Chemical and Functional Properties of Food Components

Chemical andFunctional

Properties ofFood

ComponentsSecond Edition

Chemical and Functional Properties of Food ProteinsEdited by Zdzislaw E. Sikorski

Chemical and Functional Properties of Food Components, Second EditionEdited by Zdzislaw E. Sikorski

Chemical and Functional Properties of Food Components SeriesSERIES EDITORZdzislaw E. Sikorski

Chemical and Functional Properties of Food LipidsEdited by Zdzislaw E. Sikorski and Anna Kolakowska

CRC PR ESSBoca Raton London New York Washington, D.C.

EDITED BY

Zdzislaw E. Sikorski, Ph.D.Professor of Food Science

Department of Food Chemistry and TechnologyGdansk University of Technology, Poland

Chemical andFunctional

Properties ofFood

ComponentsSecond Edition

This book contains information obtained from authentic and highly regarded sources. Reprinted materialis quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonableefforts have been made to publish reliable data and information, but the author and the publisher cannotassume responsibility for the validity of all materials or for the consequences of their use.

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Library of Congress Cataloging-in-Publication Data

Chemical and functional properties of food components / editor, E. Sikorski.--2nd ed.

p. ; cm. -- (Chemical and functional properties of food components series)Includes bibliographical references and index.ISBN 1-58716-149-4 (alk. paper)1. Food--Analysis. 2. Food--Composition. I. Sikorski, E. II. Series.

TX545 .C44 2002664

′

.07--dc21 2002276808

Zdzislaw

Zdzislaw

TX494_frame_FM Page 4 Wednesday, May 22, 2002 7:52 AM

Dedication

I am honored to dedicate this volume to Professor Owen R. Fennema.



Preface

Water, saccharides, lipids, proteins, and minerals — the main components — formthe structure of and are responsible for the sensory and nutritional properties offoods. Other constituents, present in lower quantities, especially colorants, flavorcompounds, vitamins, probiotics, and additives, also contribute to different aspectsof food quality. The catabolysis that takes place in raw materials postharvest, as wellas chemical and biochemical changes and interactions of components during storageand processing, affect all aspects of food quality. These processes can be effectivelycontrolled by the food processor who knows food chemistry.

The contents of this book go beyond that of a standard food chemistry text. Thisvolume contains a concise, yet well-documented presentation of the current state ofknowledge on the content, structure, chemical and biochemical reactivity, functionalproperties, and biological role of the components most important to food quality.The first two chapters describe in general terms the contents and role of differentconstituents in food quality and structure. The main components are presented inChapters 3–7, while Chapter 8 deals with their impact on the rheological propertiesof foods. Chapters 9 and 10 discuss the effects of different constituents on the colorand flavor of foods, while Chapters 11–14 are concerned primarily with the biolog-ical value and safety aspects of the constituents.

Most chapters have the character of monographs prepared by specialists in therespective areas. They are based on the personal research and teaching experience of thecontributors, as well as on critical evaluation of the present state of knowledge as reflectedin the current world literature. The large lists of references in the chapters include bothEnglish papers and papers published in other languages. This volume is addressed tofood scientists in industry and academia, food science graduate students, nutritionists,and all persons interested in the role and attributes of various food components.

I am honored to dedicate this volume to Professor Owen R. Fennema, Universityof Wisconsin – Madison, whom I met in person during three IUFoST congresses.Fennema’s books, especially the excellent

Food Chemistry,

have been an invaluablesource of information and inspiration to me, my students, and probably most foodprofessionals in the world.

E. SikorskiZdzislaw



Acknowledgment

As the editor, I have had the privilege to work with colleagues from universities andresearch institutions in Australia, The Netherlands, Poland, Taiwan, and the UnitedStates, who have contributed to this volume, sharing their knowledge and experience.Their acceptance of my conception of the book and of the editorial suggestions ishighly appreciated. Special thanks are due to those contributors who prepared theirchapters ahead of the deadline. It was possible to publish the book without delayonly because of the understanding of Dr. Eleanor Riemer and Sara Kreisman ofCRC Press, who agreed to accept several chapters even after the deadline.

I also want to thank several of my coworkers in the department of food chemistryand technology of the Gdansk University of Technology, Poland, who willinglyhelped me in different ways, especially in handling the computer. Last but not leastmy gratitude goes to my wife, Krystyna, who generously tolerated a husband heavilyinvolved for the past 40 years in writing and editing food science books.

E. Sikorski

Gdansk University of TechnologyZdzislaw



Editor

E. Sikorski

received his B.S., M.S., Ph.D., and D.Sc. degrees from theGdansk University of Technology (GUT) and his doctor

honoris causa

from theAgricultural University in Szczecin, Poland. He served as head of the departmentof food chemistry and technology and dean of the faculty of chemistry at GUT andwas visiting researcher and professor at the Ohio State University, Columbus, Ohio;CSIRO, Hobart, Australia; DSIR, in Auckland, New Zealand; and National TaiwanOcean University, Keelung. He is currently professor at GUT and, since 1996,chairman of the Committee of Food Technology and Chemistry of the Polish Acad-emy of Sciences. He has published 200 journal articles, 11 books (in Polish, English,Russian, and Spanish), and 8 book chapters in marine food science and food chem-istry. He holds seven patents.

Zdzislaw

TX494_frame_FM Page 11 Thursday, May 23, 2002 8:50 AM


Contributors

Agnieszka Bartoszek, Ph.D.

Department of Pharmaceutical Technology and Biochemistry

Gdansk University of TechnologyGdansk , Poland

Maria Bielecka, Ph.D.

ProfessorDivision of Food ScienceInstitute of Animal Reproduction

and Food Research of the Polish Academy of Sciences

Olsztyn, Poland

Yan-Hwa Chu, Ph.D.

Food Industry Research and Development Institute

Taiwan, Republic of China

Barbara E. Cybulska, Ph.D.

Department of Pharmaceutical Technology and Biochemistry

Gdansk University of TechnologyGdansk , Poland

Peter E. Doe, Ph.D.

ProfessorDepartment of EngineeringUniversity of Tasmania, HobartTasmania, Australia

Lucy Sun Hwang, Ph.D.

ProfessorGraduate Institute of Food Science

and TechnologyNational Taiwan UniversityTaiwan, Republic of China

Jen-Min Kuo, Ph.D.

ProfessorDepartment of Food HealthChai-Nan University of Pharmacy

and ScienceTaiwan, Republic of China

Tadeusz S. Matuszek, Ph.D.

Department of Mechanical EngineeringGdansk University of TechnologyGdansk , Poland

Julie Miller Jones, Ph.D.

Department of Home EconomicsCollege of St. CatherineSt. Paul, Minnesota

Nabrzyski, Ph.D.

Professor EmeritusDepartment of BromatologyMedical Academy of GdanskGdansk , Poland

Krystyna Palka, Ph.D.

Department of Animal Food ProductsAgricultural AcademyKraków, Poland

Bonnie Sun Pan, Ph.D.

ProfessorDepartment of Marine Food ScienceNational Taiwan Ocean UniversityTaiwan, Republic of China

Michal


Adriaan Ruiter, Ph.D.

Professor EmeritusDepartment of the Science of Food

of Animal OriginUtrecht UniversityThe Netherlands

E. Sikorski, Ph.D.

ProfessorDepartment of Food Chemistry

and TechnologyGdansk University of TechnologyGdansk , Poland

Piotr Tomasik, Ph.D.

ProfessorDepartment of ChemistryAcademy of AgricultureKraków, Poland

Alphons G.J. Voragen, Ph.D.

ProfessorDepartment of Agrotechnology and

Food SciencesWageningen UniversityThe Netherlands

Jadwiga Wilska-Jeszka, Ph.D.

Professor EmeritusInstitute of Technical BiochemistryTechnical University of £ód zLódz,´ Poland

Chung-May Wu, Ph.D.

ProfessorDepartment of Food Science and

NutritionHungkuang Institute of TechnologyTaiwan, Republic of China

Zdzislaw


Table of Contents

Chapter 1

Food Components and Their Role in Food Quality ..................................................1

E. Sikorski

Chapter 2

Chemical Composition and Structure of Foods......................................................11

Krystyna Palka

Chapter 3

Water and Food Quality ..........................................................................................25

Barbara Cybulska and Peter Edward Doe

Chapter 4

Mineral Components ...............................................................................................51

Nabrzyski

Chapter 5

Saccharides ..............................................................................................................81

Piotr Tomasik

Chapter 6

Food Lipids............................................................................................................115

Yan-Hwa Chu and Lucy Sun Hwang

Chapter 7

Proteins ..................................................................................................................133

E. Sikorski

Chapter 8

Rheological Properties of Food Systems ..............................................................179

Tadeusz Matuszek

Chapter 9

Food Colorants.......................................................................................................205

Jadwiga Wilska-Jeszka

Zdzislaw

Michal

Zdzislaw


Chapter 10

Flavor Compounds.................................................................................................231

Chung-May Wu, Jen-Min Kuo, and Bonnie Sun Pan

Chapter 11

Probiotics in Food..................................................................................................259

Maria Bielecka

Chapter 12

Major Food Additives............................................................................................273

Adriaan Ruiter and Alphons G.J. Voragen

Chapter 13

Food Safety............................................................................................................291

Julie Miller Jones

Chapter 14

Mutagenic, Carcinogenic, and Chemopreventive Compounds in Foods.............................................................................................307

Agnieszka Bartoszek

Index

......................................................................................................................337


1

1-5871-6149-4/02/$0.00+$1.50© 2002 by CRC Press LLC

Food Components and Their Role in Food Quality

E. Sikorski

CONTENTS

1.1 Main Food Components...................................................................................11.1.1 Introduction ..........................................................................................11.1.2 Contents and Role in Food Raw Materials .........................................21.1.3 Factors Affecting Food Composition...................................................4

1.2 Quality of Foods ..............................................................................................51.3 Functional Properties of Food Components....................................................51.4 Role of Chemistry and Processing Factors .....................................................6

1.4.1 Introduction ..........................................................................................61.4.2 Effect on Safety and Nutritional Value................................................71.4.3 Effect on Sensory Quality....................................................................7

References..................................................................................................................8

1.1 MAIN FOOD COMPONENTS

1.1.1 I

NTRODUCTION

Foods are derived from plant material, carcasses of animals, and single-cell organ-isms. They are composed mainly of water, saccharides, proteins, lipids, and min-erals (Table 1.1). These main components serve as nutrients by supplying thehuman body with the necessary building materials and source of energy, as wellas elements and compounds indispensable for the metabolism. Some plant polysac-charides are only partly utilized for energy. However, as dietary fiber, they affectvarious processes in the gastrointestinal tract in different ways (Kritchevsky andBonfield, 1995). Foods also contain a host of other constituents present in smallerquantities, especially nonprotein nitrogenous compounds, vitamins, colorants, fla-vor compounds, and functional additives. Many of the minor components origi-nally present in foods are nutritionally essential, e.g., vitamins (some can beutilized by the body) and amino acids. Numerous groups, including tocopherols,ubiquinone, carotenoids, ascorbic acid, thiols, amines, and several other nonprotein

1

Zdzislaw

2

Chemical and Functional Properties of Food Components

nitrogenous compounds, serve as endogenous muscle antioxidants, playing anessential role in postmortem changes in meat (Decker et al., 2000). Other minorcomponents are useless or even harmful if present in excessive amounts. Mostfood raw materials are infected with different microorganisms — putrefactive andoften pathogenic — and some contain parasites. A variety of compounds are addedintentionally during processing to serve as preservatives, antioxidants, colorants,flavorings, sweeteners, and emulsifying agents and to fulfill different other tech-nological purposes. The chemical nature and role of functional food additives arepresented in detail in Chapter 12.

1.1.2 C

ONTENTS

AND

R

OLE

IN

F

OOD

R

AW

M

ATERIALS

Polysaccharides, proteins, and lipids are involved in different structures of the plantand animal tissues used for food. The structures built from these materials are respon-sible for the form and tensile strength of the tissues and create the necessary conditionsfor the metabolic processes to occur. Compartmentation resulting from these structuresplays a crucial biological role in the organisms. Some other saccharides, proteins, andlipids are stored for reserve purposes. Other constituents are either bound to differentcell structures or distributed in soluble form in the tissue fluids.

The content of water in various foods ranges from a few percent in driedcommodities, e.g., milk powder, through about 15% in grains, 16–18% in butter,20% in honey, 35% in bread, 65% in manioc, and 75% in meat — to about 90% inmany fruits and vegetables. Most of the water is immobilized in the plant and animaltissues by the structural elements and various solutes, contributes to buttressing theconformation of the polymers, and interacts in metabolic processes.

Saccharides are present in food raw materials in quantities ranging from about1% in meats and fish, to about 4.5% in milk, 18% in potatoes, and 15–20% in sugarbeets, to about 70% in cereal grains. Polysaccharides participate in the formationof structures in plants. They are also stored in plants as starch and in muscles asglycogen. Other saccharides are dissolved in tissue fluids or perform different bio-logical functions: in free nucleotides, as components of nucleic acids, or bound toproteins and lipids.

TABLE 1.1Main Components in Typical Foods

Water Saccharides Proteins Lipids Minerals Vitamins

Juices Saccharose Soybean Oils Vegetables VegetablesFruits Honey Beans Lard Fruits FruitsMilk Cereals Meat Butter Meat Fish liverVegetables Chocolate Fish Chocolate Fish products MeatJellies Potato Wheat Nuts Dairy products CerealsLean fish Cassava Cheese Egg yolk Cereals MilkLean meat Fruits Eggs Pork Nuts Yeast


3

The protein content in foods is given mainly as crude protein, i.e., as N

×

6.25.The 6.25 nitrogen-to-protein (N:P) conversion factor has been recommended formost plant and animal food products under the assumption that the N content intheir proteins is 16% and they do not contain nonprotein N. The N content in theproteins in various foods, however, is different, since it depends on the amino acidcomposition. Furthermore, the total N consists of protein N and of N contained innumerous nonprotein compounds, e.g., free peptides and amino acids, nucleic acidsand their degradation products, amines, betains, urea, vitamins, and alkaloids. Insome foods the nonprotein N may constitute up to 30% of total N. In many of thesecompounds the C:N ratio is similar to the average in amino acids. However, the Ncontent in urea (47%) is exceptionally high. Most of the nonprotein nitrogen com-pounds can be utilized by the organism as a source of nitrogen.

The average conversion factor for estimation of true protein, based on the ratiosof total amino acid residues to amino acid N, determined for 23 various food productsis 5.68 and for different classes of foods, 5.14–6.61 (Table 1.2). The N:P factor of4.39, based on analysis of 20 different vegetables, has been proposed by Fujiharaet al. (2001) for estimating the true protein content in vegetables. A common N:Pfactor of 5.70 for blended foods or diets has been recommended by Sosulski andImafidon (1990).

Proteins make up about 1% of the weight of fruits, 2% of potatoes, 3.2% ofbovine milk, 12% of eggs, 12–22% of wheat grain, about 20% of meat, and 25–40%of different beans. They serve as the building material of muscles and other animaltissues and, in plants and animals, play crucial metabolic roles as enzymes andenzyme inhibitors, participate in the transport and binding of oxygen and metal ions,and perform immunological functions. During their development cereal grain andlegume seeds deposit large quantities of storage proteins in granules known also asprotein bodies. In soybeans these proteins constitute 60–70% of the total proteincontent, and the granules in 80% are made of proteins.

Lipids constitute below 1% of the weight of fruits, vegetables, and lean fish;3.5% of milk; 6% of beef; 32% of egg yolk; and 85% of butter. The lipids containedin the food raw materials in low quantities serve mainly as components of protein-phospholipid membranes and perform metabolic functions. In fatty commodities themajority of the lipids are stored as depot fat in the form of triacylglycerols. Thelipids of numerous food fishes, such as orange roughy, mullets, codfish, and sharks,

TABLE 1.2N:P Conversion Factors in Foods

Product Factor Product Factor

Dairy products 6.02–6.15 Potato 5.18Egg 5.73 Leafy vegetables 5.14–5.30Meat and fish 5.72–5.82 Fruits 5.18Cereals and legumes 5.40–5.93 Microbial biomass 5.78–6.61

Source:

From Sosulski, F.W. and Imafidon, G.I.,

J. Agric. Food Chem.

, 38, 1351, 1990.

4


as well as some crustaceans and mollusks, also comprise wax esters. Some sharkoils are very rich in hydrocarbons, particularly in squalene (Sikorski et al., 1990).Furthermore, the lipid fraction of food raw materials harbors different sterols, vita-mins, and pigments that are crucial for metabolism.

1.1.3 F

ACTORS

A

FFECTING

F

OOD

C

OMPOSITION

The content of different components in food raw materials depends on the speciesand variety of the animal and plant crop, the conditions of cultivation and harvestingof the plants, the feeding and age of the farm animals or the season in which fishand marine invertebrates are caught, and postharvest changes taking place in thecrop during storage. The food industry, by establishing quality requirements for rawmaterials, can encourage producers to control within limits the contents of the maincomponents in their crops, e.g., saccharose in sugar beets, starch in potatoes, fat invarious meat cuts, pigments in fruits and vegetables and in the flesh of fish fromaquaculture, or protein in wheat and barley, as well as the fatty acid composition oflipids in oilseeds and meats. The contents of desirable minor components such asnatural antioxidants can also be effectively controlled to retard the oxidation ofpigments and lipids in beef meat (Matsumoto, 2000). Contamination of the rawmaterial with organic and inorganic pollutants can be controlled by observing rec-ommended agricultural procedures in using fertilizers, herbicides, and insecticidesand by restricting certain fishing areas seasonally to avoid marine toxins. The sizeof predatory fish like swordfish, tuna, or sharks that are fished commercially can belimited to reduce the risk of too high a content of mercury and arsenic in the flesh.

The composition of processed foods depends on the applied recipe and onchanges taking place due to processing and storage. These changes are mainlybrought about by endogenous and microbial enzymes, active forms of oxygen,heating, chemical treatment, and processing at low or high pH (Haard, 2001).Examples of such changes are:

• Leaching of soluble components, e.g., vitamins and minerals during wash-ing, blanching, and cooking

• Drip formation after thawing or due to cooking• Loss of moisture and volatiles due to evaporation and sublimation• Absorption of desirable or harmful compounds during salting, pickling,

or smoking• Formation of desirable or harmful compounds due to enzyme activity,

e.g., development of a typical flavor in cheese or decarboxylation of aminoacids in fish marinades

• Generation of desirable or objectionable products due to interactions of reactivegroups induced by heating or chemical treatment, e.g., flavors or carcinogeniccompounds in roasted meats or

trans

fatty acids in hydrogenated fats• Formation of different products of oxidation of food components, mainly

of lipids, pigments, and vitamins• Loss of nutrients and deterioration of dried fish due to the attack by flies,

mites, and beetles


5

1.2 QUALITY OF FOODS

The quality of a food product, i.e., the characteristic properties that determine thedegree of excellence, is a sum of the attributes contributing to the satisfaction of theconsumer with the product. The composition and the chemical nature of the foodcomponents affect all aspects of food quality. The total quality reflects at least thefollowing attributes:

• Compatibility with the local or international food laws, regulations, andstandards, concerning mainly proportions of main components, presenceof compounds regarded as identity indicators, contents of contaminantsand additives, hygienic requirements, and packaging

• Nutritional aspects, i.e., the contents of nutritionally desirable constitu-ents, mainly proteins, essential amino acids, essential fatty acids, vitamins,fiber, and mineral components

• Safety aspects affected by the compounds that may constitute healthhazards for the consumers and affect the digestibility and nutritional useof the food, e.g., heavy metals, toxins of different origin, pathogenicmicroorganisms, parasites, and enzyme inhibitors

• Sensory attributes — color, size, form, flavor, and taste — and rheologicalproperties, obviously affected by the chemical composition of the product,as well as the effects resulting from processing and culinary preparation

• Shelf life at specific storage conditions• Convenience aspects, which are reflected by the size and ease of opening

and reclosing the container, suitability of the product for immediate useor for different types of thermal treatment, ease of portioning or spreading,and transport and storage requirements

• Ecological aspects regarding suitability for recycling of the packagingmaterial and pollution hazards

For many foods one of the most important quality criterion is freshness. This isespecially so in numerous species of vegetables, fruits, and seafood. Fish of valuablespecies at the state of prime freshness, suitable to be eaten raw, may have a marketprice that is ten times higher than that of the same fish after several days of storagein ice but still very fit for human consumption. The characteristic freshness attributesof different foods are usually evaluated by sensory examination and by determinationof specific indices, e.g., nucleotide degradation products in fish.

1.3 FUNCTIONAL PROPERTIES OF FOOD COMPONENTS

The term

functional properties

has evolved to have a broad range of meanings.That corresponding to the term

technological properties

implies that the givencomponent present in optimum concentration, subjected to processing at optimumparameters, contributes to the desirable sensory characteristics of the product,usually by interacting with other food constituents. Hydrophobic interactions,

6


hydrogen bonds, ionic forces, and covalent bonding are involved. Thus the func-tional properties of food components are affected by the number of accessiblereactive groups and by the exposure of hydrophobic areas in the given medium.Therefore the functional properties displayed in a system of given water activityand pH and in the given range of temperature can be to a large extent predictedfrom the structure of the respective saccharides, proteins, and lipids. They canalso be improved by appropriate, intentional enzymatic or chemical modificationsof the molecules, mainly those that affect the size, charge density, or hydrophilicand hydrophobic character of the compounds, or by changes in the environment,regarding both the solvent and other solutes.

The functional properties of food components make it possible to manufactureproducts of desirable quality. Thus pectins contribute to the characteristic texture ofripe apples and make perfect jellies. Various other polysaccharides are good thick-ening and gelling agents at different ranges of acidity and concentration of variousions. Alginates in the presence of Ca

2+

form protective, unfrozen gels on the surfaceof frozen products. Some starches are resistant to retrogradation, thereby retardingstaling of bread. Fructose retards moisture loss from biscuits. Mono- and diacyl-glycerols, phospholipids, and proteins are used for emulsifying lipids and stabilizingfood emulsions and foams. Antifreeze proteins decrease ice formation in variousproducts, and gluten plays a major role in producing the characteristic texture ofwheat bread.

Technologically required functional effects can also be achieved by intentionallyemploying various food additives — food colors, sweeteners, and a host of othercompounds — that are not regarded as foodstuffs per se, but are used to modify therheological properties or acidity, increase the color stability or shelf life, or act ashumectants or flavor enhancers (Rutkowski et al., 1997).

During the recent two decades the term

functional

has also been given to a largegroup of products and components, also called designer foods, pharmafoods, nutra-ceuticals, or foods for specific health use, that are regarded as health enhancing.These foods, mainly drinks, meals, confectionery, ice cream, and salad dressings,contain various ingredients (e.g., oligosaccharides, sugar alcohols, or choline) thatare claimed to have special physiological functions like neutralizing harmful com-pounds in the body and promoting recovery and general good health (Goldberg,1994). Foods containing probiotics, mainly dairy products, have been treated indetail in Chapter 11.

1.4 ROLE OF CHEMISTRY AND PROCESSING FACTORS

1.4.1 I

NTRODUCTION

The chemical nature of food components is of crucial importance for all aspectsof food quality. It decides on the nutritional value of the product, its sensoryattractiveness, the development of desirable or deteriorative changes due to inter-actions with other constituents and to processing, and the susceptibility and resis-tance to spoilage during storage. Food components that contain reactive groups,many of them essential for the quality of the products, are generally labile and


7

easily undergo different enzymatic and chemical changes, especially when treatedat elevated temperatures or in conditions promoting the generation of active speciesof oxygen.

1.4.2 EFFECT ON SAFETY AND NUTRITIONAL VALUE

Food is regarded as safe if it does not contain harmful organisms or compounds inconcentrations above the accepted limits (see Chapter 13). The nutritional value offoods depends primarily on the contents of nutrients and nutritionally objectionablecomponents in the products.

Processing may increase the safety and biological value of food by inducingchemical changes, increasing the digestibility of the components, or by inactivatingundesirable compounds, e.g., toxins or enzymes catalyzing the generation of toxicagents from harmless precursors. Freezing and short-term frozen storage of fishinactivate the parasite Anisakis, which could escape detection during visual inspec-tion of herring fillets used as raw material for cold marinades produced at mildconditions. Thermal treatment brings about inactivation of myrosinase, the enzymeinvolved in hydrolysis of glucosinolanes. This arrests the reactions that lead to theformation of goitrogenic products in oilseeds of Cruciferae. Heat pasteurization andsterilization reduce the number of vegetative forms and spores, respectively, to theacceptable level of pathogenic microorganisms. Several other examples of suchimprovements of the biological quality of foods are given in the following chaptersof this book.

However, there are also nutritionally undesirable side effects of processing:destruction of essential food components as a result of heating, chemical treatment,and oxidation. Generally known is the partial thermal decomposition of vitamins,especially thiamine, loss of available lysine and sulfur-containing amino acids, orgeneration of harmful compounds (e.g., carcinogenic heterocyclic aromatic amines,lysinoalanine, and lanthionine or position isomers of fatty acids) not originallypresent in foods. Thanks to the unprecedented development of analytical chemistry,applying efficient procedures of enrichment and separation, combined with the useof highly selective and sensitive detectors, has made it possible to determine variousproducts of chemical reactions in foods, even in very low concentrations. In recentyears new evidence of side effects has been accumulated in respect to chemicalprocessing of oils and fats. Commercial hydrogenation of oils not only brings aboutthe intended saturation of selected double bonds in the fatty acids, and thereby therequired change in the rheological properties of the oil, but also results in thegeneration of a large number of trans-trans and cis-trans isomers that are absent inunprocessed oils.

1.4.3 EFFECT ON SENSORY QUALITY

Many of the desirable sensory attributes of foods stem from the properties of theraw material: the color, flavor, taste, and texture of fresh fruits and vegetables or thetaste of nuts and milk. These properties are in many cases carried through to thefinal products.

8 Chemical and Functional Properties of Food Components

In other commodities the characteristic quality attributes are generated in pro-cessing. The texture of bread develops due to interactions of proteins, lipids, andsaccharides with each other and with various gases (Eliasson, 1998; Wrigley et al.,1998; Preston, 1998). The bouquet of wine is due to fermentation of saccharidesand a number of other biochemical and chemical reactions. The delicious color,flavor, texture, and taste of smoked salmon are generated as a result of enzymaticchanges in the tissues and the effect of salt and smoke (Doe et al., 1998). Optimumfoam performance of beer depends on the interactions of peptides, lipids, the surface-active components of hop, and gases (Hughes, 1999). The flavor, texture, and tasteof cheese result from fermentation and ripening, while the appealing color and flavorof different fried products are due to reactions of saccharides and amino acids(Sikorski, 2001).

The sensory attributes of foods are related to the contents of many chemicallylabile components. These components, however, just as most nutritionally essentialcompounds, are prone to deteriorative changes in severe heat treatment conditions,oxidizing conditions, or application of considerably high doses of chemical agents(e.g., acetic acid or salt), which are often required to ensure safety and sufficientlylong shelf life of the products. Thus loss in sensory quality takes place in overster-ilized meat products, due to degradation of sulfur containing amino acids and thedevelopment of an off-flavor; in toughening of the texture of overpasteurized hamor shellfish, due to excessive shrinkage of the tissues and drip; and in deteriorationof the texture and arresting of ripening in herring, due to preservation at too high aconcentration of salt.

Optimum parameters of storage and processing ensure the retention of thedesirable properties of the raw material and lead to development of intendedattributes of the product. In the selection of these parameters the chemistry of foodcomponents and of the effect of processing must be studied. The eager food tech-nology student can find all the necessary information in at least two excellenttextbooks on food chemistry, published by Belitz et al. (2001) and Fennema (1996);in numerous books on food lipids, proteins, and saccharides; and in current inter-national journals.

REFERENCES

Belitz, H.D., Grosch, W., and Schieberle, P., Lehrbuch der Lebensmittelchem, 4th ed.,Springer-Verlag, Berlin, 2001.

Decker, E.A., Livisay, S.A., Zhou S., Mechanism of endogenous skeletal muscle antioxidants:chemical and physical aspects, in Antioxidants in Muscle Foods: Nutritional Strategiesto Improve Quality, Decker, E., Faustman, C., and Lopez-Bote, C.J., Eds., WileyInterscience, New York, 2000, p. 25.

Doe, P. et al., Basic principles, in Fish Drying and Smoking: Production and Quality, Doe,P.E., Ed., Technomic Publishing Co., Inc., Lancaster, PA, 1998, p. 13.

Eliasson, A.C., Lipid-carbohydrate interactions, in Interactions: The Keys to Cereal Quality,Hamer, R.J. and Hoseney, R.C., Eds., American Association of Cereal Chemists, Inc.,St. Paul, MN, 1998, p. 47.

Fennema, O.R., Ed., Food Chemistry, 3rd ed., Marcel Dekker, New York, 1996.

Food Components and Their Role in Food Quality 9

Fujihara, S., Kasuga, A., and Aoyagi, Y., Nitrogen-to-protein conversion factors for commonvegetables in Japan, J. Food Sci., 66, 412, 2001.

Goldberg, I., Functional Foods: Designer Foods, Pharmafoods, Nutraceuticals, Chapman &Hall, New York, 1994.

Haard, N.F., Enzymic modification in food systems, in Chemical and Functional Propertiesof Food Proteins, Sikorski, Z.E., Ed., Technomic Publishing Co., Lancaster, PA, 2001,p. 155.

Hughes, P., Keeping a head: optimizing beer foam performance, in Bubbles in Food, Campbell,G.M. et al., Eds., Eagan Press, St. Paul, MN, 1999, p. 129.

Kritchevsky, D. and Bonfield, Ch., Eds., Dietary Fiber in Health & Disease, Eagan Press,St. Paul, MN, 1995.

Matsumoto, M., Dietary delivery versus exogenous addition of antioxidants, in Antioxidantsin Muscle Foods: Nutritional Strategies to Improve Quality, Decker, E., Faustman,C., and Lopez-Bote, C.J., Eds., Wiley Interscience, New York, 2000, p. 315.

Preston, K.R., Protein-carbohydrate interactions, in Interactions: The Keys to Cereal Quality,Hamer, R.J. and Hoseney, R.C., Eds., American Association of Cereal Chemists, Inc.,St. Paul, MN, 1998, p. 81.

Rutkowski, A., Gwiazda, S., and Dabrowski, K., Food Additives and Functional Component,Agro & Food Technology, Katowice, 1997 (in Polish).

Sikorski, Z.E., Chemical reactions in proteins in food systems, in Chemical and FunctionalProperties of Food Proteins, Sikorski, Z.E., Ed., Technomic Publishing Co., Inc.,Lancaster, PA, 2001, p. 191.

Sikorski, Z.E., , A., and Pan, B.S., The nutritive composition of the majorgroups of marine food organisms, in Seafood: Resources, Nutritional Composition,and Preservation, Sikorski, Z.E., Ed., CRC Press, Boca Raton, FL, 1990, p. 29.

Sosulski, F.W. and Imafidon, G.I., Amino acid composition and nitrogen-to-protein conversionfactors for animal and plant foods, J. Agric. Food Chem., 38, 1351, 1990.

Wrigley, C.W. et al., Protein-protein interactions: essential to dough rheology, in Interactions:The Keys to Cereal Quality, Hamer, R.J. and Hoseney, R.C., Eds., American Associ-ation of Cereal Chemists, Inc., St. Paul, MN, 1998, p. 17.

Kolakowska

111-5871-6149-4/02/$0.00+$1.50© 2002 by CRC Press LLC

Chemical Composition and Structure of Foods

Krystyna Palka

CONTENTS

2.1 Introduction ....................................................................................................112.2 Protein Food Products....................................................................................12

2.2.1 Meat....................................................................................................122.2.2 Milk and Milk Products.....................................................................142.2.3 Eggs....................................................................................................15

2.3 Saccharide Food Products..............................................................................162.3.1 Cereal and Cereal Products................................................................162.3.2 Potatoes ..............................................................................................182.3.3 Honey .................................................................................................202.3.4 Nuts ....................................................................................................202.3.5 Seeds of Pulses...................................................................................20

2.4 Edible Fats......................................................................................................212.5 Fruits and Vegetables .....................................................................................21References................................................................................................................23

2.1 INTRODUCTION

Foods are edible fragments of plant or animal tissues in a natural or processed statethat, after being eaten and digested in the human organism, may be a source ofdifferent nutrients. Taking as a base the dominant nutritional component, foodproducts may be divided into four groups:

• Protein food products• Saccharide food products• Edible fats• Fruits and vegetables

The particular groups of chemical constituents participate in building the struc-ture of food products as components of specialized tissues. For this reason thischapter presents, in addition to chemical composition, the morphology of the selectedproducts from each group.

2


2.2 PROTEIN FOOD PRODUCTS

2.2.1 MEAT

Meat is the edible part of animal, chicken, or fish carcasses. Its chemical compositionis as follows: 60–85% water, 8–23% protein, 2–15% lipids, 0.5–1.5% saccharides,and about 1% inorganic substances (Table 2.1). These quantities change significantlydepending on the kind, age, sex, level of fattening, and part of the animal carcass.The largest fluctuations are observed in the contents of water and lipids.

Water is a solvent of organic and inorganic substances and an environment ofbiochemical reactions. It also participates in the maintenance of meat proteinconformation.

Meat proteins include sarcoplasmic, myofibrillar, and connective tissue proteins.Among the sarcoplasmic proteins are heme pigments and enzymes, which influencethe color, smell, and structure of meat. Myofibrillar proteins and collagen are ableto retain and hold water in meat structure and to emulsify fat. Therefore theyinfluence the rheological properties of meat products.

Mineral elements are in enzymatic complexes and other structures that play animportant biochemical role. They can affect the technological properties of meat,e.g., water-holding capacity, as well as the sensory characteristics. Meat is also agood source of B group vitamins.

The main structural unit of striated muscle tissue is a multinucleus cell called musclefiber. Its length varies from several millimeters to hundredths of a millimeter, and thediameter is within the range 10–100 µm (Figure 2.1a). The thickness of muscle fibersaffects the meat tenderness. The muscle fiber contains typical somatic cell compounds,sarcoplasmic reticulum, and myofibrils. The sarcoplasmic reticulum has the capacityof reversible binding of calcium ions. Myofibrils are the main structural element ofmuscle fiber, making up 80% of its volume. They have a diameter of 1–2 µm and aresituated parallel to the long axis of the fiber (Figure 2.1b). The spaces between myo-fibrils are filled up with a semiliquid sarcoplasm, which forms the environment ofenzymatic reactions and takes part in conducting nervous impulses into the muscle.

Each myofibril consists of two different protein structures: myofilaments. Theseare myosin thick (15 nm × 1.5 µm) and thin (7 nm × 1 µm) filaments made fromactin, tropomyosin, and troponin.

Inside the muscle fiber there is also a cytoskeleton — the protein structuresassuring the integrity of muscle cells. Cytoskeletal proteins such as titin and nebulinare located in myofibrils and anchored in the Z line. Desmin is made up of costamers,which connect the myofibrils; vinculin connects myofibrils and sarcolemma. Post-mortem changes in cytoskeletal proteins probably play a role in the improvementof meat functional properties, especially its tenderness and water-holding capacity.

The muscle fiber is covered by a thin membrane called sarcolemma and a layerof connective tissue called endomysium. Bundles of muscle fibers are surroundedby perimysium, and whole muscle is surrounded by epimysium. At the ends of themuscle epimysium forms tendons, which connect the muscle to the bone(Figure 2.2). Both the quantity and kind of connective tissue affect the technologicaland nutritional properties of meat.

Chemical Composition and Structure of Foods 13

TABLE 2.1Chemical Composition of Foods Rich in Proteins

Product Water (%)

Crude Protein

Nx6.25 (%) Lipids (%)Saccharides

(%)

Mineral Components

(%)

Beef, leanPork, leanVealLambChicken:Light meatDark meat

HerringOyster

71.572.075.071.5

75.076.060.085.0

21.020.020.019.5

23.020.018.07.5

6.57.03.57.0

2.04.515.51.5

1.01.01.01.5

1.01.0

0.5–1.50.5–1.5

1.01.01.01.0

Cow milkSheep milkSour cream (25%)Yogurt, low fatQuargRipened cheeseMilk powder

88.082.068.085.0

64.0–75.035.0–50.0

3.0

3.06.03.05.0

9.0–14.020.0–35.0

26.0

3.56.525.01.0

12.0–18.020.0–30.0

26.0

4.54.54.07.52.52.0

38.0.

1.01.00.50.71.55.06.0

Whole egg, without shellWhiteYolk

Whole egg powder

73.588.048.53.5

13.011.016.047.5

12.0traces32.043.0

1.00.51.0

to 0.5

1.00.51.04.0

Source: Adapted from Hedrick, H.B. et al., Principles in Meat Science, Kendall-Hunt Publishing Co.,Dubuque, 1994; Kirk, R.S. and Sawyer, R., Pearson’s Composition and Analysis of Foods, LongmanScience, London, 1991; Renner, E., Cheese: Chemistry, Physics and Microbiology, Vol. 1, Fox, P.F., Ed.,Chapman & Hall, London, 1993, 557; Sikorski, Z.E., Seafood Raw Materials, WNT, Warsaw, 1992;Tamime, A.Y. and Robinson, R.K., Yoghurt: Science and Technology, CRC Press, Boca Raton, FL, 1999.

FIGURE 2.1 Scanning electron microscope (SEM) micrographs of bovine semitendinosusmuscle: transverse section (a) and longitudinal section (b). F, muscle fiber; MF, myofibril.(From Palka, K., unpublished.)


2.2.2 MILK AND MILK PRODUCTS

Milk is a liquid secretion of the mammary glands of female mammals, consisting of80–90% water and 10–20% dry mass. It is an oil-in-water (O/W) emulsion composedof fat and fat-soluble vitamins; the aqueous phase contains proteins, mineral salts, lactose,and water-soluble vitamins. The chemical composition of milk (Table 2.1) depends onspecies and breed, lactation period, and nutritional and health conditions of the animal.

The proteins of milk are made up of caseins and whey proteins. Milk proteins,caseins, and several enzymes, mainly hydrolases and oxidoreductases, are very impor-tant in the manufacturing of cheeses and yogurts (Figure 2.3). After drying they areused in the food industry as milk powder, caseinates, and casein hydrolyzates. Non-protein nitrogenous compounds constitute about 0.2% of milk..

The milk fat is made up of about 98% triacylglycerols and 1% phospholipids. Italso contains smaller amounts of di- and monoacylglycerols, sterols, higher fatty acids,

FIGURE 2.2 Schematic structure of skeletal muscle: tendon (1), epimysium (2), perimysium(3), endomysium (4), sarcolemma (5), myofibril (6), muscle fiber (7), and bundle of musclefibers (8).

FIGURE 2.3 SEM micrograph of protein matrix in yogurt. (From Domagala, J., unpublished.With permission.)


carotenoids, and vitamins. In cow milk fat over 500 fatty acid residues have beenidentified. The polyenoic fraction constitutes about 3% of the total fatty acids and iscomposed mainly of linoleic and oc-linolenic acids. The milk fat is easily digestiblebecause of a relatively low melting temperature and great dispersion (droplets of 5–10µm in diameter). Because of the latter, it is susceptible to hydrolysis and oxidation.

The main saccharide of milk is lactose. During heat treatment of milk, lactoseis involved in Maillard reactions. Lactose is used for the production of baby formulas,low-caloric foods, bread, drugs, and microbiological media.

The milk minerals are composed mainly of calcium and phosphorus in the formof calcium phosphate. Phosphorus is also present in milk in the form of phospho-proteins. These components have important nutritional and technological signifi-cance. The total content of Ca and P in milk is about 0.12 and 0.10%, respectively.

About 6–9% of milk volume is made up of gases, mainly CO2, N2, and O2.

Oxygen present in milk may cause oxidation of unsaturated fatty acids. For thisreason air is removed from milk during processing.

Milk contains vitamins essential for the growth and development of youngorganisms, especially vitamins from the B group and vitamin A. The quantity ofvitamin A depends on the season.

2.2.3 EGGS

The hen egg consists of a shell, egg white, and yolk (Figure 2.4). The 0.2- to 0.4-mm-thick shell constitutes 10–12% of the egg mass and consists of about 3.5%organic and 95% mineral components. The shell has a many-layer structure. Twoof the layers are made of keratin and collagen fibers. The next two layers arecalcinated and on the surface are covered by a thin membrane (cuticula) that containstwo thirds of the shell pigments. The shell protects the egg against microbiologicalcontamination and makes the exchange of gases possible.

FIGURE 2.4 Schematic structure of hen egg: shell (1), membranes (2), air chamber (3), rarewhite (4), dense white (5), yolk (6), and chalazae (7).


The egg white — about 60% of the egg mass — composed mainly of water anda mixture of proteins, has a many-layer structure too. Starting from the shell thereare four fractions of white: external thin, external thick, internal thin, and internalthick, which make up 23, 57, 17, and 2.5%, respectively, of the egg white mass.Mucin structures called chalazae keep the yolk in central position in the egg. Duringlong storage the chalazae lose their elasticity, and the egg white loses part of itswater, due to evaporation.

The egg yolk — about 30% of the egg mass — has a spherical shape, a diameterof about 3–3.5 cm, and a color ranging from dark to light orange, depending onthe quantity of lipids and carotenoid pigments in the fodder. It is surrounded bya thin and elastic vittelin membrane build of keratin and mucin fibers. The eggyolk, being an O/W emulsion, stabilized by lecithin, has a very high viscosity.The viscosity of the yolk decreases during storage, as a result of water permeationfrom the white through the vittelin membrane. Egg yolks are utilized as a stabilizerin manufacturing mayonnaise.

The chemical composition of the egg (Table 2.1) is rather stable. As the onlysource of food for the embryo, it contains all substances essential for life. There isabout 6.6 g of very well-balanced proteins in one egg. About two thirds of yolkmass are lipids, mainly unsaturated. Cholesterol makes up about 2.5% of the drymass of the yolk. The egg is also a source of vitamins A, B, D, E, and K and thebest dietary source of choline. The minerals S, K, Na, P, Ca, Mg, and Fe are in freeform or bound to proteins and lipids.

The eggs and egg products, thanks to their texture-improving properties, emul-sifying effect, and foaming ability, are multifunctional components used in foodtechnology in liquid or dried form.

2.3 SACCHARIDE FOOD PRODUCTS

2.3.1 CEREAL AND CEREAL PRODUCTS

Cereals are fruits of cultivated grasses that may be used as raw materials forproduction of food and feed. The major cereals are: wheat, rye, barley, oats, millet,rice, sorghum, and maize. The share of cereal products in the human diet isestimated at 50–60%.

The shape of grains varies from elongated (rye) to spherical (millet), but theanatomical structure of cereal grains is rather similar. The essential anatomicalelements of cereal grains are: seed coat (bran), endosperm, and germ. Commerciallythe most important cereal is wheat. A wheat grain is about 1 cm long and has adiameter of 0.5 cm. It is egg-shaped with a deep crease running along one side anda number of small hairs, called the beard, at one end (Figure 2.5).

The grain is surrounded by a five-layer coat called bran that makes up 15% ofthe mass of the whole grain. It is rich in B vitamins and contains about 50% of thetotal mass of minerals of the grain. The bran consists of cellulose and is indigestiblefor humans. It is separated during flour production and used as animal fodder.

The germ, about 3% of the mass of the grain, is situated at the base of the grain.It contains the embryo, which is rich in lipids, proteins, B vitamins, vitamin E, and


minerals, mainly iron. A membranous tissue called scutellum separates the germ fromthe endosperm. It is a rich source of thiamine — about 60% of all its content in the grain.

The starchy endosperm makes up 80–90% of the wheat grain and is a reserveof food for the germ. The starch granules are embedded in a protein matrix, whilethe periphery of the endosperm is composed of a single aleurone layer. The aleuronelayer is rich in proteins and contains high amounts of minerals, vitamins, andenzymes. However, it is usually removed during milling. Considering the size, mostof the starch granules in the endosperm cells of wheat may be located in two ranges— large, 15–40 µm in diameter; and small, 1–10 µm in diameter — whereas thosein the subaleurone endosperm cells are 6–15 µm in diameter.

The chemical composition of cereal (Table 2.2) is dependent on species, culti-vate, and time and conditions of growth, harvest, and storage.

The starch constitutes about 80% of the grain dry mass. In bread making themost important properties of starch are its water-holding capacity, gelatinization,and susceptibility to hydrolysis.

The protein content of cereal grains is in the range of 7–18%. From the technologicalpoint of view, proteins, mainly gluten proteins, as well as enzymes — amylases, pro-teases, and lipases — are important during dough making. Cereal grains also contain2–4% of lipids, mainly triacylglycerols of unsaturated fatty acids and phospholipids.

FIGURE 2.5 Schematic structure of wheat grain: longitudinal section (a) and transversesection (b); beard (1), bran (2), endosperm (3), crease (4), scutellum (5), and germ (6).


The mineral elements, mainly P and K, and to a smaller extent, also Mg andCa, make about 2% of the grain mass. Vitamins of the B group and vitamin E arealso present in the grains.

The milling technique can be modified to increase or decrease the yield of flourfrom a given amount of grain. The percentage of flour produced is termed theextraction rate of flour. Whole flour, containing the bran, germ, scutellum, andendosperm of the grain, has an extraction rate of 100%. An extraction rate of 70%means that the flour is almost entirely composed of crushed endosperm. As thepercentage of flour increases, the amount of dietary fiber in flour increases too. Itis an important nutritional aspect connected with cereal products.

2.3.2 POTATOES

The potato is a swollen underground stem or tuber that contains a store of foodfor the plants. In the tuber a bud end and a stem end can be distinguished. Thehollows, called eyes, are spirally arranged around the tuber surface. The tubersection is divided into the pith, parenchyma, vascular system, cortex, and peri-derm (Figure 2.6).

Each potato tuber is a single living organism, and its water is indispensable inall the vital processes. Water transports any substances moving in the interior of the

TABLE 2.2Chemical Composition of Cereals and Cereal Products

ProductWater(%)

CrudeProteinNx6.25

(%)Saccharides

(%)Lipids(%)

MineralComponents

(%)

GrainsWheatRyeMaizeRice paddyMillet

15.015.015.015.015.0

11.09.0

10.07.5

10.5

68.570.567.075.565.0

2.01.54.50.54.0

1.51.51.51.03.0

FlourWheat flour (97%)Wheat flour (50%)Rye flour (97%)Rye flour (60%)

13.513.513.513.5

10.08.57.55.5

70.575.073.078.5

3.01.52.01.5

1.50.51.50.5

BreadWheat breadRye breadRusks

37.546.07.0

8.06.58.5

57.545.075.0

1.51.05.5

2.02.01.5

Source: Adapted from Fox, B.A. and Cameron, A.G., Food Science: A Chemical Approach, Hodderand Stoughton, London, 1986; Kent, N.L., Technology of Cereals with Special Reference to Wheat,Pergamon Press, Oxford, 1975.


tuber. It also protects the tubers against overheating (by transpiration). The waterconstitutes about 75% of the potato (Table 2.3). The major constituent of the potatois starch (about 20%). With regard to starch content there are potato cultivates of alow (to 14%), medium (15–19%), and high (above 20%) starch content. Potato isalso a valuable source of ascorbic acid — up to 55 mg/100 g. Its ash consists ofabout 60% K and 15% P2O5. The chemical composition of potato tubers changesduring storage, due to evaporation and catabolic processes.

In many parts of the world potatoes are the main saccharide source inhuman food and animal fodder and are also widely used as raw material forstarch manufacture and in the fermentation industry.

FIGURE 2.6 Schematic structure of potato, longitudinal section: eye (1), periderm (skin) (2),parenchyma (3), vascular ring (4), and pith (5).

TABLE 2.3Chemical Composition of Potato and Honey

Potato % Honey %

WaterDry matter:StarchSaccharidesProteinsCelluloseLipids

Mineral components

76.024.017.51.52.01.00.51.0

WaterSaccharides:FructoseGlucoseMaltoseTrisaccharidesSaccharose

Proteins, vitamins, and mineral components

17.082.538.531.07.04.01.50.5

Source: Adapted from Lisinska, G. and Leszczynski, W., Potato Science and Technology, ElsevierApplied Science, London, 1989; Ramsay, I., Honey as a food ingredient, Food Ingredient Process.Int., 10, 16, 1992.


The shape and size of starch granules are specific for different starchy rawmaterials (Figure 2.7).

2.3.3 HONEY

Honey is produced by honeybees from the flower nectar of plants. Fresh honey is aclear, very aromatic, dark-amber-colored liquid. It is very sticky and hygroscopic, witha density of about 1.40 g/cm3. Honey is an oversaturated solution of glucose andfructose, easy crystallizing. After crystallization its color is brighter. It is a very stableproduct. At a temperature of 8–10°C and a humidity of 65–75% it may be stored formany years. Honey is a high-caloric food easy assimilated by the human organism.

Honey is used in the manufacturing of alcoholic beverages, i.e., in wine production.In medicine it is prescribed for heart, liver, stomach, skin, and eye illnesses. In thefood industry honey is used as a very effective sweetener (25% sweeter than sucrose);a very well binding, concentrating, and covering additive; and a taste intensifier.

The chemical composition of honey (Table 2.3) is dominated by glucose andfructose. Honey also contains many other valuable components, like enzymes,organic acids, mineral elements, nonprotein nitrogenous compounds, vitamins,aroma substances, and pigments.

2.3.4 NUTS

Nuts are composed of a wooden-like shell and a seed, covered by a yellow or brownskin. Each part makes up about 50% of the nut mass. Inside of the seed is a germ.The seeds of nuts consist of about 60% lipids rich in unsaturated fatty acids, 16–20%easily digested proteins, 7% saccharides, vitamins B1 (10 mg/100 g) and C (30–50mg/100 g), and P, Mg, K, and Na. With regard to their high quantity of easilyassimilated nutrients, nuts may be used in diets of convalescents and children.

2.3.5 SEEDS OF PULSES

To this group belong peas, beans, lentils, soybeans, and peanuts. All of them havefruits in the form of pods. Their shape and size depend on the cultivar. Inside thepod are seeds used as raw material in the food industry.

FIGURE 2.7 SEM micrographs of starch granules in different starchy raw materials: potato(a), wheat (b), and maize (c). (From Juszczak, L., unpublished. With permission.)


The dry mass of pulse seeds consists of saccharides (14–63%), proteins(28–44%), and lipids (1–50%). The other constituents are mineral elements (mainlyK and P) and vitamins from the B group. Soybean is the most valuable pod plant,due to its high quantity and good quality of protein. Soy products in the form ofmeat extenders and analogs are used all over the world. Soybean is also a rawmaterial in the oil industry.

2.4 EDIBLE FATS

Food products like butter, lard, margarine, and plant oils are regarded as “visible”fats. They make up about 45% of the total fat consumed by man, while the “invisible”fats, which are natural components of foods like meat, fish, eggs, and bakeryproducts, make up about 55%.

Visible fats are composed mainly of triacylglycerols. They also contain fat-soluble vitamins A, D, and E and additives added during processing, like antioxi-dants, colorants, or preservatives.

The consistency of fats depends on the content of unsaturated fatty acid residues.The oils of plant and fish origin are rich in long-chain polyenic fatty acids.

Butter consists of 16–18% water, 80–82.5% lipids, 0.5% proteins, and 0.5%saccharides.

2.5 FRUITS AND VEGETABLES

Fruits and vegetables are rich sources of vitamins and minerals, as well as terpenes,flavonoids, tannins, chinons, and phytoncides. They make food more attractivebecause of smell and color.

The fruits and vegetables are living organisms, and their chemical compositionis very changeable. The predominant constituent of fruits and vegetables is water,which may represent up to about 96% of the total weight of the crop. The water infruits and vegetables may be in free or bound form. A relatively high amount of freewater improves the taste of fruits and vegetables consumed in their raw state, aswell as the accessibility of soluble components. Most of the solid matter of fruitsand vegetables is made of saccharides and smaller amounts of protein and fat.

The total saccharide content in the fresh weight of fruits and vegetables rangesfrom about 2% in some pumpkin fruits to above 30% in starchy vegetables. Generallyvegetables contain less than 9% saccharides. The polysaccharides — cellulose andhemicellulose — are largely confined to the cell walls. The di- and monosaccharides— sucrose, glucose, and fructose — are accumulated mainly in the cell sap. Theproportions of the different saccharide constituents can fluctuate due to metabolicactivity of the plant, especially during fruit ripening.

The majority of proteins occurring in fruits and vegetables play enzymatic rolesthat are very important in the physiology and postmortem behavior of the crop. Theprotein content in vegetables is lower than 3%, except in sweet maize (above 4%).In fruits it ranges from below 1% to above 1.5%. They are found mainly in thecytoplasmic layers.


The lipids of fruits and vegetables are, like the proteins, largely confined to thecytoplasmic layers, in which they are especially associated with the surface mem-branes. Their content in fruits and vegetables is always lower than 1%. Lipid andlipid-like fractions are particularly prominent in the protective tissues at the surfacesof plant parts — epidermal and corky layers.

Plant tissues also contain organic acids formed during metabolic processes. Forthis reason fruits and vegetables are normally acidic in reaction. The quantity oforganic acids is different, from very low, about 2 miliequivalents of acid/100 g insweet maize and pod seeds, to very high, up to 40 miliequivalents/100 g in spinach.For the majority of fruits and vegetables the dominant acids are citric acid and malicacid, each of which can, in particular examples, constitute over 2% of the freshweight of the material. Lemons contain over 3% of citric acid. Tartaric acid accu-mulates in grape and oxalic acid in spinach. The fruits in general show a decreasein overall acidity during the ripening process.

The total amount of mineral components in fruits and vegetables is in the rangeof 0.1% (in sweet potatoes) up to about 4.4% (in kohlrabi). The most abundantmineral constituent in fruits and vegetables is potassium (Table 2.4). Generallyvegetables are a better source of minerals than fruits. The mineral elements influencenot only the growth and crop of fruits and vegetables, but also their texture (Ca),color (Fe), and metabolic processes (microelements).

The diversity of form shown by fruit and vegetable structures is extremely wide.Among the vegetables there are representatives of all the recognizable morphologicaldivisions of the plant body — whole shoots, roots, stems, leaves, and fruits.

Fruits may also be classified into a number of structural types. The individualseed-bearing structures of the flower called carpels constitute the gynoecium. Theseed-containing cavity of a carpel is called the ovary, and its wall develops into thepericarp of the fruit. The edible fleshy part of a fruit most commonly develops fromthe ovary wall, but it may be also derived from the enlarged tip of stem from whichfloral organs arise, and sometimes leaf-like structures protecting the flowers mayalso become fleshy, e.g., in pineapple.

TABLE 2.4Mineral Components of Fruits and Vegetables (mg/100 g of Raw Mass)

Component mg Rich Source

KNaCaMgPClSFe

35065

15050

12090802

Parsley (above 1000 mg)CelerySpinach (up to 600 mg)Sweet maizeSeeds and young growing partsCeleryPlants with higher quantity of proteinsParsley (up to 8 mg)

Source: Adapted from Duckworth, R.B., Fruit and Vegetables, Pergamon Press, London, 1966.


The most metabolic activity of plants is carried out in the tissue called paren-chyma, which generally makes up the bulk of the volume of all soft edible plantstructures. The epidermis, which sometimes is replaced by a layer of corky tissue,is structurally modified to protect the surface of the organ. The highly specializedtissues collenchyma and sclerenchyma provide mechanical support for the plant.Water, minerals, and products of metabolism are transported from one part toanother of the plant through the vascular tissues, xylem and phloem, which arethe most characteristic anatomical features of plants on the cross section.

The structure of fruits is dominated by soft parenchymatous tissue, while con-ducting and supporting structures are rather poorly developed. An exception is thepineapple, in which conducting tissues are very prominently represented. The subtlestructure and proportions of individual tissues influence the texture, properties, andsuitability for processing of fruits and vegetables.

REFERENCES

Duckworth, R.B., Fruit and Vegetables, Pergamon Press, London, 1966.Fox, B.A. and Cameron, A.G., Food Science: A Chemical Approach, Hodder and Stoughton,

London, 1986.Hedrick, H.B. et al., Principles of Meat Science, Kendall-Hunt Publishing Co., Dubuque, IA, 1994.Kent, N.L., Technology of Cereals with Special Reference to Wheat, Pergamon Press, Oxford,

1975.Kirk, R.S. and Sawyer, R., Pearson’s Composition and Analysis of Foods, Longman Science,

London, 1991.Lisinska, G. and Leszczynski, W., Potato Science and Technology, Elsevier Applied Science,

London, 1989.Ramsay, I., Honey as a food ingredient, Food Ingredient Process. Int., 10, 16, 1992.Renner, E., Nutritional aspects of cheese, in Cheese: Chemistry, Physics and Microbiology,

Vol. 1, Fox, P.F., Ed., Chapman & Hall, London, 1993, p. 557.Sikorski, Z.E., Seafood Raw Materials, WNT, Warsaw, 1992 (in Polish).Tamime, A.Y. and Robinson, R.K., Yoghurt: Science and Technology, CRC Press, Boca Raton,

FL, 1999.

251-5871-6149-4/02/$0.00+$1.50© 2002 by CRC Press LLC

Water and Food Quality

Barbara Cybulska and Peter Edward Doe

CONTENTS

3.1 Introduction ....................................................................................................253.2 Structure and Properties of Water..................................................................26

3.2.1 Water Molecule ..................................................................................263.2.2 Hydrogen Bonds ................................................................................273.2.3 Properties of Bulk Water ...................................................................283.2.4 Thermal Properties of Water..............................................................323.2.5 Water as a Solvent .............................................................................333.2.6 Water in Biological Materials............................................................36

3.2.6.1 Properties ............................................................................363.2.6.2 Water Transport...................................................................39

3.3 Water in Food.................................................................................................403.3.1 Introduction ........................................................................................403.3.2 Sorption Isotherms and Water Activity .............................................41

3.3.2.1 Principle ..............................................................................413.3.2.2 Measurement of Water Activity..........................................43

3.3.3 Water Activity and Shelf Life of Foods ............................................443.4 Water Supply, Quality, and Disposal .............................................................45

3.4.1 Water Supply......................................................................................453.4.2 Water Quality .....................................................................................45

3.4.2.1 Standards and Treatment ....................................................453.4.2.2 Water Pollution ...................................................................47

3.4.3 Wastewater Treatment and Disposal..................................................48References................................................................................................................49

3.1 INTRODUCTION

Water is the most popular and most important chemical compound on our planet. Itis a major chemical constituent of Earth’s surface, and it is the only substance thatis abundant in solid, liquid, and gaseous form. Because it is ubiquitous, it seems tobe a mild and inert substance. In fact, it is a very reactive compound characterizedby unique physical and chemical properties that make it very different from otherpopular liquids. The peculiar water properties determine the nature of the physicaland biological world.

3


Water is the major component of all living organisms. It constitutes 60% or moreof the weight of most living things, and it pervades all portions of every cell. Itexisted on our planet long before the appearance of any form of life. The evolutionof life was doubtlessly shaped by physical and chemical properties of the aqueousenvironment. All aspects of living cells’ structure and function seem to be adaptedto water-unique properties.

Water is the universal solvent and dispersing agent, as well as a very reactivechemical compound. Biologically active structures of biomacromolecules are spon-taneously formed only in aqueous media. Intracellular water is not only a mediumin which structural arrangement and all metabolic processes occur, but an activepartner of molecular interactions, participating directly in many biochemical reac-tions as a substrate or a product. Its high heat capacity allows water to act as a heatbuffer in all organisms. Regulation of water contents is important in the maintenanceof homeostasis in all living systems.

Only 0.003% of all sweet water reserve participates in its continuous circulationbetween the atmosphere and the hydrosphere. The remaining part is confined in theAntarctic ice. The geography of water availability has determined, to a large degree,the vegetation, food supply, and habitation in the various areas of the world. Forexample, Bangladesh has one of the world’s highest population densities — madepossible through the regular flooding of the Ganges River and the rich slits it depositsin its wake. In Bangladesh, the staple food — rice — grows abundantly and is readilydistributed. In other societies the food must be transported long distances or keptover winter. Stability, wholesomeness, and shelf life are significant features of suchfoods. These features are, to a large degree, influenced by the water content of thefood. Dried foods were originally developed to overcome the constraints of timeand distance before consumption. Canned and frozen foods were developed next.The physical properties, quantity, and quality of water within food have a strongimpact on food effectiveness, quality attributes, shelf life, textural properties, andprocessing.

3.2 STRUCTURE AND PROPERTIES OF WATER

3.2.1 WATER MOLECULE

Water is a familiar material, but it has been described as the most anomalous ofchemical compounds. Although its chemical composition, HOH or H2O, is univer-sally known, the simplicity of its formula belies the complexity of its behavior. Itsphysical and chemical properties are very different from compounds of similarcomplexity, such as HF and H2S. To understand the reasons for water’s unusualproperties, it is necessary to examine its molecular structure in some detail.

Although a water molecule is electrically neutral as a whole, it has a dipolarcharacter. The high polarity of water is caused by the direction of the H–O–H bondangle, which is 104.5°, and by an asymmetrical distribution of electrons within themolecule. In a single water molecule, each hydrogen atom shares an electron pairwith the oxygen atom in a stable covalent bond. However, the sharing of electronsbetween H and O is unequal, because the more electronegative oxygen atom tends

Water and Food Quality 27

to draw electrons away from the hydrogen nuclei. The electrons are more often inthe vicinity of the oxygen atom than of the hydrogen atom. The result of this unequalelectron sharing is the existence of two electric dipoles in the molecule, one alongeach of the H–O bonds. The oxygen atom bears a partial negative charge δ–, andeach hydrogen a partial positive charge δ+. Since the molecule is not linear, H–O–Hhas a dipole moment (Figure 3.1). Because of this, water molecules can interactthrough electrostatic attraction between the oxygen atom of one water molecule andthe hydrogen of another.

3.2.2 HYDROGEN BONDS

Such interactions, which arise because the electrons on one molecule can be partiallyshared with the hydrogen on another, are known as hydrogen bonds. The H2Omolecule, which contains two hydrogen atoms and one oxygen atom in a nonlineararrangement, is ideally suited to engage in hydrogen bonding. It can act both as adonor and as an acceptor of hydrogens. The nearly tetrahedral arrangement of theorbital about the oxygen atom allows each water molecule to form hydrogen bondswith four of its neighbors (Figure 3.2).

An individual, isolated hydrogen bond is very labile. It is longer and weakerthan a covalent O–H bond (Figure 3.3). The hydrogen bond’s energy, i.e., theenergy required to break the bond, is about 20 kJ/mol. These bonds are interme-diate between those of weak van der Waals interactions (about 1.2 kJ/mol) andthose of covalent bonds (460 kJ/mol). Hydrogen bonds are highly directional;they are stronger when the hydrogen and the two atoms that share it are in astraight line (Figure 3.4).

Hydrogen bonds are not unique to water. They are formed between water anddifferent chemical structures, as well as between other molecules or even withina molecule. They are formed wherever an electronegative atom (oxygen or nitro-gen) comes in close proximity to a hydrogen covalently bonded to another elec-tronegative atom. Some representative hydrogen bonds of biological importanceare shown in Figure 3.5.

FIGURE 3.1 Water molecule as an electric dipole.


Intra- and intermolecular hydrogen bonding occurs extensively in biologicalmacromolecules. A large number of the hydrogen bonds and its directionality confersvery precise three-dimensional structures upon proteins and nucleic acids.

3.2.3 PROPERTIES OF BULK WATER

The key to understanding water structure in solid and liquid form lies in the conceptand nature of the hydrogen bonds. In the crystal of ordinary hexagonal ice(Figure 3.6), each molecule forms four hydrogen bonds with its nearest neighbors.

FIGURE 3.2 Tetrahedral hydrogen bonding of five water molecules.

FIGURE 3.3 Two water molecules connected by hydrogen bonds.

Hydrogen bond0.177 nm

Covalent bond0.0965


Each HOH acts as a hydrogen donor to two of the four water molecules and as ahydrogen acceptor for the remaining two. These four hydrogen bonds are spatiallyarranged according to the tetrahedral symmetry.

The crystal lattice of ice occupies more space than the same number of H2Omolecules in liquid water. The density of solid water is thus less than that of liquidwater, whereas simple logic would have the more tightly bound solid structure more

FIGURE 3.4 Directionality of the hydrogen bonds.

FIGURE 3.5 Some hydrogen bonds of biological importance.


dense than its liquid. One explanation for ice being lighter than water at 0°C proposesa reforming of intermolecular bonds as ice melts so that, on average, a water moleculeis bound to more than four of its neighbors, thus increasing its density. But as thetemperature of liquid water increases, the intermolecular distances also increase,giving a lower density. These two opposite effects explain the fact that liquid waterhas a maximum density at a temperature of 4°C. At any given instant in liquid waterat room temperature, each water molecule forms hydrogen bonds with an averageof 3.4 other water molecules (Lehninger et al., 1993). The average translational androtational kinetic energies of a water molecule are approximately 7 kJ/mol, the sameorder as that required to break hydrogen bonds; therefore, hydrogen bonds are in acontinuous state of flux, breaking and reforming with high frequency on a picosecondtime scale. A similar dynamic process occur in aqueous media with substances thatare capable of forming hydrogen bonds.

At 100°C liquid water still contains a significant number of hydrogen bonds,and even in water vapor there is strong attraction between water molecules. Thevery large number of hydrogen bonds between molecules confers great internalcohesion on liquid water. This feature provides a logical explanation for many ofits unusual properties. For example, its large values for heat capacity, melting point,boiling point, surface tension, and heat of various phase transitions are all relatedto the extra energy needed to brake intermolecular hydrogen bonds.

That liquid water has structure is an old and well-accepted idea; however, thereis no consensus among physical chemists as to the molecular architecture of thehydrogen bond’s network in the liquid state. The available measurements on liquidwater do not lead to a clear picture of liquid water structure. It seems that the majority

FIGURE 3.6 Structure of ice.


of hydrogen bonds survive the melting process, but obviously rearrangement ofmolecules occurs. The replacement of crystal rigidity by fluidity gives moleculesmore freedom to diffuse about and to change their orientation. Any molecular theoryfor liquid water must take into account changes in the topology and geometry ofthe hydrogen bond network induced by the melting process.

Many models have been proposed, but none has adequately explained all prop-erties of liquid water. “Iceberg” models postulated that liquid water contains dis-connected fragments of ice suspended in a sea of unbounded water molecules.

The most popular, the so-called “flickering clusters” model, suggests that liquidwater is highly organized on a local basis: the hydrogen bonds break and reformspontaneously, creating and destroying transient structural domains (Figure 3.7).However, because the half-life of any hydrogen bond is less than a nanosecond,the existence of these clusters has statistical validity only; even this has beenquestioned by some authors who consider water to be a continuous polymer.

Experimental evidence obtained by x-ray and neutron diffractions strongly sup-port the persistence of a tetrahedral hydrogen bond order in the liquid water, butwith substantial disorder present.

Stillinger (1980) created a qualitatively water-like structure by computer simu-lation. The view that emerges from these results is the following: liquid water consistsof a macroscopically connected, random network of hydrogen bonds. This networkhas a local preference for tetrahedral geometry, but it contains a large proportion ofstrained and broken bonds that are continually undergoing topological reformation.The properties of water arise from the competition between relatively bulky ways

FIGURE 3.7 “Flickering clusters” of H2O molecules in bulk water.


of connecting molecules into local patterns characterized by strong bonds and nearlytetrahedral angles and more compact arrangements characterized by more strain andbond breakage.

According to the model proposed by Wiggins (1990), two types of waterstructure can be distinguished: high-density water and low-density water. In densewater the bent, relatively weak hydrogen bonds predominate over straight, stron-ger ones. Low-density water has many ice-like straight hydrogen bonds. Althoughhydrogen bonding is still continuous through the liquid, the weakness of thebonds allows the structure to be disrupted by thermal energy extremely rapidly.High-density water is extremely reactive and more liquid, whereas low-densitywater is inert and more viscous. A continuous spectrum of water structuresbetween these two extremes could be imagined. The strength of water–waterhydrogen bonding, which is the source of water density and reactivity, has greatfunctional significance; this explains solvent water’s properties and its role inmany biological events.

A common feature of all theories is that a definite structure of liquid water isdue to the hydrogen bonding between molecules and that the structure is in thedynamic state as the hydrogen bonds break and reform with high frequency.

3.2.4 THERMAL PROPERTIES OF WATER

The unusually high melting point of ice, as well as the heat of water vaporizationand specific heat, is related to the ability of water molecules to form hydrogen bondsand to the strength of these bonds.

A large amount of energy, in the form of heat, is required to disrupt the hydrogen-bonded lattice of ice. In the common form of ice, each water molecule participatesin four hydrogen bonds. When ice melts, most of the hydrogen bonds are retainedby liquid water, but the pattern of hydrogen bonding is irregular, due to the frequentfluctuation. The average energy required to break each hydrogen bond in ice hasbeen estimated to be 23 kJ/mol, while that to break each hydrogen bond in water isless than 20 kJ/mol (Ruan and Chen, 1998).

The heat of water vaporization is much higher than that of many other liquids.As is the case with melting ice, a large amount of thermal energy is required forbreaking hydrogen bonds in liquid water, to permit water molecules to dissociatefrom one another and to enter the gas phase. Perspiration is an effective mecha-nism of decreasing body temperature because the evaporation of water absorbsso much heat.

A relatively large amount of heat is required to raise the temperature of 1 g ofwater by 1°C because multiple hydrogen bonds must be broken in order to increasethe kinetic energy of the water molecules. Due to the high quantity of water in thecells of all organisms, temperature fluctuation within cells is minimized. This featureis of critical biological importance, since most biochemical reactions and macromo-lecular structures are sensitive to temperature. The unusual thermal properties ofwater make it a suitable environment for living organisms, as well as an excellentmedium for the chemical processes of life.


3.2.5 WATER AS A SOLVENT

Many molecular parameters, such as ionization, molecular and electronic structure,size, and stereochemistry, will influence the basic interaction between a solute and asolvent. The addition of any substance to water results in altered properties for thissubstance and for water itself. Solutes cause a change in water properties becausethe hydrate envelopes that are formed around dissolved molecules are more organizedand therefore more stable than the flickering clusters of free water. The properties ofsolutions that depend on solute and its concentration are different from those of purewater. The differences can be seen in such phenomena as the freezing point depres-sion, boiling point elevation, and increased osmotic pressure of solutions.

The polar nature of the water molecule and the ability to form hydrogen bondsdetermine its properties as a solvent. Water is a good solvent for charged or polarcompounds and a relatively poor solvent for hydrocarbons. Hydrophilic compoundsinteract strongly with water by an ion–dipole or dipole–dipole mechanism, causingchanges in water structure and mobility and in the structure and reactivity of thesolutes. The interaction of water with various solutes is referred to as hydration. Theextent and tenacity of hydration depends on a number of factors, including the natureof the solute, salt composition of the medium, pH, and temperature.

Water dissolves dissociable solutes readily, because the polar water moleculesorient themselves around ions and partially neutralize ionic charges. As a result, thepositive and negative ions can exist as separate entities in a dilute aqueous solutionwithout forming ion pairs. Sodium chloride is an example where the electrostaticattraction of Na+ and Cl– is overcome by the attraction of Na+ with the negativecharge on the oxygens and Cl– with the positive charge on the hydrogen ions(Figure 3.8). The number of weak charge–charge interactions between water and theNa+ and Cl– ions is sufficient to separate the two charged ions from the crystal lattice.

To acquire their stabilizing hydration shell, ions must compete with watermolecules, which need to make as many hydrogen bonds with one another aspossible. The normal structure of pure water is disrupted in solution of dissociablesolutes. The ability of a given ion to alter the net structure of water is dependenton the strength of its electric field. Among ions of a given charge type (e.g., Na+

and K+ or Mg+2 and Ca+2), the smaller ions are more strongly hydrated than thelarger ions, in which the charge is dispersed over a greater surface area. Most

FIGURE 3.8 Hydration shell around Na+ and Cl–.


cations, except the largest ones, have a primary hydration sphere containing fourto six molecules of water. Other water molecules, more distant from the ion, areheld in a looser secondary sphere. The electrochemical transfer experiments indi-cate a total of 16 molecules of water around Na+ and about 10 around K+. Thebound water is less mobile and more dense than HOH molecules in the bulk water.At some distance, the bonding arrangements melt into a dynamic configuration ofpure water.

Water is especially effective in screening the electrostatic interaction betweendissolved ions, because, according to Coulomb’s law, the force (F) between twocharges q+ and q– separated by a distance r is given as:

F = q+ · q–/εr2 (3.1)

where ε is the dielectric constant of the medium. For a vacuum, ε = 1 Debye unit,whereas for bulk water, ε = 80; this implies that the energies associated withelectrostatic interactions in aqueous media are approximately 100 times smaller thanthe energies of covalent association, but increase considerably in the interior of aprotein molecule.

In thermodynamic terms, the free energy change, ∆G, must have a negative valuefor a process to occur spontaneously.

∆G = ∆H – T∆S (3.2)

where ∆G represents the driving force, ∆H (the enthalpy change) is the energyfrom making and breaking bonds, and ∆S (the entropy change) is the increase inrandomness.

Solubilization of a salt occurs with a favorable change in free energy. As saltsuch as NaCl dissolves, the Na+ and Cl– ions leaving the crystal lattice acquire greaterfreedom of motion. The entropy (∆S) of the system increases; where ∆H has a smallpositive value and T∆S is large and positive, ∆G is negative.

Water in the multilayer environment of ions is believed to exist in a structurallydisrupted state because of conflicting structural influences of the innermost vicinalwater and the outermost bulk-phase water. In concentrated salt solutions, the bulk-phase water would be eliminated, and the water structure common in the vicinityof ions would predominate. Small or multivalent ions, such as Li+, Na+, H3O+, Ca+2,Mg+2, F–, SO4

–2, and PO4–3, which have strong electric fields, are classified as water

structure formers because solutions containing these ions are less fluid than purewater. Ions that are large and monovalent, most of the negatively charged ions andlarge positive ions, such as K+, Rb+, Cs+, NH4

+, Cl–, Br–, I–, NO–3, ClO4, and CNS–,

disrupt the normal structure of water; they are structure breakers. Solutions contain-ing these ions are more fluid than pure water (Fennema, 1985).

Through their varying abilities to hydrate and to alter water structure and itsdielectric constant, ions influence all kinds of water solute interactions. The confor-mation of macromolecules and the stability of colloids are greatly affected by thekinds and concentrations of ions present in the medium.


Water is a good solvent for most biomolecules, which are generally charged orpolar compounds. Solubilization of compounds with functional groups such asionized carboxylic acids (COO–), protonated amines (NH3

+), phosphate esters, oranhydrides is also a result of hydration and charge screening.

Uncharged but polar compounds possessing hydrogen bonding capabilities arealso readily dissolved in water, due to the formation of hydrogen bonds with watermolecules. Every group that is capable of forming a hydrogen bond to anotherorganic group is also able to form hydrogen bonds of similar strength with water.Hydrogen bonding of water occurs with neutral compounds containing hydroxyl,amino, carbonyl, amide, or imine groups. Saccharides dissolve readily in water, dueto the formation of many hydrogen bonds between the hydroxyl groups or carbonyloxygen of the saccharide and water molecules. Water–solute hydrogen bonds areweaker than ion–water interactions. Hydrogen bonding between water and polarsolutes also causes some ordering of water molecules, but the effect is less significantthan with ionic or nonpolar solutes.

The introduction into water of hydrophobic substances such as hydrocarbons,rare gases, and the apolar groups of fatty acids, amino acids, or proteins is thermo-dynamically unfavorable because of the decrease in entropy. The decrease in entropyarises from the increase in water–water hydrogen bonding adjacent to apolar entities.Water molecules in the immediate vicinity of a nonpolar solute are constrained intheir possible orientations, resulting in a shell of highly ordered water moleculesaround each nonpolar solute molecule (Figure 3.9a). The number of water moleculesin the highly ordered shell is proportional to the surface area of hydrophobic solute.In the case of dissolved hydrocarbons, the enthalpy of formation of the new hydrogenbonds often almost exactly balances the enthalpy of creation in water, a cavity of

FIGURE 3.9 Cage-like water structure around the hydrophobic alkyl chain (a) and hydro-phobic interactions (b).

Hydrophylic"head group"

(a) (b)


the right size to accommodate the hydrophobic molecule. However, the restrictionof water mobility results in a very large decrease in entropy. According to

∆G = ∆H – T∆S (3.3)

if ∆H is almost zero and ∆S is negative, ∆G is positive.To minimize contact with water, hydrophobic groups tend to aggregate; this

process is known as hydrophobic interaction (Figure 3.9b). The existence of hydro-phobic substances barely soluble in water but readily soluble in many nonpolarsolvents, and their tendency to segregate in aqueous media, has been known for along time. However, the origin of this hydrophobic effect is still somewhat contro-versial. The plausible explanation is that hydrophobic molecules disturb the hydro-gen bonded state of water, without having any compensatory ordering effects. Apolarmolecules are water structure formers: water molecules cannot use all four possiblehydrogen bonds when in contact with hydrophobic, water-hating molecules. Thisrestriction results in a loss of entropy, a gain in density, and increased organizationof bulk water.

Amphipathic molecules, i.e., compounds containing both polar or chargedgroups and apolar regions, disperse in water if the attraction of the polar group forwater can overcome possible hydrophobic interactions of the apolar portions of themolecules. Many biomolecules are amphipathics: proteins, phospholipids, sterols,certain vitamins, and pigments have polar and nonpolar regions. When amphipathiccompounds are in contact with water, the two regions of the solute molecule expe-rience conflicting tendencies: the polar or charged hydrophilic regions interact favor-ably with water and tend to dissolve, but the nonpolar hydrophobic regions tend toavoid contact with water. The nonpolar regions of the molecules cluster together topresent the smallest hydrophobic area to the aqueous medium, and the polar regionsare arranged to maximize their interactions with the aqueous solvent. In aqueousmedia, many amphipathic compounds are able to form stable structures, containinghundreds to thousands of molecules, called micelles. The forces that held the non-polar regions of the molecules together are due to hydrophobic interactions.

The hydrophobic effect is a driving force in the formation of clathrate hydratesand the self-assembly of lipid bilayers. Hydrophobic interactions between lipids andproteins are the most important determinants of biological membrane structure. Thethree-dimensional folding pattern of proteins is also determined by hydrophobicinteractions between nonpolar side chains of amino acid residues.

3.2.6 WATER IN BIOLOGICAL MATERIALS

3.2.6.1 Properties

Water behaves differently in different environments. Properties of water in hetero-genous systems such as living cells or food remain a field of debate. Water moleculesmay interact with macromolecular components and supramolecular structures ofbiological systems through hydrogen bonds and electrostatic interactions. Solvationof biomolecules such as lipids, proteins, nucleic acids, or saccharides resulting fromthese interactions determines their molecular structure and function.


Various physical techniques, i.e., nuclear magnetic resonance (NMR), x-raydiffraction, and chemical probes (exchange of H by D), indicate that there is a layerof water bound to protein molecules, phospholipid bilayers, and nucleic acids, aswell as at the surface of the cell membranes and other organelles.

Water associated at the interfaces and with macromolecular components mayhave quite different properties from those in the bulk phase. Water can be expectedto form locally ordered structures at the surface of water-soluble, as well as water-insoluble, macromolecules and at the boundaries of the cellular organelles. Bio-macromolecules generally have many ionized and polar groups on their surfaces andtend to align near polar water molecules. This ordering effect exerted by the mac-romolecular surface extends quite far into the surrounding medium.

According to the association–induction theory proposed by Ling (1962), fixedcharges on macromolecules and their associated counterions constrain water mole-cules to form a matrix of polarized multilayers having restricted motion, comparedwith pure water. The monolayer of water molecules absorbed on the polar sorptionsite of the molecule is almost immobilized and thus behaves, in many respects, likepart of the solid or like water in ice. It has different properties than additional waterlayers defined as multilayers have. The association–induction theory has been sharedby many researchers for many years. Unfortunately, elucidation of the nature ofindividual layers of water molecules has been less successful, due to the complexityof the system and lack of appropriate techniques.

Measurements of the diffusion coefficients of globular protein molecules insolution yield values for molecular size that are greater than the corresponding radiidetermined by x-ray crystallography. The apparent hydrodynamic radius can becalculated from the Stokes–Einstein relation:

D = kBT/6πηaH (3.4)

where D is the diffusion coefficient, kB is the Boltzman constant, T is the temperature,η is the solution viscosity, and aH is the molecule radius (Nossal and Lecar, 1991).

Similarly, studies utilizing NMR techniques show that there is a species ofassociated water that has a different character than water in the bulk phase. By theseand other methods it was found that, for a wide range of protein molecules, approx-imately 0.25–0.45 g of H2O is associated with each gram of protein.

The hydration forces can stabilize macromolecular association or prevent mac-romolecular interactions with a strength that depends on the surface characteristicof the molecules and the ionic composition of the medium.

The interaction between a solute and a solid phase is also influenced by water.Hydration shells or icebergs associated with one or the other phase are destroyedor created in this interaction and often contribute to conformational changes inmacromolecular structures — and ultimately to changes in biological and functionalproperties important in food processing.

Biophysical processes involving membrane transport are also influenced byhydration. The size of the hydration shell surrounding small ions and the presenceof water in the cavities of ionic channels or in the defects between membrane lipidsstrongly affect the rates at which the ions cross a cell membrane.


The idea that intracellular water exhibits properties different from those of bulkwater has been around for a long time. The uniqueness of the cytoplamic water wasdeduced from:

• The observation that cells may be cooled far below the freezing point ofa salt solution iso-osmotic with that of the cytoplasm.

• Properties of the cytoplasm, which in the same conditions should bindwater like a gel.

• Osmotic experiments in which it has often been observed that part of cellwater is not available as a solvent. This water has been described asosmotically inactive water, bound water, or compartmentalized water.

According to a recent view, three different kinds of intracellular water can bedistinguished: a percentage of the total cell water appears in the form of usual liquidwater. A relevant part is made up of water molecules that are bound to different sitesof macromolecules in the form of hydration water, while a sizeable amount, althoughnot fixed to any definite molecular site, is strongly affected by macromolecular fields.This kind of water has been termed vicinal water. Most of the vicinal water surroundsthe elements of the cell cytoskeleton. Vicinal water has been extensively investigated,and it has been found that some of its properties are different from those of normalwater. It does not have a unique freezing temperature, but an interval ranging from–70 to –50°C; it is a very bad solvent for electrolytes, but nonelectrolytes have thesame solubility properties in it as in usual water; its viscosity is enhanced, and itsNMR response is anomalous (Giudice et al., 1986).

The distribution of various types of water inside the living cells is a questionthat cannot be answered yet, especially because in many cells marked changes havebeen noted in the state of intracellular water as a result of biological activity. Thepossibility that water in living cells may differ structurally from bulk water hasincited a search for parameters of cell water that deviate numerically from those ofbulk water.

The diffusion coefficient for water in the cytoplasm of various cells has beendetermined with a satisfactory precision. It has been found that the movement ofwater molecules inside living cells is not much different and is reduced by a factorof between 2 and 6, compared with the self-diffusion coefficient for pure water.According to Mild and Løvtrup (1985), the most likely explanation of the observedvalues is that part of the cytoplasmic water, the vicinal water close to the varioussurface structures in the cytoplasm, is structurally changed to the extent that its rateof motion is significantly reduced, compared with the bulk phase.

In heterogenous biological materials and foods, water exists in different states.It is thought that water molecules in different states function differently.

Water associated with proteins and other macromolecules has traditionally beenreferred to as bound water. However, to designate such water as bound can bemisleading because, for the most part, the water molecules are probably only tran-siently associated, and at least a portion of the associated water has to be constantlyrearranged, due to the thermal perturbations of weak hydrogen bonds.


Water molecules are constantly in motion, even in ice. In fact, the translationaland rotational mobility of water directly determines its availability. Water mobilitycan be measured by a number of physical methods, including NMR, dielectricrelaxation, ESR, and thermal analysis (Chinachoti, 1993). The mobility of watermolecules in biological systems may play an important role in a biochemicalreaction’s equilibrium and kinetics, formation and preservation of chemical gra-dients and osmotic pressure, and macromolecular conformation. In food systems,the mobility of water may influence the engineering processes — such as freezing,drying, and concentrating chemical and microbial activities, and textural attributes(Ruan and Chen, 1998).

3.2.6.2 Water Transport

Water transport is associated with various physiological processes in whole livingorganisms and single cells.

When cells are exposed to hyper- or hypo-osmotic solutions, they immediatelylose or gain water, respectively. Even in an isotonic medium a continuous exchangeof water occurs between living cells and their surroundings. Most cells are so smalland their membrane so leaky that the exchange of water molecules measured withisotopic water reaches equilibrium in a few milliseconds.

The degree of water permeability differs considerably between tissues and celltypes. Mammalian red blood cells and renal proximal tubules are extremely perme-able to water molecules. Transmembrane water movements are involved in diversephysiological secretion processes.

How water passes through cells has begun to come clear only in the last fiveyears. Water permeates living membranes through both the lipid bilayer andspecific water transport proteins. In both cases water flow is passive and directedby osmosis. Water transport in living cells is therefore under the control of ATPand ion pumps.

The most general water transport mechanism is diffusion through lipidbilayers, with a permeability coefficient of 2–5 × 10-4 cm/sec. The diffusionthrough lipid bilayers depends on lipid structure and the presence of sterol(Subczynski et al., 1994). It is suggested that the lateral diffusion of the lipidmolecules and the water diffusion through the membrane is a single process(Haines, 1994).

A small amount of water is transported through certain membrane transportproteins, such as a glucose transporter or the anion channel of erythrocytes.

The major volume of water passes through water transport proteins. The firstisolated water transporting protein was the channel-forming integral protein fromred blood cells. The identification of this protein has led to the recognition of afamily of related water-selective channels, the aquaporins, that are found in animals,plants, and microbial organisms. Water flow through the protein channel is controlledby the number of protein copies in the membrane. In red blood cells, there are200,000 copies/cell; in apical brush border cells of renal tubules, it constitutes 4%of the total protein (Engel et al., 1994).


3.3 WATER IN FOOD

3.3.1 INTRODUCTION

Water, with a density of 1000 kg m-3, is denser than the oil components of foods;oils and fats typically have densities in the range 850–950 kg m-3. Glycerols andsugar solutions are denser than water.

Unlike the solid phase of most other liquids, ice is less dense than liquid water;ice has lower thermal conductivity than water. These properties have an effect onthe freezing of foods that are predominantly water based; the formation of an icelayer on the surface of liquids and the outside of solids has the effect of slowingdown the freezing rate.

Because a molecule of water vapor is lighter (molecular weight = 18) than thatof dry air (molecular weight = about 29), moist air is lighter than dry air at the sametemperature. This is somewhat unexpected, because the popular conception is thathumid air (which contains more water) is heavier than dry air.

At room temperature, water has the highest specific heat of any inorganic ororganic compound, with the sole exception of ammonia. It is interesting to spec-ulate why the most commonly occurring substance on this planet should have oneof the highest specific heats. One of the consequences of this peculiarity in thefood industry is that heating and cooling operations for essentially water-basedfoods are more energy demanding. To heat a kilogram of water from 20 to 50°Crequires about 125 kJ of energy, whereas heating the same mass of vegetable oilrequires only 44 kJ.

A sponge holds most of its water as liquid held in the intestacies of the spongestructure. Most of the water can be wrung out of the sponge, leaving a matrix of airand damp fibers. Within the sponge fibers the residual water is more tenuously held— absorbed within the fiber of the sponge.

If the sponge is left to dry in the sun, this adsorbed water will evaporate, leavingonly a small proportion of water bound chemically to the salts and to the celluloseof the sponge fibers. Like water in sponge, water is held in food by various physicaland chemical mechanisms (Table 3.1). It is a convenient oversimplification to dis-tinguish between “free” and “bound” water. The definition of bound water in sucha classification poses problems. Fennema (1985) reports seven different definitionsof bound water. Some of these definitions are based on the freezability of the “bound”component, and others rely on its availability as a solvent. He prefers a definitionin which bound water is “that which exists in the vicinity of solutes and other non-aqueous constituents, exhibits reduced molecular activity and other significantlyaltered properties as compared with ‘bulk water’ in the same system, and does notfreeze at –40°C.”

The moisture content can be measured simply by weighing a sample and thenoven drying it, usually at 105°C overnight; the difference in mass is the moisturecontent in the original sample. However, much confusion is caused by reporting themoisture content simply as a percentage without specifying the basis of the calcu-lation. It should be made clear whether the moisture content is calculated on a wetbasis (moisture content divided by original mass) or on a dry basis (moisture content


divided by the “bone dry” or “oven dry” mass). Even the term bone dry mass cancause confusion among non-English speakers; it was once misinterpreted as the“mass of the dry bones.” For example, in foods containing significant quantities offat or salt, the moisture content may be calculated as the mass of water in a sampledivided by the dry solids that are not salt or fat; in this case, the moisture contentshould be reported as calculated on a salt-free, fat-free, dry basis.

3.3.2 SORPTION ISOTHERMS AND WATER ACTIVITY

3.3.2.1 Principle

Since 1929 it has been recognized that the chemical and microbial stability, and thusthe shelf life, of foods is not directly related to its moisture content, but to a propertycalled water activity (Tomkins, 1929). Essentially, water activity is a measure of thedegree to which water is bound within the food, and thus unavailable for furtherchemical or microbial activity.

Water activity is defined as the ratio of the partial pressure of water vapor in oraround food to that of pure water at the same temperature. Relative humidity of moistair is defined in the same way, except that by convention, relative humidity is reportedas a percentage, whereas water activity is expressed as a fraction. Thus if a sampleof meat sausage is sealed within an airtight container, the humidity of the air in theheadspace will rise and eventually equilibrate to a relative humidity of say 83%,which means that the water activity (aw) of the meat sausage is 0.83.

The relationship between water activity and moisture content for most foods ata particular temperature is a sigmoidal-shaped curve called the sorption isotherm(Figure 3.10). The term equilibrium moisture content curve is also used. Sorption

TABLE 3.1Classification of Water States in Foods

Class of Water Description

Porportion of Typical 90% (Wet Basis) Moisture Content Food

Constitutional An integral part of nonaqueous constituent <0.03%Vicinal Bound water that strongly acts with specific

hydrophilic sites of nonaqueous constituents to form a monolayer coverage; water–ion and water–dipole bonds

0.1–0.9%

Multilayer Bound water that forms several additional layers around hydrophilic groups; water–water and water–solute hydrogen bonds

1–5%

Free Flow is unimpeded; properties close to those of dilute salt solutions; water–water bonds predominate

5% to about 96%

Entrapped Free water held within matrix or gel that impedes flow

5% to about 96%


isotherms at different temperatures can be calculated using the Clausius–Clapeyronequation from classical thermodynamics:

(3.5)

where aw is the water activity, T is the absolute temperature, ∆H is the heat of sorption,and R is the gas constant.

A complication arises from one of the methods of measuring sorption isothermsfor food. Food that has previously been dried and then is rehydrated will have adifferent sorption isotherm (adsorption isotherm) from that which is in the processof drying (desorption isotherm). This difference is due to a change in water-bindingcapacity in foods that have been previously dried.

Many mathematical descriptors for sorption isotherms have been proposed. Oneof the more famous is that of Brunauer et al. (1938), the B.E.T. isotherm, which isbased on the concept of a measurable amount of monomolecular layer (vicinal)water for a particular food. Wolf et al. (1985) compiled 2201 references on sorptionisotherm data for foods. An example of the type, detail, and accuracy of sorptionisotherm data available in the literature is presented in Table 3.2.

Iglesias et al. (1975) proposed the following three-parameter equation to fitsorption isotherm data for a range of foods:

aw = exp(–a' θr)

where a' and r are the parameters listed in Table 3.2, and θ = X/Xm.

FIGURE 3.10 A typical sorption isotherm for food.

Desorption

Adsorption

Water activity

Moi

stur

e co

nten

t (dr

y ba

sis)

0.2 0.4 0.6 0.8 1.0

4.0

3.0

2.0

1.0

d awln( )d 1 T⁄( )------------------- ∆H

R--------=


X is the equilibrium moisture content and Xm, in units of g/100 g dry basis, is the B.E.T.monomolecular moisture content for the food listed in Table 3.2. However, there arenearly as many equations to sorption isotherms as there are researchers in this field.

3.3.2.2 Measurement of Water Activity

Many methods of measuring water activity have been developed by researchers.These include direct vapor pressure measurement, equilibration with a stable hygro-scopic substance that has a known sorption behavior, and various types of hygrom-eters (Doe, 1998).

Water activity is most conveniently measured by the measurement of relativehumidity in the headspace over a food sample in a sealed container. Commerciallyavailable instruments for water activity determination use various methods formeasuring the relative humidity: hair hygrometer (Lluft), electrical hygrometer(Nova Sina), and dew point temperature (Aqualab). The hygrometer-based instru-ments are prone to drift and must be calibrated regularly against saturated solutionsof various inorganic salts. Hygrometer-based instruments are also prone to hys-teresis at high humidities.

The Aqualab CX2 water activity meter (Decagon Devices Inc., Pullman, WA)detects water condensation on a chilled mirror (dew point temperature). The instru-ment is sensitive to water activity units of <0.001. Readings take 5 min or less andare accurate to ±0.003 water activity units.

Care must be taken with any measurement of water activity to ensure that the sampleis representative of the food under test. Dried fish, for example, will have moisture andsalt contents, and thus water activity, varying widely from thin, exposed flesh to therelatively moist interior. If the worst-case scenario for the growth of potentially toxic orspoilage organisms is of interest, the sample of flesh for water activity determinationshould be excised from the thickest, most moist region of the fish.

TABLE 3.2Sorption Isotherm Data for Cod and Corn

ProductTemperature

(°C) Xm r a'

Coda 30 7.68 1.2398 1.3490Cornb 4.5 8.30 2.2345 1.9748

15.5 7.68 2.4862 2.094930 7.30 2.5663 1.795038 6.35 2.3711 1.861850 6.89 2.1203 1.593660 5.11 2.2185 1.7430

a Adsorption, after Jason (1958).b Desorption, after Chen and Clayton (1971).

Source: From Iglesias, H.A. et al., J. Food Technol., 10, 289, 1975.


3.3.3 WATER ACTIVITY AND SHELF LIFE OF FOODS

Many of the chemical and biological processes that cause deterioration of foods —and ultimately spoilage — are water dependent. Microbial growth is directly linkedto water activity. No microbes can multiply at a water activity below 0.6. Dehydrationis arguably the oldest form of food preservation; the sun drying of meat and fishhas been traced to the beginning of recorded history. Drying relies on removingwater, thus making it unavailable for microbial growth.

Salting or curing has the same effect. A saturated solution of common salt hasa water activity of close to 0.75. Thus, by adding sufficient salt to foods, the wateractivity can be lowered to a level where most pathogenic bacteria are inactivated,but the moisture content remains high.

Intermediate moisture content foods (IMFs) such as pet food and continentalsausages rely on fats and water-binding humectants such as glycerol to lower wateractivity. Fat, which is essentially hydrophobic, does not bind water, but acts as afiller for IMFs to increase the volume of the product.

The effect of several humectants is for each to sequester an amount of waterindependently of the other humectants that may be present in the food. Each thuslowers the water activity of the system according to the equation of Ross (1975):

awn = aw0 · a w1 · a w2 · a w3 · etc.

where awn is the water activity of the complex food system, and a w0 etc. are the wateractivities associated with each component of the system.

For example, the water activity of a food with a moisture content of 77% (wetbasis) and a salt content of 3% (wet basis) can be calculated as follows: 100 g ofthe food comprises 77 g of water, 20 g of bone dry matter, and 3 g of salt. Thecontribution to the water activity due to the salt can be calculated (according toRaoult’s law of dilute solutions), using the molecular weights of water (18) and salt(58.5), as:

a w1 = (77 × 18)/(77 × 18 + 3 × 58.5) = 0.89

The water activity for the salt-free solid matter of the food is found from itssorption isotherm at that moisture content, e.g., a w0 = 0.90. Thus the water activityof the salted food is:

a wn = a w0 · a w1 = 0.9 × 0.89 = 0.8

None of the dangerous pathogenic bacteria associated with food, such asClostridium or Vibrio spp., which cause botulism and cholera, can multiply at wateractivity values below about 0.9. Thus drying or providing sufficient water-bindinghumectants is an effective method of preventing the growth of food-poisoningbacteria. Only osmophilic yeasts and some molds can grow at water activities in therange 0.6–0.65. Thus, by reducing the water activity below this value, foods aremicrobially stable — unless the packaging is such that the food becomes locally


wet again, in which case local spoilage can occur, e.g., when condensation occurswithin a hermetically sealed package subjected to rapid cooling.

There are various chemical reactions that proceed and may be accelerated atlow values of water activity. Maillard reactions leading to lysine loss and browncolor develop peaks at aw values around 0.5–0.8. Nonenzymatic lipid oxidationincreases rapidly below aw = 0.4. Enzymic hydrolysis decreases with water activityto aw = 0.3, after which, it is negligible.

3.4 WATER SUPPLY, QUALITY, AND DISPOSAL

3.4.1 WATER SUPPLY

Just as water is an integral part of any food, the supply, quality, and disposal ofwater is of prime consideration in the establishment and operation of all foodprocessing. Potable (drinkable) water may be required for addition to the product,and will certainly be required for cleanup. Nonpotable water may be required forheat exchangers and cooling towers. Boiler feed water must be conditioned withinclose limits of pH and hardness. Brennan et al. (1990) in their book Food EngineeringOperations list four types of water used in the food and beverage industries:

• General-purpose water• Process water• Cooling water• Boiler feed water

The siting and consequent viability of a food processing plant may well dependon a guaranteed, regular supply of suitable quality water and an environmentallyacceptable method of disposal. Developed countries now have strict regulations forthe emisson of wastewater. Developing countries are becoming increasingly aware ofthe problems of wastewater disposal. At a recent symposium in Indonesia a fish-dryingprocessor was asked what his main technical problems were. He nominated waterpollution, not for reasons of meeting environmental control regulations, but becausethe fish farmers further down the river were complaining about his wastewater.

3.4.2 WATER QUALITY

3.4.2.1 Standards and Treatment

There are a number of international standards for potable (drinkable) water qualityin existence. The World Health Organization (WHO) has a standard for potablewater quality as part of the Codex Alimentarius. The standard detailed in Table 3.3is from the U.S. Departmental Protection Agency.

There is also a large Environment Circular (EC) directive relating to the qualityof water intended for human consumption (80/778/EEC) that is contained in thejoint circular from the Department of the Environment, Circular 20/82, 2 MarshamStreet, London SW1P 3EB, and the Welsh Office, Circular 33/82, Cathays Park,Cardiff CF1 3NQ, issued on 19 August 1982.


In most cases water will require some treatment to assure that it meets foodhygiene requirements and does not constitute a public health hazard. Surface waterfrom rain runoff into rivers or impoundments is likely to contain atmospheric solutes,minerals from the ground, organic matter from vegetation, microbial contaminationfrom birds and wild and domestic animals, and human waste. Water from under-ground aquifers will have much of the surface contamination filtered out, but it islikely to be high in dissolved mineral content.

Treatment for bringing water quality within the required standard may involvescreening, sedimentation, coagulation and flocculation, filtration, and other physical orchemical treatments to remove microorganisms, organic matter, or dissolved minerals.

TABLE 3.3Primary Maximum Contaminant Levels in Potable Water

Contaminant Level (mg/l unless Specified)

Arsenic 0.05Cadmium 0.010Lead 0.05Nitrate (as N) 10Silver 0.05Endrin 0.0002Methoxychlor 0.12.4 D 0.1Total trihalomethanes 0.10Carbon tetrachloride 0.005Vinyl chloride 0.002para-Dichlorobenzene 0.0751,1,1-Trichloroethane 0.2Barium 1Chromium 0.05Mercury 0.002Selenium 0.01Fluoride 4.0Lindane 0.004Toxaphene 0.0052,4,5-TP silvex 0.01Trichloroethylene 0.0051,2-Dichloroethane 0.005Benzene 0.0051,1-Dichloroethylene 0.007Radium 226 and 228, combined 5 pC/lGross β particle 4 millirem/yearGross α particle 15 pC/lTurbidity 1–5 tuColiform bacteria 1/100 ml, monthly average

Source: From the U.S. Departmental Protection Agency.


Metal screens are used to remove particles larger than about 1 mm in size.Settling ponds remove smaller particles. Insoluble, suspended matter is usuallyremoved by sand filters. Coagulating and flocculating agents act to bind smallerparticles into clumps that then settle or can be screened or filtered.

Microorganisms can be inactivated by heat, chemical disinfection, ultravioletradiation, or ultrasonic treatment. Most town water supplies are chlorinated or haveozone added for chemical disinfection.

Treatment to remove dissolved mineral matter is more complex. Dissolvedbicarbonates of calcium, magnesium, sodium, and potassium cause alkalinity; sol-uble calcium and magnesium salts cause hardness. Alkalinity and hardness may needto be adjusted for some food processing operations. For example, the formation ofa “head” on beer is critically dependent on water hardness. Excessively hard watermay cause discoloration and toughening of certain foods. On the other hand, hardnessmay be required to prevent excessive foaming in clean-up operations.

Iron and manganese salts may be present in water supplies forming organicslimes that tend to clog pipes. Aeration, filtering, and settling are effective for theremoval of iron bicarbonates. Insoluble oxides of manganese are formed throughchlorination.

Excessive amounts of dissolved gases, carbon dioxide, oxygen, nitrogen, andhydrogen sulfide cause problems in boiler feed water, corrosion, and bacterial for-mation. Treatment for this is by boiling and venting off the noncondensable gasesor by chemical dosing.

Small amounts of hydrocarbons such as kerosene and diesel cause tainting infoods. Separating fuels from processing areas, personal hygiene, cleaning of stationsaround food processing operations, and good housekeeping can prevent this problem.

3.4.2.2 Water Pollution

Polluted water is described as polluted if it poses a risk to the health of humans,fish, or other animals.

Microbiologically polluted water contains bacteria and other microorganismsthat may be hazardous or toxic. Human and animal wastes from sewage andfarmyard runoff are the principal sources of microbiological pollution. Pollutedwater can be an indirect hazard, as fish and shellfish may become contaminatedand eaten.

Water can be polluted by organic and inorganic chemicals. Domestic and indus-trial pesticides are a major source of chemical pollution, as are detergents. Many ofthese substances are slow to degrade and may be concentrated in the food chainwith disastrous consequences for fish and bird life.

Biodegradable substances tend to deplete oxygen, resulting in a reduction ofaerobic bacteria and fish. Food waste is high in biochemical oxygen demand (BOD).BOD is defined as the quantity of oxygen (in units of mg liter–1) required for amicroorganism to oxidize the waste at a particular temperature (20°C) in 5 days.Food wastes contain large quantities of organic matter that break down naturally byoxidation; however, this oxygen demand is at the expense of other natural biochem-ical processes in waterways, which become oxygen depleted and lifeless if the BOD


is too high. Food wastes can range in BOD from 500–4000 mg liter–1, which ishigher than for domestic sewage (200–400 mg liter–1).

An excess of nutrients, such as phosphorus and nitrogen in polluted water, willlead to an excessive growth of plant matter in waterways and algal blooms. Besidesclogging waterways and adding toxins, this extra plant material contributes to theBOD of the water.

Suspended matter, even if chemically and biologically inert, can contribute topollution. These particles will eventually settle out and cause silting and an anaerobicenvironment at the bottom of waterway.

Water pollution is most effectively prevented by removing the pollutants beforethey get into the waterways. This can be effected through good housekeeping prac-tices, such as not discharging fatty material and detergents into the domestic sewagesystem, proper design of landfill areas, pretreatment of industrial wastes, and sepa-ration of storm water from sewage, so as to not overload treatment plants.

3.4.3 WASTEWATER TREATMENT AND DISPOSAL

The ultimate aim of any food processing operation is to have an environmentallyneutral impact. Reuse, recycle, and sustainability are today’s catchwords. For a foodoperation to be truly environmentally sustainable, it should recycle all water notincorporated in the product or vented to the atmosphere. The reality is that it iscurrently considered uneconomic to recycle wastewater from food processing oper-ations. Current practice is to treat wastewater to limit its effect on receiving waters.

Treatment of wastewater mirrors the water treatment methods described above,i.e., a combination of physical, chemical, and biological treatments.

A physical process treats suspended, rather than dissolved, pollutants. The pol-lutants may simply be allowed to settle or float to the top naturally, or the processmay be aided mechanically, which will cause smaller particles to stick together,forming larger particles that will settle or rise faster — a process known as floccu-lation. Chemical flocculants may also be added to produce larger particles. A finaltreatment stage of filtration through a medium such as sand can result in very clearwater. Ultrafiltration, nanofiltration, and reverse osmosis are processes that forcewater through membranes and can remove colloidal material and even some dis-solved matter. Absorption (adsorption, technically) on activated charcoal is a physicalprocess that can remove dissolved chemicals. Air or steam stripping can be used toremove gas or low-boiling liquid pollutants from water; vapors removed in this wayare also often passed through beds of activated charcoal to prevent air pollution.These last processes are used mostly in industrial treatment plants, though activatedcharcoal is common in municipal plants for odor control.

Wastewater from food processing operations usually contains significant solidmatter that can be removed by physical processes. Fats and oils can be skimmedfrom the surface of settling tanks; heavier suspended matter can be removed assludge, which can then be dewatered, dried, and used as animal feed, fertilizer, orfuel. An alternative method for the removal of oils and fats is aeration, a process inwhich air bubbles blown from the bottom of a settling tank carry fine solids andgrease to the surface.


Chemical treatments of wastewater are much the same as those described abovefor process water treatment. BOD can be effectively reduced by biological treatment.Both aerobic and anaerobic fermentation of the organic material is used. Dependingon the scale of the operation, bioreactors range in size from 7.5 m diameter and 2–3m in depth to 1- to 2-m-deep lagoons covering several hectares. However, for long-term sustainable operation there must be provision for sludge removal. Where areafor treatment is not a limitation and there is sufficient isolation, so smell is not adeterrent, wastewater is sprayed directly on the ground, where it breaks down underthe action of sunlight and in-ground bacteria.

A typical municipal treatment plant would comprise a preliminary treatmentplant in which large or hard solids are removed or crushed. The effluent then passesthrough a primary settling basin in which organic suspended matter will either settleout or float to the surface to be skimmed off. The next part of the process is usuallyreferred to as secondary treatment, wherein the remaining dissolved or colloidalorganic matter is removed by aerobic biodegradation. This promotes the formationof less offensive, oxidized products. The treatment unit should be sufficiently largeto remove enough of the pollutants to prevent significant oxygen demand in thereceiving water after discharge.

Sewage and wastewater can also be treated anaerobically. Closed reactors facil-itate odor control, although anaerobic lagoons are also used. Such lagoons are deeperthan those for aerobic types, with grease allowed to accumulate on the surface tocontrol odor emission. Methane produced as an end product of the biochemicalpathway can be used for heating the reactors in cold weather. A problem with theanaerobic digestion process is its sensitivity to pH and temperature variation andthe susceptibility of the active microorganisms to chemical disinfectants.

REFERENCES

Brennan, J.G. et al., Food Engineering Operations, 3rd ed., Elsevier Applied Science, London,1990, p. 523.

Brunauer, S., Emmet, P.H., and Teller, E., Adsorption of gases in multilayers, J. Am. Chem.Soc., 60, 309, 1938.

Calabrese, E.J., Gilbert, C.E., and Pastides, H., Eds., Safe Drinking Water Act: Amendments,Regulations, and Standards, Lewis Publishers, Chelsea, MI, 1989.

Chen, C.S. and Clayton, J.T., The effect of temperature on sorption isotherms of biologicalmaterials, Trans. A.S.A.E., 14, 927, 1971.

Chinachoti, P., Water mobility and its relation to functionality of sucrose-containing foodsystems, Food Technol., 47, 134, 1993.

Doe, P.E., Ed., Fish Drying and Smoking Production and Quality, Technomic Publishing Co.Inc., Lancaster, PA, 1998, p. 22.

Engel, A., Waltz, Th., and Agre, P., The aquaporin family of membrane water channels, Curr.Opin. Struct. Biol., 4, 545, 1994.

Fennema, O.R., Food Chemistry, 2nd ed., Marcel Dekker Inc., New York, 1985.Giudice, E. et al., Water in biological systems, in Modern Bioelectrochemistry, Gutmann, F.

and Keyzer, H., Eds., Plenum Press, New York, 1986, p. 282.Haines, Th.H., Water transport across biological membranes, FEBS Lett., 346, 115, 1994.


Iglesias, H.A., Chirife, J., and Lombardi, J.L., An equation for correlating equilibrium mois-ture content in foods, J. Food Technol., 10, 289, 1975.

Jason, A.C., A study of evaporation and diffusion processes in the drying of fish muscle, inFundamental Aspects of the Dehydration of Foodstuffs, Soc. Chem. Ind., London,1958, p. 103.

Lehninger, A.L., Nelson, D.L., and Cox, M.M. Principles of Biochemistry, 2nd ed., WorthPublishers, Inc., New York, 1993, p. 181.

Ling, G.N., A Physical Theory of the Living State, Ginn (Blaisdel), Boston, MA, 1962.Mild, K., and Lovtrup, S., Movement and structure of water in animal cells. Ideas and

experiments, Biochim. Biophys. Acta, 822, 155, 1985.Nossal, R. and Lecar, H., Eds. Molecular and Cell Biophysics, Addison-Wesley Publishing

Co., Reading, MA, 1991, p. 9.Ross, K.D., Estimation of water activity in intermediate moisture foods, Food Technol., 29,

26, 1975.Ruan, R.R. and Chen, P.L., Water in Foods and Biological Materials, Technomic Publishing

Co. Inc., Lancaster, PA, 1998.Stillinger, F.H., Water revisited, Science, 209, 451, 1980.Subczynski, W.K. et al., Hydrophobic barriers of lipid bilayer membranes formed by reduction

of water penetration by alkyl chain unsaturation and cholesterol, Biochemistry, 33,7670, 1994.

Tomkins, R.G., Studies of the growth of moulds. 1., Proc. R. Soc. B, 105, 375, 1929.Wiggins, Ph.M., Role of water in some biological processes, Microbiol. Rev., 54, 432, 1990.Wolf, W., Spiess, W.E.L., and Jung, G., Sorption Isotherms and Water Activity of Food

Materials, Science and Technology Publishers, Hornchurch, Essex, England, 1985.

511-5871-6149-4/02/$0.00+$1.50© 2002 by CRC Press LLC

Mineral Components

Nabrzyski

CONTENTS

4.1 Contents and Role of Minerals in Foods ......................................................514.2 Interaction with Dietary Components............................................................54

4.2.1 Effect on Absorption ..........................................................................544.2.2 Building Body Tissue and Regulating Body Processes ....................57

4.3 Role in Food Processes..................................................................................574.3.1 Effect on Oxidation............................................................................574.3.2 Effect on Rheological Properties .......................................................674.3.3 Other Effects ......................................................................................68

4.4 Effect of Storage and Processing on the Mineral Components in Foods ....684.5 Chemical Nature of Toxicity of Some Mineral Food Components..............70

4.5.1 Introduction ........................................................................................704.5.2 Arsenic ...............................................................................................704.5.3 Mercury ..............................................................................................714.5.4 Cadmium ............................................................................................724.5.5 Lead....................................................................................................744.5.6 Interactions of Elements ....................................................................77

References................................................................................................................77

4.1 CONTENTS AND ROLE OF MINERALS IN FOODS

Minerals represent from 0.2–0.3% of the total intake of all nutrients in the diet. Theyare so potent and so important that without them the organism would not be ableto utilize the remaining 99.7% of the food. The main mass of these mineralsconstitutes the macroelements; the trace elements constitute only a hundredth of apercent of the total mass of daily eaten nutrients. Foods that are good sources ofminerals are given in Table 4.1.

Dietary minerals are necessary for maintenance of normal cellular metabolismand tissue function. These nutrients participate in a multitude of biochemical andphysiological processes important for health. Because of their broad biochemicalactivity, many of these compounds are intentionally used as functional agents in avariety of foods. On the other hand, some cations may induce a diversity of unde-sirable effects that influence the nutritional quality of foods.

4Michal


TABLE 4.1 Contents of Selected Minerals in Some Foods

Mineral Food Amount (mg/100 g) Reference

Calcium Swiss cheese, low sodiumSardines in tomato sauceCod in tomato sauceYogurt, naturalMilkOrangeCarrotTuna in own saucePotato

960437*335*189*120*424125*10

Feltman, 1990

Wojnowski, 1994Wojnowski, 1994

Wojnowski, 1994Potassium

Magnesium

Zinc

Iron

Wheat seedsPorcine liverBeefOat, flakedCarrotPorkOrangeMilkWheat meal (550)Cheese (45% fat)Sardine in tomato sauceTuna in own sauceYogurt, naturalMilkOysterPeas, yellow driedOats, flakedLiver chicken a. pigEgg (yolk)BeefWhole milk powderHard cheeseWheat mealFishBee honeyPorcine liverEgg (yolk)Oat, flakedWheat seedsPorkBeefWheat meal (550)Egg (white)

50235034233529026017715712610727*24*12*9*

up to 1004.23.1

3.6; 4.53.63.83.12.40.6

0.4–1.20.08–1

227.24.63.32.32.61.10.2

Wojnowski, 1994Wojnowski, 1994Wojnowski, 1994Wojnowski, 1994Wojnowski, 1994Wojnowski, 1994Wojnowski, 1994Wojnowski, 1994Wojnowski, 1994Wojnowski, 1994

Lopez et al., 1983Marzec et al., 1992Marzec et al., 1992Marzec et al., 1992Marzec et al., 1992Marzec et al., 1992Marzec et al., 1992Marzec et al., 1992Marzec et al., 1992Marzec et al., 1992Gajek et al., 1987Wojnowski, 1994Wojnowski, 1994Wojnowski, 1994Wojnowski, 1994Wojnowski, 1994Wojnowski, 1994Wojnowski, 1994Wojnowski, 1994

Mineral Components 53

Copper Oysters

Liver, calfLiver, beefWheat germ

Sunflower seedsTunaSalmonHam

6; 17

73

0.9; 2

20.50.2

0.03; 0.08

Lopez et al., 1983; Williams, 1982

Williams, 1982Williams, 1982Marzec et al., 1992; Williams, 1982

Williams, 1982Williams, 1982Williams, 1982Marzec et al., 1992; Williams, 1982

Chromium SpicesCacaoPaprika, pepper, curryHawthornCheese, drownedWhole-meal breadBeefKidney, liver

>0.1–0.50.2

~0.050.025>0.01~0.02

<0.004<0.0015

Wilpinger et al., 1995Wilpinger et al., 1995Wilpinger et al., 1995Wilpinger et al., 1995Wilpinger et al., 1995Wilpinger et al., 1995Wilpinger et al., 1995Wilpinger et al., 1995

Fluoride Black teas

Fish, cannedShellfish

3–34

0.09–0.80.03–0.15

Nabrzyski and Gajewska, 1995

WHO, 1984WHO, 1984

Iodide Marine fish, oyster, shrimp, lobsterMilk powder

0.02–0.10.06

Causeret, 1962Paslawska and Nabrzyski, 1975

Selenium Tortilla chipsPotato chipsPork kidney, braisedTuna, cannedSalmon, cannedMilk

1.00.970.210.120.080.002

Feltman, 1990Feltman, 1990Feltman, 1990Feltman, 1990Feltman, 1990Feltman, 1990

Note: * = author’s unpublished data.

Source: From Causeret, J., in Fish as Food, Academic Press, New York, 1962, 205; Feltman, J., inPrevention’s Giant Book of Health Facts, Rodale Press, Emmaus, PA, 1990; Gajek, O.M. et al., RocznikiPZH, 38, 14, 1987; Lopez, A. et al., J. Food Sci., 48, 1680 and 1961, 1983; Marzec, Z. et al., in Tablesof Trace Elements in Food Products, National Food and Nutrition Institute, Warsaw, 1992; Nabrzyski,M. and Gajewska, R., Z. Lebensm. Unters. Forsch., 201, 307, 1995; Paslawska, S. and Nabrzyski, M.,Bromat. Chem. Toxicol., 8, 73, 1975; WHO, in Fluorine and Fluorides, WHO, Geneva, 1984; Williams,D.M., in Clinical Biochemical and Nutritional Aspects of Trace Elements, Alan R. Liss, Inc., New York,1982; Wilpinger, M. et al., Z. Lebensm. Unters. Forsch., 201, 521, 1995; Wojnowski, W., in Chemicznei funkcjonalne wlasciwosci , Sikorski, Z.E., Ed., Wydawnictwa Naukowo-Technic-zne, Warszawa, 1994.

TABLE 4.1 (CONTINUED)Contents of Selected Minerals in Some Foods

Mineral Food Amount (mg/100 g) Reference

skladników zywnosci


Minerals play an important role in plant life. They function as catalysts ofbiochemical reactions, are responsible for changes in the state of cellular colloids,directly affect the cell metabolism, and are involved in changes in protoplasm turgorand permeability. They often become the centers of electrical and radioactive phe-nomena in living organisms.

Minerals are usually grouped in two categories: the macroelements requiredin our diets in amounts greater than 100 mg, and the microelements required inmilligram quantities or less per day. The macroelements include calcium, magne-sium, phosphorus, sodium, potassium, sulfur, and chlorine. The microelements arecomprised of iron, zinc, copper, manganese, iodine, cobalt, nickel, molybdenum,chromium, fluorine, selenium, vanadium, boron, silicon, and a few others of whichtheir biological functions have not yet been fully recognized.

Actually, mineral deficiency states are more likely to occur than vitamin insuffi-ciency states. At increased risk of mineral deficiencies are people who eat low-caloriediets, the elderly, pregnant women, people using certain drugs such as diuretics,vegetarians, and those living in areas where soils are deficient in certain minerals.There is increasing evidence that those humans whose nutritional status is suboptimalin certain trace elements, such as selenium, may be at greater risk for certain formsof cancer and heart disease. Suboptimal intake can be due to soil depletion, the effectsof acid rain, and the overrefining, overprocessing of foods and other factors.

Minerals occur in foods in many chemical forms. They are absorbed from theintestines as simple cations, as part of an anionic group, or in covalent or noncovalentassociations with organic molecules. The chemical form of minerals in foods stronglyinfluences their intestinal handling and biological availability. Thus, the iron in theform of hemoglobin in meats is more bioavailable than inorganic iron. This may alsobe true for selenium in selenomethionine and for the organic chelates of dietarychromium and zinc. Factors that affect mineral solubility or their reduction to a suitableform for cellular uptake, or those that influence the transfer through the mucosa ortransport into circulation, govern the rate and efficiency of uptake of the minerals. Forexample, iron and zinc are much more bioavailable from human breast milk than fromcow’s milk or comparable infant formula. The intrinsic molecular associations of theseminerals with low-molecular-weight binding compounds in human mammary secre-tions is thought to convey this enhanced absorbability (Rosenberg and Solmons, 1984).

Some minerals can produce chronic toxicity when absorbed and retained in excessof the body’s demands. Homeostatic mechanisms, often hormonally mediated, regulatethe absorption of certain minerals and thereby protect against excessive accumulation.

Recently developed speciation analysis makes it possible to determine the formsof minerals that are present in food and the environment, and may cause specificphysiological or pharmacological effects in organisms.

4.2 INTERACTION WITH DIETARY COMPONENTS

4.2.1 EFFECT ON ABSORPTION

Various nutritional and nonnutritional components of the diet, other nutrients invitamin–mineral supplements, or assorted medications can interact with minerals in


the gastrointestinal tract and influence their absorption. For example, amino acidsmay perform as intraluminar binders for some trace minerals. Large, complex, andpoorly digestible proteins, on the other hand, may bind minerals tightly and diminishtheir absorption. Triacylglycerols and long-chain fatty acids derived from triacyl-glycerols may form soaps with calcium and magnesium and decrease the bioavail-ability of these two nutrients.

Lactose has been implicated in the enhanced absorption of calcium from milk.Pectins, cellulose, hemicellulose, and polymers produced by the Maillard reactionduring cooking, processing, or storage may bind minerals in the lumen and thusreduce their biological availability. Interaction between and among minerals, or withanionic species, are important determinants of mineral absorption. Absorption ofiron is hindered by fiber and phosphates and promoted by ascorbic acid, copper, andmeat protein. Ascorbic acid also enhances absorption of selenium, but reduces theabsorption of copper. A high protein intake appears to increase the excretion ofcalcium, whereas vitamin D ingestion promotes the retention of calcium.

Intestinal parasites, dietary fiber phytates, and excessive sweating interferewith zinc absorption. Phytates, oxalates, and tannates can interfere with the absorp-tion of a number of minerals. Certain medications such as tetracycline can alsoinhibit absorption of minerals, while others such as didoquin or dilatin may actuallypromote uptake of certain minerals. Apparently, chemically similar minerals sharecertain “channels” for absorption, and the simultaneous ingestion of two or moresuch minerals will result in competition for absorption. When unphysiologicalimbalances among competitive nutrients exist as the result of leaching from waterpipes, storage in unlacquered tin cans, or improper formulation of vitamin–mineralsupplements, nutritionally important consequences of this mineral–mineral inter-action can result.

Finally, to participate in a nutritionally relevant process for the organism as awhole, a mineral must be transported away from the intestine. The concentration ofcirculating binding proteins and the degree of saturation of their metallic bindingsites may influence the rate and magnitude of transport of recently absorbed minerals(Rosenberg and Solomons, 1984).

Minerals require a suitable mucosal surface across which to enter the body.Resection or diversion of a large portion of small bowel obviously affects mineralabsorption. Extensive mucosal damage due to mesenteric infarction or inflamatorybowel disease or major diversion by jejunoileal bypass procedures reduces theavailable surface area. Minerals whose absorption occurs primarily in the proximalintestine, e.g., copper or iron, are affected differently than those absorbed moredistally, e.g., zinc. In addition, the integrity of the epithelium, the uptake of fluidsand electrolytes, the intracellular protein synthesis, the energy-dependent pumps,and the hormone receptors must be intact.

Intrinsic diseases of the small intestinal mucosa may impair mineral absorption.Such conditions as celiac sprue, dermatitis herpetiformis, infiltrative lymphomas,and occasionally inflammatory bowel disease produce diffuse mucosal damage.Protein energy malnutrition causes similar damage, and tropical enteropathy affectspart of the population of developing countries living under adverse nutritional andhygienic conditions.


As can be seen from above, the absorption of most metals from the gastrointes-tinal tract is variable (Table 4.2) and depends on many external and internal factors.Thus the quantity of metal ingested rarely reflects that which is bioavailable. In fact,under most circumstances, only a small fraction of ingested metals is absorbed,while the great majority passes out of the gut in the feces.

The Recommended Dietary Allowance (RDA) represents standards of nutritionset by the Food and Nutrition Board of the U.S. National Academy of Sciences(Feltman, 1990). It contains the levels of essential nutrients that are adequate tomeet the nutritional needs of the normal, healthy population. Individuals may differin their precise nutritional requirements. To take these differences into account, the

TABLE 4.2Mean Daily Intake, RDA or SAI, and Absorption Percentage of Minerals from the Gastrointestinal Tract

Milligram per Adult

Mineral Daily intake RDAa or SAIb

Percentage of Absorption

MacroelementsCalciumChlorideMagnesiumPhosphorusPotassiumSodium

960–1220 1700–5100145–358

1670–21303300

3000–7000

800–1200a

750b

280–350b

800–1200a 2000b

500b

10–50Highc

20–60Highc

Highc

Highc

MicroelementsChromium

CobaltCopperFluorineIodineIronManganeseMolybdenumNickel SeleniumVanadiumZinc

<0.15

0.003–0.0122.4

<1.4<1.015

5.6; 8>0.15

0.16–0.200.06–0.22

0.012–0.03012; 18

0.05–0.20b

0.002a,d

1.5–3.0b

1.5–4b

0.15a

10–15a 2–3b

0.075–0.250b

0.05; 0.30.055–0.0700.01–0.025

12–15a

<1 or 10–25 in form of GTF*

30–5025–60Highc

10010–40

4070–90<10~70<1

30–70

Microelements Recently Considered EssentialBoron 1–3 1–2 Highc

Silicon 21–46; 200 21–46 3; 40

c more than 40%d 0.002 mg of cobalt containing vitamin B12.


RDA provides a “margin of safety,” i.e., it sets the allowances high enough to coverthe needs of most healthy people. For additional nutrients that are necessary to keepthe body healthy for which the RDA has not yet been established, a “safe andadequate daily intake” (SAI) is estimated.

The functions of minerals in the body involve building tissue and regulatingnumerous body processes. Their role in the human body is summarized in Table 4.3.

4.2.2 BUILDING BODY TISSUE AND REGULATING BODY PROCESSES

Certain minerals, including calcium, phosphorus, magnesium, and fluorine, are com-ponents of bone and teeth. Deficiencies during the growing years cause growth tobe stunted and bone tissue to be of poor quality. A continual adequate intake ofminerals is essential for the maintenance of skeletal tissue in adulthood.

Potassium, sulfur, phosphorus, iron, and many other minerals are also structuralcomponents of soft tissue (Solomons, 1984; Eschleman, 1984).

Minerals are an integral part of many hormones, enzymes, and other compoundsthat regulate biochemical functions in the organism. For example, iodine is requiredto produce the hormone thyroxine, chromium is involved in the production of insulin,and hemoglobin is an iron-containing compound. Thus the production of thesesubstances in the organism depends on adequate intake of the involved minerals.Minerals can also act as catalysts. Calcium is a catalyst in blood clotting. Someminerals are catalysts in the absorption of nutrients from the gastrointestinal tractin the metabolism of proteins, fat, and carbohydrates, and in the utilization ofnutrients by the cell.

Minerals dissolved in the body fluids are responsible for nerve impulses and thecontraction of muscles, as well as for water- and acid-base balance. They play animportant role in maintaining the respiration, heart rate, and blood pressure in normallimits. Deficiency of minerals in the diet may lead to severe, chronic clinical signsof diseases, frequently reversible after their supplementation in the diet, or followingthe total parenteral nutrition. Their influence on biochemical reactions in livingsystems also makes it possible to use them intentionally in many food processes.

4.3 ROLE IN FOOD PROCESSES

4.3.1 EFFECT ON OXIDATION

Because minerals are an integral part of many enzymes, they play an important rolein food processing, e.g., in alcoholic and lactic fermentation, meat aging, and dairyfood production. Many compounds used as food additives or for rheological modi-fication of some foods contain metallic cations in their structure. A number of thesecompounds function as antimicrobials, sequestrants, antioxidants, flavor enhancers,and buffering agents, and sometimes even as dietary supplements (Table 4.4).

Some heavy metal ions actively catalyze lipid oxidation. Their presence even intrace amounts has long been recognized as potentially detrimental to the shelf life offats, oils, and fatty foods. They can activate molecular oxygen by producing superox-ide, which then, through dismutation and other steps of biochemical changes, turns


TABLE 4.3 Biological Role of Some Minerals

Mineral Function Deficiency Sources

MacroelementsCalcium Bone and tooth formation;

blood clotting, cell permeability; nerve stimulation; muscle contraction; enzyme activation

Stunted growth; rickets; osteomalacia; osteoporosis; tetany

Milk, hard cheese, salmon and small fish eaten with bones, some dark green vegetables, legumes

Magnesium

Phosphorus

Component of bones and teeth; activation of many enzymes; nerve stimulation; muscle contraction

Bone and tooth formation; energy metabolism component of ATP and ADP; protein synthesis component of DNA and RNA; fat transport; acid-based balance; enzyme formation

Seen in alcoholism or renal disease; tremors leading to conclusive seizures

Stunted growth; rickets

Green leafy vegetables, nuts, whole grains, meat, milk, seafood

Milk, meat, poultry, fish, eggs, cheese, nuts, legumes, whole grains

Potassium Osmotic pressure; water balance; acid-based balance; nerve stimulation; muscle contraction, synthesis of protein; glycogen formation

Nausea; vomiting; muscular weakness; rapid heart beat; heart failure

Meats, fish, poultry, whole grains, fruits, vegetables, legumes

Sodium Osmotic pressure; water balance; acid-based balance; nerve stimulation; muscle contraction; cell permeability

Rare: nausea, vomiting, giddiness, exhaustion, cramps

Table salt, salted foods, MSG and other sodium, additives, milk, meat, fish, poultry, eggs, bread

MicroelementsChromium Trivalent chromium

increases glucose tolerance and plays role in lipid metabolism; useful in prevention and treatment of diabetes; hexavalent chromium is toxic

Impaired growth; glucose intolerance; elevated blood cholesterol

Whole-grain cereals, condiments, meat products, cheese, brewer,s yeast


Cobalt Cofactor of vitamin B12; plays role in immunity

Rarely observed, but if exists, pernicious anemia with hematological and neurologic manifestations may be observed due to vitamin B12 deficiency

Organ meats (liver, kidney), fish, dairy products, eggs

Copper Necessary for iron utilization and hemoglobin formation; constituent of cytochrome oxidase; involved in bone and elastic tissue development

Anemia, neutropenia, leucopenia, skeletal demineralization

.

Liver, kidney, oysters, nuts, fruits, dried legumes

Iron

Manganese

Molybdenum

Hemoglobin and myoglobin formation; essential component of many enzymes

Cofactor of large number of enzymes; in aging process has a role as an antioxidant (Mn-superoxide dismutase); important for normal brain function, reproduction, and bone structure

Cofactor of enzymes xantine and aldehyde oxidase; copper antagonist

Anemia; decrease in oxygen transport and cellular immunity; muscle weakness

In animals: chondrodystrophy, abnormal bone development, reproductive difficulties; in humans: shortage of evidence

Reduces conversion of hypoxantine and xantine to uric acid, resulting in development of xantine renal calculi; deficiency state may be potentiated by high copper intake

Liver, lean meats, legumes, dried fruits, green leafy vegetables, whole grain, fortified cereals

Tea, whole grain, nuts moderate levels: fruits, green vegetables; organ meat and shellfish contain very absorbable manganese

Grain, legumes

Zinc

Fluoride

Constituent of many enzyme systems; carbon dioxide transport; vitamin A utilization

Resistance to dental decay

Delayed wound healing; impaired taste sensitivity; retarded growth and sexual development; dwarfism

Tooth decay in young children

Oysters, fish, meat, liver, milk, whole grains, nuts, legumes

Drinking water rich in fluoride; seafood; teas

TABLE 4.3 (CONTINUED)Biological Role of Some Minerals



into hydroxyl free radicals. Three cations are involved in the activity of superoxidedismutase (SOD). This enzyme has been patented as an antioxidant agent for foods.

Three types of metalloenzymes of SOD exist in living organisms: Cu Zn-SOD,Fe-SOD, and Mn-SOD. All three types of SOD catalyze dismutation of superoxideanions to produce hydrogen peroxide in vivo. There is evidence of increased lipidoxidation in apple fruit during senescence. SOD activity may also be involved inreactions induced by oxygen, free radicals, and ionizing radiation and could help toprotect cells from damage by peroxidation products (Du and Bramlage, 1994).

Besides SOD, catalase, ceruloplasmin, albumin, appotransferrin, and chelatingagents (e.g., ethylenediaminetetraacetic acid (EDTA), bathocupreine, cysteine, andpurine) are capable of inhibiting the oxidation of ascorbic acid induced by tracemetals. Copper-induced lipid oxidation in ascorbic acid-pretreated cooked groundfish may be inhibited in the presence of natural polyphenolic compounds, the fla-vonoids, which are effective antioxidants, and prevent the production of free radicals(Ramanathan and Das, 1993). In the presence of ADP-chelated iron and traces ofcopper, oxygen radicals are generated in the sarcoplasmic reticulum of muscle food.Muscle contains notable amounts of iron, a known prooxidant, and trace amountsof copper, also a catalyzing peroxidative reaction (Hultin, 1994; Wu and Brewer,1994). Iron occurs associated with heme compounds and as nonheme iron complexedto proteins of low molecular weight. Reactive nonheme iron can be obtained byrelease of iron from hem pigments or from the iron storage protein, ferritin. Iron is

Iodine Synthesis of thyroid hormones that regulate basal metabolic rate

Goiter; cretinism, if deficiency is severe

Iodized salt, seafood, food grown near the sea

Selenium Protects against number of cancers

Cataract; muscular dystrophy; growth depression; liver cirrhosis; infertility; cancer; aging due to deficiency of selenoglutathione peroxidase; insufficiency of cellular immunity

Broccoli, mushrooms, radishes, cabbage, celery, onion, fish, organ meats

Boron(recently considered essential; still has to be proven)

Prevents osteoporosis in postmenopausal women; beneficial in treatment of arthritis; builds muscle

Probably impairs growth and development

Foods of plant origin and vegetables

Source: Eschleman, M.M., in Introductory Nutriton and Diet Therapy, Lippincott J.B. Co., London,1984; Hendler S.S., in The Doctor’s Vitamin and Mineral Encylopedia, Simon and Schuster, New York,1990.

TABLE 4.3 (CONTINUED)Biological Role of Some Minerals



TABLE 4.4Selected Mineral Compounds Used as Food Additives

Chemical Name ofCompound and (INS)

Synonyms or Other

Chemical NameFunctional Classand Comments

ADI, TADI, PMTDI,(mg/kg of body

weight)

Calcium alginate (404)

Calcium ascorbate (302)

Calcium benzoate (213)

Calcium chloride (509)

Calcium alginate

Calcium ascorbate dihydrate

Monocalcium benzoate

Calcium chloride

Thickening agent; stabilizer

Antioxidant

Antimicrobial agent; preservative

Firming agent

ADI “not specified”


ADI 0–5.0


Calcium citrate (333) Tricalcium citrate; tricalcium salt of beta hydroxytricarballylic acid

Acidity regulator; firming agent; sequestrant


Calcium dihydrogen phosphate (341i)

Calcium dihydrogen tetraoxophosphate; monobasic calcium phosphate; monocalcium phosphate

Buffer, firming, raising, leavening and texturing agent; used in fermentation processes

MTDI 70.0

Calcium disodium ethylenediaminetetraacetace (385)

Calcium disodiumEDTA

Antioxidant; preservative; sequestrant

ADI 0–2.5

Calcium glutamate (623)

Monocalcium DI-L- glutamate

Flavor enhancer; salt substitute


Calcium hydroxide (526)

Slaked lime Neutralizing agent; buffer; firming agent

ADI “not limited”

Calcium hydrogen carbonate (170ii)

Calcium hydrogen carbonate

Surface colorant; anticaking agent; stabilizer


Calcium lactate (327) Calcium dilactate hydrate

Buffer; dough conditioner

Calcium sorbate (203) Calcium sorbate Antimicrobial, fungistatic, preservative agent

ADI 0–25.0(as sum of calcium,potassium, and sodium salt)

Magnesium chloride(511)

Magnesium chloride hexahydrate

Firming, color retention agent


Magnesium carbonate(504i)

Magnesium carbonate

Anticaking and antibleaching agent

ADI 0–50.0

continued


TABLE 4.4 (CONTINUED)Selected Mineral Compounds Used as Food Additives


Synonyms or Other



weight)

Magnesium gluconate(580)

Magnesium gluconate dihydrate

Buffer; firming agent in yeast food


Magnesium glutamate DI-L- (625)

Magnesium glutamate


ADI “not specified” (group ADI for α glutamic acid and its monosodium, potassium, calcium, magnesium, and ammonium salts)

Magnesium hydrogen phosphate (343ii)

Magnesium hydrogen ortophosphate trihydrate; dimagnesium phosphate

Dietary supplement MTDI 70 (expressed as phosphorus from all sources)

Magnesium hydroxide (528)

Magnesium hydroxide

Alkali; color adjunct ADI “not limited”

Magnesium hydroxide carbonate (504ii)

Magnesium carbonate hydroxide hydrated

Alkali; anticaking, color retention and drying agent


Magnesium lactate D,L- (also magnesium lactate L) (329)

Magnesium DI-D,L-lactate

Buffering agent; dough conditioner; dietary supplement


Magnesium oxide (530)

Magnesium oxide Anticaking and neutralizing agent


Magnesium sulfate (518)

Magnesium sulfate Firming agent ADI “not specified”

Potassium acetate (261)

Potassium acetate Antimicrobial agent; preservative; buffer

ADI “not specified” (also includes the free acid)

Potassium alginate (402)

Potassium alginate Thickening agent; stabilizer

ADI “not specified” (group ADI for alginic acid and its ammonium, calcium, and sodium salts)

Potassium aluminosilicate (555)

Potassium aluminosilicate

Anticaking agent No ADI allocated

Potassium ascorbate (303)

Potassium ascorbate Antioxidant ADI “not specified”

Potassium benzoate (212)

Potassium benzoate Antimicrobial agent; preservative

ADI 0–5,0 (expressed as benzoic acid)




Synonyms or Other



weight)

Potassium bromate (924a)

Potassium carbonate(501i)

Potassium bromate

Potassium carbonate

Oxidizing agent

Alkali; flavor

ADI withdrawn


Potassium chloride (508)

Potassium chloride, sylvine, sylvite

Seasoning and gelling agent; salt substitute


Potassium or sodium copper chlorophyllin (141ii)

Potassium dihydrogen phosphate (340i)

Potassium hydrogen carbonate (501ii)

Potassium or sodium chlorophyllin

Monopotassium dihydrogen ortophosphate; monobasic potassium phosphate

Potassium bicarbonate

Color of porphyrin

Buffer; sequestrant; neutralizing agent

Alkali; leavening agent; buffer

ADI 0–15

MTDI 70.0


Potassium hydrogen sulfite (228)

Potassium hydrogen sulfite

Preservative; antioxidant

ADI 0–0.7 (group ADI for sulfur dioxide and sulfites; expressed as sulfur dioxide, covering sodium, and potassium metabisulfite, potassium and sodium hydrogen sulfite, and sodium thiosulfate)

Potassium glutamate (622)

L-Monopotassium L-glutamate



Sodium alginate (401) Sodium alginate Thickening agent; stabilizer


Sodium aluminium phosphate acidic (541i)

Salp. Sodium trialuminium tetradecahydrogen; octaphosphate tetrahydrate (A);

Raising agent ADI 0–0.6

continued




Synonyms or Other



weight)

trisodium dialuminium pentade cahydrogen octaphosphate (B)

Sodium aluminiumphosphate basic (541ii)

Kasal. Autogenous mixture of an alkaline sodium aluminum phosphate

Emulsifier ADI 0–0.6

Sodium ascorbate(301)

Sodium L-ascorbate Antioxidant ADI “not specified”

Sodium benzoate (211)

Sodium salt of benzenecarboxylic acid

Antimicrobial, preservative

ADI 0–5.0

Sodium dihydrogen phosphate (339i)

Disodium ethylenediaminetetraacetate (386)

Monosodium dihydrogen monophosphate (ortophosphate)

Disodium EDTA Disodium edeteate

Buffer; neutralizing agent; sequestrant in cheese, milk, fish, and meat products

Antioxidant; sequestrant, preservative, synergist

MTDI 70.0

ADI 0–2.5 (as calcium disodium EDTA)

Sodium glutamate(621)

Monosodium L-glutamate (MSG); glutamic acid monosodium salt monohydrate

Flavor enhancer ADI “not specified”

Sodium iron III–ethylenediamine tetraacetatetrihydrate

Ferric sodium edeteate; sodium iron EDTA; sodium feredetate

Nutrient supplement (provisionally considered to be safe in food fortification programs)

ADI acceptable

Sodium or potassium metabisulfite (223, 224)

Disodium or potassium pentaoxodisulfate

Antimicrobial; preservative; bleaching agent; antibrowning agent

ADI 0–0.7 (group ADI for sulfur dioxide and sulfites expressed as SO2, covering sodium and potassium salt)

Sodium nitrite (250) Sodium nitrite Antimicrobial; color fixative

ADI 0–0.1

Sodium nitrate (251) Sodium nitrate; cubic or soda

niter; chile salpeter

Antimicrobial; color fixative

ADI 0–5.0




Synonyms or Other



weight)

Sodium phosphate (339iii)

Sodium or potassium sorbate (201, 202)

Trisodium phosphate; trisodium monophosphate; ortophosphate; sodium phosphate;

Sodium or potassium sorbate

Sequestrant; emulsion stabilizer; buffer

Antimicrobial; fungistatic agent

MTDI 70.0

ADI 0–25.0

Notes: INS = international numbering system; prepared by the Codex Committee for Food Additivesfor the purpose of providing an agreed upon international numerical system for identifying foodadditives in an ingredient list as an alternative to the declaration of the specific name (Codex Alimen-tarius, 2nd ed., Vol. 1, Sec. 5.1, 1992).

ADI = acceptable daily intake; estimate of the amount of a substance in food or drinking water,expressed on a body weight basis, for a standard human weight of 60 kg, that can be ingested dailyover a lifetime without appreciable risk for health.

ADI “not specified” and ADI “not limited” are terms applicable to a food substance of very low toxicitythat, on the basis of the available data — chemical, biochemical, toxicological, and other, as well astotal dietary intake of the substance, arising from its use at levels to achieve the desired effect and fromits acceptable background in food — does not, in the opinion of JECFA, represent a hazard to health.For this reason and those stated in individual evaluations, the establishment of ADI in numerical formis not deemed necessary. An additive meeting this criterion must be used within the bound of goodmanufacturing practice, i.e., it should be technologically efficacious and should be used at the lowestlevel necessary to achieve this effect; it should not conceal inferior food quality or adulteration, and itshould not create a nutritional imbalance.

TADI = temporary ADI; term established by JECFA for a substance for which toxicological data are sufficientto conclude that use of the substance is safe over a relatively short period of time during which the substancecan be evaluated for further safety data, but are insufficient to conclude that use of the substance is safe overa lifetime. A higher-than-normal safety factor is used when establishing a TADI, and an expiration date isestablished by which time appropriate data to resolve the safety issue should be submitted to JECFA.

MTDI = maximum tolerable daily intake, or provisional maximum tolerable daily intake (PMTDI); a termused for description of the end point of contaminants with no cumulative properties. Its value representspermissible human exposure as a result of the natural occurrence of the substance in food or drinking water.In the case of trace elements that are both essential nutrients and unavoidable constituents of food, a rangeis expressed, the lower value representing the level of essentiality and the upper value the PMTDI.

Source: FAO/WHO Ed., Summary of Evaluations Performed by the Joint FAO/WHO Expert Committeeon Food Additives 1956–1993, ILS Inst., Geneva, 1994; WHO, 44th Meeting of the Joint FAO/WHOExpert Committee on Food Additives, Geneva, 1996.


part of the active site of lipoxygenase, which may participate in lipid oxidaton.Reducing components of the tissue-like superoxide anion, ascorbate, and thiols canconvert the inactive ferric iron to active ferrous iron. There are also enzymic systemsthat use reducing equivalents from NADPH to reduce ferric iron. A number ofcellular components are capable of reducing ferric to ferrous iron, but under mostconditions the two major reductants are superoxide and ascorbate (Hultin, 1994).

In some cases reduction of ferric iron can be accomplished by enzymicallyutilizing electrons from NADH and, to a lesser extent, NADPH through an enzymicsystem associated with both the sarcoplasmic reticulum and mitochondria. Ferrousiron can activate molecular oxygen by producing superoxide. Superoxide may thenundergo dismutation spontaneously or by the action of SOD and produce thehydrogen peroxide that can interact with another atom of ferrous iron to producethe hydroxyl radical. The hydroxyl radical can initiate lipid oxidation. It is gen-erally accepted that ferrous iron is the reactive form of iron in oxidation reaction.Since it is likely that most iron ordinarily exists in the cell as ferric iron, the abilityto reduce ferric to ferrous iron is critical.

Development of rancidity and warmed-over flavor, a specific defect that occursin cooked and reheated meat products following short-term refrigated storage, hasbeen directly linked to autooxidation of highly unsaturated, membrane-bound phos-pholipids and to the catalytic properties of nonheme iron (Oelinngrath and Slinde,1988; Pearson et al., 1977; Hultin, 1994).

Dietary iron may influence muscle iron stores and thus theoretically may alsoaffect the lipid oxidation in muscle food, e.g., pork. There appears to be a thresholdfor dietary iron level (between 130 and 210 ppm) above which muscle and livernonheme iron and total iron, and muscle thiobarbituric acid reactive substances beginto increase because of porcine muscle lipid oxidation (Miller et al., 1994a, 1994b).

The secondary oxidation products, mainly aldehydes, are the major contributorsto warmed-over flavor and meat flavor deterioraton, because of their high reactivityand low flavor thresholds. Ketones and alcohols have a high flavor threshold, thuscausing off-flavors less often.

Exogenous antioxidants can preserve the quality of meat products. Radicalscavengers appear to be the most effective inhibitors of meat flavor deterioration.However, different substrates and systems respond in different ways. Active ferrousiron may be eliminated physically by chelation with EDTA or phosphates, or chem-ically by oxidation to its inactive ferric form.

Ferroxidases are enzymes that oxidize ferrous to ferric iron in the presence ofoxygen according to the formula:

4Fe2+ + O2 + 4H+ → 4Fe3+ + 2H2O

Ceruloplasmin, a copper protein of blood serum, is a ferroxidase. Oxidation offerrous to ferric iron tends to be favored in extracellular fluids, while chelation ismore likely intracellular (Hultin, 1994).

Sodium chloride has long been used for food preservation. Salt alters both thearoma and the taste of food. Addition of sodium chloride to blended cod muscleaccelerates the development of rancidity (Castell et al., 1965; Castell and Spears,


1968). This salt-induced rancidity is inhibited by chelating agents such as EDTA,sodium oxalate, and sodium citrate and by nordihydroguaiaretic acid and propylgallate. Although sodium chloride and other metal salts act as prooxidants, theyhave a strong inhibiting effect on Cu2+-induced rancidity in the fish muscle. Themost effective concentration of NaCl for this antioxidant effect is between 1 and8% (Castell et al., 1965; Castell and Spears, 1968). Castell and Spears (1968) alsoshowed that the other heavy metal ions were effective in producing rancidity whenadded to various fish muscles. The relative effectiveness was of the followingdecreasing order: Fe2+ > V2+ > Cu2+ > Fe3+ > Cd2+ > Co2+ > Zn2+, while Ni,2+ Ce2+,Cr3+, and Mn2+ had no effect in the used concentrations. Of those tested, Fe2+,V2+,and Cu2+ were by far the most active catalysts. There were, however, importantexceptions. The comparative effectiveness of the metal ions was not the same formuscles taken from all the species tested.

EDTA is reported to be effective as the metal ions sequester and is approved foruse in the food industry as a stabilizer and antioxidant. It acts also as an inhibitorof Staphylococcus aureus by forming stable chelates in the media with multivalentcations that are essential for cell growth. The effect is largely bacteriostatic andeasily reversed by releasing the complexed cations with other cations for whichEDTA has higher affinity (Kraniak and Shelef, 1988).

The addition of phosphate — pyro-, tripoly-, and hexametaphosphate — alsoprotects cooked meat from auto-oxidation. Ortophosphate gives no protection. Themechanism by which phosphates prevent autooxidation appears to be related to theirability to sequester metal ions, particularly ferrous iron, which is the major proox-idant (Pearson et al., 1977). The addition of NaCl increases retention of moisture inmeat and meat products.

4.3.2 EFFECT ON RHEOLOGICAL PROPERTIES

The interaction between metal ions and polysaccharides often affects the rheologicaland functional properties in food systems (Ha et al., 1989).

In aqueous media, neutral polysaccharides have little affinity for alkali metaland alkali earth metal ions. On the other hand, anionic polysaccharides have a strongaffinity for metal counterions. This association is related to the linear charge densityof the polyanions. The linear charge density is expressed as the distance betweenthe perpendicular projections of an adjacent charged group on the main axis of themolecule. The higher the linear charge density, the stronger the interaction of coun-terions with anionic groups of the molecule. Such anionic hydrocolloids (0.1%solutions) as alginate, karaya, arabic, and ghati have higher calcium-binding affinity(Ha et al., 1989). An important functional property of alginates is their capacity toform gels with calcium ions. This makes alginates extensively suited to prepareproducts such as fruit and meat analogs. They are also widely used in biotechnologyas an immobilization agent of cells and enzymes. The method involves diffusion ofcalcium ions through alginate and a cross-linking reaction with the alginate carboxy-lic group to form the gel (Ha et al., 1989; WHO, 1993a, 1993b). Carrageenans arereported to stabilize casein and several plant proteins against precipitation withcalcium and are used to prepare texturized milk products (Samant et al., 1993).


4.3.3 OTHER EFFECTS

Sodium reduction in the diet is recommended as a means of preventing hyperten-sion and subsequent cardiovascular disease, stroke, and renal failure. Reducing orsubstituting NaCl requires an understanding of the effects caused by the newfactors introduced. Several methods have been proposed for reducing the sodiumcontent in processed meat without an adverse effect on the quality (flavor, gela-tion), or shelf life of the products. This includes a slight sodium chloride reduction,replacing some of the NaCl with other chloride salt (KCl or MgCl2) or nonchloridesalt, or altering processing methods (Barbut and Mittal, 1985).

Calcium ion is a known activator of many biochemical processes. The calcium-activated neutral protease (CANP) plays an important role in postmortem tenderizingof meat. The function of the metal ion in such an enzyme is believed to be eitherneutralization of the charges on the surface, by preventing electrostatic repulsion ofsubunits, or effecting of a conformational change required for association of thesubunits. Thus the metal ions must be present in a specific state to perform this function.

The metallic cation in solution exists as aqua complex ions in equilibrium withtheir respective hydroxy complex:

The acid ionization constant (pKa) of the aqua complex ion determines whetheror not the ion would form complexes with a protein. This depends greatly on thepH of the medium. Since the ionization constant of low charge is 12.6, the ion wouldform a stable complex only with negatively charged protein in alkaline media. Itcannot bind to cationic proteins because it does not share electrons to form a covalentbond. This consideration explains why the activity of Ca2+-activated protease isoptimum in the alkaline pH range. Thus a decrease in its activity at acidic pH valuesmay partly be due to a change in the electronic state of Ca2+ (Asghar and Bhatti,1987; Barbut and Mittal, 1985).

Generally, sodium and potassium react only to a limited extent with proteins,whereas calcium and magnesium are somewhat more reactive. Transition metals,e.g., ions of Cu, Fe, Hg, and Ag, react readily with proteins, many forming stablecomplexes with thiol groups. Calcium cations and ferrous, cupric, and magnesiumcations may be integral parts of certain protein molecules or molecular associations.Their removal by dialysis or sequestration appreciably lowers the stability of theprotein structure toward heat and proteases.

4.4 EFFECT OF STORAGE AND PROCESSING ON THE MINERAL COMPONENTS IN FOODS

The effect of normal storage on mineral components is rather low and may be connectedmainly with changes of humidity or contamination; however, high changes of mineral

M(H2O)m+ ⇔ MOH(m – 1)+ + H+

aqua hydroxy-complex(weak base)complex ion


components may occur during canning, cooking, drying, freezing, peeling, and all theother steps involved in preserving, as well as in food processing, for direct consumption.

The highest losses of minerals are encountered in the milling and polishingprocess of cereals and groats. All milled cereals undergo a significant reductionof nutrients. The extent of the loss is governed by the efficiency with which theendosperm of the seed is separated from the outer seed coat (bran) and the germ.The loss of certain minerals and vitamins is deemed so relevant to health that inmany countries a supplementation procedure has been introduced for obtainedfood products to enrich them with the lost nutrients, e.g., iron to the bread. Insome countries regulations have been issued for standards of identity for enrichedbread. If bread is labeled “enriched,” it must meet these standards. In white flours,the losses of magnesium and manganese may reach up to 90%. These mineralsremain mainly in the bran — the outer part of the cereals. For this reason, it seemsreasonable to recommend consumption of bread baked from whole meals insteadfrom white meals.

Recommended, sometimes steady, consumption of bran alone, for dietary pur-pose, should be done with great care because it may also contain many differentcontaminants, such as toxic metals and organic pesticides.

During preparation for cooking or canning, vegetables should be thoroughly washedbefore cutting to remove dirt and traces of insecticide spray. Root vegetables should bescrubbed. The dark outer leaves of greens are rich in iron, calcium, and vitamins, so theyshould be trimmed sparingly. Peeling vegetables and fruit should be avoided, wheneverpossible, because minerals and vitamins are frequently concentrated just beneath theskin. Potatoes should be baked or cooked in their skins, even for hashed browns or potatosalad. However, True et al. (1979) showed that cooking potatoes by boiling whole orpeeled tubers, as well as microwave cooking and oven baking, may have a negligibleeffect on the losses of Al, B, Ca, Na, K, Mg, P, Fe, Zn, Cu, Mn, Mo, J, and Se. Microwavedpotatoes retain nutrients well, and contrary to popular belief, peeling potatoes does notstrip away their vitamin C and minerals. Whenever practical, any remaining cookingliquid should be served with the vegetable or used in a sauce or gravy soup. To retainminerals in canned vegetables, one should pour the liquid from the can into a saucepanand heat at low temperature to reduce liquid; add vegetables to remaining liquid andheat before serving. Low temperatures reduce shrinkage and loss of many other nutrients.Cooking and blanching leads to the most important nutrient losses. In the liquid of cookedvegetables about 30–65% of potassium, 15–70% of magnesium and copper, and 20 toover 40% of zinc is leached. Thus it is reasonable to use this liquid for soup preparation(Rutkowska, 1975; Trzebska-Jeske et al., 1973).

The losses depend on both the kind of vegetables cooked and the course of theapplied process. Steam blanching generally results in smaller losses of nutrients,since leaching is minimized in this process. Frozen meat and vegetables thawed atambient temperatures lose many nutrients, including minerals in the thaw drip. Toavoid these nutrients losses, the drip should be added to the pot where the meal isprepared for consumption. Frozen fruits should be eaten without delay, fresh, justafter thawing, together with the secreted juice. Foods blanched, cooked, or reheatedin a microwave oven generally retain about the same or even higher amounts ofnutrients as those cooked by conventional methods.


4.5 CHEMICAL NATURE OF TOXICITY OF SOME MINERAL FOOD COMPONENTS

4.5.1 INTRODUCTION

A diet consisting of a variety of foods provides the best protection against potentiallyharmful chemicals in food. This is because the body tolerates very small quantitiesof many toxic substances, but has only a limited ability to cope with large quantitiesof any single one. Almost any chemical can have a harmful effect if taken in a largequantity. This is especially true for trace minerals, and to some degree, also formacroelements, as well as vitamins. For this reason, it is important to understandthe difference between toxicity and hazard. Many foods contain toxic chemicals,but these chemicals do not present a hazard if consumed in allowable amounts.

Toxic compounds of such metals as arsenic, mercury, cadmium, and lead con-taminate the environment and may enter the food supply. A number of minerals canproduce chronic toxicity when absorbed and retained in excess of the body’sdemands. The proportion of elements accumulated by the organism is different thanthe proportion in the environment, and this results in their concentration within theorganism. Some of the elements are necessary to the organism for metabolic pro-cesses; others, however, that are accumulated in high proportions — sometimesspecifically in some organs — according to present knowledge do not have anymetabolic significance for the organism (e.g., arsenic, cadmium, mercury, and lead)and are recognized as toxic. Their toxicity is a function of the chemical form andthe dose that enters the body. It is also a function of accumulation in the body tissues.For this reason, it is very important to have information about the chemical form ofthe discussed metals. Currently this may be done by applying speciation analysis,which makes it possible to differentiate the chemical form of the examined elementand assess the safety level of the metal residue in foods or drinking water.

4.5.2 ARSENIC

Pentavalent and trivalent arsenicals react with biological ligands in different ways.The trivalent form reacts with the thiol protein groups, resulting in enzyme inacti-vation, structural damage, and a number of functional alterations. The pentavalentarsenicals, however, do not react with -SH groups. Arsenate can competitively inhibitphosphate insertion into the nucleotide chains of DNA of cultured human lympho-cytes, causing false formation of DNA because of instability of the arsenate esters.Dark repair mechanisms are also inhibited, leading to peristence of these errors inthe DNA molecules. Binding differences of the trivalent and pentavalent forms leadto differences in accumulation of this element. Trivalent inorganic arsenic is accu-mulated in a higher level than its pentavalent form. The organic arsenic compoundsare considered less toxic or nontoxic in comparison to inorganic arsenic, of whichtrivalent arsenicals are the most toxic forms.

Dietary arsenic represents the major source of arsenic exposure for most of thegeneral population. Consumers eating large quantities of fish usually ingest signif-icant amounts of arsenic, primarily as organic compounds, especially those withstructures similar to arsenobetaine and arsenocholine, as well as various other arsenic


derivates. Fish of many species contain arsenic between 1 and 10 mg/kg. Arseniclevels at or above 100 mg/kg have been found in bottom feeders and shellfish. Bothlipid and water-soluble organoarsenic compounds have been found, but the water-soluble forms, mainly the quaternary arsonium derivates, constitute the larger portionof the total arsenic in marine animals (Vaessen and van Ooik, 1989; WHO, 1989).

Studies in mice have demonstrated that after administration of arsenobetaineand arsenocholine over 90% of the dose was absorbed; about 98% of the adminis-tered dose of arsenobetaine was excreted unchanged in the urine, and 66 and 9% ofthe single oral dose of arsenocholine was excreted in the urine and feces, respectively,within 3 days. The majority of arsenocholine was oxidized to arsenobetaine in theanimal organism and, in this form, was excreted in the urine. The retention ofarsenocholine in the animal body, following administration, was greater than theretention of arsenobetaine. The fate of organic arsenicals in man still has not beenfully clarified.

Little available information on the organoarsenicals present in fish and otherseafood may indicate that these compounds appear to be readily excreted in theurine in an unchanged chemical form, with most of the excretion occuring within2 days of ingestion. Volunteers who consumed flounder excreted 75% of the ingestedarsenic in urine within 8 days of eating the fish.

The excreted arsenic was in the same chemical form as it was in the fish. Lessthan 0.35% was excreted in the feces. There are no data on tissue distribution ofarsenic in humans after ingestion of arsenic present in fish and other seafood. Also,there have been no reports of ill effects among ethnic populations consuming largequantities of fish that result in organoarsenic intakes of about 0.05 mg/kg of bodyweight per day (WHO, 1989). Inorganic tri- and pentavalent arsenicals are metab-olized in man, dog, and cows to less toxic methylated forms, such as monomethy-larsenic and dimethylarsenic acids (Peoples, 1983).

4.5.3 MERCURY

Organic mercury compounds, especially methylmercury, are recognized as moredangerous for man than the inorganic ones.

Most foods, except fish, contain very low amounts of total mercury (<0.01mg/kg), which is almost entirely in the form of inorganic compounds. Over 90%of mercury in fish and shellfish is in the form of methylmercury. This is so becausefish feed on aquatic organisms that contain this compound, ultimately originatingfrom microorganisms that biomethylate inorganic mercury. Marlin is the onlypelagic fish known to have more than 80% of the total muscle mercury present asinorganic mercury (Cappon and Smith, 1982). The amount of methylmercury isespecially high in large, old fish of predatory species like the shark and swordfish.In fish of freshwater species, the mercury content depends on the concentrationof mercury in water and sediment and on the pH of water. The concentration ofmethylmercury in most fish is generally less than 0.4 mg/kg, although predatorssuch as the swordfish, shark, and pike may contain up to several milligrams ofmethylmercury per kg in their muscles. The intake of methylmercury depends onfish consumption and the concentration of methylmercury in the fish consumed.


Many people eat about 20–30 g of fish per day, but certain groups eat 400–500 gper day. Thus the daily dietary intake of methylmercury can range from about 0.2to 4 µg/kg of body mass.

Studies of the kinetics of methylmercury after ingestion showed that its distri-bution in the tissues is more homogenous than that of other mercury compounds,with the exception of elemental mercury.

The most important features of the distribution pattern of methylmercury are ahigh blood concentration, a high erythrocyte/plasma concentration ratio (about 20),and a high deposition in the brain. Another important characteristic is slow demeth-ylation, which is a critical detoxification step.

Methylmercury and other mercury compounds have a strong affinity for sulfurand selenium. Although selenium has been suggested to provide protection againstthe toxic effect of methylmercury, no such effect has been demonstrated.

A variety of effects have been observed in animals treated with toxic doses, butsome of these, such as renal damage and anorexia, have not been observed in humansexposed to high doses. The primary tissues of concern in humans are the nervoussystem and particularly the developing brain, and these have been the main reasonfor the wide range of epidemiologial studies. Methylmercury passes about ten timesmore readily through the placenta than other mercury compounds. The dermalabsorption of methylmercury is similar to that of inorganic mercury salts.

The LD50 values after oral administration are 25 mg/kg of body weight in oldrats (450 g of body mass) and 40 mg/kg in young rats (200 g). The clearance halftimeof methylmercury is about 74 days for the human body and 52 days for the bloodcompartment (WHO, 2000).

4.5.4 CADMIUM

Cadmium shares chemical properties with zinc and mercury, but in contrast tomercury, it is incapable of environmental methylation, due to the instability of themonoalkyl derivate. Similarities and differences also exist in the metabolism of Zn,Cd, and Hg. Metallothioneins and other Cd-binding proteins hold or transport Cd,Zn, and Hg within the body. Metallothioneins are metal-binding proteins of relativelylow molecular mass with a high content of cysteine residues that have a particularaffinity for cadmium, as well as for zinc and copper, and can affect its toxicity.

Its synthesis in organisms is induced by the above-mentioned metals and isinvolved in the storage of these metals in organs. Zinc metallothionein can detoxifyfree radicals. Cadmium-induced metallothionein is able to bind cadmium intracel-lularly and in this way protects the organism against the toxicity of this metal.Cadmium is transported in the plasma as a complex with metallothionein and maybe toxic to the kidney when excreted in the glomerular filtrate.

Most cadmium in urine is bound to metallothionein. This protein occurs inthe organism as at least four genetic variants. The two major forms, I and II,are ubiquitous in most organs, particularly in the liver and kidney, and also inthe brain. Metallothionein isolated from adult or fetal human livers containedmainly zinc and cooper, whereas that from human kidneys contained zinc,copper, and cadmium.


The metals are bound to the peptide by mercaptide bounds and are arrangedin two distinct clusters: a four-metal cluster called the α domain and a three-metal cluster called cluster β, at the C terminal of the protein. The α cluster isan obligate zinc cluster, whereas the zinc in cluster β may be replaced by copperor by cadmium.

Interaction with metallothionein is the basis for metabolic interactionsbetween these metals. Metallothionein III is found in the human brain and differsfrom I and II by having six glutamic acid residues near the terminal part of theprotein. Metallothionein III is thought to be a growth inhibitory factor, and itsexpression is not controlled by metals; however, it does bind zinc. Anotherproposed role for metallothionein III is participation in the utilization of zinc asa neuromodulator, since metallothionein III is present in the neurons that storezinc in their terminal vesicles. Metallothionein IV occurs during differentiationof stratified squamous epithelium, but it is known to have a role in the absorptionor toxicity of cadmium.

Metallothionein in the gastrointestinal mucosa plays a role in the gastrointestinaltransport of cadmium. Its presence in cells of the placenta impairs the transport ofcadmium from maternal to fetal blood and across blood–brain barriers, but onlywhen the concentration of cadmium is low. Newborns are virtually cadmium free,whereas zinc and copper are readily supplied to the fetus. Rapid renal concentrationoccurs mainly during the early years of life.

Cadmium bound to metallothionein in food does not appear to be absorbed ordistributed in the same way as inorganic cadmium compounds. Low dietary con-centration of calcium promotes absorption of cadmium from the intestinal tractof experimental animals. A low iron status in laboratory animals and humans hasalso been shown to result in greater absorption of cadmium. In particular, womenwith low body iron stores, as reflected by low serum ferritin concentrations, hadan average gastrointestinal absorption rate that was twice as high (about 10%) asthat of a control group of women (about 5%). High iron status results in decreasingtotal and fractional cadmium accumulation from diets, whereas low iron status inorganisms promotes accumulation of cadmium. Studies in rats with reduced ironstatus showed that the inclusion of wheat bran — containing phytate hinderingthe absorption of iron, calcium, and other minerals — into their diets increasedthe uptake of cadmium.

The LD50 value for rats and mice treated orally ranges from about 100–3000mg/kg of body mass after a single dose of cadmium chloride. The high affinityof Cd for –SH groups and the ability of imparting moderate covalency in boundsresult in increased lipid solubility, bioaccumulation, and toxicity. In humans, afternormal levels of exposure, about 50% of the body burden is found in the kidneys,about 15% in the liver, and about 20% in the muscles. Like in animals, theproportion of cadmium in the kidney decreases as the liver concentrationincreases. The lowest concentrations of cadmium are found in the brain, bone,and fat. Accumulation in the kidney continues to 50–60 years of age in humansand falls thereafter, possibly due to age-related changes in the kidney integrityfunction. In contrast, cadmium levels in the muscle continue to increase over thecourse of life. The average cadmium concentration in the renal cortex of nonoc-


cupationally exposed persons, age 50, varies between 11 and 100 mg/kg indifferent regions.

The diet is the major route of human exposure to cadmium. Contamination offoods with cadmium results from its presence in soil and water. Concentrations ofcadmium in foods range widely, and the highest average concentrations are foundin mollusks, kidneys, livers, cereals, cocoa, and leafy vegetables. A daily intake ofabout 60 µg would be required to reach a concentration of 50 mg/kg in the renalcortex of persons 50 years of age, assuming an absorption ratio of 5%. About 10%of the absorbed daily dose is rapidly excreted (WHO, 1989, 2001).

4.5.5 LEAD

The Joint FAO/WHO Expert Committee on Food Additives (JECFA) and other WHOcommittees have recognized that infants and children are the groups at highest risk tolead exposure from food and drinking water. Lead as an anthropogenic contaminantfinds its way into air, water, and surface soil. Lead-containing manufactured productsalso contribute to the lead body burden. The domestic environment, in which infantsand children spend the greater part of their time, is of particular importance as a sourceof lead intake. In addition to exposure from general environmental sources, some infantsand young children, as a result of normal, typical behavior, can receive high doses oflead through mouthing or swallowing of nonfood items. Pica, the habitual ingestion ofnonfood substances, which occurs among many young children, has frequently beenimplicated in the etiolgy of lead toxicity. In the United States, on average, 2-year-oldchildren may receive about 45% of their daily lead intake from dust, 40% from food,15% from water and beverages, and 1% from inhaled air (WHO, 1986).

Lead absorption is heavily influenced by food intake; much higher rates occurafter fasting than when lead is ingested with a meal. This effect may be due mainlyto competition from other ions, particularly iron and calcium, for intestinal transportpathways. Absorption is also affected by age; the typical absorption rates in adultsand infants are 5–10% and about 50%, respectively.

Children absorb lead from the diet with greater efficiency than adults (WHO,2000). After absorption and distribution in blood, where most lead is found inerythrocytes, it is initially distributed to soft tissues throughout the body. Subse-quently, lead is deposited in the bone, where it eventual accumulates. The half-lifeof lead in blood and other soft tissues is 28–36 days. Lead that is deposited inphysiologically inactive cortical bones may persist for decades without substantiallyinfluencing the concentrations of lead in blood and other tissues. On the other hand,lead that is accumulated early in life may be released later when bone resorption isincreased, e.g., as result of calcium deficiency or osteoporosis. Lead that is depositedin physiologically active trabecular bones is in equilibrium with blood. The accu-mulation of high concentrations of lead in blood when exposure is reduced may bedue to the ability of bones to store and release lead.

Dietary lead that is not absorbed in the gastrointestinal tract is excreted in thefeces. Lead that is not distributed to other tissues is excreted through the kidneyand, to a lesser extent, by biliary clearance (WHO, 2000).


The biochemical basis of lead toxicity is its ability to bind to biologicallyimportant molecules, thereby interfering with their function by a number of mech-anisms. At the subcellular level, the mitochondrion appears to be the main targetorganelle for toxic effects of lead in many tissues. Lead has been shown toselectively accumulate in the mitochondria. There is evidence that it causes struc-tural injury to these organelles and impairs basic cellular energetics and othermitochodrial functions. It is a cumulative poison, producing a continuum of effects,primarily on the hematopoietic system, the nervous system, and the kidneys. Atvery low blood levels, lead may impair normal metabolic pathways in children.At least three enzymes of the heme biosynthetic pathway are affected. Lead atabout 10 µg/100 cm3 in blood interferes with δ-aminolevulinic acid dehydratase(WHO, 1986). Alteration in the activity of the enzymes of the heme syntheticpathway leads to accumulation of the intermediates of the pathway. There is someevidence that accumulation of δ-aminolevulinic acid exerts toxic effects on neuraltissues through interference with the activity of the neurotransmitter γ-amino-butyric acid. The reduction in heme production per se has also been reported toadversely affect nervous tissue by reducing the activity of tryptophan pyrollase,a heme-requiring enzyme. This results in an increased metabolism of tryptophanvia a second pathway, which produces high blood and brain levels of the neu-rotransmitter serotonin.

TABLE 4.5Provisional Tolerable Weekly Intake (PTWI) of Toxic Elements

Element PTWI

((((µµµµg/kg of body weight) Comments

Arsenic 15.0 For inorganic arsenicCadmium 7.0 —Lead 25.0 When blood lead levels in children exceed 25 µg/100

cm3 (in whole blood), investigations should be carried out to determine the major sources of exposure, and all possible steps should be taken to ensure that lead levels in food are as low as possible

Mercury 3.3 as methylmercury; 5.0 as total mercury

With the exception of pregnant and nursing women who are at greater risk to adverse effects from methylmercury

Note: PTWI = provisional tolerable weekly intake; this term refers to contaminants such as heavy metalswith cumulative properties. Its value represents permissible human weekly exposure to those contaminantsunavoidably associated with the consumption of otherwise wholesome and nutritious foods.

Source: WHO, 30th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Cambridge,1986; WHO, 33rd Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Cambridge,1989; WHO, 53th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 2000;WHO, 55th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 2001.

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TABLE 4.6Metal Toxicity in Man

Metal Toxic Effects

Daily Intake(mg per adult

person) Source of Exposure Absorption

Arsenic Inorganic compounds cause abnormal skin hyperpigmentation, hyperkeratosis, skin and lung cancer; organoarsenic compounds present in fish are less toxic or nontoxic

0.0–0.29 Contaminated water, food containing residue of arsenic pesticides, and veterinary drug; fish and shellfish are the richest sources of organic compounds arsenobetaine and arsenocholine

>90%, organoarsenic compounds

High, inorganic trivalent compounds

Cadmium Accumulates mainly in liver and renal cortex; nephrotoxicity, decalcification, osteoporosis, osteomalacia, and Itai Itai disease; embryo toxic in early gestation; impairs immune system, calcium and iron absorption; hypertension and cardiovascular disease; kidney is the critical organ

<0.01–0.1 Oysters, cephalopods, crops grow on land fertilized with high doses of phosphate and sewage sludge contaminated; cadmium leaching from enamel and pottery glazes; contaminated water

3–10%; cadmium bound to metallothionein is well absorbed

Lead

Mercury

At blood levels greater than 40 µg/100 cm3, exerts a significant affect on hemopoietic system, resulting in anemia; affects central nervous system

Methylmercury compounds easily pass the blood–brain and placetal barriers; causes severe neurological damage, greater in young children; in animals, also renal damage and anorexiaa

<0.1–0.2

<0.02–0.1

Food contaminated from leaching of glazes of ceramic food ware, as well as from motor vehicle exhausts, atmospheric deposits, canned foods, and water supply from plumbing system

Fish and shellfish; meat from animals fed with mercury-dressed grains

5–10% in adult person 40–50% in children

>90% as methylmercury compounds

15% as inorganic mercuric compounds

aInformation from WHO, 53th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 2000.

Source: Nabrzyski, M. and Gajewska, R., Roczniki PZH, 35, 1, 1984; Nabrzyski, M. et al., Roczniki PZH, 36, 113, 1985; WHO, Arsenic, WHO, Geneva 1981; WHO,30th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Cambridge, 1986; WHO, 33rd Meeting of the Joint FAO/WHO Expert Committee on FoodAdditives, Cambridge, 1989; WHO, 53th Meeting of the Joint FAO/WHO Expert Committee on Food Additives, Geneva, 2000; WHO, 55th Meeting of the JointFAO/WHO Expert Committee on Food Additives, Geneva, 2001.


Lead interferes with vitamin D metabolism, since it inhibits hydroxylation of25-hydroxy-vitamin D to produce the active form of vitamin D. The effect has beenreported in children, with blood levels as low as 10–15 µg/100 cm3 (WHO, 1986).Measurements of the inhibitory effects of lead on heme synthesis are widely usedin screening tests to determine whether medical treatment for lead toxicity is neededfor children in high-risk populations who have not yet developed overt symptomsof lead poisoning.

4.5.6 INTERACTIONS OF ELEMENTS

Data concerning the toxicity of the four discussed toxic minerals are presented inTables 4.5 and 4.6. The uptake of elements is not entirely independent of one another.Elements of similar chemical properties tend to be taken up together. Sometimes oneelement has an inhibiting effect on another, or there can be a synergistic effect, e.g.,enhancement of absorption of calcium in the presence of adequate amounts of phos-phorus, or cadmium and lead hindering calcium and iron absorption, or zinc andcopper antagonism and their influence on the ratio of Zn/Cu on copper deficiency.

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Rosenberg, J.H. and Solomons, N.W., Physiological and pathophysiological mechanism inmineral absorption, in Absorption and Malabsorption of Minerals, Vol. 12., Solomons,N.W. and Rosenberg, J.H., Eds., Alan R. Liss, Inc., New York, 1984, p. 1.

Rutkowska, U., The effect of the grinding process on contents of copper, zinc, and manganesein rye and wheat flour, Roczniki PZH, 26, 339, 1975 (in Polish).

Samant, S.K. et al., Protein-polysaccharide interactions: a new approach in food formulation,Int. J. Food Sci. Technol., 28, 547, 1993.

Solomons, N.W., Ed., Absorption and Malabsorption of Mineral Nutrients, Alan R. Liss, Inc.,New York, 1984, p. 269.

True, R.H. et al., Changes in the nutrient composition of potatoes during home preparation,III, Min. Am. Potato J., 56, 339, 1979.

Trzebska-Jeske, I. et al., The effect of mechanical processing on nutritional value of groatsproduced in Poland, Roczniki PZH, 24, 717, 1973 (in Polish).

Vaessen, H.A.M.G. and van Ooik, A., Speciation of arsenic in Dutch total diets: methodologyand results, Z. Lebensm. Unters. Forsch., 189, 232, 1989.

WHO, Environmental health criteria, 18, in Arsenic, WHO, Geneva, 1981.WHO, Environmental health criteria, 36, in Fluorine and Fluorides, WHO, Geneva, 1984.

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Skladniki

811-5871-6149-4/02/$0.00+$1.50© 2002 by CRC Press LLC

Saccharides

Piotr Tomasik

CONTENTS

5.1 Natural Food Saccharides, Occurrence, Role, and Applications ..................815.2 Carbohydrate Structure ..................................................................................825.3 Carbohydrate Chirality...................................................................................885.4 Carbohydrate Reactivity.................................................................................89

5.4.1 Chemical and Physical Transformations of Mono-, Di-, and Oligosaccharides Essential in Food Chemistry ..........................895.4.1.1 Reactions of Aldehyde and Ketone Functions...................895.4.1.2 Reactions of the Hydroxyl Groups ....................................925.4.1.3 Reactions of Glycosidic Bond............................................975.4.1.4 Specific Reactions of Saccharides......................................97

5.4.2 Chemical and Physical Transformations of Polysaccharides............995.4.2.1 Depolymerization of Carbohydrates.................................1025.4.2.2 Chemical Modification of Polysaccharides without

Attempted Depolymerization............................................1035.4.2.3 Cross-Linked Polysaccharides..........................................105

5.4.3 Enzymatic Transformations of Carbohydrates ................................1055.4.4 Cereal and Tuber Starches ...............................................................107

5.5 Functional Properties of Carbohydrates ......................................................1075.5.1 Taste..................................................................................................1075.5.2 Colorants ..........................................................................................1095.5.3 Flavor and Aroma ............................................................................1105.5.4 Texture..............................................................................................1105.5.5 Encapsulation ...................................................................................1115.5.6 Polysaccharide Containing Biodegradable Materials......................112

References..............................................................................................................113

5.1 NATURAL FOOD SACCHARIDES, OCCURRENCE, ROLE, AND APPLICATIONS

Nature commonly utilizes saccharides as a source of energy, structure-formingmaterial, water-maintaining hydrocolloids, and even sex attractants. All organismcells contain saccharide components in their membranes. Frequently, saccharidesexist in naturally derivatized forms, e.g., aminated, as in chitin and chitosan;

5


esterified; alkylated, as in glycosides; oxidized; reduced; or linked to proteins,lipids, and other structures, such as hemoglobin and hesperidin.

Lower monosaccharides, i.e., aldo- and keto-bioses, -trioses, and -tetroses, donot exist naturally in a free state. Glyceroaldehyde and hydroxyacetone in phospho-rylated forms are the products of alcoholic fermentation and glycolytic sequence.Erythrose and erythrulose also appear in phosphorylated forms in the pentose cycleof glucose, while ketopentose–ribulose can be found as its phosphate ester(Table 5.1).

5.2 CARBOHYDRATE STRUCTURE

Carbohydrates are either polyhydroxyaldehydes (aldoses, oses) or polyhydroxyke-tones (ketoses, uloses); there is an electron gap at their carbonyl carbon atom.Typically, aldehydes and ketones accept nucleophiles such as water to form hydratesor alcohols to form hemiketals (5.1 and 5.3) and hemiacetals (5.4 and 5.6), respec-tively. In pentoses, pentuloses, hexoses, hexuloses, and higher carbohydrates, oneof the hydroxyl groups can play the role of internal nucleophile. Thus, open-chainstructure (5.2 and 5.5) cyclizes into internal hemiacetals and ketals, all with eitherfive- (5.1 and 5.3) or six- (5.4 and 5.6) membered cycles.

Since all their carbon atoms are sp3-hybridized, the bond angles in the cycleshould be about 109ο to provide strainless conformations. It implies nonplanarconformations of the cycles (Siemion, 1985).

In some cases, the pyranose ring formation can be either obstructed or blocked,and a five-membered furanose ring dominates for the given sugar. The molecular

Structures 5.1 — 5.6

Saccharides 83

structure of di- and higher saccharides is additionally controlled by a potential energybenefit resulting from the formation of intramolecular hydrogen bonds, as in cello-biose (5.7a), lactose (5.7b), maltose (5.8 and 5.9), and sucrose (5.10).

Both maltose structures correspond to two energy minima, available thanks tointramolecular hydrogen bonds. Two hydrogen bonds might stabilize the sucrosemolecule, provided the fructosyl moiety takes the furanosyl structure. Indeed, suchpossibility is employed in nature.

In polysaccharides, the structural factors are even more important. A number ofdifferent saccharide units in the chain, branching of the chain, and the presence ofeither more-polar groups (COOH, PO3H2, and SO3H) or less-polar groups (OCH3

Structure 5.7



TABLE 5.1 Essential Natural Saccharides in Food and Their Occurrence and Applications

Saccharide Occurrence Applications

Monosaccharides and Their Natural DerivativesPentosesD-Apiose Parsley and celeryL-Arabinose Plant gums, hemicelluloses,

saponins, protopectinAlcoholic fermentation; furan-2-aldehyde production

D-Xylose Accompanies L-arabinose Reduction of xylitol; sucrose substitute; alcoholic fermentation; production of furan-2-aldehyde

HexosesL-Fucose Mother milk, algae, plant mucus,

and gumsD-Galactose Oligo- and polysaccharides, plant

mucus and gums, saponins, glycosides

Diagnostics in liver tests

D-Glucose Plants and animals, honey, inverted sugar, saponins

Alcoholic fermentation; sweetener; energy pharmacopeial material; nutrient; food preservative

D-Manose Algae, plant mucus, orangesL-Rhamnose Plant mucus and gums, pectins,

saponins, glycosidesHexulosesD-Fructose Fruits, honey, inverted sugar Non-cavity-causing sweetener;

sweetener for diabetics; food humidifier and preservative

D-Glucosylamine Chitin, chitosan Pharmaceutical aid; antiarthritic drugs; ion exchanger

L-Sorbose Rowan berries Synthesis of ascorbic acid

Disaccharides (oses)Lactose Mammalian milk Improves the taste of dairy products;

fermenting component of milkMaltose Starch, sugar beet, honeySucrose Sugar beet, sugar cane Alcoholic fermentation; common

sweetener; caramel production; food preservation

PolysaccharidesAgar Red algae Microbiological nutrient; gel-

forming agent; emulsifier; bread staling retardant; meat texturizer; meat substitute

Alginates Brown algae Thickener; gel-forming agent; food and beer foam stabilizer

Saccharides 85

and NHCOCH3) than the OH group are crucial for the overall structure of polysac-charide. Amylose and cellulose are the most regularly built; they form polymerchains of α-D- and β-D-glucose units, respectively. In very random cases, amyloseis branched with short chains (Ball et al., 1998). The amylose chain is originallylong and randomly coiled (Figure 5.1), but it turns into a more ordered, helical

Carrageenans ι, κ, γ, µ, ν Red seaweed Gel-forming agent; stabilizer; protein fiber texturizer; milk fat anticoagulant; milk clarifying agent

Cellulose Plants Saccharification to glucose; dietary fiber; chromatographic sorbent

Dextran Frozen sugar beet Chromatographic sorbent (Sephadex); blood substitute

Furcellaran Red seaweed Gel-forming agent; filler; marmalade stabilizer; protein precipitation

Gatti gum Anageissus latifolia tree Emulsifier; stabilizerGuaran gum Leguminous plants Food; cosmetics; pharmaceutical

thickener and stabilizerGum Arabic Senegal acacia Emulsifier; antistaling stabilizer;

flavor fixativeGum karaya Sterculiacea tree (India) Foam stabilizer; thickenerGum locust bean Locust bean Thickener; adhesiveGum tragacanth Astragalus species (Middle East) Thickener; stabilizerGlycogen Liver, muscle Glucose reservoirHemicelluloses:Arabinogalactan Larch Emulsifier; stabilizerGalactanMannans, xylans

Plants Alcoholic fermentation; reduction to alcohol

Heparin Liver, tongues Blood anticlotting agentHialuronic acid Connective tissues Water absorbentInulin Endive, Jerusalem artichoke PrebioticPectins Plants, mainly apples, citrus,

sugar beetGel-forming agent; beer stabilizer

Protopectin Plants and nonmatured fruits Decomposes to pectins on plant maturation and cooking

Starch Amylose, amylopectin

Tubers, grains, some fruits Food filler; thickener; gel-forming agent, bakery products; saccharification to syrups

Tamarind flour Tamarind tree (India) Thickener; marmalade; jelly; ice cream; mayonnaise stabilizer

Xanthan gum Semiartificial gum Hydrocolloid stabilizer

TABLE 5.1 (CONTINUED)Essential Natural Saccharides in Food and Their Occurrence and Applications

Saccharide Occurrence Applications


structure. Helical complexes are formed if hydrocarbons, alcohols, lipids, fatty acids,and bar-like anions, such as I5

–, OCN–, are present in the amylose environment(Tomasik and Schilling, 1998a, 1998b).

Such compounds and anions, potential guests of the complex, either havehydrophobic fragments or are fully hydrophobic. The possibility of the reductionof the energy of the system by interactions of hydrophobic sides of amylose andthe potential guest is the driving force of the formation of a helical complex.Thus, its cavity is hydrophobic and all hydroxyl groups of the D-glucose unitsare situated on the external surface of the helix, as well as on the edges of itscavity (the V-type amylose). The number of glucose units in one helix turndepends on the guest molecule present in the helical complex. With KOH as aguest, one turn involves six glucose units. Inclusion of KBr reduces the turn tofour glucose units, whereas inclusion of tert-butanol and α-naphthol requires theturns of seven and eight glucose units, respectively (Tomasik and Schilling,1998a). An additional stabilization of the amylose helix comes from the double-helix formation (Imberty et al., 1991). Depending on the helix–helix interactionsand, in consequence, their mutual arrangement, A- and B-type amylose is formed(Figure 5.2). Recently distinguished C-type amylose appears to be a combinationof both A and B patterns.The conformation of β-D-glucose units bound in cel-lulose in the 1→4' manner offers a particularly strong hydrogen bond cross-linkedmacrostructure of this polysaccharide.

Glycans with 1,2-, 1,3-, and particularly 1,6-linked units have a more irregular,loosely jointed structure. The heterogenicity of the polysaccharide structural unitsand their volumes introduce further regularities or irregularities in the macrostruc-ture. A decrease in the group polarity, e.g., by methylation, and number results in amore irregular polysaccharide structure.

An opposite effect can be achieved in the presence of more polar groups, oreven less polar, but suitably oriented groups. For instance, chitin, a polysaccharidewith acetylamino groups, has a very regular, compact structure that provides insol-ubility of chitin in water. This polysaccharide is a common insect carapace-forming

FIGURE 5.1 Randomly coiled amylose chain and its helical complex, formed as a result ofits interaction with a nonpolar fragment.

x

x

Saccharides 87

material. Because of this property, chitin has found several technical applications(Goosen, 1997).

Amylopectin (Figure 5.3) presents a special case. It is a highly branchedhomopolymer of α-D-glucose units. The 1→6-linked terminal branches, which occurat about every 8th glucose unit, contain 15–30 glucose units. These branches canalso participate in the formation of helical complexes. Some guest molecules maysituate in areas around branching sites in the amylopectin molecule. In spite of anirregular, bulky structure, amylopectin also forms a double helix (Imberty et al.,1991). Because of functional properties, the structure of the polysaccharide matrix,the tertiary structure, is also essential. In solution, polysaccharides such as amyloseform separate fibrils that, upon coiling, turn either into micelles at a low-temperaturegradient or into gels at a high-temperature gradient. Both amylose and amylopectinparticipate in the starch granule organization (Gallant et al., 1997). Their seminativemixture has specific functional properties. It strongly depends on the amylose-to-amylopectin ratio; size of granules (Table 5.2); content of residual components of

FIGURE 5.2 The crystallographic A- and B-types of amylose depend on the structure ofdouble amylose helices.

FIGURE 5.3 Scheme of amylopectin molecule.


native starch, e.g., lipids, proteins, and mineral salts; and random esterification withphosphoric acid, the latter exclusively in the case of potato amylopectin. The amy-lose-to-amylopectin ratio decides on aqueous solubility of starch and texture of itsgels, resulting from a penetration of water into starch granules (swelling) and frompushing the granule interior into a solution where the gel network is formed. Thesize of granules is essential for smoothness of products prepared from starch (pud-dings, gels). In practice, not all starch granules swell and participate in the gelformation. Larger granules are more susceptible to gelation and chemical modifica-tion (Lii et al., 2001b). The nutritional value of starches usually increases withcontent of residual components; however, in several cases, when starch is subjectedto chemical modifications or is used for specific nonnutritional purposes, such“contaminants” are nonbeneficial.

Cellulose that is completely insoluble in water forms microfibrils that are com-posed of crystallites and amorphous regions. Such regions may be also distinguishedinside of starch granules. Roughly, they form concentric crystalline and amorphouslayers surrounding the hilum, the origin of the granule growth (Gallant et al., 1997).Amorphous regions contain amylopectin (Szymonska et al., 2000). The structure ofgranules is developed on plant vegetation by enzymatic debranching of so-called-plant glycogen (Erlander, 1998). These enzymes reside inside of starch granules andcan be activated on starch processing.

5.3 CARBOHYDRATE CHIRALITY

Chirality is a property resulting from a lack of symmetry of molecules. All carbo-hydrates, including polysaccharides, have centers of asymmetry and therefore arechiral. Chirality is expressed as a concentration-independent specific rotation, [α]°:

TABLE 5.2Selected Properties of Various Botanical Origin Starches

Starch Origin

Amylose Content (%)

Granule Size (µµµµm)

Gelation Temperature

(°C)Protein

Content (%)a

Lipid Content (%)a

Barley 19–22 5–40 51–59 up to 1.22 up to 0.20Maize 21–24 10–30 67–100 0.32 0.60Oat 23–30 5–15 87–90 up to 0.39 up to 0.62Potato 18–23 1–100 59–68 0.15 0.06Rice 8–37 2–10 68–78 up to 2.82 up to 1.00Rye 24–30 8–60 55–70 0.32 0.22Triticale 23–24 2–40 55–62 0.27 0.39Waxy maize

1–2 10–30 62–72 up to 0.31 up to 0.20

Wheat 24–29 2–36 59–64 0.24 0.36

a Average values on dry basis.

Saccharides 89

[α]° = (α · 100)/lc (5.1)

where α is an angle of twist determined polarimetrically, l is the length of thepolarimetric tube, and c is the concentration of saccharide in g/100 cm3. Chiralityof freshly prepared aqueous solutions of saccharides is either variable or constantin time, which points to mutarotation or lack of mutarotation, respectively (seebelow).

5.4 CARBOHYDRATE REACTIVITY

5.4.1 CHEMICAL AND PHYSICAL TRANSFORMATIONS OF MONO-, DI-, AND OLIGOSACCHARIDES ESSENTIAL IN FOOD CHEMISTRY

5.4.1.1 Reactions of Aldehyde and Ketone Functions

Mutarotation — Only reducing sugars, e.g., those with a hydroxyl group at theanomeric carbon atom, mutarotate. They reversibly, either spontaneously, or on acidor base catalysis, transform through the pyranose and furanose ring opening followedby ring-closure (5.11.a and 5.14 into 5.12 and 5.11b). An open-chain structure isnot typical for saccharides. Aqueous D-glucose at 25°C has approximately 0.003%of the open-chain compound.



Mutarotation has limited, rather diagnostic, significance in food chemistry andtechnology. Practical use of this reaction is demonstrated in milk powder manufac-ture. Evaporation of milk at a rate lower than mutarotation of lactose yields a productwith less α-lactose isomer, which crystallizes in prism- or pyramid-like form. Fastmilk evaporation gives an amorphous mixture of α- and β-lactose (5.7b).

Reduction to Alcohols — The industrial scale reduction involves either NaBH4

or electrochemical and catalytic (Raney nickel) hydrogenation. Resulting open-chainpolyols, the sugar alcohols (5.12 and 5.13), have a new chiral center. In consequence,each ketose (5.14) yields two alcohols, whereas aldoses (5.11a and 5.11b) yieldonly one alcohol.

Addition to the Carbonyl Group — The internal, cyclic hemiacetal formationis one of the illustrations of such addition. The H2N–X nucleophiles, with X beingNH2 (hydrazine), NHAr (arylhydrazines), OH (hydroxylamine), NHCONH2 (semi-carbazide), NHCSNH2 (thiosemicarbazide), or alkyl (primary amine), producehydrazones, arylhydrazones, oximes, semicarbazones, thiosemicarbazones, and alkylimines (Schiff bases), respectively, following the following path: 5.4 + 5.15 → 5.16→ … → 5.21.

Hydrazones and arylhydrazones (5.20) react with the second molecule of thecorresponding reagent into osazones (5.21). The reactions with mono-, di-, and lower


Saccharides 91

oligosaccharides have some analytical value. Reactions with H2N–X nucleophilesin which X = CH(R)COOH, the amino acids, nucleotides, and proteins, as well asNH3

+ (ammonia) produce aldosylamino acids and aldosylamines, respectively (4.15with X = CH(R)COOH or H).

Aldoses undergo the Amadori rearrangement and subsequently turn into cara-mels, the natural brown food colorants, and/or heteroaromatic compounds — deriv-atives of pyrrole, imidazole, and pyrazine. Ketoses react similarly into ketosylaminoacids or ketosylamines, which, in the first step, undergo the Heyns rearrangement(5.17–5.23). These rearrangements are the first steps of either thermal or enzymatic(the Maillard reaction) reactions resulting in the browning of food and the aromaof roasted, baked, or fried foodstuffs.

Oxidation — The oxidation of aldoses (5.24) with bromine or chlorine inalkaline solution (hypobromites and hypochlorites, respectively) leads to aldonicacids that readily self-esterify (lactonize) into δ- (5.25) and γ- (5.26) lactonesresiding with free acid (5.27) in equilibrium. β-Conformers oxidize more readilythan α-conformers.




Glucono-δ-lactone (4.25) has found its application in baking powders, rawfermented sausages, and dairy products where the slow release of acid is required.

The oxidations with Cu2+ (the Fehling, Benedict, and Barfoed tests) and Bi3+

(the Nylander test) ions are the only analytical tests for reducing sugars, e.g., thosewith the hydroxyl group at the anomeric carbon atom.

5.4.1.2 Reactions of the Hydroxyl Groups

Esterification — Saccharides are commonly esterified with acyl chlorides, as wellas organic and inorganic acid anhydrides. These reactions can be run either exhaus-tively with involvement of all hydroxyl groups of saccharide molecules or selec-tively. In the latter case, a protection (blocking) of certain hydroxyl groups isrequired. For instance, all hydroxyl groups of D-glucose, except that at C3, canbe protected in reaction with acetone in acidic medium. Resulting 1,2,5,6-di-O-isopropylidene-α-D-glucofuranose (5.28), after acylation at a nonprotectedhydroxyl group to give monoacylated diketal (5.29), is then decomposed withcarboxylic acid into 3-monoacylated saccharide (5.30). Such reactions can beapplied to polysaccharides, although polysaccharides readily esterify carboxylicacids simply on heating of their blends (Tomasik and Schilling, 2002).

The acylation of mono- and oligosaccharides and their derivatives, mainlysorbitol and sucrose, with higher fatty acids yields surface-active agents and fatreplacers. Hydrolysis of acyl groups can be achieved by either interesterification(water or alcohols) or ammonolysis.


Saccharides 93

Etherification — There are several methods of sugar etherification. They are:

• The hydrochloride catalyzed Fischer glycosidation with alcohols• The exhaustive Haworth methylation with dimethyl sulfate in alkaline

medium, with retention of configuration at the anomeric carbon atom• The Irvine-Purdie exhaustive methylation, which involves methyl iodide

in the presence of Ag2O• The Koenigs-Knorr glycosidation, which is the substitution of an α-halo

atom of α-halopentacetyl sugars with methanol in the presence of Ag2CO3

Such reactions with small alkyl groups are important for saccharide structuralanalysis.

Halogenation — The hydroxyl group at C1 is readily substituted with a halideatom (X) when a pentacetylated saccharide is treated with HX in acetic acid. Suchsaccharides are suitable for synthesis of desoxysaccharides. Exhaustive replacementof all hydroxyl groups can be achieved with reagents suitable for such reaction withsimple alcohols, i.e., COCl2, SOCl2, POCl3, PCl3, and PCl5. Chlorination of somesugars results in products of increased sweetness (Table 5.3).

Dehydration — It is an intramolecular elimination of one water moleculeproducing 1,6- (5.31), 3,6- (5.32), or 1,2- (5.34) anhydrosugars, as well as being inequilibrium with saccharide enol (5.33) and ketone (5.35).

Anhydrosugars can be utilized for the synthesis of some derivatives, such asamino sugars and others. Dehydration is the first step of sugar caramelization. Furtherheating of dehydrated saccharides results in the formation of three subsequentcompounds called caramelan, caramelen, and caramelin (Tomasik et al., 1989):

6C12H22O11 – 12 H2O = 6C12H12O9 (caramelan)

6C12H22O11 – 18 H2O = 2C36H18O24 (caramelen)

6C12H22O11 – 27 H2O = 3C24H26O13 (caramelin)

Reduction — A multistep reaction leads to desoxysaccharides. It involves 1-halopentaacetylated saccharide, which is dehalogenated with zinc into acetylatedglucal (5.35). Hydrolyzed glucal accepts sulfuric acid, the SO3H residue of whichis readily hydrolyzed into deoxysugar (5.41).

Oxidation — Apart from CO2 and H2O, there are three series of products thatresult from the oxidation of saccharide. They are 2,3-dialdehydes (5.43 and 5.49)formed on the oxidative cleavage of saccharides (5.42 and 5.48) with periodates,the sole oxidants providing such course of oxidation. Such dialdehydes are consid-ered toxic. Further oxidation of dialdehydes leads to glyceric acid (5.45), glyoxalicacid (5.47), hydroxypyruvic acid (5.46), and erythronic acid (5.51), as shown belowfor the oxidative cleavage of sucrose (5.42) and maltose (5.48).

The oxidation of monosaccharides, e.g., D-galactose (5.52), with strong oxidantsproceeds at both C1 and C6 atoms, leaving dicarboxylic, aldaric acids (5.53). Aldaric


acids can lactonize into lactones (5.54). Lactones produce uronic acids (5.55) whenreduced with sodium amalgam.

The oxidation at C1 can be prevented by protection of the 1–OH group. Theglycosidic bond in oligosaccharides offers sufficient protection. Application of weakoxidants offers direct route to uronic acids.

Complex Formation — The hydroxyl groups offer two types of interactionswith molecules having either a clearly dipole character or charge, i.e., ions. Thehydrogen atoms of these groups are capable of interactions with electron-excessivesites of dipoles and anions, whereas lone electron pairs of the oxygen atom areelectron donors for cations and the positive side of dipolar molecules.

The complex formation is a general ability of saccharides. Fruitful resultswere noted in the cases of Ca2+

salts, preferable chloride, and hydrogen carbonate.The cation forms fairly stable compounds. This property was widely utilized in

TABLE 5.3RS of Various Substances in 10% Aqueous Solutions (RS of Sucrose = 1.0)

Substance RS

Sucrose 1.00β-D-Fructopyranose 1.80Inverted sugar 1.30D-Glucopyranose α- 0.70

β- 0.80D-Mannopyranose α- 0.30

β- ΒitterD-Galactopyranose 0.32Maltose 0.32D-Lactose, α- 0.20

β- 0.30D-Galactosucrose TastelessRaffinose 0.01Stachyose 0.101'-Chloro-1'-desoxysucrose 0.204-Chloro-4-desoxysucrose 0.056-Chloro-6-desoxysucrose Bitter1',4,6'-Trichloro-1',4,6-tridesoxygalactosucrose

20.00

Mannitol 0.40Sorbitol 0.60Xylitol 0.85–1.2Honey 0.97Molasses 0.74Saccharin 200–700Cyclamates 30–140Aspartame 200Neohesperidin dihydrochalcone 2000

Saccharides 95




sugar manufacture for the separation of sucrose from its syrups. Saccharidealcohols also coordinate metal ions. Depending on cations, their optical rotationis affected to a different extent, but always in the order of Na+ < Mg2+ < Zn2+,Ba2+ < Sr2+ < Ca2+. Complexes of saccharides with a wide variety of cations


Saccharides 97

were prepared and characterized (Angyal, 1989). Saccharides also complex toother, nonmetallic compounds, e.g., organic food components such as polysac-charides and proteins. They are sorption complexes with involvement of hydro-gen bonds. The energies of the complex formation are low and do not exceed 4kJ/mole (Tomasik et al., 1995). Nevertheless, they are essential in food textur-ization and thermal stability (Ciesielski and Tomasik, 1998; Ciesielski et al.,1998). The complexation itself can seriously affect the sugar metabolism andbiotechnological processes, as well as transport of metal ions in the organism.

5.4.1.3 Reactions of Glycosidic Bond

As a typical acetal bond, a glycosidic bond readily hydrolyzes in an acid-catalyzedreaction. In this manner, di- and oligosaccharides can be split into monosaccharides.It is a common method for manufacturing of invert sugar, a mixture of α-D-glucoseand β-D-fructose, from sucrose.

5.4.1.4 Specific Reactions of Saccharides

In strongly acidic media, saccharides produce furan derivatives in a sequence ofreactions that are rearrangements and dehydrations followed by cyclization. Similarproducts are available thermally. Pentoses and hexoses give furan-2-aldehyde and5-hydroxymethylfuran-2-aldehyde, respectively. Both of these products are respon-sible for the specific aroma of caramel and burnt sugar.

In weakly acidic and neutral media the reactions proceed at a lower rate. Reduc-tones (4.55–4.57), compounds with the carbonyl group vicinal to an endiol moiety,which are formed, are stable at pH < 6 and act as natural antioxidants. They transforminto deoxysugars, uloses (5.58). The latter undergo cyclization into 5-hydroxymeth-ylfuran-2-aldehyde (5.62). Corresponding osuloses (5.63) in similar sequences oftransformations yield diacetylformosine (5.69).



In acid-based reactions 2-acetyl-3-hydroxyfuran (isomaltol) (5.76), 3-hydroxy-2-methylpyran-4-one (5.77), and maltol (5.79) are formed. They are responsible forthe baked bread aroma.


Saccharides 99

Endiols (4.80) can isomerize into other saccharides in the Lobry de Bruyn–vanEkenstein rearrangement. Thus, D-glucose (5.4) can isomerize into mannose (5.81)and fructose, (5.1) accompanied by a small amount of D-psicose (5.83). Alkalinemedium provides isomerization to disaccharides, which turn from aldoses into ke-toses, as shown for lactose (5.7b) isomerized to lactulose (5.84).

Since the enolization is not restricted to the 2 and 3 positions, a number ofproducts are formed that undergo subsequent aldol condensations and the Cannizzarooxidation. They are all 2-hydroxy-3-methyl, 3,4-dimethyl-2-hydroxy, 3,5-dimethyl-2-hydroxy, and 3-ethyl-2-hydroxy-2-cyclopenten-1-ones; sugar acids; acetic acid;hydroxyacetone; three isomeric hydroxy-2-butanones; γ-butyrolactone; and suchfuran derivatives as furyl alcohol, 5-methyl-2-furyl alcohol, and 2,5-dimethyl-4-hydroxy-3(2H)-furanone. They are food flavoring agents.

5.4.2 CHEMICAL AND PHYSICAL TRANSFORMATIONS OF POLYSACCHARIDES

Although several polysaccharides found their large-scale applications, only few ofthem, e.g., starch, cellulose, and hemicelluloses, are modified on an industrial scale.




Saccharides 101

Products of their modifications are widely utilized in food technology and everydayfood preparations. Food processing such as cooking, baking, frying, and picklingusually deal with food carbohydrate transformations.

The functional group reactivity in polysaccharides is, to a great extent,obstructed by their macrostructure. These potential reaction sites that do not resideon the surface may be unavailable for many reagents, as they are either hiddeninside the macrostructure or involved in the formation of intra- and intermolecularhydrogen bonds crucial for the macrostructure properties. Many reactions ofpolysaccharides are governed by heterogenicity of the reaction system. Onlyrandomly reacting polysaccharides are solvent soluble. Among polysaccharidesutilized either on or after transformation, hemicelluloses are exclusive. They arewater soluble or they swell. Problems of solubility and compactness are encoun-tered particularly in cellulose and starch, which are fibrillar and granular, respec-tively. The reactivity in terms of the rate and degree of transformation can becontrolled by either application of suitable reagents or loosening of the compactstructure with involvement of a physical action. The solvent effect (water in caseof starch and higher alcohols (Ruck, 1996) in case of cellulose) is the mostcommonly used tool. But high pressure; sonication with ultrasounds; ultraviolet,microwave, and ionizing radiation; thermolysis; freezing; and glow plasma might

Structures 5.80— 5.84


also be suitable for loosening a compact polysaccharide structure (Szymonskaet al., 2000; Tomasik and Zaranyika, 1995). Pasting and gelatinization of starchby heating it in water or immersing it in aqueous alkali delivers pregelatinizedstarch. Because such processing destroyed several intra- and intermolecular bonds,pregelatinized starch is well water soluble and chemically more active. Whengranular starch is passed under pressure through narrow nozzles, so-called α-starchwith improved solubility in water is formed. However, such physical modificationsof macrostructure usually result in a depolymerization of the polysaccharide.

Starch granules are composed of amylose and amylopectin, forming crystallineand amorphous regions of granule. Polysaccharides in an amorphous region are moresusceptible to enzymatic digestion than those in crystalline regions (so-called resis-tant starch). Resistant starch is used as prebiotic — a nutrient for probiotic bacteriacolonizing human intestine. Controlled swelling of starch granules in water canremove a significant part of the amorphous interior of starch granule, producingempty domains within granules. Potentially, such granules can be utilized as naturalmicrocapsules for colorants and aromas. Functional properties of starch depend onthe amylose-to-amylopectin ratio. For some purposes, amylose-rich starch is morebeneficial, and for the others, application of an amylopectin-rich (waxy) starch hasa priority. Genetically engineered starches enriched in such components are availableon the market.

5.4.2.1 Depolymerization of Carbohydrates

If not utilized in the pulp industry, hemicelluloses are hydrolyzed in the acid-catalyzed process, mainly to monosaccharides and to furan-2-aldehyde (pen-tosanes) and 5-hydroxymethylfuran-2-aldehyde (5.62) (hexosanes). Monosac-charide-containing syrups, after purification, are either fermented or utilized aswood molasses for feeding ruminants. In another approach, xylose, the leastsoluble component of syrup, is allowed to crystallize. Separated xylose is thenhydrogenated over an Ni/Al catalyst at 120°C under 6 × 106 Pa into xylitol.Hemicelluloses, together with proteins, are capable of the Maillard reaction andmay contribute to the overall secondary aroma of processed foodstuffs (Tomasikand Zawadzki, 1998).

The acid-catalyzed hydrolysis of cellulose, the saccharification, results in split-ting the terminal D-glucose unit of the fibrilles. Thus, under thorough control of thereaction conditions, D-glucose is the sole product. Glucose syrup either is a sourceof pharmaceutical grade D-glucose or is fermented to ethanol.

The β-glycosidic bond of cellulose can be split thermally. Perhaps the mostancient polysaccharide processing — the dry wood distillation — delivers charcoal,water, tar, methanol, acetone, acetic acid, and gases. Liquid and gaseous fractionsresult from the thermolysis of thermally split D-glucose. Thermolysis of cellulosewith α-amino and α-hydroxy acids produces several aromas potentially interestingfor food and cosmetic industries. Starch and pectins also generate aromas on heatingwith these acids (Baczkowicz et al., 1991; Sikora et al., 1998). Depolymerizationof starch yields dextrins — one of the most useful products of the food industry.The most frequent dextrinization involves proton catalysis or heat. Hydrochloric

Saccharides 103

acid is a superior catalyzing proton donor, but organic acids are also capable ofstarch dextrinization. Such processes extended in time can lead in the saccharificationof starch to oligosaccharides and, finally, to D-glucose, maltose, and glucose syrups,which are used directly as sweeteners or are fermented. Thermal (up to 260°C)dextrinization of starch produces canary yellow dextrins called British gums. Theydiffer in properties and applications from dextrins from acid hydrolysis. Dextrinsare commonly used as food thickeners, plasticizers, and adhesives. The physicalmethods mentioned above can also be used in the manufacture of dextrins in readilycontrolled processes. Depolymerization of polysaccharides to formaldehyde seemsto be particularly promising to the chemical industy as the versatile, renewable sourceof and key process for utilization of polysaccharides in the 21st century (Okkerseand van Bekkum, 1996). Reduction of formaldehyde delivers methanol, one of themost important chemical reagents.

5.4.2.2 Chemical Modification of Polysaccharides without Attempted Depolymerization

Polysaccharides offer practically the same kind of reactivity as monosaccharides,except reactions on the anomeric carbon atom, because in a majority of polysaccharidesthe hydroxyl group at this atom takes part in the polysaccharide chain formation viathe glycosidic bonds. In long chains of polysaccharide, only terminal saccharide unitscontain free hydroxyl groups at the anomeric carbon atom. It should be mentionedthat even such minute modification in this position can be reflected by changes inrheological properties of polysaccharide solutions, pastes, and gels. There are somepolysaccharides naturally containing some functional groups. Thus, chitin containsacetamido groups. Alginates, many plant gums (Arabic, gatti, karaya, tragacanth, andxanthan, the latter semisynthetic), pectins, some galactans, and xylans contain carbox-ylic groups. Heparin, furcellaran, and carrageenans carry sulfate function. These groupscan be utilized in chemical modifications of these polysaccharides.

Limitations in possibility of chemical modifications of starch result fromsteric hindrance of reaction sites, solubility, viscosity of reaction medium, andsusceptibility to side reactions; among them, depolymerization almost alwaysaccompanies intended modification. As a rule, polysaccharides are soluble,although frequently only sparingly, in water and dimethyl sulfoxide. Polysaccha-rides solubilize on xanthation, i.e., on reaction with CS2 in alkaline medium, toform syrups of xanthates. On acidification polysaccharides could be recovered.Such procedure was utilized for several decades for production of artificial silkfrom cellulose.

Polysaccharides undergo hydrolysis; reduction to alcohols; oxidation to alde-hydes, ketones, and carboxylic acids; esterification with inorganic (sulfuric, phos-phoric, nitric, boric, and sillylic acids) and organic acids; etherification; acetylationwith aldehydes; halogenation with the same reagents as mono- and disaccharides;ammination (usually via halogenated polysaccharides); carbamoylation with acyla-mides or isocyanides; and metallation. Only some of the large number of potentialmodifications achieved approval by food laws of particular countries. Thus far onlystarch, cellulose, and pectin are chemically modified for nutritional purposes and


can be implemented into foodstuffs. If biodegradable materials are also considered,modification of other polysaccharides can be taken into account.

Practical modification of pectins is limited to changes in degree of their meth-ylation. In this manner the strength of their jellies can be controlled. Modificationsof cellulose for use in the food industry are limited to its esterification and etheri-fication. Mainly, cellulose acetate is produced. It is used for special membranes fortreating water and fruit juices. Among ethers, methyl- and methylhydroxypropylcelluloses pay particular attention. They are available in methylation with commonmethylating agents and propylene oxide. Carboxymethyl cellulose (CMC) is theproduct of the reaction of cellulose with chloroacetic acid. Products of degree ofsubstitution from 0.3–0.9 are available. All 2-, 3-, and 6-hydroxyl groups do react.Modified and derivatized celluloses have found their application in the food industryas nondigestible components of low-calorie meals. CMC is a texturizing agent andedible adhesive.

Chemical modification of starch for nutritional purposes involves oxidation, butonly with a limited number of oxidants; esterification, with a limited number ofesterifying reagents; etherification; and complex formation. Metal derivatives mighthave some significance as carriers of bioelements and therapeutic agents, first of all,insulin substitutes (Tomasik et al., 2001). Oxidation of starch to aldaric and uronicacid-type carboxylic starches for practical purposes should leave no more than onecarboxylic group per each 25th glucose unit. The oxidation should be carried outwith a possible high depolymerization degree and the formation of the smallestpossible number of the terminal anomeric carbon atoms. Gels from oxidized starcheshave low viscosity and good transparency. Such oxidation is provided by sodiumhypochlorite. This oxidant only randomly oxidizes the 6-hydroxymethyl groups ofstarch. The latter groups are readily oxidized with nitrogen oxides. Metal ion-catalyzed air oxidation of starch results in simultaneous formation of carboxyl andcarbonyl starches. The most useful esters of starch are phosphates, commonly usedgelating agents, acetates, and adipates — the film forming materials. Only thesepreparations are utilized in foods, which have a low degree (0.2–0.0001) of esteri-fication. The most important and widely used starch esters are those prepared byusing monochloroacetic acid (carboxymethyl starch), ethylene oxide (hydroxy-methyl starch), and propylene oxide (hydroxypropyl starch).

Side chains introduced into starch by esterification or etherification can undergodissociation. For instance, all starch sulfates, starch phosphates, and carboxymethylstarches dissociate in aqueous solution, leaving a negative charge on starch. Theyare called anionic starches. If starch was etherified with a reagent introducingtetralkylammonium salt function, the dissociation developed a positive charge onthe starch and such starch belonged to cationic starches.

Polysaccharides are important complexing agents for inorganic and organic gases,liquids, and solids. Usually surface sorption is involved, but in the case of starch,inclusion complexes inside of the amylose helix and eventually short helices of amy-lopectin, as well as inside of the amylopectin branches, and capillary complexesinvolving capillaries between starch granules are also formed. All of them exist in anatural, native form; they can also be formed in several common operations of foodprocessing, e.g., dough formation, beating of foam, and scrambling yolk with sugar.

Saccharides 105

Formation of inclusion complexes of starch becomes a more common method ofprotecting some volatile, as well air-sensitive, food components (microencapsulation).Such complexes are essential for food texturization and overall stabilization. Cationicstarches are used as detergents and cellulose pulp components, whereas anionicstarches readily form complexes with proteins (Schmitt et al., 1998). The latter areattempted in utilization as biodegradable plastics and meat substitutes.

5.4.2.3 Cross-Linked Polysaccharides

Polysaccharide cross-linking frequently occurs when it is acetalated, esterified, oretherified with bi- and polyfunctional reagents, e.g., POCl3, polyphosphates, dian-hydrides of tetraioic acids, dialdehydes, dicarboxydiamides, vinyl monomers, andso on. Usually such compounds have enhanced water-binding capacity, lower aque-ous solubility, and shear force stability.

Retrogradation is a very common reaction of gels of starch polysaccharides. Itleads to enhanced molecular-weight systems. Amylose gels retrograde even withinhours, whereas retrogradation of amylopectin gels takes days and even weeks.Retrogradation of gels is manifested by dendrite formation in the gel and in breadby bread staling. The phenomenon is due to orientation of chains of amylose inrespect to one another to aggregate with involvement of intermolecular hydrogenbonds. The retrogradation affinity depends on starch variety and decreases in theorder: potato > corn > wheat > waxy corn starch. Evidently, the retrogradation rateand nature of the formed amylose crystals depend on the starch source, amylose:amy-lopectin ratio, and storage temperature. Low temperature, around the freezing point,and polar gel additives favor retrogradation. Retrograded starch is utilized as acomponent of low-calorie food.

5.4.3 ENZYMATIC TRANSFORMATIONS OF CARBOHYDRATES

With few exceptions, enzymatic processes in carbohydrates cause degradation.Enzymes are used in the form of pure or semipure preparations or together withtheir producers, i.e., microorganisms. Currently, semisynthetic enzymes are alsoin use. Alcoholic fermentation is the most common method of utilization ofmonosaccharides, sucrose, and some polysaccharides, e.g., starch. Lactic acidfermentation is another important enzymatic process. Lactic acid bacteria metab-olize mono- and disaccharides into lactic acid. This acid has a chiral center; thuseither D(–), L(+), or racemic products can be formed. In the human organism,only the L(+) enantiomer is metabolized, whereas the D(–) enantiomer is concen-trated in blood and excreted with urine. Among lactic acid bacteria, only Strepto-coccus shows specificity in the formation of particular enantiomers, and only theL(+) enantiomer is produced.

Enzymatic reduction of glucose-6-phosphate (5.85) into inositol-1-phosphatewith cyclase and reduced NAD coenzyme, followed by hydrolysis with phosphatase,presents another nondegrading enzymatic process proceeding on hexoses.

Inositol (5.86) plays a role in the growth factor of microbes. Its hexaphosphate,phytin, resides in the aleurone layer of wheat grains.


There are also known bacteria that polymerize mono- and oligosaccharides.Leuconostoc mesenteroides polymerizes sucrose into dextran — an almost linearpolymer of 400 or more α-D-glucose units. Dextran is also generated in frozen sugarbeets. This causes difficulties in sugar manufacturing if the beets have to be storedat low temperature. Dextran serves as a blood substitute and chromatographic gel(Sephadex). Other polysaccharides synthesized by bacteria are levan, a polymer ofβ-D-fructose; pullulan, a polymer of α-D-glucose; and xanthan gum, a polymer ofβ-D-glucose and α- and β-D-mannoses.

The enzymatic oxidation of sucrose with glucose oxidase to D-glucose-δ-lactone consumes oxygen dissolved in beer and juices. In this manner the rate ofundesirable processes caused by oxidation, e.g., color and taste changes, isdecreased. All essential enzymatic polysaccharide transformations deal with deg-radation (Figure 5.4). In the case of cellulose, this degradation leads to glucose.Endoglucanase and cellobiohydrolase attack the amorphous regions of the compactstructure of cellulose, producing D-glucose and cellobiose, respectively. Starch,amylose, and amylopectin are not necessarily so deeply degraded. There are severalamylolytic enzymes capable of starch degradation. They provide high specificityof their action (Figure 5.4). Synthesis of cyclodextrins (cycloglucans, Schardingerdextrins) presents a special case. Slightly hydrolyzed starch is transformed intocyclic products composed of six, seven, and eight α-D-glucose units, α-, β-, andγ-cyclodextrins. The yield of cyclodextrins declines with the number of glucoseunits in cycles.

FIGURE 5.4 Enzymatic transformations of starch.

Dextrin

Pullulanaseand

Glcogenase

γ− β−

α− Cyclodextrin

β - Amylase

Amylo - 1.6 - α - gluconase(Dextrinase)

Bacillus macerans

Maltose

α - Glucosidase

Glucse

Glucseisomerase

Fructose

Glucoamylase

Glucose

α - Amylase

Dextrin

Saccharides 107

Although higher-membered cyclodextrins are also formed in the reaction mix-tures, their minute yield seriously limits their potential applications. Cyclodex-trins are sometimes cross-linked into cyclodextrin resins with interesting inclu-sion properties.

5.4.4 CEREAL AND TUBER STARCHES

All botanical varieties of starches can be primarily classified into tuber andcereal starches. Differences in size and shape of granules, the amylose/amy-lopectin ratio, and protein (7–13%), lipid (1.5–6%), other carbohydrate (5–23%),and mineral (1–3%) content, not necessarily on whether a given starch belongsto one of the above two classes. Potato starch, the tuber starch, has the largestgranules (up to 150 µm), and as the sole starch, it has amylopectin esterifiedwith phosphoric acid (Seidemann, 1966). However, starch granules of wild yam(Diascorea dumetrorum), which has one of the finest granules ever seen, alsooriginate from tuber starches (Nkala et al., 1994). Generally, cereal starches arericher in lipids (e.g., cornstarch), and tuber starches are richer in proteins,although the oat, a cereal starch, is one of the richest in lipids and proteins (seeTable 5.2). Polysaccharides and lipids, as well as proteins, in granules usuallyreside therein in native complexes. These complexes are stronger in cerealstarches. Thus, potato starch can readily be isolated relatively free of proteins,whereas the complete defatting of cornstarch could not be afforded. The maindifference between tuber and cereal starches comes from their crystallographicpattern: A for tuber and B for cereal starches. These two patterns result fromdifferent mutual orientations of amylose helices inside the granule, e.g., single(A-type) and double (B-type) (Figure 5.3). These differences determine severalessential properties of both classes of starches. They are swelling, gelation, andcourse of pasting, and affinity to various physical, physicochemical, and chem-ical modifications. There are also differences in the taste, digestibility, andnutritive value of particular starches.

The most common sources of starch in various regions of the world are potato,maize, cassava (manioc, tapioca, yucca), and rice. Popularity of a given starch andstarchy plants do not go together. For instance, in many regions of the world wheatand rye are very commonly used. Wheat starch is only randomly isolated, and ryestarch is only exceptionally available. Rye grains contain mucus, which seriouslyobstructs isolation of starch from this source.

5.5 FUNCTIONAL PROPERTIES OF CARBOHYDRATES

5.5.1 TASTE

Saccharides are usually associated with sweet taste, although among them are alsobitter and nonsweet saccharides (Table 5.3). Except for sucrose, the sweetnessdecreases with the number of monosaccharide units going toward oligo- and polysac-charides, because only one monosaccharide unit interacts with mucoprotein of thetongue receptor.


Because a number of powerful synthetic and natural nonsaccharide sweetenersare available on the market, apart from reduction to saccharide alcohols, otherderivatizations of saccharides, even if they increase their sweetness (Table 5.3), haveno practical significance.

The following carbohydrate sweeteners are in common use (their relative sweet-ness (RS) in respect to 10% aqueous solution of sucrose is given in Table 5.3):

• D-glucose: because of fast resorption, it is a source of immediately availableenergy. It is used in injections and infusion fluids for children and patients intheir recovery period. Its digestion requires insulin. It causes tooth cavities.

• D-fructose: the most readily water-soluble sugar. It does not crystallizefrom stored juices. Because of its hygroscopicity, it retains moisture insugar-preserved food and intensifies its flavor and aroma. Metabolism ofD-fructose delivers less energy than sucrose. This saccharide neithercauses nor accelerates tooth cavities. It accelerates ethanol metabolism.In the organism, D-fructose metabolizes into glycogen, animal starchbeing the energy reservoir stored in the liver.

• Lactose: sparingly water-soluble (20% at room temperature) sugar presentin mammalian milk (4.8–5.1%). It is utilized as a carrier of other sweet-eners. It improves flavor, produces a good image of food processed inmicrowave ovens, and improves the taste of dairy products.

• Sucrose: the most common sweetener for its pleasant taste. It is widelyused as a preservative of marmalades, syrups, and confitures. Osmoticphenomena are involved. Due to competition of microorganisms andpreserved foodstuffs for water molecules, the microorganism tissuesundergo plasmolysis. Aqueous solutions containing 30% sucrose do notferment, and 60% of the solutions are resistant to all bacteria but Zygosac-charomyces.

• Maltose: slightly hygroscopic disaccharide of mild and pure sweet impres-sion. Its solutions have low viscosity. Its color is stable regardless oftemperature.

• Starch syrups: they result from starch saccharification. The saccharification canbe carried to various stages. The first sweet product, maltotetraose syrup (RS =0.25), is viscous. As the saccharification proceeds, the viscosity of syrups declineand their RS increases. Syrups are water soluble, do not retrograde, and arereadily digested. Glucose syrup, the final product of saccharification, may beconverted by isomerization into fructose syrups (Table 5.4) or hydrogenated toD-sorbitol. Apart from the sweetness and low energetic value (17.5 kJ/g), tex-turizing and filling properties of syrups are utilized in practice.

• Malt extract from barley malt obtained by aqueous extraction: contains4–5% sucrose; spare amounts of D-glucose, D-fructose, and maltose;proteins; and mineral salts.

• Maple syrup and maple sugar from juice of Acer saccharium maple trees:contains 98% saccharides, 80–98% of which is sucrose.

• Sugar alcohols (D-sorbitol, D-xylitol, and D-mannitol): perfectly watersoluble, soluble in alcohol, and more stable at low and high pH values than

Saccharides 109

saccharides. Their sweet taste lasts for a prolonged time and is accompaniedby a cool impression. They metabolize without insulin. The energetic valuesof xylitol, sorbitol, and mannitol are 17, 17, and 8.5 kJ/g, respectively.Therefore, they can be used as sweeteners for diabetics and consumers withobesity. Because of hygroscopicity, they are used as food humectants.

• Compounded sweeteners, blends of various sweeteners: the compositionof such blends depends on the purpose they are designed for. Usually theyare blends of various saccharides, but sorbitol, sugar syrups, and evenmalic acid are also compounded.

• Honey: this natural product has a composition dependent on the harvesttime, geographical region, and origin and kind of flowers from which thenectar was collected. Even the variety of insects is a factor. Fructose,glucose, and maltose constitute approximately 90% of the total sugarcontent. There is also a rich variety of free amino acids and other organicacids, minerals, pigments, waxes, enzymes, and pollen. The latter mayact allergizing. Honey may contain toxic components from poisonousplants, although there are several poisonous plants that give nonpoisonoushoney. In some countries aqueous solutions of honey are fermented intohoney-flavored wine (mead).

5.5.2 COLORANTS

Sugars are utilized for generation of caramel, a brown colorant for food (Tomasiket al., 1989). For this purpose sugar is burnt (caramelized). Various additives(caustic soda, caustic sulfite, ammonia, and their combinations) catalyze thisprocess. In laboratory tests some proteogenic amino acids and their sodium andmagnesium salts proved to be suitable catalysts (Sikora et al., 1994). Catalystsaccelerate the process and decrease caramelization temperature, usually between130 and 200°C, providing that there is good tinctorial strength. Products preparedby noncatalyzed burning of sugars at 200–240°C have poor tinctorial strengthand serve as flavoring agents.

There is a concern about harm coming from the free radical character ofcaramels. However, they were proven (Barabasz et al., 1990) to be nonmutagenic.Thermal processing of saccharides and polysaccharides containing foodstuffs

TABLE 5.4Saccharide Content (%) in Various Starch Syrups

Syrups

Glucose Conversion

Saccharide Low High Very High Maltose Fructose

Glucose 15 43 92 10 7–52Fructose — — — — 42–90Maltose 11 20 4 40 4Higher saccharides 48 13 2 28 3–6


results in development of brown color; it originates from caramelization anddextrinization, respectively. Brown-colored dextrins, even if they contain freeradicals, are nonmutagenic because such free radicals are unusually stable(Ciesielski and Tomasik, 1996). Depending on the catalyst used, caramels differfrom one another in their isoelectric point. If colored matter does not fit theisoelectric point, micels of the caramel irreversibly discharge and the caramelseparates. Four types and several classes of caramels with widely differentproperties are manufactured. This variety provides a selection of a proper col-orant to all types of foodstuffs.

5.5.3 FLAVOR AND AROMA

Burning of sugar in noncatalyzed processes results in formation of particularly highamounts of furan-2-aldehyde and its derivatives. They constitute the flavor and aromatypical for caramels. Many foodstuffs (meat, fish, dough, potato, cocoa, coffee, andtobacco) on thermal treatment (baking, frying, roasting, and smoking) develop spe-cific aromas. They are volatile derivatives of pyrazine, imidazole, pyrrole, andpyridine formed on thermal reactions of saccharides and proteins, nucleotides, andamino acids.

Saccharides and polysaccharides — starch and cellulose (Baczkowicz et al.,1991), pectins (Sikora et al., 1998), and hemicelluloses (Tomasik and Zawadzki,1998) — heated with amino acids develop scents specific for polysaccharide, aminoacid, and reaction conditions. Thus, supplementation of saccharides and polysac-charides with amino acids and proteins, as well as supplementation of protein-con-taining products with saccharide, can be useful in generation, modification, andenrichment of flavor and aroma of foodstuffs and tobacco.

5.5.4 TEXTURE

More concentrated aqueous solutions of carbohydrates form viscous liquids. Thisproperty is most commonly utilized in practice for texturizing foodstuffs. In suchsolutions sugar–sugar interactions (complexation) are responsible for this effect. Itwas found that although interactions in various monosaccharide–monosaccharide,disaccharide–disaccharide, and monosaccharide–disaccharide combinations broughtno particularly promising texturizing result (Mazurkiewicz and Nowotny- ,1998), certain blends of either mono- or disaccharide with polysaccharides showedremarkable increase in viscosity and adhesiveness (Mazurkiewicz et al., 1993). Onsuch, edible glues and adhesives could be prepared. Such interactions are commonlyutilized in texturization of puddings, jellies, foams, and so on. Some oligosaccharidesand the majority of polysaccharides form hydrocolloids, which build up their ownmacrostructure. They give an impression of jelly formation, thickening, smoothness,stabilization against temperature and mechanical shocks, aging, and resistance tosterilization and pasteurization. Plant gums, pectins, and alginates are particularlywillingly utilized for this purpose. Recently, considerable attention was paid totextural properties of polysaccharide–polysaccharide interactions where both inter-acting polysaccharides were starches of various origins (Obanni and Bemiller, 1997;

Rózanska´.

Saccharides 111

Lii et al., 2001a). One should note that the texturizing effect of a given saccharideor polysaccharide and its various blends is developed as a function of time necessaryfor the formation of a gel network (a physical cross-linking). The pH and temperaturemay also be essential factors. If protons (pH < 7) or hydroxyl anions (pH > 7) andtemperature do not evoke any structural changes in interacting species, the textur-izing effect is reversible in pH and temperature. If retrogradation does not take place,texturization is also reversible in time.

Saccharides, oligosaccharides, and polysaccharides form also complexes withmineral salts, proteins, and lipids. Such complexes also contribute to foodstufftexture.

Apart from combinations of natural saccharides, oligosaccharides, and polysac-charides with involvement of lipids and proteins, chemically modified polysaccha-rides are also utilized for texturization. Cross-linked starches are important textur-izing agents. The degree of cross-linking is an important factor. It should not behigher than 0.2. Among cross-linked starches, those esterified with phosphoric acidare particularly favored. All starches can be cross-linked by esterification withphosphoric acid (in practice, either with salts of meta- or orthophosphates, as wellas POCl3 and PCl5), but at the same degree of substitution, phosphorylated potatostarch gives superior results, while cornstarch phosphate is the poorest.

Starch sulfate ester is used as a thickener and emulsion stabilizer. It is a typicalanionic starch used as a component of anionic starch–protein complexes constitutingmeat substitutes (Tolstoguzov, 1991, 1995). Other anionic starches, as well as pec-tins, alginic acid, carrageenans, furcellaran, heparin, xanthan gum, and carboxym-ethyl cellulose, are anionic polysaccharides; their application in food texturizationis now under study (Clark and Ross-Murphy, 1987; Schmitt et al., 1998; Zaleskaet al., 2001a, 2001b). Anionic polysaccharides are particularly good texturizingagents in the presence of mineral salt cations (Na+, K+, Mg2+, and Ca2+).

Among many available modified polysaccharides, application of only few ofthem is legal in view of the food law of particular countries. Some restrictions areput on the method of their manufacture and the purity of such products.

The replacement of saccharide sweeteners (first of all sucrose) in food withvarious natural and synthetic sweeteners of very high RS (currently, mainly saccha-rine, aspartame, and cyclamates) is a task. It is also a demand of consumers lookingfor low-calorie food. Also, diabetics are looking for food free of insulin-requiringsaccharides and polysaccharides. Following such demands, problems are encoun-tered in providing the anticipated texture of sweet products manufactured withoutsaccharides (Mazurkiewicz et al., 2001).

5.5.5 ENCAPSULATION

Various foodstuffs loose their original, beneficial flavor, aroma, taste, and coloron processing. It is a common result of evaporation of volatile components ordecomposition of certain food components under the influence of oxygen or light.In this manner the quality of foodstuffs decreases. In order to avoid such effects,volatile and unstable products are either protected in processed sources or, afterprocessing, are supplemented by fragrances, colorants, and other components.


Such goals are met by encapsulation and supplementation of microcapsule closedadditives. Saccharides are suitable for making such microcapsules. Compressionof additives (guest molecules) with a saccharide forming the matrix of the micro-capsule (the host molecule) is a common practice. It is beneficial if there are someother-than-mechanical interactions between the guest and host that decrease therate of evaporation or reaction of the guest from the microcapsule. Granular starchcan encapsulate guests in capillaries between granules; gelatinized starch, amylose,and amylopectin can trap certain molecules inside helices generated in contactwith guest molecules.

Coacervation or coprecipitation of host and guest and suspension of the guestmolecule in polysaccharide gels, followed by drying, is another common procedure.Microcapsules can be made on the formation of polysaccharide–protein complexesin the presence of a potential host. Preswelled granular starches are potential naturalmicrocapsules (Lii et al., 2001b).

α-, β-, and γ-cyclodextrins are the most effective compounds for microen-capsulation of food components (Szejtli, 1984). Cyclodextrins take a form oftoruses with cavities of 0.57, 0.78, and 0.95 nm in diameter, respectively. Theirheight is 0.78nm.

Upper and bottom edges of the toruses have secondary and primary hydroxylgroups, respectively. All hydroxyl groups reside on the external surface of toruses,making cyclodextrins hydrophilic. Simultaneously, their cavity interior is hydrophobic.

Cyclodextrins are water-soluble hosts for hydrophobic guests. The formation ofinclusion complexes is controlled by the dimensional compatibility of the guest andhost cavity. Commercially available dextrins are, in fact, inclusion complexes of cyclo-dextrins with two water molecules closing the entrance to the cavity. The formationof cyclodextrin inclusion complexes is reversible and, therefore, is governed by con-centration of guests competing for a place inside the cavity.

5.5.6 POLYSACCHARIDE CONTAINING BIODEGRADABLE MATERIALS

There is a growing concern about fully biodegradable plastic — packing and wrap-ping foils, containers, equipment of fast-food restaurants, and superabsorbents.

Currently, several products made of polyethylene modified into biodegradable mate-rial are in use throughout the world. Biodegradability of such materials was afforded byadmixture of 6–15 w-% of natural components, such as starch, cellulose, wood, orproteins, into polyethylene. Polyurethane foams used as thermal insulators and packingmaterials contain up to 20% starch. The level of starch in copolymers of ethylene witheither vinyl chloride, styrene, or acrylic acid may reach 50%. Of course, the effect ofbiodegradation of such material has more aesthetic significance than ecological. Althoughdegradation of the finely pulverized synthetic portion of such materials is accelerated, itstill takes several decades for depolymerization to come to its end.

Apparently, the simplest biodegradable plastics could be prepared of starchsolely by compression of up to 106 kPa, provided starch was moisturized up to itsnatural water-binding capacity (~20 w-%) ( and Tomasik, 1992).

Following the idea of full biodegradability of materials, attention has been paidto the compositions of plain carbohydrates with either unmodified or modified

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Saccharides 113

proteins and of modified carbohydrates with unmodified and modified proteins. Suchcompositions are processed to generate carbohydrate–protein complexes. The ther-modynamic and electrical compatibilities of components should be reached in orderto afford the best functional properties of materials. Because of the chemical natureof proteins (cationic character), carbohydrates should be anionic, i.e., on dissociationthe negative charge should be left on polysaccharide moiety. The COOH, PO3H2,and SO3H groups provide such properties. Whenever modification of a carbohydrateis required to make it anionic, the degree of derivatization should not exceed 0.1. Itshould neither increase the hydrophilicity of the product nor, if possible, decreaseits molecular weight.

REFERENCES

Angyal, S.Y., Complexes of metal cations with carbohydrates in solution, Adv. Carbohydr.Chem. Biochem., 47, 1, 1989.

Ball, S.G., van de Wal, M.H.B.J., and Visser, R.G.F., Progress in understanding the biosyn-thesis of amylose, Trend Plant Sci., 3, 462, 1998.

Baczkowicz, M. et al., Reactions of some polysaccharides with biogenic amino acids,Starch/Staerke, 43, 294, 1991.

Barabasz, W. et al., On mutagenicity of caramels, Starch/Staerke, 42, 69, 1990.Ciesielski, W. and Tomasik, P., Starch radicals. Part I, Carbohydr. Polym., 31, 205, 1996.Ciesielski, W. and Tomasik, P., Starch radicals. III, Z. Lebensm. Unters. Forsch., A207, 292,

1998.Ciesielski, W., Tomasik, P., and Baczkowicz, M., Starch radicals. IV, Z. Lebensm. Unters.

Forsch., A207, 299, 1998.Clark, A.H. and Ross-Murphy, S.B., Structural and mechanical properties of biopolymer gels,

Adv. Polym. Sci., 53, 57, 1987.Erlander, S., Biosynthesis of starch, . Technol. , Suppl. 4, 112, 1998.Gallant, D.J., Bouchet, B., and Baldwin, P.M., Microscopy of starch: evidence of a new level

of granule organization, Carbohydr. Polym., 32, 177, 1997.Goosen, M.F.A., Application of Chitin and Chitosan, CHIPS, Weimar, TX, 1997.Imberty, A. et al., Recent advances in knowledge of starch structure, Starch/Staerke, 43, 375,

1991., E. and Tomasik, P., Effect of high pressure on starch matrix, Starch/Staerke, 44, 167,

1992.Lii, C.-y. et al., Polysaccharide: polysaccharide interactions in pastes, Pol. J. Food Nutr. Sci.,

submitted, 2001a.Lii, C.-y. et al., Granular starches as dietary fiber and natural microcapsules, Int J. Food Sci.

Technol., accepted, 2001b.Mazurkiewicz, J. and Nowotny- , M., Viscosity of aqueous solutions of saccharides,

Pol. J. Food Nutr. Sci., 7/2, 171, 1998.Mazurkiewicz, J., Rebilas, K., and Tomasik, P., Aspartame as texturizing agent for foodstuffs,

Z. Lebensm. Unters. Forsch., A212, 369, 2001.Mazurkiewicz, J., Zaleska, H., and , J., Studies in carbohydrate based glues and

thickeners for foodstuffs. Part I. Glucose–sucrose–apple pectin ternary systems,Starch/Staerke, 45, 175, 1993.

Nkala, B. et al., Starch from wild yam from Zimbabwe, Starch/Staerke, 46, 85, 1994.

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Obanni, M. and Bemiller, J.N., Preparation of some starch blends, Cereal Chem., 74, 431,1997.

Okkerse, C. and van Bekkum, H., Starch 96: The Book, Van Doren, H. and Van Swaaij, N.,Eds., Carbohydrate Research Foundation, Noordwijkerhout, 1996, chap. 1.

Ruck, H., The new organosolv pupls: will they otrival starch as an industrial raw material?,. Technol. ., Suppl. 2, 138, 1996.

Schmitt, C. et al., Structure and technofunctional properties of protein-polysaccharide com-plexes. A review, Crit. Rev. Food Sci. Nutr., 38, 689, 1998.

Seidemann, J., Die Staerkeatlas, Paul Parey, Berlin, 1966.Siemion, I.Z., Biostereochemistry, PWN, Warsaw, 1985, chap. 1 (in Polish).Sikora, M., Tomasik, P., and Araki, K., Thermolysis of pectins with amino acids, Pol. J. Food

Nutr. Sci., 7/3, 391, 1998.Szejtli, J., Cyclodextrin Inclusion Complexes, Academiai Kiado, Budapest, 1984.Szymonska, J., Krok, F., and Tomasik, P., Deep freezing of potato starch, Int. J. Biol. Mac-

romol., 27, 307, 2000.Tolstoguzov, V.B., Functional properties of food protein and role of protein: polysaccharide

interaction, Food Hydrocoll., 4, 429, 1991.Tolstoguzov, V.B., Some physico-chemical aspects of protein processing foods. Multicompo-

nent gels, Food Hydrocoll., 9, 317, 1995.Tomasik, P. et al., Potato starch derivatives with some chemically bound bioelements, Acta

Pol. Pharm. Drug Res., 58, 447, 2001.Tomasik, P., Palasinski, M., and Wiejak, S., The thermal decomposition of carbohydrates.

Part I. The decomposition of mono-, di-, and oligo-saccharides, Adv. Carbohydr.Chem. Biochem., 47, 203, 1989.

Tomasik, P. and Schilling, C.H., Complexes of starch with inorganic guests, Adv. Carbohydr.Chem. Biochem., 53, 263, 1998a.

Tomasik, P. and Schilling, C.H., Complexes of starch with organic guests, Adv. Carbohydr.Chem. Biochem., 53, 346, 1998b.

Tomasik, P. and Schilling, C.H., Chemical modification of starch, Adv. Carbohydr. Chem.Biochem., in press, 2002.

Tomasik, P., Wang, Y.J., and Jane, J., Starch: sugar complexes, Starch/Staerke, 47, 185, 1995.Tomasik, P. and Zaranyika, M.F., Nonconventional methods of modification of starch, Adv.

Carbohydr. Chem. Biochem., 51, 243, 1995.Tomasik, P. and Zawadzki, W., Reaction of plant material with biogenic amino acids, Pol.

J. Food Nutr. Sci., 7/1, 29, 1998.Zaleska, H., Ring, S., and Tomasik, P., Complexes of potato starch with casein, Int. J. Food

Chem. Technol., 36, 509, 2001a.Zaleska, H., Ring, S., and Tomasik, P., Electrosynthesis of potato starch: whey protein isolate

complexes, Carbohydr. Polym., 45, 89, 2001b.

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1151-5871-6149-4/02/$0.00+$1.50© 2002 by CRC Press LLC

Food Lipids

Yan-Hwa Chu and Lucy Sun Hwang

CONTENTS

6.1 Introduction ..................................................................................................1156.2 Chemical Constituents of Oils and Fats ......................................................1166.3 Processing of Oils and Fats .........................................................................118

6.3.1 Introduction ......................................................................................1186.3.2 Receiving..........................................................................................1186.3.3 Preparation .......................................................................................1186.3.4 Extraction .........................................................................................1186.3.5 Refining ............................................................................................119

6.3.5.1 Degumming.......................................................................1196.3.5.2 Chemical Refining ............................................................1196.3.5.3 Physical Refining ..............................................................1206.3.5.4 Bleaching ..........................................................................1206.3.5.5 Deodorizing.......................................................................1206.3.5.6 Dewaxing ..........................................................................120

6.3.6 Modification .....................................................................................1216.3.6.1 Hydrogenation...................................................................1216.3.6.2 Interesterification ..............................................................1216.3.6.3 Fractionation .....................................................................121

6.4 Changes of Lipids Due to Storage ..............................................................1216.5 Interactions of Lipids with Other Components in the Food System..........1226.6 Functional Fatty Substances ........................................................................123

6.6.1 Structured Lipids..............................................................................1236.6.2 Polyenoic Fatty Acids ......................................................................1266.6.3 Vegetable Lecithin............................................................................1286.6.4 Tocopherol and Phytosterol .............................................................1296.6.5 Sesame Lignans................................................................................130

References..............................................................................................................131

6.1 INTRODUCTION

Lipids include oils, fats, and fat-like substances that have a greasy feel and areinsoluble in water but soluble in certain organic solvents such as ether, alcohol, andhexane. They are the major component of the human diet, serving as a source of

6


energy, providing essential nutrients (linoleic acid, linolenic acid, and vitamins A,D, E, and K), and facilitating the absorption of fat-soluble vitamins. In most devel-oped countries, lipids may contribute up to 40% of the energy in the diet of thepopulation; this is much higher than the 30% or less recommended by most healthorganizations. High intake of total dietary fat is associated with increased risk ofcoronary heart disease, obesity, and some types of cancers. However, oils and fatsplay a vital functional and sensory role in food products. Consumers are allured bythe flavor, texture, and aroma of fat-rich foods. Fats interact with other componentsto develop and fabricate texture, mouth feel, and the overall sensation of lubricityof foods. The role of lipids in food quality should not be disregarded by the tendencyto overemphasize dietary fat as “negative” nutrients. This chapter will review theproperties of oils and fats, oil processing, functional lipids, and utilization of someby-products from oil processing.

6.2 CHEMICAL CONSTITUENTS OF OILS AND FATS

Oils and fats are water-insoluble, hydrophobic substances of vegetable or animalorigins that consist mainly of triacylglycerols (TAGs). The esterification of onemolecule of glycerol with three molecules of fatty acids (FAs) yields three moleculesof water and one molecule of TAG. The FAs contribute both the chemical andphysical properties of the TAGs. Most FAs in nature are straight-chain acids thatcontain an even number of carbon atoms. All acids with 12-, 14-, 16-, and 18-carbonatoms are major FAs. Saturated FAs contain no double bonds, whereas unsaturatedones contain at least one double bond. Polyenoic FAs (PEFAs) contain at least twodouble bonds and mostly exist as nonconjugated PEFA types, in which double bondsbetween the carbons are separated by one carbon atom.

The geometry of double bonds, as well as the number of double bonds, deter-mines the reactivity of unsaturated FAs. A trans linkage produces less irregularityin the straight-chain structure; thus the trans FAs are usually higher melting andless reactive. Most naturally occurring FAs are cis forms. cis acids may be convertedto trans isomers in the course of processing, involving heat and hydrogenation.

The average degree of unsaturation of oils and fats is determined by the iodinevalue; the average molecular weight is measured by the saponification number. TheFA compositions of oils and fats are determined by gas liquid chromatographyanalysis of methyl esters of FAs after methanolysis of fats and oils.

The most widely distributed naturally occurring saturated FAs are lauric (C14:0),palmitic (C16:0), and stearic (C18:0) acids. The richest common sources of lauric acid arecoconut oil, palm kernel oil, and babassu butter, which contain at least 40% of this acid.Palmitic acid is a major component of palm oil (45–50%) and lard and tallow (25–30%)(Tables 6.1 and 6.2). Stearic acid can be manufactured by hydrogenation of FAs.

A variety of unsaturated FAs occur naturally in large quantities. These acidscontain an even number of carbon atoms; 18-carbon atoms containing one, two, andthree double bonds occur most frequently. The most abundant monoenic acid invegetable oils and animal fats is oleic acid (C18:1). Rich sources of C18:1 are olive oil(70%), peanut oil (40%), sesame oil (40%), rice bran oil (45%), Camellia oleiferatea seed oil (80%), beef tallow (40%), and lard (45%).

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The most important and widely distributed PEFAs are linoleic (cis,cis-9,12-octadecadienoic) and linolenic (cis,cis,cis-9,12,15-octadecatrienoic) acids. Linoleicacid, one of the nutritionally essential FAs, is the most abundant PEFA and is widelydistributed in common vegetable oils such as soybean oil (50%), sunflower oil (65%),corn oil (50%), and sesame oil (40%). Linolenic acid distributed in nature is a majoracid of the highly unsaturated vegetable oils. Rich sources are linseed (45–50%)and perilla (65%) oils.

Highly unsaturated FAs with three to six double bonds always occur in marineanimal fats. The most known and important acids are eicosapentaenoic acid (EPA,C20:5) and docosahexaenoic acid (DHA, C22:6). Fish species, location site, type of fatwithin the fish, and environmental effects cause a wide variation of FAs in marineanimal fats.

All oils and fats contain small amounts of nonglyceride components. Some ofthese components are removed from crude oils during refining to produce finalproducts with satisfactory sensory properties. These minor components includephosphatides, unsaponifiable matters, chlorophyll, and alteration products.

TABLE 6.1Fatty acid composition of some vegetable oils (%)

Oil C10:0 C12:0 C14:0 C16:0 C18:0 C18:1 C18:2 C18:3Babassu 6 44 16 8 3 15 2Canola 3.9 2 64 19 9Coconut 7 48 17 8 3 6 2Corn 12 2 27 57Cottonseed 0.8 25 2 18 53 0.1Olive 1 14 2.6 72 10 1Palm 1 46 5 39 9 0.4Palm kernel 3.6 50 16 8 2 14 2Peanut 12 3 47 31Safflower 6 2 13 77 0.4Sesame 10 5.2 41.2 43.3 0.2Soybean 11 4 23 54 7Sunflower 7 4 19 68 0.5

TABLE 6.2Fatty acid composition of animal fats (%)

OilC4:0-C12:0 C14:0 C16:0

C18:0

C18:1

C18:2

C18:3

C20:5

C22:6

Beef tallow

3 26 22 42 2 0.2

Butter 12 11 26 10 28 2 1Chicken 1 22 10 41 20 2Lard 1.3 25 16 46 9 0.3Mackerel 6 16 3 15 2 1 5 9


6.3 PROCESSING OF OILS AND FATS

6.3.1 INTRODUCTION

Crude oil contains relatively small and variable amounts of nonglyceride impurities.The quality and yield of finished oil are affected by some of the undesirable impu-rities that are not properly removed during processing.

The oil-insoluble impurities consist of seed fragments, excess moisture, mealfines, and a waxy substance. These oil-insoluble impurities are normally and readilyremoved by filtration. However, the oil-soluble impurities such as free FAs, phos-phatides, gummy or mucilaginous substances, color bodies, proteins, hydrocarbons,ketones, and aldehydes are more difficult to remove.

A series of unit operations are required to remove objectionable impurities withthe least detrimental effect on finished oil quality and minimum oil loss.

6.3.2 RECEIVING

Receiving, sampling, drying, storage, and cleaning are the typical operations of oil-bearing materials prior to oil processing. The moisture content of the raw materialis one of the prime factors for extended storage and final product quality. Highmoisture of oil-bearing materials results in reduced oil and protein content and darkercolor and increased refining loss of the extracted oil. For proper storage and subse-quent processing, the contaminants must be removed and the grains or seeds mustbe dried to around 12–13% water content prior to storage. During storage, it is aroutine practice to monitor the temperature of grains or seeds. If heating is occurring,the grains or seeds must be processed immediately. Otherwise, rotation of the grainsor seeds is required to avoid severe heating and damage.

6.3.3 PREPARATION

Proper preparation of grains or seeds is required for extraction of the oil, either bysolvent or mechanical methods. The unit operations typically involve scaling, cleaning,cracking, conditioning, and flaking. The grains or seeds are scaled and cleaned toremove contaminants. For soybeans, cracking separates the hulls from the meats andthe hulls are then removed by aspiration. After dehulling, the meats are conditionedto soften the cracks that are pliable for the subsequent flaking. During flaking, themeats are generally passed to the flaking rolls to squeeze the meats into flakes ofapproximately 0.30 mm in thickness. For oil-bearing materials with high oil content,such as sunflower, canola, peanut, or sesame, the purpose of conditioning or cookingis to break down the oil cell walls to the point where the oil is available to be expelled.In addition, protein coagulation in the meal, adjustment of the moisture content of themeal, and reduction in oil viscosity for proper pressing are also included.

6.3.4 EXTRACTION

Mechanical extraction is used to press the oil-bearing materials with high oil content.Oil from a mechanical pressing operation contains meal fines in high concentrations,

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which are removed by filtration. The filtered oil can be used either for directconsumption or for subsequent refining. Sesame and peanut oils, as the typicalpressed oils with unique flavors, are widely consumed in Oriental countries. Oliveoil, an important product in the Mediterranean area, is also obtained by mechanicalextraction from the fruit of the Olea europaea L. tree.

For oleaginous materials having a low oil content (18–20%), such as soybeanand rice bran, solvent extraction is often applied for oil recovery. Hexane is widelyaccepted as the most effective solvent used today. Most of the extractors currentlyused are designed as countercurrent flow devices. The solid material flows in anopposite direction of solvent-oil miscella with an increasing oil concentration. Themiscella containing around 25–30% oil after extraction is subjected to solventdistillation to recover the oil. The extracted solid material, commonly known aswhite flakes, is also conveyed to the desolventizing process.

A combination of mechanical and solvent extraction is often applied to oilseedswith high oil content, e.g., sunflower, safflower, corn germ, and canola. The mostefficient method of extracting the oil is mechanically expelling about 60% of the oiland then using solvent extraction of the remaining oil.

6.3.5 REFINING

6.3.5.1 Degumming

Degumming is an optional process and is used to remove phosphatides and foreignmaterials that are present in crude oil. Phosphatides are an excellent emulsifierthat interfere with the oil–water separation in the acidulation process and causeneutral oil loss. Water degumming is effective for water-hydratable phosphatides.The phosphatides contained in soybean oil from good-quality beans are 90%hydratable and can be removed by water hydration. Severely damaged beanscontain increased amounts of nonhydratable phosphatides (NHPs), mainly calciumand magnesium salts of phosphatidic acids. For the removal of NHPs, several acidtreatments are used to produce a lower phosphorus degummed oil. Pretreatmentof oil with phosphoric acid, citric acid, or other agent with proper time, temper-ature, and agitation conditions, followed by water hydration, is effective in remov-ing NHPs from the oil.

6.3.5.2 Chemical Refining

The purpose of chemical or physical refining is to remove nonglyceride impuritiesthat consist of free FAs and mucilaginous substances, phosphatides, chlorophyll,and color bodies. Alkali refining is associated with the proper choice of alkalies,amounts of alkalies, and refining practice to produce refined oil without excessivesaponification of neutral oil. The concentration and amount of caustic alkali solutionto be used for refining the crude oil varies with the content of FAs in the oil. Ifexcess caustic alkali solution is used, prolonged heating will result in saponificationof the oil and neutral oil losses.


6.3.5.3 Physical Refining

Traditional alkali refining is replaced by physical refining, in which the use ofchemicals is reduced. The most widely used method is steam refining. The crudeoil quality is very important in order to obtain high-quality refined oil. The oil beforephysical refining should be efficiently degummed to remove phospholipids, as wellas heavy metals, and bleached to remove pigments. The phospholipid content of theoil must be sufficiently low ⎯ less than 5 mg/kg phosphorus before steam strippingand less than 20 mg/kg phosphorus before bleaching. By applying superheated steamunder low pressure and at a temperature higher than 220°C, both FAs and undesirablevolatiles are removed. The quality of physically refined oil is close to that of alkali-refined oils, but losses of neutral oil are lower and the environment is less polluted(Cmolik and Pokorny, 2000).

6.3.5.4 Bleaching

The bleaching process is used to remove color bodies and other minor impurities.The bleaching adsorbent, usually a clay product, removes residual soap fromalkali refining, aldehydes and ketones from decomposed peroxides, and colorbodies. The color of bleached oil is widely measured by the Lovibond tintometercolor scale.

6.3.5.5 Deodorizing

The deodorizing process is used to improve the taste, odor, color, and stabilityof the oils by the removal of FAs; various flavor and odor compounds classifiedas aldehydes, ketones, alcohols, and hydrocarbons; and oxidation products andpigments. Deodorization is primarily a high-temperature, high-vacuum, steamdistillation process. High-temperature treatment bleaches the oil by destructionof the carotenoids. Some minor compounds, including tocopherols and phy-tosterols, are partially removed by deodorization. Typical conditions for deodor-ization of vegetable oil in semicontinuous deodorizers are: a temperature of245–260°C, a holding time of 15–40 min, an absolute pressure of 3–6 mm ofHg, 3–8% stripping and sparge steam based on oil throughput, and oil cooledto 60°C in the deodorizer.

6.3.5.6 Dewaxing

In some vegetable oils such as sunflower, safflower, corn, rice bran, and canolaoil, waxy materials may appear as sediments during storage at lower tempera-tures. To avoid a hazy appearance of oils, dewaxing is usually done by chillingthe oils in a continuous heat exchanger to about 0–5°C for 4–16 h to completethe growth of the wax crystals. After stabilization, the temperature is normallyincreased to about 15°C, and the proper amount of a filter aid is metered intothe chilled oil to facilitate filtration. The wax content of the filtered oil shouldbe reduced to a level of about 10 µg/g in order to obtain an oil with a good coldstorage stability.

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6.3.6 MODIFICATION

6.3.6.1 Hydrogenation

Hydrogenation is the reaction of oils and fats with hydrogen gas in the presence ofa catalyst. A nickel catalyst is normally used in the edible oil industry. Hydrogenationis designed to saturate the double bonds in the TAGs. Isomerization of the cisorientation to the trans position of double bonds also occurs during hydrogenation.Both the FA composition and physical properties of the oils and fats are modified.The modified oils and fats can be used for specific applications such as the manu-facture of margarines, bakery and confectionary fats, and shortenings.

6.3.6.2 Interesterification

Interesterification is a process to prepare functional plastic fats by exchanging FAwithin and between TAGs. Chemical and enzymatic methods are the two types ofinteresterification presently in use. The most commonly used catalyst for chemicalinteresterification is sodium methoxide. In order to maintain the catalyst activity,the water content of the oils and fats should be less than 0.01% (w/w), and the levelsof free FAs and peroxides should be as low as possible, preferably less than 0.05%(w/w). Lipase-catalyzed interesterifications are classified into random (no regiospec-ificity) and specific (1,3-regiospecific) categories. Random lipases include those fromCandida rugosa, Geotrichum candidum, and Staphylococcus aureus. Specific lipasesinclude pancreatic lipase and the enzymes from Mucor miehei, Aspergillus niger,Pseudomonas fluorescens, and Rhizopus arrhizus.

6.3.6.3 Fractionation

This process involves partial crystallization under controlled conditions and separa-tion of the remaining liquid from the solidified part. Dry, solvent, and detergentfractionations are normally used in this system. The first system is the simplestseparation; it involves cooling the oil to a desired end temperature and then filteringthe liquid oil on a vacuum filter or in a membrane press filter. The latter two systems,involving solvent or detergent separation of the crystallized phase from the liquidphase, are not widely used, due to their high production costs, capital investments,and contamination.

6.4 CHANGES OF LIPIDS DUE TO STORAGE

The oxidative stability of lipids depends on several factors, including the degree ofunsaturation, nature of unsaturation (position of double bonds), antioxidant content(tocopherols and synthetic antioxidants), prooxidant content (trace metals andenzymes), and storage conditions (exposure to heat, light, oxygen, and moisture).

Hydrolysis and oxidation are the two basic reactions that cause the deteriorationof fat or oil. Lipids undergo auto-oxidative degradation during storage. The higherthe storage temperature of the lipids, the faster the oxidation. Light, particularlyultraviolet light, also has a great effect on oxidation rates. Light-induced oxidation


of oleic acid occurs about 30,000 times faster than autoxidation. For the fat or oilitself, the greater the degree of unsaturation of the FA residues, the higher the rateof oxidation. Lipid oxidation leads to the formation of hydroperoxides, which arevery unstable and decompose to form secondary reaction products such as aldehydes,ketones, alcohols, acids, and hydrocarbons, which are described as having objec-tionable off-odors and off-flavors. During the initial or induction phase, oxidationproceeds at a relatively low rate. Peroxides are formed during this period. After acertain critical amount of oxidation has occurred, the reaction enters a second phase.The sample begins to smell and taste rancid in the beginning or early second phase.As fat or oil oxidation continues, the peroxides decompose to generate volatile andnonvolatile secondary products.

Lipid hydroperoxides can be measured by peroxide value (PV) and 2-thiobarbituric acid (TBA) tests. The resistance of a fat or an oil to oxidativerancidity can be measured by the Schaal oven test, Swift test, and oil stabilityindex (OSI) analysis.

Most of the vegetable oils contain natural antioxidants, the most importantof which are tocopherols. Maximizing the natural tocopherol content of the oilsduring refining is of great importance for extending the shelf life of finishedproducts. However, the addition of antioxidants is the most commonly usedmethod of retarding lipid oxidation in fat or oil. Some of the more popularsynthetic antioxidants used are phenolic compounds such as butylated hydroxy-anisole (BHA), butylated hydroxytoluene (BHT), mono-tert-butyl-hydroquinone(TBHQ), and propyl gallate (PG).

The presence of metals in the fat or oil greatly accelerates the oxidation process.Inactivation of the catalytic effect of these metals, e.g., copper, manganese, and iron,can be achieved by the use of a sequestering agent. Citric acid is one of the mostcommon chelating agents used in the fat and oil industry.

Lipid oxidation reactions can also be retarded by other means besides usingantioxidants or sequestering agents. One method is to reduce the concentration ofoxygen in the fat or oil, e.g., by packing the products under vacuum or nitrogen.Oxygen is about three times more soluble in lipids than in water. There is likely tobe sufficient oxygen present in the oil phase to cause lipid oxidation if oxygen isnot excluded from the aqueous phase.

6.5 INTERACTIONS OF LIPIDS WITH OTHER COMPONENTS IN THE FOOD SYSTEM

Lipids are indispensable to production, structure, and palatability of food, besidesbeing an essential nutrient. Lipids solubilize taste and aroma constituents of foodand act as precursors of important food aroma and flavor compounds. Lipids havebeen important bakery ingredients for shortening the texture of the finished bakedproducts. Shortening, a baker’s term, is used to tenderize baked products by actingas a shortening agent, which interferes with gluten development during mixing, andby lubricating gluten proteins, allowing expansion during proofing and baking ofyeast bread. Lipids contribute to the incorporation and retention of air in the form

Food Lipids 123

of small bubbles distributed throughout a batter; these small bubbles are importantto the grain and volume of baked products.

An emulsion is formed when oil and water are shaken together. The water phaseis dispersed in droplets in the oil phase, such as margarine, giving a water-in-oil(W/O) emulsion. Oil dispersed in an aqueous phase is called an oil-in-water (O/W)emulsion. The length of time for separation of these two phases depends on the sizeof the droplets — large droplets rise faster than small ones. The use of surfactantdecreases the free energy at the oil–water interface, lowering interfacial tension andslowing the rate of coalescence. Polar lipids, with large-charged or uncharged polargroups, giving these lipids amphiphilic nature, act as emulsifiers and surface-activeagents (surfactants) in foods and as a necessary component in food structures.

Surfactants modify the gelatinization behavior of starch by raising the swell-ing temperature. In starch solution, a helix is formed with a hollow cylinderwith a hydrophilic outer surface and a hydrophobic inner surface. Straight-chainalkyl molecules can fit into the inner space. In this way, the FA part of emulsifierssuch as glycerol monostearate (GMS) can form a complex with gelatinizedstarch, retarding starch crystallization in bread crumbs and slowing the stalingprocess. Unsaturated FAs have a bend due to the double bond in the hydrocarbonchain, limiting their ability to form complexes with helical sections of amyloseand amylopectin.

Mutual interaction of lipids and proteins contributes significantly to the phys-ical properties of many food systems of technological interest, such as emulsionsand foams. The hydrophobic regions may interact with the lipophilic parts ofsurfactants. In dough formation, the addition of anionic surfactants acting as doughstrengtheners promotes gluten protein aggregation, even at a lowered pH level, bybinding the lipophilic tail of the surfactant to the hydrophobic regions on theprotein molecule surface.

Lipids contribute to foam structure of whipped cream and constitute an essentialphase in food emulsions, such as milk, mayonnaise, and gravy. Lipids also providea pleasant creamy or oily mouth feel to many food products and contribute to thejuiciness of meat. They prevent crystallization and provide smoothness to crystallinecandies and frozen desserts.

During deep frying, lipids act as heat-transfer agents and react with the proteinand carbohydrate components of food, developing unique flavors and odors, as wellas a brown color, all of which are desirable to the consumer.

6.6 FUNCTIONAL FATTY SUBSTANCES

6.6.1 STRUCTURED LIPIDS

Structured lipids (SLs) are defined as TAGs restructured or modified to changetheir FA composition or their positional distribution in TAG molecules by chem-ical or enzymatic reaction, such as direct esterification, acidolysis, alcoholysis,or interesterification, depending on the types of substrates available (Lee andAkoh, 1998).


Direct esterification:

R1–COOH + R–OH → R1–COOR + H2O

Acidolysis:

R1–COOR + R1–COOH → R2–COOR + R1–CO–OH

Alcoholysis:

R–COOR1 + R2–OH → R–COOR2 + R1–OH

Interesterification:

R1–COOR2 + R3–COOR4 → R1–COOR4 + R3–COOR2

SLs, especially mono-long and di-medium chain-length MLM types, can providemedium-chain FAs (MCFAs) as a quick energy source and long-chain FAs (LCFAs)as essential FAs to hospital patients (Figure 6.1). Medium-chain TAGs (MCTs)primarily contain FAs with chain lengths of 6–12 carbons. Their smaller molecularsize and relatively high solubility in water contribute to different digestive andabsorptive properties, compared to those of long-chain TAGs (LCTs). MCTs aremainly metabolized via the portal vein, providing quick energy (Bach and Babayan,1982). However, MCTs alone cannot provide essential FAs. Through enzymatictransesterification, it is possible to incorporate a desired acyl group onto a specificposition of the TAG, whereas chemical transesterification does not provide for thisregiospecificity, due to the random nature of the reaction. Thus, lipase-catalyzedtransesterification can provide regio- or stereospecific SLs for nutritional, medical,

FIGURE 6.1 Structured lipids produced from an MCT and an LCT catalyzed by sn-1,3-specific lipase. M = medium chain FA; L = long chain FA.

Sn-1,3-specific lipase

M

M

MLCT

LL

L

M

L

M

L

L

L

M

M

M

L

M

M

M

L

MCT

L L

L

M

Food Lipids 125

and food applications. For example, TAG contains an n-3 or n-6 PEFA, such as EPA,DHA, γ-linolenic acid (GLA), or arachidonic acid, at the sn-2 position of the glycerolbackbone, and two MCFAs at the sn-1 and sn-3 positions. This MLM type of SLcan provide the essential FAs and retain the assimilation advantages of the MCT.Irimescu et al. (2000) developed an enzymatic procedure to produce 1,3-dicapryloyl-2-eicosapentaenoylglycerol (MLM type). The maximal molar content of the MLMin the glycerides of the reaction mixture was up to 91%; the total yield was 88%and no purification of the intermediates was necessary.

FAs liberated from food during absorption are metabolized more easily if theyare short or medium chain, i.e., C10 or below. The sn-2 monoacylglycerols can beabsorbed directly. Therefore, essential or desired FAs are most efficiently utilizedfrom the sn-2 position in acylglycerols. In accordance with this, TAGs with short-chain FAs (SCFAs) or MCFAs at the sn-1 and sn-3 positions and PEFAs at the sn-2 position are rapidly hydrolyzed with pancreatic lipase (sn-1,3-specific lipase) andabsorbed efficiently into mucosal cells. SCFAs or MCFAs are used as a source ofrapid energy for infants and patients with fat malabsorption-related diseases. LCFAs,especially DHA and arachidonic acid, are important in both the growth and devel-opment of an infant, while n-3 PEFAs have been associated with reduced risk ofcardiovascular disease in adults (Christensen et al., 1995; Jensen et al., 1995).

SLs also can be used as low-calorie fats consisting of SCFAs and LCFAs.Because SCFAs provide fewer calories per unit of weight and LCFAs are poorlyabsorbed and thus impart less energy, these fats have a lower energy density thannatural fats (Willis et al., 1998). The best-known representatives of this low-caloriefat group are Caprenin and Salatrim. Caprenin, containing one molecule of behenicacid (C22:0) and two molecules of caprylic acid (C8:0) or capric acid (C10:0), is acommercially available low-calorie SL. It has been produced by reaction of monobe-henin with free FAs (Kluesener et al., 1992). Its energy value using young rats asthe test model is 4.3 kcal/g, approximately half the energy in traditional fats andoils (Ranhotra et al., 1994). Caprenin has similar properties to cocoa butter and canbe used in chocolate candy bars to replace cocoa butter. Caprenin can also be usedin soft candy and in confectionery coating for nuts, fruits, and cookies. Accordingto a 91-day feeding study in rats, Caprenin has no observable adverse effect, becausethe amount of Caprenin is greater than 15% (w/w) in the diet or greater than 83%of total dietary fat (Webb et al., 1993).

Salatrim (an acronym for short- and long-chain acid triacylglycerol molecules)consists of a mixture of LCFAs and SCFAs esterified to glycerol. Salatrim, developedby Nabisco Inc., is a family of fats composed of TAGs that delivers fewer caloriesthan other fats. Nabisco discovered that TAGs containing mixtures of LCFAs andSCFAs functioned like normal fats but provided fewer calories when consumed. Theenergy value of Salatrim is between 4.7 and 5.1 kcal/g (Willis et al., 1998). By usingSalatrim, Hershey Foods Corporation creates a 50% reduced-fat semisweet chocolatebaking chip named Benefat. Benefat contains fewer calories than normal cocoa butterand is only partially absorbed by the body (Tarka, 1996). The SCFAs in Salatrimare acetic acid, propionic acid, butyric acid, or mixtures including any combinationof these three. The LCFAs in Salatrim are provided by completely hydrogenatedvegetable oils, such as canola or soy. The completely hydrogenated fats contain


predominantly stearic acid; this is unique among LCFAs because stearic acid isnonhypercholesterolemic. In addition, when fed as a component in Salatrim, stearicacid is poorly absorbed. Five 90-day feeding trials of rats were conducted withvarious Salatrim compositions. The results indicated that Salatrim fed to rats at levelsas high as 7.9 g/kg/day did not cause any adverse effects (Smith and Finley, 1995).

6.6.2 POLYENOIC FATTY ACIDS

Dietary PEFAs have important physiological effects on the regulation of biologicalprocesses involving eicosanoid production, signal transduction, and maintenance ofmembrane fluidity. Two families of PEFAs, designated as n-6 and n-3, normally arepresent in the tissues and body fluids. The n-6 PEFA linoleic acid (18:2, n-6) isprimarily found in plants. Arachidonic acid converted by desaturation and elongationof linoleic acid is the main substrate for synthesis of prostaglandins, thromboxane,leukotrienes, and platelet-activating factor, which are eicosanoid mediators of inflam-mation; thrombosis and bronchoconstriction; inflammation and chemotaxis, andbronchial hypersensitivity (Okuyama et al., 1997). High amounts of these moleculescause an immunosuppressive effect. The n-3 PEFAs having anti-inflammatory andimmunomodulatory effects act as inhibitors of arachidonic acid metabolism. Themetabolic pathway of n-3 PEFAs is different from that of n-6 PEFAs. These twofamilies have different physiological functions and act in concert with one anotherto regulate biological processes. The n-3 FA α-linolenic acid is converted to EPAand DHA (Figure 6.2) which are the precursors of the 3-series of prostaglandins andthe 5-series of leukotrienes.

Vegetable oils and fish are the predominant sources of n-3 PEFAs in the diet.Fish are the major source of EPA (20:5) and DHA (22:6), whereas vegetable oilsare the major source of α-linolenic acid (ALA; 18:3). ,Soybean and canola oils are

FIGURE 6.2 Metabolism of n-3 linolenic acid.

Prostaglandins (3-series)Thromboxanes (5-series)Leukotrienes

EPA(C20:5) C22:5Elongase

DHA(C22:6)

α -Linolenic C18:4 C20:4Elongase∆ 6-Desaturase ∆ 5-Desaturase

∆ 4-Desaturase

Food Lipids 127

the primary sources of ALA. The contents of ALA in soybean and canola oils arearound 7.8 and 9.2%, respectively. Flaxseed and perilla oils are rich sources of n-3PEFA, the contents of which are more than 50%.

Mackerel, menhaden, herring, cod liver, and salmon are rich in EPA andDHA. However, the content of n-3 FA can vary appreciably among fish of differenttypes. Many reports state that EPA and especially DHA are important for humandevelopment, particularly of the brain and eye (Connor et al., 1992; Uauy et al.,1992). Supplementation of infant formula with EPA and DHA clearly improvesvisual acuity; supplementation with both arachidonic acid and DHA producesright balance.

Linoleic acid, known as n-6 essential FA, is the major constituent of vegetableoils obtained from corn, safflower, soybean, and sunflower. Linoleic acid can bestored, oxidized to supply energy, or metabolized to a GLA, cis-6,9,12-octadecatri-enoic acid. GLA then can be metabolized to dihomogammalinolenic acid (DGLA)and arachidonic acid (Figure 6.3). These metabolites are critical for the developmentof many tissues, especially the brain, which by weight contains about 20% of n-6essential FA. The conversion of linoleic acid to GLA catalyzed by ∆6 desaturase inhumans is well established as a rate-limiting metabolic step (Kies, 1989), with smallamounts of linoleic acid being converted to GLA and its metabolites. This biocon-version is depressed under stressful conditions, probably resulting from the ∆6 desat-urase defect. In such cases an essential fatty acid deficient status may be avoided bydirect intake of GLA. Infants are proportionally somewhat more limited in their ∆6desaturase supply than adults. Therefore, infants may have difficulty in formingadequate amounts of all these acids if linoleic acid is the only dietary source of n-6essential FA. This is the reason why GLA, DGLA, and arachidonic acid are presentin human milk. Besides, the below-normal plasma or adipose tissue concentrationsof GLA, DGLA, or arachidonic acid may also be found in: people with diabetes,

FIGURE 6.3 Metabolism of n-6 linoleic acid.

γ - Linolenic acid

Linoleic acid∆ 6-Desaturase

Dihomo - γ - Linolenic acid

Elongase

∆ 5-Desaturase

Arachidonic acid

Prostaglandins(1-series)

Prostaglandins (2-series)Thromboxanes

Leukotrienes (4-series)

LipoxygenaseCyclooxygenase


alcoholic people, women with premenstrual syndrome, aged people, middle-agedindividuals who will develop a stroke, and middle-aged individuals who will laterdevelop heart disease (Carter, 1988). GLA and its metabolites are effective in thesuppression of inflammation and in the treatment of diabetic neuropathy, atopiceczema, age-related diseases, alcoholism, cardiovascular disease, and gastrointestinal,gynecological, neurological, and immunological disorders.

Evening primrose oil is rich in GLA (7–15%). Two seed oils other thanevening primrose oil have been found to contain substantial amounts of GLA.These are borage oil, containing 21–25% GLA, and black currant oil, containingabout 15–20% GLA. Microorganisms of the genus Spirulina are another sourceof GLA. Dried Spirulina species contain around 10% lipid, and of that, 20–25%is GLA. Fungi such as those of the Rhizopus and Mortierella species can alsoproduce GLA.

6.6.3 VEGETABLE LECITHIN

Vegetable lecithin, an edible by-product of oil processing, is primarily a mixture ofphospholipids such as phosphatidylcholine, phosphatidylethanolamine, phosphati-dylinositol, and phosphatidic acid (Figure 6.4) and contains minor quantities ofglycolipids and oligosaccharides. The degumming of oil with water yields lecithinsludge and degummed oil. Continuous agitated thin-film evaporation reduces themoisture of the lecithin sludge to less than 1%, resulting in a highly viscous semi-liquid product. The major vegetable lecithin is soybean lecithin.

Lecithin purification is of commercial importance, as the sludge is contaminatedwith carbohydrates, proteins, or other impurities. Removal of fines by filtration iseasy in the state of the miscella or crude oil. It is difficult to filter impurities in thestate of highly viscous finished lecithin. Standardized fluid lecithins typically contain

FIGURE 6.4 Some phospholipids in plants.

R" = CH2-CH2-N+(CH3)3 (Phosphatidylcholine) R" = CH2-CH2-NH3+ (Phosphatidylethanolamine)R" = C6H6-(OH)6 (Phosphatidylinositol)R" = H (Phosphatidic acid)R' = Fatty acidR = Fatty acid or -HPO4-R"

CH2 –O–R

R'O–CH O

CH2 –O–P–O–R" (α form)

(β form)

OH

Food Lipids 129

62–64% acetone insolubles (AIs) and have an acid value below 30. Treating thelecithin sludge with acetone can enhance the AI content of lecithin up to 95–98%.

Because of its surface-active properties, lecithin has been widely used in theprocessing of foods, including baked foods, beverages, and confections. Lecithincan be modified from the basic viscous W/O emulsifier type to various forms withdifferent physical and functional properties. In W/O emulsions such as margarineor ice frosting, basic lipophilic lecithin is suitably used in conjunction with mono-acylglycerols. The apparent hydrophilicity of lecithin can be increased by modifi-cation of lecithin through acetylation, hydroxylation, solvent fractionation, and de-oiling. Hydrophilic lecithin having the property of water dispersibility can be usedin O/W emulsions.

Lecithin, especially phosphatidylcholine, is an important constituent of all humancells. Diet supplementation with lecithin improved serum lipoprotein patterns. Itdecreased the levels of total cholesterol, low-density lipoprotein (LDL) cholesterol,and TAGs, and increased the levels of high-density lipoproteins (Canty, 2000).

6.6.4 TOCOPHEROL AND PHYTOSTEROL

The richest sources of vitamin E in the diet are vegetable oils. α-Tocopherol is themajor contributor to the total vitamin E activity in some oils, but others containsubstantial amounts of γ-tocopherol (Figure 6.5). Typically, wheat germ, sunflower,cottonseed, and safflower oils contain about 1700, 500, 400, and 350 mg of α-tocopherol equivalent kg–1, respectively. Tocopherols are concentrated in deodorizerdistillate (DOD) during the deodorization step. As a result, DOD is a good sourceof natural tocopherols that are used to make natural vitamin E. DOD is composedof FAs, mixed mono-, di-, or triacylglycerols, sterols, tocopherols, sterol esters,hydrocarbons, and oxidation by-products. DOD is frequently collected and sold. A

FIGURE 6.5 Structure of the tocopherols.

Compound R1 R2 R3α−Tocopherol CH3 CH3 CH3

β−Tocopherol CH3 H

H

CH3

γ−Tocopherol H CH3 CH3

δ−Τocopherol H CH3

O

R1

CH3

R2

R3

CH3

CH3 CH3CH3

CH3


series of chemical and physical treatments such as saponification, esterification,and molecular distillation can be used to concentrate tocopherols and sterols.

Plant sterols, also called phytosterols, have been reported to include over 250 dif-ferent sterols and related compounds in various terrestrial and marine materials (Akihisaet al., 1991). Sitosterol, stigmasterol, and campesterol are the commonly consumed plantsterols. The predominant sterol class in vegetable oils is 4-desmethyl sterols. Sitosterolusually contributes more than 50% of desmethyl sterols. The other most significantdesmethyl sterols include campesterol, stigmasterol, ∆5-avenasterol, ∆7-avenasterol, and∆7-stigmastenol. Brassicasterol is a typical sterol for rapeseed and other Cruciferae.Stanol occurs in significant amounts in corn bran and fiber oil (Piironen, et al., 2000).

These plant sterols have similar chemical structures to cholesterol (Figure 6.6)and the capacity to lower plasma cholesterol and LDL cholesterol. The higher thedietary intake of plant sterols from the diet, the lower the serum cholesterol level.

6.6.5 SESAME LIGNANS

Sesame (Sesamum indicum L.) is usually processed into oil with a characteristicroast flavor, which is used as a condiment in Oriental countries. Sesame seed and

FIGURE 6.6 Structures of animal and plant sterols.

HO

HO

HO

Cholesterol

β-Sitosterol

Stigmasterol

Campesterol

HO

Food Lipids 131

its oils are reported to have bioactive compounds such as sesamin, sesamolin,sesaminol, and sesamol (Kamal-Eldin et al., 1994; Umeda-Sawada et al., 1998)(Figure 6.7). All these compounds in the oil showing strong antioxidant activitygive excellent oil stability during storage. However, after oil pressing, some sesamelignans might still remain in the defatted sesame. Lignan glucosides are the majorcompounds in the defatted sesame flour. They are known to have multiple biolog-ical functions such as antioxidant activity (Yamashita et al., 1998; Hirose et al.,1992), anticarcinogenicity (Hirose et al., 1992), antihypertensive effect (Kita et al.,1995) in rats, and alleviation of liver damage caused by alcohol or carbon tetra-chloride (Akimoto et al., 1993) in mice. In addition, Sugano et al. (1990) reportedon the hypocholesterolic activity of sesamin. They showed that sesamin reducedboth blood and liver cholesterol levels of rats fed with purified diets containingsesamin and cholesterol. This phenomenon may be due to the inhibition of intes-tinal absorption of cholesterol by sesamin. Also, it was found that sesamin reducedthe activity of hepatic 3-hydroxy-3-methylglutaryl CoA reductase, the key enzymein cholesterol synthesis.

REFERENCES

Akihisa, T., Kokke, W., and Tamura, T., Naturally occurring sterols and related compoundsfrom plants, in Physiology and Biochemistry of Sterols, Patterson, G.W. and Nes,W.D., Eds., American Oil Chemists’ Society, Champaign, IL, 1991, p. 172.

Akimoto, K. et al., Protective effects of sesamin against liver damage caused by alcohol orcarbon tetrachloride, Ann. Nutr. Metab., 37, 218, 1993.

Bach, A.C. and Babayan, B.K., Medium-chain triglycerides: an update, Am. J. Clin. Nutr.,36, 950, 1982.

Canty, D., Lecithin, choline, and heart disease, INFORM, 11, 537, 2000.

FIGURE 6.7 Structures of antioxidants in sesame seed and oil.


Carter, J.P., Gamma-linolenic acid as a nutrient, Food Technol., 42, 72, 1988.Christensen, M.S., Mullertz, A., and Hoy, C.E., Absorption of triglycerides with defined or

random structure by rats with biliary and pancreatic diversion, Lipids, 30, 521, 1995.Cmolik, J. and Pokorny, J., Physical refining of edible oils, Dur. J. Lipid Sci. Technol., 102,

472, 2000.Connor, W.E., Neuringer, M., and Reisbeck, S., Essential FA: the importance of n-3 FA in

the retina and brain, Nutr. Rev., 50, 21, 1992.Hirose, N. et al., Suppressive effect of sesamin against 7,12-dimethylbenz[a]anthracene

induced rat mammary carcinogenesis, Anticancer Res., 12, 1259, 1992.Irimescu, R. et al., Enzymatic synthesis of 1,3-dicapryloyl-2-eicosapentaenoylglycerol, J. Am.

Oil Chem. Soc., 77, 501, 2000.Jensen, M.M., Christensen, M.S., and Hoy, C.E., Intestinal absorption of octanoic, decanoic and

linoleic acids: effects of triacylglycerol structure, Ann. Nutr. Metab., 38, 104, 1995.Kamal-Eldin, A., Appelqvist, L.A., and Yousif, G., Variations in the composition of sterols,

tocopherols and lignans in seed oils from four sesamum species, J. Am. Oil Chem.Soc., 71, 149, 1994.

Kies, C., Evening primrose oil: a source of gamma linolenic acid, Cereal Food World, 34,1016, 1989.

Kita, S. et al., Anthihypertensive effect of sesamin. II. Protection against two-kidney, one-clip renal hypertension and cardiovascular hypertrophy, Biol. Pharmacol. Bull., 18,1283, 1995.

Kluesener, B.W., Stipp, G.K., and Yang, D.K., Selective Esterification of Long Chain FattyAcid Monoglycerides with Medium Chain FA, U.S. Patent 5,142,071, 1992.

Lee, K.T. and Akoh, C.C., Structured lipids: synthesis and applications, Food Rev. Int., 14,17, 1998.

Okuyama, H., Kobayashi, T., and Watanabe, S., Dietary FA: the n-6/n-3 balance and chronicelderly diseases: excess linoleic acid and relative n-3 deficiency syndrome seen inJapan, Prog. Lipid Res., 35, 409, 1997.

Piironen, V. et al., Plant sterols: biosynthesis, biological function and their importance tohuman nutrition, J. Sci. Food Agric., 80, 939, 2000.

Ranhotra, G.S., Gelroth, J.A., and Glaser, B.K., Usable energy value of a synthetic fat(caprenin) in muffins fed to rats, Cereal Chem., 71, 159, 1994.

Smith, R.E. and Finley, J.W., Chemistry, testing and application of Salatrim low calorie fat,Manufacturing Confectioner, 75, 85, 1995.

Sugano, M. et al., Influence of sesame lignans on various lipid parameters in rats, Agric. Biol.Chem., 54, 2669, 1990.

Tarka, S.J., Hershey creates a new reduced fat baking chip, Candy Industry, 161, 36, 1996.Uauy, R.D. et al., Visual and brain function measurements in studies of ω-3 fatty acid

requirements in infants, J. Pediatr., 120, 168, 1992.Umeda-Sawada, U., Ogawa, M., and Igarashi, O., The metabolism and n-6/n-3 ratio of

essential FA in rats: effect of dietary arachidonic acid and mixture of sesame lignans(sesamin and episesamin), Lipids, 33, 567, 1998.

Webb, D.R. et al., A 91-day feeding study in rats with caprenin, Food Chem. Toxicol., 31,935, 1993.

Willis, W.M., Lencki, R.W., and Marangoni, A.G., Lipid modification strategies in the productionof nutritionally functional fats and oils, Crit. Rev. Food Sci. Nutr., 38, 639, 1998.

Yamashita, K. et al., Sesame seed lignans and γ-tocopherol act synergistically to producevitamin E activity in rats, J. Nutr., 122, 2440, 1998.

1331-5871-6149-4/02/$0.00+$1.50© 2002 by CRC Press LLC

Proteins

E. Sikorski

CONTENTS

7.1 Chemical Structure.......................................................................................1347.1.1 Introduction ......................................................................................1347.1.2 Amino Acid Composition ................................................................1347.1.3 Hydrophobicity.................................................................................137

7.1.3.1 Average Hydrophobicity...................................................1377.1.3.2 Surface Hydrophobicity....................................................137

7.2 Conformation ...............................................................................................1387.2.1 Native State ......................................................................................1387.2.2 Denaturation .....................................................................................141

7.3 Functional Properties ...................................................................................1417.3.1 Introduction ......................................................................................1417.3.2 Solubility ..........................................................................................142

7.3.2.1 Effect of the Protein Structure and Solvent .....................1427.3.2.2 Effect of Ions ....................................................................1437.3.2.3 Importance in Food Processing ........................................144

7.3.3 Water-Holding Capacity...................................................................1447.3.4 Gelling and Film Formation ............................................................145

7.3.4.1 Gel Structure.....................................................................1457.3.4.2 Interactions of Components..............................................1467.3.4.3 Binding Forces and Process Factors ................................1467.3.4.4 Importance in Food Processing ........................................147

7.3.5 Emulsifying Properties.....................................................................1487.3.5.1 Principle ............................................................................1487.3.5.2 Factors Affecting Emulsification ......................................1497.3.5.3 Determination of Emulsifying Properties ........................150

7.3.6 Foaming Properties ..........................................................................1507.4 Proteins as Functional Components in Foods .............................................151

7.4.1 Muscle Proteins................................................................................1517.4.2 Legume Proteins ..............................................................................1537.4.3 Milk Proteins....................................................................................1537.4.4 Egg Proteins .....................................................................................1547.4.5 Mycoprotein .....................................................................................154

7.5 Effects of Heating ........................................................................................1557.5.1 Introduction ......................................................................................155

7Zdzislaw


7.5.2 Rheological Changes........................................................................1567.5.3 Changes in Color .............................................................................1577.5.4 Development of Volatile Compounds ..............................................1587.5.5 Reactions at Alkaline pH .................................................................159

7.6 Oxidation......................................................................................................1607.7 Enzyme-Catalyzed Reactions ......................................................................162

7.7.1 Introduction ......................................................................................1627.7.2 Changes in Milk Proteins ................................................................1627.7.3 Role of Enzymes in Muscle Foods .................................................1627.7.4 Transglutaminase-Catalyzed Reactions ...........................................1667.7.5 Other Enzyme Applications in Foods..............................................167

7.8 Chemical Modifications ...............................................................................1687.8.1 Introduction ......................................................................................1687.8.2 Alkylation.........................................................................................1697.8.3 Acylation ..........................................................................................1707.8.4 N-Nitrosation....................................................................................1717.8.5 Reactions with Phosphates...............................................................172

References..............................................................................................................173

7.1 CHEMICAL STRUCTURE

7.1.1 INTRODUCTION

Proteins are linear condensation products of various α-L-amino acids (a.a.) thatdiffer in molecular weight, charge, and nonpolar character (Table 7.1), bound bytrans-peptide linkages. They differ in number and distribution of various a.a. residuesin the molecule. The chemical properties, size of the side chain, and sequence ofthe a.a. affect the conformation of the molecule, i.e., the secondary structure con-taining helical regions, β-pleated sheets, and β-turns; the tertiary structure or thespatial arrangement of the chain; and the quaternary structure — the assembly ofseveral polypeptide chains.

The conformation affects the biological activity, nutritional value, and functionalrole of proteins as food components.

7.1.2 AMINO ACID COMPOSITION

In most proteins the proportion of each of the different a.a. residues, calculated as apercent of the total number of residues, ranges from 0 to about 30%. In extreme casesit may even reach 50%. Cereal proteins are generally very poor in Lys. Several majorgrains are deficient in Thr, Leu, Met, Val, and Trp. In most collagens there are noCys and Trp residues, while the content of Gly, Pro, and Ala is 328, 118, and 104residues/1000 residues, respectively. Paramyosin, abundant in the muscles of marineinvertebrates, is rich in Glu (20–24%), Asp (12%), Arg (12%), and Lys (9%). Theantifreeze fish serum glycoproteins contain several a.a. sequences of Thr-X2-Y-X7,where X is predominantly Ala and Y a polar residue. The antifreeze proteins of typeI usually contain more than 60 mol% of Ala. Thr and Y, and in various antifreeze

Proteins 135

proteins, other polar residues, form hydrogen bonds with ice crystals, inhibitingthereby the crystal growth. The β-caseins contain 14% of Pro residues. The moleculehas a polar N-terminal region (1–43) with a charge of –12 and an apolar fragment,containing most of the Pro residues. Such sequence favors the temperature-, concen-tration-, and pH-dependent associations into threadlike polymers, stabilized mainlyby hydrophobic adherences. Lysozyme, a basic protein of egg whites and otherorganisms, containing four -S-S- cross-links in a single polypeptide, retains its enzy-matic activity in acidic solution even after heating to 100°C. The Bowman–Birktrypsin inhibitor consists of 71 a.a. residues in one polypeptide chain with loops dueto seven -S-S- bonds. The bovine serum albumin has 1 SH group and 17 intramolec-ular -S-S- bridges per molecule. Grain prolamines are very rich in Glu (up to 55%)and Pro (up to 30%). Among the 225 residues of phosvitin of egg yolk, there are 122Ser, most of them phosphorylated (SerP). The typical sequences of phosvitin are: …Asp-(SerP)6-Arg-Asp … and … His-Arg-(SerP)6-Arg-His-Lys … .

Most food proteins, however, do not differ very much in a.a. composition.Generally the contents of acidic residues are the highest, and those of His, Trp, and

TABLE 7.1Selected Properties of Proteinogenic Amino Acids

Amino Acid Abbreviation pKa1 pKa2 pKR

Isoelectric Point pI

Side Chain Hydrophobicity

(Ethanol → Water) kJ/mol

Glycine Gly 2.34 9.60 — 6.0 0Alanine Ala 2.34 9.69 — 6.0 3.1Valine Val 2.32 9.62 — 6.0 7.0Leucine Leu 2.36 9.60 — 6.0 10.1Isoleucine Ile 3.26 9.68 — 6.0 12.4Proline Pro 1.99 10.60 — 6.3 10.8Phenylalanine Phe 1.83 9.13 — 5.5 11.1Tyrosine Tyr 2.20 9.11 10.07 5.7 12.0Tryptophan Trp 2.38 9.39 — 5.9 12.5Serine Ser 2.21 9.15 13.60 5.7 0.2Threonine Thr 2.15 9.12 13.60 5.6 1.8Cysteine Cys 1.71 8.35 10.28 5.0 4.2Methionine Met 2.28 9.21 — 5.7 5.4Asparagine Asn 2.02 8.80 — 5.4 –0.04Glutamine Gln 2.17 9.13 — 5.7 –0.4Aspartic acid Asp 1.88 3.65 3.65 2.8 2.2Glutamic acid Glu 2.19 4.25 4.24 3.2 2.3Lysine Lys 2.20 8.90 10.56 9.6 6.2Arginine Arg 2.18 9.09 12.48 10.8 3.1Histidine His 1.80 5.99 6.00 7.5 2.1

Note: pKa1 = –log [H+] [a.a.+/–]/[a.a.+], pKa2 = –log [H+] [a.a.–]/[a.a.+], pKR = negative logarithm ofdissociation constant of a.a. group in aqueous solution.


sulfur containing a.a. are the lowest. However, the number of residues capable ofaccepting a positive charge is often higher, especially in plant proteins, since about50% of side chain carboxyl groups are amidated.

Many a.a. residues undergo posttranslational enzymatic amidation, hydroxyla-tion, oxidation, esterification, glycosylation, methylation, or cross-linking. Somesegments of the polypeptide chains may be removed (Figure 7.1). Modified residuesin a given protein can be used for analytical purposes, e.g., hydroxyproline (ProOH),which is characteristic for collagens.

Posttranslational modifications may result in covalent attachment of variousgroups to the proteins. They may change the ionic character of the molecule, e.g.,the phosphoric acid residues or saccharides. The residues involved in phosphoryla-tion and binding of saccharide moieties are Ser, Thr, LysOH, ProOH, His, Arg, andLys. Among the proteins containing many phosphorylated a.a. residues is αS-casein.

FIGURE 7.1 Posttranslational modifications in collagen. (From Sikorski, Z.E., Proteins, inChemical and Functional Properties of Food Components, Sikorski, Z.E., Ed., TechnomicPublishing Co. Inc., PA, 1997. With permission.)

Polyrybosome

Hydroxylases

Procollagen GlycosyltransferasesEndopeptidases

Pro - α1

Pro - α1

Pro - α2

Tropocollagen

Collagen fibers

Proteins 137

In the central region of αS1-casein SerP occurs in sequences: … SerP-Ala-Glu … ,… SerP-Val-Glu … , … SerP-Glu-SerP … , and … SerP-Ile-SerP-SerP-SerP-Glu… . Such distribution favors oligomer formation, due to hydrophobic interactionsof the apolar fragments of the molecules, with the charged sequences exposed tothe solvent. High contents of saccharides are characteristic for the allergenic glyco-proteins of soybeans (up to about 40%), several egg white proteins (up to 30%),albumins of cereal grains (up to 15%), whey immunoglobulins (up to 12%), andcollagens of marine invertebrates (up to 10%). In κ-casein there is a hydrophobicN-terminal part (1–105) and a hydrophilic macropeptide (106–169), or a glycomac-ropeptide, with a saccharide moiety (0.5%) of N-acetylneuraminic acid, D-galactose,N-acetylgalactosamine, and D-mannose residues.

7.1.3 HYDROPHOBICITY

7.1.3.1 Average Hydrophobicity

The nonpolar character of an a.a. can be expressed by hydrophobicity, i.e., changeof the free energy (Fta) accompanying the transfer of the a.a. from a less polar solventto water. Exposure of an a.a. with a large hydrocarbon side chain to the aqueousphase results in a corresponding decrease in entropy due to structuring of wateraround the chain. The hydrophobicity of the side chain of an a.a. is: Ftr = Fta – FtGly,where FtGly is the hydrophobicity of Gly.

The average hydrophobicity (Ftav) of a protein can be estimated as Ftav = ΣFta/n,where n is the number of a.a. residues in the protein molecule.

It is not possible to predict the conformation and behavior of a protein in solutionon the basis of Ftav. However, proteins of high Ftav yield bitter hydrolysates.

7.1.3.2 Surface Hydrophobicity

Most hydrophobic a.a. residues of a globular protein are burried in the interior ofthe native molecule. However, some of them form hydrophobic clefts or occur onthe surface as individual residues or patches of residues.

Phe, Tyr, and Try residues in food proteins can be monitored by measuring the intrinsicfluorescence. They absorb ultraviolet radiation and emit fluorescence in the order:

The intensity of fluorescence and the wavelength of maximum intensity dependon the polarity of the environment. Thus a Try residue located in a nonpolar regionemits fluorescence at 330–332 nm, and in complete exposure to water at 350–353nm. Furthermore, electron withdrawing groups, like carboxyl, azo, and nitro groups,as well as different salt ions, have a quenching effect on fluorescence. However,measurements of intrinsic fluorescence and of fluorescence quenching have notfound wide application in hydrophobicity determinations, because they are restrictedto the effect of aromatic a.a. residues.

Phe 260 nm 283 nmTyr 275 nm 303 nmTrp 283 nm 343 nm


The simplest and most commonly used are hydrophobic probes, based on thephenomenon that the quantum yield of the fluorescence of compounds containingsome conjugated double bond systems is about 100 times higher in a nonpolarenvironment than in water. Thus hydrophobic groups can be monitored by aromaticor aliphatic probes and fluorescence measurements. Most often used are 1-anili-nonaphthalene-8-sulfonate (ANS) (Formula 7.1) and cis-parinaric acid (CPA) (For-mula 7.2). The binding of triacylglycerols or sodium dodecylsulfate may also bedetermined.

7.2 CONFORMATION

7.2.1 NATIVE STATE

In a natural environment the proteins spontaneously fold from an extended form Lto the native conformation N, which is affected by the primary structure L ↔ N.

This is accompanied by a decrease in free energy: –RTlnK = ∆G = ∆H – T∆S,where R is the gas constant, T is the temperature, H is enthalpy, S is entropy, andK is the equilibrium constant (K = [N]/[L]).

The conformation of proteins in solutions is affected by hydrogen bondsbetween water and hydrophilic residues resulting in enthalpy changes, as well ashydrophobic effects caused by nonpolar groups in the aqueous environment, bring-ing about entropy changes. This is reflected in the total free energy change ∆Gt:∆Gt = ∆Hp + ∆Hw – T∆Sp – T∆Sw, where the subscripts p and w refer to proteinand water, respectively.

The native conformation is stabilized by various forces. The dipole–dipoleinteractions, depolarization, and dispersion forces are significant only at a veryclose distance (r) of the atoms because the energy decreases with r–6. The hydrogenbonds, abundant in proteins, differ in energy from about 2 to about 12 kJ/mol,depending on the properties and direction of the groups involved. The strength ofthe H-bonds does not depend significantly on temperature, but increases with

ˆ

Formula 7.1

Formula 7.2

NH

SO3-

CH3 4CH2 (CH = CH) 2(CH )7 COOH

Proteins 139

pressure. The energy of the ionic bonds is affected by the dielectric constant andmay reach into the hydrophobic core of a protein about 21 kJ/mol between theionized residues of Asp and Lys. The energy of hydrophobic interactions increaseswith temperature and decreases with increasing pressure. Covalent bonds otherthan those in the polypeptide chain, although of highest energy, are generally verylimited in number. However, some proteins rich in such bonds may have highthermal stability, e.g., mature collagens containing different cross-links generatedin reactions of the oxidized ε-NH2 group of Lys and LysOH:

Other examples would be in the Maillard reaction of the saccharide moieties ofthe molecules and as proteins containing many -S-S- bridges, e.g., several proteinaseinhibitors.

A very significant effect on the properties of proteins is exerted by their quater-nary structures and micellar associations.

Soybean glycinin composed of six basic and six acidic subunits has a structureof two superimposed rings. In each ring the three acidic and three basic subunitsare arranged alternatively. Thus ionic interactions are possible both within each ringand between the rings. Because the conformation of the oligomer is buttressed bynoncovalent forces, the addition of urea and changes in pH and ionic strength leadto dissociation of the protein into subunits.

Reaction 7.1

Prot NH2 Prot CH

O

lysyl

oxidase

Prot Prot

O H

C

CH

OH

CH Prot

O H

C

ProtCCH

Prot NH2

ProtO

HC C

H

OCH2 Prot+

N

NH

CH2

Prot

CHProt CH Prot

CH

N

Prot

N

N

CH2 Prot

CHProt CH Prot

C

HO

ProtCH2

N

N

H2O


In unheated milk the caseins are present as a colloidal dispersion ofparticles containing about 6–7% calcium phosphate, known as micelles, andas smaller particles without calcium phosphate. These forms are in an equi-librium that is affected by temperature, pH, and the concentration of Ca2+. Infresh milk about 80–90% of the mass of caseins is in the micellar form. Themicelles are very porous and hydrated, have a diameter ranging from a few toabout 600 nm, and have a weight average molecular mass of 600 MDa.Numerous investigations have resulted in various models of the structure ofcasein micelles. According to one group of models the micelles are formedfrom several hundreds subunits, called submicelles, that differ in compositionand size. In these models either the subunits are linked by calcium phosphateor the calcium phosphate is located as discrete packages within the submicelles.According to the calcium phosphate nanocluster model there are no subunits,but the polypeptide chains form a matrix in which calcium phosphate nano-cluster-like particles are embedded (Figure 7.2). The outer parts of the micellesare occupied by hydrophilic polypeptide chains, including the macropeptideof κ-casein and Ca2+-sensitive peptides, and form a hairy layer (Holt andRoginski, 2001).

FIGURE 7.2 Calcium phosphate nanocluster model of a casein micelle. Substructure arisesfrom the calcium phosphate nanocluster-like particles in the micelles (dark spheres). Thereis a smooth transition from the core to the diffuse outer hairy layer that confers steric stabilityon the micelle. (Courtesy of Holt and Roginski, 2001.)

Proteins 141

7.2.2 DENATURATION

The native conformation of proteins is generally stabilized by rather smallenergy. The net thermodynamic stability of the native structure of many proteinsis as low as about 40–80 kJ/mo–1. The unfolding enthalpy of metmyoglobin andlysozyme is about 285 and 368 kJ/mo1, respectively. Therefore ionizing radiation,shift in pH, change in temperature or concentration of various ions, or addition ofdetergents or solvents may cause dissociation of the oligomers into subunits, unfold-ing of the tertiary structure, and uncoiling of the secondary structure (Figure 7.3).These changes are known as denaturation.

Exposure of the a.a. residues originally buried in the interior of the moleculechanges the pI, surface hydrophobicity, and the biochemical properties of proteins.Denaturation may be reversible, depending on the degree of deconformation andenvironmental factors. This may affect the value of determinations of enzyme activityused as a measure of severity of heat processing in food operations. For monitoringmilk pasteurization the determination of γ-glutamyltransferase can be used, sincethe enzyme undergoes complete inactivation after 16 sec at 77°C and no reactivationhas been evidenced (Zehetner et al., 1995).

Generally food processing causes irreversible denaturation followed by reactionsof the thermally denatured proteins with other components that may lead to loss infood quality. However, in foods denaturation may have beneficial or detrimentaleffects. The main effects comprise changes in pI, hydration, solubility, viscosity ofsolutions, biological activity, and reactivity of a.a. residues.

7.3 FUNCTIONAL PROPERTIES

7.3.1 INTRODUCTION

The functional properties important for the processor are attributes that, at properconcentration of the respective components or additives and at appropriate condi-tions, provide for the desirable characteristics of the product. These properties ofproteins are displayed in interactions with the surrounding solvent, ions, other

FIGURE 7.3 a: Protein denaturation of native molecule. b: Molecule changes conformationwith ruptured disulfide bridges and ionic bonds. c: Denatured molecule with randomlyextended polypeptide chains. (From Sikorski, Z.E., Proteins, in Chemical and FunctionalProperties of Food Components, Sikorski, Z.E., Ed., Technomic Publishing Co. Inc., PA,1997. With permission.)

sss

s

s

s

ss

M2+

a) b) c)


proteins, saccharides, and lipids, and in surface phenomena. The most important onein food processing can be roughly grouped accordingly (Table 7.2). They affect theappearance, color, juiciness, mouth feel, and texture of a large variety of foods, aswell as cutting, mincing, mixing, formation of dough, fibers, foils, bubbles, shaping,and transporting of food materials.

The functionalities of proteins can be modified by using enzymatic and chemicalprocesses that change the structure of proteins. They depend also on the pH, ionicstrength, and temperature in the food system. Through a better understanding of thetertiary structure of many food proteins, it should be possible to modify functionalityusing genetic engineering. To evaluate the functionality of some proteins in differentsystems, the quantitative structure–activity relationship approach may be applied(Nakai and Li-Chan, 1988).

7.3.2 SOLUBILITY

7.3.2.1 Effect of the Protein Structure and Solvent

The solubility or extractability of proteins is often defined in food chemistry as thepercent of the total quantity of protein contained in the food material that can beextracted by water or a suitable solvent in specified conditions. It depends on theproperties of the protein and solvent, pH, concentration and charge of other ions,and temperature. Generally proteins rich in ionizable residues, of low surface hydro-phobicity, are soluble in water or dilute salt solutions. Here belong the proteins ofthe egg white. Those abundant in hydrophobic groups readily dissolve in organicsolvents. The classification of cereal proteins into albumins, globulins, prolamines,and glutelins soluble in water, dilute salt solutions, 60–80% aliphatic alcohols, and0.2% NaOH, respectively, may also be used for characterization of other proteins.Stabilization by cross-linking is of crucial importance; e.g., the solubility of collagenfrom different connective tissues depends on the type and age of the tissue. Youngtropocollagen can be solubilized in neutral or slightly alkaline NaCl solution; tro-pocollagen containing intramolecular covalent bonds is soluble in citric acid solutionat pH 3, while mature collagen with covalent intermolecular cross-links is not solublein cold, dilute acids and buffers. It can, however, be partially solubilized in a highly

TABLE 7.2Functional Properties of Proteins Displayed in Interactions with Different Food Constituents

Interactions with

Water Water and Proteins Lipids or Gases

Wet ability Viscosity inducing Emulsifying abilitySwelling Gelling Emulsion stabilizationRehydration Fiber forming Foaming abilityWater holding Dough forming Foam stabilizationSolubility Membrane forming

Proteins 143

comminuted state or after several hours of treatment in alkaline media. Differencesin solubility are essential for various procedures of isolation of individual proteinsand groups of proteins from foods (Kristinsson, 2001).

Denaturation may decrease solubility; e.g., fish protein concentrate produced byextraction of minced fish with boiling azeotropic isopropanol is scarcely soluble inwater. In organic solvents, due to their low dielectric constant, the energy of inter-actions between charged a.a. residues is higher than in water. This may favorunfolding of the molecules and exposition of the hydrophobic residues, which cannot be counterbalanced by entropy forces. Thermal denaturation followed by aggre-gation due to interactions of the exposed reactive groups leads generally to loss insolubility. On the other hand, if heating brings about deconformation of the quater-nary and tertiary structures, it may increase the solubility, as in collagen.

Adding antioxidants to the defatted soy flour prior to alkaline extraction enhancesthe solubility of the protein isolate in proportion to the decrease in oxidation of thiolgroups (Boatright and Hettiarachchy, 1995).

7.3.2.2 Effect of Ions

In water solutions the solubility of proteins has a minimum pI (Figure 7.4).Because at such pH there is no electrostatic repulsion between the molecules, thehydration layer alone can not prevent aggregation. Although the attraction of waterdipoles by ionized groups of opposite charges in a.a. residues largely offsets theelectrostatic binding between the ions, the net balance of the attraction and change

ˆ

FIGURE 7.4 Effect of pH on the solubility of proteins.


in solvent entropy favors salt bridge formation. At pH values below or above thepI of the protein, the solubility increases due to repelling of the positive or negativeions, as well as to increased interaction of the charged polypeptide chains withwater dipoles. The pI of a protein may shift slightly with changing concentrationof salts in the solution.

The effect of ions on the solubility of a protein depends on their ionic strengthµ:µ= 0.5 ΣmiZi

2, where mi is the molarity of the solution in respect to the given ionand Zi is the charge of the ion. The effect of ions on the solubility of a protein alsodepends on their effect on the surface tension of the solvent, the dipole moment,and the reduction of the molecular surface area of the protein upon aggregation.Various ions, depending on their size and charge, favor or decrease the solubility ofproteins. In the low range of concentration, i.e., µ = 0.5 – 1.0, the solubility increaseswith the concentration of neutral salts. This is known as salting in. The ions have ascreening effect on the charged protein molecules. Being surrounded by waterdipoles, they add to the hydration layer, which favors solubilization of the macro-molecules. At higher concentrations the effect depends mainly on the ability of thesalts to affect the water structures.

7.3.2.3 Importance in Food Processing

The solubility versus pH curve can be used for selecting parameters for extractionof proteins from different sources. Adding a required amount of salt to the meatsduring cutting and mixing in a silent cutter is a prerequisite for extracting myofibrillarproteins from the tissue structures and forming a sausage batter of adequate quality.CaCl2 is used to precipitate the whey proteins, while CaSO4 coagulates soy proteinsin tofu manufacturing.

The solubility also contributes to gelling and emulsification. It may also berequired for efficient use of various protein isolates as functional food additives inproducts differing in pH and salt content. The loss in solubility due to abuse treatmentis often indicative of protein denaturation and subsequent cross-linking. Thereforesolubility data, if used to characterize commercial protein products, should be deter-mined in standardized procedures. In the methodology of solubility assays thefollowing factors must be considered: size and disintegration of the sample, pH andionic strength of the solvent, proportion of sample size to that of the solvent, numberof extractions, foaming during blending and stirring, temperature and time of extrac-tion, and separation of nonproteinaceous material ( , 2001).

7.3.3 WATER-HOLDING CAPACITY

The ability of many foods to retain water is affected by the involvement of proteinsin different structures. In meat and fish tissues the state of water depends on variousinteractions of water structures with proteins and other solutes. Furthermore, becauseof the fibrous nature of the muscle and compartmentation, water is also held in meatby physical entrapment. Alterations in the spatial arrangement of the proteins andin the integrity of the tissue structures caused by biochemical and processing factorsare responsible for shrinking or swelling of the material and thus for retaining or

Kolakowski

Proteins 145

exudation of water. Classical investigations on the effect of pH, divalent cations,postmortem changes, freezing and thawing, heating, salting, polyphosphates, andcitrates on the water-holding capacity (WHC) of meat were made by Hamm (1960).

WHC has a large impact on the texture and juiciness of meat and fish products.Decrease in WHC brings about excessive cooking loss and thawing drip. Changesin WHC may be also used for evaluating the effect of processing on the structureof proteins and on the quality of muscle foods. To be used as a quality index,WHC should be determined in standardized procedures. WHCs are based onmeasurements of loss of water from the original sample, due to centrifugation,pressing, or capillary force, or on measuring the quantity of liquid separated underthe action of a force from a sample with added water or aqueous solution (Regen-stein and Regenstein, 1984).

7.3.4 GELLING AND FILM FORMATION

7.3.4.1 Gel Structure

A gel consists of a three-dimensional lattice of large molecules or aggregates capableof immobilizing solvent, solutes, and filling material. Food gels may be formed byproteins and polysaccharides that may participate in gel formation in the form ofsolutions, dispersions, micelles, or even in disrupted tissue structures, as in meatand fish products.

Generally gelation is a two-step phenomenon (Damodaran, 1989). The first stepusually involves dissociation of the quaternary structure of the protein, followed byunfolding. In several proteins heating to about 40°C is sufficient, and some fishprotein sols turn slowly into gels, even at 4°C. Preheating at 25–40°C, called “ashi”or setting, is applied prior to cooking in manufacturing gelled, elastic fish meatproducts. During setting the endogenous transglutaminase leads to formation ofcross-links between myosin heavy chains. In ovalbumin solutions gelling starts at61–70°C. In the second step, at higher temperatures, the unfolded molecules rear-range and interact, initially usually with their hydrophobic fragments, forming alattice. Ovalbumin gels increase in firmness when heated to about 85°C. Subsequentcooling generally stabilizes the gel structure. If the rate of the structuring stage islower than that of denaturation, the unfolded molecules can rearrange and form anordered lattice of a heat-reversible, translucent gel. Too rapid interactions in thedenatured state lead to an irreversible coagulum, due to random associations toinsoluble, large aggregates.

In the gel network there are zones, where the polymers interact, and largesegments, where the macromolecules are randomly extended. The lattice is respon-sible for the elasticity and the textural strength of the product. In multicomponentgels all constituents may form separate or coupled networks, or else one component,not involved in network formation, may indirectly affect the gelling by steric exclu-sion of the active molecules. Such exclusion increases the concentration of the activecomponent in the volume of the solution where the gel is formed. In gels made fromthe mince of squid meat at 1.5% NaCl, the added carrageenan and egg whites formseparate networks that support the structure made of squid proteins, while added


starch fills the lattice and retains water (Gomez-Guillen et al., 1996). Proteins andpolysaccharides that have opposite net charges, when in mixed solutions, may formdifferent soluble and insoluble complexes held by ionic bonds. Lipid-filled milkprotein gels containing small fat globules with a narrow particle size distributionhave a smooth texture and a high shear modulus.

A three-dimensional network of partially unfolded molecules is also in protein-aceous films. These films are usually made by preparing a protein solution at pHvalues far from the pI, controlling denaturation of the molecules due to heating orshear, adding plasticizers, degassing, casting or extruding through a nozzle, anddrying to evaporate the solvent.

7.3.4.2 Interactions of Components

The structure of gels depends on the components and the process parameters. Proteinscontaining over 30% hydrophobic residues form coagulum-type gels, e.g., hemoglobinand egg white albumin. The gelling-type proteins contain less hydrophobic residuesand are represented by some soybean proteins, ovomucoid, and gelatin.

The interaction of different macromolecules may decrease the gel strength, mayhave no influence on the rheological properties of the gel, or else may have asynergistic effect. Casein micelles in a whey protein matrix may enhance or decreasethe gelling, depending on pH. Heat coagulation of sarcoplasmic proteins impairsthe gelation of actomyosin in gels made from the meat of pelagic fish.

The proteinase-catalyzed softening known as modori in minced heated fishproducts may be decreased by adding protease inhibitors from potato, bovine plasma,porcine plasma, or egg white. Inhibitors from various legume seeds are also effectiveagainst fish muscle proteinases (Benjakul et al., 2001a, 2001b; Matsumoto andNoguchi, 1992). The impact of other factors may be controlled by applying optimumprocessing parameters.

7.3.4.3 Binding Forces and Process Factors

The hydrophobic interactions prevail at higher temperatures and probably initiatethe lattice formation, while hydrogen bonds increase the stability of the cooledsystem. The electrostatic interactions depend on pH, charge of the molecules, ionicstrength, and divalent ions. Intermolecular -S-S- bridges, as well as covalent bondsformed due to the activity of transglutaminases, may also add to the gel formation.In gelled fish products -S-S- bonding occurs during cooking at about 80°C (Hossainet al., 2001). Gels stabilized mainly at low temperatures by hydrogen bonding areheat reversible, i.e., they melt due to heating and can be set again by cooling, whilegels stabilized by hydrophobic interactions and covalent bonds are heat stable.

Depending on the properties and concentration of the protein, ionic strength, andpH, even a coagulum-type gel like that of ovalbumin can be melted by repeated heatingand set again when cooled (Shimizu et al., 1991). Heat-induced gels may melt underincreased pressure at room temperature, while cold-set gels of gelatin are resistant tosuch conditions (Doi et al., 1991). Optimum ionic strength and concentration of Ca2+

is required for producing well-hydrated heat-set gels from whey proteins.

Proteins 147

There is generally a pH range at which the gel strength in the given system ishighest. It depends on the nature of the polymers participating in cross-linking andincreases with protein concentration. At the pI of the proteins, due to the lack ofelectrostatic repulsion, the rate of aggregation is usually high, leading to less-ordered,less-expanded, and less-hydrated gels. In heat-induced gels made of water-washedchicken breast minced muscle at a pH of 6.4 and a low NaCl concentration, themyofibrils, insoluble at such conditions, form local networks of aggregates, withlarge voids between them. Increasing the pH to 7.0 results in a gel with an evenlydistributed network of myofibrils and an additional network of fine strands, smallerintramyofibrillar spaces, increased stress and strain values, and higher WHC (Fengand Hultin, 2001).

The ovalbumin gel has optimum rheological properties at pH 9, while at pH <6 it is brittle and has low elasticity. Transparent ovalbumin gel can be made byheating at a pH other than the pI at a certain salt concentration. In a two-stepprocedure transparent gels can be made from ovalbumin, bovine serum albumin,and lysozyme over a broad range of salt concentration by heating the proteinsolutions first without salt and after cooling by repeated heating in the presence ofadded salt (Tani et al., 1993). The pH range for gelation of whey proteins is 2.5–9.5,although near the pI, which is about 5, the gels are opaque, coarse, and may turninto curd-like coagulum. In the neutral to alkaline pH the gels made of fat-free wheyprotein isolates or purified β-lactoglobulin are translucent, smooth, and elastic. Inacid conditions, if high shear force is applied for a short time at denaturationtemperature, aggregation of the whey proteins to microparticles occurs. This leadsto well-hydrated gels of a smooth, nonelastic texture, similar to that of a fat emulsion.In a slightly alkaline environment at a temperature of above 60°C, insoluble aggre-gates are formed due to denaturation of β-lactoglobulin, the major component ofwhey proteins. The rheological properties of whey protein gels, at different pHvalues, depend also on the concentration of Ca2+.

The -S-S- bridges are responsible for the thermal stability of gels. Such bondsadd to the elasticity of heat-set whey protein gels at neutral to alkaline pH values,but not in acidic conditions when the thiol has low reactivity (Jost, 1993). Ascorbicacid improves the formation of heat-set gels of ovalbumin and fish proteins byundergoing rapid oxidation to dehydroascorbic acid, which affects polymerizationby intermolecular -S-S- bridges. In making edible films from wheat gluten, theexposed SH groups of the protein, heat-denatured in an alkaline solution, form -S-S- cross-links due to air oxidation during drying (Roy et al., 1999).

7.3.4.4 Importance in Food Processing

Gelling is important for the quality of comminuted-type, cooked sausages and gelledfish products. The gel strength of such commodities is mainly affected by theproperties of myosin and processing conditions. Comminuting of the meat with saltresults in unfolding of the myosin microfibrils and increases the surface hydropho-bicity. This leads to hydrophobic associations in the lattice structure. Heating to50–80°C favors deconformation of the myosin heads (Figure 7.5) and their interac-tions. Although myosin has the highest gel-forming ability of all muscle proteins,


the whole myofibrillar protein fraction, the sarcoplasm, and the connective tissueproteins are also capable of gelation. The overall gel strength depends on theconcentration and interactions of different proteins.

Edible films may be used for their barrier properties to prevent the migration ofwater, oil, oxygen, and volatile aroma compounds between food and the environment.The coatings prevent oxidative browning of sliced fruits and vegetables due to theirantioxidant properties. The oxygen radicals’ scavenging capacity of films made ofcommercial concentrated whey protein powder has been found to be higher than thatof coatings based on calcium caseinate. The addition of carboxymethyl cellulose tothe formulation increases the antioxidant capacity of the products (Le Tien et al., 2001).Films can also find application as enzyme supports and carriers of food ingredients.For edible sachets used for delivering premeasured quantities of ingredients in foodprocessing, the heat seal ability of the material is important. Antimicrobial agentsadded to edible coatings used for food protection may affect the mechanical strengthand barrier properties of the material (Ko et al., 2001). Different films have uniquefunctional properties best suited to fulfill the needs of specific food applications.

The films can be made either of proteins or of composite materials with saccharidesor lipids. For these purposes, collagen, gelatin, casein, total milk proteins, wheyproteins, wheat gluten, corn zein, water-soluble fish proteins, and soy proteins areused. The barrier properties, appearance, tensile strength, thermal stability, and heatseal ability of the products depend on the characteristics and proportions of the gellingcomponents, interactions and contents of plasticizers, and conditions of fabrication.Films made of whey protein are transparent, bland, and flexible; have very high oxygen,oil, and aroma barrier properties in an environment of low humidity; and are poorprotection against water vapor migration. Some of their characteristics depend on thedegree of thermal denaturation of the protein before casting. Increasing the degree ofdenaturation by heating leads to higher tensile strength and insolubility and to loweroxygen permeability of the films (Perez-Gago and Krochta, 2001). Water vapor per-meability may be decreased by adding lipids, either by laminating a lipid layer overa protein film or by uniformly dispersing the lipid in the proteinaceous component.The result depends on the properties and amount of added lipid.

7.3.5 EMULSIFYING PROPERTIES

7.3.5.1 Principle

Proteins help to form and stabilize emulsions, i.e., dispersions of small liquid dropletsin the continuous phase of an immiscible liquid. The decrease in the diameter of

‘

FIGURE 7.5 Schematic representation of the myosin molecule. (From Sikorski, Z.E., Pro-teins, in Chemical and Functional Properties of Food Components, Sikorski, Z.E., Ed.,Technomic Publishing Co. Inc., PA, 1997. With permission.)

Proteins 149

the droplets due to agitation exponentially increases the interfacial area. The work(W) required for the increase in surface area (∆A) can be decreased by lowering thesurface tension (z): W = z ∆A, due to attachment of proteins to the droplets. Theprotein film around the lipid globules, with its electrostatic charge and steric hin-drance, prevents flocculation, i.e., formation of clusters of globules, and thus morerapid creaming due to the action of gravitational force: V = 2 r2 g ∆P/9 µ, where Vis the velocity of the droplet, g is the gravitational force, ∆P the difference in densityof both phases, µ the viscosity of the continuous phase, and r the radius of thedroplet or cluster of droplets.

Stable films around the fat globules also prevent the coalescence of the dispersedphase, i.e., joining of the fat globules to form a continuous phase. Furthermore,soluble proteins increase the viscosity of the dispersing phase, thus reducing the rateof creaming and coalescence.

The efficiency of proteins as emulsifiers depends on their surface hydrophobicityand charge, steric effects, elasticity and rigidity, and viscosity in solution. Globularproteins that have stable structures and are very hydrophilic are good emulsifiersonly when unfolded. However, the emulsifying properties do not increase linearlywith the hydrophobicity of the protein, as they depend on the hydrophile/lipophilebalance (HLB), which is defined as: HLB = 20 Wh/Wt, where Wh is the weight ofthe hydrophilic groups and Wt is the total weight of the molecule.

The emulsifiers with HLB < 9 are regarded as hydrophobic; HLB = 11–20,hydrophilic; and HLB = 9–11, intermediate. There is an effect of protein solubility,as the molecules must be able to migrate to the surface of the fat globules. However,in comminuted sausage batters, in the presence of salt the insoluble proteins mayalso participate in the formation of fat dispersions. After a few minutes of homog-enization, about 90% of the initially insoluble meat proteins of the stroma can befound in the emulsion layer (Nakai and Li-Chan, 1988). The quantity of proteinrequired for stabilization of an emulsion increases with the volume of the dispersedphase and with the decrease in diameter of the droplets. The concentration ofproteins forming a monomolecular layer at the interface is of the order of 0.1mg/m2, and the effective concentrations are in the range of 0.5–20 mg/m2. For ahigh rate of film formation, the required concentration of protein in the emulsionmay be as high as 0.5–5%.

7.3.5.2 Factors Affecting Emulsification

The pH of the environment affects the emulsifying properties by changing the solubilityand surface hydrophobicity of proteins, as well as the charge of the protective layeraround the lipid globules. Ions alter the electrostatic interactions, conformation, andsolubility of the proteins. However, in many foods, mainly comminuted meat batters,the concentration of NaCl is considerably high for sensory reasons. Thus small changesin the salt content within the accepted range may have no significant effect on theproperties of proteins. Heating to about 40–60°C, causing partial unfolding of theprotein structure without loss in solubility, may induce gelation of the protective layer,as well as decrease the viscosity of the continuous phase. Therefore moderate heatingmay improve the emulsifying properties of proteins.


7.3.5.3 Determination of Emulsifying Properties

Several procedures are used to determine the efficiency of proteins in emulsifyinglipids and the stability that the proteins impart to the emulsions.

The emulsifying capacity is represented by the volume of oil (cm3) that isemulsified in a model system by 1 g of protein when oil is added continuously toa stirred aliquot of solution or dispersion of the tested protein. It is determined bymeasuring the quantity of oil at the point of phase inversion. The latter can bedetected by a change in color, viscosity, or electrical resistance of the emulsion, orthe power taken by the stirrer engine. The emulsifying capacity decreases with anincreasing concentration of protein in the aqueous volume. It is affected by theparameters of emulsification, depending on the equipment, as well as by the prop-erties of the oil.

The emulsion stability is measured as the final volume of the emulsion after theinitial volume has been centrifuged or standing for several hours at specified conditions.It may also be determined as the quantity of oil or cream separated from the emulsion,or the time required for the emulsion to release a specified quantity of oil.

7.3.6 FOAMING PROPERTIES

Food foams are dispersions of gas bubbles in a continuous liquid or semisolid phase.Foaming is responsible for the desirable rheological properties of many foods, e.g.,the texture of bread, cakes, whipped cream, ice cream, and beer froth. Thus foamstability may be an important food quality criterion. However, foams are often anuisance for the food processor, e.g., in the production of potato starch or sugar andin the generation of yeast. Residues of antifoaming aids in molasses may drasticallyreduce the yield in citric acid fermentation.

The gas bubbles in food foams are separated by sheets of the continuous phase,composed of two films of proteins adsorbed on the interface between a pair of gasbubbles, with a thin layer of liquid in between. The volume of the gas bubbles maymake up 99% of the total foam volume. The contents of protein in foamed productsare 0.1–10% and of the order of 1 mg/m2 interface. The system is stabilized bylowering the gas–liquid interfacial tension and formation of rupture-resistant, elasticprotein film surrounding the bubbles, as well as by the viscosity of the liquid phase.The foams, if not fixed by heat setting of the protein network, may be destabilizedby drainage of the liquid from the intersheet space, due to gravity, pressure, orevaporation, by diffusion of the gas from the smaller to the larger bubbles, or bycoalescence of the bubbles resulting from rupture of the protein films.

Factors facilitating the migration of the protein to the interface and formationof the film are important for foaming. The foaming capacity or foaming power, i.e.,the ability to promote foaming of a system, measured by the increase in volume, isaffected mainly by the surface hydrophobicity of the protein. The stability andstrength of the foam, measured by the rate of drainage and the resistance to com-pression, respectively, depend on the flexibility and the rheological properties of thefilm. Other components of the system, mainly salts, sugars, and lipids, affect thefoam formation and stability by changing either the properties of the proteins or the

Proteins 151

viscosity of the continuous phase. The standard whey protein concentrates thatcontain 4–7% of residual milk lipids have significantly inferior foaming propertiescompared with lipid-free isolates.

Excellent foaming ability is characteristic for egg white proteins, especiallyovalbumin, ovotransferrin, and ovomucoid. Chilling of egg whites below roomtemperature or the presence of sugar or lipids decreases foaming, a pH value of <6increases the foaming capacity, and heating of the dried proteins at 80°C for a fewdays before use increases foam stability. The foaming of whey protein isolates canbe improved by addition of Ca2+ or Mg2+. The ions are effective only immediatelyafter the salts are added. According to Zhu and Damodaran (1994) the ions mightcause unfolding and polymerization of the proteins at the interface via ionic linkages.On the other hand, prolonged incubation of the isolate solution with the salts slightlyreduces the film-forming ability, possibly by promoting aggregation and micelliza-tion of the protein.

7.4 PROTEINS AS FUNCTIONAL COMPONENTS IN FOODS

7.4.1 MUSCLE PROTEINS

The meat of slaughter animals, fish, mollusks, and crustaceans is predominantlyused to prepare different dishes, a variety of canned, smoked, marinated, salted, anddried products, and a large number of sausage assortments. In these products thefunctional properties of the muscle proteins are responsible for the desirable sensoryattributes. However, an increasing proportion of the raw material, mainly less suitablefor producing high-quality products of the meat, poultry, and fish industry, is usedfor manufacturing protein concentrates, preparations, and hydrolysates. These prod-ucts can be incorporated into various food products for nutritional reasons and asfunctional ingredients.

Much research has been devoted to working out optimum parameters of pro-ducing different protein concentrates from fish and krill (Lanier, 1994). While theproducts have high nutritional value and many are tasteless and odorless, some,manufactured in denaturing conditions, lack the desired functional properties. Agood example is the fish protein concentrate obtained by hot azeotropic isopro-panol extraction. On the other hand, a concentrate of myofibrillar proteins knownas surimi, produced mainly from fish and to a lesser extent from poultry and meat,is highly functional.

Surimi is originally a Japanese product obtained by washing minced fish fleshseveral times with fresh water. This treatment removes most of the sarcoplasmicproteins, including enzymes and pigments, nonprotein nitrogenous compounds, var-ious odorous substances, other soluble components, and fat. The remaining myo-fibrillar proteins have higher gel-forming ability than the original protein mixture.Nowadays fish surimi is produced mainly on board vessels (Toyoda et al., 1992).The typical commercial surimi is made from Alaska pollock. In order to preventdeterioration of its functional properties during frozen storage, different cryopro-tectants, predominantly saccharides, are added prior to freezing (Figure 7.6). Surimiis used mainly for manufacturing traditional Japanese gelled products, obtained by


mixing it with salt, grinding, forming, and steaming or broil cooking (kamaboko),or frying (tempura). Another growing outlet is the production of a variety of fabri-cated products, including molded (shrimp-type) and fiberized (crab-leg-type) shell-fish analogs (Wu, 1992). The most important topics in this area in the last twodecades have been the suitability of fish of different lean and fatty species, includingfreshwater fish, as raw material for surimi (Holmes et al., 1992; Luo et al., 2001);mechanisms of protein changes in frozen stored material and selection of optimumcryoprotectants (Matsumoto and Noguchi, 1992); the effect of different ingredientson the texture and water binding of various gelled products (Yoon and Lee, 1990);and other factors affecting gelation of surimi (Niwa, 1992; Jiang et al., 1998).

FIGURE 7.6 Flow sheet of the process used for manufacturing surimi.

Water

Water

Water

Cryoprotectants

3x

Wastewater,Scales

Wastewater,Scales

Heads, Viscera

Skin, Fins,and Bones

Water-SolubleComponents

Scraps ofSkin, Scales

Surplus Water

Meat Separatingand Mincing

Washing

HeadingGutting

Washing

Leaching

Draining

Refining

Dewatering

Mixing

Surimi

White Fish

Proteins 153

7.4.2 LEGUME PROTEINS

Soybean proteins are used as a variety of traditional products, e.g., soy milk orfermented items, defatted flour, grits, concentrates, or isolates. The traditional prod-ucts are prepared according to procedures known in the Orient, involving waterextraction, cooking, coagulation of the proteinaceous curd, roasting, and fermenta-tion, often in combinations with other components. Different forms of concentratedor isolated protein products are prepared by milling, toasting, extraction of fat andsaccharides, and isolation of protein fractions. The antinutritional factors present insoybeans are usually inactivated or removed in processing. The “beany” or “painty”off-flavor in soy milk due to volatiles generated in lipoxygenase-catalyzed reactionsis prevented by thermal denaturation of the enzyme before or during grinding withwater (Kwok and Niranjan, 1995). The protein isolates may be “tailor-made” to havethe desirable functional properties.

Grits, flours, and isolates for food applications are produced also from otherlegumes, mainly peanuts, beans, broad beans, and peas (Lampart-Szczapa, 2001).

7.4.3 MILK PROTEINS

Because of very high biological value and absence of antinutritional factors, exceptfor some allergenic activity, milk proteins have found various application in formu-lated foods and as meat extenders. Initially only the caseins were used, but recentlythe recovery of whey proteins and their fractions was made economically feasible.

Least soluble is acid casein. Its solubility and foaming properties can beimproved by glycosylation of the ε-NH2 groups. Sodium and calcium caseinatesprepared by acid precipitation and neutralization are soluble and very heat stable,and have a high WHC and emulsifying, foaming, and gelling ability. Rennet casein,richer in calcium, has low solubility in the presence of Ca2+. Precipitates producedby heat denaturation of the whey proteins and coprecipitation with casein by additionof acid or calcium salts are more soluble and have higher nutritional value than theacid and rennet casein.

Different whey protein concentrates and isolates are manufactured by com-plexing with phosphates or polysaccharides, by gel filtration, ultrafiltration, or heatdenaturation. At a pH of about 4.2 and at 55–65°C α-lactalbumin undergoesisoelectric precipitation due to dissociation of the Ca2+ and hydrophobic interac-tions (Bramaud et al., 1995). Other minor whey proteins also precipitate, whilethe soluble β-lactoglobulin is separated, concentrated by ultrafiltration, neutral-ized, and spray dried. The product has superior WHC and gelling properties inmeat products. β-lactoglobulin, however, denatures and forms insoluble aggregatesat temperatures above 60°C at pH 8. This is a limitation for the use of whey proteinisolates in pasteurized products. The thermal stability of β-lactoglobulin can beimproved by controlled hydrolysis. Doucet et al. (2001) have shown that hydrolysisof a whey protein isolate by Alcalase, when less than 16% and 4% of β-lactoglo-bulin and α-lactalbumin, respectively, remained unhydrolyzed, induced gel for-mation. Gelation was preceded by formation of aggregates. The structure of thegel was stable over a temperature range of 30–65°C. Other undenatured forms of


whey proteins are also used as foam stabilizers and gelling agents; some are solubleunder acidic conditions. The purified α-lactalbumin fraction is more suitable forinfant food formulations than whey protein concentrate, since human milk doesnot contain β-lactoglobulin.

The functional properties of milk proteins in foods have recently been expertlytreated by Holt and Roginski (2001). These authors described the antihypersensitive,opioid, immunomodulatory, and calcium-binding milk peptides, the antiviral prop-erties of various milk components, and the antimicrobial activity of lactoperoxidase,lactoferrin, lactoferricins, casein peptides, and peptides from α-lactalbumin.

7.4.4 EGG PROTEINS

Egg albumen is used in various food formulations because of its foaming propertiesand heat gelling ability, while egg yolk serves as an emulsifying agent. The functionalproperties of egg proteins have recently been treated by Ternes (2001). The strengthof egg white gels can be increased by preheating the dry protein at 80°C before use(Kato et al., 1990a). In gels formed by preheated egg whites the molecular weightof aggregates is much smaller than it is in gels made of nonpreheated proteins.Preheating of dry egg whites confers a lower enthalpy and temperature of denatur-ation on the protein. This results in increased flexibility of the molecules, leadingto more cohesive interfacial films, i.e., improved surface functional properties. Themore cohesive films composed of overlapping polypeptides are better capable ofexpanding under stress than the films formed from nonpreheated proteins (Katoet al., 1990b).

Egg white and egg yolk gels can also be prepared without heating by applyinghigh pressure (Hayashi et al., 1989). The albumen and yolk from fresh eggs formstiff gels after 30 min of exposure to a pressure above 6000 and 4000 kg/cm,2

respectively. The pressure-induced gels are more adhesive, elastic, and digestiblethan the boiled egg.

Lysozyme, which makes up 3.5% of the total egg white proteins and can be easilyseparated by ion-exchange techniques (Lesnierowski and Kijowski, 2001), is recog-nized as a safe, antimicrobial agent to be used for food preservation. It is stable up toabout 100°C, has maximum activity at a pH range of 5.3–6.4, and inhibits severalpathogenic bacteria, including Listeria monocytogenes, Clostridium botulinum, Yers-inia enterocolitica, and Campylobacter jejuni (Kijowski and Lesnierowski, 1999).

7.4.5 MYCOPROTEIN

One of the results of research of the second half of the 20th century on single-cellprotein for human food and for animal feed was the development of the process ofmycoprotein manufacturing. The product has been approved in several Europeancountries for general food use. It has the form of insoluble hyphae, typically 400–700µm × 3–5 µm with low frequency of branching. Mixing with proteinaceous binders,flavorings, and colors, followed by forming and heating, leads to meat productanalogs. The mycoprotein can also be used in extruded commodities and as fatreplacers in yogurt and ice cream (Rodger, 2001).

Proteins 155

7.5 EFFECTS OF HEATING

7.5.1 INTRODUCTION

Heating controls the rate of different enzymatic and chemical reactions. Asapplied in food processing, it affects the conformation of proteins, enzyme activ-ity, solubility, and hydration, and leads to thermal and hydrolytic rupturing ofpeptide bonds, thermal degradation and derivatization of a.a. residues, cross-linking, oxidation, and formation of sensory-active compounds. Most of thesereactions are reflected in foods as desirable or detrimental changes in color, flavor,juiciness, rheological properties, enzyme activity, and toxicity. These processesare affected by the temperature and time of heating, pH, oxidizing compounds,antioxidants, radicals, and other reactive constituents, especially reducing sac-charides. Some of the undesirable reactions can be minimized. Stabilizers, e.g.,polyphosphates and citrate, which bind Ca2+, increase the heat stability of wheyproteins at neutral pH. Lactose present in whey in sufficiently high concentrationsmay protect the proteins from denaturation during spray drying (Jost, 1993).

The heat-induced unfolding of a protein usually proceeds in several steps,since separate domains of the molecule denature at different temperatures,depending on the forces stabilizing their structure. The molecular transitiontemperature, i.e., the point at which major changes in conformation occur, canbe determined by different techniques, mainly by differential scanning calorim-etry. The susceptibility of proteins to thermal denaturation depends on theirstructure, predominantly on the number of cross-links, as well as on the simul-taneous action of other denaturing agents. Salt bridges, side chain–side chainhydrogen bonds, and a large proportion of residues in α-helical conformationincrease the thermal stability of many proteins (Kumar et al., 2000). In someproteins the first changes appear at 35–40°C. The peak maximum temperature oftransition of myosin in the myofibrils ranges from 43°C in cod muscle to 60°Cin the bovine M. semimembranosus (Howell et al., 1991). Sodium choridedecreases the thermal stability of meat proteins by up to about 30%. In theexperiments of Fernandez-Martin et al. (2000), pressurization of sausage formu-lations at 300 MPa at 10°C for 20 min significantly destabilized the proteins.However, the thermal stability of proteins in formulations heated under hydro-static pressurization was higher than that in control samples. The stabilizing effectwas related to the temperature of heating.

Heating of soluble collagen brings about uncoiling of the superhelix andunfolding and separation of the polypeptide chains from each other, if they arenot bound by stable bonds. This results in a decrease in viscosity of the solution.The denaturation temperature Td can be measured in the range of rapid changein viscosity. Insoluble collagen fibers shrink, due to heat denaturation, by up to75% of their original length. The shrinkage temperature Ts is usually about 20°Chigher than Td. It increases with cross-linking and in fish collagen with thecontents of PrOH. The denatured collagen turns into gelatin after prolongedboiling in water, due to partial hydrolysis. This phenomenon affects the rheolog-ical properties of cooked meats containing much connective tissue.


Thermal changes comprise loss in solubility due to aggregation of the proteins,e.g., β-lactoglobulin and immunoglobulins, or increase in solubility as a resultingof the breaking down superstructures, as in collagen. Heating of many proteins to105–140°C at a low water content, in conditions resembling those during extrusioncooking, leads to increased solubility. This regards proteins that have an open randomcoil structure and low number of -S-S- bonds and are not able to form many covalentnondisulfide cross-links (Mohammed et al., 2000). Further effects of heating includeformation of gels, e.g., in most types of sausages, kamaboko, meat gels, and severaltypes of cheeses; development of gas-retaining structures, as in dough and bread;hydrolytic changes; alteration of the rate of proteolysis; modification of the nutritivevalue; and inactivation of some allergens.

7.5.2 RHEOLOGICAL CHANGES

Proteins are primarily responsible for the texture of meat, poultry, fish, meat andfish gels, cheese, bread, cakes, and many other foods.The texture of muscle foodsis affected mainly by:

• The contents and cross-linking of collagen, and the morphological struc-ture of the tissues, e.g., meat, fish, and squid

• The biochemical state of the muscle, i.e., interactions of the proteins ofthe myofibril (e.g., in rigor mortis, cold shortening, and thaw rigor), aswell as the proteolytic changes during aging of the meat

• Mechanical disintegration of the muscle structure

Treatment abuse of food during storage, processing, and preparation may leadto toughening and partial loss of the gel-forming ability of frozen stored fish,shrinking and toughening of pasteurized ham, toughening and formation of thegrainy structure in casein curd, and separation of fat layers in sausages.

The thermal changes in meat commence at about 40°C — some of the meatproteins in solution coagulate at that temperature. Further heating results in shrinkageof collagen, at 50–60°C, followed by gelatinization in a moist environment. At about65°C hardening of the myofibrils occurs. The final texture of the product dependson hardening of the myofibrillar structure and gelatinization of collagen in the givenmeat at the particular state of postmortem changes, heated according to a particulartime–temperature regime. The rheological changes in meat and fish are emphasizedby drip loss, 20–40% of the original weight, and by shrinkage.

In making bread, the wheat flour, when mixed with water, forms a viscoelasticdough that retains gas and sets, due to heating during baking. The agent responsiblefor these dough properties is gluten, which develops in mixing of the flour withwater. Dry gluten contains 80–90% proteins, 5–10% saccharides, 5–10% lipids, andminerals. The gluten proteins are composed of 40–50% gliadin, 35–40% glutenin,and 3–7% soluble proteins. During mixing with water the flour particles, containingstarch granules embedded in the protein matrix, are progressively hydrated and formthe viscoelastic dough. SH/SS interchange reactions result in formation of intermo-lecular -S-S- bridges. Generally the resistance to extension of the dough increases

Proteins 157

to a peak value. Overmixing usually results in a decrease in resistance and is causedby excessive breaking of the -S-S- bonds, not accompanied by formation of newintermolecular bridges. This ends in depolymerization of the protein and thusincreased solubility and decreased viscosity of the dough. The required mixing timecan be controlled, within limits, by changing the pH, adding oxidants, or mixing inan inert atmosphere. The gas-retaining ability depends on the viscosity of thehydrated protein–carbohydrate–lipid system. Rice and corn flours do not decreasethe gas diffusion rate as effectively, because the doughs prepared from them are notas viscoelastic as the gluten-containing doughs. The relatively high gas retention ofrye flour doughs is due to the viscosity of soluble pentosans. A similar effect canbe achieved in gluten-free doughs by adding surfactants, particularly natural flourlipids, monoacylglycerols, or xanthan gum (Hoseney and Rogers, 1990). Duringbaking the expansion of the dough stops due to polymerization or cross-linking, asa result of SH/SS interchange reactions. The setting prevents further expansion ofthe dough and the collapse of the loaf of bread.

Very severe heating of foods, at much higher temperatures and times than thoserequired for sterilization, may lead to formation of isopeptide cross-links betweenthe free NH2 group of Lys and the carboxylic group of Asp or Glu:

These reactions tighten the structure of the products and may decrease thebiological availability of Lys, as well as the digestibility of the proteins.

7.5.3 CHANGES IN COLOR

Pig, sheep, beef, and whale contain about 0.2–2.4, 4.5–5.5, 1–20, and 50 mg ofmyoglobin in 1 g of muscle, respectively. The total content of all chromoproteinsin the red muscles of fish ranges from a few to 20 mg/g and is about 20 times higherthan that in the white muscles. Changes in the chromoproteins due to oxidation orreduction, denaturation, curing, and reactions with sulfur-containing compounds leadto desirable or undesirable alterations in color.

Reaction 7.2

ε - N (γ - glutamyl) lysylamidecrosslink

HN CH C

O

CH2)2

COOH

(

NH2

CH2)4

CHHN C

O

(

+heating

HN CH C

O

CH2)2

C

O

CHN CH

CH2)4

NH

O

(

(


Beef heated to 58–60°C internal temperature is rare; to 66–68°C, medium rare;to 73–75°C, medium; and to 80–82°C, well done. The recommended end pointtemperature in pork is 77°C and in poultry 77–82°C.

The reactions of myoglobin in cured, heated meat resulting in formation of theheat-stable nitrosylhemochromogen and a nitrite–protein complex proceed accordingto Killday et al. (1988) as follows:

In proteinaceous foods rich in saccharides or secondary lipid oxidation products,the Maillard reaction prevails. The generation of pyrraline from Lys can be used asan indicator of thermal changes in proteins:

7.5.4 DEVELOPMENT OF VOLATILE COMPOUNDS

Severe heating of proteinaceous foods leads not only to generation of flavor com-pounds due to the Maillard reaction, but also to thermal degradation of Met and Cysresidues in proteins, as well as of different low-molecular-weight compounds. Thesereactions are discussed in Chapter 10 of this volume.

Reaction 7.3

Formula 7.3

+

metmyoglobin nitrosyl myoglobin nitrosyl myoglobin nitrosylhemochromogen radical

NO2 Globin

NO

Fe2+heating

NO2- +

OH

Fe3+

NH

N

Globin

autoreduction

NO

NO

Fe2+

Globin

NH

Nreduction

NO

Fe2+

Globin (or Globin radical)

NH

N

OH-

N

CH2)4

C

HOH2C CHO

NH2

COOH

(

H

Pyrraline

Proteins 159

7.5.5 REACTIONS AT ALKALINE PH

Alkaline treatment is used for peeling of fruits and vegetables, for producing proteinisolates, for removing nucleic acids from single-cell protein preparations, and for inac-tivating mycotoxins and proteinase inhibitors. In protein solutions and in foods, severechanges in reactive a.a. residues take place at high pH values, even at temperatures aslow as 50°C. They lead to cross-linking and formation of nontypical a.a. residues.

Cross-linking is based on β-elimination, mainly in Cys, Ser, SerP, or Thr,followed by a nucleophilic addition of the ε-NH2 of Lys, δ-NH2 of ornithine,and SH of Cys residues, or of NH3 to the double bond of dehydroalanine or3-methyldehydroalanine:

Reactions of Cys at alkaline pH also liberate free sulfur and a sulfide ion:

Reaction 7.4

Reaction 7.5

HN CH C

CHR

Y

OOH-

H2O+ HN C C

CHR

O

Y+ -

dehydroalanine residue

where: R=H, CH3; Y=OH, OPO3H2, SH, SR+, SSR

HN C C

CHR

Y

O

ε - N (γ - glutamyl) lysylamidecrosslink

HN C C

O

CH2

NH2

CH2)4

CHHN C

O

(

+

(

HN CH C

O

CH2

NH

CH2)4

CHHN C

O

HN CH C

O

CH2

S

S

CH2

CHHN C

O

HN C C

O

CH2

OH- -S

S

CH2

CHHN C

O

H2O+-

S

CH2

CHHN C

O

S+

-OH

-S

CH2

CHHN C

O

CH2

CHN C

O

H2O S -2++

HN C C

O

CH2

S

S

CH2

CHHN C

O


At a given temperature the overall rate of reaction depends on the rate of β-elimination and on the conformation of the protein. This is because the accessibilityof the dehydroalanine residue for the nucleophilic attack depends on the spatialarrangement of the reacting groups. The reaction can be inhibited by acylating thenucleophilic groups in proteins or by adding thiol compounds, which compete witha.a. residues for the dehydroalanine double bond:

Alkaline conditions favoring cross-linking in proteins lead to racemization of a.a.:L-a.a. ↔ D-a.a., i.e., after the first step in the reaction sequence the carboanions recom-bine with protons to the L and D forms. The rate of racemization is affected mainly bythe properties of the residues — the lowest is in aliphatic a.a. — and the structure of theprotein. Generally the process rate is about 10 times higher in proteins than in free a.a.

Severe heating at an alkaline pH may decrease the digestibility and biologicalvalue of proteins that result from cross-linking and racemization. The rate of absorp-tion of some D-a.a. in an organism is lower than that of the corresponding L forms.Not all D-a.a. can be metabolized. Furthermore, some of the modified residues,mainly lysinoalanine, induce pathological kidney changes in experimental animals.

7.6 OXIDATION

In most proteinaceous foods the oxidation of a.a. residues in proteins is initiatedby radicals and different reactive forms of oxygen — singlet oxygen 1O2, superoxideanion radical O2

–, and hydroxyl radical •OH — that are generated in the wateryenvironment by light, ionizing radiation, catalytic action of cations, and the activityof enzymes. Lipid peroxides and other oxidation products are also involved.Polyphenols, present in many foods, are prone to oxidation to quinones by oxygenat neutral and alkaline pH values. They can also act as strong oxidizing agents indifferent products. H2O2, if abused as an bactericidal agent, e.g., in the treatmentof storage tanks, packaging materials, or proteinaceous meals, may also causeoxidation of proteins.

The effect of oxidative changes in proteins depends on the activity of theoxidizing agent, the presence of sensitizers, e.g., riboflavin, chlorophyll, and eryth-rosine, the temperature, and the reactivity of the a.a. residues. Several tissues containvarious prooxidants, including transition metals and heme pigments, lipoxygenases,and peroxidases, as well as endogenous antioxidants, like glutathione, superoxidedismutase, and catalase.

Abstraction of a hydrogen atom on the α-carbon or in the a.a. side chain of aprotein leads to the formation of protein radicals. These may polymerize with other

Reaction 7.6

R S- H2C C

C

NH

O

H+ R S CH2 C H

C

NH

O

+ +

Proteins 161

protein or lipid radicals. Different scission products may also be formed. H2S andfree sulfur may be generated due to oxidation of the –SH group. The sulfur-con-taining a.a. are converted to many oxidized compounds, including cysteine sulfenic,sulfinic and sulfonic acids, mono- and disulfoxides, and mono- and disulfones. Thea.a. most prone to oxidation in different model systems and in foods are Met, Cys,Trp, Tyr, and His. Oxidation of Try leads to kynurenine (Friedman and Cuq, 1988),and of His to Asp:

In food systems the oxidation of proteins is often preceded by lipid oxidation,mainly by the primary lipid peroxide products or the radicals produced due to theirbreakdown (O’Grady et al., 2001).

Reaction 7.7

Reaction 7.8

HN C O

CH2

CH

COOHH2N

CHO

H2N C O

CH2

CH

COOHH2N

OO

H2N COOHCH

CH2

N

R

O2

HNCH2

CHCOOHH2N H2N COOH

CH

CH2

NNCH2

CHCOOHH2N

kynurenine N-formylkynurenine

COOH

CH2

CHCOOHH2N

sensitizer

hν, O2

N

NH

H2N COOHCH

CH2

+ C O

NH2

NH2

+ other products


The products of oxidation affect the flavor of foods, either directly or by reactingwith precursors. Their biological value depends generally on the degree of changedue to scission, polymerization, and oxidation. Furthermore, essential a.a. in oxidizedfoods may become limiting in the diet. Formation of protein–protein and pro-tein–lipid cross-links decreases the digestibility of proteins.

7.7 ENZYME-CATALYZED REACTIONS

7.7.1 INTRODUCTION

Reactions in proteins and other nitrogenous compounds catalyzed by endogenousenzymes are responsible for desirable and undesirable sensory attributes of foods— color, flavor, and texture — as well as for the development of compounds thatare nutritionally beneficial or have detrimental effects on human health. The use ofadded enzymes or enzyme sources is also an essential part of many traditionalmethods of food processing. Since the conditions of enzymatic reactions are muchmilder than those applied in chemical treatments, different added enzymes are beingused to an increasing extent to modify the functional properties of food proteins.

Some proteins affect the sensory and functional properties of foods by exhibitingenzymatic activity in their natural environment or when added intentionally duringprocessing in the form of enzyme-rich materials, pure enzyme preparations, or startercultures of microorganisms. The examples of effects involving protein changesinclude loss of prime freshness in fish after the catch, rigor mortis and tenderizationin meat, ripening of salted fish and cheese, softening of fish gels, fermentation insoybean processing, and proteolytic changes in wheat flour. Enzymatic modificationof proteins in food systems has recently been treated exhaustively by Haard (2001).

7.7.2 CHANGES IN MILK PROTEINS

In milk the phosphatases may dephosphorylate the caseins. Thiol oxidase mayparticipate in oxidation of SH groups to disulfides. Endogenous and bacterial pro-teinases catalyze extensive modifications in milk proteins. Plasmin, the alkalineserine proteinase associated with casein micelles and milk fat membrane, attacks β-casein and αs1-casein. Several endogenous plasmin activators and inhibitors controlthe degradation of milk proteins. The enzyme activity is the highest at pH 7.5 andis only slightly reduced during high-temperature, short-time pasteurization of milk.Heat-stable extracellular proteinases produced by psychrotropic bacteria present inchilled milk hydrolyze different caseins and whey proteins. They can cause a bitternote in UHT milk, age gelation of sterilized milk, and flavor defects in fermentedproducts. Proteinases of somatic cells present in milk, especially from cows in latelactation, may also decrease the yield of cheese and lead to development of bitternessin pasteurized milk (Holt and Roginski, 2001).

7.7.3 ROLE OF ENZYMES IN MUSCLE FOODS

The sensory quality of meat and seafood is significantly affected by endogenousproteases. The lysosomes contain, among other enzymes, at least 12 cathepsins,

Proteins 163

which can exert a concerted action on proteins and peptides. The optimum pH forthe activity of cathepsins is generally in a low acidic range. However, many enzymesretain high activity at pH values one or two units away from the optimum. Cathepsinsare released from the lysosomes in stored beef into the sarcoplasm. Most of the meatcathepsins hydrolyze at least some proteins of the myofibrils. Proteolysis by cathep-sins has been regarded as one of the factors coresponsible for tenderization of meat.However, not all of these enzymes have a significant effect on intact meat proteinsin the usual temperature conditions of postslaughter handling and chilling of theanimal carcasses. Furthermore, although they are able to hydrolyze myosin and actin,only insignificant degradation of these main proteins of the myofibrils takes placeduring tenderization of meat. They can, however, participate in the concerted actionof various proteinases in aging meat and fish.

The muscles also contain nonlysosomal proteinases capable of hydrolyzingseveral myofibrillar proteins responsible for the structural integrity of the musclefibers, especially the cytoskeletal proteins. Calpains, the calcium-activated neutralmetalloproteinases, require the cysteinyl thiol group for activation. The highestactivity of calpains against isolated myofibrils is in the pH range of 7.0–7.5, whileat pH 6 and 4.5 the activity is about 80% and 40% of the maximum value, respec-tively. One form of the enzyme, called microcalpain, requires at least 0.1–0.5 mMCa2+ for activation, the optimum concentration being 1 mM; the second form, µ-calpain, is activated at micromolar concentrations of Ca2+. Due to the loss of theCa2+-retaining ability of the reticulum in the muscle postmortem, the concentrationof Ca2+ in the sarcoplasm may increase up to about 0.1 mM. There is a cause-and-effect relationship between the activity of µ-calpain and the decrease of musclestrength (Purslow et al., 2001). The enzyme rapidly degrades the cytoskeletal proteindesmin, causing depolymerization of the intermediate filaments that bind neighbor-ing Z-discs in the myofibril. The major fragments resulting from the breakdown arefurther cleaved by cathepsins. The known variations in the rate of tenderization ofvarious muscles are due to the differences in the activity of calpains and calpastatin— a family of endogenous inhibitor proteins that are strictly calpain specific andare located in the same cellular area as the enzyme. The meat tenderization processalso involves degradation of other cytoskeletal proteins — titin, nebulin, and desmin(Jiang, 2000; Kijowski, 2001).

The changes in proteins catalyzed by endogenous enzymes affect the sensoryquality of various salted, cold-smoked, and marinated fish products. In lightly saltedsalmon, sturgeon, herring, anchovy, Baltic sprats, and fish of many other species,the hydrolytic processes lead to development of tender texture. The flavor becomespredominantly fishy and salty, with meaty, cheesy, and slightly rancid notes (Sikorskiet al., 1995). The enzymes involved in ripening of salted, uneviscerated fish, likeherring, are mainly those of the pyloric appendages. The suitability of fish for saltripening is affected by the activity of the endogenous proteases, which fluctuatesseasonally and depends on the feeding intensity of the fish. Excessive proteolysis,in products stored too long at too high a temperature, leads to unacceptable softeningof the flesh. On the surface of overripe salted fish white “bloom” of crystallizedpeptides and a.a., mainly Tyr, may appear. In raw herring marinades the ripeningoccurs due to muscle cathepsins.


High activity of muscle proteases during the spawning migration may bringabout changes that increase the emulsifying ability of salmon meat during thespawning period (Kawai et al., 1990).

Different endogenous proteinases are involved in the disintegration of thestructure of fish gels known as modori that often occurs due to slow cooking inthe temperature range of 50–70°C. In such gels hydrolysis of myofibrillar proteins,particularly myosin, was evidenced. Early reports indicated the heat-stable alkalineproteinases, found in the muscles of several fish species, to be involved. Theactivity of these enzymes is usually not detectable below 50°C. Further investi-gations revealed that cathepins B, L, and L-like contribute to the disintegration ofthe gel structure by hydrolyzing the myosin heavy chain, light chains, actin, andtroponins, and that these undesirable effects can be inhibited by using cysteineproteinase inhibitors. A very thorough discussion of the role of different protein-ases in the modori softening has been presented by Jiang (2000).

A high degree of proteolysis is involved in manufacturing edible fish sauces,silage for animal feed, and hydrolyzates for use as functional ingredients in foodsand as bacterial peptones (Sikorski et al., 1995; Lopetcharat et al., 2001). Fishsauces belong to a group of traditional, fermented products typical for SoutheastAsia. They are manufactured by salting different small fish, mainly Stolephorusspp., Ristelliger spp., Sardinella spp, Engraulis spp., Clupea spp., Scomber colias,and Decapterus spp., according to a variety of recipes. The proportions of fish tosalt range from 1–6 and the fermentation time, usually at ambient temperature,from about 2–18 months. Endogenous and bacterial enzymes are involved indeveloping the typical flavor of the sauces. The undiluted filtrate of the autolysateis regarded as the first grade fish sauce; the brine extract of the nonhydrolyzedresidue is of lower sensory quality and nutritional value. Various proteolyticenzymes from animal, plant, and microbial sources added in the process canincrease the rate of proteolysis and even improve the quality of the products(Venugopal et al., 2000).

Fish silage is typically made from by-catch fish and filleting offal by mincing,acidifying with formic acid or a mixture of formic and sulfuric acid, and proteolysiscatalyzed by endogenous enzymes. After about 2 days at 30–40°C most of the tissuesare solubilized. The silage containing 70–80% water can be used as such afterremoval of the solids and the fatty layer, or else the liquid can be concentrated tothe required degree. The product, manufactured commercially in large scale, is usedas a feed component for pigs, poultry, and fish.

Fish hydrolysates are produced mainly from lean fish of underutilized speciesor from the filleting of by-products in a process catalyzed by added proteinases ofplant, animal, or microbial origin (Figure 7.7). The product can be used as a sourceof a.a. in growth media for microorganisms, as a replacement for milk in animalfeeding, or as a functional ingredient in foods (Liceaga-Gesualdo and Li-Chan, 1999;Mukhin et al., 2001).

Partial autoproteolysis has been successfully utilized for producing in industrialconditions food – grade, thermally coagulated, frozen protein gel from Antarctickrill. The protein recovery is about 80% of the protein content in the whole krill( and Sikorski, 2000).Kolakowski

Proteins 165

Other possible applications of proteolytic enzymes in seafood processing includedescaling fish, peeling and deveining shrimp, tenderizing squid, isolating pigmentsfrom shellfish waste, and reducing the viscosity of fish meal stick waters. Squidmuscles contain very active proteinases ( , 1999). High proteolyticactivity causes extensive degradation of the myofibrillar proteins in the course ofextraction of these proteins for analytical purposes. There are significant differencesin the autoproteolytic activity in the muscles of squid of different species.

Trimethylamine oxide demethylase, present in the muscles of many gadoidfishes, affects the functional properties of fish proteins indirectly by catalyzing theformation of formaldehyde:

FIGURE 7.7 Flow sheet of the process used for manufacturing fish hydrolyzates.

Reaction 7.9

Water, 1:2

Filtration

Mincing

HydrolysisOptimum Temperature

Enzyme Inactivation100oC

Evaporation

Drying

Fish Meat

Endopeptidases

NaOH or HCl

Insolubles

Vapors

Vapors

Fish Peptone

Koladziekska

+H3C N O

CH3

CH3

NH HCO

H

CH3

CH3

demethylase


which may participate in cross-linking. These reactions are most important in frozenstored gadoid fish (Sikorski and Kostuch, 1982; Sikorski and , 1994;Sotelo and Rehbein, 2000).

7.7.4 TRANSGLUTAMINASE-CATALYZED REACTIONS

Transglutaminase (TGase), or protein-glutamine γ-glutamyltransferase, catalyses thetransfer of the acyl group of glutamine residues in proteins or peptides on primaryamines or a water molecule:

It participates in several physiological processes in plant and animal organisms. Itis also produced as an extracellular enzyme by Streptoverticillium sp., Physariumsp., and other microorganisms. The red sea bream TGase cloned in Escherichia coliis an intracellular enzyme. Generally the activity of TGase of plant and microbialorigin is independent on Ca2+, while the enzyme present in animal tissues is Ca2+

dependent. However, the Ca2+ requirement depends not only on the source of theenzyme, but also on the type of substrate. In the active site of TGase is a thiol groupin the sequence -Tyr-Gly-Gln-Cys-Trp-.

TGases occur in the form of a monomer, dimer, or tetramer, soluble in the cytosolor bound in mitochondria and lysosomes. Although they have a maximum activity at50°C, they can be effectively used for modification of food proteins in the temperaturerange of 5–20°C. The optimum pH range for the activity of TGase of different originsis 6–9.5. The role of TGase in food processing is due to the protein cross-linkingeffect, incorporation of amines, and deamidation of glutamine residues. The effect ofthe enzyme activity expressed as cross-linking depends also on the concentration ofNaCl, as well as on the properties of the protein substrate (Ashie and Lanier, 2000;

and Sikorski, 2001). The deamidation activity of TGases of variousorigin is affected by the enzymes’ substrate specificity (Ohtsuka et al., 2000).

Reaction 7.10

Kolakowska

Prot (CH2)2 C NH2

O

H2N (CH2)4 Prot+

Prot (CH2)2 C NH2

O

H2O+

acyl transfer

Prot (CH2)2 C NH

O

R NH3+TGase

Prot (CH2)2 C NH

O

(CH2)4 Prot NH3+TGase

crosslinking

deamidation

Prot (CH2)2 C OH

O

NH3+TGase

Prot (CH2)2 C NH2

O

H2N R+

Kolakowski

Proteins 167

Endogenous TGase activity is responsible for the formation of ε(γ-glutamyl)lysine cross-links in dried fish (Kumazawa et al., 1993), in frozen-stored surimi (Haard et al., 1994), and in the polymerization of the myosinheavy chain during setting of surimi in manufacture of kamaboko (Kumazawaet al., 1995).

Commercially produced microbial TGase has found numerous applicationsin food processing. It can be used for increasing the gel strength of kamabokomade of surimi produced from fish of low gel-forming ability, for improvingthe rheological properties of dairy products, and in manufacturing various meatcommodities. Reactions catalyzed by added TGase can lead to “tailor-made”protein preparations, e.g., edible films of defined barrier properties from wheyproteins, and to covalent binding of saccharides to plant proteins rich in Gluresidues (Colas et al., 1993). Ca2+-independent TGase derived from Streptover-ticillium can induce gelation of glycinin and legumin at 37°C, and the gelsare more rigid and elastic than thermally gelled products (Chanyongvorakulet al., 1995). This enzyme added at optimum concentration to fish skin gelatinincreases the melting point, strength, and viscosity of the gels. The activityof TGase during storage of the product, which might change the rheologicalproperties of the gel, can be arrested by heating to 90°C just after incubationof the gelatin solution with the enzyme (Gómez-Guillen et al., 2001). Cross-linking of proteins catalyzed by TGase does not impair the nutritional valueof the products.

7.7.5 OTHER ENZYME APPLICATIONS IN FOODS

Wheat lipoxygenase and soybean lipoxygenase, catalyzing oxidation of fatty acids,generate oxidized reaction products that improve the dough-forming propertiesand baking performance of flour. A similar role is performed by polyphenol oxidaseand peroxidase.

Enrichment of proteins in specific a.a. can be achieved in the plastein reaction,i.e., protease-catalyzed transpeptidation in concentrated solutions of a.a. ethylesters and protein hydrolyzates (Figure 7.8). Incubation of a protein hydrolyzate,concentrated to 30–40%, with ethyl esters of Lys, Met, or Trp, e.g., with anappropriate endopeptidase at pH 4–7 at about 37°C, leads after a few days toaccumulation of peptides of 2–3 kDa enriched in the respective a.a. residues.Plasteins free of Phe residues can also be obtained for phenylketonuric patients.The rate of incorporation of a.a. into the plastein increases with the hydrophobicityof the a.a. Thus selective removal of hydrophobic a.a. from the hydrolyzate anddecrease of its bitter taste are possible.

Cyclic adenosine monophosphate-dependent protein kinase is useful for phos-phorylation of a.a. residues in mild conditions. The modification makes the soybeanproteins soluble in media rich in calcium and improves their emulsifying properties(Seguro and Motoki, 1990).

In a papain-catalyzed reaction, at room temperature, proteins can be acylated andenriched in SH groups using N-acetyl-homocysteinethiolactone (Sung et al., 1983):


7.8 CHEMICAL MODIFICATIONS

7.8.1 INTRODUCTION

Chemical additives and reactions are used to change the color and several propertiesof different foods and isolated proteins. Typical examples include the use of sodiumnitrite in the curing of meat, chemical modifications of dough proteins for improvingthe texture of many baked goods, and applications of polyphosphates in the meatindustry. The intended modification in the properties of proteins can be achieved bychanging the charge, hydrophobicity, and steric parameters of the molecules, due tocross-linking or alterations of the a.a. residues. Ascorbic acid and its oxidationproduct dehydroascorbic acid have been known as flour improvers in the baking ofbread. Dehydroascorbic acid and its breakdown products — threose, glyoxal,diacetyl, and methyl glyoxal — are involved in Maillard-type reactions leading toprotein cross-linking (Fayle et al., 2000). Many experiments on chemical modifica-tion of a.a. residues serve the purpose of studying the structure–function relationshipin respect to proteins in different food systems under the conditions prevailing duringprocessing and storage.

FIGURE 7.8 Utilization of the plastein reaction.

Reaction 7.11

UndesirableAmino Acids,Impurities

Amino Acids,Small Peptides

Endopeptidases

Exopeptidases,Organic Solvent

Endopeptidases,Amino Acid Asters

Ethanol

Protein

Plasteins

Extraction

Hydrolysis

Plastein Reaction

Modificationof Peptides

C

H3C CO NH CH

CH2

C

O

SH2

H2N Prot H3C CO NH CH CO NH Prot

CH2)2

SH

(

+papain

pH 10

Proteins 169

7.8.2 ALKYLATION

The carbonyl compounds formed due to autoxidation of lipids and in catabolicprocesses postmortem in muscles, or introduced with wood smoke, can bring aboutundesirable effects by interacting with a.a. residues. On the other hand, some car-bonyl compounds are used intentionally to modify the proteins. Formaldehyde canharden the collagen dope in the manufacturing of sausage casings, protect foddermeals against deamination by the rumen microflora, and bind immobilized enzymeson supports.

In reducing conditions, alkylation of amino, indole, thiol, and thioether groups,and binding of saccharides to a.a. residues are possible:

For alkylation of amino, phenol, imidazole, thiol, and thioether groups in a.a.residues of proteins, reactions with haloacetates and haloamides can also be used:

The digestibility of such derivatives is generally somewhat lower than that of theunmodified proteins.

Malonaldehyde, a typical lipid oxidation product, can form cross-links in pro-teins by reacting with two amino groups:

There is also a possibility that aliphatic monoaldehydes generated in lipidautoxidation can participate in cross-linking of proteins. Formaldehyde can reactin food systems with amino, amide, hydroxyl, and thiol groups in a.a. residues ofproteins, even at room temperature. Some of these reactions result in cross-linkingof the proteins. In cheese the biogenic formaldehyde reacts with the N-terminalHis of γ2-casein to form spinacine:

Reaction 7.12

Reaction 7.13

Reaction 7.14

Reaction 7.15

pH 9

0oC2Prot NH2 4HCHO NaCNBH3 2Prot N(CH3)2 NaHCNBO3 H2O++++ ++++

+ +Prot SH ICH2COOH Prot S CH2COOH HI

+Prot —NH2 ICH2CONH2 Prot NH CH2 CONH2 HI+

Prot N CH CH2 CH N Prot+O

HC CH2 C

O

HProt NH22 + H2O


Other carbonyl compounds produced in cheese by lactic acid bacteria form otherderivatives in reactions with His (Pellegrino and Resmini, 1996).

7.8.3 ACYLATION

Acylation of nucleophilic groups is intended to increase the hydrophobicity of theprotein, introduce additional ionizable groups, or contribute to cross-linking:

The acylating agents may react with amino, imidazole, hydroxyl, phenol, andthiol groups in a.a. residues. The rate of reaction depends on the properties of thenucleophiles, the pH, the steric factors resulting from the protein conformation, andthe presence of inhibitors. The amino and tyrosyl groups can be acylated easily,while His and Cys derivatives hydrolyze readily. Acylation of hydroxyl groups ina.a. residues of proteins proceeds in the presence of an excess of acetic anhydrideonly after the amino groups have been acylated. For the formation of isopeptidelinkages N-carboxyanhydrides of a.a. are suitable. The degree of acylation dependson the nature of the protein, the acylating agent, and the process conditions, andmay reach up to 95% of lysyl residues.

Some food proteins are rich in phosphoric acid residues. The acid may eitherform ester bonds with Ser residues, as in caseins and egg proteins, or stabilize thenative conformation of protein micelles by electrostatic interactions with negativelycharged groups and calcium ions, as in caseins. In soy proteins Ser and Thr residuescan be esterified and Lys amidated with cyclic sodium trimetaphosphate at pH 11.5and 35°C (Sung et al., 1983):

Reaction 7.16

Reaction 7.17

NH

N

CH2

CHCOOHH2N

NH

N

HN

COOH

spinacine

HCHO

-OOC (CH2)2 C NH

O

ProtO

O

O

H2N Prot+

Proteins 171

The Nεtriphospholysine residues protect the NH2 group during heating in analkaline environment and hydrolyze at pH < 5. For chemical phosphorylation otherreagents are also effective, e.g., phosphorus oxychloride and phosphorus pentoxide.The reactivity of these compounds may, however, lead to undesirable cross-linkingof the proteins:

Acylation of a.a. residues generally improves WHC, as well as emulsification andthe foaming capacity of the proteins. The pI shifts toward lower values, and the solubilityincreases over that of the unmodified protein, above the pI, and decreases in the acidicrange. This is important, e.g., for wheat gluten, which has low solubility in the neutralpH range. The positive change in the functional properties is not in all cases achievedat the highest degree of modification, since it depends on the change in surface hydro-phobicity that is affected by the nature of the protein and the acylating agent.

The biological availability of acylated proteins depends on the kind of the acylgroup and the extent of acylation. Isopeptides are generally well utilized, while theavailability of other derivatives usually decreases with the increasing size of theacylating moiety and the degree of acylation.

7.8.4 N-NITROSATION

The nitrous acid generated in foods at low pH values, from endogenous or addednitrites, decomposes easily to yield the nitrosating agents nitrous anhydrate andnitrosonium ion:

Reaction 7.18

Reaction 7.19

P

O O-

O

O

P

P

O O-

O

O-

OProt Ser OH

Prot Lys NH2

+

pH 11 - 12- H2O

pH 11 - 12

pH<5

Prot Ser O P

O-

O

O-

Prot Lys NO

O-

O

O-

O

P

P

O-O

O-O

P

H

P2O7-4

H+

+ +

+

H+

+-

Prot NH2 POCl3 Prot NH POCl2 H Cl++ +

HOOC Prot

++Prot NH CO Prot Cl2PO2-

H+


Reactions of these compounds with the secondary and tertiary amines containedin many foods lead to the known carcinogens N-nitrosoamines:

The rate of N-nitrosation increases with the pKa of the amine and depends onthe pH — it is highest at a pH range of 2–4. The reaction can be inhibited bycompounds capable of binding the nitrosating agents — in meat curing, sodiumascorbate is very effective. Foods low in amines and nitrites generally contain about1–10 ppb, while cured and heavy smoked meat and fish contain up to several hundredppb of N-nitroso compounds.

7.8.5 REACTIONS WITH PHOSPHATES

In acid environments proteins may form protein–phosphate complexes of low sol-ubility. The metaphosphates, which are less hydrated than the ortophosphates, formcomplexes that are less soluble than those with ortophosphates. This has been utilizedfor the modification of functional properties of protein concentrates and preparations,for separation of proteins in different food processing operations, and in treatmentof protein-containing food plant effluents.

Reaction 7.20

Reaction 7.21

Reaction 7.22

O N O N O H2O+2HO N O

O N O N O

H

N O HO N O+

H+

or

or

RNH

R

O N O N O

+ +

+O N

+-H

RN

RN O

HNO2

NO2-

O N OH

N ON

R

R N

H

O

RN

RR +

RN

RN O + R O N ON O R

RN

RN O N O-O

Proteins 173

Polyphosphates improve the sensory quality of many food products. They pre-vent the separation of butter fat and aqueous phases in evaporated milk, and theformation of gel in concentrated milk sterilized by high-temperature short-time(HTST). They also stabilize the fat emulsion in processed cheese by disrupting thecasein micelles and thus enhance the hydrophobic interactions between lipids andcasein. Polyphosphates are also used in meat processing for increasing the WHCand improving the texture of many cooked products. The mechanisms involved indifferent applications depend on the properties of the phosphates and the commod-ities, as well as the parameters of processing.

In meat products the increase in WHC, texture improvement, and the decreasein drip may be caused by increasing the pH, complexing of Ca2+ and Mg2+, bindingof phosphates to proteins, rupturing the cross-links between myosin and actin,and dissolving some proteins. Phosphates facilitate the manufacture of meatproducts of low sodium content. To produce an emulsion-type sausage of accept-able quality, at least 2.5% salt is required. The contents of salt can be decreasedto 1.5–2.0% without loss in product quality by adding phosphates in amounts of0.35–0.5%. Generally, proprietary blands of several polyphosphates are used, togive the best quality and to prevent precipitation of orto- and pyrophosphates inbrines rich in Ca2+.

Polyphosphates are added as cryoprotectants to frozen fish minces. They arealso applied in form of dips to fish fillets prior to freezing to prevent thaw drip lossesand to improve the texture of canned fish. Mainly, about 10% solutions of Me5P3O10

and Me4P2O7 are used for 1–2 min. Different proprietary mixtures are also applied,e.g., Na4P2O7 + Na2H2P2O7 or Na3PO4 + Na4P2O7 + Na2H2P2O7.

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1791-5871-6149-4/02/$0.00+$1.50© 2002 by CRC Press LLC

Rheological Properties of Food Systems

Tadeusz Matuszek

CONTENTS

8.1 Introduction ..................................................................................................1798.2 Flow Properties of Liquid and Semisolid Food Systems............................1818.3 Effect of Composition and Processing Parameters

on the Rheological Behavior of Food Systems...........................................1918.3.1 Energy, Stress, and Deformation .....................................................1918.3.2 Structure Development.....................................................................1938.3.3 Glass Transition and State Diagrams ..............................................1958.3.4 Dynamics Map of the Food System................................................196

8.4 Importance of the Rheological Properties of Foods for Process Design and Control...................................................................1998.4.1 Simplified Rheological Principles ...................................................1998.4.2 Case Behavior of Fluid Food System..............................................201

References..............................................................................................................203

8.1 INTRODUCTION

Most food systems are built of a network of many small particles and macromole-cules and held together by a wide range of intermolecular and colloidal forces. Theirstructure, texture, stability, and functionality are strongly influenced by the strengthof these interactions. Moreover, the texture of a final food system depends stronglyon the history of structural changes during processing. At the current state of art,we do not understand the mechanisms whereby subtle changes in food systeminteractions control the structure and mechanical properties of foods. General strat-egy in food systems is to determine quantitatively the relationships between inter-actions, structure, and rheology related to the food functionality. From the structurepoint of view, it means the complete specifications of the relative distributions ofparticle in space. In the case of rheology, it means the frequency-dependent rela-tionship between stress and strain at a small deformation rate, as well as dependentbehavior at large deformations. The food functionality in general can be expressedthrough the hurdle technological effect, which was achieved at the final stage offood processing. Each particular food product can be assessed by a certain set of

8


hurdles that differs in quality and intensity, depending on the technology used(Gorris, 1995). The hurdles might influence the stability and the sensory, nutritive,technological, and economic properties of a product.

The hurdles affecting the shelf life of foods also influence other food properties,including texture. The effects of several physical, chemical, and mechanical treat-ments should be carefully considered in developing new processes and products. Itis not enough to describe the composition of a food product and to determine theconditions and types of unit operation necessary to achieve the required quality.How the major food components, such as water, salt, hydrocolloids, starches, lipids,proteins, flavors, and additives, interact with each other and affect the product qualitywith respect to microstructure, texture, and appearance should be examined.

From a food engineering point of view, food functionality is the specific responseof foods to applied forces encountered during preparation, processing, storage, andconsumption (Kokini et al., 1993). The understanding of food at the molecular levelinvolves the application of both theoretical and experimental techniques of chemistry,physics, mathematics, fluid mechanics, biochemistry, and biophysics to understandhow the molecular properties and interactions affect the final quality of the product.If the texture is to be controlled, then the effect of individual components of theformulation should be known.

The forces affecting foods during engineering operations may include thevarious forms of energy applied, e.g., transport fluxes related to the mass and heatflow; electromagnetic energy, including light, microwave, and infrared radiation;and chemical reactions, which are responsible for transferring food from onethermodynamic state to another through changes in enthalpy, entropy, and resultingfree energies.

The energy deposited and the resulting forces usually expose their effects at anylevel in the hierarchy of food structure, i.e., from the molecular level to the formationof phases, networks, aggregates, cells, and finally, the food products themselves.

Many food systems are formed in conditions far away from thermodynamicequilibrium because all food components can potentially interact chemically withone another to varying degrees. Most food materials and their complex systems arebiologically active and physically unstable with continuous changes of their struc-ture. Those physical, chemical, and mechanical instabilities in many food systemsare a direct result of the nonequilibrium nature of these systems. During foodprocessing, the raw material has its chemical and physical properties extensivelyaltered. This results in a final product whose appearance is very different from theoriginal, primary native microstructure. Most processing operations are stronglyrelated to the structural aspects of water as a main solvent and plasticizer and to thecontribution of water to hydrodynamic properties of food systems. The thermody-namic aspects describing water relation in equilibrium, with its surroundings at acertain relative humidity, pressure, and temperature, should also be considered. Manysystems involve complex mixtures of molecules in low-water environments, andinterfacial phenomena with all forces of intermolecular interactions play a veryimportant role in food functionality. Overall, the objective of food systems is todevelop a predictive methodology for substantially improving the ability of produc-ers to create new food products of specified properties and controlled consistency

Rheological Properties of Food Systems 181

in food processing. Therefore, the kinetic and thermodynamic aspects of possiblephysical and chemical interactions have to be investigated to obtain a completeunderstanding of all dynamic processes leading to food functionality (Figure 8.1).

8.2 FLOW PROPERTIES OF LIQUID AND SEMISOLID FOOD SYSTEMS

The flow properties are critical for attaining accuracy and quality in designing foodprocessing machines and food industry plants. They are also vital in modelingprocessing operations. Various energy and heat treatments of food include thermalconductivity, thermal diffusivity, density, consistency and concentration changes,specific enthalpy, specific heat, texture, and mechanical and rheological properties.

Foods are mostly nonhomogeneous and structure formation means that variousstates of aggregation occur during processing. The engineering phase of processingusually involves changes in the structure of raw materials. The food technologistand engineer would like to be able to predict the properties of any formulation of

FIGURE 8.1 Outline of general methodology of the functional food properties seen as defor-mation and property changes. (From Matuszek, T.S., paper presented at 9th World Congressof Food Science and Technology, Budapest, 1995.)

Quantitative analysis ofdeformation

Quantitative determination of statewith influence on the

transportation phenomena withinthe structure system

Characterization of a flowwith the range of structuraland phase transition effect

Measurement of thestress/shear rate

Mathematical model Structural modelselection selection

Property calculation and itstransition in food processing


components over a wide range of processing and storage conditions. In order tomake this happen, it is necessary to understand more about factors that affect:

• All levels of food structure organization• The kinetics of competitive adsorption of the food components at fluid

interfaces• The developing time-dependent properties of food formulations• Fouling problems and their effects on processing performance for different

types of membranes that are created within the microstructure of thesystems

All these factors are related to the theory of flow for predicting the rates ofmolecular transport and their relationships to molecular and consequently foodmicrostructure properties. This molecular flow information leads to a better under-standing of surface rheological factors and of the organization and motions, togetherwith intermolecular interaction, of molecules at interfaces. Intermolecular forces areresponsible for many of the bulk properties of foods. A realistic processing descrip-tion of the relationships among pressure, volume, temperature, energy, and otherproperties of the material must include the effects of attractive and repulsive forcesbetween molecules. Repulsive forces prevent the molecules from approaching oneanother too closely and account for the low compressibility of liquids. Intermolecularforces between near and distant neighbors dictate the ordered molecular arrange-ments in crystalline solids. These forces also account for the solid elasticity of andfor a very complex, condensed phase. Furthermore, the properties of structure influ-enced by velocity of propagation of disturbances in it, such as local density, tem-perature changes, and kinetic and temperature instabilities, are neither constant noruniform. The time and energy variations for all occurrences in the various regionsof food structure correspond to their conversion to flow properties like viscosity,surface tension, and diffusion of liquids through membranes and other barriers.

In food products that are complex physiological systems containing varioustypes of solutions, as well as fibrous, cellular, and crystalline components, therelationship shown in Figure 8.2 exists. It follows that the study of food textureinvolves several areas:

• The structure, in terms of both micro- and macrostructure• The evaluation of the rheological properties considered as physical properties• The evaluation of rheological and textural properties by the human

sense organs• The interrelationship of the physical and sensory measurements of food

structure

In this respect, the texture comprises all physical characteristics of foods relatedto the response to applied force and measured objectively in terms of force, distance,and time. Texture depends on the various constituents and structural elements offoods in which the microstructure components are formed and then clearly recog-nized in terms of flow and deformation during different processing treatments.


Fluid flow may be steady or unsteady, uniform or nonuniform, and it can also belaminar or turbulent, as well as one-, two-, or three-dimensional, and rotational orirrotational. One-dimensional flow of incompressible fluid in food systems occurswhen the direction and magnitude of the velocity at all points are identical. In thiscase, flow analysis is based on the single dimension taken along the central streamlineof the flow, and velocities and accelerations normal to the streamline are negligible.In such cases, average values of velocity, pressure, and elevation are considered torepresent the flow as a whole. Two-dimensional flow occurs when the fluid particlesof food systems move in planes or parallel planes and the streamline patterns areidentical in each plane. For an ideal fluid there is no shear stress and no torque;additionally, no rotational motion of fluid particles about their own mass centers exists.

In general, food can be classified as Newtonian and non-Newtonian. Its viscositydepends strongly on the shear rate (Figure 8.3). Shear stress versus shear rate curvesmay have the shape represented by curves 1–7 (Figure 8.4).

Some of the most difficult material properties of fluid and semisolid foods todetermine experimentally are viscometric functions and steady shear rheologicalproperties. The flow properties of a liquid and semisolid food system should bemeasured in the following instances:

FIGURE 8.2 Evolution of food structure arrangements from raw materials and the processingmethod used to transform them into products.

Molecular and chemicalcomposition

(energy of primary structure)

Primary structure geometryand resistance

Food engineering operation levels(molecular ultrastructure,microstructure, andmacrostructure)

Food microstructure in and afterexit from processing plant

Rheological propertiesof food structure

Final texture Functional food Nutritional Food relatedarrangements factors value law responsibilities

Energyapplied

Wasteutilizationprocesses


• When new food products have to be manufactured with clearly specifiedrheological characteristics

• When rheological properties must be carried through various steps ofengineering operations without any changes

• When rheological properties indicate directly or indirectly the quality ofthe final product

• When rheological properties chosen to describe the texture of the productappear to be the most successful on the market

• When continuous process evaluation of the rheological properties playsan essential role in development of new products and designing betterequipment

There are three main rheological properties of materials: viscous flow, plasticflow, and elastic deformation. The stress deformation behavior of elastic materialsis represented by a straight line through the origin. However, in this case, the

FIGURE 8.3 Different types of non-Newtonian liquids and semisolid foods.

Non-Newtonian food systems

Viscoelastic Rheostable Nonrheostable

With flow limit Antithixotropic flow

Without flow limit Thixotropic flow

Nonlinear viscoplastic With flow limit

Bingham’sviscoplastic Without flow limit

Pseudoplastic flowwith relaxation

Dilatant flow withcondensationeffects


deformation is reversible upon removal of the force. Many foods show time-depen-dent rheological behavior and a combination of these, such as viscoelasticity andviscoplasticity.

To characterize Newtonian and non-Newtonian food properties, severalapproaches can be used, and the whole stress–strain curve can be obtained. One ofthe most important textural and rheological properties of foods is viscosity (orconsistency). The evaluation of viscosity can be demonstrated by reference to theevaluation of creaminess, spreadability, and pourability characteristics. All of thesedepend largely on shear rate and are affected by viscosity and different flow condi-tions. If it is related to steady flow, then at any point the velocity of successive fluidparticles is the same at successive periods of time for the whole food system. Thus,the velocity is constant with respect to time, but it may vary at different points with

FIGURE 8.4 Relationship between shear stress and shear rate for different foods’ flow char-acteristics.

(1)

types of Bingham’sliquids (2)

(3)

(4)thixotropy liquids

(5)

τ0

*

(6)dilatation and rheopexyliquids flow

(7)

Shear rate D

τSh

ear

stre

ssY

ield

str

ess

non-li

near p

lastic

flow

Bingh

am’s

plastic

flow

(idea

lized

)

non-linear plastic

flow

pseudoplastic + yield stress

pseudoplastic

flow

Newto

nian liq

uid fl

ow


respect to distance. Flow is unsteady when conditions at any point in a fluid foodsystem change with time. Most practical food engineering problems involve steadyflow conditions and are based on the Newton suggestion.

The thin layer of liquid between two small planes of area A (Figure 8.5) isconsidered to be part of a laminar flow. For a greater velocity, the middle layerpulls forward with an equal force F, while the layer below, which has lesservelocity, pulls the middle layer back with an equal force F. These two equal andopposite parallel forces form a shear couple and produce a shear stress of magni-tude F/A. Newton suggested that the shear stress is directly proportional to thevelocity gradient:

F/A ~ dV/dz (8.1)

∴ F/A = ηdV/dz (8.2)

or

τ = η ⋅ D (8.3)

where η is the constant of proportionality and is called the dynamic viscosity anddV/dz = D is called the velocity gradient, or shear rate. The two planes are separatedby a distance ∂z, and the shear strain ∂θ = ∂x/∂z. Because this has taken place intime ∂t, the rate of change of shear strain is ∂θ/∂t ≅ dV/dz = velocity gradient, wheredV is the velocity of the upper layer relative to the lower.

Newtonian liquids show a stress–strain relationship represented by a straightline (Figure 8.6a). In Figure 8.6b there are viscosities of two Newtonian fluids atdifferent shear rates. These two materials, represented by 1 and 2, may have thesame apparent viscosity when there is no direct proportionality between shear stressand the rate of shear. The flow behavior for non-Newtonian stress–strain relationship

FIGURE 8.5 Sample shear flow: definition of shear stress, strain, and shear rate.

z

1A F

V δx

2 θ

δz FA

xinterplates fluid

y


is represented by different curves (Figure 8.7). The term non-Newtonian is appliedto all materials that do not obey the direct proportionality between shear stress andrate of shear. For a non-Newtonian fluid, the viscosity has no meaning unless theshear rate is specified and the apparent viscosity is not constant. Apparent viscosity(ηapp) can be used for easy comparison between Newtonian and non-Newtonianfluids at particular shear rates. It is usually defined as the ratio of the shear stressover the rate of shear.

During food engineering operations, many fluids deviate from laminar flow whensubjected to high shear rates. The resulting turbulent flow gives rise to an apparentincrease in viscosity as the shear rate increases in laminar flow, i.e., shear stress =viscosity × shear rate. In turbulent flow, it would appear that total shear stress =(laminar stress + turbulent stress) × shear rate. The most important part of turbulentstress is related to the eddies’ diffusivity of momentum. This can be recognized asthe atomic-scale mechanism of energy conversion and its redistribution to the dynam-ics of mass transport processes, responsible for the spatial and temporal evolutionof the food system.

In general, there are three main types of non-Newtonian liquids and semisolids:

• Time-independent, for which the rate of shear depends only on the shearstress

• Time-dependent, for which the relationship between the rate of shear andshear stress depends on the time of shear

• Viscoelastic, which has characteristics of both elastic solids and viscousliquids

In time-independent liquid food products, the flow curve is linear but intersectsthe shear stress axis at a positive value of shear stress. This value is known as ayield stress. The significance of the yield stress is that it is the stress that must beexceeded before the material will flow. This type of flow can be characterized bythe following rheological equation (for the Bingham–Schwedoff model):

FIGURE 8.6 a: Newtonian liquid. b: Viscosities of two Newtonian fluids at different shearrates.

a) b)τ η

1

2

D D


τ = ηpl ⋅ D + τ0 (8.4)

where τ0 is the yield stress and ηpl is the Bingham plastic viscosity.To the same family of curves belong pseudoplastic materials. These fluids show

a decrease in apparent viscosity with an increase in the rate of shear and are typicalof the majority of non-Newtonian liquid food products. The way most often usedto describe the properties of these materials is an empirical Ostwald-de Waele powerlaw equation:

τ = k ⋅ Ds (8.5)

FIGURE 8.7 Non-Newtonian flow behavior. a: Structural viscosity (for high molecular solu-tion). b: Dilatant flow (suspension with high concentration). c: Viscoplastic with flow limits:1, ideal plastic; 2 or 3, nonlinear plastic flow. d: 1, thixotropy flow; 2, antithixotropy flow;3, viscoelastic flow; e:rheopexy flow.

a)τ η

D τb)

τ η

D τc)

τ 2 η 1

3τ0

D τ d) e)

τ τ 1

2

3

D D


where k is the consistency index and s is the flow behavior index, which forpseudoplastic materials is less than 1 and greater than zero (0 < s < 1).

This equation can be used to describe the rheological properties of any time-dependent fluid if applied over a limited range of shear rate. Many examples areknown in most of the existing procedures for solving engineering problems in thefood industry. They include the case study of processing concentrated fruit juiceswith suspended pulp particles, dairy cream, more-or-less-concentrated tomatopuree, apple puree, butter, minced meat, and infant foods. Among the food productsthat exhibit pseudoplastic behavior are all that contain soluble high-molecular-weight substances and insoluble matter. Products that contain crystals and otherparticles like fat globules dispersed in a liquid phase, e.g., molten chocolate andice cream mix, have a yield stress. The apparent viscosity for a pseudoplasticmaterial is ηapp = k ⋅ Ds – 1.

There are many pseudoplastic food products that display more complex rheo-logical behavior and with a yield stress that can be characterized in two ways, eitherby an extension of the power law rheological equation of Herschel–Bulkley:

τ = k ⋅ Ds + τ0 (8.6)

or by an equation developed by Casson:

τ1/2 = k0 + ki ⋅ D1/2 (8.7)

where k0 is the Casson yield stress and ki is the Casson plastic viscosity.Among this type of non-Newtonian materials are dilatant fluids. They show an

increase in apparent viscosity with an increase in rate of shear and are not commonlyfound among liquid food products. They can be represented by power law Equation8.5, but in this case the flow behavior index, s, would be greater than 1 and lessthan infinity (1 < s < ∞). Such “shear thickening” is observed in materials withsuspensions of solids at a high solid content, when approaching the point of tightestpacking. For example, corn-flour pastes can be dilatant.

There are other foods that possess the shear rate. Those food systems, whenplaced under steady flow at a constant rate, show a changing shear stress over timeuntil an equilibrium value is achieved. Time-dependent behavior can be interpretedfrom viscoelasticity, thixotropy, or a combination of the two, and the power lawequation is not adequate for proper evaluation of such a system (Shoemaker andFigoni, 1984). Time-dependent materials can be subdivided into two classes: thix-otropic and rheopectic. Time-dependent liquid foods for which the apparent viscositydecreases with time of shearing are known as thixotropic materials, whereas rheopec-tic fluids are those for which the apparent viscosity increases with time of shearing.In a thixotropic flow, the response to shear is instantaneous, and the time-dependentbehavior can be observed as the shearing process continually alters the structure ofthe system. These structural changes include disentanglement of polymer moleculesin solution and deflocculation of globules in emulsion. The rate of structure break-down during shearing at a given rate depends on the number of linkages availablefor breaking and therefore decreases with time. In the case with rheopectic fluids,the structure builds up in shearing; this phenomenon can be regarded as the reverse


of thixotropy. In fact, rheopectic behavior is often referred to as antithixotropy.Thixotropy is generally defined as the continuous decrease of apparent viscositywith time under shear and subsequent recovery of viscosity when the flow is dis-continued. The simplest example of such a system undergoing structural changes,known as symmetrically thixotropic fluid, is shown in Figure 8.8.

Once shearing is stopped (the external force is no longer acting), the rate of thesystem structural recovery is the same as the rate of structural breakdown understeady shear. In foods, the time needed for recovery may vary significantly fromone thixotropic product to another. The time dependency can be observed in foodsystems such as concentrated emulsions, sols, and gels.

Semisolid foods belong, in general, to a group than can be characterized byviscoelastic parameters. Viscoelasticity is due to the delayed motion and retardedresponse of a system to a shear resulting from a joint viscous and elastic nature.Jellies and deserts fall into this category. Jams are also included; however, someadditional measure of elasticity of the product is required.

Measurements of stress or viscosity decay at a constant or steady shear rate havealso been used to characterize structural breakdown. The classical approach tocharacterizing structural breakdown is the measurement of the hysteresis loop(Figure 8.7d and e). The area enclosed by the loop is the first indication of the degreeof structural breakdown and depends on the previous shear history and both the rateof change in shear and the maximum value of the shear rate. The relationship betweenrheological properties and the food hysteresis loop area is very complicated and hasa complex shear history. Many food systems show viscoelastic behavior with time-dependent flow properties similar to that shown in Figure 8.9. Among others, vis-coelastic rheological behavior of such a food system can be characterized by a creepcompliance test, where a constant stress is applied and the strain is followed as afunction of time (t). Creep compliance is generally expressed in terms of a ratio:strain (τ) over stress. In this case, stress relaxation is also normally expressed interms of a ratio: stress (τ) over strain. For an ideal elastic solid, the stress or strain

FIGURE 8.8 Flow behavior of a symmetrically thixotropic system. (Adapted from Harris,J., Rheology and Non-Newtonian Flow, Longman Group, Ltd., London, 1977.)

shear recovery

Shearstress

Time


will be independent of time, and the stress divided by the strain will be the elasticmodulus of the material.

In real food polymers, a distinction can be made between a viscoelastic solid,which contains some cross-links that are permanent, and a viscoelastic liquid, where,under the influence of stress, the relative movement of whole molecules will beobserved. As shown in Figure 8.9, in the case of a viscoelastic solid, after applicationof the stress, the strain will eventually reach a constant value, and upon removal ofthe stress, the strain will finally return to the remaining value of food primary energy,which was not entirely dissipated. For a viscoelastic liquid, a permanent deformationwill remain after removal of the stress. In the stress relaxation area, the deformationvalue will decay to zero for a viscoelastic liquid, whereas for a solid, it will reacha constant, nonzero value. It can also be seen as either a decreased value to the zeroor a constant, nonzero value, as pointed out by the dashed line. Both values char-acterize the rheology parameters of foods under certain conditions. One of thereasons for this is that the factors of time-dependent foods are not necessarily relatedto their elastic modulus. This can be explained by the series of small deformationswithout rupture, which are dependent in different ways and are based on the primarymolecular microstructure of foods. The time required for the stress to relax to adefinite fraction of its initial value is the relaxation time.

8.3 EFFECT OF COMPOSITION AND PROCESSING PARAMETERS ON THE RHEOLOGICAL BEHAVIOR OF FOOD SYSTEMS

8.3.1 ENERGY, STRESS, AND DEFORMATION

Stress and strain or deformation can be useful in microscopic or molecular descrip-tions of how the observed phenomena come about. They have directional propertiesthat distinguish an elongation from a shear, for example. When the stress and strainmay depend on time, it can be either the unchanging equilibrium state or a steady

FIGURE 8.9 Flow behavior of a viscoelastic system. Regions AB and CD represent vis-coelastic behavior; region BC represents structural breakdown during steady shear.

steady shear relaxation

Shearstress(strain orcompliance)

elastic solid B

viscoelastic liquid

viscoelastic solid

C

A

Time

D


flow in which strain increases at a constant rate. The magnitude is also important;i.e., if doubling the strain leads to a doubling of the stress, then the behavior —because of the geometry and time patterns being identical — is called linear. In foodindustrial practice, nonlinear phenomena are mostly the rule, and the way rheologicalbehavior actually appears depends on the time scale of the process in which it isobserved. The ratio of a material’s relaxation time to the time over which behavioris observed is called the Deborah number. As the Deborah number becomes smaller,the behavior changes from a solid to a fluid. In case of suspensions and dispersionsof solid particles in a fluid, the effects of concentration, size, shape, and arrangementof the dispersed particles must also be considered.

In general, for the effect of composition and processing parameters of the foodsystem, the external mechanical work needed to make a material deform or generatea flow pattern is used in three ways:

• It is stored reversibly so that the material can give back the energy asmechanical work.

• It is transformed to chemical energy in bonds or weak links betweenparticles.

• It is dissipated into heat and lost.

Among all the deformations and flow patterns investigated in food science, onein is of particular importance: steady flow. In this case, the geometry is shearing,the dependence on time is a steady increase in the shear, and the magnitude isarbitrary. The most common behavior in the food system is shear thinning or thepseudoplasticity curve, also known as a viscoelastic characteristic of materials suchas polymers. In these, elasticity arises from the tendency of the polymer segmentsto take on random equilibrium arrangements, due to their thermal motion.

A viscous contribution results from friction as one segment slides past another.The same friction also tends to drag the molecule out of its equilibrium shape.However, at low shear rates, the viscous stress is too small to do this, so the shapeof the molecule and also the food system’s viscosity do not change. At larger shearrates, the viscous stress can deform the molecule into a shape in which the flowpattern occurs with more lowering of the viscosity. At a higher shear rate, themolecules cannot be deformed anymore. The shear rate can then be increasedindefinitely without a further drop in viscosity. The equilibrium, considered as aconfiguration of the molecule, is restored when shearing stops, so that the deforma-tion is a means of storing mechanical work in a recoverable manner.

Energy can also be stored in other ways on a microscopic scale, e.g., byelectrical charges being forced near each other in colloidal systems and by emul-sion drops being distorted from the spherical shape. In this case, the surface tensiongives them stabilizing surfactant layers on dispersed particles being pressed intoeach other.

The mechanical work put into a food system with respect to the chemicaltransformation is typically associated with changes in the bonding between foodcomponents. In accordance with such changes, energy can be used to break linksinitially holding particles in chains or aggregates, leading eventually to all the


particles being unbounded. Because the aggregation of particles causes a greaterdisturbance to the flow, such a system would be shear thinning. Due to the passageof time, it would also be thixotropic when steady flow was started.

In other foods, the effect of composition and processing parameters can beachieved by different ways of storing work, e.g., shear thickening. In this case, theparticles stick together when they collide, and the link formation promoted byshearing is less likely. It would lead to rheopexy when an increase in velocity takesplace, with time at the onset of flow. These phenomena occur only in highly con-centrated dispersions of particles; i.e., randomly arranged particles interface witheach other greatly in flow conditions. If the interaction between particles allowslayering within a certain time needed to accomplish this process, rearrangement ofthe food dispersed system will be more perfect in slower flows at low shear rates.The viscosity should then increase with shear rate. This final effect of compositionand rheological behavior of such a food system is strongly related to the size ofparticles. If the particles are unequal in size, very small ones can fit into gaps betweenlarger ones, allowing flow at a higher concentration than that for equal-size particles.At the same concentration, the dispersion with a wide range of particle sizes has alower viscosity than one with uniform particles. In some cases, the effect of foodsystem composition regarding process parameters can be interpreted by catastrophicchanges in component organization, i.e., antithixotropy, hysteresis, and relaxationperiod of time. Such an abrupt change can be observed, for instance, in shearthickening when a critical shear rate has been exceeded.

In general, the rheological properties of the food system have to be describedin terms of particle sizes, shapes, surfaces, volumes, lengths, and their frequencies.Such structural characteristics of food systems are in reality the visual representa-tions of highly ordered biological molecules. By combining such structural andfunctional data in equations that can then be integrated into mathematical andrheological models, opportunities are being created for analyzing complex foodsystem responses and dissecting them into data of processing parameters and simpler,more interpretable food texture, quality, and functionality.

8.3.2 STRUCTURE DEVELOPMENT

A specific food product can be made by using a variety of recipes and processesthat differ in their demand on the functional ingredients. A detailed understandingof any effect of food system composition involves the following issues:

• Thermodynamic consideration: is the reaction feasible to be carried out in thepractice of food engineering? Is a particular process likely to take place, andcan it be ascertained by theoretical consideration of energy associated with thereaction? To what extent can it be calculated because of the enthalpy change,free energy, and entropy change, and can the equilibrium be kept constant?

• Food system reaction kinetics: it is important to know, because of the finaleffect of food system composition, how fast the reaction is. It may beperfectly feasible from a thermodynamics point of view, yet of no practicalvalue because it takes place far too slowly.


• Reaction mechanisms: it is necessary to be familiar with what actuallyhappens in all changes during a food engineering operation and to keepit under control because of the rheological parameters and their influenceon food system composition. The fullest understanding of a reactioninvolves a study of the possible mechanisms by which one set of bondsis broken, while another one is formed during the same process conditions.

• Separation of the product: a reaction mechanism intended to make oneparticular product will be useful only if it is relatively easy to separatethat product from the mixture remaining at the end of the reaction. Thereare several possible results of physical separation: interruption of liquidbridging, lubrication, competition for absorbed water, cancellation ofelectrostatic charges and molecular forces, and modification of crystal-line lattice. All these results can influence flowability and reaction mech-anisms in different food systems. They can also be used for theevaluation of flowability by the following methods: direct flow rate,angle of repose, shear and tensile strength, unconfined yield stress, angleof internal friction, and cohesion measurements, as well as plots of thewhole flow function.

All of them are worthy in order to gain knowledge relevant to the processingparameters of non-Newtonian liquid and semisolid food systems, particularly in thefollowing areas:

• Methodology adequate for characterization of non-Newtonian materialswith regard to changes taking place during shearing and heating

• Relationships between the flow properties and residual time in continuousprocesses

• Better use of flow characteristics for the design of process equipment• The effect of residual time for food quality with regard to microbiology,

nutrition, and sensory and functional properties

Understanding the thermodynamics, reaction kinetics and mechanisms, and sep-aration process requires accurate analysis of confirmation and physical interactionin the absence of water or in the low-mixture environments.

There are some processes, e.g., grinding, where the primary cell structure ischanged significantly and can liberate the internal cell components. These liberatedcomponents can be purified, and their functional properties can be exploited to createfoods whose textures are completely different from those of original raw materials,e.g., bread, biscuits, or sausages. Furthermore, by following this method, it is pos-sible to use the natural texturizing properties of certain components. Such agents asemulsifiers, hydrocolloids, and proteins have opened up — through emulsifying,whipping, softening, preventing of crystallization, thickening, gelling, and stabilizingfacilities — new development possibilities in a wide range of food products: namely,beverages, cream soup, sauce, salad dressing, bread, biscuits, pastry, sausage andmeat spreads, jam, gel, cream and whipped desserts, ice cream, and confectionery.These new agents, combined with improved processing parameters and preservation


technologies, have led to the development of new foods with varied textures, suchas those of liquids, semisolids, solids, pastes, gels, and foams. Either single or severaltexturizing agents can often lead to the desired effect for food preparation; the properingredients must be correctly selected and dosed, as well as incorporated at a preciseprocessing stage in various processing systems.

8.3.3 GLASS TRANSITION AND STATE DIAGRAMS

A complete textural evaluation with respect to the processing parameters and rheo-logical behavior of the food system may be logistically impossible. More impor-tantly, not all these data may be required, because some factors influencing thestructural composition effect are probably multicorrelated parameters and more orless sensitive than others. The complex force deformation and property frequencychange–response profiles of a variety of food materials are particularly amenable tofractal (Peleg, 1997 and Peleg and Hollenback, 1984) and to the glass phase tran-sition. Food system composition effects can be characterized in terms of their fractalor noninteger dimension, as well as through the weight fraction of solids, when theyare transformed into the viscous liquid state. The application of fractals in imageanalysis (Kalab et al., 1995) and glass transition processes related to rheologicalchanges in food systems with various aspects of food science, including textureevaluation, has only recently been addressed (Roos, 1995; Kokini et al., 1995). Thecommon view of glass transition structure is that both the short-range and long-range orders are absent, and the structure formation process is best described as acontinuous random. It has been reported (Roos, 1995) that glass transition is asecond-order phase transition. In some cases, the local ordering in food systemcomposition prevails over an intermediate range of several atomic or molecular units.In the phase transition process, for gas-to-particle conversion, the following areincluded: homogenous, heteromolecular nucleation (formation of a new, stable liquidor solid ultrafine particle involving one gaseous species only); homogeneous, het-eromolecular nucleation (formation of a new particle involving two or more gaseousspecies, typically one of these being water); and heterogeneous, heteromolecularcondensation (growth of preexisting particles due to deposition of molecules fromthe gas phase). Glass phase transition processes result in exciting changes in freevolume, molecular mobility, and physical properties of amorphous materials andcan be detected from changes in mechanical, thermal, and dielectric properties of afood system. Knowledge of the relationships between glass transition temperatureTg and physiochemical changes is very important in predicting the effects of com-position on food rheological behavior in various processes, including, among others,agglomeration, baking, extrusion, dehydration, freezing, and storage conditions. Tg

of food system components can influence food properties, cause deteriorativechanges, and be useful for visualizing processing parameters through the use of statediagrams. These drawings can also be used to show the relationships among com-ponents of a food system, temperature, and stability of food materials, as well as topredict changes under various process conditions (Figures 8.10 and 8.11). The caseof cereal proteins in the prediction of material process phases is shown in Figure 8.12.


8.3.4 DYNAMICS MAP OF THE FOOD SYSTEM

The glass transition processes in foods may result from a rapid removal of waterfrom solids. Based on that, e.g., the Tg values of anhydrous polysaccharides are high,and the food materials may decompose at temperatures below Tg (Kokini et al., 1994;Roos and Karel, 1991b). The glass temperature transition affects viscosity, stickiness,crispness, collapse, crystallization, and ice formation, and can strongly influencedeteriorative reaction rates. This provides a new theoretical and experimental frame-work for the study of food systems: to unify structural and functional aspects offoods, described in terms of water dynamics and glass dynamics.

The term water dynamics indicates the mobility of the plasticizing diluent anda theoretical approach to understanding how to control the water movement in glass-forming food systems. The term glass dynamics deals with the time and temperaturedependence of relationships among composition, structure, and thermomechanicalproperties, as well as the functional behavior of food systems.

The functional aspects, in terms of water dynamics and glass dynamics, and theappropriate kinetic description of the nonequilibrium thermomechanical behavior offood systems have been illustrated as a dynamics map, shown in Figure 8.13.

FIGURE 8.10 State diagram of water-plasticizable materials. Food solids can be trans-formed into the glassy state in processes that remove water, e.g., extrusion, dehydration, andfreezing. The glass transition temperature Tg decreases with increasing water content. Max-imally freeze-concentrated solids have a glass transition at T'g, and the corresponding con-centration of solids in the maximally freeze-concentrated phase C'g. Equilibrium melting ofice occurs at T'm. (From Roos, Y.H., Food Technol., 49, 97, 1995.)

extrusion dehydration - drying

water and solids - evaporation

freezing solids and water

Tm curve

T’m ice, solids, and water

T’g

Tg curve

-1350C

0 Weight fraction of solids C’g 1.0

Tem

pera

ture


The dynamics map represents both the equilibrium and nonequilibrium aspects.The equilibrium regions are described through two dimensions of temperature andcomposition. The major area of the dynamics map, shown in Figure 8.13, repre-sents a nonequilibrium region of the most far-reaching technological consequencesto aqueous food systems. The nonequilibrium regions require for their descriptionthe third dimension of time, expressed as t/τ, where τ is a relaxation time. Non-equilibrium physical states determine the time-dependent thermomechanical, rheo-logical, and textural properties of food systems. Based on the Williams–Lan-del–Ferry (WLF) mechanism, the glass transition, as in the food’s reference state,can be concluded and identified from the dynamics map. The dynamics map canbe used to estimate the mobility transformation in water-compatible food polymersystems in terms of the critical variables of time, temperature, moisture content,and pressure (Peleg, 1993).

The glass transition as a reference state can be used to explain all transformationin time, temperature, and structure composition effects between different relaxationstates for technologically practical food systems in their nonequilibrium nature. Amongothers, specific examples include reduced activity and shelf stability of freeze-dried

FIGURE 8.11 State diagram for food materials, showing the Tg curve and isoviscousstates above Tg. Maximally freeze-concentrated solids with a solute concentration of C'ghave Tg at T'g. Ice melting within maximally freeze-concentrated materials occurs atT'm. The equilibrium melting curve shows the equilibrium melting point Tm as a functionof concentration. (From Roos, Y.H. and Karel, M., Food Technol., 45, 66, 1991b.)

solution rubber

solubility crystallizationcollapsestickiness

eutectic pointTm

108[Pa s] equilibrium ice formation and melting

ice and rubberT’m

glassmaximum ice formation

T’gice and glass 106 [Pa s]

nonequilibrium iceformation

1011[Pa s] delayed ice formation

glass

Concentration C’g

Tem

pera

ture


FIGURE 8.12 Transformations in cereal proteins during the wetting, heating, and cooling ordrying stages of extrusion cooking, as seen on a hypothetical phase diagram. (From Kokini,J.L. et al., Trends Food Sci. Technol., 5, 281, 1994.)

FIGURE 8.13 A four-dimensional dynamics map with axes of temperature, concentration,time, and pressure, which can be used to describe mobility transformation in nonequilibriumglassy and rubbery systems. AW, water activity; RVP, relative vapour pressure. (From Slade,L. and Levin, H., Crit. Rev. Food Sci. Nutr., 30, 115, 1991.)

free-flow region

loosely held network

flashing-offmoisture

heating

expansion

cooling Tg + 1000Cwetting and

mixing rubberglass

dry material

Moisture [%]

Tem

pera

ture

mobility transformation map

reactive equilibriumvapour phasecrystalline solid

aw biological steady state

1

equilibriumRVP nonequilibrium

dilute solution room temperature

nonequilibrium 0

reference state

nonequilibrium

stable

concentrationtime

pressure

definedhere only


proteins and living cells, graininess and iciness of ice cream, lumping of dry powder,and the bloom on chocolate, as well as recipe requirements for gelatin desserts, cookingof cereals and grains, expansion of bread during baking, collapse of cake during baking,cookie baking effects of flour and sugar, and staling of baked products. Glass dynamicshas proven to be a very useful concept for elucidating the physiochemical mechanismsof structural/mechanical changes in various melting and (re)crystallization processes,including the gelatinization and retrogradation of starches. Glass dynamics can alsobe used to describe the viscoelastic behavior of amorphous polymeric network-formingproteins such as gluten and elastin (Slade and Levin, 1991).

These unified concepts, based on water dynamics and glass dynamics, have beenused to explain and predict the functional and rheological properties of food systemsduring processing and their effects on time-dependent structural and mechanicalfactors related to quality and storage stability of food microstructures.

8.4 IMPORTANCE OF THE RHEOLOGICAL PROPERTIES OF FOODS FOR PROCESS DESIGN AND CONTROL

8.4.1 SIMPLIFIED RHEOLOGICAL PRINCIPLES

The rheology of food systems is important in many food applications. Rheology asthe science concerned with the deformation and flow of matter involves, in mostrheological tests, a force to a material measuring its flow or change in shape. Mostof the textural properties that can be recognized when people consume foods arelargely rheological in nature, e.g., smoothness, hardness, tenderness, creaminess,brittleness. The stability and appearance of foods often depend on the rheologicalcharacteristics of their components.

Rheological properties of the food system materials can be divided into thosethat deform and those that flow. They can be further subdivided into ideal (strainrate independent) and nonideal (strain rate dependent) material. Ideal solid foodmaterials deform in elastic; its properties are described by Hookean manner. Idealliquid flows viscously; its properties are described by Newtonian manner. In bothcases the behaviors are independent of the strain rate. Most food systems are nonideal(strain dependent), and their rheological properties are complicated and vary withthe direction of stress application. There are three commonly applied types of stress:compressive, directed toward the material; tensile, directed away from the material;and shearing, directed tangentially to the material (Figure 8.14). Strain is theresponse of a material to stress. Therefore, there are three types of strain: compres-sive, tensile, and shear. The ratio of stress to strain is called the modulus (E). It canbe compression, tensile, or shear modulus. When an elastic material is compressed,the stress–strain relationship is a straight line at the origin, and the slope is givenby the tangent of angle β, called Young’s modulus of elasticity. Rheologically, foodsystem materials may deform in three ways: elastic, plastic, or viscous. Deformationor strain in an ideal elastic body occurs instantly at the moment stress is appliedand is directly proportional to stress; it disappears instantly and completely whenstress is removed (point P depicted in Figure 8.14, limit of the stress proportionality).


Deformation in an ideal plastic material does not begin until a certain value of stressupper yield point is reached (strain from point S to point Q). Deformation ispermanent, and no recovery occurs when the stress is removed. The strain at pointS is still elastic, but without proportionality between stress and deformation. PointR in the tensile test represents the maximum or ultimate stress of the material, andpoint Z represents the stress and deformation at rupture of the food system materials.In an ideal viscous body, deformation occurs instantly at the moment when stressis applied. In comparison with an elastic body, the strain is proportional to the rateof strain and is not recovered when stress is removed. The stress σt (tensile test) orσc (compression test) is usually referred to the original cross-sectional area (Fo). Thetest pieces are subjected to a gradually increasing tensile or compression load intesting equipment such as an Instron model. During this increasing load, the corre-sponding elongation ∆L (or shortening) over the gauge length Lo is continuouslymeasured. The elongation ∆L (or shortening) consists of an “elastic” and a “perma-nent” part of deformation. The latter can be measured by removing the stress. Usingthe principles of strength of materials, the strain is ε = ∆L/Lo.

In the rheological structure of most food systems there is a viscous elementpresent, and the deformation curves are often highly influenced by the rate of theimposed strain. This is due to the fact that the material relaxes (or flows) while testedunder compression and the resultant deformation of this flow is dependent on thenature of the viscous element (Szczesniak, 1963; Peleg and Bagley, 1983). In theviscoelastic food systems, where during processing it is caused to oscillate sinuso-idally, the strain curve may or may not be a sine wave. In cases when a periodicoscillatory strain is applied on a food system like fluid material, oscillating stresscan be observed. The ideal elastic solid produces a shear stress wave in phase with

FIGURE 8.14 Fundamental types of stress (σt-tensile or σc-compression) acting on the body.

Q Rσt

S Tensile

PFo

tgβ=E

-ε E ε

Compression

Fo P Shear S

Z Q σc

Z


the strain wave. In the perfect viscous liquid, the stress is 90° out of phase with theapplied strain. For viscoelastic materials there are both viscous and elastic properties,described by complex modulus G, known as the transversal or compression modulus.It consists of two parts that describe two viscoelastic properties of food systemmaterials. The first part is called the storage or rigidity modulus, G' = τo cosϕ/γo,and represents the elastic character of the material. The second part is called theloss modulus G′′ = τo sinϕ/γo, and represents the viscous character of the material.The angle ϕ is an intermediate phase angle with a value between 0 and 90°, and τo

and γo are the amplitudes of the stress and strain waves, respectively.In addition, the effect of time and temperature on the behavior of the materials

manifests a great influence on the rheological properties of the food systems.

8.4.2 CASE BEHAVIOR OF FLUID FOOD SYSTEM

Accurate and reliable rheological data are necessary for the design and control of fluid-moving machines, the sizing of pumps and other transport processes, the estimationof velocity, the shear and residence time distribution in continuous mixing, and theevaluation of heating rates. Temperature differences occur in heat processing of foods.The nonuniform distribution of heat is due to the fact that the heat field intensity isnot homogenous over the entire object of application. It depends on the coefficient ofretention, heat absorption, and the heat resistance at the walls of the equipment.

For many foods, the temperature effects are related to the changes in apparentviscosity:

ln ηappa = a + b/T (8.8)

where ηapp is the apparent viscosity, T is the temperature in Kelvin degrees, and aand b are constants.

The complex nature of rheological behavior in molten chocolate is demonstratedbelow. Chocolate is a suspension of solid particles in a fluid medium. The mainsolid particles in chocolate are cocoa and sugar, and the fluid is cocoa butter. Thereare other minor ingredients such as the surface active agents, water, milk solids, andbutter fat. Cocoa butter is Newtonian and time dependent. Large quantities of solidparticles, as well as surface and moisture active agents, can change the flow behaviorpattern of molten chocolate to a non-Newtonian flow. A typical flow curve for moltenchocolate has a yield stress, and the apparent viscosity falls rapidly with an increasingrate of shear (Figure 8.15). Many factors influence the flow behavior of chocolate.The most important ones are fat content, type and quantity of surface active agent,moisture content, temperature, degree of shearing, and particle size and distribution.The latter, in accordance with quality parameters and consumer acceptance, shouldnot contain cocoa particles larger than 15 µm in diameter. Molten chocolate is, inmany cases, time dependent, which can be expressed by:

τ = k ⋅ t–m (8.9)

where τ is the shear stress, t the time, k the constant, and m the index of timedependency.


Chocolate can be characterized by a yield stress and plastic viscosity, i.e., as theBingham plot. Another curve was established by Casson and reported by Holdsworth(1971) in which chocolate is characterized by the yield value and plastic viscosity.The Bingham plot is mainly used for process design and its control in the productionof plain chocolate. In the case of Casson plots, some molten chocolates, particularlythose containing active surface agents, did not give straight-line relationships. Toovercome this difficulty, another expression was developed (Elson, 1977):

τ = ηp ⋅ D + B ⋅ sinh–1 D + τ0 (8.10)

where τ is the shear stress, D is the rate of shear, ηp is the plastic viscosity, τ0 is theyield stress, and B is the interaction effect.

The flow behavior of molten chocolate can also be affected by changes inprocessing conditions. These may lead to different values, because of the effect ofnon-Newtonian flow at the walls of the processing equipment. The wall shear rateis often characterized by the Nusselt number equation, which contains the so-calledδ factor. The δ factor is the ratio of the wall shear rate for a non-Newtonian fluidto that of a Newtonian fluid at the same flow rate. For power law fluids, this factorcan be calculated:

δ = (3n + 1)/4n (8.11)

where n is the flow behavior index. The temperature-dependent properties of moltenchocolate would have a major effect on heat transfer. Some assumptions are madethat during many heating operations the temperature-dependent effects are morerelevant than the degree of pseudoplasticity of the fluid. Solutions are often obtained

FIGURE 8.15 Relationship among shear stress, viscosity, and shear rate as flow behavior ofmolten chocolate; for 1 the temperature is 35°C, and for 2 it is 45°C (arbitrary scale).

τ

η = f (D) (1)

τ = f (D)(2)

η = f (D)

(3)

D

τ


in cases where heat is generated due to viscous dissipation of energy and by phasetransition changes. The prediction of temperature and velocity profiles are also veryimportant in a wide range of different heat transfer situations. Attempts to calculateand predict the heat transfer rates in processing design, e.g., in agitated vessels, arecomplicated by difficulties in accounting for the geometry of the system and by thecomplex rheological behavior of most liquids and semisolid foods. Heat transfer toboth Newtonian and non-Newtonian food systems and the prediction of the rate ofheat transfer in both jacketed vessels and vessels containing heating coils, foragitation produced by paddles, turbines, propellers, and anchors, can be consideredby using general types of correlation:

Nu = f (Re, Pr, Vi, dimensionless geometrical factor) (8.12)

where Nu is the Nusselt number, Re is the Reynolds number, Pr is the Prandtl number,Vi is η/ηw (the viscosity ratio), and ηw is the viscosity at the wall of equipment.

For most non-Newtonian food systems, it is obvious that because the shear ratethroughout the material in the vessel varies, so does the apparent viscosity. Thisleads to a problem in specifying the viscosity, which is to be used in the Re, Pr, andVi numbers, when this type of equation (8.12) is applied in process design andcontrol. The prediction of heat transfer coefficients in the equipment handling non-Newtonian food products, based on knowledge of the flow curve and its dependency,changes for which it will be encountered, is a prerequisite to any process designand control consideration.

REFERENCES

Elson, C.R., Increased Design of Efficiency through Improved Product Characterisation, paperpresented at Symposium of Chemical Engineering, West South Branch, U.K., 1977,p. 96.

Gorris, L.M., Food Preservation by Combined Processes, paper presented at 1st Main Meeting“Copernicus Programme,” Porto, Portugal, 1995, p. 10.

Harris, J., Rheology and Non-Newtonian Flow, Longman Group, Ltd., London, 1977.Holdsworth, S.D., Applicability of rheological models to the interpretation of flow and

processing behaviour of fluid food products, J. Texture Stud., 2, 393, 1971.Kalab, M., Alan-Wojtas, P., and Miller, S.S., Microscopy and other imaging techniques in

food structure analysis, Trends Food Sci. Technol., 6, 177, 1995.Kokini, J.L. et al., The development of state diagrams for cereal proteins, Trends Food Sci.

Technol., 5, 281, 1994.Kokini, J.L., Cocero, A.M., and Madeka, M., State diagrams help predict rheology of cereal

proteins, Food Technol., 49, 74, 1995.Kokini, J.L., Eads, T., and Ludescher, R.D., Research needs on the molecular basis for food

functionality, Food Technol., 47, 36S, 1993.Matuszek, T.S., Raw Materials and Food Processing with Regard to the Predictive Micro-

structure, paper presented at 9th World Congress of Food Science and Technology,Budapest, 1995, p. 136.

Peleg, M., On the use of the WLF model in polymers and foods, Crit. Rev. Food Sci. Nutr.,32, 59, 1993.


Peleg, M., Contact and fractures as components of the rheological memory of solid foods,J. Texture Stud., 3, 194, 1997.

Peleg, M. and Bagley, E.B., Physical Properties of Foods, AVI Publishing Co., Westport, CT,1993.

Peleg, M. and Hollenbach, A.M., Flow conditioners and anti-caking agents, Food Technol.,38, 93, 1984.

Roos, Y.H., Glass transition-related physiochemical changes in foods, Food Technol., 49, 97,1995.

Roos, Y.H. and Karel, M., Plasticizing effect of water on thermal behaviour and crystallisationof amorphous food models, J. Food Sci., 56, 38, 1991a.

Roos, Y.H. and Karel, M., Applying the state diagrams in food processing and productdevelopment, Food Technol., 45, 66, 1991b.

Shoemaker, C.F. and Figoni, P.I., Time-dependent rheological behaviour of foods, FoodTechnol., 38, 112, 1984.

Slade, L. and Levin, H., Beyond water activity: recent advances based on an alternativeapproach to the assessment of food quality and safety, Crit. Rev. Food Sci. Nutr., 30,115, 1991.

Szczesniak, A.S., Objective measurement of food texture, J. Food Sci., 28, 410, 1963.

2051-5871-6149-4/02/$0.00+$1.50© 2002 by CRC Press LLC

Food Colorants

Jadwiga Wilska-Jeszka

CONTENTS

9.1 Introduction ..................................................................................................2059.2 Carotenoids...................................................................................................206

9.2.1 Structure ...........................................................................................2069.2.2 Occurrence .......................................................................................2099.2.3 Carotenoids Used as Food Colorants ..............................................2109.2.4 Physical and Chemical Properties ...................................................2129.2.5 Biological Activity ...........................................................................213

9.3 Chlorophyll...................................................................................................2159.4 Heme Pigments ............................................................................................2179.5 Anthocyanins................................................................................................219

9.5.1 Occurrence and Structure.................................................................2199.5.2 Chemical Properties .........................................................................2209.5.3 Biological Activity ...........................................................................2229.5.4 Stability of Anthocyanins’ Color in Food .......................................223

9.6 Betalains .......................................................................................................2249.6.1 Occurrence and Structure.................................................................2249.6.2 Chemical Properties .........................................................................225

9.7 Quininoid Pigments......................................................................................2269.8 Some Other Natural Pigments .....................................................................226

9.8.1 Riboflavin and Riboflavin 5′phosphate............................................2269.8.2 Turmeric, Curcumin .........................................................................2279.8.3 Caramel ............................................................................................227

9.9 Synthetic Organic Colors.............................................................................228References..............................................................................................................228

9.1 INTRODUCTION

Color is an important quality aspect of both unprocessed and manufactured foods.Natural colorants are unstable; thus the color of food products may provide anindication of biochemical and chemical changes during processing and storage.

However, color cannot be studied without considering the human sensory system.Perception of color is related to three factors: spectral composition of light source,physical object characteristics, and eye sensitivity. Fortunately the characteristic of

9


the human eye for viewing color is fairly uniform, and it is not difficult to replacethe eye by some instrumental sensor or photocell.

The color of food is the result of the presence of natural pigments or addeddyes. Natural pigments are generally considered the pigments occurring in unproc-essed food, as well as those that can be formed upon heating, processing, or storage.These pigments can be divided into five groups:

• Carotenoids: isoprenoid derivatives• Chlorophylls and hemes: porphyrin pigments• Anthocyanins: 2-phenylbenzopyrylium derivatives• Miscellaneous, naturally occurring colorants such as betalains, cochineal,

riboflavin, and curcumin• Melanoidins and caramels: formed during food heating and storage

All these natural pigments are unstable and participate in different reactions, sothe food color is strongly dependent on conditions.

The use of synthetic organic colors has been recognized for many years as the mostreliable and economical method of restoring some of the food’s original shade to theprocessed product. An even more important application of synthetic dyes is using themto improve and standardize the appearance of those products that have little or no naturalcolor present, such as dessert powders, table jellies, ice, and sugar confectioneries. Thesynthetic organic colors are superior to the natural pigments in tinctorial power, rangeand brilliance of shade, stability, ease of application, and cost-effectiveness. However,from a health safety viewpoint, they are not accepted by the consumers, so over the pastyears increasing interest in natural food colorants has been observed.

9.2 CAROTENOIDS

9.2.1 STRUCTURE

Carotenoids are the naturally occurring tetraterpene pigments widely distributedthroughout the living world. The name carotenoids has been derived from the majorpigment of the carrot (Daucus carote L). β-carotene, a symmetrical molecule of 40carbon atoms, consists of 8 isoprene units having 11 conjugated double bonds and2 β-ionone rings (Formula 9.1).

The term carotenoids designates a group of structurally related colorants thatare mainly found in plants. At present, more than 600 carotenoids have been iden-tified. Their basic structure is a symmetrical tetraterpene skeleton, formed by head-to-tail condensation of two 20-carbon units. (Formula 9.1). Based on their compo-sition, carotenoids are subdivided into two groups: carotenes, which contain onlycarbon and hydrogen atoms, e.g., α-, β-, and γ-carotenes and lycopene (Formulae9.2–9.4); and xanthophylls — oxocarotenoids — which contain at least one oxygenfunction, such as hydroxy, keto, or epoxy groups (Formulae 9.5–9.9).

Carotenoids can also contain additional isoprene chains, homocarotenoids, or ifless than 40 carbon atoms, apocarotenoids (Formulae 9.10 and 9.11). In somecarotenoids allenic or acetylenic groups are found.

Food Colorants 207

The color of carotenoid pigments is the result of the presence of a system ofconjugated double bonds. A minimum of seven conjugated double bonds is requiredfor the yellow color to appear. The increase of double bonds results in a shift of themajor adsorption bands to the longer wavelengths, and the hue of carotenoidsbecomes more red. Because of the highly conjugated double-bond system, caro-tenoids show ultraviolet and visible absorption spectrum characteristics. For mostcarotenoids, three peaks, or two peaks and a shoulder, are absorbed in the range of400–500 nm. Absorption maxima and molecular extinction values are significantlyaffected by the solvent used. Thus, for all-trans-β-carotene, the respective wave-length maximum and E1%

1cm are 435 nm and 2592 in petroleum ether, but 465 nmand 2396 in chloroform (Barua et al., 2000).

In unprocessed plants, usually all-trans (all E) double-bond configurations occur,but cis isomers of each carotenoid are also possible. Processing and storage can cause

Formulae 9.1–9.4 Carotenes

β

β

β - Carotene

(1)

β

ε

α - Carotene

(2)

Ψ

β

γ - Carotene

(3)

1

3 Ψ 58 10 12

7 Ψ

Lyckopene

(4)

14

15 14' 12'

15'

10' 8'

7'

6'

4'

2'


Formulae 9.5–9.9 Xanthophylls

HO

OH

β

Lutein

(5)

HO

OH

O

O

Violaxanthin

(6)

HO

β - Crytoxanthin

(7)

OH

O

OH

Capsanthin

(8)

O Canthaxanthin

(9)

O

Food Colorants 209

isomerization of carotenoids in foods and affect the color. The compounds withall-trans configurations have the deepest color. Increasing the number of cis bondsresults in gradual lightening of the color. The cis isomers not only absorb less stronglythan the all-trans isomer, but they also show a so-called cis peak at 330–340 nm.

Many carotenoids have chiral centers that are due to the presence of asymmetriccarbon atoms. However, natural carotenoids exist only in one of the possible enan-tiomeric forms, because the biosynthesis is enantiomere selective.

9.2.2 OCCURRENCE

Carotenoids appear to be synthesized de novo by photosynthetic higher plants,mosses, algae, and nonphotosynthetic bacteria and fungi. All photosynthetictissues contain carotenoids: higher plants in the chloroplasts, although the coloris masked by the chlorophylls, and some bacteria in photosynthetic membranes.The chloroplasts, present in green unripe fruits, in most cases gradually changeinto chromoplasts on ripening, and carotenoid synthesis, often of novel pigments,is enormously stimulated. Typical examples are the tomato and red pepper.Oxygen but not light is required for carotenoid synthesis.

In all photosynthetic organisms carotenoids have two major functions: asaccessory pigments for light harvesting and in the prevention of photooxidativedamage. In plants they are essential components of the light-harvesting antennae,where they can absorb photons and transfer the energy to chlorophyll. The majorcarotenoids that carry out this function in plants are lutein, violaxanthin, neoxan-thin, and β-carotene.

The other function of carotenoids is to protect against photooxidation processesthat are caused by the excited triplet state of chlorophyll. Carotenoid molecules,with nine or more conjugated carbon–carbon double bonds, can absorb triplet stateenergy from chlorophyll and thus prevent the formation of harmful singlet oxygen.

The main carotenoids of green leaves are lutein, violaxanthin, cryptoxanthin,and β-carotene; the others are produced in smaller quantities. Common carotenoids

Formulae 9.10 and 9.11 Apocarotenoids

β

CHO

β - Apo - 8' - carotenal

(10)

CH3O

O

COHO

Bixin

(11)


in fruits are β-carotene, lycopene, and different xanthophylls. The latter group areusually present in esterified form. Some of the carotenoids, such as β-carotene,lycopene, and zeaxanthin, are very widely distributed and so become important asfood components. However, the content of carotenoids usually does not exceed 0.1%dry weight (Table 9.1) In the plant products carotenoids may occur as simple or verycomplex mixtures; some of the most complex are found in citrus fruits. The simplestcarotenoids usually exist in animal products, because the animal organism is limitedin its ability to absorb and deposit them. The compounds, which have been isolatedonly from animal tissues, mainly xanthophylls, are the result of metabolic changes,generally oxidative, in the ingested carotenoids. Crude vegetable oils contain caro-tenoids, but bleaching and hydrogenation leads to almost complete degradation ofthese pigments. Particularly rich in carotenoids (0.05–0.2%) is crude palm oil,containing mainly α- and β-carotenes. Egg yolk contains only xanthophylls, mainlylutein, zeaxanthin, and cryptoxanthin (0.3–8.0 mg/kg).

9.2.3 CAROTENOIDS USED AS FOOD COLORANTS

The most commonly used natural carotenoid extracts for foodstuffs are annatto,paprika, and saffron. Many other sources, including alfalfa, carrot, tomato, citruspeel, and palm oil, are also utilized.

Annatto (E 160(b)) is an orange-yellow oil-soluble natural pigment extractedfrom the pericarp of the seed of a Bixa orellana L. tree. The major coloring com-ponent of this extract is the diapocarotenoid bixin (Formula 9.11). Several otherpigments, mainly degradation products of bixin, are also present, including trans-bixin, norbixin, and trans-norbixin. Bixin is a methyl ester of a dibasic fatty acidthat, on treatment with alkalis, is hydrolyzed to water-soluble norbixin. Two typesof annatto are therefore available: an oil-soluble extract containing bixin and a water-soluble extract containing norbixin.

Paprika oleoresin (E 160(c)) is an orange-red oil-soluble extract from sweet redpeppers Capsicum annum. The major coloring compounds are xanthophylls: cap-santhin (Formula 9.8), capsorubin as their dilaurate esters, and β-carotene. Thepresence of characteristic flavoring and spicy pungency components limits applica-tion of this extract in foodstuffs.

Saffron, an extract of flowers of Crocus sativus, contains the water-solublepigment crocin; the digentiobioside of apocarotenic acid, crocetin; zeaxanthin, a β-carotene; and characteristic flavoring compounds. The yellow color of this pigmentis attractive in beverages, cakes, and other bakery products. However, use of thiscolorant is restricted by its high price.

Carrot extracts (E 160(a)), carrot oil, palm oil, and related plant extract are alsoavailable on the market. Their main components are β- and α-carotenes (Formulae9.1 and 9.2, respectively). Processes for the commercial extraction of carotene fromcarrots were developed. Purified crystalline products contain 20% α-carotene and80% β-carotene and may be used for coloring fat-based products as dispersion ofmicrocrystals in oil.

Individual carotenoid compounds — β-carotene, β-apo-8'carotenal (Formula9.10), apocarotenoic ethyl ester, and canthaxanthin (Formula 9.9) — are synthesized

Foo

d C

olo

rants

211

for use as food colorants for edible fats and oils. Their properties are given in Table 9.2. The carotenoids pigments, in combination withsurface active agents, are also available as microemulsions for coloring foods with a high water content.

TABLE 9.1Quantities of Different Carotenoids in Some Vegetables and Fruits (mg/100 g of Edible Portion)

Vegetable or Fruit β-Carotene α-Carotene Lycopene Lutein Violaxanthin β-Cryptoxanthin Total

Kale 8.68 0.15 — 18.6 5.81 0.12 34.76Spinach 3.68 0.09 — 9.54 3.04 — 17.31Lettuce 1.68 0.04 — 2.92 2.36 0.03 8.48White cabbage 0.034 — — 0.08 0.07 0.002 0.25Red paprika 3.78 0.51 0.13 0.25 — — 30.37a

Green paprika 0.11 0.01 — 0.41 0.12 0.002 0.70Tomato 0.89 0.15 11.44 0.21 — — 12.7Broccoli 0.32 — — 0.8 0.18 0.011 1.56Carrot 9.54 4.89 — 0.36 — — 15.90Blackberry 0.13 0.02 — 0.65 0.06 0.008 0.90Strawberry 0.006 0.0002 — 0.04 0.003 0.0005 0.05Nectarine 0.40 0.14 — 0.98 0.51 0.08 2.40Apricot 0.90 0.02 — 0.041 0.02 0.06 1.13Grapefruit 0.59 — 2.77 0.02 0.005 0.012 3.50Orange 0.013 0.006 — 0.02 0.22 0.05 0.40

a Includes 13.94 mg/100 g of capsanthin/capsorubin and 5.0 mg/100 g of capsolutein.

Source: Adapted from Muller, H., Z. Lebensm. Unters. Forsch. A, 204, 88, 1997.


9.2.4 PHYSICAL AND CHEMICAL PROPERTIES

Carotenoids are extremely lipophilic compounds that are almost insoluble in water. Inaqueous surroundings they tend to form aggregates or adhere to surfaces. They aresoluble in nonpolar organic solvents such as hexane, halogenated hydrocarbons, ortetrahydrofurane. In oils their solubility is rather low, particularly in a pure crystallinestate. In the organism they are located in cellular membranes or in lipophilic compart-ments. In some plants hydroxylated carotenoids are esterified with various fatty acids,which make them even more lipophilic.

With their extended system of conjugated double bonds, the carotenoids containa reactive electron-rich system that is susceptible to reactions with electrophiliccompounds. This structure is responsible for high sensitivity of carotenoids to oxygenand light. The central chain of conjugated double bonds can be oxidatively cleavedat various points, giving rise to the family of apocarotenoids.

Most carotenoids (but not vitamin A) serve as singlet oxygen quenchers. Singletoxygen 1O2 interacts with carotenoid to give triplet states of both molecules. The energyof excited carotenoid is dissipated through vibrational interaction with the solvent torecover the ground state. Carotenoids are the most efficient naturally occurring quench-ers of singlet oxygen. They may also participate in the propagation step of the oxidationprocess as chain-breaking antioxidants that scavenge reactive peroxyl radicals. How-ever, carotenoids serve this function best at low oxygen tensions. At higher oxygenlevels, a carotenoid intermediate radical might add oxygen to form carotenoid peroxylradicals, which could act as prooxidants, initiating the process of lipid peroxidation.

On the other side, radicals and peroxides, occurring in food as a result of lipidoxidation, accelerate oxidative degradation of carotenoid pigments, which leads toformation of epoxides located at the β-ionone ring, β-apo-carotenones, and β-apo-carotenals of different chain lengths. Lipoxygenase involved in the decay of vegetablematter may also cause the destruction of carotenoids. Antioxidants, including ascorbicacid and its derivatives, tocopherols, and polyphenolics, are used to suppress thisoxidative degradation.

Due to oxidative degradation of carotenoids, aroma compounds are also formed,including β-ionone with an odor threshold value of 14 ng/g in water. The formation

TABLE 9.2Properties of Carotenoids Used as Food Colorants

Carotenoid Color

Solubility (g/100 ml) at 20°C

λλλλmax

Vitamin AActivity (IU/mg)Oils Ethanol

β-Carotene Yellow 0.05–0.08 0.01 455–456 1.67Apocarotenoid ester Yellow to orange 0.7 0.1 448–450 1.2Apocarotenal Orange to red 0.7–1.5 0.1 460–462 1.2Canthaxanthin Red 0.005 0.01 468–472 0

Source: Adapted from Klaui, H. and Bauernfeind, J.C., Carotenoids as Colorants and Vitamin APrecursors, CRC Press, Inc., Boca Raton, FL, 1981.

Food Colorants 213

of β-ionone in dehydrated carrots causes the undesired off-flavor “odor of violets.”Unsaturated ketones derived from carotenoid degradation are readily further oxidized.The stability of carotenoids in frozen and heat-sterilized foods is quite high, but it ispoor in dehydrated products, unless the products are packaged in inert gas. Dehydratedcarrots fade rapidly.

9.2.5 BIOLOGICAL ACTIVITY

Carotenoids are known to have different biological functions. According to Berg etal. (2000) the most important functions of some groups of carotenoids are:

• Provitamin A activity: β-carotene, α-carotene, and β-cryptoxanthin• Antioxidant activity: all carotenoids• Cell communication: β-carotene, canthaxanthin, and cryptoxanthin• Immune function enhancers: β-carotene• Ultraviolet skin protection: β-carotene and lycopene• Macula protection: lutein and zeaxanthin

The best documented and established function of some carotenoids is theirprovitamin A activity, especially of β-carotene. One mole of β-carotene can theo-retically be converted, by cleavage of C 15 = C 15' double bond, to yield two molesof retinal (Reaction 9.1). However, the physiological efficiency of this processappears to be only 50%. The observed average efficiency of intestinal β-caroteneabsorption is only two thirds of the total content. Thus, a factor of 1/6 is used tocalculate the retinol equivalent (RE) from β-carotene, but only 1/12 from the otherprovitamin A carotenoids in food (Combs, 1992). In fruits and vegetables β-carotenecontent is used as a measure of the provitamin A content.

The other very important biological function of carotenoids is linked with theirantioxidant activity. An antioxidant has been defined as a substance that, at lowconcentration relative to an oxidizable substrate, can suppress, delay, or preventoxidation of the substrate. Carotenoids act as antioxidants against lipid peroxidationby quenching singlet oxygen and trapping free peroxyl radicals. The structure ofcarotenoid, in particular the length of the polyene chain, significantly influences itsantioxidant properties.

Different methods have been used for determination of antioxidant activity.Rice-Evans et al. (1997) have used a method based on the ability to quench thecolored ABTS radicals to compare antioxidant activity of some carotenoids. Theresults were calculated as the Trolox equivalent of antioxidant capacity (TEAC).The activity of Trolox, the water soluble α-tocopherol analog, was given a valueof 1. A higher value in this assay indicated a higher activity of the carotenoid(Table 9.3).

Lipid peroxidation is a problem not only in the edible oil, but also in the humanbody. Excess production of oxygen radical species and particularly hydroxyl radicalscan affect lipid cell membranes to produce lipid peroxides and reactive oxygenspecies (ROS), which are linked to a variety of diseases, such as cancer and cardio-vascular disease, and acceleration of the aging process.


Reaction 9.1 Formation of vitamin A from b-carotene

TABLE 9.3Antioxidant Activities of Some Carotenoids

Carotenoid TEAC (mM)

Lycopene 2.9β-Cryptoxanthin 2.0β-Carotene 1.9Lutein 1.5Zeaxanthin 1.4α-Carotene 1.3

Source: Adapted from Rice-Evans, C. et al., FreeRad. Res., 26, 381, 1997.

β

β

β

β

15

15'

β - carotene

β - carotene - 15, 15' - oxygenase

CHO

CH2OH

Retinal

Retinol

retinal aldehyde

reductace

alcohol

dehydrogenase

Food Colorants 215

It was observed that people with low carotenoid intake or low blood levels havean increased risk of degenerative diseases. In a number of these diseases free radicaldamage plays a role in the pathophysiology of the disease. Earlier studies were focusedmainly on β-carotene and the lycopene protective effect against prostate and lungcancer, but there is as yet no definitive proof for a causal relationship or for a beneficialantioxidant effect of carotenoids.

The cancer-preventing effect of β-carotene has been investigated in several inter-vention trials. However, only in one of these studies, the Linxian study, was a protectiveeffect found for a combined β-carotene, vitamin E, and selenium supplementation. Inthe other studies, no protective effect was found, and in some cases, a higher risk oflung cancer has been observed after high doses of β-carotene. Therefore, the conclusionfrom these studies is that high-dose supplements of β-carotene are contradicted forheavy smokers, but could give a beneficial effect to individuals with a poor baselinecarotenoid status. Probably a diet rich in high-carotenoid-containing fruits and vege-tables is more efficacious than individual carotenoid compounds, because it representsa lower, regular intake of several constituents with several mechanisms of action asopposed to a high intake of one constituent with limited functions (Berg et al., 2000).

9.3 CHLOROPHYLL

Chlorophyll is the most widely distributed natural plant pigment and acts as a catalystin biochemical photosynthesis. In higher plants and algae, except the blue-greens,chlorophyll is found in chloroplasts, while in blue-green algae and photosyntheticbacteria, it is located on the intracellular lamellae. In living plant tissues chlorophyllis present in colloidal suspension in chloroplast cells, in the form associated withprotein and saccharides. The chlorophyll pigments are the same in all plants. Apparentdifferences in color are due to the presence of other associated pigments, in particularxanthophylls and carotenes, which always accompany the chlorophylls and act as asunscreen for the light-sensitive chlorophyll. Typical leaf material contains chloro-phylls (about 2.5 mg/g), xanthophylls (0.3 mg/g), and carotenes (0.15 mg/g ) (Hum-phrey, 1980). In many fruits chlorophyll is present in an unripe state and graduallydisappears during ripening, as the yellow and red carotenoids take over.

The chlorophylls are tetrapyrrole pigments in which the porphyrin ring is in thedihydro form, and the central metal atom is magnesium (Formula 9.12). There aretwo chlorophylls: blue-green and yellow-green, occurring in a ratio of about 3:1.The yellow-green chlorophyll differs from the blue-green chlorophyll in that themethyl group on carbon 3 is replaced with an aldehyde group. Chlorophyll is adiester: one group is esterified with methanol and the other with phytyl alcohol.

The important chemical characteristics of chlorophylls are:

• The easy loss of magnesium in dilute acids or replacement of Mg2+ byother divalent metals

• The hydrolysis of the phytyl ester in dilute alkalis or transesterificationby lower alcohols

• The hydrolysis of the methyl ester and cleavage of the isocyclic ring instronger alkalis


Removal of magnesium gives olive-green phaeophytin a and b. Replacing mag-nesium by iron or tin ions yields grayish brown compounds, while copper or zincions retain the green color. Upon removal of the phytyl group by hydrolysis in dilutealkali or by the action of chlorophyllase, green chlorophyllins or cholorphylids areformed. Removal of magnesium and the phytyl group results in phephorbide for-mation (Figure 9.1).

Chlorophylls and pheophytins are lipophylic, due to the presence of the phytolgroup, while chlorophyllins and pheophorbids without phytol are hydrophylic. Thecopper complexes of both pheophytin and pheophorbid have the metal firmly bound;it is not liberated even by the action of concentrated hydrochloric acid, and it is notremoved to any appreciable extent upon metabolism; thus it is acceptable for thecoloration of foodstuffs. Both coppered and uncoppered chlorophyll and their deriv-atives are available as food colorants.

The oil-soluble chlorophylls (uncoppered and coppered pheophytin) are notwidely used for food coloring, because commercial purification has not proven to

Formula 9.12 Chlorophyll

O

OCCH2CH2

H

1 2

3

4

6 5

8

7N

N

Mg

N

N

R

CH2CH3

CH3 CH CH2

O

H

C O

Chlorophyll a R= —CH3Chlorophyll b R= —CHO

CH3OCH3

H3C

Food Colorants 217

be as satisfactory as that for the water-soluble derivatives. Their stability is goodtoward light and heat but poor to acid and alkaline conditions. Applications are foundin canned products and confectioneries on the levels of 0.5–1 g/kg.

The water-soluble chlorophyllins (uncoppered and coppered sodium or potas-sium pheophorbide) have good stability toward light and heat and moderate stabilityto both acid and alkalis. Food color usage is in canned products, confectioneries,soups, and dairy products.

9.4 HEME PIGMENTS

The color of meat is the result of the presence of two pigments: myoglobin andhemoglobin. In both pigments the heme group is composed of the porphyrin ringsystem and the central iron atom bound with globin. In myoglobin, the proteinportion has a molecular weight of 17,000, and in hemoglobin about 67,000.

The central iron atom has six coordination bonds, each representing an electronpair accepted by the iron from five nitrogen atoms; four from the porphyrin ringand one from a histidyl residue of the globin. The sixth bond is available forbinding with any atom that has an electron pair to donate, e.g., O2 or NO. Theoxidation state of the iron atom and physical state of globin play an importantrole in meat color formation.

FIGURE 9.1 Transformation of chlorophyll pigments.

Mg2+

phytolchlorophilase

PHEOPHYTIN(olive-green)

acid

Mg2+phytol

alkali

methanol

CHLOROPHYLL(green)

phytol

acid

Mg2+

acid

PHEPHORBIDE(olive-brown)

phytol

alkali

CHLOROPHYLLIN(green)

CHLOROPHYLID(green)


In fresh meat, in the presence of oxygen, the reversible reaction of myoglobin(Mb) with oxygen occurs and results in the formation of bright-red-colored oxy-myoglobin (MbO2). In both pigments the iron is in ferrous form, and upon oxidationto ferric state, the brownish metmyoglobin (MMb) is formed.

The oxymyoglobin and myoglobin exist in a state of equilibrium with oxy-gen. The ratio of these pigments depends on oxygen pressure. In meat there isa slow oxidation of the heme pigments to metmyoglobin. Metmyoglobin cannotbind oxygen.

Heating of meat results in the denaturation of the globin linked to iron, as wellas in the oxidation of iron to the ferric state and formation of different brown hemepigments named hemichrome.

In the curing of meats, the heme pigments react with nitrite of the curing mixture,and the red-colored nitrite–heme complex nitrosomyoglobin is formed, but it is notparticulary stable. More stable is the pigment with a denatured globin portion, namednitrosylhemochromogen, found in meat heated at temperatures above. The reactions ofheme pigments in meat have been summarized in Figure 9.2 and presented in Figure 7.3.

In the presence of thiol compounds as reducing agents in the reversible reaction,myoglobin may form a green sulfmyoglobin. Other reducing agents, e.g., ascorbate,lead to formation of cholemyoglobin. This reaction is irreversible.

A potential source of red and brown heme pigments is animal blood and itsdehydrated protein extracts, which mainly consist of hemoglobin and may be usedas red and brown colorings to meat products. However, in most countries their usageas a food coloring agent is not permitted.

Reaction 9.2 Basic transformation of myoglobin

FIGURE 9.2 Transformation of myoglobin in meat; dMMb and dMbNO, denatured formsof pigments.

MbO2Mb MMb

red purplish red brownish

dMMb MMb MMbNObrownish brownish bright red

heating NO

MbO2 Mb MbNO dMbNO red purplish red bright red bright red

heating oxidation reduction reduction

-O2

+O2

NO heating

Food Colorants 219

9.5 ANTHOCYANINS

9.5.1 OCCURRENCE AND STRUCTURE

Anthocyanins are among the most important groups of plant pigments. They arepresent in almost all higher plants and are the dominant pigments in many fruitsand flowers, giving red, violet, or blue color. They play a definite role in attractinganimals in pollination and seed dispersal. They may also have a role in the mecha-nism of plant resistance to insect attack.

Anthocyanins are part of the very large and widespread group of plant constit-uents known as flavonoids, which possess the same C6–C3–C6 basic skeleton. Theyare glycosides of polyhydroxy and polymetoxy derivatives of 2-phenylbenzopyry-lium or flavylium cation (Formula 9.13). Differences between individual anthocya-nins are: the number of hydroxyl groups in the molecule; the degree of methylationof these hydroxyl groups; the nature, number, and position of glycosylation; and thenature and number of aromatic or aliphatic acids attached to the glucosyl residue.From about 20 known naturally occurring anthocyanidins, only 6 occur most fre-quently in plants: pelargonidin, cyanidin, peonidin, delphinidin, petunidin, and mal-vidin (Table 9.4). Substitution of the hydroxyl and methoxyl groups affect the color

Formula 9.13 Flavylium cation

TABLE 9.4Naturally Occurring Anthocyanidins

Anthocyanidin R3' R5' λmax(nm) Color

Pelargonidin (Pg) H H 520 OrangeCyanidin (Cy) OH H 535 Orange-redPeonidin (Pn) OCH3 H 532 Orange-redDelphinidin (Dp) OH OH 546 Bluish-redPetunidin (Pt) OCH3 OH 543 Bluish-redMalvidin (Mv) OCH3 OCH3 542 Bluish-red

O

OHOH

HO

OH

R3'

R5'

35

7

3'

5'

+2

46

8

4'

6'

2'


of the anthocyanins. An increase in the number of hydroxyl groups tends to deepenthe color to a more bluish shade. An increase in the number of methoxyl groupsincreases redness.

Because of the possibility of different -ose and acid substitutions at differentpositions, the number of anthocyanins is 15–20 times greater than the number ofanthocyanidins (Mazza and Miniati, 1993). The -ose molecules most commonlybonded to anthocyanidins are glucose, galactose, rhamnose, arabinose, and di- andtrisaccharides, formed by combinations of these four monosaccharides. The mostcommon class of anthocyanins are 3-monosides, 3-biosides, 3,5-diglycosides, and3,7-diglycosides; however, glycosylation of 3', 4', and 5' hydroxyl groups is alsopossible. The composition and content of anthocyanins in fruits are very diversified(Table 9.5).

9.5.2 CHEMICAL PROPERTIES

In aqueous media, most of the natural anthocyanins behave like pH indicators, beingred at low pH, bluish at intermediate pH, and colorless at high pH. According toBrouillard (1982), in acidic and neutral media four anthocyanin structures exist inequilibrium: the red flavylium cation (AH+), blue or red quinonoidal base (A),colorless carbinol pseudobase (B), and colorless chalcone (C) (Reaction 9.3).

The pH of the medium plays a particularly important role in the equilibriumbetween these different anthocyanin forms, and consequently in color modification.In strongly acid solution, at a pH below 2, the red cation AH+ is the dominant form.As the pH is increased, a rapid proton loss occurs to yield the red or blue quinoidalbase A, usually existing in two forms (Figure 9.3). On standing, a further reactionoccurs, i.e., hydration of flavylium cation AH+, to give colorless carbinol pseudo-base B. Relative amounts of forms AH+, A, B, and C at equilibrium vary with bothpH and the structure of anthocyanins. For the common anthocyanin 3-glycosides

TABLE 9.5Anthocyanins in Some Fruits: Composition and Content

Fruits Main AnthocyaninsTotal Anthocyanins

(mg/100 g)

Blackberry Cy 3-Glu, Cy 3-Rut 83–326Bilberry Dp 3-Gal, Mv 3-Glu, Pt 3-Glu 250–490Black current Cy 3-Rut, Cy 3-Glu, Dp 3-Rut, Dp 3-Glu 250Chokeberry Cy 3-Gal, Cy 3-Arab, Cy 3-Glu, Cy 3-Xyl 520–800Cranberry Cy 3-Gal, Cy 3-Arab, Pn 3-Gal, Pn 3-Arab 78Strawberry Pg 3-Glc, Cy 3-Glc 7–30Red grapes Mv 3-Glu, Dp 3-Glu, Pt 3-Glu, Pn 3-Glu,

3-acetylglucoside, 3-p-coumarylglucoside30–750

Source: Adapted from Macheix, J.J. et al., Fruit Phenolics, CRC Press, Boca Raton, FL, 1990; andWang, H. et al., J. Agric. Food Chem., 45, 304, 1997.

Food Colorants 221

or 3,5-diglycosides, the principal product formed on raising the pH above 3 is thecolorless carbinol pseudobase B (Figure 9.3). At this pH, however, small amountsof the blue quinoidal base and the colorless chalcones are also present and increasewith increasing pH. Between pH values of 4 and 6 very little color remains, sincethe amounts of the colored forms (AH+ and A) are very small (Reaction 9.3). Byvarying the substitution pattern of the flavylium ring, anthocyanidin, which existsprimilarly in quinoidal or chalcone form, can be prepared (Jacobucci and Sweeny,1983), but such anthocyanin compounds are not found in plants.

The color of anthocyanins containing media depends on different factors. The mostimportant are structure and concentration of anthocyanin pigments, pH, and presenceof copigments and metallic ions, all of which influence the color shade. Also importantare the temperature and presence of oxygen, phenoloxidase, ascorbic acid, and sulfurdioxide, all of which influence the anthocyanins’ degradation rate and color stability.

Reaction 9.3 Structural anthocyanin transformations in aqueous media

FIGURE 9.3 Distribution of anthocyanin structures as functions of pH.

OO

OH

O Gl

OH

O

OH

OH

HO

GlO

OHO

OH

OH

HO

GlO

OH

O

OH

O

HO

GlO OH

HOO

OHGl

O

OH

O+

OH

OH

HO

GlO

A

B

C

-H++H+ +H+

-H+

AH+: Flavylium cation

A: Quinonoidal bases

- H+/H2O

B: Carbinol pseudobase CE: E - Chalcone

CZ: Z - Chalcone

0

50

100

1 2 3 4 5 6

AH+

B

CA

pH

% o

f to

tal


The structure of the anthocyanin molecule has a marked effect on the colorintensity and stability. The increase of the number of hydroxyl groups in B-ringshifts the absorption maximum to longer wavelengths, and the color changes fromorange to bluish red. Methoxyl groups replacing hydroxyl groups reverse this trend.The hydroxyl group at C-3 is particularly significant because it shifts the color fromyellow-orange to red. The same hydroxyl, however, destabilizes the molecule; the3-deoxyanthocyanidins are much more stable than the other anthocyanidins. Simi-larly, the presence of a hydroxyl group at C-5 and a substitution at C-4 both stabilizethe colored forms. Glycosylation also affects the stability of these pigments; thehalf-life of anthocyanidins is significantly lower than that of their corresponding 3-glucosides. Anthocyanins containing two or more aromatic acyl groups, such ascinerarin or zebrinin, are stable in neutral or weakly acidic media. This is possiblya result of hydrogen bonding between phenolic hydroxyl groups in anthocyanidinsand aromatic acids. Brouillard (1981) observed that diacylated anthocyanins arestabilized by sandwich-type stacking caused by the hydrophobic interaction betweenthe anthocyanidin ring and the two aromatic acyl groups.

The increase in anthocyanins’ concentration results in an increase in absorbanceat λmax, greater than expected according to the Beer–Lambert law. It is probablyconnected with anthocyanins’ self-association.

Intermolecular copigmentation of anthocyanins with other flavonoids, somephenolic acids, alkaloids, and other compounds, including anthocyanins themselves,increases the color intensity (hyperchromic effect) and causes a shift in the wave-length (batochromic shifts), giving purple to blue colors. The intensity of the copig-mentation effect depends on several factors, including type and concentration ofboth anthocyanins and copigments, pH, and temperature of the solvent (Brouillardet al., 1991). The pH value for the maximum copigmentation effect is about 3.5 andmay vary slightly, depending on the pigment–copigment system. Color intensifica-tion by copigmentation increases with increasing ratios of copigment to anthocya-nins. Increasing temperature strongly reduces the color-intensifying effect. Thecopigmentation phenomenon is widespread in nature and also occurs in fruit andvegetable products such as juices and wines.

In the presence of metals anthocyanins can form purplish blue or slate-graypigments called lakes. This reaction may induce color changes, if fruit products,during processing or storage, are in contact with metals such as tin, aluminum,or iron.

9.5.3 BIOLOGICAL ACTIVITY

Anthocyanins are natural colorants belonging to the large family of phenolic com-pounds: flavonoids. For many years they have been known to display differentpharmacological and biological activities, such as vasoprotective, anti-inflamatory,and radioprotective agents. Additionally, they prevent cholestrol-induced arterioscle-rosis and heart disease. However, the most important properties of anthocyaninsseem to be their activities as potent free radical scavengers and powerful chain-breaking antioxidants. Similar to other flavonoids, they can react with reactiveoxygen radicals, such as hydroxyl radical, superoxide anion radicals, and lipid

Food Colorants 223

peroxyl radical, and inhibit lipid peroxidation at the early stage. This is very impor-tant because in vivo lipid peroxidation has been implicated as the primary cause ofcoronary heart disease, atherosclerosis, cancer, and aging. The antioxidant effectivityof anthocyanin pigments is structure dependent and for the main aglicons, it is abouttwo times higher than those of vitamins C and E.

Recently, increasing attention has been focused on anthocyanins as naturalantioxidants, because of their ubiquitous presence in plant products, particularly infruits, juices, and red wine. The daily intake of anthocyanins in humans is as highas 200 mg/day. Despite relatively high potential intake in humans, the physiologicalimpact of the anthocyanins is not well recognized, because of the lack of purecompounds and their low stability. Anthocyanin-enriched materials, of differentpurities, from the skin of grapes and other by-products of wine and juice manufactureare produced in different countries. One of the better known, commercially availableanthocyanin concentrates is the extract of Vaccinium myrtillus, bilberry (VMA),which contains glycosides of delphinidin and cyanidin and is used to treat variousmicrocirculation diseases resulting from capillary fragility (Wang et al., 1997). Redwine — much more than white wine and grape juice — is also recognized as a richsource of natural antioxidants. It has been demonstrated that red wine has superoxideradical scavenging potential and is able to effectively inhibit oxidation of low densitylipoproteins (LDLs) in vitro and in vivo. However, in all these products not onlyanthocyanins but also other phenolic antioxidants, such as flavonols and flavanols,are present and may influence the biological and antioxidant activity. Therefore, theconsumption of fruits rich in anthocyanins and red wine appears to be a good meansto impede the lipid oxidation process responsible for different diseases and aging.

9.5.4 STABILITY OF ANTHOCYANINS’ COLOR IN FOOD

Anthocyanins appear to have low stability in all products manufactured from fruits.This limits the use of these pigments as food colorants. Two main groups of factorsare responsible for the stability of anthocyanins’ color in fruits during processing:the initial composition of the fruit, with regard to anthocyanins and other constitu-ents, including enzymatic systems; and the processing factors, such as temperature,light, and presence of oxygen.

Several enzymes and in particular phenolases, peroxidases, and β-glucosidasescan decrease the quality of the initial product during the extraction of fruit juicesor the preparation of processed products, leading to browning and loss of color byenzymatic degradation of anthocyanins. Anthocyanins themselves are not good sub-strates for o-diphenol oxidase, but are instead oxidized by chlorogenic acid ↔chlorogenoquinone redox shuttle phenomena. Thus enzymatic oxidation of chloro-genic acid may by combined with nonenzymatic oxidation and polymerization ofanthocyanins. The same phenomenon has been observed in the presence of catechins.

Ascorbic acid may have a protective effect with regard to anthocyanins, sinceit reduces the o-quinones formed before their polymerization. However, ascorbicacid, as well as products of its degradation, increases anthocyanins’ degradation rate.

Sulfur dioxide, widely used in fruit processing, at concentrations as low as 30mg/kg, inhibits the enzymatic degradation of anthocyanins. At high concentrations


of the order of 500–2000 mg/kg, it forms a colorless SO2–anthocyanin complex.This is a reversible reaction: after removal of sulfur dioxide, the color turns red again.

Regardless of the favorable action of high temperatures on the blockage ofenzymatic activities, anthocyanins are readily destroyed by heat during processingand storage. A high-temperature, short-time process was recommended for bestpigment retention. For instance, in red fruit juices heated 12 min at 100°C, antho-cyanin losses appear to be negligible.

The reaction listed above can proceed with different rates and can bring aboutdifferent changes in color, depending on the composition of food products. Mostfrequently the red color slowly turns brown. However, in correctly processed andstored fruits, color changes are so slow that they only slightly affect consumerappreciation of fruit products.

Anthocyanin concentrate may be used as a food colorant at a pH <4.

9.6 BETALAINS

9.6.1 OCCURRENCE AND STRUCTURE

Betalains occur in centrospermae, mainly in red beets, but also in some cactus fruitsand mushrooms. They consist of red-violet betacyanins (λmax ~ 540 nm) and yellowbetaxanthins (λmax ~ 480 nm). About 50 betalains have been identified. The majorbetacyanin is betanin (Formula 9.14), glucoside of betanidin, which accounts for

75–95% of the total pigments of beets. The other red pigments are isobetanin (C-15epimer of betanin), prebetanin, and isoprebetanin. The latter two are sulfate monoestersof betanin and isobetanin, respectively. Unlike anthocyanins, betanins cannot be hydro-lyzed to aglycone by acid hydrolysis without degradation. The major yellow pigmentsare vulgaxanthin I and II (Formula 9.15). High betalain content in beetroot, on average1% of the total solids, makes this vegetable a valuable source of the food colorant.

Formula 9.14 Betanin and isobetanin

N COOH

H

HOOC

H

+

HON COO-

HGlO

N COOH

H

+

HO N COO-

HGlO

H

HOOC

Betanin Isobetanin

Food Colorants 225

9.6.2 CHEMICAL PROPERTIES

The color stability of betanin solution is strongly influenced by pH and heating.Betanin is stable at pH values of 4–6, but thermostability is greatest between pHvalues of 4 and 5. As a result of betanin degradation cyclo-DOPA and betalamicacid are formed (Reaction 9.4). This reaction is reversible (Czapski, 1985). Lightand air have a degrading effect on betanin. These effects are cumulative, but someprotection may be offered by antioxidants such as ascorbic acid. Small amountsof metallic ions increase the rate of betanin degradation. Therefore a chelatingagent can stabilize the color. Many protein systems present in food products alsohave some protective effect.

Formula 9.15 Vulgaxanthins

Reaction 9.4 Degradation of betanin

+

NH

HOOC

H

COOH

NH

RO

COO-

R = —NH2 vulgaxanthin IR = —OH vulgaxanthin II

+

N COOH

H

HOOC

H

GlO

HO N

H

COO-

GlO

HON

H

COOH

H

N COOH

H

HOOC

H

OH

H2O

H2O

+

-

+

Betanin Cyclodopa glucoside Betalamic acid


Beetroot red (E 162), available as liquid beetroot concentrate and as beetrootconcentrate powders, is suitable for products of relatively short shelf life, which donot undergo as severe heat treatment as meat and soya protein products, ice cream,and gelatin desserts.

9.7 QUININOID PIGMENTS

These pigments are widely distributed. They are the major yellow, red, and browncoloring materials of roots, wood, and bark. They also occur at high levels in certaininsects. The largest group is that of anthraquinone pigments. The most importantqininoid pigments commercially available for use in foodstuffs are cochineal andcochineal carmine.

Cochineal (E 120) is the red coloring matter extracted from the dried bodies offemale insects of the species Dactylopius coccus Costa or Coccus cacti L. Theseinsects are cultivated on the cactus plants in Peru, Equador, Guatamala, and Mexico.

The major pigment of cochineal is polyhydroxyanthraquinone C-glycoside, car-minic acid (Formula 9.16), which may be present at up to 20% dry weight of themature insects. Cochineal extract or carminic acid are rarely used as coloring mate-rials for food, but are usually offered in the form of their lake. Aluminum complexes(lakes) can be prepared with ratios of cochineal and aluminum varying from 8:1 to2:1, having corresponding shades from pale yellow to violet.

Cochineal carmine is insoluble in cold water, dilute acids, and alcohol and slightlysoluble in alkali, giving a purplish red solution. The shade becomes more blue at higherpH values. Cochineal carmine is stable toward light and heat, but the stability to sulfurdioxide is poor. In powdered form this pigment can be used for coloring various instantfoodstuffs, in alkaline solutions, and in ammonia for coloring different foods, includingbaked products, yogurts, soups, deserts, confectioneries, and syrups.

9.8 SOME OTHER NATURAL PIGMENTS

9.8.1 RIBOFLAVIN AND RIBOFLAVIN 5′′′′PHOSPHATE

Riboflavin, vitamin B2 (Formula 9.17), is a yellow pigment present in many productsof plant and animal origin. Milk and yeast are the best sources of riboflavin.

Formula 9.16 Carminic acid

HOOC

HO

CH3 O

O

OH

Gl

OH

OH

Food Colorants 227

It is an orange-yellow crystalline powder, intensively bitter tasting, that is veryslightly soluble in water and ethanol, affording a bright green-yellow fluorescentsolution. Riboflavin is stable under acidic conditions, but unstable in alkaline solutionand when exposed to light. Reduction produces a colorless leuko form, but color isregenerated again in contact with air.

Riboflavin-5'-phosphate sodium salt is much more soluble in water than theunesterified riboflavin and is not so intensely bitter. It is one of the physiologicallyactive forms of vitamin B2. It is more unstable to light than riboflavin. Both formscan be used as coloring and an enriching food additive to cereal, dressing, and cheese.

9.8.2 TURMERIC, CURCUMIN

Turmeric or curcumin is the fluorescent-yellow-colored extract from the rhizome ofvarious species of curcuma plant, Curcuma longa L. The main pigment of curcumais curcumin (Formula 9.18).

Turmeric oleoresin is insoluble in water but soluble in alkalis, alcohols, andglacial acetic acid. This pigment has a strong characteristic odor and sharp taste,and is utilized for both its taste and color properties as an additive to canned products,soups, mustards, and other products.

9.8.3 CARAMEL

Caramel is the amorphous dark brown coloring material formed by heating saccha-rides in the presence of selected accelerators. It consists of a mixture of volatile andnonvolatile low-molecular-weight compounds and high molecular compounds. Thecomposition and coloring power of caramel depend on the type of raw material and

Formula 9.17 Riboflavin

Formula 9.18 Curcumin

N

N N O

NH

O

(HCOH)3

CH2OH

CH2

H3C

H3C

HO

O

OH

O

H3CO OCH3


process used. Both Maillard-type and caramelizing reactions are involved, and thecommercial products are extremely complex in composition. More-detailed infor-mation on caramel is given in Chapter 5.

9.9 SYNTHETIC ORGANIC COLORS

The synthetic food colorants, according to their chemical structure, belong tomono-, di-, and trisazo, triarylmethane, xanthene, quinoline, and indigoid. Theycan also be divided into water-soluble, oil-soluble, insoluble (pigment), and surfacemarking colors.

Water solubility is conferred on many dyes by introducing to the molecule atleast one salt-forming group. The most common is the sulfonic group, but carboxylicacid residues can also be used. These dyes are usually isolated as sodium salts. Theyhave colored anions and are known as anionic dyes. The other dyes containing basicgroups, such as –NH2, –NH–CH3, or –N(CH3)2, form water-soluble salts with acids.These are cationic dyes and their colored ions are positively charged. If both acidicand basic groups are present, an internal salt is formed.

Oil-soluble or solvent-soluble colors lack salt-forming groups. Pigments are thecolors having no affinity for most substrates. They are thus generally insoluble inwater, fats, and solvent, so they color by dispersion in the food medium. Precipitationof water-soluble colors with aluminum, calcium, or magnesium salts (generally withaluminum) forms water-insoluble lakes. Lakes may be prepared from all classes ofwater-soluble food colors, and they are one of the most important groups of foodcolor pigments.

The stability of synthetic food colors toward the condition prevailing in foodprocessing depends on product composition, temperature, and time of exposition.Generally, they are resistant to boiling and baking, but light has a destructive effecton all of the colors. The use of synthetic colors is the most reliable and economicalmethod of coloring those products that have little or no natural color present, suchas dessert powders, table jellies, and sugar confectioneries.

The synthetic organic dyes are superior to the natural colorants in consistencyof strength, range and brilliance of shade, stability, ease of application, and cost-effectiveness. However, the manner in which synthetic colorants are employed, froma safety viewpoint, has much to be desired. Therefore, regulations were introducedto control the use of these added food colorants.

REFERENCES

Barua, A.B. et al., Vitamin A and carotenoids, in Modern Chromatographic Analysis ofVitamins, De Leenheer, A.P., Lambert, W.E., and Van Bocxlaer, J.F., Eds., MarcelDekker, Inc., New York, 2000, p. 7.

Berg, H. et al., The potential for the improvement of carotenoid levels in foods and the likelysystematic effect, J. Sci. Food Agric., 80, 880, 2000.

Brouillard, R., Origin of exceptional color stability of the Zebrina anthocyanin, Phytochem-istry, 20, 143, 1981.

Food Colorants 229

Brouillard, R., Chemical structure of anthocyanins, in Anthocyanins as Food Colours,Markakis, P., Ed., Academic Press, New York, 1982, p. 1.

Brouillard, R. et al., pH and solvent effects on the copigmentation reaction of Malvin bypolyphenols, purine and pyrimidine derivatives, J. Chem. Soc. Perkin Trans., 2, 1235,1991.

Combs, G.F., Jr., The Vitamins: Fundamental Aspects in Nutrition and Health, AcademicPress Inc., San Diego, 1992, p. 121.

Czapski, J., The effect of heating conditions on losses and regeneration of betacyanins, Z.Lebensm. Unters. Forsch., 180, 21, 1985.

Humphrey, A.M., Chlorophyll, Food Chem., 5, 57, 1980.Jacobucci, G.A. and Sweeny, J.G., The chemistry of anthocyanins, anthocyanidins and related

flavylium salts, Tetrahedron, 39, 3005, 1983.Klaui, H. and Bauernfeind, J.C., Carotenoids as food colours, in Carotenoids as Colourants

and Vitamin A Precursors, Academic Press, New York, 1981, p. 47.Macheix, J.J., Fleuriet, A., and Billot, J., Fruits Phenolics, CRC Press, Boca Raton, FL, 1990,

p. 239.Mazza, G. and Miniati, E., Anthocyanins in Fruits Vegetables and Grains, CRC Press, Boca

Raton, FL, 1993, p. 1.Muller, H., Determination of the carotenoid content in selected vegetables and fruits by HPLC

and photodiode array detection, Z. Lebensm. Unters. Forsch. A, 204, 88, 1997.Rice-Evans, C. et al., Why do we expect carotenoids to be antioxidants in vivo, Free Rad.

Res., 26, 381, 1997.Wang, H., Coa, G., and Prior, R.L., Oxygen radical absorbing capacity of anthocyanins,

J. Agric. Food Chem., 45, 304, 1997.

2311-5871-6149-4/02/$0.00+$1.50© 2002 by CRC Press LLC

Flavor Compounds

Chung-May Wu, Jen-Min Kuo, and Bonnie Sun Pan

CONTENTS

10.1 Sources of Flavors in Foods ........................................................................23210.1.1 Flavors Formed Naturally in Plants.................................................232

10.1.1.1 Spices and Herbs ..............................................................23210.1.1.2 Fruits .................................................................................23210.1.1.3 Vegetables .........................................................................233

10.1.2 Flavors Produced by Microbes or Enzymes....................................23310.1.3 Flavors Produced by Heating or Cooking .......................................23310.1.4 Flavors from Flavorants Added .......................................................233

10.2 Molecular Structure and Odor of Flavor Compounds ................................23410.2.1 Volatility and Intensity of Aroma Compounds................................23410.2.2 Flavor Compounds and Their Odors ...............................................234

10.3 Changes in Flavor During Food Storage and Processing ...........................23510.3.1 Changes Due to Nature of Flavor Compounds ...............................23510.3.2 Changes Due to Continuing Aroma Biogenesis..............................23610.3.3 Changes Due to Tissue Disruption or Enzyme Reactions ..............236

10.3.3.1 Introduction.......................................................................23610.3.3.2 Allium ...............................................................................23610.3.3.3 Brassicas ...........................................................................23710.3.3.4 Mushrooms .......................................................................23710.3.3.5 Formation of Green-Grassy Notes in Disrupted Tissues .23710.3.3.6 Glycosides as Flavor Precursors.......................................238

10.3.4 Changes Due to Processing .............................................................23810.3.4.1 Maillard Reaction .............................................................23810.3.4.2 Lipid Oxidation.................................................................23910.3.4.3 Interaction of Lipids in the Maillard Reaction ................24010.3.4.4 Extrusion ...........................................................................24110.3.4.5 Concentration and Other Processes..................................241

10.3.5 Changes Due to Storage of Food Products .....................................24110.4 Use of Flavors in Food Industry..................................................................242

10.4.1 Functional Properties of Flavor Compounds...................................24210.4.2 Collection or Production of Flavoring Materials ............................243

10.4.2.1 Natural Flavor Materials...................................................24310.4.2.2 Organic Chemicals Used in Flavorings............................244

10.4.3 Flavor Manufacturing.......................................................................245

10


10.4.3.1 Flavor Compounding ........................................................24510.4.3.2 Process Flavor...................................................................246

10.5 Biotechnological Production of Flavors ......................................................24610.5.1 Microbial Production of Flavor Compounds...................................24610.5.2 Enzymatic Generation of Flavor Compounds .................................24810.5.3 Recombinant DNA Technology for Flavor Formations ..................249

10.6 Applications of Flavors................................................................................250References..............................................................................................................251

10.1 SOURCES OF FLAVORS IN FOODS

10.1.1 FLAVORS FORMED NATURALLY IN PLANTS

10.1.1.1 Spices and Herbs

Since antiquity, spices, herbs, and condiments have been considered virtuallyindispensable in the culinary arts. They have been used to flavor foods andbeverages the world over. Spices can be grouped according to the parts of theplant used: leaves (bay and laurel); fruits (allspice, anise, capsicum, caraway,coriander, cumin, dill, fennel, paprika, and pepper); arils (mace); stigmas (saffron);flowers (safflower); seeds (cardamom, celery seed, fenugreek, mustard, poppy, andsesame); barks (cassia and cinnamon); buds (clove and scallion); roots (horseradishand lovage); and rhizomes (ginger and turmeric). Most of the spices and herbscontain volatile oils, called essential oils, which are responsible for the character-istic aroma of spices. Some spices (capsicum, ginger, mustard, pepper, and horse-radish) are pungent, while paprika, saffron, safflower, and turmeric are valued fortheir colors. Many spices have some antioxidant activities (Chen et al., 1999).Rosemary and sage are particularly pronounced in antioxidant effects. Cloves,cinnamon, mustard seed, and garlic contain antimicrobial activities (Firouzi et al.,1998). Some spices have physiological and medicinal effects. Spiced foods containsubstances that affect the salivary glands (Pruthi, 1980).

10.1.1.2 Fruits

Citrus fruits contain peel oil, the essence from which oil is obtained duringconcentration of the juice process. Citrus oils are characterized by a high per-centage of terpene hydrocarbons (limonene, C10H16), which contribute little toaroma. The unique characteristics of limonene are its relative insolubility indilute alcohol and its susceptibility to oxidation, causing off-flavor production.If the monoterpenes are removed, the resulting oil is called terpene-free orterpeneless oil. Aldehydes, esters, and alcohols are the main contributors to thearomas of citrus oil. These compounds are relatively polar and soluble in water;therefore, they are satisfactory for applications in food and beverage.

Fruits other than citrus contain much less volatile aromatic compounds andcannot form essential oil in distillates. However, their juices, juice concentrates,

Flavor Compounds 233

extracts of dehydrated fruits, and distillates (essence) can be used as flavorantsdirectly added to foods.

10.1.1.3 Vegetables

Vegetables contain some flavor compounds, the concentrations of which are mostlytoo low to obtain essential oils. In the tissues of some vegetables, volatile compoundsare enzymatically produced when they are disrupted. Vegetables have the functionof flavoring only after their cells are disrupted or after being oil-fried. Vegetableflavors are classified in the category of savory flavor, while fruit flavors are classifiedas sweet flavors.

In addition to the three natural flavor categories described above, tea, coffeebeans, cocoa beans, flowers (i.e., rose and jasmine), peppermint, and balsamare natural products with flavoring properties (Arctander, 1960; Furia andBellanca, 1975).

10.1.2 FLAVORS PRODUCED BY MICROBES OR ENZYMES

Fermentation has been known and commercially exploited for centuries. Prod-ucts like spirit, liquor, wine, beer, and other alcoholic beverages; vinegar; cheeseand yogurt; miso, soy sauce, and fermented bean curd; ham and sausage; fishsauce; cured vanilla beans, tea, and cocoa; pickles and sauerkraut; dough, bread,and other bakery products have special flavor notes that can also be used asseasonings.

Biotechnology for the production of flavoring materials has been developedin the past decade. The technology relating to the production of flavors includecell and tissue culture; microbial fermentation; and bioconversion of substratesusing whole microbial cells, plant cells, or enzymes (Harlander, 1994; Kringerand Berger, 1998). For example, in a model system, using lipoxygenase (LOX)extracted from mullet gill in place of roe LOX to react with roe lipid, resulted ina very slight decrease in unsaturated fatty acids and a pronounced increase ingreen and fresh fish-like flavor notes (Pan and Lin, 1999). Fish oil modified withalgal LOX yields an aroma more desirable than that of the untreated fish oil (Huand Pan, 2000).

10.1.3 FLAVORS PRODUCED BY HEATING OR COOKING

The flavors of foods such as wheat, peanuts, and sesame, after being cooked, arequite different from those of the raw materials. Flavor formation from flavor pre-cursors in the processed foods is primarily via the Maillard reaction, caramelization,thermal degradation, and lipid–Maillard interactions.

10.1.4 FLAVORS FROM FLAVORANTS ADDED

Flavorings play essential roles in the production of a wide range of food products versatilein aroma to allow consumer choices and to meet consumer needs. In this regard, flavor


manufacturers require expertise in flavor formulations, research, and technical services,while flavor users need fundamental knowledge of flavor applications.

10.2 MOLECULAR STRUCTURE AND ODOR OF FLAVOR COMPOUNDS

10.2.1 VOLATILITY AND INTENSITY OF AROMA COMPOUNDS

The flavor of food is largely perceived as a result of the release of odorous com-pounds, usually present in trace amounts in foods, into the air in the mouth and thento the olfactory epithelium in the nose. The volatility is caused by the evaporationor rapid sublimation of an odoriferous substance. It is proportional to the vaporpressure of the substance and inversely proportional to its molecular weight. There-fore, an aroma compound must be volatile. Other characteristics relate to aromacompounds; among them flavor intensity is the most important. Threshold is usedmost extensively for quantification of flavor intensity. Psychophysically, a thresholdcan be defined as the minimum concentration of a stimulus that can be detected(absolute threshold), discriminated (just noticeable difference), or recognized (rec-ognition threshold). In general, the detection thresholds are lower than the recogni-tion thresholds, if the difficulty in measuring both is compared (Pangborn, 1981).

The relationship between the molecular structure of an aroma compound andits threshold is still unclear. Volatility of a compound may not relate to its threshold.For example, the threshold of ethanol (boiling point is 78°C) is much higher thanoctanol (boiling point is 195°C) or other homologous alcohol. Ethanol has highvolatility but low odor intensity. It is often used as a solvent in compounded flavors.

In general, sulfur- or nitrogen-containing compounds and heterocyclic com-pounds have very low threshold values.

An odor unit is defined as the ratio of concentration to threshold. This unitquantifies the contribution of a specific component or a fraction to the total odor ofa mixture; however, it says nothing about the odor quality of the final mixture, andit does not imply anything about the relationship between the stimulus concentrationand the intensity of sensation above the threshold (Teranishi et al., 1981).

10.2.2 FLAVOR COMPOUNDS AND THEIR ODORS

The relationship between the molecular structure of a chemical compound and itsodor has been the subject of much research and conjecture. It is still not possibleto predict the aromatic profile from the structure of a given chemical, and it is notpossible to assume changes in flavor profile based on molecular structure modifica-tion. Even stereoisomers may differ in odor both qualitatively and quantitatively.Nevertheless, the relationship between structure and odor can be summarized asfollows.

Small molecules — such as ethanol, propanol, and butanol among alcohols;acetaldehyde and propionaldehyde among aldehydes; and acetic acid, propionic acid,and butyric acid among acids — are highly volatile and exhibit pungent ethereal,diffusive, harsh, or chemical odor characteristics. Only in extreme dilution of these


compounds will a desirable odor become perceptible. Bigger molecules of alcohols,aldehydes, and acids are mild and desirable at 5–10°C. Molecules containing alco-hols, aldehydes, and acids reduce their volatility and odor intensities with increasesin molecular size at temperatures higher than 10°C.

Compounds containing functional groups such as -OH, -CHO, -CO, and -COOHplay important roles in exporting the odors of a compound. Acid is sour, aldehydeyields a fresh note, and ester is fruity. However, an elongated alkyl group enhancesthe fatty or oily note. Ketones having two alkyl groups attached to a carbonyl groupgive more fatty aroma than the corresponding aldehydes.

Ester has a fruity note. When the initial alkyl group in alcohol or acid or bothis relatively large in molecular size or with its own characteristic note, the resultingester maintains this note in addition to the fruity note. Examples include citronellylacetate, having a fresh rosy–fruity odor, which inherits the rosy note from citronellol;and bornyl acetate, having a sweet herbaceous–piney odor with a balsamic under-tone, which maintains the odor of borneol.

The boiling point of ethyl acetate is 77°C, and its molecular weight is 88. Thoseof its reactant ethyl alcohol are 78°C and 46, while those of the acetic acid are 118°Cand 60, respectively. Ester has a higher molecular weight but a lower boiling pointin comparison to the precursor alcohol and acid. Many esters such as ethyl acetatehave fresh notes. Aldehyde has a relatively low boiling point. For example, acetal-dehyde has a molecular weight of 44, while its boiling point is 21°C. Therefore,aldehydes are often used for their fresh note. For example, decanal contributes tothe fresh note in orange aroma.

Lactones are cyclic compounds with relatively high boiling points and an esterfunctional group. They have the characteristic ester notes: fruity, oily, and sweet.γ-Undecalactone, with a peach-like aroma, has a boiling point of 297°C.

Heterocyclic compounds generally have very low thresholds. Thiazoles, thi-olanes, thiophenes, furans, pyrazines, and pyridines are normally present in largernumbers and higher concentrations in cooked, fermented, and processed seafoodsor meat products than in fresh ones (Pan and Kuo, 1994).

Essential oil, oleoresin, or other natural flavoring raw materials have manyvaluable trace components that play important roles in aroma. These componentsare not commercially available now because of their complexity and low threshold.It is not feasible to undergo a complicated manufacturing process for the very littleamount needed. The only source available is the natural product.

10.3 CHANGES IN FLAVOR DURING FOOD STORAGE AND PROCESSING

10.3.1 CHANGES DUE TO NATURE OF FLAVOR COMPOUNDS

A volatile compound evaporates continuously, even at room temperature. Higher tem-perature accelerates the evaporation. Some food ingredients such as lipids and proteinsmay trap flavor compounds to some extent and reduce their volatility. Different flavorcompounds have different volatility. An aged food may not only lose its total flavor, butalso change its proportions of the flavor components, resulting in a changed odor.


Many flavor compounds contain double bonds or aldehyde groups, which aresusceptible to oxidation, cleavage, polymerization, or interaction among components(Sinki et al., 1997). Alcohols can be oxidized to the corresponding aldehyde andthen acid. Alcohol and acid can react to form ester. Ester can be hydrolyzed toalcohol and acid at neutral or alkaline pH. Aldehyde and alcohol can be dehydratedby catalysis to form hemiacetal, and the reverse reaction can occur in acidic condi-tions or in water.

10.3.2 CHANGES DUE TO CONTINUING AROMA BIOGENESIS

The amount of secondary metabolites such as aroma compounds produced by a plantduring its life cycle is a balance between formation and elimination. The two opposingfunctions are directly controlled by two main groups of factors. The intrinsic factorsare comprised of all internal, or hereditary, properties (e.g., genotype and ontogeny),while extrinsic factors are comprised of all external, or environmental properties (e.g.,pressure, wind, light, temperature, soil, water, and nutrients). Therefore, a plant mate-rial such as citrus fruits (Nagy and Shaw, 1990) or the essential oils (Lawrence, 1986)may have quite a different flavor quality due to the culture conditions and maturity.The typical flavor of climatic fruit such as bananas, peaches, pears, and cherries doesnot have the flavor during early fruit formation; it develops fully during a rather shortperiod of ripening. During that time, minute quantities of lipids, carbohydrates, pro-teins, and amino acids are enzymatically converted to volatile flavors (Reineccius,1994a). During postharvest handling, the plant continues the biogenesis of aroma.

10.3.3 CHANGES DUE TO TISSUE DISRUPTION OR ENZYME REACTIONS

10.3.3.1 Introduction

Some food flavors are not present in the intact plant tissues, but are formed byenzymatic processes when the plants are cut or crushed. Under these circumstances,the cells are ruptured, and the flavor precursors are released and exposed to enzymes.Unique examples of this kind of flavor formation are described below.

10.3.3.2 Allium

Garlic, onion, shallot, green onion, and chive belong to the allium genus. Membersof this genus contain volatile sulfur compounds, including thiols, sulfides, disulfides,trisulfides, and thiosulfinates (Block and Calvey, 1994; Yamaguchi and Wu, 1975;Yu and Wu, 1989).

The enzymatic flavor formation reaction of the allium genus can be generalizedas follows:

2 RSOCH2CHNH2COOH → RSSOR + 2 NH3 + CH3COCOOH

where R is methyl, propyl, 1-propenyl, or allyl. The 1-propenyl compound has beenidentified as the lacrimator in onions. Allicin, the active odor principle of fresh garlic,


is diallyl thiosulfinate. In common with all thiosulfinates, allicin readily forms diallyldisulfide and diallyl trisulfide at room temperature. The addition of soybean oil in theprocess of garlic disruption can slow down the conversion of allicin (Kim et al., 1995).

10.3.3.3 Brassicas

The brassicas of importance as foods include turnips, rutabagas, mustards, and thecole crops — cabbage, broccoli, cauliflower, and brussels sprouts. The productionof isothiocyanates in brassicas is via an enzymatic reaction on specific glycosides.Some of the isothiocyanates, especially allylthiocyanate, are highly pungent and aremainly responsible for the odors of brown mustard, horseradish, cabbage, and othercrucifers. Any process that destroys or inactivates enzymes in these plants will causedecreases in aroma production, resulting in a less distinctive flavor. This is usuallythe case when brassica foodstuffs are commercially preserved.

10.3.3.4 Mushrooms

1-Octen-3-ol occurs in many mushroom species. It contributes significantly to the flavorof edible mushrooms, such as Agaricus campestris (Tressl et al., 1982) and Agaricusbisporus (Wurzenberger and Grosch, 1982; Chen and Wu, 1984). 1-Octen-3-ol is formedenzymatically from linoleic acid, which was shown to be the major fatty acid in A.bisporus. Enzymes involved in the pathway of formation of 1-octen-3-ol include LOX,hydroperoxide lyase, and allene oxide synthases (Grechkin, 1998).

Shiitake (Lentinus edodes) is one kind of edible mushroom highly prized inChina and Japan. Due to the difficulties of postharvest storage, the mushroom hasbeen traditionally preserved in dried form. The differences between the fresh shiitakeand the dried shiitake lie in the contents of eight-carbon compounds (i.e., 3-octanone,1-octen-3-ol, 3-octanol, n-octanol, and cis-2-octen-l-ol) and sulfurous compounds(i.e., dimethyl disulfide and dimethyl trisulfide). Fresh shiitake contains more eight-carbon compounds than dried shiitake, while dried shiitake contains more sulfurouscompounds than fresh shiitake (Chang et al., 1991). The formation of volatile shii-take is affected greatly by the pH during blending. 1-Octen-3-ol and 2-octen-l-olare predominantly formed around pH values of 5.0–5.5, while the formation ofpredominantly sulfurous compounds such as dimethyl disulfide and dimethyl trisul-fide is around pH 7.0. Two enzymatic systems are probably responsible for theformation of eight-carbon and sulfurous compounds. An enzymatic reaction is likelyto occur in dried shiitake, yielding more volatile sulfur compounds than fresh shiitake(Chen et al., 1984).

10.3.3.5 Formation of Green-Grassy Notes in Disrupted Tissues

Six-carbon compounds such as hexanal, 3Z-, and 2E-hexenal at high concentrationswere detected in ruptured tissue of apples, grapes, and tomatoes (Schreier andLorenz, 1981). These compounds, when they occur, are only in trace amounts inintact plant cells. Aliphatic C-6 components, which contribute to the green note offruits, are formed from unsaturated C-18 fatty acids by enzymatic activity aftercellular disruption. LOX is involved in the reaction (Galliard and Matthew, 1977).


(Z)-3-Hexen-l-ol, (E)-2-hexenal, hexanol, (E)-2-hexen-l-ol, and hexanal are formedin bell peppers (Capsicum annuun var. grossum, Sendt) after tissue disruption (But-tery and Ling, 1992).

10.3.3.6 Glycosides as Flavor Precursors

There are two forms of monoterpene derivatives in grapes: free and glycosidicconjugates. The free form consists of compounds with interesting flavor propertiessuch as geraniol, nerol, linalool, linalool oxides, α−terpineol, cirronellol, hotrienol,and flavorless polyhydroxylated compounds (polyols), which under mild acidichydrolysis conditions can yield odorous volatiles. The flavorless glycoside forms,cons i s t i ng o f β -D-g lucopy ranos ide s and d ig lycos ide s ; and6-O-α−L-arabinofuranosyl-β-D-glucopyranosides, 6-O-α−L-rhamnopyranosyl-β-D-glucopyranosides (rutinosides), and 6-O-β-D-apiofuranosyl-β-D-glucopyrano-sides of predominantly geraniol, nerol, and linalool, together with monoterpenes,are present at a higher oxidation state than the free forms. As most of these com-pounds have interesting sensory properties, their glycosides make up a potentialaroma reserve that is more abundant than in their free counterparts. The gly-cosidically bound volatiles can be released by either acid or enzyme hydrolysis (Wuand Liou, 1986). β-Glucosidase, the most abundant glycosidase, is present withα−arabinosidase and α−rhamnosidase in grapes and berries of various cultivars.Enzyme treatment of juice or wine increases the concentrations of volatile mono-terpene flavorants. Prolonged aging of wine or its exposure to elevated temperaturesincreases the concentration of free volatile monoterpenes through hydrolysis ofglycosidic precursors in wine (Gunata et al., 1992; Straus et al., 1986).

Other plants such as papaya (Schreier and Winterhalter, 1986), nectarine (Take-oka et al., 1992), and tea leaves (Lee et al., 1984; Kobyashi et al., 1992) also containglycosides as precursors of flavors.

10.3.4 CHANGES DUE TO PROCESSING

10.3.4.1 Maillard Reaction

The Maillard reaction plays an important role in flavor development, especially inmeat and savory flavor (Buckholz, 1988). Products of the Maillard reaction arealdehydes, acids, sulfur compounds (e.g., hydrogen sulfide and methanethiol), nitro-gen compounds (e.g., ammonia and amines), and heterocyclic compounds such asfurans, pyrazines, pyrroles, pyridines, imidazoles, oxazoles, thiazoles, thiophenes,di- and trithiolanes, di- and trithianes, and furanthiols (Martins et al., 2001). Highertemperature results in production of more heterocyclic compounds, among whichmany have a roasty, toasty, or caramel-like aroma.

Sugar, ascorbic acid, amino acids, thiamine (de Ross, 1992; Ames and Hincelin,1992; Guntert et al., 1992, 1994; Yoo and Ho, 1997), and peptides (Ho et al., 1992; Izzoet al., 1992; de Kok and Rosing, 1994) are potential reactants of the Maillard reaction.They are present in most foods, so the Maillard reaction occurs commonly when thesefoods are cooked. The conditions of cooking determine the aroma of the cooked foods.For example, the major volatiles identified from water-boiled duck meat are the common


degradation products of fatty acids, while roasted duck meat contains not only thevolatiles found in raw duck meat, but also pyrazines, pyridines, and thiazoles (Wu andLiou, 1992), which are Maillard reaction products. The wax gourd (Benincasa hispida,Cogn), also known as winter melon or gourd melon, a vegetable, is used to producebeverages, candy, and jams that are popular in Taiwan. The flesh of the gourd melon iswhite in color. The major volatile compounds of fresh gourds are (E)-2-hexenal, n-hex-anal, and n-hexyl formate, while the 2,5-dimethylpyrazine, 2,6-dimethylpyrazine,2,3,5-trimethylpyrazine, 2-methyl pyrazine, and 2-ethyl-5-methyl pyrazine are the majorvolatile compounds of the wax gourd beverage, which is brown in color. The beverageis prepared by cooking sliced wax gourd and sugar at alkaline pH for about 3–4 h, oreven longer, followed by diluting with water and serving as a nonalcoholic beverage.The pyrazine compounds not present in the fresh wax gourd are likely formed from thesugar added and the endogenous amino acids during processing of the beverage (Wuet al., 1987). This example shows changes in the flavor of foods during processing inwhich the Maillard reaction plays an important role.

Hundreds of patents have been granted worldwide for processes and reactionproducts based on Maillard technology applied to manufacturing meat and savoryflavors (Buckholz, 1988; Mottram and Salter, 1988; Ouweland et al., 1988).

The Maillard reaction may produce mutagenic components, pigments, and anti-oxidants, all of which are discussed in other sections of this book.

10.3.4.2 Lipid Oxidation

The oxidation products of lipids include volatile aldehydes and acids. Therefore,lipids are one of the major sources of flavors in foods. For example, much of thedesirable flavors of vegetables such as tomatoes, cucumbers, mushrooms, and peas(Ho and Chen, 1994); fresh fish (Hsieh and Kinsella, 1989), fish oil (Hu and Pan,2000); and cooked shrimp (Kuo and Pan, 1991; Kuo et al., 1994), as well as manydeep-fat fried foods such as French-fried potatoes (Salinas et al., 1994) and friedchicken (Shi and Ho, 1994), are contributed by lipid oxidation. LOX-catalyzed lipidoxidation produces secondary derivatives, e.g., tetradecatrienone, which is a keycompound of shrimp (Kuo and Pan, 1991). The major difference between the flavorsof chicken broth and beef broth is the abundance of 2,4-decadienal and γ-dodeca-lactone in chicken broth (Shi and Ho, 1994). Both compounds are well-known lipidoxidation products. A total of 193 compounds has been reported in the flavor ofchicken. Forty-one of them are lipid-derived aldehydes.

The core flavor of mashed potatoes consists of naturally occurring and thermallygenerated compounds. These compounds arise mainly from the oxidation of fattyacids, especially highly unsaturated fatty acids, and from the degradation and inter-action of sugar and amino acids. The extent to which these reactions affect the flavorof the final product depends on the age of the raw materials, storage conditions, andprocessing techniques. For example, both lipid oxidation and nonenzymatic brown-ing reactions increase with the age of the raw potato (Salinas et al., 1994).

Garlic develops its aroma from enzymatic reactions, as described before. Whengarlic slices are deep fried, microwave heated, or oven baked, the aroma changes(Yu et al., 1993) and contributes a different kind of garlic flavor to foods. A novel


S-compound was identified from the interaction of garlic and heated edible oil (Hsuet al., 1993). Also, alliin and deoxyalliin, two important flavor precursors of garlic,can react with 2,4-decadienal, which is one of the major oxidation products of fattyacids to form aroma (Yu et al., 1994).

Deep-fat frying is a universal cooking method. Stir frying is common in somecuisines, especially in Chinese cooking. Changes of volatile compounds in oils afterdeep-fat frying or stir frying and subsequent storage were studied (Wu and Chen,1992). Soybean oil was heated by deep frying at 200°C for 1 h, with the addition ofwater, and then stored at 55°C for 26 weeks. All samples contained aldehydes as majorvolatiles. During heating and storage, total volatiles increased 260- to 1100-fold.However, aldehyde content decreased from 62–87% to 47–67%, while volatile acidcontent increased from 1–6% to 12–33%. Hexanoic acid increased to 26–350 ppm inthe oils after storage. Hexanoic acid has a heavy, acrid-acid, fatty, rancid odor, oftendescribed as “sweat-like,” that is responsible for the rancid note. Water addition todeep-fried oils tends to retard the formation of volatile compounds during deep frying.

Freshly stir-fried Chinese food has a much better flavor quality than after it isaged. The main change in volatile constituents of stir-fried bell peppers during agingis the production of volatile carbonyl compounds from autoxidative breakdown ofunsaturated fatty acids (Wu et al., 1986).

Generally, the undesirable flavor qualities of food are associated more closelywith lipids than with proteins and carbohydrates. Lipids are responsible for therancidity of lipid-containing foods. The term warmed-over flavor (WOF) is used todescribe the rapid development of oxidized odor in cooked meat upon subsequentholding. The rancid or stale odor becomes readily apparent within 48 h, in contrastto the more slowly developed rancidity that becomes evident only after frozen storagefor a period of months. Although WOF was first recognized as occurring in cookedmeat, hence its name, it also develops in raw ground meat exposed to air. Overheatingof meat protects it against WOF by producing Maillard reaction products possessingantioxidant activity (Pearson and Gray, 1983).

Recently, phospholipids, e.g., lecithin, were classified as nutraceutical foods(Colbert, 1998). The off-flavor associated with lecithin produced in fermented dairyproducts includes 2,4-nonadienal, 2,4-decadienal, and hydrogen peroxide(Suriyaphan et al., 2001).

Flavor chemistry of lipid foods has been reviewed and compiled elsewhere inthe last decade (Ho and Chen, 1994; Min and Smouse, 1989; Shahidi and Cadwall-ader, 1997; Shahidi, 1998).

10.3.4.3 Interaction of Lipids in the Maillard Reaction

The Maillard reaction and the oxidation of lipids are two of the most importantreactions for the formation of aromas in cooked foods. Interactions between lipidoxidation and the Maillard reaction have received less attention, despite the fact thatlipids, sugars, and amino acids exist in close proximity in most foods. Lipids, uponexposure to heat and oxygen, are known to decompose into secondary products,including alcohols, aldehydes, ketones, carboxylic acids, and hydrocarbons. Alde-hydes and ketones produce heterocyclic flavor compounds reacting with amines and


amino acids, via Maillard-type reactions in cooked foods (Shibamoto and Yeo, 1992).Lipid degradation products such as 2,4-decadienal and hexanal can interact withMaillard reaction intermediates to form long-chain alkylpyrazines, as well as otherheterocyclic compounds (Farmer and Whitefield, 1993).

10.3.4.4 Extrusion

Extrusion cooking is a process whereby foodstuffs of low-moisture content (10–30%) aresubmitted to the action of heat, pressure, and mechanical shearing for a short time (20sec to 2 min). Extrusion can have a significant effect on flavor and aroma profiles of foodproducts manufactured through this process, e.g., extrusion of wheat flour products(Hwang et al., 1994). Depending on raw material composition, flavor development duringprocessing may be an important consideration for product quality. Certain mechanismssuch as nonenzymatic browning and lipid oxidation are considered to have significantimplications in the flavor characteristics of food products. Oxidation and volatility of flavorcompounds are important factors to be considered during heating and extrusion cookingat different temperatures and moisture contents. Lipid oxidation products are the majorcompounds of aroma generation in the extrudates prepared from wheat flour at a highmoisture content and low die temperature. By lowering moisture content, lipid degradationcompounds decreased, and the Maillard reaction products dominated the flavor profile.The lipid oxidation products significantly increased during storage of samples extrudedat low moisture content and high die temperature (Villota and Hawkes, 1988).

Retention of aroma compounds during extrusion cooking of different formula-tions, e.g., starch, starch-caseinate, and biscuit mix, was studied (Sadafian andCrouzet, 1987). Several aroma compounds — limonene, p-cymene, linalool, geran-iol, terpenyl acetate, and β-ionone — were added in different ways: water emulsion,oil solution, capsules, or inclusion complexes in β-cyclodextrin. During the extrusionprocess, the major loss of free volatiles reaches more than 90%. It is controlled bywater stripping during the expansion phase of the extrudate. Flavor retention isincreased through encapsulation of volatile compounds in natural or artificial wallsor as inclusion complexes in β-ionone.

10.3.4.5 Concentration and Other Processes

Some foods have special treatment in processing that may affect the compositionof volatile components. As an example, in hybrid passion fruit, the presence of about1–2% starch makes heat processing, i.e., pasteurization and concentration, impossi-ble or impractical, unless the starch is removed before processing. However, the stepof removing starch and concentration causes loss of volatile compounds of fruitjuice (Kuo et al., 1985).

10.3.5 CHANGES DUE TO STORAGE OF FOOD PRODUCTS

Food preservation is designed to prevent undesirable changes in food and food products.However, flavor changes in food products during storage occur continuously for pro-cessed foods, although the deterioration of flavor quality is not significant in most cases.


Nonenzymatic reactions that occur during processing and storage of food prod-ucts are detrimental if foods contain reducing compounds or if these compounds areproduced during storage as a result of oxidation, acid hydrolysis, enzymatic reac-tions, or physicochemical changes. Water mediates the nonenzymatic browningreaction by controlling the liquid phase viscosity; by dissolution, concentration, anddilution of reactants; and by effects on the reaction pathways, due to activationenergy limitations in dehydrated foods (Saltmarch et al., 1981).

Citrus juice can have the problem of off-flavor formation during processing andstorage. Changes in volatile components in aseptically packaged orange juice duringstorage at room temperatures were monitored. Quantities of several desirable flavorcomponents decreased during storage, while amounts of two undesirable compo-nents, α-terpineol and furfural, increased progressively with prolonged storage (Mos-honas and Shaw, 1987).

The ultrahigh temperature (UHT) processing of milk owes its commercial suc-cess to the observation that the rate of destruction of microorganisms increases morerapidly with temperature than the rates of the accompanying color and flavor changes.At very high processing temperatures, high sterility may be achieved with minimaladverse nutritional and chemical effects. However, UHT milk darkens in color duringstorage. This effect is noticeable after a few months at 20°C. It becomes morepronounced at higher temperatures and longer storage times. The milk also deteri-orates in taste. The ε-amino group of lysine in milk proteins may react extensivelywith lactose through the Maillard reaction before milk develops a marked off-flavor,discoloration, or instability (Moller, 1981). Spray-dried whey may also undergo theproblem of browning via the Maillard reaction.

10.4 USE OF FLAVORS IN FOOD INDUSTRY

10.4.1 FUNCTIONAL PROPERTIES OF FLAVOR COMPOUNDS

Taste, aroma, texture, and visual appearance play very important parts in the appealof all prepared foods. Food flavorings are compounded from natural and syntheticaromatic substances. The compounded flavors may or may not be found in nature.Reasons for using flavors in foods include (Giese, 1994a, 1994b):

• Flavors can be used to create a totally new taste. This does not happenvery often, but some new flavors have been enormously successful, suchas those used by Coca-Cola® or Pepsi-Cola®.

• Flavoring ingredients may be used to enhance, extend, round cut, orincrease the potency of flavors already present.

• Processing operations such as heating may cause a loss of flavor, whilesome flavors already present may need supplementation or strengthening.

• Flavor ingredients can simulate other more expensive flavors or replaceunavailable flavors.

• Flavors may be used to mask less desirable flavors. This function doesnot imply that flavors are being used to hide spoilage, but rather to coverharsh or undesired tastes naturally present in some processed foods.


Recent research has shown that flavor compounds provide not only sensoryquality to food, but also other functional properties, including antioxidative activity,antimicrobial activity, and health-promoting functions. The antioxidative activity wasfound in the essential oils of cloves, nutmeg (Dorman et al., 2000), Terminalia catappaL. leaves (Wang et al., 2000); aroma compounds of soybeans and mung beans (Leeand Shibamoto, 2000); and extracts of several members of the allium genus (Yin andCheng, 1998). Such aroma compounds may be used to prevent lipid oxidation in foodpreparation or food processing with health-related properties that are based on theirantioxidative activity. Antimicrobial activity was found in the essential oils of variousherbs, spices (Firouzi et al., 1998), onions, garlic (Block, 1985), mustard, and horse-radish (Delaquis and Mazza, 1995). Ninety-three different commercial essentials oilswere screened for activity against 20 Listeria monocytogene strains in vitro; the resultscorrelated with the actual chemical composition of each oil. Strong antimicrobialactivity was often correlated with essential oils containing a high percentage ofmonoterpenes, eugenol, cinnamaldehyde, thymol (Lis-Balchin and Deans, 1997), andisothiocyanates (Delaquis and Mazza, 1995). Flavors with antimicrobial activity canbe useful adjuncts in food preservation systems. Moreover, antimutagenic, anticarci-nogenic, and antiplatelet activity were found in sulfur-containing compounds ofseveral allium members (Chen et al., 1999).

10.4.2 COLLECTION OR PRODUCTION OF FLAVORING MATERIALS

10.4.2.1 Natural Flavor Materials

The main activities of flavor industries are collection or production of flavoringmaterials, manufacturing flavor, studies on flavor application, and technical services.

The sources, names, characteristics, and major flavor components of naturalflavoring materials such as spices, herbs, etc. have been summarized in several books(Arctander, 1960; Furia and Bellanka, 1975; Reineccius, 1994b). A large portion ofthe constituents in natural flavor materials is not flavor compounds. These nonflavorcompounds have to be removed to produce concentrated flavorants. There are twomajor methods to reach this purpose as follows.

Distillation — The essential oils are the distilled fraction of aromatic plants.Most often, they are steam distilled. These oils, which are primarily responsible forthe characteristic aroma of the plant material, are generally complex mixtures oforganic compounds. For example, during the concentration of citrus juices, a layerof essential oil is formed in the condensate. This oil is called essence oil. Terpenescan be removed from both essential oil and essence oil to obtain folded oil. Somefruit or vegetable distillates containing flavor compounds are called essence.Although no essential oil layer is obtained from vegetable distillate, it is used as aflavoring raw material. Citrus peels, rich in essential oils, are expressed to get cold-pressed oils.

Solvent Extraction — Essential oils do not contain hydrophilic flavoring com-ponents, antioxidants, or pigments. The nonvolatile flavoring constituents of aromaplants are recoverable by extraction. The selection of solvent is limited dependingon its toxicity, regardless of whether or not it remains in the final product. Two kinds


of solvents are used: a polar solvent such as ethanol (e.g., vanillin is soluble inethanol and therefore this alcohol is used to prepare vanilla bean extract) and anonpolar solvent such as petroleum ether. Most aroma compounds are oil soluble.Therefore, petroleum ether is used as the solvent to extract plant aroma. The extract,after removal of the solvent, is called concrete. Concrete may contain wax and fattyacids in large proportions and is further purified by ethyl alcohol extraction. Theproduct is called absolute. The nonvolatile flavoring constituents of herbs and spicesare recoverable by extraction. In practice, a solvent is chosen that dissolves both theessential oil and the nonvolatiles present. The resulting solvent-free product is knownas oleoresin. A disadvantage of the oleoresins is that they are very viscous, makingthem difficult to handle or mix in processing operations. Several products have beendeveloped into extractives, which are convenient to use and avoid handling problems.Extractives can be dispersed in salt, dextrose, or other carriers to create dry-solublespices. They may also be dispersed in fats to make fat-based soluble spices. Emul-sification of extracts with starches and gums, followed by spray drying, producesencapsulated spices. Solubilization of extracts with glycerol, isopropyl alcohol, andpropylene glycol produces liquid-soluble spices (Giese, 1994b).

10.4.2.2 Organic Chemicals Used in Flavorings

Organic chemicals used in flavorings include:

• Hydrocarbons, such as limonene, pinene, ocimene, α-phellandrene, andβ-caryophyllene

• Alcohols, such as hexanol, cis-3-hexen-l-ol, geraniol, citronellol, eugenol,and 1-menthol

• Aldehydes, such as acetaldehyde, hexanal, 2,4-decadienal, citral, and vanillin• Ketones, such as diacetyl, ionone, and nootkatone• Acids, such as acetic acid, butyric acid, and pyroligenious acid• Esters, such as ethyl acetate, linalyl acetate, ethyl phenyl acetate, and

methyl dihydrojasmonate• Lactones, such as γ-nonalactone, δ-decalactone, and γ-undecalactone• Hemiacetals, such as acetaldehyde, diethylacetal and citral dimethyl acetal• Ethers, such as diphenyl oxide and rose oxide• Nitrogen-containing compounds, such as trimethylamine• Sulfur-containing compounds, such as dimethylsulfide, thiolactic acid,

and allyl disulfide• Heterocyclic compounds, such as furans, pyrazines, pyridines, and thiazoles

The names, chemical structures, physical and sensory properties, and uses have beensummarized in several books (Arctander, 1969; Furia and Bellanca, 1975; Reinec-cius, 1994b). Many organic chemicals being used in flavorings are produced bysynthetic methods and are commercially available. More and more natural com-pounds are used in flavorings, due to the increasing demand for natural flavorings.They are produced or prepared by isolation of the compound from natural sourcesor by biotechnological methods.


Thousands of flavoring raw materials may form a flavor. A large number of theflavoring raw materials are supplied by different manufacturers and stocked. There-fore, a strict quality control system for the flavoring raw materials, as well as theproducts, is very important.

10.4.3 FLAVOR MANUFACTURING

10.4.3.1 Flavor Compounding

From thousands of flavor raw materials, 20–50 items are commonly selected andmixed with different ratios to blend a flavor. This is called flavor compounding,which is a kind of formulation. The raw material may be organic chemicals, essentialoils, extracts, oleoresins, or processed flavors. Knowledge of their nature, physicaland organoleptic properties, and applications is needed by flavorists. Flavor com-pounding requires at least 3–5 years of training.

How a flavor is formulated and modified is shown using strawberry flavor(Table 10.1). The characteristic notes of strawberry are fruity, sweet, green, and alittle bit oily and sour. Ethyl butyrate and methyl cinnamate have a fruity note;cis-3-hexen-l-ol and ethyl hexanoate are green; benzaldehyde and2,5-methyl-4-hydroxy-3 (2H) furanone are sweet; butyric acid is sour; and γ-unde-calactone is oily–fruity. Formula 1 was originally designed for use in cake mix.Therefore, compounds of low boiling points, e.g., ethyl acetate, were not used. Thesolvent was propylene glycol, which has a boiling point of 187.3°C, so the flavorcompound was heat stable. However, the application of this flavor in cake resultedin a sensory characteristic like pineapple, not strawberry. Pineapple is oily, fruity,and sweet. Since butter, sugar, and milk were among the ingredients in the cakemix, oily or fatty and sweet notes were derived from those ingredients. Therefore,formula 1 was modified by reducing the amount of γ−undecalactone, benzaldehyde,and 2,5-dimethyl-4-hydroxy-3 (2H) furanone and increasing the amount of ethylbutyrate, ethyl hexanoate, cis-hexen-l-ol, butyric acid, and methyl cinnamate. The

TABLE 10.1Formulas of Strawberry Flavors

Ingredient Formula 1 Formula 2

Ethyl butyrate 1.5 3.0Ethyl hexanoate 1.0 2.0cis-3-Hexen-1-ol 1.0 2.0Benzaldehyde 0.3 0.2Butyric acid 0.4 0.82,5-Dimethyl-4-hydroxy-3 (2H) furanone 2.0 1.0Methyl cinnamate 1.3 2.0γ-Undecalactone 0.9 0.5Propylene glycol 91.6 88.5Total 100.0 100.0


application test showed that formula 2 gave the cake a strawberry flavor, althoughthis modified flavor did not smell like strawberry before application.

10.4.3.2 Process Flavor

Process flavors include processed (reaction) flavors, fat flavors, hydrolysates, autoly-sates, and enzyme modified flavors. Production of dairy flavor by enzyme modifi-cation of butterfat is an example (Lee et al., 1986; Manley, 1994), while meat flavorproduced by enzymatic reactions has a much longer history.

Raw meat has little flavor. Characteristic meat flavor varies with the species ofanimal and temperature and type of cooking. Both water-soluble and lipid-solublefractions of meat contribute to meat flavor. The water-soluble components includeprecursors that upon heating are converted to volatile compounds described as “meaty.”Many desirable meat flavor volatiles are synthesized by heating water-soluble precur-sors such as amino acids and carbohydrates. The Maillard reaction, including formationof Strecker degradation compounds and interactions between aldehydes, hydrogensulfide, and ammonia, is important in the formation of the volatile compounds of meatflavor. Theoretically, other kinds of flavors formed during cooking could also beobtained from heat processing. The contingency is the availability of the precursors,which may be too expensive to be isolated from natural raw materials or synthesized.

The most practical way to characterize process flavorings is by their starting materialsand processing conditions, since the resulting composition of volatiles is extremelycomplex — comparable to the composition of cooked foods. Process flavorings areproduced every day by housewives in kitchens, by food industries during food processing,and by the flavor industry. The International Organization of the Flavor Industry (IOFI)has guidelines for the production and labeling of process flavorings (IOFI, 1990). Somekey points are: the reactants are strictly appointed; flavorings, flavoring substances, flavorenhancers, and process flavor adjuncts shall be added only after processing is completed;the processing conditions should not exceed 15 min at 180°C or proportionately longerat lower temperatures; and the pH should not exceed 8.0.

Process flavors are very successful in some cases, but unsuccessful in manyothers. Natural flavor materials such as meat extract or aromatic chemicals may beadded to process flavors to enrich some notes or to increase the overall intensity.

10.5 BIOTECHNOLOGICAL PRODUCTION OF FLAVORS

10.5.1 MICROBIAL PRODUCTION OF FLAVOR COMPOUNDS

Food products labeled as containing “all natural flavors” have a much higher marketprice than similar products containing artificial flavors. This preference has led to astrong upsurge in the requirement for natural flavor. The increasing demand for theseflavor compounds now exceeds their supply from traditional sources. This has moti-vated research efforts toward finding alternative, natural ways of obtaining naturalflavor compounds. In the United States, the Code of Federal Regulations states thatproducts produced or modified by living cells or their components, including enzymes,can be designated as “natural.” Thus, the use of biotechnological methods using


microorganisms, enzymes, and recombinant DNA seems to be a promising economicaland enviroment-friendly process for generating natural flavor compounds.

Traditional fermentation using microbial activity is commonly used for the pro-duction of nonvolatile flavor compounds such as acidulants, amino acids, and nucle-otides. The formation of volatile flavor compounds via microbial fermentation on anindustrial scale is still in its infancy. Although more than 100 aroma compounds maybe generated microbially, only a few of them are produced on an industrial scale. Thereason is probably due to the transformation efficiency, cost of the processes used, andour ignorance to their biosynthetic pathways. Nevertheless, the exploitation of micro-bial production of food flavors has proved to be successful in some cases. For example,the production of γ-decalactone by microbial biosynthetic pathways lead to a pricedecrease from $20,000/kg to $1,200/kg U.S. Generally, the production of lactone couldbe performed from a precursor of hydroxy fatty acids, followed by β-oxidation fromyeast bioconversion (Benedetti et al., 2001). Most of the hydroxy fatty acids are foundin very small amounts in natural sources, and the only inexpensive natural precursoris ricinoleic acid, the major fatty acid of castor oil. Due to the few natural sources ofthese fatty acid precursors, the most common processes have been developed fromfatty acids by microbial biotransformation (Hou, 1995). Another way to obtain hydroxyfatty acid is from the action of LOX. However, there has been only limited researchon using LOX to produce lactone (Gill and Valivety, 1997).

Vanillin, perhaps the most important aroma compound, occurs in the bean ofVanilla planifolia. At present in the world flavor market, only 0.2% of this compoundis extracted from beans; the remainder is produced synthetically. Thus, the produc-tion of vanillin via microbial transformation has been the most extensively investi-gated. Figure 10.1 shows some of the possible routes for the production of naturalvanillin by microorganisms. The transformation of the natural stilbene isorhapontinto vanillin is catalyzed by a microbial stilbene dioxygenase. This process has led tomany patents (Hadegorn and Kaphammer, 1994). Alternative precursors are eugenol(Washisu et al., 1993) and isoeugenol (Shimoni et al., 2000). However, the biocon-version gave relatively low yields. Direct use of ferulic acid (Figure 10.1 to producevanillin is perhaps the most promising approach, because this precursor is a constit-uent of various grasses and crops, and is a product of the microbial oxidation oflignin). An example is the use of sugar beet pulp or maize bran as the source offerulic acid to produce vanillin using two fungi (Bonnin et al., 2001). However, itsrecovery as a pure precursor is difficult, and the existence of numerous side reactionsmay explain the low bioconversion yields.

FIGURE 10.1 Proposed pathways for the biosynthesis of vanillin.

Eugenol

Isorhapontin

Coniferaldehyde

Ferulic acid

Vanillin


Benzaldehyde is the second most important material after vanillin. It is used asan ingredient in cherry and other natural fruit flavors in the flavor industry. Naturalbenzaldehyde is generally extracted from fruit kernels such as apricots. Nowadays,the fermentation of natural substrates such as phenylalanine offers an alternativeroute for the biosynthesis of natural benzaldehyde (Moller et al., 1998). However,production via the fermentation process will become commercially acceptable onlyif sufficient yields can be obtained, which has been difficult until now.

Other applications of microorganisms used in the production of flavor com-pounds are listed in Table 10.2.

10.5.2 ENZYMATIC GENERATION OF FLAVOR COMPOUNDS

More than 3000 enzymes have been described in the literature, but only 20 are availablefor use in commercial processes (Armstrong and Brown, 1994). Lipases, esterases,LOXs, glycosidases, proteases, and nucleases are the major enzymes for flavor gen-eration. Among them, lipases seem to be the most important enzyme in commercialutilization. The lipase-catalyzed reactions include hydrolysis, esterification, and trans-esterification. The reactions can be performed not only in aqueous systems, but alsoin organic solvents (Jaegar et al., 1994). Based on these outstanding features, lipasesare being increasingly used to synthesize “natural” flavoring materials such as esters(Langrand et al., 1990). (S)-2-Methylbutanoic acid methyl ester, which is known as amajor apple and strawberry flavor ingredient, was synthesized using lipase in organicmedia. The reaction efficiencies among 20 microbial lipases were compared (Kwonet al., 2000). Isoamyl acetate, one of the most employed flavor compounds in theindustry, could be produced by using immobilized lipase (Krishna et al., 2001). Low-molecular-weight esters (LMWEs) are flavoring agents for fruit-based products.Screening 27 commercial lipases showed that enzymes from Candida cylindracea,Pseudomonas fluorescens, and Mucor miehei (immobilized) promoted synthesis ofLMWEs in nonaqueous systems (Welsh et al., 1990). The LMWE has also beenproduced using plant seedling lipase (Liaquat and Apenten, 2000).

TABLE 10.2Aroma Compounds Produced by Microorganisms

Aroma Compounds Microorganisms Reference

Acetic acid Bacteria Sharpell and Stemann, 1979Diacetyl Bacteria Cheetham, 1996Geosmin Bacteria Pollak and Berger, 19962-Acetyl-pyrroline Bacteria Romanczyk et al., 1995Lactone Yeast Benedetti et al., 2001Linalool Yeast Welsh, 1994Benzaldehyde Fungi Fabre et al., 1996Vanillin Fungi Bonnin et al., 20011-Octen-3-ol Fungi Assaf et al., 1995Jasmonate Fungi Miersch et al., 1993


A green note is present in a wide variety of fresh leaves, vegetables, and fruits.The characteristic aroma compounds responsible for the green note include trans-2-hexenol, cis-2-hexenol, trans-3-hexenol, cis-3-hexenol (leaf alcohol), hexanol,hexanal, and cis-2-hexenal (Whitehead et al., 1995). These compounds are biosyn-thetically produced using LOX pathway enzymes as reported (Hatanaka, 1993; Fabreand Goma, 1999). The commercial processes for generating green odor compoundshave been established using LOX pathway enzymes as shown in Figure 10.2. Fourmajor enzymes — lipolytic enzyme, LOX, hydroperoxide lyase (HPLS), and alcoholdehydrogenase (using baker yeast as a source) — are involved in the formation of greenodor compounds (Hatanaka, 1993). Lipids — commercial soybean oil or vegetable oil— are hydrolyzed to fatty acid by lipolytic enzymes. Fatty acid 13-hydroperoxides areformed from the action of a specific LOX and then cleaved by HPLS into C6-green odorcompounds. Among the various sources containing LOX activity, soybeans (Gardner,1989), peas (Chen and Whitaker, 1986), tomatoes (Riley et al., 1996), potatoes (Galliardand Phillips, 1971), cucumbers (Hornostaj and Robinson, 1999), and microorganisms(Bisakowski et al., 1997) are worth mentioning. HPLS is not available in commercialsources. It is used as a vegetable homogenate. Mungbean seedlings (Rehbock et al.,1998) and guava (Tijet et al., 2000) show higher HPLS activity than several other sourcesin producing green odor. Continous generation of green odor volatiles using a bioreactorimmobilized with LOX and HPLS is being investigated (Cass et al., 2000).

10.5.3 RECOMBINANT DNA TECHNOLOGY FOR FLAVOR FORMATIONS

The application of recombinant DNA technology in the flavor industry is lessadvanced than it is in the pharmaceutical and food industries. However, this tech-nology seems to have the most potential in future research. Nowadays, the recom-

FIGURE 10.2 Formation of green odor compounds via lipoxygenase pathway enzymes.

hexenol

lipid

lipolytic enzyme

linoleic acid linolenic acid

lipoxygenase

13-hydroperoxide 13-hydroperoxide

hydroperoxide lyase

hexanal cis-3-hexanal

alcoholdehydrogenase


cis-3-hexenoltrans-2-hexanal

trans-2-hexenol


isomerase


binant DNA technology is being increasingly used in several areas, including theproduction of aroma chemicals, improvement of flavor profiles through geneticengineering, removal of off-flavors, and enzymatic formation of flavor aldehyde(Muheim, 1998).

Fermentative or enzymatic processes are used to produce many flavor compounds.However, most of the above-mentioned techniques have been only reasonably appliedso far, due to the fact that production of aroma chemicals in generally very smallamounts is making their recovery an expensive endeavor. Recombinant DNA technol-ogy is helping to achieve efficient production of flavor compounds. A good exampleis the production of green note compounds via LOX pathway enzymes. Many plantLOXs from soybean seeds (Steczko et al., 1991), pea seeds (Hughes et al., 1998), andpotato tubers (Royo et al., 1996), and hydroperoxide lyases from guava (Tijet et al.,2000), alfalfa (Noordermeer et al., 2000), and peppers (Matsui et al., 1996) have beencloned and expressed in Escherichia coli or yeast. The green note compounds producedfrom such recombinant yeast cells bearing enzyme genes are identical to those fromthe native enzymes. In addition, higher amounts of flavor compounds (such as leafalcohol) have been produced in the presence of such recombinant enzymes than in thepresence of native enzymes.

10.6 APPLICATIONS OF FLAVORS

In food processing, choosing the right type of flavor, dosage, and method of addingthe flavor is important in flavor applications. A flavor can be admired only aftersuitable application. Due to different application conditions, flavors are made to havedifferent characteristics, e.g., solubility in water or oil, or heat stability or unstability,to meet the requirements. There is no general rule for flavor application. Flavor usersshould have some basic knowledge of flavor, food chemistry, and processing andthen they can handle flavor applications work very well. For example, citral is thekey compound of lemon flavor. If the flavor has undergone thermal treatment severeenough to let it be oxidized, then the hemiacetal form can be added to replace citraland cause changes in flavor. Limonene is a major constituent in citrus oils. It has tobe removed to prevent off-flavor production in food processing and storage. Theextent of evaporation loss of each flavor ingredient is different in food processing.Some food components such as starch, lipids, and proteins can trap flavor compoundsand reduce their volatilities. Some foods have their own flavors or flavor production.Therefore, modification of flavor formulas is needed to meet the identity of differentprocessed foods. Studies on flavor application for each food product are required tofind the right strength, form, and step. Technical supports to flavor users are standardservices provided by flavor makers.

Flavors can be used to develop new food products. At the 1995 IFT Food Expo,flavor manufacturers created unique berry flavors that do not exist naturally and aremore exciting than ever. Mayberry, pepperberry, juneberry, mountainberry, bugle-berry, and bellberry were all fabricated by creative flavor manufacturers (Sloan,1995). Creating new flavors for innovative flavor applications is a challenge to theflavor industry, thus leading to the development of more and new quality foodproducts for quality living.


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2591-5871-6149-4/02/$0.00+$1.50© 2002 by CRC Press LLC

Probiotics in Food

Maria Bielecka

CONTENTS

11.1 Introduction ..................................................................................................25911.2 Scientific Basis of Probiotic Functionality and Justification

of Their Use .................................................................................................26011.3 Probiotic Strain Selection ............................................................................26111.4 Probiotic Effects...........................................................................................263

11.4.1 Introduction ......................................................................................26311.4.2 Intestinal Infections..........................................................................26411.4.3 Immune Stimulation.........................................................................26411.4.4 Effect on Nonspecific Immune Responses ......................................26411.4.5 Effect on Specific Immune Responses ............................................26511.4.6 Factors that Influence the Efficacy of LAB ....................................26611.4.7 Future ...............................................................................................266

11.5 Probiotic Foods ............................................................................................26611.5.1 Food Products Containing Probiotics ..............................................26611.5.2 Efficacy of Probiotic Products .........................................................26711.5.3 Safety................................................................................................26811.5.4 Critical Questions Related to Probiotics .........................................268

11.6 Recommendation for Future Research ........................................................269References..............................................................................................................269

11.1 INTRODUCTION

The increasing consumer awareness that diet and health are linked is stimulatingthe innovative development of novel products by the food industry. The new products,which should satisfy the consumer needs, are functional foods containing probioticmicroorganisms with scientifically supported health claims for improving one’s stateof well-being and helping reduce the risk of diseases. Probiotic bacteria are used asthe active ingredient in functional foods, most frequently in bioyogurt, and also indietary adjuncts and health-related products. The health benefits attributed to pro-biotic bacteria can be categorized as either nutritional benefits or therapeutic benefits.

The term probiotic is derived from the Greek language and means “for life.” Itwas first used by Lilly and Stillwell (1965) to describe “substances secreted by onemicroorganism which stimulated the growth of another” and thus was contrasted withthe term antibiotic. After several modifications, Schrezenmeir and de Vrese (2001)

11


proposed the following definition of probiotics: “A preparation of or a product con-taining viable, defined microorganisms in sufficient numbers, which alter the micro-flora (by implantation or colonization) in a compartment of the host and by that exertbeneficial health effects in this host.” This definition confines the probiotic conceptto effects produced by viable microorganisms, but is application independent of theprobiotic site of action and route of administration. Therefore, this definition mayinclude such sites as the oral cavity, the intestine, the vagina, and the skin. In thecase of probiotic foods, the health effect is usually based on alteration of the gas-trointestinal (GI) microflora and therefore based on survival during GI transit. Thusthe validity of the condition of the appropriate number in the definition is underlined.

Although there are numerous probiotic products for human consumption on themarket, there is a lot of skepticism regarding their beneficial effects. This has in partbeen due to some reports of their positive health benefits that have been publishedwith little scientific backup. Furthermore, many of the microorganisms included inthese products are not viable and have not been selected either for specific beneficialproperties or for their ability to survive in the GI tract. If health claims regardingprobiotic bacteria are to be substantiated, it is imperative to establish which strainshave been used and from which source they have been obtained.

11.2 SCIENTIFIC BASIS OF PROBIOTIC FUNCTIONALITY AND JUSTIFICATION OF THEIR USE

The total mucosal surface area of the adult human GI tract is up to 300 m2, makingit the largest body area interacting with the environment. The huge surface wouldsuggest a great capacity for effective absorptive area, for defensive exclusion ofinfections, and toxic and allergenic material from the internal milieu. The gut-associated lymphoid tissue (GALT) makes the GI tract the largest lymphoid orimmune organ in the human body. It has been estimated that there are approximately1010 immunoglobulin (Ig) (antibody)-producing cells per meter of small bowel, thusaccounting for ~80% of all immunoglobulin-producing cells in the body (Targanand Shanahan, 1994).

Sterile at birth, the GI tract rapidly acquires a commensal enteric microflora,resulting in the creation of a complex intestinal ecosystem. This microflora adds anadditional competitive component to the defense capability through competitiveexclusion. It is also essential for mucosal immune education. The balance of thiscommensal microflora may be altered by physiological changes in endogenous acidand bile secretion, diet and bowel movements, colonization by pathogens, liver orkidney diseases, pernicious anemia, cancer, radiation, oral use of antibiotics orimmunosuppressive agents, surgical operations of the GI, immune disorders, andemotional stress. Many of these parameters are influenced by age, particularly inthe late decades of life.

It is estimated that the intestines of humans contain ~1014 viable bacteria cells;this number is about 10 times higher than that of all eucariotic cells in the humanbody (Mitsuoka, 1996). The intestinal microflora of healthy humans is confined tothe distal ileum and the colon. It consists of over 400 species belonging to about 40

Probiotics in Food 261

genera. Most of them are obligatory anaerobic, and some of them attain highpopulation levels. Approximately 30–40 bacterial species constitute 99% of thecultivable fecal microflora of a healthy human. Some of these are present in popu-lations of at least 1010–11 colony forming units (cfu) per gram of feces (wet weight).These live bacteria make up ~30% of the fecal mass. The fecal microflora is arepresentative of the microflora of the colon. While the numerically predominantgenera of bacteria detected in the feces of different individuals are the same, thereis variation in the occurrence and population size of bacterial species.

Gibson (1998) distributed the gut bacteria into three groups: beneficial (Lacto-bacillus and Bifidobacterium), harmful (Pseudomonas aeruginosa, Staphylococcus,and Clostridium), and opportunistic (Enterobacteriaceae, Eubacterium, andBacteroides). In healthy subjects, well-balanced and beneficial bacteria dominate.Beneficial bacteria play useful roles in the aspects of nutrition and prevention ofdisease. They produce essential nutrients such as vitamins and organic acids, whichare absorbed from the intestines and utilized by the gut epithelium and by vitalorgans such as the liver. Organic acids also suppress the growth of pathogens in theintestines. Other intestinal bacteria produce substances that are harmful to the host,such as toxins and carcinogenic substances. When harmful bacteria dominate in theintestines, essential nutrients are not produced and the level of harmful substancesrises. These substances may not have an immediate detrimental effect on the host,but they are thought to be contributing factors to aging, cancer, liver and kidneydiseases, hypertension, arteriosclerosis, and reduced immunity. Little is knownregarding which intestinal bacteria are responsible for these effects.

The normal balance of intestinal flora may be maintained or restored to normalfrom an unbalanced state by a well-balanced diet or by oral bacteriotherapy. Oralbacteriotherapy, using intestinal strains of lactic acid bacteria (LAB), such as Lac-tobacillus and Bifidobacterium, can restore normal intestinal balance and producebeneficial effects.

11.3 PROBIOTIC STRAIN SELECTION

Although progress in probiotic research has been achieved, not all of the availableprobiotic bacteria on the market have adequate scientific documentation. If nutri-tional and health benefits are to be derived from products containing probioticbacteria, the mechanisms by which these benefits are derived should be understoodand those strains demonstrating the most promise in this regard should be used.Consequently, it is necessary to establish rational criteria for screening and selectionof candidate microorganisms and also to evaluate the efficacy of the selected strainsor food products in well-controlled human dietetic or clinical trials.

As a result of the food industry collaboration with scientists and clinicians,supported by EU-funded programs that aim to promote the generation and dissem-ination of consensus, the following criteria for the selection and assessment ofprobiotic microorganisms have been established:

• Be of human origin• Demonstrate nonpathogenic behavior


• Exhibit resistance to technological processes (i.e., viability and activityin delivery vehicles)

• Prove resistance to gastric acid and bile• Adhere to gut epithelial tissue• Be able to persist in the GI tract• Possess antimicrobial activity• Modulate immune responses• Have the ability to influence metabolic activities (e.g., β-galactosidase

activity, vitamin production, and cholesterol assimilation)

In addition, these requirements were further expanded by Berg (1998) and Salminenet al. (1996, 1998a), who stated that:

• Each potential probiotic strain should be documented.• Extrapolation of data, even from closely related strains, is not acceptable.• Only well-defined strains, products, and study populations should be used

in trials.• Where possible, all human studies should be randomized, double blind,

and placebo controlled.• Results should be confirmed by independent research groups.• Preferentially, the study should be published in a peer-reviewed journal.

In the development of probiotic foods, the strains of LAB such as Lactobacillusand Bifidobacterium have been most commonly used. This is primarily due to theperception that they are desirable members of the intestinal microflora, colonizingthe intestines of newborns as one of the first genera (Goldin and Gorbach, 1992;Berg, 1998). In addition, LAB have traditionally been used in the production offermented dairy products and have “generally recognized as safe” (GRAS) status.

The requirement that the strains of probiotic bacteria used should be of humanorigin is based on the observation that only human strains can be adhesive and colonizethe human GI tract, which is the first step in promoting colonization resistance (Huisin’t Veld et al., 1994). It has been proposed that species specificity does occur and forstrains to be beneficial to a particular host they should be isolated from that species.This is not well documented. Subsets of probiotic bacteria currently employed in thedairy food industry are not of human origin and therefore do not meet the criteria, asoutlined above, for the selection of probiotic microbes acceptable for human consump-tion. The bifidobacterial strains isolated from market bioyogurt were identified phe-notypically and genetically as Bifidobacterium animalis (Roy et al., 1996; Roy andSirois, 2000; Bielecka et al., 2000a). The results of our studies showed that these strainssurvived at low pH and bile, and adhered well to Caco-2 and HT-29 cell lines, as wellas to colon epithelium of humans and rats (Bielecka et al., 2000b). Additionally, thestrains belonging to B. animalis species, either isolated from bioyogurts or from ratsand adults consuming bioyogurts, were unusually homogenous. Recently, a Bifidobac-terium strain, isolated from market bioyogurt, was classified as Bifidobacterium lactis— the new species genetically most similar to B. animalis (Meile et al., 1997). Thename B. lactis has been given for honoring the source of isolation and justifying its


use in bioyogurt. Cai et al. (2000), comparing B. animalis JCM 1190T and B. lactisJCM 11602T found their phenotypic and genetic similarity: B. animalis and B. lactiswere the most closely related species in the phylogenetic tree and showed a highsimilarity in 16S rRNA sequences (98.8%). The levels of DNA–DNA hybridizationbetween the type strains of B. lactis and B. animalis ranged from 85.5–92.3%, showingthat they represent a single species (a genospecies is characterized by a DNA–DNAsimilarity of more than 70% and a 16S rRNA similarity of more than 95%). The mostoften isolated Bifidobacterium species from the human colon of adults areB. catenulatum, B. longum, B. adolescentis, B. bifidum, and B. pseudocatenulatum.Rarely isolated are B. angulatum and B. animalis. Among species of Lactobacillusisolated either from human feces or directly from intestinal homogenized mucosa aspotentially adherent probiotic bacteria are L. paracasei, L. salivarius, L. acidophilus,L. crispatus, L. gasseri, L. reuteri, L. rhamnosus, and L. plantarum (Molin et al.,1993). No single dominant species was found among the isolates.

A critical criterion of selection is that the probiotic strain must be tolerated bythe immune system and should not provoke the formation of antibodies against theprobiotic. This latter property, in conjunction with the ability of some LAB to surviveand colonize in the gut, has given rise to further applications, which involve their useas live vectors for oral immunization, i.e., introducing antigens targeting the GALTand aiming to induce a mucosal immune response (Marteau and Rambaud, 1993).

Strain viability and maintenance of desirable characteristics during product man-ufacture and storage is also a necessity for probiotic strains. The ability to multiplyrapidly on relatively cheap nutrients is a distinct advantage, as ease of culturing isimportant for technical application of the strains. Strain survival depends on suchfactors as the final product pH, the presence of other microflora, the storage temper-ature, and the presence or absence of microbial inhibitors in the product. Exploitationof the latest biotechnological advances in culture production, preservation, and storageshould aid in maintaining high numbers of probiotic bacteria in products.

11.4 PROBIOTIC EFFECTS

11.4.1 INTRODUCTION

A number of benefits in the ingestion of probiotics have been reported. Accordingto Vaughan et al. (1999), the beneficial effects of probiotic strains — demonstratedand proposed — are the following:

• Increased nutritional value (better digestibility and increased absorptionof minerals and vitamins)

• Alleviation of lactose intolerance• Positive influence on intestinal flora• Prevention of intestinal tract infections• Improvement of immune system• Reduction of inflammatory reactions• Prevention of cancer• Antiallergic activity


• Regulation of gut motility• Reduction of serum cholesterol• Prevention of osteoporosis• Improved well-being

11.4.2 INTESTINAL INFECTIONS

The primary claim regarding probiotics is their beneficial influence on the intestinalecosystem, which in turn may provide protection against GI infections and inflamma-tory bowel diseases. The desirable effects on human health include antagonistic activityagainst pathogens and antiallergenic action and other effects on the immune system.Whereas some of these claims remain controversial, well-planned clinical trialsincreasingly support them for carefully selected probiotic strains (Ouwehand et al.,1999). Some probiotic strains have been selected as bacteriolytic against Salmonella,Escherichia coli, and Staphylococcus aureus in associated cultures with the pathogens(Bielecka et al., 1998). The strains increased Bifidobacterium population numbers inthe colons of both healthy and Salmonella-infected rats and protected the naturalbalance of intestinal microflora (Bielecka et al., 2002). Bouhnik et al. (1996) andMatsumoto et al. (2000) observed an increase in Bifidobacterium population numbersin feces of healthy volunteers after 2 weeks of bioyogurt consumption. Bifidobacteriumspecies and L. acidophilus administered in milk were effective in reducing Candidaand Clostridium difficile occurrences in feces (Corthier et al., 1985).

The mechanism by which protection is offered by these probiotics has not yetbeen fully established. However, one or more of the following are possible: compe-tition for nutrients, secretion of antimicrobial substances, blocking of adhesion sites,attenuation of virulence, blocking of toxin receptor sites, immune stimulation, andsuppression of toxin production.

11.4.3 IMMUNE STIMULATION

One of the most interesting aspects of probiotic supplementation is directed towardimmune responses. Orally administered probiotic strains of LAB exert a positiveimpact on nonspecific and specific host immune responses. Nonspecific immuneresponses constitute the first line of host defense.

11.4.4 EFFECT ON NONSPECIFIC IMMUNE RESPONSES

The results of many experimental studies (Perdigon and Alvarez, 1992; Paubert-Braquet et al., 1995; De Petrino et al., 1995) have shown that the consumption ofcertain strains of LAB is able to enhance:

• Phagocytic activity of peritoneal and pulmonary macrophages and bloodleukocytes

• Secretion of lysosomal enzymes, reactive oxygen, nitrogen species, andmonokines by phagocytic cells

• In vivo clearance of colloidal carbon, an indicator of phagocyte functionof the reticuloendothelial system


Similar results have been reported for human subjects. Ingestion of fermentedmilk containing L. acidophilus LA1 or B. bifidum Bb12 for 3 weeks resulted inincreased phagocytic activity of peripheral blood leukocytes (Schiffrin et al., 1997).This increase in phagocytosis was coincidental with colonization by LAB.

The results of several animal studies indicate that the ability to enhance phago-cyte cell function is strain dependent. Structural differences in cell wall compositionof different LAB strains are suggested to be responsible for differences in efficacy.Furthermore, strains that are able to survive in the GI tract, adhere to the gut mucosa,and persist above a critical level are more efficient at stimulating phagocytic cells(Schiffrin et al., 1997). The results of studies of a large number of Bifidobacteriumstrains belonging to different species showed a large diversity in survival at low pHand bile, and in the adherence to the colon epithelium between strains belonging tothe same species, excluding B. animalis, in which the strains were uncommonlyhomogenous (Bielecka et al., 2000b). These and other results proved the importanceof careful probiotic strain selection.

Recent studies of Gill (1998) have shown that the magnitude of response alsodepends on the dose of LAB. Mice receiving a milk-based diet containing 1011

cfu/day of L. rhamnosus HN001 for 10 days showed significantly greater phagocyticactivity than mice receiving 109 or 107 LAB.

11.4.5 EFFECT ON SPECIFIC IMMUNE RESPONSES

Specific immune responses can be classified into broad categories: humoral immunity(HI) and cellular-mediated immunity (CMI). HI is affected by antibodies produced byplasma cells (mature B lymphocytes) that bind specifically to antigenic epitopes on thesurface of pathogenic organisms and with the aid of complement kill these pathogens.Specific classes of antibodies have specific functions. For example, IgA antibodiespredominate at the mucosal surfaces and prevent adherence of pathogens to the gutmucosa. IgG and IgM are involved in systemic neutralization of bacterial toxins andpromote phagocytosis by monocytes–macrophages via opsonization. Antibodies areeffective at neutralizing or eliminating extracellular pathogens and antigens (Gill, 1998)*.

CMI is mediated by T lymphocytes. On exposure to an antigen or pathogen, Tlymphocytes of predetermined clones proliferate or produce cytokines. Throughthese cytokines, T cells influence the activities of other immune cells, e.g., byaugmenting the ability of macrophages to kill intracellular pathogens and tumorcells. In addition, subsets of T cells act as helper cells (CD4+) for antibody produc-tion, as mediators of delayed type hypersensitivity (DTH), or as cytotoxic cells(CD8+) against virus-infected cells and cancer cells. CMI is particularly effectiveagainst intracellular pathogens and tumor cells (Gill, 1998).

Several studies in experimental animals and humans have demonstrated theimmunostimulatory effects of lactic cultures on several aspects of humoral and cell-mediated immunity (Nader de Macias et al., 1992; Perdigon et al., 1990; Kaila et al.,1992). Whether the immunoenhancing effects of LAB are related to their immuno-genicity is not known. It is well documented that mucosal antibodies prevent the

* Reprinted form Int. Dairy J. Vol. 8, pp. 535-544, 1998, El Sevier Science, Oxford, U.K. With permission.


adherence of pathogenic microorganisms to gut epithelium. It is likely, therefore,that antilactobacilli antibodies in gut secretions may interfere with the ability ofLAB to adhere and proliferate in the gut. If adherence and colonization to gutepithelium are essential for LAB to exert beneficial immunoenhancing effects, itwill be desirable to select strains that do not elicit an immune response to themselves.

11.4.6 FACTORS THAT INFLUENCE THE EFFICACY OF LAB

Several factors have an impact on the ability of LAB to influence immune function(Gill, 1998; De Petrino et al., 1995; Paubert-Braquet, 1995; Portier et al., 1993):

• A large variation exists in the ability of LAB to affect the immune system.• The effect of LAB on the immune system is dose dependent, with a higher

intake of LAB resulting in a superior response, compared with that of alower intake.

• Live cultures are more efficient at enhancing certain aspects of immunefunction than killed cultures.

• Lactic cultures delivered in fermented products induce a superiorresponse, compared to cultures given in unfermented products.

There is no information on the efficacy of LAB in relation to host age, physio-logical status, and dietary intake. All these factors may have an important bearingon the ability of LAB to influence host responses.

11.4.7 FUTURE

There is now strong evidence that certain strains of LAB are endowed with thecapacity to stimulate both nonspecific and specific immune functions. This highlightsthe opportunity for the dairy and health food industries to develop novel, value-adding, immunity-enhancing food products. However, many significant gaps remainin our knowledge. Therefore, future studies should be directed at:

• Demonstrating the relevance of immunomodulation to better health• Defining the effective dose for each strain• Elucidating the mechanisms by which LAB act on the immune system• Identifying new strains that are able to inhabit desired anatomical sites in

the gut and modulate desired immune functions

11.5 PROBIOTIC FOODS

11.5.1 FOOD PRODUCTS CONTAINING PROBIOTICS

Products containing probiotics come in a variety of formats:

• Conventional foods: probiotic-containing yogurts, fluid milk, and cottagecheese; consumed primarily for nutritional purposes, but also for probioticbenefits

• Food supplements or fermented milks: food formulations whose primarypurpose is to be a delivery vehicle for probiotic bacteria and their fermentation


end products; consumed for health effects, in monoculture (Yakult, Japan),mixed cultures (Actimel, Danone, LC1, Nestle) and others

• Dietary supplements: capsules and other formats designed to be taken byhealthy individuals to improve health

In the development of probiotic-containing food products, the product conceptmust take into account the desire of consumers for health-enhancing foods, but notat the expense of taste, convenience, and pleasurable nature of product. The abilityto communicate messages on health to the consumer is extremely important, e.g.,“promotes GI health,” “supports the body’s natural immune function,” but it mustbe scientifically accurate and in accordance with actual legislation, which may differfrom country to country. In addition to communications on health benefits of pro-biotic products, another important area of communication is on viable count or activeingredients in probiotic products. Statements as to content and counts of bacteria incommercial products are frequently not accurate, claiming the presence of certaingenera, species, or strain of probiotic, and rarely harbor any messages on probioticpotency. In countries where there is no legislation requiring this type of labeling,the consumer is unable to make an informed choice based on a guaranteed probioticcontent of a food product. In the long run, the failure of the industry to self-regulatein this regard may be its undoing. Consumers, unable to identify a potent product,may find a specific probiotic product ineffective and turn away from the entireproduct category.

11.5.2 EFFICACY OF PROBIOTIC PRODUCTS

Probiotic consumption can be justified only if a health effect or reduction in risk ofdisease can be realized by the consumer. Substantiation of health effects is a chal-lenge the probiotic industry is now facing, in large part because of the high costassociated with conducting controlled clinical or epidemiological evaluations. Thesehealth effects are believed to be genera, species, and strain specific. In many casescontrolled studies have not been done; however, a lack of proof has a great influenceon the use of health claims. There is no motivation for companies or consumers toinvest in technology supported mainly by testimonial, inference, or supposition.Therefore, the clinical evaluation of commercial products must be conducted and isessential for labeling health claims. The few probiotic strains whose effect in humanhealth is supported by clinical evaluations have a legitimate marketing advantage,even though the strains may be no more effective than other, untested bacteria.

Salminen et al. (1996) and Fonden et al. (2000) listed the number of variablesthat must be controlled for clinical evaluation of probiotics:

• Strain or combination of strains• Growth conditions of strain• Format for delivery (dried, supplemented in a food product, grown in a

food product)• Consumption level of active ingredient• Test population


• Validated biomarkers in combination with clinical end point• Clinical protocol, with preference to blinded, placebo-controlled formats

11.5.3 SAFETY

Although the safety of traditional lactic starter bacteria has never been in question,the more recent use of intestinal isolates of bacteria (bifidobacteria, intestinal lac-tobacilli, and enterococci), to be delivered as probiotics in high numbers to consum-ers with potentially compromised health, has raised the question of safety. Theseintestinal isolates do not share the centuries-old tradition of being consumed ascomponents of fermented dairy products. However, their presence in commercialproducts over the past few decades has not given any indication of a safety concern.

The safety of lactobacilli and bifidobacteria has most recently been reviewed bySalminen et al. (1998b). The general conclusion is that the pathogenic potential oflactobacilli and bifidobacteria is quite low. This is based on the prevalence of thesemicrobes in fermented foods, as commensal colonizers of the human body, and theconcomitant low level of infection attributed to them. A report from the LABIndustrial Platform (Guarner and Schaafsma, 1998) indicated that the overall riskof infection from LAB (excluding enterococci) is very low, but that L. rhamnosusdeserved particular surveillance, due to the greater proportion of infections attributedto this species, compared with infections by other lactobacilli. One commercial strainof L. rhamnosus, GG, has been used repeatedly in clinical trials and human studies,including one involving enteral feeding of premature infants (Saxelin, 1997).

Regarding the safety of enterococci, the picture is less clear. Foods containingenterococci are consumed on a regular basis. However, safety reports seem to agreethat the enterococci pose a greater threat than other LAB. Giraffa et al. (1997)concluded that the enterococci, although a group of phenotypically heterogeneousorganisms, display potential pathogenic properties. Adams and Marteau (1995)excluded the enterococci from LAB, which they regard as having low pathogenicpotential. Enterococci have been isolated from clinical infections: Enterococcus-mediated infections of the biliary tract, the abdomen, burn wounds, surgical wounds,and many others (Jett et al., 1994). Often, enterococci are isolated as pure culturesfrom these infections, showing their primary pathogenic nature (Aquire and Collins,1993). In the United States, vancomycin-resistant enterococci comprise a worrisomesource of nosocomial infections. This forms a serious threat to humans, as it isknown that gene transfer between enterococci and related organisms can occur rathereasily. In this respect, transfer of the VanA gene from Enterococcus faecium toStaphylococcus aureus has already been observed in vitro (Noble et al., 1992). Theseobservations and contradictory characteristics of enterococci make the use of thesemicroorganisms more and more questionable as food fermentation agents (Arthuret al., 1996).

11.5.4 CRITICAL QUESTIONS RELATED TO PROBIOTICS

Sanders and Huis in’t Veld (1999), in their extensive review, outlined the followingcritical questions related to probiotics:


• Identification of physiologically relevant biomarkers that can be used toassess parameters of probiotic effectiveness in humans (strain, dose, straingrowth, delivery conditions)

• Definition of active principle(s)• Stability parameters for active principle(s)• Resolution of taxonomy of probiotic species and development of user-

friendly methods for conducting speciation assessments• Science-driven implementation of findings in commercial products• Epidemiology and properly controlled human intervention studies to con-

firm probiotic efficacy

11.6 RECOMMENDATION FOR FUTURE RESEARCH

If probiotics are to be used to treat and prevent infection, the first studies that mustbe undertaken are to characterize fully (phenotypical and genotypical traits) themicroorganisms that will be used. If they do not demonstrate anti-infective traitsin vitro, it seems unlikely that they can be efficacious in humans. Scientific rationalefor the selection of the best species or strain for use as probiotics is not possiblewithout more information on the mechanisms by which probiotics exert their ben-eficial effects in vivo.

The benefits of probiotics are often demonstrated under defined experimentallaboratory conditions, but these beneficial effects fail to materialize in clinical trials,often because the trials are not properly controlled or consist of too few subjects.Large, double-blind, clinical trials are essential for establishing the practical andscientific logic of the probiotic concept.

The full potential of therapeutic manipulation of the enteric flora with probioticsmay not be optimally realized until our understanding of the normal flora is complete.The interaction between the host and the commensal flora requires basic investiga-tion.

Further information concerning the molecular basis of probiotic strains can havean impact on the development of strains with safe and effective novel probioticeffects. There is enormous potential for metabolic engineering, as has already beendemonstrated for several LAB. Indigenous bacteria vectors, such as Lactobacillus,might be considered safer than the Salmonella and virus vectors presently consideredfor these purposes.

The use of prebiotics in association with useful probiotics may be a worthwhileapproach, as prebiotics preferentially stimulate some probiotic strains. Combinationof probiotic and prebiotic as synbiotic can also enhance probiotic effectiveness.

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Arthur, M., Reynolds, P., and Courvalin, P., Glycopeptide resistance in enterococci, TrendsMicrobiol., 4, 401, 1996.

Berg, R.D., Probiotics, prebiotics or “conbiotics”? Trends Microbiol., 6, 89, 1998.Bielecka, M., Biedrzycka, E., and Biedrzycka, El., Isolation and identification of bifidobac-

terial strains, Med. Sci. Monitor Int. Med. J. Exp. Clin. Res., 6 (Suppl. 3), 123, 2000a.Bielecka, M. et al., Interaction of Bifidobacterium and Salmonella, Int. J. Food Microbiol.,

45, 151, 1998.Bielecka, M., Biedrzycka, E., and Majkowska, A., Selection of bifidobacterial strains capable

for colonisation of gastrointestinal tract, Med. Sci. Monitor Int. Med. J. Exp. Clin.Res., 6 (Suppl. 3), 123, 2000b.

Bielecka, M. et al., The influence of bifidobacteria on pathomorphological pattern and micro-flora of gastrointestinal tract in non-infected and Salmonella-administered rats, Br.J. Nutr. Suppl., in print.

Bouhnik, Y. et al., Effects of Bifidobacterium sp. fermented milk ingested with and withoutinulin on colonic Bifidobacteria and enzymatic activities in healthy humans, Eur.J. Clin. Nutr., 50, 269, 1996.

Cai, Y., Matsumoto, M., and Benno, Y., Bifidobacterium lactis Meile et al. 1997 is a subjectivesynonym of Bifidobacterium animalis (Mitsuoka 1969) Scardovi and Trovatelli 1974,Microbiol. Immunol., 44, 815, 2000.

Corthier, G., Dubos, F., and Raibaud, P., Modulation of cytotoxin production by Clostridiumdifficile in the intestinal tracts of gnotobiotic mice inoculated with various humanintestinal bacteria, Appl. Environ. Microbiol., 49, 250, 1985.

De Petrino, S.F. et al., Protective ability of certain lactic acid bacteria against an infectionwith Candida albicans in a mouse immunosuppression model by corticoid, FoodAgric. Immunol., 7, 365, 1995.

Fonden, R. et al., Effect of fermented dairy products on intestinal microflora, human nutritionand health: current knowledge and future perspectives, Bull. IDF, 352, 1, 2000.

Gibson, G.R., Dietary modulation of the human gut microflora using prebiotics, Br. J. Nutr.,80 (Suppl. 2), S209, 1998.

Gill, H.S., Stimulation of the immune system by lactic cultures, Int. Dairy J., 8, 535, 1998.Giraffa, G., Carminati, D., and Neviani, E., Enterococci isolated from dairy products: a review

of risk and potential technological use, J. Food Prot., 60, 732, 1997.Goldin, B.R. and Gorbach, S.L., Probiotics for humans, in Probiotics: The Scientific Basis,

Fuller, R., Ed., Chapman & Hall, London, 1992, p. 355.Guarner, F. and Schaafsma, G.J., Probiotics, Int. J. Food Microbiol., 39, 237, 1998.Huis in’t Veld, J.H.J., Havenaar, R., and Marteau, P., Establishing a scientific basis for probiotic

R&D, Trends Biotechnol., 12, 6, 1994.Jett, B.D., Huycke, M.M., and Gilmore, M.S., Virulence of enterococci, Clin. Microbiol. Rev.,

7, 462, 1994.Kaila, M. et al., Enhancement of the circulating antibody secreting cell response in human

diarrhoea by a human Lactobacillus strain, Pediatr. Res., 32, 141, 1992.Lilly, D.M. and Stillwell, R.H., Probiotics: Growth promoting factors produced by micro-

organisms, Science, 147, 747, 1965.Marteau, P. and Rambaud, J.C., Potential of using lactic acid bacteria for therapy and immu-

nomodulation in man, FEMS Microbiol. Rev., 12, 207, 1993.Matsumoto, M. et al., Effect of Bifidobacterium lactis LKM 512 yoghurt on fecal microflora

in middle to old aged persons, Microb. Ecol. Health Dis., 12, 77, 2000.Meile, L. et al., Bifidobacterium lactis sp. nov., a moderately oxygen tolerant species isolated

from fermented milk, Syst. Appl. Microbiol., 20, 57, 1997.Mitsuoka, T., Intestinal flora and human health: Asia Pacific, J. Clin. Nutr., 5, 1, 2, 1996.


Molin, G. et al., Numerical taxonomy of Lactobacillus spp. associated with healthy anddiseased mucosa of the human intestines, J. Appl. Bacteriol., 74, 314, 1993.

Nader de Macias, M.E. et al., Inhibition of Shigella sonnei by Lactobacillus casei and Lact.Acidophilus, J. Appl. Bacteriol., 73, 407, 1992.

Noble, W.C., Virani, Z., and Cree, R.G.A., Co-transfer of vancomycin and other resistancegenes from Enterococcus faecalis NCTC 12201 to Staphylococcus aureus, FEMSMicrobiol. Lett., 93, 195, 1992.

Ouwehand, A.C. et al., Probiotics: mechanisms and established effects, Int. Dairy J., 9, 43,1999.

Paubert-Braquet, M. et al., Enhancement of host resistance against Salmonella typhimuriumin mice fed a diet supplemented with yoghurt or milks fermented with variousLactobacillus casei strains, Int. J. Immunother., 11, 153, 1995.

Perdigon, G. and Alvarez, S., Probiotics and the immune state, in Probiotics, Fuller, R., Ed.,Chapman & Hall, London, 1992, p. 146.

Perdigon, G. et al., Prevention of gastrointestinal infection using immunobiological methodswith milk fermented with Lactobacillus casei and Lactobacillus acidophilus, J. DairyRes., 57, 255, 1990.

Portier, A. et al., Fermented milks and increased antibody responses against cholera in mice,Int. J. Immunother., 9, 217, 1993.

Roy, D. and Sirois, S., Molecular differentiation of Bifidobacterium species with amplifiedribosomal DNA restriction analysis and alignment of short regions of the ldh gene,FEMS Microbiol. Lett., 191, 17, 2000.

Roy, D., Ward, P., and Champagne, G., Differentiation of bifidobacteria by use of pulsed-field gel electrophoresis and polymeraze chain reaction, Int. J. Food Microbiol., 29,11, 1996.

Salminen, S. et al., Lactic acid bacteria in health and disease, in Lactic Acid Bacteria:Microbiology and Functional Aspects, 2nd ed., Salminen, S. and von Wright, A.,Eds., Marcel Dekker Inc., New York, 1998a, p. 211.

Salminen, S., Isolauri, E., and Salminen, E., Clinical uses of probiotics for stabilising the gutmucosal barrier: successful strains and future challenges, Antonie van Leeuwenhoek,70, 251, 1996.

Salminen, S. et al., Demonstration of safety of probiotics: a review, Int. J. Food Microbiol.,44, 93, 1998b.

Sanders, M.E. and Huis in’t Veld, J.H.J., Bringing a probiotic-containing functional food tothe market: microbiological, product, regulatory and labelling issues, Antonie vanLeeuwenhoek, 76, 293, 1999.

Saxelin, M., Lactobacillus GG: a human probiotic strain with thorough clinical documenta-tion, Food Rev. Int., 13, 293, 1997.

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2731-5871-6149-4/02/$0.00+$1.50© 2002 by CRC Press LLC

Major Food Additives

Adriaan Ruiter and Alphons G.J. Voragen

CONTENTS

12.1 Introduction ..................................................................................................27312.2 Classification ................................................................................................27412.3 Preservatives.................................................................................................275

12.3.1 Introduction ......................................................................................27512.3.2 Sulfite ...............................................................................................27612.3.3 Nitrite ...............................................................................................27712.3.4 Sorbic Acid.......................................................................................27712.3.5 Benzoic Acid ....................................................................................278

12.4 Antioxidants .................................................................................................27812.5 Flavorings, Colorants, and Sweeteners........................................................27912.6 Stabilizers, Emulsifiers, and Thickening Agents.........................................28112.7 Clarifying Agents and Film Formers...........................................................28312.8 Acidulants.....................................................................................................28312.9 Fat Substitutes and Fat Mimetics ................................................................28412.10 Prebiotics ......................................................................................................285References..............................................................................................................287

12.1 INTRODUCTION

The addition of certain substances to foodstuffs was practiced in ancient times,mostly for improving keeping properties. Salt was added to perishable foodstuffssuch as meat and fish from the prehistoric ages on. Smoke curing can also beconsidered as the fortuitous addition of constituents to food, as wood smoke containsa number of compounds that are absorbed by the food during the smoke-curingprocess or are deposited onto the surface. These treatments not only prolong theshelf life of the food but also add to the flavor.

The preparation of any food product includes the addition of a number of ingre-dients that are not considered to be additives, but clearly improve some properties ofthe food, such as keeping quality, and are originally intended as such. For example,preparation of a marinade in sour wine or vinegar is a technique for preserving fishthat was already known to the Romans, but acetic acid is not an additive in the strictsense of the word. In some cases, it is not so easy to determine whether or not thesubstance under consideration is an additive. It is helpful to keep in mind that anadditive is intended as an aid, for some purpose or another, not as an ingredient.

12


The Joint Food and Agriculture Organization/World Health Organization(FAO/WHO) Expert Committee on Nutrition (1955) defined food additives as “non-nutritive substances which are intentionally added to foodstuffs, mostly in small quan-tities, with the aim of improving the appearance, the flavor, the taste, the compositionor the shelf-life.” In a more recent wording, these food additives are described as“substances generally not intended as a foodstuff or as a characteristic ingredient ofa foodstuff which, irrespective of any nutritional value, are added, for any technologicalor sensoric reason, to a foodstuff during manufacturing, preparation, packaging, trans-port or storage, and from which it is expected that either the substance itself or reactionor decomposition products become a permanent component of the foodstuff or theraw material” (van Dokkum, 1985; Kamsteeg and Baas, 1985). In the latter definition,the term improvement is not included, and the remaining presence of the compound,or reaction products from that compound, is included in the definition.

This may be the result of a shift in the attitude toward additives. The ranking, bythe public, of actual food hazards was almost inverse to that given by Wodicka (1977),in which microbiological and nutritional risks were ranked at the top and food additivesat the very bottom. To some extent, this inversion lasts even today (Hall, 1999).

The preparation of any food product includes the addition of a number ofingredients that are not considered to be additives, but clearly improve some prop-erties of the food, such as keeping quality, taste, flavor, or texture, and are originallyintended as such.

The origin of food additives often remains a point of discussion. There is acontinuing demand, from the consumer’s side, for “natural” additives. No additive,however, is completely free from impurities. Products of chemical synthesis shouldbe purified, eliminating starting materials and compounds resulting from side reac-tions. It has to be stated that enzyme-catalyzed synthesis or modification more andmore replaces purely chemical synthesis of modification.

“Natural” compounds should be purified as well in order to remove accompa-nying substances that have no significance in the final product. Generally speaking,purification is more difficult and more complicated for “natural” additives, as it isalso much more problematic to characterize the raw material, which may contain agreat many ill-defined compounds whose toxicities are largely unknown (Ruiter,1989). Feberwee (1989) points out that official legislation does not discriminatebetween safe natural and safe artificial food additives. The main difference in safetyevaluation between these two categories is the long experience of man with naturaladditives (Lüthy, 1989).

12.2 CLASSIFICATION

Additives are mostly listed and classified into categories:

• Preservatives to extend the shelf life of foodstuffs• Antioxidants to protect lipids in food from attack by oxygen• Flavor enhancers to improve the perception of taste and flavors• Sweeteners to replace sugars in giving a sweet taste to the product• Colorants to improve the appearance of a foodstuff

Major Food Additives 275

• Emulsifying agents to enable and maintain a fine partition of oils or fatsin water (or a partition of water in oils or fats) and of gas in liquid (foam)

• Thickening and gel-forming agents• Clarifying agents• Film formers• Glazing agents• Acidulants• Fat substitutes and replacers• Substances improving nutritional value• Pro- and prebiotics• Many other substances, such as anticlotting agents, moisteners, antifoam-

ing agents, flour improvers, leavening agents, baking powders, meltingsalts, stiffening agents, complexing agents, fillers, and enzymes.

With respect to reactivity of additives, it is preferable to make another classifi-cation, in which three groups can be distinguished:

• Substances that, simply by their presence, lead to the desired improve-ment. Most colorants, sweeteners, and some preservatives belong to thisclass. Many of these additives do not display a strong reactivity towardother constituents during preparation and storage of the foodstuffs towhich they are added.

• Substances that are added because of their reactivity toward undesirablecomponents already present or arising during manufacturing or storageand that may be bound by these added substances. The reaction may bedirected toward these components themselves or toward their precursors.Antioxidants are an example of this category, as well as some peculiarsubstances reacting with matrix components to make desirable compo-nents such as flavor compounds.

• Food additives that participate, for a part, in fortuitous reactions that, insome cases, may be undesirable.

This classification, however, also has its limits. First, there is hardly any additivethat does not take part in some chemical reaction at all. Furthermore, some foodadditives may also participate in unintentional reactions. Therefore, in this presen-tation some additives are discussed individually, with emphasis on their reactivitytoward matrix compounds.

12.3 PRESERVATIVES

12.3.1 INTRODUCTION

Preservatives are added in order to protect a variety of foodstuffs against microbialspoilage. This protection is possible, in many cases, because of a chemical reactionbetween the preservative and the microorganisms. It may therefore be expected thatthese compounds show some reactivity toward food components as well.


Many preservatives are comparatively reactive compounds, e.g., sulfite, nitrite,and sorbic acid, but some show a moderate reactivity only, e.g., benzoic acid. Sulfite,nitrite, sorbic acid, and benzoic acid are discussed below.

12.3.2 SULFITE

Disinfection by the vapors of burning sulfur is an old technique that was frequentlyused to decontaminate wine casks. Some sulfur dioxide was left in these vessels,preventing the wine from unwanted microbial infections.

At present, sulfites are used both as preservatives and as agents that stop browningreactions. In food, the HSO3

– species predominates, while in dehydrated food it isexpected that S(IV) mainly exists as metabisulfite (HS2O5

2–), which is in equilibriumwith HSO3

– and SO32– (Wedzicha et al., 1991). Because of the nucleophilicity of the

sulfite ion, many reactions with food components are possible (Wedzicha, 1991), oneof these being the reversible addition to carbonyl compounds. It is suggested that thesulfite rather than the bisulfite ion acts as the nucleophilic agent (Wedzicha et al., 1991).

This reaction has many implications for foodstuffs. For example, aroma com-ponents possessing a carbonyl group become involatile and do not contribute any-more to the overall flavor. Other nucleophilic reactions include the cleavage of S–Sbonds in proteins and addition to C=C bonds of α,β-unsaturated carbonyl com-pounds. Control of nonenzymatic browning is based on this latter reaction (McWeenyet al., 1974). A key intermediate of the Maillard reaction, i.e., 3,4-deoxyhexulos-3-ene, is efficiently blocked by a fast reaction with sulfite, leading to formation of 3,4-dideoxy-4-sulfohexosulose, which is much less reactive and in which sulfite isirreversibly bound.

Ascorbic acid browning is also inhibited by the addition of sulfite (Wedzicha andMcWeeny, 1974). The same holds for polyphenol oxidase-catalyzed oxidation ofnatural phenols in fruit. The mechanism of the inhibition is by reaction of o-quinoneintermediates with sulfite, which leads to nonreactive sulfocatechols (Wedzicha, 1995).

An undesirable reaction of sulfite in food is the cleavage of thiamin by meansof an attack at the pyrimidin moiety (Zoltewicz et al., 1984). This was one of thereasons for a ban, in many countries, on the use of sulfite in meat. Another reasonis the preserving effect on the meat color, which makes stale meat look as if it werefresh. Sulfite, however, is unable to reduce metmyoglobin back to myoglobin (Wed-zicha and Mountfort, 1991).

An important reaction, in a quantitative respect, is the cleavage of disulfide bondsin meat proteins, in particular, in lean meat.

The reducing capacities of sulfite should be emphasized as well. In fact, cleavageof S–S bonds by sulfite can be considered a reduction. This property of sulfite makesit useful as an additive to flour for biscuit making (Wedzicha, 1995). The cleavageof disulfide bonds in wheat proteins speeds up and facilitates the production of asatisfactory dough.

A quite different type of reaction, which may also occur in food, is thereduction of azo dyes to colorless hydrazo compounds. Like in the reaction withcarbon compounds, the reactive species is SO3

2- and not HSO3– (Wedzicha and

Rumbelow, 1981).


12.3.3 NITRITE

lt has been known for a long time that small amounts of saltpeter (KNO3) are ableto cause a reddish discoloration of meat, which is characteristic for many meatproducts. In about 1900 it was established that it was not nitrate, but its reductionproduct, i.e., nitrite, that was responsible for this color development.

Some decades later, nitrite was recognized as a potent inhibitor of microorgan-isms, including pathogens, in many meat products. In particular, the inhibition ofClostridium botulinum, with accompanying toxin formation, was established. Therole of nitrite in the characteristic cured meat flavor was still noticed later on.

The inhibitive action of nitrite is pH dependent, which led to the assumption thatundissociated nitrous acid is the active substance. However, this is a hypothetical acidfrom which equimolar parts of H2O, NO, and NO2 are formed. In the 1960s it becameclear that nitric oxide (NO) is the active species. Nitric oxide can also be generatedthrough reduction of nitrite, e.g., by ascorbate or isoascorbate (Wirth, 1985).

Nitric oxide shows a strong binding to iron and is able to block iron atoms inbiologically active compounds important in cell metabolism, in particular in theoutgrowth of germinated spores (Woods et al., 1989). In meat products preservedwith nitrite, NO binds to heme iron, thus forming nitrosomyoglobin (Giddings, 1977).

There is some evidence that inhibition of C. botulinum outgrowth in nitrite-curedmeat products is mainly due to iron binding in such a way that this is no longeravailable for outgrowth of Clostridium spores. This strong binding also explains theantioxidative properties of nitrite in these products (Grever and Ruiter, 2001).

Fat is also able to bind some nitric oxide. The amount incorporated in fat isconsiderably higher in unsaturated than in saturated lipids. Furthermore, nitrite isable to react with intermediates of the Maillard reaction, such as 3-deoxyosulose(Wedzicha and Wei Tian, 1989).

The reaction of nitrite with secondary or tertiary amines, though unimportant inquantitative respect, leads to N-nitroso compounds, which, for a considerable part, arepotent carcinogens. These compounds may rearrange to form highly electrophilic dia-zonium ions that react with cellular nucleophiles such as water, proteins, and nucleic acids.

Nitrate ingested with food or drinking water is partially reduced to nitrite in thebody and contributes more than nitrite in meat products to the possible endogenousformation of N-nitroso compounds. A ban on the use of low amounts of nitrite asan additive is therefore not very rational and deprives the consumer of a very effectiveguard against a number of pathogenic microorganisms, in particular C. botulinum,but also Clostridium perfringens and Staphylococcus aureus.

Finally, nitrite may react in physiological concentrations and under gastric pHconditions with naturally occurring, as well as synthetic, antioxidants (Kalus et al.,1990). There are no indications for the formation of hazardous reaction conditionsfrom a viewpoint of mutagenicity.

12.3.4 SORBIC ACID

The preserving properties of sorbic acid were recognized around 1940. During thelate 1940s and the 1950s, sorbic acid became available on a commercial scale,


resulting in its extensive use as a food preservative throughout the world (Sofos andBusta, 1983). As a straight-chain trans-trans dienoic fatty acid (FA) (CH3–CH =CH–CH = CH–COOH), it is susceptible to nucleophilic attack (Khandelwal andWedzicha, 1990b). The lowest electron density is associated with position 3. Nucleo-philic groups, e.g., the thiol group, however, may bind to the carbon atom at the 5position as the terminal methyl group delocalizes the charge (Khandelwal andWedzicha, 1990a; Wedzicha, 1995). Sorbic acid inactivates several intracellularenzymes by this mechanism. It passes the cell wall in its undissociated form only,which explains its low activity at higher pH values. The pKa value at 25°C amountsto 4.76. It is mainly active against yeasts, molds, and strictly aerobic bacteria. Thetoxicity toward mammals is low.

Sorbic acid is easily oxidized. This oxidation is accompanied by the developmentof a glyoxal-like flavor in sorbic acid preparations and a brown color in a widevariety of model foods in which sorbic acid was included. Amino acids acceleratecolor development (Wedzicha et al., 1996).

12.3.5 BENZOIC ACID

This compound is relatively stable during food processing and in food products. Itwas proposed in 1875 by H. Fleck as a replacer for salicylic acid and can beconsidered as one of the first safe food preservatives. Like sorbic acid, it is mainlyactive against yeast and molds, but the growth of micrococci, Escherichia coli, andmany other bacteria is retarded as well.

As is the case with sorbic acid, benzoic acid penetrates the cell wall in theundissociated form. As a consequence, it is active at lower pH values only (pKa at25°C = 4.19) and therefore serves as a preservative for sour products such as fruitjuices and jams. In shrimp preservation it is applied as a powder that is spread overthe shrimps, passes cell walls, and then ionizes in the intracellular fluid to yieldprotons that acidify the alkaline interior of the cell. The main cause of its activity,however, is biochemical effects (Eklund, 1980) such as inhibition of oxidativephosphorylation and of enzymes from the citric acid cycle (Chipley, 1983). Inmayonnaise preserved by benzoic acid, the undissociated acid is mainly present inthe lipid phase, which can be considered as a reservoir for the aqueous phase.

Benzoic acid is often combined with sorbic acid in order to reduce its peculiarflavor. It has to be stated, however, that this is at least partly caused by impuritiesin the benzoic acid preparation used.

12.4 ANTIOXIDANTS

Antioxidants can be defined as “substances that, when present in low concentrationscompared to those of an oxidizable substrate, significantly delay or inhibit oxidationof that substrate” (Halliwell and Gutteridge, 1989).

Antioxidants are frequently added to unsaturated fats and oils in order to protectthese against oxidative deterioration. For this reason, they are also added to a varietyof food products containing unsaturated lipids. Antioxidants frequently applied areesters of gallic acid, butylated hydroxyanisole (BHA), butylated hydroxytoluene


(BHT), and tertiary butylhydroxyquinone (TBHQ). Of these, TBHQ is by far themost potent antioxidant. In both BHA and BHT, the butyl groups are also of a tertiarystructure (Figure 12.1).

Antioxidants are naturally present in many foodstuffs and are of great importanceas inactivators of radical formation. Some antioxidative enzyme systems are pro-duced in the human body and are supposed to play an important role in the cellulardefense against oxidative damage (Langseth, 1995).

Many of the antioxidants present in food have the function of terminating chainreactions. A variety of compounds such as phenols, aromatic amines, and conjugatescan function as chain-breaking antioxidants. They react with the chain-propagatingradical species, which results in the formation of radical species incapable of extract-ing hydrogen atoms from unsaturated lipids. These radicals may rapidly combinewith other radicals or, if a polyphenolic structure is present (e.g., gallic acid esters),disproportionate into their original state and a quinoid form.

Since there are synergistic effects between antioxidants, commercial preparationsusually contain mixtures of these antioxidants. As oxidative rancidity is strongly cata-lyzed by some heavy metal ions, in particular Cu++, antioxidant mixtures often containsequestrants (e.g., citric acid and ethylenediaminetetraacetic acid (EDTA)) in order tocomplex these ions. Reductants such as ascorbic acid, which decrease the local concen-tration of oxygen, are also able to decrease the formation of peroxy radicals.

Fat oxidation by bacteria can be suppressed by the addition of preservatives suchas benzoic acid or sorbic acid.

12.5 FLAVORINGS, COLORANTS, AND SWEETENERS

Artificial flavorings are frequently added to a variety of foodstuffs. These prepa-rations mostly consist of a large number of different compounds, of which some

FIGURE 12.1 Antioxidants. Top: from left to right, alkyl gallates, the two isomers of BHA.Bottom: fom left to right, BHT and TBHQ.


show a considerable reactivity. The way in which flavor components interact withthe food matrix and how this influences flavor perception has been reviewed byBakker (1995).

Many interactions are of a pure chemical nature and may result from thepresence of aldehydes and their reactivity toward amino and thiol groups ofproteins. Another frequently occurring type of interaction is the formation ofhydrogen bonds between food compounds and polar flavor components such asalcohols. Starch, starch-derived maltodextrins, and β-cyclodextrin are able to forminclusion complexes with many flavor components. Many other interactions,although of great influence on flavor perception, are of a physical nature andtherefore not mentioned in this chapter.

Food additives such as dyes and sweeteners are not intended to react with matrixcompounds or to undergo other reactions. Some reactions may occur, however, anda few examples are given here.

As for food dyes, many of these are azo compounds, which implies the possibilityof reduction, e.g., by the action of certain bacteria. The loss of color, in these cases,is an indication of spoilage. Bisulfite is also able to reduce azo dyes (Wedzicha andRumbelow, 1981).

Sweeteners have been applied to foodstuffs for many years. Compounds suchas saccharin, sodium cyclamate, aspartame, and several others are well known andhardly need to be discussed here. In later times, sweeteners such as sucralose andthaumatin appeared on the scene. Sucralose is a sucrose derivative obtained bychlorination, by which the D-glucopyranosyl unit is converted to a galactopyranosylunit chlorinated at position 4, while the fructofuranosyl unit is chlorinated at posi-tions 1 and 6. This results in an intense sweetness (600 times that of sucrose) anda greater stability toward acids (Figure 12.2).

FIGURE 12.2 Sucralose.


Thaumatin is a protein from katemfe fruit (Thaumatococcus danielli), with thestrongest sweetening properties hitherto known (2500 times as sweet as sucrose).The protein is freely soluble in water, consists of 207 amino acids, and shows amolecular weight of 22 kDa and an I.E.P. of 11.5. The electrical charge in themolecule is thought to be a major factor in the interaction with taste receptors (Boy,1994). It synergizes with aspartame and with flavor enhancers such as 5'-nucleotidesand sodium glutamate. Apart from this, it masks the aftertaste of saccharin. It alsomasks metallic and bitter taste components.

Taste interactions between sweeteners are not uncommon. Another example isthe synergism between aspartame and acesulfame K. A 70/30 blend, in some cases,shows a taste that cannot be distinguished from sugar. Acesulfam K also shortensthe long, sweet aftertaste of sucralose (Meyer, 2001). Apart from taste interactions,some sweeteners also show synergism with flavors.

Some sweeteners may undergo chemical reactions, thereby losing their sweetproperties. The instability of saccharin at higher temperatures is well known. Apartfrom this, saccharin is subject to some degradation under acidic conditions, yield-ing sulfobenzoic acid, which has a disagreeable phenolic flavor. Another exampleis aspartame, which is the methyl ester of N-L-α-aspartyl-L-phenylalanine.Because of its nature, the stability in aqueous systems is limited. The maximumstability is between pH values of 3 and 5 and decreases at higher temperatureswith concomitant loss of sweetening power. The main degradation product is 3,6-dioxo-5-(phenylmethyl)-2-piperazinoacetic acid (Furda et al., 1975). Otherdecomposition products are listed by Stamp and Labuza (1989), who added somenovel components to this group. These all have in common the absence of a sweettaste. Apart from this, aspartame shows remarkable reactivity toward a number ofaldehydes that may be present in foodstuffs and contribute to flavor (Hussein et al.,1984; Cha and Ho, 1988), and thaumatin reacts with carrageenans if these arepresent (Ohashi et al., 1990).

Many unintended and sometimes unwanted reactions of artificial dyes, sweet-eners, and other additives with the food matrix are imaginable and should alwaysbe taken into consideration when the consequences of such additions to foodare discussed.

12.6 STABILIZERS, EMULSIFIERS, AND THICKENING AGENTS

The most important representatives of these compounds are polysaccharides:starch and starch derivatives (α-1,4 D-glucans); cellulose and cellulose deriva-tives (β-1,4 D-glucans); plant extracts (pectins: α-1,4 D-galacturonans); seaweedextracts (carrageenan, agar, and alginates); seed flour (guar and locust beangalactomannans, tamarind xyloglucans, and konjac glucomannans); exudategums (arabic, karaya, and tragacanth); and microbial gums (xanthan, gellan, andcurdlan). Polymers are made of one or more types of sugar residues and arecovalently attached in linear, linearly branched, and branched structures. Theiranomeric form (α/β), types of linkages (1,2; 1,3; 1,4; 1,4,6; 1,3,6; etc.), presenceof functional groups (carboxyl, phosphate, sulfate, esters, and ethers), and molec-ular weight distribution determine their conformation in aqueous systems (stiff


or rod-like, random coil, helices), the intra- and intermolecular interactionsbetween molecules (dimerization, association, ionic interactions, hydrophobicinteractions), and the interactions with other molecules (other polysaccharides,proteins, and lipids). These interactions are the basis for viscous behavior,gelling, water binding, film forming, bulking, stabilizing, and emulsifying prop-erties. Some polysaccharides act synergistically in imparting these functions,e.g., locust bean gum and carrageenan, locust bean gum and xanthan, pectin andalginate. Important parameters for applications are pH, heat and shear stability,syneresis properties, shelf life, and compatibility with other food constituents.Derivatives of these polysaccharides with improved functional properties arealso used.

Emulsifiers are amphophilic compounds that concentrate at oil or water inter-faces, causing a significant lowering of interfacial tension and a reduction in theenergy needed to form emulsions. They can be anionic, cationic, and nonioniccompounds that have one or more of the following characteristics: surface active,viscosity enhancer, solid absorbent, or hydrophilic/lipophilic balance (HLB). Theyare added to food emulsions to increase emulsion stability and to attain an acceptableshelf life. Polysaccharides are not surface-active agents, but rather macromolecularstabilizers that generally function through enhancement of viscosity and envelopingoil droplets in oil-in-water (O/W) emulsions. The emulsifiers used in food manu-facture were categorized by Artz (1990) (cf. Table 12.1). Only lecithin is of naturalorigin. Its main source is soybean, but it is also present in corn, sunflower, cottonseed,rapeseed, and eggs.

Emulsifiers stabilize emulsions in various ways. They reduce interfacialtension and may form an interfacial film that prevents coalescence of droplets.In addition, ionic emulsifiers provide charged groups on the surface of theemulsion droplets and thus increase repulsive forces between droplets. Emulsi-fiers can also form liquid crystalline microstructures such as micelles at theinterface of emulsion droplets. These are formed only at emulsifier concentra-tions larger than the critical micelle-forming concentration. These microstruc-tures have a stabilizing effect.

TABLE 12.1Food Emulsifier Categories

Category Typical Application

Lecithin (naturally occurring) and lecithin derivativesGlycerol FA estersHydroxycarboxylic acid and FA estersLactylate FA estersPolyglycerol FA estersPolyethylene and propylene glycol FA estersEthoxylated derivatives of monoglyceridesSorbitan FA esters

——Baking goods, margarine—Baked goodsO/W emulsions—Antistaling


Proteins also have a major influence on emulsion stability, although varioustypes of instability may occur: instability caused by coalescence or flocculation, andcream layer formation caused by differences in density between oil droplets and theaqueous phase. In practice, the latter problem is the most difficult to solve.

Creaming can be retarded by increasing the viscosity of the aqueous phase andby reducing the diameter of oil droplets or the density difference. The densitydifference between an oil droplet and serum can be reduced by loading as muchprotein as possible on the oil droplet surface. An open, random-coil protein, suchas sodium caseinate, is expected to give less protein loaded on the oil surface thancompact proteins do. It has been shown that open-structure proteins show a lowerequilibrium surface load than compact structure proteins (Zwijgers, 1992). Thehigher the equlibrium surface load, the better the emulsion-stabilizing protein.

In line with the foregoing, milk protein hydrolysates are useful foamers andemulgators. The foam- and emulsion-forming properties of milk peptides are evensuperior to those of intact milk proteins, as long as these show both charged andhydrophobic areas (Caessens et al., 1999).

The selection of emulsifiers to prepare food emulsions is mainly based ontheir HLB number. This index is based on the relative percentage of hydrophilicto lipophilic groups within the emulsifier molecule. Lower HLB numbers indicatea more lipophilic emulsifier, while higher numbers indicate a more hydrophilicemulsifier. Emulsifiers showing HLB numbers between 3 and 6 are best for water-in-oil (W/O) emulsions, and emulsifiers with numbers between 8 and 18 are bestfor O/W emulsions.

12.7 CLARIFYING AGENTS AND FILM FORMERS

Clarifying agents or flocculants are used to eliminate turbidity or suspend particlesfrom liquids, e.g., chill haze in beer, precipitates in fruit juices and wines, and hazein oils. Often, they provide a nucleation site for suspended fines. Examples ofclarifying agents are lime in sugar juice clarification, pectic enzymes to break downpectins in fruit juices, and gelatin for clarification of fruit juices.

Film formers are used to coat food by providing it with a protective layer andso making it more attractive in appearance or increasing its palatability. Film formersmay not impart flavor or mouth feel of their own to the food. Examples are starchesto coat proteins to prevent Maillard reactions, mineral oils to seal pores of eggs, andsodium caseinate to encapsulate fat in whiteners.

12.8 ACIDULANTS

Food acidulants find their application, for the greater part, in beverages and infruit and vegetable processing. Apart from pH lowering, acidulants provide buffercapacity, impair sourness and tartness, enhance the effect of preservatives, and forsome acidulants such as citric acid, prevent discoloration caused by trace metals(Seifert, 1992).


Besides acids, other components that produce or release acids are applied asacidulants, in particular when a slow release of acid is of importance. A well-knownslow-release acidulant is glucono-δ-lactone (GDL), which is used in bakery products,dairy products, and in particular, meat products (Watine, 1995) (Figure 12.3).

The use of GDL in the maturation of dry sausages is well known. Duringpreparation of these sausages, GDL standardizes acidification, strongly reduces riskof contamination, and improves quality. GDL gradually lowers the pH to 5.4, andafter filling the sausage casings, the temperature is lowered to 0–4°C for some hours.During this period the growth of starters and undesirable bacteria is inhibited. Thenthe temperature is increased so that fermentation can take place normally.

12.9 FAT SUBSTITUTES AND FAT MIMETICS

Dietary fat contributes to the combined perception of mouth feel, taste, and aroma. Fatalso contributes to creaminess, appearance, palatability, texture, and lubrication propertiesof foods, and it increases the feeling of satiety during meals. Apart from this, it is ableto carry lipophilic flavor compounds and can act as a precursor for flavor development.A very important characteristic of fat is its suitability to be used for frying.

Due to their high caloric value, there is an increasing tendency to replace fatsand oils with components that are not calorific but can impart the same technologicaland sensory functionalities.

Two types of fat replacers can be distinguished: fat substitutes and fat mimetics.Fat substitutes are lipid- or fat-based macromolecules that physically and chemicallyresemble triacylglycerols (e.g., sucrose polyesters or alkyl glycoside polyesters). Fatmimetics are protein- or carbohydrate-based compounds that imitate organolepticor physical proteins or triacylglycerols (Voragen, 1998). Fat substitutes physicallyand chemically resemble fats and oils, as these are esters of polyols. They are stableat cooking and frying temperatures.

Many carbohydrate-based fat substitutes are mixtures of sucrose esters formedby chemical transesterification or interesterification of sucrose with one to eight FAs.The class with six to eight FAs are called sucrose FA polyesters. These moleculesare too large to be broken down by intestinal lipase enzymes and, for that reason,do not show any caloric value (Voragen, 1998).

FIGURE 12.3 D-Gluconolactone.


Olestra, in this respect, is a promising compound. The stability of Olestra iscomparable to natural fats and even better. Applied as a frying medium, it appearsto undergo slower oxidative and hydrolytic degradation (Lindley, 1996). The func-tionality and potential application of the sucrose FA polyesters is governed by thetype of fatty esters used in the manufacture. The melting character depends on thelength and the degree of saturation of the FA in a similar way. In theory, this meltingcharacter may be adjusted by a right choice of FA (Lindley, 1996).

The esters containing one to three FAs are called sucrose FA esters (SFEs).Unlike sucrose FA polyesters, the SFEs are easily hydrolyzed and absorbed bydigestive lipases, and are thus caloric. SFEs containing five to seven free hydroxylgroups with one to three FA esters show both hydrophilic and lipophilic propertiesand therefore give excellent emulsifying and surface-active properties. In addition,they are effective lubricants, anticaking agents, thinning agents, and antimicrobials(Voragen, 1998).

Other carbohydrates modified to FA esters are sorbitol, trehalose, raffinose,and stachyose.

Saccharide-based fat mimetics differ strongly from fats and oils. Generally theyabsorb a substantial amount of water and are therefore not suitable for frying. Asthey can carry only water-soluble flavors, they lack the flavor of fats and oils. Inulinand starch hydrolysates (dextrose equivalent ~ 2) are striking examples of a fatmimetic. The fat substitution is based on its ability to stabilize water into a creamystructure that has a fat-like mouth feel (Blomsma, 1997).

Most carbohydrate-based fat replacers are extracted from by-products rich incell wall polysaccharides. Polydextrose, which can be applied both as a carbohydrateand as a fat replacer, is obtained by vacuum thermal polymerization of glucose,using citric acid as a catalyst and sorbitol as a plasticizer (Voragen, 1998).

12.10 PREBIOTICS

In Chapter 11, it is stated that the use of prebiotics in association with usefulprobiotics may be a worthwhile approach, as prebiotics may stimulate someprobiotic strains.

The term prebiotics is derived from the Greek and can be translated as “priorto life.” Generally, prebiotics comprise food additives that are barely or not digestedin the small intestine and end up in the colon, where they may stimulate beneficialbacteria by serving as fermentation substrates. Promotion and regulation of healthis the aim of these bioactive products that present an important trend in the present-day production of foods.

Nondigestible carbohydrates are the main representatives of class of food addi-tives. There are three main types of carbohydrates that are indigestible in the humansmall intestine: nonstarch polysaccharides, resistant starch, and nondigestible oli-gosaccharides (NDOs). As the average daily ingestion of the latter group is lowerthan the level considered safe, i.e., not over 15 g/day, supplementation of NDOscould be beneficial (Voragen, 1998). These can be used in a wide range of processedfoods, including dairy products, confectioneries, bakery products, ready meals,breakfast cereals, and drinks. Other significant beneficial effects are:


• Replacement of sugar and fat• Reduction of the number of unwanted bacteria in the colon• Fiber enrichment of foods hitherto poor in fiber, e.g., white bread, dairy

products, transparent drinks• Prevention of tooth decay• Regulation of lipid metabolism (van Haastrecht, 1995)

Two specific groups of NDOs, which are commercially available, have to bementioned: fructo-oligosaccharides (FOSs), obtained by transfructosylation ofsucrose using a β-D-fructosyltransferase or by hydrolysis of inulin by endo-inuli-nase; and galacto-oligosaccharides (GOSs), obtained by transgalactosylation of lac-tose using β-galactosidase. Inulin is a virtually linear fructose polymer in which thefructose molecules are linked by β-(2-1) bonds with an average degree of polymer-ization ranging from 2–60 (average length of 10).

Most oligosaccharides have a moderate reducing power by which they are stillliable to Maillard reactions when used in food to be heat processed. FOSs of theGFn type (composed of fructofuranosyl residues and one terminal, nonreducingglucosyl residue, obtained by transfructosylation), e.g., lactosucrose and glycosyl-sucrose, have no reducing power. FOSs by hydrolysis of inulin can be of the GFn

type or of the Fm type, the latter having a reducing fructofuranosyl residue(Figure 12.4).

FIGURE 12.4 Two types of FOSs (sucrose of comparison). (After van Haastrecht, J., Int.Food Ingredients, 1995.)


At pH < 4 and treatments at elevated temperatures or prolonged storage atambient conditions, oligosaccharides present in a food can be hydrolyzed, resultingin loss of nutritional and physicochemical properties. For FOSs it is reported thatin a 10% solution of pH 3.5, less than 10% is hydrolyzed after heat treatments of10 sec at 145°C, 5 min at 45°C, or 60 min at 70°C. After 2 days at 30°C, less than5% is hydrolyzed. The stability can greatly differ for the various classes of oligosac-charides, depending on the sugar residues present, their ring form, and anomericconfiguration and linkage types. Generally β-linkages are stronger than α-linkages,hexoses are more strongly linked than pentoses and deoxysugars, and pyranoses aremore strongly linked than furanoses.

Finally, resistant starch is a class of dietary carbohydrates that are attracting anincreased interest from food manufacturers, due to the beneficial effects these mighthave on human health. These starches escape digestion and absorption in the smallintestine of humans and reaches the large bowel, where fermentation takes place.As a result, the pH in the colon is lowered and short-chain FAs are formed. Theyfurther increase fecal bulk and may protect against colon cancer, improve glucosetolerance, and lower blood lipid levels. The most important forms of resistant starchin the diet are botanically encapsulated starch present in intact foods, starches witha B-type crystalline structure present in unheated foods, starch retrogradated as aresult of full gelatinization and dispersion by processing, and thermally or chemicallymodified starches (Voragen, 1998).

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2911-5871-6149-4/02/$0.00+$1.50© 2002 by CRC Press LLC

Food Safety

Julie Miller Jones

CONTENTS

13.1 Introduction ..................................................................................................29113.2 Consumer Attitudes toward the Food Safety Problem................................29313.3 Tests to Determine Food Safety ..................................................................29413.4 Food Safety Concerns ..................................................................................29613.5 Microbial Contamination of Food ...............................................................29613.6 Risk-Benefit as It Applies to Food ..............................................................29813.7 Nutritional Evaluation of Food Processing .................................................300

13.7.1 Effects on Vitamins ..........................................................................30013.7.2 Effects on Minerals ..........................................................................302

13.8 Newer and Novel Technologies ...................................................................30213.8.1 Irradiation .........................................................................................30213.8.2 Biotechnology ..................................................................................303

13.9 Additives.......................................................................................................303References..............................................................................................................304

13.1 INTRODUCTION

Safe food — it is what every individual expects in every mouthful and everygovernment strives to give its populace. Since food is the object of our earliestpreferences and the subject of our strongest prejudices, food safety is a gut issue.Yet what seems on the surface to be both basic and imperative is not at all simple,and in fact, is not achievable in the absolute sense. It is extremely hard to accepteven the idea that food is relatively — not absolutely — safe. What appears tothreaten food, threatens in a very direct and visceral way.

An understanding of basic definitions about safety and toxicity is crucial. First,all compounds, no matter how salutary, can be ingested in some manner or in somequantity that will cause toxicity. Toxicity is the capacity of a substance to producesome adverse effect or harm. Even essential components such as water and vitaminscan be consumed at toxic levels. Too much pure water can cause renal shutdown;excessive vitamins can cause minor problems such as flushing or nausea or majorproblems such as liver damage, teratogenicity, and death. The 1538 Paracelsus motto,“Only the dose makes the poison,” operates for food components (Jones, 1992).

13


Second, what is safe for one is not safe for another. Individuals who haveallergies, inborn or acquired errors of metabolism, or certain diseases can ingestfood in a usual and customary manner and yet suffer adverse and even, in rareinstances, fatal outcomes. Thus, foods that are safe for most are not safe for all.

Third, how the food is used or produced may alter its safety. Combinations offoods and drugs or a certain food with a bizarre or poor diet can render an otherwisesafe food as harmful. A food may contain an unexpected contaminant such as amycotoxin or toxin, acquired during certain growing or feeding conditions. Thus,what is usually safe harbors a masquerading toxin.

Since absolute safety is unattainable, relative safety is what is sought. Relativesafety is the probability that no harm will come when the food is consumed in ausual and customary manner. Even relative safety when it comes to food is a bigorder, because it requires constant diligence by each party who comes in contactwith the food. Any glitch in the system from the field to the table can introduce apotential hazard.

The starting material, i.e., the food itself, must not have high levels of naturallyoccurring toxicants. Safety must be maintained by growing the food in an environ-ment free of pollutants or contaminants. Plant raw materials must be free of infes-tations, harmful residues, mold, and mycotoxins. Animal raw materials should notcontain any veterinary drug residues or any abnormal constituents transferred fromfeedstuffs. Metal particles, weed contaminants, or other incidental components fromharvesting or processing must be vigilantly prevented. During transportation fromthe field to plant or market, carriers must handle the food to maintain its quality.Care must be exercised so that proper temperatures and moisture levels are main-tained and no infestation occurs during any point of the storage, shipping, andprocessing. Handling conditions during manufacturing, storage, shipping, and mar-keting must not allow microbial or chemical contamination. Prevention of naturaldeterioration and further contamination is often done through packaging, togetherwith other techniques such as modified atmosphere packaging. Packaging and theother applied techniques must not introduce risks of their own, such as micromigra-tion of nonfood polymers into the foodstuff or alternative microbial risks.

Once in the consumer’s hands, food must provide the expected nutrients duringits shelf life. Furthermore, food must be handled properly to prevent contamination.Unfortunately, the home and food service setting are the most common places forfood mishandling. Thus the process that is taken for granted as both simple andimperative is anything but.

Even when all steps happen according to proper protocol, the food may still notbe safe, as the person ingesting it may react adversely to it, choke on it, or have afood–drug interaction that renders a usually safe food component injurious. Whilescientists know that “safe” is not risk-free, this notion is not held by consumers.

In addition to the tension created by convincing consumers that no food is risk-free, there is tension around food. One reason is because there is a vast separationbetween the food consumer and the producer. There has been a tremendous decreasein the number of people in industrialized countries who have any connection withfarming and food production. The childhood story where the little red hen growsthe wheat, harvests and mills the wheat, and bakes the bread is the closest that most

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modern consumers come to the production and processing of food. Some are evenfar removed from preparation of food. In countries like the U.S. and the U.K., safestorage and preparation techniques are no longer learned at home because very littlefood is prepared. Plated meals and deli food, which are heated to serving temperature,usually in a microwave, have become the norm for some families.

13.2 CONSUMER ATTITUDES TOWARD THE FOOD SAFETY PROBLEM

Consumer concerns about food safety are, in part, a protest to scientific and tech-nological complexity and a lack of trust in government, big business, and its adver-tising. For some, science has become the problem, not the answer. Even for thosewho believe in the promise science holds, scientific complexity can be confusing.Two experts espousing different assumptions, extrapolations, and interpretationsreach diametrically opposed positions often using the same data. Disagreement ofscientists is not the only source of confusion. Media-savvy, self-appointed expertsor consumer groups’ spokespeople with easy-to-understand messages, albeit specificagendas, add to the multiplicity of positions consumers hear. The messages fromthese sources are straightforward and are not tied, as ethical scientists are, to theconflicting evidence produced by the data. It is nearly impossible for anyone, includ-ing the consumer, to sort through the cacophony to find the truth. Groups that positionthemselves as anti big business and technology and pro consumer and environmentalso have a credibility edge. This is particularly true in areas where fear aboundsand technology such as irradiation or biotechnology is unfamiliar.

Lack of trust in government food safety agencies has been made worse by thedioxin scare in Europe, where the Belgian government failed to inform the publicwhen they were first aware of the problem. In cases where the U.K. government hashad to change its position and its statements, as in the case of mad cow disease,credibility was severely eroded.

Exacerbating the problem is the quality of information given to the public.Information about food in the media is often too simplistic, too boring, too incom-plete, or too biased. Sixty-second news bytes drastically distill a 10-year study, takean item out of context, or reflect the findings of a single study, which is not inagreement with a whole body of other studies. The news commentator has neitherthe time nor the knowledge to interpret what this news item means to someone whoeats this food once a week. Information from scientists is often filled with jargonand presented in a dry, incomprehensible manner.

Often both activist groups and advertisers select scientific literature that supportstheir point of view, but does not fairly represent the full body of knowledge. Some-times discredited data, the most egregious examples, or highly controversial dataare used to heighten worry. Some groups use statements about vulnerable groups toincrease impact and fear. For example, there was a recent report and media campaignon pesticide residues in children. Studies have shown that sources are more believableif they report that a food or component is not safe, rather than affirming that thefood is safe (Occhipinti and Siegal, 1994).


Along with increased complexity, there is in some countries such as the UnitedStates decreased scientific literacy coupled with greater fear of chemicals and tech-nology. The realization that human life has always entailed exposure to chemicalsand that everything ingested and inhaled is composed of chemicals is not a sharedassumption. Even more elusive to most consumers is the fact that naturally occurringchemicals are more abundant and can be more toxic than synthetic ones. Mostconsumers believe the converse: that natural chemicals are innocuous and syntheticones are nefarious. Ironically, for food chemicals much more is known about thesynthetic chemicals added to food than those that occur naturally. Furthermore, withrespect to food there is a romanticization of the “good old days.” Careful analysisshows much shorter life spans, long hours of preparation in the kitchen, pooravailability of produce in the late winter months, and other problems that are notseen in the romantic look at the “good old days.”

13.3 TESTS TO DETERMINE FOOD SAFETY

Human beings have always been intuitive toxicologists, relying on their senses ofsight, taste, and smell to detect harmful or unsafe food, water, and air. When asked,some consumers still feel that they are the prime determiners of food safety and tryto rely on themselves. Scientists and savvy consumers have come to recognize thatour senses are not adequate to assess the dangers inherent in exposure to a chemicalsubstance, especially one in which the ill effect is either cumulative or delayed. Thesciences of toxicology and risk assessment have developed to assess the safety offoods and their constituents; they use the following toxicity tests, which are per-formed on all compounds used as intentional additives and pesticides:

• Acute tests: using at least two species of experimental animals to deter-mine lethal dose 50 (LD50) - the dose which kills half of the animals.

• Metabolic tests: done early in the protocol to track the fate of the com-pound in the body. If metabolites are formed, their fates and toxicity mustalso be determined. Different species are used to test whether the metab-olism is the same and to see which species will be most similar to humans.

• Subacute tests: require the feeding of a range of doses below the LD50 toat least two species for 2–3 months. A threshold or no observable effectlevel (NOEL) is determined from the highest dose that produces no harmin the most sensitive species.

• Chronic tests: feeding a compound at doses 100–1000 times that whicha human would likely ingest, to determine chronic toxicity. Two to threespecies fed for a lifetime are used in these tests, which not only assessthe health of the animal but determine if there are any reproductive oroffspring abnormalities.

After the various forms of testing are done and indicate that an additive maybe safely used, the NOEL is divided by a safety factor so that the acceptabledaily intake (ADI) can be determined. The ADI is expressed as milligrams ofthe test substance per kilogram of body weight per day. The safety factor is

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arbitrary and may vary according to the test material and circumstances. Oftena factor of 100 is chosen. The rationale for 100 is that if the average sensitivityof humans to a particular compound is 10 times greater than that for the mostsensitive test animal, and if the most sensitive humans are 10 times more sensitivethan the test animals, the use of the factor 100 (10 × 10) would mean that themost sensitive individual could safely ingest the amount equivalent to the ADI(Francis, 1993).

Two possible food contaminants require special consideration in choosing asafety factor: carcinogens and prions. For carcinogens, the 100-fold safety factormay be inadequate, and factors as high as 5000 have been proposed. Somescientists adhere to the idea that there is for some carcinogens no threshold ortolerance level. Currently, more believe that there is a threshold level, but answer-ing what is a safe level is difficult for several reasons. Lag times between exposureto a carcinogen and the development of a tumor may be at least 20 years. Dietary,genetic, and environmental factors may all play a role in detoxifying or in ampli-fying the effect of a carcinogen or tumor promoter. Even the concentration of thesubstance may be critical; at some concentrations the compound may act as atumor inhibitor and at others it may act as a tumor promoter. Prions are a specialcase because no one is clear on how they get into food in the first place, let alonehow much is required to cause an effect and why some individuals are susceptible,while others may not be. Setting an ADI for a substance like this is impossiblewithout much more information.

For all chemicals, carcinogens or not, a final step must be completed afterestablishing the ADI; a value must be assigned for the amount that would be allowedin a particular foodstuff. Consumption estimates for foods or commodities that mightcontain the chemical are needed along with estimates of total intake from all sources.This calculation is used to establish the maximum residue level (MRL) for anyparticular commodity.

Constant monitoring and reevaluation of these estimated intakes make certainthat estimates reflect real exposure. Recent data indicate that the intake estimatesused to calculate the MRL may need some modification. More specific food productconsumption data for high-risk groups are needed. Sampling procedures are oftentoo aggregate to target these groups. More consideration of food consumed awayfrom home is needed, because this market segment now accounts for about half ofall U.S. consumer food expenditures.

Even with the best scientific methods, extrapolations and judgments arerequired in order to infer human health risks from animal data. Basic toxicologicalconcepts, assumptions, and interpretations were found according to a recent surveyto differ greatly between toxicologists and laypeople, as well as among toxicolo-gists working in industry, academia, and government. Toxicologists were foundto be sharply divided in their opinions about the ability to predict a chemical’seffect on human health on the basis of animal studies and other laboratory methodsbeing employed in lieu of animal tests (Ames and Gold, 2000). This differenceof opinion creates public policy tensions. Renowned toxicologist Bruce Amesstated that minimizing minuscule hypothetical risks may damage public health bydiverting resources and distracting the public from major risks. In addition,


renowned epidemiologists such as Mike Osterholm state that the avoidance ofpossible risks from processes like irradiation may continue to allow food-bornedisease that could be significantly reduced (Diaz and Noel, 2001).

13.4 FOOD SAFETY CONCERNS

Food-borne disease has always topped the list of food safety concerns for mostgovernment bodies around the world. Highly publicized outbreaks of Salmonella,Listeria, and Escherichia coli have placed food-borne disease at the top of theconsumer’s list of food safety concerns as well. This has not always been the case.Chemicals and pesticides used to be a much greater fear than food-borne disease.Not all are roughly equal as consumer concerns. Joint expert committees of the Foodand Agriculture Organization/World Health Organization (FAO/WHO) continuouslyevaluate new data to ensure that the chemicals allowed in the food supply are safeand that the levels ingested do not exceed the ADI. With science now increasing itsability to detect substances to the attogram level, more must be done to help theconsumer move from the position of “zero tolerance.”

In recent years concerns associated with food produced with antibiotics orhormones or by biotechnology or treatment with irradiation have increased. Madcow disease and other prion-related diseases have created great fear and economichavoc. The terrorist events of 2001 have shocked the food industry, government, andconsumer into recognizing the possibility that some form of bioterrorism may betransmitted through food and water.

How a food safety concern is viewed varies by the group. Scientific groupsjudge a hazard on known deaths or cases of illness. Consumers have many concernsabout potential problems that may occur but have not as yet been documented.This is also reflected in some European regulatory responses invoking the precau-tionary principle. This entails the failure to approve use of a substance becauseof a lack of ability to prove its safety, even though there is little or no good dataproving it unsafe.

13.5 MICROBIAL CONTAMINATION OF FOOD

Pathogenic bacteria are responsible for the majority of food-related outbreaks in theUnited States. Opportunity for contamination exists at every stage in the food chain.Actual incidence of food-borne disease is unknown, even in countries with fairlysophisticated monitoring systems, because the number of cases are severely under-reported. The newly installed PulseNET system by the Centers for Disease Controland Prevention (CDC) in Atlanta is an attempt to have better tracking and obtainbetter data regarding certain microorganisms.

The most recent estimates from the CDC in the United States suggest that there are76 million illnesses, 325,000 hospitalizations, and 5,000 deaths each year from food-borne disease. Surprisingly, the actual pathogen is identified in less than 20% of theillnesses. In other words, known pathogens account for an estimated 14 million illnesses,60,000 hospitalizations, and 1,800 deaths. Of the known pathogens, Salmonella, Listeria,

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and Toxoplasma species account for 75% of the cases and are responsible for 1,500deaths each year. Campylobacter jejuni is the leading reported cause of diarrheal illness(Altekruse et al., 1999). Staphylococcus aureus, Clostridium perfringens, Yersinia entero-colitica, and pathogenic strains of E. coli, as well as the parasites giardia, cyclospora,and cryptosporidium, are also problems and are in the news often for their potential tocause very large or lethal outbreaks. E. coli, Listeria, and botulism are of significantconcern because of their high degree of morbidity and mortality (Yang et al., 2000).

Unknown agents account for the remaining 62 million illnesses, 265,000 hos-pitalizations, and 3,200 deaths. Overall, food-borne diseases appear to cause moreillnesses but fewer deaths than had been previously estimated in the United States(Mead et al., 1999).

The increased incidence of all types of viral, bacterial, and parasitic infectionsis due not only to better reporting, detection, and surveillance, but also to changesin our consumption patterns. People in many Western nations buy more prepre-pared, prepackaged foods; demand out-of-season and exotic foods from all aroundthe globe; utilize new technologies, such as modified atmosphere; demand foodwith less salt and fat; and use food services and delis more often. Coupled withthese changes, consumers also desire fewer additives that might slow microbialgrowth. Greater pollution of areas such as the Gulf Stream, as in the case ofVibrios, also means more food-borne disease. More eating out and deli food meansthe possibility of greater contamination, because a greater number of people arehandling the food and there are more potential steps for errors. All these trendscan impact the microorganisms and chemicals found in food.

Another factor increasing the incidence of food-borne disease is an increase invulnerable populations: the very young, the very old, the chronically ill, and theimmunocompromised. In most countries the increase in life span, number of trans-plants, and other conditions requiring immunosuppressing drugs raises the numberof people in the at-risk groups.

Another factor that affects the incidence of food-borne disease is the lack ofknowledge about food preparation and storage. A study by the U.S. CDC traced77% of the microbial disease outbreaks to food service establishments, 20% tohomes, and 3% to food processing plants. From these data it can be seen thatwhile increased food safety programs such as Hazard Analysis Critical ControlPoint (HACCP) or Longitudinally Integrated Safety Assurance (LISA) are beingmandated in many parts of the world, there needs to be a plan to reduce problemsin food service and an education program to tell consumers about safe foodhandling and preparation.

Another contributing factor may be consumer preference. While food safety ispreferred at a logical level, it must be balanced against other attributes of the product.Flavor preference for a soft cheese made with unpasteurized milk or raw fish mayoutweigh the small risk of contracting Listeria, E. coli, or a parasite. Price mayimpact the choice of a specific food, if the safer food is more expensive to produce.Interestingly, food safety is an income-elastic good. As incomes rise, so does thepremium a consumer will pay for food that is perceived to be safer, yet at the sametime, those with more income and education often engage in riskier food safetybehaviors (Yang et al., 2000; Swinbank, 1993).


Interestingly, traditional market mechanisms do not work directly with respect tofood safety issues. First, food safety attributes are not readily determined at the pointof purchase. Competing food products are rarely appraised according to alternativelevels of microbiological spoilage or probability of contaminated cans. Second, a lesssafe product is usually not intentionally supplied. The problem often lies in accidentalcontamination or a change in the process handling, shipping, storage, or productcomposition such that microbial growth is allowed or contamination occurs.

Consumers are often unaware that there are long-term as well as short-termconsequences of food-borne disease. Sometimes the acute effects of food-bornedisease do not end in two or three days. Several significant food-borne pathogensare capable of triggering chronic disease, and even permanent tissue or organ destruc-tion, probably via immune mechanisms. Arthritis, inflammatory bowel disease,hemolytic uremic syndrome, Guillain-Barre syndrome, and possibly several autoim-mune disorders can be triggered by food-borne pathogens or their toxins. Researchis needed to more fully understand the mechanisms by which the immune systemis inappropriately activated by these common food-borne disease-causing agents(Mead et al., 1999; Bunning et al., 1997).

Understandably consumers react viscerally to a dread outcome. If a supplier makesa mistake, the company will be pilloried in all forms of media. One mistake in a million(an undetectable number) that gives rise to the death of two people will not only affectthe sales of the particular product, but those of all products of that type and by thatmanufacturer. Many companies fold in the face of such an adverse event.

To prevent such negative consequences, many industry programs are in place world-wide. Mandatory HACCP, good manufacturing practice (GMP), and other such programsrequire sanitary conditions for food production and help minimize chances for contam-ination. International Standards Organization (ISO) 9001 and ingredient specificationprograms ensure that the raw materials incorporated into food products meet requiredlow levels of contamination and reduce both corporation and consumer risk.

13.6 RISK-BENEFIT AS IT APPLIES TO FOOD

The risk-benefit concept is clear-cut in many aspects of our lives. For instance, inmedicine the treatment of disease has inherent and sometimes lethal risks, but thebenefits afforded by the treatment are believed by most to outweigh the risks. Inthis case the risk is vital and the benefit is vital. In sports, the activity may contributeto health (vital) and well-being (nonvital), but it may pose a risk of injury (vital).However, the risk is voluntary and the athlete may feel in control. With food therisk-benefit may be much less apparent to the consumer. Chemicals may inhibitmicroorganisms but may pose some risk. Since risk is present in the food, it isinvoluntary, and the consumer has a sense of outrage because there is no sense ofcontrol with respect to its use. Adding to the imbalance in the risk equation are manyreports stating the risks of its use and virtually none touting the benefits. For example,with pesticides in food the risks include a possible increase in the number of cancers,a reduction in the immune response, estrogenic effects, and environmental concerns.The benefits stating that pesticides reduce vector-borne disease, decrease the amountof fossil fuel required to mechanically cultivate a field, reduce the number of bug

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parts and droppings in food, and increase crop yield to feed a burgeoning globalpopulation are only rarely reported.

In the same manner risks of additives are often cited by various groups, whilethe benefits remain unsung in articles to which the consumer has ready access. Forinstance, a preservative can have several important benefits:

• Formation of a cancer-producing mycotoxin may be arrested by additivesinhibiting mold growth.

• Food costs can be reduced because staling and oxidation are retarded andless expensive packaging and transportation solutions are required.

• Food waste is reduced.• Oxidized fats with their attendant health risks are reduced.• Preservatives make possible foods that meet consumer wants of convenience.

Looking at the risks and not the benefits of chemicals or technologies associatedwith food is like an accountant shearing a ledger in half and considering the liabilitieswithout the assets. However, even if judgments of risk and benefit are considered,they have been found to be inversely related (Alhakami and Slovic, 1994). Activitiesor technologies that are judged high in risk tend to be judged low in benefit, andvice versa. In situations where there is high risk, there tends to be a confounding ofrisk and benefit in people’s minds. Risk gurus Paul Slovic and his colleagues atDecision Research in Eugene, OR, found that perceived risk is often not related tothe probability of injury.

Communicating risk is about trust. Trust can be easily destroyed but is verydifficult to establish. Once there is the element of distrust, it fuels more distrust.

Risk communicators should be aware that risks that people can choose to avoid(e.g., skiing) give a sense of control and that risks that are familiar (e.g., Salmonellafrom potato salad or disease from smoking) or have been around a long time (e.g.,food-borne disease) are easily tolerated and often minimized. Risks that are poorlytolerated are involuntary risks, such as exposure to small amounts of pesticideresidues in food and those risks that have unknown effects (e.g., biotechnology-produced tomatoes) or long-delayed effects (which are possible with prion exposure).

The framing of risks makes a tremendous difference in their acceptance. A studyreported in the New England Journal of Medicine showed that 44% of respondentswould select a procedure for a lung cancer treatment when told they had a 68%chance of surviving, but only 18% would select the procedure if they were told theyhad a 32% chance of dying. It is no wonder that the consuming public has aninordinate fear of some food additives and pesticides, because the information isalways reported in terms of increased risk rather than possible reduced risk, due toless mold or bacterial growth.

Some risks were accepted when consumers were faced with a choice about risks.For instance, consumers in California were asked if they would accept food irradiation.The responses were varied but had strong negative leanings. If the same consumerswere asked if they would accept irradiation as a way to use less pesticide or reduce amicrobial hazard, then irradiation acceptance was increased (Bruhn, 1999).


Consumers thus appear quite capable of understanding and using the risk-benefitconcept for making decisions about food choices. It is mandatory that all sides ofthe story get a hearing so that these informed choices can be made considering boththe risks and benefits.

The final word about risk-benefit is that the definitions of the risks and thebenefits are not the same in all cases. The definition of benefit needs to be clear.For some countries, the benefit is reduced postharvest food losses. The value of thisbenefit can vary with the country involved. Different weights may be assigned ifthere is danger of severe food shortage versus simply an increase in the cost of thesubstance. Thus, the science and art of risk assessment are difficult because eachstep in the process is value laden.

13.7 NUTRITIONAL EVALUATION OF FOOD PROCESSING

Food processing both maintains and destroys nutrients. In a few cases nutrients areeven more available after processing. This seeming paradox will be explored.

For most foods, processing reduces the nutrient content, compared to the freshlyharvested item. However, processing makes food and the nutrients within available ata later date, so the loss incurred must be compared with what would happen to thediet if no processing was utilized. For some foods, processing makes the nutrientsmore available because toxic factors and antinutrients are destroyed. Cassava, soy-beans, and corn are all examples of important classes of food that are made either lesstoxic or more nourishing through processing. Cyanide is removed from cassava withgrinding and soaking; enzyme inhibitors and lecithins are destroyed during the heatingof the soybean; and niacytin releases niacin when corn is processed with lime (CaO).

All nutrients (except water) may undergo either chemical or physical changesduring processing that render them inactive or less bioavailable. This occurs formacro- as well as micronutrients. During browning, the amino acid lysine can reactwith carbohydrates to lower the biological value of protein.

Fat oxidation can decrease the level of essential fatty acids in the diet and canlower the overall food quality by introducing free radicals and other oxidized prod-ucts into the diet. Hydrogenation alters the nutrition properties of oil by increasingthe degree of hydrogenation and by introducing trans fats to the diet. Adding plantstanols to reduce cholesterol is another way the nutritive effect of fats can be changedby processing. With each pressing of olive oil, fewer and fewer phenolics, with theiranitoxidant properties, are available.

Altering particle size of grains is one way that processing can change the physio-logical effect of nondigestible carbohydrates. Pregelatinizing starch causes greater ele-vation of blood glucose than the equivalent starch item that has not undergone pregela-tinization treatment. Heat treatment and Maillard reactions can increase resistant starchand may therefore increase the amount of material in the food behaving like fiber.

13.7.1 EFFECTS ON VITAMINS

Vitamin loss during processing and cooking of various foodstuffs has been of interestto nutritionists, processors, and consumers. Vitamin C, the most labile vitamin, is

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lost during canning, blanching, fresh or frozen storage, drying, and irradiation.Losses can be 100% if the conditions of processing and storage are not controlled.For example, a study of processed mashed potatoes fortified with vitamin C showsthe lability of this vitamin. Cumulative losses of vitamin C were: 56% for additionof the vitamin to freshly mashed potatoes, 82% for drum-dried potatoes, 82% forflakes stored 4.3 months at 25°C, and 96% for reconstituted mashed potatoes held30 min on a steam table. One serving (100 g) would contain 10 ppm — 2% of theadult U.S. Recommended Dietary Allowance (RDA). A more stable isomer used tofortify the mashed potatoes would yield about 201 ppm (about 33% of the RDA ofvitamin C per serving) (Wang et al., 1992).

Thiamin and folate, while not as labile as ascorbate, are easily lost duringprocessing. Thiamin is extremely water soluble and destroyed by heat, so much canbe leached into the cooking or storing liquids during preparation of both meats andvegetables. Losses in the making of soy flour are minimal, but losses in the makingof soy flour into tofu stored in water are 85% or greater (Fernando and Murphy,1990). In addition to losses due to leaching, thiamin content can decrease markedlywhen subjected to basic pH. The splitting under alkaline conditions of the two ringsof thiamin causes loss of all biological activity for humans. Thus, a quick breadwith bicarbonate leavenings can lose up to 75% of the thiamine in the finished bakedproduct because of the synergistic effect of both heat and pH. Sulfites used aspreservatives will also cleave thiamine.

Folic acid is easily lost during storage of fresh vegetables at room temperatureand through many heat processes. Oxidative destruction of 50–95% of the folatecan occur with protracted cooking or canning. Currently in the United States folateis added to all enriched or fortified cereal and flour products in order to increasethis nutrient to prevent neural tube defects and to reduce coronary disease and somecancers. Thus, the processed, fortified product will have more folate.

Riboflavin is unstable to light; therefore, riboflavin-containing foods subjectedto either ultraviolet or visible light can show significant losses of riboflavin. Ribo-flavin is much less water soluble than thiamin, but long-term storage in water cancause leaching. For instance, tofu stored in water can lose 80–90% of the riboflavin.

Pyridoxine (vitamin B6) losses in food are dependent on the temperature and onthe specific form of the vitamin. Thermal processing and low moisture storage ofcertain foods result in reductive binding of pyridoxal to lysine in proteins, makingit unavailable. Thus canning and drying losses can be substantial. Losses in cannedinfant formulae are of particular concern because the formulae may be an infant’sonly food source. During blanching there is not much measurable loss of vitaminB-6 content, but recent studies have shown that the loss of bioavailability or absorb-ability may be significant. Most meats, a good source of vitamin B-6, lose littleduring preparation.

Fat-soluble vitamins show somewhat greater stability than water-soluble vita-mins. They are not as easily destroyed by normal cooking and are not leachedinto the cooking water. However, vitamin A changes slowly from the all-transform, the most biologically active form, to the cis form during canning and withlong times on a steam table. Carotenoids, currently valued for their antioxidantand possible anticarcinogenic potential, also oxidize to some degree during heat


treatment. Traditional canning causes greater losses of vitamin A and carotenesthan high-temperature short-time (HTST) processing (Chen et al., 1995). Littleloss occurs in frozen blanched vegetables, but vitamin A and other carotenoidseasily oxidize in drying when no antibrowning additives such as sulfite are used.

Vitamin E is not very stable to heating followed by freezing and is lost in millingas the germ is removed from white flour. Some vitamin E isomers are lost during theprocessing of oil. In many countries the vitamin D content of food is increased throughfortification of dairy products. Vitamin K is not greatly affected by heat but is lost tolight, so vitamin K-containing oils retain their vitamin content if stored in amber bottles.

The whole class of phytochemicals that have beneficial effects on the body arealso affected by processing. These compounds can be fat soluble or water soluble.Their effects can be changed by processing, as seen in the differences between greenand black teas. Firing while the leaf is still green making green tea retains moreantioxidants than allowing the leaf to wither to make black tea. The removal of theskin in the making of white wine can change the number of phytochemicals. Theuse of sulfite to prevent browning in the drying of golden raisins causes an increasein the antioxidant capacity of the raisin over those with no sulfite present.

13.7.2 EFFECTS ON MINERALS

Minerals are lost into the cooking liquid if the liquid is not ingested. Minerals areretained in the bran and germ fragments of the grain and are therefore lost to thosewho ingest only refined grain products. However, even if the whole grain is ingestedthe bioavailability of the mineral may be impaired because the mineral is tightly boundto the bran of the germ. Furthermore, some minerals may be made more availableduring the cooking process, while others become less bioavailable. While effects ofvarious nutrients and certain nonnutrient components of food on mineral utilizationhave been studied, less is known about the effects of food processing and preparationprocedures. Fermentation during the production of beer, wine, yogurt, and Africantribal foods affects bioavailability of zinc and iron. Baking changes the chemical formof iron in fortified bread products, and these changes can affect bioavailability. Theavailability of iron in milk-based infant formula depends on whether iron is addedbefore or after heat processing. Food packaging (e.g., tin cans) can alter food compo-sition and thus potentially affect mineral bioavailability. Maillard browning has beenreported to cause slight decreases in zinc availability.

13.8 NEWER AND NOVEL TECHNOLOGIES

13.8.1 IRRADIATION

Treating fresh or frozen meats with ionizing radiation is an effective method toreduce or eliminate food-borne human pathogens. The irradiation dose, processingtemperature, and packaging conditions strongly influence the results of irradiationtreatments on both the microbiological and nutritional quality of meat. Radiationdoses up to 3.0 kGy have little effect on the vitamins in chicken and pork but havevery substantial effects on food-borne pathogens. Even vitamins such as thiamin,

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which are very sensitive to ionizing radiation, are not significantly affected by theU.S. Food and Drug Administration maximum-approved radiation dose to controlTrichinella, but at larger doses they are significantly affected (Fox et al., 1995).

13.8.2 BIOTECHNOLOGY

Biotechnology is viewed as a new process. In actuality, it is an extension of an oldprocess. Time-honored processes such as fermentation and plant and animal hus-bandry employ biotechnology. However, in the last 20 years the technology hastaken a giant step forward by using gene-splicing techniques to speed up the processand make it more precise. It allows changes that were never before achievablebecause genes that could not be incorporated with normal breeding techniques canbe with biotechnology.

Biotechnology has the potential to both increase and decrease available nutrientsin the same way that plant breeding can. Care must be exercised that the nutrientcontent of a food is not reduced when another attribute is engineered into it. Goldenrice is an example where vitamin A is incorporated into food for use in parts of theworld where the number-one cause of preventable blindness in children is vitaminA deficiency. Rice is a great vehicle because most of the regions where this deficiencyis a problem are rice-eating regions.

One food safety concern about genetic engineering is that toxic componentsnaturally found might be increased. Attempts to breed or genetically engineer plantswith natural herbicides or pesticides or herbicide-resistant plants could increase thepotential toxicity if many foods would carry a natural pesticide. Scientists must notbe lured into the common belief that nature is benign and chemicals from the labare noxious.

Another food safety concern regards allergenicity. The transfer of a protein intoa food through biotechnology could lead to allergic reactions for persons not expect-ing that particular protein in a totally different kind of food. In 2000, Starlink cornwith cry9C protein was not approved for human food use because the regulatoryauthorities thought that there were inadequate data assuring that the protein was notallergenic. This subsequently was the cause of a massive voluntary recall.

Currently the ability of laboratories and regulatory agencies to determine if afood has been produced by biotechnology is limited. Accuracy on different foodproducts varies, so much more research is needed in this area.

Another big concern is that bioengineered crops will adversely affect the envi-ronment. Some reports have suggested that BT-corn will adversely affect otherspecies or that some bioengineered products will become dominant strains.

13.9 ADDITIVES

Food additives can enhance the safety and nutritional quality of a food or vice versa.By preventing oxidation of fat and easily oxidized vitamins, antioxidants ensure thatsafety is enhanced and the intended nutritional value of the food is delivered.Antibrowning agents such as sulfite retain phytochemicals and vitamins A and Cbut lower the amount of thiamine, folate, and pyridoxal. Sorbic acid can prevent


mold and possible mycotoxins but can form protein adducts in the stomach thataffect the availability of the protein. Vitamins C and E react with nitrite to preventthe formation of nitrosamines. This reaction will use the vitamins and thus they willnot be available for other functions. Phosphates are antimicrobial because of theirsequestering capacity. This capacity can have an antinutritional effect because ofmineral-binding ability. Vitamins themselves are added to fortify and enrich prod-ucts, making food have more nutrients than it might otherwise. Sometimes food ishighly fortified to give consumers the idea that if they eat one serving, they do notneed to pay attention to other parts of their diet. Consumers need to be educatedthat there is much more to food that is beneficial than just vitamins and minerals.

New products that replace entire foods or macronutrients, such as fat replacers,must be evaluated both for their nutritional contribution and for their dietary impact.These foods may help some people reach needed dietary goals. In other cases, theyintroduce risks such as overconsumption and abuse, vitamin leaching or competition,and gastrointestinal problems. In some instances additives that were intended foruse in microamounts are now being used in macroquantities. They may exceed theADI and have effects that would make them unsafe at high levels of use.

Additives, like all food components, need to be looked at with the risks andbenefits in mind. Contrary to popular belief, food additives can be regarded as thesafest and most studied constituents of our food supply. This is as it should be.Furthermore, surveillance of food additives is a mandatory consequence of their use;their safety must be continually ensured, considering any change in usage patternsand new data. This constant vigilance can make consumers feel that science andtechnology is untrustworthy, because they perceive that science changes its mind.In fact, just the reverse should be true. Since additive safety is constantly beingchallenged to ensure that only the most wholesome food products are on the market,fear should be lessened. Unfortunately, this usually is not the case. Substances shouldnever be added to food without careful analysis and a conservative approach to theiruse. A clear benefit to the end user must be present before a food additive shouldbe allowed.

REFERENCES

Alhakami, A.S. and Slovic, P., A psychological study of the inverse relationship betweenperceived risk and perceived benefit, Risk Anal., 14, 1085, 1994.

Altekruse, S.F. et al., Campylobacter jejusi: an emerging foodborne pathogen, EmergingInfect. Dis., 5, 28, 1999.

Ames, B.N. and Gold, L.L., Paracelsus to parascience: the environmental cancer distraction,Mutat. Res., 447, 3, 2000.

Bruhn, C.M., Consumer perceptions and concerns about food contaminants, Adv. Exp. Med.Biol., 459, 1, 1999.

Bunning, V.K., Lindsay, J.A., and Archer, D.L., Chronic health effects of microbial foodbornedisease, World Health Stat. Q., 50, 51, 1997.

Chen, B.H., Peng, H.Y., and Chen, H.E., Changes of carotenoids, color, and vitamin A contentduring processing of carrot juice, J. Agric. Food Chem., 44, 1912, 1995.

Food Safety 305

Diaz, A. and Noel, C., “Beating Bacteria in the Food We Eat. Irradiation: It Sounds Bad, Butis It?” ABC news commentary, February 28, 2001.

Fernando, S.M. and Murphy, P.A., HPLC determination of thiamin and riboflavin in soybeansand tofu, J. Agric. Food Chem., 38, 163, 1990.

Fox, J.B.J. et al., Gamma irradiation effects on thiamin and riboflavin in beef, lamb, pork,and turkey, J. Food Sci., 60, 596, 1995.

Francis, F.J., How do we test for safety of food?, Sci. Food Agric., 5, 2, 1993.Jones, J.M., Food Safety, Eagan Press, St. Paul, MN, 1992.Mead, P.S. et al., Food related illness and death in the United States, Emerging Infect. Dis.,

4, 607, 1999.Occhipinti, S. and Siegal, M., Reasoning about food and contamination, J. Personality Soc.

Psychol., 66, 243, 1994.Swinbank, A., The economics of food safety, Food Policy, 18, 83, 1993.Wang, X.Y. et al., Vitamin C stability during preparation and storage of potato flakes and

reconstituted mashed potatoes, J. Food Sci., 57, 1136, 1992.Yang, S., Angulo, F.J., and Altekruse, S.F., Evaluation of safe food-handling instructions on

raw meat and poultry products, J. Food Prot., 63, 1321, 2000.

3071-5871-6149-4/02/$0.00+$1.50© 2002 by CRC Press LLC

Mutagenic, Carcinogenic, and Chemopreventive Compounds in Foods

Agnieszka Bartoszek

CONTENTS

14.1 Introduction ..................................................................................................30814.2 Role of Mutagens in Carcinogenesis...........................................................30914.3 Metabolic Activation and Formation of DNA Adducts by

Food Mutagens and Carcinogens ................................................................31014.4 Tests for Mutagenicity and Carcinogenic Properties of Food

Components..................................................................................................31514.5 Food-borne Mutagens and Carcinogens ......................................................317

14.5.1 Introduction ......................................................................................31714.5.2 Mycotoxins.......................................................................................31814.5.3 Nitrosamines.....................................................................................31914.5.4 Mutagens in Heat-Processed Foods.................................................320

14.5.4.1 Heterocyclic Aromatic Amines.........................................32014.5.4.2 Polycyclic Aromatic Hydrocarbons..................................32214.5.4.3 Effect of Commercial Processing and Cooking

Techniques ........................................................................32314.5.5 Mutagens in Tea, Coffee, and Alcoholic Beverages .......................32414.5.6 Other Risk Factors ...........................................................................325

14.6 Chemopreventive Food Components ...........................................................32614.6.1 Anticarcinogenic Food Components ...............................................32714.6.2 Cancer Chemoprevention.................................................................330

14.7 Summary ......................................................................................................331References..............................................................................................................333

14


14.1 INTRODUCTION

Factors and substances able to induce changes in the genetic code are calledmutagens. Those that can cause cancer, excluding genetic susceptibility, are calledcarcinogens. Such factors are omnipresent in the human environment; they can beof natural origin or formed as a result of numerous chemical processes. To thesefactors belong a variety of synthetic chemicals, combustion products, water and airpollutants, sunlight and ionizing radiation, cigarette smoke, alcohol, and some foodcomponents. Such factors like specific occupational exposures or cigarette smokingare clearly high-risk conditions for cancer. Diet is a major environmental variable;however, its impact on tumor development is vague, since it may both promote andinhibit carcinogenesis.

A fundamental observation in cancer epidemiology during the last century wasthat cancer incidence and mortality rates vary dramatically across the globe (Parkin,1998). In addition, rates of cancer among populations migrating from low- to high-incidence countries change markedly; in most cases they approximate the rates inthe new region within one to three generations. For instance, the replacement offoods of plant origin with foods of animal origin, notably meat products and dairyproducts, increases cancer incidence, especially the risk of breast, colon, prostate,and rectum cancers (Bingham, 1999). These cancers are virtually absent in thepopulations of some countries of the developing world; the general overall cancerburden there is strikingly lower. Similar conclusions were inevitable in the case ofepidemiological studies on prostate cancer incidence and breast cancer incidence inmigrants to the United States from Poland (Staszewski and Haenszel, 1965) andJapan (Wynder et al., 1991), respectively. These cancers are relatively infrequent inthe countries of origin, but in the investigated populations of immigrants they reachedthe level observed in the United States, even within one generation. Such lines ofevidence indicate that the primary determinants of cancer rates are not geneticfactors, but rather environmental and lifestyle factors that could, in principle, bemodified to reduce cancer risk.

It has been estimated that approximately 35% of cancer deaths in the UnitedStates are attributable to dietary habits (Anon., 1993). Not surprisingly, the presenceof potential mutagens and carcinogens, as well as anticarcinogenic substances infoods, has become of widespread interest. The majority of mutagens and carcinogensfound in foods are formed during food processing, especially thermal processing.However, the processing and heating of foods have invaluable advantages. Theyincrease shelf life of foods, which can then be economically priced, decrease therisk of diseases caused by food-borne pathogens, improve taste and nutritive valueof food, and provide easy-to-prepare and time-saving convenience foods. Therefore,it is of utmost importance to establish what processes are responsible for mutagenand carcinogen formation in food and to clarify their involvement in transformationof a normal cell into a cancerous one. This field of research is progressing rapidly,and it may be expected that the gathered knowledge should bring about new tech-nologies that will keep the current benefits of food processing, while minimizingthe formation of harmful compounds. It should also enable the elaboration of sounddietary recommendations aimed at diminishing cancer risk.

Mutagenic, Carcinogenic, and Chemopreventive Compounds in Foods 309

14.2 ROLE OF MUTAGENS IN CARCINOGENESIS

Transformation of a normal cell into a cancerous one manifests itself macroscopi-cally as an uncontrolled cellular growth, resulting in the formation of a tumorconsisting of cells that do not differentiate into their specialized tissues, may metas-tasize and invade other sites of the body, and eventually lead to the death of theorganism. Each cancer arises from a single cell. This implies that once the abnormalbehavior arises (e.g., loss of control over cell division), such capacity is handed todaughter cells. Cancer is thus a disease that fundamentally involves the structureand function of DNA. Recent developments in the area of molecular carcinogenesishave demonstrated that neoplastic transformation involves the accumulation of mul-tiple genetic alterations in critical cancer-related genes. Therefore, cancer is oftenreferred to as a disease of genes (Sugano, 1999).

Cancer-related genes are numerous and include oncogenes; tumor suppressorgenes; genes involved in regulation of the cell cycle, development, DNA repair, anddrug metabolism; genes involved in immune response and angiogenesis; and othercorrelates of metastasis. It has been evidenced that certain alleles of these genescontribute to cancer susceptibility and are mutated in tumors. The alleles conferringincreased risk for cancer might require an environmental influence to have theireffect. The genetic background modifies the risk of disease for exposed individuals(risk might be raised or lowered). In the majority of cases in which diet is involvedin the carcinogenic process, susceptibility genes are thought to be most relevant(Dean, 1998; Sinha and Caporaso, 1999).

The process of carcinogenesis in humans (originally identified in animals),resulting in genetic alterations in cancer-related genes, proceeds in a multistagemanner over a long latent period (Anon., 1997; Sugano, 1999). At the onset of cancerdevelopment, two major stages can be distinguished: initiation and promotion. Car-cinogens responsible for the changes that can lead to the conversion of a healthycell into a neoplastic cell are divided into genotoxic and epigenetic (Taylor, 1982).Genotoxic carcinogens, acting at the initiation stage, include mainly substancesdisplaying mutagenic properties. Most mutagenic and carcinogenic food componentsbelong to the group of genotoxins. The name originates from their ability to damagecellular genetic material. The damage usually involves the formation of a covalentbond between DNA and a mutagen after any required host-controlled biochemicalactivation. The sites, which most frequently undergo such modifications, are nitrog-enous bases, guanine in particular (Swenberg et al., 1985). DNA adducts interferewith proper pairing between complementary bases and diminish the fidelity of DNAreplication, which in turn may result in incorporation of incorrect nucleotides intothe daughter DNA molecule. In this way, as a result of replication, the promutageniclesion, such as a DNA adduct, unless repaired by cellular repair systems, becomesfixed in a form of mutation, i.e., as a change in the genetic code.

For genotoxic food-borne carcinogens, DNA binding is crucially important;without DNA adduct formation, such agents do not induce cancers (Swenberg et al.,1985). Not all DNA adducts are critical lesions; only those altering the importantcancer-related genes by causing specific mutations following DNA replication areessential for neoplastic transformation. The cell bearing mutated gene(s) may be


eliminated by various mechanisms, protecting the organism against development ofabnormal cells, or it may persist within tissue. However, it needs to undergo cyclesof cell duplication, involving epigenetic control mechanisms, to generate a perma-nently altered, mutated cell that expresses preneoplastic characteristics, giving riseto a clone of initiated cells. Such a clone of cells susceptible to cancerous growth,if exposed to one or more factors (mostly epigenetic), called promoters, may pro-liferate to a definable focus of preneoplastic cells. This stage is known as promotion.Epigenetic factors operating as promoters of cancer usually require high and sus-tained exposures. Their effects, unlike those of genotoxins, are reversible (Weis-burger and Williams, 2000). To such factors belong many natural and man-madechemicals, including those present in food. The mechanisms of promotion are lessunderstood than those of genotoxin action, but they are thought to involve stimulationof cell proliferation, blockage of communication pathways between normal andmutated cells, and more. Also, partially reduced oxygen molecules such as hydroxylradical or superoxide radical, often referred to as oxygen radicals, act at the stageof promotion. They arise as a side effect of normal metabolism, and their formationis believed to underlie the cancer-promoting effect of a high-protein and high-fatdiet, since these food constituents are intensively metabolized. Oxygen radicals canbind to various cellular components, including DNA; they have also been shown toinfluence gene expression (Ames et al., 1993; Burcham, 1999).

The initiation and promotion of neoplastic transformation is followed by the finalstage of the carcinogenic process, known as progression, which comprises the growthof the tumor and its spread to other body parts. There are several lines of evidencethat at least some carcinogens present in food products are able to give rise to thedescribed above sequence of events in higher and lower vertebrates (Anon., 1993).

14.3 METABOLIC ACTIVATION AND FORMATION OF DNA ADDUCTS BY FOOD MUTAGENS AND CARCINOGENS

The vast majority of carcinogens, such as those in foods, accounting for a large fractionof the human cancer burden, do not possess mutagenic and carcinogenic properties inthemselves. In order for these properties to be revealed, the metabolic activation in anorganism is required, leading to the formation of electrophilic metabolites capable ofbinding to nucleophilic centers in DNA. Therefore, in literature the name promutagenor procarcinogen is often used to describe the compounds that must be converted bycellular enzymes into ultimate genotoxic mutagens and carcinogens.

Metabolic activation of carcinogens involves many enzymatic systems, knownas phase I enzymes. The most important is the cytochrome P450 complex, consistingof several different isoenzymes, which are particularly active in the liver. Otherenzymes include peroxidases, quinone reductases, epoxide hydrolases, sulfotrans-ferases, and others. Their variety reflects the diversity of chemical structures ofcompounds to which an organism is exposed. These may be harmful substances orneeded ones, or even those indispensable for its proper functioning. One could arguethat the activation of carcinogens is an undesirable side effect of metabolic pathways,


which were developed in the course of evolution most probably in order to improvethe utilization of nutrients and elimination of unwanted or harmful substances.

Competing with enzymatic activation are detoxification processes involvingphase II enzymes. These enzymes catalyze the attachment of polar groups to increasewater solubility of normal metabolites, as well as foreign compounds, and therebyfacilitate elimination. To the enzymes responsible for removal of mutagens andcarcinogens belong most of all glutathione-S-transferases and glucuronyltrans-ferases; however, phase I enzymes are sometimes also involved in the initial stagesof detoxification. It even happens that activation and detoxification run in paralleland are catalyzed by the same enzymatic system. For instance, epoxidation ofbenzo[a]pyrene by cytochrome P450 in position 7/8 results in the formation of acarcinogenic metabolite, while in position 4/5 it produces an inactive derivativeexcreted readily from the organism. Below are given some examples of well-estab-lished metabolic activation pathways for a few classes of mutagenic compoundsfound in food, along with the major products of reaction of their main toxic metab-olites with DNA, more precisely, with guanine, which is the preferred site of bindingof electrophilic intermediates.

Metabolic activation of aflatoxin B1, belonging to the class of mycotoxins, iscatalyzed by cytochrome P450. The metabolic conversion of this compound canfollow many pathways; however, only the epoxidation in position 8/9 produces theultimate carcinogen:

This metabolite binds to the N7 position of guanine, giving an unstable adduct8,9-dihydro-8-(N7-guanyl)-9-hydroxy-aflatoxin B1, which either undergoes sponta-neous depurination or rearrangement to a stable 8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl-formamide)-9-hydroxy-aflatoxin B1, following the openingof the imidazole ring (Wakabayashi et al., 1991).

The formation of nitrosamines in the reaction of amines with nitrites under acidicconditions in the stomach can be considered as nonenzymatic activation of aminespresent in food. Nitrosamines undergo further metabolism, catalyzed enzymaticallyby cytochrome P450, involving hydroxylation (Anon., 1993).

The hydroxylated derivative is unstable and in a series of spontaneous reactionsgives rise to methyl carbo-cation, which alkylates guanine in position O6, thus inthe site taking part in the formation of hydrogen bonds in DNA with complementarybase cytosine.

Formula 14.1

O O

O

O O

OCH3 O O

O

O

O O

OCH3

cytochrome P450


Metabolic activation of benzo[a]pyrene consists of three enzymatic reactions.First, the formation of epoxide in position 7/8 is catalyzed by cytochrome P450;epoxidation in position 4/5 results in detoxification of this compound. Then, epoxidehydrolase converts the epoxide into 7,8-dihydrodiol, which is subsequently oxidizedto 7,8-diol-9,10-epoxide. The formation of four different diastereoisomers is feasible,among which anti-9,10-epoxide derived from (-)-7,8-dihydrodiol is by far most

Formula 14.2

Formula 14.3

O O

O

O

O O

OCH3

+DNA HN

NN

NO O

O

H2N

O

HO

OCH3

O O

HN

N

O

OO

O O

OCH3

N

O

NHH2N

OH

HO

sugar

sugar

N

H3C

H3C

N O + H2O

HH2C

H

N N OH

-H2OH2C N N H2C N N

N N

H3C

H2CHO

O

H

NH + NO2 +

H3C

H3C

N N

H3C

H

O + CH2O

cytochrome P450

unstable

CH3 + N2

H


carcinogenic (Dipple and Bigger, 1990). In DNA, this derivative reacts most fre-quently with guanine in such a way that position 10 of benzo[a]pyrene and positionN7 of guanine become linked together.

Aromatic compounds substituted with amino groups, e.g., heterocyclic aromaticamines present in protein food products, are usually activated by cytochrome P450to hydroxylamines. This type of metabolism is observed in the case of 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2).

After further spontaneous rearrangements, hydroxylamine derivatives produceelectrophilic intermediates, which are able to modify DNA bases (Sugimura andSato, 1983). One of the possible structures of DNA adducts formed by Trp-P-2 withguanine is given in Formula 14.7.

Formula 14.4

Formula 14.5

HN

N N

N

CH3

H2N

sugar


In this case, the position C8 of guanine has been modified. The group of hetero-cyclic aromatic amines includes so many different compounds that a large varietyof chemical structures of DNA adduction products formed by them can be expected.

The normal metabolic processes taking place in the organism generate numerouspartially reduced oxygen molecules. They are responsible for many detrimentaleffects to the cells. Oxygen radicals may cause peroxidation of cell membrane lipids,oxidation of proteins, and modification of DNA components. Reaction with DNAleads to the formation of a variety of promutagenic lesions (Ames et al., 1993;Halliwell, 1999), usually called oxygen DNA adducts. Formula 14.8 gives examplesof such adducts resulting from hydroxylation of nucleobases.

It is nowadays generally accepted that the enzymatic systems implicated in metab-olism of carcinogens may be the reason for different susceptibility of humans to cancer(van Iersel et al., 1999; Manson and Benford, 1999; Wolf, 2001). Therefore, the genescoding enzymes responsible for biotransformation of carcinogens have been includedin the list of cancer-related genes. Importantly, many dietary compounds can influencevarious phase I and II enzymes by induction or inhibition. For example, cytochromeP450 isoenzyme CYP1A2 (phase I) activity may be induced by polycyclic aromatic

Formula 14.6

Formula 14.7

N

N

H

CH3

NH2

cytochrome P450

- SO4-2

unstable

N

N

H

CH3

NH-OH

N

N

H

NH O SO 4 N

N

H

NH

N

N

N

H

CH3

H

N

N N

NH

O

NH2

H


hydrocarbons in grilled and smoked foods and inhibited by naringenin in grapefruit.Similarly, the phase II enzyme glutathione-S-transferases can be induced by manynonnutrient phytochemicals, dietary lipids, and reactive oxygen species (Sinha andCaporaso, 1999). Current research attempts to relate genetically correlated sensitivityand environmental exposures, including dietary impact, to individual cancer risk.

14.4 TESTS FOR MUTAGENICITY AND CARCINOGENIC PROPERTIES OF FOOD COMPONENTS

Food products contain thousands of compounds — some of nutritive value —nonnutritive components, numerous additives, substances formed during processing,and pesticide residues. Their safety is of utmost importance for human healthprotection, including cancer risk assessment. In order to evaluate the carcinogenicityof individual food constituents and their mixtures, often of unknown chemicalstructure, as well as the impact of cooking procedures, short-term reliable andinexpensive tests are necessary. Since cancer risk associated with chemical com-pounds is thought to stem mainly from their ability to induce mutations, mutagenicity

Formula 14.8

N

N N

N

NH2

HO

HN

N N

N

H2N

O

HO

N

N

NH2

OHO

OH

OHOH

N

N

O

CH3H

O OH

OH

sugar

adenosine guanosine

thymidine cytosine

sugar

sugarsugar


is used in the assessment of carcinogenic properties of food components. Such abilitycan be detected with the aid of bacteria whose culturing is easy, quick, and econom-ical. In the case of bacterial mutagenicity tests, it is assumed that the factors capableof damaging bacterial DNA can interact in a similar way with the DNA of higherorganisms. The evaluation of carcinogenicity, i.e., the ability of substances to inducecancers, is performed mainly in mice and rats.

The method most widely used to evaluate mutagenic activity is the Ames test(Ames et al., 1975). It utilizes mutant strains of Salmonella typhimurium unable tosynthesize histidine, thus dependent on an outer source of this amino acid. The backmutation in the appropriate gene makes the bacteria histidine independent. Thefrequency of back mutations increases in the presence of mutagenic factors. Tomimic metabolic activation of mutagens, typical for mammalian cells but oftenabsent in bacteria, microsomal fraction (usually isolated from rat liver) is addedconcomitantly with the substance studied. Currently, an array of Salmonella strainsis available that enable not only the evaluation of the overall mutagenic activity ofa given compound, but also the type of mutation it induces. Moreover, the techniquesof genetic manipulation offered by modern molecular biology allowed the construc-tion of bacterial strains expressing various animal and human genes coding enzymesimplicated in activation of chemical carcinogens. For instance, a strain of Salmonellatyphimurium expressing mammalian cytochrome CYP1A2 and NADPH cytochromeP450 reductase, two enzymes believed to be most important for the metabolism offood-borne mutagens and carcinogens, has been constructed (Aryal et al., 1999).However, as pointed out by many researchers, in vitro mutagenicity tests are in somecases overly sensitive and may not reflect exposures and mechanisms of biologicalrelevance to humans. Therefore, it is generally accepted that mutagenic propertiesof a given compound detected in bacteria need to be assessed in appropriate in vivoassays (MacGregor et al., 2000). For instance, commercially available transgenicMuta Mouse® and the Big Blue™ mouse and rat models, though they use bacterialtransgene as the mutational target, assure metabolic conversion of a compoundtypically tested for higher organisms. After exposition on mutagenic substance inan animal, the bacterial transgene is recovered and the frequency of its mutationassayed in the natural “host,” which is Escherichia coli.

To assess carcinogenicity, several doses of potential carcinogens are adminis-tered to animals. The highest of them correlates to the maximum tolerated dose(MTD) that does not cause severe weight loss or other life-threatening signs oftoxicity. As a result of such studies, the lowest dose is determined at which carci-nogenic effects are still observed. The next level below that is assumed not to havea biological effect, the so-called “no effect level.” This value, divided by a safetyfactor of either 100 or 1000, correcting for difference in sensitivity between animalsand humans, is considered the acceptable daily intake (Anon., 1988). Such studiesare usually very lengthy, so shorter alternative carcinogenicity assays are beingdeveloped. The new animal tumorigenesis models are designed with the aid of geneticengineering and are characterized by rapid development of tumors. In the literature,for example, there are described transgenic mouse models overexpressing oncogenec-myc (Ryu et al., 1999) or c-myc and tumor growth factor TGFα (Thorgeirsson


et al., 1999), immunodeficient (SCID) mice (Salim et al., 1999), and knockout p53-deficient mice not expressing the tumor suppressor p53 gene (Park et al., 1999).

There is a continuous debate regarding whether carcinogenicity of compoundscan indeed be predicted based on mutagenicity tests. The data gathered so far showthat for certain groups of chemical carcinogens a very good overlap exists betweenthe bacterial mutagen and animal carcinogen group, providing support for the Amestest as appropriate method for identifying causative agents for human cancers.However, the usage of short-lived species like rodents to estimate carcinogeniceffects in a long-lived species such as the human must be taken with caution. Inorder to achieve a long life span, humans evolved mechanisms rendering them moreresistant to cancer. In addition, essential differences were shown between metabolicactivation and detoxification, as well as the DNA adduct formation by heterocyclicfood-borne amines, i.e., a vital DNA lesion initiating cancerous transformation, inrodents and in humans. Thus rodent models do not accurately represent the humanresponse to this type of compound (Turteltaub et al., 1999).

Although neither in vitro mutagenicity tests nor carcinogenicity tests in animalscan fully reflect the consumer’s health risk associated with a given chemical, theyplay an essential role since they enable the identification of those substances in foodsthat require detailed toxicological evaluation and whose consumption in largeramounts should be avoided.

14.5 FOOD-BORNE MUTAGENS AND CARCINOGENS

14.5.1 INTRODUCTION

The idea that nutrition is an important factor in the risk of cancer is not new. Reportsfrom the 19th and 20th centuries, based on observations made during clinical prac-tice, often indicated diet as a risk factor. More recently, albeit already classic, Dolland Peto’s survey of epidemiological evidence pointed to links between meat con-sumption and increased incidence of specific cancers (Doll and Peto, 1981).

Mutagens and carcinogens found in food products can be classified into threecategories (Sugimura and Sato, 1983). (Mutagens are understood here as compoundsgiving positive results in the Ames test. Those able to induce tumors in experimentalanimals are considered to be carcinogenic.) The first category includes naturalcompounds such as mycotoxins and substances of plant origin. The second categorycontains substances formed as a result of food storage, cooking, and processing. Thethird category of food-borne mutagens and carcinogens is derived from pesticides,fungicides, and additives. Contrary to public belief, compounds belonging to thethird group appear to have only marginal significance in the etiology of humancancer, due to the very low concentrations to which people are exposed.

In this chapter, mainly mutagens and carcinogens arising as a result of food process-ing are described, because these substances are believed on one hand to represent themajor dietary cancer risk factor, and on the other hand the health hazard that can bereadily reduced by changing food storage and preparation technologies. A large groupof potential mutagenic and carcinogenic substances of plant origin was omitted, althoughhumans may consume as much as a few grams of them daily (Ames and Gold, 1990).


Potential plant mutagens and carcinogens belong to a variety of classes of chemicalcompounds, e.g., hydrazine derivatives, flavonoids, alkenylbenzenes, pyrrolizidine alka-loids, phenolics, saponins, and many other known and unknown compounds. Plantsproduce these toxins to protect themselves against fungi, insects, and animal predators.For example, cabbage contains at least 49 natural pesticides and their metabolites, fewof which were tested for carcinogenicity and mutagenicity, some of which turned outpositive. However, there is no evidence that plant-based food increases cancer risk. Incontrast, epidemiological studies demonstrate that phytochemicals found in edible plantsexhibit numerous activities preventing carcinogenesis. Therefore, their role will be dis-cussed in a chapter concerning anticarcinogenic food components.

14.5.2 MYCOTOXINS

Mycotoxins are highly toxic compounds produced by molds, mostly in the generaAspergillus, Penicillium, and Fusarium. They represent the most dangerous contam-ination, arising mainly during storage of numerous food commodities, e.g., corn orpeanuts. Tropical and subtropical climates are particularly favorable locations formycotoxin production because of often poor food harvesting and storage practices.

Among several classes of compounds belonging to the group of mycotoxins, carci-nogenic properties have been demonstrated only for three of them. These are aflatoxinsand sterigmatocystin, inducing liver cancers, and ochratoxin A, implicated in the devel-opment of kidney cancers in experimental animals (Wakabayashi et al., 1991):

Aflatoxin B1 is the most carcinogenic mycotoxin and, based on available toxi-cological and epidemiological data, has been classified as a human hepatocarcinogen(Anon., 1987).

Formula 14.9

O O

O

O O

OCH3 O O

O

O O

OCH3

O

CH2

O

CH3

Cl

OH

CCH NH

COOH O

aflatoxin B1

ochratoxin A

O

aflatoxin G1


14.5.3 NITROSAMINES

A number of nitroso compounds, N-nitrosamines among them, are potent carcino-gens. The most common carcinogenic nitrosamines, found mainly in protein food,are N-nitroso-dimethylamine (NDMA), N-nitroso-diethylamine (NDEA), N-nitroso-pyrrolidine (N-Pyr), and N-nitroso-piperidine (N-Pip). These compoundssupposedly increase the risk of colon, rectum, stomach, pancreas, and bladdercancers. Nitrosamines are most prevalent in cured meats, but have also been detectedin smoked fish, soy protein foods dried by direct flame, and food-contact elasticnettings. Dietary surveys indicated weekly mean intakes of these compoundsamounting to about 3 µg per person (Anon., 1988; Cassens, 1995). In addition, theprecursors of nitrosamines, especially nitrate, are abundant in some leafy and rootvegetables (Table 14.1).

Nitrate and nitrite are also formed endogenously in the human body. In mammalianorganisms, following enzymatic conversion of L-arginine, nitric oxide is produced,which in turn may be converted to nitrite and nitrate (Hibbs et al., 1987). A portionof nitrate, either ingested or endogenously formed, carried out in the blood, is secretedby salivary glands into the oral cavity. Here nitrate can be reduced by microbial floraand swallowed. Thus it ends up in the gastric environment, similar to the nitrite ingestedwith food. Under the acidic conditions of the stomach, the nitrosation of amines presentin food by nitrite occurs, giving rise to N-nitrosamines. Animal studies suggest, how-ever, that in vivo formation of nitrosamines does not occur to a significant extent, andfrom a cancer risk perspective, preformed N-nitroso compounds consumed in curedmeat or fish seem to be much more significant (Anon., 1997).

TABLE 14.1Most Important Sources of N-Nitrosamines and Their Precursors (Nitrites and Nitrates) in the Human Environment

Substance Source

N-Nitrosamines Cured meat (especially bacon)Smoked fishSoy protein foods dried by direct flameSome alcoholic beveragesFood-contact elastic nettingsRubber baby bottle nipplesCosmetics

Nitrites Cured meatBaked goods and cerealsVegetablesNitrate reduction in vivo

Nitrates Drinking waterNatural constituent of beets, celery, lettuceNitrate fertilizer residues


The presence of nitrites has both a positive and negative impact on food safety.On one hand, in many countries, a correlation between stomach and liver cancers,induced probably by nitrosamines, and the amount of nitrites consumed is observed(Fine et al., 1982). On the other hand, nitrites inhibit the growth of Clostridiumbotulinum, thus reducing the risk of food contamination by botulinum toxins. More-over, under the acidic conditions of the stomach, where they are involved in theformation of carcinogenic nitrosamines, nitrites are capable of neutralizing carcin-ogens formed as a result of protein pyrolysis (Pariza, 1982).

Since the presence of nitrites is mainly a consequence of vegetable cultivationand food processing, changes in technology may lead to a considerable decrease ofthe amounts of these compounds in food products, thereby diminishing the risk ofcancers induced by nitrosamines. Nonetheless, they are likely to remain a necessaryadditive of preserved foods, since an alternative to nitrites as curing agents andmicrobiological preservatives has not been found so far. It has been learned, though,that the formation of carcinogenic nitrosamines during thermal processing, e.g.,frying, of cured meats can by largely inhibited by the addition of antioxidants, e.g.,ascorbate and α-tocopherol. The addition of such compounds has now become astandard procedure (Cassens, 1995).

14.5.4 MUTAGENS IN HEAT-PROCESSED FOODS

In the 1960s, with the advent of experimental models of chemical carcinogenesisand the publication of the mutagenicity test by Ames et al. (1975), the detection ofspecific chemical carcinogens in the human diet became plausible. Surprising newswas that cooking of proteinaceous foods under normal cooking conditions promotesmutagenesis. Mutagens were found in grilled and fried meat and fish, and methanolextracts of their charred parts were found in smoke condensates produced whilecooking these foods, as well as in heated, purified proteins and amino acids. Mostof the examined mutagens proved carcinogenic in mice and rats, inducing cancersof various organs (Nagao, 1999).

The formation of mutagens in canned foods is also associated with sterilization,although temperatures applied in this case are relatively low: 110–120°C. Mutagenicsubstances produced during canning have not been chemically characterized so far(Krone et al., 1986). In the case of other protein foods, such as milk, cheese, eggs,or legumes, the presence of mutagenic substances was detected only after thermalprocessing associated with a change of color resulting from burning etc. (Robbana-Barnat et al., 1996).

14.5.4.1 Heterocyclic Aromatic Amines

Heterocyclic aromatic amines (HCAs) are formed during thermal processing ofmany kinds of foods, especially foods containing much protein. They may beassociated with increased incidence of human tumors in the colon, breast, stom-ach, liver, and other organs. However, so far gathered data do not allow final


conclusions to be drawn (Anon., 1997). Around 20 different food-derived HCAshave been isolated to date.

The products of amino acids and protein pyrolysis whose chemical structuresare given below are produced in temperatures higher than 300°C. Therefore, theyare detected mainly in the surface layers of meat and fish subjected to open-flamebroiling. These compounds are strong mutagens, though they usually are not verypotent carcinogens (Sugimura and Sato, 1983; Nagao, 1999):

Another type of HCA is generated in the dry crusts of foods baked at 150–200°C.These are derivatives of quinoline, quinoxaline, and pyridine formed in the reactionof creatine or creatinine with amino acids and sugars. All the reactants are thusnatural constituents of meat. These HCAs, examples of whose chemical structuresare given below, belong to the strongest food-borne mutagens known and are car-cinogenic in rodents (Wakabayashi et al., 1991); the compound designated IQ wasshown to be carcinogenic in nonhuman primates (Adamson et al., 1994). They arefound in the crusts of fried or broiled meat and fish, as well as in fried and bakedmeats and heated meat extracts (Krone et al., 1986):

Formula 14.10

Formula 14.11

N

N N

NH

N

N

CH3

H R

NH2

R

NH2

NH2

Trp-P-1: R=CH3Trp-P-2: R=H

Glu-P-1: R=CH3Glu-P-2: R=H

Phe-P-1

Trp-P-1: 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indoleTrp-P-2: 3-amino-1-methyl-5H-pyrido[4,3-b]indoleGlu-P-1: 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazoleGlu-P-2: 2-aminodipyrido[1,2-a:3',2'-d]imidazolePhe-P-1: 2-amino-5-phenylpyridine

N

N

NNH2

CH3

N

N N

NNH2

CH3H3C

NN

N

CH3

NH2

IQ PhIPMeIQx

IQ: 2-amino-3-methylimidazo[4,5-f]quinolineMeIQx: 2-amino-3,8-dimethylimizado[4,5-f]quinoline PhIP: 2-amino-1-methyl-6-phenylimizado[4,5-b]pyridine


Compounds PhIP and MeIQx are most prevalent of the HCAs in the humandiet. Daily consumption may be as high as several nanograms per person. Theseamounts ingested by humans may not be sufficient to induce cancers by themselves.At least such a conclusion can be drawn from comparison with animal intakes.However, many environmental factors may be implicated in neoplastic transforma-tion in man. HCAs may be one of these factors (Nagao, 1999).

Since HCAs belong to the most abundant food-borne substances possiblyaffecting cancer risk, much research is devoted to clarifying their impact ontumor induction. It was found that dietary polyenoic fat, e.g., corn oil used forfrying meat patties, significantly enhances PhIP mammary carcinogenesis in rats,and it was suggested that PhIP initiates the carcinogenic process, while dietaryfat serves as a promoter (Ghoshal et al., 1999). Particularly worrying are resultsof experiments performed in rats, which demonstrated that PhIP is passed viathe liver to the breast and is secreted to milk of lactating animals. The newbornpups received a dose sufficient to induce tumors. Such a route of exposure mayalso exist in other mammals, including humans. This would mean that humansare exposed to HCAs in foods continuously from early life, even in utero (Felton,1994; Paulsen et al., 1999).

14.5.4.2 Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) containing a system of condensed aro-matic rings are formed as a result of incomplete combustion of organic matter. PAHsare associated with elevated risk of cancers in various tissues, especially skin andlung. It has been established that for carcinogenicity of these compounds, the metab-olites arising from epoxidation of the so-called “bay region” (Chapter 15.3) areresponsible.

In food, PAHs are produced mostly during heating, especially open-flame heatingsuch as grilling of meat. Under such conditions, fat from meat drips onto a hotsurface, e.g., hot coal during grilling, and is incinerated. The smoke from the fatpyrolysis containing PAHs is adsorbed on the meat. The levels of these compoundsthat can potentially be produced are relatively large: the surface of a 2-lb well-donesteak was reported to contain an amount of benzo[a]pyrene equivalent to that foundin the smoke from 600 cigarettes (Pariza, 1982). In the case of smoked meat andfish, smoke used during processing is also a source of carcinogenic PAHs (Sikorski,1988). In addition, a number of food products contain measurable amounts of thesehydrocarbons resulting from environment pollution, e.g., fish caught in heavilyindustrialized regions.

The concentration of PAHs detected in foods is in the range of several to severalhundred nanograms per 1 g of food product (Anon., 1993). In feeding studies inwhich volunteers consumed heavily charbroiled beef, a dose-dependent formationof PAH–DNA adducts in white blood cells was observed. Their level increased after1–4 days following ingestion and they were eliminated within about 7 days. It wasthus unequivocally demonstrated that food-borne PAHs are capable of incurringdamage to human DNA (Schoket, 1999).


14.5.4.3 Effect of Commercial Processing and Cooking Techniques

The content of food-borne mutagens resulting from processing is relatively smallbut very variable and is estimated to amount to 0.1–500 ng/g of a given food product.The World Cancer Research Fund panel of experts evaluated the evidence andindicated that consumption of grilled or barbecued meat, consumption of fried foods,and a diet high in cured meats possibly increase the risk of certain human cancers.They concluded, however, that “there is no convincing evidence that any method ofcooking modifies the risk of cancer” (Anon., 1997). This statement has been arguedagainst by several researchers who demonstrate in their studies that the formationof food carcinogens depends strongly on the cooking technique applied and mustbe thus reflected by the differences in health hazard. This is of special concern inthe case of animal protein foods, because their processing involves methods partic-ularly liable to generation of carcinogenic HCAs and PAHs. Another cooking-associated exposure to PAHs and HCAs is fumes, which are produced abundantlyduring stir frying. Lung cancer is the most common cause of cancer death amongwomen in Taiwan, though most of them are nonsmokers. There are recent reportsconfirming the association between the PAH–DNA adduct level in lung tissue andlung cancer incidence in Chinese women, many of whom reported that they stir-fried meat daily (Yang et al., 2000).

The temperature applied during processing has a decisive influence on thekind of HCAs formed, while the amount depends on cooking time and method,as well as the type of food (Bartoszek, 2001). Their content, however, can beeffectively reduced. For instance, mutagens of HCA type were not detected inbeef either processed in a microwave oven or stir fried for 3 min on high heat(Miller, 1985). It has also been established that mutagenicity of cooked meatdecreases (mostly fried hamburgers were analyzed) after microwave pretreat-ment, causing the leakage of juices and thereby diminishing the content of sugarsand creatinine, i.e., precursors of some HCAs. Addition of onion and somevitamins also effectively reduced mutagenicity of cooked hamburgers (Katoet al., 1998, 2000; Edenharder et al., 1999).

Cured meat and fish are the main source of nitrite and the greatest contributorsof preformed carcinogenic N-nitrosamines in the human diet. It turns out that anothertraditional way of preserving protein foods, salting, also modifies cancer risk. Epi-demiological studies showed that cancer rates are highest in those parts of the worldwhere diets are traditionally very salty, e.g., in Japan, China, or Chile. Salt is usedextensively as a preservative and flavor enhancer throughout the world, but it wasdemonstrated to increase stomach cancer risk in a dose-dependent manner. Thiscarcinogenicity enhancement is probably due to damage to the mucosal layer facil-itating Helicobacter pylori infection (Anon., 1997).

In addition, commercial foods may contain traces of chemicals used in pack-aging and migration from food-contact materials can occur during their processing,storage, and preparation. These chemicals include monomers of polymeric mate-rials used in packaging, such as vinyl chloride and acrylamide classified by theInternational Agency for Cancer Research (1987) in group 2A (probable human


carcinogens). To this group also belongs cadmium, which along with lead, arsenic,and other carcinogenic heavy metals, may contaminate foods, especially organmeats, including the liver and kidney, in which these metals tend to concentrate(Rojas et al., 1999).

Cooked meals are characteristic of most civilizations, and preparation and enjoy-ment of cooked food is intrinsic to social and family life. Meat and fish may becooked using water, fat, more or less fierce heat, direct flame, and other methods.Curing and smoking have been used as a means of preserving meat and fish forthousands of years. Modern food technologies employ basically the same methods,only on a larger scale, to provide easy-to-prepare and time-saving convenience foodsdevoid of microbial contamination and with an increased shelf life. Relativelyrecently, it has been realized that all of the above benefits must be weighed againstthe possibility of formation of a variety of carcinogenic compounds as a result offood processing.

14.5.5 MUTAGENS IN TEA, COFFEE, AND ALCOHOLIC BEVERAGES

Coffee brewed from roasted beans and those prepared from instant powder, includingthe caffeine-free type, all display mutagenic activity. Apart from natural mutagenssuch as caffeic acid and its precursors chlorogenic and neochlorogenic acids, thesedrinks contain mutagenic products of pyrolysis: methylglyoxal and less active gly-oxal and diacetyl (Ames, 1986):

These pyrolysis products were also found in roasted tea and brandy-type alco-holic beverages (Sugimura and Sato, 1983). In addition, as a result of ethanolmetabolism, mutagenic acetaldehyde is formed, while in coffee and tea caffeine, aninhibitor of DNA repair synthesis is present and may also contribute to cancer risk.

These observations, made during studies carried out with the aid of microorgan-isms and experimental animals, suggested that tea and coffee might pose a serioushealth hazard, especially because both of these drinks are consumed in substantialamounts almost all over the world. Epidemiological studies, whose results becameavailable 10 years later, showed how misleading the extrapolation of data betweenspecies could be. No convincing evidence that daily consumption of tea or coffeeincreases cancer risk was found. In contrast, it turned out that regular green tea intakedecreases it, owing to the presence of numerous phytochemicals exhibiting anticarci-nogenic properties, which will be discussed later in this chapter. Caffeine, previouslyregarded as a harmful compound, has become an important (because of substantial

Formula 14.12

C

C

O

O

C

C

O

O

H

H3CH

H

C

C

O

O

H3C

H3C

glyoxal methylglyoxal diacetyl


intake) factor in carcinogenesis prevention, mainly because it helps to combat obesity,constituting a well-documented risk factor of many widespread diseases, includingheart ailments and cancer (Anon., 1997; El-Bayoumy et al., 1997).

The opposite must be said in the case of alcoholic beverages. Experimental resultsdid not indicate that they might play a role in the potentiation of cancer risk. Thisnotion was somehow supported by the epidemiological studies carried out in France,which lead to the discovery of the so-called “French paradox.” Contrary to the commonbelief among this country’s population, despite high alcohol intake, the frequency ofheart failures and possibly also tumor incidence is lower than that in other states.Currently, it is postulated that antioxidant substances present in colored alcoholicbeverages and particularly abundant in red wine (Figure 14.1) offer such protection.

The studies carried out in France are the only ones, they failed to demonstratealcohol as a cancer risk factor. The data gathered in other regions indicate alcoholas an important cause of carcinogenesis. The risk of cancer development increaseswith the amount of alcohol consumed and becomes particularly high when accom-panied by cigarette smoking (Anon., 1997; Doll, 1999).

14.5.6 OTHER RISK FACTORS

A number of epidemiological studies indicated that high consumption of fat contributesto the development of breast and large intestine cancers in humans (Ames, 1986). Carci-nogenic effects are also ascribed to high-calorie and protein-rich diets. Animal studiessuggest that all the mentioned risk factors come to play after initiation of tumorigenesis,while their mode of action relies on the increased production of oxygen radicals. Reactiveoxygen species are generated in the organism as a result of normal metabolism. A dietrich in nutrients increases the intensity of metabolic processes and thus also oxygen radicalproduction. These radicals are implicated in the induction of endogenous oxidative damage

FIGURE 14.1 Antioxidative properties of selected alcoholic beverages (based on Bartoszet al., Biochem. Mol. Biol. Int., 46, 519, 1998). The high antioxidative activity of beers may,to a considerable extent, result from the addition of antioxidants, vitamin C in particular.


of macromolecules, including the formation of so-called oxygen DNA adducts (e.g., 8-hydroxy-2'-deoxyguanosine) and protein carbonyl derivatives (Youngman et al., 1992;Chevion et al., 2000). This type of lesion is believed to play a significant role in the processof aging and in the variety of degenerative age-related disorders, including cancer. Theanimal studies showed that calorie and protein restriction markedly inhibits both carcino-genesis and accumulation of endogenous oxidative damage (Youngman et al., 1992;Rogers et al., 1993; Burcham, 1999). Convincing support is also lent by reports demon-strating that the diet containing ingredients with antioxidant properties considerably inhib-its cancer development (Anon., 1997; Thomas, 2000).

Moreover, although fats do not display mutagenic activity per se, some of theirconstituents, such as cholesterol and unsaturated fatty acids, are easily oxidizedduring thermal processing, giving rise to reactive molecules that in turn may triggera chain reaction of lipid peroxidation, leading to the formation of mutagens, pro-moters, and carcinogens. These include radicals, fatty acid epoxides and peroxides,aldehydes (e.g., malondialdehyde, which binds covalently with DNA), and others(Ames, 1986). Another important mechanism by which fat modulates carcinogenesis— some researchers claim the most important — involves its interference withsynthesis of prostaglandins and leukotrienes, as well as the development of insulinresistance, which in turn stimulates proliferation of cells (colonic epithelium cellsin particular) (Woutersen et al., 1999; Bruce et al., 2000).

Another class of food-borne substances that have been postulated to influencethe frequency of cancer development are xenoestrogens. Xenoestrogens penetrateinto the organisms with food and they mimic or change the activity of estrogensproduced endogeneously. To these compounds, whose ability to promote the devel-opment of estrogen-dependent cancers (e.g., breast cancer) has been documented,belong polychlorinated biphenyls (PCBs), formed during drinking water chlorina-tion; pesticide residues, DDT in particular; and some components of plastics usedfor food packaging. In the case of DDT and certain PCBs, their association withbreast cancer incidence was evidenced based on human-derived biological material.These substances are extremely stable and persist in the environment for many years,even in countries where DDT has been banned long ago. It is estimated that thedecreased exposition to xenoestrogens would decline the frequency of breast cancerby 20%, i.e., by 36,000 cases in the United States alone (Davis et al., 1993).

14.6 CHEMOPREVENTIVE FOOD COMPONENTS

Laboratory studies carried out over the past 20 years demonstrated that food, one ofthe major components of the human environment, contains numerous mutagens andcarcinogens. As described earlier in this chapter, they may be naturally occurring,but most of them are of anthropogenic origin and are found in food mainly as a resultof thermal processing of fat and protein-rich food products. These findings werefollowed by epidemiological investigations, which confirmed the health risk associ-ated with the consumption of foods with high protein and calorie content. Theyrevealed, however, that edible vegetables and fruits, apart from nutritive macroele-ments, contain numerous microelements and nonnutritive phytochemicals displayingdifferent anticarcinogenic and other health-promoting biological activities, effectively


reducing human cancer risk (for the most extensive review see Anon., 1997). Thelatter, until recently, have been regarded as unimportant to human health.

In the 1990s, the results of numerous investigations carried out in differentpopulations were published and demonstrated unequivocally a rare situation in thecase of epidemiological studies: that a high content of vegetables and fruits in thediet was associated with decreased cancer incidence. As a result of research onanticarcinogenic food components, a number of substances displaying such chemo-preventive properties have been characterized: lycopene found in tomatoes (Giovan-nucci, 1999), epigallocatechins in tea (Fujiki et al., 2000), sulforaphane in broccoli(Zhang et al., 1994), and resveratrol in grapes (Jang et al., 1997), to name only afew most extensively investigated. Chemopreventive potential exhibited by plantfoods has nowadays become one of the major and most promising fields of cancerresearch, because it may help to diminish the global cancer burden simply byimplementing specific dietary recommendations (Schatzkin, 1997; Wolf, 2001). Inaddition, phytochemicals isolated from edible plants are tested with the aim todevelop dietary supplements, which could protect humans against cancer, as well asbecome a means of cancer chemotherapy enhancement.

14.6.1 ANTICARCINOGENIC FOOD COMPONENTS

A number of natural and synthetic compounds are able to prevent cancer inductionor development when administered to animals before or concomitantly with carcin-ogens. These substances include vitamins, microelements, compounds of plant ori-gin, medicines, and others (Table 14.2). Although the studies on the modes of actionof cancer preventive agents are still on the way in many laboratories and bring newdiscoveries each day, it has been realized even before they were undertaken that anyfactor capable of counteracting the production of carcinogenic metabolites, inhibitingthe initiation or promotion of tumorigenesis, and inhibiting metastasis by malignantcells, may be considered an anticarcinogen.

Anticarcinogens are divided into three groups, depending on the stage of car-cinogenesis they act at (Ames, 1986; Anon., 1993; Caragay, 1992). The first of thesegroups includes blocking agents, which protect cells at the stage of initiation ofneoplastic transformation. The second group includes suppressing agents, which areimportant during cancer promotion and uncontrolled growth of initiated cells. Factorsmaking cells more resistant to neoplastic transformation constitute the third group.

Blocking agents protect cells against substances that could initiate changesleading to malignancy. There are three major mechanisms (groups) of their activity.First, they prevent the formation of carcinogens from precursors. For instance,vitamin C inhibits, via an unknown mechanism, the formation of carcinogenicnitrosamines from amines and nitrites present in food (Caragay, 1992). It has beenalso found that lactic acid bacteria from both fermented dairy (Gilliland, 1990) andnondairy (Thyagaraja and Hosono, 1993) foods display antimutagenic activity,owing to the ability to bind mutagens. In this binding, peptidoglycan present in thebacterial cell wall is involved, and this property is not abolished after sterilization.Similar physicochemical sequestering of mutagenic and carcinogenic aromaticsubstances is displayed by chlorophyllin, the sodium and copper salt of chlorophyll


(Ardelt et al., 2001). To the second group of blocking agents belong the factorsthat protect cells against DNA damage. These mechanisms are best recognized.They involve the reduction of synthesis or inhibition of enzymes responsible formetabolic activation of carcinogens (phase I enzymes) and induction of enzymestaking part in detoxification of harmful substances (phase II enzymes). The abilityto modulate the activity of cytochrome P450 isoenzymes, often implicated incarcinogen activation, is displayed by numerous compounds, e.g., phenols, foundin edible plants. The detoxifying enzymes, especially glutathione-S-transferases,are effectively induced by isothiocyanates present in cruciferous vegetables, e.g.,broccoli. The compounds capable of trapping DNA-damaging species belong tothe third group of blocking agents. The removal of toxic metabolites is usually

TABLE 14.2Examples of Anticarcinogenic Foodborne Substances: Their Occurrence and Major Chemopreventive Activity

Type of Preventive Factor Substance Source Chemopreventive Activity

Blocking agents Vitamin CVitamin ECarotenes

LycopeneEpigallocatechinsChlorophyllin

PeptydoglycanGlutathione

Isothiocyanates

Citrus fruitPlant oilsCarrot (and other orange vegetables)

TomatoesTeaGreen vegetables

Cell wall of lactic bacteriaGarlic

Broccoli

AntioxidantAntioxidantAntioxidant

AntioxidantAntioxidantAromatic carcinogen sequestering

Carcinogen sequesteringChemical binding of electrophiles

Detoxifying enzyme induction

Suppressing agents Genistein, daidzein

GenisteinRetinoids

Isotiocyanates

Soy, sorgo

SoyOrange-colored vegetables

Cruciferous vegetables

Antiestrogenic activity

Inhibition of angiogenesisStimulation of cell differentiation

Inhibition of oncogene activation

Factors making cells more resistant to neoplastic transformation

Isoflavones

Diallyl sulfide

Hn–3 fatty acidsVitamin D + Ca + P

Soy

Garlic

Fish oil

Restricted calorie diet containing increased levels of vitamin D + Ca + P

Stimulation of cell maturation

Anti-Helicobacter pyroli activity

Modulation of signal transduction

Inhibition of cell proliferation


accomplished by nucleophilic substances, first of all glutathione and other sulfur-containing compounds abundantly found in garlic and onion, which can bindelectrophilic DNA-reactive intermediates. Vitamins C and E, trapping oxygen rad-icals in lipid membranes, as well as β-carotene and other polypropenes, present inall chlorophyll-containing food products and particularly effective in the neutral-ization of singlet oxygen, protect DNA against oxidative damage. Compoundscontaining selenium play similar roles. Selenium is an essential component of theactive site of glutathione peroxidase, the enzyme responsible for destroying hydro-gen peroxide and other peroxides generated during lipid peroxidation. Also,polyphenols, major phytochemicals present in all kinds of foods of plant origin,display antioxidative properties.

Suppressing agents, constituting the second group of anticarcinogenic factors,influence the process of transformation of the initiated (precancerous) cell into atruly malignant cell. Numerous nonnutritive phytochemicals display the ability toslow down or inhibit cancerous growth. Also, in this case several protective mech-anisms can be distinguished (Wattenberg, 1997). They involve stimulation of celldifferentiation (retinol), inhibition of oncogene activation (isothiocyanates), andselective inhibition of proliferation of tumor cells and antiangiogenic activity(genistein present in soy), disabling the growth of new blood cells necessary tosupply neoplasm with nutrients and oxygen. Generally, the mechanisms of actionof suppressing agents are poorly understood at the moment, as are the processespreventing cancer development at the later stages of carcinogenesis.

Factors belonging to the third group render cells more resistant to neoplastic trans-formation. These mechanisms are least known. They include stimulation of cell matu-ration, activity believed to be responsible for reducing breast cancer growth by soyisoflavones, and inhibition of cell divisions in target cells. Proliferation increases theprobability of conversion of promutagenic DNA damage into mutation, and thus reduc-tion of its rate in a way protects cells against neoplastic transformation. It has beendemonstrated that dietary enrichment in calcium, phosphate, and vitamin D slows downthe rate of cell divisions (Anon., 1997; Wattenberg, 1997). Garlic components can alsobe included in this group of anticarcinogenic agents because of their antimicrobial activityagainst Helicobacter pylori, a risk factor in the case of gastric cancers. Garlic componentsinhibit the growth of these bacteria and thereby prevent damage to epithelium, makingthis tissue more resistant to harmful effects of carcinogens (Anon., 1997).

Vegetables and fruits are the major sources of dietary anticarcinogens that canprotect human organisms against neoplastic diseases by different mechanisms, atvarious stages of carcinogenesis. Thus the diet rich in plant-derived foods appears tobe a realistic, nonpharmacologic, prophylactic approach against cancer. Apart fromnumerous anticarcinogenic substances, it also provides meals of low-calorie and pro-tein content. All these factors reduce cancer risk in humans. Therefore, the food andpharmaceutical industry share an interest in edible plants as a means of cancer chemo-prevention. In the case of the food industry, the prevention will probably rely on dietaryrecommendations ensuring high intake of protective phytochemicals, as well as enrich-ments of foods with anticarcinogenic vitamins and minerals. The pharmaceuticalindustry has begun to develop preparations, based on edible plants, exhibiting desirableactivities from a prophylactic cancer perspective.


14.6.2 CANCER CHEMOPREVENTION

Cancer chemoprevention can be defined as the prevention of neoplastic diseasesby providing people with one or more chemical substances in the form of specialpreparations or as naturally occurring dietary components. Cancer developmentis a slow, multistage process that takes about 20 years on average. The number ofnew cancer cases estimated around the world for only 25 different cancers in 1990amounted to 8.1 million (Parkin, 1998). If this number is multiplied by 20 yearsof latent development, it may be expected that more than 160 million people are,at this moment, at one of the stages of neoplastic transformation, which is lifethreatening. These people are the target population of cancer prevention, thuschemoprevention.

Anticarcinogenic compounds found in edible foods display many advantagesfrom the chemoprevention point of view. Any substance consumed as a chemopre-ventive agent is supposed to be ingested by healthy people for a long time; therefore,it must be devoid of toxicity. Numerous components of fruit and vegetables fulfillthis condition. Another desirable property of edible plants is the fact that theyrepresent a well-known element of human life and thereby facilitate the decision ofadopting health-promoting activities.

For about 10 years, very extensive studies have been carried out on numerouscompounds, both natural ones and their artificial derivatives, with potential applica-bility in cancer chemoprevention. Here are four examples of promising substancesisolated from edible plants.

Formula 14.13

OHOH

H

O

O

OH OH

OH

OH

OH

OH

OH

H3CSO

NCS

OH

OH

HO

epigallocatechin gallate resveratrol

sulforaphane

lycopene


Sulforaphane is one of the isothiocyanates produced by vegetables from thecruciferous family. Broccoli is a particularly abundant source of sulforaphane. Itis capable of inducing liver phase II enzymes responsible for detoxification ofmutagens and carcinogens (Zhang et al., 1994). Another promising compound,epigallocatechin gallate, was isolated from green tea. This compound, which is avery potent antioxidant, constitutes about 50% of the dry weight of green teaextract (Mitscher et al., 1997; Fujiki et al., 2000). It is present in black tea extractsas well, though in smaller amounts. Antioxidative properties are also displayedby lycopene, one of the major carotenoids present in tomatoes, processed tomatoesin particular (Giovannucci, 1999). Another chemopreventive compound, resvera-trol, belongs to phytoalexins and was isolated from grapes. Resveratrol was dem-onstrated to activate different mechanisms preventing cancer development. Studiesin animals showed that it induced phase II enzymes, scavenged oxygen radicals,stimulated cell differentiation, and thus inhibited carcinogenesis at various stagesof neoplastic transformation. The health-promoting properties of red wine are alsoascribed to resveratrol (Jang et al., 1997).

Moreover, it has recently been postulated that dietary supplementation with foodantioxidants may provide a safe and effective means of enhancing response to cancerchemotherapy (Conklin, 2000). Much more research is needed to validate this claim;however, the stimulation of oxygen radical formation by antitumor drugs is a knowncause of side effects of chemotherapy like cardio- or nephrotoxicity. The approvedchemoprotectants used clinically to date are not neutral to the organism either. Incontrast, certain antioxidative food components, in doses that are without adverseeffects, could improve the quality of life of patients by ameliorating chemotherapy-induced side effects and also enhance activity of antitumor drugs by different mech-anisms (e.g., inhibition of topoisomerase II).

The discovery of anticarcinogenic properties of many plant-borne compoundspresent in food is undoubtedly one of the most important developments, encouragingthe hope that the cancer death toll can be diminished. The fact that these substancesare found in liked and widely appreciated food products should facilitate the utili-zation of their precious chemopreventive properties.

14.7 SUMMARY

Numerous epidemiological surveys demonstrate that consumption of protein foodsincreases cancer risk in humans. This increase can be at least partially ascribed tomutagens and carcinogens present in such foods. The majority of mutagens andcarcinogens found in foods result from preservation and processing, especiallycooking at high temperatures. The processing of foods, however, into palatableproducts available all year-round is essential to sustain life. Preservation methods,such as salting, curing, or smoking, eliminate the risk of various forms of microbialcontamination, some of which may be life threatening. Apart from this practicalsignificance, preservation and cooking give food specific taste and flavor and arethe pleasures of life and intrinsic parts of cultures.

Food can thus be a source of carcinogenic risk; however, when the appropriatedietary recommendations are followed, it may play a protective role. Figure 14.2


clearly shows that many food-borne cancer risk factors are readily avoidable. Theincorporation of elements preventing cancer development into the diet does not seemto be particularly difficult, though the change of food preferences may be a toughdecision for many people.

It is often argued that the amounts of carcinogenic substances in food are sosmall that they should be readily detoxified within the organism. Food, however, isnot the only source of mutagens and carcinogens in our surroundings. In the pollutedenvironment, there is a plethora of factors that may increase cancer risk. Carcino-genic food components thus represent an additional burden, the one perhaps mosteffectively delivered into the human body. Therefore, the levels of these substancesin food should be as small as possible. This applies to both the food industry andevery household. Modern technologies used in future food processing should ensurethat while food products retain the desirable properties, the formation of potentialcarcinogens is minimal. Equally important for reducing cancer risk are changes incooking and the dietary habits displayed by people. Widespread research on anti-carcinogenic phytochemicals may eventually result in the development of protocolsenabling the enrichment of commercially available foods in cocktails of chemopre-ventive substances, similar to current vitamin supplementation.

FIGURE 14.2 The influence of some food components and dietary preferences on the riskof development of the most frequent human cancers (based on Anon., Food, Nutrition andthe Prevention of Cancer: A Global Perspective, AICR, Washington, D.C., 1997).

Lung cancer

Pancreas cancer

Colorectal cancer

Breast cancer

Prostate cancer

Kidney cancer

Vegetables

Fruits

Carotenoids

Vitamin C

Fiber

Alcohol

Meat

Heat

processing

High calorie

content

Obesity

Decreased risk

convincing probable possible

Increased risk


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337

Index

A

Absolute, 244Absorption spectrum, visible,

207–209Acceptable daily intake (ADI), 65,

294–296, 304Acer saccharium maple tree, 108Acesulfame K., 281Acetaldehyde

boiling point of, 235flavoring from, 244formation of, 324hemiacetal, 244molecular weight of, 235odor of, 234

Acetatebornyl, 235citronellyl, 235ethyl, 235potassium, 62starch ester, 104

Acetic acidboiling point of, 235from dry wood distillation, 102for fish preservation, 273flavoring agent, 99, 244from microorganisms, 248molecular weight of, 235odor of, 234in Salatrim, 125

Acetone, 102, 128–129Acetyl-3-hydroxyfuran, 98Acetylation, 129Acetylgalactosamine, 137Acetylneuraminic acid, 137Acid casein, 153Acids

acetic, see Acetic acidacetylneuraminic, 137acid casein, 153acrylic, 112as additives, see Additivesaldaric, 93–94, 104aldosylamino, 90alginic, 111amino, see Amino acidsaminobutyric, 75aminolevulinic, 75antioxidants, see Antioxidantsantistaling agents, 282apocarotenic acid, 210arachidonic acid, 125–127aroma of, see Aromaascorbic, see Ascorbic acidaspartic, 134, 135behenic, 125benzenecarboxylic, 64

benzoic, 278–279betalamic, 225boric acid, 103butyric, see Butyric acidcaffeic acid, 324capric, 125caprylic, 125carboxylic, 35, 103, 240carminic, 226chloroacetic, 104chlorogenic, 223, 324cis-parinaric acid (CPA), 138citric, see Citric aciddehydroascorbic, 147, 168dihomogammalinolenic, 127dimethylarsenic, 71docosahexaenoic, 117EDTA, see

Ethylenediaminetetraacetic acid (EDTA)

eicosapentaenoic, 117, 125, 126erythronic, 93, 96ester formation, 236fatty, see Fatty acids (FAs)ferulic, 247folic, 301formic, 164galactaric, 97galacturonic, 97gallic, 278gastric, 262gluconic, 91glutamic, see Glutamic acidglyceric, 93, 96glyoxalic, see Glyoxalic acidhexanoic, 240hialuronic, 85hydrochloric, 102–103, 216from hydroperoxides, 122hydroxy, 102, 247hydroxycarboxylic, 282hydroxypyruvic, 93, 96hydroxytricarballylic, 61ketosylamino, 91lactic, see Lactic acid bacteria

(LAB)lauric, 116linoleic, see Linoleic acidslinolenic, see Linolenic acidlipid oxidation product, 239Maillard reactions, 238malic, 22, 109monochloroacetic, 104monomethylarsenic, 71mucic, 97neochlorogenic, 324nitric, 103nitrous, 277nordihydroguiaiaretic, 67

nucleic, 3, 37, 159oc-linolenic, 15odor of, 234–235oleic acid, 116, 121–122oxalic, 22palmitic, 116PEFA, 116–117, 125–127phenolic, 222phosphatidic, 119, 128phosphoric, see Phosphoric acidpropionic, 125, 234pyroligenious, 244ricinoleic, 247salicylic, 278SCFA, 125sillylic, 103sorbic, 277–279, 303–304stearic, 116, 125–126sulfobenzoic, 281sulfonic, 161sulfuric, 93, 103, 164tartaric, 22tetraioic, 105thiobarbituric, 66, 122thiolactic, 244trans fatty acids, 4, 7, 116uric, 59uronic, 94, 104

Acidulants, 247, 275, 283Acrylamide, 323–324Acrylic acid, 112Actin

cross-link rupture, 173hydrolyzing of, 163–164myofilaments from, 12

Activity, water, 41–45Actomyosin, 146Acute tests, 294Acylation, 170–171Additives, 61–65, 273, 303–304

as acidulants, 283–284amount of, quality attribute, 5antioxidants, see Antioxidantsbenefits of, 299benzoic acid, 278–279carcinogens and mutagens formed

from, 317as clarifying agents, 283classification of, 274–275for color, 279–281compression of, 112consumer demand, 297definition of, 274as emulsifiers, 281–283as fat substitutes, 284–285as film formers, 283for flavoring, 279–281honey, 20nitrite, see Nitrite


prebiotics, 285–287as preservatives, 275–278protein solubility, 144riboflavin, see Riboflavinsorbic acid, 277–279, 303–304as stabilizers, 281–283sulfite, 276, 301–303as sweeteners, 279–281as thickening agents, 281–283

Adducts, oxygen DNA, 314–315, 317Adenine, 29Adenosine diphosphate (ADP), 58, 60Adenosine triphosphate (ATP), 39Adhesives

CMC, 104dextrins, 103from saccharides, 85, 110

ADI, 65, 294–296, 304Adipates, 104ADP, 58, 60Adsorption isotherm, 42–43Aeration, 47–48Aflatoxins, 311, 318Agar, 84, 281Agaricus bisporus, 237Agaricus campestris, 237Agents

anticlotting, 275antifoaming, 150, 275antimicrobials, 148antistaling, 282blocking, 327–328buffering, 57, 61–65bulking, 281chelating, see Chelating agentsclarifying, 275, 283complexing, 104, 275drying, 62emulsifying, see Emulsifying

agentsemulsion forming, 283firming, 61–62flavor, 99foaming, 153–154, 283gelling, 6glazing, 275leavening, 61–63, 275neoplastic transformation

resisting, 327–329nitrosating, 172preservation, 273raising, 61–63stiffening, 275suppressing, 327–329surface active, 92, 123, 129texturing, see Texturing agentsthickening, see Thickening agentsthinning, 285vasprotective, 222

AI, 128–129ALA, 126–127; see also Linolenic

acidAlanine, 134–135Alaska pollock, 151Albumin

bovine serum, 135, 147in eggs, 146, 154oxidation of ascorbic acid, 60saccharides in, 137

solubility of, 142Alcalase, 153Alcohol

aliphatic, 142butanol, 86, 234cancer risk factor, 325, 332citronellol, 235, 244dehydration of, 236dehydrogenase, 214, 249ethanol, see Ethanolethyl, 235eugenol, 243–244, 247favor threshold of, 66flavoring from, 233, 244geraniol, 238, 241, 244hexanol, 244, 249honey in, 20from hydroperoxides, 122isopropyl, 244leaf, 249–250from lipid oxidation, 240lipid solvent, 1151-methol, 244mutagen formation in, 324–325odor of, 234–235oxidation of, 236propanol, 234reduction, 90vanillin, 244

Alcoholism, 58, 127–128, 131Aldaric acid, 93–94, 104Aldehydes

acetaldehyde, see Acetaldehydealcohols, reduction to, 90boiling point of, 235carbonyl group, addition to, 90–91in chicken, 239in chlorophyll, 215citral, 244, 250citrus peel oil aroma, 232cleavage, 2362,4-decadienal, 244dehydration of, 236from DNA, 249–250flavoring from, 240–241, 244hexanal, 237–239, 244, 249from hydroperoxides, 122lipid oxidation product, 239Maillard reactions, 238, 246molecular weight of, 235mutagen formation from, 326mutarotation, 89–90nucleophile acceptance, 82odor of, 234–235in oil, 120oxidase, 59, 66oxidation of, 91–92, 103, 236polymerization of, 236propionaldehyde, 234reactions of

to carbohydrates, 89–92to proteins, 280

retinal, 213–214in soybean oil, 240vanillin, 244, 247–248in yellow-green chlorophyll, 215

Aldol condensation, 99Aldoses, 82, 91–92, 99Aldosylamines, 90

Aldosylamino acids, 90Aleurone layer, 17, 105Alfalfa, 210, 250Algae, 84Alginate

an anionic hydrocolloid, 67in brown algae, 84calcium, 61carboxylic groups in, 67, 103emulsifier, 281gel formation, 6, 67pectins and, 282potassium, 62sodium, 63stabilizer, 281for texture, 110thickening agent, 281

Alginic acid, 111Alkali, 62–63, 119Alkaloids, 3, 222Alkenylbenzenes, 318Alkyl glycoside polyesters, 284Alkyl imines, 90Alkylation, 169–170Alkylpyrazines, 241Allene oxide, 237Allergenicity, 303Allergens, 156Alliin, 240Allium genus, 236–237, 243Allspice, 232Allyl disulfide, 244Allythiocyanate, 237Aluminium phosphate, sodium,

63–64Aluminosilicate, 62Aluminum

anthocyanins reaction to, 222complexes, lakes, 226, 228in fruits and vegetables, 69

Amadori rearrangement, 90, 91Ames test, 316–317Amidation, posttranslational

enzymatic, 136Amide, 35Amines

antioxidant, 1–2aromatic, carcinogenic

heterocyclic, 7carbohydrate reactivity, 90flavor from, 240–241incorporation of, 166Maillard reactions, 238, 240–241nonprotein N in, 3

Amino acidsalkaline pH, reaction with,

159–160alkylation of, 169–170caramel catalysts, 109cellulose thermolysis, 102chemical modification of, 168composition of, 134–137conformation, 134, 138–141denaturation of, 141destabilization of, 155in eggs, 154for emulsions and foams, 148–151enzyme-catalyzed reactions,

162–167

Index 339

in film formation, 145–148flavor from, 240–241, 247in fried food, 8functional properties of, 141–142gelation of, 145–148in gluten, 156heating of, 155–160hydrophobicity, 36, 137–138as intraluminar binders, 55in legumes, 153Maillard reactions, 238, 240–241in milk, 153–154in muscles, 151–152mycoprotein, 154N-nitrosation of, 171–172nonprotein N in, 3oxidation of, 160–162pH, effect of, 143–144phosphate reactions, 172–173in potatoes, 239pressurization of, 155process flavor from, 246in proteins, 134–173reaction to, by water, 35solubility of, 142–144, 156water retention in, 144–145

Aminobutyric acid, 75Aminolevulinic acid, 75Ammonia

catalyzation agent, 109Maillard reactions, 238, 246solvent for, 35specific heat of, vs. water, 40

Ammonium, 34Ammonolysis, 92Amnhydrides, 35Amorphous layers in starches, 88, 102Amphipathic molecules, 36Amylases, 17Amylopectin, 87–88

in potatoes, 107retrogradation, 105in starch, 85, 102, 104

Amylosesto amylopectin ratio, 102in helical complexes, 86–87, 104,

107retrogradation, 105in starch granules, 85, 88, 102structure of, 86

Anageissus latifolia tree, 85Anchovy, 163Anemia, pernicious, 59, 76, 260Angiogenesis, 328Angle of internal friction, 194Angle of repose, 194Anhydrosugars, 93Anilinonaphthalene-8-sulfonate

(ANS), 138Anionic dyes, 228Anionic starch, 104, 111Anisakis parasite, 7Anise, 232Annatto, 210Anorexia, 76ANS, 138Anthocyanin, 206, 219–224Anthocyanins, 219–224Anthraquinone, 226

Anthropogenic contaminant, 74Anti-inflammatory agent, 126, 222Antibiotics in food, 296Antibleaching agent, 61Antibodies, 265Antibrowning agent, 64, 303Anticaking agent, 61–62, 285Anticarcinogenicity, 131, 243,

326–329Anticlotting agents, 275Antiestrogenic activity, 328Antifoaming agents, 275Antifreeze proteins, 6, 134–135Antihypertensive effect, 131, 154Antimicrobials

agents, in edible coatings, 148essential oils of herbs and spices,

243lysozyme, see Lysozymein milk proteins, 154mineral compounds as, 57, 61–65spices and herbs, 232sucrose FA esters, 285

Antimutagenicity, 243Antioxidants, 243, 278–279, 303

additives as, 274–275alcoholic beverages, 325in allium genus members, 243amines, see Aminesanthocyanins, 222–223anticarcinogenic action of, 326,

328ascorbic acid, see Ascorbic acidcarotene, see Carotenecarotenoids, see Carotenoidscatalase, 60, 160cloves, 243control of, in food, 4cryptoxanthin, see CryptoxanthinEDTA, see


in essential oils, 243flavonoids, see Flavonoidsfrom flavorings, 243glutathione, see Glutathionelipid stability, 121lutein, see Luteinlycopene, see Lycopenemeat preservation, 66mineral compounds as, 57, 61–64mung bean, 243, 249nitrite, see Nitritenitrosamine formation inhibitor,

320nutmeg, 243in olive oil, 116–117, 300polyphenolics, 212, 279, 329raisins, 302reductones, 97rosemary, 232sage, 232sesame, see SesameSOD, 57–60, 66, 160sodium chloride, see Sodium

chloridesolubility of, 143soy, see Soysoybeans, see Soybeans

spices, 232in tea, 302, 331TEAC, 213Terminalia catappa L. leaves, 243thiols, see Thiolstocopherals, see Tocopherolsin tomatoes, 331ubiquinone, 1–2warmed-over flavor protection,

240zeaxanthin, 210, 213–214

Antiplatelet, 243Antistaling agents, 282Antithixotrophy, 184, 188–190, 193Antiviral properties, 154Apocarotenic acid, 210Apocarotenoids

bixin, 209–210formula for, 209properties of, 212structure of, 206vitamin A in, 212

Apoise, 84Apparent viscosity, 201, 203Apples, 6, 85, 237, 248Appotransferrin, 60Apricot, 211, 248Aquaporins, 39Arabic gum, 85

anionic hydrocolloid, 67carboxylic function in, 103emulsifier, 281stabilizer, 281thickening agent, 281

Arabinofuranosyl, 238Arabinogalactan, 85Arabinose, 84, 220Arabinosidase, 238Arachidonic acid, 125–127Arginine, 134–136, 319Arils, 232Aroma, 110

of allium plants, 236–237baked food, 91of brassicas, 237bread, baked, 98burnt sugar, 97of cake mix, before preparation,

245–246caramel, 97, 238from carotenoid degradation,

212–213from cellulose thermolysis, 102citrus peel oil, 232compounds

acetic acid, 234acetyl-pyrroline, 248benzaldehyde, 245, 248diacetyl, see Diacetylgeosmin, 248jasmonate, 248lactone, see Lactoneslinalool, 238, 241, 248from microorganisms, 248octen-3-ol, 248

from DNA, 249–250extraction of, by solvent, 244from extrusion cooking, 241from fish oil, treated, 233


fried food, 91, 123green note, 249from hemicellulose, 102ionone, 212–213from lipid oxidation, 240–241from Maillard reactions, 240–241microbial, 247from monoterpene derivatives, 238of mung beans, 243odor unit, 234–235oranges, 235from oxidation of lipids, 122, 243roasted food, 91, 238of soy, 243from starch, 102storage of, in starch granules, 102structure of, 234–235toasty food, 238undecalactone, 235vanillin, 244, 247–248

Aromatic plants, 243Arsenic, 70–71

in predatory fish, 4PTWI, 75toxic effects on humans, 76,

323–324water contamination level, 46

Arsenobetaine, 70–71Arsenocholine, 70–71Arteriosclerosis, 222–223, 261Arthritis, 60, 298Arylhydrazine, 90Arylhydrazones, 90–91Ascorbate

calcium, 61heme, reaction with, 218nitrite reduction, 277nitrosamine formation inhibitor,

320potassium, 62sodium, 64

Ascorbic acidanthocyanins, 221, 223antioxidant properties, 1–2, 212betalain, effect on, 225browning, inhibition of, 276in flour, 168gel formation, 147Maillard reactions, 238mineral absorption, 55oxidation of, 60in potatoes, 19sulfite, reaction to, 276

Ashi, 145Asparagine, 135Aspartame, 94, 111, 281Aspartic acid, 134, 135Aspergillus, 318Aspergillus niger, 121Association-induction theory, 37Astragalus, 85ATP, 39Autolysates, 246Avenasterol, 130Azo groups, 137, 276, 280

B

B vitamins; see also Riboflavin; Thiamine

in eggs, 16in infant formula, 301in meat, 12in milk, 15in minerals, 59in nuts, 20pyridoxine, 301in seeds of pulses, 21in wheat grain, 16–17

Babassu butter, 116–117Baby formula

bioavailability of minerals in, 54DHA and EPA in, 127fatty acids in, 125iron in, 302α-lactalbumin in, 154lactose in, 15vitamin B6, 301

Bacon, 319Bacteria, 248

anticarcinogenic action of, 328coliform, 46in dairy products, 327Enterobacteriaceae, 261Lactic acid bacteria (LAB), see

Lactic acid bacteria (LAB)peptones in, 164vitamins in, 261

Bacteriotherapy, 261Bacteroides, 261Bakery products, 284Baking, 101, 110Baking powder, 92Balsam, 233Baltic sprats, 163Banana, 236Barfoed test, 92Barium, 46, 96Barks, spices from, 232Barley, 16, 88, 108Bathocupreine, 60Batochromic shifts, 222Bay, 232Beans, 20–21; see also Legumes

flavoring from, 233proteins in, 3, 153

Beard, of wheat grain, 16–17Beef; see also Meat

broth, 239chromium in, 53composition of, 13fatty acids in, 117HCAs in cooked, 323iron in, 52lipids in, 3myoglobin in, 157myosin transition temperature, 155potassium in, 52temperature during cooking, 158zinc in, 52

Beeralginates in, 84antioxidant, 325fermentation of, 302

flavoring from, 233foam, 8, 84, 150oxygen in, reduction of, 106turbidity in, 283water hardness, impact on, 47

Beer-Lambert law, 222Beetles, 4Beets, 224–226, 319; see also Sugar

beetsBehenic acid, 125Bell peppers, 238, 240Bellberry, 250Benedict test, 92Benefat, 125Benincasa hispida, 239Benzaldehyde, 245, 248Benzene, 46Benzenecarboxylic acid, 64Benzoate

calcium, 61potassium, 62sodium, 64

Benzoic acid, 278–279B.E.T. isotherm, 42–43Betalains, 3, 206, 224–226Betalamic acid, 225Beverages, 233, 283, 285–286BHA, 122, 278BHT, 122, 278–279Bifidobacterium, 261–265, 268Bilberry, 220, 223Bile, 262Bingham-Schwedoff model, 187–188Bingham's viscoplastic flow,

184–185, 188, 202Biochemical oxygen demand (BOD),

47–49Biodegradable materials, 105,

112–113; see also Packaging

Biotechnology, 296, 303Bioyogurt, 262–263Bismuth, 92Bisulfite, 280Bixa orellana L. tree, see AnnattoBixin, 209–210Black currant, 128, 220Blackberry, 211, 220Blanching, 4, 69Bleaching

carotenoid degradation, 210of oil-bearing materials, 120

Blindness, 303Blocking agents, 327–328Blood

anticlotting agent, 85calcium in, clotting catalyst, 57ceruloplasmin in, 66lead in, 74lipid levels in, 287minerals in, 58probiotics, impact on, 264substitutes, 85

Bloomon chocolate, 199on fish, 163

BOD, 47–49Boiling point, 33, 235, 245Boltzman constant, 37

Index 341

Bones, 58–60, 74Borage oil, 128Boric acid, 103Borneol, 235Boron

biological function of, 60in fruits and vegetables, 69microelement, 54RDA, 56

Botulism, 44, 154, 277, 297, 320Bound water, 38, 40–41Bovine semitendinosus muscle, 13Bowman-Birk trypsin inhibitor, 135Brain development, 127, 301Bran, 16–18

cadmium uptake, 73ferulic acid source, 247mineral bioavailability, 69, 302

Brandy, 325Brassicas, 237Brassicasterol, 130Bread

ascorbic acid in, 168bicarbonate leavenings, 301chromium in, 53composition of, 18dough making, see Doughenriched, definition of, 69flavoring from, 233gas-retaining structures in, 156iron in, 302lactose in, 15lipids in, 122–123making of, 17minerals in, 58staling, see Antistaling agents;

Stalingtexture of, 8, 150thiamine in, 301water content of, 2white, 285–286

Bread crumbs, 123Brine, 173British gums, 103Broccoli

anticarcinogenic action of, 328–329

carotenoids in, 211chemopreventive properties of,

327flavor of, 237selenium in, 60sulforaphane source, 331

Bromate, potassium, 63Bromine, 34, 91–92Bronchial hypersensitivity, 126Bronchoconstriction, 126Browning of food, 45, 91Brussels sprouts, 237Bubbles, in foam, 150Buds, spices from, 232Buffering agents, 57, 61–65Bugleberry, 250Bulk-phase water

bound water vs., 40organization of, 36properties of, 28–32, 37–38structural influence of, 34

Bulking agents, 281

Burnt sugar, 97Butanol, 86, 234Butter

dietary fat in, 3, 21fat separation in, 173fatty acids in, 117water content of, 2

Butterfat, 246Butylated hydroxyanisole (BHA),

122, 278Butylated hydroxytoluene (BHT),

122, 278–279Butyric acid

flavoring from, 244odor of, 234in Salatrim, 125in strawberry flavoring, 245

Butyrolactone, 99

C

Cabbage, 60, 237, 318Cacao, 53Cactus fruits, 224Cadmium, 70, 72–74

calcium absorption, 77chloride, 73iron absorption, 77PTWI, 75for rancidity inhibition, 67toxic effects on humans, 76,


Caffeic acid, 324Caffeine, 324–325Calcium

absorption of, 55, 77alginate, 61anticarcinogenic action of, 329ascorbate, 61benzoate, 61biological function of, 57–58blood-clotting catalyst, 57in carrots, 52caseinate, 148, 153in cereals, 18in cheese, 52chloride, 61, 94citrate, 61in cod, 52compounds, food additives, 61dihydrogen phosphate, 61dilactate hydrate, 61disodium EDTA, 61in eggs, 16excretion of, 55for food texturization, 111in fruits and vegetables, 22, 69gel formation, 67, 146glutamate, 61hydrogen carbonate, 61, 94hydroxide, 61ions, in water, 33lactate, 61lead and, 74macroelement, 54in milk, 15, 52

in oranges, 52phosphate, 140RDA, 56react with proteins, 68rheological properties of whey,

147in saccharide alcohols, 96salts of phosphatidic acid, 119in sardines, 52soap formation, 55sorbate, 61transglutaminase-catalyzed

reactions, 166treatment to remove from water, 47in tuna, 52water structure former, 34in yogurt, 52

Calcium-activated neutral protease (CANP), 68

Calpains, 163Camellia oleifera tea seeds, 116Campesterol, 130Campylobacter jejuni, 154, 297Cancer, 60, 309–310

from arsenic, 76bladder, 319blocking agents, 327breast, 308, 325–326, 332causing properties, testing for,

315–317chemoprevention, 330–331colon, 287, 308, 319, 326, 332factor

alcoholic beverages, 325diet, 308, 325dietary fat, 116, 325reactive oxygen species, 213,

315, 325gastric, 329intestine, 325kidney, 318, 332Linxian study, 215liver, 318, 320lung, 215, 332neoplastic transformation resisting

agents, 327pancreas, 319, 332prevention

caffeine, 324–325β-carotene, 215carotenoids, 332fiber, 332fruits and vegetables, 327, 332probiotics, 263selenium supplements, 215vitamin C, 332vitamin E, 215

prostate, 215, 308, 332rectum, 308, 319, 332risk

alcoholic beverages, 325, 332cigarette smoking, 325heat processing, 332high calorie content, 332meat, 332obesity, 332

stomach, 319–320, 323suppressing agents, 327

Candida


cylindracea, 248probiotics impact on, 264rugosa lipase, 121

Candy, 123, 125Canning, 320Cannizzaro oxidation, 99Canola, 117–120, 126–127CANP, 68Canthaxanthin, 208, 210, 212–213Caprenin, 125Capric acid, 125Caprylic acid, 125Capsanthin, 208–210Capsicum, 232Capsicum annum, 209–210, 238Capsorubin, 210Caramel, 109–110

Amadori rearrangement before, 91aroma of, 97, 238colorant for food, 91, 109, 206,

227–228dehydration of saccharides, 93flavor, after caramelization, 233sucrose in, 84

Caraway, 232Carbohydrates

alcohols, 90, 96–97aldehyde, 89–92in biodegradable materials,

112–113carbonyl group, addition to, 90–91in cereals and cereal products, 107chirality, 88–89dehydration of, 93depolymerization of, 102–103encapsulation using, 111–112esterification, 92etherification, 93fat substitutes, 285flavor, undesirable, 240glycosidic bond, 97halogenation of, 93hydroxyl groups, 92–97ketone, 89–92modification of, 103–107mutarotation, 89–90oxidation of, 91–94process flavor from, 246reactivity of, 89–107reduction of, 93relative sweetness, 94resistant starch, see Resistant

starchretrogradation in, 105structure of, 82–88taste of, 107–109texture in, 110–111in tubers, 107

Carbon dioxidein milk, 15oxidation of saccharides, 93polysaccharides reaction to, 103transportation, cellular, 59treatment to remove from water, 47

Carbon tetrachloride, 46, 131Carbonate

magnesium, 61potassium, 63

Carbonyl compounds

aldehyde and, 90–91ketone and, 90–91protein modification, 169solvent for, 35water and, 29

Carboxylic acid, 35, 103, 240Carboxylic groups, 103, 137, 228Carboxymethyl cellulose (CMC),

104, 111, 148Carboxymethyl starch, 104Carcinogens, 308–318

N-nitrosoamines, 172, 277safety factor for, 295

Cardamom, 232Cardiovascular disease; see also Heart

diseasefactor

cadmium, 76reactive oxygen species, 213

prevention of, 68risk of, 125

Carminic acid, 226Carotene


antioxidant, 214chlorophyll and, 215formula for, 207in fruits and vegetables, 209–211intercellular communication agent,

213lycopene, see Lycopenein palm oil, 210photooxidation protection, 209properties of, 212retinal from, 213–214structure of, 206ultraviolet skin protection, 213vitamin A in, 212–213zeaxanthin, 210, 213–214

Carotenoidsin alfalfa, 210in annatto, 210anticarcinogenic action of, 332antioxidant, 1–2, 213, 331apocarotenoids, see

Apocarotenoidsbiological activity, 213carotenes, see Carotenein carrot, 210in citrus peel, 210color of, 207–209destruction of, in deodorizing of

oil, 120as food coloring, 210–212homocarotenoids, 206lycopene, see Lycopenein milk, 14–15neoxanthin, 209oxidation of, 301–302oxocarotenoids, see Xanthophyllsin palm oil, 210in paprika, 210pigments from, 16, 206properties of, 212–213in red pepper, 209–210in saffron, 210structure of, 206–209synthesis of, 209–210

in tomato, 210vitamin A in, 212–213xanthophylls, see Xanthophyllszeaxanthin, 210, 213–214

Carrageenanscasein stablizer, 67emulsifier, 281for food texturization, 111locust bean gum and, 282in red seaweed, 85in squid meat gels, 145stabilizer, 281sulfate function, 103thaumatin reactions with, 281thickening agent, 281

Carrotsanticarcinogenic action of, 328calcium in, 52carotenoids in, 206, 210, 211oil from, 210pigments from, 52, 206potassium in, 52

Caryophyllene, 244Caseins

acylation of, 170antimicrobial activity of, 154enzyme-catalyzed reactions in,

162for film formation, 148lipid interaction in cheese, 173in milk, 14, 140, 153phosphorylated amino acid

residues in, 136–137processing of, 153proline in, 135rheological changes to, 156stablizer, 67in whey, 146

Cassava, 107, 300Cassia, 232Casson equation, 189, 202Castor oil, 247Catabolic processes, 169Catalase, 60, 160Cataracts, 60Catechins, 223Cathepsins, 162–164Cationic dyes, 228Cationic starch, 104Cations, 54; see also MineralsCauliflower, 237Caustic soda, 109Celery

apiose in, 84nitrates in, 319selenium in, 60sodium in, 22spice from seeds, 232

Celiac sprue, 55Cellobiohydrolase, 106Cellobiose, 83, 106Cellular-mediated immunity (CMI),

265Cellulose

acetate, 104aroma of, 110in biodegradable materials, 112CMC, 104degradation of, 106

Index 343

depolymerization of, 102emulsifier, 281esterification, 104etherification, 104in fruits and vegetables, 21mineral bioavailability, 55modification of, 99–104in plants, 85in potatoes, 19solubility, 101–102stabilizer, 281thermolysis of, 102thickening agent, 281in wheat bran, 16

Cereals, 16–18barley, 16, 88, 108cadmium in, 74folate in, 301mineral bioavailability after

processing, 69minerals in, 58–59nitrites in, 319N:P conversion factor in, 3oats, see Oatsphase diagram, 198proteins in, 134saccharides in, 2, 137solubility of, 142starch in, 107

Cerium, 67Ceruloplasmin, 60, 66Cesium, 34Chalazae, 15–16Charcoal, 48, 102Cheese

alkylation of, 169–170calcium in, 52, 58chromium in, 53, 58composition of, 13enzyme-catalyzed reactions in,

162fat emulsion in, 173flavoring from, 233gelation of, 156milk protein in, 14minerals in, 58mutagen formation in, 320phosphorus in, 58potassium in, 52sensory attributes of, cause of, 8sequestrant for, 64yield of, 162zinc in, 52

Chelating agents, 60bathocupreine, 60betalains, 3, 206, 224–226citric acid, see Citric acidcysteine, see CysteineEDTA, 60, 66–67iron, see Ironphosphates, see Phosphatepurine, 60sodium citrate, 67sodium oxalate, 67

Chemotaxis, 126Cherry, 236, 248, 325Chicken; see also Meat

broth, 239composition of, 13

fatty acids in, 117fried, 239gels from, 147lipid oxidation in, 239radiation, effect on vitamins, 302

Chile saltpeter, 64Chinons, 21Chips, 53Chirality, 88–89, 105Chitin, 81, 86–87, 103Chitosan, 81Chive, 236Chloride

calcium, 61magnesium, 61potassium, 63RDA, 56sodium, see Sodium chloride

Chlorination, 47, 280, 326Chlorine

in fruits and vegetables, 22macroelement, 54oxidation of aldoses, 91–92water structure breaker, 34

Chloroacetic acid, 104Chlorodesoxysucrose, 94Chloroform, 207Chlorogenic acid, 223, 324Chlorogenoquinone, 223Chlorophyll, 215–217


photooxidation protection, 209pigments from, 206removal of, 119sensitizer, 160

Chloroplasts, 209Chocolate, 125, 189, 201–203Chokeberry, 220Cholemyoglobin, 218Cholera, 44Cholesterol

cancer risk factor, 326chromium impact on, 58decreasing level of, 129–131, 300in egg yolk, 16probiotics impact on, 262, 264structure of, 130

Choline, 6, 16Chondrodystrophy, 59Chromatographic sorbent, 85Chromium

in beef, 53bioavailability, 54biological function of, 58in bread, 53in cacao, 53in cheese, 53in curry, 53in hawthorn, 53for insulin production, 57in kidneys, 53in liver, 53microelement, 54in paprika, 53in pepper, 53for rancidity inhibition, 67RDA, 56in spices, 53

water contamination level, 46Chromoplasts, 209Chromoproteins, 157Chronic tests, 294Cinerarin, 222Cinnamaldehyde, 243Cinnamon, 232Cirronellol, 238Cis fatty acids, 7, 116, 121Cis-parinaric acid (CPA), 138Citral, 244, 250Citrate

calcium, 61sodium, 67for stabilizing, 155

Citric acidas catalyst, 285chelating agent, 122discoloration prevention by, 283enzymes from, inhibition of, 278fermentation of, 150in fruits and vegetables, 22as sequestrant, 279as solvent, 142treatment of oil, before

degumming, 119Citronellol, 235, 244Citrus fruit

anticarcinogenic action of, 328carotenoids in, 210oil

aroma, 232essence oil, 243limonene in, 232, 250

Clarifying agents, 275, 283Clathrate hydrates, 36Clausius-Clapeyron equation, 41–42Cleaning, 118Clostridium

botulinum, 44, 154, 277, 297, 320difficile, 264in gut, 261illness from, 297perfringens, 277, 297water activity level, 44

Cloves, 232, 243Clupea, 164CMC, 104, 111, 148CMI, 265Coacervation, 112Coalescence, 283Coatings, 125, 148Cobalt

biological function of, 59microelement, 54for rancidity inhibition, 67RDA, 56

Coca-Cola, 242Coccus cacti L., 226Cochineal, 206, 226Cocoa

aroma, 110cadmium in, 74flavoring from, 233rheological properties of, 201

Cocoa butter, 125, 201Coconuts, 116–117Code of Federal Regulations, 246Codfish


calcium in, 52DHA and EPA in, 127lipids in, 3–4myosin transition temperature, 155rancidity in, 66sorption isotherm data for, 43

Codliver oil, 127Coefficient of retention, 201Coffee, 110, 233, 324–325Cohesion, 194Colas, 242Cole crops, 237Coliform bacteria, 46Collagen

in egg shell, 15for film formation, 148formaldehyde and, 169heating of, 155–156hydroxyproline in, 136posttranslational modifications in,

136rheological properties of, 156–157saccharides in, 137solubility of, 142–143thermal stability of, 139water retention, in meat, 12

Collapse, 196Collenchyma, 23Color scale, Lovibond tintometer, 120Colorants, food, 6, 205–206

additives as, 274–275, 279–281anthocyanins, 219–224betalains, 224–226caramel, see Caramelcarotenoids, see Carotenoidschlorophyll, see Chlorophyllchromoproteins, 157curcumin, 206, 227fixative, 64from flavonoids, 219–224heme, 217–218microcapsules for, 102perception of, 205–206quininoid, 226retention agent, 62riboflavin, see Riboflavinsorbic acid, 277–279, 303–304synthetic organic colors, 228tetrapyrrole pigments, 215–217tetraterpene pigments, 206–215thermal processing, 109–110turmeric, 227, 232

Compartmentalized water, 38Complex force deformation, 195Complex formation, 104Complex modulus, 201Complexing agents, 275Compression modulus, 199, 201Compressive modulus, 199–200Compressive strain, 199–200Compressive stress, 199–200Concentration, 234Concrete, 244Conditioning, 118Confitures, 108Conformation, 155Coniferaldehyde, 247Constitutional water, 41

Containers, biodegradable, 105, 112–113; see also Packaging

Contaminants, 5; see also PollutionCookies, 125Cooking

aroma of, 240carbohydrate transformation, 101carcinogens and mutagens formed

after, 317drip formation during, 4extrusion, 241leaching of vitamins and minerals

during, 4, 69Maillard reactions, 238methods, cancer risk, 323–324mineral bioavailability, 55mutagen formation during, 320WHC impact on, 145

Copigmentation, 222Copper

bioavailability of, 55biological function of, 59catalyzation agent, 279chlorophyll, reaction with, 216deficiency, zinc effect on, 77in fruits and vegetables, 69in ham, 53lipid oxidation, 60in lipids, 122in liver, 53loss of, during processing, 69metallothioneins and, 72microelement, 54oxidations with, 92oxygen radicals, generation of, 60in oysters, 53for rancidity inhibition, 67RDA, 56react with proteins, 68in salmon, 53in sunflower seeds, 53in tuna, 53in wheat, 53

Copper chlorophyllinpotassium, 63sodium, 63

Coprecipitation, 112Coriander, 232Corn

bran, 130for film formation, 148flour, 157, 189lecithin from, 282linoleic acid in oil, 117, 127oil from, 117–120processing of, 300retrogradation in, 105sorption isotherm data for, 43Starlink, 303storage of, mycotoxin activity, 318

Cornstarch, 107Cosmetics, 85Costamers, 12Cottage cheese, 266Cottonseed, 117, 129, 282Coulomb's law, 34Covalent bonds, 27–28, 139, 146Cow's milk

bioavailability of minerals in, 54; see also Milk

composition of, 13fatty acid residues in, 15

CPA, 138Cracking, 118Cranberry, 220Creaminess, 185Creaming, 149, 283Creatine, 321Creatinine, 321Creep compliance test, 190–191Cretinism, 60Crispness, 196Crocetin, 210Crocin, 210Crocus sativus, 210Cross-linking

from acylation, 170–171from alkylation, 169of amino acid residues, 136,

159–160in gelation, 145during phosphorylation, 171polysaccharides, 105of proteins, 142rupture of, 173starches, 111in transglutaminase-catalyzed

reactions, 166Cruciferae

anticarcinogenic action of, 328brassicasterol in oilseeds, 130goitrogenic products in oilseeds, 7odor of, 237

Crude protein, 3, 13, 18Crustaceans, 3–4, 151–152Cryoprotectant, 151–152, 173Cryptosporidium, 297Cryptoxanthin

antioxidant, 214in egg yolk, 210formula for, 208in fruits and vegetables, 211in green leaves, 209–210intercellular communication agent,

213vitamin A in, 213

Crystallites in starches, 88, 102Crystallization, 196Cubic niter, 64Cucumbers, 239, 249Cumin, 232Curcumin, 206, 227Curd

flavoring from, 233from gelation of whey, 147rheological changes to, 156from soybeans, 153

Curdlan, 281Curing, 273

binding of nitrosating agents, 172color changes from, 157for food preservation, 44heme pigments, 218of meat, nitrosamines, 319nitrite in, 168, 277, 323nitrosamine formation during, 320,

323

Index 345

Curry, 53Cyanide, 300Cyanide sulfide, 34Cyanidin, 219, 223Cyclamates, 94, 111Cyclization, 97Cyclodextrins, 106–107, 112, 241Cycloglucans, 106Cyclooxygenase, 127Cyclospora, 297Cysteine, 60

alkaline pH, reaction with, 159in collagen, 134enzyme inhibitor, 164hydrolyzing of, 170oxidation of, 161properties of, 135sulfenic, 161thermal degradation of, 158in transglutaminase, 166

Cytochrome oxidase, 59Cytochrome P450 complex, 310–315Cytokines, 265Cytoskeletal proteins, 12, 163Cytosol, 166Cytotoxic cells, 265

D

Dactylopius coccus Costa, 226Daidzein, 328Dairy products, 14–15; see also

specific typesfermentation of, 240, 262, 268fiber enrichment in, 285–286flavor of, 246GDL in, 92, 284lactic acid bacteria in, 327lactose in, 108minerals in, 59N:P conversion factor in, 3rheological properties of, 167vitamin D fortification, 302

Daucus carote, 52, 206DDT, 326Deamination, 166, 169Deborah number, 192Decadienal, 240, 244Decalactone, 244, 247Decalcification, 76Decanal, 235Decapterus, 164Decarboxylation, 4Deformation

complex force, 195in an ideal body, 199–200rheological property, 181,

184–185types of, 199

Degumming oil, 119Dehydration, 44, 93, 97, 276Dehydroalanine, 159–160Dehydroascorbic acid, 147, 168Delayed type hypersensitivity (DTH),

265Delphinidin, 219, 223Demethylation, 72

Denaturation of proteins, 141color changes from, 157in egg whites, 154film formation and, 148gelation and, 145solubility after, 143in soy milk, 153temperature, 155in whey, 153, 155

Dendrite formation, 105Density of water, 29–30, 32, 36Deodorizer distillate (DOD), 129Deodorizing of oil, 120Deoiling, 129Deoxyalliin, 240Deoxysugars, 97Depot fat, 3Dermatitis herpetiformis, 55Desaturase, 126, 127Deserts, 190Designer foods, 6Desmin, 12, 163Desorption isotherm, 42–43Desoxyglucosulose, 98Desoxysaccharides, 93Detergents, 48, 105Detoxification, 72, 311Dew point temperature, 43Dewaxing of oil, 120Dextran, 85, 106Dextrins, 102, 110, 112Dextrose, 244DGLA, 127DHA, 125–126Diabetes, 58

fatty acids levels in, 127food for, 111sweeteners, 108–109

Diacetylflavoring from, 244formosine, 97, 99from microorganisms, 248mutagenic pyrolysis product, 324protein modification, 168

Diacylglycerols, 6, 14–15Dialdehydes, 93, 105Diallyl sufide, 328Diallyl thiosulfinate, 236–237Dialysis, 68Diascorea dumetrorum, 107Diaso, 228Diazonium, 277Dicarboxydiamides, 105Dichlorobenzene, 46Dichloroethane, 46Dichloroethylene, 46Didoquin, 55Dielectric constant (ε), 34Dielectric relaxation measurement, 39Diesel in water supply, 47Dietary fat, 21

cancer risk factor, 325–326composition of, 116–117edible, colorants for, 211glutathione, see GlutathioneHCA activation by, 322in milk, 14–15minetics, 284RDA, 116

substitutes, 284–285Dietary fiber

cellulose, 85in flour, 18plant polysaccharides as, 1zinc absorption, 55

Dietary supplementantioxidants, 331chemopreventives, 326–327magnesium hydrogen phosphate,

62probiotics, 275probiotics as, 267vegetable lecithin, 129

Diethylacetal, 244Differential scanning calorimetry, 155Diffusion coefficient, 37, 38Diffusivity of momentum, 187Diglycosides, 238Dihomogammalinolenic acid

(DGLA), 127Dihydrogen phosphate

calcium, 61potassium, 63sodium, 64

Diketal, monoacylated, 92Dilatant flow, 184, 185, 189Dilatin, 55Dill, 232Dimagnesium phosphate, 62Dimethyl-2-hydroxy, 99Dimethyl disulfide, 237Dimethyl-hydroxyacetone, 99Dimethyl sulfoxide, 103Dimethylarsenic acids, 71Dimethylsulfide, 244Dioxin, 293Diphenyl oxide, 244Dipole moment, 26Direct flow rate, 194Disaccharides, 84

in fruits and vegetables, 21lactose, see Lactosemaltose, see Maltoseproperties of, 89–99sucrose, see Sucrose

Disodium EDTA, 61, 64Disodium pentaoxodisulfate, 64Dispersion droplet size, 15Dissociable solutes, 33Distillation, 102, 130, 243Dithianes, 238Dithiolanes, 238DNA

adducts, 314–315, 317, 325–326arsenic impact on, 70of Bifidobacterium, 262–263cancer and, 309–310damage protection, 328for flavor compounds, 246–247flavoring from, 249–250hydrogen bond in, 29modification of, 310–315PAH damage to, 322protein synthesis of, 58repair inhibitor, 324

Docosahexaenoic acid, 117DOD, 129Dodecylsulfate, sodium, 138


Dougharoma, 110conditioner, mineral compounds

as, 61–62flavoring from, 233formation of, 17, 156–157gas-retaining structures in, 156lipids in, 123lipoxygenase in, 167proteins in, 142saccharides in, 104sulfite, additive to, 276

Drinks, 285–286Drip formation

from cooking, 4decrease in, 173in ham, 8during rheological changes, 156in shellfish, 8after thawing, 4, 69WHC impact on, 145

Drugs, 15Drying, 39Drying agents, 62DTH, 265Duck, 238–239Dwarfism, 59Dyes, 206, 228Dynamic viscosity, 186

E

Ecology, 5Eczema, atopic, 128EDTA, see Ethylenediaminetetraacetic

acid (EDTA)Effluent treatment, 48–49, 172Eggs, 15–16

acylation of, 170amino acids in, 135composition of, 13fat in, 21iron in, 52lecithin from, 282lipids in, 3lysozyme in, 135, 154mineral oil on, 283minerals in, 58–59mutagen formation in, 320N:P conversion factor in, 3phosvitin in, 135proteins in, 3, 135, 142, 154serine in, 135white, see White, eggyolk, see Yolk, eggzinc in, 52

Eicosanoid production, 126Eicosapentaenoic acid (EPA), 117,

125–126Elastic deformation, 199Elastic modulus, 191Elastin, 199Electrostatic interactions, 26–27,

143–144Elongase, 126, 127Emulsification, 144, 148–151, 171Emulsifying agents

additives as, 275, 281–283agar, 84calcium caseinate, 153egg yolk, 154HLB number of, 283mineral compounds as, 64polysaccharides, 84–85, 281–282sodium caseinate, 153

Emulsion forming agents, 283Emulsion stablizer, 65Emulsions, 190Enantiomers, 105Encapsulation, 111–112, 241, 244Endiols, 99Endive, 85Endoglucanase, 106Endoinulinase, 286Endomysium, 12, 14Endopeptidases, 136, 168Endosperm, 16–18, 69Endrin, 46Engraulis, 164Enolization, 99Enterobacteriaceae, 261Enterococcus faecium, 268Enteropathy, tropical, 55Enthalpy, 34

of egg whites, 154of hydrophobic substances in

water, 35–36of proteins, 138, 141rheological property, 193

Entrapped water, 41Entropy, 34

of hydrophobic substances in water, 35–36

of proteins, 137rheological property, 193solvent, 143–144

Environmental impact of processing, 48–49, 172

Enzymesactivity

denaturation, 141role of minerals in, 58–59

amylases, 17catalyzed reactions in proteins,

162–167cathepsins, 162–164esterases, 248flavoring from, 236–238, 246–247glycosidase, 238, 248hydrolases, 14lipases, 17, 121, 248lipoxygenase, see Lipoxygenase

(LOX)in meat, 12myrosinase, 7nucleases, 248oxidoreductases, 14phase II, 311proteases, 17, 146, 248tryptophan pyrollase, 75

EPA, 117, 125–126Epigallocatechin, 327–331Epimysium, 12, 14Epithelium, 329Epoxides, 212, 310, 326Erythrocytes, 39, 74

Erythronic acid, 93, 96Erythrose, 82Erythrosine, 160Erythrulose, 82Escherichia coli

hydroperoxide lyases in, 250illness from, 296–297in mutagenic activity testing, 316prevention

benzoic acid, 278probiotics, 264

red sea bream TGase cloned in, 166

ESR, 39Essence, 243Essential oils

antimicrobial activity of, 243aroma of, 235of cloves, 243definition of, 232distillation of, 243flavor of, 236from vegetables, 233

Esterases, 248Esterification

of amino acid residues, 136of cellulose, 104of chlorophyll, 215citrus peel oil aroma, 232lipase-catalyzed reaction, 248of starch, 104of tocopherols and sterols, 130

Estersaspartame, 94, 111, 281butylated hydroxyanisole (BHA),

122, 278butylated hydroxytoluene (BHT),

122, 278–279emulsifier, food, 282ethyl acetate, 235, 244–245fatty acids, see Fatty acids (FAs)flavoring from, 244gallic acid, 278–279glycerol fatty acid, 282hydrolyzing of, 236hydroxycarboxylic fatty acid, 282lactylate fatty acid, 282linalyl acetate, 244methyl dihydrojasmonate, 244odor of, 235polyethylene fatty acid, 282polyglycerol fatty acid, 282of polyols, 284propylene glycol fatty acid, 282raffinose, 94, 285sorbitan fatty acid, 282sorbitol, see Sorbitolstachyose, 94, 285sucrose fatty acid esters (SFE),

284–285TBHQ, 122, 278–279trehalose, 285

Estrogens, 326Ethanol

an extraction solvent, 243–244fermentation of glucose syrup, 102metabolism of, 108threshold of, 234

Ether, 115

Index 347

Etherification, 93, 104Ethers

diphenyl oxide, 244flavoring from, 244rose oxide, 244

Ethyl-2-hydroxy-2-cyclopenten-1, 99Ethyl acetate, 235, 244–245Ethyl butyrate, 245Ethyl hexanoate, 245Ethyl phenyl acetate, 244Ethylene oxide, 104Ethylenediaminetetraacetic acid

(EDTA), 60ferrous iron, elimination of, 66rancidity inhibitor, 66–67as sequestrant, 279

Eubacterium, 261Eugenol, 243–244, 247Evaporation, 4, 16Evening primrose oil, 128Extraction

alkaline, 143azeotropic isopropanol, 151of fat and saccharides from

soybeans, 153of myofibrillar proteins, 144of oil, 118–119solvent, 243–244

Extractives, 244Extrusion, 241Exudate gums

arabic, see Arabic gumemulsifiers, 281karaya, see Karaya gumstabilizers, 281thickening agents, 281tragacanth, see Tragacanth gum

Eyesight, 20, 127

F

FA, see Fatty acids (FAs)Fats, 116–117; see also Lipids

antioxidants in, 278–279density of, 40flavor of, 246as IMF filler, 44oxidation of, 279processing of, 118–122rancid odor, 66–67, 122, 240removal from water, 48storage of, 121–122substitutes, 275, 304transportation, cellular, 58

Fatty acids (FAs), 116–117cancer risk factor, 326in cereals, 17cis, 116in edible fats, 21; see also Dietary

fatesters, 282green aroma from, 249hydrogenation of, 116lactone production, 247linoleic acid, see Linoleic acidlipoxygenase catalyzing oxidation

of, 167

long-chain, 124–126medium-chain, 124–125in milk, 14–15in nuts, 20oxidation of, 15, 239polenoic, 126–128in potatoes, 239ricinoleic, 247short-chain, 125in soap formation, 55sorbic acid, 277–279, 303–304structured lipids, 124–126trans, 116unsaturated, decrease in, 233

Fehling test, 92Fennel, 232Fenugreek, 232Fermentation process

biotechnology in, 303for flavor compounds, 247flavoring from, 233mineral bioavailability in, 302mineral compounds in, 61products of, 82saccharides in, 84–85, 105, 108of soybean proteins, 153

Ferric sodium edeteate, 64Ferritin, 60, 73Ferroxidases, 66Ferulic acid, 247Fiber, 332Fillers, 85, 275Film formation, 145–149

additives for, 275, 283edible, from whey proteins, 167from egg whites, 154from phosphates, 104from polysaccharides, 281–282

Filtration, 46–48, 153Firming agents, 61–62Fischer glycosidation, hydrochloride

catalyzed, 93Fish; see also specific types

Anisakis parasite in, 7aroma, 110arsenic in, 70–71ashi, 145calcium in, 58chromoproteins in, 157cobalt in, 59cooking of, 324; see also Cookingenzyme-catalyzed reactions in,

162–167fat in, 21fatty acids in, 117feed for, 164flavoring from, 233fluoride in, 53gadoid, 165–166gelation of, 145, 146hydrolysates, 164–165iodide in, 53lipid oxidation in, 60, 239lipids in, 3marinades, decarboxylation of

amino acids in, 4mercury in, 71minerals in, 52–53, 58–60modori, 146

N:P conversion factor in, 3oil from, 116–131, 233, 328phosphorus in, 58polyphosphates in processed, 173potassium in, 58preservation agents, 273proteins in, 151–152rheological changes to, 156saccharides in, 2sauces, 164selenium in, 60sequestrant for, 64setting of, 145silage, 164smoked, 319sodium in, 58solubility of, 143storage of, 151surimi, 151trimethylamine in, 165water in tissue, 43, 144–145zinc in, 52, 59

Flaking of oil-bearing materials, 118Flavonoids

anthocyanins, 219–224antioxidant, 60carcinogenicity, 318cyanidin, 219, 223delphinidin, 219, 223in fruits and vegetables, 21malvidin, 219mutagenicity, 318pelargonidin, 219peonidin, 219petunidin, 219

Flavor, 250additives for, 6, 279–281agents, 99of allium plants, 236–237of brassicas, 237from carbohydrates, 107–109in cheese, 4Code of Federal Regulations, 246compounding, 245–246after cooking, 233distillation of, 243from DNA, 249–250enhancement, by additives, 274from enzymes, 248–249in extrusion cooking, 241fixative, 85of fresh fish, 233in fried food, 123fruit, 232–233green-grassy notes in fruit,

237–238after heating, 233of herbs, 232intensity, 234IOFI, 246Maillard reactions, 238–239manufacture of, 245–246in meat, 4, 66from microbes, 233, 247–248from minerals, 57, 61–64of mushrooms, 237natural products with flavoring

properties, 233"odor of violets", 212–213


from organic chemicals, 244–245from oxidation of lipids, 122,

239–241process, 246production of, 243–250properties of, 242–243roasted food, 130savory, 233, 238–239from sorbic acid, 278of spices, 232structure of, 234–235sweet, 233vegetable, 233

Flaxseed, 127Flickering clusters water model, 31,

33Flies, 4Flocculation, 46–48, 149, 283Flounder, 71Flour

ascorbic acid in, 168for biscuit making, 276composition of, 18corn, 157, 189dietary fiber in, 18emulsifier, 281extraction rate of, 18folate in, 301germ removal, 302from guar seeds, 281from konjac seeds, 281from locust beans, 281rice, 157rye, 157soy, 143, 301stabilizer, 281sulfite, additive to, 276tamarind, 85, 281thickening agent, 281vitamin E in, 302wheat, 156–157

Flow, analysis of, 181–191, 194, 202Flowers, 233Fluid flow, 183Fluoride, 53, 59; see also FluorineFluorine

biological function of, 57microelement, 54RDA, 56water contamination level, 46water structure former, 34

Foamadditives in, 275beating of, 104properties of, 150–151stabilization, 142, 153–154texture of, 110in whipped cream, 123

Foaming, 142, 144, 171Foaming agents

egg albumin, 154milk peptides, 283milk proteins, 153, 283

Folate, 301, 303Folded oil, 243Folic acid, 301Food

composition of, 2–4functional properties of, 5–6

groups, 11processing, see Processing of foodquality of, 5–8safety of, 7, 291–304storage of, see Storage

Food poisoning, 44Formaldehyde, 103, 165, 169Formic acid, 164FOS, 286Fractals, 195Fractionation of oil, 121Free energy change, 34–36, 137–138,

193Free peptides, 3Free radicals, 60, 72, 110; see also

Radicals, oxygenFree water, 41Freezing, 101–102, 151Freezing point

depression of, 33impact on, by water mobility, 39of vicinal water, 38of water-based foods, 40

Freshness, 5Frosting, 129Fructo-oligosaccharides (FOS), 286Fructofuranosyl, 280Fructopyranose, 94Fructose, 84, 106

in barley malt, 108from D-glucose, 99in fruits and vegetables, 21in honey, 19–20, 109to retard moisture loss, 6syrup, 108, 109

Fructosyltransferase, 286Fruits, 21–23; see also specific types

alkaline treatment of, 159analogs, 67anthocyanins in, 223anticarcinogenic action of, 329,

332from cactus, 224carotenoids in, see Carotenoidscitrus, see Citrus fruitconfectionery coating for, 125copper in, 59flavor of, 232–233, 236, 248iron in, 59katemfe, 281lipids in, 3minerals in, 58–59N:P conversion factor in, leafy, 3oxidation of, 148potassium in, 58processing of, 283proteins in, 3spices from, 232water content in, 2

Fryingaroma, 110, 240carbohydrate transformation, 101chicken, 239flavor from, 240lipid action during, 123methods, cancer risk, 323–324mutagen formation during, 320nitrosamine formation during, 320potatoes, 239

Fucose, 84Fungi, 128, 248Fungicides, 317Fungistatic agent, 61, 65Furan derivatives

arabinose in, 84aromas from, 235from burning sugar, 110in caramel, 110flavor of, 245flavoring agent, 99, 244from hemicellulose, 102Maillard reactions, 238production of, 97in strawberry flavoring, 245sucrose in, 84

Furcellaran, 85, 103, 111Furfural, 242Fusarium, 318

G

Galactan, 85, 103Galactaric acid monolactone, 97Galacto-oligosaccharides (GOS), 286Galactopyranose, 94Galactopyranosyl, 280Galactose, 84, 97

bonded to anthocyanidins, 220in casein, 137oxidation of, 93–94

Galactosidase, 262Galactosucrose, 94Galacturonans, 281Galacturonic acid, 97Gallic acid, 278–279GALT, 260Garlic


antimicrobial activity of, 232, 243aroma of, 239–240soybean oil with, 236–237

Gas, 15Gastric acid, 262Gastrointestinal disorders, 127–128,

260–261, 263Gatti gum, 85, 103GDL, 92, 284Gelatin, 146

from denatured collagen, 155for film formation, 148in fruit juice, 283

Gelatinization, 17, 88, 107, 199Gelation

of actomyosin, 146denaturation and, 145of lipids, 123of proteins, 144–146steric exclusion, 145of whey proteins, 153

Gellan gums, 281Gelling agent

additives as, 275calcium caseinate, 153egg albumen, 154β-lactoglobulin, 153

Index 349

mineral compounds as, 63phosphates, 104polysaccharides, 84–85, 281–282proteins, 142sodium caseinate, 153whey proteins, 153–154

Gelsfor coacervation, 112enzyme-catalyzed reactions in,

162–164from fish, 146formation of, 87–88, 111for frozen products, 6from heating of proteins, 156milk protein in, 146modori, 146, 164from oxidized starches, 104retrogradation, 105strength of, increasing, 167structure of, 145–146from surimi, 151–152time-dependency of, 190translucent, 145

Genistein, 328–329Geosmin, 248Geotrichum candidum lipase, 121Geraniol, 238, 241, 244Germ

corn, 119mineral bioavailability, 69, 302nut, 20removal from white flour, 302wheat, 16–18, 129

Ghati gum, 67Giardia, 297Ginger, 232GLA, 125–128Glass dynamics map, 196–198Glass phase transition, 195–199Glazing agents, 275Globulins, 142Glow plasma, 101–102Glucans, 281Gluconate, magnesium, 62Gluconic acid, 91Glucono-δ-lactone (GDL), 92, 284Glucopyranose, 94Glucopyranosides, 238Glucopyranosyl, 280Glucose, 84

in barley malt, 108bonded to anthocyanidins, 220from cellulose, 102, 106in fruits and vegetables, 21in helical complexes, 86in honey, 19–20, 109isomeritization of, 99polymerization of, 285production of, 106pullulan, 106reaction protection, 92from starch, 103structure of, 89syrup, 108, 109tolerance, 58transporter, for water, 39xanthan gum, see Xanthan gum

Glucosephosphate, 105Glucosidases, 223, 238

Glucosinolanes, 7Glucosylamine, 84Glucuronyltransferases, 311Glutamate

calcium, 61magnesium, 62potassium, 63sodium, 64

Glutamic acidcadmium and, 73in paramyosin, 134properties of, 135sodium glutamate, 64

Glutamineenzyme-catalyzed reactions in,

166–167properties of, 135in transglutaminase, 166

Glutathioneanticarcinogenic action of, 311,

328–329antioxidant, 160in dietary fat, 315

Glutelins, 142Gluten

in cereals, 17in dough, 156–157for film formation, 147–148glass dynamics of, 199texture from, 6

Glycans, 86; see also PolysaccharidesGlyceric acid, 93, 96Glyceroaldehyde, 82Glycerol, 282Glycerol monostearate (GMS), 123Glycerold, 282Glycerols

density of, 40esterification of, 116extract solubilization, 244as humectants, 44

Glycinein collagen, 134properties of, 135in transglutaminase, 166

Glycinin, 167Glycogen, 2, 85, 88, 108Glycolipids, 128Glycomacropeptide, 137Glycosidase, 238, 248Glycosides, 84Glycosidic bond, 97Glycosylation

of acid casein, 153of amino acid residues, 136of anthocyanins, 219, 222

Glycosylsucrose, 286Glycosyltransferases, 136Glyoxalic acid, 93, 96, 168, 324GMS, 123Goiter, 60GOS, 286Gourd melon, 239Grain, 59; see also Cereals; specific

typesamino acids in, 134composition of, 16, 18glutamic acid in, 135mineral bioavailability, 58–59, 302

proline in, 135water content of, 2

Grapefruit, 211, 314–315Grapes

chemopreventive properties of, 327, 331

flavor of, 237monoterpene in, 238red, anthocyanins in, 220

Gravy, 123Green onion, 236Grilling, 314–315, 320, 322Grinding, 194, 300Grits, 153Gross alpha particle, 46Gross beta particle, 46Guar, 281Guaran gum, 85Guava, 249–250Guillan-Barre syndrome, 298Gums

arabic, see Arabic gumBritish, 103curdlan, 281emulsifier, 281exudate, 281gatti, 85, 103gellan, 281ghati, 67karaya, see Karaya gumlocust bean, 85, 282microbial, 281plant, 84stabilizer, 281for texture, 110thickening agent, 281tragacanth, see Tragacanth gumxanthan, see Xanthan gum

Gut-associated lymphoid tissue (GALT), 260

Gynecological disorders, 127–128

H

HACCP, 297Halide, 93Haloacetates, 169Haloamides, 169Halogenation, 93Ham

copper in, 53flavoring from, 233overpasteurization of, 8rheological changes to, 156

Hardness of water, 47Haworth methylation, 93Hawthorn, 53Hazard Analysis Critical Control

Point (HACCP), 297, 298HDL cholesterol, 129Health foods, 6Heart disease; see also Cardiovascular

diseasefactor

arachidonic acid, 127–128dietary fat, 116

prevention of


anthocyanins, 222–223caffeine for, 324–325folate, 301

treatment of, honey for, 20Heat absorption, 201Heat pasteurization, 7Heat resistance, 201Heating, 4, 242Heavy metals, 5, 120Helical complexes, 86–87Helicobacter pylori, 323, 328–329Hematopoietic system, 75Heme; see also Nonheme

cholemyoglobin, 218compounds, 60hemichrome, 218iron, nitric oxide binding to, 277lead, impact on, 75, 77metmyoglobin, 218myoglobin in, 217–218nitrite, reaction with, 218nitrosomyoglobin, 218nitrosylhemochromogen, 158, 218oxidation of, 218oxymyoglobin, 218pigments from, 12, 160, 206,

217–218sulfmyoglobin, 218thiols, reaction to, 158

Hemiacetals, 82, 236, 244Hemicellulose

arabinogalactan, 85arabinose, 84, 220aroma of, 110in fruits and vegetables, 21galactan, 85, 103hydrolyzing of, 102mannans, 85mineral bioavailability, 55modification of, 99–102solubility, 101xylans, 85, 103

Hemichrome, 218Hemiketals, 82Hemoglobin

coagulum-type gel, 146iron in, 54, 57pigments, 12, 160, 206, 217–218saccharides in, 82transporter, for water, 39

Hemolytic uremic syndrome, 298Hemopoietic system, 76Heparin, 85, 103, 111Herbs, 232, 243, 243–245Herring

Anisakis parasite in, 7composition of, 13DHA and EPA in, 127enzyme-catalyzed reactions in,

163salt concentration in, 8

Herschel-Bulkley equation, 189Hesperidin, 82Heteroaromatic compounds, 91Heterocyclic aromatic amines (HCA),

320–324Heterocyclic compounds

flavoring from, 244furans, see Furan derivatives

mutagens, 320–324pyrazine, see Pyrazinepyridine, see Pyridinethiazoles, see Thiazolesthreshold value, 234

Heteromolecular condensation, 195Heteromolecular nucleation, 195Hexametaphosphate, 67Hexanal

flavoring from, 237–239, 244green aroma, 249

Hexanecartenoid solvent, 212lipid solvent, 115, 119

Hexanoic acid, 240Hexanol, 244, 249Hexosanes, 102Hexoses, 82, 84, 97Hexuloses, 82, 84Heyns rearrangement, 91HI, 265Hialuronic acid, 85High-density lipoproteins (HDL)

cholesterol, 129Hilum, 88Histidine

alkylating agent, 169–170hydrolyzing of, 170oxidation of, 161in phosphorylation of saccharides,

136properties of, 135residues, 135, 217

HLB, 149, 282, 283Homeostasis, 26Homeostatic mechanisms, 54Homocarotenoids, 206Honey, 20, 109

glucose in, 84maltose in, 84relative sweetness, 94water content of, 2zinc in, 52

Hops, 8Hormones in food, 296Horseradish, 232, 237, 243Hotrienol, 238HPLS, 237, 249Human breast milk

bioavailability of minerals in, 54fatty acids in, 127fucose in, 84

Humectantseffect of, on water activity, 44food additives as, 6sugar alcohols, 108–109

Humoral immunity (HI), 265Husbandry, animal and plant, 303Hydration, 33Hydration water, 38Hydrazine

carbohydrate reactivity, 90carcinogenicity, 318heating in alkaline, 171mutagenicity, 318

Hydrazo compounds, 90–91, 276Hydrocarbons

flavoring from, 244from hydroperoxides, 122

from lipid oxidation, 240reaction to water, 33, 35squalene, 4

Hydrochloric acid, 102–103, 216Hydrocolloids

alginate, 67arabic gum, see Arabic gumcalcium-binding, 67ghati, 67karaya gum, see Karaya gumsaccharides, 81tragacanth gum, see Tragacanth

gumHydrogen bonds

in gels, 146in proteins, 138–139in water, 27–39

Hydrogen carbonatecalcium, 61potassium, 63

Hydrogen peroxidedestruction of, 329off-flavor in dairy products, 240production of, 60, 66

Hydrogen phosphate, magnesium, 62Hydrogen sulfide

Maillard reactions, 238, 246treatment to remove from water, 47

Hydrogen sulfite, potassium, 63Hydrogenation

carotenoid degradation, 210of oil-bearing materials, 121, 300

Hydrolases, 14Hydrolysates

bitter, 137fish, 164–165milk protein, 283process flavor, 246starch, 285

Hydrolysisof chlorophyll esters, 215cow's milk, 15of denatured collagen, 155enzymic, 45of esters, 236of beta-lactoglobulin, 153lipase-catalyzed reaction, 248lipid deterioration, 121of myofibrillar proteins, 164of proteins, with endopeptidases,

168starch property, 17

Hydrolyzates, 164, 167Hydroperoxide, 122Hydroperoxide lyase (HPLS), 237,

249Hydrophile/lipophile balance (HLB),

149, 282, 283Hydrophilic interactions, 41Hydrophobicity, 35–36

from acylation, 170–171of proteins, 137–144, 147–151

Hydroscopic, 20Hydroxide, 61, 62Hydroxy-2-methylpyran-4, 98Hydroxy-3-methyl, 99Hydroxy acids, 102, 247Hydroxyacetone, 82, 99Hydroxycarboxylic, 282

Index 351

Hydroxycarboxylic acid, 282Hydroxylamine, 90, 313Hydroxylases, 136Hydroxylation

of amino acid residues, 136of nitrosamines, 311of vegetable lecithin, 129

Hydroxylsacylation of, 170on anomeric carbon atom, 103dehydration of, 93esterification, 92etherification, 93halogenation of, 93metal ions with, 96oxidation of, 93–94radicals, generation of, 66, 213reactions of, 92–97reduction of, 93solvent for, 35water and, 29

Hydroxymethl starch, 104Hydroxymethylfuran-2-aldehyde, 97Hydroxyproline, 136Hydroxypropyl starch, 104Hydroxypyruvic acid, 93, 96Hydroxytricarballylic acid, 61Hygienic requirements, 5Hygrometers, 43Hygroscopicity, 108Hyperchromic effect, 222Hyperkeratosis, 76Hypertension, 68, 76, 261Hypobromites, 91–92Hypochlorite, 91–92Hypoxantine, 59Hysteresis

measurement of loop, for structural breakdown, 190–191

parameter, rheological process, 193

in rheopexy flow, 188in viscoelastic flow, 188

I

Icechemical properties of, 29–31color of, 206density of, 40formation of, 196thermal properties of, 32

Ice cream, 150, 154, 189Iceberg water model, 31Icing, 129Imidazoles

acylation of, 170alkylation of, 169aromas from, 91, 110Maillard reactions, 238

Imine, 35Immune function enhancer, 213,

263–266Immunoglobulins, 137, 156, 260Immunological disorders, 126–128

Immunomodulatory effect, 154, 264–266

Indigoid, 228Indole group, 169Infant formula

B vitamins in, 301bioavailability of minerals in, 54DHA and EPA in, 127fatty acids in, 125iron in, 302lactalbumin in, 154lactose in, 15

Infertility, 60Infiltrative lymphomas, 55Inflammation, 126–128Inflammatory bowel disease, 55,

263–264, 298Inhibitors, enzyme

amount of, quality attribute, 5calpains and calpastatin, 163cysteine proteinase, 164proteins as, 3

Inositol, 105INS, 65Insulin

chromium requirement, 57glucose digestion, 108resistance, 326substitutes, 104

Interesterification, 92, 121Intermediate moisture content foods

(IMFs), 44International numbering system

(INS), 65International Organization of the

Flavor Industry (IOFI), 246Intestinal infections, 264Intrinsic fluorescence, 137–138Inulin, 85, 285–256Invert sugar, 97Iodide, 53, 86Iodine

biological function of, 57, 60in dietary fat, degree of

unsaturation, 116microelement, 54RDA, 56water structure breaker, 34

IOFI, 246Ion pumps, 39Ionic strength, 144Ionization constant, 68Ionizing radiation, 101–102Ionone, 212–213, 241, 244Iron

ADP-chelated, 60anthocyanins reaction to, 222in beef, 52bioavailability of, 54–55, 302biological function of, 57, 59–66cadmium and, 73chlorophyll, reaction with, 216dietary level, 66EDTA and, 64in eggs, 16, 52in fruits and vegetables, 22, 69in heme, 217lead and, 74in lipids, 122

in liver, 52microelement, 54nitric oxide binding to, 277in oats, 52in pork, 52for rancidity inhibition, 67RDA, 56react with proteins, 68treatment to remove from water, 47in wheat, 16–17, 52

Irradiation of food, 296, 302–303Irvine-Purdie methylation, 93ISO 9001 for food safety, 298Isoamyl acetate, 248Isoascorbate, 277Isocyanides, 103Isoelectric point of proteinogenic

amino acids, 135Isoeugenol, 247Isoflavones, 328Isoleucine, 135Isomaltol, 98, 100Isomerase, 249Isomers

cis-trans, 7trans-trans, 7

Isoprenoid derivative, see CarotenoidsIsopropyl alcohol, 244Isothiocyanates, 237, 243, 328–331Itai Itai disease, 76

J

Jams, 190, 278Jasmine, 233Jasmonate, 248Jellies

color of, 206formation of, 110pectin, 104viscoelastic food, 190

Jerusalem artichoke, 85Juices

anthocyanins in, 223benzoic acid in, 278citrus, flavor of, 242–243enzyme treatment of, 238oxygen in, reduction of, 106precipitates in, 283

Juneberry, 250

K

K, see PotassiumKale, 211Kamaboko, 151–152, 156, 167Karaya gum, 85


Katemfe fruit, 281Keratin, 15–16


Kerosene, 47Ketones, 66

alcohols, reduction to, 90carbonyl group, addition to, 90–91from carotenoid degradation, 213diacetyl, see Diacetylflavor from, 240–241from hydroperoxides, 122ionone, 244from lipid oxidation, 240mutarotation, 89–90nootkatone, 244nucleophile acceptance, 82odor of, 235in oil, 120oxidation of, 91–92, 103reactions of, 89–92saccharide dehydration, 93

Ketopentose-ribulose, 82Ketoses, 82, 99Ketosylamines, 91Ketosylamino acid, 91Kidneys

cadmium in, 74chromium in, 53lead in, 75selenium in, 53

Kinase, 167Kinetics, 193Koenigs-Knorr glycosidation, 93Kohlrabi, 22Konjac, 281Krill, 151, 164Kynurenine, 161

L

L. acidophilus, 264–265L. rhamnosus, 268Labeling, 5, 267Lactalbumin, 153–154Lactate, 61–62Lactic acid bacteria (LAB), 105,

261–269, 327–328Lactobacillus, 261–265, 268–269Lactoferricins, 154Lactoferrin, 154Lactoglobulin, 147, 153–154, 156Lactones, 93–94

decalactone, 244flavoring from, 244from microorganisms, 248nonalactone, 244odor of, 235production of, 247undecalactone, 244

Lactonize, 91–92Lactoperoxidase, 154Lactose, 108

calcium absorption, 55formation of, 83intolerance, 263isomeritization of, 99, 101Maillard reactions in, 242in milk, 15, 84mutarotation, 90relative sweetness, 94

transgalactosylation of, 286Lactosucrose, 286Lactulose, 99, 101Lactylate, 282Lakes, 222, 226, 228Lamb, 13Laminar flow, 183, 186Lanthionine, 7Larch, 85Lard, 21, 116–117Laurel, 232Lauric acid, 116Laws, regulations, & standards, 5LCFA, 124–126LCT, 124LDL cholesterol

decreasing level of, plant sterols, 130

decreasing level of, vegetable lecithin, 129

wine, oxidation inhibitor, 223Leaching, 4, 301Lead, 70, 74–77

calcium absorption, 77iron absorption, 77PTWI, 75toxic effects on humans, 76,


Leaf alcohol, 249–250Leavening agents, 61–63, 275Leaves, spices from, 232Lecithin

in egg yolk, 16emulsifier, 282as nutraceutical food, 240off-flavor in, 240vegetable, 128–129

Legumes; see also Beansgum from, 85minerals in, 58–59mutagen formation in, 320N:P conversion factor in, 3peanuts, see Peanutspeas, see Peasprotease inhibitor, 146soybeans, see Soybeans

Legumin, 167Lemons, 22, 250Lentils, 20–21Lentinus edodes, 237Lethal dose, 294Lettuce, 211, 319Leucine, 134, 135Leuconostoc mesenteroides, 106Leucopenia, 59Leukotrienes, 126, 127, 326Levan, 106Lignin, 247Lime, 61, 283, 300Limonene, 232, 241, 244, 250Linalool, 238, 241, 248Linalyl acetate, 244Lindane, 46Linear charge density, 67Ling's association-induction theory,

37Linoleic acid

in cow's milk, 15

green aroma formation, 249from lipids, 115–117octen-3-ol formation, 237in polyenoic fatty acid, 126–127

Linolenic acidgreen aroma formation, 249from lipids, 115–117in polenoic fatty acid, 126–127in structured lipids, 125from vegetable oil, 126–127

Linseed oil, 117Linxian study of carotene, 215Lipases

in cereals, 17flavor from, 248LMWE in, 248types of, 121

Lipids, 115–116, 122–123acidolysis of, 123–124alcoholysis of, 123–124alkylation of, 169autoxidation of, 169in beef, 3in beer foam, 8in butter, 3, 21in cereals and cereal products,

17–18, 107in codfish, 3–4composition of, 116–117in crustaceans, 3–4in egg yolks, 3, 16emulsification of, 148–151esterification of, 123–124in film formation, 148in fish, 3flavor from, 239in fruits and vegetables, 3, 22in gluten, 156green aroma from, 249hydrophobic interactions with

proteins, 36interesterification of, 123–124lateral vs. water diffusion, 39lecithin, 128–129Maillard reactions and, 240–241in meat, 12metabolism of, 58, 285–286in milk, 3in mollusks, 3–4in mullets, 3–4in nuts, 20in orange roughy, 3–4oxidation

in apples, 60degradation of pigments, 212flavor from, 239–241lipoxygenase, 65–66mineral catalyst, 57nonenzymatic, 45protein oxidation, 161

PEFAs, 126–128permeability, 39peroxidation, see Peroxidation,

lipidperoxides, 160phytosterols, 120, 129–130in potatoes, 19, 107processing of, 118–122

Index 353

in protein-phospholipid membranes, 3

in protein-rich food, 13rancid odor from, 66–67, 122, 240in seeds of pulses, 21in sesame, 116–119, 130–131in shark, 3–4in starches, 88storage of, 121–122structured, 123–126tocopherals, see Tocopherolsin tubers, 19, 107in vegetables, 3vitamin E, 129volatility, reduction by, 235–236warmed-over flavor from, 240water transport, cellular, 39in wheat germ, 16–17

Lipoxygenase (LOX)carotenoids, destruction of, 212fatty acid catalyzation, 167flavoring from, 233, 248green aroma, 237, 249–250hydroxy fatty acid from, 247lactone production, 247lipid oxidation, 65–66metabolism of PEFAs, 127octen-3-ol formation, 237prooxidant, 160soy milk flavor, 153

Liquid phase viscosity, 242Liquor, 233LISA, 297Listeria

illness from, 296–297monocytogenes, 154, 243

Lithium, 34Liver

cadmium in, 74chromium in, 53copper in, 53glycogen from, 85heparin from, 85iron in, 52minerals in, 59–60potassium in, 52zinc in, 52

Liver disease, 20, 60Lobry de Bruyn-van Ekenstein

rearrangement, 99Lobster, 53Locust bean, 85, 281, 282Long-chain fatty acids (LCFA),

124–126; see also Fatty acids (FAs)

Long-chain triacylglycerols (LCT), 124

Longitudinally Integrated Safety Assurance (LISA), 297

Loss modulus, 201Lovage, 232Lovibond tintometer color scale, 120Low-calorie food

CMC in, 104lactose in, 15retrograde starch in, 105structured lipids in, 125sucrose FA polyesters in, 284sweeteners for, 111

Low-density lipoprotein (LDL) cholesterol

decreasing level of, plant sterols, 130

decreasing level of, vegetable lecithin, 129

wine, oxidation inhibitor, 223Low-molecular-weight esters

(LMWE), 248LOX, see Lipoxygenase (LOX)Lubricants, 285Lumen, 55Lung cancer, 215Lutein

antioxidant, 214in egg yolk, 210formula for, 208in fruits and vegetables, 211in green leaves, 209–210macula protection, 213photooxidation protection, 209

Lycopeneanticarcinogenic action of, 328antioxidant, 214, 331chemopreventive properties of,

327formula for, 207in fruits, 210in grapefruit, 211in paprika, 211structure of, 206, 330in tomato, 211ultraviolet skin protection, 213

Lymphocytes, 265Lysine

alkaline pH, reaction with, 159amidation of, 170browning, reactions during, 300in cereals, 134in dried fish, 167in hydrolyzate, 167Maillard reactions with, 45, 242in paramyosin, 134in phosphorylation of saccharides,

136pyridoxine binding, 301processing of, 7properties of, 135

Lysinoalanine, 7, 160Lysosomes

in muscle food, 162–163probiotics, impact on, 264transglutaminase in, 166

Lysozymein eggs, 135, 154enthalpy of, 141transparent gels from, 147

M

Mace, 232Mackerel, 117, 127Macroelements, 51, 54, 70Macula protection, 213Mad cow disease, 293, 296Magnesium

biological function of, 57–58

in bread, 69carbonate, 61in cereals, 18chloride, 61, 68in chlorophyll, 215–216compounds, food additives, 61–62in eggs, 16for food texturization, 111in fruits and vegetables, 22glutamate, 62hydrogen phosphate, 62hydroxide, 62ions, in water, 33lactate, 62loss of, during processing, 69macroelement, 54in milk, 52in nuts, 20oxide, 62RDA, 56react with proteins, 68in saccharide alcohols, 96salts of phosphatidic acid, 119in sardines, 52soap formation, 55sulfate, 62treatment to remove from water, 47in tuna, 52water structure former, 34in yogurt, 52

Maillard reactionsblocking, by sulfites, 276in caramel, 228of carbohydrates, 91dehydroascorbic acid in, 168flavor development, 238–239flavoring, effect on, 233, 246of hemicelluloses, 102of lactose in heat-treated milk, 15lipid oxidation and, 240–241mineral bioavailability, 55nitrite interaction, 277oligosaccharides, 286in protein-rich foods, 102, 139,

158resistant starch, increasing, see

Resistant starchstarch, to prevent, 283warmed-over flavor protection,

240water activity level, 45zinc bioavailability after, 302

Maizecomposition of, 16, 18ferulic acid source, 247organic acid in, 22properties of, 88proteins in, 21starch source, 107

Malic acid, 22, 109Malonaldehyde, 169Malondialdehyde, 326Maltol, 98, 100Maltose, 108

in barley malt, 108formation of, 83in honey, 19, 84, 109oxidative cleavage of, 93relative sweetness, 94


from starch, 84, 103syrup, 109

Maltotetraose syrup, 108Malts, 108Malvidin, 219Manganese

biological function of, 59in bread, 69in fruits and vegetables, 69in lipids, 122microelement, 54for rancidity inhibition, 67RDA, 56treatment to remove from water, 47

Manioc, 2, 107Mannans, 85Mannitol, 89, 94, 108–109Mannopyranose, 94Mannose, 84, 89, 99, 106, 137Maple syrup, 108Margarine

fat in, 21hydroxycarboxylic acid in, 282manufacture of, 121a W/O emulsion, 129water-in-oil emulsion, 123

Marinades, 7, 273Marlin, 71Marmalade, 85, 108Maximum residue level (MRL), 296Maximum tolerable daily intake

(MTDI), 65Maximum tolerated dose (MTD), 316Mayberry, 250Mayonnaise

benzoic acid in, 278egg yolk in, 16lipids in, 123preservation of, 278

MCFA, 124–125MCT, 124–125Mead, 109Meat, 12–13; see also Beef; Chicken;

Pork; Poultryaging of, 57analogs, 67, 154aroma, 110B vitamins in, 301cancer risk factor, 317, 332chromium in, 58cobalt in, 59cooking of, 324; see also Cookingdietary fat from, 21, 115–126enzyme-catalyzed reactions in,

162–167extenders, 153flavor of, 4, 238–239, 246GDL in, 284gelation of, 145, 156HCAs in, 321iron in, 59irradiation of, 302–303magnesium in, 58manganese in, 59mineral bioavailability in, 54minerals in, 58–60mutagen formation in, 323N:P conversion factor in, 3oversterilization of, 8

phosphorus in, 58plasma, protease inhibitor, 146postmortem changes in, 1–2, 12potassium in, 58process flavor of, 246proteins in, 3, 151–152rheological changes to, 156saccharides in, 2saltpeter in, 277selenium in, 60sequestrant for, 64sodium in, 58substitutes, 84, 105, 111sulfite, reaction to, 276surimi, 151warmed-over flavor in, 66, 240water content of, 2, 144–145zinc in, 59

Medium-chain fatty acids (MCFA), 124–125; see also Fatty acids (FAs)

Medium-chain triacylglycerols (MCT), 124–125

Melanoidin, 206Menhaden, 127Mercaptide bounds, 73Mercury, 70, 71–72

metallothioneins and, 72in predatory fish, 4PTWI, 75react with proteins, 68toxic effects on humans, 76water contamination level, 46

Mesenteric infarction, 55Metabisulfite

in dehydrated food, 276potassium, 64sodium, 64

Metabolic tests, 294Metallothioneins, 72–73Methane, 49Methanethiol, 238Methanol, 102, 103Methionine

in grains, 134in hydrolyzate, 167oxidation of, 161properties of, 135thermal degradation of, 158

Methol, 244Methoxychlor, 46Methyl cinnamate, 245Methyl dihydrojasmonate, 244Methyl glyoxal, 168Methylation, 104, 136Methyldehydroalanine, 159Methylglyoxal, 324Methylmercury, 71–72Metmyoglobin, 141, 218, 276Micelles

acylation of, 170casein, 140, 173definition of, 36from emulsifiers, 282enzyme-catalyzed reactions in,

162formation of, 87in gel structure, 145in proteins, 139

in whey, 146Microbial contamination of food, 296Microbial gums, 281; see also GumsMicrocalpain, 163Microcirculation diseases, 223Microelements, 54Microencapsulation, 105, 111–112Microfibrils, 88Microwaved food

mineral loss in, 69mutagen formation in, 323polysaccharides in, 101–102

Milk, 14–15bioavailability of minerals in, 54bitterness in, 162calcium in, 52, 55, 58carrageenans used in, 67caseins in, 140clarifying agent, 85composition of, 13–14enzyme-catalyzed reactions in,

162evaporated, 173fat anticoagulant, 85fermented, probiotics in, 265–267for film formation, 148gels, protein, 146lactose in, 15, 55, 84, 108lipids in, 3, 123magnesium in, 52, 58minerals in, 58–59mutagen formation in, 320pasteurization, 141phosphorus in, 58potassium in, 52probiotics in, 266–267protein hydrolysates, 283proteins in, 3, 146, 153–154riboflavin in, 226saccharides in, 2selenium in, 53sequestrant for, 64of sheep, 13sodium in, 58soy, 153substitutes, 164ultrahigh temperature processing

of, 242zinc in, 59

Millet, 16, 18Milling

mineral bioavailability after, 69of soybeans, 153vitamin bioavailability after, 302of wheat grain, 17, 18

Minerals, 51–54; see also specific types

absorption of, 54–57in cereals and cereal products, 18,

107deficiency in, 54in fruits and vegetables, 22functions of, 57–60leaching of, from food, 4in potatoes, 19, 107processing of, 302in protein rich food, 13RDA, 56–57in tubers, 19, 107

Index 355

Miscella, 119Miso, 233Mites, 4Mitochondria, 66, 75, 166Models

Bingham-Schwedoff, 187–188Flickering clusters, 31, 33Iceberg, 31Stillinger, 31–32of water, 31–32Wiggins, 32

Modori, 146, 164Moisteners, 275Moisture content, 40–41

dynamics map, 197extrusion cooking, 241of oil-bearing materials, 118retention of, 108

Molasses, 94, 150Mold

mycotoxins in, 318prevention

benzoic acid, 278sorbic acid, 278, 303–304

water activity level, 44Molecular weight

of acetic acid, 235of dietary fat, saponification

number, 116of dry air, 40ethyl acetate, 235of katemfe fruit, 281LMWE, 248of salt, 44in volatility of aroma compounds,

234of water vapor, 40

Mollusks, 3–4, 74, 151–152Molybdenum

biological function of, 59in fruits and vegetables, 69microelement, 54RDA, 56

Mono-tert-butyl-hydroquinone (TBHQ), 122, 278–279

Monoacylglycerolsabsorption of, 125for emulsions and foams, 6in gluten-free dough, addition of,

157in milk fat, 14–15vegetable lecithin, use with, 129

Monoaso, 228Monobasic calcium phosphate, 61Monobasic potassium phosphate, 63Monobehenin, 125Monocalcium benzoate, 61Monocalcium DI-L-glutamate, 61Monocalcium phosphate, 61Monochloroacetic acid, 104Monoglycerides, 282Monokines, 264Monomethylarsenic acids, 71Monopotassium dihydrogen

ortophosphate, 63Monopotassium glutamate, 63Monosaccharides, 84

in fermentation process, 105in fruits and vegetables, 21

from hemicellulose, 102oxidation of, 93–94polymerization of, 106properties of, 89–99

Monosodium dihydrogen ortophosphate, 64

Monosodium L-glutamate (MSG), 58, 64

Monoterpenes, 232, 238, 243Mortierella, 128Mountainberry, 250MRL, 296MSG, 58, 64MTD, 316MTDI, 65Mucic acid, 97Mucin, 15–16Mucor miehei, 121, 248Mullets, 3–4, 233Multilayer water, 41Mung beans, 243, 249Muscles

activity, role of minerals in, 58–60composition of, 60glycogen from, 85structure of, 12, 14

Muscular dystrophy, 60Mushrooms

betalains in, 224flavor of, 237lipid oxidation in, 239selenium in, 60

Mustard, 232, 237, 243Mutagens, 308–318Mutarotation, 89–90Mutton, 157Mycoprotein, 154Mycotoxins, 159, 299, 311, 317–318Myofibrillar proteins

concentrate of, 151extraction of, 144in gels, 147, 151in muscle fiber, 12–14

Myoglobin, 276Myosin

cross-link rupture, 173filaments in muscle, 12in gelation, 145, 147–148hydrolyzing of, 163in modori, 164polymerization of, 167transition of, from heat, 155

Myrosinase, 7

N

NAD, 105NADH, 66NADPH, 66Nanofiltration of water, 48Naphthol, 86Naringenin, 314–315NDO, 285–286Nebulin, 12, 163Nectarine, 211, 238Neochlorogenic acid, 324Neohesperidin dihydrochalcone, 94

Neoplastic transformation resisting agents, 327–329

Neoxanthin, 209Nephrotoxicity, 76Nerol, 238Nervous system, 75Neurological disorders, 127–128Neutralizing agent, 61–62Neutropenia, 59Newtonian food systems, 183–184NHP, 119Niacin, 300Niacytin, 300Nickel

catalyzation agent, 121microelement, 54for rancidity inhibition, 67RDA, 56

Nicotinamide adenine dinucleotide (NAD)

carbohydrate enzymatic transformation, 105

NADH, 66NADPH, 66

Nitratesources of, 319water contamination level, 46water structure breaker, 34

Nitric acid, 103Nitric oxide, 277Nitrite

Clostridium botulinum inhibitor, 320

as food additives, 277protein pyrolysis neutralization,

320sodium, 64, 218sources of, 319

Nitro groups, 137Nitrogen

compounds, flavoring from, 244excessive amount of, 48Maillard reactions, 238in milk, 14–15sources of, 3threshold value, 234treatment to remove from water, 47

Nitrogen-to-protein (N:P) conversion factor, 3

Nitrosamines, 319–320blocking of

by Vitamin C, 304, 327by Vitamin E, 304

hydroxylation of, 311Nitrosation, 171–172, 319Nitrosomyoglobin, 218, 277Nitrosylhemochromogen, 158, 218Nitrous acid, 277NMR, 37, 39No observable effect level (NOEL),

294NOEL, 294Non-Newtonian food systems,

183–184, 187, 194Nonadienal, 240Nonalactone, 244Nondigestible oligosaccharides

(NDO), 285–286Nonheme iron, 60, 66


Nonhydratable phosphatides (NHPs), 119

Nonhypercholesterolemic, 125–126Nonlinear viscoplastic flow, 184Nonrheostable food systems, 184Nootkatone, 244Norbixin, 209–210Nordihydroguiaiaretic acid, 67Nuclear magnetic resonance (NMR)

imagining, 37, 39Nucleases, 248Nucleic acids, 3, 37, 159Nucleotides, 247Nusselt number equation, 202–203Nutmeg, 243Nutraceuticals, 6Nutrient supplement, 64, 84Nutrition; see also Dietary

supplementadditives, definition of, 274amount of, quality attribute, 5, 7processing of food, 300RDA, 56–57

Nuts, 20, 58–59, 125Nylander test, 92

O

Oats, 16iron in, 52potassium in, 52properties of, 88starch in, 107zinc in, 52

Obesity, 116, 324–325, 332Oc-linolenic acids, 15Ochratoxin A, 318Ocimene, 244Octanol, 234Octaphosphate tetrahydrate, 63Octen-3-ol, 237Odor, 234–235; see also AromaOil; see also Lipids; Oil-in-water

(O/W) emulsion; Water-in-oil (W/O) emulsion

aldehydes in, 120, 240antimicrobials in, 243antioxidants in, 116–117, 243,

278–279, 300aroma, 232–233bleaching of, 120borage, 128brassicasterol in, 130Camellia oleifera tea seed, 116canola, 117–120carotene in, 210carotenoids in, 120, 210from carrots, 120, 210castor oil, 247citrus fruit

aroma, 232essence oil, 243limonene in, 232, 250

cleaning of, 118coconuts, 116–117codliver, 127composition of, 116–117

conditioning of, 118corn, 117–120, 127cottonseed, 117cracking of seeds to extract, 118degumming of, 119density of, 40deodorizing of, 120dewaxing of, 120distillation of, 243essential, see Essential oilsesterification of, 232evening primrose, 128extraction of, 118–119fat in, 21fish, 116–131, 233, 239, 328flaking, 118flaxseed, 127folded, 243folded oil, 243fractionation of, 121garlic and, 239–240goitrogenic products in, 7haze in, 283heavy metals in, 120hydrogenation of, 7, 121, 300ketones in, 120lecithin, 129linseed, 117lipid peroxidation in, 213mineral, on eggshells, 283moisture content of, 118from monoterpenes, 232Oil stability index (OSI) analysis,

122olive, 116–117, 300palm, 116–117, 210peanut, 116–119perilla, 117, 127phosphatides in, 119–120phosphorus in, 120pigments in, 243pollution from processing of, 120processing of, 118–122removal from water, 48rice bran, 116, 119–120safflower, 117–120, 127saponification of, 119saturated fats in, 116scaling of, 118sesame, 116–119shark, 4soybean, 117, 236–237, 240, 249specific heat of, 40squalene in, 4storage of, 121–122sulfur compound, garlic in,

239–240sunflower, 117–120, 127temperature, 118terpene-free, 232tocopherols in, 120treatment of, 119unsaturated fat in, 116vegetable, 116–131, 210, 249Vitamin E in, 129, 302from wheat, 129

Oil-in-water (O/W) emulsion, 123; see also Water-in-oil (W/O) emulsion

egg yolk, 16milk, 14polyethylene fatty acid esters in,

282polysaccharide activity, 282propylene glycol fatty acid esters

in, 282vegetable lecithin, 129

Oil stability index (OSI) analysis, 122Olea europaea L. tree, 119; see also

Olive oilOleic acid, 116, 121–122Oleoresin, 235, 244Olestra, 285Oligosaccharides

formation of, 137galatose in, 84in health foods, 6in lecithin, 128nondigestible, 285–286polymerization of, 106properties of, 89–99from starch, 103

Olive oil, 116–117, 300Oncogene activation, 328Onion

anticarcinogenic action of, 323, 328–329

antimicrobial activity of, 243flavor of, 236lacrimator of, 236selenium in, 60

Opioid effect, 154Opsonization, 265Orange roughy, 3–4Oranges

aroma, 235calcium in, 52carotenoids in, 211mannose in, 84potassium in, 52

Organoarsenic compounds, 71Ornithine, 159Ortophosphate, 65, 67Osazones, 90OSI, 122Osmosis, 39Osmotic, 33, 38–39, 58Osteomalacia, 58, 76Osteoporosis

cadmium effect on, 76lead effect on, 74prevention of

boron for, 60calcium for, 58probiotics, 264

Ostwald-de Waele power law, 188–189

Osuloses, 97Ovalbumin, 145–147, 151; see also

White, eggOvomucoid, 146, 151; see also White,

eggOvotransferrin, 151; see also White,

eggOxalates, 55Oxalic acid, 22Oxazoles, 238Oxidation

Index 357

of amino acid residues, 136of carotenoids, 212of cholesterol, 326of chromoproteins, 157cost of food, impact on, 299of DNA, 329of fatty acids, 326flavor from, 239–241of heme, 218of lipids

alcohol from, 240in apples, 60aroma from, 240–241carboxylic acids from, 240degradation of pigments, 212deterioration from, 121flavoring from, 239–241food quality, 300hydrocarbons from, 240ketones from, 240Maillard reactions and,

240–241mineral catalysists, 57nonenzymatic, 45prevention of, 243vs. proteins, 161

lipoxygenase, see Lipoxygenase (LOX)

of milk, 15of minerals, 57–60protection from, see Antioxidantsof protein vs. lipids, 161for saccharides, 91–94of sorbic acid, 278of vegetables, 301warmed-over flavor from, 240

Oxide, magnesium, 62Oxidizing agent, 63Oxidoreductases, 14Oximes, 90Oxocarotenoids, see XanthophyllsOxygen (O)

anthocyanins, degradation rate, 221

BOD, 47–49DNA adducts, 314–315in milk, 15radicals, generation of, see

Radicals, oxygentreatment to remove from water, 47

Oysters, 13, 52–53, 59, 76

P

P-cymene, 241Packaging

biodegradable, 105, 112–113effects, on irradiation treatments,

302methods, cancer risk, 323–324type of, quality attribute, 5xenoestrogens in, 326

PAH, 322–324Palm, 116–117, 210Palmitic acid, 116Pancreatic lipase, 121, 125Papain, 167

Papaya, 238Paprika, 53, 210–211, 232Paramyosin, 134Parasites; see also specific types

amount of, quality attribute, 5illness from, 297zinc absorption, 55

Parenchyma, 23Parsley, 22, 84Passion fruit, 241Pathogens, 5, 44; see also specific

typesPCB, 326Peaches, 236Peanuts, 20–21

cooking, flavor after, 233oil from, 116–119proteins in, 153storage of, mycotoxin activity, 318

Pears, 236Peas, 20–21

lipid oxidation in, 239LOX activity in, 249–250proteins in, 153zinc in, 52

Pectinsalginate and, 282aroma of, 102, 110carboxylic groups in, 103emulsifier, 281for food texturization, 111methylation of, 104mineral bioavailability, 55modification of, 103–104a polysaccharide, 85rhamnose in, 84stabilizer, 281for texture, 110texture from, in apples, 6thickening agent, 281

Peeling, 69PEFA, 116–117, 125–127Pelargonidin, 219Penicillium, 318Pentosanes, 102Pentoses, 82, 84

apoise, 84arabinose, 84, 220furan derivatives, see Furan

derivativesxylose, 84, 102

Pentuloses, 82Peonidin, 219Pepper, 53, 232Pepperberry, 250Peppermint, 233Peppers, 250Pepsi-Cola, 242Peptides

in beer foam, 8chain, hydrogen bond in, 29Maillard reactions, 238

Peptones, bacterial, 164Peptydoglycan, 328Perchlorate, 34Perilla oil, 117, 127Perimysium, 12, 14Peroxidases, 160, 167, 223, 310Peroxidation, lipid

anthocyanins impact on, 222–223carotenoids impact on, 212–213mutagen formation after, 326selenium, effect of, 329SOD impact on, 60

Peroxide value, 122Peroxides, 326Peroxyl radicals, 279; see also

Peroxidation, lipidPesticides, 298–299, 317, 326Pet food, 44Petroleum ether, 207, 244Petunidin, 219PH

acid ionization constant, 68anthocyanins, as indicators,

220–221of aspartame, 281balance, minerals for, 57–58of benzoic acid, 278of betalains, 225in colon, 287for copigmentation, 222during emulsification, 149–150for enzymes, 163after GDL, 284for gelation, 146–147for hydrolyzates, 167lowering, by acidulants, 283of N-nitrosation, 172of plant tissue, 22for process flavor, 246reactions, alkaline, 159–160regulators, mineral compounds as,

61–63of saccharides, 97of shiitake, 237of sorbic acid, 278for texture, 111for transglutaminase, 166water-holding capacity of meat,

145of water, mercury concentration,

71water treatment for, 47

Phaeophytin, 216–217Phagocytic activity, 264–265Pharmafoods, 6Phellandrene, 244Phenolases, 223Phenolic acid, 222Phenolics, 318Phenoloxidase, 221Phenols, 169–170Phenylalanine

benzaldehyde from, 248fluorescence, intrinsic, 137plasteins, removal from, 167properties of, 135

Phenylbenzopyrylium, 206, 219–224Phenylketonuric, 167Phephorbide, 216–217Phloem, 23Phosphatases, 162Phosphate

anticarcinogenic action of, 329antimicrobial activity of, 304auto-oxidation protection, 67bioavailability of iron, 55


calcium, 140effluent treatment with, 172film formation from, 104gelling agent, 104reactions with proteins, 172–173sodium, 65solvent for, 35in starch, 104starch ester, 104wastewater treatment and disposal

with, 172water structure former, 34

Phosphatides in oil, 119–120Phosphatidic acid, 128Phosphatidylcholine, 128–129Phosphatidylethanolamine, 128Phosphatidylinositol, 128Phospholipids

as amphipathic molecules, 36in cereals, 17for emulsions and foams, 6in milk fat, 14–15as nutraceutical food, 240rancidity and warmed-over flavor,

66in vegetable lecithin, 128–129water layer in, 37

Phosphoric acid, 103, 170for food texturization, 111posttranslational modifications in,

136potato esterification, 88, 107treatment of oil, before

degumming, 119Phosphorus

biological function of, 57, 58calcium absorption, 77in cereals, 18in eggs, 16excessive amount of, 48in fruits and vegetables, 22, 69level in oil, 120macroelement, 54in milk, 15in nuts, 20oxychloride, 171pentoxide, 171RDA, 56in seeds of pulses, 21

Phosphorylationof amino acid residues, 167inhibition of by benzoic acid, 278reagents, 171of saccharides, 136

Phosvitin, 135Photooxidation, 209Physarium, 166Phytates, 55Phytin, 105Phytoalexins, 331Phytoncides, 21Phytosterols, 120, 129–130Pica, 74Pickles, 233Pickling, 4, 101Pigments

annatto, 210anthocyanin, 206, 219–224anthraquinone, 226

beetroot red, 226betalains, 3, 206, 224–226caramel, see Caramelcarotenoid, see Carotenoidschlorophyll, see Chlorophyllcochineal, 206, 226crocin, 210curcumin, 206, 227in essential oils, 243heme, 12, 160, 206, 217–218hemoglobin, 12, 160, 206,

217–218lakes, 222, 226, 228melanoidin, 206oxidation of, 4phenylbenzopyrylium, 206,

219–224polyhydroxyanthraquinone C-

glycoside, 226porphyrin, see Porphyrin pigmentsquininoid, 226riboflavin, see Riboflavinsynthetic organic colors, 228tetrapyrrole, 215–217tetraterpene, 206–215types of, 206

Pigs, 164Pike, 71Pineapple, 22–23, 245Pinene, 244Pinoresinol, 131Plant gums, 84Plant sterols, see PhytosterolsPlasma, 146Plasmin, 162Plasmolysis, 108Plasteins, 167–168Plastic deformation, 199Plasticizers, 103, 148, 180Plastics, biodegradable, 105, 112–113Platelet-activating factor, 126PMTDI, 65Polar compounds, 33Pollution

amount of, quality attribute, 5cancer risk factor, 332from oil processing, 120safety of food, impact on, 297of water, 47–49

Polychlorinated biphenyls (PCB), 326Polycyclic aromatic hydrocarbons

(PAH), 322–324Polydextrose, 285Polyenoic fatty acids (PEFAs),

116–117, 125–127Polyethylene, 112, 282Polyglycerol, 282Polyhydroxyaldehydes, 82Polyhydroxyanthraquinone C-

glycoside, 226Polyhydroxyketones, 82Polymerization, 147, 162Polyols, 238Polyphenol oxidase, 167Polyphenolic compounds


antioxidants, 212, 279, 329gallic acid esters, 278–279

oxidation inhibitor, 60oxidation of, 160, 276

Polyphosphates, 145, 155, 173Polypropenes, 329Polyrybosome, 136Polysaccharides, 84–85

acetylation, 103, 105agar, 84alginate, see Alginateamylopectin, see Amylopectinamyloses, see Amylosesarabic gum, see Arabic gumarabinogalactan, 85aroma of, 110carbamoylation, 103carrageenans, see Carrageenanscellulose, see Cellulosechirality, 88–89complexing agents, 104depolymerization of, 102dextran, 85, 106emulsifier, 281–282esterification, 92, 103, 105etherification, 103, 105fat substitutes, 285film formation in, 145furcellaran, 85, 103, 111galactan, 85, 103galatose in, 84gatti gum, 85, 103as gelling agents, 6, 145, 281–282glycogen, see Glycogenguaran gum, 85halogenation of, 103hemicellulose, see Hemicelluloseheparin, 85, 103, 111hialuronic acid, 85hydrolysis of, 103inulin, 85, 285–256karaya gum, see Karaya gumlocust bean gum, 85, 282mannans, 85metallation, 103minerals and, 67modification of, 99–107nonstarch, 285oxidation of, 103pectins, see Pectinsprotopectin, 85reduction of, 103solubility, 101stabilizer, 281–282starch, see Starchstructure of, 83–86in tamarind flour, 85texture in, 110–111as thickening agents, 6, 281–282tragacanth gum, see Tragacanth

gumxanthan gum, see Xanthan gumxylans, 85, 103

Polyurethane foams, 112Poppy, 232Pork; see also Meat

composition of, 13iron in, 52, 66myoglobin in, 157radiation, effect on vitamins, 302temperature during cooking, 158

Index 359

Trichinella in, 302–303Porphyrin pigments

chlorophyll, see Chlorophyllheme, 12, 160, 206, 217–218from potassium copper

chlorophyllin, 63from sodium copper chlorophyllin,

63Potassium

acetate, 62alginate, 62aluminosilicate, 62ascorbate, 62in beef, 52benzoate, 62bicarbonate, 63biological function of, 57–58bromate, 63carbonate, 63in carrots, 52in cereals, 18in cheese, 52chloride, 63, 68chlorophyllin, 63compounds, food additives, 62–63dihydrogen phosphate, 63in eggs, 16for food texturization, 111in fruits and vegetables, 22, 69glutamate, 63hydrogen sulfite, 63ions, in water, 33–34in liver, 52loss of, during processing, 69macroelement, 54metabisulfite, 64in milk, 52in nuts, 20in oats, 52in oranges, 52in potatoes, 19RDA, 56react with proteins, 68in seeds of pulses, 21sorbate, 65treatment to remove from water, 47water structure breaker, 34in wheat, 52

Potatoes, 18–19; see also Sweet potatoes

aroma, 110fried, 239lipid oxidation in, 239LOX activity in, 249–250mashed, 239minerals in, 69N:P conversion factor in, 3properties of, 88protease inhibitor, 146proteins in, 3retrogradation in, 105saccharides in, 2starch in, 107vitamin fortification, 301

Poultry; see also Chicken; Duck; Meat

feed for, 164Maillard reactions, 238–239minerals in, 58

surimi, 151Pourability, 185Powdered milk

composition of, 13mutarotation, 90proteins in, 14water content of, 2

Powered milkiodide in, 53zinc in, 52

Prebiotics, 285–287; see also Probiotics

additives as, 275inulin, 85, 285–256resistant starch, see Resistant

starchPremenstrual syndrome, 127–128Preservatives

acidulants, 247, 275, 283additives as, 274–278benefits of, 299benzoic acid, 278–279glucose in, 84mineral compounds as, 61–64sorbic acid, 277–279, 303–304for sour products, 278sucrose, see Sucrosesulfites, 276, 301–303

Pressure dynamics map, 197Pressurization, 101–102Prions, 295Probiotics; see also Prebiotics

additives as, 275basis of use, 260–261definition of, 259–260effects, 263–266efficacy of, 267–268research on, 268–269safety of, 268strain selection, 261–263

Processing of food, 4, 7–8cancer risk factor, 332carcinogens and mutagens formed

after, 317denaturation during, 141flavor changes during, 241–242flow analysis, 181–191gelation, 145–148methodology of, 179–181methods, cancer risk, 323–324mineral bioavailability, 55, 68–69protein solubility, 144rheological properties after,

156–157WHC impact on, 145

Procollagen, 136Prolamines, 142Proline, 134, 135Prooxidants, 212Propanol, 234Property frequency change-response

profile, 195Propionaldehyde, 234Propionic acid, 125, 234Propyl gallate, 67, 122Propylene glycol

boiling point of, 245fatty acid esters, 282as solvent, 244

Propylene oxide, 104Prostaglandins, 126, 127, 326Prostate cancer, 215Proteases

in cereals, 17flavor from, 248inhibitors of, 146

Protein bodies, 3Protein-phospholipid membranes, 3Proteinase inhibitors, 159Proteins, 134

acylation of, 170–171alkylation of, 169–170amino acid composition, 134–137as amphipathic molecules, 36in beans, 3in biodegradable materials, 112in butter, 21cancer risk factor, 331–332in cereals and cereal products, 107chemical modification of, 168conformation, 134, 138–141denaturation of, 141destabilization of, 155in eggs, 3, 154emulsifier, 283emulsion stability, 282for emulsions, 6, 148–151enzyme-catalyzed reactions,

162–167ferritin, 60film formation, 145–148flavor, undesirable, 240foams, 6, 148–151in food, 3in fruits, 3in fruits and vegetables, 21function of, in body, 3functional properties of, 141–142gelation of, 145–148in gluten, 156heating of, 155–160hydrophobicity in, 36, 137–138legume, 153in meat, 3, 12in milk, 3, 153–154mineral bioavailability, 55, 68in muscles, 151–152mycoprotein, 154myofibrillar, see Myofibrillar

proteinsN-nitrosation of, 171–172in nuts, 20oxidation of, 160–162pH, effect of, 143–144phosphate reactions, 172–173in potatoes, 3, 19, 107precipitation, 85pressurization of, 155pyrolysis, 320react to minerals, 68in seeds of pulses, 21solubility of, 142–144, 156in soybeans, 3stabilizer, 283in starches, 88thaumatin, 280–281thickening agent, 283in tubers, 19, 107


volatility, reduction by, 235–236in water, 37water retention in, 144–145water transport, cellular, 39in wheat, 3, 16–17

Proteolysis, 156, 163–164Protonated amines, 35Protopectin, 84–85Provisional maximum tolerable daily

intake (PMTDI), 65Provisional tolerable weekly intake

(PTWI), 75Pseudomonas aeruginosa, 261Pseudomonas fluorescens, 121, 248Pseudoplastic flow, 184, 188–189Psicose, 99, 101PTWI, 75Puddings, 110Pullulan, 106PulseNET system, 296Pumpkins, 21Purine, 60Pyrazine, 91

aromas from, 110, 235flavoring from, 244Maillard reactions, 238–239in roasted duck, 238–239

Pyridinearomas from, 110, 235flavoring from, 244a HCA, 321Maillard reactions, 238in roasted duck, 238–239

Pyridoxal, 303Pyridoxine, 301Pyrimidin, 276Pyroligenious acid, 244Pyrometaphosphate, 67Pyrrole, 91, 110, 238Pyrrolizidine alkaloids, 318

Q

Quarg, 13Quaternary structures

dissociation of, 145in marine animals, 71in proteins, 139solubility of, 143

Quininoid, 226Quinoline, 228, 321Quinones, 160, 310Quinoxaline, 321

R

Racemization of amino acids, 160Radiation

dosage, effect on vitamins, 302–303

irradiation, 296, 302–303radioprotective agent, 222ultraviolet, see Ultraviolet

radiationRadicals, oxygen, 160–162

in apples during senescence, 60lipid peroxidation, caused by, 314,

326promotion of mutagenic cells, 310scavenging of, 66, 148, 331trapping of, 329

Radioprotective agent, 222Radishes, 60Radium 226 and 228, 46Raffinose, 94, 285Raising agents, 61–63Raisins, 302Rancidity, 66–67, 122, 240Raney nickel catalytic hydrogenation,

90Raoult's law of dilute solutions, 44Rapeseed, 130, 282RDA, 56–57, 301Reactive oxygen species (ROS)

cancer risk factor, 213, 315, 325glutathione, see Glutathioneprobiotics, impact on, 264

Recommended Dietary Allowance (RDA), 56–57, 301

Recycling, 5Red pepper, 209–210Red sea bream, 166Red seaweed, 85Reductants, 279Reduction, 93, 157Reductones, 97Relative humidity of moist air, 41, 43Relative sweetness (RS), 94, 108Relative vapor pressure (RVP), 198Renal disease, 58, 68Renal proximal tubules, 39Rennet casein, 153Reproduction, 59Resistant starch, 102, 285, 287, 300Resveratrol, 327, 330–331Reticuloendothelial system, 264Retinal, 213–214Retinoids, 328Retinol, 329Retrogradation, 105Reverse osmosis, 48Rhamnopyranosyl, 238Rhamnose, 84, 220Rhamnosidase, 238Rheological properties, 179–181,

199–203angle of internal friction, 194angle of repose, 194calcium, impact on, 147cohesion, 194creep compliance test, 190–191of dairy products, 167Deborah number, 192deformation, 191–192, 199–200of dilatant fluids, 185, 189direct flow rate, 194dynamics map, 196–198flow analysis, 181–191, 194flow behavior index, 202foaming, 150of gel, 146–147glass phase transition, 195–199heat, 201–203of hydrogenated oil, 7

image analysis, 195kinetics, 193of materials, 184mathematical characterization of,

195of meat, 12, 155modification of, 6, 67in non-Newtonian food systems,

184–189of polysaccharides, 103of proteins, 156–157of pseudoplastic materials,

188–189quality attribute, 5reaction mechanisms, 194rheopectic, 189–190shear strength, 194shear thickening, 189, 193shear thinning, 192–193shearing, 183–191, 202steady flow, 192stress-strain relationship,

185–189, 191–192structure, 190–191, 193–195tensile strength, 194thermodynamics, 193thixotropic, 185, 189–190, 193time, 185–189viscoelastic, 190–192viscosity, 183–191yield stress, 185, 187–188, 194,

201–202Rheopetic fluids, 189–190Rheopexy flow, 188, 193Rheostable food systems, 184Rhizomes, 232Rhizopus arrhizus, 121, 128Riboflavin

pigments from, 206, 226–227processing of, 301sensitizer, 160

Rice, 16, 18bran, 116, 119–120flour, in dough, 157golden, 303properties of, 88starch source, 107for vitamin A deficiency, 303

Ricinoleic acid, 247Rickets, 58Rigidity modulus, 201Ristelliger, 164RNA, 58Roasting, 110Roe, 233Roots, 232; see also TubersROS, see Reactive oxygen species

(ROS)Rose, 233Rose oxide, 244Rosemary, 232Rotational mobility of water, 39RS, 94, 108Rubidium, 34Rutabagas, 237Rutinosides, 238RVP, 198Rye, 16, 18

flour, in dough, 157

Index 361

properties of, 88starch source, 107

S

Saccharides, 81–82alcohols, 90, 96–97aldehydes, see Aldehydesaroma of, 110binding of, to amino acid residues,

169in biodegradable materials,

112–113bonded to anthocyanidins, 220in butter, 21caramel, see Caramelcarbohydrates, see Carbohydratescarbonyl group, addition to, 90–91in cereals and cereal products, 2,

18chirality, 88–89as cryoprotectant, 151dehydration of, 93depolymerization of, 102–103encapsulation using, 111–112enol, 93esterification of, 92etherification of, 93fat mimetic, 285in fish, 2in fried food, 8fructose, see Fructosein fruits and vegetables, 21glucose, see Glucosein gluten, 156glycosidic bond, 97halogenation of, 93in honey, 19ketones, see Ketonesin meat, 2, 12in milk, 2, 15modification of, 103–107mutarotation, 89–90in nuts, 20oxidation of, 91–94phosphorylation of, 136polysaccharides, see

Polysaccharidesin potatoes, 2, 19in protein rich food, 13reactivity of, 89–107reduction of, 93relative sweetness, 94retrogradation in, 105in seeds of pulses, 21solvent for, 35structure of, 82–88sucrose, see Sucrosein sugar beets, 2taste of, 107–109texture in, 110–111

Saccharin, 94, 281Saccharine, 111Saccharose, 19Safe and adequate daily intake (SAI)

level, 56–57Safety, food, 291–304

Safflowerlinoleic acid in oil, 127oil from, 117processing of, for oil, 118–120spice from, 232tocopherol in, 129

Saffron, 210, 232Sage, 232SAI, 56–57Salatrim, 125–126Salicylic acid, 278Salmon

calcium in, 58copper in, 53DHA and EPA in, 127enzyme-catalyzed reactions in,

163–164selenium in, 53sensory attributes of, cause of, 8

Salmonellavs. Lactobacillus, for vector

choice, 269for mutagenic activity testing, 316outbreaks of, 296prevention, probiotics, 264risk of, 299typhimurium, 316

Saltextractive dispersal, 244in meat processing, 144, 273sodium chloride, see Sodium

chloridesubstitutes, 61–63, 68

Saltingabsorption of compounds during, 4for food preservation, 44in, definition of, 144methods, cancer risk, 323

Saltpeter, 64, 277Saponins, 84

carcinogenicity, 318galatose in, 84glucose in, 84mutagenicity, 318rhamnose in, 84saponification, 116, 119, 130

Sarcolemma, 12, 14Sarcoplasm, 148Sarcoplasmic proteins, 146, 151Sarcoplasmic reticulum

calcium ion binding, 12ferric iron reduction, 66oxygen radicals in, 60postmortem changes in, 163

Sardinella, 164Sardines, 52Saturated fats and oils, 116Sauerkraut, 233Sausages

fat dispersion in, 149flavoring from, 233formaldehyde in manufacture of,

169GDL in, 92, 284gelling in, 147, 156as IMFs, 44low salt, 173processing of, 144rheological changes to, 156

Scaling, 118Scallion, 232SCFA, 125Schaal oven test, 122Schardinger dextrins, 106Schiff bases, 90Scission of proteins, 162Sclerenchyma, 23Scomber colias, 164Screening, of water, 46–48Scutellum, 17–18Seafood; see also specific types

arsenic in, 70–71enzyme-catalyzed reactions in,

162–167fluoride in, 59iodine in, 60magnesium in, 58minerals in, 52–53, 58–60

Seasonings, 233Seaweed, 281Seeds of Pulses, 20–21, 22Seizures, 58Selenium

anticarcinogenic action of, 329bioavailability of, 54, 55biological function of, 60in chips, 53in fruits and vegetables, 69in kidneys, 53mercury and, 72microelement, 54in milk, 53RDA, 56in salmon, 53supplementation, 215in tuna, 53water contamination level, 46

Selenoglutathione peroxidase, 60Selenomethionine, 54Semicarbazide, 90Senegal acacia, 85Sensitizers, 160Sequestrants

antinutritional effects, 304carcinogen, 328for cheese, 64citric acid, see Citric acidEDTA, see


for fish, 64in lipids, 122for meat, 64for milk, 64mineral compounds as, 57, 61–65

Serinealkaline pH, reaction with, 159bonding with phosphoric acid, 170in phosphorylation of saccharides,

136properties of, 135

Serotonin, 75Sesame, 130–131

cooking, flavor after, 233linoleic acid in, 117oil from, 116–119spice from, 232

Setting, 145, 157, 167


Settling ponds, 47, 48Sewage, 48–49Shallot, 236Shark

lipids in, 3–4mercury in, 71size of, 4squalene in oil, 4

Shear modulus, 146, 199Shear rate, 183–192, 202Shear strain, 186, 199–200Shear strength, 194Shear stress, 183–192, 199–200Shear thickening, 189, 193Shear thinning, 192–193Shelf life, 5–6, 57Shellfish

analogs, 151–152arsenic in, 70–71fluoride in, 53manganese in, 59mercury in, 71overpasteurization of, 8

Shiitake, 237Short-chain fatty acids (SCFA), 125Shortening, 122Shrimp

iodide in, 53lipid oxidation in, 239peeling and deveining of, 165preservation of, 278tetradecatrienone in, 239

Silage, 164Silicon, 54, 56Silk, 103Sillylic acid, 103Silver, 46, 68Singlet oxygen quencher, 212–213,

329Sitosterol, 130Skin disease

honey to treat, 20hyperpigmentation, 76macula protection, 213ultraviolet radiation protection,

213Smoke curing, 273; see also Curing

absorption of compounds during, 4aroma, 110cytochrome P450 activity,

314–315of fish, nitrosamines, 319mutagen formation during, 320PAHs in, 322

SOD, 57–60, 66, 160Soda niter, 64Sodium

alginate, 63aluminum phosphate, 63ascorbate, 64, 172benzoate, 64biological function of, 58caseinate, 153, 283chlorophyllin, 63citrate, 67dihydrogen phosphate, 64dodecylsulfate, 138in eggs, 16feredetate, 64

for food texturization, 111in fruits and vegetables, 22, 69glutamate, 64, 281hypochlorite, 104ions, in water, 33–34iron EDTA, 64kasal, 64macroelement, 54metabisulfite, 64methoxide, 121nitrate, 64, 168nitrite, 64in nuts, 20oxalate, 67phosphate, 65RDA, 56react with proteins, 68reduction of, in food, 68in saccharide alcohols, 96sorbate, 65treatment to remove from water, 47trialuminum tetradecahydrogen,

63trimetaphosphate, 170water structure former, 34

Sodium chloridecross-linking in proteins, 166free energy change in water, 34in meat batters, 149–150moisture retention, 67preservation agent, 66for rancidity inhibition, 67reduction of, in food, 68as solvent, 142thermal stability of meat, 155in water, 33

Solutions, 190Solvent fractionation, 129Solvents

ethanol, see Ethanolpetroleum ether, 207, 244water, 33–36

Sonication, 101–102Sorbate, calcium, 61Sorbate, potassium, 65Sorbate, sodium, 65Sorbic acid, 277–278, 279, 303–304Sorbitan fatty acid esters, 282Sorbitol

acylation of, 92FA ester, 285formula for, 89hydrogenation of glucose syrup,

108as plasticizer, 285relative sweetness, 94

Sorbose, 84Sorghum, 16Sorgo, 328Sorption isotherm, 41–45Sour cream, 13Sour taste, 283Soy


denaturation of proteins in milk, 153

dried, 319flavoring from, 233

Soybeans, 20–21acylation of, 170in allium processing, 237antioxidant, 243degumming of, 119emulsifying properties of, 167fermentation of, 162flour, solubility of, 143frying oil from, 240gels from, 146glycoproteins in, 137green aroma from oil, 249lecithin from, 128, 282, 300linoleic acid in, 117, 127LOX activity in, 167, 249–250oil from, 117PEFAs in, 126–127processing of, 117–119, 144, 300proteins in, 3, 146, 153saccharides in, 137solubility of, in calcium, 167structure of, 139

Speciation analysis, 54, 70Specific heat

of ammonia, 40of vegetable oil, 40of water, 32, 40

Specific rotation, 88–89Spectrum, visible absorption,

207–209Spices, 53, 232, 243–245Spinach, 22, 211Spinacine, 169–170Spirulina, 128Spoilage of food, 44, 280Sprats, Baltic, 163Spreadability, 185Squalene, 4Squid, 145, 156, 165Stabilizers

additives as, 281–283carrageenans, see Carrageenanscaseins, see Caseinscitrate, 61, 67, 155EDTA, see


ester, starch sulfate, 111mineral compounds as, 61–65polyphosphates, 145, 155, 173polysaccharides, 281–282proteins, 283sodium phosphate, 65starch, 281

Stachyose, 94, 285Staked lime, 61Staling

of bread, 6cost of food, impact on, 299retardant

agar, 84GMS, 123sorbitan fatty acid esters, 282

retrogradation of gels, 105Staphylococcus aureus

gene transfer by, 268in gut, 261illness from, 297inhibitor of, 67

Index 363

lipase, 121prevention, nitrite, 277prevention, probiotics, 264

Starchalpha-starch, 102anionic, 104, 111antifoaming agents in, 150aroma of, 102, 110in biodegradable materials,

112–113carboxymethyl, 104cationic, 104from cereals, 107complex formation, 104degradation of, 106depolymerization of, 102–103dextrinization, 102–103emulsifier, 281esterification, 104etherification, 104in extrusion cooking, 241in fermentation process, 105film former, 283gelatinization of, 17, 88, 107, 199,

300granules, 20, 87–88, 107hydrolysates, see Hydrolysateshydroxymethl, 104hydroxypropyl, 104maltose in, 84modification of, 99–104oxidation of, 104phosphates, see Phosphatepolysaccharides, see

Polysaccharidesin potatoes, 19, 107pregelantinized, 102removal of, before processing, 241resistant, 102, 285, 287, 300retrogradation, 105, 199solubility, 101–102as a stabilizer, 281sulfates, 104surfactants, modification by, 123thickening agent, 281from tubers, 19, 107waxy, 102in wheat endosperm, 17

Steady flow, 192Stearic acid, 116, 125–126Sterculiacea tree, 85Steric exclusion, 145Sterigmatocystin, 318Sterilization, 7, 320Sterols

as amphipathic molecules, 36DOD in, 129in milk fat, 14–15plant, 130structure of, 130for water transport, cellular, 39

Stickiness, 196Stiffening agents, 275Stigmas, spices from, 232Stigmasterol, 130Stilbene isorhapontin, 247Stillinger water model, 31–32Stokes-Einstein relation formula, 37Stolephorus, 164

Stomach illness, 20Storage, 4, 7–8

carcinogens and mutagens formed after, 317

of eggs, 16of fish, 151flavor changes during, 235–238,

241–242flow analysis, 181–191of lipids, 121–122methods, cancer risk, 323–324mineral bioavailability, 55, 68–69modulus, 201of potatoes, 19requirements, adherence to,

quality attribute, 5retrogradation rate, 105rheological properties after,

156–157Strain, 199–200Strain rate, 199Strawberry

anthocyanins in, 220carotenoids in, 211esters in, 248formulas for, 245–246

Strecker degradation compounds, 246Streptococcus, 105Streptoverticillium, 166–167Stress, 199–200Stress-strain relationship, 186–188,

190–191Stroke, 68, 127–128Strontium, 96Structural viscosity flow, 188Structure, 181–191, 190–191Structured lipids, 123–126Sturgeon, 163Styrene, 112Subacute tests, 294Sublimation, 4Sucralose, 280, 281Sucrose, 108

acylation of, 92in barley malt, 108enzymatic oxidation of, 106in fermentation process, 105formation of, 83in fruits and vegetables, 21honey vs., 20invert sugar, 97in maple syrup, 108oxidative cleavage of, 93polymerization of, 106relative sweetness, 94substitutes, 84in sugar beets, 84in sugar cane, 84TAG substitutes, 284transfructosylation, 286

Sugaralcohol, 6, 108–109burnt, 97confectioneries, coloring for, 206invert, 97Maillard reactions, 238in potatoes, 239substitutes, additives as, 274

Sugar beets

dextran in, 85, 106ferulic acid source, 247maltose in, 84saccharides in, 2sucrose in, 84

Sugar cane, 84Sulfate, 34, 62, 103Sulfides, 236Sulfite, 276, 301–303Sulfmyoglobin, 218Sulfobenzoic acid, 281Sulfocatechols, 276Sulfonic acid, 161Sulforaphane, 327, 330–331Sulfotransferases, 310Sulfur

amino acids residues containing, 135

biological function of, 57compound

flavoring from, 244garlic in oil, 239–240

dioxide, see Sulfur dioxidein eggs, 16in fruits and vegetables, 22macroelement, 54Maillard reactions, 238mercury and, 72threshold value, 234

Sulfur dioxideanthocyanins, degradation rate,

221, 223–224cochineal carmine stability, 226in wine, 276

Sulfuric acid, 93, 103, 164Sunflower

copper in, 53lecithin from, 282linoleic acid in, 117linoleic acid in oil, 127oil from, 117processing of, for oil, 118–120tocopherol in, 129

Superoxide dismutase (SOD), 57–60endogenous antioxidant, 160hydrogen peroxide production, 66

Suppressing agents, 327–329Surface active agents, 92, 123, 129Surface tension, 192Surimi, 151–152, 167Sweet potatoes, 22Sweeteners

additives as, 274–275, 279–281glucose in, 84honey, 20sucrose, 84

Sweetnessfrom carbohydrates, 107–109increasing, 93relative, 94, 108

Swift test, 122Swordfish, 4, 71Synergist, 64Syrups

from carbohydrates, 108from depolymerization of

carbohydrates, 102, 103fructose, 108glucose, 108


maltotetraose, 108maple, 108saccharide content in, 109from starch, 85, 108sucrose in, 108of xanthates, 103

T

T cells, 265TADI, 65TAG, see Triacylglycerols (TAGs)Tallow, 116–117Tamarind, 85, 281Tannins, 21, 55Tapioca, 107Tar, 102Tartaric acid, 22Tartness, 283TBA, 66, 122TBHQ, 122, 278–279Tea

anticarcinogenic action of, 328antioxidant, 331chemopreventive properties of,

327flavor of, 238flavoring from, 233fluoride in, 53green vs. black, 302minerals in, 59mutagen formation in, 324–325processing of, 302

TEAC, 213Teeth, 58–60, 108, 285–286Temperature

apparent viscosity and, 201of carmelization, 109denaturation, 155for deodorizing of oil, 120effects

formula for, 201on irradiation treatments, 302

flow property, 181–191fluctuation within cells, 32glass phase transition, 195–199heat field intensity, 201hydrophobicity, 139Maillard reactions, 238melting, of cow's milk, 15of oil-bearing materials, 118oxidation and, 121protein heating, 155–160retrogradation rate, 105shrinkage, 155in solubility assays, 144swelling, of starch, 123for texture, 111for transglutaminase, 166ultrahigh, 242of whey proteins, 153

Temporary acceptable daily intake (TADI), 65

Tempura, 151–152Tensile modulus, 199–200Tensile strain, 199–200Tensile strength, 194

Tensile stress, 199–200Terminalia catappa L. leaves, 243Terpenes, 21, 232, 243Terpenyl acetate, 241Terpineol, 238, 242Tertiary butylhydroxyquinone

(TBHQ), 122, 278–279Tertiary structures, 143Testing of food, 294–296Tests, 294–296

acute, 294Ames, 316–317Barfoed, 92Benedict, 92for cancer, 315–317chronic, 294creep compliance test, 190–191Fehling, 92metabolic, 294for mutagens, 315–317Nylander, 92Schaal oven, 122subacute, 294Swift, 122

Tetany, 58Tetracycline, 55Tetradecatrienone, 239Tetrahydrofurane, 212Tetraioic acids, 105Tetralkylammonium salt function,

104Tetrapyrrole pigments, 215–217Tetraterpene pigments, 206–215Texture

in carbohydrates, 110–111complex formation for, 97development of, 6, 8dynamics map, 196–198flow property, 181–191of gels, 145–147, 156–157impact on, by water mobility, 39of protein-rich food, 156–157rheological properties of, 199

Texturing agentsagar, 84carrageenans, 111CMC, 104mineral compounds as, 61starch, 105

TGase, 145–146, 166–167Thaumatin, 280–281Thaumatococcus danielli, 281Thermal conductivity, 40Thermal stability

complex formation for, 97of gels, 147of beta-lactoglobulin, 153of proteins, 139, 141, 155–160

Thermodynamics, 193Thermolysis, 101–102Thiamine

antibrowning agent impact on, 303Maillard reactions, 238in nuts, 20processing of, 301radiation, effect on, 302–303sulfite, reaction to, 276thermal decomposition of, 7in wheat scutellum, 17

Thiazolesaromas from, 235flavoring from, 244Maillard reactions, 238in roasted duck, 238–239

Thickening agentsadditives as, 275, 281–283dextrins, 103mineral compounds as, 61–63polysaccharides, 84–85, 281–282proteins, 283starch sulfate ester, 111

Thinning agents, 285Thiobarbituric acid (TBA), 66, 122Thioether group, 169Thiolactic acid, 244Thiolanes, 235Thiols

acylation of, 170alkaline pH, reaction with, 160alkylation of, 169in allium, 236antioxidant, 1–2arsenical, react with, 70disulfide creation in milk, 162gels, impact on, 147heme, reaction with, 158oxidation of, 143in transglutaminase, 166transition metals and, 68

Thiophenes, 235, 238Thiosemicarbazide, 90Thixotropic flow

definition of, 189–190non-Newtonian behavior, 188in nonrheostable systems, 184shear stress vs. shear rate, 185after shear thinning, 193

Threoninealkaline pH, reaction with, 159in antifreeze fish serum

glycoproteins, 134–135esterification of, 170in phosphorylation of saccharides,

136properties of, 135

Threose, 168Threshold of flavor, 234Thrombosis, 126Thromboxanes, 126Thymine, 29Thymol, 243Thyroid, 60Thyroxine, 57Time, 187–191, 197Tin, 216, 222, 302Tissue disruption, 237–238Titin, 12, 163Toasting, 153Tobacco, 110Tocopherols, 129–130

analog, 213antioxidant, 1–2, 122, 212destruction of, in deodorizing of

oil, 120lipid storage, 121nitrosamine formation inhibitor,

320TEAC, 213

Index 365

Tofu, 144, 301Tomato

anticarcinogenic action of, 328antioxidant, 331carotenoids in, 209, 210, 211chemopreventive properties of,

327flavor of, 237lipid oxidation in, 239LOX activity in, 249

Tongues, 85Torque, 183Toxaphene, 46Toxins, 5, 70–77, 291, 294–296Toxoplasma, 296–297Tragacanth gum, 85


Trans fatty acids, 4, 7, 116Transesterification, 248Transgalactosylation, 286Transglutaminase (TGase), 145–146,

166–167Translational mobility of water, 39Transpeptidation, 167Transportation, 5, 181–191Transversal modulus, 201Trehalose, 285Tremors, 58Triacylglycerols (TAGs)

binding of, 138in cereals, 17decreasing level of, vegetable

lecithin, 129hydrogenation, 121interesterification, 121in lipids, 3, 21, 116–117in milk, 14–15minetics, 284in Salatrim, 125soap formation, 55structured lipids, 123–126substitutes, 284–285

Triarylmethane, 228Triaso, 228Tricalcium salt of beta, 61Trichinella, 302–303Trichloroethane, 46Trichloroethylene, 46Trihalomethanes, 46Trimethylamine, 165, 244Tripolymetaphosphate, 67Trisaccharides, 19Trisodium dialuminum

pentadecahydrogen octaphosphate, 64

Trithianes, 238Trithiolanes, 238Triticale, 88Trolox equivalent of antioxidant

capacity (TEAC), 213Tropocollagen, 136, 142Tropomyosin, 12Troponin, 12, 164Tryptophan

in collagen, 134

fluorescence, intrinsic, 137in grains, 134in hydrolyzate, 167oxidation of, 161properties of, 135pyrollase, 75residues, 135in transglutaminase, 166

Tuberspotatoes, see Potatoesstarch in, 107sweet potatoes, 22yam, 107

Tunacalcium in, 52copper in, 53magnesium in, 52selenium in, 53size of, 4

Turbidity, 46, 283Turbulent flow, 187Turgor, 54Turmeric, 227, 232Turnips, 237Tyrosine

bloom in fish, 163fluorescence, intrinsic, 137in grains, 134oxidation of, 161properties of, 135in transglutaminase, 166

Tyrosyls, 170

U

Ubiquinone, 1–2Ultrafiltration of water, 48Ultrasound, 47, 101–102Ultraviolet radiation, 47, 101–102

absorption of, by amino acids, 137absorption of, by carotenoid

pigments, 207–209lipid deterioration, 121riboflavin destruction, 301skin protection, 213

Undecalactone, 235, 244–245Unsaturated fats and oils, 116Urea, 3, 139Uric acid, 59Uronic acid, 94, 104

V

V-type amylose, 86Vaccinium myrtillus, 220, 223Valine, 134, 135Van der Waals interactions, 27Vanadium, 54, 56, 67Vanilla beans (Vanilla planifolia),

233, 243–244Vanillin, 244, 247–248Vaporization of water, 32Vasprotective agents, 222Veal, 13; see also Beef; Meat

Vegetables, 21–23; see also specific types

alkaline treatment of, 159anticarcinogenic action of,

328–329, 332boron in, 60cadmium in, 74calcium in, 58flavor of, 233green aroma from oil, 249iron in, 59lecithin, 128–129lipid oxidation in, 239lipids in, 3magnesium in, 58minerals in, 58–60nitrites in, 319N:P conversion factor in, leafy, 3oil from, 116–131, 210oxidation of, 148potassium in, 58processing and storage of, 69, 283storage of, 301vitamin E, 129water content in, 2

Vibrio, 44, 297Vicinal water

B.E.T. isotherm, 42definition of, 38, 41structural influence of, 34

Vinculin, 12Vinegar, 233, 273Vinyl chloride, 46, 112, 323–324Vinyl monomers, 105Violaxanthin, 208–211Viscoelastic flow, 187–188Viscoelastic food systems

creep compliance test, 190–191flow behavior in, 189–191glass dynamics of, 199in non-Newtonian flows, 184oscillating stress measurements of,

200–201Viscometric functions, 183–184Viscoplastic flow, 184Viscosity

Bingham plastic, 188of dilatant fluids, 189of egg yolk, 16glass phase transition, 196liquid phase, 242in non-Newtonian flows, 186–191of pseudoplastic flow, 188–189rheological property, 182–186of rheopetic fluids, 189of thixotropic materials, 189

Viscous deformation, 199–200Vitamin A

antibrowning agent impact on, 303in cartenoids, 212changes in during food processing,

301–302in eggs, 16fat-soluble, 21formation of from β-carotene, 214in golden rice, 303from lipids, 115–116in milk, 15oxidation of, 302


utilization of, 59Vitamin B group, see B vitaminsVitamin C

antibrowning agent impact on, 303–304

anticarcinogenic action of, 327–329, 332

antioxidant effectivity, 223blocking agent, 328fortification with, 301in nuts, 20in potatoes, 69

Vitamin Danticarcinogenic action of, 329calcium retention, 55in dairy products, 302in eggs, 16fat-soluble, 21lead interference with metabolism

of, 76from lipids, 115–116

Vitamin Eantibrowning agent impact on,

303–304anticarcinogenic action of,

328–329antioxidant effectivity, 223cancer prevention, 215changes in during food processing,

302in eggs, 16fat-soluble, 21from lipids, 115–116in vegetable oils, 129in wheat germ, 16–17

Vitamin Kin eggs, 16from lipids, 115–116storage of, 302

Vitaminsanticarcinogenic action of, 327from bacteria, 261deficiency in, 54effect on, by food processing and

storage, 300–301in eggs, 16in fruits and vegetables, 69leaching of, from food, 4in milk, 14–15nonprotein N in, 3production of, 262radiation, effect on, 302–303sources of, meat, 12thermal decomposition of, 7thiamine, 7

Vittelin membrane, 16Vodka, 325Volatility of aroma compounds, 234Vulgaxanthin, 224–225

W

Warmed-over flavor, 66, 240Washing, 4Wastewater treatment and disposal,

48–49, 172Water, 25–26

activity, 41–45alkalinity, 47bound water, 38, 40–41bulk-phase water, see Bulk-phase

waterin butter, 21carbohydrate structure, 82in cereals and cereal products, 18classes of, 41constitutional water, 41contamination levels for potable,

46cytoplamic, 37–38density of, 40drinkable, 45from dry wood distillation, 102dynamics map, 196–198electrostatic attraction in, 26–27entrapped water, 41in food, 2free water, 41in fruits and vegetables, 21in honey, 19hydration water, 38hydrodynamic radius formula, 37during interestification, 121intracellular, 37–38liquid phase viscosity, 242MCT solubility in, 124in meat, 12in milk and milk products, 14mobility of, 39models, 31–33molecular structure of, 26–32, 34Multilayer water, 41nonpotable, 45oxidation of proteins in, 160oxidation of saccharides, 93plasticizable material, state

diagram, 196pollution, 47–49polysaccharide solubility in, 103potable, 45in potatoes, 19in protein rich food, 13, 142quality, 45–47retention, starch property, 17in silage, 164as solvent, 33–36supply, 45in surimi production, 152thermal properties of, 32transportation, cellular, 39treatment, 46–48types of, 45wastewater treatment and disposal,

48–49Water-holding capacity (WHC)

acylation, impact on, 171of beta-lactoglobulin, 153calcium caseinate, 153of meat, 145, 173pH, effect on, 147sodium caseinate, 153

Water-in-oil (W/O) emulsion, 123frosting, 129icing, 129margarine, see Margarinevegetable lecithin, 129

Wax esters, 3–4Wax gourd, 239Waxy corn/maize

dewaxing of oil, 120properties of, 88retrogradation in, 105

Whale, 157WHC, see Water-holding capacity

(WHC)Wheat

acylation of, 171composition of, 16–18cooking, flavor after, 233copper in, 53extrusion cooking of, 241for film formation, 147–148flour, gluten in dough, 6, 156–157iron in, 52lipoxygenase, 167oil from, 129potassium in, 52properties of, 88proteins in, 3proteolytic changes in, 162retrogradation in, 105starch source, 107zinc in, 52

Wheycoatings from, 148enzyme-catalyzed reactions in,

162for film formation, 148foaming properties, 150–151gels from, 146–147heat stability of, 155Maillard reactions in, 242in milk, 14, 153–154processing of, 144saccharides in, 137

Whipped cream, 123, 150White cabbage, 211White, egg

composition of, 13, 15–16foaming properties, 151, 154gels from, 145–147, 154lysozyme in, 135protease inhibitor, 146proteins in, 145–147, 151saccharides in, 137solubility of, 142in squid meat gels, 145

Whiteners, 283Wiggins water model, 32Williams-Landel-Ferry (WLF)

mechanism, 197Wine

anthocyanins in, 223as an antioxidant, 325antioxidants in, 223bouquet of, 8casks, decontamination of, 276enzyme treatment of, 238fermentation of, 302flavoring from, 233grape processing for, 302honey in, 20, 109in marinades, 273precipitates in, 283resveratrol in, 331

Index 367

sulfur dioxide in, 276Winter melon, 239WLF, 197WLF mechanism, 197Wood, 112Wood molasses, 102Wounds, healing of, 59Wrappings, biodegradable, 105,

112–113; see also Packaging

X

X-ray crystallography, 37X-ray diffraction, 37Xanthan gum, 85, 103, 106

emulsifier, 281for food texturization, 111in gluten-free dough, addition of,

157locust bean gum and, 282stabilizer, 281thickening agent, 281

Xanthates, syrups of, 103Xanthation, 103Xanthene, 228Xanthophylls

in animal tissues, 210canthaxanthin, see Canthaxanthincapsanthin, see Capsanthinchlorophyll and, 215cryptoxanthin, see Cryptoxanthinin egg yolk, 210formula for, 208lutein, see Luteinin paprika, 210in red pepper, 209, 210structure of, 206violaxanthin, see Violaxanthin

Xantine, 59Xenoestrogens, 326Xylans, 85, 103Xylem, 23Xylitol, 84, 94, 102, 108–109Xylose, 84, 102

Y

Yam, 107Yeast

alcohol dehydrogenase source, 249

aroma compounds from, 248bakers, 249generation of, 150hydroperoxide lyases in, 250lactone production, 247minerals in, 58prevention

benzoic acid, 278sorbic acid, 278

riboflavin in, 226water activity level, 44

Yersinia enterocolitica, 154, 297Yield stress, 185, 187–188, 194,

201–202Yogurt

calcium in, 52composition of, 13fermentation of, 302flavoring from, 233magnesium in, 52milk protein in, 14mycoproteins in, 154probiotics in, 266

Yolk, eggcomposition of, 13, 15–16emulsifying agent, 154

lipids in, 3, 16phosvitin in, 135serine in, 135xanthophylls in, 210

Young's modulus of elasticity, 199Yucca, 107

Z

Z-disks, 163Z line, 12Zeaxanthin, 210, 213–214Zebrinin, 222Zinc

in beef, 52bioavailability, 54–55, 302biological function of, 59in cheese, 52chlorophyll, reaction with, 216copper antagonism, 77dehalogenation using, 93in eggs, 52in fish, 52in fruits and vegetables, 69in honey, 52in liver, 52loss of, during processing, 69metallothioneins and, 72–73microelement, 54in oats, 52in oysters, 52in peas, 52in powered milk, 52for rancidity inhibition, 67RDA, 56in saccharide alcohols, 96in wheat, 52

Zygosaccharomyces, 108

Chemical and Functional Properties of Food Components

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