This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1. Dairy Scienceand TechnologySecond Edition 2006 by Taylor
& Francis Group, LLC
2. FOOD SCIENCE AND TECHNOLOGY A Series of Monographs,
Textbooks, and Reference BooksEditorial Advisory Board Gustavo V.
Barbosa-Cnovas Washington State UniversityPullmanP. Michael
Davidson University of TennesseeKnoxville Mark Dreher McNeil
Nutritionals, New Brunswick, NJRichard W. Hartel University of
WisconsinMadison Lekh R. Juneja Taiyo Kagaku Company, JapanMarcus
Karel Massachusetts Institute of TechnologyRonald G. Labbe
University of MassachusettsAmherstDaryl B. Lund University of
WisconsinMadison David B. Min The Ohio State University Leo M. L.
Nollet Hogeschool Gent, BelgiumSeppo Salminen University of Turku,
Finland James L. Steele University of WisconsinMadison John H.
Thorngate III Allied Domecq Technical Services, Napa, CAPieter
Walstra Wageningen University, The NetherlandsJohn R. Whitaker
University of CaliforniaDavisRickey Y. Yada University of Guelph,
Canada 76. Food Chemistry: Third Edition, edited by Owen R. Fennema
77. Handbook of Food Analysis: Volumes 1 and 2, edited by Leo M. L.
Nollet 78. Computerized Control Systems in the Food Industry,
edited by Gauri S. Mittal 79. Techniques for Analyzing Food Aroma,
edited by Ray Marsili 80. Food Proteins and Their Applications,
edited by Srinivasan Damodaran and Alain Paraf 81. Food Emulsions:
Third Edition, Revised and Expanded, edited by Stig E. Friberg and
Kre Larsson 82. Nonthermal Preservation of Foods, Gustavo V.
Barbosa-Cnovas, Usha R. Pothakamury, Enrique Palou, and Barry G.
Swanson 83. Milk and Dairy Product Technology, Edgar Spreer 84.
Applied Dairy Microbiology, edited by Elmer H. Marth and James L.
Steele 85. Lactic Acid Bacteria: Microbiology and Functional
Aspects, Second Edition, Revised and Expanded, edited by Seppo
Salminen and Atte von Wright 2006 by Taylor & Francis Group,
LLC
3. 86. Handbook of Vegetable Science and Technology:
Production, Composition, Storage, and Processing, edited by D. K.
Salunkhe and S. S. Kadam 87. Polysaccharide Association Structures
in Food, edited by Reginald H. Walter 88. Food Lipids: Chemistry,
Nutrition, and Biotechnology, edited by Casimir C. Akoh and David
B. Min 89. Spice Science and Technology, Kenji Hirasa and Mitsuo
Takemasa 90. Dairy Technology: Principles of Milk Properties and
Processes, P. Walstra, T. J. Geurts, A. Noomen, A. Jellema, and M.
A. J. S. van Boekel 91. Coloring of Food, Drugs, and Cosmetics,
Gisbert Ottersttter 92. Listeria, Listeriosis, and Food Safety:
Second Edition, Revised and Expanded, edited by Elliot T. Ryser and
Elmer H. Marth 93. Complex Carbohydrates in Foods, edited by Susan
Sungsoo Cho, Leon Prosky, and Mark Dreher 94. Handbook of Food
Preservation, edited by M. Shafiur Rahman 95. International Food
Safety Handbook: Science, International Regulation, and Control,
edited by Kees van der Heijden, Maged Younes, Lawrence Fishbein,
and Sanford Miller 96. Fatty Acids in Foods and Their Health
Implications: Second Edition, Revised and Expanded, edited by Ching
Kuang Chow 97. Seafood Enzymes: Utilization and Influence on
Postharvest Seafood Quality, edited by Norman F. Haard and Benjamin
K. Simpson 98. Safe Handling of Foods, edited by Jeffrey M. Farber
and Ewen C. D. Todd 99. Handbook of Cereal Science and Technology:
Second Edition, Revised and Expanded, edited by Karel Kulp and
Joseph G. Ponte, Jr. 100.Food Analysis by HPLC: Second Edition,
Revised and Expanded, edited by Leo M. L. Nollet 101.Surimi and
Surimi Seafood, edited by Jae W. Park 102.Drug Residues in Foods:
Pharmacology, Food Safety, and Analysis, Nickos A. Botsoglou and
Dimitrios J. Fletouris 103.Seafood and Freshwater Toxins:
Pharmacology, Physiology, and Detection, edited by Luis M. Botana
104.Handbook of Nutrition and Diet, Babasaheb B. Desai
105.Nondestructive Food Evaluation: Techniques to Analyze
Properties and Quality, edited by Sundaram Gunasekaran 106.Green
Tea: Health Benefits and Applications, Yukihiko Hara 107.Food
Processing Operations Modeling: Design and Analysis, edited by
Joseph Irudayaraj 108.Wine Microbiology: Science and Technology,
Claudio Delfini and Joseph V. Formica 109.Handbook of Microwave
Technology for Food Applications, edited by Ashim K. Datta and
Ramaswamy C. Anantheswaran 2006 by Taylor & Francis Group,
LLC
4. 110. Applied Dairy Microbiology: Second Edition, Revisedand
Expanded, edited by Elmer H. Marth and James L. Steele 111.
Transport Properties of Foods, George D. Saravacosand Zacharias B.
Maroulis 112. Alternative Sweeteners: Third Edition, Revised and
Expanded,edited by Lyn OBrien Nabors 113. Handbook of Dietary
Fiber, edited by Susan Sungsoo Choand Mark L. Dreher 114. Control
of Foodborne Microorganisms, edited by Vijay K. Junejaand John N.
Sofos 115. Flavor, Fragrance, and Odor Analysis, edited by Ray
Marsili 116. Food Additives: Second Edition, Revised and
Expanded,edited by A. Larry Branen, P. Michael Davidson, Seppo
Salminen,and John H. Thorngate, III 117. Food Lipids: Chemistry,
Nutrition, and Biotechnology: SecondEdition, Revised and Expanded,
edited by Casimir C. Akohand David B. Min 118. Food Protein
Analysis: Quantitative Effects on Processing,R. K. Owusu- Apenten
119. Handbook of Food Toxicology, S. S. Deshpande 120. Food Plant
Sanitation, edited by Y. H. Hui, Bernard L. Bruinsma,J. Richard
Gorham, Wai-Kit Nip, Phillip S. Tong,and Phil Ventresca 121.
Physical Chemistry of Foods, Pieter Walstra 122. Handbook of Food
Enzymology, edited by John R. Whitaker,Alphons G. J. Voragen, and
Dominic W. S. Wong 123. Postharvest Physiology and Pathology of
Vegetables: SecondEdition, Revised and Expanded, edited by Jerry A.
Bartzand Jeffrey K. Brecht 124. Characterization of Cereals and
Flours: Properties, Analysis,and Applications, edited by Gnl
Kaletunand Kenneth J. Breslauer 125. International Handbook of
Foodborne Pathogens, edited byMarianne D. Miliotis and Jeffrey W.
Bier 126. Food Process Design, Zacharias B. Maroulisand George D.
Saravacos 127. Handbook of Dough Fermentations, edited by Karel
Kulpand Klaus Lorenz 128. Extraction Optimization in Food
Engineering, edited byConstantina Tzia and George Liadakis 129.
Physical Properties of Food Preservation: Second Edition,Revised
and Expanded, Marcus Karel and Daryl B. Lund 130. Handbook of
Vegetable Preservation and Processing, edited byY. H. Hui, Sue
Ghazala, Dee M. Graham, K. D. Murrell,and Wai-Kit Nip 131. Handbook
of Flavor Characterization: Sensory Analysis,Chemistry, and
Physiology, edited by Kathryn Deiblerand Jeannine Delwiche 2006 by
Taylor & Francis Group, LLC
5. 132. Food Emulsions: Fourth Edition, Revised and Expanded,
edited by Stig E. Friberg, Kare Larsson, and Johan Sjoblom 133.
Handbook of Frozen Foods, edited by Y. H. Hui, Paul Cornillon,
Isabel Guerrero Legarret, Miang H. Lim, K. D. Murrell, and Wai-Kit
Nip 134. Handbook of Food and Beverage Fermentation Technology,
edited by Y. H. Hui, Lisbeth Meunier-Goddik, Ase Solvejg Hansen,
Jytte Josephsen, Wai-Kit Nip, Peggy S. Stanfield, and Fidel Toldr
135. Genetic Variation in Taste Sensitivity, edited by John
Prescott and Beverly J. Tepper 136. Industrialization of Indigenous
Fermented Foods: Second Edition, Revised and Expanded, edited by
Keith H. Steinkraus 137. Vitamin E: Food Chemistry, Composition,
and Analysis, Ronald Eitenmiller and Junsoo Lee 138. Handbook of
Food Analysis: Second Edition, Revised and Expanded, Volumes 1, 2,
and 3, edited by Leo M. L. Nollet 139. Lactic Acid Bacteria:
Microbiological and Functional Aspects: Third Edition, Revised and
Expanded, edited by Seppo Salminen, Atte von Wright, and Arthur
Ouwehand 140. Fat Crystal Networks, Alejandro G. Marangoni 141.
Novel Food Processing Technologies, edited by Gustavo V.
Barbosa-Cnovas, M. Soledad Tapia, and M. Pilar Cano 142. Surimi and
Surimi Seafood: Second Edition, edited by Jae W. Park 143. Food
Plant Design, edited by Antonio Lopez-Gomez; Gustavo V.
Barbosa-Cnovas 144. Engineering Properties of Foods: Third Edition,
edited by M. A. Rao, Syed S.H. Rizvi, and Ashim K. Datta 145.
Antimicrobials in Food: Third Edition, edited by P. Michael
Davidson, John N. Sofos, and A. L. Branen 146. Encapsulated and
Powdered Foods, edited by Charles Onwulata 147. Dairy Science and
Technology: Second Edition, Pieter Walstra, Jan T. M. Wouters and
Tom J. Geurts 2006 by Taylor & Francis Group, LLC
6. Dairy Scienceand Technology Second EditionPieter WalstraJan
T. M. WoutersTom J. Geurts Boca Raton London New York A CRC title,
part of the Taylor & Francis imprint, a member of the Taylor
& Francis Group, the academic division of T&F Informa plc.
2006 by Taylor & Francis Group, LLC
7. Published in 2006 byCRC PressTaylor & Francis Group6000
Broken Sound Parkway NW, Suite 300Boca Raton, FL 33487-2742 2006 by
Taylor & Francis Group, LLCCRC Press is an imprint of Taylor
& Francis GroupNo claim to original U.S. Government
worksPrinted in the United States of America on acid-free paper10 9
8 7 6 5 4 3 2 1International Standard Book Number-10: 0-8247-2763-0
(Hardcover)International Standard Book Number-13: 978-0-8247-2763-5
(Hardcover)Library of Congress Card Number 2005041830This book
contains information obtained from authentic and highly regarded
sources. Reprinted material isquoted with permission, and sources
are indicated. A wide variety of references are listed. Reasonable
effortshave been made to publish reliable data and information, but
the author and the publisher cannot assumeresponsibility for the
validity of all materials or for the consequences of their use.No
part of this book may be reprinted, reproduced, transmitted, or
utilized in any form by any electronic,mechanical, or other means,
now known or hereafter invented, including photocopying,
microfilming, andrecording, or in any information storage or
retrieval system, without written permission from the
publishers.For permission to photocopy or use material
electronically from this work, please access
www.copyright.com(http://www.copyright.com/) or contact the
Copyright Clearance Center, Inc. (CCC) 222 Rosewood Drive,Danvers,
MA 01923, 978-750-8400. CCC is a not-for-profit organization that
provides licenses and registrationfor a variety of users. For
organizations that have been granted a photocopy license by the
CCC, a separatesystem of payment has been arranged.Trademark
Notice: Product or corporate names may be trademarks or registered
trademarks, and are used onlyfor identification and explanation
without intent to infringe. Library of Congress
Cataloging-in-Publication Data Walstra, Pieter.Dairy science and
technology / Pieter Walstra, Jan T.M. Wouters, T.J. Geurts.--2nd
ed.p. cm. -- (Food science and technology ; 146)Rev. ed. of: Dairy
technology / P. Walstra [et al.]. c1999.Includes bibliographical
references.ISBN 0-8247-2763-0 (alk. paper)1. Dairy processing. 2.
Milk. 3. Dairy products. I. Wouters, Jan T. M. II. Geurts, T. J.
(Tom J.) III. Dairy technology. IV. Title. V. Food science and
technology (Taylor & Francis) ; 146. SF250.5.D385 2005
637.1--dc22 2005041830Visit the Taylor & Francis Web site
athttp://www.taylorandfrancis.comTaylor & Francis Groupand the
CRC Press Web site at is the Academic Division of T&F Informa
plc. http://www.crcpress.com 2006 by Taylor & Francis Group,
LLC
8. PrefaceThe primary theme of this book is the efcient
transformation of milk into high-quality products. This needs a
thorough understanding of the composition andproperties of milk,
and of the changes occurring in milk and its products
duringprocessing and storage. Moreover, knowledge of the factors
that determine prod-uct quality, including health aspects and shelf
life, is needed. Our emphasis is onthe principles of physical,
chemical, enzymatic, and microbial transformations.Detailed
manufacturing prescriptions and product specications are not given,
asthey are widely variable. Aimed at university food science and
technology majors, the book is writtenas a text, though it will
also be useful as a work of reference. It is assumed thatthe reader
is familiar with the rudiments of food chemistry, microbiology,
andengineering. Nevertheless, several basic aspects are discussed
for the benet ofreaders who may be insufciently acquainted with
these aspects. The book con-tains no references to the literature,
but suggestions for further reading are given. The book is made up
of four main parts. Part I, Milk, discusses the chem-istry,
physics, and microbiology of milk. Besides providing knowledge of
theproperties of milk itself, it forms the basis for understanding
what happens duringprocessing, handling and storage. Part II,
Processes, treats the main unit oper-ations applied in the
manufacture of milk products. These are discussed in somedetail,
especially the inuence of product and process variables on the
(interme-diate) product resulting. A few highly specic processes,
such as churning, arediscussed in product chapters. In Part III,
Products, integration of knowledgeof the raw material and of
processing is covered for the manufacture of severalproducts. The
number of dairy products made is huge; hence, some product
groupshave been selected because of their general importance or to
illustrate relevantaspects. Procedures needed to ensure consumer
safety, product quality, and pro-cessing efciency are also treated.
Part IV, Cheese, describes the processes andtransformations
(physical, biochemical, and microbial) in the manufacture
andripening of cheese. Here, the processes are so specic and the
interactions sointricate that a separate and integrated treatment
is needed. It starts with genericaspects and then discusses specic
groups of cheeses. Several important changes have been introduced
in this second edition. Thereasons were, rst, to improve the
didactic quality of the book and, second, tomake it more useful as
a reference source. More basic and general aspects arenow treated,
especially physicochemical and microbiological ones. Part I hasbeen
substantially enlarged, one reason why the title of the book has
beenbroadened. The nutritional aspects of milk components are now
included, andthose of some products are enlarged. A section on milk
formation has been added. 2006 by Taylor & Francis Group,
LLC
9. Naturally, the text has been updated. Moreover, several
parts have been reorga-nized or rewritten. Factual information has
been increased and partly moved toan Appendix.Pieter WalstraJan
Wouters Tom Geurts Wageningen, The Netherlands 2006 by Taylor &
Francis Group, LLC
10. AcknowledgmentsFirst, we want to stress that much of the
present book derives from the substantialcontributions that our
then-coauthors, Ad Noomen, Arend Jellema, and Tiny vanBoekel, made
to the rst edition. We are grateful that we could benet from
theirextensive expertise. Several people have provided information
and advice. Professors NormanOlson (University of Wisconsin,
Madison), Marie Paulsson (Lund University, Swe-den), and Zdenko
Puhan (Technical University, Zrich, Switzerland) scrutinized(parts
of) the rst edition and gave useful advice. We consulted several
colleaguesfrom our department, from NIZO Food Research (Ede, the
Netherlands), andfrom the Milk Control Station (Zutphen, the
Netherlands). We also receivedinformation from the following Dutch
companies: Campina (Zaltbommel andWageningen), Carlisle Process
Systems (formerly Stork, Gorredijk), FrieslandFoods (Deventer), and
Numico (Wageningen). We thank all of the people involvedfor their
cooperation and for the important information given. 2006 by Taylor
& Francis Group, LLC
11. ContentsPart IMilkChapter 1Milk: Main Characteristics
.....................................................31.1Composition
and
Structure..........................................................................3
1.1.1 Principal Components
.....................................................................3
1.1.2 Structural Elements
.........................................................................41.2
Milk
Formation............................................................................................71.3
Some Properties of Milk
...........................................................................111.4
Variability
..................................................................................................121.5
Changes......................................................................................................13Suggested
Literature
...........................................................................................16Chapter
2Milk
Components..................................................................172.1
Lactose.......................................................................................................172.1.1
Chemical
Properties.......................................................................172.1.2
Nutritional Aspects
........................................................................192.1.3
Physicochemical
Aspects...............................................................202.2
Salts............................................................................................................262.2.1
Composition and Distribution among the
Phases.........................262.2.2 Properties of the Salt
Solution
......................................................302.2.3
Colloidal Calcium Phosphate
........................................................322.2.4
Nutritional Aspects
........................................................................332.2.5
Changes in Salts
............................................................................332.3
Lipids
.........................................................................................................372.3.1
Constituent Fatty Acids
.................................................................382.3.2
Lipid Classes
.................................................................................422.3.3
Nutritional Aspects
........................................................................472.3.4
Autoxidation
..................................................................................482.3.5
Triglyceride
Crystallization...........................................................522.4
Proteins
......................................................................................................632.4.1
Chemistry of
Proteins....................................................................632.4.2
Survey of Milk Proteins
................................................................722.4.3
Serum
Proteins...............................................................................762.4.4
Casein
............................................................................................792.4.5
Nutritional Aspects
........................................................................83
2006 by Taylor & Francis Group, LLC
12.
2.5Enzymes.....................................................................................................84
2.5.1 Enzyme Activity
............................................................................85
2.5.2 Some Milk Enzymes
.....................................................................88
2.5.3 Inactivation
....................................................................................922.6
Other
Components.....................................................................................93
2.6.1 Natural
Components......................................................................93
2.6.2 Contaminants
.................................................................................95
2.6.3 Radionuclides
................................................................................972.7
Variability
..................................................................................................98
2.7.1 Sources of Variability
....................................................................98
2.7.2 Nature of the Variation
................................................................103
2.7.3 Some Important Variables
...........................................................106Suggested
Literature
.........................................................................................108Chapter
3Colloidal Particles of
Milk..................................................1093.1Basic
Aspects...........................................................................................109
3.1.1 Surface Phenomena
.....................................................................111
3.1.2 Colloidal Interactions
..................................................................118
3.1.3 Aggregation
.................................................................................122
3.1.4 Size Distributions
........................................................................1253.2
Fat
Globules.............................................................................................127
3.2.1 Properties
.....................................................................................127
3.2.2 Emulsion Stability
.......................................................................130
3.2.3 Interactions with Air Bubbles
.....................................................134 3.2.4
Creaming......................................................................................136
3.2.5 Lipolysis
......................................................................................1393.3
Casein Micelles
.......................................................................................140
3.3.1
Description...................................................................................141
3.3.2
Changes........................................................................................145
3.3.3 Colloidal
Stability........................................................................150
3.3.4 Gel Formation and Properties
.....................................................155Suggested
Literature
.........................................................................................157Chapter
4Milk
Properties....................................................................1594.1Solution
Properties
..................................................................................1594.2Acidity
.....................................................................................................1604.3Redox
Potential
.......................................................................................1624.4Flavor
.......................................................................................................1644.5Density.....................................................................................................1664.6Optical
Properties
....................................................................................1674.7Viscosity
..................................................................................................169
4.7.1 Some Fluid
Rheology..................................................................169
4.7.2 Liquid Milk Products
..................................................................173Suggested
Literature
.........................................................................................174
2006 by Taylor & Francis Group, LLC
13. Chapter 5Microbiology of Milk
.........................................................1755.1General
Aspects
.......................................................................................175
5.1.1 Microorganisms
...........................................................................175
5.1.2 Bacteria
........................................................................................176
5.1.3 Yeasts and
Molds.........................................................................179
5.1.4 Enumeration of
Microorganisms.................................................181
5.1.5 Growth
.........................................................................................182
5.1.6 Milk as a Substrate for Microorganisms
....................................1875.2 Undesirable
Microorganisms...................................................................190
5.2.1 Pathogenic Microorganisms
........................................................190 5.2.2
Spoilage Microorganisms
............................................................1945.3
Sources of Contamination
.......................................................................197
5.3.1 Microbial Ecology
.......................................................................197
5.3.2 Microorganisms Present in the Udder
........................................198 5.3.3 Contamination
during and after Milking ....................................1995.4
Hygienic Measures
..................................................................................201
5.4.1 Protection of the Consumer againstPathogenic Microorganisms
........................................................202 5.4.2
Measures against Spoilage
Organisms........................................202Suggested
Literature
.........................................................................................203Part
IIProcessesChapter 6General Aspects of
Processing............................................2076.1Introduction..............................................................................................2076.2Preservation
Methods
..............................................................................2096.3Quality
Assurance....................................................................................212
6.3.1 Concepts
......................................................................................212
6.3.2 Hazard Analysis/Critical Control Points
(HACCP)....................214 6.3.3 Quality Assurance of Raw Milk
.................................................2156.4 Milk
Storage and Transport
....................................................................217
6.4.1 Milk Collection and Reception
...................................................217 6.4.2 Milk
Storage
................................................................................218
6.4.3 Transport of Milk in the Dairy
...................................................2216.5
Standardizing
...........................................................................................222Suggested
Literature
.........................................................................................223Chapter
7Heat Treatment
....................................................................2257.1
Objectives
................................................................................................2257.2
Changes Caused by Heating
...................................................................226
2006 by Taylor & Francis Group, LLC
14. 7.2.1 Overview of Changes
..................................................................226
7.2.2 Reactions of
Proteins...................................................................229
7.2.3 Reactions of Lactose
...................................................................233
7.2.4 Heat Coagulation
.........................................................................2367.3
Heating Intensity
.....................................................................................242
7.3.1 Processes of Different Intensity
..................................................242 7.3.2 Kinetic
Aspects............................................................................245
7.3.3 Inactivation of Enzymes
..............................................................252
7.3.4
Thermobacteriology.....................................................................2557.4
Methods of
Heating.................................................................................263
7.4.1 Considerations
.............................................................................263
7.4.2
Equipment....................................................................................265
7.4.3 Heat Regeneration
.......................................................................270
7.4.4 Control
.........................................................................................271Suggested
Literature
.........................................................................................272Chapter
8Centrifugation......................................................................2738.1
Cream Separation
....................................................................................2738.2
Removal of Particles
...............................................................................276Suggested
Literature
.........................................................................................277Chapter
9Homogenization
..................................................................2799.1
Objectives
................................................................................................2799.2
Operation of the
Homogenizer................................................................2809.3
Effects of Turbulence
..............................................................................2829.4
Factors Affecting Fat Globule
Size.........................................................2859.5
Surface Layers
.........................................................................................2879.6
Colloidal
Stability....................................................................................2899.7
Homogenization Clusters
........................................................................2909.8
Creaming..................................................................................................2929.9
Other Effects of Homogenization
...........................................................2939.10
Other Ways of
Working...........................................................................295Suggested
Literature
.........................................................................................296Chapter
10 Concentration
Processes......................................................29710.1
General Aspects
.......................................................................................297
10.1.1 Concentration of Solutes
.............................................................297
10.1.2 Water
Activity..............................................................................300
10.1.3 Changes Caused by Concentrating
.............................................302 10.1.4 The Glassy
State..........................................................................303
10.1.5 Reaction Rates
.............................................................................30410.2
Evaporating..............................................................................................307
2006 by Taylor & Francis Group, LLC
15. 10.3 Drying: General Aspects
.........................................................................314
10.3.1 Objectives
....................................................................................314
10.3.2 Drying
Methods...........................................................................31610.4
Spray Drying
...........................................................................................318
10.4.1 Drier Conguration
.....................................................................318
10.4.2 Atomization
.................................................................................319
10.4.3 Change of State of the Drying
Air..............................................322 10.4.4 Changes
of State of the Drying Droplets
...................................326 10.4.5 Two-Stage
Drying........................................................................332Suggested
Literature
.........................................................................................335Chapter
11 Cooling and Freezing
..........................................................33711.1
Cooling
....................................................................................................33711.2
Freezing
...................................................................................................338Suggested
Literature
.........................................................................................340Chapter
12 Membrane Processes
...........................................................34112.1
General Aspects
.......................................................................................341
12.1.1 Types of Processes
......................................................................341
12.1.2 Efciency
.....................................................................................343
12.1.3 Technical
Operation.....................................................................34512.2
Ultraltration
...........................................................................................346
12.2.1 Composition of the
Retentate......................................................346
12.2.2 Permeate
Flux..............................................................................34912.3
Reverse
Osmosis......................................................................................35112.4
Desalting
..................................................................................................354Suggested
Literature
.........................................................................................356Chapter
13 Lactic Fermentations
...........................................................35713.1
Lactic Acid Bacteria
................................................................................357
13.1.1 Taxonomy
....................................................................................357
13.1.2 Metabolism
..................................................................................360
13.1.3 Genetics
.......................................................................................373
13.1.4 Bacteriocins
.................................................................................37413.2
Acid
Production.......................................................................................37413.3
Bacteriophages.........................................................................................377
13.3.1 Phage Composition and
Structure...............................................377 13.3.2
Phage Multiplication
...................................................................377
13.3.3 Phage Resistance
Mechanisms....................................................382
13.3.4 Inactivation
..................................................................................38313.4
Ecological
Aspects...................................................................................38413.5
Starters
.....................................................................................................385
2006 by Taylor & Francis Group, LLC
16. 13.5.1
Composition.................................................................................385
13.5.2 Properties
.....................................................................................388
13.5.3 Shifts in Flora
..............................................................................388
13.5.4 Traditional Starter Manufacture
..................................................390 13.5.5 Modern
Starter Manufacture
.......................................................394Suggested
Literature
.........................................................................................396Chapter
14 Fouling and Sanitizing
........................................................39914.1
Deposit Formation
...................................................................................39914.2
Cleaning...................................................................................................40514.3
Disinfection..............................................................................................408Suggested
Literature
.........................................................................................410Chapter
15 Packaging
............................................................................41115.1
Distribution Systems
...............................................................................41115.2
Packaging Materials
................................................................................41215.3
Filling Operation
.....................................................................................415Suggested
Literature
.........................................................................................417Part
IIIProductsChapter 16 Milk for Liquid
Consumption.............................................42116.1
Pasteurized
Milk......................................................................................421
16.1.1 Manufacture
.................................................................................422
16.1.2 Shelf Life
.....................................................................................427
16.1.3 Extended-Shelf-Life Milk
...........................................................43016.2
Sterilized Milk
.........................................................................................431
16.2.1
Description...................................................................................431
16.2.2 Methods of Manufacture
.............................................................432
16.2.3 Shelf Life
.....................................................................................43616.3
Reconstituted
Milks.................................................................................43716.4
Flavor
.......................................................................................................43716.5
Nutritive
Value.........................................................................................439
16.5.1 Modication of Composition
......................................................439 16.5.2
Loss of Nutrients
.........................................................................44016.6
Infant Formulas
.......................................................................................441
16.6.1 Human Milk
................................................................................441
16.6.2 Formula Composition and Manufacture
.....................................444Suggested Literature
.........................................................................................444
2006 by Taylor & Francis Group, LLC
17. Chapter 17 Cream Products
...................................................................44717.1
Sterilized Cream
......................................................................................447
17.1.1 Manufacture
.................................................................................448
17.1.2 Heat Stability
...............................................................................448
17.1.3 Stability in Coffee
.......................................................................448
17.1.4
Clustering.....................................................................................45017.2
Whipping Cream
.....................................................................................452
17.2.1 Desirable
Properties.....................................................................452
17.2.2 Manufacture
.................................................................................453
17.2.3 The Whipping Process
................................................................45417.3
Ice
Cream.................................................................................................458
17.3.1 Manufacture
.................................................................................459
17.3.2 Physical Structure: Formation and Stability
...............................462 17.3.3 Role of the Various
Components
................................................465Suggested
Literature
.........................................................................................466Chapter
18 Butter
...................................................................................46718.1
Description...............................................................................................46718.2
Manufacture
.............................................................................................468
18.2.1 Processing Scheme
......................................................................468
18.2.2 The Churning Process
.................................................................471
18.2.3 Working
.......................................................................................47418.3
Properties
.................................................................................................478
18.3.1
Microstructure..............................................................................478
18.3.2
Consistency..................................................................................480
18.3.3 Cold Storage
Defects...................................................................48518.4
Cultured Butter from Sweet Cream
........................................................48618.5
High-Fat
Products....................................................................................489
18.5.1 Anhydrous Milk Fat
....................................................................489
18.5.2 Modication of Milk
Fat.............................................................490
18.5.3 Recombined
Butter......................................................................492
18.5.4 Low-Fat Butter Products
.............................................................494Suggested
Literature
.........................................................................................495Chapter
19 Concentrated Milks
.............................................................49719.1
Evaporated Milk
......................................................................................497
19.1.1 Manufacture
.................................................................................497
19.1.2 Product Properties
.......................................................................501
19.1.3 Heat Stability
...............................................................................502
19.1.4
Creaming......................................................................................504
19.1.5 Age Thickening and Gelation
.....................................................50519.2
Sweetened Condensed Milk
....................................................................507
2006 by Taylor & Francis Group, LLC
18. 19.2.1 Manufacture
.................................................................................507
19.2.2 Keeping
Quality...........................................................................509Suggested
Literature
.........................................................................................512Chapter
20 Milk Powder
........................................................................51320.1
Objectives
................................................................................................51320.2
Manufacture
.............................................................................................51420.3
Hygienic Aspects
.....................................................................................517
20.3.1 Bacteria in the Original
Milk......................................................517
20.3.2 Growth during
Manufacture........................................................519
20.3.3 Incidental Contamination
............................................................521
20.3.4 Sampling and Checking
..............................................................52120.4
Powder Characteristics
............................................................................522
20.4.1 The
Particle..................................................................................522
20.4.2 Extractable
Fat.............................................................................522
20.4.3
Free-Flowingness.........................................................................523
20.4.4 Specic Volume
...........................................................................525
20.4.5
Dissolution...................................................................................526
20.4.6 WPN Index
..................................................................................529
20.4.7 Flavor
...........................................................................................530
20.4.8
Conclusions..................................................................................53120.5
Deterioration
............................................................................................53120.6
Other Types of Milk
Powder...................................................................535Suggested
Literature
.........................................................................................535Chapter
21 Protein Preparations
............................................................53721.1
Manufacture
.............................................................................................538
21.1.1 Casein
..........................................................................................539
21.1.2 Whey Protein
...............................................................................540
21.1.3 Other Products
.............................................................................54221.2
Functional
Properties...............................................................................543
21.2.1 Solution Properties
......................................................................544
21.2.2 Gels
..............................................................................................546
21.2.3 Emulsions
....................................................................................548
21.2.4
Foams...........................................................................................549Suggested
Literature
.........................................................................................550Chapter
22 Fermented Milks
.................................................................55122.1
General Aspects
.......................................................................................55122.2
Types of Fermented Milks
......................................................................552
22.2.1 Mesophilic
Fermentation.............................................................552
22.2.2 Thermophilic Fermentation
.........................................................553 2006
by Taylor & Francis Group, LLC
19. 22.2.3 YeastLactic Fermentation
..........................................................555
22.2.4 Molds in Lactic
Fermentation.....................................................55722.3
Cultured
Buttermilk.................................................................................55722.4
Yogurt
......................................................................................................558
22.4.1 The Yogurt
Bacteria.....................................................................559
22.4.2 Manufacture
.................................................................................562
22.4.3 Physical Properties
......................................................................565
22.4.4 Flavor Defects and Shelf Life
.....................................................56822.5
Nutritional Aspects
..................................................................................569
22.5.1
Composition.................................................................................569
22.5.2 Nutritional
Value..........................................................................570
22.5.3 Probiotics
.....................................................................................571
22.5.4 Prebiotics
.....................................................................................572Suggested
Literature
.........................................................................................573Part
IVCheeseChapter 23 Principles of Cheese Making
..............................................57723.1
Introduction..............................................................................................57723.2
Essential Process Steps
...........................................................................57923.3
Changes Occurring
..................................................................................580Suggested
Literature
.........................................................................................582Chapter
24 Cheese
Manufacture............................................................58324.1
Milk Properties and Pretreatment
...........................................................583
24.1.1 The Raw
Milk..............................................................................583
24.1.2 Milk Treatment
............................................................................58424.2
Starters
.....................................................................................................58624.3
Enzyme-Induced
Clotting........................................................................588
24.3.1 Enzymes Used
.............................................................................588
24.3.2 The Enzyme-Catalyzed Reaction
................................................590 24.3.3
Aggregation
.................................................................................591
24.3.4 Gel
Formation..............................................................................593
24.3.5 The Renneting Time
....................................................................594
24.3.6 Clotting of Heat-Treated Milk
....................................................59624.4 Curd
Making............................................................................................596
24.4.1 Clotting
........................................................................................597
24.4.2 Accumulation of Various Components
.......................................600 24.4.3 Concentrating
before
Clotting.....................................................601
24.4.4 Syneresis
......................................................................................603
24.4.5 Acid Production and
Washing.....................................................608
24.4.6 Separation of Curd and
Whey.....................................................610 2006
by Taylor & Francis Group, LLC
20. 24.5 Shaping and Pressing
..............................................................................61324.6
Salting
......................................................................................................615
24.6.1 Mass Transport during Salting
....................................................616 24.6.2
Important
Variables......................................................................622
24.6.3 Distribution of Salt and Water after Salting
...............................62424.7 Curing, Storage, and
Handling................................................................625
24.7.1 Temperature
.................................................................................626
24.7.2 Air Conditions
.............................................................................627
24.7.3 Rind Treatment
............................................................................627
24.7.4
Packaging.....................................................................................63024.8
Cheese Composition and Yield
...............................................................631
24.8.1 Variables Involved
.......................................................................632
24.8.2
Yield.............................................................................................636
24.8.3 Standardizing the Milk
................................................................638Suggested
Literature
.........................................................................................638Chapter
25 Cheese Ripening and Properties
.........................................64125.1 Lactic
Fermentation.................................................................................64125.2
Enzyme Sources
......................................................................................64225.3
Proteolysis................................................................................................644
25.3.1 Methods of Characterization
.......................................................644 25.3.2
Milk Proteinases
..........................................................................645
25.3.3 Clotting Enzymes
........................................................................646
25.3.4 Enzymes of Lactic Acid Bacteria
...............................................648 25.3.5 Enzymes
of Nonstarter Organisms
.............................................650 25.3.6 Interaction
between Enzyme Systems ........................................650
25.3.7 Ultraltration of Cheese
Milk.....................................................65125.4
Lipolysis
..................................................................................................65325.5
Development of
Flavor............................................................................654
25.5.1
Description...................................................................................654
25.5.2 Formation of Flavor Compounds
................................................65525.6 Development
of Texture
..........................................................................659
25.6.1
Structure.......................................................................................659
25.6.2
Consistency..................................................................................66125.7
Accelerated Ripening
..............................................................................66925.8
Nutritive Value and Safety
......................................................................672Suggested
Literature
.........................................................................................675Chapter
26 Microbial
Defects................................................................67726.1Coliform
Bacteria
....................................................................................67926.2Butyric
Acid Bacteria
..............................................................................68026.3Lactobacilli
..............................................................................................68326.4Heat-Resistant
Streptococci.....................................................................684
2006 by Taylor & Francis Group, LLC
21. 26.5 Propionic Acid Bacteria
..........................................................................68426.6
Organisms on the
Rind............................................................................68526.7
Other
Aspects...........................................................................................686Suggested
Literature
.........................................................................................686Chapter
27 Cheese Varieties
..................................................................68727.1
Overview..................................................................................................687
27.1.1 Variations in Manufacture
...........................................................688
27.1.2 Types of Cheese
..........................................................................69427.2
Fresh
Cheese............................................................................................696
27.2.1 Quarg
...........................................................................................697
27.2.2 Cottage Cheese
............................................................................69927.3
Gouda-Type Cheeses
...............................................................................702
27.3.1 Manufacture
.................................................................................702
27.3.2 Properties and
Defects.................................................................70927.4
Cheddar-Type Cheeses
............................................................................712
27.4.1 Manufacture
.................................................................................712
27.4.2 Properties
.....................................................................................71627.5
Swiss and Pasta-Filata Types
..................................................................718
27.5.1
Emmentaler..................................................................................719
27.5.2 Mozzarella
...................................................................................72227.6
Cheeses with a Specic Flora
.................................................................724
27.6.1 Soft Cheese with Surface Flora
..................................................725 27.6.2
Blue-Veined
Cheese.....................................................................73427.7
Processed
Cheese.....................................................................................737Suggested
Literature
.........................................................................................739Part
VAppendixAppendix A.1 Often-Used Symbols
...........................................................743A.2Abbreviations.......................................................................745A.3Conversion
Factors..............................................................746A.4Physical
Properties of Milk Fat
..........................................747A.5Amino Acid
Composition of Milk Proteins .......................748A.6Amino
Acid Sequences of Caseins.....................................750
2006 by Taylor & Francis Group, LLC
22. A.7Some Properties of Lactose
................................................754A.8Trace
Elements in Cows Milk
...........................................755A.9Physical
Properties of Milk and Milk Products .................756A.10 Mass
Density and Viscosity of Some MilkFractions
......................................................................................757A.11
Heat Transfer
.......................................................................758A.12
Data on Some Cheese Varieties
..........................................762 2006 by Taylor &
Francis Group, LLC
23. Part IMilk 2006 by Taylor & Francis Group, LLC
24. 1Milk: MainCharacteristicsMilk is dened as the secretion of
the mammary glands of mammals, its primarynatural function being
nutrition of the young. Milk of some animals, especiallycows,
buffaloes, goats and sheep, is also used for human consumption,
either assuch or in the form of a range of dairy products. In this
book, the word milk willbe used for the normal milk of healthy
cows, unless stated otherwise. Occasion-ally, a com-parison will be
made with human milk. This chapter is meant as a general
introduction. Nearly all that is mentioned with the exception of
parts of Section 1.2 is discussed in greater detail in
otherchapters. However, for readers new to the eld it is useful to
have some idea of theformation, composition, structure, and
properties of milk, as well as the variation including natural
variation and changes due to processing that can occur inthese
characteristics, before starting on the main text.1.1 COMPOSITION
AND STRUCTURE1.1.1 PRINCIPAL COMPONENTSA classication of the
principal constituents of milk is given in Table 1.1. Theprincipal
chemical components or groups of chemical components are those
presentin the largest quantities. Of course, the quantity (in
grams) is not paramount in allrespects. For example, vitamins are
important with respect to nutritive value; en-zymes are catalysts
of reactions; and some minor components contribute markedlyto the
taste of milk. More information on milk composition is given in
Table 1.3. Lactose or milk sugar is the distinctive carbohydrate of
milk. It is a disac-charide composed of glucose and galactose.
Lactose is a reducing sugar. The fat is largely made up of
triglycerides, constituting a very complicatedmixture. The
component fatty acids vary widely in chain length (2 to 20
carbonatoms) and in saturation (0 to 4 double bonds). Other lipids
that are present includephospholipids, cholesterol, free fatty
acids, monoglycerides, and diglycerides. About four fths of the
protein consists of casein, actually a mixture of fourproteins:
S1-, S2-, -, and -casein. The caseins are typical for milk and have
somerather specic properties: They are to some extent
phosphorylated and have littleor no secondary structure. The
remainder consists, for the most part, of the milkserum proteins,
the main one being -lactoglobulin. Moreover, milk contains
nume-rous minor proteins, including a wide range of enzymes. The
mineral substances primarily K, Na, Ca, Mg, Cl, and phosphate are
not equi-valent to the salts. Milk contains numerous other elements
in trace3 2006 by Taylor & Francis Group, LLC
25. 4 Milk: Main CharacteristicsTABLE 1.1Approximate
Composition of MilkAverage ContentRangea Average Content
inComponent in Milk (% w/w) (% w/w) Dry Matter (% w/w)Water87.1
85.388.7 Solids-not-fat8.97.910.0 Fat in dry matter31 2238 Lactose
4.63.85.3 36Fat 4.02.55.5 31Proteinb3.32.34.4 25casein2.61.73.5
20Mineral substances0.7 0.570.83 5.4Organic acids 0.170.120.21
1.3Miscellaneous 0.15 1.2Note: Typical for milks of lowland
breeds.a These values will rarely be exceeded, e.g., in 1 to 2% of
samples of separatemilkings of healthy individual cows, excluding
colostrum and milk drawn shortlybefore parturition.b Nonprotein
nitrogen compounds not included.quantities. The salts are only
partly ionized. The organic acids occur largely asions or as salts;
citrate is the principle one. Furthermore, milk has many
miscel-laneous components, often in trace amounts.The total content
of all substances except water is called the content of drymatter.
Furthermore, one distinguishes solids-not-fat and the content of
fat in thedry matter.The chemical composition of milk largely
determines its nutritional value; theextent to which microorganisms
can grow in it; its avor; and the chemicalreactions that can occur
in milk. The latter include reactions that cause off-avours.1.1.2
STRUCTURAL ELEMENTSStructure can be dened as the geometrical
distribution of the (chemical) compo-nents in a system. It may
imply, as it does in milk, that the liquid contains particles.This
can have important consequences for the properties of the system.
Forinstance, (1) chemical components are present in separate
compartments, whichcan greatly affect their reactivity; (2) the
presence of particles greatly affects somephysical properties, like
viscosity and optical appearance; (3) interaction forcesbetween
particles generally determine the physical stability of the system;
and (4)the separation of some components (fat and casein) is
relatively easy. Figure 1.1 shows the main structural elements of
milk. Of course, the gureis schematic and incomplete. Some
properties of the structural elements are given 2006 by Taylor
& Francis Group, LLC
26. 1.1 Composition and Structure5A5 MilkBPlasma 500 Fat
globulesFat MembraneC Serumglobule 50000CaseinmicellesFIGURE 1.1
Milk viewed at different magnications, showing the relative size of
struc-tural elements (A) Uniform liquid. However, the liquid is
turbid and thus cannot behomogeneous. (B) Spherical droplets,
consisting of fat. These globules oat in a liquid(plasma), which is
still turbid. (C) The plasma contains proteinaceous particles,
which arecasein micelles. The remaining liquid (serum) is still
opalescent, so it must contain otherparticles. The fat globules
have a thin outer layer (membrane) of different constitution.(From
H. Mulder and P. Walstra, The Milk Fat Globule, Pudoc, Wageningen,
1974.)in Table 1.2, again in a simplied form; the numerical data
mentioned are meantonly to dene orders of magnitude. The table
clearly shows that aspects of colloidchemistry are essential for
understanding the properties of milk and the manychanges that can
occur in it. All particles exhibit Brownian motion; they have
anelectrostatic charge, which is negative at the pH of milk. Their
total surface areais large. Fat globules. To a certain extent, milk
is an oil-in-water emulsion. But thefat globules are more
complicated than emulsion droplets. In particular, thesurface layer
or membrane of the fat globule is not an adsorption layer of one
2006 by Taylor & Francis Group, LLC
27. 6 Milk: Main CharacteristicsTABLE 1.2Properties of the Main
Structural Elements of Milk Milk Plasma SerumGlobularLipoprotein
Fat GlobulesCasein MicellesProteinsParticlesMain components
FatCasein, water, Serum proteinLipids, proteinssaltsTo be
considered as Emulsion Fine dispersionColloidalColloidal solution
dispersionContent 42.80.60.01 (% dry matter)Volume fraction 0.05
0.10.006104Particle diametera0.110 m20400 nm36 nm 10 nmNumber per
ml 1010 1014 1017 1014Surface area7004000050000100 (cm2/ml
milk)Density 9201100 1300 1100 (20C; kg m3)Visible withMicroscope
Ultramicroscope ElectronmicroscopeSeparable withMilk separator
High-speed Ultraltration UltraltrationcentrifugeDiffusion
rate0.00.10.30.60.4 (mm in 1h)aIsoelectric pH3.8 4.6 454Note:
Numerical values are approximate averages.a For comparison, most
molecules in solution are 0.4 to 1 nm diameter, and diffuse, say, 5
mmin 1 h. 1 mm = 103 m = 106 nm = 107 .single substance but
consists of many components; its structure is complicated.The dry
mass of the membrane is about 2.5% of that of the fat. A small part
ofthe lipids of milk is found outside the fat globules. At
temperatures below 35C,part of the fat in the globules can
crystallize. Milk minus fat globules is calledmilk plasma, i.e.,
the liquid in which the fat globules oat.Casein micelles consist of
water, protein, and salts. The protein is casein.Casein is present
as a caseinate, which means that it binds cations, primarilycalcium
and magnesium. The other salts in the micelles occur as a
calciumphosphate, varying somewhat in composition and also
containing a small amountof citrate. This is often called colloidal
phosphate. The whole may be
calledcalcium-caseinate/calcium-phosphate complex. The casein
micelles are notmicelles in the colloid-chemical sense but just
small particles. The micelles have 2006 by Taylor & Francis
Group, LLC
28. 1.2 Milk Formation 7an open structure and, accordingly,
contain much water, a few grams per gramof casein. Milk serum,
i.e., the liquid in which the micelles are dispersed, is milkminus
fat globules and casein micelles.Serum proteins are largely present
in milk in molecular form or as very smallaggregates.Lipoprotein
particles, sometimes called milk microsomes, vary in quantityand
shape. Presumably, they consist of remnants of mammary secretory
cellmembranes. Few denitive data on lipoprotein particles have been
published.Cells, i.e., leukocytes, are always present in milk. They
account for about0.01% of the volume of milk of healthy cows. Of
course, the cells contain allcytoplasmic components such as
enzymes. They are rich in catalase.Table 1.3 gives a survey of the
average composition and structure of milk.1.2 MILK FORMATIONMilk
components are for the most part formed in the mammary gland (the
udder)of a cow, from precursors that are the results of digestion.
Digestion. Mammals digest their food by the use of enzymes to
obtain simple,soluble, low-molar-mass components, especially
monosaccharides; small pep-tides and amino acids; and fatty acids
and monoglycerides. These are taken upin the blood, together with
other nutrients, such as various salts, glycerol, organicacids,
etc. The substances are transported to all the organs in the body,
includingthe mammary gland, to provide energy and building blocks
(precursors) formetabolism, including the synthesis of proteins,
lipids, etc. In ruminants like the cow, considerable predigestion
occurs by means ofmicrobial fermentation, which occurs for the most
part in the rst stomach orrumen. The latter may be considered as a
large and very complex bio-fermenter.It contains numerous bacteria
that can digest cellulose, thereby breaking downplant cell walls,
providing energy and liberating the cell contents. From
celluloseand other carbohydrates, acetic, propionic, butyric and
lactic acid are formed, whichare taken up in the blood. The
composition of the organic acid mixture dependson the composition
of the feed. Proteins are broken down into amino acids. Therumen
ora uses these to make proteins but can also synthesize amino acids
fromlow-molar-mass nitrogenous components. Further on in the
digestive tract themicrobes are digested, liberating amino acids.
Also, food lipids are hydrolyzed inthe rumen and partly metabolized
by the microorganisms. All these precursors canreach the mammary
gland. Milk Synthesis. The synthesis of milk components occurs for
the greaterpart in the secretory cells of the mammary gland. Figure
1.2 illustrates such acell. At the basal end precursors of milk
components are taken up from the blood,and at the apical end milk
components are secreted into the lumen. Proteins areformed in the
endoplasmic reticulum and transported to the Golgi vesicles,
inwhich most of the soluble milk components are collected. The
vesicles grow insize while being transported through the cell and
then open up to release theircontents in the lumen. Triglycerides
are synthesized in the cytoplasm, forming 2006 by Taylor &
Francis Group, LLC
29. TABLE 1.3Composition and Structure of Milka 8FAT GLOBULE
CASEIN MICELLE SERUM Water790 g Organic acidsProteinsProtein
citrate 1600 mg casein + Glycerides casein 26 g triglycerides 40 g
proteose peptone + Carbohydrates formate40 mg-lactoglobulin 3.2 g
diglycerides0.1 gSalts2g monoglycerides10 mg 850 mglactose46
gacetate30 mg-lactalbumin 1.2 gCa Fatty acids 60 mgphosphate1000
mgglucose70 mg lactate20 mgserum albumin 0.4 g Sterols 100 mg
citrate150 mg Carotenoids 0.3 mg K, Mg, Na others oxalate20
mgimmunoglobulins 0.8 g Vitamins A, D, E, KWater~80 g others 10
mgproteose peptone + Water 60 mgEnzymes
OthersMineralsotherslipaseplasmin Ca, bound 300 mg Gases Nonprotein
nitrogenous MEMBRANE Ca, ions 90 mg oxygen6 mg compounds water +Mg
70 mg nitrogen 16 mgpeptides + protein 700 mgLEUKOCYTEphospholipids
250 mg K 1500 mg Lipids amino acids50 mg cerebrosides30 mg
LIPOPROTEINNa450 mg glycerides +urea250 mg glycerides+ PARTICLE
fatty acids 15 mgCl1100 mgfatty acids20 mgammonia10 mgMany enzymes
streols 15 mg other lipids lipidsphosphate 1100 mgphospholipids 100
mgothers300 mg e.g., catalaseprotein enzymessulfate 100 mg
cerebrosides 10 mg Enzymes Nucleic acids alkaline phosphatase
enzymes Water xanthine oxidase water bicarbonate 100 mg sterols15
mgacid phosphatase Milk: Main Characteristics many others
othersperoxidase Cu4 g Fe100 gTrace elementsmany othersZn3 mg
Vitamins, e.g.Phosphoric esters~300 mgFe120 g riboavin 2 mg
OthersCu 20 g ascorbic acid20 mg many othersa Approximate average
quantities in 1 kg milk. Note: The water in the casein micelles
contains some small-molecule solutes. 2006 by Taylor & Francis
Group, LLC
30. 1.2 Milk Formation 9LUMEN Microvillus Golgi vesicle with
casein micelles Junctional complex Golgi apparatus
CytosolNascentfat globule Lysosome Mitochondrion Outer cell
membrane Nucleus
(plasmalemma)EndoplasmicRibosomesreticulumBasementmembrane5 mFIGURE
1.2 Stylized diagram of a mammary secretory cell. Below is the
basal part, ontop the apical part of the cell. The cell is bounded
by other secretory cells to form theglandular epithelium. See text
for further details. (From P. Walstra and R. Jenness,
DairyChemistry and Physics, Wiley, New York, 1984. With
permission.)small globules, which grow while they are transported
to the apical end of thecell. They become enrobed by the outer cell
membrane (or plasmalemma) whilebeing pinched off into the lumen.
This type of secretion is called merocrine,which means that the
cell remains intact. Table 1.4 gives some information about the
synthesis of specic components.Most are synthesized in the cell.
Others are taken up from the blood but, generally,not in the same
proportion as in the blood; see, especially, the salts. This
meansthat the cell membranes have mechanisms to reject, or allow
passage of, speciccomponents. Some substances, notably water and
small lipophilic molecules, can 2006 by Taylor & Francis Group,
LLC
31. TABLE 1.410Synthesis of Important Milk ComponentsMilk
Component Precursor in Blood Plasma Synthesis of
ComponentConcentration Concentration In theSpecic Specic forName(%
w/w) Name(% w/w) Secretory Cell?for Milk? the
Species?Water86Identical 91No NoNoLactose4.7 Glucosea0.05YesYes
NoProteinCaseins2.6 YesYes Yesb-lactoglobulin0.32 Amino acids
0.04YesYes Yes-lactalbumin0.12 YesYes YesLactoferrin 0.01
YesNoYesSerum albumin0.04Identical 3.2 No
NoYesImmunoglobulins0.07Most are identical1.5 No NoYesEnzymesTrace
Various Yesc Noc YesLipids Acetic acid 0.01 Triglycerides4 -Hydroxy
butyric acid 0.006 Partly Partly Acylglycerols
Phospholipids0.03Some lipids 0.3Milk: Main CharacteristicsCitric
Acid0.17Glucosea0.05YesNoNoMinerals Identical No NoNoCa 0.130.01Pd
0.090.01Na 0.040.34K0.150.03Cl 0.110.35a Glucose can also be formed
in the secretory cells from some amino acids.b All proteins are
species specic, but comparable proteins occur in the milk of all
ruminants.c Is not true for all enzymes.d In various phosphates.
2006 by Taylor & Francis Group, LLC
32. 1.2 Milk Formation11pass the cell more or less unhindered.
Some other components, such as serumalbumin and chlorides, can leak
from the blood into the milk by passing throughthe spaces between
secretory cells. Also, some leukocytes somehow reach thelumen.
Finally, cell remnants, such as part of the microvilli depicted in
Figure 1.2and tiny fragments of cytoplasm that occasionally adhere
to a fat globule, aresecreted and form the lipoprotein particles of
Table 1.2.Excretion. The glandular epithelium, consisting of layers
of secretory cells,form spherical bodies called alveoli. Each of
these has a central lumen into whichthe freshly formed milk is
secreted. From there, the milk can ow through smallducts into
larger and still larger ones until it reaches a cavity called the
cistern.From the cistern, the milk can be released via the teat. A
cow has four teats andhence four separate mammary glands, commonly
called (udder) quarters.Excretion of the milk does not happen
spontaneously. The alveoli have tocontract, which can be achieved
by the contraction of muscle tissue around thealveoli. Contraction
is induced by the hormone oxytocin. This is released intothe blood
by stimulation of the teats of the animal, be it by the suckling
youngor by the milker. The udder is not fully emptied.Lactation.
When a calf is born, lactation i.e., the formation and secretionof
milk starts. The rst secretion greatly differs in composition from
milk (seeSubsection 2.7.1.5). Within a few days the milk has become
normal and milk yieldincreases for some months, after which it
declines. The yield greatly varies amongcows and with the amount
and the quality of the feed taken by the cow. For milchcows,
milking is generally stopped after about 10 months, when yield has
becomequite low. The duration from parturition to leaving the cow
dry is called thelactation period, and the time elapsed after
parturition is the stage of lactation.1.3 SOME PROPERTIES OF
MILKMilk as a Solution. Milk is a dilute aqueous solution and
behaves accord-ingly. Because the dielectric constant is almost as
high as that of pure water, polarsubstances dissolve well in milk
and salts tend to dissociate (although this dis-sociation is not
complete). The ionic strength of the solution is about 0.073 M.
ThepH of milk is about 6.7 at room temperature. The viscosity is
low, about twice thatof water, which means that milk can readily be
mixed, even by convection currentsresulting from small temperature
uctuations. The dissolved substances give milkan osmotic pressure
of about 700 kPa (7 bar) and a freezing-point depressionclose to
0.53 K. The water activity is high, about 0.995. Milk density ( 20)
equalsabout 1029 kgm3 at 20C; it varies especially with fat
content.Milk as a Dispersion. Milk is also a dispersion; the
particles involved aresummarized in Table 1.2. This has several
consequences, such as milk beingwhite. The fat globules have a
membrane, which acts as a kind of barrier betweenthe plasma and the
core lipids. The membrane also protects the globules
againstcoalescence. The various particles can be separated from the
rest.The fat globules can be concentrated in a simple way by
creaming, whicheither occurs due to gravity or more efciently is
induced by centrifugation. 2006 by Taylor & Francis Group,
LLC
33. 12Milk: Main CharacteristicsIn this way cream and skim milk
are obtained. Skim milk is not identical to milkplasma, though
quite similar, because it still contains some small fat
globules.Cream can be churned, leading to butter and buttermilk;
the latter is rather similarin composition to skim milk.Likewise,
casein micelles can be concentrated and separated from milk,
forinstance, by membrane ltration. The solution passing through the
membrane isthen quite similar to milk serum. If the pores in the
membrane are very small, alsothe serum proteins are retained. When
adding rennet enzyme to milk, as is donein cheese making, the
casein micelles start to aggregate, forming a gel; whencutting the
gel into pieces, these contract, expelling whey. Whey is also
similarto milk serum but not quite, because it contains some of the
fat globules and partof the -casein split off by the enzyme. Casein
also aggregates and forms a gelwhen the pH of the milk is lowered
to about 4.6.Moreover, water can be removed from milk by
evaporation. Altogether, arange of liquid milk products of various
compositions can be made. Some exam-ples are given in Table
1.5.Flavor. The avor of fresh milk is fairly bland. The lactose
produces somesweetness and the salts some saltiness. Several small
molecules present in verysmall quantities also contribute to avor.
The fat globules are responsible for thecreaminess of whole
milk.Nutritional value. Milk is a complete food for the young calf,
and it canalso provide good nutrition to humans. It contains
virtually all nutrients, most ofthese in signicant quantities.
However, it is poor in iron and the vitamin Ccontent is not high.
It contains no antinutritional factors, but it lacks dietary
bre.Milk as a Substrate for Bacteria. Because it is rich in
nutrients, manymicroorganisms, especially bacteria, can grow in
milk. Not all bacteria that needsugar can grow in milk, some being
unable to metabolize lactose. Milk is poorin iron, which is an
essential nutrient for several bacteria, and contains
someantibacterial factors, such as immunoglobulins and some enzyme
systems. More-over, milk contains too much oxygen for strictly
anaerobic bacteria. Altogether,the growth of several bacteria is
more or less restricted in raw milk, but severalothers can
proliferate, especially at high ambient temperatures.1.4
VARIABILITYFreshly drawn milk varies in composition, structure, and
properties. Even within themilk from a single milking of one cow,
variation can occur. The fat globules varyin size and, to some
extent, in composition, and the same applies to casein micelles.
Natural Variation. The main factors responsible for natural
variation in milkare the following: Genetic factors: Breed and
individual. The stage of lactation: This can have a signicant
effect. Especially the milk obtained within 2 or 3 d after
parturition tends to have a very different composition; it is
called colostrum or beestings. 2006 by Taylor & Francis Group,
LLC