Frying Technology and Practices

Frying Technologyand Practices

Frying/FM/wBluesChanges 8/19/05 11:39 AM Page 1

Copyright 2004 by AOCS Press. All rights reserved.

Editors

Monoj K. GuptaMG Edible Oil Consulting International

Richardson, Texas

Kathleen WarnerNational Center for Agricultural Utilization Research

U.S. Department of AgriculturePeoria, Illinois

Pamela J. WhiteDepartment of Food Science

Iowa State UniversityAmes, Iowa

Champaign, Illinois

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Frying Technologyand Practices



AOCS Mission StatementTo be the global forum for professionals interested in lipids and related materials throughthe exchange of ideas, information science, and technology.

AOCS Books and Special Publications CommitteeM. Mossoba, chairperson, U.S. Food and Drug Administration, College Park, MarylandR. Adlof, USDA, ARS, NCAUR, Peoria, IllinoisJ. Endres, The Endres Group, Fort Wayne, IndianaT. Foglia, USDA, ARS, ERRC, Wyndmoor, PennsylvaniaL. Johnson, Iowa State University, Ames, IowaH. Knapp, Deaconess Billings Clinic, Billings, MontanaA. Sinclair, RMIT University, Melbourne, Victoria, AustraliaP. White, Iowa State University, Ames, IowaR. Wilson, USDA, REE, ARS, NPS, CPPVS, Beltsville, Maryland

Copyright © 2004 by AOCS Press. All rights reserved. No part of this book may be reproducedor transmitted in any form or by any means without written permission of the publisher.

The paper used in this book is acid-free and falls within the guidelines established to ensurepermanence and durability.

Library of Congress Cataloging-in-Publication DataFrying Technology and practices / editors, Monoj K. Gupta, Kathleen Warner, Pamela J.White

p. cm.Includes bibliographical references and index.ISBN 1-893997-31-6 (hardcover : alk. paper)

1. Frying. 2. Oils and fats, Edible. I. Gupta, Monoj K. II. Warner, Kathleen. III. White,Pamela J. 612′.01577--dc21

TX689.F79 2004 641.7′7--dc22

2004003927

Printed in the United States of America.08 07 06 05 04 5 4 3 2 1



P re f a c e

The frying of food products for culinary delight has been known to humans for cen-turies. Frying was one of the fastest ways to prepare foods. Most of the products werepan fried. The Chinese wok, Indian Kadai, and the Western frying pan were used forfrying food at home. These early frying pans eventually evolved into kettles and fin a l-ly into the sophisticated continuous fryers of today. Precise moisture- and texture-con-trolling devices have been developed to fry diverse types of food products. These foodsinclude sliced potatoes to make potato chips, sheeted and cut corn chips, extrudedproducts, pellets that expand to large volumes and shapes, as well as batter- c o a t e dproducts, ranging from chicken, to fish, to various vegetables.

Improved packaging techniques and packaging materials have increased theshelf life of various products, which has helped in their distribution. Partly dehy-drated food (also known as par-fried) products, such as French fries and fried chick-en, have reduced the cost and increased the production efficiency of food serviceand restaurant operations.

The processes of extraction and refining of vegetable oil have improved signif-icantly over the past three decades. During the same period, the oil-refining equip-ment and refining techniques have greatly improved. The oil processors are nowable to deliver refined vegetable oils with higher quality and stability to the foodindustry.

Numerous publications are available on frying that describe the effect of thefrying process on the oil quality and flavor stability of the fried product. These pub-lications constitute a tremendous source of information regarding the chemistry offrying oil and the fried food.

Overall frying equipment, oil quality, packaging, and the distribution systemhave improved greatly. However, there has been very little advancement in theprocess of training personnel in the frying operation to improve their knowledge ofthe properties of the oil and the impact of frying on its degradation. Of all compo-nents in the frying operation, the oil has the greatest impact on the flavor stability ofthe fried product, plant personnel are insufficiently trained to apply appropriatetechniques in a frying operation that would allow them to maintain the highest levelof oil quality in the process.

The personnel in a frying operation require a thorough understanding of thephysical and chemical properties of the frying oil and the effect of the frying processon oil quality. This knowledge would enable them to protect the oil against unduedamage, thus enabling them to avoid the operating techniques that can cause oildegradation in the frying process. An oil with a minimum amount of damage candeliver fried foods with high flavor stability.

A number of books and technical papers have been published on frying. Mostof them explain oil chemistry and degradation products of the oil. Some describecertain frying processes. This book is a unique compilation of theoretical discus-



sions of oil chemistry and the mechanism of oil breakdown as well as the practicalaspects related to frying. For example, this book includes: (i) basic frying-oil chem-istry and the techniques for the protection of the frying oil; (ii) frying techniquesinvolving coated foods; (iii) food safety and regulatory aspects related to frying andthe practical issues; and (iv) the proper techniques required for the day-to-day oper-ation of a frying process.

Kathleen Warner and Pamela J. White have been known for many years as fun-damental as well as applied researchers in the field of fats and oils. Ron Sassiela isa well-known scientist and author in the field of coated-food technology. DavidFirestone has been a renowned figure in the fats and oils area for many decades,Rick Stier is a food scientist who has devoted many years to understanding andassisting the frying industry. Finally, Monoj K. Gupta has had a long history in veg-etable-oil processing as well as years of experience in the frying industry. His famil-iarity with vegetable-oil processing allowed him to develop an in-depth understand-ing of the frying process. He was able to envision opportunities to improve the shelflife of fried products by applying oil-quality management techniques that areapplied in vegetable-oil processing to produce high-quality oil and to protect itagainst degradation. This accumulated experience along with specific techniques arediscussed in several chapters of this book, culminating in the suggestion of practi-cal solutions to numerous situations faced by frying operators and supervisors intheir industry.

Monoj K. GuptaKathleen WarnerPamela J. White



Contents

Chapter 1 Preface

Chapter 1 The Frying IndustryMonoj K. Gupta

Chapter 2 Chemical and Physical Reactions in Oil During FryingK. Warner

Chapter 3 Selection of Frying OilMonoj K. Gupta

Chapter 4 Role of Antioxidants and Polymerization Inhibitors inProtecting Frying OilsKathleen Warner, Caiping Su, and Pamela J. White

Chapter 5 Procedures for Oil Handling in a Frying OperationMonoj K. Gupta

Chapter 6 The Effect of Oil Processing on Frying Oil StabilityMonoj K. Gupta

Chapter 7 Critical Factors in the Selection of an Industrial FryerMonoj K. Gupta, Russ Grant, and Richard F. Stier

Chapter 8 Critical Elements in the Selection and Operationof Restaurant FryersMonoj K. Gupta

Chapter 9 Technology of Coating and Frying Food ProductsRonald J. Sasiela

Chapter 10 Fried Foods and Their Interaction with PackagingKenneth S. Marsh

Chapter 11 Toxicology of Frying Fats and OilsRichard F. Stier

Chapter 12 Regulatory Requirements for the Frying IndustryDavid Firestone



Chapter 1

The Frying Industry

Monoj K. Gupta

MG Edible Oil Consulting International, 9 Lundy’s Lane, Richardson, TX 75080

Introduction: Historical BackgroundMankind has consumed fried food for centuries. Long ago, fried foods were pre-pared and consumed by the family at meal times or at gatherings with friends.Today, fried foods can be purchased in various forms. Shelf-stable packaged saltysnack food has become common in every country. Fried foods are also served inrestaurants, by food services, and at home. In the United States, nearly 2 billionpounds of oil is used annually for frying salty snack foods. The French fry manu-facturers, breaded chicken and fish processors, as well as the restaurants and foodservices use several billion pounds of oil annually for frying. Freshly fried donuts,although not a salty snack, are popular as a snack or breakfast item.

Fried salty snack food is a source of culinary delight throughout the world.The advanced countries in the West can provide some documents showing the ori-gins of certain types of snack foods. Countries with old cultures and traditionshave had snack foods for centuries but do not have any formal documentationshowing when or how these products were introduced. For example, the people ofIndia have consumed popped corn kernels for centuries. The corn was popped in abed of hot sand. The people of the Indian subcontinent have used several othersalty snack foods for centuries. These snack foods include nuts, grains, leguminousproducts, and extruded grains. Fried wafers were served on all social occasions inIndia. However, there are no documents showing the dates of origin for any ofthese products. The original inhabitants of North, Central and South America con-sumed fire-roasted corn and other vegetables. People in the Orient also have theirindigenous snack foods but no historical data can be obtained to establish theirsource and the date of origin.

United States of America. Probably the most documented snack food develop-ment can be traced in the United States. According to information recorded in theHistory of Snacks (1), the modern potato chip began as a joke in 1853 in aSaratoga Springs resort in New York. The railroad magnate Commodore CorneliusVanderbilt was dining at the resort one evening when he sent the fried potatoesback to the kitchen because they were too thick. George Gum, the cook on duty,decided to thinly slice potatoes, deep fry and salt the fried chips. The chips werethin, crispy, and salty. What was meant to be a joke turned out to be the birth of

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modern day potato chips. The product was an instant hit. The Saratoga Chipsbecame a fad with the resort’s socialite patrons. Soon the recipe spread throughoutthe eastern region of the country.

In 1890, Cleveland entrepreneur, William Tappenden, started delivering pota-to chips that had been fried in his kitchen to the neighborhood stores. As the busi-ness grew, his barn became the first potato chip–producing factory in the country.Products were made in different parts of the country, and were delivered to thestores in sacks. It became apparent that this packaging could not protect the prod-uct well against moisture. In 1926, Laura Scudder first introduced potato chipbags. She and her employees used a hot iron to seal the edges of folded wax paper.They filled the formed bag and sealed the top in the same manner. Before thistime, the retailers had to dispense potato chips from cracker barrels or large glassdisplay jars. In 1933, the Dixie Wax Paper Company of Dallas introduced the first“pre-print” wax glassine bags, called “Dixie's Fresheen.” Nonbleeding ink wasused to print on one side of the paper.

The National Potato Chip Institute (NPCI) was founded in 1937. The firstchallenge of the NPCI was to educate both retailers and the consumers about pota-to chips and their uses. Some retailers believed that potato chips were similar tosoap chips and were to be used on washday. Other retailers suggested to the con-sumers that they should place the chips in a bowl, and add sugar and cream to thechips. In 1959, the National Potato Chip Institute (NPCI) changed its name toPotato Chip Institute International (PCII), to reflect the worldwide membership.Later in 1976, there was yet another name change to Potato Chip/Snack FoodAssociation (PC/SFA) to reflect the existence of snack foods other than potatochips. The headquarters of the PC/SFA also was moved from Cleveland to theWashington, DC area. In 1986, the PC/SFA again changed its name. It celebratedits Golden Anniversary with the new name Snack Food Association (SFA).

Today’s leader, Frito-Lay of Texas, has brought about the most dramatic evo-lution in the American snack food industry. It all started in 1932, with two individ-uals who were producing two entirely different products in two separate parts ofthe country. Mr. Elmer Doolin of San Antonio started the Fritos brand corn chips.The Frito company expanded and moved its headquarters to Dallas in 1933. Mr.Doolin came across a corn product that had a very unique flavor and texture. Hesought out the company owner and purchased the company with all the rights tothe secret process, formula, and the process equipment in 1938. The kitchen of Mr.Doolin’s mother was the first manufacturing plant for the Fritos brand corn chips.

Elsewhere, Mr. Herman W. Lay started to sell potato chips to the stores inNashville TN, the same year that Mr. Doolin started to sell his product in SanAntonio. Mr. Lay was delivering his potato chips to the stores using his 1929Model A Ford truck. By 1934, his company had established six delivery routes. In1938, through reorganization the company’s name was changed to H.W. Lay &Company. The company started to flourish under the new name and organization,selling Lay’s brand Potato Chips.



The industry suffered from a short supply of raw material and fuel from 1941to 1945, when United States was engaged in the Second World War. Businessexpansion and development were essentially halted during those years because offood and fuel rationing. In 1945, the Frito Company granted a license to the H.W.Lay Company to be the first exclusive franchise to manufacture and distributeFritos corn chips in the Southeast. A close relationship grew between the two com-panies. In September of 1961, just 29 years after they had begun their ventures, theFrito Company and H.W. Lay Company merged to become the Frito-LayCompany. Mr. Doolin died in 1958. He did not see the merger of the two compa-nies but he saw his Frito Company become a dominant snack food enterprisebefore his death. In 1965, Frito-Lay and Pepsi-Cola merged.

Today, Frito-Lay is the leading snack food–producing company in the world.The company sells numerous salty snack food products including include potatochips, corn chips, extruded products, nuts, and a variety of other products.

Salty snack foods in the United States have gone through significant changesduring the past two decades. In the 1980s, the presence of high saturated fatty acidsin animal fats was linked to coronary heart disease. This finding caused theremoval not only of animal fats but also palm oil, palm olein, and coconut oil fromU.S. snack foods. Palm oil, palmolein, and coconut oils were called “TropicalOils” and were labeled as “Bad for You Oils.” The name Tropical Oil was laterdropped because the FDA disallowed this form of labeling. Unfortunately, palmoil, palm olein, and coconut oils were replaced with hydrogenated soybean oil. Noquestions were raised about the increased saturated fatty acids in hydrogenatedsoybean oil.

In the late 1980s and early 1990s, there was a heavy promotion of “Low-Fat”and “Fat-Free” salty snack foods. Some low-fat baked products were also intro-duced with partial or total replacement of fat using fat-replacers available in themarket. The idea was to reduce the “fat calories” in the snack food. However, mostof these products exhibited poor consumer acceptance after the initial trial periodwas over. In reality, the U.S. Surgeon General’s report indicated that introductionof these products did not help the general public lose weight. There are probablymany reasons for the discrepancy between the low calories per serving and lack ofweight loss (or even weight gain) by the users of these low-fat and fat-free prod-ucts. Probably the most significant development in the fat-free salty snack foodarea was the introduction of Olestra, better known as Olean by its inventor, Procter& Gamble Company of Cincinnati, OH. Olestra is a sucrose polyester, in which thefatty acids can be derived from soybean, cottonseed, or other vegetable oils.Olestra is indigestible. It can fry snack food like regular vegetable oils, which iswhat made Olestra very attractive to the snack food manufacturers.

The FDA approved Olestra for making salty snack food in 1996. Frito-Layintroduced potato chips and tortilla chips fried in Olestra in the late 1990s and mar-keted the products under the brand name “WOW.” The brand expansion was quitepromising but it never reached the level of prominence in the snack food arena



because of some complaints from consumers of gastrointestinal discomfort anddiarrhea. Also, there were negative reports from the consumer advocates onOlestra. Fried salty snack foods are considered to be an indulgence food and areconsumed for pleasure. Most of the low-fat and no-fat products are lacking in fla-vor, texture, and mouth-feel attributes compared with products fried in oils.Consumers began to move away from the low-fat and no-fat products after havingconsumed them for a period of time. It seems that the majority of the salty snackfood users still prefer the taste of the full-fat products.

United Kingdom. Potato chips are one of the most popular and oldest savorysnacks sold in the UK. It is believed that Sir Walter Raleigh and Sir Francis Drakebrought potatoes to England from Peru in 1570. Soon the crop expanded into vari-ous parts of Europe, and by the end of the 18th century, potatoes were availablealmost everywhere on the European continent. A man named Frank Smith startedhis potato chip plant and sold the product in the early 1900s. The chips were soldin bags made of grease-proof paper.

Germany. Frank Flessner and his wife Ella started their Stateside Potato ChipCompany in Germany in 1951. The chips were made at home, packaged in glassinebags, and delivered to the U.S. Army base in Germany. U.S. soldiers were his primaryclients. By 1961, the company had established two manufacturing plants. Flessnerconvened a meeting in Frankfurt, Germany among Flessner, Harvey Noss (USA),David Sword (UK), and John Zweifel (Switzerland). This marked the beginning ofsemiannual meetings whose participants would eventually form the European SnackFood Association (ESA). Both ASA and ESA provide numerous valuable services tothe members of the respective Associations including information on legislative, eco-nomic, technical, and political issues related to the snack food industry.

Other Cultures and Regions. The history of the snack-food industry or of itsproducts is difficult to obtain in other countries because of the lack of documentedinformation. For example, Indians consume at least 300 different varieties of saltysnacks that are fried in vegetable oils. These products contain grains, pounded rice,nuts, vegetables, raisins, legumes, coconut, and seasoning to suit the palates of thepeople in the various parts of the country. Although these products have been usedfor centuries, no one can determine the date or the place of origin of most of theseproducts. This market has advanced from a cottage industry to the manufacturingsector in the past three decades. A large number of these products are exported tothe United Kingdom, the United States, Canada, and many European countries.

The salty snack food industry is now entering into the area of “Natural” and tosome degree “Organic” products that are being fried in nonhydrogenated vegetableoils. This sector is expected to grow rapidly. However, the limiting factors are avail-ability and cost of the ingredients. This situation is not expected to improve in the nearfuture, although the demand for this category of product has already increased.



Major Categories of Salty Snack Foods in the United States

Potato chips, the number one salty snack food in the United States, are celebratingtheir 150th year. The growth, flavor categories, and presentation of the product havegone through several revolutionary changes. The process has evolved from the kitchenfryer to the most modern automated continuous fryers. The packaging has changedfrom paper sack to glassine paper bags to the metallized film packaging with nitrogenflush for better shelf life. In 2001, potato chips sales in the United States were estimat-ed at 1.848 billion pounds, with approximate sales of $6.039 billion.

Tortilla chips were the next biggest sellers, with ~1.5 billion pounds and anestimated revenue of $4.1 billion in the United States in 2001. Table 1.1 lists thepredominant salty snack foods sold in the United States in 2001 and 2000.

Sales of potato chips, the number one salty snack food product in the UnitedStates, have grown at an annual rate of 3–4%. The product is sold in the countrythrough various channels as listed in Table 1.2. Table 1.3 lists the top 20 brands ofpotato chips in the United States and their sales figures for the year 2001. The fat-free category showed a significant decline in sales in 2001 compared with previousyears. This decline occurred in part because of reduced interest in the niche marketas well as the negative reports on Olestra by various consumer advocates.

TABLE 1.1 Year 2001 and 2000 Salty Snack Food Sales in the United Statesa,b

Sales Change Volume ChangeSegment (million $) (%) (million lbs) (%)

Potato chips2001 6039.2 +7.0 1848.6 +3.02000 4955.3 +5.7 1610.8 +4.7

Tortilla/Tostada chips2001 4148.2 +5.0 1501.9 +1.32000 3950.7 +5.4 1483.2 +3.6

Corn snacks2001 933.7 +2.1 279.1 –0.32000 914.5 +7.9 280.0 +2.8

Pretzels2001 1204.1 +0.9 580.1 –1.12000 1193.4 –2.2 586.3 +3.1

Snack nuts2001 1839.6 +1.5 515.9 +2.32000 1812.4 +7.7 503.9 +4.2

Microwave popcorn2001 1273.3 +2.2 453.9 +1.32000 1245.9 +7.7 448.1 +5.5

Ready-to-eat popcorn2001 466.9 –4.8 124.5 –5.12000 490.4 –0.5 130.9 –0.5

Continued



Tortilla chips are the second largest category of salty snack food sold in theUnited States as shown in Table 1.1. In 2001, the sales of tortilla chips in the coun-try was $4.148 billion, with an average growth of 5%. Like potato chips, tortillachips are also sold in the United States through various channels as listed in Table1.4. Table 1.5 lists the top 20 brands of tortilla chips in the United States. As withpotato chips, fat-free tortilla chips showed a significant loss in sales volume.

The snack food business has grown from a $13.8 billion industry in 1992 to$21.8 billion in 2001. Table 1.6 lists snack food sales chronologically for the pastdecade. The volume growth for the snack food industry has been 3–4%, with a few

TABLE 1.1 (Cont.)

Sales Change Volume ChangeSegment (million $) (%) (million lbs) (%)

Unpopped popcorn2001 78.1 –2.8 87.1 –3.92000 80.3 +0.6 90.6 –1.4

Cheese snacks2001 1027.1 +3.7 332.6 +2.52000 990.4 +7.7 324.2 +4.4

Pumpkin/Sunflower seeds2001 138.3 +5.5 52.4 +2.42000 131.1 +15.7 51.2 +11.7

Meat snacks2001 2011.2 +15.6 139.5 +14.92000 1739.8 +31.7 121.4 +26.2

Pork rind2001 498.5 –2.6 83.7 +0.72000 511.8 +21.8 83.1 +24.9

Variety pack2001 345.9 –2.6 76.6 –11.82000 347.6 +3.1 86.8 +4.9

Others2001 1794.2 +3.5 392.4 –1.62000 2325,6 –0.4 597.5 –0.8

Total2001 21,798.3 +3.5 6468.3 +1.42000 20,689.2 +6.4 6398.0 +3.6

aSource: Reference 3, p-SI-5.bAccording to the Snack Food Association, the consumption of snack food in the United States, based on apopulation number of 272 million, for the year 2000 was as follows:

The U.S. consumed 1680 potato chips per person.The number of potato chips consumed in the U.S. was 451,024,000,000 (451 billion).The number of pounds of snack foods consumed per person was 23 lbs.Meat snacks posted the highest increase in sales with a >30% gain.The total snack sales worldwide were an estimated $55 billion (U.S. Commerce Department).According to the U.S. AgExporter (4), U.S. exports of savory snacks were $1.6 billion.



exceptionally high and low growth years. The revenue increase has been steadyexcept in 1995, when the snack food market lost both volume and net dollar sales.The general economy and the cost of ingredients were believed to be responsiblefor the low sales volume.

TABLE 1.2 Sales Channels for Potato Chips in the United Statesa

Product soldLocation (%)

Supermarket 43.1Grocery stores 10.0Mass merchandiser 8.1Warehouse club 2.5Drug store 2.6Convenience Store 15.6Vending machine 5.0Food service 4.7Other 8.3

aSource: Reference 3, p-SI-49.

TABLE 1.3Top 20 Brands of Potato Chips in the United States During 2001a

Volume Change $ Share Volume ChangeRank Brand (million $) (%) (%) (million lb) (%)

1 Lay’s 834.2 +2.2 29.9 266.3 –1.42 Ruffles 334.6 +1.0 12.0 92.5 –4.13 Wavy Lay's 290.3 +54.3 10.4 91.9 +48.94 Pringles 224.4 +7.4 8.0 67.5 +1.65 Private label 149.8 +3.7 5.4 68.0 +2.96 Utz 68.0 +8.5 2.4 21.8 +5.37 Wise 59.4 –1.5 2.1 19.9 –1.78 Ruffles Flavor Rush 56.6 –18.6 2.0 14.5 –16.79 Lay’s Bistro Gourmet 51.0 N/A 1.8 11.4 N/A

10 Ruffles WOW 50.2 –5.8 1.8 8.5 –19.611 Pringles Right Crisps 49.1 –13.8 1.8 13.4 –20.212 Herr 47.5 +10.0 1.7 15.9 +1.013 Jay’s 43.1 +3.7 1.5 14.3 +5.314 Cape Cod 42.8 +13.3 1.5 8.5 +12.715 Lay’s WOW 41.5 –10.6 1.5 6.9 –23.416 Old Dutch 37.1 +10.9 1.3 13.1 +8.917 Golden Flake 27.9 +1.6 1.0 9.0 +2.318 Pringles Fat Free 27.0 –14.5 1.0 5.5 –15.119 Pringles Cheesums 20.2 +7.6 0.7 5.9 +4.120 Mike-Sells 19.8 –0.9 0.7 6.5 –2.5aSource: Reference 3, p-SI-50.



Other Categories of Snack Foods

In addition to chips, popcorn and nuts, there are many different fried snack foodssold in almost every country. Some of these are made from extruded dough,whereas others are made from pellets. The products are generally fried at ≥190°C.

TABLE 1.4 Sales Channels for Tortilla Chips in the United Statesa

Product soldLocation (%)

Supermarket 40.1Grocery stores 12.8Mass merchandiser 7.5Warehouse club 3.9Drug store 1.9Convenience Store 13.5Vending machine 5.8Food service 4.7Other 9.8


TABLE 1.5Top 20 Brands of Tortilla Chips in the United States During 2001a

Volume Change $ Share Volume ChangeRank Brand (million $) (%) (%) (million lb) (%)

1 Doritos 709.9 +4.7 37.6 220.5 +2.72 Tostitos 594.5 –2.7 31.5 175.1 –7.13 Private Label 85.7 +4.5 4.5 45.6 +1.84 Santitas 68.7 +7.3 3.6 39.7 +8.75 Mission 47.9 +3.6 2.5 27.3 –1.66 Baked Tostitos 40.3 –19.9 2.1 9.8 28.77 Tostitos Scoops 36.6 N/A 1.9 9.2 N/A8 Doritos Extremes 29.3 N/A 1.5 8.6 N/A9 Tostitos WOW 24.1 9.6 1.3 4.3 20.8

10 Doritos WOW 19.6 10.0 1.0 3.3 21.311 Old Dutch 15.7 +4.0 0.8 6.4 +3.012 Tostitos Santa Fe Gold 12.3 +2172.0 0.6 3.5 +2204.513 Pardinos 11.7 38.5 0.6 4.5 42.914 Herr 9.7 +6.7 0.5 3.8 +3.915 Snyder's of Hanover 9.3 +4.5 0.5 4.7 5.216 Garden of Eatin Blue Chips 8.8 +43.5 0.5 2.0 +45.117 Utz 8.3 +9.4 0.4 3.4 +4.618 Daines 7.4 3.7 0.4 3.4 12.019 Guiltless Gourmet 7.0 +2.6 0.4 1.3 0.220 Chi Chi Fiesta 6.6 +7.0 0.3 2.8 +1.2aSource: Reference 3, p-SI-56.



The fried products are dusted with seasonings and packaged. This is one of thegrowing segments in the snack food area.

Types of Oil Used in Making Salty Snack Foods

It is interesting to note that the oils used in making salty snack foods follow the“rule of availability and cost.” For example, in the United States, potato chips werefried in liquid cottonseed oil from the beginning. Other oils such as peanut andcorn, were also used. The potato chips fried in cottonseed oil became the GoldStandard for potato chips in the United States because of the taste of the productand the availability of the oil in the country. However, as the supply of cottonseedoil began to fall in recent years and that of corn oil began to rise at a moderateprice increase, the snack food industry switched over to corn oil. Sesame seed oiland sunflower oils have been traditionally used more commonly in Mexico to frysnack foods because the consumers like the taste of the products fried in these oils.However, the supply of partially hydrogenated soybean oil and palmolein atreduced cost prompted many snack food processors to switch over to these oils.People in India and China like food fried in peanut oil. Here the people have start-ed to use palmolein, palm oil, and other less costly oils to remain profitable in thebusiness. In many African and South American countries, almost any indigenousoil is used for frying. Malaysians use palm and palmolein for frying. ThePhilippinos and South Indians have used coconut oil for frying and cooking foodsfor centuries, simply because these oils have been available in the region.

In today’s snack food industry, the frying oil is chosen on the basis of the fol-lowing criteria: (i) product flavor; (ii) texture; (iii) mouth-feel; (iv) aftertaste; (v)product shelf life; (vi) availability; (vii) cost; and (viii) nutritional requirements.The snack food companies in the advanced countries use the first four criteria list-ed above to determine the acceptability of any oil for a given product. Items (v)–

TABLE 1.6 Snack Food Sales from 1992 to 2001a

Sales Growth Volume GrowthYear (billion $) (%) (billion lbs) (%)

2001 21.80 +5.1 6.47 +3.32000 20.69 +6.3 6.38 +3.31999 19.38 +6.2 6.17 +4.41998 18.17 +7.3 5.90 +2.21997 16.84 +8.5 5.77 +2.81996 15.41 +2.1 5.61 +1.31995 15.09 +0.3 5.54 –2.71994 15.05 +2.6 5.69 +3.01993 14.66 +5.9 5.52 +6.21992 13.80 +2.7 5.18 +5.0




(vii) are related to the company’s profitability. The last item is becoming more impor-tant in affluent countries in which consumers are able to pay the high price for theproduct fried in the so-called “healthful oils” that are low in saturated fats and are nothydrogenated. The prime examples are high oleic sunflower, high oleic canola, mid-oleic canola, mid-oleic sunflower (NuSun), and low-linolenic canola oils.

For the most part, even in countries such as the United States, the cost andavailability of oil are very critical for the sustenance of a snack food manufacturer.The reason is that there is a huge price gap between the more abundant oils such aspalmolein or soybean compared with high-oleic sunflower, NuSun (mid-oleic sun-flower), or high oleic safflower oils.

Soybeans, the largest source of vegetable oil in the world, are grown predomi-nantly in the United States, Argentina, and Brazil. Some other countries, such asIndia and China, also produce soybeans. Palm oil is the second largest source ofvegetable oil in the world. Worldwide, palm oil production is growing at a muchfaster rate than is soybean oil. Malaysia and Indonesia are the principal growers ofpalm oil. Palm oil is also produced in Central America, South America, Africa, andIndia. Canola (low erucic acid rapeseed), the third largest oilseed crop in the world,grows mainly in Canada and Europe. In addition to soybeans, China and India alsoproduce mentionable quantities of low erucic acid rapeseeds.

Sunflower is the fourth largest oilseed crop growing primarily in the formerSoviet Union, the United States, Argentina, Canada, and Europe. Other countries suchas South Africa and India also produce sunflower seeds for crushing. Table 1.7 liststhe latest world oilseed and oil production figures (2). Palmolein is used for fryingsalty snack food in almost every country except the United States. Cottonseed, corn,partially hydrogenated soybean, canola and sunflower oils are used in the UnitedStates for frying. In addition, small amounts of liquid canola, high-oleic sunflower andhigh-oleic safflower and NuSun oils are also used for frying snack foods in the U.S.

A review of the data in Table 1.7 shows that soybean oil is the world leader involume, followed by palm oil. However, in the salty snack food area, palmoleinand palm oil are used in more countries than soybean oil. Soybean oil is used heav-ily in baked foods. Cottonseed, sunflower, and peanut oils are produced in muchsmaller volumes and are generally consumed locally by the producing countries.

Evolution of the Frying Industry into Diverse Products

The frying industry has evolved significantly from the early days of chips. The fry-ers have become larger and more sophisticated in terms of product-feed, internalconstruction, oil temperature control, and distribution. Efforts have been made toreduce the volume of oil in the frying system to reduce the oil turnover time, thuspreserving the quality of the oil.

Batch fryers have been traditionally used to produce smaller volumes andharder texture in the fried chips. New continuous fryers have successfully duplicat-ed the harder texture of the kettle-fried chips, but at a much higher production rate.



Continuous fryers with a very specialized design of the frying bed have been intro-duced to fry preformed chips with a very low oil turnover time. Normally, theseproducts require a very short fry time.

Par-fried products, such as French fries, potato nuggets, chicken, or chickenfried steaks, are all par-fried products that are frozen immediately after frying andstored at –5 to –10°F. The product is distributed in freezer trucks. These productsare fried directly from “Freezer to Fryer” without any thawing and served immedi-ately in restaurants, through food services, and even at home. These products havethe great advantage of convenience and reduced cost. Products, such as par-friedFrench fries, chicken, and coated vegetables require shortening with a fairly highlevel of solids, which can be achieved through the standard hydrogenation processas it is done in the United States and several other countries. Batter-coated fish fil-lets are fried in either lightly hydrogenated oil or nonhydrogenated oil. The storagetemperature of –5 to –10°F helps protect the oil from rapid oxidation. This allowsthe food processors to use nonhydrogenated oils.

Three countries, the United States, Canada, and the Netherlands, are the majorproducers and exporters of frozen French fries. According to the Department ofCommerce, the U.S. Census Bureau, Foreign Trade Statistics, the United Statesexported nearly $316 million worth of frozen French fries in 2002. The export sta-tistics on frozen French fries for the past 6 years are listed in Table 1.8. Other par-fried frozen products include fish sticks, breaded shrimp, and par fried chicken asmentioned above. Table 1.9 lists the production and sales figures of fish sticks andbreaded shrimp from 1992 to 2001.

An alternative shortening for French fries or heavy-duty industrial frying canbe made v i a fractionation of palm oil and/or the interesterification process. Thisapproach has been applied successfully in several countries outside of NorthAmerica. These shortenings have higher amounts of palmitic and stearic acids than

TABLE 1.7 World Production Figures of the Major Oilseeds and Oilsa

Seeds Seeds Oils Oilsproduced produced produced produced2001/02 2000/01 2001/02 2000/01

Type of oil (million metric tons)

Soybean 184.21 175.20 29.37 27.05Palm — — 24.73 23.83Canola 37.47 37.14 13.51 13.95Sunflower 23.11 24.41 7.38 8.67Cottonseed 36.43 37.27 4.27 3.94Corn — — 1.11 1.09Peanut (groundnut) 24.11 22.94 5.46 4.87Coconut — — 3.19 3.51aSource: Reference 2.



the conventional hydrogenated shortening. However, if the t r a n s fatty acids areconsidered as fatty acids that behave like saturated fatty acids, the interesterifiedproduct contains a significantly lower amount of cholesterol-promoting fatty acids(combined saturated and t r a n s fatty acids). At present, these products are moreexpensive than the conventionally hydrogenated shortening. Possibly the concerno v e r t r a n s fatty acid might encourage the oil processing industry to look into amore economical way to produce interesterified shortening in the near future.

Pourable shortening, made from fully hydrogenated soybean (or canola) oiland lightly hydrogenated soybean or canola oil can provide the functionality of theheavy-duty frying shortening with a significantly lower trans fatty acid content.The trans fatty acid content of the pourable shortening can be reduced practicallyto zero by replacing partially hydrogenated soybean or canola oil with liquid oils,such as high-oleic sunflower, canola, safflower, or NuSun, corn or cottonseed,which are low in linolenic acid. This, of course, is a costlier proposition.

Comments on the Par-Frying Process

Although par-frying is a very attractive means for large-scale product distribution, thismethod will not produce a shelf-stable product if one attempts to par-fry the saltysnack product and distribute it to the large-scale snack food manufacturers, who in turnpull the product from the freezer, fry it, package, and distribute it. The product willdevelop a rancid flavor very rapidly. This is because the product in the par-fryingprocess absorbs less oil than in the full-frying process. This increases the oil turnovertime in the fryer, causing more damage to the oil and forms a higher concentration offree radicals in the oil. These free radicals are carried by the product and further cat-alyze the oxidative degradation of the oil in the product during storage.

TABLE 1.8 French Fries Production Data for the United States (1997–2001)

Year 1997 1998 1999 2000 2001

Volume (million lbs) 13,162.8 14,293.2 14,019 14,686 12,671

TABLE 1.9 Fish Sticks and Breaded Shrimp Production Data for the United States (1997–2001)

Fish sticks Breaded shrimp

Year (million lbs) (million $) (million lbs) (million $)

1997 31.37 64.30 117.47 334.941998 31.19 63.47 109.48 333.261999 29.49 63.40 119.15 351.892000 18.11 42.55 121.40 375.452001 19.51 41.53 152.19 539.63



There is always an exchange of oil between the food product and the fryingoil. A high concentration of free radicals in the fryer feed will result in higher con-centration of free radicals in the final fryer. This will accelerate the autoxidationprocess in the frying oil and reduce the shelf life of the re-fried product even whenit is packaged in nitrogen flushed and metallized bags. The product will have afraction of the shelf life of the same product fried under normal processes (not par-fried and refried).

Miscellaneous Fried Snacks

Donuts. Freshly fried donuts are very popular and used for breakfast or snack.These products are yeast-raised and fried in hydrogenated shortening to providethe taste. Interesterified shortening or that made from fractionated palm oil compo-nents can be used to fry donuts. Shelf-stable donuts are sold in the supermarkets,convenience stores, or gas stations. These products are generally baked, instead offried for longer shelf life.

Fried Nuts. Peanuts, cashews, sunflower seeds, and pumpkin seeds are sold in vari-ous forms, such as fried, dry roasted, coated, and glazed. In frying nuts, there is verylittle oil pick up by the product. This greatly increases the oil turnover time in a fryer.It will be clear from the discussions in the later chapters in this book that the type ofoil used in this process must have good oxidative stability to obtain good shelf life forthe product. Some manufacturers use nonhydrogenated canola oil in this process. Thehigh-linolenic acid in liquid canola oil does not provide good shelf life for the product.The liquid oil used in this process must have a low linolenic acid content, e.g., cotton-seed, corn, high-oleic sunflower, NuSun, low-linolenic canola, or high-oleic canola.Otherwise, one must use lightly hydrogenated canola or soybean oil to achieve goodshelf life. Stuffed vegetables, breaded vegetables, breaded shrimp, for example, arefried at the restaurants and served immediately. These products are generally fried inliquid oils or in pourable shortening.

Snack Food Market in Europe

As mentioned earlier, the snack food industry is quite large and extensive in Europe. Itis more difficult, however, to obtain comprehensive data on all types of snack foods inEuropean countries compared with the United States. The overall tonnage of potatochips and other snack foods and snack nuts are shown in Table 1.10. In comparisonwith the United States, per capita consumption of snack food in the European Union ismuch lower.

SummaryThe frying industry includes restaurant as well as restaurant operations. Restaurantsfry fresh foods or use a wide variety of par-fried products such as French fries, potatowedges, stuffed cheese sticks, potato skins, vegetable/cheese stuffing, or batter-coated



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vegetables. These products are fried and served immediately. The frozen par-friedproducts are fried at the restaurants without thawing. This helps the product to retaingood oil flavor as well as a crunchy crust.

Packaged salty snack food products require a long shelf life after frying andpackaging. This makes it essential to use an oil that has good oxidative and flavorstability. Par-fried foods use oils ranging from liquid [refined, bleached, deodor-ized (RBD)] oil to heavily hydrogenated shortening. Shelf-stable snack foods mustuse oils such as RBD oils with low or no linolenic acid, lightly hydrogenated soy-bean, or canola oil with a linolenic acid content of <2%.

The snack food industry must be constantly engaged in product innovation toretain the customer base. To achieve this objective, the industry has to maintainseveral core-brand products, such as salted potato chips, tortilla chips, or extrudedcorn products. In addition to the core brands, most companies have to maintain avariety of flavor extensions of the same core product base. Some of these productsmay even appear as novelty items.

Snack food companies have to constantly monitor acceptability of the prod-ucts and take appropriate action when the product sales begin to show a decline.Many companies use an “in-and-out” strategy for new line extension of any brand.This means that the companies introduce a novel flavor applied to the salted prod-uct for a limited time and then change to some other flavor. The flavors might evenbe rotated over a period of time depending on the consumer acceptance.

The consumer trend in Western countries and elsewhere has become dynamic.The favorite seasonings from India and the Far East have become popular inEurope. Several Mexican flavors such as jalapeno and salsa have become house-hold products in the United States. Some of the Western flavors, such as cheeseand salt and vinegar, are gaining approval in the Eastern markets.

References

1 . Snack Food Association web site, History of Snacks (http://www.sfa.org/news.html)(2002).

2 . Oil World (http://www.oilworld.de) (2002).3 . Snack Food & Wholesale Bakery (2002) Vol. 91. 4 . United States Department of Agriculture, Foreign Agricultural Service, U.S. AgExporter:

(http://www.fas.usda.gov) (2002).



http://www.sfa.org/

www.oilworld.de

http://www.fas.usda.gov/

Chapter 2

Chemical and Physical Reactions in Oil During Frying

K. Warner

National Center for Agricultural Utilization Research, 1815 North University Street, Peoria, IL61604

IntroductionFoods are fried to provide desirable color, texture, and flavor. These positiveattributes result from the many chemical and physical reactions that take place dur-ing frying. Without these reactions, fried foods would not be crisp and goldenbrown nor would they have that characteristic deep-fried flavor. Frying can alsonegatively affect frying oils and fried food. At high temperatures, the oil changessignificantly because of the many chemical and physical reactions that producedegradation compounds that affect the functional, sensory, and nutritional qualitiesof oils and fried food. In the early stages of frying, many of these changes are gen-erally required to provide the desirable characteristics typical of fried food.However, if the oil is allowed to deteriorate too much, then poor quality food andshortened fry life of the oil results. The physical and chemical changes that occurduring frying have been studied extensively to develop new frying oils, as well asadditives and handling procedures that help protect oils from extreme changes dur-ing frying. This chapter will describe the objectives of frying as well as the physi-cal and chemical changes in oils during frying. The positive and negative effects ofthese changes on the oils and fried food will be discussed. Practical methods tomeasure and inhibit oil deterioration will be described.

Objectives of Frying/Frying CyclesDuring deep fat frying, food is cooked by a direct transfer of heat from the hot oilto the cold food. The following processes occur in a well-maintained frying opera-tion. As food is added to the hot oil, the temperature of the oil decreases. Moisturefrom the food forms steam rapidly before subsiding as the water in the food dissi-pates. Steam bubbles are created in the oil. As frying continues, the food becomesbrown in color. Oil is absorbed into the food creating a crisp texture and deep-friedflavor in the food. As frying continues, oils deteriorate because of the frying condi-tions used, including high heat and moisture. Unless procedures are followed tokeep the oil from continuing to deteriorate, oils will degrade with increasing fryingas they proceed through the five stages in the life cycle of frying oil.

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The first stage of the cycle begins when the oil is fresh; however, oils in thisphase provide only a little browning and food may look undercooked. Deep-friedflavor intensity of the food is usually also low. Frying operations will often condi-tion the oils by using a blend of used and fresh oil at the start and then adding theused oil in the fryer at a certain rate along with some fresh oil. This conditions theoil rapidly and at no additional cost. The oil is at its optimum during the secondphase of the cycle. The food has a desirable golden brown color, it is fully cooked,and it has optimal deep-fried flavor. The small amount of oil deterioration that hastaken place by this point is actually required to provide the desirable deep-fried fla-vor in the food. Some oils will develop this characteristic deep-fried food flavormore quickly than others depending on the fatty acid composition of the oil. Forexample, cottonseed oil with high (50–55%) linoleic acid produces significantlyhigher intensities of fried food flavor in potato chips and French fried potatoes thando oils with low (10%) linoleic acid, such as high (80–90%) oleic oils. As fattyacids decompose at high temperature conditions, volatile degradation products pro-duce characteristic flavors. Some oxidation products, such as 2,4-decadienal,which is a break down product of linoleic acid, are important in the formation ofthe typical deep-fried flavor. One objective of the frying operation should be to tryto keep the oil at or near this stage of the cycle.

During the third part of the cycle, the oil continues to deteriorate; it is lower inquality than at the second stage, but is still acceptable. The fried food has a darkerbrown color and slight off-flavors may be detectable in the food at this phase. Bythe fourth stage, the oil has deteriorated even further and the oil quality is margin-al. The food has a dark brown color and moderate-to-strong off-flavors, and the oilhas begun to foam. Foaming will prevent the uniform cooking of the food, so thatthe fried food may not be fully cooked. By the time the oil reaches the fifth and lastcycle of its fry life, severe oil degradation is occurring. Foaming of the oil is amajor problem; the fried food has an unacceptable flavor and may not be fullycooked in the center because foaming has limited the direct contact of oil and food.Unless frying conditions are adjusted to maintain the oil in the second phase of thecycle, the oil will continue to deteriorate and may have to be discarded.

General Physical and Chemical Changes in the Frying Oil

Physical changes in oils that occur during heating and frying include increased vis-cosity, darkening in color, and increased foaming as frying time continues. At thesame time, the smoke point of the oil decreases. The frying operator may notnotice these effects until the oil has been used for prolonged periods of time.Although many frying operations rely simply on visual inspection of the oil todetermine that these negative effects are occurring, specific methods exist to mea-sure degradation processes and products quantitatively. For example, free fattyacids (FFA), carbonyl compounds, and high-molecular-weight products willincrease with increased frying time and can be measured chemically or by chro-

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matography. We will discuss later how these chemical compounds form and causethe physical changes in the oil. With the increase in these compounds, unsatura-tion, flavor quality, and the level of essential fatty acids (linoleic and linolenic)decreases concurrently and can be monitored by chromatography and by smellingthe frying oil. Some frying operations, such as restaurants, discard frying oils whenfrying causes excessive foaming of oil, when the oil tends to smoke excessively, orwhen the oil color darkens. In addition, abused oil increases in off-odors, such asacrid and burnt, and the fried food develops off-flavors as well. Procedures toinhibit frying oil deterioration will be discussed later in the chapter.

Physical Changes in Oils During Frying

During deep-frying, heat is transferred from the oil to the food, while water isevaporated from the food and oil is absorbed by the food (Fig. 2.1). Oil is alsoadsorbed onto the surface of the fried food. Factors, such as shape and size of thefood, and oil temperature, significantly affect these processes. Understanding thephysical processes of how food fries will help in optimizing the frying process toproduce good quality food and oil with longer fry life. Oil losses depend on thetype of fried food; for example, potatoes absorb more oil than does meat. The typeof frying vat also affects the oil stability. For example, oil heated in a pressuredeep-fat fryer deteriorates less than oil heated in an open vat. Physical changes in

Fig. 2.1. Physical and chemical reactions that occur during frying.



oils that occur during heating and frying include increased viscosity, color darken-ing, increased foaming, and decreased smoke point. Methods are available to mea-sure these physical changes quantitatively, but they are usually evaluated subjec-tively by visual inspection during practical frying. Although visual inspections areusually not used in research studies, they are often used by restaurants to determinewhen to discard frying oils. For example, a visual inspection could determine whenthere is excessive foaming of the oil, when the oil begins to smoke excessively, orwhen the oil color becomes too dark. Smelling the odors from the heating oil willalso identify deteriorated oil if the odors are sharp, pungent, and burnt. The rela-tionship of physical and chemical changes in oil is usually predictable because thedecomposition products from the chemical breakdown of the oil cause the physicalchanges in frying oil, such as increases in viscosity, color, and foaming.

Chemical Changes in Oils During Frying

The primary purpose of frying is to produce the distinctive fried food flavor andcrisp texture that are so desirable. A small number of chemical changes are neces-sary so that we have food with golden brown color and deep-fried flavor. As men-tioned previously, oil that has just been heated to frying temperature will not pro-duce the color and flavor typical of oil that has been conditioned or heated for sev-eral hours before frying. During deep-fat frying, various deteriorative chemicalprocesses, such as hydrolysis, oxidation, and polymerization, take place, and oilsdecompose to form volatile products and nonvolatile monomeric and polymericcompounds (Fig. 2.1). Chemical changes during frying increase FFA, carbonylcompounds, and polymeric compounds and decrease fatty acid unsaturation. Withcontinued heating and frying, these compounds further decompose until break-down products accumulate to levels that produce off-flavors and potentially toxiceffects, leaving the oil no longer suitable for frying. The amounts of these com-pounds that are formed and their chemical structures depend on many factors,including oil and food types, frying conditions, and oxygen availability. In addi-tion, these chemical reactions (hydrolysis, oxidation, and polymerization) are inter-related, producing a complex mixture of products.

Hydrolysis. As food is fried in oil, air and water cause chemical reactions. Waterand steam hydrolyze triacylglycerols producing monoacylglycerols and diacylglyc-erols, and eventually FFA and glycerol (Fig. 2.2). Glycerol will partially evaporatebecause it volatilizes at temperatures >150°C, and the reaction equilibrium is shift-ed in favor of other hydrolysis products. The extent of hydrolysis is a function ofvarious factors such as oil temperature, interface area between the oil and the aqueousphases, and amount of water and steam, because water will hydrolyze oil more quick-ly than steam. FFA and low-molecular-weight acidic products produced from oil oxi-dation enhance hydrolysis in the presence of steam during frying. Degradation prod-ucts from hydrolysis decrease the fry life of the oil. The level of the FFA is a measureof the degree of hydrolysis in the oil.



Oxidation. Oxygen is present in fresh oil and more is added to the frying oil whenfood is placed in the fryer. Heat, along with the addition of food, produces a seriesof reactions including the formation of free radicals, hydroperoxides, and conjugat-ed dienoic acids. The chemical reactions that occur during the oxidation processhelp to form both volatile and nonvolatile decomposition products. For example,ethyl linoleate oxidation leads to the formation of conjugated hydroperoxides,which can form noncycling long-chain products or they can cyclize and form per-oxide polymers. The oxidation mechanism in frying oils is similar to autoxidationat room temperature; however, the unstable primary oxidation products (hydroper-oxides) decompose rapidly at frying temperatures into secondary oxidation prod-ucts, such as aldehydes and ketones (Fig. 2.3). Secondary oxidation products thatare volatile contribute significantly to the odor of the oil and flavor of the friedfood. For example, unsaturated aldehydes, such as 2,4-decadienal, 2,4-nonadienal,2,4-octadienal, 2-heptenal, or 2-octenal, contribute to the desirable, characteristicdeep-fried flavor in oils during the second phase of the frying cycle. However, sat-urated and unsaturated aldehydes such as hexanal, heptanal, octanal, nonanal, and2-decenal, produce distinctive off-odors in the frying oil. The fruity and plastic off-odors typical of heated high-oleic oils can be attributed primarily to heptanal,octanal, nonanal, and 2-decenal. In deteriorated frying oil, acrolein is primarilyresponsible for the typical acrid odor. Analysis of primary oxidation products, suchas hydroperoxides, at any one point in the frying process provides little informa-tion because their formation and decomposition fluctuate rapidly and are not easilypredicted. During frying, oils with polyunsaturated fatty acids (PUFA), such as

Fig. 2.2. Hydrolysisprocess for frying oils.



linoleic acid, have a distinct induction period of hydroperoxide formation followedby a rapid increase in peroxide values, then a rapid destruction of peroxides.Measuring levels of PUFA, such as linoleic acid, can help determine the extent ofthermal oxidation. Oxidative degradation will produce oxidized triacylglycerolscontaining hydroperoxide-, epoxy-, hydroxy-, and keto-groups and dimeric fattyacids or dimeric triacylglycerols. Volatile degradation products can be saturatedand monounsaturated hydroxy-, aldehydic-, keto-, and dicarboxylic-acids, hydro-carbons, alcohols, aldehydes, ketones, and aromatic compounds.

Polymerization. Polymerization results in the formation of compounds with highmolecular weight and polarity (Fig. 2.4). Polymers can form from free radicals ortriacylglycerols by the Diels-Alder reaction. Cyclic fatty acids can form within onefatty acid; dimeric fatty acids can form between two fatty acids, either within orbetween triglycerides; and polymers with high molecular weight are obtained asthese molecules continue to cross-link. As polymerized products increase in thefrying oil, the viscosity of the oil also increases.

Causes of Oil Deterioration

Degradation of frying oil is affected by many factors, such as unsaturation of fattyacids, oil temperature, oxygen absorption, metals in the food and in the oil, andtype of food (Table 2.1). The type of food being fried alters the composition of thefrying oil because fatty acids are released from fat-containing foods, such as meatand fish, and their concentration in the frying oil increases with continued use.Breaded and battered food can degrade frying oil more quickly than nonbreaded

Fig. 2.3. Oxidationprocess for frying oils.



food. For example, onion rings are more detrimental to the oil than potato chips,possibly because of the breading material that accumulates in the oil. However,even foods such as potatoes degrade oil stability because of the increased additionof oxygen as the food is added to the frying oil. Food particles accumulating in theoil also deteriorate oil quickly; therefore, filtering oils will help remove these parti-cles along with other oxidation products and can help to extend oil fry life.

Frying protocols of intermittent or continuous frying affect fry life. For exam-ple, cottonseed oil heated intermittently had as much polar material as oil heatedcontinuously for three times as long. This difference may be caused by the

Fig. 2.4. P o l y m e r i z a t i o nprocess for frying oils.

TABLE 2.1 Factors Affecting Frying Oil and Fried Food Degradation

Oil/food• Balance amount of unsaturated and saturated fatty acids for optimal oil fry life,

healthfulness, flavor quality, and stability of fried food• Choose oils with moderate-to-high stability• Consider nature of food: nonbreaded/battered foods degrade oils less than do breaded/

battered foods• Chelate metals in oil with use of metal chelator, such as citric acid• Use oils with good initial quality• Do not allow degradation products to accumulate in oil• Use antioxidants and antifoam additives

Process• Keep oil temperature neither too high nor too low• Avoid prolonged frying time• Minimize aeration/oxygen absorption• Keep frying equipment in good condition• Maintain continuous frying, which is better than intermittent frying• Add makeup oil to ensure good oil turnover rate• Filter oil and clean fryer



increased amounts of fatty acyl peroxides that decompose upon repeated heatingand cooling, causing further oil damage. Replenishing the fryer with fresh oil iscommonly done in most frying operations; however, in the snack food industry inwhich more make-up oil is added than in restaurant-style frying, a completeturnover time of 8–12 h can be achieved in a continuous fryer. Levels of the reac-tion products in frying oil can also be affected by absorption into the fried food.Evaporation of aldehydes and ketones takes place, but fatty acids are not distilledunder frying conditions. Some amount could be removed from the fryer as entrain-ment in the water vapor leaving the fryer and being removed through the exhaustduct. However, the accumulation of degradation products in the frying oil and theireventual absorption in fried foods is of primary concern when commercial frying isdone under abusive conditions. In summary, the following characteristics of the oiland/or food affect the amount of oil deterioration during frying: type of food, typeof oil, unsaturation/saturation of fatty acids, metals in food or oil, initial oil quality,degradation products in the oil and additives to the oils, such as antioxidants andantifoam agents. The following frying procedures also affect oil deterioration: fry-ing time and rate, oxygen, fryer type, surface-to-volume ratio of the oil, oil temper-ature, continuous or intermittent frying, addition of makeup oil, and filtering of oil.

Products from Oil Deterioration

In deep fat frying, both thermal and oxidative decomposition of the oil occur, pro-ducing volatile and nonvolatile decomposition products. These two types of com-pounds are of interest because the volatile compounds affect the flavor of the foodand the room odor of the frying oil, whereas the nonvolatile compounds affect howlong the oil can be used for frying and how long the fried food can be stored beforeit is consumed. Not only do these compounds adversely affect the stability of thefrying oil as already discussed, but the foods fried in deteriorated oils may alsocontain a significant amount of decomposition products that have potentiallyadverse effects on the food safety, flavor, and flavor stability of the fried food. Thevolatile compounds are responsible primarily for flavor (both positive and nega-tive) in the fried food. Undesirable off-flavors can be produced if frying oil isallowed to deteriorate. Nonvolatile compounds, such as polymers, at low levels,may not have much effect on the flavor of a food that is consumed immediatelyafter frying; however, they do affect the fry life of the oil and the shelf life of agedfried food. Thermal polymers may exist in an edible product, but the conditions fortheir formation are not usually encountered in commercial practice because snackfood frying processes are found to be less drastic when good operating protocolsare followed.

Effects of Volatile Compounds on Flavor of Fried Food

When oils are heated to frying temperatures, many compounds are produced as thefatty acids decompose. For example, when pure linoleic acid, a major fatty acid in



most vegetable oils, is heated, the primary volatile compounds include pentane,acrolein, pentanal, 1-pentanal, hexanal, 2- and/or 3-hexanal, 2-heptenal, 2-octenal,2,4-nonadienal, 2,4-octadienal, and 2,4-decadienal. All of these compounds pro-duce characteristic odors and flavors that affect the room odor of the frying oil andthe flavor of the fried food. The 2,4-decadienal is the major contributor to deep-fried flavor, but 2-heptenal, 2-octenal, 2,4-nonadienal, 2,4-nonadienal, and 2,4-octadienal also are described as producing a deep-fried odor. Some compoundslisted above will usually produce off-odors. For example, an acrid odor is a resultof acrolein, and grassy odor is produced by hexanal and 2- and/or 3-hexanal.Frying oils such as high-oleic sunflower have undesirable fruity and plastic odorsbecause of the volatile compounds that decompose from oleic acid. Heptane,octane, heptanal, octanal, nonanal, 2-decenal, and 2-undecenal can be found inmost oils because they arise from the oxidation of the oleic acid. But when oleicacid is a major component of the oil, such as in high-oleic (>80%) oils, the off-fla-vor and odors such as plastic/waxy and fruity are noticeable. Fruity flavors are pro-duced from octanal and nonanal, and plastic/waxy from 2-decenal and 2-undece-nal. This information helps explain the origin of the deep-fried flavor that is char-acteristic of high-linoleic frying oils, but that is present only at low levels in high-oleic oils. In addition, the types of chemical compounds derived from oleic acidhelp explain why high-oleic oils have plastic, waxy and fruity odors that are hardlynoticeable in oils with low levels of oleic acid.

Effects of Nonvolatile Compounds on Fry Life of Oil

Nonvolatile products in deteriorated frying oils include polymeric triacylglycerols,oxidized triacylglycerol derivatives, and cyclic compounds. Polymeric triacylglyc-erols result from condensation of two or more triacylglycerol molecules to formpolar and nonpolar high-molecular-weight compounds. The nonpolymerized partof the oil contains mainly unchanged triacylglycerols in combination with theiroxidized derivatives. In addition, it contains monoacylglycerols and diacylglyc-erols, partial glycerides containing chain scission products, triacylglycerols withcyclic and/or dimeric fatty acids, and any other nonvolatile products. However,much oil deterioration is required for a significant amount of these polymers toform. In continuous potato chip processing, this is not usually a problem becausefrying conditions are monitored carefully and a high oil turnover rate is achieved.However, oil used in industrial batch fryers (kettle fryers) or small-scale batch fry-ing operations, such as restaurants, is found to deteriorate more because of high oilturnover time.

Measuring Deterioration Products

The physical and chemical changes occurring in frying oils and the many com-pounds formed in deteriorated frying oil have been reported extensively. Althoughthese compounds often are used to measure degradation, many of the existing



methods are based on measuring nonspecific compounds that may or may not relate tooil degradation or fried food quality. Therefore, it is not surprising that frying is oftendescribed as more of an art than a science. In fact, the frying industry is still searchingfor the ultimate criteria to rapidly evaluate frying stability of oils and fried food flavorquality and stability. The standard methods used to measure degradation products infrying oils include polar components, conjugated dienes and fatty acids, as well asrapid analyses, such as the dielectric constant (Table 2.2). Four well-known rapid testsinclude Food Oil Sensor (FOS) (Northern Instruments, Lino Lakes MN), which mea-sures the dielectric constant in frying fat relative to fresh oil; the RAU-Test, which is acolorimetric test-kit that contains redox indicators reacting with the total amount ofoxidized compounds; Fritest (E Merck, Darmstadt, Germany), which is a calorimetrictest-kit sensitive to carbonyl compounds; and the Spot Test, which assays FFA to indi-cate hydrolytic degradation and FFA. The Food Oil Sensor correlates better with polarcompounds than do the RAU-Test, Fritest, and Spot test. The amounts of FFA are usu-ally not a reliable indication of deteriorated frying fat. Practically, commercial fryingoil operators want to know “When should frying oil be discarded?” Because there aremany variables that affect oil degradation as discussed previously, a specific methodmay be useful for one operation, but not for another. Determining the endpoint of afrying oil requires good judgment, knowledge of the particular frying operation, aswell as the type of frying oil, appropriate analytical measurements, and the expectedshelf life of the fried food. Some of the laboratory methods used to measure degrada-tion products in frying oil include column chromatography and high-performance size-exclusion chromatography to detect both polar and nonpolar compounds. Several tech-

TABLE 2.2 Methods to Measure Deterioration Products in Frying Oil

Nonvolatile compounds and related processes Method/Reference

Iodine value AOCS Cd 1–25/93 (1)Fatty acid composition AOCS Ce 1–6293 (1)Total polar compounds AOCS Cd 20–91/97 (1)Free fatty acids AOCS Ca 5a-40/93 (1)Dielectric constant (Fritsch, 1981) (2)Nonurea adduct–forming esters (Firestone, 1961) (3)Fryer oil color AOCS Td 3a-64/93 (1)Viscosity (Stevenson, 1984) (4)Smoke point AOCS Cc 9a-48/93 (1)Foam height (Billek, 1978) (5)

Volatile compounds and related processes Method/Reference

Peroxide value AOCS Cd 8–53 (1)Conjugated dienes AOCS Ti 1a-64 (1)Volatile compounds AOCS Cg 4–94 (1)Sensory analysis of odor and flavor (Warner, 1995) (6)



niques, including direct injection, static headspace, dynamic or purge-and-trap head-space, and solid phase microextraction, all of which use capillary gas chromatography,can analyze volatile compounds. The rapid methods mentioned above, such as theFood Oil Sensor, can be used successfully to estimate frying stability in restaurant-typefrying operations.

Measuring Deterioration Products Related to Fry Life

Nonvolatile decomposition products are a better measure of degradation of fryingoil than are volatile products because volatile compounds are constantly formingand decomposing. Nonvolatile higher-molecular-weight compounds are reliableindicators of fat deterioration because their accumulation is steady and they are notvolatile. For example, total polar compounds usually increase linearly with increas-ing frying time and polymers have also been shown to increase with increasingheating time. High statistical correlations have been obtained between number offryings and amounts of decomposition products in the oil, including total polarcompounds, diacylglycerols, triacylglycerol polymers, and triacylglycerol dimers.FFA may not correlate significantly with the number of fryings. Changes fromhydrolysis and oxidation parallel each other during frying as indicated by the highcorrelations between levels of triacylglycerol polymers and triacylglycerol dimers(from oxidation) and diacylglycerols (from hydrolysis) with the number of fryings.Four methods to assess frying oils are commonly used in European laboratoriesand include gel permeation chromatography (GPC), liquid chromatography (LC)on a silica gel column, polar and nonpolar components column chromatography onsilica gel (CC), and petroleum ether–insoluble oxidized fatty acids. Measuringpetroleum ether–insoluble oxidized fatty acids is usually time consuming and inac-curate. The GPC method is able to determine dimeric and oligomeric triacylglyc-erols in frying oil irrespective of the presence of oxidized compounds, whereas theLC method can indicate the total amount of polar and oxidized compounds.Separating polar and nonpolar components by CC is simpler and faster than theother three methods mentioned above.

The formation and accumulation of nonvolatile compounds are responsible forphysical changes in frying oil, such as increased viscosity, darkening in color,increased foaming, and decreased smoke point as described earlier. Most methodsfor assessing deterioration of frying oils are often based on these changes.Nonspecific methods for measuring nonvolatile compounds in deteriorated fryingoil include FFA, nonurea adduct-forming esters, peroxide value, benzidine value,acid value, ultraviolet absorbance, refractive index, and petroleum ether–insolubleoxidized fatty acids. None of these methods are considered good measures of heatabuse. In Europe, values of 24–27% polar materials are common endpoints for dis-carding frying oil in restaurant frying. However, if fried foods are to be stored for aperiod of time before they are consumed, the level of polar materials must be muchless than the 24% endpoint, with recommendations of <10% polar materials.



Measuring Deterioration Products Related to Flavor

Because many of the volatile decomposition products volatilize during frying, it isdifficult to obtain an accurate representation of oil deterioration by instrumentaland chemical analyses of these compounds. Methods that measure volatile com-pounds directly or indirectly include peroxide value, gas chromatographic volatilecompound analysis, and sensory analysis. These methods are much better for mea-suring the quality and stability of the fresh and aged fried food than for measuringthe quality of the frying oil itself. The peroxide value is not a good measure of heatabuse in frying oils because peroxides are unstable at frying temperature. Peroxidesdecompose very easily into secondary oxidation products; therefore, analysis ofperoxides at random times of oil use tells little about the overall quality of the oil.Gas chromatographic volatile compound analysis measures compounds that aredirectly related to the flavor of the fried food. The fatty acid composition of fryingoils has a major effect on the volatile compounds detected in the oil and on the fla-vor of the fried food. Although frying oils are complex mixtures of triacylglyc-erols, a wide variety of fatty acids, and many minor constituents, degradation com-pounds are primarily from the fatty acids. As expected, unsaturated fatty acids con-tribute significantly more to the formation of volatile compounds than do thosefrom the more stable saturated fatty acids, such as palmitic and stearic. The stability ofoleic acid, a monounsaturated fatty acid, is between that of the PUFA and the satu-rated fatty acids.

Identifying volatile compounds in fried food is important because these com-pounds help in understanding the chemical reactions that occur during frying, andbecause the flavor of deep fat fried food is caused by the volatile compounds.Although the volatile compounds are continually changing in the frying oil, mea-suring these compounds in the frying oil can give some indication of oil deteriora-tion; however, care should be taken in interpreting data on volatile compounds inused frying oil because of the fluctuations in formation and degradation of thecompounds at frying temperature. Gas chromatography/mass spectrometry can beused to identify volatile compounds in the frying oils such as hydrocarbons, alde-hydes, alcohols, furans, esters, ethers, acids, and lactones. The total amounts ofvolatile compounds increase as the oil temperature increases, but they then candecompose to form other compounds, thereby creating a cycling pattern of volatilecompound formation and degradation. Volatile compounds can be identified andquantified from fresh and aged fried food. The amounts and types of volatile com-pounds in the food depend on the type of frying oil, the quality of the fryer oil atthe time of product collection, and on the length of storage of the food.

Sensory evaluation is still the method most often used by different countries todetermine when to discard frying oil. Scientific groups in Germany use sensoryassessment of frying oils; however, if the assessment does not give a clear indica-tion that the oil is deteriorated, then instrumental or chemical analysis is used tosupport a final decision on oil quality. The 3rd International Symposium on Deep-



Fat Frying (7) recommended that sensory parameters of the fried food be the prin-cipal quality index for deep fat frying. To further confirm oil abuse, total polarmaterials should be <24% and polymeric triacylglycerols <12%. Sensory analysisof frying oil and fried food quality may be conducted by analytical descriptive/dis-criminative panels using trained, experienced panelists or by consumer panelsusing untrained judges. However, results from consumer panels that measure theflavor likeability of food are usually dependent upon individual likes and dislikesrather than objective standards used by trained panels. Consumer panels may findno differences in fried food flavors, whereas a trained, experienced analyticaldescriptive panel can usually detect significant differences in the type and intensityof flavors in fried food prepared in various oil types. More research is required tounderstand the relationship between fried food flavor and the volatile and non-volatile decomposition compounds produced in frying oils.

Inhibiting Frying Oil Deterioration

The factors affecting hydrolysis, oxidation, and polymerization, which eventuallyproduce oil deterioration, can be controlled and their effects can be limited. Forexample, to help inhibit frying oil deterioration, choose a fresh oil with good initialquality, no prior oxidation, low levels of PUFA, and low amounts of catalyzingmetals. The extent of these degradation reactions can be controlled by carefullymanaging frying conditions, such as temperature and time, exposure of oil to oxy-gen, continuous or intermittent frying, oil filtration, and turnover of oil. The effectsof adding antioxidants and antifoam additives, which can help maintain oil quality,will be discussed in another chapter.

References

1. AOCS, Official Methods and Recommended Practices of the American Oil Chemists’Society, 5th edn., edited by D. Firestone, AOCS Press, Champaign, IL, 1998.

2. Fritsch, C.W., Measurements of Frying Fat Deterioration: A Brief View, J. Am. OilChem. Soc. 58:272 (1981).

3 . Firestone, D.W., Horwitz, L., Friedman, and G.M. Shue, Heated Fats I. Studies of theEffects of Heating on the Chemical Nature of Cottonseed Oil, Ibid. 38:253 (1961).

4 . Stevenson, S.G., M. Vaisey-Genser, and N.A.M. Eskin, Quality Control in the Use of DeepFrying Oils, J. Am. Oil Chem. Soc. 61: 1102 (1984).

5. Billek, G., G. Guhr, and J. Waibel, Quality Assessment of Used Frying Fats: A Comparisonof Four Methods, Ibid. 55: 728 (1978).

6 . Warner, K., Sensory Evaluation of Oils and Fat-Containing Foods in Methods to AssessQuality and Stability of Oils and Fat-Containing Foods, edited by K. Warner, and N.A.M.Eskin, American Oil Chemists’ Society, Champaign, IL, 1995, p. 30.

7. Anonymous, Recommendations of the 3rd International Symposium on Deep FatFrying, Eur. J. Lipid Sci. Technol. 102:594 (2000).



Chapter 3

Selection of Frying Oil

Monoj K. Gupta

MG Edible Oil Consulting International, 9 Lundy's Lane, Richardson, TX 75080

I n t ro d u c t i o nIt is very important to select an oil that is appropriate for each individual type ofsnack food because the oil plays an essential role in developing the proper taste ofthe fried product. A wide variety of snack food is sold in the market, such as pota-to chips, tortilla chips, cheese-coated extruded snacks, fried noodles, batter-coatedproducts such as fish fillet, coated or filled vegetables, chicken, and French fries.Each of these products has specific requirements for flavor, texture, appearance,and keeping quality. In each case, the oil either complements the base ingredientsor enhances the overall flavor of the product. The oil can also influence the flavorrelease from the seasoning applied on the product. In short, the oil contributes tothe success or failure of a product in gaining consumer acceptance.

Basis for Oil Selection

Oil is used for frying and also for spraying on the surface of the fried product toapply seasoning. The seasoning can be dairy powder or a blend of spices and dairycomponents to impart a flavor to the product that is very appealing to most con-sumers. In most cases, the frying oil and spray oil are the same for a given product.However, some exceptions might exist.

As mentioned in Chapter 1, the following criteria are used by the snack foodindustry for selecting oil for a given product: (i) appearance; (ii) aroma/flavor; (iii)texture; (iv) mouth-feel; (v) aftertaste; (vi) product shelf life; (vii) availability;(viii) cost; and (ix) nutritional requirements.

Appearance, Aroma/Flavor, and Texture. The appearance of the snack foodmakes the first impression on the consumer. The consumer notices the aroma andthen the flavor of the product is captured as it is tasted. The texture of the productis noticed after the product appearance and flavor have made an impression. If theproduct does not have an appealing appearance or appetizing aroma and flavorappeal, the consumer may not even try it or may try it with reservation. This mayinfluence the judgment made concerning the texture of the product.

Texture. Texture is the next most important attribute for the snack food. Thechips must be crispy to the first bite but not necessarily too hard for potato chips or

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tortilla chips. The crispness/hardness can be a function of the frying condition, consis-tency (solids content) of the oil, the composition and thickness of the food being fried,frying temperature, and fry time. For example, hard-bite potato chips are fried in liquidcottonseed, corn, or peanut oil at temperatures <330°F (lower than the 350–360°F usedfor regular potato chips) for 3–6 min to obtain the hard texture. Batter-coated chickenor French fries have to be fried in a hydrogenated fat to obtain the crisp texture.

Mouth-Feel. Mouth-feel is also very important. The product must not be dry orsticky, and it must cause little or no packing between and on the surface of thetooth, known as tooth packing. The fried chips must have neither an oily nor awaxy mouth-feel. Generally, hydrogenated oils and palm oil produce a waxymouth-feel in fried chips. It is a common experience among palm oil users that theproduct tastes waxy especially when the weather is cold. This is because palm oilsolidifies at 38°C, which is higher than the normal body temperature. Products donot leave a waxy mouth-feel when they are fried in one of the following oils: pal-molein (melting point 22–24°C), liquid cottonseed or liquid corn oil (do not solidi-fy even at 15°C). Products fried in liquid cottonseed oil and liquid corn oil mayappear oily on the surface and may leave oil on the fingertips.

Aftertaste. The product must have a pleasant aftertaste, i.e. the consumer shouldnot experience any lingering unpleasant taste after swallowing the snack food.

Shelf Life. Shelf life is very important for both technical as well as commercialsuccess of the product. It is important to note that a product may exhibit poor shelflife even if the fresh product had very good flavor and texture. This can occur forone or both of the following reasons: (i) Development of poor texture due to mois-ture gain by the product during storage; (ii) development of oxidized or rancid fla-vor due to oxidation of the oil in the product during storage.

Moisture permeation through the packaging film is the cause for the moisturegain and the loss of product texture. This can also be accompanied by the develop-ment of a stale flavor in the product. Moisture gain by the product can be signifi-cantly reduced by using a packaging film with high moisture barrier properties andby proper moisture control in the product during frying.

An oxidized or rancid flavor is observed in the packaged product if the incom-ing frying oil is of poor quality or has been damaged in the frying process. Both ofthe above-mentioned phenomena greatly reduce the time required by the companyfor the distribution and sale of the product. The shelf life of a product can bedefined in different ways as shown below:

1. The product is as good as fresh when it is tasted on the last date printed on thepackage.

2. The product has developed unacceptable flavor and/or or texture at any pointduring storage. The code date on the package might not have expired at thetime the product became unacceptable.



Many product manufacturers seem to have confused notions about shelf lifeand the code date for the product. They seem to feel that code date and shelf lifeare identical. It must be remembered that the code date for the product is based onthe time required by the company for warehousing, distribution, and retail sales ofthe product. Some of these activities may be out of the company's own system and,therefore, cannot be fully controlled by the company. In such cases, the companyhas to look at the realistic time of product delivery to the store shelf, and the timeneeded for sale of the product at the store. The product must be either as good asfresh or acceptable to the consumers at the point the product is consumed. Thistime period may be long. The existing packaging material may not provide therequired shelf life to the product to meet the necessary code date. In this case, thecompany may have to use a packaging film either with higher moisture or gas bar-rier property (or both), possibly a different type of oil for frying, nitrogen flush inbags, and have a proper oil quality management system in operation. These are theeconomic factors that a company must take into account to arrive at an appropriatecode date for the product.

The first six criteria—appearance, aroma/flavor, texture, mouth-feel, after-taste, and product shelf life—are often considered to be the “criteria for technicalsuccess” for the product. One must note that in the process of achieving these suc-cess criteria, the oil used in frying must have high oxidative and thermal stability.However, one must be careful about choosing the oil for the product, i.e., avoidingthe selection of an oil that has low availability and a high price. In that case, thetechnical success will lead to economic failure. Therefore, one should exercisegood judgment to achieve a proper balance between the technical success and theeconomic success for the company.

Nutritional Needs. Nutritional concern has been on the top of the list of all pro-gressive-minded snack food companies. Unfortunately, availability of the “healthful”oils at an affordable price and ample supply has been the Achilles’ heel for theadvancement of these oils in the snack food industry. Some companies are usingthese oils in their niche market products. At present, the volume is small comparedwith the total snack food market. Most well-known healthful oils are low in saturatedfat and low in linolenic acid. Examples of such oils are listed below:

• High-oleic sunflower• High-oleic safflower• Low-linolenic canola• High-oleic canola• Mid-oleic sunflower (NuSun)

These oils do not require hydrogenation for heavy-duty industrial frying.Unfortunately, the combined production volume of all of these oils is not sufficientto meet the current demand for frying oil in the industry. The snack food industry



used nearly 2 billion pounds of oil in the year 2001 in the United States. The com-bined production of all of the oils listed above falls short of 500 million pounds.Their supply is not expected to match the need for cottonseed, palmolein, and par-tially hydrogenated soybean oil within the foreseeable future. Therefore, manufac-turers of snack food in the United States will continue to use the oil that is readilyavailable and is reasonably priced in their respective countries.

Specific Applications. For products such as cheese snacks, or snacks with filling,a certain amount of solid fat is required at ambient temperature for two reasons: (i)to prevent run-off of the coating or the filling material from the surface or inside ofthe product; and (ii) to provide a certain amount of fat melting in the mouth duringchewing so that there is a release of fat-soluble flavor from the seasoning and, insome instances, the added perception of a cooling effect caused by the melting ofthe fat crystals. Partially hydrogenated soybean oil, canola oil, cottonseed oil, andcorn oil are used in this type of application. Where available, palm oil becomes anatural choice as a coating oil.

For spray oil on tortilla chips, it can be demonstrated that each type of oil bringsout a distinctive flavor character of the seasoning. Some of the oils bring out thedairy note from the cheese coating, whereas others can bring out a more garlic oronion note. The mechanism for these phenomena has not been investigated. For thisreason, one must experiment with each type of oil and determine the best combina-tion between the type of spray oil and the seasoning used for topical application.

For frying batter-coated fish or vegetables, a crispy outer crust and a tenderand moist interior are required. This is accomplished primarily by selecting thecoating material applied on the product. Therefore, liquid oil or lightly hydrogenat-ed oil can be used to make these products. These products are par-fried, frozenimmediately, packaged, and then stored at –5 to –10°F (–20 to –23°C). The prod-uct is distributed in trucks with refrigeration and then stored again at –5 to –10°Fin freezers at the final destination. The frozen product is fried (without thawing)and served immediately in restaurants or food services. The liquid oil used in thepar-fry process must have good oxidative stability; otherwise, these products candevelop oxidized flavor even when they are stored in freezers at –5 to –10°F. Finalfrying of the product can be done either in liquid oil or hydrogenated fat.

Pre-cooked chicken is also prepared and delivered in the same manner asdescribed above. The only difference is that the oil used in this case requires moresolids to maintain the extra crispy crust. Final frying of the product is generallydone in hydrogenated fat.

French fries are one of the most popular products throughout the world. Thepotatoes are cut, water-washed, pretreated with citric acid, calcium and magnesiumsalts, blanched, par-fried, and frozen like fish or chicken. The fat system requires acertain amount of fully hydrogenated fat to maintain the dry surface appearanceand crispy taste of the fried product. The fried product must maintain its crispnessat the restaurant or in a food service for 5–7 min after it is removed from the fryer.



In the absence of fully hydrogenated fat, the product loses its crispness very quick-ly and the restaurant or the food service employee has to throw away the friedproduct. Although the process of making French fries includes steps in which thecut potatoes are soaked in calcium and magnesium salts to impart some firmness tothe raw product, the absence of a fully hydrogenated fraction in the frying shorten-ing still makes the product less acceptable.

It was mentioned earlier that the oil plays a large role in determining the flavorand texture of the fried product to be accepted by consumers. For example, in theUnited States, mostly liquid cottonseed oil is used to fry potato chips, with veryfew exceptions. Liquid cottonseed oil is considered to be the gold standard for fry-ing potato chips in this country. Liquid corn oil, lightly hydrogenated sunfloweroil, NuSun (mid-oleic sunflower oil), and blends of cottonseed and corn oil havebeen used to substitute for the liquid cottonseed oil with good success. In fact,Procter & Gamble Company has found NuSun oil to be a better choice for theirPringles brand potato chips for flavor and consumer acceptability. In all of thesecases, the oil has complemented the potato base and has developed the flavor char-acter desired by the U.S. consumers. Peanut oil (groundnut) and sesame seed oilalso produce very pleasing flavor character in potato chips. However, they are bothscarce and costly.

Palmolein is used extensively throughout the world for frying potato chips. Theproduct has a pleasant flavor character and an agreeable aftertaste. Unfortunately,the snack food and other industries in the U.S. market discontinued the use of pal-molein and palm oil in late 1980s because of the high saturated fatty acid content.Since that time, many nutritionists around the world have shown that palm oil is notas harmful as it was labeled by certain entities in the U.S. (1–3). The oil is currentlyused extensively in Europe, Latin America, the United Kingdom, Canada, Mexico,Africa, and Asia. Palmolein has been sold as single-, double- or triple-fractionatedoils to offer more liquid fractions for application in various products including snackf o o d .

La Fabril in Ecuador introduced a fractionated palmolein that is low in trisatu-rated and tripolyunsaturated triglycerides. Potato chips and tortilla chips fried inthis oil demonstrate excellent flavor character and stability. Unfortunately, the oilis somewhat more expensive than palmolein. Snack food manufacturers in theregion blended this oil with soybean oil to reduce the cost. This practice resulted inproducts with poor flavor character and stability.

Liquid soybean oil, as well as liquid canola oil, contains ~7–8% linolenic acid,which makes the oils very unstable in frying. Both oils are hydrogenated to reduce thelinolenic acid content to <2% to achieve oxidative stability in these oils. Soybean oiland canola oil are found to be less desirable in frying potato chips in the United States,Mexico, and a few other countries. On the other hand, partially hydrogenated canolaoil is used in Canada for frying potato chips and other snack foods.

The growth of the tortilla chip industry has been somewhat faster than that ofthe potato chip segment in the United States. Lightly hydrogenated soybean oil



(iodine value of 100 ± 4) is considered to be the gold standard for frying tortilla chipsin the United States. Use of corn oil is increasing in the country to fry tortilla chips.Certain niche markets use high-oleic safflower and high-oleic sunflower oils. Inaddition, certain manufacturers in the United States also use various grades of liquidcanola oil including partially hydrogenated canola oil, high-oleic canola oil, or low-linolenic canola oil. Palmolein, again, is used quite extensively in various other coun-tries to fry tortilla chips to impart excellent flavor character and stability.

Standard sunflower oil contains >60% linoleic acid, which makes the oilunsuitable for frying shelf-stable products. The oil has to be hydrogenated to aniodine value of 100 ± 2, or have a linoleic acid content of 35 ± 2%. Both potatochips and tortilla chips fried in this lightly hydrogenated sunflower oil demonstrategood flavor character and shelf-life stability.

Steps for the Selection of Oil for a Snack Food

Selection of oil for a specific snack food is important for achieving a product thatis liked by the consumer for flavor and texture and so on. A snack food companyfaces the challenge of selecting oil for a product under the following situations:

• Is the oil needed to formulate a new product?• Is the oil to be used as an alternate to an oil already in use for an existing prod-

uct?

New Product. In the case of a new product, the frying oil must be carefullyselected on the basis of consumer acceptability, and acceptable product shelf life.In addition to meeting the above requirements, one must make sure that the select-ed oil also meets the requirements of availability and cost as well as any nutritionalrequirements provided by the corporation.

Alternate Oil For an Existing Product. Selecting alternative oils is a commonpractice in the industry when the company requires flexibility to change the type ofoil in an existing product. This is an economic decision based solely on the avail-ability and cost of the oil without sacrificing product acceptability and shelf life.The oil must meet the following criteria to be certified as an alternative to theexisting oil in use:

1. Test product must be tested against the existing product (control) preparedunder identical process conditions based on consumer tests.

2. An approved consumer testing protocol must be used. Test product must beequal to the control in all product attributes both when fresh and at the end ofthe desired code date.

3. Test product must have shelf-life stability equal to or better than the control.4. The test oil should handle the same way as the control oil. No special equip-

ment should be required to handle the new oil.



At this point, the oil is technically approved and must go through the standardeconomic evaluation by the procurement department. However, for all practicalpurposes, it works better if the technical group is in close communication with pro-curement from the very beginning of the process. At this juncture, procurementshould identify more than one supplier for the new oil. The technical group shouldanalyze the samples chemically for confirmation of the quality. Sometimes asmall-scale test might be advisable for a disaster check on the oil from a differentsupplier. This is because on some occasions, the same type of oil with apparentlyidentical chemical analyses may not deliver the same product flavor. This can hap-pen for a variety of reasons as described in Chapter 8. A case study on this subjectis outlined below:

• U.S. consumers do not like potato chips fried in partially hydrogenated soy-bean oil. The consumers can detect the difference in the flavor of the potatochips, when they are fried in an oil blend that contains a very small amount ofsoybean oil in liquid cottonseed oil.

• Soybean oil was specially processed, hydrogenated to <2% linolenic acid con-tent, deodorized, and then blended with liquid cottonseed oil.

• The blended oil was used to make potato chips and then compared against thecontrol product made with 100% liquid cottonseed oil. The test results showedthat the fresh potato chips made with blended oil, containing 25–50% of the spe-cially processed soybean oil, had acceptability identical to that of the control.

• The acceptability for the test products made with the blended oils was margin-ally lower than the control at the end of the code date.

• Consumers found the potato chips flavor unacceptable when the oil blend con-tained 10% of conventionally processed soybean oil with the chemical analy-ses identical to those specially processed.

The test oils were prepared by different oil processors. The oil from one of theprocessors could be added up to 50% with cottonseed oil and the experts as well asthe consumers could not detect any difference between the test product and control.The oils from the other processors could be added only up to 25% in the oil blend toproduce similar results. All three companies obtained the crude soybean oils fromgarden variety soybeans. The finished oils from the three processors had identicalchemical analyses. Therefore, this kind of difference could be attributed only to thespecific processing techniques applied by the individual processors. It is alwaysadvisable to test the oil from a new supplier on a small scale to ensure that all prod-uct criteria are met before the supplier is accepted as a qualified oil supplier.

Selection of Oil For Frying at Restaurants. Selection of oil for a restaurant fol-lows the basic laws of supply and cost. The food service industry operates under verytight profit margins. As a result, the restaurant owner chooses the least expensive oilthat produces a satisfactory product and has a satisfactory fry life. Restaurants use



partially hydrogenated soybean oil, pourable shortening, all-purpose frying short-ening, and various other oils to fry a wide variety of products. Palm oil and pal-molein can also be used in restaurants, although these oils are not currently used inthe United States.

SummaryThe selection of oil for any product, whether new or existing, is determined by thefollowing criteria:

• Successful product performance as determined by consumer acceptance and/orpreference test.

• No plant modification is required to use a new type of oil. Any plant modifica-tion should be justifiable by either direct saving on the cost of oil or frompotential increase of sales.

• The oil must be available as a commodity for economic reasons. It must be agood technical as well as economic fit for the company.

• The oil must show high consumer acceptability in a new product category ormust be at least as good as the control in the case of an existing product.

References

1. Hornstra, G., A.A.H.M. Hennissen, D.T.S. Tan, and R. Kalafusz, Life Science, PlenumPublishing Co., 1987, p. 69.

2. Hornstra, G., and R.B. Lussenburg, Relationship Between the Type of Dietary FattyAcid and Arterial Thrombosis Tendency in Rats, Atherosclerosis 22:499–519 (1975).

3. Sundram, K., K.C. Hayes, and O.H. Siru, Dietary Palmitic Acid Results in a LowerSerum Cholesterol than a Lauric-Myristic Acid Combination in Normolipemic Humans,Am. J. Clin. Nutr. 59:841–846 (1994).



Chapter 4

Role of Antioxidants and Polymerization Inhibitorsin Protecting Frying Oils

Kathleen Warnera, Caiping Sub, and Pamela J. Whiteb

aNational Center for Agricultural Utilization Research, U.S. Department of Agriculture,Peoria, IL, and bFood Science and Human Nutrition Department and Center for CropsUtilization Research, Iowa State University, Ames, IA

IntroductionThe fatty acid composition of oils has a major effect in determining how stable anoil will be during frying, but other factors, such as the amounts and types of natu-rally occurring minor oil constituents and of chemical and natural additives, canaffect oil stability and the quality of fried food. Minor oil constituents, includingtocopherols, β-carotene, and chemical antioxidants, have been shown to improvethe quality and stability of salad oils. Oil processors put additives, such as methylsilicone and antioxidants, into frying oils during or after processing. This chapterpresents information about the effects on fry life of several types of naturallyoccurring compounds and other additives.

Protective Properties of Tocopherols

Tocopherols are natural antioxidants found in oilseeds, but the amounts of the fourprimary homologs, α, β, γ, and δ-tocopherol, vary widely in oils. Tocopherols arephenolic antioxidants that react with free radicals in oils to interrupt the oxidativereaction, thereby inhibiting oxidation of the fatty acids (Fig. 4.1). Utilizing oilswith these naturally occurring antioxidants is one way in which to enhance the fry-ing life of oils and the storage stability of fried foods. Another option is to add thenatural antioxidative components as extracts to oils.

Tocopherols degrade much faster in oils heated to frying temperature than atambient temperature. Because the tocopherol concentration is reduced as oils areheated at frying temperatures, their loss has been used as a measure of the level ofoil deterioration. Many studies have shown the changes in tocopherol content ofoils as they are used for frying and the different rates at which the various toco-pherol homologs degrade. Gordon and Kourismska (1) reported that α-tocopherolin rapeseed oil was lost much more quickly than γ- and δ-tocopherols. Barrera-Arellano et al. (2) confirmed the finding that α-tocopherol losses were rapid whenthey heated triolein, trilinolein, and a 1:1 blend of these two lipids. Marquez Ruiz

Ch4/PcFry/37-49/25 Feb/F 6/7/05 2:29 PM Page 37


et al. (3) also found that the natural levels of tocopherol affected the fry life of sun-flower oil. Potatoes fried in sunflower oil oxidized more slowly than potatoes fried inhigh-oleic sunflower oil even though the sunflower oil contained 19% polar com-pounds, whereas the potatoes fried in high-oleic sunflower oil had 16% polar com-pounds. The authors attributed the differences in stability to the fact that the sunfloweroil had 100 ppm α-tocopherol and the high-oleic sunflower oil had only 10 ppm at thestart of the storage study. On the other hand, the greatest losses were for γ- t o c o p h e r o lin peanut oil used for frying (4) and in a blend of soybean and rapeseed oil (5).Miyagaura et al. (5) also found that the tocopherols were retained more if potatoesfried in the oil were coated with a batter than if the potatoes had no batter.

Much of the research indicates that α-tocopherol degrades more quickly thando other tocopherols. This conclusion, coupled with the finding that only one of itsoxidation products showed antioxidant activity, favors the use of γ-tocopherols infrying oil. Warner et al. (6) found that γ-tocopherol inhibited the formation of totalpolar compounds in triolein used for frying potato chips and prevented rancidity inthe aged chips even though very low or no amount of α-tocopherol remained in theoil or in the oil extracted from the potato chips. The oxidation products of α-toco-pherol were assumed to have helped inhibit the deterioration of the oil and thechips.

Some researchers found that the loss of tocopherols is inhibited by combiningtocopherols with other additives in the frying oil. For example, Gordon andKourimska (7) ststudied changes in tocopherol content of oil used for deep-fat fry-ing of potatoes and found that α-tocopherol was lost much more quickly than γ- orδ-tocopherol. Without added antioxidants in the frying oil, α-tocopherol wasreduced by 50% after 4–5 fryings, but it required 7 and 7–8 fryings for γ- and δ-tocopherol, respectively, to reach 50% depletion. However, the presence of rose-mary extract or ascorbyl palmitate in the frying oil caused a significant reductionin the rate of loss of the tocopherols.

CH3

HO

5,7,8 Trimethyl α-Tocopherol 7,8 Dimethyl γ-Tocopherol

5,8 Dimethyl β-Tocopherol 8 Methyl δ-Tocopherol

HO HO

H3CH3C

HO

CH3CH3

CH3

CH3CH3

CH3CH3 CH3CH3

CH3|[CH2CH2CH2CH3]3

CH3|[CH2CH2CH2CH3]3

CH3|[CH2CH2CH2CH3]3

CH3|[CH2CH2CH2CH3]3

Fig. 4.1. Structures of α, β, γ, and δ-tocopherols.



The fatty acid composition of the oil also affects the rate of tocopherol loss inoils. Yuki and Isikawa (8) found that the loss of tocopherols was much greater insaturated fats than in more unsaturated ones. These results are similar to those ofFrankel et al. (9) who found that tocopherol loss was significantly less in highlyunsaturated oils than in more saturated ones, such as lard and cottonseed oil. Theytheorized that hydroperoxides formed in the polyunsaturated oils decomposedbefore they reacted with the tocopherols because they are very unstable comparedwith the very stable hydroperoxides formed in monounsaturated oil. The hydroper-oxides from saturated oils do not decompose before they can react with the toco-pherols because of their high stability.

Although most oils contain tocopherols, some oils contain other compoundsthat can help inhibit oxidation as well. Adding the natural antioxidative compo-nents from one type of oil to other oils that lack much antioxidant protection isanother option to enhance frying oil stability. Some oils are processed to preservenatural antioxidants including olive oil, rice bran oil, sesame oil, and red palm oil.Abdalla (10) found that 1% of the unsaponifiable matter from olive oil distillateimproved the frying life of the oil and the oxidative stability of potato chips friedin sunflower oil. The positive effects were attributed to the tocopherols, squaleneand avenasterol, in the olive oil distillate. Red palm olein is processed to preservenaturally occurring high levels of β-carotene, tocopherols, and tocotrienols. In fry-ing tests, red palm olein had better frying stability than did corn oil or palm oleinon the basis of free fatty acids, viscosity, and iodine value (11). They also reportedthat crackers fried in the red palm olein had better oxidative stability than thosefried in the other oils. Warner and Zhang (12) found that rice bran oil improvedthe frying stability of both cottonseed and sunflower oils when blended at a 1:3ratio.

Protective Properties of Chemical Antioxidants

Oil processors usually add chemical antioxidants to processed oil to retard undesirablechanges during frying and to extend the shelf life of the food fried in the oil.Antioxidants, such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene(BHT ) (Fig. 4.2), are effective in inhibiting oil oxidation at ambient temperatures, butthese additives volatilize easily at frying temperatures, especially when water ispresent. In tests on heated palm olein with no frying, the oil lost 70% of its originalBHT and 60% of the original BHA after 8 h (13). Freeman et al. (14) reported noprotective effects of 200 ppm BHT in heated sunflower oils. The effects of BHT inheated cottonseed oil with water added showed that BHT had no inhibitory effecton the deterioration of the oil during frying (15). A large portion of BHT was lostthrough steam distillation. Warner et al. (16) reported that 80% of the 70 ppm ofBHT was lost from lard after frying six batches of French fried potatoes, possiblyas a result of steam distillation. None of the 50 ppm of original BHA remainedafter frying four batches of potatoes.



Tertiary butylhydroquinone (TBHQ) (Fig. 4.2) has been reported to have bet-ter stability in frying oils than do BHA and BHT (1); therefore, it can protect thefrying life longer and also carry through to help protect the fried food during stor-age. Carlson and Tabacchi (17) found that added TBHQ as well as added α-toco-pherol decreased the rate of α-tocopherol loss in partially hydrogenated soybeanoil, hydrogenated soybean/palm oil, and corn oil used for frying French fries. Theα-tocopherol loss in the frying oils increased significantly with increasing fattyacid oxidation. No significant changes in α-tocopherol levels in the French friesoccurred during 4 d of frying, but these authors observed a 40% reduction in α-tocopherol in the frying oils.

TBHQ, lecithin, ascorbyl palmitate, rosemary extract, BHA, BHT, and toco-pherol were studied in rapeseed oil during the frying of French fries (1). The rose-mary extract and ascorbyl palmitate both inhibited dimer formation during deep-fatfrying and retarded losses of natural tocopherols in the oil. The stability of the fry-ing oil decreased as the tocopherols were depleted along with an increase inhydroperoxides generated in oil samples after frying. Che Man et al. (18) foundthat TBHQ was better than α-tocopherol in decreasing free fatty acids, polar com-pounds, and polymers in palm olein used for frying. On the other hand, α- t o c o-pherol was better than TBHQ in reducing anisidine values. They found no syner-gistic effects as reported in some studies.

Some reports in the literature indicate that TBHQ may not have much effecton frying oil stability. Rhee (19) showed that the combination of 200 ppm TBHQand 1 ppm methyl silicone worked synergistically to reduce oxidation and poly-merization of partially hydrogenated soybean oil, but that methyl silicone playedthe major role. BHA and BHT had the same effect as TBHQ. The effects of methylsilicone will be discussed later in this chapter. In a study of the effects of oil addi-tives on room odors of heated soybean oil and hydrogenated soybean oils, Warnerand co-workers (20) found that the addition of 200 ppm TBHQ did not affect theintensities of the odors. They found that the combination of TBHQ and methyl sili-

Fig. 4.2. Structures of butylated hydroxyanisole (BHA), butylated hydroxytoluene(BHT), and tertiary butylhydroquinone (TBHQ).

2-+3-tert-butyl- 2,6-di-tert-butyl- tert-4-hydroxyanisole p-hydroxytoluene butylhydroquinone



cone did decrease odor intensities; however, the methyl silicone was primarilyresponsible for this effect. Frankel et al. (21) also showed that TBHQ was lesseffective in frying oils alone than when added with methyl silicone.

Protective Properties of Herbal Extracts

The addition of natural antioxidants has been studied extensively in frying oils andhas shown positive effects. Jaswir and co-workers (22–25) found that herbalextracts of rosemary and sage improved the sensory acceptability of potato chips.In another study using rosemary and sage extracts with BHA and BHT, Che Manand Tan (26) found that the oxidation of the palm olein frying oil was inhibited inthe following order of effectiveness: rosemary oleoresin > BHA > sage extract >BHT > control. The same order was reported in potato chip stability. Rapeseed oilcontaining rosemary extract and methyl silicone had lower levels of polar com-pounds and polymers, and French fried potatoes had improved flavor quality (27).The effect of the rosemary extract alone was not measured. Even breading materialfrom cottonseed flour has been shown to inhibit frying oil degradation because theflour contained polyphenolic compounds (28).

Protective Properties of Antioxidant Decomposition Products

As previously discussed, the breakdown products of antioxidant compounds canhave antioxidant properties. Kim and Pratt (29) identified and characterized thedecomposition products of TBHQ heated at frying temperatures, including tertiarybutylbenzoquinone (TBBQ) as the primary and major oxidation product of TBHQ.They reported that the interconversion between TBHQ and TBBQ played thegreatest part in the antioxidant effectiveness and carry-through effect of TBHQ.

Silicone (Methyl Silicone, Polydimethylsiloxane)

Definition and Uses. A silicone is an organo-silicon polymer with a silicon-oxy-gen framework (30). The most basic silicone compound, polydimethylsiloxane, isa high-molecular-weight liquid polymer having a very low vapor pressure (<1 mmHg) (31). Polydimethylsiloxane also has very low water solubility (<100 ppb).Because it has a specific gravity of <1 g/cm3 (less than that of water), it will initial-ly form a surface film if discharged into water. Its formula, shown in Figure 4.3, isthe simplest form of any silicone (30). Polydimethylsiloxane products are fluidswith varied viscosities, depending on the molecular weight of the polydimethyl-siloxane. These fluids are clear, colorless, and odorless; thermally, chemically, andshear stable; and soluble and emulsifiable with many organic materials. Thus, theyhave many applications in industrial and food processes. Generally, silicones havelow toxicity. Silicones meet the requirements for evaluation methods and testinglevels under CFR 177.2710, are food-grade and, thus, are approved by the Food



and Drug Administration (FDA) for use in food materials and equipment that mayincidentally come in contact with foods (32). The use of polydimethylsiloxane tosuppress foaming in aqueous systems is well known and widely applied. It wasfirst reported by Martin (33) that a concentration of 0.03 ppm of polydimethyl-siloxane was sufficient to inhibit the oxidation of frying oil over a prolonged heat-ing period. Since then, numerous studies (14,20,34,35) have reported antioxidanteffects (more accurately referred to as antipolymerization effects) in frying oils ofsilicone-based additives at levels of 0.01–5 ppm with surface concentrationbetween 0.03 and 12.7 µg/cm2 (Table 4.1). Yan and White (35) showed that theaddition of 1.0 ppm methyl silicone (2.8 µg/cm2) significantly reduced the loss offatty acids in lard with two times the added cholesterol. Babayan (36) also showedthat low concentrations of polydimethylsiloxane would raise the smoke point of anoil by as much as 25°F (4°C).

Proposed Mechanisms. Although the antipolymerization effects of polydi-methylsiloxane in frying or at static high temperatures have been studied, themechanism by which methyl silicone protects oil is not completely understood.According to Gordon (37), four possible explanations exist for the protectiveeffects of polydimethylsiloxane. First, the methyl silicone may represent a physicalbarrier that prevents the penetration of oxygen into the oil from the atmosphere.Freeman et al. (14) argued against this first explanation, however, which assumesthat oxygen diffuses through the silicone layer less rapidly than through the surfacelayer of oil molecules. He concluded that there is no reason why this should be so.

Fig. 4.3. Formula structure ofpolydimethylsiloxane (31).

TABLE 4.1Different Concentrations of Methyl Silione Used by Different Researchers

Concentration used Amount of silicone(ppm)

Oil Surface(µg/cm2)

Minimum Full weight area Minimum Fulleffective protective (g) (cm2) effective protective Ref.

0.01 0.02 30 10.2 0.03 0.06 (14)0.06 0.10 30 33.2 0.05 0.09 (14)

2 NAa NA NA NA (34)5 200 78.5 12.7 (20)1 500 176.6 2.8 (35)0.2 600 176.6 0.7 (35)

aNA, not available.



A second explanation for the molecule's effect may be that polydimethylsilox-ane presents an inert surface to the atmosphere, thus inhibiting oxidation at the sur-face. Third, it may act as a chemical antioxidant, being oxidized and inhibiting thepropagation of free-radical chains with its effectiveness arising from its concentra-tion at the surface where oxidation occurs. Fourth, and finally, polydimethylsilox-ane may inhibit convection currents in the surface layer, which in turn inhibits theabsorption of oxygen from the atmosphere and the distribution of oxygen throughthe fat. Indeed, other researchers (14,38) demonstrated that silicone prevented con-vection currents in the surface layer, and that the rate of oxidation of the oil wasdependent on the rate and duration of the convection currents. An alternative find-ing is that the temperature of the air-oil interface is approximately 100°F (38°C)lower than that in the fryer. It is reasonable to think that convection currents wouldplay a part. This reasoning also may explain the results of a study by Rock et al.(34), who showed that methyl silicone could both promote and inhibit polymeriza-tion at a level of 2 ppm in frying fats, depending upon the method of heating.When thermostatically heated in a fryer at 375°F (190°C), with or without frying,fats containing methyl silicone deteriorated more slowly than did controls withoutthe additive. The reverse was true when these fats were heated and maintained at375°F (190°C) in an oven. The most reasonable conclusion from the above possi-ble mechanisms is that the protective effect of methyl silicone is caused by amonolayer of silicone on the oil-to-air surface. Further, Freeman et al. (14) showedthat the critical concentration for autopolymerization activity of methyl silicone infrying oil responded to this monolayer on the air-to-oil surface. Indeed, it is thesurface concentration, rather than the bulk concentration that governs the protec-tive effect. Freeman’s results suggested that, in general, the minimum effectivesurface concentration must be between 0.05 and 0.06 µg/cm2 of surface, as notedearlier in this chapter.

Interaction of Silicones with Fried Foods. Freeman et al. (14) further investigat-ed the fate of silicone in relation to the fried product. When potato chips were friedin an oil containing ≥2 ppm silicone, the silicone content of the used oil wasreduced to <1 ppm and the surplus was taken up by the potato chips. It was recom-mended that silicone should not be used at levels >2 ppm in frying oils because sil-icones picked up by the fried food can affect the results of experiments designed tomeasure oxidation in fried foods (14). Silicone products are also widely used forlubricating laboratory glassware; thus, trace amounts can easily contaminate sam-ples. This fact, coupled with the small amounts required to inhibit oil oxidation,can give misleading results in experiments designed to study oxidation phenome-na. Researchers should be aware of the potential contamination and take precau-tions to avoid anomalous results.

General Recommendations on Amounts of Silicones. Overall, it is recom-mended that silicone-based additives to oils used for frying foods be present at lev-



els of 0.02–2 ppm, with the minimum effective surface concentration between 0.05and 0.06 µg/cm2 and full protective surface concentration between 0.06 and 0.09µg/cm2 (14).

Plant Sterols and Components with Related Effective Structures

Studies (39,40) have demonstrated that some plant sterols (Fig. 4.4), isolated fromoat, olive, corn, wheat germ, and Vernonia anthelmintica exhibited antipolymer-ization properties in oils heated at 180°C (41,42). One of these sterols, Δ5-avena-sterol (Fig. 4.4), was similar to methyl silicone in its effectiveness at 100–180°Cwhen the oil was heated on a hotplate, but not in an oven (Gordon and Williamson,unpublished data). In addition, Δ5-avenasterol seemed to be concentrated in a layer

Fig. 4.4. Structures of ethylidene side chain, undecylenic acid, linalool, linalyl acetate,and plant sterols (44,45).

P l a n t Double s t e r o l s bond Δ5- A v e n a s t e r o l 5 , 2 4 ( 2 8 )Δ5- A v e n a s t e r o l 7 , 2 4 ( 2 8 )V e r n o s t e r o l 8 , 1 4 , 2 4 ( 2 8 )F u c o s t e r o l 5 , 2 4 ( 2 8 )S t i g m a s t e r o l 5 , 2 2β- S i t o s t e r o l 5C i t r o s t a d i e n o l 7 , 2 4 ( 2 8 )S p i n a s t e r o l 7 , 2 2Lanosterol (30 carbons) 8 , 2 7Ergosterol (29 carbons) 5 , 2 2Cholesterol (27 carbons) 5



at the surface (37). These findings suggest that Δ5-avenasterol acts as a chemicalantipolymerizer on the surface of frying oils, where oxygen is present. Other plantsterols exhibiting antipolymerization effectiveness include Δ7-avenasterol, fuco-sterol, citrostadienol, and vernosterol (Fig. 4.4) (39). However, sterols, includingcholesterol, stigmasterol, ergosterol, lanosterol, β-sitosterol, and spinasterol, wereeither ineffective or slightly increased polymerization (43).

Gordon and Magos (39) theorized that the presence of unhindered hydrogenatoms on an allylic carbon atom in the ethylidene side chain (Fig. 4.4) leads torapid reaction with lipid free radicals. Isomerization leads to a relatively stableallylic tertiary free radical, which is slow to react further, and this interrupts theautoxidation chain (Fig. 4.5). Stigmasterol does not have antipolymerization(antioxidant) activity, presumably because the rate of loss of hydrogen atoms at thetertiary carbon atoms (C-20 and C-24) is slow, as a result of steric hindrance to theapproach of a free radical. Thus, sterols with unhindered hydrogen atoms in theethylidene side chain are most effective.

Gordon and Magos (39) also proposed that further antipolymerization effectsmay arise from the presence and position of one or more endocyclic double bonds.For example, vernosterol has an effect arising from the rapid formation of free rad-icals at C-29, but slower formation of free radicals at C-11 or C-16. The latter freeradicals are stabilized by delocalization over two double bonds, which also con-tribute to the antipolymerization activity of the sterol. Thus, vernosterol should bemore effective than sterols with one endocyclic double bond, such as fucosterol.This effect was, indeed, demonstrated by Sims et al. (1972), who showed the orderof effectiveness of the sterols in safflower oil at 180°C to be as follows: verno-sterol > Δ7-avenasterol > fucosterol. Other compounds having these structuralproperties include linalool and undecylenic acid (Fig. 4.4). Both compounds have aterminal double bond, or one that will shift to the terminal position with heat.Linalool, which is relatively volatile at frying temperatures, was reacted withacetate to form the more stable linalyl acetate (LA), for testing in frying oils. Theaddition of LA at 0.04% was as effective as methyl silicone at 0.3 ppm (35). Thehigh-temperature antipolymerization effect of undecylenic acid on soybean oilheated at 180°C also was reported, but at a reduced effectiveness compared withthat of LA (35,42).

Fig. 4.5. Mechanism for the antipolymerization (antioxidant) activity of sterols (N = sterolring) (39).



Although these plant sterols are currently not commercially available as fryingfat additives, they can promote frying oil stability in their native form, eitherleached out from foods fried in the oil, or from the oil source itself. Perhaps thesecompounds will be developed commercially to provide an alternate choice to thesilicones as a natural polymerization inhibitor in frying fats.

Effects of Silicone Combined with Other Antioxidantsor Polymerization Inhibitors

The antipolymerization effect of silicone also has been studied in comparison to orin combination with other active components (14,20,35,41,43), such as citric acid(CA), BHT, TBHQ, polymeric antioxidant-Anoxomer (polymeric AO), LA, andplant sterols. Freeman et al. (14) hypothesized that in normal frying practices, thealternate heating and cooling operation should give more rapid deterioration of theoil than would an equivalent continuous heating period (see Chapter 5 in thisbook). Conventional phenolic type antioxidants, discussed earlier in this chapter,protect the oil during the cool periods; thus they would be expected to providegreater protection with the alternating regimen than with continuous heating. In astudy evaluating alternate heating and cooling periods, however, BHT had no pro-tective effect on the oil, whereas silicone had a very marked effect (14). The inac-tivity of the antioxidant suggests that BHT was substantially destroyed during thefirst hot period, but not silicone.

Warner et al. (20) showed that methyl silicone had the strongest effect of anyadditive (CA, TBHQ, or a polymeric antioxidant, polymeric AO) when used alone,in decreasing objectionable room odors in statically heated soybean oils. In all soy-bean oils tested in the study, the additive treatment responsible for the greatestdecrease in room odor intensity was methyl silicone, in combination with eitherCA or CA + TBHQ, indicating a synergistic effect.

General Overall Recommendations for Additives in Frying Fats/Oils

• Antioxidants naturally present in oils can help extend frying oil life and shelflife of the fried food.

• Blending oil containing high levels of naturally occurring antioxidants with oilcontaining low levels may improve its stability.

• The loss of tocopherols in oils may be retarded by the addition of other antiox-idants.

• Tocopherol loss is lower in less saturated oils than in more saturated oils.• Use of herbal extracts and chemical antioxidants has been shown to have a

wide range of effectiveness in frying oils. • Antipolymerization compounds, such as silicone and some plant sterols, can

be used alone or in combination with other additives in frying to protect oildecomposition and the fried food.



• Silicone can be used in frying at levels of 0.02–2 ppm, with the minimumeffective surface concentration between 0.05 and 0.06 µg/cm2, and a full pro-tective surface concentration between 0.06 and 0.09 µg/cm2.

• Plant sterols, such as vernosterol, Δ7-avenasterol, and fucosterol, may be goodalternate choices as natural polymerization inhibitors in frying fats.

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Prooxidant? J. Am. Oil Chem. Soc. 44:102A (1967).35. Yan, P.S., and P.J. White, Linalyl Acetate and Methyl Silicone Effects on Cholesterol

and Triglyceride Oxidation in Heated Lard, J. Am. Oil. Chem. Soc. 68:763–768 (1991).36. Babayan, V.K., Silicones to Raise the Smoke Point, U.S. Patent 2,998,319; Aug. 29,

1961.37. Gordon, M.H., The Mechanism of Antioxidant Action In Vitro, in Food Antioxidants,

edited by B.J.F. Hudson, Elsevier Applied Science, London, 1990, pp. 13–18.



www.silicones.net

www.appliedsilicone.com

38. Rock, S.P., and H. Roth, Factors Affecting the Rate of Deterioration in the FryingQuality of Fats II, J. Am. Oil Chem. Soc. 41:531–533 (1964).

39. Gordon, M.H., and P. Magos, The Effect of Sterols on the Oxidation of Edible Oils,Food Chem. 10:141–147 (1983).

40. White, P.J., and L.S. Armstrong, Effect of Selected Oat Sterols on the Deterioration ofHeated Soybean Oil, J. Am. Oil. Chem. Soc. 63:525–529 (1986).

41. Boskou, D., and I.D. Morton, Effect of Plant Sterols on the Rate of Deterioration ofHeated Oils, J. Sci. Food Agric. 27:928–932 (1976).

42. Yan, P.S., and P.J. White, Linalyl Acetate and Other Compounds with RelatedStructures as Antioxidant in Heated Soybean Oil, J. Agric. Food Chem. 38:1904–1908(1990).

43. Sims, R.J., J.A. Fioriti, and M.J. Kanuk, Sterol Additives as Polymerization Inhibitorsfor Frying Oils, J. Am. Oil Chem. Soc. 49:298–301 (1972).

44. Cyberlipid.org, Sterols, http://www.cyberlipid.org/sterols/ster0003.htm (2003).45. Eskin, M., Plant Food Can Be an Important Factor in the Reduction of Risk for Chronic

Disease, http://www.cjche.ca/News/protect/may99/pg17–41.pdf (2003).



http://www.cyberlipid.org/

http://www.cjche.ca/

Chapter 5

Procedures for Oil Handling in a Frying Operation

Monoj K. Gupta


IntroductionFried food products constitute one of the major sectors in the food industry. Theoperation requires careful selection of raw materials and control of processing andpackaging to deliver a product with the highest quality. Therefore, it is importantfor the frying operation to implement and follow certain procedures. Like all otherprocessing or manufacturing operations, the frying operation begins with a soundspecification for the fresh incoming raw materials, accompanied by well-definedoperating standards. In the area of raw materials, we will focus primarily on theoil. Different types of oil are used for frying a wide range of snack foods. The oilsdiffer, for example, in melting points, the degree of saturation, or color. However,there are many common analytical standards that apply to all types of oil used inthe snack food industry. These are discussed in detail.

The oil is subjected to very harsh physical and chemical conditions in a fryer.Thus, the frying oil must have very high stability. This is why the frying oil shouldhave more stringent analytical standards than those required for making salad oilsor margarine products. In addition to the quality standards for the fresh oil, thereare essential elements required for successful frying performance of the oil. Theseinclude the procedures for oil receiving, oil unloading, oil storage, fryer operation,fryer shutdown, fryer sanitation, and storage of used oil, in addition to properpackaging of the product.

Fresh Oil Quality Specifications

Normally, different oils are used for frying different snack foods. As mentioned inChapter 3, most of these oils are not interchangeable among the products. For anygiven product, the frying oil is chosen on the basis of the following criteria: (i)product flavor; (ii) product texture; (iii) mouth-feel; (iv) aftertaste; (v) availability;(vi) product shelf life; (vii) cost; and (viii) nutritional requirements. Items (i)–(iv)are related to product quality and consumer acceptability. These are establishedthrough consumer tests for preference and acceptance. Item (vi) is establishedthrough shelf-life test protocols suitable for the type of product, the distributionsystem, and the packaging material. Neither consumer acceptability nor shelf lifefor a product can be achieved if the incoming oil quality is unsatisfactory. Items



(v), (vi), and (vii) are economic factors that determine the cost of the final product.Recently, item (viii) has been receiving more attention because of the new knowl-edge about trans fat and saturated fat intake in our diet.

Frying is a process in which heat transfer, mass transfer, and chemical reac-tions occur simultaneously. Hot oil supplies the thermal energy and removes mois-ture from the food. The food develops fried food flavor and darker surface colorthrough the Maillard reaction. At the same time, several simple and complexchemical reactions take place in the oil. The principal reactions in the oil are thefollowing: hydrolysis, autoxidation, and polymerization. Hydrolysis is the reactionbetween the triglyceride and water, which produces free fatty acids (FFA), diglyc-erides, and monoglycerides during frying. Oil and water must be in perfect solutionfor this reaction to occur. Oil and water, however, are not intersoluble, except atvery high temperature (>500°F), a temperature far beyond the range of normal fry-ing and achieved only under high pressure.

The intersolubility of oil and water can be greatly increased by adding a smallamount of surfactant (emulsifier), such as soap or natural emulsifiers (phospho-lipids, diglycerides, and monoglycerides). Vegetable oils always contain smallamounts of phospholipids, diglycerides, and monoglycerides. The chemical refin-ing process can produce appreciable quantities of diglycerides and monoglyceridesin the refined oil if the crude oil is of poor quality, if there is a caustic overdose inthe refining process, or if the oil is refined a second time for some reason. Most ofthe monoglycerides, but not the diglycerides, are distilled in the deodorizer. Thus,fresh oil may contain an appreciable amount of diglycerides and a small amount ofmonoglycerides.

These natural surfactants present in the fresh oil can increase the intersolubili-ty of oil and water and promote hydrolysis of the oil in frying. Therefore, fresh oilfor frying applications must contain very low levels of these natural emulsifyingagents (see Table 5.1). Monoglycerides and diglycerides depress the smoke pointof oil. This may prevent the operator from heating the oil to the proper frying tem-perature, resulting in underfried products. A low smoke point of the oil can also bea fire hazard in the frying operation. Diglycerides decompose to produce mono-glycerides during frying. Therefore, fresh oil for frying must contain these com-pounds at low levels. Lower than normal smoke point indicates incomplete refin-ing of the oil. This can have an adverse effect on the shelf life of an industrialproduct. A low initial smoke point in the fresh oil may lead to excessive discardingof oil in a restaurant or food service operation.

In addition to the above compounds, the oil may contain high levels of calci-um and magnesium as natural trace impurities. These impurities are especiallynoticed in the refined oil when very poor quality crude oil is used. Sometimes,these impurities can be found at high levels in refined oils due to inadequate refin-ing and bleaching of the crude oil.

Calcium and magnesium form soap when they react with the FFA or the neu-tral oil. These soaps then act as emulsifying agents. Therefore, frying oils must



have very low concentrations of calcium and magnesium (Table 5.1). Copper cancatalyze the hydrolysis of oil, but the copper content of refined vegetable oils inthe United States is extremely low. Metals, such as iron, can initiate autoxidation.Freshly processed oils always contain trace amounts of iron. Autoxidation is one ofthe major modes of oil degradation in frying. Autoxidation of oil leads to poor fla-vor and reduced shelf life in a fried product. Therefore, frying oil must contain avery low level of iron (Table 5.1).

Conjugated dienes are formed at the onset of autoxidation in the oil and areindicative of the oxidative state of the oil. Conjugated dienes are formed from thepolyunsaturated fatty acids in the oil. For example, in linoleic acid, the double

TABLE 5.1 Analytical Standards Recommended for Frying Oils

Not > Analytical methodAnalysis Desired standard (Not <) (AOCS)

Triglyceride (%) 96–98 96 Cd 11c-93Monoglyceride (%) <0.3? 0.4 Cd 11b-91 Cd 11d-96Diglycerideb (%) <1.0? 1.5 Cd 11b-91 Cd 11d-96Free fatty acid (%) <0.03 0.05 Ca 5a-40Peroxide value (mEq/kg) <0.5 1.0 Cd 8b-90para-Anidisine value <4.0 6 Cd 18-90Soap (ppm) 0.0 0.0 Cc 17-95Phosphorus (ppm) <0.5 1.0 Ca 12b-92Iron (ppm) <0.2 0.5 Ca 18b-91Calcium (ppm) <0.2 0.5 Ca 15b-87Magnesium (ppm) <0.2 0.5 Ca 15b-87Sodium (ppm) Trace 0.2 Ca 15b-87Chlorophyllc (ppb) 30 70 Cc 13d-55Lovibond colord Depends on oil type — Cc 13b-45Tocopherolse (ppm) 800–1000 1200 (700) Ce 8-89Polar compounds (%) 0–2 4.0 Cd 20-91Polymers (%) 0–1 2.0 Cd 22-91Conjugated dienes (%) 0–1.0 1.5 Ti 1a-64Active oxygen methodf (h) Depends on oil type Cd 12-57Oxidative Stability Index (h)g Depends on oil type (7) Cd 12d-92Smoke point (°F)h See footnote Cc 9a-48Flavor grade �8 (7) Cg 2-83aCommercial palm oil or palmolein contains a higher concentration (as much as 1%).bCommercial palm oil or palmolein contains a higher concentration (4–11%).c<30 ppb for soybean and canola. Promotes photooxidation at higher concentrations.d<0.1 for soybean, canola, sunflower; <3.0 for cottonseed and palm; <2.0 for corn.e800 ppm in cottonseed, soybean; 500–600 ppm in sunflower, corn and canola.f15–20 h in corn, and cottonseed; 12–15 h in soybean, canola and sunflower (with no antioxidants); 30–40 hfor high-oleic sunflower; 40–50 h for palm oil; 50–60 h for palmolein; 100 h for heavy-duty frying shortening;150–200 h heavy-duty frying shortening with tert-butylhydroquinone as antioxidant.g8–9 h at 110°C test for cottonseed, corn, soybean (100 iodine value).h460°F minimum for chemically refined fresh seed oils; 410–428°F for physically refined palmolein.



bonds are located between the following carbon atoms in the fatty acid molecule: 9and 10; 12 and 13; 15 and 16. The double bonds in this molecule are separated bytwo single bonds between the carbon atoms. At the onset of autoxidation, the dou-ble bonds shift to the following positions: between carbon atoms 10 and 11; 12 and13 (remains unchanged); 14 and 15. Here, the double bonds are separated by onesingle bond between two carbon atoms. A high value of conjugated dienes in theoil indicates that the oil will undergo oxidation rapidly, when it is exposed to hightemperature and oxygen. Therefore, it is important to receive fresh oils containinglow levels of conjugated dienes for frying (Table 5.1).

The peroxide value (PV) indicates the primary state of oil oxidation. A low PV isrequired for frying oil. The p a r a-anisidine value (pAV), which indicates the secondarystate of oil oxidation, is a very important indicator of frying oil stability. Crude oil con-taining a high PV can be refined, bleached, and deodorized to a low PV, but the pAVwould remain high in such an oil, indicating a poor history or abuse of the oil beforerefining. Such oil would oxidize rapidly in the fryer. Therefore, it is important to setlow values for both PV and pAV for the fresh oil (Table 5.1).

FFA are readily removed in the refining and deodorization steps. Therefore, prop-erly refined oil should always have a low FFA content (0.02–0.04%). A FFA content>0.05% in the fresh oil indicates improper or incomplete refining and deodorizing ofthe crude oil. Therefore, one can expect the oil to perform poorly in frying, showingboth rapid hydrolysis and autoxidation. Therefore, the FFA in a fresh frying oil mustbe <0.05%. Some argue that the addition of citric acid or phosphoric acid as a chelatorin the deodorized oil increases the FFA. Therefore, a maximum value of 0.05% forFFA may be too low. In the author's experience, the amount of chelator added in theoil increases the FFA by 0.006%. Therefore, in the opinion of the author, this is a weakargument. A value of FFA >0.05% indicates that there might be some trace impuritiesleft in the oil, which can reduce the shelf life of the fried product.

Polymers are formed when the oil is heated. The amount of polymers formedduring frying depends on: (i) frying temperature; (ii) type of oil; (iii) type and com-position of the food being fried; (iv) type of fryer; and (v) operating conditions in agiven fryer. The frying process generates two types of polymers, i.e., thermal p o l y-mers and oxidative polymers. Thermal polymers are formed when heat is applied tothe oil. Oxidative polymers are formed when two or more of the free radicals fromthe autoxidation reaction react together to form a larger molecule (commonlyreferred to as the termination step in autoxidation). Thermal polymers can impart abitter aftertaste to the freshly fried product. Oxidative polymers may not always indi-cate a problem with flavor in the fresh product, but may cause rapid deterioration ofthe flavor of the product during storage. The formation of thermal polymers in fryingcan be avoided through proper fryer operating practices. The presence of trace metalsand natural emulsifiers can produce oxidative polymers in the oil during frying; thus,the fresh oil must contain low levels of these components.

Table 5.1 lists the recommended analytical standards for fresh frying oil. Thislist does not include the melting points, solid fat contents or Lovibond colors,



because these values vary with the type of oil. Table 5.1 indicates that ~96–98% ofthe oil is comprised of triglycerides (or neutral oil). The rest of the components arenontriglycerides.

All vegetable oils contain tocopherols, which are natural antioxidants. Thegoal of proper oil refining is to retain a high level of these tocopherols in thedeodorized oil. The most common tocopherols in vegetable oils are α, β- (smallamounts), γ-, and δ-tocopherols. α-Tocopherol provides resistance to photooxida-tion of the oil; γ- and δ-tocopherols provide autoxidative stability to the oil.Therefore, oils with higher levels of γ- and δ-tocopherols, low linolenic acid, andlow levels of trace impurities exhibit higher oxidative stability in the fryingprocess. Table 5.1 indicates that the level of tocopherols must not exceed certainupper limits (shown for soybean oil). A high concentration of tocopherols cancause rapid oxidation of the oil in frying because some of the decomposition prod-ucts of tocopherols are prooxidants.

The PV of the oil must be 0.0 mEq/kg in freshly deodorized oil. A higher valuemay indicate either a poor vacuum in the deodorizer or improper cooling and storageof the deodorized oil. The PV must be <1.0 mEq/kg as received at the frying plant. Inaddition, the oil must be treated with citric acid at the end of the deodorization cycleby the processor to chelate and reduce trace metals in the oil. The flavor of the oilmust be bland, weak buttery, or weak nutty. The color of the oil must be typical andthere must be absolutely no off- or foreign odor in the fresh oil.

Oil Loading at the Oil Processor and Transportation

Oil Loading. The snack food manufacturing company must specify the methodfor loading fresh oil into a truck or rail car. They also must specify sampling andsanitation procedures related to oil storage, loading, and the mode of filling thevessel. Table 5.2 presents the list of procedures a snack food manufacturer shouldinsist upon from an oil supplier (processor). The oil manufacturer’s operationshould be inspected by the snack food company staff to confirm compliance. Someof these procedures are related to oil quality and stability, whereas others relate toproduct safety or regulatory requirements. The specific items are designated as Q,P S, or R, to indicate quality, product safety, and regulatory compliance, respec-tively, in the specific areas indicated.

Oil Transportation. Trucks are generally used for shipping oil relatively shortdistances, requiring 2–12 h of travel time. A team of two drivers is used for longerdistances where nonstop driving is needed. Hydrogenated oils can solidify duringtravel, especially in the winter. Heated and insulated trucks with proper tempera-ture control can be used. The heating coils should preferably be located in an outerjacket to avoid scorching of the oil, but this type of truck is rare. Some trucks usethe heat from the truck exhaust to prevent oil solidification, but this practice usual-ly results in poor temperature control and can cause scorching of the oil during



transit. Refined oil is also transported in rail cars in the United States, generally forlong distance deliveries. Two thousand-pound totes are used for smaller users.These totes are very convenient. Some of them are reusable, which makes thispractice environmentally friendly.

Receiving Oil at the Snack Food Plant. It is necessary for a snack food manu-facturer to have well-defined procedures for oil receiving, unloading, and storage.The oil receiving procedure is outlined in Table 5.3. The oil must not be unloadeduntil all quality, product safety, and regulatory conditions as outlined in Table 5.3are met.

Oil Unloading. After the oil is released for unloading, certain unloading proce-dures as outlined in Table 5.4 must be followed. However, sometimes the hydro-

TABLE 5.2 Oil Loading Procedures at the Oil Processora

1 . Both the inside and outside of the truck must be clean (PS, Q) .2 . There should be no foreign odor in the truck (Q, PS) .3 . Cleanliness certificate must indicate the material transported in the previous load and it must

be food compatible (P S) .4 . The certificate must show where the truck was washed and when (P S) .5 . Oil is stored in the storage tank under nitrogen protection (Q) .6 . Headspace oxygen in the oil storage tank should be <0.5% (Q) .7 . The oil storage tank must have temperature control (Q) .8 . Liquid oil temperature must be <110°F (Q) .9 . Hydrogenated oil temperature must be no >10°F above the melting point of the oil (Q) .

1 0 . The oil passes through a bag filter with a 25- to 100-µm opening before filling the truck (P S) .1 1 . The oil is saturated with nitrogen as it is being pumped into the truck, using an in-line nitrogen

diffuser (Q) .1 2 . The track is loaded from the bottom (bottom filled) (Q) .1 3 . Oil samples are taken from the top, middle, and bottom of the truck after loading is completed

by using a zone sampler, mixed in a clean container, and then analyzed. This is the official oilloading analysis (not from the storage tank) (Q) .

1 4 . A loading sample is shipped along with the truck (Q , R) .1 5 . A Cerificate of Analysis must be signed by the supplier showing the type of oil and all pertinent

analyses. This certificate is sent along with all shipping documents (Q, R) .1 6 . The truck must be filled to the fullest capacity. A minimum air space is left on top of the oil (Q) .1 7 . Do not transport partially filled trucks (Q) .1 8 . Use a smaller or a compartmentalized truck for smaller loads (Q) .1 9 . After the truck is loaded, the headspace in the truck is purged with nitrogen and then the hatch

is closed (Q) .2 0 . Seals are applied at the appropriate locations (top hatch, discharge line, or any other port

through which one could access the oil inside the truck) (P S) .2 1 . Seal numbers are recorded on the Bill of Lading (P S) .2 2 . The supplier should retain a representative shipping sample of the oil for future reference

(Q, PS) .aP S, product safety; Q, oil quality; R, regulatory compliance.



genated oil has to be melted before sampling and unloading. The key in meltingthe solidified fat in the vessel is to use low-pressure (<25 psi, preferably <15 psi)saturated steam, a thermodynamic steam trap to condense the steam in the heatingcoil, and discharge the condensate at a preset temperature. Table 5.5 outlines theprocedure for heating an oil truck or rail car. Figure 5.1 shows the schematic dia-gram for the oil heating system to prepare the truck or the rail car for unloading,and Figure 5.2 shows the schematic diagram for the oil unloading system.

Heating a Truck or Rail Car to Melt the Solidified Fat. Trucks or rail cars areheated with low-pressure, saturated steam. Steam contains thermal energy. Most ofthe energy in steam is present as latent heat of condensation. Nearly 1000 Btu ofheat is released when 1 lb of low pressure steam is condensed. Therefore, forcingcomplete condensation of the steam increases the energy utilization from the

TABLE 5.3 Oil Receiving and Unloading at the Snack Food Planta

1 . Check the appearance of the truck. It must be clean on the outside. If not, the truck should berejected (P S) .

2 . Inspect the seals. They must not be broken. Do not accept the oil if one or more seals arebroken or missing (P S) .

3 . Do not unload the oil if the numbers on the seals do not match (PS, R, Q) those recorded on theBill of Lading.

4 . Resolve the discrepancy with the help of the purchasing department and the supplier. Do notunload the oil until the matter has been resolved (PS, R, Q) .

5 . Check the Bill of Lading for the type of oil and compare it against the Certificate of Analysis.These two must match (Q, R) .

6 . If there is a disagreement between the two, the type of oil in the truck or rail car, it must beresolved with the help of the supplier and/or analytical tests (Q, R) and the purchasing d e p a r t m e n t .

7 . The oil can be considered for unloading only after the oil is positively identified (Q, R) .8 . Once the issue is resolved, open the top hatch and check the interior of the truck or rail car. Do

not accept the oil if one or more of the following occur:• The truck has a foreign odor (P S) .• The oil contains foreign matter (P S) .• The oil has an unusual color (PS, Q) .9 . If the oil passes through steps 1–9, check oil temperature. It must be <110°F for liquid oil (Q) .

1 0 . Hydrogenated oil may have to be melted first. Use the procedure outlined under oil unloading(Table 5.4).

1 1 . Collect oil samples from top, middle, and bottom of the track using a zone sampler, mix them ina container, and analyze for free fatty acids (FFA), peroxide value (PV), color, odor, and flavor(Q) .

1 2 . Accept the oil for unloading if:F F A 0.05%, maximum (Q) P V <1.0 mEq/kg, maximum (Q)O d o r None (Q, PS)F l a v o r Sweet, buttery or nutty (Q)

aSee Table 5.2 for abbreviations.



steam. Presetting the condensate discharge temperature to a low limit reduces therisk of overheating or scorching the oil at the heating surface.

Oil Storage

The oil must be stored properly after it is unloaded. During storage, the oil must bemonitored daily. The following daily checks are recommended: (i) oxygen in the tankhead space; (ii) PV of the oil; (iii) FFA of the oil; and (iv) temperature of the oil.

The oxygen in the tank head space must be maintained at <0.5%. The tankhead space should be purged with nitrogen if the oxygen content is high. Purgingof the tank head space should continue until the oxygen in the tank head spacedrops below 0.5%.

A rise in PV indicates the presence of dissolved oxygen in the oil. Using a cin-tered metal diffuser at the bottom of the tank, one should sparge the oil with nitrogento remove the dissolved oxygen from it. The sparging procedure should continue untilthe PV stabilizes. The oil should be used rapidly if the PV continues to rise.

The FFA in oil does not rise during storage when the oil is properly processed;however, its constant value should be confirmed by resampling. A rise in FFA in

TABLE 5.4 Oil Unloading Procedure

1 . Check and verify inventory space in the designated tank for unloading the oil. Dedicated tanksmust be used for each type of oil (Q, R) .

2 . Check if there is any oil left in the tank. If so, collect a sample and analyze for free fatty acids(FFA), peroxide value (PV), and flavor. The results must indicate the following:F F A <0.05% (Q) .P V <2.0 (if the tank is nitrogen blanketed) (Q) .

<4.0 (if the tank is not nitrogen blanketed) (Q) .F l a v o r Good (Q) .

3 . Discard the oil if the FFA is >0.05% (Q), and/or the PV is >4.0 mEq/kg.4 . Do not unload fresh oil on top of the used oil if the analysis of the residential oil in the tank

does not meet the above standards (Q) .5 . Use up the oil rapidly if the FFA is <0.05% but the PV is >2.0 mEq/kg (Q). The upper limit for

PV is 4.0 mEq/kg (Q) .6 . Start the oil-unloading pump.7 . The oil must pass through a filter located on the suction side of the unloading group. Use a

basket filter with a 150-mesh stainless steel screen (P S) .8 . Inspect the basket after every load is finished for any foreign material (P S) .9 . The oil from the filter should pass through an in-line nitrogen diffuser to saturate the oil with

nitrogen (Q) .1 0 . Discharge the oil into the storage tank. The discharge pipe must extend to the bottom of the

tank, near the floor (Q) .1 1 . Blow the line clear with nitrogen at the end of unloading the vessel to clear the line (Q, R) .1 2 . Check the oxygen content in the tank after unloading the oil (Q) .1 3 . Sparge the tank with nitrogen if the oxygen content is >0.5% and continue to sparge the tank

until the oxygen in the tank is <0.5% (Q)aSee Table 5.2 for abbreviations.



fresh oil during storage can be caused by the following: high oil storage tempera-ture, a leak on the heating coil, especially if it is steam heated, or high phosphorus(>3 ppm) in the fresh oil. The oil must not be used if the FFA rises during storageand exceeds 0.05% because this indicates some basic problem with the oil and the riskof early development of rancid flavor in the packaged snack food in storage. The tem-perature of the oil and the possibility of a coil leak must be investigated and corrected

TABLE 5.5 Heating Truck or Rail Cara

1 . Have a supply of 10–15 psig saturated (not superheated) steam.2 . Have a thermodynamic steam trap. The capacity of the steam trap should be based on:• The amount of oil to be melted in certain number of hours.• Condensate discharge temperature is set at 140–150°F.3 . Spot the truck or rail car at the unloading station of heating.4 . Connect the steam supply line to the inlet of the heating coil.5 . Crack open the steam valve to purge the condensate from the line and the heating coil in the

v e s s e l .6 . Close the valve.7 . Connect the thermodynamic steam trap at the discharge side of the heating coil.8 . Slowly open the steam valve.9 . Steam will flow into the coil and start condensing.

1 0 . Condensate will discharge through the trap as it reaches the preset discharge temperature.1 1 . These steps will greatly reduce the time to melt the solidified fat in the vessel.

N o t e :• The bulk temperature in the vessel will remain <130°F when the procedure is followed

p r o p e r l y .aRefer to Figure 5.1.

Fig. 5.1. Schematic diagram for steam heating system.

Thermodynamic stream trays.



immediately. In the absence of high oil temperature or coil leaks, phosphorus in the oilshould be checked. The oil must be returned to the supplier for reprocessing if it has ahigh phosphorus content (see Table 5.1). The liquid oil temperature must be main-tained below 110°F in storage. The storage temperature for hydrogenated oil willdepend on its melting point. Overheating of oil in storage must be avoided. Immediatecorrective action should be taken if there is any sign of overheating of oil in a tank.

Fryer Operation: (Start-up, Shutdown, Steady-State Operation,Temporary Shutdown, Used Oil Storage, and Sanitation)

There are strict requirements for each of the pertinent steps in a fryer operation,start-up, shutdown, steady-state operation, temporary shutdown, used oil storage,and sanitation. For ease of explanation, the description will begin with a completeshutdown procedure and used oil storage. Some of the typical shutdown practicesused by the snack food industry are discussed below:

Intermittent Operation (for 8 or 16 h/d). Practice 1: At the end of the operation,the oil is left in the fryer to cool down naturally. Practice 2: The oil is naturallycooled, filtered, and put back into the fryer. Practice 3: Practice 2 is followed butthe fryer is sanitized before the oil is returned to the fryer. Practice 4: The oil isnaturally cooled, filtered, and stored in a holding tank under atmospheric condi-tions. The fryer is sanitized. The oil remains in the holding tank.

In all of the above cases, the fryer is started with the used oil, plus a small amountof fresh makeup oil added to reach the fryer fill-volume. Fresh oil is then added to thefryer to replenish the fryer volume during frying. The above practices seriously dam-age the oil, and produce snack foods that have poor shelf-life stability.

None of the above practices are good for oil quality. The underlying causes forthe degradation of oil in the these practices are discussed:

Fig. 5.2. Schematic diagram for the oil unloading system.



• The oil left in the fryer can absorb oxygen from the air and undergo primaryoxidation, forming peroxides (measured as PV). This PV increase may not benoticed because the peroxides rapidly decompose when the oil is heated in thefryer the next day and the PV drops to a lower value. When the peroxidesdecompose, the pAV value increases and catalyzes further oil decomposition.This process will be discussed in detail later in this chapter.

• Unfiltered oil retains all of the crumbs, which become charred with the heat.These charred materials in the oil can absorb a large amount of the oil decom-position products and can catalyze oxidative, and to some degree, hydrolyticreactions in the oil during subsequent frying.

• The suspended material in the oil can alter the color and flavor of the productbeing fried, and may result in product rejection for color and/or flavor.

The above-mentioned fryer shutdown procedures may be satisfactory for par-fried frozen products because the product is stored in the freezer until the productis fried and served. Normally, a par-fried product is consumed immediately after itgoes through the final frying step in the restaurant or food service operation. Inthese instances, the effect of poor oil quality is less evident. However, even thefrozen par-fried products can develop off-flavor, depending on the absolute levelof oil degradation at the time the product is collected.

Continuous Operation. Like the intermittent processes, the shut-down procedurecan vary greatly in a continuous frying operation. Typical practices are listed.Practice 1: The oil is circulated through the oil recirculating system where a built-inatmospheric cooling device cools the oil. The cooled oil is left in the fryer for thenext start-up. Practice 2: Typically, the oil is cooled to 250–260°F by circulating theoil. The oil is filtered and stored in a temporary holding tank. The fryer is sanitizedand the oil is transferred back into the fryer. In this type of operation, the same tem-porary holding tank is used in conjunction with different fryers. Practice 3: The oil iscooled and filtered as described in Practice 2. The oil from each fryer is stored in itsown holding tank under atmospheric conditions. The fryer is sanitized.

The procedures outlined above are slightly better than those described for theintermittent operations. However, there are some concerns regarding oil degrada-tion because absorption of oxygen by the oil is directly proportional to the surfacearea of the oil. Therefore, leaving the oil in the fryer, as described under Practices1 and 2, increases oxygen absorption by the oil and causes high oil oxidation dur-ing storage. In addition to the large surface area, the fryer contains a large amountof residual heat from the tons of metal around the fryer pan. This heat is transmit-ted back into the oil as it is left in the fryer, causing a rise in temperature and poly-merization, in addition to oxidation of the oil. Sharing the same temporary holdingtank raises the following concerns: (i) It increases the chances for cross-mixing ofoils from fryers that are frying different products, which may affect product flavor;(ii) cross contamination of oils may violate the product-labeling requirement,



which can become a regulatory issue; and (iii) the cooling of the oil to 250–260°Fis not enough to minimize oil degradation during storage.

Fryer Shutdown and Used Oil Transfer Procedure

To achieve proper shutdown and maintain good oil quality, it is necessary to havea cooling system that cools the oil rapidly at the end of the operation. The oil isthen saturated with nitrogen before it is stored in a holding tank maintained undernitrogen protection. This practice minimizes the oxidative degradation of the oil asit is generally experienced in the frying industry. In reality, the oil in the fryer isdamaged most during the following operating steps: (i) shutdown; (ii) start-up; (iii)temporary fryer shutdown; and (iv) low fryer throughput.

Oxidative degradation of oil can be monitored simply by following the PV valuesduring shut down because under this condition, the rate of formation of PV exceedsthat of its breakdown. Figure 5.3 shows the PV data from a continuous potato chipfryer with natural cooling. The PV rose from 4 to 35 in 120 min while the oil tem-perature dropped from 350 to 245°F. The PV of the oil was 6 at 15 min and 8 after30 min of cooling. The PV rose sharply after 30 min and reached a value of 35 after120 min of oil circulation. These changes suggest that the sharp increase in PV dur-ing shutdown could be controlled if the fryer oil is cooled rapidly and immediatelywhen frying is stopped. The oil could be protected further by saturating it with nitro-gen and then storing it in a holding tank, which itself is maintained under a nitrogenblanket (like fresh oil). The head-space oxygen content must be <0.5%. Purging andsparging requirements for the holding tank are the same as those described for oil stor-age. Table 5.6 outlines recommended fryer shutdown procedures. The schematic dia-gram for the oil cooling system is shown in Figure 5.4.

Comment: It is important to cool the oil as soon as the frying process stops, tominimize the increase in the PV of the oil caused by the reaction with oxygen. Thisis because the secondary and tertiary oxidation products are formed as the perox-ides break down. Peroxides do not impart off-flavor to the fried product but thebreakdown components impart off-flavor to the fried product and reduce its shelflife. Nitrogen sparging helps remove the dissolved oxygen from the oil. Some of

Cooling time, 15-min intervalFig. 5.3. Peroxide value(PV) in fryer oil at shutdown.



the dissolved nitrogen comes out of the oil as the oil enters the holding tank. Inaddition, the nitrogen blanket in the holding tank (not shown in the diagram) pre-vents additional oxygen absorption at the surface of the oil in storage.

Figure 5.5 shows the PV data when the oil is cooled down rapidly through anexternal cooler using a system like the one shown in Figure 5.4. The oil tempera-ture dropped to 140°F in 25 min and the PV of the oil rose only from 4 to 6mEq/kg during cooling.

Fryer Sanitation

It is always recommended that the fryer and the accessories be sanitized at the endof the operation. The purpose of sanitation is to remove the residual oil and theparticulate matter accumulated in the system. If not sanitized, the residual oil in the

TABLE 5.6 Recommended Oil Cooling Procedures

1 . Make sure that the city water supply is on, the surge tank is full, and the mechanical float isworking before fryer shutdown.

2 . Turn off the heat as soon as the last product enters the fryer.3 . Sample the oil and check the peroxide value (PV) and free fatty acids (FFA) just before cooling

s t a r t s .4 . Open the manual valve MV-2.5 . Open the manual valves at the inlet and outlet of the filter and the cooler (not shown in the

d i a g r a m ) .6 . Start cooling water pump P-2 as soon as the last product leaves the fryer.7 . Open the 3-way valve to recirculate the oil back to the fryer.8 . Start oil pump P-1.9 . Open the 3-way valve to the holding tank when the oil temperature (leaving the cooler) reaches

2 6 0 – 2 7 0 ° F .1 0 . Alternatively, cool the oil to 140°F by recirculating it through the cooler and then transfer it to

the holding tank.1 1 . Open the nitrogen feed into the in-line diffuser as soon as oil transfer begins.1 2 . Adjust nitrogen flow to 0.12–0.15 ft3/gal oil flow per minute.1 3 . Continue to transfer the oil to the holding tank until the fryer is empty.1 4 . Close the nitrogen valve.1 5 . Stop the water pump and oil pump.1 6 . Drain the fryer, heat exchanger, piping, and accessories by using a positive displacement

scavenger pump and send the oil to the holding tank.1 7 . Prepare for sanitation.1 8 . Check the PV and FFA in the oil in the holding tank immediately after the oil has been

t r a n s f e r r e d .

N o t e s :• The FFA in the oil will be the same as it was before the oil was cooled and transferred.• The PV in the oil from the holding tank must be no greater than 5 units above what was

observed in Step #3.• Used oil stored for >5 d may not be suitable for use.

Refer to Figure 5.4.



system will continue to be oxidized, producing free radicals that catalyze further oildecomposition during the subsequent operation. The crumbs act as a sponge andabsorb the decomposed oil components, creating a concentrated source of catalyst foroil decomposition. Nonsanitized fryers show rapid hydrolysis and oxidation of the oilin subsequent operation. Table 5.7 lists the recommended steps for fryer sanitation.

Fryer Start-Up

Several prestart-up checks are recommended to have a smooth fryer start-up, aswell as to obtain good product shelf life. These include the following: (i) check thefresh oil quality (PV, FFA, pAV, and flavor); (ii) check the used oil quality (PV,FFA and pAV); (iii) check all preparatory and feed systems; and (iv) precheck thepackaging system, seasoner, salt applicator, and the conveyor to packaging.

Fig. 5.4. Schematic diagram for oil cooling and transfer.

Cooling time, 15-min interval

Fig. 5.5. Peroxide value(PV) in fryer oil duringshutdown with rapidcooling.



The above inspection must be completed 3–4 h before actual frying of theproduct to prevent undue delays at start-up while the hot oil remains in the idlefryer. Any issue with the equipment must be corrected even before the oil is

TABLE 5.7 Fryer Sanitation Procedures

1 . Open the manual drain valves to remove the last bit of oil remaining in the system.2 . Close the valves.3 . Fill the fryer with water (no caustic or detergent), heat the water to 170–180°F, and circulate it

for 15 min to remove most of the oil from the system.4 . Drain the water.5 . Close all drain valves.6 . Refill the fryer with water, heat it to 170–180°F, and start recirculating the water.7 . Add sufficient caustic into the fryer to make a 5% solution (no stronger).8 . Circulate the caustic solution for 4–6 h. Maintain the heat.9 . Drain the water from the fryer.

1 0 . Refill the system with water, circulate for 15 min and drain it.1 1 . Refill the fryer with water for a second rinse.1 2 . Add one quart to two gallons of vinegar into the fryer, depending on the size of the fryer and

continue recirculation for 15 min.1 3 . Rinse the fryer once more.1 4 . Check the pH of the water in the fryer while recirculating. The pH of the sample should be the

same as that of the city water, and not always 7. This is because the pH of the city water is notalways 7. The pH must be read on a pH meter, for accuracy, and not with pH paper.

1 5 . Empty the fryer.1 6 . Open all drain valves to drain the residual water.1 7 . Close the drain valves.1 8 . Check the fryer pan for cleanliness. For small direct-fired fryers, the pans are sometimes cleaned

with sanitizing foam, containing detergent. The pan must be thoroughly rinsed and the pH ofthe rinse water also must be checked.

N o t e s :• The residual oil from the fryer system is pumped out using a scavenger pump during shutdown.

However, the residual water from the fryer system is not removed at the end of sanitation in thesame manner.

• Because water can remain in the frying system, one can expect the caustic solution also to bepresent after sanitation unless proper neutralization is done with the vinegar.

• Caustic remaining in the system reacts readily with the FFA and the neutral oil, as the fryer isfilled and the oil dewatering step is begun. The presence of soap in the oil causes a rapidincrease in FFA in the fryer oil, rapid oil oxidation, and loss of product shelf life.

• Proper neutralization and careful drainage of the residual water is therefore important to reducethe start-up time and the risk of having any leftover caustic or detergent in the system.

• There is a misconception among the snack food operations that the pH of the rinse water mustbe 7.0. This is incorrect. The pH of the water after the final rinse must match that of the citywater used for rinsing the fryer. City water may have a pH ranging from 6.5 to 8.5, dependingon the soil condition in the area. Therefore, checking for a pH of 7.0 can allow either acid oralkali to remain in the system.

• The pH of the rinse water is checked with pH paper in most plants. A pH meter should be usedfor better accuracy.



pumped into the fryer. Oil analyses must be performed on the fresh and used oils toconfirm their suitability for use. Recommended oil analyses are listed below:

Fresh Oil: FFA < 0.05% and no higher than at receiptTPV <2, preferably <1PAV <6, preferably <4Flavor: Bland, sweet, or buttery

Note: The above values of PV and pAV for fresh oil are higher than the ones shown inTable 5.1. This is because there is always some increase in these values while the oilis stored, even under nitrogen.

Used Oil: FFA <0.5%, and no higher than at shutdownPV <5 mEq/kg, preferably no >2 mEq/kg units above the PVvalue at shutdown

After all prechecks are made and found satisfactory, the plant has to prepare forstart-up. The recommended procedure is listed in Table 5.8.

Comment: A layer of foam on the surface of the oil during dewatering indicates thepresence of soap left in the system due to poor rinsing during sanitation. The soapthen catalyzes the hydrolysis and oxidation of the fryer oil. The oil must beremoved from the fryer and discarded. The fryer must be rinsed and refilled withnew oil. The presence of soap in the fryer oil can greatly reduce product shelf life.In addition, contamination of fryer oil with soap can be considered adulteration incertain countries. This may result in a fine from the local or federal regulatoryagency. Therefore, the contaminated oil must be discarded.

Fryer Operation

A fryer is like a chemical reactor. It requires a uniform feed, proper temperaturecontrol, and replenishment of reactant (oil) at a steady rate as it is depleted by theoil absorption in the fried product by uniformly feeding the fryer with product atthe designed rate. This concept suggests that the following conditions must bemaintained: the fryer is operated at the maximum designed capacity at all times;the inlet and outlet temperatures of the oil are maintained according to the processspecifications; the oil makeup is done automatically, using a level control system;and the fryer is not shut down frequently such as for lunch and coffee breaks.

During normal operation of a continuous fryer, the FFA rises, reaches asteady-state value within 24 h of frying, and remains essentially unchanged unlessprocess interruptions occur. The steady-state value for FFA depends on the follow-ing factors: (i) type of product being fried; (ii) temperature of frying; (iii) type offryer; and (iv) impurities in the incoming oil. In a single-zone fryer, potato chipsare fried in oil with an inlet temperature of 350–365°F and a temperature drop of



40–45°F, between the inlet and the outlet of the fryer. In a multizone fryer, the oilenters the fryer at different locations; this helps to retain a more even temperaturealong the fryer and can also significantly increase the oil volume unless the designis done with utmost care. Frying time for potato chips is generally 2–3 min.Tortilla chips are fried in oil with an inlet temperature of 350–360°F for ~60 s.There is a temperature drop of 8–10°F in the oil between the inlet and exit of thetortilla chip fryer. The fryer pan can be designed in the shape of a horseshoe orstraight, like that of a potato chip fryer. Extruded products and pellets are fried for<60 s at higher temperatures, ranging from 380 to 420°F.

Free Fatty Acids

The FFA value of the fryer oil is checked in almost every frying operation to deter-mine oil quality during frying. The FFA ranges between 0.24 and 0.28% in a contin-uous potato chip fryer, and between 0.30 and 0.35% in a continuous tortilla chipfryer. The FFA can be somewhat lower for a tortilla chip fryer, if the chips are madefrom masa and not from corn freshly cooked with lime. The FFA of the fryer oil is

TABLE 5.8 Fryer Start-Up Procedure

1 . Check the quality of the used and fresh oil and make sure they meet the required standards.2 . Using the analytical data, determine the ratio of used and fresh to be used at the start.3 . The fresh oil to used oil ratio should be varied from 50:50 to 80:20, depending on the peroxide

value (PV) and free fatty acids (FFA) of the used oil, assuming that PV of the fresh oil is still<2.0. Note that after storage, the fresh oil PV may go up to 2.0 even under nitrogen protection.

4 . Check the fryer pan for cleanliness. If satisfied, check and make sure all drain valves are closed.5 . Start filling the fryer no more than 2 h before actual frying.6 . Heat the oil to 210°F with recirculation (where applicable) for dewatering the oil. Do not

exceed 220°F. This step is followed to remove any residual water from sanitation.7 . After dewatering, hold the oil at low heat.8 . Start heating the oil immediately after dewatering. Heat the oil to the desired frying temperature

and start frying as soon as the oil reaches the frying temperature.9 . Bring the fryer throughput to its designed rate within 15–30 min.

1 0 . Use fresh oil only for make-up for at least 2 h.1 1 . Start using a blend of fresh and used oil (50:50 or some other ratio) until the used oil is finished.

N o t e s :• Heating the oil to a higher temperature during detwatering does not decrease the drying time

significantly. On the other hand, it oxidizes the oil before start-up.• Use of an oil blend improves the shelf life of the start-up product compared with 100% used oil

at start-up.• Use of 100% fresh oil is not recommended because of the underdeveloped fried flavor,

sometimes called “green flavor,” in the product. Some snack food companies use 100%fresh oil at the start and then use 100% used oil for make-up. This procedure is also notrecommended because the oil takes a long time to recover after all of the used oil isconsumed. Using a blend of fresh and used oil for make-up after the fryer has been startedup with 100% fresh oil is the recommended procedure.



higher in the case of pellets or extruded products, which are fried at a much highertemperature as indicated above. Figure 5.6 shows typical FFA trends in a continuouspotato chip fryer. One can see that the FFA stabilized at 0.24–0.26% and did not riseduring frying. Figure 5.7 helps explain why the oil degrades rapidly when it is leftidle at a high temperature.

The FFA is expected to remain unchanged when the process runs smoothlyand without frequent interruptions. However, as mentioned earlier, many opera-tions have two coffee breaks and a lunch break during every shift. No product isfried during this time and the oil remains in the fryer with full heat and sometimeswith recirculation through the oil heater. Because of the many reactions occurringsimultaneously in the fryer as mentioned earlier, the fryer is like a chemical reac-tor. The following example will explain the effect of fryer idle time on oil quality:

• The fresh oil introduces some reactants into the fryer during frying, for exam-ple FFA or oxidation products. Let this be called Input (I).

• The fryer generates products of the reaction, depending on the fryer tempera-ture and the product being fried. Let this be called Generation (G).

• Some products of the reaction are carried out by the fried products. Let it becalled Outlet (O).

• Some minute amounts of reaction products leave through the vent and the oilloss. These will not be counted.

Frying time (h)

Fig. 5.6. Free fatty acids(FFA) in a continuouspotato chip fryer.

Fig. 5.7. Fryer/reactor.



The general material balance can be expressed as follows:

Output (O) – Input (I) + Generation (G) = Accumulation (A) [1]

or,

O – I + G = A [2]

At steady-state operation at the designed temperature and throughput, no increasein FFA is observed. The product carries out the FFA coming in with the fresh oiland that generated in the fryer. The same is true for the other oil breakdown prod-ucts. Therefore, there is no accumulation of FFA and the value of A in the aboveequation is 0. Thus, at steady state, the equation reduces to:

O – I + G = 0 [3]

or,

O = I + G [4]

This sequence explains why no increase in FFA is seen under steady-state opera-tion at the designed production rate.

During a temporary fryer shutdown, there is no output or input but the genera-tion continues. Starting from Eq. [2], I – O + G = A, Input, I = 0 (zero) and,Output, O = 0 (zero). Therefore,

G = A [5]

At temporary shutdown, the reactions in the oil continue, and the products of thereaction accumulate in the oil. There is no product to carry out the oil breakdownproducts that are accumulated during temporary shutdown. As a consequence, theFFA and other products of the reaction in the fryer oil rise to a higher plateau thanbefore. This is why the fryer oil tends to exhibit a higher FFA and higher PV afterevery temporary shutdown. This scenario explains why frequent fryer shutdownswill lead to higher FFA and other oil breakdown products in the fryer oil.Generally, one can see a steep rise in the PV and other analyses of the fryer oilafter every temporary shutdown. Figure 5.8 shows an example of the rise in theFFA with each temporary shutdown. Eventually, the FFA went out of control.

Fryer Turnover Time. The definition of fryer turnover time is the theoreticalnumber of hours required to use up all of the oil in a frying system (e.g., fryer pan,piping, heater, filter) through absorption by the product fried in it if no make-up oilwere supplied. Generally, it is calculated on the basis of designed throughput of thefryer as follows:



Total amount of oil in the frying system 4000 lbsProduction rate 2000 lbs/hAmount of oil in the product 40%Amount of oil picked up by the product 0.4 × 2000 = 800 lbs/hTheoretical oil turnover time 4000/800 = 5 h

The actual oil turnover time for the fryer will be somewhat higher becausethere is low product throughput during start-up and none during normal shut downand brand changeovers or temporary shutdowns. As a general rule, the best fryerutilization is between 85 and 90% of its designed capacity. Using this guideline,one would expect the oil turnover time for the fryer in the above example to bebetween 5.55 and 5.88 h.

Importance of the Steady-State Operation at Full Production. On the basis ofthe above discussions on the reaction in the fryer and the oil turnover rate, one canappreciate the value of operating the fryer at full capacity and with few or no inter-ruptions. The following events occur at low fryer throughput:

Product output L o wProduct input L o wG e n e r a t i o n Continues at the same rate because it is temperature dependentOil turnover time Becomes significantly higher. It is infinity during temporary

shutdown, start-up, and final shutdownA c c u m u l a t i o n Increases significantly

At lower fryer throughput, the turnover time for the oil in the fryer increases,generating more oil breakdown products, which increases the accumulation factor(A) in Eq. [1]. As the production continues at reduced throughput, the accumula-tion of the oil breakdown products continues to increase. Many of these com-pounds are catalytic in nature, i.e., they promote further hydrolysis and oxidationof the oil, which results in a very rapid increase of FFA and oxidation products inthe fryer. The product picks up these compounds at higher levels, which reducesthe product shelf life. Figure 5.9 shows a typical example of a potato chip fryer

Frying time (h)Fig. 5.8. Free fatty acids (FFA) in a continuous potato chip fryer with interrupted operation.



operated at 60% of the designed throughput. The FFA level in the fryer oil became>0.5% in <24 h. In comparison, at normal steady-state production, the FFAreached 0.24–0.26% and remained unchanged during the operation (Fig. 5.8).

The level of FFA in the fryer oil is generally used as the primary indicator ofoil quality. Indeed, decisions regarding partial or total replacement of the oil in thefryer are made on the basis of the FFA value. Therefore, there is a general feelingamong snack food processors that the shelf life of the product is related to the FFAcontent of the oil in the fryer. Although this concept has merit, the shelf life ofsnack food is not totally dependent on the FFA content of the oil in the fryer. Inreality, the FFA do not impart poor flavor to the product until they begin tobecome oxidized. Therefore, there must be other compounds that are formed fromthe FFA or the fatty acid moieties on the triglycerides during frying that contributeto the poor flavor of the fresh product. Many of these compounds also reduce theshelf life of the product. Oxidation and degradation of the FFA and the triglyc-erides are the primary causes for poor flavor and shelf life of snack foods.

Peroxide Value. The first step in oil oxidation is the formation of the peroxides.These compounds are formed from the reaction between the unsaturated fatty acidsand oxygen. The reacting fatty acids may come from the FFA or the triglyceridesin the oil. Peroxides do not impart any off-flavor to the product. The peroxides,however, are very unstable. They decompose and form various types of com-pounds, such as aldehydes or ketones. Most of these compounds impart poor flavorto the product and also reduce its shelf life. A group of these compounds can beanalyzed and results expressed as the pAV. Thus, the oil is expected to have a highpAV if the oil had a high PV at some point. The compounds that constitute pAVcan react further to form more complex compounds, such as polar compounds,polymers, cyclic fatty acids, and many other compounds.

Controlling pAV in the fresh oil is important. The recommended value forfresh frying oil is <4.0 as shown in Table 5.1. Measurement of pAV in the fryer oil

Frying time (h)

Fig. 5.9. Free fatty acids (FFA) in a continuous potato chip fryer operated at 60%throughput.



also can provide information on the long-term stability of certain types of snackfoods. The PV in fryer oil increases during dewatering (drying) of the oil, whichoccurs at the start-up. It decreases rapidly, soon after frying starts, resulting in anincrease in pAV. This scenario explains why the time for the entire process ofdewatering and beginning of frying must be short.

Figure 5.10 shows the typical PV values in a continuous potato chip fryer. Onecan see how they increase during dewatering and heating of the oil and the sharpdrop that occurs as soon as frying begins. Figure 5.10 indicates that the PVincreased sharply during dewatering. Some PV breaks down, but the rate of forma-tion of PV at this stage is far greater than that of decomposition until frying starts.After the start of frying, the PV decreases to a low value, ranging from 2 to 4. Atsteady state, the rate of formation of PV and the rate of its decomposition are near-ly equal, which explains why the PV remains low throughout actual frying. ThePV in the fryer oil will increase under the following conditions: (i) the oil comes incontact with air in the frying system; and (ii) the production rate drops. The PV willplateau at a higher level after the fryer has undergone several temporary shutdownsand the oil is not cooled during these occurrences.

There is a belief among snack food processors that determining PV in a hotfryer oil is inaccurate. Some experts even recommend not checking the PV in afryer oil. The author of this chapter is of a different opinion. Measurement of PV isextremely important! The oil must be analyzed for PV immediately after sampling,and via techniques that slow down the reaction in the oil immediately after sam-pling. A continuous fryer for potato chips or tortilla chips would have a PV of2.0–4.0 mEq/kg under the steady-state condition. A higher number indicates addi-tional oil oxidation and should be investigated.

In addition to hydrolysis and oxidation, there are several other reactions thatoccur simultaneously in a fryer. The oil undergoes the primary reactions of hydrolysis

During dewatering and start-upFig. 5.10. Typical peroxide value (PV) in a continuous potato chip fryer.

AFTERPRODUCTIONSTARTS

AT STEADYSTATE

DURING DEWATERINGAND HEATING



and peroxide formation. The secondary and tertiary reactions occur at later stagesof oil decomposition. These reactions are more rapid under the following condi-tions: (i) the fryer is operated intermittently; (ii) the product throughput is lowerthan the designed capacity; (iii) the product is made in batch fryers in which the oilturnover time is very high.

Normally, the reactions become autocatalytic in the tertiary reaction stage, andare manifested as uncontrolled FFA in the fryer oil. In addition, the oil increases inits content of alcohol, acids other than FFA, polymers, and other decompositioncompounds. Oxidative polymers also are formed at this stage. Figure 5.11 showsthe complete picture of the various paths of oil reaction that can occur in a fryer.

Oxidative polymers contain high amounts of oxygen. They also are highlyreactive and decompose into other free radicals that degrade the oil in the product,even if the latter has been packaged in bags made with high gas barrier film andflushed with nitrogen. Badly abused oils are generally high in oxidative as well asthermal polymers. Generally, a high level of thermal polymers in the fryer oil willimpart a bitter aftertaste to the fresh product. Oxidative polymers, on the other hand,may not affect the fresh product flavor. However, the product tends to develop an

Fig. 5.11. Oil decomposition in frying. Source: JAOCS 58: 272 (1981).



oxidized flavor shortly after production and storage, resulting in an early productfailure during storage. Table 5.9 lists the recommended analyses for the oil andproduct samples during production and the frequency of testing.

Temporary Fryer Shut Down

Although it is desirable to have continuous fryer operation, there are temporaryfryer shutdowns that occur fairly regularly for one or more of the following rea-sons: (i) down time for two coffee breaks and one lunch break in every shift; (ii)mechanical issues on the product feed side of the operation; (iii) operational issueswith the salt applicator, seasoning applicator, or the conveying system leading topackaging; and (iv) mechanical breakdown on the packaging line. Item (i) causesthe most damage to the fryer oil in any frying operation. This practice is discre-tionary and should always be avoided. Items (ii)–(iv) arise from unforeseen situa-tions. Some of these breakdowns may require hours for correction. The oildegrades rapidly when the oil is hot and left in the fryer.

As noted earlier, oil decomposition products accumulate in the fryer while thefryer is down (Fig. 5.7). This increases the concentration of the free radicals andother oil breakdown products that catalyze oil breakdown. The effect of these reac-tions can be observed in the fryer oil at restart. Figure 5.9 demonstrates the effectof frequent fryer shutdowns on FFA in the fryer oil.

Figure 5.12 shows the PV and pAV data in a continuous potato chip fryer inwhich frying was interrupted three times. The PV in the fryer oil increased eachtime the fryer went down. The PV value decreased each time the fryer was restart-ed. However, the steady-state value of PV attained a higher plateau after everyrestart of the fryer. Similar phenomena were observed with FFA in which it

TABLE 5.9 Recommended Frequency for Oil and Product Analysesa

A n a l y s i s F r e q u e n c y Normal limit Shutdown limit

O i lF F A Every 2 h 0 . 0 2 – 0 . 0 3 5 < 0 . 5P V Every 2 h V a r i a b l eb —p A V Every 2 h Depends on the product Depends on the product

P r o d u c tM o i s t u r e Every 2 h < 1 . 5 %c < 1 . 5 %c

Oil content Every 2 h Depends on the product Depends on the productS a l t Every 2 h Depends on the product Depends on the productS e a s o n i n g Every 2 h Depends on the product Depends on the productT a s t e / f l a v o r Every 2 h Must meet standards Unacceptable flavor

aFFA, free fatty acids; PV, peroxide value; pAV, p a r a-anisidine value.bNormally the PV in a potato chip or tortilla chip fryer is 3–4, at steady state.cMost fresh fried snack foods have a moisture content of 1–1.5%.



TABLE 5.10 Recommended Procedures for Oil Handling During Temporary Fryer Shutdown

1 . Turn off the following items as soon as the fryer goes down:• Oil heater• Oil recirculation pump• Paddle wheels 2 . Remove the conveyor.3 . Obtain the best estimate on the anticipated down time for the fryer whenever it goes down.4 . If the down time is going to be >30 min, start cooling the oil using the oil cooling system

shown in Figure 5.4.5 . Continue cooling the oil and hold it in the fryer; when the temperature reaches 140°F, shut

down the recirculation pump and hold the oil in the fryer.6 . If the fryer is ready to be restarted while the oil is still being cooled, stop cooling, start

reheating the oil and proceed with the operation.7 . Take an oil sample to check the free fatty acids (FFA) and peroxide value (PV) before restart,

to monitor the oil quality. Establish a quality guideline for the use of the oil, based on productshelf-life data.

8 . If the maintenance work takes more than 4–6 h, the oil must be transferred to the holding tank, by using the proper shutdown procedures described in Table 5.6.

9 . Sanitize the fryer as described in Table 5.7.

N o t e :• Certain specialists in fryer design and operation believe that heating and cooling the oil causes

more damage than keeping the oil hot in the fryer during temporary fryer shut down. This beliefis not correct. The oil decomposes many times faster while it is hot than when it is cooled downand reheated later.

Frying time (h)

Fig. 5.12. Peroxide value (PV) and p a r a-anisidine value (pAV) in fryer oil during frequents h u t d o w n s .



increased after each temporary shutdown (see Fig. 5.8). Oil oxidation during tem-porary fryer shutdowns can be minimized by rapidly cooling the oil in the fryer assoon as the fryer goes down. Table 5.10 outlines the recommended procedure foroil cooling. The oil cooling system is shown in Figure 5.4.

Special Comments

The process for making tortilla chips uses lime in the corn-cooking step, whichloosens the hulls and incorporates some flavor into the chips. The corn is washedin a washer to remove the excess lime on the corn. This part of the operation isoften overlooked by the operators. Sometimes the flow of wash water is interrupt-ed or the spray nozzles are plugged. In these situations, the excess lime on the cornsurface enters the fryer, reacts with the FFA to form soap, and causes a very rapidrise in FFA in the fryer oil.

Transferring oil from one fryer to another is common in a frying operation.This practice can result in poor product flavor and poor shelf life of the product. Inaddition, the plant may face some labeling issues, these may not be addressed by theproduct label, if the personnel are not careful about mingling the oils from differentfryers.

SummaryFrying involves very complex reactions. There is simultaneous heat and masstransfer. Many chemical reactions take place between the oil and oxygen, the oiland moisture, and the oil and the food being fried. All of these processes occurunder high heat, which increases the reaction rates geometrically, compared withthose at ambient temperature. The type of fryer, method of fryer operation, and thetype of food being fried also influence these reactions. Oil will always undergosome reactions in frying. Adherence to the procedures outlined above can signifi-cantly reduce these reactions and greatly enhance the quality of the oil and theshelf life of the fried products.

References

1. Seifensieder, L.L., Zig 64:122 (1937).2. Chang, S.S., and F.A. Kummerow, J. Am. Oil Chem. Soc. 31:324 (1954).3. Frankel, E.N., in Flavor Chemistry of Fats and Oils, American Oil Chemists’ Society,

Champaign, IL, 1985, p. 1.4. Nawar, W.W., in Flavor Chemistry of Fats and Oils, American Oil Chemists’ Society,

Champaign, IL, 1985, p. 39.5. Fritsch, C.W., J. Am. Oil Chem. Soc. 58:272 (1981).6. Gupta, M.K., INFORM 4:1267 (1993).



Chapter 6

The Effect of Oil Processing on Frying Oil Stability

Monoj K. Gupta


IntroductionFried foods, whether deep-fried, pan-fried, or stir-fried are one of the most popularculinary delights enjoyed by consumers throughout the world. This is true regardlessof nationality or ethnic background. In many parts of the world, fried snacks orentrees are prepared and consumed fresh, but packaged, shelf-stable snack foods aremarketed in both industrialized and developing countries. As frying and storagetechnologies have advanced, so has the technology of packaging.

Partially dehydrated (par-fried) products are increasingly packaged and storedin freezers for later distribution. These products are transported in the frozen stateto food service establishments where they are immediately stored in freezers. Thefrozen products are then prepared in small restaurant-style fryers and served. Somepar-fried frozen products also are sold in supermarkets.

Frying oils are derived largely from vegetable sources, such as soybean, palm,canola, sunflower, cottonseed, corn, peanut (groundnut), and sesame seed. Theseoils are refined, bleached, and deodorized. Soybean, canola, and sunflower oils arelightly hydrogenated for use in frying applications. In addition to these products,coconut oil is widely used in the Philippines and parts of South India for cookingand frying. In some rural parts of the world, rendered, unrefined animal fats arestill used in food preparation, including fried foods.

Home-fried foods or those fried in restaurants are consumed soon after they areprepared. The effect of oil off-flavor in these foods is usually not perceived unless theoil is badly abused in the fryer. The snack food industry has established that the flavorof fresh products, as well as those stored frozen, is highly dependent upon the qualityof the oil in the fryer at the time the product was initially collected. Shelf-stable friedsnack foods are packaged and distributed; thus, several weeks or even months maypass before the product is sold and consumed. During that period, the oil in the friedfood continues to degrade. Therefore, it is necessary to maintain a minimum level ofoil quality standards for the oil during frying to ensure that consumers enjoy good fla-vor quality in the fried product even weeks after the product has been packaged.Additionally, the use of packaging with nitrogen flush and proper conditions for distri-bution and storage can greatly prolong the shelf life of the products.

All packaged fried food products require certain code dates for freshness.Some packages state that a product will retain its freshness until the date printed



on the package. In reality, some products do last even a little longer than the code date,but the converse is also true. The code date and shelf life of a product are related butare not synonymous. The code date for a product is established on the basis of the timerequired for warehousing and distribution of the product, plus the time required for theproduct to be purchased from the retail store and consumed. On the other hand, a prod-uct is considered to have reached the end of its shelf life when consumer taste testsindicate that the product either does not taste fresh or it has an unacceptable flavor ortexture (or both). Oil quality affects the product flavor, and the texture of the product isaffected by the excess moisture pickup by the product during storage.

The shelf life of a product is established through storage stability studies,using consumer acceptance tests as a barometer. These tests help select the type ofpackaging required to obtain the desired shelf life for the product based on thecode date required for the product. Occasionally, the code date required by saleslead time may be unrealistic for maintaining the shelf life of the product, even withthe added expense of the highest quality oil and the best packaging material avail-able. The product code date and the selection of packaging material for a productmust be balanced carefully to obtain maximum shelf life and, at the same time,maximize the financial return for the corporation.

Oil continues to degrade while the product is in storage. Nitrogen flush andthe use of gas barrier packaging can enhance shelf life. However, these precautionsdo not provide absolute protection from oil degradation. If the oil in the fryer washeavily degraded at the time the product was packaged, all safeguards and laterprocedures become useless. Therefore, it is very important to implement strictoperating standards for oil handling as described in Chapter 5.

Mechanism of Frying

Frying is a combined process of mass and heat transfer and chemical reactionsbetween oil and air, oil and moisture (from the food), and oil and various food con-stituents, such as proteins, carbohydrates, or chemical additives. The combinedreactions between the proteins and carbohydrates in the food and the hot oil in thefryer generate fried flavor and surface color v i a the Maillard reaction and someoxidative reactions in the oil itself.

Most frying operations are conducted at an oil temperature of 300–365°F.Extruded products and pellets are typically fried at 380–420°F. Heat from the fry-ing oil penetrates the product and vaporizes its internal moisture. The water vapormigrates to the surface of the food and escapes as steam. As the moisture contentdrops, the surface of the product turns from a golden yellow to a light- or medium-brown color. Figure 6.1 is a pictorial representation of these physical phenomenathat take place during frying.

The oil also undergoes a series of chemical reactions during frying. Theseinclude hydrolysis, oxidation (autoxidation, photosensitized oxidation, and photo-chemical oxidation), and thermal decomposition (polymerization).



Hydrolysis

Hydrolysis is the reaction between a water molecule and a triglyceride molecule. Thereaction can be described as shown in Figure 6.2. Hydrolysis produces a molecule offree fatty acid (FFA) and a molecule of diglyceride. The reaction can continuebetween a diglyceride molecule and another molecule of water to produce a moleculeof monoglyceride and another molecule of FFA. Ultimately, the reaction can yield amolecule of glycerol and three molecules of FFA; however, the occurrence of thiscomplete reaction in a fryer is rare. The hydrolysis of oil can occur only when oil andwater are in perfect solution. Oil and water do not mix, but they do become solublewhen subjected to very high temperatures (500°F) and high pressure. Hydrolysis canoccur at normal frying temperatures in the presence of a small amount of surfactant. Asurfactant (emulsifier) can come from various sources:

1. Processed oil• High amounts of phospholipids, left in the oil resulting from poor refining and

bleaching conditions.• Higher than normal levels of diglycerides and monoglycerides present in the

oil. Normally, excess caustic treat is required to refine poor quality crude oil,which produces higher diglycerides and monoglycerides in the processed oil.

Fig. 6.1. Heat and masstransfer in frying.

Fig. 6.2. Hydrolytic reaction. R1, R2, and R3 represent fatty acid moieties such aspalmitic, stearic, oleic, etc.



• Soap left in the refined oil resulting from poor bleaching processes.• Incompletely refined and bleached oil may contain higher than normal levels

of calcium and magnesium. These metals form soaps with the FFA in the fryeroil and become surfactants.

2. Food to be fried• Certain food products contain naturally occurring alkali (e.g., sodium, potassi-

um) and alkaline earth metals (e.g., calcium, magnesium) that can form soapswith the FFA in the fryer oil, thus providing the necessary surfactant to pro-mote hydrolysis of triglycerides during frying.

• Leavenings, used in certain batter coatings, contain mono- and dicalciumphosphates, sodium aluminum phosphate, and sodium bicarbonate. Thesemetal ions can form soaps with the FFA during frying, which provides thenecessary surfactant for hydrolysis of the fryer oil.

• Sodium acid pyrophosphate (SAPP), used in the wash water to minimize enzy-matic reactions in vegetables, also can produce soap with the FFA during frying.

3. Operation• Caustic (or soap), left in the fryer system from sanitation procedures, can pro-

mote hydrolysis in the fryer oil.• Several oil decomposition products have surface-active properties and can

promote hydrolysis of oil during frying.

Oxidation

Autoxidation. Autoxidation is a free-radical mechanism. Free radicals are formedwhenever the oil is heated. These free radicals then carry on an autoxidative reac-tion in the presence of a metal ion, such as iron. The reaction steps in autoxidationare shown below:

Step #Unsaturated fatty acid (RH) + Initiator (Metal) → R• (Free radical) (1)R + O2 → ROO• (Peroxy radical) (2)ROO• + RH → ROOH (Hydroperoxide) + R• (Free radical) (3)R• + R• → RR (4)

Step 1 (Initiation): unsaturated fatty acid forms a free radical through catalyticreactions with a metal ion initiator.

Step 2 (Oxidation): the free radical reacts with oxygen and forms a peroxy radical.Step 3 (Propagation): the peroxy radical reacts with an unsaturated fatty acid and

forms hydroperoxide and a free radical. The free radical continues the reac-tion cycle as shown in Scheme 1:



This reaction cycle continues until there is no more unsaturated fatty acidleft in the oil or no more oxygen is available.

Step 4 (Termination): two or more free radicals can react with each other to formdimeric or polymeric compounds; this happens primarily when there is nomore oxygen or no more unsaturated fatty acid left in the system. However,the reaction between the free radicals occurs even during propagation (Step 3).

The frying process itself is one of the biggest sources for generating free radi-cals in the oil. However, this is not the only source of free radicals in a fryer oil.The fresh oil itself may contain free radicals under the following conditions:

1. The crude oil is derived from seeds that have either been damaged or storedunder high heat and high humidity, triggering enzymatic reactions.

2. The oil is derived from crude oil that has been stored for a long time and hasdeveloped a high peroxide value.

3. The oil is unduly heated in the refinery without nitrogen protection, causingfree radical formation.

4. The oil is bleached under poor vacuum, allowing air exposure to the oil. Thiscondition leads to a high peroxide value (PV), and the peroxides rapidly breakdown to form various free radicals.

5. Hot bleached oil is stored in atmospheric storage tanks before it is deodorized.6. The vacuum in the deodorizer is poor, which allows the oil to react with the

oxygen present to form dimers, polymers, cyclic fatty acids and various otherfree radicals.

7. The deodorized oil is stored in atmospheric storage tanks.8. Deodorized oil is loaded into the storage tanks by discharging it at the top of

the tank. The free fall through the air space in the tank increases oxygenabsorption, which leads to a high PV in the oil, and eventually results in a highfree-radical content in the oil.

9. Loading a truck or a rail car by dropping the oil from the top and not from thebottom (bottom-loading) can cause oxygen absorption by the oil that eventuallyincreases the PV of the oil.

Therefore, one can appreciate the great number of possibilities for the fresh oilto develop a high concentration of free radicals via oxidation. Such oils undergo

Scheme 1.



rapid degradation in the fryer and produce oxidized or rancid flavor in the finishedproduct during storage.

Photosensitized Oxidation. Photosensitized oxidation can occur when a productcontains a photosensitizer, and the product is exposed to fluorescent or daylightthrough clear packaging material. In this process, peroxides are formed via the sin-glet oxygen reaction mechanism, which is 1500 times faster than the autoxidationreaction mechanism. Chlorophylls and their breakdown components (pheophytins,pheophorbides, and pyropheophorbides) are 10 times stronger photosensitizersthan their corresponding parent compounds. Chlorophylls are present primarily insoybean and canola oil, but they also can be found in sunflower and cottonseed oilsat much lower levels. Inadequate or improper bleaching may leave a high amountof chlorophyll in oil, or produce high levels of chlorophyll decomposition, causingphotooxidation in the packaged snack food.

Photochemical Oxidation. This type of oxidation occurs when oil is exposed toultraviolet (UV) light in the presence of a metal ion. Unsaturated fatty acids in theoil oxidize under these conditions. This reaction is as rapid as autoxidation. A pho-tochemical reaction in fried foods can be observed when the fried foods are keptunder UV light to keep them warm.

Oxidation Promoted by Surfactants. Surfactants in the oil can also promoteautoxidation, in addition to hydrolysis. For example, a high phospholipid contentin the frying oil can reduce the interfacial tension between the oil and air duringfrying, causing excessive foaming. This increases the oxygen uptake by the oilcausing rapid oxidation. Soap in fresh oil also reacts in the same manner andincreases oil oxidation during frying. High levels of diglycerides or monoglyc-erides react similarly to phospholipids or soap, causing rapid oil oxidation. Highlevels of calcium or magnesium in the fresh oil can also form soap in the fryer, andreact in the same manner as the other surfactants described above.

The consequence of having high levels of these impurities can be devastatingto the frying process. This is why fresh oil used for frying must meet very stringentspecifications. Oils that are satisfactory for margarine and shortening formulation(for baking) may not always exhibit good stability during heavy-duty industrialfrying. Table 5.1 in the preceding chapter shows the recommended oil specifica-tions for frying applications. The oil must be low in trace impurities, monoglyc-erides and diglycerides, and must have zero soap.

Thermal Decomposition

Oil undergoes thermal decomposition in the fryer. Overheating of the oil in fryingproduces high levels of thermal polymers in the fryer oil. Frequent fryer shutdownsand restarts generally increase oxidation and hydrolysis of the oil. It was men-



tioned earlier that heating causes the formation of free radicals in the oil, whichleads to the formation of oxidative polymers in fryer oil. Thus, heat can produceboth thermal and oxidative polymers. Vegetable oil is subjected to high heat duringthe refining process. Therefore, inappropriate heating of the oil during processingcan also produce high polymers in the freshly refined oil. A high polymer level infresh oil indicates poor oil quality and the potential for poor shelf life for the prod-uct fried in it. Thermal polymers can impart a bitter taste to a fresh product.Oxidative polymers may not have any initial effect on product flavor but can pro-duce an oxidized or rancid flavor in stored products, even with a nitrogen flush.Table 5.1 shows that the fresh oil must have a maximum polymer content of 1.0%.

Discussion

The reactions in the oil during frying, such as hydrolysis, autoxidation, and thermaldecomposition are temperature dependent. These reactions are expected to proceedrapidly during frying because of the high oil temperature. Unfortunately, no fryingoperation can be carried out without high oil temperature. It is possible, however,to minimize breakdown reactions by using a good quality oil containing minimalamounts of impurities. Each impurity has a different role in oil degradation. Thus,understanding the type of degradation can help pinpoint the impurity involved.With this knowledge, one can outline an appropriate course of action to prevent oildegradation, starting from fresh oil quality and carrying it through the fryingprocess. For example, hydrolysis requires a surfactant to solubilize oil and water.Therefore, fresh oil for frying must have the levels of impurities specified in Table5.1, i.e., the phosphorus content must be low (1.0 ppm maximum), the soap contentmust be 0, and the monoglyceride content must be low.

Table 5.1 indicates that the maximum FFA in the fresh oil for frying applica-tion should be <0.05%. Some may argue that the FFA can be higher because of theaddition of citric acid to the oil. Therefore, 0.05% may not be a realistic upper limitfor the FFA. In the experience of this author, all new refineries in the United Statesand Mexico have been obtaining 0.02–0.04% FFA in fresh oils with 50 ppm of cit-ric acid added at the cooling stage of the deodorizer. Use of 50 ppm of citric acidincreases the titrated FFA value in the processed oil by 0.005–0.006%. Therefore,the addition of citric acid to the deodorized oil should not be a major contributor tothe FFA value of the oil.

Arguments have been raised by many oil processors that a value of 0.07% oreven 0.1% FFA in fresh oil should be acceptable for frying applications. The authorbelieves that a value of 0.1% FFA in fresh oil is satisfactory for making baking short-ening and margarine. A high initial value of 0.1% for FFA can greatly reduce the fry-life of the oil in a snack food operation in which the fryer oil is terminated at a FFAvalue of 0.5%. Depending on the mode of operation, as will be described in Chapter 7,one can experience a very rapid rise in FFA in the fryer oil. This can result in a highereconomic losses because part or all of the fryer load of oil is discarded frequently due



to the rapid rise of FFA in the fryer oil. FFA >0.05% also indicates less than satisfac-tory refining and bleaching. A higher concentration of phosphorus can increase thevalue of FFA in freshly deodorized oil. It is experienced occasionally that the FFA incorn oil cannot be reduced to a lower value in the deodorizer. This has been associatedwith high phosphorus in the incoming oil to the deodorizer. Physically refined pal-molein, containing high phosphorus, exhibits similar behavior. High phosphorus inthe fresh oil can rapidly increase the fryer oil FFA, even if the operation is conductedunder standard operating conditions. Therefore, rapidly increasing FFA during fryingmay be an indication of insufficient refining and bleaching of the oil. Sometimes theoil supplier demands a higher price for fresh oil with guaranteed low FFA. It is aneconomic decision that the snack food processor has to make to create a balancebetween the marginally higher oil price against the cost of oil thrown away due to therapid rise in the FFA during frying.

Case Study 1. FFA in a continuous potato chip fryer rose from 0.04 to 0.2% in <4 h.Normal progression of FFA in a fryer is 0.04–0.08% in 8 h. Further investigationrevealed that the oil contained 3 ppm of phosphorus. Table 5.1 recommends a maxi-mum phosphorus content of 1.0 ppm in fresh oil for frying.

Case Study 2. In this case, the FFA in a fresh oil storage tank rose from 0.03% (atreceipt) to 0.08% after 2 wk, at a storage temperature of <100°F. Fresh oil shouldnot exhibit any increase in FFA when stored under ambient conditions. Furtherinvestigation showed that the oil contained 4 ppm of phosphorus.

Autoxidation requires metal ions to initiate the formation of free radicals. Freeradicals are formed not only in the frying process but also at various stages of veg-etable oil processing as stated below:

1. Decomposition of oil starts from the moment the seeds are harvested, stored,and subsequently cracked for extraction.

2. Free radicals are formed whenever the unsaturated fatty acids are exposed totrace metals, oxygen, light, and heat. The formation can happen in crude oilextraction, refining, bleaching, deodorization, oil storage, transportation,unloading, and storage at the point of use.

An oil processor could prevent or minimize the formation of the free radicals in the oilby being aware of the sources and taking the appropriate preventive steps. In the veg-etable oil processing industry, it is common knowledge that refined oil obtained frompoor quality crude (oil) exhibits poor stability. There are various reasons for this. Poorquality crude oil generally contains high levels of free radicals, lower tocopherols, andhas a high PV. Generally, these oils do not have good flavor stability. The followingexample illustrates this point.

In a controlled experiment, Evans et al. allowed the PV of crude oil to increasebefore refining the oil. The PV in the crude oil ranged from 8.0 to 73 mEq/kg. Theoils were refined, bleached, deodorized, and then stored at 60°C in the dark. The



oil samples were pulled out of storage and flavors were examined by an expertpanel. The results are shown in Figure 6.3. The freshly deodorized oils had accept-able flavor; however, the flavor grades for samples with the initial PV values of22.1, 56, and 73 in the crude oil dropped sharply after 3 d of storage.

When an oil with a high PV is deodorized, 90% of the triglyceride moleculescontaining cleavaged unsaturated fatty acid moieties (origin of peroxides) remain inthe oil. Although these amounts would be at levels of parts per million, these com-pounds are highly reactive free radicals that catalyze autoxidation in the processed oil,even if the PV has been reduced to zero v ia bleaching and deodorization. In addition,these compounds promote secondary and tertiary oxidation steps in the oil, resultingin poor oil stability. Food fried in oil made from highly oxidized crude oil exhibitspoor flavor during storage. Sometimes, even with 100% fresh oil at start-up, the fryeroil exhibits rapid oxidation within a few hours after the start. Generally, oil refiners donot monitor the PV of the crude oil. It is critical that they do so, especially if they aresupplying frying oil to snack food manufacturers.

Case Study. Frying oil was obtained that met standard specifications on FFA(<0.05%) and PV (<1.0 mEq/kg.). The oil started to develop a high para-anisidinevalue (pAV) value soon after frying began. The fried snack food had unacceptableflavor. Further investigation indicated the following: (i) the incoming oil had apAV ranging from 9 to 15; (ii) the crude oil used in making this processed oil hadvery high PV, ranging from 18 to 27 mEq/kg before the oil was processed. Thiscase illustrates why frying oil must not be made from a crude oil that has alreadydeveloped a high PV.

Storing crude soybean oil for several months before refining is not an issueunless the oil has been exposed to air (oxygen). Soybean oil is known to develop afishy flavor, even after the oil is hydrogenated, deodorized, and properly stored.Researchers have proposed various hypotheses for the development of this flavor.However, one described in Figure 6.4 seems to explain this phenomenon well.

It has been proposed that if oxidized crude soybean oil is left in contact withthe lecithin, the oil can develop a fishy flavor in storage, even if the oil is properlyprocessed later. It is suggested that the formation of the secondary amines in thereaction process is responsible for the fishy flavor. Lecithin forms trimethyl amine

Fig. 6.3. Oil flavor stability with a high peroxide value (PV) in the crude oil.

Storage time (d)



oxide in the presence of oxygen, which reacts with the hydroperoxide formed insoybean oil and produces secondary amines and formaldehyde. The secondaryamines impart a fishy odor and flavor to the oil. Research has shown that soybeanoil with a fishy odor/flavor contains formaldehyde and nitrogen. Lecithin is asource of nitrogen. Therefore, it is important for oil refiners to make sure the crudeoil is not exposed to oxygen during handling and storage. It has also been suggest-ed that soybean oil be water degummed to a phosphorus content ≤50 ppm, dried,and then stored for better long-term flavor quality.

Bleaching reduces trace impurities such as phosphorus, iron, calcium, magne-sium, chlorophyll, and various oil breakdown compounds. The addition of anappropriate amount of citric acid along with acid-activated clay facilitates theremoval of the trace impurities. In addition, the use of a vacuum and mechanicalagitation are critical for proper bleaching with minimum oil oxidation. Insufficientbleaching of the oil can leave high concentrations of trace impurities in the oil dueto the following: (i) low bleaching temperature; (ii) insufficient amount of bleach-ing clay and/or citric acid; (iii) poor quality bleaching clay; and (iv) inadequate orinsufficient contact time between acid-activated clay, citric acid, and oil. Highbleaching temperature, on the other hand, can oxidize the oil, greatly reducing theamount of tocopherols and increasing the free radical content in the oil.

The atmospheric bleaching process also can oxidize the tocopherols of the oiland increase the concentration of the free radicals in bleached oil. Oxidation oftocopherols can also affect the flavor and color stability of the oil. In the presenceof oxygen and acidic pH, chlorophyll undergoes decomposition to form pheo-phytins, pheophorbides, and pyropheophorbides. These breakdown compounds ofchlorophyll are 10 times stronger photosensitizers than their parent compounds.There are two types of chlorophyll present in the soybean oil, i.e., chlorophyll-Aand chlorophyll-B. Chlorophyll-B and its decomposition products are strongerphotosensitizers than chlorophyll-A or its decomposition compounds. Productsfried in oils containing high chlorophyll and its decomposition products will exhib-it poor photooxidative stability if the products are packaged in clear bags.

Thus, improper bleaching can significantly reduce the stability of the friedproduct. Snack food companies must make oil processors aware of these factors so

Fig. 6.4. Suggested mechanism for the development of fishy flavor in soybean oil.



they will begin to use appropriate equipment and implement proper process condi-tions to obtain a high quality bleached oil.

In certain oil processing operations, hot bleached oil is stored in atmospherictanks for several hours or days before the oil is deodorized. This can significantlyincrease the concentration of free radicals in the oil. One can expect poor flavorstability in the fried products in storage. To obtain better oil stability, one must fol-low the steps outlined below:

• Cool to <110°F before storage.• Saturate the oil with nitrogen before it is discharged into the storage tank.• Have a nitrogen blanket in the storage tank.• Discharge the oil as close as possible to the floor of the tank.

Hot oil can be stored for a few hours with full nitrogen protection; however, thisstep does not completely prevent formation of free radicals. Therefore, cooling theoil before storage is the preferred option.

Deodorization is the final step in the oil refinery, where the FFA and othervolatile matter are steam-distilled under vacuum. Critical variables in deodoriza-tion are:

• Vacuum (operating pressure)• Deaeration time• Heat bleaching time• Deodorization temperature• Distillation time• Quality of feed oil• Volume of stripping steam• Distribution of stripping steam• Differential pressure across the packed column• Internal cooling temperature• Citric addition temperature• Final cooling

The operating pressure or conversely the operating vacuum in a deodorizer is oneof the most important process variables from the standpoint of oil oxidation. Mostmodern deodorizers are designed for an absolute operating pressure of <3 mmHg.Some equipment manufacturers continue to design deodorizers for an operating pres-sure of <6 mmHg. In either case, the FFA are removed easily from the oil. The odor-bearing compounds take somewhat longer to distill. The purpose of low operatingpressure (conversely high vacuum) is to facilitate the removal of these volatile impuri-ties. The high vacuum also removes the dissolved oxygen from the oil in the deaera-tion step before the oil is subjected to high temperature for heat bleaching and deodor-i z a t i o n .



Under higher operating pressure, dissolved oxygen is not sufficiently removedfrom the oil. Consequently, oil produced under poor vacuum (high operating pres-sure) exhibits higher levels of dimers, polymers, and oil oxidation products.Deodorized oil, containing a high concentration of dimers, develops poor flavorduring storage, which can reduce product shelf life if the oil is used for fryingshelf-stable snack foods. Davies and his co-workers prepared mixtures of deodor-ized oil with dimers as shown in Table 6.1.

Properly refined and deodorized oil was added with dimers at the levels shownin Table 6.1. The oil samples were stored at 60°C and in the dark. The oil sampleswere checked for flavor by a group of trained panelists. The results are shown inFigure 6.5. The following results were observed: (i) the control and the samplewith 0.5% dimers maintained similar flavor grades during the test; (ii) the fresh oilsample containing 1% dimers had an acceptable flavor but it deteriorated rapidlyduring the test; and (iii) the sample containing 2% dimers had unacceptable flavoreven in the fresh oil sample.

It is well established in the oil processing industry that operating the deodoriz-er under poor vacuum increases the level of dimers in the deodorized oil. Theresults of the above test clearly explain why oils deodorized under poor vacuum donot retain their flavor well in storage. One should expect that such oils would pro-duce fried foods with a poor shelf life.

Deodorized oil must be saturated with nitrogen at the point it leaves the final cool-er. At this point, the oil temperature should be ~100°F, but absolutely no higher than110°F. The hydrogenated oil temperature must not be >10°F above its melting point.Storage tanks must have a nitrogen blanket with temperature indicators. The oxygencontent in a tank must be <0.5%. Atmospheric storage of deodorized oil causes the PVto increase. The typical scenario in an atmospheric storage tank is shown in Figure 6.6.

After the tank is loaded, the PV should be low. Dissolved oxygen in the oilstarts reacting with any unsaturated fatty acids present. This reaction is more pro-nounced at the top of the tank because of the presence of air above the oil surface;this is evident when the PV of the oil increases as the oil level goes down. The PVreaches a maximum at a low oil level in the tank and drops sharply to a low valueas the tank receives a load of fresh oil. This process is repeated over and over again

TABLE 6.1 Mixtures of Deodorized Oil and Dimersa

Deodorized oil Dimers(%)

100.0 (Control) 0.099.5 1.098.5 1.598.0 2.0

aSource: Reference 15.



as shown in Figure 6.6. The rise and fall pattern of the PV has a graphic represen-tation very much like a sawtooth.

The PV in the oil does not rise in a similar manner when the oil is protected bynitrogen. This process involves saturating the deodorized oil with nitrogen andmaintaining a nitrogen blanket in the tank. Figure 6.6 shows that the PV of the oilremained low when the oil was protected with nitrogen.

SummaryAs discussed earlier, oil undergoes simultaneous hydrolysis, autoxidation, andthermal decomposition during frying. These reactions are accelerated because of

Fig. 6.5. Effect of dimers (Dim) on oil flavors.Storage time (d)

Fig. 6.6. The peroxide value (PV) of deodorized oil after each week of storage underatmospheric and nitrogen atmosphere.

Time (wk)

–n– Atmospheric



the high temperature in the fryer. Hydrolysis requires a surfactant to solubilize oiland water to react and form FFA. Fresh oil can carry high phospholipids, diglyc-erides, monoglycerides, calcium, magnesium, and even soap if the oil is derivedfrom poor quality seeds, poor quality crude oil, or is improperly processed.

Free radical reaction is the primary source for oxidation of the oil, both in thefryer and during storage of the fried products. A certain amount of free radicals isalways present in fresh oil. However, excessive oxidation of oil during processing,storage, loading, and transport can significantly increase the amount of the freeradicals in oil, which can reduce both the fry-life of a sample of oil as well as theshelf life of products fried with that oil. Although decomposition of oil can be min-imized in the fryer by implementing proper procedures (as discussed in Chap. 5),success in that area is rather limited when the fresh oil contains a high level of freeradicals. The presence of high levels of trace metals is indicative of either poorquality crude oil or poor processing. High levels of trace metals in fresh oil alwaysreduce its performance in frying and storage stability of the fried product.

RecommendationsThe following recommendations are made:

1. Oil processors must recognize that frying is the most difficult application for theoil. The oil must be able to withstand the harsh environment of heat, agitation,exposure to oxygen, and chemical reactions with the food ingredients in the fry-ing process. Current oil quality parameters used in the oil industry are adequatefor manufacturing margarine and baking fat. However, these quality parametersmay not be sufficient for the oil to be used in heavy-duty industrial frying for allof the reasons that have been discussed in this chapter. Therefore, the oil proces-sors must take special care in making frying oil so that the oil is low in phospho-rus, trace metals, and also low in factors causing oil decomposition as outlinedin Table 5.1.

2. Reducing the PV in the oil through bleaching and deodorization does not com-pletely guarantee good oil quality. Autoxidation produces several compoundsthat impart desirable, as well as undesirable flavor to the fried products. Someof these compounds are volatile, but the majority (90%) of them are not. Thesenonvolatile compounds are highly reactive and are primarily responsible forthe development of poor flavor in the fried products during storage.

3. The specifications for frying oil should include pAV, dimers, polymers, andpreconjugated dienes in addition to the other standard analyses. The oilprocessors do not normally test fresh oils for these attributes. Therefore, thiswill require special negotiations with the oil suppliers.

4. The breakdown of chlorophyll must be minimized. Avoiding excessive con-tact between the oil and air as well as atmospheric bleaching can reducechlorophyll breakdown.



5. To avoid the development of off-flavor in stored products, phosphorus in crudesoybean oil must be reduced to a very low level before it is refined.

6. Deodorized oil must always be protected with nitrogen to minimize the forma-tion of peroxides during storage and handling after deodorization.

7. The PV in the crude oil must not be allowed to rise above a value of 8.0 mEq/kgfor good flavor stability.

8. Snack food companies and the oil processors must communicate openly so thateach party comes to understand the other’s needs. This dialogue will enable oilprocessors to understand issues and variables involved in frying and respond tothe needs of snack food companies.

Oil processors may have to upgrade their equipment and/or operating controls toimplement proper process and product standards that satisfy the requirements of theirsnack food manufacturing clients.

References

1 . Gupta, M.K., in Proceedings of the World Conference on Oilseeds Technology andP r o c e s s i n g, American Oil Chemists’ Society, Champaign, IL, 1992.

2 . Seifensieder, L.L., Zig 64:122 (1937).3 . Frankel, E.N., in Flavor Chemistry of Fats and Oils, American Oil Chemists’ Society,

Champaign, IL, 1985.4 . Lomano, S.S., and W.W. Nawar, J. Food Sci., 47:744 (1982).5 . Nawar, W.W., in Flavor Chemistry of Fats and Oils, American Oil Chemists’ Society,

Champaign, IL, 1985.6 . Mistry, B., and D.B. Min, J. Am. Oil Chem. Soc. 65:528 (1988).7 . Ward, K.R., J.K. Daun, and C.T. Thornstainson, INFORM 4:519 (1993).8 . Min, D.B., in Flavor Chemistry of Fats and Oils, American Oil Chemists’ Society,

Champaign, IL, 1989.9 . Frankel, E.N., Handbook of Soy Oil Processing and Utilization, American Oil Chemists’

Society, Champaign, IL, 1987.1 0 . Paulose, M.M., and S.S. Chang, J. Am. Oil Chem. Soc. 50:147 (1970).1 1 . Gupta, M.K., INFORM 4:1267 (1993).1 2 . Evans, C.D., E.N. Frankel, P.M. Cooney, and H.A. Moser, J. Am. Oil Chem. Soc. 37: 452

( 1 9 6 0 ) .1 3 . Robertson, J.A., W.H. Morrison, and O. Burdick, Ibid. 50:443 (1973).1 4 . Evans, C.D., G.R. List, R.E. Beal, and L.T. Black, Ibid. 51:544 (1974).1 5 . Davies, W.L., and E. Gill, J. Soc. Chem. Ind. 55:141 (1936).1 6 . Blumenthal, M.M., J.R. Trout, and S.S. Chang, J. Am. Oil Chem. Soc. 53:496 (1976).1 7 . List, G.R., T.L. Mounts, and A.C. Lancer, Ibid. 69:443 (1992).1 8 . Gupta, M.K., Improvement of Soybean Oil Flavor Through Processing, Presented at the

Annual Meeting of the AOCS, Atlanta, GA, May, 1994.



Chapter 7

Critical Factors in the Selection of an Industrial Fryer

Monoj K. Guptaa, Russ Grantb, and Richard F. Stierc

aMG Edible Oil Consulting International, 9 Lundy’s Lane, Richardson, TX 75080, bRich-Seapak Corporation, Brunswick, GA, and cConsulting Food Scientists, 627 Cherry Avenue,Sonoma, CA 95476

IntroductionFood preparation requires a certain amount of dehydration. This can be completedehydration (fried snack foods) or only partial dehydration such as in stir-frying andsautéing. Frying provides the fastest means for food dehydration, allowing shelf-sta-ble snack foods to be made. This is why industrial frying has evolved into a multibil-lion dollar industry in the United States and abroad. The frying process is quite simplewhen dealing with frying at home or small-scale production. It becomes quite com-plex once the process crosses the threshold from a small frying operation to a large-scale production. Today’s consumer expects consistent quality in a packaged friedfood. Success of a food processor depends on the consistency of product qualitydelivered at a reasonable cost. Therefore, it is important to make a methodical evalua-tion of available frying systems and their suitability for a specific application.

Batch frying is used only for low-volume production and, in some cases, tomake products with specific characteristics. Crunchy kettle-fried chips are a goodexample. However, this process is more costly. Some snack food processors havebeen using continuous fryers to produce hard-bite chips by manipulating the fryingconditions. In this chapter, we will discuss the criteria for selection of a fryer.

Types of Industrial FryersThere are three types of industrial fryers, namely, batch fryers, continuous fryers,and vacuum fryers.

Batch Fryers

These fryers resemble the so-called restaurant fryers, except that they are muchlarger in size, capable of frying several hundred pounds of product per batch (Fig.7.1). Batch fryers are used for small-scale production or for frying very specialtypes of products such as kettle-fried Hawaiian-style potato chips. The oil is placedin a large pan where it is heated by gas burners located under the pan. A level con-trol maintains the oil level and a temperature control device maintains the tempera-ture of the oil in the pan. In certain installations, the oil is heated in an external



heat exchanger. The oil is continuously taken out of the fryer, circulated throughthe oil heater and returned back into the fryer pan. The former method of heatingthe oil is known as the “direct heating” system (Figs. 7.2 and 7.3) and the latter iscalled the “indirect heating” system (Figs. 7.2 and 7.4). The external oil heaterscan be either steam-heated or gas-fired. The steam heat exchangers are generallyshell and tube type with the oil passing through the tubes and steam on the jacketside. Moderate pressure (180–200 psi) steam is used. The gas-fired heaters are ofdifferent designs. In some of the heaters, the oil in tubes is directly in the path ofthe flue gas. Others use the hot flue gas from the burners to heat air, which in turnheats the oil in the tubes. The following sequence of events occurs during the oper-ation of a batch fryer:

1. The oil temperature is allowed to reach the desired steady state condition.2. The product is added in discrete amounts to the pan.3. The oil temperature drops sharply and then recovers at the point at which the

product reaches the desired end-point moisture content.4. The product is stirred either with a manual stirrer or with an automatic stirrer.

Fig. 7.1. Batch fryer (cour-tesy of Heat & Control).

Fig. 7.2. Direct and indirectheating systems (courtesy ofHeat & Control).

Direct heated fryer

Indirect heated fryer

Oillevel

Oil level

Filter

Filter

Heat exchanger



5. The product is removed from the fryer with a take-out conveyor.6. The product is sometimes centrifuged to remove the excess oil on the surface.7. The product is then seasoned and packaged.

Continuous Fryers

Continuous fryers are used for large-scale production of fried snacks. The oil is heatedin a straight or horseshoe-shaped pan with temperature and level controls. The productis fed into the fryer at one end and the fried product is taken out from the opposite endby a take-out conveyor. The internal construction of the fryer varies greatly with thetype of product fried. This is described later in this chapter. As in batch fryers, the oilin a continuous fryer is heated either in direct or indirect oil heaters.

Fig. 7.3. Direct fired heating system (courtesy of Heat & Control).

Fig. 7.4. Indirect heated fryer (courtesy of Heat & Control).



Vacuum Fryers

A vacuum fryer is used to fry fruits or vegetables whose original product color isretained with minimum browning. These fryers are very expensive and generallydo not have high production capacity. The most commonly used fryers of this cate-gory are batch fryers. Continuous vacuum fryers are extremely costly and arerarely used. These fryers have several distinctive features including the following:

1. The fryer is operated under vacuum. Typical operating pressure is <100mmHg.

2. The frying is conducted at ~250°F. The food can be dehydrated at this temper-ature under vacuum.

3. The food is placed in a basket.4. The basket is inserted and placed in the vacuum chamber above the surface of

the oil.5. The vacuum is applied.6. The basket is lowered into the hot oil at ~250°F.7. Frying begins and the oil temperature drops (as described in a batch fryer).8. The oil is circulated continuously through an external heater.9. The oil regains the temperature when the moisture content of the product

reaches the predetermined value.10. The vacuum in the fryer is broken slowly.11. The fryer is opened and the product basket is taken out.12. The excess oil is allowed to drain and the product is cooled before packaging.

Criteria for Fryer SelectionSelection of a fryer is very important for producing a given end product. The fryermust meet the process criteria that are necessary to fry the product; otherwise, itbecomes difficult to achieve the desired attributes in the finished product. Thisrequires an understanding of the product and the appropriate process(es) to createit. The following is a list of items that are considered to be important for selectinga fryer for a given product: (i) product characteristics desired; (ii) production vol-ume (fryer capacity); (iii) heat load requirement; (iv) oil turnover time required; (v)fines removal and oil filtration; (vi) cleaning and maintenance; (vii) emission;(viii) specific fryer equipment; (ix) mode of heating oil, i.e., direct heating or indi-rect heating; and (x) technical support from the fryer manufacturer.

For the fried product to be appealing to consumers, it must exhibit the follow-ing attributes: flavor, texture, aroma, appearance, mouth feel, aftertaste, and overallsatisfaction. Fried products can be classified into two broad groups, e.g., (i) non-coated products, such as salty chips, seasoned or simply salted, donuts, nuts, andmiscellaneous extruded and sheeted products, meatballs, turkey breasts; (ii) coated



products, such as breaded seafood, chicken, vegetables, or corn dogs. Each productis unique in terms of texture, flavor, appearance, color, and taste.

Par-fried (partially dehydrated) products can be both coated and noncoated.These products are partially dehydrated in the frying process and immediatelyfrozen in blast-freezers. The products are then stored at –10 to –20°F (–23 to28°C). Freezer-trucks are used for their distribution. Restaurants and food servicesare the principal users of par-fried products although many of these products aresold in supermarkets. These products are kept in the freezer at –10 to –20°F untilthey are ready to be fried and are put directly into the fryer without thawing. Themost common par-fried products include the following: French fries, various otherpotato products, coated vegetables, cheese-filled peppers and other vegetables,poultry products, and batter-coated fish fillets.

Food coating is typically done through a multistep process in which layers ofcoating materials are applied in several steps. A wide variety of coatings is used,including tempura batter, seasoned flour, or various grades of breadcrumbs that arecalled J-Crumb.

Product Characteristics

As discussed earlier, each type of fried product has its own characteristic texture,color, and appearance. They are also made from different raw materials. The feedmaterials have different properties and the fried products have different bulk densi-ties. One needs to be aware of the characteristics of the fried products in order tobe able to select appropriate designs for the fryer and the feed systems.

Some important product attributes that should be considered for the selectionof a frying system are as follows: (i) type of product to be fried; (ii) product buoy-ancy; (iii) coating system applied to the product; (iv) surface color and product tex-ture desired; (v) types of fines produced during frying.

Type of Product to be Fried. Once the product type and its characteristics aredefined, it becomes important to investigate any special features that might berequired to prepare, feed, and fry the product. If no special features are required,the food manufacturer should evaluate the fryers already available in the marketthat would produce the desired product. However, one must consider the versatili-ty of the design so that more than one product could be fried in the same fryerwithout sacrificing efficiency or quality. In most instances, the basic fryer designmight be suitable for frying many products. However, one should expect toencounter differences in the feed system, conveyor, submerger, the take-out sys-tem, and oil filtration device in systems that are intended to produce differenttypes of product.

Product Buoyancy. This is an important consideration in selecting the requiredfeatures in a fryer. Different conveyor designs are used in the fryers to handleproducts with different buoyancy. There are products that naturally float and are



allowed to do so in the fryer. Typical examples of this type of product are donutsand nuts. There are other products that change their specific gravity and float asthey are being fried. An example of such a product is pork rinds. Potato chips haveto be submerged part of the time during frying. There are products that remain sub-merged in the oil throughout the frying time. Typical examples include breadedchicken and chicken fried steaks.

Two types of feed systems are used to feed products into the fryer. They arethe dough, slurry, or extruded product feed system, and the individual product feedsystem. Doughnuts, corn chips, or formulated potato products use the first-men-tioned feed system. The products are fed as viscous fluids or as solids (or semi-solids). They are extruded directly into the frying oil. Product feed (the latter sys-tem) is used when solid or semisolid products are conveyed into the fryer. Thisincludes potato chips, pastries (fried Danish), French fries, fish sticks, meat patties,pellets, and most coated products. The solid products may be dropped directly intothe cooking oil. Kettle-style chips are an example in which the feed material issliced directly into the oil. Free starch on the surface, sugars in the feed materialtogether with the frying condition provide the unique flavor, color, and bite tothese kettle-fried chips.

The following are some guidelines for the selection of fryer: (i) one mustknow whether the food product sinks in the fryer oil or it floats; (ii) for “semi-buoyant” product the fryer will require only a main (bottom) conveyor if the prod-uct sinks or a submerger conveyor if the product is buoyant. This keeps the productsubmerged in the oil for a certain period during frying while the main conveyorcarries the product through the fryer. For those products that change buoyancy dur-ing frying, the fryers must have a main and submerger conveyor.

Coating System Applied to the Product. Coating of the product highly compli-cates the fryer design and the overall process. The following are some importantconsiderations for the selection of a fryer for coated products: (i) Determinewhether a still-bath of oil fryer (typically direct-fired fryer) would be suitable forthe desired application. (ii) Generally, an indirect-heat fryer produces better resultsbecause the oil flows through the fryer bed.

Surface Color and Product Texture Desired. Sometimes there is a need to “set”the outer surface of the coating in hot oil before the product touches the internalconveyor of the fryer. This is called the “free-fry” zone, which is located at thebeginning of the fryer. This applies to many tempura-coated products, as well aspotato chips and various other fried products. This prevents the product piecesfrom sticking to the fryer conveyor or to each other (clumping) before the productreaches the frying zone. The “free-fry” or “convey-in” varies with the products tobe fried.



Types of Fines Produced. The fines accumulate in the fryer pan during frying.These are primarily carbohydrate material (or proteinaceous material from poultry,meat, or fish). The crumbs become charred during frying. Thus, accumulation offines can darken the fryer oil. This leads to a darker colored product with a burnttaste. This is why it is necessary to remove the fines from the fryer either continu-ously or at certain frequency.

One could use a fryer with a still-bath for products that generate low or moderateamounts of fines. The fines can be removed in a continuous filtration system. In addi-tion, the fryers are sanitized (boil-out) every night at the end of frying. This removesall of the fines that accumulate in the fryer even after continuous filtration of the oil.Continuous oil filtration is more desirable for products that generate large amounts offines during frying. Indirect-heat fryers with continuous and high oil flow make it easi-er to remove a large portion of the fines from the fryer via continuous oil filtration.However, with a very high accumulation of crumbs or sludge, it is recommended tohave a set of bottom-dredging bars that push the accumulated material from the fryerpan into a filter. The filtered oil is returned at an appropriate location on the fryer.

Production Volume (Fryer Capacity)

The fryer capacity is chosen on the basis of the production volume required for thebusiness. Various factors are taken into account to determine the actual capacity of afryer including the following: (i) the number of operating hours per day (8, 16, or 24);(ii) frying time needed for proper moisture and texture control of the product; (iii) fre-quency of fryer sanitation required; (iv) company's warehousing and distribution sys-tem; and (v) required product code date based on the shelf life and sales and distribu-tion requirements.

The above information is used to determine the physical dimensions of the fryer,the belt width, and belt loading, which is defined as: (i) product in lb/ft2 area of thebelt, (ii) product in lb/ft of belt, or (iii) the number of pieces per linear foot of the belt.

Some key points in determining the fryer size include the desired productionrate in pounds per hour, the physical dimensions of the product, the fry timerequired, and the belt loading, typically in lb/ft2. The following is an example forcalculating belt-loading (lb/ft2):

Desired production rate = 3000 lb/hRecommended product loading = 1.5 lb/ft2

Cook area required = (3000 lb/f)/(1.5 lb/ft2 × 60 min) = 33.3 ft2

For calculating fryer length:

Process (fry-time) = 1 minFryer width = 3.33 ftFryer length = 33.3ft2/3.33 ft = 10 ft



Heat Load Requirement

The primary function of a fryer is to remove the moisture from the product beingfried. The fryer oil supplies the heat to vaporize the free water present in the foodand heat required to bring the product to the frying temperature. The majority ofthe heat is required for vaporizing the free moisture from the product. There areseveral points in the process during which thermal energy is lost. Therefore, thethermal capacity of the fryer must be in excess of the theoretical amount of energyrequired for the dehydration and heating of the product alone. Areas in which heatis lost during frying that must be taken into account in designing the oil heatingsystem include the following:

• Heating the product feed from room temperature to the final fryer temperature• Dehydration of the fried product• Rate of dehydration of the product• Heating of all physical equipment, including the piping and filters• Radiation heat loss from the fryer, furnace, and other ancillaries• Heat loss through the fryer exhaust• Heat loss through the gas heater flue• Thermal efficiency of the heat exchange system

Heat load calculations are made to determine the actual heat load requirementfor a fryer designed for a specific product type and production volume. The typicalheat (number of BTU) required for various products is listed in Table 7.1. Thesenumbers clearly vary with the type of product. Potato chips require the highestamount of heat energy because of the very high moisture content of the raw pota-toes (~80% moisture).

The calculation of the frying heat load is made as follows: product type, 3-passcoated (predust, batter, bread) Chicken Tender; production rate, 4000 lb/h; BTU

TABLE 7.1 Heat Load Requirements for Frying Various Products

Frying oil temperature Heat requirementProduct (°F) (BTU/lb)

Potato chips 370 4500Tortilla chips 375 1500Corn chips 390 2250Batter-coated and breaded par-fried producta 375 350Egg rolls and burritosb 365 200Nuts 325 500Fried snack pies 365 1000–1500aThis heat is only for setting the crust and not for cooking the meat or fish inside.bThis is only to fry the shell. The filling inside is precooked.



requirement, 350 BTU/lb; heat required = 4000 × 350 = 1,400,000 BTU/h. Thisamount must be corrected for the various sources of heat loss listed above. The properheat load design for a fryer must also take the following factors into consideration: (i)temperature differential across the length of the fryer, known as “Delta-T,” (ii) therecovery time or response time for the heating system to maintain proper oil tempera-ture, and (iii) minimizing temperature overshoot.

Delta-T Through the Fryer. This is the temperature difference between inlet (feed-end) and outlet (discharge-end) seen in the fryer when it is operated at its designedcapacity. When the fryer is idle, the temperatures at the inlet and outlet of the fryer areessentially the same (i.e., Delta-T = 0). A temperature differential is establishedbetween the inlet and the outlet of the fryer once frying resumes. This temperature dif-ferential is critical to achieve the desired product characteristics (e.g., dehydration rate,amount of dehydration, development of texture, or color). In an indirect-heat oil flowfryer (Fig. 7.4), this temperature differential can be designed into the system to a pre-cise degree. By designing the oil flow through the fryer within a specific velocityrange, the energy (heat) absorbed by the product at the fryer inlet can produce a pre-dictable temperature gradient (Delta-T) down the length of the fryer. Most direct-firedfryers (Fig. 7.3) have dual control heat banks (either fire-tubes or thermal radiators)that can be set to different temperature set-points at each end of the fryer, thus provid-ing a fairly reliable Delta-T.

Recovery (Response) Time. This represents the capability of the fryer to respond toincreased frying load and is influenced by the following two factors: (i) availability ofexcess thermal energy beyond the amount of heat required to fry the product and com-pensate for the losses, and (ii) the type of heat exchanger in the system. Typically,tube-fired fryers (Figs. 7.2 and 7.3) are the slowest in reacting to major heat loadchanges. These systems are the slowest to both cool down and heat up. There is alwaysa time lag between the heat supplied to the tubes and the transfer of heat to the fryeroil. This results in large temperature swings. A temperature swing of 10–15°F is fairlycommon in this type of direct-fired fryer. Thermal fluid radiator direct-fired fryers arefaster and more predictable because they utilize thermal fluid flow through the radiatorto regulate the heat availability. Once the fryer’s internal thermocouple senses the needfor a temperature change to remain on set-point, the thermal fluid flow valve adjusts tothe correct thermal fluid flow requirement, thereby sending less or more hot thermalfluid to the radiator. A temperature swing within the range of 7 to 10°F is fairly com-mon. Indirect-heat external heat exchangers have the fastest response to any change inheat load and can react almost instantaneously. A temperature swing of ±2°F is typi-cal. This can be further reduced by precision control of the oil flow.

Oil Turnover Time Required

This is a ratio of the weight of the oil in a system to the hourly rate of oil picked upby the product. Turnover is expressed in hours. This is one of the major factors in



designing the frying system. An example of the calculation of oil turnover time isas follows:

Oil content in the frying system (fryer pan and accessories, including piping) = 4000 lb

Production throughput = 2000 lb/hAmount of oil in the product = 25%Oil carried out by the product = 500 lb/hTheoretical oil turnover time = (4000 lb oil)/ (500 lb/h oil pick-up) = 8 h

This number is based on a production rate of 100% designed throughput withno down time. In reality, it takes time for fryer start-up, shut down, and brandchangeover. In addition, there are needs for mechanical repair from time to timeand there is also a short period after the start-up when the production rate is not at100% of the designed capacity. This brings the fryer utilization down to ~80–90%.Therefore, actual turnover time for the above fryer would be as follows: 8/0.8 =10.0 h , or 8/0.9 = 8.9 h. For potato chips fryers, a theoretical oil turnover time of 8h is considered highly desirable. For tortilla chips, the desired theoretical oilturnover time is 6 h, and that for extruded corn products is 4 h. Oil turnover time ischosen on the basis of the type of product and the frying temperature. Highturnover time increases oil degradation and reduces product shelf life. Therefore,for any fryer, it is preferable to have the lowest oil turnover time.

Fines Removal and Oil Filtration

As mentioned earlier, fines from the fryer should be removed to minimize darken-ing of the fryer oil and prevent burnt flavor in the product. Figure 7.5 displays vari-ous types of filters used to remove fines. Paper filters are not ideal. They causehigh oil loss and also allow the hot oil to be exposed to air for a long period. Thefryer system generally contains a filter to remove the coarse material from the oil.Sometimes this is augmented with a finer filter that removes the smaller particlesfrom the fryer oil. In many applications, one must use a combination of a motor-ized and a centrifugal filter (or a rotary drum filter, Fig. 7.6).

The type of filter for a fryer should be chosen carefully on the bases of thesize, the amount, and the degree of hardness of the fines to be removed from thefryer oil. For products that produce heavy amounts of fines, such as breaded prod-ucts or sugar-infused products, a bottom-dredging system is used as mentioned ear-lier. This is a specially designed conveyor system. The fryer manufacturer shouldbe informed of the need for heavy fine removal during frying.

Sometimes a continuous filtration system is used to clean the fryer oil. In thisprocess, it is recommended that ~5% of the fryer oil be removed, filtered throughan in-line filter, and returned to the fryer. This system can be good, but in mostcases, the flow of oil through the fryer is not uniformly distributed due to various



factors. This allows fines to accumulate on the fryer pan at various spots; these arenot removed by the filter. In other words, a continuous filter of this type is as goodas the system's capability to push all of the fines through the filter, with minimumaccumulation in the fryer.

Continuous paper filter

Centrifugal Motorized catch box filter

Dual basket filter

Fig. 7.5. Various types of filters for fines (courtesy of Heat & Control).

Fig. 7.6. Rotary drum filter(courtesy of Heat & Control).



In many operations, an oil treatment system is used. This takes out the finesand also treats the oil to reduce free fatty acids, color, oxidized material, and soapfrom the fryer oil. This has been proven to improve the fry life of the oil and alsoto extend product shelf life. The oil can be treated at the end of frying or duringfrying. In the former case, a batch system is used. In the latter case, a small amount(typically 5%) of the fryer oil is treated through a system similar to the schematicdiagram shown in Figure 7.7.

There are many treatment agents that are commercially available for oil treat-ment. Although such treatment can be beneficial, not every treatment material onthe market is satisfactory. Some of them reduce free fatty acids via an acid/basereaction. The base metals in these treatment agents are typically calcium and mag-nesium salts, which react with the free fatty acid, forming calcium and magnesiumsoaps. These soaps in the oil cause a rapid rise in free fatty acids and also causerapid oil oxidation. Reactions in the fryer oil have been discussed in several chap-ters in this book. It is important, then, that the reduction in free fatty acids is notaccomplished via an acid/base reaction.

Cleaning and Maintenance

Fryers must be sanitized at the end of production. This can occur at the end of theweek as in a continuous potato chip or tortilla chip fryer. If the operation is carriedout for only one or two shifts a day, the fryer must be sanitized at the end of theday's production. Without sanitation, the frying system can contain a certainamount of degraded oil, which acts as catalyst for rapid oil degradation when thefryer is restarted the next day. The fryer pan and the accessories are sanitized eitherwith dilute caustic solution or commercial sanitizing detergents. Fryer cleaning and

Fig. 7.7. A fryer oil treatment system.



sanitation procedure were discussed in Chapter 5. Inaccessible parts, such as thehood and stack, are sanitized by an automatic sanitizing device called CIP (clean-ing in place) process.

Emission

The fryer emits steam, odor, and volatile chemicals. In several states in the UnitedStates and also in many other countries, it is mandatory to install a scrubber on thefryer stack to control emission from the fryer.

Specific Fryer Equipment

The fryer is the centerpiece of the entire frying system (Fig. 7.8). The industrialfrying system consists of a multitude of accessories (Fig. 7.9), including the fol-lowing: a continuous potato chip fryer, continuous tortilla chip frying system, andextruded products.

Continuous Potato Chip Fryer. An industrial potato chip fryer has many componentsas follows: a potato washer that washes the potatoes to clean the mud or sand from thesurface of the potatoes; a destoner to remove rocks coming with the potatoes; a peelerwith which the peels are removed with a minimum loss of the tuber (this can be eithera mechanical or a steam peeler); an inspection belt from which the defective potatoesare manually removed; a water-vat in which the peeled potatoes are held before theyare sliced, which protects the potato surface from browning.

Very large tubers are cut into smaller pieces. The potatoes are sliced to thedesired thickness in high-speed slicers. Water is added to the slicer along with pota-toes to wash off the starch separated during slicing. This starch is recovered for sale.The potato slices are further washed to remove the surface starch from the slices to

Fig. 7.8. Potato chip fryer (courtesy of Heat & Control).



minimize darkening of the oil due to charring of the starch. This also protects thepotato chips from turning brown and developing a burnt flavor during frying.

The slices are fed into the fryer in a single layer via a high-speed draining/feedbelt. This reduces the formation of clusters and minimizes the amount of waterentering the fryer along with the feed. The potato slices come into contact with thehighest temperature oil in the fryer and pass through a section called the “free-fry”zone. The slices (chips) then enter the frying zone where their forward flow alongthe length of the fryer is controlled by a set of paddle wheels. The paddles rotate atsome preset rate (rpm) and the intermeshing of the adjoining paddles is set careful-ly by the fryer manufacturer to move the product evenly along the length of thefryer without causing any interference or product breakage. The chips then passthrough a zone in which a submerger belt holds the product under the oil surfaceand moves it along the direction of product flow. This completes the product dehy-dration and texture development of the product.

The fried product is carried out of the fryer by a take-out conveyor, which allowsthe excess oil to drain from the product and also cools the product as it is conveyed topackaging. Salting is done soon after the product leaves the fryer, if the chips are notto be seasoned. However, care must be exercised to prevent any salt from blowinginto the fryer. Salt in the fryer oil can adversely affect the oil quality. Seasoning isapplied in a tumbler (Fig. 7.10). This unit (as shown in Fig. 7.10) is part of the tortillachip process. The basic difference between the tumblers used for the two products isshown in Table 7.2. Most seasonings come preblended with salt. Therefore, no addi-tional salt is required. The temperature of the product and that of the spray oil can becritical for many types of seasoning. High temperature can adversely affect the stabili-ty of the seasoning during product storage.

The seasoned product is packaged. Sometimes snack food manufacturers usemetallized bags and nitrogen flush for retaining product freshness. The bags areplaced in cases and are sent to the warehouse for distribution. The product qualityis checked after frying, after applying the seasoning, and after it is filled in bags.The fryer oil quality is checked at a certain frequency. This is discussed in detail inChapter 5. At the end of operation, the fryer oil is cooled, filtered, and stored in a

Fig. 7.9. Typical continuous frying sys-tem (courtesy of Heat & Control).



holding tank. The fryer is sanitized. An external oil cooler is beneficial for the usedoil quality. Some manufacturers of snack food use nitrogen protection for theirused oil in the holding tank (as well as in the fresh oil storage tank).

Continuous Tortilla Chip Frying System. The main ingredient in tortilla chips iscorn. The corn is used in two difjferent ways, i.e., freshly cooked corn or corn flour(masica). Processing of the former is described in detail.

Corn is cooked in a vat or in a continuous cooker. A certain amount of lime(calcium hydroxide) is added. The lime helps soften the outer shell of the corn. The

TABLE 7.2 Differences in Seasoning Tumblers Used for Potato and Tortilla Chips

Oil spray added beforeProduct applying the seasoning General description

Potato chips No Powdered seasoning is applied to the product.

Tortilla chips Yes A small amount of oil is sprayed on the productsurface before the seasoning is applied. The oilhelps the seasoning to adhere.

Fig. 7.10. Tortilla chip production line with seasoning tumbler (courtesy of Heat &Control).



lime also adds flavor to the product. The cooked corn is washed thoroughly toremove the excess lime from the surface. The corn is then ground to make dough,called masa. Grinding is done to produce the masa with a very specific degree ofgrinding of the corn. Water is also added to the masa in the grinder (also known asa mill) to provide a water content of ~50%. The masa is then sheeted and cut tospecific size and shape.

The raw chips then pass through a gas-fired toaster oven. The raw chips losesome moisture and also develop some toast-points on the surface. This gives thepleasant toasted flavor in the finished product. The degree of toasting is carefullycontrolled. Overtoasting as well as undertoasting of the chips produces undesirableflavor in the fried chips. The chips from the toaster-oven then pass through a proofer(also known as an equilibrator). This is a chamber with open sides. The chips passthrough a series of special conveyor belts. The object is to achieve an even distribu-tion of moisture in the chips. This also makes the chip color and texture of the friedchips more uniform. The product is then fried either in a horseshoe fryer or astraight-through fryer. The frying time is very short compared with potato chips.

In principle, the product removal, salting, and the seasoning application tech-niques are very similar to those in the potato chips operation. However, tortilla chipshave a much lower oil content and less surface oil compared with potato chips.Therefore, a small amount of oil is sprayed on the chips to obtain better adhesion ofthe seasoning. The seasoned product is filled mostly in clear bags. Some manufactur-ers use metallized bags with nitrogen flush. The fryer is sanitized and the used oil isplaced in a holding tank similar to that discussed for potato chips. The fryer is sani-tized. The general scheme of the tortilla chip frying system is shown in Figure 7.11.

Extruded Products. There are many extruded snack products that are fried or bakedafter extrusion, then seasoned and packaged for distribution. One of the popular prod-ucts is an extruded corn chips product. This product is made either from the cookedcorn or from masica but is pressed out through extruders. The product is fried at asomewhat higher temperature than either tortilla chips or potato chips. A baked ver-sion is also produced, but it is made from masica as the primary raw material. Thereare many other extruded ethnic products with savory flavors on the market in the

Fig. 7.11. Tortilla chip fryersystem (courtesy of CasaHerera, Inc.).



United States. They have a wide range of ethnic flair, from Asian, to Indian, toM e x i c a n .

Mode of Heating Oil

In practice, there are two major heating systems used for heating the cooking oil,i.e., direct internal heating and external heating. Many determining factors comeinto play when deciding what type of fryer may be selected. Among these factorsare the type of product being produced, the equipment cost, space availability,manufacturer’s experience, and environmental issues. Other factors exist as well.

In a direct internal heating system, gas (natural or propane) and to a lesser extentelectrical heaters are used to heat the oil in the fryer. On rare occasions fuel oil may beused. The heating elements are immersed in the cooking oil directly below the productzone. Heating is achieved by firing (igniting gas) inside these heating tubes or ele-ments. The heat is transferred directly into the oil by conduction through the heatingelement. Temperature control is achieved by modulating the fuel input to the burnersor switching the electrical elements on and off. A thermocouple or temperature probein the oil is used to sense oil temperature and a controller regulates the burners to pro-vide heat to the oil. Immersion tubes can be run across the fryers or lengthwise. Foodsthat are processed in direct-heated systems include kettle-style chips, battered andbreaded products (fish, meat, poultry, and vegetables), oil-roasted nuts, doughnuts,and other snack foods. Figure 7.2 shows a direct heating system. This kind of heatingsystem has a number of disadvantages. The primary one is the lack of temperaturecontrol as described earlier.

An external heating system uses either high-pressure saturated steam or natural gasas the source of heat. In a steam heater, the oil is pumped through a bank of tubes withsteam condensing on the outside. This is an excellent system for heating frying oil.Heating oil with saturated steam prevents overheating of the oil. It is highly recom-mended to avoid superheated steam so as not to overheat or scorch the oil. Overheatingof the oil is common in gas-fired heaters, due to the high skin temperature of the heat-ing coil surface. A modified design for the gas-fired system can reduce overheating ofthe oil. In this design, the hot flue gas from the gas burner heats inducted air. The hotair then passes across the tubes through which the fryer oil is recirculated.

An indirect heating system is superior to direct heating for better oil flow anddistribution through the fryer. The system also allows better temperature control. Thedisadvantage is that the external heating system increases the oil volume. This canincrease oil turnover time for the fryer. Therefore, the system must be carefullydesigned to minimize the oil volume.

Technical Support from the Fryer Manufacturer

Care must be exercised in selecting the fryer from any manufacturer. The past per-formance, customer service, and technical support are important considerations forselecting a fryer from a given manufacturer.



The Changing Market

Low Oil Snacks. Since the 1990s, consumers have been looking for reduced-fatsnack foods. The demand for reduced-fat and no-fat products was rising in the 1990sbut appears to have reached a plateau. However, there is a market for reduced-fatsnack foods. According to the Food and Drug Administration, a food can be labeled“Reduced Fat” if the oil content is reduced by 331/3% of the original (standard) level.Fabricated snack foods can be prepared with reduced fat in the formula v i a reduced oilpickup. Potato chips are par-fried and the remainder of the moisture is removed in achamber using high-velocity steam, hot air, or nitrogen. The final product is similar inappearance to standard fried potato chips, except that the low-oil product is far lessoily on the surface. The low-oil product has a reduced “fried food flavor” comparedwith regular potato chips.

Baked Potato Chips. The demand for low-fat cookies and crackers increased in the1990s. There was also an increased demand for baked potato chips at that time. Theproduct is made with potato flakes as the primary ingredient. The dough is sheeted,cut into desired size and shape, and then baked. Although the product met the demandfrom a specific segment of the general consumer group, the popularity of the productnever grew. As a matter of fact, the sales of low-oil and no-oil products have declined.Chapter 1 of this book provides some statistics on snack food consumption in theUnited States. There has been a shift in consumer demand as well as industry patternsfor low-oil and no-oil products. The current thrust is on healthful products made withnatural, organic ingredients using nonhydrogenated oil.

Fryers with Special Features

Multizone Fryers. Large-scale production lines use multizone fryers. The heatedoil enters the fryer at several entry points (Fig. 7.12). Dehydration of the product

Fig. 7.12. Multizone fryer(courtesy of Heat &Control).



can be controlled better with this system. A disadvantage of this design is that onemust take extra care to ascertain that the oil volume is not too high; otherwise theoil turnover time can increase and cause rapid oil degradation.

Heat Wave Fryers. This is an innovation of the Heat & Control company (Hayward,CA). Hot oil is allowed to come down on the product like a curtain as the productpasses through on a special belt. The fryer has the ability to fry a variety of products.The oil volume required is low and the actual oil flow and contact with the food isgentle, thus minimizing oil degradation.

This type of fryer is capable of frying coated products, fabricated, formed prod-ucts and various products that are individually fed on the fryer-in feed.

The oil volume is much lower than required in a standard design fryer of equalproduction capacity. These fryers are more costly but are more efficient in terms ofheat utilization and attaining product characteristics.

Fryer manufacturers are constantly looking for ways to improve fryer design,heat efficiency, and oil filtration capability in order to meet the challenge of the fried-feed industry.

Fig. 7.13. (Courtesy ofHeat & Control).



Chapter 8

Critical Elements in the Selection and Operationof Restaurant Fryers

Monoj K. Gupta


IntroductionRestaurants serve freshly fried foods to their customers. These products are fried insmall countertop or floor-model fryers. Food-service operations or fast-foodrestaurants generally fry par-fried fish, meat and vegetable products in floor-modelfryers. Selection of a specific type of fryer depends on the application. For exam-ple, in small restaurants in which the demand is sparse and the volume is not high,a countertop fryer is adequate for the service. In a fast-food restaurant, the fryermust have a high capacity and quicker heat recovery for fast service. Typically, afloor-model fryer with large oil volume and high heat capacity is used. A floor-model pressure fryer is used for frying chicken, breaded shrimp, or breaded fish.Turkey fryers in which a whole bird is fried and served have become common incertain areas.

Some floor-model fryers are equipped with oil filters, in which the oil is fil-tered at a certain frequency. Very few floor-model fryers provide a continuous oilfiltering system. Oil cooling devices are not provided. Oil in the vat cools naturallywhen frying stops and the fryer is turned off.

Restaurant fryers are most damaging to the oil because of the prolonged expo-sure of the oil to high temperatures and frequent down times during the day whenno frying is conducted. The oil is filtered once or twice each day in most restau-rants. Some restaurants use powders that remove the free fatty acids (FFA) andcolor from the oil. This procedure has both advantages and disadvantages, whichwill be discussed later.

Types of Restaurant Fryers

The principal categories of restaurant fryers are:

• Countertop fryers• Floor-type fryers that are used by fast-food and food-service operations• Pressure fryers• Turkey fryers

Ch8/Fry/110-124/Feb 16/F 6/7/05 3:16 PM Page 110


Countertop Fryers. These fryers are very convenient for frying small quantitiesof food at a time, and can have single or dual baskets. The oil capacity can rangefrom 15 to 30 lbs, with ~15 to 20 lbs in single-basket fryers. These fryers areequipped with temperature control systems that can heat the oil to 400°F(204.4°C) and automatically shut off the heat to let the oil cool down to 200°F(93.3°C) if the fryer is left idle for several minutes. The oil remains at this temper-ature until frying is resumed. The heat capacity of these fryers ranges from 25,000to 45,000 BTU/h. There are countertop pressure fryers that are typically used forfrying fish or shrimp. These fryers are normally equipped with a single pressuresetting and automatic shut-off, and are very convenient to use for small-scalerestaurants and also for research projects. Examples of countertop fryers are pic-tured in Figure 8.1.

Floor-Model Fryers. Floor-type fryers (Fig. 8.2) are most common in restaurantsand food-service institutions. The capacity varies greatly. The oil-holding capacityof the frying pan ranges from 40 to 90 lbs. The fryers can have single or dual bas-kets or split frying pans with individual temperature controls. The oil is heated byeither gas or electricity. The heat capacities of these fryers can range from 90,000to 200,000 BTU/h. Some fryers are designed to have rapid heat recovery torespond to the high demand of fast-food restaurants.

Generally, the fryer controllers have an on-off power switch that turns onpower either to the gas control system or to the heating elements, if the fryers areelectrically heated. The control system typically has two operating modes, i.e.,standby and high heat (or fry). The fryer is kept on standby when the demand islow, such as after the lunch rush or in the late evening.

Most restaurant frying is carried out at 335–375°F (168–190.6°C). A specificamount of food is placed in a basket, which is lowered into the vat. The tempera-ture drops immediately and then it gradually recovers. It is important for the oiltemperature to recover within a specific period of time to obtain proper texture,appearance, and flavor of the fried food. This recovery time is especially critical

Fig. 8.1. Three types of countertop fryer.

Single basket Dual basket Pressure fryer



for chicken, fish, and other meat products because the interior of the product mustreach a specific temperature to prevent food-borne diseases associated with suchproducts. For other products, such as French fries, vegetables, funnel cakes, orcoated cheese, the temperature profile for the frying oil is important to maintainthe desired product characteristics. Table 8.1 shows a typical oil temperature pro-file during frying of French fries in a twin-pan countertop fryer, Model 5301Amanufactured by Star Manufacturing International, (Smithville, TN). The individ-ual vats had an oil capacity of 15 lbs and a total thermal capacity of 45,000BTU/h. Table 8.2 indicates the temperature profile for frying par-fried coatedc h i c k e n .

These floor-type fryers generally have V-shaped frying pans. The narrow lowerpart of the pan is known as the cool zone, where the oil temperature is much lowerthan that in the frying zone, above. This physical arrangement allows the food crumbsto accumulate in the cool zone, which minimizes scorching of this material. Scorchedfood material can darken the fried food and also impart a burnt taste.

Fig. 8.2. Typical floor-type restaurant fryer.

TABLE 8.1 Fryer Oil Temperature Profile During Frying of French Friesa

Fryer oil temperatureSteps [°F (°C)]

Initial fryer oil temperature 375 ± 2 (190.6 ± 1.1°C)Fryer oil temperature dropped immediately <330 (165.6°C) Temperature after first 1 min 30 s 330 (165.6°C) Temperature after 2 min 45 s 345–350 (173.9–176.7°C)Product is taken out and temperature is allowed to recover to fry 375 ± 2 (190.6 ± 1.1°C)

the next batchaThe batch size was 0.75 lb; the total fry time/batch was 2 min 45 s.



Some manufacturers offer floor-model fryers with built-in filters (see Fig. 8.3).These filters are made of stainless steel mesh, a layer of filter paper normally used onthe screen. A built-in pump circulates the oil through the screen for several min-utes. The filtered oil is used to flush the residual solids in the fryer pan. The fil-tered oil is put back in the fryer pan and stored until the next operation. Generallythe oil is filtered once or twice daily. Certain restaurants perform filtration threetimes a day. External filters (see schematic diagram in Fig. 8.4) are also availableto filter the fryer oils. These filters are very similar to the built-in filters; they canbe hazardous, however, because of the high oil temperature and more manual oper-ation. Burns from hot oil are one of the most common accidents in a fast-foodrestaurant. Continuous oil filtration systems are also available in certain fryerbrands.

Pressure Fryers. Pressure fryers are used for frying almost any type of product,although they are used largely for frying chicken, meat products, and breadedshrimp. The fryer is equipped with a lid that can be held tightly to maintain specif-ic pressure inside the frying vat. The pressure can range from 5 to 15 psi (lbs/in2).The United States Department of Agriculture (USDA) established the standard

TABLE 8.2 Fryer Oil Temperature Profile During Frying of Par-Fried Chickena

Steps Fryer oil temperature [°F (°C)]

Initial fryer oil temperature 360 ± 2° (182.2 ± 1.1°C)The fryer oil temperature dropped rapidly 330 (165.6°C)Temperature after 4 min 350 (176.7°C)Interior temperature of the product 160 (71.1°C)Product was taken out and temperature was allowed to 360 (182.2 ± 1.1°C)

recover to fry the next batchaThe batch size was 1 lb; the total fry time/batch was 4 min.

Fig. 8.3. Floor fryer with oil filter system.



pressure setting of 15 psig (lbs/in2 gauge) in 1917. This was done primarily forfood and operator safety. The older model fryers operated only at a single pressuresetting of 15 psig by the jiggle-top load setting. By changing the load on the jiggle-top relief valve, one could reduce the operating pressure. The newer fryers canoperate at low (5 psig), medium (8–10 psig), and high pressure (15 psig). Typicalapplications for the various operating pressures are listed in Table 8.3.

Par-fried foods or other prepared foods have specific recipes that recommendthe pressure settings to be used. This makes it essential to have a pressure fryer thatis not simply preset at a specific operating pressure, limiting the capability of therestaurant. The primary benefit of a pressure fryer is the rapid fry time. Anotherclaimed benefit is the retention of good flavor in the product. For example, theOriginal Recipe of Kentucky Fried Chicken (KFC) is fried in pressure fryers. It isclaimed that the subtle volatile flavor components are better retained in the productdue to enclosed pressure frying. This is a reasonable claim because, in contrast,

Fig. 8.4. Schematic diagram for a general filter system for a restaurant fryer.

TABLE 8.3Applications for Various Operating Pressures in Pressure Fryers

Low Medium HighOperating pressure (psig) 5 8–10 15

Operating temperature (°F) 220 235 250Type of food fried Fish, breaded shrimp, Rice, Every

soft-textured pudding, typevegetables or custard of food



during conventional frying, the food aroma is released and lost into the surround-ing area, such as the kitchen. Some of the volatile flavor components are strippedfrom the food by the evaporating water during frying. The flavor components pen-etrate into the product more in a pressure fryer. Like the other restaurant fryers,pressure fryers are available in countertop as well as floor models. Figure 8.5shows both types of fryers.

Turkey Fryers. These fryers have become common in recent years. The fryer iscylindrical in shape and has a perforated basket to hold the food. The fryer cancook a whole turkey or chicken in ≤6 min. The heat source is normally natural gasand is supplied from the bottom of the frying pan. The entire system includes thefollowing components: (i) stainless steel stock pot; (ii) a vented lid perforatedbasket (or rack) for the poultry; (iii) a grab hook on the basket; (iv) thermometer;(v) a gas cooker; and (vi) a seasoning injector to inject oil and seasoning into thebird. The heating system has a temperature regulator and a thermal capacity of150,000 to 200,000 BTU/h. Figure 8.6 shows a typical turkey fryer with its acces-sories.

Typical Fryer Operation at a Restaurant

The typical restaurant operation involves starting up the fryer early in the morn-ing. The frying temperature can range from 335 to 375°F (168–190.6°C), depend-ing on the product. The oil is maintained at a certain minimum temperature whenthere are no customers. The typical routine in a restaurant fryer operation is as fol-lows: The fryer is started in the morning with lunch and dinner as the busiesttimes; the rest of the time, business is slow. The oil must be kept hot at all times;it is filtered once each day, or sometimes two or three times a day. The fryer iscleaned at night and refilled with the used oil. A small amount of fresh oil isadded for make-up.

Fig. 8.5. Two types of pressure fryer.

Countertop type Floor type



Selection of Oil for Restaurant Frying

Oil receives the harshest treatment in a restaurant fryer. The oil remains hot for16–18 h/d; during this time, the hot oil remains in the fryer without any food beingfried. Under these conditions, the oil is damaged rapidly. It can develop anunpleasant abused odor, which can produce unappetizing fried food flavor.Because food at a restaurant is consumed within minutes after frying, the effect ofbad oil quality is not always apparent to the consumers. However, occasionally,such food held under ultraviolet (UV) light develops an off-flavor reminiscent ofoxidized or abused oil.

The type of fat used in a restaurant is generally made from partially and fullyhydrogenated oils. The oils are derived from various sources, such as soybean, cot-tonseed, palm, canola, and animal fat such as tallow. Table 8.4 lists the typicalshortenings and oils used in a restaurant.

Effect of Restaurant Frying on Oil and Food

The restaurant serves fried food to receive customer satisfaction. This can beachieved only by meeting the following criteria:

1. Produce palatable food2. Maintain good product flavor3. Maintain good product texture4. Do not produce oil-soaked product5. Do not have the coating fall off the food6. Maintain long fry-life for the oil

Fig. 8.6. Turkey fryer with its accessories.



However, the restaurant has to operate under certain constraint which have agreat effect on the success or failure in meeting the above criteria. Typical exam-ples of the constraints in a restaurant operation are as follows: (i) prolonged expo-sure of the frying oil to high heat; (ii) contamination of the oil with the metals,phosphorus, calcium, magnesium, aluminum, and other impurities from the foodcoating and pretreatment; and (iii) reactions from the accumulated crumbs in thefryer.

All of these affect the oil quality. When the oil becomes dark, the food mayreflect the dark oil color or burnt flavor, and may even appear underfried, depend-ing on the quality of the oil in the fryer. The common effects on the oil in the fryerare as follows: (i) decomposition of the oil; (ii) darkening of the oil; (iii) develop-ment of off-flavor in the food; (iv) incomplete frying; and (v) the accumulation ofcrumbs in the fryer.

A large number of impurities are also formed in the fryer during operation.These compounds are damaging to the oil in many ways. Some cause hydrolysis of

TABLE 8.4 Typical Oils and Shortenings Used in Restaurant Frying

Product Frying fat Comments

Extra crispy chicken Hydrogenated shortening Made from soybean,French fries with a melt point of cottonseed, palm, orBatter-coated vegetables 105–115°F (40–46°C) canola oil with

varying degrees of hydrogenation.

Pourable shortening with Frying shortenings alsoa melt point of 108–115°F contain synthetic antioxidant(42.2–46°C) (TBHQ) and, in most cases,

an antifoaming agent such aspolydimethyl siloxane.

Batter-coated shrimp Lightly hydrogenated soybean Soybean oil with an iodine Batter-coated fish fillet or canola oil, palm oil or value (IV) of 90–100 isOnion rings palm olein commonly used in theLightly coated chicken Pourable shortening with a melt United States.

for pressure frying point of 100–105°F Canola oil with an IV ofHigh-oleic sunflower, high-oleic 80–90 is used.

canola, low-linolenic canola; Palm oil is used in Asia, NuSun can also be used Europe, Africa, Central

America and South America. All restaurant frying oils should containTBHQ and polydimethylsiloxane for goodperformance.

Abbreviation: TBHQ, tert-butylhydroquinone.



the oil, forming FFA, whereas others cause oxidation and polymerization of theoil. Specific impurities accumulated in the fryer oil include phosphorus and tracemetals from the food and the coating material; protein from the meat product; car-bohydrates from vegetable products and the coatings; carbon particles formed fromthe starch and other carbohydrates; and oxidation products from the oil breakdown.

Phosphates of calcium, magnesium, and aluminum are used in the batter coat-ing and in the pretreatment of French fries. These metals form soap with the FFAin the oil. The soap then catalyzes the hydrolysis process, causing rapid formationof more FFA. At some point, this reaction becomes autocatalytic when the FFAcontent in the oil rises very rapidly.

Protein causes darkening of the oil through the Browning reaction process thatdevelops the fried food flavor. Carbohydrates react with the oil and eventually leadto hydrolysis. Charred products from both carbohydrate and protein sources accu-mulate in the oil, causing darkening, as well as the development of off-flavor in thefried food. The charred materials act as adsorbents of the oil decomposition prod-ucts, which are polar in nature. These compounds are free radicals and cause fur-ther oxidation of the oil in the fryer. This is why the oil in restaurant fryers has thefollowing characteristics: high FFA, excessive oil oxidation, and high polymeriza-tion.

During frying of foods containing lipids at a measurable level (such as par-fried French fries, chicken, or fish fillet), there is always an exchange of fatsbetween the fryer oil and the oil/fat from the food being fried. Table 8.5 shows atypical fatty acid composition in a restaurant fryer, in which the par-fried chickenwas fried in corn oil for 80 h. The data indicate that the oil in the fryer had a signif-icant increase in palmitic, stearic, and oleic acids and a significant reduction inlinoleic acid concentrations. This indicates an exchange of oil between the foodand the fryer oil.

Improving Restaurant Fryer Operation

The quality of fried food and the performance of the fryer at a fast-food restaurantor in food-service operations can be significantly improved by implementing cer-tain operation procedures as listed below:

1. Clean the fryer thoroughly every night. Remove all gums and deposits byscrubbing the fryer pan and the heating coils.

2. Look for hot spots, indicated by discoloration of the fryer pan surface, andrepair or replace the pan if there are hot spots.

3. Filter the oil at least once or twice each day.4. Add fresh oil to the fryer at regular intervals, such as every 2 h.5. Treat the oil once or twice each day with proper treating agents, which are

commercially available.6. Develop a plan to discard the fryer oil on the basis of product taste and flavor.



Measuring Oil Quality in the Fryer

Measuring oil quality to decide whether to discard it is one of the most ill-definedand empirical operations conducted in a restaurant. In most operations, the restau-rant manager or a senior employee decides when the oil from a fryer should be dis-carded. Generally, oil color and/or the foam height in the fryer are used to deter-mine the termination point for the oil. Both approaches are subjective and can leadto error, with the oil either being discarded prematurely or used beyond its limit foroptimal product flavor and taste.

There are several physical and chemical quick tests available to restaurants. Inmost cases, they have either operational or cost limitations. In addition, restaurantsundergo very high rates of turnover of personnel in the kitchen. The personnel whooperate the kitchen do not always feel comfortable with the test kits. Therefore,testing oil at a restaurant is a major challenge.

There are no Food and Drug Administration (FDA) regulations on frying oilquality in the United States. Chile and most countries in Europe have adopted someform of regulations to control the quality of frying oil at restaurants. This, to somedegree, compels the restaurant personnel to learn the techniques of testing fryer oil forquality and to determine when to discard it. Several test methods have been intro-duced to make a quick determination of oil quality in the fryer. These methods anddevices may be classified as physical and chemical.

Physical Tests: Noninstrumental. These include oil color, clarity, and foamheight. In the past, color wands and color strips were promoted to determine the oilquality in a restaurant fryer. These were not very successful because they did notprovide any practical help to the restaurant personnel. This is because a universalcolor standard does not apply for all types of oil. Sometimes cottonseed oil, cornoil, and palm olein turn darker than soybean or sunflower oil in a restaurant-typefryer even though the oil quality is perfect for frying foods. The restaurant operatorwould believe that darker colored oil was bad, and therefore throw away perfectlygood oil just because of its darker color.

Oil clarity diminishes as the oil is used. Kentucky Fried Chicken (KFC) intro-duced a visual tester that they called the “visibility tester.” It is a stainless steel rod

TABLE 8.5 Composition Change of Fatty Acids in the Fryer During Chicken Frying

Fat extracted from Fresh corn oil Fryer oil afterFatty acid fresh par-fried chicken in the fryer (%) 80 h of frying

Palmitic (C16:0) 13.2 10.70 11.83Stearic (C18:0) 7.3 1.97 4.45Oleic (C18:1) 45.7 28.59 37.81Linoleic (C18:2) 32.5 57.33 44.37Linolenic (C18:3) 1.2 0.97 1.04



attached to a shiny silver disk at the end. The rod has a linear scale showing threeindented marks, which are used to judge shortening quality. The shiny disk is low-ered into the oil with the depth of insertion monitored on the rod. A penlight isheld next to the rod, turned on and the disk observed. The oil is discarded if thedisk is not visible at a certain depth. All of the above tests are highly subjective.They may or may not help the restaurant personnel to manage the oil quality anddecide when to discard it.

Physical Tests: Instrumental. These include Fri-Check, viscosity meter, food oilsensor, and the 3M PCT tester. Dr. Christian Gertz of Hagen, Germany developedthe Fri-Check testing device. The test relates the viscosity and density of the oil toits degradation as determined by the concentration of polar material and polymers.The unit consists of an electronic box with a removable steel tube. The tube isfilled with the oil to be tested and maintained at constant temperature. A cylindri-cal metal piece is then carefully released at the top of the tube filled with oil. Thetime required by this object to fall a measured height is noted. This time is depen-dent on the density and viscosity of the oil. Because the density and viscosity ofthe oil increase with the formation of polar materials and polymers in frying, the“falling-time” can be related to the degree of oil decomposition. In actual tests, theFri-Check data correlated well with the percentage of polar material and polymersin the oil. The system is relatively simple and can be used for monitoring degrada-tion of used frying fats in a restaurant.

G.E.C. Marconi of Chelmsford, England and the scientists at LeatherheadFood Research developed an instrument to measure viscosity of oil. The principleof operation is similar to that of a tuning fork. Dampening of the vibration dependson the viscosity of the surrounding fluid, and resonance depends on density. Thisinstrument could be used at a restaurant; however, determination of the actualpoint of termination for the oil can be difficult at a restaurant. The NorthernInstrument Company has been marketing the Food Oil Sensor since the late 1970s.The instrument monitors the change in the value of the dielectric constant in fryingfat. This value increases as the oil is degraded due to the formation of polar materi-al in the oil. Operation of this instrument is simple but is prone to error due toimproper cleaning of the instrument. This makes the instrument less suitable forrestaurants. This is a good tool for a research laboratory. The 3M Company(Europe) introduced an instrument called the Polar Compound Tester or PCT 120.This instrument operates on the principle of polarity developed in the oil with fry-ing. Although the instrument is easy to use and provides good information, somerestaurant operators find it difficult to use.

Chemical Tests. These include Oxifrit and Fri-Test (Merck, Darmstadt,Germany); alkaline contaminant material/polar component material (ACM/PCM;Mir-Oil); total polar material (TPM), FFA, and water emulsion titratables (WET;Test Kit Technologies); acid value (AV; Advantek; and Shortening Monitor-3M).



The Merck Company developed the Oxifrit and Fri-Test to measure oil qualityin frying operations, especially in restaurants. The Fri-Test measures the alkalicolor number to indicate oxidized fatty acid (OFA) and the Oxifrit Test measuresoxidation products in the fryer oil. Both tests are colorimetric and use a solvent-based reagent system. The only drawback to these tests is that like many othermethods, they are complicated for restaurant personnel.

The ACM and PCM tests were developed and patented by Libra Laboratories.Patent and distribution rights are now owned by Oil Process Systems of Allentown,PA. Oil Process Systems, also known by the name of Mir-Oil, manufactures and dis-tributes filter materials. The ACM test measures alkaline contaminant materials,which include soaps. The PCM test measures polar contaminant materials (accumu-lated polar), which are solvent-based colorimetric tests. These tests produce quickresults and could be used at a restaurant. However, the addition of a solvent makes itdifficult for restaurant personnel.

Test Kit Technologies has been manufacturing and marketing rapid tests formeasuring TPM, FFA percentage, and WET for >10 y. The Gel-in-Tube InstantChemistry (GITIC) technique is used. With the GITIC technology, hot oil sam-ples are collected from the fryer, filtered, and added directly to the gel. The oilmelts the gel and the components of the gel react with the oil to produce a color.While still hot, the tube is placed in a small colorimeter and a reading isobtained. The reading may be related directly to oil quality and used for monitor-ing oil oxidation. The TPM test is a single-phase test, whereas the FFA and WETtests have two phases, producing a colored bottom layer, all of which are read bythe instrument. The users must establish their own color limits to reflect the oilquality standards for their product. This instrument is simple but the cost of thetubes can be prohibitive for many restaurants. In addition, the restaurants are nottrained to develop their own oil quality criteria for discard as required by thisi n s t r u m e n t .

The 3M Company of St. Paul, Minnesota developed the Shortening Monitor,which consists of a white strip of paper, measuring 0.3 × 3.75 in., with four bluebands across it. The strips are used as a dip test to measure accumulated FFA, sim-ilar to commonly used pH papers. The tests were developed to provide users, espe-cially those in the fast-food industry, with an inexpensive means to objectivelymeasure FFA in cooking oil. This test might be suitable for restaurants because theFFA in restaurant fryers tend to run high and might be effective in predicting theimminence of a lower smoke point in the fryer oil.

Advantec manufactures and distributes test strips for measuring the acid value(AV) in the fryer oil. The product is marketed in Asia through Ajinomoto. This issimilar to the 3M test-strip, and monitors acid value in the oil. The operator placesa plastic strip with an indicator on the tip into the cooking oil. The color indicatorchanges from dark blue to a light olive green color depending on the acid value ofthe oil. The color chart is given in Table 8.6. This test strip can be a useful additionto FFA percentages for assessing oil quality criteria in a restaurant fryer.



Filtration and Treatment of Oil

The oil from the fryer must be cleaned routinely to obtain good fried food quality.Oil filtration can be done through an external filter in which the oil is collected in apot with a screen at the bottom. In many operations, a filter paper or filter cloth isused on top of the filter screen. The oil is circulated through the screen with thehelp of a pump. The fryer pan is rinsed with the clean oil and then the filtered oil isput back into the fryer pan. This process removes most of the particulate matteraccumulated at the bottom of the pan (cool zone) during frying. This can helpreduce the burnt color and flavor in fried food. Some fryers have built-in filters(see Fig. 8.3). The external type filter is shown in Figure 8.4.

Impurities in the oil can be removed more effectively by treating the oil withtreatment powders. These materials remove the soap and polar materials from theoil. This can significantly improve the fry life for the oil. There are several oiltreatment powders that are available in the market to treat the fryer oil during fil-tration. Manufacturers of these chemicals claim that the frying oil can be usedlonger when these treatment chemicals are used. Some of these materials can sig-nificantly reduce the FFA and color in the fryer oil. Restaurant owners like to havelighter color oil because the point of oil discard is based mainly on the darkness ofthe oil. However, some of these treatment materials reduce FFA by chemicallyreacting with alkali, which produces soap in the oil due to the reaction between theFFA and the alkali metal present in the treatment material. The presence of soap inthe fryer oil can lead to the following phenomena:

• Foaming in the fryer, which can increase oxidation of the oil and reduce its frylife

• Development of an unpleasant flavor in the fried food• Change in the appearance of the fried food • Food adulteration; according to the regulatory guidelines in many countries

including the United States, the presence of soap in a frying oil may adulteratethe food Therefore, one must select a treatment powder that does not react chemically

with the FFA, but removes the oil impurities by a physical adsorption process.

TABLE 8.6 Color Chart Used to Gauge the Acid Value of the Oil

Color Acid value (%)

Blue 0.0Dark green 0.5Green 1.0Light green 2.0Olive 3.0Very light olive 4.0



While selecting the material from a supplier, the restaurant owner or manager mustlook at the test data from the company and make sure that the soap content in theoil after treatment is not higher than before treatment. In addition, one must beknowledgeable about the recommended oil temperature for the addition of thesechemicals in the oil. The temperature of contact can be critical in the case of cer-tain treatment ingredients. For example, certain treatment materials contain citricacid. Citric acid is a metal chelator and is expected to remove the excess metal ionsthat are absorbed by the fryer oil during frying. Unfortunately, citric acid breaksdown if the oil temperature is >284°F (140°C). Oil, transferred to the filter basin, canbe hotter because the frying temperature in a restaurant fryer is much higher and theoperator may not allow sufficient time for the oil to cool under the ambient conditionbefore the treatment material is added to the oil. Incidentally, restaurant fryers do nothave any oil cooling capability. The oil temperature is not necessarily checked beforethe treatment starts. Therefore, the oil treatment will produce variable results in theday-to-day operation in part because of the destruction of the citric acid.

Some manufacturers claim that their material does not have to be removedfrom the oil. This would be against the Good Manufacturing Practices (GMP)according to the U.S. FDA and the Food Codex. The treatment material, added intothe oil should be circulated through the filter screen for 5–15 min, as described ear-lier. The cleaned oil is then put back into the fryer. The fry life of the oil isincreased by 25–50% in some instances. The flavor of the fried food also improveswith the oil treatment, which is significant. However, one must look at the overalleconomics. The cost of oil treatment material, the recommended frequency oftreatment, dosage of the treatment material, and the savings on oil must be checkedcarefully to justify the use of the material.

SummaryRestaurant fryers are designed to fry small quantities of foods on demand andserve them promptly after they are fried. The oil in a restaurant fryer is damagedmore than in a continuous industrial fryer. A kettle fryer used in the industrialoperation comes close to a restaurant fryer in terms of oil damage.

There is a wide range of sizes of fryers available to meet the need of a restau-rant. Countertop fryers are especially suited to small restaurants. Floor-type fryers,which have much larger frying pan and production capability, are used in fast-foodrestaurants and large food-service operations. Pressure fryers can be used for fry-ing various food products for quick frying. However, this type of fryer provides theadded advantage that the flavor is retained better in the food and the oil generallyhas a longer fry life. Turkey fryers are unique. These are being used more andmore by restaurants to fry the whole birds.

Oil quality is important in producing good product flavor at a restaurant.Because the food is consumed soon after it is fried, one could allow a higher degra-dation of the fryer oil quality compared with that for packaged snack food. Fresh



oil quality standards for restaurant frying must be similar to those listed in Table5.1 (Chap. 5). One must remember that not all of these analyses are performed rou-tinely by the oil processors. Therefore, it may cost more for the oil if one wants allof those analyses to be performed on every receipt of oil. This is cost prohibitivefor any type of operation. In the United States, there is very little problem with themono- and diglycerides in seed oils. Therefore an occasional check on the traceimpurities, such as iron, FFA, calcium, and magnesium may be sufficient for freshoils for restaurants.

Oil filtration at the fryer is required to improve the flavor and appearance ofthe fried food at a restaurant. In addition, treatment of the oil with some treatmentmaterial in a proper manner can improve the fry life of the oil. This, in turn, canprovide a significant improvement in the product flavor and appearance. One mustbe careful about choosing the type of treatment material and make sure that it doesnot produce soap in the oil. Extra soap in the oil will reduce the frying performanceof the oil after treatment.

There are no good procedures or gadgets to check the oil quality in a restau-rant fryer. The procedure or the gadget must be simple and foolproof for it to beeffective in a restaurant kitchen. Some of the gadgets described earlier are relative-ly simple, but still are difficult to monitor when one has to depend on a fryer oper-ator who does not have the basic skills to operate an instrument or a testing devicethat requires specific operational procedures to be followed. One must use the pro-cedures outlined above for typical restaurant fryer operations along with goodjudgment to enhance the performance of a restaurant fryer.

References

1. Anonymous, Test Strip for Frying Fats, J. Am. Oil Chem. Soc. 63:838 (1986).2. Anonymous, Oils and Fats Research at Leatherhead Food RA, Inform 3:586 (1992).3. Anonymous, Viscosity Tester Method, KFC Corporation R & D/QC (1995).4. Gertz, C., Chemical and Physical Parameters as Quality Indicators of Used Frying Oils,

Eur. J. Lipid Technol. 102:566 (2000).5. Graziano, V.J., Portable Instrument Rapidly Measures Quality of Frying Fat in Food

Service Operations, Food Technol. 33:52 (1979).6. Kress-Rogers, E., P.N. Gillatt, and J.B. Rossell, Development and Evaluation of a Novel

Sensor for In Situ Assessment of Frying Oil Quality, Food Control xx:163 (1990).



Chapter 9

Technology of Coating and Frying Food Products

Ronald J. Sasiela

Icelandic USA Incorporated, Cambridge, MD 21613

IntroductionThe frying of coated food products is a complex subject studied by many specialtycompanies that market batter and breading ingredients and equipment companiesthat supply coating and frying systems to food processors and restaurants. Thischapter provides a broad overview of these two segments of the industry; the inter-ested reader is referred to the extensive reference list, as well as web sites of thosemajor corporations.

Why Coat Products Before Frying? This question may appear trivial at first, butit is subtle in many ways. The art, and it is often more an art than a science, ofcoated food products is replete with many stories of successful new products andthose that were relegated to the “scrap heap.” Certainly there are few individualswho do not know about the start and popularity of Kentucky Fried Chicken by anastute businessman “Colonel” Harlan Sanders back in the 1950s. Using a secretrecipe of 16 herbs and spices, he commercialized the “finger-lick’n good” tastethat has grown to nearly 10,000 restaurants in >40 different countries, with currentannual sales of $9.7 billion (1,2). Escoffier, in his classic 1941 text Guide Culinaire,devoted no less than eight full pages to explaining the then true art of sautéing andfrying. He states in a succinct manner: “All products . . . must be put into the fatwhen it is very hot in order that a hardened coating may form on their surfaceswhich will keep their juices in” (3).

Perhaps the key and most important reason for coating food products is to add totheir taste. Whether it be for adding flavor to a somewhat bland food (the spices ofHarlan Sanders’s chicken coating) or the coating’s antidrying effect on Escoffier’sveal cutlet, without their respective farinaceous enrobing, the final creations wouldnot have made it, so to speak, “to the radar screen” in present-day marketing jargon.

Coatings also have a profound effect on the cost of the final product, almostalways reducing its price per pound to the consumer, while providing a value-added feature. For example, by starting with chicken tender strips at $2.00/lb andapplying 30% batter and breading at a hydrated cost of $0.30/lb, the ingredientcost of the final coated chicken tender strip would be $1.49/lb, or a reduction incost of 25.5%. Of course, the labor expense and equipment amortization charges

Ch9/PFry/125-155/Feb 14/F 6/7/05 2:17 PM Page 125


would partially offset that cost difference, yet the added benefits to the restaurantowner or retail customer in convenience are often incalculable. They would nowhave a consistent tasty coated food product that could simply be dropped into therestaurant fryer for a quick 3- to 4-min service, or be baked at home, both withoutthe laborious, time-consuming procedure of preparing the individual coated pieces.Deep-frying at home is regarded as a great inconvenience by U.S. consumers espe-cially, who prefer not having to deal with the safety issues of hot frying oil and thelingering frying oil aroma that can extend well beyond the kitchen. In fact, afamous jingle coined by an early New York chain pioneer in take-out fried chickenwent, “Don't cook tonight, call Chicken Delight!” Product convenience was a cor-nerstone of their successful marketing strategy when established in 1964.

Mr. Clarence Birdseye’s 1932 pioneering of commercial freezing systems andthe advent of a frozen distribution system in the United States paved the way for anew frozen fish dinner. When he helped invent the ubiquitous fish stick in the 1950s,it was the convenience of oven baking a crumb-coated fish fillet segment that attract-ed the attention of consumers, especially those not close to a coastline where freshseafood would have been readily available (Dr. Aaron Brody, personal communica-tion, 2003). This author can personally attest to the marvel and celebration thataccompanied the arrival of the first large chest freezer in his parents’ small cornergrocery store in Brooklyn, New York at that time. The advent of the novelty andconvenience of quick-frozen foods was underway. The development of the frozenfish block, a boneless, skinless cohesive mass of fillet, subsequently opened the pathfor low-cost, mass-produced seafood that surged to popularity. Arthur Treacher’sFish & Chips similarly increased to nearly a 2000-unit franchise based on the origi-nal patented technique of making true English-style, batter-coated cod fillets foreagerly awaiting diners (4). No doubt, their use of peanut oil as a frying medium con-tributed a subtle taste preferred by patrons (Neil J. Trager, personal communication,2003). The popularity of the famous Wisconsin Friday-night fish fry for which virtu-ally every restaurant in that state serves batter-coated fish fillets, further attests to theinsatiable longing for the mouthfeel delivered by (i) the flavor of the moist food sub-strate, in this case often codfish, (ii) the crispy, mildly seasoned, puffed batter coat-ing, and (iii) the sensory experience of the warm frying oil on the palate.

Types of Coatings Used on Food Products

Food coatings can be broken down into several classification systems. Forinstance, one could refer to liquid coatings or dry granular particles as being thefinal covering on the product before frying (5). The type of processing equipmentalso could dictate how one refers to a certain type of product (6). It can be helpfulto initially classify the product, keeping in mind (i) its intended final method ofcooking, and (ii) its desired surface texture (7). This approach clearly delineatesthe ingredients and process to be used to create the final consumed product. “Startwith the end in mind” might be an appropriate expression. Secondary considera-



tions of crust color, seasoning levels, visuals in the crust (e.g., herbs or seeds) can beregarded as cosmetic in nature, always being subservient to the two lead objectives.Such an approach would initially require that the product be predetermined for finalpreparation by the following techniques: regular, impingement, or convection ovenbaking; deep fat frying; grilling; microwave oven; quartz oven; broiling; and pansautéing, or other heating appliance or a combination of two or more intended cookingp r o c e d u r e s .

The second group of selection criteria would resonate from the food's surfacetextural considerations. These include a choice of the following: cracker meal;American-style bread crumbs; Japanese-style bread crumbs; fresh bread crumbs;coarse crushed crackers; extruded crumbs; root vegetables, e.g., shredded potatoes;“chicken-fried steak” coating; tempura batter; fish and chip batter; and corn dogbatter.

Annual Amounts of Coated Products Manufactured

The annual combined volume of the commonly coated food substrates processed inthe United States well exceeds billions of pounds. Consumption of French fried pota-toes alone in the United States is 45 lb/capita (~10 billion lb/y) with an increasing per-centage of that switching to unique coated versions exhibiting extended heat-lampsuperiority and tantalizing coated seasoned crusts. Once a commodity, the lowlyFrench fry has been elevated to near pedestal status because it is now used by fast foodchains to differentiate themselves in an ever increasingly competitive market segment.Indeed, French fry “wars” have been fought between the two leading fast food ham-burger chains in the United States, based on a coating technology arsenal (8)! Frenchfry manufacturing companies have begun advertising lines of spicy options for restau-rants to select from. Names such as “Flamethrower FriesT M” (9) and “RedstoneC a n y o nT M Seasoned Fries with Spirited Flavor Kickin’ Crunch” (10) leave little to theimagination of their intent. That latter potato processor's ad even boasts “. . . the worldleader in French fries and an innovator in batters and coatings.” Similarly, seafoodconsumption in the United States is currently 15 lb/capita, with much of that consumedwith a batter or breading coating. In 2001, U.S. production of fish sticks reached43,014,000 lb, fish portions sold 189,186,000, and breaded shrimp sold 152,192,000 lbfor a combined economic value of $816,362,000 (11). Nearly 26.4% of Germany’s167,000 tons of seafood consumed annually is in battered and breaded forms (Dr.Reinhard Schubring, personal communication, 2003). Processed poultry parts, coatedvegetables, cheese, and corn dogs are the other major contributors to the multibillion-pound market for coated foods.

A fast food chain’s need for quick service resulted in increasing use of theirdeep-fat fryers. Demands for signature coated foods that can be cooked rapidly,utilizing the limited culinary skill level of their staff, have followed. This list(Table 9.1) is not meant to be exhaustive, but purely illustrative and a primer forfurther innovative thought.



Ingredients and Processing Equipment Commonly Usedfor Batter, Breading, and Frying

Types of Batters and Their Commercial Applicators

Adhesion-Type Batters. These are pumpable, meaning they can be recirculatedwithin applicator machines without adversely affecting their functionality. Theyare used as the initial fluid over which dry breading is then applied. Adhesion-typebatters usually consist of a blend of wheat flour, food starch, corn flour, gums,milk, eggs, and seasonings. Commercially, batters of this type, as well as others,are produced by batter and breading companies staffed by food technologists expe-rienced in cereal science (see web sites in the References). Batter mixes are conve-niently sold in 50-lb multiwall bags that provide protection during storage andtransportation, yet are relatively easy to open. Some have pull-tabs on their outer-most paper ply, which allows it to be readily stripped off (Fig. 9.1 foreground).Removal of this outer paper layer eliminates the introduction of extraneous matterthat may be clinging to the outside of the bag into the batter mixing system and is aGood Manufacturing Practice (GMP). Water is the usual liquid used to hydrate thedry batter mix. It is inexpensive, sanitary, readily available, and does not vary incharacteristics. Virtually any other fluid can be used such as beer, carbonated

TABLE 9.1 Commonly Battered and Breaded Food Products

Seafood VegetablesFish sticks Onion rings, strips, chips, “blossom”Fish fillets and portions Bell peppersOysters OkraShrimp EggplantClam strips Sauerkraut ballsCalamari rings Cucumbers

CauliflowerPoultry Potatoes

Bone-in chicken parts MushroomsChicken strips (tenders) ZucchiniChicken patties Stuffed jalapeño peppersChicken “nuggets”Turkey cutlets Meat products

Corn dogsCheese sticks Pork fritters

Veal cutlet pattiesGround meat patties

“Fried ice cream” Nuts

Fruit RavioliApple frittersFried bananas



water, corn syrup, honey, or buttermilk, either full strength or diluted. One manu-facturer recently introduced a coated seafood product line based on the use of apopular Buffalo wing hot sauce as its hydrating fluid (12). The actual mixing of thedry batter mix with the water is accomplished by several methods. The most com-mon and efficient technique is to use equipment that has been specifically designedto accomplish that task. Large orbital mixing bowls with a wire whisk, or batchbox mixers that automatically meter in a predetermined amount of water for 50 lb ofdry mix are useful. However, equipment that (i) prepares the batter as it is needed,(ii) senses the batter’s viscosity and records it on a continuous chart, (iii) adjustsviscosity accordingly, (iv) chills the batter and (v) pumps it back to the batterapplicator, can be well worth the additional investment by reducing downtime anddelivering a more consistent quality product (Fig. 9.1 background).

By preparing the batter only at the time it is needed, rather than in large batch-es ahead of time, the potential for waste of unused, leftover liquid batter is reducedand more importantly, the possibility of microbiological growth in the batter isminimized. Commercial stainless steel machines for application of adhesion battersvary from small 6-in wide tabletop models (13) to 40-in wide high-capacity units(Fig. 9.2). Note in the photograph the double weir design of the overflow trough,

Fig. 9.1. Foreground: Batter mixes are sold commercially in 50-lb bags and often fea-ture a GMP strip tab to remove their outer ply. Background: A fully automatic battermixer with a continuous viscosity chart recorder.



air blower piping at the discharge, and a rod handle to a strainer basket (unseen) atthe pump’s sump reservoir. All of these features are useful to guarantee completeand uniform controlled batter coverage at the top, sides, and bottom of the foodpieces. Batters of this type have to be prepared within a solids/liquid ratio that doesnot exceed the engineering limits of the recirculating pump in the batter applicator.Batter viscosity is directly influenced by the ratio of dry mix to water (Table 9.2).Note that the viscosity of high-starch batters is extremely sensitive to its batter’ssolids/liquid ratios. They have a relatively narrow range of functionality andmachinability. At higher solid ratios (>45%), the batter becomes too thick to be

Fig. 9.2. A 40-inch wide commercial SureCoat® batter applicator. Photo courtesywww.heatandcontrol.com.

TABLE 9.2 Effect of the Percentage of Solids on Batter Viscosity

Equivalent lb water/ Viscosity (cps) Viscosity% Batter solids 50 lb dry mixa at 20°C (cm) at 15 s

25 150 25 23+33.3 100 50 23+40 75 103 23+50 50 7720 3.7560 33.3 TTTM TTTM66.6 25 TTTM TTTMaKerry Industries starch batter mix #4630; TTTM, too thick to measure.



www.heatandcontrol.com

handled by the equipment, and at low solid ratios (<35%), the batter is nearly waterthin and its adhesive functionality is compromised. When processing frozen sub-strates, the freezing point of the batter is critical for subsequent crumb adhesion. Ifthe batter is too thin, it may form an undesirable ice film on the food's surfaceb e f o r e the battered piece has an opportunity to reach the crumb applicatormachine, thereby resulting in poor coating adhesion and inadequate weight gain.Conversely, if the batter is excessively thick, it will contribute to “tailings,” i.e.,unsightly attached tabs at the trailing edge of the breaded food piece.

High-starch batters exhibit rapid settling when not under agitation. Thedeposited slurry from such settling can adversely affect pumps upon start-up due tothe high shear forces they create. In a prototype development unit, one must watchthe batter and periodically stir it to prevent settling of solids to the bottom (Fig.9.3). The photograph illustrates three common batter viscosity-measuring devices:from front to back, a Bostwick consistometer for thicker tempura batters (14), twodrain cup (Zahn, Stein, Norcross–not shown) viscometers for thinner batters, and auniversal Brookfield rotating-spindle viscometer (15). A cross spirit level is usedto calibrate the interior of the trough of the Bostwick unit so that it is always plumbin both directions, i.e., side-to-side and front-to-back. A thermometer is used inconjunction with the viscometer because viscosity is a function of temperature.Viscosity measurement, not accompanied by its temperature, is suspect. Other so-called all-purpose batters do not have the high level of modified food starch com-monly found in fish applications. However, they do not display that tenaciousadhesion function and offer a broader range for the viscosity/solids ratio.

Puff-Type, Tempura Batters. These differ from the above described adhesion bat-ters as follows: They have significantly higher viscosity; their leavening content ismuch higher; they are not coated with any breading material; the food is simplydipped into the batter, excess batter removed, and then placed in hot frying oil to

Fig. 9.3. Using a wire whip toperiodically stir settling batterensures consistent samplecharacteristics. Viscositymeasuring devices can rangefrom the simple to the sophis-ticated.



set the coating; and they often result in a smooth surface texture. The typicalarrangement of process steps to produce a batter-coated food product is illustratedin Figure 9.4. The food is prepared for tempura coating in any number of ways. Forexample: (i) A 16-lb commercial fish block can be cut into attractive 1.0-ozwedges (16). (ii) The pieces of fish are predusted with a fine-mesh flour. (iii) Theyare passed through the prepared liquid batter. (iv) They are conveyed under an airblower that removes excess liquid batter. (v) The product is then dropped into acontinuous fryer at 375°F for 25 s. (vi) The fried product is passed through a con-tinuous freezer to drop its internal temperature to ~0°F. Finally, the frozen productis packaged as a two-ounce finished product.

Both the batter applicator and the fryer have unique design features (Fig. 9.5) thatallow for handling of the wet drippy batter. In the late 1960s, Kris Gunnarsson, plantmanager at Coldwater Seafood Corporation (now Icelandic USA, Inc.) overcame thechallenges required to pioneer this new product category (17). This same coatingsequence would be followed for virtually any food product with desired variationsin the substrate-to-coating ratio. Unique formulations continue to be created forthis coating category. Low-fat absorption rice coatings (18) and “enhanced texturalcharacteristics” (19) are but two such recent examples. The liquid tempura applica-tor is of a nonrecirculating type, meaning that the batter is deposited in the batterreservoir and is not pumped. It is a static bath, through which the food products arepassed. Because of the thickness of the batter and its high leavening content, thefood pieces are generally conveyed in place, i.e., they are held in their orientationbeneath the thick viscous batter by the friction of both an upper and lower openweave belt (Fig. 9.6). The food pieces have an extended dwell time in the batter,

Fig. 9.4. The puff-type tempura process.



during which the batter hydrates the food’s surface predust, thereby providingsuperior coating adhesion.

Corn Dog-Type Batters. These are used as a coating for skewered hot dogs,breakfast sausage on a stick, and other similar novelty items. Historically, they arecharacterized by a yellow cornmeal profile, moderate leavening puff, and often aslightly sweet taste. The consistency of this batter is critical to its proper adhesion,coverage, and flow on the skewered frankfurter. The working viscosity has a nar-row operating range because of the unique manner with which the batter is appliedto the hot dog. The racked skewered franks are first conveyed through the corn-meal-rich batter. Then they are withdrawn from the batter tank and rapidly invert-ed. The batter is thus allowed to partially flow back (by gravity) from the free endof the frank toward its wooden skewer. At the correct moment of that inverted,reversed flow, the rack is reinverted and placed into the hot frying fat, resulting ina longitudinally uniform thickness of smoothly expanding batter clinging to the hotdog (Fig. 9.7). Too viscous a batter will result in excess coating pickup, a doughyinterface, splits in the outer crust, with lack of flow toward the skewered end, and a

Fig. 9.5. An illustration ofthe interior of a tempurafryer with Teflon® slats ontowhich the wet battered foodis deposited. Oil is notshown. Photo courtesywww.heatandcontrol.com.

Fig. 9.6. Commercial tempura batter applicators must transport the food piece through athick batter while maintaining alignment and orientation. Courtesy of FMC FoodTech.




bulged free end. Similarly, too thin a batter results in a thin coating at the free endof the corn dog and excess batter running onto the wooden skewer. Careful con-trols at the batter mix manufacturer’s facility and similar controls at the processorlevel are critical for a satisfactory end product. Products in this category includebreakfast sausage coated with a pancake-type batter, regular corn dogs with chick-en, turkey, beef, or a beef/pork/cheese bit blend. Jalapeno peppers can be found insome products sold in the market. Batter flavors such as crunchy honey and chiliare also available. Mini corn dogs (nonskewered) and even a cheeseburger corndog have been marketed in this unique corn dog product form.

Factors Influencing Fryer Oil Absorption in Coated Products. Frying fat that isabsorbed into a batter, or battered and breaded food product is influenced by sever-al factors (20). Because the absorption is a surface effect, the primary contributorto fat absorption is the amount of surface area of the product exposed to the fryingmedium. A general rule of thumb is to anticipate an amount between 8 and 12% byweight of the raw breaded product. However, secondary factors will affect theactual amount. Some of the most common factors are listed in Table 9.3. In addi-tion to these factors, there are many adjuncts to conventional coating systems thatare available that can help curb excess fat absorption. Many of these are propri-etary in nature, and are offered by both coating supply and basic ingredient manu-facturing companies (22–37).

Types of Breading Materials and Their Commercial Applicators

Cracker Meal. Cracker meal is a commercial term that is used to identify anolder, yet still commonly used, low-cost granular breading material. It is typically

Fig. 9.7. Commercial corndog illustrating its woodenskewer, the interiorexpanded batter crumb(exposed) uniformly wrap-ping the hot dog, and thefree end that enters thehot frying oil first.



processed in large band ovens as wide sheets of flour and water dough whosemoisture level is 35–40%. That moisture, and the heat of the oven act to gelatinizethe starch component of the flour. Quick-acting chemical leavening may be addedto the dough to tenderize it and provide some porosity. Because of the relativelyshort dough-mixing cycle time, yeast does not have adequate time to work as aleavening agent in this material. The baked hot dough sheets are then coarsely bro-ken and dried to a moisture level that will allow milling to the desired mesh size.The resulting breading contains <12% moisture and exhibits several unique proper-ties for use as a food-coating agent. With its starch now fully activated (pregela-tinized), it will have high water absorption. When it comes in contact with wet bat-ter enrobing a food, it will rapidly absorb the batter's moisture. This will cause thecoating to become rigid and the food can then withstand belt transfers on a high-speed production line and subsequent packaging. The cracker meal will completethe two-step coating sequence initiated by the wet batter dip and provide an attrac-tive appearance to the final surface of the fried food. When used as a predust in amultiple-pass coating system, its granulation is generally kept to no coarser than a20-mesh size (Fig. 9.8). The breading will seal the surface to help retain the food’smoisture, and can be further used as a vehicle to deliver seasonings, flavors, andtextures to the consumer. It also helps retard freezer burn of the frozen stored food.

Granulation Considerations, and Their Relationship to Fryer Operations. Ofall the possible attributes of a breading material, it is its granulation that has themost profound influence on its functionality. Collectively, Figures 9.9–9.12 graph-ically display the important characteristics of granulation. The aesthetic attributesof coverage and absence of coating voids (Fig. 9.9) must be considered whendeveloping a coated food product. Coating pickup (Fig. 9.10) directly influencesthe cost of a battered and breaded food. The sensory attributes of fried crust color(Fig. 9.11), and crispness (Fig. 9.12) can be enhanced by selection of the propergranulation. A coarse granulation is generally an 8-, 6-, or 4-mesh crumb.

Excessive coarseness of a coating can contribute positively to the texturalappearance of a fried food, but may also result in greater particle falloff when friedand during subsequent handling, including shipping and distribution because of theweak bond to the batter film. Careful packaging of the coarsely coated product is

TABLE 9.3 Factors Affecting Increased and Reduced Fat Absorption by Coating

Increased absorption Reduced absorption

Higher surface area/volume ratio Lower surface area/volume ratioGreater crumb porosity Denser crumb consistencyHigher leavening content Lower leavening contentLow fryer oil temperatures (21) Higher fryer oil temperaturesA floating fried food Totally submerged fried foodUsing broken down oil Using new oil



one approach to maintain the optimal texture for the consumer. A cost analysisshould be made of the package’s added cost vs. deliverable sensory benefit.

Maillard Reaction Agents. In 1912, L.C. Maillard elucidated the various, nowwell-recognized variables that affect product flavor and color (38). They areresponsible for some of the unique flavor of coated foods, as well as color develop-ment. By understanding the dependency of each of the reactants, a food technolo-gist can use the Maillard reaction somewhat like an artist’s pallet, to create a spec-trum of crust colors, ranging from very light to dark golden brown and with shadesof red. The two reactants are classically described as a “reducing” sugar and a pro-tein. The reducing sugar, generally a monosaccharide, is either naturally occurringin the coating ingredients or added to the coating formulation. Possible candidatesinclude dextrose (glucose or corn sugar), lactose (milk sugar), maltose, and fruc-tose present in corn syrup and invert sugar. The higher the percentage of the mono-saccharide, the greater will be the crust color development. Often as little as 0.5%dextrose will be sufficient to achieve a significant increase in the crust color, which

Fig. 9.8. The breading process.

Prepare food substrate(deglaze, slice, blanch, devein)

Fine-mesh predustcracker meal

Dipping and coating in slightlythicker second batter

Coating in first batter

Outer crumb coating

Freezing

Packing



will be a brown shade. Dry dairy whey (a lactose source) is a low-cost ingredientthat is often used to enhance color. However, compared with dextrose, about threetimes as much whey is required to achieve the same degree of crust color darkness.The shade will also have a slight reddish hue in addition to the brown color. Drypotato flour has the unique ability to produce a distinctive reddish hue in a friedcoating. One coating supplier has created a convenient ring-bound, dual-color huechart for use with both brown and reddish colored coatings (Fig. 9.13). Althoughthe disaccharide sugar does not enter into the Maillard reaction, it produces thesame crust color darkening as a monosaccharide when it is used as a fermentablecarbohydrate in yeast-leavened breads (Neil J. Trager, personal communication,2003).

In addition to the two chemical reactants, the Maillard reaction depends on: (i)temperature, (ii) pH, (iii) time, and (iv) moisture level. The Maillard reactionrequires a minimum temperature of 239°F for activation. The reaction rate acceler-ates with temperature rise. Typical deep fat fryers operate at 325–400°F, whichaccounts for the characteristic coloring of fried foods. The Maillard reaction pro-ceeds rapidly in basic pH (>7) and slows down under acidic pH (<7). Therefore,the pH and the concentration of the two reactants can be used to customize the

Good

Fair

Poor

Fine Medium CoarseGranulation

Fig. 9.9. As the breadingparticles become coarser,coating coverage lessens.

High

LowFine Medium Coarse

Granulation

Fig. 9.10. Coating weightpickup passes through amaximum as the bread-ing granulation varies.



crust color of fried products requiring different cooking times. Time is also impor-tant in crust color development and directly affects the end product’s appearance.The Maillard reaction is inhibited by high moisture levels in the coating, whichaccounts for the lack of crust color development when a par-fried product is ovenbaked. For regular or microwave coated products, the desired crust color must befully developed before the products are frozen because no significant colorincrease will be gained by the consumer’s oven baking cycle in a microwave oven.It is important to note that the high moisture level of the coating inhibits theMaillard reaction even in a 425°F oven and prevents darkening of the crust. Bycontrast, the same product, deep-fried at 350°F, will shortly become darkerbecause the hot frying oil will quickly desiccate the coating and allow the Maillardreaction to proceed swiftly.

Bread Crumbs

There are four generally accepted types of bread crumbs used commercially forcoating food products. In contrast to cracker meals, bread crumbs are leavenedwith yeast, have a porous cell structure, a significantly lower bulk density, andexhibit exceptional crispness on a coated food.

D a r k

M e d i u m

L i g h t


Fig. 9.11. Fry colorincreases with coarse-ness of the breading.

High

Low


Fig. 9.12. A baked orfried product’s crispnesswill be influenced by thecoating’s granulation.



American-Style Breadcrumbs. These are made by a conventional bread-makingtechnique. This consists of the development of a true elastic bread dough that isallowed to ferment; the dough is then deposited into loaf pans (1–2 lb), where theproofing step takes place. The pans are then transferred into a hot oven to bake for20–30 min. The loaves are removed from the pans, allowed to cool, and stale. Thestale loaves are then shredded, dried to a moisture level of ~10%, milled to thedesired granulation, and then packed into 25- to 35-lb bags. These crumbs arecharacterized by their generally spherical particle size, porous cell structure, andboth pale interior crumb and darker exterior crust color (39). When used as a coat-ing, they offer the benefit of a highlighted crust, meaning there are multicolored(light and dark) particles on the surface that add to its aesthetic appeal. The doughitself can be left plain or colored with paprika, annatto, or caramel. The porouscell structure provides a greater level of crispness, both initially out of the fryer/oven compared with cracker meal and during holding time under a commercialfood service heat lamp or similar storage appliance. Because the loaves’ proofingstage can be regulated, it is possible to achieve crumb textures from very tender tovery firm and crunchy. The latter are useful for coatings designed for microwavereheating, although they still do not result in the level of crispness achievable byf r y i n g .

Fig. 9.13. Using a color chart is a convenient way to quantify the subjective attributeof crust color. Use of a calibrated digital thermometer confirms that the fryer’s ther-mostat is functioning properly.



Japanese-Style Bread Crumbs. These are characterized by their unique sliveredparticle appearance. They are made from a yeast-leavened dough, but unlikeAmerican-style bread crumbs, they are baked in much larger pans (10–20 lb) by adialectic heating, rather than hot oven, process. The loaf pans have two opposingmetal faces, separated by a nonconductive 4- to 6-in spacer. High voltage electriccurrent is automatically attached to each of the metal plates, which causes thedough to heat by electrical resistance. The dough’s salt level must be generally<2%; otherwise, pan arching and excessive heat buildup will be experienced. Asthe dough reaches >200°F it begins to release steam (loose moisture) and graduallyloses conductivity, thereby bringing the bake cycle to its self-limiting end. Thisprocess can be carried out in ambient air, i.e., no hot oven air contacts the loaf;thus, it bakes to a crustless finish. The large baked dough loaf is removed from itspan and allowed to cool and stale overnight. The shredding of the loaf is carriedout with special mills that retain the highly desired striated, elongated pure whitecrumbs, sometimes mistakenly confused with rice. Because of the full gelatiniza-tion of the flour starch throughout the loaf, these crumbs exhibit very high waterabsorption. Their shape produces extremely crisp coatings, both when fried, aswell as oven baked. They are the coating of choice for premium shrimp. Versionsare sold colored with hues of yellow, red, and brown (40). A toasted crumb hasbeen the basis of a popular retail shakable breading mix for many years (41). Onecoating manufacturer uses a continuous extrusion process that stretches the rope-like dough to elongate the pores in the dough and thereby mimic the traditionaldialectic process result (42). The use of these coarse crumbs requires specializedbreading equipment designed to avoid their breakdown due to their fragility andevenly coat all sides of the food (Fig. 9.14).

Fresh bread crumbs are used only to a limited extent by food processorsbecause of the troublesome logistical considerations associated with handling aperishable commodity in their facility when the option of using dry, shelf-stablebreading is available (43). The selection of processing equipment that will proper-ly handle the moist fragile crumbs is also a hurdle that prevents entrants into thatingredient’s use (44). Consumer preferences for fresher foods, however, mayeventually see both an increase in development in this coating area, as well asimproved equipment design for the processor beyond those already in the market-place (45). Extruded crumbs are manufactured by HHST (high heat short time)equipment that produces an e x p a n d e d granule mimicking conventional baked-loafbread crumbs. They offer an additional opportunity to provide consumers with aspectrum of textures and grains that ordinarily do not allow processing by conven-tional techniques described above. Because the hot extrusion process does not relyon gluten development in the dough, non-gluten grains such as soy, rice, and oatscan also be processed by this technique. They are available in a wide assortmentof textures such as light, brittle, crispy, crunchy, or tender. Bright colors, a mar-keting trend in the new millennium, are easily incorporated into these extrudedcrumbs (46).



Flour-Type Breading

Flour-type breading is probably one of the earliest types of dry coating materialsused in food preparation. As the name implies, the primary ingredient is simplywheat flour. Historically, it has been the coating used to prepare bone-in poultryparts, after they were first dusted and dipped in a milk and egg wash. This baselayer of dusting and batter on the food has a tendency to remain pliable when sub-sequently coated with the flour and tossed about in a breading pan or in commer-cial breading equipment. The resultant surface texture is rough and flaky. The sur-face also develops finger marks and smudge marks from contact with adjacentpieces of substrate. The flour selected for the breading is generally “patent” flour,with a higher protein content than that associated with other types of breadings.Although most cracker meals are made with 8–9% protein flour, the use of 12%high-gluten flour for this coating is common. The extra protein acts to both absorbthe surface moisture more quickly and to create a crispier texture. The fact that thecoating remains pliable is crucial to the in situ creation of the rough surface.Because of the lack of gelatinization of this fine flour-based breading material, ithas much more of a tendency to stay suspended in the frying medium and can

Fig. 9.14. Commercial Japanese-style bread crumb machines have special sifter platesthat aid in the uniform application of coarse particles. Courtesy of FMC FoodTech.

Sifter platepattern

Sifterplate

Pressurerolls Blower

tubes

Crossfeedscrew (tovertical screw)



cause the oil’s premature breakdown. It also can contribute a burnt taste to the finalfried food. Chicken parts are fried at a significantly lower temperature than otherfoods to allow the heat to penetrate to the bone. This avoids the presence ofunsightly wet blood being noted by the consumer, as well as ensuring the controlof pathogenic bacteria, especially Salmonella. Quick-service restaurants will oper-ate their fryers at 325°F for chicken cooking (vs. 360°F for most other foods), andmay need up to ~15 minutes fry time, depending upon the thickness of the chickenpieces. The low native browning characteristics of patent flour allow the food to becooked for this length of time without becoming too dark. Frequently filtering thefryer oil through a fine mesh filtering medium removes the suspended flour in thefrying oil. The breaded chicken is allowed to rest for 2–5 minutes before it isplaced in the frying oil. This hydrates the surface flour by the moisture from thebatter, which helps to prevent excessive flour fall-off in the fryer. In commercialbreading applications, a drum-type breading machine is often selected to preventflour dust in the work environment. Air blowers are used to remove excess flourfrom the coated food pieces. Recent innovations have occurred in the design of thisbasic equipment. A convertible drum that can repeatedly tumble the food, or breadit in a level plane, and then spread the food out evenly onto a conveyor belt forsubsequent frying has gained popularity (47–49). Conversely, earlier drum dustersleft a pyramid-shaped stream at their exit, which resulted in coating damage andloss of production rates. The result of continuous drum-process equipment is todeliver an aesthetically pleasing product with a so-called “homestyle” textured sur-face as described above.

Composite Breading

Composite breading is a mixture of the above six described breading agents to cre-ate unique signature coating. Examples include simple blends of the individualbreadings alone. However, when a two-part blend is anticipated, it is cost effectiveto add other agents as well. Seasonings, herbs, flavors, salt, seeds, colorings, andnutmeats are but some of such coating-enhancing agents. For example, one manu-facturer offers a Thai gourmet breader made of “a blend of traditional complemen-tary flavors including creamy coconut, ginger, lemongrass, and red chili, served upin a festive crispy breader” (50). The frying of such compounded, often coarse,breading materials must take into account the adhesion of those particles to thefood surface and the risk of inadvertently introducing unwanted allergens into thefrying medium (51,52).

Root Vegetables

Root vegetables have recently begun to be used as coating agents on commerciallyavailable seafoods (53). The use of shredded potatoes, sweet potatoes, carrots, andother such ingredients is still a “sleeper,” primarily because of the logistical issuesconcerning their efficient preparation at the processor level and a marketing recog-



nition of their full potential (54). Consumer appeal is widely recognized by “potatocrusted. . .” entrees on leading fine restaurant menus and is expected to expand itsappearance into the casual and fast food service sector with time.

Types of Commercial Fryers

Direct-Fired Fryers. This refers to commercial fryers that have their oil heatingsource within the body of the fryer itself. This could consist of heating tubes thatare either traverse or longitudinal to the length of the fryer (Fig. 9.15). Electricalheating elements inserted within tubes, or natural or propane gas that is fired fromone side and vented out the opposite side can supply the BTU input. The advan-tages of a direct-fired fryer are its low initial cost and small footprint within theplant. These fryers react instantly to surges in product throughput via thermostatsstrategically located at the beginning and exit of the oil bath. A continuous crumband sediment removal system helps control the amount of suspended charredcrumbs in the oil, thereby adding to product quality (Fig. 9.16). When heated bycombustion gases, direct-heated fryers have a tendency to develop a circular oilcurrent that can influence crust color uniformity across the width of the fryer. Theoil directly above where the flame enters the heating tube is always hotter than thatat the opposite exhaust side of the fryer. The hot oil rises and circulates across thetop of the fryer to the cooler side. It also tends to sweep the product to the coolerside of the fryer, causing an uneven exit pattern at the fryer discharge. Tube baf-fles, to more evenly distribute the heat, are only marginally effective in controllingthese dissymmetry phenomena. The use of a chart-recording thermometer is essen-tial to monitor the fryer’s performance and aid in future troubleshooting of fryerperformance (Fig. 9.17). One manufacturer has designed a totally novel method offrying that relies on repeated exposure of the food to a succession of thin curtainsof hot frying oil (Fig. 9.18) (55,56).

Indirectly Heated Fryers. These rely on an external heater in which the oil isheated either directly or indirectly by natural gas (Fig. 9.19). The other forms of

Fig. 9.15. Direct-heated fryers have heating tubes submerged in the oil. Courtesy ofFMC FoodTech.

Cooking oil

Heat source

Sediment

G e n t l eSediment settlesto the cold zoneT u b e s



heating are steam or thermal fluids. Electrical heaters are rare in this type of fryer.These are much more costly to install because of the remote furnace, pumps, andpiping, but offer many advantages over the direct-heat fryers. The latter offer moreuniform heating of the oil, less noise and heat level in the vicinity of the fryer, andbetter oil temperature control.

Fig. 9.16. Charred crumbparticles can be depositedonto the surface of prefriedfoods (top), whereas wellfiltered oil leaves productsclean of defects (bottom).

Fig. 9.17. Continuous chart recorder for a fryer can provide important temperature historyuseful for troubleshooting.



Mathematical Relationships for Coated Products

P i c k u p is an expression that represents the percentage of coating in the final product.For example, if a 50-g food piece were coated to 75 g, the pickup would be: [(75 g/50 g) /75 g] × 100 = 33.3% pickup. The final product is considered to be the total col-lective weight additions of the coating steps, i.e., heating, such as partial or fully fry-ing, or oven baking, and includes the weight of any frying oil, water glaze, or sauce.

Yield is the percentage change of the product’s weight using its starting weightas the basis of the calculation. Using the same data as above: (75 g/50 g) × 100 =150% yield. Belt loading is useful in determining the anticipated production rate of a

Fig. 9.18. HeatWave® fry-ing system uses curtainsof hot oil to repeatedlybaste the food. Photocourtesy www.heatand-control.com.

Fig. 9.19. Indirect heated fryers have oil heated by a remote furnace. Courtesy of FMCFoodTech.

Cooking oil S e d i m e n t

T u r b u l e n tOil is stirred up–sediment settles on product

B o i l e rcooking oil direction

Heat source





coated food product. It can be measured simply by laying out a 1-ft2 area and arrang-ing the raw food product in that square as if it were being supplied to the beginning ofthe processing line. Proper spacing of the food pieces on the grid must take intoaccount the tendency of adjacent pieces to contact one another further along in the pro-duction process when defects called “doubles” or “marriages” will occur. Conversely,excess spacing between pieces has a direct influence on achieving the line’s maximumoutput and optimizing the fryer’s oil turnover rate (Fig. 9.20).

Conveyor speed is useful to calculate the expected production rate of a produc-tion line. It is generally measured in ft/min with a typical value of 15–100 ft/min.For example, if a 3-ft wide processing line has a belt loading capacity of 1.5 lb anda speed of 25 ft/min, its rate would be: (1.5 lb/ft2) × (3 ft) × (25 ft/min) × (60 min/h) =6750 lb/h.

In addition to belt loading as a means of projecting production rates, it may benecessary to use a particular piece of equipment on that processing line that has alimiting capacity. Such could be the case in the following examples: (i) a patty-forming machine that can cycle no faster than perhaps 40 strokes/min; (ii) the fryertime required to reach a regulatory-required internal temperature; (iii) freezer cool-ing capacity; or (iv) packaging limitations. It is not desirable to operate conveyorsat any higher rate than that minimum limiting resource.

Transfer is the term generally used to indicate the movement of the food beingcoated from one piece of processing equipment to the next in line. Proper selectionand control are critical to maintain maximum coating quality and production out-put in such transfers. Transfers can be level or they can be overlapped. In the latterarrangement, the discharge of the first conveyor is slightly projected over the sec-ond one. This arrangement allows the piece to drop a short distance, and is usedwhen the food will not properly transfer in a level plane, such as with round foodslike mushrooms or scallops. Conveyor speeds are generally adjusted to increase ~2ft/min at each transfer. This differential helps maintain spacing as the food piecesaccumulate coating material. Selection of a transfer is perhaps most important forbatter-coated products where the drippy, liquid batter-coated item is being moveddirectly into hot frying oil (Fig. 9.21).

Target

Low output Doubles

Too low Balanced Too highBelt loading

Fig. 9.20. Awareness ofbelt loading balancesline output and productquality.



Critical Control Points

The U.S. FDA Hazard Guide for Seafoods provides guidelines to protect againsttoxin formation by Staphylococcus aureus (57) in the hydrating batter. The recom-mended cumulative critical temperatures limits for the use of hydrated batter are:(i) not to exceed 50°F for >12 h, or (ii) not to exceed 70°F for >3 h. The tempera-ture of the hydrated batter is constantly monitored. The batter and the associatedproduct must be destroyed if there is any deviation from the recommended condi-tions during operation. Refrigeration equipment or ice can be used to manage thetemperature condition of the hydrated batter in the process. A temperature recorderis recommended to constantly monitor the temperature of the batter. This can limitthe risk of any deviation in the process.

Regulatory Considerations for Coated Products

The regulation of coated food products is under the auspices of three federal agencies.The manufacture of meat and poultry products is handled by the U.S. Department ofAgriculture (USDA) with no fee required for the inspection service. That agency alsoissues regulations and label approval for all child nutrition (CN) foods that are servedas part of the national school lunch program. Coated beef and poultry products arelimited to a coating content of 30%. Thereafter, they are required to use the expression“fritter” rather than “patty.” The USDA places its distinctive shield on everyprocessed package.

The National Marine Fisheries Service, a subagency of the National Oceanic andAtmospheric Administration (NOAA), is the fee-paid organization that is responsiblefor on-site seafood inspection at processing plants that desire an optional governmentshield to be placed on their packages. It has established a detailed listing (Table 9.4) ofminimum fishery content percentages for the full range of processed products man-ufactured under their jurisdiction. This subagency has established “Standards ofIdentity” for many of the most commonly coated seafood products (58). For instance,

Fryer

Star rollers

Topsubmergerbelt

Teflon slat Mainfryer infeed conveyor conveyor

Fig. 9.21. The transfer of batter-coated food is accomplished using a pointed rollerinto a Teflon® slatted fryer. Courtesy of FMC FoodTech.



TABLE 9.4 Minimum Flesh Content Requirements for USDC-Inspected Productsa,b

USDC grade mark PUFI mark(%) (%)

FishRaw breaded fillets —c 50Precooked breaded fillets — 50Precooked crispy/crunchy fillets — 50Precooked battered fillets — 40

Fish portionsRaw breaded portions 75 50Precooked breaded portions 65 50Precooked battered portions — 40

Fish sticksRaw breaded sticks 72 50Precooked breaded sticks 60 50Precooked battered sticks — 40

ScallopsRaw breaded scallops 50 50Precooked breaded scallops 50 50Precooked crispy/crunchy scallops — 50Precooked battered scallops — 40

ShrimpLightly breaded shrimpd 65 65Raw breaded shrimpd 50 50Precooked crispy/crunchy shrimp — 50Precooked battered shrimp — 40Imitation breaded shrimpe — No minimum; encouraged

to put % on labelOystersf

Raw breaded oysters — 50Precooked breaded oysters — 50Precooked crispy/crunchy oysters — 50Precooked battered oysters — 40

MiscellaneousFish and seafood cakes — 35Extruded and breaded products — 35

aThis list of minimum flesh requirements for standardized and nonstandardized breaded and battered products isprovided to ensure that all users of U.S. Department of Commerce (USDC)-inspected fishery products are aware ofthe minimum flesh requirements. These requirements apply to all species of battered and breaded fish and shellfish.PUFI, Processed Under Federal Inspection.bNOTE: USDC will certify coated, nongraded products without a standard of identity, etc., such as breaded fishsticks, breaded portions, and similar breaded fish products that contain less than 50% fish flesh if a statement imme-diately follows as part of the statement of identity declaring the amount of fish flesh actually present; e.g., “BreadedFish Sticks Containing 45% Fish.”cNo USDC grading standard exists for products without Grade A percentages.dFDA Standard of Identity requires that the product contain 50% shrimp flesh by weight. If a product is labeled“lightly” breaded, it must contain 65% shrimp flesh.eAny product with a Standard of Identity that contains less flesh than the standard requires must be labeled“imitation.”fFlesh content on oyster products can be determined only on an input weight basis during production.



there is a distinction made between “frozen raw breaded shrimp” that requires atleast 50% shrimp content and “frozen raw lightly breaded shrimp,” that stipulatesat least 65% shrimp content (59). Breaded shrimp with >50% coating is required tobe labeled “imitation” shrimp.

The FDA is the agency with regulatory authority over all non-meat or non-poultry plants, including seafood facilities. Labeling of coated vegetables, cheese,seafood, fruit, or nuts, for example, must comply with that agency’s guidelines,which in some instances may be different from the USDA provisions.

Finished Product Sensory Issues

The critical sensory factors that influence consumer response to a coated foodproduct are as follows:

1. Crispness—both initially and as the food continues to be masticated.2. Oiliness—the sensation of warm oil on the palate is a universally enjoyed

experience. However, in excess, it causes the food to appear to be “greasy”and undesirable. An excessively low fat level makes the food dry, tough,chewy and unpleasant tasting.

3. Flavor—the trend in coated foods is to enhance the seasoning level, with somemarkets expecting very intense “Buffalo Wing”-type heat. The salt content ofsome coated food products can reach high levels; chicken breadings are anexample. Variety and balance are important in formulating a winning product.

4. Crust color—plays an important role in the initial visual acceptance or rejec-tion of a coated product. A fried color chart is a useful tool. One coating man-ufacturer even has placed a color chart on its web site.

5. Heat lamp holding capacity—is the time that the fried food can be kept underthe heat lamp and still maintain acceptable flavor. This is particularly impor-tant for fast food restaurants and food services that have to keep some productunder the heat lamp for ready service to the customers.

6. Durability—is the ability of the coated cooked product to withstand anticipat-ed handling abuse at the cooking site. A cheese stick that blows out its coreinto the frying oil before it reaches the desired internal temperature is notgoing to be acceptable to consumers. Similarly, a fish portion that breaks easi-ly when handled with tongs as it is being assembled into a sandwich will resultin delayed service and increased cost. In both these examples, corrective mea-sures with the coating system can offer a solution.

Common Fryer Problems and Troubleshooting Them

Scorched particles are the cause of burnt flavor and sometimes darker productcolor. This can be corrected. Initially, it is imperative that the source of the prob-lem be minimized; then, proper operating procedures are put in place. Generally,



the problem originates from a high concentration of loose flour or dusting materialon the food surface. Introduction of excessive breading particles into the fryercauses scorching of the released material in the fryer. The situation is generallycreated by the following factors: (i) using a breading that is too coarse; (ii) impropertransfer of products into the fryer; (iii) excess fryer oil turbulence; and (iv) contactwith the fryer’s submerger belt, which allows abrasion of the coating. Adequatecontinuous filtration of the fryer helps remove particles as they are released intothe oil.

Off-flavors are often associated with a lack of sufficient turnover rate in thefryer, thus allowing breakdown products to build up in the frying oil. If a fryerholds 500 gal of frying oil (~3750 lb) and the fat absorption of the cooked food is8%, the minimum 7.5-h production rate should be 6250 lb/h to utilize the 500 gal.Less than that rate accelerates oil breakdown and leads to the development of off-odors. Another contributor to undesirable flavors is the cross-transfer of flavorsfrom the previous cooking of a high-intensity coated food followed by a muchblander food. The frying oil can become the source of flavor carryover. Suitablefiltration and treatment with appropriate filtering aids can offer relief for this quali-ty issue. Discarding of the oil is an option.

Excessive crust color arises from out-of-control Maillard reactions. One subtleaddition is the phenomenon found when the product fries to the proper crust colorin the manufacturer’s facility yet is excessively dark at the subsequent restaurantsite. This condition can often be traced to partial warming of the frozen productduring storage or distribution. Under these conditions, the enzyme system withinthe coating becomes activated and may combine with proteinaceous fluids fromthe thawing food core. The enzymes then convert the flour in the coating to sugars,which in turn become available for the Maillard browning reaction. Frost in thepackages generally indicates temperature abuse of the frozen product. Excess elec-trolytes in the coating, depressing the coating’s freezing point, can exacerbate thecondition.

Batter texture issues and coating blow-off during frying are generally causedby the following: (i) Lack of control of the batter viscosity; (ii) excessive free fattyacid levels (or oil breakdown) in the frying oil; (iii) incorrect product entry fromthe batter applicator into the hot oil; (iv) excessively high oil temperature; (v) lackof adequate rinsing of the fryer after caustic cleaning; and (vi) an incorrectly for-mulated batter. Strict process controls during tempura batter processing will reapmany benefits to the processor by reducing waste and maintaining consistent prod-uct quality, thereby providing complete customer satisfaction.

Acknowledgments

The author would like to express his appreciation to James Padilla and Bill Klein of Heatand Control, Inc. for supplying several of the photographs, FMC FoodTech for several ofthe figures; Monoj Gupta, Neil J. Trager, Andrea Pohl, Terry L. Hogan, and Dr. Christy A.Sasiela for offering valuable critical review of the chapter draft.



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C h a r a c t e r i s t i c s, J. Baur, K.S. Darley, J.J. Janda, J.R. Martin, D.B. Bernacchi, I.G.Donhowe; Griffith Laboratories International, Inc., September 11, 2001.

20. Guillaumin, R. (Institut des Corps Gras) Kinetics of Fat Penetration in Food, in Frying ofF o o d, edited by G. Varela, A.E. Bender, I.D. Morton, VCH-Ellis Horwood, C h i c h e s t e r ,UK, 1988.

21. Flick, G., Y. Gwo, W. Baran, R. Sasiela, J. Boling, C. Vinnett, R. Martin, and G.Arganosa, Effects of Cooking Conditions and Post-Preparation Procedures on theQuality of Battered Fish Portions, J. Food Qual. 12:227–242, (1989).



www.brookfieldengineering.com

22. U.S. Patent 5,527,549, Method of Making Improved Fried Battered and Breaded Foods,Griffith Laboratories Worldwide, Inc., 1996.

23. U.S. Patent 5,601,861, Method of Making Battered and Breaded Food CompositionsUsing Calcium Pectins, T. Gerrish, C. Higgins, and K. Kresl; 1997.

24. U.S. Patent 5,753,286, Coated Food and Method of Coating, Kerry Industries, 1998.25. Fry ShieldTM, The Healthier, Lower-Fat Frying Choice, two-page advertising bulletin,

Kerry Industries, Beloit, WI, 1996.26. U.S. Patent 5,217,736, Potato and Other Food Products Coated with Edible Oil Barrier

Films, Opta Food Ingredients, Inc., 1993.27. U.S. Patent 4,917,909, Low Fat Potato Chips and Process for Preparing, GAF

Chemicals Corp., 1990.28. Reduced Oil Absorption and Increased Moisture Retention in Batter-Coated Fried

Foods with Methocel Premium Food Gums, four-page technical information bulletin,Dow Chemical USA, Midland, MI, undated.

29. U.S. Patent 5,372,829, Process for Preparing Low-Fat Fried Food, Merck & Co., 1994.30. U.S. Patent 5,492,707, Process for Preparing Low-Fat Fried-Type or Baked Food

Products, Monsanto Co., 1996.31. Dip System Cuts Fat in Fried Foods, Food Product Design, Newlyweds Foods, May

1994.32. An Innovative Approach to Enhance the Value and Quality of Breaded Fried Foods,

NewlyWeds Fat Barrier 2000®, two-page advertising bulletin, Newlyweds Foods,Chicago, IL, undated.

33. U.S. Patent 4,943,438, Bread Crumb Coating Composition and Process for ImpartingFried-Like Texture and Flavor to Food Product, ConAgra, Inc., 1990.

34. U.S. Patent 4,518,620, Process for Breading Food, Central Soya Company, 1985.35. What is Newly CrispT M?, two-page advertising bulletin, NewlyWeds Foods, Chicago,

IL, undated.36. U.S. Patent 5,770,252, Process for Preparing a Breaded Food, L. McEwen, M.

Yurchesyn, K. Wypior; National Sea Products, 1998.37. U.S. Patent 6,013,292, Low Fat Food Product, Schechter, S., Superior Nutrition Corp.,

2000.38. Baking & Confectionary Section, The Maillard Reaction, Food Technology

International, May 2002, p. 112.39. American Style Bread Crumbs—Your Formula for Success, two-page advertising bul-

letin, Golden Dipt/Modern Maid Division, Fenton, MI, undated.40. Kerry Coatings, The Unexpected, 12-page advertising booklet, Beloit, WI, distributed

2003.41. U.S. Patent 4,068,009, Bread Crumb Coating Composition and Process, J. Rispoli, M.

Rogers, and J. Russo; General Foods Corp., 1978.42. U.S. Patent 4,423,078, Production of Oriental-Style Breading Crumbs, D. Darley, D.

Dyson, and D. Grimshaw; The Griffith Laboratories, Ltd., 1983.43. Coating Handbook for Prepared Foods Processors, Heat and Control, Inc., Hayward,

CA, 1999, p. 17.44. Fresh BreadcrumbTM Fish Portions Coated with Freshly Ground Loaves of Bread, four-

page sales booklet #S324, Icelandic USA, Inc., Norwalk, CT, 2002.45. U.S. Patent 4,936,248, Breader for Coating Edible Food Products with Fresh Bread

Crumbs, Stein Associates, 1990.



46. Breadings, eight-page advertising booklet, NewlyWeds Foods, Chicago, IL, 1999.47. U.S. Patent 6,158,332, Convertible Drum-Type Coating Apparatus, R. Nothum, Sr., and

R. Nothum, Jr., 2000.48. U.S. Patent 5,728,216, Continuous Tumble Coating and Breading Apparatus, E.J.

London; Stein, Inc., 1998.4 9 . Food Processing Equipment, A.K. Robins, LLC, advertising booklet, Baltimore, MD,

u n d a t e d .5 0 . Gourmet Breaders—Thai, one-page advertising sheet, Kerry Ingredients, Beloit, WI, 2003.51. Taylor, S.L., Allergies to Oil, Food Allergy News, 3:4, 2001.52. Food Allergy Awareness: An FDA Priority, Food Safety Magazine, Bailey, C., ed.,

February–March 2001, Washington, DC.53. Tater CrustTM—Shredded Potato Coated Fish Portions, four-page advertising booklet

#S325, Icelandic USA, Inc., Norwalk, CT, 2000.54. Sasiela, R.J., Troubleshooting Seafood Products—Shredded Potato Coatings, F o o d

Industry J. 5:2, pp. 146–148, Leatherhead Food Research Association, Surry, UK, 2002.55. HeatWave® Frying System, six-page brochure, Heat and Control, Inc., Hayward, CA,

2000.56. U.S. Patent 6,067,899, Breaded Products Fryer, A. Caridis, L. Murgel, C. Beitsayadeh,

J. Silverter; Heat and Control, Inc., Hayward, CA, 2000.57. U.S. Food and Drug Administration, Hazards and Controls Guidance, Chapter 15, 3rd

edn., Washington, DC, June 2001.58. Title 21 Code of Federal Regulations, 1–1404.59. Title 21 Code of Federal Regulations 161.175, 6.

A p p e n d i xSome Coated Foods Web Sites*

Coated foods regulatory and related web sites:www.fda.gov U.S. Food & Drug Administration: the lead agency for

processed seafood, vegetable, cheese, etc., a primaryresource for HACCP regulations

www.nmfs.noaa.gov National Marine Fisheries Service: a U.S. agencyresponsible for the inspection of coated seafood

www.usda.gov United States Department of Agriculture: a U.S. agencyresponsible for the inspection and labeling of coated meatand poultry products

www.uspto.gov United States Patent and Trademark Office: access to U.S.food patents

Batter and breading suppliers’ web sites:www.griffithlabs.com Griffith Laboratories: a global supplier of batter, breading, and

seasoning ingredientswww.kerryingredients.com Kerry Ingredients: a global supplier of coating, and ingredients,

and extrusion technologywww.mccormickflavor.com McCormick Foods: a major seasoning and coating ingredient

supplier. Print out a useful fry color chart from this sitewww.newlywedsfoods.com NewlyWeds Foods: a global coating and seasoning

ingredient supplier



www.fda.gov

www.usda.gov

http://www.nmfs.noaa.gov/

http://www.uspto.gov/

http://www.griffithlabs.com/

www.kerryingredients.com

www.mccormickflavor.com

http://www.newlywedsfoods.com/

www.premiereblending.com Premiere Blending Company: a supplier of seasoning and coating ingredients

www.richmondbaking.com Richmond Baking Company: an Indiana-based manufacturerof unique coarse cracker meals

www.washingtonquality Washington Quality Foods: a mid-Atlantic global supplier of foods.com coating ingredients and bakery mixes

www.sagevfoods.com Sage Foods: a rice-based coating ingredient supplierwww.semills.com Southeast Mills: a supplier of flour-based coating ingredientshttp://www.extension.iastate. Iowa State University basic primer about batter formulation

edu/Publications/N2857.pdf ingredients

Batter and breading equipment web sites:www.akrobbins.com A Maryland-based custom manufacturer of coating and other

food processing equipmentwww.bettcher.com Bettcher Industries: an Ohio manufacturer of coating equipmentwww.fmcfoodtech.com FMC: parent corporation of Stein Equipment Company: an early

developer of a broad range of coating and frying equipmentwww.heatandcontrol.com A major California-based supplier of a broad range of batter,

breading, frying, grilling and marinating equipmentwww.koppens.com A major Holland-based, coating equipment supplierwww.nothum.com A Missouri-based coating equipment supplierwww.orbitalfoods.com Used batter, breading and frying equipmentwww.barsso.com/engels.htm Used batter, breading and frying equipmentwww.used-food-processing- Used batter, breading and frying equipment

machinery.co.uk/stock_list.htm

Coated seafood related sites:Website U R L Brief descriptionwww.nfi.org National Fisheries Institute: a U.S. seafood trade organizationwww.icelandic.com Icelandic® brand: a Maryland-based leading supplier of

processed seafood products, Icelandic USA, Inc.www.seaclam.com Sea Watch International, Ltd.: Maryland processor of clam

www.seaclam.com strips, calamari, etc.www.frionor.com Frionor: a Rhode Island supplier of processed seafood items,

Division of American Seafood Corp.www.blountseafood.com./ Blount Seafood: a Rhode Island processor of coated scallops,

breaded_items.htm shrimp, musselswww.tampamaid.com Tampa Maid Foods Inc.: a Florida processor of breaded shellfishwww.conagrafoods.com/ Singleton Seafoods: a Florida processor of shrimp, and otherbrands/singleton.jsp? coated seafoodBrandID=anywww.icelandseafoodcorp.com Samband of Iceland brand, division of SIF: a Virginia

processor of battered and breaded seafoodwww.seapak.com Rick-Sea Pak Corporation: a Georgia processor of coated

shellfishwww.gortons.com Gorton’s: a major U.S. national retail brand of assorted seafood

productswww.phillipsfoods.com Phillips Foods Inc.: a Maryland processor of coated crab and

seafoodwww.sealord.com Sealord: a New Zealand based seafood processor



www.richmondbaking.com

www.washingtonqualityfoods.com

www.sagevfoods.com

www.semills.com

http://www.extension.iastate.edu/

www.bettcher.com

www.fmcfoodtech.com


www.koppens.com

www.nothum.com

www.orbitalfoods.com

www.barsso.com/

www.nfi.org

www.icelandic.com

www.seaclam.com

www.frionor.com

www.blountseafood.com./

www.tampamaid.com

www.conagrafoods.com/

www.seapak.com

www.gortons.com

www.phillipsfoods.com

www.sealord.com

www.vikingseafoods.com Viking Seafood Co.: a New England-based processor of breaded fish products

www.seafood.ucdavis.edu/ Battered fish HACCP guidelinesHACCP/Compendium/chapt02.htm

www.mackayeeffish.com/ Mackay Reef Fish Supplies Pty. Ltd.: an Australian fish processor crumbed.htm

www.unilever.ca/Divisions/ BlueWater Seafoods: a major Canadian seafood processorbluewater.html

www.fpil.com Fishery Products International: Newfoundland-based seafood processor

www.mrspauls.com Mrs. Paul’s Kitchens: part of the Aurora Foods group which also includes major U.S. retail brand Van De Kamps

www.kpseafood.com King & Prince Seafood, a Georgia-based processor of shrimp

www.tridentseafoods.com Trident Seafoods, a Seattle-based processor of seafoodwww.unisea.com UniSea Corporation: owner of the Mrs. Friday’s brand, a Los

Angeles-based seafood processorwww.st.nmfs.gov/st1 U.S. Fisheries Statistics and Economicshttp://ag.ansc.perdue.edu/ London Annual Seafood Report

aquanic/publicat/govagen/fas/uk5075.htm

Coated poultry related web sites:www.tysonfoodsinc.com Tyson Foods: an Arkansas-based world leader in processed

poultry productswww.perdue.com Perdue foodservice: a major East coast processor of poultry

Other informative coated products’ web sites:www.1800Poppers.com Formerly Anchor Food Products: a major coated appetizer

processor (aka Poppers®), now a division of McCain Foodswww.giorgiofoods.com Giorgio Foods: Pennsylvania processor of coated mushrooms,

cheese sticks, appetizerswww.phillipsfoodsinc.com Phillips Foods: a manufacturer of breaded mushrooms and

appetizerswww.jon-linfoods.com Jon-Lin Frozen Foods: a California manufacturer of breaded

onion rings, squash, fruit, and battered French toast stickswww.simplotfoods.com Simplot Foods: a major processor of coated potato, and finger

foodswww.lambweston.com Lamb-Weston: another potato powerhouse with seasoned and

coated frieswww.mccainusa.com Manufacturer of seasoned French fries and other appetizershttp://www.fosterfarms.com California-based processor of poultry and various corn dogswww.jimmydean.com Corn dog manufacturer

*Note: Web sites often change and are solely guidelines; therefore, conduct a search if a listing is not responsive.Some sites require registration. No company or product endorsement is made by its listing here or elsewhere in thisc h a p t e r .



www.vikingseafoods.com

www.unilever.ca/

www.fpil.com

www.mrspauls.com

www.kpseafood.com

www.tridentseafoods.com

www.unisea.com

www.st.nmfs.gov/

www.tysonfoodsinc.com

www.perdue.com

www.1800Poppers.com

www.giorgiofoods.com

www.phillipsfoodsinc.com

www.jon-linfoods.com

www.simplotfoods.com

www.lambweston.com

www.mccainusa.com

www.fosterfarms.com

www.jimmydean.com

Chapter 10

Fried Foods and Their Interaction with Packaging

Kenneth S. Marsh

Kenneth S. Marsh & Associates, Ltd., Seneca, SC

Packaging FunctionsPackaging plays a number of critical roles for fried foods. Consistent with virtuallyany food product, it must contain the product, protect it against moisture, oxygen, andsometimes light, and protect it against shock, vibration, and mishandling during stor-age and shipping. The packaging must present information consistent with the regula-tory requirements. In addition to these protection functions, packaging helps presentthe product in a manner that differentiates it from competitive products to attract pur-c h a s e r s .

This diversity of functions crosses company departmental boundaries, which canlead to conflicts and disagreements, with various groups working on the product hav-ing different objectives. For example, purchasing may seek the least expensive pack-age material; marketing prefers the most impressive option; production is easier with aloose package, but distribution damage is reduced with a snug package. Therefore, theselection of packaging material for a product can become a complicated process in acorporation in which multiple groups are involved in making the decision.

A humorous manifestation of this occurred when the corporate director ofpackaging for a Fortune 500 company put a nonmoisture-, nonoxygen-sensitivefood product packaged in a Kraft bag (commonly referred to as a brown paperbag). He presented the bag at a marketing meeting that included senior manage-ment. To the incredulous committee he stated that his proposed package satisfiedthe protection requirements, and anything more should be considered as marketingexpense. The point is that the package must both protect and present the product.

Consumers are exposed to many packages during their supermarket ventures.Any package, therefore, has little opportunity to grab the consumer’s attention.Competition for attention in the supermarket is extremely fierce. Studies suggestthat the time to gain the consumer's attention ranges between a few seconds andtenths of seconds. Mr. Harckham recommends that the company line thereforemake a statement as the consumer comes down the aisle, and then each individualproduct differentiate itself when the consumer is in front of the shelf. His examplewas not fried foods, but illustrates the concept. Lipton soups (as do Campbell's)exhibit a strong presence with strong red and white bands, which tell the consumer“Here are Lipton soups.” The graphics presented to consumers looking directly atthe shelf, however, clearly differentiate one flavor from others. A critical look at

Ch10/PFry/156-177/25 Feb. 6/7/05 2:20 PM Page 156


other company products will show whether their products compete as a companyor as individual products. Company identity through creative packaging and pre-sentation can greatly influence a consumer's attention.

Procedures to specify protection functions and distribution requirements willbe presented later in this chapter. The following will present generalized require-ments for various types of foods.

Packaging Examples

Bakery. Bakery products typically require a short shelf life because their “raisond’être” is freshness. Products may require some moisture protection, and oftenrequire grease protection, not for the product, but for the product presentation.Grease spots on a package would detract from the clean appearance of a freshproduct. Typical materials are coated board and coated papers in which the coat-ings may be polyethylene or wax, either of which provides both limited moistureprotection (if sealed) and resistance to grease wicking.

Packaging examples for bakery items will utilize donuts. Similar packagesalso apply to other bakery items. Figure 10.1 shows donuts in a thermoformedpolystyrene (PS) tray. This represents an inexpensive packaging material, withhigh clarity, rigid feel, a hinged cover, which facilitates reclosure, but which offerslittle moisture or oxygen protection. As with the following examples, low barrierprotection is appropriate because of short shelf-life requirements. Figure 10.2

Fig. 10.1. Thermoformed polystyrene tray.



exhibits a window box, which offers product visibility in a coated board box,whereas Figure 10.3 illustrates windowed bags, which contain a grease-resistantcoating or treatment to avoid wicking and polymer bags for donuts. The polymerbag, which shows the entire product, is also formed on the packaging line andoffers faster line speeds to the manufacturer.

Fig. 10.2. Use of a window box in a coated board box.

Fig. 10.3. Window bags with a grease-resistant coating and polymer bags.



Figure 10.4 shows donuts in a tray with overwrapped film. The tray can beexpanded polystyrene (EPS), PS, polyolefin, polyester, or expanded polyolefin.The overwrap may be polyvinyl chloride (PVC), polyolefin, or other polymers.This package offers a fresh bakery look and shows the product. A final option ispresented in Figure 10.5, which shows fresh bakery, i.e., no package. This option

Fig. 10.4. A tray with overwrapped film.

Fig. 10.5. An example of no packaging—fresh baked goods.



provides the shortest shelf life, but suggests freshness. It offers the customers theopportunity to mix and match different varieties into a single purchase. From theenvironmental perspective, “no package” offers a nonpolluting option, but alsogives no protection to the product. It makes labeling difficult (must be suppliedthrough external media).

Snacks. Snack items usually require oxygen and moisture protection becausethese products are typically low in moisture (to provide crispness) and high in oilcontent. The protection requirements will relate to the expected shelf life, i.e., thelength of time between production and consumption, which in turn relates to thedistribution system and the distribution environment. A number of possible trade-offs exist. Controlled temperature (and possibly relative humidity) during ware-housing will influence the amount of moisture pick-up and oil degradation in theproduct. However, this is a costly proposition. A distribution that allows morerapid deployment of the product distribution, such as the Frito Lay system, canreduce the packaging protection requirements.

In addition to chemical protection, packaging must offer protection from phys-ical abuse from shock, vibration, and compression. Much of this function is borneby the distribution package, typically a corrugated shipper, or overwrapped tray.The primary package (the package in direct contact with the product) also plays arole. Cans provide stacking strength and shock protection. Corrugated boxes offerless stacking strength than cans, but actually can provide more shock protectionbecause paperboard will absorb rather than transmit shock pulses. Polymer pouchesalso provide shock protection if the pouch is inflated before sealing. Potato or cornchip pouches, for example, are typically inflated, often with nitrogen to reduce oxi-dation and to provide protection against shocks.

Tip: Testing protocols for distribution packages, such as the ASTM D4169 (1)and ISTA procedures suggest drops be made on different orientations of the ship-per, and on surfaces, edges, and corners. Usually the different orientations (bottom,side, end, top) are included to test shippers falling on these alternate panels, withthe “normal” (bottom facing down) orientation set. It is recommended that onemust look at the results to determine whether an alternate orientation offers betterprotection [by exhibiting a higher effective free fall drop height than the normalconfiguration (2)]. If this is true, consider changing the product orientation in theshipper to provide additional protection with virtually no cost increase.

Unlike the donut examples above, snacks typically have longer shelf lives andtherefore require more barrier protection than that offered by coated paperboardcontainers. Therefore, most snacks are packaged in polymeric films with a widerange of moisture and gas barrier properties. The amount of protection relates tothe shelf-life requirements, and the storage environment.

An important trade-off is possible in which the distribution system affects thepackaging requirements. Frito Lay has developed a system consisting of ~50 man-ufacturing plants and 900 distribution centers (DC). This system allows products to



be manufactured and delivered to the retail facilities within weeks, and more oftenwithin days after production. This rapid deployment reduces the protection require-ments of the package. Therefore, Frito Lay can present fresher products (or moreoxygen-sensitive products) to the store shelves more rapidly than would be feasiblewith a more modest grocery distribution system with fewer plants and DC, simplybecause they can obtain product. The simplest and least expensive snack packageis a polyolefin bag, such as the linear low-density polyethylene (LLDPE) bags.These bags offer moisture protection but no oxygen protection; therefore, they areused for products that will sell quickly, or are not expected to exhibit rancidity dur-ing the time they remain on the shelf. Orientation of the polymeric films improvesboth clarity and barrier properties. Figure 10.6 presents an example of bags withthese properties. Clear bags can be made from single or multiple films. Laminatedor co-extruded structures allow for combinations of properties that are more suit-able for a given product than those available through any single film. For example,oriented polypropylene (OPP) provides a moisture barrier but little oxygen barrier.Incorporating a barrier layer, such as ethylene vinyl alcohol (EVOH) or polyvinyli-dene chloride (PVDC) can add substantial oxygen barrier to the package. Becausethese barrier materials are usually more difficult to seal, a heat seal layer is addedas the inside layer. Clear bags with the added barrier properties have the advantageof showing the product, as seen above in Figure 10.6.

Aluminum may add high oxygen and light protection to a laminate. Aluminumfoil is essentially impermeable to oxygen and moisture as long as it is free of pin-

Fig. 10.6. Clear bags made of linear low-density polyethylene.



holes or cracks. Because foil does not provide an easy sealing mechanism and isprone to tearing in thin films, the barrier is achieved by incorporating thin foils intoa laminated structure. Pouches with a foil barrier provide excellent oxygen protec-tion. These gusseted pouches will stand vertically on the shelf and help sell theproduct.

Foil can also be incorporated into structures in which paperboard is utilized toprovide strength and rigidity. A Pure-Pak container can be incorporated with alu-minum foil to achieve the barrier properties. Composite cans of various shapes andsizes (Fig. 10.7) use a thicker paperboard layer to add rigidity and stackingstrength to the packaging. The preformed potato sticks cans in Figure 10.7 wereinitially protected from impact with a corrugated medium placed between the chipsand the composite can, but this protection is no longer used. Aluminum providesother attributes that allow the container to become part of the product. The foil pan(Fig. 10.8), which is thicker than foils used in laminates, is used to cook the pop-corn, and clearly differentiates the enclosed product from competitors with value-added features.

Although many snack foods are packaged in foil laminates, most current snackpackages now use metallized substrates (Fig. 10.9). Aluminum is sputtered ontofilms in extremely thin layers, thereby using considerably less aluminum than eventhe thinnest foils. One can differentiate foil structures from metallized structures bycupping a bag snugly against one’s face and looking directly into the bag toward abright light. The presence of pinholes of light and thin lines (cracks in the foil)indicate that the structure contains foil. Metallized films will transmit light throughthe material, and the amount of light transmitted will be inversely proportional tothe amount of aluminum lay-down, and the amount of printing inks. If little light

Fig. 10.7. Compositecans have a thickerpaperboard layer toimprove rigidity andstacking.



comes through, the lay-down is heavy; if light comes through easily, the lay-downis light. The degree of barrier properties in a packaging film is a function of theamount of aluminum and the contiguity of the layer. Extremely thin lay-downs ofaluminum may provide a bright metallic appearance to the package and printing,but provide little barrier properties. For example, an overseas airlines company dis-covered that their peanuts were becoming rancid. The degree of metallization onthe peanut pouches was found to be very light so that the oxygen barrier was notsignificantly enhanced over the base material. The perception was that they wereemploying a barrier material, which was not the case. The aluminum metallizationin this case gave a metallic appeal to the graphics, but offered almost no barrierenhancement. The solution was to improve the amount and integrity of the alu-minum lay-down and thereby improve the barrier properties of the film.

The attraction of a metallized substrate can be combined with a presentationthat shows the product by using pattern-metallized films, which leave a clear win-dow. The dynamic graphics that resulted from inks printed on foils or metallizedfilms became so ubiquitous that one company introduced a matte finish to differen-tiate their product. This finish was identified as a deli look, which suggested fresh-ness. An extension of packaging snacks as individual products is the multipack,which allows a forum for consumers to try other products in a company's line.

Snacks that are less susceptible to environmental influences, such as popcornkernels, may be packaged in boxes. This option is also used for more sensitiveproducts, such as butter-flavored popcorn (oxygen sensitive) with a bag-in-box

Fig. 10.8. Use of an aluminum container as part of the product (foil pan) clearly differ-entiates it from competing products (bottle and gusset pouch).



package. Consumer benefits may be enhanced with susceptor inserts which focusmicrowave energy to concentrate heat and promote browning or popping (Fig.10.10). Additional convenience was mentioned earlier with the popping pan. Otherpresentations of snack packaging include bags clipped to a display rack, or lowbarrier snack bags.

Potato chips represent a large portion of fried snack products and illustratemany packaging challenges. Additional discussion of the technical aspects of pota-to chips (as a representative of this and other fried chips) is therefore warranted.The bulk density of potato chips is typically 0.056 g/mL. This is a light productwith a very large surface area. As a result, the headspace in the package, if air,would contain sufficient oxygen to oxidize the oils used in the frying process. Airallows uptake exceeding 3 mL O2/g at STP (standard temperature and pressure).With sufficient oxygen within the package, the oxygen barrier will provide disap-pointing results. The solution is to exclude the oxygen from the package beforesealing, and then maintain low oxygen within the package by appropriate barriermaterials. Therefore, an inert gas, typically nitrogen, is used in the packaging offried snacks. Very significant increases in storage life are realized if:

• Oxygen (O2) levels in the headspace are kept below 2% • Oxygen (O2) barrier films are employed• A light barrier is incorporated into the packaging film

Fig. 10.9. Metallized substrates (aluminum).



Studies that compare different materials used for potato chip pouches were com-piled by Robertson (3). A polyethylene bag whether high density (HDPE) or lowdensity (LDPE) (moisture barrier, but poor oxygen barrier) provided a 15-d shelflife at 27°C, 65% relative humidity. A PVC/PVDC copolymer-coated polypropy-lene bag provided 8–10 wk shelf life before the chips were unsalable due to loss ofcrispness. Potato chips packaged in polypropylene (PP)/aluminum foil poucheslasted ~27 wk before becoming unsalable due to rancid flavor development.

Chips packaged in OPP/LDPE/PVC, HDPE/EVA copolymer with an ultravio-let light (UV) absorber developed a distinct oxidized flavor within 7 d of storage at21°C and 55% relative humidity under 140–230 foot-candles of continuous fluo-rescent light. Potato chips stored under similar conditions, but with a brown light-absorbing pigment or an aluminum foil/LDPE construction were stable for 10 wkof storage.

The code date for a product is dictated primarily by the distribution system ofthe company. The product can fail due to moisture uptake and/or oil oxidation dur-ing distribution and storage. Shelf life of the product can be ensured by carefulselection of a packaging material that offers the required moisture and oxygen bar-rier properties. The extended code date for a product is achievable at a cost. Thisrequires a careful evaluation of the overall need for product protection, distributiontime, and the systems that are in place for a given product.

Frozen Fried Foods. Frozen foods are protected by temperatures that slow oxida-tive, chemical and biological reactions and bind water (in the form of ice), thuseliminating possible access by microorganisms. The storage temperature is themajor player in protecting frozen foods. Fried foods require little packaging protec-tion. However, no freezer maintains a constant temperature. Frost-free freezerseliminate frost by periodically heating the freezer walls and thereby driving offfrost. In addition, the temperature rises every time the freezer door is opened, andis brought down again after closing. As a result, temperatures fluctuate in thefreezer.

Fig. 10.10. Use of bags in a box for microwave products.



The water-holding capacity of warmer air is greater than that of colder air.Even if the freezer temperature rises just a few degrees, the air space in a packagewill hold more water. Water sublimes (converts from ice directly to vapor) fromthe product in the package and increases the relative humidity in the package head-space. When temperatures fall, water-holding capacity decreases and water con-denses onto the colder surface. Because the chilling is external, the colder surfaceis the package, and ice crystals form on the inside surface of the package. Thecycle, therefore, is that water leaves the product and condenses inside the package,resulting in “freezer burn,” which is a textural change in the product caused bylocalized drying. Reduced headspace in the package can minimize this problem.The tighter the package, the smaller the effect, with vacuum packaging being themost effective for this purpose. The recommendation for frozen foods, therefore, isto make the package as tight as feasible for any product.

A simple package is a polyethylene bag (Fig. 10.11). It has the advantages oflow cost and resistance to fats and oils. Paperboard is also used (Fig. 10.12), butpaperboard consists of hydrophilic cellulose fibers, which can wick oils and makethe package unsightly (as mentioned above with bakery products). Coatings orpolymers are used to prevent wicking. This is why most paperboard containers thatare in direct contact with frozen fried products are coated. Another way to separateproduct from contacting a paperboard container is to employ an internal container,such as a bag or tray, for the product (Fig. 10.13).

Other Fried Products and Outlets. Most of the products mentioned above aresold through traditional grocery systems or smaller retail outlets such as conve-nience stores and gas stations. Bakeries, which used to be separate facilities, areincreasingly incorporated into supermarket chains. Additional trends are home

Fig. 10.11. Frozen product in polyethylene bag.



meal replacement (HMR) systems in which prepared meals are offered at super-markets in competition with restaurants, and kiosks in which specialty products aregrouped for sale. Both of these developments offer freshly prepared foods fortoday’s meal. They also offer new snacks such as fried pies with overwrap.

Fig. 10.12. Frozen product in paperboard container.

Fig. 10.13. Paperboard container with an internal container, e.g., a bag or tray.



Packaging Systems for Fried Foods: Selection and Evaluation

The previous section illustrates the many options for packaging of various friedfoods. This section will cover the technical aspects of the packaging choice, that is,those aspects that provide suitable protection for the product itself. This protectionincludes the barrier requirements, which define the shelf life of the product, andphysical protection, which allows the product to survive the distribution system.The primary protection, which defines the shelf life of the product, will be dis-cussed first. Distribution protection will follow.

Shelf Life. The company manufacturing and distributing the product must definethe shelf-life requirements for any product. Often a group of employees (a commit-tee) performs the task of specifying the desired shelf life for a product. Thisprocess might be based on experience with existing products and past experience.The company’s product distribution system plays an important part in determiningthe desired shelf life of the product. The choice of shelf life has a significant effecton the image and profitability of the product.

A major consideration for shelf life is the stability of the product itself. Anyproduct containing unsaturated fats or oils will be prone to oxidation; thus, theproduct will be oxygen sensitive. Fried products are also dried (moisture flashesoff during frying) and are usually also moisture sensitive. It deserves mention thatthe type of package will directly affect product shelf life. For example, a snackitem, which (in packed form) becomes soggy in 1 mo, and becomes unacceptablyrancid in 4 mo, will be viewed as moisture sensitive because it first becomes unac-ceptable through a moisture gain. The same product, with a moisture barrier that isadequate for maintaining crispness will be viewed as an oxygen-sensitive product.In addition to the primary protection for shelf life, the package must protect theproduct through the distribution environment. This has been mentioned earlier andwill be discussed in detail later in this chapter.

Company philosophy affects the packaging choice. A company that competeson price may choose an inexpensive package providing limited shelf life (mini-mum barrier), and possibly simplified graphics for cost containment. Alternatively,a company may choose a premium image, with better packaging, longer shelf life(or higher quality within the shelf life through better barrier), and more attractiveart work. The distribution system, as previously mentioned, also affects the selec-tion of the packaging material. The goals for packaging can be stated as follows: toprovide adequate protection for the product from production to consumption, to becost effective, to be able to be handled by the packaging machinery at the plant,and to be environmentally responsible. In addition, it must also present, inform,and help sell the product.

Many criteria are used to define shelf life. As a general rule, business efficien-cy is enhanced when the production capacity, inventory capability, and distributionsystem are taken into consideration to define the shelf-life requirement for a prod-



uct. This requires knowledge of the distribution system and the production of suffi-cient product to maintain the pipeline with product plus sufficient surplus to main-tain the supply. The business model, therefore, is to produce product with a shelflife that matches the distribution system and meets the product quality standards asdesired by the customers.

The packaging barrier properties required to provide the needed shelf life for aproduct will vary with the package size. The same product packaged in a smallersize has a shorter shelf life than that in a larger package because the larger packagehas less film surface area per unit weight of the product in it. Therefore, the prod-uct in a larger package comes in contact with a smaller amount of moisture andoxygen diffused into the package compared with a smaller package within thesame time span. Therefore, for a given product and package shape, the larger theproduct size, the lower the barrier requirements necessary for a given shelf life.With this in mind, let us discuss barrier properties of different packaging materials.

When choosing a packaging material, it is prudent to remember that the barrierproperties of packaging materials vary widely. Glass and metal (such as cans orfoils) are the only materials that provide an absolute barrier to gases (such as oxy-gen) and vapor (such as moisture). Even these materials supply an absolute barrieronly if they have full integrity. Rigid containers of either glass or metal must besealed, and the sealant materials also have a finite barrier property. Some gases andvapors can permeate through the sealant. Therefore, metal cans or glass containersprovide good protection but are not absolute. Foils are good barriers as long as t h e yhave no pinholes or cracks. However, thin unprotected foils are prone to both pin-holes and cracking. This is why foils are usually laminated to polymers and/or paperto make the material more resistant to damage in handling. The ultimate barrier prop-erty of the packaging film depends on the choice of laminate and the thickness of thelayers, including the foils.

Plastics can provide a wide range of barrier properties to both gases and mois-ture. No polymeric material supplies an absolute barrier. Figure 10.14 presents anumber of packaging materials that are currently used or have historically beenused for packaging snack foods. The values are representative of particular poly-mers, but keep in mind that different resins with the same name may vary in per-meability characteristics (i.e., check with suppliers). The graph shows that somepolymers, such as polyolefins, comprise a relatively good moisture barrier, butpoor oxygen barrier. Other materials, such as EVOH, are excellent oxygen barriers,but poor moisture barriers. PVDC and METPET (metallized polyester, with goodlay-down) are excellent barriers to both gases and moisture.

Figure 10.15 presents the barrier properties in a different format, i.e., the costof sufficient polymer to provide an arbitrary unit of barrier performance. All of theoxygen barriers are the same, as are all of the moisture barriers. The graph showsthat using polyethylene for the oxygen barrier, for example, would be very costlybecause an unreasonable wall thickness would be required to obtain the desiredlevel of oxygen barrier. This material, however, provides a cost-effective moisture



barrier at a reasonable thickness, although HDPE, a more expensive resin, is morecost effective for moisture protection. A very thin EVOH film will provide anexcellent oxygen barrier, but would be too thin to provide a suitable package.EVOH is therefore typically incorporated into a laminate to provide the gas barrierwhile other components add mechanical strength, moisture barrier, and heat stability.Specific strength and barrier properties, therefore, can be designed in a cost-effec-tive manner with an appropriate choice of polymer combinations in a lamination orcoextrusion.

Packaging materials must be evaluated to determine the shelf life that they willprovide for a given product. This is usually determined through storage studies atboth ambient and accelerated conditions. High-temperature/high-humidity storagestudies do accelerate degradation and allow for more rapid assessment of perfor-mance than ambient studies, but the kinetics (reaction rates) will vary with prod-ucts and must be evaluated with the specific product before accelerated tests can beevaluated correctly. Any program that states that an accelerated condition is somemultiple of ambient is valid only if it has been verified on a specific productthrough a statistically validated test.

Mathematical modeling can be employed to shorten the time required to testpackaging materials. The first step is to determine limits for any agent that defines

Fig. 10.14. Film permeabilities. Source: Kenneth S. Marsh & Associates, 1985, withpermission.

–WVTR –02TR



the quality of the product. For snack products, this often includes moisture, whichaffects texture, and oxygen, which promotes rancidity. For all products, there is anupper limit for moisture content and the degree of oil oxidation in the fresh prod-uct. A threshold value for each of these parameters also exists to define the endpoint for consumer acceptance. It is necessary to meet the maximum moisture andoil oxidation standards in manufacturing. The packaging material is then chosen tomatch the desired shelf life, given the product distribution system in place.

Although a target value may be specified for any critical parameter, produc-tion variability exists. Furthermore, the acceptable range, which is defined by thecompany, is ideally wider than the production range (Figure 10.16). If this werenot true, the product would have no shelf life. The amount of oxygen or moisturethat can be tolerated is the amount that can be absorbed between production andthreshold or acceptable levels. Again, the quality acceptance criteria will be relatedto those points that are chosen on the basis of consumer acceptance data.

Once an acceptability range is established and a quantity of permeant is speci-fied, barrier requirements can be calculated. For example, if a product is known tobe able to tolerate x grams of oxygen before it becomes unacceptable, one can cal-culate the barrier required to allow x grams during the shelf-life requirement at aspecified storage environment. A simple calculation is to define the oxygen trans-

Fig. 10.15. Relative cost of different barriers. Source: Kenneth S. Marsh & Associates,1985, with permission.

–WVTR Protection –02TR P r o d u c t i o n



mission per day and match that to barrier specifications of films. However, such aprocedure will overspecify barrier because transmission changes as oxygen levelsincrease within the package (Figure 10.17). A more accurate procedure will com-pensate for the changes in oxygen level.

Calculations of minimum barrier requirements for a given shelf life provide ameans to choose suitable barrier materials. It is still prudent to verify the choiceswith storage studies, but such studies can be restricted to confirming materials thatare likely to succeed and eliminating those that are not likely to provide therequired shelf life. Furthermore, if both ambient and accelerated shelf-life studiesare performed, the kinetics can be determined such that accelerated studies can beproperly evaluated for future studies. In addition to barrier requirements, othermeans can be used to extend shelf life. For example, nitrogen flushing removesoxygen from the package. Oxygen or moisture absorbers (active packaging) canalso be employed to reduce the effects of agents that permeate the package.Packaging films are now available that absorb oxygen as it is permeating the film,thereby reducing the influx into the product.

Shelf life can be influenced by changing environmental conditions, which aretypical for noncontrolled distribution systems (controlled is refrigerated and frozendistribution). High-temperature, high-humidity conditions experienced early in thedistribution cycle will have a more detrimental effect on shelf life than similar con-ditions experienced later. Figure 10.18 shows the shelf life of a food product vs.month of production. Products shipped during the summer months had shortershelf lives than those produced during cooler periods. Furthermore, as expected,

Fig. 10.16. Quality profile. Source: Kenneth S. Marsh & Associates, 1991, with per-mission.

Process condition



Fig. 10.17. Permeant accumulation. S o u r c e : Kenneth S. Marsh & Associates, 1991, withp e r m i s s i o n .

Time (mo)

Fig. 10.18. Shelf life vs. month of production. Source: Kenneth S. Marsh & Associates,1984, with permission.

Month of production



the shelf life of products shipping to warmer locations had reduced shelf life(unless stored in climate controlled warehouses). Such information could be usedto improve product performance by possibly changing packaging requirements (ifregionally produced) or advertising to improve product flow through more criticalregions.

Physical Protection. Physical protection can be achieved through the primarypackaging container, such as nitrogen injection into potato chip bags as mentionedearlier, or through the distribution packaging, such as a corrugated shipper.Additional cushioning may be employed if necessary.

The physical requirements are typically defined through distribution testing. Inyears past, this was performed with shipping tests in which product was sentthrough distribution and evaluated for damage. Simulated testing is now typicallyperformed on packaged products. In this test, packages are shock-tested to simulateimpacts, vibration-tested to simulate transportation forces, and compression-testedto simulate warehouse stacking. Standard procedures are available through theAmerican Society for Testing and Materials (ASTM) and International SafeTransit Association (ISTA). The simulated testing procedure must be appropriatefor the distribution system through which the product is shipped. Applications thatvary widely from standard conditions should be carefully evaluated against the testresults. For example, field supplies for military operations may need to pass a stan-dard for helicopter drops (150-ft drop at 100 knots with 75% survival) that is sig-nificantly greater than grocery distribution, but designed for an appropriate criticaloperation. The distribution packaging must be designed to withstand the shockexperienced through the distribution system. The ability to do so is often expressedas the effective free-fall drop height (EFFDH), i.e., the highest level from whichthe product can be dropped and withstand an acceptable level of damage (Table10.1). The greater this value is, the greater the height from which it can be safelydropped. Keep in mind that heavier products typically experience lower drops in

TABLE 10.1 Fragility Evaluation Drop Tests

Effective free fall drop(in)

Product Base Side End

Chips I 14 14 32Chips II 17 11 17Snack I 24 6 30Snack II 24 52 19Snack III 34 60 25Snack IV 18 18 18



distribution. For example, a unitized shipment on a pallet will experience muchlower drops than a single package.

Vibration occurs during transportation, and varies with the mode of transport,such as truck, rail, ship, or air. Most food products do not have sufficient profit mar-gins to justify additional cushioning materials to dampen vibration. Compressionstrength is critical for stacking strength, and specifies how high pallets may bestacked. The distribution testing is performed with packages that have been equilibrat-ed to standard conditions, usually 73°F/50% relative humidity. This is done to allowcomparison among different studies and different testing laboratories. If storage con-ditions differ from standard conditions, it is important to recognize that compressionstrength may not match expectations. Storage in hotter, humid environments willseverely reduce the compression strength of corrugated packaging.

The author strongly advises that anyone who specifies packaging for food (orany) product should follow the product through the entire production and distribu-tion system. This includes observing incoming quality assurance for the raw mate-rials and the packaging material that are used to make the product, production,transport to the warehouse, warehouse operation, transport to retail outlets, the log-ging of product, stacking onto the retail shelves, and use of the product. Such ananalysis may uncover anomalies in the system that alter the product in a dispropor-tionate manner. Many companies either assume that they know these systems, oranticipate a certain level of performance. Actual observations of these various sys-tems may suggest ways to improve the product, improve the package, or improvethe distribution system, and ways to improve profitability.

Improving profitability with packaging systems does not necessarily meandecreasing packaging costs. The author evaluated the distribution system for a frozenproduct and discovered that a disproportionate amount of damage was caused duringthe log-in process at the supermarket chain. In high humidity environments, moisturecondensed onto the product, which had to be exposed to be logged in. A cartonimprovement and moisture-protective coating increased packaging costs by $200,000per year, but resulted in a $1.7 million reduction in damages.

Reducing Distribution Costs. It is recommended that the product be followedthrough the distribution system to better understand the following:

• How the packaging performs throughout the distribution system• Where damage may occur in the system

Once the information is collected and the system performance is understood, onemust take the following steps: (i) define the action steps needed to correct theissues; and (ii) take appropriate action to improve performance. These principlesmay be extended with increased knowledge of the entire system. The above discus-sion of shelf life included a description of changes in shelf life that result fromchanging environmental conditions. Analysis and documentation of these changesmay offer additional means for improving profits. It is possible to utilize this infor-



mation to improve profitability if one studies the effects of various city climates inrelationship to the actual product shelf life obtained in the various geographic loca-tions. The company could try to better match distribution system to productturnover rates as suggested in Figure 10.18. One could modify advertising andcoupons to accelerate the sale of products in warmer climates if the packaging wasdesigned for these more critical regions. Such action may enable the company toreduce the cost of packaging, thereby resulting in a major savings. It suggests thatone could design the package for the entire market as opposed to the worst geo-graphic location.

Another option for varying regional performance is to vary regional packag-ing. This requires additional product codes, which obviously means additionalexpense. However, if the savings in packaging materials exceeds these costs, profitimprovement is achieved. The practicality of this option depends on its economicviability. An additional benefit of studying distribution environments is that itallows comparison between new and existing markets. For example, a domesticcompany that wishes to expand to foreign markets may evaluate additional packag-ing requirements to meet the needs for those markets.

Modern technology can be employed to carry this concept further. The authorhas proposed a Computer-Aided Distribution in which temperature/humidity sen-sors could be installed in distribution centers and possibly transport vehicles andcontainers. These sensors could record the actual conditions that specific productshave experienced, and be used to pull products on the basis of available shelf lifeinstead of first-in/first-out systems that cannot compensate for abused product.This system would require a database consisting of all shipments with dates, desti-nations, and environmental readings, a computer program to calculate availableshelf life, and an interface that modifies pull dates of products in the specific distri-bution center. Needless to say, it would require a highly sophisticated computersystem that the distribution staff would have to follow exactly.

ConclusionsThe author strongly advises any person who is responsible for the design or speci-fication of a packaging system to follow the product through its entire manufactur-ing and distribution system periodically and observe products in the entire distribu-tion system. Such action will demonstrate how well the system is performing.Viewing products in distribution will also suggest how products compare withcompetition, which may well lead to ideas that may benefit the company. Testingand evaluation of actual product through distribution conditions can pinpoint prob-lem areas. Any aspect of these areas that results in a disproportionate amount ofproduct damage makes them the focus of opportunity for profit improvement.

Packaging can reduce damage and improve sales. A relatively common prac-tice is to choose the lowest cost packaging material for a given product. This mayappear to be a sound business option, but it may compromise profitability in the



long run. Often there is a trade-off among product, packaging, distribution, and amore protective package. The final decision should be based on profitability.Packaging that promotes sales through better presentation, and convenience fea-tures such as easy opening, resealable pouch, and so on may not only enhancesales, but also allow for consumer acceptance of a higher price. Packaging attractscustomers at the supermarket and plays the role of principal salesman for the prod-uct at the store. Therefore, it is directly related to the company's profitability. Thepackage will influence the initial sale; the product quality will determine repeatsales.

References

1. ASTM D4169-94, Standard Practice for Performance Testing of Shipping Containersand Systems, American Society for Testing and Materials, Philadelphia, 1994.

2. Marsh, K.S., Influence of Product Orientation on Shock Resistance of Snack Foods,Packaging Technol. Eng. 8:36 (1999).

3. Robertson, G.L., Food Packaging: Principles and Practice, Marcel Dekker, New York,1993.



Chapter 11

Toxicology of Frying Fats and Oils

Richard F. Stier

Consulting Food Scientists, 627 Cherry Avenue, Sonoma, CA 95476

IntroductionFatty foods, especially fried foods, are enjoyed by people of all countries, and fathas been used for thousands of years by almost every civilization. No matter whereone travels, these delicious products are offered as part of the daily fare. In Europe,frites and fried pastries are mainstays of the diet. The Chinese produce a frieddough product bearing a name that literally translates as fried rope. Tempura, afried battered product, is a staple of Japanese cookery. Fried and seasoned grains,chips and wafers have been part of daily snacks in the subcontinent of India for cen-turies. A small sampling of popular fried foods in the United States includes Frenchfries, fried chicken, fried snack foods (chips and nuts), donuts, pastries, and pies.

Modern day consumers have been made to believe that the foods that are tastyand rich in taste are bad for one's health. Many physicians have called all fried foods“bad” because they are fried in oil and are rich in fat calories. To some degree, this istrue because overindulgence of any type of food, whether it is rich or lean in energy,could be harmful to health. In addition, some consumer advocates have indicatedthat frying generates compounds that could pose health hazards.

Deep-fat frying is probably one of the most dynamic processes in all of foodprocessing. The oil, as well as the fried food, undergoes dramatic chemical changesduring the frying process. The oil is subjected to prolonged heat stress that canbreak down the oil, producing a large number of compounds that can affect the fla-vor, taste, and storage life of the product. Some of the oil breakdown products maycause some gastrointestinal distress when the food is consumed in very large quan-tities. In reality, properly operated fryers do not heavily damage frying oil, and theoil does not pose any toxicological danger. Concern over the health implications ofoil and fried foods have led to a great deal of research in this area.

A considerable amount of research has been performed over the past sixdecades. Researchers have tried to understand whether normal frying generatesany harmful compounds in the oil or fried foods and whether heated and/or abusedoils are safe for human consumption. Most of these studies were conducted on lab-oratory animals to determine: (i) the effect on health and longevity of the test ani-mals, their organs, and survival; and (ii) food utilization, absorption of nutrients,and the growth pattern of the test animals.

The majority of the feeding studies utilized oils that were heated and abusedexcessively. No frying operation, whether industrial or restaurant, would treat the



fryer oils in the way these researchers did. Therefore, one must exercise proper judg-ment when drawing conclusions from the studies. However, this kind of laboratoryresearch has been and will continue to be extremely important. Studies with heated fatsand oils do provide the regulatory agencies with the background information for enact-ing laws and/or establishing guidelines to protect the health and welfare of the con-sumers. This chapter will review the effect of heated oils on human health.

Dietary IssuesThere have been several major changes during the past two decades in consumer,industry, and government attitudes toward the consumption of fats and oils. Fats oroils have been labeled as one of the less desirable constituents in our daily diet.These findings have spawned the proliferation of so-called “Low-Fat” and “Fat-Free” products in almost every category of packaged foods. Unfortunately, fats andoils (lipids), along with proteins and carbohydrates, are the primary nutrients in thehuman diet. Without some fat, the diet is incomplete. The studies conducted by theSurgeon General of the United States indicate that consumption of low-fat and no-fat products has not produced a leaner population. Unfortunately, the contrary istrue, and the U.S. population is getting fatter.

Early Research Work on Heated Oils

Research on frying fat and oils began in the early part of the 20th century. The homeeconomics departments of various universities in the Midwest took the pioneering rolein this area. Studies were conducted in the early 1930s to determine the nutritionaleffects of heat on fats. Morris and his colleagues (1) reported that rats given heatedlard as their diet developed vitamin E deficiency. Their work also showed that ratssuffered growth failure and weight loss when their diet contained 50% lard that washeated for 120 min at 300°C.

Roffo (2) reported that rats developed tumors when their diet consisted of sun-flower oil, olive oil, lard, tallow, or cholesterol that had been heated for 30 min at350°C. Later workers refuted these findings on the basis that the tumors failed tomeet the established criteria for cancer.

Crampton and Millar (3) observed that rats had a high rate of mortality whenthey were fed a diet consisting partly of polymerized linseed oil. The linseed oilwas heated for 6–15 h at 275°C with carbon dioxide sparged through the oil toexclude air. Harris (4) reported that laboratory rats suffered impaired growth and illhealth when they consumed fish oils heated for 8–12 h at 280°C. Lane et al. (5)observed no tumor formation in rats when the diet consisted of oil browned for 30min at 350°C. These rats, however, seemed to have a higher incidence of papillonand ulcers. Lassen et al. (6) showed that sardine oil that had been heated to hightemperatures was less digestible than unheated oil.

Crampton and his colleagues reported results in a series of papers in 1951 (7). Inone study, the rats received a diet of baked feed consisting of 10–20% of linseed, soy,



cottonseed, rapeseed, corn, peanut, or herring oil. The oils were individually heatedfor 30 h at 275°C and then incorporated into a baked product. Baking was done at375°F for 20 min. Test rats receiving the diet containing 20% heated oil showedincreased weight loss. The linseed oil diet seemed to have the worst effect on the rats.

In a second study by Crampton et al. (8), the heated linseed oil was fractionat-ed by a distillation process into distillate and residue. Heavy mortality and overallpoor health were observed in the group administered the residue fraction in theirdiet. The distillate fraction was found to be relatively less harmful to the rats, butwas more deleterious than the unheated oil.

Deuel et al. (9) made citric acid esters of glycerol. The esters were heated for8 h at 205°C and potato chips were fried with the heated ester. Rats were fed a dietconsisting of heated esters and fried potato chips. Neither diet had any adverseeffects on the test rats.

Frahm et al. (10) observed deleterious effects in mice fed heat-polymerizedwhale oil. Crampton et al. (11) showed impaired weight gain in rats whose dietswere high in polymerized oils. They also fractionated the heated oils into six frac-tions, ranging from straight-chain compounds to cyclic compounds. They observedthat the diet containing 20% of the cyclic monomers (non-urea–adducting fraction)caused high mortality in the test rats. The diet containing 20% of the straight-chaincompounds did not have any adverse effect on the rats.

Raju and Rajagopalan (12) heated sesame, peanut, and coconut oils in openpans at 270°C. The thermal polymers thus produced in the oils caused depressedgrowth rates in test animals. Kaunitz and co-workers (13) heated lard and cotton-seed oils with aeration for 200 h at 95°C. The heated lard contained 17% polymersand the heated cottonseed oil contained 40% polymers. Rats fed the diet containing20% of these oxidized and polymerized fats suffered from high mortality. Adverseeffects were also noted in rats fed diets consisting of 10% of these oxidized andpolymerized fats. The adverse trends reversed when the rats were fed diets contain-ing fresh oils.

Crampton et al. (14) fed the non-urea adduct–forming components from lin-seed, soy, and sunflower oils to rats. The fractions from linseed oil had the mostdeleterious effects on the test rats. The effects from the soybean oil were less pro-nounced and the sunflower oil had the least effect.

Johnson et al. (15) observed that corn oil, thermally oxidized at room tempera-ture, depressed growth in rats. The growth rate became normal once the diet waschanged to fresh corn oil. All of the above-mentioned work and the results aresummarized in Table 11.1.

Subsequent Feeding Studies on Heated Fats

Neither commercial fryers nor restaurant fryers are operated under the test conditionsdiscussed in the previous section. These are extreme heating conditions and theresults obtained do not represent real-life situations in the frying industry. Melnick



(16) called many of these early studies “impractical.” He presented information onused oils gathered from 89 commercial chip-frying operations and indicated that therewas little change in the iodine value of the oils as a result of frying, and polymer con-tents were not an issue. Rice et al. (17) examined fats from restaurants, bakeries, andchip producers. They observed that rats experienced only slight decreases in energyand slight increases in liver size when the diet contained even the most abused oils inthis group of products. Alfin-Slater et al. (18) noted that growth, reproduction, lacta-tion, and longevity in rats were not impaired when cottonseed oil was heat-polymer-ized to effect a drop of 5% of its fresh iodine value.

Witting et al. (19) suggested that the incorporation of a single peroxide groupinto fatty acid molecules was enough to cause toxicity in rats and mice. Nishida etal. (20), on the other hand, reported that the test rats fed heated oils had reducedcholesterol. Perkins and Kummerow (21) heated corn oil for 48 h with agitation.The abused oil was then fractionated via distillation. Weanling rats died within 7 dwhen they were fed the residue fraction from the non-urea–adducting fatty acids.Alfin-Slater et al. (22) heated various vegetable oils for 60–100 min at 610°Funder vacuum. In their feeding studies, no evidence of nutritional impairment wasnoted, except for soybean oil, which was found to be highly polymerized under thetest conditions. A slight decline in digestibility was also observed with this oil.

Custot (23) warned that improper frying could severely damage the oils.Keane et al. (24) conducted a study using heated oils from commercial operations.No toxicity was observed in the rats; in fact, those rats fed the heated fats gainedweight. The same study reported that oils heated and oxidized under laboratoryconditions produced lower growth rates in test rats, but no toxicity was observed inthese rats.

R i c e et al. (25) reported that there was “no reason to believe that fats werenutritionally damaged by normally accepted good practices in present-day foodpreparation.” They also observed that the frying oils suffered undesirable changes

TABLE 11.1 Early Research on Heated and Oxidized Oils

O i l P a r a m e t e r s R e s u l t s R e f e r e n c e

L a r d 20 min at 300°C Depressed growth; weight loss ( 1 )S u n f l o w e r 30 min at 350°C Tumors ( 2 )L i n s e e d 6–30 h Depressed growth ( 3 )S o y 2 7 5 ° C Weight loss ( 8 )C o t t o n s e e d D e a t h ( 1 4 )R a p e s e e dP e a n u tC o r nF i s h 8–12 h at 280°C Depressed growth; ill health ( 4 )S e s a m e Open pans at 270°C Depressed growth ( 1 2 )P e a n u t



in viscosity, browning, and product flavor before the oils reached the state at whichbiological effects could be observed. They observed biological activity on labora-tory rats when they were fed the oil that had been foaming in a potato chip fryer.No specific cause for the foaming was reported.

Perkins (26) presented a review of earlier work in the area of frying fat toxici-ty and posed three questions: (i) Are polymers formed in unsaturated oils duringdeodorization, processing, and use? (ii) Are polymeric materials absorbed on foodproducts in the fryer; if so, to what extent? (iii) What are the physiologic and nutri-tional effects of these polymeric materials? The researchers determined that the oilcan be polymerized during oil refining if proper precautions are not taken. Thepolymers are also absorbed by the fried food, but no partitioning effect has beenproven.

Firestone et al. (27) and Friedman et al. (28) reported that heating cottonseed oilfor 190 h at 225°C increased its viscosity. They reported that heating the oilsincreased viscosity and molecular weight and lowered the iodine value. Theyobserved that rats fed this abused oil suffered from a lack of nutrient absorption. Theyhypothesized that such abused oils might have interfered with absorption of othernutrients. The forced feeding of urea filtrate monomers and dimers to weanling miceresulted in death. Similar adverse effects were observed when the non-urea–adductingfatty acids were included in the diet. These researchers were the first ones to proposeusing this class of compounds as an indicator of the quality of heated oils.

In 1962, Poling et al. (29) studied the influence of temperature, heating time,and aeration on the nutritive value of heated cottonseed oil. They found that thechanges in the oil were proportional to the severity of the conditions. They alsoreported that the oils with a high level of change were subjected to conditions thatwere more severe than those encountered in the normal frying process. Test ani-mals had enlarged livers when they were fed damaged oils in their diet. Fleischmanet al. (30) recommended against both reusing and overheating oils because thesewould cause additional hydrolysis and oxidation in the oil. They commented thatfrying appears to decrease the hypocholesteremic effect of the high concentrationof polyenoic acids in raw oils.

Raju et al. (31) heated peanut, sesame, and coconut oils in an open iron panfor 8 h at 270°C. Rats fed a diet containing 15% of these oils had reduced growthrates, reduced food intake, increased liver weight, reduced vitamin-B storage,reduced carbohydrate absorption, and higher blood glucose and cholesterol.Perkins and Van Akkeren (32) demonstrated that intermittent heating and coolingof cottonseed oil caused the oil to break down rapidly. Oil heated intermittently for66 h and oil heated continuously for 166 h contained the same amount of polarmaterials. They concluded that oils in small operations in which the turnover is lowmay be damaged more rapidly than those in large operations in which oil turnoveris more rapid. This was found to be the case in actual practice.

Kaunitz et al. (33) conducted long-term feeding studies in which rats were feda diet that included up to 30% fat. The fat had been oxidized for 40 h at 60°C, with



airflow of 1–2 L/min. Cottonseed, chicken fat, beef fat, and olive oils were used.They found that death rates and lesions observed after death were greater in ratsthat had consumed the oxidized oils, except for the oxidized olive oil. A year later,Kaunitz (34) participated in an IFT-sponsored symposium on the Chemistry andTechnology of Deep Fat Frying. In his summary concerning the effects of cookingand storage he noted that: “Intelligent cooking or even storage procedures mayimprove the quality of some dietary fats.”

Nolen et al. (35) conducted a feeding study on rats using hydrogenated soy-bean oil, cottonseed oil, and lard. These oils were used under restaurant conditionsuntil they were judged to be unfit for use. These fats made up 15% of the diet. Theused fats were slightly less absorbable and gave correspondingly slower growthrates. There were no clinical, pathologic, or metabolic criteria to suggest that theused fats adversely affected the population consuming them. Distillable non-urea–adducting fractions from used fats proved somewhat toxic when high concen-trations were administered to weanling rats. Their conclusion was: “Although heat-ing of fats under actual frying conditions does cause the formation of substanceswhich can be shown to be toxic, the level of such substances and the degree oftheir toxicity are so low as to have no practical dietary significance.” Nolen con-ducted additional studies (36,37) with hydrogenated fats. He concluded that hydro-genated fats, either fresh or used, did not affect reproduction in rats.

Poling et al. (38) conducted long-term feeding studies on laboratory rats. Therats were fed heated (182°C for 120 h) cottonseed salad oil, corn oil, lard, and hydro-genated vegetable shortening. They found no significant differences between theheated and unheated oils. They stated that, “The absence of adverse effects attribut-able to the heated fats during the life span of the rats is further evidence of the safetyof these fats of the quality customarily consumed by the human population.”

In 1972 and 1973, Ohfuji and his colleagues in Japan conducted a series ofstudies on the nutritive value of heated oils (39–41). They found a toxic dimer inabused oils, and concluded that this was found in the most polar fraction of theoils. This dimer itself was more digestible than the thermally oxidized oil. The oilswere heated for 90 h at 275°C in the presence of air or nitrogen. They did reportthat they were able to recover small amounts of the dimer in some commercialcooking oils.

Billek et al. (42,43) presented their findings on sunflower oil obtained fromthe commercial production of fish fingers. They isolated different fractions fromthe oil before and after it had been used for frying, and used these for feeding stud-ies. They found that rats consuming the polar fraction had significantly lowerweight gains than the other test animals. As a result of this study, they proposedthat the polar fraction could be used as an index of oil quality. They concluded that30% polar material in fryer oil represented a safe number, a value that was reducedlater to 27% for regulatory purposes. This is the non-urea–adducting fraction. This,indeed, was a revival of the work done by Firestone et al. in 1960–1961. Polarmaterials are, in fact, now used in several European nations as a quality index in



restaurant fryer oils. At the AOCS meeting in 1978, Clark presented a review on thestate of heated oils, reporting that there was no evidence that oils used in commercialoperations were abused to the point that they would create health problems.

In 1978, Lang et al. ( 4 5 ) published a study based on 10 years of animal feedingstudies, in which three generations of rats were fed heated and unheated oils at a levelof 10% of their diet. The study concluded, “Frying fats heated under conditions ofgood commercial practice are not detrimental to the health of test animals.” Billek( 4 6 ) commented that even after 20 years, the study made by Lang et al. has not beencriticized and its conclusions are still valid.

F o n g et al. (47) used the Ames test (microcosms) as a means of evaluatingChinese peanut oils for aflatoxins. They detected mutagenic activity in fresh oils,an activity that decreased with repeated cooking. This study demonstrated thatheating could remove certain undesirable components from fresh oils, i.e., the afla-toxins. Aflatoxins can be present in cold-pressed peanut oil. This is not the case forpeanut oil produced in Western countries because the oil is processed at a hightemperature.

Taylor and his colleagues (48,49) conducted two studies to determine whethermutagens were present in fried foods and the effect of frying conditions on mutagenformation. Their work agreed with that of many others, i.e., mutagens are not a prob-lem if oils are not abused. Goethart et al. (50) conducted a study on frying oils andfoods from canteens in The Netherlands and also conducted their own frying studies.Their work indicated that there was a slight decline in weight gain and some differ-ences in liver and kidney size in animals fed more abused oils (frying up to 14 d).They did not find any evidence of mutagens in fried foods or heated oils.

Hageman et al. (51–53) also conducted work using the Ames test on heatedoils and foods. These workers observed increased mutagenicity in the polar frac-tion of the oil with increasing abuse. They were unable to isolate the mutageniccomponents within the polar fraction. In 1990, Addis (54) postulated that choles-terol oxides and other oxidative materials formed as result of heating oil may act asinitiators of arterial damage. These materials allegedly damage the arterial walls,setting the stage for plaque deposition. Marquez-Ruiz (55) indicated that thermallyoxidized fats might have adverse effects on human health.

Industry and Food Service Practices

Researchers in the field of nutrition have stated that handling of frying oils undernormal operating conditions does not pose any health hazards, even though mostfried foods are rich in oil or fat. This was reiterated at the 3rd InternationalSymposium on Frying sponsored by the DGF (56). They made the following state-ment: “There are no health concerns associated with consumption of frying fatsand oils that have not been abused at normal frying conditions.” The next questionis whether oil abuse is indeed a problem in the food processing and food serviceindustries. There are a number of studies that indicate that oils used in commercial



frying are not abused (16,57,58). The oils from these studies did not pose anyhealth concern.

When abused, oils break down into hundreds of compounds. Many of thesecompounds are detrimental to the shelf life of the oils and the products made withthem. Complaints from German consumers about fried food quality at restaurantsand their aftermath that prompted scientists in that country to initiate studies onfryer oil quality in restaurants, which led to the first recommendations for regulat-ing frying fats (59).

Blumenthal (60) evaluated hundreds of oil samples from industrial and foodservice frying operations and related those samples to actual practices. He foundthat the oils from the commercial chip fryers were least abused. This is primarilydue to high oil-takeout by the food and constant replenishment with fresh oil(Table 11.2). Industrial fryers are used for foods such as French fries and batter-coated and breaded products; these are much more abused than the products pro-duced in chip fryers. The fast food, coffee-shop doughnut, and institutional fryingoperations are the most abusive to frying oil. This agrees with the observations ofPerkins and Van Akkeren (32). Table 11.2 compares average values of oil qualitiesfor these industries (60). As noted in Table 11.2, the fast food and restaurant busi-nesses do create abused oils. However, in actual practice, very few restaurant oper-ations allow their oils to reach such high polar concentrations.

Trans Fatty Acids

Trans fatty acids are the trans isomers of unsaturated fatty acids. Most naturallyoccurring unsaturated fatty acids are found in the cis form. The cis and trans formsrefer to the position of the hydrogen around the double bonds on the fatty acidchain. These hydrogen atoms are held in place at the double bond. When the atomsare on the same geometric side of the chain, they are referred to as being in the cisposition; those on opposite sides of the chain are in the trans position.

Trans fatty acids, however, are not simply the products of human chemistry.There are several naturally occurring sources of trans acids. They may be found insome plant oils, such as tung and pomegranate oil. However, these are not commonedible oils. They are also formed in fats from ruminants, such as cattle and sheep.

TABLE 11.2 Approximate Levels of Polar Materials at Which Various Industry Segments Discard Oila

Polars at discardI n d u s t r y ( % )

Snack foods 1 1 – 1 3I n d u s t r i a l 1 5 – 1 7Restaurant and institutional 2 2 – 2 7

aS o u r c e : Reference 82.



The bacteria in the rumen produce trans acids, found in these animals. The levelsof trans acids found in natural sources is quite low (1–5% of total fat).

If the triglyceride being examined has a high level of trans acids, these willpack together, forming a solid fat. This is a function of the straight chains formedby t r a n s acids. Because they are straight, they will pack more tightly and formcrystals or hard fats. Harder fats have higher melting points (Table 11.3). In fact,the melting points of trans acids are midway between those of saturated and the cisunsaturated isomer.

The development of the hydrogenation process is credited to a French chemistnamed Sabatier. The process is now >100 years old. Hydrogenation allows oil refin-ers to “harden” fats using hydrogen in the presence of a catalyst. The most commoncatalyst used is nickel. One common misunderstanding is that hydrogenation pro-duces only saturated fats from the unsaturated fats. In fact, a percentage of existingunsaturated fatty acids is converted to both saturated fats and the t r a n s isomers of thenaturally occurring c i s forms. As described above, the t r a n s isomers have highermelting points than do the original c i s isomers, which allows processors to manufac-ture a variety of plastic fats from the hydrogenated fats. These plastic fats have awide range of functional characteristics, depending upon their makeup.

Over the years, oil refiners have continually refined the hydrogenation process.The makeup of the finished product is a function of the type of processing the oilundergoes. By controlling process time, pressure, temperature, catalyst quality, rate ofagitation, and quality of the feedstock and filtration, a range of products may be pro-duced. One of the most critical quality control points is the catalyst. Old or poisonedcatalysts produce finished products with higher levels of t r a n s acids. The greater thedegree of hydrogenation, the harder the fat. In a fully hydrogenated product, all of thedouble bonds are eliminated and the resulting product is hard and brittle. Fully hydro-genated oil has essentially zero t r a n s fat content (Table 11.4).

Fats and oils are prone to oxidation and other reactions. In particular, soybeanand canola oils are susceptible to oxidation. Soybean and canola oils used for fry-ing shelf-stable snacks are typically “brush” or lightly hydrogenated to reduce thelinolenic acid content in the oil, which enhances oxidative stability. Oils used fordoughnut, food service, or restaurant frying are more heavily hydrogenated.

It is logical to ask how much t r a n s fatty acids do people consume and does thispose a potential health risk? It is difficult to determine the consumption of t r a n s fat in

TABLE 11.3 Melting Points of C1 8 Fatty Acids

Fatty acid F o r m u l a Melting point (°C)

Stearic acid C1 8 : 0 6 9 . 9Oleic acid (c i s) C1 8 : 1 1 0 . 0 – 1 3 . 0Linoleic acid (c i s) C1 8 : 2 – 5 . 0Elaidic acid (t r a n s) C1 8 : 1 4 4 . 5



our daily diet, because the daily diet comprises a very complex mixture of differentfoods and it varies with individual eating habits. Dr. David Firestone of the UnitedStates Food and Drug Administration (FDA) and Dr. W.M.N. Ratnayake (61) showedthat there was no single method applicable for all samples.

One major barrier to determining the amount of trans fatty acids in the diet isthat no one has yet developed a comprehensive database on the subject. As anexample, the FDA allows food processors to utilize nutritional databases, such asthose in the USDA Handbook 8 series (62), or those developed by suppliers fortheir products to prepare nutritional labels. The databases listing t r a n s fatty acidcontents in various foods are not readily available; thus, anyone who wishes todetermine whether their foods contain these materials must have the food analyzed.Dickey and Caughman (63) from the USDA have developed a compilation of fattyacid profiles, including trans acids, for >100 foods, but more work is needed.

The amount of trans fatty acids in the daily diet has been a subject of debatefor a number of years. In the United States, estimates vary from 7.6 to 15.2 g/d. In1985, an expert panel report prepared for the FDA (64) estimated daily consump-tion to be 8.3 g/d. Estimates prepared by the edible oil industry in 1984 and 1989were 7.6 and 8.1 g/d, respectively. Hunter and Applewhite’s 1986 estimate fordaily consumption was 2.3–6.6 (65). Enig et al. (66,67) determined the averagedaily consumption to be 13.3 g for adolescents and 14.9 g for adults. These latterestimates have been criticized by the edible oil industry as not being realistic basedon hydrogenated oil production. There have been reports that in some countriesdaily consumption of trans fatty acids may be as much as 48 g/d.

Even though there is debate over the exact average daily consumption of transacids, it is clear that there are a number of foods that may have high levels of transacids. Many of these foods are, unfortunately, common snack foods. Doughnutscontain >30% fat, a third of which is trans fat; this computes to ~5 g of trans fatper doughnut. It is estimated that 10 potato chips, which contain 10 g of total fat,contain 2.2 g of trans fat when they are fried in partially hydrogenated soybean orcanola oil.

TABLE 11.4 Proportion of T r a n s Fatty Acids in Food Products

Total fatty acids as t r a n sFood category ( % )

Margarine (stick) 2 5 – 3 0Margarine (tub) 1 3 – 2 0Household salad/cooking oils 0Household shortenings 1 4 – 1 8Foodservice frying fats and oils 6 – 4 0Baking fats (foodservice) 1 0 – 3 5B u t t e r 2 – 9

aS o u r c e : Reference 63.



The expert panel report from 1985 mentioned above concluded: “The avail-able scientific information suggests little reason for concern with the safety ofdietary trans fatty acids at present and expected use levels of linoleic acid.” Thisreport also called for additional studies to clarify certain issues (64).

In 1988, the Institute of Shortening and Edible Oils (68) concluded that:“Concerns that have been raised about possible relationships between atheroscleroticdisease or cancer are not supported by reliable data.” In their 1994 “Food Fats andOils” report (69), their position changed somewhat concluding that: “Overall, the dataindicate that t r a n s acids behave similarly to saturates with respect to raising plasmacholesterol; however, the extent of cholesterol raising was less than that by saturates.”

A 1995 report issued by ILSI (70), the International Life Sciences Institute, con-cluded that the existing data did not support a link between consumption of t r a n s f a t t yacids and coronary heart disease. Publications by a number of researchers, especiallyHunter and Applewhite (65,71), support the position that there are no health concernsfrom consumption of hydrogenated fats and oils.

On the other hand, a large number of people and organizations indicate thattheir research data suggest health concerns related to the consumption of t r a n sfatty acids. There is concern that trans fats act more like saturated fats. Table 11.5presents the time line of health concerns regarding dietary fatty acids. Although thereports that support the safety of hydrogenated fats focus on coronary heart dis-ease, this table indicates that there are other possible health concerns. A 1994report by the Danish Nutrition Council (72) concluded that, “T r a n s fatty acids

TABLE 11.5 Time Line of Concerns About Health Issues Regarding Dietary T r a n s Fatty Acidsa , b

D a t e R e s e a r c h e r Concerns expressed

1 9 5 6 H. Sinclair Increased cancer EFA deficiency1 9 5 8 A. Keys Increased heart disease1 9 7 0 s W.E. Connor and others Adverse effect on serum cholesterol1 9 7 0 s F.A. Kummerow Adverse effect on serum cholesterol1 9 7 7 G.V. Mann Increased heart disease1 9 7 8 M.G. Enig Increased cancer mortality1 9 8 0 s University of Maryland Altered mixed function oxidase enzymes;

Enig, Teter, and Barnard milk fat depression; decreased insulin binding1 9 8 9 T. Hamis et al. Decreased testosterone, abnormal sperm1 9 9 0 s Mensink and Katan Adverse effect on CHD risks; total cholesterol;

LDL-C; HDL-C; LP(a)1 9 9 0 s B. Koletzko Low birth weight infants, altered n-3

EFA status1 9 9 3 – 9 4 Harvard University Increased heart disease, increased cancer risk

Willet et al.1 9 9 4 G.V. Mann Increased heart diseaseaSource: Reference 83.bAbbreviations: EFA, essential fatty acids; CHD, coronary heart disease; LDL-C, low density lipoprotein cholesterol;HDL-C, high density lipoprotein cholesterol; LP(a), lipoprotein a.



increase the likelihood of developing atherosclerosis and possibly have a harmfuleffect on the growth of the fetus.”

As a result of this study, the Danish Council requested a reduction in t r a n sfatty acid content of foods. The continuing research of the Dutch workers, Mensink(73,74) and Katan (75,76), and of the German researcher, Koletzko (77,78), all ofwhom have indicated that trans fats increase health risk suggests that the effect oftrans fatty acid on human health requires further clarification.

The American Council on Science and Health (79) has made one of the bestand most objective overviews of the t r a n s fatty acid situation on science andhealth. Their report indicates that consumption of trans acids has an adverse effecton blood lipoproteins compared with unmodified vegetable oils. They indicate thatmore work is required to compare trans and saturated fats, and that studies on pop-ulations that have linked high intakes of t r a n s fats with heart disease have hadweaknesses in their methodology.

One wonders what the future will hold for hydrogenated fats and oils. These fatsoffer a wide range of functions useful for the processing industry, especially the bakingindustry. The alternative to using hydrogenated fats would be to return to using animalfats or the so-called tropical oils, something that is not likely to happen. The AmericanCouncil on Science and Health suggests using less fat and a more intelligent selectionof types of foods, which is a good common sense recommendation no matter whatone’s diet (79). It is likely that there will be some changes in foodservice frying fatsand maybe even industrial oils. These products are highly hydrogenated for stabilityand extended fry life. Even though members of the edible oil industry defend hydro-genation, they are cognizant of the increasing consumer awareness of t r a n s fats andare looking for alternatives. An example of an alternative product is one created byCargill Specialty Oils. In 1998, they released a line of no or low t r a n s-fatty acid prod-ucts, and used the no-t r a n s feature as a tool for marketing the products as healthy oils.According to Cargill spokespeople, “We now have a line of oils which fit the all-natur-al definition and have no hydrogenation required so they’re a healthier alternativewithout any compromise on flavor or shelf-life stability.”

Environmental Concerns

There are literally thousands of compounds formed in the oil during deep-frying offoods. Fritsch (57) summarized the many classes of materials that are formed dur-ing frying. A fryer has been compared to a large steam distillation apparatus. Asthe water in food boils off, the steam removes volatile compounds from the oil. Atone time, these went up the stack and into the environment, but today, thesevolatile materials are either trapped in a spray tower or burned as fuel.

One of the volatile degradation products of deep-fat frying is a mutageniccompound, called acrolein, also known as acrylaldehyde, acrylic aldehyde, and 2-propenal. This compound is a clear or yellow compound with a disagreeable odor.The presence of blue smoke indicates that the oil is degrading and that acrolein



may be released. It vaporizes much more easily than water. The chemical formula is:H2C=CH-CHO. Small amounts of acrolein may be found in fried foods and cookingoils. Acrolein that is inhaled will leave the body within minutes. As with any com-pound, the effects on health vary with the amount and length of exposure. Short expo-sures to low levels of the compound may cause eye watering and throat irritation andsoreness. Acrolein exposure at 170–430 ppb will result in irritation. These effects dis-appear within minutes after the exposure stops. Higher levels of the compound andlonger exposure times may affect the lungs so severely that death could result. There isno available information on the effects of consuming foods or beverages containingacrolein. The Occupational Safety and Health Administration (OSHA) has establishedlimits for acrolein of 0.1 ppm (100 ppb) in workroom air to protect workers during an8-h workday over a 40-h work week. NIOSH (National Institute for OccupationalSafety and Health) recommends that the concentration in workroom air be limited to0.1 ppm averaged over an 8-h shift (Table 11.6).

TABLE 11.6Health Effects from Breathing Acrolein

Short-term exposure (�1 4 d)

Levels in air (ppm) Length of exposure (min) Description of effects

0 . 0 0 0 0 5 Minimum risk level0 . 1 7 4 0 Eye irritation0 . 2 6 4 0 Nose irritation0 . 4 3 4 0 Throat irritation

Long-term exposure (�1 4 d)

Levels in air (ppm) Length of exposure (min) Description of effects

0 . 0 0 0 0 9 x x x Minimum risk level based on animal studies x x x x x x The health effects of long term exposure to

humans to air containing specific levels of acrolein are not known

Exposure to acrolein

Concentration (ppm) E f f e c t s

1 . 0 – 2 . 3 Medium to severe eye irritation in 5 minutes1 . 2 Extremely irritating to all mucous membranes within 5 min; lacrimation0 . 8 – 0 . 9 Changes in amplitude of respiratory membranes; slightly increased

respiratory frequency; decreased eye sensitivity to light; changes in opticalc h r o n a x y

0 . 3 – 0 . 5 Slight eye and nose irritation; no effect on respiratory frequency oramplitude; odor perceived

0 . 1 4 – 0 . 1 5 30% felt eye irritation in 2 min; increased annoyance and no eye or noseirritation during repeated exposure

0 . 0 3 – 0 . 0 3 4 Odor threshold for most acrolein sensitive people0 . 0 2 Threshold for affecting electrocortical activityaS o u r c e : Reference 84.



Some scientists have theorized that this compound may have had severalinsidious effects on the industry, particularly fast food and restaurant operations.Dr. Michael Blumenthal (personal communication) suggested that acrolein in thework environment has contributed in part to the rapid turnover in that industry.This may be true, although the work environment itself in a fast food restaurant is alarge factor in the high turnover rate among workers. At an IFT short course in1994, Eskin (80) addressed the acrolein issue at length. He presented materialsrelating to cancer risk in Chinese women and cooking with oil. Because acrolein isa prime degradation compound, the implication was that it could be a contributorto the development of the disease. This is supported by a recent publication byChinese scientists who isolated a series of mutagens from fumes of peanut oil usedfor cooking.

The issue of heated fats and public health has not been a focus in the UnitedStates, but as noted earlier, this is an issue in Europe. Firestone et al. (81) first pre-sented a review of the regulatory situation pertaining to heated fats and oils at the1990 meeting of the Institute of Food Technologists. In that publication, it wasnoted that Belgium, France, Germany, Spain, and Switzerland were among thecountries who had established regulatory limits for polar materials in restaurantfrying oils, the segment most likely to abuse oil in the restaurants. It was, in fact,abuse of frying fats at the restaurant level that led to the studies that resulted in therecommendations to establish regulatory limits for frying fats and oils. Ironically,Germany, where this work was done, has not established regulations on the nation-al level, but only in its individual states. Since that time, other EU nations have fol-lowed the Germans in establishing regulatory limits for restaurant oils. Theseguidelines and regulations are presented in Table 11.7.

SummaryThe basic belief in the scientific community is that heated oils, particularly thosethat have not been abused, are not a health hazard. Some compounds found inabused oils are potential mutagens, but the levels at which they are found are low,and the consequent health effect is considered to be small. Test animals fed largequantities of abused oil or fractions tend to gain weight at a slower rate than thosegiven fresh or less abused oils, apparently due to the indigestible compounds(polymers) formed in the fryer oil. Other studies using these same badly abusedoils have even resulted in the development of tumors or worse in test animals.Conversely, other studies have shown that slightly heated oils are more digestiblethan fresh oils. When conducting animal feeding studies using heated oils, it wasshown that it is essential to ensure that diets are balanced so that the actual effectsof the oils may be observed. Some of the early work has been questioned becauseof this exact point.

The most deleterious compounds were found in the non-urea–adducting frac-tion of abused oils, which contains highly polar materials. As early as 1961, polar



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compounds were proposed as an index for oil quality and safety for fryer oils. A30% limit was recommended. Many years after this initial recommendation, theenactment of regulations or guidelines in several European nations has occurred,targeted at ensuring the production of safe and wholesome foods in the restaurantand food service industries. This discard point for polar materials generally coin-cides with the best practices of cooks in restaurants in the United States.

The basic message to users of frying fats was clearly stated in the DGF recom-mendations of 2000. To ensure that there are no health concerns, it is essential that thequality of frying oil be controlled. If oil quality is allowed to degrade, health concernsare only part of the issue. In a cost-conscious world, the real issue is economics. Theuse of abused oil for frying produces poor quality food. Consumers may reject suchfood because of poor flavor. Because the food industry relies on repeat business, suchactions may result in a long-term loss of business for the operation.

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32. Perkins, E.G., and L.A. Van Akkeren, (1965) Heated Fats. IV. Chemical Changes inFats Subjected to Deep Fat Frying Processes, J. Am. Oil Chem. Soc. 42:782–786.

33. Kaunitz, H., R.E. Johnson, and L. Pegus, A Long-Term Nutritional Study with Fresh andMildly Oxidized Vegetable and Animal Fats, J. Am. Oil Chem. Soc. 42:770–774 (1965).

34. Kaunitz, H., Nutritional Aspects of Thermally Oxidized Fats and Oils, Food Technol.21:278–281 (1967).



35. Nolen, G.A., J.C. Alexander, and N.R. Artman, Long-Term Rat Feeding Study withUsed Frying Fats, J. Nutr. 93:337–348 (1967).

36. Nolen, G.A., Effects of Fresh and Used Hydrogenated Soybean Oil on Reproduction andTeratology in Rats, J. Am. Oil Chem. Soc. 49:688–693 (1972).

37. Nolen, G.A., A Feeding Study of a Used, Partially Hydrogenated Soybean Oil, FryingFat in Dogs, J. Nutr. 103:1248–1255 (1973).

38. Poling, C.E., E. Eagle, E.E. Rice, A.M.A. Durand, and M. Fisher, Long-TermResponses of Rats to Heat-Treated Dietary Fats: IV. Weight Gains, Food and EnergyEfficiencies, Longevity, and Histopathology, Lipids 5:128–136 (1970).

39. Ohfuji, T., and T. Kaneda, Characterization of the Toxic Compounds in ThermallyOxidized Oil, Lipids 8:353–359 (1973).

40. Ohfuji, T., H. Igarashi, and T. Kaneda, Studies on the Relationship Between theNutritive Value and the Structure of Polymerized Oils. VIII. Presence of Toxic DimerGlycerides in Used Frying Oils, Yakagaku 21:21 (1972).

41. Ohfuji, T., K. Sakurai, and T. Kaneda, Studies on the Relationship Between NutritiveValue and the Structure of Polymerized Oils. VII. Absorption and Metabolism of the ToxicSubstance Separated from Thermally Oxidized Oil in Rats, Yakagaku 21:68 (1972).

42. Billek, G., G. Guhr, and W. Sterner, presented at 69th Annual Meeting of the AmericanOil Chemists’ Society, New York, NY, 1977.

43. Billek, G., G. Guhr, and W. Sterner, Feeding Experiments with Heated Fats and FatFractions, Fette Seifen Anstrichm. 81:562–566 (1979).

44. Clark, W., Nutritional Aspects of Frying Fats—An Overview, presented at the 70thAnnual Meeting of the AOCS, Chicago, Illinois, 1978.

45. Lang, K., G. Billek, J. Führ, J. Henschel, E. von Jan, J. Kracht, H. Scharmann, H.-J.Strauss, M. Unbehend, and J. Waibel, Ernährungsphysiologische Eigenschaften vonFritierfetten. U. Ernährungswiss. Supplement 21:1–61 (1978).

46. Billek, G. Eur. J. Lipid Sci. and Tech.: Special Edition, 102:8–9, 587–593 (2000).47. Fong, L.Y.Y., C.C.T. Ton, P. Koonanuwatchaidet, and D.P. Huang, Mutagenicity of

Peanut Oils and Effect of Repeated Cooking, Food Cosmet. Toxicol. 18:467–470 (1980).48. Taylor, S.M., C.M. Berg, N.H. Shoptaugh, and V.N. Scott, Lack of Mutagens in Deep-

Fat Fried Foods Obtained at the Retail Level, Food Chem. Toxicol. 20:209–212 (1982).49. Taylor, S.M., C.M. Berg, N.H. Shoptaugh, and E. Traisman, Mutagen Formation in

Deep-Fat Fried Foods as a Function of Frying Conditions, J. Am. Oil Chem. Soc. 60: 576–580 (1983).

5 0 . Goethart, R.L.D., H. Hoekman, E.J. Sinkeldam, L.J. Van Gamert, and R.J.J. Hermus,Cooking in Oil: The Stability of Frying Oils with a High Linoleic Acid Content, V o e d i n g4 6:300–306 (1985).

51. Hageman, G., R. Kikken, F. ten Hoor, and J. Kleinjans, Assessment of Mutagenic Activityof Repeatedly Used Frying Fats, Mutat. Res. 204:593–604 (1988).

5 2 . Hageman, G., R. Kikken, F. ten Hoor, and J. Kleinjans, Linoleic Acid HydroperoxideConcentration in Relation to Mutagenicity of Repeatedly Used Deep Frying Fats, L i p i d s2 4:899–902 (1989).

53. Hageman, G., R. Hermans, F. ten Hoor, and J. Kleinjans, Mutagenicity of Deep Frying Fat,and Evaluation of Urine Mutagenicity in Man After Consumption of Fried Potatoes, F o o dChem. Toxicol. 28:75–80 (1990).

54. Addis, P.B., Coronary Heart Disease: An Update with Emphasis on Dietary LipidOxidation Products, Nutr. News 62:7–10 (1990).



55. Marquez-Ruiz, G., and Dobarganes, M.C., Nutritional and Physiological Effects ofUsed Frying Fats, in Deep Frying: Chemical, Nutrition and Practical Applications,edited by E.G. Perkins and M.D. Erickson, AOCS Press, Champaign, IL, 1996.

56. DGF, Recommendations of the 3rd International Symposium on Deep Fat Frying—Optimal Operation, Eur. J. Lipid Sci. Technol. 102:594 (2000).

57. Fritsch, C.W., Measurements of Frying Fat Deterioration, J. Am. Oil Chem. Soc. 58:272(1981).

58. Blumenthal, M.M., Optimum Frying: Theory and Practice, Libra Laboratories,Piscataway, NJ, 1987.

59. DGF, Meeting Summary: German Society for Fat Research, Fette Seifen Anstrichm.75:49 (1973).

60. Blumenthal, M.M., A New Look at the Chemistry and Physics of Deep Fat Frying,Food Technol. 45:68–71, 94 (1990).

61. Ratnayake, W.M., Determination of Trans Unsaturation by Infrared Spectroscopy andDetermination of Fatty Acid Composition of Partially Hydrogenated Vegetable Oils andAnimal Fats by Gas Chromatography/Infrared Spectrophotometry: Collaborative Study,J. Assoc. Off. Anal. Chem. 78:703–802 (1995).

62. USDA, Composition of Foods: Agriculture Handbook No. 8, Agriculture ResearchService, United States Department of Agriculture, Superintendent of Documents, 1975.

63. Dickey, L.E., and Caughman, C.R., Fatty Acid Profiles Including Trans Isomers in 123Food Sources Presented as Grams of Fatty Acid per 100 Grams of Foods, 1995.

64. United States Food and Drug Administration (1985)65. Hunter, J.E., and T.H. Applewhite, Isomeric Fatty Acids in the U.S. Diet: Levels and

Health Perspectives, Am. J. Clin. Nutr. 44:707–717 (1986).66. Enig, M.G., S, Atal, J. Sampugna, and M. Keeney, Trans Fatty Acids in the U.S. Diet,

J. Am. Coll. Nutr. 9:471–521 (1990).67. Enig, M.G., S. Atal, J. Sampugna, and M. Keeney, Responses to Letters to the Editor, J.

Am. Coll. Nutr. 10:512–514, 517–518, 519–521 (1991).68. Anonymous, Food Fats and Oils, 7th edn., Institute of Shortening and Edible Oils, New

York, NY, 1994.69. Anonymous, Food Fats and Oils, 6th edn., Institute of Shortening and Edible Oils, New

York, NY, 1988.70. International Life Sciences Institute (ILSI) Expert panel on T r a n s Fatty Acids and

Coronary Heart Disease, Trans Fatty Acids and Coronary Heart Disease, edited by P.M.Kris-Etherton, Am. J. Clin. Nutr. 62:518–519 (1995).

71. Hunter, J.E., and T.H. Applewhite (1991).72. Danish Nutrition Council Task Group, The Influence on Health of Trans Fatty Acids,

Transfedtsyers Betydning for Sundheden (1994); Danish Nutrition Council, Trans FattyAcids, Clin. Sci. 88:375–392 (1995).

73. Mensink, R.P., and G. Hornstra, The Proportion of Trans Monounsaturated Trans FattyAcids in Serum Triacylglycerols or Platelet Phospholipids as Objective Indicator ofTheir Short-Term Intake in Healthy Men, Br. J. Nutr. 73:605–612 (1995).

74. Mensink, R.P., Summary Statement: Isomeric Fatty Acids, World Rev. Nutr. Diet.75:173–174 (1994).

75. Katan, M.B., Commentary on the Supplement Trans Fatty Acids and Coronary HeartRisk, Am. J. Clin. Nutr. 62:518–519 (1995).

76. Katan, M.B., Exit Trans Fatty Acids, Lancet 346:1245–1246 (1995).



77. Koletzko, B., and T. Decsi, Adipose Tissue T r a n s Fatty Acids and Coronary HeartDisease, Lancet 345:273–278 (1995).

78. Koletzko, B., Trans Fatty Acids and the Human Infant, World Rev. Nutr. Diet.75:82–85 (1994).

79. Meister, K., Facts About Fats: Health Effects of Dietary Fats and Oils, AmericanCouncil on Science and Health, New York, NY, 1995.

80. Eskin, N.A.M., Toxicological Concerns with Frying Fats and Oils, presented at IFTsponsored short course, Understanding Deep Frying of Foods, Atlanta, Georgia, June24–25, 1994.

81. Firestone, D.D., R.F. Stier, and M.M. Blumenthal, Regulation of Frying Fats and Oils,Food Technol. 45:90–94 (1990).

82. Stier, R.F., and M.M. Blumenthal, Multifunctional Fats & Oils, Baking & Snack 13:29(1991).

83. Enig, M.G., Trans Fatty Acids in the Food Supply, Enig & Associates, Silver Spring,MD, 1995.

84. Beauchamp, R.O., Jr., D.A. Andjelkovich, A.D. Kligerman, K.T. Morgan, and H. Heck, ACritical Review of the Literature on Acrolein Toxicity, CRC Crit. Rev. Toxicol. 14: 3 0 9( 1 9 8 5 ) .

Suggested Reading

Allen, R.R., Hydrogenation, J. Am. Oil Chem. Soc. 58:166–169 (1981).Anonymous, Fat Trans-Formation, Snack Food & Wholesale Bakery, December 4, 1988.Blumenthal, M.M., Presented at IFT Sponsored Short Course, Understanding Deep Frying

of Foods, Atlanta, Georgia, June 24–25, 1994.Brooks, D., Some Perspectives on Deep-Fat Frying, INFORM 2:1091–1095 (1991).Brown, M.H., Here’s the Beef: Fast Foods Are Hazardous to Your Health, Sci. Dig.:31–36,

76–77 (April, 1986).Buxtorf, U.P., W. Manz, and M. Schupbach, Gebiete Lebensm. Hyg. 67:429 (1976).Castang, J. Ann. Fals. Exp. Chim. 74:701 (1981).Chang, S.S., R.J. Peterson, and C.T. Ho, Chemical Reactions Involved in Deep Fat Frying

of Food, J. Am. Oil Chem. Soc. 55:718 (1979).Clark, W.L., and G.W. Serbia, Safety Aspects of Frying Fats and Oils, Food Technol.

45:84–86 (1991).Dickey, L.E., Trans Fatty Acid Content of Selected Foods, INFORM 6:484 (1995).Firestone, D., Worldwide Regulation of Frying Fats, INFORM 4:1366–1371 (1993).Gao, Y.-T, W.J. Blot, W. Zheng, A.G. Ershow, C.W. Hsu, L.I. Levin, R. Zhang, and J.F.

Frameni, Jr., Lung Cancer Among Chinese Women, Int. J. Cancer 40:604–609 (1987).Gertz, C., Analytical Aspects and Possibilities of the Development of Acrylamide in Fried

Foods, Eur. J. Lipid Sci. Technol. 104:762–771 (2002). Guhr, G., and J. Waibel, Untersuchung an Friterfetten: Zusammenhange Zwischen dem

Gehalt an Petrolather—Unloslichen Oxidierten Fettsauren und dem Gehalt an PolarenSubstanzen bzw. dem Gehalt an Polymeren Triglyceriden, Fette Seifen Anstrichm.80:106 (1978).

Hayes, K.C., Designing a Cholesterol-Removed Fat Blend for Frying and Baking, F o o dTechnol. 50:92–97 (1996).



Jones, L.A., and C.C. King, Cottonseed Oil, National Cottonseed Products Association andCotton Foundation, Memphis, TN, 1990.

Kamal-Eldin, A., L.A. Appelqvist, C. Gertz, and F.R. Stier (1996) Enhancing the FryingPerformance of High Oleic Sunflower Oil Using a Specially Manufactured Sesame andRice Bran Oil, presented at the Annual Meeting of the AOCS, Indianapolis, IN.

Kochkar, S.P., Stabilisation of Frying Oils with Natural Antioxidant Components, Eur. J.Lipid Sci. Technol. 102:552–559 (2000).

Mankel, A., Zur Analytik und Beurteilung von Fritürenfetten II. Fette Seifen Anstrichm.72:677–688 (1970).

Marquez-Ruiz, G., M.C. Perez-Camino, and M.C. Dobarganes, J. Am. Oil Chem. Soc. 69:930 (1992).

Melton, S.L., Nutritional Needs for Fat and the Role of Fat in the Diet, in Deep Frying:Chemical, Nutrition and Practical Applications, edited by E.G. Perkins and M.D.Erickson, AOCS Press, Champaign, IL, 1996.

Potter, N.N., Food Science, 2nd edn., AVI Publishing, Westport, CT (1973).Silkeberg, A., Stable Oil Composition, U.S. Patent Pending (1996).Stevenson, S.G., M. Vaisey-Genser, and N.A.M. Eskin, (1984) Quality Control in the Use

of Deep Frying Oils, J. Am. Oil Chem. Soc. 61:1102.Stier, R.F., The Functions of Trans Fatty Acids, Baking & Snack 19:78–86 (1997).Tareke, E., P. Rydberg, P. Karlsson, S. Eriksson, and Tornqvist, Analysis of Acrylamide, A

Carcinogen Formed in Heated Foodstuffs, J. Agric. Food Chem. 50:4998–5006 (2002).Thompson, J.A., M.M. Paulose, B.R. Reddy, R.G. Krishnamurthy, and S.S. Chang, A

Limited Survey of Fats and Oils Used for Deep Fat Frying, Food Technol. 21:405–412(1967).

United States Food and Drug Administration, FDA Proposes New Rules for T r a n s F a t t yAcids in Nutritional Labeling, Nutrient Content Claims and Health Claims, HHS News,November 12, 1999.

United States Food and Drug Administration, Detection and Quantitation of Acrylamide inFoods Draft Method, United States Food and Drug Administration, Center for FoodSafety and Applied Nutrition, July 23, 2002.

United States Food and Drug Administration, FDA Draft Plan for Acrylamide in Food,United States Food and Drug Administration, Center for Food Safety and AppliedNutrition, September 20, 2002.

United States Food and Drug Administration, Food Labeling: T r a n s Fatty Acids in NutritionLabeling and Nutrition Content Claims, Fed. Regist. 63:216, p. 61711, November 9, 1998.

Wolfram, G., Recent Findings on Nutritional Properties of Heated Fats—A General Review,Fette Seifen Anstrichm. 81:559–562 (1979).

Wu, S.-C., G.-C.Yen, and F. Sheu, Mutagenicity and Identification of Mutagenic Compounds ofFumes Obtained from Heated Peanut Oil, J. Food Protect. 64:240–245 (2001).



Chapter 12

R e g u l a t o ry Requirements for the Frying Industry

David Firestone

Food and Drug Administration, Washington, DC 20204

IntroductionImproper frying operations result in degradation of frying fats and diminish thequality and wholesomeness of fried food. Although there are no worldwide regula-tions and guidelines for control of frying fats and frying operations, a number ofEuropean countries, concerned with the quality of fried foods and possible healthrisks to consumers, have issued regulations and guidelines for control of frying fatsand frying operations (1,2). State and local agencies in the United States as well asthe Food and Drug Administration (FDA) have not promulgated specific regula-tions or guidelines controlling the quality of frying fats because it has not beendetermined that frying fats used in the preparation of fried foods are injurious tohealth. However, the Department of Agriculture's Food Safety and InspectionService (USDA/FSIS) Meat and Poultry Inspection Manual contains several gener-al guidelines for frying meat and poultry products (3), and the agency has issued aplant sanitation directive requiring cleaning of frying equipment at regular inter-vals (4). Safety and other aspects of frying technology have been discussed at sym-posia of the Institute of Food Technologists and German Society for Fat Science(Deutsche Gesellschaft für Fettwissenschaft, DGF) (5–8).

Quality Control

After the 1979 symposium on frying fats and oils (6), the DGF recommended thattotal polar compounds be determined to complement traditional organoleptic (senso-ry) evaluation of frying fat quality. This method (9), involving silica gel columnchromatography, became a standard reference method in many European countriesconcerned with possible health risks from improper use of frying fats. Determinationof polymerized (dimeric and polymeric) triglycerides by gel permeation (sizeexclusion) high-pressure liquid chromatography (HPLC) (10) is also used widelyfor the control of frying fat quality. Many analytical tests have been proposed forevaluation of frying fat quality (Table 12.1). Quick tests are also available for car-rying out in situ evaluations at the fryer. These include the Oxifrit Test (redox indi-cator) and the Fritest (carbonyl compounds) distributed by E. Merck (Darmstadt,Germany), and the Veri-Fry quick tests available from Libra Laboratories(Metuchen, NJ).



FDA Regulations

The FDA has not established specific regulations to control the quality of fryingfats. However, frying fats are regulated by the general provisions of the FederalFood, Drug, and Cosmetic Act, which states that a food is deemed adulterated if it“contains any poisonous or deleterious substance which may render it injurious tohealth” [sec. 402 (a)(1)], if it contains “any added poisonous or added deleterioussubstance (other than specified substances such as pesticides” [402 (a)(2)], if it“consists in whole or in part of any filthy, putrid or decomposed substance, or if itis otherwise unfit for food” [sec. 402 (a)(3)], or if it “has been prepared, packed orheld under insanitary conditions whereby it may have been contaminated withfilth, or whereby it may have been rendered injurious to health” [402 (a)(4)]. Also,section 404 of the Act mandates the Secretary of Health and Human Services topromulgate regulations to control contamination of food with microorganisms dur-ing the manufacture, processing, or packing of food products distributed in inter-state commerce. Concerned about food safety, the FDA has been leading an effortin the United States to improve coordination among public health and food regula-tory officials to improve food safety programs to minimize outbreaks of food-borne illness (11,12). This effort has included programs to apply Hazard Analysisand Critical Control Point (HACCP) plans to food preparation facilities as well asthe establishment of a national database on the occurrence of food-borne diseaserisk factors within the retail segment of the food industry, which included improperhandling of food and poor sanitation (13).

Five practices and behaviors were noted that resulted in the most significant“out of compliance” rate:

1. Cold holding of potentially hazardous food (PHF) at ≤5°C.2. Ready-to-eat (RTE), PHF cold holding at ≤5°C.3. Commercially processed RTE, PHF date marked.4. Surfaces/utensils cleaned/sanitized.5. Proper, adequate hand washing.

TABLE 12.1 Laboratory Tests for Oil Quality Determination

Acid value Epoxides Refractive indexAnisidine value Fatty acid composition Smoke pointCarbonyl value Free fatty acids TBA testa

Color Iodine value Total polar compoundsCyclic fatty acids Peroxide value Trans fatty acidsDielectric constant Polymeric triglycerides ViscosityConjugated diene value Total volatilesaTBA, thiobarbituric acid.



In addition, a set of procedures were developed for standardizing and certifyingretail food inspection and training officers to ensure that retail foods are safe,unadulterated, and honestly presented to the consumer (14).

FDA programs to reduce food-borne illness, encourage voluntary HACCP-basedefforts from industry, and standardize food inspection procedures include use of theFood Code (15) as a general reference document by state and local government agen-cies responsible for overseeing food safety in retail establishments. Although the FoodCode is neither federal law nor federal regulation, it represents the FDA’s best advicefor a uniform system of regulation to ensure that food at retail is safe. The various sec-tions of the Food Code cover employee health; personal cleanliness and hygiene prac-tices; food handling, preparation, and presentation; equipment installation, use, andsanitation; water plumbing and waste handling; physical facilities; storage and use oftoxic materials (e.g., sanitizers, drying agents, pesticides, fruit and vegetable washingchemicals); and compliance and enforcement procedures including approval ofHACCP plans. Section 3–401.11 of the Food Code specifies that all parts of a food beheated to minimum temperatures and holding times to ensure that the foods are safe.Section 4–301.14 states that ventilation hood systems should be sufficient in numberand capacity to prevent grease or condensation from collecting on walls and ceilings.Section 6–202.12 states that heating, ventilating, and air conditioning systems shouldbe designed and installed so that make-up air intake and exhaust vents do not causecontamination of food, food-contact surfaces, equipment, or utensils. An Annex speci-fies a series of enforcement mechanisms and references including management andpersonnel guidelines for ensuring food safety, food establishment inspection, andpreparation of inspection reports; HACCP guidelines including procedures to ensurethat HACCP systems are working, plus typical flow diagrams; food processingrequirements; and a set of model forms and guides including HACCP guidelines andHACCP Food Inspection Report forms. The Food Code does not specifically specifyoptimum frying temperatures because it is concerned primarily with the destruction ofmicroorganisms that cause food-borne illness. However, the Food Code specifies thatall parts of a food be heated to 63°C for 3 min (minimum) and for longer holding timesat lower temperatures (121 min at 54°C).

In 1998, FDA drafted a document “Managing Food Safety: A HACCP PrinciplesGuide for Operators of Food Establishments at the Retail Level” (16), based on inputfrom industry, academia, and consumers, as well as state and local food regulators, toassist food establishment employees in preparing safe food. The document is intendedto serve as a guide for preparing a simple plan based on HACCP principles. It includessections on identifying critical control points, developing corrective actions, carryingout verification procedures (e.g., checking monitoring and corrective action records),and maintaining facilities equipment.

USDA/FSIS Guidelines and Directives

The Meat and Poultry Inspection Manual of the Food Safety and InspectionService of the Department of Agriculture (FSIS/USDA) (17) contains some gener-



al guidelines for frying meat and poultry products. Observing that deep fat fryingtimes vary with the temperature of the fat, the amount of replacement fat addedperiodically, and treatment of the fat during use, the guidelines state that “exces-sive foaming, darkened color and objectionable odor or flavor are evidence ofunsuitability and require fat rejection.” The guidelines also state that the frying fatshould be discarded “when it foams over the vessel's side during cooking or whenits color becomes almost black as viewed through a colorless glass container.” Theserviceable life of fat can be extended by holding the frying temperature below204°C (400°F), replacing one third or more each day, filtering as needed, andcleaning the system at least weekly. Adding an antifoam agent (dimethylpolysilox-ane) to fresh fat is recommended. For poultry, the FSIS guidelines advise that “tocompletely fry poultry parts, time and temperature required depends upon producttype and weight, and upon equipment. Acceptable frying operation should be carriedout at approximately 190°C (375°F) or higher for 10–13 min when parts are not pre-cooked . . . commercially prepared fats may contain antioxidants or antifoamingagents . . . used fat may be made satisfactory by filtering, adding fresh fat, and regu-larly cleaning the equipment. Large amounts of sediment and free fatty acid contentin excess of 2% are usual indicators that frying fats are unwholesome and requirereconditioning or replacement. Sediment is usually removed by filtering. Addingfresh fat or new fat reduces the free fatty acid to acceptable levels.”

The guidelines note that fat used for fish products is not satisfactory for fryingpoultry. Solid frying fat may be kept liquid if the holding temperature does not fallbelow 54°C (130°F) to prevent localized excess heating and fat breakdown duringmelting.

FSIS directive 11.000.2 (18) requires cleaning of frying equipment at regularintervals and allows continuous filtering or flushing with clean fat for limited periodsof time and notes that “complete drainage, followed by dismantling and scouring orotherwise thorough cleaning, is necessary for acceptable sanitizing. Traces of waterand detergents increase rate of fat breakdown. They must be completely removedfrom pipelines, valves, filters, and pumps, must be of sanitary construction, readilyaccessible to cleaning, and preferably constructed of stainless steel. Rubber and sometypes of plastic connecting lines are not acceptable.”

State and City Regulations in the United States

Inquiries were made at intervals during 1989–2001 to 35 U.S. State health depart-ments and food control agencies to determine whether regulations and guidelineswere available for control of frying fats and frying operations in restaurants andprocessing plants. The replies generally indicated that there were no specific regu-lations other than those requiring that fats used in food preparation and food ser-vice establishments be obtained from approved sources and are not adulterated.Many health departments replied that there were no specific regulations for fryingfats, frying operations, and fried foods other than the general regulations for sanita-tion and recommendations in the 1999 Food Code or earlier versions of the Code.



The State of Wisconsin’s Department of Health and Social Services statedcandidly that its Restaurant Inspection Program does not have any procedures forchecking frying fats in restaurants. “Our only concern is that frying fats and oils beobtained from an approved source and be maintained in a reasonably clean condi-tion. Due to high cooking temperatures used in deep frying operations, frying fatsand oils have not been considered a public health hazard as it relates to bacterialcontamination. Deep-frying operations in restaurants are viewed as an issue offood ‘quality’ rather than food ‘safety’. Typically, deep-frying operation problemsare related to exhausting fumes and concerns regarding consumer complaints relat-ed to food odors and off taste that may result.”

The Food Protection Division of the Allegheny County Health Department(Pittsburgh, PA) has no specific regulations for control of frying fat or fried foodquality other than regulations designed to protect consumers from food that con-tains pathogens. The Department does note that “when oxidation occurs or fattyacids increase in oils due to usage, the oils will have a lower smoke point or afishy, rancid taste thus rendering them unusable from a quality standpoint.” TheChicago Department of Health regulates fats and oils under the general provisionsof chapter 4–344 of the Municipal Code of Chicago, which addresses sanitationpractices in food establishments. Food products require approved labels and shouldbe free of rancidity. When routine inspections are made, frying fats are checked forcolor, sediments, and foreign objects as well as excessive smoke. If necessary, fatand oil samples are collected for determination of rancidity by the Kreis test. TheFulton County (Atlanta, GA) Food Service Sanitation Regulations do not mentionfrying fats except for the cleaning of frying equipment and proper disposal of spentcooking fats. The State Department of Health regulates Food Service establish-ments in South Dakota. Cooking equipment that utilizes oil or grease is required tobe located under exhaust hoods that vent to the outside. Plumbing systems mustcomply with the state Plumbing Code that requires grease-traps to prevent greasefrom entering wastewater systems.

The FDA’s Division of Federal-State Relations advised the ConnecticutDepartment of Health (in response to an inquiry to FDA in 1990) that (i) there isno standard frequency for filtering fat used in deep-fat frying operations (the filter-ing material should be clean and the oil should be clear and properly stored); (ii)any presence of “off” odors or visible evidence of foreign material, filth, or otheradulterants would warrant discarding the fat; and (iii) fat must be adequately pro-tected from contamination during use, storage, or filtering.

The State of Montana’s Food and Consumer Safety Section regulationsrequire the following:

• Ventilation hoods in food service establishments to be installed at or above allcommercial type deep fryers, broilers, fry grills, steam-jacketed kettles, hot-topranges, ovens, barbecues, rotisseries, dishwashing machines, and similar equip-ment which produces comparable amounts of steam, smoke, grease, or heat.



• Ventilation hoods and devices shall be designed to prevent grease or condensationfrom collecting on walls and ceilings, and from dropping into foods or onto food-contact surfaces. Filters or other grease-extracting equipment shall be readilyremovable for cleaning and replacement if not designed to be cleaned in place.

The Denver Department of Health requires in addition to adequate ventilatinghoods, use of a velometer to test equipment in restaurants to ensure that the hoodsmaintain adequate air velocities. The St. Louis Department of Health’s Food ServiceEstablishment ordinances also require that ventilating hoods be designed to preventgrease or condensation from collecting on ceilings and walls or from dripping ontofood contact surfaces, and specifies that grease extracting equipment be readilyremovable for cleaning if not designed to be cleaned in place.

The New Orleans Department of Health requires food service establishmentsto have grease control devices for separating and retaining water-borne fats, oil,and grease before the wastewater exits the trap and enters the sanitary sewer col-lection and treatment system. Discharged wastewater should be free of oil orgrease exceeding 250 mg/L. Specifications and instructions are provided for greaseinterceptors and operation of oil and grease waste disposal systems.

Regulations and Guidelines in Europe and Other Countries

Although federal, state and local agencies in the United States are concerned pri-marily with greater control or elimination of food-borne pathogens from the foodsupply, other countries, chiefly in Europe, have issued regulations and guidelinesintended to assist in providing better quality as well as safe fried foods. Between1990 and 2001, 53 countries were contacted about regulations for frying fats andfried food. Responses were received from 34 countries, including 19 of 21European countries. Austria, Belgium, Chile, France, Hungary, Italy and Spainhave specific laws, regulations, or standards for frying fats. Other countries haveno specific laws or regulations for frying fats although several countries (Finland,Germany, The Netherlands, Norway, Portugal and Sweden) enforce measures forpractical control in food establishments. Regulations or guidelines of individualcountries are shown in Table 12.2. Additional information follows on regulation offrying fats and fried foods in these and several other countries.

Australia

The National Food Authority, established in August 1992, is responsible for thedevelopment of food standards and food safety education. Enforcement of foodstandards and surveillance of food establishments are carried out by the states andterritories, which have their own food laws and regulations. Frying fats are not reg-ulated in detail by the 1987 Australian Food Standards Code, which does prescribestandards for various foods, including frying fats, and states that edible fats andoils used in frying may contain sorbitans and polysorbates as well as not >10mg/kg dimethylpolysiloxane.



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Australian Defense Force specification 5–5-2 (November 1984) requires thatdeep-fat frying be in accordance with good manufacturing practice and complywith state and territory food regulations. Solid fat for deep-fat frying should com-ply with the following: (i) moisture, not >3 g/kg; (ii) free fatty acids, not >1 g/kg;(iii) slip melting point between 38 and 49°C; (iv) peroxide value, not >2 mEq/kg;(v) gallates, not >0.1 g/kg; and (vi) clean flavor and free from objectionable odor.Liquid fat for deep-frying should comply with similar requirements for moisture,free fatty acids, peroxide value, and gallate content. In addition, saturated fatty acidcontent should not be >500 g/kg total fatty acids. Fats for deep-frying should notcontain mineral oil or >50g/kg erucic acid.

According to the Victoria Health Department, municipal councils are responsiblefor monitoring food premises. Frying oils are subject to collection and analysis foriodine value, saponification value, acid value, peroxide value, and unsaponifiable mat-ter, as well as qualitative tests for adulterants. Some local councils use Oxifrit Test kitsto determine the degree of deterioration of frying fats used in kitchens and bakeries.

Austria

The Austrian Codex Alimentarius (Austrian Foodstuffs Book) states that frying fatshould not exhibit unpleasant odor and taste, unacceptable appearance (dark color,foaming), or a high level of carbonaceous residue. Also, frying fats should have anacid value <2.5, smoke point >170°C, and total polar compounds <27%, or oxi-dized fatty acids insoluble in petroleum ether <1%. Frying fats should not be heat-ed above 180°C.

Belgium

A royal decree issued in 1974 defined quality standards for edible fats and oils. Anadditional royal decree issued in 1978 authorized additives in edible oils, includingup to 3-mg/kg dimethylpolysiloxane in frying oils. Oils intended for frying must belabeled “Oil for Frying,” and dimethylpolysiloxane, if present, must be listed onthe label. A royal decree issued in 1988 (19,20) forbade preparation of fried foodin frying fat heated above 180°C or with a free fatty acid content >2.5%, DPTG>10%, total polar compounds >25%, viscosity >37 mPa⋅s at 50°C (food fats) or 27mPa ⋅ s at 50°C (food oils), or smoke point <170°C. Frying oils and fats may notcontain >2% linolenic acid. The law specifically forbids preparation of fried foodin equipment not provided with temperature control. Frying fats should not transferto the fried food improper odor or taste. The sale of used oils and fats for subse-quent use in processing food products for human consumption as well as direct orindirect reuse in the food industry is forbidden.

Chile

Paragraph V, Article 226 of the 1998 Food Law requires that vegetable oils andlard used for frying should be discarded if (i) free acidity expressed as oleic acid is



>1%; (ii) smoke point is <170°C; or (iii) oxidized fatty acids not soluble in petrole-um ether are >1%, or total polar compounds are >25%.

Czech Republic

Guidelines of the National Health Institute effective January 1, 1995 include rec-ommendations that total polar compounds in frying oils should be <25% and thatDPTG be <10%.

France

A 1905 constitutional law allowed French authorities to regulate food preparationand to specify conditions for analysis (21). A 1973 regulation specified that deep-frying fat should not contain >2% linolenic acid. Synthetic antioxidants (butylatedhydroxyanisole, butylated hydroxytoluene, and gallates) are permitted, as are nat-ural tocopherol concentrates in oils and fats intended for industrial use (in mini-mum 5-kg containers). Silicone additives are prohibited. Decree No. 86–857 ofJuly 18, 1986 (21) specifies that fats and oils with >25% total polar compounds areunfit for human consumption.

Germany

There are no specific laws or regulations in Germany for control of frying fats.Recommendations resulting from the first two DGF symposia on frying fats (5,6),however, have been generally applied to the control of edible fats and oils and fry-ing fats. These recommendations were established following reports of gastroin-testinal distress after fried food was eaten. According to A. Seher of the FederalInstitute for Fat Research in Münster, an epidemiological group was unable to linkabused fat with these episodes, but it revealed that many restaurants were abusingfat, particularly those frying meaty foods.

According to the 1973 DGF recommendations, used frying fats are consideredto have deteriorated if (i) taste or flavor is unacceptable, (ii) smoke point is <170°Cand the content of oxidized fatty acids insoluble in petroleum ether is ≥0.75%, or(iii) the content of oxidized fatty acids insoluble in petroleum ether is >1%. Afterdevelopment of the method for determining total polar compounds in 1979, theDGF recommended allowing no >27% total polar compounds in food fats. Thebasic recommendations of the DGF are still valid. Recommendations adopted bythe Arbeitskreis Lebensmittelchemischer Sachverstandiger der Lander und desBundesgesundheitsamtes (ALS) (Working Sector of the Food ChemicalAuthorities of the Local and State Health Offices) in 1991 are as follows: sensorycharacteristics (appearance, odor, and taste) of frying fats are of primary impor-tance; petroleum ether–insoluble fatty acids, maximum 0.7%; total polar com-pounds, maximum 24%; smoke point, minimum 170°C; smoke point difference(from unheated fat), maximum 50°C; acid value, maximum 2.0%.



A third International Symposium on Deep-Fat Frying, held March 20–21,2000 in Hagen/Westphalia, Germany, resulted in adoption of the following recom-mendations for frying oils (8):

1. The principal quality index for deep fat frying should be the sensory parame-ters of the food being fried.

2. Analysis of suspect frying fats and oils should utilize two tests to confirmabuse, as follows:

Total polar compoundsPolymeric materials (polymerized triglycerides)

3. The use of rapid tests for monitoring oil quality is recommended. Rapid testsshould exhibit the following characteristics:

Correlate with internationally recognized standard methodsProvide an objective indexBe easy to useBe safe for use in food processing/preparation areasQuantify the oil degradationBe field rugged

4. Affirming previous work: There are no health concerns associated with con-sumption of frying fats and oils that have not been abused at normal fryingconditions.

5. Encourage development of new and improved methods that provide fats andoils chemists and the food industry with tools to conduct work more quicklyand easily. Work should strive to develop methods that are environmentallyfriendly, using lower quantities of and less hazardous solvent systems.

6. Encourage and support basic research focused on understanding the dynamicsof deep fat frying and the frying process. Research should be cross-discipli-nary, encompassing oil chemistry, food engineering, sensory science, foodchemistry, and nutritional sciences.

7. One of the basic tools to ensure food and oil quality is the use of filtration.Filter materials should be used to maintain oil quality as needed.

8. Used, but not abused, frying oils may be topped up or diluted with fresh oilwith no adverse effects on quality. Abused fats and oils were defined in thefirst two recommendations.

The symposium delegates left for further discussion the subject of what constitutesa long-life frying oil claim in keeping with recommendations 1 and 2.

Hungary

There are no mandatory regulations in Hungary for frying oil quality. Standard No.Msz-08–1907–87, valid January 6, 1988, recommends determination of total polar



compounds for estimation of fat quality as follows: <25%, acceptable quality;between 25 and 30%, frying fat should be changed; >30%, frying fat is unusable.

The National Institute of Food Hygiene and Nutrition recommended that ironand copper fryers should not be used, and that frying temperatures should be keptbetween 160 and 180°C. Smoke point <180°C indicates that the fat has deteriorat-ed and should be discarded. The surface-to-volume ratio of fryers should be mini-mized. Sunflower oil may be used for up to 8–10 h of frying, if treated carefully.Corn oil may be used for 10–13 h, and lard, for 18–20 h, if treated carefully. Afterfrying, the oil should be filtered and stored at a low temperature. Deteriorated fry-ing oils should not be used for human consumption or for animal feed.

Iceland

Guidelines issued by the Environmental and Food Agency of Iceland are as fol-l o w s :

1. Use fats and oils intended for deep frying. Many types of salad oil do notmaintain their quality at the temperatures used for deep frying.

2. Do not mix used fats or oils with new ones because that would accelerate dete-rioration.

3. Clean all frying equipment regularly and filter the fat. All dirt and residue ofdetergents and cleaning products adversely affect the quality of fats and oils.Avoid contact of copper or copper compounds with fat. Do not apply salt tofoodstuffs above the frying pan because metal compounds in salt could resultin deterioration of the fat.

4. The appropriate frying temperature is 165–190°C. Higher temperatures resultin dark color, oxidation, hydrolysis, and polymerization. If the temperature istoo low, the frying time is too long, affecting the quality of foodstuffs. Tominimize the drop in temperature, it is important not to overload the fryingpan.

5. When the fat is heated, the temperature should not be set higher than the tem-perature to be used for frying.

6. Durability of fat can be prolonged by keeping the temperature between 90 and120°C when the fat is not in use.

7. Because the heat transfer in solid fat is low, it should be melted at low temper-atures to avoid overheating certain parts of the fat. Slight burning or overheat-ing of fat can accelerate deterioration and spoil all of the fat in the pan.

8. Remember that spoiled frying fat can have adverse health effects.

Israel

Although Israel has no specific regulations for cooking and frying oils, guidelinespublished by the Swedish National Food Administration (22) are recommended for



application by Food Control Administration inspectors. Israel’s Food ControlAdministration submitted a request to the Standards Institution of Israel in 1992that a requirement for total polar compounds be added to the vegetable oil stan-dard, but the request was rejected.

Italy

The Ministry of Health issued a regulation January 1, 1991 for fats and oils used forfrying “to prevent possible risks to consumers from improper or excessive use of fatsfor frying.” The regulation specifies the following: (i) use only those oils and fats forfrying that are resistant to heat; (ii) avoid frying temperatures >180°C; (iii) total polarcompounds should not be more than 25 g/100 g; (iv) prepare the food to be fried prop-erly, avoiding the presence of water and addition of salt and spices, which acceleratechanges in frying fat, as much as possible; (v) allow excess oil to drain from the food;(vi) change the oil frequently, check the quality of the oil or fat during frying, and donot use oil too long (indicated by darkened color, viscosity, and tendency to smoke);(vii) filter the oil if it will be used again and clean the filter and fryer because charredcrust, viscous oily residue, or old oil accelerates alteration of the oil; (viii) avoid“reconditioning” oil (addition of fresh oil) because fresh oil changes rapidly when incontact with used oil; and (ix) protect frying oils and fats from light.

Japan

There are no formal regulations in Japan regarding the quality of frying oil. Withrespect to food establishments, however, the following guidelines exist for deter-mining when to discard frying oil: (i) if the smoke point is <170°C; (ii) if the acidvalue is >2.5; and (iii) if the carbonyl value is >50.

Luxembourg

There are no specific regulations for frying fat in Luxembourg. General regulationsin force for all foods, however, also apply to frying fats. For practical control infood establishments preparing fried food, the food inspector uses E. Merck’sFritest. If the Fritest is positive, then frying fat is checked for free fatty acids, totalpolar compounds, taste, color, odor, and appearance. Use is allowed of up to 3mg/kg of dimethylpolysiloxane in frying fats.

The Netherlands

Food laws in The Netherlands are enforced by 16 food inspection services, eachcovering an inspection area of about one million people. Inspectors sample the fry-ing oil or fat in restaurants, snack bars, fish shops, and so forth. Samples arebrought to the laboratory where they are checked for odor, taste, acid value, andDPTG content. Frying fat or oil is “unfit for human consumption” if the acid valueis >4.5 and/or DPTG content is >16%.



Portugal

There are no specific regulations for frying fats and oils in Portugal. However, theMinistry of Agriculture’s Food Quality Institute examines frying and cooking oilfor color and odor and also by E. Merck’s Fritest and Oxifrit Test and LibraLaboratories’ Veri-Fry quick tests. If positive, the oil is analyzed for content oftotal polar compounds, which should be no >25%. It is recommended that fryingtemperatures should be not be greater than 180°C.

Scandinavian Countries

The Scandinavian countries have no specific laws or regulations applicable to fryingfats. General regulations applicable to edible fats and oils apply to frying fat.Norway’s laws require foods to be free of pollutants and toxic substances and specifythat only tocopherols and citric acid may be added to fats and oils. For practical con-trol in restaurants and fast-food establishments, Norwegian inspectors may useorganoleptic evaluation or the Fritest. In Sweden, the Oxifrit Test is used as a quicktest, and the method for total polar compounds is used as a reference method.

In Finland, fat is considered spoiled when color, odor, and taste are <1 whenchecked using a scale of 1 to 5, or when the acid value is >2.5 and the smoke point is<170°C (23). Vegetable oil is spoiled when color, odor, and taste are <1, or when theFritest is >2, acid value is >2, and smoke point is <180°C. It is also considered spoiledwhen the decrease in iodine value (compared to that of unused oil) is >16, acid value is>2, and smoke point is <180°C. These guidelines have been used since 1976.

In 1991, the National Food Administration of Finland issued a circular that was tobe observed by all public health boards outlining procedures for sampling and analysisof frying fat. Test criteria are as follows: sensory evaluation (smell, taste, color); totalpolar compounds, maximum 25%; acid value, vegetable oil, 2.0; acid value, solid fat,2.5; smoke point, vegetable oil, minimum 180°C; smoke point, solid fat, minimum170°C; Fritest, vegetable oil, maximum 2 (scale 1–3); Oxifrit Test, <3 (scale 1–4);food oil sensor, <4 (scale 0–6). In addition, information is provided on the choice ofkettle material (stainless steel is recommended) and the proper use and cleaning of fry-ing equipment. Last, an inspection form is presented (Fig. 12.1) to be completed by thehealth inspector and provided to the food laboratory.

The Swedish National Food Administration (NFA) prepared a document in 1989presenting advice and guidelines on handling frying fat. A summary of the NFAguidelines is shown in Table 12.3. An English edition was issued in June 1990 (22). Itspurpose is to encourage the employees of food establishments to prepare high qualityfried food. The NFA recommends the use of the Oxifrit Test as a quick test for kitchenstaff or local food control inspectors. According to Food Control Ordinance SLV FS1990:10, food producers must have some form of quality control program approved bycontrol officials. The NFA recommended use of the Oxifrit Test as part of compulsoryquality control programs. In Sweden, antifoam agents, such as silicones, are not per-mitted in frying oil because they mask natural foaming in deteriorated oil.



Singapore

The Food Control Department of the Ministry of the Environment has no specificregulations controlling frying fats. However, the quality of fats and oils is moni-tored by checking physical appearance, and peroxide value of used fats is checkedto ensure that it is not >10 mEq/kg.

Fig. 12.1. Food laboratory inspection form (Finland National Food Administration).



Spain

Royal decrees of 1981 and 1983 regulate transportation, processing, and commerceof edible fats and oils but are not applicable to frying. However, a more recentdecree protecting consumers (24) specifies that frying oils and fats must not con-tain foreign compounds, must contain <25% total polar compounds, should satisfysensory evaluations, must not alter the quality of fried foods, and must not be soldfor subsequent use in preparing food products after use in preparing fried food.

Switzerland

Food control is carried out by the individual member states (cantons) of the Swissconfederation. Basic food legislation is contained in the federal law of 1905 (25).A 1936 ordinance deals with labeling and advertising of food and food additives,as well as investigation and inspection of food establishments. Laboratories of thelarge cantons are responsible for food control in each region.

The Swiss Food Ordinance controls frying oils and fats in restaurants andcatering facilities and gives guidelines for food preparation and sale. The SwissPublic Health Office issued a list of permitted additives and maximum levels in

TABLE 12.3 Swedish National Food Administration Guidelines for Deep-Fat Frying

1. All fat in the fryer must be changed before it smokes or foams. Use tests such as Food OilSensor or Oxifrit Test to indicate when it is time to change.

2. Strain the fat and clean the fryer once daily. Rinse carefully after cleaning. Solid materialand detergent residue in the fat accelerate breakdown of the fat. Store the strained fat atroom temperature or at lower temperatures in a covered stainless steel vessel. If iron potsare used, they should be rinsed only with hot water. Detergents remove the protective filmof polymerized fat that builds up during use.

3. Frying temperature should be 160–180°C (320–356°F). At lower temperatures, the productabsorbs more fat. At higher temperatures, the fat deteriorates more quickly.

4. Use fat specially intended for frying.

5. Avoid salting or seasoning fried food over the fryer. Salt and seasoning can acceleratebreakdown of the fat.

6. Lower the temperature when not frying and protect the fat from light.

7. The fryer should have no iron, copper, or brass parts that come in contact with the heatedfat.

8. Keep a constant level of fat in the fryer. Fry a little at a time to keep the temperature as evenas possible. Prefry when large amounts will be prepared.

9. Use a separate fryer, if possible, for potatoes. The fat deteriorates more rapidly when meator fish are fried than when only potatoes are fried.

10. Caution: Do not overheat. If the fat temperature rises above 300°C (572°F), the fat may burn.



foods, including coloring agents, antioxidants, and emulsifiers allowed in food fatand oil (these additives do not improve frying performance and are not used in fry-ing oils). Silicone additives are forbidden.

Food inspectors check frying oil for odor, taste, color, and smoking and observethe state of hygiene in food establishments. Suspect frying oil quality is checked onthe spot by the Fritest. If positive, the oil is checked in the laboratory for the level oftotal polar compounds. Food control officials generally follow the DGF recommenda-tion that frying oil should not contain >27% total polar compounds.

Frying oil is considered to be deteriorated if odor and taste are objectionable,or if not clearly objectionable, the smoke point is <170°C and total polar com-pounds are >21%, or total polar compounds exceed 27%. These criteria are basedon the assumption that a careful, experienced cook monitors not only the quality ofthe frying oil, but also the hygiene of the kitchen. If the frying oil does not adhereto the recommendations, owners of establishments deemed sanitary are warned totake care of the frying oil in use. Owners of unsanitary establishments are asked toimprove conditions as well as frying oil quality.

SummaryFrying fats in the United States are subject to control under the general provisionsof the Federal Food, Drug and Cosmetic Act. The FDA has not issued specific reg-ulations because it has not been determined that frying fats used in deep-frying areinjurious to health. The Meat Inspection Manual of the USDA’s Food Safety andInspection Service contains several general guidelines for frying meat and poultryproducts. Several other countries, mainly in Europe, have issued regulations orguidelines for control of frying fats and fried food because of interest in improvingthe quality and acceptability of fried foods.

References

1. Firestone, D., R.F. Stier, and M.M. Blumenthal, Regulation of Frying Fats and Oils,Food Technol. 45:90–94 (1991).

2. Firestone, D., Worldwide Regulation of Frying Fats and Oils, INFORM 4:1366–1371(1993).

3. Meat and Poultry Inspection Manual, Food Safety and Inspection Service, U.S.Department of Agriculture, Washington, D.C., December 1990, Section 1840, p. 125.

4. Combined Compilation of Meat and Poultry Inspection Issuances for 1984–1990, FoodSafety and Inspection Service, U.S. Department of Agriculture, Washington, D.C., FSISDirective 11.000.2, April 28, 1987, Section cc, p. 14.

5. Anonymous, Meeting Summary, D.F. Symposium on Frying and Cooking Fats, FetteSeifen Anstrichm. 75:449 (1973).

6. Baltes, J., C.H. Krauch, A. Seher, V. Wolf, and N. Zollner, D.F. Symposium on Fryingand Cooking Fats, Fette Seifen Anstrichm. 81 (Special Issue):493–574 (1979).

7. Blumenthal, M.M., and R.A. Carr, Symposium on the Chemistry and Technology ofDeep-Fat Frying, Food Technol. 45:67–96 (1991).



8. Anon., 3rd International Symposium on Deep-Fat Frying, March 20–21, 2000, Eur. J.Lipid Sci. Technol. 102:507–593 (2000).

9. Official Methods and Recommended Practices of the American Oil Chemists’ Society,5th edn., American Oil Chemists’ Society, Champaign, IL, 2001, Official Method Cd20–91.

10. Official Methods and Recommended Practices of the American Oil Chemists’ Society,5th edn., American Oil Chemists’ Society, Champaign, IL, 2001, Official Method Cd22–91.

11. Food Safety Initiate Update, Center for Food Safety and Applied Nutrition (CFSAN),FDA, Washington, D.C., January 28, 2000 (see http://www.cfsan.fda.gov).

12. National Food Safety Programs, December 24, 2001 (see http://vm.cfsan.fda.gov/~dms/fs-toc.html or www.foodsafety.gov).

13. Report of the FDA Retail Food Program Database of Foodborne Illness Risk Factors,Center for Food Safety and Applied Nutrition (CFSAN), FDA, Washington, D.C.,August 10, 2000 (see http://www.cfsan.fda.gov/~dms/retrsk.html).

14. FDA Procedures for Standardization and Certification of Retail Food Inspection/Training Officers, Food and Drug Administration, Washington, DC, August 28, 2000(see http://www.cfsan.fda.gov/~ear/rfi-toc.html).

15. Food Code, 1999 Recommendations of the United States Public Health Service Foodand Drug Administration, Washington, D.C., PB 99-115925.

16. Managing Food Safety: A HACCP Principles Guide for Operators of Food Establishmentsat the Retail Level, Food and Drug Administration, Washington, DC, April 15, 1998 (seeh t t p : / / v m . c f s a n . f d a . g o v / ~ d m s / ) .

17. Meat and Poultry Inspection Manual, Food Safety and Inspection Service, U.S.Department of Agriculture, Washington, D.C., December 1990, section 18.90, p. 125.

18. Combined Compilation of Meat and Poultry Inspection Issuances for 1984–1990, FoodSafety and Inspection Service, U.S. Department of Agriculture, Washington, D.C., FSISDirective 11.000.2, 4–28–87, section cc, p. 14.

19. Dehaene, J.-L. and W. Demeester-de Meyer, Royal Decree on Use of Edible Fats and Oilsfor Preparation of Fried Foods, Belgian State J. 20:1544–1545 (1988).

20. Rev. Fr. Corps Gras 38:224 (1991).21. J. Officiel de la Republic Francaise 118:9126 (July 24, 1986).2 2 . General Advice on Handling Frying Fats (SLV FS 1990:2), National Food Administration,

Uppsala, Sweden, 1990.23. Marcuse, R., Fette Seifen Anstrichm. 81:4 (1979).24. Quality Standard for Heated Fats and Oils, Official State Bull. (Spain), No. 26, January 31,

1989, pp. 2665–2667.25. Public Health in Europe 28, Food Safety Services, 2nd edn., World Health Organization

(WHO) Regional Office for Europe, WHO, Copenhagen, 1988, pp. 177–180.



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