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Food Biochemistry andFood Processing

EditorY. H. Hui

Associate EditorsWai-Kit Nip

Leo M.L. NolletGopinadhan PaliyathBenjamin K. Simpson

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Food Biochemistry andFood Processing

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iv

©2006 Blackwell PublishingAll rights reserved

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First edition, 2006

Library of Congress Cataloging-in-Publication Data

Food biochemistry and food processing / editor, Y.H.Hui ; associate editors, Wai-Kit Nip . . . [et al.].—1st ed.

p. cm.Includes index.ISBN-13: 978-0-8138-0378-4 (alk. paper)ISBN-10: 0-8138-0378-0 (alk. paper)1. Food industry and trade—Research. I. Hui,

Y. H. (Yiu H.)TP370.8.F66 2006664—dc22

2005016405

The last digit is the print number: 9 8 7 6 5 4 3 2 1

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v

Contents

Contributors viiPreface xiii

Part I: Principles1. Food Biochemistry—An Introduction 3

W. K. Nip2. Analytical Techniques in Food Biochemistry 25

M. Marcone3. Recent Advances in Food Biotechnology Research 35

S. Jube and D. Borthakur4. Browning Reactions 71

M. Villamiel, M. D. del Castillo, and N. Corzo

Part II: Water, Enzymology, Biotechnology, and Protein Cross-linking

5. Water Chemistry and Biochemistry 103C. Chieh

6. Enzyme Classification and Nomenclature 135H. Ako and W. K. Nip

7. Enzyme Activities 155D. J. H. Shyu, J. T. C. Tzen, and C. L. Jeang

8. Enzyme Engineering and Technology 175D. Platis, G. A. Kotzia, I. A. Axarli, and N. E. Labrou

9. Protein Cross-linking in Food 223J. A. Gerrard

10. Chymosin in Cheese Making 241V. V. Mistry

11. Starch Synthesis in the Potato Tuber 253P. Geigenberger and A. R. Fernie

12. Pectic Enzymes in Tomatoes 271M. S. Kalamaki, N. G. Stoforos, and P. S. Taoukis

Part III: Muscle Foods13. Biochemistry of Raw Meat and Poultry 293

F. Toldrá and M. Reig

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vi Contents

14. Biochemistry of Processing Meat and Poultry 315F. Toldrá

15. Chemistry and Biochemistry of Color in Muscle Foods 337J. A. Pérez-Alvarez and J. Fernández-López

16. Biochemistry of Seafood Processing 351Y. H. Hui, N. Cross, H. G. Kristinsson, M. H. Lim, W. K. Nip, L. F. Siow, and P. S. Stanfield

17. Seafood Enzymes 379M. K. Nielsen and H. H. Nielsen

18. Proteomics: Methodology and Application in Fish Processing 401O. T. Vilhelmsson, S. A. M. Martin, B. M. Poli, and D. F. Houlihan

Part IV: Milk19. Chemistry and Biochemistry of Milk Constituents 425

P. F. Fox and A. L. Kelly20. Biochemistry of Milk Processing 453

A. L. Kelly and P. F. Fox

Part V: Fruits, Vegetables, and Cereals21. Biochemistry of Fruits 487

G. Paliyath and D. P. Murr22. Biochemistry of Fruit Processing 515

M. Oke and G. Paliyath23. Biochemistry of Vegetable Processing 537

M. Oke and G. Paliyath24. Nonenzymatic Browning of Cookies, Crackers, and

Breakfast Cereals 555M. Villamiel

25. Rye Constituents and Their Impact on Rye Processing 567T. Verwimp, C. M. Courtin, and J. A. Delcour

Part VI: Fermented Foods26. Dairy Products 595

T. D. Boylston27. Bakery and Cereal Products 615

J. A. Narvhus and T. Sørhaug28. Biochemistry of Fermented Meat 641

F. Toldrá29. Biochemistry and Fermentation of Beer 659

R. Willaert

Part VII: Food Safety30. Microbial Safety of Food and Food Products 689

J. A. Odumeru31. Emerging Bacterial Foodborne Pathogens and Methods

of Detection 705R. L. T. Churchill, H. Lee, and J. C. Hall

Index 745

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Contributors

vii

Harry Ako (Chapter 6)Department of Molecular Biosciences and

BioengineeringUniversity of Hawaii at ManoaHonolulu, HI 96822, USAPhone: 808-956-2012Fax: 808-956-3542Email: [email protected]

I. A. Axarli (Chapter 8)Enzyme Technology LaboratoryDepartment of Agricultural BiotechnologyAgricultural University of AthensIera Odos 7511855 Athens, Greece

Dulal Borthakur (Chapter 3)Department of Molecular Biosciences and

BioengineeringUniversity of Hawaii at ManoaHonolulu, Hawaii 96822, USAPhone: 808-956-6600Fax: 808-956-3542Email: [email protected]

Terri D. Boylston (Chapter 26)Food Science and Human NutritionIowa State University2547 Food Sciences BuildingAmes, IA 50011, USAPhone: 515-294-0077Fax: 515-294-8181Email: [email protected]

Chung Chieh (Chapter 5)Department of Chemistry

University of WaterlooWaterloo, Ontario N2L 3G1, CanadaPhone (office): 519-888-4567 ext. 5816Phone (home): 519-746-5133Fax: 519-746-0435Email: [email protected]

Robin L.T. Churchill (Chapter 31)Department of Environmental BiologyUniversity of GuelphGuelph, Ontario N1G 2W1, Canada

Nieves Corzo (Chapter 4)Instituto de Fermentaciones Industriales (CSIC)c/Juan de la Cierva, 328006 Madrid, SpainPhone: 34 91 562 2900Fax: 34 91 564 4853Email: [email protected]

C. M. Courtin (Chapter 25)Department of Food and Microbial TechnologyFaculty of Applied Bioscience and EngineeringKatholieke Universiteit LeuvenKasteelpark Arenberg 20B-3001 Leuven, BelgiumPhone: �32 16 321 634Fax: �32 16 321 997Email: [email protected]

N. Cross (Chapter 16)Cross Associates4461 North Keokuk AvenueApt. 1Chicago, IL 60630, USAPhone: 773-545-9289Email: [email protected]

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viii Contributors

Maria Dolores del Castillo (Chapter 4)Instituto de Fermentaciones Industriales (CSIC)c/Juan de la Cierva, 328006 Madrid, SpainPhone: 34 91 562 2900Fax: 34 91 564 4853Email: [email protected]

J. A. Delcour (Chapter 25)Department of Food and Microbial TechnologyFaculty of Applied Bioscience and EngineeringKatholieke Universiteit LeuvenKasteelpark Arenberg 20B-3001 Leuven, BelgiumPhone: �32 16 321 634Fax: �32 16 321 997Email: [email protected]

Juana Fernández-López (Chapter 15)Departamento de Tecnología AgroalimentariaEscuela Politécnica Superior de OrihuelaUniversidad Miguel HernándezCamino a Beniel s/n 03313 DesamparadosOrihuela (Alicante), SpainPhone: �34 6 674 9656Fax: �34 6 674 9609/674 9619Email: [email protected] [email protected]

Alisdair R. Fernie (Chapter 11)Max Planck Institute of Molecular Plant PhysiologyAm Mühlenberg 114476 Golm, Germany

Patrick F. Fox (Chapter 19, 20)Food Science and TechnologyUniversity College CorkCork, IrelandPhone: 00 353 21 490 2362Fax: 00 353 21 427 0001Email: [email protected]

Peter Geigenberger (Chapter 11)Max Planck Institute of Molecular Plant PhysiologyAm Mühlenberg 114476 Golm, GermanyEmail: [email protected]

Juliet A. Gerrard (Chapter 9)School of Biological SciencesUniversity of Canterbury,Christchurch, New ZealandPhone: �64 03 364 2987

Fax: �64 03 364 2950Email: [email protected]

J. Christopher Hall (Chapter 31)Department of Environmental BiologyUniversity of GuelphGuelph, Ontario N1G 2W1, CanadaPhone: 519-824-4120 ext. 52740Fax: 519-837-0442Email: [email protected]

Dominic F. Houlihan (Chapter 18)School of Biological SciencesUniversity of Aberdeen, Aberdeen, UK

Y. H. Hui (Editor, Chapter 16)Science Technology SystemP.O. Box 1374West Sacramento, CA 95691, USAPhone: 916-372-2655Fax: 916-372-2690Email: [email protected]

Chii-Ling Jeang (Chapter 7)Department of Food ScienceNational Chung Hsing UniversityTaichung, Taiwan 40227, Republic of ChinaPhone: 886 4 228 62797Fax: 886 4 228 76211Email: [email protected]

Sandro Jube (Chapter 3)Department of Molecular Biosciences and


Mary S. Kalamaki (Chapter 12)Department of Pharmaceutical SciencesAristotle University of Thessaloniki54124 Thessaloniki, GreecePhone: �30 2310 412238Fax: �30 2310 412238Email: [email protected]

Alan L. Kelly (Chapter 19, 20)Food Science and TechnologyUniversity of CorkCork, IrelandPhone: 00 353 21 490 3405Fax: 00 353 21 427 0001Email: [email protected]

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Contributors ix

G. A. Kotzia (Chapter 8)Enzyme Technology LaboratoryDepartment of Agricultural BiotechnologyAgricultural University of AthensIera Odos 7511855 Athens, Greece

H. G. Kristinsson (Chapter 16)University of FloridaLaboratory of Aquatic Food Biomolecular ResearchAquatic Food Products ProgramDepartment of Food Science and Human NutritionGainesville FL 32611, USAPhone: 352-392-1991 ext. 500Fax: 352-392-9467Email: [email protected]

Michael Krogsgaard Nielsen (Chapter 17)Food Biotechnology and Engineering GroupFood BiotechnologyBioCentrum-DTUTechnical University of DenmarkPhone: 45 45 25 25 92Email: [email protected]

N. E. Labrou (Chapter 8)Enzyme Technology LaboratoryDepartment of Agricultural BiotechnologyAgricultural University of AthensIera Odos 7511855 Athens, GreecePhone and Fax: �30 210 529 4308Email: [email protected]

Hung Lee (Chapter 31)Department of Environmental BiologyUniversity of GuelphGuelph, Ontario N1G 2W1, Canada

M. H. Lim (Chapter 16)Department of Food ScienceUniversity of OtagoDunedin, New ZealandPhone: 64 3 479 7953Fax: 64 3 479 [email protected]

Massimo Marcone (Chapter 2)Department of Food ScienceUniversity of GuelphGuelph, Ontario N1G 2W1, CanadaPhone: 519-824-4120, ext. 58334Fax: 519-824-6631Email: [email protected]

Samuel A. M. Martin (Chapter 18)School of Biological SciencesUniversity of Aberdeen, Aberdeen, UK

Vikram V. Mistry (Chapter 10)Dairy Science DepartmentSouth Dakota State UniversityBrookings SD 57007, USAPhone: 605-688-5731Fax: 605-688-6276Email: [email protected]

Dennis P. Murr (Chapter 21)Department of Plant AgricultureUniversity of GuelphGuelph, Ontario N1G 2W1, CanadaPhone: 519-824-4120 ext. 53578Email: [email protected]

Judith A. Narvhus (Chapter 27)Dept of Chemistry, Biotechnology,

and Food ScienceNorwegian University of Life SciencesBox 50031432 Aas, NorwayEmail: [email protected]

Henrik Hauch Nielsen (Chapter 17)Danish Institute for Fisheries ResearchDepartment of Seafood ResearchSøltofts PladsTechnical University of Denmark, Bldg. 221DK-2800 Kgs. Lyngby, DenmarkPhone: �45 45 25 25 93Fax: �45 45 88 47 74Email: [email protected]

Michael Krogsgaard Nielsen (Chapter 17)Food Biotechnology and Engineering GroupFood BiotechnologyBioCentrum-DTUTechnical University of Denmark, Bldg. 221DK-2800 Kgs. Lyngby, DenmarkPhone: �45 45 25 25 92Fax: �45 45 88 47 74Email: [email protected]

Wai-kit Nip (Associate Editor, Chapters 1, 6, 16)Department of Molecular Biosciences and


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x Contributors

Leo M. L. Nollet (Associate Editor)Hogeschool GentDepartment of Engineering SciencesSchoonmeersstraat 52B9000 Gent, BelgiumPhone: 00 329 242 4242Fax: 00 329 243 8777Email: [email protected]

Joseph A. Odumeru (Chapter 30)Laboratory Services DivisionUniversity of Guelph95 Stone Road WestGuelph, Ontario N1H 8J7, CanadaPhone: 519-767-6243Fax Number: 519-767-6240Email: [email protected]

Moustapha Oke (Chapters 22, 23)Ontario Ministry of Agriculture and Food1 Stone Road West, 2nd Floor SWGuelph, Ontario N1G 4Y2, CanadaEmail: [email protected]

Gopinadhan Paliyath (Associate Editor, Chapters21, 22, 23)Department of Plant AgricultureUniversity of GuelphGuelph, Ontario N1G 2W1, CanadaPhone: 519-824-4120, ext. 54856Email: [email protected]

José Angel Pérez-Alvarez (Chapter 15)Departamento de Tecnología AgroalimentariaEscuela Politécnica Superior de OrihuelaUniversidad Miguel HernándezCamino a Beniel s/n 03313 DesamparadosOrihuela (Alicante), SpainPhone: �34 06 674 9656Fax: �34 06 674 9609/674 9619Email: [email protected]

D. PlatisLaboratory of Enzyme TechnologyDepartment of Agricultural BiotechnologyAgricultural University of AthensIera Odos 7511855 Athens, Greece

Bianca M. Poli (Chapter 18)Department of Animal ProductionUniversity of FlorenceFlorence, Italy

Milagro Reig (Chapter 13)Instituto de Agroquímica y Tecnología de Alimentos (CSIC)P.O. Box 7346100 Burjassot (Valencia), Spain

Douglas J.H. Shyu (Chapter 7)Graduate Institute of BiotechnologyNational Chung Hsing UniversityTaichung, Taiwan 40227, Republic of ChinaPhone: 886 4 228 840328Fax: 886 4 228 53527Email: [email protected]

Benjamin K. Simpson (Associate Editor)Department of Food ScienceMcGill University, MacDonald Campus21111 Lakeshore RoadSt. Anne Bellevue PQ H9X3V9, CanadaPhone: 514-398-7737Fax: 514-398-7977Email: [email protected]

L. F. Siow (Chapter 16)Department of Food ScienceUniversity of OtagoDunedin, New ZealandPhone: 64 3 479 7953Fax: 64 3 479 7567

Terje Sørhaug (Chapter 27)Department of Chemistry, Biotechnology,

and Food ScienceNorwegian University of Life SciencesBox 50031432 Aas, NorwayEmail: [email protected]

P. S. Stanfield (Chapter 16)Dietetic Resources794 Bolton St.Twin Falls, ID 83301, USAPhone: 208-733-8662Email: [email protected]

Nikolaos G. Stoforos (Chapter 12)Department of Chemical EngineeringAristotle University of Thessaloniki54124 Thessaloniki, GreecePhone: �30 2310 996450Fax: �30 2310 996259Email: [email protected]

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Contributors xi

Petros S. Taoukis (Chapter 12)Laboratory of Food Chemistry and TechnologySchool of Chemical EngineeringNational Technical University of AthensIroon Polytechniou 515780 Athens, GreecePhone: �30 210 772 3171Fax: �30 210 772 3163Email: [email protected]>

Fidel Toldrá (Chapters 13, 14, 28)Instituto de Agroquímica y Tecnología de Alimentos (CSIC)Apt. 7346100 Burjassot (Valencia), SpainPhone: 34 96 390 0022Fax: 34 96 363 6301Email: [email protected]

Jason T.C. Tzen (Chapter 7)Graduate Institute of BiotechnologyNational Chung Hsing UniversityTaichung, Taiwan 40227, Republic of ChinaPhone: 886 4 228 840328Fax: 886 4 228 53527Email: [email protected]

T. Verwimp (Chapter 25)Department of Food and Microbial TechnologyFaculty of Applied Bioscience and EngineeringKatholieke Universiteit LeuvenKasteelpark Arenberg 20

B-3001 Leuven, BelgiumPhone: �32 16 321 634Fax: �32 16 321 997Email: [email protected]

Oddur T. Vilhelmsson (Chapter 18)Faculty of Natural Resource SciencesUniversity of AkureyriBorgum, Room 243IS-600 Akureyri, IcelandPhone: �354 460 8503Fax: �354 460 8999Mobile: �354 697 4252Email: [email protected]

Mar Villamiel (Chapters 4, 24)Instituto de Fermentaciones Industriales (CSIC)c/Juan de la Cierva, 328006 Madrid, SpainPhone: 34 91 562 2900Fax: 34 91 564 4853Email: [email protected]

Ronnie Willaert (Chapter 29)Department of UltrastructureFlanders Interuniversity Institute for BiotechnologyVrije Universiteit BrusselPleinlaan 2B-1050 Brussels, BelgiumPhone: 32 2 629 18 46Fax: 32 2 629 19 63Email: [email protected]

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Preface

In the last 20 years, the role of food biochemistryhas assumed increasing significance in all major dis-ciplines within the categories of food science, foodtechnology, food engineering, food processing, andfood biotechnology. In the five categories men-tioned, progress has advanced exponentially. Asusual, dissemination of information on this progressis expressed in many media, both printed and elec-tronic. Books are available for almost every special-ty area within the five disciplines mentioned, num-bering in the hundreds. As is well known, the twoareas of food biochemistry and food processing areintimately related. However, books covering a jointdiscussion of these topics are not so common. Thisbook attempts to fill this gap, using the followingapproaches:

• Principles of food biochemistry,• Advances in selected areas of food biochemistry,• Food biochemistry and the processing of muscle

foods and milk,• Food biochemistry and the processing of fruits,

vegetables, and cereals,• Food biochemistry and the processing of

fermented foods, and• Microbiology and food safety.

The above six topics are divided over 31 chapters.Subject matters discussed under each topic arebriefly reviewed below.

• The principles of food biochemistry are exploredin definitions, applications, and analysis and inadvances in food biotechnology. Specificexamples used include enzymes, protein cross-linking, chymosin in cheesemaking, starchsynthesis in the potato tuber, pectinolytic

enzymes in tomatoes, and food hydrationchemistry and biochemistry.

• The chemistry and biochemistry of muscle foodsand milk are covered under the color of musclefoods, raw meat and poultry, processed meat and poultry, seafood enzymes, seafood pro-cessing, proteomics and fish processing, milkconstituents, and milk processing. The chemistryand biochemistry of fruits, vegetables, andcereals are covered in raw fruits, fruits pro-cessing, vegetable processing, rye flours, andnonenzymatic browning of cereal bakingproducts. The chemistry and biochemistry offermented foods touch on four groups ofproducts: dairy products, bakery and cerealproducts, fermented meat, and beer.

• The topic of microbiology and food safety coversmicrobial safety and food processing, andemerging bacterial foodborne pathogens.

This reference and classroom text is a result of thecombined effort of more than 50 professionals fromindustry, government, and academia. These profes-sionals are from more than 15 countries and havediverse expertise and background in the discipline of food biochemistry and food processing. Theseexperts were led by an international editorial team of five members from three countries. All these in-dividuals, authors and editors, are responsible forassembling in one place the scientific topics of foodbiochemistry and food processing, in their immensecomplexity. In sum, the end product is unique, bothin depth and breadth, and will serve as

• An essential reference on food biochemistry and food processing for professionals in thegovernment, industry, and academia.

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xiv Preface

• A classroom text on food biochemistry and foodprocessing in an undergraduate food scienceprogram.

The editorial team thanks all the contributors forsharing their experience in their fields of expertise.They are the people who made this book possible.We hope you enjoy and benefit from the fruits oftheir labor.

We know how hard it is to develop the content ofa book. However, we believe that the production of a

professional book of this nature is even more diffi-cult. We thank the editorial and production teams atBlackwell Publishing for their time, effort, advice,and expertise. You are the best judge of the qualityof this book.

Y. H. HuiW. K. Nip

L. M. L. NolletG. Paliyath

B. K. Simpson

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Part IPrinciples

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Food Biochemistry and Food ProcessingEdited by Y. H. Hui

Copyright © 2006 by Blackwell Publishing

1Food Biochemistry—An

IntroductionW. K. Nip

3

IntroductionBiochemical Changes of Carbohydrates in Food

Changes in Carbohydrates in Food SystemsChanges in Carbohydrates during Seed GerminationMetabolism of Complex CarbohydratesMetabolism of Lactose and Organic Acids in Cheese

ProductionRemoval of Glucose in Egg Powder ProductionProduction of Starch Sugars and Syrups

Biochemical Changes of Proteins and Amino Acids inFoods

Proteolysis in Animal TissuesTransglutaminase Activity in Seafood ProcessingProteolysis during Cheese FermentationProteolysis in Geminating SeedsProteases in Chill-Haze Reduction in Beer Production

Biochemical Changes of Lipids in FoodsChanges in Lipids in Food SystemsChanges in Lipids during Cheese FermentationLipid Degradation in Seed GerminationBiogeneration of Fresh-Fish OdorBiochemically Induced Food Flavors

Biochemical Degradation and Biosynthesis of PlantPigments

Degradation of Chlorophyl in Fruit MaturationMevalonate and Isopentyl Diphosphate Biosynthesis

prior to Formation of CarotenoidsNaringenin Chalcone Biosynthesis

Selected Biochemical Changes Important in the Handlingand Processing of Foods

Production of Ammonia and Formaldehyde fromTrimethylamine and Its N-Oxide

Production of Biogenic AminesProduction of Ammonia from UreaAdenosine Triphosphate DegradationPolyphenol Oxidase Browning

Ethylene Production in Fruit RipeningReduction of Phytate in Cereals

Biotechnology in Food Production, Handling, andProcessing

Biotechnology-Derived Food EnzymesGenetically Modified Microorganisms Useful in Food

ProcessingConclusionAcknowledgementsReferences

INTRODUCTION

Food losses and food poisoning have been recog-nized for centuries, but the causes of these problemswere not understood. Improvements in food prod-ucts by proper handling and primitive processingwere practiced without knowing the reasons. Foodscientists and technologists started to investigatethese problems about 60 years ago. Currently, someof these causes are understood, and others are stillbeing investigated. These causes may be microbio-logical, physical (mechanical), and/or chemical (in-cluding biochemical). Food scientists and technolo-gists also recognized long ago the importance of abackground in biochemistry, in addition to the basicsciences (chemistry, physics, microbiology, andmathematics). This was demonstrated by a generalbiochemistry course requirement in the first Rec-ommended Undergraduate Course Requirements ofthe Institute of Food Technologists (IFT) in theUnited States in the late 1960s. To date, food bio-chemistry is still not listed in the IFT recommendedundergraduate course requirements. However, many

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Food Biochemistry and Food ProcessingEdited by Y. H. Hui

Copyright © 2006 by Blackwell Publishing

4 Part I: Principles

universities in various countries now offer a gradu-ate course in food biochemistry as an elective orhave food biochemistry as a specialized area ofexpertise in their undergraduate and graduate pro-grams. One of the reasons for not requiring such acourse at the undergraduate level may be that a bio-chemistry course is often taken in the last two tothree semesters before graduation, and there is noroom for such a course in the last semesters. Also,the complexity of this area is very challenging andrequires broader views of the students, such as thoseat the graduate level. However, the importance offood biochemistry is now recognized in the subdis-cipline of food handling and processing, as many ofthese problems are biochemistry related. A content-specific journal, the Journal of Food Biochemistry,has also been available since 1977 for scholars toreport their food biochemistry–related researchresults, even though they can also report their find-ings to other journals.

Understanding of food biochemistry followed bydevelopments in food biotechnology in the pastdecades resulted in, besides better raw materials andproducts, improved human nutrition and food safety,and these developments are applied in the foodindustry. For example, milk-intolerant consumers inthe past did not have the advantage of consumingdairy products. Now they can, with the availabilityof lactase (a biotechnological product) at the retaillevel in some developed countries. Lactose-free milkis also produced commercially in some developedindustrial countries. The socially annoying problemof flatulence that results from consuming legumescan be overcome by taking “Beano™” (alpha-galac-tosidase preparation from food-grade Aspigillusniger) with meals. Shark meat is made more palat-able by bleeding the shark properly right after catchto avoid the biochemical reaction of urease on urea,both naturally present in the shark’s blood. Propercontrol of enzymatic activities also resulted in betterproducts. Tomato juice production is improved byproper control of its pectic enzymes. Better color inpotato chips is the result of control of the oxidativeenzymes and removal of substrates from the cutpotato slices. More tender beef is the result of prop-er aging of carcasses and sometimes the addition ofprotease(s) at the consumer level; although thisresult had been observed in the past, the reasonsbehind it were unknown. Ripening inhibition ofbananas during transport is achieved by removal ofthe ripening hormone ethylene in the package to

minimize the activities of the ripening enzymes,making bananas available worldwide all year round.Proper icing or seawater chilling of tuna after catchavoids/controls histamine production by inhibitingthe activities of bacterial histamine producers, thusavoiding scombroid or histamine poisoning. Theseare just a few of the examples that will be discussedin more detail in this chapter and in the commoditychapters in this book.

Problems due to biochemical causes are numer-ous; some are simple, while others are fairly com-plex. These can be reviewed either by commoditygroup or by food component. This introductorychapter takes the latter approach by grouping thevarious food components and listing selected relatedenzymes and their biochemical reactions (withoutstructural formulas) in tables and presenting briefdiscussions. This will give the readers another wayof looking at food biochemistry, but as an introduc-tion to the following material, effort is taken to avoidredundancy with the chapters on commodities thatcover the related biochemical reactions in detail.

This chapter presents first selected biochemicalchanges in the macrocomponents of foods (carbohy-drates, proteins, and amino acids), then lipids, thenselected biochemical changes in flavors, plant pig-ments, and other compounds important in food handling and processing. Biotechnological develop-ments as they relate to food handling and processingare introduced only briefly, as new advances areextensively reviewed in Chapter 3. As an example ofcomplexity in the food biochemistry area, a diagramshowing the relationship of similar biochemical re-actions of selected food components (carbohy-drates) in different commodities is presented. Ex-amples of serial degradation of selected foodcomponents are also illustrated with two other dia-grams.

It should be noted that the main purpose of thischapter is to present an overview of food biochem-istry by covering some of the basic biochemicalactivities related to various food components andtheir relations with food handling and processing. Asecond purpose is to get more students interested infood biochemistry. Purposely, only essential refer-ences are cited in the text, to make it easier to read;more extensive listings of references are presentedat the ends of tables and figures. Readers shouldrefer to these references for details and also consultthe individual commodity chapters in this book (andtheir references) for additional information.

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1 Food Biochemistry—An Introduction 5

BIOCHEMICAL CHANGES INCARBOHYDRATES IN FOOD

CHANGES IN CARBOHYDRATES IN FOODSYSTEMS

Carbohydrates are abundant in foods of plant origin,but are fairly limited in quantity in foods of animalorigin. However, some of the biochemical changesand their effect(s) on food quality are common to allfoods regardless of animal or plant origin, while oth-ers are specific to an individual food. Figure 1.1shows the relationship between the enzymatic de-gradation of glycogen and starch (glycolysis) andlactic acid and alcohol formation, as well as the citricacid cycle. Even though glycogen and starch are glu-cose polymers of different origin, after they are con-verted to glucose by the appropriate respective en-zymes, the glycolysis pathway is common to allfoods. The conversions of glycogen in fish and mam-malian muscles are now known to utilize differentpathways, but they end up with the same glucose-6-phosphate. Lactic acid formation is an importantphenomenon in rigor mortis and souring and cur-dling of milk, as well as in the manufacturing ofsauerkraut and other fermented vegetables. Ethanolis an important end product in the production ofalcoholic beverages, bread making, and to a muchsmaller extent in some overripe fruits. The citric acidcycle is also important in alcoholic fermentation,cheese maturation, and fruit ripening. In bread mak-ing, �-amylase, either added or from the flour itself,partially hydrolyzes the starch in flour to release glu-cose units as an energy source for yeast to grow anddevelop so that the dough can rise during the fermen-tation period before punching, proofing, and baking.

CHANGES IN CARBOHYDRATES DURING SEEDGERMINATION

Table 1.1 lists some of the biochemical reactionsrelated to germination of cereal grains and seeds,with their appropriate enzymes, in the production ofglucose and glucose or fructose phosphates fromtheir major carbohydrate reserve, starch. They arethen converted to pyruvate through glycolysis, asoutlined in Figure 1.1. From then on, the pyruvate isutilized in various biochemical reactions. The glu-cose and glucose/fructose phosphates are also usedin the building of various plant structures. The lattertwo groups of reactions are beyond the scope of thischapter.

METABOLISM OF COMPLEX CARBOHYDRATES

Besides starch, plants also possess other subgroupsof carbohydrates, such as cellulose, �-glucans, andpectins. Both cellulose and �-glucans are composedof glucose units but with different �-glycosidic link-ages. They cannot be metabolized in the humanbody, but are important carbohydrate reserves inplants and can be metabolized into smaller mole-cules for utilization during seed germination. Pecticsubstances (pectins) are always considered as the“gluing compounds” in plants. They also are notmetabolized in the human body. Together with cel-lulose and �-glucans, they are now classified in thedietary fiber or complex carbohydrate category.

Interest in pectin stems from the fact that inunripe (green) fruits, pectins exist in the propectinform, giving the fruit a firm/hard structure. Uponripening, propectins are metabolized into smallermolecules, giving ripe fruits a soft texture. Propercontrol of the enzymatic changes in propectin iscommercially important in fruits, such as tomatoes,apples, and persimmons. Tomato fruits usually don’tripen at the same time on the vines, but this can beachieved by genetically modifying their pecticenzymes (see below). Genetically modified toma-toes can now reach a similar stage of ripeness beforeconsumption and processing without going throughextensive manual sorting. Fuji apples can be kept inthe refrigerator for a much longer time than othervarieties of apples before getting to the soft grainytexture stage because the Fuji apple has lower pecticenzyme activity. Persimmons are hard in the unripestage, but can be ripened to a very soft texture due topectic enzyme activity as well as the degradation ofits starches. Table 1.2 lists some of the enzymes andtheir reactions related to these complex carbohy-drates.

METABOLISM OF LACTOSE AND ORGANICACIDS IN CHEESE PRODUCTION

Milk does not contain high molecular weight carbo-hydrates; instead its main carbohydrate is lactose.Lactose can be enzymatically degraded to glucoseand galactose-6-phosphate by phospho-�-galactosi-dase (lactase) by lactic acid bacteria. Glucose andgalactose-6-phosphate are then further metabolizedto various smaller molecules through various bio-chemical reactions that are important in the flavordevelopment of various cheeses. Table 1.3 lists some

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Figure 1.1. Degradation of glycogen and starch. �-Amylase (EC 3.2.1.1), Hexokinase (EC 2.7.1.1), Glucose-6-phosphate isomerase (EC 5.3.1.9), 6-Phosphofructokinase (EC 2.7.1.11), Fructose bisphosphate aldolase (EC4.1.2.13), Triose phosphate isomerase (EC 5.3.1.1), L-lactic dehydrogenase (EC 1.1.1.27), Pyruvate dehydrogenase(NADP) (EC 1.2.1.51), Alcohol dehydrogenase (EC 1.1.1.1), Xylose isomerase (EC 5.3.15). [Eskin 1990, Lowrie1992, Huff-Lonergan and Lonergan 1999, Cadwallader 2000, Gopakumar 2000, Simpson 2000, Greaser 2001,IUBMB-NC website (www.iumb.org)]

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of these enzymatic reactions. This table also listssome enzymes and reaction products of organic acidspresent in very small amounts in milk. However, theyare important flavor components (e.g., propionate,butyrate, acetaldehyde, diacetyl, and acetoine).

REMOVAL OF GLUCOSE IN EGG POWDERPRODUCTION

Glucose is present in very small quantities in eggalbumen and egg yolk. However, in the productionof dehydrated egg products, this small amount ofglucose can undergo nonenzymatic reactions thatlower the quality of the final products. This problemcan be overcome by the glucose oxidase–catalasesystem. Glucose oxidase converts glucose to glu-conic acid and hydrogen peroxide. The hydrogenperoxide is then decomposed into water and oxygen

by the catalase. Application of this process is usedalmost exclusively for whole egg and other yolk-containing products. However, for dehydrated eggalbumen, bacterial fermentation is applied to re-move the glucose. Application of yeast fermentationto remove glucose is also possible. The exact pro-cesses of glucose removal in egg products are theproprietary information of individual processors(Hill 1986).

PRODUCTION OF STARCH SUGARS AND SYRUPS

The hydrolysis of starch by means of enzymes (�-and �- amylases) and/or acid to produce glucose(dextrose) and maltose syrups has been practiced formany decades. Application of these biochemical reactions resulted in the availability of variousstarch (glucose and maltose) syrups, maltodextrins,

Table 1.1. Starch Degradation during Cereal Grain Germination

Enzyme Reaction

�-amylase (EC 3.2.1.1) Starch → glucose � maltose � maltotriose � �-limited dextrins � linear maltosaccharides

Hexokinase (EC 2.7.1.1) D-hexose (glucose) � ATP → D-hexose (glucose)-6-phosphate � ADP

�-glucosidase (maltase, EC 3.2.1.20) Hydrolysis of terminal, nonreducing 1,4-linked �-D-glucose residues with release of �-D-glucose

Oligo-1,6 glucosidase (limited dextrinase, �-limited dextrin → linear maltosaccharidesisomaltase, sucrase isomerase, EC 3.2.1.10)

�-amylase (EC 3.2.1.2) Linear maltosaccharides → MaltosePhosphorylase (EC 2.4.1.1) Linear maltosaccharides � phosphate → �-D-glucose-

1-phosphatePhosphoglucomutase (EC 5.4.2.2) �-D-glucose-1-phosphate → �-D-glucose-6-phosphateGlucosephosphate isomerase (EC 5.3.1.9) D-glucose-6-phosphate → D-fructose-6-phosphateUTP-glucose 1-phosphate uridyl (UDP- UTP � �-D-glucose-1-phosphate → UDP-glucose �

glucose pyrophosphorylase, Glucose- pyrophosphate transferase1-phosphate uridyltransferase, EC 2.7.7.9)

Sucrose phosphate synthetase UDP-glucose � D-fructose-6-phosphate → sucrose (EC 2.4.1.14) phosphate � UDP

Sugar phosphatase (EC 3.1.3.23) Sugar phosphate (fructose-6-phosphate) → sugar (fructose) � inorganic phosphate

Sucrose phosphatase (EC 3.1.3.24) Sucrose-6-F-phosphate → sucrose � inorganic phosphateSucrose synthetase (EC 2.4.1.13) NDP-glucose � D-fructose → sucrose � NDP�-fructose-furanosidase (invertase, Sucrose → glucose � fructose

succharase, EC 3.2.1.26)

Sources: Duffus 1987, Kruger and Lineback 1987, Kruger et al. 1987, Eskin 1990, Hoseney 1994, IUBMB-NC web-site (www.iubmb.org).

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maltose, and glucose for the food, pharmaceutical,and other industries. In the 1950s, researchers dis-covered that some xylose isomerase (D-xylose-keto-isomerase, EC 5.3.1.5) preparations possessed theability to convert D-glucose to D-fructose. In theearly 1970s, researchers succeeded in developingthe immobilized enzyme technology for various ap-plications. Because of the more intense sweetness offructose as compared to glucose, selected xyloseisomerase was successfully applied to this new tech-nology with the production of high fructose syrup(called high fructose corn syrup in the United States).High fructose syrups have since replaced most of the

glucose syrups in the soft drink industry. This isanother example of the successful application ofbiochemical reactions in the food industry.

BIOCHEMICAL CHANGES OFPROTEINS AND AMINO ACIDS INFOODS

PROTEOLYSIS IN ANIMAL TISSUES

Animal tissues have similar structures even thoughthere are slight differences between mammalian landanimal tissues and aquatic (fish and shellfish) animal

Table 1.2. Degradation of Complex Carbohydrates

Enzyme Reaction

Cellulose degradation during seed germinationa

Cellulase (EC 3.2.1.4) Endohydrolysis of 1,4-�-glucosidic linkages in cellulose and cereal �-D-glucans

Glucan 1,4-�-glucosidase Hydrolysis of 1,4 linkages in 1,4-�-D-glucan so as to remove (Exo-1,4-�-glucosidase, EC 3.2.1.74) successive glucose units

Cellulose 1,4-�-cellubiosidase Hydrolysis of 1,4-�-D-glucosidic linkages in cellulose and (EC3.2.1.91) cellotetraose releasing cellubiose from the nonreducing

ends of the chainsb-galactosan degradationa

�-galactosidase (EC 3.21.1.23) �-(1→4)-linked galactan → D-galactoseb-glucan degradationb

Glucan endo-1,6-�-glucosidase Random hydrolysis of 1,6 linkages in 1,6-�-D-glucans(EC 3.2.1.75)

Glucan endo-1,4-�-glucosidase Hydrolysis of 1,4 linkages in 1,4-�-D-glucans so as to (EC 3.2.1.74) remove successive glucose units

Glucan endo-1,3-�-D-glucanase Successive hydrolysis of �-D-glucose units from the (EC 3.2.1.58) nonreducing ends of 1,3-�-D-glucans, releasing �-glucose

Glucan 1,3-�-glucosidase 1,3-�-D-glucans → �-D-glucose(EC 3.2.1.39)

Pectin degradationb

Polygalacturonase (EC 3.2.1.15) Random hydrolysis of 1,4-�-D-galactosiduronic linkages in pectate and other galacturonans

Galacturan 1,4-�-galacturonidase (1,4-�-D-galacturoniside)n � H2O → (1,4-�-D-[Exopolygalacturonase, poly galacturoniside)n-1 � D-galacturonate(galacturonate) hydrolase, EC 3.2.1.67)

Pectate lyase (pectate transeliminase, Eliminative cleavage of pectate to give oligosaccharides with EC 4.2.2.2) 4-deoxy-�-D-galact-4-enuronosyl groups at their

nonreducing endsPectin lyase (EC 4.2.2.10) Eliminative cleavage of pectin to give oligosaccharides with

terminal 4-deoxy-6-methyl-�-D-galact-4-enduronosylgroups

Sources: aDuffus 1987, Kruger and Lineback 1987, Kruger et al. 1987, Smith 1999.bEskin 1990, IUBMB-NC website (www.iubmb.org).

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tissues. The structure will break down slowly afterthe animal is dead. The desirable postmortem situa-tion is meat tenderization, and the undesirable sit-uation is tissue degradation/spoilage.

In order to understand these changes, it is impor-tant to understand the structure of animal tissues.Table 1.4 lists the location and major functions ofmyofibrillar proteins associated with contractile ap-paratus and cytoskeletal framework of animal tis-sues. Schematic drawings and pictures (microscopic,scanning, and transmission electronic microscopicimages) of tissue macro- and microstructures areavailable in various textbooks and references. Chap-ter 13 in this book, Biochemistry of Raw Meat andPoultry, also shows a diagram of meat macro- andmicrostructures. To avoid redundancy, readers notfamiliar with meat structures are advised to refer to

Figure 13.1 when reading the following two para-graphs that give a brief description of the musclefiber structure and its degradation (Lowrie 1992,Huff-Lonergan and Lonergan 1999, Greaser 2001).

Individual muscle fibers are composed of myofib-rils 1–2 �m thick and are the basic units of muscularcontraction. The skeletal muscle of fish differs fromthat of mammals in that the fibers arranged betweenthe sheets of connective tissue are much shorter. Theconnective tissue is present as short transverse sheets(myocommata) that divide the long fish muscles intosegments (myotomes) corresponding in numbers tothose of the vertebrae. A fine network of tubules, thesarcoplasmic reticulum separates the individual myo-fibrils. Within each fiber is a liquid matrix, referredto as the sarcoplasm, that contains mitochondria, en-zymes, glycogen, adenosine triphosphate, creatine,

Table 1.3. Changes in Carbohydrates in Cheese Manufacturing

Action, Enzyme or Enzyme System Reaction

Formation of lactic acidLactase (EC 3.2.1.108) Lactose � H2O → D-glucose � D-galactoseTagatose pathway Galactose-6-P → lactic acidEmbden-Meyerhoff pathway Glucose → pyruvate → lactic acid

Formation of pyruvate from citric acidCitrate (pro-3S) lyase (EC 4.1.3.6) Citrate → oxaloaceateOxaloacetate decarboxylase Oxaloacetate → pyruvate � CO2

(EC 4.1.1.3)Formation of propionic and acetic acids

Propionate pathway 3 lactate → 2 propionate � 1 acetate � CO2 � H2O3 alanine → propionic acid � 1 acetate � CO2 � 3 ammonia

Formation of succinic acidMixed acid pathway Propionic acid � CO2 → succinic acid

Formation of butyric acidButyric acid pathway 2 lactate → 1 butyrate � CO2 � 2H2

Formation of ethanolPhosphoketolase pathway Glucose → acetylaldehyde → ethanolPyruvate decarboxylase (EC 4.1.1.1) Pyruvate → acetylaldehyde � CO2Alcohol dehydrogenase (EC 1.1.1.1) Acetylaldehyde � NAD � H� → ethanol � NAD�

Formation of formic acidPyruvate-formate lyase (EC 2.3.1.54) Pyruvate � CoA → formic acid � acetyl CoA

Formation of diacetyl, acetoine, 2-3 butylene glycolCitrate fermentation pathway Citrate → pyruvate → acetyl CoA → diacetyl → acetoine

→ 2-3 butylene glycolFormation of acetic acid

Pyruvate-formate lyase (EC 2.3.1.54) Pyruvate � CoA → formic acid � acetyl CoAAcetyl-CoA hydrolase (EC 3.1.2.1) Acetyl CoA � H2O → acetic acid � CoASources: Schormuller 1968; Kilara and Shahani 1978; Law 1984a,b; Hutlins and Morris 1987; Kamaly and Marth

1989; Eskin 1990; Khalid and Marth 1990; Steele 1995; Walstra et al. 1999; IUBMB-NC website (www.iubmb.org).

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myoglobin, and other substances. Examination ofmyofibrils under a phase contrast light microscopeshows them to be cross-striated due to the presenceof alternating dark or A-bands and light or I-bands.These structures in the myofibril appear to be verysimilar in both fish and meat. A lighter band or H-zone transverses the A-band, while the I-band has adark line in the middle known as the Z-line. A furtherdark line, the M-line, can also be observed at thecenter of the H-zone in some cases (not shown inFig. 13.1). The basic unit of the myofibril is the sar-comere, defined as the unit between adjacent Z-lines.Examination of the sarcomere by electron micro-scope reveals two sets of filaments within the fibrils, athick set consisting mainly of myosin and a thin setcontaining primarily of F-actin. In addition to theparacrystalline arrangement of the thick and thin setof filaments, there is a filamentous “cytoskeletalstructure” composed of connectin and desmin.

Meat tenderization is the result of the synergeticeffect of glycolysis and actions of proteases such ascathepsins and calpains. Meat tenderization is a verycomplex multifactorial process controlled by a num-ber of endogenous proteases and some as yet poorlyunderstood biological parameters. With currently

available literature, the following explanation can beconsidered. At the initial postmortem stage, cal-pains, having optimal near neutral pH, attack certainproteins of the Z-line, such as desmin, filamin, neb-ulin, and to a lesser extent, connectin. With the pro-gression of postmortem glycolysis, the pH drops to5.5 to 6.5, which favors the action of cathepsins onmyosin heavy chains, myosin light chains, �-actinin,tropnin C, and actin. This explanation does not ruleout the roles played by other postmortem proteolyticsystems that can contribute to this tenderization.(See Eskin 1990, Haard 1990, Huff-Lonergan andLonergan 1999, Gopakumar 2000, Jiang 2000, Simp-son 2000, Lowrie 1992, and Greaser 2001.)

Table 1.5 lists some of the more common enzymesused in meat tenderization. Papain, ficin, and brome-lain are proteases of plant origin that can breakdownanimal proteins. They have been applied in meat ten-derization or in tenderizer formulations industriallyor at the household or restaurant levels. Enzymessuch as pepsins, trypsins, cathepsins, are well knownin the degradation of animal tissues at various sitesof the protein peptide chains. Enteropeptidase (en-terokinase) is also known to activate trypsinogenby cleaving its peptide bond at Lys6-Ile7. Plasmin,

Table 1.4. Locations and Major Functions of Myofibrillar Proteins Associated with the ContractileApparatus and Cytoskeletal Framework

Location Protein Major Function

Contractile apparatusA-band Myosin Muscle contraction

c-protein Binds myosin filamentsF-, H-, I-proteins Binds myosin filaments

M-line M-protein Binds myosin filamentsMyomesin Binds myosin filamentsCreatine kinase ATP synthesis

I-band Actin Muscle contractionTropomyosin Regulates muscle contractionTroponins T, I, C Regulates muscle contraction�-, �-actinins Regulates actin filaments

Cytoskeletal frameworkGAP filaments Connectin (titin) Links myosin filaments to Z-lineN2-Line Nebulin UnknownBy sarcolemma Vinculin Links myofibrils to sarcolemmaZ-line �-actinin Links actin filaments to Z-line

Eu-actinin, filamin Links actin filaments to Z-lineDesmin, vimmentin Peripheral structure to Z-lineSynemin, Z-protein, Z-nin Lattice structure of Z-line

Sources: Eskin 1990, Lowrie 1992, Huff-Lonergan and Lonergan 1999, Greaser 2001.

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Table 1.5. Proteases in Animal Tissues and Their Degradation

Enzyme Reaction

Acid/aspartyl proteasesPepsin A (Pepsin, EC 3.4.23.1) Preferential cleavage, hydrophobic, preferably aromatic,

residues in P1 and P�1 positionsGastricsin (pepsin C, EC 3.4.23.3) More restricted specificity than pepsin A; high preferential

cleavage at Tyr bondCathepsin D (EC 3.4.23.5) Specificity similar to, but narrower than that of pepsin A

Serine proteasesTrypsin (�- and �-trypsin, EC 3.4.21.4) Preferential cleavage: Arg-, Lys-Chymotrypsin (Chymotrypsin A and B, Preferential cleavage: Tyr-, Trp-, Phe-, Leu-

EC 3.4.21.1)Chymotrysin C (EC 3.4.21.2) Preferential cleavage: Leu-, Tyr-, Phe-, Met-, Trp-, Gln-, Asn-Pancreatic elastase (pancreato- Hydrolysis of proteins, including elastin. Preferential

peptidase E, pancreatic elastase I, cleavage: Ala�EC 3.4.21.36)

Plasmin (fibrinase, fibrinolysin, Preferential cleavage: Lys- � Arg-; higher selectivity EC 3.4.21.7) than trypsin

Enteropeptidase (enterokinase, Activation of trypsinogen be selective cleavage of Lys6-Ile7

EC 3.4.21.9) bondCollagenase General term for hydrolysis of collagen into smaller

moleculesThio/cysteine proteases

Cathepsin B (cathepsin B1, EC 3.4.22.1) Hydrolysis of proteins, with broad specificity for peptide bonds, preferentially cleaves -Arg-Arg- bonds in smallmolecule substrates

Papain (EC 3.4.22.2) Hydrolysis of proteins, with broad specificity for peptide bonds, but preference for an amino acid bearing a largehydrophobic side chain at the P2 position. Does not acceptVal in P1�

Fiacin (ficin, EC 3.4.23.3) Similar to that of papainBromelain (3.4.22.4) Broad specificity similar to that of pepsin A�-glutamyl hydrolase (EC 3.4.22.12 Hydrolyzes �-glutamyl bonds

changed to 3.4.1.99)Cathepsin H (EC 3.4.22.16) Hydrolysis of proteins; acts also as an aminopeptidase

(notably, cleaving Arg bond) as well as an endopeptidaseCalpain-1 (EC 3.4.22.17 changed to Limited cleavage of tropinin I, tropomyosin, and C-protein

3.4.22.50) from myofibrils and various cytoskeletal proteins fromother tissues. Activates phosphorylase, kinase, and cyclic-nucleotide-dependent protein kinase

MetalloproteasesProcollagen N-proteinase (EC 3.4.24.14) Cleaves N-propeptide of procollagen chain �1(I) at Pro�

Gln and �1(II) and �2(I) at Ala�Gln

Sources: Eskin 1990, Haard 1990, Lowrie 1992, Huff-Lonergan and Lonergan 1999, Gopakumar 2000, Jiang 2000,Simpson 2000, Greaser 2001, IUBMB-NC website (www.iubmb.org).

01CH_Hui_277065 10/18/05 7:36 AM Page 11


pancreatic elastase and collagenase are responsiblefor the breakdown of animal connective tissues.

TRANSGLUTAMINASE ACTIVITY IN SEAFOODPROCESSING

Transglutaminase (TGase, EC 2.3.2.13) has the sys-tematic name of protein-glutamine �-glutamyltrans-ferase. It catalyzes the acyl transfer reaction between�-carboxyamide groups of glutamine residues in pro-teins, peptides, and various primary amines. Whenthe �-amino group of lysine acts as acyl acceptor, itresults in polymerization and inter- or intramolecularcross-linking of proteins via formation of �-(�-glu-tamyl) lysine linkages. This occurs through exchangeof the �-amino group of the lysine residue for ammo-nia at the carboxyamide group of a glutamine residuein the protein molecule(s). Formation of covalentcross-links between proteins is the basis for TGase tomodify the physical properties of protein foods. Theaddition of microbial TGase to surimi significantlyincreases its gel strength, particularly when the suri-mi has lower natural setting abilities (presumablydue to lower endogenous TGase activity). Thus far,the primary applications of TGase in seafood pro-cessing have been for cold restructuring, cold gela-tion of pastes, or gel-strength enhancement throughmyosin cross-linking. In the absence of primaryamines, water may act as the acyl acceptor, resultingin deamination of �-carboxyamide groups of gluta-mine to form glutamic acid (Ashie and Lanier 2000).

PROTEOLYSIS DURING CHEESE FERMENTATION

Chymosin (rennin) is an enzyme present in the calfstomach. In cheese making, lactic acid bacteria(starter) gradually lower the milk pH to the 4.7 thatis optimal for coagulation by chymosin. Most lacticacid starters have limited proteolytic activities. How-ever, other added lactic acid bacteria have muchstronger proteolytic activities. These proteases andpeptidases break down the milk caseins to smallerprotein molecules and, together with the milk fat,provide the structure of various cheeses. Other en-zymes such as decarboxylases, deaminases, andtransaminase are responsible for the degradations ofamino acids into secondary amines, indole, �-ketoacids, and other compounds that give the typical fla-vor of cheeses. Table 1.6 lists some of these en-zymes and their reactions.

PROTEOLYSIS IN GERMINATING SEEDS

Proteolytic activities are much lower in germinatingseeds. Only aminopeptidase and carboxypeptidaseA are better known enzymes (Table 1.7). They pro-duce peptides and amino acids that are needed in thegrowth of the plant.

PROTEASES FOR CHILL-HAZE REDUCTION INBEER PRODUCTION

In beer production, a small amount of protein is dis-solved from the wheat and malt into the wort.During extraction of green beer from the wort, thisprotein fraction is also carried over to the beer.Because of its limited solubility in beer at lowertemperatures, it precipitates out and causes hazing inthe final product. Proteases of plant origin such aspapain, ficin, and bromelain, and possibly othermicrobial proteases, can break down these proteins.Addition of one or more of these enzymes is com-monly practiced in the brewing industry to reducethis chill-haze problem.

BIOCHEMICAL CHANGES OFLIPIDS IN FOODS

CHANGES IN LIPIDS IN FOOD SYSTEMS

Research reports on enzyme-induced changes inlipids in foods are abundant. In general, they areconcentrated on changes in the unsaturated fattyacids or the unsaturated fatty moieties in acylglyc-erols (triglycerides). The most studied are linoleate(linoleic acid) and arachidonate (arachidonic acid)as they are quite common in many food systems(Table 1.8). Because of the number of double bondsin arachidonic acid, enzymatic oxidation can occurat various sites, and the responsible lipoxygenasesare labeled according to these sites (Table 1.8).

CHANGES IN LIPIDS DURING CHEESEFERMENTATION

Milk contains a considerable amount of lipids andthese milk lipids are subjected to enzymatic oxida-tion during cheese ripening. Under proper cheesematuration conditions, these enzymatic reactionsstarting from milk lipids create the desirable flavorcompounds for these cheeses. These reactions arenumerous and not completely understood, so only

01CH_Hui_277065 10/18/05 7:36 AM Page 12


Table 1.6. Proteolytic Changes in Cheese Manufacturing

Action and Enzymes Reaction

CoagulationChymosin (rennin, EC 3.4.23.4) �-Casein → Para-�-casein � glycopeptide, similar to

pepsin AProteolysis

Proteases Proteins → high molecular weight peptides � amino acidsAmino peptidases, dipeptidases, Low molecular weight peptides → amino acids

tripeptidasesProteases, endopeptidases, High molecular weight peptides → low molecular weight

aminopeptidases peptidesDecomposition of amino acids

Aspartate transaminase (EC 2.6.1.1) L-Asparate � 2-oxoglutarate → oxaloacetate � L-glutamateMethionine �-lyase (EC 4.4.1.11) L-methionine → methanethiol � NH3 � 2-oxobutanolateTryptophanase (EC 4.1.99.1) L-tryptophan � H2O → indole � pyruvate � NH3Decarboxylases Lysine → cadaverine

Glutamate → aminobutyric acidTyrosine → tyramineTryptophan → tryptamineArginine → putrescineHistidine → histamine

Deaminases Alanine → pyruvateTryptophan → indoleGlutamate → �-ketoglutarateSerine → pyruvateThreonine → �-ketobutyrate

Sources: Schormuller 1968; Kilara and Shahani 1978; Law 1984a,b; Grappin et al. 1985; Gripon 1987; Kamaly andMarth 1989; Khalid and Marth 1990; Steele 1995; Walstra et al. 1999; IUBMB-NC website (www.iubmb.org).

Table 1.7. Protein Degradation in Germinating Seeds

Enzyme Reaction

Aminopeptidase (EC 3.4.11.11* deleted in 1992, Neutral or aromatic aminoacyl-peptide � H2O →referred to corresponding aminopeptidase) neutral or aromatic amino acids � peptide

Carboxypeptidase A (EC 3.4.17.1) Release of a C-terminal amino acid, but little or no action with -Asp, -Glu, -Arg, -Lys, or -Pro

Sources: Stauffer 1987a,b; Bewley and Black 1994; IUBMB-NC website (www.iubmb.org).

general reactions are provided (Table 1.9). Readersshould refer to chapters 19, 20, and 26 in this bookfor a detailed discussion.

LIPID DEGRADATION IN SEED GERMINATION

During seed germination, the lipids are degradedenzymatically to serve as energy source for plantgrowth and development. Because of the presence ofa considerable amount of seed lipids in oilseeds,

they have attracted the most attention, and variouspathways in the conversion of fatty acids have beenreported (Table 1.10). The fatty acids hydrolyzedfrom the oilseed glycerides are further metabolizedinto acyl-CoA. From acyl-CoA, it is converted toacetyl-CoA and eventually used to produce energy.It is reasonable to believe that similar patterns alsoexist in other nonoily seeds. Seed germination isimportant in production of malted barley flour forbread making and brewing. However, the changes of

01CH_Hui_277065 10/18/05 7:36 AM Page 13


Table 1.9. Changes in Lipids in Cheese Manufacturing

Enzyme or Actions Reaction

LipolysisLipases, esterases Triglycerides → �-keto acids, acetoacetate, fatty

acidsAcetoacetate decarboxylase (EC 4.1.1.4) Acetoacetate � H� → acetone � CO2Acetoacetate-CoA ligase (EC 6.2.1.16) Acetoacetate � ATP � CoA → acetyl CoA �

AMP � diphosphateEsterases Fatty acids → esters

Conversion of fatty acids�-oxidation and decarboxylation �-Keto acids → methyl ketonesSources: Schormuller 1968, Kilara and Shahani 1978, IUBMB-NC website (www.iubmb.org).

Table 1.10. Lipid Degradation in Seed Germination

Enzyme or Enzyme System Reaction

Lipase (oil body) Triacylglycerol → diacylglycerol � fatty acidTriacylglycerol → monoacylglycerol � fatty acidsDiacylglycerol → monoacylglycerol � fatty acidFatty acid � CoA → acyl CoA

�-oxidation (glyoxysome) Acyl CoA → acetyl CoAGlyoxylate cycle (glyoxysome) Acetyl CoA → succinateMitochondrion Succinate → phosphoenol pyruvateReverse glycolysis (Cytosol) Phosphoenol pyruvate → hexoses → sucrose

Sources: Bewley and Black 1994, Murphy 1999.

Table 1.8. Enzymatic Lipid Oxidation in Food Systems

Enzyme Reaction

Arachidonate-5-lipoxygenase (5-lipoxygenase, Arachidonate � O2 → (6E, 8Z, 11Z, 14Z)-(5S)-EC 1.13.11.34) 5-hydroperoxyicosa-6-8-11,14-tetraenoate

Arachidonate-8-lipoxygenase (8-lipoxygeanse, Arachidonate � O2 → (5Z, 9E, 11Z, 14Z)-(8R)-EC 1.13.11.40) 8-hydroperoxyicosa-5,9,11,14-tetraenoate

Arachidonate 12-lipoxygenase (12-lipoxygenase, Arachidonate � O2 → (5Z, 8Z, 10E, 14Z)-(12S)-EC 1.13.11.31) 12-hydroperoxyicosa-5,8,10,14-tetraenoate

Arachidonate 15-lipoxygenase (15-lipoxygenase, Arachidonate � O2 → (5Z, 8Z, 11Z, 13E)-(15S)-EC 1.13.11.33) 15-hydroperoxyicosa-5,8,11,13-tetraenoate

Lipoxygenase (EC 1.13.11.12) Linoleate � O2 → (9Z, 11E)-(13S)-13-hydroperoxyoctadeca-9, 11-dienoate

Sources: Lopez-Amaya and Marangoni 2000a,b; Pan and Kuo 2000; Kolakowska 2003; IUBMB-NC website(www.iubmb.org).

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lipids in these seeds are of less importance than theactivity of �-amylase.

BIOGENERATION OF FRESH-FISH ODOR

The main enzymes involved in biogeneration of thearoma in fresh fish have been reported as the 12- and15-lipoxygenases (Table 1.8) and hydroperoxidelyase. The 12-lipoxygenase acts on specific polyun-saturated fatty acids and produces n-9-hydroperox-ides. Hydrolysis of the 9-hydroperoxide of eicos-apentenoic acid by specific hydroperoxide lyasesleads to the formation of mainly (Z,Z)-3-6-nonadi-enal, which can undergo spontaneous or enzyme-catalyzed isomerization to (E,Z)-2,6-nonadienal.These aldehydes may undergo reduction to theircorresponding alcohols. This conversion is a signifi-cant step in the general decline of the aroma intensi-ty due to the fact that alcohols have somewhat higherodor detection thresholds than the aldehydes (John-son and Linsay 1986, German et al. 1992).

BIOCHEMICALLY INDUCEDFOOD FLAVORS

Many fruits and vegetables produce flavors that aresignificant in their acceptance and handling. Thereare a few well-known examples (Table 1.11). Garlicis well known for its pungent odor due to the enzy-matic breakdown of its alliin to the thiosulfonateallicin, with the characteristic garlic odor. Straw-berries have a very typical pleasant odor when theyripen. Biochemical production of the key compound

responsible for strawberry flavor [2,5-dimethyl-4-hydroxy-2H-furan-3-one (DMHF)] is now known. Itis the result of hydrolysis of terminal nonreducing�-D-glucose residues from DMHF-glucoside withrelease of �-D-glucose and DMHF. Lemon andorange seeds contain limonin, a bitter substance thatcan be hydrolyzed to limonate, which creates a lessbitter taste sensation. Many cruciferous vegetablessuch as cabbage and broccoli have a sulfurous odordue to the production of a thiol after enzymatichydrolysis of its glucoside. These are just someexamples of biochemically induced fruit and veg-etable flavors. Brewed tea darkens after it is exposedto air due to enzymatic oxidation. Flavors fromcheese fermentation and fresh-fish odor have al-ready been described earlier. Formation of fishyodor will be described later (see below). Readersinterested in this subject should consult Wong(1989) for earlier findings of chemical reactions.Huang’s review on biosynthesis of natural aromacompounds derived from amino acids, carbohy-drates, and lipids should also be consulted (2005).

BIOCHEMICAL DEGRADATIONAND BIOSYNTHESIS OF PLANTPIGMENTS

DEGRADATION OF CHLOROPHYL IN FRUITMATURATION

Green fruits are rich in chlorophylls that are gradu-ally degraded during ripening. Table 1.12 shows

Table 1.11. Selected Enzyme-Induced Flavor Reactions

Enzyme Reaction

Alliin lyase (EC 4.4.1.4), (garlic, onion) An S-alkyl-L-cysteine S-oxide → an alkyl sufenate � 2-aminoacrylate

�-glucosidase (EC 3.2.1.21) (strawberry) Hydrolysis of terminal nonreducing �-D-glucose residues with release of �-D-glucose

[2,5-Dimethyl-4-hydroxy-2H-furan-3-one (DMHF)-glucoside → DMHF]

Catechol oxidase (EC 1.10.3.1), (tea) 2 Catechol � O2 → 2 1,2-benzoquinone � 2 H2OLimonin-D-ring-lactonase (EC 3.1.1.36) (lemon Limonoate-D-ring-lactone � H2O → limonate

and orange seeds)Thioglucosidase (EC 3.2.1.147) (cruciferous A thioglucoside � H2O → A thiol � a sugar

vegetables)

Sources: Wong 1989, Eskin 1990, Chin and Lindsay 1994, Orruno et al. 2001, IUBMB-NC website (www.iubmb.org).

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some of the enzymatic reactions proposed in thedegradation of chlorophyll a (Table 1.12).

MEVALONATE AND ISOPENTYL DIPHOSPHATEBIOSYNTHESIS PRIOR TO FORMATION OFCAROTENOIDS

Table 1.13 lists the sequence of reactions in the for-mation of (R)-mevalonate from acetyl-CoA, andfrom (R)-mevalonate to isopentyl diphosphate. Iso-pentyl diphosphate is a key building block for caro-tenoids (Croteau et al. 2000). Carotenoids are thegroup of fat-soluble pigments that provides the yel-low to red colors of many common fruits such asyellow peaches, papayas, and mangoes. During post-harvest maturation, these fruits show intense yellowto yellowish orange colors due to synthesis of caro-tenoids from its precursor isopentyl diphosphate,which is derived from (R)-mevalonate. Biosynthesesof carotenoids and terpenoids have a common pre-

cursor, (R)-mevalonate derived from acetyl-CoA(Table 1.13). (R)-mevalonate is also a building blockfor terpenoid biosynthesis (Croteau et al. 2000;IUBMB website).

NARINGENIN CHALCONE BIOSYNTHESIS

Flavonoids are a group of interesting compoundsthat not only give fruits and vegetables various red, blue, or violet colors, but also are related to the group of bioactive compounds called stilbenes.They have a common precursor of trans-cinnamatebranching out into two routes, one leading to theflavonoids, and the other leading to stilbenes (Table1.14; IUBMB website). Considerable interest hasbeen given to the stilbene trans 3,5,4’-trihydroxystil-bene (commonly called reveratrol or resveratrol) inred grapes and red wine that may have potent antitu-mor properties and to another stilbene, combretas-tatin, with potential antineoplastic activity (Croteau

Table 1.12. Degradation of Chlorophyll

Enzyme Reaction

Chlorophyllase (EC 3.1.1.4) Chlorophyll → chlorophyllide � phytolMagnesium dechelatase (EC not available) Chlorophyllide a → phyeophorbide a � Mg2�Phyeophorbide a oxygenase (EC not available) Phyeophorbide a � O2 → red chlorophyll

catabolite (RCC)RCC reductase (EC not available) RCC → fluorescent chlorophyll catabolite (FCC)Various enzymes FCC → nonfluorescent chlorophyll catabolites

(NCC)

Sources: Eskin 1990, Dangl et al. 2000, IUBMB-NC website (www.iubmb.org).

Table 1.13. Mevalonate and Isopentyl Diphosphate Biosyntheses

Enzyme Reaction

Acetyl-CoA C-acetyltransferase (EC 2.3.1.9) 2 acetyl-CoA → acetoacetyl-Co-A � CoAHydroxymethylglutaryl-CoA-synthase Acetoacetyl-CoA � acetyl-CoA � H2O → (S)-

(EC 2.3.3.10) 3-hydroxy-3-methylglutaryl CoA � CoAHydroxymethylglutaryl-CoA reductase (NADPH2) (S)-3-hydroxy-3-methylglutaryl-CoA � 2 NADPH2

(EC 1.1.1.34) → (R)-mevalonate � CoA � 2 NADPMevaldate reductase (EC 1.1.1.32) (R)-mevalonate � NAD → mevaldate � NADH2Mevalonate kinase (EC 2.7.1.36) (R)-mevalonate � ATP → (R)-5-

phosphomevalonate �ADPPhosphomevalonate kinase (EC 2.7.4.2) (R)-5-phosphomevalonate � ATP → (R)-5-

diphosphomevalonate � ADPDiphosphomevalonate decarboxylase (EC 4.1.1.33) (R)-5-diphosphomevalonate � ATP → isopentyl

diphosphate � ADP � phosphate � CO2Sources: Croteau et al. 2000, IUBMB-NC Enzyme website (www.iubmb.org).

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et al. 2000). Table 1.14 gives the series of reactionsin the biosynthesis of naringenin chalcone. Naring-enin chalcone is the building block for flavonoidbiosynthesis. The pathway for the biosynthesis of astilbene pinosylvin and 3,4’5’-trihydroxystilbenehas been postulated (IUBMB website).

SELECTED BIOCHEMICALCHANGES IMPORTANT IN THEHANDLING AND PROCESSING OFFOODS

PRODUCTION OF AMMONIA ANDFORMALDEHYDE FROM TRIMETHYLAMINE ANDITS N-OXIDE

Trimethylamine and its N-oxide have long beenused as indices for freshness in fishery products.Degradation of trimethylamine and its N-oxide leadsto the formation of ammonia and formaldehyde withundesirable odors. The pathway on the production offormaldehyde and ammonia from trimethylamineand its N-oxide is shown in Figure 1.2.

PRODUCTION OF BIOGENIC AMINES

Most live pelagic and scombroid fish (e.g., tunas,sardines, and mackerel) contain an appreciableamount of histidine in the free state. In postmortemscombroid fish, the free histidine is converted by thebacterial enzyme histidine decarboxylase into freehistamine. Histamine is produced in fish caught 40–50 hours after death when fish are not properlychilled. Improper handling of tuna and mackerelafter harvest can produce enough histamine to causefood poisoning (called scombroid or histamine poi-soning). The common symptoms of this kind of foodpoisoning are facial flushing, rashes, headache, and

gastrointestinal disorder. These disorders seem to bestrongly influenced by other related biogenic amines,such as putrescine and cadaverine, produced by sim-ilar enzymatic decarboxylation (Table 1.15). The

Table 1.14. Naringenin Chalcone Biosynthesis

Enzyme Reaction

Phenylalanine ammonia-lyase (EC 4.3.1.5) L-phenylalanine → trans-cinnamate � NH3Trans-cinnamate 4-monoxygenase (EC 1.14.13.11) Trans-cinnamate � NADPH2 � O2 → 4-

hydroxycinnamate � NADP � H2O4-Coumarate-CoA ligase (EC 6.2.1.12) 4-hydroxycinnamate (4-coumarate) � ATP � CoA

→ 4-coumaroyl-CoA � AMP � diphosphateNaringinin-chalcone synthase (EC 2.3.1.74) 4-coumaroyl-CoA � 3 malonyl-CoA → naringinin

chalcone � 4 CoA � 3 CO2Sources: Eskin 1990, Croteau et al. 2000, IUBMB-NC Enzyme website (www.iubmb.org).

Figure 1.2. Degradation of trimethylamine and its N-oxide. Trimethylamine N-oxide reductase (EC 1.6.6.9),Trimethylamine dehydrogenase (EC 1.5.8.2),Dimethylamne dehydrogenase (EC 1.5.8.1), Aminedehydrogenase (EC 1.4.99.3). [Haard et al. 1982,Gopakumar 2000, Stoleo and Rehbein 2000, IUBMB-NC website (www.iubmb.org)]

01CH_Hui_277065 10/18/05 7:36 AM Page 17

POLYPHENOL OXIDASE BROWNING

Polyphenol oxidase (PPO, EC 1.10.3.1, systematicname 1,2 benzenediol:oxygen oxidoreductase) isalso labeled as phenoloxidase, phenolase, monophe-nol and diphenol oxidase, and tyrosinase. This en-zyme catalyzes one of the most important color re-actions that affects many fruits, vegetables, andseafood, especially crustaceans. This postmortemdiscoloration in crustacean species such as lobster,shrimp, and crab is also called melanosis or blackspot. It connotes spoilage, is unacceptable to con-sumers, and thus reduces the market value of theseproducts.

Polyphenol oxidase is responsible for catalyzingtwo basic reactions. In the first reaction, it catalyzesthe hydroxylation of phenols with oxygen, to the o-position adjacent to an existing hydroxyl group.For example, tyrosine, a monohydroxy phenol, ispresent naturally in crustaceans. PPOs from shrimpand lobster are activated by trypsin or by a trypsin-like enzyme in the tissues to hydroxylate tyrosinewith the formation of dihydroxylphenylamine(DOPA). The second reaction is the oxidation of thediphenol to o-benzoquinones, which are further oxi-dized to melanins (brown to dark products), usuallyby nonenzymatic mechanisms.

The major effect of reducing agents or antioxi-dants in the prevention of browning is their ability toreduce the o-quinones to the colorless diphenols, orto react irreversibly with the o-quinones to form stable colorless products. The use of reducing com-pounds is the most effective control method for PPObrowning. The most widespread antibrowning treat-ment used by the food industry was the addition ofsulfiting agents. However, because of safety con-cerns, other methods have been developed, includingthe use of other reducing agents (such as ascorbicacid and analogs, cysteine and glutathione), chelat-ing agents (phosphates, EDTA), acidulants (citric


presence of putrescine and cadaverine is more sig-nificant in shellfish, such as shrimp. The detectionand quantification of histamine is fairly simple andinexpensive. However, the detection and quantifica-tion of putrescine and cadaverine are more compli-cated and expensive. It is suspected that histaminemay not be the real and main cause of poisoning, ashistamine is not stable under strong acidic condi-tions such as pH 1 in the stomach. However, theU.S. Food and Drug Administration (FDA) has strictregulations governing the amount of histamine per-missible in canned tuna, as an index of freshness ofthe raw materials, because of the simplicity of hista-mine analysis (Gopakumar 2000).

PRODUCTION OF AMMONIA FROM UREA

Urea is hydrolyzed by urease (EC 3.5.1.5) to ammo-nia, which is one of the components of total volatilebase (TVB). TVB nitrogen has been used as a qualityindex of seafood acceptability by various agencies(Johnson and Linsay 1986, Cadwallader 2000, Go-pakumar 2000). A good example is shark, whichcontains fairly high amounts of urea in the live fish.Under improper handling, urea is converted to am-monia by urease, giving shark meat an ammoniaodor that is not well accepted by consumers. Toovercome this problem, the current practice ofbleeding the shark near its tail right after harvest isvery promising.

ADENOSINE TRIPHOSPHATE DEGRADATION

Adenosine triphosphate (ATP) is present in all bio-logical systems. Its degradation in seafood has oftenbeen reported (Fig. 1.3) (Gill 2000, Gopakumar2000). The degradation products, such as inosineand hypoxanthine, have been used individually or incombination as indices of freshness for many years.

Table 1.15. Secondary Amine Production in Seafoods

Enzyme Reaction

Histidine decarboxyalse (EC 4.1.1.22) L-Histidine → histamine � CO2Lysine decarboxylase (EC 4.1.1.18) L-Lysine → cadaverine � CO2Ornithine decarboxylase (EC 4.1.1.17) L-Ornithine → putrescine � CO2

Sources: Gopakumar 2000, IUBMB-NC website (www.iubmb.org).

01CH_Hui_277065 10/18/05 7:36 AM Page 18


acid, phosphoric acid), enzyme inhibitors, enzymetreatment, and complexing agents. Application ofthese inhibitors of enzymatic browning is strictlyregulated in different countries (Eskin 1990, Gopa-kumar 2000, Kim et al. 2000).

ETHYLENE PRODUCTION IN FRUIT RIPENING

Ethylene acts as one of the initiators in fruit ripen-ing. Its concentration is very low in green fruits butcan accumulate inside the fruit and subsequentlyactivates its own production. Table 1.16 lists theenzymes in the production of ethylene starting frommethionine. The effect of ethylene is commonlyobserved in the shipping of bananas. The banana is aclimacteric fruit with a fast ripening process. Duringshipping of green bananas, ethylene is removedthrough absorption by potassium permanganate torender a longer shelf life.

REDUCTION OF PHYTATE IN CEREALS

Phytic acid (myo-inositol hexaphosphate) is themajor phosphate reserve in many seeds. Since itexists as a mixed salt with elements such as potassi-um, magnesium, and calcium (and as such is calledphytin or phytate), it is also a major source of thesemacronutrient elements in the seed. However, thissalt form of macronutrients renders them unusableby the human body. During seed germination, phy-tase (4-phytase, phytate-6-phosphatase, EC 3.1.3.26)hydrolyzes the phytic acid to release phosphate, itsassociated phosphate cation, and 1-D-myo-inositol1,2,3,4,5-pentakisphosphate. Breakdown of phytateis rapid and complete (Stauffer 1987a,b; Berger1994; Bewley 1997). This enzymatic reaction re-leases the macronutrients from their bound forms sothey are more easily utilized by the human body.This explains why breads utilizing flour from germi-nated wheat are more nutritious than those madefrom regular wheat flour.

BIOTECHNOLOGY IN FOODPRODUCTION, HANDLING, ANDPROCESSING

BIOTECHNOLOGY-DERIVED FOOD ENZYMES

With the advancement of biotechnology, the foodindustry was not slow in jumping on the wagon for

Figure 1.3. Degradation of adenosine triphosphate(ATP) in seafoods. ATP phosphohydrolase (EC3.6.3.15), ADPase (EC 3.6.1.6), AMP deaminase (EC3.5.4.6), 5’-nucleotidase (EC 3.1.3.5), Inosine nucleoti-dase (EC 3.1.3.5), Xanthine oxidase (EC 1.1.3.22). [Gill2000, Gopakumar 2000, IUBMB-NC website(www.iubmb.org)]

01CH_Hui_277065 10/18/05 7:36 AM Page 19


better processing aids. At least six biotechnology-derived enzymes have been developed: acetolactatedecarboxylase, �-amylase, amylo-1,6-glucosidase,chymosin, lactase, and maltogenic �-amylase (Table1.17). Chymosin has now been well adopted by thecheese industry because of reliable supply and rea-sonable cost. Lactase is also well accepted by thedairy industry for the production of lactose-free milkand as a dietary supplement for lactose-intolerantconsumers. Amylases are also being used for theproduction of high fructose corn syrup and as ananti-staling agent for bread. The application of pec-tic enzymes in genetically modified tomatoes wasmentioned earlier. It should be noted that each coun-try has its own regulations governing the use ofthese biotechnology-derived enzymes.

GENETICALLY MODIFIED MICROORGANISMSUSEFUL IN FOOD PROCESSING

Like the biotechnology-derived food enzymes, ge-netically modified microorganisms are being devel-oped for specific needs. Lactic acid bacteria andyeast have been developed to solve problems in the

dairy, baking, and brewing industries (Table 1.18).As with the biotechnology-derived food enzymes,their use is governed by the regulations of individualcountries.

CONCLUSION

The Institute of Food Technologists (IFT), formed inthe United States in 1939, was the world’s first suchorganization to pull together those working in foodprocessing, chemistry, engineering, microbiology,and other subdisciplines who were trying to betterunderstand food and help solve some of its relatedproblems. Now, most countries have similar organi-zations, and the IFT has developed into a worldorganization and the leader in this field.

When we look back into the history of food sci-ence as a discipline, we see that it started out with afew universities in the United States, mainly in com-modity departments, such as animal science, dairyscience, horticulture, cereal science, poultry science,and fishery. Now, in the United States and Canada,most of these programs (about 50 in total) haveevolved into a food science or food science and

Table 1.16. Ethylene Biosynthesis

Enzyme Reaction

Methionine adenosyltransferase L-methionine � ATP � H2O → S-adenosyl-�-(adenosylmethionine synthase, EC 2.5.1.6) methionine � diphosphate � phosphate

Aminocyclopropane carboxylate synthetase S-adenosyl-�-methionine → 1-aminocyclopropane-(EC 4.4.1.14) 1-carboxylate � 5�-methylthio-adenosine

Aminocyclopropane carboxylate oxidase 1-aminocyclopropane-1-carboxylate � ascorbate(EC 4.14.17.4) � 1⁄2 O2 → ethylene � dedroascorbate � CO2

� HCN � H2O

Sources: Eskin 1990, Bryce and Hill 1999, Crozier et al. 2000, Dangl et al. 2000, IUBMB-NC website(www.iubmb.org).

Table 1.17. Selected Commercial Biotechnology-Derived Food Enzymes

Enzyme Application

Acetolactate decarboxylase (EC 4.1.1.5) Beer aging and diacetyl reduction�-amylase (EC 3.2.1.1) High fructose corn syrup (HFCS) productionAmylo-1,6-glucosidase (EC 3.2.1.33) High fructose corn syrup (HFCS) productionChymosin (EC 3.4.23.4) Milk clotting in cheese manufacturingLactase (EC 3.2.1.108) Lactose hydrolysisGlucan 1,4-�-maltohydrolase (maltogenic Anti-staling in bread

�-amylase, EC 3.2.1.133)

Sources: Roller and Goodenough 1999, Anonymous 2000, IUBMB-NC website (www.iubmb.org).

01CH_Hui_277065 10/18/05 7:36 AM Page 20


human nutrition department. The IFT has played animportant role in these developments. There are alsoprograms in other countries where food science isgrouped under other traditional disciplines such asbiology or chemistry. However, some universities ina few countries put more emphasis on food scienceand form a school or a college. Many food sciencedepartments with a food biochemistry emphasis arenow available all over the world, and they promotetheir programs through the Internet. These depart-ments place their emphases on one or more com-modities.

Research reports on various topics of food sci-ence and food technology have been published invarious journals including the Journal of FoodScience, Food Technology, and others. Food-relatedbiochemical studies were published in various jour-nals until 1977, when the first issue of Journal ofFood Biochemistry was published. Although foodbiochemistry–related reports are still published inother journals, establishment of this journal is amilestone for this subdiscipline of food science. Afew books with emphasis on food biochemistry ingeneral and on specific commodities/componentshave also become available in the past 40 years.

Over the past several decades, many food bio-chemistry–related problems have been resolved, andthese solutions have resulted in industry applica-tions. Examples of such achievements as lactase,lactose-free milk, “Beano™,” transgenic tomatoeswith easier ripening control, application of transglu-taminase to control seafood protein restructuring,proteases for meat tenderization, production of highfructose syrups, and others have been discussed ear-lier. With the recent interest and development inbiotechnology, food biochemists are trying to applythis new technique to help solve many food-relatedbiochemical problems. These may include but not

be limited to those in food safety, improved nutrientcontent, delayed food spoilage, better raw materialsfor processing and product development, better pro-cessing technology, and less expensive flavoringmaterials. In the near future, we should not be sur-prised when researchers report breakthroughs thatare food biochemistry related. In fact, this is expect-ed, as we now have better trained researchers andmore advanced research tools. Although its studyrequires a diversified background, food biochem-istry is gaining more interest in the food science dis-cipline. It is an area that will attract more students,especially with the current interest in biotechnology.

ACKNOWLEDGEMENTS

I would like to thank Prof. C. S. Tang, Departmentof Molecular Biosciences and Bioengineering, Uni-versity of Hawaii at Manoa, Honolulu, Hawaii, andProf. Mike Morgan, Proctor, Department of FoodScience, University of Leeds, United Kingdom, fortheir constructive suggestions on the chapter outlineand critical comments in the preparation of thischapter.

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Table 1.18. Selected Genetically Modified Microorganisms Useful in Food Processing

Microorganisms Application

Lactobacillus lactis Phage resistance, lactose metabolism, proteolytic activity, bacteriocin production

Saccharomyces (Baker’s yeast) Gas (carbon dioxide) production in sweet, high-sugar dough

Saccharomyces cervisiae (Brewer’s yeast) Manufacture of low-calorie beer (starch degradation)

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