Geoffrey Campbell-Platt€¦ · BLBK179-Campbell-Platt June 29, 2009 11:45 This edition ﬁrst...

BLBK179-Campbell-Platt June 29, 2009 11:45

Food Science and Technology

Edited by

Geoffrey Campbell-PlattProfessor Emeritus of Food Technology, University of Reading

President of IUFoST 2008–2010

A John Wiley & Sons, Ltd., Publication

iii



i


ii



Edited by

Geoffrey Campbell-PlattProfessor Emeritus of Food Technology, University of Reading

President of IUFoST 2008–2010

A John Wiley & Sons, Ltd., Publication

iii


This edition first published 2009C© 2009 Blackwell Publishing Ltd

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Library of Congress Cataloging-in-Publication Data

Food science and technology / edited by Geoffrey Campbell-Platt.p. ; cm.

Includes bibliographical references and index.ISBN 978-0-632-06421-2 (hardback : alk. paper)1. Food industry and trade. 2. Biotechnology. I. Campbell-Platt, Geoffrey.

II. International Union of Food Science and Technology.[DNLM: 1. Food Technology. 2. Biotechnology. 3. Food Industry.

4. Nutritional Physiological Phenomena. TP 370 F6865 2009]TP370.F629 2009664–dc22 2009001743

A catalogue record for this book is available from the British Library.

Set in 9.5/12pt Palatino by Aptara R© Inc., New Delhi, IndiaPrinted in Singapore

1 2009

iv

http://www.wiley.com/wiley-blackwell

http://www.wiley.com/wiley-blackwell


Contents

List of contributors viii

1 Introduction 1Geoffrey Campbell-Platt

1.1 Food science and technology courseelements 1

1.2 Evolution of the book 11.3 Food safety assurance 21.4 The International Union of Food

Science and Technology (IUFoST) 21.5 The book 3

2 Food chemistry 5Richard A. Frazier

2.1 Introduction 52.2 Carbohydrates 52.3 Proteins 122.4 Lipids 202.5 Minor components of foods 242.6 Water in foods 252.7 Physical chemistry of dispersed

systems 272.8 Chemical aspects of organoleptic

properties 30

3 Food analysis 33Heinz-Dieter Isengard and Dietmar Breithaupt

3.1 Macro analysis 333.2 Instrumental methods 45

4 Food biochemistry 57Brian C. Bryksa and Rickey Y. Yada

4.1 Introduction 574.2 Carbohydrates 58

4.3 Proteins 674.4 Lipids 734.5 Nucleic acids 774.6 Enzymology 794.7 Food processing and storage 814.8 Summary 82

5 Food biotechnology 85Cherl-Ho Lee

5.1 History of food biotechnology 855.2 Traditional fermentation technology 865.3 Enzyme technology 1025.4 Modern biotechnology 1055.5 Genetic engineering 1095.6 Tissue culture 1115.7 Future prospects 111

6 Food microbiology 115Tim Aldsworth, Christine E.R. Doddand Will Waites

6.1 Introduction 1156.2 Microorganisms important to the

food industry 1166.3 Microscopic appearance of

microorganisms 1166.4 Culturing microorganisms 1176.5 Microbial growth 1196.6 Methods of measuring growth 1196.7 Microbial biochemistry and

metabolism 1206.8 Agents of foodborne illness 1216.9 Outbreaks 1406.10 An outbreak that wasn’t! 1426.11 Incidence of foodborne illness 143

v


vi Contents

6.12 The Richmond Report on themicrobiological safety of food 144

6.13 Water-borne diseases 1446.14 Traditional and novel methods of

microbial detection 1466.15 Microbiological sampling plans 1536.16 Hazard Analysis and Critical

Control Points 1586.17 Hygienic factory design 1606.18 Microbial fermentation 162

7 Numerical procedures 175R. Paul Singh

7.1 SI system of units 1757.2 Rules for using SI units 1797.3 Equation 1817.4 Graphs – linear and exponential

plots 1857.5 Calculus 186

8 Food physics 193Keshavan Niranjan and Gustavo FidelGutierrez-Lopez

8.1 Physical principles 1938.2 Material properties 202

9 Food processing 207Jianshe Chen and Andrew Rosenthal

9.1 Fundamentals of fluid flow 2089.2 Principles of heat transfer 2159.3 Unit operations 2199.4 Food preservation 2349.5 Food processes and flowcharts 243

10 Food engineering 247R. Paul Singh

10.1 Engineering aspects of hygienicdesign and operation 247

10.2 Cleaning and sanitizing 25010.3 Process controls 25310.4 Storage vessels 25910.5 Handling solid foods in a

processing plant 26010.6 Storage of fruits and vegetables 26410.7 Refrigerated transport of fruits

and vegetables 26610.8 Water quality and wastewater

treatment in food processing 271

11 Food packaging 279Gordon L. Robertson

11.1 Requirements of packagingmaterials 279

11.2 Classification of packagingmaterials 280

11.3 Permeability characteristics ofplastic packaging 284

11.4 Interactions between packagingmaterials and food 290

11.5 Packaging systems 29211.6 Package closures and

integrity 29411.7 Environmental impacts of

packaging 295

12 Nutrition 299C. Jeya Henry and Lis Ahlstrom

12.1 Introduction 29912.2 Human energy requirements 29912.3 Protein 30512.4 Carbohydrates 31112.5 Lipids and energy density 31412.6 Micronutrients – vitamins,

minerals and trace minerals 317

13 Sensory evaluation 323Herbert Stone and Rebecca N. Bleibaum

13.1 Introduction 32313.2 Background and definition 32413.3 Facilities 32613.4 Subjects 32813.5 Methods 331

14 Statistical analysis 341Herbert Stone and Rebecca N. Bleibaum

14.1 Introduction 34114.2 Descriptive statistics 34214.3 Inferential statistics 34314.4 Correlation, regression, and

multivariate statistics 344

15 Quality assurance and legislation 353David Jukes

15.1 Introduction 35315.2 Fundamentals of food law 35415.3 Food quality management

systems 36415.4 Statistical process control 378


Contents vii

16 Regulatory toxicology 399Gerald G. Moy

16.1 Introduction 39916.2 Regulatory toxicology 40016.3 Chemical hazards in food 40316.4 Conclusions 408

17 Food business management: principlesand practice 411Michael Bourlakis, David B. Grant andPaul Weightman

17.1 Introduction 41117.2 The food business environment 41117.3 The UK food chain system 41317.4 Characteristics of UK food retailers 41417.5 Characteristics of UK food

processors 41617.6 Marketing in food business

management 41717.7 Food operations management 41717.8 Human resource management 42417.9 Finance and accounting for food

firms 42517.10 Conclusions 430

18 Food marketing 433Takahide Yamaguchi

18.1 Introduction 43318.2 Marketing principles 434

18.3 Marketing research 43518.4 Strategic marketing and the

marketing plan 441

19 Product development 447Ray Winger

19.1 Introduction 44719.2 Background 44819.3 Class protocols 453

20 Information technology 463Sue H.A. Hill and Jeremy D. Selman

20.1 PC software packages 46320.2 Managing information 46920.3 Electronic communication 472

21 Communication and transferable skills 479Jeremy D. Selman and Sue H.A. Hill

21.1 Study skills 48021.2 Information retrieval 48221.3 Communication and

presentational skills 48721.4 Team and problem solving

skills 490

Index 495

Color plate section after page 340


Contributors

Chapter 1

Professor Geoffrey Campbell-PlattProfessor Emeritus of Food

TechnologyUniversity of Reading; President of IUFoST

2008–2010WhiteknightsReadingRG6 6APUnited Kingdom

Chapter 2

Dr Richard A. FrazierSenior Lecturer in Food

BiochemistryDepartment of Food BiosciencesUniversity of ReadingWhiteknightsReadingRG6 6APUnited Kingdom

Chapter 3

Professor Heinz-Dieter IsengardUniversity of HohenheimInstitute of Food Science and

BiotechnologyD-70593 StuttgartGermany

Professor Dietmar BreithauptUniversity of HohenheimInstitute of Food ChemistryD-70593 StuttgartGermany

Chapter 4

Mr Brian C. BryksaDepartment of Food ScienceUniversity of GuelphGuelphOntario N1G 2W1Canada

Professor Rickey Y. YadaCanada Research Chair in Food Protein StructureScientific Director, Advanced Foods and Materials

Network (AFMNet)Department of Food ScienceUniversity of GuelphGuelphOntario N1G 2W1Canada

Chapter 5

Professor Cherl-Ho LeeDivision of Food Bioscience and TechnologyCollege of Life Sciences and BiotechnologyKorea University1 Anamdong, Sungbukku,Seoul136-701 Korea

viii


Contributors ix

Chapter 6

Dr Tim AldsworthThe University of HertfordshireCollege Lane CampusHatfieldAL10 9ABUnited Kingdom

Professor Christine E.R. Doddand Professor Will Waites

Division of Food SciencesUniversity of NottinghamSutton Bonington CampusLoughboroughLeicestershireLE12 5RDUnited Kingdom

Chapter 7

Professor R. Paul SinghDistinguished Professor of Food EngineeringDepartment of Biological and Agricultural

EngineeringDepartment of Food Science and TechnologyUniversity of CaliforniaOne Shields Avenue DavisCA 95616USA

Chapter 8

Professor Keshavan NiranjanProfessor of Food BioprocessingEditor, Journal of Food EngineeringUniversity of ReadingWhiteknightsPO Box 226ReadingRG6 6APUnited Kingdom

Professor Gustavo Fidel Gutierrez-LopezProfessor of Food EngineeringHead, PhD Program in Food Science and TechnologyEscuela Nacional de Ciencias BiologicasInstituto Politecnico NacionalCarpio y Plan de Ayala S/NSanto Tomas, 11340Mexico, DFMexico

Chapter 9

Dr Jianshe ChenDepartment of Food Science and NutritionUniversity of LeedsLeedsLS2 9JTUnited Kingdom

Dr Andrew RosenthalNutrition and Food Science GroupSchool of Life SciencesOxford Brookes UniversityGipsy Lane CampusOxfordOX3 0BPUnited Kingdom

Chapter 10

Professor R. Paul SinghDistinguished Professor of Food

EngineeringDepartment of Biological and Agricultural

EngineeringDepartment of Food Science and TechnologyUniversity of CaliforniaOne Shields Avenue DavisCA 95616USA


x Contributors

Chapter 11

Professor Gordon L. RobertsonUniversity of Queensland andFood • Packaging • Environment6066 Lugano DriveHope IslandQLD 4212Australia

Chapter 12

Professor C. Jeya HenryProfessor of Food Science and Human NutritionSchool of Life SciencesOxford Brookes UniversityGipsy LaneOxfordOX3 OBPUnited Kingdom

Ms Lis AhlstromResearcherSchool of Life SciencesOxford Brookes UniversityGipsy LaneOxfordOX3 0BPUnited Kingdom

Chapters 13 and 14

Dr Herbert Stone and Dr Rebecca N. BleibaumTragon Corporation350 Bridge ParkwayRedwood ShoresCA 94065-1061USA

Chapter 15

Dr David JukesSenior Lecturer in Food RegulationDepartment of Food BiosciencesUniversity of ReadingWhiteknightsReadingRG6 6APUnited Kingdom

Chapter 16

Dr Gerald G. MoyGEMS/Food ManagerDepartment of Food Safety, Zoonoses and

Foodborne DiseaseWorld Health OrganizationGenevaSwitzerland

Chapter 17

Dr Michael BourlakisSenior LecturerBrunel UniversityBusiness SchoolElliot Jaques BuildingUxbridgeMiddlesexUB8 3PHUnited Kingdom

Professor David B. GrantLogistics InstituteBusiness SchoolUniversity of HullKingston upon HullHU6 7RXUnited Kingdom

Dr Paul WeightmanSchool of Agriculture, Food and Rural

DevelopmentNewcastle UniversityAgriculture BuildingNewcastle upon TyneNE1 7RUUnited Kingdom

Chapter 18

Professor Takahide YamaguchiProfessor of ManagementGraduate School of

AccountancyUniversity of HyogoKobe-Gakuentoshi CampusKobe, 651-2197Japan


Contributors xi

Chapter 19

Professor Ray WingerProfessor of Food TechnologyInstitute of Food, Nutrition and

Human HealthMassey UniversityPrivate Bag 102 904North Shore Mail CentreAlbanyAucklandNew Zealand

Chapters 20 and 21

Dr Sue H.A. Hill and Professor Jeremy D. SelmanManaging Editor and Head of Editorial and

Productionand Managing DirectorInternational Food Information Service

(IFIS Publishing)Lane End HouseShinfield RoadShinfieldReadingRG2 9BBUnited Kingdom


xii


1Introduction

Geoffrey Campbell-Platt

Food science and technology is the understandingand application of science to satisfy the needs of soci-ety for sustainable food quality, safety and security.

At several universities worldwide, degree pro-grammes in food science and technology have beendeveloped in the past half-century. This followed thelead of the University of Strathclyde (then the RoyalCollege of Science and Technology) in Glasgow, Scot-land, under the leadership of the first Professor ofFood Science, who also became President of the In-ternational Union of Food Science and Technology(IUFoST), the late John Hawthorn.

The aim of these courses has been to provide foodscience and technology graduates with the ability,through multidisciplinary studies, to understand andintegrate the scientific disciplines relevant to food.They would then be able to extend their knowledgeand understanding of food through a scientific ap-proach, and to be able to apply and communicate thatknowledge to meet the needs of society, industry andthe consumer for sustainable food quality, safety andsecurity of supply.

1.1 Food science and technologycourse elements

Students studying food science and technology inhigher education need to have undertaken coursesin the basic scientific disciplines of chemistry, bi-ology, mathematics, statistics and physics. Theseare developed in food science and technology de-gree programmes through course elements in Food

Chemistry, Food Analysis, Food Biochemistry, FoodBiotechnology, Food Microbiology, Numerical Proce-dures and Food Physics. These are all covered bychapters in this book, followed by chapters cover-ing Food Processing, Food Engineering and Packag-ing. Further courses are required in Nutrition, Sen-sory Evaluation, Statistical Techniques, and QualityAssurance and Legislation. Regulatory Toxicologyand Food Safety is addressed, as is Food BusinessManagement. Other course elements in Food Market-ing and Product Development are included, togetherwith chapters on Information Technology, and Com-munication and Transferable Skills.

Food science and technology are science-basedcourses, requiring a good grounding in science andthe use of laboratory and pilot-plant facilities, to rein-force the theoretical knowledge acquired. As well asacquiring practical laboratory and observation skills,laboratory experiments need to be written up, devel-oping important reporting and interpretation skills.Universities therefore require up-to-date facilities forchemical, microbiological laboratory exercises, andprocessing pilot-plant facilities for teaching the prin-ciples of unit processing and engineering operations,as well as sufficient well-qualified staff to teach therange of disciplines covered in this book.

1.2 Evolution of the book

The book has evolved from a working group of theCommittee of University Professors of Food Scienceand Technology (CUPFST), United Kingdom, who

1


2 Food Science and Technology

sought to agree a framework of common course el-ements for the various food science and technologycourses established in the UK. Newer universities ad-vised that each course element should be based onoutcomes, which should be achieved on successfulcompletion, and it is these outcome headings thathave largely been used as subject headings in eachchapter of this book. This approach is popular inter-nationally and is used by professional institutes suchas the Institute of Food Science and Technology (IFST)in the UK, and the book has evolved in consulta-tion with the recommended Education Standards forFood Science of the Institute of Food Technologists(IFT) in the USA.

The IFT recognises food science as the discipline inwhich engineering, biological and physical sciencesare used to study the nature of foods, the causes ofdeterioration, the principles underlying food process-ing, and the improvement of foods for the consumingpublic. Food technology is recognised as the appli-cation of food science to the selection, preservation,processing, packaging, distribution and use of safe,nutritious and wholesome food. In short, it could besaid that the food scientist analyses and takes apartfood materials, whilst the food technologist puts allthat knowledge into use in producing safe, desiredfood products. In practice, as recognised throughoutthe world, the terms are often used interchangeably,and practising food scientists and technologists haveto both understand the nature of food materials andproduce safe, nutritious food products.

It is understood, and desirable, that the variousfood science and technology courses offered willvary, reflecting particular research interests and ex-pertise, in different institutions, and students willwant to develop their own interests through spe-cific module choices or individual research projects.However, the purpose of establishing the core com-petencies, reflected in the chapters of this book, isto recognise what a food science or food technologygraduate can be expected to achieve as a minimum,so that employers and regulators know what to ex-pect of a qualified graduate, who could then expect,after suitable relevant experience, to become a mem-ber of a professional body, such as IFT or IFST, or aChartered Scientist.

1.3 Food safety assurance

In our increasingly interdependent globalised world,food safety is an implied term in the ‘food purchas-

ing or food service’ consumer contract, which oftenappears to be addressed publicly only when some-thing goes wrong. In fact, food control agencies andfood retailers require processors and manufactur-ers to apply Hazard Analysis Critical Control Points(HACCP) to all their processes. This, combined withgood practices, such as Good Manufacturing Practice(GMP), and traceability, build quality and safety as-surance into the food chain, which is inherently betterwith the very large number of food items producedand eaten frequently, and when individual item ordestructive testing can only give a limited picture ofthe total production. Both HACCP and GMP requiregood teamwork by all involved in food processing,and it is the multidisciplinary-trained food scientistor technologist who usually is called upon to lead andguide these operations.

In our modern world where food ethics are to thefore, in terms of sustainable production practices,care of our environment, fair-trade, packaging re-cycling and climate-change concerns, food scientistsand technologists will have an increasing role to play,in keeping abreast of these issues and the science thatcan be applied to help address them. Food scientists,to be successful, already need good interpersonal,communication and presentation skills, which maybe learned through example, mentoring and prac-tice in as many different situations as possible; inthe future, these skills promise to be in even greaterdemand, as scientists engage with increasingly de-manding members of the public.

1.4 The International Union ofFood Science and Technology(IUFoST)

IUFoST is the international body representing some65 member countries and some 200,000 food scien-tists and technologists worldwide. IUFoST organisesWorld Congresses of Food Science and Technologyin different locations around the world, normally ev-ery 2 years, at which the latest research and ideas areshared, and the opportunity is provided for youngfood scientists to present papers and posters and tointeract with established world experts. Higher ed-ucation in food science and technology has been ofgreat interest for several years, with many devel-oping countries looking for guidance in establish-ing courses in the subject, or to align them moreclosely with others, to help graduates move more suc-cessfully between countries and regions. IUFoST is


Introduction 3

also helping the development of Distance Education,where people are in employment and not able toattend normal university courses. IUFoST thereforesees the publication of this book as an important partof its contribution to helping internationally in shar-ing knowledge and good practice.

IUFoST has also established the InternationalAcademy of Food Science and Technology (IAFoST),to which eminent food scientists can be elected bypeer review, and are designated as Fellows of IAFoST.The Fellows have acted as lead authors and advis-ers in the increasing range of authoritative ScientificInformation Bulletins published by IUFoST, throughits Scientific Council, which help summarise key foodissues to a wider audience.

1.5 The book

In writing this book, we have been honoured to havethe 20 chapters written by 30 eminent authors, from10 different countries. All authors are experts in theirrespective fields, and together represent 15 of the

world’s leading universities in food science and tech-nology, as well as four leading international organ-isations. We are particularly honoured that severalof the authors are distinguished Fellows of IAFoST,so helping directly to inspire younger potential foodscientists and technologists through this textbook forstudents.

It is therefore hoped that this book is adoptedwidely, providing tutors and students with the ba-sic content of the core components of food scienceand technology degrees, while providing guidancethrough references to further knowledge and formore advanced study. If this work provides the op-portunity to help students worldwide in sharing acommon ideal while developing their own interestsand expertise, the original aim of Professor JohnHawthorn in developing this vital subject, so essen-tial for all of us, from Scotland to a worldwide disci-pline, will have been achieved.

Supplementary material is available atwww.wiley.com/go/campbellplatt


4


2Food chemistry

Richard A. Frazier

Key points� Carbohydrate chemistry: structures, properties and reactions of major monosaccharides,

oligosaccharides and polysaccharides in foods.� Proteins: chemistry of the amino acids and their role in protein structure, a description of the major

forces that stabilize protein structure and how they are disrupted during protein denaturation.� Lipids: structure and nomenclature, polymorphism of triglycerides, oil and fat processing (hydrogenation

and interesterification), and lipid oxidation.� Chemistry of minor components in foods: permitted additives, vitamins and minerals.� Role of water in foods: water activity, its determination and the importance for microbial growth, chemical

reactivity and food texture.� Physical chemistry of dispersed systems: solutions, lyophilic and lyophobic dispersions, colloidal

interactions and the DLVO theory, foams and emulsions.� Chemical aspects of organoleptic properties of foods.

2.1 Introduction

Food chemistry is a fascinating branch of appliedscience that combines most of the sub-disciplines oftraditional chemistry (organic, inorganic and phys-ical chemistry) together with elements of biochem-istry and human physiology. Food chemists attemptto define the composition and properties of food, andunderstand the chemical changes undergone duringproduction, storage and consumption, and how thesemight be controlled. Foods are fundamentally biolog-ical substances and are highly variable and complex;therefore, food chemistry is a constantly evolving andexpanding field of knowledge that underpins other

areas of food science and technology. This chaptercannot hope to encompass all of the intricacies anddetails of food chemistry, but instead attempts to pro-vide an overview of the fundamental areas that con-stitute this important area of science. To delve deeper,the reader is encouraged to refer to one or more ofthe excellent texts relating to food chemistry that arelisted as further reading at the end of this chapter.

2.2 Carbohydrates

Carbohydrate is the collective name for polyhy-droxyaldehydes and polyhydroxyketones, and these

5



compounds form a major class of biomolecules thatperform several functions in vivo, including the stor-age and transport of energy. Indeed, carbohydratesare the major source of energy in our diet. Thename carbohydrate derives from their general em-pirical formula, which is (CH2O)n; however, the car-bohydrate group contains several derivatives andclosely related compounds that do not fit this generalempirical formula but are still considered to be carbo-hydrates. There are three distinct classes of carbohy-drates: monosaccharides (1 structural unit), oligosaccha-rides (2–10 structural units) and polysaccharides (morethan 10 structural units).

2.2.1 Monosaccharides

The monosaccharides are also termed simple sugars,are given the suffix -ose and classified as aldoses orketoses depending on whether they contain an alde-hyde or ketone group. The most common monosac-charides are either pentoses (containing a chain of fivecarbon atoms) or hexoses (containing a chain of sixcarbon atoms). Each carbon atom carries a hydroxylgroup, with the exception of the atom that forms thecarbonyl group, which is also known as the reducinggroup.

Simple sugars are optically active compounds andcan contain several asymmetrical carbon atoms. Thisleads to the possibility for the formation of mul-tiple stereoisomers or enantiomers of the same basicstructure. To simplify matters, monosaccharides areassigned optical configurations with respect to com-parison of their highest numbered asymmetric car-bon atom to the configuration of D-glyceraldehyde orL-glyceraldehyde (see Fig. 2.1). By convention, thecarbon atoms in the monosaccharide molecule arenumbered such that the reducing group carries thelowest possible number; therefore, in aldoses the re-ducing group carbon is always numbered 1 and inketoses the numbering is started from the end ofthe carbon chain closest to the reducing group. Mostnaturally occurring monosaccharides belong to the

CHO

HOH2COH

H

D-glyceraldehyde L-glyceraldehyde

CHO

HOH2C OHH

Figure 2.1 The D and L stereoisomers of glyceraldehyde.

CHO

CH2OH

D-glucose(aldose)C6O6H12

D-fructose(ketose)C6O6H12

CH2OH

CH2OH

H

HO

H

H

HO

H

H

OH

H

OH

OH

O

H

OH

OH

Figure 2.2 Fischer projections of the structures of D-glucoseand D-fructose.

D-series, i.e. their highest numbered carbon has asimilar optical configuration to D-glyceraldehyde.

The stereochemistry of the monosaccharides isdepicted using the Fischer projection as shown forD-glucose and D-fructose in Fig. 2.2. All bonds aredepicted as horizontal or vertical lines; all horizontalbonds project toward the viewer, while vertical bondsproject away from the viewer. The carbon chain isdepicted vertically with the C1 carbon at thetop.

Aldoses and ketoses commonly exist in equilib-rium between their open-chain form and cyclic struc-tures in aqueous solution. Cyclic structures formthrough either a hemiacetal or a hemiketal linkage be-tween the reducing group and an alcohol group ofthe same sugar. In this way sugars form either a five-membered furanose ring or a six-membered pyranosering as shown in Fig. 2.3 for D-glucose. The formationof a furanose or pyranose introduces an additionalasymmetric carbon; hence two anomers are formed (�-anomer and �-anomer) from each distinct open-chainmonosaccharide. The interconversion between thesetwo anomers is called mutarotation.

The cyclic structures of carbohydrates are com-monly shown as Haworth projections to depict theirthree-dimensional structure. However, this projectiondoes not account for the tetrahedral geometry of car-bon. This is most significant for the six-memberedpyranose ring, which may adopt either a chair or aboat conformation as depicted in Fig. 2.4. Of these, thechair conformation is favoured due to its greater ther-modynamic stability. Within this conformation thebulky CH2OH group is usually found in an equato-rial position to reduce steric interactions.


Food chemistry 7

CH2OH

CH2OH

OHO

β-D-glucopyranose

HH

H

H

H

OH

OH

OH

CH2OH

HO

α-D-glucopyranose

HH

OH

H

H

OH

OH

OH

CH2OH H

H

Ö

D-glucose

HH

O

H

H

OH

OH

OH C

Figure 2.3 The formation of a hemiacetallinkage between the C1 carbon of D-glucoseand the hydroxyl group of its C5 carbonleading to two anomers of D-glucopyranose.The rings are depicted as Haworth projections.

2.2.2 Oligosaccharides

Oligosaccharides contain 2–10 sugar units and arewater soluble. The most significant types of oligosac-charide occurring in foods are disaccharides, whichare formed by the condensation (i.e. water is elim-inated) of two monosaccharide units to form a gly-cosidic bond. A glycosidic bond is that between thehemiacetal group of a saccharide and the hydroxylgroup of another compound, which may or may notbe itself a saccharide. Disaccharides can be homoge-neous or heterogeneous and fall into two types:

1 Non-reducing sugars in which the monosaccharideunits are joined by a glycosidic bond formed be-tween their reducing groups (e.g. sucrose and tre-halose). This inhibits further bonding to other sac-charide units.

H H

H

H

H

H

H

H

H

H

OH OH

OH

OH

HO

HO

HOHOOH

OH

Chair Boat

O

O

Figure 2.4 Chair and boat conformations ofα-D-glucopyranose.

2 Reducing sugars in which the glycosidic bond linksthe reducing group of one monosaccharide unit tothe non-reducing alcoholic hydroxyl of the secondmonosaccharide unit (e.g. lactose and maltose). Areducing sugar is any sugar that, in basic solu-tion, forms an aldehyde or ketone allowing it toact as a reducing agent, and therefore includes allmonosaccharides.

Of the disaccharides, sucrose, trehalose and lactoseare found free in nature, whereas others are found asglycosides (in which a sugar group is bonded throughits anomeric carbon to another group, e.g. a pheno-lic group, via an O-glycosidic bond) or as buildingblocks for polysaccharides (such as maltose in starch),which can be released by hydrolysis. Probably thethree most significant disaccharides in food are su-crose, lactose and maltose, whose structures are de-picted in Fig. 2.5.

Sucrose is the substance known commonly inhouseholds as sugar and is found in many plant fruitsand saps. It is isolated commercially from sugar caneor the roots of sugar beet. Sucrose is composed of an�-D-glucose residue linked to a �-D-fructose residueand is a non-reducing sugar. Its systematic name is �-D-glucopyranosyl-(1↔2)-�-D-fructofuranoside (hav-ing the suffix -oside, because it is a non-reducingsugar). It is the sweetest tasting of the disaccharidesand is an important source of energy.



H

H

H

H

H

H

H

CH2OH

CH2OH

OH

HOHO

OH OH

O

OSucrose

O

OH

H

H

H

O

OH

HHO

OH

H

OH

H

H

H

OH

OH

HOOH

H

Lactose

O

H

H

H

H

H

OH

HOOH

OH

O

H

H

H

H

H

OH

HOHO

OH

O

Maltose

O

Figure 2.5 The structures of some common disaccharides:sucrose, lactose and maltose.

Lactose is found in mammalian milk and its sys-tematic name is �-D-galactopyranosyl-(1↔4)-�-D-glucopyranose. To aid the digestion of lactose, theintestinal villi of infant mammals secrete an enzymecalled lactase (�-D-galactosidase), which cleaves themolecule into its two subunits �-D-glucose and �-D-galactose. In most mammals the production of lac-tase gradually reduces with maturity into adulthood,leading to the inability to digest lactose and so-calledlactose intolerance. However, in cultures where cattle,goats and sheep are milked for food there has evolveda gene for lifelong lactase production.

Maltose is formed by the enzymatic hydrolysis ofstarch and is an important component of the barleymalt used to brew beer. It is a homogeneous disaccha-ride consisting of two units of glucose joined with an�(1→4) linkage, and is systematically named 4-O-�-

D-glucopyranosyl-D-glucose. Maltose is a reducingsugar and the addition of further glucose unit yieldsa series of oligosaccharides known as maltodextrinsor simply dextrins.

2.2.3 Polysaccharides

Polysaccharides are built of repeat units of monosac-charides and are systematically named with the suf-fix -an. The generic name for polysaccharides is gly-can and these can be homoglycans consisting of the onetype of monosaccharide or heteroglycans consisting oftwo or more types of monosaccharide.

Polysaccharides have three main functions in bothanimals and plants: as sources of energy, as structuralcomponents of cells, and as water-binders. Plant andanimal cells store energy in the form of glucans, whichare polymers of glucose such as starch (in plants) andglycogen (in animals). The most abundant structuralpolysaccharide is cellulose, which is also a glucan andis found in plants. Water-binding substances in plantsinclude agar, pectin and alginate.

Polysaccharides occur as several structural types:linear (e.g. amylose, cellulose), branched (e.g. amy-lopectin, glycogen), interrupted (e.g. pectin), block (e.g.alginate) or alternate repeat (e.g. agar, carrageenan).According to the geometry of the glycosidic link-ages, polysaccharide chains can form various con-formations, such as disordered random coil, extendedribbons, buckled ribbons or helices. One of the most im-portant properties of a great number of polysaccha-rides in foods is that they are able to form aqueousgels and thereby contribute to food structure and tex-tural properties (e.g. mouth-feel).

2.2.3.1 Starch

Starch occurs in the form of semi-crystalline gran-ules ranging in size from 2 to 100 µm, and con-sists of two types of glucan: amylose and amylopectin.Amylose is a linear polymer of �(1→4) linked �-D-glucopyranose and constitutes 20–25% of moststarches. Amylopectin is a randomly branched poly-mer of �-D-glucopyranose consisting of linear chainswith �(1→4) linkages with 4–5% of glucose units alsobeing involved in �(1→6) linked branches. On aver-age the length of linear chains in amylopectin is about20–25 units. The chemical structures of amylose andamylopectin are shown in Fig. 2.6.

Amylose molecules contain in the region of 103 glu-cose units and form helix structures which entrap


Food chemistry 9

CH2OH

OH

OH

OH

O

CH2OH

OH

OH

O

O

CH2OH

OH

OH

O

CH2OH

OH

OH

OHO

n

Amylose

Amylopectin

O

CH2OH

OH

OH

OO

O

O

CH2OH

OH

OH

O

CH2OH

OH

OH

O

Figure 2.6 Chemical structures of amylose and amylopectin.

other molecules such as organic alcohols or fattyacids to form clathrates or helical inclusion com-pounds. Indeed, the blue colour that results when io-dine solution is used to test for starch is thought to bedue to the formation of an inclusion compound.

Amylopectin is a much larger molecule than amy-lose, containing approximately 106 glucose units permolecule, and forms a complex structure. This struc-ture is described by the cluster model and has threetypes of chain (see Fig. 2.7): A chains that are un-branched and contain only �(1→4) linkages, B chainsthat contain �(1→4) and �(1→6) linkages, and Cchains that contain �(1→4) and �(1→6) linkages plusa reducing group. The linear A chains in this structureform clusters that are crystalline in nature, whereasthe branched B chains give amorphous regions.

Starch granules undergo a process called gelatiniza-tion if heated above their gelatinization temperature(55–70◦C depending on the starch source) in the pres-ence of water. During gelatinization granules firstbegin to imbibe water and swell, and as a conse-

Reducing endC chain

B chain

A chain

Figure 2.7 Amylopectin cluster model.

quence they progressively lose their organized struc-ture (detected as a loss of birefringence). As time



progresses, granules become increasingly permeableto water and solutes, thus swelling further and caus-ing the viscosity of the aqueous suspension to in-crease sharply. Swollen starch granules leach amy-lose, which further increases viscosity to the extentthat a paste is formed. As this paste is allowed to cool,hydrogen-bonding interactions between amylopectinand amylose lead to the formation of a gel-likestructure.

Prolonged storage of a starch gel leads to the on-set of a process termed retrogradation, during whichamylose molecules associate together to form crys-talline aggregates and starch gels undergo shrinkageand syneresis. Retrogradation can be viewed as a re-turn from a solvated, dispersed, amorphous state toan insoluble, aggregated or crystalline condition. Toavoid retrogradation in food products, waxy starchescan be used that contain only amylopectin. Chemi-cally modified starches are also available that havebeen depolymerized (i.e. partially hydrolysed), ester-ified or crosslinked to tailor their properties for par-ticular end uses.

2.2.3.2 Glycogen

The polysaccharide that animals use for the short-term storage of food energy in the liver and muscles isknown as glycogen. Glycogen is similar in structure toamylopectin, but has much higher molecular weightand a higher degree of branching. Branching aids therapid release of glucose since the enzymes that re-lease glucose attack on the non-reducing ends, cleav-ing one glucose molecule at a time. More branchingequates to more non-reducing ends meaning morerapid release of energy. The metabolism of glyco-gen continues post-mortem, which means that by thetime meat reaches the consumer it has lost all of itsglycogen.

2.2.3.3 Cellulose

The most abundant structural polysaccharide is cellu-lose. Indeed, there is so much cellulose in the cell wallsof plants that it is the most abundant of all biologicalmolecules. Cellulose is a linear polymer of �(1→4)linked glucopyranose residues. The �-linkage incellulose is not susceptible to attack by salivary amy-lases that break down starch �-linkages, and there-fore cellulose forms a major part of dietary fibre. Di-etary fibre is not digested by enzymes in the smallintestine and is hence utilized by colonic microflora

via fermentation processes. So-called hemicelluloses,including xylans, which are major constituents of ce-real bran, are another major component of dietaryfibre.

2.2.3.4 Pectins

Pectins are mainly used in food as gelling agents.Pectins are heteroglycans and have complex struc-tures that are based on a polygalacturonan back-bone of �(1→4)-linked D-galacturonic acid residues,some of which are methylated. Into this backbone,there are regions where D-galacturonic acid is re-placed by L-rhamnose, bonded via (1→2) linkagesto give an overall rhamnogalacturonan chain. Pectinsare characterized by smooth regions that are free ofL-rhamnose residues and hairy regions consisting ofboth D-galacturonic acid and L-rhamnose residues.The hairy regions are so-called because they carryside chains of neutral sugars including mainly D-galactose, L-arabinose and D-xylose, with the typesand proportions of neutral sugars varying with theorigin of pectin.

As stated above, pectins are mainly applied infoods for their gelling properties, especially in jamsand preserves. Gels consist of a three-dimensionalpolymeric network of chains that entrap water. Pectingels are stabilized by junction zones, which are crys-talline regions where smooth regions align them-selves and interact. The hairy regions of pectindisrupt these junction zones, preventing extensiveaggregation that could lead to precipitation as occursduring amylose retrogradation.

2.2.3.5 Gums

Distinct from those polysaccharides that form gelsare a group of polysaccharides that are called gums.Gums have a high affinity for water and give high-viscosity aqueous solutions, but are not able to formgels. The reason for this is that all gums possessstructures that incorporate a very high degree ofbranching or highly interrupted chains. This preventsthe formation of junction zones (such as in pectins)that are a feature of polysaccharide gels. A notablegum that is commonly employed in foods is xanthangum, which is secreted by Xanthomonas campestrisand has a backbone of �(1→4)-linked glucopyra-nose with trisaccharide branch points every fiveresidues.


Food chemistry 11

CH2OH

D-glucose(aldose)

D-fructose(ketose)

H

HO

H

H

H

OH

OH

OHH

OH

C

C

C

C

CH2OH

HO

H

H

H

OH

O

OHH

OH

C

C

C

C

CH2OH

1,2-cis-enediol

H

H+HO

H

H

H

OH

O

OH

OH

C

C

C

C

CH2OH

CH2OH

HO

H

H

H

OH

O

OH

C

C

C

C

Figure 2.8 The isomerization of sugars to form an enediol intermediate prior to caramelization.

2.2.4 Reactions of carbohydrates

2.2.4.1 Caramelization

When a concentrated solution of sugars is heatedto temperatures above 100◦C, various thermal de-composition reactions can occur leading to formationof flavour compounds and brown-coloured prod-ucts. This process, which particularly occurs dur-ing the melting of sugars, is called caramelization.Caramelization is a non-enzymic browning reaction likethe Maillard reaction discussed below.

During caramelization, the first reaction step isthe reversible isomerization of aldoses or ketoses intheir open chain forms to form an enediol intermedi-ate (Fig. 2.8). This intermediate can then dehydrateto form a series of degradation products – in thecase of hexoses the main product is 5-hydroxymethyl-

2-furaldehyde (HMF), whereas pentoses yield mainly2-furaldehyde (furfural). HMF and furfural are consid-ered useful indicators of accurate storage tempera-ture of food samples.

2.2.4.2 Maillard browning

The Maillard reaction is the chemical reaction betweenan amino acid and a reducing sugar that, via the for-mation of a pool of reactive intermediates, leads tothe formation of flavour compounds and melanoidinpigments (non-enzymic browning). The initial stepin this complex series and network of reactions isthe condensation of reducing sugar and amino acid.The reactive carbonyl group of the sugar reacts withthe nucleophilic amino group of the amino acid toform an Amadori compound as shown in Fig. 2.9. This

NH2

−H2O

R

OH OH

O

+

OH

Reducing sugar

Amadori compound

Rearrangement

OH

OHR

NH

OH

OH OH OH

OR

NH

OH

OH OH

OHR

N

OH

OH OHFigure 2.9 The formation of an Amadoricompound during the initial stage of theMaillard reaction.



reaction normally requires heat (usually >100◦C), ispromoted by low moisture content, and is acceler-ated in an alkaline environment as the amino groupsare deprotonated and hence have an increased nu-cleophilicity. Various reducing sugars have differingrates of reaction in the Maillard reaction; pentosessuch as ribose, xylose and arabinose are more reactivethan hexoses such as glucose, fructose and galactose.Different sugars give different breakdown productsand hence unique flavour and colour.

2.2.4.3 Toxic sugar derivatives

The Maillard reaction, while desirable in many re-spects, does have certain implications for the lossof essential amino acids (cysteine and methionine),the formation of mutagenic compounds and the for-mation of compounds that can cause protein cross-linking, which is implicated in diabetes. The mostconcerning aspect is the potential for toxic sugarderivatives with mutagenic properties, primarily thegroup of compounds called heterocyclic amines. Theseare particularly associated with cooked meat, espe-cially that which has been grilled at high temperaturefor long cooking times. In recent times the formationof acrylamide has been an issue of concern in potato-based snack foods.

2.3 Proteins

Proteins are polymers of amino acids linked togetherby peptide bonds. They can also be referred to aspolypeptides. Proteins are key constituents of food,contributing towards organoleptic properties (partic-ularly texture) and nutritive value. Proteins partici-pate in tissue building and are therefore abundant inmuscle and plant tissues.

2.3.1 Amino acids – the building blocksof proteins

2.3.1.1 Amino acid structure

The general structure of an amino acid is depicted inFig. 2.10, and consists of an amino group (NH2), acarboxyl group (COOH), a hydrogen atom and a dis-tinctive R group all bonded to a single carbon atom,called the �-carbon. The R group is called the sidechain and determines the identity of the amino acid.

COOH

RH

NH2

Un-ionized form Zwitterionic form

COO–

RH

+NH3

Figure 2.10 The general structure of an amino acid.

Amino acids in solution at neutral pH are predom-inantly zwitterions. The ionization state varies withpH: at acidic pH, the carboxyl group is un-ionizedand the amino group is ionized; at alkaline pH, thecarboxyl group is ionized and the amino group isun-ionized.

There are 20 different amino acids that are com-monly found in proteins. The R group is differentin each case and can be classified according to sev-eral criteria into four main types: basic, non-polar (hy-drophobic), polar (uncharged) and acidic. Tables 2.1,2.2 and 2.3 categorize the amino acids accordingto these types. The four different functional groupsof amino acids are arranged in a tetrahedral arrayaround the �-carbon atom; therefore, all amino acidsare optically active apart from glycine. Of the possi-ble L- or D-isomers, proteins contain only L-isomersof amino acids.

Some proteins contain non-standard amino acids inaddition to the 20 standard amino acids (Fig. 2.11).These are formed by modification of a standardamino acid following its incorporation into thepolypeptide chain (post-translational modification).Two examples that are encountered often in foodproteins are hydroxyproline and O-phosphoserine.Hydroxyproline occurs in collagen and O-phospho-serine occurs in caseins.

2.3.1.2 Peptide bonds

The peptide bond is the covalent bond between aminoacids that links them to form peptides and polypep-tides (Fig. 2.12). A peptide bond is formed betweenthe �-carboxyl group and the �-amino group of twoamino acids by a condensation (or dehydration syn-thesis) reaction with the loss of water. Peptides arecompounds formed by linking small numbers ofamino acids (up to 50). A polypeptide is a chain of50–100 amino acid residues. A protein is a polypep-tide chain of 100+ amino acid residues and has a pos-itively charged nitrogen-containing amino group atone end (N-terminus) and a negatively charged car-boxyl group at its other end (C-terminus).


Food chemistry 13

Table 2.1 Basic and acidic amino acids.

Single SingleAmino acid letter code Structural formula Amino acid letter code Structural formula

Basic: Acidic:Arginine (Arg) R Aspartic acid (Asp) D

Histidine (His) H Glutamic acid (Glu) E

Lysine (Lys) K



Table 2.2 Non-polar amino acids.


Alanine (Ala) A Phenylalanine (Phe) F

Isoleucine (IIe) I Proline (Pro) P

Leucine (Leu) L Tryptophan (Trp) W

Methionine (Met) M Valine (Val) V


Food chemistry 15

Table 2.3 Polar amino acids.


Asparagine (Asn) N Serine (Ser) S

Cysteine (Cys) C Threonine (Thr) T

Glutamine (Gln) Q Tyrosine (Tyr) Y

Glycine (Gly) G

A special feature of the peptide bond is its par-tial double bond character. This arises because thepeptide bond is stabilized by resonance hybridizationbetween two structures, one single bonded betweenthe carbon and nitrogen atoms, the other doublebonded. As a consequence, the peptide bond is planarand stable. This has implications for the possible con-formations adopted by a polypeptide chain, since norotation is possible around the peptide bond. How-ever, rotation is possible around bonds between the�-carbons and the amino nitrogen and carbonyl car-bon of their residue.

H

OH

H3N

CH2

CH

O

P

C

O

O

HydroxyprolineO-phosphoserine

H

N

O

OC+

+

O

O O

Figure 2.11 Chemical structures of some non-standardamino acids common in food proteins.



H H H

H

Amide planeO

N

R3

R2

R1 H H O

CC C

CN

N C

Figure 2.12 Peptide bonds in a polypeptide. The partialdouble bond character is represented by the dashed doublebonds. The shaded boxes highlight atoms that exist within thesame plane.

2.3.2 Molecular structure of proteins

2.3.2.1 Primary structure

The primary structure of a protein is simply thesequence of amino acids listed from the N-terminalamino acid. There are more than a billion possible se-quences of the 20 amino acids and every protein willhave a unique primary structure which determineshow the protein folds into a three-dimensional con-formation. If we compare the primary sequence Leu-Val-Phe-Gly-Arg-Cys-Glu-Leu-Ala-Ala with Gly-Leu-Arg-Phe-Cys-Val-Ala-Glu-Ala-Leu, these twopeptides have the same number of amino acids,the same kinds of amino acids, but have differentprimary structures.

2.3.2.2 Secondary structure

The secondary structure of a protein describes thearrangement of the protein backbone (polypeptidechain) due to hydrogen bonding between its amino acidresidues. Hydrogen bonding can occur between anamide hydrogen atom and a lone pair of electrons ona carbonyl oxygen atom, as shown in Fig. 2.13.

The peptide bond is planar, offering no rotationaround its axis. This leaves only two bonds withineach amino acid residue that have free rotation,namely the �-carbon to amino nitrogen and �-carbonto carboxyl carbon bonds. The rotations around thesebonds are represented by the dihedral angles � (phi)and � (psi), as shown for a tripeptide of alaninein Fig. 2.14. Ramachandran plotted � and � com-binations from known protein structures and foundthat there are certain sterically favourable combina-tions that form the basis for the preferred secondarystructures. He also found that unfavourable orbitaloverlap precludes some combinations: � = 0◦ and� = 180◦; � = 180◦ and � = 0◦; � = 0◦ and � = 0◦.

OHH

N

R

R

NN

H

R

O

H OH

OHH

N

R

R

NN

H

R

O

Hydrogen bond

H OH

Figure 2.13 Hydrogen bonding between two polypeptides.

Two kinds of hydrogen bonded secondary struc-tures occur frequently with features that repeat at reg-ular intervals. These periodic structures are the �-helixand the �-pleated sheet. The �-pleated sheet can givea two-dimensional array and can involve more thanone polypeptide chain.

�-HelixThe �-helix is a coiled rod-like structure and involvesa single polypeptide chain. The ‘�′ denotes that ifyou were to view the helix down its axis then youwould note that it spirals clockwise away from you.The �-helix is stabilized by hydrogen bonding par-allel to the helix axis and the carbonyl group of eachresidue is hydrogen bonded to the amide group of theresidue that is four residues away if counting fromthe N-terminus. There are 3.6 residues for each turnof the helix and the dihedral angles are � = −57◦ and� = −48◦. The R group of each residue protrudesfrom the helix and plays no role in the formation of

H H

H

O

H3N+

CH3

H3C H3CH H O

φ

ψ

CC C

CN C

O

ON C

Figure 2.14 Bonds adjacent to peptide bonds with freerotation are depicted in bold with their respective dihedralangles φ and ψ .

Geoffrey Campbell-Platt€¦ · BLBK179-Campbell-Platt June 29, 2009 11:45 This edition ﬁrst...

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Transcript of Geoffrey Campbell-Platt€¦ · BLBK179-Campbell-Platt June 29, 2009 11:45 This edition ﬁrst...