Food processing handbook (vol 1 and 2) ( PDFDrive com )

Front Matter Edited by James G Brennan and Alistair S Grandison Food Processing Handbook Volume 1 Related Titles Rychlik, Michael (ed ) Fortified Foods with Vitamins Analytical Concepts to Assure Bett.Front Matter Edited by James G Brennan and Alistair S Grandison Food Processing Handbook Volume 1 Related Titles Rychlik, Michael (ed ) Fortified Foods with Vitamins Analytical Concepts to Assure Bett.Front Matter Edited by James G Brennan and Alistair S Grandison Food Processing Handbook Volume 1 Related Titles Rychlik, Michael (ed ) Fortified Foods with Vitamins Analytical Concepts to Assure Bett.Front Matter Edited by James G Brennan and Alistair S Grandison Food Processing Handbook Volume 1 Related Titles Rychlik, Michael (ed ) Fortified Foods with Vitamins Analytical Concepts to Assure Bett.

Related Titles

Rychlik, Michael (ed.)

Fortified Foods with Vitamins

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Global Legislation for Food Packaging

2009 ISBN: 978-3-527-31674-8 Chen, X D., Mujumdar, A S (eds.)

Drying Technologies in Food Processing

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Edited by James G Brennan and Alistair S Grandison

Food Processing Handbook

2nd edition

Volume 1

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carefully produced Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

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© 2012 Wiley-VCH Verlag & Co KGaA, Boschstr 12, 69469 Weinheim, Germany All rights reserved (including those of translation into other languages) No part

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Contents

Preface to the Second Edition XV

Preface to the First Edition XVII

List of Contributors XIX

Content of Volume 1

1 Postharvest Handling and Preparation of Foods for Processing 1

Alistair S Grandison

1.2 Properties of Raw Food Materials and Their Susceptibility to

Deterioration and Damage 2

1.2.3 Deterioration of Raw Materials 6

1.2.5 Improving Processing Characteristics through Selective Breeding and

2.1.2 Safety and Quality Issues 33

2.4.2.2 Tunnel (Spray) Pasteurizers 51

2.4.2.3 Extended Shelf Life Products 52

2.6.2 Fundamental Principles of Ohmic Heating 67

2.6.2.1 Electrochemical Reaction on Electrodes 68

2.6.2.2 Heating Pattern of Multiphase Food in Ohmic System 69

2.6.2.3 Modeling of Ohmic Heating 70

3.1.5 Applications for Evaporation 86

3.1.5.1 Concentrated Liquid Products 86

3.1.5.2 Evaporation as a Preparatory Step to Further Processing 88

3.1.5.3 The Use of Evaporation to Reduce Transport, Storage, and Packaging

3.2.2 Drying Solid Foods in Heated Air 92

3.2.3 Equipment Used in Hot Air Drying of Solid Food Pieces 94

3.2.3.1 Cabinet (Tray) Dryer 94

3.2.3.3 Conveyor (Belt) Dryer 95

3.2.3.5 Fluidized Bed Dryer 96

3.2.3.6 Pneumatic (Flash) Dryer 98

3.2.4 Drying of Solid Foods by Direct Contact with a Heated Surface 99

3.2.5 Equipment Used in Drying Solid Foods by Contact with a Heated

3.2.5.1 Vacuum Cabinet (Tray or Shelf) Dryer 100

3.2.6 Freeze Drying (Sublimation Drying, Lyophilization) of Solid

3.2.7 Equipment Used in Freeze Drying Solid Foods 102

3.2.7.1 Cabinet (Batch) Freeze Dryer 102

3.2.7.2 Tunnel (Semi-continuous) Freeze Dryer 103

3.2.7.3 Continuous-Freeze Dryers 104

3.2.8 Drying by the Application of Radiant (Infrared) Heat 105

3.2.9 Drying by the Application of Dielectric Energy 105

3.2.10 Electrohydrodynamic Drying (EHD) 107

3.2.13 Drying Food Liquids and Slurries in Heated Air 111

VIII Contents

3.2.13.1 Spray Drying 111

3.2.14 Drying Liquids and Slurries by Direct Contact With a Heated

3.2.14.1 Drum (Roller, Film) Dryer 116

3.2.14.2 Vacuum Band (Belt) Dryer 117

3.2.14.3 Refractance Window Drying System 118

3.2.15 Other Methods Used for Drying Liquids and Slurries 118

3.2.16 Applications of Dehydration 119

3.2.16.1 Dehydrated Vegetable Products 119

3.2.16.2 Dehydrated Fruit Products 121

3.2.16.3 Dehydrated Dairy Products 122

3.2.16.4 Instant Coffee and Tea 123

3.2.16.5 Dehydrated Meat Products 123

3.2.16.6 Dehydrated Fish Products 123

3.2.17 Stability of Dehydrated Foods 124

References 126

Jos´e Mauricio Pardo and Keshavan Niranjan

4.2.2 Gas Contact Refrigerators 132

4.2.3 Immersion and Liquid Contact Refrigeration 133

4.3.1 Mechanical Refrigeration Cycle 135

4.3.1.1 The Pressure and Enthalpy Diagram 137

4.3.1.2 The Real Refrigeration Cycle (Standard Vapor Compression

4.3.3.3 Refrigerant Flow Rate 144

4.3.3.4 Work Done by the Compressor 145

4.3.3.5 Heat Exchanged in the Condenser and Evaporator 145

4.4.1 Formation of the Microstructure during Solidification 146

4.4.2 Mathematical Models for Freezing Kinetics 147

5.5 Effects on the Properties of Food 165

5.7 Applications and Potential Applications 168

5.7.1 General Effects and Mechanisms of Irradiation 169

5.7.2 Applications to Particular Food Classes 172

5.7.2.1 Meat and Meat Products 172

5.7.2.2 Fish and Shellfish 173

5.7.2.3 Fruits and Vegetables 174

5.7.2.4 Bulbs and Tubers 174

5.7.2.5 Spices and Herbs 175

5.7.2.6 Cereals and Cereal Products 175

5.7.2.7 Other Miscellaneous Foods 175

References 176

6 High Pressure Processing 179

Margaret F Patterson, Dave A Ledward, Craig Leadley, and Nigel Rogers

X Contents

6.2.6 Strain Variation within a Species 185

6.2.7 Stage of Growth of Microorganisms 185

6.2.8 Magnitude and Duration of the Pressure Treatment 185

6.2.9 Effect of Temperature on Pressure Resistance 185

6.2.11 Combination Treatments Involving Pressure 186

6.2.12 Effect of High Pressure on the Microbiological Quality of Foods 187

6.10 Current and Potential Applications of HPP for Foods 200

References 201

7 Emerging Technologies for Food Processing 205

Liliana Alamilla-Beltr´an, Jorge Welti-Chanes, Jos´e Jorge Chanona-P´erez,

Ma de Jes ´us Perea-Flores, and Gustavo F Guti´errez-L´opez

7.2 Pulsed Electric Field Processing 206

7.2.2 Effects of PEF on Microorganisms 208

7.2.3 Factors Affecting the Ability of PEF to Inactivate Microorganisms 209

7.2.3.1 Processing Factors 209

7.2.3.2 Microorganism Factors 210

8.2 Factors Affecting the Choice of a Packaging Material and/or Container

for a Particular Duty 226

8.3 Materials and Containers Used for Packaging Foods 233

8.3.1 Papers, Paperboards, and Fiberboards 233

XII Contents

8.3.8 Packaging in Flexible Films and Laminates 245

8.3.9 Rigid and Semi-rigid Plastic Containers 247

8.3.11 Glass and Glass Containers 255

8.7.3 Quality Indicators and Sensors 273

8.7.3.1 Chemical Indicators 273

8.7.3.2 Microbial Indicators 273

8.7.3.3 Gas Concentration Indicators 273

8.7.4 Radiofrequency Identification Devices (RFID) 274

8.7.5 Other Intelligent Packaging Devices 274

8.7.6 Consumer Attitudes, Safety, and Legal Aspects of Active and Intelligent

Packaging 275

References 276

Contents XIII

Content of Volume 2

9 Separations in Food Processing Part 1 281

James G Brennan and Alistair S Grandison

10 Separations in Food Processing: Part 2 – Membrane Processing, Ion

Exchange, and Electrodialysis 331

Michael J Lewis and Alistair S Grandison

11 Mixing, Emulsification, and Size Reduction 363

18 Process Control in Food Processing 559

Keshavan Niranjan, Araya Ahromrit, and Ashok S Khare

19 Environmental Aspects of Food Processing 571

Niharika Mishra, Ali Abd El-Aal Bakr, Keshavan Niranjan, and Gary

22 Microscopy Techniques and Image Analysis for the Quantitative

Evaluation of Food Microstructure 667

Maria de Jes ´us Perea-Flores, Ang´elica Gabriela Mendoza-Madrigal, Jos´e Jorge Chanona-P´erez, Liliana Alamilla-Beltr´an, and Gustavo Fidel

Gutierrez-L´opez

Preface to the Second Edition

In this second edition of Food Processing Handbook the chapters in the first editionhave been retained and revised by including information on recent developments

in each field and updating the reference lists Some of the most notable changesare: the inclusion of a new section on ohmic heating in the Chapter on thermalprocessing (Chapter 2); extending the packaging chapter to cover intelligent pack-aging (Chapter 8); explaining the calculation of greenhouse gas emissions (carbonfootprints) and providing a case study in the chapter on environmental aspects offood processing (Chapter 19) The original chapter entitled Baking, Extrusion andFrying has been split into three individual chapters providing extended coverage ofthese three important processes (Chapters 12, 13, and 14) Several new topics havebeen added to reflect recent trends and concerns in the food industry These includechapters on: traceability in food processing and distribution (Chapter 16); hygienicdesign of food processing plant (Chapter 17); process realisation (Chapter 21);microscopy techniques and image analysis for the quantitative evaluation of foodmicrostructure (Chapter 22); nanotechnology in the food sector (Chapter 23) andfermentation and the use of enzymes (Chapter 24) These changes have necessi-tated dividing the book into two volumes, the first consisting of the more basicfood preservation processes and packaging, while volume 2 includes other man-ufacturing processes and other considerations relating to safety and sustainablemanufacturing

It is hoped that this much extended edition will be of interest to scientists andengineers involved in food manufacture and research and development in industry,and to staff and students participating in food related courses at undergraduate andpostgraduate levels

James G Brennan, Alistair S Grandison

Preface to the First Edition

There are many excellent texts available which cover the fundamentals of foodengineering, equipment design, modelling of food processing operations etc.There are also several very good works in food science and technology dealing withthe chemical composition, physical properties, nutritional and microbiologicalstatus of fresh and processed foods This work is an attempt to cover the middleground between these two extremes The objective is to discuss the technologybehind the main methods of food preservation used in today’s food industry

in terms of the principles involved, the equipment used and the changes inphysical, chemical, microbiological and organoleptic properties that occur duringprocessing In addition to the conventional preservation techniques, new andemerging technologies, such as high pressure processing and the use of pulsedelectric field and power ultrasound are discussed The materials and methods used

in the packaging of food, including the relatively new field of active packaging, arecovered Concerns about the safety of processed foods and the impact of processing

on the environment are addressed Process control methods employed in foodprocessing are outlined Treatments applied to water to be used in food processingand the disposal of wastes from processing operations are described

Chapter 1 covers the postharvest handling and transport of fresh foods andpreparatory operations, such as cleaning, sorting, grading and blanching, appliedprior to processing Chapters 2, 3 and 4 contain up-to-date accounts of heat process-ing, evaporation, dehydration and freezing techniques used for food preservation

In Chapter 5, the potentially useful, but so far little used process of irradiation isdiscussed The relatively new technology of high pressure processing is covered inChapter 6, while Chapter 7 explains the current status of pulsed electric field, powerultrasound, and other new technologies Recent developments in baking, extrusioncooking and frying are outlined in Chapter 8 Chapter 9 deals with the materialsand methods used for food packaging and active packaging technology, includingthe use of oxygen, carbon dioxide and ethylene scavengers, preservative releasersand moisture absorbers In Chapter 10, safety in food processing is discussed andthe development, implementation and maintenance of HACCP systems outlined.Chapter 11 covers the various types of control systems applied in food processing.Chapter 12 deals with environmental issues including the impact of packagingwastes and the disposal of refrigerants In Chapter 13, the various treatments

XVIII Preface to the First Edition

applied to water to be used in food processing are described and the physical,chemical and biological treatments applied to food processing wastes are outlined

To complete the picture, the various separation techniques used in food processingare discussed in Chapter 14 and Chapter 15 covers the conversion operations ofmixing, emulsification and size reduction of solids

The editor wishes to acknowledge the considerable advice and help he receivedfrom former colleagues in the School of Food Biosciences, The University ofReading, when working on this project He also wishes to thank his wife, Anne,for her support and patience

List of Contributors

Araya Ahromrit

Assistant Professor

Department of Food Technology

Khon Kaen University

and Director of the Manchester

Food Research Centre

Old Hall Lane

Santiago 6904411Chile

James G Brennan

16 Benning WayWokinghamBerkshireRG40 1XXUK

Stanley P Cauvain

BakeTran

1 Oakland closeFreelandWitney

OX 29 8AXUK

Jos´e Jorge Chanona-P´erez

National School of BiologicalSciences-National PolytechnicInstitute

Department of Food Science andTechnology

Carpio y Plan de Ayala s/n Sto

Tom´as 11340Mexico City

XXIV List of Contributors

Ali Abd El-Aal Bakr

Food Science and Technology

Gustavo Fidel Gutierrez-L´opez

National School of Biological

Soojin Jun

University of Hawaii at ManoaCollege of Tropical Agricultureand Human ResourcesDepartment of Human NutritionFood and Animal Sciences

1955 East West Rd 302FHonolulu, HI 96822USA

Ashok S Khare

University of ReadingDepartment of Food andNutritional SciencesP.O Box 226WhiteknightsReading RG6 6APUK

Christopher J Kirby

Pharmaterials Ltd

Unit B

5 Boulton RoadReading RG2 0NHUK

Christopher Knight

Head of AgricultureCampden BRIChipping CampdenGlos GL55 6LDUK

A A 140013 ChiaColombia

Ang´elica Gabriela Mendoza-Madrigal

National School of BiologicalSciences-National PolytechnicInstitute

Department of Food Science andTechnology

Carpio y Plan de Ayala s/n Sto

Tom´as 11340Mexico City

Niharika Mishra

Agricultural and BiologicalEngineering

717 W Cherry laneApt # 2

State College, PA 16803USA

Keshavan Niranjan

University of ReadingDepartment of Food andNutritional SciencesP.O Box 226WhiteknightsReading RG6 6APUK

XXVI List of Contributors

Maria de Jes´us Perea-Flores

National School of Biological

School of SportTourism and the OutdoorsPreston

Lancashire PR1 2HEUK

Jorge Welti-Chanes

Technological Institute ofAdvanced Studies of MonterreyFood and Biotechnology Unit

Av Eugenio Garza Sada 2501 SurCol Tecnol´ogico

64849 MonterreyN.L

Mexico

R Andrew Wilbey

The University of ReadingDepartment of Food andNutritional SciencesWhiteknightsReading RG6 6APUK

in the United Kingdom, so beet sugar production is confined to the autumnand winter, yet demand for sugar is continuous throughout the year Even inthe case of raw materials that are available throughout the year, such as milk,there are established peaks and troughs in volume of production, as well asvariations in chemical composition Availability may also be determined by lesspredictable factors, such as weather conditions, which may affect yields or limitharvesting In other cases demand is seasonal, for example, ice cream or saladsare in greater demand in the summer, whereas other foods are traditionally eaten

in the winter months, or even at more specific times, such as Christmas orEaster

In an ideal world, food processors would like a continuous supply of rawmaterials, whose composition and quality are constant and whose prices arepredictable Of course this is usually impossible to achieve In practice, proces-sors contract ahead with growers to synchronize their needs with raw materialproduction

The aim of this chapter is to consider the properties of raw materials in relation

to food processing, and to summarize important aspects of handling, transport,storage, and preparation of raw materials prior to the range of processing operationsdescribed in the remainder of this book The bulk of the chapter will deal with solidagricultural products including fruits, vegetables, cereals, and legumes, althoughmany considerations can also be applied to animal-based materials such as meat,eggs, and milk

Food Processing Handbook, Second Edition Edited by James G Brennan and Alistair S Grandison.

© 2012 Wiley-VCH Verlag GmbH & Co KGaA Published 2012 by Wiley-VCH Verlag GmbH & Co KGaA.

2 1 Postharvest Handling and Preparation of Foods for Processing

or poor-quality units, it is vital to procure materials whose properties most closelymatch the requirements of the process Quality is a wide-ranging concept and

is determined by many factors It is a composite of those physical and chemicalproperties of the material which govern its acceptability to the ‘‘user.’’ The latter may

be the final consumer, or more likely in this case, the food processor Geometricproperties, color, flavor, texture, nutritive value, and freedom from defects are themajor properties likely to determine quality

An initial consideration is selection of the most suitable cultivars in the case

of plant foods (or breeds in the case of animal products) Other preharvestfactors (such as soil conditions, climate, and agricultural practices), harvestingmethods and postharvest conditions, maturity, storage, and postharvest handlingalso determine quality These considerations, including seed supply and manyaspects of crop production, are frequently controlled by the processor or even theretailer

The timing and method of harvesting are determinants of product quality.Manual labor is expensive, therefore mechanized harvesting is introduced wherepossible Cultivars most suitable for mechanized harvesting should mature evenly,producing units of nearly equal size that are resistant to mechanical damage

In some instances, the growth habits of plants (e.g., pea vines, fruit trees) havebeen developed to meet the needs of mechanical harvesting equipment Uniformmaturity is desirable as the presence of over-mature units is associated withhigh waste, product damage, and high microbial loads, while under-maturity isassociated with poor yield, lack of flavor and color, and hard texture For economicreasons, harvesting is almost always a ‘‘once over’’ exercise, hence it is importantthat all units reach maturity at the same time The prediction of maturity isnecessary to coordinate harvesting with processors’ needs, as well as to extendthe harvest season It can be achieved primarily from knowledge of the growthproperties of the crop combined with records and experience of local climaticconditions

The ‘‘heat unit system,’’ first described by Seaton [1] for peas and beans, can

be applied to give a more accurate estimate of harvest date from sowing date

in any year This system is based on the premise that growth temperature isthe overriding determinant of crop growth A base temperature, below which nogrowth occurs, is assumed, and the mean temperature of each day through thegrowing period is recorded By summing the daily mean temperatures minus basetemperatures on days where mean temperature exceeds base temperature, thenumber of ‘‘accumulated heat units’’ can be calculated By comparing this withthe known growth data for the particular cultivar, an accurate prediction of harvest

1.2 Properties of Raw Food Materials and Their Susceptibility to Deterioration and Damage 3

date can be computed In addition, by allowing fixed numbers of accumulated heatunits between sowings, the harvest season can be spread, so that individual fieldsmay be harvested at peak maturity Sowing plans and harvest date are determined

by negotiation between the growers and the processors, and the latter may evenprovide the equipment and labor for harvesting and transport to the factory

An important consideration for processed foods is that it is the quality of theprocessed product, rather than the raw material, that is important For minimallyprocessed foods, such as those subjected to modified atmospheres, low doseirradiation, mild heat treatment, or some chemical preservatives, the characteristics

of the raw material are a good guide to the quality of the product For moresevere processing, including heat preservation, drying, or freezing, the qualitycharacteristics may change markedly during processing Hence, those raw materialswhich are preferred for fresh consumption may not be most appropriate forprocessing For example, succulent peaches with delicate flavor may be lesssuitable for canning than harder, less flavorsome cultivars, which can withstandrigorous processing conditions Similarly, ripe, healthy, well-colored fruit may beperfect for fresh sale, but may not be suitable for freezing due to excessive driploss while thawing For example, Maestrelli [2] reported that different strawberrycultivars with similar excellent characteristics for fresh consumption, exhibited awide range of drip loss (between 8 and 38%), and hence would be of widely differentvalue for the frozen food industry

1.2.1

Raw Material Properties

The main raw material properties of importance to the processor are geometry,color, texture, functional properties, and flavor

Agricultural products do not come in regular shapes and exact sizes Size andshape are inseparable, but are very difficult to define mathematically in solid foodmaterials Geometry is, however, vital to packaging and controlling fill-in weights

It may, for example, be important to determine how much mass or how manyunits may be filled into a square box or cylindrical can This would require a vastnumber of measurements to perform exactly, and thus approximations must bemade Size and shape are also important to heat processing and freezing, as theywill determine the rate and extent of heat transfer within food units Mohsenin [3]describes numerous approaches by which the size and shape of irregular food units

4 1 Postharvest Handling and Preparation of Foods for Processing

may be defined These include the development of statistical techniques based on alimited number of measurements and more subjective approaches involving visualcomparison of units to charted standards Uniformity of size and shape is alsoimportant to most operations and processes Process control to give accurately anduniformly treated products is always simpler with more uniform materials Forexample, it is essential that wheat kernel size is uniform for flour milling.Specific surface (area/mass) may be an important expression of geometry,especially when considering surface phenomena, such as the economics of fruitpeeling, or surface processes such as smoking and brining

The presence of geometric defects, such as projections and depressions, cate any attempt to quantify the geometry of raw materials, as well as presentingprocessors with cleaning and handling problems, and yield loss Selection ofcultivars with the minimum defect level is advisable

compli-There are two approaches to securing optimum geometric characteristics: first,the selection of appropriate varieties, and second, sorting and grading operations.1.2.1.2 Color

Color and color uniformity are vital components of the visual quality of fresh foods,and play a major role in consumer choice However, it may be less important in rawmaterials for processing For low-temperature processes, such as chilling, freezing,

or freeze drying, the color changes little during processing, and thus the color

of the raw material is a good guide to suitability for processing For more severeprocessing, the color may change markedly during the process Green vegetablessuch as peas, spinach, or green beans change color on heating from bright green

to a dull olive green This is due to the conversion of chlorophyll to pheophytin It

is possible to protect against this by addition of sodium bicarbonate to the cookingwater, which raises the pH However, this may cause softening of texture, and theuse of added colorants may be a more practical solution Some fruits may losetheir color during canning, while pears develop a pink tinge Potatoes are subject

to browning during heat processing due to the Maillard reaction Therefore, somevarieties are more suitable for fried products, where browning is desirable, thanfor canned products, in which browning would be a major problem

Again there are two approaches: procuring raw materials of the appropriatevariety and stage of maturity, and sorting by color to remove unwanted units.1.2.1.3 Texture

The texture of raw materials is frequently changed during processing Texturalchanges are caused by a wide variety of effects, including water loss, proteindenaturation which may result in loss of water-holding capacity or coagulation,hydrolysis, and solubilization of proteins In plant tissues, cell disruption leads toloss of turgor pressure and softening of the tissue, while gelatinization of starch,hydrolysis of pectin, and solubilization of hemicelluloses also cause softening ofthe tissues

The raw material must be robust enough to withstand the mechanical stressesduring preparation, for example, abrasion during cleaning of fruit and vegetables

1.2 Properties of Raw Food Materials and Their Susceptibility to Deterioration and Damage 5

Peas and beans must be able to withstand mechanical podding Raw materialsmust be chosen so that the texture of the processed product is correct, such ascanned fruits and vegetables in which raw materials must be able to withstand heatprocessing without being too hard or coarse for consumption

Texture is dependent on the variety as well as the maturity of the raw material,and may be assessed by sensory panels or commercial instruments One widelyrecognized instrument is the tenderometer used to assess the firmness of peas Thecrop would be tested daily and harvested at the optimum tenderometer reading

In common with other raw materials, peas at different maturities can be usedfor different purposes, so that peas for freezing would be harvested at a lowertenderometer reading than peas for canning

1.2.1.4 Flavor

Flavor is a rather subjective property which is difficult to quantify Flavor quality ofhorticultural products is influenced by genotype and a range of pre- and postharvestfactors [4] Optimizing maturity/ripeness stage in relation to flavor at the time ofprocessing is a key issue Again, flavors are altered during processing, and followingsevere processing, the main flavors may be derived from additives Hence, the lack

of strong flavors may be the most important requirement In fact, raw materialflavor is often not a major determinant as long as the material imparts only thoseflavors which are characteristic of the food Other properties may predominate.Flavor is normally assessed by human tasters, although sometimes flavor can belinked to some analytical test, such as sugar/acid levels in fruits

1.2.1.5 Functional Properties

The functionality of a raw material is the combination of properties which mine product quality and process effectiveness These properties differ greatly fordifferent raw materials and processes, and may be measured by chemical analysis

deter-or process testing

For example, a number of possible parameters may be monitored in wheat.Wheat for different purposes may be selected according to protein content Hardwheat with 11.5–14% protein is desirable for white bread, and some whole wheatbreads require even higher protein levels (14–16%) [5] On the other hand, soft orweak flours with lower protein contents are suited to chemically leavened productswith a lighter or more tender structure Hence protein levels of 8–11% are adequatefor biscuits, cakes, pastry, noodles, and similar products Varieties of wheat forprocessing are selected on this basis, and measurement of protein content would

be a good guide to process suitability Furthermore, physical testing of doughusing a variety of rheological testing instruments may be useful in predicting thebreadmaking performance of individual batches of wheat flours [6] A further test

is the Hagberg Falling Number which measures the amount ofα-amylase in flour

or wheat [7] This enzyme assists in the breakdown of starch to sugars, and highlevels give rise to a weak bread structure Hence, the test is a key indicator of wheatbaking quality and is routinely used for bread wheat, and often determines theprice paid to the farmer

6 1 Postharvest Handling and Preparation of Foods for Processing

Similar considerations apply to other raw materials Chemical analysis of fat andprotein in milk may be carried out to determine its suitability for manufacturingcheese, yoghurt, or cream

1.2.2

Raw Material Specifications

In practice, processors define their requirements in terms of raw material tions for any process on arrival at the factory gate Acceptance of, or price paid for,the raw material depends on the results of specific tests Milk deliveries would beroutinely tested for hygienic quality, somatic cells, antibiotic residues, extraneouswater, as well as possibly fat and protein content A random core sample is takenfrom all sugar beet deliveries and payment is dependent on the sugar content Forfruits, vegetables, and cereals, processors may issue specifications and tolerances

specifica-to cover the size of units, the presence of extraneous vegetable matter, foreignbodies, levels of specific defects (e.g., surface blemishes, insect damage), and so

on, as well as specific functional tests Guidelines for sampling and testing manyraw materials for processing in the United Kingdom are available from Campden

of demand for organic foods in the United Kingdom and western Europe, whichobviously introduces further demands on production methods that are beyond thescope of this chapter

1.2.3

Deterioration of Raw Materials

All raw materials deteriorate following harvest, by some of the followingmechanisms:

• Endogenous enzymes: Postharvest senescence and spoilage of fruit and

veg-etables occurs through a number of enzymic mechanisms, including oxidation

of phenolic substances in plant tissues by phenolase (leading to browning);sugar–starch conversion by amylases; postharvest demethylation of pectic sub-stances in fruits and vegetables leading to softening tissues during ripening andfirming of plant tissues during processing

• Chemical changes: These include deterioration in sensory quality by lipid

oxida-tion; non-enzymic browning; and breakdown of pigments such as chlorophyll,anthocyanins, and carotenoids

• Nutritional changes: Breakdown of ascorbic acid is an important example.

1.2 Properties of Raw Food Materials and Their Susceptibility to Deterioration and Damage 7

• Physical changes: These include dehydration and moisture absorption.

• Biological changes: Examples are the germination of seeds and sprouting.

• Microbiological contamination: Both the organisms themselves and their toxic

products lead to deterioration of quality, as well as posing safety problems

1.2.4

Damage to Raw Materials

Damage may occur at any point from growing through to the final point of sale Itmay arise through external or internal forces

External forces result in mechanical injury to fruits and vegetables, cereal grains,eggs, and even bones in poultry They occur due to rough handling as a result

of careless manipulation, poor equipment design, incorrect containerization, andunsuitable mechanical handling equipment The damage typically results fromimpact and abrasion between food units, or between food units and machinerysurfaces and projections, excessive vibration or pressure from overlying material.Increased mechanization in food handling must be carefully designed to minimizethis

Internal forces arise from physical changes such as variation in temperature andmoisture content, and may result in skin cracks in fruits and vegetables, or stresscracks in cereals

Either form of damage leaves the material open to further biological or chemicaldamage including enzymic browning of bruised tissue, or infestation of puncturedsurfaces by molds and rots

1.2.5

Improving Processing Characteristics through Selective Breeding

and Genetic Engineering

Selective breeding for yield and quality has been carried out for centuries inboth plant and animal products Until the twentieth century, improvements weremade on the basis of selecting the most desirable looking individuals, whilemore systematic techniques have been developed more recently, based on greaterunderstanding of genetics The targets have been to increase yield as well asaiding factors of crop or animal husbandry such as resistance to pests anddiseases, suitability for harvesting, or development of climate-tolerant varieties(e.g., cold-tolerant maize or drought-resistant plants) [8] Raw material quality,especially in relation to processing, has become increasingly important There aremany examples of successful improvements in processing quality of raw materialsthrough selective plant breeding including:

• improved oil percentage and fatty acid composition in oilseed rape;

• improved milling and malting quality of cereals;

• high sugar content and juice quality in sugar beets;

8 1 Postharvest Handling and Preparation of Foods for Processing

• development of specific varieties of potatoes for the processing industry, based

on levels of enzymes and sugars, producing appropriate flavor, texture and color

in products, or storage characteristics;

• Brussels sprouts which can be successfully frozen

Similarly, traditional breeding methods have been used to improve yields ofanimal products such as milk and eggs, as well as improving quality – for example,fat/lean content of meat Again the quality of raw materials in relation to pro-cessing may be improved by selective breeding This is particularly applicable tomilk, where breeding programs have been used at different times to maximizebutterfat and protein content, and would thus be related to the yield and quality

of fat- or protein-based dairy products Furthermore, particular protein geneticvariants in milk have been shown to be linked with processing characteristics,such as curd strength during manufacture of cheese [9] Hence, selective breed-ing could be used to tailor milk supplies to the manufacture of specific dairyproducts

Traditional breeding programs will undoubtedly continue to produce ments in raw materials for processing, but the potential is limited by the gene poolavailable to any species Genetic engineering extends this potential by allowingthe introduction of foreign genes into an organism, with huge potential benefits.Again many of the developments have been aimed at agricultural improvementssuch as increased yield, or introducing herbicide, pest, or drought resistance.Other developments have aimed to improve the nutritional quality of foods Forexample, transgenic ‘‘Golden’’ rice as a rich source of vitamin A; cereal grainswith increased protein quantity and quality; oilseeds engineered to contain higherlevels of omega-3 fatty acids However, there is enormous potential in geneticallyengineered raw materials for processing [10] The following are some exampleswhich have been demonstrated:

improve-• Tomatoes which do not produce pectinase and hence remain firm while colorand flavor develop, producing improved soup, paste, or ketchup

• Potatoes with higher starch content, which take up less oil and require less energyduring frying

• Canola (rape seed) oil tailored to contain high levels of lauric acid to improveemulsification properties for use in confectionery, coatings, or low-fat dairyproducts; high levels of stearate as an alternative to hydrogenation in manufacture

of margarine; and high levels of polyunsaturated fatty acids for health benefits

• Wheat with increased levels of high molecular weight glutenins for improvedbreadmaking performance

• Fruits and vegetables containing peptide sweeteners such as thaumatin ormonellin

• ‘‘Naturally decaffeinated’’ coffee

There is, however, considerable opposition to the development of geneticallymodified foods in the United Kingdom and elsewhere, due to fears of humanhealth risks and ecological damage, discussion of which is beyond the scope of this

1.3 Storage and Transportation of Raw Materials 9

book It therefore remains to be seen if, and to what extent, genetically modifiedraw materials will be used in food processing

be available throughout the year Effective transportation and storage systems forraw materials are essential to meet this need

Storage of materials whose supply or demand fluctuate in a predictable manner,especially seasonal produce, is necessary to increase availability It is essential thatprocessors maintain stocks of raw materials, therefore storage is necessary to bufferdemand However, storage of raw materials is expensive for two reasons: storedgoods have been paid for and may therefore tie up quantities of company money,and secondly, warehousing and storage space are expensive All raw materialswill deteriorate during storage The quantities of raw materials held in store andthe times of storage vary widely for different cases, depending on the aboveconsiderations The ‘‘just in time’’ approaches used in other industries are lesscommon in food processing

The primary objective is to maintain the best possible quality during storage,and hence avoid spoilage during the storage period Spoilage arises through threemechanisms:

1) Living organisms such as vermin, insects, fungi, and bacteria – these may feed

on the food and contaminate it

2) Biochemical activity within the food leading to quality reduction, such as piration in fruits and vegetables; staling of baked products; enzymic browningreactions; rancidity development in fatty food

res-3) Physical processes, including damage due to pressure or poor handling;physical changes such as dehydration or crystallization

The main factors that govern the quality of stored foods are temperature,moisture/humidity, and atmospheric composition Different raw materials providevery different challenges

Fruits and vegetables remain as living tissues until they are processed and themain aim is to reduce respiration rate without damage to the tissue Storage timesvary widely between types Young tissues such as shoots, green peas, and immaturefruits have high respiration rates and shorter storage periods, while mature fruitsand roots, and storage organs such as bulbs and tubers (e.g., onions, potatoes,sugar beets) respire much more slowly, and hence have longer storage periods

10 1 Postharvest Handling and Preparation of Foods for Processing

Table 1.1 Storage periods of some fruits and vegetables under typical storage conditions.

Commodity Temperature ( ◦ C) Humidity (%) Storage period

Some examples of conditions and storage periods of fruits and vegetables are given

in Table 1.1 Many fruits (including bananas, apples, tomatoes, and mangoes)display a sharp increase in respiration rate during ripening, just before the point

of optimum ripening, known as the ‘‘climacteric.’’ The onset of the climacteric

is associated with the production of high levels of ethylene, which is believed

to stimulate the ripening process Climacteric fruit can be harvested unripe andripened artificially at a later time It is vital to maintain careful temperature controlduring storage or the fruit will rapidly over-ripen Non-climacteric fruits (e.g., citrusfruit, pineapples, strawberries) and vegetables do not display this behavior, andgenerally do not ripen after harvest Quality is therefore optimal at harvest, and thetask is to preserve quality during storage

Harvesting, handling, and storage of fruit and vegetables are discussed in moredetail by Thompson [11], while Nascimento Nunes [12] visually depicts the effects

of time and temperature on the appearance of fruit and vegetables throughoutpostharvest life

With meat storage the overriding problem is growth of spoilage bacteria, whileavoiding oxidative rancidity Cereals must be dried before storage to avoid germi-nation and mold growth, and subsequently must be stored under conditions whichprevent infestation with rodents, birds, insects, or molds

Hence, very different storage conditions may be employed for different rawmaterials The main methods employed in raw material storage are the control oftemperature, humidity, and composition of atmosphere

1.3.1.1 Temperature

The rate of biochemical reactions is related to temperature, such that lower storagetemperatures lead to slower degradation of foods by biochemical spoilage, as well

as reduced growth of bacteria and fungi There may also be limited bacteriocidal

effects at very low temperatures Typical Q values for spoilage reactions are

1.3 Storage and Transportation of Raw Materials 11

approximately 2, implying that spoilage rates would double for each 10◦C rise,

or conversely that shelf life would double for each 10◦C reduction This is an

oversimplification as Q10 may change with temperature Most insect activity isinhibited below 4◦C, although insects and their eggs can survive long exposure tothese temperatures In fact grain and flour mites can remain active and even breed

at 0◦C

The use of refrigerated storage is limited by the sensitivity of materials to lowtemperatures The freezing point is a limiting factor for many raw materials,

as the tissues will become disrupted on thawing Other foods may be subject

to problems at temperatures above freezing Fruits and vegetables may displayphysiological problems that limit their storage temperatures, probably as a result ofmetabolic imbalance leading to a build-up of undesirable chemical species in thetissues Some types of apples are subject to internal browning below 3◦C, whilebananas become brown when stored below 13◦C, and many other tropical fruitsdisplay chill sensitivity Less obvious biochemical problems may occur even where

no visible damage occurs For example, storage temperature affects starch/sugarbalance in potatoes; in particular, below 10◦C a build up of sugar occurs, which ismost undesirable for fried products Examples of storage periods and conditionsare given in Table 1.1, illustrating the wide ranges seen with different fruits andvegetables It should be noted that predicted storage lives can be confounded if theproduce is physically damaged, or by the presence of pathogens

Temperature of storage is also limited by cost Refrigerated storage is expensive,especially in hot countries In practice, a balance must be struck incorporating cost,shelf life, and risk of cold injury Slower growing produce such as onions, garlic,and potatoes can be successfully stored at ambient temperature and ventilatedconditions in temperate climates

It is desirable to monitor temperature throughout raw material storage anddistribution

Precooling to remove the ‘‘field heat’’ is an effective strategy to reduce the period

of high initial respiration rate in rapidly respiring produce prior to transportationand storage For example, peas for freezing are harvested in the cool early morningand rushed to cold storage rooms within 2–3 h Other produce, such as leafyvegetables (lettuce, celery, cabbage) or sweetcorn, may be cooled using water sprays

or drench streams Hydrocooling obviously reduces water loss

1.3.1.2 Humidity

If the humidity of the storage environment exceeds the equilibrium relativehumidity (ERH) of the food, the food will gain moisture during storage, and viceversa Uptake of water during storage is associated with susceptibility to growth ofmicroorganisms, while water loss results in economic loss, as well as more specificproblems such as cracking of seed coats of cereals, or skins of fruits and vegetables.Ideally the humidity of the store would equal the ERH of the food so that moisture

is neither gained nor lost, but in practice a compromise may be necessary The

water activity (aw) of most fresh foods (e.g., fruit, vegetables, meat, fish, milk)

is in the range 0.98–1.00, but they are frequently stored at a lower humidity

12 1 Postharvest Handling and Preparation of Foods for Processing

Some wilting of fruits or vegetable may be acceptable in preference to mold growth,while some surface drying of meat is preferable to bacterial slime Packaging may

be used to protect against water loss of raw materials during storage and transport(see Chapter 8)

1.3.1.3 Composition of Atmosphere

Controlling the atmospheric composition during storage of many raw materials

is beneficial The use of packaging to allow the development or maintenance ofparticular atmospheric compositions during storage is discussed in greater detail

in Chapter 8

With some materials the major aim is to maintain an oxygen-free sphere to prevent oxidation (e.g., coffee, baked goods), while in other casesadequate ventilation may be necessary to prevent anaerobic fermentation leading

With fresh meat, controlling the gaseous environment is useful in combinationwith chilling The aim is to maintain the red color by storage in high O2concen-trations, which shifts the equilibrium in favor of high concentrations of the brightred oxymyoglobin pigment At the same time, high levels of CO2 are required tosuppress the growth of aerobic bacteria

1.3.1.4 Other Considerations

Odors and taints can cause problems, especially in fatty foods such as meat anddairy products, as well as less obvious commodities such as citrus fruits, whichhave oil in the skins Odors and taints may be derived from fuels or adhesivesand printing materials, as well as other foods (e.g., spiced or smoked products).Packaging and other systems during storage and transport must protect againstcontamination

Light can lead to oxidation of fats in some raw materials (e.g., dairy products)

In addition, light gives rise to solanine production and the development of greenpigmentation in potatoes Hence, storage and transport under dark conditions isessential

1.4 Raw Material Cleaning 13

1.3.2

Transportation

Food transportation is an essential link in the food chain, and is discussed indetail by Heap [15] Raw materials, food ingredients, fresh produce, and processedproducts are all transported on a local and global level, by land, sea, and air Inthe modern world, where consumers expect year-round supplies and non-localproducts, long-distance transport of many foods has become commonplace, andair transport may be necessary for perishable materials Transportation of food

is really an extension of storage; a refrigerated lorry is basically a cold store onwheels However, transport also subjects the material to physical and mechanicalstresses, and possibly rapid changes in temperature and humidity, which arenot encountered during static storage It is necessary to consider both the stressesimposed during the transport and those encountered during loading and unloading

In many situations transport is multimodal Air or sea transport would commonlyinvolve at least one road trip before and one road trip after the main journey Therewould also be time spent on the ground at the port or airport where the materialcould be exposed to wide-ranging temperatures and humidities, or bright sunlight,and unscheduled delays are always a possibility During loading and unloading,the cargo may be broken into smaller units where more rapid heat penetration mayoccur

The major challenges during transportation are to maintain the quality of thefood during transport, and to apply good logistics – in other words, to move thegoods to the right place at the right time and in good condition

1.4

Raw Material Cleaning

All food raw materials are cleaned before processing The purpose is obviously toremove contaminants, which range from innocuous to dangerous It is important tonote that removal of contaminants is essential for protection of process equipment

as well as the final consumer For example, it is essential to remove sand, stones,

or metallic particles from wheat prior to milling to avoid damaging the machinery.The main contaminants are:

• unwanted parts of the plant such as leaves, twigs, husks;

• soil, sand, stones, and metallic particles from the growing area;

• insects and their eggs;

• animal excreta, hairs, and so on;

• pesticides and fertilizers;

• mineral oil;

• microorganisms and their toxins

Increased mechanization in harvesting and subsequent handling has generallyled to increased contamination with mineral, plant, and animal contaminants,

14 1 Postharvest Handling and Preparation of Foods for Processing

while there has been a general increase in the use of sprays, leading to creased chemical contamination Microorganisms may be introduced preharvestfrom irrigation water, manure fertilizer, or contamination from feral or domes-tic animals, or postharvest from improperly cleaned equipment, wash waters, orcross-contamination from other raw materials

in-Cleaning is essentially a separation process, in which some difference in physicalproperties of the contaminants and the food units is exploited There are a number ofcleaning methods available, classified into dry and wet methods, but a combinationwould usually be used for any specific material Selection of the appropriate cleaningregime depends on the material being cleaned, the level and type of contaminationand the degree of decontamination required In practice a balance must be struckbetween cleaning cost and product quality, and an ‘‘acceptable standard’’ should bespecified for the particular end-use Avoidance of product damage is an importantcontributing factor, especially for delicate materials such as soft fruit

1.4.1

Dry Cleaning Methods

The main dry cleaning methods are based on screens, aspiration, or magneticseparations Dry methods are generally less expensive than wet methods and theeffluent is cheaper to dispose of, but they tend to be less effective in terms ofcleaning efficiency A major problem is recontamination of the material with dust.Precautions may be necessary to avoid the risk of dust explosions and fires

Screens Screens are essentially size separators based on perforated beds or wiremesh by which larger contaminants are removed from smaller food items (e.g.,

straw from cereal grains, or pods and twigs from peas) This is termed ‘‘scalping’’

(Figure 1.1a) Alternatively ‘‘de-dusting’’ is the removal of smaller particles (e.g.,sand or dust) from larger food units (Figure 1.1b) The main geometries are rotary

drums (also known as reels or trommels) and flatbed designs Some examples

are shown in Figure 1.2 Abrasion, either by impact during the operation of themachinery, or aided by abrasive disks or brushes, can improve the efficiency ofdry screens Screening gives incomplete separations and is usually a preliminarycleaning stage

Aspiration This exploits the differences in aerodynamic properties of the foodand the contaminants It is widely used in the cleaning of cereals, but is alsoincorporated into equipment for cleaning peas and beans The principle is to feedthe raw material into a carefully controlled upward air stream Denser material willfall, while lighter material will be blown away depending on the terminal velocity

Terminal velocity in this case can be defined as the velocity of upward air stream in

which a particle remains stationary, and depends on the density and projected area

of the particles (as described by Stokes’ equation) By using different air velocities,

it is possible to separate, say, wheat from lighter chaff (Figure 1.3) or denser smallstones Very accurate separations are possible, but large amounts of energy are

1.4 Raw Material Cleaning 15

(b)

Figure 1.1 Screening of dry particulate materials: (a) scalping and (b) de-dusting.

required to generate the air streams Obviously the system is limited by the size

of raw material units, but is particularly suitable for cleaning legumes and cereals.Air streams may also be used simply to blow loose contaminants from larger itemssuch as eggs or fruit

Magnetic cleaning This is the removal of ferrous metal using permanent orelectromagnets Metal particles derived from the growing field or picked up duringtransport or preliminary operations constitute a hazard both to the consumer and

to processing machinery (e.g cereal mills) The geometry of magnetic cleaningsystems can be quite variable: particulate foods may be passed over magnetizeddrums or magnetized conveyor belts, or powerful magnets may be located aboveconveyors Electromagnets are easy to clean by turning off the power Metaldetectors are frequently employed prior to sensitive processing equipment as well

as to protect consumers at the end of processing lines

Electrostatic cleaning This can be used in a limited number of cases wherethe surface charge on raw materials differs from contaminating particles Theprinciple can be used to distinguish grains from other seeds of similar geometrybut different surface charge, and has also been described for cleaning tea The feed

is conveyed on a charged belt and charged particles are attracted to an oppositelycharged electrode according to their surface charge (Figure 1.4)

16 1 Postharvest Handling and Preparation of Foods for Processing

Feed

Feed

Stock

Oversized refuse

Oversize

Product Screen 1

Screen 2

Undersize

Vibrating drive unit

(a)

(b)

Figure 1.2 Screen geometries: (a) rotary screen and (b) principle of flatbed screen.

1.4 Raw Material Cleaning 17

Lower surface positive charge

Figure 1.4 Principle of electrostatic cleaning.

1.4.2

Wet Cleaning Methods

Wet methods are necessary if large quantities of soil are to be removed, andare essential if detergents are used They are, however, expensive as large quan-tities of high purity water are required, and the same quantity of dirty effluent

18 1 Postharvest Handling and Preparation of Foods for Processing

is produced Treatment and reuse of water can reduce costs Employing thecountercurrent principle can reduce water requirement and effluent volumes ifaccurately controlled Sanitizing chemicals such as chlorine, citric acid, and ozoneare commonly used in wash waters, especially in association with peeling and sizereduction, where reducing enzymic browning may also be an aim [16] Levels of100–200 mg l−1 chlorine or citric acid may be used, although their effectivenessfor decontamination has been questioned and they are not permitted in somecountries

Soaking is a preliminary stage in cleaning heavily contaminated materials such

as root crops, permitting softening of the soil, and partial removal of stonesand other contaminants Metallic or concrete tanks or drums are employed,and these may be fitted with devices for agitating the water, including stirrers,paddles, or mechanisms for rotating the entire drum For delicate produce such

as strawberries or asparagus, or products which trap dirt internally (e.g., celery),sparging air through the system may be helpful The use of warm water or includingdetergents improves cleaning efficiency, especially where mineral oil is a possiblecontaminant, but adds to the expense and may damage the texture

Spray washing is very widely used for many types of food raw material Efficiencydepends on the volume and temperature of the water and time of exposure As

a general rule, small volumes of high-pressure water give the most efficient dirtremoval, but this is limited by product damage, especially to more delicate produce.With larger food pieces it may be necessary to rotate the unit so that the wholesurface is presented to the spray (Figure 1.5a) The two most common designs

Fruit piece

(a)

(b)

Figure 1.5 Water spray cleaning: (a) spray belt washer and (b) drum washer.