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Handbook ofPostharvest Technology

Cereals, Fruits, Vegetables,Tea, and Spices

edited byAmalendu ChakravertyIndian Institute of TechnologyKharagpur, India

Arun S. MujumdarNational University of SingaporeSingapore

G. S. Vijaya RaghavanHosahalli S. RamaswamyMcGill UniversitySainte-Anne-de-BellevueQuebec, Canada

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and Wolfgang BarzHandbook of Postharvest Technology Cereals, Fruits, Vegetables, Tea, and Spices,

edited by Amalendu Chakraverty, Arun S Mujumdar, G S Vijaya Raghavan,and Hosahalh S Ramaswamy

Handbook of Soil Acidity, edited by Zdenko Rengel

Additional Volumes in Preparation

Humic Matter: Issues and Controversies in Soil and Environmental Science, Kim H.Tan

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Preface

In order to prevent huge quantitative as well as qualitative losses of fruits, vegetables,cereals, pulses, spices, and plantation crops, all steps of improved postharvest technology(PHT) must be carefully designed and implemented, beginning with harvesting and endingwith consumption and utilization of their products and by-products.

To derive optimal benet from production techniques, the engineering principlesand practice of harvesting and threshing and their effects on grain yield have been outlinedin this book. Drying is one of the most important operations in PHT. Hence, the theory,principles, methods, and commercial dryers associated with grain-drying systems havebeen narrated systematically. A chapter on the drying of fruits, vegetables, and spices isincluded as well. This book also deals with the principles of grain storage, infestationcontrol and pesticide applications, warehouses, silos, and special storage methods. Presentmilling technologies of grains, especially processing and milling of rice and pulses, areillustrated and described. Rice husks and other agro-industrial by-products pose a seriousdisposal problem. Therefore, a chapter is devoted to the conversion and utilization ofbiomass, with an emphasis on combustion and furnaces, gasication and gasiers, andchemical processing of biomass and by-products. Moreover, utilization of fruit and vegeta-ble by-products is incorporated. Importance has also been placed on the structure, compo-sition, properties, and grades of food grains. Postharvest technology of tea, coffee, cocoa,and spices has been included as well. Postharvest technology of fruits and vegetables isdiscussed, covering in detail postharvest physiology, maturity, quality, grades, cooling,storage, disease detection, packaging, transportation, handling, and irradiation.

Although PHT has been introduced as a eld of study at various agricultural univer-sities and food technological institutes all over the world in the last few decades, practicallyno attempt has been made to develop a comprehensive handbook of PHT that deals withengineering principles and modern technologies.

iii

iv Preface

Thus, a comprehensive handbook covering both fundamentals and present practiceof PHT of grains, fruits, and vegetables for the production of food, feed, chemicals, andenergy should serve as a valuable source of information to a worldwide audience con-cerned with agricultural sciences and engineering, food technology, and other alliedsubjects.

Postharvest technology is an interdisciplinary subject. Therefore, the contributingauthors of this book are specialists recognized in their respective disciplines.

We take this opportunity to express our heartfelt thanks to the chapter authors fortheir timely and valuable contributions. We wish to pay homage to the contributorsDr. A. C. Datta and Dr. R. S. Satake, who are no longer with us in person. Sincere thanksare due to the editorial staff of Marcel Dekker, Inc., and all the other people who assistedus directly and indirectly. The wholehearted cooperation of our families is also deeplyappreciated.

Amalendu ChakravertyArun S. Mujumdar

G. S. Vijaya RaghavanHosahalli S. Ramaswamy

Introduction: Production, Trade,Losses, Causes, and Preservation

The need to increase food production to meet the requirements of a rapidly growing worldpopulation is widely recognized. Cereals, pulses, fruits, and vegetables are the importantfood crops in the world as these are the bulk sources of calories, proteins, and nutrients,and spices and plantation crops play an important role in the economies of many countries.To supply an adequate quantity of grains and other food to the expanding world populationis a challenge to mankind. Rice and wheat have an added importance in national andinternational trade with political and social implications.

The supply of grains and other food crops can be augmented by increasing produc-tion as well as by reducing postharvest losses. The production of food has increased sig-nicantly during the last few decades due to successful research and development effortsin both areas. The use of recently developed high-yielding crops has created a high yieldpotential when it is supplemented with suitable application of fertilizer and modern man-agement practice. The term green revolution is used to reveal the impact of high-yielding cultivars on the world of agriculture.

1 PRODUCTION AND TRADEWorldwide wheat production has increased remarkably since the 1960s, as has the world-wide production of rice. In the period from 1950 to 1971, the world grain productionnearly doubled. This dramatic increase is strongly due to the higher use of fertilizers andimproved cultivars. Wheat and rough rice production in different countries is shown inTable 1.

Table 2 shows the major grain exporting and importing countries in 1997. The pro-duction of pulses and some fruits and vegetables in 1996 is shown in Tables 3 and 4,

v

vi Introduction

Table 1 Wheat and Paddy Production (1000 MT) in SomeCountries

Wheat production, Paddy production,Country 1996 1996

India 62620.0 120012.0China 109005.0 190100.0Russian Fed. 87000.0 2100.0U.S.A. 62099.0 7771.0Canada 30495.0 France 35946.0 116.0Australia 23497.0 951.0Pakistan 16907.0 5551.0Argentina 5200.0 974.0World 584870.0 562260.0

Source: FAO Production Year Book, Vol. 50, FAO, Rome, 1996.

Table 2 Grain Export and Import (million tonnes) ThroughMajor Seaports of the World, 1997Country Export Country Import

3 Canadian ports 27.202 3 Egyptian ports 2.7597 U.S. ports 94.804 7 Chinese ports 1.4664 European ports 13.401 3 S. Korean ports 12.0004 Australian ports* 12.509 7 Japanese ports* 8.674

* 19971998.Source: World Grain, Nov. 1998.

Table 3 Pulse Production (1000 MT) inSome Continents/Countries

Continent/country Production, 1996

Asia 28222Africa 7651Europe 9380N. America 5541S. America 3770Australia 2186India 14820China 4979Brazil 2862France 2636World 56774

Source: IndiaFAO Production Year Book, Vol.49, FAO, Rome, 1995; othersFAO ProductionYear Book, Vol. 50, FAO, Rome, 1996.

Introduction vii

Table 4 Fruit and Vegetable Production (million tonnes) in SelectedCountries

Production, 1996

Country Apple Orange Mango Potato

China 16.00 2.26 1.21 46.03India 1.20 2.00 10.00 17.94Russian Fed. 1.80 38.53Poland 1.70 22.50Brazil 0.65 21.81 0.44 2.70Mexico 0.65 3.56 1.20France 2.46 6.46Germany 1.59 13.60U.S.A. 4.73 10.64 22.55World 53.67 59.56 19.22 294.82

Source: FAO Production Year Book, Vol. 50, FAO, Rome, 1996.

respectively. The world supply, demand, and stock (19971998) of some importantgrainswheat, rice, maize, and barleyalong with their cultivation area and yield arepresented in Table 5. In addition, Figures 1 and 2 represent the world prices of wheatfrom 19701971 to 19971998 and maize from 19811982 to 19971998, respectively.These reveal the international status of grains, fruits, and vegetables.

As regards the world trade activity (19961997) of food and feed grainswheat,maize, barley, soybean, rice, and sorghumit is interesting to note that some countriesare perennial powerhouses in grain exports, such as the United States, Australia, Canada,the European Union countries, and Argentina, whereas Egypt, Japan, China, and Mexiconearly always rank among the top grain importers (World Grain, Nov. 1998).

2 LOSSES AND CAUSESHunger and malnutrition can exist in spite of adequate food production. These can be theresult of uneven distribution, losses, and deterioration of available food resources. Hence,maximum utilization of available food and minimization of postharvest food losses areabsolutely essential.

Losses vary by crop variety, year, pest, storage period, methods of threshing, drying,handling, storage, processing, transportation, and distribution according to both the climateand the culture in which the food is produced and consumed. With such an enormousvariability, it is not surprising that reliable statistics of postharvest food losses are notavailable. It is also very difcult to determine the exact magnitude of losses. Fortunately,research and development and education activities related to postharvest technology ofcrops have been growing. For each postharvest operation there is a possibility of somelosses either in quantity or in quality of crop product. For cereals, the overall postharvestlosses are usually estimated to be in the range of 520%, whereas for fruits and vegetablesit may vary from 20% to 50%. If these losses can be minimized, many countries of theworld may become self-sufcient in food.

The major purpose of food processing is to protect food against deterioration. Allfood materials are subject to spoilage. The rate of spoilage of raw food commodities may

viii Introduction

Table 5 World Grain Position (in million tonnes and hectares), 19971998WHEAT

Supply Demand Ending stocks 132.0

Beginning stocks 109.7 Food use 420.5Production 609.3 Feed use 99.9 Wheat area 230.8Total 719.0 Other 66.6 Yield (tonnes/ha) 2.65

Total 587.0

RICE (milled)Supply Demand Ending stocks 52.1

Beginning Stocks 51.2 All usesProduction 384.6 Rice area 148.2Total 435.8 Yield (tonnes/ha) 2.6

MAIZE

Supply Demand Ending stocks 87.7

Beginning Stocks 91.3 Feed 405.6Production 578.6 Other 176.6 Maize area 136.9Total 669.9 Total 582.2 Yield (tonnes/ha) 4.23

BARLEY

Supply Demand Ending stocks 31.3

Beginning Stocks 91.3 All uses 147.2Production 154.5 Barley area 65.3Total 178.5 Yield (tonnes/ha) 2.37Source: World Grain, Nov. 1998

be very high for fruits and vegetables and not as rapid in the case of cereals and pulses.The spoilage of food is due to three main causes: 1) microbial, 2) enzymatic, and 3)chemical.

All foods during storage are more or less infected with microbes, which cause de-composition of the food constituents, often with the production of evil-smelling and toxicsubstances. Hence, prevention of microbiological spoilage is essential in any preservationmethod.

Enzymes, being normal constituents of food, can break down its proteins, lipids,carbohydrates, etc., into smaller molecules and are also responsible for enzymatic brow-ning or discoloration of food. Hence, no food can be preserved properly if its enzymesare not inactivated.

The different chemical constituents of food also react with one another or with theambient oxygen, causing alteration in color, avor, or nutrients.

3 PRESERVATIONIdeally, any method of food preservation should prevent all the above three types of spoil-age, but none of the present industrial methods fullls the requirements completely. All

Introduction ix

Fig. 1 Export wheat prices, 19701971 through 19971998 (JulyJune). (From World Grain,Nov. 1998.)

Fig. 2 Export maize prices, 19811982 through 19971998 (JulyJune). (From World Grain,Nov. 1998.)

x Introduction

these methods must prevent microbial spoilage, but they may be effective to varying de-grees in preventing enzymatic and chemical spoilage.

Leaving aside potential innovative preservation techniques such as ohmic heating,pulsed electric eld, edible coating, and encapsulation, generally, industrial methods offood preservation include:

Removal of moisturedrying/dehydration, concentration, etc.Removal of heatrefrigeration/cold-storage, freezing, etc.Addition of heatcanning, pasteurization, etc.Addition of chemicals/preservativesFermentationOther methodsapplication of high-frequency current, irradiation, etc.

Apart from these, various other technologies such as pyrolysis, gasication, combus-tion, and chemical and biochemical processing are also used for conversion of biomassand grain by-products to chemicals, energy, and other value-added products.

Amalendu Chakraverty

BIBLIOGRAPHYA Chakraverty. Postharvest Technology. Eneld, NH: Science Publishers, 2001.JG Ponte, K Kulp, eds. Handbook of Cereal Science and Technology, Second Edition, Revised and

Expanded. New York: Marcel Dekker, 2000.

Contents

Preface iiiIntroduction vContributors xv

Part I: Properties, Grades, Harvesting, and Threshing

1. Structure and Composition of Cereal Grains and Legumes 1Esmaeil Riahi and Hosahalli S. Ramaswamy

2. Physical and Thermal Properties of Cereal Grains 17Shyam S. Sablani and Hosahalli S. Ramaswamy

3. Grain-Grading Systems 41Rajshekhar B. Hulasare, Digvir S. Jayas, and Bernie L. Dronzek

4. Harvesting and Threshing 57Adhir C. Datta

Part II: Drying

5. Grain Drying: Basic Principles 119Arun S. Mujumdar and Janos Beke

xi

xii Contents

6. Grain-Drying Systems 139Susanta Kumar Das and Amalendu Chakraverty

7. Commercial Grain Dryers 167G. S. Vijaya Raghavan

Part III: Storage and Handling

8. Grain Storage: Perspectives and Problems 183Somiahnadar Rajendran

9. Structural Considerations: Warehouse and Silo 215Ananada P. Gupta and Sriman K. Bhattacharyya

10. Controlled Atmosphere Storage of Grain 235Noel D. G. White and Digvir S. Jayas

Part IV: Milling

11. Grain-Milling Operations 253Ashok K. Sarkar

12. Specialty Milling 327Ashok K. Sarkar

13. Rice Milling and Processing 373Robert S. Satake

14. Dehulling and Splitting Pulses 397Shahab Sokhansanj and Rhambo T. Patil

15. Milling of Pulses 427Hampapura V. Narasimha, N. Ramakrishnaiah, and V. M. Pratape

Part V: Postharvest Technology of Fruits and Vegetables

16. Postharvest Physiology of Fresh Fruits and Vegetables 455Jennifer R. DeEll, Robert K. Prange, and Herman W. Peppelenbos

17. Maturity and Quality Grades for Fruits and Vegetables 485Thomas H. J. Beveridge

18. Cooling and Storage 505Timothy J. Rennie, Clement Vigneault, Jennifer R. DeEll, and G. S.Vijaya Raghavan

Contents xiii

19. Packaging of Fruits and Vegetables 539James P. Smith, Hosahalli S. Ramaswamy, Byrappa Ranganna, andG. S. Vijaya Raghavan

20. Transportation and Handling of Fresh Fruits and Vegetables 555Catherine K. P. Hui, Denyse I. LeBlanc, Clement Vigneault, JenniferR. DeEll, and Samson A. Sotocinal

21. Potential Applications of Volatile Monitoring in Storage 585Peter Alvo, Georges Dodds, G. S. Vijaya Raghavan, Ajjamada C.Kushalappa, and Cristina Ratti

22. Irradiation of Fruits, Vegetables, Nuts, and Spices 623Monique Lacroix, Miche`le Marcotte, and Hosahalli S. Ramaswamy

23. Drying of Fruits, Vegetables, and Spices 653Stefan Grabowski, Miche`le Marcotte, and Hosahalli S. Ramaswamy

Part VI: Postharvest Technology of Coffee, Tea, and Cocoa24. Coffee: A Perspective on Processing and Products 697

Kulathooran Ramalakshmi and Bashyam Raghavan

25. Tea: An Appraisal of Processing Methods and Products 741Srikantayya Nagalakshmi

26. Postharvest Technology of Cocoa 779Kamaruddin Abdullah

Part VII: Biomass, By-Products, and Control Aspects27. Conversion and Utilization of Biomass 797

Amalendu Chakraverty

28. Utilization of By-Products of Fruit and Vegetable Processing 819Waliaveetil E. Eipeson and Ramesh S. Ramteke

29. Control Aspects of Postharvest Technologies 845Istvan Farkas

Index 867

Contributors

Peter Alvo, M.Sc. Department of Agricultural and Biosystems Engineering, McGillUniversity, Sainte-Anne-de-Bellevue, Quebec, Canada

Janos Beke, Ph.D. Department of Automotive and Thermal Technology, Faculty ofMechanical Engineering, Szent Istvan University, Godollo, Hungary

Thomas H. J. Beveridge, Ph.D. Pacic Agri-Food Research Centre, Agriculture andAgri-Food Canada, Summerland, British Columbia, Canada

Sriman K. Bhattacharyya, Ph.D. Department of Civil Engineering, Indian Institute ofTechnology, Kharagpur, India

Amalendu Chakraverty, Ph.D. Post Harvest Technology Centre, Department of Ag-ricultural and Food Engineering, Indian Institute of Technology, Kharagpur, India

Susanta Kumar Das, M.Tech, Ph.D. Post Harvest Technology Centre, Department ofAgricultural and Food Engineering, Indian Institute of Technology, Kharagpur, India

Adhir C. Datta, Ph.D. Department of Agricultural and Food Engineering, Indian Insti-tute of Technology, Kharagpur, India

Deceased.

xv

xvi Contributors

Jennifer R. DeEll, Ph.D, P.Ag. Fresh Market Quality Program, Ontario Ministry ofAgriculture and Food, Vineland Station, Ontario, Canada

Georges Dodds Department of Agricultural and Biosystems Engineering, McGill Uni-versity, Sainte-Anne-de-Bellevue, Quebec, Canada

Bernie L. Dronzek, Ph.D. Department of Plant Science, University of Manitoba, Winni-peg, Manitoba, Canada

Waliaveetil E. Eipeson, Ph.D.* Department of Fruit and Vegetable Technology, Cen-tral Food Technological Research Institute, Mysore, India

Istvan Farkas, D.Sc. Department of Physics and Process Control, Szent Istvan Univer-sity, Godollo, Hungary

Stefan Grabowski, Ph.D. Food Research and Development Centre, Agriculture andAgri-Food Canada, Saint-Hyacinthe, Quebec, Canada

Ananada P. Gupta Department of Civil Engineering, Indian Institute of Technology,Kharagpur, India

Catherine K. P. Hui Horticultural Research and Development Centre, Agriculture andAgri-Food Canada, Saint-Jean-sur-Richelieu, Quebec, Canada

Rajshekhar B. Hulasare, Ph.D. Department of Biosystems Engineering, University ofManitoba, Winnipeg, Manitoba, Canada

Digvir S. Jayas, Ph.D., P.Eng., P.Ag. Department of Biosystems Engineering, Univer-sity of Manitoba, Winnipeg, Manitoba, Canada

Kamaruddin Abdullah, Dr. Department of Agricultural Engineering, Institut PertanianBogor, Bogor, Indonesia

Ajjamada C. Kushalappa, Ph.D. Department of Plant Science, McGill University,Sainte-Anne-de-Bellevue, Quebec, Canada

Monique Lacroix, Ph.D. Research Centre in Applied Microbiology and Biotechnology,Canadian Irradiation Centre and INRSInstitute Armand-Frappier, University of Quebec,Laval, Quebec, Canada

Denyse I. LeBlanc, M.Sc. Atlantic Food and Horticulture Research Centre, Agricultureand Agri-Food Canada, Kentville, Nova Scotia, Canada

* Retired.

Contributors xvii

Miche`le Marcotte, Ph.D. Food Research and Development Centre, Agriculture andAgri-Food Canada, Saint-Hyacinthe, Quebec, Canada

Arun S. Mujumdar, Ph.D. Department of Mechanical Engineering, National Univer-sity of Singapore, Singapore and Department of Chemical Engineering, McGill University,Quebec, Canada

Srikantayya Nagalakshmi, M.Sc.* Department of Plantation Products, Spices, and Fla-vour Technology, Central Food Technological Research Institute, Mysore, India

Hampapura V. Narasimha, M.Sc., Ph.D. Department of Grain Science and Technol-ogy, Central Food Technological Research Institute, Mysore, India

Rhambo T. Patil, Ph.D. Central Institute for Agricultural Engineering, Bhopal, India

Herman W. Peppelenbos, Dr. Postharvest Quality of Fresh Products, Agrotechnologi-cal Research Institute (ATO-DLO), Wageningen, The Netherlands

Robert K. Prange, Ph.D, P.Ag. Atlantic Food and Horticulture Research Centre, Agri-culture and Agri-Food Canada, Kentville, Nova Scotia, Canada

V. M. Pratape Department of Grain Science and Technology, Central Food Technologi-cal Research Institute, Mysore, India

Bashyam Raghavan, M.Sc. Department of Plantation Products, Spices, and FlavourTechnology, Central Food Technological Research Institute, Mysore, India

G. S. Vijaya Raghavan, B.E., M.Sc., Ph.D. Department of Agricultural and BiosystemsEngineering, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada

Somiahnadar Rajendran, Ph.D. Department of Food Protectants and Infestation Con-trol, Central Food Technological Research Institute, Mysore, India

N. Ramakrishnaiah Department of Grain Science and Technology, Central Food Tech-nological Research Institute, Mysore, India

Kulathooran Ramalakshmi, M.Sc. Department of Plantation Products, Spices, andFlavour Technology, Central Food Technological Research Institute, Mysore, India

Hosahalli S. Ramaswamy, Ph.D. Department of Food Science and Agricultural Chem-istry, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada

Ramesh S. Ramteke, Ph.D. Department of Fruit and Vegetable Technology, CentralFood Technological Research Institute, Mysore, India

* Retired.

xviii Contributors

Byrappa Ranganna, Ph.D. Division of Agricultural Engineering, University of Ag-ricultural Sciences, Bangalore, India

Cristina Ratti Departement des Sols et de Genie Agroalimentaire, Universite Laval,Sainte-Foy, Quebec, Canada

Timothy J. Rennie, M.Sc. Horticultural Research and Development Centre, Agricultureand Agri-Food Canada, Saint-Jean-sur-Richelieu, Quebec, Canada

Esmaeil Riahi, Ph.D. Department of Food Science and Agricultural Chemistry, McGillUniversity, Sainte-Anne-de-Bellevue, Quebec, Canada

Shyam S. Sablani, Ph.D. Department of Bioresource and Agricultural Engineering, Sul-tan Qaboos University, Al-Khod, Muscat, Oman

Ashok K. Sarkar Milling Technology and Quality Control, Department of Food Tech-nology, Canadian International Grains Institute, Winnipeg, Manitoba, Canada

Robert S. Satake, D.Eng. Satake Corp., Hiroshima, Japan

James P. Smith, Ph.D. Department of Food Science and Agricultural Chemistry,McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada

Shahab Sokhansanj, Ph.D. Department of Agriculture and Bioresource Engineering,University of Saskatchewan, Saskatoon, Saskatchewan, Canada

Samson A. Sotocinal, Ph.D. Department of Agricultural and Biosystems Engineering,McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada

Clement Vigneault, Ph.D. Horticultural Research and Development Centre, Agricultureand Agri-Food Canada, Saint-Jean-sur-Richelieu, Quebec, Canada

Noel D. G. White, Ph.D. Cereal Research Centre, Agriculture and Agri-Food Canada,Winnipeg, Manitoba, Canada

Deceased.

1Structure and Composition of CerealGrains and Legumes

ESMAEIL RIAHI and HOSAHALLI S. RAMASWAMYMcGill University, Sainte-Anne-de-Bellevue, Quebec, Canada

1 INTRODUCTIONCereals are monocotyledonous plants that belong to the grass family. Based on botanistsapproximation, there are about 350,000 plant species, of which about 195,000 species areeconomically important owering plants. Nearly 50 species are cultivated worldwide andas few as 17 species provide 90% of human food supply and occupy about 75% of the totaltilled land on earth. They consist of wheat, rice, corn, potato, barley, sweet potato, cassava,soybean, oat, sorghum, millet, rye, peanut, eld bean, pea, banana, and coconut. The cerealgrains such as wheat, rice, corn, barley, oat, rye, sorghum, and millet provide 50% of thefood energy and 50% of the protein consumed on earth. Wheat, rice, and corn togethermake up three-fourths of the worlds grain production. In general, cereal grains have beenconsidered as the source of carbohydrates to supply food energy to the diet. Cereal grains,especially rice and wheat, provide the bulk of energy consumed on earth (Stoskopf, 1985).

The cereal crops that are grown for their edible fruit are generally called grain, butbotanically referred to as caryopsis. The cereal seed consists of two major components,the endosperm and embryo or germ. The endosperm encompass the bulk of the seed andis the energy source of stored food. An outer wall called the pericarp that develops fromthe ovary wall encases the endosperm. A semipermeable layer under the pericarp, whichis called testa, surrounds the embryo and is derived from the inner ovary wall. The testais permeable to water, but not to dissolved salts, and is important for germination. Thethird layer, which is called aleurone, contains thick-walled cells that are free of starch.The pericarp, testa, and aleurone layer are collectively called the bran.

The legumes such as chickpea, black gram, mung bean, and pigeon pea, have anestimated 16,00019,000 species in 750 genera. Asia ranks rst both in area harvested

1

2 Riahi and Ramaswamy

and production. India accounts for 75 and 96% of the total global production of thechickpea and pigeon pea, respectively. The term legume originated from the Latin le-gumen, which means seed harvested in pods. The expression food legumes usually meansthe immature pods and seeds as well as mature dry seeds used as food by humans. Basedon Food and Agricultural Organization (FAO) practice, the term legume is used for allleguminous plants. Legumes such as French bean, lima bean, or others, that contain asmall amount of fat are termed pulses, and legumes that contain a higher amount of fat,such as soybean and peanuts, are termed leguminous oilseeds. Legumes are importantsources of food in developing countries. Soybean, groundnut, dry bean, pea, broad bean,chickpea, and lentil are the common legumes in the most countries. In some countries,depending on the climatic condition and food habits, other legumes are grown. Legumesare next to cereals in terms of their economic and nutritional importance as human foodsources. They are cultivated not only for their protein and carbohydrate content, but alsobecause of the oil content of oilseed legumes such as soybeans and peanuts.

Legumes are reasonably priced sources of protein, generally about double that ofmost cereals, and have a high food value; also, they are fair sources of some vitaminsand minerals. Legumes have almost the same caloric value per unit weight as cereals.Legumes are a better source of calcium than cereals and contain 100200 mg of calciumper 100 g. Legumes, when compared with cereals, are a better source of iron, thiamine,riboavin, and nicotinic acid. The utilization of legumes is highest in India and LatinAmerica owing to religious restriction and food attitude. Legumes also contain someantinutritional factors, such as trypsin and chymotrypsin, phytate, lectins, polyphenols,atulence-provoking and cyanogenic compounds, lathyrogens, estrogens, goitrogens,saponins, antivitamins, and allergens. However heat treatment is known to destroy theantinutrients, such as protease inhibitors and lectins, although it also destroys the vitaminsand amino acids. Legumes are a good source of dietary ber; the crude ber, protein, andlipid components have a hypocholesterolemic effect.

The following is a brief account of the structure and composition of the major cerealcrops and legumes.

2 CEREAL CROPS2.1 Structure2.1.1 Wheat

Wheat is a single-seeded fruit, 4- to 10-mm long, consisting of a germ and endospermenclosed by an epidermis and a seed coat. The fruit coat or pericarp (45- to 50-m thick)surrounds the seed and adheres closely to the seed coat. The wheat color, depending onthe species and other factors, is red to white, and is due to material present in the seedcoat. Wheat also is classied based on physical characteristics such as red, white, soft,hard, spring, or winter. The wheat kernel structure is shown in Fig. 1. The outer pericarpis composed of the epidermis and hypodermis. The epidermis consists of a single layerof cells that form the outer surface of the kernel. On the outer walls of the epidermal cellsis the water-impervious cuticle. Some epidermal cells at the apex of the kernel are modiedto form hairs. The hypodermis is composed of one to two layers of cells. The inner pericarpis composed of intermediate cells and cross-cells inward from the hypodermis. Long andcylindrical tube cells constitute the inner epidermis of the pericarp. In the crease, the seedcoat joins the pigment strand, and together they form a complete coat about the endosperm

Structure and Composition of Cereal Grains 3

Fig. 1 Diagrammatic illustrations of wheat structure. (From Lasztity, 1999.)

and germ. Three layers can be distinguished in the seed coat: a thick outer cuticle, a colorlayer that contains pigment, and a very thin inner cuticle. The bran comprises all outerstructures of the kernel inward to, and including, the aleurone layer. This layer is the outerlayer of the endosperm, but is considered as part of the bran by millers. The aleuronelayer is usually one cell thick and almost completely surrounds the kernel over the starchyendosperm and germ. The endosperm is composed of peripheral, prismatic, and centralcells that are different in shape, size, and position within the kernel. The endosperm cellsare packed with starch granules, which lie embedded in a matrix that is largely protein.Additional details on the wheat structure can be found in Lasztity (1999).2.1.2 CornCorn or maize (Zea mays L.) is an important cereal crop in North America. Maize withina few weeks, develops from a small seed to a plant, typically 2- to 3.5-m tall. Corn appar-ently originated in Mexico and spread northward to Canada and southward to Argentina.The corn seed is a single fruit called the kernel. It includes an embryo, endosperm, aleu-rone, and pericarp. The pericarp is a thin outer layer that has a protection role for theendosperm and embryo. Pericarp thickness ranges from 25 to 140 m among genotypes.Pericarp adheres tightly to the outer surface of the aleurone layer and is thought to impartsemipermeable properties to the corn kernel. All parts of the pericarp are composed of

4 Riahi and Ramaswamy

Fig. 2 Diagram of a corn kernel. (From Potter, 1986.)

dead cells that are cellulosic tubes. The innermost tube-cell layer is a row of longitudinaltubes pressed tightly against the aleurone layer. This layer is covered by a thick and rathercompact layer, known as the mesocarp, composed of closely packed, empty, elongatedcells with numerous pits. A waxy cutin layer that retards moisture exchange covers anouter layer of cells, the epidermis. The endosperm usually comprises 8284% of the kerneldry weight and 8689% starch by weight. The outer layer of endosperm or the aleuronelayer is a single layer of cells of an entirely different appearance. This layer covers theentire starchy endosperm. The germ is composed of the embryo and the scutellum. Thescutellum acts as the nutritive organ for the embryo, and the germ stores nutrients andhormones that are necessary for the initial stage of germination. A typical longitudinalsection of a kernel of corn is shown in Fig. 2 and additional details can be found in Potter(1986).2.1.3 RiceRice (Oryza sativa L.) is one of the major food staples in the world. The ripe rice isharvested as a covered grain (rough rice or paddy), in which the caryopsis is enclosed ina tough hull or husk composed mostly from silica. The pericarp is fused to the seed andcomprises seed coat, nucellus, endosperm, and embryo. The caryopsis is covered by hull,composed of two modied leaves: the palea and larger lemma. The hull provides protectionfor the rice caryopsis. The hull also protects the grain from insect infestation and fungaldamage. The hull consist of four structural layers: (a) an outer epidermis of highly siliciedcells; (b) sclerenchyma or hypoderm bers two- or three-celllayers thick; (c) crushed,spongy parenchyma cells; and (d) inner epidermis of generally isodiametric cells. The

Structure and Composition of Cereal Grains 5

Fig. 3 Structure of the rice grain. (From Juliano, 1985.)

embryo or germ is very small and is located on the central side at the base of the grain.The typical structure of the rice grain is shown in Fig. 3; additional details can be foundin Juliano (1985).2.1.4 BarleyBarley (Hordeum vulgare L.) also belongs to the grass family and is one of the majorancient worlds crops. It contributes to the human food, malt products, ranks the top tencrops, and is fourth among the cereals. In the commercial barley, the owering glumesor husk is attached to the grain, whereas some varieties are hull-less and the grain isseparate from the husk. The husk is usually pale yellow or buff and is made up of fourtypes of cells, which are dead at maturity. The caryopsis is located in the husk and thepericarp is fused to the seed coat or testa. Within the seed coat the largest tissue is thestarchy endosperm that is bonded to the aleurone layer. The embryo is located at the baseof the grain. The longitudinal section of the mature barley is shown in Fig. 4, and furtherdetails can be found in MacGregor and Bhatty (1993).2.1.5 OatOat is grown for both grain and forage needs. The hull contributes to about 30% of thetotal kernel weight. It consists of leaf-like structures that tightly enclose the groat andprovide protection during seed growth. At the early stage of growth, the hull assists innutrient transport and contributes signicantly to groat nutrition. Contribution of hulls tothe total dietary ber content of oat is considerable; the hemicellulose content of the oat

6 Riahi and Ramaswamy

Fig. 4 Structure of the mature barley. (From MacGregor and Bhatty, 1993.)

hull is between 30 and 50%. After removing the hulls, the morphology of remaining groatis not unlike other common cereals. The groat is longer and more slender than wheatand barley and, mostly, is covered extensively with hairs. The groat consists of threemorphological and chemically distinct components: bran, germ, and starchy endosperm.These components are traditional descriptions of commercial fractions and do not accu-rately reect the genetic, chemical, or fractional characteristics of each fraction. The struc-ture of the oat kernel is shown in Fig. 5 (Webster, 1986).2.1.6 RyeRye (Secale cereale L.), another member of the grass family, has two species: S. fragileand S. cereale. Rye is used mostly in bread making. The mature rye grain is a caryopsis,dry, one-seeded fruit, grayish yellow, ranging from 6 to 8 mm in length and 2 to 3 mmin width. The ripe grain is free-threshing and normally grayish yellow. The seed consistsof an embryo attached-through a scutellum to the endosperm and aleurone tissues. Theseare enclosed by the remnants of the nucellar epidermis, the testa or seed coat, and thepericarp or fruit coat. The aleurone is botanically the outer layer of the endosperm and,in rye, is generally one-cell thick. The aleurone layer surrounds the starchy endospermand merges into the scutellum located between the endosperm and embryo. In the maturegrain, the aleurone is characterized by the presence of numerous intensely staining aleu-rone granules. The starchy endosperm represents the bulk of the kernel and is composedof three types of cells: peripheral or subaleurone, prismatic, and central, which differ inshape, size, and location within the kernel. Figure 6 is a schematic of the longitudinalsection of a rye cell (Kulp and Ponte, 2000).

Structure and Composition of Cereal Grains 7

Fig. 5 Oat kernel structure. (From Webster, 1986.)

Fig. 6 Diagrammatic view of longitudinal section of rye grain. (From Bushuk and Campbell,1976.)

8 Riahi and Ramaswamy

2.1.7 SorghumSorghum (Sorghum bicolor L.) is a major source of energy and protein in developingcountries, especially in Africa and Asia. The sorghum kernel is roughly spherical and iscomposed of three main components: the seed coat, embryo, and endosperm. The seedcoats consist of the fused pericarp and testa. The extreme outer layer is pericarp that issurrounded by a waxy cuticle. Some sorghums contain a complete testa that may or maynot contain spots of pigment. The embryo consists of a large scutellum, an embryonicaxis, a plumule, and a primary root. The embryo is relatively rmly embedded and difcultto remove by dry milling. The endosperm is the largest proportion of the kernel and con-sists of an aleurone layer. The peripheral layer is made up of cells containing a highproportion of protein. The layer after the peripheral layer, called the corneous layer, con-tains less protein and a higher proportion of starch than the peripheral layer. Figure 7shows the structure of a sorghum grain; additional details can be found in Hulse et al.(1980) and Kulp and Ponte (2000). The mature sorghum grain comprises about 10% em-

Fig. 7 Cross section of the sorghum grain: P, pericarp; CE, corneous endosperm; FE, ouryendosperm; SA, stylar area; S, Scutellum; EA, embryonic axis. (From Hulse et al., 1980.)

Structure and Composition of Cereal Grains 9

bryo, 8% pericarp or bran layers, and 80% endosperm. These proportions may vary withvariety, environmental condition, and degree of maturity. The embryo is rich in protein,lipid, minerals, and B vitamin groups.

2.2 CompositionThe chemical composition of the cereals varies widely and depends on the environmentalconditions, soil, variety, and fertilizer. The proximate composition of selected cereals isgiven in Table 1 along with typical values of vitamin and mineral composition. The distri-bution of different amino acids in cereal grains is tabulated in Table 2.

Wheat has a higher protein content than other cereals: The protein content variesfrom 7 to 22% depending on the variety. However, because of low availability of someessential amino acids in wheat (see Table 2), its biological value requires addition orsupplementation with other amino acids. Several research efforts have focused on produc-ing different wheat varieties with higher protein and essential fatty acids content.

Carbohydrates are the major chemical composition of the corn. However, the maizecorn kernel is more than a rich source of carbohydrates, it is a source of enzymes for thestudy of biosynthesis, and genetic markers for genetic, biochemical, and genetic engi-neering studies. The starch granule is formed inside an amyloplast and arranged in aninsoluble granule. Starch is the major carbohydrate in the kernel and comprises close to72% of its dry weight. Starch also is found in the embryo, bran, and tip cap. Amylosemakes up 2530% of the starch, whereas amylopectin composes 7075% of the starch.Monosaccharides, such as fructose and glucose, are found in equal proportions in theendosperm. Among the disaccharides, sucrose is the major sugar in kernels that compriseonly 48% of kernel dry weight; maltose is also found at less than 0.4% of the kerneldry weight. The corn bran consists of 70% hemicelluloses, 23% cellulose, and 0.1% ligninon a dry weight basis. The protein content of the corn shows that it is poor in essentialamino acids, such as tryptophan, lysine, and threonine, valine, and sulfur amino acids (seeTable 2). The corn has only 4.4% oil (dry basis), but the amount of corn oil productionis enormous, even though it is not considered as an oil seed crop. Triglycerides are themajor composition (98.8%) of the rened commercial corn oil. Other types of lipids,such as phospholipids, glycolipids, hydrocarbons, sterols, free fatty acids, carotenoids,and waxes, are also found in corn oil. Corn has a high level of unsaturated fatty acid(linoleic acid). Corn oil is very stable compared with other seed oils owing to its lowlevel of linolenic acid and the presence of natural antioxidant.

The composition of rice and its fraction depends on the cultivars, environmentalconditions, and processing. The rice components distributed differently in aleurone, em-bryo, and other parts of the grain. The average brown rice protein content ranges from4.3 to 18.2% with a mean value of 9.2%. Protein is the second most important rice compo-nent after carbohydrates. The outer tissues of the rice grain are rich in water-soluble pro-teins (albumin) and also salt-soluble proteins (globulin), but the endosperm is rich inglutelin. The milling fraction of the rice grain has a limited prolamin (alcohol-solubleproteins), and the nonprotein nitrogen (NPN) of the rice is about 24%. Rice starch iscomposed of a linear fractionamyloseand branched fractionamylopectinthat isa major factor in the eating and cooking quality of the rice. The waxy rice starch hasapproximately 0.81.3% amylose, whereas nonwaxy milled rice contain 733% amylose.The amylose content of the rice can be classied as 12% (waxy), 720% (intermediate),2025% (high), and more than 25% (very high). Waxy rice has a higher free-sugar level,

10 Riahi and RamaswamyTa

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Structure and Composition of Cereal Grains 11

Table 2 Amino Acid Composition of Cereals

Amino acid (%) Wheat Rye Corn Barley Oats Rice SorghumArginine 0.80 0.53 0.51 0.60 0.80 0.51 0.40Cystine 0.20 0.18 0.10 0.20 0.20 0.10 0.20Histidine 0.30 0.27 0.20 0.30 0.20 0.10 0.03Isoleucine 0.60 0.53 0.51 0.60 0.60 0.40 0.60Leucine 1.00 0.71 0.11 0.90 1.00 0.60 1.60Lysine 0.50 0.51 0.20 0.60 0.40 0.30 0.30Methionine 0.20 0.50 0.10 0.20 0.20 0.20 0.10Phenylalanine 0.70 0.70 0.51 0.70 0.70 0.40 0.51Threonine 0.40 0.40 0.40 0.40 0.40 0.30 0.30Tryptophan 0.20 0.10 0.10 0.20 0.20 0.10 0.10Tyrosine 0.51 0.30 0.50 0.40 0.60 0.70 0.40Valine 0.60 0.70 0.40 0.70 0.70 0.51 0.60

Source: Pomeranz, 1971.

especially maltodextrine. Lipids are in the form of spherosomes or lipid droplets, with adifferent size in the aleurone layer, subaleurone, and embryo. Rice has about 0.4% non-starch lipid at 14% moisture. Starch lipid from brown rice is close to 0.60.7% for non-waxy rice and 0.2% for waxy rice. Rice is also a source of several vitamins and minerals.

Carbohydrates represent the major source of energy in barley, accounting for about80% of grain weight. Starch is the most abundant single component, accounting for upto 65%, and is composed mainly of amylose and amylopectin. Cellulosic microbrils arefound in the cell walls that reinforce a matrix that mainly comprises arabinoxylans and-glucans. Proteins are the minor components in barley and consist 815% of the dryweight of the mature grain. Albumins and globulins represent 2.8 and 18.1% of the totalproteins in barley, whereas glutelins account for 738% of the total. In barley, lipids arestored in oil droplets or spherosomes bounded by a simple membrane. The principal corelipid is triacylglycerol and small amounts of other nonpolar lipids. Total lipid content ofwhole barley grain among different varieties has been reported from 2.4 to 3.9%. The totallipids comprise 6778% nonpolar lipids, 813% glycolipids, and 1421% phospholipids.

The starch content of the oats has a higher lipid content (1.2%) than other cereals.The oury endosperm of the high-protein species contains a smaller proportion of starchgranules than the lower-protein species. Oat starch is more like rice starch in both sizeand shape and is highly aggregated. Physical properties of the oat starch are inuencedby the climate, genetic, and agronomic condition. The amylose content of the oat rangesbetween 16 and 27%. Oat has superior nutritional value when compared with other cerealsowing to its higher protein quality and concentration (1520%). Oats also have higherlipid concentrations than found among other cereal grain. The free-lipid percentage ofoats is 5.09.0%, whereas wheat, rice, maize, barley, and rye have 2.13.8, 0.83.1, 3.95.8, 3.34.6, and 3.34.6% lipid, respectively. The lipids are distributed in different partsof the grain, but over 50% of the lipids are stored in the endosperm.

The starch composition of the rye our is mostly the same as wheat our. However,the individual granules are different in size and also the -amylase activity in the maturekernel is high and, therefore, the viscosity of the dough is lower than wheat. Rye proteinsare considered superior to other cereals in biological value; rye has a higher proportionof water- and salt-soluble proteins compared with the other cereals that have an effect in

12 Riahi and Ramaswamy

improving the amount of the essential amino acid lysine (see Table 2). The principalcomponent of the rye is starch that is inversely related to the protein content. The crudefat content of rye is similar to that of wheat and barley, ranging from 1.5 to 2.0%. Theunsaturated fatty acid content of rye is very high and is characterized by a higher linolenicacid content than found in other cereal grain.

In sorghum (nonwaxy), amylose is reported to range from 20 to 30% and, in somevarieties, from 12 to 13% of the starch. Glucose appears to be the principal free sugar insorghum. Compared with other cereal grains, cellulose and pentosan contents are high.Pentosans are located mostly in the pericarp and cell walls. Removal of the outer pericarpsignicantly reduces crude ber of the sorghum. The mineral content of the sorghum,such as calcium, iron, and phosphorus, and also B vitamins, is reduced by removal of theouter pericarp and is also affected by phytic acid that affects their availability.

3 LEGUMES3.1 StructureUsually the food legumes are classied in two categories: the legumes in which energyis stored as fat (such as peanut and soybean), and those in which energy is stored asstarch (chickpeas). The structure of the food leguminous plants is generally similar. Maturelegume seeds have three major components: the seed coat, the cotyledons, and the embryoaxis, which constitute 8, 90, and 2% of the seed, respectively. The structure of typicallegume seeds and their various anatomical parts of the seed are shown in Figs. 8 and 9.The outer layer of the seed is the testa or seed coat. In most legumes, the endosperm isshort-lived and, at maturity, it is reduced to a thin layer surrounding the cotyledons orembryo. The external structure of the seed includes helium, micropyle, and raphe. Aftersoaking and removing the seed coat of a bean, the endosperm comes off, and the reminderis composed of embryonic structure. The embryonic structure includes the shoot, whichconsists of two cotyledons, and a short axis above and below the cotyledons, which has

Fig. 8 Cross sections of a mature broad seed with one cotyledon removed. (From Kadam et al.,1989.)

Structure and Composition of Cereal Grains 13

Fig. 9 Mung bean seed coat and cotyledon. (From Kadam et al., 1989.)

several foliage leaves, and terminates in the short tip. The embryonic stem and plumuleare fairly well developed in the resting seed and lie between two cotyledons or seed leaves.The radicle or embryonic root has almost no protection except that provided by the seedcoat. Therefore, the seed is unusually breakable, especially when it is dried and roughlytreated.

Usually, legumes have a moderately thick seed coat. Legume seeds having thickseed coats have higher amounts of lipids. The outermost layer of the seed coat is usuallyknown as the cuticle. The other two important features in the external topography of theseed include the hilum and micropyle. The hilum of the legume is different from othersin shape and size, ranging from round to oblong, oval, or elliptical. The micropyle showsvariation, ranging from circular and triangular to fork-shaped. The cotyledons of legumesseeds are composed of numerous oarenchymatous cells. The size of the parenchymatouscells ranges from 70 to 100 m, and the most abundant structures in this region are starch.The distribution of nutrients in different seed fractions, calculated on a percentage of thewhole seed, shows that the major portion of protein, ether extract, phosphorus, and ironis present in cotyledons, whereas 8090% of crude ber and 3250% of calcium arepresent in seed coat.

3.2 CompositionThe chemical composition of the legumes depends on the cultivars, geographical location,and growth condition. The proximate composition of selected legumes is given in Table3, along with typical values of vitamin and mineral composition. Legumes usually containa large amount of carbohydrates ranging from 24 to 68%. The carbohydrates includemono- and oilgosaccharides. Starch is the main carbohydrate in legumes similar to pinto

14 Riahi and Ramaswamy

Tabl

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ofD

iffer

entR

awLe

gum

es

Pean

utPi

geon

Chickp

eaSo

ybea

nLe

ntils

Larg

eBlack

Gre

enFa

vaM

ugCo

wpe

a

Prox

imate

Moi

sture

5.6

10.6

10.7

8.6

10.5

10.9

10.6

10.7

10.6

9.7

11.7

com

posit

ion

Prot

ein

22.7

19.8

19.5

34.3

24.7

21.2

21.8

23.9

24.8

23.6

22(%

)Fa

t44

.51.

35.

718

.71

1.1

1.4

1.3

1.4

1.4

1.3

Carb

ohyd

rate

25.5

65.2

61.7

31.6

61.2

62.7

63.5

62.4

60.4

61.6

63.4

Crud

eb

er2.

95.

54

3.8

4.1

5.3

3.

47

4.4

4.5

Neu

tral

ber

5.5

13.6

6.1

1210

.411

.313

.35.

714

.99.

27.

7Ash

2.2

3.7

2.7

5.1

2.6

4.2

3.4

2.5

3.3

3.3

3.3

Vita

min

Thiam

ine

0.90

0.60

0.51

0.87

0.54

0.64

0.99

0.79

0.52

0.61

0.94

com

posit

ion

Rib

oav

in0.

183

0.16

60.

228

0.33

00.

238

0.18

00.

201

0.25

40.

286

0.24

50.

227

(mg,

%)

Niacin

15.4

42.

941.

722.

352.

31.

611.

932.

942.

522.

462.

36Vita

min

B6

0.58

20.

264

0.56

00.

627

0.54

90.

601

0.28

50.

153

0.37

40.

410

0.44

0To

talf

olac

in0.

401

0.34

30.

481

0.25

00.

432

0.30

80.

470.

322

0.43

10.

490

0.54

5Pa

ntot

heni

cac

id2.

921.

351.

321.

731.

781.

320.

991.

911

1.71

1.39

-Car

oten

e

36.2

29.1

46.3

34.9

160.

247

.454

.128

.0M

iner

alPh

osph

orus

460.

431

7.4

365.

747

740

8.5

366.

538

0.3

332.

937

3.3

348.

842

6.5

com

posit

ion

Potass

ium

786.

612

00.4

1044

.218

2097

020

17.3

1424

.310

49.5

1503

.111

92.2

1450

.3(m

g,%

)So

dium

34.4

26.1

22.7

6.9

16.6

6.6

5.2

18.4

11.6

5.6

23Ca

lciu

m66

.012

9.1

165

223.

159

.398

.692

.349

.197

.812

4.8

80.3

Mag

nesiu

m26

8.3

171

202.

728

4.5

180.

723

6.2

195.

615

7.2

214.

724

3.6

250.

2Zi

nc5.

282.

873.

544.

483.

512.

973.

962.

733.

352.

623.

77M

anga

nese

2.99

1.79

2.14

5.43

1.31

1.67

1.17

1.13

4.59

1.06

1.28

Copp

er3.

151.

090.

811.

430.

770.

960.

770.

760.

821.

050.

94Iron

5.92

8.26

6.23

8.66

8.07

7.43

4.82

5.02

6.66

8.80

7.54

Sour

ce:M

atth

ews,

1989

.

Structure and Composition of Cereal Grains 15

beans, but in soybean and lupine seeds starch content ranges from 0.2 to 3.5%. The oligo-saccharides, such as those of the rafnose family (rafnose, stachyose, and verbascose),are the most predominant in legumes and are 31.176% of total soluble sugars. In somelegumes, the percentage of the oligosaccaride is higher.

Consumption of large amount of beans causes atulence in humans and animals thatresults in discomfort, abdominal rumblings, cramps, pain, and diarrhea, which is caused bythe rafnose family. Legumes also contain large amounts of crude ber, ranging from1.213.5%. Cellulose is a major component of crude ber in pink beans, whereas in otherlegumes, such as red gram and lentil, hemicelluloses are the major components of ber.The legume starch usually contains more amylose than amylopectin. The starch structureis both crystalline and amorphous.

Legumes contain an appreciable amount of protein. The protein content depends onthe species of legume and ranges from 15 to 45%. The crude protein content is a mixtureof nitrogenous compounds, such as free amino acids, amines, lipids, purine and pyramidinebases, nucleic acid, and alkaloids. Globulins constitute most of the storage proteins inmost legume seeds. The biological value of legume proteins is low owing to their contentof sulfur amino acids. However, addition of methionine in the diet has a benecial effecton the protein efciency ratio in all legumes.

Some legumes, such as peanuts, soybeans, and winged beans, have a considerableamount of lipid, 50, 21, and 17%, respectively. However, lipid content of other speciesvaries from 1 to 7.2%. The lipid content of the legumes depends on variety, origin, loca-tion, climate, soil, and environmental conditions. The major fatty acid contents of thelegume are oleic, linoleic, and linolenic acid; the legume lipids consist of natural lipid,phospholipids, and glycolipids. The natural lipids are the predominant lipids in most le-gumes. Total lipid content of the legumes, especially natural lipids, increase to more than20% during seed maturation. These lipids are highly sensitive to enzymatic and nonenzy-matic oxidation, which results in the aldehydes, ketones, esters, and acids.

Legumes are a good source of minerals, such as calcium, iron, copper, zinc, potas-sium, and magnesium. Potassium is the main mineral of the legume and comprises about2530% of the total mineral content of the food legumes. Legumes also are a moderatesource of iron and also have a sufcient amount of phosphorous, which exists as phyticacid. Legumes are a good source of thiamin, riboavin, and niacin, whereas the carotenecontent of most species is very limited. Drying and storage diminish most of the vitamins.Legumes contain more vitamin E than cereal grains. Legumes also contain a considerableamount of folic acid; a high quantity of polysaccharides and lignin reduce the availabilityof B vitamins, especially B6.

REFERENCESBushuk W, Campbell WP (1976). Morphology and chemistry of the rye grain. In Drews E, Evans

LE, Rozsa TA, Scoles GJ, Seibel W, Simmonds DH, Starzycki S, eds. Rye: Production, Chem-istry, and Technology. American Association of Cereal Chemists, St. Paul, MN, p. 63105.

Egli DB (1998). Seed Biology and Yield of Grain Crops. Cab International, Wallingford, Englandp. 178.

Hulse JH, Laing EM, Pearson OE (1980). Sorghum and the Millets: Their Composition and NutritiveValue. Academic Press, New York, p. 997.

Juliano BO (1985). Rice: Chemistry and Technology. American Association of Cereal Chemists,St. Paul, MN, p. 774.

16 Riahi and Ramaswamy

Kulp K, Ponte JG (2000). Handbook of Cereal Science and Technology, 2nd ed. Marcel Dekker,New York, p. 790.

Lasztity R (1999). Cereal Chemistry. Akademiai Kiado, Budapest. p. 308.MacGregor AW, Bhatty RS (1993). Barley Chemistry and Technology. American Association of

Cereal Chemists, St. Paul, MN, p. 486.Matthews HR (1989). Legumes: Chemistry, Technology and Human Nutrition. Marcel Dekker, New

York, p. 389.Pomeranz Y (1971). Wheat Chemistry and Technology. American Association of Cereal Chemists,

St. Paul, MN, p. 821.Potter NN (1986). Food Science. AVI New York, p. 735.Reddy NR, Pearson MD, Sathe SK, Salunkhe DK (1984). Chemical, nutritional and physiological

aspects of dry bean carbohydrates: a review. Food Chem 13:2568.Kadam SS, Deshpande SS, Jambhale ND (1982). Seed structure and composition, In: Handbook of

World Food Legumes: Nutritional Chemistry, Processing Technology and Utilization, vol 1.Salunkhe DK, Sathe SK, Reddy NR, CRC Press, Boca Raton, FL, pp. 2345.

Stoskopf NC (1985). Cereal Grain Crops. Reston Publishing Reston, VA. p. 516.Watson SA (1987). Structure and composition. In: Watson SA, Ramstad PE, eds. Corn: Chemistry

and Technology. American Association of Cereal Chemists, St. Paul, MN, pp. 5382.Webster FH (1986). Oats: Chemistry and Technology. American Association of Cereal Chemists,

St. Paul, MN, p. 433.

2Physical and Thermal Propertiesof Cereal Grains

SHYAM S. SABLANISultan Qaboos University, Al-Khod, Muscat, OmanHOSAHALLI S. RAMASWAMYMcGill University, Sainte-Anne-de-Bellevue, Quebec, Canada

1 INTRODUCTIONData on physical properties of grain are essential for the design of equipment for handling,aeration, and storage, as well as processing cereal grains and other agricultural materials.Basic thermal and moisture transport properties are also required for simulating heat andmoisture transport phenomena during drying and storage. The most important such proper-ties are the grain weight, sphericity, roundness, size, volume, shape, surface area, bulkdensity, kernel density, fractional porosity, static coefcient of friction against differentmaterials and angle of repose, heat capacity, thermal conductivity, thermal diffusivity,moisture diffusivity, equilibrium moisture content, and latent heat of vaporization. Theseproperties vary widely, depending on moisture content, temperature, and density of cerealgrains. The experimental measurement of the physical and thermal properties of cerealgrains is the concern of postharvest technologists and researchers.

Substantial research has been carried out, over the years, on gathering data for mate-rial property evaluation, and some excellent review articles have been published in variousscientic journals on the physical, thermal, and moisture transport properties of plant andanimal food materials (Nelson, 1973; Polley et al., 1981; Miles et al., 1983; Sweat, 1974).Several excellent books have also been published highlighting data on physical, thermal,chemical, and electromagnetic radiation properties of food and agricultural products cov-

17

18 Sablani and Ramaswamy

ering a broad range of plant and animal food products (Mohsenin, 1980, 1981, 1984, 1986;Okos, 1986; Rahman, 1995; Rao and Rizvi, 1995). In most published books and reviews,the importance of these properties and the fundamentals involved in their measurementare highlighted, but compilation of some properties are limited mostly to fruits, vegetables,and other food products of plant or animal origin. Property data for grains is generallyscarce and scattered. This chapter is designed to present relevant data for cereal grainsand also a brief review of the methods commonly used for their estimation. It is hopedthat this review will be helpful to postharvest technologists, as well as equipment designand process engineers, who are interested in the storage and handling of cereal grains.

2 PHYSICAL PROPERTIES2.1 1000-Grain WeightIn handling and processing of grains, it is customary to know the weight of 1000 grainkernels. The 1000-grain weight is a good indicator of the grain size, which can varyrelative to growing conditions and maturity, even for the same variety of a given crop.When compared with other crops at the same moisture level, the 1000-kernel weight willalso provide an idea of relative size of the kernel for handling purposes. Pabis (1967)used 1000-grain weight and kernel density to determine the effective diameter of a kernel.Generally, this is measured directly by taking the weight of 1000 grain kernels. Fraser etal. (1978) measured the weight of 1000 kernels of fababeans (also known as fava beans)and presented a correlation of grain weight as a function of moisture content. Dutta et al.(1988a) found that the 1000-kernel weight of gram increased linearly with increasingmoisture content from 10.9 to 28.4%. Bala and Woods (1991) measured the weight ofrandomly selected 100 malt grains and multiplied by 10 to give a 1000-grain weight. Theyalso presented a linear regression equation for the 1000-kernel weight as a function ofmoisture content. Shepherd and Bharadwaj (1986a) assumed a linear relation between the1000-kernel weight of pigeon pea and the moisture content, and measured the 1000-kernelweight at 0 and 14.7% moisture content to evaluate regression parameters. Deshpande etal. (1993) also observed a linear relation between 1000-kernel weight of soybean and itsmoisture content in the range 8.020.0%. Data on the 1000-grain weight of selected cerealgrains are given in Table 1.

2.2 Sphericity and RoundnessAccurate estimation of shape-related parameters are important for determination of termi-nal velocity, drag coefcient, and Reynolds number. It is also important to know the shapebefore any heat or moisture transport analysis can be performed. Sphericity is dened asthe ratio of the surface area of a sphere, which has the same volume as that of the solid,to the surface area of the solid. Roundness of a solid is a measure of the sharpness of itscorners and is dened as the ratio of the largest projected area of an object in its naturalrest position to the area of the smallest circumscribing circle (Curray, 1951). Higher valuesof sphericity and roundness indicate that the objects shape is closer being spherical. Cur-ray (1951) suggested the following relation for calculation of sphericity and roundness ofthe grain:

Sphericity d idc

(1)

Properties of Cereal Grains 19

Tabl

e1

1000

-Gra

inW

eigh

t,Sp

heric

ity,a

nd

Rou

ndne

ssofG

rain

s

Moi

sture

content

Prod

uct

(%w.b

.)10

00-g

rain

weigh

t(kg

)Sp

heric

ityRou

ndne

ssRef

s.

Faba

[fava

]bea

ns8.

534

.90.

371

3.7

10

3 m

Fr

aser

etal.,

1978

Gra

m12

.432

.40.

156

1.56

2

10

3 m0.

735

0.69

7Dut

taet

al.,

1988

a0.

810a

0.81

3aM

alt

4.89

41

.66

0.03

52

0.62

7

10

3 m

Bala

and

Woo

ds,1

991

Oilb

ean

seed

4.3

0.60

5

0.27

70.

398

0.35

7Oje

and

Ugb

or,1

991

Pige

onpe

a12

.80.

076

0.82

20.

818

Shep

herd

and

Bha

rdwaj,

1986

aSo

ybea

n8.

020

0.10

1

0.10

5m

0.80

3

0.06

m

Des

hpan

deet

al.,

1993

aW

ithou

troot:

m,m

oist

ure

content

.

20 Sablani and Ramaswamy

Roundness ApAc

(2)

where dc and Ac represent the diameter and area of the smallest circumscribing circle,respectively, di denotes the diameter of the largest inscribing circle. Ap is the projectedarea of the grain.

Dutta et al. (1988a) used shadowgraphs of a grain in three mutually perpendicularpositions to determine the sphericity and roundness of gram, with and without roots. Ifthe root of gram is ignored, the sphericity and roundness values were higher. Oje andUgbor (1991) found that 95% of oilbean seeds had a roundness of less than 0.55 andsphericity of less than 0.75, which explained the difculty in getting the seeds to roll.They suggested that this property should help in the design of hoppers and dehullingequipment for the seed. Shepherd and Bharadwaj (1986a) approximated the shape of pi-geon pea as a prolate spheroid and estimated the sphericity and roundness of pigeon peaat 12.8% moisture level using 20 shadowgraphs. They reported the sphericity and round-ness values of pigeon pea as 0.822 and 0.818, respectively, with a standard deviation ofless than 0.056. Deshpande et al. (1993) measured the linear dimensions of grains witha micrometer (reading to 0.01 mm) and used the relation [sphericity (LWT )0.33/L, whereL length, W width, T thickness], as proposed in Mohsenin (1981). They observedthat the sphericity of soybean grain increased linearly with increasing moisture contentfrom 8.0 to 20.0%. The sphericity and roundness values for selected grains are also in-cluded in Table 1.

2.3 Bulk DensityThe bulk density of cereal grains is determined by measuring the weight of a grain sampleof known volume. The grain sample is placed in a container of regular shape, and theexcess on the top of the container is removed by sliding a string or stick along the topedge of the container. After the excess is removed completely the weight of the grainsample is measured. The bulk density of the grain sample is obtained simply by dividingthe weight of the sample by the volume of the container. The bulk density gives a goodidea of the storage space required for a known quantity of particular grain. Bulk densityalso inuences the effective conductivity and other transport properties. From the storagepoint of view, it is important to determine the effect of moisture content on the bulkdensity of grains because the bulk density of some grains increase with an increasingmoisture content, whereas it decreases for some other grains. The bulk densities of roughrice (Wratten et al., 1969) and short rice (Morita and Singh, 1979) were reported to in-crease linearly with an increasing moisture content between 12 and 18%, whereas thebulk densities of canola (Sokhansanj and Lang, 1996), fababeans (Fraser et al., 1978;Irvine et al., 1992), axseed (Irvine et al., 1992), gram (Dutta et al., 1988a), lentils (Irvineet al., 1992; Carman, 1996), malt (Bala and Woods, 1991), and soybean (Deshpande etal., 1993) decreased linearly with an increasing moisture content. Shephard and Bhardwaj(1986a) reported that the bulk density of pigeon pea is higher than that of soybean andgrain sorghum but lower than that of fababean in the same moisture range. The bulkdensities of rice bran (Jones et al., 1992; Tao et al., 1994), pigeon pea (Shepherd andBhardwaj, 1986b; rice (Jones et al., 1992; Chandrasekhar and Chattopadhyay, 1989), andwheat (Jones et al., 1992) have also been determined as a function of moisture contentfor the different grains, which along with their associated moisture contents, are given in(Table 2).

Properties of Cereal Grains 21

2.4 Kernel DensityThe kernel (true) density of a grain is dened as the ratio of the mass of a grain sampleto the solid volume occupied by the sample. For the determination of kernel density ofan average grain, two methods have been suggested: one involved the displacement of agas, whereas the other used displacement of a liquid. In both methods, Archimedes princi-ple of uid displacement is used to determine the volume. Wratten et al. (1969) determinedthe density of medium- and long-grain rice using an air-comparison pycnometer. Thekernel density varied from 1324 to 1372 kg/m3 for medium-grain rice (Saturn) and from1362 to 1385 kg/m3 for long-grain rice (Bluebonnet-50). The true density of pigeon peagrain was determined by measuring the grain volume using the water displacement method(Shepherd and Bhardwaj, 1986a). They found that the true density of pigeon pea decreasedlinearly with increasing moisture content in the range 5.922.0%. On comparing the truedensity of pigeon pea with that of other cereal grains, it was higher than that of soybean,but lower than that of corn in the moisture range selected for this study. Dutta et al. (1988a)used water displacement method and determined the true density of gram in the range ofmoisture content 8.823.7%. The true density of gram decreased linearly with increasingmoisture content. Oje and Ugbor (1991) used the water displacement method and foundthe mean true density of oilbean seed was 1120 kg/m3 at a moisture content level of 4.3%.Chang (1988) used a gas pycnometer with helium to determine the true density of corn,wheat, and sorghum kernels. Irvine et al. (1992) used an air comparison pycnometer tomeasure the grain volume of preweighed samples and determined the densities of axseed,lentils, and fababeans at different moisture content. They found that the true densities ofEston lentils, Laird lentils, and fababeans decreased by 1.3, 2.8, and 1.6%, respectively,when moisture content of these seeds increased between 10 and 18%. The kernel densityof axseed remained relatively constant at approximately 1149 kg/m3 between 8.2 and12.6% moisture content. Deshpande et al. (1993) measured the kernel density of soybeanusing a liquid displacement method. The grains were coated with a very thin layer ofepoxy resin adhesive (Araldite) to avoid any absorption of water during the experimentas used earlier by Dutta et al. (1988a). The adhesive was insoluble in water, resistant toheat, humidity, solvents, and acids. The increase in weight of the grain owing to adhesivecoating was less than 1.5%, and there was no change in weight of the grain even if it waskept submerged in distilled water for 2 h. The effect of moisture content on kernel densityof soybean grain showed a linear decrease with moisture content. Tao et al. (1994) usedan indirect method to determine the volume of preweighed rice bran. They obtained thevolume of the rice bran samples from porosity determination. The true densities of branof long and medium rice were reported to be 1080 kg/m3, and 1000 kg/m3, respectively.The densities of wheat and canola kernels have also been determined using liquid displace-ment method (Sokhansanj and Lang, 1996). Kernel density values for different grains aresummarized in Table 2.

2.5 PorosityThe porosity of grain is an important parameter that affects the kernel hardness, breakagesusceptibility, milling, drying rate, and resistance to fungal development (Chang, 1988).Porosity is a property of grain that depends on its bulk and kernel densities. The grainporosity can be measured with the help of an air comparison pycnometer or by the mercurydisplacement method. The values of grain porosity of various grains, as measured withthe former method, tend to be 510% higher (Thompson and Issacs, 1967). Fractional

22 Sablani and Ramaswamy

Tabl

e2

Bul

kDen

sity,

Ker

nelD

ensit

y,an

dPo

rosit

yofG

rain

s

Moi

sture

content

Bul

kde

nsity

Ker

neld

ensit

yPr

oduc

t(%

wb)

(kg/m

3 )(kg

/m3 )

Poro

sity

Ref

s.

Bra

n13

.623

5

Jo

neset

al.,

1992

Cano

laa

5.0

19.0

672

661

1122

11

180.

401

0.40

9So

khan

sanj

and

Lang

,199

6Ca

nola

b67

866

111

2611

180.

403

0.40

9Co

rn(B

oJac

)11

.814

52(0.

53)

Chan

g,19

88Co

rn(S

tauffe

r)12

.014

50(1.

29)

Chan

g,19

88Fa

ba[fa

va]b

eans

8.5

34.9

883

4.44

m

Fr

ease

ret

al.,

1978

Faba

[fava

]bea

ns12

.621

.981

576

113

9313

73

Irvi

neet

al.,

1992

Flax

seed

7.0

15.1

634

574

1148

11

43

Irvi

neet

al.,

1992

Gra

m8.

823

.781

4.8

3.45

m13

402.

73m

39.1

0.14

5m

Dut

taet

al.,

1988

aLe

ntil

6.1

24.6

1212

8.

95m

27

.3

0.15

9m

Carm

an,1

996

Lent

ils(E

ston)

11.4

18

.082

578

314

1013

92

Irvi

neet

al.,

1992

Lent

ils(L

aird)

11.7

17

.780

476

714

3113

93

Irvi

neet

al.,

1992

Malt

4.89

32

.452

74.

48m

Bala

and

Woo

ds,1

991

Oilb

ean

seed

4.3

1120

34Oje

and

Ugb

or,1

991

Pige

onpe

a12

.878

212

83Sh

ephe

rdan

dBha

rdwaj,

1986

aRice

bran

b

290

1080

0.73

Tao

etal.,

1994

Rice

bran

d

280

1000

0.72

Tao

etal.,

1994

Rice

(roug

h)c

1218

598

648

1324

13

7258

.553

.1W

ratte

net

al.,

1969

Rice

(roug

h)b

1218

586

615

1362

13

8359

.656

.9

Properties of Cereal Grains 23

Rice

(short

)11

.24

19.4

563

266

4

M

orita

and

Sing

h,19

79Rice

(padd

y)8.

963

9Jo

neset

al.,

1992

Rice

(whit

e)a12

.985

1Jo

neset

al.,

1992

Rice

(whit

e)a13

.382

3Jo

neset

al.,

1992

Rice

(whit

e)d13

.283

9Jo

neset

al.,

1992

Rice

(Pan

oli)

10.5

780

1465

0.47

Chan

dras

ekha

rand

Chatto

padh

yay,

1989

Sorg

hum

(Ferr

yMor

se)

12.7

1471

(0.68

)Ch

ang,

1988

Sorg

hum

(Fun

k)11

.214

48(0.

60)

Chan

g,19

88So

ybea

n8.

020

.074

8.9

166.

3m

1254

.852

5.8

m0.

405

0.13

6m

Des

hpan

deet

al,1

993

Whe

ata

8.0

22.0

790

686

1374

13

320.

425

0.48

5So

khan

sanj

and

Lang

,199

6W

heat

b76

668

636

033

20.

419

0.48

5W

heat

9.1

827

Jone

set

al.,

1992

Who

lem

eal

9.3

542

Jone

set

al.,

1992

Whe

at(ha

rd)(N

ewton

)13

.814

76(0.

42)

Chan

g,19

88W

heat

(hard)

(Cen

turk)

13.8

1469

(0.54

)Ch

ang,

1988

Whe

at(so