Handbook of vegetables and vegetable processing

This chapter re-views and explains the biology and classification of vegetables.Biology and Classification of Vegetables A primary reason for the diversity amongvegetable crops is the br

Handbook of Vegetables

and Vegetable Processing

Handbook of Vegetables

and Vegetable Processing

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Handbook of vegetables and vegetable processing/editor, Nirmal K Sinha; administrative editor, Y.H Hui; associate editors, E ?zg?l Evranuz, Muhammad Siddiq, Jasim Ahmed.

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ISBN 978-0-8138-1541-1 (hardback : alk paper)

1 Vegetables–Processing–Handbooks, manuals, etc 2 Vegetables–Composition–Handbooks, manuals, etc 3 Botanical chemistry–Handbooks, manuals, etc I Sinha, Nirmal K II Hui, Y H (Yiu H.) TP443.H35 2011

2010020449

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1 2011

Part I Biology, Biochemistry, Nutrition, Microbiology, and Genetics

1 Biology and Classificatio of Vegetables 3

Theodore J K Radovich

2 Biochemistry of Vegetables: Major Classes of Primary (Carbohydrates,

Amino Acids, Fatty Acids, Vitamins, and Organic Acids) and SecondaryMetabolites (Terpenoids, Phenolics, Alkaloids, and Sulfur-Containing

N Hounsome and B Hounsome

3 Flavor and Sensory Characteristics of Vegetables 59

Peter K C Ong and Shao Quan Liu

4 Genetic Engineering of Vegetable Crops 83

Jiwan S Sidhu and Sudarshan Chellan

5 Nutritional Profil of Vegetables and Its Significanc to Human Health 107

Masood Sadiq Butt and Muhammad Tauseef Sultan

6 Bioactive Phytochemicals in Vegetables 125

Fereidoon Shahidi, Anoma Chandrasekara, and Ying Zhong

7 Microbiology of Fresh and Processed Vegetables 159

Annemarie L Buchholz, Gordon R Davidson, and Elliot T Ryser

Part II Postharvest Technology and Storage Systems

8 Postharvest Handling Systems and Storage of Vegetables 185

P S Raju, O P Chauhan, and A S Bawa

9 Postharvest Physiology of Vegetables 199

Peter M A Toivonen

v

vi Contents

Part III Processing and Packaging of Vegetables

10 Fresh-Cut Vegetables 221

W Krasaekoopt and B Bhandari

11 Principles of Vegetable Canning 243

Dharmendra K Mishra and Nirmal K Sinha

12 Refrigeration and Freezing Preservation of Vegetables 259

Kasiviswanathan Muthukumarappan and Brijesh Tiwari

13 Drying of Vegetables: Principles and Dryer Design 279

Jasim Ahmed

14 Drying Vegetables: New Technology, Equipment, and Examples 299

E ¨Ozg¨ul Evranuz

15 Minimal Processing and Novel Technologies Applied to Vegetables 317

Jasim Ahmed and Tanweer Alam

16 Processing of Vegetable Juice and Blends 335

James S.B Wu and S-C Shen

17 Vegetable Fermentation and Pickling 351

Nejib Guizani

18 Vegetable Parts, Herbs, and Essential Oils 369

Sri Yuliani and Bhesh Bhandari

19 Processing and Computer Technology 387

Gokhan Bingol and Y Onur Devres

20 Packaging for Fresh Vegetables and Vegetable Products 405

Melvin A Pascall

21 Waste Management and Utilization in Vegetable Processing 423

Dalbir S Sogi and Muhammad Siddiq

Part IV Product and Food Plant Safety and HACCP

22 Controlling Food Safety Hazards in the Vegetable Industry—The HACCP

Luke F LaBorde

23 Good Agricultural Practices and Good Manufacturing Practices for

Elizabeth A Bihn and Stephen Reiners

24 Microbial Safety of Fresh and Processed Vegetables 483

Jaheon Koo

Part V Commodity Processing

25 Asparagus, Broccoli, and Caulifl wer: Production, Quality, and Processing 507

Paramita Bhattacharjee and Rekha S Singhal

Contents vii

26 Avocado: Production, Quality, and Major Processed Products 525

Tasleem Zafar and Jiwan S Sidhu

27 Dry Beans: Production, Processing, and Nutrition 545

Muhammad Siddiq, Masood S Butt, and M Tauseef Sultan

B C Sarkar and H K Sharma

29 Chili, Peppers, and Paprika 581

Lillian G Po

30 Peas, Sweet Corn, and Green Beans 605

Muhammad Siddiq and Melvin A Pascall

31 Garlic and Onion: Production, Biochemistry, and Processing 625

Wieslaw Wiczkowski

32 Edible Mushrooms: Production, Processing, and Quality 643

Ramasamy Ravi and Muhammad Siddiq

33 Table Olives and Olive Oil: Production, Processing, Composition, and

Kostas Kiritsakis, Apostolos Kiritsakis, Elena Manousaki-Karacosta, and Fivos Genigeorgis

34 Potatoes: Production, Quality, and Major Processed Products 683

Edgar Po and Nirmal K Sinha

35 Green Leafy Vegetables: Spinach and Lettuce 705

Gurbuz Gunes and Esra Dogu

V D Truong, R Y Avula, K Pecota, and C G Yencho

37 Tomato Processing, Quality, and Nutrition 739

Ali Motamedzadegan and Hoda Shahiri Tabarestani

Fresh and processed vegetables are a growing segment of the food industry andoccupy an important place in the global com-merce and economy of many countries Vari-ous studies have demonstrated the importance

fast-of vegetables to human health, ing fibe , vitamins, minerals, bioactive phy-tochemicals, and other nutrients in our diet

contribut-Botanically and organoleptically diverse etables are primarily grown on regional andseasonal basis Because of their highly per-ishable nature, search for efficien and bettermethods of preservation has been continuingalong side the developments in production,postharvest handling, processing, and qualityimprovements This handbook with 37 chap-ters contributed by more than 50 authors fromNorth America, Europe, Australia, Asia, andMiddle East is organized in fi e parts, whichreview and discuss important developments

veg-in vegetables and vegetable processveg-ing

Part I of the handbook has 7 chapters onphysiology, biochemistry, sensory and fl vorproperties, nutrition, phytochemical proper-ties, genetic engineering, and microbiology

Part II has 2 chapters on postharvest iology and technology

phys-Part III has 12 chapters covering ous aspects of vegetable processing includingfresh-cut vegetables, vegetable parts, herbsand essential oils, vegetable juices, minimalprocessing and new technologies, refrigera-tion and freezing, drying, computer applica-tions, packaging, and waste management

vari-Part IV includes 3 chapters on product andplant safety, including microbial safety, GAPand GMP, and HACCP

Part V covers processing of important etables including green, leafy, tuber and root,and other vegetables It also includes chapters

veg-on dry beans, olives, and avocadoes which areused as vegetables

This handbook is intended as a porary source book on vegetable and veg-etable processing for the industry, students,academia, libraries, research institutes, lab-oratories, and other interested professionals

contem-To our knowledge, there are few books onvegetables and vegetable processing with as-sociated coverage of scientifi aspects and in-dustrial practices Although the readers arethe fina judge, we hope this handbook wouldmeet the growing need for a quality book

in this field The editorial team edges many individuals for their supportsduring the conception and development ofthis book Our sincere thanks and gratitude

acknowl-to all authors for their contributions andfor bearing with us during the review pro-cess We would like to thank the publish-ing and copy editing departments, especially,Mark Barrett, Susan Engelken and RonaldD’souza for their supports to this project

We are grateful to the institutions we are sociated with and to our families for theirsupports

as-Nirmal K SinhaY.H Hui

E ¨Ozg¨ul EvranuzMuhammad SiddiqJasim Ahmed

ix

Jasim AhmedPolymer Source Inc

Dorval, Montreal, Qu´ebec H9P 2X8, Canada

Tanweer AlamBanaras Hindu UniversityVaranasi, Uttar Pradesh, India

R.Y AvulaDepartment of Food Science andTechnology

University of GeorgiaAthens, GA 30602, USA

A.S BawaDefence Food Research LaboratorySiddarthanagar, Mysore, India

Bhesh BhandariSchool of Land, Crop and Food SciencesThe University of Queensland

Brisbane QLD 4072, Australia

Paramita BhattacharjeeDepartment of Food Technology andBio-chemical EngineeringJadavpur University

Kolkata, West Bengal, India

Elizabeth A BihnDepartment of Food ScienceCornell University

Ithaca, NY 14853, USA

Gokhan BingolUnited States Department of Agriculture,Agricultural Research Service

Pacifi Western Area, Western RegionalResearch Center, Processed FoodsResearch

Albany, CA 94710, USA

Annemarie L BuchholzDepartment of Food Science and HumanNutrition

Michigan State UniversityEast Lansing, MI 48824, USA

Masood Sadiq ButtNational Institute of Food Science andTechnology

University of AgricultureFaisalabad, Pakistan

Anoma ChandrasekaraDepartment of BiochemistryMemorial University of Newfoundland

St John’s, NL A1B 3X9, Canada

O.P ChauhanDefence Food Research LaboratorySiddarthnagar, Mysore, India

Sudarshan ChellanBiotechnology DepartmentKuwait Institute for Scientifi ResearchSafat, Kuwait

xi

xii Contributors

S-C ShenDepartment of Human Development andFamily Studies

National Taiwan Normal UniversityTaipei, 10610, Taiwan

Gordon R DavidsonDepartment of Food Science and HumanNutrition

Michigan State UniversityEast Lansing, MI 48824, USA

Y Onur DevresFood Engineering DepartmentIstanbul Technical University

34469 Maslak, Istanbul, TurkeyEsra Dogu

Food Engineering DepartmentIstanbul Technical University

34469 Maslak, Istanbul, Turkey

E ¨Ozg ¨ul EvranuzFood Engineering DepartmentIstanbul Technical University

34469 Maslak, Istanbul, TurkeyFivos Genigeorgis

School of Food Technology and NutritionAlexander Technological Education InstituteSindos, Thessaloniki, Greece

Nejib GuizaniDepartment of Food Science and Nutrition,College of Agricultural and MarineSciences

Sultan Qaboos UniversitySultanate of OmanGurbuz GunesFood Engineering DepartmentIstanbul Technical University

34469 Maslak, Istanbul, Turkey

B HounsomeCollege of Health and Behavioural Sciences,Institute of Medical and Social CareResearch

Bangor UniversityBangor, LL57 1UT, Wales, UK

N HounsomeCollege of Health and Behavioural Sciences,Institute of Medical and Social CareResearch

Bangor UniversityBangor, LL57 1UT, Wales, UK

Apostolos (Paul) KiritsakisSchool of Food Technology and NutritionAlexander Technological Education InstituteSindos, Thessaloniki, Greece

Kostas KiritsakisSchool of Food Technology and NutritionAlexander Technological Education InstituteSindos, Thessaloniki, Greece

Jaheon KooDepartment of AgricultureUniversity of Arkansas at Pine BluffPine Bluff, AR 71601, USA

W KrasaekooptDepartment of Food TechnologyFaculty of Biotechnology, AssumptionUniversity

Huamark, Bankkok, Thailand

Luke F LaBordeDepartment of Food SciencePenn State UniversityUniversity Park, PA 16802, USA

Shao Quan LiuFood Science and Technology Program,Department of Chemistry

National University of SingaporeSingapore

Elena Manousaki-KaracostaSchool of Food Technology and NutritionAlexander Technological Education InstituteSindos, Thessaloniki, Greece

Contributors xiii

Dharmendra K MishraBiosystems and Agricultural EngineeringMichigan State University

E Lansing, MI 48824, USAAli MotamedzadeganDepartment of Food Science, College ofAgricultural Engineering

Sari Agricultural Sciences and NaturalResources University

Sari, Mazandaran, IranKasiviswanathan MuthukumarappanDepartment of Agricultural and BiosystemsEngineering

South Dakota State UniversityBrookings, SD 57007, USAPeter K.C Ong

Food Science and Technology Program,Department of Chemistry

National University of SingaporeSingapore

Melvin A PascallDepartment of Food Science and TechnologyOhio State University

Columbus, OH 43210, USA

K PecotaDepartment of Horticultural ScienceNorth Carolina State UniversityRaleigh, NC 27695, USAEdgar Po

Department of Industrial and ManufacturingSystems Engineering

University of ColumbiaMissouri, MO 65211, USALillian G Po

Department of Food ScienceUniversity of MissouriColumbia, MO 65211, USATheodore J.K RadovichDepartment of Tropical Plant and SoilSciences

University of Hawai’i at M¯anoaHonolulu, HI 96822, USAP.S Raju

Defence Food Research LaboratorySiddarthnagar, Mysore, IndiaRamasamy Ravi

Department of Sensory ScienceCentral Food Technological ResearchInstitute

Mysore 570 020, IndiaStephen ReinersDepartment of Horticultural SciencesNew York State Agricultural ExperimentStation

Geneva, NY 14456, USAElliot T Ryser

Department of Food Science and HumanNutrition

Michigan State UniversityEast Lansing, MI 48824, USAB.C Sarkar

Department of Food Engineering andTechnology

Sant Longowal Institute of Engineering andTechnology

Longowal, Sangrur, IndiaFereidoon ShahidiDepartment of BiochemistryMemorial University of Newfoundland

St John’s, NL A1B 3X9, CanadaH.K Sharma

Department of Food Engineering andTechnology

Sant Longowal Institute of Engineering andTechnology

Longowal, Sangrur, IndiaMuhammad SiddiqDepartment of Food Science and HumanNutrition

Michigan State UniversityEast Lansing, MI 48824, USA

xiv Contributors

Jiwan S SidhuDepartment of Family SciencesCollege for Women, Kuwait UniversitySafat, Kuwait

Rekha S SinghalDepartment of Food Engineering andTechnology

Institute of Chemical TechnologyMumbai, India

Nirmal K SinhaGraceland Fruit Inc

1123 Main StreetFrankfort, MI 49635, USA

Dalbir S SogiDepartment of Food Science and TechnologyGuru Nanak Dev University

Amritsar, India

Hoda Shahiri TabarestaniDepartment of Food ScienceTajan High Education InstituteGhaemshahr, Mazandaran, Iran

Muhammad Tauseef SultanNational Institute of Food Science andTechnology

University of AgricultureFaisalabad, Pakistan

Brijesh TiwariDepartment of Food and TourismHollings Faculty,

Manchester Metropolitan UniversityManchester, M14 6 HR, UK

Peter M.A ToivonenPostharvest Physiology, Food Safety andQuality Program, Agriculture andAgri-Food Canada

Pacifi Agri-Food Research CentreSummerland, British Columbia V0H 1Z0,Canada

Van-Den TruongUSDA-ARS Food Science Research Unit,Department of Food, Bioprocessing andNutrition Sciences

North Carolina State UniversityRaleigh, NC 27695, USAWieslaw WiczkowskiInstitute of Animal Reproduction and FoodResearch

Polish Academy of Sciences in OlsztynOlsztyn, Poland

James S.B WuGraduate Institute of Food Science andTechnology

National Taiwan UniversityTaipei, Taiwan

C.G YenchoDepartment of Horticultural ScienceNorth Carolina State UniversityRaleigh, NC 27695, USASri Yuliani

Indonesian Center for Postharvest Researchand Development

Bogor, IndonesiaTasleem ZafarDepartment of Family SciencesCollege of Women

Kuwait UniversitySafat 13060, KuwaitYing ZhongDepartment of BiochemistryMemorial University of Newfoundland

St John’s, NL A1B 3X9, Canada

Part I

Biology, Biochemistry, Nutrition, Microbiology, and Genetics

in many parts of the world, particularly inthe tropics Although vegetables account forless than 1% of the world’s plants, the ge-netic, anatomical, and morphological diver-sity of vegetables as a group is astounding(Graham et al 2006; Maynard and Hochmuth2007) Hundreds of vegetable taxa are grownfor food in subsistence and commercial agri-cultural systems worldwide This chapter re-views and explains the biology and classification of vegetables.

Biology and Classification of Vegetables

A primary reason for the diversity amongvegetable crops is the broad definitio of theword “vegetable” itself Any plant part con-sumed for food that is not a mature fruit

or seed is by definitio a vegetable These

include petioles (e.g., celery, Apium

grave-olens Dulce group), entire leaves (e.g., tuce, Lactuca sativa), immature fruits (e.g., cucumber, Cucumis sativus), roots (e.g., car- rot, Dacus carota), and specialized structures such as bulbs (e.g., onion, Allium cepa Cepa group) and tubers (e.g., white potato, Solanum tuberosum).

let-Further expanding this already generousdefinitio is the inclusion of mature fruitsthat are consumed as part of a main meal

rather than dessert (e.g., tomato, Solanum copersicum) This culinary exception to the

ly-anatomical rule was given legal precedence inthe US Supreme Court decision Nix v Hed-den (1893) that confirme common usage of

“vegetable” in reference to tomato This hassince been extended to beans and other fruits

Even dessert melons (e.g., cantaloupe, cumis melo Cantalupensis group), which are

Cu-fruits by every botanical, legal, and culinarydefinition are frequently “lumped” in withvegetables because of similarities in biologyand culture that they share with their more

vegetal cousins in the Cucurbitaceae (Iltis and

Doebley 1980) (Table 1.1)

The biological diversity among vegetablesnecessitates a systematic method for groupingvegetables in order to efficientl access in-formation and make management decisions.Understanding the biology of vegetable cropswill aid decision making associated with pro-duction, postharvest handling, and market-ing Ultimately, vegetable classificatio is in-extricably linked with crop biology Three

Handbook of Vegetables and Vegetable Processing Edited

by N K Sinha
c 2011 Blackwell Publishing Ltd.

3

Biology and Classification of Vegetables 11

Table 1.2 Definitions of selected terms relating to vegetable anatomy, biology, and classification

Andromonoecious Staminate and hermaphrodite fl wers on same plant Annual Plant that completes life cycle (sets seed) and dies in one year Axillary bud Bud occurring in the leaf axil, as in Brussels’ sprouts

Biennial Plant that completes life cycle (sets seed) and dies in two years Bolt Develop inflorescenc prematurely, as in lettuce and spinach Bract Modifie leaf or scale at base of fl wer

Bulb Bud surrounded by flesh and papery scales attached to stem plate Calyx Sepals or outer whorl of perianth

Carpel Individual unit of compound pistil Caryopsis Fruit (grain) of grass, as in sweet corn Corm Vertically oriented flesh , solid stem at or below soil surface, e.g., taro Cortex Storage tissues of root or stem, between epidermis and vascular tissue Cultivar Group of cultivated plants with distinguishing characteristics that are retained when

plants are reproduced Curd Fleshy inflorescenc with fl wer buds undifferentiated, e.g., caulifl wer Determinant Branch stops growing at fl wering

Dioecious Staminate (male) and pistillate (female) fl wers on separate plants Endocarp Inner layer of flesh fruit wall

Endodermis Inner layer of cortex, adjacent to vascular tissue Epidermis Thin outer layer of leaf, stem, or root

Exocarp Outermost layer (e.g., rind or skin) of fruit wall Floret Small fl wer on inflorescence e.g., artichoke

Gynoecious Producing predominantly, or only, female fl wers Indeterminant Branch continues to grow after fl wering starts Legume Single carpel fruit with two sutures, seed attached along one suture Lenticel Raised, unsuberized dot or pore for gas exchange

Mesocarp Middle layer of pericarp or fruit wall Locule Seed cavity of fruit Also compartment of ovary or anther Midrib Pronounced central vein of leaf

Monoecious Male and female fl wers on same plant Node Enlarged area on stem where buds emerge Pedicel Stalk or stem of individual fl wer or flore Peduncle Primary fl wer stalk of inflorescenc Pepo Cucurbit fruit, leathery or woody exocarp inseparable from endocarp Perfect fl wer Flower with both male and female parts

Perennial Plants persisting for three years or more

Rhizome Horizontally oriented underground stem modifie for storage, with nodes capable of

forming new roots and shoots Scales Fleshy or dry modifie leaves of a bulb Silique Specialized fruit of Brassicaceae, with two fused carpels Stele Central core of vascular strengthening tissue in roots and stems Tuber Fleshy, enlarged stems occurring at end of rhizomes

basic approaches toward classificatio ofvegetables that are based on commonalitiesamong groups are as follows:

1 Tissues and organs consumed

2 Ecological adaptation

3 Taxonomy

All three of the above approaches toward sificatio are based on some level of com-monality in crop biology, with the precision

clas-of classificatio varying from relatively low(plant part consumed) to very high (taxo-nomic) Table 1.2 gives definition of selectedterms related to vegetable anatomy, biologyand classification

12 Handbook of Vegetables and Vegetable Processing

Vegetable Tissues and Organs

The phenotypic diversity among vegetables

is actually based on relatively few types ofspecialized cells and tissues Dermal, ground,and vascular tissue make up the three basic tis-sue systems Ultimately, the structure of thesecells and tissues determine their function

Dermal Tissues

Epidermal cells, together with cutin and ular waxes, make up the outer layers of leaves,fruit, and other above-ground structures andprotect against water loss and other adverseabiotic and biotic factors The periderm (cork)layer of mature roots and stems is analogous

cutic-to the epidermis, but consists of nonlivingcells supplemented with suberin Stomatalguard cells are epidermal cells specialized

in regulating gas exchange, and are cially dense on the abaxial surface of leaves

espe-Lenticels are specialized, unsuberized mal structures (appearing as raised dots orbumps) that regulate gas exchange on roots,stems, and fruits Trichomes and root hairsare dermal cells with excretory, absorptive,and other functions critical to the ecology ofvegetables

der-Ground Tissues

Ground tissues are comprised of the

scle-renchyma Parenchyma cells are thin-walledcells that make up much of the ground tissues

of vegetables Parenchyma cells often serve

to store starch and other compounds Thecortex and pith of white potato are examples

of ground tissues dominated by parenchyma

Collenchyma cells have alternating thin andthick cell walls that provide fl xible support

for stems, as in the strings of celery (Apium graveolens) Sclerenchyma tissues include

sclerids and fiber with tough cell walls

Sclerenchyma cells are typically scarce inedible vegetable organs, but are importantcomponents of seed coats, nut shells, and the

stony endocarps of peaches (Prunus persica)

and related fruits

Conducting Tissues

Vascular tissues conduct water, minerals, tosynthates, and other compounds throughoutthe plant The xylem is part of the apoplast andconsists primarily of nonliving tracheids andvessel elements The xylem transports wa-ter, mineral nutrients, and some organic com-pounds, generally from the roots to leaves.The phloem is part of the symplast, con-sists primarily of sieve cells and compan-ion cells, and is important in conducting sug-ars, amino acids, and other compounds fromsource (usually leaves) to sink (actively grow-ing meristems, roots, developing fruits, andseeds) Both xylem and phloem are supported

pho-by parenchyma cells and fibe Some xylemcells (i.e., tracheids) have thickened cell wallsthat contribute significantl to the structuralsupport of tissues

The differentiation and variable structure

of plant tissues result in diverse functionsamong the plant organs (stems, roots, andleaves) and organ systems (e.g., fruits, fl w-ers, buds, and bulbs) consumed as vegetables.The classificatio of vegetables by edibleparts has been termed “Supermarket Botany”(Graham et al 2006) Although broad andnot always anatomically correct, the group-ing of commodities as leafy, fruit, and rootvegetables has value to growers, distribu-tors, and others in the market chain be-cause of similarities in cultural and posthar-vest requirements within groups In addition

to being practical, the division of vegetables

by anatomical structure highlights the pressive crop improvement accomplishments

im-of the early agriculturalists, which both ploited and expanded the structural diversityinherent in the plant kingdom

ex-Leafy Vegetables

Leaves are the primary site of photosynthesis

in plants and are generally the most nutrient

Biology and Classification of Vegetables 13

dense and most perishable of the vegetables

Leaves, particularly dark green leaves, tain relatively high levels of minerals (e.g.,

con-Fe, Mg, Ca), enzymes (protein), and ondary metabolites (e.g., carotenes and xan-thophylls) These compounds, important tohuman nutrition, are required by the plantfor light collection, electron transport, pho-toprotection, carbon fixation and many otherbiochemical processes abundant in leaves

sec-Stomata are especially dense on the abaxialsurface of leaves and are the terminal point

of transpiration, which is the primary nism for dissipating heat accumulated fromintercepting solar radiation High stomataldensity combined with the high surface areamake leafy vegetables more susceptible topostharvest water loss than other vegetables

mecha-Subsequently, rapid cooling after harvest andstorage under high humidity are particularlyimportant postharvest procedures for leafyvegetables (Kader 2002)

Leafy vegetables are concentrated in

the Asteraceae (Compositae), Brassicaceae (Crucifereae), and Chenopodiaceae Culi- nary herbs, dominated by the Lamiaceae (Labiatae), are also categorized as leafy veg-

etables Other vegetables consumed primarily

for leaf structures include Impomea ica (Convolvulaceae), celery (Apiaceae), and Amaranthus spp (Amaranthaceae) The

aquat-leaves of many plants grown primarily forother organs (fruits, roots, specialized struc-tures) are often utilized to supplement the

diet The leaves of taro (Colocasia esculenta) and cassava (Manihot esculenta), as well as

the young leaves and shoots of sweet potato

(Ipomea batatas) and many cucurbits bitaceae) are typical examples of vegetables

(Cucur-in this category

Leafy vegetables that are generally cookedbefore consumption to soften texture and im-prove fl vor (e.g., mature leaves of many

Brassica spp and Chenopodiaceae) are

sometimes classifie as “greens” to entiate them from leafy vegetables that thatare consumed raw, often as salad (e.g., most

differ-Compositae and the very young leaves of many Brassica) “Potherb” is used to describe

greens used in small quantity for fl voring incooking

While generally softer and lighter in flavor than cooking greens, salad crops vary intheir texture and fl vor, and these differencesare important in differentiating among leafyvegetables consumed raw Examples includetextural differences among lettuce (crisphead

vs butterhead types) and variable levels of ture and pungency in species used in mesclunmixes Textural and fl vor differences arecaused by variability in leaf structure (cuti-cle thickness), cell type, succulence, as well

tex-as type and quantity of phyochemicals (e.g.,glucosinolates) present (Figure 1.1)

Root Vegetables

Root vegetables include true roots (carrot,sweet potato and cassava) as well as special-ized structures such as tubers, bulbs, corms(e.g., taro), and hypocotyls (e.g., radish,

Raphanus sativus) These specialized

struc-tures are classifie as root vegetables because

of their full or partial subterranean habit,their physical proximity to true roots, andtheir function as storage organs for starchand other compounds Most of these special-ized structures consist primarily of stem tis-sue, with bulbs being a notable exception.Although significan variability in caloricvalue and shelf life exists within the rootscrops, they are typically higher in calories andless perishable than other vegetables due totheir storage function, suberized periderm orprotective skin, and high dry matter content(Figure 1.2)

True Roots

The biology and anatomy of true root etables are exemplifie by a comparison ofthree important crops: carrot, sweet potato,and cassava All true roots consist of sec-ondary vascular tissue arising from a cambial

veg-14 Handbook of Vegetables and Vegetable Processing

Figure 1.1 Anatomy of select leafy vegetables.

layer, with phloem (cortical) tissue ing outward and xylem tissue inward Sec-ondary plant products are found throughoutroot tissues, but many are particularly abun-dant in the pericycle, which is closely associ-ated with the periderm and is removed uponpeeling

extend-In carrot (a primary tap root), the jority of the edible portion is comprised

ma-of sugar-storing parenchyma associated withsecondary phloem tissue Sucrose is the dom-inant sugar in mature roots, and roots con-tain little starch The tissue associated withthe secondary xylem in the center of roots(pith) is of coarser texture and small pith is de-sirable in commercial carrots (Rubatzky andYamaguchi 1997) In contrast, the majority

of the edible portions of sweet potato andcassava are internal to the vascular ring of en-larged secondary roots and consist of starch-containing storage parenchyma, which sur-round a matrix of xylem vessels In cassava,all cortical tissue is removed along with theperiderm (collectively, the peel) prior to cook-

ing, and a dense bundle of fibrou vasculartissue in the center of roots is also removedbefore consumption Although the majority

of sweet potato and cassava starch is lopectin, variation in the minority quantity ofamylose affects texture of the cooked product.Glutinous texture, stickiness, or waxiness ofthe product increases with a decreasing ratio

under-and the yams (Dioscorea spp.).

Potato tubers form at the end of rhizomesoriginating from the main stem Recessedbuds (eyes) and leaf scars (eyebrows) on theskin surface are conspicuous indicators thatthe potato is derived from stem rather than

Biology and Classification of Vegetables 15

Figure 1.2 Anatomy of select vegetables classified as “root crops.”

root tissue (Figure 1.2) In the absence of mancy or chemical inhibition, these buds willsprout and allow for the vegetative reproduc-tion of potato from “seed” pieces or smallwhole potatoes In contrast to potato, yam tu-bers lack conspicuous buds, leaf scars, andother outward signs of being derived fromstem tissue Sprouts will form from yam tu-bers and tuber pieces, but generate most read-ily from the proximal end of tubers As withtrue roots, cooking quality of tubers is influenced by starch type, dry matter content, andcell size

dor-The swollen hypocotyl tissues of table

beet (Beta vulgaris group Crassa) and radish (Rhaphanus sativus) are closely associated

with the taproot, and the edible portion is scribed as the hypocotyl-root axis The multi-ple cambia and differentially pigmented vas-cular tissues in beet result in the characteristicbanding observed in cross sections of the veg-etable (Figure 1.2)

de-Corms are a third type of modifie stemgrouped with the root vegetables and are ex-

emplifie by taro (Colocasia esculenta) and other members of the Araceae Corms are

vertically oriented, apically dominant, pressed starchy stem bases that initiate under-ground, but continue to grow partially aboveground Adventitious shoots eventually arisefrom the parent corm to form secondary corms

com-or ccom-ormels

Bulb vegetables, mainly in the Alliaceae,

are comprised primarily of swollen, fles yleaves (scales) specialized for storage ofcarbohydrates and other compounds (Figure1.2) These leaves arise in a whorl from acompressed conical stem called a basal plate.Dry, papery scales of the bulb exterior protectthe bulb

Fruit Vegetables

Fruit vegetables are concentrated in the naceae, Cucurbitaceae, and Fabaceae, but

Sola-occur in other families as well Large fruited

annual vegetables of the Cucurbitaceae and Solanaceae are generally warm- and

16 Handbook of Vegetables and Vegetable Processing

Figure 1.3 Anatomy of select vegetables composed of fruits and fruiting bodies (mushroom).

hot-season crops because their wild itors evolved in tropical and subtropical lati-tudes where growing seasons are long enough

progen-to produce enough vegetative growth progen-to port large fruits in a single year (see ecolog-ical adaptation below) Other vegetables in

sup-this group are okra (Abelmochus esculentus) and Phaseolus spp Intensive selection has

since resulted in early cultivars of most ing vegetables that will produce fruit in theshort growing periods of northern latitudes

fruit-Among the commercial vegetables, ple fruits dominate Berry, pepo, and legumeare the characteristic fruit types of the

sim-Solanaceae, Cucurbitaceae, and Fabaceae,

respectively Specialized pods produced by

okra (capsule) and the Brassicaceae and

Morigaceae (silique) are dry and at least

par-tially dehiscent at maturity but are consumedimmature green, while still succulent Eachkernel on an ear of corn is a simple indehis-cent fruit (caryopsis) (Figure 1.3)

In many fruit vegetables, the whole fruit

is edible although not necessarily consumed

In tomato, eggplant (Solanum melogena),

cu-cumber, and other vegetables, the entire carp along with placenta and other tissue isconsumed These vegetables may be peeled

peri-to soften texture and lighten fl vor by moving toughened dermal cells as well ascutin, waxes, and other secondary metabolitesthat are associated with organ protection, andwhich are concentrated in the epidermis andouter pericarp (exocarp) Immature fruit of

re-Biology and Classification of Vegetables 17

bittermelon (Momordica charantia) may also

be peeled to reduce bitterness caused by mordicosides and other compounds concen-trated in the outer pericarp, while the toughendocarp and spongy placenta of bittermelonare discarded along with the seeds The edible

mo-portion of mature Cucurbita fruit is pericarp tissue In Cucumis melo (e.g., cantaloupe and

muskmelon) the most internal portions of thepericarp (endocarp and mesocarp) are eaten,with the leathery rind (exocarp and some

mesocarp) discarded In watermelon lus lanatnus) the rind includes much of the

(Citrul-pericarp, with placental tissue making up asubstantial portion of what is consumed, al-though succulent parts of the rind can be pick-led and otherwise prepared

oler-ers of many plant taxa are consumed ther raw or cooked Important vegetablescomprised of flora structures include broc-

ei-coli and globe artichoke (Cynara scolymus)

(Figure 1.4)

Ecological Adaptation of Vegetables

The environmental optima (e.g., temperature,light, and soil moisture) of vegetable cropswill depend greatly on the center of origin oftheir wild progenitors For example, vegeta-bles whose center of origin lies in the tropicsare often generally classifie as warm-season,short-day plants In contrast, crops with tem-perate origins are often considered cool-season, long-day plants Our need for foodand fibe has resulted in strong, artificial selection pressure for broad adaptabil-ity in many vegetables crops (Wien 1997;

Sung et al 2008) Nevertheless, many etables can be grouped with regard totheir environmental requirements, and knowl-edge of these requirements is critical forcrop managers to make effective decisions(Table 1.3)

veg-Temperature

Classificatio of vegetable crops by ature is based on three sets of values, or car-dinal temperatures, that describe the mini-mum, maximum, and optimum temperatureranges for crop growth Minimum and max-imum temperatures represent the limits atwhich growth and development are thought

temper-to stemper-top or at least slow temper-to a negligible rate,while plant growth and normal developmentare most rapid within the optimum tempera-ture range Krug (1997) stratifie the simpleclassificatio of “warm” and “cool” seasoncrops to account for subtle but significandifferences in cardinal temperatures For ex-ample, the effective growth range for hot-season crops does not include temperatures

as low as the minima for warm-season crops,while heat-tolerant cool crops have tempera-ture maxima that exceed those of other cool-season crops (Figure 1.4)

A practical application resulting from thedominant influenc of temperature on veg-etable crop biology is the use of a heat unitsystem (or temperature sum concept) to pre-dict plant growth The most simple and oft-cited example is that used to predict harvestdates for corn Daily heat units (HU) accu-mulated are often calculated using the equa-

tion HU = ⌺ (Tavg − Tbase), where Tavg is

the average daily temperature and Tbase isthe minimum temperature for the crop, belowwhich no growth is expected Cool-seasoncrops grown during the summer in temperatezones will frequently be exposed to supraop-timal temperatures, and HU calculations mustaccount for the negative effect of high temper-atures on crop growth In head cabbage, HUcalculations using upper and lower threshold

18 Handbook of Vegetables and Vegetable Processing

Figure 1.4 Anatomy of select vegetables composed of flowers and associated structures Asterisk (∗) indicates

“floret” used as an industry designation for individual branches of inflorescence in broccoli.

temperatures of 21 and 0◦C have been usedeffectively to explain seasonal variability inhead size and weight (Radovich et al 2004;

Figure 1.5) If the daily maximum

tempera-ture (Tmax) falls below the upper threshold,then HU are calculated as described above

for corn If Tmax exceeds 21◦C, then an termediate cutoff method is employed, where

in-HU = [(Tmin+ 21)/2)] − [(Tmax− 21) ∗ 2]

Using this cutoff method, HU = 0 when

Tmax≥ 30◦C

Unfortunately, single factor models such

as HU are not adequate to predict all mental events In the cabbage example above,variation in HU fails to explain year-to-yearvariability in head density Similarly, whileestimation of head density changes in lettuce

develop-is improved by the inclusion of light intensityinto the HU equation (i.e., photothermalunits), the inclusion of an additional factor isnot adequate to satisfactorily predict densitychanges (Jenni and Bourgeois 2008) This

Biology and Classification of Vegetables 19

Table 1.3 Classification of vegetables based on lifecycle, temperature growth requirements, and photoperiodicity

Life cycle

Perennial Asparagus officinal , Capsicum spp., Ipomea batatas, Solanum sp.

Biennial Beta vulgaris, Brassica oleracea Capitata group, Dacus carota

Annual Spinacia oleracea, Cucurbita spp., Brassica oleracea Italica group

Temperature demand∗(temperature range for effective growth)

Hot (18–35 ◦ C) Abelmochus esculentus, Citrullus lanatus, Capsicum chinense

Warm (12–35 ◦ C) Cucumis sativus, Cucurbita spp., Zea mays, Capsicum annuum

Cool (heat tolerant) (7–30 ◦ C) Colocasia escultenta, Allium spp., Cynara scolymus, Brassica rapa L.

Chinensis group Cool (7–25 ◦ C) Brassica oleracea, Raphanus sativus, Latuca sativa, Solanum tuberosm

Photoperiod

Short day Amaranthus spp., Pachyrhizus erosus, Solanum tuberosum

Day neutral Solanum lycopersicum, Phaseolus spp., Cucurbita spp.

Long day Allium cepa Cepa group, Spinacia oleracea Source: After Pierce (1987).

∗ After Krug (1997).

highlights the potentially complex ship between ontogeny and environmentalfactors

relation-While heat drives vegetative growth inmost vegetables, a certain number of coldunits (time of exposure to temperatures be-low some critical minimum) are required toinitiate fl wering in many temperate biennialvegetables This phenomenon, termed vernal-

ization, is exhibited by Brassica, beets, and

other vegetables In crops that are tive to photoperiod, cold units may be cal-culated similarly as described above, whilephotothermal units are employed for photope-riodic crops

insensi-Light

All plants require light for photosynthesis

While a degree of shading will improve thegrowth of some vegetables, this is often a tem-perature response to cooling resulting fromreduced solar radiation Similarly, while thequality (i.e., wavelength) of light significantlaffects crop phenology, light quantity (inten-sity and daylength) generally impacts veg-etable crops in a similar manner However,crops often differ substantially in their re-sponse to photoperiod

As a rule, plants exhibit some sensitivity

to photoperiod in their development, ularly with regard to fl wering and storageorgan development (Waycott 1995; Martinez-Garcia et al 2002) As mentioned previously,tropical and temperate crops are frequentlyconsidered short- and long-day plants respec-tively, although the actual stimulus is theduration of the dark period and day neu-tral cultivars have been developed for manycrops Short-day crops include yam bean,cowpea, sweet potato, and potato Onion,lettuce, and spinach are examples of long-day vegetables (Mettananda and Fordham1997)

partic-Taxonomy of Vegetables

Botanical classificatio is the most preciseand ultimately most useful method of orga-nizing plants by biological commonality Thevast majority of vegetables are Angiosperms(subclass Monocotyledons and Dicotyledons)

in the division Spermophyta The Tallophyta(algae and fungi) are also important

The broadest taxonomic grouping vant to vegetable production and management

rele-is the Family Similarities in structure and

20 Handbook of Vegetables and Vegetable Processing

Figure 1.5 Relationship between growing degree-days and head traits of cabbage (Brassica oleracea Capitata

group) grown in 2001 (full symbols) and 2002 (open symbols) at the Ohio Agricultural Research and Development Center Treatment means of cultivars “Bravo,” “Bronco,” and “Transam,” are represented by circles, squares, and triangles, respectively (from Radovich et al 2004).

adaptation among plants within Families aregenerally conspicuous enough to be useful

in olericulture For example, ecological andphysiological differences among Families areoften adequate enough to be resistant to many

of each other’s specifi pathogens A cal application of this by crop managers is toavoid successive planting of crops from thesame Family when designing vegetable rota-tions in production

practi-Subordinate to the Family is Genus, lowed by the species designation Members of

fol-a species fol-are usufol-ally geneticfol-ally isolfol-ated fromthose of other species, and can freely inter-breed with individuals from the same species.Biological differences tend to be minor belowthe species level, but infraspecifi variability

in vegetable morphology and ecological tation is relevant enough to warrant furtherclassification

adap-Biology and Classification of Vegetables 21

Significan confusion and a lack of sistency in vegetable nomenclature at thesubspecifi level centers around three terms:

con-subspecies, varietas, and group All are

cate-gories of vegetables sharing distinct features

of functional relevance and have been used

interchangeably Subspecies and varietas are

botanical terms, while group is used sively by horticulturalists The differences be-

exclu-tween subspecies (ssp.) and varietas (also

variety, var.) have been recognized as tle but distinct, with the latter subordinate

sub-to the former (Kapadia 1963) However, bycurrent convention, the terms are used inter-changeably, with ssp more frequently used inEurope and var more common in the UnitedStates (Hamilton and Reichard 1992) Char-acteristics that distinguish ssp and var areexpected to go beyond the morphological andhave geographic, ecologic, or evolutionary in-tegrity (Hamilton and Reichard 1992; Peraltaand Spooner 2001) In contrast, horticulturalgroups may be define exclusively by func-tional similarities in morphology, as governed

by the International Code of Nomenclaturefor Cultivated Plants (ICNCP or CultivatedPlant Code) (Brickell et al 2004)

Botanical precedence has been cited forpreferential use of “variety” over “group” ininfraspecifi classificatio (Kays and SilvaDias 1996) However, botanical classification is dynamic and botanical variety statusmay change Also, while botanical varieties

of cultivated plants by definitio qualify forstatus as horticultural groups, the reverse isnot true Consequently, variety is used forone species and group for another in sometexts, and important authors differ in theiruse of variety and group for the same vegeta-bles (Rubatzky and Yamaguchi 1997; May-nard and Hochmuth 2007) This inconsistentusage can easily lead to confusion There-fore, this author proposes that “group” beused in lieu of “variety” (if not “subspecies”)

as a consistent, inclusive, and uniquely ticultural term to describe subspecifi cate-gories of vegetables sharing distinct features

hor-of functional relevance The vegetables hor-of

Brassica oleracea, including broccoli (Italica

group), kohlrabi (Gongylodes group), sels sprouts (Gemmifera group), head cab-bage (Capitata group), and collards (Acephalagroup) are well-known examples

Brus-The cultivated variety (cultivar, cv.) is ordinate to the group classification and isused to distinguish plants with one or moredefinin characteristics Although the termvariety is sometimes used in lieu of culti-var, cultivar should not be confused with the

sub-botanical variety (varietas, var.) as described

above To qualify for cultivar status, guishing characteristics must be preservedwhen plants are reproduced

distin-Although not preferred, the term “strain” issometimes used for vegetables derived from

a well-known cultivar, but with minor ences in form “Clone” is used to describegenetically uniform plants vegetatively prop-agated from a single individual The term

differ-“line” generally refers to inbred, sexuallypropagated individuals

Writing Nomenclature

As with other organisms, the Latin binomial

of vegetables is written in italics, with thefirs letter of the generic name capitalizedand the specifi name in lowercase letters.Current convention is to use single quotation

marks to indicate cultivar status, e.g., olus vulgaris ‘Manoa Wonder’, while use of

Phase-cv preceding the cultivar name is considered

obsolete (Brickell et al 2004) As a nation, the word “group” may either precede

desig-or follow the group name, and is listed inparentheses prior to the cultivar name, e.g.,

Brassica oleracea (Capitata group) “Bravo.”

The name of the person (authority) who firsdescribed the taxon may also be included

in the complete name For example, bita moschata Duchesne indicates that the species was named by Duchesne, while Cu- curbita moschata (Duchesne) Poir indicates

Cucur-22 Handbook of Vegetables and Vegetable Processing

that credit for the naming is given to esne in Poir (Paris 2000)

Duch-Acknowledgements

We thank Dr Arthur D Wall for his view of this chapter, and Jessica W Radovichfor assistance with graphic design of figuresChristina Theocharis is also gratefully ac-knowledged for her technical assistance

Society for Horticultural Science (ISHS).

Graham LE, Graham JM, Wilcox LW 2006 Plant Biology, 2nd edition Upper Saddle River, NJ:

Pearson/Prentice-Hall.

Hamilton CW, Reichard SH 1992 Current practice in the use of subspecies, variety, and forma in the classi-

ficatio of wild plants Taxon 41:485–498.

Iltis HH, Doebley JF 1980 Taxonomy of Zea (Gramineae) II Subspecifi Categories in the Zea

Mays Complex and a Generic Synopsis Am J Bot

67:994–1004.

Jeffery C 1990 Systematics of the Cucurbitaceae: an overview In: Bates DM, Robinson RW, Jeffrey C (ed-

itors), Biology and Utilization of the Cucurbitaceae.

New York: Cornell University Press, pp 1–28.

Jenni S, Bourgeois G 2008 Quantifying phenology

and maturity in crisphead lettuce HortTechnology

18:553–558.

Kader AA 2002 Postharvest biology and technology:

an overview In: Kader AA (editor), Postharvest nology of Horticultural Crops Berkeley, CA: Univer-

Tech-sity of California Agriculture and Natural Resources,

pp 39–48.

Kapadia ZJ 1963 Varietas and subspecies: a suggestion

for greater uniformity Taxon 12:257–259.

Kays SJ, Silva JC 1996 Cultivated Vegetables of the World Athens, GA: Exon Press.

Krug H 1997 Environmental influence of development

growth and yield In: Wein HC (editor), The Physiology

of Vegetable Crops New York: CAB International, pp.

101–206.

Martinez-Garcia JF, Garcia-Martinez JL, Bou J, Prat S.

2002 The interaction of gibberellins and photoperiod

in the control of potato tuberization J Plant Growth Regul 20:377–386.

Maynard DN, Hochmuth GJ 2007 Knott’s Handbook for Vegetable Growers, 5th edition New York: John

Wiley & Sons, Inc.

Mettananda KA, Fordham R 1997 The effects of 12 and

16 hour daylength treatments on the onset of bulbing in

21 onion cultivars (Allium cepa L) and its application

to screening germplasm for use in the tropics J Hort Sci 72:981–988.

Nix v Hedden 1893 Supreme Court Decision 149 U.S.

304 May 10, 1893 http://laws.findl w.com/us/149/ 304.html (accessed on June 9, 2010).

Paris HS 2000 Duchesne is the Botanical authority for

Cucurbita moschata and Cucurbita maxima Cucurbit Genetics Cooperative Report 23:56–57.

Peirce L 1987 Vegetables: Characteristics, Production and Marketing New York: John Wiley and Sons.

Peralta IE, Spooner DM 2001 Granule-bound starch synthase (Gbssi) gene phylogeny of wild toma-

toes (Solanum L section Lycopersicon Mill Wettst Subsection Lycopersicon) Am J Bot 88(10):1888–

1902.

Radovich TJK, Kleinhenz MD, Honeck NJ 2004 tant cabbage head traits at fi e points in development.

Impor-J Veg Crop Prod 10:19–32.

Rubatzky VE, Yamaguchi M 1997 World Vegetbales: Principles, Production, and Nutritive Values New

York: Chapman & Hall, 572 pp.

Sung Y, Cantliffe DJ, Nagata RT, Nascimento WM.

2008 Structural changes in lettuce seed during nation at high temperature altered by genotype, seed

germi-maturation temperature and seed priming J Am Soc Hort Sci 133:300–311.

Waycott W 1995 Photoperiodic response of

geneti-cally diverse lettuce accessions J Am Soc Hort Sci

120:460–467.

Wien HC (editor) 1997 The Physiology of Vegetable Crops New York: CAB International.

Chapter 2

Biochemistry of Vegetables: Major Classes of Primary (Carbohydrates, Amino Acids, Fatty Acids, Vitamins, and Organic Acids) and Secondary Metabolites (Terpenoids, Phenolics, Alkaloids, and Sulfur-Containing Compounds) in Vegetables

N Hounsome and B Hounsome

Introduction

Historically, major plant constituents were vided as primary and secondary metabolites

di-K¨ossel (1891) define primary metabolites

as present in every plant cell that is capable

of reproduction, while secondary metabolitesare present only “accidentally.” Plant metabo-lites determine the food’s nutritional qual-ity, color, taste, and smell, and its antiox-idative, anticarcinogenic, antihypertension,anti-inflammator , antimicrobial, immunos-timulating, and cholesterol-lowering proper-ties Primary metabolites are found acrossall species within broad phylogenetic groups,and are produced using the same (or nearlythe same) biochemical pathways Primarymetabolites, such as carbohydrates, aminoacids, fatty acids, and organic acids, are in-volved in growth and development, respira-tion and photosynthesis, and the synthesis ofhormones and proteins A general scheme of

major primary metabolic pathways in plants

is shown in Figure 2.1

Secondary metabolites include terpenoids,phenolics, alkaloids, and sulfur-containingcompounds such as glucosinolates Theydetermine the color of vegetables, protectplants against herbivores and microorgan-isms, attract pollinators and seed-dispersinganimals, and act as signal molecules understress conditions (Seiger 1998; Crozier et al.2006) Secondary metabolism is charac-terized by the high “degree of chemicalfreedom,” which is thought to evolve underthe selection pressure of a competitiveenvironment (Hartmann 1996)

Primary and secondary metabolites not readily be distinguished on the basis ofprecursor molecules, chemical structures, orbiosynthetic origins For example, terpenoidsinclude primary as well as secondary metabo-lites (e.g., phytol and gibberellins are pri-mary metabolites, while limonene and men-thol are secondary metabolites) A compoundsuch as phylloquinone (vitamin K1) is usuallyclassifie as terpenoid quinone, rather than

can-Handbook of Vegetables and Vegetable Processing Edited

by N K Sinha
c 2011 Blackwell Publishing Ltd.

23

24 Handbook of Vegetables and Vegetable Processing

Carbohydrates

CO 2

Calvin cycle

Pentose phosphate pathway

Shikimic acid pathway

Aromatic amino acids amino acids Aliphatic

Phenylpropanoid pathway

Amines

Phenolic

Tricarboxylic acid cycle

Terpenoids Chlorophylls

Alkaloids Glucosinolates

Figure 2.1 General scheme of primary metabolic pathways in plants.

phenolic, while other quinones, such as zoquinones and anthraquinones, are regarded

ben-as phenolic compounds Nonprotein aminoacids (e.g., canavanine and citrulline) aresometimes discussed as primary metabolitessince they act as intermediates in the synthe-sis of the protein amino acids (Morot-Gaudry

et al 2001) At the same time, they can be garded as secondary metabolites due to theirinvolvement in plant defense mechanisms(Rosenthal 2001; Besson-Bard et al 2008)

re-In this chapter, we provide an overview ofthe major classes of plant metabolites found

in vegetables, emphasizing their roles inhuman health and nutrition The chapter alsocontains information about plant metaboliteswith reported antioxidant properties Thecontent of selected primary and secondarymetabolites in vegetables is presented inTables 2.1 and 2.2

Primary Metabolites

Carbohydrates

Carbohydrates are a class of organic pounds originating from the Calvin Cycleand consisting of carbon, hydrogen, andoxygen (CH2O)n In plants, carbohydratesoccur as monosaccharides (e.g., arabinose,

com-glucose, fructose, galactose, and rhamnose),disaccharides (e.g., sucrose, maltose, andtrehalose), sugar alcohols (e.g., sorbitol,mannitol, and xylitol), oligosaccharides (e.g.,raffinose stachyose, and fructooligosac-charides), and polysaccharides (e.g., starch,cellulose, hemicellulose, and pectins) Thechemical structure of selected carbohydrates

is shown in Figure 2.2

Monosaccharides, sucrose, and charides are present in all vegetables.Raffinos and stachyose have been found inbeetroot, broccoli, lentil, pea, onion, and soy-bean (Obendorf et al 1998; Frias et al 1999;Peterbauer et al 2001; Muir et al 2009).Fructooligosaccharides (e.g., kestose andnystose) are accumulated in artichoke,broccoli, garlic, leek, and onion (Shiomi1992; Benkeblia and Shiomi 2006; Muir

polysac-et al 2007; Muir polysac-et al 2009) Sorbitol wasfound in broccoli, cabbage, caulifl wer, kale,maize corn, and tomato; mannitol in broccoli,caulifl wer, celery, and fennel (Cataldi et al.1998; Nilsson et al 2006; Muir et al 2009)

In terms of their physiological or tional role, carbohydrates are often classifie

nutri-as available and unavailable Available bohydrates are those that are hydrolyzed byenzymes of the human gastrointestinal sys-tem to monosaccharides, such as sucrose and