Handbook of Vegetables and Vegetable Processing

Nirmal Sinha, Y. H. Hui, E. Özgül Evranuz, Muhammad Siddiq, Jasim Ahmed

• Publisher: Wiley-Blackwell
• Year: 2010
• Print ISBN: 9780813815411
• eBook ISBN: 9780470958445
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Vegetables are an important article of commerce both in developed and developing economies. Many studies point to importance of vegetables in our diet. Handbook of Vegetables and Vegetable Processing serves as a reference handbook on vegetables and vegetable processing containing the latest developments and advances in this fast growing field. The book can be considered as a companion to Y. H. Hui's popular Handbook of Fruits and Fruit Processing (2006). Handbook of Vegetables and Vegetable Processing is contemporary in scope, with in-depth coverage of new interdisciplinary developments and practices in the field of vegetables emphasizing processing, preservation, packaging, and nutrition and food safety. Coverage includes chapters on the biology, horticultural biochemistry, microbiology, nutrient and bioactive properties of vegetables and their significant commercialization by the food industry worldwide. Full chapters are devoted to major vegetables describing aspects ranging from chemistry to processing and preservation. World-renowned editors and authors have contributed to this essential handbook on vegetables and their production, technology, storage, processing, packaging, safety and commercial product development.

Special Features:

• Coverage includes biology and classification, physiology, biochemistry, flavor and sensory properties, microbial safety and HACCP principles, nutrient and bioactive properties
• In-depth descriptions of key processes including, minimal processing, freezing, pasteurization and aseptic processing, fermentation, drying, packaging, and application of new technologies
• Entire chapters devoted to important aspects of over 20 major commercial vegetables including avocado, table olives and textured vegetable proteins
• Unparalleled expertise on important topics from more than 50 respected authors

Part I

Biology, Biochemistry, Nutrition, Microbiology, and Genetics

Chapter 1

Biology and Classification of Vegetables

Theodore J. K. Radovich

Introduction

Vegetables enrich and diversify the human diet. They are the primary source of mineral nutrients, vitamins, secondary plant metabolites, and other compounds that support human health and nutrition. Vegetables, especially roots and tubers, can also possess significant caloric value, serving as staple crops in many parts of the world, particularly in the tropics. Although vegetables account for less than 1% of the world's plants, the genetic, anatomical, and morphological diversity of vegetables as a group is astounding (Graham et al. 2006; Maynard and Hochmuth 2007). Hundreds of vegetable taxa are grown for food in subsistence and commercial agricultural systems worldwide. This chapter reviews and explains the biology and classification of vegetables.

Biology and Classification of Vegetables

A primary reason for the diversity among vegetable crops is the broad definition of the word “vegetable” itself. Any plant part consumed for food that is not a mature fruit or seed is by definition a vegetable. These include petioles (e.g., celery, Apium graveolens Dulce group), entire leaves (e.g., lettuce, Lactuca sativa), immature fruits (e.g., cucumber, Cucumis sativus), roots (e.g., carrot, Dacus carota), and specialized structures such as bulbs (e.g., onion, Allium cepa Cepa group) and tubers (e.g., white potato, Solanum tuberosum).

Further expanding this already generous definition is the inclusion of mature fruits that are consumed as part of a main meal rather than dessert (e.g., tomato, Solanum lycopersicum). This culinary exception to the anatomical rule was given legal precedence in the US Supreme Court decision Nix v. Hedden (1893) that confirmed common usage of “vegetable” in reference to tomato. This has since been extended to beans and other fruits. Even dessert melons (e.g., cantaloupe, Cucumis melo Cantalupensis group), which are fruits by every botanical, legal, and culinary definition, are frequently “lumped” in with vegetables because of similarities in biology and culture that they share with their more vegetal cousins in the Cucurbitaceae (Iltis and Doebley 1980) (Table 1.1).

Table 1.1 Botanical names, common names, and edible parts of select vegetables by family. Families in the Monocotyledons are listed first (shaded) followed by families in Dicotyledons

Source: Abridged and modified from Maynard and Hochmuth (2007).

The biological diversity among vegetables necessitates a systematic method for grouping vegetables in order to efficiently access information and make management decisions. Understanding the biology of vegetable crops will aid decision making associated with production, postharvest handling, and marketing. Ultimately, vegetable classification is inextricably linked with crop biology. Three basic approaches toward classification of vegetables that are based on commonalities among groups are as follows:

1. Tissues and organs consumed

2. Ecological adaptation

3. Taxonomy

All three of the above approaches toward classification are based on some level of commonality in crop biology, with the precision of classification varying from relatively low (plant part consumed) to very high (taxonomic). Table 1.2 gives definitions of selected terms related to vegetable anatomy, biology and classification.

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

Term	Definition
Andromonoecious	Staminate and hermaphrodite flowers 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
Berry	Fruit fleshy throughout
Biennial	Plant that completes life cycle (sets seed) and dies in two years
Bolt	Develop inflorescence prematurely, as in lettuce and spinach
Bract	Modified leaf or scale at base of flower
Bulb	Bud surrounded by fleshy 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 fleshy, 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 inflorescence with flower buds undifferentiated, e.g., cauliflower
Determinant	Branch stops growing at flowering
Dioecious	Staminate (male) and pistillate (female) flowers on separate plants
Endocarp	Inner layer of fleshy 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 flower on inflorescence, e.g., artichoke
Fruit	Mature ovary.
Gynoecious	Producing predominantly, or only, female flowers
Indeterminant	Branch continues to grow after flowering 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 flowers on same plant
Node	Enlarged area on stem where buds emerge
Pedicel	Stalk or stem of individual flower or floret
Peduncle	Primary flower stalk of inflorescence
Pepo	Cucurbit fruit, leathery or woody exocarp inseparable from endocarp
Perfect flower	Flower with both male and female parts
Pericarp	Fruit wall
Perennial	Plants persisting for three years or more
Petiole	Leaf stalk
Rhizome	Horizontally oriented underground stem modified for storage, with nodes capable of forming new roots and shoots
Scales	Fleshy or dry modified 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

Vegetable Tissues and Organs

The phenotypic diversity among vegetables is actually based on relatively few types of specialized cells and tissues. Dermal, ground, and vascular tissue make up the three basic tissue systems. Ultimately, the structure of these cells and tissues determine their function.

Dermal Tissues

Epidermal cells, together with cutin and cuticular waxes, make up the outer layers of leaves, fruit, and other above-ground structures and protect against water loss and other adverse abiotic and biotic factors. The periderm (cork) layer of mature roots and stems is analogous to the epidermis, but consists of nonliving cells supplemented with suberin. Stomatal guard cells are epidermal cells specialized in regulating gas exchange, and are especially dense on the abaxial surface of leaves. Lenticels are specialized, unsuberized dermal structures (appearing as raised dots or bumps) that regulate gas exchange on roots, stems, and fruits. Trichomes and root hairs are dermal cells with excretory, absorptive, and other functions critical to the ecology of vegetables.

Ground Tissues

Ground tissues are comprised of the parenchyma, collenchyma, and sclerenchyma. Parenchyma cells are thin-walled cells that make up much of the ground tissues of vegetables. Parenchyma cells often serve to store starch and other compounds. The cortex and pith of white potato are examples of ground tissues dominated by parenchyma. Collenchyma cells have alternating thin and thick cell walls that provide flexible support for stems, as in the strings of celery (Apium graveolens). Sclerenchyma tissues include sclerids and fibers with tough cell walls. Sclerenchyma cells are typically scarce in edible vegetable organs, but are important components of seed coats, nut shells, and the stony endocarps of peaches (Prunus persica) and related fruits.

Conducting Tissues

Vascular tissues conduct water, minerals, photosynthates, and other compounds throughout the plant. The xylem is part of the apoplast and consists primarily of nonliving tracheids and vessel elements. The xylem transports water, mineral nutrients, and some organic compounds, generally from the roots to leaves. The phloem is part of the symplast, consists primarily of sieve cells and companion cells, and is important in conducting sugars, amino acids, and other compounds from source (usually leaves) to sink (actively growing meristems, roots, developing fruits, and seeds). Both xylem and phloem are supported by parenchyma cells and fiber. Some xylem cells (i.e., tracheids) have thickened cell walls that contribute significantly to the structural support of tissues.

The differentiation and variable structure of plant tissues result in diverse functions among the plant organs (stems, roots, and leaves) and organ systems (e.g., fruits, flowers, buds, and bulbs) consumed as vegetables. The classification of vegetables by edible parts has been termed “Supermarket Botany” (Graham et al. 2006). Although broad and not always anatomically correct, the grouping of commodities as leafy, fruit, and root vegetables has value to growers, distributors, and others in the market chain because of similarities in cultural and postharvest ...

Table of contents

• Cover
• Half Title Page
• Title Page
• Copyright
• Preface
• Contributors
• Part I: Biology, Biochemistry, Nutrition, Microbiology, and Genetics
• Part II: Postharvest Technology and Storage Systems
• Part III: Processing and Packaging of Vegetables
• Part IV: Product and Food Plant Safety and HACCP
• Part V: Commodity Processing
• Index