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Vegetables and Fruits: Clssification, structure, composition and nutritive value.pptx

Fruits and vegetables constitute a fundamental part of human nutrition, supplying essential micronutrients, dietary fibre, antioxidants, and various bioactive compounds that promote health and prevent chronic diseases. Their classification, cellular structure, chemical composition, and nutritive profile influence their functional properties, sensory attributes, and overall dietary significance. This presentation presents a systematic and scientific overview of the classification, structural organization, compositional characteristics, and nutritional importance of fruits and vegetables, with specific relevance to Food Science, Food Technology, and Nutrition disciplines.

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VEGETABLES AND FRUITS: CLASSIFICATION, STRUCTURE, COMPOSITION AND NUTRITIVE VALUE Aktarafun Zannat Assistant Professor (Food and Nutrition) Govt. College of Applied Human Science, Dhaka
CLASSIFICATION • Vegetables: • Vegetables are classified according to the parts of the plants consumed or colour of the vegetable or according to the nutritive values. Nutritionally they are classified into 3 groups- 1. Green leafy vegetables 2. Roots and Tubers 3. Other vegetables Botanical Classification- B Srilakshmi book (page- 197) Fruits: B Srilakshmi book (page- 227)
Structure (a) Cell Wall System 1. Primary Wall • The outermost living boundary of the cell. Composed mainly of cellulose, hemicellulose, and pectic substances. It is thin, flexible, and permeable, allowing exchange of water and solutes. Provides shape, rigidity, and protection to the cell. 2. Middle Lamella • The intercellular layer that cements adjacent plant cells together. Composed largely of pectin compounds. Responsible for firmness and cohesion of fruits and vegetables. During ripening or cooking, pectin becomes soluble, causing the tissue to soften. 3. Intercellular Space • Small air-filled gaps between cells. Influences texture, crispness, and light reflection, affecting appearance. The amount of intercellular space differs among fruits and vegetables.
(b) Plasmalemma (Cell Membrane) • A semi-permeable membrane located inside the cell wall. Controls the movement of water, ions, and solutes in and out of the cytoplasm. Maintains the integrity of the protoplast. (c) Protoplasmic Components • The protoplasm includes all living parts of the cell, enclosed by the plasmalemma.  Cytoplasm: • Jelly-like substance containing organelles such as the nucleus and plastids. Site of metabolic activities and enzyme reactions.  Nucleus: • The control center of the cell. Contains the nucleolus and chromatin material (DNA). Directs cell metabolism, growth, and reproduction.
 Plastids: • Specialized organelles responsible for color and storage. Three main types: Chloroplasts (photosynthesis), Chromoplasts (pigments), Leucoplasts (storage).  Vacuole: • Large central cavity filled with cell sap (water, sugars, salts, acids, pigments). Surrounded by the tonoplast. Maintains turgor pressure, keeping tissues firm and crisp.  Tonoplast: • Membrane surrounding the vacuole. Regulates the exchange of substances between vacuole and cytoplasm.  Starch Grains: • Found mainly in leucoplasts (amyloplasts). Serve as storage form of carbohydrates. Quantity and size vary with type of fruit or vegetable.
FUNCTIONAL IMPORTANCE OF CELL STRUCTURE a) Mechanical and Structural Functions • The cell wall and middle lamella provide mechanical strength and rigidity. These features maintain shape and resist deformation during handling and cooking. The firmness of tissues depends on pectin structure and cell turgor. (b) Physiological and Sensory Functions • Vacuole and cytoplasm contain organic acids, sugars, and pigments responsible for flavor and color. Air spaces between cells influence crispness and appearance. Loss of turgor pressure results in softening or wilting. Texture changes during cooking occur due to pectin solubilization and cell wall breakdown. (c) Nutritional Importance • Cell wall polysaccharides (cellulose, hemicellulose, and pectic substances) form dietary fiber. Plastids store essential nutrients such as starch and pigments (carotenoids, chlorophyll). Vacuole stores soluble nutrients like vitamin C and organic acids.
COMPARISON WITH ANIMAL CELLS •Plant parenchyma cells differ from animal cells in several ways: -Have rigid cell walls made of cellulose. -Contain vacuoles and plastids. -Possess a middle lamella for adhesion, absent in animal cells. •These structures provide firmness, storage capacity, and turgidity, all of which influence the edible quality of fruits and vegetables.
COMPOSITION AND NUTRITIVE VALUES OF VEGETABLES 1. Nutritive Value of Green Leafy Vegetables • Green leafy vegetables are the manufacturing organs of plants where photosynthesis takes place. • They are low in carbohydrates and energy but are good sources of β- carotene, calcium, riboflavin, folic acid, and ascorbic acid (Vitamin C). • The nutritive value depends on the variety and freshness of the leaves.
Vitamin and Mineral Content • Rich sources of vitamins and minerals, especially B-vitamins (riboflavin, folic acid), β- carotene, and Vitamin C. • β-carotenes act as antioxidants and precursors of Vitamin A. • The greener the leaves, the higher the carotene content due to more chlorophyll pigments. • Drying and withering reduce the content of Vitamin C and riboflavin. Iron and Calcium Content • Rich in iron — help in preventing anaemia. • Amaranth, fenugreek, gogu are good iron sources. • Agathi, colocasia, drumstick, and fenugreek leaves contribute calcium, though absorption is limited by oxalic acid.
Other Nutrients and Fibre • High moisture content; therefore, they wither easily and need proper preservation. • Not good sources of protein, fat, or carbohydrates. • Excellent sources of fibre, aiding digestion and preventing degenerative diseases. • Discarded leaves like cauliflower leaves, beetroot leaves, and pumpkin leaves also contain iron and should be used.
2. NUTRITIVE VALUE OF ROOTS AND TUBERS Energy and Starch • Provide more calories than leafy vegetables because they contain more starch. • Important energy-giving foods. Carotene and Vitamin C • Carrots are rich in carotenes. • Roots and tubers are fairly good sources of Vitamin C. • Deficiency in Other Nutrients • Poor sources of calcium, iron, and B-vitamins. • Also low in protein.
3. NUTRITIVE VALUE OF OTHER VEGETABLES General Composition • Contain high moisture, making them highly perishable. • Contribute fibre to the diet. Vitamins and Pigments • Tomatoes are rich in carotenoids (especially lycopene). • Cluster beans, capsicum (green, red, yellow) — good sources of iron, carotenoids, and Vitamin C. • Capsicum contributes to both colour and Vitamin C content.
Antioxidant Activity of Vegetables • Antioxidants protect cells against oxidative damage caused by free radicals. • Measured by DPPH (2,2’-Diphenyl-1-picryl hydrazyl) radical scavenging activity. • Okra and broad beans have the highest antioxidant activity among other vegetables. Beetroot shows the highest antioxidant activity among roots and tubers. Pigments in Vegetables • Classification • Pigments give colour and visual appeal to vegetables. • Classified into: • Water-insoluble pigments: Chlorophyll and Carotenoids • Water-soluble pigments: Anthocyanins, Anthoxanthins, and Betalains
WATER-INSOLUBLE PIGMENTS Chlorophyll • Found in chloroplasts; responsible for green colour. • Two forms: • Chlorophyll-a: blue-green • Chlorophyll-b: yellow-green • Present in a 3 : 1 ratio in most plants. • Masked by other pigments in some vegetables. • Present in leafy vegetables, capsicum, beans, peas, and chillies. Carotenoids • Fat-soluble pigments: yellow, orange, red in colour. • Include β-carotene, α-carotene, γ-carotene, lycopene, xanthophyll, cryptoxanthin. • Function as antioxidants and precursors of Vitamin A.
WATER-SOLUBLE PIGMENTS Anthocyanins • Water-soluble red to purple pigments; derivatives of cyanidin. • Found in cherries, red apples, berries, grapes, pomegranates, and currants. • Responsible for red colour in radish skin, sweet potato, red cabbage, and purple brinjal. • Sensitive to pH and heat; colour fades on cooking. Anthocyanidins • Anthocyanins without sugar. • Examples: • Pelargonidin – red • Cyanidin – reddish blue • Delphinidin – blue
Anthoxanthins • Colourless to yellow pigments related to anthocyanins. • Present in onions, spinach, and other pale-coloured vegetables. • Sensitive to pH – become darker in acidic medium. • Subgroups include flavones, flavonols, flavanones, catechins, etc. Betalains • Found in certain families instead of anthocyanins. • Two pigments: Betacyanin (red-violet) and Betaxanthin (yellow). • Present in beetroot.
ORGANIC ACIDS •Vegetables contain formic, oxalic, malic, citric, tartaric, and succinic acids. •Give flavour and slightly acidic pH (5.0–6.3). •Tomatoes and grapes have low pH due to high organic acid content.
ENZYMES IN VEGETABLES • Act as catalysts in biochemical reactions. • Two major groups: Hydrolytic enzymes and Oxido-reductases.  Functions • Responsible for ripening (e.g., in tomatoes and bananas). • Cause browning in potato, brinjal, plantain. • Papain in papaya: used in tenderising meat and stabilising beer. • Can cause loss of anthocyanin pigments (by anthocyanase). • Heat treatment inactivates undesirable enzymes.
FLAVOUR COMPOUNDS • Result from sugars, acids, salts, aldehydes, ketones, alcohols, tannins, and sulphur compounds. • Sweetness mainly from glucose, fructose, galactose. • Astringency from tannins and phenolics. Sulphur-Containing Compounds • Found in onion, garlic, leek (Allium group) and cruciferous vegetables (cabbage, turnip, cauliflower, kale, mustard). • Responsible for characteristic odour and strong flavour. • Overcooking or improper cooking enhances sulphur odour.
BITTER COMPOUNDS • Cucurbitacins – found in cucumber and gourds, cause bitterness. • Solanine and chaconine – steroidal glycoalkaloids in potatoes; toxic if sprouted or damaged. • Cooking destroys most toxic alkaloids. • Proper storage reduces sprouting and bitterness.
Addition of Chemicals • Preservative Treatment • Studies at Agriculture College and Research Institute, Madurai: • Onions treated with maleic hydrazide (2000 ppm) inhibited rooting and sprouting. • Prolonged storage life up to 150 days. Factors That Extend Shelf Life •Harvesting at optimum maturity with minimum injury. •Maintaining proper sanitation during handling and storage. •Optimum storage conditions: proper temperature, humidity, and sanitation. •Controlled atmosphere during all marketing and transport steps.
COMPOSITION AND NUTRITIVE VALUE OF FRUITS • Fruits are generally poor sources of protein and fat. • Avocado is an exception, containing 13.8 % fat. • ω-3 fatty acids are present in plum, papaya, and guava — these fruits contribute to dietary ω-3 fatty-acid intake (NIN 1999–2000). • Contain high moisture, hence are highly perishable. • Good sources of fibre aiding digestion. Caloric Value • Fruits are not high in calories. • Bananas give a fairly good amount of energy compared to most fruits. • Ripe fruits have a higher percentage of sugars than unripe ones. • Major sugars: sucrose, fructose, and glucose. Mineral Content • Generally, fruits are poor in iron, but dry fruits are a fairly good source of iron.
VITAMINS AND CAROTENOIDS β-Carotene and Carotenoids • Mangoes are excellent sources of carotenes. • Research at NIN, Hyderabad found Alphonso richest in β-carotene. • Banganapally and Pedda Rasalu are fairly good sources. • Indian dates, papaya, and oranges also contain β-carotene. • Carotenoids provide yellow-orange colour and act as vitamin A precursors. Vitamin C (Ascorbic Acid) • Guavas and citrus fruits are excellent sources of vitamin C. • Cashew apple is inexpensive yet rich in vitamin C (≈ 180 mg/100 g). • Gooseberry (Amla) is the richest natural source of vitamin C (≈ 252 mg/100 g). • Variation exists from fruit to fruit, but all fresh fruits contain some ascorbic acid. • Loss of Vitamin C occurs when fruits are: • Bruised or peeled, • Cooked or exposed to air, alkali, or copper.
Antioxidant Value •Antioxidant activity measured as DPPH (Trolox equivalent mg/100 g). •Guava shows the highest antioxidant activity among fresh fruits. Water Content • Fruits contain 75–90 % water. • Water dissolves sugars, salts, organic acids, and pigments within vacuoles. • Insoluble substances remain colloidally dispersed. • Pigments in Fruits • Like vegetables, fruits owe their colour to several pigment groups. Chlorophyll • Found in guava, gooseberry, and country apple. • Imparts green colour, though masked by carotenoids in ripe fruits.
Carotenoids • Present in mango, papaya, orange, watermelon (lycopene), muskmelon (β- carotene), jackfruit, peach (violaxanthin), tomato, grape pink (lycopene + β- carotene), pineapple (violaxanthin + β-carotene). • Contribute yellow, orange, and red hues. Anthocyanins • Found in grapes, blueberries, plums, and cherries. • Provide red-blue-violet shades. Anthoxanthins • Present in guava, apple, gooseberry, pear, custard apple, banana. • Yield pale yellow to creamy colours.
CELLULOSE AND PECTIC SUBSTANCES • Fruit framework built from cellulose forming the cell-wall matrix. • Hemicellulose and pectic substances fill intercellular spaces and bind cells. Pectic Compounds • Include protopectin, pectinic acid, and pectin. • Act as cementing substances giving firmness. • Heat or ripening converts insoluble protopectin to soluble pectin, softening fruit. • Acids make tissue firm; alkalis disintegrate fibres. • Apples and guavas are rich in pectin (a soluble dietary fibre).
FLAVOUR CONSTITUENTS Volatile Compounds • Include esters, aldehydes, acids, alcohols, ketones, ethers. • Example: jackfruit flavour due to 13 esters (mostly 3-methyl butanoates), 9 alcohols, 5 aldehydes, 5 acids, and 2 acetyl-1-pyrroline compounds. Other Influencing Substances • Sugars, tannins, acids, and mineral salts also modify fruit flavour. • Some fruits have essential oils contributing to characteristic aroma.
POLYPHENOLS Nature and Occurrence • Include tannins, catechins, leuco-anthocyanins, hydroxy acids. • Present in apples, peaches, grapes, almonds, pears, absent in most herbs. • Confer astringency and affect colour and flavour. • Skins and seeds are high in tannin content. Effects on Fruit Quality • Cause a puckering sensation (astringency) in mouth. • Lead to haze or precipitate formation in juice, beer, and wine due to protein- phenolic interactions. • Cause brown discolouration in cut fruits via oxidation (chlorogenic acid, catechins).
BITTERNESS IN FRUITS AND VEGETABLES Compounds Responsible • Limonoids (triterpenes) and flavanone glycosides (naringin). • Found especially in citrus fruits (grapefruit). Mechanism • Bitter flavour develops when precursor (limonoate A-ring lactone) reacts with acid during juice extraction, forming limonin. • Naringin, a major flavonoid in grapefruit, also contributes to bitterness. Other Examples • Cucumber contains cucurbitacins (oxygenated tetracyclic triterpenes) that impart bitterness. • Bitter compounds may exist both free and glycosidic forms.
IMPORTANCE OF VEGETABLES • Vegetables are important for human health because oftheir vitamins, minerals, phytochemical compounds, and dietary fiber content. • Especially antioxidant vitamins (vitamin A, vitamin C, and vitamin E). • Adequate vegetable consumption protects from some chronic diseases such as diabetes, cancer, obesity, cardiovascular diseases.
ANTI-NUTRIENTS • “Anti-nutrients” are substances that can block the absorption of nutrients. Anti-nutrients are naturally found in animals and many plant-based foods. In plants, they are compounds designed to protect from bacterial infections and being eaten by insects. • Glucosinolates in cruciferous vegetables (broccoli, cabbage) can prevent the absorption of iodine, which may then interfere with thyroid function and cause goiter. Those already with an iodine deficiency or a condition called hypothyroidism are most susceptible. • Lectins in legumes (beans, peanuts, soybeans), whole grains can interfere with the absorption of calcium, iron, phosphorus, and zinc.
• Oxalates in green leafy vegetables, tea can bind to calcium and prevent it from being absorbed. • Phytates (phytic acid) in whole grains, seeds, legumes, some nuts can decrease the absorption of iron, zinc, magnesium, and calcium. • People who are at high risk for diseases related to mineral deficiencies, such as osteoporosis with calcium deficiency or anemia with iron deficiency, may wish to monitor their food choices for anti-nutrient content.
References • Srilakshmi, B. (2019). Food Science (8th Edition). New Age International Publishers.
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