Overview
This lecture covers the classification, nutritional value, composition, and storage of vegetables and fruits, along with their pigments, enzymes, and post-harvest handling processes.
Classification and Characteristics of Vegetables
- Vegetables are horticultural plants with a lifespan of less than one year and high water and fiber content.
- Main groups: leaf, root, fruit, seed/pod, stem, and flower vegetables.
- Leaf vegetables include spinach, mustard greens, kale, and lettuce; they have high water and cellulose but low protein and energy.
- Fruit vegetables include chayote, tomatoes, cucumbers, and eggplant; they are high in water and vitamins.
- Seed/pod vegetables (e.g., long beans, green beans, peas) are low in water and high in carbohydrates, protein, and vitamin B-complex.
- Root vegetables (e.g., carrots, loba) have high water, vitamin A, iron, and magnesium.
- Stem (e.g., bamboo shoots) and flower vegetables (e.g., broccoli, cauliflower) have moderate vitamins and cellulose.
- Selection of vegetables should focus on freshness, color, absence of damage, and firmness.
Composition and Nutritional Value of Vegetables
- Vegetables contain 70–95% water, carbohydrates (mainly cellulose), vitamins (A, B, C), and minerals (calcium, iron).
- Dark green vegetables are high in vitamin A and iron.
- Cassava leaves are high in vitamin A, C, protein, and calcium.
- Turgor pressure (cell water content) affects vegetable texture and freshness.
Pigments and Enzymes in Vegetables
- Chlorophyll gives a green color and changes to brown on cooking.
- Carotenoids (carotene, xanthophyll, lycopene) give orange, yellow, and red colors.
- Flavonoids (anthocyanin, anthoxanthin, tannin) contribute yellow, red, blue, and colorless pigments.
- Enzymes like phenolase cause browning; papain and bromelain can tenderize meat.
Classification and Composition of Fruits
- Fruit is formed from the ovary and consumed as a dessert.
- Fruit organs: skin (epidermis), basic tissue (parenchyma, collenchyma, sclerenchyma), and transport tissue (xylem, phloem).
- Fruits are climacteric (e.g., mango, banana—continue ripening) or non-climacteric (e.g., orange, grape—do not ripen after harvest).
- Main components: carbohydrates (sugar, starch, pectin), protein (<1%), fat (<1%), vitamins A, B, C, calcium, and iron.
Pigments, Enzymes, and Organic Acids in Fruits
- Fruit pigments: chlorophyll (green), carotenoids (orange, yellow, red), flavonoids (purple, white, astringent).
- Main organic acids: citric (orange), malic (apple), tartaric (grape).
- Enzymes such as catecholase and polyphenolase cause browning.
Post-Harvest Handling and Preservation
- Storage: lower oxygen levels (2–3%) slow metabolism and delay ripening.
- Cooling (5–8°C) inhibits respiration; some fruits (banana, avocado) are cold-sensitive.
- Wax coating retains moisture, slows respiration, and increases shine.
- Preservation methods: drying, adding sugar (jam), acidification, and fermentation (kimchi, pickles).
Key Terms & Definitions
- Turgor — The pressure of cell contents against cell walls, affecting texture.
- Climacteric fruit — Fruits that ripen after harvest with increased respiration (e.g., banana).
- Non-climacteric fruit — Fruits that do not ripen further after harvest (e.g., orange).
- Chlorophyll — Green pigment in plant leaves.
- Carotenoids — Group of pigments giving yellow, orange, and red colors.
- Flavonoids — Pigments responsible for various colors (yellow, red, blue, purple).
- Phenolase — Enzyme that causes browning in fruits and vegetables.
Action Items / Next Steps
- Review and memorize vegetable and fruit classifications and selection criteria.
- Study nutritional value tables for common vegetables and fruits.
- Read about post-harvest handling and preservation methods.