December 20, 2017 belezza 0Comment

More About Vegetables


More About Vegetables

  • Are plants or parts of plants used as food.
  • Supply many nutrients & variety to the diet
  • Make food attractive by their colour, texture and flavour

Indian Context

  • Intake of vegetables has been too low in daily diet
  • Expensive, need more preparation time or due to ignorance of their importance
  • Unavailability in a particular place/season results in less consumption
  • As they are perishable, the consumption would be limited if storage facilities are not available.

Composition and Nutritive Value

  • Protective Foods as they are rich in minerals and vitamins
  • Nutritionally they are classified into 3 groups:

-Green leafy vegetables

-Roots and Tubers

-Other vegetables

Green leafy vegetables

  • Low in carbohydrates and energy
  • Good sources of beta carotene, calcium, riboflavin, folic acid, ascorbic acid and iron.
  • Exception-Drumstick leaves as has high content of protein.
  • Beet greens are excellent sources of iron and riboflavin.
  • Dark green leafy vegetables have more carotenes than light ones e.g outer layers of cabbage gives more carotene than the inner leaves.

Roots and Tubers

  • Give more calories compared to GLV as they contain more starches.
  • Carrots contain high amount of carotene though this amount is lower when compared to the content present in green leafy vegetables.

Roots and Tubers

  • Roots and Tubers are fairly good source of vitamin C
  • Poor source of calcium, iron, B vitamins and proteins.

Other Vegetables

  • High amount of moisture
  • Highly perishable.
  • Good source of vitamin C and rich in fiber content e.g capsicum, bitter gourd

Pigments and effect of cooking

  • Appealing bright colours of many vegetables are result of the various pigments contained in their tissues.
  • Chief pigments present in vegetables and fruits are:
  1. i) Water insoluble pigments e.g. chlorophyll, carotenoids
  2. ii) Water soluble pigments e.g. anthocyanins, anthoxanthins

Water insoluble or fat soluble pigments

Chlorophyll

  • Green pigments of leaves and stems – close to the cell wall in small bodies called chloroplasts.
  • Insoluble in water & dominant in unripe fruits.
  • Other pigments present are masked by it.
  • Green leafy vegetables, capsicum, beans, peas and chillies.
  • Two types of chlorophyll are there
  • a) Chlorophyll-a
  • b) Chlorophyll-b

Vegetables

Cooking

  • Green vegetables in acid retain a percentage of chlorophyll when they are cooked than do   acid vegetables.
  • To minimize the effect of acids, they should be cooked in an uncovered pan to eliminate volatile acids in the first few minutes
  • Use enough water to cover the vegetables to dilute those acids which are not volatile.

Carotenoids

  • Are groups of yellow, orange, red, fat soluble pigments.
  • Alpha-carotene, beta–carotene, gamma–carotene.
  • Beta carotene is synthesized to Vitamin A.
  • Ordinary cooking conditions have little effect on the colour or the nutritive value of carotenoid.

Water soluble pigments

  • Flavonoids are classified into anthocyanins and anthoxanthins.
  • Anthocyanins are highly water soluble pigments that range in color from red to purple.
  • The anthoxanthins are colourless or white.

Anthocyanins

  • Their solubility in water makes them disperse freely.
  • Cherries, red apples, various berries, blue and red grapes, pomegranates, currants, skin of radishes and sweet potato, red cabbage achieve their colour appeal because of predominance of anthocyanins.
  • On the addition of alkali, anthocyanins turn blue

Cooking

  • Cooking in a steamer or in a pressure pan which limits the contact of the vegetable with water are better methods than boiling in water.
  • Pickles are usually low in pH and anthocyanins change to deep crimson red.

Anthoxanthins

  • Colourless or pale yellow pigments.
  • They are so widely distributed that it is exceptional to find a plant in which anthoxanthins are not present.
  • Give colour to cauliflower, onions, and spinach or other leafy vegetables.
  • In green leafy vegetables the colour is masked by chlorophyll.
  • The colour of the vegetable will be whiter if little acid such as lime juice or vinegar is added during cooking.
  • If the water in which cauliflower is cooked is slightly alkaline, it will have a distinctly yellow colour to
  • They turn yellow or orange in the presence of alkali.
  • On the addition of alkali, the anthoxanthins turn yellow while anthocyanins turn blue and the mixture of the two appears green in colour, as seen in red cabbage.
  • Hence, red cabbage is frequently cooked with the addition of some slices of tart apple to ensure that the pH is sufficiently acidic to avoid the development of a blue, highly unpalatable pigment colour.

Selection

Desirable characteristics

  • Beans: tender, fresh, crisp, clean, firm velvety to touch, seeds should be less than half grown, should break easily with a sharp sound.
  • Cabbage: fresh , should be compact , no insect holes ,no yellow or withered leaves
  • Carrots : firm, fresh, smooth, yellow orange in colour, there should not be any wilted, soft or flabby portion
  • Cauliflower: compact, no insects , fine heads, tender green leaves , should not be rough, flowers should not be spread out or yellow as they indicate maturity.
  • Brinjal: firm ,bright, uniform dark rich purple or green colour, free of scars or decay, should not be wilted, flabby or soft, no insect holes
  • Ladies finger: young, tender, fresh tips should be broken easily, should not have any holes which indicates infestation, should not be hard while cutting
  • Greens : tender, fresh bright green ,no holes in leaves, no withered leaves, not with too much of water, no soft portion of leaves
  • Tomatoes : bright red in colour, firm, should not be soft, plump body with uniform red colour, no hole, no black, no over ripened areas, no cracks

Changes during cooking

  • Vegetables are cooked to

-improve colour, flavour, texture

-improve digestibility

-add variety to diet

  • Cooking of vegetables brings about various changes.
  • Water may be

-Absorbed if the vegetables are cooked in water

-Water gets removed during baking.

-Excess water absorption produces sogginess in the cooked vegetables.

  • Cellulose and hemi cellulose are softened by cooking. These changes make vegetables easier to chew.

Losses of nutrients during cooking

Some losses occurs during cooking  as the food gets exposed to different  conditions

  • Mechanical losses

During pre- preparation activities like peeling, the vitamins under the skin may be lost.

Throwing outer leaves of cabbage can result in loss of carotene as greener leaves contain higher amount of

carotene.

  • Action of water

Water soluble nutrients like

  • thiamine,
  • riboflavin,
  • niacin,
  • pyridoxine,
  • pantothenic acid,
  • folic acid,
  • ascorbic acid

may be dissolved during cooking and nutrients may be lost.

Methods to reduce losses

  1. Cut the vegetables into bigger pieces so  that the exposure of the vitamins to water is less. e.g. when carrots are cut crosswise, the loss of ascorbic acid is greater than that when they are cut lengthwise.
  2.  Soaking or washing time should be reduced. So that enough time is not given  for the water soluble nutrients to get dissolved in water.
  3. Wash the vegetables with skin and then peel or cut.
  4. Use as small quantity of water as possible so that there is no extra water e.g steaming and pressure cooking.
  5. Cook for a short time. As period of cooking increases more and more of ascorbic acid leaches into the water.
  6. Cover the vessel with a lid to hasten the cooking process.
  7. Cook the vegetables with the skin so that leaching of vitamins into water would be less.
  8. Leached water can be used in cooking.
  9. Oxidation and chemical decomposition
  10. Loss of nutrients can occur by chemical decomposition which may be caused by the reaction of the cooking water or by heat.
  11. Vitamin C is readily oxidisable and is lost readily.
  12. Vitamin A gets oxidized by dehydration or application of dry heat.
  13. Riboflavin is sensitive to light. Foods which are exposed to sunlight before cooking cause riboflavin loss.
  14. Minerals are not easily destroyed by cooking.
  15. Addition of baking soda
  16. Sometimes baking soda is added to Vegetables to improve the colour or to hasten cooking process.This creates alkaline medium in which losses of vitamins like ascorbic acid, thiamine, folic acid may be more.

The three R’s of cooking to conserve nutrients are:

  • Reduce the amount of water used
  • Reduce the length of cooking period
  • Reduce the amount of surface area exposed

Storage of vegetables

  • Most green vegetables may be kept fresh and crisp in covered containers or plastic bags in the refrigerator.
  • If they are washed before storing they should be drained thoroughly because too much moisture can increase the possibility of a spoilage and decay.
  • Seeds such as peas can remain fresh longer if left in the pods.
  • Tubers and bulbs can be stored in a cool place without refrigeration

 

 

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