India is the second largest producer of vegetables (59 million tonnes i.e.12.94% of the world production of 456 million tonnes) and fruits (27.3 million tonnes i.e. 7.37% of the world production). Vegetables are susceptible to the action of a variety of microorganisms, which leads to substantial decay, losses during post harvest handling. 
Vegetables and fruits have a limited shelf life and hence it warrants great scope for processing.

Vegetables can be classified into three groups according to their nutritive value.

i. Green Leafy Vegetables

They are an inexpensive rich source of many nutrients such as – carotene, ascorbic acid, folic acid, calcium, iron and fibre. They are a poor source of protein.

ii. Roots and Tubers

Roots and tubers are rich in carbohydrates and are a source of energy in the diet. Carrot and yellow varieties of yam are rich in carotene and potato contains Vitamin C. Tapioca and yam are rich in calcium. Roots and tubers are a poor source of iron, protein and a fair source of B – Vitamins.

iii. Other Vegetables

These are a good source of dietary fibre and add variety to the diet. They are a fairly good source of vitamins and minerals. (Eg.) brinjal, ladies finger, cauliflower, cucumber, gourd varieties.

Cleaning

Thorough washing in water is essential. If vegetables are consumed raw extra care is needed in cleaning them. Cauliflower flowerets are washed with hot salt water to remove the insects. Greens are put in a large basin of water. The impurities like dirt and sand settle to the bottom and leaves are lifted from the top. Vegetables can be washed under running tap water.

Peeling

Roots and tubers are peeled before cooking. It is better to remove the skin after cooking because the nutrients would seep inside during the process of cooking. Skin can be removed easily. Loss of colour can be prevented and sweetness of the carrots is better retained if the skin is removed after blanching.

Blanching

This is done to destroy microorganisms, denature enzymes, to remove the skin easily and to improve the colour. Apart from these preliminary preparations, cutting, grating, grinding and stringing are also done before cooking.

Effect of pickling

Pickles are usually low in pH and anthocyanins change to deep crimson red in colour.

Changes during cooking

Vegetables are cooked to improve the colour, flavour and texture by which over all palatability is improved. Digestibility is also improved. The fibre becomes softened, starch gets gelatinised and protein gets coagulated. Cooking vegetables adds variety to the diet. Cooking destroys microorganisms.

Effect of method of cooking

Anthocyanins are water soluble cell sap pigments, which can be leached from a vegetable by the cooking water. Cooking in a steamer or in a pressure pan which limit the contact of the vegetable with water are better methods than boiling in water. To retain the red colour in red cabbage, the cooking water should be acidified. Otherwise the pigment will change to a dull and unappetising blue.

Storage of vegetables

Most fresh vegetables retain their top quality for only a few days. All green vegetables of high water content are best when fresh. If allowed to stand long after gathering the vegetables becomes wilted and tough through loss of moisture. The flavour is also impaired because of enzyme action and the conversion of sugar to starch. Mature vegetables particularly roots and tubers and bulbs deteriorate less in storage than do fresh immature vegetables. One reason for the short storage life of many vegetables is that they are rapidly respiring.

Most fresh green vegetable 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 can peas can remain fresh longer it left in the pots. Tubers and bulbs can be stored in a cool place without refrigeration. Many vegetables, especially the leafy ones, spoil quickly after harvest. CFTRI, Mysore has developed technology to keep them fresh for extended periods.

Factors affecting storage life

Loss of water

Transpirational loss of water is one of the main process that affect the commercial and physiological deterioration of vegetables after harvest. The moisture loss adversely affects the appearance, texture, flavour and weight of the products. Most noticeable effect of moisture is the softening of the tissues caused by loss of turgidity.

Respiration and metabolism

Vegetables are living commodities and continue to respire even after harvest. Respiration uses the stored food, leading to its depletion and consequently the loss of quality. Hence, storage life of vegetables is influenced by rate of respiration and is associated with biochemical activity.

Role of vegetables in cookery

Vegetables are used universally in all recipes.
They are used in curries salads and in sambar.
They are used as garnishing agents e.g. shredded carrot and coriander leaves.
They are used as stuffing in samosa and parathas.
They are used as thickening agents in gravies and soups.
They are used as in of chutneys (onion) and pickles (tomato, onion).
As part of recipes like pulao, aluvadi and in nonvegetarian dishes.

DEHYDRATION OF VEGETABLES

Dehydration means the process of removal of moisture by the application of artificial heat under controlled conditions of temperature, humidity and air low. In this process a single layer of fruits or vegetables, whole or cut into pieces or slices are spread on trays which are placed inside the dehydrator. The initial temperature of the dehydrator is usually 43°C which is gradually increased to 60-66°C in the case of vegetables and 66-71°C for fruits.

Shade drying

Shade drying is carried out for products which can lose their colour and / or turn brown if put in direct sunlight. Therefore, shade drying is carried out under a roof or thatch which has open sides.

Osmotic dehydration

In osmotic dehydration the prepared fresh material is soaked in a heavy sugar solution and / or a strong salt solution and then the material is sun or solar dried.

Blanching : Exposing vegetable to hot or boiling water as a pre-treatment before drying has the following advantages :
*    It helps clean the material and reduce the amount of microorganisms present on the surface;
*    It preserves the natural colour in the dried products; for example, the carotenoid (orange and yellow) pigments dissolve in small intracellular oil drops during blanching and in this way they are protected from oxidative breakdown during drying;
*    It shortens the soaking and/or cooking time during reconstitution.
During hot water blanching, some soluble constituents are leached out; water-soluble flavours; vitamins (vitamin C) and sugars.

Rehydration ratio

If the weight of the dehydrated sample (a) used for the test is 5 g and the drained weight of the rehydrated sample (b) 30g, then

The preservation of food in common salt or in vinegar is known as pickling. Pickling is the result of fermentation by lactic acid-forming bacteria, which are generally present in large numbers on the surface of fresh vegetables.