Food Science and Processing

FOOD SCIENCE AND PROCESSING 3 (2+1)

Lesson 15 : Vegetables- Processing and Preparation

Changes during cooking

Vegetables are cooked to improve the colour, flavor and texture by which overall palatability is improved. Digestibility is also improved. The fibre becomes softened, starch gets gelatinized and protein gets coagulated. Cooking destroys microorganisms.

Water content

1. Water may be absorbed if the vegetable is cooked submerged in water or steam.
2. Removal of water occurs during baking.
3. Excess water absorption tends to produce sogginess in the cooked vegetable.
4. The bulk of the leafy vegetables is greatly decreased as they wilt during cooking.

Cellulose and peptic substances

1. Cellulose and hemicelluloses are softened by cooking.
2. The pectic substances undergo some chemical changes. Pectic substances make it easier to chew and cut cooked vegetables.
3. Sodium bicarbonate added to the cooking water disintegrates the hemicelluloses and cellulose and produces a soft texture in a short cooking period. Potatoes should be boiled or fried before adding to tomatoes or acidic medium.
4. Calcium chloride or saturated solution of calcium hydroxide has the effect of making the vegetable tissues more firm forming insoluble calcium salts with pectic substances. Calcium chloride is used to prevent softening of canned tomatoes.

Other carbohydrates:
1. Gelatinisation of starch takes place during boiling e.g., potatoes get gelatinized during boiling.
2. Dextrinisation of starch takes place when potatoes are fried.
3. Hydrolysis of starch occurs and they are converted to simple sugars.
4. Caramelisation of sugar occurs when vegetables get scorched or burnt e.g., onions.

Protein

Protein gets coagulated completely or partly during cooking.