Milling or decortications: Legumes are generally milled to remove the outer husk by wet or dry process. The dal obtained by the dry method is hemispherical in shape, softens rapidly on cooking and gives good flavour. Dal prepared by wet method is usally flat,has a small depression in the center due to shrinkage and softens slowly during cooking. Legumes are consumed as a whole or dehusked ones.
Milling yield can be increased by lower seed coat percentages, regular shaped grain variety, having loose-husked varieties and heating seeds before dehulling. Normally the percentage of yield is 82 per cent during milling. Advantages:
Protein digestibility is improved. Net protein utilisation of dal is higher than those of whole seeds.
Removal of hull facilitates a reduction of fiber. Nutrients availability is increased.
Seed coats account for 80-90 per cent of the total seed polyphenols. Dehusking removes this antinutritional factor.
This improves appearance, texture, cooking quality and palatability.
Keeping quality is improved.
In dehusking , germ may be removed with skin and may result in loss of thiamine.
Soaking: Many pulses particularly whole grams which have hard outer covering need soaking prior to cooking. During soaking, water enters through the hilum or scar where the bean is attached to pod. From there, it seeps around the periphery of the bean and causes the seed coat to wrinkle. Whole pulses are soaked in cold water overnight or in warm water (60-70oC) for 4-5 hours. Soaking makes the pulse tender and hastens the process. It also reduces phytic acid and oligosaccharides.
Soaking in salt solution is preferred to loosen the seed coat and enhance water absorption. Addition of soda to water reduces cooking time significantly by about one-third. This saving in cooking time is compensated for the amount of thiamine lost as a result of the alkaline environment.
Germination: Whole grams are soaked overnight and should be drained away and seeds should be tied in a loosely woven cotton cloth and hung. Water should be sprinkled twice or thrice day. In a day or two germination takes place. Moisture and warmth are essential for germination.
During sprouting, dormant enzymes get activated and digestibility and availability of nutrients is improved. Starched and proteins are converted to simpler substances as germination proceeds, the ratio of essential amino acids changes providing more of essential amino acids, Sprouting reduces trypsin inhibiting factors due to the release of enzymes. Germinated seeds have more of maltose. The action of cytases and pectinases are releases during sprouting and the cell walls are broken down and the availability of nutrients increase.
During sprouting minerals like calcium, zinc and iron are released from bound form. Phytic acid amount is reduced so the availability of proteins and minerals are increased.
Riboflavin, niacin, folic acid, choline and biotin content are increased.
Vitamin C is synthesised during germination hence germinated pulses can be substituted for fruits. The increase in vitamin C is around 7-20 mg per 100 g of pulses. Vitamin C content is maximal after about 30 hrs of germination.
Sprouting decreases cooking time. The thick outer coat bursts open the grain and the grain becomes soft making it easier for the cooking water to penetrate the grain.
Dehusking is easier when the grains are sprouted and dried.
Germination decreases the mucus inducing property of legumes.
Thickening power of starch is reduced due to conversion of starch to sugars.
Germination metabolises oligosaccharides and hence do not produce gas or flatulence.
Germination improves taste and texture and without much cooking also sprouts like green gram can be consumed.
Germinated pulses add variety to diet.
Fermentation: This process increases the digestibility, since the microbial enzymes break down the legume protein and enhances cooking process. It also improves palatability and nutritive value (B and C vitamins). Toxic substances of pulses can be eliminated by fermentation. In idli making, fermentation process improves the availability of essential amino acids and thus nutritional quality of protein is improved. Idli and dosa are examples of fermented foods.
Parching and puffing: Legumes such as Bengal gram and peas are parched to give highly-acceptable products. The traditional Indian household practice for roasting or parching pulses involves initially sprinkling the grains with a little water. Then the pulse is mixed with the pre-heated sand in a frying pan kept on an open fire and maintained at a temperature ranging from 200 to 250o C depending on the pulse species for 2-3 minutes.
Puffed pulse grains are prepared in the country in a manner similar to that used for roasting. For puffing, seeds are soaked in water, mixed with sand that has been heated to 250o C and then heated for short time. The more common legumes prepared in this manner are thick peas and field peas. Parched Bengal gram has been used successfully in the treatment of protein calorie malnutrition in children.