Reducing tannins in Black gram

Legumes are an important source of protein in the diets. The presence of tannins, saponins, phytic acid and other antinutritional substances hinder their utilization in the human body. Tannins affect the availabilityof amino acids, utilization of protein and inhibit the activities of digestive enzymes. Soaking of legumes before cooking is a common practice to soften texture and hasten the cooking process. Soaking in salt solution results in a considerable reduction in cooking time and improvement in protein quality. Black gram, Vigna mungo (Linn.) Hepper, HindiUrd is an important food legume. It contains 24% dietary protein but it is necessary to reduce tannins before use in order to increase their protein digestibility.Sodium chloride and sodium bicarbonate are the salts usually used in traditional soaking process or before cooking. Rehman and Shah from Pakistan studied the effects of varietal differences, and soaking and cooking methods on the tannin contents and protein digestibilityof black grams. Sodium bicarbonate soaking extracted about 2.5 times more tannins compared to tap water. Soaking temperature and time also played a significant role in the extraction of tannins. At 100°C, less time was required for the extraction of tannins than at 30°C. Soaking in water and salt solution also improved the protein digestibility. Significant reduction in tannins and improvement in protein digestibilityof black grams was also observed after cooking the soaked black grams [Rehman & Shah, Plant Food Hum Nutr, 2001,56(3),265-273].