Insoluble dietary fibre components of food legumes as affected by soaking and cooking processes

Effects of soaking and cooking methods were studied on neutral detergent fibre (NDF), acid detergent fibre (ADF), cellulose, hemicellulose and lignin contents of five food legumes. Black grams, chickpeas, lentils, and red and white kidney beans were soaked in tap water and sodium bicarbonate solution (1% w/v). Slight but significant increases in ADF (0.85-4.57%) and cellulose (344-6.59%) were observed on soaking food legumes in tap water. Soaking in sodium bicarbonate solution led to appreciable increase of hemicellulose (44.43-58.86%) and cellulose (5.67-12.5%) but lignin contents remained unchanged. The insoluble dietary fibre components were reduced to various contents on cooking water-presoaked legumes, by three different methods. However, pressure cooking showed a more pronounced effect on the reduction of these insoluble dietary fibre components than ordinary and microwave cooking methods. Pressure cooking caused reduction in NDF (28.5-35.3%), ADF (11.6-21.8%), cellulose (17.0-35.8 and hemicellulose (37.5-42.4%) whereas increase in lignin content (15.2-27.8%) was observed. Reduction in hemicellulose content was distinctly more than cellulose content as a result of cooking the food legumes by these three cooking methods. (C) 2003 Published by Elsevier Ltd.