Domestic processing effects on some insoluble dietary fibre components of various food legumes

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 (3.44–6.59%) were observed on soaking food legumes in tap water. Soaking in sodium bicarbonate solution led to an appreciable increase of hemicellulose (44.4–58.9%) and cellulose (5.67–12.5%) but lignin contents remained unchanged. The dietary fibre components were variously reduced up on cooking the water-presoaked legumes by three different methods. However, pressure cooking showed a more pronounced effect on the reduction of these dietary fibre components than ordinary or microwave cooking methods. Pressure cooking caused reductions in NDF (28.5–35.3%), ADF (11.6–23.9%), cellulose (17.0–35.8%) and hemicellulose (37.6–42.4%) whereas increase in lignin content (15.2–27.8%) was observed. Reduction in hemicellulose was distinctly greater than that of cellulose content as a result of cooking the food legumes by these three cooking methods.