Dietary fibre and fermentability characteristics of root crops and legumes

Abstract

The dietary fibre and fermentability characteristics of local root crops and legumes were determined. Total, soluble and insoluble fibre were determined in six root crops (kamote, gabi, potato, tugi, ube, cassava) and ten legumes (mungbean, soyabean, peanut, pole sitao, cowpea, chickpea, green pea, lima bean, kidney bean and pigeon pea) using Association of Official Analytical Chemists methods. The dietary fibre from test foods was isolated and fermented in vitro using human faecal inoculum simulating conditions in the human colon. The SCFA, e.g. acetate, propionate, butyrate, produced after fibre fermentation was measured using HPLC. The dietary fibre content of root crops ranged from 4.6 to 13.5 g/100 g while legumes ranged from 20.9 to 46.9 g/100 g, suggesting that root crops and legumes are good sources of dietary fibre. Significant amounts of SCFA were produced after in vitro fermentation of the fibre isolate of both root crops and legumes. The best sources (as mmol/g fibre isolate) of acetate among the legumes were pole sitao (5.6 (SEM 0.5)) and mungbean (5.3 (SEM 0.1)) and among the root crops, tugi (2.5 (SEM 0.4)) and cassava (2.4 (SEM 0.1)); of propionate, kidney bean (7.2 (SEM 1.5)) and pigeon pea (3.3 (SEM 0.2)) for legumes, and tugi (1.8 (SEM 0.2)) for root crops; and of butyrate, peanut (6.0 (SEM 0.2)) and cowpea (5.4 (SEM 0.2)) for legumes, and tugi (0.8 (SEM 0.0)) and cassava (0.8 (SEM 0.0)) for root crops. In conclusion, root crops and legumes are good sources of dietary fibre and produced SCFA after fibre fermentation, such as acetate, propionate and butyrate. SCFA production after in vitro fermentation can be estimated using human faecal inoculum and can be used to model the human colon.