Effect of cooking methods on available and unavailable carbohydrates of some tropical grain legumes

The available and unavailable carbohydrate contents of eleven tropical legumes from different seed lines were investigated in raw, cooked and autoclaved forms. Raw legumes contained small amounts of glucose and fructose which ranged from 0.05 to 0.22 g/100 g and 0.24 to 0.90 g/100 g, respectively, sucrose varied between 1.49 g/100 g and 3.76 g/100 g. Reducing sugars were higher in bambara groundnut than other legumes. Starch was the principal carbohydrate, ranging from 35.4 to 50.0 g/100 g. African yam beans, lima beans and kidney beans had fairly high levels of oligosaccharides ( raffinose + stachyose) than bambara groundnuts. Non-cellulosic polysaccharides and cellulose contents were highest in jack bean followed by pigeon pea TUc5537-1 and least in bambara groundnut KAB-3. Lignin was low and fairly uniform in all the legumes. The available carbohydrates were reduced to various extents by cooking, whereas the unavailable carbohydrates were not affected appreciably by heat treatment.