Enzymic Availability of Starch in Cooked Black Beans (Phaseolus vulgaris L) and Cowpeas (Vigna sp.)

The starch content of black beans and cowpeas was assessed enzymatically in freshly cooked as well as in cooked, stored, and reheated samples. The available starch contents of the variously treated seeds were greater in cowpeas (32-33%, dmb) than in black beans (25-28%, dmb). All samples exhibited relatively high levels of retrograded resistant starch (RS) (8-20%, total starch basis), although beans showed higher contents of this fraction. No major difference in RS formation was observed between conventional and microwave reheating. Total starch was slightly decreased in stored/reheated black beans compared to that in the freshly cooked seeds. In vitro enzymic hydrolysis indices (HI) and corresponding predicted glycemic indices (pGI) of cowpea samples were 2-fold greater than those registered for beans. Reheating, and particularly microwaving, increased the amylolysis course parameters of black beans without altering the enzymic availability of cowpea starch.