Effect of processing on blood glucose and insulin responses to starch in legumes

Postprandial glycemic and insulinemic responses to variously processed red kidney beans were evaluated in normal subjects. The dried seeds were (a) boiled; (b) autoclaved; (c) boiled, freeze-dried, and milled to obtain a precooked flour (PCF) rich in cell-enclosed starch; or (d) milled, steam-cooked, and freezedried to yield a flour containing free starch (FSF). All bean products elicited lower metabolic responses than white wheat bread, used as a reference. Judged from the glycemic and insulinemic indices and the postprandial peak concentrations, autoclaved beans, PCF, and FSF had a more “rapid” behavior than the boiled seeds. Responses to autoclaved beans and PCF were intermediate between boiled beans and the FSF. The insulinemic indices of a lentil PCF and white bread were similar, indicating that different legumes may have different susceptibilities to processing. It is concluded that both the cellular and the cotyledon tissue structures are important determinants of the metabolic responses to legumes.