Importance of physical form rather than viscosity in determining the rate of starch hydrolysis in legumes

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Abstract
These studies were designed to determine whether the slow rate of carbohydrate absorption after oral ingestion of legumes is due to the viscosity of leguminous fibers or rather to the physical inaccessability of the carbohydrate to the intestinal hydrolytic enzymes. Using lentils as an example of a legume known to be slowly absorbed in vivo, we examined factors that could potentially modulate the rate of formation of glucose from the starch in lentils in vitro. The slow rate of hydrolysis of lentil starch does not appear to be due to increased viscosity (or the presence of gelling fibers) since 1) the rate of release of free glucose from a dialysis sac into the dialysate was not affected by the presence of lentils, and 2) the rate of hydrolysis of lentil starch was not affected by increasing the shaking rate of the incubation vessel from 0 to 150 oscillations per minute. In contrast, the physical form of lentils appeared to be critical in determining the rate of starch hydrolysis. Grinding the lentils before cooking increased the starch hydrolysis rate 5-fold, while blending them after cooking gave an intermediate rate.