Food Structure


The common bean (Phaseolus vulgaris) requires cooking for extended periods of time prior to consumption. In this investigation both quantitative and microstructural changes in common bean dietary fiber as a result of cooking were examined. Cooking resulted in a slight decrease in soluble dietary fiber and a marked increase in insoluble dietary fiber. The increase in insoluble dietary fiber was responsible for a 15 -30 percent increase in total dietary fiber.

Scanning electron microscopy was used to examine the microstructure of uncooked and cooked bean flours and the insoluble and soluble dietary fiber fractions of these two fl ours. In uncooked whole bean flour large (10 -30 um) spherical starch granules and small (1 -5 um) protein bodies characteristic of the common bean were observed. However, after cooking, only amorphous material containing gelatinized starch and denatured proteins was visible.

Few microstructural differences were observed between uncooked and cooked insoluble dietary fiber fractions. Doth fractions consisted primarily of cell wall remnants from which starch and protein storage bodies had been removed. Also present in both insoluble fiber fractions were partially digested fragments of the seed coat palisade cell layer, and long, thin fibers which appear to be remnants of the nutrient transporting phloem. The cooked and uncooked soluble dietary fiber fractions were microstructurally similar consisting of thin, irregularly shaped sheets and long, thin rods.

Included in

Food Science Commons