STARCH ALTERATIONS IN HARD-TO-COOK BEANS (PHASEOLUS-VULGARIS)

Dry common bean seeds (Phaseolus vulgaris cv. Carioca) were stored und er conditions favorable for the development of hardness in order to in vestigate possible alterations in the starch component due to the hard -to-cook (HTC) phenomenon. Examination of isolated starch granules or seed fractures observed under scanning electron microscopy revealed th at hard beans were more resistant to amyloglucosidase attack. Under po larized light microscopy, starch granules of HTC beans appeared more b irefringent than those of the control beans. Differential scanning cal orimeter thermograms showed an increase of the temperature of gelatini zation of starch isolated from HTC-and-old beans (5 years of storage), whereas starch isolated from control (soft) bean seeds and HTC seeds stored for a short period of time (2 months) showed no such increase.