Histochemical and ultrastructural characterization of easy-to-cook and hard-to-cook carioca bean genotypes

Carioca beans (Phaseolus vulgaris L.) stored under high temperature and humidity are subjected to the hard-to-cook phenomenon (HTC), which result in loss of technological and sensory quality. Cotyledon cells of easy-to-cook (ETC) and HTC bean were examined by histochemical and transmission electron microscopy methods to identify structural differences resulting from the hardening phenomenon. Results showed that during bean hardening there is a disruption of primary and secondary walls, as well as disintegration of the plasmatic membrane. The level of cell wall damage depends on the genotype studied, with that more susceptible to the HTC (BRS-Pontal and Pérola) presenting more intense structural changes than that less susceptible to the HTC (BRSMG-Madrepérola). The involvement of starch or protein in the hardening phenomenon of bean genotypes was not identified. These results confirm the involvement of cell wall-middle lamella in the hardening phenomenon of carioca bean.