HARD-TO-COOK DEFECT IN BLACK BEANS - HARDENING RATES, WATER IMBIBITION AND MULTIPLE MECHANISM HYPOTHESIS

The existence of a slower initial hardening period during storage of dry black beans, independent of cooking time and heat pretreatment, was corroborated. Water vapor production during storage for 1 year at 25 and 35-degrees-C did not change appreciably the moisture in dry beans stored at 10 and 12% moisture content. Further support to the hypothesis that water in soaked hard beans is held differently from that in soft beans was based on differences in the rate of drying and microstructural evidence. A dual contribution to the hardening mechanism, one reversible and another irreversible, was postulated based on soaking experiments with monovalent salts and chelating agents. Cell separation was not changed by salt treatment although the cell wall morphology was modified.