HEAT TREATMENT: A PROCESS TO CONTROL THE DEVELOPMENT OF THE HARD-TO-COOK PHENOMENON IN BLACK BEANS (Phaseolus vulgaris)

Whole black beans were heat treated for 2, 5 and 10 mm at 121°C and 10, 20 and 30 mm under steam (98°C). Heat treatments did not affect the physical appearance of the grams but significantly (P < 0.05) decreased the development of the hard-to-cook phenomenon in seeds stored at 25°C and 70% RH for 9 months. After 9 months of storage no significant difference (P < 0.05) was found between hardness of cooked beans subjected to the shortest heat treatments and control samples kept at 4°C. Nitrogen solubility in 0.01N NaOH increased significantly (P < 0.05) in all samples as well as solubility in 5% KCl except in samples subjected to the longer heat treatments. Water absorption of the beans was favored by the heat treatments evaluated A high correlation (r = 0.91) was found between the cooked beans hardness value and the lignified protein content of the cotyledon.