PHYSICOCHEMICAL STUDIES OF HARD-TO-COOK BEANS (PHASEOLUS-VULGARIS)

Model aqueous systems were used for the study of the cooking quality o f beans (Phaseolus vulgaris). These systems were created using graded contents of calcium and magnesium ions, in a ratio of 4:1, to prepare aqueous media with cation content corresponding to 0-400 mg litre(-1) of calcium carbonate. The model systems were used to measure the quali ty of boiled beans in water of low and high divalent cation content. A boiling time of 60 min was used and the hardness of the boiling beans was measured by an Instron Universal Testing Machine. Cooking of bean s in water of low divalent cation content equivalent to 0-50 mg litre( -1) CaCO3 resulted in well-boiled beans for both types (easy-to-cook a nd hard-to-cook) of beans. Boiling in water of high divalent cation co ntent led to the formation of very hard beans for both types of bean, while boiling in water of moderate divalent cation content (normal dri nking water: 150-250 mg litre(-1) CaCO3) differentiated between the tw o categories of beans. These results were further tested by adsorption experiments with divalent cations, on beans boiled (a) in different p roportions of boiling water, and (b) in model aqueous systems. The div alent cation content of boiling water and the phytic acid content of t he beans proved to be the crucial factors in the hard-to-cook phenomen on of beans.