Influence of variety, growth location and storage conditions on development of hard-to-cook defect in common bean ( Phaseolus vulgaris L).

Abstract

Storage of beans, especially at temperature higher than 25 degrees C and relative humidity greater than 65%, lead to development of the hard-to-cook (HTC) defect, which leads to increased cooking time, fuel and water use. This has a negative effect on the acceptability and utilization of beans. This study investigated the influence of bean cultivar, moisture content, growth location and storage containers on the development of HTC defect. Freshly harvested (within one month of storage) beans of cultivars K131, K132, NABE4 and NABE 11 were first assessed for susceptibility to the HTC defect and then evaluated for chemical changes associated with differences in moisture content and storage conditions. Bean samples were obtained from farmers at initial moisture content of about 15%. Some of the beans were dried to moisture content of 12 and 9%. Samples at 15, 12 and 9% were stored in plastic buckets, earthenware, polypropylene and sisal bags at ambient temperature (22-28 degrees C). Samples were drawn at monthly intervals and analysed for cooking time, lignin, acid detergent fibre, calcium and magnesium content. Extent of HTC defect was found to be in the order K131> K132> NABE11> NABE4. Higher the moisture content resulted in greater extent of HTC development. HTC was found to be associated with increase in lignin content (r2=0.72). A significant increase in acid detergent fibre (ADF) was observed in samples stored in all the 4 storage containers. The increase was highest for beans stored in polypropylene bags and plastic buckets, while beans stored in the sisal bags and earthenware had the least increase. Storage in sisal bags (25 degrees C, RH 74%), which allowed equilibration of the temperature and relative humidity with that of the environment, controlled HTC defect development more than other methods, i.e. pot (22 degrees C, RH 93%) polypropylene bags (25.8 degrees C, RH 80%) and plastic bucket (27.9 degrees C, RH 84%). Based on the results of this study, drying beans to lower moisture content and prevention of heat build up during storage are recommended as strategies to control HTC development.