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

Storage of beans, especially at temperatures higher than 25ºC, and relative humidity greater than 65%, lead to development of the hard-to-cook (HTC) defect which results in increased cooking time, fuel and water use. This has a negative effect on acceptability and utilization of beans. This study was aimed at investigating the influence of bean variety, moisture content, growth location and storage containers on the development of HTC defect. Freshly harvested (within one month of storage) beans of varieties K131, K132, NABE4 and NABE 11 collected from farmers were first assessed for susceptibility to the HTC defect and then chemical changes associated with differences in moisture content and storage conditions were determined. 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 oC). Samples were drawn at monthly intervals and analyzed for cooking time, lignin, acid detergent fiber, calcium and magnesium content. Extent of HTC defect was found to be in the order K131> K132> NABE11> NABE4. The higher the moisture content the greater the 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 (25ºC, RH 74%) which allowed equilibration of the temperature and relative humidity with that of the environment controlled HTC defect development more than other methods; pot (22ºC, RH 93%) polypropylene bags (25.8ºC, RH 80%) and plastic bucket (27.9ºC, 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. Keywords: Hard –to-cook, Legumes, Grain storage, Lignification. AJFAND Vol. 8 (3) 2008: pp. 333-348