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 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