Impact of Storage Conditions on the Physical Properties and Cooking Characteristics of Two Bean Varieties Grown in Kenya

Abstract

Common beans are highly nutritious and widely consumed in Kenya. Storage of common beans under adverse conditions of high temperature and high humidity renders them susceptible to the hard-to-cook (HTC) defect. This results in increased cooking time, fuel and water use which has a negative effect on acceptability and utilization of beans. The objective of this study was to determine effects of storage temperature and relative humidity on development of the HTC defect in Rose coco and Red Kidney bean varieties. Bean samples were obtained from Kenya Agricultural and Livestock Research Organization (K ALRO) - Thika. The beans were stored at varying temperature (25ºC, 35˚ C and 45˚ C) and relative humidity (RH=75% and 83%) combinations. Apart from beans stored at 25ºC/75%, samples from each treatment condition were sampled after every two months and analyzed for physical properties. Soaking pretreatments in deionized water, sodium carbonate and calcium chloride solutions were carried out to determine their effect on the cooking time. There was a significant increase in conductivity and leached solutes paralleled by decreasing hydration and swelling coefficients with increasing storage time under all the storage conditions. Characteristic dimensions and one hundred seed weight were not significantly different among the bean varieties under various storage conditions. Moisture uptake reduced by 19% for Rose coco and 23% for Red kidney under 35˚C/83%  storage whereas 45˚C/75% had a 29% reduction for Rose coco and 39% reduction for Red kidney over the 6 months storage period. Cooking time increased for all the bean varieties with increasing storage time, the most pronounced increase (100%) being observed at 45˚C and 75% RH. Across the 6 months storage period, Na₂CO₃ soaking pretreatment reduced the cooking time by 75% for Rose coco and 70% for Red kidney in comparison to beans cooked without prior soaking. Based on the results of this study, it was concluded that storage under high temperature and relative humidity conditions accelerated the development of the HTC defect in beans resulting in changes in physical and cooking properties.

Keywords: hard-to-cook, storage, physical properties, cooking quality