INFLUENCE OF STORAGE CONDITIONS ON DEVELOPMENT OF HARD TO COOK DEFECT IN COMMON BEANS AND THE SUBSEQUENT NUTRITIONAL CHANGES

Abstract

Common beans form one of the main sources of proteins in poor sub-Saharan Africa. However, common beans are succumbed to the Hard-to-cook (HTC) defect which is suggested to develop due to storage at temperatures higher than 25ºC and relative humidity of more than 70%. This results in increased cooking time, fuel consumption and water use thus lowering the rate of utilization of beans at domestic level. This study was aimed at understanding the development and the effects of hard to cook on an easy and hard to cook bean varieties. Samples were collected from KARI (Kenya Agricultural Research Institute), Thika. The hard (Pinto) and easy (Red Haricot) to cook beans were stored at varying temperatures (25, 35, and 45°C) and humidity (75 and 85%) levels, followed by pre-treatment (soaking in deionized water, sodium carbonate and calcium chloride) and thermal treatment. The samples were assessed for physical (Seed density, seed porosity, characteristic dimension of beans, hydration coefficient, and swelling coefficient) changes. Beans stored at 45ºC at 75% RH were significantly harder than those stored at 25ºC/75% and 35ºC/85% after 2 months. The hydration coefficient and swelling coeffient decreased with increasing storage time while the geometric properties did not change. Bean hardness, solutes and electrolytes leaching after 16hr soaking substantially increased with increased temperature. It was concluded that the longer the beans are stored at higher temperatures the more they develop the hard to cook defect.