Instability of common beans during storage causes hardening: The role of glass transition phenomena

Abstract Long-term storage of common beans leads to loss of cooking quality and an ill-defined solution, appropriate storage, is recommended. Therefore, the polymer science theory of glasses that hypothesizes stability of a system below its glass transition temperature (T g ) was applied to determine bean stability during storage in relation to cooking behavior. Since composition influences T g , powders of cotyledons and seed coats in addition to whole beans were equilibrated above different saturated salt solutions in order to generate materials with different moisture contents. A thermal mechanical compression test which measures compressibility changes in a system upon reaching its glass-rubber transition temperature region was conducted to obtain the T g . A T g -moisture relation was established, whose relevance was confirmed by storage and cooking experiments which showed development of hard-to-cook in beans stored above T g but not below it. Therefore, this relation constitutes a stability map for storage of common beans.