Hard‐to‐cook phenomenon in beans: Changes in antinutrient factors and nitrogenous compounds during storage

Abstract

Abstract Five different bean varieties ( Phaseolus vulgaris ) from Kenya, which were either freshly collected or stored for 5 years in tropical conditions (30–40°C; >75% humidity), were compared for their cooking characteristics. The beans under storage develop an irreversible phenomenon classified as ‘hard‐to‐cook’ (HTC) which results in undesirable characteristics limiting their acceptability. Our aims were to determine the effects of the HTC phenomenon on the proteins and antinutrient factors in these beans. Both fresh and HTC beans contained nutritionally significant amounts of lectins, trypsin and α‐amylase inhibitors. HTC samples had higher lectin and lower α‐amylase inhibitor contents, while the amounts of trypsin and chymotrypsin inhibitors were the same. Storage appeared to reduce water‐extractable nitrogen. Fractionation with sodium dodecyl sulphate also showed that less protein may be available in HTC than fresh beans. We established that the undesirable changes in beans, such as increased cooking time, which often accompany the storage of harvested seeds under tropical conditions produce an overall decrease in soluble‐N fractions, particularly proteins. The results can provide guidelines on how to utilise these seed(s) and their products. Furthermore, appropriate processing is needed to reduce their antinutrients for human nutrition.