Hard-to-cook (HTC) phenomenon associated changes in protein and lipid profile of faba and adzuki beans

Abstract

High-temperature and high-humidity storage of beans is known to impact their hydration properties and functional characteristics in both whole-cooked beans and bean flour. However, the role of proteins and lipids in these changes remains unexplored, particularly for vicilin and legumin-rich legumes. This study investigated protein and lipid modifications during storage at 40 °C under 60 % and 80 % relative humidity (RH) for 9 months to induce Hard-to-Cook (HTC) phenomenon. Adzuki protein (rich in vicilin) showed significant changes in solubility, while faba protein (rich in legumin) was unaffected. Molecular size distribution revealed increased protein aggregates and decreased legumin and vicilin fractions in faba proteins. In adzuki proteins, the vicilin fraction decreased and the legumin fraction completely disappeared after storage at 40 °C for 9 months. Nano differential scanning calorimetry showed double endothermic peaks for faba proteins: a small peak at 82 °C for vicilin and a second major peak at 95 °C for legumin. For control adzuki proteins, the pattern was opposite to that seen in faba beans. The first major peak occurred at 84 °C for vicilin and a later minor peak was observed for legumin. During storage, both peaks shifted to the left, indicating a decrease in the denaturation temperature. Fatty acid analysis revealed a decrease in short and medium-chain fatty acids (C8:0, C14:0) and an increase in long-chain fatty acids (C20:0). Exploring the changes in protein structure, aggregation, and functionality during high-temperature and humidity storage, along with lipid profile could provide a more comprehensive understanding of how storage conditions affect bean quality.