Changes in Physicochemical Properties of Dry Beans (Phaseolus vulgaris L.) during Long-Term Storage

Abstract

Five different bean varieties (Phaseolus vulgaris L.) from Kenya, which were obtained either freshly collected or after having been stored for 5 years in tropical conditions (30−40 °C, >75% RH), were compared for their cooking characteristics. Beans under storage were susceptible to the hard-to-cook (HTC) defect, and the bean cooking time was up to 12 times that of the fresh beans, limiting their acceptability. A study was undertaken to investigate changes in nutritionally relevant physicochemical properties of beans during storage. Chemical analysis showed that storage resulted in a decrease in pH and an increase in titratable acidity in all varieties. Total polyphenol, non-tannin polyphenol, tannin, and lignin contents were determined; storage-induced HTC beans contained lower levels of total polyphenols (especially, non-tannin polyphenols) than the fresh beans but higher levels of tannins in all cultivars. Significant increases in lignin and lignified protein were also detected and accompanied by increases in cooking time. A reduction in phytic acid was also observed. These results are discussed in relation to the mechanisms which may underlie the development of the HTC defect. Keywords: Beans; hard-to-cook; phenolic compounds; storage