A POSSIBLE ROLE FOR CONDENSED TANNINS IN BEAN HARDENING

Bean seeds stored at high temperatures and humidities are susceptible to the hard-to-cook (HTC) defect in which they do not soften sufficiently during cooking. Hard shell is a defect in which beans do not imbibe sufficient water during soaking. This paper explores the possibility that polymerized leucoanthocyanins (condensed tannins) play a role in these reactions. Tannin measurements of extracts from hard and soft beans and from isolated cell wall material suggest that the high temperatures and relative humidity conditions encountered during tropical storage lead to migration of tannins from the seed coat to the cotyledon where they condense and bind with macromelecular components of the cell wall and middle lamella, leading to HTC. Oxidation of tannins in the seed coat may restrict water mobility and thus contribute to the hard shell condition in stored legume seeds.