Variation of phenolic compounds of Phaseolus vulgaris L. during storage and its relationship with the hardening

摘要

A major limiting for consumption of legumes in tropical countries is the hardening of the grains during storage at high temperature and high relative humidity. The aim of this study was to determine the effect of storage conditions on phenolic compounds and antioxidant capacity of the cotyledons and seed coat of Phaseolus vulgaris L. and their relation to hardening. Grain samples were stored at 5 ?°C - 34 % RH and 37 ?°C - 75 % RH for 120 days. The physical properties (hardness, cooking time, imbibition capacity, electrical conductivity of the soaking water, moisture, and water activity) were measured in the whole grain, while phenolic compounds (total polyphenols, hydroxycinnamic acids, flavonoids, soluble condensed tannins, and lignin) and antioxidant capacity were measured in cotyledons and testa. Hydroxycinnamic acids and flavonoids were analyzed by HPLC-DAD/ESI-MS, the free compounds were extracted by methanol, and those bound to insoluble fiber were released by alkaline hydrolysis. Storage at 37 ?°C - 75 % RH increased grain hardness and decreased its imbibition capacity. Also, it generated a greater reduction in phenolic compounds concentration (except by ferulic acid, which increased) and antioxidant capacity of the cotyledons and the seed coat, compared with storage at 5 ?°C - 34 % RH. The significant increase detected in concentration of free and conjugated ferulic acid, only when stored at 37 ?°C - 75 % RH, could be directly related to the grain hardening.