Abstract
Purpose: Adzuki beans are generally eaten by boiling them in water with their seed coats and grinding them to make a paste. Adzuki-bean-seed coats contain a large amount of polyphenols (PPs) with physiological functions, but approximately 80% of the seed-coat PPs are dissolved into water during boiling. However, some of the PPs diffuse into the cotyledons and may bind to proteins. This study was conducted to determine which proteins in adzuki beans bind more easily to PPs.
Methods: PPs were extracted from seed coats, while albumin, globulin, prolamin and glutelin were from cotyledons. Each protein was mixed with PP solution and heated. Trichloroacetic acid was added to precipitate protein. The amount of PPs bound with proteins was calculated from the free PP concentration measured by Folin-Ciocalteu method. Precipitated proteins were analyzed by SDS-PAGE.
Results: The extracted proteins were most abundant in the order of globulin, glutelin, albumin and prolamin. The amount of bound PPs was higher in albumin and glutelin than globulin. SDS-PAGE showed that the band intensities of the higher molecular-mass (>200 kDa) bands increased with the addition of PPs in a concentration dependent manner. Furthermore, 7S globulin, the major protein in adzuki beans, is suggested to interact with PPs.
