Removal of bound polyphenols and its effect on structure, physicochemical and functional properties of insoluble dietary fiber from adzuki bean seed coat

Abstract

Adzuki bean seed coat is an underutilized by-product of the adzuki bean paste process, rich in insoluble dietary fibers and bound polyphenols, which have diverse bioactivities. This work aimed to investigate the content of bound polyphenols in adzuki bean seed coat insoluble dietary fiber (AIDF) and their effects on the structure, physicochemical properties, and functional properties of insoluble dietary fiber. Alkaline treatment was used to remove the bound polyphenols from AIDF, resulting in dephenolized dietary fiber (AIDF-DF). The FT-IR, XRD and SEM results showed that there was no considerable structural difference between AIDF and AIDF-DF. The CLSM demonstrated that bound polyphenols could be removed from AIDF by alkaline treatment. Compared with AIDF, the water retention capacity, oil retention capacity, and swelling capacity of AIDF-DF were decreased by 6.87%, 34.42%, and 15.71%, respectively. AIDF also showed strong hypolipidemic capacities in vitro. What's more, DPPH decreased by 88.98%–92.22%, ABTS+ decreased by 74.60%–75.61%, and FRAP value decreased by 76.29%–89.44% in AIDF-DF when compared with AIDF. Therefore, the results will provide a better understanding of the interaction between cereal-based DF and its bound polyphenols.