Dietary fiber-bound polyphenols in Canavalia gladiata seed coat: Optimization of conditions, identification and bioactivity assessment of acid, alkaline, and enzymatic extraction

In this paper, the optimal conditions for extracting dietary fiber-bound polyphenols in Canavalia gladiata seed coat using three hydrolysis methods, namely alkali, acid and enzyme, were obtained using response surface methodology. The total phenolic content of alkali hydrolysis products was 2635.97 μg GAE/g DW, which was much higher than that of the acid (1418.87 μg GAE/g DW) and the enzyme method (1316.39 μg GAE/g DW). Qualitative analysis identified a total of 38 compounds, 33 of which were quantified. The results showed that CGDF-BPs were dominated by phenolic acids, especially gallic acid. Overall the alkaline method hydrolyzed dietary fibers more thoroughly, releasing a higher diversity of compounds. However, their in vitro antioxidant and α-glucosidase inhibitory activities were inconsistent at equivalent concentration due to differences in bound polyphenol composition caused by the alkali, acid, and enzyme methods, which served as a reference for studying of the composition and activity of natural plant polyphenols.