Structures, physicochemical properties, and hypoglycemic activities of soluble dietary fibers from white and black glutinous rice bran: A comparative study

To extend the applications of glutinous rice bran, a by-product of the glutinous rice processing industry, soluble dietary fibers (SDF) isolated from Chinese white (WSDF) and black (BSDF) glutinous rice bran were compared for their structures, physicochemical properties, and hypoglycemic activities in this study. Results showed that BSDF had higher glucose content while lower rhamnose, arabinose, xylose, and mannose contents, similar molecular weight, and a particular presence of anthocyanin compared to WSDF. Owing to the smaller particle size, higher viscosity, and more abundant network structures, BSDF had higher glucose adsorption capacity and retarding glucose diffusion ability than WSDF. The evaluations in vitro kinetics showed that addition of BSDF in starch led to a smaller glucose absorption rate constant and expected glucose index than WSDF, although BSDF showed lower α-amylase inhibitory ability. Interactions between the SDF and α-amylase, which were mediated by van der Waals force and hydrogen bond (WSDF-α-amylase) and hydrophobic interaction (BSDF-α-amylase), induced partial transformation of α-amylase from α-helix and β-sheet to β-turn and random coil. In summary, both WSDF and BSDF could be used as natural food additives for the reduction of postprandial blood glucose level and the enhancement of antioxidant activity in food products, while BSDF may show better efficacy.