Optimization and identification of bound polyphenols from rice bean (Vigna umbellata) skin dietary fiber, antioxidant activities and α-glucosidase inhibition mechanism

Vigna umbellata is an important homologous medicinal and food legume, and its fruit is rich in polyphenols. Acidic, alkaline (highest yield) and enzymatic methods were used to release bound polyphenols from rice bean skin dietary fiber. 44 compounds were identified from the alkaline hydrolysis products. With the increase of polyphenol concentration within a specific range, the scavenging rate of DPPH• and ABTS + • radicals and the reduction ability of ferric ions were increased. Rice bean skin dietary fiber bound polyphenols (RBSDF-BP) showed significant α -glucosidase inhibitory activity. The results showed that Hydrogen bonding and hydrophobic forces were the binding forces for RBSDF-BP to form a stable polyphenol-enzyme complex with α -glucosidase. Molecular docking revealed that the three polyphenols of RBSDF-BP had a strong affinity for the active site in the hydrophobic cavity of the enzyme. This study provides valuable discoveries for the potential application of RBSDF-BP as natural inhibitors of α -glucosidase. Chemical compounds Protocatechuic acid (PubChem CID: 72); Malic acid (PubChem CID: 525); Isoferulic acid (PubChem CID: 736186); p-Hydroxybenzoic acid (PubChem CID: 135); Citric acid (PubChem CID: 311), (+)-Catechin (PubChem CID: 9064), Fumaric acid (PubChem CID: 444972), Gallic acid (PubChem CID: 370), Azelaic acid (PubChem CID: 2266), (−)-Epicatechin (PubChem CID: 72276).