Purple red rice bran anthocyanins reduce the digestibility of rice starch by forming V-type inclusion complexes

Purple red rice bran, a by-product of the rice polishing process, contained abundant anthocyanins. However, most of them were discarded resulting in a waste of resources. This study investigated the effects of purple red rice bran anthocyanin extracts (PRRBAE) on the physicochemical properties and digestive properties of rice starch and its mechanism of action. Infrared spectroscopy and X-ray diffraction indicated that PRRBAE could interact with rice starch through non-covalent bonds to form intrahelical V-type complexes. The DPPH and ABTS⁺ assays showed that PRRBAE could confer better antioxidant activity on rice starch. In addition, the PRRBAE could increase the resistant starch content and decrease the enzyme activities by changing the tertiary and secondary structure of starch-digesting enzymes. Further, molecular docking suggested that aromatic amino acids play a key role in the interaction of starch-digesting enzymes with PRRBAE. These findings will contribute to a better understanding of the mechanism of PRRBAE reducing starch digestibility, and to the development of high value-added products and low glycemic index (GI) foods.