Inhibition of starch digestion by phenolic acids with a cinnamic acid backbone: Structural requirements for the inhibition of -amylase and -glucosidase

This study investigated the inhibition mechanism of cinnamic acid-based phenolic acids (cinnamic acid: CIA, 3,4dimethoxy cinnamic acid: 3,4-mCIA, caffeic acid: CA, ferulic acid: FA) on starch digestion. CA, FA, and 3,4-mCIA contributed to reducing the rapidly digested starch content and increasing the resistant starch content. The enzyme activity inhibition results responded that the four phenolic acids inhibited alpha-amylase activity better than alpha-glucosidase. The order of IC50 against alpha-amylase and alpha-glucosidase was CA > FA > 3,4-mCIA > CIA. Phenolic acid's benzene ring formed conjugated Pi-systems with the amino acid residues of alpha-amylase. Salt-bridge interactions were the main driving forces for the binding of phenolic acids to alpha-glucosidase. The binding was stabilized by the hydroxyl (OH) group and the methoxy on the benzene ring, where the OH exerted a better effect. These results illuminate the inhibition mechanism of starch digestion with cinnamic acid-based phenolic acids from an interaction perspective.