Binding interactions between protein and polyphenol decreases inhibitory activity of the polyphenol against α-amylase: A new insight into the effect of dietary components on starch-hydrolyzing enzyme inhibition

The influence of three proteins on α-amylase inhibition of by tannic acid (TA, a typical phenolic competitive inhibitor) were studied. It was found that bovine serum albumin (BSA) and isolated whey protein (IWP) significantly decreased the inhibitory activity of TA against α-amylase with the decreasing effect in the order of BSA > IWP, while egg albumin (EA) hardly affected the enzyme inhibition. TA interacted with both α-amylase and the proteins through non-covalent forces, including hydrogen bondings and π-stackings. The binding affinity of TA to three proteins followed the order of BSA > IWP > EA. Therefore, the similar order in the influence of three proteins on TA-amylase binding interactions was observed, resulting in the respective strongest and weakest decreasing effects of BSA and EA on α-amylase inhibition by TA. Interestingly, the proteins maintained the quenching effect of TA on α-amylase fluorescence. These results indicated that there formed a respective protein-TA-amylase ternary complex, in which TA-protein binding interactions maintained π-stacking between TA and α-amylase but weakened hydrogen bondings between TA and the enzyme active site. Therefore, the competitive inhibition intensity of TA was reduced by BSA and IWP. Conclusively, proteins should be considered as an influencing factor of dietary polyphenols regarding the regulation of starch digestion.