Pectin enhances the inhibition of α-amylase via the mixture of rutin and quercetin

The human dietary system, which contains a variety of compounds such as polyphenols and polysaccharides, is very complex. Whether polysaccharides affect the inhibitory of polyphenol mixtures on α-amylase needs to be further investigated. The aim of this study was to analyze the effect and mechanism of pectin on the inhibition of α-amylase by a mixture of rutin and quercetin (R–Q). Results revealed that the inhibition and quenching affinity of R–Q for α-amylase was enhanced by pectin. The Stern-Volmer quenching constant of R–Q–α-amylase was increased by pectin from (6.08 ± 0.453) × 10 3  mL/mg to (9.80 ± 0.285) × 10 3  mL/mg. Pectin enhanced the ability of R–Q to inhibit α-amylase for two main reasons. On the one hand, it was owing to the binding of pectin to rutin, which increased the opportunity for quercetin to bind to the active center of α-amylase, thus enhancing the inhibitory effect of R–Q on α-amylase. On the other hand, pectin and quercetin simultaneously bound to different sites of α-amylase by noncovalent interactions to form the ternary complex of pectin–α-amylase–quercetin. The conformation of α-amylase and the hydrophobicity of amino acid residues were altered by the ternary complex, thereby enhancing the hydrogen bonding in the reaction system.