Effects of Oolong Tea Polyphenols, EGCG, and EGCG3″Me on Pancreatic α‑Amylase Activity in Vitro

In order to investigate the inhibitory effects and possible mechanisms of Oolong tea polyphenols, (−)-epigallocatechin gallate (EGCG) and (−)-epigallocatechin 3-O-(3-O-methyl) gallate (EGCG3″Me) on pancreatic α-amylase, the inhibition, enzyme kinetics, ultraviolet (UV) absorption spectrum and fluorescence spectrum of α-amylase were investigated. The results showed that Oolong tea polyphenols, EGCG, and EGCG3″Me all exhibited inhibitory effects against α-amylase, and their half inhibitory concentration (IC50) values were 0.375, 0.350, and 0.572 mg/mL, respectively. The results of Lineweaver–Burk double reciprocal plot indicated that the inhibitory types of Oolong tea polyphenols and EGCG were competitive, whereas EGCG3″Me was in a noncompetitive pattern. Oolong tea polyphenols, EGCG, and EGCG3″Me all induced red-shift of UV absorbance and quenching of fluorescence of α-amylase, suggesting possible changes in the conformation of α-amylase. The differences of inhibitory effects and inhibition types for EGCG and EGCG3″Me might be due to their structural difference (the hydroxyl group at C-3 in D ring of EGCG substituted by methoxy group, forming EGCG3″Me).