Enzymic catalyzing affinity to substrate affects inhibitor-enzyme binding interactions: Inhibition behaviors of EGCG against starch digestion by individual and co-existing α-amylase and amyloglucosidase

•Epigallocatechin gallate(EGCG) inhibits amylase(AA) at slowly-digestible-starch phase.•EGCG inhibited amyloglucosidase(AMG) and AA/AMG in the whole digestion process.•Binding of EGCG with AA and AMG causes more unbound AMG in AA/AMG system.•Although EGCG-AA binding affinity was higher than EGCG-AMG, AA inhibition was weaker.•High catalytic affinity of AA to starch weakens EGCG-AA binding in digestion system. The inhibition of (-)-epigallocatechin-gallate (EGCG) against starch digestion by α-amylase (AA), amyloglucosidase (AMG) and co-existing enzymes (AA/AMG) were comparatively studied. EGCG inhibited AA only at slowly-digestible-starch (SDS) phase. This resulted from high catalytic efficiency of AA for rapidly-digestible-starch (RDS), counteracting the inhibition at this phase. EGCG inhibited AMG and AA/AMG during whole process. At RDS phase, the catalytic velocity of AMG was always higher than AA/AMG because of an antagonistic effect of two enzymes. However, at SDS phase with EGCG, the catalytic velocity of AA/AMG was higher than AMG. This is because binding of EGCG with both enzymes caused more unbound AMG that generated more glucose in co-existing AA/AMG than AMG. Although EGCG-AA binding affinity was higher than EGCG-AMG, competitive inhibition of EGCG against AA was weaker than AMG, indicating relatively higher binding/catalyzing affinity of AA to starch significantly weakened EGCG-AA binding due to competitive relationship between starch and EGCG.