The inhibitory activities of three tea extracts (TEs) and individual phenolic compounds in TEs against porcine pancreatic α-amylase (PPA) were studied by measuring their half inhibitory (IC50) concentrations. The kinetics of inhibition by these extracts and compounds were investigated through Dixon, Cornish-Bowden, and Lineweaver–Burk plots. The results showed that green, oolong and black tea extracts, epigallocatechin gallate, theaflavin-3, 3′-digallate and tannic acid were competitive inhibitors of PPA, whereas epicatechin gallate, theaflavin-3′-gallate and theaflavin were mixed-type inhibitors with both competitive and uncompetitive inhibitory characteristics. Only catechins with a galloyl substituent at the 3-position showed measurable inhibition. The competitive inhibition constants (Kic) were lower for theaflavins than catechins, with the lowest value for theaflavin-3, 3′-digallate. The lower Kic than the uncompetitive inhibition constant for the mixed-type inhibitors suggests that they bind more tightly with free PPA than with the PPA–starch complex. A 3 and/or 3′-galloyl moiety in catechin and theaflavin structures was consistently found to increase inhibition of PPA through enhanced association with the enzyme active site.
... gallate (EGCG, C 22 H 18 O 11 ), (-)epicatechin gallate (ECG, C 22 H 18 O 10 ), theaflavin (TF, C 29 H 24 O 12 ), theaflavin-3′-gallate (TF1, C 36 H 28 O 16 ), and theaflavin-3, 3′-digallate (TF2, C 43 H 32 O 20 ) were obtained from Chengdu Biopurify Phytochemicals Ltd. ...
