Changes of porcine pancreas α-amylase in activity and secondary conformations under inhibition of tea polyphenols

Mechanisms Underlying the Effect of Tea Extracts on In Vitro Digestion of Wheat Starch

The effect of extracts from four types of tea made from Camelia sinensis (green, white, black, and oolong) on in vitro amylolysis of gelatinized starch and the underlying mechanisms were studied. Of the four extracts, black tea extract (BTE) gave the strongest inhibition of starch digestion and on α-amylase activity. Fluorescence quenching and surface plasmon resonance (SPR) showed compounds in BTE bound to α-amylase more strongly than those in the green, white, and oolong tea extracts. Individual testing of five phenolic compounds abundant in tea extracts showed that theaflavins had a greater inhibitory effect than catechins on α-amylase. SPR showed that theaflavins had much lower equilibrium dissociation constants and therefore bound more tightly to α-amylase than catechins. We conclude that BTE had a stronger inhibitory effect on in vitro enzymatic starch digestion than the other tea extracts, mainly due to the higher content of theaflavins causing stronger inhibition of α-amylase.

Inhibition of starch digestion by flavonoids: Role of flavonoid-amylase binding kinetics

In this study, kinetics of binding between α-amylase and green tea flavonoids were investigated by fluorescence quenching (FQ). Their effect on α-amylase inhibition was evaluated. Whereas epicatechin (EC) and epigallocatechin (EGC) exhibited slow binding kinetics (in the order of minutes), epicatechin gallate (ECG) and epigallocatechin gallate (ECGC) exhibited very rapid binding (in the order of seconds) with Human Salivary α-amylase (HSA) and Porcine Pancreatic α-amylase (PPA). EGCG reached maximum inhibition of HSA and PPA with short incubation time whereas maximum inhibition of HSA and PPA by EC was reached only after 45 to 60 min of incubation. Similar results with ECG and EGC, but not in line with FQ kinetics, highlighted possible interferences of starch-flavonoid interaction in the binding and inhibition process. These results suggest that incubation times of enzymes and flavonoids shall be evaluated prior to enzyme inhibition testing in order to ensure consistent and reliable results.