Tea polyphenols enhance binding of porcine pancreatic α-amylase with starch granules but reduce catalytic activity

The effects of tea polyphenols on binding of porcine pancreatic α-amylase (PPA) with normal maize starch granules were studied through solution depletion assays, fluorescence spectroscopy and initial rate kinetics. Only polyphenols which have inhibitory activity against PPA increased the binding of PPA with starch. The results are consistent with a binding equilibrium between polyphenols, starch and PPA. The dissociation constant (Kd) for PPA binding was decreased by tea polyphenols, with the effects greater for theaflavins than catechins and for galloylated than non-galloylated polyphenols. Tea polyphenols were also shown to increase the binding rate of PPA to starch. In addition, there were positive linear correlations between 1/Kd and reciprocal of competitive inhibition constant (1/Kic) and between 1/Kd and fluorescence quenching constant (KFQ). Despite the greater amount of PPA on the granules, starch hydrolysis is reduced because the polyphenol inhibition of PPA persists after binding to starch.