Grade identification of ripened Pu-erh teas, and their differences of phenolic components, in vitro antioxidant capacity and hypoglycemic effect

Tea grade causes chemical differences. To reveal its detailed impact, chemical constitute and in vitro antioxidant capacity were determined in 20 ripened Pu-erh teas (RiPT). Their inhibitory activity on <i>α</i>-amylase and <i>α</i>-glucosidase were calculated to evaluate hypoglycemic effect. Results confirmed pile-fermentation as the main effective factor for chemical and functional differences among four series of RiPT. Furthermore, partial least squares-discriminant analysis and heat map analysis both accomplished the discrimination of high grade (G1) from middle grade (G3 and G5) and low grade (G7 and G9). Particularly, several phenolics like theaflavins, (-)-epigallocatechin (EGC), rutin and quercetin contributed to grade identification. Due to phenolics difference, RiPT grade showed positive correlation with antioxidant capacity and hypoglycemic effect. Characteristic antioxidants and inhibitors existed in RiPT with significantly positive (<i>P</i> < 0.05 and <i>r</i> > 0.75) correlations. Concretely, theaflavins, EGC, theabrownins, gallic acid, rutin and quercetin enhanced its antioxidant capacity and hypoglycemic effect.