Black Tea Polyphenols Suppress Postprandial Hyperglycemia In Vivo in Mice and Inhibit α-Glucosidase Activity In Vitro

Black tea is reported to have various beneficial effects on health. Activated charcoal-treated black tea (ACBT) did not contain catechins nor caffeine and included small amount of theaflavins (TFs). We had further fractionated ACBT to obtain black tea polymerized polyphenols (BTPP), TFs-poor fraction and TFs-rich fraction and studied in vitro and/or in vivo effect of the fractions to elucidate the effect of ACBT. Sucrose-loading test in mice showed that ACBT and BTPP at the dose of, 1000 and 560 mg/kg, respectively, suppressed the increase of blood glucose level while secretion of insulin was not affected. We found that this effect is caused by inhibition of α-glucosidase activity. BTPP contained TFs, but the content was not at all enough to explain the activity of ACBT, 1H NMR analysis of BTPP was carried and showed the existence of many benzotropolone ring containing substances as active compounds.