Condensed tannin content in the extracts was determined by the
vanillin/HClmethod of with some modifications. An aliquot of the extracts (1 mL) was added to the vanillin
reagent (2 mL), which had been prepared by dissolving vanillin in
methanol (0.5%, w/v). Sequentially, an aqueous HCl solution (2 mL,4%, v/v) was added to the mixture, and then the mixture was incubated in the dark. The absorbance was measured at 500 nm after
20 min of incubation. To calculate CTC, (+)-catechin standards at
different concentrations (500–3000 g/mL) were used.