Sample 0.1 g was extracted twice for 2 h with 10 mL of 80% methanol containing 1% HCl at room temperature on a reciprocal shaker. Extract (100 μL) was mixed with 2 mL of 2% (w/v) Na2CO3 solution. After incubation for 3 min, 100 μL of Folin-Ciocalteu reagent was added.