Polyphenol content was determined by the Folin–Ciocalteu assay (Kanaya, 2006). Each powdered sample (100 mg) was ground in a mortar with 10 ml of 99.7% methanol and stored for 2 h at 12 ◦C. After centrifugation at 1700 x g for 10 min, the supernatant was used for analysis. Extract (0.5 ml)was mixed with 0.2 ml Folin–Ciocalteu reagent (Wako), 0.5 ml saturated Na2CO3, and 4.3 ml Milli-Q water and stored for 1 h at room temperature. The spectrum was recorded at 765 nm. The polyphenol concentration was expressed as gallate equivalent