The total phenolic content (TPC) was determined by the
Folin–Ciocalteu method (Singleton et al., 1999). The
extract (0.1 g) was dissolved with methanol and up to
100 mL, and then the extract solution (0.5 mL) was mixed
with 0.5mL of the Folin–Ciocalteau reagent and 0.5mL of
100 mg/mL sodium carbonate (added 2 min after the
Folin–Ciocalteau reagent). After initial mixing the opaque
flasks were allowed to stand for 2 h. The optical density of
the blue-colored samples was measured at 765nm. The
total phenolic contents were expressed as mg gallic acid
equivalent (GAE)/g dry basis.