The TPC was determined using the Folin-Ciocalteu method according to the procedure reported by Zhang et al. (2006) with some modifications. Briefly, a volume of 20 μL of standards or test samples was mixed with 100 μL of Folin-Ciocalteu reagent in 96-well plates. After 5 minutes, 80 μL of 7.5% sodium carbonates was added to each well.