Determination of total phenolic content (TPC)
Total phenolic content was determined according to Zheng and Wang (2001) by using Folin–Ciocalteu reagent. Twenty ll of sample was mixed with 1.58 ml of distilled water followed by 100 ll of Folin–Ciocalteus reagent. The mixture was vortexed vigorously, left to stand at room temperature for 15 min and 300 ll of sodium carbonate solution (20%) was added. The mixture was left to stand at room temperature for 2 h then the absorbance was measured with a spectrum UV–ViS Spectrophotometer at 765 nm.