2.5. Determination of total phenols by Folin-Ciocalteu
reagent method
Folin-Ciocalteu reagent was used to determine the total phenolic content (TPC) of the various organic crude extracts[14]. Gallic acid was used as a reference standard (20-100 μg/mL) for plotting calibration curve. A volume of 0.5 mL of the plant extract (100 μg/ mL) was mixed with 1.5 mL of Folin-Ciocalteu reagent (diluted 1:10 with de-ionized water) and were neutralized with 3 mL of sodium carbonate solution (7.5%, w/v). The reaction mixture was kept in dark at room temperature for 30 min with intermittent shaking for color development. The absorbance of the resulting blue color was measured by using double beam UV-Vis spectrophotometer (UV Analyst-CT 8200) at fixed wavelength of 765 nm. The TPCs were determined using linear regression equation obtained from the standard plot of gallic acid. The content of total phenolic compounds was calculated as mean依SD (n=3) and expressed as mg/g gallic acid equivalent (GAE) of dry extract.