2.5. Determination of total phenolic content
TPC in each sample was determined by using the Folin-Ciocalteu colorimetric method that was previously described (Cai et al., 2004) with a slight modification. In brief, aliquots (0.1 mL) of appropriately diluted sample or standard solutions were mixed with 0.5 mL of 0.5 N Folin–Ciocalteu’s phenol reagent, and the reaction was neutralized with 1.0 mL of saturated sodium carbonate (75.0 g/L). The absorbance of the resulting blue color was measured at 760 nm with a UV–vis spectrophotometer after incubation for 2 h at room temperature (∼23 ◦C). A calibration curve was prepared using gallic acid solution (5–100 g/mL). TPCs were expressed as grams of gallic acid equivalent (g GAE) per 100 g of dry weight. The determination was performed in triplicate.