2.4.2. ABTS assay
The free radical-scavenging activity was carried out using a spectrophotometer by the improved ABTS radical cation decolorization method as described (Cai et al., 2004; Wojdylo et al.,2007). ABTS radical cation (ABTS•+) was produced by reacting 7.0 mmol/L ABTS solution with 2.45 mmol/L potassium persulfate at 2:1 (v/v) and allowing the mixture to stand in the dark at room temperature for 16 h prior to use. The ABTS•+ solution was diluted with 80% ethanol to yield an absorbance of 0.700 ± 0.02 at 734 nm. The ABTS•+ solution (4.0 mL, absorbance of 0.700 ± 0.02) was added to 0.1 mL of appropriately diluted sample and was mixed thoroughly. The reaction mixture was stored at room temperature for 6 min, and absorbance was immediately measured at 734 nm. Trolox standard solution (final concentration 50–700 mol/L) was prepared and assayed under the same conditions. Results were expressed in terms of mmol TEAC.