2.6. Determination of Antioxidant Activities by DPPH Radical Scavenging Assay and ABTS Radical Cation Decolorization Assay

DPPH radical scavenging activity was determined according to the modified method by Yamasaki et al. [25]. DPPH solution in absolute ethanol was freshly prepared before use and protected from light. The extracts were prepared in various concentrations (1, 10, 50, and 100 μg/ml). A portion of the sample solution 0.1 ml was mixed with the DPPH solution (ratio 1 : 1) in 96-well plates and protected from light for 30 minutes at room temperature, and the absorbance was measured at 520 nm using a spectrophotometer.

The ABTS radical cation decolorization assay followed the method by Re et al. [26]. The solution was produced by reacting 7 mM ABTS stock solution in distilled water with 2.45 mM potassium persulfate to produce the ABTS^•+ solution. The extracts were examined by the ABTS assay. A portion of the sample solution 0.02 ml was mixed with ABTS^•+ solution (ratio 1 : 10) in 96-well plates and kept in the dark. The reaction was carried out for 6 min, and the absorbance was measured at 734 nm. BHT was used as a positive control in both antioxidant assays.