The ABTS free radical scavenging capacity assays were carried using a modified method as
described by Fang and Re [26,27]. Potassium persulfate was added to 7 mM of ABTS+ and kept for
12–16 h at room temperature in dark. The ABTS+ solution was diluted with PBS (potassium
phosphate-buffered saline, pH 7.4) to an absorbance of 0.70 ± 0.02 at 734 nm before analysis. ABTS+
solution (3.0 mL) was added to sample fractions (0.1 mL, 25–800 g/mL) or individual pure compounds
(6.25–200 g/mL) in DMSO at different concentrations and mixed by hand for 20 s. The reaction
mixture was kept at room temperature for 6 min, and the absorbance was recorded at 734 nm on a
Shimadzu UV-2550 spectrophotometer. Trolox® was used as the positive control. The ABTS free
radical-scavenging capacity (%) was calculated using the following equation: