For producing ABTS radicals, the ABTS
solution was mixed to 2.45 mM potassium persulfate (final
concentration) at a ratio of ABTS/potassium persulfate of
1: 0.5, M/M and allowing the mixture to stand in the dark
at room temperature for 24 h before use. The ABTS
solution was diluted with water to an absorbance of 0.7 ±
0.02 at 734 nm. To the diluted ABTS solutions (200 L),
which were put into 24 well-plates, were added the sample
solutions (2L) dissolved in 95% ethanol, and then the
absorbance at 734 nm was measured after 10 min
incubation at room temperature.