The method of Arnao, Cano, and Acosta (2001) with some modifications
was adopted. Stock solutions of 7.4 mM ABTS in water
and 2.6 mM potassium persulfate (K2S2O8) were prepared. Before
use, equal volumes of the two solutions were mixed and allowed
to react in the dark for 12–16 h at room temperature to generate
the ABTS radical cation. The solution was then diluted with methanol
until an absorbance of 1.1 at 734 nm (diluted 30-fold) was
achieved. A compound (20 lL, 1.5 mM in methanol) or methanol
(control) was diluted to 3.0 ml with the freshly prepared ABTS+
solution (final concentration 10.0 lM) then the decrease in absorbance
was recorded after 6 min in the dark at 734 nm against a
blank of methanolic solution of the compound. All experiments
were done in duplicates. A standard curve of trolox (1.0–6.5 mM)
was prepared. Results are presented as trolox equivalent of antioxidant
capacity (TEABTS or TEAC value). The % of ABTS+ scavenging
activity was calculated by the following equation