ABTS+ is a well-known nitrogen-centred synthetic radical and is
widely used to determine antioxidant activity. The ABTS radical is
generated by oxidation of ABTS with potassium persulphate and
when extracts are added to the ABTS radical, it is converted to a
non-radical form. Different concentrations of extracts, ranging
from 0.125 to 2.0 mg/ml, were examined for scavenging activity
and it ranged from 27.8% to 96.4% for the water-based GJE extract
to between 19.0% and 94.3% for the ethanol-based extract. The radical-
scavenging activity of the water extract was (96.4%), significantly
higher than the ethanol extract (94.3%) at a concentration
of 2 mg/ml (Table 2). A higher phenolic content might be responsible
for higher ABTS+ scavenging activity of water extract (Sayd,
Hanan, Taie, & Taha, 2010). However, the ethanol extract (at
2 mg/ml) and BHT (95.2%, at 0.125 mg/ml) did not show any significant
difference (P > 0.05) in ABTS+-scavenging activity. Water extract
of the 2 mg/ml concentration showed a stronger activity than
that of 0.125 mg/ml BHT (P < 0.05; Table 2). In addition, IC50 values
were 0.21 and 0.39 mg/ml for water and ethanol extracts, respectively
(Table 2). The antioxidant activity in the ABTS assay was also
strongly correlated with phenolic and flavonoid contents
(r2 = 0.9986 and 0.9848, respectively, for water extract and
r2 = 0.9995 and 0.9997, respectively, for the ethanol extract). The
same correlation between antioxidant activity and total phenolic
content in Gardenia jasminoides shootlets and calli was observed
by Sayd et al. (2010).