reaction and the influence of the selected time-point of
measurement on the reported antioxidant activity; thus
the determinants of the antioxidant activity are the extent
of reduction and rate of reduction of the radical. For
example, whereas caffeic acid and kaempferol demonstrate
the lower extent of inhibition than ferulic acid and
luteolin, respectively, the reactions of the former are
essentially complete after 1 min reaction. Flavonoids
varied in the range of times over which the reaction took
place (Fig. 5). Whereas most phenolics had completed
the reaction at 4 min, some compounds especially luteolin
and naringenin were still reacting. Expressing the
results as area under the curve can take these factors into
account.
The major improvement in the assay for lipophilic
compounds such as carotenoids is the design improvement
incorporating the radical cation and the antioxidant
both in the lipophilic phase. The reaction between the
carotenoids and ABTS•1 is essentially complete after 1
min, little further reaction taking place thereafter. The
antioxidant activity of lycopene was of the same order as
obtained using previous methodology that produced the
radical cation using manganese dioxide as oxidant [20].
The value for b-carotene was significantly higher. This
method improves the assay also on the grounds that
application of manganese dioxide as oxidizing agent can
involve molecular chemistry with the potential to produce
a two electron oxidation of ABTS to the radical
dication, that limits its definition and applicability.
The antioxidant activities of the plasma antioxidants,
ascorbic acid, a-tocopherol, and uric acid, as well as that
of glutathione, are shown in Table 1. The TEAC values
obtained are close to those obtained by myoglobin/ABTS
assay [1,13], with the latter two being slightly higher.
There are differences between the TEAC values for
the flavonoids and hydroxycinnamates at 1 min, 4 min
and 6 min by the ABTS•1 decolorization assay compared
with the myoglobin/ABTS assay monitored at 6 min. The
latter assay involved continuous formation of the ABTS
radical cation from ferryl myoglobin, derived from met