The crude extract of G. changii was screened for DPPH
radical scavenging activity according to the method described
and the results of the screening are shown in Figure 1 as
comparable with known antioxidant.
The methanolic extract tested showed a lower reducing
power activity than BHT and vitamin E. BHT showed the
highest reducing power activity (66.0%) followed by Vitamin
E (40.1%) and the methanolic extract (4.3%) respectively at the
concentration tested (1 mg/ml). We therefore suggest that at
proper concentration of the crude extracts of G. changii may
act as free radicals scavenger and may react with free radicals
to convert them to more stable products and terminate radical
chain reaction [12]. Our result demonstrated that crude extract
of G. changii thereby has moderate free radical scavenging
activity.
All these properties are involved in the overall anti-oxidant
activity, which makes it suitable for the prevention of human
disease in which free radicals play an important role [13-14].
Dose inhibition curve and IC50 values of the crude extract
are shown in Fig 2. In the dose-response experiment it could
be observed that total inhibition of the enzymes was never
achieved. Maximal inhibition was in the range of 75-85%,
in the presence of 25 mg/ml extract. With the addition of
larger amount of extract to DPPH assay mixture, the degree
of inhibition decreased, indicating a pro-oxidant effect. The
explanation for the higher IC50 (IC50 = 14.70 mg/ml) value
found in the experiment was because the sample used was a
crude extract with the compound(s) react as antioxidant.
Result of the TLC-DPPH separation and determination of
radical scavenging activity showed in Figure 3. Our thin layer
chromatography study showed that the crude extract of G.
changii contained 7 major bands. A major part of compounds
in G. changii crude extract was found to be inactive based on
DPPH scavenging area. Only one DPPH radical scavenging
band was separated and detected with Rf
value 0.63 (Figure. 3).
In such situation, the real concentration for the compound(s),
which reacts as an antioxidant, was very low in the crude
extract.
The phenolic content of the sample was determined using
Folin-Ciocalteu reagent and was 5.0 mg/g dry weight expressed
as gallic acid equivalents (GAE). Typical phenolics that possess
antioxidant activity have been characterized as phenolic acids
and flavonoids [15]. Phenolic acids have repeatedly been
implicated as natural antioxidants in fruits, vegetables, and
other plants. For example, caffeic acid, ferulic acid, and vanillic
acid are widely distributed in the plant kingdom [16].
From these results it can concluded that the crude extract
of G. changii are promising starting material for the isolation
of compound(s) with antioxidant activities. There is lack of
information available on the chemical composition of G. changii,
which exhibit antioxidant activity. Further phytochemical work
need to be done on these extracts including fractionation to
isolate active constituent and subsequent pharmacological
evaluation.