Several chemical and biochemical assays were used to screen
the antioxidant properties: reducing power (measuring the conversion
of a Fe3+/ferricyanide complex to the ferrous form), scavenging
activity on DPPH radicals (measuring the decrease in
DPPH radical absorption after exposure to radical scavengers),
inhibition of b-carotene bleaching (by neutralizing the linoleatefree
radical and other free radicals formed in the system which attack
the highly unsaturated b-carotene models), and inhibition of
lipid peroxidation in brain tissue (measured by the colour intensity
of MDA–TBA complex). The assays were performed in the whole
extract, since it could be more beneficial than isolated constituents;
a bioactive individual component can change its properties
in the presence of other compounds present in the extracts.
According to Liu (2003), additive and synergistic effects of phytochemicals
in fruits and vegetables are responsible for their potent
bioactive properties and the benefit of a diet rich in fruits and vegetables
is attributed to the complex mixture of phytochemicals
present in whole foods. This explains why no single antioxidant
can replace the combination of natural phytochemicals to achieve
health benefits