Polyphenolic
compounds, widely distributed in plant kingdom, have been exhaustively studied
for their bioactive properties specially antioxidant activity. However, they
are extensively metabolized by human organism and the resulting metabolites are
largely responsible for their effects. Furthermore, they may interact with the
endogenous antioxidant network being this possibility scarcely studied. Plasma
antioxidant network encompasses antioxidant enzymes and other substances such
as uric acid. In addition, ascorbic acid is the major compound representing
water soluble compartment both in foods and human body. The interaction of this
vitamin with phenolic compound is largely unexplored. This work aims to study
if there is a synergic effect between phenolic metabolites and main
antioxidants (uric and ascorbic acid). For this purpose, the antioxidant
activity was evaluated in terms of ORAC (oxygen radical absorbance capacity)
and FRAP (ferricreducing antioxidant power) as these tests involved either HAT
(Hydrogen Atom Transfer) or SET (Single Electron Transfer) mechanisms. Additionally,
a kinetic studied was developed to test if the rate constant presented a
synergic effect. Protocatechuic acid, 3,4-dihydroxyphenylacetic acid,
3,4-dihydroxyphenylpropionic acid and 3-hydroxyphenylacetic acid were selected
as they were metabolites of polyphenol compounds such as anthocyanins,
quercetin, neohesperidin, chlorogenic acid and hesperetin present in wines,
orange and strawberries. A synergic effect was proved for the combination of ascorbic
acid with 3,4-dihydroxyphenylacetic acid, both in terms of antioxidant activity and
potent increase of velocity of the antioxidant reaction that took place.