oxidants and antioxidants in biology - Oxygen Club of California

Effect of ferric ions on the antioxidant activity of
olive polyphenols
FÁTIMA PAIVA-MARTINS A , MICHAEL H. GORDON* , B
a CIQ, Dep. de Química, Faculdade de Ciências, Universidade do Porto, R. do
Campo Alegre, nº 687, 4169-007 Porto, Portugal
b School of Food Biosciences, The University of Reading, Whiteknights PO Box
226, Reading RG6 6AP, UK
The effects of five phenolic compounds, occurring in olives
and virgin olive oil, namely oleuropein, hydroxytyrosol, hydroxytyrosol
acetate and 3,4-dihydroxyphenylethanol-elenolic acid (3,4-
DHPEA-EA) and 3,4-dihydroxyphenylethanol-elenolic acid dialdehyde
(3,4-DHPEA-EDA), on the oxidative stability of stripped
olive oil and stripped olive oil-in-water emulsions were studied in
the presence or absence of ferric chloride. The addition of phenolic
compounds in bulk oil, even in the presence of ferric ions, significantly
extended the induction time of lipid oxidation. The effect of
the presence of ferric ions on the antioxidant activity was more severe
for compounds with lower antiradical power and more reducing
capacity.
In emulsions, oleuropein and hydroxytyrosol enhanced the
prooxidant effect of ferric chloride at pH 3.5 and pH 5.5. 3,4-
DHPEA-EDA reduced the prooxidant effect of ferric chloride at pH
5.5 and pH 7.4 but at pH 3.5 prooxidant effects were evident at
higher phenol concentration. 3,4-DHPEA-EA reduced the prooxidant
effect of ferric ions at all pH values tested. In this system, in
addition to the antiradical power and reducing capacity, the stability
of chelates formed play an important role on the antioxidant capacity
of these compounds in the presence of ferric ions.
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