ANTIOXIDANT/PROOXIDANT EFFECTS OF GARLIC ON LINOLEIC ACID PEROXIDATION INDUCED BY COPPER(II)

Abstract

Antioxidant compounds in food have proven health-protecting effects. Garlic (Allium
sativum) has been cultivated since ancient times and used as a spice and condiment for
many centuries. Garlic contains polyphenol and sulphur compounds, which are responsible
for its antioxidant activity.
In this study the peroxidation of linoleic acid (LA) in the presence of copper (II) [Cu(II)] ions
alone and with garlic extract was investigated in aerated and incubated emulsions at 37oC
and pH 7. Cu(II)-induced LA peroxidation followed pesudo-first order kinetics with respect
to primary (hydroperoxides) and secondary (aldehydes- and ketones-like) oxidation
products, which were determined by ferric thiocyanate (FeIII-SCN) and thiobarbituric acidreactive
substances (TBARS) methods, respectively [1]. In accordance with theoretical
expectations [2], garlic extract showed a distinct dose-dependent antioxidant effect on
inhibition of LA peroxidation with respect to hydroperoxide formation, as measured by FeIIISCN
colorimetry. Surprisingly, TBARS results were contradictory to this finding, possibly
showing the prooxidative effect of garlic extract on secondary product formation during
peroxidation. This unexpected result may stem from the generation of reactive sulfur
species (RSS) from garlic extract under the Cu(II)-induced oxidizing conditions of the
TBARS assay, enhancing (rather than retarding) sulfhydryl and LA oxidation in model
systems of lipid oxidation which is better expressed in secondary product formation [3].

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