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

Abstract

Antioxidant compounds in food have proven health-protecting effects. Garlic (Alliumsativum) 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].