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 formany centuries. Garlic contains polyphenol and sulphur compounds, which are responsiblefor its antioxidant activity.In this study the peroxidation of linoleic acid (LA) in the presence of copper (II) [Cu(II)] ionsalone and with garlic extract was investigated in aerated and incubated emulsions at 37oCand pH 7. Cu(II)-induced LA peroxidation followed pesudo-first order kinetics with respectto primary (hydroperoxides) and secondary (aldehydes- and ketones-like) oxidationproducts, which were determined by ferric thiocyanate (FeIII-SCN) and thiobarbituric acidreactivesubstances (TBARS) methods, respectively [1]. In accordance with theoreticalexpectations [2], garlic extract showed a distinct dose-dependent antioxidant effect oninhibition of LA peroxidation with respect to hydroperoxide formation, as measured by FeIIISCNcolorimetry. Surprisingly, TBARS results were contradictory to this finding, possiblyshowing the prooxidative effect of garlic extract on secondary product formation duringperoxidation. This unexpected result may stem from the generation of reactive sulfurspecies (RSS) from garlic extract under the Cu(II)-induced oxidizing conditions of theTBARS assay, enhancing (rather than retarding) sulfhydryl and LA oxidation in modelsystems of lipid oxidation which is better expressed in secondary product formation [3].