Cationic surfactants (S) were found to protect lipids in O/W emulsions from oxidation in some extent [1]. However, in reverse systems, micelles and microemulsions of W/O type, cationic surfactants such as alkyltrimethyl ammonium halides, alkylpyridinium salts, cause accelerated oxidation of hydrocarbons and lipids. Hydroperoxides (ROOH), which are the primary oxidation products, were found to be more surface-active than initial hydrocarbons or lipids. So, in nonpolar organic media, hydroperoxides form joint reverse micelles with S, in which ROOH decompose into free radicals with a greater rate in comparison with the bulk decomposition. It resulted in the increase of oxidation rate.

Because the most of known antioxidants (AO) include a polar group (phenolic, sulfuric, or amine) in their molecules, and physical location of AO changes in the presence of S as well as that of ROOH, this partitioning can dramatically influence AO effectiveness. The behavior of various natural (α-tocopherol, quercetin, -carotene) and synthetic (hydrogenated quinolines, nitroxyl radical, dimer 2,2´-bis[2-(p-dimethylaminophenyl)indane-1,3-dione]) antioxidants in the presence of hydroperoxides (derived from cumene and limonene oxidation) and cationic surfactants, which differ in their polar heads, counter ions, and hydrophobic parts, has been studied. Analysis of the AO consumption kinetics and AO transformation products had shown that there are two routes for AO consumption which are accelerated in the presence of cationic S: i) interaction with free radicals, derived from ROOH decomposition, catalyzed by S; ii) direct interaction with ROOH activated in joint micelles. The latter rout is not valid for completely hydrophobic β-carotene. Kinetic parameters characterizing the reaction rates and catalytic effects of S have been estimated.

Financial support of this work by the Russian Foundation for Basic Research (grant No 04-03-32569) and Scientific School (No 5236.2006.3) is gratefully acknowledged.

[1] C. D.Nuchi, P. Hernandes, J. McClements, E. A. Decker. J. Agric. Food. Chem. 2002, 50, 5445.

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