Impact of Surface Active Compounds on Iron Catalyzed Oxidation of Methyl Linolenate in AOT–Water–Hexadecane Systems

Abstract

Edible oils contain minor surface active components that form micro-heterogeneous environments, such as reverse micelles, which can alter the rate and direction of chemical reactions. However, little is known about the role of these micro-heterogeneous environments on lipid oxidation of bulk oil. Our objective was to evaluate the ability of water, cumene hydroperoxide, oleic acid, and phosphatidylcholine to influence the structure of reverse micelles in a model oil system: sodium bis(2-ethylhexyl) sulfosuccinate (aerosol-OT; AOT) in n-hexadecane. The influence of reverse micelle structure on iron catalyzed lipid oxidation was determined using methyl linolenate as an oxidizable substrate. The size and shape of the reverse micelle were investigated by small-angle x-ray scattering, and water contents was determined by Karl Fischer titrations. Lipid hydroperoxides and thiobarbituric acid reactive substances were used to follow lipid oxidation. Our results showed that AOT formed spherical reverse micelles in hexadecane. The size of the reverse micelles increased with increased water or phosphatidylcholine concentration, but decreased upon addition of cumene hydroperoxide or oleic acid. Iron catalyzed oxidation of methyl linolenate in the reverse micelle system decreased with increasing water concentration. Addition of phosphatidylcholine into the reverse micelle systems decreased methyl linolenate oxidation compared to control and reverse micelles with added oleic acid. These results indicate that water, cumene hydroperoxide, oleic acid, and phosphatidylcholine can alter reverse micelle size and lipid oxidation rates. Understanding how these compounds influence reverse micelle structure and lipid oxidation rates could provide information on how to modify bulk oil systems to increase oxidative stability.