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J. Cosmet. Sci.J 55, 281-289 (May/June 2004) Investigation of atmospheric oxidation of propyl gallate in an anionic surfactant system in the absence and presence of ascorbic acid M. SZYMULA, Department of Radiochemistry & Colloid Chemistry, Faculty of Chemistry} Maria Curie-Sktodowska University, M. Curie-Sktodowska Sq. 3J 20-031 Lublin} Poland. Accepted for publication March I SJ 2004. Synopsis The antioxidant efficiency of two hydrophilic species, ascorbic acid (AA) and propyl gallate (PG), in an anionic surfactant system are studied. Ascorbic acid and propyl gallate are dissolved/solubilized in a microemulsion formed by water, pentanol, and sodium dodecyl sulfate. The determination of propyl gallate decomposition/oxidation kinetics shows enhanced oxidation of PG with increasing pentanol concentration in the system. When ascorbic acid and propyl gallate are both present in water, in surfactant aqueous solution, and in the studied microemulsion systems, the molecular complex AAPG is formed. After some time the complex decomposes. INTRODUCTION Microemulsions and liquid crystals are the most popular delivery systems for functional cosmetics and pharmaceutical ingredients. Aggregated systems of self-assembling mol­ ecules are able to prevent chemical degradation of the active ingredient. We examined the phase behavior of the system stabilized by sodium dodecyl sulfate (SDS). Studies of the pseudoternary phase diagram of the system comprising SDS as surfactant, water, and pentanol as cosurfactant showed the existence of oil-in-water and water-in-oil microemulsion regions connected by a narrow channel of bicontinuous structure and a lamellar region (1-3). A medium-chain-length alcohol as cosurfactant (e.g., pentanol) plays a crucial role in the formation, phase behavior, and properties of microemulsions (4). We are concerned with an effect of the colloidal properties of micellar systems on the activities of different types of antioxidants (3,5-8). Apart from the kind of micellar system used, the antioxidant molecule polarity was the main property that changed in our experiment. The antioxidants examined were ascorbic acid (AA, vitamin C, H2A), a-tocopherol (a-T, vitamin E), and �-carotene. Their polarity (water solubility, which 281