Antioxidant activity of alpha-tocopherol and Trolox in different lipid substrates: Bulk oils vs oil-in-water emulsions

This study was aimed at evaluating the antioxidant effectiveness of alpha-tocopherol and its water-soluble analogue, Trolox, in different lipid systems. The oxidative stability of lipids in bulk and emulsion systems at 37 degrees C decreased in the order corn oil triglycerides > methyl linoleate > linoleic acid. In both bulk and emulsified linoleic acid, Trolox was a better inhibitor of hydroperoxide formation and decomposition than alpha-tocopherol. However, in bulk methyl linoleate and corn oil triglycerides, although Trolox was a better inhibitor of hydroperoxide formation, in emulsions, alpha-tocopherol was a better inhibitor of both the formation and decomposition of hydroperoxides. In emulsified methyl linoleate and corn oil, the partition coefficients of Trolox between lipids and water at high concentrations were not affected by Tween 20, and the antioxidant activity of Trolox decreased because it partitioned into the water phase and Tween 20 micelles. In contrast, in linoleic acid emulsified with Tween 20, the formation of mixed micelles of linoleic acid and Tween 20 increased the percentage of Trolox in the water phase and Trolox was more effective as an antioxidant than alpha-tocopherol because it diffused in the water phase and into mixed micelles. The physical states of lipid systems affect the distribution of antioxidants and thus significantly influence their antioxidant behavior. Because Linoleic acid has unique physical properties in aqueous micelles, it may not be a valid substrate for evaluating food antioxidants.