The physical location of antioxidants in oil-in-water emulsions can have significant influence on their free radical scavenging activity and ability to inhibit lipid oxidation. We aimed to determine the effect of the surfactant concentration on the partitioning behavior of tocopherols (α, γ, and δ) in oil-in-water emulsions. Tween 20 (0.1, 0.5, and 1%) increased the partitioning of the tocopherols into the aqueous phase via the formation of Tween 20-tocopherol comicelles. Partitioning behavior of antioxidants was dependent upon the number of methyl groups and, thus, polarity of the tocopherols. δ-Tocopherol (one methyl group) exhibited the most partitioning into the aqueous phase, while α-tocopherol (three methyl groups) had the lowest partitioning. Lipid oxidation studies showed that the antioxidant activity of δ- and α-tocopherols was enhanced by adding Tween 20 to oil-in-water emulsions. This work suggests that surfactant micelles could increase the antioxidant activity of tocopherols by changing their physical location.
Keywords: antioxidant; lipid oxidation; oil-in-water emulsion; surfactant; tocopherol.