Effects of natural antioxidants on iron-catalyzed lipid oxidation of structured lipid-based emulsions

The effects of iron, pH, and natural antioxidants (alpha-tocopherol, gallic acid, and quercetin) on oxidation of structured lipid-based emulsions were evaluated. Ten percent oil-in-water emulsions were formulated with a canola oil/caprylic acid structured lipid and stabilized with 0.5% whey protein isolate. The PV, anisidine values, and Totox values of emulsions stored at 50degreesC were measured over a 15-d period. Iron significantly (P < 0.05) increased lipid oxidation rates compared to control emulsions. Greater iron-catalyzed lipid oxidation occurred in the pH 3.0 emulsions compared to their pH 7.0 counterparts. Quercetin and gallic acid exhibited significant (P < 0.05) prooxidant effects on total oxidation in the pH 3.0 emulsions. Emulsions at pH 7.0 were relatively stable to oxidation throughout the storage period. Because of the ability of some of these natural antioxidants to exhibit prooxidant activity, care should be exercised when adding them to food systems containing transition metals.