29B-20

The food industry would like to incorporate structured lipids into their product formulations.  However, a better understanding of the reaction mechanism and factors that influence their oxidation in food matrices is needed.  Lipids often exist as oil-in-water emulsions in foods, and therefore, their oxidation properties should be examined in this medium. 

Our objective was to evaluate the effects of iron (50 and 100 μM), pH (3.0 and 7.0), and natural antioxidants (α-tocopherol, gallic acid, and quercetin) on oxidation of structured lipid-based emulsions. 

Ten percent oil-in-water emulsions were formulated with a canola oil/caprylic acid structured lipid and stabilized with 0.5% whey protein isolate.  Antioxidants were added at 0.02% weight of the oil.  The peroxide values, anisidine values, and TOTOX values of emulsions stored at 50°C were measured over a 15-day period. 

Iron significantly (p < 0.05) increased lipid oxidation rates compared to control emulsions that contained no added metals.  Low pH further increased the iron-catalyzed lipid oxidation.  α-Tocopherol did not affect total oxidation in emulsions at pH 3.0, or at pH 7.0 in the presence of lower concentrations of iron (50 μM).  However, at pH 7.0 in the presence of greater concentrations of iron (100 μM), α-tocopherol had a prooxidant effect.  Quercetin and gallic acid had a significant (p < 0.05) prooxidant effect on total oxidation in the pH 3.0 emulsions and at pH 7.0 when higher concentrations of iron (100 μM) were added to the emulsions. 

The results of this study will help in optimizing product formulations and understanding the complexity of lipid oxidation in real food emulsions prepared with canola oil/caprylic acid structured lipids.  Due to the ability of α-tocopherol, gallic acid, and quercetin to exhibit prooxidant activity under some conditions, care should be exercised when adding them to food systems containing transition metals.