Influence of molecular environment on lipid oxidation of structured lipid-based model emulsions
Osborn, Hannah Terry
MetadataShow full item record
A structured lipid (SL) was enzymatically synthesized from canola oil and caprylic acid. The reaction mechanism and factors that influence oxidation of SL-based oil-in-water model emulsions were evaluated. Peroxide values, anisidine values, and TOTOX values were utilized to determine the oxidative stability of emulsions stored at 50°C. Emulsion samples were prepared by admixing emulsifiers such as sucrose fatty acid ester (SFE) or whey protein isolate (WPI) with 10 or 30% oil, and then homogenized at 1000 or 10,000 psi to form different particle sizes. Oil concentration and emulsifier type significantly affected lipid oxidation rates in the emulsions, whereas particle size had no effect. Oxidation properties of SL emulsions containing copper were evaluated at pH 3.0 and 7.0. Increased lipid oxidation occurred in the pH 7.0 emulsions. The addition of 0.5 M NaCl increased oxidation in the acidic emulsions. Both á-tocopherol and citric acid performed as antioxidants in the pH 3.0 emulsions. The effects of pH and natural antioxidants (á-tocopherol, gallic acid, and quercetin) on iron-catalyzed oxidation of SL emulsions stabilized by WPI were evaluated for 15 days of storage. Greater iron-catalyzed lipid oxidation occurred in the pH 3.0 emulsions compared to their pH 7.0 counterparts. Quercetin and gallic acids had prooxidant effects on total oxidation in the pH 3.0 emulsions. The prooxidant effect of the phenolic compounds was only observed at pH 7.0 when higher concentrations of iron (100 µM) were added to the emulsions. á-Tocopherol did not affect total oxidation in the pH 3.0 emulsions. At pH 7.0, á-tocopherol had a prooxidant effect in the presence of higher concentrations of iron (100 µM). The antioxidant efficacies of á-tocopherol, â-carotene, genistein, and daidzein in SL emulsions with no added transition metals were evaluated over a 30-day period. Less total oxidation occurred in the WPI emulsions compared to their SFE counterparts. â-carotene and soy isoflavones exhibited prooxidant activities in the SFE emulsions. Soy isoflavones also increased oxidation in WPI emulsions, but â-carotene did not exhibit prooxidant activity in these emulsions. á-Tocopherol did not affect the final TOTOX value of either WPI or SFE emulsions.