Lipid oxidation in emulsions as affected by charge status of antioxidants and emulsion droplets

The influence of charge status of both lipid emulsion droplets and phenolic antioxidants on lipid oxidation rates was evaluated using anionic sodium d odecyl sulfate (SDS) and nonionic polyoxyethylene 10 lauryl ether (Brij)-st abilized emulsion droplets and the structurally similar phenolic antioxidan ts gallamide, methyl gallate, and gallic acid. In nonionic, Brij-stabilized salmon oil emulsions at pH 7.0, gallyol derivatives (5 and 500 mu M) inhib ited lipid oxidation with methyl gallate > gallamide > gallic acid. In the Brij-stabilized salmon oil emulsions at pH 3.0, low concentrations of the g alloyl derivatives were prooxidative or ineffective while high concentratio ns were antioxidative. In SDS-stabilized salmon oil emulsions, oxidation ra tes were faster and the galloyl derivatives were less effective compared to the Brij-stabilized emulsions. Differences in antioxidant activity were re lated to differences in the ability of the galloyl derivatives to partition into emulsion droplets and to increase the prooxidant activity of iron at low pH.