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 dodecyl sulfate (SDS) and nonionic polyoxyethylene 10 lauryl ether (Brij)-stabilized emulsion droplets and the structurally similar phenolic antioxidants gallamide, methyl gallate, and gallic acid. In nonionic, Brij-stabilized salmon oil emulsions at pH 7.0, gallyol derivatives (5 and 500 mu M) inhibited lipid oxidation with methyl gallate > gallamide > gallic acid. In the Brij-stabilized salmon oil emulsions at pH 3.0, low concentrations of the galloyl derivatives were prooxidative or ineffective while high concentrations were antioxidative. In SDS-stabilized salmon oil emulsions, oxidation rates were faster and the galloyl derivatives were less effective compared to the Brij-stabilized emulsions. Differences in antioxidant activity were related 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.