The antioxidant mechanisms of whey proteins in a Tween 20-stabilized salmon oil-in-water emulsion were investigated. The antioxidant activity of the high molecular weight (HMW) fraction of whey from pasteurized milk was found to increase with concentration, as determined by its ability to inhibit TBARS and lipid peroxide formation. The ability of sulfhydryl-blocked whey to inhibit TBARS formation was reduced 60% compared to the HMW fraction alone at 7 days of storage. HMW fraction was able to scavenge peroxyl radicals, with scavenging decreasing approximately 20% when sulfhydryls were blocked. HMW fraction was able to chelate iron away from the surface of negatively charged BSA-stabilized emulsion droplets, indicating that the whey proteins were able to chelate iron. A better understanding of the mechanisms by which whey proteins inhibit lipid oxidation could increase the use of whey proteins as food antioxidants.