Effect of temperature, time, medium form and casein on lipid oxidation of polyunsaturated fatty acids in algae oil

The oxidative stability of algae oil either in solution in inert oil (OO) or present as an oil-in-water emulsion diluted in water (EW) or skim milk (EM) was investigated as a function of time. The OO and EM samples were more oxidatively stable than the EW samples. The lower oxidative stability of the EW samples was attributed to a water-soluble catalyst, probably iron. Iron is bound by milk proteins in the EM samples contributing to its higher oxidative stability. Approximately 7 mg ml^-1 casein (-25% of the level in skim milk) was shown to be sufficient to bind 100 ppm of an added iron catalyst and this level of added casein was also shown to effectively inhibit lipid oxidation in a similar sample. Further addition of casein had no effect on the amount of unbound iron or on the oxidation kinetics. We hypothesize iron binding by casein is responsible for the antioxidant properties of milk.