Studies on the antioxidant activity of milk caseins

The antioxidant properties of milk casein subunits (alpha-casein, beta-casein and kappa-casein) were evaluated in liposomal models. All the subunits of casein are able to inhibit Feinduced peroxidation of arachidonic acid inserted into multilamellar liposomes of dipalmitoylphosphatidylcholine (0.2mM and 0.8mM, respectively). The peroxidation was monitored as thiobarbituric acid reactive substances, and the strongest inhibitory effect occurred when 500 mug of alpha-casein were added to 0.5ml of liposomal suspension. At this concentration, peroxidation was completely inhibited in our experimental conditions (incubation for 2h at room temperature, with a mixture of ferrous sulfate and ascorbate, 50 and 500muM final concentration, respectively). The mechanisms of antioxidant action are complex, but the strongest effect is achieved by modifying the Fe2+/Fe3+ equilibrium; in fact, caseins seem to favour the autoxidation of iron, and thus inhibit lipid peroxidation.