Milk casein: inhibitor of lipoxygenase-catalyzed lipid peroxidation

Various milk products inhibited lipoxygenase-catalyzed lipid peroxidation in a model system consisting of linoleic acid, one of the two purified soybean isozymes, and the inhibitor to be tested. The inhibition by milk was not dependent on its fat content, pasteurization, dialyzation, or heating. The inhibitory effect was associated with the isoelectrically precipitated casein fraction. This effect was verified with a commercial casein product. However, on the basis of kinetic grounds neither did the absoption of substrate to casein nor did calcium cause the inhibition. Luminometric measurements showed that casein inhibition was acommpanied by a loss of chemiluminescence emission.