Antioxidative factors in milk

Lipid auto-oxidation in milk is affected by a complex interplay of pro- and antioxidants. Several of these compounds are also important nutrients in the human diet and may have other physiological effects in the gastrointestinal tract and other tissues. Among antioxidative enzymes superoxide dismutase catalyses the dismutation of superoxide anion to hydrogen peroxide. The degradation of hydrogen peroxide can be catalysed by catalase and the selenoprotein glutathione peroxidase. The latter enzyme can also degrade lipid peroxides. Lactoferrin may have an important role by binding pro-oxidative iron ions. The occurrence of different forms of these antioxidative proteins in milk and available data on their functional role are reviewed. More remains to be learnt of individual compounds and as an example the potential role of seleno compounds in milk is virtually unknown. Antioxidative vitamins in milk can provide an important contribution to the daily dietary intake. Moreover vitamin E and carotenoids act as fat-soluble antioxidants, e.g. in the milk fat globule membrane, which is regarded as a major site of auto-oxidation. Vitamin C is an important water-soluble antioxidant and interacts in a complex manner with iron and fat-soluble antioxidants. The concentrations of these compounds in milk are affected by cow feeding rations and milk storage conditions. Since milk contains a number of antioxidants many reactions are possible and the specific function of each antioxidant cannot easily be defined. There are indications that other compounds may have antioxidative function and measurement of total antioxidative capacity should be a useful tool in evaluating their relative roles.