Antioxidative activity of urate in bovine milk

The antioxidative effects of urate on peroxidase-induced protein oxidation and light-induced riboflavin degradation and lipid oxidation in whole milk were studied. In addition, experiments using ascorbate were conducted to di rectly compare the antioxidative activity of urate and ascorbate. The prese nce of urate and/or ascorbate (10-30 mg/L) lowered peroxidase-induced forma tion of dityrosine by 44-96% in unpasteurized whole milk. No synergistic ef fect of urate and ascorbate on peroxidase-induced dityrosine formation was registered, but merely an additive effect. Light exposure of pasteurized wh ole milk showed that ascorbate was oxidized at the expense of urate, which indicated ascorbate-mediated recycling of the urate radical. Moreover, both urate and ascorbate (30 mg/L) retarded light-induced lipid oxidation in pa steurized whole milk as measured by formation of lipid hydroperoxides with urate being the most effective (28% reduction in Lipid hydroperoxides) comp ared with ascorbate (14%). Finally, addition of urate or ascorbate (300 mg/ L) to pasteurized whole milk showed a slight protective effect against ligh t-induced degradation of riboflavin with urate being the most effective.