Effects of skimmed milk powder, whey or casein on tissue trace element status and antioxidant enzyme activities in rats fed control and copper-deficient diets

Abstract

Results from a number of studies have suggested that milk-based diets are particularly effective at inducing copper (Cu) deficiency. In the current study, groups (n=5) of weanling Wistar rats were provided with control (14.4 mg Cu/kg diet) and Cu-deficient (1.1 mg Cu/kg diet) diets containing skimmed milk powder (SMP; 385 g/kg), whey (270 g/kg) or casein (103 g/kg) and deionised water for 91 days after which they were exsanguinated and the liver and heart removed. Tissue Cu levels, copper-zinc superoxide dismutase (CuZnSOD) and cytochrome c oxidase activities were significantly (P<0.05) lower in control animals fed SMP compared with those fed casein. Animals fed whey exhibited intermediate values for these indices of Cu status. Although hepatic iron levels were significantly (P<0.05) lower in animals fed the SMP diet, hepatic zinc was significantly (P<0.05) higher as were the hepatic activities of glutathione reductase and the selenium-dependent glutathione peroxidase. There were no significant differences, however, in hepatic levels of thiobarbituric acid reactive substances (TBARS) among any of the experimental groups. It is proposed that these changes in tissue trace elements and enzyme activities may be related to dietary interactions involving casein and soluble milk proteins.