Selenium content and distribution of human, cow and goat milk

Studies were undertaken to compare the content and distribution of selenium in human, cow and goat milk. Selenium content of cow milk was found to be lower than that of either human or goat milk. Regardless of source, less than 3% of total milk selenium was associated with the lipid fraction. Selenium within the 120,000 X g supernatant accounted for 72, 62 and 30% of the total in cow, human and goat milk, respectively. Glutathione peroxidase occurred in all milk samples with goat greater than human greater than cow. Percent of total peroxidase activity associated with glutathione peroxidase was 29, 27 and 65 for human, cow and goat milk, respectively. Approximately 20-28% of the selenium in milk was removed by dialysis (molecular exclusion of 6-8 kDa). After gel chromatography, 8-12 selenoprotein fractions were detected in undialyzed skim milk from each species. Most of the glutathione peroxidase activity was found in the fractions corresponding to 170 and 96 kDa in milk from all species examined. The diameric form of glutathione peroxidase also appeared in dialyzed and undialyzed milk. Distinct differences in the content and distribution of selenoproteins among these species in fresh and dialyzed milk are discussed.