Selenium concentration and glutathione peroxidase activity in cow’s milk
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Samples of raw or pasteurized cow’s milk and infant formula were assayed for glutathione peroxidase (GSH-Px) activity, selenium (Se), and total protein. GSH-Px activity was detected in raw milk, but not in market-pasteurized milk or infant formula. The correlation between GSH-Px activity and Se levels was significant, even when the influence of protein level was removed. This result implies a role of GSH-Px as one of biologically active forms of Se in raw milk. Absence of GSH-Px activity in pasteurized milk and infant formula result from the heating process in these productions, because the heating of raw milk gave an irreversible inactivation of GSH-Px. Both GSH-Px activity and Se levels had significant correlation with protein level, but not so when the respective influences of Se and GSH-Px levels were removed. In raw cow’s milk, Se content was 23 ng/mL and GSH-Px activity was 20 U/mL. About 12% of Se was bound to GSH-Px, and 0.003% of protein was GSH-Px. Raw milk obtained in July contained higher levels of Se, GSH-Px, and protein than that in November. Data for cow’s milk were discussed in relation to those for human milk and those in New Zealand.
Index EntriesSelenium glutathione peroxidase raw cow’s milk pasteurized cow’s milk infant formula infant nutrition active forms of selenium correlation between glutathione peroxidase and selenium levels
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