Improved zinc bioavailability from colloidal calcium phosphate-free cow's milk

The lower bioavailability of zinc in cow’s milk compared with human milk is well documented, but the basis of this difference has yet to be adequately explained. Over 90% of the Zn in cow’s milk is associated with casein micelles and it has been shown (Lonnerdal et al., 1985) that the bioavailability to rats of this fraction of Zn is similar to that in cow’s milk, but lower than that of human skim milk. We have recently obtained evidence that 60–70% of the Zn in bovine casein micelles is associated with colloidal calcium phosphate (CCP), while the remainder is directly bound to casein (Singh et al., 1987). The object of this study was to investigate whether the CCP fraction influences the bioavailability of Zn in cow’s milk.