Comparison of the structure of micellar calcium phosphate in milk from six species by extended X-ray absorption fine structure spectroscopy

SUMMARY Extended X-ray absorption fine structure spectra, above the Ca K absorption edge, were recorded from lyophilized casein micelles obtained from the milk of cow, pig, goat, rabbit and rat. A spectrum was also obtained from the calcium phosphate prepared from the casein micelles of human milk. Comparison of these spectra showed that the short-range environment of calcium in the micellar calcium phosphate was the same in all six species. Furthermore, these spectra closely resembled that of brushite (CaHP04. 2H20). However, X-ray diffraction showed no evidence for an extensive crystal lattice in micellar calcium phosphate.