Colloidal calcium phosphates in casein micelles studied by slow-speed-spinning 31P magic angle spinning solid-state nuclear magnetic resonance

The composition of bovine casein micelles was analyzed by P-31 magic angle spinning solid-state nuclear magnetic resonance spectroscopy. By looking at isotropic and anisotropic P-31 chemical shift parameters, resonance line shapes, the combination of single-pulse and H-1 to P-31 cross-polarization spectra, and comparison with spectra for various model compounds combined with multiple-component simulation and iterative fitting procedures, we were able to identify and quantify a variety of inorganic and organic phosphates in the micelles. These include phosphates from mobile and immobile inorganic hydroxyapatite-type phosphates as well as phosphates from kappa -casein and the Ca2+-binding phosphoserines from alpha (s1)-, alpha (s2)-, and beta -casein. This information is discussed in relation to previous knowledge and various models for the colloid formation.