Calcium phosphate micellar

These different casein monomers combine with calcium phosphate to form discrete particles on the nano-size scale. The phosphoserines of the caseins are seemingly clustered for the purpose of linking within the micelle to putative calcium phosphate microcrystallites, also known as nanoclusters (Holt, 1992 Home, 1998, 2002, 2003, 2006 Holt et al., 2003 Home et al., 2007). Structural evidence for the existence of such nanoclusters has come from neutron and X-ray scattering (de Kruif and Holt, 2003 Holt et al., 2003 Pignon et al., 2004 Marchin et al., 2007). The presence of nanoclusters allows native casein micelles to be effective natural suppliers of essential calcium salts in the human diet in a readily assimilated functional form. Protein-nanocluster interactions are the central concept of the cross-linking mechanism in Holt s model of casein micellar assembly (Holt et al., 2003 de Kruif and Holt, 2003). Any analogy with conventional soap-like micelles is considered to be... 

Salt and Ester P Composition of Casein Micelles and Micellar Calcium Phosphate... 

The amino acid and ionic composition of micellar calcium phosphate can be used to estimate the degree of protonation of the phosphate groups. By summing the positive and negative charges, a charge... 

Griffin et al. (1988) reported that when the colloidal calcium phosphate was depleted, by addition of a EDTA solution to a micellar dispersion, there was essentially no selective dissociation of the individual caseins. This difference from the results of Holt et al. (1986) could reflect a difference of methodology. The method of Griffin et al. (1988) could bring about an almost complete and therefore non-selective disintegration of some micelles in the immediate vicinity of the added EDTA while leaving others virtually intact. In the dialysis method of Holt et al. (1986), the free Ca2+ concentrations is never depressed and hence micelles dissociate only because of the solubi-lazation of the colloidal calcium phosphate. 

It is now believed that the coUoidal micelles are formed from sub-miceUar casein units which are held together by Ca + and linked through the ester phosphate groups to regions of calcium phosphate of one kind or another. The spherical micelles are 120 nm diameter and the sub-micellar units are 10-20 nm diameter. Reported molecular weights of the sub-micelles lie in the range 250,000-1,000,000. They are believed to contain 25-30 casein molecules with apk varieties in about the same proportions as found for whole milk. 

Reported studies on native casein micelles have indicated that P NMR spectroscopy was useful to determine the nature of phosphate molecules as phosphoserins and inorganic calcium phosphate" . Quantitative assessment of the various micellar components was also probed by Rasmussen et al (1997). Nevertheless, in the case of cheeses which are highly-hydrated and heterogeneous samples, investigations by high-field NMR appear as a true challenge. The NMR technique implies some evident technical limitations as for instance, the sample preparation (introduction in NMR tubes or rotor), but NMR is also dependant on the intrinsic sample properties such as heterogeneity and multi-phase liquid/solid nature which induce some susceptibility effects and the presence of anisotropic interactions. The feasibility of the P NMR spectroscopy to study cheeses has been first probed on the milk powder, main component of these dairy products. 

It is well known that the addition of soluble calcium salts reduces the heat stability of milk, whereas the addition of calcium complexing agents with the appropriate control of pH improves heat stability. Phosphates and citrates have often been used to increase the heat stability of concentrated milks (Augustin and Clarke, 1990 Pouliot and Boulet, 1991 Sweetsur and Muir, 1982a). A reduction in activity by the addition of these salts contributes to the improved heat stability of concentrated milks, but the effects of salts on the equilibrium of caseins between the serum and micellar phases of milk also affect heat stability. 

Acylation affects the casein micelles of milk. The main effects are increased dissolution of the calcium and phosphate from the micelle and increased solubilization of caseins as a consequence of acylation (Vidal et al., 2002). As the equilibria of caseins between the micellar and serum phases are known to affect a number of functional properties (e.g., gelation, emulsification), it may be expected that acylation will affect functionality. 

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