Nanoclusters, calcium phosphate

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... 

FIGURE 7.2 Calcium phosphate nanocluster model of a casein micelle. Substructure arises from the calcium phosphate nanocluster-like particles in the micelles (dark spheres). There is a smooth transition from the core to the diffuse outer hairy layer that confers steric stability on the micelle. (Courtesy of Holt and Roginski, 2001.)... 

Another example of oxide—phosphate synergic interaction is the immobilization of calcium phosphate nanoclusters into sol—gel Ti02 [26]. 

Caseins are similar in structure and found in milk as nanoparticles called micelle. Casein micelles are composed of several thousand molecules, bonded via calcium phosphate nanoclusters. All other proteins present in milk are grouped together and termed whey proteins. The primary whey protein in cow milk is ) -lacto-globulin. A very interesting feature of milk proteins is their potential as nanovehicles for bioactive compounds. The potential of deUvering high nutritional value components by milk proteins has opened new opportunities in food and nonfood industrial sectors. Fortunately, the huge volume of milk production enables the manufacture of non-expensive purified proteins possible [77]. 

Gel-like structure is another model that states casein molecules are located in micelle in a tangle manner and comphcated situation, forming a sphere. In addition, /c-caseins stretch out of the micelle and form a hairy layer. In this model, which was proposed by Holt [35], calcium phosphate nanoclusters act as linkers of thread-like casein monomers by cross-linking [2, 29, 36, 37]. In this model the calcium phosphate nanoclusters are responsible for linking the caseins molecules to each other whereas in previous proposed model nanoclusters are the joiners for submicelles. 

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