Casein micelles hairy layer

Van der Waals forces There has been some success in relating these forces to micellar stability. However, the steric stabilization has been found to be also of some importance. Especially, the hairy layer interferes with the interparticle approach. There are several factors that will affect the stability of the casein micelle system ... 

Historically, ideas of casein micelle structure and stability have evolved in tandem. In the earlier literature, discussions of micellar stability drew on the classical ideas of the stability of hydrophobic colloids. More recently, the hairy micelle model has focused attention more on the hydrophilic nature of the micelle and steric stabilization mechanisms. According to the hairy micelle model, the C-terminal macropeptides of some of the K-casein project from the surface of the micelle to form a hydrophilic and negatively charged diffuse outer layer, which causes the micelles to repel one another on close approach. Aggregation of micelles can only occur when the hairs are removed enzymatically, e.g., by chymosin (EC 3.4.23.4) in the renneting of milk, or when the micelle structure is so disrupted that the hairy layer is destroyed, e.g., by heating or acidification, or when the dispersion medium becomes a poor solvent for the hairs, e.g., by addition of ethanol. 

Thus, the NMR spectra support the contention that the hairy layer of micelles is formed predominantly from the C-terminal peptide of a proportion (possibly as much as half) of the K-casein molecules. However, the mobile fraction will include contributions from any caseins that have dissociated from the micelles as a result of suspension in the 2H20 buffers and any mobile side chains inside the micelle, as well as the mobile external surface fraction. 

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.)... 

K-casein on the other (31). Moreover, these simple systems show appreciable differences from native casein micelles in their response to Ca ". In casein micelles, the binding sites for Ca appear to be some distance from the surface of the hairy layer (13) and the same argument can be presumably used for the individual caseins, and show that the calcium binding sites in the synthetic particles are within the surface of shear. On the other hand, the binding of Ca may cause conformational changes in the interfacial layer. 

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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