Review: Casein Micelle Structure; An Examination of Models

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Abstract
The casein micelle system of bovine milk is unique because protein aggregates of similar spherical shape but extreme variability of size are formed by the self-assembly of 3 major nonidentical subunits. The monomeric subunits appear to be approximately the same size and shape with similar amphiphilic natures, the chief difference in properties being in the carbohydrate-containing .kappa.-casein which acts to stabilize the system against precipitation by calcium ion. Micelle models with .kappa.-casein exclusvely in the interior lack a stabilization mechanism and can be eliminated. Statistical considerations of a chain polymer model also lead to its rejection. EM reveals spherical submicellar aggregates which at present can be accounted for by only 3 models. Of these 3, the experimental data are predicted only by 1 in which .alpha.s1, .beta. and .kappa.-casein subunits are associated into spherical soap-micelle-like particles with the .kappa.-casein segregated into 1 portion, giving these submicelles an amphiphilic nature. The .alpha.s1 and .beta.-caseines are hydrophobic while the .kappa.-casein portion of the submicelle surface is hydrophilic. Of particular interest is the ability of this micelle model to explain the formation of a minimum micelle which is larger than a submicellar particle.

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