Casein micelles appearance

Changes in hydration. As would be expected from many of the changes discussed above, the hydration of the casein micelles decreases with the duration of heating at 140CC. The decrease appears to be due mainly to the fall in pH - if samples are adjusted to pH 6.7 after heating, there is an apparent increase in hydration on heating. 

All the heat-induced changes discussed would be expected to cause major alterations in the casein micelles, but the most significant change with respect to heat coagulation appears to be the decrease in pH - if the pH is readjusted occasionally to pH 6.7, milk can be heated for several hours at 140°C without coagulation. The stabilizing effect of urea is, at least partially,... 

Freeman, N. W. and Mangino, M. E. 1981. Effects of ultra-high temperature processing on size and appearance of casein micelles in bovine milk. J. Dairy Sci. 64, 1772-1780. 

Casein exists in milk as a calcium caseinate-calcium phosphate complex the ratio of these components is approximately 95.2 to 4.8. The dispersed casein particles appear to be spherical m shape and of various sizes. The size distribution of the casein micelles is nol constant, hut varies with aging, heating, concentration, and other processing treatments. Processing alters ihe water-binding of casein and this in turn affects the apparent viscosity of products that contain casein Changes in hydration have not been measured quantitatively although the casein panicles of raw milk... 

Although casein micelles are more or less spherical particles, their appearance in electron micrographs is not smooth but has been lik-... 

When casein micelles are dissociated, spherical particles are observed with a size similar to the scale of the substructure. Moreover, the number of spherical particles formed by dissociation appears to correspond roughly to the number of substructural elements in the micelle. In electron micrographs of mammary gland secretory cells, some of the Golgi vesicles contain particles of a size similar to that of the particles formed by dissociation of micelles, whereas others contain larger particles. Buchheim and Welsch (1973) proposed that the smaller particles are not small micelles but subunits that are to be assembled into full-sized micelles. The envisaged sequence of assembly is as follows ... 

To elucidate the surface morphology and size distribution of pressure treated casein micelles and their irreversible fragments, AFM experiments were performed. The samples were pressure-treated for 30 min in discrete steps (0.1-400 MPa) across the dissociation transition (Figure 19.22). Instead of a continuous evolution of the structure with pressure three characteristic morphologies can be observed The native micelles, existent up to 50 MPa, appear to be composed of sub-elements, suggesting... 

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