Casein aggregation

Helstad, K., Rayner, M., van Vliet, T., Paulsson, M., and Dejmek, P. (2007). Liquid dropletlike behaviour of whole casein aggregates adsorbed on graphite studied by nanoindentation with AFM. Food Hydrocolloids 21, 726-738. 

K-casein aggregates in aqueous medium are more complicated than those of p-casein, being composed of star-like sub-micelles, where each submicelle contains nine K-casein chains and the total degree of association may reach about 140 (Thum el al., 1987a). Payens and Vreeman (1982) used sedimentation measurements to infer a critical micelle concentration for K-casein of 0.5 mg/ml. 

It is pertinent to note here the observed increase in the value of the structure-sensitive parameter p from 1 to 2. This implies that the architecture of the sodium caseinate aggregates, as modified by interaction with the surfactant, becomes generally more open, despite the inferred collapse of their constituent protein nanoparticles. In contrast, a shell-like aggregation structure can be inferred for the self-assembly of sodium caseinate as a result of its interaction with the non-ionic surfactant PGE (this surfactant is based on a mixture of the esters of stearic and palmitic acids in chemical combination with polyglycerol (Krog, 1997)). 

Ruis, H.G.M., Venema, P., van der Linden, E. (2007). Relation between pH-induced stickiness and gelation behaviour of sodium caseinate aggregates as determined by light scattering and rheology. FoodHydrocolloids, 21, 545-554. 

Vetier, N., Desobry-Banon, S., Ould Eleya, M.M., Hardy, J. (1997). Effect of temperature and acidification rate on the fractal dimension of acidified casein aggregates. Journal of Dairy Science, 80, 3161-3166. 

Sejersen, M.T., Salomonsen, T., Ipsen, R., Clark, R., Rolin, C., Engelsen, S.B. (2007). Zeta potential of pectin-stabilized casein aggregates in acidified milk drinks. International Dairy Journal, 17, 302-307. 

The most thorough study of the formation of artificial casein micelles is that of Schmidt and co-workers (1977 1979 Schmidt and Koops, 1977 Schmidt and Both, 1982 Schmidt and Poll, 1989), who not only studied the properties of the casein aggregates but also attempted to relate them to the solution conditions under which they were formed. In the precipitation of calcium phosphate from solution, the means by which solutions are mixed together is of crucial importance Schmidt et al. (1977) described a method in which four solutions were pumped simultaneously into a reaction vessel while keeping the pH constant. As a result of careful, slow mixing, the reproducibility of the size distributions of particles, measured by electron microscopy on freeze-fractured and freeze-etched specimens, was very good. In the first series of experiments, the objective was to produce milk like concentrations of the most important ions while... 

At pH 5.2, i.e., the pH at the onset of gelation, a heterogeneous distribution of casein aggregates (composed of aggregated casein micelles and new casein particles) with a range of sizes is observed. 

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