The biological roles of casein molecules include the sequestration of amorphous calcium phosphate, as calcium phosphate nanoclusters (CPN), to form stable complexes in milk. Here, the most amphiphilic of the calcium binding caseins, �-casein, play a particular important role. The adsorption of �-casein is of relevance for biomineralisation and has been studied by ellipsometry, surface force measurements, neutron reflectivity, and wetting force measurements.The common model emerging from these studies is that the protein forms a monolayer at hydrophobic surfaces, with the �hydrophobic� part of the protein sticking to the surface and the highly charged N-terminal portion protruding into the solution.  On hydrophilic surfaces the protein is suggested to adsorb as micellar type of aggregates. These observations can be related to the �-casein's ability to self-assembly in bulk solution. Recent results on the co-adsorption of calcium phosphate nanoclusters (CPN) and �-casein at hydrophobized and hydrophilic silica-water interfaces will be discussed. The structural characteristics of the adsorbed layer, determined by neutron reflectivity showed that the calcium phosphate nanoclusters profoundly affected the rate of adsorption and structure of the interface compared to the adsorption of �-casein alone. For the hydrophobic interface the effects depended on the point at which the nanoclusters were added. It is proposed that the nanoclusters become surface active because whole �-casein molecules can replace one or more of the hydrophilic peptides in the shell of the nanoclusters.

Self-assembly of caseins and their interaction with interfaces

243rd National Meeting (2012)

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