CASEIN MICELLES - DIFFUSIVITY AS A FUNCTION OF RENNETING TIME

The diffusivity of kappa-casein micelles in renneted skim milk was measured by dynamic light scattering. By use of the Stokes-Einstein relation, the apparent particle radius was calculated. As a result of the enzymatic proteolysis of the kappa-casein peptides that provide the steric stabilization of the casein micelles, the hydrodynamic radius diminishes. However, as a result of the increasing attractive interactions the apparent micelle radius increases. Depending on the length scale, one can distinguish collective diffusion and self-diffusion. For both phenomena, theoretical descriptions exist. Combining this theory with an adhesive-hard-sphere model for the casein micelles allows a quantitative prediction of the experimental results. In this way a clear insight into the initial stages of the renneting proces is gained and this can be used for further modeling and control of the cheesemaking process.