Changes in the physico-chemical properties of casein micelles during ultrafiltration combined with diafiltration

The objective of this work was to determine if after membrane processing, the physical properties of casein micelles change. Milk was concentrated by ultrafiltration, and also subjected to various levels of diafiltration, by addition of water to the retentate. After the membrane concentration process, the retentates were diluted back to their original concentration, to study their physico-chemical properties. For better comparison, all the samples were dialyzed against the original milk, to obtain similar serum compositions. For the first time, the effect of different levels of diafiltration was studied. Diafiltration induced losses of colloidal calcium phosphate and caused changes in the turbidity parameter (1/l*) measured by light scattering, as well as in the ultrasonic properties (velocity and attenuation) of the casein micelles. When tested in a similar serum environment, the reconstituted micelles after diafiltration showed a lower susceptibility to aggregation and the rennet induced gels had a lower storage modulus than those formed with the original milk, at the same protein concentration. This work brings for the first time evidence of the differences in the physical properties of the casein micelles as a function of membrane processing history.