Pressurisation of raw skim milk and of a dispersion of phosphocaseinate at 9 degrees C or 20 degrees C: effects on the distribution of minerals and proteins between colloidal and soluble phases

The effects of high pressure treatments (100-300 MPa; 15 min; 9 degrees C or 20 degrees C) on the distribution of minerals and proteins of raw skim milk (RSM) and of a dispersion of industrial phosphocaseinate (PC) were studied after separation of the micellar and soluble phases by ultracentrifugation (UCF). Whatever the temperature of high pressure treatments, the pressure-induced dissociation of the casein micelles was accompanied by calcium (Ca), phosphorus (P) and casein release from the micelles. The released Ca and P were or became bound to soluble proteins since progressive increases in Ca and P concentrations were observed in the UCF supernatants of RSM and of the PC dispersion but not in the ultrafiltrates from these UCF supernatants (free of soluble proteins). Simultaneously, alpha(S1-), alpha(S2-), beta- and kappa-caseins were progressively released from the micelles, as seen by electrophoretic analysis. The pressure-induced solubilisation of alpha(S1-) and alpha(S2-)caseins, essentially located in the core of the micelles, suggests that high pressure de-stabilized micelles including their internal structure.