Pressurisation of raw skim milk and of a dispersion of phosphocaseinate at 9 degrees C or 20 degrees C: effects on casein micelle size distribution

Raw skim milk (RSM) and a dispersion of industrial phosphocaseinate (PC) were pressurised for 15 min at 100-300 MPa and 9degreesC or 20degreesC. Treatment at 100-150 MPa and 9degreesC or 20degreesC induced an increase in the hydrodynamic volume of the main micelle population (30-70 nm) of RSM and PC and a slight dissociation of the largest micelles (300-600 nm), as determined by photon correlation spectroscopy (PCS). At 9degreesC, micelle dissociation increased progressively with pressure from 150 to 300 MPa, since turbidity and micelle diameters (PCS) of both RSM and PC decreased. At 20degreesC, pressurisation at greater than or equal to 200 MPa induced both micelle dissociation and aggregation phenomena. However, dissociation predominated over aggregation, for both RSM and PC, since small-sized micelles were mainly detected either by PCS (in particle number frequency) or by atomic force microscopy. Treatment at 300 MPa and 9degreesC or 20degreesC induced irreversible changes in casein micelles, with resulting diameters half the size of the original micelles. (C) 2003 Elsevier Ltd. All rights reserved.