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

Abstract

Abstract Raw skim milk (RSM) and a dispersion of industrial phosphocaseinate (PC) were pressurised for 15 min at 100–300 MPa and 9°C or 20°C. Treatment at 100–150 MPa and 9°C or 20°C 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 9°C, micelle dissociation increased progressively with pressure from 150 to 300 MPa, since turbidity and micelle diameters (PCS) of both RSM and PC decreased. At 20°C, pressurisation at ⩾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 9°C or 20°C induced irreversible changes in casein micelles, with resulting diameters half the size of the original micelles.