Casein Micelles at Non-Ambient Pressure Studied by Neutron Scattering

The disruption of casein micelles, as found in cows’ milk, was investigated at pressures up to 300 MPa with small angle neutron scattering (SANS). From the decrease of the overall level of scattering, the expected disruption of the micelles was concluded. This disruption was incomplete, and stable at 300 MPa, independent of pressure history. At intermediate pressures, pressure history, (step-wise increase from ambient, or stepwise decrease from 300 MPa) had a strong effect on the scattering patterns. At high pressures, where scattering patterns were sufficiently structured, sizes of scattering entities could be deduced. The scattering entities at high pressure showed a bimodal size distribution. One size was outside the window of quantitative observation and may be similar to that of the native micelles or residual fat globules, the other smaller size, found under high pressure is in the 10–20 nm range and may correspond clusters of about 10 separate casein molecules. The pressure-induced disruption of casein micelles is partially reversed after return to ambient pressure, but small scattering entities, absent before pressure treatment, remain.