Appearance of submicronic particles in the milk fat globule size distribution upon mechanical treatments

In this study, we show the appearance of particles with a diameter smaller than 400 nm in the fat globule size distribution of mechanically damaged raw milks, measured by Laser Light Scattering and Dynamic Light Scattering. These submicronic particles appeared upon homogenization above 3 MPa, upon ultrasonication, and upon pumping coupled with shear greater than 50 x 10(3) s(-1). They were sometimes observed in raw milk received from the dairy plant. This may indicate bad handling or pumping, and caused the milk fat globule specific surface area to increase dramatically. Ultracentrifugal fractionation of homogenized milks revealed the presence of particles of around 100 and 400 nm that floated and sinking particles of 200-300 nm. The thickness of their surrounding layer, affected by urea treatment, was different. Hypotheses about the nature of the particles are given. The knowledge of such submicronic particles in mechanically damaged milk can bring new insights in the understanding of interactions between fat and the protein network in dairy products such as gels.