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 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. milk fat globule / particle size distribution / laser light scattering / homogenization / shear stress / mechanical treatment / casein micelle Rsum -Apparition de particules submicroniques dans la distribution de taille de globules gras du lait soumis des traitements mcaniques. Dans cette tude, nous montrons par granulomtrie laser l'apparition de particules de diamtre infrieur 400 nm dans la distribution de taille des globules gras de laits crus qui ont t endommags mcaniquement. Ces particules submicroniques apparaissent lors d'une homognisation suprieure 3 MPa, d'une exposition aux ultrasons et lors d'un pompage coupl un cisaillement suprieur 50 10 3 s -1 . Elles apparaissent aussi parfois dans du lait cru de grand mlange reu d'une laiterie industrielle : cela peut indiquer que le lait a subi des pompages et un transport indadapts et entrane une augmentation importante de la surface spcifique des globules gras du lait. Un fractionnement par ultracentrifugations de laits homogniss montre l'existence de particules autour de 100 et 400 nm qui crment et des particules de 200-300 nm qui