Lipid domains in the milk fat globule membrane: Dynamics investigated in situ in milk in relation to temperature and time

Abstract

The microstructure of the milk fat globule membrane (MFGM) is still poorly understood. The aim of this study was to investigate the dynamics of the MFGM at the surface of milk fat globules in relation to temperature and time, and in relation to the respective lipid compositions of the MFGM from bovine, goat and sheep milks. In-situ structural investigations were performed using confocal microscopy. Lipid domains were observed over a wide range of temperatures (4-60°C). We demonstrated that rapid cooling of milk enhances the mechanisms of nucleation and that extended storage induces lipid reorganization within the MFGM with growth, leading to circular lipid domains. Diffusion of the lipid domains, coalescence and reduction in domain size were observed upon heating. Different MFGM features could be related to the respective cholesterol/sphingomyelin molar ratio in the three milk species. These structural changes may affect the interfacial properties of the MFGM, with consequences for the functional properties of fat globules and the mechanisms of their digestion.

Keywords: Cholesterol; Confocal microscopy; Lipid phase transition; Phase separation; Sphingomyelin.