Emulsification and dilatational surface rheology of ultrasonicated milk fat globule membrane (MFGM) materials

Herein milk fat model emulsions (MFMEs) of infant formulas were prepared with ultrasonication-processed milk fat globule membrane (MFGM) materials (as well as MFGM/Lecithin blend and lecithin). The emulsion stability during storage was determined with a turbiscan. The microstructure of MFMEs was examined with confocal laser scanning microscopy (CLSM) at different pH values. Besides, the adsorption kinetics and linear/nonlinear dilatational rheological properties of oil/water interfaces were measured with a droplet tensiometer. After ultrasonication process, the average particle size of MFGM fragments decreased from 800 +/- 100 nm to 230 +/- 10 nm. The surface tension (at 100 s) of MFGM-stabilized interfaces was 17.4 mN/m (0.5 g/L), 12.9 mN/m (1.0 g/L and 2.0 g/L) and 11.0 mN/m (4.0 g/L), indicating a good emulsifying capacity of ultrasonicated MFGM materials. At neutral and acidic pH, MFMEs stabilized with MFGM dispersions or MFGM/Lecithin (1:1) at a total concentration of 4.0 g/L showed strong resistance against coalescence (CLSM). MFGM dispersions exhibited different surface rheological behaviour from pure phospholipids, proteins or a simple phospholipid/protein mixture, which suggested a heterogeneous structure of MFGM-stabilized interfaces, mainly consisting of MFGM fragment particles, interspersed with free phospholipids and proteins. These findings could provide a better understanding of emulsifying properties of MFGM materials.