Composition and Structure of Fat Globule Surface Layers in Recombined Milk

Protein coverage, composition and structure of surface layers of fat globules in recombined milk were determined. Average protein load was ∼6 mg/m 2 fat surface. Both casein and whey proteins were present in the fat globule surface layer, with casein adsorbed in preference to whey proteins and α s (α sl +α s2 )‐casein adsorbed in preference to β‐casein. Transmission electron microscopy showed that the surface layer of fat globule was made up of casein micelles, fragments of casein micelles and a thin layer of protein, possibly whey proteins. Experiments with surface layers that had been dispersed in EDTA showed that the extent of dissociation of caseins followed the order: β‐casein > α s ‐casein ≦ K‐casein, suggesting that most of the K‐casein was probably associated directly with the fat surface.