The molecular structure of the surface of commercial cow's milk

Abstract

The structure of the top 100 Å of the air/liquid interface of commercial cow's milk has been determined by X-ray reflectometry. The excellent reflectivity from the surface of this dilute emulsion indicates the accessibility of other emulsion structures to the reflectivity method. The surface structure has been studied as a function of fat content (0.1–8.6 wt.%), aging and heating at temperatures up to 37°C. The interfacial structure is dominated by the presence of β-casein in this system, with a two layer model consisting of a more dense top layer, 18 Å thick, and a less dense second layer, 29 Å thick. Removal of the fat component by skimming hardly changes the surface density profile for fresh milk but clear differences are observed (presumably in the protein distribution) for aged and heated samples.