THE POSSIBLE CONFORMATIONS OF MILK-PROTEINS ADSORBED ON OIL-WATER INTERFACES

The dimensions of the milk proteins β-casein and β-lactoglobulin when adsorbed to polystyrene latices have been measured. In addition, the effect of one protein on the other in mixed adsorption systems has been measured. These studies were used as baselines to study the effect of the proteolytic enzyme, trypsin, on the adsorbed β-casein. When trypsin attacked the casein, the diameter of the latex casein complex decreased by about 20 nm. An effect of similar dimension was observed when trypsin was used to attack the β-casein in an emulsion prepared using soya oil and β-casein, indicating that the conformation of the protein in the emulsion was similar to that in the model latex system. The results on the changes in the thickness of the protein layer surrounding the latex or the emulsion can be correlated with observations of the peptides produced by the trypsin action. The decrease in the thickness of the protein layer appears to be associated with the breaking of one of two bonds in the adsorbed β-casein, which allows a possible structure of the protein on the interface to be defined. © 1991.