Maximum disjoining pressure in protein stabilized concentrated oil-in-water emulsions

A model for the prediction of the equilibrium profile of film thickness and continuous phase liquid holdup profile in a concentrated oil-in-water (O/W) emulsion is proposed. This model is employed to infer the maximum disjoining pressure in a concentrated corn oil-in-water emulsion stabilized by bovine serum albumin (BSA) from the experimental measurements of different proportions of oil, polyhedral O/W foam, and aqueous layers at different centrifugal accelerations. The inferred maximum disjoining pressures were found to be higher at higher concentrations of BSA, lower ionic strengths as well as at pH values farther away from pI. The predicted variations of disjoining pressure with film thickness for a concentrated O/W emulsion stabilized by BSA exhibited two maxima due to steric and electrostatic interactions, respectively. The experimental maximum disjoining pressures for toluene-in-water emulsion stabilized by BSA were found to be about two to three times the predicted maxima due to steric interactions but were two to three orders of magnitude higher than the maxima due to electrostatic interactions, thus indicating that steric interaction is the dominant stabilizing mechanism. The discrepancy between the experimental and predicted maximum disjoining pressures is believed to be mainly due to lack of information with regard to the thickness of the adsorbed protein layer at the oil—water interface.