Factors affecting the stability of O/W emulsion in BSA solution: stabilization by electrically neutral protein at high ionic strength.

Bovine serum albumin (BSA) was used as an emulsifier to disperse corn oil in aqueous media with various protein concentration, pH, and ionic strength. Quantitative estimation was made on the homogenizing activity of BSA and dispersion stability of oil particles by measuring particle size, turbidity, and creaming rate. Dispersion stability strongly depended on pH and became a minimum around pH 5.0 which was the isoelectric point of BSA. The interfacial tension between BSA solution and corn oil was minimized at pH 5.0. Interesting results were obtained concerning the ionic-strength dependence of stability. When the ionic strength was set below 30 mM, the emulsions became more stable with the increase of BSA concentration at pH 6.7 but the opposite behavior (enhanced destabilization) was confirmed at pH 5.0 with the BSA content. In high ionic strength conditions (ca. > or = 80 mM NaCl), however, BSA-stabilized emulsions became fairly stable even at pH 5.0. These results suggested that BSA molecules having no net charge induced some attractive interactions (e.g., bridging or depletion) in low ionic strength but steric stabilization in high ionic strength, respectively.