pH DEPENDENT EMULSIFYING PROPERTIES OF B-LACTOGLOBULIN

ABSTRACT

The emulsifying properties of B-Lactoglobulin (B-Lg) seem to be highly dependent on pH. Coarse emulsions which showed rapid creaming were obtained in the pH range 4.3 - 5.0, whereas emulsions with fine droplets were obtained at pH > 7.5. The emulsion formed at pH 2.8 showed high polydispersity and intermediate behavior. The amount of B-Lg adsorbed (2-10 mg/m²) at the oil/water interface was determined at different pH and they followed the order of pH: 5.0 > 4.3 > 2.8 > 7.6 > 9.7. Higher aggregates seem to be adsorbed near the isoelectric pH of B-Lg whereas a decrease in adsorption occured as pH was changed from the isoelectric pH. This correlated well with the known decrease in aggregative ability of B-Lg. The stabilities of these emulsions however apparently were not related to the thickness of the interfacial layer. The emulsions were found to be most stable at the alkaline pH and least near the isoelectric pH. The results did not correlate with the measured surface hydrophobicities of B-Lg at different pH. It seems that the conformational flexibility of B-Lg is most important in determining emulsion stability. Coalescence also depended on the droplet size and bigger droplets were found to coalesce faster than the smaller ones.