O/W emulsions stabilized by whey protein: Influence of heat treatment and high pressure homogenization

The objective of this work was to study the physical properties of O/W emulsions stabilized by whey proteins. Coarse emulsions were prepared with 30% (w/w) soy oil and water phase containing 7% w/w of non heated and denatured whey proteins at 70 or 90oC. These emulsions were high pressure homogenized at 250, 450 and 600 bar in order to obtain fine emulsions. Creaming kinetics of the emulsions obtained after and before high pressure homogenization was measured. At equilibrium conditions of phase separation it was also evaluated the droplet size distribution and flow curves of the separated phases. The effect of highpressure homogenization on the protein denaturation degree were evaluated by polyacrylamide gel electrophoresis (PAGE) and associated with emulsion properties. A cream phase separation was observed after 1 day of coarse emulsions prepared with non heated and treated at 70oC and after 15 days for 90oC heat denatured proteins. After pressure homogenization all emulsions were stable with no phase separation even after 30 days of observation. Fine emulsions showed the smallest droplet size and Newtonian flow behaviour with non heated protein in contrast to all emulsions containing heat denatured proteins that showed shearthinning, thixotropic behavior and gel formation. The SDS PAGE of non-heat treated emulsions showed whey proteins unfolding and some aggregation as a consequence of high-pressure homogenization. It was observed the presence of high molecular weight protein aggregates stabilized for disulfide bonds and concentrated into the cream phase, mainly in fine emulsions homogenized at 250 bar. However, the increase in pressure homogenization caused the disruption of these aggregates, particularly of β-lactoglobulin. The decrease in the particle size in fine emulsions homogenized at 450 bar was related to disruption of these aggregates.