Influence of glycerol and sorbitol on thermally induced droplet aggregation in oil-in-water emulsions stabilized by β-lactoglobulin

The influence of polyol cosolvents (glycerol and sorbitol) on the flocculation stability of hydrocarbon oil-in-water emulsions stabilized by a globular protein was examined. Salt (150 mM NaCl) and polyols (0-40 wt%) were added to n-hexadecane oil-in-water emulsions stabilized by β-lactoglobulin (β-Lg, pH 7.0) either before or after isothermal heat treatments (30-90 °C for 20 min). When salt was added to emulsions before heat treatment, appreciable droplet flocculation was observed below the thermal-denaturation temperature of the adsorbed β-Lg (Tm∼70 °C), and more extensive flocculation was observed above Tm. On the other hand, when salt was added after heat treatment, appreciable droplet flocculation still occurred below Tm, but little flocculation was observed above Tm. Addition of cosolvents to the emulsions increased the temperature where extensive droplet flocculation was first observed when they were heated in the presence of salt, which was attributed to their ability to increase Tm and to reduce the droplet collision frequency, with sorbitol being more effective than glycerol. Our results are interpreted in terms of the influence of the cosolvents on protein conformational stability, protein-protein interactions and the physiochemical properties of aqueous solutions. This study has important implications for the formulation and production of protein stabilized oil-in-water emulsions for industrial applications, such as foods, pharmaceuticals and cosmetics.