Influence of alginate, pH and ultrasound treatment on palm oil-in-water emulsions stabilized by β-lactoglobulin

The influence of pH (3–7), sodium alginate (0–0.5 wt%) and high intensity sonication (1 min, 20 kHz, 70% amplitude) on the properties of palm oil-in-water emulsions stabilized by 0.45 wt% β-lactoglobulin (β-Lg, 5 mM phosphate buffer) was determined using a variety of analytical techniques: ζ-potential, light scattering, creaming index, and optical microscopy. At pH 3–5, anionic alginate adsorbed to the surfaces of β-Lg coated droplets due to electrostatic attraction. At pH 6 and 7 adsorption did not occur because of the strong electrostatic repulsion between the anionic alginate and anionic droplets. Emulsion droplets coated by β-Lg-alginate complexes were prone to bridging flocculation, which promoted creaming instability. However, high intensity ultrasound treatment was able to reduce the degree of droplet flocculation in these emulsions, thereby increasing their creaming stability. These results suggest that stable emulsions containing droplets surrounded by β-Lg–alginate interfacial complexes can be produced (at pH 4 and 5) by using ultrasound treatment to disrupt any flocs formed when the polysaccharide and emulsion are mixed together. This manuscript continues our work of identifying proteins and polysaccharides that are suitable for formation of multilayer emulsions with improved stability to environmental stresses or with novel functional properties that could be used in the food industry.