Competitive adsorption and displacement of anionic polysaccharides (fucoidan and gum arabic) on the surface of protein-coated lipid droplets

Abstract

The electrostatic deposition of polysaccharides on protein-coated lipid droplets can improve emulsion stability and performance. Emulsions often contain a mixture of different polysaccharides, which may compete for attachment to the lipid droplet surfaces. The purpose of this study was to investigate the competitive adsorption and displacement of two anionic polysaccharides with different molecular properties (fucoidan and gum arabic) to caseinate-coated lipid droplets, using a combination of electrophoresis, light scattering, and isothermal titration calorimetry methods. Fucoidan had a higher negative charge, molecular weight, and radius of gyration than gum arabic. Both fucoidan and gum arabic were capable of absorbing to the caseinate-coated lipid droplets due to electrostatic attraction, but fucoidan adsorbed at a higher pH (pH 6) than gum arabic (pH 4.5), and required a lower amount to saturate the droplet surfaces (around 0.03 wt% versus 0.04 wt% for saturating 0.5 wt% emulsion). The ζ-potential of the lipid droplets saturated with polysaccharide was considerably more negative for fucoidan (−40 mV) than for gum arabic (−22 mV). In the presence of a mixture of the two polysaccharides, fucoidan preferentially adsorbed to the droplet surfaces rather than gum arabic. Furthermore, fucoidan rapidly displaced gum arabic from gum arabic-coated lipid droplet surfaces, which promoted droplet aggregation and led to an exothermic enthalpy change. In contrast, gum arabic was unable to displace fucoidan from fucoidan-coated lipid droplets, which was attributed to the higher charge density of the fucoidan. These results have important implications for designing polysaccharide/protein-coated multilayer emulsions for specific applications.