Physicochemical and rheological properties of oil-in-water emulsions prepared with sodium caseinate/gellan gum mixtures

This work discusses physicochemical properties (particle size distribution, electrokinetic potential, interfacial tension) and rheological responses of oil-in-water emulsions prepared with 30% sunflower oil and different sodium caseinate/gellan gum mixtures, at pH 5.4 and 25 °C. The characteristics of caseinate, gellan gum, and caseinate/gellan mixture solutions were studied first. They showed low viscosity values and almost Newtonian behavior. Addition of 5 mM CaCl2 to the gellan solutions induced shear-thinning behavior, as well as the development of viscoelasticity. Both the viscosity and the elastic modulus of polysaccharide solutions were attenuated by the presence of protein. Emulsions without gellan in the aqueous phase were almost Newtonian, with relatively low viscosity values. When gellan concentration was 0.03% or higher, shear-thinning behavior and viscoelasticity were observed; these effects were negatively influenced by the addition of CaCl2. Casein-covered oil droplets are dispersed in the background matrix formed by the polysaccharide and casein aggregates (filler particles). The emulsion is thus stabilized against both flocculation and creaming, while the rheological behavior strongly depends on the structural state of the polysaccharide. The interaction between caseinate and gellan appears to be the key factor to understand the resulting macroscopic behavior.