Interfacial composition and stability of sodium caseinate emulsions as influenced by calcium ions

The changes in droplet size distribution, surface protein concentration and composition, microstructure and creaming stability were examined when CaCl2 was incorporated into oil-in-water emulsions (30%, w/w, soya oil) made with 0.5 or 3%, w/w, sodium caseinate. The droplet size distribution of emulsions made with 0.5 or 3% was monomodal until a critical CaCl2 concentration (4 mm in 0.5%, 20 mm in 3% sodium caseinate) after which the distribution shifted towards larger size range. The shape of the size distribution curve was dependent on whether CaCl2 added before or after homogenization. Surface protein concentration increased with CaCl2 addition, which was largely due to enhanced adsorption of the αs (αs1-+αs2-) casein at interface of emulsion droplets in all emulsion systems studied. Addition of CaCl2 before or after homogenization caused a decrease in the creaming stability of emulsions made with 0.5% caseinate. In contrast, addition of CaCl2 up to ∼10 mM increased the creaming stability of 3% caseinate emulsions, although the stability decreased again above 20 mm CaCl2. The confocal microscopy confirmed that the extent of depletion flocculation in 3.0% caseinate emulsions decreased by addition of CaCl2, but irreversible flocculation occurred when added CaCl2 exceeded 20 mM.