Strategies to improve the physical stability of sodium caseinate stabilized emulsions: A literature review

Sodium caseinate (NaCas) is widely used as an emulsifier to stabilize emulsions via electrostatic and steric repulsions. However, the stability of NaCas-stabilized emulsions is affected by various compositional and environmental factors, e.g., pH, temperature, ionic strength and protein concentration. Hence, methods to improve the stability of NaCas emulsions against compositional and environmental conditions are reviewed in this paper. The first part introduces the structure of NaCas and its stabilization mechanisms. Furthermore, the effect of environmental circumstances on NaCas emulsion stability is discussed in detail. Lastly, two optimization methods to improve emulsion stability, are highlighted: (1) emulsion preparation methods using high pressure homogenization, ultrasonication or microfluidization and (2) addition of biopolymers (such as protein and polysaccharide) and Tween 20/80, either complexed (covalent or non-covalent bonding) or non-complexed with NaCas. For the first method, nanoscale particle sizes, created by the high-energy methods, reduce droplet aggregation and improve emulsion stability. In method (2), conjugation of biopolymers with NaCas increases the thickness of the adsorbing layers, providing more electrostatic or steric repulsion, or increasing the viscosity of the continuous phase to improve the stability of the NaCas emulsions against environmental conditions.