The formation mechanism of multilayer emulsions studied by isothermal titration calorimetry and dynamic light scattering

The formation of multilayer interfaces in oil-in-water (O/W) systems has many advantages in delivering lipid-soluble active compounds. In this study, isothermal titration calorimetry (ITC) and dynamic light scattering (DLS) were used to investigate the formation mechanism of multilayer emulsions by mixing low methoxyl pectin (LMP) and sodium caseinate (CAS) stabilized O/W emulsion. Thermodynamic properties and ζ-potential curves were studied as a function of polymer ratio, suggesting that ITC could provide more accurate information about the polymer concentration effect. ITC titration confirmed that LMP binds CAS-coated droplets mainly through electrostatic forces, which was a spontaneous exothermic process (ΔG < 0). Furthermore, stable multilayer emulsions were obtained by titrating CAS-stabilized droplets into LMP instead of back-titrating. Finally, the effects of mixing methods on the stability of multilayer emulsions were evaluated. The results suggest that titration rather than direct mixing can produce uniform and smaller-sized droplets and delay the onset of droplets aggregation.