pH-, ion- and temperature-dependent emulsion gels: Fabricated by addition of whey protein to gliadin-nanoparticle coated lipid droplets

Emulsion gels were prepared by addition of whey protein isolate (WPI) to gliadin nanoparticles (GNP)-stabilized emulsion and controllable gel strength were achieved by altering temperature, and pH values and ionic concentration. The effects of temperature, pH and ionic concentration on rheological properties, droplet size distribution, ζ-potential and microstructure of these systems were characterized. The elastic modulus of WPI and GNP-stabilized emulsion gels were strongly temperature-dependent. Weak emulsion gels were formed at ambient temperature by addition of WPI to the GNP-stabilized emulsions, whereas strong gels were formed by heating above the thermal denaturation temperature of the proteins. The addition of WPI has a positive effect on improving gel strength of the emulsion gels, with the strongest gels being formed at 2% WPI. The gel strength could also be modulated by adjusting pH and ionic strength, with the strongest gels being formed near the isoelectric point of the proteins (pH 5 and 6.8) and at low ionic strengths (0–200 mM). Changes in the physicochemical properties of the emulsion gels were attributed to alterations in the structural arrangement and interactions of the nanoparticle-coated lipid droplets, which was supported by the results of electrophoresis and confocal laser scanning microscopy. These findings show that the rheological properties of GNP and WPI-stabilized emulsion gel could be easily regulated by temperature, pH or ionic strength, which may make them suitable for various applications in the food industry.