Pickering emulsions stabilized by egg white protein-alginate nanoparticles: Freeze-thaw stability after heating

Egg white protein (EWP)-sodium alginate (SA) nanoparticles were fabricated by controlled heating (75 degrees C, 10 min) of an aqueous solution containing EWP and SA (pH 7.0). The nanoparticles formed had a relatively small average diameter (350-460 nm) and polydispersity index (PDI< 0.3). Hydrogen bonding and electrostatic interactions were the main forces involved in particle formation as determined by Fourier transform infrared spectra and intrinsic fluorescence analyses. The composite nanoparticles had contact angles (theta) of about 90 degrees, which allowed them to be used as particle-based emulsifiers to form and stabilize concentrated oil-in-water Pickering emulsions (70% oil). Inverted fluorescence microscopy showed that the composite nanoparticles adsorbed to the surfaces of the oil droplets in these emulsions. Rheological analysis showed that the Pickering emulsions had predominantly elastic-like properties and exhibited strong shear thinning behavior. The apparent shear viscosity, elastic modulus, and viscous modulus of the emulsions depended on particle size and alginate concentration. A heat treatment (90 degrees C, 20 min) greatly increased the viscoelastic properties of the emulsions, which was attributed to protein unfolding and aggregation. Heating improved the resistance of the Pickering emulsions to freezing and thawing. This study provides a simple and convenient method to fabricate semi-solid Pickering emulsions using natural ingredients. These emulsions may have a variety of applications in foods, including as edible inks for 3D food printing.