Fabrication and Characterization of Quinoa Protein Nanoparticle-Stabilized Food-Grade Pickering Emulsions with Ultrasound Treatment: Effect of Ionic Strength on the Freeze–Thaw Stability

The development of multilayered interfacial engineering on the emulsion freeze–thaw properties has recently attracted widespread attention, because of the essential freeze–thaw storage process in some emulsion-matrix food products. In this research, we studied the role of salt concentration on the freeze–thaw properties of quinoa protein (QPI) nanoparticles-stabilized Pickering emulsions. The QPI nanoparticles (particle concentration c = 2%, w/v) with increasing particle size and surface hydrophobicity (H0) were fabricated by ultrasound treatment at 100 W for 20 min, by varying the NaCl addition (salt concentrations, 0–500 mM). The sonicated QPI nanoparticles with increasing salt concentrations showed higher β-sheet structure contents and stronger hydrophobic interactions, which were attributed to the decreasing charged groups and particle aggregation by electrostatic interactions. As compared to the sonicated QPI nanoparticles-stabilized Pickering emulsions (c = 2%, oil fraction φ = 0.5) without salt accretion, the emulsions with salt accretion exhibited better freeze–thaw properties after three freeze–thaw circulations, which might be mainly caused by the generation of gel-like three-dimensional structure and multilayered network at the droplets’ interface with smaller droplet sizes. Increasing the salt concentration progressively enhanced the freeze–thaw properties of sonicated QPI nanoparticles-stabilized Pickering emulsions probably due to the inhibit formation of ice crystal by the “salting-out” effects. The results of this study would provide great significance to investigate the role of salt concentration in the freeze–thaw properties of protein-stabilized Pickering emulsions.