Fabrication of pea protein isolate-stabilized oil-in-water emulsions with high freeze-thaw stability: Effect of high intensity ultrasonic on emulsions and interfacial protein structure

The poor freeze-thaw stability of plant protein-based emulsions posed a major challenge for their application in the cold chain foods. The present study successfully prepared oil-in-water emulsions stabilized solely with pea protein isolate (PPI) with excellent freeze-thaw stability using a facile high intensity ultrasonic (HIU)-assisted method. The optimized emulsion can endure three freeze-thaw cycles without stratification or oil leakage, maintaining oil droplet sizes at the nanometer scale. Furthermore, changes of interfacial protein structure induced by HIU were systematically investigated to reveal the stabilizing mechanism. The freeze-thaw stability of emulsions treated under varying intensities was evaluated based on changes in the appearance and oil drop size distribution. The results showed that the oil drop size of emulsions decreased from micron to nanometer and the freeze-thaw stability was significantly enhanced with the increase of HIU intensity. The emulsion exhibited optimized freeze-thaw stability under 800W. Subsequently, the effect of HIU on the structure of interfacial protein was analyzed through SDS-PAGE, -SH/S-S contents, UV spectrum, surface hydrophobicity, protein adsorption percentage, emulsifying activity and interfacial dilatational rheology. It was found that HIU triggered crosslinking of disulfide bonds among interfacial PPI molecules and enhanced the strength of the interface layer. Additionally, HIU promoted the unfolding of interfacial PPI structure, resulting in the improvement of surface hydrophobicity, emulsifying activity, and interfacial adsorption percentage of PPI. The study demonstrated the feasibility of using HIU to improve the freeze-thaw stability of oil-in-water emulsions stabilized with PPI and provided references for the fabricating of plant protein-based frozen emulsion foods.