Synergistic Effects of Ultrasound and pH-Shifting on the Solubility and Emulsification Properties of Peanut Protein

Peanut protein is a byproduct of peanut oil extraction with limited applications within the food sector due to its low solubility and emulsifying properties. This study investigated the influences and mechanisms of high-intensity ultrasound (HIU, 200~600 W) and pH-shifting (pH 12), either individually or jointly, on the structure, solubility, and emulsifying properties of PP. Results indicated that the solubility of PP significantly increased after the combined treatment, particularly when the HIU power was 300 W (p < 0.05). Accordingly, emulsions prepared from it exhibited highest storage stability. Structural analysis indicated that the increased PP solubility (9.95% to 54.37%, p < 0.05) is mainly attributed to the structural changes that occur during protein unfolding, resulting in the uncovering of hydrophobic groups (7181.43 to 14,083.00, p < 0.05) and the reduction of α-helices (24.43% to 18.17%, p < 0.05). Moreover, confocal laser scanning microscopy of the emulsions revealed that the combination-treated PP resulted in smaller protein particle sizes (50.09 μm to 15.68 μm, p < 0.05), tighter adsorption on the oil–water interface, and a denser and more stable interfacial film compared to the native and the individual treatment, thereby enhancing the stability of the system. A rheological analysis confirmed that the combined treatment improved the interfacial properties of the protein, which was advantageous for emulsion stability. In conclusion, HIU combined with pH12-shifting can appreciably improve the solubility and emulsifying properties of PP to broaden its application prospects.