Soy protein is wildly used in food industry due to its high nutritional value and good functionalities. However, the poor storage stability of commercial soy protein products has puzzled both the producers and the users for a long time. The current study assessed the changes in protein solubility, aggregation, oxidation, and conformation of soy protein isolate (SPI) with various soluble aggregates formed at different pH values (pH 5–8) during storage. During storage, SPI samples showed a reduced protein solubility (p < .05), an increased protein oxidation (p < .05), and an attenuated conformational enthalpy (∆H). SPI with a higher pH produced more disulfide‐mediated aggregates at the expense of sulfhydryl groups and experienced greater losses of protein tertiary structure and a faster reduction in solubility. Yet, all samples nearly shared similar rising trend during 8‐week storage, which indicated the production of protein carbonyls was insensitive to pH. Soluble aggregates present in fresh SPI samples appeared to induce instability of SPI during storage. These findings suggested SPI prepared at pH 6 was in favor of its storage stability, and soluble aggregates presented in fresh samples should be paid more attention for further study of storage stability kinetics.

The effect of alkali-induced oxidation of three phenolic acids, namely gallic acid, epigallocatechin gallate, and tannic acid, on the structure and gelation of ginkgo seed protein isolate (GSPI) was investigated. A mixture of 12% (w/v) GSPI and different concentrations of alkali-treated phenolic acids (0, 0.06, 0.24, and 0.48% w/w) were heated at 90 °C, pH 6.0, for 30 min to form composite gels. The phenolic treatment decreased the hydrophobicity of the GSPI sol while enhancing their rheological properties. Despite a reduced protein solubility, water holding capacity, stiffness, and viscoelasticity of the gels were improved by the treatments. Among them, the modification effect of 0.24% (w/v) EGCG was the most prominent. Through the analysis of microstructure and composition, it was found to be due to the covalent addition, disulfide bond formation, etc., between the quinone derivatives of phenolic acids and the side chains of nucleophilic amino acids. Phenolic acid modification of GSPI may be a potential ingredient strategy in its processing.

The solubility of soybean isolate protein (SPI) undergoes significant degradation during storage and transportation. This study investigates the formulation and assessment of SPI-stabilized medium internal phase emulsions (MIPEs) with different solubilities, namely SPI80, SPI70, SPI60, and SPI50, corresponding to solubility levels of about 80%, 70%, 60%, and 50%, respectively. The contact angles of these SPI variants ranged from 79.35 to 86.55 degrees, with SPI60 and SPI50 exhibiting significantly higher values compared to SPI80 and SPI70. All SPI samples were successfully utilized for the preparation of MIPEs. However, as SPI solubility decreases, emulsion stability progressively declines, accompanied by a reduction in the absolute value of zeta potential. Additionally, interfacial protein adsorption in emulsions decreases with decreasing SPI solubility, a trend that is similarly observed in viscosity characteristics, storage modulus (G′), and loss modulus (G″). Confocal laser scanning microscopy (CLSM) and cryo-scanning electron microscopy (Cryo-SEM) analyses revealed that emulsions exhibit reduced uniformity and a less interconnected microstructural network as SPI solubility decreases. These findings provide a theoretical foundation for utilizing low-solubility SPI in MIPEs applications.