Physicochemical integration of egg white proteins and milk casein based on phase separation as a stable and optimized colloidal complex

Egg white proteins (EWP) are shown a tendency to phase separation and sedimentation in response to changes in pH levels and ionic strength, which restricts their use in egg milk beverages. Herein, casein (CN) was used to enhance the stability of EWP and the EWP-CN complex phase separation behavior and structural properties were studied. In the method, the complex physiochemistry, protein microstructure, intermolecular interactions, and its formed bonds were evaluated accordingly. The results showed that the EWP-CN optimal coacervation ratio was 2:1. At this ratio, the soluble complex and insoluble coacervate occurred at pH 6.5 and 5.35, respectively. Besides, EWP-CN exhibited high solubility at pH 2.0, 2.5, 3.0, and 6.5, while low solubility at pH 5.0 was based on the NaCl isotonic impact. Additionally, FTIR analysis demonstrated that the formation of coacervate was driven by the electrostatic interactions between the -COO- of one protein and the -NH3+ of the other protein, resulting in a change in secondary and tertiary structure. For surface hydrophobicity, the EWP-CN complex showed higher values (3201.4) than EWP (1899.4). The TEM micrographs demonstrated that EWP-CN at pH 5.0 formed dense and highly crosslinked aggregates as a result of protein folding change. In conclusion, the current study's novelty came from the significant improvement in EWP-CN coacervates by optimizing the complex isocritical condition. Whereas, it presents a potential solution and lays a theoretical basis for overcoming the problems facing hydrocolloidal beverages such as sedimentation and thermal instability, especially in EWP-based beverages.