pH-mediated inhibition of water-induced egg white precipitation: A structural and quantitative proteomic analysis

Water dilution induces undesirable precipitation in egg white, hindering its industrial use. This study investigated the inhibitory effect of alkaline pH (9.5-10.5) on this phenomenon. Increasing the buffer pH dramatically reduced the turbidity and particle size (from 1395.4 nm to 418.2 nm) of egg white solutions. This was attributed to enhanced electrostatic repulsion, as evidenced by a more negative zeta-potential (from -8.0 mV to -23.8 mV). Paradoxically, precipitate mass initially increased at pH 9.5 despite improved solution clarity, contradicting the conventional expectation that higher solids content yields higher turbidity. This was resolved by discovering a fundamental shift in aggregate structure: the opaque, flocculent precipitates in the control, characterized by high surface hydrophobicity and a loose microstructure, transformed into a transparent, hydrogel-like matrix at alkaline pH. This new structure, composed of a dense nanoparticle network with low surface hydrophobicity, minimized light scattering. Quantitative proteomics revealed this transformation was driven by a stoichiometric shift, not a change in protein types. Alkaline pH solubilized primary turbidity-causing proteins (e.g., Metalloproteinase inhibitor 3) while promoting an ordered assembly of others, a process potentially mediated by the electrostatic bridging role of lysozyme. This study uncovers a dual mechanism of electrostatic solubilization and structural reorganization, offering a practical, pH-based strategy to control egg white precipitation.