Abstract

This study investigated the regulatory effects of alkaline extraction pH (8.0-11.0) on the composition, structure, and emulsifying properties of walnut protein (WP). As the pH increased from 8 to 9-11, the protein recovery yield increased sharply from 55.46% to 79.80%-85.26% attributed to the increased solubility of glutelin and globulin. In contrast, the proportion of albumin was higher at pH 8 than at pH 9-11. Given that albumin possesses inherently weak emulsifying capacity, this compositional difference provided a basis for the pH-dependent variation in emulsifying properties. Structural analysis revealed that with increasing pH, the WP structure became looser and underwent unfolding. Surface hydrophobicity increased continuously from pH 8 to pH 10, peaked at pH 10, and then slightly decreased at pH 11 due to enhanced intermolecular interactions. Meanwhile, the absolute ζ-potential and conformational flexibility reached their maximum at pH 11. As the extraction pH increased, the ability of WP to reduce interfacial tension was enhanced. The droplet size (d4,3) of the stabilized emulsions decreased from 68.0 μm (pH 8-E) to 5.53 μm (pH 11-E), and the flocculation index dropped from 833% to 189%. In summary, over the pH range of 8 to 11, synergistic changes in the composition and structure of WP drove the improvement in emulsifying properties.