Divalent cation-mediated regulation of the hierarchical structure and rheological properties of ovalbumin fibrils

Mg²⁺, Zn²⁺, Ca²⁺ and Fe²⁺ increased antiparallel β-sheet content in preformed ovalbumin fibrils. • Cation treatment shortened apparent fibril contours and increased interfibrillar aggregation. • Divalent cations increased the viscosity and storage modulus of ovalbumin fibril dispersions. • Cation treatment reduced the zeta potential and apparent surface hydrophobicity of ovalbumin fibrils. • ITC showed relatively weak, ion-dependent association between divalent cations and preformed fibrils. Metal ions can regulate the structural organization and macroscopic properties of protein fibrillar assemblies. Although previous studies have extensively examined ion-mediated regulation of protein fibrillation, the effects of divalent cations on the hierarchical organization of preformed egg-protein fibrils remain poorly understood. In this study, OVA fibrils were prepared by heating the protein at pH 2.0 and 90 °C for 8 h, after which Mg 2+ , Zn 2+ , Ca 2+ , or Fe 2+ was added to evaluate the effect of each ion on the post-formation organization and properties of the preformed fibrils. Divalent-cation treatment caused ion-dependent changes in the secondary-structure distribution, colloidal properties, microscopic morphology, and rheological behavior of the preformed OVA fibrils. These changes were attributed to post-formation interfibrillar association, aggregation, and structural reorganization rather than enhanced fibril formation. All OVA fibril systems showed partial precipitation at 500 mM, indicating loss of colloidal stability rather than homogeneous hydrogel formation. ICP-MS revealed ion-dependent differences in apparent metal retention. Collectively, these findings demonstrated that divalent cations regulated the hierarchical organization and rheological properties of preformed OVA fibrils through ion-dependent post-formation structural reorganization, providing a basis for controlling the functionality of egg-protein fibrillar materials. Download: Download high-res image (340KB) Download: Download full-size image