Interaction and Characterisation Analysis of Calcium Ion-crosslinked Catechin-Ovalbumin Amyloid Fibril Hydrogels

To investigate the effects of different Ca²⁺ concentrations (control group, Ca₁ 0.86 mmol/L, Ca₂ 2.58 mmol/L, Ca₃ 17.2 mmol/L, Ca₄ 34.4 mmol/L) on the structure and physicochemical properties of catechin-ovalbumin amyloid fibril hydrogels (C-OVAF), we conducted a systematic analysis using techniques such as thioflavin T fluorescence spectroscopy, circular dichroism spectroscopy, rheology, low-field NMR, particle size analysis, Zeta potential measurement, surface hydrophobicity assessment, antioxidant experiments, scanning electron microscopy, and molecular docking. The results showed that, compared with the control group, Ca²⁺ cross-linking significantly altered the secondary structure (α-helix increased from 6% in the control to 12% in Ca₄, β-turns increased from 16% (control) to 29% (Ca₄), β-sheets decreased from 50% (control) to 43% (Ca₄), and random coils decreased from 28% (control) to 15% (Ca₃). As Ca²⁺ concentration increased, the storage modulus (G') first rose and then fell, with the Ca²⁺ group exhibiting the highest G' (indicating the highest network density and elasticity). Low-field nuclear magnetic resonance confirmed an increase in the proportion at this concentration, with significantly optimized water retention, the lowest surface hydrophobicity, and DPPH, ABTS⁺ radicals reached 61.9% and 53.4%, respectively, with optimal antioxidant activity, while the system’s particle size and Zeta potential stabilized. Scanning electron microscopy revealed that the Ca₂ group formed a regular, continuous network structure, and molecular docking confirmed that C-OVAF forms complexes via hydrophobic interactions and hydrogen bonding, with Ca²⁺ in the Ca₂ group enhancing intermolecular interactions through coordination. In summary, Ca²⁺ crosslinking significantly improves the structure and properties of C-OVAF hydrogels. A Ca²⁺ concentration of 2.58 mmol/L balances molecular intermolecular forces to simultaneously optimize water retention and antioxidant activity. This study provides theoretical guidance for the performance regulation, preparation optimization, and food processing applications of metal ion-crosslinked polyphenol-protein hydrogels.