Regulation of on zein/epicatechin gallate interaction by CaCl₂ and the complex structure: Insights from multiple...

The regulatory effect of CaCl₂ on interaction between zein and epicatechin gallate (ECG), as well as structural and physicochemical properties of their complexes, were investigated. Molecular docking results indicated Ca²⁺ lowered binding affinity while altering their binding mode. UV-vis spectroscopy revealed CaCl₂ does not directly alter structure of individual molecules. Instead, it indirectly modified conformation of zein and its chromophore microenvironment by modulating its strength and interaction modes. FT-IR spectroscopy showed Ca²⁺ induced unwinding of zein α-helix and promoted β-sheet formation. Additionally, by tuning specific interactions, CaCl₂ created an ordered intermolecular network and preserved complex's spherical surface, as was evident from SEM images. QCM-D demonstrated zein-ECG interactions were strongest at 0.2 mol/L Ca²⁺, affording the most thermally stable complex, while treatment with 0.8 mol/L Ca²⁺ maximized the solubility. These findings indicated Ca²⁺ modulated interaction patterns between zein and ECG, as well as structure and physicochemical properties of the resulting complexes.