Preparation, characterization, assembly, and stability of walnut peptide - zinc complexes and its ability to promote zinc transport in Caco-2 cells

Walnut peptides (WP) are promising metal-ion carriers that are expected to improve the bioavailability of dietary micronutrients. In this study, walnut peptide zinc complexes (WP-Zn), a novel zinc supplement differentiated from conventional zinc salts, was successfully fabricated. The morphology analysis and particle size distribution result displayed that WP folded and aggregated to create spherical particles with increased particle size upon Zn²⁺ complexation. FTIR spectra, amino acid profiles and conformational dissociation tests demonstrated that WP covalently chelated Zn²⁺ first via carboxy oxygen, carbonyl oxygen and amino nitrogen atoms. Then, they further self-assembled to homogeneous complexes via non-covalent interactions including hydrophobic interactions, hydrogen bonds and electrostatic forces. Remarkably, WP-Zn possessed superior thermal, acid-base and gastrointestinal digestive stability compared to ZnSO₄. WP-Zn was primarily transported via ZIP4 and the paracellular pathway in Caco-2 cell monolayer model. These findings suggest that WP-Zn has great potential for development and application as a novel zinc supplement.