Zinc Chelates from Low-Molecular-Weight Donkey-Hide Gelatin Peptides: Preparation, Characterization, and Evaluation of In Vitro Antioxidant Activity

This study synthesized a low-molecular-weight donkey-hide gelatin peptide-zinc chelate (LMW DHGP-Zn) using peptides derived from donkey-hide gelatin. Under optimized conditions (zinc concentration of 32 mg/mL, peptide-to-zinc mass ratio of 8:1, pH 6.5, 60 °C, 70 min), a maximum chelation rate of 41.34% ± 0.23% was achieved. Comprehensive characterization via scanning electron microscopy, ultraviolet-visible spectroscopy, fluorescence spectroscopy, zeta potential, particle size, Fourier transform infrared spectroscopy, and circular dichroism confirmed substantial structural and physicochemical alterations post-chelation. After chelation, the surface charge is neutralized, and the distribution of particles is more even. Furthermore, analysis indicated an elevated content of acidic amino acids (glutamic acid and aspartic acid), and spectroscopic data confirmed the coordination of zinc ions with amino and carboxyl groups on the peptide. Consequently, the LMW DHGP-Zn chelate demonstrated significantly enhanced ABTS radical cation scavenging activity. These results provide a scientific foundation for its potential application as a natural antioxidant in the food, cosmetic, and pharmaceutical industries.