This study aimed to explore the structural characteristics and antioxidant mechanism of donkey-hide gelatin peptides. After hydrolysis and ultrafiltration treatment, five gelatin peptides with different molecular weights (MWs) were obtained. Amino acid analysis showed that gelatin peptides with different MWs contained a large number of amino acids, including G, P, E, N, A, and R, and differences were noted in the content of various amino acids. Fourier transform infrared spectroscopy and circular dichroism revealed that these gelatin peptides differed in terms of the peak strength of functional groups and number of secondary structures. Moreover, 26 pentapeptides/hexapeptides were identified. Among them, we investigated by molecular docking how PGPAP, which has the best antioxidant activity, may interact with the Keap1 protein. The results showed that the PGPAP-Keap1 complex had a stable conformation, and Arg415, Gly462, Phe478, and Tyr572 were the key residues involved in the binding of the peptide PGPAP to Keap1. Our results demonstrated that PGPAP could serve as a bioactive peptide with antioxidant activity.

Iron deficiency is a global health issue, making the development of novel iron supplements to enhance iron absorption critically important. In this study, low molecular weight donkey-hide gelatin peptides (LMW DHGP) were enzymatically hydrolyzed from donkey-hide gelatin. Experimental results demonstrated that the iron chelating capacity of LMW DHGP reached 249.98 μg/mg. Key amino acids (Asn, Gly, Cys, Lys) may participate in chelation. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis showed rough, porous amorphous structures of LMW DHGP-iron complexes. The results of circular dichroism spectroscopy (CD) indicated that the self-assembly of LMW DHGP-iron complexes appears to be primarily mediated by peptide α-helical structural conformations. Fourier transform infrared (FTIR) spectroscopy further indicated that the interaction between LWM DHGP and Fe²⁺ likely occurs through carboxyl and amino functional groups. In vitro digestion stability studies demonstrated that LMW DHGP-iron complexes exhibited superior iron ion solubility compared to FeSO₄ in simulated gastrointestinal conditions. PGPAG-iron complexes exhibited the highest antioxidant activity, with scavenging rates of 71.64% (DPPH radical) and 88.79% (ABTS radical). These findings collectively suggest that LMW DHGP-iron complexes possess significant potential as a novel iron supplement in food applications, which provides valuable theoretical insights for the development of innovative iron supplementation strategies.

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.

Gelatin from bovine hide, especially yak hide, is valued in the food and pharmaceutical industries; however, as the most common domestic cattle in China, gelatin made from yellow cattle hide remains unexplored. Thus, the physicochemical properties, nutritional components, and flavor characteristics of gelatin produced from yellow cattle hides and yak hides, both before and after hair removal, were analyzed. It was found that yellow cattle hide gelatin (YCHG) not only had a higher protein content (68.45–71.51%) than yak hide gelatin (YHG) (66.81–67.56%) but also had a higher Fe content (86.75 ± 1.650 mg/kg). Additionally, 17 amino acids were detected in the four bovine hide gelatin samples; among them, dehaired yellow cattle hide gelatin (DYCHG) was richer in sweet-tasting amino acids than the others. Notably, non-dehaired yellow cattle hide gelatin (NDYCHG) featured 4-methyl-3-penten-2-one (with a honey aroma), whereas non-dehaired yak hide gelatin (NDYHG) featured β-pinene, 1-nonanal, acetic acid-D, (E)-2-pentenal, and allyl sulfide. Therefore, yellow cattle hide gelatin (YCHG) exhibits prominent nutritional and flavor properties, suggesting its potential as an alternative raw material for food industry applications.