Green Extraction and Characterization of Collagen from Different Fish Scales and Cell Culture-Based Bioactive Evaluation of Its Combinations with Zingiber officinale

Fish processing by-products represent a valuable and sustainable source of collagen for biomedical and functional applications. In the present study, collagen was extracted from the scales of red mullet (Mullus barbatus), gilthead sea bream (Sparus aurata), and European sea bass (Dicentrarchus labrax) using a green extraction approach based on a natural deep eutectic solvent (NADES) system composed of citric acid, xylitol, and water. The extracted collagens were comprehensively characterized by SDS-PAGE, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses. The results confirmed the presence of Type I collagen and demonstrated that the characteristic triple-helical structure and molecular organization were preserved throughout the extraction process. To preliminarily evaluate their potential as matrices for incorporating bioactive compounds, collagen matrices were combined with Zingiber officinale (ginger) extract at different ratios. The resulting combinations were evaluated for antioxidant, antimicrobial, and cytocompatibility properties. Antioxidant activity increased significantly with increasing ginger concentration, with the highest radical scavenging activity observed in combinations containing the greatest proportion of ginger extract. Similarly, antimicrobial activity against Escherichia coli and Staphylococcus aureus was enhanced by ginger incorporation, with stronger inhibition observed against the Gram-positive bacterium. Cytocompatibility studies performed on human dermal fibroblast (HDFa) cells revealed that selected collagen–ginger combinations maintained high cell viability and did not induce substantial membrane damage, nuclear abnormalities, apoptosis, or necrosis at appropriate concentrations. Overall, the findings demonstrate that fish scale-derived collagen obtained through a sustainable NADES-based extraction process possesses favorable structural and biological properties and may serve as a potential carrier matrix for plant-derived bioactive compounds. These findings provide preliminary evidence supporting the future development of environmentally friendly functional biomaterials with prospective applications in pharmaceutical, biomedical, and tissue engineering fields.