Sequential extraction of collagen and gelatin from the skins of codfish, meagre and blue shark in the perspective of application in healthcare

The valorization of marine by-products has emerged as a sustainable strategy to obtain highvalue biopolymers such as collagen and gelatin. In this study, collagen was extracted using acetic acid from the skins of two warm-water fish species (meagre and blue shark) and one cold-water species (codfish, both salted and non-salted), with subsequent extraction of gelatin from the remaining biomass, and a comparative analysis of their physicochemical properties was carried out. Collagen extraction yields varied across species, with blue shark exhibiting the highest yield (8.3%), followed by salted codfish (5.1%), meagre (4.8%), and non-salted codfish (4.5%). Rheological profiling revealed species-specific thermal responses, with meagre collagen displaying the highest viscosity across all tested temperatures and the highest denaturation temperature (30.3 °C), indicating superior thermal stability. FTIR and CD spectroscopy confirmed the preservation of the triple-helical structure in all samples, with characteristic amide bands observed, although minor wavenumber shifts suggest subtle structural differences among species. SDS-PAGE electrophoresis revealed typical collagen α1 and α2 chains along with β and γ components, with meagre and blue shark samples exhibiting cleaner profiles with fewer degradation products and slightly heavier α- chain bands thus suggesting higher molecular integrity compared to codfish-derived collagens. A comparison between salted and non-salted cod collagens revealed that salting improved extraction yield but negatively impacted rheological, thermal and structural stability, suggesting a detrimental effect over collagen integrity. Moreover, high molecular weight gelatin could be obtained from the remaining biomass of skins of all fish species, adding another level to the proposed strategy for valorization of fish by-products. Overall, these findings emphasize the impact of species origin and habitat temperature on collagen characteristics and suggest that meagre collagen holds strong potential for biomedical applications due to its favorable rheological and structural properties.