Sustainable extraction of chitosan from blue crabs (Callinectes sapidus) by green solvents

Chitosan, one of the significant marine polysaccharides, has attracted widespread attention due to its excellent biocompatibility and broad application prospects. This study proposes a novel green extraction method based on Brønsted acid-base deep eutectic solvents (DESs) for the efficient production of chitosan from the exoskeleton of blue crabs, achieving a green alternative to traditional inorganic acid-base chemical processes. Unlike conventional processes, this study innovatively replaces inorganic acids with acidic DESs and sodium hydroxide with alkaline DES, establishing an environmentally friendly deacetylation route. The effects of four different acidic DESs on chitosan purity were systematically compared. The produced chitosan was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and nuclear magnetic resonance (¹H NMR). Characteristic NMR peaks at 4.6 and 4.8 ppm confirm the formation of glucosamine structures, indicating that the purity of the resulting chitosan is comparable to that of commercial one. Furthermore, this study established a process technology roadmap and life cycle assessment (LCA) model to identify environmental impact hotspots during the extraction process. The results showed that electricity consumption during the manufacturing phase was the primary source of environmental burden, providing clear guidance for subsequent energy optimization and industrial scale-up.