Eco-friendly chitosan production from diverse biowastes: deep eutectic solvents outperform conventional methods

Chitosan, one of the most abundant biopolymers, has gained increasing attention due to its biocompatibility, biodegradability, and versatile applications. This study introduces gentle extraction approach that combines deep eutectic solvents (DES) for chitin extraction with an optimized deacetylation step using only 35 % NaOH instead of the conventional 50 % to obtain chitosan. A comparative evaluation was performed across insect (Hermetia illucens pupae, Black Soldier Fly) and marine (shrimp and crab) sources under identical conditions to assess the effect of solvents on extraction behavior and chitosan characteristics. Two DES systems were employed: the slightly basic choline chloride-urea (Ch:U) and the acidic choline chloride-lactic acid (Ch:LA). In-depth analysis including SEM, FTIR, XRD, TGA, DSC, NMR, rheological assessments, and biological activities were used. The green extraction significantly enhanced yields across all sources with the urea-based method outperforming the lactic acid-based system. NMR analysis revealed high deacetylation degrees (85-87 % for crab, 81 % for BSF and 69-79 % for shrimp). The conventional chemical method achieved DD of 88 % (crab), 83 % (shrimp), and 68 % (BSF). All chitosan samples exhibited shear-thinning behavior with variable viscoelastic properties, along with notable antioxidant and antimicrobial activities, particularly in lactic acid-based extracts of BSF chitosan. The urea-based method enhanced thermal stability, with crab chitosan exhibiting the highest stability, followed by shrimp chitosan. These findings highlight the advantages of sustainable DES-based extraction of chitosan for reducing environmental impact and improving industrial scalability. Future research should prioritize the direct extraction of chitosan from shells using DES to improve process efficiency and environmental sustainability.