Deep eutectic solvents for the extraction of β-chitin from Loligo vulgaris squid pens: a sustainable way to valorize fishery by-products

β-chitin, a promising biopolymer for the production of chitosan and biomaterials, is sourced from fishery by-products. Herein, β-chitin has been extracted using Deep Eutectic Solvents (DES) for the first time, only the α-polymorph having been extracted using these solvents until now. Six acid, neutral, and alkaline DES systems were trialed, with only the alkaline DES systems, in particular potassium carbonate: glycerol (KGLY) at 100 or 120 °C for 2 or 3 h, resulting in high-purity β-chitin. The ensuing β-chitin was characterized in terms of chemical and physical structure, morphology, crystallinity, and thermal properties. Under the best extraction conditions, using the DES KGLY system, the β-chitin samples were highly pure, presenting an acetylation degree between 77 and 88%, a high crystallinity between 88 and 91%, and a maximum degradation temperature of around 350 °C. Moreover, the solvent system was easily recyclable with consistent performance over 3 cycles of re-use. The extraction method is well-suited for the extraction of crystalline β-chitin and could be integrated into future works in the production process of chitosan.