Fractionation of Squid Pens with Ionic Liquids─An Upgraded β-Chitin and Shellfish Protein Production

Abstract

This study investigates the utilization of squid pen waste through a biocompatible ionic liquid approach, focusing on choline acetate, [Ch][OAc]. This ionic liquid effectively extracts over 80 wt % of protein from squid pen waste. To optimize the extraction process, a factorial design of experiments was employed to achieve a protein recovery of 75% at an estimated purity of 86%, along with highly acetylated, crystalline β-chitin with a purity of up to 95%. The extracted protein was subsequently used to create biocomposite films from α- and β-chitosan, demonstrating impressive tensile strengths of 93.15 ± 7.9 and 83.5 ± 6.2 MPa, respectively, while maintaining hydrophilic properties (θ_water < 90°). Molecular dynamics simulations revealed that the anion [OAc]⁻ exhibits a stronger affinity for protein surfaces compared to other anions, while its combination with the cation [Ch]⁺ optimally facilitates protein recovery. A material mass balance indicated that from 1 kg of dry squid pen, 0.526 kg of protein and 0.34 kg of chitin were recovered. However, high solvent usage significantly impacts energy demands and CO₂ emissions, generating approximately 4.27 kg of CO₂ per kg of product, with 61% attributed to protein production. Technoeconomic analysis demonstrated that solvent costs account for nearly 65% of the minimum selling price of the protein, estimated at $9 kg^–1, which decreases to $0.6 for each kilogram of coproduced β-chitin. Technoeconomic analysis showed that solvent costs comprise nearly 65% of the minimum selling price of the protein, which can reach $9 kg^–1, but this price decreases to $0.6 for each kilogram of coproduced β-chitin. This research underscores the potential of squid pen waste as a valuable resource while highlighting the need for sustainable solvent management strategies.