Recovery of astaxanthin from Antarctic krill (<i>Euphausia superba</i>) waste by using thermo-reversible ionic liquid-water systems: Phase behavior, extraction and residue utilization

In this study, astaxanthin was recovered from Antarctic krill waste via thermo-reversible biphasic system composed of phosphonium-based ionic liquids (ILs) and water. The phase behavior and physical properties of the mixtures were investigated. The astaxanthin extraction was compared with organic solvents and pure ILs, and the extraction mechanism was revealed through Quantum chemical computation. Moreover, the stability of the extract was evaluated. The extracted residue was further used as a biosorbent to remove methyl blue and Congo red from waste water. Results showed the [P₄₄₄₄]CF₃COO-water system presented lower critical solution temperature (LCST)-type phase behavior, while the [P₄₄₄₈]CF₃COO-water system presented an upper critical solution temperature (UCST)-type phase behavior. Astaxanthin has a tendency to migrate to the IL-rich phase due to the hydrogen bond between ILs and astaxanthin. The highest extraction yield of astaxanthin reached 35.78 μg/g by using the [P₄₄₄₄]CF₃COO-water system at 308.15 K at a solid–liquid ratio of 1:40 g/mL and an extraction time of 75 min. In addition, the extracted residue with spongy and porous surface showed high removal efiiciency of Congo red (92.6%) and methylene blue (97.31%). The study provides an efficient and environmentally friendly method to selectively extract astaxanthin from natural bioresources.