Extraction of astaxanthin from Haematococcus pluvialis utilizing acidic deep eutectic solvents: A comparison with ionic liquids and organic solvents

Ionic liquids (ILs) and organic solvents have been extensively utilized for the extraction of astaxanthin (Ast). Nonetheless, the large-scale extraction of Ast still necessitates enhancements in extraction efficiency, environmental sustainability, and a decrease in economic costs. Acidic deep eutectic solvents (DESs) formulated with DL-menthol and fatty acids was designed to extract Ast from Haematococcus pluvialis ( H. pluvialis ). The properties of the DESs, along with its extraction efficiency, antioxidant activity, stability, and recycling were assessed and contrasted with tributyloctylphosphine chloride ([P 4448 ]Cl) and ethanol. Quantum chemical calculation was applied to understand the extraction mechanism of DES. The extraction efficiency peaked at 91.25 % when using a DL-menthol:acetic acid (MAA) mixture at an ultrasonic power of 300 W for 30 min, with a solid-to-liquid ratio of 1:20 g/ml, surpassing that of [P 4448 ]Cl extraction (69.91 %) and ethanol extraction (59.34 %). Furthermore, the extracts demonstrated the highest storage stability after MAA extraction, and MAA also showed the best recycling capabilities as compared with [P 4448 ]Cl and ethanol. However, the DPPH· and intracellular ROS scavenging capacities were slightly lower than those after [P 4448 ]Cl extraction. In general, acidic DESs exhibit the highest extraction efficiency and stability of Ast as compared with ILs and organic solvents, while their antioxidant activity requires further improvement. In addition, 25 % of sugar could be released by enzymatic hydrolysis the H. pluvialis residue to further produce bioethanol. This study will provide a theoretical foundation for the extraction of biomolecules and the design of efficient method to comprehensive utilization of microalgae resources.