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

Abstract

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 ([P₄₄₄₈]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 [P₄₄₄₈]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 [P₄₄₄₈]Cl and ethanol. However, the DPPH· and intracellular ROS scavenging capacities were slightly lower than those after [P₄₄₄₈]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.