Correlating chemico-physical features of thymol-based deep eutectic solvents with astaxanthin extraction performances

Hydrophobic/water-insoluble Deep Eutectic Solvents (DESs), such as the thymol-based ones, are widely used and studied for the extraction and pre-concentration of valuable compounds from various matrices. In this paper, a structure-activity approach was used to determine the factors that influence the efficacy of a series of thymolbased hydrophobic DESs applied for the extraction of astaxanthin from genetically-modified Picosynechococcus sp. PCC 11901, a recently discovered cyanobacterium. As expected, the polarity of the media plays a significant role, but surprisingly, the intimacy of the molecules forming the DESs has a relevant role in the process as well, showing this parameter to be crucial for their performances. This parameter is also linked to the viscosity, which is also playing a key role in the processes. Moreover, the comparison of the results with an ideal non-DES mixture showed a non-correlation of this liquid with the set of DESs used, underlining the importance of the liquid's identity determination in this field