###### Abstract
However, the use of these chemicals presents significant environmental and health issues, given their toxic and non-biodegradable nature [16]. As an alternative, neoteric solvents can be used for the extraction of target compounds from biomass. Among the options for the extraction of microalgal components are supercritical fluids--mainly supercritical carbon dioxide--which are safer while still offering high extraction yields. For example, extraction with supercritical CO\({}_{2}\) is a method in which it is possible to achieve high efficiencies by adjusting parameters such as pressure and temperature [17; 18]. Other relevant neoteric solvents include ionic liquids (IL) and deep eutectic solvents (DES). IL are low melting-point salts that present a high extractive capacity [19; 20], although they still have high costs and their synthesis can be challenging [19; 21; 22]. Conversely, DES offer simpler preparation and reduced costs, and they are typically more biodegradable [23]. These consist of two or more components that combine to form a structure of hydrogen bonds. One of these components is a hydrogen bond donor (HBD), which is a compound that provides hydrogen bonds, and the other is a hydrogen bond acceptor (HBA), which captures the hydrogen bonds. The combination of these two compounds in the appropriate proportions and at a specific temperature will form the DES [24]. While HBAs are formed, basically, from quaternary ammonium salts, HBDs can include amines, carboxylic acids, or urea [25; 26]. Regarding the toxicity of DES, these compounds are commonly regarded as non-toxic substances. However, there is a lack of systematic studies that comprehensively address their potential health effects and environmental toxicity, and these issues are still controversial. The harmless characteristics of the individual components lead to this assumption, especially in the case of natural deep eutectic solvents (NADES) which are a subgroup of DES formed by primary metabolites (e.g., sugar, polyols, and amino acids at a specific molar proportion). Nevertheless, it is essential to consider the potential synergistic effects that might arise from the combination of these DES components, as they could influence the overall hazardous properties and ecological footprint of these eutectic mixtures [27]. It is anticipated that the number of studies on the toxicity of these compounds will increase in the future. However, compared to traditional organic solvents, DES offer clear advantages, such as their negligible vapor pressure and non-flammability. They also exhibit good chemical and thermal stability, ensuring their reliability in various applications. Several studies have shown that, in general, DES can offer less toxicity in comparison to other neoteric solvents such as ILs [27]. One of the key properties of DES is their formation temperature. Unlike many mixtures with a formation temperature that is the average of the melting points of its components, DES have a lower melting point than the respective melting points of their individual constituents. This property is quite relevant in terms of energy cost-savings since less energy is required for DES formation [28; 29]. Previously, in our research group, a study was conducted on the efficiency of fatty acid extraction with eutectic solvents from untreated and ultrasound- and osmotic shock-pretreated microalgal biomass [25]. The results showed that the most promising phases were those based on choline chloride. As a novelty in this work, the effect of water content in choline chloride-based eutectic phases on the extraction capacity of the fatty acids present in untreated microalgal biomass is addressed, in order to perform a direct extraction from the starting material. Elsewhere, it has been reported that the use of hydrophilic DES helps disrupt the cell walls of microalgae, eliminating the necessity for pre-treatment procedures [30].