###### Abstract  
In this work, a review about the applicability of eutectic solvents, mainly deep eutectic solvents (DES) and natural deep eutectic solvents (NADES), for the extraction of bioactive compounds from natural products has been carried out. These alternative solvents have shown not only to have high extraction yields but also to be environmentally friendly, exhibiting very low or almost no toxicity, compared to conventional organic solvents. The last trends and main extraction methods that have been most widely used in studies using these emerging solvents have been reviewed, as well as the varied natural sources in which they have been used, including agro-food by-products. Besides the toxicity, biodegradability of these solvents is reviewed. Likewise, different reported bioactivity tests have been included, in which extracts obtained with these ecological solvents have been tested from antioxidant activity analysis to in vivo studies with rats, through in vitro cytotoxicity tests. bioactivity; deep eutectic solvent; extraction; biomass; by-products +
Footnote †: journal: Medical Biology  
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are recognized as GRAS, besides, most of them are polar, not capable of solubilizing apolar molecules, making extractions very limited. In addition, due to the climatic drift observed in recent years, there is a significant concern for the environment. Therefore, there is a desire to reduce energy, water and solvent consumption, and carbon emissions, increasing the demand of ecological extraction processes. Green technologies are being tested, taking into account the need to be effective and efficient, increasing throughput, improving process selectivity, and reducing energy consumption. A solution to this problem is the use of alternative solvents: ionic liquid (ILs) solvents, deep eutectic solvents (DESs), and natural eutectic solvents (NADESs), generally reported as green solvents. Some authors have discussed the application of these solvents for the extraction of bioactive compounds, but they have been focused on specific applications or compounds. This review attempts to explain the role of DESs and NADESs, to extract bioactive compounds from natural products, which have shown not only to have high yields but also to be eco-friendly and to present low or almost zero toxicity and will provide an updated discussion of the most relevant trends in this area [2]. Eutectic solvents are homogenous liquids whose melting points are lower than the individual melting points of the individual components in the mixture. In fact, the name comes from the Greek words \"\(\epsilon\)%\" (eu = well) and \"\(\epsilon\)%%\" (texis = melting). In this category of liquids, we can find mainly two types: ILs and DESs. Ionic liquids are molten salts that remain liquid at room temperature. Generally, they are the result of the combination of organic cations with organic or inorganic anions. More than \(10^{8}\) possible combinations are estimated [3]. Their main characteristic is having lower melting points than their elements. These substances have physicochemical properties that can be easily modified by the appropriate cation/anion combination, providing ideal properties such as thermal stability, polar variability, high boiling points, good dissolving, and extractability. Besides, ILs have low volatility and flammability, which make them safer than organic solvents. Despite this, ILs have faced difficulties since they have been regulated by the Food and Drug Administration (FDA), the Codex Alimentarius, the Food and Agriculture Organization of the United Nations (FAO), the World Health Organization (WHO) or the European Food Safety Authority (EFSA), because of the toxicity observed in some anions and cations managed, low biodegradability, and complex purification [2]. Fortunately, emerging solvents, ILs analogs, called DESs, appeared some years ago.