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.
Highlights
The valorization of agricultural by-products by extracting their bioactive compounds is a very interesting alternative to their incineration or even composting, as addressed by FAO [1] in their proposed food waste recovery hierarchy
Regarding the type of deep eutectic solvents (DES) applied in this area, the use of choline chloride (ChCl)-based natural deep eutectic solvents (NADES) has been the most extended combined with different types of hydrogen bond donors (HBD), combinations of lactic acid and glucose have demonstrated their suitability for the extraction of phenolic and acidic compounds [35,36]
The use of eutectic solvents for extraction and isolation of bioactive compounds from natural raw materials, agro-industrial products and by-products has sharply increased due to the particular characteristics of these solvents and the advantages that their use provides in this field
Summary
The valorization of agricultural by-products by extracting their bioactive compounds is a very interesting alternative to their incineration or even composting, as addressed by FAO [1] in their proposed food waste recovery hierarchy. An essential characteristic of DESs, and especially NADEs, is their low toxicity These solvents can be applied directly in food and pharmaceutical formulations if made with primary metabolites of cells, which have recently been called NADESs [7]. Most of studies using DESs as extraction solvents to recover bioactive phytochemicals are mainly based on plants, other natural sources such as vegetables, fruits and byproducts from food and agro-food industry have been investigated. Several combinations of DESs have been tested for their ability to extract bioactive compounds from different plants, covering a broad range of phytochemicals such as flavonoids, phenolic acids, anthocyanins, and alkaloids as they will be seen below. The main bioactive compounds extracted using DESs are summarized along with the best extraction conditions for each use
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