# Deep Eutectic Solvents as Extraction Media for
## 3 Conclusions  
The use of DES in the extractions of flavonoids has yielded overwhelmingly promising results. All of the applications reviewed have reported success in isolation and extraction of the target compounds, as well as competitive, if not superior, extraction rates compared with conventional solvents, in addition to the satisfactory behavior of the extract in the latter applications (such as direct analysis, synthesis or catalysis), wherever attempted.  
The issue of selectivity of the DES or NaDES used for the extraction of flavonoids has not been extensively researched yet. In fact, the majority of the published works focus on the extraction efficiency evaluated in terms of total flavonoid or total phenolic content, or anti-oxidant activity, and do not usually analyze the selectivity of the solvents on the extraction of certain molecules. Obviously, this is the next step that should be investigated. As a very good indicative example, [PERSON] et al. [65] have screened a series of DES comprised of ChCl and carboxylic acids as solvents for the extraction of phytochemicals from the leaves of walnut trees (_Juglans. regia_ L.). They found differences in selectivity in the extraction of 3-O-caffeoylquinic acid, quercetin 3-O-glucose, and quercetin O-pentoside among the various DES, and these results enabled them to choose the optimum system for their process.  
DES are extremely versatile, with variables such as the number of ingredients, their ratios, and the ingredients themselves. This versatility limits their number to the foresight and the resilience of the researcher, who can design and apply any DES to any system, through any method, with the promise that the resulting extraction will be efficient while being green, given the general properties of DES. The relatively low cost of DES ingredients coupled with an increased selectivity after careful planning means that a lean-process future would definitely involve DES in the extraction compendium.  
The fact that the DES extract system has a satisfactory performance in analytical methods [12] or chemical processes means that there is the potential for circumventing the last stage of extraction (separating the extract from the DES), using the system in its entirety instead. DES, being perfectly capable solvents, albeit viscous, can act as the solvent or carrier for the extract in its following stages, in some cases aiding in the reactions it might partake in or in the overall environment the extract will inhabit. The natural origin of NaDES would mean that such systems can be used in their entirety, even in products to be used or consumed by people (such as cosmetics or pharmaceuticals), without the need for extract isolation and further processing.  
A pioneer example of NaDES being utilized as both an extraction medium and a biocompatible, consumer-grade carrier is the patented process by [PERSON] et.al. [74], which encompasses all of the advantages and the potential they provide. This patent officially links the laboratory research results regarding the use of betaine-based NaDES, mixed with glycerol or water, for the extraction and storage of natural extracts from plants or microorganisms, and the subsequent use of the extract directly as a uniform, natural-origin product. Evidently, the patent of such a method means that the industry is ready and willing to employ NaDES as an immediate extraction-carrier system, even on a consumer level.  
This summary of flavonoid extractions via DES incorporates the essence of green chemistry, and the future of chemistry in general. Tailor-made solvents are applied to carefully designed conditions to collect a very valuable substance from a natural source with as little waste as possible. The simplicity of this sentence is deceptive, since careful design and research is required to replace conventional methods, however, these promising results can only act as fuel for future research.  
This research received no external funding.  
The authors declare no conflict of interest.