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thorough cross-comparison of literature data. The issue is far from being easy, notably because experimental evidence of deep eutectic solvent formation is still challenging. Indeed, some mixtures are not necessarily deep eutectic solvent, i.e.,
presenting an anomalous fusion temperature lower than that resulting from the ideal
mixture of the components. They also include a significant amount of water that is
intrinsically part of the mixture. In the same context, we have also observed esterification reaction between components of deep eutectic solvents formed by the combination of acids and alcohols. Comparison of extraction efficiencies in each
component of deep eutectic solvents beyond deep eutectic solvent itself should be
equally important to achieve (providing that the component would be a liquid) or
alternatively by using different mixture compositions. Such an evaluation has not
been performed in any of publications in the field. It will be of great interest to
highlight any added value of having a deep eutectic solvent rather than a simple
solvent mixture. Another key point is related to the methodologies for quantifying
polyphenols in extracts. While most of chromatography techniques are compatible
with deep eutectic solvents, care has to be taken with colorimetric protocols.
Although a meta-analysis of published works remains difficult to achieve in
order to assess the benefit of deep eutectic solvents for polyphenol extraction, several points are worth mentioning, making them highly promising media. Regarding
the performance of extraction, deep eutectic solvents are not necessarily better than
conventional solvents or ionic liquids. However, many authors have highlighted that
deep eutectic solvents allow a better stability and a better conservation of the
extracted polyphenols. As a result, recovery extraction could be bypassed while
systematically required when ionic liquids are used as extractant media. Many
authors have shown that eutectic solvents could retain the antioxidant properties of
polyphenols longer than conventional organic solvents. Interestingly, due to the
harmlessness of natural deep eutectic solvent, natural deep eutectic solvent extracts
can be anticipated to be used directly for many applications of polyphenol extracts,
namely, cosmetics. In that case, natural deep eutectic solvent could even be designed
as a part of product formulation.
To summarize, deep eutectic solvents may offer broader industrial perspectives
than classical solvents because they are globally cheaper, eco-friendly, and more
socially acceptable at the moment.
References
Abbott AP, Capper G, Davies DL et al (2001) Preparation of novel, moisture-stable, Lewisacidic ionic liquids containing quaternary ammonium salts with functional side chains. Chem
Commun:2010–2011. https://doi.org/10.1039/b106357j
Abbott AP, Capper G, Davies DL et al (2003) Novel solvent properties of choline chloride/urea
mixtures. Chem Commun:70–71. https://doi.org/10.1039/b210714g
Abbott AP, Boothby D, Capper G et al (2004) Deep eutectic solvents formed between choline chloride and carboxylic acids: versatile alternatives to ionic liquids. J Am Chem Soc
126:9142–9147. https://doi.org/10.1021/ja048266j
L. Percevault et al.
thorough cross-comparison of literature data. The issue is far from being easy, notably because experimental evidence of deep eutectic solvent formation is still challenging. Indeed, some mixtures are not necessarily deep eutectic solvent, i.e.,
presenting an anomalous fusion temperature lower than that resulting from the ideal
mixture of the components. They also include a significant amount of water that is
intrinsically part of the mixture. In the same context, we have also observed esterification reaction between components of deep eutectic solvents formed by the combination of acids and alcohols. Comparison of extraction efficiencies in each
component of deep eutectic solvents beyond deep eutectic solvent itself should be
equally important to achieve (providing that the component would be a liquid) or
alternatively by using different mixture compositions. Such an evaluation has not
been performed in any of publications in the field. It will be of great interest to
highlight any added value of having a deep eutectic solvent rather than a simple
solvent mixture. Another key point is related to the methodologies for quantifying
polyphenols in extracts. While most of chromatography techniques are compatible
with deep eutectic solvents, care has to be taken with colorimetric protocols.
Although a meta-analysis of published works remains difficult to achieve in
order to assess the benefit of deep eutectic solvents for polyphenol extraction, several points are worth mentioning, making them highly promising media. Regarding
the performance of extraction, deep eutectic solvents are not necessarily better than
conventional solvents or ionic liquids. However, many authors have highlighted that
deep eutectic solvents allow a better stability and a better conservation of the
extracted polyphenols. As a result, recovery extraction could be bypassed while
systematically required when ionic liquids are used as extractant media. Many
authors have shown that eutectic solvents could retain the antioxidant properties of
polyphenols longer than conventional organic solvents. Interestingly, due to the
harmlessness of natural deep eutectic solvent, natural deep eutectic solvent extracts
can be anticipated to be used directly for many applications of polyphenol extracts,
namely, cosmetics. In that case, natural deep eutectic solvent could even be designed
as a part of product formulation.
To summarize, deep eutectic solvents may offer broader industrial perspectives
than classical solvents because they are globally cheaper, eco-friendly, and more
socially acceptable at the moment.
References
Abbott AP, Capper G, Davies DL et al (2001) Preparation of novel, moisture-stable, Lewisacidic ionic liquids containing quaternary ammonium salts with functional side chains. Chem
Commun:2010–2011. https://doi.org/10.1039/b106357j
Abbott AP, Capper G, Davies DL et al (2003) Novel solvent properties of choline chloride/urea
mixtures. Chem Commun:70–71. https://doi.org/10.1039/b210714g
Abbott AP, Boothby D, Capper G et al (2004) Deep eutectic solvents formed between choline chloride and carboxylic acids: versatile alternatives to ionic liquids. J Am Chem Soc
126:9142–9147. https://doi.org/10.1021/ja048266j
L. Percevault et al.