287
performed a multivariate study using the RSM method (Bi et al. 2013). The correlation of several parameters makes it possible to highlight the effects of the solvents
and/or the technologies used. The response surface methodology (RSM) is a practical tool for optimizing complex extraction procedures and can evaluate multiple
parameters and their interactions (Yang et al. 2008). The RSM is always used in
combination with the Box-Behnken design (BBD). Compared to the central composite design (CCD), the BBD avoids the axial points outside the experiment level
and requires fewer runs (Marcet et al. 2018). In the case of studies with eutectic
solvents, the number of parameters is even greater than in the case of conventional
studies. Indeed, it is necessary to consider not only the type of solvent but also the
stoichiometries of the components or the proportion of water involved. This makes
the studies based on the RSM methods particularly relevant.
The difficulty in choosing the parameters of extraction using eutectic solvents is
due to the range of parameters to be controlled (plant-to-solvent ratio, extraction
temperature, extraction duration, eutectic mixture used, percentage of water, technology extraction, etc.), often addressed in an empirical manner. Studying parameters screening by using the response surface method allows a rationalization of the
impact of the different factors on extraction rates or even on the type of metabolites
extracted. This method allows a multifactorial study that highlights the synergies of
the parameters studied.
7.4.5 Polyphenol Recovery
When the objectives are to obtain polyphenol metabolites free from solvents, especially deep eutectic solvent herein, recovery of polyphenols is necessary. Several
methods for separating eutectic solvents from extracted polyphenols have already
been described in the literature. Most of these methods are based on what had
already been developed with ionic liquids. The elimination of the solvent was generally regarded as a brake for the development of ionic liquids and now eutectics in
industrial extraction processes. Indeed, these solvents have a low vapor pressure
that makes them safe but almost impossible to evaporate with traditional protocols.
Elimination of eutectic solvents often leads to a significant decrease in the overall
efficiency of the extraction protocol.
The use of microporous resin type AB-8 was found to be efficient for the separation of the eutectic solvent from the extracted polyphenols with a recovery rate of
almost 72% (Cui et al. 2018). The major drawback of this method remains the large
amount of solvent necessary to separate the compounds. Indeed, for 24 mL of
extract, 270 mL of deionized water and 270 mL of 95% ethanol were necessary (Cui
et al. 2018). Similarly, C18 type SPE columns were used to separate the eutectic
solvents from the extracted flavonoids (Mansur et al. 2019). An excellent recovery
rate of 97% was obtained. But here again, a large amount of solvents was required:
for 0.5 mL of extract, 6 mL of acidified water and 8 mL of methanol were employed.
7 Extraction of Plant and Algal Polyphenols Using Eutectic Solvents
performed a multivariate study using the RSM method (Bi et al. 2013). The correlation of several parameters makes it possible to highlight the effects of the solvents
and/or the technologies used. The response surface methodology (RSM) is a practical tool for optimizing complex extraction procedures and can evaluate multiple
parameters and their interactions (Yang et al. 2008). The RSM is always used in
combination with the Box-Behnken design (BBD). Compared to the central composite design (CCD), the BBD avoids the axial points outside the experiment level
and requires fewer runs (Marcet et al. 2018). In the case of studies with eutectic
solvents, the number of parameters is even greater than in the case of conventional
studies. Indeed, it is necessary to consider not only the type of solvent but also the
stoichiometries of the components or the proportion of water involved. This makes
the studies based on the RSM methods particularly relevant.
The difficulty in choosing the parameters of extraction using eutectic solvents is
due to the range of parameters to be controlled (plant-to-solvent ratio, extraction
temperature, extraction duration, eutectic mixture used, percentage of water, technology extraction, etc.), often addressed in an empirical manner. Studying parameters screening by using the response surface method allows a rationalization of the
impact of the different factors on extraction rates or even on the type of metabolites
extracted. This method allows a multifactorial study that highlights the synergies of
the parameters studied.
7.4.5 Polyphenol Recovery
When the objectives are to obtain polyphenol metabolites free from solvents, especially deep eutectic solvent herein, recovery of polyphenols is necessary. Several
methods for separating eutectic solvents from extracted polyphenols have already
been described in the literature. Most of these methods are based on what had
already been developed with ionic liquids. The elimination of the solvent was generally regarded as a brake for the development of ionic liquids and now eutectics in
industrial extraction processes. Indeed, these solvents have a low vapor pressure
that makes them safe but almost impossible to evaporate with traditional protocols.
Elimination of eutectic solvents often leads to a significant decrease in the overall
efficiency of the extraction protocol.
The use of microporous resin type AB-8 was found to be efficient for the separation of the eutectic solvent from the extracted polyphenols with a recovery rate of
almost 72% (Cui et al. 2018). The major drawback of this method remains the large
amount of solvent necessary to separate the compounds. Indeed, for 24 mL of
extract, 270 mL of deionized water and 270 mL of 95% ethanol were necessary (Cui
et al. 2018). Similarly, C18 type SPE columns were used to separate the eutectic
solvents from the extracted flavonoids (Mansur et al. 2019). An excellent recovery
rate of 97% was obtained. But here again, a large amount of solvents was required:
for 0.5 mL of extract, 6 mL of acidified water and 8 mL of methanol were employed.
7 Extraction of Plant and Algal Polyphenols Using Eutectic Solvents