288
However, for certain applications (e.g., cosmetics or food supplements), it is possible to retain the solvent with the extracted polyphenols and use this mixture
directly (Jeong et al. 2017; Choi and Verpoorte 2019). Thus, Jeong and coworkers
noted that eutectic solvents based on betaine and glycerol did not give better extraction results than traditional organic solvents. It has been however proposed to use
the extracts without separating the metabolites from the eutectic solvents. The
eutectic solvent would be an integral part of the formulation. As a result, the choice
of the components of the eutectics should be compatible with cosmetic regulations.
Taken together, the results of this study demonstrate that the mixture composed of
betaine, glycerol, and glucose can be applied on a large scale as a multifunctional
and cheap medium, i.e., for efficient extraction and stable storage of catechins,
being at the same time an active ingredient. For example, green tea extracts prepared in this way could be readily used in cosmetic products or in pharmaceutical
formulations for skin (Jeong et al. 2017).
We can mention now that beyond the separation from the deep eutectic solvent
extracting media, the goal of recovery is to obtain metabolites from complex matrices with different degrees of purity. In some cases, such as in the pharmaceutical
field, it is necessary to obtain molecules of the highest purity. In other areas such as
cosmetics or the food industry, it is sufficient to obtain a mixture of molecules.
7.5 Quantification, Identification and Antioxidant
Activity of Polyphenols
7.5.1 Identification and Quantification of Polyphenols
An important point is the identification and quantification of the polyphenolics in
the extracts. Different methods have been employed taking into account that solvents cannot be simply evaporated as in the case of traditional solvents. Figure 7.10
gathers all the different methods that have been employed. Two major approaches
currently exist, direct characterization or characterization after removal of the eutectic solvent, notably by using liquid/liquid extraction or chromatographic separation
systems such as solid phase extraction (SPE) columns.
The amount of total phenolic contents in extracts is generally quantified by colorimetric methods based on calibration curves derived from known amounts of purified standards such as gallic acid or catechin. The most widely employed assay is
the Folin-Ciocalteu method (Fig. 7.11), which displays several advantages
(Singleton et al. 1999). It is quite easy to handle and rapid and does not require
heavy equipment. It covers all the range of phenolics including monophenolics,
contrariwise to other colorimetric methods based on iron or aluminum salts that
cannot react with monophenols (Singleton et al. 1999). For instance, the determination of total flavonoids is very often conducted by using AlCl 3 and expressed as rutin
or (+)-catechin equivalent.
L. Percevault et al.
However, for certain applications (e.g., cosmetics or food supplements), it is possible to retain the solvent with the extracted polyphenols and use this mixture
directly (Jeong et al. 2017; Choi and Verpoorte 2019). Thus, Jeong and coworkers
noted that eutectic solvents based on betaine and glycerol did not give better extraction results than traditional organic solvents. It has been however proposed to use
the extracts without separating the metabolites from the eutectic solvents. The
eutectic solvent would be an integral part of the formulation. As a result, the choice
of the components of the eutectics should be compatible with cosmetic regulations.
Taken together, the results of this study demonstrate that the mixture composed of
betaine, glycerol, and glucose can be applied on a large scale as a multifunctional
and cheap medium, i.e., for efficient extraction and stable storage of catechins,
being at the same time an active ingredient. For example, green tea extracts prepared in this way could be readily used in cosmetic products or in pharmaceutical
formulations for skin (Jeong et al. 2017).
We can mention now that beyond the separation from the deep eutectic solvent
extracting media, the goal of recovery is to obtain metabolites from complex matrices with different degrees of purity. In some cases, such as in the pharmaceutical
field, it is necessary to obtain molecules of the highest purity. In other areas such as
cosmetics or the food industry, it is sufficient to obtain a mixture of molecules.
7.5 Quantification, Identification and Antioxidant
Activity of Polyphenols
7.5.1 Identification and Quantification of Polyphenols
An important point is the identification and quantification of the polyphenolics in
the extracts. Different methods have been employed taking into account that solvents cannot be simply evaporated as in the case of traditional solvents. Figure 7.10
gathers all the different methods that have been employed. Two major approaches
currently exist, direct characterization or characterization after removal of the eutectic solvent, notably by using liquid/liquid extraction or chromatographic separation
systems such as solid phase extraction (SPE) columns.
The amount of total phenolic contents in extracts is generally quantified by colorimetric methods based on calibration curves derived from known amounts of purified standards such as gallic acid or catechin. The most widely employed assay is
the Folin-Ciocalteu method (Fig. 7.11), which displays several advantages
(Singleton et al. 1999). It is quite easy to handle and rapid and does not require
heavy equipment. It covers all the range of phenolics including monophenolics,
contrariwise to other colorimetric methods based on iron or aluminum salts that
cannot react with monophenols (Singleton et al. 1999). For instance, the determination of total flavonoids is very often conducted by using AlCl 3 and expressed as rutin
or (+)-catechin equivalent.
L. Percevault et al.