194
extraction solvent, hence reducing the environmental pollution. In addition, the
used deep eutectic solvent showed high stability, low density, and a melting point
near room temperature (Habibollahi et al. 2018).
Deep Eutectic Solvent-Based Subcritical Water Extraction
When increasing the temperature of water above its boiling point (between 100 and
374 °C) but keeping the pressure tuned for liquid state, subcritical water is obtained.
At these conditions, water acts like an organic solvent that can dissolve a wide range
of analytes of low polarities, hence presenting the advantage of using only water as
the extraction solvent. New approaches on using deep eutectic solvent in a certain
percentage with subcritical water are being reported. Nevertheless, one should
underline the high amount of water added to the deep eutectic solvent (generally
superior to 50% volume), thus questioning the remaining structure of the deep
eutectic solvent. For example, Machmudah et al. (2018) tested the effect of the addition of 10–30% volume of deep eutectic solvent to pure water on the extraction of
xanthone (Machmudah et al. 2018). Table 6.3 presents some examples of the application of subcritical water extraction technique with deep eutectic solvents as
extraction solvents.
Saravana et al. (2018a, b) proved that the yield of polysaccharides obtained using
the optimal deep eutectic solvent (choline chloride/glycerol (1:2 molar ratio) + 70%
water) was at least twice of that obtained from a solution of HCl/water mixture, usually used to extract polysaccharides (Saravana et al. 2018a, b). Through adding
10–30% citric acid/alanine (1:1 molar ratio) deep eutectic solvent to water media,
Machmudah et al. (2018) proved the efficacy of the resulting subcritical water
extraction method to extract xanthones. Accordingly, scanning electron microscope
images showed the disruption of the surface of the pericarps of mangosteen after
treatment by this method at high temperature. The formation of pores was obviously
observed via the pronounced cleavage of intermolecular and intramolecular bonds
in and/or between lignin, cellulose, and hemicellulose by deep eutectic solvent
(Machmudah et al. 2018).
Deep Eutectic Solvent-Based Aqueous Two-Phase System
Such system is formed when two polymers, one polymer, and one salt or two salts
are mixed in the presence of water, forming two distinct aqueous phases. K 2 HPO 4 is
the frequently used salt because it demonstrated a better phase-forming ability than
other salts (for example, Na 2 HPO 4 and KH 2 PO 4 ) (Li et al. 2016). This technique is
widely used to extract proteins. It prevents proteins denaturation and preserves their
biological activity. Also, it is used for the extraction of genetic materials, drugs,
cells, and organelles (Zeng et al. 2014; Li et al. 2016). The detailed process of the
aqueous two-phase system is illustrated in Fig. 6.5.
L. Nakhle et al.
extraction solvent, hence reducing the environmental pollution. In addition, the
used deep eutectic solvent showed high stability, low density, and a melting point
near room temperature (Habibollahi et al. 2018).
Deep Eutectic Solvent-Based Subcritical Water Extraction
When increasing the temperature of water above its boiling point (between 100 and
374 °C) but keeping the pressure tuned for liquid state, subcritical water is obtained.
At these conditions, water acts like an organic solvent that can dissolve a wide range
of analytes of low polarities, hence presenting the advantage of using only water as
the extraction solvent. New approaches on using deep eutectic solvent in a certain
percentage with subcritical water are being reported. Nevertheless, one should
underline the high amount of water added to the deep eutectic solvent (generally
superior to 50% volume), thus questioning the remaining structure of the deep
eutectic solvent. For example, Machmudah et al. (2018) tested the effect of the addition of 10–30% volume of deep eutectic solvent to pure water on the extraction of
xanthone (Machmudah et al. 2018). Table 6.3 presents some examples of the application of subcritical water extraction technique with deep eutectic solvents as
extraction solvents.
Saravana et al. (2018a, b) proved that the yield of polysaccharides obtained using
the optimal deep eutectic solvent (choline chloride/glycerol (1:2 molar ratio) + 70%
water) was at least twice of that obtained from a solution of HCl/water mixture, usually used to extract polysaccharides (Saravana et al. 2018a, b). Through adding
10–30% citric acid/alanine (1:1 molar ratio) deep eutectic solvent to water media,
Machmudah et al. (2018) proved the efficacy of the resulting subcritical water
extraction method to extract xanthones. Accordingly, scanning electron microscope
images showed the disruption of the surface of the pericarps of mangosteen after
treatment by this method at high temperature. The formation of pores was obviously
observed via the pronounced cleavage of intermolecular and intramolecular bonds
in and/or between lignin, cellulose, and hemicellulose by deep eutectic solvent
(Machmudah et al. 2018).
Deep Eutectic Solvent-Based Aqueous Two-Phase System
Such system is formed when two polymers, one polymer, and one salt or two salts
are mixed in the presence of water, forming two distinct aqueous phases. K 2 HPO 4 is
the frequently used salt because it demonstrated a better phase-forming ability than
other salts (for example, Na 2 HPO 4 and KH 2 PO 4 ) (Li et al. 2016). This technique is
widely used to extract proteins. It prevents proteins denaturation and preserves their
biological activity. Also, it is used for the extraction of genetic materials, drugs,
cells, and organelles (Zeng et al. 2014; Li et al. 2016). The detailed process of the
aqueous two-phase system is illustrated in Fig. 6.5.
L. Nakhle et al.