12 Industrial Extraction of Microalgal Pigments
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the targeted pigment and to recycle the organic solvent. In order to reduce the energy
requirement of distillation, the selected solvent for industrial-scale pigment extraction should be relatively volatile and have a low boiling point. Since the extracted
pigments will likely be used for nutraceutical or food applications, it is also important
to use green solvents or solvents of low toxicity for the extraction (e.g. acetone and
ethanol instead of chloroform and methanol).
12.3.2 Pressurised Liquid Extraction (PLE)
Pressurised liquid extraction (PLE), also known as pressurised solvent extraction or
accelerated solvent extraction, is an organic solvent extraction that is performed at
elevated temperature and pressure. (Halim et al. 2012a; Herrero et al. 2006; Jaime
et al. 2010). Solvent is maintained in its liquid state throughout the operation. The
temperature and pressure elevation help to disintegrate cellular structures and accelerate mass transfer kinetics. As a result, PLE uses less solvent and can complete the
extraction process in a shorter timeframe compared to a conventional organic solvent
extraction (Halim et al. 2012a; Herrero et al. 2006; Jaime et al. 2010). However, PLE
has a higher energy requirement than conventional solvent extraction due to its use
of elevated temperature and pressure. High temperature (up to 200 °C) may also
lead to the degradation of thermally sensitive proteins and pigments (Halim et al.
2012a; Herrero et al. 2006; Jaime et al. 2010). In their study investigating the use of
PLE (with either hexane or ethanol) to obtain astaxanthin from red-cyst H. pluvialis,
Jaime et al. (2010) found that temperature increase during PLE improved extraction
yield but had a negative effect on the structural integrity and thus the antioxidant
activity of the extract (Table 12.3). PLE (with hexane, ethanol, water or acetone) has
also been applied for the extraction of β-carotene from D. salina (Denery et al. 2004;
Herrero et al. 2006) (Table 12.4).
12.3.3 Ionic Liquid Extraction
Ionic liquids are salts of loosely held anions and cations that remain in liquid state
over a wide range of temperature (melting point < 100 °C) (Desai et al. 2016;
Praveenkumar et al. 2015; Rodrigues et al. 2018). Many of their physical properties, such as polarity, hydrophobicity and viscosity, are adjustable and can be
controlled by the exchange or combination of ions. Such physical versatility means
that their solvating power can be specifically tailored to the target compound in
order to enhance solvent-solute interaction and increase extraction efficiency. This
makes ionic liquids a potent extracting solvent and an attractive alternative to organic
solvents for various extraction systems, including pigments from microalgae (Desai
et al. 2016; Praveenkumar et al. 2015; Rodrigues et al. 2018). Most ionic liquids,
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the targeted pigment and to recycle the organic solvent. In order to reduce the energy
requirement of distillation, the selected solvent for industrial-scale pigment extraction should be relatively volatile and have a low boiling point. Since the extracted
pigments will likely be used for nutraceutical or food applications, it is also important
to use green solvents or solvents of low toxicity for the extraction (e.g. acetone and
ethanol instead of chloroform and methanol).
12.3.2 Pressurised Liquid Extraction (PLE)
Pressurised liquid extraction (PLE), also known as pressurised solvent extraction or
accelerated solvent extraction, is an organic solvent extraction that is performed at
elevated temperature and pressure. (Halim et al. 2012a; Herrero et al. 2006; Jaime
et al. 2010). Solvent is maintained in its liquid state throughout the operation. The
temperature and pressure elevation help to disintegrate cellular structures and accelerate mass transfer kinetics. As a result, PLE uses less solvent and can complete the
extraction process in a shorter timeframe compared to a conventional organic solvent
extraction (Halim et al. 2012a; Herrero et al. 2006; Jaime et al. 2010). However, PLE
has a higher energy requirement than conventional solvent extraction due to its use
of elevated temperature and pressure. High temperature (up to 200 °C) may also
lead to the degradation of thermally sensitive proteins and pigments (Halim et al.
2012a; Herrero et al. 2006; Jaime et al. 2010). In their study investigating the use of
PLE (with either hexane or ethanol) to obtain astaxanthin from red-cyst H. pluvialis,
Jaime et al. (2010) found that temperature increase during PLE improved extraction
yield but had a negative effect on the structural integrity and thus the antioxidant
activity of the extract (Table 12.3). PLE (with hexane, ethanol, water or acetone) has
also been applied for the extraction of β-carotene from D. salina (Denery et al. 2004;
Herrero et al. 2006) (Table 12.4).
12.3.3 Ionic Liquid Extraction
Ionic liquids are salts of loosely held anions and cations that remain in liquid state
over a wide range of temperature (melting point < 100 °C) (Desai et al. 2016;
Praveenkumar et al. 2015; Rodrigues et al. 2018). Many of their physical properties, such as polarity, hydrophobicity and viscosity, are adjustable and can be
controlled by the exchange or combination of ions. Such physical versatility means
that their solvating power can be specifically tailored to the target compound in
order to enhance solvent-solute interaction and increase extraction efficiency. This
makes ionic liquids a potent extracting solvent and an attractive alternative to organic
solvents for various extraction systems, including pigments from microalgae (Desai
et al. 2016; Praveenkumar et al. 2015; Rodrigues et al. 2018). Most ionic liquids,