trilaminated structure (Yamada and Sakaguchi 1982); hence, the cell disruption of
Chlorophyta is hard because they have rigid and thick cell walls (Baudelet et al.
2017). Additionally, culture conditions could alter the cell wall structure and
composition (Eppink et al. 2017).
According to Parniakov et al. (2015), the pulse electric field (PEF) seems
promising for a controlled cell wall disruption as pre-treatment or combined with
other treatment processes, such as sonication or extraction with a green solvent
(Postma et al. 2016). But this technology has some disadvantages; e.g., the solution
must be free of ions, and energy consumption is strongly dependent on biomass
concentration (Günerken et al. 2015). Nevertheless, more research is needed to
improve the efficiency of the cell wall disruption for different microalgae biomass
concentrations and the liberation of products needs to be increased. Electrical arc
treatment is a relatively recent technique for extraction from biomass. This technique was applied for polyphenol extraction and resulted in lower energy consumption, 16 kJ/kg compared to 53–267 kJ/kg for PEF (Boussetta et al. 2013). This
could be of high interest for microalgae biorefinery. Two other processes are
promising: the subcritical water use and the high-pressure homogenization (Roux
et al. 2017), which suggest a positive energy balance for cell disruption.
3.1.3 Metabolite Extraction
After cell disruption, the next step is the extraction of products. Extraction methods
include the use of solvents, super- or subcritical fluids, polymers, ionic liquids,
membranes, or resins (see Table 3). The main objective of extraction is to obtain all
fractions with no loss either in quantity or in quality (avoiding alteration/loss in
functions). Reviews about this topic have been done by Eppink et al. (2017), Gong
et al. (2017), González-Delgado and Kafarov (2011), Michalak and Chojnacka
(2014), Postma et al. (2016), Roux et al. (2017), and improvements have mainly
focused on fuel/lipid extraction by either solvent or supercritical fluid extraction.
Conventional extraction procedures for lipids are hydraulic pressing, expeller
pressing, and solvent extraction (Cuellar-Bermudez et al. 2015; Ranjith Kumar
et al. 2015). For solvent extraction, hexane, hexane-isopropanol, or
chloroform-methanol are the main solvents used (Cuellar-Bermudez et al. 2015;
Ranjith Kumar et al. 2015). The adequate solvent blend must be chosen depending
on lipid polarity and solubility (Cuellar-Bermudez et al. 2015). The ideal solvent
blend for lipid extraction from microalgae seems to be chloroform-methanol in a
1:1 (%v/v) proportion (Ryckebosch et al. 2012). A wet technology for lipid
extraction was studied by the NAABB (National Alliance for Advanced Biofuels
and Bioproducts) at laboratory-scale and showed good performance with selective
separation of free fatty acids and tocopherol; this alternative offers energy savings
because harvesting and drying operations are not necessary (Marrone et al. 2017).
Recent advances have also been made in supercritical fluid extraction (SFE) (Nobre
et al. 2013; Yen et al. 2015). One advantage of SFE is the application for extraction
of both lipids and pigments. Nobre et al. (2013) achieved 33g lipid /100 g dry biomass
102
P.-L. Gorry et al.
Chlorophyta is hard because they have rigid and thick cell walls (Baudelet et al.
2017). Additionally, culture conditions could alter the cell wall structure and
composition (Eppink et al. 2017).
According to Parniakov et al. (2015), the pulse electric field (PEF) seems
promising for a controlled cell wall disruption as pre-treatment or combined with
other treatment processes, such as sonication or extraction with a green solvent
(Postma et al. 2016). But this technology has some disadvantages; e.g., the solution
must be free of ions, and energy consumption is strongly dependent on biomass
concentration (Günerken et al. 2015). Nevertheless, more research is needed to
improve the efficiency of the cell wall disruption for different microalgae biomass
concentrations and the liberation of products needs to be increased. Electrical arc
treatment is a relatively recent technique for extraction from biomass. This technique was applied for polyphenol extraction and resulted in lower energy consumption, 16 kJ/kg compared to 53–267 kJ/kg for PEF (Boussetta et al. 2013). This
could be of high interest for microalgae biorefinery. Two other processes are
promising: the subcritical water use and the high-pressure homogenization (Roux
et al. 2017), which suggest a positive energy balance for cell disruption.
3.1.3 Metabolite Extraction
After cell disruption, the next step is the extraction of products. Extraction methods
include the use of solvents, super- or subcritical fluids, polymers, ionic liquids,
membranes, or resins (see Table 3). The main objective of extraction is to obtain all
fractions with no loss either in quantity or in quality (avoiding alteration/loss in
functions). Reviews about this topic have been done by Eppink et al. (2017), Gong
et al. (2017), González-Delgado and Kafarov (2011), Michalak and Chojnacka
(2014), Postma et al. (2016), Roux et al. (2017), and improvements have mainly
focused on fuel/lipid extraction by either solvent or supercritical fluid extraction.
Conventional extraction procedures for lipids are hydraulic pressing, expeller
pressing, and solvent extraction (Cuellar-Bermudez et al. 2015; Ranjith Kumar
et al. 2015). For solvent extraction, hexane, hexane-isopropanol, or
chloroform-methanol are the main solvents used (Cuellar-Bermudez et al. 2015;
Ranjith Kumar et al. 2015). The adequate solvent blend must be chosen depending
on lipid polarity and solubility (Cuellar-Bermudez et al. 2015). The ideal solvent
blend for lipid extraction from microalgae seems to be chloroform-methanol in a
1:1 (%v/v) proportion (Ryckebosch et al. 2012). A wet technology for lipid
extraction was studied by the NAABB (National Alliance for Advanced Biofuels
and Bioproducts) at laboratory-scale and showed good performance with selective
separation of free fatty acids and tocopherol; this alternative offers energy savings
because harvesting and drying operations are not necessary (Marrone et al. 2017).
Recent advances have also been made in supercritical fluid extraction (SFE) (Nobre
et al. 2013; Yen et al. 2015). One advantage of SFE is the application for extraction
of both lipids and pigments. Nobre et al. (2013) achieved 33g lipid /100 g dry biomass
102
P.-L. Gorry et al.