12 Industrial Extraction of Microalgal Pigments
301
in the studies as well as specific key findings from each investigation. The extraction efficiency of phycobiliproteins is almost entirely dependent on the degree of
cell disruption as the water-soluble pigments are readily transferred to the aqueous
solvent after being liberated from the biomass. This is in contrast to the extraction
efficiency of water-insoluble pigments (such as chlorophylls and carotenoids), which
is determined by both the degree of cell disruption during biomass pretreatment and
the affinity of the incoming extraction solvent (organic solvent, pressurised organic
solvent or supercritical carbon dioxide) to the pigment molecules.
12.4.4 Pycoerythrin
Phycoerythrin (PE) is a red phycobiliprotein that is primarily found in the chloroplasts of cyanobacteria (such as Synechococcus sp., Phormidium sp., Leptolyngbya
sp.), red algae (such as Porphyridium cruentum) and cryptophytes (Rhodomonas
salina) (Benavides and Rito-Palomares 2006; Cuellar-Bermudez et al. 2015; Jubeau
et al. 2013; Thoisen et al. 2017; Viskari and Colyer 2003). Most studies on PE
recovery have used either filtered or concentrated wet biomass as their starting material (Tables 12.5 and 12.6). The most suitable cell rupture method for PE extraction will depend on the cell wall structure and is therefore species specific. Instead
of a cell wall, each cryptophyte cell possesses a fragile periplast underneath the
plasma membrane that can easily be ruptured through freeze-drying action (freezing
the biomass at −20 °C and then thawing it to room temperature). Freeze-thawing
Rhodomonas salina cells suspended in a phosphate buffer has been shown to be able
to achieve almost complete PE recovery from the biomass (Lawrenz et al. 2011;
Thoisen et al. 2017). On the other hand, cyanobacterial species have tougher cell
walls made of peptidoglycan that can only be disrupted with a mechanical pretreatment step, such as ultrasonication (Porphyridium cruentum) and nitrogen cavitation (Synechococcus CCMP 833) (Benavides and Rito-Palomares 2006; Viskari and
Colyer 2003). In their study investigating PE recovery from red algae (Porphyridium
cruentum), Jubeau et al. (2013) were able to extract almost 100 wt% of available
PE by using a 2-stage high-pressure homogenisation which permeabilised the cell
membrane in its first step (< 100 MPa) to recover low molecular-weight protein and
then ruptured the cell wall in its second step (> 100 MPa) to selectively recover PE.
Microalgal or cyanobacterial PE has to undergo a number of post-recovery purification steps (refer to Sect. 12.5) in order to meet the strict standards of pharmaceutical
or molecular biology field. The A585/A280 value indicates the molar ratio of PE
to other contaminating proteins in the solution and is used to determine PE purity
(Cuellar-Bermudez et al. 2015). Diagnostic and pharmaceutical-grade PE must have
an A585/A280 value greater than 4.
301
in the studies as well as specific key findings from each investigation. The extraction efficiency of phycobiliproteins is almost entirely dependent on the degree of
cell disruption as the water-soluble pigments are readily transferred to the aqueous
solvent after being liberated from the biomass. This is in contrast to the extraction
efficiency of water-insoluble pigments (such as chlorophylls and carotenoids), which
is determined by both the degree of cell disruption during biomass pretreatment and
the affinity of the incoming extraction solvent (organic solvent, pressurised organic
solvent or supercritical carbon dioxide) to the pigment molecules.
12.4.4 Pycoerythrin
Phycoerythrin (PE) is a red phycobiliprotein that is primarily found in the chloroplasts of cyanobacteria (such as Synechococcus sp., Phormidium sp., Leptolyngbya
sp.), red algae (such as Porphyridium cruentum) and cryptophytes (Rhodomonas
salina) (Benavides and Rito-Palomares 2006; Cuellar-Bermudez et al. 2015; Jubeau
et al. 2013; Thoisen et al. 2017; Viskari and Colyer 2003). Most studies on PE
recovery have used either filtered or concentrated wet biomass as their starting material (Tables 12.5 and 12.6). The most suitable cell rupture method for PE extraction will depend on the cell wall structure and is therefore species specific. Instead
of a cell wall, each cryptophyte cell possesses a fragile periplast underneath the
plasma membrane that can easily be ruptured through freeze-drying action (freezing
the biomass at −20 °C and then thawing it to room temperature). Freeze-thawing
Rhodomonas salina cells suspended in a phosphate buffer has been shown to be able
to achieve almost complete PE recovery from the biomass (Lawrenz et al. 2011;
Thoisen et al. 2017). On the other hand, cyanobacterial species have tougher cell
walls made of peptidoglycan that can only be disrupted with a mechanical pretreatment step, such as ultrasonication (Porphyridium cruentum) and nitrogen cavitation (Synechococcus CCMP 833) (Benavides and Rito-Palomares 2006; Viskari and
Colyer 2003). In their study investigating PE recovery from red algae (Porphyridium
cruentum), Jubeau et al. (2013) were able to extract almost 100 wt% of available
PE by using a 2-stage high-pressure homogenisation which permeabilised the cell
membrane in its first step (< 100 MPa) to recover low molecular-weight protein and
then ruptured the cell wall in its second step (> 100 MPa) to selectively recover PE.
Microalgal or cyanobacterial PE has to undergo a number of post-recovery purification steps (refer to Sect. 12.5) in order to meet the strict standards of pharmaceutical
or molecular biology field. The A585/A280 value indicates the molar ratio of PE
to other contaminating proteins in the solution and is used to determine PE purity
(Cuellar-Bermudez et al. 2015). Diagnostic and pharmaceutical-grade PE must have
an A585/A280 value greater than 4.