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R. Halim
12.2.3 Ultrasonication
During ultrasonication, sonic waves are transmitted to the suspending medium to
create a continuous cycle of microbubble formation (rarefaction phase) and implosion (compression phase). The collapse of microbubbles releases shock waves which
bombard microalgal cells and shear their cell walls (Dong et al. 2016; Halim et al.
2013). The technology has successfully been used to enhance the yield of both
water-insoluble (e.g. astaxanthin) and water-insoluble (e.g. phycocyanin and phycoerythrin) pigments from various microalgal biomass (Benavides and Rito-Palomares
2006; Dong et al. 2014; Furuki et al. 2003; Lawrenz et al. 2011; Rodrigues et al.
2018; Zou et al. 2013). Ultrasonication, however, has been shown to have a slower
disruption rate than HPH and a relatively high energy requirement (Halim et al.
2013).
12.2.4 Pulse Electric Field (PEF)
PEF treatment subjects cells to pulses of high-intensity electric field. At sufficiently
high transmembrane voltage (0.5–1 V), the field causes cell membrane to become
irreversibly permeable (a phenomenon known as ‘electropermeabilisation’) (Dong
et al. 2016; Eing et al. 2013; Luengo et al. 2015; Sheng et al. 2011). Unlike the
other mechanical methods, PEF generally does not result in cell rupture and can
be particularly useful for the selective extraction of small intracellular components
that can pass through the permeabilised cell membrane/wall complex, such as watersoluble enzymes and ionic compounds (Dong et al. 2016; Eing et al. 2013; Luengo
et al. 2015; Sheng et al. 2011). Since PEF treatment requires an electrically nonconductive medium for its operation, saltwater algal species will have to be dewatered and washed with a large amount of fresh water prior to being subjected to the
treatment. In Luengo et al. (2015), PEF treatment was shown to be able to substantially increase (by a factor of 4) the yield of lutein extraction from Chlorella vulgaris
biomass.
12.2.5 Osmotic Shock
Sudden change in the solute concentration of culture medium creates pressure difference between the cell cytoplasm and the medium. This can potentially result in cell
rupture if the species has a relatively weak cell wall (Dong et al. 2016). For freshwater
species (such as Botryococcus sp., Chlorella vulgaris and Scenedesmus sp.), osmotic
shock is carried out at hypertonic shift, triggered by adding solutes (such as NaCl and
sorbitol) to the culture medium. For saltwater species (such as Dunaliella viridis),
osmotic shock is performed at hypotonic shift, induced by transferring biomass to a
R. Halim
12.2.3 Ultrasonication
During ultrasonication, sonic waves are transmitted to the suspending medium to
create a continuous cycle of microbubble formation (rarefaction phase) and implosion (compression phase). The collapse of microbubbles releases shock waves which
bombard microalgal cells and shear their cell walls (Dong et al. 2016; Halim et al.
2013). The technology has successfully been used to enhance the yield of both
water-insoluble (e.g. astaxanthin) and water-insoluble (e.g. phycocyanin and phycoerythrin) pigments from various microalgal biomass (Benavides and Rito-Palomares
2006; Dong et al. 2014; Furuki et al. 2003; Lawrenz et al. 2011; Rodrigues et al.
2018; Zou et al. 2013). Ultrasonication, however, has been shown to have a slower
disruption rate than HPH and a relatively high energy requirement (Halim et al.
2013).
12.2.4 Pulse Electric Field (PEF)
PEF treatment subjects cells to pulses of high-intensity electric field. At sufficiently
high transmembrane voltage (0.5–1 V), the field causes cell membrane to become
irreversibly permeable (a phenomenon known as ‘electropermeabilisation’) (Dong
et al. 2016; Eing et al. 2013; Luengo et al. 2015; Sheng et al. 2011). Unlike the
other mechanical methods, PEF generally does not result in cell rupture and can
be particularly useful for the selective extraction of small intracellular components
that can pass through the permeabilised cell membrane/wall complex, such as watersoluble enzymes and ionic compounds (Dong et al. 2016; Eing et al. 2013; Luengo
et al. 2015; Sheng et al. 2011). Since PEF treatment requires an electrically nonconductive medium for its operation, saltwater algal species will have to be dewatered and washed with a large amount of fresh water prior to being subjected to the
treatment. In Luengo et al. (2015), PEF treatment was shown to be able to substantially increase (by a factor of 4) the yield of lutein extraction from Chlorella vulgaris
biomass.
12.2.5 Osmotic Shock
Sudden change in the solute concentration of culture medium creates pressure difference between the cell cytoplasm and the medium. This can potentially result in cell
rupture if the species has a relatively weak cell wall (Dong et al. 2016). For freshwater
species (such as Botryococcus sp., Chlorella vulgaris and Scenedesmus sp.), osmotic
shock is carried out at hypertonic shift, triggered by adding solutes (such as NaCl and
sorbitol) to the culture medium. For saltwater species (such as Dunaliella viridis),
osmotic shock is performed at hypotonic shift, induced by transferring biomass to a