12 Industrial Extraction of Microalgal Pigments
285
An SCCO 2 extraction setup can be divided into 3 separate parts (Fig. 12.2b). Part
I consists of a feed pump which compresses and delivers liquid CO 2 to the extraction
vessel. Part II comprises an extraction vessel where the microalgal biomass is placed
and an oven module that heats incoming CO 2 and converts it into supercritical fluid
in the extraction vessel. Part III consists of a heated micrometering valve that depressurises the outgoing SCCO 2 . Once completely decompressed, CO 2 evaporates back
to the ambient as a gas and the recovered pigment is forced to precipitate out as a
solvent-free liquid extract.
The use of SCCO 2 extraction for the recoveries of astaxanthin from Haematococcus pluvialis (Fujii 2012; Machmudah et al. 2006; Reyes et al. 2014) and βcarotene from Dunaliella salina has been demonstrated (Pour Hosseini et al. 2017)
(Tables 12.2–12.4). Because of its non-polar nature, SCCO 2 is unable to effectively
interact with polar pigment molecules such as astaxanthin. A polar modifier (also
known as co-solvent or entrainer), such as ethanol, is therefore often added to the
solvent during the extraction process in order to enhance its affinity towards the
targeted pigment and increase extraction yield.
12.4 Processing Pathways for Pigment Recovery
from Microalgal Biomass
This section examines the different biomass processing pathways used for extracting
pigments from microalgae. We focus our discussion on the extraction of four industrially relevant and highly valuable microalgal pigments: astaxanthin, β-carotene,
phycoerythrin and phycocyanin.
12.4.1 Astaxanthin Recovery
Tables 12.2 and 12.3 summarise previous studies that have investigated astaxanthin
recovery from microalgal biomass (Denery et al. 2004; Desai et al. 2016; Dong
et al. 2014; Jaime et al. 2010; Kang and Sim 2007; Kobayashi et al. 1997; Molino
et al. 2018; Sarada et al. 2006; Zhao et al. 2009; Zou et al. 2013). The tables
report the biomass pretreatment (cell rupture) and the extraction method used in
each study as well as key findings obtained from each investigation. As can be seen
from the tables, Haematococcus pluvialis was the species used in majority of the
studies. H.pluvialis cells can accumulate significant amounts of astaxanthin (up to 7
wt%) in their cytoplasm during the encystment phase of their life cycles. The cells,
however, are protected by thick, robust and exceedingly tough bilayered cell walls
that consist of an outer trilaminar sheath (made of algaenan) and an inner secondary
polysaccharide wall (made of mannan). Astaxanthin recovery from H.pluvialis
generally subsribes to a two-step cell rupture and extraction procedure. During
the cell rupture step, the biomass is subjected to a mechanical pretreatment (bead
miling/ultrasonication/microwave), a chemical pretreatment (HCl hydrolysis/ionic
285
An SCCO 2 extraction setup can be divided into 3 separate parts (Fig. 12.2b). Part
I consists of a feed pump which compresses and delivers liquid CO 2 to the extraction
vessel. Part II comprises an extraction vessel where the microalgal biomass is placed
and an oven module that heats incoming CO 2 and converts it into supercritical fluid
in the extraction vessel. Part III consists of a heated micrometering valve that depressurises the outgoing SCCO 2 . Once completely decompressed, CO 2 evaporates back
to the ambient as a gas and the recovered pigment is forced to precipitate out as a
solvent-free liquid extract.
The use of SCCO 2 extraction for the recoveries of astaxanthin from Haematococcus pluvialis (Fujii 2012; Machmudah et al. 2006; Reyes et al. 2014) and βcarotene from Dunaliella salina has been demonstrated (Pour Hosseini et al. 2017)
(Tables 12.2–12.4). Because of its non-polar nature, SCCO 2 is unable to effectively
interact with polar pigment molecules such as astaxanthin. A polar modifier (also
known as co-solvent or entrainer), such as ethanol, is therefore often added to the
solvent during the extraction process in order to enhance its affinity towards the
targeted pigment and increase extraction yield.
12.4 Processing Pathways for Pigment Recovery
from Microalgal Biomass
This section examines the different biomass processing pathways used for extracting
pigments from microalgae. We focus our discussion on the extraction of four industrially relevant and highly valuable microalgal pigments: astaxanthin, β-carotene,
phycoerythrin and phycocyanin.
12.4.1 Astaxanthin Recovery
Tables 12.2 and 12.3 summarise previous studies that have investigated astaxanthin
recovery from microalgal biomass (Denery et al. 2004; Desai et al. 2016; Dong
et al. 2014; Jaime et al. 2010; Kang and Sim 2007; Kobayashi et al. 1997; Molino
et al. 2018; Sarada et al. 2006; Zhao et al. 2009; Zou et al. 2013). The tables
report the biomass pretreatment (cell rupture) and the extraction method used in
each study as well as key findings obtained from each investigation. As can be seen
from the tables, Haematococcus pluvialis was the species used in majority of the
studies. H.pluvialis cells can accumulate significant amounts of astaxanthin (up to 7
wt%) in their cytoplasm during the encystment phase of their life cycles. The cells,
however, are protected by thick, robust and exceedingly tough bilayered cell walls
that consist of an outer trilaminar sheath (made of algaenan) and an inner secondary
polysaccharide wall (made of mannan). Astaxanthin recovery from H.pluvialis
generally subsribes to a two-step cell rupture and extraction procedure. During
the cell rupture step, the biomass is subjected to a mechanical pretreatment (bead
miling/ultrasonication/microwave), a chemical pretreatment (HCl hydrolysis/ionic