12 Industrial Extraction of Microalgal Pigments
267
Phycobiliproteins are found in prokaryotic cyanobacteria and eukaryotic red algae.
They are divided into four main classes according to their molecular structure: allophycocyanin (bluish-green in colour), phycocyanin (blue in colour), phycoerythrin
(red in colour), phycoerythrocyanin (orange in colour) (Cuellar-Bermudez et al.
2015; Khanra et al. 2018). Phycoerythrin (PE), a red phycobiliprotein with an
absorption peak at 565 nm, is primarily found in the chloroplast of cyanobacteria
(such as Synechococcus sp., Leptolyngbya sp.) and red algae (such as Porphyridium
cruentum), while phycocyanin (PC), a blue phycobiliprotein with an absorption peak
at 610—620 nm, is almost exclusively found in cyanobacteria (such as Spirulina
platensis) (Cuellar-Bermudez et al. 2015; Khanra et al. 2018; Rammuni et al. 2019).
Unlike chlorophylls and carotenoids, phycobiliproteins are soluble in water and
aqueous buffers (e.g. phosphate buffer) and can thus be recovered from microalgal
biomass without the use of organic solvents (Cuellar-Bermudez et al. 2015; Khanra
et al. 2018; Rammuni et al. 2019).
12.1.1.1 Astaxanthin and H.Pluvialis
H.pluvialis has received significant industrial attention because of its ability to
accumulate astaxanthin during the encystment stage. Astaxanthin is a red-coloured
alipathic carotenoid (C 40 H 52 O 4 ) with powerful antioxidant, anti-inflammatory and
immunoprotective properties (Cuellar-Bermudez et al. 2015; Denery et al. 2004;
Molino et al. 2018; Rammuni et al. 2019). It is currently used as an oral tablet
for treating Alzheimer’s disease, Parkinson’s disease, stroke, high cholesterol, liver
disease and age-related macular degeneration, a feed additive in aquaculture for fish
growth as well as a food colorant to provide salmon, trouts and crustaceans their characteristic pink colours. With astaxanthin content up to 7 wt% of its dry biomass (or
90 wt% total carotenoid), red-phase H.pluvialis cells accumulate significantly more
astaxanthin than any other known natural sources, such as yeast (Phaffia rhodozyma)
or other algal cells (e.g. B braunii, Chlorella sp. Chlorococcum sp. Dunaliella sp.
and Scenedesmus sp.) (Cuellar-Bermudez et al. 2015; Denery et al. 2004; Molino
et al. 2018; Rammuni et al. 2019).
H.pluvialis cells only accumulate astaxanthin in their cytoplasm during the encystment stage. The onset of the stage is triggered by unfavourable growth conditions,
such as nitrogen and phosphorous starvation, high solar intensities, salt stress and
elevated temperature. The encystment process is, however, accompanied by the
formation of a new thick, physically resistant and multi-layered cell wall (Sect. 12.1)
which limits the accessibility of the accumulated intracellular astaxanthin. Because of
the presence of hydroxyl (–OH) and keto (–C = O) bonds in its molecule, astaxanthin
is easily esterified with fatty acids and thus typically accumulated in its ester forms
(Cuellar-Bermudez et al. 2015; Denery et al. 2004; Molino et al. 2018; Rammuni
et al. 2019). In terms of distribution, up to 95% of astaxanthin in the cells can exist
in its ester forms (70% monoester and 25% diester) and only 5% in its free form.
Despite having a much stronger antioxidant property than the corresponding ester
forms, astaxanthin in its free form is unstable and highly susceptible to oxidation,
267
Phycobiliproteins are found in prokaryotic cyanobacteria and eukaryotic red algae.
They are divided into four main classes according to their molecular structure: allophycocyanin (bluish-green in colour), phycocyanin (blue in colour), phycoerythrin
(red in colour), phycoerythrocyanin (orange in colour) (Cuellar-Bermudez et al.
2015; Khanra et al. 2018). Phycoerythrin (PE), a red phycobiliprotein with an
absorption peak at 565 nm, is primarily found in the chloroplast of cyanobacteria
(such as Synechococcus sp., Leptolyngbya sp.) and red algae (such as Porphyridium
cruentum), while phycocyanin (PC), a blue phycobiliprotein with an absorption peak
at 610—620 nm, is almost exclusively found in cyanobacteria (such as Spirulina
platensis) (Cuellar-Bermudez et al. 2015; Khanra et al. 2018; Rammuni et al. 2019).
Unlike chlorophylls and carotenoids, phycobiliproteins are soluble in water and
aqueous buffers (e.g. phosphate buffer) and can thus be recovered from microalgal
biomass without the use of organic solvents (Cuellar-Bermudez et al. 2015; Khanra
et al. 2018; Rammuni et al. 2019).
12.1.1.1 Astaxanthin and H.Pluvialis
H.pluvialis has received significant industrial attention because of its ability to
accumulate astaxanthin during the encystment stage. Astaxanthin is a red-coloured
alipathic carotenoid (C 40 H 52 O 4 ) with powerful antioxidant, anti-inflammatory and
immunoprotective properties (Cuellar-Bermudez et al. 2015; Denery et al. 2004;
Molino et al. 2018; Rammuni et al. 2019). It is currently used as an oral tablet
for treating Alzheimer’s disease, Parkinson’s disease, stroke, high cholesterol, liver
disease and age-related macular degeneration, a feed additive in aquaculture for fish
growth as well as a food colorant to provide salmon, trouts and crustaceans their characteristic pink colours. With astaxanthin content up to 7 wt% of its dry biomass (or
90 wt% total carotenoid), red-phase H.pluvialis cells accumulate significantly more
astaxanthin than any other known natural sources, such as yeast (Phaffia rhodozyma)
or other algal cells (e.g. B braunii, Chlorella sp. Chlorococcum sp. Dunaliella sp.
and Scenedesmus sp.) (Cuellar-Bermudez et al. 2015; Denery et al. 2004; Molino
et al. 2018; Rammuni et al. 2019).
H.pluvialis cells only accumulate astaxanthin in their cytoplasm during the encystment stage. The onset of the stage is triggered by unfavourable growth conditions,
such as nitrogen and phosphorous starvation, high solar intensities, salt stress and
elevated temperature. The encystment process is, however, accompanied by the
formation of a new thick, physically resistant and multi-layered cell wall (Sect. 12.1)
which limits the accessibility of the accumulated intracellular astaxanthin. Because of
the presence of hydroxyl (–OH) and keto (–C = O) bonds in its molecule, astaxanthin
is easily esterified with fatty acids and thus typically accumulated in its ester forms
(Cuellar-Bermudez et al. 2015; Denery et al. 2004; Molino et al. 2018; Rammuni
et al. 2019). In terms of distribution, up to 95% of astaxanthin in the cells can exist
in its ester forms (70% monoester and 25% diester) and only 5% in its free form.
Despite having a much stronger antioxidant property than the corresponding ester
forms, astaxanthin in its free form is unstable and highly susceptible to oxidation,