5 Carotenoid Overproduction in Microalgae: Biochemical …
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that is produced during the first step is stressed for accumulating astaxanthin. Consequently, two growth media might be required. For instance Nahidian et al. (2018)
optimized a growth medium for the biomass production of Haematococcus pluvialis
TMU1 while Azizi et al. (2020) optimized a medium for astaxanthin production
by Haematococcus pluvialis NIES 144 and Haematococcus pluvialis UTEX 2505.
The optimization of the growth medium includes the selection of an adequate CO 2
source and/or aeration system. The optimization of all these parameters allowed
Azizi et al. (2020) to increase significantly the astaxanthin production by Haematococcus pluvialis. It is generally assumed that sodium carbonate is more economically
feasible because it is transported in an easier manner than gaseous carbon dioxide
and it exhibits a higher solubility than carbon dioxide (Hsueh et al. 2007) allowing
saturation of the growth medium in DIC (Sampathkumar and Gothandam 2019).
An often overlooked parameter in microalgal biotechnological at large scale is
the changing weather conditions, not only the light-dark cycle and the seasonality
but also the unpredictable and daily variations. Zhang et al. (2020) reported that in
Yunnan Province (China) the light intensity can reach 2000 μmol m
−2 s
−1 at noon
but the frequent rains and cloudy conditions reduce it at 150 μmol m
−2 s
−1 for
long period, therefore affecting astaxanthin production. To overcome this difficulty,
authors have suggested the use of organic carbon source as its utilization does not
rely on the photosynthetic activity.
Carotenoids are mostly hosted in the photosynthetic membranes where they serve
to harvest light and/or as antioxidant molecules. In eukaryotic organisms, the photosynthetic membranes are located in the chloroplasts (Solymosi 2012). When Cars
accumulate under stress, they are associated with lipids and proteins into droplets that
accumulate in the chloroplasts (β-carotene: Ben-Amotz et al. (1982); Derwenskus
et al. (2019)) or in the cytosol as in Haematoccoccus sp. (Lemoine et al. 2008). The
hydrophobic nature of carotenoids as well as their cellular localization lowers the
efficiency of the extraction procedures. This, together with the high cost of the downstream processes (Vinayak et al. 2015; Postma et al. 2016) have slowed down the
exploitation of microalgae as a source of carotenoids. To accelerate this development,
alternative extraction methods are developed. Supercritical CO 2 extraction, sometimes using a co-solvent (e.g. Chronopoulou et al. (2019)), pressurized extraction
(Derwenskus et al. 2019), ultrasound (Plaza et al. 2012), microwaves (Pasquet et al.
2011) and pulsed electric fields (Parniakov et al. 2015) are among these possibilities.
Nevertheless, these methods are destructive for the biomass and energy consuming
and the generated wastes need to be treated (Vinayak et al. 2015). To reduce the impact
of the biotechnological processes on the environment, biorefinery and biocompatible extraction concepts have been proposed. Both propose a holistic view of blue
biotechnology based on microalgae.
Clearly, carotenoids are among the molecules with an attractive future. Although
carotenoids are common molecules found in microalgae, they can be over accumulated in cells using environment constraints. Despite of this potential, there are not
enough data to make microalgae a real platform for the production of carotenoids.
More studies should be dedicated to the different aspects of the regulation of
111
that is produced during the first step is stressed for accumulating astaxanthin. Consequently, two growth media might be required. For instance Nahidian et al. (2018)
optimized a growth medium for the biomass production of Haematococcus pluvialis
TMU1 while Azizi et al. (2020) optimized a medium for astaxanthin production
by Haematococcus pluvialis NIES 144 and Haematococcus pluvialis UTEX 2505.
The optimization of the growth medium includes the selection of an adequate CO 2
source and/or aeration system. The optimization of all these parameters allowed
Azizi et al. (2020) to increase significantly the astaxanthin production by Haematococcus pluvialis. It is generally assumed that sodium carbonate is more economically
feasible because it is transported in an easier manner than gaseous carbon dioxide
and it exhibits a higher solubility than carbon dioxide (Hsueh et al. 2007) allowing
saturation of the growth medium in DIC (Sampathkumar and Gothandam 2019).
An often overlooked parameter in microalgal biotechnological at large scale is
the changing weather conditions, not only the light-dark cycle and the seasonality
but also the unpredictable and daily variations. Zhang et al. (2020) reported that in
Yunnan Province (China) the light intensity can reach 2000 μmol m
−2 s
−1 at noon
but the frequent rains and cloudy conditions reduce it at 150 μmol m
−2 s
−1 for
long period, therefore affecting astaxanthin production. To overcome this difficulty,
authors have suggested the use of organic carbon source as its utilization does not
rely on the photosynthetic activity.
Carotenoids are mostly hosted in the photosynthetic membranes where they serve
to harvest light and/or as antioxidant molecules. In eukaryotic organisms, the photosynthetic membranes are located in the chloroplasts (Solymosi 2012). When Cars
accumulate under stress, they are associated with lipids and proteins into droplets that
accumulate in the chloroplasts (β-carotene: Ben-Amotz et al. (1982); Derwenskus
et al. (2019)) or in the cytosol as in Haematoccoccus sp. (Lemoine et al. 2008). The
hydrophobic nature of carotenoids as well as their cellular localization lowers the
efficiency of the extraction procedures. This, together with the high cost of the downstream processes (Vinayak et al. 2015; Postma et al. 2016) have slowed down the
exploitation of microalgae as a source of carotenoids. To accelerate this development,
alternative extraction methods are developed. Supercritical CO 2 extraction, sometimes using a co-solvent (e.g. Chronopoulou et al. (2019)), pressurized extraction
(Derwenskus et al. 2019), ultrasound (Plaza et al. 2012), microwaves (Pasquet et al.
2011) and pulsed electric fields (Parniakov et al. 2015) are among these possibilities.
Nevertheless, these methods are destructive for the biomass and energy consuming
and the generated wastes need to be treated (Vinayak et al. 2015). To reduce the impact
of the biotechnological processes on the environment, biorefinery and biocompatible extraction concepts have been proposed. Both propose a holistic view of blue
biotechnology based on microalgae.
Clearly, carotenoids are among the molecules with an attractive future. Although
carotenoids are common molecules found in microalgae, they can be over accumulated in cells using environment constraints. Despite of this potential, there are not
enough data to make microalgae a real platform for the production of carotenoids.
More studies should be dedicated to the different aspects of the regulation of