258
poultry, livestock and fish (Cazzonelli 2011); in cosmetics; and as active ingredients
in medicinal pharmaceuticals. The global market for carotenoids is expected to
increase from US $1.2 billion in 2010 to $1.4 billion by 2018 (D’Alessandro and
Antoniosi Filho 2016). The nutraceutical industries synthetically manufacture five
major carotenoids (lycopene, β-carotene, canthaxanthin, zeaxanthin and astaxanthin)
on an industrial scale. Nowadays, natural sources of carotenoids are generally preferred over chemical synthesis as these are devoid of stereoisomers. Their mono- or
diesters form may improve their stability by providing greater shelf life. Moreover,
there is an increasing demand of natural products from consumers. This has promoted
major efforts to improve carotenoid production from biological sources instead of
chemical synthesis (del Campo et al. 2007).
Among various microalgae, Haematococcus pluvialis, Dunaliella salina and
Chlorella zofingiensis are the extensively studied taxa as they are widely used in the
commercial production of β-carotene and astaxanthin in medium- and large-scale
cultures (Lemoine and Schoefs 2010). Carotenoid accumulation in H. pluvialis was
first reported by Flotow (1844), which is well reviewed by Lemoine and Schoefs
(2010). Under favourable environmental conditions, H. pluvialis grow as large flagellated green macrozoids. When conditions become unfavourable (e.g. light stress,
deficiency of nitrogen, etc.), the cells become spherical, induce cyst formation and
change colour from green to red. This resting stage corresponds to large red cells
with a thick and heavy resistant cell wall. Tischer (1936) identified the pigment in
resting cells and named ‘haematochrom’ as astaxanthin. Under oxidative stress,
biosynthesis of astaxanthin enhances in these cyst cells (Kobayashi et al. 1993;
1997a, b) which is considered as a survival strategy developed by this organism
(Boussiba 2000). Under stress conditions, H. pluvialis accumulates astaxanthin up
to 2–3% (w/w) on a dry weight basis or 43 μg/g on a fresh weight basis (Boussiba
et al. 1999; Lemoine and Schoefs 2010).
Tolerance to excessive ROS has been shown to be higher in astaxanthin-rich
cysts than in vegetative cells (Kobayashi et al. 1997a, b; Li et al. 2010). In cysts,
astaxanthin molecules are present as fatty acid esters and thus have both hydrophilic
groups and hydrophobic esters at both β-ionone rings. Compared to nonesterified
molecules, the esterified astaxanthin molecules have better capacity to detoxify
1
O 2 .
This suggests their ability to function as stabilizers to maintain high antioxidant
ability between hydrophilic and hydrophobic conditions (Hagen et al. 1993;
Kobayashi et al. 1997a; Kobayashi and Sakamoto 1999). The proteomic analysis
identified 70 proteins whose expression pattern changed in H. pluvialis following
stress induction (Wang et al. 2004a, b). Proteins from the families SOD, CAT and
POX were quickly upregulated within the first 12–48 h and then downregulated
when astaxanthin molecules accumulated. This suggests primary enzymatic defence
response of the cells that plays a critical role upon onset of stress and during the
transition of green vegetative cells to cyst formation (Wang et al. 2004a, b).
Kobayashi (2000) also observed decrease in the ROS formation in H. pluvialis with
the increase in intracellular astaxanthin content. Compared to cyst cells, vegetative
cells with no astaxanthin had higher ROS formation. Thus, vegetative cells might be
more sensitive to ROS than cyst cells, suggesting the importance of morphological
K. Chokshi et al.
poultry, livestock and fish (Cazzonelli 2011); in cosmetics; and as active ingredients
in medicinal pharmaceuticals. The global market for carotenoids is expected to
increase from US $1.2 billion in 2010 to $1.4 billion by 2018 (D’Alessandro and
Antoniosi Filho 2016). The nutraceutical industries synthetically manufacture five
major carotenoids (lycopene, β-carotene, canthaxanthin, zeaxanthin and astaxanthin)
on an industrial scale. Nowadays, natural sources of carotenoids are generally preferred over chemical synthesis as these are devoid of stereoisomers. Their mono- or
diesters form may improve their stability by providing greater shelf life. Moreover,
there is an increasing demand of natural products from consumers. This has promoted
major efforts to improve carotenoid production from biological sources instead of
chemical synthesis (del Campo et al. 2007).
Among various microalgae, Haematococcus pluvialis, Dunaliella salina and
Chlorella zofingiensis are the extensively studied taxa as they are widely used in the
commercial production of β-carotene and astaxanthin in medium- and large-scale
cultures (Lemoine and Schoefs 2010). Carotenoid accumulation in H. pluvialis was
first reported by Flotow (1844), which is well reviewed by Lemoine and Schoefs
(2010). Under favourable environmental conditions, H. pluvialis grow as large flagellated green macrozoids. When conditions become unfavourable (e.g. light stress,
deficiency of nitrogen, etc.), the cells become spherical, induce cyst formation and
change colour from green to red. This resting stage corresponds to large red cells
with a thick and heavy resistant cell wall. Tischer (1936) identified the pigment in
resting cells and named ‘haematochrom’ as astaxanthin. Under oxidative stress,
biosynthesis of astaxanthin enhances in these cyst cells (Kobayashi et al. 1993;
1997a, b) which is considered as a survival strategy developed by this organism
(Boussiba 2000). Under stress conditions, H. pluvialis accumulates astaxanthin up
to 2–3% (w/w) on a dry weight basis or 43 μg/g on a fresh weight basis (Boussiba
et al. 1999; Lemoine and Schoefs 2010).
Tolerance to excessive ROS has been shown to be higher in astaxanthin-rich
cysts than in vegetative cells (Kobayashi et al. 1997a, b; Li et al. 2010). In cysts,
astaxanthin molecules are present as fatty acid esters and thus have both hydrophilic
groups and hydrophobic esters at both β-ionone rings. Compared to nonesterified
molecules, the esterified astaxanthin molecules have better capacity to detoxify
1
O 2 .
This suggests their ability to function as stabilizers to maintain high antioxidant
ability between hydrophilic and hydrophobic conditions (Hagen et al. 1993;
Kobayashi et al. 1997a; Kobayashi and Sakamoto 1999). The proteomic analysis
identified 70 proteins whose expression pattern changed in H. pluvialis following
stress induction (Wang et al. 2004a, b). Proteins from the families SOD, CAT and
POX were quickly upregulated within the first 12–48 h and then downregulated
when astaxanthin molecules accumulated. This suggests primary enzymatic defence
response of the cells that plays a critical role upon onset of stress and during the
transition of green vegetative cells to cyst formation (Wang et al. 2004a, b).
Kobayashi (2000) also observed decrease in the ROS formation in H. pluvialis with
the increase in intracellular astaxanthin content. Compared to cyst cells, vegetative
cells with no astaxanthin had higher ROS formation. Thus, vegetative cells might be
more sensitive to ROS than cyst cells, suggesting the importance of morphological
K. Chokshi et al.