Algae-Mediated Carbon Dioxide Sequestration for Climate Change Mitigation and Conversion to Value-Added Products - Biotechnological Applications of Microalgae - page 170

H. pluvialis transform into resting cyst cells, the aplanospores, and develop a distinct
red color due to astaxanthin accumulation. After maturation, the cysts germinate,
releasing flagellated cells (Margalith, 1999). The transformation of vegetative micro-
algal cells to astaxanthin-accumulating resting cells could be achieved by subjecting
the microalgal culture to environmental and nutritional stress, for example, nitrogen
and phosphorus limitation, increases in culture temperature, increases in the salinity
of the culture medium, and exposure of the culture to high irradiance (Del Campo
et al., 2007). The astaxanthin content of Haematococcus cells can go up to 3%, mak-
ing them an attractive source of the carotenoid pigment.
The accumulation of astaxanthin in Haematococcus cells in the resting phase
necessitates a two-phase cultivation protocol where in the first phase the microalga
is grown under optimal growth conditions to achieve high biomass yields, and then
the green biomass is subjected to nutritional and environmental stress in a second
phase to induce cyst (aplanospore) formation and the accumulation of astaxanthin
(Del Campo et al., 2007). Complete outdoor cultivation of Haematococcus has not
been feasible due to its high sensitivity to contamination and extreme environmen-
tal conditions during the growth phase. Commercial production of Haematococcus
biomass is generally carried out in closed photobioreactors, or it combines closed
photobioreactors and open ponds where the first stage of biomass generation is car-
ried out in closed photobioreactors, followed by a short residence period of culture in
open ponds for the second phase of induction of astaxanthin accumulation (Olaizola
and Huntley, 2003; Cysewski and Lorenz, 2004; Del Campo, 2007).
Astaxanthin has major commercial application in aquaculture as a source of
pigmentation for salmon, trout, and red sea bream (Lorenz and Cysewski, 2000;
Guerin et al., 2003; Cysewski and Lorenz, 2004), and the market is dominated by
synthetic astaxanthin. Natural astaxanthin from Haematococcus is not competitive
with synthetic astaxanthin for aquaculture applications due to high production costs
(Guerin et al., 2003; Olaizola, 2003). Therefore, the economic viability of large-
scale cultivation of Haematococcus to produce natural astaxanthin for aquaculture
applications alone may not be feasible, but finding high-value markets is important.
Human nutraceuticals have emerged as the high-value market for natural astaxan-
thin from Haematococcus . Several in vitro and in vivo studies have demonstrated
the beneficial health effects of Haematococcus -derived natural astaxanthin (Guerin
et al, 2003; Olaizola, 2003; Kamath et al., 2008; Yuan et al., 2011). Haematococcus
has been cleared by the U.S. FDA for application as an ingredient in dietary supple-
ments for humans and has also been approved for human consumption in several
European countries (Lorenz and Cysewski, 2000). This has paved the way for mar-
keting Haematococcus biomass for application as a food supplement.
11.4.3 o ther v alue -a dded p roduCts (vap s )
Microalgae have also been recognized as potential sources of various other VAPs
for food applications. Green microalgae and cyanobacteria could be used as a
rich source of the photosynthetic pigment chlorophyll. Chlorophyll acts as a che-
lating agent and can be used in ointments, and in the treatment of liver recovery
and ulcers (Puotinen, 1999). Chlorophyll can also be used as a natural colorant in