Algae-Mediated Carbon Dioxide Sequestration for Climate Change Mitigation and Conversion to Value-Added Products - Biotechnological Applications of Microalgae - page 169

as lipid globules in interthylakoid spaces of chloroplasts of alga (Vorst et al., 1994).
It contributes to light harvesting and protects the alga from oxidative damage dur-
ing excessive irradiance by quenching the triplet-state chlorophyll or by reacting
with singlet oxygen ( 1 O 2 ), thus preventing the formation of reactive oxygen species
(Demming-Adams and Adams, 2002; Del Campo et al., 2007; Raja et al., 2007;
Telfer, 2002). The beneficial effects of β-carotene on human health are attributed to
its antioxidant properties (Guerin et al., 2003; Higuera-Ciapara et al., 2006; Hussein
et al., 2006), and several studies have indicated that adequate intake of carotenoids
has the ability to prevent degenerative diseases (Astorg, 1997; Demming-Adams and
Adams, 2002; Krinsky and Johnson, 2005). β-Carotene also has the ability to act as
provitamin A (Garcia-Gonzalez et. al., 2005; Gouveia and Empis, 2003). Because of
these properties, β-carotene has found applications as a food supplement and colorant.
The extent of β-carotene accumulation in Dunaliella biomass is a function of
high salinity, temperature stress, high light intensity, and nitrogen limitation. Being
an extremophile, by virtue of its ability to grow at high salinity, it is possible to grow
Dunaliella biomass in open-pond cultivation systems in photo-autotrophic mode. The
production ponds are typically located in areas that could provide high solar irradi-
ance, warm temperatures, and hypersaline waters (Ben-Amotz, 1999). Commercial
cultivation facilities of Dunaliella are located in Australia, Israel, China, and the
United States (Del Campo et al., 2007), with global production estimates at about
1,200 MT y −1 (Pulz and Gross, 2004). The open-pond cultivation systems used are
either very large ponds (without mixing) of up to 250 ha or paddle-mixed raceway
ponds of about 3,000 m 2 surface area (Del Campo, 2007). Commercial producers are
offering Dunaliella biomass directly as a powder for application as an ingredient in
human dietary supplements and functional foods (Spolaore et al., 2006).
Downstream processing of Dunaliella biomass is carried out to extract
β-carotene for use as a natural food colorant and food supplement. The natural
β-carotene from Dunaliella must compete with cheaper synthetic β-carotene in
the marketplace. Synthetic β-carotene is dominated by all- trans -β-carotene (Von
Laar et al., 1996), whereas natural β-carotene from Dunaliella contains more than
50% 9- cis -β-carotene (Johnson et al., 1996). Therefore, although more expensive,
natural β-carotene provides the natural isomers in their natural ratio (Guerin et al.,
2003; Garcia-Gonzalez et al., 2005; Spolaore et al., 2006), and the natural isomer of
β-carotene is accepted as superior to the synthetic all- trans -isomer (Radmer, 1996;
Vilchez et al., 1997; Lorenz and Cysewski, 2000; Becker, 2004; Spolaore et al.,
2006). Although not yet cost compared to synthetic β-carotene, production of natu-
ral β-carotene from Dunaliella has been reported as an economically viable and
growing industry (Singh et al., 2005; Chisti, 2006). The algal meal of Dunaliella
after extraction of β-carotene is reported to contain about 40% protein and therefore
could find application in fish and poultry feed (Iwamoto, 2004).
11.4.2 a staxanthin
A freshwater green microalga, Haematococcus pluvialis , has been cultivated as a
source of natural astaxanthin, a ketocarotenoid. Astaxanthin in microalgal cells
is located in the cytoplasmic lipid globules. The biflagellate and motile cells of