Biology Reference
In-Depth Information
Biotechnological applications of dinofl agellates are limited because
most dinofl agellates cannot be easily cultured. The microalgae
Dunaliella
salina
and the
diatoms (
Nitzschia
spp.), when grown under controlled
conditions of temperature, pH, photon fl ux density and salinity, can
give high total lipid contents up to 28% in the cells on dry weight basis
(Renaud et al., 1994). The green microalga,
Chlorella zofi ngiensis
has been
cultivated for astaxanthin. The alga showed excellent growth on glucose-
supplemented media in batch culture. In the absence of light, formation
of secondary carotenoids was mostly dependent on the initial carbon and
nitrogen balance in the medium. Enhanced biosynthesis of astaxanthin is
dependent on a high C/N ratio of 180. The light-independent astaxanthin-
producing ability of
C. zofi ngiensis
suggests that the alga might be
potentially employed for commercial production of astaxanthin on a large-
scale (Ip and Chen, 2005). The infl uence of culture conditions on yield and
carotenoid production has also been shown in the case of
D. salina.
Under
stress conditions, such as formation of excessive free radicals, cell division
inhibition, nitrogen starvation, high salinity and temperature, this balance
is disturbed and the cells generate additional amounts of the carotene.
With nitrogen starvation, β-carotene production can be enhanced about
seven-fold. Maximum carotene (8.28 pg/cell) could be obtained upon
exposure of the cells to high light irradiance (6000 lux) at a temperature of
35
o
C (Pisal and Lele, 2005) The green microalga
Chlorella protothecoides
has
been shown to produce enhanced quantity of lutein under a combination
of nitrogen limitation and high-temperature stress when grown in batch
mode in a 3.7 litre fermenter containing 40 g/L glucose and 3.6 g/L urea,
followed by a relatively reduced supply of nitrogen source to establish a
nitrogen-limited culture. This N-limited fed-batch culture was scaled up
to 30 l, and a three-step cultivation process was developed for high yield of
the carotene. (Shi et al., 2002) The process of isolation of lutein consists of
extraction of the crude pigment with dichloromethane from the microalga
after saponifi cation, which gives the carotenoid a minimum purity of 90%
and yield of 91% (Gouveia et al., 2007). A functional food oil, rich in fatty
acids and antioxidants, colored with carotenoids extracted from
Chlorella
vulgaris
has been produced. The alga was subjected to supercritical CO
2
extraction at a pressure of 300 bar or using acetone containing vegetable
oil at room and high temperatures. The recovery of carotenoids was
100% with oil at room temperature for 17 h. In supercritical extraction the
degree of crushing strongly infl uenced the extraction recovery and higher
pigment recoveries were obtained with well-crushed biomass (Gouveia et
al., 2007; Tokusoglu and Unal, 2003). Production of β-carotene by
Spirulina
algae is very high, and depends upon light intensity. The natural β-carotene
extracted from the algae is a mixture of numerous carotenoids and essential
nutrients that are not present in synthetic β-carotene. On an average,
