Microalgae as an Attractive Source for Biofuel Production - Environmental Sustainability: Role of Green Technologies - page 132

amount of lipids (20-50 %) and, when conditions
are optimized, higher productivity can be reached.
The lipid content (% dry weight) of different
marine and freshwater microalgae species has
shown signifi cant differences among the species
(Table 2 ). The other factors are taken into
account, such as lipid profi le and the ability to
grow under specifi c environmental conditions.
The factors that affect the lipid profi le are nutri-
tional, processing, and cultivation conditions.
Factors such as growth rate, quality and quantity
of lipid, and strong adaptability in a changing
environment to determine the preferred nutrients
and nutrient uptake rates are very important in
selecting better strains (Amaro et al. 2011 ).
The composition of fatty acids plays an impor-
tant role in the characteristics of the biodiesel
they produce and differs between species.
Biodiesel is composed of saturated and unsatu-
rated fatty acids with 12-22 carbon atoms, some
of them of

attained 204 mg/L/day (with an average biomass
productivity of 0.30 g/L/day and more than 60 %
lipid content) in nitrogen-deprived media
(Rodolfi et al. 2009 ; Veillette et al. 2012 ).
Navicula accumulates 58 % (g lipid/g dry weight)
under nitrogen defi ciency, whereas the lipid con-
tent is very low (i.e.) 22-49 % (g lipid/g dry
weight) under silicon (Si) defi ciency. The above
results clearly prove that nitrogen deprivation has
a positive effect on lipid accumulation.
On the other hand, phosphate deprivation
could have an effect on lipid content (Khozin-
Goldberg and Cohen 2006 ; Xin et al . 2010 ). For
example, when the P concentration was increased
from 0.14 to 0.37 mg/L, an increase in the bio-
mass was recorded, while the lipid content
decreased from 53 to 23.5 % (g lipid/g dry
weight). Silicon depletion also leads to an
increase in the cellular lipid content. Under sili-
con starvation in the diatom, an increase of 60 %
of the lipid content of Navioua pelliculosa is pos-
sible. Lipid fractions as high as 70-85 % on a dry
weight basis have been reported. Such high lipid
contents exceed that of most terrestrial plants.
How it is that diatoms rapidly switch over from
carbohydrate accumulation to lipid accumulation
remains unclear. However, diatoms have great
potential to accumulate microalgal lipids
(Miyamoto 1997 ). At the initial stage of growth,
more polar lipids and polyunsaturated C 16 and C 18
fatty acids are produced. The stationary growth
phase generally consists of neutral saturated 18:1
and 16:0 long-chain fatty acids.
Light also plays an important role in lipid
accumulation. Under high light intensity, Euglena
gracilis and Ch. vulgaris produce polyunsatu-
rated C 16 and C 18 fatty acids as well as mono- and
di-galactosyl-diglycerides, sphingolipids, and
phosphoglycerides. Under low temperature con-
ditions, Monochrysis lutheri produce polyunsatu-
rated C 18 fatty acids, but in Dunaliella salina the
fatty acid composition changes (Takagi et al.
2006 ). The above fi ndings clearly deny that light
intensity also plays a crucial role in fatty acid
composition. Osmotic shock might also enhance
lipid production. However, salt stress may affect
the quantity of lipid within the algal cells. For
example, Dunaliella cells can grow well in high

6 families. The seven fresh-
water microalgae showed similar fatty acid com-
position patterns, showing that all microalgae
synthesize C14:0, C16:0, C18:1, C18:2, and
C18:3 fatty acids. The relative intensity of other
individual fatty acid chains is species specifi c,
e.g. Ankistrodesmus sp. consists of C16:4 and
C18:4; Isochrysis sp. consists of C18:4; and
Nannochloris sp. consists of C22:6, C16:2,
C16:3, C20:5, C16:2, and C16:3; and Nitzschia
sp. consists of C20:5 (Thomas et al. 1984 ; Mata
et al. 2010 ).
Some microalgae oil yield is higher than veg-
etable oil; this is strain dependent. Different
nutritional and environmental factors may affect
the fatty acid composition. The high amount of
oil production is induced under stress conditions
such as nitrogen defi ciency, high light intensity,
phosphorous defi ciency, silicon defi ciency,
salt stress, and other factors. For example,
Botryococcus braunii under nitrogen defi ciency
and salt stress induced the accumulation of C20:5
whereas, all other species accumulated C18:1
(

ˉ 3 and ˉ

and Pire 2001 ; Pratoomyot et al. 2005 ;
Natrah et al. 2007 ; Hu et al. 2008 ; Gouveia and
Oliveira 2009 ; Mata et al. 2010 ). Some microal-
gae have the ability to accumulate lipids under
nitrogen deprivation. Nannochloropsis

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sp.