Ecofriendly Approach for Bioethanol Production …
307
2.6 Light Intensity
Light is the main energy provider for photosynthetic microalgae. Providing suitable
light intensity does not only improve biomass productivity, but also can change the
biochemical compositions of microalgae (Hu 2007). Through illumination with high
light intensity, the carbohydrate and lipid content in microalgae cells could be further
enhanced (Lv et al. 2010). Recent study have shown that supplying light intensity
between 200 and 420 μmol m
−2 s
−1 could enhance the carbohydrate content of
Scenedesmus obliquus (Ho et al., 2012). At a light intensity of 420 μmol m
−2 s
−1 ,
Scenedesmus obliquus accumulated the highest carbohydrate content of 38%; which
was about 2.3 times higher compared to cultivation supplied with a light intensity
of 60 μmol m
−2 s
−1 . The same observation was also reported by Brányiková et al.
(2011), in which the starch content in Chlorella was increased from 8.5% to 40%
when the light intensity was switched from 215 μmol m
−2 s
−1 to 330 μmol m
−2
s
−1 . However, it should be noted that providing extremely high light intensity could
reduce the biomass productivity of microalgae, which is generally known as photoinhibition (Chisti 2008). The carbohydrate productivity in Scenedesmus obliquus
was reported to reduce by about 45% when high intensity was increased from 420
to 540 μmol m
−2 s
−1 (Ho et al. 2012).
3 Carbohydrate in Microalgae
Microalgae cells are composed by different polysaccharides (polymeric carbohydrate
molecules that bonded by glycosidic linkages of long chains of monosaccharides
unit) that can be broken down into monosaccharides through pre-treatments and
hydrolysis processes. The produced monosaccharides (e.g. glucose) can be converted
to bioethanol through fermentation (Barsanti and Gualtieri 2014). Microalgae species
such as Chlorella, Chlamydomonas, Dunaliella, and Scenedesmus consists of high
carbohydrates content, which is suitable to be used as the feedstock for bioethanol
production (Harun et al. 2014). Cellulose structure has been the research focus in
recent reported studies, particularly in bioethanol production.
The types of classes of polysaccharides that found in green microalgae are cellulose, chrysolaminarin, floridean starch, paramylon and starch (Barsanti and Gualtieri
2014). Among the listed polysaccharides, cellulose and starch are the widely studied
classes in microalgae research for bioethanol production.
3.1 Cellulose
The microalgae phyla that have cellulose storage are Chlorophyceae (Chlorophyta), Dinophyta, Phaeophyta (Ochrophyta), Prymnesiophyceae, Rhodophyceae
307
2.6 Light Intensity
Light is the main energy provider for photosynthetic microalgae. Providing suitable
light intensity does not only improve biomass productivity, but also can change the
biochemical compositions of microalgae (Hu 2007). Through illumination with high
light intensity, the carbohydrate and lipid content in microalgae cells could be further
enhanced (Lv et al. 2010). Recent study have shown that supplying light intensity
between 200 and 420 μmol m
−2 s
−1 could enhance the carbohydrate content of
Scenedesmus obliquus (Ho et al., 2012). At a light intensity of 420 μmol m
−2 s
−1 ,
Scenedesmus obliquus accumulated the highest carbohydrate content of 38%; which
was about 2.3 times higher compared to cultivation supplied with a light intensity
of 60 μmol m
−2 s
−1 . The same observation was also reported by Brányiková et al.
(2011), in which the starch content in Chlorella was increased from 8.5% to 40%
when the light intensity was switched from 215 μmol m
−2 s
−1 to 330 μmol m
−2
s
−1 . However, it should be noted that providing extremely high light intensity could
reduce the biomass productivity of microalgae, which is generally known as photoinhibition (Chisti 2008). The carbohydrate productivity in Scenedesmus obliquus
was reported to reduce by about 45% when high intensity was increased from 420
to 540 μmol m
−2 s
−1 (Ho et al. 2012).
3 Carbohydrate in Microalgae
Microalgae cells are composed by different polysaccharides (polymeric carbohydrate
molecules that bonded by glycosidic linkages of long chains of monosaccharides
unit) that can be broken down into monosaccharides through pre-treatments and
hydrolysis processes. The produced monosaccharides (e.g. glucose) can be converted
to bioethanol through fermentation (Barsanti and Gualtieri 2014). Microalgae species
such as Chlorella, Chlamydomonas, Dunaliella, and Scenedesmus consists of high
carbohydrates content, which is suitable to be used as the feedstock for bioethanol
production (Harun et al. 2014). Cellulose structure has been the research focus in
recent reported studies, particularly in bioethanol production.
The types of classes of polysaccharides that found in green microalgae are cellulose, chrysolaminarin, floridean starch, paramylon and starch (Barsanti and Gualtieri
2014). Among the listed polysaccharides, cellulose and starch are the widely studied
classes in microalgae research for bioethanol production.
3.1 Cellulose
The microalgae phyla that have cellulose storage are Chlorophyceae (Chlorophyta), Dinophyta, Phaeophyta (Ochrophyta), Prymnesiophyceae, Rhodophyceae