refers to conditions that satisfy the critical temperature and critical pressure
simultaneously. In the case of water, the critical point is a critical temperature of
374 °C and a critical pressure of 221 bar (218.3 atm). “Critical temperature” refers
to a state where a substance’s temperature is high enough that no amount of
pressure causes liquefaction, while “critical pressure” refers to a state where a
substance’s pressure is high enough that it does not evaporate no matter how high
the temperature (Matsumoto et al. 2003).
C. Ethanol Fermentation
Fermentation is the transformation of monosugars into ethanol once complex
components have been reduced to low molecular weight. The sugars that serve as
the main materials in ethanol fermentation include glucose and mannitol in brown
algae, and glucose, galactose, and xylose in green and red algae. Microorganisms
such as yeasts and bacterial play a role in ethanol fermentation. The optimal
approach in this case would be to allow single microorganisms to convert all
components into ethanol. The characteristics of the enzymes made available to the
microorganisms in fermentation, however, are such that this cannot be relied upon.
Research has indicated the possibility of using gene improvement to produce yeasts
with a wider range of substrate specificity, which raises hopes for the future.
Glucose can be converted to ethanol by a range of microorganisms. Yeasts that
can produce ethanol from glucose include Saccharomyces cerevisiae, Pachysolen
tannophilus, and Pichia angophorae; bacteria include Zymomonas mobilis. Ethanol
can also be produced from galactose, which is present in large volumes in red algae,
after its conversion to glucose-6-phosphate. The sugar alcohol mannitol is converted into ethanol through the actions of the yeast Pichia angophorae and the
bacteria Zymobacter palmae. Various microorganisms contained in Aspergillus
oryzae, a fungus used in traditional forms of Korean liquor, have been found to
produce ethanol as they break down the alginic acid in kelp; mannitol was found to
be the source of this ethanol.
Takeda et al. were the first to succeed in using genetically manipulated bacteria
from Sphingomonas sp. to produce ethanol for alginic acid, which is present in
large quantities in brown algae. As an example of a major brown algae sugar being
converted entirely through ethanol fermentation, this marked a great advancement
in ethanol production from algae biomass, which is one of the most abundant of
resources (Takeda 2011; Wang et al. 2011; Lee and Lee 2012).
9.2.2 Future Tasks
In bioethanol production, the ethanol produced from a single glucose molecule is
limited to two molecules. This requires a overall manufacturing process of efficient
ethanol fermentation with low energy consumption. More specifically, algae containing large amounts of sugars suitable for ethanol fermentation must be sought
and developed, and farming and harvesting methods must be established for these
9.2 Producing Ethanol with Algae
303
simultaneously. In the case of water, the critical point is a critical temperature of
374 °C and a critical pressure of 221 bar (218.3 atm). “Critical temperature” refers
to a state where a substance’s temperature is high enough that no amount of
pressure causes liquefaction, while “critical pressure” refers to a state where a
substance’s pressure is high enough that it does not evaporate no matter how high
the temperature (Matsumoto et al. 2003).
C. Ethanol Fermentation
Fermentation is the transformation of monosugars into ethanol once complex
components have been reduced to low molecular weight. The sugars that serve as
the main materials in ethanol fermentation include glucose and mannitol in brown
algae, and glucose, galactose, and xylose in green and red algae. Microorganisms
such as yeasts and bacterial play a role in ethanol fermentation. The optimal
approach in this case would be to allow single microorganisms to convert all
components into ethanol. The characteristics of the enzymes made available to the
microorganisms in fermentation, however, are such that this cannot be relied upon.
Research has indicated the possibility of using gene improvement to produce yeasts
with a wider range of substrate specificity, which raises hopes for the future.
Glucose can be converted to ethanol by a range of microorganisms. Yeasts that
can produce ethanol from glucose include Saccharomyces cerevisiae, Pachysolen
tannophilus, and Pichia angophorae; bacteria include Zymomonas mobilis. Ethanol
can also be produced from galactose, which is present in large volumes in red algae,
after its conversion to glucose-6-phosphate. The sugar alcohol mannitol is converted into ethanol through the actions of the yeast Pichia angophorae and the
bacteria Zymobacter palmae. Various microorganisms contained in Aspergillus
oryzae, a fungus used in traditional forms of Korean liquor, have been found to
produce ethanol as they break down the alginic acid in kelp; mannitol was found to
be the source of this ethanol.
Takeda et al. were the first to succeed in using genetically manipulated bacteria
from Sphingomonas sp. to produce ethanol for alginic acid, which is present in
large quantities in brown algae. As an example of a major brown algae sugar being
converted entirely through ethanol fermentation, this marked a great advancement
in ethanol production from algae biomass, which is one of the most abundant of
resources (Takeda 2011; Wang et al. 2011; Lee and Lee 2012).
9.2.2 Future Tasks
In bioethanol production, the ethanol produced from a single glucose molecule is
limited to two molecules. This requires a overall manufacturing process of efficient
ethanol fermentation with low energy consumption. More specifically, algae containing large amounts of sugars suitable for ethanol fermentation must be sought
and developed, and farming and harvesting methods must be established for these
9.2 Producing Ethanol with Algae
303