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Bioethanol has been recognized as a potential alternative to
petroleum-derived transportation fuels. Even if cellulosic biomass
is less expensive than corn and sugarcane, the higher costs for its
conversion make the near-term price of cellulosic ethanol higher
than that of corn ethanol and even more than that of sugarcane
ethanol. Conventional process for bioethanol production from
lignocellulose includes a chemical/physical pre-treatment of
lignocellulose for lignin removal, mostly based on auto hydrolysis
and acid hydrolysis, followed by saccharification of the free
accessible cellulose portions of the biomass. The highest yields of
fermentable sugars from cellulose portion are achieved by means of
enzymatic hydrolysis, currently carried out using a mix of
cellulases from the fungus Trichoderma reesei. Reduction of
(hemi)cellulases production costs is strongly required to increase
competitiveness of second generation bioethanol production. The
final step is the fermentation of sugars obtained from
saccharification, typically performed by the yeast Saccharomyces
cerevisiae. The current process is optimized for 6-carbon sugars
fermentation, since most of yeasts cannot ferment 5-carbon sugars.
Thus, research is aimed at exploring new engineered yeasts
abilities to co-ferment 5- and 6-carbon sugars. Among the main
routes to advance cellulosic ethanol, consolidate bio-processing,
namely direct conversion of biomass into ethanol by a genetically
modified microbes, holds tremendous potential to reduce ethanol
production costs. Finally, the use of all the components of
lignocellulose to produce a large spectra of biobased products is
another challenge for further improving competitiveness of second
generation bioethanol production, developing a biorefinery.
Bioethanol has been recognized as a potential alternative to
petroleum-derived transportation fuels. Even if cellulosic biomass
is less expensive than corn and sugarcane, the higher costs for its
conversion make the near-term price of cellulosic ethanol higher
than that of corn ethanol and even more than that of sugarcane
ethanol. Conventional process for bioethanol production from
lignocellulose includes a chemical/physical pre-treatment of
lignocellulose for lignin removal, mostly based on auto hydrolysis
and acid hydrolysis, followed by saccharification of the free
accessible cellulose portions of the biomass. The highest yields of
fermentable sugars from cellulose portion are achieved by means of
enzymatic hydrolysis, currently carried out using a mix of
cellulases from the fungus Trichoderma reesei. Reduction of
(hemi)cellulases production costs is strongly required to increase
competitiveness of second generation bioethanol production. The
final step is the fermentation of sugars obtained from
saccharification, typically performed by the yeast Saccharomyces
cerevisiae. The current process is optimized for 6-carbon sugars
fermentation, since most of yeasts cannot ferment 5-carbon sugars.
Thus, research is aimed at exploring new engineered yeasts
abilities to co-ferment 5- and 6-carbon sugars. Among the main
routes to advance cellulosic ethanol, consolidate bio-processing,
namely direct conversion of biomass into ethanol by a genetically
modified microbes, holds tremendous potential to reduce ethanol
production costs. Finally, the use of all the components of
lignocellulose to produce a large spectra of biobased products is
another challenge for further improving competitiveness of second
generation bioethanol production, developing a biorefinery.
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