Biomass to Xylose
Rozina Rashid, Uroosa Ejaz, and Muhammad Sohail
Abstract
Lignocellulosic (LC) feedstock is the most economical
and renewable natural feedstock of chemicals and energy.
It is primarily composed of lignin, cellulose, and hemicellulose which are woven together and render the
biomass recalcitrant to degradation. Hemicellulose is the
second largest component of this biomass that is degraded
to obtain large quantities of xylose. The effective
utilization of the xylose is one of the most significant
pre-requirement for economical bioconversion of LC
biomass into biochemicals and biofuels. However, there
are still some bottlenecks in the bioconversion of xylose,
due to limitations to exploit xylose metabolism pathways.
To overcome these issues, various research works have
been carried out to engineer the transporters and enzymes
involved in xylose utilization. Successful progress in this
regard will boost xylose yield and titer, leading to the
economical bioprocessing of the LC biomass. In order to
understand biomass transformation strategies, firstly
structural composition of LC biomass is introduced that
is followed by the discussion on the chemical and
enzymatic hydrolysis of biomass. Moreover, the importance of pretreatment as a prerequisite operation to
biomass saccharification has also been highlighted along
with an overview on various pretreatment methods.
Finally, the significance of xylose as a raw material, its
efficient utilization and the challenges concerning
co-fermentation of sugars for the production of biofuels
and other value-added chemicals by yeasts have been
discussed.
Keywords
Biomass Á Chemical degradation Á Enzymatic
degradation Á Hemicellulose Á Xylose
1 Introduction
The reliance of modern world on fossil fuels as chemical and
energy feedstock is at stake due to high cost, volatile
geopolitical scenarios, limited reserves, irregular prices, and
harmful consequences on the environment (Vennestrøm
et al. 2011). Extensive research on coal and biomass was
started in Germany and in few other countries during world
wars I and II for the production of chemicals and fuels (Faith
1945). Since, plant biomass is natural, abundant, and
renewable source and has less impact on environment, it has
become a choice for today’s world to use it for the synthesis
of fuels and chemicals (Vennestrøm et al. 2011; Perlack
2005).
2 Plant Biomass
The plant biomass as defined by Roberts et al. (1985) is the
mass of plant present above or below ground and is produced (just by terrestrial plants) at the annual rate of
2.3 Â 10
11 metric tons of wood that can replace 66% of
world’s energy or 7 Â 10
11 metric tons of coal (Lynd et al.
2002). Plant biomass has been proven to be a great renewable feedstock for the synthesis of chemicals, fuels, heat, and
power generation and has potential to displace petroleum
products (Brown et al. 2015) mainly because of its cost
competitiveness and for being environmentally friendly.
R. Rashid Á U. Ejaz Á M. Sohail (&)
Department of Microbiology, University of Karachi, Karachi,
75270, Pakistan
e-mail: msohail@uok.edu.pk
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
Inamuddin and A. Khan (eds.), Sustainable Bioconversion of Waste to Value Added Products, Advances in Science,
Technology & Innovation, https://doi.org/10.1007/978-3-030-61837-7_15
247
Rozina Rashid, Uroosa Ejaz, and Muhammad Sohail
Abstract
Lignocellulosic (LC) feedstock is the most economical
and renewable natural feedstock of chemicals and energy.
It is primarily composed of lignin, cellulose, and hemicellulose which are woven together and render the
biomass recalcitrant to degradation. Hemicellulose is the
second largest component of this biomass that is degraded
to obtain large quantities of xylose. The effective
utilization of the xylose is one of the most significant
pre-requirement for economical bioconversion of LC
biomass into biochemicals and biofuels. However, there
are still some bottlenecks in the bioconversion of xylose,
due to limitations to exploit xylose metabolism pathways.
To overcome these issues, various research works have
been carried out to engineer the transporters and enzymes
involved in xylose utilization. Successful progress in this
regard will boost xylose yield and titer, leading to the
economical bioprocessing of the LC biomass. In order to
understand biomass transformation strategies, firstly
structural composition of LC biomass is introduced that
is followed by the discussion on the chemical and
enzymatic hydrolysis of biomass. Moreover, the importance of pretreatment as a prerequisite operation to
biomass saccharification has also been highlighted along
with an overview on various pretreatment methods.
Finally, the significance of xylose as a raw material, its
efficient utilization and the challenges concerning
co-fermentation of sugars for the production of biofuels
and other value-added chemicals by yeasts have been
discussed.
Keywords
Biomass Á Chemical degradation Á Enzymatic
degradation Á Hemicellulose Á Xylose
1 Introduction
The reliance of modern world on fossil fuels as chemical and
energy feedstock is at stake due to high cost, volatile
geopolitical scenarios, limited reserves, irregular prices, and
harmful consequences on the environment (Vennestrøm
et al. 2011). Extensive research on coal and biomass was
started in Germany and in few other countries during world
wars I and II for the production of chemicals and fuels (Faith
1945). Since, plant biomass is natural, abundant, and
renewable source and has less impact on environment, it has
become a choice for today’s world to use it for the synthesis
of fuels and chemicals (Vennestrøm et al. 2011; Perlack
2005).
2 Plant Biomass
The plant biomass as defined by Roberts et al. (1985) is the
mass of plant present above or below ground and is produced (just by terrestrial plants) at the annual rate of
2.3 Â 10
11 metric tons of wood that can replace 66% of
world’s energy or 7 Â 10
11 metric tons of coal (Lynd et al.
2002). Plant biomass has been proven to be a great renewable feedstock for the synthesis of chemicals, fuels, heat, and
power generation and has potential to displace petroleum
products (Brown et al. 2015) mainly because of its cost
competitiveness and for being environmentally friendly.
R. Rashid Á U. Ejaz Á M. Sohail (&)
Department of Microbiology, University of Karachi, Karachi,
75270, Pakistan
e-mail: msohail@uok.edu.pk
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
Inamuddin and A. Khan (eds.), Sustainable Bioconversion of Waste to Value Added Products, Advances in Science,
Technology & Innovation, https://doi.org/10.1007/978-3-030-61837-7_15
247