release D-glucose that can be used to produce biofuels or chemical feedstock by
fermentation or chemical transformation. However, the heterogeneous quality of
the material, the presence of crystalline insoluble cellule and lignin molecules,
makes the degradation of this material difficult (Turner et al. 2007).
Although biomass degradation is an efficient natural process, it is not fast
enough to provide energy or chemicals at a sustainable pace. Inspite of pretreatments of chemical and physical nature proposed to disrupt lignin which is the main
obstacle in lignocellulose degradation, the degradation of each one of the components of Lignocellulosic biomass remains a slow and expensive process, and
many of the monomers released cannot be used efficiently by microorganisms or
easily transformed in some other economically interesting molecules. Hence,
lignocellulosic biomass conversion to energy and fine chemicals requires intensive
research effort if it is to really substitute oil as the main source of energy and
precursors to the world. Many advances have to be done in several fields such as
lignocellulose pretreatment, microbial strain improvement, enzyme activity
modification and enhancement, wastes management, and a new understanding of
the whole process.
A promising approach to overcome many limitations in the integral management of lignocellulosic biomass is the productive systems known as biorefineries.
A biorefinery is an industrial facility that integrates biomass conversion processes
to produce fuels, power, and value-added chemicals from biomass (Kamm and
Kamm 2004).
7.2 Lignocellulosic Biomass and Degradation
Lignocellulosic biomass is a heterogeneous material formed by cellulose, that is, a
linear polymer formed by D glucose connected by beta-1,4 glycosidic bonds;
every two glucose residues are arranged in opposite directions and form a cellobiose unit, and these units are repeated thousand of times creating cellulose chains
that are packed by hydrogen bonds to form elementary microfibrils. These
microfibrils are attached to each other by hemicelluloses that are heterogeneous
polymer of pentoses, hexoses, and sugar acids as pectins, and are covered by
lignin, a polymer formed mainly by conferyl, sinapyl, and p-coumaryl alcohols.
Lignin gives the material its structural strength and serves as a barrier to the
penetration of solutions or enzymes to the interior of the lignocellulose structure;
this is the hardest component of the biomass to degrade (Ha et al. 1998; Balan
et al. 2009; Hamelinck et al. 2005).
The proposed idea about lignocellulose degradation is that in which cellulose
fibers are attacked initially by endoglucanases that break the bonds in the chains at
random sites to reveal free and nonfree reducing ends. The ends are then attacked
by cellobiohydrolases (exoglucanases) that move along both chain threads
releasing cellobiose units. The cellobiose units are hydrolyzed by beta-glucosidases to render glucose; this step is essential to preserve the reaction rate as it
7 Integral Management of Lignocellulosic Biomass by Biorefining
237
fermentation or chemical transformation. However, the heterogeneous quality of
the material, the presence of crystalline insoluble cellule and lignin molecules,
makes the degradation of this material difficult (Turner et al. 2007).
Although biomass degradation is an efficient natural process, it is not fast
enough to provide energy or chemicals at a sustainable pace. Inspite of pretreatments of chemical and physical nature proposed to disrupt lignin which is the main
obstacle in lignocellulose degradation, the degradation of each one of the components of Lignocellulosic biomass remains a slow and expensive process, and
many of the monomers released cannot be used efficiently by microorganisms or
easily transformed in some other economically interesting molecules. Hence,
lignocellulosic biomass conversion to energy and fine chemicals requires intensive
research effort if it is to really substitute oil as the main source of energy and
precursors to the world. Many advances have to be done in several fields such as
lignocellulose pretreatment, microbial strain improvement, enzyme activity
modification and enhancement, wastes management, and a new understanding of
the whole process.
A promising approach to overcome many limitations in the integral management of lignocellulosic biomass is the productive systems known as biorefineries.
A biorefinery is an industrial facility that integrates biomass conversion processes
to produce fuels, power, and value-added chemicals from biomass (Kamm and
Kamm 2004).
7.2 Lignocellulosic Biomass and Degradation
Lignocellulosic biomass is a heterogeneous material formed by cellulose, that is, a
linear polymer formed by D glucose connected by beta-1,4 glycosidic bonds;
every two glucose residues are arranged in opposite directions and form a cellobiose unit, and these units are repeated thousand of times creating cellulose chains
that are packed by hydrogen bonds to form elementary microfibrils. These
microfibrils are attached to each other by hemicelluloses that are heterogeneous
polymer of pentoses, hexoses, and sugar acids as pectins, and are covered by
lignin, a polymer formed mainly by conferyl, sinapyl, and p-coumaryl alcohols.
Lignin gives the material its structural strength and serves as a barrier to the
penetration of solutions or enzymes to the interior of the lignocellulose structure;
this is the hardest component of the biomass to degrade (Ha et al. 1998; Balan
et al. 2009; Hamelinck et al. 2005).
The proposed idea about lignocellulose degradation is that in which cellulose
fibers are attacked initially by endoglucanases that break the bonds in the chains at
random sites to reveal free and nonfree reducing ends. The ends are then attacked
by cellobiohydrolases (exoglucanases) that move along both chain threads
releasing cellobiose units. The cellobiose units are hydrolyzed by beta-glucosidases to render glucose; this step is essential to preserve the reaction rate as it
7 Integral Management of Lignocellulosic Biomass by Biorefining
237