in the plant cell walls, acting as barrier against enzymatic hydrolysis and other
external threats to its structure (Zhu et al. 2010). It has been confirmed that
hemicellulose removal improves glucose yield after enzymatic hydrolysis of material (Chen et al. 2015). Lignin causes another problem besides providing a physical
barrier like hemicelluloses. Lignin causes a non-productive adsorption of enzymes
employed in cellulose hydrolysis, deactivating them along the process (Ximenes
et al. 2011). Lignin removal with pretreatments can reduce loss of active enzymes
(Yang and Pan 2016). Changes in biomass structure are observed by looking at
superficial cavities, gaps, and hollow spaces created by hemicellulose elimination
and/or lignin amendment by pretreatments like dilute acid, peroxide, steam explosion, and alkaline methods (Karimi and Taherzadeh 2016). A quantification of these
components (cellulose, hemicelluloses, and lignin) can determine biomass quality
and drive its application. The pretreatment processes improve lignocellulosic biomass quality allowing its conversion into biofuel, organic acids, and other chemicals
with high industrial interest.
2.8
Biomass Genetic Improvement
Modification of cell wall structure of lignocellulosic biomass is the key step in
improving the quality of bioenergetic crops. However, genetic improvement of
energy crops is still a challenge to increase the production of biomass and biofuels
on large scale. A genetic modification in the plant cell wall structure is desired to
specifically alter the cell wall interconnections (cellulose crystallinity) and reducing
lignin levels and increasing carbohydrate content. The genetic manipulation must
select appropriate genes, which is a fundamental step to meet the expected
objectives. However, there are more than 1,000 genes related to biosynthesis,
degradation, and regulation of the plant cell wall (Xie and Peng 2011). As complementary techniques for genetic improvement of biomass quality, several tools have
been developed: high-throughput genotyping, generation sequencing, and molecular
breeding techniques such as marker assisted selection and genomic selection. These
modern tools have been applied in a wide variety of bioenergetic species such as
sugarcane, elephant grass, sorghum, and miscanthus (Allwright and Taylor 2016).
In order to optimize the biomass conversion from sugarcane into bioethanol, it is
imperative to use genetically improved hybrids with better biomass degradability.
However, genetic engineering is still a challenge due to limited understanding of the
large and complex genome of this plant (Hoang et al. 2015).
Modern sugarcane represents the extreme example of polyploidy, with a doublegenome structure, where genotypes resulting from the same crossover may vary in
amount of homologous and homologous chromosomes. Mapping of genetic linkages
is particularly difficult to construct in polyploid species because (i) the statistics are
much more complicated for polyploids than for diploids, (ii) a wide variety of
genotypes are expected in a segregating population, (iii) there are several ways of
forming gametes and random pairs of multiple homologous chromosomes,
(iv) alleles segregation with different dosage levels makes it impossible for the
48
F. L. Shimizu et al.
external threats to its structure (Zhu et al. 2010). It has been confirmed that
hemicellulose removal improves glucose yield after enzymatic hydrolysis of material (Chen et al. 2015). Lignin causes another problem besides providing a physical
barrier like hemicelluloses. Lignin causes a non-productive adsorption of enzymes
employed in cellulose hydrolysis, deactivating them along the process (Ximenes
et al. 2011). Lignin removal with pretreatments can reduce loss of active enzymes
(Yang and Pan 2016). Changes in biomass structure are observed by looking at
superficial cavities, gaps, and hollow spaces created by hemicellulose elimination
and/or lignin amendment by pretreatments like dilute acid, peroxide, steam explosion, and alkaline methods (Karimi and Taherzadeh 2016). A quantification of these
components (cellulose, hemicelluloses, and lignin) can determine biomass quality
and drive its application. The pretreatment processes improve lignocellulosic biomass quality allowing its conversion into biofuel, organic acids, and other chemicals
with high industrial interest.
2.8
Biomass Genetic Improvement
Modification of cell wall structure of lignocellulosic biomass is the key step in
improving the quality of bioenergetic crops. However, genetic improvement of
energy crops is still a challenge to increase the production of biomass and biofuels
on large scale. A genetic modification in the plant cell wall structure is desired to
specifically alter the cell wall interconnections (cellulose crystallinity) and reducing
lignin levels and increasing carbohydrate content. The genetic manipulation must
select appropriate genes, which is a fundamental step to meet the expected
objectives. However, there are more than 1,000 genes related to biosynthesis,
degradation, and regulation of the plant cell wall (Xie and Peng 2011). As complementary techniques for genetic improvement of biomass quality, several tools have
been developed: high-throughput genotyping, generation sequencing, and molecular
breeding techniques such as marker assisted selection and genomic selection. These
modern tools have been applied in a wide variety of bioenergetic species such as
sugarcane, elephant grass, sorghum, and miscanthus (Allwright and Taylor 2016).
In order to optimize the biomass conversion from sugarcane into bioethanol, it is
imperative to use genetically improved hybrids with better biomass degradability.
However, genetic engineering is still a challenge due to limited understanding of the
large and complex genome of this plant (Hoang et al. 2015).
Modern sugarcane represents the extreme example of polyploidy, with a doublegenome structure, where genotypes resulting from the same crossover may vary in
amount of homologous and homologous chromosomes. Mapping of genetic linkages
is particularly difficult to construct in polyploid species because (i) the statistics are
much more complicated for polyploids than for diploids, (ii) a wide variety of
genotypes are expected in a segregating population, (iii) there are several ways of
forming gametes and random pairs of multiple homologous chromosomes,
(iv) alleles segregation with different dosage levels makes it impossible for the
48
F. L. Shimizu et al.