Therefore, considering the importance of enzymatic system in the field of
biorefinery, the main focus must be on finding new strains which can produce a
large amount of xylanases along with other hydrolytic enzymes. Along with these,
new methods should be found to enhance the production of fermentable sugar that
can be further converted into biofuel. This chapter includes the brief overview of the
process involved in the biorefinery system via microbial xylanases. A brief overview
of the biorefinery process has been shown in Fig. 7.1.
7.2 Raw Material for Biorefinery
Residues obtained from agricultural industries such as wheat straw and bran, rice
straw and husk, sugarcane bagasse, cotton stalk some of the most abundant lignocellulosic biomass. Lignocellulosic plant biomass have been recognized as an
efficient raw material for the biorefinery processes which can replace huge sections
of fossil resources (Maiti et al. 2018). The biorefinery process can produce three
main end-products, i.e. biofuels, bioenergy and biochemicals. As compared to other
renewable resources such as sun, wind and water, use of lignocellulosic biomass has
some advantages as it contains carbon materials in addition to fossils (Pachapur et al.
2019). Biorefinery processes comprises of a broad range of methods which can
separate plant biomass (cellulose, hemicellulose) resources, such as rice, wheat,
wood, grass, corn, etc., into carbohydrates, triglycerides, proteins, etc, which can
further be converted into value-added end-products such as biofuels and biochemicals (De Jong et al. 2009; Saba et al. 2015) via various physical, chemical or
biological processes (Juodeikiene et al. 2011).
7.3 Structure of Lignocellulosic Plant Biomass
In the complete structure of the plant cell wall, cellulose is the principal component
which is present in a complex but systematic framework fibrous structure (Kumar
et al. 2009). This fibrous structure is made up of approximately 500–15,000 anhydrous glucose units linked with β-1,4-glycosidic linkages which form a linear homopolysaccharide with the series of small cellobiose units. Extremely crystalline
structure of cellulose comprises inter- and intra-molecular H-bonds that are formed
by β-1,4 arrangement of the glucoside bonds (Saini et al. 2015). Hemicellulose
which is found in the upper layer of cellulose and below the lignin in the plant cell
wall (Saini et al. 2015) contains a short polypeptide chain with 50–200 units of
pentose and hexose sugar which is highly branched such as D-xylose, L-arabinose
and D-mannose-galactose-glucose, respectively. The hemicellulose part also has an
acetate group which is arranged randomly to the hydroxyl groups of the pentose
sugar ring with ester linkages (Saini et al. 2015). Lignin is the third important
component of the plant cell wall which is a highly crosslinked aromatic amorphous
7 Xylanases: A Helping Module for the Enzyme Biorefinery Platform
163
biorefinery, the main focus must be on finding new strains which can produce a
large amount of xylanases along with other hydrolytic enzymes. Along with these,
new methods should be found to enhance the production of fermentable sugar that
can be further converted into biofuel. This chapter includes the brief overview of the
process involved in the biorefinery system via microbial xylanases. A brief overview
of the biorefinery process has been shown in Fig. 7.1.
7.2 Raw Material for Biorefinery
Residues obtained from agricultural industries such as wheat straw and bran, rice
straw and husk, sugarcane bagasse, cotton stalk some of the most abundant lignocellulosic biomass. Lignocellulosic plant biomass have been recognized as an
efficient raw material for the biorefinery processes which can replace huge sections
of fossil resources (Maiti et al. 2018). The biorefinery process can produce three
main end-products, i.e. biofuels, bioenergy and biochemicals. As compared to other
renewable resources such as sun, wind and water, use of lignocellulosic biomass has
some advantages as it contains carbon materials in addition to fossils (Pachapur et al.
2019). Biorefinery processes comprises of a broad range of methods which can
separate plant biomass (cellulose, hemicellulose) resources, such as rice, wheat,
wood, grass, corn, etc., into carbohydrates, triglycerides, proteins, etc, which can
further be converted into value-added end-products such as biofuels and biochemicals (De Jong et al. 2009; Saba et al. 2015) via various physical, chemical or
biological processes (Juodeikiene et al. 2011).
7.3 Structure of Lignocellulosic Plant Biomass
In the complete structure of the plant cell wall, cellulose is the principal component
which is present in a complex but systematic framework fibrous structure (Kumar
et al. 2009). This fibrous structure is made up of approximately 500–15,000 anhydrous glucose units linked with β-1,4-glycosidic linkages which form a linear homopolysaccharide with the series of small cellobiose units. Extremely crystalline
structure of cellulose comprises inter- and intra-molecular H-bonds that are formed
by β-1,4 arrangement of the glucoside bonds (Saini et al. 2015). Hemicellulose
which is found in the upper layer of cellulose and below the lignin in the plant cell
wall (Saini et al. 2015) contains a short polypeptide chain with 50–200 units of
pentose and hexose sugar which is highly branched such as D-xylose, L-arabinose
and D-mannose-galactose-glucose, respectively. The hemicellulose part also has an
acetate group which is arranged randomly to the hydroxyl groups of the pentose
sugar ring with ester linkages (Saini et al. 2015). Lignin is the third important
component of the plant cell wall which is a highly crosslinked aromatic amorphous
7 Xylanases: A Helping Module for the Enzyme Biorefinery Platform
163