However, use of single enzymatic system has been reported with higher yield for the
downstream processing of microalgal biomass (Vanegas et al. 2015); cocktails could
be more hopeful for the hydrolysis of different biopolymers of plant biomass
(Ehimen et al. 2013).
7.5.2 In Enzymatic Hydrolysis
For the economic generation of ethanol from cellulosic plant biomass, enzyme-based
hydrolysis is an advantageous process as it is a very cost-effective method, with a
probably vast yield when compared to chemical treatment. Long chain of carbohydrate present in the plant cell wall can be deconstructed by hydrolysis method with
the help of enzyme catalysis process. By forming a physical barrier, hemicellulose
restricts the cellulase accessibility to cellulose (Zhang et al. 2012). Hence, supplying
enzymes such as xylanases which can degrade them can be the most suitable method
to enhance the release of overall fermentable sugar from various pretreated lignocellulosic plant biomass (Kumar et al. 2009; Öhgren et al. 2007). Xylanases,
e.g. endo-β-1,4-xylanases (EC 3.2.1.8) and β-xylosidase (EC 3.2.1.37), can act in
the main chains along with the side chain residues of the complex structure of xylan.
Endo-β-1,4-xylanase disrupts the long chain of xylan into smaller ones (Aditiya et al.
2016); similarly, xylopyranose is produced by β-xylosidase which is a pyranose unit
made up of xylose monomers which are formed by continuous cleaving of oligosaccharide. Other xylanolytic accessory enzymes such as feruloyl esterase
(EC 3.1.139) and acetyl xylan esterase (EC 3.1.1.72) cleave the outer chains (Aditiya
et al. 2016). Due to their more amorphous nature, hemicelluloses are quite different
from celluloses, and also hemicellulolytic enzymes are more complicated but with
very particular actions. Hence, it can be confirmed that destruction of xylan by
enzymatic hydrolysis may remove the cellulose covering and also it can help in the
improvement of cellulase performance (Zhang et al. 2012).
7.6 Enzyme Synergy: A Conceptual Strategy
Synergistic action of enzymes can be stated as the combination of pretreatment and
hydrolysis steps to convert most of the polymeric components to fermentable sugar
(Ang et al. 2015). In this process, some attention must be taken that the process
should not degrade or irreversibly transform the sugars, which will eventually lead to
the loss in fermentable sugar. Further, the slurries generated after the pretreatment
may have some unwanted physical and chemical characteristics which may hinder
the catalysis process of enzymatic proteins. Thus, to avoid the extent of degradation,
less severe pretreatment methodologies must be selected, e.g. biological
pretreatment via enzymes and microorganisms like fungi (Teter et al. 2014; Zhang
et al. 2012).
7 Xylanases: A Helping Module for the Enzyme Biorefinery Platform
167
downstream processing of microalgal biomass (Vanegas et al. 2015); cocktails could
be more hopeful for the hydrolysis of different biopolymers of plant biomass
(Ehimen et al. 2013).
7.5.2 In Enzymatic Hydrolysis
For the economic generation of ethanol from cellulosic plant biomass, enzyme-based
hydrolysis is an advantageous process as it is a very cost-effective method, with a
probably vast yield when compared to chemical treatment. Long chain of carbohydrate present in the plant cell wall can be deconstructed by hydrolysis method with
the help of enzyme catalysis process. By forming a physical barrier, hemicellulose
restricts the cellulase accessibility to cellulose (Zhang et al. 2012). Hence, supplying
enzymes such as xylanases which can degrade them can be the most suitable method
to enhance the release of overall fermentable sugar from various pretreated lignocellulosic plant biomass (Kumar et al. 2009; Öhgren et al. 2007). Xylanases,
e.g. endo-β-1,4-xylanases (EC 3.2.1.8) and β-xylosidase (EC 3.2.1.37), can act in
the main chains along with the side chain residues of the complex structure of xylan.
Endo-β-1,4-xylanase disrupts the long chain of xylan into smaller ones (Aditiya et al.
2016); similarly, xylopyranose is produced by β-xylosidase which is a pyranose unit
made up of xylose monomers which are formed by continuous cleaving of oligosaccharide. Other xylanolytic accessory enzymes such as feruloyl esterase
(EC 3.1.139) and acetyl xylan esterase (EC 3.1.1.72) cleave the outer chains (Aditiya
et al. 2016). Due to their more amorphous nature, hemicelluloses are quite different
from celluloses, and also hemicellulolytic enzymes are more complicated but with
very particular actions. Hence, it can be confirmed that destruction of xylan by
enzymatic hydrolysis may remove the cellulose covering and also it can help in the
improvement of cellulase performance (Zhang et al. 2012).
7.6 Enzyme Synergy: A Conceptual Strategy
Synergistic action of enzymes can be stated as the combination of pretreatment and
hydrolysis steps to convert most of the polymeric components to fermentable sugar
(Ang et al. 2015). In this process, some attention must be taken that the process
should not degrade or irreversibly transform the sugars, which will eventually lead to
the loss in fermentable sugar. Further, the slurries generated after the pretreatment
may have some unwanted physical and chemical characteristics which may hinder
the catalysis process of enzymatic proteins. Thus, to avoid the extent of degradation,
less severe pretreatment methodologies must be selected, e.g. biological
pretreatment via enzymes and microorganisms like fungi (Teter et al. 2014; Zhang
et al. 2012).
7 Xylanases: A Helping Module for the Enzyme Biorefinery Platform
167