In order to avoid the loss of fermentable sugar, all the three major steps,
i.e. pretreatment, hydrolysis and fermentation, of biomass conversion can be incorporated together which will lead to the reduction in multistep process. Hence,
different enzymes can be mixed together in sufficient ratio to prepare the suitable
enzyme cocktail (Bhardwaj et al. 2019). These enzymes will work synergistically
and will lead to the enhanced biomass conversion and release of maximum sugar as
compared to other physical and chemical methods (Chaturvedi and Verma 2013).
Later the released sugar in the slurry can further be converted into bioethanol by the
use of ethanologenic microorganisms such as Saccharomyces cerevisiae (Bhardwaj
et al. 2019). Although bio-based methods have various advantages such as high
specificity, no formation of toxic and inhibitory chemicals and expensive and
sophisticated instruments are not required, they have some limitations also like
high enzyme cost, limited temperature and pH stability (Bala and Singh 2019a).
A study has been reported on the use of thermo-alkali-stable lignohemicellulolytic enzyme laccase from Myrothecium verrucaria (Agrawal et al.
2019), xylanase from Aspergillus oryzae (Bhardwaj et al. 2017) and cellulase from
Schizophyllum commune (Kumar et al. 2018) cocktails (crude, partially purified) in
combination with Saccharomyces cerevisiae MTCC-173, by using simultaneous
delignification, saccharification and fermentation (SDSF) in combination with Saccharomyces cerevisiae MTCC-173 (Bhardwaj et al. 2019). Various forms of
xylanase were produced by some thermophilic fungi such as Malbranchea
cinnamomea (Mahajan et al. 2014), Pyrenophora phaeocomes (Rastogi et al.
2016) and Trametes versicolor, Pleurotus ostreatus and Piptoporus betulinus
(Valášková and Baldrian 2006). Similarly, thermophilic mould such as
T. aurantiacus was found capable of producing xylanase and cellulases by using
agricultural biomass (Jain et al. 2015).
Similarly, in coculturing method, combination of enzyme produced by Aspergillus niger and Trichoderma reesei resulted in a three-fold higher hydrolysis rate of
unwashed pretreated sugarcane bagasse with only 0.7 FPU activity/g glucan enzyme
load when compared to 5–15 times enzyme loading (Florencio et al. 2016). Therefore, it can be stated that cocktails of various enzymes and coculture of microorganisms could be a better approach to enhance the fermentable sugar production (Kolasa
et al. 2014).
7.7 Factors Affecting Biological Pretreatment
In order to get highest yield via enzymatic pretreatment, it is required to understand
the factor affecting the microbial growth and metabolism (Wan and Li 2012). The
factors which may affect the process are nature, moisture content and particle size of
the biomass or substrates, microorganism type and inoculum concentration, enzyme
type and conditions like time, pH and temperature. Biomass surface contains internal
and external area where the particle size and shape is important for the maintenance
of biomass component capillary structure (Maurya et al. 2015). Further, particles
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N. Bhardwaj and P. Verma
i.e. pretreatment, hydrolysis and fermentation, of biomass conversion can be incorporated together which will lead to the reduction in multistep process. Hence,
different enzymes can be mixed together in sufficient ratio to prepare the suitable
enzyme cocktail (Bhardwaj et al. 2019). These enzymes will work synergistically
and will lead to the enhanced biomass conversion and release of maximum sugar as
compared to other physical and chemical methods (Chaturvedi and Verma 2013).
Later the released sugar in the slurry can further be converted into bioethanol by the
use of ethanologenic microorganisms such as Saccharomyces cerevisiae (Bhardwaj
et al. 2019). Although bio-based methods have various advantages such as high
specificity, no formation of toxic and inhibitory chemicals and expensive and
sophisticated instruments are not required, they have some limitations also like
high enzyme cost, limited temperature and pH stability (Bala and Singh 2019a).
A study has been reported on the use of thermo-alkali-stable lignohemicellulolytic enzyme laccase from Myrothecium verrucaria (Agrawal et al.
2019), xylanase from Aspergillus oryzae (Bhardwaj et al. 2017) and cellulase from
Schizophyllum commune (Kumar et al. 2018) cocktails (crude, partially purified) in
combination with Saccharomyces cerevisiae MTCC-173, by using simultaneous
delignification, saccharification and fermentation (SDSF) in combination with Saccharomyces cerevisiae MTCC-173 (Bhardwaj et al. 2019). Various forms of
xylanase were produced by some thermophilic fungi such as Malbranchea
cinnamomea (Mahajan et al. 2014), Pyrenophora phaeocomes (Rastogi et al.
2016) and Trametes versicolor, Pleurotus ostreatus and Piptoporus betulinus
(Valášková and Baldrian 2006). Similarly, thermophilic mould such as
T. aurantiacus was found capable of producing xylanase and cellulases by using
agricultural biomass (Jain et al. 2015).
Similarly, in coculturing method, combination of enzyme produced by Aspergillus niger and Trichoderma reesei resulted in a three-fold higher hydrolysis rate of
unwashed pretreated sugarcane bagasse with only 0.7 FPU activity/g glucan enzyme
load when compared to 5–15 times enzyme loading (Florencio et al. 2016). Therefore, it can be stated that cocktails of various enzymes and coculture of microorganisms could be a better approach to enhance the fermentable sugar production (Kolasa
et al. 2014).
7.7 Factors Affecting Biological Pretreatment
In order to get highest yield via enzymatic pretreatment, it is required to understand
the factor affecting the microbial growth and metabolism (Wan and Li 2012). The
factors which may affect the process are nature, moisture content and particle size of
the biomass or substrates, microorganism type and inoculum concentration, enzyme
type and conditions like time, pH and temperature. Biomass surface contains internal
and external area where the particle size and shape is important for the maintenance
of biomass component capillary structure (Maurya et al. 2015). Further, particles
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N. Bhardwaj and P. Verma