11.2 Cellulases
Many researchers and industries chiefly focused on cellulases as they are the most
unbeaten group of lignocellulolytic enzymes used in disparate economically related
processes. Principally, cellulases are enzymatic proteins which operate slowly by
one to two orders of amplitude compared to the rest of the carbohydrate-degrading
enzymes (Himmel et al. 2007) leading to the biotransformation of lignocelluloses to
efficacious requisites. The noteworthy usage of cellulose biomass is thought to be
associated with economic process for the enzyme cultivation (Solomon et al. 1999;
Wu and Lee 1997).
Based on their catalytic site in the cellulosic substrate, cellulases are categorised
into three groups:
Endoglucanase: During the solubilisation of cellulosic material, CMCase proceeds
in associated action with exoglucanases and β-D-glycosidase (Zhang et al. 2006)
by breaking the internal glycosidic bonds present in the cellulosic chains producing cellooligosaccharides.
Exoglucanases: (Cellobiohydrolases (CBHs)) – It acts on cellulose by cleaving the
disaccharide units initiating from the non-reducing terminal of the chain. It also
acts on swollen, partially degraded amorphous substrates and cellodextrins.
However, soluble derivatives of cellulose such as hydroxyl ethyl cellulose and
carboxymethyl cellulose were not hydrolysed. A non-significant constituent to be
noticed in few cellulase systems is glucohydrolase (Joshi and Pandey 1999).
β-Glycosidase: (Cellobiose) – β-Glycosidase hydrolyses cellobiose to glucose,
contributing an easily metabolised source of carbon to the fungus. Numerous
cellobioses were reported in wide Aspergillus members with different molecular
weights. A great number of these enzymes except a few fail to exert action on
H3 P O4 – swollen, CM celluloses and other polymeric substrates such as cotton,
Avicel and filter paper (Bhat and Hazlewood 2003).
The two foremost enzymes termed “absolute cellulases” directly act on cellulose to
give off glucose. The so formed cellobiose later fragmented into glucose by the third
enzyme in sequence (Dincer and Telefoncu 2006; Andersen 2007) (Fig. 11.1).
11.3 Fungal Cellulases
The most robust and widespread biomass fragmenting microbes that have evolved in
nature are fungi showing assorted modes of life for the bioconversion of green
cellulosic deposits on the biosphere. The secretion of multifarious set of oxidative
and hydrolytic enzymes (cellulases) mould fungi to be capable of decomposing
green biomass (Elzaher and Fadel 2010; Amir et al. 2011). Therefore, the scale of
notable performance and potentiality of the production were presented with ease at
uplifted activities on industrial scale. Industrial biorefinery applications are largely
dependent on cellulase mixture of fungal origin.
11 Significance of Process Parameters on Fungal Cellulase Production
301
Many researchers and industries chiefly focused on cellulases as they are the most
unbeaten group of lignocellulolytic enzymes used in disparate economically related
processes. Principally, cellulases are enzymatic proteins which operate slowly by
one to two orders of amplitude compared to the rest of the carbohydrate-degrading
enzymes (Himmel et al. 2007) leading to the biotransformation of lignocelluloses to
efficacious requisites. The noteworthy usage of cellulose biomass is thought to be
associated with economic process for the enzyme cultivation (Solomon et al. 1999;
Wu and Lee 1997).
Based on their catalytic site in the cellulosic substrate, cellulases are categorised
into three groups:
Endoglucanase: During the solubilisation of cellulosic material, CMCase proceeds
in associated action with exoglucanases and β-D-glycosidase (Zhang et al. 2006)
by breaking the internal glycosidic bonds present in the cellulosic chains producing cellooligosaccharides.
Exoglucanases: (Cellobiohydrolases (CBHs)) – It acts on cellulose by cleaving the
disaccharide units initiating from the non-reducing terminal of the chain. It also
acts on swollen, partially degraded amorphous substrates and cellodextrins.
However, soluble derivatives of cellulose such as hydroxyl ethyl cellulose and
carboxymethyl cellulose were not hydrolysed. A non-significant constituent to be
noticed in few cellulase systems is glucohydrolase (Joshi and Pandey 1999).
β-Glycosidase: (Cellobiose) – β-Glycosidase hydrolyses cellobiose to glucose,
contributing an easily metabolised source of carbon to the fungus. Numerous
cellobioses were reported in wide Aspergillus members with different molecular
weights. A great number of these enzymes except a few fail to exert action on
H3 P O4 – swollen, CM celluloses and other polymeric substrates such as cotton,
Avicel and filter paper (Bhat and Hazlewood 2003).
The two foremost enzymes termed “absolute cellulases” directly act on cellulose to
give off glucose. The so formed cellobiose later fragmented into glucose by the third
enzyme in sequence (Dincer and Telefoncu 2006; Andersen 2007) (Fig. 11.1).
11.3 Fungal Cellulases
The most robust and widespread biomass fragmenting microbes that have evolved in
nature are fungi showing assorted modes of life for the bioconversion of green
cellulosic deposits on the biosphere. The secretion of multifarious set of oxidative
and hydrolytic enzymes (cellulases) mould fungi to be capable of decomposing
green biomass (Elzaher and Fadel 2010; Amir et al. 2011). Therefore, the scale of
notable performance and potentiality of the production were presented with ease at
uplifted activities on industrial scale. Industrial biorefinery applications are largely
dependent on cellulase mixture of fungal origin.
11 Significance of Process Parameters on Fungal Cellulase Production
301