different enzymes as they can produce thermostable enzymes. As compared to
mesophilic enzymes, thermophiles have high resistance for denaturing agents and
high-pressure tolerance. Hence, they may be considered as the valuable domain for
the production of biofuels at higher temperatures (Haki and Rakshit 2003), because
high temperature may enhance the penetration of enzymes via cell wall of lignocellulosic plant biomass and can behave as a physical factor for the disorganization of
the cell wall of lignocellulosic biomass (Paës and O’Donohue 2006). Among various
pretreatment methods, enzymatic degradation of lignocellulosic biomass using cellulase and xylanase is found to be the most suitable and specific with no other toxic
effects or product formation and no loss of substrate. Thermostable xylanases and
cellulases play a very important role in the pharmaceutical, chemical, food and paper
and pulp industries. Xylanases have been found to be an alternative of chlorine in
paper and pulp industry due to their involvement in the leaching of xylan from
carbohydrate-lignin complex. This way xylanase can be useful in the replacement of
chlorine and in pulp bleaching process and can reduce the environmental pollution
caused by them. A thermostable xylanase obtained from Myceliophthora
thermophila was found suitable as compared to a thermolabile xylanase obtained
from Trichoderma reesei in paper and pulp industry. A thermostable xylanase from
Bacillus sp. NCIM5 was utilized in the bagasse pulp pre-bleaching by simultaneously reducing the demand of chlorine (Kulkarni and Rao 1996). Various bacterial
strains such as Bacillus sp. and Dictyoglomus sp. were successful at commercial
scale (Rani and Nand 2000). Although, for many xylanolytic and cellulolytic
enzymes, the temperature and pH optima were found to be below 50
C and acidic
or neutral pH (Gessesse 1998), various thermophilic fungi are found to be the good
producers of xylanases and cellulases which were successfully used in the lignocellulosic biomass saccharification (Kaur and Satyanarayana 2004).
7.9 The Products of Biorefinery
A list of some recent xylanases involved in the biorefinery process has been shown
in Table 7.1 and discussed as follows.
7.9.1 Bioethanol
Bioethanol produced from lignocellulosic plant biomass is ecological process that
can be enhanced by using suitable enzymes and microorganisms. Previous studies
have reported that thermophilic microorganism can produce more amount of
bioethanol via simultaneous delignification, saccharification and fermentation process. Thermal stability has been found to be an important and desirable property for
cellulolytic and xylanolytic enzymes required for successful saccharification. The
hydrolysis rate of Trichoderma is low as it has less β-glucosidase level (Mohanram
170
N. Bhardwaj and P. Verma
mesophilic enzymes, thermophiles have high resistance for denaturing agents and
high-pressure tolerance. Hence, they may be considered as the valuable domain for
the production of biofuels at higher temperatures (Haki and Rakshit 2003), because
high temperature may enhance the penetration of enzymes via cell wall of lignocellulosic plant biomass and can behave as a physical factor for the disorganization of
the cell wall of lignocellulosic biomass (Paës and O’Donohue 2006). Among various
pretreatment methods, enzymatic degradation of lignocellulosic biomass using cellulase and xylanase is found to be the most suitable and specific with no other toxic
effects or product formation and no loss of substrate. Thermostable xylanases and
cellulases play a very important role in the pharmaceutical, chemical, food and paper
and pulp industries. Xylanases have been found to be an alternative of chlorine in
paper and pulp industry due to their involvement in the leaching of xylan from
carbohydrate-lignin complex. This way xylanase can be useful in the replacement of
chlorine and in pulp bleaching process and can reduce the environmental pollution
caused by them. A thermostable xylanase obtained from Myceliophthora
thermophila was found suitable as compared to a thermolabile xylanase obtained
from Trichoderma reesei in paper and pulp industry. A thermostable xylanase from
Bacillus sp. NCIM5 was utilized in the bagasse pulp pre-bleaching by simultaneously reducing the demand of chlorine (Kulkarni and Rao 1996). Various bacterial
strains such as Bacillus sp. and Dictyoglomus sp. were successful at commercial
scale (Rani and Nand 2000). Although, for many xylanolytic and cellulolytic
enzymes, the temperature and pH optima were found to be below 50
C and acidic
or neutral pH (Gessesse 1998), various thermophilic fungi are found to be the good
producers of xylanases and cellulases which were successfully used in the lignocellulosic biomass saccharification (Kaur and Satyanarayana 2004).
7.9 The Products of Biorefinery
A list of some recent xylanases involved in the biorefinery process has been shown
in Table 7.1 and discussed as follows.
7.9.1 Bioethanol
Bioethanol produced from lignocellulosic plant biomass is ecological process that
can be enhanced by using suitable enzymes and microorganisms. Previous studies
have reported that thermophilic microorganism can produce more amount of
bioethanol via simultaneous delignification, saccharification and fermentation process. Thermal stability has been found to be an important and desirable property for
cellulolytic and xylanolytic enzymes required for successful saccharification. The
hydrolysis rate of Trichoderma is low as it has less β-glucosidase level (Mohanram
170
N. Bhardwaj and P. Verma