29
can be kept minimum and fed as per demand (Shibuya et al. 1981). The use of a
soluble carbon source in lieu of (ligno) cellulose has obvious advantages as this will
allow better mixing and aeration and greater control over the fermentation process.
Also the fermentation would no longer be dependent on the hydrolysis of lignocellulose (Allen and Mortensen 1981). While sophorose is the best inducer of cellulase
in Trichoderma reesei, it is also the most expensive and difficult to manufacture.
Recently, Danisco Inc. has patented a process using concentrated glucose, containing appreciable quantities of sophorose as carbon source/inducer for cellulase production using T. reesei (England et al. 2015). Here the inducing mixture of sugars
was generated through transglycosylation activity employing whole cellulase preparations from T. reesei.
It may be concluded that the choice of method for cellulase production depends
on the end application and the cost evaluations also need to consider the efficacy of
the enzyme preparation on the chosen lignocellulosic substrate. While SSF and
SmF have their own advantages and disadvantages, it is not prudent to state one
method is better than the other, since the choice is often made depending on the
context of application, rather than on the mere advantages of a particular method.
1.6
Strategies for Cost-Efficient Cellulase Preparations
Attaining cost efficiency of biomass-hydrolyzing enzymes is a complex R&D problem considering the fact that the cost of cellulases for biomass conversion depends
not just on the cost of their production, but also on various factors that determine
their efficiency for the hydrolysis of biomass. The production costs of cellulase are
tightly connected to the productivity of the enzyme-producing strain and the final
activity yield in the fermentation broth. The hydrolytic efficiency of the multienzyme complex depends on both the properties of the individual enzymes and synergies between them, and their ratio in the cocktail (Gusakov et al. 2014). While the
knowledge on the number and type of enzymes and proteins that are involved in
biomass hydrolysis is far from complete, the minimum set of enzymes required is
probably easy to gauge. Moreover, in actual practice, the enzymes used may never
be in their pure form, which means that preparations enriched for a component
enzyme would still contain other activities and accessory proteins, albeit in smaller
amounts. This would probably take care of the requirements of those accessory
activities which may be needed only in lesser proportions, in analogy with nature’s
own arsenal for plant cell wall degradation that uses the accessory activities in far
lesser amounts compared to the main enzymes – cellobiohydrolases and endoglucanases. Commercial enzyme cocktails for biomass hydrolysis contain several different enzymes and accessory proteins of suboptimal activities and relative proportions,
and it is important to know the optimal concentrations of each enzyme and their
relative proportions to develop efficient cocktails for hydrolysis of biomass. For
example, the typical T. reesei cellulase preparation, though rich in cellobiohydrolase, contains only low concentrations of beta glucosidase, and hence the biomasshydrolyzing cocktails produced by enzyme manufactures often blend in large
1 Enzymes for Bioenergy
can be kept minimum and fed as per demand (Shibuya et al. 1981). The use of a
soluble carbon source in lieu of (ligno) cellulose has obvious advantages as this will
allow better mixing and aeration and greater control over the fermentation process.
Also the fermentation would no longer be dependent on the hydrolysis of lignocellulose (Allen and Mortensen 1981). While sophorose is the best inducer of cellulase
in Trichoderma reesei, it is also the most expensive and difficult to manufacture.
Recently, Danisco Inc. has patented a process using concentrated glucose, containing appreciable quantities of sophorose as carbon source/inducer for cellulase production using T. reesei (England et al. 2015). Here the inducing mixture of sugars
was generated through transglycosylation activity employing whole cellulase preparations from T. reesei.
It may be concluded that the choice of method for cellulase production depends
on the end application and the cost evaluations also need to consider the efficacy of
the enzyme preparation on the chosen lignocellulosic substrate. While SSF and
SmF have their own advantages and disadvantages, it is not prudent to state one
method is better than the other, since the choice is often made depending on the
context of application, rather than on the mere advantages of a particular method.
1.6
Strategies for Cost-Efficient Cellulase Preparations
Attaining cost efficiency of biomass-hydrolyzing enzymes is a complex R&D problem considering the fact that the cost of cellulases for biomass conversion depends
not just on the cost of their production, but also on various factors that determine
their efficiency for the hydrolysis of biomass. The production costs of cellulase are
tightly connected to the productivity of the enzyme-producing strain and the final
activity yield in the fermentation broth. The hydrolytic efficiency of the multienzyme complex depends on both the properties of the individual enzymes and synergies between them, and their ratio in the cocktail (Gusakov et al. 2014). While the
knowledge on the number and type of enzymes and proteins that are involved in
biomass hydrolysis is far from complete, the minimum set of enzymes required is
probably easy to gauge. Moreover, in actual practice, the enzymes used may never
be in their pure form, which means that preparations enriched for a component
enzyme would still contain other activities and accessory proteins, albeit in smaller
amounts. This would probably take care of the requirements of those accessory
activities which may be needed only in lesser proportions, in analogy with nature’s
own arsenal for plant cell wall degradation that uses the accessory activities in far
lesser amounts compared to the main enzymes – cellobiohydrolases and endoglucanases. Commercial enzyme cocktails for biomass hydrolysis contain several different enzymes and accessory proteins of suboptimal activities and relative proportions,
and it is important to know the optimal concentrations of each enzyme and their
relative proportions to develop efficient cocktails for hydrolysis of biomass. For
example, the typical T. reesei cellulase preparation, though rich in cellobiohydrolase, contains only low concentrations of beta glucosidase, and hence the biomasshydrolyzing cocktails produced by enzyme manufactures often blend in large
1 Enzymes for Bioenergy