Xylanases that belong to GH8, GH43, and GH98 display an inverting mechanism of
catalysis. Unlike other families, at the time of writing, the GH134 family comprises
only β-mannanases which are distinct from other β-mannanases by its inverting
catalytic mechanism [149]. However, the catalytic residues and the displacement
mechanism of this enzyme is yet to be identified.
6 Applications of Alkaline Active Hemicellulases
With the growing interest in “greener” industrial processes and the discovery of
more amenable enzymes that fit to industrial requirements, the application of
enzymes is expanding both in volume and diversity. This seems reflected in the
ever-increasing market value of industrial enzymes. It is believed that hydrolases are
the major commercial enzymes which roughly account for 75% of the total industrial
enzyme market [150]. Hemicellulases are among these commercially important
hydrolases. The annual market value of xylanases alone is estimated to be over
200 million USD [151], and recently the compound annual growth rate of the global
xylanase market has been projected to be about 6.6% [152]. Although neutralophiles
have been the dominant sources for commercial hemicellulases, in recent years
alkaliphiles and alkali-tolerant organisms are also becoming important. Xylanases
and mannanases which are significantly active and stable in high pH conditions are
the ideal choices for applications such as biobleaching of Kraft pulp and detergent
formulation which require alkaline conditions. Moreover, as shown in Tables 2 and
4, most alkaline active hemicellulases are often active in a wide range of pH, from
slightly acidic to highly alkaline milieu. Thus, potentially, at least some of these
hemicellulases of alkaliphiles can be used in areas where enzymes of neutralophiles
are being used like in food, beverage, and feed industries. Below, some of the
important real and potential applications of alkaline active hemicellulases are
discussed.
6.1 Pulp and Paper
The pulp and paper industries use different methods of recovering cellulose fibers
from lignocellulosic biomass, most of which is from wood. Chemical pulping which
includes Kraft, sulfite, and semichemical processes is the dominant method among
the pulping processes. Kraft pulping accounts for over 90% of the total chemical
pulping. The Kraft process which is also called the sulfate process involves an
alkaline treatment with solutions of sodium sulfide and sodium hydroxide at about
170
C for 2 h resulting in the degradation and solubilization of lignin. The resulting
pulp from this alkaline cooking has brownish color primarily due to the residual
lignin and lignin derivatives which are covalently attached to the hemicellulose
fraction. Removal of this lignin involves a multistage bleaching process, which
involves elemental chlorine. Although chlorine-based bleaching of pulp is effective,
270
G. Mamo
catalysis. Unlike other families, at the time of writing, the GH134 family comprises
only β-mannanases which are distinct from other β-mannanases by its inverting
catalytic mechanism [149]. However, the catalytic residues and the displacement
mechanism of this enzyme is yet to be identified.
6 Applications of Alkaline Active Hemicellulases
With the growing interest in “greener” industrial processes and the discovery of
more amenable enzymes that fit to industrial requirements, the application of
enzymes is expanding both in volume and diversity. This seems reflected in the
ever-increasing market value of industrial enzymes. It is believed that hydrolases are
the major commercial enzymes which roughly account for 75% of the total industrial
enzyme market [150]. Hemicellulases are among these commercially important
hydrolases. The annual market value of xylanases alone is estimated to be over
200 million USD [151], and recently the compound annual growth rate of the global
xylanase market has been projected to be about 6.6% [152]. Although neutralophiles
have been the dominant sources for commercial hemicellulases, in recent years
alkaliphiles and alkali-tolerant organisms are also becoming important. Xylanases
and mannanases which are significantly active and stable in high pH conditions are
the ideal choices for applications such as biobleaching of Kraft pulp and detergent
formulation which require alkaline conditions. Moreover, as shown in Tables 2 and
4, most alkaline active hemicellulases are often active in a wide range of pH, from
slightly acidic to highly alkaline milieu. Thus, potentially, at least some of these
hemicellulases of alkaliphiles can be used in areas where enzymes of neutralophiles
are being used like in food, beverage, and feed industries. Below, some of the
important real and potential applications of alkaline active hemicellulases are
discussed.
6.1 Pulp and Paper
The pulp and paper industries use different methods of recovering cellulose fibers
from lignocellulosic biomass, most of which is from wood. Chemical pulping which
includes Kraft, sulfite, and semichemical processes is the dominant method among
the pulping processes. Kraft pulping accounts for over 90% of the total chemical
pulping. The Kraft process which is also called the sulfate process involves an
alkaline treatment with solutions of sodium sulfide and sodium hydroxide at about
170
C for 2 h resulting in the degradation and solubilization of lignin. The resulting
pulp from this alkaline cooking has brownish color primarily due to the residual
lignin and lignin derivatives which are covalently attached to the hemicellulose
fraction. Removal of this lignin involves a multistage bleaching process, which
involves elemental chlorine. Although chlorine-based bleaching of pulp is effective,
270
G. Mamo