APPLICATIONS OF XYLANOLYTIC ENZYMES

Xylanolytic enzymes from microorganism have attracted a great deal of attention in the last decade, particularly because of their biotechnological potential in various industrial processes (Wong and Saddler, 1992; Kuhad and Singh, 1993; Niehaus et al., 1999; Bajpai 1999). Cellulases and hemicellulases have numerous applications in various industries including chemicals, fuel, food, brewery and wine, animal feed, textile and laundry, pulp and paper and agriculture (Bhat, 2000; Sun and Cheng, 2002; Beauchemin et al., 2001, 2003). The strains reported for the commercial production of xylanases include Trichoderma reesei (Tenkanen et al., 1992), Thermomyces lanuginosus (Gubitz et al., 1997; Bajpai 1999), Aureobasidium pullulans (Christov et al., 1999), Bacillus subtilis (Khanongnuch et al., 1999), and Streptomyces lividans (Senior et al., 1992; Ragauskas et al., 1994).

Currently, the most promising application of xylanases is in the prebleaching of kraft pulps (Bajpai, 1999). Potential industrial applications with special reference to biobleaching have been reviewed by Beg et al., (2001). Enzyme application improves pulp fibrillation and water retention, reduction of beating times in virgin pulps, restoration of bonding and increased freeness in recycled fibers, and selective removal of xylans from dissolving pulps. Xylanases are also useful in yielding cellulose from dissolving pulps for rayon production and biobleaching of wood pulps (Viikari et al., 1994; Srinivasan and Rele, 1999). Chauhan et al., (2006) has recently reported application of xylanase enzyme of Bacillus coagulans as a prebleaching agent on non-wood pulps.

Xylanases are routinely used for the improvement of animal feed (Silva and Smithard, 2002) and in pretreatment of forage crops to improve the digestibility of ruminant feeds (Gilbert and Hazlewood, 1993). 

The efficiency of xylanases in improving the quality of bread has been seen with an increase in specific bread volume (Courtin et al., 1999; Ingelbrecht et al., 2000). Use of glycoside hydrolase family 8 xylanase in baking has recently reviewed by Collins et al., (2006).

Xylan is present in large amounts in wastes from agricultural and food industries. The most challenging application is the development of an economic process for the solubilizaition of ligno-cellulose material to serve as a renewable energy and carbon source (Galbe and Zacchi, 2002). Xylanase in synergism with several other enzymes, such as mannanases, ligninase, xylosidase, glucanase, glucosidase, etc., can be used for the generation of biological fuels, such as ethanol and xylitol, from ligno-cellulosic biomass (Kuhad and Singh 1993; Olsson and Hahn-Hagerdal, 1996; Dominguez 1998).

Many biologically important compounds including various oligosaccharides, glycoconjugate and neoglycoproteins can readily be synthesized using the transglycosylation potency of glycosidases. Eneyskaya et al., (2003) reviewed the application of xylanase and β-xylosidase for the regio-stereoselective synthesis of oligosaccharides. Enzymatic synthesis of di and trisaccharides (Ajisaka et al., 1998; Komba and Ito, 2001) more rarely, tetrasaccharides (Kono et al., 1999), synthesis of spacer linked oligosaccharide for the preparation of neoglycoproteins (Lio et al., 1999) and glycosyl-containing drugs (Scheckermann et al., 1997) have been reported using exoglycosidases.

Xylanase treatment of plant cells can induce glycosylation and fatty acylation of phytosterols. Treatment of tobacco suspension cells (Nicotiana tabacum CV. KY 14) with a purified endoxylanase from Trichoderma viride caused a 13-fold increase in the levels of acylated sterol glycosides and elicited the synthesis of phytoalexins (Moreau et al., 1994).

Xylanase are used concurrently with cellulase and pectinase for clarifying must and juices, and for liquefying fruits and vegetables (Biely, 1985). α-L-Arabinofuranosidase and β-D-glucopyranosidase have been employed in food processing for aromatizing musts, wines, and fruit juices (Spagna et al., 1998). Some xylanases may be used to improve cell wall maceration for the production of plant protoplasts (Wong et al., 1986).

A potential application of the xylanolytic enzyme system in conjunction with the pectinolytic enzyme system is in the degumming of bast fibers such as flax, hemp, jute, and ramie (Sharma, 1987; Puchart et al., 1999). A xylanase-pectinase combination is also used in the debarking process, which is the first step in wood processing (Wong and Saddler, 1992; Bajpai, 1999). The fiber liberation from plants is affected by retting, i.e., the removal of binding material present in plant tissues using enzymes produced in situ by microorganisms. Replacement of slow natural retting by treatment with artificial mixtures of enzymes could become a new fiber liberation technology in the near future (Bajpai, 1999).

The most recent researches in bio-fuel industry reveal that bacterial and fungal xylanases  do have important roles to play in hydrolysis of ligno-cellulosic materials in much effiecient manner to produce fermentable sugars (Garcia-Aparicio et al., 2007; Lopez-Casado et al., 2008; Damaso et al., 2007; Sanderson, 2006).