Paper production (Biobleaching)
The use of enzymes to reduce the use of chemicals in bleaching of kraft pulps has been studied extensively. The research has focused on two areas. The first area of study is oxidation of the lignin in the pulp using a variety of lignin degrading systems. Lignin degradation systems are found in only a limited number of fungal species, limiting the range of conditions the enzymes can be applied in. The enzyme systems also require oxygen, metals, and possibly chemical mediators. The second area of study is the use of biomass degrading enzymes to hydrolyze xylan and mannan present in the pulp, splitting the linkage between hemicellulose and lignin, and giving a whiter pulp.
Xylan contains a backbone of β-1,4 linked xylose residues. Depending on the source, the backbone can be substituted with α-1,2 linked glucuronic acid (glucuronoxylan, GX), α-1,2 and α-1,3 linked arabinose (arabinoxylan, AX) or α-1,2 linked glucuronic acid and α-1,3 linked arabinose (glucuronoarabinoxylan, GAX) (Figure 1). Additional substitutions such as acetyl and methyl groups can be present, and the material can be crosslinked to components of lignin such as ferrulic acid. Xylanases (technically endoxylanases) cleave β-1,4 xylose linkages in the backbone. β-xylosidases cleave xylose from the nonreducing end of the xylan chain. α-Glucuronidases cleave the α-1,2 linked glucuronic acid from the backbone and α-arabinosidases (arabinofuranosidases) cleave the α-1,2 and α-1,3 linked arabinose from the backbone.
The research in this area has centered on the use of xylanases from bacterial and fungal sources. Enzymes with a wide range of pH and temperature optimum have been tested for this application and have been shown to be somewhat, but not completely effective. Treatment of kraft pulp with xylanase results in reduced usage of chemicals and increased brightness. The mechanism of this improvement is believed to be hydrolysis of xylan-lignin molecules that have been redeposited on the cellulose fibers. Research has shown that the xylanases tested in the literature were highly effective in hydrolyzing xylan isolated from kraft pulp, but much less effective on the same xylan when bound to cellulose fibers.
C5-6 supplies a complete set of xylan-degrading activities to advance your research. Xylanases from C. thermocellum, D. turgidum, and Geobacillus sp. all possess the stability to work under the conditions of paper production. All these enzymes are free of contaminating cellulase activity that decreases the yield of paper from your pulp. All these enzymes can be easily scaled-up for pilot and production testing.
Enzymes for mannan degradation
There are three types of mannans. Mannan has a backbone of β-1,4 linked mannose residues. Glucomannan has a backbone of β-1,4 linked mannose residues with β-1,4 linked glucose residues interspersed within the chain (Figure 2). Galactomannan has a backbone of β-1,4 linked mannose residues with α-1,6 linked galactose residues interspersed along the chain.
C5-6 supplies a complete set of mannan-degrading activities to advance your research. We offer the thermostable C. thermocellum ManA that cleaves the β-1,4 linkages between mannose residues. From D. turgidum, we offer two enzymes. The thermostable CelA possesses both glucanase and mannanase activitities and hydrolyzes mannan, glucomannan, and galactomannan. We also offer thermostable Mannanase 8, Dtur_0671 that cleaves the β-1,4 linkages between mannose residues. Thermostable α-galactosidases are available from both C. thermocellum and D. turgidum for cleavage of the α-1,6 linked galactose. Non-thermostable versions of these enzymes are also available. These are cloned from F. succinogenes.
Enzymes for xyloglucan degradation
Xyloglucan consists of β-1,4 linked glucose chains, similar to cellulose, substituted with α-1,6 linked xylose. Depending on the plant source, the xylose can be further substituted with galactose or galactose and fucose. Xyloglucanases cleave the β-1,4 linkages in xyloglucan. Most endocellulases and β-glucanases cannot cleave xyloglucan, however exceptions exist. The xylose resiudes can be cleaved from xyloglucan using an α-xylosidase (Figure 3). β-Glucosidases cleave glucose from the non-reducing end of the chain.
C5-6 supplies a number of enzymes with xyloglucanase activity including Streptomyces flavogriseus xyloglucanase and F. succinogenes xyloglucanase. Other available enzymes with xyloglucanase activity include D. turgidum CelA and C. thermocellum CelD, CelE and CelH. C5-6 is the only supplier of fungal α-xylosidase from A. niger. The most popular β-glucosidase with our customers is the A. acidocaldarius β-glucosidase.