Hydrolysis of xylans by enzyme systems from solid cultures of Trichoderma harzianum strains

Abstract

Xylanase activity was isolated from crude extracts of Trichoderma harzianum strains C and 4 grown at 28 o C in a solid medium containing wheat bran as the carbon source. Enzyme activity was demonstrable in the permeate after ultrafiltration of the crude extracts using an Amicon system. The hydrolysis patterns of different xylans and paper pulps by xylanase activity ranged from xylose, xylobiose and xylotriose to higher xylooligosaccharides. A purified ß-xylosidase from the Trichoderma harzianum strain released xylose, xylobiose and xylotriose from seaweed, deacetylated, oat spelt and birchwood xylans. The purified enzyme was not active against acetylated xylan and catalyzed the hydrolysis of xylooligosaccharides, including xylotriose, xylotetraose and xylopentaose. However, the enzyme was not able to degrade xylohexaose. Xylanase pretreatment was effective for hardwood kraft pulp bleaching. Hardwood kraft pulp bleached in the XEOP sequence had its kappa number reduced from 13.2 to 8.9 and a viscosity of 20.45 cp. The efficiency of delignification was 33%.

Purification and characterization of a low molecular weight xylanase from solid-state cultures of Aspergillus fumigatus Fresenius

“…Xylanase activity was determined by mixing 25 µl of enzyme solution with 50 µl of oat spelt xylan (3.0-50 mg/ml) in 100 mM sodium acetate buffer, pH 5.0 at 50 O C for 30 min. The release of reducing sugar was measured using the dinitrosalicylic reagent method (19,24). Xylanase activity was expressed as µmol reducing sugar formed min -1 ml -1 enzyme solution, i.e., as IU ml -1 and IU mg -1 protein.…”

“…The activity against filter paper was measured as described by Mandels et al (18). ß-Xylosidase, α-arabinofuranosidase, ß-glucosidase and ß-mannosidase activities were determined as reported elsewhere (24). For the kinetic experiments, soluble and insoluble samples from oat spelt and birchwood xylans were used as substrates in a concentration range of 0.05-8.0 mg/ml.…”

Purification and characterization of a new Xylanase from Humicola grisea var. Thermoidea

“…Xylanases have potential applications in the food, chemical, pharmaceutical and paper industries (8,17). These enzymes are produced by several fungal species, including Humicola grisea var.…”

“…Some properties of these purified enzymes have been published (13,22). Solid-state cultivation on wheat bran as a substrate is an efficient procedure for xylanase production (17,23). Some of the advantages of the use of solidstate cultivation over liquid medium are described such as lower costs and the production of enzymes with higher specific activities (11).…”

Wood production, wood technology, and biotechnological impacts

“…6) are removed by α-glucuronidase (EC 3.2.1.139) (Pell et al 2004). A high degree of hydroxyl groups of sugar residues in xylans are esterified by acetyl groups (see above) which also prevents enzymatic cleavage by hydrolytic enzymes (Kormelink & Voragen 1993, Wood & McCrae 1986, Cybinski et al 1999, Silveira et al 1999. During fungal degradation of wood, acetyl esterase (EC 3.1.1.6) removes O-acetyl groups from the positions C-2 and C-3 of β-D-xylopyranosyl residues in the xylan backbones (Halgasova et al 1994, Tenkanen 1998, Cybinski et al 1999, Chung et al 2002).…”