RESUMO
OBJECTIVE: To develop an endo-ß-1,4-xylanase with high specificity for production of prebiotic xylooligosaccharides that optimally works at moderate temperature desirable to reduce the energy cost in the production process. RESULTS: The xylB gene, encoding for a glycosyl hydrolase family 11 xylanase from a thermoresistant fungus, Aspergillus niger BCC14405 was expressed in a methylotrophic yeast P. pastoris KM71 in a secreted form. The recombinant XylB showed a high specific activity of 3852 and 169 U mg-1 protein on beechwood xylan and arabinoxylan, respectively with no detectable side activities against different forms of cellulose (Avicel Ò PH101 microcrystalline cellulose, phosphoric acid swollen cellulose and carboxymethylcellulose). The enzyme worked optimally at 45 °C, pH 6.0. It showed a specific cleavage pattern by releasing xylobiose (X2) as the major product from xylooligosaccharides (X3 to X6) substrates. The highest XOS yield of 708 mg g-1 substrate comprising X2, X3 and X6 was obtained from beechwood xylan hydrolysis. CONCLUSION: The enzyme is potent for XOS production and for saccharification of lignocellulosic biomass.
