RESUMO
Aspergillus terricola and Aspergillus ochraceus, isolated from Brazilian soil, were cultivated in Vogel and Adams media supplemented with 20 different carbon sources, at 30 degrees C, under static conditions, for 120 and 144 h, respectively. High levels of cellulase-free xylanase were produced in birchwood or oat spelt xylan-media. Wheat bran was the most favorable agricultural residue for xylanase production. Maximum activity was obtained at 60 degrees C and pH 6.5 for A. terricola, and 65 degrees C and pH 5.0 for A. ochraceus. A. terricola xylanase was stable for 1 h at 60 degrees C and retained 50% activity after 80 min, while A. ochraceus xylanase presented a t(50) of 10 min. The xylanases were stable in an alkali pH range. Biobleaching of 10 U/g dry cellulose pulp resulted in 14.3% delignification (A. terricola) and 36.4% (A. ochraceus). The brightness was 2.4-3.4% ISO higher than the control. Analysis in SEM showed defibrillation of the microfibrils. Arabinase traces and beta-xylosidase were detected which might act synergistically with xylanase.
Assuntos
Aspergillus ochraceus/classificação , Aspergillus ochraceus/enzimologia , Celulose/metabolismo , Endo-1,4-beta-Xilanases/química , Endo-1,4-beta-Xilanases/metabolismo , Madeira/química , Endo-1,4-beta-Xilanases/isolamento & purificação , Ativação Enzimática , Estabilidade Enzimática , Especificidade da EspécieRESUMO
This study describes the production of xylanases from Aspergillus niveus, A. niger, and A. ochraceus under solid-state fermentation using agro-industrial residues as substrates. Enzyme production was improved using a mixture of wheat bran and yeast extract or peptone. When a mixture of corncob and wheat bran was used, xylanase production from A. niger and A. ochraceus increased by 18%. All cultures were incubated at 30 degrees C at 70-80% relative humidity for 96 h. For biobleaching assays, 10 or 35 U of xylanase/g dry cellulose pulp were incubated at pH 5.5 for 1 or 2 h, at 55 degrees C. The delignification efficiency was 20%, the brightness (percentage of ISO) increased two to three points and the viscosity was maintained confirming the absence of cellulolytic activity. These results indicated that the use of xylanases could help to reduce the amount of chlorine compounds used in cellulose pulp treatment.