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
Ochratoxin A (OA) is a mycotoxin that has been found in coffee beans and coffee beverages. Its toxicological profile includes carcinogenicity, nephrotoxicity, and immunotoxicity. Aspergillus ochraceus is the major species responsible for OA production in Brazilian coffee beans. The genetic relationships among 25 A. ochraceus strains collected from Brazilian coffee-bean samples were determined based on RAPD and internal transcribed spacer (ITS) sequence data. The isolates were resolved into 2 distinct groups, one with 4 strains (group A) and the other with 21 strains (group B). Specific nucleotide variations characterizing group A and B were found for both ITS1 and ITS2 regions. Group B is a new group proposed here to accommodate the majority of the Brazilian isolates. Each group was found to contain both toxigenic and nontoxigenic strains, indicating that there is no association between molecular genotypes and the ability to produce OA.