RESUMO
In recent years, xylanases have expanded their use in many processing industries, such as pulp and paper, food and textile. Thermomyces lanuginosus IOC-4145 was able to produce a very high level of cellulase-free xylanase in shaken cultures using corncob as substrate (500 U/ml). An optimization of the medium composition in submerged fermentation was carried out aiming at a low cost medium composition for enzyme production. Statistical experiment design ws employed for this purpose, pointing out corncob as the most important parameter, which affects enzyme production. Additionally, the influence of several chemicals on zulanase activity was investigated in the crude extract. A slight stimulation of the enzyme (5-15 percent) was achieved with NaCl and urea, both at 3 mM of concentration. On the other hand, dithiothreitol and ß-mercaptoethanol at a molarity of 5mM have caused a strong stimulation of the enzyme (40-53 percent). The crude xylanase displayed appreciable thermostability, retaining almost 50 percent of activity during 24 hours of incubation at 50oC; about 50 percent of activity was present at 60oC even after4 hours of incubation. The enzyme also exhibited good storage stability at û20oC without any stabilizing agent.
