Selection and production of insoluble xylan hydrolyzing enzyme by newly isolated Thermomyces lanuginosus
Forty-two strains of Thermomyces lanuginosus isolated from various sources in Thailand were divide into 4 groups based on the soluble xylan hydrolyzing (SXH) and insoluble xylan hydrolyzing (IXH) enzyme activities in the supernatant obtained from 5-day culture at 50°C in the liquid medium using corncob as substrate. The strains which exhibited high IXH enzyme activity, showed high binding ability to insoluble xylan. Ten strains of T. lanuginosus produced high activity towards insoluble xylan. Among these, T. lanuginosus THKU-56 could produce considerable activity of insoluble xylan hydrolyzing enzyme with the highest stability that remained 28.2 and 58.9% of the original activity after treating at pH 3.5 and 37°C and at pH 6.0 and 70°C for 1 h, respectively. The optimized concentration of corncob, yeast extract, KH2PO4 and Tween80 were determined in shaking condition for the production of insoluble xylan hydrolyzing enzyme by T. lanuginosus THKU56 using a central composite design. Unlike other components, only corncob and yeast extract were found to affect the xylanase production. The optimal concentration of the active nutrients for xylanase production were 41 gl-1 of corncobs and 24 gl-1 of yeast extract, which gave a predicted and experimental yield of 526.7 and 541 Uml-1 at 5th day of culture, respectively.
Key words: Thermomyces lanuginosus, insoluble xylan hydrolyzing enzyme, xylan-binding ability, central composite design.