Sawdust and digestive bran as cheap alternate substrates for xylanase production

Abstract

Xylanases are a major group of enzymes, mostly produced from microbial fermentation processes, and  have wide industrial and biotechnological applications. The production cost of xylanase is the major  factor limiting its use, thus indicating the need for low cost production systems for market of this  enzyme. In this study, therefore, sawdust and digestive bran were investigated as substrates for  xylanase production by Bacillus strains. The xylanase titre ranging between 30.849 to 45.206 nkat/ml  and 6.633 to 22.717 nkat/ml was produced by these Bacillus strains, using sawdust and wheat bran as  the substrate, respectively. The optimum temperature for the production of xylanase was found to be  between 45 and 55°C, while the optimum pH was 8.0 for all the strains tested. The xylanases produced  by these Bacillus strains were found to be stable over a wide range of temperature tested (40 to 90°C).  Up to 98 and 95% of the initial activity was retained by the crude extract of two of the Bacillus strains  tested, while 10.3 to 56% loss in activity was observed for the other isolates after one hour incubation at 70°C. Addition of metal salts or additives to the crude extract was found to inhibit the enzyme activity to a varying degree, with the following order Hg 2+> EDTA > Na > Urea > Mg 2+> Ca 2+observed. Findings from this study indicate the potential use of sawdust and digestive bran as cheaper alternatives for the production of xylanases.    Key words: Bacillus sp, digestive bran, sawdust, thermostability, xylanase.