Statistical methods for optimization of xylanase production by solid state fermentation from Aspergillus foetidus mtcc 4898
Xylanolytic enzymes consist of endo-1,4-β-xylanase, β-xylosidase, α-glucuronidases, α-L-arabinofuranosidas, acetylxylan esterase. Their potential applications are mainly in the pulp and paper industry but also in the bioconversion of lignocellulosic materials to fuels and chemicals. In the present work, strains of Aspergillus foetidus MTCC 4898, Trichoderma ressei NCIM 1186 and Trichoderma viride NCIM 1051 were screened for maximum production of xylanases by solid state fermentation (SSF). Aspergillus foetidus MTCC 4898 produced maximum extracellular xylanases, and hence was selected for further work. Among a few easily available lignocellulosics tested, combination of corn cob and wheat bran (3:2) was found to be the best substrate for xylanase production (2100 U/gds) in SSF. In a first step the one factor at-a-time method was used to investigate the effects of media constituents and fermentation parameters like moisture content, nitrogen source, additional carbon source, temperature and pH on production of xylanases. Maximum xylanase production was obtained at 75% moisture content, pH 5.5at 28±2°C for 4 days. In a second step the statistical method of Taguchi L-16 and the response surface methodology were used for further optimization of media components. The final optimized medium produced 3500 U/gds of xylanase which increased xylanase production by 1.94 fold compared to unoptimized medium. Ammonium sulphate precipitation gave 65.23% yield with 2.12 fold purity as compared to the crude broth. Aqueous two phase extraction (ATPS) of xylanase by 17.5 (w/w) PEG-1500 and 30%(w/w) ammonium sulphates gave 97.52% yield with 5.21 fold purity as compared to crude broth.