Bioprocessing of agro-industrial residues for optimization of xylanase production by solid-state fermentation in flask and tray bioreactor

Xylanases encompass a broad spectrum of industrial applications like food, animal feed, textile and biofuel. This study aimed at optimization of solid-state fermentation by Aspergillus niger CCUG33991 for maximum xylanase production using low-cost agro-industrial residues(1) in tray bioreactor. SSF2 was performed using wheat bran, sorghum stover, corn cob and soybean meal in flasks for investigation of appropriate substrate, initial pH, media composition and minerals solution. Thereafter, the obtained results combined with results of earlier experiments were used for exploring the effects of particle size, initial moisture content and temperature in tray bioreactor. OFAT method(3) was followed to select optimum level of each parameter. Next, effect of air-drying and pelleting condition were tested on enzyme stability. Finally, the extracted enzymes were subjected to zymography. The highest xylanase activity of 2919 +/- 174 U/g-IDW4 at 48 h was achieved using wheat bran with particle size range of 0.3-0.6 mm, initial moisture level of 70%, moistened by distilled water containing 1% (v/v) glycerol and 1% (w/v) of (NH4)(2)SO4, and controlled bed temperature in the range of 28-35 degrees C with surface aeration. As a result, a 2.5-fold higher and 24 h faster xylanase production in trays than in flasks was attained. The enzyme also showed a great deal of stability to air-drying and pelleting condition. Zymogram analysis confirmed multiple isoforms of xylanase. SSF in tray bioreactor is a potential method for xylanase production. Wheat bran as lowcost, time-saving and xylan-containing hemicellulosic agro-waste is preferable to use as the carbon and energy sources for maximum production of xylanase.