Purification and characterization of a highly-stable fungal xylanase from Aspergillus tubingensis cultivated on palm wastes through combined solid-state and submerged fermentation.

Fungal xylanase was produced from lignocellulosic palm wastes through combined solid-state fermentation (SSF) and submerged fermentation (SmF) by Aspergillus tubingensis TSIP9 in a helical-impeller equipped bioreactor. The combined SSF-SmF promoted the xylanase production by 15 and 70% higher than SSF and SmF, respectively. Sequential purification yielded 7.4-fold purified xylanase with 9.07% recovery. The maximum activities of crude and purified xylanase were observed at the same pH of 5.0 and the same temperature of 50 °C while purified xylanase is more active and highly stable at a wider pH range of 3-8 and temperature of 30-60 °C. The half-life of purified xylanase at various temperatures was also much improved by 2-8 folds compared to crude xylanase. Michaelis-Menten constants, Vmax and Km, for purified xylanase are 2,602.8 U/mg and 32.4 mg/mL, respectively. Purified xylanase activity was most enhanced with Ca2+ followed by Zn2+ and Fe2+ at 10 mM while significantly inhibited by Co2+, Cu2+, Pb2+, and Ag+. This study has shown the effectiveness of combined SSF-SmF for xylanase production and superior properties of purified xylanase for industrial processes.