Characterization of xylanase produced by aspergillus niger fermented on corn cob

ABSTRACT

The use of waste as raw material is important for government economy and natural balance. This article investigates a strain of Aspergillus niger for xylanase production in solid state fermentation [SSF] using different agricultural residues without pretreatment. The organism produced 164.4 [micro mol/ ml/min] of xylanase in static flask on corn cob, an inexpensive lignocellulosic biomass, without enrichment of medium [only distilled water]. Using surfactant solution [Tween 80, 1%] for enzyme extraction from solid substrate increased the yield by 515%. Maximum xyianase activity was recorded at 55°C, with high activity at wide range of temperature [50-60°C]. The enzyme produced on corn cob showed good thermal stability with residual activity of 62.1 and 54.3% after 2 hr incubation at 50 and 60°C, respectively, Addition of glycerol [50%] improved stability against temperature by 19.9% after incubation at 60°C for 1hr, and 17.8% after incubation at 60°C for 2 hr. The optimum pH for the enzyme activity was 4.5, increasing pH causing decreasing in activity. Xylanase enzyme was stable at different pH's after 1 hr with remaining activity of 89.6% and 55.0%, respectively at pH 4.0 and 9.0. The enzyme possessed 70.6 and 37.6% of its activity by storage at room temperature after 10 and 30 days. In presence of metal ions such as Na[2+], Ca[2+] and protein disulphide reducing agents such as dithiothreitol [DTT], the activity of enzyme was increased by 34.9, 10.7 and 32.8%, respectively. Sodium dodecyl sulphate [SDS] and Cu[2+] ion strongly inhibited the enzyme by 56,8 and 23.7%, respectively. Saccarification of different wastes by the enzyme was studied. The highest yield of reducing sugars [20.3 mg/ 200 mg dry weight substrate] was obtained from corn cob with maximum saccharification after 72 hr [71.8%] as compared to other wastes