Purification and immobilization of an Aspergillus terreus xylanase: Use of continuous fluidized bed column reactor

An Aspergillus terreus extracellular xylanase produced by solid state fermentation was purified and characterized. A 6.4 fold purified xylanase was obtained by ammonium sulphate (in 30-40% saturation) precipitation followed by dialysis. Molecular weight of the xylanase was 67.0 kDa as estimated by SDS-PAGE. The enzyme was immobilized in barium alginate gel. Both free and immobilized enzyme showed maximum activity at pH 5.5 and 60 degree C (8.0 lU/mg & 5.25 IU/mg, respectively) and were most stable at pH 5.5 and thermostable up to 55 degree C. Co super(2+) stimulated free enzyme activity (9.27 IU/mg) and Mg super(2+) stimulated activity of immobilized enzyme (5.54 IU/mg). V sub(max) and K sub(m) for free and immobilized xylanases were 6.6 mu mole/mg/min, 0.75% and 1.25 mu mole/mg/min, 0.625%, respectively. 23.4% conversion of substrate (0.1% birchwood xylan) was possible in 7 h using a continuous fluidized bed column reactor under the following conditions: bed height 16 cm, temperature 40 degree C, and dilution rate 4.09 h super(-1).