Performance of Aspergillus niger B 03 β-xylosidase immobilized on polyamide membrane support

The dynamics of beta-xylosidase biosynthesis from Aspergillus niger B 03 was investigated in laboratory bioreactor. Maximum xylosidase activity. 5.5 U/ml was achieved after 80 h fermentation at medium pH 4.0. The isolated beta-xylosidase was immobilized on polyamide membrane support and the basic characteristics of the immobilized enzyme were determined. Maximum immobilization and activity yield obtained was 30.0 and 6.8%, respectively. A shift in temperature optimum and pH optimum was observed for immobilized beta-xylosidase compared to the free enzyme. Immobilized enzyme exhibited maximum activity at 45 degrees C and pH 4.5 while its free counterpart at 70 degrees C and pH 3.5. respectively. Thermal stability at 40 and 50 degrees C and storage stability of immobilized beta-xylosidase were investigated at pH 5.0. Kinetic parameters K-m, V-max and K-i were determined for both enzyme forms. Free and immobilized beta-xylosidase were tested or xylose production from birchwood xylan. The substrate was preliminarily depolymerized with xylanase to xylooligosaccharides and the amount of xylose obtained after their hydrolysis with free and immobilized beta-xylosidase was determined by HPLC analysis. Continuous enzyme hydrolysis of birchwood xylan was performed with xylanase and free or immobilized beta-xylosidase. The maximum extent of hydrolysis was 25 and 30% with free and immobilized enzyme, respectively. Immobilized preparation was also examined for reusability in 20 consecutive cycles at 40 degrees C. (C) 2008 Elsevier B.V. All rights reserved.