Comparative biochemical characterization of soluble and chitosan immobilized beta-galactosidase from Kluyveromyces lactis NRRL Y1564

An investigation was conducted on the production of beta-galactosidase (beta-gal) by different strains of Kluyveromyces, using lactose as a carbon source. The maximum enzymatic activity of 3.8 +/- 0.2 U/mL was achieved by using Kluyveromyces lactis strain NRRL Y1564 after 28 h of fermentation at 180 rpm and 30 degrees C. beta-gal was then immobilized onto chitosan and characterized based on its optimal operation pH and temperature, its thermal stability and its kinetic parameters (K-m and V-max) using o-nitrophenyl beta-D-galactopyranoside as substrate. The optimal pH for soluble beta-gal activity was found to be 6.5 while the optimal pH for immobilized beta-gal activity was found to be 7.0, while the optimal operating temperatures were 50 degrees C and 37 degrees C, respectively. At 50 degrees C, the immobilized enzyme showed an increased thermal stability, being 8 times more stable than the soluble enzyme. The immobilized enzyme was reused for 10 cycles, showing stability since it retained more than 70% of its initial activity. The immobilized enzyme retained 100% of its initial activity when it was stored at 4 degrees C and pH 7.0 for 93 days. The soluble beta-gal lost 9.4% of its initial activity when it was stored at the same conditions. (C) 2013 Elsevier Ltd. All rights reserved.