Hydrolysis of lactose in whole milk catalyzed by β-galactosidase from Kluyveromyces fragilis immobilized on chitosan-based matrix

beta-Galactosidase (beta-gal) from Kluyveromyces fragilis was immobilized on chitosan-based matrices and agarose beads by different protocols to catalyze the hydrolysis of whole milk lactose in a batch system. The best derivative was obtained by immobilizing the enzyme on chitosan coagulated with KOH and activated with glutaraldehyde, both steps carried out at 50 degrees C. The immobilization yield and recovered activity were 100%. Maximum activity was achieved at pH 7.0 and 45 degrees C for both soluble and immobilized beta-gal. The maximum beta-gal load immobilized on chitosan-glutaraldehyde support was around 21 mg of enzyme per gram of support. Immobilized beta-gal was 3-5-fold more stable than the soluble enzyme at 40 and 20 C, respectively. The biocatalyst retained 80% of its initial activity after 3 months at 10 degrees C and pH 7.0 in the presence of the cofactors Mn2+ and Mg2+, twice more stable than soluble enzyme. The immobilized biocatalyst was capable to efficiently hydrolyze lactose into the whole milk at 25 degrees C (above 95% conversion), showing similar performance after four consecutive batches. (C) 2013 Elsevier B.A. All rights reserved.