Galacto-oligosaccharide synthesis by immobilized Aspergillus oryzae β-galactosidase

Aspergillus oryzae beta-galactosidase was immobilized by three different techniques, namely adsorption on celite, covalent coupling to chitosan and aggregation by cross-linking. These techniques were compared in terms of the yield of immobilized preparation, enzymatic characteristics, stability and efficiency in oligosaccharide synthesis. Immobilization led to increase in K-m in each case. Immobilization on chitosan gave maximum enzyme yield and oligosaccharide synthesis. At 60 degrees C, the chitosan-immobilized enzyme was stabilized (by 1.6-fold) due to protection effect of the matrix. However, at 65 degrees C, the t(1/2) of cross-linked enzyme aggregates (CLEA) of beta-galactosidase was 1.07 h as compared to 0.79 h in the case of free enzyme. Both chitosan-immobilized enzyme and CLEA were used for oligosaccharide synthesis. Using 20% (w/v) lactose, the chitosan-immobilized enzyme gave maximum oligosaccharide yield (17.3% of the total sugar) as compared to free enzyme (10.0%) in 2 h at 40 degrees C. CLEA were instead found effective in lactose hydrolysis yielding 78% monosaccharide in 12 h. (C) 2005 Elsevier Ltd. All rights reserved.