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Aspergillus oryzae β-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°C, the chitosan-immobilized enzyme was stabilized (by 1.6-fold) due to protection effect of the matrix. However, at 65°C, the t_1/2 of cross-linked enzyme aggregates (CLEA) of β-galactosidase was 1.07h as compared to 0.79h 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 …