Reversible immobilization of K. fragilis β-galactosidase onto magnetic polyethylenimine-grafted nanospheres for synthesis of galacto-oligosaccharide

A nanosized support for reversible immobilization of enzymes, magnetic poly(glycidyl methacrylate-ethylene glycol dimethacrylate-hydroxyethyl methacrylate) nanospheres grafted with polyethyleneimine, was prepared and characterized by scanning electron microscopy and vibrating sample magnetometry. The novel support displayed 3.2-fold higher adsorption capacity for Kluyveromyces fragilis β-galactosidase than commercial ion exchange resin DEAE-Sepharose, the maximum amount of the enzyme adsorbed on the support reached 86.7 mg/g with enzyme activity recovery of 92.5%. The adsorbed K. fragilis β-galactosidase showed high catalytic activity and operational stability for synthesis of galacto-oligosaccharide (GOS), 4.5 kg of GOS were produced per gram of adsorbed enzyme from lactose during 15 consecutive batch reactions by reuse of the same biocatalyst, and the immobilized biocatalyst retained about 84.6% of its initial activity after 15 cycles of batch operation. The support could be regenerated and reused, remaining 93.0% of its original adsorption capacity at the end of the twentieth adsorption–desorption cycle.