β-Galactosidase-immobilised microreactor fabricated using a novel technique for enzyme immobilisation and its application for continuous synthesis of lactulose

In this study, several surface functionalisation techniques were used to immobilise beta-galactosidase in a microreactor. beta-Galactosidase was pretreated with lactose before immobilisation, and functionalised multi-walled carbon nanotubes (MWNTs), DNA-wrapped single-walled carbon nanotubes and glutaraldehyde as a linker were used to immobilise beta-galactosidase on a microchannel surface. When functionalised MWNTs were used as a linker for immobilisation of pretreated beta-galactosidase, the enzyme microreactor showed the highest performance. The K-m(app) and V-max were 2.84 mM and 0.52 mM/min, respectively, and the conversion of o-nitrophenyl-beta-D-galactopyranoside (ONPG) reached 78.3% during the continuous flow reaction at a flow rate of 2.5 mu L/min. In an enzyme microreactor, continuous synthesis of lactulose was performed, and the lactulose concentration was maintained at about 1.29 g/L for 48 h. (C) 2012 Elsevier Ltd. All rights reserved.