Hydrolysis of Lactose by Immobilized β-galactosidase using a Horizontal Rotary Column Reactor

Abstract

The rate of hydrolysis of lactose by β-galactosidase, immobilized into cellulose triacetate fibers, was studied using a horizontal rotary column reactor. The rotary column reactor, developed by us, consists of wire-mesh cylinder, separated into four chambers by punched plates. A feed shaft, with many orifices, runs down the center of the cylinder. This shaft is covered with wire mesh. After placing the immobilized β-galactosidase in the chambers, lactose solution was fed from a tank to the cylinder through the orifices and wire mesh, to contact the immobilized β-galactosidase. The results were as follows. (1) The rotary column reactor could be operated without a channeling or a severe pressure drop through the column that was observed in a packed bed rector. (2) The reaction rate in the rotary column reactor could be increased suddenly by increasing the rotational speed from 11 to 21rpm and increased gently by increasing the rotational speed from 21 to 47rpm at a lactose solution concentration above 4% (w/w). (3) The reaction rate in the rotary column reactor at 21rpm was 1.16 times of the reaction rate in a packed bed reactor at 75.1ml/s. Thus, the rotary column reactor has a higher reaction efficiency than a packed bed reactor. This may be because the contact efficiency between the lactose and cellulose triacetate fibers, which support the β-galactosidase, is improved by the rotation of the column. (4) The rate of lactose transfer into the immobilized β-galactosidase in the rotary column reactor was improved by increasing the rotational speed. The reason was considered, as follows, by discussion of the JD-factor. The fibers become highly dispersed in the lactose solution as the rotational speed increases, increasing the effective specific area for lactose transfer. (5) From an orthogonal experiment, L₈, it was found that the reaction rate is affected greatly by the packed density of immobilized β-galactosidase.