초록
<P><B>Abstract</B></P><P>In this work, we have investigated the kinetics of the biotechnological production of lactobionic acid (<I>LBA</I>) and sorbitol by the catalytic action of glucose–fructose oxidoreductase (<I>GFOR</I>) and glucono-δ-lactonase (<I>GL</I>) enzymes. The cells of bacterium <I>Zymomonas mobilis</I> ATCC 29191 containing this enzymatic complex were submitted to permeabilization and reticulation procedures. The effect of the concentration of substrates on the rate of product formation using a mobilized cell system was investigated. The application of higher fructose concentration seems to not affect the initial rate of formation of the bionic acid. Under conditions of low initial concentration of lactose, the experimental kinetic data of the bi-substrate reaction were modelled by assuming a rate equation of the classical ping-pong mechanism. The found kinetic parameters displayed a low affinity of the <I>GFOR</I> enzyme for both substrates. The enzymatic system did not exhibit normal <I>Michaelis–Menten</I> kinetics in response to a change of concentration of lactose, when fructose was held constant, presenting a sigmoid relationship between initial velocity and substrate concentration. A rate equation based on <I>Hill</I> kinetics was used to describe the kinetic behaviour of this enzyme-substituted reaction at higher lactose concentrations. The results from batch experiments using immobilized cells within Ca-alginate beads revealed that there is no pronounced occurrence of mass transfer limitations on <I>LBA</I> production for beads with 1.2mm in average diameter. This discussion aids for defining the best operating conditions to maximize the productivity for <I>LBA</I> and sorbitol in this bioconversion and also for reducing the complexity of downstream separation processes.</P>