Studies on modelling and simulation of lactose hydrolysis by free and immobilized β-galactosidase from Aspergillus niger

β-Galactosidase from Aspergillus niger was immobilized effectively on a porous ceramic monolith by adsorption and intermolecular cross-linking. The binding efficiency reached 80% and no enzyme leaching was observed even under vigorous mechanical agitation. Immobilization did not change the pH optimum of lactose hydrolysis. The enzyme decay followed first-order kinetics and the thermal stability of the immobilized lactase was considerably enhanced. At 50 °C and pH 3.6 the half-life of the immobilized lactase was 180 days and that of the free enzyme 24 days. The kinetics of lactose hydrolysis by both free and immobilized lactase were studied in a batch reactor system in the absence of any mass transfer limitations. In both cases the totally competitive galactose inhibition kinetic model predicted the experimental data. Simulation of the performance of a laboratory continuous flow immobilized lactase reactor system showed that experimental results could be predicted by the ideal plug flow model when an apparent effectiveness factor n_f=0.65 is used to take into account the external mass transfer limitations.