Performance of the dialytic reactor with product inhibited enzyme reactions: a model study

Many hydrolytic enzymatic reactions are product inhibited. In a previous paper we reported that an enzyme reactor using dialysis to continually extract cleavage products could be advantageously used to hydrolyze whey proteins. Continuous dialysis of the reaction mixture produces a dilute product stream and requires large volumes of purified water. Both difficulties are eliminated by use of a closed loop reverse osmosis system to regenerate the dialysate. Low molecular weight products are thus removed from the reaction circuit as they are formed and concentrate in an accumulator with time through the dialysate stream. In this paper, we present an integral model for the description of mass transport in such dialytic reactor. Dimensional analysis of the model equations yielded a set of dimensionless parameters determining reactor performance. Reactor performance was found to depend not only on the enzyme, product and substrate concentrations, as in batch reactors, but also on the dialyzer selectivity. The model was validated experimentally with respect to the hydrolysis of a modified soluble starch by β-amylase from sweet potato. The dialytic reactor permitted a more efficient use of enzyme activity than the corresponding batch reactor. However, as outlined by the model, extraction of partially degraded substrate, as well as product, into the dialysate with only partially selective membranes limited the reactor performance despite the predictable relief of product inhibition.