Abstract
In this study combined cross-linked aggregates of catalase from bovine liver and glucose-oxidase from Aspergillus niger were prepared, and the effects of the precipitant and crosslinking agents, as well as the use of bovine serum albumin (BSA) as a feeder protein, on enzyme immobilization yield and thermal stability of both enzymes, were evaluated. Combi- crosslinking of enzyme aggregates (CLEAs) prepared using dimethoxyethane as precipitant, 25 mM glutaraldehyde and BSA/enzymes mass ratio of 5.45 (w/w), exhibited the highest enzyme activities and stabilities at 40 degrees C, pH 6.0, and 250 rpm for 5 h. The stability of both immobilized enzymes was fairly similar, eliminating one of the problems of enzyme coimmobilization. Combi-CLEAs were used in gluconic acid (GA) production in a bubble column reactor operated at 40 degrees C, pH 6.0 and 10 vvm of aeration, using 26 g L-1 glucose as the substrate. Results showed conversion of around 96% and a reaction course very similar to the same process using free enzymes. The operational half-life was 34 h, determined from kinetic profiles and the first order inactivation model. Combi-CLEAs of glucose-oxidase and catalase were shown to be a robust biocatalyst for applications in the production of gluconic acid from glucose.