Immobilized enzyme tri-phase reactors for oxidation of cephalosporin C

The enzymatic oxidation of Cephalosporin C (CEPHC) was catalyzed by D-aminoacid oxidase, from the red yeast Trigonopsis variabilis, immobilized on Duolite A365. The study was performed in two different three phase bioreactors, gas-liquid-solid (immobilized enzyme): the fluidized-bed batch reactor, fed continuously with oxygen and discontinuously with CEPHC, and the UF-membrane reactor continuously fed with both substrates. Only the first reactor allowed significant product yield (> 70%) while the second was a very useful tool for laboratory investigation of both bioconversion kinetics and enzyme stability. Optimum reaction temperature was 15°C for the control of CEPHC spontaneous degradation (roughly 15% in 30 h), and enzyme deactivation (half-life greater than 30 h). Immobiliza tion improved (one order of magnitude longer half-life) enzyme resistance to mechanical stresses induced by liquid stirring and gas bubbling. Roughly 0.04 g of CEPHC was adsorbed per gram of enzyme carrier. The limiting step in oxygen transfer was the gas to liquid transport. In order to attain kinetic control of the bioconversion the mildest conditions were atmospheric gas pressure and oxygen flow rate equal to 2 x 10-2 NmLs per mL of liquid phase.