l-Malic acid production within a microreactor with surface immobilised fumarase

In recent years, microreactors have evolved from a technical novelty to a useful tool in many scientific laboratories. On the other hand, their implementation in industry proceeds with a slower pace. In this work, we present a microreactor system for continuous l-malic acid production that demonstrates potentials of microfluidic systems for production of this widely used organic acid. APTES and glutaraldehyde were used to covalently immobilise fumarase on glass microreactor walls in order to allow product–catalyst separation. The system was tested at different substrate concentrations and flow rates and conversion up to 80% could be obtained in appropriate conditions. The reaction was precisely predicted by the developed mathematical model. Kinetic studies were performed with both free and immobilised enzyme and the later was found to retain approximately 25% of free enzyme activity and had the activity half-life of 9 days.