Malic acid production through the whole-cell hydration of fumaric acid with immobilised Rhizopus oryzae

The production of malic acid from fumaric acid using Rhizopus oryzae as a whole-cell bioconversion process was investigated. Biomass preparation and immobilisation were more straightforward compared with Bravibacterium flavum and Saccharomyces cerevisiae. Anaerobic operation greatly increased the process half-life, which also increased with an increasing sodium concentration in the medium. A model was proposed and validated using repeat-batch and continuous experiments. The results indicated a maximum specific productivity of 3.78 g g−1 h−1 and a process half-life of 40 h, which compares favourably with both B. flavum and S. cerevisiae. No other by-products were formed during the hydration reaction.