L ‐Malic Acid Production by Fumarase

Abstract Malic acid is an intermediate metabolite in the tricarboxylic acid cycle. It is widely used in pharmaceutical, food processing, and other industries. Malic acid was produced commercially by chemical synthesis or through fermentation processes that convert fumaric acid to L ‐malic acid by using fumarase. In this article, we introduce several methods to produce L ‐malic acid by fumarase. Brevibacterium ammoniagenes MA‐2 and Brevibacterium flavum MA‐3 were selected for producing fumarase. The fermentation results of these two strains showed that the internal‐loop airlift reactor was more suitable than the stirred reactor. In addition, a comparison of cell collection methods showed that flocculation and coagulation were more suitable. We also established several methods of cell immobilization using mixed gels, which were better than the conventional single κ‐Carrageenan entrapment. When the immobilized cells of B. ammoniagenes MA‐2 and B. flavum MA‐3 catalyzed the ammonia fumarate to L ‐malic acid, the product concentrations were 210 g/L and 218 g/L respectively. Furthermore, the apparent kinetic parameters and the intrinsic kinetic parameters of immobilized cells were obtained. In order to cut down the residual fumaric acid, a conversion system was established to produce L ‐malate coupling with immobilized Escherichia coli No. 1 cells for converting the remnant fumarate to L ‐aspartic acid. A system‐integrated reaction and separation process, which produced L ‐malic acid from free cells containing fumarase, was established. The yield was up to 99.9% under the optimum reaction conditions, giving us a satisfactory and economical result for industrial application. Finally, the mechanism for the system‐integrated reaction and separation process was studied.