BIOTECHNOLOGY - V. G. Herasymenko - 2006

Part II. Special Biotechnologies

CHAPTER 10. APPLICATIONS OF IMMOBILIZED ENZYMES IN BIOTECHNOLOGY

10.4. BIOTECHNOLOGY OF L-MALIC ACID PRODUCTION

L-Malic acid is in high demand on the global market as a substitute for citric acid in the food and pharmaceutical industries. Chemical synthesis (via the Hydrolysis of maleic/malic anhydride) yields only a racemic mixture of optical D, L-isomers, whereas the microbiological synthesis of L-malic acid is unfeasible for industrial-scale production due to its high cost.

However, L-malic acid can be produced via the Fermentation of fumaric acid—the same precursor used to obtain L-aspartic acid. Catalyzed by the enzyme fumarase, fumaric acid undergoes Hydration (The addition of Water across a double bond) to form L-malic acid. Microbial Cells containing the fumarase enzyme are used as the biocatalyst.

To produce L-malic acid on a large scale, the Japanese company Tanabe Seiyaku utilizes Immobilized Microbial Cells entrapped in a polyacrylamide gel. In addition to the primary process of L-malic acid synthesis, these cells catalyze an unwanted side reaction: The formation of succinic acid. To inhibit this reaction, the immobilized microbial cells undergo additional Treatment. Immobilization significantly enhances the stability of cellular fumarase, yielding a half-inactivation time of 55 days at 37 ^oC, compared to just 6 days for intact (untreated) cells.

For The production of L-malic acid, the Italian company Snamprogetti employs fumarase immobilized by entrapment within Cellulose triacetate hollow fibers. Furthermore, for the immobilization of whole microbial cells, the company uses a carrageenan-based gel (a polysaccharide derived from seaweeds) instead of polyacrylamide gel. This modification increased the half-inactivation time of the enzyme to 160 days.