l-Malic acid is an intermediate metabolite in the tricarboxylic
acid (TCA) cycle of living cells [9]. Because it causes greater
tartness and taste retention than other food acids, it is commonly
used as a food additive [10]. Besides food industry, malic
acid has also its application in the pharmaceutical and cosmetic
industry [11]. In medicine only l-enantiomer of this acid is efficient
in the treatment of liver dysfunction and hyperammonemia
[12]. l-Malic acid can be prepared by isolating it from natural
fruit juices or by separating it from the racemic mixture produced
by chemical synthesis. Industrially, it is formed enzymatically
from fumaric acid by the action of the enzyme fumarase. For
that purpose microbial cells that contain fumarase are employed.
In 1974 an industrial process in which whole cells of Brevibacterium
ammoniagenses with high fumarase activity were
immobilized in gel matrices of polyacrylamide was developed
by Yamamoto et al. [13]. In 1977 productivity of this process,
as well as operation stability were improved by changing B.
ammoniagenses cells with the B. flavum [14,15]. Also immobilization
process with polyacrylamide was changed to the more
economical –carrageenan immobilization method [16]. A disadvantage
of this system was that by-product like succinic acid