It is produced as a racemic mixture by chemical synthesis
(hydration of maleic or fumaric acid) or as enantiomerically
pure L-malate by the enzymatic hydration of fumarate (immobilized
cells or fumarase) (3, 9, 30). Substrates for the synthesis
of malic acid (maleic acid, fumaric acids, maleic anhydride) are
derived from petroleum (32). Increases in oil and gas prices
coupled with concerns about climate change and global warming
have renewed interest in the production of malic acid by
microbial fermentation