How Can the High Molar Yield of Fumaric Acid be Explained

1 How Can the High Molar Yield of Fumaric Acid be Explained  

Although Felix Ehrlich was the first to show in 1911 that fumaric acid is produced by R. nigricans, it took 28 years until Foster and Waksman (1939) identified an overproducer Rhizopus strain, which was (probably) used shortly after in the industry for the production of fumaric acid on a large scale (see above, 15.2.1). 

Fumaric acid (molar yield of approximately 100% moles of acid produced per moles of glucose utilized x 100), L-malic acid (15 mol%), and succinic acid (5 mol%) were the major acids formed during the fermentation. C4 acid (fumaric, L-malic, and succinic acid) molar yields of 120-145%, with a maximal fumaric acid concentration of 107 g/L, were obtained after 4-5 days (Goldberg and Stieglitz, 1985,1986 Kenealy et al., 1986 Ng et al., 1986). These high yields confirmed earlier data obtained by Rhodes et al. (1959, 1962). 

How can we explain the unusually high molar yield of fumaric acid obtained by a Rhizopus strain  

According to Rhodes et al. (1959) the accumulation of fumaric acid maybe attributed to low activity or absence of fumarase. However, a high in vitro activity of fumarase was measured during the fumaric acid production stage (Osmani and Scrutton, 1985 Kenealy et al., 1986). 

---