Controlling Substrate Concentration in Fed‐Batch Candida magnoliae Culture Increases Mannitol Production

Candida magnoliae HH‐01, a yeast strain that is currently used for the industrial production of mannitol, has the highest mannitol production ever reported for a mannitol‐producing microorganism. However, when the fructose concentration exceeds 150 g/L, the volumetric mannitol production rate decreases because of a lag in mannitol production, and the yield decreases as a result of the formation of side products. In fed‐batch culture, the volumetric production rate and mannitol yield from fructose vary substantially with the fructose concentration and are maximal at a controlled fructose concentration of 50 g/L. In continuous feeding experiments, the maximum mannitol yield was 85% (g/g) at a glucose/fructose feeding ratio of 1/20. A high glucose concentration in the production phase resulted in the formation of ethanol followed by a decrease in yield and productivity. NAD(P)H‐dependent mannitol dehydrogenase was purified to homogeneity from C . magnoliae . In vitro , mannitol dehydrogenase was inhibited by increasing ethanol concentration. Mannitol product was also found to be inhibitory with a K i of 183 mM. Under optimum conditions, a final mannitol production of 213 g/L was obtained from 250 g fructose/L after 110 h.