LACTIC-ACID PRODUCTION BY PELLET-FORM RHIZOPUS-ORYZAE IN A SUBMERGED SYSTEM

Rhizopus oryzae NRRL, 395 produces optically pure L(+)-lactic acid tha t is highly preferred for the production of environmentally benign pol ymers. With xylose as the carbon source for cultivation, it can be sel f-immobilized as pellets with a size of about 1 mm. Repeated usage of the same pellets by transferring them into fresh media every time when the glucose was exhausted over a period of 22 d yielded 1742 or 2001 g/L lactic acid total (based on 100-mL working volume) depending on th e media used. Lactic acid is known to be a strong inhibitor for both g rowth and production, and it can be removed continuously by the adsorp tion on the PVP resin. With the fermenter-adsorber system, the ferment ation can be performed as effectively as the ones with added neutraliz ing agents, such as calcium carbonate and sodium hydroxide. One proble m of the fermenter-adsorber system is that lower production was obtain ed than in shake flasks; hence, proper reactor design is necessary to improve the process.