FED-BATCH FERMENTATION WITH AND WITHOUT ONLINE EXTRACTION FOR PROPIONIC AND ACETIC-ACID PRODUCTION BY PROPIONIBACTERIUM-ACIDIPROPIONICI

Fed-batch propionic and acetic acid fermentations were performed in se mi-defined laboratory medium and in corn steep liquor with Propionibac terium acidipropionici strain P9. On average, over four experiments, 3 4.5 g/l propionic acid and 12.8 g/l acetic acid were obtained in about 146 h in laboratory medium with 79 g/l glucose added over five feedin g periods. The highest concentration of propionic acid, 45 g/l, was ob tained when the glucose concentration was not allowed to drop to zero. In corn steep liquor 35 g/l propionic acid and 11 g/l acetic acid wer e produced in 108 h from 59.4 g/l total lactic acid provided as seven feedings of corn steep liquor. Extractive fed-batch fermentations were conducted in semi-defined medium using either flat-sheet-supported li quid membranes or hollow-fiber membrane extraction to remove organic a cids from the culture medium. As operated during the course of the fer mentation, these systems extracted 25% and 22% of the acetic acid and 36.5% and 44.5% of the propionic acid, respectively, produced in the f ermentation. Total amounts of acids produced were about the same as in comparable nonextractive fermentations: 30-37 g/l propionic acid and 13 g/l acetic acid were produced in 150 h. Limitations on acid product ion can be attributed to limited substrate feed, not to failure of the extraction system.