FERMENTATION METABOLISM AND KINETICS IN THE PRODUCTION OF ORGANIC-ACIDS BY PROPIONIBACTERIUM-ACIDIPROPIONICI

The genus Propionibacterium acidipropionici was grown under pH-control led batch fermentation conditions for the production of acetic and pro pionic acids using 19.1 g/L glucose as a carbon source. The optimum pH range was found to be between 5.5 and 6.5. Bacterial metabolism and f ermentation pathways were altered at pH values outside this range. Lac tic acid was produced as a key intermediate, with the final acetic and propionic acid production entirely dependent on the cell's ability to metabolize the lactic acid. Most of the glucose in the medium was con sumed in less than 20 h of fermentation and converted to lactic acid. Batch fermentation at PH 6 showed that lactic acid was completely util ized to produce 8.5 g/L propionic acid and 5.7 g/L acetic acid. Howeve r, the bacteria were unable to metabolize lactic acid at pH 7, resulti ng in 0.7 g/L propionic acid and 7.0 g/L acetic acid in the fermenter. A kinetic study of batch fermentation at pH 6 showed two distinct gro wth phases during the fermentation. Most of the cell growth was achiev ed in the exponential growth stage when glucose was consumed as a main substrate. A nonexponential growth stage was observed when lactic aci d was utilized as a carbon source, producing propionic and acetic acid s as secondary metabolites.