PROPIONIC-ACID PRODUCTION BY IMMOBILIZED CELLS OF A PROPIONATE-TOLERANT STRAIN OF PROPIONIBACTERIUM-ACIDIPROPIONICI

Cells of the propionate-tolerant strain Propionibacterium acidipropion ici P200910, immobilized in calcium alginate beads, were tested for pr opionic and acetic acid production both in a semidefined laboratory me dium and in corn steep liquor in batch, fed-batch, and continuous ferm entation. Cell density was about 9.8 x 10(9) cells/g (wet weight) of b eads, and beads were added to the medium at 0.1 g (wet weight) beads/m l. Beads could be reused for several consecutive batch fermentations; propionic acid production in the tenth cycle was about 50%-70% of that in the first cycle. In batch culture complete substrate consumption ( glucose in semidefined medium, lactate in corn steep liquor) and maxim um acid production were seen within 36 h, and acid yields from the sub strate were higher than in free-cell fermentations. Fed-batch fermenta tions were incubated up to 250 h. Maximum propionic acid concentration s obtained were 45.6 g/l in corn steep liquor and 57 g/l in semidefine d medium; this is the highest concentration achieved to date in our la boratory. Maxi mum acetic acid concentrations were 17 g/l and 12 g/l, respectively. In continuous fermentation of semidefined medium, diluti on rates up to 0.31 h(-1) could be used, which gave higher volumetric productivities (0.96 g l(-1) h(-1) for propionic acid and 0.26 g l(-1) h(-1) for acetic acid) than we have obtained with free cells. Corn st eep liquor shows promise as an inexpensive medium for production of bo th acids by immobilized cells of propionibacteria.