EFFECT OF AERATION ON ORGANIC-ACID PRODUCTION BY PROPIONIBACTERIUM-SHERMANII

Propionibacteria have been reported as being oxygen sensitive bacteria . Nevertheless, in this work, we intend to show that Propionibacterium shermanii CDB 10014 is able to grow even at high volumetric oxygen tr ansfer coefficients (K(L)a). Similar final cell concentrations were ac hieved in experiments at different K(L)a values, with increasing cell yield from 0.08 g/g cells in anaerobic conditions to 0.22 g/g at K(L)a 61 h(-1). The organic acid production pattern changes depending on th e K(L)a. At K(L)a higher than 36 h(-1), propionic acid was not produce d and acetic acid was the main product. At K(L)a higher than 20 h(-1), lactic acid began to be produced. In further studies, no important di fferences in the growth yield were observed in the pH range 5.5-7.0, w hile the cell production was enhanced by temperatures in the range 30- 35 degrees C.