Influence of environmental parameters on propionic acid upstream bioprocessing by Propionibacterium acidi-propionici

Abstract

Accumulation of propionic acid as the predominant product in anaerobic mixed acid bioprocessing is influenced by pH, temperature and redox. The effect of temperature on the bioprocess showed that while the specific growth rate increased from 0.05 h −1 to 0.115 h −1 between 26°C and 37°C, specific propionic acid formation rate did not increase above 30°C and the ratio of propionic to acetic acid decreased with an increase in temperature. pH was found to influence the lag time, specific growth rate, yield of cells and product per g substrate. Ratio of propionic to acetic acid was also greatly influenced by pH. While lower pH gave better ratios of propionic to acetic acid (5:1), the propionic acid productivity was low (0.11 g l −1 h −1) while at pH values above 6 (up to 7.5) lower ratios of propionic acid to acetic acid was obtained (2.5:1) but productivity of propionic acid was higher (0.2 g l −1 h −1). A pH cycling strategy was adopted which gave high ratios of propionic to acetic acid (5.4) with good productivity of propionic acid (0.22 g l −1 h −1).