The effect of ethanol on the growth and propionic acid formation of propionibacterium acidipropionici

This study aimed to assess the effect of ethanol on the growth and propionic acid production of Propionibacterium acidipropionici, and develop a mixed-cultures method to improve propionic acid production. At natural pH, low amount of ethanol (less than 0.5%, v/v) showed significantly stimulatory effects on the growth and propionic acid production of P. acidipropionici, while not at pH 6.5 controlled. Based on these results, a mixed cultures strategy to improve propionic acid fermentation of P. acidipropionici was developed. The addition of Candida sp. BS-1 (2%, v/v) to the flasks of P. acidipropionici, the glycerol consumption rates (0.218 g/l/h), and the maximal propionic acid yield (11.3 g/l) were about 24.8% and 20.9% higher than those of the single culture fermentation. The results indicated a mixed-culture method would be a potential way to improve propionic acid production.