Substrate-limited co-culture for efficient production of propionic acid from flour hydrolysate.

Propionic acid is presently mainly produced by chemical synthesis. For many applications, especially in feed and food industries, a fermentative production of propionic acid from cheap and renewable resources is of large interest. In this work, we investigated the use of a co-culture to convert household flour to propionic acid. Batch and fed-batch fermentations of hydrolyzed flour and a process of simultaneous saccharification and fermentation were examined and compared. Fed-batch culture with substrate limitation was found to be the most efficient process, reaching a propionic acid concentration of 30 g/L and a productivity of 0.33 g/L*h. This is the highest productivity so far achieved with free cells on media containing flour hydrolysate or glucose as carbon source. Batch culture and culture with controlled saccharification and fermentation delivered significantly lower propionic acid production (17-20 g/L) due to inhibition by the intermediate product lactate. It is concluded that co-culture fermentation of flour hydrolysate can be considered as an appealing bioprocess for the production of propionic acid.