Propionic acid production via two-step sequential repeated batch fermentations on whey and flour

In this study, two-stage process was developed for propionic acid production via repeated batch and fed-batch fermentations. In the first step, either whey lactose or flour hydrolysate was used as carbon source to produce lactic acid using Lactobacillus plantarum in repeated batch and fed-batch fermentations. Then, produced lactic acid was used as a carbon source for propionic acid fermentation using Propionibacterium freudenreichii in repeated batch fermentations. Maximum lactic acid concentrations were achieved as 100 g/L at 250th hour of incubation (corresponding to 6th cycle of repeated batch fermentation) on whey lactose and 97 g/L at 500th hour (1st cycle) on flour hydrolysate as substrate. For propionic acid production, maximum propionic acid concentrations were obtained as 28 g/L at 700th hour (13th cycle) on lactic acid obtained from whey and 35 g/L at 3600th hour (10th cycle) on lactic acid obtained from flour hydrolysate. Lactic acid and propionic acid productivities were 0.80 g/Lh and 0.050 g/Lh on whey lactose higher than the values 0.12 g/Lh and 0.025 g/Lh obtained on flour hydrolysate respectively. •Repeated batch fermentations are advantageous over batch fermentations allowing reuse of biomass at biomass limited fermentations.•Two-stage fermentation allows to produce organic acids to be used as a substrate from several complex bio-based feedstocks.•Productivities of propionic acid fermentations on whey are higher than those on flour.•The product yields are higher on whey compared to on flour.•Developing a long-term process on semi solid mediums such as flour are important to control contamination.