Propionic acid production by Propionibacterium sp. using low-cost carbon sources in submerged fermentation

Abstract

Abstract: Propionic acid is widely used as additive in animal feed and also in the manufacturing of cellulose-based plastics, herbicides, and perfumes. Salts of propionic acid are used as preservative in food. Propionic acid is mainly produced by chemical synthesis. Nowadays, propionic acid production by fermentation of low-cost carbon sources has been an interesting alternative. At the present investigation, propionic acid production by eight propionibacteria strains was studied using a basal medium with sugarcane molasses (BMSM), glycerol (BMG) or lactate (BML) in small batch fermentation at 30 and 36°C, in order to select the best one for further experiments in stirred-tank bioreactor. Bacterial growth was carried out under low dissolved oxygen concentration and without pH control in 1L batch assays. Results indicated that P. zeae (DSM 20274) was the most adapted propionibacteria to BMG, reaching 8.98g/L of propionic acid at 36ºC and 2.86g/L of dry biomass at 30ºC in small bacth model and the pH controlled fermentation did not improve significantly these productions. In addition, P. arabinosum (ATCC 4965) produced more biomass in BMSM than in other media at 30°C (7.55g/L) as well as at 36°C (3.71g/L) and achieved 8.23g/L of propionic acid concentration at 30ºC. When fermentation with pH controlled at 7 was performed using ATCC 4965 in BMSM, its fermentative parameters increased a lot, reaching an improvement of 490% for biomass concentration and 315% for propionic acid concentration. Afterwards, this fermentative broth was tested for antifungal activity and it affected Aspergillus flavus and A. ochraceaus growth. The best propionic acid productivity was obtained by ATCC 9614 using BML (0.126g.L-1.h-1), although the yielding of this metabolite was higher when using glycerol as carbon source by ATCC 4868 (0.962g/g) because there was no detection of acetic acid. Besides, when using the BML or BMSM, acetic acid emerged as an undesirable by-product for further propionic acid purification.