Fed-batch fermentation of propionic, acetic and lactic acid production

Abstract

Propionibacterium is capable of producing many important industrial products such as propionic acid, vitamin B 12 and bacteriocin. Also it shows some probiotic health benefits and produces stimulator of intestinal bacteria. The aim of this research is to evaluate the effect of pH control on biomass, propionic, acetic and lactic acids production in fed-batch system by Propionibacterium freudenreichii ssp. shermanii and Lactobacillus acidophilus. Fermentation was conducted in a 3-L fermentor containing base medium and molasses as the carbon source in which milk feeding were added in 36th hour and maintained at 30 °C. Total fermentation time was 144 h. Every 24 h sampling has been done to measure the biomass and organic acids. Yield of biomass and acid production were compared in two separate trials: one treatment without pH control and another in which pH was maintained at 6.5 by using NaOH 1N. Content of biomass and organic acid were measured by freeze drying method and HPLC, respectively. The final concentration of the obtained responses in treatments with and without pH control is as following (g/L): biomass 6.22±0.04 and 13.76 ±0.04; propionic acid, 5.25±0.02 and 5.67±0.01; acetic acid 5.86±0.02 and 6.33±0.06; and lactic acid 11.34±0.09 and 7.40±0.07. In treatment which pH has not been controlled, production of dried biomass, propionic and acetic acid were higher than controlled treatment. So production of a beverage containing propionic acid could be recommended due to satiety-inducing and saturation effect in consumer.