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

Propionibacteria are capable of producing many important industrial products such as propionic acid، vitamin B12 and bacteriocins. Also these bacteria show some probiotic health benefits and produce prebiotics as stimulator of intestinal bacteria. The aim of this research is evaluation of pH control on production of biomass propionic، acetic and lactic acids in fed-batch system، with feeding of molasses and lactose as carbon sources of co-fermentation of Propionibacterium freudenreichii ssp. shermanii and Lactobacillus acidophilus. Fermentation was conducted in a 3-liter fermentor containing base medium and molasses as the carbon source in which lactose was fed after 36th hat temperature at 30 °C. Total fermentation time was 96 hand sampling was done in every 24 h intervals to measure the biomass and organic acids. Two treatments were compared to each other: in one trial، pH was maintained at 6. 5 by using NaOH 1N، but in another، during fermentation pH was not controlled. Content of biomass and organic acid were measured by freeze drying and HPLC methods، respectively. The final concentration of the dependent variables for the two treatments with and without pH control obtained as following (g/L): biomass 1. 97±0. 07 and 1. 72 ±0. 07، propionic acid، 4. 87±0. 13 and 4. 16±0. 04، acetic acid 4. 87±0. 13 and 4. 16±0. 04 and lactic acid 7. 93±0. 06 and 6. 10±0. 09. In this study it was shown that production of mentioned organic acids was not affected significantly by adding NaOH for control of pH in medium.