Prospects For The Application Of Ultrasonic Membrane Extractors In The Submerged Cultivation Of Lactic Acid And Propionic Acid Bacteria
D. A. Durnikin, M. M. Silantyeva, O. V. Ereshchenko
The industrial production of lactic acid and propionic acid bacteria, which produce lactic, acetic and propionic acids and used as the components of biological preservatives of feed and fodder, requires to maintain a total concentration of organic acids in fermentation broth at a level of one percent during the whole fermentation process. The higher concentration inhibits the growth and development of these microorganisms, so their cell concentration in fermentation broth does not exceed 0.6·109 ml-1. Under laboratory conditions, pH of cultivation medium can be regulated by the neutralization of organic acids with alkaline, but under the large-scale production, the loss of produced lactic, acetic, and propionic acids is inexpedient, since they are widely used in various industrial segments including the conservation of rich fodder. One of the possible solutions is the use of a membrane extractor to remove organic acids, which represent valuable metabolites, from the cultural broth directly during the cultivation process. In this study, the efficiency of a specially designed membrane extractor equipped with additional ultrasonic transducers, which reduced diffusion limitations near the membrane surface, has been assessed in the process of submerged cultivation of three bacterial cultures: Lactococcus lactis VPKM B-2092, Lactobacillus plantarum VPKM B-4173, and Propionibacterium acidipropionici VPKM B-5723. The extractor was connected to the fermenter as external device and consisted of a cartridge filter preventing the biomass uptake into the extractor and a membrane extractor of a “liquid-liquid”type equipped with pH-state and hydrodynamic ultrasonic transducers. Whereas classic pH-states feed a pH-correcting solution into a fermenter according to a signal from a pH sensor, the developed pH-state construction turned on the US membrane extractor to remove excess organic acids from the fermentation broth. Due to the maintenance of optimum pH, the final concentration of L. lactis, L. plantarum, and P. acidipropionici cells increased in 5.8, 3.6, and 3.2 times, respectively. The equipping of a membrane extractor with ultrasonic transducers accelerated the removal of organic acids from fermentation broth of L. lactis, L. plantarum, and P. acidipropionici in 5.25, 5, and 6.25 times, respectively, i.e., provided a more rapid and efficient fermentation. The proposed technology improves the economical efficiency of the process and provides the required diversity of technical solutions for its use in a microbiological production.