An overview of biotechnological production of propionic acid: from upstream to downstream processes

The increasing demand for propionic acid (PA) production and its wide applications in several industries, especially the food industry (as a preservative and satiety inducer), have led to studies on the low-cost biosynthesis of this acid. This paper gives an overview of the biotechnological aspects of PA production and introduces Propionibacterium as the most popular organism for PA production. Moreover, all process variables influencing the production yield, different simple and complex carbon sources, the metabolic pathway of production, engineered mutants with increased productivity, and modified tolerance against high concentrations of acid have been described. Furthermore, possible methods of extraction and analysis of this organic acid, several applied bioreactors, and different culture systems and substrates are introduced. It can be concluded that maximum biomass and PA production may be achieved using metabolically engineered microorganisms and analyzing the most significant factors influencing yield. To date, the maximum reported yield for PA production is 0.973 g·g-1, obtained from Propionibacterium acidipropionici in a three-electrode amperometric culture system in medium containing 0.4 mM cobalt sepulchrate. In addition, the best promising substrate for PA bioproduction may be achieved using glycerol as a carbon source in an extractive continuous fermentation. Simultaneous production of PA and vitamin B12 is suggested, and finally, the limitations of and strategies for competitive microbial production with respect to chemical process from an economical point of view are proposed and presented. Finally, some future trends for bioproduction of PA are suggested.

[ effects of betaine on vitamin B12 production by Propionibacterium freudenreichii]

Chemical production of vitamin B12 is a complicated process. The purpose of this study, done for the first time in Iran, was to produce vitamin B12 by Propionibacterium freudenreichii and investigate the effect of adding betaine on its yield. Propionibacterium freudenreichii was added to a fermention culture medium containing filtrated soaked corn. This was followed by incubation at 30°C and, then, adding betaine at six concentrations [0, 5, 10, 15, 20 and 30 g/l]. Separation and purification were done and the presence and the amount of vitamin B[12] produced were determined by HPLC. The most effective concentration of betaine for vitamin B[12] production [318.33 Pg/ml] was 10 g/l, which had a negative effect on dry weight of the cells [22.37 g/l]. The results demonstrated that betaine could greatly stimulate vitamin B[12] biosynthesis by Propionibacterium freudenreichii and inhibit cell growth. Based on the findings of this study, betaine added to the culture medium of Propionibacterium freudenreichii at a suitable concentration could increase the yield of vitamin B[12], paving the way to a commercial, more economic method for its production