Propionic acid fermentation of glycerol and glucose by Propionibacterium acidipropionici and Propionibacterium freudenreichii ssp shermanii

A comparative study was carried out in anaerobic batch cultures on 20 g/l o f either glycerol or glucose using two propionibacteria strains, Propioniba cterium acidipropionici and Propionibacterium freudenreichii ssp. shermanii . In all cases, fermentation end-products were the same and consisted of pr opionic acid as the major product, acetic acid as the main byproduct and tw o minor metabolites, n-propanol and succinic acid. Evidence was provided th at greater production of propionic acid by propionibacteria was obtained wi th glycerol as carbon and energy sources. P. acidipropionici showed higher efficiency in glycerol conversion to propionic acid with a faster substrate consumption (0.64 g l(-1) h(-1)) and a higher propionic acid production (0 .42 g l(-1) h(-1) and 0.79 mol/mol). The almost exclusive production of pro pionic acid from glycerol by this bacterium suggested an homopropionic tend ency of this fermentation. Acetic acid final concentration was two times lo wer on glycerol (2 g/l) than on glucose (4 g/l) for both micro-organisms. P . freudenreichii ssp. shermanii exhibited a glycerol fermentation pattern t ypical of non-associated glycerol-consumption-product formation. This could indicate a particular metabolism for P. freudenreichii ssp. shermanii orie nted towards the production of other specific components. These results ten d to show that glycerol could be an excellent alternative to conventional c arbon sources such as carbohydrates for propionic acid production.