Propionic acid fermentation from corn stover hydrolysate by Propionibacterium acidipropionici

Propionibacterium acidipropionici ATCC 4875 is capable of utilizing lignocellulosic biomass-derived sugars to produce propionic acid, which can be used as a precursor to synthesize renewable propylene. In order to systematically study propionic acid production from corn stover, mock-hydrolysate containing similar concentrations of major sugars and known inhibitors found in corn stover hydrolysate slurry, was first used to test propionic acid fermentation. The effect of CO₂ and N₂ on mock-hydrolysate fermentation was investigated. Results demonstrated that sparging N₂, instead of CO₂, through the medium led to a higher yield and productivity. Cultures composed of varying initial concentrations of sugars and inhibitors showed that the highest propionic acid productivity and yield were achieved in the mock-hydrolysate medium corresponding to 2.7-fold diluted slurry. Going forward, to enhance the propionic acid production and simplify downstream purification, an integrated fermentation/solvent extraction process will be applied. To date, tertiary and quaternary amines dissolved in oleyl alcohol were selected as solvent extractant and their toxicity on cell growth was investigated.  Fermentation was severely inhibited by the quaternary amine; however, it was less influenced by tertiary amine and even enhanced by oleyl alcohol alone.