S23: Development of an industrializable fermentation process for propionic acid production

Propionic acid is a short chain fatty acid with wide industrial application including uses in pharmaceuticals, herbicides, cosmetics and food preservatives.   This work summarizes the research advancements made towards developing an industrially feasible fermentation based route to propionic acid.  Seventeen propionic acid producing strains were screened on glucose and sucrose to identify the strain with the highest productivity, titer and propionic acid purity.  Propionibacterium acidipropionici ATCC 4875 was selected as the superior strain and was used for subsequent fermentation process and media optimization studies that were performed to maximize fermentation performance.  Fermentation productivity was improved more than three-fold to exceed 2 g/L/h by densifying the fermentation inoculum source.  Byproduct levels, particularly lactic acid and succinic acid, were reduced significantly by optimizing fermentor headspace pressure and agitation shear.  Replacing the lab grade medium components with industrial grade yeast extract and hydrolyzed soy protein significantly reduced fermentation costs, but did not improve final productivity or yield.  However, a novel medium based on pure enzymatically treated corn mash (ECM) resulted in significantly improved propionic acid yields, but a reduction in productivity was observed.   Supplementation of ECM with cyanocobalamin partially restored productivity, while supplementation with various minerals and other vitamins had no effect on fermentation performance. With the optimized ECM fermentation recipe, a fermentation productivity of 0.5 g/L/h with a substrate yield of 0.60 g/g was achieved resulting in a cost of production less than 1 USD/kg of propionic acid.