Production of propionic acid by microbiological way. Part 2. Effect of the pH value on cell growth and acid production

The batch propionic acid fermentation of sugar cane molasses by Propionibacterium acidi propionici PP-1 was studied at various pH values ranging from 5 to 7. The optimum pH range for cell growth was between 6 and 7, whereas the specific growth rate decreased with the pH in the acidic range down to 0.197 h^?1 at pH 5. The propionic acid yield increased with decreasing pH; it changed from 22% (wt/wt) at pH 7 to 38% at pH 5. It has been obvious that this process is inhibited by the products of the fermentation and more severely in the acidic range where the acids are in an unionized state. A generalized equation of the non-competetive inhibition was adjusted for each pH value, and kinetic inhibition constants were estimated.