Ninety strains of Propionibacterium were screened for their ability to lower the pH of maltose broths. Strains attaining a pH <5 in enriched maltose broth consisted of 12 strains of Propionibacterium acidipropionici, 2 of Propionibacterium jensenii, and 3 of Propionibacterium thoenii. These 17 strains were further tested for their ability to produce propionic acid on maltose, lactose, lactate, and starch and their ability to produce propionic acid on various concentrations of maltose and lactate between 0.5 and 5.0%. On the basis of these tests, strains were selected to be tested in a batch fermentor for their ability to produce propionic acid on a substrate of partially hydrolyzed corn. P. acidipropionici P9 proved to be one of the most productive strains and achieved concentrations of 3.25% propionic acid and 14 g/L biomass in 140 h.
Journal Paper No. J-15135 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Project No. 3122.