Propionic acid (PA) is a colorless, pungent, fuming liquid. The formula for propionic acid is CH3CH2COOH. PA and its calcium, sodium, and potassium salts are important C-3 platform chemicals that are widely used as preservatives in animal feed and human foods. PA is also an important chemical intermediate in the synthesis of cellulose fibers, herbicides, perfumes, and pharmaceuticals. According to the US Department of Energy, PA is among the top 30 candidate platform chemicals with various uses. 

Chemical Synthesis

Commercial production of PA is mainly achieved through chemical synthesis from petroleum feedstocks33; however, fermentation is an attractive alternative method for the production of PA from renewable resources. Due to the exhaustion of petroleum resources and the serious environmental pollution caused by the utilization of fossil resources, production of PA by microbial fermentation from renewable resources has attracted increasing attention. The species that have been used for the microbial production of PA include Propionibacterium freudenreichii, Propionibacterium acidipropionici, Propionibacterium thoenii, and Propionibacterium jensenii.

Uses

Propionic acid (PA) is an important organic molecule of vast economic importance that includes food preservatives, flavoring agents, pharmaceutical formulations, textile and rubber auxiliaries, plasticizers, cosmetics, etc. Most importantly, PA acts as an antimicrobial agent and is supplied as poultry feed to reduce acidogenesis in the metabolism of ruminants. The salt of PA as a food preservative is considered to be “Generally Regarded as Safe” (GRAS). The market value of PA ranges from 1 to 3 USD/kg calcium propionate for food additive purposes. Acidogenesis is the major biochemical pathway involved in the fermentative production of PA.