propionic

Propionic, in chemical nomenclature, refers primarily to propionic acid (propanoic acid) and related derivatives such as propionates and propionate esters. Propionic acid is a carboxylic acid with three carbon atoms, CH3-CH2-COOH. It is a colorless liquid at room temperature with a sharp, penetrating odor and is produced both industrially and by microbial fermentation.

Propionic acid is a weak acid (pKa around 4.87). It forms salts with metals, notably sodium propionate and calcium propionate, which are widely used as food preservatives to inhibit mold and some bacteria. The acid and its salts are miscible with water and many organic solvents. Industrial production occurs by chemical synthesis and by microbial fermentation of carbohydrates.

Propionic acid is produced by certain bacteria during fermentation, most famously by Propionibacterium species in Swiss-type cheeses, where it contributes flavor and carbon dioxide that creates holes. It also occurs in small amounts in various fermented foods and is used industrially as a chemical intermediate in the manufacture of plastics, fragrances, and various propionate esters.

In biochemistry, propionic acid is an intermediate in the metabolism of certain amino acids and odd-chain fatty acids. It is converted to propionyl-CoA and then to methylmalonyl-CoA, ultimately entering the citric acid cycle as succinyl-CoA. Defects in this pathway cause propionic acidemia, a metabolic disorder. Safety wise, propionic acid and its salts can be irritants to skin and eyes; salts used as food preservatives are approved for use in many jurisdictions at established levels.