propionica

Propionic acid, or propanoic acid, is a carboxylic acid with the formula CH3-CH2-CO2H. It is a colorless liquid at room temperature with a sharp, sour odor and a pKa around 4.87. It is miscible with water and many organic solvents. Propionic acid occurs naturally in dairy products and is produced by certain bacteria during fermentation.

Natural occurrence and biological relevance include production by Propionibacterium species, notably Propionibacterium freudenreichii in Swiss cheese, where it contributes to flavor and the formation of characteristic holes by releasing carbon dioxide. In humans, propionate is a short-chain fatty acid produced by gut microbiota and can serve as a metabolic substrate in the liver.

Production and sources can be both biological and industrial. Industrially, propionic acid is produced by oxidation of propionaldehyde or by catalytic routes starting from propanol or related precursors. It is also derived from biological fermentation processes. The acid forms salts, known as propionates, such as sodium propionate and calcium propionate, which are widely used as food preservatives and acidity regulators.

Applications include use as a preservative (notably in bread and baked goods) to inhibit mold growth, as a food acidity regulator, and as a chemical intermediate in the manufacture of esters, fragrances, and various plastics. It also appears in some cosmetics and pharmaceutical formulations in small amounts.

Safety and metabolism: In humans, propionate is metabolized in the liver via propionyl-CoA to succinyl-CoA through biotin-dependent propionyl-CoA carboxylase and methylmalonyl-CoA mutase, linking it to the citric acid cycle. Propionic acid and its salts can irritate skin or eyes and may cause gastrointestinal discomfort if ingested in large quantities. Propionates are generally considered safe at approved food-use levels.