Product Code Database
Propionic acid (, from the Greek language words πρῶτος : prōtos, meaning "first", and πίων : píōn, meaning "fat"; also known as propanoic acid) is a naturally occurring carboxylic acid with chemical formula . It is a liquid with a pungent and unpleasant smell somewhat resembling body odor. The anion as well as the Carboxylate salt and of propionic acid are known as propionates or propanoates.
About half of the world production of propionic acid is consumed as a preservative for both animal feed and food for human consumption. It is also useful as an intermediate in the production of other chemicals, especially polymers.
Propionic acid displays the general properties of carboxylic acids: it can form amide, ester, acid anhydride, and acyl chloride derivatives. It undergoes the Hell–Volhard–Zelinsky reaction that involves α-halogenation of a carboxylic acid with bromine, catalyst by phosphorus tribromide, in this case to form 2-bromopropanoic acid, . This product has been used to prepare a racemic mixture of alanine by ammonolysis.
It is also produced by the aerobic oxidation of propionaldehyde. In the presence of cobalt or manganese salts (manganese propionate is most commonly used), this reaction proceeds rapidly at temperatures as mild as 40–50 °C:
Large amounts of propionic acid were once produced as a byproduct of acetic acid manufacture. At the current time, the world's largest producer of propionic acid is BASF, with approximately 150 kt/a production capacity.
Alternative methods of production have been trialled, by genetically engineering strains of Escherichia coli to incorporate the necessary pathway, the Wood-Werkman cycle.
Propionic acid is also useful as an intermediate in the production of other chemicals, especially polymers. Cellulose-acetate-propionate is a useful thermoplastic. Vinyl propionate is also used. In more specialized applications, it is also used to make and . The of propionic acid have fruit-like odors and are sometimes used as or artificial flavorings.
In biogas plants, propionic acid is a common intermediate product, which is formed by fermentation with propionic acid bacteria. Its degradation in anaerobic environments (e.g. biogas plants) requires the activity of complex microbial communities.
In production of the Jarlsberg cheese, a propionic acid bacterium is used to give both taste and holes. www.jarlsberg.com quote: " In the production of Jarlsberg®, propionic acid bacteria (the Secret Recipe!) is used to give the cheese its characteristic taste and holes."
The metabolism of propionic acid begins with its conversion to propionyl coenzyme A, the usual first step in the metabolism of . Since propionic acid has three carbons, propionyl-CoA cannot directly enter either beta oxidation or the citric acid cycles. In most , propionyl-CoA is carboxylation to D-methylmalonyl-CoA, which is Isomerisation to L-methylmalonyl-CoA. A vitamin B12-dependent enzyme catalyzes rearrangement of L-methylmalonyl-CoA to succinyl-CoA, which is an intermediate of the citric acid cycle and can be readily incorporated there.
Propionic acid serves as a substrate for hepatic gluconeogenesis via conversion to succinyl-CoA. Additionally, Exogeny propionic acid administration results in more endogenous glucose production than can be accounted for by gluconeogenic conversion alone. Exogenous propionic acid may upregulate endogenous glucose production via increases in norepinephrine and glucagon, suggesting that chronic ingestion of propionic acid may have adverse metabolic consequences.
In propionic acidemia, a rare inherited genetic disorder, propionate acts as a metabolic toxin in liver cells by accumulating in mitochondria as propionyl-CoA and its derivative, methylcitrate, two tricarboxylic acid cycle inhibitors. Propanoate is metabolized oxidatively by glia, which suggests astrocytic vulnerability in propionic acidemia when intramitochondrial propionyl-CoA may accumulate. Propionic acidemia may alter both neuronal and glial gene expression by affecting histone acetylation. When propionic acid is infused directly into rodents' brains, it produces reversible behavior (e.g., hyperactivity, dystonia, social impairment, perseveration) and brain changes (e.g., innate neuroinflammation, glutathione depletion) that may be used as a means to model autism in rats.
A study in mice suggests that propionate is produced by the bacteria of the genus Bacteroides in the gut, and that it offers some protection against Salmonella there. Another study finds that fatty acid propionate can calm the immune cells that drive up blood pressure, thereby protecting the body from damaging effects of high blood pressure.
Propionates should not be confused with propenoates (commonly known as ), the ions/salts/esters of propenoic acid (also known as 2-propenoic acid or acrylic acid).
Biology
Propionic acid is produced biologically as its coenzyme A ester, propionyl-CoA, from the metabolism breakdown of fatty acids containing of carbon atoms, and also from the breakdown of some . Bacteria of the genus Propionibacterium produce propionic acid as the end-product of their anaerobic metabolism. This class of bacteria is commonly found in the stomachs of and the sweat glands of humans, and their activity is partially responsible for the odor of Emmental cheese, American "Swiss cheese" and sweat.
Human occurrence
The human skin is host of several species of Propionibacteria. The most notable one is the Cutibacterium acnes (formerly known as Propionibacterium acnes), which lives mainly in the of the skin and is one of the principal causes of acne. Propionate is observed to be among the most common short-chain fatty acids produced in the large intestine of humans by gut microbiome in response to indigestible carbohydrates (dietary fiber) in the diet. The role of the gut microbiota and their metabolites, including propionate, in mediating brain function has been reviewed.
Bacteriology
The Bacteria species Coprothermobacter platensis produces propionate when fermenting gelatin. Prevotella brevis and Prevotella ruminicola also generate propionate when fermenting glucose.
Propionate salts and esters
The propionate , or propanoate, ion is , the conjugate base of propionic acid. It is the form found in biological systems at physiological pH. A propionic, or propanoic, compound is a carboxylate salt or ester of propionic acid. In these compounds, propionate is often written in shorthand, as or simply .
Examples
Salts
Esters
See also
External links
|
|
