Propionic acid (/proʊpiˈɒnɪk/, from the Greek words πρῶτος : prōtos, meaning "first", and πίων : píōn, meaning "fat"; also known as propanoic acid) is a naturally occurring carboxylic acid with chemical formulaCH 3CH 2CO 2H. It is a liquid with a pungent and unpleasant smell somewhat resembling body odor. The anionCH 3CH 2CO− 2 as well as the salts and esters of propionic acid are known as propionatesorpropanoates.
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 was first described in 1844 by Johann Gottlieb, who found it among the degradation products of sugar.[10] Over the next few years, other chemists produced propionic acid by different means, none of them realizing they were producing the same substance. In 1847, French chemist Jean-Baptiste Dumas established all the acids to be the same compound, which he called propionic acid, from the Greek words πρῶτος (prōtos), meaning first, and πίων (piōn), meaning fat, because it is the smallest H(CH 2) nCOOH acid that exhibits the properties of the other fatty acids, such as producing an oily layer when salted out of water and having a soapy potassiumsalt.[11]
Propionic acid has physical properties intermediate between those of the smaller carboxylic acids, formic and acetic acids, and the larger fatty acids. It is miscible with water, but can be removed from water by adding salt. As with acetic and formic acids, it consists of hydrogen bonded pairs of molecules in both the liquid and the vapor.
It is also produced by the aerobic oxidationofpropionaldehyde. In the presence of cobaltormanganese 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.
Biotechnological production of propionic acid mainly uses Propionibacterium strains.[16] However, large scale production of propionic acid by Propionibacteria faces challenges such as severe inhibition of end-products during cell growth and the formation of by-products (acetic acid and succinic acid).[17] One approach to improve productivity and yield during fermentation is through the use of cell immobilization techniques, which also promotes easy recovery, reuse of the cell biomass and enhances microorganisms' stress tolerance.[18] In 2018, 3D printing technology was used for the first time to create a matrix for cell immobilization in fermentation. Propionic acid production by Propionibacterium acidipropionici immobilized on 3D-printed nylon beads was chosen as a model study. It was shown that those 3D-printed beads were able to promote high density cell attachment and propionic acid production, which could be adapted to other fermentation bioprocesses.[19] Other cell immobilization matrices have been tested, such as recycled-glass Poraver and fibrous-bed bioreactor.[20][21]
Alternative methods of production have been trialled, by genetically engineering strains of Escherichia coli to incorporate the necessary pathway, the Wood-Werkman cycle.[22]
Propionic acid inhibits the growth of mold and some bacteria at levels between 0.1 and 1% by weight. As a result, some propionic acid produced is consumed as a preservative for both animal feed and food for human consumption. For animal feed, it is used either directly or as its ammonium salt. This application accounts for about half of the world production of propionic acid. The antibiotic monensin is added to cattle feed to favor propionibacteria over acetic acid producers in the rumen; this produces less carbon dioxide and feed conversion is better. Another major application is as a preservative in baked goods, which use the sodium and calcium salts.[15] As a food additive, it is approved for use in the EU,[23] US,[24] Australia and New Zealand.[25]
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 pesticides and pharmaceuticals. The esters of propionic acid have fruit-like odors and are sometimes used as solvents or artificial flavorings.[15]
Inbiogas 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.[26]
In production of the Jarlsberg cheese a propionic acid bacteria is used to give both taste and holes.[27]
The metabolism of propionic acid begins with its conversion to propionyl coenzyme A, the usual first step in the metabolism of carboxylic acids. Since propionic acid has three carbons, propionyl-CoA cannot directly enter either beta oxidation or the citric acid cycles. In most vertebrates, propionyl-CoA is carboxylatedtoD-methylmalonyl-CoA, which is isomerisedtoL-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.[28]
Propionic acid serves as a substrate for hepaticgluconeogenesis via conversion to succinyl-CoA.[29][30] Additionally, exogenous propionic acid administration results in more endogenous glucose production than can be accounted for by gluconeogenic conversion alone.[31] 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.[32]
Inpropionic 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.[33][34] 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.[33]
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 sebaceous glands of the skin and is one of the principal causes of acne.[35] Propionate is observed to be among the most common short-chain fatty acids produced in the large intestine of humans by gut microbiota in response to indigestible carbohydrates (dietary fiber) in the diet.[36][37] The role of the gut microbiota and their metabolites, including propionate, in mediating brain function has been reviewed.[38]
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.[39] 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.[40]
The propionate/ˈproʊpiəneɪt/, or propanoate, ionisC 2H 5COO− , 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 saltorester of propionic acid. In these compounds, propionate is often written in shorthand, as CH 3CH 2CO 2 or simply EtCO 2.
Propionates should not be confused with propenoates (commonly known as acrylates), the ions/salts/esters of propenoic acid (also known as 2-propenoic acid or acrylic acid).
^ abcdefPropanoic acid in Linstrom, Peter J.; Mallard, William G. (eds.); NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg (MD) (retrieved 13 June 2014)
^Johann Gottlieb (1844) "Ueber die Einwirkung von schmelzendem Kalihydrat auf Rohrzucker, Gummi, Stärkmehl und Mannit" (On the effect of molten potassium hydroxide on raw sugar, rubber, starch powder, and mannitol), Annalen der Chemie und Pharmacie, 52 : 121–130. After combining raw sugar with an excess of potassium hydroxide and distilling the result, Gottlieb obtained a product that he called『Metacetonsäure』(meta-acetone acid) on p. 122: "Das Destillat ist stark sauer und enthält Ameisensäure, Essigsäure und eine neue Säure, welche ich, aus unten anzuführenden Gründen, Metacetonsäure nenne." (The distillate is strongly acidic and contains formic acid, acetic acid, and a new acid, which for reasons to be presented below I call "meta-acetone acid".)
^Dumas, Malaguti, and F. Leblanc (1847) "Sur l'identité des acides métacétonique et butyro-acétique" [On the identity of metacetonic acid and butyro-acetic acid], Comptes rendus, 25 : 781–784. Propionic acid is named on p. 783: "Ces caractères nous ont conduits à désigner cet acide sous le nom d'acide propionique, nom qui rappelle sa place dans la séries des acides gras: il en est le premier." (These characteristics led us to designate this acid by the name of propionic acid, a name that recalls its place in the series of fatty acids: it is the first of them.)
^Liu, Long; Zhu, Yunfeng; Li, Jianghua; Wang, Miao; Lee, Pengsoon; Du, Guocheng; Chen, Jian (2012). "Microbial production of propionic acid from propionibacteria: Current state, challenges and perspectives". Critical Reviews in Biotechnology. 32 (4): 374–381. doi:10.3109/07388551.2011.651428. PMID22299651. S2CID25823025.
^Alonso, Saúl; Rendueles, Manuel; Díaz, Mario (2015). "A novel approach to monitor stress-induced physiological responses in immobilized microorganisms". Applied Microbiology and Biotechnology. 99 (8): 3573–3583. doi:10.1007/s00253-015-6517-1. PMID25776062. S2CID860853.
^Belgrano, Fabricio dos Santos; Diegel, Olaf; Pereira, Nei; Hatti-Kaul, Rajni (2018). "Cell immobilization on 3D-printed matrices: A model study on propionic acid fermentation". Bioresource Technology. 249: 777–782. Bibcode:2018BiTec.249..777B. doi:10.1016/j.biortech.2017.10.087. PMID29136932.
^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."
^ abD. F. MacFabe; D. P. Cain; K. Rodriguez-Capote; A. E. Franklin; J. E. Hoffman; F. Boon; A. R. Taylor; M. Kavaliers; K.-P. Ossenkopp (2007). "Neurobiological effects of intraventricular propionic acid in rats: Possible role of short-chain fatty acids on the pathogenesis and characteristics of autism spectrum disorders". Behavioural Brain Research. 176 (1): 149–169. doi:10.1016/j.bbr.2006.07.025. PMID16950524. S2CID3054752.