Butanoic Acid Information
Butyric acid (from Greek βούτυρο, meaning "butter"), also known under the systematic name butanoic acid, is a carboxylic acid with the structural formula C H3CH2CH2-COOH. Salts and esters of butyric acid are known as butyrates or butanoates. Butyric acid is found in butter, Parmesan cheese, and vomit, and as a product of anaerobic fermentation (including in the colon and as body odor). It has an unpleasant smell and acrid taste, with a sweetish aftertaste (similar to ether). It can be detected by mammals with good scent detection abilities (such as dogs) at 10 ppb, whereas humans can detect it in concentrations above 10 ppm.
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Chemistry
Butyric acid is a fatty acid occurring in the form of esters in animal fats and plant oils. The triglyceride of butyric acid makes up 3% to 4% of butter. When butter goes rancid, butyric acid is liberated from the glyceride by hydrolysis, leading to the unpleasant odor. It is an important member of the fatty acid subgroup called short-chain fatty acids. Butyric acid is a weak acid with a pKa of 4.82, similar to acetic acid, which has pKa of 4.76.[1] The similar strength of these acids results from their common -CH2COOH terminal structure.[2] Pure butyric acid is 10.9 molar.
The acid is an oily, colorless liquid that is easily soluble in water, ethanol, and ether, and can be separated from an aqueous phase by saturation with salts such as calcium chloride. Potassium dichromate and sulfuric acid oxidize it to carbon dioxide and acetic acid, while alkaline potassium permanganate oxidizes it to carbon dioxide. The calcium salt, Ca(C4H7O2)2·H2O, is less soluble in hot water than in cold.
Butyric acid has a structural isomer called isobutyric acid (2-methylpropanoic acid).
Production
It is industrially prepared by the fermentation of sugar or starch, brought about by the addition of putrefying cheese, with calcium carbonate added to neutralize the acids formed in the process. The butyric fermentation of starch is aided by the direct addition of Bacillus subtilis. Salts and esters of the acid are called butyrates or butanoates.
Butyric acid or fermentation butyric acid is also found as a hexyl ester hexyl butyrate in the oil of Heracleum giganteum (a type of hogweed) and as the octyl ester octyl butyrate in parsnip (Pastinaca sativa); it has also been noticed in the fluors of the flesh and in perspiration.
Uses
Butyric acid is used in the preparation of various butyrate esters. Low-molecular-weight esters of butyric acid, such as methyl butyrate, have mostly pleasant aromas or tastes. As a consequence, they find use as food and perfume additives. It is also used as an animal feed supplement, due to the ability to reduce pathogenic bacterial colonisation.[3] It is an approved food flavouring in the EU FLAVIS database (number 08.005).
Due to its powerful odor, it has also been used as a fishing bait additive.[4] Many of the commercially available flavours used in carp (Cyprinus carpio) baits use butyric acid as their ester base; however, it is not clear whether fish are attracted by the butyric acid itself or the additional substances added to it. Butyric acid was, however, one of the few organic acids shown to be palatable for both tench and bitterling.[5]
The substance has also been used as a noxious, nausea-inducing repellent by antiwhaling protesters to disrupt Japanese whaling crews,[6] as well as by antiabortion protesters to disrupt abortion clinics.[7]
Biochemistry
Biosynthesis
Butyrate is produced as end-product of a fermentation process solely performed by obligate anaerobic bacteria. Fermented Kombucha "tea" includes butyric acid as a result of the fermentation. This fermentation pathway was discovered by Louis Pasteur in 1861. Examples of butyrate-producing species of bacteria:
- Clostridium acetobutylicum
- Clostridium butyricum
- Clostridium kluyveri
- Clostridium pasteurianum
- Fusobacterium nucleatum
- Butyrivibrio fibrisolvens
- Eubacterium limosum
The pathway starts with the glycolytic cleavage of glucose to two molecules of pyruvate, as happens in most organisms. Pyruvate is then oxidized into acetyl coenzyme A using a unique mechanism that involves an enzyme system called pyruvate-ferredoxin oxidoreductase. Two molecules of carbon dioxide (CO2) and two molecules of elemental hydrogen (H2) are formed as waste products from the cell. Then,
| Action | Responsible enzyme |
|---|---|
| Acetyl coenzyme A converts into acetoacetyl coenzyme A | acetyl-CoA-acetyl transferase |
| Acetoacetyl coenzyme A converts into β-hydroxybutyryl CoA | β-hydroxybutyryl-CoA dehydrogenase |
| β-hydroxybutyryl CoA converts into crotonyl CoA | crotonase |
| Crotonyl CoA converts into butyryl CoA (CH3CH2CH2C=O-CoA) | butyryl CoA dehydrogenase |
| A phosphate group replaces CoA to form butyryl phosphate | phosphobutyrylase |
| The phosphate group joins ADP to form ATP and butyrate | butyrate kinase |
ATP is produced, as can be seen, in the last step of the fermentation. Three molecules of ATP are produced for each glucose molecule, a relatively high yield. The balanced equation for this fermentation is
- C6H12O6 → C4H8O2 + 2CO2 + 2H2.
Several species form acetone and n-butanol in an alternative pathway, which starts as butyrate fermentation. Some of these species are:
- Clostridium acetobutylicum, the most prominent acetone and butanol producer, used also in industry
- Clostridium beijerinckii
- Clostridium tetanomorphum
- Clostridium aurantibutyricum
These bacteria begin with butyrate fermentation, as described above, but, when the pH drops below 5, they switch into butanol and acetone production to prevent further lowering of the pH. Two molecules of butanol are formed for each molecule of acetone.
The change in the pathway occurs after acetoacetyl CoA formation. This intermediate then takes two possible pathways:
- acetoacetyl CoA → acetoacetate → acetone
- acetoacetyl CoA → butyryl CoA → butanal → butanol
Highly-fermentable fiber residues, such as those from resistant starch, oat bran, pectin, and guar are transformed by colonic bacteria into short-chain fatty acids (SCFA) including butyrate, producing more SCFA than less fermentable fibers such as celluloses.[8] One study found that resistant starch consistently produces more butyrate than other types of dietary fiber.[9] The production of SCFA from fibers in ruminant animals such as cattle is responsible for the butyrate content of milk and butter.[10]
Cancer and life span
The role of butyrate changes differs between normal and cancerous cells. This is known as the "butyrate paradox". Butyrate inhibits colonic tumor cells, and promotes healthy colonic epithelial cells;[11] but the signaling mechanism is not well understood.[12] A review suggested the chemopreventive benefits of butyrate depend in part on amount, time of exposure with respect to the tumorigenic process, and the type of fat in the diet.[8] The production of volatile fatty acids such as butyrate from fermentable fibers may contribute to the role of dietary fiber in colon cancer.[8]
Butyric acid can act as an HDAC inhibitor, inhibiting the function of histone deacetylase enzymes, thereby favoring an acetylated state of histones in the cell. Acetylated histones have a lower affinity for DNA than nonacetylated histones, due to the neutralization of electrostatic charge interactions. In general, it is thought that transcription factors will be unable to access regions where histones are tightly associated with DNA (i.e., nonacetylated, e.g., heterochromatin). Therefore, butyric acid is thought to enhance the transcriptional activity at promoters, which are typically silenced or downregulated due to histone deacetylase activity.
Two HDAC inhibitors, sodium butyrate (NaB) and trichostatin A (TSA), increase lifespan in experimental animals.[13]
See also
- Indole-3-butyric acid
- Acids in wine
- Gamma-Hydroxybutyric acid
References
This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press.
- ^ "Adimix Sodium Butanoate information". http://linkan.se/files/pdf/product_sheets/INVE/adimix_presentation.pdf.
- ^ "Using the pKa table". http://web.chem.ucla.edu/~harding/tutorials/acids_and_bases/pKa_table.html.
- ^ Supplementation of Coated Butyric Acid in the Feed Reduces Colonization and Shedding of Salmonella in Poultry
- ^ Freezer Baits, nutrabaits.net
- ^ Kasumyan, A.O.; Døving, K.B. (2003). "Taste preferences in fishes". Fish and Fisheries 4 (4): 289–347. doi:10.1046/j.1467-2979.2003.00121.x.
- ^ Japanese Whalers Injured by Acid-Firing Activists, newser.com, February 10, 2010
- ^ National Abortion Federation, HISTORY OF VIOLENCE Butyric Acid Attacks
- ^ a b c Lupton, Joanne R. (2004). "Microbial Degradation Products Influence Colon Cancer Risk: the Butyrate Controversy". Journal of Nutrition 134 (2): 479–82. PMID 14747692. http://jn.nutrition.org/cgi/content/full/134/2/479.
- ^ Cummings JH, Macfarlane GT, Englyst HN (2001). "Prebiotic digestion and fermentation". American Journal of Clinical Nutrition 73 (suppl): 415S–20S. PMID 11157351.
- ^ Grummer, Ric R. (1991). "Effect of feed on the composition of milk fat". J Dairy Sci 74 (9): 3244–57. doi:10.3168/jds.S0022-0302(91)78510-X. PMID 1779073. http://download.journals.elsevierhealth.com/pdfs/journals/0022-0302/PIIS002203029178510X.pdf.
- ^ Vanhoutvin, SA; Troost, FJ; Hamer, HM; Lindsey, PJ; Koek, GH; Jonkers, DM; Kodde, A; Venema, K et al. (2009). Bereswill, Stefan. ed. "Butyrate-Induced Transcriptional Changes in Human Colonic Mucosa". PloS one 4 (8): e6759. doi:10.1371/journal.pone.0006759. PMC 2727000. PMID 19707587. http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0006759.
- ^ Klampfer, L; Huang, J; Sasazuki, T; Shirasawa, S; Augenlicht, L (2004). "Oncogenic Ras Promotes Butyrate-induced Apoptosis through Inhibition of Gelsolin Expression". The Journal of biological chemistry 279 (35): 36680–8. doi:10.1074/jbc.M405197200. PMID 15213223. http://www.jbc.org/content/279/35/36680.full.pdf.
- ^ Zhang, M; Poplawski, M; Yen, K; Cheng, H; Bloss, E; Zhu, X; Patel, H; Mobbs, CV et al. (2009). Dillin, Andy. ed. "Role of CBP and SATB-1 in Aging, Dietary Restriction, and Insulin-Like Signaling". PLoS biology 7 (11): e1000245. doi:10.1371/journal.pbio.1000245. PMC 2774267. PMID 19924292. http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1000245.
External links
- International Chemical Safety Card 1334
- 2004 review of the scientific evidence on butanoate/butyrate vs. colon cancer
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