Geosmin
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| IUPAC name
(4S,4aS,8aR)-4,8a-Dimethyl-1,2,3,4,5,6,7,8-octahydronaphthalen-4a-ol
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| Other names
4,8a-Dimethyl-decahydronaphthalen-4a-ol; Octahydro-4,8a-dimethyl-4a(2H)-naphthalenol
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| Identifiers | |
3D model (JSmol)
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| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.039.294 |
PubChem CID
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CompTox Dashboard (EPA)
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| Properties | |
| C12H22O | |
| Molar mass | 182.307 g·mol−1 |
| Boiling point | 270 to 271 °C (518 to 520 °F; 543 to 544 K) |
| Hazards | |
| Flash point | 104 °C (219 °F; 377 K) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Geosmin is an organic compound with a distinct earthy flavor and aroma produced by a type of Actinobacteria, and is responsible for the earthy taste of beets and a contributor to the strong scent (petrichor) that occurs in the air when rain falls after a dry spell of weather or when soil is disturbed.[1] In chemical terms, it is a bicyclic alcohol with formula Template:Chemical formula, a derivative of decalin. Its name is derived from the Greek γεω- "earth" and ὀσμή "smell".
Production
Geosmin is produced by the gram-positive bacteria Streptomyces, a genus of Actinobacteria in the order Actinomycetales, and released when these microorganisms die. Communities whose water supplies depend on surface water can periodically experience episodes of unpleasant-tasting water when a sharp drop in the population of these bacteria releases geosmin into the local water supply. Under acidic conditions, geosmin decomposes into odorless substances.[2]
In 2006, the biosynthesis of geosmin by a bifunctional Streptomyces coelicolor enzyme was unveiled.[3][4] A single enzyme, geosmin synthase, converts farnesyl diphosphate to geosmin in a two-step reaction.
Streptomyces coelicolor is the model representative of a group of soil-dwelling bacteria with a complex lifecycle involving mycelial growth and spore formation. Besides the production of volatile geosmin, it also produces many other complex molecules of pharmacological interest; its genome sequence is available at the Sanger Institute.[5]
Effects
The human nose is extremely sensitive to geosmin and is able to detect it at concentrations as low as 5 parts per trillion.[6]
Geosmin is responsible for the muddy smell in many commercially important freshwater fish such as carp and catfish. Geosmin combines with 2-methylisoborneol, which concentrates in the fatty skin and dark muscle tissues. Geosmin breaks down in acid conditions; hence, vinegar and other acidic ingredients are used in fish recipes to help reduce the muddy flavor.
The smell after a rainstorm is also attributed to geosmin. (The smell before the rain is ozone.)[7]
References
- ^ The earth's perfume, Protein Spotlight, Issue 35, June 2003.
- ^ Gerber, NN; Lechevalier, HA (November 1965). "Geosmin, an earthly-smelling substance isolated from actinomycetes". Applied microbiology. 13 (6): 935–8. PMC 1058374. PMID 5866039.
- ^ Jiang, J.; He, X.; Cane, D.E. (2006). "Geosmin biosynthesis. Streptomyces coelicolor germacradienol/germacrene D Synthase converts farnesyl diphosphate to geosmin". J. Am. Chem. Soc. 128 (25): 8128–8129. doi:10.1021/ja062669x. PMID 16787064.
- ^ Jiang, J.; He, X.; Cane, D.E. (2007). "Biosynthesis of the earthy odorant geosmin by a bifunctional Streptomyces coelicolor enzyme". Nat. Chem. Biol. advanced online publication. 3 (11): 711–5. doi:10.1038/nchembio.2007.29. PMC 3013058. PMID 17873868.
{{cite journal}}: Italic or bold markup not allowed in:|journal=(help) - ^ "The genome of Streptomyces coelicolor A3(2) producing geosmin". Sanger Institute. Retrieved 2009-01-31.
- ^ Polak, E.H.; Provasi, J. (1992). "Odor sensitivity to geosmin enantiomers". Chemical Senses. 17: 23. doi:10.1093/chemse/17.1.23.
- ^ Yuhas, Daisy (18 July 2012). "Storm Scents: You Can Smell Oncoming Rain". Scientific American.
Further reading
- Bear, I.J.; R.G. Thomas (1964). "Nature of argillaceous odour". Nature. 201 (4923): 993–995. doi:10.1038/201993a0.
- Bear, I.J.; R.G. Thomas (1965). "Petrichor and plant growth". Nature. 207 (5005): 1415–1416. doi:10.1038/2071415a0.