Geosmin
| Geosmin | |
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(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 | |
| CAS number | 19700-21-1  |
| PubChem | 29746 |
| ChemSpider | 27642 |
| ChEBI | CHEBI:46702 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | C12H22O |
| Molar mass | 182.30 g mol−1 |
| Boiling point |
270-271 °C, 543-544 K, 518-520 °F |
| Hazards | |
| Flash point | 104 °C (219 °F) |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Geosmin is an organic compound with a distinct earthy flavor and aroma, 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. It is produced by a variety of microorganisms. Chemically, it is a bicyclic alcohol with formula C12H22O, a derivative of decalin. Its name is derived from the Greek γεω- "earth" and ὀσμή "smell".
Contents |
Production [edit]
Geosmin is produced by several classes of microbes, including cyanobacteria and actinobacteria (especially Streptomyces), and released when these microbes 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.[1]
In 2006, the biosynthesis of geosmin by a bifunctional Streptomyces coelicolor enzyme was unravelled.[2][3] 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 life cycle 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.[4]
Effects [edit]
Geosmin is responsible for the earthy taste of beets and a contributor to the strong scent that occurs in the air when rain falls after a dry spell of weather (petrichor) or when soil is disturbed.[5] 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 bottom-dwelling freshwater fish such as carp and catfish. Cyanobacteria produce geosmin and 2-methylisoborneol, which concentrate in the skin and dark muscle tissue. Geosmin breaks down in acid conditions; hence vinegar and other acidic ingredients in fish recipes help reduce the muddy flavor.
The smell after a rainstorm is also attributed to geosmin. (The smell before the rain is ozone.)[7]
References [edit]
- ^ 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.; X. He, D.E. Cane (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.; X. He, D.E. Cane (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.
- ^ "The genome of Streptomyces coelicolor A3(2) producing geosmin". Sanger Institute. Retrieved 2009-01-31.
- ^ The earth's perfume, Protein Spotlight, Issue 35, June 2003.
- ^ 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 [edit]
- 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.
