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 | 182.3 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, which literally translates to "earth smell", is an organic compound with a distinct earthy flavour and aroma, and 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.
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[edit] Production
Geosmin is produced by several classes of microbes, including cyanobacteria (blue-green algae) 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 by Jiang et al.[2][3] A single enzyme, the germacradienol/germacrene D synthase converts farnesyl diphosphate to geosmin in a two-step reaction.
Streptomyces coelicolor is the model representative of a group of soil-dwelling organisms with a complex life cycle involving mycelial growth and spore formation. Beside 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]
[edit] Effects
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 also 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.
[edit] See also
[edit] References
- ^ Gerber, NN; Lechevalier, HA (November 1965). "Geosmin, an earthly-smelling substance isolated from actinomycetes.". Applied microbiology 13 (6): 935–8. PMC 1058374. PMID 5866039. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1058374.
- ^ 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. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3013058.
- ^ "The genome of Streptomyces coelicolor A3(2) producing geosmin". Sanger Institute. http://www.sanger.ac.uk/Projects/S_coelicolor/. 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.
[edit] 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.
