Geosmin

Geosmin
Names
IUPAC name
(4S,4aS,8aR)-4,8a-Dimethyl-1,2,3,4,5,6,7,-octahydronaphthalen-4a-ol
Other names
4,8a-Dimethyl-decahydronaphthalen-4a-ol; Octahydro-4,8a-dimethyl-4a(2H)-naphthalenol
Identifiers
19700-21-1 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:46702 YesY
ChemSpider 27642 YesY
ECHA InfoCard 100.039.294
PubChem 29746
Properties
C12H22O
Molar mass 182.31 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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Infobox references

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 C12H22O, 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.[7][8] 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.[9]

The smell after a rainstorm is also attributed to geosmin. (The smell before the rain is ozone.)[10]

References

  1. ↑ The earth's perfume, Protein Spotlight, Issue 35, June 2003.
  2. ↑ Gerber, NN; Lechevalier, HA (November 1965). "Geosmin, an earthly-smelling substance isolated from actinomycetes.". Applied microbiology. 13 (6): 935–8. PMC 1058374Freely accessible. PMID 5866039.
  3. ↑ 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.
  4. ↑ 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 3013058Freely accessible. PMID 17873868.
  5. ↑ "The genome of Streptomyces coelicolor A3(2) producing geosmin". Sanger Institute. Retrieved 2009-01-31.
  6. ↑ Polak, E.H.; Provasi, J. (1992). "Odor sensitivity to geosmin enantiomers". Chemical Senses. 17: 23. doi:10.1093/chemse/17.1.23.
  7. ↑ Vallod, D.; Cravedi, J. P.; Hillenweck, A.; Robin, J. (2007-04-03). "Analysis of the off-flavor risk in carp production in ponds in Dombes and Forez (France)". Aquaculture International. 15 (3-4): 287–298. doi:10.1007/s10499-007-9080-7. ISSN 0967-6120.
  8. ↑ Lovell, Richard T.; Lelana, Iwan Y.; Boyd, Claude E.; Armstrong, Martin S. (1986-05-01). "Geosmin and Musty-Muddy Flavors in Pond-Raised Channel Catfish". Transactions of the American Fisheries Society. 115 (3): 485–489. doi:10.1577/1548-8659(1986)1152.0.CO;2. ISSN 0002-8487.
  9. ↑ Winkler, Lawrence (2012-08-06). Westwood Lake Chronicles. Lawrence Winkler. ISBN 9780991694105.
  10. ↑ Yuhas, Daisy (18 July 2012). "Storm Scents: You Can Smell Oncoming Rain". Scientific American.

Further reading

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