Geosmin

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Geosmin
IUPAC name

(4S,4aS,8aR)-4,8a-Dimethyl-1,2,3,4,5,6,7,8-octahydronaphthalen-4a-ol

Other names

4,8a-Dimethyl-decahydronaphthalen-4a-ol; Octahydro-4,8a-dimethyl-4a(2H)-naphthalenol

Identifiers
CAS number 19700-21-1 YesY
PubChem 29746
ChemSpider 27642 YesY
ChEBI CHEBI:46702 YesY
Jmol-3D images {{#if:O[C@]12[C@H](CCC[C@]2(CCCC1)C)C|Image 1
Properties
Molecular formula C12H22O
Molar mass 182.30 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
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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 type of Actinobacteria. 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.[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 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.[4]

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 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

  1. ↑ Gerber, NN; Lechevalier, HA (November 1965). "Geosmin, an earthly-smelling substance isolated from actinomycetes.". Applied microbiology 13 (6): 935–8. PMC 1058374. PMID 5866039. 
  2. ↑ 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. 
  3. ↑ 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. 
  4. ↑ "The genome of Streptomyces coelicolor A3(2) producing geosmin". Sanger Institute. Retrieved 2009-01-31. 
  5. ↑ The earth's perfume, Protein Spotlight, Issue 35, June 2003.
  6. ↑ Polak, E.H.; Provasi, J. (1992). "Odor sensitivity to geosmin enantiomers". Chemical Senses 17: 23. doi:10.1093/chemse/17.1.23. 
  7. ↑ 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. 
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