Geosmin

Geosmin

Geosmin
Names
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 Y
ChEBI	CHEBI:46702 Y
ChemSpider	27642 Y
Jmol 3D model	Interactive image
PubChem	29746
InChI InChI=1S/C12H22O/c1-10-6-5-8-11(2)7-3-4-9-12(10,11)13/h10,13H,3-9H2,1-2H3/t10-,11+,12-/m0/s1 Y Key: JLPUXFOGCDVKGO-TUAOUCFPSA-N Y InChI=1/C12H22O/c1-10-6-5-8-11(2)7-3-4-9-12(10,11)13/h10,13H,3-9H2,1-2H3 /t10-,11+,12-/m0/s1
SMILES O[C@]12[C@H](CCC[C@]2(CCCC1)C)C
Properties
Chemical formula	C12H22O
Molar mass	182.31 g·mol−1
Boiling point	270 to 271 °C (518 to 520 °F; 543 to 544 K)
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y verify (what is YN ?)
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. 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.

In 2006, the biosynthesis of geosmin by a bifunctional Streptomyces coelicolor enzyme was unveiled. 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.

Effects

The human nose is extremely sensitive to geosmin and is able to detect it at concentrations as low as 5 parts per trillion.

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.)

Further reading

• The earth's perfume, Protein Spotlight, Issue 35, June 2003.