Geosmin
Geosmin is an organic chemical compound with a distinct earthy odor produced by certain bacteria and fungi. The name is derived from the Greek words "geo" (earth) and "osme" (smell). Geosmin is responsible for the characteristic earthy taste in beets, and is a contributor to the muddy flavor sometimes found in drinking water and fish, particularly catfish.
Sources:
Geosmin is primarily produced by Streptomyces bacteria, cyanobacteria (blue-green algae), and some fungi. These microorganisms are commonly found in soil and water. When these organisms die, geosmin is released into the environment. Rain falling on soil can aerosolize geosmin, contributing to the characteristic "earthy" smell after a rain shower. In aquatic environments, geosmin produced by cyanobacteria can accumulate in the water, imparting an off-flavor to drinking water sources and affecting the taste of fish.
Impact on Water and Food:
Even at extremely low concentrations (as low as 5 parts per trillion), geosmin can be detected by humans. This high sensitivity makes it a significant concern for water treatment facilities and aquaculture. Geosmin is generally harmless, but its unpleasant taste and odor can make water and food unpalatable. Water treatment plants employ various methods to remove geosmin, including activated carbon filtration, ozone treatment, and biofiltration. In aquaculture, managing algae blooms and water quality is crucial to minimizing geosmin production.
Impact on Animal Behavior:
Geosmin has been shown to attract certain insects, including fruit flies. The compound acts as an olfactory cue, guiding them to suitable habitats for reproduction. Specific receptors on the fruit fly antenna bind to geosmin, triggering behavioral responses.
Chemical Properties:
Geosmin is a bicyclic alcohol with the chemical formula C12H22O. It is a colorless or pale yellow liquid that is soluble in organic solvents but only slightly soluble in water. The molecule contains a hydroxyl group and has a distinct stereochemistry, contributing to its unique odor profile.