The smell of red beetroot gives off a bit of moisture, and we perceive it as normal. However, if our nose gets the same feeling from water or fish, then the food may be spoiled. The “earthy” smell of a compound called geosmin corresponds to this. German scientists have discovered and identified the olfactory receptors that respond to it.
Geosmin is a volatile organic compound produced by soil microbes. People perceive it as an earthy, musty odor. It usually comes from the soil after rain. It is found in plants such as cacti and beets.
Many animals experience geographic change. Some are repelled, others are attracted. For example, fruit flies are warned by the smell that food is spoiling. Camels, on the contrary, go to moisture because it indicates its proximity.
“This shows that geosmin acts as a chemical signal in the animal kingdom, including humans,” explained Lena Ball from the Leibniz Institute, first author of the paper published in the journal. Agricultural and Food Chemistry.
According to food chemist Stephanie Frank, a person can detect even small concentrations of geosmin in water: 4–10 nanograms per liter, which corresponds to a teaspoon dissolved in 200 Olympic-sized swimming pools.
Geosmin was discovered in 1965 and is an important ingredient in food production. However, it was still unknown which odor receptors in the nose detect it. This is now known thanks to research by scientists from the Leibniz Institute for Food Systems Biology at the Technical University of Munich (Germany), led by Dietmar Krautwurst.
The scientists tested 616 variants, only one of which responded to a physiologically important concentration of geosmin – OR11A1. They also checked whether it responded to other food odors. Of the 177 compounds, the receptor showed activity only for 2-ethylphenol, which smells like earth and is produced by microbes.
The researchers tested how the olfactory receptors of some of the animals most genetically similar to humans respond to geographic variation. These include kangaroo jumpers, mice, rhesus macaques, Sumatran orangutans, polar bears and camels. The scientists wanted to know if the same pre-geographic receptors had persisted throughout 100 million years of mammalian evolution, Ball said. The human and ape receptors turned out to be the least sensitive. Kangaroo-hopping rodents recognize geographic variation a hundred times better.
This study confirmed that geographic variation acts as a signal substance. Furthermore, its results will help to develop a recognition system to monitor the quality of food production, storage or to control freshwater quality.
Source: Port Altele
