“Caramel Receptor” Found
The research results of the Leibniz Institute of Food Systems Biology (LSB) contribute to a better understanding of the molecular coding of food flavors
© C. Schranner / LSB
Scientists in the laboratory of PD Dr. Krautwurst
“The test system we have developed is unique worldwide. We have genetically modified the test cells so that they act like small biosensors for odorants. In doing so, we specify exactly which type of odorant receptor they present on their cell surface. In this way, we can specifically investigate which receptor reacts how strongly to which odorant.”
PD Dr. Dietmar Krautwurst
Leibniz Institute of Food Systems Biology at the Technical University of Munich (LSB)
When the scent of caramel wafts through the house, hardly anyone can resist – almost everyone loves and knows this sweet, slightly burnt smell. So far unknown: the appropriate olfactory receptor that conveys this sensory impression. On Friday, October 12, 2021, the Leibniz Institute of Food Systems Biology at the Technical University of Munich (LSB) has now announced that the research team led by PD Dr. Dietmar Krautwurst has found the so-called “caramel receptor”.
Furaneol receptor previously unknown
When food is consumed, chemical odor codes are transferred into olfactory stimulus patterns. For this to happen, key odorants – such as furaneol in this case – must cooperate with one or more of the 400 olfactory receptors in the nose. As a natural odorant, furaneol is not only found in bread or coffee; it also gives many fruits such as strawberries or pineapples a special caramel-like scent. The substance is also used in food production. The type of odorant receptor through which the caramel odorant furaneol with the chemical name 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) is perceived by humans was unknown until now. This is true for 80 percent of human odorant receptor types, for which the odorant spectrum has not yet been identified despite intensive research efforts.
Targeted screening of human olfactory receptors
The team led by PD Dr. Dietmar Krautwurst is using a collection of all human olfactory receptor genes and their most common genetic variants for its research in order to decipher their function using a test cell system. In their current study, the researchers reviewed a total of 391 human olfactory receptor types and 225 of their most common variants. According to Dr. Krautwurst, their developed test system is unique in the world: the test cells were genetically modified to function like small biosensors for odorants. This allowed them to specifically analyze which receptor reacts to which odorant and at what strength.
© G. Olias / LSB
Furaneol and strawberries: The odorant furaneol gives strawberries and other foods a caramel-like aroma.
Furaneol and coffee: The odorant furaneol gives coffee and other foods a caramel-like aroma.
Receptor OR5M3 with specific recognition spectrum
According to Dr. Franziska Haag, first author of the study, the study results show that furaneol activates only the odor receptor OR5M3. “Here, even one thousandth of a gram of the odorant per liter is sufficient to generate a signal,” Dr. Haag explains. To find out whether the receptor reacts to other odorants, the LSB researchers analyzed 186 other so-called key food odorants. They found only one more: Homofuraneol, which is also responsible for a caramel-like aroma, among others in fruits such as durian (civet fruit).
Commenting on the results, Dr. Dietmar Krautwurst said, “We assume that the receptor OR5M3 we identified has a very specific recognition spectrum for food ingredients that smell caramel-like.” In the future, this knowledge could be used to develop new biotechnologies that can be used to quickly and easily check the sensory quality of corresponding foods along the entire value chain, the molecular biologist said. “In the future, we at the institute will continue to use our extensive odorant and receptor collections to help elucidate the molecular basis of human olfactory perception. After all, this significantly influences our food choices and thus our health,” adds Prof. Dr. Veronika Somoza, Director of the Leibniz Institute in conclusion.
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