Who doesn’t love the smell of caramel? However, the olfactory receptor that decisively contributes to this sensory impression was hitherto unknown. Researchers at the Leibniz Institute for Food Systems Biology at the Technical University of Munich (LSB) have now solved the mystery of its existence and identified the “caramel receptor”. The new knowledge contributes to a better understanding of the molecular coding of food flavourings.
Furaneol is a natural odorant that gives many fruits such as strawberries, but also coffee or bread, a caramel smell. Likewise, the substance has long played an important role as a flavoring agent in food production. Nevertheless, until now it was unknown which of the approximately 400 different types of olfactory receptors that humans use to perceive this odorant.
Olfactory receptors put to the test
This is not an isolated case. Despite intensive research, only about 20% of human olfactory receptors are still known which odor spectrum they recognize. To help elucidate recognition spectra, the team led by Dietmar Krautwurst at LSB is using a collection of all human olfactory receptor genes and their most common genetic variants to decipher their function using a cell system of testing.
“The test system we have developed is unique in the world. We have genetically modified the test cells so that they act as small biosensors for odorants. In doing so, we specify exactly what type of odorant receptor they present on their cell surface. In this way, we can specifically study which receptor reacts with which strength to which odorant, “explains Dietmar Krautwurst. In the present study, the researchers examined a total of 391 types of human olfactory receptors and 225 of their most common variants.
Only two odorants for one receiver
“As our results show, furaneol only activated the odorant receptor OR5M3. Even one thousandth of a gram of the odorant per liter is enough to generate a signal,” explains the study’s first author Franziska Haag. Additionally, the team investigated whether the receptor also reacted to other odorants. To this end, the team looked at 186 other substances that are key odorants and therefore play a major role in the formation of food aroma. Of these, however, only homofuranol was able to significantly activate the receptor.
This odorant is structurally closely related to furaneol. As previous studies on LSB have shown, it imparts a caramel flavor to fruits such as durian. “We hypothesize that the receptor we have identified, OR5M3, has a very specific recognition spectrum for food ingredients that smell like caramel. In the future, this knowledge could be used to develop new biotechnologies that can be used to quickly and easily check the quality of food throughout the value chain”, says Dietmar Krautwurst. Although there is still a long way to go to understand the complex interplay between the approximately 230 key odorants linked to the food and human olfactory receptors, a start has been made, adds the molecular biologist.
Veronika Somoza, Director of the Leibniz Institute adds: “In the future, we will continue to use our vast collections of odorants and receptors at the Institute to help elucidate the molecular basis of human olfactory perception. After all, it greatly influences our food choices and thus our health.”