The aroma of caramel is liked by most, but to date, the olfactory receptor that contributes decisively to this sensory impression was not known. Scientists from the Leibniz Institute for Food Systems Biology at the Technical University of Munich (LSB) recently solved the mystery of its existence and discovered the “caramel receptor”. This understanding may help comprehend the molecular coding of food flavors.
The odorant furaneol gives coffee and other foods a caramel-like aroma. Image Credit: Leibniz Institute for Food Systems Biology at the Technical University of Munich
Furaneol, a natural odorant, provides various fruits like strawberries and also coffee or bread a caramel-like scent. In food production too, the substance has played a vital role as a flavoring agent. However, to date, it was not known which of the approximately 400 various types of olfactory receptors humans employ to perceive this odorant.
Odorant receptors put to the test
In spite of in-depth research, only for about 20% of human olfactory receptors it is known which odorant spectrum they recognize. To illustrate the recognition spectra, the researchers headed by Dietmar Krautwurst at LSB employed a collection of all human olfactory receptor genes and their most common genetic variants to decode their function with a test cell system.
The test system we developed is unique in the world. 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.”
Dietmar Krautwurst, Leibniz Institute for Food Systems Biology, Technical University of Munich
In the current research, the scientists analyzed a total of 391 human odorant receptor types and 225 of their most common variants.
Only two odorants for one receptor
As our results show, furaneol activated only the OR5M3 odorant receptor. Even one thousandth of a gram of the odorant per liter is sufficient to generate a signal.”
Franziska Haag, Study First Author, Leibniz Institute for Food Systems Biology, Technical University of Munich
Moreover, the researchers also examined whether the receptor also reacts to other odorants. Until recently, the researchers analyzed 186 other substances that are major odorants and hence perform a vital role in shaping the aroma of food. But, of these, only homofuraneol could activate the receptor.
The odorant is structurally similar to furaneol. Earlier research works by LSB show that it provides a caramel-like aroma to fruits like durian.
Dietmar Krautwurst also adds, “We hypothesize that the receptor we identified, OR5M3, 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 foods along the entire value chain.”
The molecular biologists also state that even though there is a great deal to be done, to comprehend the complex interplay between the approximately 230 key food-related odorants and human olfactory receptors, this research proves a start to it.
In the future, we will continue to use our extensive odorant and receptor collections at the Institute to help elucidate the molecular basis of human olfactory perception. After all, this significantly influences our food choices and thus our health.”
Veronika Somoza, Director, Leibniz Institute for Food Systems Biology, Technical University of Munich
Haag, F., et al. (2021) Key Food Furanones Furaneol and Sotolone Specifically Activate Distinct Odorant Receptors. Journal of Agricultural and Food Chemistry. doi.org/10.1021/acs.jafc.1c03314.