The olfactory receptor that contributes decisively to this sensory impression was recently uncovered by researchers at the Leibniz Institute for Food Systems Biology at the Technical University of Munich (LSB), in Germany.

Identifying the existence of the “caramel receptor” is hailed as a significant step toward a better understanding of the molecular coding of food flavors.

“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,” says Dietmar Krautwurst, lead researcher of the study.

The receptor is sensitive to furaneol, a natural odorant that gives numerous fruits such as strawberries – but also coffee or bread – a caramel-like scent. 

The substance has long played an important role as a flavoring agent in food production. Nevertheless, until now it was unknown which of the estimated 400 different types of olfactory receptors humans use to perceive this odorant.

Odorant receptors put to the test
Despite intensive research, scientists have uncovered the functions of roughly 20% of human olfactory receptors.

Although there is still a long way to go to understand the complex interplay between the approximately 230 key food-related odorants and human olfactory receptors, a start has been made, notes Krautwurst.

Despite intensive research, scientists have uncovered the functions of roughly 20% of human olfactory receptors.To help elucidate this recognition spectra, the team led by 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 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,” explains Krautwurst.

“In this way, we can specifically investigate which receptor reacts and how strongly to which odorant.”

In the study, the researchers examined a total of 391 human odorant receptor types and 225 of their most common variants. 

only two odorants for one receptor
As the results show, furaneol only activated the OR5M3 odorant receptor. 

“Even one thousandth of a gram of the odorant per liter is sufficient to generate a signal,” remarks first author of the study, Franziska Haag. 

In addition, the team investigated whether the receptor also reacts to other odorants. To this end, the team examined 186 other key odorants that play a major role in shaping the aroma of food. 

Of these, however, only homofuraneol was able to significantly activate the receptor.

This odorant is structurally closely related to furaneol. As shown by previous LSB studies, it imparts a caramel-like aroma to fruits, such as durian. 

“We will continue to use our extensive odorant and receptor collections at the Institute to help elucidate the molecular basis of human olfactory perception,” says Veronika Somoza, director of the Leibniz Institute.

“After all, this significantly influences our food choices and thus our health.”

Craving caramel
Caramel, particularly salted caramel, is still a key flavor in trend-driven indulgent product development. 

Beneficial health properties have been newly attributed to the ingredient. A recent study found that the greater the degree of caramelization, the greater its antioxidant activities could be, with the daily ingestion of caramel colors said to be “almost equivalent to a glass of orange juice.”

Barry Callebaut recently tapped into consumer appetite for this profile in its launch of Caramel Aura, a warm and golden-hued chocolate emulating decadence.