The smell was one of the senses that remained a mystery for the science community for a long time. It was in 1991 when Linda Buck and Richard Axel discovered the large family of genes associated with the olfactory receptors and realized that neurons in the olfactory epithelium have only one kind of receptor. For their findings, they received the Nobel Prize in 2004 (1) and this promoted a lot of research on the topic.
Today we know that we can smell because of our olfactory sensory neurons present in our nose epithelia. Each of these neurons has one kind of odor receptor, which binds the different molecules that we are constantly inhaling from the environment (Image 1). These volatile molecules are known as odorants(2), and once the neuron detects the odorant, it sends a message to the brain, which recognizes the smell(3). The human has 400 types of olfactory receptors allowing a lot of possibilities for different patterns.
There are innumerable odorants in nature. Geraniol (Image 2) for example, is a terpenic alcohol present in roses and citronellas, and is commonly used in fragrances for its floral, sweet and fruity smell. Aldehydic compounds, like aldehydes C-10, C-11 and C-12 are characterized by a metallic and citrusy smell, in fact, these three molecules are present in the famous perfume Chanel N°5 (4). Sometimes, odor compounds with the same functional group have similar odors (like the case of aldehydes), but in other cases, really small changes in the molecule's structure can present a different odor profile(5). The stereoisomers of the carvone (Image 3) present different aromas, the R-carvone has a minty and sweetish smell while the S-carvone is mentholated and spicy(6). A lot of studies have tried to find if there is a relation between the structure and the smell, but it is definitely not an easy job, it depends on which receptors the odorant binds.
Even though the effort to uncover the mystery of smell has increased during the last decades, we still have a lot of orphan receptors. The term orphan receptor refers to a receptor whose ligands (in this case odorants) haven't been identified, so we don't know what type of molecule can activate it. But what if we were able to recognize which receptors are activated during a really pleasant smell, or during an unpleasant one, could we use other molecules to increase or block a specific odor? Could we manipulate the smell? Turns out that Chemcom, a company in Brussels is already working on this: they even developed an artificial human nose (7), amazing, isn´t it? This company has deorphanized more than 120 olfactory receptors, but this is not the best part: Chemcom has identified which of our receptors are involved in an enjoyable smell, like a floral, marine, or fruity odor and also knows which receptors are active when we smell sweat or mildew. With this information, the company can develop and recognize enhancers and antagonists to reduce or increase the type of smell we are interested in.
This kind of technology offers a lot of possibilities and has different applications. It allows a new approach to eliminating the malodors (present not only in the environment but also in some personal care products due to an active or raw material). Instead of covering the malodor with a likable and intense smell, we can use antagonists, molecules that block the receptors and reduce the interaction with the specific odorant, so the response to that particular odor is significantly decreased. By contrast, we can use enhancers to intensify the perception of certain compounds, which are especially useful for raw materials in fragrances that are expensive, allergens, or are restricted because of the effects on the environment.
Therefore, the answer is yes, we can modify the smell! And it is pretty useful, we can combat malodors, reduce the cost of a fragrance, make it safer and also friendlier with the environment. We can do more, with less.
1. The Nobel Prize in Physiology or Medicine 2004. (2004). Retrieved 28 November 2021, from https://www.nobelprize.org/prizes/medicine/2004/press-release/
2. Di Pizio, Antonella; Niv, Masha Y. (2014). Computational Studies of Smell and Taste Receptors. Israel Journal of Chemistry, 54(8-9), 1205–1218. doi:10.1002/ijch.201400027
3. Smell Disorders. (2017). Retrieved 30 November 2021, from https://www.nidcd.nih.gov/health/smell-disorders
4. Aldehydes - The Perfume Society. Retrieved 28 November 2021, from https://perfumesociety.org/ingredients-post/aldehydes/
5. Genva, M., Kenne Kemene, T., Deleu, M., Lins, L., & Fauconnier, M. (2019). Is It Possible to Predict the Odor of a Molecule on the Basis of its Structure?. International Journal Of Molecular Sciences, 20(12), 3018. doi: 10.3390/ijms20123018
6. Morcia, C., Tumino, G., Ghizzoni, R., & Terzi, V. (2016). Carvone (Mentha spicata L.) Oils. Essential Oils In Food Preservation, Flavor And Safety, 309-316. doi: 10.1016/b978-0-12-416641-7.00035-3
7. ChemCom. (2022). Retrieved 7 December 2021, from http://chemcom.be/