The smell of vanilla is a favorite in 10 different cultures Listen to this article

The aroma of vanilla or orange blossoms is pleasant for New Yorkers, aunts from the jungles of northern Ecuador, or students at Ubon Ratchathani University in Thailand. On the other hand, the smell of rotting onions or feet is unpleasant for residents of Mexico City, the Mah Meri fishermen of the Malay Peninsula or the hunter-gatherer seri of the Gulf of California. A recently published study suggests that, with great individual variability, the positive or negative valence of odors is universal.

Science has not advanced as much with smell as with other senses. Visually, for example, by knowing the wavelength of light, you can guess what color it is. With the ear, the frequency of the sound wave allows us to know what sound it is. But knowing the chemical structure of a molecule cannot predict well what it will smell like. In addition to the thousands of possible combinations of a compound (atomic structure, molecular weight, concentration…) each one’s environment, in the aroma that accompanies it since childhood. In fact, for a good portion of scientists in this field, smelling good or bad basically depended on the culture.

A study published on Monday current biology It downplays the importance of culture and bets on the universal validity of smell. The researchers selected 10 molecules from a previous study from a large sample of about 500 scents and presented them to 235 people from 10 different cultures over multiple sessions. In addition to some twenty residents of Mexico City and New York, the sample also included people from traditional communities from Malaysia to Ecuador, more or less exposed to Western culture. The hypothesis was that if odor is shaped by culture, the results must be very different.

Studies show that there is a great deal of variability within each community. But, on average, they all like similar fragrances and dislike similar smells. 4-Hydroxy-3-methoxybenzaldehyde, i.e. vanillin, the parent compound of vanilla pods, is the most pleasant molecule for the communities participating in the study. Ethyl butyrate, present in many fruits and which gives that distinctive aroma to pineapple or mango, is also highly appreciated in different parts of the planet. Synthesized, it is an essential additive in packaged citrus juices. Linalool, a component of many aromatic plants, or phenethyl alcohol from roses, carnations, orange blossom or green pine also appears to be highly graded.

“Culture plays a very small role in determining how pleasant a smell is”

Asifa Majid, Professor at the University of Oxford and expert in the perception of smell and language

Professor Asifa Majid of the University of Oxford, co-author of the research, acknowledges that “a number of previous ethnographic studies in different communities have suggested that cultures may vary widely in terms of smells perceived as pleasant and unpleasant, but he Did not test experimentally with a wide range of cultures. Their study, he says, “fills in this gap by testing them in very different settings, including hunter-gatherers and small-scale farmers, as well as people living in large cities in different parts of the world.” Majid, who did this work at the University of York, concludes that “culture plays a very small role in determining how pleasant a smell is. Neuroscientist Artin Arshmian, her colleague at the Karolinska Institute in Stockholm, Sweden, and the study’s first author, agrees: “We are not saying that learning does not affect odor (or taste) preferences. Of course they do! What we are saying is that culture has little effect on the perception of pure smell.”

Bad smell also seems universal. At the opposite end of vanilla’s spectrum, the molecule ranked worst by participants, whether Malaysian, Mexican or Ecuadorian, was isovaleric acid, which was present in both human sweat and rancid animal and vegetable fats. It smells of some French or Northern Spanish cheeses. Diethyl disulfide is also the most stinky that comes from overripe onions or rotten potatoes. And a third malodorous compound is octanoic or caprylic acid, which is naturally present in the fat of palm or coconut oil and mammalian milk.

One possible limitation of the work is that they only used 10 molecules. But Arshmian explains: “We selected odorants based on a previous study with industrialized urban residents in the United States (New York City), which evaluated the pleasantness of 476 different molecules.” From them he selected a category “which covers the validity from unpleasant to pleasant”, he added. They used the remaining 466 odorants to build a prediction model based on the molecular structure of each odorant. “Thus, although the odors to be tested are few, the model is based on a very large set. It is important to note that ten odorants were not included while constructing the model and yet the model was able to predict the classification of odors”, concludes the researcher.

The study with nearly 500 of those odors was published in 2016, So 480 molecules with very different molecular weights or complexity were used. 0 were compounds with molecular complexity, such as water or iodine, up to molecules, such as androstenedione, a steroid related to a pheromone, the value of which indicates a very complex structure of 564 macromolecules. That work also elevated vanillin and buried isovaleric acid with the most extreme valence. The accumulation of data served them to confirm previous findings or to obtain new ones. Thus, as long as hydrogen was not in the formula, the degree of pleasantness of the aroma depended more on molecular complexity. The presence of oxygen or a greater number of atoms also led to speculation that this substance would smell good. In the extreme, anything that involved sulfur atoms was going to go bad.

“A good chemist would need some sociology, genetics and knowledge of artificial intelligence to be able to find a universally pleasant smell”

Pablo Meyer, researcher at IBM Research and director of the Dreams Challenge

In 2017, Science published the second part of that study, But this time, dream olfactory prediction challenge He was looking for a series of algorithms to predict the pleasantness or not of a scent based on the 4,884 physico-chemical properties that might be behind the smell. Massive computing, inspired by centuries of chemical knowledge, went against the subjective descriptions of various groups, who had to describe the smell of each molecule with words, such as “sour”, “baked bread”, “musty”, “fruity”. , “chemical” … the models managed to predict both the intensity and valence of the odor very well. They also struck down half of the semantic descriptors used by humans to define each odor. Hardly anyone had the guts to describe the smell of water.

Mexican Pablo Meyer is director of the Dream Challenge at IBM Research and a co-author of the study Science, “Most people’s view is that language doesn’t describe smell well, but we’ve shown that whether you like something or not, we’re able to accurately describe the olfactory sensation with words, They say. Regarding Arshmian and Majid’s study, they highlighted that “indeed, the most obvious variation is individual, it leads to the idea that you like (or don’t like) the smell or that they give you a particular smell.” A reminder of what is beyond culture”. Regarding the possibility that science, in its computing of matter, predicts odor as predicted by its fundamental properties of color or sound, Meyer believes that valence can be reconstructed. Although it will not be easy: “To be a good chemist I would need a little knowledge of sociology (cultural differences), genetics and artificial intelligence to be able to find a universally pleasant smell (and as far as I know, disgusting too). to happen.

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