Smell

People can discern thousands of odors, although there is great variability among people in the ability to detect particular odors. Some of the differences in this detection ability are believed to be genetically determined.

Odor is a sensation, a stimulus and perception captured by the sense of smell by the interaction of an organic substance with the olfactory receptors in the nostrils. This interaction is influenced by many factors such as the composition of the substance, its volatility or the number and type of olfactory receptors of each individual.

In the olfaction process, odorant substances are transported through the air, reach the olfactory epithelium where they are detected by the receptors of the sensory receptor neurons. The olfactory epithelium has between 20 and 30 million receptor cells which, when activated, transmit the signal to the cerebral cortex and, from there, to the limbic system and hippocampus where olfactory memory is established and memories are associated with certain odors.

It is estimated that humans have the ability to differentiate up to ten thousand different odors, but most of us will only perceive a fraction of them in our lifetime, so the description of an odor often varies from person to person. In addition, olfactory perception is also influenced by cultural, emotional or physiological aspects.

One of the best known odorant compounds are ionones, which are natural compounds found naturally in the scent of flowers where they serve as an attractant to pollinating insects. They are widely used in perfumery and as food flavorings.

The ability to determine to a greater or lesser extent b-ionone compounds is strongly conditioned by genetics. Several studies have determined that the only major region of genetic association for b-ionone sensitivity discovered so far is located on human chromosome 11, in the OR5A1 gene, which is responsible for producing the olfactory receptor 5A1 that initiates a neuronal response that triggers odor perception.

Individuals carrying genotypes for b-ionone can more easily differentiate between olfactory stimuli and foods and beverages with and without added b-ionone. These responses associated with the genotypes of the marker found in the OR5A1 gene were confirmed in 96% of the individuals who participated in the study conducted.

Number of observed variants

13.5 million variants

Number of variants analyzed in the study

1 variant

Bibliography

Jaeger SR, McRae JF, Bava CM, Beresford MK, Hunter D, Jia Y, et al. A mendelian trait for olfactory sensitivity affects odor experience and food selection. Curr Biol [Internet]. Elsevier Ltd; 2013;23(16):1601–5.

Aloum L, Alefishat E, Adem A, Petroianu G. Ionone Is More than a Violet's Fragrance: A Review. Molecules. 2020 Dec 10;25(24):5822. doi: 10.3390/molecules25245822. PMID: 33321809; PMCID: PMC7764282.

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