Have you ever wondered why you like certain foods, and dislike others? Or why you think some recipes are inedible while others seem to enjoy the taste? Baring the cultural aspect, a lot of it comes down to how you perceive the smell of the foods.
All of us, at some point, have disagreed on what a particular food tastes or smells like (think coriander, durian, wine). And while you might think that the other person might be mistaken or have a poorly developed sense of smell, sensory scientists at The New Zealand Institute for Plant & Food Research have dissected some of the genetics behind flavour preferences and shown that we all live in our own unique world when it comes to odour perception.
A pair of studies published by Sara Jaeger, Jeremy McRae, Richard Newcomb and colleagues published in an August edition of journal Current Biology identified the genetic variations that underpin the differences in smell sensitivity and perception between individuals, which explain some of the reasons why people appear to have ‘blind spots’ in their tasting abilities.
The researchers tested nearly 200 people for their sensitivity to ten different chemical compounds that occur in foods and searched through the subjects’ genomes for areas of the DNA that differed between people who could smell a given compound compared to people who could not. This approach — known as a genome-wide association study or GWAS — is widely used to identify genetic differences, for instance, between healthy and diseased individuals in the hope of identifying genes that underpin certain diseases, such as diabetes or cancers.
McRae and colleagues found a genetic association for four (malt (isobutyraldehyde), apple (β-damascenone), blue cheese (2-heptanone) and β-ionone) of the ten odors tested suggesting that differences in the genetics determine the likelihood of a person being able to smell these compounds. There was no regional difference, and the ability to smell one odour does not predict the ability to detect the others.
The genetic variants associated all lie in or near genes that encode odorant receptors. Odorant receptors are a large family of genes -humans have about 400 functional odorant receptors, while mice have over three times as many. The odorant receptors sit on the surface of sensory nerve cells in our nose. When they bind a chemical compound drifting through the air, the nerve cell sends an impulse to the brain, leading ultimately to the perception of a smell.
In the case of β-ionone, the smell associated closely with violets, McRae and colleagues managed to pinpoint the exact mutation (a change in the DNA sequence) in the odorant receptor gene OR5A1 that underlies the sensitivity to smell the compound and to perceive it as a floral note — people who are less able at smelling β-ionone also describe the smell differently as sour or pungent and are less likely to find it pleasant. I took part in the trial, and found that I am very sensitive to β-ionone. At high concentrations, the smell was overly perfumey and quite unpleasant, it reminded me of turkish delight (which makes me gag) and the scent of some air fresheners.
While we can train our palates and refine our sensory perception, your DNA will ultimately decide if you are a super smeller and cultural backgrounds can affect whether you like what you are smelling. On top of that landscape, with odorant receptors acting independently of each other, we are all living in our own little world of smells.
1. Jaeger et al. A Mendelian Trait for Olfactory Sensitivity Affects Odor Experience and Food Selection, Current Biology 2013 23(16) pp. 1596 – 1600
2. McRae et al., Identification of Regions Associated with Variation in Sensitivity to Food-Related Odors in the Human Genome, Current Biology 2013, 23(16) pp. 1601 – 1605