Why Do Some Things Taste Bitter To Some People But Not To Others?

Unne Fung

Have you ever wondered why some things taste more bitter to some than others? This revelation goes all the way back to 1931 when a chemist named Arthur Fox accidentally released synthesized Phenylthiocarbamide. His colleague complained about its bitter taste, but he could not taste its bitterness!

This kickstarted a series of taste testing investigations. The compounds Phenylthiocarbamide and Propylthiouracil cause a bitter taste and although they are not naturally present, they are used to determine bitter sensitivity. In fact, these compounds are bitter to 75% of the population and tasteless to 25%.

We now know that genetics is the main reason bitterness varies from person to person. The bitter gene receptors (TAS2R38) lie on the surface of the tongue. There are three possible SNPS (single nucleotide polymorphisms- mutations where one nucleotide is swapped for another letter) that result in the two main haplotypes; the AVI recessive ‘non- taster’ and the PAV dominant ‘taster.’ *Haplotypes are sets of SNPs on 1 chromosome. (Those with the PAV/PAV genotype are more likely to be ‘supertasters,’ others with the PAV/AVI genotype range from 'super to medium to non-tasters’ and lastly, those with the AVI/AVI genotype are most likely ‘non tasters.’ Just as the name suggests, ‘supertasters’ are more sensitive to bitterness, ‘medium tasters’ are in the middle and ‘non-tasters’ are the least sensitive. AAI and AAV are rare, PAI and PVI are really rare and AVV and PVV (only evident when there are diseases) do not affect taste. When paired with a haplotype, the level of bitterness varies. And, although studies show that supertasters have a higher density of fungiform papillae (mushroom like protrusions) on the tip of their tongues than ‘non-tasters.’ More recent studies have shown that there is no correlation between the number of fungiform papillae and taste perceptions.

*SNPs in the TARS238 gene:

rs714598 causes the gene to change from proline (P) to alanine (A) in the 49th amino acid

rs7126866 causes the gene to change from alanine (A) to valine (V) in the 262nd amino acid

rs10246939 causes the gene to change from valine (V) to isoleucine (I) in the 296th amino acid

What’s the point of food being bitter, you may ask? This goes back to evolution. The perception of bitterness was probably useful in determining if plants were toxic or not when humans had to regularly hunt and forage for food. A modern example can be seen in potatoes. Normally, potatoes contain low levels of the toxic glycoalkaloids, solanine and alpha-chaconine. However, if a potato is left in the sun for a long time, more chlorophyll is produced and glycoalkaloid levels increase. These compounds result in a bitter taste, and it stops us from eating the potato. To put its toxicity into perspective, 140-350 mg of glycoalkaloids would be enough to kill a human weighing 70kg! The differences in our ancestor’s diets according to nationality may be a reason why different people have different genotypes.

So, what kind of taster are you?

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