Bitter taste perception

Sensitivity to bitter taste plays an important role in regulating the intake of some toxic substances in food, which could otherwise produce intoxication.

Taste is the sensation produced by certain bodies in the organ of taste. It is determined primarily by chemical sensations detected by taste (tongue) as well as smell (odor).

Although the human soft palate contains taste buds, the main organ of taste is classically considered to be the tongue and the main structure that houses the sensory endings are the papillae. These are able to distinguish between a wide variety of tastes: sweet, bitter, sour, salty and umami, catalogued as a new taste since 2010.

Sour and salty substances are linked to ion channels, while sweet, bitter and umami tastes are transmitted through G-protein-linked receptors, which are expressed in taste cells on the surface of the tongue. These proteins are encoded by the TAS2R gene family.

According to the Dictionary of the Royal Spanish Academy (RAE), bitterness has the characteristic taste of gall, quinine and other alkaloids and when it is particularly intense it produces an unpleasant and long-lasting sensation.

The perception of bitterness is considered a key defense mechanism against intoxication with potentially toxic substances. Although so far no direct relationship between bitterness and food toxicity has been established, many common bittering agents, such as strychnine and nicotine, are toxic at low or high concentrations.

The sensation of bitterness arises when precise chemicals come into contact with specialized cell receptors on the human tongue. But not everyone perceives the same bitterness for a given stimulus; this character variant is partly decided genetically and can have an effect on food perception, preferences and consumption.

Taste sensation, as well as its intensity, can be affected by various factors such as smoking, age and genetics. Several studies have repeatedly identified the role of 3 markers in the taste sensitivity to the bitter-tasting substance phenylthiocarbamide (PTC). The ability to perceive PTC is correlated with the ability to perceive other naturally bitter substances and is dependent on bitter taste receptors. These receptors are determined by the TAS2R38 gene, where the identified mutations occur; therefore, variations in its sequence can lead to a loss of function of this receptor and this would explain the variability in the ability to detect bitter taste among individuals.

It is estimated that the TAS2R38 gene may be responsible for up to 85% of the phenotypic variation in sensitivity to PTC.

Number of observed variants

13.5 million variants

Number of variants analyzed in the study

3 variants

Bibliography

Jeruzal-Swiatecka J., Fendler W., et al. Clinical Role of Extraoral Bitter Taste Receptors. Int J Mol Sci. 2020 Jul; 21(14): 5156.

Drayna D. Human taste genetics. Annu Rev Genomics Hum Genet. 2005;6:217–35.

Smail H.O. The roles of genes in the bitter taste. AIMS Genet. 2019; 6(4): 88–97.

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