Bitterness perception plays a key role in human evolution while taste remains essential for food perception. Toxins typically produce bitter flavors which makes human sensitivity to bitterness biologically important. Research indicates that the detection of bitterness depends primarily on type 2 taste receptor (TAS2R) genes and individual sensitivity to bitter flavors varies significantly due to TAS2R gene polymorphism.
The TAS2R receptor family comprises G protein-coupled receptors which primarily function to detect bitter substances. The taste buds of the tongue contain these receptors which send signals to the brain via the bitter signaling pathway. In addition, TAS2R receptors not only play a role in the taste system, but also function in tissues such as the airways, intestines, and immune cells, affecting the body's metabolism, immune response, and disease risk.
Related Product
Biological Basis of Bitterness Perception
Taste receptor cells on our tongue detect bitterness as a fundamental taste and send these signals to the brain. Research indicates that bitter taste receptors consist primarily of the TAS2R family which predominantly resides on the taste receptor cells located within taste buds. Bitter compounds including alkaloids and flavonoids Bitter compounds activate the G protein-coupled receptor signaling pathway when they bind to TAS2R receptors which enables signal transmission to the brain that creates the perception of bitterness.
Taste System
TAS2R receptors serve to identify bitter substances which help protect organisms from consuming toxic materials. The evolutionary mechanism protected humans from consuming dangerous plants and substances by helping to identify potential toxins through taste. TAS2R38 gene variation between PAV and AVI determines taste sensitivity for PTC and PROP which influences how people accept cruciferous vegetables like broccoli and cabbage. The TAS2R16 receptor detects amygdalin as a toxic substance available in various foods like cherry pits and almonds.
Respiratory System
TAS2R receptors serve functions beyond the taste system because they are expressed in airway epithelial cells where they support antimicrobial defense and airway relaxation. The receptor detects specific bacterial metabolites which trigger immune reactions that defend against bacterial infections including sinusitis and COPD. Mutations in TAS2R38 (AVI/AVI) can make people more prone to respiratory infections.
Digestive System
TAS2R receptor expression in the intestinal region affects gastrointestinal hormone release together with appetite control and glucose metabolism management. Bitter compounds activate TAS2R receptors which cause GLP-1 and CCK release to lower appetite and enhance insulin sensitivity. Immune cells such as macrophages and dendritic cells exhibit TAS2R receptors which help detect pathogens and regulate inflammation. The system detects bacterial lipopolysaccharide (LPS) and metabolites which activates innate immune responses thereby enhancing antibacterial efficiency.
Bitter Taste Is Represented by the Type 2 Taste Receptor (TAS2R) Gene Family
The TAS2R gene family consists of 25-30 functional genes that encode different bitter taste receptors responsible for detecting different types of bitter compounds.
| TAS2R Receptors |
Bitter compounds identified |
Function/Relevance |
| TAS2R38 |
Phenylthiocarbamide (PTC), 6-propyl-2-thiouracil (PROP) |
Influences sensitivity to bitter taste |
| TAS2R16 |
Amygdalin, glucosides |
Involved in the perception of some plant toxins |
| TAS2R46 |
Flavonoids, terpenes |
Recognizes a variety of plant secondary metabolites |
| TAS2R50 |
Quinine, certain drugs |
May affect medication compliance |
| TAS2R19 |
Caffeine, quinine |
Influences acceptance of bitter beverages |
| TAS2R31 |
Acetaldehyde, bitter drugs |
May be related to alcohol metabolism |
| TAS2R14 |
Broad-spectrum bitter taste perception |
Recognizes a variety of compounds, possibly involved in immune function |
Genetic Differences in Bitterness Sensitivity in Humans
The sensitivity of different populations to bitterness varies greatly, and this difference is mainly determined by single nucleotide polymorphisms (SNPs) of the TAS2R gene. For example:
Polymorphism of the TAS2R38 gene
TAS2R38 is one of the most intensively studied bitter receptor genes. It has polymorphisms at three loci (A49P, V262A, I296V), forming two major haplotypes:
- PAV type (sensitive type): highly sensitive to bitter substances such as PTC (phenylthiourea) and PROP (6-propyl-2-thiouracil).
- AVI type (insensitive type): low perception of these bitter substances.
The influence of other TAS2R genes
- Genetic differences in TAS2R16 determine how sensitive someone is to amygdalin which exists in bitter almonds and cherry pits.
- Genetic differences in TAS2R19 and TAS2R31 influence how people perceive bitter compounds including caffeine and quinine.
- The bitter taste perception of specific drugs including cardiovascular medications can be influenced by genetic variations in TAS2R50.
Impact of Bitter Taste Sensitivity on Diet and Health
Vegetable Intake
People with high sensitivity to bitter flavors like PAV/PAV homozygotes often avoid bitter vegetables such as broccoli and cabbage which results in a lower intake of dietary fiber and antioxidants.
Alcohol and Coffee Consumption
Those with a lower sensitivity to bitter flavors tend to consume more coffee along with alcoholic beverages because they accept their bitter tastes better.
Medication Compliance
Specific bitter receptors play a role in how drugs are perceived by humans. Individuals with a sensitivity to bitterness when tasting drugs tend to reject taking those medications which subsequently impacts the treatment results.
Evolutionary Adaptation
The distribution of TAS2R gene polymorphisms across populations varies because of distinct dietary patterns and environmental factors in different regions. For example, Africans generally have higher bitter sensitivity, while bitter insensitive variants are more common in Europeans.
TAS2R Causes Differences in Human Sensitivity to Bitter Taste
TAS2R receptors are central to bitter taste perception because genetic variations in TAS2R genes change how sensitive individuals are to bitter tastes. The variance in sensitivity to bitter taste impacts dietary preferences, health outcomes and evolutionary changes in humans. Research into genetics and taste science will deepen our understanding of bitter taste perception and help develop personalized nutrition and health interventions.
References
- Behrens, M., et al. The human bitter taste receptor TAS2R7 facilitates the detection of bitter salts. Biochemical and Biophysical Research Communications. 2019, 512(4): 877-881.
- Roura, E., et al. Variability in human bitter taste sensitivity to chemically diverse compounds can be accounted for by differential TAS2R activation. Chemical Senses. 2015, 40(6): 427-435.
.
