What is taste sensitivity?
Taste sensitivity refers to the intensity with which you perceive different tastes and flavors.
What determines a person's taste sensitivity?
There are three aspects of taste sensitivity that we need to consider in answering this question:
People differ in the number and appearance of their taste papillae
While there is little variation from person to person in the number of foliate and circumvallate papillae, the number and shape of the fungiform papillae, located on the anterior portion of the tongue, are highly variable. It is easy to see fungiform papillae if you stain your tongue with blue food coloring, as we have done for the pictures here. The fungiform papillae do not stain, so they stand out as pink against the blue background.
Tongue of a mildly sensitive taster.
The fungiform papillae are the small pinkish dots on this tongue. Note that they are small and seed-shaped.
Tongue of a moderately sensitive taster.
The fungiform papillae on this tongue are larger and more rounded than those on the tongue above.
Tongue of a highly sensitive taster.
This tongue is covered with fungiform papillae. Note that this tongue does not have any blue areas like those in the tongues shown above.
As you can imagine, the more fungiform papillae you have the greater the number of taste buds you will have, and the stronger the signals sent from the mouth to the brain can be. People with large numbers of taste papillae, coupled with high sensitivity of their nerve endings, experience tastes, and usually smells as well, as being very strong. They are also able to distinguish individual flavors in a mixture easily. By contrast, people with fewer taste buds and low sensitivity, tastes, smells, and flavors are not as strong, and they come as a "package deal."
People differ in the sensory capacities for bitter, sweet, and umami
The sensory capacities of your taste buds are dictated by the structure of the receptors on your taste cells, and on their capacity to excite the process of transmitting the taste message. These receptors capture the molecules that come into contact with the tips of the taste cells, and send a message through the cell to the neve endings surrouding the base of the cells.
The structure of these receptors is genetically programmed. For example, the receptor for phenylthiocarbamide (PTC, the substance on the taste strips you may have tried in school - see sidebar) comes in at least three different genetic variants. The receptor produced by the original gene can transmit the nasty bitter taste of the compound. The receptors produced by the mutated versions of the gene transmit the taste poorly or not at all.
Much of the research on taste senstivity has been done using a chemical called 6-n-propylthiouracil, or PROP for short. This chemical has many of the same properties as PTC, but is safer to use. However, when we use this compound as a single measure of taste sensitivity, we confound sensitivity to PROP with sensitivity to a wide array of very different compounds. In other words we can be insensitive to PROP or PTC, but quite sensitive to other compounds, and in particular other bitter compounds.
Indeed we humans seem to have quite a repertoire of genes for receptors for bitter tastes, with multiple genetic variants - there seem to be about 30 different genes that are each broadly tuned to capture a large variety of bitter molecules from food, so that we each experience a broad array of compounds that we consider "bitter."
While we know a great deal about the genetic basis for sensitivity to bitter compounds, much less is known about sensitivity to other tastants. Here a problem is that sensitivity as measured by thresholds to sensing simple compounds such as sucrose (sugar) varies hugely by state of hunger, body weight, hormonal status, pre-diabetic state, and more. That being said, gene studies in which researchers looked at variations in the gene structure for the sweet and umami taste receptors have found variations that are associated with differences in umami sensitivity, and even more commonly, with differences in sweet taste sensitivity.
This discussion of genes only touches one aspect of taste sensitivity. As noted above, taste sensitivity is also dependent on the number of taste buds you have, and of course on what happens in nerves, brainstem and brain.
Individual differences in trigeminal sensitivity
We have become interested in differences in trigeminal senstivity, which manifests itself in differences in responses to hot and cold, and to compounds that activate temperature receptors such as menthol for cool and cold receptors and cinnamon for warm and hot receptors. This interest stems from the fact that all foods not only activate the classic tastes, but also activate the trigeminal nerve to a greater or lesser degree.
Data on genetic variability of trigeminal receptors is lacking, but we have found empirically that people differ considerably in their response to the cooling effect of mint. The same seems to go for the warming effect of cinnamon.