What is taste sensitivity?
Taste sensitivity refers to the intensity with which you perceive tastes and flavors. People with high taste sensitivity experience tastes, and usually smells, too, as being very strong. They are also able to distinguish individual flavors in a mixture very well. For people with low taste sensitivity, tastes, smells, and flavors are not as strong, and they come as a "package deal." Taste senstivity depends on multiple factors, inculding the nature and number of taste receptors on taste bud cells, and the number of taste buds a person has.
How do we know what a person's taste sensitivity is?
In our research, we have primarily used two methods for finding out what a person's taste sensitivity is. In the first method, we use a chemical called 6-n-propylthiouracil, or PROP for short, and in the second we have people rate the intensity of the taste of a peppermint LifeSaver(TM).Ý We and others have also used sucrose for sweet senstivity, citric acid for sour sensitivity, and of course sodium chloride for salt senstivity. There are number of bitter compounds that can be used as well. These give differing results, because they appear to bind to different receptors for bitter compounds - there appears to be more than forty of these bitter receptors!
What is PROP?
The full chemical name of PROP is 6-n-propylthiouracil. It is a chemical that is usually used to treat hyperthyroidism, for which high doses are used over a long time. In taste testing, we use a very tiny amount, just enough to get the taste. Some people can taste PROP, and some people can't - for very sensitive tasters, the taste of PROP is very intense. It tastes like a nasty "bitter" chemical. People who can't taste PROP say it tastes like water, if we use PROP in solution. If we use PROP on a piece of filter paper, people who are highly senstive want to get the paper out of their mouths as quickly as possible. People who can't taste PROP say that they only taste the filter paper itself.
How do you test for taste sensitivity?
For PROP testing, we have used solutions containing PROP at different concentrations. When we do large scale studies, we use filter papers which have been soaked in PROP and then dried. You place the filter paper on your tongue, and then rate the intensity of the taste.
For peppermint tasting, we also ask you to indicate the intensity of the flavor before and after crunching down on it. Once you have crunched down on the peppermint, we ask you to rate the intensity of the cooling sensation you may experience. You mark the intensity on a line divided into sections, corresponding to intensities from barely detectable to strongest imaginable. We then measure the distance between the baseline and the mark you place on the line indicating the intensity of your experience. The resulting intensity ratings run from 0 to 100, with the higher the rating the more sensitive you are. These ratings allow us to classify people according to taster type.
People also differ in their taste papillae
It is easy to see fungiform papillae if you stain your tongue with blue food coloring, as we have done in the pictures at below. 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.