The Etiology of Taste

Taste or gustation is a chemical sense that includes five primary tastes: sour, sweet, bitter, salty and umami (savory). Basic taste was once described as being specific to certain tongue locations and this was referred to as “Tongue Mapping,” but we now know taste can occur at multiple locations in the mouth and taste is also intertwined with the sense of smell (along with all the memories we have stored that cause association with certain scents). All taste sensations occur throughout the mouth and may be a combination of all the five tastes as originally mentioned. When mixed with saliva, flavors and taste are disbursed throughout the mouth and perceived as those listed previously. Supertasters are more often detected in children because of their eating habits and food preferences. It is suggested a bitter sensitivity may be modified during life and may decrease somewhat in later life through “adaptation” but food preference is especially noted in children. The olfactory and tactile sensations also play major roles in our ability to perceive these taste sensations and tactile sensations. An example is that some children will not eat certain foods - and this is not only because of taste but also simply because of the texture. They are often described as “picky eaters.”

Papillae of the tongue:

  • The fungiform papillae have taste buds on their dorsal surface. Generally, supertasters have an increased number and density of fungiform papillae on their tongue and especially on the anterior two thirds of the tongue.
  • The filiform papillae are conical epithelial projections with thick cornified layers and they do not contain taste buds. These papillae act as an abrasive coating that aids in cleaning the mouth with the help of saliva. They also assist in moving food through the mouth.
  • The vallate papillae contain numerous taste buds on their lateral surface. These papillae are eight to ten in number and are a V-shaped line at the base of the tongue. Each bud is a small ovoid or barrel-shaped organ that extends from the basal lamina to the surface of the epithelium. The outer surface is covered with epithelium.
  • The foliate papillae are located on either side of the tongue, posterior to the vallate papillae. These papillae contain taste buds as well.

Taste buds are made up of gustatory cells (receptor cells), basal cells and supporting cells. As stated previously, each cell has a function. The taste pore is an opening to the outer surface of the papillae allowing the gustatory hair (only seen with electron micrography) found in the taste bud to reach the outside environment. Within each taste bud, there are gustatory cells (10 to 12 neuroepithelial cells) that are the receptors of taste stimuli (Figure 12).

Figure 12. Histology of a papillae.
Image: Diagram showing histology of a papillae.

These microscopic hair like processes reach into the space beneath the taste pore. Taste occurs when a chemical substance contacts a receptor cell in the taste bud and the chemical fires the nerve in that area of the taste bud. The electric impulse is then sent to the brain and the brain perceives this sensation as taste when it reaches the brain.

When viewing fungiform papillae microscopically, they have a fairly distinct appearance. They show a slight elevation of the surface that is typically broad and flat-topped. The taste buds are found primarily on the flat top surface of fungiform papillae. In the circumvallate and foliate papillae, there is a crypt-like space around the structure and taste buds (the neuroepithelial cells that act as taste receptors) are found in the epithelium adjacent to the crypt-like space. A very prominent sub-epithelial nerve plexus is present in the connective tissue. As food is beginning to be broken down by the saliva, the chemicals responsible for taste are dissolved into the saliva that seeps into the crypt and is subsequently picked up by the receptors and interpreted as taste. The dissolution of the food also produces some aerosolization of the chemicals, which is picked up by the olfactory apparatus in the nose. So supertasters can sometimes be identified because they have a very strong sense of smell-they often can detect the most subtle of scents such as a light perfume or normal dental office scents. Hayes and Keast 2011 state there is continuing supporting evidence supertasters have a greater chemosensory acuity.15 This concept fits into the current information that many supertasters are involved in food evaluation and food tasting (e.g., chefs, wine tasters) because these individuals are able to discern subtle taste changes. Some supertasters can identify even the least of ingredients that have been added to foods such as spices.33 Wine tasters fall into this category and actually use these abilities to make a living. Hayes also suggests a more defined use of the terminology suggesting the term “Hyperguesia” as a heightened taste response.15 More research needs to be conducted in chemosensory variation and the classification of all taste variations.

Taste sensations occur because they are conducted by three nerves that have direct supply to the tongue and oral tissues; they are the Facial nerve, the Glossophargyngeal and the Vagas nerve (Figure 11).

Figure 11. Nerve Diagram.
Image: Diagram of a head showing nerves.

Surgery to the middle ear may affect the chorda tympani causing a change in the sense of taste. In some cases, a tonsillectomy may damage the glossopharngeal nerve causing this change.11 Chronic ear infections and upper respiratory infections may also damage the middle ear since the cranial nerve passes through this area (refer to Figure 11 for the nerves involved).

The taste sensation is not recognized until it is mixed with certain chemicals when dissolved in saliva and then detected by the receptors in the taste buds. Various causes of xerostomia should be evaluated as well. A dry mouth limits taste perception because the food is not mixed with saliva and does not circulate throughout the mouth. Clinicians report that a dry mouth is often a complaint by patients describing a metallic taste, phantom taste and sometimes a bitter taste as voiced by supertasters. Some of the taste, dry mouth and taste-associated factors have been found in patients with BMS as well.32 Patients with this complaint tend to be found more often in women.14,20 Saliva acts to dissolve strong concentrations in the mouth, so a certain taste may be more accentuated within a dry mouth because it is not circulated throughout the taste buds. The patient may complain of somatosensory sensations that are subjective feelings of oral sandiness, roughness, phantom tastes or dryness.4 Supertasters tend to avoid very textured foods and descriptions by patients are qualitative in nature with great variation. Supertasters also avoid very fatty foods, again because of the unpleasant texture they sense. A key point should be made here: although these sensations may be reported by some patients, supertasters are supertasters from birth because of the genetic component; therefore, the patient may not know any difference in taste or be able to describe these taste changes since they have always reacted the same way to foods and/or scents and have no comparison. Some confusion with other disorders may tend to overlap and need to be differentiated.17

Spicy foods like capsaicin (the substance that makes chili peppers taste hot) can sometimes be tolerated but the adjustment is not made by taste buds. Rather, the receptors that respond to hot spices are called “polymodal nociceptors,” and the oral burn produced by these receptors projects to the brain via the trigeminal nerve (Figure 11). These receptors can desensitize the burning sensation over time.18 If you eat foods containing capsaicin, the burn will diminish through desensitization. However, this adjustment is only temporary. If the person decides to discontinue the process and begin to use capsaicin again at a later time, the burning sensation will return. Even the airlines have begun to take notice of the way that individuals taste. This perception of taste is accentuated or diminished, while flying in pressurized cabins. Passengers often complain about tasteless food and how terrible the food is on an airplane. When flying at normal altitudes, our perception of sweet and saltiness drops by 30%. Pressurized cabins cause our mucous membranes to swell, blocking the pathway to the olfactory receptors in the nose. As stated previously, taste and smell work together to provide the wide range of tastes we experience. Airlines are introducing new ways to accommodate the different modes of tastes to address the wide range of tasters. Multiple airlines have been researching this problem and it is possible that we will see changes in the types of foods that are served.34 Additional information on this subject can be found in the resources section.

The sense of taste evolved to discriminate beneficial foods from environmental poisons as a critical system to ensure human survival.26 Recent studies by Herbert et al. looked at the startle reflex response or eye blink response.17 Results from the study indicate a link between PROP positive tasters (supertasters) and relevant patterns of emotional responding. This link with supertasters may reinforce the survival mechanism and the heightened sense of both taste and emotional responding.

The characteristics of supertasters include their ability to taste foods with an increased awareness but also an increased intensity as well. Bartoshuk describes supertasters as being in a “neon taste world.”4 Supertasters tend to use more salt on their food and they eat less vegetables that have a bitter taste such as kale, brussels sprouts and broccoli.34 These individuals report an aversion to dark coffee, radishes, hard liquor, chocolate, and any vegetable that has a somewhat bitter taste including the cruciferous vegetable category. See Appendix 1 for a list of foods that supertasters “like” and “dislike.”