SENSE OF TASTE: TYPES OF FLAVORS, RECEPTORS AND PERCEPTION - BIOLOGY - 2024

The sense of taste is located on the tongue and allows human beings to perceive the different flavors of the substances they eat, such as food and drinks. There are five basic flavors or taste qualities: sour or sour, bitter, sweet, salty, and umami.

Umami means "tasty" and is the latest flavor discovered. It comes from receptors stimulated by monosodium glutamate, a substance naturally present in many foods. It is also added as a flavor enhancer.

Green (bitter), yellow (sour or sour), black (sweet), white (salty).

Almost all vertebrates have all five taste qualities, with the exception of felines that do not perceive sweetness. Most animals tend to ingest sweet or salty substances, but avoid acidic or bitter ones, since they are associated with the deterioration of food.

This means that the sense of taste also has a protective function, since if we eat something poisonous or in bad condition, our reaction will be to expel it immediately because it has a bad taste; This prevents it from reaching the stomach and causing disease.

Taste and taste are not the same. The taste differs from taste in that both smell and taste are involved in the former. For this reason, a person who has lost the sense of smell is not able to distinguish flavors.

Both taste and smell are classified as chemoreceptors, as they work by reacting to the molecular chemicals in substances.

In order for something to be tasted, it must be dissolved in saliva so that it reaches the receptors. Specialized receptor cells for taste are found primarily in the taste buds of the tongue, the fundamental organ of taste.

Types of flavors

Gabrielzerrisuela

What we generally understand as flavor is a set of sensations that includes smell, temperature and texture. The sense of smell is very important, since if we have it altered, the ability to capture flavors decreases dramatically.

Taste and smell influence our behavior, and are part of the autonomic nervous system. That is why when we perceive a bad taste, we can feel nauseous and vomit. Our behavior is probably to avoid this type of food; On the contrary, when we feel an appetizing taste, the production of saliva and gastric juices increases, and we will want to continue eating.

There are five types of flavors or basic flavor qualities, although there may be a combination, for example, bittersweet. The basic flavors are:

Sweet

This taste is generally caused by sugar, fructose, or lactose. However, there are other substances that are perceived as sweet. For example, some proteins, amino acids or some alcohols present in fruit juices or alcoholic beverages.

Acid

This sensation is caused by hydrogen ions (H +). The foods that naturally contain this flavor the most are lemon, orange, and grapes.

Salty

This is the simplest flavor receptor and is produced mainly by sodium ions. We usually feel it in foods that contain salt. Other minerals, such as potassium or magnesium salts, can cause this sensation.

Bitter

This taste is caused by several different substances. There are about 35 different proteins in sensory cells that take up bitter substances. This is explained from the evolutionary point of view, since man has had to detect which substances were poisonous in order to survive.

Umami

It is generally caused by glutamic acid or aspartic acid. This flavor was identified in 1908 by the Japanese scientist Kikuane Ikeda.

This taste quality is similar to the taste of a meat broth. Ripe tomatoes, cheese, and meat are high in glutamic acid. In Chinese cuisine, glutamate is widely used as a flavor enhancer.

Taste receptors

The taste cell receptors are located on the taste buds. A young adult can have up to 10,000 recipients. Most of these are found on the tongue; however, they are also found on the soft palate, pharynx, and epiglottis (cartilage above the larynx).

There are even taste buds in the mucosa that lines the upper part of the esophagus, which causes food to be tasted as we swallow it.

-Taste buds

The taste buds are sensory receptors found primarily on the tongue. There are 4 types:

Antimoni

- Goblet papillae: they are smaller in number, but larger. They are located at the base of the tongue, and go to the back forming a V (called V lingual). They contain about 250 taste buds, grouped together from 20 to 50 receptor cells.

- Mushroom papillae: they have a mushroom shape and are located throughout the tongue, especially in front of the V lingual. They have a reddish color, contain up to 8 taste buds and receptors for temperature and touch.

- Filiform papillae: its function is thermal and tactile. They are found throughout the tongue, from the center to the edges.

- Foliate papillae: they are located on the edges, on the back of the tongue. They have taste buds on the sides, about 1,300.

-Taste buttons

Most of the taste buds are located on the taste buds. They are microscopic, being 20 to 40 millionths of an inch in size, and contain 30 to 80 receptor cells. Many of these cells connect to nerve fiber endings.

Taste bud in which 6 taste buds can be observed. Possible2006

The taste buds are on the surface of the papillae and communicate with the outside through a duct called the taste pore. They have three types of epithelial cells: support cells, taste receptor cells, and basal cells.

• There are about 50 taste receptor cells in each taste bud. They are surrounded by supporting cells.
• Receptor cells run from the base of the button upward, projecting vertically into the taste pore. These cells live for only about ten days and are renewed regularly.
• Basal cells are on the periphery of the taste bud and produce support cells.

Structure of a taste bud (Health, 2016)

What parts of the tongue does each taste detect?

There is a misconception that the tongue has specific zones for each type of flavor. In reality, all flavors can be detected by all parts of the tongue, although there are sides that are somewhat more sensitive to certain flavors.

About half of the sensory cells perceive the five basic tastes. The other half is responsible for transmitting the intensity of the stimulus. Each cell has a range of specific flavors, and therefore can be more sensitive to each taste quality.

Location of taste receptors. From left to right: sweet, sour, salty and acid Distribution and types of papillae (Health, 2016)

For example, the back of the tongue is very sensitive to bitter tastes. This seems to be that it is a protection of the body to be able to expel bad food or poisonous substances before they are swallowed and harm us.

The complete taste sensation occurs when the perceptions of all the sensory cells of the entire tongue are combined. Taking into account that there are 5 basic flavors and 10 intensity levels, it is possible that up to 100,000 different flavors are perceived.

Taste information perception: from the tongue to the brain

The first step to perceive a flavor is that it comes into contact with our tongue and internal parts of the mouth. The information is transmitted to our brain so that it can be interpreted.

Taste buttons

What allows us to capture certain characteristics of food are the taste buds. These are bulb-shaped, and have a hole at the top called the gustatory pore. Inside are the cells of taste.

Chemicals from food dissolve in saliva and come into contact with taste cells through the taste pore.

Specific taste receptors are found on the surface of these cells that interact with chemicals in food.

As a consequence of this interaction, electrical changes are generated in taste cells. In short, they emit chemical signals that are translated into electrical impulses that are sent to the brain.

Thus, the stimuli that the brain interprets as basic taste qualities (sweet, sour, salty, bitter and umami) are produced by various chemical reactions in taste cells.

Salty foods

Sweet flavor signal transduction pathway. Object A is a taste bud, Object B is a taste bud cell, and Object C is the neuron attached to the taste cell. Source: Transduction of Taste Signals. US National Library of Medicine.

In salty foods, taste cells are activated when sodium ions (Na +) enter ion channels, penetrating the cell. When sodium accumulates inside the cell, it depolarizes, opening calcium channels. This causes neurotransmitters to be released that send messages to the brain.

Acidic or sour flavors

Sour taste signal transduction pathway. Object A is a taste bud, Object B is a taste receptor cell within Object A, and Object C is the neuron attached to Object B. Source: Transduction of Taste Signals. US National Library of Medicine.

Something similar happens with acidic flavors. The hydrogen ions present in them flow into the recipient cells through ion channels. This causes depolarization of the cell and release of neurotransmitters.

Sweet, sour and umami

Bitter taste signal transduction pathway. Object A is a taste bud, Object B is a taste cell, and Object C is a neuron attached to Object B. Source: Transduction of Taste Signals. US National Library of Medicine

With the sweet, sour and umami tastes the mechanism is different. The substances capable of producing these tastes do not enter the receptor cells by themselves, but bind to receptors indirectly connected to others.

Proteins activate other chemicals (second messengers) that cause depolarization, releasing the neurotransmitter.

Cranial nerves

There are three cranial nerves that connect to taste neurons. The facial nerve transmits stimuli to the taste buds of the anterior two thirds of the tongue, the glossopharyngeal nerve of the posterior third of the tongue, and the vagus nerve innervates the buttons in the throat and epiglottis.

The nerve impulses reach the medulla oblongata. From there, some impulses project to the limbic system and the hypothalamus. While others travel to the thalamus.

Subsequently, these impulses are projected from the thalamus to the primary taste area in the cerebral cortex. This enables conscious perception of tastes.

Due to the projections in the hypothalamus and the limbic system there appears to be a connection between taste and emotions. Sweet foods produce pleasure, while bitter foods cause rejection even in babies.

This explains why people and animals quickly learn to avoid a food if it can affect their digestive system, and to look for the one that was most pleasant.

Research and other possible flavors

The latest research is looking for other flavors that can be captured by sensory cells. It is believed that there could be a greasy taste, as there are probably specific receptors for fat.

In fact, it seems that there are certain fatty acids that the enzymes in saliva differentiate. This is something that is currently being investigated.

Taste of calcium?

It is also studied whether there is a taste of calcium, since it has been found that there are two receptors for this taste on the tongue of mice. A similar receptor has been observed in the human tongue, although its role in tasting has not yet been determined.

What does seem clear in the research is that this "taste" is not liked by mice or humans. It is described as a bitter and chalky taste. Scientists think that, if there was a taste of calcium, its purpose would be to avoid ingesting excessively foods that contain it.

Alkaline and metallic

Currently working to discover if there are other tastes such as alkaline and metallic. Some Asian cultures put on top of their curry dishes what they call "silver or gold leaves." Although they generally lack flavor, a different flavor can sometimes be perceived.

Scientists have pointed out that this sensation has something to do with electrical conductivity, since it adds some electrical charge to the tongue.

Spicy taste?

It should also be clarified that the sensation of hot or spicy is not a flavor in a technical sense. It is actually a pain signal sent by the nerves that transmit the sensations of touch and temperature.

Some pungent compounds like capsaicin activate receptors other than the taste buds. The key receptor is called TRPV1 and it acts like a molecular thermometer.

Normally these receptors send itchy signals to the brain when exposed to high temperatures (over 42 degrees). Capsaicin binds to that receptor and lowers the activation temperature to 35 degrees. For this reason, the receptors send high-temperature signals to the brain, even if the food is not very hot.

Freshness

Something similar happens with the flavor of freshness, with substances such as mint or menthol. In this case, the touch receptors, called TPRM8, are activated. In this case, the brain is tricked into detecting cold at normal temperatures.

Both spiciness and freshness are transmitted to the brain through the trigeminal nerve instead of the classic nerves for taste.

References

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