The role of taste sensitivity in the life of the organism is reduced, first of all, to the regulation of eating behavior (the choice of a certain type of food, the formation of preference reactions, etc.). Taste perception does not remain constant for a long period, it changes depending on the state of the body and, in particular, on the momentary need for a given substance. It can be said that the taste system serves as a kind of control device, thanks to which the selection of adequate nutrients is carried out.

The structure of the taste system

Receptors. The upper surface of the tongue is covered with numerous folds of the mucous membrane, in the thickness of which specialized epithelial formations of a rounded shape are located. These are taste buds or taste buds. A person has an average of 9-10 thousand bulbs. In the thickness of the bulb there is a cavity that communicates with the external environment through a hole - a pore.

Each taste bud includes from 30 to 80 flattened, elongated spindle-shaped cells, closely adjacent to each other like orange slices (Fig. 10).

On the surface of each taste cell facing the pore, there are microvilli that come into contact with solutes. There are three types of cells - sensory, supporting and basal, performing different functions. Sensory cells are mature taste receptors belonging to the type of secondary sensory. Basal cells are immature receptors; they give rise to sensory cells in the process of ontogenesis. Supporting cells perform an auxiliary function.

Pathways of the gustatory system. Each taste cell is innervated by one, and more often by several taste fibers. It has been found that up to 30 fibers can form synaptic contacts with one receptor cell.

Fibers of the facial, glossopharyngeal, vagus, and trigeminal nerves are involved in the transmission of sensory information from taste buds. The main and, apparently, the most specialized information is associated with the facial and glossopharyngeal nerves.

From the taste buds of the anterior two-thirds of the tongue, fibers extend that go as part of the facial nerve. From the posterior third of the tongue, tonsils, hard palate and pharynx, taste impulses enter the glossopharyngeal nerve.

Central divisions of the gustatory system. All taste fibers entering the brain stem end in the nucleus of a single bundle that runs throughout the medulla oblongata. This nucleus is common to the facial, glossopharyngeal, and vagus nerves. Fibers depart from the nucleus of a single bundle, which are directed to the arcuate nucleus, which is part of the ventrobasal complex of the thalamus. From there, information is transmitted to the cortical centers of taste, mainly to the lower part of the postcentral gyrus.

Physiology of the taste system

A single taste cell in most cases reacts to substances of different taste qualities, i.e. is not strictly specific. However, the sensitivity threshold for one of these substances is usually lower than for others. The process of interaction of the gustatory stimulus molecule with the receptor has not been fully elucidated to date. Most researchers believe that there are specialized active centers on the membrane of taste cells, on which the stimulus molecule is adsorbed. It is possible that during the interaction of the receptor with the substance, a change in the conformation of membrane proteins occurs, which, in turn, leads to the development of the receptor potential. The amplitude of the receptor potential depends on the concentration of the stimulating substance.

Among the taste fibers that carry information, fibers were found that selectively respond to stimuli of a certain quality. With an increase in the concentration of the solution, both the frequency of discharges and the number of fibers involved in the reaction (due to different thresholds) increase. However, most taste fibers are not strictly specific. Thus, many fibers of the glossopharyngeal nerve react especially strongly to substances with a bitter taste. And if we consider that this nerve innervates the posterior third of the tongue, it becomes clear why the root of the tongue is most sensitive to bitter. This, however, does not mean that the glossopharyngeal nerve is insensitive to other substances. Its fibers can also react to other substances if their concentration is high enough. The fibers of the facial nerve are more strongly excited by the action of salty, sweet or sour: some of them are more responsive to sugar than to salt, others to salt than to sugar, and so on. Thus, the number of excited fibers and the level of their excitation create a peculiar pattern of impulse activity, which encodes information about the quality and intensity of the stimulus.

When considering the physiology of the central parts of the taste analyzer, it should be noted that most of the neurons in the nucleus of the solitary tract exhibit polymodal sensitivity. They react not only to different taste qualities, but also to tactile and temperature irritations of the surface of the tongue. At the same time, each cell has its own “activity profile”, i.e. a certain level of reaction and response pattern under the action of a substance in a certain concentration.

At higher levels of the sensory system, the number of neurons with highly specific taste sensitivity increases. Thus, when recording the activity of single neurons in the arcuate nucleus, neurons specialized for taste, temperature, and tactile modality were found. A number of cortical cells react only to substances with one taste quality.

Main characteristics of taste sensitivity

The main characteristics of taste sensitivity are the levels of absolute, differential thresholds, latent (hidden) periods of taste sensation and taste adaptation.

Under absolute threshold understand the minimum concentration of a chemical substance that causes a taste sensation in a person. The absolute threshold of perception of different flavoring substances can vary significantly (by several orders of magnitude). As a rule, the detection thresholds for bitter substances are much lower than those for sweet, sour, and salty substances. This is due to the fact that many toxic compounds that are dangerous to the health and life of the body have a bitter taste. Therefore, in the process of evolution, a subtle sensitive mechanism has been formed that can prevent the damaging effect of such substances. In addition, the threshold can change for the same substance both in different subjects and in the same individual in different periods of time. It depends on the place of application and the temperature of the testing solution, the individual characteristics of the subject, the functional state of the subject at the time of the experiment, the body's need for this substance. Due to the complexity of this relationship, it is believed that irritation is not a simple chemical interaction of a substance with a taste cell.

Difference (differential) threshold- this is the value of the minimum perceptible difference in the perception of the same taste stimulus when moving from one concentration to another (expressed in units of concentration). Relative differential threshold is the ratio of the difference threshold to the initial concentration (expressed in relative units). The value of the difference and differential thresholds depends on the concentration of the testing solution and the place of its application. It is shown that the minimum differential threshold takes place at medium concentrations of the substance; at low and high concentrations, the threshold increases.

Hidden (latent) taste period is the time between the application of irritation and the appearance of a sensation of taste. The latent period decreases with an increase in the concentration of the testing solution and an increase in the irritated surface of the tongue.

Phenomenon adaptation It consists in increasing the absolute threshold and reducing the intensity of the taste sensation during prolonged exposure to the stimulus. Depends on the type and concentration of the substance. After the termination of the stimulus, sensitivity is restored. Adaptation to sweet and salty substances occurs faster than to bitter and sour ones.

Questions and tasks for self-control

1. Describe the structure of the taste bud.

2. What is the cause of the receptor potential in the taste cell?

3. How does the value of the receptor potential change with an increase in the concentration of an odorous substance?

4. Why are the detection thresholds for bitter substances lower than for other compounds?

Table of contents of the subject "Vestibular sensory system. Taste. Taste sensitivity. Olfactory sensory system. Smell (smells). Classification of smells.":
1. Vestibular sensory system. function of the vestibular system. vestibular apparatus. Bone labyrinth. Webbed labyrinth. Otoliths.
2. Hair cells. Properties of receptor cells of the vestibular apparatus. Stereocilia. Kinocilium.
3. Otolith apparatus. otolith organ. Adequate stimuli receptors of otolithic organs.
4. Semicircular canals. Adequate stimuli of the receptors of the semicircular canals.
5. The central part of the vestibular system. vestibular nuclei. Kinetoses.
6. Taste. Taste sensitivity. Taste sensory system. Taste reception. Taste time.

8. Central department of the taste system. Pathways of taste sensitivity. Taste kernels.
9. Taste perception. Olfactory sensory system. Macromatics. Microsmatics.
10. Smell (smells). Odor classification. Stereochemical theory of smells.

Membrane of microvilli of taste cells contains specific sites (receptors) designed to bind chemical molecules dissolved in the liquid environment of the oral cavity. There are four taste sensations, or four taste modalities: sweet, sour, salty, and bitter. A strict relationship between the chemical nature of the substance and the taste sensation is not: for example, not only sugars have a sweet taste, but also some inorganic compounds (salts of lead, beryllium), and the sweetest substance is saccharin, which is not absorbed by the body. Most taste cells are polymodal, that is, they can respond to stimuli from all four taste modalities.

Joining specific receptors molecules with a sweet taste, activates the system of secondary messengers of adenylate cyclase - cyclic adenosine monophosphate, which close the membrane channels of potassium ions, and therefore the membrane of the receptor cell is depolarized. Substances with a bitter taste activate one of two systems of secondary messengers: 1) phospholipase C - inositol-3-phosphate, which leads to the release of calcium ions from the intracellular depot with subsequent release of the mediator from the receptor cell; 2) the specific G-protein gastducin, which regulates the intracellular concentration of cAMP, which controls the cation channels of the membrane and this determines the occurrence of the receptor potential. The action of molecules that have a salty taste on receptors is accompanied by the opening of controlled sodium channels and depolarization of the taste cell. Substances with a sour taste close the membrane channels for potassium ions, which leads to depolarization of the receptor cell.

The value of the receptor potential depends on taste quality and chemical concentration acting on the cell. The appearance of a receptor potential leads to the release of a mediator by the taste cell, which acts through the synapse on the afferent fiber of the primary sensory neuron, in which, after 40-50 ms from the onset of the stimulus, the frequency of action potentials increases. Nerve impulses that have arisen in afferent fibers are conducted to the nuclei of single bundles of the medulla oblongata. With an increase in the concentration of the active substance, the total number of reacting sensory fibers increases due to the involvement of high-threshold afferents in the transmission of information from the receptors.

Taste sensitivity

Thresholds of taste sensitivity are detected by alternately applying solutions of substances with different taste qualities to the surface of the tongue (Table 17.4). The absolute threshold of sensitivity is the appearance of a certain taste sensation, which differs from the taste of distilled water. Taste the same substance can be perceived differently depending on its concentration in solution; for example, at a low concentration of sodium chloride, it feels sweet, and at a higher concentration - salty. The maximum ability to distinguish the concentration of solutions of the same substance and, accordingly, the lowest differential threshold of taste sensitivity are characteristic of the middle range of concentrations, and at high concentrations of the substance, the differential threshold increases.

Table 17.4. Absolute Perception Thresholds for Substances with a Characteristic Taste

Absolute taste thresholds vary individually, but the vast majority of people have the lowest threshold for determining substances with a bitter taste. This feature of perception arose in evolution, it contributes to the rejection of the use of bitter-tasting substances in food, to which the alkaloids of many poisonous plants belong. Taste thresholds differ in the same person depending on his need for certain substances, they increase due to prolonged use of substances with characteristic taste(for example, sweets or salty foods) or smoking, drinking alcohol, burning drinks. Different areas of the tongue differ in taste sensitivity to various substances, which is due to the peculiarities of the distribution of taste buds. The tip of the tongue is more sensitive than other regions to sweet, the sides of the tongue to sour and salty, and the root of the tongue to bitter. Taste sensations in most cases are multimodal and are based not only on the selective chemical sensitivity of taste receptor cells, but also on food irritation. thermoreceptors and mechanoreceptors of the oral cavity, as well as the action of volatile food components on olfactory receptors.

Introduction

The laboratory workshop is intended for undergraduates studying in the direction 260100 "Food from vegetable raw materials."

Tasks for laboratory classes and guidelines for their implementation are drawn up in accordance with the current program and meet the requirements of the Federal Educational Standard of Higher Professional Education in the direction of training 260100 "Food from plant materials" (qualification (degree) "Master"). The purpose of laboratory classes is to acquire special knowledge on the synthesis and isolation from natural raw materials of substances used as flavor, color and aroma enhancers in the food industry, to get acquainted with the features of standardization and analysis of these compounds. When performing laboratory work, students must use the knowledge gained in the study of such disciplines as "Food Chemistry", "Analytical Chemistry. Physical and chemical methods of analysis”, “Organic chemistry”, “Physical chemistry”.

Laboratory work is performed by each student independently. Upon completion of the work, the student must issue a report.

Works requiring the use of volatile and flammable liquids (petroleum ether, ethanol, chloroform, etc.) must be carried out under draft in polished dishes.

Taste is the body's response to molecular stimuli. All higher animals have separate responses to taste and smell. In less highly organized animals, such as invertebrates, the separation of taste and smell is less distinct.

There are four main types of taste : sour, sweet, salty and bitter.

To these four main types of taste, which were described in the 19th century by the German physiologist Adolf Fick, a fifth one was officially added recently - the umami taste. This taste is typical for protein products: meat, fish and broths based on them; it is produced by monosodium glutamate. Other types of taste include metallic, tart, etc.

Flavoring substances of foodstuffs conditionally divided into the following groups:

1. Glucophoric (sweet) substances– mono- and disaccharides, saccharin, glycerol and glycine.

According to the glucophoric theory of sensation, the carriers of sweetness are the glucophoric groups -CH 2 (OH); -CH(OH), and auxoglucone groups -CH- are the regulators.

2. Acidic substances- mineral and organic acids, acidic salts - cause a sour taste due to the presence of hydrogen ions. The exceptions are amino acids such as glycine, which has a sweet taste, butyric and nitrosulfonic acids, which have a bitter taste.

3. Salt substances- chlorine salts with low molecular weight. The salty taste is determined by the presence of free chloride ions. The exceptions are salts that have a salty-sour taste (KBr, etc.) and bitter (KI, CaCl 2 , MgCl 2, etc.). Their admixture in table salt worsens the salty taste, giving unpleasant shades.

4. bitter substances– the aforementioned salts, glycosides, essential oils, e.g. bulbous vegetables, citrus fruits (naringin, hespiridin); alkaloids (theobromine, caffeine). Thus, the bitter taste, just like the sweet one, arises when substances of various structures act on the receptors. The bitter taste of some substances appears only in combination with other substances. An example is limonin, which acquires a bitter taste when combined with citric acid, which is observed when citrus fruits freeze and rot.

To influence the nerve endings that cause taste sensations, a certain minimum concentration of substance molecules is required, called taste threshold.

The thresholds of taste sensitivity are revealed by alternately applying solutions of substances with different taste qualities to the surface of the tongue (Table 1). The absolute threshold of sensitivity is the appearance of a certain taste sensation, which differs from the taste of distilled water. The taste of the same substance can be perceived differently depending on its concentration in solution; for example, at a low concentration of sodium chloride, it feels sweet, and at a higher concentration - salty. The maximum ability to distinguish the concentration of solutions of the same substance and, accordingly, the lowest differential threshold of taste sensitivity are characteristic of the middle range of concentrations, and at high concentrations of the substance, the differential threshold increases.

Absolute thresholds for taste sensitivity vary from person to person, but the vast majority of people have the lowest threshold for detecting substances with a bitter taste. This feature of perception arose in the process of evolution, it contributes to the rejection of the use of bitter-tasting substances in food, to which the alkaloids of many poisonous plants belong. Taste thresholds differ in the same person depending on his need for certain substances, they increase due to long-term use of substances with a characteristic taste (for example, sweets or saltiness) or smoking, drinking alcohol, burning drinks.

Taste sensitivity depends on the following factors:

1. The chemical composition of saliva. Saliva, which dissolves food, is a complex mixture of chemical compounds containing both inorganic substances - chlorides, phosphates, sulfates, carbonates, thiocyanates, and organic compounds - proteins and digestive enzymes. After prolonged washing of the tongue with distilled water, as a result of which the taste buds are freed from saliva, the sensitivity threshold for salt is significantly reduced;

2. The chemical nature of the gustatory compound and its concentration;

3. From what the person ate to exposure to that compound;

4. Temperatures of the consumed product: the lowest threshold values ​​of sensitivity are obtained in the range of 22 - 32°C.

5. Places and areas of the stimulated area of ​​the tongue, which is due to the peculiarities of the distribution of taste buds. The tip of the tongue is more sensitive than other regions to sweet, the sides of the tongue to sour and salty, and the root of the tongue to bitter.

6. Age: taste sensitivity in the elderly decreases, the tendency to decrease in sensitivity becomes noticeable by about 60 years;

7. Individual characteristics of a person.

Table 1. Absolute thresholds of taste sensitivity of substances with a characteristic taste

Food products have either one taste (sugar is sweet, table salt is salty), or they differ in a combination of the main types of taste. In this case, they speak of a harmonious and inharmonious combination of taste. So, harmoniously, as a whole, sweet or salty tastes are combined with sour or bitter. For example, the sweet-sour taste of fruits, some confectionery; bittersweet taste of chocolate; sour-salty taste of pickled vegetables; salty-bitter taste of olives.

Combinations of salty-sweet, bitter-sour are considered inharmonious, these combinations are perceived as two different tastes, they are unusual for food products, are rare and occur, as a rule, as a result of spoilage.

Different types of taste, when combined, can soften or enhance each other. So, sweet taste softens sour and bitter, sour enhances salty and bitter, astringent and pungent enhance sour and bitter, but soften sweet.

With the simultaneous exposure to different tastes, the weakest of them can sometimes be observed to disappear, even if the substance that causes it is contained in quantities exceeding the threshold of sensation. The disappearance of a weak taste can also be facilitated by other factors that change or compensate for the taste (pH of the medium, juiciness, fat content, etc.). Salty, sweet and sour tastes easily disappear.

The taste of most substances has not yet been established. It is generally accepted that many proteins, polysaccharides, fats are devoid of taste. However, knowledge in this area is still incomplete. Thus, specific proteins of plant origin, which have a high taste activity, have recently been discovered. Two of them (monellin, thaumatin) have an intensely sweet taste and can be considered as taste proteins.

In addition, substances have been found that are taste modifiers(substances that can change the taste quality), for example, miraculin glycoprotein. After miraculin, acid is perceived as a sweet substance (this phenomenon is called taste illusion). It is assumed that miraculin binds to the plasma membrane. The acid changes the conformation of the membrane, stimulating its sweet site. Modifiers are of particular interest to the food industry.

Usually, in the organoleptic evaluation of food products, taste refers to sensations resulting from stimulation of chemoreceptor cells, and tactile and olfactory sensations. The former are related to the consistency of the product or the effect of chemicals on the oral mucosa. In this regard, taste can be characterized by such a concept as astringency. It is caused by tannins that act on the inner surface of the oral cavity, resulting in a feeling of tightening of the surface and its dryness. A sharp, burning taste is felt due to a burn of the mucous membrane, for example, pepper capsaicin, mustard sinalbin.

To characterize the complex of impressions of taste, smell and touch during the distribution of the product in the oral cavity, determined quantitatively and qualitatively, the definition is applied - deliciousness of food.

Flavoring substances are widely used in food production, their use is controlled by the State Sanitary and Epidemiological Supervision of the Russian Federation.

Laboratory works

Taste sensitivity assessment

The test of sensory sensitivity to recognize the main types of taste is carried out on model solutions of chemically pure substances:

sweet - 1% sucrose solution

salty - 0.4% sodium chloride solution

sour - 0.05% tartaric acid solution

bitter - 0.5% magnesium sulfate solution

To prepare the solution, distilled water treated with activated carbon is used. The solutions are stored in flasks with ground stoppers at a temperature of 18-20°C. Pour 35 ml of solution into tasting glasses. In total, nine samples are prepared: two glasses with any three solutions and three glasses with the fourth solution. The test subject does not need to know the order in which samples are submitted. Between the samples make a 1-2 minute break, be sure to rinse your mouth with clean water. With seven or more correct answers, the candidate for tasters is recommended to perform the following test tasks.

To determine the threshold sensitivity to the main taste sensations, the evaluator is asked to try a series of solutions of increasing concentration. Each series consists of 12 solutions. The concentration is considered detected if the test solution is identified in three triangular comparisons. In each triple of solutions, two contain water, and one contains the test solution. They are served in a sequence unknown to the subject. Solutions are prepared in accordance with table 2.

Table 2. - Solutions used in the determination of threshold taste sensitivity

Solution number	Substance (g/l)
sucrose	NaCl	wine acid	MgSO4
	1.0	0.1	0.05	1.0
	1.3	0.2	0.07	1.3
	1.7	0.3	0.1	1.7
	2.0	0.4	0.15	2.1
	2.7	0.5	0.20	2.7
	3.5	0.7	0.27	3.5
	4.5	1.0	0.35	5.5
	5.7	1.5	0.45	5.7
	7.3	2.0	0.6	7.3
	9.4	2.8	0.8	9.4
	12.0	4.0	1.00	12.0

The threshold sensitivity to the main types of taste for candidates for tasters should be: for sweet taste - 7 g/l of sucrose; for a salty taste - 1.5 g / l for sodium chloride; for sour taste - 0.5 g / l of tartaric acid; for a bitter taste - 5.0 g / l of magnesium sulfate.

TASTE SENSITIVITY

Taste stimuli are perceived by the taste buds. The bulbs are located in the mucous membrane. They occupy almost the entire thickness of the stratified epithelium, but do not reach the free surface. Taste buds are also found in the mucous membrane of the back of the tongue, soft palate, anterior surface of the epiglottis and vocal cords, posterior pharyngeal wall, and upper esophagus. In the mucous membrane of the oral cavity, taste buds are found as separate inclusions.

There are four types of basic taste sensations - sweet, salty, sour and bitter. With prolonged exposure to a taste substance, sensitivity to it gradually decreases due to taste adaptation. However, adaptation to one gustatory substance does not affect sensitivity to other gustatory stimuli.

Complex taste sensations that occur when eating a variety of foods are caused by irritation not only of taste buds, but also of surface sensitivity receptors (tactile, temperature), as well as olfactory ones.

Different parts of the mucous membrane of the tongue are not equally sensitive to the main stimuli. Sweet is perceived by all points of the tongue, but this feeling is more pronounced at its tip. Bitterness is also perceived by all points of the tongue, but the foliate and vallate papillae are most sensitive to it. Salty is best perceived with the tip of the tongue.

There are several methods for testing taste sensitivity. So, if it is necessary to find out whether there are violations of taste sensitivity to all or to some types of irritants, the patient is offered to rinse his mouth with 10 ml of a certain solution (temperature 20-25 ° C) for 3-5 s with intervals for bitter 3 minutes, and for other stimuli 2 min. For research, you can use a 20% sugar solution, 10% sodium chloride solution, 0.2% hydrochloric acid solution and 0.1% quinine sulfate solution.

When studying the taste sensitivity of individual parts of the tongue, a drop of the corresponding solution is applied to them with a thin brush or glass rod. To avoid spreading the liquid over the entire surface of the tongue, the patient indicates on the plate with the designations of the four main stimuli the one that corresponds to his sensation. Before the study and after each test, the patient should rinse his mouth thoroughly. According to some authors, the order of application of taste stimuli does not play a role, from the point of view of others, taste sensitivity to sour should be evaluated last, since sour reduces taste sensitivity in general.

There is also evidence that weak (subthreshold) solutions of quinine and sodium chloride increase sensitivity to sugar. If it is necessary to determine the threshold, use solutions of increasing concentration. The threshold is considered to be the concentration at which the patient first establishes the type of stimulus.

In the study of threshold concentrations, individual fluctuations of the body must be taken into account.

Different types of taste sensitivity are characterized by a certain latent period of sensation, i.e., the time interval between the application of a stimulus and the occurrence of a particular sensation (Table 1).

The taste buds on the tongue respond to stimuli located in the mouth. In other words, taste sensitivity in all vertebrates is involved in orientation at close range. At the same time, in fish, the sense of taste can also serve as orientation at a long distance. In water, flavoring substances move by diffusion and convection from very distant sources to taste buds, which can be dispersed over the entire surface of the fish's body.

In addition to its role in orientation at close range, the human sense of taste performs an important function by triggering a series of reflexes. For example, washing the tongue with a secret from the serous glands is controlled by a reflex, which is under the influence of taste buds. The secretion of saliva is also triggered reflexively by appropriate stimulation of the taste buds. Even the composition of saliva varies depending on the nature of the stimuli acting on sensory cells, and gustatory stimuli also affect the secretion of gastric juice. Finally, it has been proven that vomiting is induced with the participation of taste sensitivity.

Literature

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• 2. Lectures on the physiology of the central nervous system: Textbook. Faculty of Biology and Chemistry, UdSU, Pronichev I.V. -- Powered by swift.engine.edu, 2003. - 162 p.
• 3. Shulgovskiy VV Fundamentals of neurophysiology: Textbook for university students. -- M.: Aspect Press, 2000. p. 277.
• 4. Shulgovsky VV Physiology of higher nervous activity with the basics of neurobiology: Textbook for students of biol. specialties of universities. - M .: Publishing Center "Academy", 2003. - 464 p.