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Photo Source: Pixabay if saliva deceives you, don't be sad, don't be sad, because it not only deceives you.

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The tropical regions of West Africa are rich in a plant called Synsepalum dulcificum.

Photo Source: Hamale Lyman via Wikimedia Commons its fruit itself tastes sour, but when humans eat it and put a piece of lemon in their mouth, they will feel that the lemon is sweet. The magic of "sweetening" sour food lasts about an hour.

Mysterious fruit can deceive human taste because of a special glycoprotein-mysterious fruit protein (miraculin). This substance has no taste in a neutral environment, but in acidic conditions, it binds to sweet receptors in taste buds. In this way, when the mysterious fruit protein stays on the tongue, people will regard sour things as sweet.

So, without using such taste modifiers, humans will be able to taste the real taste of food? It's not that simple. You think your taste buds can communicate directly with the food, but in fact, the taste you eat is not the flavor of the food itself, but the taste when it is trained by saliva.

When the mystery fruit suddenly tells us that lemons are sweet, we at least know that it is a lie. But if saliva quietly modifies our sense of taste, can we still find out very tactfully?

If you eat too much, it won't taste bad. Saliva is a lubricant in the mouth. With its protection, we can speak and eat smoothly without getting hurt in these daily activities. But the processing of food by saliva does not just reduce the particles in it, turning the food into an easy-to-swallow ball.

For example, when we eat a bar of chocolate, the taste substances in it, such as sweet compounds, bitter compounds, etc., usually dissolve in saliva and then bind to the receptors on the taste buds, so that we have a chance to feel it. It's not so much tasting chocolate as tasting a mixture of saliva and chocolate-there's nothing you can do about it. after all, it's hard to taste without saliva.

Ensuring the normal functioning of our sense of taste is one of the tasks of saliva. In addition, saliva may also unwittingly transform our sense of taste. In your memory, have you ever encountered a kind of food that at first felt so bad that you wanted to throw up after a bite, but after eating it a few times, you found that it didn't taste so bad, and even slowly liked it?

Photo: in the year of Pixabay2017, a group of scientists trained rats' sense of taste with special "delicacies". The diet they designed for rats contains 0.375% quinine, a bitter irritant that is not a friendly ingredient for ordinary mice who are not used to suffering. The rats in the experimental group ate normal food without quinine for 14 days, and then ate the food with quinine for 14 days, while the rats in the control group enjoyed a diet without quinine all the time.

The rats that just started eating quinine were very uncomfortable and their food intake decreased sharply. But two weeks later, they became much more receptive to bitter foods and ate back to baseline levels. By contrast, there was no significant change in the amount of food eaten by the rats who had never eaten quinine. So, the rats trained with quinine diet become able to endure hardship, is it that they are used to that bitterness? Or has the taste of quinine changed in their mouths?

Scientists have found that during quinine feeding, a variety of salivary proteins are secreted in the mouth of rats more than before. Moreover, these salivary proteins did not return to baseline levels when the rats that had eaten bitterness for two weeks returned to a normal diet. The researchers confirmed through experiments that these changes in protein secretion were not due to changes in the amount of food eaten in rats, but precisely because quinine was added to the diet.

Later, the same research team did another experiment in which saliva from rats that had developed the ability to endure bitterness was put into the mouths of rats that had not experienced bitterness, and the rats that had not been trained by bitterness were able to tolerate bitterness. At the same time, rats who had no bitter experience and did not get "bitter saliva" from their peers were still very resistant to the sudden arrival of bitter food.

Although scientists are not quite sure which proteins help rats endure bitterness, different saliva does seem to give rats a different sense of taste. So, will human beings who have been trained to endure hardship and those who have not been trained have different tastes?

In 2018, a team of scientists recruited 64 volunteers to drink bitter chocolate almond milk three times a day, each time to rate the taste of almond milk. The taste test lasted a week, and the bitterness scores reported by the volunteers declined over time.

In addition to the subjective feeling that almond milk became less bitter, the saliva composition of the volunteers also changed: the content of several proline-rich proteins (proline-rich proteins,PRP) gradually increased. Some of these proteins can bind to bitter molecules such as tannins. And the reduction in bitterness people perceive may have something to do with it.

Sometimes, our evaluation of a food will change from bad to not bad, or even to delicious, perhaps as a result of a change in saliva composition. The researchers speculate that this may be an adaptation that can help humans reduce their negative feelings about bitter substances (or other unacceptable taste substances).

In addition to changing the chemical composition of saliva, some physical methods can also be used to change our taste perception.

An important prerequisite for us to feel sweetness or bitterness when cola is out of breath is that sweet or bitter compounds successfully reach the taste buds and bind to the corresponding taste receptors. But even if you have these flavor molecules in your mouth, you don't always reach the taste buds. If there is a way to block the path of some flavor molecules to the taste buds, it can change the way humans perceive taste.

For example, in a study published in 2021, scientists believe that this may be part of the reason why aerated colas are not as sweet as breathless colas.

In fact, there is a better-known explanation for this phenomenon, which is that when carbon dioxide is converted into carbonic acid, it stimulates the nociceptor (nociceptor) on the tongue, causing pain, distracting the brain and not feeling too sweet. But the team insisted on exploring the issue from another perspective.

Photo Source: Pixabay they focus on the lubrication mechanism in the mouth. In the course of human diet, there will be sliding between the tongue and the upper jaw, when saliva as a lubricant is critical, it can reduce the damage caused by the friction between the uneven tongue and the upper jaw.

For example, when the saliva film is too thin to completely avoid direct contact between the tongue and the upper jaw, this lubrication mode is called boundary lubrication (boundary lubrication); and when the saliva film is enough to completely separate the two surfaces without any contact, the lubrication mode becomes full-film lubrication (full-film lubrication). There is also an intermediate state between different lubrication modes, called mixed lubrication (mixed lubrication).

In the laboratory, scientists used an artificial oral model to simulate the situation when the tongue and upper jaw were lubricated with liquid. They found that when the tongue moves slowly relative to the upper jaw in the artificial mouth, the liquid provides boundary lubrication. As the sliding speeds up, more liquid will be dragged into the contact surface between the tongue and the upper jaw, the hydrodynamic pressure will push the two surfaces away, and the lubrication mode will change to mixed lubrication and eventually to full-film lubrication.

The friction force in the mouth will also be different between different lubrication modes. The researchers found that under mixed lubrication (speed 3-15 mm / s), when the thickness of the film formed by the liquid (~ 25 nm) was close to the roughness of the tongue surface in the artificial mouth (~ 20 nm), the friction caused by soda is more than 3 times that of non-soda (under the same pressure).

This is because carbon dioxide in soda accumulates at the entrance to the interface between the tongue and the upper jaw, limiting fluid flow, reducing hydrodynamic pressure and increasing friction, the researchers explained. Scientists are so concerned about the friction in the mouth because it often affects the taste of food and the taste that people perceive.

Image source: Vl coach descu et al, 2021 in addition, the researchers found another factor that increases friction in soda. They found that soda reduced the thickness of the saliva membrane in the artificial mouth by 80%. If you destroy the lubricating saliva membrane, it will bring more friction to the mouth.

Scientists say that one reason why aerated colas are not as sweet as breathless colas may be that friction-related mechanisms affect the flow of flavor molecules to taste buds when we drink aerated colas. Of course, this does not mean that they want to overturn their predecessors' explanations, but just provide another way of thinking.

So, what's the use of this kind of thinking? Knowing more about the laws of taste perception, food scientists will be better able to deceive people's taste perception. But it doesn't matter. We've never tasted the real taste of food anyway.

Eating bird's nest is the taste of saliva and saliva?

Reference:

Https://knowablemagazine.org/article/health-disease/2018/gut-feelings

Https://pubmed.ncbi.nlm.nih.gov/29162505/

Https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7656233/

Https://www.eurekalert.org/news-releases/654605

Https://www.sciencedirect.com/science/article/abs/pii/S0021979720314193

Https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7733011/

This article comes from the official account of Wechat: global Science (ID:huanqiukexue)

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