Do you know how many lemons China produces in a year? In 2021 alone, about 1 million tons of lemons will be produced in China. Lemons are popular all over the world. In recent years, the demand for lemons in my country has also increased year by year. Whether in cities or towns, lemons are often seen in fruit stalls and supermarkets. The domestic sales of lemon may not be large, but it is already a “regular customer” on the fruit shelf.
Why do sour lemons capture the hearts of so many diners? Digging deeper into this question, why do many people like sour taste?
The whole world loves my sour taste
the taste of happiness
Lemon is not the most sour fruit, its acidity is far behind that of the “king of sourness” – green plum. Green plums are too acidic to be eaten raw, and can only be eaten as candied fruit such as sour plums.
After eating a sour plum, as the teeth cut the sour plum flesh, various acidic components in the sour plum spread rapidly in the mouth, collide with our taste buds, and activate the taste receptors in the taste buds. The activated taste receptors release a variety of specialized signals, informing some specific nerve cells on the tongue to transmit the “sour” signal to the brain.
One of the most tart fruits, green plums are used to make preserves
Scientists have found that eating sour foods causes the body to release serotonin, an inhibitory neurotransmitter that regulates appetite, sleep, memory, mood, and more. Those who are familiar with serotonin know that it can make people feel happy (for example, caffeine can temporarily raise serotonin levels, making people feel good for a short period of time). As a widely used neurotransmitter, serotonin exists in many areas in the human body, of which 80% to 90% of serotonin is produced in the intestine, and the central nervous system also produces a small amount of serotonin. It can also produce serotonin. Meanwhile, some scientists have speculated that serotonin’s role may be to transmit sour taste signals between taste receptors and the lingual nerve.
To confirm this hypothesis, scientists designed a special protein that emits green fluorescence (hereafter referred to as chlorophyll), which just happens to bind to the serotonin receptors on nerve cells in the tongue. The experimental results showed that when the mice were hungry after eating sour food, a large amount of chlorophyllin was accumulated in the area of the tongue where the sour taste was felt. This shows that serotonin is indeed produced on the tongue, and further confirms that serotonin is the neurotransmitter that sends acid signals to the brain.
Serotonin is the neurotransmitter that transmits sour taste signals
It can be seen that those who pour half a bottle of vinegar every time they eat noodles must have their brains occupied by the “happiness” transmitted by serotonin when they drink a big mouthful of sour noodle soup. The sour taste can be regarded as a veritable taste of happiness.
Our tongues can sense the five senses of sour, sweet, salty, bitter, and fresh, but not all animals have these five senses. For example, carnivores such as cats, otters, and hunting dogs have lost their ability to sense sweetness; giant pandas who are accustomed to vegetarian food cannot taste umami. But the ability to sense sour taste is very common in the animal kingdom.
Taste helps animals survive. Animals like sweetness because sugar is an important energy substance; umami is mainly produced by amino acids such as ornithine and glutamic acid, so liking umami food is caused by animals’ demand for protein; salty taste is produced by sodium ions, and sodium Ions are an important element to ensure the normal work of cells. Eating salty foods can ensure the normal work of cells; foods that can induce bitter tastes are generally toxic, and the perception of bitterness can keep us away from these toxic foods as much as possible.
Of the five flavors, however, the reason for the need for sourness remains elusive. A sour taste does not mean the food is poisonous, nor does it mean that the food is nutritious. Sour foods contain free-moving hydrogen ions. The higher the concentration of these hydrogen ions, the lower the pH of the food and the more sour the food tastes.
The meaning of taste to animals
Scientists sampled 84 species from the five major vertebrate groups of birds, mammals, reptiles, amphibians and fish and tested their ability to sense sour taste. The results found that all 84 species can sense sour taste. Why do animals perceive sour taste?
The taste of survival
Sensing sour taste can help animals survive better.
Night monkeys’ food is mainly plant fruits, and they especially like to eat some overripe, slightly fermented fruits. These fruits commonly contain acetic acid or lactic acid. Scientists don’t yet know exactly why, but one hypothesis is that the sour taste helps night monkeys discover the fruits. Interestingly, wild boars also prefer tart carrion or fermented plant tubers. Wild boars have a more sensitive sense of smell than night monkeys, and wild boars use sniffing to find food such as plant tubers or fungi buried in the ground.
Night monkeys like sour fruits
Wouldn’t it be dangerous to eat these stale foods? Some scientists believe that the sour taste of these foods is due to the predominance of lactic acid bacteria or acetic acid bacteria, which by themselves are not harmful to wild boars and can inhibit the growth of other microorganisms.
Many animals, including humans, that cannot synthesize vitamin C by themselves, like foods with a certain degree of sourness. This may be because vitamin C has a sour taste, and the perception of sour taste can help these animals discover foods that may contain vitamin C.
Slightly acidic foods can enhance digestion and stimulate saliva production; relatively sweet and sour flavors indicate a higher degree of fruit ripeness; and, of course, extremely acidic foods can also make animals resistant to eating them. In the 1970s, scientists fed unripe tomatoes and lemons to sheep, and the poor sheep cried out with sourness.
In sour fruits, soft acid bacteria or acetic acid bacteria already dominate
taste of evolution
Fish are the oldest vertebrates, and scientists have assessed and confirmed that the vast majority of fish can sense sour taste. Not only can fish sense sour taste, but they also have a lot of taste buds. Not only are there taste buds in the mouth, some fish also have taste buds on the gills, tentacles near the lips, and on the jaws, and some fish have taste buds except for the head. Some also have taste buds, a few fish have taste buds all over the body, and very few fish even have taste buds on their fins.
Why do fish have so many taste buds? Why do all fish sense sourness? This is because all vertebrates need to maintain the acid-base balance in the body, that is, to maintain an appropriate pH value of body fluids, which is one of the prerequisites for the smooth progress of biochemical reactions in the body. Compared with vertebrates living on land, the acid-base balance of fish living in water is more easily affected by the environment, which is one of the important reasons why fish must sense the acidity of water body.
Catfish have taste buds almost all over the body
Excessive dissolved carbon dioxide in the water can lead to acidification of the water body, and the fish in the water are susceptible to the acidity of the water body, resulting in hypercapnia. As a result, the brain function of the fish is affected and the fish is disoriented. This is another important reason why fish values sour perception. Some scientists speculate that as some fish landed and evolved into other types of vertebrates, the fish’s perception of sourness was inherited by subsequent vertebrates, including humans, of course.
Sensitivity to acidity also helps carnivorous fish find prey. Some fish, such as catfish, rely on outer taste buds on their tentacles to sense the presence of prey (such as the carbon dioxide produced when animals lurking in river bottom mud breathe).
The taste of creation
Vinegar is an important invention of mankind. The “National Food Safety Standard Vinegar” defines vinegar as: “a liquid acidic condiment brewed by microbial fermentation using various materials containing starch, sugar, edible alcohol, alone or in combination.” Vinegar is made by two Step-by-step extraction from sugary foods: The first stage is anaerobic fermentation, in which sugars are broken down by yeast in the absence of oxygen to produce ethanol and carbon dioxide; the second stage is aerobic fermentation, in which aerobic fermentation such as Acetobacter Microorganisms convert ethanol into acetic acid.
Vinegar was originally called “醯” (xī) in ancient Chinese. There is a record in “Xunzi: Encouraging Learning” that “acidic acid gathers together”. Later, people called vinegar “酢” (cù). According to legend, Heita, the son of the god of wine, Dukang, made a mistake in making wine and got vinegar on the 21st day of the fermentation of the lees. This sweet and sour seasoning is named “酢”, which means “you” and “twenty-one” respectively.
Vinegar is one of the important cultural labels in Shanxi
Vinegar is produced in many places in China, such as Duliu old vinegar in Tianjin, Qishan vinegar in Shanxi, and red yeast rice vinegar in Henan. Among the local vinegars, the most famous are Yongchun old vinegar, Langzhong Baoning vinegar, Zhenjiang balsamic vinegar and Shanxi old mature vinegar.
There are more than 3,000 vinegar enterprises in China. Although there are only about 130 vinegar enterprises in Shanxi, their annual output accounts for 20% of the national annual output of vinegar. According to statistics, each Shanxi person consumes an average of 7.5 to 10 kilograms of vinegar every year. In the past, relatively wealthy Shanxi people were proud to drink 10-year-old or 20-year-old vinegar. Shanxi people believe that vinegar is like old wine, the more it ages, the more fragrant it is.
The arid climate is an important reason why Shanxi people love to drink vinegar. The tall and majestic Taihang Mountains prevent the humid monsoon from the Pacific Ocean from further penetrating into the Loess Plateau. In the climate that is arid and rainy all the year round, it is easy for people living there to lose their appetite. Old mature vinegar can just add flavor to food, so that Shanxi people can have a good appetite in hot summer.
The flavor of Shanxi aged vinegar is complex, in which microorganisms contribute a lot. Fang Xinfang, a famous microbiologist in my country, once pointed out that Shanxi Qingyuan vinegar has a unique smell and its fermentation temperature exceeds 40 ℃, so microorganisms other than acetic acid bacteria must be involved in the fermentation process. Today, with the help of advanced analytical equipment, scientists know that the acid-producing microorganisms in the fermentation process of Shanxi aged vinegar are mainly acetic acid bacteria and lactic acid bacteria, which determine the sour tone of Shanxi aged mature vinegar. Microorganisms such as Bacillus, Acetobacter pasteuri and Lactobacillus plantarum are responsible for producing rich aroma substances in Shanxi aged vinegar. These aroma substances include ethyl acetate with fruity sweetness, ethyl isovalerate with banana aroma and sweet and sour smell, ethyl isobutyrate with sweet rum aroma, isopentyl with apple brandy aroma and spicy taste Alcohol etc. Shanxi old mature vinegar contains such rich aromatic substances, it is no wonder that Shanxi people are so hard to let go of it.
Shanxi old mature vinegar is delicious, no wonder Shanxi people love to drink vinegar
Animals have learned to survive better by sensing sour taste in the long evolutionary history. Humans not only inherited the ability to sense sour taste from ancestral species, but also creatively created unique sour foods. The sour taste enriches our love for food and deeply affects human civilization.
Balsamic vinegar – grapes can make wine and vinegar
Modena in Italy has three famous icons: supercars, tenor Pavarotti and balsamic vinegar.
Traditional balsamic vinegar is made from Trebbiolo white grapes. Workers simmer the must in copper pots for 24 hours, and the resulting thick must be transferred to large oak barrels for open fermentation. During this process, the concentrated grape juice is constantly oxidized and the water is constantly evaporated, and workers have to transfer the fermentation broth to smaller oak barrels at regular intervals. After 12 years of aging and 4 to 5 transfers, balsamic vinegar is drinkable. It is estimated that to make 250ml of balsamic vinegar requires at least 36kg of grapes.