What is the function of three green leaves?

The existing research data show that there are as many as 500 chemical components in tea, including more than 450 organic compounds and about 30 inorganic compounds. The chemical components in tea can be divided into two parts: moisture and dry matter. See table 1 for its specific categories.

Table 1- Classification of chemical constituents in tea:

Classification names account for% of fresh leaves and% of dry matter.

Humidity 75 ~ 78

2-4 parts of dry matter (22%-25% of fresh leaves) water-soluble inorganic compound.

Water insoluble fraction 1.5 ~ 3.0

20-30 parts of organic compound egg white

Amino acid 1 ~ 4

3-5 parts of alkaloid

20-35 parts of tea polyphenols

Sugar 20-25

Organic acid 3 or so

The lipid is about 8.

Chromatin 1.

0.005-0.03 of aromatic substance

Vitamin 0.6 ~ 1.0

enzyme

As can be seen from the table, the chemical components in tea are various and complex, but the biochemical reaction pathways of their synthesis and transformation are interrelated and mutually restricted.

1, moisture

Water is an essential component in the life activities of tea trees, and it is also an important medium for a series of chemical changes in the process of making tea. In the process of making tea, the change of tea color and fragrance is accompanied by the change of water content. Therefore, the change of water content is often regarded as an important biochemical index to control the quality of tea. The water content of fresh tea leaves is generally 75% ~ 78%, which varies with tea varieties and seasons. Generally, the water content of tender leaves, rainy leaves, exposed leaves and big leaves is higher in rainy season and spring, and the high water content can reach about 84%. The water content of old leaves, middle and small leaf species and leaves is low in dry season and sunny day. See Table 2 for the moisture control indexes in the process of tea making.

Table 2- Changes of water content during processing of fried green tea (%):

Nominal water content

Fresh leaves 75 ~ 78

60-64 fixing leaves

Knead about 60 leaves.

35-40 parts of second light liquid

Sanqing liquid 10 ~ 15

5 ~ 6 dry foot leaves

2. protein and amino acids

The content of protein in tea is 20% ~ 30% of dry matter, and the content of protein which can be directly used in water is only 1% ~ 2%. This part of water-soluble protein is one of the ingredients that form the taste of tea soup. Amino acids are the basic substances that constitute protein, accounting for 1% ~ 4% of the total dry matter. Tea contains more than 25 kinds of amino acids, including theanine, glutamic acid, aspartic acid, asparagine, arginine, serine, alanine, histidine, threonine, glutamine, phenylalanine, glycine, valine, tyrosine, leucine and isoleucine, in which theanine accounts for more than 50% of the total amino acids. Amino acids, especially theanine, are important components in the formation of tea aroma and freshness, and are closely related to the formation of green tea aroma.

3. Alkaloids

The alkaloids in tea include caffeine, theobromine and striatum. Among them, the content of caffeine is the most, accounting for about 2% ~ 5%; Other contents are very few, so the alkaloid content in tea is often expressed by the determination of caffeine content. Caffeine is easily soluble in water and is an important substance to form tea flavor. The "muddy after cooling" in black tea soup is a macromolecular compound formed by caffeine and polyphenols in tea, which is one of the indexes to measure the quality of black tea. Caffeine can be used as one of the characteristics to distinguish true and false tea. Caffeine has many pharmacological effects on human body, such as refreshing, diuresis, promoting blood circulation and helping digestion.

4. Tea polyphenols

Tea polyphenols are the general name of more than 30 polyphenols in tea, including catechins, flavonoids, anthocyanins and phenolic acids. The content of tea polyphenols accounts for 20% ~ 35% of the total dry matter. In the total amount of tea polyphenols, catechin accounts for about 70%, which is an important component that determines the color, aroma and taste of tea. Its oxidative polymerization products, such as theaflavins and thearubigins, play a decisive role in the red color and taste of black tea soup. Flavonoids, also known as anthoxanthin, are one of the main substances that form the color of green tea soup, accounting for 1% ~ 2% of the total dry matter. Anthocyanins are bitter, and the content of anthocyanins in purple buds is high. If there are too many anthocyanins and the quality of tea is poor, it will make it difficult to ferment black tea and affect the redness of soup. It is even worse for the quality of green tea, which will cause bitterness and green leaves. The content of phenolic acids in tea is low, including gallic acid, catechin, chlorogenic acid, caffeic acid and so on.

5. sugar

Sugar in tea includes monosaccharide, disaccharide and polysaccharide. Its content accounts for 20% ~ 25% of the total dry matter. Monosaccharide and disaccharide, also known as soluble sugars, are easily soluble in water, with a content of 0.8% ~ 4%, and are one of the substances that constitute the taste of tea. Polysaccharides in tea include starch, cellulose, hemicellulose and lignin, accounting for more than 20% of the total dry matter of tea. Polysaccharide is insoluble in water and is an important component to measure the tenderness of tea. Tea has low tenderness and high polysaccharide content; High tenderness and low polysaccharide content.

Pectin and other substances in tea are metabolites of sugar, accounting for about 4% of the total dry matter. Water-soluble pectin is one of the main components that form the thickness and luster of tea soup.

6. Organic acids

Tea contains a variety of organic acids, accounting for about 3% of the total dry matter. Organic acids in tea are mostly free organic acids, such as malic acid, citric acid, succinic acid and oxalic acid. Organic acids formed in the process of making tea include palmitic acid, linoleic acid and ethylene acid. Organic acid is one of the main aroma components in tea. It has been found that there are 25 organic acids in the aroma components of tea. Although some organic acids have no fragrance, they are transformed into aroma components after oxidation, such as linoleic acid. Some organic acids are good adsorbents for aroma components, such as palmitic acid.

7. Lipids

Lipids in tea include fat, phospholipids, glycerides, sugar esters and thioesters, accounting for about 8% of the total dry matter. It has a positive effect on the formation of tea aroma. Lipids in tea protoplasm play a regulatory role in the penetration of substances into human cells.

8. pigment

Pigments in tea include fat-soluble pigments and water-soluble pigments, and their contents only account for about 65438 0% of the total dry matter of tea. Fat-soluble pigments are insoluble in water, including chlorophyll, lutein and carotene. Water-soluble pigments, including flavonoids, anthocyanins and theaflavins, lycopene and theabrownins, are all oxidation products of tea polyphenols. Fat-soluble pigment is the main component that forms the color of dry tea and the color of leaf bottom. In particular, the color of green tea and dry tea and the yellow-green color at the bottom of leaves are mainly determined by the total content of chlorophyll and the composition ratio of chlorophyll a and chlorophyll b. Chlorophyll a is dark green, chlorophyll b is yellow-green, and the chlorophyll b content in new shoots is high, so the color of dry tea is mostly light yellow or light green. In the fermentation process of black tea processing, chlorophyll is destroyed a lot, resulting in dark brown substances and oxidation products of tea polyphenols. Protein, pectin, sugar and other substances in tea combine to make the dry color of black tea brown or dark black, and the leaf bottom is red. The colors of green tea, black tea, yellow tea, white tea, oolong tea and black tea are closely related to the content, composition and transformation of pigments in tea.

9. Aromatic substances

Aromatic substances in tea refer to the general name of volatile substances in tea. In the total chemical composition of tea, the content of aromatic substances is not much. Generally, fresh leaves contain 0.02%, green tea contains 0.005% ~ 0.02%, and black tea contains 0.0 1% ~ 0.03%. Although there are not many aromatic substances in tea, the types are very complicated. According to analysis, there are usually more than 300 kinds of aroma components in tea, and there are about 50 kinds of aroma components in fresh leaves. Green tea contains 1O0. There are as many as 300 kinds of aroma components in black tea. The main components of tea aroma substances are alcohol, phenol, aldehyde, ketone, acid, ester, lactone, nitrogen-containing compounds, sulfur-containing compounds, hydrocarbons, oxides and so on. Alcohols are the main aromatic substances in fresh leaves, and low-boiling gray-green alcohols have strong grass fragrance, high-boiling linalool, phenylethanol and so on. It has the characteristics of fragrance and floral fragrance. The aroma components of finished green tea are mainly alcohols and pyrazines, and pyrazines are mostly formed in the baking and frying process of green tea processing. The main aroma components of black tea are alcohols, aldehydes, ketones, esters and other aroma compounds, most of which are oxidized during the processing of black tea.

10, vitamins

Tea is rich in vitamins, accounting for 0.6% ~ 1% of the total dry matter. Vitamins are divided into water-soluble and fat-soluble. Fat-soluble vitamins include vitamin A, vitamin D, vitamin E and vitamin K, etc. Vitamin a content is more. Fat-soluble vitamins are insoluble in water and cannot be directly absorbed and utilized when drinking tea. Water-soluble vitamins include vitamin C, vitamin B 1, vitamin B2, vitamin B3, calcium pantothenate, vitamin B 1 1, vitamin P and inositol. Vitamin C content is the highest, especially high-grade and famous green tea. Generally, the vitamin C content per 100 g of high-grade green tea can reach about 250 mg, and the highest can reach more than 500 mg. It can be seen that people can absorb certain nutrients by drinking green tea.

1 1, enzyme

Enzyme is a kind of egg white body, which participates in a series of chemical changes caused by tea plant life activities and enzymatic activities in tea processing, so it is also called biocatalyst. There are many kinds of enzymes in tea, including oxidoreductase, hydrolase, lyase, phosphorylase, transposase and isomerase. Enzymatic proteins have the characteristics of general protein, and are easily denatured and inactivated at high or low temperature. All kinds of enzymes have their optimum temperature range, and the enzyme activity is the strongest in the range of 30 ~ 50℃. If the enzyme is inactivated and denatured, it will lose its catalytic ability. The catalysis of enzymes is specific, such as polyphenol oxidase, which can only oxidize tea polyphenols and polymerize into theaflavins, thearubigins and theabrownins. Protease can only promote the decomposition of protein into amino acids. Tea processing is to use this characteristic of enzyme to inactivate or stimulate the activity of enzyme through technical means, so that it can carry out enzymatic reaction along the requirements of tea, thus obtaining the unique color and aroma of various teas. For example, in the process of green tea processing, a series of chemical changes caused by enzymes are prevented in a short time by using high temperature enzyme deactivation, and the quality characteristics of green leaf green soup are formed. The purpose of fermentation in the processing of black tea is to intensify the activity of enzymes, promote the oxidative polymerization of tea polyphenols under the catalysis of polyphenol oxidase, and generate oxidation products such as theaflavins and thearubigins, thus forming the quality characteristics of black tea Hongye Red Soup.

12, inorganic compound

Inorganic compounds in tea account for 3.5% ~ 7.0% of the total dry matter, which are divided into water-soluble parts and water-insoluble parts. These inorganic compounds are called "ash" after high temperature combustion. The water-soluble part of ash is called water-soluble ash, which accounts for 50% ~ 60% of the total ash. Tea with good tenderness has higher water-soluble ash, and tea with thick stems has higher total ash. Ash content is one of the indexes for quality inspection of exported tea, and it is generally required that the total ash content should not exceed 6.5%.