teapolyphenols (TPs) is a general term for polyhydroxyphenolic compounds in tea, including flavanols (catechins), flavandiols, flavonoids and phenolic acids. Catechins are a class of important substances in tea polyphenols, accounting for about 60% to 80% of the total amount of tea polyphenols. They mainly contain 8 monomers, including epigallocatechin gallate, epigallocatechin, gallocatechin, epicatechin gallate, epicatechin gallate, catechin gallate, epicatechin gallate, epicatechin gallate, epicatechin gallate, epicatechin gallate, epicatechin and epicatechin.

In the process of tea processing, polyphenol oxidase and peroxidase oxidize catechins to obtain thearubin, theaflavin and theaflavin three tea pigments. These TPs not only give the tea its complex taste and color, but also benefit human health.

Today, while pursuing high-quality economic development, people also consider green development and recycling. Tea polyphenols have antioxidant, antibacterial, anticancer and anti-obesity activities, so researchers have used them in medicine and food.

In medicine, researchers are using delivery systems to protect easily degradable drugs and improve their bioavailability; In addition, tea polyphenols are combined with proteins and polysaccharides to make new sunscreen products and drugs, which are used for skin care, anti-allergy, anti-pathogen, maintaining oral health and regulating lipid metabolism.

In the field of food research, tea polyphenols are mainly combined with polysaccharides, proteins, etc., through the interaction of molecules to improve the sensory quality of food, prolong the storage period of food, and make food packaging materials. Based on this, we discussed the application research of tea polyphenols in the field of food and medicine, in order to provide reference for the in-depth research of tea polyphenols in food and medicine.

1.Physical and chemical properties of tea polyphenols

Tea polyphenols are derived from tea leaves and are a mixture of organic polyhydroxyl compounds, including catechins, anthocyanins, flavonols and phenolic acids, etc. The main antioxidant component is catechins. Among them, epigallocatechin gallate accounted for 50% to 60%, epicatechin gallate accounted for 15% to 20%, epigallocatechin accounted for 10% to 15%, gallatechin accounted for 6% to 8% and epicatechin accounted for 4% to 6%. At room temperature, tea polyphenols are a light yellow or light green powder, astringent taste, strong acid resistance, stable in pH 2~7; Tea polyphenols have certain hygroscopicity and are easy to change color in alkaline environment.

2.Biological activity of tea polyphenols

Tea polyphenols have various biological activities such as antioxidant, antibacterial and anti-mutation, EGCG is the most abundant in catechins and plays the main antioxidant activity. The biological activity comes from the phenolic hydroxyl group in tea polyphenols, which plays different biological activities in different food types. These special functions make tea polyphenols widely used in food.

Application of tea polyphenols in food

1.Food preservation and preservation

Tea polyphenols can be widely used in food preservation and preservative, its non-toxic side effects and edible safety characteristics make it an ideal choice. It can prevent food oxidation discoloration, improve the stability of cellulose, and protect the nutrients in food.

2.Replace synthetic antioxidants

With the attention paid to food safety, tea polyphenols are gradually replacing artificial antioxidants as natural antioxidants. It can not only be used in animal and vegetable oils, meat products, aquatic products, fruit and vegetable foods, etc., but also can be used in pastry, candy and so on. It is worth noting that the antioxidant activity of tea polyphenols was first used in fats and oily foods. Due to the activity of phenol hydroxyl on the benzene ring of catechins to supply hydrogen, it has a strong reducing ability and becomes an ideal natural antioxidant for fats.

The antioxidative mechanism of tea polyphenols is that the active phenol hydroxyl group, as a hydrogen donor, binds to the free group of fatty acids, interrupts the chain reaction of fatty acid oxidation, and thus inhibits the formation of hydroperoxide. At the same time, fat-soluble tea polyphenols can chelate with trace variable metal elements in oil, so that it loses catalytic activity and terminates free radical chain reaction from the source. In addition, the phenol hydroxyl group itself is easily oxidized, which reduces the oxygen content in the oil and delays the oxidation of the oil.

3.Functional food development

Tea polyphenols show great potential in the development of functional food, and its unique chemical structure determines that it has a strong ability to remove free radicals. Tea polyphenols have low REDOX potential, polyo-phenol hydroxyl group can provide hydrogen to interrupt or terminate the free radical chain reaction, and its unique chemical structure determines that it has a strong ability to remove free radicals. Tea polyphenols can activate the scavenging system of free radicals, and inhibit the production of free radicals by inhibiting the oxidation-inducing transition metal ions of the oxidase system. As a natural free radical scavenger, tea polyphenols are beneficial for maintaining human health. Although China is still in its infancy in this field, it has broad prospects for future development.

4.Application in the preservation of meat products and aquatic products

The common pathogenic bacteria in meat products are pseudomonas, Enterobacter, staphylococcus and salmonella, and the main bacteria causing the spoilage of aquatic products are pseudomonas bacteria. Tea polyphenols can effectively inhibit the reproduction of a variety of bacteria, slow down the oxidation of fat, delay the deterioration, thus extending the freshness of meat products and aquatic products.

In recent years, tea polyphenols in pork, beef, mutton and other meat products and a variety of fish slices, surimi, fish balls and shrimp and other aquatic products have been reported one after another, is an ideal natural fresh-keeping agent. A large number of studies have shown that the higher the concentration of tea polyphenol preservation solution, the better the inhibition effect on the microorganisms of meat products and aquatic products, but tea polyphenols will have adverse effects on the sensory perception of meat, resulting in the color of meat. Tea polyphenols can inhibit the growth of many kinds of bacteria, but its mechanism is not clear.

5.Application in fruit and vegetable preservation

Better control of pathological water loss caused by harmful microorganisms on fruit damage; Tea polyphenols have high antioxidant effect, which can slow down the oxidative damage of fruits and vegetables, regulate the activity of polyphenol oxidase, and activate the defense system of fruits and vegetables. At the same time, tea polyphenol molecules contain a number of active phenolic hydroxyl groups, which can directly provide the hydrogen in the molecules to vitamin C in fruits and vegetables, so that it can maintain a reduced state and reduce the loss of vitamin C.

The low concentration of tea polyphenols sprayed or coated on the surface of fresh fruits and vegetables can inhibit bacterial reproduction and extend the fresh life of fruits and vegetables. The fresh-keeping mechanism is complex, and the dominant factors are different with different types of fruits and vegetables. In addition, tea polyphenols can also delay the post-ripening period of fruits and vegetables, because it has a slowing effect on the biochemical activity of fruits and vegetables. However, the preservation mechanism of tea polyphenols for different fruits and vegetables is not the same, and the required dosage and use conditions of different objects are different, which also needs further research.

Application of tea polyphenols in medicine

1, anti-oxidation and anti-radiation

Because of its unique chemical structure, tea polyphenols have very strong antioxidant capacity, which is far more than common antioxidants such as VC, VE and artificial antioxidants BHT, BHA and so on. In addition, tea polyphenols can also remove harmful free radicals, enhance the body's immunity, and catechin derivatives can also reduce the toxicity of heavy metals on the human body and anti-radiation effect, so it is also known as "radiation busters".

2.Hemostatic function

Tea polyphenols have antioxidant and antibacterial activities, so they can inhibit oxidative stress and bacterial reproduction at the wound site, promote the formation of blood vessels in vitro and the deposit of collagen, activate red blood cells and neutrophils, and quickly stop bleeding. Proteins, coagulation factors, platelets and fibrin at the wound site combine with tea polyphenols to produce coagulation components and accelerate wound healing.

3.Antitumor therapy

Tea polyphenols, especially catechin derivatives, have anti-mutation and anti-cancer effects, which can hinder and inhibit the lipid peroxidation process, maintain and improve the enzyme activity in human body, and show good effects in the prevention and adjuvant treatment of stomach cancer, bowel cancer and other diseases.

4, reduce blood lipids, inhibit atherosclerosis

Tea polyphenols can significantly inhibit the increase of cholesterol content in plasma and liver, have the effect of promoting the excretion of lipid compounds from feces, not only can prevent atherosclerosis, but also have the effect of weight loss. Among them, EGCG and other catechins regulate lipid metabolism by inhibiting the absorption of nutrients in the gastrointestinal tract, controlling the formation of fat cells and lipids, regulating intestinal flora, and improving insulin resistance.

5.Cardiovascular disease prevention

Tea polyphenols have good preventive and therapeutic effects on cardiovascular diseases, especially in the inhibition of atherosclerosis caused by high cholesterol and triglyceride content. In addition, tea polyphenols can also help maintain and lower blood pressure and regulate sugar metabolism to lower blood sugar levels.

6.Anti-oxidation and anti-aging

Tea polyphenols can remove excessive free radicals in the human body and slow down the aging of the human body. The antioxidant activity of tea polyphenols is stronger than VE, and it is better when combined with VC and VE.

7.Caries prevention

It has been proved that tea polyphenols can strongly inhibit cariogenic bacteria and significantly reduce plaque and periodontal index.

8.Antibacterial and antiviral

Polyphenols can precipitate cell protein, denaturate and deactivate cell protein. Using the principle of antibacterial and antiviral tea polyphenols, catechins have been used in air conditioners abroad. EGCG in TPs can bind to the lipid membrane of bacteria and affect the folate metabolism of bacteria by inhibiting the cytoplasmic enzyme dihydrofolate reductase, thus achieving the purpose of antibacterial.