Deep processing of tea: analysis of extraction process of green tea extract

The main components of green tea extract include tea polyphenols, caffeine, aromatic oil, water, minerals, pigments, carbohydrates, proteins, amino acids and multivitamins, which have blood pressure lowering, anti-blood coagulation, lowering blood fat, lowering blood sugar, and losing weight. , prevention and treatment of atherosclerosis, prevention of skin allergies, skin pigmentation and anti-caries, plaque, periodontitis and bad breath. In particular, tea polyphenols, as natural antioxidants, have strong antibacterial and anti-enzyme effects, and have broad application prospects in food, medicine, health care and many other fields.

As a natural antioxidant preservative for food, tea polyphenols are generally sold at a price of 100-1.5 million yuan/ton; as a raw material for health care products, the price can reach 1.6-2 million yuan/ton. In the next five years in which synthetic food antioxidants and natural products coexist, the annual demand for tea polyphenols will gradually transition from 500 tons to 5,000 tons, and the annual demand will rise to tens of thousands of tons in the future; as a huge added value The main ingredient of health care products, tea polyphenols will gradually increase from the current tens of tons of demand to hundreds of tons.

Tea polyphenols are the general term for catechins, flavonoids, phenolic acids and anthocyanidic compounds in tea, accounting for about 15% to 25% of the dry weight of tea. The most important ingredient in tea polyphenols is the various catechins of the flavanols.

The research on tea polyphenols developed in the 1980s and reached its climax after the 1990s. At present, the research on the purification and application of tea polyphenols has attracted attention at home and abroad, and is still in the ascendant stage.

The research on the preparation of tea polyphenols from tea is mainly found in some patents and literatures. It can be divided into three categories according to different separation methods: solvent extraction, ion precipitation and column separation.

The solvent extraction method is to leach from the tea leaves with a polar solvent, and then the liquid extract is separated by liquid-liquid extraction, and finally concentrated to obtain a product. At present, the industrial production of tea polyphenols is mainly produced by this method, the product yield is 5% -10%, the purity of the product is about 80% - 98%, and the caffeine is 4% - 7%. The organic solvents used are acetone, ***, methanol, hexane, and ***. However, this method uses a variety of organic solvents, and the production cost is high. Some organic solvents of toxic substances make the products and operations insecure and easily cause environmental pollution.

The ion precipitation method utilizes a metal capable of precipitating tea polyphenols and separating them from caffeine such as copper salts, lead salts or aluminum trichloride. Since this method uses heavy metals that are toxic to humans as a precipitant, its products are not accepted by the food and pharmaceutical industries.

Column separation preparation methods which have been reported so far include a gel column, an adsorption column and an ion exchange column. Recently, more research has been focused on improving purity. For this reason, there are many studies on column separation. The key to this technology is column packing and rinsing. Studies have shown that the yield of tea polyphenols by column separation preparation is between 4% and 8%, and the purity can reach 98.1%. If the separation by gel column is high, the residual amount of caffeine is only 0.1%. However, column packing materials such as adsorption type resins, lipophilic gels and the like are very expensive, and a variety of organic solvents are used in the rinsing, which is obviously not suitable for the industrial production of tea polyphenols.

At present, there are about thirty or forty tea polyphenol plants built and under construction in China, but only three or four are truly competitive (product quality, scale, cost and benefit). The main reason is that the existing factories use the traditional solvent extraction method and sedimentation separation. Without high-tech means, the color, purity, solvent residue and caffeine content of the products cannot meet the requirements of increasingly domestic and foreign merchants. In particular, due to the use of a large number of flammable and explosive organic solvents in the process, some even use solvents such as toxic chloroform, resulting in poor safety, poor quality and high comprehensive cost. In the food additive industry, the price cannot be combined with some synthetic antioxidants. Competition, the purity of the health care products industry can not meet the requirements. These problems cannot be solved by existing traditional processes.

The use of supercritical carbon dioxide extraction technology, combined with traditional processes to produce high-purity tea polyphenols, can produce high-quality tea polyphenols, but also solve some of the drawbacks of traditional processes.

The supercritical carbon dioxide extraction technology is combined with the traditional extraction, concentration and extraction techniques to obtain a new process for preparing high-purity tea polyphenols. The advantages are as follows: 1. The amount of organic solvent is reduced, the safety is good, and the pollution is less; The rate is high; 3. The residual solvent can be completely removed; 4. The comprehensive cost is low. The process not only improves the purity and yield of the tea polyphenol, but also makes the content more than 90%, the caffeine content is less than 2%, the solvent residue is zero, and the industrial production is safe for the raw materials, the solvent used, the production route and the production process. Sexuality and the requirements of color, yield and purity of the product to facilitate more effective application in the food and pharmaceutical industries.

It is also reported that the combined production process of tea polyphenols and caffeine by resin adsorption method, such as green tea, crushed old tea tablets, tea clothes, tea and other raw materials, can make the absorption rate of tea polyphenols and caffeine reach dry tea respectively. Weighed 8.6% and 1.6%.