Preparation method of catechin

Abstract

The invention belongs to the technical field of medicine extraction, and relates to a preparation method of catechin. The preparation method comprises the following steps: dissolving extraction, HPD-400 macroporous resin column chromatography, first extraction, first HPD-100 macroporous resin column chromatography, second extraction, first crystallization, second HPD-100 macroporous resin column chromatography, third extraction, second crystallization, recrystallization and yield calculation. In the preparation method, the components are simple, the result is clear, the purity is more than 99%, the single impurity content is less than or equal to 0.1%, the residue detection is less than or equal to 0.1%, and the quality standard of product bulk drugs is met. In addition, the preparation method provided by the invention has the advantages of simple steps, convenience in quality control, stable process, no environmental pollution and higher purity, and is suitable for industrial large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of drug extraction, and particularly relates to a method for preparing catechins. Background Art

[0002] Tea polyphenols (also known as antioxidants and vitamin polyphenols) is the general name for polyphenols in tea, and is known as the "radiation killer" by the health and medical community. It is an amorphous powder, easily soluble in water, soluble in ethanol, methanol, ethyl acetate, and insoluble in chloroform. Its main components are six types of compounds: flavanones, anthocyanidins, flavonols, anthocyanidins, phenolic acids, and phenolic acids. The catechins involved in the present invention are flavanones in the tea polyphenols component, accounting for 60%-80% of the total tea polyphenols. Catechins have multiple pharmacological effects such as anti-tumor, anti-oxidation, anti-bacteria, and protection of heart and brain organs. Among them, EGCG (epigallocatechin gallate) has the most outstanding antioxidant properties, which can effectively balance free radicals in the human body by removing reactive oxygen species (ROS), NO, or reacting with ROS to generate stable compounds. As the research on catechins becomes more in-depth, more pharmacological functions have been discovered. Catechins can inhibit cancer cell proliferation and induce cancer cell apoptosis by regulating related enzyme activities or specifically binding to related enzyme proteins, but there are obvious differences between different catechin monomers. Catechins can also prevent cardiovascular and cerebrovascular diseases and protect the kidneys, liver and nervous system.

[0003] However, the preparation method of catechins is usually complicated, and the purity is difficult to reach above 99%. Therefore, it is necessary to simplify the equipment requirements and process to facilitate the scale-up of industrial production. Summary of the invention

[0004] In order to solve the above problems, the purpose of the present invention is to provide a method for preparing catechins, which uses a resin column filtration method to achieve the purpose and provide a theoretical basis for the preparation of anti-tumor catechins. The product prepared by the method is simple to operate, high in purity and low in energy consumption. Through HPLC detection and analysis, its purity is above 99%.

[0005] In order to achieve the above-mentioned object, the present invention adopts the following technical scheme: a method for preparing catechins, comprising the following steps: 1) Dissolve the extract material - tea polyphenols, and dilute it with water to obtain a diluted liquid. This step is to better dissolve and clear the column; 2) Add the diluted material from step 1) to a HPD-400 macroporous resin column, and elute with purified water + 20% ethanol and 95% ethanol in sequence. The elution with purified water and 20% ethanol is to wash more material and increase the yield as much as possible, and the elution with 95% ethanol is to rinse the resin column for next use; 3) The receiving solution obtained in step 2) is concentrated under reduced pressure at 60°C-65°C, and ethyl acetate is added with half volume and one quarter volume for extraction respectively, the temperature during extraction is not higher than 40°C, and the extraction is stirred; the combined extracts are concentrated under reduced pressure at 55-65°C into a paste, and purified water is added to dissolve at 55-65°C to obtain a feed liquid; 60-65°C can keep the feed liquid in a state of slight boiling but not boiling, and ethyl acetate can be concentrated under reduced pressure faster, and no higher than 40°C can make the material dissolve in ethyl acetate to the maximum extent without destroying the active properties, so that the extraction is successful, and purified water is added to dissolve at 55-65°C because tea polyphenols have the best solubility at 40-80°C; 4) Add the liquid obtained in step 3) to a macroporous resin column of HPD-100 and elute with 15-25% ethanol; this concentration of ethanol can minimize the impurities of the eluted material and increase the yield; 5) The eluate is concentrated under reduced pressure at 60-65°C, and one-half and one-quarter volumes of ethyl acetate are added for extraction, respectively. The temperature during extraction is not higher than 40°C, and the extraction is stirred; the combined extracts are concentrated under reduced pressure at 55-65°C to a paste, and purified water is added to dissolve at 55-65°C to obtain a feed solution; 6) crystallizing the liquid obtained in step 5) at 4-10° C. for 24-48 hours, centrifuging and washing to obtain intermediate A; 7) Add 15-25% ethanol in an amount of 8-12 times the dry weight of intermediate A to dissolve at 60℃-65℃, add to the HPD-100 macroporous resin column, and elute with 15-25% ethanol; the crystallization environment of 4-8℃ is the most suitable crystallization condition for tea polyphenols. Tea polyphenols will precipitate crystals as the temperature decreases, but when the temperature is below zero, the material will freeze and affect the crystallization amount; 8) The liquid obtained in step 7) is concentrated under reduced pressure at 60°C-65°C, and extracted by adding one-half and one-quarter volumes of ethyl acetate respectively, the temperature during extraction is not higher than 40°C, and the extraction is stirred; the combined extracts are concentrated under reduced pressure at 60°C-65°C into a paste, and purified water is added to dissolve at 60°C-65°C; 9) crystallizing the liquid obtained in step 8) at 4-10° C. for 24-48 hours, centrifuging and washing to obtain an EGCG intermediate B, wherein the EGCG is epigallocatechin gallate; 10) Dissolve the EGCG intermediate B in purified water and then recrystallize it, filter and wash it to obtain a refined EGCG product; 11) Drying the refined EGCG product.

[0006] During extraction, the temperature is not higher than 40°C because higher temperature makes catechins, especially EGCG, unable to dissolve in the ethyl acetate extraction phase but dissolve in its own solvent phase (ethanol aqueous solution), which greatly reduces the yield of catechins, especially EGCG; the extraction should be carried out within a certain stirring speed range. Too low stirring speed reduces the extraction efficiency, while too high stirring speed causes the entire extraction system to emulsify (emulsification was observed when the extraction stirring speed reached 85r / min in the experiment), making it impossible to achieve extraction separation.

[0007] In the present invention, different resin columns are used successively. Purification with different resin columns can fully retain not only EGCG, but also other epicatechins, catechins and other structural components similar to EGCG, and the HPD-400 macroporous resin column is used for primary screening first, and then the HPD-100 macroporous resin column is used for purification. In the present invention, EGCG intermediate B and EGCG refined product are actually catechin products, and other epicatechins, catechins and other structural components similar to EGCG are all catechins, which are all effective ingredients of catechins as medicines, and are also effective ingredients of the final product, and are not counted as impurities; and EGCG is the main component of the catechin product, so it is named EGCG intermediate B and EGCG refined product.

[0008] In the present invention, the extraction step is performed after the eluent is concentrated under reduced pressure, and then concentrated under reduced pressure, and water is added to the column, which is used to extract more materials and maintain the high purity of the EGCG refined product. Compared with the method of "concentrating under reduced pressure to dryness and then adding water to the column" without extraction, the present invention adopts this method to obtain a high-purity EGCG refined product, and greatly shortens the preparation time, from more than 12 hours to about 8 hours.

[0009] In a preferred embodiment, the results of the two crystallizations of EGCG are: the purity of intermediate A is ≥90%, and the purity of intermediate B is ≥99%.

[0010] In a preferred embodiment, in step 1), the temperature when dissolving the extract material is 55°C-70°C, and the time is 0.4-0.6h (preferably 0.5h).

[0011] In a preferred embodiment, when the feed solution passes through the HPD-400 and HPD-100 macroporous resin columns, the upper and lower flow rates (referring to the flow rates at the upper and lower parts of the macroporous resin column) should be kept consistent.

[0012] In a preferred embodiment, vacuum drying is adopted in step 11), the temperature is 60°C±5°C, and the drying time is 8-10 hours.

[0013] In a preferred embodiment, in steps 3), 5) and 8), the stirring speed during extraction is 50-80 r / min.

[0014] In a preferred embodiment, in steps 3), 5) and 8), the extraction temperature is 25°C-35°C.

[0015] Furthermore, in steps 3), 5), and 8), the solution is concentrated under reduced pressure at 60°C-65°C to half of the original volume. Half and quarter volumes refer to half and quarter volumes after reduced pressure concentration. In steps 3), 5), and 8), during extraction, first add half the volume of ethyl acetate of the solution after reduced pressure concentration, extract and separate to obtain a first extract, and then add a quarter the volume of ethyl acetate of the solution after reduced pressure concentration to the remaining solution (referring to the remaining solution after the first extraction except the first extract), extract and separate to obtain a second extract, and combine the first extract and the second extract.

[0016] In step 3) and step 10), preferably, four times the amount of purified water is added; in step 5) and step 8), preferably, two times the amount of purified water is added; in step 7), preferably, 10 times the dry weight of intermediate A is added with 20% ethanol.

[0017] Compared with the prior art, the EGCG prepared by the present invention has the following advantages: the experimental equipment used in the experimental process is simple; in the preparation and purification process of EGCG, the raw materials used are of low cost and easy to obtain; the technical solution of the present invention can obtain a high-purity EGCG product by designing reaction parameters and purification process parameters, and in their coordinated cooperation, only simple purification and crystallization are required; based on the prior art, the equipment requirements and process are simplified to facilitate industrial scale-up production.

[0018] The EGCG finished product obtained by the preparation method of the present invention has low impurities, a finished product purity of more than 99%, a single impurity content of ≤0.1%, a residue detection of ≤0.1%, and a moisture content of ≤5%, which meets the quality standards of the product raw material medicine. DETAILED DESCRIPTION

[0019] The present invention is described in detail below with reference to specific embodiments.

[0020] The preparation method of the present invention comprises the following steps: dissolution and extraction, HPD-400 macroporous resin column chromatography, first extraction, first HPD-100 macroporous resin column chromatography, second extraction, first crystallization, second HPD-100 macroporous resin column chromatography, third extraction, second crystallization, recrystallization, and calculation of yield. The preparation method has simple ingredients and clear results, a purity of more than 99%, a single impurity content of ≤0.1%, and a residue detection of ≤0.1%, which meets the quality standards of the product raw material medicine. In addition, the preparation method of the present invention has simple steps, convenient quality control, stable process, no environmental pollution, and high purity, and is suitable for large-scale industrial production.

[0021] Example 1: Add 100g of tea polyphenols to 400ml of purified water, stir and dissolve at 60℃ for 0.5h, add to a HPD-400 macroporous resin column, and after loading, elute with 10.2L (3.4L of purified water and 6.8L of 20% ethanol) and 5L of 95% ethanol respectively. The eluted part was concentrated under reduced pressure at 60°C to 5.1L, and 2.6L and 1.3L of ethyl acetate were added for extraction (extraction temperature was 30°C, and the stirring speed was 50r / min during extraction). The combined extracts were concentrated under reduced pressure at 60°C to a paste, 200g of purified water solution was added, and then added to a HPD-100 macroporous resin column, and 3.6L was eluted with 20% ethanol. The eluate was concentrated under reduced pressure at 60°C to 1.6L, and 0.8L and 0.4L of ethyl acetate were added for extraction (extraction temperature was 30°C, and the stirring speed was 50r / min during extraction). The combined extracts were concentrated under reduced pressure at 60°C to a paste, 53g of purified water solution was added, and then placed at 4°C for crystallization for 48h. After centrifugation, add 325ml of 20% ethanol to dissolve at 60℃, add to the HPD-100 model macroporous resin column, elute 6.6L with 20% ethanol after loading, concentrate the eluate to 3.3L under reduced pressure at 60℃, add 1.6L and 0.8L of ethyl acetate to extract (extraction temperature 30℃, stirring speed 50r / min), combine the extracts to be concentrated to a paste at 60℃, add 30g of purified water to dissolve, and then put it at 4℃ to start crystallization for 48h. Filter and wash with cold water once to obtain EGCG intermediate B. Add 60g of purified water to it and put it in a 4℃ environment to recrystallize to obtain EGCG refined product, put the refined product into a vacuum drying oven, and dry it at 60℃ for 8h. The yield is calculated to be 10.64%.

[0022] HPLC analysis showed that the purity of intermediate A was 94.1%, the purity of the finished product was 99.543%, the single impurity was 0.015%, the residue detection was 0.081%, and the moisture content was 3.65%, which met the quality standards of the product raw materials.

[0023] Example 2: Add 100g of tea polyphenols to 400ml of purified water, stir and dissolve at 63°C for 0.5h, add to a HPD-400 macroporous resin column, and after loading, elute with 10.2L (3.4L with purified water and 6.8L with 20% ethanol) and 5L with 95% ethanol respectively. The eluted part was concentrated under reduced pressure to 5.1 L at 63°C, and 2.6 L and 1.3 L of ethyl acetate were added for extraction (extraction temperature: 25°C, stirring speed: 60 r / min), the combined extracts were concentrated under reduced pressure to a paste at 63°C, 258 g of purified water solution was added, and then added to a HPD-100 macroporous resin column, and 3.6 L was eluted with 20% ethanol, the eluate was concentrated under reduced pressure to 1.6 L at 63°C, and 0.8 L and 0.4 L of ethyl acetate were added for extraction (extraction temperature: 25°C, stirring speed: 60 r / min), the combined extracts were concentrated under reduced pressure to a paste at 60°C, 68 g of purified water solution was added, and then placed at 6°C for crystallization for 48 hours. After centrifugation, 355 ml of 20% ethanol was added to dissolve at 63°C, and added to the HPD-100 macroporous resin column. After the sample was loaded, 6.6 L was eluted with 20% ethanol. The eluate was concentrated to 3.3 L under reduced pressure at 63°C, and 1.6 L and 0.8 L of ethyl acetate were added for extraction (extraction temperature 25°C, stirring speed 60r / min), respectively. The combined extracts were concentrated to a paste under reduced pressure at 63°C, 24 g of purified water was added to dissolve, and then placed at 6°C for crystallization for 48 hours. Filter and wash with cold water once to obtain EGCG intermediate B. Add 48 g of purified water and place it in a 6°C environment for recrystallization to obtain EGCG refined product, and place the refined product in a vacuum drying oven and dry it at 63°C for 9 hours. The yield was calculated to be 9.96%.

[0024] HPLC analysis showed that the purity of intermediate A was 93.283%, the purity of the finished product was 99.101%, the single impurity was 0.085%, the residue detection was 0.076%, and the moisture content was 2.73%, which met the quality standards of the product raw materials.

[0025] Example 3: Add 100g of tea polyphenols to 400ml of purified water, stir and dissolve at 60℃ for 0.5h, add to a HPD-400 macroporous resin column, and after loading, elute with 10.2L (3.4L with purified water and 6.8L with 20% ethanol) and 5L with 95% ethanol respectively. The eluted part was concentrated under reduced pressure at 65°C to 5.1L, and 2.6L and 1.3L of ethyl acetate were added for extraction (extraction temperature was 35°C, and the stirring speed was 50r / min during extraction). The combined extracts were concentrated under reduced pressure at 65°C to a paste, 282g of purified water solution was added, and then added to a HPD-100 macroporous resin column, and 3.6L was eluted with 20% ethanol. The eluate was concentrated under reduced pressure at 60°C to 1.6L, and 0.8L and 0.4L of ethyl acetate were added for extraction (extraction temperature was 35°C, and the stirring speed was 50r / min during extraction). The combined extracts were concentrated under reduced pressure at 65°C to a paste, 51g of purified water solution was added, and then placed at 10°C for crystallization for 48h. After centrifugation, add 300ml of 20% ethanol to dissolve at 65℃, add to the HPD-100 model macroporous resin column, and after loading, elute 6.6L with 20% ethanol. The eluate is concentrated to 3.3L under reduced pressure at 65℃, and 1.6L and 0.8L of ethyl acetate are added for extraction (extraction temperature 35℃, stirring speed 50r / min), respectively. The combined extracts are concentrated to a paste under reduced pressure at 65℃, and 22g of purified water is added to dissolve and then placed at 10℃ for crystallization for 48h. Filter and wash with cold water once to obtain EGCG intermediate B. Add 44g of purified water and place it in a 4℃ environment to recrystallize to obtain EGCG refined product, and place the refined product in a vacuum drying oven and dry it at 65℃ for 10h. The yield is calculated to be 11.82%.

[0026] HPLC analysis showed that the purity of intermediate A was 96.823%, the purity of the finished product was 99.7%, the single impurity was 0.0212%, the residue detection was 0.071%, and the moisture content was 2.65%, which met the quality standards of the product raw materials.

[0027] Comparative Example 1 Add 100g of tea polyphenols into 400ml of purified water, stir and dissolve at 60℃ for 0.5h, add into HPD-400 macroporous resin column, and after loading, elute with 10.2L (3.4L with purified water and 6.8L with 20% ethanol) and 5L with 95% ethanol respectively. The eluted part was concentrated under reduced pressure at 60°C to 5.1L, and 2.6L and 1.3L of ethyl acetate were added for extraction (extraction temperature 55°C, stirring speed 50r / min), the combined extracts were concentrated under reduced pressure at 60°C to a paste, 200g of purified water solution was added to a HPD-100 macroporous resin column, and 3.6L was eluted with 20% ethanol, the eluate was concentrated under reduced pressure at 60°C to 1.6L, 0.8L and 0.4L of ethyl acetate were added for extraction (extraction temperature 55°C, stirring speed 50r / min), the combined extracts were concentrated under reduced pressure at 60°C to a paste, 53g of purified water solution was added, and crystallization began at 4°C for 48h. After centrifugation, add 325ml of 20% ethanol to dissolve at 60℃, add to the HPD-100 model macroporous resin column, elute 6.6L with 20% ethanol after loading, concentrate the eluate to 3.3L under reduced pressure at 60℃, add 1.6L and 0.8L of ethyl acetate to extract (extraction temperature 55℃, stirring speed 50r / min), combine the extracts to be concentrated to a paste at 60℃, add 30g of purified water to dissolve, and then put it at 4℃ to start crystallization for 48h. Filter and wash with cold water once to obtain EGCG intermediate B. Add 60g of purified water to it and put it in a 4℃ environment to recrystallize to obtain EGCG refined product, put the refined product into a vacuum drying oven, and dry it at 60℃ for 8h. The yield is calculated to be 5.73%.

[0028] HPLC analysis showed that the finished product had a purity of 98.101%, a single impurity of 0.174%, and a moisture content of 4.3%, which met the quality standards of the product raw material drug.

[0029] Comparative Example 2 Add 100g of tea polyphenols into 400ml of purified water, stir and dissolve at 60℃ for 0.5h, add into HPD-400 macroporous resin column, and after loading, elute with 10.2L (3.4L with purified water and 6.8L with 20% ethanol) and 5L with 95% ethanol respectively. The eluted part was concentrated under reduced pressure at 60°C to 5.1L, and 2.6L and 1.3L of ethyl acetate were added for extraction (extraction temperature was 30°C, and the stirring speed was 100r / min during extraction). The combined extracts were concentrated under reduced pressure at 60°C to a paste, 200g of purified water solution was added, and then added to a HPD-100 macroporous resin column, and 3.6L was eluted with 20% ethanol. The eluate was concentrated under reduced pressure at 60°C to 1.6L, and 0.8L and 0.4L of ethyl acetate were added for extraction (extraction temperature was 30°C, and the stirring speed was 100r / min during extraction). The combined extracts were concentrated under reduced pressure at 60°C to a paste, 53g of purified water solution was added, and then placed at 4°C for crystallization for 48h. After centrifugation, add 325ml of 20% ethanol to dissolve at 60℃, add to the HPD-100 model macroporous resin column, and after loading, elute 6.6L with 20% ethanol. The eluate is concentrated to 3.3L under reduced pressure at 60℃, and 1.6L and 0.8L of ethyl acetate are added for extraction (extraction temperature 30℃, stirring speed 100r / min), respectively. The combined extracts are concentrated to a paste under reduced pressure at 60℃, and 30g of purified water is added to dissolve and then placed at 4℃ for crystallization for 48h. Filter and wash with cold water once to obtain EGCG intermediate B. Add 60g of purified water and place it in a 4℃ environment to recrystallize to obtain EGCG refined product, and place the refined product in a vacuum drying oven and dry it at 60℃ for 8h. The yield is calculated to be 5.76%.

[0030] HPLC analysis showed that the finished product had a purity of 98.036%, a single impurity of 0.182%, and a moisture content of 4.1%, which met the quality standards of the product raw material drug.

[0031] Comparative Example 3 Add 100g of tea polyphenols into 400ml of purified water, stir and dissolve at 60℃ for 0.5h, add into HPD-400 macroporous resin column, and after loading, elute with 10.2L (3.4L with purified water and 6.8L with 75% ethanol) and 5L with 95% ethanol respectively. The eluted part was concentrated under reduced pressure at 60°C to 5.1L, and 2.6L and 1.3L of ethyl acetate were added for extraction (extraction temperature was 30°C, and the stirring speed was 50r / min during extraction). The combined extracts were concentrated under reduced pressure at 60°C to a paste, and 200g of purified water solution was added to a HPD-100 macroporous resin column, and 3.6L was eluted with 75% ethanol. The eluate was concentrated under reduced pressure at 60°C to 1.6L, and 0.8L and 0.4L of ethyl acetate were added for extraction (extraction temperature was 30°C, and the stirring speed was 50r / min during extraction). The combined extracts were concentrated under reduced pressure at 60°C to a paste, and 53g of purified water solution was added and placed at 4°C for crystallization for 48h. After centrifugation, add 325ml of 20% ethanol to dissolve at 60℃, add to the HPD-100 model macroporous resin column, and after loading, elute 6.6L with 75% ethanol. The eluate is concentrated to 3.3L under reduced pressure at 60℃, and 1.6L and 0.8L of ethyl acetate are added for extraction (extraction temperature 30℃, stirring speed 50r / min), respectively. The combined extracts are concentrated to a paste under reduced pressure at 60℃, and 30g of purified water is added to dissolve and then placed at 4℃ to start crystallization for 48h. Filter and wash with cold water once to obtain EGCG intermediate B. Add 60g of purified water and place it in a 4℃ environment to recrystallize to obtain EGCG refined product, and place the refined product in a vacuum drying oven and dry it at 60℃ for 8h. The yield is calculated to be 13.62%.

[0032] HPLC analysis showed that the purity of the finished product was 88.509%, the single impurity was 1.401%, and the moisture content was 3.67%, which did not meet the quality standards of the product raw material.

[0033] The yield in this article is the yield. As can be seen from Comparative Example 1, the high extraction temperature greatly reduces the yield; as can be seen from Comparative Example 2, the high extraction stirring speed causes the extract to emulsify and make it difficult to separate, which greatly reduces the yield and the purity of the product; in Comparative Example 3, the ethanol concentration is high during elution, resulting in more impurities being eluted, so the yield is higher but the product purity is significantly reduced and the impurities are significantly increased.

[0034] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form, and any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for preparing catechins, characterized in that: The steps include: 1) Dissolve the extract material - tea polyphenols, and dilute with water to obtain a diluted liquid; 2) Add the diluted solution in step 1) to a HPD-400 macroporous resin column, and elute with purified water + 20% ethanol and 95% ethanol in sequence; 3) The receiving solution obtained in step 2) is concentrated under reduced pressure at 60°C-65°C, and extracted by adding half and quarter volumes of ethyl acetate respectively, the temperature during extraction is not higher than 40°C, and the extraction is stirred; the combined extracts are concentrated under reduced pressure at 55-65°C to a paste, and purified water is added to dissolve at 55-65°C to obtain a feed solution; 4) Add the liquid obtained in step 3) into a HPD-100 macroporous resin column and elute with 15-25% ethanol; 5) The eluate is concentrated under reduced pressure at 60-65°C, and one-half and one-quarter volumes of ethyl acetate are added for extraction, respectively. The temperature during extraction is not higher than 40°C, and the extraction is stirred; the combined extracts are concentrated under reduced pressure at 55-65°C to a paste, and purified water is added to dissolve at 55-65°C to obtain a feed solution; 6) crystallizing the liquid obtained in step 5) at 4-10° C. for 24-48 hours, centrifuging and washing to obtain intermediate A; 7) Add 15-25% ethanol (8-12 times the dry weight) to the intermediate A and dissolve it at 60℃-65℃, add it to the HPD-100 macroporous resin column, and elute it with 15-25% ethanol; 8) The liquid obtained in step 7) is concentrated under reduced pressure at 60°C-65°C, and extracted by adding one-half and one-quarter volumes of ethyl acetate respectively, the temperature during extraction is not higher than 40°C, and the extraction is stirred; the combined extracts are concentrated under reduced pressure at 60°C-65°C into a paste, and purified water is added to dissolve at 60°C-65°C; 9) crystallizing the liquid obtained in step 8) at 4-10° C. for 24-48 hours, centrifuging and washing to obtain an EGCG intermediate B, wherein the EGCG is epigallocatechin gallate; 10) Dissolve the EGCG intermediate B in purified water and then recrystallize it, filter and wash it to obtain a refined EGCG product; 11) Drying the refined EGCG product.

2. The method for preparing catechins according to claim 1, characterized in that: The results of the two crystallizations of EGCG are: the purity of intermediate A is ≥90%, and the purity of intermediate B is ≥99%.

3. The method for preparing catechins according to claim 1, characterized in that: In step 1), the temperature when dissolving the extract material is 55°C-70°C and the time is 0.4-0.6h.

4. The method for preparing catechins according to claim 1, characterized in that: When the feed liquid passes through the HPD-400 and HPD-100 macroporous resin columns, the flow rates up and down should be kept consistent.

5. The method for preparing catechins according to claim 1, characterized in that: In step 11), vacuum drying is adopted, the temperature is 60°C ± 5°C, and the drying time is 8-10h.

6. The method for preparing catechins according to claim 1, characterized in that: In steps 3), 5) and 8), the stirring speed during extraction is 50-80 r / min.

7. The method for preparing catechins according to claim 1, characterized in that: In steps 3), 5) and 8), the extraction temperature is 25°C-35°C.

8. The method for preparing catechins according to claim 1, characterized in that: In steps 3), 5) and 8), during extraction, first add ethyl acetate in a volume half times that of the concentrated feed solution under reduced pressure, perform extraction and separation to obtain a first extract, and then add ethyl acetate in a volume one quarter times that of the concentrated feed solution under reduced pressure to the remaining solution (referring to the remaining solution after the first extraction except the first extract), perform extraction and separation to obtain a second extract, and combine the first extract and the second extract.

9. The method for preparing catechins according to claim 1, characterized in that: In step 3) and step 10), four times the amount of purified water was added; in step 5) and step 8), two times the amount of purified water was added.

10. The method for preparing catechins according to claim 1, characterized in that: In step 7), add 20% ethanol in an amount 10 times the dry weight of intermediate A.