Method for extracting tea polyphenols and removing caffeine from tea leaves

Abstract

The application relates to the technical field of tea polyphenol extraction and purification, and particularly discloses a method for extracting tea polyphenols and removing caffeine from tea leaves. The method comprises the following steps: extracting tea polyphenol extract, and contacting the tea polyphenol extract with modified montmorillonite powder to remove caffeine, wherein the amount of the modified montmorillonite powder is 2-8 wt% of the tea polyphenol extract; and the modified montmorillonite powder is obtained by loading carboxyl modified nanofiber whiskers on montmorillonite powder. The method has the advantages of high caffeine removal rate and high tea polyphenol retention rate.

Description

Technical Field

[0001] This application relates to the technical field of tea polyphenol extraction and purification, and more specifically, it relates to a method for extracting tea polyphenols and removing caffeine from tea leaves. Background Technology

[0002] Tea has numerous health benefits, including lowering blood sugar and lipids, anti-cancer, anti-aging, and anti-radiation effects. These benefits are inseparable from the effective functional components in tea. The effective components in tea include tea polyphenols, tea polysaccharides, caffeine, theanine, and tea proteins. Among these, tea polyphenols are the most important functional substances in tea, accounting for approximately 16-34 wt%, and are the collective term for all phenolic compounds in tea. The main chemical components of tea polyphenols are catechins, anthocyanins, flavonoids and flavonols, phenolic acids and condensed phenolic acids, etc. Among these, catechins are the main components of tea polyphenols, accounting for 60-80 wt% of the total tea polyphenols.

[0003] Currently, extraction methods for tea polyphenols include solvent extraction, enzymatic extraction, ultrasound-assisted extraction, microwave-assisted extraction, supercritical CO2 extraction, and pulsed electric field-assisted extraction. Solvent extraction methods, including water extraction and organic solvent extraction, suffer from high levels of impurities such as tea pigments, caffeine, and tea polysaccharides, leading to purification difficulties. Enzymatic extraction, in particular, inhibits polyphenol activity due to strong complexation between enzymes and polyphenols. Ultrasound, microwave-assisted extraction, and supercritical CO2 extraction are several methods that significantly improve the extraction rate and activity of tea polyphenols; however, supercritical CO2 extraction has the problem of high equipment costs. Regardless of the extraction method, the resulting tea polyphenols inevitably contain impurities such as tea pigments and caffeine; therefore, purification is essential to obtain high-purity tea polyphenols.

[0004] Caffeine, an impurity found in tea polyphenols, is a central nervous system stimulant. However, it has side effects for people with neurasthenia, atherosclerosis, hypertension, and pregnant women, such as causing palpitations, excitement, and insomnia. High levels of caffeine can also cause stomach cramps, excessive gastric acid secretion, and inhibited nutrient absorption in sensitive individuals. Furthermore, high caffeine intake can lead to dependence and even cause bodily dysfunction. Therefore, removing caffeine from tea polyphenols is necessary.

[0005] Current methods for purifying caffeine include solvent extraction, metal ion precipitation, macroporous resin adsorption, microbial degradation, and adsorption and ion exchange. Studies have shown that when using macroporous resins such as AL-2, NKA-9, AB-8, and HPD to remove caffeine, the adsorption rate is generally 55-75%, but the adsorption rate of tea polyphenols is only 45-55%. When using AL-1 resin, although the caffeine adsorption rate is as high as 98%, the adsorption rate of tea polyphenols remains as high as 38%. This indicates that macroporous resin adsorption for caffeine removal suffers from a high loss rate of tea polyphenols. However, when using adsorbents to remove caffeine from tea polyphenols, studies using montmorillonite as the adsorbent have shown a 92% removal rate of caffeine and an 86% retention rate of tea polyphenols in oolong tea, and a 92% removal rate of caffeine and a 75% retention rate of tea polyphenols in black tea.

[0006] Therefore, it is necessary to provide a method with both high caffeine removal rate and high tea polyphenol retention rate. Summary of the Invention

[0007] In order to improve the removal rate of caffeine and the retention rate of tea polyphenols during the process of removing caffeine from tea polyphenols, this application provides a method for extracting tea polyphenols and removing caffeine from tea leaves.

[0008] The method for extracting tea polyphenols and removing caffeine from tea provided in this application adopts the following technical solution:

[0009] A method for extracting tea polyphenols and removing caffeine from tea leaves includes the following steps:

[0010] A tea polyphenol extract is obtained by extraction, and the tea polyphenol extract is contacted with modified montmorillonite powder to remove caffeine. The amount of modified montmorillonite powder is 2-8 wt% of the tea polyphenol extract.

[0011] The modified montmorillonite powder is obtained by processing montmorillonite powder through a step including loading carboxyl-modified nanofiber whiskers.

[0012] By adopting the above technical solution, the adsorbent of this application is obtained by loading carboxyl-modified nanofiber whiskers onto montmorillonite powder. Compared with cellulose, the nanofiber whiskers exhibit superior solubility and thermal stability. After carboxyl modification, the carboxyl-modified nanofiber whiskers contain more carboxyl groups, and their adsorption capacity, stability, and hydrophilicity are significantly improved. When carboxyl-modified nanofiber whiskers are loaded onto montmorillonite powder, the carboxyl groups and the polyhydroxy structures of tea polyphenols exhibit charge repulsion in the solution, thus reducing the loss of tea polyphenols during adsorption. Furthermore, the loading of carboxyl-modified nanocellulose onto montmorillonite powder significantly enhances its adsorption capacity. This solution reduces the loss of tea polyphenols through charge repulsion between carboxyl groups and tea polyphenols, and also synergistically improves the removal efficiency of caffeine through the combined action of carboxyl-modified nanofiber whiskers and montmorillonite powder.

[0013] In some embodiments, the modified montmorillonite powder is used at 2-2.5 wt%, 2.3-3.6 wt%, 3.2-4.7 wt%, 3.6-5.8 wt%, 4.7-6.9 wt%, or 5.2-8 wt% of the tea polyphenol extract.

[0014] In one embodiment, the modified montmorillonite powder is used at 2.3 wt%, 3.2 wt%, 4 wt%, 4.7 wt%, 5.1 wt%, 5.8 wt%, 6.7 wt%, 7.3 wt%, or 8.6 wt% of the tea polyphenol extract.

[0015] Optionally, the preparation method of the modified montmorillonite powder includes the following steps: dispersing the carboxyl-modified nanofiber whiskers in an acidic solution and mixing and stirring with montmorillonite powder, then separating the solid and liquid and collecting the solid, drying and pulverizing to obtain modified montmorillonite powder.

[0016] By adopting the above technical solution, the adsorption capacity of montmorillonite powder is significantly improved under acidic conditions, while the carboxyl groups of the carboxyl-modified nanofiber whiskers are retained, so that the carboxyl-modified nanofiber whiskers are stably loaded on the montmorillonite powder.

[0017] Optionally, after dispersing the carboxyl-modified nanofiber whiskers in an acidic solution, the pH of the resulting carboxyl-modified nanofiber whisker dispersion is 3.0-4.0.

[0018] In some embodiments, the pH of the carboxyl-modified nanofiber whisker dispersion is 3.0-3.2, 3.2-3.5, 3.5-3.8, or 3.8-4.0.

[0019] Optionally, the mass ratio of the carboxyl-modified nanofiber whiskers to the montmorillonite powder is (0.06-0.09):1.

[0020] In some embodiments, the mass ratio of the carboxyl-modified nanofiber whiskers to the montmorillonite is (0.06-0.07):1, (0.07-0.08):1, or (0.08-0.09):1.

[0021] In one embodiment, the mass ratio of the carboxyl-modified nanofiber whiskers to the montmorillonite is 0.06:1, 0.065:1, 0.072:1, 0.078:1, 0.084:1, or 0.089:1.

[0022] Optionally, when the carboxyl-modified nanofiber whiskers are dispersed in an acidic solution, the weight ratio of the carboxyl-modified nanofiber whiskers to the acidic solution is (0.001-0.005):1.

[0023] In some embodiments, when the carboxyl-modified nanofiber whiskers are dispersed in an acidic solution, the weight ratio of the carboxyl-modified nanofiber whiskers to the acidic solution is (0.001-0.0015):1, (0.0015-0.003):1, (0.003-0.0048):1, or (0.0048-0.005):1.

[0024] In one embodiment, when the carboxyl-modified nanofiber whiskers are dispersed in an acidic solution, the weight ratio of the carboxyl-modified nanofiber whiskers to the acidic solution is 0.001:1, 0.0013:1, 0.0018:1, 0.0023:1, 0.0027:1, 0.0032:1, 0.0039:1, 0.0041:1, 0.0048:1, or 0.005:1.

[0025] Optionally, the method for preparing the carboxyl-modified nanofiber whiskers includes the following steps:

[0026] Nanofiber whisker dispersion and acrylic acid were mixed at a mass ratio of (2-4):1, and then mixed with a photoinitiator and reacted under ultraviolet light. After solid-liquid separation, the solid was collected, washed with water and dried to obtain carboxyl-modified nanofiber whiskers.

[0027] By adopting the above technical solution, photoinitiation is used to stably graft acrylic acid onto nanofiber whiskers to obtain stable carboxyl-modified nanofiber whiskers.

[0028] Optionally, the reaction time under ultraviolet light irradiation is 10-15 min.

[0029] Optionally, the contact time between the tea polyphenol extract and the modified montmorillonite powder adsorbent is 10-20 minutes, accompanied by stirring at a speed of 7000-8000 rpm.

[0030] The tea polyphenol extract of this application can be obtained by existing methods, such as hot water boiling, ethanol extraction, ultrasound-assisted organic solvent extraction, or micro-assisted organic solvent extraction.

[0031] Optionally, the method for obtaining tea polyphenol extract includes the following steps:

[0032] Step 1: Mix tea powder with 40-50% ethanol solution and extract by ultrasonic-microwave combined extraction. The weight of the tea powder is 10-20 wt% of the 40-50% ethanol solution.

[0033] Step 2: Then add 40-50% ethanol solution to make the material-to-liquid ratio 1:20-35, extract, separate solids and liquids, and concentrate the supernatant to obtain tea polyphenol extract.

[0034] By adopting the above technical solution, tea polyphenol extract with high tea polyphenol content can be obtained by using ultrasound-microwave combined with ethanol solution.

[0035] Optionally, in step 1, during ultrasonic-microwave synergistic extraction, the microwave power is 300-500W, the ultrasonic power is 40-70W, the extraction time is 100-200s, and the extraction temperature is 60-80℃.

[0036] The extraction time in step 2 is 30-70 minutes.

[0037] In summary, this application has the following beneficial effects:

[0038] 1. This application uses modified montmorillonite to adsorb caffeine from tea polyphenol extract. By loading carboxyl-modified nanofiber whiskers onto montmorillonite powder, the caffeine removal rate is improved while the loss of tea polyphenols is reduced.

[0039] 2. In this application, the modified montmorillonite powder is prepared by using carboxyl-modified nanofiber whiskers and montmorillonite powder at a mass ratio of (0.06-0.09):1 to obtain a higher caffeine removal rate and tea polyphenol retention rate. Detailed Implementation

[0040] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0041] Nanofiber whiskers are commercially available or prepared. One feasible preparation method includes the following steps:

[0042] Cellulose raw material is mixed with 60-68 wt% concentrated sulfuric acid and reacted at 40-45℃ for 1-3 hours. Water is then added to stop the reaction, and the mixture is centrifuged to obtain nanofiber whiskers.

[0043] The cellulose raw material is selected from any one or two of degreased cotton and filter paper.

[0044] The ratio of cellulose raw material to 60-68 wt% concentrated sulfuric acid is 1 g cellulose raw material : (15-22) mL concentrated sulfuric acid.

[0045] Concentrated sulfuric acid refers to an aqueous solution of concentrated sulfuric acid prepared by using sulfuric acid as a solute and water as a solvent.

[0046] Example of preparation of nanocellulose whiskers

[0047] Preparation Example 1

[0048] Degreased cotton and 60wt% concentrated sulfuric acid were mixed at a ratio of 1g fiber raw material to 15mL concentrated sulfuric acid, ensuring complete saturation of the cotton. The mixture was then reacted in a constant temperature water bath at 40℃ for 3 hours. The reaction was then stopped by adding 5 times the volume of water to the concentrated sulfuric acid. After centrifugation, the supernatant was acidic, and the lower precipitate was nanofiber whiskers. The supernatant was discarded, and the lower precipitate was washed 5 times with water and then dried to obtain the nanofiber whiskers.

[0049] Preparation Example 2

[0050] Degreased cotton and 64wt% concentrated sulfuric acid were mixed at a ratio of 1g fiber raw material to 18mL concentrated sulfuric acid, ensuring complete saturation of the cotton. The mixture was then reacted in a constant temperature water bath at 43℃ for 2 hours. The reaction was then stopped by adding 5 times the volume of water to the concentrated sulfuric acid. After centrifugation, the supernatant was acidic, and the lower precipitate was nanofiber whiskers. The supernatant was discarded, and the lower precipitate was washed 5 times with water and then dried to obtain the nanofiber whiskers.

[0051] Preparation Example 3

[0052] Degreased cotton and 68wt% concentrated sulfuric acid were mixed at a ratio of 1g fiber raw material to 22mL concentrated sulfuric acid, ensuring the cotton was completely soaked in the sulfuric acid. The mixture was then reacted in a constant temperature water bath at 45℃ for 1 hour. The reaction was then stopped by adding 5 times the volume of water to the concentrated sulfuric acid. After centrifugation, the supernatant was acidic, and the lower precipitate was nanofiber whiskers. The supernatant was discarded, and the lower precipitate was washed 5 times with water and then dried to obtain the nanofiber whiskers.

[0053] Preparation example of carboxyl-modified nanofiber whiskers

[0054] The preparation method of the carboxyl-modified nanofiber whiskers includes the following steps:

[0055] Nanofiber whisker dispersion and acrylic acid were mixed at a mass ratio of (2-4):1, and then mixed with a photoinitiator and reacted under ultraviolet light. After solid-liquid separation, the solid was collected, washed with water and dried to obtain carboxyl-modified nanofiber whiskers.

[0056] The reaction time under ultraviolet light irradiation is 10-15 minutes.

[0057] Preparation Example 4

[0058] Nanofiber whiskers were dispersed in water, and acrylic acid was added and mixed thoroughly; the acrylic acid was added at a mass ratio of nanofiber whiskers to acrylic acid of 2:1. Then, photoinitiator Darocur 2959 was added at a concentration of 3 wt% of the nanofiber whiskers. After all raw materials were evenly dispersed, the mixture was heated at 60 mW / cm². 2 The reaction mixture was irradiated with ultraviolet light at a specific intensity for 15 min, then filtered, washed three times with water, and dried to obtain carboxyl-modified nanofiber whiskers. In this preparation example, the nanofiber whiskers were prepared using the method described in Preparation Example 1.

[0059] Preparation Example 5

[0060] Nanofiber whiskers were dispersed in water, and acrylic acid was added and mixed thoroughly; the acrylic acid was added at a mass ratio of nanofiber whiskers to acrylic acid of 3:1. Then, photoinitiator Darocur 2959 was added at a concentration of 4 wt% of the nanofiber whiskers. After all raw materials were evenly dispersed, the mixture was heated at 75 mW / cm². 2 The reaction mixture was irradiated with ultraviolet light for 10 min, then filtered, washed three times with water, and dried to obtain carboxyl-modified nanofiber whiskers. In this preparation example, the nanofiber whiskers were prepared using the method described in Preparation Example 2.

[0061] Preparation Example 6

[0062] Nanofiber whiskers were dispersed in water, and acrylic acid was added and mixed thoroughly; the acrylic acid was added at a mass ratio of nanofiber whiskers to acrylic acid of 4:1. Then, Darocur 2959 photoinitiator was added at a concentration of 5 wt% of the nanofiber whiskers. After all raw materials were evenly dispersed, the mixture was heated at 80 mW / cm². 2 The reaction mixture was irradiated with ultraviolet light at a specific intensity for 8 min, then filtered, washed three times with water, and dried to obtain carboxyl-modified nanofiber whiskers. In this preparation example, the nanofiber whiskers were prepared using the method described in Preparation Example 3.

[0063] Preparation example of modified montmorillonite powder

[0064] Preparation Example 7

[0065] The modified montmorillonite powder was prepared as follows: 10g of carboxyl-modified nanofiber whiskers were dispersed in 10kg of hydrochloric acid solution to obtain a carboxyl-modified nanofiber whisker dispersion. The pH of the carboxyl-modified nanofiber whisker dispersion was adjusted to 3.1 by adjusting the amount of hydrochloric acid. 167g of montmorillonite powder was added to the carboxyl-modified nanofiber whisker dispersion and stirred for 10h. The mixture was then centrifuged and the precipitate was collected. The precipitate was dried to constant weight and then pulverized into powder to obtain the modified montmorillonite powder. The carboxyl-modified nanofiber whiskers were prepared in Preparation Example 4.

[0066] Preparation Example 8

[0067] The modified montmorillonite powder was prepared as follows: 10g of carboxyl-modified nanofiber whiskers were dispersed in 3.33kg of hydrochloric acid solution to obtain a carboxyl-modified nanofiber whisker dispersion. The pH of the carboxyl-modified nanofiber whisker dispersion was adjusted to 3.5 by adjusting the amount of hydrochloric acid. 125g of montmorillonite powder was added to the carboxyl-modified nanofiber whisker dispersion and stirred for 12h. The mixture was then centrifuged and the precipitate was collected. The precipitate was dried to constant weight and then pulverized into powder to obtain the modified montmorillonite powder. The carboxyl-modified nanofiber whiskers were prepared in Preparation Example 5.

[0068] Preparation Example 9

[0069] The modified montmorillonite powder was prepared as follows: 10g of carboxyl-modified nanofiber whiskers were dispersed in 2kg of hydrochloric acid solution to obtain a carboxyl-modified nanofiber whisker dispersion. The pH of the carboxyl-modified nanofiber whisker dispersion was adjusted to 4.0 by adjusting the amount of hydrochloric acid. 111g of montmorillonite powder was added to the carboxyl-modified nanofiber whisker dispersion and stirred for 14h. The mixture was then centrifuged and the precipitate was collected. The precipitate was dried to constant weight and then pulverized into powder to obtain the modified montmorillonite powder. The carboxyl-modified nanofiber whiskers were prepared in Preparation Example 6.

[0070] Preparation Example 10

[0071] The difference between this preparation example and preparation example 8 is that the carboxyl-modified nanofiber whiskers are replaced with an equal weight of nanofiber whiskers, otherwise the same as preparation example 8.

[0072] Preparation Example 11

[0073] The difference between this preparation example and preparation example 8 is that, in preparing the modified montmorillonite powder, the mass ratio of carboxyl-modified nanofiber whiskers to montmorillonite powder is 0.03:1.

[0074] Specifically, the preparation method of modified montmorillonite powder is as follows: 10g of carboxyl-modified nanofiber whiskers are dispersed in 3.33kg of hydrochloric acid solution to obtain a carboxyl-modified nanofiber whisker dispersion. The pH of the carboxyl-modified nanofiber whisker dispersion is adjusted to 3.5 by adjusting the amount of hydrochloric acid. 333g of montmorillonite powder is added to the carboxyl-modified nanofiber whisker dispersion and mixed and stirred for 12h. Then, the mixture is centrifuged and the precipitate is collected. The precipitate is dried to constant weight and then pulverized into powder to obtain modified montmorillonite powder. The carboxyl-modified nanofiber whiskers are prepared by Preparation Example 5.

[0075] Preparation Example 12

[0076] The difference between this preparation example and preparation example 8 is that, in preparing the modified montmorillonite powder, the mass ratio of carboxyl-modified nanofiber whiskers to montmorillonite powder is 0.12:1.

[0077] Specifically, the preparation method of modified montmorillonite powder is as follows: 10g of carboxyl-modified nanofiber whiskers are dispersed in 3.33kg of hydrochloric acid solution to obtain a carboxyl-modified nanofiber whisker dispersion. The pH of the carboxyl-modified nanofiber whisker dispersion is adjusted to 3.5 by adjusting the amount of hydrochloric acid. 83g of montmorillonite powder is added to the carboxyl-modified nanofiber whisker dispersion and mixed and stirred for 12h. Then, the mixture is centrifuged and the precipitate is collected. The precipitate is dried to constant weight and then pulverized into powder to obtain modified montmorillonite powder. The carboxyl-modified nanofiber whiskers are prepared by Preparation Example 5.

[0078] Example

[0079] The tea mentioned in this application can be of various varieties and origins. For example, it can be Pu-erh tea, green tea, oolong tea, black tea, or dark tea, etc.

[0080] The following uses Pu-erh tea (raw tea) as an example to illustrate the method for extracting tea polyphenols and removing caffeine in this application. The Pu-erh tea used contains 28.32 wt% tea polyphenols and 3.68 wt% caffeine.

[0081] Example 1

[0082] A method for extracting tea polyphenols and removing caffeine from tea leaves, comprising the following steps:

[0083] (1) Extraction of tea polyphenols

[0084] Step 1: Grind the Pu-erh tea leaves to obtain tea powder. Take 200g of tea powder and mix it with 2000g of 40% ethanol solution. Place the mixture in an ultrasonic-microwave extractor and perform ultrasonic-microwave synergistic extraction. Set the microwave power to 300w, the ultrasonic power to 40w, the extraction time to 200s, and the extraction temperature to 60℃ to obtain the initial extraction mixture (the initial extraction mixture contains solvent, tea powder, and tea components dissolved or dispersed in the solvent).

[0085] Step 2: Then, add a fresh 40 vol.% ethanol solution to all the initial extraction mixtures to make the material-to-liquid ratio 1:20, extract for 30 min, then centrifuge and take the supernatant. Concentrate to 1 / 2 of the supernatant volume to obtain the tea polyphenol extract.

[0086] (2) Take 1000g of tea polyphenol extract, add 20g of modified montmorillonite powder prepared in Preparation Example 7, and stir at 7000rpm for 20min to remove caffeine. Then centrifuge and take the supernatant to obtain the purified tea polyphenol solution. Distill the tea polyphenol solution under reduced pressure to obtain the purified tea polyphenol.

[0087] Example 2

[0088] A method for extracting tea polyphenols and removing caffeine from tea leaves, comprising the following steps:

[0089] (1) Extraction of tea polyphenols

[0090] Step 1: Grind the Pu-erh tea leaves to obtain tea powder. Take 300g of tea powder and mix it with 2000g of 45% ethanol solution. Place the mixture in an ultrasonic-microwave extractor and perform ultrasonic-microwave synergistic extraction. Set the microwave power to 400w, the ultrasonic power to 55w, the extraction time to 150s, and the extraction temperature to 70℃ to obtain the initial extraction mixture (the initial extraction mixture contains solvent, tea powder, and tea components dissolved or dispersed in the solvent).

[0091] Step 2: Then, add a fresh 45% ethanol solution to all the initial extraction mixtures to make the material-to-liquid ratio 1:30, extract for 50 minutes, then centrifuge and take the supernatant. Concentrate the supernatant to 1 / 2 of its volume to obtain the tea polyphenol extract.

[0092] (2) Take 1000g of tea polyphenol extract, add 50g of modified montmorillonite powder prepared in Preparation Example 8, and stir at 7500rpm for 15min to remove caffeine. Then centrifuge and take the supernatant to obtain the purified tea polyphenol solution. Distill the tea polyphenol solution under reduced pressure to obtain the purified tea polyphenol.

[0093] Example 3

[0094] A method for extracting tea polyphenols and removing caffeine from tea leaves, comprising the following steps:

[0095] (1) Extraction of tea polyphenols

[0096] Step 1: Grind the Pu-erh tea leaves to obtain tea powder. Take 400g of tea powder and mix it with 2000g of 50% ethanol solution. Place the mixture in an ultrasonic-microwave extractor and perform ultrasonic-microwave synergistic extraction. Set the microwave power to 500w, the ultrasonic power to 70w, the extraction time to 100s, and the extraction temperature to 80℃ to obtain the initial extraction mixture (the initial extraction mixture contains solvent, tea powder, and tea components dissolved or dispersed in the solvent).

[0097] Step 2: Then, add a fresh 50% ethanol solution to all the initial extraction mixtures to make the material-to-liquid ratio 1:35, extract for 70 minutes, then centrifuge and take the supernatant. Concentrate the supernatant to 1 / 2 of its volume to obtain the tea polyphenol extract.

[0098] (2) Take 1000g of tea polyphenol extract, add 80g of modified montmorillonite powder prepared in Preparation Example 9, and stir at 8000rpm for 10min to remove caffeine. After centrifugation, take the supernatant to obtain the purified tea polyphenol solution. Distill the tea polyphenol solution under reduced pressure to obtain the purified tea polyphenols.

[0099] Examples 4-5

[0100] The difference between Examples 4-5 and Example 2 is that the modified montmorillonite powder was prepared using different preparation examples; specifically, Example 4 uses the modified montmorillonite powder from Preparation Example 11, Example 5 uses the modified montmorillonite powder from Preparation Example 12, and the rest is the same as Example 2.

[0101] Examples 6-7

[0102] The difference between Examples 6-7 and Example 2 lies in the amount of modified montmorillonite powder used; specifically, in Example 6, the amount of modified montmorillonite powder used is 2 wt% of the tea polyphenol extract, and in Example 7, the amount of modified montmorillonite powder used is 8 wt% of the tea polyphenol extract, with the other aspects being the same as in Example 2.

[0103] Comparative Example

[0104] Comparative Examples 1-2

[0105] The difference between Comparative Examples 1-2 and Example 2 lies in the amount of modified montmorillonite powder used; specifically, in Comparative Example 1, the amount of modified montmorillonite powder used was 0.5 wt% of the tea polyphenol extract, and in Comparative Example 2, the amount of modified montmorillonite powder used was 11 wt% of the tea polyphenol extract, with the other aspects being the same as in Example 2.

[0106] Comparative Example 3

[0107] The difference between this comparative example and Example 2 is that the modified montmorillonite powder was prepared in Preparation Example 10, while the rest is the same as in Example 2.

[0108] Comparative Example 4

[0109] The difference between this comparative example and Example 2 is that the modified montmorillonite powder is replaced with an equal weight of montmorillonite powder; otherwise, they are the same as in Example 2.

[0110] Comparative Example 5

[0111] The difference between this comparative example and Example 2 is that the modified montmorillonite powder is replaced with an equal weight of carboxyl-modified nanofiber whiskers. The carboxyl-modified nanofiber whiskers were prepared in Preparation Example 5, and the rest is the same as in Example 2.

[0112] Comparative Example 6

[0113] The difference between this comparative example and Example 2 lies in the adsorbent and the adsorption method, as detailed below:

[0114] The steps of a method for extracting tea polyphenols and removing caffeine from tea are as follows:

[0115] S1. Extract tea polyphenols to obtain tea polyphenol extract. The specific steps are the same as step (1) in Example 2.

[0116] S2. Take 1000g of tea polyphenol extract and add 50g of adsorbent, specifically a mixture of 3.7g of carboxyl-modified cellulose whiskers and 46.3g of montmorillonite powder. Stir at 7500rpm for 15min to remove caffeine. After centrifugation, collect the supernatant to obtain a purified tea polyphenol solution. Distill the tea polyphenol solution under reduced pressure to obtain purified tea polyphenols.

[0117] Performance testing

[0118] 1. Determination of tea polyphenol content

[0119] The content of tea polyphenols in the tea polyphenol extract was determined according to the relevant methods in GB / T8313-2018, and the tea polyphenol retention rate (%) was calculated based on the tea polyphenol content before and after purification of the tea polyphenol extract. The specific results are shown in Table 1. Among them, the tea polyphenol retention rate (%) = tea polyphenol content after purification of tea polyphenol extract / tea polyphenol content before purification of tea polyphenol extract × 100%.

[0120] 2. Caffeine content determination

[0121] The caffeine content in the tea polyphenol extract was determined according to the relevant methods in GB / T 8312-2013, and the caffeine removal rate (%) was calculated based on the caffeine content before and after purification of the tea polyphenol extract. The specific results are shown in Table 1. Among them, the caffeine removal rate (%) = (caffeine content before purification of tea polyphenol extract - caffeine content after purification of tea polyphenol extract) / caffeine content before purification of tea polyphenol extract × 100%.

[0122] Table 1. Retention rate of tea polyphenols and removal rate of caffeine by different methods

[0123]

[0124]

[0125] As shown in Table 1, the method of this application significantly improves the retention rate of tea polyphenols while ensuring a high removal rate of caffeine. This application significantly improves the removal rate of caffeine using montmorillonite powder and carboxyl-modified nanofiber whiskers loaded on montmorillonite powder, and significantly improves the retention rate of tea polyphenols using carboxyl-modified nanofiber whiskers.

[0126] In this scheme, Examples 2 and 6-7, and Comparative Examples 1-2 demonstrate that the amount of modified montmorillonite powder used in this method is 2-8 wt% of the tea polyphenol extract. Too little powder will directly affect the removal rate of caffeine, but too much powder will not have a significant impact on the removal rate of caffeine, but will significantly reduce the retention rate of tea polyphenols.

[0127] The modified montmorillonite powder, which is the main agent for caffeine removal, primarily functions through carboxyl-modified nanofiber whiskers supported on it. In Comparative Example 3, the modified montmorillonite powder was obtained by directly loading nanofiber whiskers onto the powder. Since the nanofiber whiskers were not carboxyl-modified, they suffer from the following drawbacks: 1. Reduced adsorption capacity of the nanofiber whiskers; 2. Decreased binding stability between the nanofiber whiskers and montmorillonite powder, leading to a significant reduction in their collaborative caffeine adsorption capacity; 3. Significantly affected tea polyphenol retention, further reducing the selective adsorption capacity of the modified montmorillonite powder for caffeine. Therefore, the method in Comparative Example 3 resulted in significantly lower tea polyphenol retention and caffeine removal rates.

[0128] The modified montmorillonite powder exerts its adsorption effect through the synergistic action of carboxyl-modified nanofiber whiskers supported on the montmorillonite powder. Comparative Examples 4-5 demonstrate that while montmorillonite powder or carboxyl-modified nanofiber whiskers alone achieve some caffeine removal, the removal rate is significantly reduced. Furthermore, in Comparative Example 4, because it uses only montmorillonite powder without the addition of carboxyl-modified nanofiber whiskers, the tea polyphenol retention rate is significantly lower. However, compared to Comparative Example 3, because the adsorbent in Comparative Example 3 works synergistically with montmorillonite powder, its adsorption effect is stronger than that in Comparative Example 4, resulting in a higher caffeine adsorption rate.

[0129] In addition, this application attempted to use a mixture of montmorillonite powder and modified nanofiber whiskers as an adsorbent to adsorb caffeine. It was found that the caffeine adsorption effect was significantly reduced compared with Example 2. Furthermore, the retention rate of tea polyphenols was also significantly reduced. While adsorbing caffeine, montmorillonite powder still adsorbed a large amount of tea polyphenols, which reduced the retention rate of tea polyphenols.

[0130] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for extracting tea polyphenols and removing caffeine from tea, characterized in that, Includes the following steps: A tea polyphenol extract was obtained, and the tea polyphenol extract was then contacted with modified montmorillonite powder to remove caffeine. The amount of modified montmorillonite powder used was 2-8 wt% of the tea polyphenol extract. The preparation method of the modified montmorillonite powder includes the following steps: dispersing carboxyl-modified nanofiber whiskers in an acidic solution and mixing and stirring with montmorillonite powder, then separating the solid and liquid and collecting the solid, drying and pulverizing to obtain modified montmorillonite powder; The preparation method of the carboxyl-modified nanofiber whiskers includes the following steps: mixing nanofiber whisker dispersion and acrylic acid at a mass ratio of (2-4):1, and then mixing with a photoinitiator and reacting under ultraviolet light irradiation. After solid-liquid separation, the solid is collected, washed with water, and dried to obtain carboxyl-modified nanofiber whiskers.

2. The method for extracting tea polyphenols and removing caffeine from tea according to claim 1, characterized in that, After dispersing the carboxyl-modified nanofiber whiskers in an acidic solution, the resulting carboxyl-modified nanofiber whisker dispersion has a pH of 3.0-4.

0.

3. The method for extracting tea polyphenols and removing caffeine from tea according to claim 1, characterized in that, The mass ratio of the carboxyl-modified nanofiber whiskers to the montmorillonite powder is (0.06-0.09):

1.

4. The method for extracting tea polyphenols and removing caffeine from tea according to claim 1, characterized in that, When the carboxyl-modified nanofiber whiskers are dispersed in an acidic solution, the weight ratio of the carboxyl-modified nanofiber whiskers to the acidic solution is (0.001-0.005):

1.

5. The method for extracting tea polyphenols and removing caffeine from tea according to claim 1, characterized in that, The reaction time under ultraviolet light irradiation is 10-15 min.

6. The method for extracting tea polyphenols and removing caffeine from tea according to claim 1, characterized in that, The contact time between the tea polyphenol extract and the modified montmorillonite powder is 10-20 minutes, accompanied by stirring at a speed of 7000-8000 rpm.

7. The method for extracting tea polyphenols and removing caffeine from tea according to claim 1, characterized in that, The method for obtaining tea polyphenol extract includes the following steps: Step 1: Mix tea powder with 40-50% ethanol solution and extract using ultrasound-microwave synergistic extraction. The weight of the tea powder is 10-20 wt% of the 40-50% ethanol solution. Step 2: Then add 40-50% ethanol solution to make the material-to-liquid ratio 1:20-35, extract, separate solids and liquids, and concentrate the supernatant to obtain tea polyphenol extract.

8. The method for extracting tea polyphenols and removing caffeine from tea according to claim 7, characterized in that, In step 1, during the ultrasonic-microwave synergistic extraction, the microwave power is 300-500W, the ultrasonic power is 40-70W, the extraction time is 100-200s, and the extraction temperature is 60-80℃. The extraction time in step 2 is 30-70 minutes.

Images