A method for separating and purifying tea polyphenols and caffeine in a tea extract

Abstract

The application belongs to the technical field of natural product extraction and separation, and specifically discloses a separation and purification method for tea polyphenols and caffeine in tea extract, which comprises the following steps: S1, raw material grading pretreatment: according to the categories, parts and seasons of tea, the raw materials are divided into three grades A, B and C, and are crushed, and defatting treatment is performed according to the grades of the raw materials; S2, grading extraction, to obtain a clear filtrate; S3, membrane method impurity removal and concentration, to remove macromolecular impurities and concentrate the extract; S4, two-stage resin adsorption process, the first stage is a caffeine selective adsorption resin, and the second stage is a tea polyphenol selective adsorption resin, and the adsorption flow rate and elution gradient are adjusted according to the grades of the raw materials; and S5, concentration and drying, to obtain high-purity tea polyphenol and caffeine products. The separation and purification method for tea polyphenol and caffeine in tea extract is adopted, so that the efficient separation and purification of green tea, Yunnan red tea and white tea are realized, tea polysaccharides are recovered, and the comprehensive utilization rate of raw materials is improved.

Description

Technical Field

[0001] This invention relates to the field of natural product extraction and separation technology, and in particular to a method for separating and purifying tea polyphenols and caffeine from tea extract. Background Technology

[0002] Due to the differentiated layout of tea industry bases, multiple categories of tea, including Yunnan black tea, green tea, and white tea, have developed rapidly, and consumers have shifted from simply drinking tea to "tea + health." Tea polyphenols and caffeine are the two most important active ingredients in tea, possessing a wide range of physiological functions and applications. However, the separation and purification processes for tea polyphenols and caffeine are primarily designed for green tea, exhibiting poor compatibility with other tea types such as Yunnan black tea and white tea. Therefore, the separation and purification processes for tea polyphenols and caffeine cannot be directly applied to green tea and must be specifically adjusted.

[0003] Different types of tea, different parts of the plant, and tea leaves from different seasons exhibit significant differences in their composition. For example, green tea has a high content of tea polyphenols and a moderate content of caffeine; Yunnan black tea has a low content of tea polyphenols but a high content of caffeine and contains a large amount of tea pigment impurities; white tea has a high content of amino acids and polysaccharides, but also contains many waxy impurities. In addition, spring tea has a high content of tea polyphenols and a low content of caffeine; summer tea has a high content of caffeine and a low content of tea polyphenols; tender leaves have a high content of target components and few impurities; older leaves have a high fiber content and complex impurities.

[0004] In existing technologies, resin adsorption and membrane separation are currently the mainstream green processes for separating and purifying tea polyphenols and caffeine, offering advantages such as good selectivity, high purity, reusable resin, and no toxic solvent residues. However, they cannot be adapted to multiple types of tea simultaneously, resulting in low efficiency and unstable product quality when processing different raw materials. In particular, the tea pigments in Dianhong tea and the waxes in white tea can easily cause irreversible contamination of the resin.

[0005] Therefore, developing a universal separation and purification method that can adjust parameters according to tea type, part, and season is of great significance for improving the utilization rate of tea resources, reducing production costs, and promoting the diversified development of the tea industry. Summary of the Invention

[0006] The purpose of this invention is to provide a method for separating and purifying tea polyphenols and caffeine in tea extracts. This method allows for targeted parameter adjustments based on tea type, part, and season, achieving efficient separation and purification of green tea, Yunnan black tea, and white tea, while simultaneously recovering tea polysaccharides and improving the comprehensive utilization rate of raw materials.

[0007] To achieve the above objectives, the present invention provides a method for separating and purifying tea polyphenols and caffeine from tea extract, comprising the following steps: S1. Raw material grading and pretreatment: According to the tea category, part and season, the raw materials are divided into three grades: A, B and C, and crushed to 40-80 mesh. Degreasing treatment is carried out according to the raw material grade. S2. Staged extraction: A staged hot water extraction process is adopted. The extraction temperature, time and material-liquid ratio are adjusted according to the grade of the raw materials. The extract is centrifuged and filtered to obtain a clear filtrate. S3. Membrane-based impurity removal and concentration: A three-stage membrane separation system of microfiltration-ultrafiltration-nanofiltration is adopted. The membrane pore size and operating pressure are adjusted according to the raw material grade to remove macromolecular impurities and concentrate the extract. S4. Selective resin adsorption: A two-stage resin adsorption process is adopted. The first stage is a caffeine selective adsorption resin, and the second stage is a tea polyphenol selective adsorption resin. The adsorption flow rate and elution gradient are adjusted according to the raw material grade. S5. Concentration and Drying: The eluent is concentrated and spray-dried separately to obtain high-purity tea polyphenols and caffeine products.

[0008] Preferably, in S1, the tea categories include green tea, Yunnan black tea, and white tea; the parts include bud tips, one bud and one leaf, one bud and two leaves, mature leaves, and old leaves; and the seasons include spring tea, summer tea, and autumn tea.

[0009] Preferably, in S1, the three levels A, B, and C are specifically as follows: Grade A raw materials: Green or white tea with one bud and one to two leaves from spring tea, with a tea polyphenol content ≥25% and a caffeine content ≥10%. Grade B raw materials: mature leaves of spring tea, green tea, white tea or Yunnan black tea with one bud and one to two leaves of autumn tea, with a tea polyphenol content of 15-25% and a tea polyphenol content: caffeine content = 5-10; Grade C raw materials: summer tea, old leaves of green tea, white tea or Yunnan black tea, with tea polyphenol content ≤15% and tea polyphenol content and caffeine content ≤5%.

[0010] Preferably, in S1, the degreasing treatment is as follows: Grade A raw materials: not degreased; Grade B raw materials: supercritical CO2 degreasing, pressure 20~25MPa, temperature 35~40℃, time 1~1.5h; Grade C raw materials: supercritical CO2 degreasing is used, with a pressure of 25~30MPa, a temperature of 40~45℃, and a time of 1.5~2h.

[0011] Tea leaves contain 0.5-5% fat-soluble impurities, mainly including epidermal waxes, triglycerides, free fatty acids, chlorophyll, carotenoids, and phytosterols. These impurities are key factors leading to low efficiency, poor product quality, and short equipment lifespan in traditional separation and purification processes. Tea waxes (mainly composed of C24-C34 long-chain fatty acids and fatty alcohols) preferentially adsorb onto the resin surface, covering active sites and clogging resin pores, resulting in a significant decrease in the resin's adsorption capacity and selectivity for the target components. While solid at room temperature, they dissolve in the aqueous phase after heating extraction, and precipitate as tiny particles upon cooling, physically clogging membrane pores and forming a dense filter cake layer on the membrane surface.

[0012] Degreasing treatment avoids irreversible fouling of the membrane system and reduces the adsorption performance and selectivity of the resin. On the other hand, it can remove fat-soluble pigments such as chlorophyll and carotenoids to improve color, remove fat-soluble off-flavor substances (such as fatty acid oxidation products) to enhance flavor, and remove easily oxidized lipids to extend the shelf life of the product.

[0013] Grade B raw materials achieve maximum CO2 solubility for waxes and fats under pressure of 20-25 MPa, with a degreasing rate ≥90% and a tea polyphenol loss rate ≤1.5%. Due to the high impurity content of Grade C raw materials, higher pressure is required to improve solubility. Grade C raw materials achieve a degreasing rate ≥85% and a tea polyphenol loss rate ≤2.2% under pressure of 25-30 MPa, temperature of 40-45℃, and time of 1.5-2.0 h, with a membrane flux recovery rate ≥72%, effectively solving the problems of membrane and resin fouling.

[0014] Preferably, in S2, the segmented hot water extraction process specifically includes: Grade A raw materials: extraction temperature 75~80℃, extraction time 20~30min, material-liquid ratio 1:15~20, two-stage extraction; Grade B raw materials: extraction temperature 80~85℃, extraction time 30~40min, material-liquid ratio 1:20~25, two-stage extraction; Grade C raw materials: extraction temperature 90~95℃, extraction time 40~60min, material-liquid ratio 1:25~30, three-stage extraction, before extraction, add 0.2~0.5% compound enzyme and pre-treat at 50℃ for 30~60min.

[0015] Preferably, the compound enzyme is specifically cellulase and pectinase, with a mass ratio of cellulase to pectinase of 2:1.

[0016] Tea cell walls are mainly composed of cellulose, hemicellulose, pectin, and lignin. Tea polyphenols and caffeine are primarily found in the vacuoles of mesophyll cells, and the cell wall is the main barrier preventing their leaching. In C-grade older leaves, the cell walls are highly lignified, and the cellulose and pectin structures are dense, making them difficult for hot water to penetrate. Therefore, enzymatic hydrolysis is necessary to break down the cell wall structure. A binary system of cellulase and pectinase is used to avoid introducing additional impurities such as proteases and hemicellulases. The pH of the raw material solution is kept stable between 4.2 and 4.8, eliminating the need for intermediate pH adjustments and ensuring consistency with the subsequent resin adsorption pH. After enzymatic hydrolysis, no further adjustments are required, and the solution directly proceeds to membrane separation and resin adsorption processes, avoiding the oxidation loss of tea polyphenols caused by pH adjustments. If the pH exceeds the above range, it can be adjusted by slowly adding hydrochloric acid and stirring thoroughly to prevent abnormal conditions (such as the use of severely aged raw materials, raw materials from abnormal production areas, or batches with severe membrane contamination leading to increased pH in the permeate) from affecting the resin adsorption process.

[0017] Preferably, in S3, the microfiltration-ultrafiltration-nanofiltration three-stage membrane separation system specifically comprises: Microfiltration: 0.2~0.45μm ceramic membrane is used, and the operating pressure is 0.1~0.2MPa; Ultrafiltration: Grade A feed uses a 10kDa ultrafiltration membrane, while Grade B and Grade C feeds use a 5kDa ultrafiltration membrane. The operating pressure is 0.2~0.3MPa. Nanofiltration: Using a 1kDa nanofiltration membrane, operating pressure 0.3~0.4MPa, concentrating to a solids content of 10~15%.

[0018] Preferably, in S4, the two-stage resin adsorption process specifically comprises: First-stage selective adsorption resin for caffeine: HPD-100, a highly hydrophilic macroporous adsorption resin, was used. The pH of the loading solution was 4.0~5.0, the adsorption flow rate was 0.8~2 BV / h, impurities were removed by washing with water for 2~3 BV, and caffeine was eluted with 30~40% ethanol. Second-stage selective adsorption resin for tea polyphenols: Spherical polyamide resin is used, the sample solution is the first-stage effluent, the adsorption flow rate is 1~2 BV / h, impurities are removed by washing with water for 2~3 BV, and tea polyphenols are eluted with 60~70% ethanol.

[0019] HPD-100 is a highly cross-linked, non-polar polystyrene-divinylbenzene macroporous adsorption resin. Its adsorption primarily stems from hydrophobic interactions. Caffeine, being more hydrophobic, exhibits a higher affinity for the non-polar resin. Furthermore, the larger molecular size of caffeine allows it to more easily enter the resin pores and diffuse more rapidly. Under acidic conditions, caffeine exists in molecular form, while tea polyphenols partially dissociate. By controlling the sample loading pH between 4.0 and 5.0, at pH > 4, the phenolic hydroxyl groups of tea polyphenols begin to dissociate, increasing polarity and decreasing affinity for the non-polar resin. Conversely, at pH < 10, caffeine primarily exists in molecular form, exhibiting strong hydrophobicity and readily adsorbed by the non-polar resin.

[0020] Preferably, in S4, adjusting the adsorption flow rate and elution gradient according to the raw material grade is specifically as follows: Grade A raw materials: adsorption flow rate 1.5~2 BV / h, the sample loading amount of the first-stage caffeine selective adsorption resin is 80~90% of the saturation adsorption capacity, and the sample loading amount of the second-stage tea polyphenol selective adsorption resin is 70~80% of the saturation adsorption capacity; Grade B raw materials: adsorption flow rate 1~1.5 BV / h, the sample loading amount of the first-stage caffeine selective adsorption resin is 90~100% of the saturation adsorption capacity, and the sample loading amount of the second-stage tea polyphenol selective adsorption resin is 80~90% of the saturation adsorption capacity; Grade C raw materials: adsorption flow rate 0.8~1 BV / h, the sample loading amount of the first-stage caffeine selective adsorption resin is 100~120% of the saturated adsorption capacity, and the sample loading amount of the second-stage tea polyphenol selective adsorption resin is 90~100% of the saturated adsorption capacity.

[0021] Preferably, the concentration and drying process is as follows: Concentration: Vacuum concentration is performed at a temperature of 50~60℃ and a vacuum degree of -0.08~-0.09MPa until the solid content reaches 30~40%. Drying: Spray drying is adopted, with an inlet air temperature of 160~180℃ and an outlet air temperature of 80~90℃.

[0022] Preferably, it also includes tea polysaccharide recovery: the ultrafiltration retentate from the three-stage membrane separation system of microfiltration-ultrafiltration-nanofiltration in S3 is concentrated and dried to obtain tea polysaccharides.

[0023] Therefore, the present invention employs the above-mentioned method for separating and purifying tea polyphenols and caffeine from tea extract, and the beneficial effects are as follows: This invention is highly versatile: it establishes a raw material grading system and parameter adjustment model based on tea category, part, and season, which can be adapted to three types of tea: green tea, Yunnan black tea, and white tea. It solves the problem of the single processing method in traditional methods, and realizes the simultaneous extraction and separation of tea polyphenols, caffeine, and tea polysaccharides, thereby improving the comprehensive utilization rate of raw materials and significantly increasing economic benefits. At the same time, through raw material grading and parameter standardization, it ensures the stability of product quality in different batches, making it suitable for large-scale industrial production.

[0024] This invention offers excellent separation performance: it employs a two-stage resin adsorption process, with the first stage selectively adsorbing caffeine and the second stage selectively adsorbing tea polyphenols. Caffeine is removed first, followed by tea polyphenol recovery. The process leverages the pH value's influence on the adsorption selectivity of HPD-100 to enhance separation selectivity, resulting in high product purity. Tea polyphenol purity reaches 90-98%, caffeine content is ≤0.2-0.8%, and caffeine purity reaches 97-99%.

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0026] Figure 1 This is a diagram showing the product purity results of an embodiment and a comparative example of a method for separating and purifying tea polyphenols and caffeine in tea extract according to the present invention. Figure 2 This is a graph showing the product yield results of an example and a comparative example of a method for separating and purifying tea polyphenols and caffeine in tea extract according to the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0028] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0029] Example 1 A method for separating and purifying tea polyphenols and caffeine from tea extract, using Grade A raw material (spring tea with one bud and two leaves), includes the following steps: S1. Raw material pretreatment: Take 100kg of spring tea with one bud and two leaves, with a tea polyphenol content (TP) of 28.5% and a caffeine (CAF) content of 2.6%, and a TP:CAF ratio of 11:1. It belongs to Grade A raw material. Grind it to 60 mesh and do not perform degreasing treatment.

[0030] S2. Fractional Extraction: Add 2000L of deionized water and extract at 80℃ for 30 min, then filter. Add 1500L of deionized water to the filter residue and extract at 80℃ for 20 min, then filter. Combine the two filtrates, centrifuge and filter to obtain a clear filtrate.

[0031] S3. Membrane-based impurity removal and concentration: The clarified filtrate is microfiltered through a 0.2 μm ceramic membrane at an operating pressure of 0.15 MPa; the microfiltration permeate is ultrafiltered through a 10 kDa ultrafiltration membrane at an operating pressure of 0.25 MPa; the ultrafiltration permeate is concentrated through a 1 kDa nanofiltration membrane to a solids content of 12% at an operating pressure of 0.35 MPa. The ultrafiltration retentate is concentrated and dried to obtain 2.1 kg of tea polysaccharides with a purity of 86.3%.

[0032] S4. Selective Resin Adsorption: At pH 4.5, the sample was passed through an HPD-100 macroporous resin column at a flow rate of 1.8 BV / h, with a sample loading volume of 85% of the resin's saturated adsorption capacity. Impurities were eluted with 2.5 BV of deionized water, followed by elution of caffeine with 35% ethanol, and the eluent was collected. The effluent was then passed through a spherical polyamide resin column at a flow rate of 1.6 BV / h, with a sample loading volume of 75% of the resin's saturated adsorption capacity. Impurities were eluted with 2 BV of deionized water, followed by elution of tea polyphenols with 65% ethanol, and the eluent was collected.

[0033] S5. Concentration and Drying: The caffeine eluent and tea polyphenol eluent were concentrated under vacuum at 55℃ and -0.085MPa to a solid content of 35%, respectively, and then spray-dried at an inlet air temperature of 170℃ and an outlet air temperature of 85℃. 23.7 kg of tea polyphenols were obtained with a purity of 98.2% and a yield of 23.7%; 2.1 kg of caffeine was obtained with a purity of 99.1% and a yield of 2.1%.

[0034] Example 2 A method for separating and purifying tea polyphenols and caffeine from tea extract, specifically for the separation and purification of Grade B raw material (autumn tea, one bud and two leaves, white tea), includes the following steps: S1. Raw material pretreatment: Take 100kg of autumn tea (one bud and two leaves), with a TP content of 21.3% and a CAF content of 3.2%, TP:CAF = 6.7:1, belonging to grade B raw materials. Grind to 60 mesh and degrease using supercritical CO2 at a pressure of 22MPa, a temperature of 38℃, and a time of 1.2h.

[0035] S2. Fractional Extraction: Add 2200L of deionized water and extract at 82℃ for 35 min, then filter. Add 1800L of deionized water to the filter residue and extract at 82℃ for 25 min, then filter. Combine the two filtrates, centrifuge, and filter to obtain a clear filtrate.

[0036] S3. Membrane-based impurity removal and concentration: The clarified filtrate is microfiltered through a 0.2 μm ceramic membrane at an operating pressure of 0.18 MPa; the microfiltration permeate is ultrafiltered through a 5 kDa ultrafiltration membrane at an operating pressure of 0.28 MPa; the ultrafiltration permeate is concentrated through a 1 kDa nanofiltration membrane to a solids content of 13% at an operating pressure of 0.38 MPa. The ultrafiltration retentate is concentrated and dried to obtain 2.8 kg of tea polysaccharides with a purity of 83.5%.

[0037] S4. Selective Resin Adsorption: At pH 4.3, the sample was passed through an HPD-100 macroporous resin column at a flow rate of 1.2 BV / h, with a loading volume of 95% of the resin's saturated adsorption capacity. Impurities were eluted with 2.5 BV of deionized water, followed by elution of caffeine with 38% ethanol, and the eluent was collected. The effluent was then passed through a spherical polyamide resin column at a flow rate of 1.3 BV / h, with a loading volume of 85% of the resin's saturated adsorption capacity. Impurities were eluted with 2.5 BV of deionized water, followed by elution of tea polyphenols with 68% ethanol, and the eluent was collected.

[0038] S5. Concentration and Drying: The caffeine eluent and tea polyphenol eluent were concentrated under vacuum at 58℃ and -0.088MPa to a solid content of 38%, respectively, and then spray-dried at an inlet air temperature of 175℃ and an outlet air temperature of 88℃. 17.2 kg of tea polyphenols were obtained with a purity of 95.6% and a yield of 17.2%; 2.7 kg of caffeine was obtained with a purity of 98.3% and a yield of 2.7%.

[0039] Example 3 A method for separating and purifying tea polyphenols and caffeine from tea extract, specifically for the separation and purification of Grade C raw material (ripe summer tea leaves of Dianhong black tea), includes the following steps: S1. Raw material pretreatment: Take 100kg of mature summer Dianhong black tea leaves with a TP content of 11.7% and a CAF content of 4.3% (TP:CAF = 2.7:1), which belongs to grade C raw materials. Grind to 50 mesh and degrease using supercritical CO2 at a pressure of 28MPa, a temperature of 42℃, and a time of 1.8h.

[0040] S2. Fractional Extraction: Add 0.3% compound enzyme (cellulase: pectinase = 2:1), pretreatment at 50℃ for 45 min; then add 2800 L of deionized water, extract at 92℃ for 50 min, and filter; add 2200 L of deionized water to the residue, extract at 92℃ for 35 min, and filter; add 1800 L of deionized water to the residue again, extract at 92℃ for 25 min, and filter. Combine the three filtrates, add 0.08% vitamin C, centrifuge and filter to obtain a clear filtrate.

[0041] S3. Membrane-based impurity removal and concentration: The clarified filtrate is microfiltered through a 0.2 μm ceramic membrane at an operating pressure of 0.2 MPa; the microfiltration permeate is ultrafiltered through a 5 kDa ultrafiltration membrane at an operating pressure of 0.3 MPa; the ultrafiltration permeate is concentrated through a 1 kDa nanofiltration membrane to a solids content of 14% at an operating pressure of 0.4 MPa. The ultrafiltration retentate is concentrated and dried to obtain 3.5 kg of tea polysaccharides with a purity of 79.2%.

[0042] S4. Selective Resin Adsorption: At pH 4.0, the sample was passed through an HPD-100 macroporous resin column at a flow rate of 0.9 BV / h, with a loading volume of 115% of the resin's saturated adsorption capacity. Impurities were eluted with 3 BV of deionized water, followed by elution of caffeine with 40% ethanol, and the eluent was collected. The effluent was then passed through a spherical polyamide resin column at a flow rate of 0.9 BV / h, with a loading volume of 95% of the resin's saturated adsorption capacity. Impurities were eluted with 3 BV of deionized water, followed by elution of tea polyphenols with 70% ethanol, and the eluent was collected.

[0043] S5. Concentration and Drying: The caffeine eluent and tea polyphenol eluent were concentrated under vacuum at 60℃ and -0.09MPa to a solid content of 40%, respectively, and then spray-dried at an inlet air temperature of 180℃ and an outlet air temperature of 90℃. 8.9 kg of tea polyphenols were obtained with a purity of 90.3% and a yield of 8.9%; 3.7 kg of caffeine was obtained with a purity of 97.2% and a yield of 3.7%.

[0044] Comparative Example 1 A traditional green tea processing method for summer Dianhong black tea involves using 100 kg of mature summer Dianhong black tea leaves (similar to Example 3) for extraction at 85℃ for 40 min (material-to-liquid ratio 1:20), a two-stage extraction process, followed by 0.2 μm microfiltration + 10 kDa ultrafiltration, and single-stage polyamide resin adsorption at a flow rate of 2 BV / h, eluted with 70% ethanol. This yields 6.5 kg of tea polyphenols (82.1% purity, 6.5% yield) and 0.5 kg of caffeine (85.7% purity, 0.5% yield). The resin lifespan is reduced to 25 cycles, and the membrane cleaning cycle is shortened to 8 batches.

[0045] Comparative Example 2 A method for separating and purifying tea polyphenols and caffeine from ungraded mixed raw materials is disclosed. Grade A, B, and C raw materials are mixed in a 1:1:1 ratio. The method differs from Example 1 in that it uses uniform process parameters: extraction at 80℃ for 35 min, material-to-liquid ratio of 1:20, two-stage extraction; 0.2 μm microfiltration + 10 kDa ultrafiltration; two-stage resin adsorption, flow rate of 1.5 BV / h. The average purity of tea polyphenols was 91.5%, with an average yield of 18.3%, and the average purity of caffeine was 81.5%, with an average yield of 0.62%. Product quality fluctuated significantly, with batch-to-batch purity differences exceeding 8%.

[0046] The purity and content of tea polyphenols and caffeine products in each embodiment and comparative example are as follows: Figure 1 and Figure 2 As shown, by classifying raw materials and adjusting targeted parameters, the separation and purification effect of tea leaves from different types, parts, and seasons can be effectively improved. The products have high purity, high yield, and stable quality, while significantly extending the service life of resins and membranes, making them suitable for large-scale industrial production.

[0047] Test For supercritical CO2 degreasing, extraction pressure (A), extraction temperature (B), and extraction time (C) were used as key factors, and degreasing rate (60%), tea polyphenol loss rate (25%), and membrane flux recovery rate (15%) were used as evaluation indicators. A three-factor, three-level orthogonal experimental design was adopted.

[0048] Degreasing rate: The content of fat-soluble impurities in the raw materials before and after degreasing is determined by gravimetric method, and the degreasing rate is calculated.

[0049] Tea polyphenol loss rate: The content of tea polyphenols in the raw materials before and after defatting was determined by the Folin-Ciocalteu method, and the loss rate was calculated.

[0050] Membrane flux recovery rate: The initial flux of the extract before and after defatting was measured after filtration through a ceramic membrane, and the flux recovery rate was calculated.

[0051] 1. The experimental raw material was Yunnan white tea with one bud and two leaves in autumn (Grade B raw material), with a total fat-soluble impurity content of 2.47%, tea polyphenol content of 21.3%, and caffeine content of 3.2%. The orthogonal experimental design is shown in Table 1, the orthogonal experimental results are shown in Table 2, and the range analysis is shown in Table 3.

[0052] Table 1 Orthogonal Experimental Design Table

[0053] Table 2. Results of Orthogonal Experiments

[0054] Table 3 Range Analysis Table

[0055] As shown in Tables 1-3, the optimal degreasing process parameters for Grade B raw materials are: A3B3C3: extraction pressure 25MPa, extraction temperature 40℃, and extraction time 1.5h. The verification results showed a degreasing rate of 93.7%, a tea polyphenol loss rate of 1.5%, and a membrane flux recovery rate of 92.1%, consistent with the orthogonal experimental results.

[0056] 2. The experimental raw material was mature summer tea leaves of Dianhong black tea (Grade C raw material), with a total fat-soluble impurity content of 5.12%, a tea polyphenol content of 11.7%, and a caffeine content of 4.3%. The orthogonal experimental design is shown in Table 4, the orthogonal experimental results are shown in Table 5, and the range analysis is shown in Table 6.

[0057] Table 4 Orthogonal Experimental Design Table

[0058] Table 5. Results of Orthogonal Experiments

[0059] Table 6 Range Analysis Table

[0060] As shown in Tables 4-6, the optimal degreasing process parameters for Grade C raw materials are: A3B3C3: extraction pressure 30MPa, extraction temperature 45℃, and extraction time 2.0h. The verification results showed a degreasing rate of 96.9%, a tea polyphenol loss rate of 2.1%, and a membrane flux recovery rate of 88.2%, consistent with the orthogonal experimental results.

[0061] In summary, extraction time has the greatest impact on degreasing efficiency, followed by extraction pressure, while extraction temperature has the least impact. This is because mass transfer rate is the limiting factor during extraction; extending the extraction time allows CO2 to fully penetrate into the cells to extract impurities. Considering economic efficiency, the process parameters A3B3C3 effectively solve the problems of membrane and resin fouling while maintaining moderate equipment energy consumption.

[0062] Therefore, the present invention adopts the above-mentioned method for separating and purifying tea polyphenols and caffeine in tea extract, which achieves efficient separation and purification of green tea, Yunnan black tea and white tea, while recovering tea polysaccharides and improving the comprehensive utilization rate of raw materials.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for separating and purifying tea polyphenols and caffeine from tea extract, characterized in that, Includes the following steps: S1. Raw material grading and pretreatment: According to the tea category, part and season, the raw materials are divided into three grades: A, B and C, and crushed to 40-80 mesh. Degreasing treatment is carried out according to the raw material grade. S2. Staged extraction: A staged hot water extraction process is adopted. The extraction temperature, time and material-liquid ratio are adjusted according to the grade of the raw materials. The extract is centrifuged and filtered to obtain a clear filtrate. S3. Membrane-based impurity removal and concentration: A three-stage membrane separation system of microfiltration-ultrafiltration-nanofiltration is adopted. The membrane pore size and operating pressure are adjusted according to the raw material grade to remove macromolecular impurities and concentrate the extract. S4. Selective resin adsorption: A two-stage resin adsorption process is adopted. The first stage is a caffeine selective adsorption resin, and the second stage is a tea polyphenol selective adsorption resin. The adsorption flow rate and elution gradient are adjusted according to the raw material grade. S5. Concentration and Drying: The eluent is concentrated and spray-dried separately to obtain high-purity tea polyphenols and caffeine products.

2. The method for separating and purifying tea polyphenols and caffeine in tea extract according to claim 1, characterized in that, In S1, tea categories include green tea, Yunnan black tea, and white tea; parts include buds, one bud and one leaf, one bud and two leaves, mature leaves, and old leaves; and seasons include spring tea, summer tea, and autumn tea.

3. The method for separating and purifying tea polyphenols and caffeine in tea extract according to claim 2, characterized in that, In S1, the three levels A, B, and C are specifically as follows: Grade A raw materials: Green or white tea with one bud and one to two leaves from spring tea, with a tea polyphenol content ≥25% and a caffeine content ≥10%. Grade B raw materials: mature leaves of spring tea, green tea, white tea or Yunnan black tea with one bud and one to two leaves of autumn tea, with a tea polyphenol content of 15-25% and a tea polyphenol content: caffeine content = 5-10; Grade C raw materials: summer tea, old leaves of green tea, white tea or Yunnan black tea, with tea polyphenol content ≤15% and tea polyphenol content and caffeine content ≤5%.

4. The method for separating and purifying tea polyphenols and caffeine in tea extract according to claim 3, characterized in that, In S1, the degreasing process is as follows: Grade A raw materials: not degreased; Grade B raw materials: supercritical CO2 degreasing, pressure 20~25MPa, temperature 35~40℃, time 1~1.5h; Grade C raw materials: supercritical CO2 degreasing is used, with a pressure of 25~30MPa, a temperature of 40~45℃, and a time of 1.5~2h.

5. The method for separating and purifying tea polyphenols and caffeine in tea extract according to claim 4, characterized in that, In S2, the segmented hot water extraction process is specifically as follows: Grade A raw materials: extraction temperature 75~80℃, extraction time 20~30min, material-liquid ratio 1:15~20, two-stage extraction; Grade B raw materials: extraction temperature 80~85℃, extraction time 30~40min, material-liquid ratio 1:20~25, two-stage extraction; Grade C raw materials: extraction temperature 90~95℃, extraction time 40~60min, material-liquid ratio 1:25~30, three-stage extraction, before extraction, add 0.2~0.5% compound enzyme and pre-treat at 50℃ for 30~60min.

6. The method for separating and purifying tea polyphenols and caffeine in tea extract according to claim 5, characterized in that, The complex enzymes specifically consist of cellulase and pectinase, with a mass ratio of 2:

1.

7. The method for separating and purifying tea polyphenols and caffeine in tea extract according to claim 1, characterized in that, In S4, the two-stage resin adsorption process is specifically as follows: First-stage selective adsorption resin for caffeine: HPD-100, a highly hydrophilic macroporous adsorption resin, was used. The pH of the loading solution was 4.0~5.0, the adsorption flow rate was 0.8~2 BV / h, impurities were removed by washing with water for 2~3 BV, and caffeine was eluted with 30~40% ethanol. Second-stage selective adsorption resin for tea polyphenols: Spherical polyamide resin is used, the sample solution is the first-stage effluent, the adsorption flow rate is 1~2 BV / h, impurities are removed by washing with water for 2~3 BV, and tea polyphenols are eluted with 60~70% ethanol.

8. The method for separating and purifying tea polyphenols and caffeine in tea extract according to claim 7, characterized in that, In S4, the adsorption flow rate and elution gradient are adjusted according to the raw material grade as follows: Grade A raw materials: adsorption flow rate 1.5~2 BV / h, the sample loading amount of the first-stage caffeine selective adsorption resin is 80~90% of the saturation adsorption capacity, and the sample loading amount of the second-stage tea polyphenol selective adsorption resin is 70~80% of the saturation adsorption capacity; Grade B raw materials: adsorption flow rate 1~1.5 BV / h, the sample loading amount of the first-stage caffeine selective adsorption resin is 90~100% of the saturation adsorption capacity, and the sample loading amount of the second-stage tea polyphenol selective adsorption resin is 80~90% of the saturation adsorption capacity; Grade C raw materials: adsorption flow rate 0.8~1 BV / h, the sample loading amount of the first-stage caffeine selective adsorption resin is 100~120% of the saturated adsorption capacity, and the sample loading amount of the second-stage tea polyphenol selective adsorption resin is 90~100% of the saturated adsorption capacity.

9. The method for separating and purifying tea polyphenols and caffeine in tea extract according to claim 1, characterized in that, This also includes tea polysaccharide recovery: The ultrafiltration retentate from the three-stage membrane separation system of microfiltration-ultrafiltration-nanofiltration in S3 was concentrated and dried to obtain tea polysaccharides.

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