High-efficiency extraction method of high-purity tea polyphenol without residual solvent

Abstract

The application discloses a kind of high-efficiency extraction methods of high-purity tea polyphenols without residual solvent, belongs to the technical field of tea extract.The method uses choline chloride-lactic acid eutectic solvent as medium, after dilution and acidification by water, green tea powder is extracted by ultrasonic-microwave pulse cooperation, and the initial concentrated solution is obtained by ultrafiltration membrane, the initial concentrated solution is selectively adsorbed by biomass hybrid core-pDES photopolymerization imprinting magnetic particles prepared by waste tea residue, and then eluted by tartaric acid eluent and ethanol-tartaric acid-acetic acid compound eluent, and finally purified by nanofiltration membrane, finally, it is dried by nitrogen protection spray drying, and then supercritical CO2 is removed, and the finished product is obtained by flash evaporation under reduced pressure.The application solves the difficulties of solvent residue, heat-sensitive components easy to oxidize and caffeine removal in traditional process, and the obtained tea polyphenol is high in purity, without solvent residue, and the process is green, suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of tea extract technology, and in particular to a highly efficient method for extracting high-purity tea polyphenols with no residual solvent. Background Technology

[0002] Tea polyphenols are a general term for polyphenolic substances in tea, mainly composed of catechins (especially EGCG), flavonoids, anthocyanins, and phenolic acids. Due to their strong antioxidant, free radical scavenging, anti-tumor, and lipid-lowering physiological activities, they have been widely used in functional foods, pharmaceuticals, daily cosmetics, and fine chemicals. With the increasing demands for raw material quality from downstream markets, developing a tea polyphenol preparation process that achieves high extraction rates, high product purity, and no harmful solvent residues has become a research hotspot in the field of natural product processing.

[0003] Currently, the mainstream technology for industrial production of tea polyphenols still relies on traditional organic solvent extraction methods, typically using volatile organic solvents such as methanol, ethanol, acetone, and ethyl acetate as extraction media. However, this method has many inherent drawbacks: on the one hand, organic solvents are generally flammable, explosive, and highly toxic, and during extraction and subsequent evaporation and recovery processes, they are prone to leaving trace residues in the final product, making it difficult to meet the stringent safety standards of the modern food and pharmaceutical industries; on the other hand, the high-temperature, long-duration reflux extraction process easily leads to the oxidative degradation or isomerization of heat-sensitive catechin components, resulting in reduced product yield and impaired bioactivity.

[0004] In recent years, while physical field enhancement technologies such as ultrasound-assisted and microwave-assisted extraction have improved mass transfer efficiency, they still remain within the framework of organic solvent use. Diethyl eutectic solvents (DES) have been introduced as novel green solvents for tea polyphenol extraction. Choline chloride-carboxylic acid DES have shown good solubility for polyphenols, but they still face two major bottlenecks: First, the high viscosity of the DES system leads to high mass transfer resistance, and DES is difficult to completely separate from the aqueous product after extraction, easily forming new types of solvent residues. Second, existing DES-water systems lack simple phase separation and recovery methods, creating a contradiction between DES recycling and the goal of "zero residual solvent" in the product. Furthermore, tea polyphenol extracts often contain structurally similar caffeine. Traditional de-caffeine removal processes such as polyamide resin adsorption or ethyl acetate extraction suffer from high solvent consumption, poor selectivity, and easy polyphenol saponification loss. In the post-processing stage, conventional vacuum thin-film evaporation or spray drying, without inert gas protection, easily triggers oxidative browning of the phenolic hydroxyl groups and EGCG isomerization in tea polyphenols, affecting product color and activity. Trace amounts of residual solvent trapped in the micropores of the dry powder are also difficult to completely remove through conventional drying.

[0005] Therefore, in response to the problems of high solvent residue risk, difficulty in phase-breaking recovery of DES system, insufficient selectivity of caffeine removal, easy damage to thermosensitive activity and difficulty in deep removal of residual solvent in the final product in existing tea polyphenol extraction technologies, it is urgent to construct a new whole-chain process from source DES medium design, extraction mass transfer enhancement, selective adsorption de-caffeine removal to final inert protection drying and supercritical residual solvent removal, so as to achieve efficient, green and high-purity preparation of tea polyphenols. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and propose a highly efficient extraction method for high-purity tea polyphenols with no residual solvent.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a highly efficient extraction method for high-purity tea polyphenols with no residual solvent, comprising the following steps:

[0009] S1. Preparation of extraction medium: Weigh choline chloride and lactic acid, place them in a reaction vessel, heat to 60-80℃, stir at 300-500 rpm for 1.0-1.5h to form a homogeneous, transparent eutectic solvent, which is called DES. Add ultrapure water to the DES stock solution for dilution, and control the volume fraction of DES in the system to be 35-40%. Adjust the pH of the solution to 5.0±0.2 with citric acid to obtain the extraction medium. Store it in a dark, sealed container for later use.

[0010] S2. DES Extraction: Take green tea raw material, crush it and pass it through a 20-40 mesh sieve. Add the sieved tea powder to the extraction medium prepared in step S1 at a mass-volume ratio of 1g:30-35mL. Start the ultrasonic-microwave synergistic extraction device, set the ultrasonic power to 200-400W and the microwave power to 100-200W, and use the pulse working mode. Extract for 20-40 minutes under constant temperature conditions of 55-60℃. After extraction, filter while hot, collect the filtrate, add fresh extraction medium under the same conditions to the filter residue, and repeat the above extraction process once. Combine the two filtrates.

[0011] S3.DES phase breakage recovery and initial concentration: Add 1-2 times the volume of ultrapure water to the filtrate after combining the steps of S2 for dilution. Pass the diluted solution through an ultrafiltration membrane with a molecular weight cutoff of 8-10 kDa. The ultrafiltration permeate is distilled under reduced pressure to recover choline chloride and lactic acid, which can be recycled for S1. The retentate is the initial concentrate.

[0012] S4. Adsorption and Elution: Adjust the pH of the initial concentrated solution from step S3 to 4.5-5.0 with HCl or dilute NaOH. Add the biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles at a solid-liquid ratio of 1ml:20-30mg. Adsorb at 25-30℃ and 100-150rpm in the dark for 30-40min. After adsorption, place the particles on a 0.5-0.6T permanent magnet wall for 30-60s. Decant and discard the supernatant. Add ultrapure water for light suspension and rinsing. Magnetic separation and discard the washing liquid. Repeat 1-2 times. Then perform stepwise elution. First, use tartaric acid acidic elution buffer, add it over 0.8-1.2h, and collect the eluent. Then switch to ethanol-tartaric acid-acetic acid composite elution buffer, add it over 1.5-2h, and collect the eluent. This yields the crude tea polyphenol solution.

[0013] S5. pH-sensitive nanofiltration final purification: The crude tea polyphenol solution obtained in S4 is distilled under reduced pressure at a temperature of 55-70℃ for 30-90 min. The residue is redissolved with 3-5 times the volume of ultrapure water, and the pH is adjusted to 5.5-6.0 using NaOH solution. Then, it is pumped into a nanofiltration system. A nanofiltration membrane with a molecular weight cutoff of 200-300 Da is selected, and separation is carried out at a pressure of 1.5-2.5 MPa and a temperature ≤35℃. The retentate phase is collected.

[0014] S6. Supercritical CO2 Residue Removal and Spray Drying: Take the retentate obtained in step S5 and spray dry it under nitrogen protection to obtain a crude product. Put the crude product into a supercritical CO2 reactor for treatment and then perform depressurized flash removal. After the process is completed, pass it through an 80-100 mesh sieve to obtain a high-purity tea polyphenol product with no residual solvent.

[0015] Preferably, the molar ratio of choline chloride to lactic acid in S1 is 1:2-3.

[0016] Preferably, in the pulse working mode of S2, the working time is 30-40 seconds with an interval of 10-15 seconds.

[0017] Preferably, the ratio of ultrapure water to biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles in S4 is 10-15 ml: 1 g.

[0018] Preferably, the tartaric acid eluent in S4 is a 0.8-1.2wt% L-tartaric acid aqueous solution, and the ratio of its amount to the amount of biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles is 10-15ml:1g.

[0019] Preferably, the ethanol-tartaric acid-acetic acid composite eluent in S4 consists of 70-80% ethanol by volume, 0.4-0.6% L-tartaric acid by mass, 5-10% acetic acid by mass, and the remainder is deionized water. The ratio of its volume to the volume of biomass hybrid nucleus-pDES-based photopolymerized imprinted magnetic particles is 15-20 ml: 1 g.

[0020] Preferably, in step S6, the spray drying process involves a feed flow rate of 300-500 mL / h, an inlet air temperature of 120-130℃, an outlet air temperature of 45-50℃, and a residence time of 10-30 s.

[0021] Preferably, the supercritical CO2 reactor in S6 has a CO2 flow rate of 20-30 kg / h, a pressure of 15-20 MPa, a temperature of 40-50°C, and uses edible ethanol, accounting for 2-3 wt% of the CO2, as an entrainer for 1.5-2.5 h.

[0022] Preferably, the decompression flashover in S6 is performed at a pressure of 0.01-0.03 MPa, a temperature of 35-45°C, and a time of 10-15 min.

[0023] Preferably, the method for preparing the biomass hybrid core-pDES-based photopolymerization imprinted magnetic particles in S4 includes the following steps:

[0024] A1. Preparation of porous biochar powder: Collect waste tea residue after green tea extraction, wash with deionized water until colorless, dry with forced air at 50-60℃ to constant weight, place in a tube furnace, heat to 400-450℃ at 4-6℃ / min under nitrogen protection, carbonize for 2-3h, cool and soak in 0.1M hydrochloric acid for 2-3h, filter, wash the filter cake again with fresh 0.1M hydrochloric acid 1-2 times, then wash with deionized water until the pH of the washing liquid is neutral, vacuum dry at 60-80℃ for 4-6h, grind through a 300-mesh sieve to obtain porous biochar powder;

[0025] A2. Magnetic Coating and Silanization Modification: The porous biochar powder obtained in step A1 was dispersed in deionized water at a ratio of 1g:20-40mL, transferred to a three-necked flask, and ferric chloride hexahydrate and ferrous chloride tetrahydrate were added sequentially. High-purity nitrogen gas was bubbled through the flask to remove oxygen for 30-40 minutes. The temperature was raised to 60-65℃, and 28% ammonia was added dropwise to adjust the pH of the system to 9.0-9.5. The mixture was stirred at 300-500 rpm for 30-40 minutes to co-precipitate. After the reaction was complete, a magnetic field was applied for separation, and the supernatant was discarded. The resulting precipitate was the Fe3O4@C intermediate. This intermediate was then re-separated... Disperse the mixture in an ethanol-water mixture at a ratio of 1g:30-40mL, wherein the volume ratio of ethanol to water in the ethanol-water mixture is 4:1. Then add 28% ammonia, γ-aminopropyltriethoxysilane and γ-(methacryloyloxy)propyltrimethoxysilane, and stir the mixture in a constant temperature water bath at 50-60℃ for 300-500rpm for 4-5h. After the reaction is completed, magnetically separate the mixture and wash it alternately with deionized water and anhydrous ethanol until the filtrate is neutral. Dry the filtrate under vacuum at 40-50℃ for 2-3h to obtain the vinyl hybrid magnetic core (denoted as Fe3O4@C@SiO2-Vinyl).

[0026] A3. Weak acid loading of EGCG template: The vinylized hybrid magnetic cores obtained in step A2 were dispersed in citrate-disodium hydrogen phosphate buffer at pH 4.5-5.0 at a ratio of 1g:50-80mL. Then, EGCG template molecules equivalent to 0.8-1.0wt% of the magnetic core mass were added. The mixture was shaken in a constant temperature shaker at 30-40℃ and 150-250rpm in the dark for 1.0-1.5h. After the shaker was incubated, an external magnetic field was applied to magnetically separate the mixture until the supernatant was clear. The supernatant was discarded, and the same volume of fresh citrate-disodium hydrogen phosphate buffer at pH 4.5-5.0 was added. The mixture was gently rinsed once, and the washings were magnetically separated and discarded. The product was collected to obtain the template-loaded hybrid magnetic core (denoted as Fe3O4@C@SiO2-Vinyl@EGCG).

[0027] A4. In-situ photopolymerization imprinting of polymerizable pDES: Weigh choline chloride and methacrylic acid, place them in a reaction flask, heat to 60-80℃, stir at 300-500rpm for 1.0-1.5h to form a homogeneous and transparent polymerizable eutectic solvent, denoted as pDES. Take the template-supported hybrid magnetic core obtained in step A3 and disperse it in N,N-dimethylformamide. Add the above pDES, ethylene glycol dimethacrylate and photoinitiator in sequence. Bubble high-purity nitrogen gas to remove oxygen for 15-25min under ice bath conditions. Move the reaction flask to a 365nm ultraviolet lamp with the lamp source 4-6cm vertically from the liquid surface and the power 30-40W. Irradiate to initiate polymerization for 15-20min, maintaining the system at a low stirring speed of 200-300rpm during the process. After polymerization is complete, magnetically separate and collect the solid product, which is the biomass hybrid core-DES-mediated photopolymerization imprinted magnetic particle.

[0028] A5. Template Elution and Post-treatment: After polymerization in step A4, the product is transferred to a Soxhlet extractor. First, an ethanol-tartaric acid composite eluent is used for ultrasonic-assisted elution at 70-80℃ for 30-40 min. Then, the eluent is switched to ammonia-methanol, with an ammonia concentration of 0.06-0.08 mol / L and an ammonia-to-methanol volume ratio of 1:3.0-3.5. The product is then soaked and washed at 35-45℃ for 8-10 min. These two elution programs are alternated 3-4 times. Finally, the product is washed 1-2 times with an acetone-water solution at a volume ratio of 4:1. It is then vacuum dried at 40-50℃ for 4-6 h and pulverized through a 200-mesh sieve to obtain biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles (denoted as Bio-MIP).

[0029] Preferably, the mass ratio of ferric chloride hexahydrate to ferrous chloride tetrahydrate in A2 is 2.6-2.8:1, and the total amount of both is 0.8-1.2 times the mass of the porous biochar powder.

[0030] Preferably, in A2, the volume ratio of 28% ammonia, γ-aminopropyltriethoxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane used for the second time is 0.8-1.2:1.0:0.5-0.6.

[0031] Preferably, the ratio of the total amount of γ-aminopropyltriethoxysilane and γ-(methacryloyloxy)propyltrimethoxysilane in A2 to the amount of Fe3O4@C intermediate is 1.5-2.0 ml: 1 g.

[0032] Preferably, the EGCG template molecule in A3 is epigallocatechin gallate with an HPLC purity of ≥98%.

[0033] Preferably, the molar ratio of choline chloride to methacrylic acid in A4 is 1:2-3.

[0034] Preferably, the ratio of template-loaded hybrid magnetic core to N,N-dimethylformamide in A4 is 1g:20-30ml.

[0035] Preferably, the amount of pDES in A4 is 20-30 wt% of the mass of the template hybrid magnetic core.

[0036] Preferably, the mass ratio of ethylene glycol dimethacrylate to pDES in A4 is 1.4-1.6:1.

[0037] Preferably, the photoinitiator in A4 is Irgacure 2959, and its amount is 0.5-0.8 wt% of the total mass of pDES and ethylene glycol dimethacrylate.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] 1. This invention constructs a green and safe process route from the source of extraction to the drying of the final product. In the extraction stage, a eutectic solvent prepared with choline chloride-lactic acid system is used as the extraction medium. This solvent has the characteristics of being non-toxic and biodegradable, which fundamentally avoids the use of traditional organic solvents (such as methanol, acetone, ethyl acetate, etc.) and the risk of residues in the product. In the post-processing stage, supercritical CO2 treatment technology is further combined to deeply remove any trace entrainers (such as edible ethanol), ultimately ensuring that the finished tea polyphenol product meets the high safety standard of "no residual solvent".

[0040] 2. This invention achieves efficient extraction and preservation of bioactivity of tea polyphenols through the synergistic effect of multiple technologies. First, the DES extraction medium can effectively disrupt plant cell walls and promote the dissolution of polyphenols. Second, the ultrasonic-microwave synergistic extraction utilizes the cavitation effect of ultrasound and the rapid penetrating heating of microwaves to significantly shorten the extraction time and improve the extraction rate. At the same time, the entire extraction and subsequent nanofiltration process are carried out under mild conditions, effectively avoiding the oxidative degradation or isomerization of heat-sensitive catechins (especially EGCG) caused by high temperatures, thereby maximizing the preservation of the product's bioactivity.

[0041] 3. This invention employs biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles (Bio-MIP) for selective adsorption. Using EGCG as a template, this molecularly imprinted material exhibits high specificity for target catechin components, effectively separating tea polyphenols from structurally similar impurities such as caffeine. Combined with a step-elution strategy (first tartaric acid eluent, then ethanol-tartaric acid-acetic acid composite eluent), highly selective enrichment of the target product is achieved. Furthermore, the magnetic material can be rapidly separated using an external permanent magnet, making the operation simple and easily scalable. Detailed Embodiments

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0043] Preparation Example 1: A method for preparing biomass hybrid core-pDES-based photopolymerization imprinted magnetic particles, comprising the following steps:

[0044] A1. Preparation of porous biochar powder: Waste tea residue after green tea extraction was collected, washed with deionized water until colorless, and dried at 55℃ to constant weight. 30g of dried tea residue was placed in a tube furnace and carbonized for 2.5h at 5℃ / min under nitrogen protection. After cooling, it was soaked in 0.1M hydrochloric acid for 2.5h, filtered, and the filter cake was washed twice with fresh 0.1M hydrochloric acid. Then it was washed with deionized water until the pH of the washing liquid was neutral. It was vacuum dried at 70℃ for 5h and ground through a 300-mesh sieve to obtain porous biochar powder.

[0045] A2. Magnetic Coating and Silanization Modification: 5g of porous biochar powder prepared in step A1 was dispersed in 150mL of deionized water and transferred to a three-necked flask. 3.65g of ferric chloride hexahydrate and 1.35g of ferrous chloride tetrahydrate were added sequentially. The mixture was bubbled with high-purity nitrogen for 35min to remove oxygen, heated to 62℃, and 28% ammonia was added dropwise to adjust the pH to 9.2. The mixture was then stirred at 400rpm for 35min to co-precipitate. Separation was performed using an external magnetic field, and the supernatant was discarded to obtain the Fe3O4@C intermediate. 6g of this intermediate was taken... The Fe3O4@C intermediate was redispersed in 210 mL of an ethanol-water mixture (ethanol to water volume ratio 4:1). Then, 6.97 mL of 28% ammonia, 6.97 mL of γ-aminopropyltriethoxysilane, and 3.83 mL of γ-(methacryloyloxy)propyltrimethoxysilane were added sequentially. The mixture was stirred at 400 rpm for 4.5 h in a 55 °C water bath. After the reaction, magnetic separation was performed, and the mixture was washed alternately with deionized water and anhydrous ethanol until neutral. The mixture was then vacuum dried at 45 °C for 2.5 h to obtain the vinyl-modified hybrid magnetic core (Fe3O4@C@SiO2-Vinyl).

[0046] A3. Weak acid loading of EGCG template: Take 6g of the vinyl-modified hybrid magnetic core prepared in step A2, disperse it in 390mL of citrate-disodium hydrogen phosphate buffer (pH 4.8), add 0.054g of EGCG template molecules, and shake in a constant temperature shaker at 35℃ and 200rpm for 1.2h in the dark. After the shaking is completed, apply an external magnetic field for magnetic separation, discard the supernatant, add the same volume of fresh buffer, gently suspend and wash once, magnetically separate and discard the washing solution, collect the product, and obtain the template-loaded hybrid magnetic core (Fe3O4@C@SiO2-Vinyl@EGCG).

[0047] A4. In-situ photopolymerization imprinting of polymerizable DES: Weigh 0.59g of choline chloride and 0.91g of methacrylic acid, place them in a reaction flask, heat to 70℃, and stir at 400rpm for 1.2h to form a homogeneous and transparent polymerizable eutectic solvent (pDES). Take 6g of the template-supported hybrid magnetic core prepared in step A3, disperse it in 150mL of N,N-dimethylformamide, and add 1.5g of the above pDES, 2.25g of ethylene glycol dimethacrylate, and 0.0224g of photoinitiator Irgacure 2959 in sequence. Under ice bath conditions, bubble high-purity nitrogen gas to remove oxygen for 20min. Move the reaction flask to a 365nm ultraviolet lamp with the lamp source 5cm vertically from the liquid surface and a power of 35W. Irradiate to initiate polymerization for 18min, maintaining low-speed stirring at 250rpm during the process. After polymerization is complete, magnetic separation is used to collect the solid product.

[0048] A5. Template Elution and Post-treatment: The polymerization product was transferred to a Soxhlet extractor. First, an ethanol-tartaric acid composite eluent, consisting of 75% (v / v) edible ethanol aqueous solution and 0.5 wt% L-tartaric acid, was used for ultrasonic-assisted elution at 75°C for 35 min. Then, an ammonia-methanol eluent was used, with an ammonia concentration of 0.07 mol / L and an ammonia-to-methanol volume ratio of 1:3.2. The product was soaked and washed at 40°C for 9 min. The two elution programs were alternated three times. Finally, an acetone aqueous solution (acetone-to-water volume ratio of 4:1) was used for washing twice. The product was then vacuum dried at 45°C for 5 h and pulverized through a 200-mesh sieve to obtain biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles (Bio-MIP).

[0049] Preparation Example 2: A method for preparing biomass hybrid core-pDES-based photopolymerization imprinted magnetic particles, comprising the following steps:

[0050] A1. Preparation of porous biochar powder: Waste tea residue after green tea extraction was collected, washed with deionized water until colorless, and dried at 55℃ to constant weight. 30g of dried tea residue was placed in a tube furnace and carbonized for 2h at 4℃ / min under nitrogen protection. After cooling, it was soaked in 0.1M hydrochloric acid for 2h, filtered, and the filter cake was washed once with fresh 0.1M hydrochloric acid. Then it was washed with deionized water until the pH of the washing liquid was neutral. It was vacuum dried at 60℃ for 6h and ground through a 300-mesh sieve to obtain porous biochar powder.

[0051] A2. Magnetic Coating and Silanization Modification: 5g of porous biochar powder prepared in step A1 was dispersed in 100mL of deionized water and transferred to a three-necked flask. 2.89g of ferric chloride hexahydrate and 1.11g of ferrous chloride tetrahydrate were added sequentially. High-purity nitrogen gas was bubbled through the flask to remove oxygen for 30min. The temperature was raised to 60℃, and 28% ammonia was added dropwise to adjust the pH to 9. The mixture was stirred at 500rpm for 30min to co-precipitate. A magnetic field was applied for separation, and the supernatant was discarded to obtain the Fe3O4@C intermediate. 6g of this intermediate was taken. The Fe3O4@C intermediate was redispersed in 180 mL of an ethanol-water mixture (ethanol to water volume ratio 4:1). Then, 4.8 mL of 28% ammonia, 6 mL of γ-aminopropyltriethoxysilane, and 3 mL of γ-(methacryloyloxy)propyltrimethoxysilane were added sequentially. The mixture was stirred at 500 rpm for 5 h in a 50 °C water bath. After the reaction, magnetic separation was performed. The mixture was washed alternately with deionized water and anhydrous ethanol until neutral, and then vacuum dried at 40 °C for 3 h to obtain the vinyl hybrid magnetic core (Fe3O4@C@SiO2-Vinyl).

[0052] A3. Weak acid loading of EGCG template: Take 6g of the vinyl-modified hybrid magnetic core prepared in step A2, disperse it in 300mL of pH 4.5 citrate-disodium hydrogen phosphate buffer, add 0.048g of EGCG template molecules, and shake in a constant temperature shaker at 30℃ and 150rpm for 1.5h in the dark. After the shaking is completed, apply an external magnetic field for magnetic separation, discard the supernatant, add the same volume of fresh buffer and gently suspend and wash once, discard the washing solution after magnetic separation, and collect the product to obtain the template-loaded hybrid magnetic core (Fe3O4@C@SiO2-Vinyl@EGCG).

[0053] A4. In-situ photopolymerization imprinting of polymerizable DES: Weigh 0.537g of choline chloride and 0.663g of methacrylic acid, place them in a reaction flask, heat to 60℃, and stir at 300rpm for 1.5h to form a homogeneous and transparent polymerizable eutectic solvent (pDES). Take 6g of the template-supported hybrid magnetic core prepared in step A3, disperse it in 120mL of N,N-dimethylformamide, and add 1.2g of the above pDES, 2.88g of ethylene glycol dimethacrylate, and 0.0204g of photoinitiator Irgacure 2959 in sequence. Under ice bath conditions, bubble high-purity nitrogen gas to remove oxygen for 15min. Move the reaction flask to a 365nm ultraviolet lamp with the lamp source 4cm vertically from the liquid surface and a power of 30W. Irradiate to initiate polymerization for 15min, maintaining low-speed stirring at 200rpm during the process. After polymerization is complete, magnetic separation is used to collect the solid product.

[0054] A5. Template Elution and Post-treatment: The polymerization product was transferred to a Soxhlet extractor. First, an ethanol-tartaric acid composite eluent was used, consisting of 70% (v / v) edible ethanol aqueous solution and 0.6 wt% L-tartaric acid. Elution was performed at 70°C with ultrasonic assistance for 30 min. Then, an ammonia-methanol eluent was used, with an ammonia concentration of 0.06 mol / L and a volume ratio of ammonia to methanol of 1:3. The product was soaked and washed at 35°C for 10 min. The two elution programs were alternated three times. Finally, an acetone aqueous solution (acetone to water volume ratio of 4:1) was used for washing once. The product was then vacuum dried at 40°C for 6 h and pulverized through a 200-mesh sieve to obtain biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles (Bio-MIP).

[0055] Preparation Example 3: A method for preparing biomass hybrid core-pDES-based photopolymerization imprinted magnetic particles, comprising the following steps:

[0056] A1. Preparation of porous biochar powder: Waste tea residue after green tea extraction was collected, washed with deionized water until colorless, and dried at 55℃ to constant weight. 30g of dried tea residue was placed in a tube furnace and carbonized for 3h at 6℃ / min under nitrogen protection. After cooling, it was soaked in 0.1M hydrochloric acid for 3h, filtered, and the filter cake was washed twice with fresh 0.1M hydrochloric acid. Then it was washed with deionized water until the pH of the washing liquid was neutral. It was vacuum dried at 80℃ for 4h and ground through a 300-mesh sieve to obtain porous biochar powder.

[0057] A2. Magnetic Coating and Silanization Modification: 5g of porous biochar powder prepared in step A1 was dispersed in 200mL of deionized water and transferred to a three-necked flask. 4.42g of ferric chloride hexahydrate and 1.58g of ferrous chloride tetrahydrate were added sequentially. The mixture was bubbled with high-purity nitrogen for 40min to remove oxygen, heated to 65℃, and 28% ammonia was added dropwise to adjust the pH to 9.5. The mixture was then stirred at 300rpm for 40min to co-precipitate. Separation was performed using an external magnetic field, and the supernatant was discarded to obtain the Fe3O4@C intermediate. 6g of the intermediate was taken... The Fe3O4@C intermediate was redispersed in 240 mL of an ethanol-water mixture (ethanol to water volume ratio 4:1). Then, 9 mL of 28% ammonia, 7.5 mL of γ-aminopropyltriethoxysilane, and 4.5 mL of γ-(methacryloyloxy)propyltrimethoxysilane were added sequentially. The mixture was stirred at 300 rpm for 4 h in a 60 °C water bath. After the reaction, magnetic separation was performed. The mixture was washed alternately with deionized water and anhydrous ethanol until neutral, and then dried under vacuum at 50 °C for 2 h to obtain the vinyl hybrid magnetic core (Fe3O4@C@SiO2-Vinyl).

[0058] A3. Weak acid loading of EGCG template: Take 6g of the vinylized hybrid magnetic core prepared in step A2, disperse it in 480mL of pH 5 citrate-disodium hydrogen phosphate buffer, add 0.06g of EGCG template molecules, and shake in a constant temperature shaker at 40℃ and 250rpm for 1h in the dark. After the shaking is completed, apply an external magnetic field for magnetic separation, discard the supernatant, add the same volume of fresh buffer and gently suspend and wash once, discard the washing solution after magnetic separation, and collect the product to obtain the template-loaded hybrid magnetic core (Fe3O4@C@SiO2-Vinyl@EGCG).

[0059] A4. In-situ photopolymerization imprinting of polymerizable DES: Weigh 0.632 g of choline chloride and 1.168 g of methacrylic acid, place them in a reaction flask, heat to 80 °C, and stir at 500 rpm for 1 h to form a homogeneous and transparent polymerizable eutectic solvent (pDES). Take 6 g of the template-supported hybrid magnetic core prepared in step A3, disperse it in 180 mL of N,N-dimethylformamide, and add 1.8 g of the above pDES, 3.53 g of ethylene glycol dimethacrylate, and 0.0426 g of photoinitiator Irgacure 2959 in sequence. Under ice bath conditions, bubble high-purity nitrogen gas to remove oxygen for 25 min. Move the reaction flask to a 365 nm ultraviolet lamp with the lamp source 6 cm vertically from the liquid surface and a power of 40 W. Irradiate to initiate polymerization for 20 min, maintaining low-speed stirring at 300 rpm during the process. After polymerization is complete, magnetically separate and collect the solid product.

[0060] A5. Template Elution and Post-treatment: The polymerization product was transferred to a Soxhlet extractor. First, an ethanol-tartaric acid composite eluent was used, consisting of 80% (v / v) edible ethanol aqueous solution and 0.4 wt% L-tartaric acid. Elution was performed at 80°C with ultrasonic assistance for 40 min. Then, an ammonia-methanol eluent was used, with an ammonia concentration of 0.08 mol / L and a volume ratio of ammonia to methanol of 1:3.5. The product was soaked and washed at 45°C for 8 min. The two elution programs were alternated and cycled four times. Finally, an acetone aqueous solution (acetone to water volume ratio of 4:1) was used for washing twice. The product was then vacuum dried at 50°C for 4 h and pulverized through a 200-mesh sieve to obtain biomass hybrid nucleus-pDES-based photopolymerized imprinted magnetic particles (Bio-MIP).

[0061] Comparative Preparation Example 1: The difference between Comparative Preparation Example 1 and Preparation Example 1 is that in step A1, the tea residue is not carbonized; instead, commercially available powdered wood-based activated carbon (analytical grade, specific surface area approximately 700-1000 m²) is purchased directly. 2 5g of the prepared porous biochar powder was used instead of the prepared powder, and the remaining steps were the same as in Preparation Example 1.

[0062] Comparative Preparation Example 2: The difference between Comparative Preparation Example 2 and Preparation Example 1 is that in step A2, after obtaining the Fe3O4@C intermediate, γ-aminopropyltriethoxysilane and γ-(methacryloyloxy)propyltrimethoxysilane are not added, nor is the silanization reaction in the ethanol-water system carried out. Instead, the Fe3O4@C intermediate is directly dried and used as a "vinyl hybrid magnetic core" in step A3. The remaining steps are completely consistent with Preparation Example 1.

[0063] Comparative Preparation Example 3: The difference between Comparative Preparation Example 3 and Preparation Example 1 is that: in step A4, the self-made pDES (choline chloride + methacrylic acid) is not added. 6g of the template-supported hybrid magnetic core obtained in step A3 is taken and dispersed in 180mL of acetonitrile. Then, 0.91g of methacrylic acid, 2.25g of ethylene glycol dimethacrylate, and 0.0224g of photoinitiator Irgacure 2959 are added sequentially. The remaining steps are consistent with Preparation Example 3.

[0064] Example 1: A highly efficient extraction method for high-purity tea polyphenols with no residual solvent, comprising the following steps:

[0065] S1. Preparation of extraction medium: Weigh 120g of choline chloride and 194g of lactic acid, place them in a reaction vessel, heat to 70℃, and stir at 350rpm for 1.2h to obtain a homogeneous and transparent DES stock solution. Take 247mL of the DES stock solution, add purified water to 650mL, and adjust the pH to 5±0.2 with 10wt% citric acid aqueous solution to obtain the extraction medium. Store in a light-proof and sealed container.

[0066] S2. DES Extraction: Take 10g of green tea, crush it and pass it through a 30-mesh sieve. Add it to 325mL of the extraction medium prepared in step S1. Start the ultrasonic-microwave synergistic extraction device, set the ultrasonic power to 300W and the microwave power to 150W, and adopt the pulse working mode: work for 35s and pause for 12s. Extract at a constant temperature of 58℃ for 30min. After extraction, filter while hot and collect the filtrate. Add 325mL of fresh extraction medium to the filter residue again and repeat the extraction once. Combine the two filtrates.

[0067] S3.DES phase breakage recovery and initial concentration: Add 1.5 times the volume of ultrapure water to the filtrate after combining the steps of S2 for dilution, and pass the diluted solution through an ultrafiltration membrane with a molecular weight cutoff of 9kDa. The ultrafiltration permeate is distilled under reduced pressure to recover choline chloride and lactic acid, which can be recycled for S1. The retentate is the initial concentrate.

[0068] S4. Adsorption and Elution: Adjust the pH of the initial concentrated solution from step S3 to 4.8, and add biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles (prepared in Preparation Example 1) at a solid-liquid ratio of 25 mg: 1 ml. Adsorb at 28°C and 125 rpm in the dark for 35 min. After adsorption, place the solution on a 0.6T permanent magnet wall for 45 s. Decant and discard the supernatant, add ultrapure water for gentle resuscitation and rinsing (the ratio of ultrapure water to the amount of biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles is 12 ml: 1 g). Magnetic separation and discard the washing solution. Repeat twice. Then perform stepwise elution, first with alcohol... The tartaric acid eluent is a 1 wt% L-tartaric acid aqueous solution. The ratio of its volume to the amount of biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles is 12 ml: 1 g. The addition is completed within 1 hour, and the eluent of this stage is collected. The ethanol-tartaric acid-acetic acid composite eluent is then switched to, consisting of 75% ethanol (volume fraction), 0.5% L-tartaric acid (mass fraction), 8% acetic acid (mass fraction), and the remainder being deionized water. The ratio of its volume to the amount of biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles is 18 ml: 1 g. The addition is completed within 1.8 hours, and the eluent of this stage is collected to obtain the crude tea polyphenol solution.

[0069] S5. pH-sensitive nanofiltration final purification: The crude tea polyphenol solution obtained in S4 was distilled under reduced pressure at a temperature of 65℃ for 60 min. The residue was redissolved with 4 times the volume of ultrapure water. The pH of the solution was adjusted to 5.8 using 0.3 mol / L NaOH solution. The solution was then pumped into a nanofiltration system. A nanofiltration membrane with a molecular weight cutoff of 250 Da was selected. Separation was carried out under a pressure of 2 MPa and a temperature of ≤35℃. The retentate phase was collected.

[0070] S6. Supercritical CO2 Residue Removal and Spray Drying: The retentate obtained in step S5 was spray dried under nitrogen protection at a feed flow rate of 400 mL / h, an inlet air temperature of 125℃, an outlet air temperature of 48℃, and a residence time of 20 s to obtain a crude product. The crude product was then fed into a supercritical CO2 reactor for treatment at a CO2 flow rate of 25 kg / h, a pressure of 18 MPa, and a temperature of 45℃. Edible ethanol, accounting for 2.5 wt% of the CO2 dosage, was used as an entrainer. The treatment lasted for 2 h, followed by depressurized flash removal at a pressure of 0.02 MPa, a temperature of 40℃, and a time of 12 min. After the treatment, the product was passed through a 90-mesh sieve to obtain a high-purity tea polyphenol product with no residual solvent.

[0071] Example 2: A highly efficient extraction method for high-purity tea polyphenols with no residual solvent, comprising the following steps:

[0072] S1. Preparation of extraction medium: Weigh 120g of choline chloride and 158g of lactic acid, place them in a reaction vessel, heat to 60℃, and stir at 400rpm for 1.5h to obtain a homogeneous and transparent DES stock solution. Take 227.5mL of the DES stock solution, add purified water to 600mL, and adjust the pH to 5±0.2 with 10wt% citric acid aqueous solution to obtain the extraction medium. Store in a light-proof and sealed container.

[0073] S2. DES Extraction: Take 10g of green tea, crush it and pass it through a 20-mesh sieve. Add it to 300mL of the extraction medium prepared in step S1. Start the ultrasonic-microwave synergistic extraction device, set the ultrasonic power to 200W and the microwave power to 100W, and adopt the pulse working mode: work for 30s and pause for 10s. Extract at a constant temperature of 55℃ for 40min. After extraction, filter while hot and collect the filtrate. Add 300mL of fresh extraction medium to the filter residue again and repeat the extraction once. Combine the two filtrates.

[0074] S3.DES phase breakage recovery and initial concentration: Add 2 times the volume of ultrapure water to the filtrate after combining the steps of S2 for dilution, and pass the diluted solution through an ultrafiltration membrane with a molecular weight cutoff of 8kDa. The ultrafiltration permeate is distilled under reduced pressure to recover choline chloride and lactic acid, which can be recycled for S1. The retentate is the initial concentrate.

[0075] S4. Adsorption and Elution: Adjust the pH of the initial concentrated solution from step S3 to 4.5, and add biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles (prepared in Preparation Example 2) at a solid-liquid ratio of 20 mg: 1 ml. Adsorb at 25°C and 100 rpm in the dark for 40 min. After adsorption, place the solution on a 0.5T permanent magnet wall for 60 s. Decant and discard the supernatant, add ultrapure water for gentle resuscitation and rinsing (the ratio of ultrapure water to the amount of biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles is 15 ml: 1 g). Magnetic separation and discard the washing solution. Repeat once. Then perform stepwise elution, first washing with tartrate acid. The eluent was a 0.8 wt% L-tartaric acid aqueous solution, with a volume ratio of 15 ml to 1 g of biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles. The addition was completed within 0.8 h, and the eluent from this stage was collected. The ethanol-tartaric acid-acetic acid composite eluent was then switched to a solution consisting of 70% ethanol (volume fraction), 0.6% L-tartaric acid (mass fraction), 10% acetic acid (mass fraction), and the remainder being deionized water. The volume ratio of this solution to the biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles was 20 ml to 1 g, and the addition was completed within 1.5 h. The eluent from this stage was collected, yielding the crude tea polyphenol solution.

[0076] S5. pH-sensitive nanofiltration final purification: The crude tea polyphenol solution obtained in S4 was distilled under reduced pressure at a temperature of 55℃ for 90 min. The residue was redissolved with 3 times the volume of ultrapure water. The pH of the solution was adjusted to 6 using 0.3 mol / L NaOH solution, and then pumped into a nanofiltration system. A nanofiltration membrane with a molecular weight cutoff of 200 Da was selected, and separation was carried out at a pressure of 1.5 MPa and a temperature ≤35℃. The retentate phase was collected.

[0077] S6. Supercritical CO2 Residue Removal and Spray Drying: The retentate obtained in step S5 is spray dried under nitrogen protection at a feed flow rate of 300 mL / h, an inlet air temperature of 130℃, an outlet air temperature of 50℃, and a residence time of 30 s to obtain a crude product. The crude product is then fed into a supercritical CO2 reactor for treatment at a CO2 flow rate of 30 kg / h, a pressure of 20 MPa, and a temperature of 50℃. Edible ethanol, accounting for 3 wt% of the CO2 dosage, is used as an entrainer. The treatment lasts for 1.5 h, followed by depressurized flash removal at a pressure of 0.03 MPa, a temperature of 45℃, and a time of 10 min. After the treatment, the product is passed through an 80-mesh sieve to obtain a high-purity tea polyphenol product with no residual solvent.

[0078] Example 3: A highly efficient extraction method for high-purity tea polyphenols with no residual solvent, comprising the following steps:

[0079] S1. Preparation of extraction medium: Weigh 140g of choline chloride and 270g of lactic acid, place them in a reaction vessel, heat to 80℃, and stir at 500rpm for 1h to obtain a homogeneous and transparent DES stock solution. Take 280mL of the DES stock solution, add purified water to 700mL, and adjust the pH to 5±0.2 with 10wt% citric acid aqueous solution to obtain the extraction medium. Store in a light-proof and sealed container.

[0080] S2. DES Extraction: Take 10g of green tea, crush it and pass it through a 40-mesh sieve. Add it to 350mL of the extraction medium prepared in step S1. Start the ultrasonic-microwave synergistic extraction device, set the ultrasonic power to 400W and the microwave power to 200W, and adopt the pulse working mode: work for 40s and intermittent for 15s. Extract at a constant temperature of 60℃ for 20min. After extraction, filter while hot and collect the filtrate. Add 350mL of fresh extraction medium to the filter residue again and repeat the extraction once. Combine the two filtrates.

[0081] S3.DES phase breakage recovery and initial concentration: Add 1 volume of ultrapure water to the filtrate after combining the steps of S2 for dilution, and pass the diluted solution through an ultrafiltration membrane with a molecular weight cutoff of 10kDa. The ultrafiltration permeate is distilled under reduced pressure to recover choline chloride and lactic acid, which can be recycled for S1. The retentate is the initial concentrate.

[0082] S4. Adsorption and Elution: Adjust the pH of the initial concentrated solution from step S3 to 5, and add biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles (prepared in Preparation Example 3) at a solid-liquid ratio of 30 mg: 1 ml. Adsorb at 30°C and 150 rpm in the dark for 30 min. After adsorption, place the solution on a 0.6T permanent magnet wall for 30 s. Decant and discard the supernatant, add ultrapure water for gentle resuscitation and rinsing (the ratio of ultrapure water to the amount of biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles is 10 ml: 1 g). Magnetic separation and discard the washing solution. Repeat twice. Then perform stepwise elution, first washing with tartrate acid. The eluent was a 1.2 wt% L-tartaric acid aqueous solution, with a volume ratio of 10 ml to 1 g of biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles. The addition was completed within 1.2 h, and the eluent from this stage was collected. The eluent was then switched to an ethanol-tartaric acid-acetic acid composite eluent, consisting of 80% ethanol (volume fraction), 0.4% L-tartaric acid (mass fraction), 5% acetic acid (mass fraction), and the remainder being deionized water. The volume ratio of this eluent to the biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles was 15 ml to 1 g, and the addition was completed within 2 h. The eluent from this stage was collected, yielding the crude tea polyphenol solution.

[0083] S5. pH-sensitive nanofiltration final purification: The crude tea polyphenol solution obtained in S4 was distilled under reduced pressure at 70℃ for 30 min. The residue was redissolved with 5 times the volume of ultrapure water. The pH of the solution was adjusted to 5.5 using 0.3 mol / L NaOH solution. The solution was then pumped into a nanofiltration system. A nanofiltration membrane with a molecular weight cutoff of 300 Da was selected. Separation was carried out at a pressure of 2.5 MPa and a temperature ≤35℃. The retentate phase was collected.

[0084] S6. Supercritical CO2 Residue Removal and Spray Drying: The retentate obtained in step S5 is spray dried under nitrogen protection at a feed flow rate of 500 mL / h, an inlet air temperature of 120℃, an outlet air temperature of 45℃, and a residence time of 10 s to obtain a crude product. The crude product is then fed into a supercritical CO2 reactor for treatment at a CO2 flow rate of 20 kg / h, a pressure of 15 MPa, and a temperature of 40℃. Edible ethanol, accounting for 2 wt% of the CO2 dosage, is used as an entrainer. The treatment lasts for 2.5 h, followed by depressurized flash removal at a pressure of 0.01 MPa, a temperature of 35℃, and a time of 15 min. After the treatment, the product is passed through a 100-mesh sieve to obtain a high-purity tea polyphenol product with no residual solvent.

[0085] Comparative Example 1: Based on Example 1, the difference is that step S4 uses the biomass hybrid core-pDES-based photopolymerization imprinted magnetic particles prepared in Comparative Preparation Example 1, and the rest is the same as in Example 1.

[0086] Comparative Example 2: Based on Example 1, the difference is that step S4 uses the biomass hybrid core-pDES-based photopolymerization imprinted magnetic particles prepared in Comparative Preparation Example 2, and the rest is the same as in Example 1.

[0087] Comparative Example 3: Based on Example 1, the difference is that step S4 uses the biomass hybrid core-pDES-based photopolymerization imprinted magnetic particles prepared in Comparative Preparation Example 3, and the rest is the same as in Example 1.

[0088] Comparative Example 4: Based on Example 1, the difference is that the biomass hybrid core-pDES-based photopolymerization imprinted magnetic particles used in step S4 were replaced with a polyamide resin column. The initial concentrate was loaded onto a 70-mesh polyamide resin column at a flow rate of 1.5 BV / h, with a column bed volume of 500 mL and a diameter-to-height ratio of 1:8. After loading, 2.5 BV of ultrapure water was pumped in at a flow rate of 1.5 BV / h. Then, the elution was switched to tartaric acid: 1 wt% L-tartaric acid aqueous solution, 2 BV, at a flow rate of 1.5 BV / h. Then, the elution was switched to ethanol-tartaric acid composite elution: 75% (v / v) edible ethanol aqueous solution containing 0.5 wt% L-tartaric acid, 3.5 BV, at a flow rate of 1.5 BV / h. The last eluent was collected to obtain the crude tea polyphenol solution. The rest was the same as in Example 1.

[0089] Performance testing:

[0090] The tea polyphenol products obtained in Examples 1-3 and Comparative Examples 1-4 were subjected to the following performance tests. All tests were conducted at a temperature of 25±2℃ and a relative humidity of 50±5%. Each group of experiments was repeated 3 times and the average value was taken.

[0091] 1. Determination of tea polyphenol purity: Referring to GB / T 8313-2018, weigh 0.2 g of tea polyphenol sample dried to constant weight, place it in a 100 mL volumetric flask, dissolve and dilute to the mark with 70% methanol solution, shake well to obtain the sample mother liquor, pipette 1.0 mL of the mother liquor into a 100 mL volumetric flask, add ultrapure water to the mark, shake well, pipette 1.0 mL of the above diluted solution into a 25 mL volumetric flask, add 5.0 mL of Folin-Ciocalteu reagent, shake well, and within 3-8 min, add 4.0 mL of 75 g / L sodium carbonate solution, add ultrapure water to the mark, shake well, and let stand at room temperature in the dark for 60 min. At the same time, use gallic acid as a standard to plot a standard curve, and use a UV-Vis spectrophotometer to measure the absorbance at a wavelength of 765 nm. Calculate the tea polyphenol purity (%) based on the standard curve.

[0092] 2. Determination of tea polyphenol yield: Accurately weigh the dried tea polyphenol product m1 to constant weight, and weigh the raw material dry tea m0 used for extraction. Tea polyphenol yield (%) = m1 / m0 × 100%.

[0093] 3. Determination of caffeine content: Referring to GB / T 8312-2013, high performance liquid chromatography (HPLC) was used for quantitative analysis. The chromatographic column was a C18 reversed-phase column (250 mm × 4.6 mm, 5 μm), the mobile phase was methanol:water = 35:65 (v / v), the flow rate was 1.0 mL / min, the column temperature was 30 ℃, the detection wavelength was 273 nm, and the injection volume was 10 μL. An appropriate amount of sample was weighed, dissolved in methanol by ultrasonication and diluted to volume, filtered through a 0.45 μm organic filter membrane, and injected. The caffeine content (%) in the product was calculated by external standard method based on peak area.

[0094] 4. Determination of Total Organic Solvent Residue: Focus on monitoring potentially residual solvents such as methanol, ethanol, acetone, ethyl acetate, and lactic acid. Weigh 0.5 g of the sample and place it in a headspace vial. Add 2 mL of N,N-dimethylformamide to dissolve it. Seal the vial. Headspace injection conditions: equilibrium temperature 80℃, equilibrium time 30 min, DB-624 capillary column (30 m × 0.32 mm × 1.8 μm), flame ionization detector (FID), and high-purity nitrogen as the carrier gas. Calculate the total residual amount (μg / g) of each solvent in the sample based on the standard curves of each solvent.

[0095] 5. Product color: The L value of the product is measured using a colorimeter. An appropriate amount of sample powder is placed in a measuring dish, compacted and smoothed. Three different points are selected for measurement for each sample, and the average value is taken. The higher the L value, the better the product brightness and the lower the degree of browning.

[0096] Table 1. Performance Test Results

[0097]

[0098] Note: "Not detected" means that the content of each target solvent is below the method detection limit (<5 μg / g).

[0099] Data Analysis:

[0100] Examples 1–3 show that the purity of tea polyphenols is 97.1-97.8%, the yield is 26.9-27.6%, the caffeine residue is controlled at 0.12-0.15%, the total organic solvent residue is undetectable (<5 μg / g), and the product L value reaches 91.9-92.5. This is due to the fact that the biomass hybrid core-pDES-based photopolymerization imprinted magnetic particles used in this invention have a high selective recognition ability for target components, and the step elution strategy can achieve precise separation of tea polyphenols from impurities such as caffeine and pigments.

[0101] In Comparative Example 1, the self-made porous charcoal made from tea residue in step A1 of the preparation of biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles was replaced with commercially available wood-based activated carbon. The resulting product had a tea polyphenol purity of 89.5%, a yield of 20.8%, an increase in caffeine to 0.38%, a residual solubility of 11.2 μg / g, and an L value of 86.3. It can be seen that although commercially available activated carbon has a comparable specific surface area, it lacks the hierarchical pore structure and oxygen-containing groups on the surface unique to carbonized tea residue. Its pre-enrichment of polyphenols and uniformity of magnetic core coating are inferior to those of self-made carbon, and the overall adsorption capacity and selectivity of the imprinted magnetic particles are reduced.

[0102] In Comparative Example 2, the silanization modification of γ-aminopropyltriethoxysilane and γ-(methacryloyloxy)propyltrimethoxysilane was omitted in step A2 of the biomass hybrid core-pDES-based photopolymerization imprinted magnetic particles. The Fe3O4@C intermediate was directly fed into subsequent processes without grafting vinyl groups. The purity of the product tea polyphenols further decreased to 87.2%, the yield was 19.6%, the caffeine content was 0.52%, the residual solubility was 12.6 μg / g, and the L value was 84.7. This indicates that silanization not only provides the vinyl anchor point but also affects the stable construction of the pDES imprinted layer on the magnetic core surface. After the regularity of the imprinted cavity was damaged, the size / functional group matching of EGCG was significantly weakened.

[0103] In Comparative Example 3, in step A4 of the biomass hybrid core-pDES-based photopolymerization imprinted magnetic particle, the polymerizable pDES (choline chloride-methacrylic acid) was replaced with acetonitrile as the polymerization medium. The product had a tea polyphenol purity of 88.1%, a yield of 20.1%, caffeine of 0.44%, a residue of 12.1 μg / g, and an L value of 85.5. pDES itself contains a hydrogen bond donor-acceptor network, which can form a "pre-assembly" with the EGCG template before UV polymerization. Acetonitrile does not have this effect, confirming that pDES-mediated photopolymerization is one of the key innovations of this imprinted magnetic particle.

[0104] Comparative Example 4 replaced the biomass hybrid core-pDES-based photopolymerization imprinted magnetic particle adsorption and elution in step S4 with the traditional polyamide resin column process. The product had a tea polyphenol purity of only 84.7%, a yield of 18.3%, a caffeine content as high as 0.95%, a residual solubility of 38.5 μg / g, an L value of 81.2, and obvious browning. Although polyamide resin has a certain polyphenol adsorption capacity, it has weak selectivity for caffeine and irreversible loss of target components on the column.

[0105] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A highly efficient extraction method for high-purity tea polyphenols with no residual solvent, characterized in that, Includes the following steps: S1. Preparation of extraction medium: Weigh choline chloride and lactic acid, place them in a reaction vessel, heat to 60-80℃, stir at 300-500 rpm for 1.0-1.5h to form a homogeneous, transparent eutectic solvent, which is called DES. Add ultrapure water to the DES stock solution for dilution, and control the volume fraction of DES in the system to be 35-40%. Adjust the pH of the solution to 5.0±0.2 with citric acid to obtain the extraction medium. Store it in a dark, sealed container for later use. S2. DES Extraction: Take green tea raw material, crush it and pass it through a 20-40 mesh sieve. Add the sieved tea powder to the extraction medium prepared in step S1 at a mass-volume ratio of 1g:30-35mL. Start the ultrasonic-microwave synergistic extraction device, set the ultrasonic power to 200-400W and the microwave power to 100-200W, and use the pulse working mode. Extract for 20-40 minutes under constant temperature conditions of 55-60℃. After extraction, filter while hot, collect the filtrate, add fresh extraction medium under the same conditions to the filter residue, and repeat the above extraction process once. Combine the two filtrates. S3.DES phase breakage recovery and initial concentration: Add 1-2 times the volume of ultrapure water to the filtrate after combining the steps of S2 for dilution. Pass the diluted solution through an ultrafiltration membrane with a molecular weight cutoff of 8-10 kDa. The ultrafiltration permeate is distilled under reduced pressure to recover choline chloride and lactic acid, which can be recycled for S1. The retentate is the initial concentrate. S4. Adsorption and Elution: Adjust the pH of the initial concentrated solution from step S3 to 4.5-5.0 with HCl or dilute NaOH. Add the biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles at a solid-liquid ratio of 1ml:20-30mg. Adsorb at 25-30℃ and 100-150rpm in the dark for 30-40min. After adsorption, place the particles on a 0.5-0.6T permanent magnet wall for 30-60s. Decant and discard the supernatant. Add ultrapure water for light suspension and rinsing. Magnetic separation and discard the washing liquid. Repeat 1-2 times. Then perform stepwise elution. First, use tartaric acid acidic elution buffer, add it over 0.8-1.2h, and collect the eluent. Then switch to ethanol-tartaric acid-acetic acid composite elution buffer, add it over 1.5-2h, and collect the eluent. This yields the crude tea polyphenol solution. S5. pH-sensitive nanofiltration final purification: The crude tea polyphenol solution obtained in S4 is distilled under reduced pressure at a temperature of 55-70℃ for 30-90 min. The residue is redissolved with 3-5 times the volume of ultrapure water, and the pH is adjusted to 5.5-6.0 using NaOH solution. Then, it is pumped into a nanofiltration system. A nanofiltration membrane with a molecular weight cutoff of 200-300 Da is selected, and separation is carried out at a pressure of 1.5-2.5 MPa and a temperature ≤35℃. The retentate phase is collected. S6. Supercritical CO2 Residue Removal and Spray Drying: Take the retentate obtained in step S5 and spray dry it under nitrogen protection to obtain a crude product. Put the crude product into a supercritical CO2 reactor for treatment and then perform depressurized flash removal. After the process is completed, pass it through an 80-100 mesh sieve to obtain a high-purity tea polyphenol product with no residual solvent.

2. The efficient extraction method for high-purity tea polyphenols with no residual solvent according to claim 1, characterized in that, The molar ratio of choline chloride to lactic acid in step S1 is 1:2-3.

3. The efficient extraction method for high-purity tea polyphenols with no residual solvent according to claim 1, characterized in that, The pulse working mode described in step S2 is to work for 30-40 seconds with an interval of 10-15 seconds.

4. The efficient extraction method for high-purity tea polyphenols with no residual solvent according to claim 1, characterized in that, The preparation method of biomass hybrid core-pDES-based photopolymerization imprinted magnetic particles in step S4 includes the following steps: A1. Preparation of porous biochar powder: Collect waste tea residue after green tea extraction, wash with deionized water until colorless, dry with forced air at 50-60℃ to constant weight, place in a tube furnace, heat to 400-450℃ at 4-6℃ / min under nitrogen protection, carbonize for 2-3h, cool and soak in 0.1M hydrochloric acid for 2-3h, filter, wash the filter cake again with fresh 0.1M hydrochloric acid 1-2 times, then wash with deionized water until the pH of the washing liquid is neutral, vacuum dry at 60-80℃ for 4-6h, grind through a 300-mesh sieve to obtain porous biochar powder; A2. Magnetic Coating and Silanization Modification: The porous biochar powder obtained in step A1 was dispersed in deionized water at a ratio of 1g:20-40mL, transferred to a three-necked flask, and ferric chloride hexahydrate and ferrous chloride tetrahydrate were added sequentially. High-purity nitrogen gas was bubbled through the flask to remove oxygen for 30-40 minutes. The temperature was raised to 60-65℃, and 28% ammonia was added dropwise to adjust the pH of the system to 9.0-9.

5. The mixture was stirred at 300-500 rpm for 30-40 minutes to co-precipitate. After the reaction was complete, a magnetic field was applied for separation, and the supernatant was discarded. The resulting precipitate was Fe3O4@C. The intermediate was redispersed in an ethanol-water mixture at a ratio of 1 g to 30-40 mL, wherein the volume ratio of ethanol to water in the ethanol-water mixture was 4:

1. Then, 28% ammonia, γ-aminopropyltriethoxysilane and γ-(methacryloyloxy)propyltrimethoxysilane were added, and the mixture was stirred in a constant temperature water bath at 50-60℃ at 300-500 rpm for 4-5 h. After the reaction was completed, the mixture was magnetically separated and washed alternately with deionized water and anhydrous ethanol until the filtrate was neutral. The filtrate was then vacuum dried at 40-50℃ for 2-3 h to obtain the vinyl hybrid magnetic core. A3. Weak acid loading of EGCG template: The vinyl hybrid magnetic cores obtained in step A2 were dispersed in citrate-disodium hydrogen phosphate buffer at pH 4.5-5.0 at a ratio of 1g:50-80mL. Then, EGCG template molecules equivalent to 0.8-1.0wt% of the magnetic core mass were added. The mixture was shaken in a constant temperature shaker at 30-40℃ and 150-250rpm in the dark for 1.0-1.5h. After the shaker was completed, an external magnetic field was applied to magnetically separate the mixture until the supernatant was clear. The supernatant was discarded, and the same volume of fresh citrate-disodium hydrogen phosphate buffer at pH 4.5-5.0 was added. The mixture was gently rinsed once, and the washing solution was discarded after magnetic separation. The product was collected to obtain the template-loaded hybrid magnetic cores. A4. In-situ photopolymerization imprinting of polymerizable pDES: Weigh choline chloride and methacrylic acid, place them in a reaction flask, heat to 60-80℃, stir at 300-500rpm for 1.0-1.5h to form a homogeneous and transparent polymerizable eutectic solvent, denoted as pDES. Take the template-supported hybrid magnetic core obtained in step A3 and disperse it in N,N-dimethylformamide. Add the above pDES, ethylene glycol dimethacrylate and photoinitiator in sequence. Bubble high-purity nitrogen gas to remove oxygen for 15-25min under ice bath conditions. Move the reaction flask to a 365nm ultraviolet lamp with the lamp source 4-6cm vertically from the liquid surface and the power 30-40W. Irradiate to initiate polymerization for 15-20min, maintaining the system at a low stirring speed of 200-300rpm during the process. After polymerization is complete, magnetically separate and collect the solid product, which is the biomass hybrid core-DES-mediated photopolymerization imprinted magnetic particle. A5. Template elution and post-treatment: After polymerization in step A4, the product is transferred to a Soxhlet extractor. First, an ethanol-tartaric acid composite eluent is used for ultrasonic-assisted elution at 70-80℃ for 30-40 min. Then, the eluent is switched to ammonia-methanol, with an ammonia concentration of 0.06-0.08 mol / L and a volume ratio of ammonia to methanol of 1:3.0-3.

5. The product is then soaked and washed at 35-45℃ for 8-10 min. The above two elution programs are alternated and cycled 3-4 times. Finally, the product is washed 1-2 times with an acetone-water solution at a volume ratio of 4:

1. The product is then vacuum dried at 40-50℃ for 4-6 h and pulverized through a 200-mesh sieve to obtain biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles.

5. The efficient extraction method for high-purity tea polyphenols with no residual solvent according to claim 4, characterized in that, In the preparation of the biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles, the mass ratio of ferric chloride hexahydrate to ferrous chloride tetrahydrate in step A2 is 2.6-2.8:1, and the total amount of both is 0.8-1.2 times the mass of the porous biochar powder. In the second use, the volume ratio of 28% ammonia, γ-aminopropyltriethoxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane is 0.8-1.2:1.0:0.5-0.6, and the ratio of the total amount of γ-aminopropyltriethoxysilane and γ-(methacryloyloxy)propyltrimethoxysilane to the amount of Fe3O4@C intermediate is 1.5-2.0 ml:1 g.

6. The efficient extraction method for high-purity tea polyphenols with no residual solvent according to claim 4, characterized in that, In the preparation of the biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles, the EGCG template molecule in step A3 is epigallocatechin gallate with an HPLC purity ≥98%.

7. The efficient extraction method for high-purity tea polyphenols with no residual solvent according to claim 4, characterized in that, In the preparation of the biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles, the molar ratio of choline chloride to methacrylic acid in step A4 is 1:2-3; the ratio of the template-supported hybrid magnetic core to N,N-dimethylformamide is 1g:20-30ml; the amount of pDES is 20-30wt% of the mass of the template-supported hybrid magnetic core; the mass ratio of ethylene glycol dimethacrylate to pDES is 1.4-1.6:1; the photoinitiator is Irgacure 2959, and its amount is 0.5-0.8wt% of the total mass of pDES and ethylene glycol dimethacrylate.

8. The efficient extraction method for high-purity tea polyphenols with no residual solvent according to claim 1, characterized in that, In step S4, the ratio of ultrapure water to biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles is 10-15 ml: 1 g; the tartaric acid eluent is a 0.8-1.2 wt% L-tartaric acid aqueous solution, and its volume to the biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles is 10-15 ml: 1 g; the ethanol-tartaric acid-acetic acid composite eluent consists of 70-80% ethanol (volume fraction), 0.4-0.6% L-tartaric acid (mass fraction), 5-10% acetic acid (mass fraction), and the remainder is deionized water, and its volume to the biomass hybrid core-pDES-based photopolymerized imprinted magnetic particles is 15-20 ml: 1 g.

9. The efficient extraction method for high-purity tea polyphenols with no residual solvent according to claim 1, characterized in that, In step S6, the spray drying process involves a feed flow rate of 300-500 mL / h, an inlet air temperature of 120-130℃, an outlet air temperature of 45-50℃, and a residence time of 10-30 s. The supercritical CO2 reactor treatment involves a CO2 flow rate of 20-30 kg / h, a pressure of 15-20 MPa, a temperature of 40-50℃, and the use of edible ethanol (2-3 wt% of CO2) as an entrainer for 1.5-2.5 h. The depressurization flashover process involves a pressure of 0.01-0.03 MPa, a temperature of 35-45℃, and a time of 10-15 min.

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