Method for effectively improving water solubility of tea polyphenol

Abstract

The invention discloses a method for effectively improving water solubility of tea polyphenol, which comprises the following steps: crushing a tea leaf raw material, and carrying out ultrasonic low-temperature cold extraction to obtain a tea polyphenol extracting solution; centrifugally separating the extracting solution at low temperature, and collecting supernate; performing counter-current extraction on the supernate through a back extraction device to remove caffeine so as to obtain an intermediate product; performing ultrasonic-assisted freeze concentration on the intermediate product, performing programmed cooling, forming ice crystals with specific particle sizes in the presence of a specific food-grade nucleating agent, and separating the ice crystals to obtain a tea polyphenol concentrated solution; and finally, drying the concentrated solution to obtain the cold-soluble tea polyphenol powder. According to the method, through ultrasonic cold extraction, serial reverse extraction and freeze concentration, the technical problems that traditional tea polyphenol is poor in cold water solubility and prone to muddy after cooling are effectively solved, the dissolution time of the prepared product in cold water of 10 DEG C is shorter than 30 seconds, the solution is clear and transparent, and the applicability of the tea polyphenol in low-temperature application scenes such as cold drinks is improved.

Description

Technical Field

[0001] This invention relates to the field of tea polyphenol processing technology, and more specifically to a method for effectively improving the water solubility of tea polyphenols. Background Technology

[0002] Tea polyphenols, as important natural active ingredients in tea, have broad application prospects in health foods, beverages, and daily chemical products due to their excellent antioxidant and antibacterial activities. However, tea polyphenols prepared by traditional methods have poor solubility in low-temperature aqueous solutions and are prone to "cold-induced turbidity," which seriously affects their application in low-temperature scenarios such as cold drinks and ready-to-eat products. This technical bottleneck not only limits the expansion of the application range of tea polyphenols but also fails to meet the growing demand of the modern consumer market for natural, convenient, and functional ingredients.

[0003] Cold-soluble tea polyphenols, as an alternative to traditional tea polyphenols, can rapidly dissolve in liquids at low temperatures of 4-10℃ while maintaining a clear and transparent state, thus preserving the natural biological activity of tea polyphenols. This characteristic allows them to be directly applied to product systems such as cold drinks, ice cream, and dairy products, greatly expanding the application scope of tea polyphenols in the food industry. However, achieving both good cold solubility and high activity retention rates presents numerous technical challenges.

[0004] Current technologies still have significant limitations in improving the water solubility of tea polyphenols. Conventional physical or chemical modification methods often fail to simultaneously achieve both solubility and retention of active ingredients, easily leading to the degradation of core functional substances in tea polyphenols, such as catechins, and loss of product flavor. At the same time, key impurities affecting solubility and taste, such as caffeine, are difficult to remove effectively. These problems collectively restrict the development and industrialization of high-quality cold-soluble tea polyphenol products.

[0005] With consumers increasingly demanding healthy, natural, and convenient products, the market demand for high-quality tea polyphenol products with good cold solubility continues to rise. This is particularly evident in the ready-to-drink tea beverage, functional frozen drink, and sports nutrition sectors, where there is an urgent need for tea polyphenol raw materials that can be directly added to low-temperature systems.

[0006] Therefore, the industry urgently needs to develop a new method for preparing tea polyphenols that can effectively balance low-temperature solubility, activity retention, and flavor stability to meet the demand of downstream applications for high-performance tea polyphenol raw materials. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art, improve the water solubility of tea polyphenols at low temperatures, increase the clarity of tea polyphenols after dissolution, and reduce or avoid the phenomenon of "turbidity after cooling".

[0008] To achieve the above objectives, the technical solution provided by the present invention is as follows.

[0009] A method for effectively improving the water solubility of tea polyphenols includes the following steps: S001. After crushing the tea raw material, mix it with the extraction solvent at a temperature below 35°C and apply ultrasonic extraction to obtain tea polyphenol extract. S002. Centrifuge the tea polyphenol extract at a temperature of 1~10℃ to remove insoluble impurities and collect the tea polyphenol supernatant. S003. Transfer the supernatant of tea polyphenols to at least two stages of back-extraction device connected in series, and perform countercurrent extraction with water as the back-extraction solvent to remove caffeine and obtain intermediate product. S004. Place the intermediate product in a freeze concentration apparatus, mix it with distilled water, cool it to -5~-3℃ and maintain it, then sonicate it for 30~180 minutes to form ice crystals in the intermediate product, then separate the ice crystals and collect the tea polyphenol concentrate. S005. Dry the concentrated tea polyphenol solution to obtain cold-soluble tea polyphenol powder.

[0010] As a preferred technical solution, in step S001, the frequency of the ultrasound is 20-50kHz, the extraction time is 30-120 minutes, and the extraction solvent is water, ethanol with a volume fraction of 30%-70%, and ethyl acetate solution with a volume fraction of 50%-100%.

[0011] As a preferred technical solution, in step S002, a high-speed centrifuge is used for centrifugal separation, with the speed of the high-speed centrifuge controlled at 5000-15000 rpm and the centrifugation time controlled at 15-60 min.

[0012] As a preferred technical solution, in step S003, the number of stages of the back-extraction device is 2-4, and the back-extraction temperature is 5-30℃.

[0013] As a preferred technical solution, in step S004, after placing the intermediate product in a freeze concentration device, a food-grade nucleating agent accounting for 0.01%-0.5% of the total mass of the intermediate product is added to it, and after mixing, cooling and ultrasonic treatment are performed; the frequency of the ultrasonic treatment is 25-40kHz, and the ice crystals are separated by centrifugation or pressure filtration.

[0014] As a preferred technical solution, in step S004, the particle size distribution D90 of the ice crystals formed by the intermediate product is 10-50 μm.

[0015] As a preferred technical solution, in step S004, the ultrasonic treatment is applied intermittently. The working mode is as follows: working at a power density of 50-150 W / L for 10-30 seconds, then stopping for 30-90 seconds. This is one cycle, and this cycle is repeated until the treatment is completed.

[0016] As a preferred technical solution, in step S004, the cooling process first cools the room temperature to 0-2℃ at a rate of 0.5-1.5℃ / min and holds it for 10-20 minutes; then it slowly cools the room temperature to the target temperature of -5 to -3℃ at a rate of 0.2-0.5℃ / min.

[0017] As a preferred technical solution, the food-grade nucleating agent is at least one of microcrystalline cellulose, gellan gum, and sodium alginate.

[0018] As a preferred technical solution, in step S005, the drying is spray drying, with an inlet air temperature of 160-210℃ and an outlet air temperature of 60-100℃.

[0019] The advantages and beneficial effects of this invention are as follows: This invention employs ultrasonic low-temperature cold extraction technology, achieving efficient extraction of tea polyphenols at temperatures below 35°C. Utilizing the cavitation, mechanical, and thermal effects of ultrasound, the cell structure of tea leaves is disrupted, while avoiding the oxidative degradation of tea polyphenols and loss of aroma components caused by high-temperature extraction. Secondly, by employing tandem back-extraction and freeze concentration, the difference in partition coefficients between tea polyphenols and caffeine between the two phases is utilized to achieve efficient caffeine removal. Ultrasonic-assisted freeze concentration, by controlling ice crystal growth kinetics and in conjunction with nucleating agents and cooling treatment, forms ice crystals with uniform particle size distribution, eliminating hydrophilic impurities and improving the cold solubility and solution clarity of the final product. This invention balances product yield and quality stability; the resulting cold-soluble tea polyphenol product can completely dissolve in 10°C cold water within 30 seconds, with a solution transmittance of over 95%, while maintaining nutrient loss of less than 12%. Attached Figure Description

[0020] Figure 1 This is a flowchart of the method for improving the water solubility of tea polyphenols according to the present invention. Detailed Implementation

[0021] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not the entire structure. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0022] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0023] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly or implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0024] Please see Figure 1 This invention provides a method for improving the water solubility of tea polyphenols. Without damaging the natural structure and bioactivity of tea polyphenols, it systematically solves the problems of poor solubility and easy turbidity after cooling in traditional tea polyphenols at low temperatures. The method mainly includes the following steps: ultrasonic low-temperature cold extraction, low-temperature centrifugation, multi-stage tandem back-extraction for caffeine removal, ultrasonic-assisted freeze concentration, and final drying and shaping.

[0025] Step S001 involves pulverizing the tea leaves and passing them through a 20-40 mesh sieve to increase the contact area with the extraction solvent. Subsequently, the pulverized tea leaves and the extraction solvent are mixed at a low temperature below 35°C. Traditional hot extraction processes are typically carried out at temperatures above 60°C. While this results in a faster extraction rate, it leads to the oxidative degradation of heat-sensitive components in tea polyphenols (such as catechins, especially EGCG) and a significant loss of volatile aroma components in the tea. This invention deliberately controls the temperature below 35°C to avoid heat damage.

[0026] When ultrasound propagates in a liquid medium, it generates cavitation, where tiny bubbles rapidly form, grow, and violently collapse, producing localized high temperatures, high pressures, and intense shock waves. This extreme physical environment effectively disrupts the cell wall structure of tea leaves, allowing for a faster and more complete release of active ingredients such as tea polyphenols into the solvent. Simultaneously, the mechanical vibrations and microjets of ultrasound enhance the mass transfer process, achieving rates comparable to or exceeding those of traditional thermal extraction, even at low temperatures. More importantly, the effects of ultrasound are instantaneous and localized, without causing a significant increase in the overall temperature of the system.

[0027] This invention preferably uses water, an ethanol solution with a volume fraction of 30%-70%, or an ethyl acetate solution with a volume fraction of 50%-100%. Water, as the safest and most economical solvent, has good solubility for tea polyphenols; ethanol solutions, especially around 50% ethanol, have high extraction efficiency due to their polarity being similar to that of many tea polyphenol components, and also possess a certain bactericidal effect; ethyl acetate has good selective solubility for catechins, which is beneficial for subsequent purification. The choice of solvent needs to be weighed based on the specific specifications of the target product and cost.

[0028] Step S002: After extraction, the obtained tea polyphenol extract is rapidly transferred to a temperature-controlled centrifuge and centrifuged at a low temperature of 1-10°C. The purpose of this step is to remove insoluble impurities that precipitate due to decreased solubility at low temperatures, such as proteins, starches, pectins, some large-molecule tannins, and some fat-soluble pigments. Many impurities soluble at room temperature (such as certain proteins and polysaccharides) show a significant decrease in solubility as the temperature decreases. At a low temperature of 1-10°C, these impurities will fully coagulate and precipitate, forming larger particles, thus allowing for more thorough removal during subsequent centrifugation. If the temperature is too high (e.g., room temperature), these impurities cannot precipitate effectively and will remain in the supernatant, becoming a potential factor affecting the cold solubility and clarity of the final product.

[0029] This invention employs a high-speed centrifuge, with the rotation speed controlled between 5000 and 15000 rpm and the centrifugation time controlled between 15 and 60 minutes. Too low a rotation speed or too short a time will prevent the effective sedimentation of fine, insoluble particles, affecting the separation effect; too high a rotation speed or too long a time, while improving the separation degree, will increase energy consumption and equipment wear, and may also cause some of the already formed flocs to be re-dispersed. Centrifugation can be performed continuously or in batches using a tubular centrifuge or a disc centrifuge. After separation, the supernatant (i.e., the tea polyphenol supernatant) is carefully collected. The sediment at the bottom mainly consists of insoluble impurities, which can be discarded or repeatedly extracted after concentration. Considering efficiency, secondary extraction is usually not performed.

[0030] Step S003: The obtained tea polyphenol supernatant is pumped into at least two stages of countercurrent extraction apparatus, using pure water as the extraction solvent, and countercurrent extraction is performed at a temperature of 5-30°C to selectively remove caffeine. The difference in partition coefficients (K values) between tea polyphenols (mainly catechins and flavonoids) and caffeine between the oil and water phases is considered. Under specific pH and temperature conditions, caffeine has a relatively higher affinity in the aqueous phase compared to most catechins. When the organic phase (or aqueous loaded phase) containing caffeine and tea polyphenols is fully contacted with the fresh aqueous phase in the countercurrent extraction tower, caffeine preferentially partitions and transfers to the aqueous phase, while tea polyphenols are mainly retained in the original phase.

[0031] It is worth noting that after step S003, in order to facilitate concentration, preferably, the tea polyphenols can be transferred to distilled water by back extraction at this time, and then concentrated into an aqueous solution of tea polyphenols.

[0032] Experiments have shown that single-stage extraction often fails to achieve the desired caffeine removal rate, while multi-stage countercurrent extraction can simulate the concept of a theoretical plate, maximizing the mass transfer driving force. The optimal number of extraction stages is 2-4. Too few stages result in incomplete caffeine removal; too many stages increase equipment investment and operational complexity, and may lead to a slight loss of tea polyphenols. The operating temperature should be controlled between 5-30℃. This temperature range ensures sufficient mass transfer rate while preventing oxidation of tea polyphenols due to excessive heat. This step effectively reduces the caffeine content in the product, weakening the ability of caffeine to form cold-complexed complexes with tea polyphenols and proteins.

[0033] Step S004: The decaffeinated intermediate product (mainly an aqueous solution of tea polyphenols) is mixed with an appropriate amount of distilled water and placed in a freeze-concentration apparatus. First, a programmed temperature-controlled cooling process is executed: the temperature is lowered from room temperature to 0-2°C at a rate of 0.5-1.5°C / min, and held near this freezing point for 10-20 minutes. This pre-cooling and holding stage is to ensure uniform heat distribution in the system and prepare for uniform nucleation of ice crystals. Subsequently, the temperature is lowered to the target final temperature of ~5-~3°C at a slower rate. This slow, stepwise cooling promotes the formation of numerous small ice crystals of uniform size, avoiding the formation of large dendritic ice crystals with excessive impurities due to excessively rapid cooling.

[0034] Before cooling, 0.01% to 0.5% of a food-grade nucleating agent, such as microcrystalline cellulose, gellan gum, or sodium alginate, can be added to the system. These nucleating agents provide a large number of heterogeneous nucleation sites, reducing the supercooling required for ice crystal nucleation and inducing ice crystals to form more uniformly at higher temperatures. This avoids sudden explosive crystallization due to excessive supercooling, thus ensuring the uniformity and controllability of ice crystal formation.

[0035] Throughout the freeze-concentration process, ultrasound at a frequency of 25–40 kHz is applied in an intermittent operating mode (e.g., operating for 10–30 seconds, then stopping for 30–90 seconds). The cavitation effect and microfluidic action of ultrasound can break up the initial ice crystals, preventing them from growing too large. At the ice crystal growth front, solutes (tea polyphenols and impurities) are expelled, forming a boundary layer with a high concentration. Ultrasound can effectively disperse this boundary layer, preventing tea polyphenol molecules from being encapsulated by the continuously growing ice crystals (i.e., reducing encapsulation loss). More importantly, the energy input of ultrasound helps hydrophilic impurities with stronger interactions with water molecules and higher freezing points (such as some polysaccharides, inorganic salts, and certain hydrophilic colloids) to be fixed within the ice crystal framework or at the interface during ice crystal growth, i.e., eutectic freezing occurs.

[0036] During slow freezing, the system tends to reach solid-liquid equilibrium. Ideally, pure water will preferentially freeze into ice crystals. Due to their polyphenolic hydroxyl structure, tea polyphenol molecules have strong hydrogen bonding with water molecules, but their molecular structure and size make them more likely to remain in the liquid phase. Hydrophilic impurities that form stronger hydrogen bond networks or hydration with water molecules have freezing points closer to pure water, and are therefore more easily incorporated into the solid phase during ice crystal growth. By controlling the ice crystal growth kinetics, we actively guide these impurities affecting cold solubility into the ice crystal phase, while allowing the target product, tea polyphenols, to accumulate in the remaining unfrozen liquid phase.

[0037] When a solution is cooled to its freezing point, water molecules preferentially condense into ice crystals, while solute molecules are excluded from the ice lattice and accumulate in the remaining unfrozen liquid. In actual freezing processes, the growth rate, morphology, and purity of ice crystals require careful control of mass and heat transfer processes. If ice crystals grow too quickly, the expelled tea polyphenols and impurity molecules will not have enough time to diffuse away from the growth interface and will be encased or carried away by the advancing ice front, leading to the loss of the target product and a decrease in purification efficiency.

[0038] After processing for 30–180 minutes, a large number of impurity-rich ice crystals with a particle size distribution D90 (over 90% of the total mass) of 10–50 μm are formed in the system. Subsequently, these ice crystals are completely separated from the concentrated tea polyphenol-rich liquid at low temperature by centrifugation or pressure filtration. Centrifugation can be performed using a high-speed refrigerated centrifuge; pressure filtration can be performed using a plate and frame filter press with a cooling jacket, using filter cloth with a pore size matching the ice crystal particle size, and at a pressure of 0.1–0.5 MPa to expel the concentrated liquid entrained by the ice crystals, further improving the recovery rate. The separated ice crystals are discarded as waste, and the collected tea polyphenol concentrate is then used in the next process.

[0039] Step S005 involves drying the aforementioned high-purity, high-concentration tea polyphenol concentrate to obtain a free-flowing, cold-soluble tea polyphenol powder. Spray drying is the preferred drying method. The inlet air temperature is controlled between 160 and 210°C. This temperature range is sufficient to allow the moisture on the droplet surface to evaporate slowly. The outlet air temperature is strictly controlled between 60 and 100°C. The outlet air temperature is a more direct indicator of the actual heat history of the product. Controlling it within this relatively low range ensures that the tea polyphenol particles will not suffer excessive loss of active ingredients or flavor deterioration due to overheating immediately after leaving the drying process and in subsequent processes.

[0040] The following examples provide a clearer and more complete description of the invention. Cold water dissolution time: Following the solubility determination method in GB / T21733-2008 Tea Beverages, accurately weigh (1.00 ± 0.01) g of tea polyphenol powder sample and place it in a 200 mL beaker. Add (100 ± 0.5) mL of purified water at (10 ± 0.5) °C. Immediately turn on the magnetic stirrer and stir at a fixed speed of 300 rpm. Using a stopwatch, the time required from the addition of the sample until no visible particles are visible in the solution and no sediment is found at the bottom of the beaker is the cold water dissolution time. Solution transmittance: Take the tea polyphenol solution prepared in the above solubility test, let it stand for 5 minutes, and then pour it into a quartz cuvette with a 1 cm optical path. Using a UV-Vis spectrophotometer, with purified water at the same temperature (10 °C) as a reference, measure its transmittance at a wavelength of 660 nm. The nutrient loss rate is mainly calculated by comparing the core active ingredients (represented by total catechins) of the final product with those of the initial tea raw materials or intermediate products. Referring to GB / T 8313-2018 "Determination Method of Tea Polyphenols and Catechins in Tea", high performance liquid chromatography (HPLC) was used to determine the total catechins in a known mass of initial tea raw materials (after extraction with the same solvent as in pretreatment step S001).

[0041] [Example 1] A method for effectively improving the water solubility of tea polyphenols includes the following steps: S001. After crushing the tea raw material, mix it with the extraction solvent water at a temperature of 25°C, and apply ultrasonic extraction at a frequency of 20kHz for 30 minutes to obtain tea polyphenol extract.

[0042] S002. The tea polyphenol extract is centrifuged at 5000 rpm for 15 minutes at 1°C to remove insoluble impurities and the supernatant of tea polyphenols is collected.

[0043] S003. The supernatant of tea polyphenols is transferred to a two-stage back-extraction device connected in series. Water is used as the back-extraction solvent for countercurrent extraction at 5°C to remove caffeine and obtain an intermediate product.

[0044] S004. Place the intermediate product in a freeze concentration apparatus, mix with distilled water, and add 0.01% (by mass) of food-grade nucleating agent microcrystalline cellulose. After mixing, perform programmed temperature control cooling: first, cool from room temperature to 0℃ at a rate of 0.5℃ / min and hold for 10 minutes; then, slowly cool from 0℃ to the target temperature of -5℃ at a rate of 0.2℃ / min and maintain this temperature. During the cooling process, apply intermittent ultrasonic treatment at a frequency of 25kHz for 30 minutes. The ultrasonic working mode is: operate at a power density of 50W / L for 10 seconds, then stop for 30 seconds; this constitutes one cycle. Repeat the cycle until the treatment is completed. This causes the intermediate product to form ice crystals with a particle size distribution D90 of 10μm. Then, separate the ice crystals by centrifugation and collect the concentrated tea polyphenol solution.

[0045] S005. The concentrated tea polyphenol solution is dried by spray drying, with the inlet air temperature at 170℃ and the outlet air temperature controlled at 80℃, to obtain cold-soluble tea polyphenol powder.

[0046] The product obtained in this embodiment has the following properties: dissolution time in cold water at 10°C is 28 seconds, the solution transmittance is 96%, and the nutrient loss rate is 10%.

[0047] [Example 2] A method for effectively improving the water solubility of tea polyphenols includes the following steps: S001. After crushing the tea raw material, mix it with an ethanol solution with a volume fraction of 30% at 30°C and apply ultrasonic extraction at a frequency of 30kHz for 60 minutes to obtain tea polyphenol extract.

[0048] S002. The tea polyphenol extract is centrifuged at 8000 rpm for 30 minutes at 5°C to remove insoluble impurities and the supernatant of tea polyphenols is collected.

[0049] S003. The supernatant of tea polyphenols is transferred to a three-stage back-extraction device in series. Water is used as the back-extraction solvent for countercurrent extraction at 15°C to remove caffeine and obtain an intermediate product.

[0050] S004. Place the intermediate product in a freeze concentration apparatus, mix with distilled water, and add 0.1% (by mass) of food-grade nucleating agent gellan gum. After mixing, perform programmed temperature control cooling: first, cool from room temperature to 1°C at a rate of 1.0°C / min and hold for 15 minutes; then, slowly cool from 1°C to the target temperature of -4°C at a rate of 0.3°C / min and maintain this temperature. During the cooling process, apply intermittent ultrasonic treatment at a frequency of 30kHz for 90 minutes. The ultrasonic working mode is: operate at a power density of 100W / L for 20 seconds, then stop for 60 seconds, which constitutes one cycle. Repeat the cycle until the treatment is completed. This causes the intermediate product to form ice crystals with a particle size distribution D90 of 25μm. Then, separate the ice crystals by pressure filtration and collect the concentrated tea polyphenol solution.

[0051] S005. The concentrated tea polyphenol solution is dried by spray drying, with the inlet air temperature at 180℃ and the outlet air temperature controlled at 85℃, to obtain cold-soluble tea polyphenol powder.

[0052] The product obtained in this embodiment has the following properties: dissolution time in cold water at 10°C is 25 seconds, the solution transmittance is 97%, and the nutrient loss rate is 8%.

[0053] [Example 3] A method for effectively improving the water solubility of tea polyphenols includes the following steps: S001. After crushing the tea raw material, mix it with an ethanol solution with a volume fraction of 50% at 32°C and apply ultrasonic extraction at a frequency of 40kHz for 90 minutes to obtain tea polyphenol extract.

[0054] S002. The tea polyphenol extract is centrifuged at 12,000 rpm for 45 minutes at 8°C to remove insoluble impurities and the supernatant of tea polyphenols is collected.

[0055] S003. The supernatant of tea polyphenols is transferred to a four-stage back-extraction device in series. Water is used as the back-extraction solvent for countercurrent extraction at 25°C to remove caffeine and obtain the intermediate product.

[0056] S004. Place the intermediate product in a freeze concentration apparatus, mix with distilled water, and add 0.3% (by mass) of food-grade sodium alginate (a nucleating agent) to the mixture. After mixing, perform programmed temperature control cooling: first, cool from room temperature to 2°C at a rate of 1.2°C / min and hold for 18 minutes; then, slowly cool from 2°C to the target temperature of -3°C at a rate of 0.4°C / min and maintain this temperature. During the cooling process, apply intermittent ultrasonic treatment at a frequency of 35kHz for 150 minutes. The ultrasonic working mode is: operate at a power density of 120W / L for 25 seconds, then stop for 80 seconds; this constitutes one cycle. Repeat the cycle until the treatment is completed. This causes the intermediate product to form ice crystals with a particle size distribution D90 of 40μm. Then, separate the ice crystals by centrifugation and collect the concentrated tea polyphenol solution.

[0057] S005. The concentrated tea polyphenol solution is dried by spray drying, with the inlet air temperature at 160℃ and the outlet air temperature controlled at 100℃, to obtain cold-soluble tea polyphenol powder.

[0058] The product obtained in this embodiment has the following properties: dissolution time in cold water at 10°C is 22 seconds, the solution transmittance is 98%, and the nutrient loss rate is 7%.

[0059] [Example 4] A method for effectively improving the water solubility of tea polyphenols includes the following steps: S001. After crushing the tea raw material, mix it with an ethanol solution with a volume fraction of 70% at 28°C and apply ultrasonic extraction at a frequency of 50kHz for 120 minutes to obtain tea polyphenol extract.

[0060] S002. The tea polyphenol extract is centrifuged at 15,000 rpm for 60 minutes at 10°C to remove insoluble impurities and the supernatant of tea polyphenols is collected.

[0061] S003. The supernatant of tea polyphenols is transferred to a two-stage back-extraction device connected in series. Water is used as the back-extraction solvent for countercurrent extraction at 30°C to remove caffeine and obtain an intermediate product.

[0062] S004. The intermediate product is placed in a freeze concentration apparatus and mixed with distilled water. A mixture of food-grade nucleating agent microcrystalline cellulose and gellan gum, accounting for 0.5% of the total mass of the intermediate product, is added and mixed thoroughly. A programmed temperature control cooling process is then executed: first, the temperature is lowered from room temperature to 2°C at a rate of 1.5°C / min and held for 20 minutes; then, the temperature is slowly lowered from 2°C to the target temperature of -3°C at a rate of 0.5°C / min and maintained at this temperature. During the cooling process, intermittent ultrasonic treatment at a frequency of 40kHz is applied for 180 minutes. The ultrasonic working mode is: operating at a power density of 150W / L for 30 seconds, followed by a 90-second pause; this constitutes one cycle, which is repeated until the treatment is completed. This causes ice crystals to form in the intermediate product, with a particle size distribution D90 of 50μm. The ice crystals are then separated by pressure filtration, and the concentrated tea polyphenol solution is collected.

[0063] S005. The concentrated tea polyphenol solution is dried by spray drying, with the inlet air temperature at 180℃ and the outlet air temperature controlled at 95℃, to obtain cold-soluble tea polyphenol powder.

[0064] The product obtained in this embodiment has the following properties: dissolution time in cold water at 10°C is 20 seconds, the solution transmittance is 99%, and the nutrient loss rate is 6%.

[0065] [Example 5] A method for effectively improving the water solubility of tea polyphenols includes the following steps: S001. After crushing the tea raw material, mix it with an ethyl acetate solution with a volume fraction of 100% at 22°C and apply ultrasonic extraction at a frequency of 25kHz for 40 minutes to obtain tea polyphenol extract.

[0066] S002. The tea polyphenol extract is centrifuged at 3°C ​​and 6000 rpm for 20 minutes to remove insoluble impurities and collect the tea polyphenol supernatant.

[0067] S003. The supernatant of tea polyphenols is transferred to a three-stage back-extraction device, and countercurrent extraction is performed at 10°C using water as the back-extraction solvent to remove caffeine and obtain an intermediate product.

[0068] S004. Place the intermediate product in a freeze concentration apparatus, mix with distilled water, and add a mixture of food-grade nucleating agent sodium alginate and microcrystalline cellulose at 0.05% of the total mass of the intermediate product. After mixing, perform programmed temperature control cooling: first, cool from room temperature to 0℃ at a rate of 0.8℃ / min and hold for 12 minutes; then, slowly cool from 0℃ to the target temperature of -4℃ at a rate of 0.25℃ / min and maintain this temperature. During the cooling process, apply intermittent ultrasonic treatment at a frequency of 28kHz for 60 minutes. The ultrasonic working mode is: operate at a power density of 80W / L for 15 seconds, then stop for 40 seconds, which constitutes one cycle. Repeat the cycle until the treatment is completed. This causes the intermediate product to form ice crystals with a particle size distribution D90 of 15μm. Then, separate the ice crystals by centrifugation and collect the concentrated tea polyphenol solution.

[0069] S005. The concentrated tea polyphenol solution is dried by spray drying, with the inlet air temperature at 210℃ and the outlet air temperature controlled at 60℃, to obtain cold-soluble tea polyphenol powder.

[0070] The product obtained in this embodiment has the following properties: dissolution time in cold water at 10°C is 26 seconds, the transmittance of the solution is 96.5%, and the nutrient loss rate is 9%.

[0071] [Example 6] A method for effectively improving the water solubility of tea polyphenols includes the following steps: S001. After crushing the tea raw material, mix it with an ethanol solution with a volume fraction of 60% at 35°C and apply ultrasonic extraction at a frequency of 45kHz for 100 minutes to obtain tea polyphenol extract.

[0072] S002. The tea polyphenol extract is centrifuged at 10,000 rpm for 50 minutes at 6°C to remove insoluble impurities and the supernatant of tea polyphenols is collected.

[0073] S003. The supernatant of tea polyphenols is transferred to a four-stage back-extraction device in series. Water is used as the back-extraction solvent for countercurrent extraction at 20°C to remove caffeine and obtain an intermediate product.

[0074] S004. The intermediate product is placed in a freeze concentration apparatus and mixed with distilled water. A mixture of food-grade nucleating agent gellan gum and sodium alginate, accounting for 0.2% of the total mass of the intermediate product, is added and mixed thoroughly. The mixture is then subjected to programmed temperature control: first, it is cooled from room temperature to 1°C at a rate of 1.3°C / min and held at this temperature for 17 minutes; then, it is slowly cooled from 1°C to the target temperature of -5°C at a rate of 0.35°C / min and maintained at this temperature. During the cooling process, intermittent ultrasonic treatment at a frequency of 38kHz is applied for 120 minutes. The ultrasonic working mode is: operating at a power density of 130W / L for 22 seconds, followed by a 70-second pause; this constitutes one cycle, which is repeated until the treatment is completed. This causes ice crystals to form in the intermediate product, with a particle size distribution D90 of 35μm. The ice crystals are then separated by pressure filtration, and the concentrated tea polyphenol solution is collected.

[0075] S005. The concentrated tea polyphenol solution is dried by spray drying, with the inlet air temperature at 175℃ and the outlet air temperature controlled at 60℃, to obtain cold-soluble tea polyphenol powder.

[0076] The product obtained in this embodiment has the following properties: dissolution time in cold water at 10°C is 23 seconds, the transmittance of the solution is 97.5%, and the nutrient loss rate is 7.5%.

[0077] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for effectively improving the water solubility of tea polyphenols, characterized in that, The method comprises the following steps: S001, crushing tea raw materials, mixing with an extraction solvent at a temperature below 35℃, and applying ultrasonic wave extraction to obtain a tea polyphenol extract; S002, centrifugal separation of the tea polyphenol extract at a temperature of 1-10℃ to remove insoluble impurities, and collection of tea polyphenol supernatant; S003, transferring the tea polyphenol supernatant to at least two stages of counter-current extraction devices in series, using water as a counter-current solvent to remove caffeine, and obtaining an intermediate product; S004, placing the intermediate product in a freeze concentration device, mixing with distilled water, cooling to -5~-3℃ and maintaining, and then ultrasonic treatment for 30-180 minutes to form ice crystals in the intermediate product, and then separating the ice crystals and collecting a tea polyphenol concentrate; S005, drying the tea polyphenol concentrate to obtain a cold-soluble tea polyphenol powder.

2. The method of claim 1, wherein, In step S001, the frequency of the ultrasonic wave is 20-50 kHz, and the extraction time is 30-120 minutes; the extraction solvent is water, an ethanol solution with a volume fraction of 30%-70%, or an ethyl acetate solution with a volume fraction of 50%-100%.

3. The method according to claim 1 or 2, characterized in that, In step S002, the centrifugal separation uses a high-speed centrifuge with a rotation speed controlled at 5000-15000 rpm and a centrifugal time controlled at 15-60 min.

4. The method of claim 1, wherein, In step S003, the counter-current extraction device has 2-4 stages, and the counter-current extraction temperature is 5-30℃.

5. The method of claim 1, wherein, In step S004, after the intermediate product is placed in the freeze concentration device, 0.01%-0.5% of a food-grade nucleating agent based on the total mass of the intermediate product is added thereto, mixed uniformly, and then cooled and ultrasonic treated; the ultrasonic treatment has a frequency of 25-40 kHz, and the ice crystals are separated by centrifugal separation or pressure filtration separation.

6. The method of claim 5, wherein, In step S004, the ice crystals formed from the intermediate product have a particle size distribution D90 of 10-50 μm.

7. The method of claim 5, wherein, In step S004, the ultrasonic treatment is intermittently applied, and the working mode is as follows: working at a power density of 50-150 W / L for 10-30 seconds, and then stopping for 30-90 seconds, which is one cycle, and the cycle is repeated until the treatment is completed.

8. The method of claim 5, wherein, In step S004, the cooling treatment uses a program-controlled temperature mode: first, cooling from room temperature to 0-2℃ at a rate of 0.5-1.5℃ / min, and maintaining for 10-20 minutes; and then slowly cooling from 0-2℃ to the target temperature of -5~-3℃ at a rate of 0.2-0.5℃ / min.

9. The method of claim 5, wherein, The food-grade nucleating agent is at least one of microcrystalline cellulose, gellan gum, and sodium alginate.

10. The method of claim 1, wherein, In step S005, the drying is spray drying, and the inlet air temperature is 160-210℃, and the outlet air temperature is controlled at 60-100℃.

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