Method for preparing a sweet tea beverage

Abstract

The application discloses a preparation method of a sweet tea beverage and belongs to the technical field of plant beverage processing. The method comprises the following steps: mixing sweet tea leaf powder with cellulase and pectinase for enzymolysis extraction, performing solid-liquid separation to obtain a crude extract; after the crude extract is cooled, tannase and naringinase are added for enzymolysis debittering, and enzyme inactivation is performed to obtain an enzymolysis liquid; the pH of the enzymolysis liquid is adjusted to the isoelectric point of sweet tea protein, a protein-polyphenol compound is precipitated and removed by centrifugation to obtain a clarified liquid; the clarified liquid is subjected to cross-flow ultrafiltration, an ultrafiltration membrane with a molecular weight cut-off that can cut off tannase and naringinase and allow sweet tea glycosides to pass through is selected, and a permeate is collected; the permeate is mixed with auxiliary materials, sterilized and filled to obtain the sweet tea beverage. The technical scheme of the application, which comprises the steps of compound enzyme wall-breaking extraction, double-enzyme directional debittering, isoelectric point precipitation and removal of turbidity and cross-flow ultrafiltration separation, solves the problems of heavy bitterness and turbidity and precipitation during storage of the sweet tea beverage, and achieves the effects of fully retaining sweetness, pure taste and long-term clarity and stability.

Description

Technical Field

[0001] This invention relates to the field of plant-based beverage processing technology, and more particularly to a method for preparing sweet tea beverages. Background Technology

[0002] Sweet tea refers to the dried leaves of *Rubus idaeus*, a plant belonging to the genus *Rubus* in the Rosaceae family. It is traditionally used as a natural sweetener and a throat-soothing beverage. Sweet tea leaves contain high-sweetness, low-calorie glycosides, as well as polyphenols, flavonoids, soluble proteins, and other components, giving it a natural advantage in developing sugar-free or low-sugar plant-based beverages. With the increasing consumer demand for healthy drinks, ready-to-drink tea products made from sweet tea are gradually entering the market.

[0003] Currently, the most common practice in producing sweet tea beverages is to directly extract the dried leaves of sweet tea using hot water to obtain an extract containing water-soluble components such as catechins. This extract is then filtered, blended, sterilized, and bottled. While this hot water extraction method is simple, prolonged high-temperature soaking causes a large amount of bitter substances, such as tannins and flavonoids, to dissolve along with the catechins. The resulting extract has a noticeable astringent taste and a bitter aftertaste, making it rough and unpalatable to the average consumer. Simultaneously, soluble proteins in the extract interact with polyphenols under heat, forming soluble or colloidal protein-polyphenol complexes. These complexes gradually aggregate during cooling, refrigeration, or prolonged standing, producing visible flocculent turbidity and even precipitation—a phenomenon known in the tea beverage industry as "cold turbidity," which severely affects the product's appearance and shelf-life stability.

[0004] To reduce the bitterness of sweet tea beverages, some processors employ physical adsorption methods, such as adding activated carbon, diatomaceous earth, or macroporous adsorption resins to the extract for debittering. These adsorbents utilize their porous structure and surface chemistry to non-selectively adsorb some polyphenols and flavonoids, thus reducing bitterness. However, while adsorbing bitter components, materials like activated carbon also adsorb large amounts of glycoside molecules, significantly reducing the sweetness of the extract. This often necessitates the addition of exogenous sweeteners to compensate for the sweetness loss, increasing ingredient costs and deviating the product's intended natural, zero-calorie sweetness. Furthermore, the waste residue generated after adsorption treatment requires solid waste disposal, increasing the environmental burden. Some manufacturers use flavorings or cyclodextrins to mask the bitterness, but this does not eliminate the bitter precursors at the source; the bitterness reappears after prolonged storage, indicating insufficient flavor stability.

[0005] In terms of clarification, the current common method is to place the extract in a low-temperature environment for an extended period of time, allowing the precipitate to settle naturally by gravity, and then collect the supernatant for bottling. This settling period often lasts for several days, resulting in low production efficiency, occupying a large amount of storage tank space, and the sedimentation effect is unstable between different batches of raw materials due to fluctuations in protein and polyphenol content. Centrifugation and diatomaceous earth filtration can accelerate the clarification process to some extent, but these physical separation methods have limited removal capabilities for dissolved protein-polyphenol complex precursors that have not yet aggregated and precipitated. The residual trace precursors will re-aggregate and form visible turbidity under the thermal shock of the sterilization process and in the temperature fluctuations during the shelf life, causing the product, which is qualified at the time of leaving the factory, to become turbid during distribution and storage.

[0006] Therefore, in the field of sweet tea beverage processing, there is a need for a preparation method that can systematically solve the above problems. This method should not only retain the natural sweetness of sweet tea glycosides while removing bitterness, but also remove as much as possible the protein-polyphenol complex precursors that cause turbidity after cooling. The goal is to obtain sweet tea beverages with a pure taste, clear appearance, and long-term shelf life without spoilage through a stable process. Summary of the Invention

[0007] This invention overcomes the problems of strong bitterness and easy turbidity and precipitation in sweet tea drinks during storage. By using compound enzyme cell wall breaking extraction, dual enzyme directional debittering, isoelectric point precipitation to remove turbidity, and cross-flow ultrafiltration separation, it achieves the effect of fully retaining sweetness, pure taste, and long-term clarity and stability.

[0008] To achieve the above objectives, the present invention adopts the following solution: The preparation method of sweet tea beverage includes the following steps: S1: Pulverize sweet tea leaves to obtain sweet tea powder, mix the sweet tea powder with water to form a slurry, add cellulase and pectinase to the slurry, carry out enzymatic extraction at the enzymatic hydrolysis temperature, heat to inactivate the enzyme after extraction, then perform solid-liquid separation, collect the liquid part to obtain crude extract; S2: Cool the crude extract to the temperature at which tanninase and naringinase act, add tanninase and naringinase to carry out enzymatic hydrolysis to degrade bitter substances, and heat to inactivate enzymes after the reaction to obtain enzymatic hydrolysate. S3: Adjust the pH of the enzymatic hydrolysate to the isoelectric point of sweet tea protein using a food-grade acidity regulator, let it stand to allow the protein-polyphenol complex to precipitate, remove the precipitate by centrifugation, and collect the supernatant as the clarified liquid. S4: The clarified liquid is subjected to cross-flow ultrafiltration. The molecular weight cutoff of the ultrafiltration membrane is set to cut off tanninase and naringinase while allowing catechins to pass through. The permeate is collected. S5: Mix the permeate and excipients evenly, sterilize and fill to obtain a sweet tea beverage.

[0009] Preferably, step S1 includes: After the sweet tea leaves are chopped, they are pulverized using a low-temperature ultrafine pulverizer in a nitrogen atmosphere to obtain sweet tea powder with a particle size not exceeding 80 mesh. Mix sweet tea powder and deoxygenated pure water in a mixing tank at a mass ratio of 1:15 to 1:25, turn on the stirrer, and stir continuously at a speed of 200-500 rpm for 10-20 minutes to obtain the slurry; Heat the slurry to 45-55℃, add 1%-3% cellulase and 0.5%-1.5% pectinase relative to the weight of sweet tea powder to the slurry, keep warm at the enzymatic hydrolysis temperature and stir continuously, and the enzymatic extraction time is 60-120 minutes. After enzymatic extraction, the slurry is heated to 85-95℃ and kept at that temperature for 10-15 minutes to inactivate the enzymes. After enzyme inactivation, the slurry is subjected to solid-liquid separation using a plate and frame filter press. The filtrate is collected to obtain the crude extract.

[0010] Preferably, step S2 includes: The crude extract is pumped into an enzymatic hydrolysis tank with a jacket for cooling. The crude extract is cooled to 40-55℃ with continuous stirring. The pH of the crude extract is adjusted to 4.0-5.5 using a food-grade acidity regulator to obtain the enzymatic hydrolysis solution. Add 0.05%-0.3% tanninase and 0.02%-0.2% naringinase relative to the volume of crude extract to the enzymatic hydrolysis solution. Both tanninase and naringinase are added in the form of immobilized enzymes. Incubate and stir for 30-90 minutes for enzymatic hydrolysis. During the enzymatic hydrolysis reaction, the bitterness value in the reaction solution is monitored in real time by an online bitterness sensor. When the bitterness value decreases to less than 50% of the initial bitterness value, the end point of the enzymatic hydrolysis reaction is determined. After the enzymatic hydrolysis reaction is completed, the reaction solution is heated to 85-95℃ and kept at this temperature for 10-15 minutes to inactivate the enzyme. The inactivated immobilized enzyme is then separated from the liquid by filtration, and the filtrate is collected to obtain the enzymatic hydrolysate.

[0011] Preferably, step S3 includes: The enzymatic hydrolysate was transferred to a sedimentation tank equipped with an online pH monitoring and automatic acid addition system. Under continuous stirring, a food-grade acidity regulator was added dropwise to the enzymatic hydrolysate through the automatic acid addition system. The pH value and corresponding turbidity value of the enzymatic hydrolysate were recorded in real time. The pH value corresponding to the peak turbidity value was the isoelectric point of sweet tea protein. Acid addition was stopped and the pH value was locked as the sedimentation endpoint. The protein-polyphenol complex was allowed to stand in a sedimentation tank at the isoelectric point of the sweet tea protein for 1-3 hours to aggregate and form a precipitate. Stirring was stopped during the standing period. After settling, the enzymatic hydrolysate containing the precipitate is sent to a disc centrifuge and centrifuged at 6000-10000 rpm. The precipitate phase is continuously discharged and the liquid phase is collected to obtain the initial clear liquid. The initial filtrate is filtered through a plate and frame filter press with a filter aid to remove residual fine suspended particles. The filtrate is collected, and the supernatant is obtained as the clarified liquid.

[0012] Preferably, in step S3, after the initial clarified liquid is finely filtered through a plate and frame filter press with a filter aid and the filtrate is collected to obtain a clarified liquid, the clarified liquid is further subjected to pH swing treatment, including the following steps: Transfer the clarified liquid to another container equipped with a stirrer. Add a food-grade acidity regulator to the clarified liquid while stirring to adjust the pH of the clarified liquid from the isoelectric point of sweet tea protein to 2.5-3.5. Keep stirring under acidic conditions for 20-40 minutes. Add a food-grade alkalinity regulator to the clarified liquid to adjust the pH of the clarified liquid from acidic back to the isoelectric point of sweet tea protein, and let it stand again for 30-60 minutes under the isoelectric point condition; After the second settling period, the clarified liquid containing the secondary precipitate was centrifuged a second time using a disc centrifuge at a speed of 6000-10000 rpm. The supernatant was collected as the final clarified liquid and subjected to cross-flow ultrafiltration.

[0013] Preferably, step S4 includes: The clarified liquid is fed into a cross-flow ultrafiltration membrane module via a feed pump. The ultrafiltration membrane of the cross-flow ultrafiltration membrane module has a molecular weight cutoff of 5kDa-20kDa, an operating temperature of 10-30℃, and a transmembrane pressure of 0.1-0.5MPa. Circulation filtration is carried out under the condition of a cross-flow velocity of 2-5m / s. Tanninase and naringinase in the clarified liquid are retained on the membrane concentration side, while catechins in the clarified liquid are allowed to pass through the ultrafiltration membrane with the solvent and enter the membrane permeation side. Continuously replenish the membrane concentration side of the cross-flow ultrafiltration membrane module with cleaning pure water at the same rate as the permeate discharge, and perform equal-volume washing filtration to elute the residual catechins in the membrane concentration side to the membrane permeate side until the catechin concentration on the membrane permeate side drops to the level of the catechin concentration in the replenished cleaning pure water, and then stop washing filtration. Collect all the permeate liquid from the membrane permeate side and combine them to obtain the permeate liquid.

[0014] Preferably, in step S4, during the equal-volume filtration process, an alternating rinsing step is also included to reduce fouling on the membrane surface. After running the equal volume filtration for a total of 15-30 minutes, stop adding pure water for cleaning to the membrane concentration side, and at the same time close the permeate discharge valve on the membrane permeate side. Increase the cross-flow velocity from 2-5 m / s to 6-8 m / s and circulate to rinse the membrane surface for 5-10 minutes. After rinsing, restore the crossflow velocity to 2-5 m / s, reopen the permeate discharge valve on the membrane permeate side, and resume replenishing the membrane concentration side with pure water for rinsing, and continue the equal volume filtration process. Alternately perform the above-mentioned speed-up rinsing step and speed-up equal-volume filtration step until the concentration of stevia on the membrane permeate side drops to the level of stevia concentration in the added cleaning pure water. Terminate all operations at this point, and combine all the permeate collected on the membrane permeate side to obtain the permeate.

[0015] Preferably, step S5 includes: The permeate was transferred to a mixing tank, and stirring was started. Microencapsulated sweet tea flavor extract, vitamin C, and sodium bicarbonate were added to the permeate. Stirring was continued until completely dissolved to obtain the mixing solution. The microencapsulated sweet tea flavor extract was prepared by spray drying a mixture of aromatic substances recovered from the sweet tea leaves after solid-liquid separation in step S1 by steam distillation and cyclodextrin. The amount of sodium bicarbonate added was adjusted to adjust the pH of the mixing solution to 6.0-6.5. Preheat the preparation solution to 60-70℃, and put it into a degassing tank for vacuum degassing under a gauge pressure of -0.06MPa to -0.09MPa for 5-15 minutes to obtain a degassed liquid. The degassed liquid is sent into an ultra-high temperature instantaneous sterilizer and sterilized at 135-140℃ for 4-6 seconds. After sterilization, it is immediately cooled to 25-30℃ to obtain the sterilized liquid. The sterilized liquid is filled into containers that have been sterilized by spraying with hydrogen peroxide in a sterile environment, and then sealed with screw caps to produce a sweet tea beverage.

[0016] As a preferred embodiment, the method for preparing the microcapsule-encapsulated sweet tea flavor extract is as follows: The sweet tea leaves retained by the plate and frame filter in step S1 are put into a steam distillation kettle, steam is introduced under normal pressure for distillation, the distillate is collected, the distillate is extracted with food-grade n-hexane, and the organic phase is removed by vacuum distillation to remove the solvent, thus obtaining the sweet tea aromatic substances. Mix β-cyclodextrin and γ-cyclodextrin in a mass ratio of 3:1 to 5:1, add deionized water to prepare a cyclodextrin mixture with a mass concentration of 15%-25%, and stir at 40-50℃ until completely dissolved. While stirring, the sweet tea aromatic substances are slowly added dropwise to the cyclodextrin mixture at an amount of 0.5-1.5 times the total mass of cyclodextrin in the cyclodextrin mixture. After the addition is completed, the mixture is stirred for 1-3 hours under nitrogen protection to encapsulate the inclusion mixture and obtain an inclusion emulsion. The inclusion complex emulsion was spray-dried at an inlet air temperature of 160-190℃ and an outlet air temperature of 70-90℃. The dried powder was collected to obtain the microcapsule-encapsulated sweet tea flavor extract.

[0017] This invention includes at least the following beneficial effects: (1) By using cellulase and pectinase to synergistically break down cell walls, the dissolution efficiency of intracellular substances such as catechins is effectively improved, and the utilization rate of raw materials is significantly improved compared with conventional hot water extraction; by using tanninase and naringinase synergistically to perform targeted enzymatic debittering, selective hydrolysis of ester-type catechins and flavonoids that produce bitterness is achieved, significantly purifying the taste without losing the sweetness of catechins; combined with isoelectric point precipitation and centrifugation to remove protein-polyphenol complexes, and cross-flow ultrafiltration at room temperature to separate enzyme proteins and catechins, the final beverage has both a sweet and pure taste and long-term storage stability without turbidity, and the overall quality is significantly better than traditional physical adsorption debittering and cold precipitation clarification. Processing method; (2) By using low-temperature nitrogen-filled pulverization and deoxygenated pure water to prepare the slurry, the polyphenol oxidase activity was inhibited from the source, and the crude extract was bright in color and had a slight raw green taste; Immobilized tannin enzyme and immobilized naringinase were used, and an online bitterness sensor was introduced during the enzymatic hydrolysis process to monitor the bitterness value in real time to determine the reaction endpoint, so that the degree of debittering can be quantitatively controlled, avoiding insufficient or excessive debittering. At the same time, the immobilized enzyme can be recycled and reused through simple filtration, reducing the subsequent carryover of exogenous enzyme protein and reducing the consumption cost of enzyme preparation; (3) The isoelectric point of sweet tea protein in each batch of material was automatically determined by online turbidity combined with pH, ​​realizing the precise matching of precipitation conditions. Disc centrifugation combined with filter aid and fine filtration made the turbidity before The removal of the substance is more thorough; the molecular weight cutoff of the ultrafiltration membrane is set to cut off tannins and naringin while allowing sweet tea glycosides to pass through. The separation is completed at low temperature, avoiding the flavor deterioration caused by enzyme inactivation at high temperature. The equal volume washing and filtration operation fully recovers the sweet tea glycosides remaining on the membrane concentration side with less pure water. The product sweetness yield is maintained at a high level, and there is no residue of added enzyme protein; (4) The aromatic substances are recovered by steam distillation of the extracted sweet tea leaves. Microcapsules are made by compounding β-cyclodextrin and γ-cyclodextrin and then added back to the blending liquid, realizing the closed-loop recovery and stabilization protection of natural aroma in the processing by-products; with vacuum degassing and ultra-high temperature instantaneous sterilization, the product can still be preserved within a long shelf life. It retains the natural sweet tea aroma and bright color, effectively solving the problem of aroma decay that is difficult to avoid by simply relying on the process to preserve the aroma; (5) By adding pH swing treatment after isoelectric point precipitation, the soluble protein-polyphenol precursors remaining after the first precipitation will aggregate and settle again after acid dissociation, thus removing the secondary turbidity source from the solution. The risk of the final clarified liquid becoming turbid during subsequent ultrafiltration and storage is greatly reduced; In the cross-flow ultrafiltration equal volume washing process, high cross-flow velocity flushing steps are alternately inserted to dynamically remove the scale on the membrane surface using the high shear force of the self-circulating liquid, maintaining stable membrane flux, reducing the frequency of chemical cleaning shutdowns, and ensuring continuous production efficiency and membrane module service life. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the principle of the method of the present invention. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0020] like Figure 1 As shown, the method for preparing a sweet tea beverage provided by the present invention includes the following steps: S1: The sweet tea leaves are pulverized to disrupt their dense structure, significantly increasing the contact area between the solid and liquid phases, resulting in sweet tea powder. The sweet tea powder is then mixed with water in a specific ratio and thoroughly stirred to form a uniform slurry. Cellulase and pectinase are added to the slurry. Cellulase specifically hydrolyzes the long cellulose chains that form the cell wall skeleton, while pectinase degrades the pectin polysaccharides that fill the intercellular spaces. The two enzymes work synergistically to promote the release of intracellular target components such as sweet tea glycosides, polyphenols, and other soluble substances into the aqueous phase. Enzymatic extraction is carried out at a temperature suitable for the activity of cellulase and pectinase, controlled between 40°C and 60°C. This temperature range is maintained with continuous stirring to ensure sufficient contact and reaction between the enzymes and the substrate. After enzymatic extraction, the slurry is heated to 85°C to 95°C and maintained for a period of time. This high temperature denatures and inactivates the cellulase and pectinase proteins, stopping the enzymatic reaction and preventing further action in subsequent processes that could alter the quality of the extract. After enzyme inactivation, the slurry undergoes solid-liquid separation, such as by plate and frame filtration, horizontal spiral centrifugation, or three-legged centrifuge, to separate the liquid portion from the residue after the contents have been released. The collected liquid portion yields a crude extract rich in glycosides.

[0021] S2: The temperature of the crude extract is lowered to the optimal range for tanninase and naringinase to exert their catalytic effects, typically between 40°C and 55°C, through heat exchange or jacket cooling. Tanninase hydrolyzes the ester bonds in gallotannins and ellagitannins, particularly acting on ester-type catechins that cause strong bitterness, degrading them into non-ester-type catechins with weaker astringency. Naringinase breaks the glycosidic bonds in flavonoid glycosides such as naringin, releasing aglycones with weaker bitterness, thus directionally reducing the bitterness of the crude extract. Tanninase and naringinase are added to the cooled crude extract, and the enzymatic hydrolysis reaction is carried out under incubation and stirring conditions. The reaction duration can be adjusted according to the desired degree of debittering. After the enzymatic hydrolysis reaction is completed, the reaction solution is heated again to 85°C to 95°C and incubated to inactivate tanninase and naringinase, yielding the enzymatic hydrolysate. This operation, through specific enzyme modification, significantly reduces unpleasant bitterness without sacrificing the sweetness of the catechins.

[0022] S3: Add a food-grade acidity regulator, such as citric acid, malic acid, phosphoric acid, or other food additives with acid-base regulating properties, to the enzymatic hydrolysate to adjust its pH to the isoelectric point of sweet tea protein. The isoelectric point of sweet tea protein can be determined in a preliminary small-scale test. Under isoelectric point conditions, the number of positive and negative charges on the surface of protein molecules is equal, the net charge approaches zero, the electrostatic repulsion between molecules is minimized, and protein molecules readily bind to polyphenols through hydrophobic interactions and hydrogen bonds, forming large protein-polyphenol complex aggregates. After adjusting the pH, allow sufficient time for the complex to aggregate and settle. Then, use centrifugation, such as a high-speed disc centrifuge, to rapidly separate the precipitate from the liquid phase using the centrifugal force field. Collect the supernatant as the clarified liquid, removing the protein-polyphenol precursor complex, which is prone to secondary turbidity during subsequent storage and low-temperature environments, at the source.

[0023] S4: Cross-flow ultrafiltration is performed on the clarified liquid. The selected ultrafiltration membrane must have a molecular weight cutoff sufficient to retain tanninase and naringinase while allowing the permeation of stevia. The molecular weights of tanninase and naringinase are typically in the tens of kilodaltons, while the molecular weight of stevia is approximately 642 Daltons. Therefore, an ultrafiltration membrane with a molecular weight cutoff of around 5 kDa can be selected. During cross-flow ultrafiltration, the clarified liquid flows tangentially at high speed along the membrane surface, and the resulting shear force continuously washes the membrane surface, mitigating concentration polarization and membrane fouling. Water and small-molecule stevia pass through the membrane pores as the permeate, while large-molecule tanninase, naringinase, and potentially residual trace amounts of protein-polyphenol complexes are retained on the membrane concentration side. This achieves non-thermal separation of the sweet functional components from the added enzymes and proteins, recovering stevia and preventing the introduction of enzymes and proteins into the finished product. The permeate is collected and proceeds to the next process.

[0024] S5: The permeate and excipients are mixed evenly in a mixing tank. Excipients can be antioxidants such as vitamin C or sodium isoascorbate to protect color and flavor, and may also include flavor-enhancing ingredients or pH buffers. The mixed liquid is then sterilized, using methods such as ultra-high temperature instantaneous sterilization or aseptic cold filling combined with microfiltration to ensure the product meets commercial sterility requirements. It is then filled into clean and sterilized containers, sealed, and the sweet tea beverage is obtained.

[0025] This solution addresses the core issues of strong bitterness and poor storage stability in sweet tea beverage production. The compound enzyme cell-wall breaking extraction significantly increases the dissolution rate of effective components in sweet tea, resulting in a marked improvement in raw material utilization. The use of tanninase and naringinase to specifically modify bitterness molecules provides stronger debittering selectivity and minimizes the loss of sweet components compared to traditional physical adsorption or masking methods, resulting in a purer sweet taste. Isoelectric point precipitation and centrifugation remove turbidity precursors, significantly shortening processing time and improving clarification efficiency compared to simple low-temperature settling. Cross-flow ultrafiltration simultaneously removes enzymes and recovers sweet tea glycosides at low temperatures, preventing flavor degradation. This allows the product to maintain a clear color and natural sweetness while achieving excellent cold and heat stability, preventing turbidity and sedimentation during long-term storage. Overall flavor quality and production economics are significantly improved.

[0026] In another technical solution, step S1 includes: In the pulverization stage, the sweet tea leaves are first chopped to reduce the load per processing run, and then pulverized using a low-temperature ultrafine pulverizer in a nitrogen-filled atmosphere. The low-temperature ultrafine pulverizer utilizes mechanical shearing force and high-frequency vibration to refine the material. Its working chamber can be circulated with liquid nitrogen or a low-temperature refrigerant to maintain a low temperature, while nitrogen is continuously introduced into the pulverization chamber to replace air. The low-temperature environment inhibits polyphenol oxidase activity, while the nitrogen atmosphere slows down the enzymatic browning and oxidative deterioration of polyphenols by reducing oxygen partial pressure. Both work synergistically to protect the original color and flavor precursors of the sweet tea leaves. The pulverized tea leaves yield sweet tea powder with a particle size no larger than 80 mesh, and the refined particle size significantly increases the exposed cell wall area. The sweet tea powder is then mixed with deoxygenated pure water at a mass ratio of 1:15 to 1:25 in a mixing tank. The deoxygenated pure water is purified water that has undergone boiling or vacuum degassing treatment, resulting in a low dissolved oxygen content, further inhibiting oxidation reactions in the aqueous phase. Stir continuously at 200 rpm to 500 rpm for 10 to 20 minutes to fully disperse and hydrate the sweet tea powder, forming a uniform and fluid slurry.

[0027] During the enzymatic hydrolysis stage, the slurry is heated to 45°C to 55°C, which is the optimal temperature range for cellulase and pectinase. 50°C is typically preferred. 1% to 3% cellulase and 0.5% to 1.5% pectinase (based on the mass of the sweet tea powder) are added to the slurry. Cellulase hydrolyzes long cellulose chains into oligosaccharide and glucose units through endo- and exo-cleavage, while pectinase disrupts the intercellular adhesive layer by cleaving the pectin polysaccharide backbone and side chains. The simultaneous action of both enzymes dissolves the cell wall from the skeleton to the filler, fully opening the pathways for the release of intracellular soluble substances. Enzymatic extraction is carried out for 60 to 120 minutes under incubation and continuous stirring. After enzymatic hydrolysis, the slurry is heated to 85°C to 95°C and incubated for 10 to 15 minutes. The high temperature causes irreversible denaturation of the protein structures of cellulase and pectinase, achieving complete enzyme inactivation.

[0028] In the separation stage, the enzyme-inactivated slurry is fed into a plate and frame filter press, which consists of alternating filter plates and frames. Under pressure, the slurry passes through the filter cloth, while solid leaf residue is trapped in the filter chamber to form a filter cake. The filtrate is collected and discharged through a flow channel. The collected filtrate yields a crude extract, in which stevia and various soluble components have been fully transferred to the aqueous phase. Low-temperature nitrogen-purified pulverization and deoxygenated pure water preparation effectively inhibit oxidative browning during processing, maintaining the crude extract's bright color and fresh plant flavor. Compound enzyme cell-wall breaking extraction significantly improves the dissolution efficiency of stevia compared to single hot water extraction. The gentle process conditions throughout avoid the burnt taste and nutrient loss caused by prolonged high-temperature cooking.

[0029] In another technical solution, step S2 includes: In the pretreatment stage, the crude extract is pumped into a jacketed hydrolysis tank with cooling. Cooling water or chilled water is circulated through the jacket to exchange heat with the tank walls. Under continuous stirring, the temperature of the crude extract is reduced to 40°C to 55°C. Stirring enhances heat transfer, ensuring uniform temperature throughout the tank and preventing localized overheating or undercooling. Subsequently, a food-grade acidity regulator is used to adjust the pH of the crude extract to 4.0 to 5.5. This pH range is suitable for the subsequent catalytic activity of tanninase and naringinase, and also provides a suitable acid-base environment for the conformational stability of the enzyme proteins, resulting in the hydrolysate.

[0030] During the enzymatic hydrolysis stage, 0.05% to 0.3% of tanninase and 0.02% to 0.2% of naringinase relative to the volume of the crude extract are added to the solution to be hydrolyzed. Both enzymes are added in the form of immobilized enzymes. Immobilized enzymes are formulations in which enzyme proteins are fixed on inert carriers such as calcium alginate gel beads, chitosan microspheres, or porous ceramic particles through covalent bonding, cross-linking, or embedding. After the reaction, the enzymes and reaction solution can be physically separated by simple filtration, and they have the potential for repeated use. Tanninase specifically breaks the ester bonds in gallotannins and ellagitannins, especially acting on ester-type catechins that cause strong astringency and bitterness, causing them to be converted into non-ester-type catechins with significantly reduced astringency after degalloylation. Naringinase hydrolyzes the glycosidic bonds of flavonoid glycosides such as naringin, cleaving the glycosyl ligand and releasing aglycones with higher bitterness threshold concentrations. The two enzymes work together for 30 to 90 minutes under conditions of incubation and continuous stirring. This time range is relatively wide and can be flexibly adjusted to modify and reduce the perceived intensity of bitterness at the molecular level.

[0031] During the endpoint determination and separation stage, the bitterness value in the reaction solution is monitored in real time by an online bitterness sensor during the enzymatic hydrolysis reaction. Based on the principle of an electronic tongue, the online bitterness sensor utilizes an array of taste sensor membranes to generate a potential response to bitter substances, converting the chemical signal into a quantifiable bitterness intensity value. The endpoint of the enzymatic hydrolysis reaction is determined when the monitored bitterness value decays to less than 50% of the initial bitterness value. This threshold is merely a common example and can be adjusted according to the flavor requirements of the target product. After the enzymatic hydrolysis reaction is completed, the reaction solution is heated to 85℃ to 95℃ and held for 10 to 15 minutes to inactivate the enzyme. The high temperature denatures both the residual enzyme protein in the solution and any enzyme protein that may detach from the immobilized enzyme surface. Furthermore, the heating process promotes thermal aggregation between the immobilized enzyme carrier and the denatured free enzyme protein in the reaction solution. The denatured protein molecules cross-link through hydrophobic interactions and disulfide bonds to form larger particles that adsorb onto the carrier surface. The inactivated immobilized enzyme, along with the aggregates, is then separated from the liquid by filtration, and the filtrate is collected as the enzymatic hydrolysate.

[0032] This method utilizes the synergistic effect of immobilized tanninase and naringinase to selectively cleave the molecular structures that produce bitterness. Compared to activated carbon adsorption for debittering, it better preserves the sweet components of stevia, exhibiting strong debittering selectivity and minimal sweetness loss. Real-time monitoring by an online bitterness sensor allows for quantifiable and controllable debittering, avoiding the problems of insufficient or excessive debittering caused by relying on experience. The use of immobilized enzymes simplifies enzyme-product separation, and the enzyme preparation can be recycled and reused, significantly reducing batch-to-batch fluctuations in enzyme dosage and costs.

[0033] In another technical solution, step S3 includes: The enzymatic hydrolysate was transferred to a settling tank equipped with an online pH monitoring and automatic acidification system. The online pH monitoring system consists of a pH composite electrode, transmitter, and controller inserted below the liquid surface. It can collect the acidity / alkalinity signal of the hydrolysate in real time and display it digitally. The automatic acidification system includes a metering pump and an acid storage tank linked to the controller. The controller issues commands based on the deviation between the monitored pH value and the set target, driving the metering pump to add food-grade acidity regulator to the settling tank in a pulsed or continuous manner. Under continuous stirring, the acidity regulator is rapidly and evenly dispersed, and the pH of the hydrolysate gradually changes. Simultaneously, an online turbidimeter is installed in the settling tank. Based on the principle of scattered or transmitted light, it can continuously measure the optical changes caused by suspended particles in the liquid and output turbidity values. When the turbidity value reaches a peak during pH adjustment, it indicates that the protein-polyphenol complex in the solution is aggregating in large quantities, forming a state with the strongest light scattering. At this point, the net charge of the protein molecules approaches zero, and the electrostatic repulsion between molecules is minimal. This peak pH is the isoelectric point of the sweet tea protein in this batch of sweet tea material. The specific isoelectric point value will fluctuate within a certain range due to differences in the origin, harvesting season, and variety of sweet tea leaves, typically falling between pH 3.0 and 4.5. The method described above allows for precise calibration of each batch of material. The system automatically stops adding acid and locks that pH value as the precipitation endpoint upon detecting a turbidity peak.

[0034] The sedimentation tank is then transferred to a settling stage under the locked isoelectric point condition of sweet tea protein, with a settling time of 1 to 3 hours. During settling, stirring is stopped, allowing the liquid to remain still. The aggregated protein-polyphenol complex particles slowly settle under gravity, while Brownian motion promotes continued collisions and flocculation between the particles, resulting in a visible precipitate. The tank is kept undisturbed during sedimentation to prevent further disturbance and dispersion of the sediment layer. The enzymatic hydrolysate containing the precipitate after settling is then fed into a disc centrifuge. The disc centrifuge contains a set of conical discs. The drum rotates at a high speed of 6000 to 10000 rpm, generating a strong centrifugal force field. The liquid enters through the central feed pipe and is distributed between the discs. The precipitate, due to its higher density, moves outward under centrifugal force and slides out along the lower surface of the discs, being discharged continuously or intermittently through the discharge port. The liquid phase moves towards the center and is collected through the overflow port, yielding the initial clarified liquid. A small amount of fine suspended particles that could not be separated by centrifugation may still remain in the initial filtrate. Therefore, the initial filtrate is further filtered by a plate and frame filter press with a filter aid. Diatomaceous earth or perlite can be used as the filter aid. A layer of filter aid is pre-laid on the filter cloth. When the feed liquid passes through the filter cloth and the filter aid layer, the microporous channels inside the filter aid further remove the residual fine particles through interception, adsorption and bridging. The supernatant obtained by collecting the filtrate is the clarified liquid.

[0035] By automatically determining the isoelectric point of sweet tea protein using online turbidity and pH coupling, precipitation conditions are precisely matched to the actual characteristics of each batch of material, eliminating the problem of unstable effects of fixed formulas due to raw material fluctuations. The combination of disc centrifugation and fine filtration aids makes the separation of protein-polyphenol precipitation more thorough, significantly reducing the risk of turbidity recurrence in the resulting clarified liquid during low-temperature storage and shelf life, and greatly improving the clarity of the product appearance.

[0036] In another technical solution, after step S3 has been completed by filtering the initial clarified liquid through a plate and frame filter press lined with filter aid and collecting the filtrate to obtain a clarified liquid, the clarified liquid can be transferred to an independent container equipped with a stirring device instead of immediately undergoing cross-flow ultrafiltration. The stirring is then turned on to ensure uniform liquid flow. A food-grade acidity regulator, such as citric acid, malic acid, or phosphoric acid solution, is added to the clarified liquid to further adjust its pH from the isoelectric point of sweet tea protein (the pH value corresponding to the previously measured turbidity peak) to a strongly acidic range of 2.5 to 3.5. The isoelectric point of sucrose protein is typically between pH 3.0 and 4.5. At this isoelectric point, the protein molecule has zero net charge, and aggregation occurs primarily driven by hydrophobic interactions and hydrogen bonds. However, deviating from the isoelectric point, especially under strongly acidic conditions, the carboxyl groups on the protein molecule surface are protonated, resulting in a positive net charge. This generates electrostatic repulsion between molecules, causing the protein-polyphenol complex precursor that was originally aggregated at the isoelectric point to dissociate, opening the aggregated structure. Simultaneously, the protein peptide chain partially unfolds in the strongly acidic environment, exposing the hydrophobic amino acid residues that were originally embedded within the molecule, significantly increasing the hydrophobic region. Stirring for 20 to 40 minutes under acidic conditions ensures the complete dissociation reaction and structural unfolding.

[0037] After the acidic dissociation step, a food-grade alkalinity adjuster is added to the clarified solution. Sodium bicarbonate solution or food-grade sodium phosphate can be used as the alkalinity adjuster to bring the pH of the clarified solution back from the acidic range to the previously locked isoelectric point of the sweet tea protein. As the pH gradually rises, the net positive charge on the surface of the protein molecules is gradually neutralized, and the electrostatic repulsion gradually weakens until it disappears. When the pH returns to the isoelectric point, the net charge of the protein molecules returns to zero. At this point, unlike the initial isoelectric point precipitation, after strong acid dissociation and structural unfolding treatment, the protein molecules expose more hydrophobic groups, and the conformation of some hydrophobic regions has changed, resulting in a richer number of sites for hydrophobic interactions between molecules. After standing again at the isoelectric point for 30 to 60 minutes, the protein-polyphenol complex precursor, whose structure has partially unfolded and whose hydrophobic regions are more exposed, re-aggregates at the isoelectric point, forming a secondary precipitate that is denser and covers a wider area than the initial precipitate. This process essentially utilizes pH oscillation to incorporate protein-polyphenol complex precursors, originally existing in soluble or metastable forms in the solution, into the precipitation system. This is an operation that deeply removes potential sources of turbidity from the solution environment. After the second settling period, the clarified liquid containing the secondary precipitate is sent to a disc centrifuge for a second centrifugation at 6000 to 10000 rpm, allowing the secondary precipitate to settle rapidly and separate from the liquid phase. The supernatant is collected. After undergoing a complete pH oscillation cycle of initial isoelectric point precipitation, acid hydrolysis and re-aggregation, and a second centrifugation, the residual protein-polyphenol complex precursors have been deeply removed. This supernatant is used as the final clarified liquid to replace the original clarified liquid for cross-flow ultrafiltration. By adding the pH oscillation treatment step, trace amounts of protein-polyphenol complex precursors existing in soluble or metastable forms in the clarified liquid are fully incorporated into the precipitation and completely separated during the acid hydrolysis and re-aggregation cycle. The final clarified liquid after this treatment has a significantly reduced tendency to cause secondary turbidity during subsequent ultrafiltration and finished product storage. The clarification stability of the product over a long shelf life is qualitatively improved compared to the single isoelectric point precipitation method, solving the problem of unreliable clarification caused by material differences or limited settling time in conventional methods.

[0038] In another technical solution, step S4 includes: The clarified solution is fed into the cross-flow ultrafiltration membrane module via a feed pump, which can be a sanitary centrifugal pump or a screw pump, providing the driving pressure required for the feed solution to circulate within the membrane module. The cross-flow ultrafiltration membrane module has a molecular weight cutoff of 5 kDa to 20 kDa. This molecular weight cutoff is selected based on the molecular weight differences of the target analytes: tanninases typically have a molecular weight between 30 kDa and 60 kDa, and naringinase typically has a molecular weight between 20 kDa and 50 kDa. Both are much larger than the maximum pore size of the selected ultrafiltration membrane and therefore cannot pass through the membrane pores and are retained on the membrane concentration side; while betaine has a molecular weight of approximately 642 Daltons, which is a small molecule and can freely pass through the membrane pores into the membrane permeate side. The operating temperature is maintained between 10°C and 30°C. Low temperatures inhibit microbial growth and slow down the oxidation of active substances such as polyphenols in the feed solution. The transmembrane pressure is controlled between 0.1 MPa and 0.5 MPa, and the cross-flow velocity is maintained between 2 m / s and 5 m / s. The high cross-flow velocity causes the feed solution to flow tangentially along the membrane surface at high speed, and the resulting shear force continuously scours the membrane surface, effectively mitigating concentration polarization and the formation of a fouling layer on the membrane surface. During the circulating filtration process, tanninase and naringinase in the clarified solution are retained on the membrane concentration side, while stevia in the clarified solution permeates through the ultrafiltration membrane with the solvent to the permeate side, achieving the separation of the target sweet components from exogenous enzymes and proteins.

[0039] As filtration proceeds, the concentration of stevia in the membrane concentration side decreases due to continuous permeation, but some stevia remains in the liquid and gel layers on the concentration side. To fully recover this residual stevia, washing water is continuously added to the membrane concentration side of the cross-flow ultrafiltration membrane module at the same rate as the permeate discharge, performing equal-volume washing. This equal-volume washing maintains a constant total volume on the membrane concentration side; for every unit of water added, one unit of permeate containing stevia is discharged. The stevia concentration on the membrane concentration side decreases exponentially with increasing washing volume. The washing water continuously dilutes the residual stevia on the membrane concentration side, further eluting it to the membrane permeate side. The endpoint of the washing is determined by online monitoring of the stevia concentration on the membrane permeate side. Washing is terminated when the stevia concentration on the membrane permeate side drops to the level of the stevia concentration in the added washing water, indicating that all elutable stevia in the membrane concentration side has been recovered. After filtration is terminated, the permeate collected from the membrane during all operations is combined to obtain a permeate rich in stevia and free of added enzymes and proteins. This method utilizes a cross-flow ultrafiltration membrane with precisely matched molecular weight cutoff to simultaneously purify stevia and remove enzymes and proteins at low temperatures, avoiding flavor degradation and additional energy consumption. The equal-volume filtration operation maximizes the recovery of stevia with minimal pure water usage, maintaining a high level of product sweetness while ensuring no added enzymes or proteins remain in the beverage, significantly improving drinking safety and clarification stability.

[0040] In another technical solution, after equal-volume washing begins, the circulating fluid on the membrane concentration side contains retained tannins, naringinase, and possibly incompletely removed trace amounts of protein-polyphenol complexes. These substances gradually accumulate in the concentration polarization layer near the membrane surface, while some macromolecules adsorb and deposit on the membrane surface, forming a dense gel layer and filter cake layer. This leads to a continuous increase in transmembrane resistance and a gradual decrease in flux on the membrane permeate side. Equal-volume washing is a continuous steady-state operation, meaning that pure water for washing is continuously added to the membrane concentration side while the permeate is discharged at the same rate. The entire process is carried out at a fixed cross-flow velocity of 2 to 5 m / s. The membrane shear force generated at this velocity is sufficient to maintain an acceptable membrane flux in the initial stage, but the thickness and density of the gel layer increase with the extension of the operating time. After a cumulative 15 to 30 minutes of equal-volume filtration, initiate a flushing step, temporarily stopping the supply of cleaning pure water to the membrane concentration side and simultaneously closing the permeate drain valve on the membrane permeate side. This seals the membrane permeate outlet, causing the pressure on the membrane permeate side to gradually converge with that on the membrane concentration side. The driving force of the transmembrane pressure difference temporarily disappears, and no more liquid passes through the membrane pores. At this point, increase the cross-flow velocity from the original 2-5 m / s to 6-8 m / s. The increased cross-flow velocity significantly enhances the fluid shear force on the membrane surface. According to fluid mechanics principles, the wall shear stress is proportional to the square of the flow velocity. Circulate and flush the membrane surface at this high cross-flow velocity for 5 to 10 minutes. The high shear force washes away the gel layer and trapped material deposited on the membrane surface during operation. The washed-off aggregates are redispersed back into the circulating liquid on the membrane concentration side, allowing the membrane surface to return to a near-clean state and effectively restoring membrane permeability.

[0041] After the flushing step is completed, the crossflow velocity is restored to the specified normal operating range of 2 m / s to 5 m / s. The permeate discharge valve on the membrane permeate side is reopened, and pure water for cleaning is resumed to be added to the membrane concentration side. The equal-volume washing filtration operation continues. The above flushing step and equal-volume washing filtration step are performed alternately to form a dynamic filtration and self-cleaning cycle. The flushing can be triggered by the cumulative running time or by the membrane flux decaying to a certain threshold of the initial flux. Both triggering methods are preferred. The alternating execution continues until the concentration of stevia on the membrane permeate side drops to the level of stevia concentration in the added pure water for cleaning, at which point all operations are terminated. Finally, all membrane permeate side liquids collected in each stage are combined to obtain the permeate. By embedding a periodic hydraulic flushing step, online self-cleaning of the membrane surface is achieved by utilizing the high shear force of the system's own circulating liquid without introducing chemical cleaning agents, disassembling the membrane module, or interrupting the overall production cycle. The alternating mode keeps the average membrane flux at a high level, shortens the overall filtration time, and significantly reduces the frequency of shutdowns for chemical cleaning due to severe membrane fouling. This extends the effective service life of the membrane modules and significantly improves production continuity and economy.

[0042] In another technical solution, step S5 includes: The permeate is transferred to a mixing tank, and stirring is started to ensure uniform flow. Microencapsulated sweet tea flavor extract, vitamin C, and sodium bicarbonate are added to the permeate. The microencapsulated sweet tea flavor extract is a recycled product formed from multiple process steps. Its preparation path is as follows: After solid-liquid separation in step S1, the sweet tea leaves retained by a plate and frame filter are collected. The leaves are then placed in a steam distillation kettle, and steam is introduced for atmospheric pressure distillation. Volatile aromatic substances in the sweet tea leaves are distilled out with the steam. After condensation, the distillate is collected. The aromatic components in the distillate can be extracted with food-grade n-hexane and the solvent removed under reduced pressure to obtain the sweet tea aromatic substances. These aromatic substances are then mixed with a cyclodextrin aqueous solution for encapsulation. The encapsulated emulsion is spray-dried to obtain the microcapsule powder. The cyclic molecular cavities of cyclodextrin, the wall material of the microcapsule, encapsulate aromatic substances within, physically protecting volatile and easily oxidized aroma components. This ensures stability in a dry state, and once dissolved in water in a liquid beverage, the cyclodextrin cavities slowly release the aromatic substances, imparting a natural sweet tea fragrance to the product. Vitamin C, as an antioxidant, scavenges dissolved oxygen and free radicals in the formulation, preventing oxidative browning and flavor degradation during subsequent processing and storage. Sodium bicarbonate is used to adjust the pH of the system to 6.0 to 6.5; this slightly acidic to near-neutral environment results in a smoother taste and protects the stability of vitamin C during subsequent sterilization. The materials are completely dissolved and mixed evenly under continuous stirring to obtain the formulation.

[0043] The prepared liquid is preheated to 60°C to 70°C. At this temperature, the viscosity of the liquid is significantly reduced, and the solubility of dissolved gases decreases, which is beneficial for subsequent degassing. The preheated liquid is then sent to a degassing tank, a sealed pressure-resistant container. A vacuum pump is used to maintain the vacuum level inside the tank at a relative vacuum of -0.06MPa to -0.09MPa. Under this negative pressure condition, oxygen and other gases dissolved in the liquid escape from the liquid phase due to the partial pressure difference and are removed by the vacuum system. The degassing time is controlled between 5 and 15 minutes, resulting in a significant reduction in the dissolved oxygen content of the degassing liquid. Thorough degassing yields a degassed liquid, which effectively prevents oxidation reactions during subsequent high-temperature sterilization and shelf-life quality degradation caused by residual oxygen in the headspace after filling.

[0044] The degassed liquid is fed into an ultra-high temperature (UHT) instantaneous sterilizer, which consists of a heat exchange section, an insulation tube, and a cooling section. The liquid is first rapidly heated to 135°C to 140°C in the preheating and heating sections, and then held in the insulation tube for 4 to 6 seconds. This extremely short high-temperature treatment is sufficient to inactivate all pathogenic bacteria and putrefactive spores required for commercial sterility. The liquid is then immediately cooled to 25°C to 30°C in the cooling section. Compared to traditional long-duration pasteurization or high-temperature autoclave sterilization, UHT instantaneous sterilization provides sufficient sterilization intensity while having an extremely low heat load, resulting in minimal thermal degradation of glycosides, polyphenols, and flavor compounds in the liquid. After sterilization, the sterilized liquid is sent to the aseptic filling room and filled into containers that have been sterilized by hydrogen peroxide spraying under the protection of a Class 100 laminar flow hood. The container sterilization system usually uses 30% to 35% hydrogen peroxide to atomize and spray the inner wall of the container and then dry it with hot air to ensure that the inner surface of the container reaches a commercially sterile state. After filling, the container is immediately capped and sealed to produce a sweet tea beverage.

[0045] This solution incorporates a sweet tea flavor extract recovered by steam distillation from self-produced leaf residue and microencapsulated during the blending process. This transforms processing byproducts into natural flavor enhancers, achieving a closed-loop flavor utilization throughout the entire process. Microencapsulation technology effectively protects volatile aromatic substances during processing and storage, resulting in a fuller and more natural aroma release upon opening. The combination of vacuum degassing and ultra-high temperature instantaneous sterilization allows the beverage to achieve a long shelf life without the addition of preservatives, while maintaining a clear color and minimal flavor loss, significantly improving overall quality compared to conventional hot-fill processes.

[0046] In another technical solution, the method for preparing the microcapsule-encapsulated sweet tea flavor extract is as follows: The sweet tea leaves retained by the plate and frame filter press in step S1 are used as the starting material. These leaves have undergone enzymatic hydrolysis with cellulase and pectinase, followed by high-temperature enzyme inactivation, which partially destroys the cell wall structure but still retains a large amount of volatile aromatic components. The leaves are then placed in a steam distillation kettle, a normal-pressure operating device equipped with a steam distributor at the bottom. Saturated steam is introduced from the bottom of the kettle, carrying away the volatile aromatic substances from the sweet tea leaves as it passes through the leaves. The mixed steam enters the condenser through a pipe at the top of the kettle and is condensed into a liquid. The distillate is collected. The distillate is an aqueous phase containing aromatic substances. Since many aromatic components have limited solubility in water, food-grade n-hexane is added to the distillate as an extraction solvent for liquid-liquid extraction. Food-grade n-hexane has excellent solubility selectivity for non-polar or weakly polar aroma components such as terpenes, aromatic alcohols, and esters. After extraction, the mixture is allowed to stand and separate into layers. The upper organic phase is then taken and distilled under reduced pressure in a rotary evaporator or falling film evaporator. Hexane evaporates at a low temperature and is condensed and recovered. The residue is the concentrated sweet tea aroma substance, which fully preserves the original fragrance and floral notes of the sweet tea leaves.

[0047] To convert the aforementioned volatile and easily oxidized aromatic substances of sweet tea into a stable form, β-cyclodextrin and γ-cyclodextrin were blended at a mass ratio of 3:1 to 5:1 as encapsulation wall materials. β-cyclodextrin consists of 7 glucose units with an inner cavity diameter of approximately 0.60 nm to 0.65 nm, while γ-cyclodextrin consists of 8 glucose units with an inner cavity diameter of approximately 0.75 nm to 0.83 nm. Sweet tea aromatic substances are a mixture of various volatile compounds, and the molecular sizes and geometries of each component differ. The cavity size of a single cyclodextrin is insufficient to efficiently encapsulate all aromatic components simultaneously. Therefore, using a blend of two cyclodextrins expands the overall size distribution range of the encapsulation cavity, allowing aroma molecules of different sizes to find matching encapsulation cavities. Prepare a cyclodextrin mixture with a mass concentration of 15% to 25% by adding the mixed cyclodextrins to deionized water. Stir at a mild temperature of 40°C to 50°C until completely dissolved. This temperature range promotes the dissolution of cyclodextrins without causing heat loss of aromatic substances during subsequent additions. While continuously stirring, slowly add the sweet tea aromatic substances dropwise to the cyclodextrin mixture at a rate of 0.5 to 1.5 times the total mass of cyclodextrins in the mixture. This slow addition allows the aromatic substances to be captured and encapsulated by the cyclodextrin molecules upon introduction, preventing them from agglomerating as free oil droplets. After the addition is complete, continue stirring for 1 to 3 hours under nitrogen protection to ensure thorough encapsulation. The nitrogen atmosphere replaces oxygen in the reaction vessel, preventing oxidation of the aromatic substances during prolonged stirring. After inclusion, an inclusion emulsion is obtained. This emulsion is then spray-dried at an inlet air temperature of 160°C to 190°C and an outlet air temperature of 70°C to 90°C. The liquid is dispersed into fine droplets by an atomizer and then comes into contact with hot air. The moisture evaporates instantly, and the cyclodextrin inclusion complex precipitates out as a dry powder. Collecting the dry powder yields the microcapsule-encapsulated sweet tea flavor extract.

[0048] The optimal ratio of β-cyclodextrin to γ-cyclodextrin allows for the efficient encapsulation of aromatic components in sweet tea of ​​varying molecular sizes, resulting in high aroma retention during storage. Reusing microencapsulated flavor extracts in sweet tea beverage formulations ensures that the drinks retain their natural and full-bodied sweet tea aroma even after sterilization and long-term storage, significantly mitigating the aroma degradation inherent in traditional aroma preservation methods.

[0049] To further demonstrate the technical advantages of the sweet tea beverage preparation method provided by this invention, the following experimental examples are provided: Preparation of experimental materials and equipment: The sweet tea leaves are selected from dried leaves of *Rubus idaeus* from Guangxi. After harvesting, impurities are removed, and the moisture content is controlled below 10%. The tea contains cellulase (100,000 U / g), pectinase (50,000 U / g), tanninase (500 U / g), and naringinase (300 U / g). It also contains food-grade citric acid, malic acid, vitamin C, and sodium bicarbonate. β-cyclodextrin and γ-cyclodextrin are also included, along with food-grade n-hexane. The equipment includes an ultrafine pulverizer, mixing tank, enzymatic hydrolysis tank, plate and frame filter, disc centrifuge, cross-flow ultrafiltration membrane module (5kDa to 20kDa molecular weight cutoff), online pH monitoring and automatic acidification system, online turbidimeter, online bitterness sensor, vacuum degassing tank, ultra-high temperature instantaneous sterilizer, and aseptic filling equipment. High-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), and turbidity meter are also included.

[0050] <Comprehensive Implementation Example> Sweet tea leaves were chopped and then pulverized using a low-temperature ultrafine pulverizer under a nitrogen atmosphere until the particle size was no larger than 80 mesh. The sweet tea powder was mixed with deoxygenated pure water at a mass ratio of 1:20 in a mixing tank and stirred at 300 rpm for 15 minutes to obtain a slurry. The slurry was heated to 50°C, and 2% (by weight of the sweet tea powder) of cellulase and 1% (by weight of pectinase) of pectinase were added. The mixture was kept at this temperature and stirred for 90 minutes for enzymatic hydrolysis. After enzymatic hydrolysis, the temperature was raised to 90°C and held for 12 minutes to inactivate the enzymes. The mixture was then subjected to solid-liquid separation using a plate and frame filter press, and the filtrate was collected to obtain the crude extract.

[0051] The crude extract was pumped into a jacketed cooling enzymatic hydrolysis vessel and cooled to 45°C with stirring. The pH was adjusted to 4.5 with citric acid. Immobilized tanninase and immobilized naringinase (0.15% and 0.08% of the crude extract volume) were added, and the mixture was kept warm and stirred to carry out the enzymatic hydrolysis reaction. The bitterness value was monitored in real time using an online bitterness sensor. The reaction was terminated when the bitterness value decreased to below 45% of the initial bitterness value. The temperature was raised to 90°C and held for 12 minutes to inactivate the enzyme. The immobilized enzyme was separated by filtration, and the filtrate was collected as the enzymatic hydrolysate.

[0052] The enzymatic hydrolysate was transferred to a precipitation tank equipped with an online pH monitoring and automatic acid addition system. Citric acid solution was added dropwise with stirring, and the pH and turbidity values ​​were recorded in real time. Acid addition was stopped when the turbidity value reached a peak, and this pH value was locked as the isoelectric point of the sweet tea protein. After standing for 2 hours, the solution was centrifuged at 8000 rpm in a disc centrifuge, and the liquid phase was collected as the primary supernatant. The primary supernatant was then filtered through a plate and frame filter press lined with diatomaceous earth filter aid, and the filtrate was collected as the clarified liquid.

[0053] Transfer the clarified liquid to a stirred container, add citric acid solution to adjust the pH to 3.0, and stir for 30 minutes. Then add sodium bicarbonate solution to adjust the pH back to the previously determined isoelectric point, and let stand for 45 minutes. Centrifuge twice in a disc centrifuge at 8000 rpm, and collect the supernatant as the final clarified liquid.

[0054] The final clarified liquid was fed into a cross-flow ultrafiltration membrane module via a feed pump. The ultrafiltration membrane had a molecular weight cutoff of 10 kDa, an operating temperature of 25°C, a transmembrane pressure of 0.3 MPa, and a cross-flow velocity of 3 m / s. Isovolous washing was performed, with pure water continuously added to the membrane concentration side at the same rate as the permeate discharge. After a cumulative 20 minutes of isovolous washing, water replenishment and discharge were paused, and the cross-flow velocity was increased to 7 m / s to circulate and flush the membrane surface for 7 minutes. After flushing, the normal flow rate and isovolous washing were resumed, alternating between these two processes until the concentration of stevia on the permeate side of the membrane decreased to the level of stevia in the added pure water. All permeate was then collected.

[0055] The permeate was transferred to a mixing tank, and 0.05% of the microencapsulated sweet tea flavor extract, 0.03% vitamin C, and sodium bicarbonate were added to adjust the pH to 6.2. The mixture was stirred to dissolve. The preparation of the microencapsulated sweet tea flavor extract involved steam distilling the leaf residue from step S1, extracting the distillate with food-grade n-hexane, and removing the solvent by vacuum distillation to obtain the sweet tea aroma substance. β-cyclodextrin and γ-cyclodextrin were mixed at a mass ratio of 4:1, and deionized water was added to prepare a 20% (w / w) cyclodextrin mixture, which was then stirred to dissolve at 45°C. While stirring, the sweet tea aroma substance was slowly added dropwise at a rate equal to one times the total mass of the cyclodextrin, and stirring continued for 2 hours under nitrogen protection to achieve encapsulation. The encapsulated emulsion was spray-dried at an inlet air temperature of 175°C and an outlet air temperature of 80°C, and the powder was collected.

[0056] The prepared solution was preheated to 65°C and then degassed in a degassing tank under a gauge vacuum of -0.08 MPa for 10 minutes. It was then sterilized in an ultra-high temperature sterilizer at 138°C for 5 seconds and cooled to 25°C. The solution was then aseptically filled into PET bottles sterilized by spraying with 30% hydrogen peroxide, and the bottles were screwed on and sealed to obtain the finished product.

[0057] Comparative Example 1 Sweet tea leaves were extracted in 90℃ hot water for 30 minutes at a material-to-liquid ratio of 1:20. Activated carbon (2% of the filtrate mass) was added to the filtrate, and the mixture was stirred and adsorbed at 50℃ for 30 minutes. The activated carbon was then removed by filtration. The filtrate was allowed to settle naturally in a 4℃ cold storage for 48 hours. The supernatant was then filtered through diatomaceous earth. Vitamin C (0.03%) was added to the filtrate, and the mixture was then UHT sterilized and bottled.

[0058] <Comparative Example 2> Compared with the comprehensive embodiment, the sweet tea flavor extract without microcapsule encapsulation is not added, the clarified liquid after isoelectric point precipitation is directly fed into the ultrafiltration without pH swing treatment, and the constant flow rate is not interspersed with water jet during equal volume washing. All other operations and parameters are exactly the same as those in the comprehensive embodiment.

[0059] Comparative Example 3 Compared with the comprehensive embodiment, step S2 is skipped, that is, the crude extract does not undergo enzymatic debittering by tanninase and naringinase, and directly enters isoelectric point precipitation and subsequent processes, while the rest is exactly the same as the comprehensive embodiment.

[0060] The following key indicators were measured: The content and retention rate of stevia glycosides were determined by HPLC. Samples were taken at three stages: the crude extract, the enzymatic hydrolysate after debittering or the corresponding intermediate liquid, and the final product to determine the stevia glycoside concentration. The stevia glycoside retention rate was calculated as the percentage of the total mass of stevia glycosides in the final product divided by the total mass of stevia glycosides in the crude extract. For Comparative Example 1, since there was no crude extract stage, the extract filtrate was used as the initial baseline. For Comparative Example 3, since there was no debittering process, the two stages—the clarified liquid after isoelectric point precipitation of the crude extract and the final product—were compared with the corresponding stages of the comprehensive example.

[0061] Bitterness value was measured using an electronic tongue bitterness sensor and expressed as a bitterness intensity value. The measurement endpoints were the same as those for catechins. Simultaneously, 10 sensory evaluators scored the bitterness intensity according to GB / T 16291.1, with 0 points indicating no bitterness and 10 points indicating extreme bitterness.

[0062] The debitterness selectivity coefficient is expressed as the ratio of the decrease in bitterness value to the loss rate of glycosides. The glycoside loss rate is 1 minus the glycoside retention rate. A coefficient greater than 1 indicates that the rate of debitterness loss is greater than the rate of sweetness loss.

[0063] Turbidity was measured using a diffuse turbidimeter, with units of NTU. The initial turbidity was measured on the day of filling, and the turbidity was measured on days 30, 90, and 180 under constant temperature and light-protected storage conditions at 25°C. The difference between the 180-day turbidity value and the initial turbidity was used as the core indicator for judging long-term clarification stability.

[0064] Clarification stability: Record the time when visible flocculent matter or precipitate first appears under storage conditions at 25°C. If it does not appear within 180 days, record it as if it has been more than 180 days.

[0065] Aroma components were analyzed using headspace solid-phase microextraction combined with gas chromatography-mass spectrometry. The total peak area of ​​characteristic aroma components in the initial sample on the day of bottling and the sample stored at 25°C for 90 days was determined. Aroma retention was expressed as the percentage of the total peak area of ​​the 90-day sample divided by the total peak area of ​​the initial sample.

[0066] Sensory evaluation was conducted by 10 sensory evaluators who scored the samples on four aspects: aroma intensity, purity of sweet tea characteristic aroma, bitterness residue, and overall preference, using a linear scale from 0 to 10.

[0067] The overall yield of catechins is calculated as the percentage of the total mass of catechins in the finished product divided by the total mass of catechins in the raw sweet tea leaves. The catechin content in the raw materials must also be determined simultaneously.

[0068] The average flux of the ultrafiltration membrane is calculated by recording the permeate flow rate every 10 minutes throughout the entire ultrafiltration operation cycle, calculating the permeate volume per unit membrane area per unit time, and taking the average value over the entire process.

[0069] Total batch processing time, measured in minutes, is the total time from the start of raw material feeding to the end of filling and sealing.

[0070] Three batches of samples were prepared independently for each group under the same conditions of using the same batch of sweet tea leaves, the same operators, and the same equipment. The results of each indicator measurement are expressed as the mean plus or minus the standard deviation of the three batches. To analyze the differences in each indicator between the comprehensive examples and the comparative examples, an independent samples t-test was used, with a significance level set at p-value less than 0.05.

[0071] The following results were obtained from experiments conducted on the comprehensive embodiment and the comparative example: Table 1 Comparison of results between the comprehensive embodiment and Comparative Example 1 As can be seen from the data in Table 1, the retention rate of catechins in the comprehensive embodiment is much higher than that in Comparative Example 1. This is because the present invention uses enzymatic debittering to selectively hydrolyze bitter molecules, while the non-selective adsorption of activated carbon leads to the removal of a large amount of catechins. The turbidity increase of the comprehensive embodiment after 180 days is only 0.2 NTU, and no precipitation occurs. In contrast, Comparative Example 1 shows obvious turbidity and precipitation in the early stage of storage due to the ineffective removal of protein-polyphenol complexes. This indicates that the combination of isoelectric point precipitation and cross-flow ultrafiltration in the present invention has an essential advantage in terms of clarification stability. Regarding aroma retention and sensory aroma intensity, the microencapsulated flavor extract of the comprehensive embodiment effectively compensates for the loss of natural aroma during processing, while the high-temperature long-term extraction and activated carbon adsorption in Comparative Example 1 both resulted in severe aroma loss.

[0072] Table 2 Comparison of results between the comprehensive embodiment and Comparative Example 2 As can be seen from the data in Table 2, although no visible precipitation appeared in Comparative Example 2 within 180 days, the increase in turbidity was significantly higher than that of the Comprehensive Example. This indicates that the lack of pH swing treatment caused some residual protein-polyphenol precursors to slowly accumulate and produce slight turbidity during long-term storage, while the Comprehensive Example showed better deep clarification. Regarding aroma, Comparative Example 2 experienced a significant decrease in aroma after 90 days of storage due to the lack of refilling of microcapsule flavor extract, while the Comprehensive Example demonstrated a significant advantage in closed-loop flavor compensation. In terms of ultrafiltration membrane flux, the alternating hydraulic flushing of the Comprehensive Example effectively controlled membrane fouling, maintained a high average flux, and reduced the total time by about one-third, demonstrating the actual contribution of hydraulic flushing to process efficiency.

[0073] Table 3 Comparison of results between the comprehensive embodiment and Comparative Example 3 As can be seen from the data in Table 3, after skipping the debittering process, the bitterness value of the finished product in Comparative Example 3 reached as high as 5.8, and the sensory bitterness residue score reached 7.2, resulting in a strong bitter taste that is difficult for the average person to accept. However, its glycoside retention rate and turbidity stability were basically the same as those of the comprehensive example. This indicates that the debittering process independently solves the taste problem and does not affect the subsequent clarification process. This set of comparisons clearly demonstrates the indispensability of step S2 and the technical logic of the clear division of labor and synergistic cooperation among the steps of this invention.

[0074] It should be noted that although the steps are described in a specific order above, this does not mean that they must be performed in that order. In fact, some of these steps can be executed concurrently, or even in a different order, as long as the required functionality is achieved. The number of devices and processing scale described herein are for simplification of the invention; applications, modifications, and variations of this invention will be readily apparent to those skilled in the art.

[0075] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing a sweet tea beverage, characterized in that, Includes the following steps: S1: Pulverize sweet tea leaves to obtain sweet tea powder, mix the sweet tea powder with water to form a slurry, add cellulase and pectinase to the slurry, carry out enzymatic extraction at the enzymatic hydrolysis temperature, heat to inactivate the enzyme after extraction, then perform solid-liquid separation, collect the liquid part to obtain crude extract; S2: Cool the crude extract to the temperature at which tanninase and naringinase act, add tanninase and naringinase to carry out enzymatic hydrolysis to degrade bitter substances, and heat to inactivate enzymes after the reaction to obtain enzymatic hydrolysate. S3: Adjust the pH of the enzymatic hydrolysate to the isoelectric point of sweet tea protein using a food-grade acidity regulator, let it stand to allow the protein-polyphenol complex to precipitate, remove the precipitate by centrifugation, and collect the supernatant as the clarified liquid. S4: The clarified liquid is subjected to cross-flow ultrafiltration. The molecular weight cutoff of the ultrafiltration membrane is set to cut off tanninase and naringinase while allowing catechins to pass through. The permeate is collected. S5: Mix the permeate and excipients evenly, sterilize and fill to obtain a sweet tea beverage.

2. The method for preparing the sweet tea beverage according to claim 1, characterized in that, Step S1 includes: After the sweet tea leaves are chopped, they are pulverized using a low-temperature ultrafine pulverizer in a nitrogen atmosphere to obtain sweet tea powder with a particle size not exceeding 80 mesh. Mix sweet tea powder and deoxygenated pure water in a mixing tank at a mass ratio of 1:15 to 1:25, turn on the stirrer, and stir continuously at a speed of 200-500 rpm for 10-20 minutes to obtain the slurry; Heat the slurry to 45-55℃, add 1%-3% cellulase and 0.5%-1.5% pectinase relative to the weight of sweet tea powder to the slurry, keep warm at the enzymatic hydrolysis temperature and stir continuously, and the enzymatic extraction time is 60-120 minutes. After enzymatic extraction, the slurry is heated to 85-95℃ and kept at that temperature for 10-15 minutes to inactivate the enzymes. After enzyme inactivation, the slurry is subjected to solid-liquid separation using a plate and frame filter press. The filtrate is collected to obtain the crude extract.

3. The method for preparing the sweet tea beverage according to claim 1, characterized in that, Step S2 includes: The crude extract is pumped into an enzymatic hydrolysis tank with a jacket for cooling. The crude extract is cooled to 40-55℃ with continuous stirring. The pH of the crude extract is adjusted to 4.0-5.5 using a food-grade acidity regulator to obtain the enzymatic hydrolysis solution. Add 0.05%-0.3% tanninase and 0.02%-0.2% naringinase relative to the volume of crude extract to the enzymatic hydrolysis solution. Both tanninase and naringinase are added in the form of immobilized enzymes. Incubate and stir for 30-90 minutes for enzymatic hydrolysis. During the enzymatic hydrolysis reaction, the bitterness value in the reaction solution is monitored in real time by an online bitterness sensor. When the bitterness value decreases to less than 50% of the initial bitterness value, the end point of the enzymatic hydrolysis reaction is determined. After the enzymatic hydrolysis reaction is completed, the reaction solution is heated to 85-95℃ and kept at this temperature for 10-15 minutes to inactivate the enzyme. The inactivated immobilized enzyme is then separated from the liquid by filtration, and the filtrate is collected to obtain the enzymatic hydrolysate.

4. The method for preparing the sweet tea beverage according to claim 1, characterized in that, Step S3 includes: The enzymatic hydrolysate was transferred to a sedimentation tank equipped with an online pH monitoring and automatic acid addition system. Under continuous stirring, a food-grade acidity regulator was added dropwise to the enzymatic hydrolysate through the automatic acid addition system. The pH value and corresponding turbidity value of the enzymatic hydrolysate were recorded in real time. The pH value corresponding to the peak turbidity value was the isoelectric point of sweet tea protein. Acid addition was stopped and the pH value was locked as the sedimentation endpoint. The protein-polyphenol complex was allowed to stand in a sedimentation tank at the isoelectric point of the sweet tea protein for 1-3 hours to aggregate and form a precipitate. Stirring was stopped during the standing period. After settling, the enzymatic hydrolysate containing the precipitate is sent to a disc centrifuge and centrifuged at 6000-10000 rpm. The precipitate phase is continuously discharged and the liquid phase is collected to obtain the initial clear liquid. The initial filtrate is filtered through a plate and frame filter press with a filter aid to remove residual fine suspended particles. The filtrate is collected, and the supernatant is obtained as the clarified liquid.

5. The method for preparing the sweet tea beverage according to claim 4, characterized in that, In step S3, after the initial clarified liquid is finely filtered through a plate and frame filter press with a filter aid and the filtrate is collected to obtain a clarified liquid, the clarified liquid is further subjected to pH oscillation treatment, including the following steps: Transfer the clarified liquid to another container equipped with a stirrer. Add a food-grade acidity regulator to the clarified liquid while stirring to adjust the pH of the clarified liquid from the isoelectric point of sweet tea protein to 2.5-3.

5. Keep stirring under acidic conditions for 20-40 minutes. Add a food-grade alkalinity regulator to the clarified liquid to adjust the pH of the clarified liquid from acidic back to the isoelectric point of sweet tea protein, and let it stand again for 30-60 minutes under the isoelectric point condition; After the second settling period, the clarified liquid containing the secondary precipitate was centrifuged a second time using a disc centrifuge at a speed of 6000-10000 rpm. The supernatant was collected as the final clarified liquid and subjected to cross-flow ultrafiltration.

6. The method for preparing the sweet tea beverage according to claim 1, characterized in that, Step S4 includes: The clarified liquid is fed into a cross-flow ultrafiltration membrane module via a feed pump. The ultrafiltration membrane of the cross-flow ultrafiltration membrane module has a molecular weight cutoff of 5kDa-20kDa, an operating temperature of 10-30℃, and a transmembrane pressure of 0.1-0.5MPa. Circulation filtration is carried out under the condition of a cross-flow velocity of 2-5m / s. Tanninase and naringinase in the clarified liquid are retained on the membrane concentration side, while catechins in the clarified liquid are allowed to pass through the ultrafiltration membrane with the solvent and enter the membrane permeation side. Continuously replenish the membrane concentration side of the cross-flow ultrafiltration membrane module with cleaning pure water at the same rate as the permeate discharge, and perform equal-volume washing filtration to elute the residual catechins in the membrane concentration side to the membrane permeate side until the catechin concentration on the membrane permeate side drops to the level of the catechin concentration in the replenished cleaning pure water, and then stop washing filtration. Collect all the permeate liquid from the membrane permeate side and combine them to obtain the permeate liquid.

7. The method for preparing the sweet tea beverage according to claim 6, characterized in that, In step S4, during the equal-volume filtration process, an alternating rinsing step is also included to reduce fouling on the membrane surface: After running the equal volume filtration for a total of 15-30 minutes, stop adding pure water for cleaning to the membrane concentration side, and at the same time close the permeate discharge valve on the membrane permeate side. Increase the cross-flow velocity from 2-5 m / s to 6-8 m / s and circulate to rinse the membrane surface for 5-10 minutes. After rinsing, restore the crossflow velocity to 2-5 m / s, reopen the permeate discharge valve on the membrane permeate side, and resume replenishing the membrane concentration side with pure water for rinsing, and continue the equal volume filtration process. Alternately perform the above-mentioned speed-up rinsing step and speed-up equal-volume filtration step until the concentration of stevia on the membrane permeate side drops to the level of stevia concentration in the added cleaning pure water. Terminate all operations at this point, and combine all the permeate collected on the membrane permeate side to obtain the permeate.

8. The method for preparing the sweet tea beverage according to claim 1, characterized in that, Step S5 includes: The permeate was transferred to a mixing tank, and stirring was started. Microencapsulated sweet tea flavor extract, vitamin C, and sodium bicarbonate were added to the permeate. Stirring was continued until completely dissolved to obtain the mixing solution. The microencapsulated sweet tea flavor extract was prepared by spray drying a mixture of aromatic substances recovered from the sweet tea leaves after solid-liquid separation in step S1 by steam distillation and cyclodextrin. The amount of sodium bicarbonate added was adjusted to adjust the pH of the mixing solution to 6.0-6.

5. Preheat the preparation solution to 60-70℃, and put it into a degassing tank for vacuum degassing under a gauge pressure of -0.06MPa to -0.09MPa for 5-15 minutes to obtain a degassed liquid. The degassed liquid is sent into an ultra-high temperature instantaneous sterilizer and sterilized at 135-140℃ for 4-6 seconds. After sterilization, it is immediately cooled to 25-30℃ to obtain the sterilized liquid. The sterilized liquid is filled into containers that have been sterilized by spraying with hydrogen peroxide in a sterile environment, and then sealed with screw caps to produce a sweet tea beverage.

9. The method for preparing a sweet tea beverage according to claim 8, characterized in that, The preparation method of the microcapsule-encapsulated sweet tea flavor extract is as follows: The sweet tea leaves retained by the plate and frame filter in step S1 are put into a steam distillation kettle, steam is introduced under normal pressure for distillation, the distillate is collected, the distillate is extracted with food-grade n-hexane, and the organic phase is removed by vacuum distillation to remove the solvent, thus obtaining the sweet tea aromatic substances. Mix β-cyclodextrin and γ-cyclodextrin in a mass ratio of 3:1 to 5:1, add deionized water to prepare a cyclodextrin mixture with a mass concentration of 15%-25%, and stir at 40-50℃ until completely dissolved. While stirring, the sweet tea aromatic substances are slowly added dropwise to the cyclodextrin mixture at an amount of 0.5-1.5 times the total mass of cyclodextrin in the cyclodextrin mixture. After the addition is completed, the mixture is stirred for 1-3 hours under nitrogen protection to encapsulate the inclusion mixture and obtain an inclusion emulsion. The inclusion complex emulsion was spray-dried at an inlet air temperature of 160-190℃ and an outlet air temperature of 70-90℃. The dried powder was collected to obtain the microcapsule-encapsulated sweet tea flavor extract.

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