Preparation method of low-temperature high-aroma instant tea

Abstract

The traditional tea processing temperature is high, the fragrance is easy to volatilize, and the dissolvability is poor; instant tea in the market is insufficient in fragrance and poor in taste. The invention provides the preparation method of the low-temperature high-aroma instant tea so as to maintain the original aroma of the tea leaves and improve the solubility. Comprising the following steps: water bath extraction: chopping tea leaves, adding a cellulase solution, and carrying out vacuum water bath for 40 minutes in an environment with the pH value of 5 and the temperature of 50-70 DEG C; recovering fragrance; the pervaporation device enriches aroma and condenses the aroma into tea essence; wall-breaking extraction: after cooling with cold water, performing low-temperature wall-breaking extraction for 15 minutes; performing centrifugal ultrafiltration by using a 200nm microfiltration membrane; performing vacuum drying on the extract; adding fragrance, namely spraying tea essence obtained by recovering the fragrance onto the dry extract in vacuum; and breaking vacuum to obtain the high-aroma instant tea product. The method has the advantages that the tea aroma is efficiently extracted, the aroma is rich and lasting, the dissolving property is improved, the tea is quickly dissolved in cold water, the taste is rich, the aroma is subjected to pressurized low-temperature treatment and vacuum drying, the production cost is reduced, and the product is wide in application and can be expanded to food additives or raw materials.

Description

Technical Field

[0001] The invention relates to the technical field of tea processing, in particular to a method for preparing low-temperature high-fragrance instant tea. Background Art

[0002] my country is the country of origin of tea and the world's largest tea consumer. It has a long history of tea production and consumption and a profound cultural heritage. Although traditional tea processing methods, such as frying and fermentation, can produce tea products with different flavors, they often have problems such as high processing temperature, volatile aroma, and poor solubility. With the acceleration of the pace of modern life, consumers have higher and higher requirements for the convenience, solubility and quality of tea products. Therefore, it is particularly important to develop a method for preparing low-temperature, high-fragrance instant tea that can maintain the original aroma of tea, improve solubility, and meet the needs of modern consumers.

[0003] At present, although there are many kinds of instant tea products on the market, most of them have problems such as insufficient aroma and poor taste. This is mainly because in the traditional instant tea preparation method, the effective ingredients of tea are easily destroyed at high temperatures, resulting in aroma volatilization and quality degradation. At the same time, the existing instant tea preparation technology is often difficult to ensure the stability and uniformity of the product, resulting in differences in solubility, taste and other aspects of the product. Therefore, there is an urgent need for a method that can overcome the defects of the existing technology and prepare high-quality, high-aroma, high-solubility low-temperature high-fragrance instant tea.

[0004] The present invention is proposed in this context, and aims to prepare a low-temperature, high-fragrance instant tea by optimizing various parameters and technical means in the tea processing process to meet the modern consumers' requirements for the convenience, instant solubility and quality of tea products. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing low-temperature high-fragrance instant tea, which achieves efficient extraction of tea aroma and good solubility of the product through specific process steps and parameter optimization.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing low-temperature high-fragrance instant tea, characterized in that the method comprises the following steps:

[0008] (1) Water bath: Chop the tea leaves and add them to the reaction tank at a solid-liquid ratio of 1:10 (g / mL). At the same time, add 10 mL of enzyme solution (preferably cellulase), adjust the pH value to 5, and then water bath for 40 minutes at 50-70°C in a vacuum environment. In this step, the enzyme solution can destroy the cell wall of the tea leaves and promote the release of the active ingredients in the tea leaves. At the same time, by controlling the temperature and time of the water bath, it can be ensured that the aroma components and active ingredients in the tea leaves are fully released without being destroyed due to excessive temperature or excessive time, preparing for the aroma recovery in the next step.

[0009] (2) Aroma recovery: After the water bath treatment in step (1), the aroma components in the tea leaves in the liquid are gradually dissolved and evaporated with the water vapor. In order to collect these aroma components, the reaction tank is connected to a pervaporation device. The device is provided with a primary low-temperature section and a secondary high-temperature section, which are respectively used to enrich the aroma components with low boiling points and high boiling points. Through pervaporation, the aroma components in the tea leaves can be separated from the water vapor, and a water vapor mixture rich in aroma can be collected. Subsequently, the water vapor mixture rich in aroma is sent to a condensation device for condensation treatment. The water vapor is condensed into liquid tea essence by the cooling effect of the condenser. The condensed liquid (i.e., tea essence) is collected and stored through pipeline diversion for subsequent use.

[0010] (3) Cooling: After completing the water bath and aroma recovery steps, add cold water to the liquid after the aroma recovery treatment in step 2 to a liquid-to-liquid ratio of 1:20 (g / mL), and cool to room temperature. Under vacuum conditions, more soluble components in the tea leaves can gradually dissolve in water, and low temperature conditions help to keep the aroma components of the tea leaves from being destroyed. This step further promotes the release of active ingredients in the tea leaves and provides a better raw material basis for subsequent steps.

[0011] (4) Cell wall breaking extraction: The cell walls of the tea leaves in the liquid cooled to room temperature in step (3) have been partially softened. At this time, cell wall breaking extraction can more effectively release the effective ingredients in the tea leaves. The cell wall breaking extraction is carried out at low temperature for 15 to 20 minutes. The mechanical force generated by the cell wall breaking equipment destroys the cell walls of the tea leaves, allowing the aroma components and soluble substances inside the tea leaves to be fully released. This step improves the extraction efficiency of the tea leaves, and the low temperature condition helps to maintain the stability of the aroma components.

[0012] (5) Centrifugal ultrafiltration: In order to further improve the purity of the tea essence and remove impurities and particulate matter therein, the extract obtained in the sampling step (4) is subjected to centrifugal ultrafiltration using a 200 nm microfiltration membrane. In this step, macromolecular substances, impurities and particulate matter in the extract are separated from the tea essence by the action of centrifugal force, thereby obtaining a tea essence with higher purity.

[0013] (6) Concentration and drying: The extract obtained in step (5) is vacuum dried to obtain a dry extract, and the tea essence obtained in step (2) is sprayed onto the dry extract under vacuum. Under vacuum conditions, water molecules in the vacuum dried tea extract evaporate, leaving gaps on the surface and the whole of the extract. By spraying the tea essence onto the dried tea extract under vacuum conditions, the tea essence adheres to the gaps on the surface of the extract. In this step, by controlling parameters such as vacuum degree and temperature, it can be ensured that the aroma components and active ingredients in the tea essence will not be destroyed due to excessive temperature during the drying process.

[0014] (7) Breaking the vacuum to obtain a highly fragrant instant tea product. Through this step, the tea essence on the surface of the extract enters the interior of the tea extract along with the air, making the tea essence and the tea extract more closely mixed and not easily separated, and the subsequent batch continuous production is more uniform.

[0015] Preferably, the enzyme solution in step (1) is cellulase.

[0016] Preferably, the step (5) is centrifugal ultrafiltration, and the centrifugal ultrafiltration is performed using a 200-500 nm microfiltration membrane.

[0017] Preferably, in step (5), the extract is subjected to centrifugal ultrafiltration using a 200 nm microfiltration membrane.

[0018] Preferably, in step (1), the water bath is performed by placing the reaction tank in a water bath at a temperature of 50° C. for 40 minutes.

[0019] Preferably, the temperature in step (6) is controlled to be a vacuum degree of 50°C.

[0020] Preferably, the cell wall breaking extraction in step (4) is a cyclic extraction with a cycle time of 15 minutes.

[0021] Preferably, in step (2) aroma recovery, the condensation device comprises a pervaporation liquid receiving tube, a semiconductor temperature difference plate assembly, a condensate collector, and a heat exchange pipe, one end of the pervaporation liquid receiving tube is connected to the pervaporation device, and the other end of the pervaporation liquid receiving tube is connected to the semiconductor temperature difference plate assembly, the condensate collector is located below the semiconductor temperature difference plate assembly, and the heat exchange pipe is connected to the reaction tank.

[0022] The pervaporation liquid receiving pipe is responsible for receiving the aroma-rich water vapor mixture from the pervaporation device. The pipe is connected to the outlet of the pervaporation device to ensure that the water vapor mixture can smoothly enter the condensation device.

[0023] Semiconductor thermocouple: As the core component of the condensing device, the semiconductor thermocouple uses the Peltier effect to produce a cooling effect on one side and heat on the other side when powered on. The cooling side is used to condense water vapor, while the heating side can recover energy through heat exchange.

[0024] Heat sink: connected to the heating side of the semiconductor thermocouple, used to dissipate heat and prevent the temperature on the heating side from being too high. The heat sink is generally designed as a large-area multi-fin structure to improve heat dissipation efficiency.

[0025] Condenser: Fits tightly on the cooling side of the semiconductor thermocouple to receive and condense the water vapor mixture. The inside of the condenser is smooth to reduce resistance during condensation and facilitate the smooth discharge of the condensate.

[0026] Condensate collector: Located below the condenser tube, it is used to collect the condensed liquid tea essence. The condensate collector is designed with a drain port to facilitate the discharge of the tea essence and subsequent processing.

[0027] Heat exchange pipe: connects the heating side of the semiconductor temperature difference plate and the reaction tank, used to recover the heat generated by the heating side and feed it back to the tea soup extraction process to improve energy utilization.

[0028] Preferably, a control system is also included: including a temperature sensor, a pressure sensor and a controller, etc., which are used to monitor the working status of the condensing device in real time and adjust the current of the semiconductor temperature difference plate according to preset parameters to control the condensing temperature and pressure.

[0029] Preferably, an insulating layer is provided between the semiconductor temperature difference plate and the external environment to reduce heat transfer and improve condensation efficiency.

[0030] Preferably, the semiconductor thermocouple assembly includes a semiconductor thermocouple, a heat sink, and a condenser. The semiconductor thermocouple includes a cooling side and a heating side. The heat sink is connected to the heating side, the condenser is attached to the cooling side, one end of the heat exchange pipe is connected to the heating side of the semiconductor thermocouple, and the other end is connected to the reaction tank.

[0031] When the aroma-rich water vapor mixture enters the condensing device, it first passes through the pervaporation liquid receiving tube and enters the condensing tube. At this time, the semiconductor temperature difference plate is powered on and a low temperature environment is generated on the refrigeration side, which reduces the temperature of the inner wall of the condensing tube. When the water vapor mixture contacts the inner wall of the condensing tube, it condenses into liquid tea essence due to the decrease in temperature. The liquid tea essence then flows into the condensate collector and is discharged through the drain port.

[0032] At the same time, the heating side of the semiconductor thermocouple generates heat, which is dissipated to the external environment through the heat sink. Part of the heat is recovered through the heat exchange pipe and fed back to the reaction tank to heat the tea to a suitable temperature and promote the precipitation of aromatic substances.

[0033] As a further improvement of the present invention, an appropriate amount of antioxidant or stabilizer can be added in the water bath extraction step to improve the stability and antioxidant properties of the tea essence. These additives can effectively prevent the tea essence from oxidation or degradation during storage and processing, thereby maintaining the quality and aroma of the product.

[0034] In addition, the present invention can also be combined with other tea processing technologies, such as tea fermentation, tea rolling, etc., to further enrich the taste and aroma of the product. By adjusting and optimizing the parameters and step sequence of these processing technologies, low-temperature, high-fragrance instant tea products with different flavors and characteristics can be prepared.

[0035] The method for preparing low-temperature high-fragrance instant tea of ​​the present invention has the following advantages:

[0036] (1) Rich and long-lasting aroma: Through the pervaporation device and the condensation device, the aroma components in the tea can be effectively collected and retained in the tea essence. At the same time, corresponding measures are taken in the subsequent processing to prevent the loss and destruction of the aroma components. Therefore, the prepared instant tea product has a rich aroma and a long-lasting aroma effect.

[0037] (2) After vacuum drying, water molecules in the tea extract evaporate and leave gaps on the surface and the whole of the extract. Under vacuum conditions, the tea essence is sprayed onto the dried tea extract in the form of a spray, and the tea essence adheres to the gaps on the surface of the extract. After the vacuum is broken, the tea essence on the surface of the extract enters the interior of the tea extract along with the air, making the tea essence and the tea extract more closely mixed and not easy to separate, and the subsequent batch continuous production is more uniform.

[0038] (2) Good solubility: Through the treatment of centrifugal ultrafiltration and vacuum drying, high-purity and uniform-sized instant tea powder can be obtained. This tea powder can also dissolve quickly in cold water and release a rich tea aroma and taste, meeting the needs of modern consumers for convenient, efficient and high-quality tea products.

[0039] (3) Low production cost: The preparation method of the present invention adopts low temperature treatment and vacuum drying and other technical means, avoiding the energy consumption and cost problems caused by traditional high temperature treatment. At the same time, by optimizing the process parameters and step sequence, the production efficiency and product quality stability can be further improved, thereby reducing the production cost and improving the market competitiveness.

[0040] (4) The microfiltration membrane is used for centrifugal ultrafiltration treatment. The solid content and tea polyphenol content in the ultrafiltered broken wall extract are increased, which can effectively inhibit the formation of microorganisms in the filtrate, reduce the total number of colonies, and remove some volatile components and moisture, preparing for the subsequent drying step.

[0041] (5) The preparation method utilizes the refrigeration effect of the semiconductor thermocouple to achieve efficient condensation, ensuring that the water vapor mixture can be quickly converted into liquid tea essence. At the same time, the heat exchange pipe recovers the heat generated on the heating side and feeds it back to the tea soup extraction process, thereby improving energy utilization and reducing production costs. The efficient operation and precise control of the condensation device help maintain the original aroma and quality of the tea, so that the final low-temperature high-fragrance instant tea has a rich aroma and a long-lasting aroma effect.

[0042] (6) Wide application of the product: The low-temperature, high-fragrance instant tea product of the present invention can not only be consumed directly as a beverage, but can also be used as a food additive or raw material in other food fields (such as pasta products, biscuits, etc.), providing the possibility for the development of new health tea foods. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Analysis of tea extract components under different extraction processes

[0044] Figure 2 Average membrane flux of tea leaves microfiltered by membranes with different pore sizes

[0045] Figure 3 Membrane flux curves of tea leaves microfiltered by membranes with different pore sizes

[0046] Figure 4 Tea essence yield and sensory evaluation results of membranes with different pore sizes

[0047] Figure 5 Cleaning experiment after microfiltration of Tieguanyin with three membranes

[0048] Figure 6 Cleaning experiment after microfiltration of Pu'er tea with two membranes

[0049] Figure 7 The content of water and tea polyphenols in tea essence. DETAILED DESCRIPTION

[0050] Example 1

[0051] 1. Material preparation: Select high-quality fresh tea leaves as raw materials, ensuring that they are free of impurities, diseases and pests. Perform preliminary processing on the tea leaves, including stem removal, impurity removal, and cleaning, to ensure the quality of subsequent processing. In addition, prepare an appropriate amount of cellulase solution (enzyme activity unit is U / mL), antioxidants (such as vitamin C), stabilizers (such as sodium alginate) and other auxiliary materials.

[0052] 2. Water bath: Chop the processed tea leaves and add them to the reaction tank at a solid-liquid ratio of 1:10 (g / mL). At the same time, add 10mL of cellulase solution (enzyme activity is 1000U / mL), adjust the pH value to 5, and then vacuum the water bath for 40 minutes at 50°C. In this step, the action of cellulase can destroy the cell walls of tea leaves and promote the release of active ingredients in tea leaves. By controlling the temperature and time of the water bath, it can be ensured that the aroma components and active ingredients in the tea leaves are fully released without being destroyed due to excessive temperature or excessive time. At the same time, the addition of antioxidants can effectively prevent the active ingredients in the tea leaves from undergoing oxidation reactions during the extraction process, thereby maintaining the quality and aroma of the product.

[0053] 3. Aroma recovery: During the water bath, the aroma components in the tea leaves gradually dissolve and evaporate with the water vapor. In order to collect these aroma components, the reaction tank is connected to a pervaporation device. The device is equipped with a primary low-temperature section (temperature of 20°C) and a secondary high-temperature section (temperature of 50°C), which are used to enrich the aroma components with low boiling points and high boiling points, respectively. Through pervaporation, the aroma components in the tea leaves can be separated from the water vapor, and a water vapor mixture rich in aroma can be collected. Subsequently, the water vapor mixture rich in aroma is sent to the condensation device for condensation treatment. The cooling effect of the condenser is used to condense the water vapor into liquid tea essence. The condensed liquid (i.e., tea essence) is collected and stored through pipeline diversion for subsequent use.

[0054] 4. Cooling: After completing the water bath and aroma recovery steps, add cold water to the tea leaves to a material-liquid ratio of 1:20 (g / mL) and cool to room temperature. More soluble components in the tea leaves can gradually dissolve in water, and low temperature conditions help to keep the aroma components of the tea leaves intact. This step further promotes the release of active ingredients in the tea leaves and provides a better raw material basis for subsequent steps.

[0055] 5. Cell wall breaking extraction: After soaking in a water bath, the cell walls of the tea leaves have been partially softened. At this time, cell wall breaking extraction can more effectively release the active ingredients in the tea leaves. Cell wall breaking extraction is carried out at a low temperature (10°C) for 15 minutes. The mechanical force generated by the cell wall breaking equipment destroys the cell walls of the tea leaves, allowing the aroma components and soluble substances inside the tea leaves to be fully released. This step improves the extraction efficiency of tea ingredients, and low temperature conditions help maintain the stability of the aroma components. In order to improve the effect of cell wall breaking extraction, cyclic extraction can be used.

[0056] 6. Centrifugal ultrafiltration: In order to further improve the purity of the broken cell extract and remove impurities and particulate matter therein, the extract is subjected to centrifugal ultrafiltration using a 200nm microfiltration membrane. In this step, the macromolecular substances, impurities and particulate matter in the extract are separated from the broken cell extract by the action of centrifugal force, thereby obtaining a broken cell extract with higher purity. The solid content and tea polyphenol content in the broken cell extract after ultrafiltration are increased, which can effectively inhibit the formation of microorganisms in the filtrate and reduce the total number of colonies. At the same time, centrifugal ultrafiltration can also remove some volatile components and moisture, preparing for the subsequent drying step.

[0057] 7. Concentration and drying: The extract obtained in step (5) is vacuum dried to obtain a dry extract. Under vacuum, the tea essence obtained in step (2) is sprayed onto the dry extract. Under vacuum, water molecules in the vacuum dried tea extract evaporate and leave gaps on the surface and the whole of the extract. By spraying the tea essence onto the dried tea extract under vacuum, the tea essence adheres to the gaps on the surface of the extract. In this step, by controlling parameters such as vacuum degree and temperature, it can be ensured that the aroma components and active ingredients of the tea essence will not be destroyed due to excessive temperature during the drying process.

[0058] During the concentration and drying process, a stabilizer (such as sodium alginate) can be added to further improve the stability of the tea essence and prevent it from being degraded during the drying process.

[0059] 8. Break the vacuum to obtain a high-flavor instant tea product. Through this step, the tea essence on the surface of the extract enters the interior of the tea extract along with the air, making the tea essence and the tea extract more closely mixed and not easy to separate, and the subsequent batch continuous production is more uniform

[0060] Example 2

[0061] This embodiment is basically the same as Embodiment 1, except that:

[0062] In the water bath step, the amount of cellulase solution was increased to 15 mL and the pH value was adjusted to 4.5. This can further improve the release efficiency of the active ingredients in the tea leaves while maintaining the stability of the aroma.

[0063] In the aroma recovery step, the temperature of the first low temperature section of the pervaporation device is adjusted to 15° C., and the temperature of the second high temperature section is adjusted to 50° C. This can better enrich the aroma components with different boiling points and increase the aroma concentration of the tea essence.

[0064] In the cell wall breaking extraction step, the extraction time is extended to 20 minutes, which can further reduce the loss of aroma components in tea leaves and improve the aroma quality of the product.

[0065] In the centrifugal ultrafiltration step, a 500nm microfiltration membrane is used for centrifugal ultrafiltration treatment. This can further remove impurities and particulate matter in the extract and improve the purity of the tea essence.

[0066] In the concentration and drying step, the vacuum degree is adjusted to 400Pa, which can ensure that the tea essence maintains stable quality during the drying process while improving the drying efficiency.

[0067] In the concentrated drying step, the temperature parameters are adjusted (the initial temperature is -10°C for 5 hours; then gradually increased to 30°C for 3 hours). In the initial stage of drying, the temperature can be lower to slow down the drying rate and avoid the formation of a hard shell on the surface of the product. As the drying progresses, the temperature can be gradually increased to speed up the drying rate. The heating rate can be controlled between 2°C and 10°C per hour to ensure that the aroma components and active ingredients of the tea essence will not be destroyed due to excessive temperature during the drying process.

[0068] Embodiment 3 (optimization and improvement)

[0069] 1. Tea pretreatment: Select high-quality Tieguanyin as the raw material and chop it into uniform particles. The chopped tea leaves need to be strictly screened and removed to ensure the purity and quality of the raw materials.

[0070] 2. Water bath and ultrasonic assistance: Add the chopped Tieguanyin into the reaction tank at a material-liquid ratio of 1:10 (g / mL), and add an appropriate amount of cellulase solution (such as 0.5% cellulase solution). Adjust the pH value of the solution to 5, and then place it in a water bath under a vacuum environment at 60°C. In order to improve the extraction efficiency, ultrasonic-assisted extraction technology can also be used. Ultrasonic equipment uses a high-frequency vibrator to generate strong ultrasonic vibrations to destroy the cell walls of tea leaves and promote the release of active ingredients in tea leaves. During the ultrasonic-assisted extraction process, parameters such as the frequency, power and time of the ultrasound need to be controlled to ensure the extraction effect and product quality.

[0071] 3. Aroma recovery and condensation: Connect the extract to the pervaporation device for aroma recovery. The pervaporation device uses multi-stage separation technology to enrich aroma components with different boiling points. During the condensation process, a high-efficiency condenser is used to adjust the flow and temperature of the cooling medium to achieve temperature uniformity and stability during the condensation process. The condensed tea essence needs to be collected and stored for subsequent use.

[0072] 4. Cooling: After completing the water bath and ultrasonic-assisted extraction steps, add cold water to the tea leaves to a solid-liquid ratio of 1:20 (g / mL) and cool to room temperature. More soluble components in the tea leaves can gradually dissolve in water, and low temperature conditions help to keep the aroma components of the tea leaves intact. This step further promotes the release of active ingredients in the tea leaves and provides a better raw material basis for subsequent steps.

[0073] 5. Cell wall breaking extraction: After soaking in a water bath, the cell wall of the tea leaves has been partially softened. At this time, cell wall breaking extraction can more effectively release the effective ingredients in the tea leaves. Cell wall breaking extraction is carried out at a low temperature of 5-10°C for 15-20 minutes. The mechanical force generated by the cell wall breaking equipment destroys the cell wall of the tea leaves, allowing the aroma components and soluble substances inside the tea leaves to be fully released. This step improves the extraction efficiency of tea ingredients, and the low temperature condition helps to maintain the stability of the aroma components.

[0074] 6. Centrifugal ultrafiltration and membrane separation: The condensed tea essence is subjected to centrifugal ultrafiltration to remove suspended matter, colloids and other macromolecular impurities. In order to further purify the tea essence, membrane separation technology can also be used. Membrane separation equipment uses different types of membrane components such as microfiltration, ultrafiltration or nanofiltration. The appropriate membrane components and process parameters are selected according to the characteristics and requirements of the tea essence. During the membrane separation process, parameters such as pressure, flow and temperature need to be controlled to ensure the separation effect and product quality. After the centrifugal ultrafiltration step, a decolorization step can also be added to remove the pigment components in the extract and improve the transparency and purity of the product.

[0075] 7. The extract obtained by the broken wall extraction is vacuum dried to obtain a dry extract. Under vacuum, the tea essence obtained by aroma recovery is sprayed onto the dry extract. Under vacuum, the water molecules of the vacuum dried tea extract evaporate and leave gaps on the surface and the whole of the extract. The tea essence is sprayed onto the dried tea extract in the form of a spray under vacuum conditions, and the tea essence is attached to the gaps on the surface of the extract. In this step, by controlling parameters such as vacuum degree and temperature, it can be ensured that the aroma components and active ingredients of the tea essence will not be destroyed due to excessive temperature during the drying process.

[0076] 8. Break the vacuum to obtain a high-flavor instant tea product. Through this step, the tea essence on the surface of the extract enters the interior of the tea extract along with the air, making the tea essence and the tea extract more closely mixed and not easy to separate, and the subsequent batch continuous production is more uniform.

[0077] The test results of Example 1 and the comparative example are as follows Figure 1 Said:

[0078] Three extraction processes were used: traditional hot extraction (70°C hot water immersion extraction for 30 minutes, solid-liquid ratio of 1:20), cell wall extraction (room temperature water cell wall extraction for 15 minutes, solid-liquid ratio of 1:20), and hot reflux extraction (hydrothermal reflux extraction for 60 minutes, solid-liquid ratio of 1:20).

[0079] The results of solid content (extraction rate) show that broken wall extraction is better than traditional extraction methods. Combined with the process advantage of "broken wall extraction saves time compared to hot reflux extraction", based on the extraction rate and extraction time, broken wall extraction has more production advantages. The results of tea polyphenol content also show that broken wall extraction has a better extraction effect (57.42%), followed by hot reflux extraction (51.79%), and traditional thermal extraction has the lowest rate (50.95%). The caffeine content shows a small gradient increase, that is: traditional hot extraction (2.80%) < broken wall extraction (3.22%) < hot reflux extraction (3.54%). Comprehensive comparison, the broken wall extraction method has a higher process efficiency.

[0080] The membrane pore size-average membrane flux of the whole process of tea microfiltration was compared, such as Figure 2 and Figure 3 As shown. The 200nm microfiltration membrane has the best effect, followed by the 500nm membrane, and the 50nm membrane is the worst. During the whole microfiltration process, the 500nm and 200nm membranes have larger fluxes, which means that when dialyzing the same volume of Tieguanyin liquid, the 50nm membrane takes longer than the 200nm membrane and the 500nm membrane (90 minutes more). When microfiltering tea leaves, the average flux of the 200nm membrane is 13.4% higher than that of the 500nm membrane and 89.2% higher than that of the 50nm membrane.

[0081] Combination Figure 4 Data show that in the tea experiment, the yield of the 200nm membrane was 12.24% higher than that of the 500nm membrane.

[0082] After sensory evaluation, the tea extract dry powder obtained by 50nm membrane treatment has a sour and rancid taste, which may be attributed to the fact that bubbles are easily generated during the concentration and drying process, making vacuum concentration more difficult; and because of the process requirement that "the microfiltration clear liquid of the 50nm membrane needs to be left overnight before concentration", the sour and rancid taste of the tea extract dry powder is inevitable.

[0083] After sensory evaluation, the tea essence obtained by 200nm membrane treatment had better sensory experience.

[0084] After production, various membranes were cleaned to investigate their degree of contamination and recovery. The relevant results are as follows: Figure 5 , Figure 6As shown. For the 200nm and 500nm membranes, in the microfiltration experiment, as the membrane pore size increases, the degree of membrane contamination decreases slightly, indicating that the anti-fouling performance of the microfiltration membrane may be affected by the pore size. In general, the recovery rate of the 200nm membrane after cleaning is at a high level, indicating that the 200nm membrane is easier to clean (or the cleaning effect is better).

[0085] The moisture content and tea polyphenols content of the concentrated and dried tea essence were measured. The results are as follows: Figure 7 As shown in Figure 2, for Tieguanyin, as the membrane pore size gradually decreases, the water content in the corresponding essence gradually decreases, and the tea polyphenol content in the active ingredient gradually increases.

[0086] The above description is merely an exemplary embodiment of the present invention and is not intended to limit the protection scope of the present invention. The protection scope of the present invention is determined by the appended claims.

Claims

1. A method for preparing low-temperature high-fragrance instant tea, characterized in that The method comprises the following steps: (1) Water bath: Chop the tea leaves, add 10 mL of enzyme solution at a solid-liquid ratio of 1:10 (g / mL), set the pH value to 5, evacuate the environment at a temperature of 50-70°C, and place the reaction tank in a water bath for 40 min; (2) Aroma recovery: The aroma components in the tea leaves in the water bath treatment liquid in step (1) are gradually dissolved and evaporated with the water vapor, and the pervaporation liquid is enriched with the aroma components through pervaporation to obtain an aroma-rich water vapor mixture. The aroma-rich water vapor mixture is cooled by a condenser to condense the water vapor into liquid, and the condensed liquid (i.e., tea essence) is collected and stored through diversion. (3) Cooling: Add cooling water to the liquid after the aroma recovery treatment in step 2 to a material-liquid ratio of 1:20, add cold water to a material-liquid ratio of 1:20 (g / mL), and cool to room temperature; (4) cell wall breaking extraction: the liquid cooled to room temperature in step (3) is subjected to cell wall breaking extraction at low temperature for 15 min to 20 min; (5) Centrifugal ultrafiltration: The extract obtained in the sampling step (4) is subjected to centrifugal ultrafiltration using a microfiltration membrane; (6) Aroma addition: the extract obtained in step (5) is vacuum dried to obtain a dry extract, and the tea essence obtained in step (2) is sprayed onto the dry extract under vacuum. (7) Break the vacuum to obtain a highly fragrant instant tea product.

2. The method for preparing low-temperature high-fragrance instant tea according to claim 1, characterized in that: The enzyme solution in step (1) is cellulase.

3. The method for preparing low-temperature high-fragrance instant tea according to claim 1, characterized in that: In the step (5), the extract is subjected to centrifugal ultrafiltration using a 200-500 nm microfiltration membrane.

4. The method for preparing low-temperature high-fragrance instant tea according to claim 3, characterized in that: The step (5) of centrifugal ultrafiltration: the extract is subjected to centrifugal ultrafiltration using a 200 nm microfiltration membrane.

5. The method for preparing low-temperature high-fragrance instant tea according to any one of claims 1 to 4, characterized in that: In the step (1), the reaction tank is placed in a water bath at a temperature of 50° C. for 40 minutes.

6. The method for preparing low-temperature high-fragrance instant tea according to claim 5, characterized in that: In the step (6), the temperature is controlled to be a vacuum degree of 50°C.

7. The method for preparing low-temperature high-fragrance instant tea according to claim 5, characterized in that: The step (2) of aroma recovery: the aroma components of the tea leaves in the liquid after the water bath treatment in step (1) are gradually dissolved and evaporated with the water vapor; the reaction tank is connected to a pervaporation device, a primary low-temperature section and a secondary high-temperature section are provided, which are respectively used to enrich the low-boiling point and high-boiling point aroma components; the pervaporation liquid is collected to obtain an aroma-rich water vapor mixture; the aroma-rich water vapor mixture is sent to a condensing device; the water vapor is condensed into a liquid by the cooling effect of the condenser; the liquid is diverted through a pipeline; and the condensed liquid (i.e., tea essence) is collected and stored.

8. The method for preparing low-temperature high-fragrance instant tea according to claim 5, characterized in that: The step (4) cell wall breaking extraction: the cell wall breaking extraction is a cyclic extraction with a cycle time of 15 minutes.

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