Extraction method of black tea extract

Abstract

The invention relates to the technical field of dark tea cream, and particularly provides a dark tea cream extraction method. The method comprises the following steps: adding dark tea leaves into an extraction solvent; at a target temperature, the extraction solvent after the dark tea leaves are put is subjected to ultrasonic oscillation for 30-40 minutes, dispersion liquid is obtained, and the ultrasonic oscillation frequency is 20-80 kHz; performing rough filtration on the dispersion liquid through a filter screen to obtain a crude extracting solution, and performing centrifugal separation on the crude extracting solution to obtain a clarified extracting solution; performing low-temperature concentration on the clarified extracting solution at 20-40 DEG C through a reverse osmosis membrane system to obtain a clarified concentrated solution; filtering the clarified concentrated solution through a filtering membrane to obtain a membrane separation solution; and concentrating and drying the membrane separation liquid to obtain black tea powder. According to the method, oxidative polymerization products such as theabrownin and the like in the dark tea leaves can be fully extracted, so that a large amount of loss of the oxidative polymerization products such as theabrownin and the like is avoided.

Description

Technical Field

[0001] This application relates to the technical field of dark tea tea essence, and particularly relates to a method for extracting dark tea tea essence. Background Art

[0002] Dark tea is one of the six major types of tea, named after its black appearance. Dark tea belongs to the post-fermented tea, and can usually be made by pressing and compacting with relatively coarse and old dark tea raw materials. Its specific tea-making process generally includes four processes: fixation, rolling, piling, and drying. Through these fermentation processes, the tea polyphenols in the dark tea raw materials can undergo deep oxidation and polymerization reactions, and then the resulting dark tea leaves include some specific oxidation and polymerization products such as tea brown pigment. The presence of oxidation and polymerization products such as tea brown pigment is also the key to the color of the dark tea infusion and the unique flavor of dark tea. Moreover, oxidation and polymerization products such as tea brown pigment also have certain physiological activities, such as being able to play a role in regulating intestinal microorganisms and promoting digestion.

[0003] In practical applications, in order to improve the unique flavor and nutritional effects of dark tea, it is usually necessary to further process dark tea into dark tea tea essence. However, the current methods for extracting dark tea tea essence are prone to causing the loss of oxidation and polymerization products such as tea brown pigment in dark tea. Summary of the Invention

[0004] The purpose of the embodiments of this application is to provide a method for extracting dark tea tea essence, which is used to solve the technical problem that the extraction of dark tea tea essence in the prior art is prone to causing the loss of oxidation and polymerization products such as tea brown pigment.

[0005] The first aspect of the embodiments of this application provides a method for extracting dark tea tea essence, including:

[0006] Put dark tea leaves into an extraction solvent, where the mass ratio between the extraction solvent and the dark tea leaves is 15:1 to 20:1;

[0007] At a target temperature, ultrasonically vibrate the extraction solvent with dark tea leaves put in for 30 to 40 minutes to obtain a dispersion liquid, where the frequency of the ultrasonic vibration is 20 to 80 kHz;

[0008] Coarsely filter the dispersion liquid through a filter screen to obtain a crude extract, and perform centrifugal separation on the crude extract to obtain a clarified extract;

[0009] Perform low-temperature concentration on the clarified extract through a reverse osmosis membrane system at 20 to 40 °C to obtain a clarified concentrated liquid;

[0010] Filter the clarified concentrated liquid through a filter membrane to obtain a membrane separation liquid;

[0011] Concentrate and dry the membrane separation liquid to obtain dark tea tea essence powder.

[0012] Preferably, the extraction solvent is deionized water containing cellulase and pectinase, wherein the mass ratio of cellulase is 0.2% - 0.3%, and the mass ratio of pectinase is 0.1% - 0.2%.

[0013] Preferably, before ultrasonic oscillation of the extraction solvent with black tea leaves added for 30 - 40 minutes, the method further includes:

[0014] Adjusting the pH value of the extraction solvent with black tea leaves added to 4.5 - 5;

[0015] Letting the extraction solvent after pH adjustment stand for enzymatic hydrolysis at 45 - 50°C for 1 - 2 hours; and,

[0016] At the target temperature, ultrasonic oscillation of the extraction solvent with black tea leaves added for 30 - 40 minutes to obtain a dispersion liquid, specifically including:

[0017] At the target temperature, ultrasonic oscillation of the extraction solvent after standing for enzymatic hydrolysis for 30 - 40 minutes to obtain a dispersion liquid.

[0018] Preferably, filtering the clarified concentrate through a filter membrane to obtain a membrane separation liquid, specifically including: ultrafiltration of the clarified concentrate using an ultrafiltration membrane with a cut-off molecular weight of less than 35 kDa to obtain a membrane separation liquid, wherein the pressure during ultrafiltration is 0.1 - 0.2 MPa.

[0019] Preferably, before adding black tea leaves to the extraction solvent, the method further includes:

[0020] Selecting high-quality black tea leaves;

[0021] Crushing the high-quality black tea leaves, wherein the particle size of the crushed black tea leaves is 2 - 5 mm; and,

[0022] Adding black tea leaves to the extraction solvent, specifically including:

[0023] Adding the crushed black tea leaves to the extraction solvent.

[0024] Preferably, the target temperature is determined according to the active temperature of endogenous enzymes in black tea leaves, the solubility characteristics of theabrownin, and the stability of the chemical structure of theabrownin.

[0025] Preferably, the target temperature is 80 - 95°C.

[0026] Preferably, the filter screen for rough filtration is a filter screen with 200 - 400 meshes; and,

[0027] The rotation speed for centrifugal separation is 3000 - 8000 revolutions per minute.

[0028] Preferably, the molecular weight cut-off of the reverse osmosis membrane in the reverse osmosis membrane system is less than 700 Da.

[0029] Preferably, the membrane separation liquid is concentrated and dried, specifically including: concentrating and drying the membrane separation liquid under vacuum conditions by a vacuum drying oven, wherein the set drying temperature is 70-80 °C.

[0030] Using the method for extracting dark tea tea essence provided by the embodiment of the present application, including putting dark tea leaves into an extraction solvent, the mass ratio between the extraction solvent and the dark tea leaves is 15:1-20:1, and then at the target temperature, ultrasonically vibrating the extraction solvent after putting in the dark tea leaves for 30-40 minutes to obtain a dispersion liquid, wherein the frequency of the ultrasonic vibration is 20-80 kHz, and then filtering the dispersion liquid through a filter screen to obtain a crude extract, and centrifuging the crude extract to obtain a clarified extract, and then performing low-temperature concentration on the clarified extract through a reverse osmosis membrane system at 20-40 °C to obtain a clarified concentrated liquid, and then filtering the clarified concentrated liquid through a filter membrane to obtain a membrane separation liquid, and then concentrating and drying the membrane separation liquid to obtain a dark tea tea essence powder. This method can fully extract the oxidation polymerization products such as theabrownin in dark tea leaves, avoid the large loss of oxidation polymerization products such as theabrownin, and thus can increase the content of oxidation polymerization products such as theabrownin in the extracted dark tea tea essence. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0032] Figure 1 It is a specific process schematic diagram of the method for extracting dark tea tea essence provided by an embodiment of the present application. Detailed Embodiments

[0033] The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application. In the description of the present application, terms such as "first" and "second" are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance or sequence.

[0034] As described above, the current method for extracting dark tea tea essence is likely to cause the loss of oxidation polymerization products such as theabrownin in dark tea. In view of this, the embodiment of the present application provides a method for extracting dark tea tea essence, as Figure 1 shown in the specific process schematic diagram of this method, this method includes the following steps:

[0035] Step S11: Put dark tea leaves into the extraction solvent, where the mass ratio between the extraction solvent and the dark tea leaves is 15:1 to 20:1.

[0036] For example, the extraction solvent can be added to the reaction kettle first. The extraction solvent can be deionized water, for example. Then, dark tea leaves are put into the reaction kettle. The mass ratio between the extraction solvent put into the reaction kettle and the dark tea leaves can be 15:1 to 20:1, such as 15:1, 16:1, 17:1, 18:1, 19:1, 20:1 or other values between 15:1 and 20:. The reason for selecting the range of 15:1 to 20:1 for the mass ratio of the two is that the following two aspects need to be considered comprehensively. First, it is necessary to improve the extraction efficiency and yield as much as possible. Generally speaking, the higher the mass ratio of the extraction solvent, the easier it is for oxidation polymerization products such as theabrownin in dark tea leaves to dissolve and diffuse into the extraction solvent. Therefore, the efficiency and yield can be better improved. At this time, especially when the extraction solvent is too low (such as less than 15:1), the oxidation polymerization products such as theabrownin in dark tea leaves may be difficult to dissolve quickly, resulting in low extraction efficiency and yield.

[0037] Second, the content of product impurities also needs to be considered. Generally speaking, the higher the mass ratio of the extraction solvent, the more impurities (such as tea polyphenols, caffeine, etc.) will be extracted while improving the extraction efficiency and yield. These impurities may affect the taste and quality of tea essence. For example, when the extraction solvent is too high (such as higher than 20:1), the oxidation polymerization products such as theabrownin will be quickly dissolved out, and various impurities will also be quickly dissolved out. Therefore, it is easy to cause too high impurity content in the final product. Therefore, in practical applications, these two factors are often considered comprehensively, and the mass ratio between the extraction solvent and the dark tea leaves is determined to be 15:1 to 20:1.

[0038] As mentioned above, the extraction solvent in this application can be deionized water. In practical applications, in order to further improve the efficiency, considering the chemical components in the cell structure of dark tea leaves, a certain amount of cellulase and pectinase can also be added to the deionized water. Thus, the deionized water containing cellulase and pectinase is used as the extraction solvent. Among them, the mass ratio of the cellulase can be 0.2% to 0.3%, such as 0.2%, 0.3% or other values between them. The mass ratio of the pectinase can be 0.1% to 0.2%, such as 0.%, 0.2% or other values between them.

[0039] For example, a 50 L reactor can be used as the reaction vessel, and 30 L of extraction solvent can be added to the reactor. The extraction solvent is deionized water with a mass ratio of cellulase of 0.25% and a mass ratio of pectinase of 0.15%. Then, 2 kg to 1.5 kg of dark tea leaves can be added to the extraction solvent.

[0040] Of course, in order to improve the yield and efficiency of dark tea essence, the dark tea leaves in step S11 can be high-quality dark tea leaves. Before adding the high-quality dark tea leaves to the extraction solvent, they can be crushed first. Therefore, before step S11, the method can also include selecting high-quality dark tea leaves and then crushing the selected high-quality dark tea leaves. The particle size of the crushed dark tea leaves is 2 to 5 mm. At this time, step S11 can specifically be adding the crushed dark tea leaves to the extraction solvent.

[0041] Among them, the high-quality dark tea leaves can specifically be dark tea leaves whose production period is within a preset number of years (such as within 3 years). A tea leaf crushing device can be used to crush the high-quality dark tea leaves, and then the part with a particle size of 2 to 5 mm can be selected by sieving and then added to the extraction solvent.

[0042] Step S12: At the target temperature, ultrasonically vibrate the extraction solvent with dark tea leaves added for 30 to 40 minutes to obtain a dispersion liquid, where the frequency of the ultrasonic vibration is 20 to 80 kHz.

[0043] In this step S12, the extraction solvent with dark tea leaves added is ultrasonically vibrated at the target temperature for 30 to 40 minutes, and the frequency of its ultrasonic vibration is 20 to 80 kHz, so that the dark tea leaves are dispersed in the extraction solvent to obtain a dispersion liquid.

[0044] It should be noted that the target temperature can be, for example, 80 to 95 °C. That is to say, the extraction solvent with dark tea leaves added can be ultrasonically vibrated under the temperature condition of 80 to 95 °C to obtain the dispersion liquid. The reason for selecting the temperature of 80 to 95 °C is that considering the characteristics of dark tea leaves themselves, the temperature condition of 80 to 95 °C is selected. Specifically, through the analysis of dark tea leaves, it is found that dark tea leaves themselves contain some endogenous enzymes, such as polyphenol oxidase. Further, the relationship data between the relative activity of polyphenol oxidase and temperature as shown in Table 1 is obtained by analyzing the activity of polyphenol oxidase at different temperatures. Among them, from the data in Table 1, it can be concluded that polyphenol oxidase has a relatively high relative activity at 60 to 80 °C and has a certain relative activity under the temperature condition of 80 to 95 °C.

[0045] Table 1

[0046] Temperature (°C) Relative activity of polyphenol oxidase (%) 30 25 40 45 50 70 60 90 65 95 70 98 75 92 80 85 85 70 90 50 95 30

[0047] Therefore, in order to prevent these endogenous enzymes from being completely inactivated and avoid excessive reactions caused by overly high activity, the target temperature is selected to be 80 - 95°C. Thus, under the temperature condition of 80 - 95°C, it is convenient to better control the reaction process. In this way, during the ultrasonic oscillation process in step S12, the endogenous enzymes in dark tea leaves can possess a certain activity to continue catalyzing the oxidation reactions of related components such as tea polyphenols and pigment substances in dark tea leaves, thereby contributing to the further formation and transformation of oxidation polymerization products such as theabrownine, and further increasing the content of theabrownine in tea essence.

[0048] Among them, the tea polyphenols in dark tea are mainly composed of catechins, flavonoids, anthocyanins, phenolic acids, etc. Under the action of polyphenol oxidase, catechins will undergo oxidation polymerization reactions to form substances such as theabrownine, which play a key role in the formation of the soup color, taste, and quality of dark tea. The pigment substances in dark tea mainly include pigments such as chlorophyll and carotenoids. Endogenous enzymes can participate in the conversion or degradation process of these pigments, reduce the content of these pigment substances, indirectly increase the content of theabrownine, and thus affect the color change of tea leaves, making them mainly present characteristic colors such as dark brown.

[0049] In addition, through physical property analysis of oxidation polymerization products such as theabrownine in dark tea leaves, it is found that its solubility in hot water increases with the increase in temperature. Considering that the boiling point of water under normal pressure is 100°C, the target temperature is selected to be 80 - 95°C, which can more fully dissolve oxidation polymerization products such as theabrownine from the cells of dark tea leaves, further improving the extraction efficiency and extraction amount. Of course, theabrownine is a type of complex oxidation polymer, and too high a temperature may change its chemical structure. However, the temperature of 80 - 95°C in this application is not sufficient to damage the structure of theabrownine. Extracting theabrownine under this temperature condition can also maximize the retention of the structure and activity of components such as theabrownine.

[0050] Therefore, in this application, three aspects of factors are comprehensively considered, namely the activity temperature of the endogenous enzymes in dark tea leaves themselves, the solubility characteristics of oxidation polymerization products such as theabrownine (that is, the higher the temperature, the higher the solubility), and the stability of the chemical structure of theabrownine, to determine the target temperature. And finally, 80 - 95°C is selected as the target temperature. Then, under the temperature condition of 80 - 95°C, ultrasonic oscillation is carried out to obtain a dispersion liquid.

[0051] In practical applications, for the specific implementation method of step S12, for example, the reaction kettle can be heated to 80 - 95°C, and then ultrasonic oscillation is carried out at a frequency of 20 - 80 kHz for 30 - 40 minutes, so that the dark tea leaves are fully dispersed in the leaching solvent to obtain a dispersion liquid.

[0052] In addition, it was also mentioned in the above step S11 that the leaching solvent can specifically be deionized water containing cellulase and pectinase. Among them, the mass ratio of cellulase is 0.2% - 0.3%, and the mass ratio of pectinase is 0.1% - 0.2%. At this time, in order to fully exert the effects of cellulase and pectinase, before performing step S12, the method can further include adjusting the pH value of the leaching solvent after adding dark tea leaves to 4.5 - 5, and then allowing the leaching solvent with the adjusted pH value to stand for enzymatic hydrolysis at 45 - 50°C for 1 - 2 hours. In this way, for step S12, it can be to ultrasonically vibrate the leaching solvent after standing enzymatic hydrolysis at the target temperature for 30 - 40 minutes to obtain a dispersion liquid.

[0053] Among them, the optimal pH value of pectinase is usually in a weak acid environment of 4 - 6, and the optimal pH value of cellulase is usually in a weak acid environment of 4 - 5. Both enzymes have relatively high activities at 45 - 50°C, which promotes the enzymatic hydrolysis reaction. Therefore, considering the optimal pH values and active temperatures of cellulase and pectinase comprehensively, before performing step S12 in this application, the pH value of the leaching solvent after adding dark tea leaves can be adjusted to 4.5 - 5 first, so that cellulase and pectinase reach the optimal pH value environment. Then, let it stand for enzymatic hydrolysis at 45 - 50°C for 1 - 2 hours, so that both enzymes can fully exert their effects to decompose the cell structure of dark tea leaves. In this way, in step S12, the dark tea leaves can be more fully and efficiently dispersed in the leaching solvent.

[0054] Step S13: Coarsely filter the dispersion liquid through a filter screen to obtain a crude extract, and perform centrifugal separation on the crude extract to obtain a clarified extract.

[0055] In this step S13, for the filter screen of the coarse filtration, a filter screen with 200 - 400 meshes can be selected for coarse filtration. Among them, the pore size of a 200 - mesh filter screen is about 74 microns, and the pore size of a 400 - mesh filter screen is about 38 microns. Therefore, by selecting a filter screen with 200 - 400 meshes for filtration, solid particles such as the residue of dark tea leaves in the dispersion liquid can be intercepted to obtain a relatively clarified crude extract.

[0056] Of course, the specific method of coarsely filtering the dispersion liquid through a filter screen can be to slowly pour the dispersion liquid into the filter screen and let the dispersion liquid filter down naturally. Of course, it can also be filtered by means of vacuum filtration, etc. After that, the tea residue can be squeezed to improve the filtration efficiency, so as to obtain a crude extract.

[0057] After obtaining the crude extract, the crude extract can be further centrifuged to obtain a clarified extract (i.e., this clarified extract). Among them, the rotational speed of this centrifugation can be 3000 - 8000 revolutions per minute. For example, it can be 3000 revolutions per minute, 5000 revolutions per minute, 8000 revolutions per minute, or other rotational speeds between 3000 revolutions per minute and 8000 revolutions per minute. Of course, the duration of centrifugation can be 5 - 15 minutes.

[0058] Therefore, in this step S13, the dispersion can be roughly filtered using a filter screen with 200 - 400 meshes to obtain a crude extract, and then a centrifugation device is used to centrifuge the crude extract at a rotational speed of 3000 - 8000 revolutions per minute, where the duration of centrifugation can be 5 - 15 minutes, so as to centrifuge and obtain a clarified extract.

[0059] Step S14: The clarified extract is subjected to low-temperature concentration at 20 - 40 °C through a reverse osmosis membrane system to obtain a clarified concentrated solution.

[0060] Among them, the reverse osmosis system is a membrane separation operation that uses the pressure difference as the driving force to separate the solvent in the solution through a reverse osmosis membrane (usually a reverse osmosis membrane made of polymer materials). In this step S14, the clarified extract is subjected to low-temperature concentration at 20 - 40 °C through the reverse osmosis membrane system, so as to separate the solvent, that is, deionized water, and then the concentration of the clarified extract is increased by separating the solvent to obtain a clarified concentrated solution.

[0061] Among them, in order to prevent the loss of active ingredients, the reverse osmosis membrane in this reverse osmosis membrane system is usually a spiral wound composite membrane module. And through the analysis of the chemical components of oxidation polymerization products such as theabrownin, it is found that the molecular weight distribution range of theabrownin is 700 - 40 kDa (i.e., 700 - 40000 Da), and the average molecular weight is approximately 6200. Therefore, in this application, the cut-off molecular weight of this reverse osmosis membrane can be less than 700 Da. For example, the cut-off molecular weight can be 200 Da, 300 Da, 400 Da, 500 Da, 600 Da, 700 Da, or other values less than 700 Da, so as to retain molecules with a molecular weight greater than this cut-off molecular weight, and thus retain oxidation polymerization products such as theabrownin as much as possible.

[0062] Of course, to prevent the reverse osmosis membrane from being affected by high temperatures, the operating temperature of low-temperature concentration in the reverse osmosis system can be 20-40°C. For example, under the conditions of 20-40°C, the reverse osmosis system can be used to perform low-temperature concentration on the clarified extract. Among them, the molecular weight cut-off of the reverse osmosis membrane in the reverse osmosis system is less than 700 Da, so as to retain molecules with a molecular weight greater than 700 Da and filter out part of the deionized water, realizing the concentration of the clarified extract and obtaining a clarified concentrated solution.

[0063] Step S15: Filter the clarified concentrated solution through a filter membrane to obtain a membrane separation solution.

[0064] As mentioned above, the molecular weight distribution range of theabrownin is 700-40 kDa, and the average molecular weight is approximately 6200. Specifically, among the organic molecules in the clarified extract, the content of oxidation polymerization products such as theabrownin with an organic molecular weight less than 700 is significantly reduced. Therefore, in step S14 above, the molecular weight cut-off of the reverse osmosis membrane can be less than 700 Da. And among the organic molecules with a molecular weight greater than 35 kDa, the content of oxidation polymerization products such as theabrownin will also be significantly reduced. Therefore, in order to reduce the content of impurities, in this step S15, an ultrafiltration membrane with a molecular weight cut-off of less than 35 kDa can be used to ultrafilter the clarified concentrated solution to obtain a membrane separation solution. Among them, the pressure during ultrafiltration can be 0.1-0.2 MPa, and the operating temperature can be 20-40°C.

[0065] In this way, through step S14 and step S15, it is finally possible to retain the organic molecules with a molecular weight of 700-35 kDa in the clarified extract. This molecular weight range is mainly oxidation polymerization products such as theabrownin. And through the reverse osmosis membrane in step S14, low-temperature concentration can be achieved. Finally, for the membrane separation solution obtained in step S15, on the one hand, the concentration of oxidation polymerization products such as theabrownin increases, facilitating subsequent concentration. On the other hand, organic molecules with a molecular weight less than 700 and a molecular weight greater than 35 kDa are filtered out, improving the purity of oxidation polymerization products such as theabrownin in the membrane separation solution.

[0066] Step S16: Concentrate and dry the membrane separation solution to obtain theabrownin tea powder.

[0067] There are various specific implementation methods for this step S16. For example, one method can be to directly heat up the membrane separation solution to achieve its concentration and drying. In practical applications, in order to further improve the efficiency, vacuum drying can also be performed on the membrane separation solution. For example, the membrane separation solution can be placed in a vacuum drying oven, and the drying temperature can be set to about 70-80°C. Then, the membrane separation solution is concentrated and dried under vacuum conditions through the vacuum drying oven to finally obtain theabrownin tea powder.

[0068] Of course, a spray dryer can also be used to spray-dry the membrane separation liquid. Among them, the inlet air temperature of the spray dryer can be 120-150°C, and the outlet air temperature can be 60-80°C. Then, under the conditions of this inlet air temperature and outlet air temperature, the membrane separation liquid is spray-dried by the spray dryer, and finally, the dark tea tea essence powder is obtained.

[0069] In practical applications, the current method for extracting dark tea tea essence is adopted. Specifically, the dark tea is crushed and then soaked in water (as the extraction solvent) at 80°C for 3 hours; then the extract is filtered, concentrated, and dried, and then the dark tea tea essence powder prepared by the prior art (as a comparative example) is obtained. Through the component analysis of this comparative example, the content of oxidation polymerization products such as theabrownin in this comparative example is about 20% (mass fraction).

[0070] Table 2

[0071]

[0072]

[0073] For the dark tea tea essence powder prepared by using the method provided in the embodiment of the present application, since the ultrasonic oscillation, low-temperature concentration, and membrane separation liquid and other conditions at the target temperature in the method provided in the embodiment of the present application are more conducive to the generation and retention of theabrownin, the content of oxidation polymerization products such as theabrownin in the finally obtained dark tea tea essence powder can be increased.

[0074] Specifically, in Example 1, by controlling the mass ratio between the extraction solvent and the dark tea leaves in step S11 to be 15:1, the ultrasonic frequency in step S12 to be 20 kHz, the ultrasonic oscillation time to be 30 minutes, and the concentration temperature during low-temperature concentration in step S14 to be 20°C. In the finally prepared dark tea tea essence powder, through the component analysis of this dark tea tea essence powder, the content of oxidation polymerization products such as theabrownin is 25% (mass fraction). Similarly, by controlling different preparation conditions, the dark tea tea essence powders of Examples 2 to 9 are obtained respectively, and component analysis is carried out respectively, and the data shown in Table 2 are obtained. Among them, the differences between Examples 2 to 9 and Example 1 are that the mass ratio between the extraction solvent and the dark tea leaves, the ultrasonic frequency, the ultrasonic oscillation time, and the concentration temperature during low-temperature concentration are different.

[0075] By comparing the data of Examples 1 to 9 shown in Table 2 above with the content data of oxidation polymerization products such as theabrownin in the comparative example (i.e., 20%), obviously, the theabrownin content in Examples 1 to 9 is between 25% and 30%, which is greater than the content of oxidation polymerization products such as theabrownin in the comparative example. Therefore, the method provided in the embodiment of the present application can increase the content of oxidation polymerization products of theabrownin in the finally obtained dark tea tea essence powder.

[0076] Using the method for extracting dark tea tea essence provided by the embodiments of the present application, which includes putting dark tea leaves into an extraction solvent, the mass ratio between the extraction solvent and the dark tea leaves being 15:1 to 20:1, then at a target temperature, ultrasonically vibrating the extraction solvent with the dark tea leaves put in for 30 to 40 minutes to obtain a dispersion liquid, wherein the frequency of the ultrasonic vibration is 20 to 80 kHz, then filtering the dispersion liquid through a filter screen to obtain a crude extract, and centrifuging the crude extract to obtain a clarified extract, then performing low-temperature concentration on the clarified extract through a reverse osmosis membrane system at 20 to 40 °C to obtain a clarified concentrated liquid, then filtering the clarified concentrated liquid through a filter membrane to obtain a membrane separation liquid, and then concentrating and drying the membrane separation liquid to obtain a dark tea tea essence powder. This method can fully extract oxidation polymerization products such as theabrownin in dark tea leaves, avoid a large loss of oxidation polymerization products such as theabrownin, and thus can increase the content of oxidation polymerization products such as theabrownin in the extracted dark tea tea essence. Moreover, this method can also purify these oxidation polymerization products such as theabrownin, thereby improving the quality of the dark tea tea essence.

[0077] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for extracting dark tea essence, characterized in that, Including: Put dark tea leaves into the extraction solvent, where the mass ratio between the extraction solvent and the dark tea leaves is 15:1 to 20:1; At the target temperature, ultrasonically vibrate the extraction solvent with dark tea leaves added for 30 to 40 minutes to obtain a dispersion liquid, where the frequency of the ultrasonic vibration is 20 to 80 kHz; Coarsely filter the dispersion liquid through a filter screen to obtain a crude extract, and perform centrifugal separation on the crude extract to obtain a clarified extract; Perform low-temperature concentration on the clarified extract through a reverse osmosis membrane system at 20 to 40 °C to obtain a clarified concentrated liquid; Filter the clarified concentrated liquid through a filter membrane to obtain a membrane separation liquid; Concentrate and dry the membrane separation liquid to obtain dark tea essence powder.

2. The method for extracting dark tea tea essence according to claim 1, characterized in that, The extraction solvent is specifically deionized water containing cellulase and pectinase, where the mass proportion of cellulase is 0.2% to 0.3%, and the mass proportion of pectinase is 0.1% to 0.2%.

3. The method for extracting dark tea tea essence according to claim 2, wherein, Before ultrasonically vibrating the extraction solvent with dark tea leaves added for 30 to 40 minutes, the method further includes: Adjust the pH value of the extraction solvent with dark tea leaves added to 4.5 to 5; Let the extraction solvent after adjusting the pH value stand for enzymatic hydrolysis for 1 to 2 hours at 45 to 50 °C; and, At the target temperature, ultrasonically vibrate the extraction solvent with dark tea leaves added for 30 to 40 minutes to obtain a dispersion liquid, specifically including: At the target temperature, ultrasonically vibrate the extraction solvent after standing for enzymatic hydrolysis for 30 to 40 minutes to obtain a dispersion liquid.

4. The method for extracting dark tea tea essence according to claim 1, wherein Filter the clarified concentrated liquid through a filter membrane to obtain a membrane separation liquid, specifically including: Ultrafilter the clarified concentrated liquid using an ultrafiltration membrane with a cut-off molecular weight less than 35 kDa to obtain a membrane separation liquid, where the pressure during the ultrafiltration process is 0.1 to 0.2 MPa.

5. The method for extracting dark tea tea essence according to claim 1, wherein Before putting dark tea leaves into the extraction solvent, the method further includes: Select high-quality dark tea leaves; Crush the high-quality dark tea leaves, where the particle size of the crushed dark tea leaves is 2 to 5 mm; and, Put dark tea leaves into the extraction solvent, specifically including: Put the crushed dark tea leaves into the extraction solvent.

6. The method for extracting dark tea tea essence according to claim 1, wherein The target temperature is determined according to the active temperature of the endogenous enzymes in the dark tea leaves, the solubility characteristics of the theafulvin, and the stability of the chemical structure of the theafulvin.

7. The method for extracting dark tea tea essence according to claim 1 or 6, characterized in that, The target temperature is 80 to 95 °C.

8. The method for extracting dark tea tea essence according to claim 1, characterized in that, The filter screen for the coarse filtration is a 200-mesh to 400-mesh filter screen; and, The rotation speed for the centrifugal separation is 3000 to 8000 revolutions per minute.

9. The method for extracting dark tea tea essence according to claim 1, wherein The cut-off molecular weight of the reverse osmosis membrane in the reverse osmosis membrane system is less than 700 Da.

10. The method for extracting dark tea tea essence according to claim 1, wherein Concentrate and dry the membrane separation liquid, specifically including: Concentrate and dry the membrane separation liquid under vacuum conditions through a vacuum drying oven, where the set drying temperature is 70 to 80 °C.

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