Pueraria green tea and preparation method thereof

Abstract

The invention discloses a preparation method of kudzu green tea, and belongs to the technical field of tea processing. The method comprises the following core steps: carrying out fixation on tender kudzu shoots at 190-210 DEG C for 40-80 seconds; rolling at the temperature of lower than 25 DEG C, and spraying a compound treatment solution consisting of a radix puerariae extract and L-cysteine; and finally, carrying out three-stage gradient drying (60-65 DEG C, 75-80 DEG C and 85-90 DEG C) until the water content is less than or equal to 6%. According to the invention, a processing system capable of efficiently inhibiting thermal degradation of theanine is constructed through the synergistic effect of the composite treatment liquid and specific de-enzyming and drying processes. According to the technology, the processing retention rate of theanine can be remarkably increased, compared with a traditional direct baking technology, the content of theanine in a finished product can be increased by multiple times, meanwhile, the high total flavonoid content is kept, and therefore the kudzu vine green tea product fresh and refreshing in flavor and high in nutritive value is prepared, and high-value utilization of kudzu vine resources is achieved.

Description

Technical Field

[0001] This invention belongs to the field of tea processing technology, and specifically relates to a kudzu green tea and its preparation method. Background Technology

[0002] As an important plant used for both food and medicine, the development and application of its underground tubers are relatively mature. However, the in-depth development and high-value utilization of its abundant above-ground vines (i.e., kudzu vines) are still significantly insufficient. Currently, apart from a small amount used as animal feed, the potential of kudzu vines as a beverage ingredient has not been fully explored.

[0003] Existing technologies have made some attempts to use kudzu vine as a substitute tea, but these solutions mainly suffer from two limitations: First, the focus of the process is on the compounding of raw materials rather than the refined processing of kudzu vine itself. For example, Chinese patent CN107125397A discloses a compound substitute tea containing multiple plants including kudzu vine. Its core technology lies in the compatibility and mixing of raw materials, without designing a specific tea-making process for the physicochemical properties of kudzu vine as a single raw material. Second, existing solutions fail to systematically design for the retention of the core quality component—theanine—during the tea-making process. For example, Chinese patent CN105475566A involves compounding kudzu root extract with mountain green tea, which essentially uses kudzu root as a functional additive rather than developing tea with kudzu vine as the main component, and does not address the transformation and retention of the internal components of kudzu vine during the tea-making process.

[0004] Theanine is a key water-soluble amino acid that determines the quality and health value of green tea. Its content directly affects the fresh, mellow, and rich flavor of the tea infusion and is also one of its important health-promoting active ingredients. However, theanine is significantly heat-sensitive and is easily degraded or volatilized during heat treatment processes such as fixation and drying, leading to a decline in the flavor and nutritional value of the finished tea. In traditional tea leaf processing, this loss is difficult to completely avoid. Kudzu vine, as a novel tea-making raw material, has a fundamentally different tissue structure, enzyme system composition, and internal components compared to fresh tea leaves, making conventional green tea processing experience unsuitable. Existing technologies, whether simple compounding schemes or borrowing from traditional processing methods, have not proposed an effective solution to systematically address the specific technical problem of significant theanine loss during the conversion of kudzu vine into green tea.

[0005] Therefore, how to improve the theanine retention rate in kudzu green tea has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of the above, it is necessary to provide a method for preparing kudzu green tea. This method can effectively suppress the loss of theanine during processing by using a specific combination of processes, thus significantly improving the retention rate of theanine in the finished product and improving the flavor, taking into account the characteristics of low background theanine content and thermal instability of kudzu raw material.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing kudzu green tea with high theanine content includes the following steps:

[0009] (1) Raw material processing: Pick tender shoots of kudzu vine, wash and drain them, and then cut them into sections;

[0010] (2) Blanching: Blanch the kudzu vine segments at 190-210℃ for 40-80 seconds to deactivate polyphenol oxidase activity;

[0011] (3) Kneading and treatment: During or after kneading, a composite treatment liquid is evenly sprayed onto the surface of the kudzu vine segments; the kneading is carried out under conditions where the ambient temperature is below 25°C;

[0012] (4) Drying: Dry the kudzu vine segments after spraying the treatment solution to reduce their moisture content to below 6%.

[0013] In this invention, further, the drying in step (4) is carried out in stages, specifically: drying at 60-65℃ for 20-40 minutes, then drying at 75-80℃ for 15-30 minutes, and finally drying at 85-90℃ for 10-20 minutes until the moisture content is ≤6%.

[0014] In this invention, the composite treatment solution is further composed of kudzu root extract and L-cysteine.

[0015] In this invention, the preparation method of the composite treatment liquid further includes: extracting kudzu root powder with an ethanol aqueous solution of 60-70% concentration, concentrating the extract to obtain a concentrated kudzu root extract, and then adding 0.8-1.2% of L-cysteine ​​by mass to the concentrated extract, mixing evenly and adjusting the pH value to 5.5-6.5.

[0016] In this invention, the amount of the composite treatment liquid sprayed is 5-10% of the weight of the kudzu vine segments.

[0017] In this invention, further, in step (2), the blanching temperature is 200°C and the blanching time is 60 seconds.

[0018] In this invention, the variety of kudzu shoots in step (1) is "Guige No. 8".

[0019] Another object of the present invention is to provide a kudzu green tea, which is prepared by the method described above.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects:

[0021] 1. This application proposes a method for preparing kudzu green tea. By introducing a composite treatment solution composed of kudzu root extract and L-cysteine, and spraying it during the low-temperature rolling stage, a synergistic effect is achieved with the subsequent specific drying process, specifically creating a stable processing environment that inhibits the thermal degradation of theanine. The synergistic effect of this composite treatment solution is considered to stem from the complementary functions of its components: the flavonoids in kudzu root extract have excellent antioxidant activity, while L-cysteine, as a recognized reducing agent and metal ion chelating agent, can effectively block oxidative degradation pathways. The combination of these two components may work together on the surface and within the internal microenvironment of the material, thereby providing a protective efficacy for heat-sensitive theanine that surpasses conventional methods during multiple thermal processing stages such as fixation and drying.

[0022] 2. This application proposes a finely controlled processing parameter. By limiting the fixation conditions to a short-duration high-temperature range of 190-210℃ for 40-80 seconds, and designing the drying process as a three-stage gradient temperature increase program of 60-65℃, 75-80℃, and 85-90℃, an optimal balance is achieved between efficient enzyme inactivation and minimal thermal damage. This series of parameters is an interconnected and synergistic overall design. Its beneficial effects are that rapid fixation can instantly inactivate polyphenol oxidase, reducing the enzymatic oxidation loss of theanine; while the unique three-stage gradient drying follows the principle of first removing a large amount of moisture at low temperature and then gradually increasing the temperature to solidify, avoiding non-enzymatic thermal decomposition of theanine under long-term high-temperature exposure. This precise process control is specifically designed for the characteristics of kudzu vine raw materials, with the direct aim of maximizing the retention of theanine.

[0023] 3. This application proposes a complete processing technology for kudzu green tea. Its most significant and ultimate benefit is that it can increase the retention rate of theanine in the finished product by several times compared to traditional direct drying processes. Example data shows that the method of this invention can significantly increase the theanine content from approximately 85 μg / g in the control process to 289 μg / g, an increase of 240%. This unexpected technical effect confirms the significant synergistic effect of the overall process chain of "specific fixation—low-temperature addition of compound treatment liquid—three-stage gradient drying." This method not only overcomes the technical challenge of insufficient flavor in kudzu products due to the low background value of theanine and its easy loss during processing, but also provides a practical and effective new path for the high-value and flavorful development and utilization of kudzu resources. Detailed Implementation

[0024] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0025] Example 1:

[0026] This embodiment proposes a method for preparing a composite treatment solution, as follows:

[0027] Take dried kudzu root of variety "Guige No. 8", pulverize it, and pass it through a 60-mesh sieve. Weigh 100g of kudzu root powder and add 1200mL of 65% (v / v) ethanol aqueous solution. Stir and extract at 65℃ for 2 hours, then filter. Add 800mL of the same concentration of ethanol aqueous solution to the filter residue and repeat the extraction once more under the same conditions. Combine the two extracts and concentrate them under reduced pressure at 50℃ and -0.08 MPa to about 1 / 5 of the original volume. Add 2.0g of L-cysteine ​​(equivalent to 1.0% of the mass of the concentrated extract) to this concentrated extract, stir until completely dissolved, and adjust the pH to 6.0 with 1mol / L dilute citric acid solution to obtain the composite treatment solution described in this invention, denoted as treatment solution A.

[0028] Example 2:

[0029] This embodiment proposes a method for preparing high-theanine kudzu green tea, including the following steps:

[0030] (1) Raw material processing: Pick the tender shoots of "Guige No. 8" kudzu vine (from the stem tip to the second unopened leaf), wash and drain them, and cut them into sections with a length of 2 cm.

[0031] (2) Blanching: Blanch the kudzu vine segments at 200℃ for 60 seconds, then remove them from the pan and let them cool to room temperature.

[0032] (3) Kneading and treatment: Knead for 20 minutes at an ambient temperature below 25°C. Five minutes after the start of kneading, spray the treatment liquid A prepared in Example 1 evenly, with the spray amount being 8% of the weight of the kudzu vine segment.

[0033] (4) Segmented drying: The kneaded kudzu segments are dried in a three-stage gradient, as follows:

[0034] First step: Dry at 63℃ for 30 minutes;

[0035] Second step: Dry at 78℃ for 22 minutes;

[0036] The third step: Dry at 88℃ for 15 minutes. The moisture content of the finished product after drying is 5.5%.

[0037] (5) Packaging: After cooling, seal the package.

[0038] Example 3:

[0039] This embodiment proposes a method for preparing high-theanine kudzu green tea, including the following steps:

[0040] (1) Raw material processing: Pick the tender shoots of "Guige No. 8" kudzu vine (from the stem tip to the second unopened leaf), wash and drain them, and cut them into sections with a length of 2 cm.

[0041] (2) Blanching: Blanch the kudzu vine segments at 190℃ for 80 seconds, then remove them from the pan and let them cool to room temperature.

[0042] (3) Kneading and treatment: Knead for 20 minutes at an ambient temperature below 25°C. Five minutes after the start of kneading, spray the composite treatment solution prepared according to the method in Example 1 evenly (wherein, the amount of L-cysteine ​​added is adjusted to 0.8% of the mass of the concentrated kudzu extract, and the pH value is adjusted to 5.5 with dilute sodium hydroxide solution), and the amount of spray is 5% of the weight of the kudzu vine segment.

[0043] (4) Segmented drying: The kneaded kudzu segments are dried in a three-stage gradient, as follows:

[0044] First step: Dry at 60℃ for 40 minutes;

[0045] Second step: Dry at 75℃ for 30 minutes;

[0046] The third step: Dry at 85℃ for 20 minutes. The moisture content of the finished product after drying is 5.0%.

[0047] (5) Packaging: After cooling, seal the package.

[0048] Example 4:

[0049] This embodiment proposes a method for preparing high-theanine kudzu green tea, including the following steps:

[0050] (1) Raw material processing: Pick the tender shoots of "Guige No. 8" kudzu vine (from the stem tip to the second unopened leaf), wash and drain them, and cut them into sections with a length of 2 cm.

[0051] (2) Blanching: Blanch the kudzu vine segments at 210℃ for 40 seconds, then remove them from the pan and let them cool to room temperature.

[0052] (3) Kneading and treatment: Knead for 20 minutes under an ambient temperature below 25°C. Five minutes after the start of kneading, spray the composite treatment liquid prepared according to the method in Example 1 (wherein, the amount of L-cysteine ​​added is adjusted to 1.2% of the mass of the kudzu root concentrated extract, and the pH value is adjusted to 6.5), and the amount of spray is 10% of the weight of the kudzu vine segment.

[0053] (4) Segmented drying: The kneaded kudzu segments are dried in a three-stage gradient, as follows:

[0054] First step: Dry at 65℃ for 20 minutes;

[0055] Second step: Dry at 80℃ for 15 minutes;

[0056] Third step: Dry at 90℃ for 10 minutes. The moisture content of the finished product after drying is 6.0%.

[0057] (5) Packaging: After cooling, seal the package.

[0058] Comparative Example 1: Comparison of the effects of different treatment solutions

[0059] This comparative example verifies the necessity of the composite treatment solution and its specific composition. The following treatment solutions were used, with all other steps and parameters identical to those in Example 2.

[0060] Comparative Example 1A: No treatment solution was sprayed.

[0061] Comparative Example 1B: Spray an equal volume (8%) of pure water.

[0062] Comparative Example 1C: Spray an equal amount (8%) of kudzu root extract aqueous solution, which was obtained by diluting the concentrated kudzu root extract obtained in Example 1 to the same content as the kudzu root extract in the composite treatment solution A.

[0063] Comparative Example 1D: Spray an equal volume (8%) of an aqueous solution of L-cysteine ​​(concentration 0.8%, pH adjusted to 6.0).

[0064] Comparative Example 1E: Spray an equal volume (8%) of 0.1% vitamin C solution.

[0065] Comparative Example 2: Comparison of Different Blanching Processes

[0066] Treatment liquid A (spraying amount 8%) was used consistently, only the blanching process was changed, and other steps and parameters were the same as in Example 2.

[0067] Comparative Example 2A: Blanching at 160℃ for 120 seconds.

[0068] Comparative Example 2B: Blanching at 240℃ for 30 seconds.

[0069] Comparative Example 3: Comparison of Different Drying Processes

[0070] The treatment solution A (spraying amount 8%) and the blanching conditions of Example 2 were kept constant, only the drying method was changed.

[0071] Comparative Example 3A (constant temperature drying): dried once at 88℃ until the moisture content is ≤6%.

[0072] Comparative Example 3B (two-stage drying): First, dry at 70°C for 50 minutes, then dry at 90°C for 25 minutes until the moisture content is ≤6%.

[0073] Comparative Example 3C (direct drying): The same "Guige No. 8" raw material as in Example 2 was used, but the process was changed to: the fresh kudzu vines after being cut into sections were directly dried at 80°C to a moisture content of ≤6% in one go, without going through the steps of blanching, kneading and spraying with treatment liquid.

[0074] Comparative Example 4: Comparison of Different Raw Material Varieties

[0075] The steps and parameters of Example 2 were followed exactly, except that the raw material was changed to the tender shoots of "Guige No. 1" kudzu vine.

[0076] Tests and Results Analysis:

[0077] The following key quality indicators were tested on the kudzu green tea products prepared by the above embodiments and comparative methods:

[0078] 1. Theanine content: The theanine in tea was determined by high performance liquid chromatography (HPLC) according to GB / T 23193-2017 "Determination of theanine in tea by high performance liquid chromatography".

[0079] 2. Total flavonoid content: The total flavonoid content was determined using the aluminum nitrate-sodium nitrite colorimetric method, with rutin as the standard.

[0080] The main test results are shown in the table below (the data in the table are the average of three parallel experiments):

[0081] Table 1. Content of main components in kudzu green tea prepared by different processes

[0082]

[0083] Based on the results in Table 1, it can be concluded that the product prepared using the method of this application (Example 2) has a significantly higher theanine content (289 μg / g) than all comparative examples that did not use or used incomplete treatment solutions. The theanine contents of Comparative Example 1C (using only kudzu root extract) and Comparative Example 1D (using only L-cysteine) were 198 μg / g and 162 μg / g, respectively, both significantly lower than those of Example 2. This indicates that kudzu root extract and L-cysteine ​​in this process are not simply additive, but rather produce a synergistic effect. This synergistic effect is also superior to that of Comparative Example 1E (175 μg / g), which uses the conventional antioxidant vitamin C. This unexpected effect may stem from the complementary functions of the two: kudzu root extract is rich in flavonoids, which have good antioxidant properties, while L-cysteine, as a recognized reducing agent and metal ion chelating agent, can effectively inhibit oxidative degradation pathways. The combination of the two may create a more efficient composite protective environment in the processing system, thereby significantly reducing the loss of theanine.

[0084] The theanine content in Comparative Example 2A (low temperature, long time, 182 μg / g) and Comparative Example 2B (high temperature, short time, 150 μg / g) was significantly lower than that in Example 2 (200℃, 60 seconds, 289 μg / g). This indicates that excessively high blanching temperatures can lead to the instantaneous loss of heat-sensitive theanine, while excessively low temperatures cannot completely inactivate polyphenol oxidase, potentially leading to indirect oxidation of theanine in subsequent processes. The blanching parameter range defined in the claims of this application (190-210℃, 40-80 seconds) represents the optimal balance between rapid enzyme inactivation and maximum theanine retention. Comparative Example 3A (88℃ constant temperature drying, 168 μg / g) showed significant theanine loss. Comparative Example 3B (70 / 90℃ two-stage drying, 208 μg / g) showed some improvement, but still fell short of the three-stage gradient drying method of this application (Example 2, 289 μg / g). This confirms that the three-stage gradient drying process of this application (e.g., 60-65℃→75-80℃→85-90℃) can more effectively avoid the degradation of theanine in the later stage of drying due to prolonged exposure to high temperatures by gradually and gently removing moisture. This specific combination produces significant technical effects.

[0085] The products prepared by the present invention (Examples 2-4) have a stable theanine content of 273-289 μg / g. Compared to Comparative Example 3C (direct drying process, 85 μg / g), which simulates the simplest existing technology, the theanine content of Example 2 is 3.4 times higher, representing an increase of 240%. This significantly demonstrates that the "specific blanching-low-temperature addition of compound treatment liquid-three-stage gradient drying" of the present invention is a complete and interconnected technical solution with synergistic effects. Its overall effect far exceeds the simple sum of the effects of each part and is comprehensively superior to all comparative examples that only change a single process condition. Meanwhile, although the theanine content of Comparative Example 4 (using "Gui Ge No. 1", 208 μg / g) is lower than that of Example 2, it is still significantly higher than that of Comparative Example 3C, indicating that the process of the present invention is universally applicable to different kudzu varieties and can significantly increase the theanine content in all cases. Data also shows that "Gui Ge No. 8" (Example 2), when combined with the specific process of the present invention, exhibits superior theanine enrichment and retention potential, making it the preferred raw material for achieving the best results.

[0086] In summary, the examples and systematic comparative experimental data jointly confirm that the technical solution provided by this invention solves the technical problem of the difficulty in retaining theanine in the processing of kudzu green tea. Through the synergistic combination of three key features—"fixed-green tea with specific parameters," "addition of the compound treatment liquid during the low-temperature rolling stage," and "specific three-stage gradient drying"—high-quality kudzu green tea with a significantly higher theanine content than that produced by conventional methods was successfully prepared, providing an innovative and effective solution for the high-value utilization of this resource.

[0087] The above embodiments are merely examples of several implementations of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention.

Claims

1. A method for preparing kudzu green tea with high theanine content, characterized in that, Includes the following steps: (1) Raw material processing: Pick tender shoots of kudzu vine, wash and drain them, and then cut them into sections; (2) Blanching: Blanch the kudzu vine segments at 190-210℃ for 40-80 seconds; (3) Kneading and treatment: During or after kneading, a composite treatment liquid is evenly sprayed onto the surface of the kudzu vine segments; the kneading is carried out under conditions where the ambient temperature is below 25°C; (4) Drying: Dry the kudzu vine segments after spraying the treatment solution to reduce their moisture content to below 6%.

2. The method according to claim 1, characterized in that, The drying in step (4) is carried out in stages, specifically: drying at 60-65℃ for 20-40 minutes, then drying at 75-80℃ for 15-30 minutes, and finally drying at 85-90℃ for 10-20 minutes until the moisture content is ≤6%.

3. The method according to claim 1, characterized in that, The composite treatment solution consists of kudzu root extract and L-cysteine.

4. The method according to claim 3, characterized in that, The preparation method of the composite treatment solution includes: extracting kudzu root powder with an ethanol aqueous solution of 60-70% concentration, concentrating the extract to obtain a concentrated kudzu root extract, and then adding 0.8-1.2% of L-cysteine ​​by mass to the concentrated extract, mixing evenly and adjusting the pH value to 5.5-6.

5.

5. The method according to claim 4, characterized in that, The amount of the composite treatment liquid sprayed is 5-10% of the weight of the kudzu vine segments.

6. The method according to claim 1, characterized in that, In step (2), the blanching temperature is 200℃ and the blanching time is 60 seconds.

7. The method according to claim 1, characterized in that, The variety of kudzu shoots in step (1) is "Guige No. 8".

8. A kudzu green tea, characterized in that, It is prepared by the method according to any one of claims 1-7.

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