Method for processing berry tea by microwave combined with carbon dioxide

Abstract

This invention provides a method for processing wild berry tea using a microwave combined with carbon dioxide, relating to the field of wild berry tea processing technology. The method mainly involves pre-cooling and spreading fresh wild berry tea leaves, followed by microwave fixation, kneading, and then treatment with supercritical carbon dioxide. The leaves are then placed in an ice-water bath for crystallization, followed by resting at room temperature, and subsequently baked and dried while using a carbon dioxide atmosphere for aroma enhancement. This invention overcomes the shortcomings of existing technologies, enabling the precipitation of a greater amount of dihydromyricetin from the wild berry tea in a shorter time, which then forms a white frost on the tea surface. Simultaneously, combined with subsequent operations, it prevents the tea leaves from darkening in color, comprehensively improving the quality of the finished wild berry tea.

Description

Technical Field

[0001] This invention relates to the field of berry tea processing technology, specifically to a method for processing berry tea using microwave combined with carbon dioxide. Background Technology

[0002] Berry tea, also known as vine tea, sweet tea, or white tea, is made from the tender stems and leaves of Ampelopsis grossedentata, a plant resource unique to my country that is both a food and a medicine. Its surface is covered with white frost, and it has a slightly bitter taste with a distinct sweet aftertaste. It has been used as a tea for over a thousand years.

[0003] The processing method for wild berry tea is similar to that of traditional tea, involving withering, fixation, rolling, and roasting. However, the key difference lies in the additional crystallization process after rolling. This crystallization process causes flavonoids to crystallize on the surface of the tea leaves. This process typically combines high-temperature fixation with pile fermentation, using prolonged fermentation to promote the release of flavonoids and form a white frost on the tea leaves. The fermentation temperature is generally between 25-45℃. This white frost is a unique characteristic of wild berry tea, facilitating the dissolution of more flavonoids, especially dihydromyricetin, in the tea liquor during short brewing. To achieve greater dihydromyricetin crystallization, a longer fermentation and fixation period is often used during wild berry tea processing. However, prolonged processing can cause the tea leaves to turn yellow or red, and may even result in a sour and astringent taste in subsequent brews.

[0004] When brewed, berry tea has a dark reddish-brown color, giving it a poor overall appearance and resulting in a lower market rating. The market generally prefers green tea liquor. To prevent leaf discoloration during processing, the piling time is often reduced, resulting in a lighter-colored berry tea. However, this produces less white bloom on the surface and less dihydromyricetin in the brewed tea, thus lowering its nutritional value. Therefore, improving the dihydromyricetin content in the tea liquor while maintaining a green hue is a major direction for current berry tea processing technology improvement. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for processing berry tea using microwave combined with carbon dioxide. This method can cause a greater amount of dihydromyricetin to precipitate from the berry tea in a shorter time, which then forms a white frost on the surface of the tea leaves. Simultaneously, combined with subsequent operations, it prevents the color of the berry tea leaves from darkening, thereby comprehensively improving the quality of the finished berry tea.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for processing wild tea using microwave combined with carbon dioxide, the method comprising the following steps:

[0008] S1. Fresh leaf processing: After picking, the fresh tea leaves are pre-cooled and spread out at 2-4℃, and then microwaved to kill the green, and the green leaves are ready for use.

[0009] S2. Rolling treatment: Place the above-mentioned blanched leaves in a rolling machine for rolling treatment to obtain rolled leaves;

[0010] S3. Carbon dioxide treatment: Place the kneaded leaves in a sealed container and keep them at 35±2℃. Increase the pressure to 7.5-8.5Mpa and fill them with supercritical carbon dioxide for 10-15 minutes. Then restore the pressure to normal and remove the excess gas. Then ventilate and let them stand at room temperature to obtain carbon dioxide treated leaves.

[0011] S4. Rapid cooling crystallization treatment: Place the carbon dioxide treated leaf in an ice-water bath for rapid cooling until crystals appear on the surface, then restore it to room temperature and let it stand to obtain the pretreated leaf.

[0012] S5. Roasting and aroma enhancement: Roast the pretreated leaves at 60-70℃ until the moisture content is ≤6%, then cool down to 40-50℃ and adjust the atmosphere to carbon dioxide for heat preservation and aroma enhancement to obtain the finished berry tea.

[0013] Preferably, the pre-cooling and drying time in step S1 is 2-4 hours.

[0014] Preferably, the microwave blanching temperature in step S1 is 65-70℃, and the blanching time is 2-3 minutes.

[0015] Preferably, the kneading time in step S2 is 8-12 minutes.

[0016] Preferably, the amount of supercritical carbon dioxide introduced in step S3 is 2-3 times the total mass of the kneading leaves.

[0017] Preferably, the time for standing at room temperature in step S3 is 30-40 minutes.

[0018] Preferably, in step S4, the thickness of the carbon dioxide-treated leaves is kept at 1-2 cm during the ice-water bath treatment, the treatment time is ≤2 hours, and the subsequent resting time at room temperature is 1-2 hours.

[0019] Preferably, the baking process in step S5 is carried out in a vacuum environment.

[0020] Preferably, the aroma extraction process in step S5 takes 30-40 minutes.

[0021] This invention provides a method for processing wild tea using microwave combined with carbon dioxide, which has the following advantages compared to existing technologies:

[0022] This invention employs pre-cooling followed by microwave fixation and then rolling to prevent the early microwave treatment from darkening the color of the wild tea leaves. Furthermore, it combines this with supercritical carbon dioxide treatment, which precipitates dihydromyricetin from the wild tea leaves at a lower temperature and in a shorter time. Subsequent ice-water bath crystallization, combined with roasting and carbon dioxide treatment to enhance aroma, effectively further inhibits the darkening of the wild tea leaves and prevents acidification. The use of supercritical carbon dioxide and subsequent crystallization reduces the loss of flavonoids due to high temperatures, increasing the content of total flavonoids and dihydromyricetin in the wild tea leaves. It also effectively removes the grassy smell of the wild tea leaves, enhances the flavor of the tea soup, and comprehensively improves the quality of the wild tea. Attached Figure Description

[0023] Figure 1 This is a chromatogram of dihydromyricetin reference standard used in the detection of DMY concentration in tea in an embodiment of the present invention;

[0024] Figure 2 This is a chromatogram of the tea infusion from Example 1 when detecting the DMY concentration in the tea infusion in this embodiment of the invention;

[0025] Figure 3 These are schematic diagrams illustrating the morphology of tea leaves and the appearance of tea soup after brewing in various embodiments and comparative examples of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The fresh tea leaves used in the following examples and comparative examples were 6-12 cm buds harvested in May 2025 from the same batch.

[0028] Example 1:

[0029] Processing of strawberry tea leaves:

[0030] (1) After picking, the fresh tea leaves are pre-cooled and spread out at 2℃ for 4 hours, then microwaved to fix the green, controlling the fixing temperature at 65℃ and the fixing time at 3 minutes, and the green leaves are prepared for use.

[0031] (2) Place the above-mentioned blanched leaves in a kneading machine (RTY-6 type kneading machine, speed controlled at 40 rpm) and knead for 8 minutes to obtain kneaded leaves;

[0032] (3) Place the kneaded leaves in a sealed container, adjust the temperature to 35±2℃, increase the pressure to 7.5MPa, then fill the container with supercritical carbon dioxide twice the total mass of the kneaded leaves, let it stand for 15 minutes, then restore the normal pressure, expel the excess gas, then open the container and let it stand for 30 minutes to obtain carbon dioxide treated leaves.

[0033] (4) Spread out the carbon dioxide-treated leaves and control the thickness of the spread to 1-2 cm. Then place them on an ice water bath and let them stand for 1.5 h. White crystals will appear on their surface. Remove them from the ice water bath and let them stand at room temperature for 1 h to obtain the pretreated leaves for use.

[0034] (5) The pretreated leaves were baked at 60°C until the moisture content was ≤6%, then cooled to 40°C and the atmosphere was adjusted to carbon dioxide. The leaves were kept warm and the aroma was enhanced for 40 minutes to obtain the finished berry tea.

[0035] Example 2:

[0036] Processing of strawberry tea leaves:

[0037] (1) After picking, the fresh tea leaves are pre-cooled and spread out at 4℃ for 2 hours, then microwaved to fix the green, controlling the fixing temperature at 70℃ and the fixing time at 2 minutes, and the green leaves are prepared for use.

[0038] (2) Place the above-mentioned blanched leaves in a kneading machine (RTY-6 type kneading machine, speed controlled at 40 rpm) and knead for 8 minutes to obtain kneaded leaves;

[0039] (3) Place the kneaded leaves in a sealed container, adjust the temperature to 35±2℃, increase the pressure to 7.5MPa, then fill the container with supercritical carbon dioxide twice the total mass of the kneaded leaves, let it stand for 15 minutes, then restore the normal pressure, expel the excess gas, then open the container and let it stand for 30 minutes to obtain carbon dioxide treated leaves.

[0040] (4) Spread out the carbon dioxide-treated leaves and control the thickness of the spread to 1-2 cm. Then place them on an ice water bath and let them stand for 2 hours. White crystals will appear on the surface. Remove them from the ice water bath and let them stand at room temperature for 2 hours to obtain pre-treated leaves for later use. Bake the pre-treated leaves at 70°C until the moisture content is ≤6%. Then cool them down to 50°C and adjust the atmosphere to carbon dioxide. Keep them warm and enhance the aroma for 30 minutes to obtain the finished berry tea.

[0041] Comparative Example 1:

[0042] Processing of strawberry tea leaves:

[0043] (1) After picking, the fresh tea leaves are spread out at room temperature for 3 hours, then microwaved to fix the green, controlling the fixing temperature at 70℃ and the fixing time at 2 minutes, and the green leaves are prepared for use.

[0044] Steps (2)-(5) are the same as in Example 1.

[0045] Comparative Example 2:

[0046] Processing of strawberry tea leaves:

[0047] The processing steps (1), (2), (4), and (5) are the same as in Example 1. The specific steps (3) are as follows:

[0048] (3) Place the kneaded leaves in a sealed container, adjust the temperature to 35±2℃, increase the pressure to 7.5MPa, then fill the container with supercritical carbon dioxide twice the total mass of the kneaded leaves, let it stand for 20 minutes, then restore the normal pressure, expel the excess gas, then open the container and let it stand for 30 minutes to obtain carbon dioxide treated leaves.

[0049] Comparative Example 3:

[0050] Processing of strawberry tea leaves:

[0051] The processing steps (1) and (2) are the same as in Example 1. The specific steps (3) are as follows:

[0052] (3) Place the kneaded leaves in a sealed container, adjust the temperature to 35±2℃, increase the pressure to 7.5MPa, then fill the container with supercritical carbon dioxide twice the total mass of the kneaded leaves, let it stand for 5 minutes, then restore the normal pressure, expel the excess gas, then open the container and let it stand for 30 minutes to obtain carbon dioxide treated leaves.

[0053] (4) Spread out the carbon dioxide-treated leaves and control the thickness of the spread to 1-2 cm. Then place them on an ice water bath and let them stand for 3 hours. If almost no white crystals are visible on the surface, then no further processing is required. That is, a short-term supercritical carbon dioxide treatment cannot fully extract the flavonoids from the berry tea.

[0054] Comparative Example 4:

[0055] Processing of strawberry tea leaves:

[0056] (1) After picking, the fresh tea leaves are pre-cooled and spread out at 3±1℃ for 3 hours, then microwaved to fix the green, controlling the fixing temperature at 70℃ and the fixing time at 2 minutes, and the green leaves are prepared for use.

[0057] (2) Place the above-mentioned blanched leaves in a kneading machine (RTY-6 type kneading machine, speed controlled at 40 rpm) and knead for 10 minutes to obtain kneaded leaves;

[0058] (3) Place the kneaded leaves in a fermentation tank, adjust the temperature to 30℃, and pile them up for 12 hours to obtain piled leaves;

[0059] (4) The above-mentioned fermented leaves are baked at 65°C until the moisture content is ≤6%, then cooled to 45°C and the atmosphere is adjusted to carbon dioxide. The leaves are kept warm and the aroma is enhanced for 35 minutes to obtain the finished berry tea.

[0060] Comparative Example 5:

[0061] Processing of strawberry tea leaves:

[0062] The processing steps (1), (2), and (3) are the same as in Example 1. The specific steps (4) and (5) are as follows:

[0063] (4) Spread out the carbon dioxide-treated leaves and let them stand at room temperature for 2.5 hours to obtain pretreated leaves for later use.

[0064] (5) The pretreated leaves were baked at 60°C until the moisture content was ≤6%, then cooled to 40°C and the atmosphere was adjusted to carbon dioxide. The leaves were kept warm and the aroma was enhanced for 40 minutes to obtain the finished berry tea.

[0065] Detection:

[0066] 1. The content of each component in the berry tea prepared in Examples 1-2, Comparative Examples 1-2, and Comparative Examples 4-5 was detected using the following specific methods:

[0067] (1) The determination of water extracts shall be carried out in accordance with GB / T 8305-2013 "Determination of Water Extracts of Tea";

[0068] (2) Soluble sugars were detected using the anthrone-sulfuric acid colorimetric method;

[0069] (3) The content of free amino acids was determined according to the method in GB / T 8314-2013 "Determination of Total Free Amino Acids in Tea";

[0070] (4) Dihydromyricetin (DMY) was determined by HPLC: (the samples of each group of mulberry tea were pulverized and extracted with methanol by ultrasonication) Welchrom C18 column (250 mm × 4.6 mm, 5 μm), flow rate 1 mL / min, column temperature 30℃, injection volume 10 μL, detection wavelength 292 nm. Mobile phase A was methanol-acetonitrile solution (95:5, V / V), mobile phase B was 0.2% phosphoric acid solution, gradient elution conditions: 0.01 min, 15% A, 85% B; 0.01–25 min, 60% A, 40% B; 25–27 min, 15% A, 85% B; 27–37 min, 15% A, 85% B.

[0071] The specific results are shown in Table 1 below:

[0072] Table 1

[0073]

[0074] As shown in the table above, the DMY content of the strawberry tea leaves obtained by conventional pile fermentation method in Comparative Example 4 was the lowest, while the content of effective components in the other groups was not significantly different.

[0075] 2. Brew each group of berry tea leaves at a mass ratio of 1:150 with hot water at 90℃, let stand for 10 minutes, separate the tea soup, cool to room temperature, detect the concentration of DMY in the tea soup, and further detect the color difference of the tea soup.

[0076] (1) The concentration of DMY in tea infusion was determined as follows: a Welchrom C18 column (250 mm × 4.6 mm, 5 μm) was selected, with methanol and 0.1% phosphoric acid aqueous solution as the mobile phase, a flow rate of 1.0 mL / min, and a detection wavelength of 290 nm; dihydromyricetin reference standard was accurately weighed, prepared into a standard solution, and injected for analysis. A standard curve was plotted with peak area as the ordinate and concentration as the abscissa (the chromatogram of the sample is shown in the figure). Figure 1 As shown in the figure, samples of each group of tea soup were taken for analysis, the peak area was recorded, and the concentration of dihydromyricetin in each tea soup was calculated by substituting it into the standard curve.

[0077] (2) Color difference detection of tea soup: Using Yibao purified water as a control, the L*, a*, and b* values ​​of the three tea soups were measured using an SMY-2000 colorimeter. The operation method is as described in the instrument manual. The larger the L* value, the brighter the color of the tea soup; the a* value indicates the degree of red and green of the tea soup, with a positive value for red and a negative value for green; the b* value indicates the degree of yellow and blue of the tea soup, with a positive value for yellow and a negative value for blue.

[0078] The specific test results are shown in Table 2 below:

[0079] Table 2

[0080]

[0081] As shown in the table above, the DMY concentration in the tea soup of Examples 1, 2 and Comparative Examples 1-2 was the highest after short-time brewing. The tea soup of Examples 1 and 2 was relatively clear and the color was yellow-green, which was refreshing. The tea soup of Comparative Example 1 was slightly less clear, while the tea soup of Comparative Examples 2, 4 and 5 was generally reddish.

[0082] 3. Sensory evaluation of each group of berry teas:

[0083] Each group of berry tea leaves was brewed with 90℃ hot water at a mass ratio of 1:150. Twenty sensory evaluators were selected to conduct sensory evaluations of the tea infusion after 5 minutes of brewing. Appearance (15 points), color (20 points), aroma (30 points), and taste (35 points) were selected as evaluation indicators. The specific sensory evaluation scoring criteria are shown in Table 3 below (the specific appearance of the tea infusion and tea leaf samples are as follows). Figure 3 (as shown)

[0084] Table 3

[0085]

[0086] The specific scoring results are shown in Table 4 below:

[0087] Table 4

[0088]

[0089] As shown in the table above, Examples 1 and 2 received the highest overall sensory evaluation.

[0090] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for processing strawberry tea using microwave combined with carbon dioxide, characterized in that, The method for processing berry tea includes the following steps: S1. Fresh leaf processing: After picking, the fresh tea leaves are pre-cooled and spread out at 2-4℃ for 2-4 hours, and then microwaved to fix the green leaves for later use. S2. Rolling treatment: Place the above-mentioned blanched leaves in a rolling machine for rolling treatment to obtain rolled leaves; S3. Carbon dioxide treatment: Place the kneaded leaves in a sealed container and keep them at 35±2℃. Increase the pressure to 7.5-8.5Mpa and fill them with supercritical carbon dioxide for 10-15 minutes. Then restore the pressure to normal and remove the excess gas. Then ventilate and let them stand at room temperature to obtain carbon dioxide treated leaves. S4. Rapid cooling crystallization treatment: The carbon dioxide treated leaves are placed in an ice-water bath for rapid cooling until crystals appear on the surface, and then restored to room temperature for static treatment to obtain pre-treated leaves; and the thickness of the carbon dioxide treated leaves is kept at 1-2 cm during the ice-water bath treatment, and the treatment time is ≤2h, and the subsequent room temperature static time is 1-2h. S5. Roasting and aroma enhancement: Roast the pretreated leaves at 60-70℃ until the moisture content is ≤6%, then cool down to 40-50℃ and adjust the atmosphere to carbon dioxide for heat preservation and aroma enhancement to obtain the finished berry tea.

2. The method for processing strawberry tea according to claim 1, characterized in that: In step S1, the microwave blanching temperature is 65-70℃, and the blanching time is 2-3 minutes.

3. The method for processing strawberry tea according to claim 1, characterized in that: The kneading time in step S2 is 8-12 minutes.

4. The method for processing wild tea according to claim 1, characterized in that: In step S3, the amount of supercritical carbon dioxide introduced is 2-3 times the total mass of the kneading leaves.

5. The method for processing berry tea according to claim 1, characterized in that: In step S3, the time for standing at room temperature is 30-40 minutes.

6. The method for processing strawberry tea according to claim 1, characterized in that: In step S5, baking is performed in a vacuum environment.

7. The method for processing strawberry tea according to claim 1, characterized in that: The aroma extraction process in step S5 takes 30-40 minutes.

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