Processing method and application of golden bud dark tea

Abstract

The invention discloses a processing method and application of golden bud dark green tea, and the method comprises the following steps: steaming golden bud green tea, cooling, inoculating a bacterial suspension on the surface of the cooled golden bud green tea, putting the inoculated golden bud tea in a constant-temperature and constant-humidity incubator for fermentation, and drying after fermentation to obtain the golden bud dark green tea. The fermentation time is controlled to be 21 days, the fermentation temperature is 28 DEG C, and the humidity is controlled in stages. The method disclosed by the invention breaks through the industry limitation of the prior art on the production of the golden bud dark tea, and not only can enable the golden bud dark tea to have good in-vitro and in-vivo lipid-lowering activity, but also can enable the golden bud dark tea to have unique fragrance and taste, flower fragrance, fruit fragrance, mushroom fragrance and fresh and soft astringent taste.

Description

Technical Field

[0001] The invention discloses a processing method and application of golden bud dark tea, and specifically relates to a method and application of synergistically improving the lipid-lowering activity of golden bud dark tea through staged humidity control and cooling process, and belongs to the technical field of dark tea processing. Background Art

[0002] Golden Bud ( Camellia sinensis cv. Huangjinya) is a unique albino tea cultivar known for its photosensitivity. Its leaves are bright yellow due to photosensitivity, and its amino acid content is significantly higher than that of traditional green tea varieties (such as Fuding Da Baicha), forming a unique fresh and refreshing taste. At present, the fresh leaves of Huangjinya tea are mainly processed into green tea through green tea technology, and a small number of them are processed into black tea through black tea technology, but there are no reports on its use in black tea production. Existing research mainly focuses on the effects of environmental factors such as light and temperature on the secondary metabolites of Huangjinya (such as flavonoids, chlorophyll, and carotenoids), while the exploration of its deep processing potential (especially black tea fermentation) is extremely limited.

[0003] Dark tea has attracted much attention due to its unique flavor and health benefits such as improving lipid metabolism disorders. Studies have shown that the metabolite spectrum of green tea changes significantly during the fermentation process into dark tea, and the accumulation of bioactive ingredients (such as flavonoid glycosides and theabrownin) can enhance the lipid-lowering function. However, the existing dark tea processing technology (such as the fermentation method of Eurotium coronatum disclosed in patent CN107502561B) has the following defects: (1) The cooling step is missing: the fungus is inoculated directly after steaming. The high temperature environment can easily damage the activity of the fungus, and the moisture distribution of the tea leaves is uneven, resulting in low fermentation efficiency. (2) Single humidity control: A fixed humidity (e.g., 70-80%) is used throughout the process, which makes it impossible to regulate the activity of key enzymes such as polyphenol oxidase and glycosidase, resulting in insufficient accumulation of active substances such as flavonoid glycosides; (3) Poor adaptability of raw materials: The amino acid content of traditional black tea raw materials is low (≤1%), while the amino acid content of golden bud tea is as high as 1.45%. The existing process fails to effectively utilize its high amino acid characteristics to convert it into lipid-lowering active ingredients (such as flavonoid glycoside-amino acid complexes), which limits the improvement of its functionality.

[0004] Therefore, based on the above-mentioned defects of the existing black tea processing technology, it is necessary to study and develop a new black tea processing method that can efficiently enhance the lipid-lowering effect of active substances in golden buds based on the high amino acid characteristics of golden bud tea. Summary of the invention

[0005] The present invention aims to solve the problems of insufficient accumulation of active substances in golden bud tea and limited lipid-lowering effect in the prior art, and provides a processing method and application of golden bud black tea, which breaks through the industry limitations of the prior art on the production of golden bud black tea, and can not only make the golden bud black tea have good in vitro and in vivo lipid-lowering activity, but also make the golden bud black tea have a unique aroma and taste, with floral, fruity and mushroom aromas, as well as fresh and soft astringency.

[0006] The present invention is achieved through the following technical scheme: a processing method of golden bud black tea, which comprises steaming golden bud green tea and then spreading it out to cool, then inoculating the surface of the cooled golden bud green tea with a bacterial suspension, then placing the inoculated golden bud green tea in a constant temperature and humidity incubator for fermentation, and controlling the fermentation time, temperature and humidity, and drying after the fermentation to obtain the golden bud black tea. The control conditions are as follows: a. Control the fermentation time to 21 days; b. Control the fermentation temperature to 28°C; c. Control humidity in stages: 1-4 days after fermentation, the humidity is 75-85%; 5-14 days after fermentation, the humidity is 65-75%; 15-18 days after fermentation, the humidity is 60-70%; 18-21 days after fermentation, the humidity is 40-50%.

[0007] The steaming step is to place the golden bud green tea in a container, cover it, and steam it at 95-105° C. for 20-40 minutes.

[0008] The air-drying cooling method is to evenly air-dry the steamed golden bud green tea in a basket, with an air-drying thickness of 1 to 3 cm, an air-drying temperature of 20 to 30° C., and an air-drying time of 1 to 3 hours.

[0009] The inoculation is to spray the suspension of Eurotium rubrum PW-1 evenly on the surface of the cooled golden bud green tea and stir evenly. Eurothumcristatum PW-1) was deposited in the China Center for Type Culture Collection, Wuhan University, China on June 21, 2017, with the deposit number CCTCC NO: M 2017355.

[0010] The inoculum size of the bacterial suspension was 10 4 ~10 6 CFU / g tea leaves.

[0011] The drying process is to place the fermented golden bud tea in an oven and dry it at 40-60° C. for 24-72 hours to obtain golden bud black tea with a final moisture content of ≤6%.

[0012] The present invention also provides the use of the above processing method in preparing golden bud dark tea with high lipid-lowering activity, wherein the content of theabrownin (TB) in the golden bud dark tea is ≥2.58%.

[0013] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The present invention realizes the reasonable control of process conditions such as fermentation time, temperature and humidity during the pile fermentation stage. By realizing staged humidity control under specific temperature control within a specific fermentation time, the fermentation process can be precisely controlled under humidity control at different stages, including promoting bacterial colonization, accelerating polyphenol oxidation, promoting flavonoid glycoside accumulation, inhibiting miscellaneous bacteria and stabilizing metabolites. This can improve the efficient conversion of active substances in golden bud tea and enhance the lipid-lowering effect of golden bud black tea.

[0014] (2) The present invention utilizes staged humidity control in coordination with the cooling process to optimize the microbial growth environment, inhibit bacterial contamination, and promote the accumulation of metabolites. Specifically, the present invention provides a low-microbial, high-activity colonization environment for the inoculated Eurotium cristatum by controlling the spreading parameters (thickness, temperature, time, and water content) during the cooling process, and then dynamically adjusts the environmental humidity during the fermentation process through staged humidity control, thereby guiding the metabolic direction of the strain and achieving precise control of the fermentation process.

[0015] (3) The method of the present invention is specifically aimed at the efficient conversion of lipid-lowering active ingredients in golden bud black tea. In the cooling stage, low temperature (20-30°C) is used to inhibit the proliferation of foreign bacteria. In the later stage (such as ultra-low humidity of 45% from the 18th to the 21st day), the humidity is controlled in stages to further inhibit the metabolism of foreign bacteria, thereby synergistically ensuring the dominant position of the target fungus (Ectopus cristatus).

[0016] (4) The method of the present invention can effectively retain the endogenous enzyme activity (such as β - glucosidase), and work together with staged humidity control to accelerate the oxidation of polyphenols to produce theabrownin, promote the synthesis of flavonoid glycosides, stabilize the structure of metabolites such as theabrownin, and keep the theabrownin content in the golden bud black tea stable at 2.58-2.66%.

[0017] It should be noted that the control of the thickness, temperature, time and moisture content of the tea leaves during the cooling process is particularly important. If the thickness is too thick (>3cm), the bottom layer of tea leaves will be cooled unevenly and water will be retained, which may easily lead to the growth of bacteria; if the thickness is too thin (<1cm), it may accelerate water loss and affect the colonization of bacteria. If the cooling temperature is too high, it may activate the metabolism of bacteria and increase the risk of contamination. If the temperature is too low, it will reduce the colonization efficiency of Eucommia cristatum. If the cooling time is too short (<1h), it will lead to insufficient cooling, and the enzyme activity inside the tea leaves will not be completely passivated, which may cause excessive oxidation. If the time is too long (>3h), it may lead to excessive water loss (less than 18%), which will inhibit the colonization of bacteria. If the moisture content is too low, the bacteria cannot effectively absorb nutrients and their metabolic activities are blocked. If the moisture content is too high, it will easily cause the tea leaves to mold and increase the risk of contamination by bacteria.

[0018] (5) Experiments have shown that the golden bud black tea produced by the processing method of the present invention has an inhibitory effect on pancreatic lipase activity and cholesterol esterase activity, and animal model experiments have shown that the golden bud black tea has good lipid-lowering activity in vivo.

[0019] (6) The processing method of the present invention can also retain the unique aroma and taste of the golden bud black tea, making it have floral, fruity, mushroom aroma, as well as fresh and soft astringency. DETAILED DESCRIPTION

[0020] The invention objectives, technical solutions and beneficial effects of the present invention are further described in detail below.

[0021] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the claimed invention, and unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs.

[0022] The present invention aims at the deficiencies of the prior art, breaks through the industry limitation that most of the golden bud tea is used for green tea, a small part is used for black tea, and there is no industry limitation of making black tea, and provides a novel golden bud black tea processing method. The processing method is proposed for the first time to address the problem that the active substances (such as theabrownin) in the golden buds are insufficiently accumulated during the process of making black tea, so that the lipid-lowering active ingredients cannot be efficiently converted. In this way, the golden bud black tea with unique aroma and taste and good lipid-lowering activity can be produced, so that the golden bud black tea has floral, fruity and mushroom aromas, fresh and soft astringency, as well as good in vitro and in vivo lipid-lowering activity.

[0023] The specific implementation modes of the present invention are described below in conjunction with the embodiments. Of course, the protection scope of the present invention is not limited to the following embodiments.

[0024] Example 1: Preparation of Golden Bud Dark Tea The specific operations for making golden bud dark tea in this embodiment are as follows: Steaming: After humidifying the golden bud green tea raw materials, place them in a container, cover them and steam them at 100℃ for 30 minutes.

[0025] Cooling: Spread the steamed golden bud green tea raw materials evenly in a basket with a thickness of about 2 cm, a temperature of 25°C, and a time of 2 hours.

[0026] Inoculation: PW-1 (CCTCC NO: M 2017355) was inoculated at a rate of 10 5 CFU / g tea leaves ratio to prepare bacterial suspension, directly spray the bacterial suspension evenly on the surface of steamed golden bud green tea, and stir evenly.

[0027] Pile fermentation: Place the inoculated golden bud tea in a constant temperature and humidity incubator set at 28°C for fermentation. The humidity is 80% for 1 to 4 days, 70% for 5 to 14 days, 65% for 15 to 18 days, and 45% for 18 to 21 days. The total fermentation time is 21 days.

[0028] Drying: Place the fermented samples in an oven and dry at 50°C for 48 hours.

[0029] Example 2: Preparation of Golden Bud Dark Tea The specific operations for making golden bud dark tea in this embodiment are as follows: Steaming: After humidifying the golden bud green tea raw materials, place them in a container, cover them and steam them at 95℃ for 20 minutes.

[0030] Cooling: Spread the steamed golden bud green tea raw materials evenly in a basket with a thickness of about 1 cm, a temperature of 20°C, and a time of 3 hours.

[0031] Inoculation: PW-1 (CCTCC NO: M 2017355) was inoculated at a rate of 10 4 CFU / g tea leaves ratio to prepare bacterial suspension, directly spray the bacterial suspension evenly on the surface of steamed golden bud green tea, and stir evenly.

[0032] Pile fermentation: Place the inoculated golden bud tea in a constant temperature and humidity incubator set at 28°C for fermentation. The humidity is 75% for 1 to 4 days, 65% for 5 to 14 days, 70% for 15 to 18 days, and 50% for 18 to 21 days, with a total fermentation period of 21 days.

[0033] Drying: Place the fermented samples in an oven and dry at 60°C for 24 hours.

[0034] Example 3: Preparation of Golden Bud Dark Tea The specific operations for making golden bud dark tea in this embodiment are as follows: Steaming: After humidifying the golden bud green tea raw materials, place them in a container, cover them and steam them at 105℃ for 35 minutes.

[0035] Cooling: Spread the steamed golden bud green tea raw materials evenly in a basket with a thickness of about 3 cm, a temperature of 25°C, and a time of 2 hours.

[0036] Inoculation: Inoculate 10 6 CFU / g tea leaves ratio to prepare bacterial suspension, directly spray the bacterial suspension evenly on the surface of steamed golden bud green tea, and stir evenly.

[0037] Pile fermentation: Place the inoculated golden bud tea in a constant temperature and humidity incubator set at 28°C for fermentation. The humidity is 85% for 1 to 4 days, 70% for 5 to 14 days, 65% for 15 to 18 days, and 40% for 18 to 21 days. The total fermentation time is 21 days.

[0038] (4) Drying: Place the fermented sample in an oven and dry it at 40°C for 72 hours.

[0039] Example 4: Preparation of Golden Bud Dark Tea The specific operations for making golden bud dark tea in this embodiment are as follows: Steaming: After humidifying the golden bud green tea raw materials, place them in a container, cover them and steam them at 100℃ for 40 minutes.

[0040] Inoculation: PW-1 (CCTCC NO: M 2017355) was inoculated at a rate of 10 5 CFU / g tea leaves ratio to prepare bacterial suspension, directly spray the bacterial suspension evenly on the surface of steamed golden bud green tea, and stir evenly.

[0041] Pile fermentation: Place the inoculated golden bud tea in a constant temperature and humidity incubator set at 28°C for fermentation. The humidity is 80% for 1 to 4 days, 75% for 5 to 14 days, 60% for 15 to 18 days, and 45% for 18 to 21 days. The total fermentation time is 21 days.

[0042] (4) Drying: Place the fermented sample in an oven and dry it at 55°C for 36 hours.

[0043] Comparative Example 1: The difference between this comparative example and Example 1 is that when making the golden bud black tea, the steamed golden bud green tea is not cooled, but the steamed golden bud green tea is directly inoculated, and the remaining operations (such as steaming, inoculation, pile fermentation and drying) and parameter conditions are the same as those in Example 1.

[0044] Comparative Example 2: The difference between this comparative example and Example 1 is that when making the golden bud black tea, the inoculated golden bud tea is not subjected to pile fermentation, but is directly dried, and the remaining operations (such as steaming, cooling, inoculation and drying) and parameter conditions are the same as those in Example 1.

[0045] Comparative Example 3: The difference between this comparative example and Example 1 is that the pile fermentation operation used in making the golden bud dark tea is different, and the other operations (such as steaming, cooling, inoculation and drying) and parameter conditions are the same as those in Example 1.

[0046] In this comparative example, during the pile fermentation, the inoculated golden bud tea was placed in a constant temperature and humidity incubator set at 28° C. for fermentation, and the humidity was controlled at 70%, and the fermentation lasted for a total of 21 days.

[0047] Comparative Example 4: The difference between this comparative example and Example 1 is that the pile fermentation operation used in making the golden bud dark tea is different, and the other operations (such as steaming, cooling, inoculation and drying) and parameter conditions are the same as those in Example 1.

[0048] In this comparative example, during the pile fermentation, the inoculated golden bud tea was placed in a constant temperature and humidity incubator set at 28°C for fermentation, the humidity was 80% from 1 to 10 days, and 70% from 11 to 21 days, and the fermentation lasted for a total of 21 days.

[0049] Comparative Example 5: The difference between this comparative example and Example 1 is that the pile fermentation operation used in making the golden bud dark tea is different, and the other operations (such as steaming, cooling, inoculation and drying) and parameter conditions are the same as those in Example 1.

[0050] In this comparative example, during the pile fermentation, the inoculated golden bud tea was placed in a constant temperature and humidity incubator set at 28°C for fermentation, the humidity was 80% for 1 to 4 days, 75% for 5 to 7 days, 70% for 8 to 14 days, 65% for 15 to 18 days, and 45% for 19 to 21 days, and the fermentation lasted for a total of 21 days.

[0051] The following tests were conducted on the golden bud dark tea prepared in Examples 1 to 4 and Comparative Examples 1 to 5, respectively.

[0052] 1. Detection of lipid-lowering active ingredients Theabrownin (TB) is the main lipid-lowering active ingredient in dark tea. The hydroxyl and carboxyl functional groups in its molecular structure can exert lipid-lowering effects through multiple mechanisms such as directly inhibiting the activity of pancreatic lipase and cholesterol esterase, combining with bile acid to reduce cholesterol absorption, activating the AMPK pathway to promote fat decomposition and inhibit cholesterol synthesis. The present invention takes the golden bud dark tea of ​​Examples 1 to 4 and Comparative Examples 1 to 5, and determines the content of theabrownin, the main lipid-lowering active ingredient, in dark tea samples with different processing techniques. The experimental method is as follows: First, weigh 3.0 g of tea powder in a conical flask, add 125 mL of boiling water, extract in a boiling water bath for 30 min, filter while hot, collect the filtrate and cool it to room temperature, measure 25 mL of the filtrate, add an equal volume of n-butanol in a separatory funnel and shake for 3 min to stand and separate, take 2 mL of the water layer, add 2 mL of saturated oxalic acid solution and 6 mL of ultrapure water in a volumetric flask, and dilute to 25 mL with 95% ethanol to obtain solution A. Next, use 95% ethanol as a blank control, measure the absorbance EA of solution A at 380 nm, and calculate the content of theabrownin according to the following formula, where m is the water content of the tea leaves: The test results are shown in Table 1 below: Table 1 Comparison of theabrownin content in Examples 1-4 and Comparative Examples 1-5 Comparing the theabrownin content in the golden bud black tea prepared by Examples 1-4 and Comparative Examples 1-5 (Table 1), it can be seen that the method of the present invention is significantly better than Comparative Examples 1 to 4. Among them, the theabrownin content of Example 1 (four-stage humidity control) is the highest, followed by Examples 2 to 4, but the difference is not significant, and the lowest is Comparative Example 2 (no pile fermentation), and Comparative Example 1 (no cooling) and Comparative Example 3 (no staged humidity) are in the middle, which shows that the four-stage humidity control described in the method of the present invention can significantly improve the synthesis of theabrownin by promoting microbial metabolism in stages; while the lack of cooling step (Comparative Example 1) or no staged control (Comparative Example 3) leads to reduced fermentation efficiency and insufficient accumulation of theabrownin. The results of Comparative Example 5 (five-stage humidity control) and Example 1 (four-stage humidity control) are slightly different, indicating that excessive subdivision of stages does not bring additional advantages to the method of the present invention.

[0053] 2. Inhibition of pancreatic lipase activity Pancreatic lipase is essential for lipid metabolism. Inhibiting the activity of pancreatic lipase can effectively reduce fat absorption and energy intake. The present invention prepares solutions of golden bud dark tea of ​​Example 1 and Comparative Examples 1 to 5, and measures the inhibitory activity of dark tea samples with different processing techniques on pancreatic lipase. The experimental method is as follows: Solution preparation: Weigh 50 mg of pancreatic lipase and dissolve it in 20 mL of ultrapure water, centrifuge (10000×g, 5 min, 20°C), and take the supernatant to obtain a pancreatic lipase solution; use 0.1 M Tris-HCl solution to prepare different groups of golden bud black tea solutions obtained in Example 1 and Comparative Examples 1 to 5 with a concentration of 400 μg / mL, and orlistat solutions of corresponding concentrations; use acetonitrile to prepare 10 mM p-nitrophenyl palmitate solution.

[0054] 150 μL pancreatic lipase solution was taken, and 600 μL sample solutions of different groups were added, with orlistat solution and 0.1 M Tris-HCl solution as positive control and blank control, respectively. After reacting at 37 °C for 15 min, 25 μL p-nitrophenyl palmitate solution was added, and the volume was made up to 1 mL with 0.1 M Tris-HCl solution. After reacting at 37 °C for 30 min, the enzyme was inactivated in an ice water bath, and the absorbance was measured at 405 nm. The calculation formula of pancreatic lipase activity inhibition rate is as follows: Among them A max is the absorbance of the blank control group, A S is the absorbance of the sample group or positive control group, A S0 It is the absorbance of the sample or positive control group in which the pancreatic lipase solution is replaced by 0.1 M Tris-HCl solution.

[0055] The experimental results are shown in Table 2 below: Table 2 Comparison of pancreatic lipase inhibition rates of Example 1 and Comparative Examples 1-5 Comparing the inhibition rate of pancreatic lipase by the golden bud black tea prepared in Example 1 and Comparative Examples 1-5 (Table 2), it can be seen that the method of the present invention is significantly better than Comparative Examples 1 to 4. Among them, the golden bud black tea prepared in Example 1 (four-stage humidity control) has the highest inhibition rate of pancreatic lipase (58%), which is significantly better than Comparative Examples 1 and 2, and better than Comparative Examples 3-5. Since the staged humidity control promotes the formation of theabrownin (TB) (1.70-2.66%), the hydroxyl and carboxyl groups in its structure directly bind to the enzyme active site to block lipid hydrolysis. Comparative Example 1 (uncooled) has a low colonization efficiency of the strain, with a TB content of only 1.70%, and the inhibition rate drops to 50%; Comparative Example 3 (unstaged humidity) has an inhibition rate of 55% due to uneven fermentation. Comparative Example 5 (five-stage humidity control) is not significantly different from Example 1 (four-stage humidity control), indicating that the over-segmentation stage does not further enhance the enzyme inhibition effect.

[0056] 3. Inhibition of cholesterol esterase activity Cholesterol esterase is crucial to lipid metabolism. Inhibiting the activity of cholesterol esterase can reduce cholesterol absorption and lower plasma cholesterol levels. The present invention prepares solutions from the golden bud dark tea of ​​Example 1 and Comparative Examples 1 to 5, and measures the inhibitory activity of dark tea samples with different processing techniques on cholesterol esterase. The experimental method is as follows: Method: NaCl was dissolved in 0.1 M PBS solution to a final concentration of 0.1 M to obtain a buffer solution; a 24 mM sodium taurocholate solution, different groups of golden bud dark tea solutions obtained in Example 1 and Comparative Examples 1 to 5 with a concentration of 400 μg / mL were prepared using the buffer solution, and simvastatin solutions of corresponding concentrations were prepared using acetonitrile to prepare an 8 mM 4-nitrophenylbutyrate solution; cholesterol was dissolved in 0.1 M PBS according to the instructions.

[0057] 400 μL of sample solutions from different groups were pipetted into EP tubes, with simvastatin solution and buffer as positive control and blank control, respectively. 200 μL of sodium taurocholate solution and 40 μL of 4-nitrophenylbutyrate solution were added in sequence, mixed and reacted at 25 °C for 10 min, then 160 μL of cholesterol esterase solution was added, mixed, reacted at 25 °C for 5 min, and the absorbance was measured at 405 nm. The inhibition rate of cholesterol esterase activity was calculated as follows: Among them A max is the absorbance of the blank control group, A S is the absorbance of the sample group or positive control group, A S0 It is the absorbance of the sample or positive control group in which the cholesterol esterase solution is replaced by 0.1 M PBS solution.

[0058] The experimental results are shown in Table 3 below: Table 3 Comparison of cholesterol esterase inhibition rates between Example 1 and Comparative Examples 1-5 Comparing the inhibition rate of cholesterol esterase of the golden bud black tea prepared in Example 1 and Comparative Examples 1-5 (Table 3), it can be seen that the method of the present invention is significantly better than Comparative Examples 1 to Comparative Examples 4. Among them, the golden bud black tea prepared in Example 1 (four-stage humidity control) has the best inhibition rate (78%) for cholesterol esterase, which mainly depends on the binding ability of TB and bile acid to reduce the formation of cholesterol micelles. Comparative Example 2 (no pile fermentation) has the lowest inhibition rate due to almost lack of TB, but because its raw material is green tea, green tea itself has a certain lipid-lowering effect, so the inhibition rate of cholesterol esterase is still 62%; Comparative Example 3 (no stage humidity) has an inhibition rate of 72% due to insufficient TB generation. The cooling process (Experimental Example 1) ensures that the crown-like cysticercus metabolizes to produce highly active TB by controlling the moisture content of the air-drying (20-22%), while the inhibition rate of the uncooled group (Comparative Example 1) is only 68% due to the unstable structure of the metabolite. The effects of Comparative Example 5 (five-stage humidity control) and Example 1 (four-stage humidity control) are comparable, and the difference is not significant, indicating that the four-stage humidity control adopted by the method of the present invention has reached the optimal balance.

[0059] 4. Sensory evaluation test The golden bud dark tea prepared in the above-mentioned embodiment 1 and comparative examples 1 to 5 were respectively subjected to sensory evaluation to test the intensity of their flavor attributes. The test method is as follows: Before the sensory evaluation test, 3.0 grams of tea sample was brewed with 150 ml of freshly boiled ultrapure water and steeped at room temperature for 4 minutes. Subsequently, the filtered tea soup was cooled to room temperature and used for analysis. A total of 14 professionally trained sensory assessors (including 5 men and 9 women, aged between 20 and 35 years old) were invited to score the tea soup using a 10-point scoring standard (where 0 points indicate no or almost imperceptible intensity, 3 points indicate weak intensity, 5 points indicate medium intensity, 7 points indicate high intensity, and 10 points indicate extremely high intensity). The taste attributes in the study include umami, sweetness, bitterness, astringency, bitter aftertaste, and astringent aftertaste.

[0060] The test results are shown in Table 4 below.

[0061] Table 4 Comparison of sensory scores of taste attributes of Example 1 and Comparative Examples 1-5 Comparing the sensory scores of the golden bud black tea prepared in Example 1 and Comparative Examples 1-5 (Table 4), it can be seen that the method of the present invention is significantly better than Comparative Examples 1 to 4. Among them, the umami and sweetness scores of Example 1 (four-stage humidity control) are higher than those of other groups, and the bitterness, astringency and aftertaste are the weakest. The cooling process (Example 1) avoids excessive oxidation of tea leaves by controlling the thickness and temperature of the drying, and retains umami substances such as amino acids; the staged humidity control balances the oxidation of polyphenols and the synthesis of flavonoid glycosides, and reduces the accumulation of bitter substances. Comparative Example 3 (not divided into stages) has an unbalanced taste due to excessively high or low humidity, and the bitterness and astringency are prominent. There is no obvious difference in the sensory between Comparative Example 5 (five-stage humidity control) and Example 1 (four-stage humidity control), indicating that the more humidity control stages are divided, the better.

[0062] (V) In vivo lipid-lowering activity test in zebrafish The golden bud dark tea prepared in Example 1, Comparative Example 1 and Comparative Example 3 were respectively taken to test their lipid-lowering activity using a high-fat zebrafish model, and the test method was as follows: The zebrafish hyperlipidemia model was constructed by treating 5-day-old zebrafish larvae with 0.1% (m / v) egg yolk powder for 48 h. At the same time, the egg yolk powder was replaced with fresh fish water as a blank control. The zebrafish with hyperlipidemia model were fed with simvastatin, 0.1% DMSO, and 125 μg / mL of the golden bud black tea sample obtained in Example 1, Comparative Example 1 and Comparative Example 3 for 48 h. The zebrafish larvae in different treatment groups were collected, washed with PBS, and fixed with 4% paraformaldehyde solution in a 4 ℃ refrigerator overnight. After the zebrafish was fixed, it was washed three times with PBS to remove the fixative, and then immersed in 60% (v / v) isopropanol solution for 30 min dehydration. After the dehydration, it was stained with a freshly prepared 0.3% (m / v) Oil Red O solution for 3 h. After the staining was completed, 60% isopropanol solution was used to wash away the floating color for microscopic observation and photography. The optical density of the stained zebrafish was measured by Image-ProPlus software (IPP software), and the optical density value was used to represent the lipid level in the zebrafish.

[0063] The test results are shown in Table 5 below.

[0064] Table 5 Comparison of lipid accumulation content in vivo between Example 1 and Comparative Examples 1 and 3 As can be seen from Table 5 above, in the lipid-lowering activity experiment in zebrafish, Example 1 (four-stage humidity control) has the best lipid-lowering effect, with a lipid accumulation rate of only 21%, which is significantly lower than Comparative Example 1 (no cooling, 34%) and Comparative Example 3 (no staged humidity control, 29%). This difference is due to the synergistic effect of the staged humidity control and cooling process in Example 1. Specifically, Example 1 promotes the directional accumulation of theabrownin (2.66%) through precise staged humidity control (80%→70%→65%→45%), while the cooling process retains the bioavailability of the active ingredient. The lack of cooling in Comparative Example 1 leads to a decrease in the colonization efficiency of the strain (water content <18%), insufficient metabolite production, and a theabrownin content of only 1.70%. The lack of staged humidity control (fixed humidity) in Comparative Example 3 leads to an imbalance in the fermentation process, which may lead to excessive oxidation of polyphenols and obstruction of flavonoid glycoside synthesis, and a reduction in the total amount of active ingredients. The experimental results verify the synergistic necessity of the staged humidity control and cooling process involved in the method of the present invention for improving the lipid-lowering activity of dark tea.

[0065] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for processing golden bud dark tea, characterized in that: The golden bud green tea is steamed and then spread out to cool, and then the bacterial suspension is inoculated on the surface of the cooled golden bud green tea. The inoculated golden bud tea is then placed in a constant temperature and humidity incubator for fermentation, and the fermentation time, temperature and humidity are controlled. After the fermentation is completed, the tea is dried to obtain the golden bud black tea. The control conditions are as follows: a. Control the fermentation time to 21 days; b. Control the fermentation temperature to 28°C; c. Control humidity in stages: 1-4 days after fermentation, the humidity is 75-85%; 5-14 days after fermentation, the humidity is 65-75%; 15-18 days after fermentation, the humidity is 60-70%; 18-21 days after fermentation, the humidity is 40-50%.

2. The processing method according to claim 1, characterized in that: The steaming step is to place the golden bud green tea in a container, cover it and steam it at 95-105° C. for 20-40 minutes.

3. The processing method according to claim 1, characterized in that: The air-drying cooling method is to evenly air-dry the steamed golden bud green tea in a basket, with an air-drying thickness of 1 to 3 cm, an air-drying temperature of 20 to 30° C., and an air-drying time of 1 to 3 hours.

4. The processing method according to claim 1, characterized in that: The inoculation is to spray the bacterial suspension of Eurotium cristatum PW-1 evenly on the surface of the cooled golden bud green tea, and stir it evenly.

5. The processing method according to claim 4, characterized in that: The inoculum size of the bacterial suspension was 10 4 ~10 6 CFU / g tea leaves.

6. The processing method according to claim 1, characterized in that: The drying process is to place the fermented golden bud tea in an oven and dry it at 40-60° C. for 24-72 hours to obtain golden bud black tea with a final moisture content of ≤6%.

7. The use of the processing method according to any one of claims 1 to 6 in preparing golden bud dark tea with high lipid-lowering activity, characterized in that: The content of theabrownin in the golden bud dark tea is ≥2.58%.

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