Brewing process and quality evaluation method of high-quality tea soup

Abstract

The invention relates to a brewing process and a quality evaluation method of high-quality tea soup. The method comprises the following steps: weighing 1g of tea, preheating ultrapure water at different temperatures, brewing the tea soup in a water bath kettle at the same temperature according to a tea-water ratio of 1: 50 at different time intervals, immediately filtering and separating the tea soup from the tea leaves after the time is up, and respectively collecting the tea soup to be detected. Chemical compositions of the selenium-rich black tea, the selenium-rich green tea, the common black tea and the common green tea are compared, and leaching rules and sensory evaluation of quality components in the selenium-rich black tea and the selenium-rich green tea under different brewing conditions are explored. By establishing a daily tea drinking model, the antioxidant activity, the hypoglycemic activity and the antibacterial activity of tea soup before and after digestion are determined. Compared with the prior art, the method for evaluating the quality of different tea leaves is established, the brewing process of high-quality tea soup is optimized on the basis of the quality component leaching amount, sensory evaluation and biological activity, and guidance is provided for consumers in the aspect of selecting the optimal tea brewing conditions with flavor and nutritional characteristics.

Description

Technical Field

[0001] The invention relates to the technical field of tea application, and in particular to a brewing process and a quality evaluation method for high-quality tea soup. Background Art

[0002] The biological activity of tea lies in its rich active compound ingredients, which not only bring a rich taste to tea soup, but also give tea a variety of potential health benefits to the human body, most of which are water-soluble organic matter. Taking tea polyphenols and catechins as examples, they have significant hypoglycemic and hypotensive activities, which help maintain the metabolic balance of the human body. Flavonoids and theanine in tea are natural antioxidants that can effectively delay the aging process and enhance immunity. Tea can also reduce the incidence of neurological diseases and prevent different types of cancer, metabolic syndrome, cardiovascular disease and other diseases. Due to different varieties, origins and processing methods, the content of flavor substances in different types of tea varies. In general, the flavor components in tea soup mainly include bitter polyphenol compounds and caffeine, umami amino acids, soluble sugars and pectin. The taste of tea soup is the coordination of multiple substances, so it is very necessary to study the dissolution rules of flavor substances in tea under different conditions to provide a theoretical basis for deep processing of tea or daily drinking of tea. Previous studies have found that as the ratio of tea to water, brewing time, and temperature increase, the content of dissolved tea polyphenols, amino acids, caffeine, total sugar, theaflavins, theabrownins, and thearubigins increases, and the taste of the tea soup becomes more distinct and richer in taste.

[0003] China's tea drinking habits have a long history and are rich and diverse. Influenced by factors such as geographical environment, historical culture, and ethnic customs, different tea drinking customs have been formed in various places. Slow tea drinking is more popular in South China, such as the morning tea culture in Guangdong, and Kung Fu tea is popular in Chaozhou and Shantou, Guangdong. The integration of tea and food is more common among China's ethnic minorities, such as Tibetan butter tea and Mongolian salty milk tea. In mountainous areas, it is common to use tea as medicine, such as the Tujia people in Hunan, Hubei, Guizhou and Sichuan drinking lei cha. Lei cha is to put tea leaves and ingredients into a mortar and grind them finely, and then pour boiling water to brew. In addition, there are preferences and specific customs in the choice of tea in different regions. For example, Beijing drinks more scented tea, Shanghai consumes more green tea, Fujian and Guangdong are popular in Oolong tea, and Pu'er tea is the main drink in the southwest. This way of drinking tea emphasizes brewing tea directly with boiling water without adding any condiments to experience the true color and aroma of tea. In summary, the study of the impact of different tea drinking methods on the dissolution law of tea components should fully consider the tea drinking habits of consumers in various regions. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems and provide a high-quality tea brewing process and quality evaluation method, which determines the tea ingredients based on the national standard method, fits and calculates the dissolution rate and dissolution time of the tea ingredients, simulates daily tea drinking, etc., to provide data for understanding the dissolution rules of various ingredients in the tea brewing process, and provide a scientific basis for the reasonable selection of tea brewing conditions based on high biological activity.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] The purpose of the present invention is to provide a brewing process and quality evaluation method for high-quality tea soup, the method comprising the following steps:

[0007] S1. Pre-treating tea leaves of different years and varieties to obtain pre-treated tea leaves;

[0008] S2. Determine the chemical content of the pretreated tea leaves and conduct significance analysis to verify the stability of different varieties of tea leaves in different years;

[0009] S3, brewing tea soup, and preparing tea soup samples obtained under different temperature and time conditions;

[0010] S4. Calculate the dissolution rate of tea soup samples obtained under different temperature and time conditions. By logarithmic fitting, with time as the independent variable and component content dissolution rate as the dependent variable, obtain the dissolution rate fitting curve of tea soup samples under different temperature conditions, obtain the dissolution concentration change of tea soup samples under different temperature and time conditions, and calculate the half dissolution time t of the components in the tea soup samples under different conditions. 50 and complete dissolution time t 100 ;

[0011] S5. Use sensory evaluation to score the taste, color, and aroma of tea soup at different temperatures and time conditions, and build a tea soup sensory evaluation database;

[0012] S6, combining the dissolution rate fitting curve of the tea soup sample under different temperature conditions obtained in step S4 and the tea soup sensory evaluation database obtained in step S5, establishing a daily tea drinking model;

[0013] S7. The bioavailability of the daily tea drinking model is verified by determining the in vitro hypoglycemic activity, antioxidant activity and in vitro antibacterial activity through in vitro simulated digestion experiments.

[0014] Furthermore, step S1 specifically includes the following process: placing the tea leaves to be tested in a grinder and grinding them for 30 seconds, adding a little tea leaves, stirring evenly, grinding them for a second time for about 60 seconds, filtering with a 200-mesh nylon cloth, obtaining the pretreated tea leaves under dry conditions, storing them in a sealed bag, marking them, and storing them in a 4°C refrigerator for a short period of time for use in subsequent content determination experiments.

[0015] Furthermore, in step S2, the determination of the chemical substance content in the pretreated tea leaves includes one or more of the following determinations: determination of tea polyphenols in tea leaves, determination of the total soluble sugar content in tea leaves, determination of the total amount of free amino acids in tea leaves, determination of catechins in tea leaves, determination of theanine and γ-aminobutyric acid in tea leaves, determination of soluble protein content in tea leaves, determination of total selenium content in tea leaves, determination of chlorophyll content in tea leaves, determination of tea pigment content in tea leaves, and determination of total flavonoids in tea leaves.

[0016] Further, step S3 includes the following process: weighing 1g of tea leaves, preheating ultrapure water at different temperatures, adding 50mL of water at a tea-to-water ratio of 1:50, and brewing tea soup in a water bath at the same temperature at different time intervals, filtering immediately after the time is up to separate the tea soup and the tea leaves, and collecting the tea soup for testing; the different temperatures include the following temperature conditions: 65°C, 75°C, 85°C, 100°C; the different time intervals include the following time intervals: 1min, 3min, 5min, 7min, 9min, 15min, 30min, 40min.

[0017] Furthermore, the tea leaves are selected from one or more of selenium-enriched black tea, ordinary black tea, selenium-enriched baked green tea, and ordinary baked green tea. The year of the tea leaves is selected from one or more of 2021, 2022, and 2023.

[0018] Furthermore, in step S4, the dissolution rate of tea components measured under the conditions of 100° C. and 40 min is defined as 100%, thereby calculating the dissolution rates of tea soup samples obtained under different temperature and time conditions.

[0019] Furthermore, in step S6, a daily tea drinking model is established by combining the dissolution rate fitting curve of the tea samples under different temperature conditions obtained in step S4 and the tea sensory evaluation database obtained in step S5, and the following conditions are selected as the daily tea drinking model: water temperature 100 degrees (Celsius), tea-to-water ratio 1:50, 50 mL of water is added to each type of tea, and a total of four cups of tea are brewed. The brewing time of the first, second, and third cups of tea is designed to be 5 minutes, the fourth cup of tea is regarded as the last brew, and the brewing time is designed to be 1 hour.

[0020] Furthermore, in step S7, the in vitro simulated digestion experiment includes one or more of a simulated saliva experiment, a simulated gastric juice experiment, and a simulated intestinal juice experiment. In step S7, the determination of in vitro hypoglycemic activity includes one or more of determining α-glucosidase inhibition rate activity and determining α-amylase inhibition rate activity. In step S7, the determination of antioxidant activity includes one or more of determining DPPH clearance rate and conducting ABTS free radical scavenging experiment.

[0021] Furthermore, the national standard method is used to determine tea ingredients, fit and calculate the dissolution rate and dissolution time of tea ingredients, and simulate daily tea drinking, so as to provide data for people to understand the dissolution rules of various ingredients in the tea brewing process, and provide a scientific basis for the reasonable selection of tea brewing conditions based on high biological activity. The main contents are as follows:

[0022] (1) In order to summarize the quality component correlation of (selenium-enriched) roasted green tea and (selenium-enriched) black tea of ​​twelve different years, the basic tea components and the content of tea characteristic quality components of ordinary roasted green tea, selenium-enriched roasted green tea, ordinary black tea and selenium-enriched black tea of ​​three years were systematically tested using the national standard method, including tea polyphenols, soluble sugars, protein, total free amino acids, theanine, catechins, total flavonoids, chlorophyll, tea pigments, selenium content, etc. By studying the impact of different years on tea quality components and conducting significance analysis, the stability of tea quality between different years was verified.

[0023] (2) In order to study the effects of different brewing conditions such as time and temperature on the dissolution process of selenium-enriched roasted green tea and selenium-enriched black tea and the dissolution characteristics of various components, the theoretical half-dissolution time t was calculated by linear fitting and 50 , complete dissolution time t 100 , and obtain the most suitable brewing conditions, and combine them with sensory evaluation to give a comprehensive score, providing a theoretical basis and data support for the follow-up.

[0024] (3) According to the consumer's living habits, national standard methods, and previous experimental conclusions, a simulated daily tea drinking model was constructed. The first, second, third, and last tea soups (all brewed for 5 minutes) were prepared at 100°C, and digested in vitro to determine the in vitro hypoglycemic activity, antioxidant activity, and antibacterial activity. The bioavailability of the daily tea drinking model was verified and maximized under appropriate conditions. By conducting an in vitro simulated digestion experiment on tea leaves, determining the in vitro free radical scavenging activity of tea soup, the inhibition rate of tea soup on sugar metabolism-related enzymes, and the antibacterial experiment of tea soup, the antioxidant activity, in vitro hypoglycemic activity, and antibacterial activity of tea soup were determined, thereby screening the possible biological activities of tea soup, providing a reference for subsequent in-depth research on the digestion and absorption of tea soup in the human body and the related mechanisms of biological activity.

[0025] Furthermore, the present invention relates to a brewing process and quality evaluation method for high-quality tea soup. 1g of tea leaves are weighed, ultrapure water of different temperatures (65℃, 75℃, 85℃, 100℃) is preheated, 50mL of water is added to each tea leaf at a tea-water ratio of 1:50, and the tea soup is brewed in a water bath at the same temperature at time intervals of 1, 3, 5, 7, 9, 15, 30, and 40min. After the time is up, the tea soup is immediately filtered to separate the tea soup from the tea leaves, and the tea soup is collected for testing. The chemical composition of selenium-enriched black tea (SeBT), selenium-enriched green tea (SeGT), ordinary black tea (BT) and ordinary green tea (GT) is compared, and the leaching rules and sensory evaluation of the quality components in SeGT and SeBT under different brewing conditions are further explored. By establishing a daily tea drinking model, the antioxidant activity, hypoglycemic activity and antibacterial activity of tea soup before and after digestion are determined. On the whole, brewing at 100℃ for 5 minutes can effectively extract the quality components of tea leaves, while brewing at 85℃ for 5 minutes can reduce the bitterness of tea soup.

[0026] Compared with the prior art, the beneficial effects of the present invention are embodied in the following aspects:

[0027] 1) The present invention proposes a high-quality tea brewing process and quality evaluation method, which determines tea ingredients based on the national standard method, fits and calculates the dissolution rate and dissolution time of tea ingredients, simulates daily tea drinking, etc., to provide data for people to understand the dissolution rules of various ingredients in the tea brewing process, and provides a scientific basis for the reasonable selection of tea brewing conditions based on high biological activity.

[0028] 2) The present invention proposes a brewing process and quality evaluation method for high-quality tea soup, establishes a quality evaluation method for different teas, optimizes the brewing process of high-quality tea soup based on the extraction amount of quality components, sensory evaluation and biological activity, and provides guidance for selecting the best brewing conditions for tea with both flavor and nutritional properties.

[0029] 3) The invention provides a method for brewing high-quality tea soup and evaluating its quality, which provides technical support for the brewing process and quality evaluation of high-quality tea soup, has the advantages of data quantification, objective results, and high judgment accuracy, and can be applied to selecting the best brewing conditions for tea with both flavor and nutritional characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1Schematic diagram of the contents of chemical components in tea leaves in the embodiments of the present invention, including soluble sugar (A); total flavonoids (B); water (C); soluble protein (D); tea polyphenols (E); catechins and caffeine in green tea (F); catechins and caffeine in black tea (G); tea pigments in green tea (H); tea pigments in black tea (I); chlorophyll a and chlorophyll b in green tea (J) and chlorophyll a and chlorophyll b in black tea (K); selenium (L); total free amino acids (M) (* indicates significant differences compared with other groups, *, p<0.05; **, p<0.01; ***, p<0.001).

[0031] Figure 2 The figures show the effects of different temperatures and times on the dissolution patterns of tea polyphenols (A), flavonoids (B), soluble sugars (C), free amino acids (D), caffeine (E) and L-theanine (F) in the tea soup of selenium-enriched green tea (SeGT) in the embodiments of the present invention; the effects of different temperatures and times on the dissolution patterns of tea polyphenols (G), flavonoids (H), soluble sugars (I), free amino acids (J), caffeine (K) and L-theanine (L) in the tea soup of selenium-enriched black tea (SeBT).

[0032] Figure 3 It is a sensory evaluation radar chart of selenium-enriched green tea (A) and selenium-enriched black tea (B) in the embodiments of the present invention; the appearance of selenium-enriched green tea soup (C) and selenium-enriched black tea soup (D) at different brewing temperatures and times.

[0033] Figure 4 The DPPH free radical scavenging rate (A) and ABTS free radical scavenging rate (B) of the tea soups with different brewing times before and after digestion in the embodiments of the present invention; the α-glucosidase inhibition rate (C) and α-amylase inhibition rate (D) of the tea soups with different brewing times before and after digestion (Note: 1-4 means the first to fourth brewing, AD means after digestion, **** means p<0.0001).

[0034] Figure 5 It is a schematic diagram of the process of brewing high-quality tea soup and the quality evaluation method in an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The present invention is described in detail below in conjunction with specific embodiments, but is by no means intended to limit the present invention. Features such as preparation methods, materials, structures or composition ratios not explicitly described in this technical solution are considered to be common technical features disclosed in the prior art.

[0036] Example 1

[0037] This embodiment provides a brewing process and quality evaluation method for high-quality tea soup, the method comprising the following steps:

[0038] S1. Pre-treat tea leaves of different years and varieties to obtain pre-treated tea leaves. The specific process is as follows: place the tea leaves to be tested in a grinder and grind them for 30 seconds, then add a little tea leaves, stir evenly, grind them for a second time for about 60 seconds, filter them with a 200-mesh nylon cloth, obtain the pre-treated tea leaves under dry conditions, store them in sealed bags, mark them, and store them in a 4°C refrigerator for short-term storage, so as to facilitate the subsequent content determination experiments;

[0039] S2. Determine the content of chemical substances in the pretreated tea leaves and conduct significance analysis to verify the stability of different varieties of tea leaves in different years, wherein the determination of the content of chemical substances in the pretreated tea leaves includes the following determinations: determination of tea polyphenols in tea leaves, determination of total soluble sugar content in tea leaves, determination of total free amino acids in tea leaves, determination of catechins in tea leaves, determination of theanine and γ-aminobutyric acid in tea leaves, determination of soluble protein content in tea leaves, determination of total selenium content in tea leaves, determination of chlorophyll content in tea leaves, determination of tea pigment content in tea leaves, and determination of total flavonoids in tea leaves;

[0040] S3, brewing tea soup, preparing tea soup samples obtained under different temperature and time conditions, the specific process is as follows: weighing 1g of tea leaves, preheating ultrapure water at different temperatures, adding 50mL of water at a tea-water ratio of 1:50, and brewing tea soup in a water bath at the same temperature at different time intervals, filtering immediately after the time is up to separate the tea soup and tea leaves, and collecting the tea soup for testing; the different temperatures include the following temperature conditions: 65°C, 75°C, 85°C, 100°C; the different time intervals include the following time intervals: 1min, 3min, 5min, 7min, 9min, 15min, 30min, 40min;

[0041] S4. Calculate the dissolution rate of tea soup samples obtained under different temperature and time conditions. By logarithmic fitting, with time as the independent variable and component content dissolution rate as the dependent variable, obtain the dissolution rate fitting curve of tea soup samples under different temperature conditions, obtain the dissolution concentration change of tea soup samples under different temperature and time conditions, and calculate the half dissolution time t of the components in the tea soup samples under different conditions. 50 and complete dissolution time t 100 ;

[0042] S5. Use sensory evaluation to score the taste, color, and aroma of tea soup at different temperatures and time conditions, and build a tea soup sensory evaluation database;

[0043] S6, combining the dissolution rate fitting curve of the tea soup sample under different temperature conditions obtained in step S4 and the tea soup sensory evaluation database obtained in step S5, establishing a daily tea drinking model;

[0044] S7. Through in vitro simulated digestion experiments, which include simulated saliva experiments, simulated gastric juice experiments, and simulated intestinal juice experiments, the in vitro hypoglycemic activity, antioxidant activity, and in vitro antibacterial activity are determined to verify the bioavailability of the daily tea drinking model.

[0045] In this embodiment, the different teas selected are selenium-enriched black tea, ordinary black tea, selenium-enriched baked green tea, and ordinary baked green tea. In this embodiment, the years of the different teas selected are 2021, 2022, and 2023, respectively.

[0046] In step S4, the dissolution rate of tea components measured under the conditions of 100° C. and 40 min is defined as 100%, thereby calculating the dissolution rates of tea soup samples obtained under different temperature and time conditions.

[0047] In step S6, the following conditions are selected as the daily tea drinking model: water temperature 100 degrees, tea-to-water ratio 1:50, a total of four cups of tea are brewed, the brewing time of the first, second and third cups of tea is designed to be 5 minutes, the fourth cup of tea is regarded as the last brew, and the brewing time is designed to be 1 hour.

[0048] In step S6, the determination of in vitro hypoglycemic activity includes one or more of determining α-glucosidase inhibition rate activity and α-amylase inhibition rate activity. In step S6, the determination of antioxidant activity includes one or more of determining DPPH scavenging rate and performing ABTS free radical scavenging experiment.

[0049] Determination of tea polyphenols in tea: refer to the spectrophotometric method in GB / T 8313-2018 "Determination of tea polyphenols and catechins in tea".

[0050] Determination of total soluble sugar content in tea: refer to the phenol-sulfuric acid method in SN / T 4260-2015 for determination.

[0051] Total amount of free amino acids in tea: refer to GB / T 8314-2013 "Determination of total amount of free amino acids in tea".

[0052] Determination of catechins in tea: refer to the spectrophotometric method and high performance liquid chromatography (HPLC) in GB / T 8313-2018 for determination, and make appropriate modifications. The details are as follows:

[0053] Preparation of the sample to be tested: Weigh 1g (accurate to 0.01g) of tea powder into a 200mL beaker, add 50mL of 70% methanol solution preheated to 70℃, stir evenly, and seal to prevent methanol from volatilizing. Extract in a 70℃ water bath for 1h, shake, and filter. After extraction, transfer to a 100mL volumetric flask, cool, dilute to the mark with water, and mix well. Filter with a 0.45μm aqueous filter membrane, and then analyze using liquid chromatography.

[0054] Liquid phase conditions: using high performance liquid chromatography LC-20AT (Shimadzu, Tokyo, Japan), mobile phase A: ultrapure water, mobile phase B: methanol (0.1% formic acid), flow rate 0.8 mL / min, column temperature: 35°C, injection volume 40 μL, detection wavelength 254 nm.

[0055] The time program settings of HPLC in the determination of catechins in tea are shown in Table 1.

[0056] Table 1. HPLC time program.

[0057]

[0058]

[0059] Determination of theanine and γ-aminobutyric acid in tea: refer to GB / T 23193-2017 "Determination of theanine in tea by high performance liquid chromatography". The details are as follows:

[0060] Preparation of the sample to be tested: weigh 1.0g (accurate to 0.01g) tea powder in a 200mL beaker, add 100mL boiling distilled water. Place in a constant temperature water bath at 100℃ for 30min, filter, transfer to a 100mL volumetric flask, cool, dilute to scale with water, mix well. Filter with a 0.45μm aqueous filter membrane, and then analyze by liquid chromatography.

[0061] Liquid phase conditions: High performance liquid chromatography LC-20AT (Shimadzu, Tokyo, Japan) was used, mobile phase A was ultrapure water, mobile phase B was pure acetonitrile, pre-filtered with two 0.45 μm filter membranes, and ultrasonicated for half an hour to remove bubbles. The flow rate was set to 0.8 mL / min, column temperature: 35 °C, injection volume 40 μL, and detection wavelength 190 nm.

[0062] The time program settings of the HPLC in the determination of theanine and γ-aminobutyric acid in tea are shown in Table 2.

[0063] Table 2 HPLC time program.

[0064]

[0065] Determination of soluble protein content in tea: refer to the Coomassie Brilliant Blue method in SN / T 3926-2014 for determination.

[0066] Determination of total selenium content in tea: Refer to GB 5009.93-2017 "National Food Safety Standard Determination of Selenium in Foods" and use atomic fluorescence method to determine the selenium content.

[0067] Determination of chlorophyll content in tea: refer to NY / T 3082-2017 "Spectrophotometric method for determination of chlorophyll content in fruits, vegetables and their products" and modify it appropriately.

[0068] Determination of the content of tea pigments in tea: The process of determining the content of theaflavins, thearubigins and theabrownins is as follows: first weigh the tea leaves and grind them and mix them with boiling water; soak the tea powder in a boiling water bath for 10 minutes, stirring 2-3 times during the soaking; after the soaking is completed, filter the solution while it is hot and cool it to room temperature; absorb the cooled extract, add ethyl acetate and shake for 5 minutes; after standing and stratifying, separate the ethyl acetate layer and the water layer for use; absorb the ethyl acetate extract, dilute with ethanol to obtain solution a; absorb the ethyl acetate extract and mix it with 2.5% NaHCO3 solution, shake for 30 10 seconds, after standing and stratifying, discard the NaHCO3 aqueous layer, absorb the upper layer of ethyl acetate, and dilute to volume with 95% ethanol solution to obtain liquid c; absorb the aqueous layer extract, mix it with saturated oxalic acid solution and water, and dilute to volume with 95% ethanol to obtain liquid d; absorb the extract and n-butanol solution in containers respectively, shake for 3 minutes, separate the aqueous layer after stratification, mix the aqueous layer liquid with saturated oxalic acid solution and distilled water, and dilute to volume with 95% ethanol to obtain liquid b; use a 1 cm colorimetric dish and 95% ethanol as a blank control to measure the absorbance A of each solution at 380 nm.

[0069] After the absorbance A of each solution is measured by the spectrophotometric method, the calculation formula of the content of theaflavins, thearubigins and theabrownins is as follows:

[0070] Theaflavins (%) = Ac × 2.25 / (m × w) × 100%

[0071] Thearubigins (%) = (2Aa + 2Ad-Ac-2Ab) × 7.06 / (m × w) × 100%

[0072] Theabrownin (%)=7.06×2Ab / (m×w)×100%

[0073] In the formula, m is the mass of instant tea powder (g); w is the dry matter content of instant tea powder (%); Aa is the absorbance of solution a; Ab is the absorbance of solution b; Ac is the absorbance of solution c; Ad is the absorbance of solution d; 2.25 and 7.06 are conversion coefficients under the same operating conditions.

[0074] Determination of total flavonoids in tea: Preparation of test samples: Accurately weigh 12 kinds of tea powder (0.1g) in a 10mL centrifuge tube, add 3mL of anhydrous ethanol, ultrasonically extract for 60min, shake once every 20min. Filter with a 0.45μm filter membrane, dilute to 5mL with anhydrous ethanol, and then measure with a UV spectrophotometer.

[0075] The process of sensory evaluation of tea soup is as follows: a 30-member review panel composed of experienced relevant personnel is selected to taste and score the tea soup under the above-mentioned different conditions. The specific scoring criteria are shown in Table 3.

[0076] Table 3 Sensory evaluation scoring criteria

[0077]

[0078]

[0079] In the process of establishing the daily tea drinking model, the leaching rate, leaching speed, daily tea drinking habits and tea evaluation methods specified in national standards of the main components' dissolution rules were comprehensively considered, and the following conditions were selected as the daily tea drinking model for subsequent research: water temperature of 100 degrees, tea-to-water ratio of 1:50, a total of four cups of tea were brewed, and combined with consumers' living habits, the brewing time of the first, second and third cups of tea was designed to be 5 minutes, the fourth cup of tea was regarded as the last brew, and the brewing time was designed to be 1 hour to study whether the dissolution rate was sufficient.

[0080] In vitro simulated digestion experiment, including the following process:

[0081] (1) Preparation of simulated saliva: KCl (15.1 mM), CaCl2(H2O)2 (1.5 mM), MgCl2(H2O)6 (0.15 mM), KH2PO4 (3.7 mM), (NH4)2CO3 (0.06 mM), NaHCO3 (13.6 mM) and HCl (1.1 mM) were mixed. 50 mL of tea sample solution, 15 mg of α-amylase (1000 U / mg) and 100 mL of simulated saliva were mixed and incubated at 37°C (pH = 7.0). After 0.5 h, 2 mL of the mixture was collected for further analysis.

[0082] (2) Preparation of simulated gastric fluid: KCl (6.9 mM), CaCl2 (H2O) 2 (0.15 mM), MgCl2 (H2O) 6 (0.12 mM), KH2PO4 (0.9 mM), (NH4) 2CO3 (0.5 mM), NaHCO3 (25.0 mM), NaCl (47.2 mM) and HCl (15.6 mM) were mixed. 30 mL of salivary digestion solution, 0.04 g of pepsin (3000 U / g) and 30 mL of simulated gastric fluid were mixed and quickly adjusted to pH = 3.0 to trigger simulated gastric digestion. After incubation at 37°C for 0.5 h, 2 mL of the mixture was collected for further analysis.

[0083] (3) Preparation of simulated intestinal fluid: KCl (6.8 mM), CaCl2 (H2O)2 (0.6 mM), MgCl2 (H2O)6 (0.33 mM), KH2PO4 (0.8 mM), NaHCO3 (85 mM), NaCl (38.4 mM) and HCl (8.4 mM) were mixed in. 30 mL of digestion sample, 0.245 g of bile salt, 0.3 g of pancreatic enzyme (4000 U / g) and 30 mL of simulated intestinal fluid were mixed and quickly adjusted to pH = 7.0 to trigger simulated intestinal digestion. Then, after incubation at 37°C for 0.5 h, 2 mL of the mixture was obtained for further analysis.

[0084] All collected samples were first used for activity determination, then freeze-dried and coded separately.

[0085] The determination of DPPH clearance rate includes the following process:

[0086] Add 200μL sample solution to a 10mL test tube. Add 3.8mL of DPPH·ethanol solution (50.0μg / mL) to the test tube in group A, and add 3.8mL of ethanol to the test tube in group B. Shake well and react at room temperature in the dark for 30min. After the reaction is completed, measure the absorbance at a wavelength of 517nm. Use ethanol as a blank control A0. Calculate the DPPH·scavenging rate (ID) as follows:

[0087] ID(%)=[1-(A1-A2) / A0]×100%

[0088] Where:

[0089] A1: absorbance of 0.2mL sample solution + 3.8mL DPPH·ethanol solution; A2: absorbance of 0.2mL sample solution + 3.8mL ethanol; A0: absorbance of 0.2mL ethanol + 3.8mL DPPH·ethanol solution. The ABTS·free radical scavenging experiment includes the following process:

[0090] In the test tubes of group A, add 400 μL of sample solution and 3.6 mL of ABTS solution respectively and mix them evenly; in the test tubes of group B, add 0.4 mL of ethanol solution and 3.6 mL of ABTS solution and mix them evenly. React at room temperature in the dark for 5 minutes. After the reaction is completed, measure the absorbance at a wavelength of 734 nm. Calculate the ABTS clearance rate (P) according to the following formula:

[0091] P(%)=(A0-A1) / A b ×100%

[0092] Where:

[0093] P: clearance rate; A0: absorbance of the mixture of ABTS· solution and sample solvent solution; A1: absorbance of the mixture of ABTS· solution and test solution.

[0094] The determination of α-glucosidase inhibition rate activity includes the following process:

[0095] The steps for determining the α-glucosidase inhibition rate of tea samples are as follows: First, prepare the substrate solution PNPG (4-nitrophenyl-α-pyranoglucoside) with a sodium phosphate buffer (pH 6.8) at a concentration of 0.1 mol. Then add 20 μL of a-glucosidase solution (1U / μL). After the above solutions are mixed, they are incubated at 37.5°C for 10 minutes. After the reaction is completed, 200 μL of saturated PNPG solution is added and incubated at 37.5°C for another 20 minutes. Subsequently, 10 μL of a 0.1 mol / L Na2CO3 solution is added to terminate the reaction. No α-glucosidase solution is added to the blank group, and no tea extract sample solution is added to the background group. Acarbose is used as a positive control group. Sodium phosphate buffer (pH6.8) is used as a zeroing solution, and its absorbance is measured at a wavelength of 400 nm. To evaluate the α-glucosidase inhibitory activity of the sample, the inhibition rate is calculated according to the following formula:

[0096] Inhibition rate % = [A 空白- (A 样品 -A 背景 )]x100% / A 空白

[0097] The determination of α-amylase inhibition rate activity includes the following process:

[0098] 500 μL of tea soup was added to 500 μL of 13U / mL α-amylase solution (0.02M sodium phosphate buffer pH 6.9) and incubated in a test tube at 25°C for 10 minutes, then 500 μL of 1% soluble starch solution (previously dissolved in sodium phosphate buffer and boiled for 15 minutes) was added to each test tube and incubated for another 25 minutes. Finally, 1 mL of DNS reagent was added and the test tube was placed in a 100°C water bath for 5 minutes. The mixture was diluted with 100 mL of distilled water. The absorbance was read at 520 nm. The results were expressed as percentage inhibition according to the following formula.

[0099] Inhibition rate % = [A 空白 -(A 样品 -A 背景 )]x100% / A 空白

[0100] The antibacterial test of tea soup includes the following process:

[0101] (1) Drug-sensitive tablets. A puncher was used to prepare the drug-sensitive tablets, and they were sterilized by high pressure sterilization to ensure their sterility. Subsequently, the drug-sensitive tablets were placed in tea soup, penicillin solution (40 μg / mL) and sterile ultrapure water, respectively, and the soaking time was 12 hours. The drug-sensitive tablets were observed to be fully soaked in different soaking media. In order to ensure the accuracy of the experimental results, a blank group and a positive control group were set up. Blank group: sterile water was used as the soaking medium to exclude the influence of non-drug factors on the experimental results; positive control group: penicillin solution (40 μg / mL) to verify the reliability of the experimental method.

[0102] (2) Bacterial activation and inoculation stage. Incubate the E. coli suspension on a shaker overnight. After bacterial activation, pipette 100 μL of 10 7 CFU / mL E. coli suspension and evenly spread it on LB solid medium. Then, stick the soaked drug sensitive sheet on the plate coated with E. coli so that the drug can fully contact with the strain.

[0103] (3) Bacterial culture. The experimental conditions were set to culture in a constant temperature incubator at 37°C for 24 hours to observe the inhibitory effect of the drug-sensitive tablet on Escherichia coli. After the experiment, a vernier caliper was used to accurately measure the diameter of the inhibition zone, which was used as an indicator to evaluate the effect of the drug-sensitive tablet.

[0104] Example 2

[0105] This embodiment, based on Embodiment 1, includes the following contents:

[0106] Chemical composition (determination of chemical substance content)

[0107] 1. Main components in tea (specifically, the test objects are selenium-enriched black tea (SeBT) in 2021, selenium-enriched green tea (SeGT) in 2021, ordinary black tea (BT) in 2021, and ordinary green tea (GT) in 2021, selenium-enriched black tea (SeBT) in 2022, selenium-enriched green tea (SeGT) in 2022, ordinary black tea (BT) in 2022, and ordinary green tea (GT) in 2022, selenium-enriched black tea (SeBT) in 2023, selenium-enriched green tea (SeGT) in 2023, ordinary black tea (BT) in 2023, and ordinary green tea (GT) in 2023)

[0108] The composition of tea leaves determines the quality of tea soup. The content of tea ingredients is affected by many factors, such as the planting process, which affects the composition of tea leaves during growth, including geographical environment, soil conditions, planting density, fertilization, pruning and picking. In addition, tea processing techniques such as fixing, rolling, fermentation, etc., will also affect the composition of tea leaves after maturity and picking, leading to secondary changes.

[0109] like Figure 1 As shown in Figure A, the soluble sugar content in tea leaves ranged from 1.12±0.06% to 5.16±0.12%. There were significant differences in the total soluble sugar content of the same type of tea leaves in different years. Figure 1 B shows the total flavonoid content of tea leaves. Flavonoids are the most abundant polyphenols in tea leaves and have antioxidant, anti-inflammatory, anti-allergic and antibacterial properties. The total flavonoid content in tea leaves ranged from 0.36 ± 0.05% to 0.83 ± 0.05%. The total flavonoid content in normal black tea remained stable over the three years and was lower than that in green tea. There was a difference in the total flavonoid content of selenium-enriched black tea between 2021 and 2023, while the total flavonoid content of selenium-enriched green tea and normal green tea fluctuated greatly. The stability order of total flavonoid content was: BT>SeBT>SeGT>GT. Within the same year, significant differences in total flavonoid content were observed when comparing SeBT with BT and SeGT with GT. When considering different tea types, it was found that the total flavonoid content of BT was lower than that of GT, which was attributed to the metabolic shift that occurred during the fermentation of BT. During the fermentation process, the total flavonoid content gradually increased with increasing temperature, reaching a peak and then rapidly decreased.

[0110] like Figure 1 As shown in Figure C, the moisture content in tea leaves ranges from 1.63±0.25% to 5.60±0.47%. It is worth noting that there are significant differences in moisture content between various teas of different years, and the moisture content of older teas is lower. The tea leaves with the highest moisture content all come from the 2023 batch, among which the 2023 selenium-rich black tea has the highest moisture content of 5.60±0.47%. The soluble protein content in tea leaves fluctuates between 0.56±0.07% and 1.16±0.05% ( Figure 1D). Soluble protein is the most stable element among the basic components of tea. Generally speaking, the relative stability of the four core components in different years is in the following order: soluble protein, total flavonoids, water, and then total soluble sugars.

[0111] 2. Tea polyphenols, catechins and caffeine

[0112] like Figure 1 As shown in Figure E, the content of tea polyphenols in unfermented green tea is usually higher than that in fully fermented black tea. The content of tea polyphenols in all green teas (including selenium-enriched green tea and normal green tea) is about 9.43±0.15 to 16.27±0.83%, while the total amount of tea polyphenols in all black teas is about 4.69±0.32 to 9.34±0.28%. Except for a few years, there are significant differences in the content of tea polyphenols between most years (p<0.0001). During the fermentation process of black tea, suitable temperature and humidity provide good reaction conditions for polyphenol oxidase. Catechins undergo oxidative polymerization under the catalysis of polyphenol oxidase to form key flavor substances such as theaflavins and thearubigins. Catechins have multiple physiological activities for human health. Green tea rich in catechins and caffeine is a more effective enhancer of sympathetic-mediated thermogenesis than caffeine itself, which helps to better control obesity. Catechins are the main bitter and astringent substances and are the key factor in determining the thickness of tea soup. Catechins include eight monomers: catechin (+C), gallocatechin (GC), catechin gallate (CG), gallocatechin gallate (GCG), epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG). As a purine alkaloid, caffeine not only has the effect of refreshing the mind, but also constitutes the taste of tea. Figure 1 As shown in Figure F, the contents of various monomers in different teas vary, but EGCG is the most abundant catechin in most green teas. The EGCG content in selenium-enriched green tea in 2023 is the highest, at 47.10±0.59 mg / g. The second most abundant monomer is caffeine, which has the highest caffeine content in normal green tea in 2021, at 32.55±1.38 mg / g, followed by 31.14±0.48 mg / g in selenium-enriched green tea in 2023, and the lowest caffeine content in selenium-enriched green tea in 2022, at 26.91±1.02 mg / g. In black tea, the two most abundant monomers are +C and caffeine, with the highest +C content in normal black tea in 2021 at 50.37±0.56 mg / g ( Figure 1 G). The caffeine content in selenium-enriched black tea in 2022 was the highest, at 38.13±1.03 mg / g, and the caffeine content remained stable overall. At low fermentation degrees (10-15%), the caffeine content remained unchanged, while at high fermentation degrees (85%), the caffeine content increased significantly.

[0113] 3.Tea pigment

[0114] The content of tea pigments Figure 1 H and I. The total amount of tea pigments in green tea is lower than that in black tea, accounting for about 7%, while the total amount of tea pigments in black tea is between 13% and 16%. Among them, theaflavins are the most abundant tea pigments in green tea, accounting for about 5%. The content of theabrownins ranges from 2.10±0.39% to 2.57±0.12%, while the content of theaflavins ranges from 0.03% to 0.35%. In black tea, the content of theaflavins ranges from 5.39±0.58% to 7.39±0.24%, theabrownins range from 7.16±0.58% to 9.43±0.34%, and theaflavins are relatively scarce. Chlorophyll is a natural pigment present in fresh tea leaves, of which chlorophyll b is the main form in plants. Among green teas, selenium-enriched green tea in 2023 has the highest chlorophyll content, which is 0.64±0.03% ( Figure 1 J), while the chlorophyll content of normal green tea in 2022 was the lowest, at 0.39±0.02%. For black tea, the chlorophyll content of selenium-enriched black tea in 2023 was the highest, at 0.51±0.05%, while the chlorophyll content of normal black tea in 2023 was the lowest, at 0.43±0.02% ( Figure 1 K).

[0115] The composition of polyphenolic compounds varies in different types of tea. The main components of green tea are catechins and gallic acid, while the main components of black tea are theaflavins, thearubigins, and other polymers of catechins. During the fermentation process of black tea, polyphenol oxidase catalyzes the conversion of catechins into theaflavins (TFs). Theaflavins mainly present astringency, but their astringency threshold is significantly lower than that of catechins, which contributes to the brightness of the black tea soup. It is generally believed that the formation of low molecular weight oxidation products such as theaflavins marks the initial stage of the development of thearubigins (TRs). The oxidation products, including theaflavins, can further condense to form dimers, trimers, and tetramers. Therefore, thearubigins are regarded as high molecular weight polymers of catechin oxidation products. The ratio of theaflavins / thearubigins is an important quality indicator and is positively correlated with the brightness of the tea soup.

[0116] 4. Selenium

[0117] As an essential trace element for the human body, selenium has biological functions such as anti-cancer, anti-aging, anti-oxidation and immune enhancement, and is of great significance to human health. Figure 1As shown in Figure 1, the selenium (Se) content in normal green tea was continuously detected between 2021 and 2023, ranging from 0.10±0.01 to 0.83±0.06 mg / kg. Similarly, for normal black tea, the Se content remained stable during the same period, fluctuating between 0.27±0.06 and 0.45±0.10 mg / kg. No significant annual Se content differences were observed between normal black teas, which may be attributed to the fact that the Se in ordinary tea leaves mainly comes from the environment and soil, rather than exogenous Se fertilizers.

[0118] There were significant differences in the selenium content of selenium-enriched green tea over the three years (p<0.0001). Notably, the selenium content in selenium-enriched green tea was the highest in 2023, reaching 7.66±0.39 mg / kg. Similarly, the selenium content in selenium-enriched black tea (SeBT) also fluctuated over the three years, with the highest selenium content in 2022 at 3.19±0.20 mg / kg. The significant annual differences in selenium content in selenium-enriched tea may be attributed to the manual application of glucosamine selenium fertilizer and the biotransformation of selenium in tea leaves. In addition, the application of selenium fertilizer can increase the content of most nutritional and functional components in tea, such as soluble sugars, tea polyphenols, catechins, flavonoids, soluble proteins and amino acids.

[0119] 5. Total free amino acids, L-theanine and gamma-aminobutyric acid (GABA)

[0120] Tea contains a variety of free amino acids, including L-theanine (L-The), aspartic acid (Asp), glutamic acid (Glu), asparagine (Asn), glutamine (Gln), glycine (Gly), histidine (His), threonine (Thr), alanine (Ala), serine (Ser), arginine (Arg), tryptophan (Trp), phenylalanine (Phe) and lysine (Lys). Among them, theanine accounts for about half of the total free amino acids. Theanine accounts for a relatively high proportion of the free amino acids in green tea, white tea and black tea. Figure 1 As shown in Figure 2, the total amount of free amino acids in the four types of tea are ranked from high to low as follows: selenium-rich green tea (1.23±0.42% in 2021, 1.04±0.06% in 2022, and 1.82±0.13% in 2023), ordinary green tea (1.44±0.22% in 2021, 1.23±0.13% in 2022, and 1.45±0.03% in 2023), ordinary black tea (0.82±0.07% in 2021, 0.81±0.05% in 2022, and 0.60±0.11% in 2023), and selenium-rich black tea (0.39±0.01% in 2021, 0.84±0.27% in 2022, and 0.39±0.08% in 2023).

[0121] Theanine is a unique amino acid found only in tea trees and mushrooms and has been shown to have a variety of health benefits for the human body. Theanine can improve brain concentration, learning ability and memory. GABA is an important neurotransmitter that has a major inhibitory effect on the central nervous system of mammals. Theanine and GABA can improve sleep disorders and maintain circadian rhythms. In addition, GABA has a hypotensive effect, and GABA tea has been shown to reduce blood pressure in rats. The contents of L-theanine and GABA in the four teas are shown in Table 1. The highest content of L-theanine was in ordinary green tea in 2021, which was 10.23±0.22mg / mL, and the lowest content was in ordinary black tea in 2022, which was 4.80±0.55mg / mL. The content of GABA was higher in green tea than in black tea, with the highest content of GABA in ordinary green tea in 2021, which was 1.41±0.02mg / mL, and the lowest content of GABA in ordinary black tea in 2023, which was 0.32±0.01mg / mL. The contents of L-theanine and GABA in different teas are shown in Table 4.

[0122] Table 4 Content of L-theanine and GABA in different teas (mg / g)

[0123]

[0124] Extraction rules of different active ingredients in selenium-enriched tea (dissolution rates of tea samples obtained under different temperatures and time conditions)

[0125] 1. Tea polyphenols

[0126] Tea polyphenols are the main components of selenium-enriched green tea and selenium-enriched black tea, accounting for about 20% of the dry weight of tea leaves, and play a decisive role in the color, aroma and taste of tea soup. The key components that determine the bitter taste of tea include alkaloids, catechins, anthocyanins, phenolic acids, flavonoid glycosides and theaflavins. After brewing at 100℃ for 40 minutes, the tea polyphenol concentration of selenium-enriched green tea is 201.30±1.85mg / 100mL, while the tea polyphenol concentration of selenium-enriched black tea is 160.40±1.46mg / 100mL.

[0127] Figure 2A and G show the dissolution patterns of tea polyphenols in selenium-enriched black tea and selenium-enriched green tea at different temperatures, with brewing time as the independent variable and the amount of tea polyphenols dissolved as the dependent variable. Compared with selenium-enriched green tea, the dissolution process of tea polyphenols in selenium-enriched black tea is more significantly affected by temperature conditions. The increase in temperature significantly increased the dissolution rate of tea polyphenols, and the dissolution rates of both teas gradually decreased with the increase in brewing time. With the increase in brewing time, the difference in tea polyphenol concentrations in tea soup at different temperatures gradually increased. Specifically, the tea polyphenol concentration after brewing at 100°C for 40 minutes was twice that of brewing at 65°C. The logarithmic fitting curve shows that after complete dissolution, the content of tea polyphenols in selenium-enriched black tea is less than that in selenium-enriched green tea. This difference is due to the conversion of tea polyphenols into theaflavins and theabrownins during the fermentation of black tea, resulting in a decrease in the content of tea polyphenols. Excessive tea polyphenols in tea can change the taste of tea soup from fresh to bitter. Therefore, selenium-enriched black tea with less tea polyphenols dissolved is more suitable for people who do not like the bitter taste of tea.

[0128] As shown in Table 5, the dissolution rate of tea polyphenols brewed at 100°C for 40 minutes was defined as 100%, and the dissolution rates at different temperatures and brewing times were calculated accordingly. Through logarithmic fitting, a fitting formula with time as the independent variable and tea polyphenol dissolution rate as the dependent variable was obtained to show the changes in the dissolution concentration of tea polyphenols in selenium-enriched black tea and selenium-enriched green tea under different time and temperature conditions was calculated. The half-dissolution time t 50 and complete dissolution time t 100 (Table 6). When brewing selenium-enriched green tea at 100°C, it takes 4.47 minutes to dissolve 50% of the tea polyphenols. However, it takes 7.66 minutes, 11.05 minutes, and 17.25 minutes to achieve the same dissolution amount at 85°C, 75°C, and 65°C, respectively. It is worth noting that it is challenging to achieve 100% dissolution of tea polyphenols in selenium-enriched green tea at 75°C and 65°C. At 85°C, complete dissolution takes about 1.5 hours, which is not practical for daily brewing of tea.

[0129] For selenium-enriched black tea, it takes 6.39 minutes to dissolve 50% of the tea polyphenols at 100°C. The same task takes 13.52 minutes, 35.70 minutes, and 112.97 minutes at 85°C, 75°C, and 65°C, respectively. It is equally difficult to achieve complete dissolution of tea polyphenols in selenium-enriched black tea at 75°C and 65°C. At 85°C, it takes nearly 198.83 minutes to completely dissolve all tea polyphenols, which is much longer than the typical 15-minute brewing time, so achieving 100% dissolution is unlikely. However, this reduced dissolution may help reduce the bitter taste of black tea, which may be a welcome result for people who prefer lighter tea flavors.

[0130] Table 5 Effects of different temperatures and times on the dissolution rate of tea polyphenols in SeGT and SeBT

[0131]

[0132] Table 6 Fitting curves of tea polyphenols dissolution rate at different temperatures

[0133]

[0134] 2. Flavonoids

[0135] The concentration of flavonoids in the selenium-enriched green tea infusion was 0.36±0.02 mg / 100 mL, while the concentration of flavonoids in the selenium-enriched black tea infusion was 0.45±0.06 mg / 100 mL, both of which were measured after brewing at 100°C for 40 minutes. Figure 2 B and H show the dissolution patterns of flavonoids in selenium-enriched green tea and selenium-enriched black tea at different brewing temperatures, respectively, with brewing time as the independent variable and the amount of flavonoids dissolved as the dependent variable. Processing technology has a significant effect on the quality components of tea. Even in the withering and drying stages of light fermentation of white tea, flavonoid glycosides are converted into flavonoid aglycones, and the content of water-soluble sugars increases, causing the taste of the tea soup to change from bitter to slightly sweet. After fermentation, the amount of flavonoids dissolved in selenium-enriched black tea at 100°C is higher than that in selenium-enriched green tea. Similar to tea polyphenols, the dissolution of flavonoids in selenium-enriched black tea is more affected by temperature conditions than that of selenium-enriched green tea. The dissolution rate of flavonoids in both teas gradually decreases with time, but the rate of decrease in selenium-enriched green tea is significantly faster than that in selenium-enriched black tea. The difference in the concentration of flavonoids in tea soup at different temperatures gradually increases with the extension of brewing time. The concentration of flavonoids after brewing at 100°C for 40 minutes is twice that of brewing at 65°C.

[0136] As shown in Table 7, assuming that the dissolution rate of flavonoids brewed at 100°C for 40 minutes is 100%, the dissolution rates at different temperatures and brewing times were calculated. Through logarithmic fitting, a fitting equation with time as the independent variable and flavonoid dissolution rate as the dependent variable was obtained to show the changes in the dissolved concentration of flavonoids in selenium-enriched black tea and selenium-enriched green tea under different time and temperature conditions was also calculated. 50 and t 100 (Table 8). When brewing selenium-enriched green tea at 100°C, it only takes 3.66 minutes to dissolve 50% of the flavonoids, while at 85°C, 75°C and 65°C, it takes 5.89 minutes, 12.37 minutes and 15.59 minutes, respectively. When brewing selenium-enriched black tea at 100°C, it takes 6.34 minutes to dissolve 50% of the flavonoids, while at 85°C, 75°C and 65°C, it takes 10.25 minutes, 18.45 minutes and 71.73 minutes, respectively. Therefore, the dissolution rate of flavonoids in selenium-enriched green tea is faster than that in selenium-enriched black tea.

[0137] Table 7 Effect of different temperatures and time on the dissolution rate (%) of flavonoids in SeGT and SeBT

[0138]

[0139]

[0140] Table 8 Dissolution rate fitting curves of flavonoids at different temperatures

[0141]

[0142] 3. Soluble sugar

[0143] The sweetness of tea soup is directly related to the content of soluble sugars in it. In some high-sugar green teas, soluble sugars account for 5-10% of the total soluble substances. According to previous research results, the soluble sugar content in tea leaves is about 1.12±0.06% to 5.16±0.12%. After brewing at 100℃ for 40 minutes, the soluble sugar concentrations in selenium-enriched green tea and selenium-enriched black tea were 90.92±0.99mg / 100mL and 98.56±1.10mg / 100mL, respectively. In general, black tea contains higher levels of soluble sugars, including sucrose, fructose, glucose, and sorbitol, compared with green tea. Figure 2 C and I respectively show the dissolution patterns of soluble sugars in selenium-enriched black tea and selenium-enriched green tea at different brewing temperatures, where brewing time is the independent variable and the amount of soluble sugar dissolved is the dependent variable. Specifically, the change in temperature has no significant effect on the dissolution of soluble sugars in selenium-enriched black tea. The dissolution rates of soluble sugars in selenium-enriched green tea and selenium-enriched black tea gradually decrease over time, and the rate of decrease is similar. Within the first 1-5 minutes of brewing, the dissolved concentrations of soluble sugars in tea soup at different brewing temperatures are similar. However, from 5 minutes to 40 minutes, the difference in the concentration of soluble sugars in tea soup at different brewing temperatures gradually increases. As shown in Table 9, after brewing at 65°C for 40 minutes, the dissolution rate of soluble sugars in selenium-enriched green tea soup reached 67.02%, exceeding the dissolution rates of tea polyphenols and flavonoids at the same temperature. As shown in Table 10, when brewing selenium-enriched green tea at 100°C, it takes 4.34 minutes to dissolve 50% of the soluble sugar, while it takes 5.24 minutes, 9.22 minutes and 13.72 minutes at 85°C, 75°C and 65°C, respectively. In addition, when brewing selenium-enriched black tea at 100°C, it takes 4.46 minutes to dissolve 50% of the soluble sugar, while it takes 5.24 minutes, 9.30 minutes and 15.34 minutes at 85°C, 75°C and 65°C, respectively.

[0144] Table 9 Effect of different temperatures and times on the dissolution rate of soluble sugars in SeGT and SeBT

[0145]

[0146] Table 10 Soluble sugar dissolution rate fitting curves at different temperatures

[0147]

[0148] 4. Free amino acids

[0149] The free amino acids in tea help enrich the flavor of tea. The sensory evaluation score of tea is significantly positively correlated with theanine and the ratio of sweet and umami amino acids. Figure 2 As shown in D and J, the amount of free amino acids dissolved in tea soup at different brewing temperatures and times was measured, and the nonlinear dissolution curve of free amino acids was fitted according to the brewing time under each temperature condition. The observation results show that the extension of brewing time increases the amount of free amino acids dissolved in tea soup. Specifically, after brewing at 100°C for 40 minutes, the concentration of free amino acids in selenium-enriched green tea soup was 115.82±0.58mg / 100mL, while the concentration in selenium-enriched black tea was 105.38±0.72mg / 100mL.

[0150] Assuming that the dissolution rate of brewing at 100°C for 40 minutes is 100%, the fitting equation with the free amino acid dissolution rate as the dependent variable was calculated by logarithmic fitting to show the changes in the concentration of free amino acids dissolved in selenium-enriched black tea and selenium-enriched green tea under different time and temperature conditions (Table 11). As shown in Table 12, when brewing selenium-enriched green tea at 100°C, it only takes 5.18 minutes to dissolve 50% of the free amino acids, while it takes 7.88 minutes, 10.20 minutes and 17.03 minutes at 85°C, 75°C and 65°C, respectively. When brewing selenium-enriched black tea at 100°C, it only takes 4.02 minutes to dissolve 50% of the free amino acids, while it takes 5.79 minutes, 8.05 minutes and 12.88 minutes at 85°C, 75°C and 65°C, respectively. In short, compared with selenium-enriched green tea, the dissolution rate of free amino acids in selenium-enriched black tea is faster.

[0151] Table 11 Effects of different temperatures and times on the dissolution rate of free amino acids in SeGT and SeBT

[0152]

[0153] Table 12 Free amino acid dissolution rate fitting curves at different temperatures

[0154]

[0155] 5. Caffeine

[0156] Purine alkaloids, mainly caffeine and theobromine, are the key compounds that give tea its unique bitter taste. It is generally believed that when the caffeine concentration in tea reaches 500μmol / L, the tea will taste bitter. The dissolved caffeine content in tea at different brewing temperatures and brewing times was measured, and a nonlinear dissolution curve of the caffeine dissolved content changing with time was fitted at each single temperature ( Figure 2 E and K). At a constant temperature, the caffeine content in the tea soup increased with the increase of brewing time. Specifically, after brewing for 40 minutes at 100°C, the caffeine concentrations in selenium-enriched green tea and selenium-enriched black tea were 76.52±0.34mg / 100mL and 58.91±0.93mg / 100mL, respectively. Regardless of the temperature, selenium-enriched black tea and green tea dissolved fastest within the first 1-3 minutes of brewing. It is worth noting that the dissolution rate in this initial stage is faster than that of flavonoids and soluble sugars, but slower than that of tea polyphenols.

[0157] A caffeine dissolution rate of 100% is defined as the amount of caffeine dissolved when brewed at 100°C for 40 minutes. As shown in Table 13, selenium-enriched green tea dissolves more caffeine than selenium-enriched black tea, which is due to differences in processing methods, and the total caffeine content in green tea is lower than that in black tea. As shown in Table 14, when brewing selenium-enriched green tea at 100°C, it takes 4.22 minutes to dissolve 50% of the caffeine, while when brewing at 85°C, 75°C, and 65°C, it takes 6.79 minutes, 9.65 minutes, and 17.16 minutes, respectively. When brewing selenium-enriched black tea at 100°C, it takes 3.93 minutes to dissolve 50% of the caffeine, and when brewing at 85°C, 75°C, and 65°C, the dissolution time is extended to 5.94 minutes, 11.26 minutes, and 28.45 minutes, respectively.

[0158] Table 13 Effects of different temperatures and times on the dissolution rate of caffeine in SeGT and SeBT

[0159]

[0160] Table 14 Caffeine dissolution rate fitting curves at different temperatures

[0161]

[0162] L-Theanine

[0163] Theanine accounts for the largest proportion of free amino acids in green tea, white tea, black tea and Pu'er tea, accounting for 48% to 63% of the total free amino acids. Theanine plays a key role in giving tea soup a fresh and refreshing taste, and can synergistically enhance this fresh feeling with other free amino acids. However, when the concentration of theanine rises to 35mg / 100mL, it will exhibit a bitter taste. The content of theanine dissolved in the tea soup at different brewing temperatures and durations was measured, and a nonlinear dissolution curve of theanine content changing with time was fitted at each single temperature ( Figure 2 F and L). Under the same temperature conditions, the brewing time of tea is positively correlated with the dissolved content of theanine. After brewing selenium-enriched green tea and selenium-enriched black tea at 100°C for 40 minutes, the theanine concentrations in the tea soup reached 52.69±1.49mg / 100mL and 54.04±0.82mg / 100mL, respectively (Table 15).

[0164] By using logarithmic fitting to calculate the fitting equation with theanine dissolution rate as the dependent variable, the changes in theanine dissolution concentration of selenium-enriched black tea and selenium-enriched green tea during the brewing process are shown. As shown in Table 16, 50% of theanine can be dissolved in 4.30 minutes of brewing selenium-enriched green tea at 100°C, while it takes 5.66 minutes, 8.79 minutes and 11.32 minutes when brewing at 85°C, 75°C and 65°C, respectively. 50% of theanine can be dissolved in 4.43 minutes of brewing selenium-enriched black tea at 100°C, while it takes 5.60 minutes, 8.12 minutes and 13.08 minutes when brewing at 85°C, 75°C and 65°C, respectively. It is worth noting that in order to keep the tea soup pleasant and not astringent, it is recommended to brew selenium-enriched green tea at 85°C for no more than 15 minutes, or at 100°C for no more than 10 minutes. For selenium-rich black tea, the brewing time at 85℃ should not exceed 13 minutes, or the brewing time at 100℃ should not exceed 9 minutes, which can ensure that theanine content remains below 35mg / 100mL, thus avoiding the bitter taste of the tea soup.

[0165] Table 15 Effect of different temperatures and times on the dissolution rate of theanine in SeGT and SeBT

[0166]

[0167] Table.16 Theanine dissolution rate fitting curve at different temperatures

[0168]

[0169] Sensory evaluation of tea soup under different extraction temperatures and times (using sensory evaluation to score the taste, color, and aroma of tea soup under different temperatures and time conditions, and construct a tea soup sensory evaluation database)

[0170] Figure 3A and B show the sensory evaluation radar charts of selenium-rich green tea and selenium-rich black tea at different brewing temperatures and times, respectively. On the whole, 100°C is considered to be the best brewing temperature for the sensory evaluation of tea soup. For selenium-rich green tea, the only condition for the sensory evaluation score to exceed 95 is brewing at 100°C for 5-7 minutes, while the brewing condition for the sensory evaluation score to reach above 90 is brewing at 100°C for 3-9 minutes. The sensory evaluation score of selenium-rich black tea can only exceed 95 when brewed at 100°C for 3-7 minutes. Under appropriate brewing time, brewing temperatures of 100°C and 85°C can increase the sensory evaluation score of selenium-rich black tea to above 90. The sensory evaluation score is positively correlated with theanine, sweetness, and umami amino acid ratios. Combined with the dissolution law of tea soup, when brewed at 100°C for 5 minutes, most of the quality components of selenium-rich black tea and selenium-rich green tea showed a dissolution rate of 50%, which is consistent with the good scores of aroma, color and taste in the sensory evaluation, thus making the tea soup at 100°C present a better sensory evaluation score.

[0171] In general, brewing at 100°C for 5 minutes can effectively extract the quality components of tea, while brewing at 85°C for 5 minutes can reduce the bitterness of tea. As the number of brewing times and digestion time increase, the biological activity of tea decreases. Therefore, the following conditions were selected as a daily tea drinking model for subsequent research: water temperature of 100 degrees, tea-to-water ratio of 1:50, a total of four brews of tea, combined with consumer living habits, the first, second, and third brewing times are designed to be 5 minutes, the fourth brew is regarded as the last brew, and the brewing time is designed to be 1 hour to study whether the dissolution is sufficient.

[0172] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A high-quality tea brewing process and quality evaluation method, characterized in that: The method comprises the following steps: S1. Pre-treating tea leaves of different years and varieties to obtain pre-treated tea leaves; S2. Determine the chemical content of the pretreated tea leaves and conduct significance analysis to verify the stability of different varieties of tea leaves in different years; S3, brewing tea soup, and preparing tea soup samples obtained under different temperature and time conditions; S4. Calculate the dissolution rate of tea soup samples obtained under different temperature and time conditions. By logarithmic fitting, with time as the independent variable and component content dissolution rate as the dependent variable, obtain the dissolution rate fitting curve of tea soup samples under different temperature conditions, obtain the dissolution concentration change of tea soup samples under different temperature and time conditions, and calculate the half dissolution time t of the components in the tea soup samples under different conditions. 50 and complete dissolution time t 100 ; S5. Use sensory evaluation to score the taste, color, and aroma of tea soup at different temperatures and time conditions, and build a tea soup sensory evaluation database; S6. Establish a daily tea drinking model by combining the dissolution rate fitting curve of the tea soup sample under different temperature conditions obtained in step S4 and the tea soup sensory evaluation database obtained in step S5.

2. A high-quality tea brewing process and quality evaluation method according to claim 1, characterized in that: Step S1 specifically includes the following process: Place the tea leaves to be tested in a grinder and grind them for 30 seconds, then add a little tea leaves, stir evenly, grind them for a second time for about 60 seconds, filter them with 200-mesh nylon cloth, and obtain the pretreated tea leaves under dry conditions. Store them in sealed bags, mark them, and store them in a 4°C refrigerator for a short period of time for use in subsequent content determination experiments.

3. The brewing process and quality evaluation method of high-quality tea soup according to claim 1, characterized in that: In step S2, the determination of the chemical substance content of the pretreated tea leaves includes one or more of the following determinations: Determination of tea polyphenols in tea, determination of total soluble sugar content in tea, determination of total free amino acids in tea, determination of catechins in tea, determination of theanine and γ-aminobutyric acid in tea, determination of soluble protein content in tea, determination of total selenium content in tea, determination of chlorophyll content in tea, determination of tea pigment content in tea, and determination of total flavonoids in tea.

4. The brewing process and quality evaluation method of high-quality tea soup according to claim 1, characterized in that: Step S3 includes the following process: Weigh 1g of tea leaves, preheat ultrapure water at different temperatures, add 50mL of water at a tea-water ratio of 1:50, and brew the tea soup in a water bath at the same temperature at different time intervals. After the time is up, filter immediately to separate the tea soup and tea leaves, and collect the tea soup for testing; The different temperatures include the following temperature conditions: 65°C, 75°C, 85°C, 100°C; The different time intervals include the following time intervals: 1 min, 3 min, 5 min, 7 min, 9 min, 15 min, 30 min, and 40 min.

5. A high-quality tea brewing process and quality evaluation method according to claim 4, characterized in that: The tea leaves are selected from one or more of selenium-enriched black tea, ordinary black tea, selenium-enriched roasted green tea, and ordinary roasted green tea.

6. The brewing process and quality evaluation method of high-quality tea soup according to claim 1, characterized in that: In step S6, a daily tea drinking model is established by combining the dissolution rate fitting curve of the tea soup sample under different temperature conditions obtained in step S4 and the tea soup sensory evaluation database obtained in step S5, and the following conditions are selected as the daily tea drinking model: water temperature 100 degrees, tea-to-water ratio 1:50, a total of four cups of tea are brewed, the brewing time of the first, second and third cups of tea is designed to be 5 minutes, the fourth cup of tea is regarded as the last brew, and the brewing time is designed to be 1 hour.

7. The brewing process and quality evaluation method of high-quality tea soup according to claim 1, characterized in that: After step S6, the following steps are performed: S7. The bioavailability of the daily tea drinking model is verified by determining the in vitro hypoglycemic activity, antioxidant activity and in vitro antibacterial activity through in vitro simulated digestion experiments.

8. A high-quality tea brewing process and quality evaluation method according to claim 7, characterized in that: In step S7, the in vitro simulated digestion experiment includes one or more of a simulated saliva experiment, a simulated gastric juice experiment, and a simulated intestinal juice experiment.

9. The brewing process and quality evaluation method of high-quality tea soup according to claim 7, characterized in that: In step S7, the determination of the in vitro hypoglycemic activity includes one or more of determining the α-glucosidase inhibition rate activity and determining the α-amylase inhibition rate activity.

10. The brewing process and quality evaluation method of high-quality tea soup according to claim 7, characterized in that: In step S7, the antioxidant activity determination includes one or more of determining DPPH scavenging rate and performing ABTS free radical scavenging experiment.

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