Visual judgment method for green tea varieties

Abstract

The invention discloses a visual identification method of different varieties of green tea, which comprises the following steps: decomposing H2O2 by nanogold pseudoperoxidase (GSH-AuNPs) to generate hydroxyl free radicals (. OH) so as to oxidize TMB (Tetramethylbenzidine) and generate a blue oxidation product (oxTMB); the antioxidant active substances such as tea polyphenol contained in the green tea inhibit the oxidation of TMB through the removal effect on. OH and the reduction effect on oxTMB. As the antioxidant activities of different varieties of green tea are different, the sensing system has different color changes, and accurate identification of different varieties of green tea is realized. Compared with existing detection methods based on chromatography and the like, the detection method has the advantages of being high in stability, rapid in response, easy and convenient to operate, portable in device and the like, has wide application prospects and can be put into industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical analysis and detection, and particularly relates to a method for visually distinguishing green tea varieties. Background Art

[0002] Green tea is one of the most popular beverages in the world, with physiological functions such as antioxidant, anti-inflammatory, cardiovascular protection and anti-obesity. As a "non-fermented" tea, green tea undergoes fewer processing steps and can retain the original polyphenolic compounds of fresh tea leaves to the greatest extent. Due to the large number of green tea varieties, uneven quality and lack of strict grading standards, it is imperative for consumers to achieve rapid identification and quality evaluation of green tea. Therefore, it is of great significance to accurately identify the varieties and grades of green tea.

[0003] Traditional methods for identifying green tea varieties and grades mostly rely on manual sensory evaluation. This method is simple and fast, but the results are easily disturbed and affected by many factors such as the environment and the physical and mental state of the reviewers, and there is a certain degree of subjectivity. At present, high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS), ultra-high-performance liquid chromatography-high-resolution mass spectrometry (UPLC-HRMS), electronic nose / tongue and spectroscopy have been developed for tea quality evaluation. These large-scale instrumental methods are costly, complex to operate, and time-consuming. They can only be limited to laboratories and cannot be accepted by the general public, making them difficult to popularize.

[0004] Therefore, it is of great practical significance to further establish a method with high sensitivity, good specificity, low cost and rapid and convenient identification of green tea varieties. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for visually distinguishing green tea varieties in view of the problems and shortcomings of the prior art. Nanogold pseudoperoxidase (GSH-AuNPs) decomposes H 2 O 2 Hydroxyl radicals (·OH) are generated to oxidize TMB and generate blue oxidation products (oxTMB). Antioxidant active substances such as tea polyphenols contained in green tea inhibit the oxidation of TMB by scavenging ·OH and reducing oxTMB. Due to the different antioxidant activities of different varieties of green tea, the sensing system undergoes different color changes, which enables accurate identification of different varieties of green tea; this method is simple in process, green and environmentally friendly, low in cost, easy to popularize, can be put into industrial production, and is suitable for promotion and application.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for visually distinguishing green tea varieties comprises the following steps:

[0008] The tea polyphenols extracts of different varieties of green tea samples were mixed with GSH-AuNPs-H 2 O 2 -TMB sensing system was mixed evenly, allowed to react, and the resulting detection system was based on GSH-AuNPs-H 2 O 2 -TMB sensing visualization image, using the color difference of the color response of different varieties of green tea samples, according to the color of the detection system obtained after the reaction of the tea polyphenol extract of the green tea sample to be tested, to achieve visual discrimination of the green tea variety to be tested. Among them, GSH-AuNPs represents glutathione-modified nanogold, and TMB is tetramethylbenzidine.

[0009] In the above scheme, the GSH-AuNPs-H 2 O 2 -TMB sensing system includes buffer and GSH-AuNPs-H 2 O 2 -TMB sensing solution, GSH-AuNPs-H 2 O 2 -TMB sensing solution contains GSH-AuNPs, H 2 O 2 and TMB solution. 2 O 2 The order of adding each solution in the TMB sensing solution is the order in which the solutions are presented. 2 O 2 The preparation method of the -TMB sensing solution comprises: mixing GSH-AuNPs, H 2 O 2 The solutions were mixed and reacted for 2-3 minutes, and finally TMB solution was added and reacted for 8-10 minutes.

[0010] In the above scheme, the static reaction time is 15-18 minutes.

[0011] In the above scheme, the pH of the obtained detection system is 3.6-3.8; the concentration of GSH-AuNPs in the obtained detection system is (0.79-1.79)×10 -5 mol / L; H 2 O 2 The concentration is 0.3-0.35 mol / L; the concentration of TMB in the obtained detection system is 0.9-1.5 mmol / L; the content of green tea components in the detection system is 0.09-0.15 mg of green tea raw materials / mL based on the green tea raw materials introduced during the preparation of the extract.

[0012] Preferably, the concentration of GSH-AuNPs in the obtained detection system is 1.20×10 -5 mol / L; H 2 O 2 The concentration of TMB is 0.326 mol / L; the concentration of TMB in the obtained detection system is 1.0 mmol / L.

[0013] In the above scheme, in the visual identification method of green tea varieties, color information is obtained by means of naked eye observation or photographing equipment, and a visual identification atlas library of different varieties of green tea is obtained by comparison.

[0014] Preferably, the photographing means further photographs under the condition of LED light illumination.

[0015] In the above scheme, the green tea variety visual identification method specifically comprises the following steps:

[0016] 1) obtaining extracts of green tea samples of different varieties to be tested;

[0017] 2) GSH-AuNPs-H 2 O 2 -TMB sensing system was mixed with the green tea extract to be tested, allowed to react, and the obtained detection system was collected based on GSH-AuNPs-H 2 O 2 -Visualization of TMB sensing;

[0018] 3) According to the relationship between the visualization images and green tea varieties, a visualization recognition model library based on green tea varieties is established to realize the recognition of different varieties of green tea products.

[0019] In the above scheme, the method for establishing the visual recognition model library includes: extracting RGB values ​​from the visual images obtained from the green tea samples of different varieties, and constructing colorimetric cards corresponding to the green tea samples of different varieties.

[0020] In the above scheme, the varieties of green tea samples corresponding to the colorimetric card vary from dark blue-green to colorless.

[0021] In the above scheme, the preparation method of GSH-AuNPs comprises the following steps: adding glutathione (GSH) to HAuCl 4 The solution was stirred evenly at room temperature in the dark, and then freshly prepared ice-cold NaBH 4 The solution was stirred vigorously at room temperature in the dark to obtain a yellow clear solution emitting red light. After high-speed centrifugation, the supernatant was filtered through a microporous filter to remove insoluble impurities and obtain a glutathione-modified nanogold solution.

[0022] In the above scheme, the glutathione (GSH), HAuCl4 , NaBH 4 The molar ratio is 1:(0.57~0.77):(0.0010~0.0012).

[0023] In the above scheme, the concentration of the obtained GSH-AuNPs solution is (0.79-1.79)×10 -3 mol / L.

[0024] In the above scheme, the centrifugal speed is 10000-12000 rpm, and the time is 15-25 min; the obtained supernatant is filtered with a 0.22 μm microporous filter membrane.

[0025] In the above scheme, the extract is prepared by ultrasonic alcohol extraction process, and the extraction solvent used is 50-70 vol% methanol aqueous solution.

[0026] In the above scheme, the ultrasonic alcohol extraction process conditions include: green tea is crushed and ground to pass through a 50-200 mesh sieve to obtain green tea powder, the green tea powder is mixed with a 50-70 vol% methanol aqueous solution according to a solid-liquid ratio of 0.1 g:9-11 mL, and ultrasonic extraction is performed at 35-40°C for 0.3-0.5 hours to obtain a crude extract, and the obtained crude extract is then centrifuged at 4000-5000 rpm for 5-15 minutes, and the supernatant is filtered through a 0.22 μm microporous filter membrane to obtain a green tea extract.

[0027] In the above scheme, the varieties of green tea to be tested include Dongting Biluochun (DT-BLC), Kaihua Longding (KHLD), Huangshan Maofeng (HS-MF), Xinyang Maojian (XY-MJ), Duyun Maojian (DY-MJ), Lu'an Guapian (LAGP) or Zhuyeqing (ZYQ).

[0028] In the above scheme, a 96-well plate was used to detect green tea varieties, as follows: acetate buffer, GSH-AuNPs, H 2 O 2 , TMB solution and different varieties of green tea extracts, and add the above solutions into a 96-well plate in sequence and incubate for 25-30 minutes; then, under LED light, use a digital camera (Nikon D3300) to take pictures of the different green tea reactions, and at the same time, the green tea varieties can be identified by naked eyes.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1) The present invention utilizes GSH-AuNPs to decompose H 2 O 2Hydroxyl radicals (·OH) are generated to oxidize TMB, generating blue oxidation products (oxTMB). The effective ingredients in green tea, such as tea polyphenols, scavenge ·OH and reduce oxTMB, thereby inhibiting the oxidation of TMB. Due to the different antioxidant activities of different varieties of green tea, the sensing system undergoes different color changes, thus achieving accurate identification of different varieties of green tea.

[0031] 2) The present invention further improves the biocompatibility and stability of AuNPs by modifying them with glutathione (GSH). GSH-AuNPs not only retain the basic catalytic properties of AuNPs, but also increase the affinity for biomolecules due to the presence of GSH, making them more potential in sensing. The pseudoenzyme activity is better than some of the nanozymes and natural peroxidases reported previously.

[0032] 3) Compared with the traditional chromatography-based detection method, the identification method of the present invention has the advantages of higher stability, faster response, simpler operation, and more portable device. It can meet the needs of ordinary people, has broad application prospects, and can be put into industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1A The different varieties of green tea and GSH-AuNPs-H in the embodiments of the present invention 2 O 2 -Visualization result diagram after TMB reaction;

[0034] Figure 1B The ultraviolet absorption spectra of different varieties of green tea in the embodiments of the present invention;

[0035] Figure 2 The tea polyphenols standard and GSH-AuNPs-H of different concentrations of green tea active ingredients in the examples are shown in Table 1. 2 O 2 -Visual results after TMB reaction;

[0036] Figure 3 In order to explore the mechanism of the method described in the present invention, tea polyphenols and GSH-AuNPs-H 2 O 2 -UV spectra of TMB before and after reaction;

[0037] Figure 4 In the mechanism study of the method described in the present invention, different concentrations of tea polyphenols and GSH-AuNPs-H 2 O 2 -UV-visible spectrum of TMB sensor after reaction (A) and spectral intensity-concentration linear graph at 652nm (B);

[0038] Figure 5TEM image (A) and UV-visible spectrum (B) of GSH-AuNPs of the present invention;

[0039] Figure 6 The steady-state kinetic analysis diagram of GSH-AuNPs of the present invention, wherein: (AB) is the Michaelis-Menten curve of GSH-AuNPs to TMB and the corresponding double linewever-burk diagram; (CD) is the GSH-AuNPs to H 2 O 2 The Michaelis-Menten curve and the corresponding double linewever-burk diagram. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] In the following examples, the method for preparing the GSH-AuNPs solution comprises the following steps: adding 400 μL of 0.213 mol / L glutathione (GSH) to 40 mL of 1.42 mmol / L HAuCl 4 The solution was stirred at room temperature in the dark for 20 min. Then, 10 μL of 0.01 mol / L freshly prepared ice-cold NaBH 4 The solution was stirred vigorously at room temperature in the dark for 25 min to obtain a yellow clear solution with red light. The solution was centrifuged at 12000 rpm for 20 min. The supernatant was filtered through a 0.22 μm microporous membrane to remove unadsorbed glutathione and other insoluble impurities to obtain a GSH-AuNPs solution with a concentration of 1.20 × 10 -3 mol / L, stored in a 4°C refrigerator away from light. During specific use, dilute 10 times the volume with deionized water to obtain a concentration of 1.20×10 -4 mol / L GSH-AuNPs solution.

[0042] The morphology, particle size and ultraviolet absorption characteristics of the GSH-AuNPs solution were characterized by transmission electron microscopy (TEM) and ultraviolet visible spectrophotometer (UV-Vis). Figure 5 .like Figure 5 As shown in (A), GSH-AuNPs are regular spherical with an average particle size of 12 nm and are evenly dispersed in the solution. Figure 5 As can be seen in (B), the prepared GSH-AuNPs have no ultraviolet absorption at 652nm, indicating that the material itself has no effect on the final discrimination result of the sensing system.

[0043] The colorimetric discrimination of different varieties of green tea is based on the reaction of tea polyphenols (TP) in green tea with pseudo-peroxidase-catalyzed H 2 O 2 The generated hydroxyl radical (·OH) has a scavenging effect and a reducing effect on oxidized TMB (oxTMB). The stronger the activity of the pseudoperoxidase, the better the catalytic effect, the faster the rate of generating ·OH and oxTMB, and the higher the sensitivity of the sensing system to TP.

[0044] The steady-state kinetics of the enzymatic reaction of GSH-AuNPs nanomaterials on TMB and H 2 O 2 The activity of pseudoperoxidase. Michaelis-Menten constant (Km) and maximum initial velocity (Vmax) are two important index parameters of enzymatic reaction. Km can represent the affinity of enzyme to substrate. It is generally believed that the smaller the Km value, the stronger the affinity between enzyme and substrate and the better the enzyme activity. Vmax directly indicates the progress of enzymatic reaction. A high Vmax value indicates that the substrate develops color quickly, indicating strong enzyme activity.

[0045] The typical Michaelis-Menten curve was obtained according to the Michaelis-Menten equation (V = Vmax [S] / (Km + [S])), and the Linewever-Burk plot was obtained according to the corresponding double inverse equation (1 / V = (Km / Vmax) [S] + 1 / Vmax) to calculate Km and Vmax. The results are shown in Table 1. 2 O 2 The Km values ​​(324 and 24.03) are lower than those of other reported nanozymes and natural horseradish peroxidase (Fe-Ag 2 S: 821 and 1250; HRP: 434 and 3700), and the Vmax values ​​(2.033 and 16.58) were higher than those of other peroxidase mimics and natural peroxidase (Fe-Ag 2 S: 0.683 and 0.0692; HRP: 0.201 and 0.334). This explains the rapid recovery of the substrate color and is also the fundamental reason for rapid detection in colorimetric sensing. The above steady-state kinetic results show that GSH-AuNPs have strong peroxidase mimetic activity.

[0046] Table 1

[0047]

[0048] [1]HUANG X,NAN Z.Porous 2D FeS2 nanosheets as a peroxidase mimic forrapid determination ofH2O2[J].Talanta,2020,216:120995.

[0049] [2] SHI W, WANG Q, LONG Y, et al. Carbon nanodots as peroxidase mimetics and their applications to glucose detection [J]. Chemical Communications, 2011, 47(23): 6695–6697.

[0050] [This article] The concentration of GSH-AuNPs was 1.20×10 -4 mol / L, TMB and H 2 O 2 The substrate concentrations were (1, 1.5, 2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20)×10 -3 mol / L.

[0051] In the following examples, the tea polyphenols standards used were provided by Shanghai Yuanye Biological Co., Ltd.

[0052] In the following examples, the extraction method of the green tea sample to be tested includes the following steps: all green tea samples are crushed, ground, and passed through a 50-mesh sieve to obtain tea powder. 0.1 g of tea powder is mixed with 10 mL of a 60 vol% methanol aqueous solution, and ultrasonically extracted at 37°C and 100 Hz for 20 min to obtain a crude extract. After making up for the weight loss, the crude extract is centrifuged at 4000 rpm for 15 min, and the obtained supernatant is passed through a 0.22 μm microporous filtration membrane to obtain a green tea extract, which is stored in a 4°C refrigerator. During specific use, it is diluted 10 times the volume with deionized water.

[0053] In the following examples, all volumes involved were accurately measured using a pipette.

[0054] Example 1

[0055] A method for visually distinguishing green tea varieties comprises the following steps:

[0056] 1) extracting green tea samples of seven different known varieties (Dongting Biluochun, Kaihua Longding, Huangshan Maofeng, Xinyang Maojian, Duyun Maojian, Lu'an Guapian, Zhuyeqing) to obtain green tea extracts;

[0057] 2) The obtained green tea extract was mixed with GSH-AuNPs-H 2 O 2 -TMB sensor system is mixed, allowed to react for 25 minutes, and the color change of the sensor system after the reaction is observed; the specific steps include:

[0058] a) Construction of GSH-AuNPs-H 2 O 2 -TMB sensor system: 600 μL of 0.2 mol / L acetate buffer at pH 3.6 was mixed with 100 μL of 1.20×10 -4 mol / L GSH-AuNPs solution was mixed, and then 100 μL 3.26 mol / L H 2 O 2 solution, react for 2 min, and finally add 100 μL 0.01 mol / L TMB solution and react for 8 min;

[0059] b) Take 70 GSH-AuNPs-H 2 O 2 -TMB sensor system, 100 μL of 10-fold dilution of the seven different varieties of green tea extracts extracted above were added thereto respectively, and each green tea sample was repeated 10 times, and the reaction was allowed to stand for 15 minutes. On the LED light board, a digital camera (model Nikon D3300) was used to take photos of the different green tea reactions. The results are shown as follows: Figure 1A As shown; the ultraviolet absorption spectra of seven different varieties of green tea are shown in Figure 1B .

[0060] Principle research

[0061] Since tea polyphenols are one of the important functional ingredients of green tea, their content is significantly correlated with the variety of green tea. At the same time, the content of tea polyphenols in different varieties of green tea varies greatly. In order to explore the effect of tea polyphenol content on the visualization of green tea varieties, tea polyphenol standard samples with different concentrations and green tea samples of different varieties were taken for visual identification, which specifically included the following steps:

[0062] 1) Weigh appropriate amounts of tea polyphenols and prepare tea polyphenol standard solutions with deionized water at concentrations of 0.3, 0.2, 0.15, 0.1, 0.06, 0.03, and 0.01 mg / mL;

[0063] 2) Construction of GSH-AuNPs-H 2 O 2 -TMB sensing system: 600 μL of 0.2 mol / L acetate buffer at pH 3.6 was mixed with 100 μL of 10-fold dilution of GSH-AuNPs solution, and then 100 μL of 3.26 mol / L H 2 O2 solution, react for 2 min, and finally add 100 μL 0.01 mol / L TMB solution and react for 8 min; take 24 GSH-AuNPs-H 2 O 2 -TMB sensing system, 100 μL of the above series of concentrations of tea polyphenols standard solution was added thereto respectively, each standard solution was repeated 3 times, and the reaction was allowed to stand for 15 min. The blank group was replaced with an equal volume of deionized water instead of the standard solution with added tea polyphenols. On the LED light board, a digital camera (model Nikon D3300) was used to take colorimetric photos of tea polyphenols at different concentrations after reaction. The results are shown in Figure 2 , Figure 2 In the experiment, the concentration of the tea polyphenol (TP) standard solution added from a to h gradually decreased, and h was the blank group.

[0064] Figure 3 The standard solution of tea polyphenols (0.3 mg / mL) and GSH-AuNPs-H 2 O 2 -UV spectra of the TMB sensing system before and after reaction.

[0065] Figure 4 The standard solutions of tea polyphenols with different concentrations and GSH-AuNPs-H 2 O 2 -TMB sensing system after reaction (A) UV spectrum, (B) linear diagram.

[0066] Figure 1- Figure 2 The test results show that due to the differences in the content of tea polyphenols, an antioxidant active ingredient in different varieties of green tea, the addition of GSH-AuNPs-H 2 O 2 -TMB sensing system, the scavenging effect on ·OH and the reducing effect on oxTMB are also different, resulting in different color changes in the sensing system, corresponding to different degrees of dark blue-green to colorless visible to the naked eye. For colors that are very close, a digital camera can be used to take photos and then the RGB values ​​of the corresponding photos can be extracted using software for chemometric algorithm (PLS-DA algorithm code, written internally by the research group) analysis; it shows that the above method of the present invention can be used to visualize and identify different varieties of green tea well by the naked eye or with the help of a visual color recognition tool.

[0067] Depend on Figure 3-Figure 4 It can be seen that GSH-AuNPs-H 2 O 2 -TMB sensor system has a significant difference in the UV absorption intensity after responding to tea polyphenols in green tea (significantly weakened). 2 O 2The UV absorption peak intensity of the -TMB sensing system at 652nm gradually decreased with the increase of tea polyphenols concentration, and showed a good linear relationship within a certain concentration range (0.01-0.3mg / mL), indicating that GSH-AuNPs-H 2 O 2 -The change of color depth of the TMB sensing system is negatively correlated with the content of tea polyphenols; tea polyphenols is a general term for polyphenols in tea leaves, and the content of tea polyphenols in green tea is 15%-30% of dry matter. The theoretical concentration of tea polyphenols introduced into the green tea extract obtained by ultrasonic alcohol extraction process of the present invention is 0.1×(15%-30%) / 10=(1.5-3) mg / mL, and the extract used for sensing is diluted 10 times, that is, (0.15-0.3) mg / mL, and within the concentration range below 0.3 mg / mL, the content of tea polyphenols in green tea and the change of color from dark to light have a negative correlation. It is inferred that the tea polyphenols and other antioxidant active substances contained in the green tea of ​​the present invention inhibit the oxidation of TMB through the scavenging effect on ·OH and the reduction effect on oxTMB. Due to the different antioxidant activities of different varieties of green tea, the sensing system undergoes different color changes, thereby achieving accurate identification of different varieties of green tea.

[0068] The above embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here, so the obvious changes or modifications derived are still within the protection scope of the invention.

Claims

1. A visual identification method for green tea varieties. It is characterized in that The following steps are involved: The tea polyphenols extracts of different varieties of green tea samples were mixed with GSH-AuNPs-H 2 O 2 -TMB sensing system was mixed evenly, allowed to react, and the resulting detection system was based on GSH-AuNPs-H 2 O 2 - The visual image of TMB sensing uses the color difference of the color response of green tea samples of different varieties to achieve visual discrimination of the green tea varieties to be tested based on the color of the detection system obtained after the tea polyphenol extract of the green tea sample to be tested is reacted; Among them, GSH-AuNPs represents glutathione-modified gold nanoparticles, and TMB is tetramethylbenzidine.

2. The method for visually distinguishing green tea varieties according to claim 1, It is characterized in that The standing reaction time is 15-18 minutes; and / or The GSH-AuNPs-H 2 O 2 The preparation method of the -TMB sensing solution comprises: mixing GSH-AuNPs, H 2 O 2 The solutions were mixed and reacted for 2-3 minutes, and finally TMB solution was added and reacted for 8-10 minutes.

3. The method for visually distinguishing green tea varieties according to claim 1, It is characterized in that The pH of the obtained detection system was 3.6-3.8; the concentration of GSH-AuNPs in the obtained detection system was (0.79-1.79)×10 -5 mol / L; H 2 O 2 The concentration is 0.3-0.35 mol / L; the concentration of TMB in the obtained detection system is 0.9-1.5 mmol / L; the content of green tea components in the obtained detection system is 0.09-0.15 mg of green tea raw materials / mL based on the green tea raw materials introduced during the preparation of the extract.

4. The method for visually distinguishing green tea varieties according to claim 1, It is characterized in that Color information is obtained by visual observation or photographic equipment.

5. The method for visually distinguishing green tea varieties according to claim 1, It is characterized in that The preparation method of GSH-AuNPs comprises the following steps: adding glutathione to HAuCl 4 The solution was stirred evenly at room temperature in the dark, and then freshly prepared ice-cold NaBH 4 The solution was stirred vigorously at room temperature in the dark to obtain a yellow clear solution emitting red light. After high-speed centrifugation, the supernatant was filtered through a microporous filter to remove insoluble impurities and obtain a glutathione-modified nanogold solution.

6. The method for visually distinguishing green tea varieties according to claim 5, It is characterized in that The glutathione, HAuCl 4 , NaBH 4 The molar ratio is 1:(0.57~0.77):(0.0010~0.0012).

7. The method for visually distinguishing green tea varieties according to claim 1, It is characterized in that The extract adopts ultrasonic alcohol extraction process, and the extraction solvent used is 50-70 vol% methanol aqueous solution.

8. The method for visually distinguishing green tea varieties according to claim 7, It is characterized in that The ultrasonic alcohol extraction process conditions adopt a solid-liquid ratio of 0.1 g:9-11 mL, a temperature of 35-40° C., and a time of 0.3-0.5 h.

9. The method for visually distinguishing green tea varieties according to claim 1, It is characterized in that The green tea samples to be tested include Dongting Biluochun, Kaihua Longding, Huangshan Maofeng, Xinyang Maojian, Duyun Maojian, Lu'an Guapian or Zhuyeqing.

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