Tea preparation method for reducing harmful substances in tea

Abstract

The invention relates to a tea preparation method capable of reducing harmful substances in tea, and belongs to the technical field of tea preparation. The tea leaf preparation method capable of reducing harmful substances in tea leaves comprises the following steps: performing microwave heating stir-frying on raw tea to obtain pre-prepared raw tea; uniformly mixing the pre-prepared raw tea with an adsorbent, performing baking treatment, and screening out the adsorbent to obtain the tea. According to the preparation method, after montmorillonite is acidized, sodium bicarbonate is used as a pore-foaming agent, then imine bond connected compounds are formed between chitosan oligosaccharide and vanillin, and after hydrochloric acid soaking, the specific surface area of the adsorbent is increased, and adsorption removal of caffeine is promoted.

Description

Technical Field

[0001] The invention belongs to the technical field of tea preparation and relates to a tea preparation method for reducing harmful substances in tea. Background Art

[0002] The tea soup obtained after brewing tea contains rich nutrients such as tea polyphenols, amino acids and vitamins, showing excellent antioxidant, radiation protection, anti-cancer and anti-aging health effects. However, tea soup also contains a certain amount of caffeine, which can stimulate the central nervous system and effectively relieve fatigue. But it is worth noting that long-term excessive intake of caffeine may have adverse effects on the cardiovascular and nervous systems, especially posing a significant threat to the health of children and pregnant women.

[0003] In view of the increasing attention paid by modern young people to a healthy lifestyle, if a technology can be developed that can effectively remove caffeine from tea while retaining beneficial ingredients such as tea polyphenols to the maximum extent, it will undoubtedly meet the needs of a wider range of people and open up a broader market space.

[0004] At present, there are many methods for removing caffeine from tea, covering a variety of technologies such as supercritical extraction, adsorption, aqueous solution elution and organic solvent extraction. Among them, the adsorption method is favored because of its economy and efficiency. In this method, adsorption materials such as ion exchange resin, activated carbon and montmorillonite play a key role. Montmorillonite, in particular, is particularly outstanding for its unique selective adsorption capacity for caffeine. However, it should also be noted that the adsorption process may have a certain impact on the color of the tea soup, thereby slightly reducing the overall quality of the tea soup. Summary of the invention

[0005] The purpose of the present invention is to provide a tea preparation method for reducing harmful substances in tea. The present invention acidifies montmorillonite, uses sodium bicarbonate as a pore-forming agent, and then utilizes a compound formed by imine bond connection between chitosan oligosaccharide and vanillin, and after soaking in hydrochloric acid, increases the specific surface area of ​​the adsorbent, thereby promoting the adsorption and removal of caffeine.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing tea leaves with reduced harmful substances in tea leaves, the method comprising the following steps:

[0008] Step 1: Fry the raw tea by microwave heating to obtain pre-made raw tea;

[0009] Step 2: Mix the pre-made raw tea and the adsorbent, then bake them, and then remove the adsorbent to obtain the tea.

[0010] As a preferred technical solution of the present invention, in step 1, the raw tea is obtained by withering, rolling and drying picked tea leaves to make raw tea with a water content of 7-9%.

[0011] As a preferred technical solution of the present invention, in step 1, the microwave heating and frying is rolling frying at a microwave power of 0.5-1kW and a rotation speed of 260-300r / min until the water content of the pre-prepared raw tea is 3-5%.

[0012] As a preferred technical solution of the present invention, in step 2, the baking treatment is baking at a temperature of 170-200° C. for 1.5-2.0 h.

[0013] The present invention discloses a method for preparing the adsorbent, comprising the following steps:

[0014] 1) placing montmorillonite in an acidic solution, mixing it, and then refluxing it, cooling it to room temperature, filtering it, washing it, and placing it in an oven for vacuum drying to obtain pretreated montmorillonite;

[0015] 2) After the pretreated montmorillonite and the chitosan oligosaccharide solution are stirred and mixed, an auxiliary agent and a vanillin solution are added, heated and stirred, and then the supernatant is removed by centrifugation, washed, immersed in a hydrochloric acid solution, filtered, washed, and placed in an oven for vacuum drying to obtain an adsorbent.

[0016] As a preferred technical solution of the present invention, in step 1), the mixing is stirring and mixing at a speed of 200-300r / min for 30-40min; the reflux treatment is reflux at a temperature of 80-90°C for 2-3h; the cleaning is cleaning with distilled water five times; and the vacuum drying is vacuum drying at a temperature of 60-70°C for 4-5h.

[0017] As a preferred technical solution of the present invention, in step 1), the mass ratio of the montmorillonite to the acidic solution is 4-5:80-100; and the acidic solution is a 25% sulfuric acid aqueous solution.

[0018] As a preferred technical solution of the present invention, in step 2), the stirring and mixing is stirring at a speed of 600-800 r / min for 40-60 min; the heating and stirring is stirring at a temperature of 60-72°C for 4-5 h; the centrifugation is centrifugation at 9000-10000 r / min for 30-40 min; the cleaning is cleaning three times with anhydrous ethanol; the soaking treatment is soaking at a temperature of 50°C for 6-8 h; the washing is washing with distilled water until the filtrate is neutral; the vacuum drying is vacuum drying at a temperature of 70-80°C to constant weight.

[0019] As a preferred technical solution of the present invention, in step 2), the mass fraction of the hydrochloric acid solution is 12%; the vanillin solution is prepared by mixing vanillin and ethanol in a mass ratio of 1:5; the mass ratio of the pretreated montmorillonite, chitosan oligosaccharide solution, auxiliary agent, vanillin solution and hydrochloric acid solution is 15-16:10-12:0.12-0.15:20-25:40-50.

[0020] As a preferred technical solution of the present invention, in step 2), the chitosan oligosaccharide solution is prepared by mixing chitosan oligosaccharide and deionized water in a mass ratio of 1.0-1.2:5-6; the molecular weight of the chitosan oligosaccharide is 2000-2400Da; and the auxiliary agent is sodium bicarbonate.

[0021] Beneficial effects of the present invention:

[0022] The present invention increases the specific surface area of ​​montmorillonite, increases the number of effective pores and surface bond breaks, facilitates the insertion of small molecule chitosan oligosaccharides into the interlayers of montmorillonite, adds sodium bicarbonate as a porogen, and then utilizes the chitosan oligosaccharides and vanillin to form a compound with good thermally stable imine bond connection. After sodium bicarbonate is soaked in hydrochloric acid, more adsorption sites are exposed on the surface of the compound, thereby further increasing the specific surface area of ​​the adsorbent and promoting the adsorption and removal of caffeine. DETAILED DESCRIPTION

[0023] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with the embodiments.

[0024] Example 1

[0025] A method for preparing tea leaves with reduced harmful substances in tea leaves comprises the following steps:

[0026] Step 1: Fry the raw tea by microwave heating to obtain pre-made raw tea;

[0027] Step 2: Mix the pre-made raw tea and the adsorbent, then bake them, and then remove the adsorbent to obtain the tea.

[0028] In step one, the raw tea is prepared by withering, rolling and drying the oolong tea leaves, and the raw tea has a moisture content of 7%. The microwave heating and frying is performed by frying the raw tea at a microwave power of 0.5 kW and a rotation speed of 260 r / min until the moisture content of the pre-prepared raw tea is 3%.

[0029] In step 2, the baking treatment is baking at 170° C. for 1.5 hours.

[0030] The preparation method of the adsorbent comprises the following steps:

[0031] 1) placing montmorillonite in an acidic solution, mixing it, and then refluxing it, cooling it to room temperature, filtering it, washing it, and placing it in an oven for vacuum drying to obtain pretreated montmorillonite;

[0032] 2) After the pretreated montmorillonite and the chitosan oligosaccharide solution are stirred and mixed, an auxiliary agent and a vanillin solution are added, heated and stirred, and then the supernatant is removed by centrifugation, washed, immersed in a hydrochloric acid solution, filtered, washed, and placed in an oven for vacuum drying to obtain an adsorbent.

[0033] In step 1), the mixing is performed by stirring and mixing at a speed of 200 r / min for 30 minutes; the reflux treatment is performed by reflux at a temperature of 80° C. for 2 hours; the cleaning is performed by cleaning with distilled water five times; the vacuum drying is performed by vacuum drying at a temperature of 60° C. for 4 hours; the mass ratio of the montmorillonite to the acidic solution is 4:80; and the acidic solution is a 25% aqueous solution of sulfuric acid.

[0034] In step 2), the stirring and mixing is stirring at a speed of 600 r / min for 40 minutes; the heating and stirring is stirring at a temperature of 60°C for 4 hours; the centrifugation is centrifugation at 9000 r / min for 30 minutes; the cleaning is cleaning three times with anhydrous ethanol; the soaking treatment is soaking at a temperature of 50°C for 6 hours; the washing is cleaning with distilled water until the filtrate is neutral; the vacuum drying is vacuum drying at a temperature of 70°C to constant weight; the mass fraction of the hydrochloric acid solution is 12%; the vanillin solution is formed by mixing vanillin and ethanol in a mass ratio of 1:5; the mass ratio of the pretreated montmorillonite, chitosan oligosaccharide solution, auxiliary agent, vanillin solution and hydrochloric acid solution is 15:10:0.12:20:40; the chitosan oligosaccharide solution is formed by mixing chitosan oligosaccharide and deionized water in a mass ratio of 1.0:5; the molecular weight of the chitosan oligosaccharide is 2000Da; and the auxiliary agent is sodium bicarbonate.

[0035] Example 2

[0036] A method for preparing tea leaves with reduced harmful substances in tea leaves comprises the following steps:

[0037] Step 1: Fry the raw tea by microwave heating to obtain pre-made raw tea;

[0038] Step 2: Mix the pre-made raw tea and the adsorbent, then bake them, and then remove the adsorbent to obtain the tea.

[0039] In step one, the raw tea is prepared by withering, rolling and drying the oolong tea leaves, and the raw tea has a moisture content of 7.5%. The microwave heating and frying is performed by frying the raw tea at a microwave power of 0.7 kW and a rotation speed of 270 r / min until the moisture content of the pre-prepared raw tea is 3.5%.

[0040] In step 2, the baking treatment is baking at 180° C. for 1.5 hours.

[0041] The preparation method of the adsorbent comprises the following steps:

[0042] 1) placing montmorillonite in an acidic solution, mixing it, and then refluxing it, cooling it to room temperature, filtering it, washing it, and placing it in an oven for vacuum drying to obtain pretreated montmorillonite;

[0043] 2) After the pretreated montmorillonite and the chitosan oligosaccharide solution are stirred and mixed, an auxiliary agent and a vanillin solution are added, heated and stirred, and then the supernatant is removed by centrifugation, washed, immersed in a hydrochloric acid solution, filtered, washed, and placed in an oven for vacuum drying to obtain an adsorbent.

[0044] In step 1), the mixing is performed by stirring and mixing at a speed of 230 r / min for 35 minutes; the reflux treatment is performed by reflux at a temperature of 83° C. for 2.5 hours; the cleaning is performed by cleaning with distilled water five times; the vacuum drying is performed by vacuum drying at a temperature of 63° C. for 4.5 hours; the mass ratio of the montmorillonite to the acidic solution is 4.3:87; and the acidic solution is a 25% aqueous solution of sulfuric acid.

[0045] In step 2), the stirring and mixing is stirring at a speed of 660 r / min for 45 minutes; the heating and stirring is stirring at a temperature of 64°C for 4.5 hours; the centrifugation is centrifugation at 9300 r / min for 35 minutes; the cleaning is cleaning three times with anhydrous ethanol; the soaking treatment is soaking at a temperature of 50°C for 6.5 hours; the washing is cleaning with distilled water until the filtrate is neutral; the vacuum drying is vacuum drying at a temperature of 73°C to constant weight; the mass fraction of the hydrochloric acid solution is 12%; the vanillin solution is formed by mixing vanillin and ethanol in a mass ratio of 1:5; the mass ratio of the pretreated montmorillonite, chitosan oligosaccharide solution, auxiliary agent, vanillin solution and hydrochloric acid solution is 15.5:10.5:0.13:22:43; the chitosan oligosaccharide solution is formed by mixing chitosan oligosaccharide and deionized water in a mass ratio of 1.1:5.3; the molecular weight of the chitosan oligosaccharide is 2200Da; and the auxiliary agent is sodium bicarbonate.

[0046] Example 3

[0047] A method for preparing tea leaves with reduced harmful substances in tea leaves comprises the following steps:

[0048] Step 1: Fry the raw tea by microwave heating to obtain pre-made raw tea;

[0049] Step 2: Mix the pre-made raw tea and the adsorbent, then bake them, and then remove the adsorbent to obtain the tea.

[0050] In step one, the raw tea is prepared by withering, rolling and drying the oolong tea leaves, and the raw tea has a moisture content of 8.5%. The microwave heating and frying is performed by frying the raw tea at a microwave power of 0.8 kW and a rotation speed of 280 r / min until the moisture content of the pre-prepared raw tea is 4.5%.

[0051] In step 2, the baking treatment is baking at 190° C. for 1.8 hours.

[0052] The preparation method of the adsorbent comprises the following steps:

[0053] 1) placing montmorillonite in an acidic solution, mixing it, and then refluxing it, cooling it to room temperature, filtering it, washing it, and placing it in an oven for vacuum drying to obtain pretreated montmorillonite;

[0054] 2) After the pretreated montmorillonite and the chitosan oligosaccharide solution are stirred and mixed, an auxiliary agent and a vanillin solution are added, heated and stirred, and then the supernatant is removed by centrifugation, washed, immersed in a hydrochloric acid solution, filtered, washed, and placed in an oven for vacuum drying to obtain an adsorbent.

[0055] In step 1), the mixing is performed by stirring and mixing at a speed of 260 r / min for 35 minutes; the reflux treatment is performed by reflux at a temperature of 85° C. for 2.5 hours; the cleaning is performed by cleaning with distilled water five times; the vacuum drying is performed by vacuum drying at a temperature of 67° C. for 4.5 hours; the mass ratio of the montmorillonite to the acidic solution is 4.7:93; and the acidic solution is a 25% aqueous solution of sulfuric acid.

[0056] In step 2), the stirring and mixing is stirring at a speed of 730 r / min for 55 minutes; the heating and stirring is stirring at a temperature of 68°C for 4.5 hours; the centrifugation is centrifugation at 9600 r / min for 35 minutes; the cleaning is cleaning three times with anhydrous ethanol; the soaking treatment is soaking at a temperature of 50°C for 7.5 hours; the washing is cleaning with distilled water until the filtrate is neutral; the vacuum drying is vacuum drying at a temperature of 75°C to constant weight; the mass fraction of the hydrochloric acid solution is 12%; the vanillin solution is formed by mixing vanillin and ethanol in a mass ratio of 1:5; the mass ratio of the pretreated montmorillonite, chitosan oligosaccharide solution, auxiliary agent, vanillin solution and hydrochloric acid solution is 15.5:11.5:0.14:23:47; the chitosan oligosaccharide solution is formed by mixing chitosan oligosaccharide and deionized water in a mass ratio of 1.1:5.7; the molecular weight of the chitosan oligosaccharide is 2200Da; and the auxiliary agent is sodium bicarbonate.

[0057] Example 4

[0058] A method for preparing tea leaves with reduced harmful substances in tea leaves comprises the following steps:

[0059] Step 1: Fry the raw tea by microwave heating to obtain pre-made raw tea;

[0060] Step 2: Mix the pre-made raw tea and the adsorbent, then bake them, and then remove the adsorbent to obtain the tea.

[0061] In step one, the raw tea is prepared by withering, rolling and drying the oolong tea leaves, and the raw tea has a moisture content of 9%. The microwave heating and frying is performed by frying the raw tea at a microwave power of 1 kW and a rotation speed of 300 r / min until the moisture content of the pre-prepared raw tea is 5%.

[0062] In step 2, the baking treatment is baking at 200° C. for 2.0 h.

[0063] The preparation method of the adsorbent comprises the following steps:

[0064] 1) placing montmorillonite in an acidic solution, mixing it, and then refluxing it, cooling it to room temperature, filtering it, washing it, and placing it in an oven for vacuum drying to obtain pretreated montmorillonite;

[0065] 2) After the pretreated montmorillonite and the chitosan oligosaccharide solution are stirred and mixed, an auxiliary agent and a vanillin solution are added, heated and stirred, and then the supernatant is removed by centrifugation, washed, immersed in a hydrochloric acid solution, filtered, washed, and placed in an oven for vacuum drying to obtain an adsorbent.

[0066] In step 1), the mixing is performed by stirring and mixing at a speed of 300 r / min for 40 minutes; the reflux treatment is performed by reflux at a temperature of 90° C. for 3 hours; the cleaning is performed by cleaning with distilled water five times; the vacuum drying is performed by vacuum drying at a temperature of 70° C. for 5 hours; the mass ratio of the montmorillonite to the acidic solution is 5:100; and the acidic solution is a 25% aqueous solution of sulfuric acid.

[0067] In step 2), the stirring and mixing is stirring at a speed of 800 r / min for 60 minutes; the heating and stirring is stirring at a temperature of 72°C for 5 hours; the centrifugation is centrifugation at 10000 r / min for 40 minutes; the cleaning is cleaning three times with anhydrous ethanol; the soaking treatment is soaking at a temperature of 50°C for 8 hours; the washing is cleaning with distilled water until the filtrate is neutral; the vacuum drying is vacuum drying at a temperature of 80°C to constant weight; the mass fraction of the hydrochloric acid solution is 12%; the vanillin solution is formed by mixing vanillin and ethanol in a mass ratio of 1:5; the mass ratio of the pretreated montmorillonite, chitosan oligosaccharide solution, auxiliary agent, vanillin solution and hydrochloric acid solution is 16:12:0.15:25:50; the chitosan oligosaccharide solution is formed by mixing chitosan oligosaccharide and deionized water in a mass ratio of 1.2:6; the molecular weight of the chitosan oligosaccharide is 2400Da; and the auxiliary agent is sodium bicarbonate.

[0068] Comparative Example 1

[0069] Compared with Example 2, the difference in Comparative Example 1 is that step one is not performed, the raw tea in step one replaces the pre-made raw tea, and the other components, preparation steps and parameters are the same.

[0070] Comparative Example 2

[0071] Compared with Example 2, the difference in Comparative Example 2 is that montmorillonite replaces the pretreated montmorillonite, and the other components, preparation steps and parameters are the same.

[0072] Comparative Example 3

[0073] Compared with Example 2, the difference in Comparative Example 3 is that chitosan replaces chitosan oligosaccharide, and the other components, preparation steps and parameters are the same.

[0074] Comparative Example 4

[0075] Compared with Example 2, Comparative Example 4 is different in that chitosan oligosaccharide is not used, and the remaining components, preparation steps and parameters are the same.

[0076] Comparative Example 5

[0077] Compared with Example 2, Comparative Example 5 is different in that no auxiliary agent is used, and the remaining components, preparation steps and parameters are the same.

[0078] Comparative Example 6

[0079] Compared with Example 2, Comparative Example 6 is different in that vanillin is not used, and the other components, preparation steps and parameters are the same.

[0080] The tea leaves obtained from Examples 1-4 and Comparative Examples 1-6 were tested as follows. The test results are shown in Table 1.

[0081] Caffeine content determination: according to GB / T8312-2013;

[0082] Table 1

[0083] Caffeine(%) Example 1 0.75 Example 2 0.72 Example 3 0.78 Example 4 0.83 Comparative Example 1 4.58 Comparative Example 2 5.14 Comparative Example 3 3.65 Comparative Example 4 4.51 Comparative Example 5 3.29 Comparative Example 6 3.73

[0084] From the test results in Table 1, it can be seen that compared with Comparative Examples 1-6, the tea leaves prepared in Examples 1-4 of the present invention have a lower caffeine content, and the adsorbent has a significant effect in removing caffeine; from the analysis of Examples 1-4 and Comparative Examples 1-6 combined with Table 1, it can be seen that the present invention uses microwave heating and frying to open the compactness and pore structure of the tea leaves, and the moisture in the tea leaves will be heated and converted into steam. This process will drive the caffeine to migrate to the surface of the tea leaves and evaporate therewith, thereby promoting the reduction of the caffeine content and facilitating the subsequent adsorption of caffeine by the adsorbent; in addition, after the present invention acidifies the montmorillonite, the specific surface area of ​​the montmorillonite can be increased, and the number of effective pores and surface broken bonds can be increased, which is conducive to the insertion of small molecule chitosan oligosaccharides into the montmorillonite interlayer, while the large molecule chitosan is not easy to insert into the montmorillonite interlayer. Sodium bicarbonate was added as a pore-forming agent, and then a compound with a good thermally stable imine bond was formed between chitosan oligosaccharide and vanillin. After sodium bicarbonate was soaked in hydrochloric acid, more adsorption sites were exposed on the surface of the compound, further increasing the specific surface area of ​​the adsorbent and promoting the adsorption and removal of caffeine.

[0085] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing tea leaves for reducing harmful substances in tea leaves, characterized in that: The tea preparation method comprises the following steps: Step 1: Fry the raw tea by microwave heating to obtain pre-made raw tea; Step 2: Mix the pre-made raw tea and the adsorbent, then bake them, and then remove the adsorbent to obtain the tea.

2. A method for preparing tea leaves for reducing harmful substances in tea leaves according to claim 1, characterized in that: In step 1, the raw tea is obtained by withering, rolling and drying the picked tea leaves to obtain raw tea with a water content of 7-9%.

3. The method for preparing tea leaves for reducing harmful substances in tea leaves according to claim 1, characterized in that: In step 1, the microwave heating and frying is performed by rolling and frying at a microwave power of 0.5-1 kW and a rotation speed of 260-300 r / min until the water content of the pre-prepared raw tea is 3-5%.

4. The method for preparing tea leaves for reducing harmful substances in tea leaves according to claim 1, characterized in that: In step 2, the baking treatment is baking at a temperature of 170-200° C. for 1.5-2.0 hours.

5. The method for preparing tea leaves for reducing harmful substances in tea leaves according to claim 1, characterized in that: The preparation method of the adsorbent comprises the following steps: 1) placing montmorillonite in an acidic solution, mixing it, and then refluxing it, cooling it to room temperature, filtering it, washing it, and placing it in an oven for vacuum drying to obtain pretreated montmorillonite; 2) After the pretreated montmorillonite and the chitosan oligosaccharide solution are stirred and mixed, an auxiliary agent and a vanillin solution are added, heated and stirred, and then the supernatant is removed by centrifugation, washed, immersed in a hydrochloric acid solution, filtered, washed, and placed in an oven for vacuum drying to obtain an adsorbent.

6. A method for preparing tea leaves for reducing harmful substances in tea leaves according to claim 5, characterized in that: In step 1), the mixing is performed by stirring and mixing at a speed of 200-300 r / min for 30-40 min; the reflux treatment is performed by reflux at a temperature of 80-90° C. for 2-3 h; the cleaning is performed by cleaning with distilled water five times; and the vacuum drying is performed by vacuum drying at a temperature of 60-70° C. for 4-5 h.

7. The method for preparing tea leaves for reducing harmful substances in tea leaves according to claim 5, characterized in that: In step 1), the mass ratio of the montmorillonite to the acidic solution is 4-5:80-100; the acidic solution is a 25% sulfuric acid aqueous solution.

8. The method for preparing tea leaves for reducing harmful substances in tea leaves according to claim 5, characterized in that: In step 2), the stirring and mixing is stirring at a speed of 600-800 r / min for 40-60 min; the heating and stirring is stirring at a temperature of 60-72°C for 4-5 h; the centrifugation is centrifugation at 9000-10000 r / min for 30-40 min; the cleaning is cleaning three times with anhydrous ethanol; the soaking treatment is soaking at a temperature of 50°C for 6-8 h; the washing is washing with distilled water until the filtrate is neutral; the vacuum drying is vacuum drying at a temperature of 70-80°C to constant weight.

9. The method for preparing tea leaves for reducing harmful substances in tea leaves according to claim 5, characterized in that: In step 2), the mass fraction of the hydrochloric acid solution is 12%; the vanillin solution is prepared by mixing vanillin and ethanol in a mass ratio of 1:5; the mass ratio of the pretreated montmorillonite, chitosan oligosaccharide solution, auxiliary agent, vanillin solution and hydrochloric acid solution is 15-16:10-12:0.12-0.15:20-25:40-50.

10. A method for preparing tea leaves with reduced harmful substances in tea leaves according to claim 5 or 9, characterized in that: In step 2), the chitosan oligosaccharide solution is prepared by mixing chitosan oligosaccharide and deionized water in a mass ratio of 1.0-1.2:5-6; the molecular weight of the chitosan oligosaccharide is 2000-2400Da; and the auxiliary agent is sodium bicarbonate.