Preparation method of oolong tea extract with high tea aroma

Abstract

The invention relates to the technical field of food processing, and particularly discloses a preparation method of an oolong tea extract. Pure water extraction is adopted, no organic solvent is introduced for extraction, the loss of flavor substances is reduced, and the method is green and environmentally friendly; high-temperature extraction is used in early-stage extraction, the extraction frequency can be reduced, the extraction efficiency can be improved, the energy consumption can be reduced, one of vitamin C, sodium erythorbate and astaxanthin is added to serve as an antioxidant, the pH is adjusted to be faintly acid, the antioxidant can keep the maximum activity and stability, and the antioxidant effect is achieved; according to the method, a molecular distillation technology, an enzymolysis technology and a membrane concentration technology are combined, so that the extraction efficiency of the oolong tea extract is improved, the flavor of the oolong tea extract is remarkably improved, and the method is simple in used equipment, low in energy consumption, easy to operate and suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing, and particularly relates to a method for preparing an oolong tea high-tea aroma extract. Background Art

[0002] Oolong tea is also known as green tea and semi-fermented tea. At present, the varieties of oolong tea in China are quite diverse, and oolong tea is also a unique tea variety in my country. Oolong tea is also one of the six traditional types of tea in my country. As a semi-fermented tea, oolong tea has a natural floral and fruity aroma and the characteristics of "green leaves with red edges". It also has the fragrance of green tea and the mellow taste of black tea, which makes oolong tea different from other teas. Oolong tea has a strong flavor, a rich tea soup, and contains a variety of active organisms such as tea polyphenols, alkaloids and theanine. Therefore, oolong tea relies on its unique taste and flavor, as well as good efficacy characteristics. With the popularization of the concept of healthy living, oolong tea is deeply loved by consumers for its rich nutrients and health functions, such as anti-oxidation, lowering blood lipids, and lowering blood sugar, and the market continues to expand. Oolong tea extract is an oolong tea extract commonly used in beverages and milk tea shops. The extract has the characteristic flavor of oolong tea. It is widely used in food and beverage processing.

[0003] At present, the oolong tea extract used in my country's beverage and food industry is extracted using an alcohol solution of a certain concentration, and then concentrated under reduced pressure to obtain the oolong tea extract. This method has low extraction efficiency, high energy consumption, environmental pollution, and serious loss of tea flavor and poor quality. During the concentration process, a large amount of oolong tea flavor substances are entrained by the solvent, and the recovered alcohol solution contains a large amount of flavor substances, which makes it difficult to recover the flavor substances. The tea aroma substances are seriously lost during the processing process, and the resulting product lacks flavor. Among them, the alcohol extract extracts more bitterness, which limits its application in the product in the later stage and affects the sensory performance. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing an oolong tea high tea aroma extract, which has the characteristics of high extraction rate and rich flavor of the prepared product.

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

[0006] A method for preparing an oolong tea extract, the specific process of the preparation method is as follows:

[0007] S1: mixing oolong tea leaves and deionized water in a mass ratio of 1:(2-3) and soaking them for 15-30 minutes, and crushing the soaked oolong tea leaves using a grinder;

[0008] S2: Mix the crushed oolong tea leaves in S1 with deionized water in a mass ratio of 1:(30-60), adjust the pH value with an alkaline solution to 5.5-6, add an antioxidant, extract at a temperature of 80-85° C. for 1.5-2.5 h, and cool to room temperature after the extraction to obtain an oolong tea extract;

[0009] S3: filtering the oolong tea extract obtained in S2 using a filter to obtain an oolong tea filtrate, extracting the oolong tea aroma from the oolong tea filtrate using a molecular distillation device, the operating conditions of the molecular distillation device being: temperature 40-60° C., vacuum degree 0.1 mbar-10 mbar, rotation speed 350 r / min, obtaining a tea aroma extract and tea residue, and concentrating the tea aroma extract using a membrane concentration device to obtain a tea aroma extract A;

[0010] S4: adding 1-3 wt % of an enzyme preparation to the tea residue obtained after distillation in S3 for enzymatic hydrolysis, wherein the enzyme preparation comprises tannase, glycosidase, flavor protease, bromelain, acid protease and fungal lipase in a mass ratio of (3-5): (3-5): (3-4): (3-4): (1-2): (1-2), the enzymatic hydrolysis temperature is 40-50° C., the enzymatic hydrolysis time is 4-12 h, and after the enzymatic hydrolysis is completed, an enzyme inactivation treatment is performed to obtain enzymatically hydrolyzed tea residue;

[0011] S5: filtering the enzymatically hydrolyzed tea residue obtained in S4, and concentrating the obtained filtrate by high multiple using a concentration device to obtain an oolong tea extract B;

[0012] S6: Compounding the tea aroma extract A obtained in S3 and the oolong tea extract B obtained in S5 at a ratio of 1:(0.5-2) to obtain an oolong tea extract.

[0013] Preferably, the alkaline solution in S2 is a saturated sodium bicarbonate solution.

[0014] Preferably, the antioxidant in S2 is one of vitamin C, sodium erythorbate or astaxanthin.

[0015] Preferably, the filter in S3 is a plate and frame filter.

[0016] Preferably, the filter screen of the filter in S3 is 100-200 mesh.

[0017] Preferably, the membrane concentration equipment in S3 is a reverse osmosis membrane equipment or a pervaporation membrane equipment.

[0018] Preferably, the temperature of the enzyme inactivation treatment in S4 is 80-90° C., and the treatment time is 30-60 min.

[0019] Preferably, the filtration in S5 uses a 0.1 μm ceramic membrane or a 0.1 μm PTFE filter membrane.

[0020] Preferably, the concentrating equipment in S5 is a vacuum concentrator or a scraped film concentrator.

[0021] Preferably, the tea aroma extract A, oolong tea extract B and oolong tea extract are used in food preparation.

[0022] The invention adopts the method of soaking oolong tea leaves in water and then crushing them through a crusher. Compared with direct extraction without crushing, the crushing extraction efficiency is higher and the number of extractions is less. The method of soaking oolong tea leaves in water and then crushing them has less dust and reduces the loss of flavor.

[0023] The invention adopts pure water extraction, does not introduce organic solvent extraction, reduces the loss of flavor substances, and is green and environmentally friendly. The invention uses high temperature extraction in the early stage of extraction. Extraction at a higher temperature can reduce the number of extractions, increase extraction efficiency, and reduce energy consumption. Vitamin C, sodium isoascorbate, and one of astaxanthin are added as an antioxidant, and the pH is adjusted to weak acidity so that the antioxidant can maintain maximum activity and stability and exert an antioxidant effect.

[0024] Oolong tea contains rich flavor substances, which are prone to oxidation during high-temperature extraction, resulting in degradation of beneficial ingredients in tea leaves. Adding vitamin C, sodium isoascorbate or astaxanthin can effectively inhibit this oxidation reaction, effectively prevent the oxidation of polyphenol compounds, amino acids and aroma substances in oolong tea leaves, protect the active ingredients in tea leaves, and maintain their flavor and nutritional value. By preventing oxidation reactions, the tea aroma and other flavor substances can be better retained and released. Vitamin C, sodium isoascorbate and astaxanthin can effectively delay the oxidation process. After adding them, the subsequent oolong tea extract usually has a longer shelf life, can better maintain its color, aroma and taste, and is suitable for long-term storage and sales. Vitamin C is a well-known immune enhancer with anti-aging and collagen synthesis promotion functions. Astaxanthin helps to fight inflammation and protect cardiovascular health. Adding these ingredients to oolong tea extract can provide consumers with additional health value and increase the attractiveness of the product.

[0025] The present invention uses molecular distillation technology and membrane concentration technology to extract the tea fragrance of oolong tea filtrate. The molecular distillation temperature is low, and some heat-sensitive substances in some tea fragrances can be protected. Molecular distillation is operated under very low pressure, the distillation liquid film is thin, the heat transfer efficiency is high, the heating time of oolong tea filtrate is short, the distance between the heated liquid surface and the condensation surface is less than the average free path of light molecules, so the light molecules escaping from the liquid surface reach the condensation surface almost without collision, so the tea fragrance substances in the tea fragrance extract are not easy to be oxidized and damaged, and the tea fragrance is preserved. At the same time, reverse osmosis membrane equipment is used to concentrate the tea fragrance extract. This process does not have the introduction of additional solvents, will not affect the tea fragrance substances, and has a high concentration multiple, simple and easy to operate equipment, low energy consumption, and high recovery rate of tea fragrance substances.

[0026] The present invention uses molecular distillation technology in combination with enzymatic hydrolysis technology, which can protect and release the flavor substances in the tea leaves to the greatest extent during extraction, thereby improving the extraction efficiency. The tea leaves are heated for a short time during molecular distillation, and the residence time at the distillation temperature is generally between a few seconds and tens of seconds, which reduces the chance of thermal decomposition of the tea leaves, and avoids the situation in which the tea leaves are heated all the time during traditional heating distillation, resulting in serious loss of nutrients. The present invention uses tannase, glycosidase, flavor protease, bromelain, acid protease and fungal lipase as enzyme preparations, and adjusts the pH to weak acidity during the early extraction to ensure the activity of the enzyme preparation. Tannase reduces the bitterness of the tea leaves by degrading tannins, while glycosidase decomposes glycoside compounds to release more flavor substances, making the tea leaves more fragrant and flavorful. The combination of the two can improve the taste of the tea leaves, making it both smooth and fragrant. Flavor protease, bromelain and acid protease can decompose the protein in the tea leaves to produce amino acids and peptide substances , providing a richer taste and freshness. Acidic protease also helps to enhance the antioxidant capacity of tea base and helps to preserve the freshness of tea base. Fungal lipase can decompose the fat in tea leaves and release fatty acids and other volatile compounds. Fatty acids are the key precursors for the formation of oolong tea aroma. The degradation of fatty acids can produce cyclic aroma products, which increase the aroma layering of tea base. The combination of fungal lipase with flavor protease, bromelain and acidic protease can further enhance the complexity of the flavor of the tea base and significantly improve the flavor quality of the prepared oolong tea extract.

[0027] The invention uses molecular distillation technology, enzymatic hydrolysis technology and membrane concentration technology in combination to improve the extraction efficiency of oolong tea extract and significantly improve the flavor of oolong tea extract. The equipment used is simple, the energy consumption is low, the operation is easy, and the method is suitable for industrial production.

[0028] The beneficial effects of the present invention are as follows: the present invention adopts pure water extraction, does not introduce organic solvent extraction, reduces the loss of flavor substances, and is green and environmentally friendly. High-temperature extraction is used in the early stage of extraction, which reduces the number of extractions, increases extraction efficiency, and reduces energy consumption. Vitamin C, sodium isoascorbate, and one of astaxanthin are added as antioxidants during extraction, and the pH is adjusted to weak acidity so that the antioxidant can maintain maximum activity and stability and exert an antioxidant effect. The addition of antioxidants can effectively prevent the degradation of beneficial components in oolong tea leaves, protect the active components in the tea leaves, maintain their flavor and nutritional value, and enable the subsequently prepared oolong tea extract to generally have a longer shelf life, better maintain its color, aroma, and taste, and be suitable for long-term storage and sales.

[0029] The present invention uses a combination of molecular distillation technology and membrane concentration technology to extract the tea aroma of oolong tea filtrate. The molecular distillation temperature is low, which can protect some heat-sensitive substances in the tea aroma. At the same time, a reverse osmosis membrane device is used to concentrate the tea aroma extract. This process does not introduce any additional solvent and will not affect the tea aroma substances. The concentration multiple is high, the equipment is simple and easy to operate, the energy consumption is low, and the recovery rate of the tea aroma substances is high.

[0030] The present invention uses molecular distillation technology in combination with enzymolysis technology, which can protect and release the flavor substances in the tea leaves to the greatest extent during extraction, thereby improving the extraction efficiency. The present invention adjusts the pH to weak acidity during early extraction to ensure the activity of the enzyme preparation, degrades tannins through tannase and glycosidase, decomposes glycoside compounds, reduces the bitterness of the tea leaves, releases more flavor substances, and makes the tea leaves more fragrant and flavorful. Three proteases are used to produce amino acids and peptide substances, providing a richer taste and freshness, wherein the acidic protease also helps to enhance the antioxidant property of the tea leaves, helps to preserve the freshness of the tea leaves, and the combination of fungal lipase and the three proteases can further enhance the complexity of the flavor of the tea leaves, and significantly improve the flavor quality of the prepared oolong tea extract.

[0031] The invention uses molecular distillation technology, enzymatic hydrolysis technology and membrane concentration technology in combination to improve the extraction efficiency of oolong tea extract and significantly improve the flavor of oolong tea extract. The equipment used is simple, the energy consumption is low, the operation is easy, and the method is suitable for industrial production. DETAILED DESCRIPTION

[0032] 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.

[0033] Example 1

[0034] S1: Weigh 10 kg of oolong tea leaves using a balance, mix the oolong tea leaves with deionized water in a mass ratio of 1:2 and soak for 15 minutes, then grind the soaked oolong tea leaves using a grinder;

[0035] S2: Add the crushed oolong tea leaves in S1 into 300 kg of water, adjust the pH value to 5.5 with a saturated sodium bicarbonate solution, add 25 g of sodium isoascorbate, extract at 83° C. for 1.5 h, and cool to room temperature after the extraction to obtain an oolong tea extract;

[0036] S3: filtering the oolong tea extract obtained in S2 using a 200-mesh plate-and-frame filter to obtain an oolong tea filtrate, extracting the oolong tea aroma from the oolong tea filtrate using a molecular distillation device, the operating conditions of the molecular distillation device being: temperature 50° C., vacuum degree 1 mbar, rotation speed 350 r / min, to obtain a tea aroma extract and tea residue, and the tea aroma extract is highly concentrated through a reverse osmosis membrane to obtain a tea aroma extract A;

[0037] S4: adding 2 wt % of an enzyme preparation to the tea residue obtained after distillation in S3 for enzymatic hydrolysis, wherein the enzyme preparation comprises tannase, glycosidase, flavor protease, bromelain, acid protease and fungal lipase in a mass ratio of 4:4:4:3:2:1, the enzymatic hydrolysis temperature is 45° C., the enzymatic hydrolysis time is 6 h, and after the enzymatic hydrolysis is completed, the temperature is raised to 85° C. for enzyme inactivation treatment, and the enzyme inactivation treatment time is 30 min, to obtain enzymatically hydrolyzed tea residue;

[0038] S5: filtering the enzymatically hydrolyzed tea residue obtained in S4 using a 0.1 μm PTFE filter membrane, and concentrating the obtained filtrate using a vacuum concentrator to obtain an oolong tea extract B;

[0039] S6: The tea aroma extract A obtained in S3 and the oolong tea extract B obtained in S5 are compounded in a ratio of 1:1 to obtain an oolong tea extract.

[0040] In this example, the extraction rate of oolong tea extract A is 70%, and the extraction rate of oolong tea extract B is 85%. The flavor evaluation results of the oolong tea extracts in this example are shown in Table 1.

[0041] Example 2

[0042] S1: Weigh 10 kg of oolong tea leaves using a balance, mix the oolong tea leaves with deionized water in a mass ratio of 1:1.5 and soak for 15 minutes, then grind the soaked oolong tea leaves using a grinder;

[0043] S2: adding the crushed oolong tea leaves in S1 into 300 kg of water, adjusting the pH value to 5.5 with a saturated sodium bicarbonate solution, adding 25 g of vitamin C, extracting at 83° C. for 2 h, and cooling to room temperature after the extraction to obtain an oolong tea extract;

[0044] S3: filtering the oolong tea extract obtained in S2 using a 200-mesh plate-and-frame filter to obtain an oolong tea filtrate, extracting the oolong tea aroma from the oolong tea filtrate using a molecular distillation device, the operating conditions of the molecular distillation device being: temperature 50° C., vacuum degree 0.5 mbar, rotation speed 350 r / min, to obtain a tea aroma extract and tea residue, and the tea aroma extract is highly concentrated through a reverse osmosis membrane to obtain a tea aroma extract A;

[0045] S4: adding 2 wt % of an enzyme preparation to the tea residue obtained after distillation in S3 for enzymatic hydrolysis, wherein the enzyme preparation comprises tannase, glycosidase, flavor protease, bromelain, acid protease and fungal lipase in a mass ratio of 5:4:3:3:1:1, the enzymatic hydrolysis temperature is 45° C., the enzymatic hydrolysis time is 8 h, and after the enzymatic hydrolysis is completed, the temperature is raised to 85° C. for enzyme inactivation treatment, and the enzyme inactivation treatment time is 30 min to obtain enzymatically hydrolyzed tea residue;

[0046] S5: filtering the enzymatically hydrolyzed tea residue obtained in S4 using a 0.1 μm PTFE filter membrane, and concentrating the obtained filtrate using a vacuum concentrator to obtain an oolong tea extract B;

[0047] S6: The tea aroma extract A obtained in S3 and the oolong tea extract B obtained in S5 are compounded in a ratio of 1:1 to obtain an oolong tea extract.

[0048] In this example, the extraction rate of oolong tea extract A is 71%, and the extraction rate of oolong tea extract B is 81%. The flavor evaluation results of the oolong tea extracts in this example are shown in Table 1.

[0049] Example 3

[0050] S1: Weigh 10 kg of oolong tea leaves using a balance, mix the oolong tea leaves with deionized water in a mass ratio of 1:1.5 and soak for 15 minutes, then grind the soaked oolong tea leaves using a grinder;

[0051] S2: Add the crushed oolong tea leaves in S1 into 500 kg of water, adjust the pH value to 5.5 with a saturated sodium bicarbonate solution, add 35 g of astaxanthin, extract at 83° C. for 2 h, and cool to room temperature after the extraction to obtain an oolong tea extract;

[0052] S3: filtering the oolong tea extract obtained in S2 using a 200-mesh plate-and-frame filter to obtain an oolong tea filtrate, extracting the oolong tea aroma from the oolong tea filtrate using a molecular distillation device, the operating conditions of the molecular distillation device being: temperature 50° C., vacuum degree 0.5 mbar, rotation speed 350 r / min, to obtain a tea aroma extract and tea residue, and the tea aroma extract is highly concentrated through a reverse osmosis membrane to obtain a tea aroma extract A;

[0053] S4: adding 2 wt % of an enzyme preparation to the tea residue obtained after distillation in S3 for enzymatic hydrolysis, wherein the enzyme preparation comprises tannase, glycosidase, flavor protease, bromelain, acid protease and fungal lipase in a mass ratio of 4:5:4:4:2:1, the enzymatic hydrolysis temperature is 45° C., the enzymatic hydrolysis time is 8 h, and after the enzymatic hydrolysis is completed, the temperature is raised to 85° C. for enzyme inactivation treatment, and the enzyme inactivation treatment time is 30 min to obtain enzymatically hydrolyzed tea residue;

[0054] S5: filtering the enzymatically hydrolyzed tea residue obtained in S4 using a 0.1 μm PTFE filter membrane, and concentrating the obtained filtrate using a vacuum concentrator to obtain an oolong tea extract B;

[0055] S6: Compounding the tea aroma extract A obtained in S3 and the oolong tea extract B obtained in S5 at a ratio of 1:2 to obtain an oolong tea extract.

[0056] In this example, the extraction rate of oolong tea extract A is 75%, and the extraction rate of oolong tea extract B is 87%. The flavor evaluation results of the oolong tea extracts in this example are shown in Table 1.

[0057] Example 4

[0058] S1: Weigh 10 kg of oolong tea leaves using a balance, mix the oolong tea leaves with deionized water in a mass ratio of 1:2 and soak for 15 minutes, then grind the soaked oolong tea leaves using a grinder;

[0059] S2: Add the crushed oolong tea leaves in S1 into 500 kg of water, adjust the pH value to 5.5 with a saturated sodium bicarbonate solution, add 35 g of sodium isoascorbate, extract at 83° C. for 2 h, and cool to room temperature after the extraction to obtain an oolong tea extract;

[0060] S3: filtering the oolong tea extract obtained in S2 using a 200-mesh plate-and-frame filter to obtain an oolong tea filtrate, extracting the oolong tea aroma from the oolong tea filtrate using a molecular distillation device, the operating conditions of the molecular distillation device being: temperature 50° C., vacuum degree 1 mbar, rotation speed 350 r / min, to obtain a tea aroma extract and tea residue, and the tea aroma extract is highly concentrated through a reverse osmosis membrane to obtain a tea aroma extract A;

[0061] S4: adding 2 wt % of an enzyme preparation to the tea residue obtained after distillation in S3 for enzymatic hydrolysis, wherein the enzyme preparation comprises tannase, glycosidase, flavor protease, bromelain, acid protease and fungal lipase in a mass ratio of 4:5:4:4:2:1, the enzymatic hydrolysis temperature is 45° C., the enzymatic hydrolysis time is 6 h, and after the enzymatic hydrolysis is completed, the temperature is raised to 85° C. for enzyme inactivation treatment, and the enzyme inactivation treatment time is 30 min, to obtain enzymatically hydrolyzed tea residue;

[0062] S5: filtering the enzymatically hydrolyzed tea residue obtained in S4 using a 0.1 μm PTFE filter membrane, and concentrating the obtained filtrate using a vacuum concentrator to obtain an oolong tea extract B;

[0063] S6: Compounding the tea aroma extract A obtained in S3 and the oolong tea extract B obtained in S5 at a ratio of 1:2 to obtain an oolong tea extract.

[0064] In this example, the extraction rate of oolong tea extract A is 73%, and the extraction rate of oolong tea extract B is 84%. The flavor evaluation results of the oolong tea extracts in this example are shown in Table 1.

[0065] Comparative Example 1

[0066] S1: Weigh 10 kg of oolong tea leaves using a balance, mix the oolong tea leaves with deionized water in a mass ratio of 1:2 and soak for 15 minutes, then grind the soaked oolong tea leaves using a grinder;

[0067] S2: adding the crushed oolong tea leaves in S1 into 300 kg of water, adjusting the pH value to 5.5 with a saturated sodium bicarbonate solution, extracting at 83° C. for 1.5 h, and cooling to room temperature after the extraction to obtain an oolong tea extract;

[0068] S3: filtering the oolong tea extract obtained in S2 using a 200-mesh plate-and-frame filter to obtain an oolong tea filtrate, extracting the oolong tea aroma from the oolong tea filtrate using a molecular distillation device, the operating conditions of the molecular distillation device being: temperature 50° C., vacuum degree 1 mbar, rotation speed 350 r / min, to obtain a tea aroma extract and tea residue, and the tea aroma extract is highly concentrated through a reverse osmosis membrane to obtain a tea aroma extract A;

[0069] S4: adding 2 wt % of an enzyme preparation to the tea residue obtained after distillation in S3 for enzymatic hydrolysis, wherein the enzyme preparation comprises tannase, glycosidase, flavor protease, bromelain, acid protease and fungal lipase in a mass ratio of 4:4:4:3:2:1, the enzymatic hydrolysis temperature is 45° C., the enzymatic hydrolysis time is 6 h, and after the enzymatic hydrolysis is completed, the temperature is raised to 85° C. for enzyme inactivation treatment, and the enzyme inactivation treatment time is 30 min, to obtain enzymatically hydrolyzed tea residue;

[0070] S5: filtering the enzymatically hydrolyzed tea residue obtained in S4 using a 0.1 μm PTFE filter membrane, and concentrating the obtained filtrate using a vacuum concentrator to obtain an oolong tea extract B;

[0071] S6: The tea aroma extract A obtained in S3 and the oolong tea extract B obtained in S5 are compounded in a ratio of 1:1 to obtain an oolong tea extract.

[0072] No antioxidant was added in this comparative example. The extraction rate of oolong tea extract A in this comparative example was 63%, and the extraction rate of oolong tea extract B in this comparative example was 70%. The flavor evaluation results of the oolong tea extracts in this comparative example are shown in Table 1.

[0073] Comparative Example 2

[0074] S1: Weigh 10 kg of oolong tea leaves using a balance, mix the oolong tea leaves with deionized water in a mass ratio of 1:2 and soak for 15 minutes, then grind the soaked oolong tea leaves using a grinder;

[0075] S2: Add the crushed oolong tea leaves in S1 into 300 kg of water, adjust the pH value to 5.5 with a saturated sodium bicarbonate solution, add 25 g of sodium isoascorbate, extract at 83° C. for 1.5 h, and cool to room temperature after the extraction to obtain an oolong tea extract;

[0076] S3: filtering the oolong tea extract obtained in S2 using a 200-mesh plate-and-frame filter to obtain an oolong tea filtrate, extracting the oolong tea aroma from the oolong tea filtrate using a heating distillation device to obtain a tea aroma extract and tea residue, and concentrating the tea aroma extract by a high multiple through a reverse osmosis membrane to obtain a tea aroma extract A;

[0077] S4: adding 2 wt % of an enzyme preparation to the tea residue obtained after distillation in S3 for enzymatic hydrolysis, wherein the enzyme preparation comprises tannase, glycosidase, flavor protease, bromelain, acid protease and fungal lipase in a mass ratio of 4:4:4:3:2:1, the enzymatic hydrolysis temperature is 45° C., the enzymatic hydrolysis time is 6 h, and after the enzymatic hydrolysis is completed, the temperature is raised to 85° C. for enzyme inactivation treatment, and the enzyme inactivation treatment time is 30 min, to obtain enzymatically hydrolyzed tea residue;

[0078] S5: filtering the enzymatically hydrolyzed tea residue obtained in S4 using a 0.1 μm PTFE filter membrane, and concentrating the obtained filtrate using a vacuum concentrator to obtain an oolong tea extract B;

[0079] S6: The tea aroma extract A obtained in S3 and the oolong tea extract B obtained in S5 are compounded in a ratio of 1:1 to obtain an oolong tea extract.

[0080] In this comparative example, molecular distillation equipment was not used, but ordinary heating distillation equipment was used. The extraction rate of oolong tea extract A in this comparative example was 61%, and the extraction rate of oolong tea extract B was 74%. The flavor evaluation results of the oolong tea extracts in this comparative example are shown in Table 1.

[0081] Comparative Example 3

[0082] S1: Weigh 10 kg of oolong tea leaves using a balance, mix the oolong tea leaves with deionized water in a mass ratio of 1:2 and soak for 15 minutes, then grind the soaked oolong tea leaves using a grinder;

[0083] S2: Add the crushed oolong tea leaves in S1 into 300 kg of water, adjust the pH value to 5.5 with a saturated sodium bicarbonate solution, add 25 g of sodium isoascorbate, extract at 83° C. for 1.5 h, and cool to room temperature after the extraction to obtain an oolong tea extract;

[0084] S3: filtering the oolong tea extract obtained in S2 using a 200-mesh plate-and-frame filter to obtain an oolong tea filtrate, extracting the oolong tea aroma from the oolong tea filtrate using a molecular distillation device, the operating conditions of the molecular distillation device being: temperature 50° C., vacuum degree 1 mbar, rotation speed 350 r / min, to obtain a tea aroma extract and tea residue, and the tea aroma extract is highly concentrated through a reverse osmosis membrane to obtain a tea aroma extract A;

[0085] S4: The tea residue obtained after distillation in S3 is filtered using a 0.1 μm PTFE filter membrane, and the obtained filtrate is highly concentrated using a vacuum concentrator to obtain oolong tea extract B;

[0086] S5: The tea aroma extract A obtained in S3 and the oolong tea extract B obtained in S4 are compounded in a ratio of 1:1 to obtain an oolong tea extract.

[0087] In this comparative example, the tea residue was not subjected to enzymatic hydrolysis. The extraction rate of oolong tea extract A in this comparative example was 69%, and the extraction rate of oolong tea extract B was 71%. The flavor evaluation results of the oolong tea extracts in this comparative example are shown in Table 1.

[0088] Comparative Example 4

[0089] S1: Weigh 10 kg of oolong tea leaves using a balance, mix the oolong tea leaves with deionized water in a mass ratio of 1:2 and soak for 15 minutes, then grind the soaked oolong tea leaves using a grinder;

[0090] S2: Add the crushed oolong tea leaves in S1 into 300 kg of water, adjust the pH value to 5.5 with a saturated sodium bicarbonate solution, add 25 g of sodium isoascorbate, extract at 83° C. for 1.5 h, and cool to room temperature after the extraction to obtain an oolong tea extract;

[0091] S3: filtering the oolong tea extract obtained in S2 using a 200-mesh plate-and-frame filter to obtain an oolong tea filtrate, extracting the oolong tea aroma from the oolong tea filtrate using a molecular distillation device, the operating conditions of the molecular distillation device being: temperature 50° C., vacuum degree 1 mbar, rotation speed 350 r / min, to obtain a tea aroma extract and tea residue, and the tea aroma extract is highly concentrated through a reverse osmosis membrane to obtain a tea aroma extract A;

[0092] S4: adding 2 wt % of an enzyme preparation to the tea residue obtained after distillation in S3 for enzymatic hydrolysis, wherein the enzyme preparation comprises tannin, glycosidase and bromelain in a mass ratio of 4:5:4, the enzymatic hydrolysis temperature is 45° C., the enzymatic hydrolysis time is 6 h, and after the enzymatic hydrolysis is completed, the temperature is raised to 85° C. for enzyme inactivation treatment, and the enzyme inactivation treatment time is 30 min, to obtain enzymatically hydrolyzed tea residue;

[0093] S5: filtering the enzymatically hydrolyzed tea residue obtained in S4 using a 0.1 μm PTFE filter membrane, and concentrating the obtained filtrate using a vacuum concentrator to obtain an oolong tea extract B;

[0094] S6: The tea aroma extract A obtained in S3 and the oolong tea extract B obtained in S5 are compounded in a ratio of 1:1 to obtain an oolong tea extract.

[0095] In this comparative example, the extraction rate of oolong tea extract A is 69%, and the extraction rate of oolong tea extract B is 75%. The flavor evaluation results of the oolong tea extracts in this example are shown in Table 1.

[0096] Table 1 Flavor evaluation test results

[0097]

[0098]

[0099] As can be seen from Table 1, the present invention uses antioxidants to effectively prevent the oxidation and degradation of beneficial ingredients in oolong tea leaves during high-temperature extraction, protect the active ingredients in the tea leaves, and maintain their flavor and nutritional value. The molecular distillation technology, reverse osmosis membrane equipment, and enzymatic hydrolysis technology are used in combination to improve the extraction efficiency, and the flavor substances in the tea base and tea aroma are protected to the greatest extent. Through the combination of six enzymes, tannins are degraded, flavor substances are released, amino acids and peptide substances are generated, and a richer taste and fresh feeling are provided, which significantly increases the complexity and quality of the flavor of the oolong tea extract.

[0100] When the present invention is used:

[0101] 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 an oolong tea extract, characterized in that: The specific process of the preparation method is as follows: S1: mixing oolong tea leaves and deionized water in a mass ratio of 1:(2-3) and soaking them for 15-30 minutes, and crushing the soaked oolong tea leaves using a grinder; S2: Mix the crushed oolong tea leaves in S1 with deionized water in a mass ratio of 1:(30-60), adjust the pH value with an alkaline solution to 5.5-6, add an antioxidant, extract at a temperature of 80-85° C. for 1.5-2.5 h, and cool to room temperature after the extraction to obtain an oolong tea extract; S3: filtering the oolong tea extract obtained in S2 using a filter to obtain an oolong tea filtrate, extracting the oolong tea aroma from the oolong tea filtrate using a molecular distillation device, the operating conditions of the molecular distillation device being: temperature 40-60° C., vacuum degree 0.1 mbar-10 mbar, rotation speed 350 r / min, obtaining a tea aroma extract and tea residue, and concentrating the tea aroma extract using a membrane concentration device to obtain a tea aroma extract A; S4: adding 1-3 wt % of an enzyme preparation to the tea residue obtained after distillation in S3 for enzymatic hydrolysis, wherein the enzyme preparation comprises tannase, glycosidase, flavor protease, bromelain, acid protease and fungal lipase in a mass ratio of (3-5): (3-5): (3-4): (3-4): (1-2): (1-2), the enzymatic hydrolysis temperature is 40-50° C., the enzymatic hydrolysis time is 4-12 h, and after the enzymatic hydrolysis is completed, an enzyme inactivation treatment is performed to obtain enzymatically hydrolyzed tea residue; S5: filtering the enzymatically hydrolyzed tea residue obtained in S4, and concentrating the obtained filtrate by high multiple using a concentration device to obtain an oolong tea extract B; S6: Compounding the tea aroma extract A obtained in S3 and the oolong tea extract B obtained in S5 at a ratio of 1:(0.5-2) to obtain an oolong tea extract.

2. The method for preparing an oolong tea extract according to claim 1, characterized in that: The alkaline solution in S2 is a saturated sodium bicarbonate solution.

3. The method for preparing an oolong tea extract according to claim 1, characterized in that: The antioxidant in S2 is one of vitamin C, sodium erythorbate or astaxanthin.

4. The method for preparing an oolong tea extract according to claim 1, characterized in that: The filter in S3 is a plate-and-frame filter.

5. The method for preparing an oolong tea extract according to claim 4, characterized in that: The filter screen of the filter in S3 is 100-200 meshes.

6. The method for preparing an oolong tea extract according to claim 1, characterized in that: The membrane concentration equipment in S3 is a reverse osmosis membrane equipment or a pervaporation membrane equipment.

7. The method for preparing an oolong tea extract according to claim 1, characterized in that: The temperature of the enzyme inactivation treatment in S4 is 80-90° C., and the treatment time is 30-60 min.

8. The method for preparing an oolong tea extract according to claim 1, characterized in that: The filtration in S5 uses a 0.1 μm ceramic membrane or a 0.1 μm PTFE filter membrane.

9. The method for preparing an oolong tea extract according to claim 1, characterized in that: The concentrating device in S5 is a vacuum concentrator or a scraped film concentrator.

10. The method for preparing an oolong tea extract according to claim 1, characterized in that: The tea aroma extract A, oolong tea extract B and oolong tea extract are used in food preparation.

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