Antioxidant tea oil and method for preparing the same

Abstract

The application belongs to the technical field of edible oil processing, and particularly relates to an antioxidant tea oil and a preparation method thereof. The preparation method comprises the following steps: preparation of tea polyphenol modified lignin based polyurethane open elastic microtubes; low-oxygen permeation conditioning of oil-tea camellia seed kernels; and gradient pressure relief rebound pressing of the oil-tea camellia seed kernels. The prepared tea polyphenol modified lignin participates in the polyurethane reaction of hexamethylene diisocyanate and polytetrahydrofuran ether diol 2000, and then is formed in a pipe mold, cut and slit to obtain the tea polyphenol modified lignin based polyurethane open elastic microtubes. In the pressing and pressure relief in the oil pressing process, the hard oil cake formed inside can be loosened and an oil guiding structure is formed, so that the oil in the inner layer can be smoothly discharged. Meanwhile, the phenolic hydroxyl groups on the outer surface and the near surface layer of the elastic microtubes can act as hydrogen donors when contacting with newly precipitated tea oil, so as to play an antioxidant role at the oil-solid interface where the tea oil is just precipitated from the oil-tea camellia seed kernels.

Description

Technical Field

[0001] This invention belongs to the field of edible oil processing technology, specifically relating to an antioxidant tea oil and its preparation method. Background Technology

[0002] Camellia oil is a vegetable oil made from camellia seeds. It contains unsaturated fatty acids, tocopherols, phytosterols, and endogenous phenolic substances. Its quality is not only affected by the variety and maturity of camellia seeds, but also closely related to the drying, crushing, conditioning, pressing, and oil separation conditions of the camellia seeds.

[0003] Mechanical pressing has advantages such as simple process, no use of organic extraction solvents, and more natural flavor of finished oil. Low-temperature mechanical pressing helps to reduce the adverse effects of high temperature on natural active ingredients and improve the quality of tea oil. However, at lower temperatures, the cell tissue and protein structure of tea seed kernels are not easily softened, and the material layer is prone to caking during continuous pressure. This can cause the oil migration channels to be blocked by compacted particles and fine powder, resulting in a high residual oil content in the pressed cake.

[0004] To improve pressing efficiency, existing technologies typically employ methods such as conditioning, high-temperature steaming and roasting, extending pressing time, or increasing final pressure. However, excessively high steaming and roasting temperatures and prolonged high-pressure residence times can easily increase frictional heat generation within the material layer. This causes the oil just extracted from the camellia seed kernels to come into contact with air at higher temperatures and with a larger specific surface area, thereby increasing the risk of initial oxidation, leading to a decline in camellia oil quality and poor antioxidant capacity. Conventional conditioning methods, which involve directly adding water, can easily result in either excessively high local moisture content or insufficient internal moisture content, leading to poor conditioning effects and an inability to effectively improve oil extraction rates. Summary of the Invention

[0005] To address the aforementioned technical deficiencies, this invention has developed an antioxidant tea oil and its preparation method. This method can solve the problems of low oil extraction rate caused by easy caking of the material layer, obstructed oil migration, and poor conditioning effect during low-temperature pressing. It can also enable the newly extracted tea oil to have good antioxidant capacity.

[0006] A method for preparing antioxidant tea oil includes the following steps: S1: Preparation of tea polyphenol-modified lignin-based polyurethane open elastic microtubules 10-12 parts by weight of enzymatically hydrolyzed lignin and 6-8 parts by weight of tea polyphenols were subjected to an acid-catalyzed phenolation reaction in the presence of sulfuric acid. The tea polyphenols were food-grade and contained 70-75% by weight of catechins. The resulting reaction mixture was added to 1,4-dioxane, stirred, and filtered. The filtrate was precipitated by diethyl ether as a reverse solvent. After washing and drying the precipitate, tea polyphenol-modified lignin was obtained. 4.5-4.75 parts by weight of polytetrahydrofuran ether diol 2000 and hexamethylene diisocyanate were then subjected to an acid-catalyzed phenolation reaction. Under the action of the agent, a prepolymerization reaction is carried out, and then 0.4-0.5 parts by weight of tea polyphenol-modified lignin is added to carry out a cross-linking reaction to obtain tea polyphenol-modified lignin-based polyurethane reaction liquid. The reaction liquid is injected into the pipe mold for gradient curing and hot pressing, and then demolded. A through slit of 0.15-0.3 mm is opened along the pipe wall axial direction and cut to obtain C-shaped pipe. The C-shaped pipe is cleaned by vibration with purification liquid, washed with water and dried to obtain tea polyphenol-modified lignin-based polyurethane open elastic microtube. S2: Low-oxygen osmotic conditioning of camellia seed kernels 100 parts by weight of camellia seeds were dried at low temperature, dehulled, crushed and sieved to obtain camellia seed kernel granules. The camellia seed kernel granules were placed under a vacuum of 0.02-0.03 MPa at 30-38℃ for vacuum degassing. Then, 2-2.5 parts by weight of deoxygenated deionized water were sprayed in the form of atomization. After adding water, nitrogen was backfilled to make the pressure reach 0.07-0.08 MPa. The camellia seed kernel granules were turned over and the operation of vacuuming-atomizing water-adding-nitrogen backfilling was repeated 3 times. The final moisture content of the camellia seed kernel granules was adjusted to 7-7.5% to obtain conditioned camellia seed kernels. Under nitrogen protection, the conditioned camellia seed kernels and tea polyphenol modified lignin-based polyurethane open elastic microtubes were mixed evenly. The tea polyphenol modified lignin-based polyurethane open elastic microtubes accounted for 2-2.5% of the mass of the conditioned camellia seed kernel granules to obtain camellia seed kernels to be pressed. S3: Gradient pressure relief and rebound pressing of camellia seed kernels The camellia seeds to be pressed are added to a hydraulic pressing device and subjected to low-pressure circulating pressing, medium-pressure circulating pressing and high-pressure final pressing in sequence at 30-38℃. The crude camellia oil obtained by pressing is centrifuged and microporous filtered under nitrogen protection to obtain antioxidant camellia oil.

[0007] Further, step S1, the preparation of tea polyphenol-modified lignin-based polyurethane open elastic microtubes, specifically includes the following steps: S1.1: Place 10-12 parts by weight of enzymatically hydrolyzed lignin and 6-8 parts by weight of tea polyphenols in a container equipped with a reflux device, then add 80-100 parts by weight of sulfuric acid solution with a mass fraction of 70-75%, and reflux at 75-80℃ for 2-3 hours to obtain a reaction mixture. Add the reaction mixture to 1,4-dioxane at a mass ratio of 1:(3-4), stir for 20-30 minutes, filter to remove solid impurities, collect the filtrate, and add it dropwise to diethyl ether at a mass ratio of 1:(12-15) to precipitate. Filter to collect the precipitate, wash it with diethyl ether 3-4 times, and vacuum dry it at 40-45℃ to constant weight to obtain tea polyphenol modified lignin. S1.2: Weigh 4.5-4.75 parts by weight of polytetrahydrofuran ether glycol 2000 and 0.4-0.5 parts by weight of tea polyphenol modified lignin. Add polytetrahydrofuran ether glycol 2000 to a reaction vessel and dehydrate it at 120°C under vacuum for 2 hours. Then cool it down to 70-75°C and keep it warm. Add 10-12 parts by weight of anhydrous N,N-dimethylacetamide and stir until polytetrahydrofuran ether glycol 2000 is fully dissolved. Then add 0.002-0.005 parts by weight of catalyst and hexamethylene diisocyanate and prepolymerize at 70-75°C for 2-3 hours to obtain the prepolymer. S1.3: Add the tea polyphenol-modified lignin weighed in step S1.2 to 5 parts by weight of anhydrous N,N-dimethylacetamide, stir at 1000-1500 rpm for 20-30 min, then add to the prepolymer obtained in step S1.2, stir and react at 70-75℃ for 4-6 h to obtain tea polyphenol-modified lignin-based polyurethane reaction solution; S1.4: Inject the tea polyphenol-modified lignin-based polyurethane reaction solution into the pipe mold. The pipe mold consists of a fixed polytetrafluoroethylene (PTFE) mandrel and an annular outer shell. The diameter of the PTFE mandrel is 1-1.5 mm, and the gap between the PTFE mandrel and the annular outer shell is 0.5-0.7 mm. Let it stand at room temperature for 5-7 hours, then heat it to 50℃ and hold it for 3-5 hours, then heat it to 70℃ and hold it for 10-12 hours. Then place the pipe mold in a 70℃ vacuum drying oven to dry and remove N,N-dimethylacetamide. Remove the annular outer shell and keep the PTFE mandrel. Hot press it at 145-160℃ and 3-5 MPa for 5-10 minutes. After cooling, remove the PTFE mandrel and demold to obtain a continuous elastic hollow tube. S1.5: Cut a continuous elastic hollow tube along the tube wall axially to form a through slit with a width of 0.3-0.5mm, making the cross-section C-shaped, and cut the length to 2-3mm to obtain C-shaped tubes. Then, place the C-shaped tubes in a purification solution at a mass ratio of 1:(10-15) and oscillate them at 70-75℃ at a speed of 80-120rpm for 2-3 hours. Then, rinse them with deionized water 2-3 times and dry them in a vacuum drying oven at 60-70℃ until constant weight to obtain tea polyphenol modified lignin-based polyurethane open elastic microtubes.

[0008] Furthermore, the tea polyphenols in step S1.1 are food-grade tea polyphenols, containing 70-75% by mass of catechins.

[0009] Further, in step S1.2, the amount of hexamethylene diisocyanate added is calculated based on the molar ratio of NCO groups to total effective hydroxyl groups of (0.8-0.85):1, where the total effective hydroxyl groups are the sum of the effective hydroxyl groups of polytetrahydrofuran ether diol 2000 and tea polyphenol-modified lignin.

[0010] Furthermore, the catalyst in step S1.2 is an organozinc catalyst ZCAT-T50.

[0011] Furthermore, the purified liquid in step S1.5 consists of anhydrous food-grade ethanol and glycerol, wherein the mass fraction of glycerol is 3-6%.

[0012] Furthermore, step S2, the low-oxygen osmotic conditioning of camellia seed kernels, specifically includes the following steps: S2.1: Select mature camellia seeds that are free from mold and insect infestation, dry them at a low temperature of 45℃ to reduce the moisture content of the camellia seeds to 4%, then remove the shells to obtain camellia seed kernels, crush the camellia seed kernels through a 20-mesh sieve to obtain camellia seed kernel granules. S2.2: Add 100 parts by weight of camellia seed kernels to a sealed conditioning container. Adjust the vacuum level inside the sealed conditioning container to 0.02-0.03 MPa and maintain it for 2-3 minutes. Then, spray 2-2.5 parts by weight of deoxygenated deionized water into the sealed conditioning container in the form of atomization with an average droplet size of 20-80 μm. At the same time as spraying, start the automatic stirrer to stir the camellia seed kernels at a speed of 180-200 rpm. Then, backfill nitrogen into the sealed conditioning container to make the pressure inside the sealed conditioning container reach 0.07-0.08 MPa. Then, turn the camellia seed kernels at a speed of 30-50 rpm for 8-12 minutes. Perform the vacuuming-atomization-water-backfilling-nitrogen operation a total of 3 times. Adjust the final moisture content of the camellia seed kernels to 7-7.5%. Maintain the temperature at 30℃ during the conditioning process to obtain the conditioned camellia seed kernels. S2.3: Under nitrogen protection, tea polyphenol-modified lignin-based polyurethane open elastic microtubes are added to the conditioned camellia seed kernel particles. The tea polyphenol-modified lignin-based polyurethane open elastic microtubes account for 2-2.5% of the mass of the conditioned camellia seed kernel particles. The mixture is then stirred at 80-100 rpm for 5-8 minutes and allowed to stand for 20-30 minutes to obtain the camellia seed kernels to be pressed.

[0013] Furthermore, step S3, the gradient pressure relief and rebound pressing of camellia seed kernels, specifically includes the following steps: S3.1: Add the camellia seed kernels to be pressed into the hydraulic pressing device, control the pressing temperature to 30-38℃, then increase the pressing pressure to 8-10MPa, hold the pressure for 90-120s, then release the pressure to 1-2MPa and hold for 20-30s, repeat the process twice to complete the low-pressure circulating pressing. S3.2: Increase the pressing pressure to 18-20MPa, hold the pressure for 120-180s, then reduce the pressure to 3-5MPa and hold for 30-45s. Repeat this process twice to complete the medium-pressure circulating pressing. S3.3: Increase the pressing pressure to 40-44MPa for high-pressure final pressing until no more tea oil is extracted. Collect the crude tea oil from each pressing process and place it in a sealed oil storage container under nitrogen protection. Centrifuge at 4000-6000rpm for 10-15min at 25-30℃ to separate water, fine solid particles and colloidal impurities. Then filter the mixture using a microporous membrane with a filtration precision of 1-3μm to obtain antioxidant tea oil.

[0014] Furthermore, the depressurization rate in steps S3.1 and S3.2 is 0.2-0.5 MPa / s.

[0015] An antioxidant tea oil is prepared by the above-mentioned method for preparing an antioxidant tea oil.

[0016] The beneficial effects are: 1. This invention utilizes sulfuric acid solution to catalyze the enzymatic hydrolysis of lignin and tea polyphenols to induce phenolic condensation, introducing a tea polyphenol structure containing multiple phenolic hydroxyl groups into lignin. Then, it participates in the polyurethane reaction of hexamethylene diisocyanate and polytetrahydrofuran ether diol 2000. During the reaction, the polyhydroxy structure in the lignin modified by tea polyphenols can form a large number of chemical cross-linking nodes. This not only improves the strength of open elastic microtubules through the aromatic ring structure, but also allows the hydroxyl groups in lignin and tea polyphenols that did not participate in the isocyanate reaction to form multi-point hydrogen bonds with the polyurethane. The combined effect of the chemical cross-linking network and the hydrogen bond physical cross-linking network allows the tube wall to dissipate mechanical energy through flexible segment extension, hydrogen bond breakage, and tube wall bending when subjected to external forces. After unloading, the tube wall recovers its shape through polyether segment retraction and hydrogen bond reconstruction. This loosens the hard oil cake formed inside during the pressing-depressurization process and forms an oil-conducting structure, allowing the inner layer of oil to be discharged smoothly and improving the oil extraction rate. Meanwhile, the unreacted phenolic hydroxyl groups on the outer surface and near-surface of the open elastic microtubes can act as hydrogen donors when in contact with the newly extracted tea oil. They can truncate initial lipid free radicals and peroxide free radicals and can coordinate with some iron, copper, and other pro-oxidizing metal ions. This provides an antioxidant effect at the oil-solid interface where the tea oil is just extracted from the tea seed kernel, improving the quality and antioxidant capacity of the newly pressed oil.

[0017] 2. This invention first performs vacuum degassing on the camellia seed kernels after low-temperature drying, expelling air from the gaps between the kernels, cell cavities, and capillaries, reducing the resistance of internal gas to water entry. After turning off the vacuum pump, pre-calculated deoxygenated deionized water is sprayed in the form of fine droplets, allowing water to evenly adhere to the surface of the camellia seed kernels. Then, nitrogen is backfilled to create a positive pressure higher than the internal pore pressure of the kernels. The external gas pressure drives the surface water to penetrate into the kernels along cell fissures and capillaries. This reduces surface clumping, excessively high local moisture content, and insufficient internal moisture content caused by direct one-time water addition. It also allows for more uniform softening of the cell walls and protein structure in the camellia seed kernels, reducing local clumping and fine powder blockage during pressing. This improves the pressing plasticity of the camellia seed kernels without the need for prolonged high-temperature steaming and roasting, thus ensuring a good oil extraction rate in subsequent pressing processes while maintaining low peroxide value and low acid value.

[0018] 3. This invention improves the pressing efficiency of tea oil through gradient pressure relief and rebound pressing. Multiple pressure holding and releasing operations during the low and medium pressure stages allow the open elastic microtubes to compress and store energy during pressure holding and rebound during pressure relief. This slightly expands the already compacted tea seed kernel layer, reconstructing the oil guiding channels. This allows the oil to be quickly discharged along the newly formed channels during subsequent high-pressure pressing. Compared to continuous high-pressure pressing, this method reduces premature caking of the material layer and localized frictional heating, increasing the effective pressing degree while maintaining a lower outlet oil temperature, thereby improving the oil extraction rate. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 A method for preparing antioxidant tea oil, specifically including the following steps: S1: Preparation of tea polyphenol-modified lignin-based polyurethane open elastic microtubules S1.1: 10 parts by weight of enzymatically hydrolyzed lignin and 6 parts by weight of food-grade tea polyphenols were placed in a container equipped with a reflux device. The catechin mass fraction of the food-grade tea polyphenols was 70%. Then, 80 parts by weight of sulfuric acid solution with a mass fraction of 70% were added. The mixture was refluxed at 75°C for 2 hours to obtain a reaction mixture. The reaction mixture was added to 1,4-dioxane at a mass ratio of 1:3. After stirring for 20 minutes, the mixture was filtered to remove solid impurities. The filtrate was collected and precipitated by adding diethyl ether at a mass ratio of 1:12. The precipitate was collected by filtration and washed three times with diethyl ether. The precipitate was then vacuum dried at 40°C to constant weight to obtain tea polyphenol-modified lignin. S1.2: Weigh 4.5 parts by weight of polytetrahydrofuran ether glycol 2000 and 0.4 parts by weight of tea polyphenol modified lignin. Add polytetrahydrofuran ether glycol 2000 to the reaction vessel and dehydrate it under vacuum at 120°C for 2 hours. Then, cool it down to 70°C and keep it warm. Add 10 parts by weight of anhydrous N,N-dimethylacetamide and stir until polytetrahydrofuran ether glycol 2000 is fully dissolved. Then add 0.002 parts by weight of organic zinc catalyst ZCAT-T50 and hexamethylene diisocyanate. The amount of hexamethylene diisocyanate added is based on a molar ratio of NCO groups to total effective hydroxyl groups of 0.8:1. The total effective hydroxyl groups are the sum of the effective hydroxyl groups of polytetrahydrofuran ether glycol 2000 and tea polyphenol modified lignin. Prepolymerize at 70°C for 2 hours to obtain the prepolymer. S1.3: Add the tea polyphenol-modified lignin weighed in step S1.2 to 5 parts by weight of anhydrous N,N-dimethylacetamide, stir at 1000 rpm for 20 min, then add it to the prepolymer prepared in step S1.2, stir and react at 70℃ for 4 h to obtain tea polyphenol-modified lignin-based polyurethane reaction solution. S1.4: The tea polyphenol-modified lignin-based polyurethane reaction solution is injected into the pipe mold. The pipe mold consists of a fixed polytetrafluoroethylene (PTFE) mandrel and an annular shell. The PTFE mandrel has a diameter of 1 mm and the gap between the PTFE mandrel and the annular shell is 0.5 mm. The mixture is left to stand at room temperature for 5 hours, then heated to 50°C and held for 3 hours, and then heated to 70°C and held for 10 hours. The pipe mold is then placed in a 70°C vacuum drying oven to dry and remove N,N-dimethylacetamide. The annular shell is removed, leaving the PTFE mandrel. The mixture is then hot-pressed at 145°C and 3 MPa for 5 minutes. After cooling, the PTFE mandrel is removed and the pipe is demolded to obtain a continuous elastic hollow tube. S1.5: A continuous elastic hollow tube is cut along the tube wall axially to form a through slit with a width of 0.3 mm, making the cross-section C-shaped, and the length is cut to 2 mm to obtain a C-shaped tube. Then, the C-shaped tube is placed in a purification solution at a mass ratio of 1:10. The purification solution consists of anhydrous food-grade ethanol and glycerol, with the glycerol mass fraction being 3%. The tube is treated by shaking at 80 rpm at 70°C for 2 hours, then rinsed twice with deionized water, and dried in a vacuum drying oven at 60°C until constant weight to obtain a tea polyphenol-modified lignin-based polyurethane open elastic microtube. S2: Low-oxygen osmotic conditioning of camellia seed kernels S2.1: Select mature camellia seeds that are free from mold and insect infestation, dry them at a low temperature of 45℃ to reduce the moisture content of the camellia seeds to 4%, then remove the shells to obtain camellia seed kernels, crush the camellia seed kernels through a 20-mesh sieve to obtain camellia seed kernel granules. S2.2: Add 100 parts by weight of camellia seed kernels to a sealed conditioning container, adjust the vacuum degree inside the sealed conditioning container to 0.02 MPa, maintain for 2 min, and prepare deoxygenated deionized water by passing nitrogen gas with a purity of not less than 99.9% into deionized water at 20℃ for 20 min. Then, spray 2 parts by weight of deoxygenated deionized water into the sealed conditioning container in the form of atomization with an average droplet diameter of 20 μm. At the same time as spraying, start the automatic stirrer to stir the camellia seed kernels at a speed of 180 rpm. Then, backfill nitrogen gas into the sealed conditioning container to make the pressure inside the sealed conditioning container reach 0.07 MPa. Then, turn the camellia seed kernels at a speed of 30 rpm for 8 min. Perform the vacuuming-atomization water addition-nitrogen backfilling operation a total of 3 times, and adjust the final moisture content of the camellia seed kernels to 7%. The temperature during the conditioning process is maintained at 30℃ to obtain the conditioned camellia seed kernels. S2.3: Under nitrogen protection, tea polyphenol-modified lignin-based polyurethane open elastic microtubes are added to the conditioned camellia seed kernel particles. The tea polyphenol-modified lignin-based polyurethane open elastic microtubes account for 2% of the mass of the conditioned camellia seed kernel particles. The mixture is then mixed at 80 rpm for 5 minutes and allowed to stand for 20 minutes to obtain camellia seed kernels to be pressed. S3: Gradient pressure relief and rebound pressing of camellia seed kernels S3.1: Add the camellia seed kernels to be pressed into the hydraulic pressing device, control the pressing temperature at 30℃, then increase the pressing pressure to 8MPa, hold the pressure for 90s, then reduce the pressing pressure to 1MPa at a depressurization rate of 0.2MPa / s and hold for 20s. Repeat this process twice to complete the low-pressure circulating pressing. S3.2: Increase the pressing pressure to 18MPa, hold the pressure for 120s, then reduce the pressing pressure to 3MPa at a depressurization rate of 0.2MPa / s and hold for 30s. Repeat this process twice to complete the medium-pressure circulating pressing. S3.3: Increase the pressing pressure to 40MPa for high-pressure final pressing until no more tea oil is extracted. Collect the crude tea oil from each pressing process and place it in a sealed oil storage container under nitrogen protection. Centrifuge at 4000rpm for 10 minutes at 25℃ to separate water, fine solid particles and colloidal impurities. Then filter the mixture using a microporous membrane with a filtration precision of 1μm to obtain antioxidant tea oil.

[0021] Example 2 A method for preparing antioxidant tea oil, specifically including the following steps: S1: Preparation of tea polyphenol-modified lignin-based polyurethane open elastic microtubules S1.1: 11 parts by weight of enzymatically hydrolyzed lignin and 7 parts by weight of food-grade tea polyphenols were placed in a container equipped with a reflux device. The catechin mass fraction of the food-grade tea polyphenols was 75%. Then, 90 parts by weight of 70% sulfuric acid solution were added, and the mixture was refluxed at 80°C for 2 hours to obtain a reaction mixture. The reaction mixture was added to 1,4-dioxane at a mass ratio of 1:3.5. After stirring for 25 minutes, the mixture was filtered to remove solid impurities. The filtrate was collected and precipitated by adding diethyl ether at a mass ratio of 1:14. The precipitate was collected by filtration and washed three times with diethyl ether. The precipitate was then vacuum dried at 42°C to constant weight to obtain tea polyphenol-modified lignin. S1.2: Weigh 4.6 parts by weight of polytetrahydrofuran ether glycol 2000 and 0.45 parts by weight of tea polyphenol-modified lignin. Add polytetrahydrofuran ether glycol 2000 to the reaction vessel and dehydrate it under vacuum at 120°C for 2 hours. Then, cool it down to 75°C and keep it warm. Add 11 parts by weight of anhydrous N,N-dimethylacetamide and stir until polytetrahydrofuran ether glycol 2000 is fully dissolved. Then add 0.003 parts by weight of organic zinc catalyst ZCAT-T50 and hexamethylene diisocyanate. The amount of hexamethylene diisocyanate added is based on the molar ratio of NCO groups to total effective hydroxyl groups of 0.82:1. The total effective hydroxyl groups are the sum of the effective hydroxyl groups of polytetrahydrofuran ether glycol 2000 and tea polyphenol-modified lignin. Prepolymerize at 75°C for 3 hours to obtain the prepolymer. S1.3: Add the tea polyphenol-modified lignin weighed in step S1.2 to 5 parts by weight of anhydrous N,N-dimethylacetamide, stir at 1500 rpm for 20 min, then add it to the prepolymer prepared in step S1.2, stir and react at 75℃ for 4 h to obtain tea polyphenol-modified lignin-based polyurethane reaction solution. S1.4: The tea polyphenol-modified lignin-based polyurethane reaction solution is injected into the pipe mold. The pipe mold consists of a fixed polytetrafluoroethylene (PTFE) mandrel and an annular shell. The PTFE mandrel has a diameter of 1.2 mm and the gap between the PTFE mandrel and the annular shell is 0.6 mm. The mixture is left to stand at room temperature for 6 hours, then heated to 50°C and held for 4 hours, and then heated to 70°C and held for 11 hours. The pipe mold is then placed in a 70°C vacuum drying oven to dry and remove N,N-dimethylacetamide. The annular shell is removed, leaving the PTFE mandrel. The mixture is then hot-pressed at 160°C and 3 MPa for 8 minutes. After cooling, the PTFE mandrel is removed and the pipe is demolded to obtain a continuous elastic hollow tube. S1.5: A continuous elastic hollow tube is cut along the tube wall axially to form a through slit with a width of 0.4 mm, making the cross-section C-shaped. The length is then cut to 3 mm to obtain a C-shaped tube. The C-shaped tube is then placed in a purification solution at a mass ratio of 1:12. The purification solution consists of anhydrous food-grade ethanol and glycerol, with the glycerol mass fraction being 5%. The tube is treated by shaking at 120 rpm at 70°C for 3 hours. It is then rinsed twice with deionized water and dried in a vacuum drying oven at 65°C until constant weight is obtained, resulting in a tea polyphenol-modified lignin-based polyurethane open elastic microtube.

[0022] S2: Low-oxygen osmotic conditioning of camellia seed kernels S2.1: Select mature camellia seeds that are free from mold and insect infestation, dry them at a low temperature of 45℃ to reduce the moisture content of the camellia seeds to 4%, then remove the shells to obtain camellia seed kernels, crush the camellia seed kernels through a 20-mesh sieve to obtain camellia seed kernel granules. S2.2: Add 100 parts by weight of camellia seed kernels to a sealed conditioning container, adjust the vacuum degree inside the sealed conditioning container to 0.03 MPa, maintain for 2 min, and prepare deoxygenated deionized water by passing nitrogen gas with a purity of not less than 99.9% into deionized water at 25℃ for 20 min. Then, spray 2.2 parts by weight of deoxygenated deionized water into the sealed conditioning container in the form of atomization with an average droplet size of 50 μm. At the same time as spraying, start the automatic stirrer to stir the camellia seed kernels at a speed of 200 rpm. Then, backfill nitrogen gas into the sealed conditioning container to make the pressure inside the sealed conditioning container reach 0.07 MPa. Then, turn the camellia seed kernels at a speed of 50 rpm for 8 min. Perform the vacuuming-atomization water addition-nitrogen backfilling operation a total of 3 times, and adjust the final moisture content of the camellia seed kernels to 7%. The temperature during the conditioning process is maintained at 35℃ to obtain the conditioned camellia seed kernels. S2.3: Under nitrogen protection, tea polyphenol-modified lignin-based polyurethane open elastic microtubes are added to the conditioned camellia seed kernel particles. The tea polyphenol-modified lignin-based polyurethane open elastic microtubes account for 2.2% of the mass of the conditioned camellia seed kernel particles. The mixture is then mixed at 80 rpm for 8 minutes and allowed to stand for 25 minutes to obtain the camellia seed kernels to be pressed.

[0023] S3: Gradient pressure relief and rebound pressing of camellia seed kernels S3.1: Add the camellia seed kernels to be pressed into the hydraulic pressing device, control the pressing temperature at 35℃, then increase the pressing pressure to 9MPa, hold the pressure for 105s, then reduce the pressing pressure to 1.5MPa at a depressurization rate of 0.3MPa / s and hold for 25s. Repeat this process twice to complete the low-pressure circulating pressing. S3.2: Increase the pressing pressure to 19MPa, hold the pressure for 150s, then reduce the pressing pressure to 4MPa at a depressurization rate of 0.4MPa / s and hold for 38s. Repeat this process twice to complete the medium-pressure circulating pressing. S3.3: Increase the pressing pressure to 42MPa for high-pressure final pressing until no tea oil is extracted. Collect the crude tea oil from each pressing process and place it in a sealed oil storage container under nitrogen protection. Centrifuge at 4000rpm for 15min at 30℃ to separate water, fine solid particles and colloidal impurities. Then filter the mixture using a microporous membrane with a filtration precision of 2μm to obtain antioxidant tea oil.

[0024] Example 3 A method for preparing antioxidant tea oil, specifically including the following steps: S1: Preparation of tea polyphenol-modified lignin-based polyurethane open elastic microtubules S1.1: 12 parts by weight of enzymatically hydrolyzed lignin and 8 parts by weight of food-grade tea polyphenols were placed in a container equipped with a reflux device. The catechin mass fraction of the food-grade tea polyphenols was 75%. Then, 100 parts by weight of sulfuric acid solution with a mass fraction of 75% were added. The mixture was refluxed at 80°C for 3 hours to obtain a reaction mixture. The reaction mixture was added to 1,4-dioxane at a mass ratio of 1:4. After stirring for 30 minutes, the mixture was filtered to remove solid impurities. The filtrate was collected and precipitated by adding it dropwise to diethyl ether at a mass ratio of 1:15. The precipitate was collected by filtration and washed 4 times with diethyl ether. The precipitate was then vacuum dried at 45°C to constant weight to obtain tea polyphenol-modified lignin. S1.2: Weigh 4.75 parts by weight of polytetrahydrofuran ether glycol 2000 and 0.5 parts by weight of tea polyphenol modified lignin. Add polytetrahydrofuran ether glycol 2000 to the reaction vessel and dehydrate it under vacuum at 120°C for 2 hours. Then, cool it down to 75°C and keep it warm. Add 12 parts by weight of anhydrous N,N-dimethylacetamide and stir until polytetrahydrofuran ether glycol 2000 is fully dissolved. Then add 0.005 parts by weight of organozinc catalyst ZCAT-T50 and hexamethylene diisocyanate. The amount of hexamethylene diisocyanate added is based on the molar ratio of NCO groups to total effective hydroxyl groups of 0.85:1. The total effective hydroxyl groups are the sum of the effective hydroxyl groups of polytetrahydrofuran ether glycol 2000 and tea polyphenol modified lignin. Prepolymerize at 75°C for 3 hours to obtain the prepolymer. S1.3: Add the tea polyphenol-modified lignin weighed in step S1.2 to 5 parts by weight of anhydrous N,N-dimethylacetamide, stir at 1500 rpm for 30 min, then add to the prepolymer obtained in step S1.2, stir and react at 75℃ for 6 h to obtain tea polyphenol-modified lignin-based polyurethane reaction solution. S1.4: The tea polyphenol-modified lignin-based polyurethane reaction solution is injected into the pipe mold. The pipe mold consists of a fixed polytetrafluoroethylene (PTFE) mandrel and an annular shell. The PTFE mandrel has a diameter of 1.5 mm and the gap between the PTFE mandrel and the annular shell is 0.7 mm. The mixture is left to stand at room temperature for 7 hours, then heated to 50°C and held for 5 hours, and then heated to 70°C and held for 12 hours. The pipe mold is then placed in a 70°C vacuum drying oven to dry and remove N,N-dimethylacetamide. The annular shell is removed, leaving the PTFE mandrel. The mixture is then hot-pressed at 160°C and 5 MPa for 10 minutes. After cooling, the PTFE mandrel is removed and the pipe is demolded to obtain a continuous elastic hollow tube. S1.5: A continuous elastic hollow tube is cut along the tube wall axially to form a through slit with a width of 0.5 mm, making the cross-section C-shaped, and the length is cut to 3 mm to obtain a C-shaped tube. Then, the C-shaped tube is placed in a purification solution at a mass ratio of 1:15. The purification solution consists of anhydrous food-grade ethanol and glycerol, with the glycerol mass fraction being 6%. The tube is treated by shaking at 120 rpm at 75°C for 3 hours, then rinsed 3 times with deionized water, and dried in a vacuum drying oven at 70°C until constant weight to obtain a tea polyphenol modified lignin-based polyurethane open elastic microtube. S2: Low-oxygen osmotic conditioning of camellia seed kernels S2.1: Select mature camellia seeds that are free from mold and insect infestation, dry them at a low temperature of 45℃ to reduce the moisture content of the camellia seeds to 4%, then remove the shells to obtain camellia seed kernels, crush the camellia seed kernels through a 20-mesh sieve to obtain camellia seed kernel granules. S2.2: Add 100 parts by weight of camellia seed kernels to a sealed conditioning container, adjust the vacuum degree inside the sealed conditioning container to 0.03 MPa, maintain for 3 min, and prepare deoxygenated deionized water by passing nitrogen gas with a purity of not less than 99.9% into deionized water at 25℃ for 30 min. Then, spray 2.5 parts by weight of deoxygenated deionized water into the sealed conditioning container in the form of atomization with an average droplet diameter of 80 μm. At the same time as spraying, start the automatic stirrer to stir the camellia seed kernels at a speed of 200 rpm. Then, backfill nitrogen gas into the sealed conditioning container to make the pressure inside the sealed conditioning container reach 0.08 MPa. Then, turn the camellia seed kernels at a speed of 50 rpm for 12 min. Perform the vacuuming-atomization-water-backfilling-nitrogen gas operation a total of 3 times, and adjust the final moisture content of the camellia seed kernels to 7.5%. The temperature during the conditioning process is maintained at 38℃ to obtain the conditioned camellia seed kernels. S2.3: Under nitrogen protection, tea polyphenol-modified lignin-based polyurethane open elastic microtubes are added to the conditioned camellia seed kernel particles. The tea polyphenol-modified lignin-based polyurethane open elastic microtubes account for 2.5% of the mass of the conditioned camellia seed kernel particles. The mixture is then mixed at 100 rpm for 8 minutes and allowed to stand for 30 minutes to obtain the camellia seed kernels to be pressed. S3: Gradient pressure relief and rebound pressing of camellia seed kernels S3.1: Add the camellia seed kernels to be pressed into the hydraulic pressing device, control the pressing temperature to 38℃, then increase the pressing pressure to 10MPa, hold the pressure for 120s, then reduce the pressing pressure to 2MPa at a depressurization rate of 0.5MPa / s and hold for 30s. Repeat this process twice to complete the low-pressure circulating pressing. S3.2: Increase the pressing pressure to 20MPa, hold the pressure for 180s, then reduce the pressing pressure to 5MPa at a depressurization rate of 0.5MPa / s and hold for 45s. Repeat this process twice to complete the medium-pressure circulating pressing. S3.3: Increase the pressing pressure to 44MPa for high-pressure final pressing until no more tea oil is extracted. Collect the crude tea oil from each pressing process and place it in a sealed oil storage container under nitrogen protection. Centrifuge at 6000rpm for 15min at 30℃ to separate water, fine solid particles and colloidal impurities. Then filter the mixture using a microporous membrane with a filtration precision of 3μm to obtain antioxidant tea oil.

[0025] Comparative Example 1 The difference from Example 1 is that, in this comparative example, the tea polyphenol-modified lignin-based polyurethane open elastic microtubes were not added to the conditioned camellia seed kernel particles in step S2.3, and the remaining steps were the same as in Example 1.

[0026] Comparative Example 2 The difference from Example 1 is that step S1.1 of this comparative example is removed, and the enzymatic hydrolyzed lignin is not modified with tea polyphenols. The remaining steps are the same as in Example 1.

[0027] Comparative Example 3 The difference from Example 1 is that the pressure relief operation in steps S3.1 and S3.2 is removed in this comparative example, and continuous pressure pressing is performed directly. The remaining steps are the same as in Example 1.

[0028] Comparative Example 4 The difference from Example 1 is that this comparative example did not add the tea polyphenol-modified lignin-based polyurethane open elastic microtubes to the conditioned camellia seed kernel particles in step S2.3, and removed the pressure relief operation in steps S3.1 and S3.2, and directly carried out continuous pressure pressing. The remaining steps are the same as in Example 1.

[0029] Comparative Example 5 The difference from Example 1 is that step S2.2 in this comparative example is replaced by: soaking the camellia seed kernels in deoxygenated deionized water under nitrogen protection, stirring at 100 rpm at 34°C until the moisture content of the camellia seed kernels reaches 7% after draining the surface water, thus obtaining conditioned camellia seed kernels. The remaining steps are the same as in Example 1.

[0030] Comparative Example 6 Camellia seeds are pressed into thin slices and then placed in a steaming and frying pan at 120°C to adjust the moisture and temperature, so that the moisture content before pressing is 3% and the pressing temperature is 120°C. Then, the oil is pressed using a hydraulic press, with the pressing temperature adjusted to 110°C and the pressing pressure to 40MPa, to obtain camellia oil.

[0031] Pressing performance: Take 5 kg of camellia seed kernels and press them according to the processes of Examples 1-3 and Comparative Examples 1-5. Press them three times in parallel to obtain camellia oil samples and pressed cakes.

[0032] The oil content of the pressed cake was determined according to the standard GB / T 14488.1—2008. The oil extraction rate was calculated as: tea oil sample mass / (tea oil sample mass + oil content of pressed cake) × 100%. The recorded data are shown in Table 1.

[0033] Table 1: Oil extraction rate of different processes

[0034] As can be seen from the data in Table 1, the average oil extraction rate of the tea oil prepared in Examples 1-3 all reached over 85%, proving that the process of this application can significantly improve the oil extraction rate of the cold pressing process. In contrast, Comparative Example 1, which did not incorporate tea polyphenol-modified lignin-based polyurethane open elastic microtubes, had an oil extraction rate of only 71%, demonstrating that pressure relief pressing alone cannot fully restore the oil migration channels. The tea polyphenol-modified lignin-based polyurethane open elastic microtubes can loosen the hard oil cake formed inside during the pressing-depressurization process and form an oil-guiding structure, allowing the inner layer of oil to be discharged smoothly and improving the oil extraction rate.

[0035] Comparative Example 2, which was not modified with tea polyphenols, also showed a decrease in oil extraction rate. This indicates that the polyhydroxy structure in the lignin modified with tea polyphenols can form a large number of chemical cross-linking nodes, which enhances the mechanical strength of open elastic microtubules and can improve the oil extraction rate.

[0036] Comparative Example 3 retained the tea polyphenol-modified lignin-based polyurethane open elastic microtubes, but did not depressurize during the low and medium pressure stages; instead, it employed a continuous pressurization method. Its average oil extraction rate was not only lower than Examples 1-3, but also lower than Comparative Example 1, and similar to Comparative Example 4, which had neither tea polyphenol-modified lignin-based polyurethane open elastic microtubes nor depressurization. This result demonstrates that open elastic microtubes need to be used in conjunction with a depressurization process to fully function. Under continuous pressurization conditions, the microtubes remain in a compressed state, the tube walls cannot recover outwards, and the hollow channels and axial openings cannot reopen. Therefore, they cannot repeatedly expand the already compacted camellia seed kernel layer; they can only statically increase the voids in the layer as ordinary filler, slightly increasing the oil extraction rate under low and medium pressure.

[0037] Comparative Example 5 did not employ a conditioning process combining vacuum degassing, atomized water addition, and nitrogen positive pressure permeation. Instead, it directly added camellia seed kernels to deoxygenated deionized water under nitrogen protection and stirred until the moisture content reached 7%. Its oil extraction rate was lower than that of Examples 1-3. This indicates that during direct soaking and stirring, moisture tends to concentrate preferentially on the particle surface, leading to excessive softening or sticking of some camellia seed kernels on the surface, while water penetration into the particle interior is relatively insufficient. This results in the presence of both overly wet and under-conditioned particles in the material layer. In contrast, this invention first uses vacuum to remove air from the particle pores, then applies pre-calculated deoxygenated deionized water to the particle surface via secondary atomization, and uses nitrogen positive pressure to drive the water to migrate inward along capillaries and small cracks. This allows the camellia seed kernels to achieve a more uniform degree of plasticization, reducing localized clumping and fine powder blockage during pressing, thereby improving the oil extraction rate.

[0038] Determination of acid value and peroxide value: Three portions of tea oil samples prepared in Examples 1-3, Comparative Examples 2 and 6 were taken respectively. The acid value was determined according to GB5009.229-2016 and the peroxide value was determined according to GB5009.227-2023. The tea oil samples were then placed at room temperature for 2 months, and the peroxide value was measured again. The average value was recorded as shown in Table 2.

[0039] Table 2: Acid value and peroxide value of tea oil

[0040] As shown in Table 2, the peroxide value and acid value of the tea oil prepared in Examples 1-3 are at a low level. Furthermore, the increase in peroxide value after two months of room temperature storage is small, far lower than that of the tea oil prepared by conventional hot pressing in Comparative Example 6. This indicates that while improving pressing efficiency, the present invention does not exacerbate the hydrolysis or oxidation of tea oil due to the addition of polyurethane elastic microtubes and repeated pressure cycles. This allows the antioxidant components of the tea oil to be preserved, while also avoiding the quality decline caused by high-temperature treatment and improving the antioxidant capacity of the tea oil.

[0041] The only difference between Comparative Example 2 and Example 1 is whether the lignin has been modified with tea polyphenols. This shows that tea polyphenol modification can introduce more polyphenol structures into lignin, making the microtubule surface and near-surface layer have more accessible phenolic hydroxyl groups, thereby improving the free radical truncation and coordination ability of oxidizing metal ions, allowing tea oil to retain more natural antioxidant components, and thus strengthening its own antioxidant capacity.

[0042] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing antioxidant tea oil, characterized in that, Includes the following steps: S1: Preparation of tea polyphenol-modified lignin-based polyurethane open elastic microtubules 10-12 parts by weight of enzymatically hydrolyzed lignin and 6-8 parts by weight of tea polyphenols were subjected to acid-catalyzed phenolation reaction under the action of sulfuric acid. The resulting reaction mixture was added to 1,4-dioxane, stirred and filtered. The filtrate was precipitated by diethyl ether antisolvent. After washing and drying the precipitate, tea polyphenol-modified lignin was obtained. 4.5-4.75 parts by weight of polytetrahydrofuran ether diol 2000 and hexamethylene diisocyanate were subjected to prepolymerization reaction under the action of catalyst. Then, 0.4-0.5 parts by weight of tea polyphenol-modified lignin were added to carry out crosslinking reaction to obtain tea polyphenol-modified lignin-based polyurethane reaction solution. The solution was injected into a pipe mold for gradient curing and hot pressing, and then demolded. A through slit of 0.3-0.5 mm was opened along the pipe wall axial direction and cut to obtain C-shaped pipe. After washing and drying with purification solution, tea polyphenol-modified lignin-based polyurethane open elastic microtube was obtained. S2: Low-oxygen osmotic conditioning of camellia seed kernels Camellia seeds are dried at low temperature, dehulled, crushed and sieved to obtain camellia seed kernels. At 30-38℃, 100 parts by weight of camellia seed kernels are placed under a vacuum of 0.02-0.03MPa for one vacuum degassing. Then, 2-2.5 parts by weight of deoxygenated deionized water are sprayed in the form of atomization. After adding water, nitrogen is backfilled to make the pressure reach 0.07-0.08MPa. The camellia seed kernels are turned over. The vacuuming-atomization water addition-nitrogen backfilling operation is performed a total of 3 times. The final moisture content of the camellia seed kernels is adjusted to 7-7.5% to obtain conditioned camellia seed kernels. Under nitrogen protection, the conditioned camellia seed kernels are mixed evenly with tea polyphenol modified lignin-based polyurethane open elastic microtubes to obtain camellia seed kernels to be pressed. S3: Gradient pressure relief and rebound pressing of camellia seed kernels The camellia seeds to be pressed are added to a hydraulic pressing device, and low-pressure circulating pressing, medium-pressure circulating pressing and high-pressure final pressing are carried out in sequence at 30-38℃. The crude camellia oil obtained by pressing is centrifuged and microporous filtered under nitrogen protection to obtain antioxidant camellia oil.

2. The method for preparing an antioxidant tea oil as described in claim 1, characterized in that, The tea polyphenols in step S1 are food-grade tea polyphenols, containing 70-75% by mass of catechins.

3. The method for preparing antioxidant tea oil as described in claim 1, characterized in that, In step S1, the amount of hexamethylene diisocyanate added is calculated based on the molar ratio of NCO groups to total effective hydroxyl groups of (0.8-0.85):1, where the total effective hydroxyl groups are the sum of the effective hydroxyl groups of polytetrahydrofuran ether diol 2000 and tea polyphenol-modified lignin.

4. The method for preparing an antioxidant tea oil as described in claim 1, characterized in that, The catalyst in step S1 is an organozinc catalyst ZCAT-T50.

5. The method for preparing an antioxidant tea oil as described in claim 1, characterized in that, The purification solution in step S1 consists of anhydrous food-grade ethanol and glycerol, wherein the mass fraction of glycerol is 3-6%.

6. The method for preparing an antioxidant tea oil as described in claim 1, characterized in that, The pipe mold in step S1 consists of a fixed polytetrafluoroethylene (PTFE) mandrel and an annular outer shell. The diameter of the PTFE mandrel is 1-1.5 mm, and the gap between the PTFE mandrel and the annular outer shell is 0.5-0.7 mm.

7. The method for preparing an antioxidant tea oil as described in claim 1, characterized in that, In step S2, the tea polyphenol-modified lignin-based polyurethane open elastic microtubules account for 2-2.5% of the mass of the conditioned camellia seed kernel particles.

8. The method for preparing an antioxidant tea oil as described in claim 1, characterized in that, In step S3, the low-pressure circulating pressing is carried out at 8-10 MPa for 90-120 seconds, then the pressure is released to 1-2 MPa and held for 20-30 seconds, and this process is repeated twice. The medium-pressure circulating pressing is carried out at 18-20 MPa for 120-180 seconds, then the pressure is released to 3-5 MPa and held for 30-45 seconds, and this process is repeated twice. The high-pressure final pressing is carried out at 40-44 MPa until no tea oil is extracted.

9. The method for preparing an antioxidant tea oil as described in claim 8, characterized in that, In low-pressure circulating pressing and medium-pressure circulating pressing, the pressure release rate after pressure holding is 0.2-0.5 MPa / s.

10. An antioxidant tea oil, characterized in that, It is prepared by any one of the antioxidant tea oil preparation methods of claims 1-9.

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