A method for refining idesia oil

Abstract

This invention discloses a refining method for *Vernicia fordii* oil, relating to the field of oil processing technology. It solves the problems of long heating time in the high-temperature range and uncontrolled decolorization catalysis leading to trans fatty acid formation during existing *Vernicia fordii* oil refining processes. The key technical points are: phosphoric acid degumming treatment, alkali refining pre-dehydration, color-protecting temperature-controlled decolorization, two-stage crystallization dewaxing, and graded temperature-controlled deodorization; after alkali refining and water washing, free water is pre-removed by vacuum drying; decolorization uses a compound of activated clay and coconut shell activated carbon, and the vacuum is removed after cooling; deodorization uses graded temperature control under high vacuum and stripping with a mixture of direct steam and food-grade nitrogen. This invention is mainly used for the refining of *Vernicia fordii* crude oil to obtain *Vernicia fordii* finished oil with low trans fatty acid content.

Description

Technical Field

[0001] This invention relates to the field of oil processing technology, and in particular to a refining method for tung oil. Background Technology

[0002] Mountain tung oil is a food ingredient, belonging to the high-end woody plant oil category. Its raw material, the mountain tung tree, is a native species with strong adaptability and wide distribution, possessing great potential for oil resource development. Mountain tung oil is rich in essential polyunsaturated fatty acids, and long-term consumption has positive effects on cardiovascular health, giving it a unique position in the high-end edible vegetable oil market. With increasing public awareness of health and the development of the woody edible oil industry, mountain tung oil, as a high-quality oil resource, has received widespread attention, and its product quality and food safety have increasingly become the focus of industry attention. From crude oil to edible finished oil, a series of refining processes are required, and the processing methods directly affect the final quality of the oil.

[0003] Currently, the main methods for extracting crude oil from *Vernicia fordii* include pressing, solvent extraction, aqueous enzymatic extraction, and supercritical carbon dioxide extraction. Regardless of the method used, the crude oil produced has problems such as high impurities and acid value, and it also has a bitter and unpleasant odor, making it unsuitable for direct consumption. It must undergo refining before it can be used as edible oil. Furthermore, *Vernicia fordii* oil contains a significant amount of wax, which severely affects the appearance and transparency of the finished oil. Therefore, wax removal is necessary during refining, and the refining process directly determines the final quality of the finished oil. However, existing refining processes for *Vernicia fordii* oil have some shortcomings, particularly regarding the alkali refining and water washing processes. Oils are typically transferred directly to the decolorization process. The free water carried in the oil enters the subsequent high-temperature stage along with the oil, forcing the deodorization stage to use long-term high-temperature vacuum dehydration, which prolongs the heating time of the oil at high temperatures. Activated clay is usually added separately in the decolorization process. The acidic sites on the surface of the activated clay adsorb pigments and catalyze the polyunsaturated fatty acids in the oil. Furthermore, the residual metal ions in the oil after decolorization further intensify the isomerization reaction under subsequent high-temperature conditions. The deodorization process often uses a method of raising the temperature to a high temperature in one go and maintaining it for a long time. The oil stays in the high-temperature range for a long time, making it easy for the cis double bonds to undergo isomerization and generate trans fatty acids. Summary of the Invention

[0004] To address the above shortcomings, this invention provides a refining method for *Vernicia fordii* oil. This method pre-removes free water from the oil through a vacuum drying step following alkali refining and water washing, ensuring controlled water content in the oil before decolorization and deodorization processes. This eliminates the need for prolonged vacuum dehydration in subsequent high-temperature stages, thus shortening the oil's heating time in the high-temperature range. In the decolorization process, activated clay and coconut shell activated carbon are added in combination, and the decolorization reaction is completed in a medium-low temperature range. After the reaction, the vacuum is released only after the oil has cooled to a lower temperature. The catalytic effect of the acidic sites of the activated clay on polyunsaturated fatty acids is inhibited at lower temperatures, while the coconut shell activated carbon simultaneously adsorbs metal ions and pigments. This method, while completing decolorization and wax removal, prepares the oil for subsequent high-temperature processes. This method reduces the inducing factors of isomerization reactions. By employing a staged temperature control method under high vacuum in the deodorization stage, low-molecular-weight odor substances are first removed by introducing direct steam at a low temperature, and then a mixture of direct steam and food-grade nitrogen is introduced at a high temperature for deep deodorization. The food-grade nitrogen forms an inert atmosphere inside the oil layer and evenly agitates the oil. Steam stripping is fully effective at a lower temperature, and the cumulative time the oil exceeds the set temperature is limited. This method uses high vacuum to lower the volatilization temperature of odor components and uses inert gas-assisted stripping instead of simply extending the high-temperature time. Under the premise of fully removing bitterness and unpleasant odors, the exposure time of polyunsaturated fatty acid cis double bonds in the high-temperature range is controlled, and the flavor and transparency of the finished oil are maintained well.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a refining method for tung oil, the specific steps of which are as follows: Phosphoric acid degumming treatment: After heating the crude tung oil, add the food additive phosphoric acid to carry out the degumming reaction, then add hot water to settle and separate the gums to obtain degummed oil; Alkali refining and pre-dehydration: Degummed oil is added to an aqueous solution of sodium hydroxide (a food additive) for alkali refining reaction. The soap residue is separated to obtain alkali-refined oil. The alkali-refined oil is washed with hot water and dried under vacuum conditions. The free water content is controlled to be reduced to below a set value to obtain pre-dried oil. Color protection and temperature-controlled decolorization: Pre-dried oil is added to food additive activated clay and food additive coconut shell activated carbon under vacuum conditions for decolorization reaction. After the reaction is completed, it is cooled to the set temperature and then the vacuum is removed. Food additive activated clay and food additive coconut shell activated carbon are filtered out to obtain decolorized oil. Two-stage crystallization dewaxing: The decolorized oil is pumped into the first crystallization tank for cooling and crystallization. After adding food additive diatomaceous earth, it is filtered through a plate and frame filter. The filtered decolorized oil is then pumped into the second crystallization tank for low-temperature crystallization. After adding food additive diatomaceous earth, it is filtered through a plate and frame filter to obtain dewaxed oil. Staged temperature-controlled deodorization: The dewaxed oil is pumped into the deodorization tank. Under high vacuum conditions, direct steam is first introduced for the first stage of deodorization, and then a mixture of direct steam and food-grade nitrogen is introduced for the second stage of deep deodorization. After deodorization, the oil is cooled and the vacuum is removed. The oil is then filtered to obtain the finished tung oil.

[0006] Furthermore, in the phosphoric acid degumming process, the crude tung oil is stirred and heated to 50-55°C, and 0.1-0.2% by weight of tung oil is added with 85% by mass of food additive phosphoric acid. The mixture is stirred for 10-15 minutes, and then 8-10% by weight of tung oil and 80-85°C of hot water are added. After stirring evenly, the temperature is raised to 80-85°C and the mixture is allowed to stand for 4-5 hours to separate the gums and obtain degummed oil.

[0007] Furthermore, in the alkali-refined pre-dehydration process, the degummed oil is stirred and heated to 30-35°C. The theoretical amount of sodium hydroxide aqueous solution required to neutralize the free fatty acids is determined based on the acid value of the degummed oil. The actual amount added is 1.15-1.25 times the theoretical amount, and the mass fraction of the sodium hydroxide aqueous solution is 12-15%. After the reaction, the temperature is raised to 60-65°C, and stirring is stopped after 30 minutes. The mixture is then allowed to stand for 4-5 hours to allow the soap granules to settle, and the soap residue is separated to obtain the alkali-refined oil.

[0008] Furthermore, in the alkali pre-dehydration process, the alkali-refined oil after separating the soapstock is heated to 50-60°C, and hot water at 80-85°C (10-12% by weight of the alkali-refined oil) is added for hot water washing. The mixture is stirred and heated to 80-85°C for 30 minutes, then stirring is stopped. The mixture is allowed to stand for 4-5 hours to allow the water layer to settle. After separating the water layer, the hot water washing is repeated 1-2 times.

[0009] Furthermore, in the alkali refining pre-dehydration process, the alkali refining oil after washing is dried at 70-80℃ and a vacuum degree ≥0.08MPa for 20-30 minutes. During the drying process, the alkali refining oil is continuously stirred and the vacuum degree is maintained at 0.08-0.09MPa. After drying, the free water mass fraction is 0.03-0.05%, thus obtaining pre-dried oil.

[0010] Furthermore, in the color-protecting and temperature-controlled decolorization process, food additive activated clay is added at 1-1.5% of the weight of the pre-dried oil, and food additive coconut shell activated carbon is compounded at 0.2-0.4% of the weight of the pre-dried oil. The food additive activated clay and food additive coconut shell activated carbon are pre-mixed in a mixing tank before being added to the pre-dried oil.

[0011] Furthermore, in the color-protecting and temperature-controlled decolorization process, the pre-dried oil is dehydrated in a decolorization reaction tank under a vacuum of ≥0.09MPa to remove trace amounts of residual moisture. Then, a mixture of food additive activated clay and food additive coconut shell activated carbon is added, and the decolorization reaction is carried out at 95-105℃ for 30-40 minutes. After the reaction is completed, the temperature is cooled to 50-55℃ and the vacuum is removed. After the vacuum is removed, the food additive activated clay and food additive coconut shell activated carbon are filtered out by a plate and frame filter press to obtain the decolorized oil.

[0012] Furthermore, in the two-stage crystallization dewaxing process, the decolorized oil is pumped into the first crystallization tank and stirred. Under normal pressure, it is slowly cooled to 25°C for the first stage of crystallization for 24 hours. After crystallization, 0.3-0.5% of the weight of the decolorized oil is added as food additive diatomaceous earth. After stirring for 2 hours, it is filtered for the first time using a plate and frame filter press. The filtered decolorized oil is then pumped into the second crystallization tank and crystallized for the second stage at 4-6°C for 48 hours. After crystallization, 0.5-0.8% of the weight of the decolorized oil is added as food additive diatomaceous earth. After stirring for 2 hours, it is filtered for the second time using a plate and frame filter press to obtain dewaxed oil.

[0013] Furthermore, in the staged temperature-controlled deodorization process, the dewaxed oil is pumped into the deodorization tank and a vacuum of ≥0.09MPa is maintained. The temperature is first raised to 155-165℃ and direct steam is introduced for the first stage of deodorization for 1.0-1.5h. Then, the temperature is raised to 175-185℃ for the second stage of deep deodorization for 1.0-1.5h. The total time for the two stages of deodorization is 2.0-3.0h.

[0014] Furthermore, in the graded temperature-controlled deodorization process, during the second stage of deep deodorization, a mixture of direct steam and food-grade nitrogen is introduced below the oil layer of the dewaxed oil. The volume fraction of food-grade nitrogen in the mixture is 20-30%. The mixture is introduced into the interior of the dewaxed oil through a distributor. The cumulative time for the oil temperature to exceed 180°C during the deodorization process is 1.0-1.5 hours. After deodorization, the oil is cooled to 60-65°C by a shell-and-tube heat exchanger before the vacuum is removed. The oil is then filtered to obtain the finished tung oil.

[0015] Compared with the prior art, the beneficial effects of the present invention are: I. This invention removes free water from the oil beforehand through a vacuum drying process following alkali refining and water washing, ensuring that the water content of the oil entering the decolorization and deodorization processes is under control. This eliminates the need for prolonged vacuum dehydration in subsequent high-temperature stages, thus shortening the heating time of the oil in the high-temperature range. In the decolorization process, activated clay and coconut shell activated carbon are added in combination and the decolorization reaction is completed in a medium-low temperature range. After the reaction, the vacuum is released only after the oil has cooled to a lower temperature. The catalytic effect of the acidic sites of the activated clay on polyunsaturated fatty acids is inhibited at lower temperatures, while the coconut shell activated carbon simultaneously adsorbs metal ions and pigments. This method, while completing decolorization and dewaxing, reduces the inducing factors for isomerization reactions in subsequent high-temperature stages.

[0016] II. This invention employs a staged temperature control method under high vacuum during the deodorization stage. First, direct steam is introduced at a low temperature to remove low-molecular-weight odor substances. Then, a mixture of direct steam and food-grade nitrogen is introduced at a high temperature for deep deodorization. The food-grade nitrogen forms an inert atmosphere inside the oil layer and uniformly agitates the oil. Steam stripping is fully effective at a lower temperature, and the cumulative time the oil exceeds the set temperature is limited. This method uses high vacuum to lower the volatilization temperature of odor components and uses inert gas-assisted stripping instead of simply extending the high-temperature time. Under the premise of fully removing bitterness and unpleasant odors, the exposure time of polyunsaturated fatty acid cis double bonds in the high-temperature range is controlled, and the flavor and transparency of the finished oil are maintained well. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0018] Figure 1 A flowchart of a refining method for tung oil; Figure 2 A framework diagram of a refining method for tung oil; Figure 3 This is a framework diagram of color protection and temperature-controlled decolorization in a refining method for tung oil. Detailed Implementation

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

[0020] It should be understood that, when used in this specification, the terms “comprising” and “including” indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0021] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” are intended to include the plural forms.

[0022] It should also be further understood that the term "and / or" as used in this specification refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0023] Example 1 (e.g.) Figure 1 , Figure 2 (as shown) Weigh 250 kg of crude tung oil and pump it into a degumming tank equipped with a stirring device. Turn on the stirring and heat the crude tung oil to 52°C. Add 0.3 kg of 85% phosphoric acid (food additive) at 0.12% of the crude tung oil's weight. Stir for 12 minutes to ensure the phosphoric acid fully contacts the crude tung oil, allowing it to convert non-hydrated phospholipids into hydrated phospholipids. Then add 22 kg of hot water at 82°C and continue stirring until homogeneous. Raise the temperature to 83°C and keep it at that temperature for 4.5 hours to allow the gums in the crude tung oil to fully absorb water, swell, and settle. After settling, release the settled gums from the bottom of the degumming tank. The upper layer of oil is the degummed oil. The acid value of the degummed oil was measured to be 4.9 mg KOH / g.

[0024] The degummed oil was pumped into an alkali refining tank and heated to 32°C with stirring. Based on the acid value of the degummed oil, the theoretical amount of sodium hydroxide solution required to neutralize free fatty acids was determined. The actual amount added was 1.2 times the theoretical amount. 9.2 kg of 13% sodium hydroxide solution was added evenly. During the addition of alkali, stirring was maintained to ensure that the alkali solution and the degummed oil were fully mixed. The sodium hydroxide solution and the free fatty acids in the degummed oil underwent a neutralization reaction to form soap granules. After the acid-base reaction was completed, the material was heated to 62°C and stirred for another 30 minutes before stirring was stopped. The mixture was then allowed to stand for 5 hours to allow the soap granules to settle completely. The soap residue was discharged from the bottom of the alkali refining tank, and the upper layer of oil was the alkali-refined oil. The free fatty acid content in the alkali-refined oil was significantly reduced.

[0025] The alkali-refined oil was heated to 55°C, and 28 kg of hot water at 83°C was added. The mixture was stirred and heated to 82°C. After stirring for 30 minutes, the stirring was stopped, and the mixture was allowed to stand for 5 hours to allow the water layer to settle. The wastewater layer was then discharged from the bottom. The same steps were repeated once more. After the second wash, the discharged water layer was clear and transparent, with no residual soap precipitated. The alkali-refined oil sample had no alkaline smell. The washing was completed, and the soap residue and residual alkali liquid carried in the alkali-refined oil were removed.

[0026] The washed alkali-refined oil was pumped into a pre-drying tank and dried at 75°C and a vacuum of 0.085 MPa for 25 minutes. During the drying process, the alkali-refined oil was continuously stirred and the vacuum was kept stable. After drying, a sample was taken for testing. The free water content in the alkali-refined oil was 0.04%, and the pre-dried oil was obtained. The low free water content in the pre-dried oil can avoid the extension of high-temperature heating time due to moisture introduction in the subsequent decolorization and deodorization processes.

[0027] Pre-dried oil was pumped into a decolorizing reaction tank, and trace amounts of residual moisture were removed under a vacuum of 0.095 MPa. 3.0 kg of food-grade activated clay (1.2% of the pre-dried oil weight) and 0.75 kg of food-grade coconut shell activated carbon (0.3% of the pre-dried oil weight) were weighed and pre-mixed evenly in a mixing tank before being added to the decolorizing reaction tank. After even mixing, the mixture was added to the decolorizing reaction tank along with the pre-dried oil, and the decolorization reaction was carried out at 100°C for 35 minutes, maintaining a vacuum of 0.095 MPa during the reaction. After the decolorization reaction was completed, the material was cooled to 55°C and the vacuum was removed. After vacuum removal, the food-grade activated clay and coconut shell activated carbon were filtered out using a plate and frame filter press to obtain the decolorized oil. Figure 3 As shown; cooling before removing the vacuum can prevent the high-temperature decolorized oil from oxidizing upon contact with air. The food additive coconut shell activated carbon and food additive activated clay are used in combination to adsorb pigments and lighten the color of the decolorized oil, while also adsorbing residual metal ions in the decolorized oil, thus reducing the inducing factors of isomerization reaction in subsequent high-temperature processes.

[0028] The decolorized oil was pumped into the first crystallization tank, stirred, and slowly cooled to 25°C under normal pressure. It was then kept at this temperature for 24 hours to allow the wax in the decolorized oil to gradually crystallize and precipitate. After crystallization, 0.9 kg of food additive diatomaceous earth was added at 0.36% of the weight of the decolorized oil. After stirring for another 2 hours, the oil was filtered for the first time using a plate and frame filter press to remove most of the wax. The decolorized oil after the first filtration was pumped into the second crystallization tank, and the temperature was controlled at 5°C. It was kept at this temperature for 48 hours to allow the remaining wax in the decolorized oil to crystallize and precipitate further. After crystallization, 1.6 kg of food additive diatomaceous earth was added at 0.64% of the weight of the decolorized oil. After stirring for another 2 hours, the oil was filtered for the second time using a plate and frame filter press to obtain dewaxed oil. The two-stage crystallization process, combined with two stages of diatomaceous earth filtration, ensured thorough wax removal and produced dewaxed oil with good transparency.

[0029] The dewaxed oil was pumped into a deodorization tank, maintaining a vacuum of 0.095 MPa. The temperature was first raised to 160°C, and direct steam was introduced above the oil layer for the first stage of deodorization for 1.2 hours, removing low-molecular-weight odor components. The temperature was then raised to 180°C, and a mixture of direct steam and food-grade nitrogen was introduced below the oil layer, with the food-grade nitrogen comprising 25% of the mixture. This mixture was evenly distributed into the dewaxed oil via a distributor for the second stage of deep deodorization for 1.3 hours. The total time the dewaxed oil temperature exceeded 180°C during the deodorization process was 1.3 hours. After deodorization, the dewaxed oil was cooled to 62°C via a tubular heat exchanger, the vacuum was removed, and the oil was filtered to obtain the finished *Vernicia fordii* oil. This staged temperature control, combined with food-grade nitrogen-assisted stripping, allowed for the removal of odor components from the dewaxed oil at a relatively low temperature, thus controlling the exposure time of the dewaxed oil in the high-temperature range.

[0030] Finished product testing: The acid value of the finished tung oil was determined by titration, the peroxide value by peroxide titration, the total trans fatty acid content by gas chromatography, the moisture and volatile matter by loss on drying, and the transparency by visual inspection. The test results were: acid value 0.18 mg KOH / g, peroxide value 0.08 g / 100g, moisture and volatile matter 0.03%, and total trans fatty acid content 0.52%. The finished tung oil sample was clear and transparent, without bitterness or unpleasant odor. The obtained finished tung oil showed balanced indicators and low trans fatty acid content, making it suitable for daily household consumption and retail sales in supermarkets.

[0031] Example 2: Weigh 220 kg of crude tung oil and pump it into a degumming tank. Stir and heat to 50°C. Add 0.25 kg of 85% food additive phosphoric acid at 0.11% of the weight of the crude tung oil. Stir for 10 min. Add 18 kg of hot water at 80°C. Stir evenly and then heat to 80°C. Keep warm and let stand for 4 h. Separate and settle the gums to obtain degummed oil. The acid value of the degummed oil is 5.1 mg KOH / g.

[0032] The degummed oil was heated to 30°C. Based on the acid value of the degummed oil, the theoretical amount of sodium hydroxide aqueous solution required to neutralize free fatty acids was determined. The actual amount added was 1.15 times the theoretical amount. 8.5 kg of 12% sodium hydroxide aqueous solution was added evenly. After the reaction, the temperature was raised to 60°C, and stirring was stopped after 30 min. The mixture was allowed to stand for 4 h, and the soap residue was separated to obtain alkali-refined oil. The alkali-refined oil was heated to 50°C, and 24 kg of hot water at 80°C was added. The mixture was stirred and heated to 80°C. After stirring for 30 min, the mixture was allowed to stand for 4 h, and the water layer was separated. The oil was washed once more in the same manner until the water layer was clear and free of soap residue. After washing, the alkali-refined oil was dried at 70°C and a vacuum of 0.08 MPa for 20 min, with continuous stirring during the drying process. After drying, the free water mass fraction in the alkali-refined oil was 0.05%, resulting in pre-dried oil.

[0033] The pre-dried oil was pumped into a decolorizing reaction tank, and trace amounts of residual moisture were removed under a vacuum of 0.09 MPa. 2.4 kg of food additive activated clay was added at 1.1% of the weight of the pre-dried oil, and 0.5 kg of food additive coconut shell activated carbon was added at 0.23% of the weight of the pre-dried oil. The two were mixed evenly before being added to the decolorizing reaction tank, and the decolorization reaction was carried out at 95°C for 30 minutes. After the reaction was completed, the temperature was cooled to 50°C and the vacuum was removed. The adsorbent was filtered out by a plate and frame filter press to obtain the decolorized oil.

[0034] The decolorized oil was pumped into the first crystallization tank and cooled to 25°C under normal pressure for 24 hours to crystallize. 0.77 kg of food additive diatomaceous earth was added at 0.35% of the weight of the decolorized oil. After stirring for 2 hours, the mixture was filtered through a plate and frame filter. The filtered decolorized oil was then pumped into the second crystallization tank and crystallized at 4°C for 48 hours. 1.2 kg of food additive diatomaceous earth was added at 0.55% of the weight of the decolorized oil. After stirring for 2 hours, the mixture was filtered through a plate and frame filter to obtain dewaxed oil.

[0035] The dewaxed oil is pumped into a deodorization tank. Under a vacuum of 0.09 MPa, the temperature is first raised to 155°C and direct steam is introduced for the first stage of deodorization for 1.0 h. Then, the temperature is raised to 175°C and a mixture of direct steam and food-grade nitrogen is introduced for the second stage of deep deodorization for 1.0 h. The food-grade nitrogen component is 20%, and the cumulative time when the dewaxed oil temperature exceeds 180°C is 1.0 h. After deodorization, the dewaxed oil is cooled to 60°C through a shell-and-tube heat exchanger to remove the vacuum. After filtration, the finished tung oil is obtained.

[0036] Finished product testing: The test was conducted using the same method as in Example 1. The results were as follows: acid value 0.22 mg KOH / g, peroxide value 0.10 g / 100g, moisture and volatile matter 0.04%, total trans fatty acid content 0.61%, and the finished tung oil sample was clear and transparent. Furthermore, the deodorization temperature and time in this preparation process were relatively low, resulting in a shorter production cycle and reduced energy consumption. The finished tung oil obtained still met the requirements for food use and is suitable for large-scale industrial production and bulk purchase by catering companies.

[0037] Example 3: Weigh 200 kg of crude tung oil and pump it into a degumming tank. Stir and heat to 55°C. Add 0.35 kg of 85% food additive phosphoric acid at 0.18% of the weight of the crude tung oil. Stir for 15 min. Add 19 kg of hot water at 85°C. Stir evenly and then heat to 85°C. Keep warm and let stand for 5 h. Separate and settle the gums to obtain degummed oil. The acid value of the degummed oil is 4.6 mg KOH / g.

[0038] The degummed oil was heated to 35°C. Based on the acid value of the degummed oil, the theoretical amount of sodium hydroxide aqueous solution required to neutralize free fatty acids was determined. The actual amount added was 1.25 times the theoretical amount. 7.0 kg of 15% sodium hydroxide aqueous solution was added evenly. After the reaction, the temperature was raised to 65°C, and stirring was stopped after 30 min. The mixture was allowed to stand for 5 h, and the soap residue was separated to obtain alkali-refined oil. The alkali-refined oil was heated to 60°C, and 22 kg of hot water at 85°C was added. The mixture was stirred and heated to 85°C. After stirring for 30 min, the mixture was allowed to stand for 5 h, and the water layer was separated. The oil was washed twice in the same manner until the water layer was clear and free of soap residue. After washing, the alkali-refined oil was dried at 80°C and a vacuum of 0.09 MPa for 30 min, with continuous stirring during the drying process. After drying, the free water mass fraction in the alkali-refined oil was 0.03%, resulting in pre-dried oil.

[0039] The pre-dried oil was pumped into a decolorizing reaction tank, and trace amounts of residual moisture were removed under a vacuum of 0.095 MPa. 2.8 kg of food additive activated clay was added at 1.4% of the weight of the pre-dried oil, and 0.7 kg of food additive coconut shell activated carbon was added at 0.35% of the weight of the pre-dried oil. The two were pre-mixed evenly and then added to the decolorizing reaction tank. The decolorization reaction was carried out at 105℃ for 40 minutes. After the reaction was completed, the temperature was cooled to 55℃ and the vacuum was removed. The adsorbent was filtered out by a plate and frame filter press to obtain the decolorized oil.

[0040] The decolorized oil was pumped into the first crystallization tank and cooled to 25°C under normal pressure for 24 hours to crystallize. 0.9 kg of food additive diatomaceous earth was added at 0.45% of the weight of the decolorized oil, and the mixture was stirred for 2 hours before being filtered through a plate and frame filter. The filtered decolorized oil was then pumped into the second crystallization tank and crystallized at 6°C for 48 hours. 1.5 kg of food additive diatomaceous earth was added at 0.75% of the weight of the decolorized oil, and the mixture was stirred for 2 hours before being filtered through a plate and frame filter to obtain dewaxed oil.

[0041] The dewaxed oil is pumped into a deodorization tank. Under a vacuum of 0.095 MPa, the temperature is first raised to 165°C and direct steam is introduced for the first stage of deodorization for 1.5 hours. Then, the temperature is raised to 185°C and a mixture of direct steam and food-grade nitrogen is introduced for the second stage of deep deodorization for 1.5 hours. The food-grade nitrogen component is 30%, and the cumulative time when the dewaxed oil temperature exceeds 180°C is 1.5 hours. After deodorization, the dewaxed oil is cooled to 65°C through a shell-and-tube heat exchanger to remove the vacuum. After filtration, the finished tung oil is obtained.

[0042] Finished product testing: The test was conducted using the same method as in Example 1. The results were as follows: acid value 0.15 mg KOH / g, peroxide value 0.07 g / 100g, moisture and volatile matter 0.03%, total trans fatty acid content 0.45%. The finished tung oil sample was clear and transparent, without bitterness or unpleasant odor. Furthermore, the deodorization process involved a higher deodorization temperature, a higher vacuum degree, and a longer deodorization time, resulting in a lower acid value and peroxide value, and a lower trans fatty acid content in the finished tung oil. This makes it suitable for the high-end food market, as well as for consumers and food processing companies with high requirements for oil quality.

[0043] Comparative example: 250 kg of crude tung oil from the same batch as in the example was weighed and processed using conventional tung oil refining technology: After degumming with phosphoric acid, the crude tung oil entered the alkali refining process. The alkali-refined oil after water washing was directly pumped into the decolorization tank without pre-drying. 3.75 kg of food additive activated clay was added at 1.5% of the weight of the crude tung oil. The decolorization reaction was carried out at 110°C and 0.08 MPa vacuum for 30 min. After decolorization, the temperature was cooled to 60°C and the vacuum was removed. The decolorized oil was obtained by plate and frame filtration. The decolorized oil underwent two-stage crystallization dewaxing: the first stage was crystallized at 25°C for 24 h, and the second stage was crystallized at 5°C for 48 h. Both stages were filtered with food additive diatomaceous earth as a filter aid and then plate and frame filtration to obtain dewaxed oil.

[0044] The dewaxed oil is pumped into a deodorization tank, heated to 160°C under a vacuum of 0.08 MPa, and deodorized by direct steam for 2 hours. After deodorization, the steam valve is not closed, and the temperature is continued to rise to 220°C. The oil is then dehydrated under vacuum at 220°C for 3 hours. After dehydration, the oil is cooled to 60°C to release the vacuum, and then filtered to obtain the finished tung oil.

[0045] Finished product testing: The test was conducted using the same method as in Example 1. The results were as follows: acid value 0.25 mg KOH / g, peroxide value 0.28 g / 100g, moisture and volatile matter 0.06%, total trans fatty acid content 2.15%, and the finished tung oil sample was clear and transparent, but the oil color was dark and it had a slight cooked taste after high-temperature deodorization.

[0046] In summary, a comparison of Examples 1, 2, and 3 with the comparative example shows that the total trans fatty acid content of the *Vernicia fordii* oil obtained in the three examples is between 0.45% and 0.61%, while the total trans fatty acid content of the *Vernicia fordii* oil obtained in the comparative example is 2.15%, a significant difference. Furthermore, the peroxide value of the comparative example is 0.28 g / 100g, significantly higher than the 0.07-0.10 g / 100g of the three examples, and the *Vernicia fordii* oil in the comparative example has a darker color and a slightly ripened appearance. The process involves three steps: 1) Alkali refining and water washing followed by vacuum drying to remove free moisture; 2) Decolorization using a combination of food-grade activated clay and coconut shell activated carbon; 3) Deodorization using high-vacuum graded temperature control and stripping with a mixture of direct steam and food-grade nitrogen. These three steps work together to ensure the deodorization depth, transparency, and dewaxing effect of the finished tung oil, while minimizing the oil's exposure time in the high-temperature range. This effectively controls the formation of trans fatty acids during refining.

[0047] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for refining Idesia oil, characterized by, The specific steps of this method are as follows: Phosphoric acid degumming treatment: After heating the crude tung oil, add food additive phosphoric acid to carry out the degumming reaction, then add hot water to settle and separate the gums to obtain degummed oil; Alkali refining and pre-dehydration: Degummed oil is added to an aqueous solution of sodium hydroxide (a food additive) for alkali refining reaction. The soap residue is separated to obtain alkali-refined oil. The alkali-refined oil is washed with hot water and dried under vacuum conditions. The free water content is controlled to be reduced to below a set value to obtain pre-dried oil. Color protection and temperature-controlled decolorization: Pre-dried oil is added to food additive activated clay and food additive coconut shell activated carbon under vacuum conditions for decolorization reaction. After the reaction is completed, it is cooled to the set temperature and then the vacuum is removed. Food additive activated clay and food additive coconut shell activated carbon are filtered out to obtain decolorized oil. Two-stage crystallization dewaxing: The decolorized oil is pumped into the first crystallization tank for cooling and crystallization. After adding food additive diatomaceous earth, it is filtered through a plate and frame filter. The filtered decolorized oil is then pumped into the second crystallization tank for low-temperature crystallization. After adding food additive diatomaceous earth, it is filtered through a plate and frame filter to obtain dewaxed oil. Staged temperature-controlled deodorization: The dewaxed oil is pumped into the deodorization tank. Under high vacuum conditions, direct steam is first introduced for the first stage of deodorization, and then a mixture of direct steam and food-grade nitrogen is introduced for the second stage of deep deodorization. After deodorization, the oil is cooled and the vacuum is removed. The oil is then filtered to obtain the finished tung oil.

2. The method of refining Idesia oil according to claim 1, characterized by, In the phosphoric acid degumming process, the crude tung oil is stirred and heated to 50-55°C. Phosphoric acid (85% by mass) is added at 0.1-0.2% of the crude tung oil weight and stirred for 10-15 minutes. Then, hot water at 80-85°C (8-10% by weight of the crude tung oil) is added and stirred until homogeneous. The mixture is then heated to 80-85°C and allowed to stand for 4-5 hours to separate the gums and obtain degummed oil.

3. The refining method for *Vernicia fordii* oil according to claim 1, characterized in that, In the alkali-refining pre-dehydration process, the degummed oil is stirred and heated to 30-35°C. The theoretical amount of sodium hydroxide aqueous solution required to neutralize the free fatty acids is determined according to the acid value of the degummed oil. The actual amount added is 1.15-1.25 times the theoretical amount, and the mass fraction of the sodium hydroxide aqueous solution is 12-15%. After the reaction, the temperature is raised to 60-65°C, and stirring is stopped after 30 minutes. The mixture is allowed to stand for 4-5 hours to allow the soap granules to settle. The soap residue is then separated to obtain the alkali-refined oil.

4. The refining method for *Vernicia fordii* seed oil according to claim 3, characterized in that, In the alkali pre-dehydration process, the alkali-refined oil after separating the soapstock is heated to 50-60°C, and hot water at 80-85°C (10-12% by weight of the alkali-refined oil) is added for hot water washing. The temperature is raised to 80-85°C by stirring for 30 minutes, and then stirring is stopped. The mixture is allowed to stand for 4-5 hours to allow the water layer to settle. After separating the water layer, the hot water washing is repeated 1-2 times.

5. The refining method for *Vernicia fordii* seed oil according to claim 4, characterized in that, In the alkali refining pre-dehydration process, the alkali refining oil after water washing is dried at 70-80℃ and vacuum degree ≥0.08MPa for 20-30 minutes. During the drying process, the alkali refining oil is continuously stirred and the vacuum degree is maintained at 0.08-0.09MPa. After drying, the free water mass fraction is 0.03-0.05%, and pre-dried oil is obtained.

6. The refining method for *Vernicia fordii* seed oil according to claim 1, characterized in that, In the color-protecting and temperature-controlled decolorization process, food additive activated clay is added at 1-1.5% of the weight of the pre-dried oil, and food additive coconut shell activated carbon is compounded at 0.2-0.4% of the weight of the pre-dried oil. The food additive activated clay and food additive coconut shell activated carbon are pre-mixed in a mixing tank before being added to the pre-dried oil.

7. The refining method for *Vernicia fordii* oil according to claim 6, characterized in that, In the color-protecting and temperature-controlled decolorization process, the pre-dried oil is dehydrated in a decolorization reaction tank under a vacuum of ≥0.09MPa to remove trace amounts of residual moisture. Then, a mixture of food additives activated clay and coconut shell activated carbon is added, and the decolorization reaction is carried out at 95-105℃ for 30-40 minutes. After the reaction is completed, the temperature is cooled to 50-55℃ and the vacuum is removed. After the vacuum is removed, the food additives activated clay and coconut shell activated carbon are filtered out by a plate and frame filter press to obtain the decolorized oil.

8. The refining method for *Vernicia fordii* seed oil according to claim 1, characterized in that, In the two-stage crystallization dewaxing process, the decolorized oil is pumped into the first crystallization tank and stirred. Under normal pressure, it is slowly cooled to 25°C for the first stage of crystallization for 24 hours. After crystallization, diatomaceous earth food additive is added at 0.3-0.5% of the weight of the decolorized oil. After stirring for 2 hours, it is filtered for the first time by a plate and frame filter press. The filtered decolorized oil is pumped into the second crystallization tank and crystallized for the second stage at 4-6°C for 48 hours. After crystallization, diatomaceous earth food additive is added at 0.5-0.8% of the weight of the decolorized oil. After stirring for 2 hours, it is filtered for the second time by a plate and frame filter press to obtain dewaxed oil.

9. The refining method for *Vernicia fordii* seed oil according to claim 1, characterized in that, In the staged temperature-controlled deodorization process, the dewaxed oil is pumped into the deodorization tank and a vacuum of ≥0.09MPa is maintained. The temperature is first raised to 155-165℃ and direct steam is introduced for the first stage of deodorization for 1.0-1.5h. Then, the temperature is raised to 175-185℃ for the second stage of deep deodorization for 1.0-1.5h. The total time for the two stages of deodorization is 2.0-3.0h.

10. The refining method for *Vernicia fordii* oil according to claim 9, characterized in that, In the graded temperature-controlled deodorization process, during the second stage of deep deodorization, a mixture of direct steam and food-grade nitrogen is introduced below the oil layer of the dewaxed oil. The volume fraction of food-grade nitrogen in the mixture is 20-30%. The mixture is introduced into the interior of the dewaxed oil through a distributor. The cumulative time for the oil temperature to exceed 180°C during the deodorization process is 1.0-1.5 hours. After deodorization, the oil is cooled to 60-65°C by a shell-and-tube heat exchanger before the vacuum is removed. The oil is then filtered to obtain the finished tung oil.

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