Method for squeezing edible oil at low temperature

Abstract

The invention relates to the technical field of green grain and oil processing, and discloses a low-temperature edible oil squeezing method which comprises the following steps: raw material pretreatment, low-temperature tempering, low-temperature squeezing, primary filtration, low-temperature precipitation, precise filtration, low-temperature dehydration and nitrogen protection and filling. Through a low-temperature squeezing process system, sectional type temperature and pressure control is adopted in the squeezing process, grease oxidation and deterioration caused by traditional high-temperature squeezing are avoided, meanwhile, low-temperature conditioning and enzymolysis effects in the pretreatment stage are combined, oil cell tissues are mildly softened, natural active ingredients and inherent flavor substances in oil are reserved to the maximum extent, and the flavor of the oil is improved. According to the present invention, the crude oil is subjected to physical sedimentation and filtration, such that the finished product grease has the good nutritional value and the good sensory quality, and the suspended impurities, the colloidal substances and the small particles in the crude oil are removed through the layer-by-layer progressive effect of the physical sedimentation and the filtration, such that the transparency and the stability of the grease are improved, and the quality deterioration risk caused by the existence of the impurities during the subsequent storage process is reduced.

Description

Technical Field

[0001] This invention relates to the field of green grain and oil processing technology, specifically a method for low-temperature pressing of edible oil. Background Technology

[0002] Low-temperature pressed oils refer to edible and medicinal oils extracted through mechanical pressing at temperatures below 65℃. This process avoids harmful impurities generated by high temperatures, preserving the natural flavor of the oilseeds and active ingredients such as vitamin E, squalene, and sterols. The crude oil is lighter in color and has a lower acid value, typically requiring no refining or only simple processing. It avoids the harmful impurities produced during high-temperature pressing, maintains the natural flavor of the oilseeds, and possesses high nutritional value.

[0003] Currently, in the production process of low-temperature pressed edible oil, due to the imprecise control of pressing temperature and the lack of effective pretreatment methods, it is difficult to fully destroy the cell wall structure of oil crops, resulting in a low oil extraction rate. At the same time, excessively high local temperatures during the pressing process can easily cause the oxidative decomposition of unsaturated fatty acids and heat-sensitive nutrients, affecting the nutritional quality of the finished oil.

[0004] Therefore, a method for low-temperature pressing of edible oil is proposed to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for low-temperature pressing of edible oil, which solves the problems mentioned in the background art, such as low oil extraction rate and oxidative decomposition of unsaturated fatty acids and heat-sensitive nutrients, which affect the nutritional quality of the finished oil.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for low-temperature pressing of edible oil, the method comprising the following steps: Step 1: Raw material pretreatment. Select whole oilseed crop seeds, clean, screen and destone them to remove impurities, moldy grains and immature grains; Step 2: Low-temperature conditioning. Place the pretreated oilseed crop seeds in a conditioning tank, control the temperature at 30-55℃ and the humidity at 50%-70%, and carry out softening treatment for 1-4 hours. Step 3: Low-temperature pressing. The conditioned oilseed crop seeds are fed into a low-temperature screw press and pressed at a temperature range of 30-55℃ and a pressure range of 10-50MPa to obtain crude oil and oil cake. Step 4: Primary filtration. The crude oil obtained from pressing is immediately transferred to the primary filtration system and coarsely filtered at 35-60℃ using a plate and frame filter press to remove large solid impurities. Step 5: Low-temperature sedimentation. Pump the crude oil after primary filtration into a sedimentation tank and let it settle at 15-25℃ for 6-24 hours under light-protected conditions. Step 6: Precision filtration. The supernatant after sedimentation is introduced into a precision filtration device and finely filtered at 20-40℃ using a filter membrane with a pore size of 0.1-5μm to further remove micron- and submicron-sized suspended particles. Step 7: Low-temperature dehydration. The finely filtered oil is sent to a vacuum dehydration tower and dehydrated for 0.5-2 hours under an absolute pressure of 0.08-0.095MPa and a temperature of 40-55℃, so that the moisture content of the oil is reduced to below 0.05%. Step 8: Nitrogen protection and filling. The dehydrated oil is cooled to 20-30℃ under nitrogen atmosphere protection and then aseptically filled to obtain the finished low-temperature pressed edible oil.

[0007] Preferably, the raw material pretreatment in step one specifically includes: Cleaning and impurity removal: Use a gravity destoner and a flat rotary screen to preliminarily clean the oilseed crop seeds, removing dust, sand, metal fragments and light impurities; Color sorting and grading: A CCD color sorter is used to sort the cleaned seeds to remove moldy and discolored seeds, and a drum grading screen is used to grade the seeds according to their particle size to ensure the uniformity of the raw materials. Washing and surface drying: The graded seeds are sent to a bubble washing machine and washed with pure water. After washing, the surface moisture is removed by a low-speed centrifuge and then dried with a low-temperature airflow of 35-45℃ to make the surface moisture content of the seeds less than 12%.

[0008] Preferably, in the cleaning and surface drying process, the water-to-material mass ratio of the bubble cleaning machine is 3:1-5:1, the cleaning time is 5-15 minutes, the rotation speed of the low-speed centrifuge is 300-800 r / min, the dehydration time is 3-8 minutes, the low-temperature airflow is clean air that has been sterilized and filtered, the wind speed is 2-5 m / s, and the drying time is 5-20 minutes.

[0009] Preferably, the specific parameters for the low-temperature conditioning process in step two are controlled as follows: The conditioning tank uses a jacketed hot water circulation heating system, with the hot water temperature controlled at 40-60℃ and the material temperature inside the tank uniformly maintained at 30-55℃. The relative humidity inside the tank is controlled within the range of 50%-70% using an ultrasonic humidifier, with humidity fluctuations not exceeding ±5%. A variable frequency agitator is used to intermittently stir the material in the tank at a speed of 10-30 r / min, with a 10-minute interval between 5 minutes of stirring.

[0010] Preferably, the low-temperature conditioning process in step two further includes adding a compound enzyme preparation for enzymatic hydrolysis, specifically: The compound enzyme preparation includes cellulase, hemicellulase, and pectinase in a weight ratio of 1-2:1-1.5:0.5-1. The total amount added is 0.01%-0.1% of the weight of the oilseed crop seeds. Before enzymatic hydrolysis, the moisture content of the oilseed crop seeds is adjusted to 18%-25%, and the pH value of the material system is adjusted to 4.5-6.0. The enzymatic hydrolysis time is 0.5-2 hours, and the treatment temperature is 30-55℃. During enzymatic hydrolysis, intermittent stirring is used at a stirring speed of 15-25 r / min. Stirring is stopped for 15-20 minutes after every 8-12 minutes of stirring.

[0011] Preferably, the specific operating conditions for low-temperature pressing in step three are as follows: A segmented low-temperature screw press is adopted, the press includes at least three pressing zones: the first zone has a temperature of 30-40℃ and a pressure of 10-20MPa; the second zone has a temperature of 40-50℃ and a pressure of 20-35MPa; and the third zone has a temperature of 45-55℃ and a pressure of 30-50MPa. The screw speed of the press is controlled at 15-40 r / min, and the cake thickness is adjusted to 1-3 mm. During the pressing process, the temperature of the press cylinder is controlled by a cooling water circulation system to ensure that the material temperature does not exceed 55℃.

[0012] Preferably, the filtration operations in steps four and six further include adding a filter aid; In the primary filtration, the filter aid is food-grade diatomaceous earth, and the addition amount is 0.5%-2% of the crude oil weight. The filtration pressure of the plate and frame filter press does not exceed 0.4MPa. In the precision filtration, the filter aid is food-grade perlite powder that has been calcined and activated at 400-600℃, and the amount added is 0.1%-0.5% of the weight of crude oil. The filter membrane is made of polyvinylidene fluoride or polytetrafluoroethylene, and the filtration pressure difference is controlled at 0.1-0.3MPa.

[0013] Preferably, the low-temperature precipitation process in step five is as follows: after the crude oil after primary filtration is introduced into the precipitation tank, it is stirred at a speed of 20-40 r / min for 5-15 minutes to make it evenly mixed; then the stirring is stopped, and the mixture is allowed to settle at 18-22℃ for 12-20 hours under light-proof conditions.

[0014] Preferably, the low-temperature dehydration process in step seven further includes the addition of natural antioxidants; The natural antioxidant is one or more of vitamin E, rosemary extract, or tea polyphenols, and the total amount added is 0.01%-0.05% of the weight of the oil. The vacuum dehydration tower is equipped with a packing layer or trays, and the residence time of the grease in the tower is 0.5-2 hours; After dehydration, the moisture content of the oil is controlled at 0.02%-0.05%, and the peroxide value is below 2.0 meq / kg.

[0015] Preferably, the specific process of nitrogen protection and filling in step eight is as follows: The dehydrated grease from step seven is first pumped into a tubular heat exchanger, where circulating cooling water at 20-25°C is used to lower the grease temperature to 20-30°C. The cooled grease is transferred to a temporary storage tank with a floating top cover. A nitrogen protective layer is formed between the top cover and the oil surface. Nitrogen is continuously introduced to keep the oxygen content in the tank top space below 0.5%. During filling, nitrogen gas at a pressure of 0.2-0.6 MPa is introduced into the top of the temporary storage tank to pressurize the grease to the filling head. A regulating valve is installed on the delivery pipeline to control the grease flow rate. A nitrogen curtain generator is concentrically arranged on the outside of the filling head, which continuously sprays nitrogen gas at a flow rate of 3-8L / min and a temperature of 18-25℃ during the filling process to form a uniform nitrogen curtain that isolates the filling head from the surrounding air. Under nitrogen protection, the oil is directly injected into the pre-emptied packaging container at a flow rate of 100-300 mL / s.

[0016] Compared with the prior art, the present invention provides a method for low-temperature pressing of edible oil, which has the following beneficial effects: 1. In this invention, a low-temperature pressing process system is used, and segmented temperature and pressure control is adopted during the pressing process to avoid the oxidation and deterioration of oil caused by traditional high-temperature pressing. At the same time, combined with the low-temperature conditioning and enzymatic hydrolysis in the pretreatment stage, the cell tissue of the oilseed is gently softened, and the natural active ingredients and inherent flavor substances in the oilseed are preserved to the maximum extent, so that the finished oil has better nutritional value and sensory quality.

[0017] 2. In this invention, a multi-stage synergistic filtration and low-temperature sedimentation process is adopted in the crude oil purification stage. Through the progressive action of physical sedimentation and filtration, suspended impurities, colloidal substances and microparticles in the crude oil are removed. This not only improves the transparency and stability of the oil, but also reduces the risk of quality deterioration caused by impurities during subsequent storage and extends the shelf life of the product.

[0018] 3. In this invention, an inert gas protection mechanism is introduced throughout the dehydration and filling process. By immediately cooling at low temperature after dehydration and completing storage and filling in a nitrogen atmosphere, a complete antioxidant protection system is constructed, which isolates the oil from contact with oxygen, thereby preventing the oxidative rancidity of unsaturated fatty acids and ensuring the pure flavor and long-lasting stable quality of the finished oil. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1: A method for low-temperature pressing of edible oil, the method comprising the following steps: Step 1: Raw material pretreatment. Select whole oilseed crop seeds, clean, screen and destone them to remove impurities, moldy grains and immature grains; Step 2: Low-temperature conditioning. Place the pretreated oilseed crop seeds in a conditioning tank, control the temperature at 30℃ and the humidity at 50%, and carry out softening treatment for 1 hour. Step 3: Low-temperature pressing. The conditioned oilseed crop seeds are fed into a low-temperature screw press and pressed at a temperature of 30°C and a pressure of 10MPa to obtain crude oil and oil cake. Step 4: Primary filtration. The crude oil obtained from pressing is immediately transferred to the primary filtration system and coarsely filtered at 35°C using a plate and frame filter press to remove large solid impurities. Step 5: Low-temperature sedimentation. Pump the crude oil after primary filtration into a sedimentation tank and let it settle at 15°C for 6 hours under light-proof conditions. Step Six: Precision filtration. The supernatant after sedimentation is introduced into a precision filtration device and finely filtered at 20°C using a filter membrane with a pore size of 0.1μm to further remove micron- and submicron-sized suspended particles. Step 7: Low-temperature dehydration. The finely filtered oil is sent to a vacuum dehydration tower and dehydrated for 0.5 hours under an absolute pressure of 0.08 MPa and a temperature of 40°C, so that the moisture content of the oil is reduced to below 0.05%. Step 8: Nitrogen protection and filling. The dehydrated oil is cooled to 20°C under nitrogen atmosphere protection and then aseptically filled to obtain the finished low-temperature pressed edible oil.

[0021] The raw material pretreatment in step one specifically includes: Cleaning and impurity removal: Use a gravity destoner and a flat rotary screen to preliminarily clean the oilseed crop seeds, removing dust, sand, metal fragments and light impurities; Color sorting and grading: A CCD color sorter is used to sort the cleaned seeds to remove moldy and discolored seeds, and a drum grading screen is used to grade the seeds according to their particle size to ensure the uniformity of the raw materials. Washing and surface drying: The graded seeds are sent to a bubble washing machine and washed with pure water. After washing, the surface moisture is removed by a low-speed centrifuge and then dried with a low-temperature airflow of 35°C to make the surface moisture content of the seeds less than 12%.

[0022] During the cleaning and surface drying process, the water-to-material mass ratio of the bubble cleaner is 3:1, the cleaning time is 5 minutes, the speed of the low-speed centrifuge is 300 r / min, the dehydration time is 3 minutes, the low-temperature airflow is clean air that has been sterilized and filtered, the wind speed is 2 m / s, and the drying time is 5 minutes.

[0023] The specific parameter control for the low-temperature conditioning process in step two is as follows: The conditioning tank uses a jacketed hot water circulation heating system, with the hot water temperature controlled at 40℃ and the material temperature inside the tank uniformly maintained at 30℃. The relative humidity inside the tank is controlled at 50% using an ultrasonic humidifier, with humidity fluctuations not exceeding ±5%. A variable frequency agitator is used to intermittently stir the material in the tank at a speed of 10 r / min, with a 10-minute interval between 5 minutes of stirring.

[0024] Step two, the low-temperature conditioning process, also includes adding a compound enzyme preparation for enzymatic hydrolysis, specifically: The compound enzyme preparation includes cellulase, hemicellulase, and pectinase in a weight ratio of 1:1:0.5. The total amount added is 0.01% of the weight of the oilseed crop seeds. Before enzymatic hydrolysis, the moisture content of the oilseed crop seeds is adjusted to 18%, and the pH value of the material system is adjusted to 4.5. The enzymatic hydrolysis time is 0.5 hours, and the treatment temperature is 30℃. During enzymatic hydrolysis, an intermittent stirring method is adopted, with a stirring speed of 15 r / min. Stirring is stopped for 15 minutes after every 8 minutes of stirring.

[0025] The specific operating conditions for low-temperature pressing in step three are as follows: A segmented low-temperature screw press is adopted, which includes at least three pressing zones: the first zone has a temperature of 30℃ and a pressure of 10MPa, the second zone has a temperature of 40℃ and a pressure of 20MPa, and the third zone has a temperature of 45℃ and a pressure of 30MPa. The screw speed of the press is controlled at 15 r / min, and the cake thickness is adjusted to 1 mm. During the pressing process, the temperature of the press cylinder is controlled by a cooling water circulation system to ensure that the material temperature does not exceed 55℃.

[0026] The filtration operations in steps four and six also include adding filter aids; In the primary filtration, the filter aid is food-grade diatomaceous earth, and the addition amount is 0.5% of the crude oil weight. The filtration pressure of the plate and frame filter press does not exceed 0.4 MPa. In precision filtration, the filter aid is food-grade perlite powder that has been calcined and activated at 400℃, and the amount added is 0.1% of the weight of crude oil. The filter membrane is made of polyvinylidene fluoride or polytetrafluoroethylene, and the filtration pressure difference is controlled at 0.1MPa.

[0027] The specific steps of the low-temperature precipitation process in step five are as follows: After the crude oil after primary filtration is introduced into the precipitation tank, it is stirred at a speed of 20 r / min for 5 minutes to make it evenly mixed; then the stirring is stopped, and the mixture is allowed to settle at 18°C ​​for 12 hours under light-proof conditions.

[0028] Step seven, the low-temperature dehydration process, also includes the addition of natural antioxidants; The natural antioxidant is vitamin E, added at a total amount of 0.01% of the fat weight. The vacuum dehydration tower is equipped with a packing layer or trays, and the residence time of the grease in the tower is 0.5 hours. After dehydration, the moisture content of the oil is controlled at 0.02%, and the peroxide value is below 2.0 meq / kg.

[0029] The specific process of nitrogen protection and filling in step eight is as follows: The dehydrated grease from step seven is first pumped into a tubular heat exchanger, where the temperature of the grease is reduced to 20°C using circulating cooling water at 20°C. The cooled grease is transferred to a temporary storage tank with a floating top cover. A nitrogen protective layer is formed between the top cover and the oil surface. Nitrogen is continuously introduced to keep the oxygen content in the tank top space below 0.5%. During filling, nitrogen gas at a pressure of 0.2 MPa is introduced into the top of the temporary storage tank to pressurize the grease to the filling head. A regulating valve is installed on the delivery pipeline to control the grease flow rate. A nitrogen curtain generator is concentrically installed on the outside of the filling head. During the filling process, nitrogen gas with a flow rate of 3L / min and a temperature of 18℃ is continuously sprayed to form a uniform nitrogen curtain, which isolates the filling head from the surrounding air. The oil is injected directly into the pre-emptied packaging container at a flow rate of 100 mL / s under the protection of a nitrogen curtain.

[0030] Example 2: A method for low-temperature pressing of edible oil, the method comprising the following steps: Step 1: Raw material pretreatment. Select whole oilseed crop seeds, clean, screen and destone them to remove impurities, moldy grains and immature grains; Step 2: Low-temperature conditioning. Place the pretreated oilseed crop seeds in a conditioning tank, control the temperature at 45℃ and the humidity at 60%, and carry out softening treatment for 2.5 hours. Step 3: Low-temperature pressing. The conditioned oilseed crop seeds are fed into a low-temperature screw press and pressed at a temperature of 45℃ and a pressure of 35MPa to obtain crude oil and oil cake. Step 4: Primary filtration. The crude oil obtained from pressing is immediately transferred to the primary filtration system and coarsely filtered at 50°C using a plate and frame filter press to remove large solid impurities. Step 5: Low-temperature sedimentation. Pump the crude oil after primary filtration into a sedimentation tank and let it settle at 20°C for 12 hours under light-proof conditions. Step 6: Precision filtration. The supernatant after sedimentation is introduced into a precision filtration device and finely filtered at 30°C using a filter membrane with a pore size of 2μm to further remove micron- and submicron-sized suspended particles. Step 7: Low-temperature dehydration. The finely filtered oil is sent to a vacuum dehydration tower and dehydrated for 1.5 hours under an absolute pressure of 0.09 MPa and a temperature of 45°C, so that the moisture content of the oil is reduced to below 0.05%. Step 8: Nitrogen protection and filling. The dehydrated oil is cooled to 25°C under nitrogen protection and then aseptically filled to obtain the finished low-temperature pressed edible oil.

[0031] The raw material pretreatment in step one specifically includes: Cleaning and impurity removal: Use a gravity destoner and a flat rotary screen to preliminarily clean the oilseed crop seeds, removing dust, sand, metal fragments and light impurities; Color sorting and grading: A CCD color sorter is used to sort the cleaned seeds to remove moldy and discolored seeds, and a drum grading screen is used to grade the seeds according to their particle size to ensure the uniformity of the raw materials. Washing and surface drying: The graded seeds are sent to a bubble washing machine and washed with pure water. After washing, the surface moisture is removed by a low-speed centrifuge and then dried with a low-temperature airflow of 40°C to make the surface moisture content of the seeds less than 12%.

[0032] During the cleaning and surface drying process, the water-to-material mass ratio of the bubble cleaner is 4:1, the cleaning time is 10 minutes, the speed of the low-speed centrifuge is 500 r / min, the dehydration time is 5 minutes, the low-temperature airflow is clean air that has been sterilized and filtered, the wind speed is 3 m / s, and the drying time is 15 minutes.

[0033] The specific parameter control for the low-temperature conditioning process in step two is as follows: The conditioning tank uses a jacketed hot water circulation heating system, with the hot water temperature controlled at 50℃ and the material temperature inside the tank uniformly maintained at 40℃. The relative humidity inside the tank is controlled at 60% using an ultrasonic humidifier, with humidity fluctuations not exceeding ±5%. A variable frequency agitator is used to intermittently stir the material in the tank at a speed of 20 r / min, with a 10-minute interval between 5 minutes of stirring.

[0034] Step two, the low-temperature conditioning process, also includes adding a compound enzyme preparation for enzymatic hydrolysis, specifically: The compound enzyme preparation includes cellulase, hemicellulase, and pectinase in a weight ratio of 1.5:1.2:0.7. The total amount added is 0.05% of the weight of the oilseed crop seeds. Before enzymatic hydrolysis, the moisture content of the oilseed crop seeds is adjusted to 22%, and the pH value of the material system is adjusted to 5.5. The enzymatic hydrolysis time is 1.5 hours, and the treatment temperature is 45℃. During enzymatic hydrolysis, an intermittent stirring method is adopted, with a stirring speed of 20 r / min. Stirring is stopped for 17 minutes after every 10 minutes of stirring.

[0035] The specific operating conditions for low-temperature pressing in step three are as follows: A segmented low-temperature screw press is adopted, which includes at least three pressing zones: the first zone has a temperature of 35℃ and a pressure of 15MPa, the second zone has a temperature of 45℃ and a pressure of 25MPa, and the third zone has a temperature of 50℃ and a pressure of 40MPa. The screw speed of the press is controlled at 30 r / min, and the cake thickness is adjusted to 2 mm. During the pressing process, the temperature of the press cylinder is controlled by a cooling water circulation system to ensure that the material temperature does not exceed 55℃.

[0036] The filtration operations in steps four and six also include adding filter aids; In the primary filtration, the filter aid is food-grade diatomaceous earth, and the addition amount is 1% of the crude oil weight. The filtration pressure of the plate and frame filter press does not exceed 0.4 MPa. In precision filtration, the filter aid is food-grade perlite powder that has been calcined and activated at 500℃, and the amount added is 0.3% of the weight of crude oil. The filter membrane is made of polyvinylidene fluoride or polytetrafluoroethylene, and the filtration pressure difference is controlled at 0.2MPa.

[0037] The specific steps of the low-temperature precipitation process in step five are as follows: After the crude oil after primary filtration is introduced into the precipitation tank, it is stirred at a speed of 30 r / min for 10 minutes to make it evenly mixed; then the stirring is stopped and the mixture is allowed to settle at 20°C for 16 hours under light-proof conditions.

[0038] Step seven, the low-temperature dehydration process, also includes the addition of natural antioxidants; The natural antioxidant is vitamin E, added at a total amount of 0.03% of the fat weight. The vacuum dehydration tower is equipped with a packing layer or trays, and the residence time of the grease in the tower is 1 hour. After dehydration, the moisture content of the oil is controlled at 0.03%, and the peroxide value is below 2.0 meq / kg.

[0039] The specific process of nitrogen protection and filling in step eight is as follows: The dehydrated grease from step seven is first pumped into a tubular heat exchanger, where the temperature of the grease is reduced to 25°C using circulating cooling water at 22°C. The cooled grease is transferred to a temporary storage tank with a floating top cover. A nitrogen protective layer is formed between the top cover and the oil surface. Nitrogen is continuously introduced to keep the oxygen content in the tank top space below 0.5%. During filling, nitrogen gas at a pressure of 0.4 MPa is introduced into the top of the temporary storage tank to pressurize the grease to the filling head. A regulating valve is installed on the delivery pipeline to control the grease flow rate. A nitrogen curtain generator is concentrically installed on the outside of the filling head. During the filling process, nitrogen gas with a flow rate of 5L / min and a temperature of 22℃ is continuously sprayed to form a uniform nitrogen curtain, which isolates the filling head from the surrounding air. The oil is injected directly into the pre-emptied packaging container at a flow rate of 200 mL / s under the protection of a nitrogen curtain.

[0040] Example 3: A method for low-temperature pressing of edible oil, the method comprising the following steps: Step 1: Raw material pretreatment. Select whole oilseed crop seeds, clean, screen and destone them to remove impurities, moldy grains and immature grains; Step 2: Low-temperature conditioning. Place the pretreated oilseed crop seeds in a conditioning tank, control the temperature at 55℃ and the humidity at 70%, and carry out softening treatment for 4 hours. Step 3: Low-temperature pressing. The conditioned oilseed crop seeds are fed into a low-temperature screw press and pressed at a temperature of 55°C and a pressure of 50MPa to obtain crude oil and oil cake. Step 4: Primary filtration. The crude oil obtained from pressing is immediately transferred to the primary filtration system and coarsely filtered at 60°C using a plate and frame filter press to remove large solid impurities. Step 5: Low-temperature sedimentation. Pump the crude oil after primary filtration into a sedimentation tank and let it settle at 25°C for 24 hours under light-protected conditions. Step Six: Precision filtration. The supernatant after sedimentation is introduced into a precision filtration device and finely filtered at 40°C using a filter membrane with a pore size of 5μm to further remove micron- and submicron-sized suspended particles. Step 7: Low-temperature dehydration. The finely filtered oil is sent to a vacuum dehydration tower and dehydrated for 2 hours under an absolute pressure of 0.095 MPa and a temperature of 55°C, so that the moisture content of the oil is reduced to below 0.05%. Step 8: Nitrogen protection and filling. The dehydrated oil is cooled to 30°C under nitrogen atmosphere protection and then aseptically filled to obtain the finished low-temperature pressed edible oil.

[0041] The raw material pretreatment in step one specifically includes: Cleaning and impurity removal: Use a gravity destoner and a flat rotary screen to preliminarily clean the oilseed crop seeds, removing dust, sand, metal fragments and light impurities; Color sorting and grading: A CCD color sorter is used to sort the cleaned seeds to remove moldy and discolored seeds, and a drum grading screen is used to grade the seeds according to their particle size to ensure the uniformity of the raw materials. Washing and surface drying: The graded seeds are sent to a bubble washing machine and washed with pure water. After washing, the surface moisture is removed by a low-speed centrifuge and then dried with a low-temperature airflow of 45°C to make the surface moisture content of the seeds less than 12%.

[0042] During the cleaning and surface drying process, the water-to-material mass ratio of the bubble cleaner is 5:1, the cleaning time is 15 minutes, the speed of the low-speed centrifuge is 800 r / min, the dehydration time is 8 minutes, the low-temperature airflow is clean air that has been sterilized and filtered, the wind speed is 5 m / s, and the drying time is 20 minutes.

[0043] The specific parameter control for the low-temperature conditioning process in step two is as follows: The conditioning tank uses a jacketed hot water circulation heating system, with the hot water temperature controlled at 60℃ and the material temperature inside the tank uniformly maintained at 55℃. The relative humidity inside the tank is controlled at 70% using an ultrasonic humidifier, with humidity fluctuations not exceeding ±5%. A variable frequency agitator is used to intermittently stir the material in the tank at a speed of 30 r / min, with a 10-minute interval between 5 minutes of stirring.

[0044] Step two, the low-temperature conditioning process, also includes adding a compound enzyme preparation for enzymatic hydrolysis, specifically: The compound enzyme preparation includes cellulase, hemicellulase, and pectinase in a weight ratio of 2:1.5:1. The total amount added is 0.1% of the weight of the oilseed crop seeds. Before enzymatic hydrolysis, the moisture content of the oilseed crop seeds is adjusted to 25%, and the pH value of the material system is adjusted to 6.0. The enzymatic hydrolysis time is 2 hours, and the treatment temperature is 55℃. During the enzymatic hydrolysis, an intermittent stirring method is adopted, with a stirring speed of 25 r / min. Stirring is stopped for 20 minutes after every 12 minutes of stirring.

[0045] The specific operating conditions for low-temperature pressing in step three are as follows: A segmented low-temperature screw press is adopted, which includes at least three pressing zones: the first zone has a temperature of 40℃ and a pressure of 20MPa, the second zone has a temperature of 50℃ and a pressure of 35MPa, and the third zone has a temperature of 55℃ and a pressure of 50MPa. The screw speed of the press is controlled at 40 r / min, and the cake thickness is adjusted to 3 mm. During the pressing process, the temperature of the press cylinder is controlled by a cooling water circulation system to ensure that the material temperature does not exceed 55℃.

[0046] The filtration operations in steps four and six also include adding filter aids; In the primary filtration, the filter aid is food-grade diatomaceous earth, and the addition amount is 2% of the crude oil weight. The filtration pressure of the plate and frame filter press does not exceed 0.4 MPa. In precision filtration, the filter aid is food-grade perlite powder that has been calcined and activated at 600℃, and the amount added is 0.5% of the weight of crude oil. The filter membrane is made of polyvinylidene fluoride or polytetrafluoroethylene, and the filtration pressure difference is controlled at 0.3MPa.

[0047] The specific steps of the low-temperature precipitation process in step five are as follows: After the crude oil after primary filtration is introduced into the precipitation tank, it is stirred at a speed of 40 r / min for 15 minutes to make it evenly mixed; then the stirring is stopped and the mixture is allowed to settle at 22°C for 20 hours under light-proof conditions.

[0048] Step seven, the low-temperature dehydration process, also includes the addition of natural antioxidants; The natural antioxidant is vitamin E, added at a total amount of 0.05% of the fat weight. The vacuum dehydration tower is equipped with a packing layer or trays, and the residence time of the grease in the tower is 2 hours. After dehydration, the moisture content of the oil is controlled at 0.05%, and the peroxide value is below 2.0 meq / kg.

[0049] The specific process of nitrogen protection and filling in step eight is as follows: The dehydrated grease from step seven is first pumped into a tubular heat exchanger, where the temperature of the grease is reduced to 30°C using circulating cooling water at 25°C. The cooled grease is transferred to a temporary storage tank with a floating top cover. A nitrogen protective layer is formed between the top cover and the oil surface. Nitrogen is continuously introduced to keep the oxygen content in the tank top space below 0.5%. During filling, nitrogen gas at a pressure of 0.6 MPa is introduced into the top of the temporary storage tank to pressurize the grease to the filling head. A regulating valve is installed on the delivery pipeline to control the grease flow rate. A nitrogen curtain generator is concentrically installed on the outside of the filling head. During the filling process, nitrogen gas with a flow rate of 8L / min and a temperature of 25℃ is continuously sprayed to form a uniform nitrogen curtain, which isolates the filling head from the surrounding air. The oil is injected directly into the pre-emptied packaging container at a flow rate of 300 mL / s under the protection of a nitrogen curtain.

[0050] Comparative Example 1: The difference between this comparative example and Example 1 is that no compound enzyme preparation was added for enzymatic hydrolysis during the low-temperature conditioning process in this comparative example.

[0051] Comparative Example 2 differs from Example 1 in that no natural antioxidants were added during the low-temperature dehydration process in this comparative example.

[0052] Comparative Example 3 differs from Example 1 in that a nitrogen curtain was not used to protect the filling head during the filling process, and the grease was filled in normal air.

[0053] Comparative Example 4: The difference between this comparative example and Example 1 is that no filter aid was added in either the primary filtration or the precision filtration in this comparative example.

[0054] The quality of the low-temperature pressed edible oils prepared in Examples 1-3 and Comparative Examples 1-4 was tested. The test items and methods are as follows: The peroxide value test is performed by titration. A certain mass of oil sample is weighed and dissolved in a mixed solution of glacial acetic acid and chloroform. After adding saturated potassium iodide solution and reacting, the solution is titrated to the endpoint with sodium thiosulfate standard titrant. The peroxide value is calculated based on the amount consumed.

[0055] For acid value testing, the cold solvent indicator titration method is used. The oil sample is dissolved in a mixed solvent of ether and ethanol, and phenolphthalein is used as an indicator. The titration is performed with potassium hydroxide or sodium hydroxide standard titrant until a faint red color appears and does not fade within 30 seconds. The acid value is calculated based on the amount consumed.

[0056] The moisture and volatile matter content was tested using the Karl Fischer coulometric titration method. Under specified instrument parameters, the oil sample was injected into the titration cell, and the iodine generated by electrolysis reacted quantitatively with the water in the sample. The moisture content was calculated by measuring the amount of electricity consumed.

[0057] Oxidative stability testing was conducted using an accelerated oxidation tester. Clean air at 110°C was introduced into an oil sample that had been heated to a specified temperature of 120°C. The volatiles were introduced into a measuring cell containing deionized water, and the changes in conductivity were continuously monitored. The oxidative stability of the oil was characterized by the induction time.

[0058] The test data of the low-temperature pressed edible oils prepared in Examples 1-3 and Comparative Examples 1-4 are recorded in the table below: Comparison and analysis of the data in the table show that the low-temperature pressed edible oils prepared using the processes in Examples 1-3 exhibit superior performance in key indicators compared to the edible oils prepared using the processes in Comparative Examples 1-4. This indicates that the low-temperature pressing process, employing segmented temperature and pressure control during pressing, avoids the oxidative deterioration of oils caused by traditional high-temperature pressing. Simultaneously, the low-temperature conditioning and enzymatic hydrolysis in the pretreatment stage gently soften the oilseed cell structure, maximizing the retention of natural active ingredients and inherent flavor substances, resulting in finished oils with better nutritional value and sensory quality. In the crude oil purification stage, a multi-stage synergistic filtration combined with low-temperature sedimentation removes suspended impurities, colloidal substances, and microparticles through the progressive action of physical sedimentation and filtration. This not only improves the transparency and stability of the oil but also reduces the risk of quality deterioration due to impurities during subsequent storage, extending the product's shelf life. An inert gas protection mechanism is introduced throughout the dehydration and filling process. By immediately cooling the oil at low temperature after dehydration and completing storage and filling in a nitrogen atmosphere, a complete antioxidant protection system is constructed, which isolates the oil from contact with oxygen, thereby preventing the oxidative rancidity of unsaturated fatty acids and ensuring the pure flavor and long-lasting stable quality of the finished oil.

[0059] By comparing and analyzing the relevant data in the table, it can be seen that the low-temperature pressed edible oil prepared by the process of this invention exhibits excellent performance in terms of oxidative stability, freshness, and purity, and has excellent comprehensive properties.

[0060] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0061] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for low-temperature pressing of edible oil, characterized in that: The method includes the following steps: Step 1: Raw material pretreatment. Select whole oilseed crop seeds, clean, screen and destone them to remove impurities, moldy grains and immature grains; Step 2: Low-temperature conditioning. Place the pretreated oilseed crop seeds in a conditioning tank, control the temperature at 30-55℃ and the humidity at 50%-70%, and carry out softening treatment for 1-4 hours. Step 3: Low-temperature pressing. The conditioned oilseed crop seeds are fed into a low-temperature screw press and pressed at a temperature range of 30-55℃ and a pressure range of 10-50MPa to obtain crude oil and oil cake. Step 4: Primary filtration. The crude oil obtained from pressing is immediately transferred to the primary filtration system and coarsely filtered at 35-60℃ using a plate and frame filter press to remove large solid impurities. Step 5: Low-temperature sedimentation. Pump the crude oil after primary filtration into a sedimentation tank and let it settle at 15-25℃ for 6-24 hours under light-protected conditions. Step 6: Precision filtration. The supernatant after sedimentation is introduced into a precision filtration device and finely filtered at 20-40℃ using a filter membrane with a pore size of 0.1-5μm to further remove micron- and submicron-sized suspended particles. Step 7: Low-temperature dehydration. The finely filtered oil is sent to a vacuum dehydration tower and dehydrated for 0.5-2 hours under an absolute pressure of 0.08-0.095 MPa and a temperature of 40-55℃, so that the moisture content of the oil is reduced to below 0.05%. Step 8: Nitrogen protection and filling. The dehydrated oil is cooled to 20-30℃ under nitrogen atmosphere protection and then aseptically filled to obtain the finished low-temperature pressed edible oil.

2. The method for low-temperature pressing of edible oil according to claim 1, characterized in that: The raw material pretreatment in step one specifically includes: Cleaning and impurity removal: Use a gravity destoner and a flat rotary screen to preliminarily clean the oilseed crop seeds, removing dust, sand, metal fragments and light impurities; Color sorting and grading: A CCD color sorter is used to sort the cleaned seeds to remove moldy and discolored seeds, and a drum grading screen is used to grade the seeds according to their particle size to ensure the uniformity of the raw materials. Washing and surface drying: The graded seeds are sent to a bubble washing machine and washed with pure water. After washing, the surface moisture is removed by a low-speed centrifuge and then dried with a low-temperature airflow of 35-45℃ to make the surface moisture content of the seeds less than 12%.

3. The method for low-temperature pressing of edible oil according to claim 2, characterized in that: In the cleaning and surface drying process, the water-to-material mass ratio of the bubble cleaning machine is 3:1-5:1, the cleaning time is 5-15 minutes, the speed of the low-speed centrifuge is 300-800 r / min, the dehydration time is 3-8 minutes, the low-temperature airflow is clean air that has been sterilized and filtered, the wind speed is 2-5 m / s, and the drying time is 5-20 minutes.

4. The method for low-temperature pressing of edible oil according to claim 1, characterized in that: The specific parameter control for the low-temperature conditioning process in step two is as follows: The conditioning tank uses a jacketed hot water circulation heating system, with the hot water temperature controlled at 40-60℃ and the material temperature inside the tank uniformly maintained at 30-55℃. The relative humidity inside the tank is controlled within the range of 50%-70% using an ultrasonic humidifier, with humidity fluctuations not exceeding ±5%. A variable frequency agitator is used to intermittently stir the material in the tank at a speed of 10-30 r / min, with a 10-minute interval between 5 minutes of stirring.

5. The method for low-temperature pressing of edible oil according to claim 1, characterized in that: The low-temperature conditioning process in step two also includes adding a compound enzyme preparation for enzymatic hydrolysis, specifically: The compound enzyme preparation includes cellulase, hemicellulase, and pectinase in a weight ratio of 1-2:1-1.5:0.5-1. The total amount added is 0.01%-0.1% of the weight of the oilseed crop seeds. Before enzymatic hydrolysis, the moisture content of the oilseed crop seeds is adjusted to 18%-25%, and the pH value of the material system is adjusted to 4.5-6.

0. The enzymatic hydrolysis time is 0.5-2 hours, and the treatment temperature is 30-55℃. During enzymatic hydrolysis, intermittent stirring is used at a stirring speed of 15-25 r / min. Stirring is stopped for 15-20 minutes after every 8-12 minutes of stirring.

6. The method for low-temperature pressing of edible oil according to claim 1, characterized in that: The specific operating conditions for low-temperature pressing in step three are as follows: A segmented low-temperature screw press is adopted, the press includes at least three pressing zones: the first zone has a temperature of 30-40℃ and a pressure of 10-20MPa; the second zone has a temperature of 40-50℃ and a pressure of 20-35MPa; and the third zone has a temperature of 45-55℃ and a pressure of 30-50MPa. The screw speed of the press is controlled at 15-40 r / min, and the cake thickness is adjusted to 1-3 mm. During the pressing process, the temperature of the press cylinder is controlled by a cooling water circulation system to ensure that the material temperature does not exceed 55℃.

7. The method for low-temperature pressing of edible oil according to claim 1, characterized in that: The filtration operations in steps four and six also include adding a filter aid; In the primary filtration, the filter aid is food-grade diatomaceous earth, and the addition amount is 0.5%-2% of the crude oil weight. The filtration pressure of the plate and frame filter press does not exceed 0.4MPa. In the precision filtration, the filter aid is food-grade perlite powder that has been calcined and activated at 400-600℃, and the amount added is 0.1%-0.5% of the weight of crude oil. The filter membrane is made of polyvinylidene fluoride or polytetrafluoroethylene, and the filtration pressure difference is controlled at 0.1-0.3MPa.

8. The method for low-temperature pressing of edible oil according to claim 1, characterized in that: The low-temperature precipitation process in step five is as follows: After the crude oil after primary filtration is introduced into the precipitation tank, it is stirred at a speed of 20-40 r / min for 5-15 minutes to make it evenly mixed; then the stirring is stopped, and the mixture is allowed to settle at 18-22℃ for 12-20 hours under light-proof conditions.

9. The method for low-temperature pressing of edible oil according to claim 1, characterized in that: The low-temperature dehydration process in step seven also includes the addition of natural antioxidants; The natural antioxidant is one or more of vitamin E, rosemary extract, or tea polyphenols, and the total amount added is 0.01%-0.05% of the weight of the oil. The vacuum dehydration tower is equipped with a packing layer or trays, and the residence time of the grease in the tower is 0.5-2 hours; After dehydration, the moisture content of the oil is controlled at 0.02%-0.05%, and the peroxide value is below 2.0 meq / kg.

10. The method for low-temperature pressing of edible oil according to claim 1, characterized in that: The specific process of nitrogen protection and filling in step eight is as follows: The dehydrated grease from step seven is first pumped into a tubular heat exchanger, where circulating cooling water at 20-25°C is used to lower the grease temperature to 20-30°C. The cooled grease is transferred to a temporary storage tank with a floating top cover. A nitrogen protective layer is formed between the top cover and the oil surface. Nitrogen is continuously introduced to keep the oxygen content in the tank top space below 0.5%. During filling, nitrogen gas at a pressure of 0.2-0.6 MPa is introduced into the top of the temporary storage tank to pressurize the grease to the filling head. A regulating valve is installed on the delivery pipeline to control the grease flow rate. A nitrogen curtain generator is concentrically arranged on the outside of the filling head, which continuously sprays nitrogen gas at a flow rate of 3-8L / min and a temperature of 18-25℃ during the filling process to form a uniform nitrogen curtain that isolates the filling head from the surrounding air. Under nitrogen protection, the oil is directly injected into the pre-emptied packaging container at a flow rate of 100-300 mL / s.

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