Press cake residual oil removal method based on Ostwald curing principle and oil pressing method

Abstract

The invention relates to an Ostwald curing principle-based press cake residual oil removal method and an oil expression method, and the press cake residual oil removal method comprises the following steps: crushing a press cake raw material, then adding press oil obtained at the same time as the press cake raw material during pressing into the crushed raw material, sealing and standing, and carrying out oil extraction on the press cake raw material. On the basis of an Ostwald curing principle, oil drops with different particle sizes are agglomerated into a whole, and then squeezing is performed to obtain a deoiled squeezed cake and squeezed oil; the method is simple in process and convenient to operate, the residual oil rate in the pressed cake is greatly reduced, the content of endogenous phenol in the oil is increased, the whole process is carried out at room temperature, heat treatment is not carried out, an organic solvent is not used, bottleneck equipment influencing industrial operation does not exist, and the method can be used in industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and vegetable protein processing, and particularly relates to a method for removing residual oil from a pressed cake and an oil pressing method based on the Ostwald ripening principle. Background Art

[0002] There are two main methods for oil production from oilseeds: extraction and pressing. The oil in oilseeds mainly exists in the organelle "oil body". The oil body is a stable natural emulsified oil droplet with a biological membrane (i.e., oil body membrane) formed by phospholipids and oil body membrane proteins on the surface, and its inner core is neutral fats such as triglycerides and diglycerides (i.e., the target of oil production). In oil seeds, the oil body membrane can effectively prevent the release of neutral fats in the inner core of the oil body. Among them, the extraction method uses organic solvents to dissolve the neutral fats in the oil body of the oilseed, while the pressing method destroys the oil body through mechanical pressure, so that the neutral fat is released from the oil body and squeezed out of the oilseed. Since the pressing method is a physical method, no chemical substances are added, it is safe and healthy and is very popular.

[0003] The pressing method is divided into two technologies: hot pressing and cold pressing. Among them, the oil pressing temperature of the hot pressing method is usually higher than 100℃, so it has the characteristics of high oil yield, but it will cause serious denaturation of protein in the pressed cake, reduce its subsequent utilization value, and thus affect its economic benefits. The cold pressing method is relative to the hot pressing method. There are currently two methods, one is to use a screw press (dynamic pressing) and the other is a hydraulic press (static pressing). In China, in order to increase the oil yield to a certain extent, a pressing temperature of about 60℃ is generally used during the pressing process. At this temperature, the residual oil content in most oil pressed cakes is 15-20%. The screw press can reach the above temperature through the friction between the materials during the screw pressing process, while the hydraulic press reaches the above temperature through hot water or steam system. Although this method does increase the oil yield to a certain extent compared to the non-heat condition, due to the presence of heat treatment, it still causes a certain degree of deterioration of protein and oil. Studies have shown that heat treatment at 60℃ will lead to an increase in the acid value and peroxide value of pressed oils such as peanuts and walnuts. Therefore, some domestic companies have been pressing oils at room temperature throughout the process. In addition, in 2022, the EU officially stipulated that only olive oils pressed or centrifuged at a temperature below 27°C can be labeled "first cold pressing" or "cold extraction". It can be seen that the oils produced at room temperature are of high quality, but the residual oil content in the pressed cake is higher, which is the main problem currently faced by the use of room temperature cold pressing to produce high-quality oils.

[0004] The main methods for removing residual oil that have been disclosed are as follows: 1. Using cold ethanol soaking and then pressing, using the fluid properties of ethanol to bring out the residual oil in the pressed cake. The advantage is that the residual oil removal effect is good, and the residual oil rate of the deoiled pressed cake is low. Although ethanol is a green solvent compared to n-hexane, it is still a flammable and explosive solvent and requires explosion protection in actual use; in addition, the oil and ethanol mixture obtained after pressing also needs to be separated from the oil, which increases the separation equipment; finally, an ethanol recovery and distillation system is required to achieve the reuse of ethanol; in addition, it also exists in vegetable oils. The problems of low endogenous phenol content and high peroxide value are not conducive to the storage stability of vegetable oil; 2) Organic solvent extraction method, which has the advantage of good residual oil removal effect, but the disadvantage is that the organic solvent is usually an alkane solvent such as n-hexane, which is toxic and has residues, is not conducive to healthy diet, and will cause environmental pollution. At the same time, oil-organic solvent separation equipment and organic solvent recovery system are also required; although ethanol can also be used for extraction, since oil is insoluble in cold ethanol and can only be dissolved in hot ethanol, it is necessary to perform heat treatment at 60-80°C, which will undoubtedly cause protein denaturation in the pressed cake, thereby affecting its subsequent utilization value.

[0005] Therefore, developing a method for removing residual oil from pressed oil cake and an oil pressing method based on the Ostwald ripening principle, without heating throughout the process, is of great significance for improving the oil yield, reducing the residual oil rate in the pressed cake, and increasing the content of endogenous phenols in vegetable oil. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects in the prior art and provide a method for removing residual oil from a pressed cake and an oil pressing method based on the Ostwald ripening principle, which not only has a good residual oil removal effect and a low residual oil rate in the deoiled pressed cake, but also promotes the dissolution of endogenous phenols, increases the content of endogenous phenols in vegetable oils, and improves the storage stability of vegetable oils.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A method for removing residual oil from a pressed cake based on the Ostwald ripening principle, comprising: crushing a pressed cake raw material, then adding pressed oil obtained simultaneously with the pressed cake raw material during pressing to the crushed raw material, sealing and standing the raw material, agglomerating oil droplets of different particle sizes into one based on the Ostwald ripening principle, and then pressing to obtain a deoiled pressed cake and pressed oil;

[0009] As a further technical solution, the amount of the pressed oil added back is at least 90% of the pressed oil obtained simultaneously with the raw material pressed cake during pressing.

[0010] As a further technical solution, the pressed cake raw material is the pressed cake obtained by the first pressing of oil and / or the deoiled pressed cake obtained by the method for removing residual oil from pressed cake according to claim 1.

[0011] As a further technical solution, the pressing adopts a cold pressing process.

[0012] As a further technical solution, the cold pressing process uses a hydraulic oil press (static pressing), and the temperature is controlled at ≤30°C throughout the pressing process, and the operation is performed at room temperature without any heat treatment.

[0013] As a further technical solution, the pressing pressure is ≥60MPa, and the pressing time is ≥25min.

[0014] As a further technical solution, the sealing and standing time is ≥12h; and the sealing and standing temperature is room temperature.

[0015] As a further technical solution, the screening rate of the crushed material through a 40-mesh sieve is ≥70%.

[0016] An oil pressing method comprises the following steps:

[0017] Step 1, squeezing the oil plants to obtain plant pressed cakes and pressed oil;

[0018] Step 2: removing residual oil from the pressed cake 1-3 times using the method for removing residual oil from the pressed cake as described in claim 1 to obtain deoiled vegetable pressed cake and vegetable oil.

[0019] As a further technical solution, the oil includes one or more of sunflower seeds, peanuts, walnut kernels, rapeseed, and sesame.

[0020] As a further technical solution, the vegetable oil obtained in step 2 needs to be left to stand or filtered to remove solid precipitates.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The thermodynamic principle of Ostwald ripening is that in a mixed system of small droplets (small bubbles) and large droplets (large bubbles), small droplets (small bubbles) will spontaneously coalesce with large droplets (large bubbles) to form larger droplets (bubbles) to minimize the total surface area of ​​all droplets (bubbles), thereby minimizing the total surface energy of all droplets (bubbles) and achieving a thermodynamically stable state. The present invention first destroys the oil cells and oil body structure of the pressed cake by crushing, and then adds back the pressed oil. After the pressed oil is mixed into the crushed material of the pressed cake, the pressed oil is dispersed in the crushed material in the form of large oil droplets, while the residual oil in the crushed material exists in the form of small oil droplets. By utilizing the thermodynamic principle of spontaneous Ostwald ripening, during the closed static process, the added pressed oil is effectively in contact with the residual oil in the pressed cake, and these small oil droplets continuously undergo spontaneous aggregation with the large oil droplets to form larger oil droplets, thereby promoting the extraction of oil during the pressing process, improving the residual oil removal effect of the pressed cake, and reducing the residual oil rate of the deoiled pressed cake.

[0023] 2. The present invention adopts a hydraulic press for pressing, and the temperature will not rise during the pressing process. The whole process can be controlled at room temperature, which greatly suppresses the quality deterioration of the pressed oil and cake.

[0024] 3. The present invention uses a method of adding back pressed oil to remove oil. Compared with the traditional direct room temperature pressing process, a higher oil yield can be obtained, and the residual oil content in the pressed cake is lower; in addition, since the mixture of pressed oil and crushed pressed cake needs to stand for a long time, this process allows active ingredients such as phenols to dissolve into the oil, so that the final pressed oil contains more active ingredients such as phenols than the direct room temperature pressed oil. On the one hand, it improves the shelf life of the pressed oil, and on the other hand, it can also improve the nutritional functionality of the pressed oil and increase the economic value of the pressed oil.

[0025] 4. The present invention adopts the method of adding back the pressed oil to remove the oil, and the crushing process destroys the oil cells and the oil body structure. Compared with the method of removing the residual oil by leaching with organic solvents and removing it with cold ethanol, the separation process of the organic solvent and the oil is omitted, and the organic solvent recovery and purification process is also omitted. Most importantly, the processing process is safer and more environmentally friendly.

[0026] In summary, the process of the present invention is simple and easy to operate, greatly reduces the residual oil rate in the pressed cake, and increases the content of active ingredients such as endogenous phenol in the oil. Moreover, the whole process is carried out at room temperature, without heat treatment, without using organic solvents, and there is no bottleneck equipment that affects industrial operation, so the present invention can be used in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1The thermodynamic principle diagram of Ostwald ripening;

[0028] Figure 2 This is the effect of the accelerated oxidation days of oil on the peroxide value of sunflower oil in effect example 1;

[0029] Figure 3 This is a graph showing the effect of the number of days of accelerated oxidation of oil on the acid value of sunflower seed oil in Effect Example 1. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0032] In the present invention,

[0033] Crusher: small multifunctional powder maker, model: LM6350, Joyoung;

[0034] Hydraulic press: Xinzhaofeng hydraulic oil press, model: YZL-230, Luoyang Zhaoge Environmental Protection Technology Co., Ltd.;

[0035] In the present invention, the raw materials used are all commercially available unless otherwise specified.

[0036] The following is a detailed introduction to the residual oil removal process and oil pressing process using oil-bearing sunflower seeds as an example.

[0037] Example 1: Effect of standing time on residual oil rate

[0038] 1. Raw material preparation and test methods

[0039] Raw material preparation: 3 kg of sunflower seed kernels were cleaned and hydraulically pressed using a hydraulic oil press (60 MPa, 25 min) to obtain pressed cake A and pressed oil A; the obtained pressed cake A and pressed oil A were divided into 3 equal parts and used as raw materials for each group of experiments to carry out the pressed cake residual oil removal test based on the Ostwald ripening principle.

[0040] The test method is as follows: crush the pressed cake A with a pulverizer for 1.5 minutes, then add all the pressed oil A of the group back into it, mix evenly, and seal it with a food-grade plastic bag. Each group is sealed and left to stand at room temperature for 8, 12, and 24 hours, and then hydraulically press it with a hydraulic oil press at room temperature (60MPa, 25min) to obtain pressed cake B, and filter the pressed oil to obtain pressed oil B;

[0041] 2. Residual oil rate detection

[0042] 1. Residual oil rate: The residual oil in the pressed cake B was determined by the chloroform-methanol method;

[0043] 3. Test results and analysis

[0044] Table 1 Effect of standing time on residual oil rate

[0045] 8h 12h 24h Residual oil rate% 8.25 7.49 7.45

[0046] Since the viscosity of oil is relatively high at room temperature, a longer standing time is often required to ensure sufficient contact and agglomeration between the oil and the residual oil in the pressed cake. It can be seen from Table 1 that the standing time has an impact on the residual oil rate. Only when the standing time reaches 12 hours can the returned oil be ensured to be fully contacted and agglomerated with the residual oil in the pressed cake. Insufficient standing time will affect its residual oil rate. After sufficient standing time, it does not require too long a time.

[0047] Example 2: Effect of crushing time and particle size on residual oil rate

[0048] 1. Raw material preparation and test methods

[0049] Raw material preparation: 4 kg of sunflower seed kernels were cleaned and hydraulically pressed using a hydraulic oil press (60 MPa, 25 min) to obtain pressed cake A and pressed oil A; the obtained pressed cake A and pressed oil A were divided into 4 equal parts and used as raw materials for each group of experiments to carry out the pressed cake residual oil removal test based on the Ostwald ripening principle.

[0050] The test method is as follows: each group uses a crusher to grind the pressed cake A for 0.5 min (the screening rate of 40 mesh screen is about 45%), 1 min (the screening rate of 40 mesh screen is about 65%), 1.5 min (the screening rate of 40 mesh screen is about 70%), and 3 min (the screening rate of 40 mesh screen is about 80%), and then add all the pressed oil A of the group back into it, mix well, and seal it with a food-grade plastic bag. Each group is sealed and left to stand at room temperature for 12 hours, and then hydraulically press it at room temperature with a hydraulic oil press (60MPa, 25min) to obtain pressed cake B, and filter the pressed oil to obtain pressed oil B;

[0051] 2. Detection of residual oil rate

[0052] 1. Residual oil rate: The residual oil in the pressed cake B was determined by the chloroform-methanol method;

[0053] 3. Test results and analysis

[0054] Table 2 Effect of crushing time on residual oil rate

[0055] 0.5min 1min 1.5min 3min Residual oil rate% 9.16 8.21 7.58 7.56

[0056] As can be seen from Table 2, the longer the crushing time (the smaller the particle size of the material), the more favorable it is to reduce the residual oil rate. However, compared with 1.5 min, the longer crushing time (3 min) has little effect on reducing the residual oil rate. In addition, it can be found that the screening rate of the 40-mesh sieve does not show a linear relationship with the crushing time. This is because some components in the raw materials (such as cell wall fiber components) are difficult to be crushed into small particles, which leads to a gradual decrease in the increase in the screening rate of the 40-mesh sieve after the crushing time is extended.

[0057] Example 3: Effect of back-pressing oil and its back-pressing amount on residual oil rate

[0058] 1. Raw material preparation and test methods

[0059] Raw material preparation: 5 kg of sunflower seed kernels were cleaned and hydraulically pressed with a hydraulic oil press (60 MPa, 25 min) to obtain pressed cake A and pressed oil A; the obtained pressed cake A and pressed oil A were divided into 5 equal parts, among which 4 parts of pressed cake A were used for the experiment, and the last part was not used and used as the raw material for each group of experiments to carry out the pressed cake residual oil removal test based on the Ostwald ripening principle.

[0060] Test method:

[0061] Test groups 1-4: four portions of pressed cake A were crushed by a pulverizer for 1.5 min (the screening rate of 40 mesh sieve was about 70%), and then 90%, 100%, 110%, and 120% of the total amount of pressed oil A in each group were added back thereto (when the amount of pressed oil A added back exceeded 100%, it was supplemented by taking the extra 5th portion of pressed oil A in the raw material), mixed evenly, and sealed with food-grade plastic bags. Each group was sealed and left to stand at room temperature for 12 h, and then hydraulically pressed (60 MPa, 25 min) by a hydraulic oil press at room temperature to obtain pressed cake B, and the pressed oil was filtered to obtain pressed oil B;

[0062] 2. Detection of residual oil rate

[0063] 1. Residual oil rate: The residual oil in the pressed cake B was determined by the chloroform-methanol method;

[0064] 3. Test results and analysis

[0065] Table 3 Effect of re-pressurized oil extraction on residual oil rate

[0066] Add back 90% Add back 100% Add back 110% Add 120% back Residual oil rate% 7.93 7.51 7.49 7.52

[0067] As shown in Table 3, if the pressed oil is not fully added back, the residual oil content will increase; if more is added back, the residual oil content will not be affected much. In view of the actual processing, it is recommended to add all the pressed oil back, which is a practical method.

[0068] Example 4: Effect of pressing pressure on residual oil rate

[0069] 1. Raw material preparation and test methods

[0070] Raw material preparation: 3 kg of sunflower seed kernels were cleaned and hydraulically pressed using a hydraulic oil press (60 MPa, 25 min) to obtain pressed cake A and pressed oil A; the obtained pressed cake A and pressed oil A were divided into 3 equal parts and used as raw materials for each group of experiments to carry out the pressed cake residual oil removal test based on the Ostwald ripening principle.

[0071] Test method:

[0072] The three portions of pressed cake A were crushed by a pulverizer for 1.5 min, and then 100% of the total amount of pressed oil A in each group was added back into the three portions, mixed evenly, and sealed with a food-grade plastic bag. Each group was sealed and left to stand at room temperature for 12 h, and then hydraulically pressed at 40, 50 and 60 MPa for 25 min at room temperature using a hydraulic oil press to obtain pressed cake B. The pressed oil was filtered to obtain pressed oil B.

[0073] 2. Detection of residual oil rate

[0074] 1. Residual oil rate: The residual oil in the pressed cake B was determined by the chloroform-methanol method;

[0075] 3. Test results and analysis

[0076] Table 4 Effect of pressing pressure on residual oil rate

[0077] 40MPa 50MPa 60MPa Residual oil rate% 15.63 10.37 7.46

[0078] Embodiment 5:

[0079] 1. Test methods

[0080] An oil pressing method comprises the following steps:

[0081] Step 1, one-time pressing: 1 kg of sunflower seed kernels were cleaned and hydraulically pressed by a hydraulic oil press (60 MPa, 25 min) to obtain pressed cake A and pressed oil A;

[0082] Step 2, first residual oil removal: The pressed cake A obtained in step 1 is crushed by a pulverizer for 1.5 min (the screening rate of 40 mesh screen is about 70%), and then all the pressed oil A obtained in step 1 is added back thereto, mixed evenly, sealed with a food-grade plastic bag, and sealed and left to stand at room temperature for 12 hours, so that oil droplets of different particle sizes are aggregated into one based on the Ostwald ripening principle, and then hydraulically pressed by a hydraulic oil press at room temperature (60 MPa, 25 min), to obtain pressed cake B and pressed oil B;

[0083] Step 3, second residual oil removal: The pressed cake B obtained in step 2 is crushed by a pulverizer for 10 seconds (the screening rate of a 40-mesh sieve is about 71%), and then all the pressed oil B obtained in step 2 is added back thereto, mixed evenly, sealed with a food-grade plastic bag, and sealed and left to stand at room temperature for 12 hours, so that oil droplets of different particle sizes are aggregated into one based on the Ostwald ripening principle, and then hydraulically pressed by a hydraulic oil press at room temperature (60 MPa, 25 min) to obtain pressed cake C and pressed oil C;

[0084] Step 4, third residual oil removal: The pressed cake C obtained in step 3 is crushed by a pulverizer for 10 seconds (the screening rate of 40 mesh screen is about 72%), and then all the pressed oil C obtained in step 3 is added back thereto, and after being evenly mixed, it is sealed with a food-grade plastic bag, and sealed and left to stand at room temperature for 12 hours, and oil droplets of different particle sizes are aggregated into one based on the Ostwald ripening principle, and then hydraulic pressing is performed at room temperature (60MPa, 25min) by a hydraulic oil press to obtain pressed cake D and pressed oil D; the pressed cake D is the de-oiled pressed cake, that is, the final pressed cake;

[0085] Step 5, filtration: The pressed oil D obtained in step 4 is filtered to obtain sunflower seed oil (state: transparent).

[0086] Comparative Example 1:

[0087] An oil pressing method comprises the following steps:

[0088] Step 1, one-time pressing: 1 kg of sunflower seed kernels were cleaned and hydraulically pressed by a hydraulic oil press (60 MPa, 25 min) to obtain pressed cake A and pressed oil A;

[0089] Step 2, first residual oil removal: The pressed cake A obtained in step 1 is crushed by a pulverizer for 1.5 min (the screening rate of a 40-mesh sieve is about 70%), and then hydraulically pressed by a hydraulic oil press at room temperature to obtain pressed cake B and pressed oil B;

[0090] Step 3, second residual oil removal: The pressed cake B obtained in step 2 is crushed by a crusher for 10 seconds (the screening rate of a 40-mesh sieve is about 71%), and then hydraulically pressed by a hydraulic oil press at room temperature to obtain pressed cake C and pressed oil C;

[0091] Step 4, third residual oil removal: The pressed cake C obtained in step 3 is crushed by a pulverizer for 10 seconds (the screening rate of a 40-mesh screen is about 72%), and then hydraulically pressed by a hydraulic oil press at room temperature to obtain pressed cake D and pressed oil D; the pressed cake D is the deoiled pressed cake, that is, the final pressed cake;

[0092] Step 5, filtration: combining the pressed oils AD obtained in steps 1-4 and filtering them to obtain sunflower seed oil;

[0093] Comparative Example 2:

[0094] An oil pressing method comprises the following steps:

[0095] Step 1, 1 kg of sunflower seed kernels were cleaned and hydraulically pressed using a hydraulic oil press (60 MPa, 25 min) to obtain pressed cake A and pressed oil A;

[0096] Step 2: The pressed cake A obtained in step 1 is crushed by a pulverizer for 1.5 min (the screening rate of a 40-mesh sieve is about 70%), put into a glass container, and then an equal mass of anhydrous ethanol at room temperature (25 degrees Celsius) is added thereto. After mixing evenly, the mixture is sealed, and the mixture is sealed and allowed to stand at room temperature (25 degrees Celsius) for 12 hours. Then, a hydraulic oil press is used to perform hydraulic pressing at room temperature (60 MPa, 25 min) to obtain a pressed cake B and a pressed oil B-alcohol mixture.

[0097] Step 3: Place the pressed oil B-alcohol mixture in step 2 into a separatory funnel, let stand to separate layers, and obtain pressed oil B.

[0098] Comparative Example 3:

[0099] An oil pressing method comprises the following steps:

[0100] 1kg of sunflower kernels were cleaned and crushed in a crusher for 1.5min (the 40-mesh screen screening rate was only 8%), and then hydraulically pressed in a hydraulic oil press at room temperature (60MPa, 25min) to obtain a pressed cake (i.e., the final pressed cake), and the pressed oil was filtered to obtain sunflower seed oil; the residual oil content in the pressed cake was 18.68%. In addition, it can be seen that due to the presence of oil, the 40-mesh screen screening rate of the crushed material was much lower than that of the pressed cake after the same crushing time.

[0101] Effect Example 1: Effects of different oil extraction methods on residual oil rate, endogenous phenol content and storage stability

[0102] 1. Determination of residual oil rate: The residual oil rates of pressed cake A, pressed cake B, pressed cake C and pressed cake D in Example 5 and Comparative Example 1 were respectively determined. The determination method is shown in Example 1, and the determination results are as follows: In Example 5, the residual oil rates of pressed cake A, pressed cake B, pressed cake C and pressed cake D were 24.11%, 7.38%, 5.81% and 3.11%, respectively; in Comparative Example 1, the residual oil rates of pressed cake A, pressed cake B, pressed cake C and pressed cake D were 24.21%, 15.44%, 10.83% and 8.08%, respectively.

[0103] 2. The contents of vitamin E and phenol in the final sunflower oil obtained in Example 5 and Comparative Example 1 were measured respectively. The measuring method was as follows: vitamin E was measured by the vitamin E measuring method in GB 5009.82-2016; phenols in the oil were first extracted with a 60% (v / v) methanol aqueous solution, and then the phenol content was measured by the Folin phenol method. The measuring results were as follows: the contents of vitamin E and phenol in the sunflower oil in Example 5 were 72.0 mg / 100 g and 112 mg / 100 g, respectively; the contents of vitamin E and phenol in the sunflower oil in Comparative Example 1 were 69.7 mg / 100 g and 93 mg / 100 g, respectively; the content of phenol in Example 5 increased by 20% compared with that in Comparative Example 1; the content of vitamin E in Example 5 increased by 3.3% compared with that in Comparative Example 1;

[0104] 3. The peroxide value and acid value of the final sunflower seed oil obtained in Example 5 and Comparative Example 1 were measured respectively, and the measurement method adopted the measurement method of peroxide value and acid value in GB 5009.227-2016. The measurement results are as follows: the peroxide value and acid value of the sunflower seed oil in Comparative Example 1 are 4.10 meq / kg and 0.16 mg KOH / g, respectively; the peroxide value and acid value of the sunflower seed oil in Example 5 are 1.34 meq / kg and 0.21 mg KOH / g, respectively, and its peroxide value is much lower than that of Comparative Example 1, while the acid value is slightly higher than that of Comparative Example 1, indicating that the quality of the sunflower seed oil obtained in Example 5 is significantly better than that of the sunflower seed oil obtained in Comparative Example 1.

[0105] 4. Grease accelerated test:

[0106] The final pressed oils prepared in Example 5 and Comparative Example 1 were placed in an oven at 60 degrees Celsius for 15 days, and samples were taken on the 0th, 1st, 2nd, 3rd, 5th, 7th, 9th, 11th, 13th and 15th days to measure the acid value and peroxide value of the pressed oils. The results are shown in Table 1. Figure 2-3 ;

[0107] from Figure 2-3 It can be seen that:

[0108] Peroxide value: Example 5 is always lower than Comparative Example 1; while the acid value after the third day, Comparative Example 1 is higher than Example 5. The results show that compared with the sunflower seed oil obtained by direct pressing at room temperature (Comparative Example 1), the sunflower seed oil prepared by the method of the present invention has better storage properties, which is closely related to the fact that more antioxidant components such as phenols are dissolved during the static process.

[0109] Effect Example 2: Effects of different oil extraction methods on the acid value, peroxide value, vitamin E and endogenous phenol content of pressed oil

[0110] The effect of the method of the present invention on removing residual oil from the pressed cake is similar to that of Comparative Example 2, and therefore, the quality of the pressed oil of the two is mainly compared.

[0111] 1. Acid value and peroxide value: The acid value and peroxide value of the pressed oils A and B in Comparative Example 2 were measured according to the method in Effect Example 1. The results are as follows: Acid value: 0.16 mgKOH / g for pressed oil A and 0.14 mgKOH / g for pressed oil B; Peroxide value: 4.05 meq / kg for pressed oil A and 3.39 meq / kg for pressed oil B. Compared with the acid value (0.21 mgKOH / g) and peroxide value (1.34 meq / kg) of the pressed oil in Example 5, it can be seen that the acid value of the pressed oil in Example 5 is similar to that of Comparative Example 2, but the peroxide value of the pressed oil in Example 5 is significantly lower than that of Comparative Example 2. From the perspective of acid value and peroxide value, the quality of the pressed oil in Example 5 is better than that of Comparative Example 2.

[0112] 2. Vitamin E and phenol content: The vitamin E and phenol content of the pressed oils A and B in Comparative Example 2 were measured according to the method in Effect Example 1. The measurement results are as follows: Vitamin E: 69.5 mg / 100 g for pressed oil A and 57.3 mg / 100 g for pressed oil B; phenol content: 91 mg / 100 g for pressed oil A and 75 mg / 100 g for pressed oil B. Compared with the vitamin E (72 mg / 100 g) and phenol content (112 mg / 100 g) of the pressed oil in Example 5, it can be seen that the vitamin E and phenol content of the pressed oil A in Comparative Example 2, especially the pressed oil B, are significantly lower than those of the pressed oil in Example 5. This is related to the fact that vitamin E and phenol are soluble in ethanol to a certain extent, which leads to a reduction in the amount of vitamin E and phenol dissolved in the pressed oil.

[0113] In general, the quality of the pressed oil obtained by the present invention is better than that of Comparative Example 2 in terms of peroxide value, vitamin E and phenol content.

[0114] The above-described embodiments are only preferred embodiments of the present invention, and are not exhaustive of the feasible implementations of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

Claims

1. A method for removing residual oil from pressed cake based on the Ostwald ripening principle, characterized in that: The pressed cake raw material is crushed, and then the pressed oil obtained simultaneously with the pressed cake raw material during pressing is added back into the crushed raw material, and the raw material is sealed and allowed to stand, and the oil droplets of different particle sizes are coalesced into one based on the Ostwald ripening principle, and then pressed to obtain the deoiled pressed cake and pressed oil; The amount of the pressed oil added back is at least 90% of the pressed oil obtained simultaneously with the raw material pressed cake during pressing.

2. The method for removing residual oil from press cake based on the Ostwald ripening principle according to claim 1, characterized in that: The pressed cake raw material is the pressed cake obtained by first pressing the oil material and / or the deoiled pressed cake obtained by the method for removing residual oil from pressed cake according to claim 1.

3. A method for removing residual oil from press cake based on the Ostwald ripening principle according to claim 1 or 2, characterized in that: The pressing adopts a cold pressing process.

4. The method for removing residual oil from press cake based on the Ostwald ripening principle according to claim 1 or 2, characterized in that: The cold pressing process adopts a hydraulic oil press, and the temperature is controlled at ≤30°C throughout the pressing process.

5. The method for removing residual oil from press cake based on the Ostwald ripening principle according to claim 4, characterized in that: The pressing pressure is ≥60MPa, and the pressing time is ≥25min.

6. The method for removing residual oil from press cake based on the Ostwald ripening principle according to claim 1, characterized in that: The sealing is left to stand for ≥12 hours.

7. The method for removing residual oil from press cake based on the Ostwald ripening principle according to claim 1, characterized in that: The screening rate of the crushed material through a 40-mesh sieve is ≥70%.

8. An oil pressing method, characterized in that: The steps include: Step 1, squeezing the oil plants to obtain plant pressed cakes and pressed oil; Step 2: removing residual oil from the pressed cake 1-3 times using the method for removing residual oil from the pressed cake as described in claim 1 to obtain deoiled vegetable pressed cake and vegetable oil.

9. An oil pressing method according to claim 8, characterized in that: The oil material comprises one or more of sunflower seeds, peanuts, walnut kernels, rapeseed and sesame.

10. An oil pressing method according to claim 8, characterized in that: The vegetable oil obtained in step 2 needs to be left to stand or filtered to remove solid precipitates.

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