Preparation method of soybean oil

Abstract

The invention provides a preparation method of soybean oil, which comprises three parts of soybean raw material selection, raw material pretreatment and extraction process, firstly, the soybean raw material is selected from fresh soybeans harvested within 6 months, and is stored in a place with the temperature of 15-30 DEG C, the humidity of below 12% and the ventilation rate of 1-3 times per hour, and secondly, the pretreatment comprises baking for 20-40 minutes at the temperature of 150-190 DEG C, and cooling at room temperature; finally, the soybean oil is obtained in a supercritical fluid extraction mode, supercritical carbon dioxide is selected as a solvent for supercritical fluid extraction, the temperature ranges from 35 DEG C to 70 DEG C, and the pressure ranges from 8 MPa to 35 MPa. Through proper raw material selection and processing technology, the obtained soybean oil has the characteristics of low acid value, high oxidation resistance and long shelf life, and has important market value.

Description

Technical Field

[0001] The invention relates to the technical field of soybean oil processing, in particular to a method for preparing soybean oil. Background Art

[0002] Soybean is an important oil crop in my country. Soybean oil, as the main oil product, accounts for 29.6% of my country's edible oil market. However, due to its easy production of oil smoke and "bean smell", it is gradually being replaced by oils with high proportion of unsaturated fatty acids such as peanut oil and walnut oil.

[0003] The reason is that the current soybean oil production usually adopts solvent dissolution or pressing. The solvent dissolution method uses organic solvent extraction to obtain soybean oil. The advantage is high yield, but the disadvantage is that the obtained soybean oil will have solvent residues, and the solvent recovery process will also take away the flavor substances in the soybean oil, making the final soybean oil have no fragrance. As a traditional soybean oil processing technology, the pressing method is divided into cold pressing and hot pressing. The advantage of the cold pressing method is that the flavor substances in the soybean are completely retained, but the disadvantage is that the yield is low, and some of the retained flavor substances are the source of the "bean smell". After increasing the pressure to increase the yield, the "bean smell" will also increase significantly; the advantage of the hot pressing method is that the yield is high, but the disadvantage is that high temperature will destroy antioxidant substances or nutrients such as vitamin E and sterols, and may also produce harmful substances such as trans fatty acids and oil polymers, affecting the taste and quality of the final soybean oil.

[0004] The fatty acids in the soybean oil obtained by the above method are unstable and easily oxidized and degraded, which leads to a high acid value in the finished soybean oil, which not only affects the taste of the soybean oil, but is also not good for health. In addition, the soybean oil will be oxidized during storage, resulting in an increase in low-level fatty acids, which further increases the acid value, and the antioxidant substances such as vitamin E existing in the soybeans are lost during the soybean oil extraction process. Therefore, a soybean oil preparation method that can maintain the aroma of soybean oil, antioxidant substances, and low acid value is urgently needed. Summary of the invention

[0005] The invention provides a method for preparing soybean oil, which is used to solve the problems in the prior art of loss of soybean oil aroma or bean odor, high acid value, and loss of antioxidant substances during a short shelf life, and achieves the prepared soybean oil having the characteristics of good flavor, low acid value, high antioxidant substances, and long shelf life.

[0006] The invention provides a method for preparing soybean oil, comprising the following steps.

[0007] In a first aspect, the present invention provides a method for preparing soybean oil, comprising the following steps: pre-treating fresh soybeans under good storage conditions by baking at 150° C.-170° C. for 20-40 minutes, and obtaining soybean oil by supercritical fluid extraction.

[0008] Ensure that the soybeans are picked fresh and stored in good conditions. Freshly picked soybeans can better retain their rich nutrients, such as protein, fatty acids, vitamins and minerals. Good storage conditions can prevent oxidation and degradation, ensuring the integrity of nutrients. Controlling the baking process temperature before extraction at 155℃-170℃ can significantly improve the quality of soybean oil and give it good flavor and stability. The reason is that high-temperature baking can cause the amino substances in soybeans to undergo Maillard reaction with sugar, which can enhance the flavor substances and reduce the beany smell. However, when the temperature is too high, it will cause the antioxidants to denature and inactivate, reducing the antioxidant capacity of the finished soybean oil. When the temperature is too low, the Maillard reaction is insufficient, the aroma is insufficient, and the beany smell cannot be effectively removed.

[0009] Supercritical fluid extraction technology can retain flavor substances and nutrients while avoiding solvent residues. In particular, it can retain natural vitamin E in soybean oil in an active state, which can not only improve the nutrition of soybean oil but also exert its antioxidant properties to extend the shelf life of the oil.

[0010] Preferably, the preparation method comprises the following steps: pre-treating fresh soybeans under good storage conditions by baking at 155°C-165°C for 25-35 minutes, and extracting soybean oil by supercritical fluid. Preferably, the supercritical fluid extraction uses supercritical carbon dioxide with a purity of more than 99.5% at 35-70° C. and 8-35 MPa for extraction.

[0011] Further preferably, the supercritical fluid extraction uses supercritical carbon dioxide with a purity of more than 99.5% at 50-70° C. and 20-30 MPa for extraction.

[0012] Preferably, the extraction time of the supercritical fluid extraction is 100-140 minutes, and the flow rate is 1-5 mL / min.

[0013] Preferably, the baking pretreatment temperature is 160° C. and the time is 25-35 minutes. At this temperature, the content of various flavor substances in the soybeans is maximized and vitamin E can be retained as much as possible.

[0014] Preferably, the good storage conditions include a storage temperature of 15°C-30°C, a humidity of less than 12%, an air exchange rate of 1 to 3 times per hour, and no direct sunlight. Too high a temperature will significantly increase the content of low-level fatty acids in soybeans, too high a humidity will easily lead to mildew and affect the flavor, good ventilation can prevent agglomeration and heat from causing soybean deterioration, and light will accelerate oil oxidation and increase low-level fatty acids.

[0015] Preferably, the fresh soybeans are soybeans harvested within 6 months. If the soybeans are stored for too long, especially for more than one year, the oil may oxidize, affecting the flavor and quality of the oil.

[0016] In a second aspect, the present invention provides application of the soybean oil preparation method in soybean oil production.

[0017] The soybean oil preparation method provided by the present invention obtains a soybean oil product with good flavor (see Table 1), low acid value, high antioxidant content and long shelf life by strictly limiting the source of raw materials, storage conditions, pretreatment methods and extraction processes. The extraction rate exceeds 19.5%, the peroxide value is less than 0.5 PV, O2 / kg on average, and the acid value is lower than 0.03AV, mg KOH / g. Compared with soybean oil obtained by traditional methods, the acid value is reduced by more than 95%, and the peroxide value is reduced by more than 90%, which is of great significance to the development of soybean oil commodities in my country. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not 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.

[0019] Example 1 Pretreatment of soybean raw materials Roasting soybean seeds at a specific temperature and time can significantly improve the quality of soybean oil and give it good flavor and stability. The specific steps are as follows: (1) Weigh 500 g of well-preserved fresh soybean seeds, wash and remove impurities, and dry them.

[0020] (2) Use DHG-9040A electric constant temperature blast drying oven (Jiaxing Zhongxin Medical Instrument Co., Ltd.), preheat the oven to 160°C to ensure temperature stability, spread the soybeans evenly on the baking tray, and ensure that there is space between the soybean particles to facilitate even heating.

[0021] (3) Place the baking tray in the preheated oven and start timing for 30 minutes.

[0022] (4) Check every 5 minutes to observe the changes in the color and aroma of the soybeans. During the roasting process, notice that a nutty aroma begins to emanate and the color gradually changes from light to golden yellow.

[0023] (5) After the set time is reached, remove the baking tray, use baking tongs to avoid burns, and place the roasted soybeans at room temperature to cool.

[0024] The roasted soybeans were extracted with supercritical fluid to extract soybean oil, and the flavor substances were detected by the following method: 2.0 g soybean oil sample was weighed into a 20 mL headspace bottle, 10 μL of gamma-lactone was added as an internal standard, and the Shimadzu GCMS-QP2020NX gas chromatograph-mass spectrometer was used for detection. The detection method was as follows: the instrument was equipped with a DB-wax capillary column (30 m × 0.25 mm, 0.5 μm), automatic injection splitless mode, injection port temperature 230 ° C, carrier gas He, flow rate 1.93 mL / min, gradient temperature program as follows: initial temperature 40 ° C, maintained for 3 min, then increased to 120 ° C at a rate of 5 ° C / min, and then increased to 230 ° C at a rate of 4 ° C / min, and maintained for 10 min. MS conditions: electron energy 70 eV, ion source temperature 200 ° C.

[0025] The test results are shown in Table 1. The content of various flavor substances in soybean oil extracted from roasted soybeans is significantly increased, which can give soybean oil a unique aroma and reduce the beany smell.

[0026] Example 2 Supercritical Fluid Extraction of Soybean Oil Using a supercritical fluid extraction device (Waters SFE preparation system), soybeans (500 g) before and after roasting were placed in the extraction device, and the equipment operating temperature was set to 60°C, pressure to 25 MPa, extraction time to 120 minutes, flow rate to 2 mL / min, and supercritical carbon dioxide was started to flow. After the extraction was completed, the extract was collected.

[0027] Comparative Example 1 500 g of fresh soybean seeds were selected and an ultra-high pressure HY-320 oil press from Shandong Suixing Machinery Company was used to extract soybean oil at 60 MPa until no oil was squeezed out.

[0028] Comparative Example 2 The only difference from Example 1 is that the baking temperature is changed to 180° C., and soybean oil is extracted according to the method described in Example 2.

[0029] Test Example 1 Shelf Life Experiment The Schaal oven accelerated oxidation experiment was carried out using a DHG-9040A electric constant temperature blast drying oven (Jiaxing Zhongxin Medical Instrument Co., Ltd.). The temperature was set to 63°C ± 1°C for 20 days. Samples were taken every two days. The acid value and peroxide value were determined according to the methods specified in GB 5009.229-2016 and GB / T21121-2007. The results are shown in Table 3. As shown in Table 3, after the accelerated test, the acid value and peroxide value of the soybean oil squeezed by the traditional method in Comparative Example 1 increased significantly, and the increase of the soybean oil supercritically extracted after baking at a higher temperature in Comparative Example 2 was weaker than that in Comparative Example 1, while the soybean oil treated by the method of Example 1 of the present invention still maintained a lower acid value and peroxide value after the accelerated test, proving that it has a longer shelf life.

[0030] Test Example 2 Quality detection of soybean oil obtained by different preparation methods The soybean oil extraction rate, peroxide value and acid value in Example 3 and Comparative Examples 1 and 2 were tested according to the methods specified in GB 5009.229-2016 and GB / T21121-2007, with 5 samples in each group. The results are shown in Tables 3 and 4.

[0031] From the comparison results of Tables 3, 4, and 5, it can be seen that the soybean oil prepared by the preparation method of the present application has a higher extraction rate (over 19.5%), lower peroxide value (less than 0.5 PV, O2 / kg on average) and acid value (all lower than 0.03AV, mg KOH / g) compared to the soybean oil extracted by the traditional method and after baking at a higher temperature. It has a better taste and is more beneficial to health. In addition, due to the low peroxide value, it is less likely to deteriorate and has a longer shelf life.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing soybean oil, characterized in that: The following steps are involved: Fresh soybeans under good storage conditions are roasted at 150-170°C for 20-40 minutes for pretreatment, and soybean oil is obtained by supercritical fluid extraction.

2. The method for preparing soybean oil according to claim 1, characterized in that: The following steps are involved: Fresh soybeans under good storage conditions are roasted at 155°C-165°C for 25-35 minutes for pretreatment, and soybean oil is obtained by supercritical fluid extraction.

3. The preparation method according to any one of claims 1 or 2, characterized in that The supercritical fluid extraction uses supercritical carbon dioxide with a purity of more than 99.5% to perform extraction at 35-70° C. and 8-35 MPa.

4. The preparation method according to any one of claims 1 to 3, characterized in that The supercritical fluid extraction uses supercritical carbon dioxide with a purity of more than 99.5% to perform extraction at 50-70° C. and 20-30 MPa.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The extraction time of the supercritical fluid extraction is 100-140 minutes, and the flow rate is 1-5 mL / min.

6. The preparation method according to any one of claims 1 or 2, characterized in that: The baking pretreatment temperature is 160° C. and the time is 25-35 minutes.

7. The preparation method according to any one of claims 1 or 2, characterized in that: The good storage conditions include storage temperature of 15°C-30°C, humidity below 12%, air exchange rate of 1 to 3 times per hour, and no direct sunlight.

8. The preparation method according to any one of claims 1 or 2, characterized in that: The fresh soybeans are soybeans harvested within 6 months.

9. Application of the method for preparing soybean oil according to any one of claims 1 to 8 in soybean oil production.

10. A soybean oil, characterized in that The method is described in any one of claims 1 to 8.

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