Preparation method of corn crude oil

Abstract

The invention relates to the field of oil preparation, and discloses a preparation method of crude corn oil. The preparation method comprises the following steps: S1, extracting embryos from corn to obtain refined embryos; s2, crushing the refined germs to obtain germ powder; s3, pressing the germ powder into germ particles; s4, the germ particles are subjected to oil immersion, and the corn crude oil is prepared. The preparation process does not need the processes of drying, flaking, steaming and frying, pre-pressing and the like, the temperature for preparing the crude corn oil is relatively low, the influence of high-temperature treatment on the quality of the oil is avoided, and the utilization rate of starch in the corn germ meal subjected to oil immersion can also be improved.

Description

Technical Field

[0001] The invention relates to the field of oil production, and in particular to a method for preparing crude corn oil. Background Art

[0002] China is a major producer and consumer of corn, but the corn oil industry is in a weak position in my country's edible oil family. In Europe and the United States, corn oil is widely used as a high-grade edible oil, with a market share of 70%, while in China, the market share of corn oil is less than 20%. Corn oil is rich in vitamin E and unsaturated fatty acids, which are essential for the human body, with a content of more than 80%, mainly linoleic acid and oleic acid. Among them, linoleic acid accounts for more than 50% of the total oil. The special nutrients contained in corn oil can play a health care role for cardiovascular and cerebrovascular patients. At present, the raw materials of corn oil in my country mainly come from local raw materials, and there are no genetically modified ingredients. From a safety perspective, corn oil is safer. The development of the corn oil industry can not only improve the domestic oil self-sufficiency rate, avoid food safety risks caused by long-term reliance on foreign raw materials, but also promote the development of the agricultural economy.

[0003] The traditional corn oil production process requires germ drying, embryo rolling, steaming, frying, and pre-pressing before entering the leaching process. The traditional corn oil production process has the following disadvantages: 1. High energy consumption. Drying and steaming require a large amount of steam heating to reduce the moisture content to meet the process requirements of the pre-pressing machine; various equipment are cumbersome and increase the use of electricity. 2. The operation is complicated and it is not easy to realize automated production. The quality and moisture content of corn will change in daily production, which will affect the effect of embryo rolling. In order to complete the production volume, the rollers of the embryo rolling machine are usually designed to be more than 1 meter long. The uneven feeding will make it difficult for the rollers to keep the roller spacing consistent, resulting in a skewed roller phenomenon. In this case, some germs that cannot be rolled will enter the next section for oil extraction, which greatly affects the oil extraction efficiency and causes the fat content of the germ meal to fluctuate. 3. The oil extracted from the leaching process is a secondary heated oil, which reduces the quality of the oil. Under the action of mechanical force extrusion, the temperature in the pressing chamber of the pre-pressing machine can reach above 130°C. After entering the leaching process, the mixed oil needs to be extracted, evaporated, and separated under a high temperature of 125°C. The two high temperatures affect the quality of the oil and increase the acid value of the oil. 4. Semi-dry germ extraction and pre-pressing affect the utilization rate of starch. Starch particles swell and rupture under high temperature, the double helix structure of amylose is destroyed, starch particles disintegrate, water is released from the molecular network, and finally re-fused to form large aggregates. Starch and lipid compounds undergo a series of interactions, and the aggregates finally appear in the form of gelatinous fragments. This type of starch is not easily hydrolyzed by enzyme preparations. In the alcohol industry, corn germ meal after oil extraction is returned to the fermentation system for alcohol production, and the starch denaturation caused by high temperature will lead to a decrease in starch utilization, affecting the ethanol yield, while aggravating the Maillard reaction in the DDGS production process and affecting the product color.

[0004] In summary, the traditional corn oil production process has the disadvantages of high energy consumption, complex operation that is not convenient for automated production, secondary heating that reduces the quality of the oil, and pre-pressing that reduces the utilization rate of residual starch in germ meal, which affects the quality of corn oil and increases production costs.

[0005] Therefore, a method for preparing corn oil at low temperature is urgently needed. Summary of the invention

[0006] The purpose of the present invention is to overcome the problems of high energy consumption in the prior art, reduced oil quality due to secondary heating, and reduced utilization rate of residual starch in germ meal due to pre-pressing, and to provide a method for preparing crude corn oil. The method uses a relatively low temperature to prepare crude corn oil, thereby avoiding the influence of high-temperature treatment on the quality of the oil and improving the utilization rate of starch in the corn germ meal after oil pressing.

[0007] In order to achieve the above object, the present invention provides a method for preparing crude corn oil, wherein the preparation method comprises the following steps:

[0008] S1, pre-treating corn to obtain refined germ;

[0009] S2, crushing the refined germ to obtain germ powder;

[0010] S3, pressing the germ powder into germ granules;

[0011] S4, soaking the germ particles in oil.

[0012] Through the above technical solution, the beneficial effects of the present invention are:

[0013] After the corn germ is extracted, the refined germ is crushed into powder and then pressed into granules, and then oil can be soaked to obtain the crude corn oil. The preparation process of the present invention does not require drying, embryo rolling, steaming and frying, pre-pressing and other processes, and the temperature for preparing the crude corn oil is relatively low, which avoids the influence of high temperature treatment on the quality of the oil and greatly reduces the adverse reactions generated in the process of preparing the crude corn oil.

[0014] In addition, starch is easy to denature under high temperature. The corn germ meal after soaking in oil is returned to the fermentation system for alcohol production. The starch denaturation caused by high temperature will lead to a decrease in starch utilization, affecting the ethanol yield, and at the same time aggravate the Maillard reaction in the DDGS production process, affecting the product color. The process for preparing corn crude oil of the present invention not only avoids the influence of high temperature treatment on the quality of oil, but also can improve the utilization of starch, and the starch hydrolysis digestibility is higher. DETAILED DESCRIPTION

[0015] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0016] The first aspect of the present invention provides a method for preparing crude corn oil, wherein the preparation method comprises the following steps:

[0017] S1, extracting the germ of corn to obtain refined germ;

[0018] S2, crushing the refined germ to obtain germ powder;

[0019] S3, pressing the germ powder into germ granules;

[0020] S4, soaking the germ particles in oil.

[0021] The oil extraction efficiency of the traditional process of rolling embryos is low, and in order to reduce the moisture content of the refined germ to meet the process requirements of the pre-pressing machine, a large amount of steam heating is required for drying and steaming, and various equipment are cumbersome, which increases the use of electricity. The temperature of pre-pressing is also very high, which can reach above 130°C. The mixed oil needs to be extracted, evaporated and separated under high temperature conditions of 125°C. The two high temperatures affect the quality of the oil and increase the acid value of the oil. After the corn is germinated, the refined germ is crushed into powder and pressed into granules, and then the oil can be soaked to obtain the corn crude oil. The preparation process of the present invention does not require processes such as drying, rolling embryos, steaming and pre-pressing, and the temperature for preparing corn crude oil is relatively low, which avoids the influence of high temperature treatment on the quality of the oil. The corn in S1 in the present invention refers to corn kernels.

[0022] In addition, starch is easy to denature under high temperature. The corn germ meal after soaking in oil is returned to the fermentation system for alcohol production. The starch denaturation caused by high temperature will lead to a decrease in starch utilization, affecting the ethanol yield, and at the same time aggravate the Maillard reaction in the DDGS production process, affecting the product color. The process for preparing corn crude oil of the present invention not only avoids the influence of high temperature treatment on the quality of oil, but also can improve the utilization of starch.

[0023] The present invention has no particular limitation on the method of pulverization, and the conventional pulverization process in the art can be used, and the pulverization can be performed by a pulverizer. In order to make the particle size of the germ powder suitable and uniform, the leaching can be performed directly after being pressed into particles, preferably, in S2, the sieving rate of the germ powder through a 14-mesh sieve is greater than or equal to 92%.

[0024] The present invention has no particular limitation on the granulation method, and a conventional granulation process in the art may be used. Preferably, a double-roll extrusion granulator is used for granulation.

[0025] In order to further improve the oil extraction effect of subsequent extraction, preferably, in S3, the average particle size of the germ particles is 5-10 mm, and the density is 350-650 kg / m 3 .

[0026] Furthermore, the density of the germ particles is 450-550 kg / m 3 .

[0027] According to the present invention, preferably, in S1, the process of extracting germs comprises: soaking, crushing, grinding, screening and winnowing.

[0028] In the present invention, the purpose of infiltration is to soften the cortex and embryo of corn kernels, enhance the toughness of the cortex, reduce the binding force between the cortex and the endosperm, expand the embryo, and increase the elasticity. This is to reduce the damage to the embryo during the process of corn peeling and embryo removal, and improve the efficiency of peeling and embryo removal. Preferably, the time of the infiltration is such that the water content in the infiltrated corn obtained after the infiltration is 16-19wt%. Further, the time of the infiltration is 6-10h.

[0029] After the germ is extracted, it is not necessary to dry the corn. After the corn is soaked, some water will be lost in the subsequent grinding, screening, air separation and other processes, as well as the crushing and pressing process. In a preferred case, the water content in the germ particles obtained by pressing is 7-12wt%.

[0030] In the present invention, the purpose of corn slag breaking is to remove the germs from the corn, which can be carried out by using conventional corn slag breaking processes and equipment in the art, for example, a corn germ removal and slag breaking machine can be used for corn slag breaking.

[0031] In the present invention, the purpose of grinding is to separate corn grits and germ, which can be carried out using conventional processes and equipment in the art, such as a grain corn mill. Preferably, the grinding conditions are such that the average particle size of the material after the grinding is less than or equal to 2 mm.

[0032] In the present invention, the purpose of screening and air separation is to improve the purity of germ and reduce the content of starch and fiber. The present invention has no particular limitation on the screening and air separation methods, and conventional methods in the art can be used. For example, screening can use a flat rotating screen or a high square screen to separate fine corn grits, and air separation can use a germ cyclone to separate the germ and fiber according to their different specific gravities.

[0033] In a preferred embodiment, the content of germ in the refined germ is greater than or equal to 75 wt %.

[0034] According to the present invention, preferably, in S4, the oil immersion process includes: extraction, solid-liquid separation and evaporation.

[0035] By adopting the preparation method of the present invention, the germ particles can be extracted at a relatively low temperature, thereby obtaining a higher oil yield. In order to obtain a higher oil yield while avoiding the adverse effects of high temperature on oil quality and reducing production pressure, preferably, in S4, the extraction temperature is 55-65°C and the extraction time is 90-120 minutes.

[0036] Furthermore, the extraction temperature is 58-62°C.

[0037] According to the present invention, preferably, the extraction is performed using a solvent, and the solvent is n-hexane.

[0038] The present invention has no particular restrictions on the specifications of n-hexane, and n-hexane reagents of various specifications on the market can be used. Preferably, n-hexane reagents with a content of 30wt% and / or n-hexane reagents with a content of 70wt% are used. In the present invention, the amount of n-hexane used is calculated based on the total amount of n-hexane reagents used.

[0039] In order to further improve the effect of extracting oil, preferably, the weight ratio of the solvent to the germ particles is (1-2):1, more preferably (1.2-1.5):1.

[0040] After extraction, the obtained material is subjected to solid-liquid separation to separate the corn germ meal after oil extraction, and the corn germ meal can be returned to the fermentation system for alcohol production. The entire process of preparing corn crude oil in the present invention is carried out at a relatively low temperature, which can avoid the color change of the product caused by the Maillard reaction, and can also avoid the reduction of starch utilization rate caused by starch denaturation, thereby improving the yield of ethanol.

[0041] The present invention has no particular limitation on the method of solid-liquid separation, and conventional solid-liquid separation processes in the art may be used, such as filtration separation, sedimentation separation, and the use of a liquid-solid fluidized bed.

[0042] After solid-liquid separation, the obtained liquid phase separation is evaporated to remove the extraction solvent. Preferably, the evaporation temperature is 105-115°C and the time is 1-2 minutes.

[0043] According to a preferred embodiment of the present invention, the method for preparing crude corn oil comprises the following steps:

[0044] S1. Soaking corn in water for 6-10 hours, so that the moisture content of the soaked corn is 16-19wt%; then using a slag crusher to crush the soaked corn, and using a grinder to grind the corn, so that the average particle size of the ground material is less than or equal to 2mm; after grinding, sieving through a high square sieve, and then using a germ cyclone to air select, to obtain refined germ with a germ content greater than or equal to 75wt%.

[0045] S2. The refined germ obtained in S1 is crushed by a crusher, so that the screening rate of the obtained germ powder through a 14-mesh sieve is greater than or equal to 92%.

[0046] S3, using a roller extrusion granulator to press the germ powder obtained in S2 into particles with an average particle size of 5-10 mm and a density of 450-550 kg / m 3 The germ particles have a water content of 7-12wt%.

[0047] S4. Extracting the germ particles obtained in S3 with n-hexane solvent at a temperature of 58-62° C. for 90-120 min, wherein the weight ratio of n-hexane solvent to germ particles is (1.2-1.5):1; after solid-liquid separation, evaporating at a temperature of 105-115° C. for 1-2 min to remove the solvent and obtain the crude corn oil.

[0048] The second aspect of the present invention provides a crude corn oil prepared by the preparation method provided by the present invention, wherein the acid value of the crude corn oil is less than or equal to 5 mg KOH / g. The acid value of the crude corn oil specifically refers to: the number of milligrams of KOH required to neutralize the free fatty acids in 1 g of crude corn oil. A high acid value indicates that the oil is hydrolyzed to produce more free fatty acids, and the crude corn oil should have a lower acid value. The lower the acid value, the better the quality of the oil.

[0049] The present invention will be described in detail below through examples and comparative examples. In the following examples and comparative examples, unless otherwise specified, all are conventional methods; the reagents and materials used, unless otherwise specified, can be obtained from commercial channels. The determination methods involved in each example and comparative example are as follows:

[0050] The calculation formula of oil yield is: oil yield % = oil yield weight ÷ total weight of corn kernel raw material × 100%.

[0051] The acid value of crude corn oil is determined using the method of "GB 5009.229-2016 National Food Safety Standard Determination of Acid Value in Food".

[0052] Starch utilization % = enzyme hydrolyzed starch content ÷ acid hydrolyzed starch content × 100%; where,

[0053] Determination of starch content by enzyme hydrolysis: Weigh 2-5g of sample and place it in a funnel with folded filter paper. First, use 50ml of ether to wash away fat 5 times (Note: If the fat content is low, this step can be omitted), then use about 100ml of 85% ethanol to wash away soluble sugars, transfer the residue into a 250ml beaker, and wash the filter paper and funnel with 50ml of water. The washing liquid is added to the beaker. Heat the beaker in a boiling water bath for 15min to gelatinize the starch, cool it to below 60℃, add 20ml of amylase solution, and keep it warm at 55-60℃ for 1h, stirring from time to time. Then take 1 drop of this solution and add 1 drop of iodine solution. It should not turn blue. If it turns blue, heat it again to gelatinize and add 20ml of amylase solution. Continue to keep warm until the iodine does not turn blue. Heat to boiling, cool it and transfer it to a 250ml volumetric flask, add water to the scale, mix well, and filter. Discard the initial filtrate, take 50ml of the filtrate, place it in a 250ml conical flask, add 5ml of 6mol / L hydrochloric acid, install a reflux condenser, reflux in a boiling water bath for 1h, add 2 drops of methyl red indicator after cooling, neutralize to neutrality with 5mol / L sodium hydroxide solution, transfer the solution to a 100ml volumetric flask, wash the conical flask, add the washing liquid to a 100ml volumetric flask, add water to the scale, and prepare the enzymatic solution. The reducing sugar content in the enzymatic solution was measured by redox titration, and the starch content of the sample was calculated.

[0054] Determination of starch content by acid hydrolysis: Weigh 2-5g of sample ground through a 40-mesh sieve, place it in a funnel with slow filter paper, wash the fat in the sample with 30ml of ether three times, and discard the ether. Then wash the residue with 150ml of 85% ethanol solution several times to remove soluble sugars. Filter the ethanol solution, wash the residue in the funnel with 100ml of water and transfer it to a 250ml conical flask, add 30ml of 6mol / L hydrochloric acid, connect the condenser, and reflux in a boiling water bath for 2h. After the reflux is completed, immediately cool it in running water. After the sample is hydrolyzed and cooled, add 2 drops of methyl red indicator, first adjust it to yellow with 40% sodium hydroxide solution, and then calibrate it with 6mol / L hydrochloric acid until the hydrolyzate just turns red. If the hydrolyzate is darker in color, it can be tested with precision pH test paper to make the pH of the sample hydrolyzate about 7. Then add 20ml of 20% lead acetate solution, shake well, and let it stand for 10min. Add 20ml of 10% sodium sulfate solution to remove excess lead. After shaking, transfer all the solution and residue into a 500ml volumetric flask, wash the conical flask with water, combine the washings in the volumetric flask, and dilute to scale with water. Filter, discard 20ml of the initial filtrate, and use the filtrate for determination. Use redox titration to measure the reducing sugar content in the filtrate and calculate the starch content of the sample.

[0055] The following examples are used to illustrate the preparation of crude corn oil.

[0056] Example 1

[0057] S1. Soak corn kernels in water for 8 hours, so that the moisture content of the soaked corn is 17wt%; then use a slag crusher to crush the soaked corn kernels, and use a grinder to grind the corn kernels, so that the average particle size of the ground material is 1.7mm; after grinding, sieve through a high square sieve, and then use a germ cyclone to air select, so as to obtain refined germ with a germ content of 82wt%.

[0058] S2. The refined germ obtained in S1 is crushed by a crusher, so that the screening rate of the obtained germ powder through a 14-mesh sieve is 94%.

[0059] S3, using a roller extrusion granulator to press the germ powder obtained in S2 into particles with an average particle size of 7 mm and a density of 500 kg / m 3 Germ particles; the water content in the germ particles is 9wt%.

[0060] S4. Using 70 wt% n-hexane solvent to extract the germ particles obtained in S3 at 60° C. for 100 min, the weight ratio of n-hexane solvent to germ particles is 1.3:1; after solid-liquid separation, evaporate at 110° C. for 1.5 min to remove the solvent and obtain crude corn oil.

[0061] Example 2

[0062] S1. Soak corn kernels in water for 8 hours, so that the moisture content of the soaked corn is 18wt%; then use a slag crusher to crush the soaked corn kernels, and use a grinder to grind the corn kernels, so that the average particle size of the ground material is 1.7mm; after grinding, sieve through a high square sieve, and then use a germ cyclone to air select, so as to obtain refined germ with a germ content of 82wt%.

[0063] S2. The refined germ obtained in S1 is crushed by a crusher, so that the screening rate of the obtained germ powder through a 14-mesh sieve is 96%.

[0064] S3, using a roller extrusion granulator to press the germ powder obtained in S2 into particles with an average particle size of 9 mm and a density of 540 kg / m 3 The germ particles have a water content of 9wt%.

[0065] S4 is the same as S4 in Example 1 to obtain crude corn oil.

[0066] Example 3

[0067] S1. Soak corn kernels in water for 8 hours, so that the moisture content of the soaked corn is 16wt%; then use a slag crusher to crush the soaked corn kernels, and use a grinder to grind the corn kernels, so that the average particle size of the ground material is 1.7mm; after grinding, sieve through a high square sieve, and then use a germ cyclone to air select, so as to obtain refined germ with a germ content of 82wt%.

[0068] S2. The refined germ obtained in S1 is crushed by a crusher, so that the screening rate of the obtained germ powder through a 14-mesh sieve is 95%.

[0069] S3, using a roller extrusion granulator to press the germ powder obtained in S2 into particles with an average particle size of 6 mm and a density of 460 kg / m 3 The germ particles have a water content of 9wt%.

[0070] S4 is the same as S4 in Example 1 to obtain crude corn oil.

[0071] Example 4

[0072] Corn crude oil was prepared according to the method of Example 1, except that in S2, "the screening rate of the obtained germ powder through a 14-mesh sieve is 90%" was used to replace "the screening rate of the obtained germ powder through a 14-mesh sieve is 94%". Corn crude oil was obtained.

[0073] Example 5

[0074] Corn crude oil was prepared according to the method of Example 1, except that in S3, "the germ powder obtained in S2 was pressed into germ particles with an average particle size of 7 mm using a double-roll extrusion granulator" was used instead of "the germ powder obtained in S2 was pressed into germ particles with an average particle size of 15 mm using a double-roll extrusion granulator". Corn crude oil was obtained.

[0075] Example 6

[0076] Corn crude oil was prepared according to the method of Example 1, except that in S3, the germ powder obtained in S2 was pressed into a pellet with an average density of 700 kg / m 3 The germ powder obtained from S2 is pressed into a pellet mill with an average density of 500 kg / m 3 Germ particles". Corn crude oil is obtained.

[0077] Comparative Example 1

[0078] Corn crude oil is prepared according to the method of Example 1, except that after obtaining refined germ, drying, embryo rolling and pre-pressing are performed, and then extraction, solid-liquid separation and evaporation are performed. The specific steps are as follows:

[0079] S1 is the same as S1 in Example 1.

[0080] S2, drying the refined germ obtained in S1 at a drying temperature of 75° C. to make the moisture content in the refined germ reach 5wt%.

[0081] The dried refined germs obtained in S3 and S2 are fed into a flaking mill for flaking to a thickness of 0.8 mm and a flaking rate of 98%.

[0082] The germ flakes obtained in S4 and S3 enter the pre-pressing machine and are pre-pressed at a temperature of 140° C. The fat content of the pre-pressed cake obtained after pre-pressing is 14 wt %.

[0083] S5. The pre-pressed cake obtained in S4 was extracted with 70 wt % n-hexane solvent at 60° C. for 100 min, with the weight ratio of n-hexane solvent to pre-pressed cake being 1.3:1. After solid-liquid separation, the pre-pressed cake was evaporated at 110° C. for 1.5 min to remove the solvent and obtain crude corn oil.

[0084] Test Case

[0085] The oil yield and acid value of the crude corn oil, the utilization rate of germ meal starch and the steam consumption of the crude corn oil prepared in each embodiment and comparative example were measured respectively. The results are shown in Table 1.

[0086] Table 1

[0087] serial number Oil yield, % Acid value, mg KOH / g Germ meal starch utilization, % Steam consumption, tons Example 1 2.52 3.86 95.3 1.87 Example 2 2.49 3.92 95.2 1.95 Example 3 2.47 3.89 95.4 1.92 Example 4 2.08 4.04 94.6 2.04 Example 5 2.01 4.05 94.3 2.13 Example 6 2.04 4.03 93.9 2.07 Comparative Example 1 2 5.23 73.6 3.86

[0088] From the results in Table 1, it can be seen that the crude corn oil prepared by the method of the present invention in Examples 1-6 has a higher oil yield, a lower acid value, a higher utilization rate of germ meal starch, and a lower steam consumption. Comparative Example 1 uses a different process to prepare crude corn oil. After obtaining refined germ, it is dried, rolled and pre-pressed, and then soaked in oil. Compared with Examples 1-6, the crude corn oil prepared in Comparative Example 1 has a lower oil yield, a significantly higher acid value, a significantly lower utilization rate of germ meal starch, and a significantly higher steam consumption. This shows that the method for preparing crude corn oil provided by the present invention can obtain a higher oil yield, and can effectively improve the quality of crude corn oil, and can also effectively improve the utilization rate of starch and reduce energy consumption.

[0089] In addition, the screening rate of the germ powder through the 14-mesh sieve in Example 4 was reduced to 90%, the average particle size of the germ granules pressed in Example 5 was increased to 15 mm, and the average density of the germ granules pressed in Example 6 was increased to 700 kg / m 3Compared with Example 1, the oil yield of the crude corn oil obtained in Examples 4-6 is reduced, the acid value is increased, the utilization rate of germ meal starch is reduced, and the steam consumption is also increased. This shows that when the screening rate of germ powder through a 14-mesh sieve, the average particle size and average density of the pressed germ particles meet the preferred conditions, the oil yield of the crude corn oil and the utilization rate of germ meal starch can be further improved, and the acid value of the crude corn oil and the energy consumption of the preparation process can be further reduced.

[0090] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing crude corn oil, characterized in that: The preparation method comprises the following steps: S1, extracting the germ of corn to obtain refined germ; S2, crushing the refined germ to obtain germ powder; S3, pressing the germ powder into germ granules; S4, soaking the germ particles in oil.

2. The preparation method according to claim 1, characterized in that: In S2, the sieving rate of the germ powder through a 14-mesh sieve is greater than or equal to 92%.

3. The preparation method according to claim 1 or 2, characterized in that: In S3, the average particle size of the germ particles is 5-10 mm, and the density is 350-650 kg / m 3 .

4. The preparation method according to any one of claims 1 to 3, characterized in that: In S1, the process of extracting germs includes: soaking, crushing, grinding, screening and winnowing.

5. The preparation method according to claim 4, characterized in that: The soaking time is such that the moisture content of the soaked corn obtained after the soaking is 16-19wt%; Preferably, the water content in the germ particles is 7-12 wt %.

6. The preparation method according to claim 4, characterized in that: The grinding conditions are such that the average particle size of the material after the grinding is less than or equal to 2 mm.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The content of germ in the refined germ is greater than or equal to 75wt%.

8. The preparation method according to any one of claims 1 to 7, characterized in that: In S4, the oil immersion process includes: extraction, solid-liquid separation and evaporation; Preferably, the extraction temperature is 55-65°C, preferably 58-62°C, and the extraction time is 90-120 min.

9. The preparation method according to claim 8, characterized in that: The extraction is performed using a solvent, wherein the solvent is n-hexane; Preferably, the weight ratio of the solvent to the germ particles is (1-2):1, preferably (1.2-1.5):

1.

10. The preparation method according to claim 8 or 9, characterized in that: The evaporation temperature is 105-115°C and the evaporation time is 1-2 minutes.