Preparation and production process of natto soybean milk

Abstract

The invention discloses a preparation and production process of natto soybean milk, which comprises the following steps: (1) preparing soybean milk: preparing soybeans into soybean milk, conveying the soybean milk into a first vacuum heat preservation tank, and cooling the soybean milk to 37 DEG C; (2) auxiliary material pretreatment: preparing sugar, a thickening agent and clear water, putting the sugar, the thickening agent and the clear water into a second vacuum heat preservation tank, sterilizing the interior of the second vacuum heat preservation tank, and cooling to 37 DEG C to prepare premixed auxiliary material liquid; (3) performing primary fermentation, namely aseptically conveying the premixed auxiliary material liquid prepared in the step (2) into a first vacuum heat preservation tank in a pipeline manner, adding bacillus natto into the first vacuum heat preservation tank, and performing micro-pressure fermentation for 24 hours under the pressure condition of 0.05-0.10 MPa to prepare nattokinase; and (4) secondary fermentation: cooling the nattokinase prepared in the step (3) to 20-28 DEG C, adding mucor into the first vacuum heat preservation tank, and performing micro-pressure fermentation for 24 hours to prepare the natto soybean milk.

Description

Technical Field

[0001] The present invention relates to the technical field of natto processing and preparation, and particularly relates to a preparation production process of natto soymilk. Background Art

[0002] Natto contains all the nutrients of soybeans and special nutrients added after fermentation, including saponins, isoflavones, unsaturated fatty acids, lecithin, folic acid, dietary fiber, calcium, iron, potassium, vitamins, and various amino acids and minerals, and is suitable for long-term consumption to maintain health.

[0003] It is known from the research of Japanese medical scientists and physiologists that the protein in soybeans is insoluble, but after being made into natto, it becomes soluble and produces amino acids, and various enzymes that do not exist in the raw materials will be produced by natto bacteria and related bacteria to help the gastrointestinal tract digest and absorb.

[0004] As a plant-based food, it is the richest in crude protein and fat. Natto is a high-protein nourishing food. The enzymes contained in natto can remove some cholesterol in the body and decompose acidified lipids in the body after consumption, and restore abnormal blood pressure to normal.

[0005] Nattokinase (NK) can be extracted from natto. Nattokinase is a serine protease that can significantly dissolve thrombi in vivo and in vitro, significantly shorten the euglobulin lysis time (ELT), and can stimulate venous endothelial cells to produce tissue plasminogen activator (t-PA), thereby more effectively exerting the thrombolytic effect.

[0006] The traditional preparation process of natto is: soaking soybeans → steaming → inoculating Bacillus natto spores → controlling the temperature (37 - 42°C) for fermentation for 18 - 24 hours → refrigerated storage. This process relies on natural fermentation. Although it can generate key functional components, it also brings significant edible defects and storage limitations: (1) Characteristic odor: Amines (such as histamine, putrescine), volatile fatty acids (such as butyric acid), and sulfides (such as methanethiol) produced during the fermentation process form a strong "fermentation odor". According to detection, the sulfur-containing compounds in its volatile components account for 30% - 40%, causing acceptance barriers for people with sensitive olfaction. (2) Bitter taste and sticky texture: Bitter peptides (such as hydrophobic short peptides) produced by the hydrolysis of soy protein, residual soy saponins (content about 0.1% - 0.3%), and viscous polysaccharides (poly-γ-glutamic acid) secreted by natto bacteria result in a bitter and sticky taste in the mouth, especially not meeting the taste preferences of non-fermented food consumption areas.

[0007] (3) Short shelf life: Natto has a high water content (≥65%) and is rich in active enzymes. It is easy to breed miscellaneous bacteria (such as Escherichia coli, mold) within 24 hours at room temperature, resulting in souring and mildew; even when refrigerated (4°C), the shelf life is only 7 - 10 days, limiting long-distance transportation and the application of ready-to-eat scenarios. (4)Single consumption scenario: Traditional natto is in solid granular form and is mostly directly consumed in its original flavor. It needs to be paired with seasonings such as soy sauce and mustard to cover up the unpleasant smell, which does not match the diverse needs of modern convenient foods (such as instant snacks and instant cooking packs). Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a preparation production process for natto soymilk. This preparation production process for natto soymilk can retain nattokinase while effectively removing the stinky substances and bitter components in natto, increasing the shelf life, and increasing the consumption scenarios. The technical solutions adopted are as follows: A preparation production process for natto soymilk includes the following steps: Step (1) Prepare soymilk: Make soybeans into soymilk, transport the soymilk to the first vacuum insulation tank, and cool the soymilk to 37°C. Step (2) Pretreatment of auxiliary materials: Prepare sugar, thickener, and clear water. Put the sugar, thickener, and clear water into the second vacuum insulation tank, sterilize the inside of the second vacuum insulation tank, then stir the sugar, thickener, and clear water, and cool to 37°C to obtain a premixed auxiliary material liquid. Step (3) Primary fermentation: Sterilely transport the premixed auxiliary material liquid prepared in step (2) to the first vacuum insulation tank through a pipeline, add Bacillus natto spores to the first vacuum insulation tank, and conduct primary fermentation. It is characterized in that: in step (3), after adding Bacillus natto spores, then introduce sterile air into the first vacuum insulation tank, stir the soymilk, premixed auxiliary material liquid, and Bacillus natto spores to make Bacillus natto spores evenly distributed in the soymilk, promote the full contact between Bacillus natto spores and soymilk, and conduct micro-pressure fermentation for 24 hours under a pressure condition of 0.05 MPa - 0.10 MPa to obtain nattokinase. It further includes step (4) Secondary fermentation: Cool the nattokinase prepared in step (3) to 20°C - 28°C, add Mucor to the first vacuum insulation tank, stir the nattokinase and Mucor, and conduct micro-pressure fermentation for 24 hours under a pressure condition of 0.05 MPa - 0.10 MPa to obtain natto soymilk.

[0009] In the above step (2), using the second vacuum insulation tank to hold sugar and thickener and sterilizing the inside of the second vacuum insulation tank can avoid contact with external air and prevent secondary pollution (such as mold spores, dust), ensuring pure culture in the subsequent fermentation process.

[0010] In the above step (3), Bacillus natto can secrete a variety of proteases. Introducing sterile air provides the necessary oxygen for Bacillus natto to meet its growth and metabolic needs; the sugar in the premixed auxiliary liquid provides a carbon source for Bacillus natto, enabling it to carry out metabolic activities. Under aerobic conditions, Bacillus natto can carry out respiration more effectively, synthesize more enzymes and metabolites, and ensure the smooth progress of the fermentation process. During the primary fermentation process, Bacillus natto utilizes the nutrients in the soybean milk for growth and reproduction, and secretes nattokinase, providing a fermentation broth rich in nattokinase for the subsequent preparation of natto soybean milk. Bacillus natto also secretes proteases, and the proteases secreted by Bacillus natto can hydrolyze the soybean protein in the soybean milk into bitter peptides (such as hydrophobic short peptides), soybean saponins and viscous polysaccharides (such as poly-γ-glutamic acid).

[0011] In the above step (4), 20°C - 28°C is the optimal growth temperature of Mucor. At this temperature, Mucor can secrete many kinds of enzymes, including fibrinolytic protease, aminopeptidase, β-glucosidase, γ-PGA degrading enzyme. The activities of these enzymes at 20°C - 28°C are 1.5 times that at 37°C, and can inhibit the excessive mucus production of Bacillus natto. Bacillus natto will produce polysaccharides during the fermentation process, which will increase the viscosity of the fermentation broth in the secondary fermentation. When Mucor grows in the fermentation broth with high viscosity, a large number of microspheres will be formed, and these microspheres can encapsulate a large number of Bacillus natto, which can mitigate the harmful effect of gastric acid in the human body on Bacillus natto, increase the survival ability of Bacillus natto in the gastrointestinal tract, and greatly enhance the health care function of natto soybean milk.

[0012] The thickener in the premixed auxiliary liquid is not decomposed by Bacillus natto or Mucor, and only increases the viscosity of the system through physical action. Since the cell wall of the bacteria in natto soybean milk has a layer of polysaccharide, it is easily adhered by the thickener. The thickener forms protective microspheres in natto soybean milk, and each protective microsphere encapsulates the bacteria in natto soybean milk, Bacillus natto and Mucor spores. If the prepared natto soybean milk is stored frozen, the bacteria in the natto soybean milk taken out after freezing will not die due to thawing, thus greatly extending the shelf life of natto soybean milk; while if traditional natto is stored frozen, the bacteria in traditional natto are not protected at all. Once thawed, the cell membrane of the bacteria in traditional natto is broken, and most of them die, making it impossible to extend the shelf life of traditional natto by frozen storage.

[0013] After the above-mentioned soybeans are ground into soybean milk to form a homogeneous liquid state, and on the basis of adding Bacillus natto, the nattokinase, bitter peptides, soybean saponins and viscous polysaccharides produced in the soybean milk are all dispersed in a dissolved state, enabling the added Mucor to evenly contact with each substance in the soybean milk and undergo the following reactions and effects: The fibrinolytic protease secreted by Mucor synergizes with nattokinase in soymilk, retains and enhances thrombolytic activity, and improves thrombolytic efficiency; The aminopeptidase secreted by Mucor can hydrolyze amino acids one by one from the N-terminus of the peptide chain. This amino acid can break down the bitter peptides produced in soymilk, enabling the aminopeptidase secreted by Mucor to specifically enzymatically hydrolyze the bitter peptides, reducing the bitterness value of natto soymilk, so that natto soymilk does not need to rely on exogenous seasonings to cover up the bitterness; The β-glucosidase secreted by Mucor can directly act on the glycosidic bond of soyasaponin molecules in soymilk to generate non-bitter aglycones, which can reduce the content of astringent substances in natto soymilk; The γ-PGA degrading enzyme secreted by Mucor can partially hydrolyze the viscous polysaccharides in soymilk, reduce the molecular weight and system viscosity of the viscous polysaccharides, and form a smooth and delicate natto soymilk, rather than the sticky filament state of traditional solid natto.

[0014] The present invention adopts two-stage fermentation. The first fermentation is the fermentation of Bacillus subtilis natto in step (3). However, this bacterium has insufficient protease, and it will produce bitterness after decomposing proteins. At the same time, it will also produce ammonia. Ammonia has a high solubility in water, which is harmful to the human liver function and has a bad taste. Then, the second fermentation in step (4) is carried out. Since Mucor can secrete many kinds of enzymes at 20°C - 28°C, adding Mucor is to supplement protease, eliminate the bitterness in natto soymilk, and at the same time quickly convert the ammonia in natto soymilk into microbial protein, increase the nutrition of the fermentation broth, improve the flavor, and eliminate the substances harmful to the human liver function.

[0015] In a preferred embodiment, in step (1), the soybeans are washed, soaked, drained, ground, filtered, and cooked to obtain soymilk, which is then aseptically transported to the first vacuum insulation tank by pipeline. More preferably, the above pipeline is made of 316L stainless steel pipeline and is combined with steam sterilization to aseptically transfer the soymilk.

[0016] In a preferred embodiment, in step (2), the interior of the second vacuum insulation tank is sterilized by high-temperature short-time sterilization or pasteurization. The conditions of the above high-temperature short-time sterilization refer to a temperature of 100°C - 130°C and a time of 20 seconds - 40 seconds. The conditions of the above pasteurization refer to a temperature of 70°C - 90°C and a time of 10 minutes - 20 minutes. The above high-temperature sterilization combined with the aseptic environment of the vacuum insulation tank ensures that the miscellaneous bacteria (such as Escherichia coli, yeast) in the sugar and thickening agent are killed.

[0017] In a preferred embodiment, in step (2), the sugar is sucrose.

[0018] In a preferred embodiment, in step (2), the thickener is one of xanthan gum, sodium carboxymethyl cellulose, and sodium alginate. The above-mentioned xanthan gum can significantly improve the system stability and inhibit water separation. The above-mentioned sodium carboxymethyl cellulose (CMC-Na) can enhance emulsification and prevent fat from floating. The above-mentioned sodium alginate forms protective microspheres through ionic cross-linking and endows the product with intestinal targeting release and dietary fiber health attributes, especially suitable for scenarios with higher requirements for probiotic activity protection and function enhancement.

[0019] In a preferred embodiment, in step (3), the outer wall of the first vacuum insulation tank is provided with a sandwich layer, and a thermometer is connected to the sandwich layer; warm water at 37°C is introduced into the sandwich layer to control the temperature of the soymilk, premixed auxiliary liquid, and Bacillus natto in the first vacuum insulation tank for fermentation.

[0020] In a further preferred embodiment, in step (4), cooling water or a refrigerant is added to the sandwich layer to reduce the temperature of the nattokinase prepared in step (3) from 37°C to 20°C - 28°C, and the cooling rate is controlled within 1°C per minute. Controlling the cooling rate within 1°C per minute can avoid the influence of sudden temperature changes on the cell activity.

[0021] In a further preferred embodiment, in step (4), the temperature of the cooling water is 15°C - 20°C. The initial temperature of nattokinase is 37°C, the target temperature is 20°C - 28°C, and the cooling water temperature is 15°C - 20°C, forming a temperature difference of 17°C - 12°C (superior to overcooling with lower temperature cooling water), which not only ensures the heat exchange rate (Fourier's law: the greater the temperature difference, the higher the heat transfer), but also avoids local overcooling (for example, when the cooling water is 10°C, the nattokinase near the container wall is prone to form a temperature difference layer of 5°C, resulting in the inactivation of Mucor in the low-temperature area).

[0022] In a further preferred embodiment, in step (4), the refrigerant is ethylene glycol solution. The ethylene glycol solution has a low freezing point and good thermal conductivity, meeting food-grade safety requirements.

[0023] In a preferred embodiment, in step (4), during the fermentation for 0 - 4 hours, low-speed stirring at a speed of 50 rpm - 80 rpm is adopted; the stirring is stopped during the fermentation for 4 - 24 hours to form a static fermentation environment. Adopting low-speed stirring in the initial stage of fermentation (0 - 4 hours) can promote the uniform dispersion of Mucor spores. Stopping the stirring in the middle and later stages of fermentation (4 - 24 hours) to form a static fermentation environment is conducive to the attachment of Mucor mycelia on the surface of protein particles and improves the decomposition efficiency.

[0024] Compared with the prior art, the present invention has the following advantages: The soymilk of the present invention forms a sterile matrix after preliminary sterilization. The mucor is evenly dispersed in the liquid state, and combined with vacuum fermentation, so that various substances in the mucor can evenly contact and react with various substances in the soymilk, which can remove the bitterness and astringency in natto, make the prepared natto soymilk have a smooth texture, avoid the problem of bacteria hidden in the gaps of soybeans in solid-state fermentation, reduce the contamination rate of miscellaneous bacteria, and the shelf life can be appropriately extended at room temperature (without adding preservatives). Detailed implementation mode

[0025] The following further describes the preferred implementation mode of the present invention.

[0026] Example 1. The preparation production process of the natto soymilk in this example includes the following steps: (1) Prepare soymilk: Make soybeans into soymilk, transport the soymilk to the first vacuum heat preservation tank, and cool the soymilk to 37°C; (2) Pretreatment of auxiliary materials: Prepare sugar, thickener and clear water, put the sugar, thickener and clear water into the second vacuum heat preservation tank, sterilize the inside of the second vacuum heat preservation tank, then stir the sugar, thickener and clear water, and cool to 37°C to obtain a premixed auxiliary material liquid; (3) Primary fermentation: Sterilely transport the premixed auxiliary material liquid prepared in step (2) to the first vacuum heat preservation tank through a pipeline, add Bacillus natto spores to the first vacuum heat preservation tank, and then introduce sterile air into the first vacuum heat preservation tank. Stir the soymilk, premixed auxiliary material liquid and Bacillus natto spores to make Bacillus natto spores evenly distributed in the soymilk, promote the full contact of Bacillus natto spores and soymilk, and carry out micro-pressure fermentation for 24 hours under the pressure condition of 0.05MPa - 0.10MPa to obtain nattokinase; (4) Secondary fermentation: Cool the nattokinase prepared in step (3) to 20°C - 28°C, add mucor to the first vacuum heat preservation tank, stir the nattokinase and mucor, and carry out micro-pressure fermentation for 24 hours under the pressure condition of 0.05MPa - 0.10MPa to obtain natto soymilk.

[0027] After the above-mentioned soybeans are ground into soymilk, a homogeneous liquid state is formed. On the basis of adding Bacillus natto spores, nattokinase, bitter peptides, soyasaponins, and viscous polysaccharides produced in the soymilk are all dispersed in a dissolved state, so that the added mucor can evenly contact with various substances in the soymilk and undergo the following reactions and effects: The fibrinolytic protease secreted by mucor synergizes with nattokinase in the soymilk, retains and enhances the thrombolytic activity, and improves the thrombolytic efficiency; The aminopeptidase secreted by Mucor can hydrolyze amino acids one by one from the N-terminus of the peptide chain, and this amino acid can break down the bitter peptides produced in soya milk, enabling the aminopeptidase secreted by Mucor to specifically enzymatically hydrolyze the bitter peptides, reduce the bitterness value of natto soya milk, and make it unnecessary for natto soya milk to rely on exogenous seasonings to cover up the bitterness; The β-glucosidase secreted by Mucor can directly act on the glycosidic bond of the soyasaponin molecule in soya milk to generate aglycone without bitterness, which can reduce the content of astringent substances in natto soya milk; The γ-PGA degrading enzyme secreted by Mucor can partially hydrolyze the viscous polysaccharides in soya milk, reduce the molecular weight and system viscosity of the viscous polysaccharides, and form a smooth and delicate natto soya milk, rather than the sticky filament state of traditional solid natto.

[0028] In step (1), the soybeans are washed, soaked, drained, ground, filtered, and steamed to obtain soya milk, which is then aseptically transported to the first vacuum insulation tank in a pipeline manner. More preferably, the above pipeline is made of 316L stainless steel pipeline and is combined with steam sterilization to aseptically transfer the soya milk.

[0029] In step (2), the interior of the second vacuum insulation tank is sterilized by high-temperature short-time sterilization or pasteurization. The conditions of the above high-temperature short-time sterilization refer to a temperature of 100°C - 130°C and a time of 20 seconds - 40 seconds. The conditions of the above pasteurization refer to a temperature of 70°C - 90°C and a time of 10 minutes - 20 minutes. The above high-temperature sterilization combined with the aseptic environment of the vacuum insulation tank ensures that the miscellaneous bacteria (such as Escherichia coli, yeast) in the sugar and thickener are killed.

[0030] In step (2), the sugar is sucrose.

[0031] In step (2), the thickener is sodium alginate. The above xanthan gum can significantly improve the system stability and inhibit water separation. The above carboxymethyl cellulose sodium (CMC-Na) can enhance the emulsification and prevent fat floating. The above sodium alginate forms protective microspheres through ionic cross-linking and endows the product with intestinal targeting release and dietary fiber health attributes, especially suitable for scenarios with higher requirements for the protection of probiotic activity and function enhancement.

[0032] In step (3), the outer wall of the first vacuum insulation tank is provided with a sandwich, and the sandwich is connected with a thermometer; warm water at 37°C is introduced into the sandwich to control the temperature of the soya milk, premixed auxiliary liquid, and Bacillus natto spores in the first vacuum insulation tank for fermentation.

[0033] In step (4), cooling water is added to the sandwich to reduce the temperature of the nattokinase prepared in step (3) from 37°C to 20°C - 28°C, and the cooling rate is controlled within 1°C / minute. Controlling the cooling rate within 1°C / minute can avoid the sudden change in temperature affecting the cell activity.

[0034] In step (4), the temperature of the cooling water is 15°C - 20°C. The initial temperature of nattokinase is 37°C, the target temperature is 20°C - 28°C, and the cooling water temperature is 15°C - 20°C, forming a temperature difference of 17°C - 12°C (superior to overcooling with lower temperature cooling water). This not only ensures the heat exchange rate (Fourier's law: the greater the temperature difference, the higher the heat transfer), but also avoids local overcooling (for example, when the cooling water is at 10°C, nattokinase near the container wall is prone to form a temperature difference layer of 5°C, resulting in the inactivation of Mucor in the low-temperature area).

[0035] In step (4), during the fermentation for 0 - 4 hours, low-speed stirring at a rotation speed of 50 rpm - 80 rpm is adopted; stirring is stopped during the fermentation for 4 hours - 24 hours to form a static fermentation environment. Adopting low-speed stirring in the initial stage of fermentation (0 - 4 hours) can promote the uniform dispersion of Mucor spores. Stopping stirring in the middle and later stages of fermentation (4 - 24 hours) to form a static fermentation environment is conducive to the attachment of Mucor mycelia to the surface of protein particles and improves the decomposition efficiency.

[0036] Comparative example 1: Operate according to the traditional nattō preparation process, specifically: After washing and soaking soybeans, steam them until cooked, cool them, inoculate Bacillus natto spores, and ferment under suitable conditions. After fermentation is completed, a traditional nattō sample is obtained.

[0037] Operate according to the production process for the preparation of nattō soy milk in Example 1 above to prepare a nattō soy milk sample. The traditional nattō sample and the nattō soy milk sample are compared respectively using the following tests.

[0038] 1. Take an appropriate amount of samples from the prepared traditional nattō sample and nattō soy milk sample, and detect the nattokinase activity using the fibrin plate method.

[0039] 2. Select 10 professionally trained sensory evaluation personnel to form a sensory evaluation group. Take an appropriate amount of samples from the prepared traditional nattō sample and nattō soy milk sample, and let the sensory evaluation personnel conduct a sensory score on the odor of the samples. The scoring standard is a 10-point system, with 10 points being the strongest odor and 1 point being no odor. The evaluation personnel sniff the samples separately, score independently, and then take the average value.

[0040] 3. Adopt a method combining sensory tasting with the detection of the content of bitter peptides and saponins. Select multiple tasting personnel to taste the samples and record the lowest concentration at which the bitter taste can be perceived. At the same time, use high-performance liquid chromatography (HPLC) to detect the content of bitter peptides and saponins in the samples.

[0041] 4. Take appropriate samples from the prepared traditional natto samples and natto soymilk samples, and conduct tests on the samples at room temperature (25°C) at regular intervals (such as 1 day, 3 days, 5 days, etc.). The tests include microbiological tests (total number of colonies, coliforms, etc.), sensory evaluation (appearance, odor, taste, etc.), and physical and chemical index tests (such as pH value, natto kinase activity, etc.).

[0042] 5. Take appropriate samples from the prepared traditional natto samples and natto soymilk samples, and place them in a refrigerated environment (0 - 5°C) for testing at regular intervals (such as 7 days, 14 days, 21 days, etc.).

[0043] 6. Take appropriate samples from the prepared traditional natto samples and natto soymilk samples, and place them in a frozen environment (-18°C) for testing at regular intervals (such as 30 days, 60 days, 90 days, 365 days, etc.). The test contents include microbiological tests, sensory evaluation, and detection of active ingredients, etc.

[0044] 7. According to the method of "Determination of Total Number of Colonies in Food Microbiology Examination" in the national standard GB4789.2 - 2016, conduct tests on the total number of colonies of samples stored for different periods of time.

[0045] Based on the above tests and relevant investigations, the following table is prepared: Performance indicators Comparative example 1 Example 1 Technical breakthrough points Nattokinase activity (FU / mL) 1500±200 2500±150 Liquid fermentation + temperature control for activity preservation, 67% increase in activity Odor sensory score (10 points) 7.5±0.5 2.5±0.3 67% reduction in odor Bitter taste threshold (mM) 0.05 (obvious) 0.5 (imperceptible) Degradation rate of bitter substances > 85% Normal temperature shelf life (days) 1 2-3 Low Aw + acid antibacterial, shelf life extended by 2 - 3 times Refrigerated shelf life (days) 7-10 30-45 Shelf life extended by 3 - 4 times Frozen shelf life (days) Cannot be frozen 365 Greatly extend the shelf life Peak total colony count <![CDATA[1×10 5 CFU / mL]]> 5×10³CFU / mL 95% reduction Number of consumption scenarios 3 (for meals, seasonings, side dishes) 8 (such as for immediate drinking, baking, meal replacement, etc.) Liquid state + function enhancement, scenario expansion by 2.7 times Through the detailed experimental data in the above table, the differences between the natto soymilk in Example 1 and traditional natto in various performance indicators are clearly shown, fully verifying that the natto soymilk in Example 1 can remove the bitterness and astringency in natto, making the prepared natto soymilk have a smooth texture, avoiding the problem of bacteria hidden in the gaps of soybeans in solid - state fermentation, reducing the contamination rate of miscellaneous bacteria, and the shelf life can be appropriately extended at room temperature (without adding preservatives), and the shelf life is greatly extended when stored in refrigeration / frozen conditions.

[0046] In addition, it should be noted that for the specific embodiments described in this specification, the names of their respective parts, etc. can be different. Any equivalent or simple changes made according to the structure, characteristics, and principles described in the inventive concept of this invention patent are included in the protection scope of this invention patent. Those skilled in the technical field to which this invention belongs can make various modifications, supplements, or use similar methods for substitution to the specific embodiments described, as long as they do not deviate from the structure of this invention or exceed the scope defined by this claim book, they should all belong to the protection scope of this invention.

Claims

1. A process for preparing natto soymilk, comprising the following steps: Step (1) preparing soybean milk: preparing soybean milk from soybeans, transferring the soybean milk to a first vacuum insulation tank, and cooling the soybean milk to 37° C.; Step (2) auxiliary material pretreatment: preparing sugar, thickener and clean water, placing the sugar, thickener and clean water into a second vacuum insulation tank, sterilizing the interior of the second vacuum insulation tank, stirring the sugar, thickener and clean water, and cooling to 37° C. to obtain a premixed auxiliary material liquid; Step (3) primary fermentation: the premixed auxiliary material liquid prepared in step (2) is aseptically transported to a first vacuum insulation tank through a pipeline, and Bacillus natto is added to the first vacuum insulation tank to perform primary fermentation; Features: In the step (3), after adding Bacillus natto, sterile air is introduced into the first vacuum insulation tank, and the soybean milk, the premixed auxiliary liquid and the Bacillus natto are stirred to make the Bacillus natto evenly distributed in the soybean milk, promote the full contact between the Bacillus natto and the soybean milk, and perform micro-pressure fermentation for 24 hours under a pressure condition of 0.05MPa-0.10MPa to obtain nattokinase; The method further comprises step (4) of secondary fermentation: cooling the nattokinase obtained in step (3) to 20°C-28°C, adding Mucor into the first vacuum insulation tank, stirring the nattokinase and Mucor, and performing micro-pressure fermentation for 24 hours under a pressure of 0.05MPa-0.10MPa to obtain natto soymilk.

2. The process for preparing natto milk according to claim 1, characterized in that: In the step (1), soybeans are washed, soaked, drained, ground, filtered, and steamed to obtain soybean milk, which is then aseptically transported to the first vacuum insulation tank through a pipeline.

3. The process for preparing natto milk according to claim 1, characterized in that: In the step (2), the interior of the second vacuum insulation tank is sterilized by high-temperature instantaneous sterilization or pasteurization.

4. The process for preparing natto milk according to claim 1, characterized in that: In the step (2), the sugar is sucrose.

5. The process for preparing natto milk according to claim 1, characterized in that: In the step (2), the thickener is one of xanthan gum, sodium carboxymethyl cellulose and sodium alginate.

6. The process for preparing natto milk according to claim 1, characterized in that: In the step (3), the outer wall of the first vacuum insulation tank is provided with an interlayer, and the interlayer is connected to a thermometer; warm water at 37° C. is introduced into the interlayer to perform temperature-controlled fermentation of the soybean milk, premixed auxiliary material liquid and natto Bacillus subtilis in the first vacuum insulation tank.

7. The process for preparing natto milk according to claim 6, characterized in that: In the step (4), cooling water or refrigerant is added to the interlayer to reduce the temperature of the nattokinase prepared in the step (3) from 37°C to 20°C-28°C, and the cooling rate is controlled within 1°C / min.

8. The process for preparing natto milk according to claim 7, characterized in that: In the step (4), the temperature of the cooling water is 15°C-20°C.

9. The process for preparing natto milk according to claim 7, characterized in that: In the step (4), the refrigerant is an ethylene glycol solution.

10. The process for preparing natto milk according to claim 1, characterized in that: In the step (4), the fermentation is carried out for 0-4 hours with low-speed stirring at a rotation speed of 50 rpm-80 rpm; stirring is stopped after 4 hours to 24 hours of fermentation to form a static fermentation environment.