Fermented bean curd rich in nattokinase and preparation method thereof

Abstract

The invention relates to the technical field of fermented bean products, in particular to fermented bean curd rich in nattokinase and a preparation method of the fermented bean curd. Comprising the following steps: carrying out strain activation and enlarged culture on bacillus natto, centrifuging, and removing supernatant to obtain a bacillus natto precipitate; uniformly mixing mucor and bacillus natto precipitates with sterile water in proportion to prepare a strain suspension; preparing a bean curd blank, spraying the strain suspension, and carrying out primary fermentation to obtain a bean curd blank; spreading table salt on the surface of the bean curd blank to pickle the bean curd blank to obtain a salted blank; preparing a soup base, inoculating the bacillus natto precipitate, fermenting, and preparing a fermented bean curd soup base; and putting the salt blank and the fermented bean curd soup base into a container, sealing, and carrying out post-fermentation under the condition of constant temperature, so as to obtain the fermented bean curd rich in nattokinase. The method has the advantages that the biological activity of the nattokinase in a salt environment is improved by a method of reducing the use amount of the salt and performing multiple fermentation on the bacillus natto; and a fermentation microbial enzyme system is enriched.

Description

Technical Field

[0001] The present invention relates to the technical field of fermented soy products, and particularly relates to a fermented bean curd rich in nattokinase and a preparation method thereof. Background Art

[0002] There are various varieties of fermented bean curd, such as red fermented bean curd, green fermented bean curd, white fermented bean curd, sauce fermented bean curd, and fancy fermented bean curd. It can be eaten alone or used to cook dishes with unique flavors. During the production process of traditional fermented bean curd, proteins in soybeans are fermented by microorganisms to produce amino acids and polypeptides. The activities of microorganisms also decompose anti-nutritional factors in soybeans and synthesize vitamin B group, which not only provides delicious taste, but also improves the digestibility and absorption rate of soy products and brings essential nutrients for the human body.

[0003] However, there are some technical problems in the production of fermented bean curd in the prior art. First of all, most traditional fermented bean curds use Mucor or Rhizopus alone as fermentation microorganisms, and use bioactive components such as proteases produced by them to degrade macromolecular substances to produce amino acids. Taking the common Actinomucor elegans as an example, the protease system produced by its metabolism is relatively single, and the small molecular substances obtained by decomposing soy protein contain a relatively large proportion of tyrosine and tyrosine short peptides, which will make the fermented bean curd produce bitterness and form white dot-like tyrosine crystals during the post-fermentation and shelf life stages, affecting the sensory quality of the product. Secondly, the fermented bean curd produced by traditional processes needs to be pickled with salt to achieve a certain degree of anti-corrosion effect. Eating too much fermented bean curd will lead to excessive salt intake and affect human health.

[0004] In addition to the typical nutritional components of fermented soy products, natto also contains a large amount of nattokinase, which can specifically dissolve fibrin, activate the human thrombolytic system, and at the same time inhibit blood coagulation and prevent bleeding, and can prevent cerebral thrombosis, assist in the treatment of thrombus sequelae, vasculitis and other diseases. Although natto has recognized health care effects, its special flavor (stink) and appearance (viscous, stringy) produced by fermentation cannot be accepted by the vast majority of people, which to a certain extent limits its wide circulation worldwide. In recent years, there have also been relevant studies hoping to add nattokinase to fermented bean curd to improve the economic value and utilization value of the product. However, it has been found through experiments that components such as salt in fermented bean curd will inhibit the activity of nattokinase. The nattokinase fermented bean curd produced by existing methods not only increases the production cost of the product, but also fails to achieve the purpose of increasing value and efficiency. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a fermented bean curd rich in nattokinase and a preparation method thereof.

[0006] The first object of the present invention is to provide a preparation method of a fermented bean curd rich in nattokinase, which specifically includes the following steps: S1. Activate the Bacillus natto strain. After activation, perform an enlarged culture using a liquid medium to obtain a Bacillus natto culture solution; centrifuge the Bacillus natto culture solution and remove the supernatant to obtain a Bacillus natto precipitate; S2. Mix the Mucor with the Bacillus natto precipitate in a certain proportion, and then fully mix the mixture with sterile water in a ratio of 1:200 - 800 to prepare a strain suspension; S3. Prepare the tofu blank; spray the strain suspension obtained in step S2 on the tofu blank for pre - fermentation; after fermentation, obtain a tofu blank with Mucor hyphae growing on it; S4. Sprinkle salt on the surface of the tofu blank and pickle the tofu blank in a food fermentation container. The weight of the salt accounts for 6 - 10% of the weight of the tofu blank, and the pickling time is 48 - 72 hours; after pickling, obtain a salted blank; S5. Prepare the soup stock, inoculate the Bacillus natto precipitate and ferment for 20 - 30 hours to obtain a fermented soup stock; mix the fermented soup stock, water and auxiliary liquid evenly to prepare the tofu - cheese soup stock; S6. Put the salted blank obtained in step S4 and the tofu - cheese soup stock fermented in step S5 into a container, seal it with a lid to obtain a semi - finished tofu - cheese product; perform post - fermentation on the semi - finished tofu - cheese product under constant temperature conditions to obtain the tofu - cheese rich in nattokinase.

[0007] Preferably, in step S2, the weight ratio of Mucor to the Bacillus natto precipitate is 1:0.2 - 15.

[0008] Preferably, the pre - fermentation conditions in step S3 are: temperature 26 - 28°C, relative humidity 70 - 95%, and fermentation time 22 - 60 hours.

[0009] Preferably, in step S4, the weight of the salt accounts for 6% of the weight of the tofu blank, and the pickling time is 72 hours; or the weight of the salt accounts for 10% of the weight of the tofu blank, and the pickling time is 48 hours.

[0010] Preferably, in step S5, the fermentation temperature is 30 - 45°C; the Bacillus natto precipitate accounts for 1 - 4% of the total dry matter in the soup stock.

[0011] Preferably, the soup stock includes drinking water, red yeast rice, rice cake and monosodium glutamate; the auxiliary liquid is edible alcohol, and the volume ratio of the fermented soup stock, water and edible alcohol is 28 - 30:27 - 29:12 - 14.

[0012] Preferably, the soup stock is the yellow slurry water at 35 - 45°C; the auxiliary liquid is the hair - like brine containing monosodium glutamate; the volume ratio of the fermented soup stock, water, hair - like brine and monosodium glutamate is 170 - 190:720 - 800:25 - 35:0.4 - 0.6.

[0013] Preferably, the mass ratio of the salted blank to the fermented bean curd soup in step S6 is 1:0.8 - 1.5; the post-fermentation conditions are: the fermentation temperature is 15 - 30°C, and the fermentation time is 1 - 3 months.

[0014] Preferably, the liquid medium is LB liquid medium; the mucor is Actinomucor elegans.

[0015] The second object of the present invention is to provide a fermented bean curd rich in nattokinase, which is prepared by using the preparation method of the fermented bean curd rich in nattokinase; the nattokinase activity in the fermented bean curd rich in nattokinase is greater than 1200 FU / g.

[0016] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) Enrich the enzyme system of fermenting microorganisms: The protease derived from Bacillus subtilis natto and the protease derived from mucor act on soybean protein together, optimize the amino acid ratio of the enzymatic hydrolysate, and achieve multiple purposes of enriching the sensory flavor, reducing bitter components, and reducing white spots (tyrosine crystals).

[0017] (2) Reduce the salt content of the fermented bean curd product: Natural antibacterial components such as bacitracin, 2,6-pyridinedicarboxylic acid, and polymyxin produced during the metabolism of Bacillus subtilis natto have an inhibitory effect on various harmful bacteria in the fermentation process, and can partially replace the antibacterial effect of salt, reducing the amount of salt used in the pickling process.

[0018] (3) Avoid the bad flavor and sensory experience brought by consumers' intake of nattokinase through eating natto foods: The product produced by the method of the present invention has the taste and appearance form of fermented bean curd. Bacillus subtilis natto is applied in the production of fermented bean curd. While utilizing nattokinase and other bioactive components, it will not produce the bad smell and bad appearance of traditional natto.

[0019] (4) Ensure the biological activity of nattokinase in the salt environment of the fermented bean curd product: By means of reducing the salt usage and multiple fermentations of Bacillus subtilis natto, it is ensured that the human body can intake highly active nattokinase by eating fermented bean curd. Description of the Drawings

[0020] Figure 1 is a flow chart of a preparation method of a fermented bean curd rich in nattokinase provided by the present invention.

[0021] Figure 2 is a graph of the sensory evaluation results of Example 1, Comparative Example 1, Comparative Example 3, and Comparative Example 5 of the present invention.

[0022] Figure 3 is a graph of the sensory evaluation results of Example 2, Comparative Example 2, Comparative Example 4, and Comparative Example 6 of the present invention. Detailed implementation manners

[0023] In the following, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are denoted by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, their detailed descriptions will not be repeated.

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation to the present invention.

[0025] The present invention provides a method for preparing fermented bean curd rich in nattokinase, which specifically includes the following steps: S1. Activate the Bacillus natto strain, and after activation, perform an enlarged culture with a liquid medium to obtain a Bacillus natto culture solution; centrifuge the Bacillus natto culture solution and remove the supernatant to obtain a Bacillus natto precipitate; Specifically, the liquid medium is an LB liquid medium.

[0026] S2. Prepare a strain suspension: mix the Mucor with the Bacillus natto precipitate in a ratio, and then fully mix the mixture with sterile water in a ratio of 1:200 - 800 to prepare a strain suspension; Specifically, the weight ratio of the Mucor to the Bacillus natto precipitate is 1:0.2 - 15; the Mucor is Mucor radians var. elegans, and the strain number is BNCC336125.

[0027] S3. Prepare a tofu blank; spray the strain suspension obtained in step S2 on the tofu blank for pre-fermentation; after the fermentation is completed, obtain a tofu blank with Mucor hyphae growing on it; Method for preparing tofu embryo: Wash the soybeans and soak them fully for 6 - 8 hours, grind them and filter to obtain soy milk; boil the soy milk, keep it warm at not less than 95°C, add a coagulant to curdle the soy milk to obtain bean curd; let the bean curd stand to remove water, and cut it into tofu blanks of uniform size after pressing.

[0028] Specifically, the pre-fermentation conditions are: temperature 26 - 28°C, relative humidity 70 - 95%, and fermentation time 22 - 60 hours.

[0029] S4. Sprinkle salt on the surface of the tofu blank, pickle the tofu blank in a food fermentation container, and obtain a salted blank after pickling; Specifically, the weight of the salt accounts for 6 - 10% of the weight of the tofu blank, and the pickling time is 48 - 72 hours.

[0030] S5. Prepare the soup base, inoculate it with the Bacillus natto precipitate and ferment for 20 - 30 hours to obtain the fermented soup base; mix the fermented soup base, water and the auxiliary liquid evenly to formulate the fermented bean curd soup base; the fermentation temperature is 30 - 45°C; the Bacillus natto precipitate accounts for 1 - 4% of the total dry matter in the soup base. Specifically, the soup base includes drinking water, red yeast rice, rice cake and monosodium glutamate; the auxiliary liquid is edible alcohol, and the volume ratio of the fermented soup base, water and edible alcohol is 28 - 30:27 - 29:12 - 14; in a specific embodiment, the mass ratio of drinking water, red yeast rice, rice cake and monosodium glutamate in the soup base is 200:14:80:0.3; the volume ratio of the fermented soup base, water and edible alcohol is 294.3:280:130; the Bacillus natto precipitate accounts for 3% of the total dry matter in the soup base. Specifically, the soup base is the yellow soybean milk at 35 - 45°C; the auxiliary liquid is the brine containing monosodium glutamate; the volume ratio of the fermented soup base, water, the brine containing monosodium glutamate and monosodium glutamate is 170 - 190:720 - 800:25 - 35:0.4 - 0.6; in a specific embodiment, the volume ratio of the fermented soup base, water, the brine containing monosodium glutamate and monosodium glutamate is 180:750:30:0.5.

[0031] S6. Load the salted blank obtained in step S4 and the fermented bean curd soup base obtained in step S5 into a container, seal it with a lid to obtain the semi-finished fermented bean curd; perform post-fermentation on the semi-finished fermented bean curd under constant temperature conditions to obtain the fermented bean curd rich in nattokinase. Specifically, the mass ratio of the salted blank and the fermented bean curd soup base is 1:0.8 - 1.5; the post-fermentation conditions are: the fermentation temperature is 15 - 30°C, and the fermentation time is 1 - 3 months.

[0032] Example 1 This example provides a method for preparing fermented bean curd rich in nattokinase, which specifically includes the following steps: S1. Activate the Bacillus natto strain, and after activation, perform enlarged cultivation with LB liquid medium to obtain the Bacillus natto culture solution; centrifuge the Bacillus natto culture solution (rotation speed 5000 rpm), remove the supernatant to obtain the Bacillus natto precipitate. S2. Prepare the strain suspension: mix the Mucor with the Bacillus natto precipitate in proportion, and then fully mix the mixture with sterile water at a ratio of 1:800 to make the strain suspension; the weight ratio of Mucor to the Bacillus natto precipitate is 1:15; the Mucor is Mucor radians var. elegans. S3. Prepare the bean curd blank; spray the strain suspension obtained in step S2 on the bean curd blank for pre-fermentation; after the fermentation is completed, obtain the bean curd blank with Mucor hyphae grown; control the pre-fermentation conditions as: temperature 28°C, relative humidity 95%, fermentation time 60 hours. S4. Sprinkle table salt on the surface of the tofu blank, and marinate it in 5 layers in a food turnover box. The total weight of table salt used in one box accounts for 6% of the weight of the tofu blank, and the marinating time is 72 hours. After marinating, a salted blank is obtained; S5. Prepare the soup stock by adding various substances in the mass ratio of drinking water, red yeast rice, flour cake, and monosodium glutamate of 200:14:80:0.3; inoculate the Bacillus natto precipitate in the soup stock, and the Bacillus natto precipitate accounts for 3% of the total dry matter in the soup stock; after inoculation, ferment at 40 °C for 24 hours to obtain the fermented soup stock; mix the fermented soup stock, water, and edible alcohol evenly in the volume ratio of 294.3:280:130 to prepare the fermented bean curd soup stock; S6. Bottle the salted blank obtained in step S4 and the fermented bean curd soup stock obtained in step S5 according to the mass ratio of 1:1.5, cover and seal to obtain the semi-finished fermented bean curd; carry out post-fermentation of the semi-finished fermented bean curd under the constant temperature condition of 30 °C for 2 months to obtain the fermented bean curd rich in nattokinase.

[0033] Example 2 This example provides a method for preparing fermented bean curd rich in nattokinase, which specifically includes the following steps: S1. Activate the Bacillus natto strain, and after activation, carry out enlarged culture with LB liquid medium to obtain the Bacillus natto culture solution; centrifuge the Bacillus natto culture solution (rotation speed 5000 rpm), remove the supernatant to obtain the Bacillus natto precipitate; S2. Prepare the strain suspension: mix the Mucor with the Bacillus natto precipitate in proportion, and then fully mix the mixture with sterile water in a ratio of 1:200 to make the strain suspension; the weight ratio of Mucor to the Bacillus natto precipitate is 1:0.2; the Mucor is Mucor radians var. elegans; S3. Prepare the tofu blank; spray the strain suspension obtained in step S2 on the tofu blank for pre-fermentation; after fermentation is completed, a tofu blank with Mucor hyphae is obtained; control the pre-fermentation conditions as: temperature 26 °C, relative humidity 70%, and fermentation time 22 hours; S4. Sprinkle table salt on the surface of the tofu blank, and marinate it in 5 layers in a food turnover box. The total weight of table salt used in one box accounts for 10% of the weight of the tofu blank, and the marinating time is 48 hours. After marinating, a salted blank is obtained; S5. Use the yellow soybean milk at 40 °C as the soup stock; inoculate the Bacillus natto precipitate in the soup stock, and the Bacillus natto precipitate accounts for 1% of the total dry matter in the soup stock; after inoculation, ferment at 40 °C for 24 hours to obtain the fermented soup stock; mix the fermented soup stock, water, maohua brine, and monosodium glutamate evenly in the volume ratio of 180:750:30:0.5 to prepare the fermented bean curd soup stock; S6. Bottles are filled with the salt blanks obtained in step S4 and the fermented fermented bean curd soup stock from step S5 according to a mass ratio of 1:0.8, sealed with a lid, and a semi-finished product of fermented bean curd is obtained; the semi-finished product of fermented bean curd is post-fermented for 2 months under a constant temperature condition with a fermentation temperature of 20 °C to obtain fermented bean curd rich in nattokinase.

[0034] Comparative Example 1 This comparative example provides a method for preparing red fermented bean curd in which Bacillus natto participates in the fermentation process. Among them: in step S2, only Mucor is used to make a strain suspension, and Bacillus natto is not used; the remaining preparation steps are the same as in Example 1.

[0035] Comparative Example 2 This comparative example provides a method for preparing green fermented bean curd in which Bacillus natto participates in the fermentation process. Among them: in step S2, only Mucor is used to make a strain suspension, and Bacillus natto is not used; the remaining preparation steps are the same as in Example 2.

[0036] Comparative Example 3 This comparative example provides a method for preparing red fermented bean curd in which Bacillus natto participates in the fermentation process. Among them: in step S5, the prepared soup stock is not inoculated with Bacillus natto and is not fermented by Bacillus natto; then the soup stock, water and edible alcohol are mixed evenly according to a volume ratio of 294.3:280:130 to prepare the fermented bean curd soup stock; the remaining preparation steps are the same as in Example 1.

[0037] Comparative Example 4 This comparative example provides a method for preparing green fermented bean curd in which Bacillus natto participates in the fermentation process. Among them: in step S5, the yellow slurry water is not fermented by Bacillus natto, and the yellow slurry water, water, mao hua brine and monosodium glutamate are directly mixed evenly according to a volume ratio of 180:750:30:0.5 to prepare the fermented bean curd soup stock; the remaining preparation steps are the same as in Example 2.

[0038] Comparative Example 5 This comparative example provides a common red fermented bean curd: 300g of red fermented bean curd of the commercially available Zhu Laoliu brand.

[0039] Comparative Example 6 This comparative example provides a common green fermented bean curd: 300g of green fermented bean curd of the commercially available Zhu Laoliu brand.

[0040] The physical and chemical indexes of the fermented bean curd in Examples 1-2 and Comparative Examples 1-6 are measured and sensory evaluations are carried out. Take the fermented bean curd samples of each group, compare the nattokinase activity and the free amino acid content, conduct sensory scoring on each sample, and comprehensively evaluate each group of samples.

[0041] I. Comparison of Nattokinase Activity The nattokinase in each group of samples reacts with fibrin to hydrolyze the peptide bonds of fibrin. The hydrolysis reaction causes the absorbance of the solution to change at 275 nm of ultraviolet light. The change in absorbance before and after the hydrolysis reaction was measured by an ultraviolet spectrophotometer, and the activity of nattokinase was indirectly obtained by conversion, and the unit is expressed in FU. One activity unit (1 FU) refers to the amount of enzyme consumed when the absorbance value increases by 0.01 at 275nm. The activity of nattokinase was determined by referring to the ultraviolet spectrophotometry method in DBS44 / 013-2019, and the test results are shown in Table 1.

[0042] Table 1 Comparison of nattokinase activity of samples in each group

[0043] As can be seen from Table 1, the nattokinase activity of the samples in Example 1 and Example 2 is significantly higher than that of other groups, which shows that the method of using Bacillus natto and performing multiple fermentations can significantly increase the nattokinase content in fermented bean curd. Except for Comparative Examples 5 and 6 in Table 1 (ND means not detected), nattokinase activity can be detected in all samples, which shows that reducing the amount of salt used in the production process of fermented bean curd has a significant effect on protecting the nattokinase activity.

[0044] 2. Amino Acid Analysis The free amino acids in the test product were 6-aminoquinoline- N -Hydroxysuccinimidyl carbamate was derivatized to generate fluorescent derivatives, which were separated by liquid chromatography and determined by fluorescence detector. The retention time was used for qualitative analysis and the external standard working curve method was used for quantitative analysis. The free amino acid level was determined by high performance liquid chromatography (method 2) in GB / T 30987-2020. The test results are shown in Table 2.

[0045] Table 2 Comparison of free amino acid content in each group of samples

[0046]

[0047] As can be seen from Table 2, the bitter amino acid levels of the samples in Example 1 and Example 2 are significantly lower than those in other groups, and the umami amino acid levels are significantly higher than those in other groups. This indicates that the use of the natto Bacillus subtilis multiple fermentation process combined with the combined action of the dual-bacteria enzyme system can significantly optimize the free amino acid level of fermented bean curd products, reduce bitterness, and enhance umami taste.

[0048] 3. Sensory Evaluation 1. Sensory evaluation was performed on Example 1, Comparative Example 1, Comparative Example 3 and Comparative Example 5 of the present invention; the sensory scoring criteria are shown in Table 3 below.

[0049] Table 3 Sensory scoring criteria for red fermented bean curd

[0050] The sensory evaluation results are shown in Figure 2 . It can be seen from the figure that among the four samples, the area enclosed by the radar chart of Example 1 is relatively complete, indicating that the evaluation result of Example 1 is the best, with the best evaluations in terms of appearance, taste, etc., and Comparative Example 1 ranks second. The shape of the radar chart of Comparative Example 5 is irregular and small, and it has the worst evaluation result among the four samples.

[0051] 2. Conduct sensory evaluations on Example 2, Comparative Example 2, Comparative Example 4, and Comparative Example 6 of the present invention; the sensory scoring criteria are shown in Table 4 below.

[0052] Table 4 Sensory Scoring Criteria for Blue Moldy Tofu

[0053] The sensory evaluation results are shown in Figure 3 . It can be seen from the figure that among the four samples, the area enclosed by the radar chart of Example 2 is relatively complete, indicating that the evaluation result of Example 2 is the best, with the best evaluations in terms of appearance, taste, etc. The shape of the radar chart of Comparative Example 4 is irregular and small, and it has a relatively poor evaluation result among the four samples.

[0054] For the experimental methods involved in the above examples, unless otherwise specifically mentioned, they are all conventional methods in the art. For example, they can refer to the relevant national standards and regulations or recommended conditions in the art. For the experimental materials and reagents involved in the above examples, unless otherwise specified, they can all be obtained from regular commercial channels.

[0055] It should be understood that various forms of the processes shown above can be used, reordering, adding or deleting steps. For example, the steps recorded in the disclosure of the present invention can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present invention can be achieved, and no limitations are imposed herein.

[0056] The above specific embodiments do not constitute a limitation to the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub - combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing fermented bean curd rich in nattokinase, characterized in that, Specifically, it includes the following steps: S1. Activate the Bacillus natto strain, and after activation, perform enlarged culture with a liquid medium to obtain a Bacillus natto culture solution; centrifuge the Bacillus natto culture solution and remove the supernatant to obtain a Bacillus natto precipitate; S2. Mix the Mucor with the Bacillus natto precipitate in a certain proportion, and then fully mix the mixture with sterile water in a ratio of 1:200 - 800 to prepare a strain suspension; S3. Prepare the tofu blank; spray the strain suspension obtained in step S2 on the tofu blank for pre-fermentation; after fermentation, obtain a tofu blank with Mucor hyphae grown on it; S4. Sprinkle salt on the surface of the tofu blank and pickle the tofu blank in a food fermentation container. The weight of the salt accounts for 6 - 10% of the weight of the tofu blank, and the pickling time is 48 - 72 hours; after pickling, obtain a salted blank; S5. Prepare the soup stock, inoculate the Bacillus natto precipitate and ferment for 20 - 30 hours to obtain a fermented soup stock; mix the fermented soup stock, water and auxiliary liquid evenly to prepare the tofu curd soup stock; S6. Put the salted blank obtained in step S4 and the tofu curd soup stock fermented in step S5 into a container, seal it with a lid to obtain a semi-finished tofu curd; perform post-fermentation on the semi-finished tofu curd under constant temperature conditions to obtain the tofu curd rich in nattokinase.

2. The preparation method of a fermented bean curd rich in nattokinase according to claim 1, characterized in that: In step S2, the weight ratio of Mucor to the Bacillus natto precipitate is 1:0.2 - 15.

3. The preparation method of a fermented bean curd rich in nattokinase according to claim 1, characterized in that: The pre-fermentation conditions in step S3 are: temperature 26 - 28 °C, relative humidity 70 - 95%, and fermentation time 22 - 60 hours.

4. The preparation method of a fermented bean curd rich in nattokinase according to claim 1, characterized in that: In step S4, the weight of the salt accounts for 6% of the weight of the tofu blank, and the pickling time is 72 hours; or the weight of the salt accounts for 10% of the weight of the tofu blank, and the pickling time is 48 hours.

5. The preparation method of a fermented bean curd rich in nattokinase according to claim 1, characterized in that: In step S5, the fermentation temperature is 30 - 45 °C; the Bacillus natto precipitate accounts for 1 - 4% of the total dry matter in the soup stock.

6. The preparation method of a fermented bean curd rich in nattokinase according to claim 5, characterized in that: The soup stock includes drinking water, red yeast rice, rice cake and monosodium glutamate; the auxiliary liquid is edible alcohol, and the volume ratio of the fermented soup stock, water and edible alcohol is 28 - 30:27 - 29:12 - 14.

7. The preparation method of a fermented bean curd rich in nattokinase according to claim 5, characterized in that: The soup stock is yellow slurry water at 35 - 45 °C; the auxiliary liquid is hairy flower brine containing monosodium glutamate; the volume ratio of the fermented soup stock, water, hairy flower brine and monosodium glutamate is 170 - 190:720 - 800:25 - 35:0.4 - 0.

6.

8. A method for preparing fermented bean curd rich in nattokinase according to claim 1, characterized in that: In step S6, the mass ratio of the salted blank to the tofu curd soup stock is 1:0.8 - 1.5; the post-fermentation conditions are: fermentation temperature 15 - 30 °C, and fermentation time 1 - 3 months.

9. A method for preparing a fermented bean curd rich in nattokinase according to any one of claims 1-8, characterized in that: The liquid medium is LB liquid medium; the Mucor is Actinomucor elegans.

10. A fermented bean curd rich in nattokinase, characterized in that: Prepared by using the preparation method of a kind of tofu curd rich in nattokinase described in any one of claims 1 - 9; the nattokinase activity in the tofu curd rich in nattokinase is greater than 1200 FU / g.

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