Method for increasing content of amino nitrogen in soybean paste through bacteria-enzyme synergy and temperature-controlled fermentation

Abstract

The invention discloses a method for increasing the content of amino nitrogen in soybean paste through bacteria-enzyme synergy and temperature-controlled fermentation, which comprises the following steps: performing superheated steam treatment on flour, soaking soybeans, and steaming; aspergillus oryzae is used as a leavening agent and is inoculated into steamed flour for fermentation, and finished koji is prepared; uniformly mixing the finished koji with a compound enzyme agent, steamed soybeans and saline water to obtain sauce mash, and performing temperature-controlled fermentation on the sauce mash in three stages. The content of amino acid nitrogen in the prepared soybean paste is 0.50-0.72 g / 100g. The method is simple and convenient to operate, the amino acid nitrogen content of the soybean paste can be remarkably increased, the flavor is improved, and wide application and popularization prospects are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of food processing, and particularly relates to a method for improving the amino nitrogen content of miso through the synergistic action of bacteria and enzymes and temperature-controlled fermentation. Background Art

[0002] The fermentation of traditional miso usually includes two parts: koji making and fermentation. Since microorganisms mainly rely on the fermentation environment and the expansion culture of dominant strains cannot be achieved, the fermentation period is relatively long and the ripening speed is slow, usually taking 2 - 3 months. At present, in production, the combination of inoculating a fermentation agent and heat preservation fermentation can improve the fermentation rate of miso, shorten the fermentation time, and reduce production costs. However, the amino acid nitrogen content in the miso fermented by this method is relatively low, affecting the nutritional quality of miso products, and the flavor is relatively thin and lacks mellowness.

[0003] Although in the reported published literature, it is found that the patent "A Fermentation Process and Preparation Method of Soybean Paste with High Amino Acid Content" with the publication number CN117837744A discloses a fermentation process of soybean paste, which improves the contents of threonine, serine, glycine, alanine, and proline in soybean paste by using a low-temperature long-time fermentation process, but this method cannot be applied to the rapid fermentation of miso. The patent "A Method for Improving the Amino Acid Nitrogen Content of Broad Bean Paste" with the publication number CN107259367A uses the expansion culture of koji seeds to increase the number of dominant microorganisms in the fermentation process and thus improve the amino acid nitrogen content in broad beans. However, the steps of koji essence expansion culture in this method are relatively cumbersome and require high-pressure sterilization, making it difficult to apply in industrial production. Summary of the Invention

[0004] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this part, as well as in the abstract and title of the specification of this application, to avoid obscuring the purpose of this part, the abstract, and the title. However, such simplifications or omissions cannot be used to limit the scope of the present invention.

[0005] In view of the above and / or problems existing in the prior art, the present invention is proposed.

[0006] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for improving the amino nitrogen content of miso through the synergistic action of bacteria and enzymes and temperature-controlled fermentation.

[0007] To solve the above technical problems, the present invention provides the following technical solution: A method for improving the amino nitrogen content of miso through the synergistic action of bacteria and enzymes and temperature-controlled fermentation, characterized by including:

[0008] Treating flour with superheated steam, soaking and steaming soybeans;

[0009] Using Aspergillus oryzae as a starter culture, inoculate it into the steamed flour and ferment to obtain the koji.

[0010] Mix the koji, complex enzyme preparation, steamed soybeans, and brine evenly to obtain the sauce mash, and ferment the sauce mash in three stages.

[0011] As a preferred embodiment of the method of the present invention, wherein: the temperature of the overheated steam treatment of the flour is 120-180°C, and the treatment time is 150-250 s; when the soybeans are soaked, the mass ratio of soybeans to water is 1:2, and the soaking time is 15-21 h.

[0012] As a preferred embodiment of the method of the present invention, wherein: the addition amount of Aspergillus oryzae is 0.03%-0.05% of the mass of the flour after overheated steam treatment.

[0013] As a preferred embodiment of the method of the present invention, wherein: the mass ratio of the koji to the steamed soybeans is 10:1-5.

[0014] As a preferred embodiment of the method of the present invention, wherein: the complex enzyme preparation includes one or several of lipase, protease, and amylase.

[0015] As a preferred embodiment of the method of the present invention, wherein: the mass ratio of lipase, protease, and amylase is 1:1-3:1-3; the total addition amount of the complex enzyme preparation is 0.2%-0.8% of the total mass of the sauce mash.

[0016] As a preferred embodiment of the method of the present invention, wherein: the three-stage fermentation is respectively the first stage: the temperature is 32-35°C, and the fermentation is 5-7 days; the second stage: the temperature is 28-30°C, and the fermentation is 3-5 days; the third stage: the temperature is 38-42°C, and the fermentation is 10-16 days.

[0017] Another object of the present invention is to overcome the deficiencies in the prior art and provide a high amino nitrogen content miso prepared by a method for increasing the amino nitrogen content of miso through fermentation.

[0018] As a preferred embodiment of the miso of the present invention, wherein: the amino acid nitrogen content of the miso is 0.50-0.72 g / 100 g.

[0019] Advantages of the present invention:

[0020] (1) The present invention improves the content of amino acid nitrogen in miso through a method of combining bacteria and enzymes with stage-controlled temperature fermentation. Specifically: during the fermentation process, protease and amylase act synergistically to effectively decompose nutrients such as proteins and carbohydrates in flour and cooked soybeans, thereby promoting the growth of fermenting microorganisms such as Aspergillus oryzae. In the first stage, an appropriate fermentation temperature helps the formation of Aspergillus oryzae spores, further enhancing the growth advantage of Aspergillus oryzae; in the second stage, the fermentation temperature is conducive to the secretion of protease by Aspergillus oryzae, thus increasing the content of protease in the fermentation system; in the third stage, the fermentation temperature is suitable for the rapid action of protease, significantly increasing the content of amino acid nitrogen and other flavor substances. By adopting this process of combining bacteria and enzymes with stage-controlled temperature fermentation, compared with the control group (without using the process of combining bacteria and enzymes or stage-controlled temperature fermentation), the content of amino acid nitrogen in miso has increased by 25.97% - 135.43%.

[0021] (2) The present invention utilizes the growth characteristics of Aspergillus oryzae and the action characteristics of protease to design and prepare a stage-controlled temperature miso fermentation technology, achieving an increase in the content of amino acid nitrogen in miso.

[0022] (3) The process involved in the present invention is simple, and the additives are green and clean, having broad application and promotion prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. Among them:

[0024] Figure 1 is the flow chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the following will provide a detailed description of the specific embodiments of the present invention in conjunction with the embodiments of the specification.

[0026] Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar promotions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0027] Second, the "one embodiment" or "embodiment" mentioned herein refers to specific features, structures, or characteristics that may be included in at least one implementation manner of the present invention. The "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0028] In the embodiments of the present invention, the raw materials used are all commercially available unless otherwise specified. For details, see Table 1.

[0029] Table 1 Raw materials used in the embodiments

[0030] Name Commercial sales channels Article number Soybean JD.com 100081230377 Flour JD.com 100006026428 Salt JD.com 100021329022

[0031] Example 1

[0032] (1) Pretreatment of raw materials: The flour is treated with superheated steam at a treatment temperature of 150 °C for a treatment time of 200 s. The soybeans are soaked in water with a volume ratio of soybeans to water of 1:2 for 18 h.

[0033] (2) Koji making: Aspergillus oryzae with a final concentration of 1.0×10 6 spores / g of flour is inoculated into the flour treated with superheated steam and cultured at 37 °C for 36 h to obtain mature koji.

[0034] (3) Mash preparation: The soaked soybeans, mature koji, and brine are mixed evenly. The mass ratio of the soaked soybeans to the koji is required to be 10:3, and the salt content of the mixed material is required to be 10.0 g / 100 g.

[0035] (4) Fermentation is carried out in three stages: The first stage: Ferment at 32 °C for 5 days; The second stage: Ferment at 28 °C for 5 days, and the third stage: Ferment at 38 °C for 10 days.

[0036] Example 2

[0037] The difference from Example 1 is that in step (4), the first stage: Ferment at 34 °C for 5 days; The second stage: Ferment at 30 °C for 5 days, and the third stage: Ferment at 40 °C for 10 days.

[0038] Example 3

[0039] (1) Pretreatment of raw materials: The flour is treated with superheated steam at a treatment temperature of 150 °C for a treatment time of 200 s. The soybeans are soaked in water with a volume ratio of soybeans to water of 1:2 for 18 h.

[0040] (2) Koji making: Aspergillus oryzae with a final concentration of 1.0×10 6 spores / g of flour is inoculated into the flour treated with superheated steam and cultured at 37 °C for 36 h to obtain mature koji.

[0041] (3) Making fermented soybean paste: Mix the soaked soybeans, the mature koji, and brine evenly. The mass ratio of the soaked soybeans to the mature koji is required to be 10:3, and the salt content of the mixed material is required to be 10.0 g / 100 g;

[0042] Add the compound enzyme preparation to the fermented soybean paste. Among them, the addition ratio of the compound enzyme preparation is 0.5% of the mass of the fermented soybean paste, and the ratio of lipase: protease: amylase is 1:1:3;

[0043] (4) Fermentation is carried out in three stages:

[0044] The first stage: Ferment at 32 °C for 5 days; the second stage: Ferment at 28 °C for 5 days, and the third stage: Ferment at 38 °C for 10 days.

[0045] Example 4

[0046] (1) Pretreatment of raw materials: Treat the flour with superheated steam at a treatment temperature of 150 °C for a treatment time of 200 s. Soak the soybeans in water with a volume ratio of soybeans to water of 1:2 for 18 h;

[0047] (2) Koji making: Inoculate Aspergillus oryzae with a final concentration of 1.0×10 6 spores / g of flour into the flour treated with superheated steam and culture it at 37 °C for 36 h to obtain mature koji;

[0048] (3) Making fermented soybean paste: Mix the soaked soybeans, the mature koji, and brine evenly. The mass ratio of the soaked soybeans to the koji is required to be 10:3, and the salt content of the mixed material is required to be 10.0 g / 100 g;

[0049] Add the compound enzyme preparation to the fermented soybean paste. Among them, the addition ratio of the compound enzyme preparation is 0.5% of the mass of the fermented soybean paste, and the ratio of lipase: protease: amylase is 1:2:2;

[0050] (4) Fermentation is carried out in three stages:

[0051] The first stage: Ferment at 32 °C for 5 days; the second stage: Ferment at 28 °C for 5 days, and the third stage: Ferment at 38 °C for 10 days.

[0052] Example 5

[0053] (1) Pretreatment of raw materials: Treat the flour with superheated steam at a treatment temperature of 150 °C for a treatment time of 200 s. Soak the soybeans in water with a volume ratio of soybeans to water of 1:2 for 18 h;

[0054] (2) Koji making: Inoculate Aspergillus oryzae with a final concentration of 1.0×10 6 spores / g of flour into the flour treated with superheated steam and culture it at 37 °C for 36 h to obtain mature koji;

[0055] (3) Mash preparation: Mix the soaked soybeans, the mature koji, and brine evenly. The mass ratio of the soaked soybeans to the mature koji is required to be 10:3, and the salt content of the mixed material is required to be 10.0 g / 100 g.

[0056] Add the compound enzyme preparation to the mash. Among them, the addition ratio of the compound enzyme preparation is 0.5% of the mass of the mash, and the ratio of lipase: protease: amylase is 1:3:1.

[0057] (4) Fermentation is carried out in three stages:

[0058] The first stage: Ferment at 32 °C for 5 days; the second stage: Ferment at 28 °C for 5 days, and the third stage: Ferment at 38 °C for 10 days.

[0059] Example 6

[0060] (1) Pretreatment of raw materials: Treat the flour with superheated steam at a treatment temperature of 150 °C and a treatment time of 200 s. Soak the soybeans in water with a volume ratio of soybeans to water of 1:2 for 18 h.

[0061] (2) Koji making: Inoculate Aspergillus oryzae with a final concentration of 1.0×10 6 spores / g of flour into the flour treated with superheated steam, and culture it at 37 °C for 36 h to obtain mature koji.

[0062] (3) Mash preparation: Mix the soaked soybeans, the mature koji, and brine evenly. The mass ratio of the soaked soybeans to the mature koji is required to be 10:3, and the salt content of the mixed material is required to be 10.0 g / 100 g.

[0063] Add the compound enzyme preparation to the mash. Among them, the addition ratio of the compound enzyme preparation is 0.5% of the mass of the mash, and the ratio of lipase: protease: amylase is 1:2:2.

[0064] (4) Ferment at 37 °C for 20 days.

[0065] Example 7

[0066] (1) Pretreatment of raw materials: Treat the flour with superheated steam at a treatment temperature of 150 °C and a treatment time of 200 s. Soak the soybeans in water with a volume ratio of soybeans to water of 1:2 for 18 h.

[0067] (2) Koji making: Inoculate Aspergillus oryzae with a final concentration of 1.0×10 6 spores / g of flour into the flour treated with superheated steam, and culture it at 37 °C for 36 h to obtain mature koji.

[0068] (3) Mash preparation: Mix the soaked soybeans, koji, and brine evenly. The mass ratio of the soaked soybeans to the mature koji is required to be 10:3, and the salt content of the mixed material is required to be 10.0 g / 100 g;

[0069] Add the compound enzyme preparation to the mash. Among them, the addition ratio of the compound enzyme preparation is 0.5% of the mass of the mash, and the ratio of lipase: protease: amylase is 1:1:3;

[0070] (4) Incubate at 37 °C for 20 days.

[0071] Example 8

[0072] (1) Pretreatment of raw materials: Treat the flour with superheated steam at a treatment temperature of 150 °C for a treatment time of 200 s. Soak the soybeans in water with a volume ratio of soybeans to water of 1:2 for 18 h;

[0073] (2) Koji making: Inoculate Aspergillus oryzae with a final concentration of 1.0×10 6 spores / g of flour into the flour treated with superheated steam and incubate at 37 °C for 36 h to obtain mature koji;

[0074] (3) Mash preparation: Mix the soaked soybeans, mature koji, and brine evenly. The mass ratio of the soaked soybeans to the mature koji is required to be 10:3, and the salt content of the mixed material is required to be 10.0 g / 100 g;

[0075] Add the compound enzyme preparation to the mash. Among them, the addition ratio of the enzyme preparation is 0.5% of the mass of the mash, and the ratio of lipase: protease: amylase is 1:3:1;

[0076] (4) Incubate at 37 °C for 20 days.

[0077] Comparative Example 1

[0078] (1) Pretreatment of raw materials: Treat the flour with superheated steam at a treatment temperature of 150 °C for a treatment time of 200 s. Soak the soybeans in water with a volume ratio of soybeans to water of 1:2 for 18 h;

[0079] (2) Koji making: Inoculate Aspergillus oryzae with a final concentration of 1.0×10 6 spores / g of flour into the flour treated with superheated steam and incubate at 37 °C for 36 h to obtain mature koji;

[0080] (3) Mash preparation: Mix the soaked soybeans, koji, and brine evenly. The mass ratio of the soaked soybeans to the koji is required to be 10:3, and the salt content of the mixed material is required to be 10.0 g / 100 g;

[0081] (4) Incubate at 38 °C for 20 days.

[0082] Comparative Example 2

[0083] (1) Pretreatment of raw materials: The flour was treated with superheated steam at a treatment temperature of 150 °C and a treatment time of 200 s. The soybeans were soaked in water with a volume ratio of soybeans to water of 1:2 for 18 h.

[0084] (2) Koji making: Aspergillus oryzae with a final concentration of 1.0×10 6 spores / g of flour was inoculated into the flour treated with superheated steam and cultured at 37 °C for 36 h to obtain mature koji.

[0085] (3) Making of soybean paste mash: The soaked soybeans, koji and brine were mixed evenly. The mass ratio of the soaked soybeans to koji was required to be 10:3, and the salt content of the mixed material was required to be 10.0 g / 100 g.

[0086] (4) Fermentation was carried out at 28 °C for 20 days.

[0087] Comparative Example 3

[0088] (1) Pretreatment of raw materials: The flour was treated with superheated steam at a treatment temperature of 150 °C and a treatment time of 200 s. The soybeans were soaked in water with a volume ratio of soybeans to water of 1:2 for 18 h.

[0089] (2) Koji making: Aspergillus oryzae with a final concentration of 1.0×10 6 spores / g of flour was inoculated into the flour treated with superheated steam and cultured at 37 °C for 36 h to obtain mature koji.

[0090] (3) Making of soybean paste mash: The soaked soybeans, koji and brine were mixed evenly. The mass ratio of the soaked soybeans to koji was required to be 10:3, and the salt content of the mixed material was required to be 10.0 g / 100 g.

[0091] (4) Fermentation was carried out at 37 °C for 20 days.

[0092] Method for determining the amino acid nitrogen content of soybean paste: Weigh 6.0 g of the sample and grind it until there are no particles. Weigh about 5.0 g of the sample, denoted as m g, and make up the volume to 100 mL and filter. Take 10 mL of the filtrate and add 60 mL of water. Adjust the pH to 8.2 with 0.05 mol / L sodium hydroxide solution, add 10.0 mL of formaldehyde aqueous solution, and titrate with 0.05 mol / L sodium hydroxide standard solution until the pH is 9.2, and record the volume of sodium hydroxide solution consumed as V1. Take 80 mL of water, adjust the pH to 8.2 with 0.05 mol / L sodium hydroxide solution, add 10.0 mL of formaldehyde aqueous solution, and titrate with 0.05 mol / L sodium hydroxide standard solution until the pH is 9.2, and record the volume of sodium hydroxide solution consumed as V2.

[0093] Content of amino acid nitrogen (g / 100g) = ((V1 - V2) × 0.05 × 0.014) / (m × 10 / 100) × 100

[0094] The content of amino acid nitrogen in the miso added with protease is shown in Table 1.

[0095] The miso of Examples 1 - 13 and Comparative Examples 1 - 2 (control group) was determined for the content of amino acid nitrogen:

[0096] Table 2 Effects of enzyme - bacterium synergy and stage - controlled temperature fermentation on the content of amino acid nitrogen in miso

[0097]

[0098]

[0099] As shown in Table 2, the content of amino acid nitrogen in Comparative Example 1 without adding enzyme agent or without stage - controlled temperature fermentation was 0.39 g / 100g, the content of amino acid nitrogen in Comparative Example 2 was 0.31 g / 100g, and the content of amino acid nitrogen in Comparative Example 3 was 0.38 g / 100g. The contents of amino acid nitrogen in Examples 1 - 8 were all higher than those in Comparative Examples 1 - 3, and the content of amino acid nitrogen increased by 30% - 90% compared with Comparative Example 3. This result indicates that the addition of enzyme agent or stage - controlled temperature fermentation technology can increase the content of amino acid nitrogen in miso; in addition, the contents of amino acid nitrogen in Examples 1 - 2 increased by 25% and 37% respectively compared with Comparative Example 1, and increased by 61% and 76% respectively compared with Comparative Example 2. This result indicates that the stage - controlled temperature fermentation technology can increase the content of amino acid nitrogen in miso; the contents of amino acid nitrogen in Examples 3 - 5 increased by 73% - 83% compared with Comparative Example 1, increased by 122% - 135% compared with Comparative Example 2, and increased by 79% - 90% compared with Comparative Example 3. This result indicates that the addition of enzyme agent can increase the content of amino acid nitrogen in miso; the contents of amino acid nitrogen in Examples 6 - 8 increased by 57% - 73% compared with Comparative Example 3. This result indicates that the addition of enzyme agent can increase the content of amino acid nitrogen in miso; particularly, the contents of amino acid nitrogen in Examples 3 - 5 were higher than those in Examples 1 - 2 and Examples 6 - 8. This result indicates that the combination of enzyme agent and stage - controlled temperature fermentation technology has a more significant promoting effect on the content of amino acid nitrogen in miso.

[0100] Refer to "GB 4789.15 - 2016 National Food Safety Standard Food Microbiology Examination - Enumeration of Molds and Yeasts" to count the molds in the koji of Examples 1 - 8 and Comparative Examples 1 - 3 (control group).

[0101] The number of molds in the miso added with enzyme agents or fermented with stage temperature control is shown in Table 3.

[0102] Table 3 Effects of enzyme-microbe synergy and stage temperature control fermentation on the number of molds in koji

[0103]

[0104]

[0105] As shown in Table 3, in Comparative Example 1 without added enzyme agents or stage temperature control fermentation, the number of molds is 4.87×10 6 CFU / g, in Comparative Example 2 the number of molds is 4.92×10 6 CFU / g, and in Comparative Example 3 the number of molds is 4.35×10 6 CFU / g. The number of molds in Examples 1 - 8 is higher than that in Comparative Examples 1 - 3. This result indicates that the addition of enzyme agents or the stage temperature control fermentation technology can promote the growth of molds during fermentation; in addition, the number of molds in Examples 1 - 2 is 68% and 73% higher than that in Comparative Example 1, 67% and 71% higher than that in Comparative Example 2, and 89% and 94% higher than that in Comparative Example 3. This result shows that the stage temperature control fermentation technology can promote the growth of molds during miso fermentation; the number of molds in Examples 3 - 5 is 347% - 604% higher than that in Comparative Example 1, 343% - 597% higher than that in Comparative Example 2, and 401% - 688% higher than that in Comparative Example 3. This result shows that the addition of enzyme agents promotes the growth of molds during miso fermentation; the number of molds in Examples 6 - 8 is 91% - 318% higher than that in Comparative Example 3. This result shows that the addition of enzyme agents promotes the growth of molds during miso fermentation;

[0106] In summary, the above results all prove that in the composite enzyme agent, lipase: protease: amylase is 1:3:1 and the fermentation process of fermenting at 32°C for 5 days, 28°C for 5 days, and 38°C for 10 days can increase the content of amino acid nitrogen in miso. The above results all prove that the method of enzyme-microbe synergy combined with stage temperature control fermentation can increase the content of amino acid nitrogen in miso. Based on the characteristics of Aspergillus oryzae fermenting agent, the present invention promotes the growth of Aspergillus oryzae by the method of enzyme-microbe synergy. At the same time, based on the optimal action conditions of protease, the stage temperature control fermentation promotes the exertion of protease action. The prepared miso has a high content of amino acid nitrogen, a simple process, and has broad application and promotion prospects.

[0107] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the present invention.

Claims

1. A method for increasing the amino nitrogen content of soybean paste by bacterial enzyme synergy and temperature-controlled fermentation, characterized in that: The method comprises the following steps: treating flour with superheated steam, soaking and steaming soybeans; using Aspergillus oryzae as a fermentation agent and inoculating it into the steamed flour for fermentation to obtain finished koji; uniformly mixing the finished koji with a complex enzyme, steamed soybeans and salt water to obtain a sauce mash, and fermenting the sauce mash in three stages.

2. The method according to claim 1, characterized in that: The temperature of the flour superheated steam treatment is 120-180° C., and the treatment time is 150-250 seconds. The mass ratio of soybeans to water during the soybean soaking is 1:2, and the soaking time is 15-21 hours.

3. The method according to claim 2, characterized in that: The amount of Aspergillus oryzae added is 0.03% to 0.05% of the mass of the flour after hot steam treatment.

4. The method according to claim 1, characterized in that: The mass ratio of the koji to the steamed soybeans is 10:1-5.

5. The method according to claim 1, characterized in that: The complex enzyme agent includes one or more of lipase, protease and amylase.

6. The method according to claim 5, characterized in that: The mass ratio of the lipase, protease and amylase is 1:1-3:1-3; the total added amount of the complex enzyme agent is 0.2%-0.8% of the total mass of the fermented mash.

7. The method according to claim 1, characterized in that: The three stages of fermentation are respectively the first stage: temperature 32-35°C, fermentation 5-7 days; the second stage: temperature 28-30°C, fermentation 3-5 days; the third stage: temperature 38-42°C, fermentation 10-16 days.

8. Soybean paste with high amino nitrogen content obtained by the method according to claims 1 to 7.

9. The soybean paste with high amino nitrogen content according to claim 8, characterized in that: The amino acid nitrogen content of the soybean paste is 0.50-0.72 g / 100g.

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