Natto, method for producing the same, packaging container, and film

Abstract

To provide natto having a longer shelf life than existing products, a preparation method thereof, a packaging container, and film.SOLUTION: A first preparation method includes: a step (i) of preparing a packaging container that satisfies (1) an oxygen permeation rate of 70-850 cc / cm2*day*atm and / or (2) average pore area of less than 10000 μm2; a step (ii) of inoculating Bacillus natto; and a step (iii) of performing fermentation that satisfies (1) that average oxygen concentration is lower than that of an outside of the packaging container and (2) that a product temperature of the fermented product during the fermentation period is 37°C-53°C. A second preparation method includes: a step (i) of preparing a packaging container; a step (ii) of inoculating Bacillus natto; and a step (iii) of performing fermentation that all satisfies (1) that an average oxygen concentration is lower than that of an outside of the packaging container, (2) that a product temperature of the fermented product during the fermentation period is 37°C-53°C, and (3) that a period when an oxygen concentration inside the packaging container during the fermentation is 10% or lower is 8 hours or longer.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to natto, a method for producing the same, a packaging container, and a film. More specifically, the present invention relates to natto having excellent storage stability, a method for producing the same, a packaging container, and a film.

Background Art

[0002] A method for producing natto with improved umami and stringiness and suppressed generation of ammonia odor, and natto produced by this method are disclosed in Patent Document 1 below.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The production method of Patent Document 1 above is characterized in that, following the fermentation in the stationary phase during the fermentation process, the fermentation process is continued while maintaining the oxygen concentration in the air in the fermentation chamber within a low oxygen concentration range of 2 to 8%. Thereby, it is excellent in that natto with improved umami and stringiness and suppressed generation of ammonia odor can be obtained.

[0005] On the other hand, as shown in Patent Document 1, the production of natto involves fermentation and thus takes time, but its shelf life is generally as short as 10 days. For this reason, it is necessary to adjust the production volume in anticipation of the shipment volume. However, there are fluctuations in demand due to trends, weather, etc., and it is not easy to predict them. For this reason, there is a problem that food loss is caused by fluctuations in demand. As a countermeasure against such fluctuations in demand, an option of extending the shelf life of the product can be considered. This is because by extending the shelf life, it becomes easier to manage inventory and the ability to counter fluctuations in demand can be increased. However, the technology disclosed in the above Patent Document 1 has a problem that it is not possible to produce natto with a longer shelf life than the current situation.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide natto having a longer shelf life than conventional natto, a method for producing the same, a packaging container, and a film.

Means for Solving the Problems

[0007] The inventors repeatedly reexamined the method for producing natto from the perspective of extending the shelf life. As a result, they focused on the fact that the technology in Patent Document 1 above is a technology for maintaining the oxygen concentration in the air in the fermentation chamber within an extremely low oxygen concentration range of 2 to 8%. This environment is an environment for producing natto with improved umami and stringiness and suppressed generation of ammonia odor, but it is an environment for forming throughout the fermentation chamber. For this reason, in order to make the packaging container for accommodating natto the same as the environment in the fermentation chamber, it has been necessary to use a highly breathable packaging container. That is, it is necessary to make the environment the same by using a highly breathable packaging container and circulating the atmosphere in the fermentation chamber and the atmosphere in the packaging container. However, the packaging container for natto is designed to function as a fermentation container during fermentation and as a product storage container after the product is completed from the perspective of cost performance, etc., and the fermentation container and the product storage container are common. For this reason, the breathability of the packaging container, which acts advantageously during fermentation, becomes a factor that makes it difficult to prevent the invasion of bacteria other than natto bacteria during product distribution, and it has been found that this is one of the reasons for shortening the shelf life. However, since natto bacteria are bacteria that consume a large amount of oxygen during fermentation, it has also been found that in a packaging container that highly prioritizes preventing the invasion of bacteria other than natto bacteria, oxygen in the packaging container becomes deficient during fermentation, making fermentation itself difficult. Therefore, the inventors have found that by enabling oxygen supply from the atmosphere in the fermentation chamber into the packaging container and using a packaging container with lower breathability than conventional ones, it is possible to significantly extend the shelf life.

[0008] As a result, it was found that the possibility of generating hood loss can be significantly reduced in proportion to the extension of the above-mentioned shelf life. Furthermore, it was found that the risk of a significantly hypoxic state in the fermentation chamber can be reduced. That is, the atmosphere in the fermentation chamber in a significantly hypoxic state is highly dangerous for living organisms. For this reason, it is preferable that the oxygen concentration in the fermentation chamber is closer to the oxygen concentration in the atmosphere. In this regard, it was found that the manufacturing method of the present application is a method capable of reducing the risk during manufacturing because it can maintain the oxygen concentration in the fermentation chamber higher than conventional ones.

[0009] That is, the present invention includes the following inventions. [1] A method for producing natto, characterized by comprising the following steps (i) to (iii). (i) Preparing a packaging container having a low oxygen permeation site satisfying at least one of the following (1) and (2); (1) The oxygen permeability is 70 cc / cm 2 ·Day·atm or more and 850 cc / cm 2 ·Day·atm or less; (2) Having through holes with an average pore area of less than 10,000 μm 2 ; (ii) Inoculating Bacillus natto; (iii) Performing fermentation satisfying the following (1) and (2): (1) During the fermentation period, the average oxygen concentration in the packaging container is relatively lower than the average oxygen concentration outside the packaging container; (2) During the fermentation period, the temperature of the material to be fermented is 37°C or higher and 53°C or lower. [2] A method for producing natto, characterized by comprising the following steps (i) to (iii). (i) Preparing a packaging container; (ii) Inoculating Bacillus natto; (iii) Performing fermentation satisfying all of the following (1) to (3): (1) During the fermentation period, the average oxygen concentration in the packaging container is relatively lower than the average oxygen concentration outside the packaging container; (2) During the fermentation period, the temperature of the material to be fermented is 37°C or higher and 53°C or lower; (3) During the fermentation period, the time when the oxygen concentration in the packaging container becomes 10% or less is 8 hours or more. [3] The method for producing natto according to [1] above, further satisfying the following (3) in the above (iii). (3) During the fermentation period, the time when the oxygen concentration in the packaging container becomes 10% or less is 8 hours or more. [4] The method for producing natto according to [2] above, wherein in the above (i), the packaging container has a low oxygen permeation site satisfying at least one of the following (1) and (2). (1) The oxygen permeability is 70 cc / cm2 ·Day·atm or more, 850 cc / cm 2 ·Day·atm or less (2) The average pore area is 10,000 μm 2 Having through-holes less than [5] The method for producing natto according to any one of [1] to [4] above, further satisfying the following (4) in (iii) above. (4) The time when the oxygen concentration in the packaging container becomes 8% or less is 5 hours or more. [6] The method for producing natto according to any one of [1] to [5] above, further satisfying the following (5) in (iii) above. (5) The time when the oxygen concentration in the packaging container becomes 6% or less is 2.5 hours or more and 15 hours or less. [7] The method for producing natto according to any one of [1] to [6] above, further satisfying the following (6) in (iii) above. (6) The temperature outside the packaging container is 30°C or more. [8] The method for producing natto according to any one of [1] to [7] above, wherein the aperture ratio of the low-oxygen permeable part is 0.022% or less. [9] The method for producing natto according to any one of [1] to [8] above, wherein the low-oxygen permeable part is a film.

[10] The method for producing natto according to any one of [1] to [9] above, wherein the content of (a) lysine contained in the fermented product continuously stored at 10°C for 10 days after (iii) is 90 mg% or less.

[11] The method for producing natto according to any one of [1] to

[10] above, wherein the content of (b) ammonia contained in the fermented product continuously stored at 10°C for 10 days after (iii) is 160 mg% or less.

[12] The method for producing natto according to any one of [1] to

[11] above, wherein the content of (c) glutamic acid contained in the fermented product continuously stored at 10°C for 10 days after (iii) is 125 mg% or less.

[13] The method for producing natto according to any one of [1] to

[12] above, wherein the content of (d) tyrosine contained in the fermented product continuously stored at 10°C for 10 days after (iii) is 120 mg% or less.

[14] The method for producing natto according to any one of [1] to

[13] above, wherein the total content of (e) bitter amino acids contained in the fermented product continuously stored at 10°C for 10 days after (iii) is 580 mg% or less.

[15] The method for producing natto according to any one of [1] to

[14] above, further comprising the following step (iv) after (iii). (iv) Adjust the temperature of the fermented product after (iii) so that the product temperature exceeds 53°C.

[16] The method for producing natto according to

[15] above, wherein step (iv) is performed within 3.5 hours after (iii).

[17] The method for producing natto according to

[15] or

[16] above, wherein the time during which the product temperature exceeds 53°C is 3.5 hours or less.

[18] The method for producing natto according to any one of

[15] to

[17] above, wherein the content of (f) valine contained in the fermented product continuously stored at 10°C for 30 days after (iv) is 90 mg% or less.

[19] The method for producing natto according to any one of

[15] to

[18] above, wherein the content of (a) lysine contained in the fermented product continuously stored at 10°C for 30 days after (iv) is 115 mg% or less.

[20] The method for producing natto according to any one of

[15] to

[19] above, wherein the content of (b) ammonia contained in the fermented product continuously stored at 10°C for 30 days after (iv) is 190 mg% or less.

[21] The method for producing natto according to any one of

[15] to

[20] above, wherein the content of (d) tyrosine contained in the fermented product continuously stored at 10°C for 30 days after (iv) is 200 mg% or less.

[22] The method for producing natto according to any one of

[15] to

[21] above, wherein the total content of (e) bitter amino acids contained in the fermented product continuously stored at 10°C for 30 days after (iv) is 1100 mg% or less.

[23] The method for producing natto according to any one of

[15] to

[22] above, further satisfying the following (g) after the above (iv). (g) The enzyme activity is 7 U / g or less.

[24] Natto characterized by being produced through the following steps (i) to (iii). (i) A step of preparing a packaging container having a low oxygen permeation site satisfying at least one of the following (1) to (2): (1) The oxygen permeability is 70 cc / cm 2 ·Day·atm or more and 850 cc / cm 2 ·Day·atm or less. (2) Having through-holes with an average pore area of less than 10000 μm 2 (ii) A step of inoculating Bacillus natto. (iii) A step of performing fermentation satisfying the following (1) and (2): (1) During the fermentation period, the average oxygen concentration inside the packaging container is relatively lower than the average oxygen concentration outside the packaging container. (2) During the fermentation period, the temperature of the material to be fermented is 37°C or higher and 53°C or lower.

[25] Natto characterized by being produced through the following steps (i) to (iii). (i) A step of preparing a packaging container. (ii) A step of inoculating Bacillus natto. (iii) A step of performing fermentation satisfying all of the following (1) to (3): (1) During the fermentation period, the average oxygen concentration inside the packaging container is relatively lower than the average oxygen concentration outside the packaging container. (2) During the fermentation period, the temperature of the material to be fermented is 37°C or higher and 53°C or lower. (3) During the fermentation period, the time when the oxygen concentration inside the packaging container becomes 10% or less is 8 hours or more.

[26] A packaging container characterized by being used for the production of natto having a low oxygen permeation site satisfying at least one of the following (1) to (2). (1) The oxygen permeability is 70 cc / cm 2 ·Day·atm or more and 850 cc / cm 2·Day·atm or less (2) having through-holes with an average pore area of less than 10,000 μm 2

[27] Further, the packaging container according to

[26] above, which is used for storage at 10 °C for 14 days or less after the fermentation is completed.

[28] Further, the packaging container according to

[26] or

[27] above, wherein the aperture ratio of the low oxygen permeation part is 0.022% or less.

[29] Further, the packaging container according to any one of

[26] to

[27] above, which is used in the method for producing natto according to [1] above.

[30] A film characterized by being used in a natto production container satisfying at least one of the following (1) to (2). (1) The oxygen permeability is 70 cc / cm 2 ·Day·atm or more and 850 cc / cm 2 ·Day·atm or less (2) having through-holes with an average pore area of less than 10,000 μm 2

[31] Further, the film according to

[30] above, which is used for storage at 10 °C for 14 days or less after the fermentation is completed.

[32] Further, the film according to

[30] or

[31] above, wherein the aperture ratio of the low oxygen permeation part is 0.022% or less.

[33] Further, the film according to any one of

[30] to

[32] above, which is used in the method for producing natto according to [1] above. [Advantages of the Invention]

[0010] According to the method for producing natto of the present invention, natto with a longer shelf life can be produced compared to the prior art. The natto of the present invention can be made into natto with a longer shelf life compared to the prior art. According to the packaging container of the present invention, natto with a longer shelf life can be produced compared to the prior art. According to the film of the present invention, natto with a longer shelf life can be produced compared to the prior art. [Embodiments for Carrying Out the Invention]

[0011] ​​Hereinafter, the present invention will be described based on specific embodiments. However, the present invention is not limited to these embodiments. These embodiments are merely exemplary examples shown for convenience of explanation, and the present invention is not limited to them in any sense, and the present invention can be variously modified according to the purpose and application. Also, all publications, patents, and patent applications cited in this specification are hereby incorporated by reference in their entirety into this specification.

[0012] In addition, in this specification, with respect to the expression "and / or", it includes the meanings of both "and" and "or". For example, "A and / or B" includes both the meanings of A and B and A or B, indicating three cases: A alone, B alone, and both A and B. Furthermore, in this specification, when defining a numerical range with multiple upper limit values and / or multiple lower limit values, even if not specifically stated, it is directly described that the numerical range defined by combining at least the maximum value of the upper limit regulation and the minimum value of the lower limit regulation is included, and furthermore, all numerical ranges obtained by combining any upper limit value among the upper limit values and any lower limit value among the lower limit values are included in one embodiment of the present invention. Also, in this specification, a numerical range connected by "~" means a numerical range including the numerical values before and after "~" as the lower limit value and the upper limit value. When multiple lower limit values and multiple upper limit values are shown separately, any lower limit value and upper limit value can be selected and connected by "~".

[0013] [1] Method for producing natto (First form) The method for producing natto according to the first form in the present invention is characterized by comprising the following steps: (i) preparing a packaging container, (ii) inoculating, and (iii) performing fermentation.

[0014] [1-1] Step (i) Step (i) is a step of preparing a packaging container having a low oxygen permeation site satisfying at least one of the following (1) to (2) (packaging container preparation step). (1) The oxygen permeability is 70 cc / cm 2·Day·above 850 cc / cm 2 ·Day·atm or less (2) The through-hole having an average pore area of less than 10,000 μm 2

[0015] The packaging container is a container that can accommodate, as the main contents (which may be collectively referred to as the fermentable substance), a raw material that is a fermentable substance by fermenting bacteria and the fermenting bacteria inoculated thereto. In the present invention, the fermenting bacteria are Bacillus natto, and the fermentable substances include soybeans, chickpeas, peas, etc. From this perspective, it has a function as a container for the fermentable substance. Further, after filling the fermentable substance, it can be sealed and directly subjected to fermentation. That is, from this perspective, it has a function as a fermentation container. Further, after the fermentation is completed, it can be directly aged. That is, from this perspective, it can have a function as an aging container. Further, after the aging is completed, if necessary, it can be packaged and shipped as a product as it is, and further, it is a container for distribution. That is, from this perspective, it can have functions as a shipping container and a distribution container. Further, it is a container that can be used in a manner of directly serving as a tableware. That is, it is a container without holes or the like through which liquid seasonings or the like flow out at the bottom and the lower part of the side surface of the container, and from this perspective, it can have a function as a tableware. Note that since the intake modes of the fermentable substance vary depending on the intaker or the like, whether or not the packaging container is used as a tableware is not limited.

[0016] ​This packaging container satisfies at least one of (1) an oxygen permeability within a predetermined range and (2) an average pore area within a predetermined range. Among the above, (1) the oxygen permeability within a predetermined range may be satisfied in any manner. That is, for example, the oxygen permeability may be satisfied by only a part of the packaging container having oxygen permeability, or the oxygen permeability may be satisfied by the entire packaging container having oxygen permeability. For example, it may be achieved by providing through-holes, and it may be achieved not only by visible openings such as through-holes but also by the oxygen permeation power of the member (for example, film) itself. Note that the packaging container that requires the oxygen permeability is a container that is in contact with the outside air. Also, when (1) is satisfied, (2) may or may not be satisfied.

[0017] The oxygen permeability of the packaging container is usually 70 cc / cm 2 ·Day·atm or more and 850 cc / cm 2 ·Day·atm or less, and can be further 150 cc / cm 2 ·Day·atm or more and 750 cc / cm 2 ·Day·atm or less, and can be further 230 cc / cm 2 ·Day·atm or more and 600 cc / cm 2 ·Day·atm or less, and can be within this range. By being within this range, the activity of Bacillus natto during the fermentation period can be effectively suppressed. Note that for the packaging container after (iii), (i)(1) and (i)(2) may or may not satisfy at least one of them. The upper limit within the above range is 850 cc / cm 2 ·Day·atm or less, but can be further 830 cc / cm 2 ·Day·atm or less, 810 cc / cm 2 ·Day·atm or less, 800 cc / cm 2 ·Day·atm or less, 780 cc / cm 2 ·Day·atm or less, 760 cc / cm 2 ·Day·atm or less, 750 cc / cm 2 ·Day·atm or less, 730 cc / cm 2 ·Day·atm or less, 700 cc / cm2 ·Per day·atm or less, 680 cc / cm 2 ·Per day·atm or less, 650 cc / cm 2 ·Per day·atm or less, 630 cc / cm 2 ·Per day·atm or less, 600 cc / cm 2 ·Per day·atm or less, 590 cc / cm 2 ·Can be ·Per day·atm or less. On the other hand, the lower limit in the above range is 70 cc / cm 2 ·Is ·Per day·atm or more, but further 100 cc / cm 2 ·Per day·atm or more, further 120 cc / cm 2 ·Per day·atm or more, 150 cc / cm 2 ·Per day·atm or more, 180 cc / cm 2 ·Per day·atm or more, 200 cc / cm 2 ·Per day·atm or more, 210 cc / cm 2 ·Per day·atm or more, 230 cc / cm 2 ·Per day·atm or more, 240 cc / cm 2 ·Per day·atm or more, 250 cc / cm 2 ·Can be ·Per day·atm or more. The above upper and lower limits can be each combination. That is, for example, the oxygen permeability can be 120 cc / cm 2 ·Per day·atm or more and 850 cc / cm 2 ·Per day·atm or less, and 100 cc / cm 2 ·Per day·atm or more and 800 cc / cm 2 ·Per day·atm or less, and 200 cc / cm 2 ·Per day·atm or more and 650 cc / cm 2 ·Per day·atm or less, and 230 cc / cm 2 ·Per day·atm or more and 750 cc / cm 2 ·Per day·atm or less, and 230 cc / cm 2 ·Per day·atm or more and 600 cc / cm 2 ·Per day·atm or less can be. Moreover, by satisfying the above configuration, the activity of Bacillus natto after fermentation can be effectively suppressed, so that a Bacillus natto fermented product (especially natto) with a longer shelf life than usual can be obtained. Specifically, after the fermentation is completed, the shelf life can be set to 14 days or less, or 10 days or less at an average storage temperature of 10°C. The lower limit is not particularly limited, but it may usually be 1 day or more, or 3 days or more. Furthermore, by satisfying the above configuration, it can be used as a packaging container for use in applications where the shelf life is 14 days or less, or 10 days or less when stored at an average storage temperature of 10°C. Furthermore, the film satisfying the above configuration may be used in a manner of being used in a natto production container, or may be used in a manner of attaching the film to the opening of the natto production container.

[0018] The oxygen permeability is measured in accordance with JIS K-7126-2. Specifically, using a gas barrier test apparatus (model "OX-TRAN 1 / 50", manufactured by MOCON), the oxygen permeability (unit: cc / cm 2 ·Day·atm) is measured at a temperature of 23 ± 2°C and a relative humidity of 50%. When the packaging container is composed of one type of member, the oxygen permeability per unit area of the member is measured, and the value obtained by multiplying the area of the member used for one packaging container is taken as the oxygen permeability. When the packaging container is composed of two or more types of members, the oxygen permeability per unit area of each member is measured, and the total value of the values obtained by multiplying the area of each member used for one packaging container is taken as the oxygen permeability. Furthermore, when the constituent member of the packaging container has a through hole, all other through holes are masked with aluminum tape, and the oxygen permeability of only one through hole to be measured is measured. Then, it is calculated as the total value of the value obtained by multiplying the oxygen permeability by the total area of the through holes (measured using a microscope) and the value obtained by multiplying the oxygen permeability of the area of the member without through holes by the area of the area without through holes.

[0019] As a packaging container capable of achieving such an oxygen permeability, for example, there is a cup-shaped part having a bottom part and side parts without through-holes through which liquid can flow out when used as a tableware, and an open part (a part opened upward) that allows the material to be fermented to be stored from above when storing the material to be fermented, etc., and a top film part that seals the open part after storing the material to be fermented in the cup-shaped part. When achieving the above-mentioned oxygen permeability by the top film part, the above-mentioned oxygen permeability may be achieved by only a part of the top film part, or may be achieved by the entire (entire surface) of the top film part.

[0020] On the other hand, among the above, (2) the average pore area within a predetermined range may be satisfied in any way. That is, for example, the average pore area may be satisfied by through-holes provided only in a part of the packaging container, or the average pore area may be satisfied by through-holes provided in the entire packaging container. Note that the packaging container that requires the average pore area is a container that is in contact with the outside air. Also, when (2) is satisfied, (1) may or may not be satisfied.

[0021] When the packaging container has through-holes, the average pore area is not limited, but from the viewpoint of effectively suppressing the activity of Bacillus natto during the fermentation period, its upper limit can be less than 10000 μm 2 and can be further 9500 μm 2 or less, and can be further 9000 μm 2 or less, and can be further 8500 μm 2 or less, and can be further 8000 μm 2 or less, 7000 μm 2 or less, 6000 μm 2 or less, 5000 μm 2 or less, 4500 μm 2 or less, 4200 μm 2 or less, 4000 μm 2 or less, 3800 μm 2 or less, 3500 μm 2 or less, 3400 μm 2 or less, 3300 μm 2 or less, 3200 μm2 The following can be adopted. The above ranges can more effectively prevent the invasion of mold from the through-holes. On the other hand, the lower limit can be 500 μm 2 or more, and further 700 μm 2 or more, 800 μm 2 or more, 900 μm 2 or more, 1000 μm 2 or more, 1100 μm 2 or more, 1200 μm 2 or more. The above ranges can ensure better oxygen circulation inside and outside the packaging container. The above-mentioned upper and lower limits can be in each combination. That is, for example, the average pore area can be 500 μm 2 or more and less than 10000 μm 2 and further 800 μm 2 or more and 8000 μm 2 or less, further 1000 μm 2 or more and 5000 μm 2 or less, further 1100 μm 2 or more and 4000 μm 2 or less, further 1200 μm 2 or more and 3500 μm 2 or less. Also, by satisfying the above configuration, the activity of Bacillus natto after fermentation can be effectively suppressed, so that a Bacillus natto fermented product (especially natto) with a longer shelf life than usual can be obtained. Specifically, after the fermentation is completed, the shelf life can be set to 14 days or less, or 10 days or less at an average storage temperature of 10°C. The lower limit is not particularly limited, but it can usually be 1 day or more, or 3 days or more. Furthermore, by satisfying the above configuration, it can be used as a packaging container for use in applications where the shelf life is 14 days or less, or 10 days or less when stored at an average storage temperature of 10°C. Particularly, in a household refrigerator where regular mold cleaning is not thorough, it is useful because it can be used for natto bacteria fermented products stored for 3 days or more, or 5 days or more, reducing the risk of mold contamination during storage in the household refrigerator. The upper limit is not particularly restricted, but it may be 14 days or less, or 10 days or less. Furthermore, by satisfying the above configuration, it can be used as a packaging container for use in a household refrigerator for storage for 3 days or more, or 5 days or more. Furthermore, the film satisfying the above configuration may be used in a mode for a natto production container, or may be used in a mode of attaching the film to the opening of the natto production container.

[0022] The average pore area means the average value of the pore areas of the through-holes in a plan view when the through-holes are provided in the packaging container. The average pore area represents the arithmetic mean of the pore areas of any 10 through-holes among the through-holes provided in the packaging container. When the number of through-holes is less than 10, it represents the arithmetic mean of the oxygen permeation degrees of all the through-holes in the packaging container. Also, as the pore area, the average pore area on the outer surface of the packaging container shall be adopted. Also, for the pore area, the through-holes are observed with a digital microscope VHX-7000 (manufactured by KEYENCE Corporation), and for the obtained image, the image analysis software installed in the microscope is used, and "automatic area measurement" is selected for area measurement to measure the pore area. Furthermore, the total of the pore areas is defined as the total pore area. This total pore area is a value calculated by multiplying the average pore area by the number of holes in the entire packaging container.

[0023] Furthermore, when through-holes are provided in the packaging container, the total pore area is not limited, but it can effectively suppress the activity of natto bacteria during the fermentation period. This total pore area can be, for example, 120,000μm 2 or more and 1,600,000μm 2 or less, and can further be 300,000μm 2 or more and 1,500,000μm 2 or less, and can further be 450,000μm 2 or more and 1,400,000μm 2It can be as follows. Furthermore, the upper limit in each of the above ranges is 1,600,000 μm 2 or less, 1,500,000 μm 2 or less, 1,400,000 μm 2 or less, 1,350,000 μm 2 or less, 1,300,000 μm 2 or less, 1,250,000 μm 2 or less, 1,200,000 μm 2 or less, 1,150,000 μm 2 or less, 1,100,000 μm 2 It can be as follows. On the other hand, the lower limit in each of the above ranges is 120,000 μm 2 or more, 150,000 μm 2 or more, 180,000 μm 2 or more, 200,000 μm 2 or more, 250,000 μm 2 or more, 300,000 μm 2 or more, 350,000 μm 2 or more, 400,000 μm 2 or more, 450,000 μm 2 or more can be set.

[0024] The aperture ratio (%) of the packaging container is not limited, but from the viewpoint of suppressing the invasion of mold, it can be, for example, 0.0015% or more and 0.022% or less, 0.004% or more and 0.019% or less, and further 0.006% or more and 0.015% or less. Furthermore, the upper limit in each of the above ranges can be 0.022% or less, 0.021% or less, 0.020% or less, 0.019% or less, 0.018% or less, 0.017% or less, 0.016% or less. On the other hand, the lower limit in each of the above ranges can be 0.0015% or more, 0.002% or more, 0.003% or more, 0.004% or more, 0.005% or more, 0.006% or more. The aperture ratio is the ratio (%) of the total area of the actually opened through-holes to the total area of the surfaces of the packaging container where the through-holes are provided. Also, the actual number of through-holes is not limited, but for example, it can be 30 or more and 1000 or less, further 70 or more and 850 or less, and further 120 or more and 750 or less. Moreover, since mold invasion can be suppressed by satisfying the above configuration, it is possible to obtain natto with an extended expiration date compared to normal. Specifically, after the fermentation is completed, the expiration date can be set to 14 days or less, or 10 days or less at an average storage temperature of 10°C. The lower limit is not particularly limited, but it may usually be 1 day or more, or 3 days or more. Furthermore, by satisfying the above configuration, it can be used as a packaging container for use in applications where the expiration date is stored at 14 days or less, or 10 days or less at an average storage temperature of 10°C.

[0025] Also, the planar shape of the through-hole is not limited. For example, an elliptical hole, a circular hole, a rhombus hole, a triangular hole, a trapezoidal hole, a linear hole, a rectangular hole, or a cross shape, X shape, Y shape, H shape, etc. can be used. Also, the hole punching position of the lid material for the natto container may be punched evenly over the entire lid area, or may be punched partially. The method of punching fine holes is not particularly limited, and examples include mechanically punching, thermal needle punching, or laser punching that are generally used, but mechanical punching by a roller method is convenient.

[0026] When adopting the top film part, the material of the film constituting the top film part is not limited. For example, paper, styrofoam, various plastics, etc. (for example, paper, styrene-modified polyolefin resin, polystyrene, high-impact polystyrene, polystyrene resin such as styrene-ethylene copolymer, polyethylene, polypropylene, polyolefin resin such as ethylene-vinyl acetate copolymer, polyester resin such as polyethylene terephthalate, etc., a film formed of a foamed sheet made of various synthetic resins) can be used. These may be used alone or in combination of two or more. Also, the thickness of the film is not limited, but for example, it can be 100 μm or less, 80 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, 30 μm or less.

[0027] The material constituting the packaging container is not limited, and materials generally used as packaging containers can be used. That is, paper, styrofoam, various plastics, etc. (for example, cup-shaped paper or styrene-modified polyolefin resin, polystyrene, high-impact polystyrene, polystyrene-based resins such as styrene-ethylene copolymer, polyethylene, polypropylene, polyolefin-based resins such as ethylene-vinyl acetate copolymer, containers formed of foamed sheets made of various synthetic resins such as polyethylene terephthalate, etc.) can be used. These may be used alone or in combination of two or more.

[0028] These materials may be appropriately selected and combined according to the characteristics of the combination with the fermenting bacteria. In addition, from the viewpoints of heat retention during fermentation, lightness during stacking during mass production, lightness during shipping, shock buffering property, shape retention during eating, lightness, and manufacturing cost, it is preferably made of paper or styrofoam, and more preferably made of styrofoam (specifically, made of polystyrene) as an example. Regarding the light transmittance, if photosynthesis or activation of fermentation by light is desired, a material with high transparency may be selected, but if the action by light is not required, it can be made opaque. From the viewpoint of light deterioration of quality associated with light irradiation during distribution and sales, it can be made opaque.

[0029] In addition, as the contents within the packaging container, other than the main contents described above (the material to be fermented by the fermenting bacteria (soybeans, chickpeas, peas, especially soybeans) and the fermenting bacteria (Bacillus subtilis var. natto) inoculated onto the material to be fermented), general liquid / gel / powder / solid seasonings, etc. may be enclosed by means of a separate structure such as a sachet or a container, as long as it does not affect the fermentation of the material to be fermented. Also, in order to prevent the material to be fermented from coming into contact with and adhering to the lid of the container and inhibiting ease of eating, laying a film-like thin film on the material to be fermented is also an aspect that does not affect the fermentation of the material to be fermented, and as long as it is within such a manner, there is no restriction whatsoever on its presence or absence. Whether or not to make holes in the film-like thin film is similarly not particularly limited. Furthermore, from the perspective of enhancing instant edibility, it is also possible to enclose tableware such as spoons and forks. Note that these are distinguished from the material to be fermented within the container.

[0030] The size of the packaging container is not limited, but from the perspective of being suitable for individual consumption, it is preferable that the internal volume of the material to be fermented before fermentation can be enclosed in a size of, for example, 20 g or more and 300 g or less. More specifically, when the container is substantially cylindrical, it is preferable that the minimum diameter is, for example, 4 cm or more and 15 cm or less, and the height is, for example, 4 cm or more and 10 cm or less. When the container is substantially rectangular parallelepiped or substantially square, it is preferable that the minimum width is 5 cm or more and 15 cm or less, and the height is 2 cm or more and 5 cm or less.

[0031] [1-2] Step (ii) Step (ii) is the step of inoculating Bacillus subtilis var. natto (inoculation step). That is, it is the step of accommodating the fermenting bacteria necessary for fermentation within the packaging container prepared in step (i). In the present invention, the fermenting bacteria are Bacillus subtilis var. natto. Any Bacillus natto can be used. For example, common commercially available strains such as Miyagino strain (product name: Pure Cultured Bacillus natto (Miyagino Bacillus natto)) (manufactured by Miyagino Manufacturing Co., Ltd.), Takahashi strain (product name: Nattozyme) (manufactured by Takahashi Yuzo Research Institute Co., Ltd.), Naruse strain (product name: Powdered Bacillus natto) (manufactured by Naruse Fermentation Chemical Research Institute) can be used. However, various strains such as mutant strains and genetically modified strains with specific properties can also be utilized. Among them, it is preferable to use K-245 strain or No.7 strain, and it is particularly preferable to use K-245 strain. The K-245 strain was internationally deposited on February 25, 2014, under the name of Bacillus subtilis K-245 strain with the accession number NITE BP-01804 at the Patent Biological Depositary, National Institute of Technology and Evaluation, 2-5-8 Kazusa Kamashima, Kisarazu, Chiba, Japan. This K-245 strain is a mutant strain obtained by mutating the Bacillus natto strain (Bucillus subtilis K-2; NITE BP-1577) described in Japanese Patent Publication No. 5-60335. In addition, the No.7 strain was internationally deposited on February 25, 2014, at the Patent Microorganisms Depositary, National Institute of Technology and Evaluation (NPMD) (Room 122, 2-5-8 Kazusa Kamashima, Kisarazu, Chiba, Japan, Zip Code 292-0818) under the accession number NITE BP-01805 (identification label: Bacillus subtilis No.7). Incidentally, Bacillus natto is classified as Bacillus subtilis, but generally it is classified separately from Bacillus subtilis as Bacillus subtilis var. natto, or Bacillus subtilis (natto), or as a closely related species of Bacillus subtilis, Bacillus natto.

[0032] In step (ii), the state of the Bacillus natto added as the Bacillus natto starter is not particularly limited, but it is preferable to use the spore state that can be directly inoculated into the high-temperature raw material to prevent contamination by miscellaneous bacteria. Inoculation of the above-mentioned Bacillus natto starter into the raw material is preferably carried out by inoculation or spraying so that the raw material and the Bacillus natto are uniform, and then mixing or the like is carried out in order to perform fermentation uniformly. Preferably, it is suitable to prepare the spore suspension of the above-mentioned Bacillus natto and add and use it in a liquid state.

[0033] Here, as the spore suspension, a culture solution obtained by culturing the above-mentioned Bacillus natto in a liquid medium having components suitable for spore formation can be used. The components of the above liquid medium are not particularly limited as long as they are liquid media containing medium components such as carbon sources, nitrogen sources, and inorganic salts that enable spore formation and growth of Bacillus natto and are usually used for culturing Bacillus natto, and may be synthetic media or natural media. Among the medium components, examples of the carbon source include sugars such as glucose, sucrose, galactose, mannose, starch, and starch degradation products, and organic acids such as citric acid. Examples of the nitrogen source include peptone, meat extract, casein hydrolyzate, ammonia, ammonium sulfate, and ammonium chloride. Examples of the inorganic salts include sodium chloride, potassium chloride, calcium chloride, sodium sulfate, sodium hydrogen sulfate, sodium nitrate, potassium phosphate, ferric chloride hexahydrate, magnesium sulfate heptahydrate, manganese chloride tetrahydrate, and ferrous sulfate. In addition, the medium may contain yeast extract, malt extract, soybean powder, vitamins (such as biotin), etc. When using a Bacillus natto mutant strain that requires specific nutritional components due to gene deletion or the like, the medium composition may be changed in a timely manner.

[0034] The inoculum amount is usually 1 / 100 to 1 / 50 amount based on the steamed soybeans. More specifically, the number of Bacillus natto to be inoculated is not particularly limited by the bacterial concentration according to the conventional method, but it is 1×10 3 ~1×10 6 per gram of soybeans, preferably 1×10 3 ~1×10 5 per gram, and more preferably 1×103 ~1×10 4 pieces.

[0035] When inoculating Bacillus natto, the temperature of the soybeans can be 55 - 95°C, preferably 60 - 95°C, more preferably 65 - 95°C, still more preferably 70 - 90°C, and particularly preferably 75 - 90°C. Within the above range, contamination by miscellaneous bacteria can be more effectively prevented, and the death of Bacillus natto spores can be more effectively prevented, thereby preventing fermentation failure.

[0036] In the method for producing natto of the present invention, any raw material that can be used in the production of ordinary natto can be used as the material to be fermented. For example, whole soybeans, halved soybeans, crushed soybeans (raw material for ground natto), defatted soybeans, chickpeas, peas, etc. can be used, and in particular, whole soybeans, halved soybeans, crushed soybeans (raw material for ground natto), and defatted soybeans can be used. In particular, medium - sized and large - sized ones used in the production of high - quality natto are preferred. These soybeans can be used raw, but it is common to use those that have been subjected to a drying treatment (dried products).

[0037] In the present invention, the raw material soybeans are heated in a liquid to obtain steamed soybeans or boiled soybeans by a conventional method. In terms of preventing the loss of components, steamed soybeans are preferred. Before performing the steaming or boiling operation, it is desirable to immerse the raw material soybeans in water and swell them. Here, as a specific preparation procedure for steamed soybeans, a method can be adopted in which the soybeans are immersed in water at normal temperature for about 6 - 24 hours, then drained, and subjected to a steaming treatment with steam at 100 - 135°C for 10 - 30 minutes. Also, a method of pressure steaming under high - pressure conditions of 0.12 - 0.22 MPa can be adopted. As a specific preparation procedure for boiled soybeans, a method can be adopted in which the soybeans are immersed in water at normal temperature for about 6 - 24 hours, and then boiled in hot water at 90 - 100°C for 20 - 50 minutes.

[0038] Specifically, the packaging container prepared in step (i) needs to contain the material to be fermented (soybeans, chickpeas, peas, especially soybeans). Therefore, it can include a step of accommodating the material to be fermented in the packaging container. The inoculation step (ii) may be performed before or after the step of accommodating the material to be fermented. Furthermore, the inoculation step (ii) and the step of accommodating the material to be fermented may be performed simultaneously. Furthermore, the packaging container preparation step (i) and the inoculation step (ii) may be performed simultaneously, or the inoculation step (ii) may be performed after the packaging container preparation (i). Also, if possible, the packaging container preparation step (i) may be performed after the inoculation step (ii).

[0039] [1-3] Step (iii) In the method for producing natto according to the first embodiment, step (iii) is a step of performing fermentation (fermentation step) that satisfies the following (1) and (2). (1) During the fermentation period, the average oxygen concentration inside the packaging container is relatively lower than the average oxygen concentration outside the packaging container (2) During the fermentation period, the temperature of the material to be fermented is 37°C or higher and 53°C or lower

[0040] “(1) During the fermentation period, the average oxygen concentration inside the packaging container is relatively lower than the average oxygen concentration outside the packaging container” means that during the entire fermentation process from the start to the end of fermentation, the average oxygen concentration inside the packaging container is relatively lower than the average oxygen concentration outside the packaging container. The “fermentation process” in the present invention refers to the process of raising the temperature of the material to be fermented (soybeans, chickpeas, peas, especially soybeans) inoculated with natto bacteria in step (ii) to 37°C or higher, and generally, the temperature is managed so that the temperature does not fall below 37°C. In addition, even if the temperature of the material to be fermented temporarily drops below 37°C due to a temporary temperature decrease, it is still regarded as part of the fermentation process. That is, it does not mean that the temperature range is completely outside the specified range. For example, if the temperature deviation is within a certain temperature range (e.g., within 2°C, preferably within 1°C) and for a certain period of time (less than 15 minutes, within 10 minutes, preferably within 5 minutes), even if the temperature of the material to be fermented deviates from the specified temperature range, it still satisfies the fermentation process.

[0041] Here, the start of fermentation refers to the state where the material to be fermented (soybeans, chickpeas, peas, especially soybeans) and the fermenting bacteria (Bacillus subtilis var. natto) coexist, and it is the point in time when the temperature of the material to be fermented first continuously reaches 37°C or higher for 15 minutes. Also, the end of fermentation refers to the point in time when, after fermentation stage (iii), the temperature of the material to be fermented continuously drops below 37°C for 15 minutes. Further, when adopting the inactivation step (iv) in which the temperature of the material to be fermented described later is set to exceed 53°C, it may be an embodiment in which the inactivation step (iv) is provided in the latter half (50% or more, especially 75% or more) of the entire fermentation process.

[0042] The "average oxygen concentration" represents the arithmetic mean value of the oxygen concentrations measured at a finite number of measurement points in the fermentation process. In addition, the average value (which may sometimes be simply referred to as "average" or "arithmetic mean value") in the disclosure of this embodiment refers to the "additive average value" unless otherwise specified. The "average oxygen concentration" can be obtained by continuously measuring the oxygen concentration every 5 minutes by the method described later and calculating the arithmetic mean of these measured values. In addition, the average oxygen concentration inside and outside the packaging container during the fermentation period is preferably the arithmetic mean value of the oxygen concentrations when the temperature of the material to be fermented (soybeans, chickpeas, peas, especially soybeans) is 37°C or higher and 53°C or lower during the fermentation period, and the time when the temperature during the fermentation period drops below 37°C may be included.

[0043] The oxygen concentration inside the packaging container can be measured using an oxygen concentration meter. The oxygen concentration meter can be composed of a main body and an O2 probe. As the main body, for example, "FireSting O2-C (4ch)" can be used, and as the O2 probe, "O2 mini sensor OXF900PT-OI (fixed needle)" can be used. For specific measurement, after sticking a rubber sheet to the ceiling of the packaging container to be measured, the detection part of the measuring instrument (the fixed needle in the above O2 probe) is inserted through the rubber sheet so as to be disposed inside the packaging container, and the oxygen concentration inside the packaging container is continuously measured every 5 minutes. In addition, in this specification, the unit of the oxygen concentration is "%", which is the volume ratio occupied by oxygen when the entire measurement target atmosphere is 100% by volume.

[0044] The oxygen concentration outside the packaging container can be measured using an oxygen concentration meter. The same device as the oxygen concentration meter for measuring the oxygen concentration inside the packaging container can be used. For specific measurement, the detection part of the measuring instrument (the fixed needle in the above O2 probe) is positioned on the outer surface of the packaging container, and the oxygen concentration outside the packaging container is continuously measured every 5 minutes.

[0045] The specific difference between the average oxygen concentration inside the packaging container and the average oxygen concentration outside the packaging container is not limited, but it is preferably 2% or more. By this difference being 2% or more, the activity of Bacillus natto during the fermentation period can be effectively suppressed. The lower limit of this difference can be 2% or more, and can further be 2.5% or more, 3% or more, 3.5% or more, 4% or more, 4.5% or more, 5% or more. On the other hand, the upper limit of this difference is not limited, but can be 16% or less, and can further be 15% or less, 14% or less, 13% or less, 12%. The above-mentioned upper limit and lower limit can be each combination. That is, for example, it can be 2% or more and 16% or less, and can further be 3% or more and 14% or less, and can further be 5% or more and 12% or less.

[0046] The average oxygen concentration inside the packaging container is not limited, but from the perspective of suppressing the activity of Bacillus natto, for example, it can be 5% or more and 12% or less, and can further be 6% or more and 11% or less, and can further be 7.5% or more and 10% or less. Furthermore, the upper limit in each of the above ranges can be 12% or less, 11.5% or less, 11% or less, 10.5% or less, 10% or less. On the other hand, the lower limit in each of the above ranges can be 5% or more, 6% or more, 6.5% or more, 7% or more, 7.5% or more. On the other hand, the average oxygen concentration outside the packaging container is not limited either, but for example, it can be 10% or more and 21% or less.

[0047] The total time of the fermentation process from the start to the end of fermentation is not limited. However, from the perspective of obtaining natto with excellent taste (especially bitterness), texture, aroma, and stretchability (yieldsilk property), usually, the lower limit is 5 hours or more, which can be 6 hours or more, and can further be 7 hours or more, 7.5 hours or more, 8 hours or more, 9 hours or more, 10 hours or more. On the other hand, usually, the upper limit is 23 hours or less, which can be 22 hours or less, and can further be 21 hours or less, 20 hours or less. The above-mentioned upper and lower limits can be in various combinations. That is, for example, it can be 5 hours or more and 23 hours or less, 7.5 hours or more and 22 hours or less, 10 hours or more and 20 hours or less.

[0048] The oxygen concentration in the packaging container (the oxygen concentration at the time of measurement, not the average oxygen concentration) is not limited. However, during the fermentation period, it is preferable from the perspective of effectively suppressing the activity of Bacillus natto during the fermentation period that the packaging container has a period during which the oxygen concentration is 10% or less. Although the lower limit of the length of this period (the period during which the oxygen concentration in the packaging container is 10% or less) is not limited, from the perspective of suppressing the activity of Bacillus natto during the fermentation period, it can be 8 hours or more, and can further be 8.1 hours or more, 8.2 hours or more, 8.3 hours or more, 8.4 hours or more, 8.5 hours or more. On the other hand, although the upper limit of the length of this period is not limited, it can be 20 hours or less, and can further be 18 hours or less, 15 hours or less, 13 hours or less, 10 hours or less, 9.7 hours or less. The above-mentioned upper and lower limits can be in various combinations. That is, for example, it can be 8 hours or more and 20 hours or less, can further be 8.2 hours or more and 15 hours or less, and can further be 8.4 hours or more and 10 hours or less.

[0049] Furthermore, during the fermentation period, it is preferable from the viewpoint of effectively suppressing the activity of Bacillus natto during the fermentation period that there is a period in which the oxygen concentration in the packaging container becomes 8% or less. Although the lower limit of the length of this period (the period in which the oxygen concentration in the packaging container becomes 8% or less) is not limited, from the viewpoint of suppressing the activity of Bacillus natto during the fermentation period, it can be set to 5 hours or more, and further can be set to 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, 9.2 hours or more. On the other hand, although the upper limit of the length of this period is not limited, it can be set to 20 hours or less, and further can be set to 18 hours or less, 15 hours or less, 13 hours or less, 11 hours or less, 10.7 hours or less. The above-mentioned upper and lower limits can be combined in various ways. That is, for example, it can be set to 5 hours or more and 20 hours or less, and further can be set to 7 hours or more and 15 hours or less, and further can be set to 9 hours or more and 11 hours or less.

[0050] Furthermore, during the fermentation period, it is preferable from the viewpoint of effectively suppressing the activity of Bacillus natto during the fermentation period that there is a period in which the oxygen concentration in the packaging container becomes 6% or less. Although the lower limit of the length of this period (the period in which the oxygen concentration in the packaging container becomes 6% or less) is not limited, from the viewpoint of suppressing the activity of Bacillus natto during the fermentation period, it can be set to 2.5 hours or more, and further can be set to 4 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, 9.5 hours or more, 9.7 hours or more. On the other hand, although the upper limit of the length of this period is not limited, it can be set to 15 hours or less, and further can be set to 14 hours or less, 13 hours or less, 12 hours or less, 11 hours or less, 10.7 hours or less. The above-mentioned upper and lower limits can be combined in various ways. That is, for example, it can be set to 2.5 hours or more and 15 hours or less, and further can be set to 5 hours or more and 13 hours or less, and further can be set to 9.5 hours or more and 11 hours or less.

[0051] In the fermentation stage (iii), the statement that "during the fermentation period, the temperature of the material to be fermented is 37°C or higher and 53°C or lower" means that throughout the entire fermentation process from the start to the end of fermentation, the temperature of the material to be fermented (soybeans, chickpeas, peas, especially soybeans) is managed so that it generally does not fall below 37°C (as described above, a temperature drop below 37°C for less than 15 minutes is allowed). From the perspective of obtaining natto with excellent taste (especially bitterness), texture, aroma, and stringiness (drawability), the lower limit of this temperature can be 37°C or higher, and can further be 38°C or higher, 39°C or higher, 40°C or higher, 41°C or higher, 42°C or higher. On the other hand, the upper limit of this temperature can be 53°C or lower, and can further be 52°C or lower, 51°C or lower, 50°C or lower, 49°C or lower, 48°C or lower, 46°C or lower. The above-mentioned upper and lower limits can be in various combinations. That is, for example, it can be 42°C or higher and 53°C or lower, and can further be 42°C or higher and 46°C or lower.

[0052] The management of the temperature can be achieved by using various air-conditioning facilities in the fermentation chamber. Examples of air-conditioning facilities include air conditioners, ventilation fans, electric fans, blowers, heaters (including warm air by steam heating and hot water heating), dimming facilities, etc. Only one type of these can be used, or two or more types can be used in combination. Specifically, in the fermentation stage (iii), heat is generated due to the activity of natto bacteria. Also, the temperature in the fermentation chamber can be affected by the weather. Therefore, cooling or heating can be carried out as necessary to reflect it in the temperature of the material to be fermented.

[0053] In the fermentation stage (iii), the temperature outside the packaging container (ambient temperature) is not particularly limited, but it can be 30°C or higher. The lower limit of the temperature outside the packaging container can be 30°C or higher, and can further be 33°C or higher, 35°C or higher, 37°C or higher. On the other hand, the upper limit of the temperature outside the packaging container can be 67°C or lower, and can further be 66°C or lower, 65°C or lower. The above-mentioned upper and lower limits can be in various combinations. That is, for example, it can be 30°C or higher and 67°C or lower, and can further be 35°C or higher and 66°C or lower. Note that the temperature outside the packaging container refers to the temperature of the outer surface of the packaging container.

[0054] [Stages (iv) of [1-4]] In the first form of the method for producing natto, after the fermentation stage (iii), a deactivation stage (iv) can be provided in which the product temperature of the material to be fermented (soybeans, chickpeas, peas, especially soybeans) is maintained above 53°C. That is, by maintaining the product temperature above 53°C, the promotion of sporulation and / or the reduction / elimination of vegetative cells can inhibit the production of enzymes by live bacteria. Also, by inactivating various enzyme activities through heating, the quality can be stabilized. Therefore, the natto in the state produced so far can be maintained, and further fermentation can be prevented. As a result, the taste (especially bitterness), texture, smell, and stringiness (yields threadability) can be kept in a good state.

[0055] The product temperature in this deactivation stage (iv) only needs to be above 53°C, but from the viewpoint of maintaining the taste (especially bitterness), texture, smell, and stringiness (yields threadability) of natto well, it can be 67°C or lower. The product temperature in this deactivation stage (iv) can be above 53°C and 67°C or lower, can be above 53°C and 66°C or lower, and can be above 53°C and 65°C or lower. Also, the maintenance time of the above product temperature is not limited, but from the viewpoint of ensuring deactivation, it can be 0.1 hour or more and 3.5 hours or less, can be further 0.3 hour or more and 3 hours or less, and can be further 0.5 hour or more and 2 hours or less.

[0056] Also, the deactivation stage (iv) only needs to be carried out after the fermentation stage (iii), but from the viewpoint of stringiness, it can be carried out within 0 hours or more and 3.5 hours from the end of the fermentation in the fermentation stage (iii), can be further carried out within 0.1 hour or more and 3 hours, and can be further carried out within 0.5 hour or more and 2 hours.

[0057] In the first form of the method for producing natto, when the inactivation step (iv) is provided, the degree of enzyme activity is not limited. However, from the perspective of shelf life, the upper limit of the enzyme activity measured in the inactivation step (iv) can be set to 7 U / g or less, and further can be set to 6.5 U / g or less, 6 U / g or less, 5.5 U / g or less, 5 U / g or less, 4.5 U / g or less, 4 U / g or less, 3.5 U / g or less, 3 U / g or less, 2.5 U / g or less. On the other hand, the lower limit can be set to 0.01 U / g or more, and further can be set to 0.03 U / g or more, 0.05 U / g or more, 0.07 U / g or more, 0.1 U / g or more, 0.3 U / g or more, 0.5 U / g or more, 0.7 U / g or more, 1 U / g or more, 1.3 U / g or more, 1.5 U / g or more, 1.7 U / g or more, 2 U / g or more. The above-mentioned upper and lower limits can be in each combination. That is, for example, it can be set to 0.01 U / g or more and 7 U / g or less, further can be set to 0.1 U / g or more and 6 U / g or less, and further can be set to 1 U / g or more and 5 U / g or less. In addition, the enzyme activity in the present application refers to neutral protease activity.

[0058] In addition, the method for measuring the enzyme activity described above is as follows. <Preparation of enzyme solution> Add 200 ml of Na phosphate (20 mM, pH 7) to 20 g of natto, and stir with a stirrer at 4 °C (in ice) for 30 minutes. Then, transfer only the supernatant to a Falcon tube so that no solid content enters. Further, centrifuge at 15000 rpm for 10 minutes, store the supernatant in another Eppendorf (store 1 ml × 5 in a 1.5 ml tube), and store at -80 °C. <Measurement of enzyme activity> Mix 50 μL of the enzyme solution prepared above, 800 μL of the substrate (casein (1% in 20 mM NaPi pH 7)), and 750 μL of the buffer solution (NaPi pH 7), and react at 37 °C for 30 minutes. Add 2400 μl of 5% TCA to stop the reaction, and leave it at room temperature for 30 minutes. Then, centrifuge at 15000 rpm for 10 minutes, take the supernatant into a test tube, and measure the absorbance (280 nm) of the supernatant. Similarly, mix 100 μL of the enzyme solution prepared above, 800 μL of the substrate (casein (1% in 20 mM NaPi pH 7)), and 700 μL of the buffer solution (NaPi pH 7), react at 37 °C for 30 minutes, and measure the absorbance (280 nm) of the supernatant. Note that for the blank, mix the substrate (casein (1% in 20 mM NaPi pH 7)) and the buffer solution (NaPi pH 7) to react, and add the enzyme solution after adding 5% TCA. <Calculation of enzyme activity> At 37 °C, the enzyme activity that cleaves 1 μg of tyrosine from casein per minute is defined as 1 U, and the unit number is calculated using the following calculation formula. Unit number (U): Absorbance (280 nm) / 1.34 / 4 / 30 (1.34: Molar absorbance coefficient of tyrosine, 4: Volume of the reaction vessel (mL), 30: Reaction time (minutes)) Furthermore, using the following calculation formula, divide the unit number by the natto weight converted from the amount of natto extract used in the reaction system to calculate the enzyme activity per 1 g of natto. Enzyme activity (U / g) = Unit number (U) * Volume of the reaction vessel (4000 μL) / Amount of enzyme solution (μL) / (Buffer + natto) (g) / Natto (g) By calculating the arithmetic mean of these, the enzyme activity in the present invention can be determined.

[0059] In the first form of the method for producing natto, other steps can be provided in addition to the above-described packaging container preparation step (i), fermentable substance accommodation step, inoculation step (ii), fermentation step (iii), and inactivation step (iv). Other steps include a cooling step, an aging step, etc. These other steps may use only one type or may use two or more types in combination. For example, after going through a cooling step of cooling to 30°C or lower (desirably about 25°C or lower), it can be moved to an aging chamber and enter the aging step. The aging step can usually be carried out at 4 to 10°C for about 24 to 72 hours after the fermentation is completed. By going through the aging step, the product natto can be obtained.

[0060] [2] Method for manufacturing natto (Second form) The method for manufacturing natto in the second form of the present invention is characterized by including the following steps: (i) a step of preparing a packaging container, (ii) a step of inoculating natto bacteria, and (iii) a step of performing fermentation.

[0061] [2-1] Step (i) Step (i) is a step of preparing a packaging container (packaging container preparation step). The packaging container has, except for not having at least one of (1) an oxygen permeability of 70 cc / cm 2 ·Day·atm or more and 850 cc / cm 2 ·Day·atm or less, and (2) an average pore area of less than 10,000 μm 2 in its essential configuration, is common to the packaging container in the method for manufacturing natto in the first form described above. Also, although it does not have at least one of (1) an oxygen permeability of 70 cc / cm 2 ·Day·atm or more and 850 cc / cm 2 ·Day·atm or less, and (2) an average pore area of less than 10,000 μm 2 in its essential configuration, as described in the method for manufacturing natto in the first form described above, it can satisfy these conditions.

[0062] That is, the packaging container is a container that can accommodate, as the main contents (which may be collectively referred to as the fermentable material), the raw material that is the material to be fermented by the fermenting bacteria and the fermenting bacteria inoculated thereto. And it can have functions as a container for the fermentable material, a fermenting container, an aging container, after the aging is completed, a shipping container, a distribution container, etc., and further, it is a container that can be used in a mode of being directly provided as a tableware. Regarding these points, the description in the method for producing natto of the first embodiment is directly applicable.

[0063] The packaging container can satisfy a predetermined range of oxygen permeability as required. The predetermined range of oxygen permeability may be satisfied in any manner, and the description in the method for producing natto of the first embodiment is directly applicable.

[0064] The oxygen permeability of the packaging container is less than 70 cc / cm 2 ·Day·atm or more than 850 cc / cm 2 ·Day·atm may be acceptable, but it is preferably 70 cc / cm 2 ·Day·atm or more and 850 cc / cm 2 ·Day·atm or less. As described in the first embodiment, being within this range can effectively suppress the activity of Bacillus subtilis natto during the fermentation period. Regarding the upper limit within the above range, the lower limit within the above range, and their combinations, the description in the method for producing natto of the first embodiment is directly applicable.

[0065] Examples of the packaging container that can achieve such oxygen permeability include, for the point that there is a packaging container provided with a cup-shaped part and a top film part that seals the open part after accommodating the fermentable material in the cup-shaped part, it is common with the packaging container in the method for producing natto of the first embodiment described above. The oxygen permeability may be satisfied by only a part of the top film part, or may be satisfied by the entire (whole surface) of the top film part. Regarding this point, the description in the method for producing natto of the first embodiment is directly applicable.

[0066] Also, when a through-hole is provided in the packaging container, the average hole area is not limited, but it can be set within the same range from the same perspective as the packaging container in the method for producing natto of the first embodiment. Also, when a through-hole is provided in the packaging container, the total hole area is not limited, but it can be set within the same range from the same perspective as the packaging container in the method for producing natto of the first embodiment. Furthermore, the aperture ratio (%) of the packaging container is not limited, but it can be set within the same range from the same perspective as the packaging container in the method for producing natto of the first embodiment.

[0067] Also, the number of through-holes is not limited, but it can be set within the same range from the same perspective as the packaging container in the method for producing natto of the first embodiment. Furthermore, the shape of the through-hole is not limited, but it can be set to the same shape from the same perspective as the packaging container in the method for producing natto of the first embodiment. When adopting a top film portion, the material of the film constituting the top film portion is not limited, but it can be made of the same material from the same perspective as the packaging container in the method for producing natto of the first embodiment. Also, the thickness of the film is not limited, but it can be set within the same range from the same perspective as the packaging container in the method for producing natto of the first embodiment. In addition, the material constituting the packaging container is not limited, and it can be made of the same material from the same perspective as the packaging container in the method for producing natto of the first embodiment.

[0068] Also, as the content in the packaging container, in addition to the main content described above in the method for producing natto of the first embodiment, within a range that does not affect the fermentation of the material to be fermented, other things may be enclosed in the same manner as the content in the packaging container in the method for producing natto of the first embodiment. Also, regarding laying a film-like thin film on the material to be fermented, whether to make holes in the film-like thin film, enclosing tableware such as spoons and forks, etc., it is the same as the content in the packaging container in the method for producing natto of the first embodiment. Furthermore, the size of the packaging container is also the same as that in the method for producing natto of the first embodiment.

[0069] [2-2] Step (ii) Step (ii) is the step of inoculating Bacillus natto (inoculation step). That is, it is the step of accommodating the fermenting bacteria necessary for fermentation in the packaging container prepared in the step of (i). In the present invention, the fermenting bacteria are Bacillus natto. Regarding Step (ii), the description regarding Step (ii) described in the method for producing natto of the first embodiment is applied as it is.

[0070] [2-3] Step (iii) Step (iii) is the step of performing fermentation (fermentation step) that satisfies all of the following (1) to (3). (1) During the fermentation period, the average oxygen concentration in the packaging container is relatively lower than the average oxygen concentration outside the packaging container (2) During the fermentation period, the temperature of the material to be fermented is 37°C or higher and 53°C or lower (3) During the fermentation period, the time when the oxygen concentration in the packaging container becomes 10% or less is 8 hours or more

[0071] In Step (iii), regarding "(1) During the fermentation period, the average oxygen concentration in the packaging container is relatively lower than the average oxygen concentration outside the packaging container", the description in the method for producing natto of the first embodiment is applied as it is. And the specific difference between the average oxygen concentration in the packaging container and the average oxygen concentration outside the packaging container is not limited, but the description in the method for producing natto of the first embodiment is applied as it is. Also, the average oxygen concentration in the packaging container and the average oxygen concentration outside the packaging container are not limited, but the description in the method for producing natto of the first embodiment is applied as it is. Furthermore, the total time of the fermentation process from the start of fermentation to the end of fermentation is not limited, but the description in the method for producing natto of the first embodiment is applied as it is. In Step (iii), regarding "(2) During the fermentation period, the temperature of the material to be fermented is 37°C or higher and 53°C or lower", the description in the method for producing natto of the first embodiment is applied as it is.

[0072] In step (iii), by "the time when the oxygen concentration in the packaging container (the oxygen concentration at the time of measurement, not the average oxygen concentration) becomes 10% or less during the fermentation period is 8 hours or more", the activity of Bacillus natto can be effectively suppressed during the fermentation period. The lower limit of the length of this period (the period when the oxygen concentration in the packaging container becomes 10% or less) is 8 hours or more from the viewpoint of suppressing the activity of Bacillus natto, but it can be further 8.1 hours or more, 8.2 hours or more, 8.3 hours or more, 8.4 hours or more, 8.5 hours or more. On the other hand, although the upper limit of the length of this period is not limited, it can be 20 hours or less, and can be further 18 hours or less, 15 hours or less, 13 hours or less, 10 hours or less, 9.7 hours or less. The above-mentioned upper and lower limits can be in each combination. That is, for example, it can be 8 hours or more and 20 hours or less, and can be further 8.2 hours or more and 15 hours or less, and can be further 8.4 hours or more and 10 hours or less.

[0073] Furthermore, from the viewpoint of effectively suppressing the activity of Bacillus natto during the fermentation period, it is preferable that during the fermentation period, there is a period when the oxygen concentration in the packaging container becomes 8% or less. Although the lower limit of the length of this period (the period when the oxygen concentration in the packaging container becomes 8% or less) is not limited, from the viewpoint of suppressing the activity of Bacillus natto, it can be 5 hours or more, and can be further 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, 9.2 hours or more. On the other hand, although the upper limit of the length of this period is not limited, it can be 20 hours or less, and can be further 18 hours or less, 15 hours or less, 13 hours or less, 11 hours or less, 10.7 hours or less. The above-mentioned upper and lower limits can be in each combination. That is, for example, it can be 5 hours or more and 20 hours or less, and can be further 7 hours or more and 15 hours or less, and can be further 9 hours or more and 11 hours or less.

[0074] Furthermore, during the fermentation period, it is preferable from the viewpoint of effectively suppressing the activity of Bacillus natto during the fermentation period that there is a period in which the oxygen concentration in the packaging container becomes 6% or less. Although the lower limit of the length of this period (the period in which the oxygen concentration in the packaging container becomes 6% or less) is not limited, from the viewpoint of suppressing the activity of Bacillus natto, it can be 2.5 hours or more, and further can be 4 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, 9.5 hours or more, 9.7 hours or more. On the other hand, although the upper limit of the length of this period is not limited, it can be 15 hours or less, and further can be 14 hours or less, 13 hours or less, 12 hours or less, 11 hours or less, 10.7 hours or less. The above-mentioned upper and lower limits can be each combination. That is, for example, it can be 2.5 hours or more and 15 hours or less, further can be 5 hours or more and 13 hours or less, and further can be 9.5 hours or more and 11 hours or less.

[0075] [2-4] Step (iv) In the second form of the method for producing natto, after the fermentation step (iii), a deactivation step (iv) for maintaining the product temperature of the material to be fermented (soybeans, chickpeas, peas, especially soybeans) above 53°C can be provided. Regarding the deactivation step (iv), the description in the method for producing natto of the first form is applied as it is.

[0076] In the second form of the method for producing natto, when the deactivation step (iv) is provided, the degree of enzyme activity is not limited, but can be in the same range from the same viewpoint as the method for producing natto of the first form.

[0077] [3] Natto obtained by this method (the first form and the second form) (3-1) The natto obtained by the method for producing natto of the first form is natto characterized by being produced through the following steps (i) to (iii). (i) A step of preparing a packaging container satisfying at least one of the following (1) to (2), (1) The oxygen permeability is 70 cc / cm 2 ·Day·atm or more and 850 cc / cm2 ·Below ·day·atm (2) The average pore area is 10,000 μm 2 Less than (ii) The step of inoculating natto bacteria (iii) The step of performing fermentation satisfying the following (1) and (2) (1) During the fermentation period, the average oxygen concentration in the packaging container is relatively lower than the average oxygen concentration outside the packaging container (2) During the fermentation period, the temperature of the material to be fermented is 37 °C or higher and 53 °C or lower Details are as described above

[0078] (3-2) The natto obtained by the method for producing natto of the second form Is natto characterized by being produced through the following steps (i) to (iii) (i) The step of preparing a packaging container (ii) The step of inoculating natto bacteria (iii) The step of performing fermentation satisfying all of the following (1) to (3) (1) During the fermentation period, the average oxygen concentration in the packaging container is relatively lower than the average oxygen concentration outside the packaging container (2) During the fermentation period, the temperature of the material to be fermented is 37 °C or higher and 53 °C or lower (3) During the fermentation period, the time when the oxygen concentration in the packaging container becomes 10% or less is 8 hours or more Details are as described above

[0079] The natto obtained by this method can contain one or more free amino acids selected from 20 types including aspartic acid, threonine, serine, glutamic acid, proline, glycine, alanine, valine, cysteine, methionine, isoleucine, leucine, tyrosine, phenylalanine, histidine, lysine, tryptophan, arginine, asparagine, and glutamine. "Free amino acid" refers to an amino acid that exists alone in a free state in the composition, separate from the amino acids that make up proteins and peptides. Incidentally, the free amino acid may contain any number of the above-mentioned 20 types. In addition, for amino acids having optical isomers (i.e., amino acids other than glycine), unless otherwise specified, the types of optical isomers are not particularly limited. That is, each amino acid may be in the L-form, the D-form, or a DL-form containing the L-form and the D-form in an arbitrary ratio.

[0080] Natto obtained by this method, the total content of free amino acids contained in the fermented product (natto) continuously stored at 10°C for 10 days after the fermentation stage (iii) is not limited, but can be 50 mg% or more in terms of the total content measured by the method for measuring the amino acid content described below. Thereby, natto with excellent storage stability can be obtained. The lower limit in the total content of these free amino acids can be further 70 mg% or more, 100 mg% or more, 130 mg% or more, 150 mg% or more, 180 mg% or more, 200 mg% or more, 210 mg% or more, 220 mg% or more, 230 mg% or more. On the other hand, the upper limit in the total content of free amino acids is not limited, but can be, for example, 930 mg% or less, and can be further 900 mg% or less, 870 mg% or less, 850 mg% or less, 830 mg% or less, 800 mg% or less, 780 mg% or less, 750 mg% or less, 730 mg% or less. The above-mentioned upper and lower limits can be each combination. That is, for example, it can be 50 mg% or more and 930 mg% or less, and can be further 150 mg% or more and 800 mg% or less, and can be further 210 mg% or more and 750 mg% or less. In addition, even when the storage temperature becomes not 10°C due to a temporary temperature change, it is regarded as natto continuously stored at 10°C for 10 days. That is, it does not mean that the temperature is completely out of the range. For example, within a certain temperature range (for example, within 2°C, preferably within 1°C) and for a certain time (less than 15 minutes, within 10 minutes, preferably within 5 minutes), even when out of the temperature range, it means that the requirements for the natto are satisfied.

[0081] <Method for Measuring Amino Acid Content> After crushing 5 g of natto and suspending it in 5% TCA, put it into a 50 ml volumetric flask and fill it up with 5% TCA. Then, place the volumetric flask in an ultrasonic cleaner and leave it for 30 minutes. After that, transfer the suspension to a centrifuge tube and centrifuge it at 7,500 rpm for 5 minutes. After centrifugation, dilute the supernatant 10-fold with 0.02 N hydrochloric acid, and then filter it through a 0.22 μm filter. The filtrate is used as a sample and measured using an amino acid analyzer (high-speed amino acid analyzer, manufactured by Hitachi High-Tech Corporation, model "LA8080").

[0082] Natto obtained by this method, where the fermented product (natto) is continuously stored at 10°C for 10 days after the fermentation stage (iii), satisfies at least one of the following (a) to (e). That is, it may satisfy one or more of the following (a) to (e), two or more, three or more, four or more, or all five. Furthermore, it may satisfy the total content of the aforementioned free amino acids. (a) The lysine content is 90 mg% or less (b) The ammonia content is 160 mg% or less (c) The glutamic acid content is 125 mg% or less (d) The tyrosine content is 120 mg% or less (e) The total content of bitter amino acids is 580 mg% or less

[0083] Regarding natto obtained by this method, the content of (a) lysine (Lys) contained in the fermented product (natto) continuously stored at 10°C for 10 days after the fermentation stage (iii) is not limited, but the content measured by the aforementioned amino acid content measurement method can be made 90 mg% or less. Thereby, natto with suppressed bitterness can be obtained. The upper limit of this lysine content can further be 85 mg% or less, 80 mg% or less, 75 mg% or less, 73 mg% or less, 70 mg% or less, 68 mg% or less, 65 mg% or less, 60 mg% or less, 58 mg% or less, 55 mg% or less, 53 mg% or less, 50 mg% or less. On the other hand, the lower limit of the lysine content is not limited, but for example, it can be 5 mg% or more, and further 10 mg% or more, 13 mg% or more, 15 mg% or more, 18 mg% or more, 20 mg% or more. The above-mentioned upper and lower limits can be in each combination. That is, for example, it can be 5 mg% or more and 90 mg% or less, further 10 mg% or more and 75 mg% or less, further 20 mg% or more and 65 mg% or less.

[0084] Natto obtained by this method, the content of (b) ammonia (NH3) in the fermented product (natto) continuously stored at 10°C for 10 days after the fermentation stage (iii) is not limited, but the content measured by the amino acid content measurement method described above can be made 160 mg% or less. Thereby, natto with suppressed odor (ammonia odor) can be obtained. The upper limit of the ammonia content can further be 150 mg% or less, 140 mg% or less, 135 mg% or less, 130 mg% or less, 125 mg% or less, 120 mg% or less, 115 mg% or less, 110 mg% or less, 100 mg% or less, 95 mg% or less, 90 mg% or less. On the other hand, the lower limit of the ammonia content is not limited, but for example, it can be 5 mg% or more, and can further be 10 mg% or more, 15 mg% or more, 20 mg% or more, 25 mg% or more, 30 mg% or more. The above-mentioned upper and lower limits can be in each combination. That is, for example, it can be 5 mg% or more and 160 mg% or less, can further be 15 mg% or more and 130 mg% or less, can further be 30 mg% or more and 110 mg% or less. In addition, the degree of fermentation suppression that occurs after the fermentation stage (iii) of the produced natto (when the above-described inactivation stage (iv) is provided, after the inactivation stage (iv)) can be determined using the amount of ammonia contained in the natto as an index. Ammonia is considered to be generated by the assimilation of various nitrogen compounds contained in soybeans by natto bacteria.

[0085] Natto obtained by this method, the content of (c) glutamic acid (Glu) contained in the fermented product (natto) continuously stored at 10°C for 10 days after the fermentation stage (iii) is not limited, but can be made 125 mg% or less by the measurement method of the amino acid content described above. Thereby, natto with suppressed astringency can be obtained. The upper limit of the content of this glutamic acid can further be 120 mg% or less, 115 mg% or less, 110 mg% or less, 105 mg% or less, 100 mg% or less, 95 mg% or less. On the other hand, the lower limit of the content of glutamic acid is not limited, but can be, for example, 5 mg% or more, and can further be 10 mg% or more, 15 mg% or more, 20 mg% or more, 25 mg% or more, 30 mg% or more, 35 mg% or more. The above-mentioned upper and lower limits can be each combination. That is, for example, it can be 5 mg% or more and 125 mg% or less, and can further be 15 mg% or more and 115 mg% or less, and can further be 25 mg% or more and 110 mg% or less.

[0086] Natto obtained by this method, the content of (d) tyrosine (Tyr) contained in the fermented product (natto) continuously stored at 10°C for 10 days after the fermentation stage (iii) is not limited, but can be made 120 mg% or less by the measurement method of the amino acid content described above. Thereby, it is possible to suppress the occurrence of a crispy texture in natto. The upper limit of the content of this tyrosine can further be 115 mg% or less, 110 mg% or less, 100 mg% or less, 95 mg% or less. On the other hand, the lower limit of the content of tyrosine is not limited, but can be, for example, 5 mg% or more, and can further be 10 mg% or more, 15 mg% or more, 20 mg% or more, 25 mg% or more. The above-mentioned upper and lower limits can be each combination. That is, for example, it can be 5 mg% or more and 120 mg% or less, and can further be 15 mg% or more and 110 mg% or less, and can further be 20 mg% or more and 100 mg% or less.

[0087] Natto obtained by this method, wherein the content of (e) bitter amino acids in the fermented product (natto) continuously stored at 10°C for 10 days after the fermentation step (iii) is not limited, but can be made 580 mg% or less in terms of the total content measured by the above-described amino acid content measurement method. Thereby, natto with suppressed bitterness can be obtained. This bitter amino acid means eight kinds of amino acids: valine (Val), methionine (Met), isoleucine (Ile), leucine (Leu), tyrosine (Tyr), phenylalanine (Phe), lysine (Lys), and arginine (Arg). Therefore, the content of (e) bitter amino acids is the total of the contents of these eight kinds of amino acids. The upper limit in the total content of this bitter amino acid can further be 570 mg% or less, 560 mg% or less, 550 mg% or less, 540 mg% or less, 530 mg% or less, 520 mg% or less, 510 mg% or less, 500 mg% or less, 490 mg% or less, 480 mg% or less, 470 mg% or less, 460 mg% or less. On the other hand, the lower limit in the total content of bitter amino acids is not limited, but can be, for example, 80 mg% or more, and can further be 90 mg% or more, 100 mg% or more, 110 mg% or more, 120 mg% or more, 130 mg% or more. The above-described upper and lower limits can be in each combination. That is, for example, it can be 80 mg% or more and 580 mg% or less, can further be 100 mg% or more and 530 mg% or less, and can further be 120 mg% or more and 500 mg% or less.

[0088] In the natto obtained by including the inactivation step (iv) in this method, although the total content of free amino acids contained in the fermented product (natto) continuously stored at 10°C for 30 days after the inactivation step (iv) is not limited, it can be made 1900 mg% or less in terms of the total content measured by the above-described method for measuring amino acid content. Thereby, natto excellent in storability can be obtained. The upper limit in the total content of these free amino acids can further be 1850 mg% or less, 1800 mg% or less, 1750 mg% or less, 1700 mg% or less, 1680 mg% or less, 1650 mg% or less, 1630 mg% or less, 1600 mg% or less. On the other hand, although the lower limit in the total content of free amino acids is not limited, for example, it can be 300 mg% or more, and can further be 400 mg% or more, 500 mg% or more, 550 mg% or more, 600 mg% or more, 630 mg% or more, 650 mg% or more, 670 mg% or more. The above-described upper and lower limits can be each combination. That is, for example, it can be 300 mg% or more and 1900 mg% or less, and can further be 450 mg% or more and 1750 mg% or less, and can further be 600 mg% or more and 1650 mg% or less. In addition, even when the storage temperature becomes not 10°C due to a temporary temperature change, it is regarded as natto continuously stored at 10°C for 30 days. That is, it does not mean that the temperature is completely deviated. For example, even when the temperature is outside the range within a certain temperature range (for example, within 2°C, preferably within 1°C) for a certain time (less than 15 minutes, within 10 minutes, preferably within 5 minutes), it means that the requirements of the natto are satisfied.

[0089] The natto obtained by this method, wherein the fermented product (natto) continuously stored at 10°C for 30 days after the fermentation step (iii) satisfies at least one of the following (a) to (b) and (d) to (f). That is, it may satisfy one or more of the following (a) to (b) and (d) to (f), or may satisfy two or more, or may satisfy three or more, or may satisfy four or more, or may satisfy all five. Further, the total content of the above-described free amino acids may be satisfied. (a) The content of lysine is 115 mg% or less (b) The ammonia content is 190 mg% or less (d) The tyrosine content is 200 mg% or less (e) The total content of bitter amino acids is 1100 mg% or less (f) The valine content is 90 mg% or less

[0090] In the natto obtained by including the inactivation step (iv) in this method, although the content of (f) valine (Val) contained in the fermented product (natto) continuously stored at 10°C for 30 days after the inactivation step (iv) is not limited, the content measured by the above-described amino acid content measurement method can be made 90 mg% or less. Thereby, natto with suppressed bitterness can be obtained. The upper limit of this valine content can be further 88 mg% or less, 87 mg% or less, 85 mg% or less, 83 mg% or less, 82 mg% or less, 81 mg% or less, 80 mg% or less, 79 mg% or less. On the other hand, although the lower limit of the valine content is not limited, for example, it can be 10 mg% or more, 15 mg% or more, 20 mg% or more, 25 mg% or more, 30 mg% or more, 35 mg% or more, 38 mg% or more. The above-described upper and lower limits can be each combination. That is, for example, it can be 10 mg% or more and 90 mg% or less, further 20 mg% or more and 85 mg% or less, further 35 mg% or more and 80 mg% or less.

[0091] In the natto obtained by including the inactivation step (iv) in this method, although the content of (a) lysine (Lys) in the fermented product (natto) continuously stored at 10°C for 30 days after the inactivation step (iv) is not limited, the content measured by the above-described amino acid content measurement method can be made 115 mg% or less. Thereby, natto with suppressed bitterness can be obtained. The upper limit of the content of this lysine can further be 110 mg% or less, 105 mg% or less, 100 mg% or less, 95 mg% or less, 90 mg% or less, 85 mg% or less. On the other hand, although the lower limit of the content of lysine is not limited, for example, it can be 25 mg% or more, and further 30 mg% or more, 35 mg% or more, 40 mg% or more, 45 mg% or more, 50 mg% or more. The above-described upper and lower limits can be each combination. That is, for example, it can be 25 mg% or more and 115 mg% or less, further 35 mg% or more and 105 mg% or less, further 50 mg% or more and 95 mg% or less.

[0092] In the natto obtained by including the inactivation step (iv) in this method, although the content of (b) ammonia (NH3) in the fermented product (natto) continuously stored at 10°C for 30 days after the inactivation step (iv) is not limited, the content measured by the above-described amino acid content measurement method can be made 190 mg% or less. Thereby, natto with suppressed odor (ammonia odor) can be obtained. The upper limit of the content of this ammonia can further be 180 mg% or less, 170 mg% or less, 165 mg% or less, 160 mg% or less, 155 mg% or less, 150 mg% or less, 145 mg% or less, 140 mg% or less. On the other hand, although the lower limit of the content of ammonia is not limited, for example, it can be 50 mg% or more, and further 60 mg% or more, 70 mg% or more, 80 mg% or more, 85 mg% or more, 90 mg% or more. The above-described upper and lower limits can be each combination. That is, for example, it can be 50 mg% or more and 190 mg% or less, further 70 mg% or more and 170 mg% or less, further 80 mg% or more and 150 mg% or less.

[0093] In the natto obtained by including the inactivation step (iv) in this method, although the content of (d) tyrosine (Tyr) contained in the fermented product (natto) continuously stored at 10°C for 30 days after the inactivation step (iv) is not limited, the content measured by the above-described amino acid content measurement method can be made 200 mg% or less. Thereby, it is possible to suppress the occurrence of a crispy texture in the natto. The upper limit of the content of this tyrosine can further be 195 mg% or less, 193 mg% or less, 190 mg% or less, 187 mg% or less, 185 mg% or less, 183 mg% or less, 180 mg or less. On the other hand, although the lower limit of the content of tyrosine is not limited, for example, it can be 20 mg% or more, and further 30 mg% or more, 40 mg% or more, 50 mg% or more, 60 mg% or more, 70 mg% or more. The above-described upper limit and lower limit can be each combination. That is, for example, it can be 20 mg% or more and 200 mg% or less, and further 40 mg% or more and 190 mg% or less, and further 60 mg% or more and 180 mg% or less.

[0094] In the natto obtained by including the inactivation step (iv) in this method, although the content of (e) bitter amino acids in the fermented product (natto) continuously stored at 10°C for 30 days after the inactivation step (iv) is not limited, it can be made 1100 mg% or less in the total content measured by the amino acid content measurement method described above. Thereby, natto with suppressed bitterness can be obtained. This bitter amino acid means eight kinds of amino acids: valine (Val), methionine (Met), isoleucine (Ile), leucine (Leu), tyrosine (Tyr), phenylalanine (Phe), lysine (Lys), and arginine (Arg). Therefore, the content of (e) bitter amino acids is the total of the contents of these eight kinds of amino acids. The upper limit in the total content of this bitter amino acid can be further 1080 mg% or less, 1060 mg% or less, 1050 mg% or less, 1030 mg% or less, 1020 mg% or less, 1000 mg% or less, 980 mg% or less, 970 mg% or less, 960 mg% or less. On the other hand, the lower limit in the content of bitter amino acids is not limited, but for example, it can be 300 mg% or more, and further 320 mg% or more, 340 mg% or more, 350 mg% or more, 380 mg% or more, 390 mg% or more, 400 mg% or more. The above-mentioned upper and lower limits can be each combination. That is, for example, it can be 300 mg% or more and 1100 mg% or less, further 350 mg% or more and 1000 mg% or less, and further 400 mg% or more and 980 mg% or less.

Example

[0095] Hereinafter, the present invention will be described in more detail according to examples, but these examples are merely examples shown for convenience of explanation, and the present invention is not limited to these examples in any sense.

[0096] [1] Production of natto 〈1〉 Production of natto in Experimental Examples 1 to 15 and 17 to 31 (1) Packaging container preparation step (i) A container (natto container) having a cup-shaped part made of polystyrene foam (PSP), and the aperture ratio shown in Tables 1 to 6 (×10―4 (%), and average pore area (μm 2 ) and a top film were prepared. The container having a cup-shaped portion has a substantially negligible oxygen permeability, and the oxygen permeability of the packaging container (Tables 1 to 6) is achieved by the through-holes provided in the top film.

[0097] Note that the oxygen permeability of the packaging container was measured in accordance with JIS K-7126-2. Specifically, using a gas barrier test apparatus (model "OX-TRAN 1 / 50", manufactured by MOCON), the oxygen permeability of the packaging container (that is, the packaging container in which the top film is attached to the cup opening of the container having the cup-shaped portion to form a top film portion) at a temperature of 23 ± 2 °C and a relative humidity of 50% (unit: cc / cm 2 ·Day·atm) was measured. Note that the acidity permeability of the packaging container was measured by masking all other through-holes with aluminum tape, measuring the oxygen permeability of only one through-hole to be measured, multiplying the oxygen permeability by the total area of the through-holes (measured using a microscope), and adding the value obtained by multiplying the oxygen permeability of the region of the member without through-holes by the area of the region without through-holes. The oxygen permeability of the entire packaging container was calculated as the total value and shown in Tables 1 to 6.

[0098] (2) Inoculation stage (ii) The dried soybeans were immersed in water for 16 hours, drained, and then pressure-cooked at 1.6 kg / cm 2 for 30 minutes. A natto bacteria solution containing K-245 strain: Bacillus subtilis K-245; NITE BP-01804, which is natto bacteria, was added so that 5000 natto bacteria were contained per 1 g of the cooked soybeans, and the mixture was gently homogenized to obtain a material to be fermented. Forty grams of the obtained material to be fermented was placed in a container having the cup-shaped portion described above, and then covered with the top film described above.

[0099] (3) Fermentation stage (iii) The packaging container containing the material to be fermented and covered was placed stationary in a programmable incubator set at a gas phase temperature of 43 °C, and fermentation was carried out over 16 hours. During the fermentation period, the average oxygen concentration in the packaging container was measured using an oxygen concentration meter (composed of a main body and an O2 probe, with "FireSting O2-C (4ch)" as the main body and "O2 mini sensor OXF900PT-OI (fixed needle)" as the O2 probe). Specifically, after pasting a rubber sheet on the ceiling of the packaging container, the detection part of the measuring device (the fixed needle of the above O2 probe) was inserted through the rubber sheet so as to be placed in the packaging container, and the oxygen concentration in the packaging container was continuously measured every 5 minutes, and calculated as the average value of the oxygen concentration measured every 5 minutes over 16 hours. The results are shown in Tables 1 to 6.

[0100] Similarly, the average oxygen concentration outside the packaging container during the fermentation stage was measured using the same oxygen concentration meter. Specifically, the detection part of the measuring device (the fixed needle in the above O2 probe) was positioned on the outer periphery of the packaging container, and the oxygen concentration outside the packaging container was continuously measured every 5 minutes, and calculated as the average value of the oxygen concentration measured every 5 minutes over 16 hours. The results are shown in Tables 1 to 6. Also, from the above measurement results, the time when the oxygen concentration in the packaging container reached 6% or less, the time when the oxygen concentration in the packaging container reached 8% or less, and the time when the oxygen concentration in the packaging container reached 10% or less were calculated, and the results are shown in Tables 1 to 6. Furthermore, when measuring the temperature of the material to be fermented during the fermentation period, the product temperature was 46 - 50 °C. The product temperature increased with the fermentation heat and reached a steady state. Also, the temperature of the outer surface of the packaging container during the fermentation period was constantly 30 °C or higher. These temperatures were measured using a TPF1100 fixed needle temperature mini sensor.

[0101] (4) Cooling stage · Aging stage After the fermentation stage was completed, the product temperature was cooled to 20 °C. Then, it was transferred to a refrigerator at 4 °C and left to stand for 8 hours in a state where the product temperature was about 5 °C for aging to obtain natto.

[0102] 〈2〉 Production of natto in Experimental Example 16 In the same manner as in Experimental Examples 1 to 15 and 17 to 31, the packaging container preparation step (i) and the inoculation step (ii) were carried out. Then, the fermentation step (iii) was carried out in the same manner as in Experimental Examples 1 to 15 and 17 to 31, except that outside air was forcibly introduced into the packaging container throughout the fermentation period so that the average oxygen concentration in the packaging container in Table 2 became 8.0%. Thereafter, further, in the same manner as in Experimental Examples 1 to 15 and 17 to 31, natto was obtained through the cooling step and the aging step.

[0103] 〈3〉Production of Natto in Experimental Examples 32 to 46 In the same manner as in Experimental Examples 1 to 15 and 17 to 31, the packaging container preparation step (i), the inoculation step (ii), and the fermentation step (iii) were carried out. Next, the inactivation step (iv) was carried out for 0.5 hours with the gas phase temperature of the incubator set at 60°C. Thereafter, further, in the same manner as in Experimental Examples 1 to 15 and 17 to 31, natto was obtained through the cooling step and the aging step from the fermentation step (iii).

[0104] [2] Evaluation 〈1〉Measurement of Various Amino Acids and Ammonia Each of the natto samples obtained in Experimental Examples 1 to 31 in the above [1]<1> and [1]<2> was continuously stored at 10°C for 10 days. After that, 5 g of each stored natto was crushed and suspended in 5% TCA, then placed in a 50-ml volumetric flask and filled up with 5% TCA. Then, the volumetric flask was placed in an ultrasonic cleaner and left for 30 minutes. After that, the suspension was transferred to a centrifuge tube and centrifuged at 7,500 rpm for 5 minutes. The supernatant after centrifugation was diluted 10-fold with 0.02N hydrochloric acid and then filtered through a 0.22-μm filter. The filtrate was used as a sample to measure the contents of various amino acids (lysine, glutamic acid, tyrosine, valine, methionine, isoleucine, leucine, phenylalanine, and arginine) and the content of ammonia using an amino acid analyzer (high-speed amino acid analyzer, manufactured by Hitachi High-Tech Corporation, model "LA8080"). Among them, the content of lysine was shown in the column of "Lys (mg%) 10°C × 10 days" in Tables 1 to 4, the content of ammonia was shown in the column of "NH3 (mg%) 10°C × 10 days" in Tables 1 to 4, the content of glutamic acid was shown in the column of "Glu (mg%) 10°C × 10 days" in Tables 1 to 4, the content of tyrosine was shown in the column of "Tyr (mg%) 10°C × 10 days" in Tables 1 to 4, and the total amount of 8 amino acids including valine, methionine, isoleucine, leucine, tyrosine, phenylalanine, lysine, and arginine was shown in the column of "Bitter amino acids (mg%) 10°C × 10 days" in Tables 1 to 4, respectively.

[0105] <2>Measurement of drawability Each of the natto samples obtained in Experimental Examples 1 to 31 in the above [1]<1> and [1]<2> was continuously stored at 10°C for 10 days. After stirring the natto 30 times / 10 seconds with chopsticks, the degree of difficulty of the natto grains falling from the chopsticks when lifting a lump of natto grains (about 20 grams) with chopsticks was evaluated. A comprehensive evaluation was carried out according to the following evaluation criteria, and the results are shown in Tables 1 to 4. 5: Very strong (when lifting a lump of mixed natto grains with chopsticks, it is held in the air for more than 3 seconds and does not fall) 4: Strong (when lifting a lump of mixed natto grains with chopsticks, it takes 1 second or more and 3 seconds or less to be held in the air until it falls) 3: Normal (when lifting a lump of mixed natto grains with chopsticks, the natto grains fall without being able to be held in the air) 2: Weak (the thread can be pulled, but no lumps of natto grains are formed) 1: Very weak (the thread cannot be pulled)

[0106] 〈3〉Sensory evaluation The sensory evaluation was conducted according to the following procedure. First, as sensory examiners for each sensory test, after conducting discrimination training on the taste, texture, appearance, etc. of foods in advance, examiners who were particularly excellent in performance, had experience in product development, had rich knowledge about the quality of foods such as taste, texture, and appearance, and were capable of making absolute evaluations regarding each sensory test item were selected. Specifically, after conducting the following discrimination trainings A) to C), examiners who were particularly excellent in performance, had rich knowledge about the quality of foods such as taste and texture, and were capable of making absolute evaluations regarding each sensory test item were selected.

[0107] A) Regarding the five basic tastes (sweetness: the taste of sugar, sourness: the taste of tartaric acid, umami: the taste of sodium glutamate, saltiness: the taste of sodium chloride, bitterness: the taste of caffeine), one aqueous solution with a concentration close to the threshold value of each component was prepared, and two distilled waters were added to these, making a total of seven samples. A taste quality discrimination test was conducted to accurately identify each taste sample. B) A concentration difference discrimination test was conducted to accurately identify the concentration differences of five types of aqueous sodium chloride solutions and aqueous acetic acid solutions with slightly different concentrations. C) A three-point discrimination test was conducted to accurately identify soy sauce from manufacturer B from a total of three samples, two from manufacturer A and one from manufacturer B.

[0108] Next, ten selected sensory examiners conducted a sensory evaluation on the bitterness of each natto in Experimental Examples 1 to 31 obtained in the above [1]〈1〉and [1]〈2〉, which were continuously stored at 10°C for 10 days, according to the following evaluation criteria. The evaluation was conducted in such a way that each examiner selected one number closest to their own evaluation from among the five-level scoring system. The total of the evaluation results was calculated as the arithmetic mean value of the scores of the ten examiners, and the decimal part was rounded off. The results were shown in the columns of "Sensory evaluation (bitterness)" in Tables 1 to 4. 5: No bitterness is felt, which is very preferable. 4: Almost no bitterness is felt, which is preferable. 3: The bitterness is not felt much and is somewhat preferable. 2: The bitterness is slightly felt and is somewhat less preferable. 1: The bitterness is felt and is not preferable.

[0109] 〈4〉Comprehensive evaluation Regarding each of the natto samples in Experimental Examples 1 to 31 obtained in the above [1]〈1〉and [1]〈2〉, and the natto stored continuously at 10°C for 10 days, a comprehensive evaluation was performed according to the following evaluation criteria, and the results are shown in Tables 1 to 4. Note that for Experimental Example 1, since it was not fermented or had poor fermentation, almost no thread pulling was observed and the texture was also poor. 5: The taste (especially bitterness), texture, smell, and thread pulling (yarn-drawing property) are very excellent and are very preferable. 4: The taste (especially bitterness), texture, smell, and thread pulling (yarn-drawing property) are excellent and are preferable. 3: The taste (especially bitterness), texture, smell, and thread pulling (yarn-drawing property) are somewhat excellent and are somewhat preferable. 2: The taste (especially bitterness), texture, smell, and thread pulling (yarn-drawing property) are somewhat less excellent and are somewhat less preferable. 1: The taste (especially bitterness), texture, smell, and thread pulling (yarn-drawing property) are not excellent and are not preferable.

[0110] 〈5〉Measurement of enzyme activity Using each of the natto samples in Experimental Examples 32 to 46 obtained in the above [1]〈3〉(natto before being stored continuously at 10°C for 30 days), an enzyme solution was prepared according to the following procedure, and the enzyme activity was measured from the enzyme solution according to the following procedure, and the results are shown in Tables 5 to 6. <Preparation of enzyme solution> Add 200 ml of Na phosphate (20 mM, pH 7) to 20 g of natto, stir with a stirrer at 4°C (in ice) for 30 minutes, and then transfer only the supernatant to a Falcon tube so that no solid content enters. Further, centrifuge at 15,000 rpm for 10 minutes, store the supernatant in another Eppendorf (store 1 ml × 5 in 1.5 ml tubes), and store at -80°C.

[0111] <Measurement of enzyme activity> 50 μL of the enzyme solution prepared above, 800 μL of the substrate (casein (1% in 20 mM NaPi pH 7)), and 750 μL of the buffer (NaPi pH 7) were mixed and reacted at 37°C for 30 minutes. 2400 μl of 5% TCA was added to stop the reaction, and it was left at room temperature for 30 minutes. Then, it was centrifuged at 15000 rpm for 10 minutes, the supernatant was taken into a test tube, and the absorbance (280 nm) of the supernatant was measured. Similarly, 100 μL of the enzyme solution prepared above, 800 μL of the substrate (casein (1% in 20 mM NaPi pH 7)), and 700 μL of the buffer (NaPi pH 7) were mixed and reacted at 37°C for 30 minutes, and the absorbance (280 nm) of the supernatant was measured. Note: For the blank, the substrate (casein (1% in 20 mM NaPi pH 7)) and the buffer (NaPi pH 7) were mixed and reacted, and the enzyme solution was added after adding 5% TCA.

[0112] <Enzyme activity calculation> At 37°C, the enzyme activity that cuts out 1 μg of tyrosine from casein per minute is defined as 1 U, and the unit number is calculated using the following calculation formula. Unit number (U): Absorbance (280 nm) / 1.34 / 4 / 30 (1.34: Molar absorbance coefficient of tyrosine, 4: Volume of the reaction vessel (mL), 30: Reaction time (minutes)) Furthermore, using the following calculation formula, the unit number is divided by the natto weight converted from the amount of natto extract used in the reaction system to calculate the enzyme activity per 1 g of natto. Enzyme activity (U / g) = Unit number (U) * Volume of the reaction vessel (4000 μL) / Amount of enzyme solution (μL) / (Buffer + Natto) (g) / Natto (g) The enzyme activity was determined by calculating the arithmetic mean of these.

[0113] 〈6〉Measurement of various amino acids and ammonia Each of the natto samples obtained in Experimental Examples 32 to 46 in the above [1]<3> was continuously stored at 10°C for 30 days. After that, for each of the stored natto samples, in the same manner as in the above [2]<1>, the contents of various amino acids (lysine, glutamic acid, tyrosine, valine, methionine, isoleucine, leucine, phenylalanine, and arginine) and the content of ammonia were measured. Among these, the content of tyrosine was shown in the column of "Tyr (mg%) 10°C × 30 days" in Tables 5 to 6, the content of valine was shown in the column of "Val (mg%) 10°C × 30 days" in Tables 5 to 6, the content of lysine was shown in the column of "Lys (mg%) 10°C × 30 days" in Tables 5 to 6, the content of ammonia was shown in the column of "NH3 (mg%) 10°C × 30 days" in Tables 5 to 6, and the total amount of 8 amino acids, namely valine, methionine, isoleucine, leucine, tyrosine, phenylalanine, lysine, and arginine, was shown in the column of "Bitter amino acids (mg%) 10°C × 30 days" in Tables 5 to 6, respectively.

[0114] <7> Sensory evaluation Ten sensory examiners selected in the same manner as in the above [2]<3> conducted a sensory evaluation on the bitterness of each of the natto samples obtained in Experimental Examples 32 to 46 in the above [1]<3> that had been continuously stored at 10°C for 30 days, according to the same evaluation criteria as in the above [2]<3>. The evaluation method and the tabulation of the evaluation results were also the same as in the above [2]<3>, and the results were shown in the column of "Sensory evaluation (bitterness)" in Tables 5 to 6.

[0115] <8> Comprehensive evaluation For each of the natto samples obtained in Experimental Examples 32 to 46 in the above [1]<3> that had been continuously stored at 10°C for 30 days, a comprehensive evaluation was conducted according to the following evaluation criteria, and the results were shown in Tables 5 to 6. 5: Taste (especially bitterness), texture, smell, and silk pulling (dragging silk property) are extremely excellent and very preferable. 4: Taste (especially bitterness), texture, smell, and silk pulling (dragging silk property) are excellent and preferable. 3: Taste (especially bitterness), texture, smell, and silk pulling (dragging silk property) are slightly excellent and slightly preferable. 2: Taste (especially bitterness), texture, smell, and silk pulling (dragging silk property) are not slightly excellent and not slightly preferable. 1: The taste (especially bitterness), texture, smell, and thread drawing (yarn-drawing property) are not excellent and are not preferable.

[0116]

Table 1

[0117]

Table 2

[0118]

Table 3

[0119]

Table 4

[0120]

Table 5

[0121]

Table 6

Industrial Applicability

[0122] The natto of the present invention, its production method, packaging container, and film are widely used in the food field.

Claims

1. A method for producing natto, comprising the following steps (i) to (iii). (i) Preparing a packaging container having a low oxygen permeation site that satisfies the following (2); (2) having a top film portion that seals an open portion opened upward, the top film portion being a film with a thickness of 100 μm or less composed of at least one selected from paper, expanded polystyrene, styrene-modified polyolefin resin, polystyrene resin, polyolefin resin, and polyester resin, having a low oxygen permeation site in part or all of the top film portion, The low oxygen permeability part has through holes with an average pore area of 500 μm2 or more and less than 10,000 μm ２ and an aperture ratio of 0.0015% or more and 0.022% or less (ii) Enclosing a material to be fermented and natto bacteria in the packaging container; (iii) Performing fermentation that satisfies the following (1) and (2) on the contents in the packaging container, (1) During the fermentation period, the average oxygen concentration in the packaging container is relatively lower than the average oxygen concentration outside the packaging container (2) During the fermentation period, the product temperature of the contents is 37°C or higher and 53°C or lower

2. A method for producing natto, comprising the following steps (i) to (iii). (i) Preparing a packaging container having a low oxygen permeation site; (ii) Enclosing a material to be fermented and natto bacteria in the packaging container; (iii) Performing fermentation that satisfies all of the following (1) to (3) on the contents in the packaging container, (1) During the fermentation period, the average oxygen concentration in the packaging container is relatively lower than the average oxygen concentration outside the packaging container (2) During the fermentation period, the product temperature of the contents is 37°C or higher and 53°C or lower (3) By supplying oxygen consumed by the natto bacteria from the atmosphere in the fermentation chamber through the low oxygen permeation site, the time during which the oxygen concentration in the packaging container becomes 10% or less during the fermentation period is 8 hours or more and 20 hours or less

3. The method for producing natto according to claim 1, further satisfying the following (3) in the above (iii). (3) By supplying oxygen consumed by the natto bacteria from the atmosphere in the fermentation chamber through the low oxygen permeation site, the time during which the oxygen concentration in the packaging container becomes 10% or less during the fermentation period is 8 hours or more and 20 hours or less

4. The method for producing natto according to claim 2, wherein in the above (i), the packaging container has a low oxygen permeation site that satisfies the following (2). (2) having a top film portion that seals an open portion opened upward The top film part is a film with a thickness of 100 μm or less, made of at least one selected from paper, styrofoam, styrene-modified polyolefin resin, polystyrene resin, polyolefin resin, and polyester resin. A part or all of the top film part has a low oxygen permeation site. The low oxygen permeation part has through holes with an average pore area of 500 μm2 or more and less than 10,000 μm ２ and a porosity of 0.0015% or more and 0.022% or less

5. Furthermore, in the above (iii), the method for producing natto according to claim 1 or 2, which satisfies the following (4). (4) The time when the oxygen concentration in the packaging container becomes 8% or less is 5 hours or more and 20 hours or less.

6. Furthermore, in the above (iii), the method for producing natto according to claim 1 or 2, which satisfies the following (5). (5) The time when the oxygen concentration in the packaging container becomes 6% or less is 2.5 hours or more and 15 hours or less.

7. Furthermore, in the above (iii), the method for producing natto according to claim 1 or 2, which satisfies the following (6). (6) The temperature outside the packaging container is 30°C or more and 67°C or less.

8. The method for producing natto according to claim 2, wherein the low oxygen permeation site is a film.

9. The method for producing natto according to claim 1 or 2, wherein the content stored continuously at 10°C for 10 days after the above (iii) satisfies at least one of the following (a) to (e). (a) The lysine content is 90 mg% or less. (b) The ammonia content is 160 mg% or less. (c) The glutamic acid content is 125 mg% or less. (d) The tyrosine content is 120 mg% or less. (e) The total content of bitter amino acids is 580 mg% or less.

10. Furthermore, the method for producing natto according to claim 1 or 2, which includes the following step (iv) after the above (iii). (iv) Adjust the temperature of the content after the above (iii) so that the product temperature becomes more than 53°C and 67°C or less.

11. The method for producing natto according to claim 10, wherein the time when the product temperature becomes more than 53°C and 67°C or less is 0.1 hour or more and 3.5 hours or less.

12. The method for producing natto according to claim 10, wherein the content stored continuously at 10°C for 30 days after the above (iv) satisfies at least one of the following (a) to (b) and (d) to (f). (a) The lysine content is 115 mg% or less. (b) The ammonia content is 190 mg% or less. (d) The tyrosine content is 200 mg% or less. (e) The total content of bitter amino acids is 1100 mg% or less. (f) The valine content is 90 mg% or less.

13. The method for producing natto according to claim 10, further satisfying the following (g) after the above (iv). (g) The enzyme activity is 0.01 U / g or more and 7 U / g or less

14. Natto characterized by being produced through the following steps (i) to (iii). (i) A step of preparing a packaging container having a low oxygen permeation site (ii) A step of enclosing the material to be fermented and natto bacteria in the packaging container (iii) A step of performing fermentation that satisfies all of the following (1) to (3) on the contents in the packaging container (1) During the fermentation period, the average oxygen concentration in the packaging container is relatively lower than the average oxygen concentration outside the packaging container (2) During the fermentation period, the product temperature of the contents is 37°C or higher and 53°C or lower (3) By supplying the oxygen consumed by the natto bacteria from the atmosphere in the fermentation chamber through the low oxygen permeation site, the time during which the oxygen concentration in the packaging container becomes 10% or less during the fermentation period is 8 hours or more and 20 hours or less

15. A packaging container characterized by being used for the purpose of producing natto having a low oxygen permeation site that satisfies at least one of the following (1) to (2). (1) The oxygen permeability is 70 cc / cm ２ ·Day·atm or more and 850 cc / cm ２ ·Day·atm or less (2) It has a top film part that seals an opening part opened upward The top film part is a film with a thickness of 100 μm or less composed of at least one or more selected from paper, styrofoam, styrene-modified polyolefin resin, polystyrene resin, polyolefin resin, and polyester resin The top film part has a low oxygen permeation site in part or in whole The low oxygen permeation site has through holes with an average pore area of 500 μm2 or more and less than 10,000 μm ２ and an aperture ratio of 0.0015% or more and 0.022% or less

16. Further, the packaging container according to claim 15, which is used for the purpose of storing at 10°C for 1 day or more and 14 days or less after the fermentation is completed

17. Further, the packaging container according to claim 15 or 16, which is used in the method for producing natto according to claim 1

18. A film characterized by being used for a natto production container that satisfies at least one of the following (1) to (2). (1) The oxygen permeability is 70 cc / cm ２ ·Day·atm or more and 850 cc / cm ２ ·Day·atm or less (2) It is a film with a thickness of 100 μm or less composed of at least one or more selected from paper, styrofoam, styrene-modified polyolefin resin, polystyrene resin, polyolefin resin, and polyester resin It has a low oxygen permeation site in part or in whole The low-oxygen permeation part has through holes with an average pore area of 500 μm2 or more and less than 10,000 μm ２ and a porosity of 0.0015% or more and 0.022% or less

19. Further, the film according to claim 18, which is used for the purpose of storing at 10°C for 14 days or less after the fermentation is completed

20. Furthermore, the film according to claim 18 or 19, which is used as a top film portion for sealing an opening portion opened upward of the packaging container in the method for producing natto according to claim 1.

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