Natto, preparation method thereof, 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, and a packaging container and film. More specifically, the present invention relates to natto having excellent storage stability, a method for producing the same, and a packaging container and film. [Background technology]

[0002] A method for producing natto that has improved flavor and stringiness and also suppresses the generation of an ammonia odor, and natto produced by this method are disclosed in the following Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-000127 A Summary of the Invention [Problem to be solved by the invention]

[0004] The method of Patent Document 1 is characterized in that, following stationary fermentation in the fermentation process, the fermentation process is continued while maintaining the oxygen concentration in the air in the fermentation chamber in a low oxygen concentration range of 2 to 8%. This is excellent in that it is possible to obtain natto that has improved flavor and stringiness, and in which the generation of ammonia odor is suppressed.

[0005] On the other hand, as shown in Patent Document 1, the production of natto requires time because it involves fermentation, but its expiration date is generally short, about 10 days. For this reason, it is necessary to adjust the production volume in anticipation of the shipping volume. However, there are fluctuations in demand due to trends, weather, etc., and these are not easy to predict. For this reason, there is a problem that food loss occurs due to demand fluctuations. As a countermeasure against this demand fluctuation, an option to extend the shelf life of the product can be considered. This is because extending the shelf life makes it easier to manage stock and can increase the countermeasure against demand fluctuations. However, there is a problem that the technology disclosed in the above Patent Document 1 cannot produce natto with a longer shelf life than the current situation.

[0006] The present invention has been made in consideration of the above problems, and aims to provide natto having a longer shelf life than conventional natto, a method for producing the same, and a packaging container and film. [Means for solving the problem]

[0007] The present inventors have repeatedly reexamined the method of producing natto from the viewpoint of extending the shelf life. As a result, they have focused on the fact that the technology of Patent Document 1 is a technology that maintains the oxygen concentration in the air inside the fermentation chamber at an extremely low oxygen concentration range of 2 to 8%. This environment is an environment for producing natto with improved flavor and stringiness and suppressed generation of ammonia odor, but it is an environment to be formed in the entire fermentation chamber. For this reason, in order to make the packaging container that contains natto common to the environment inside the fermentation chamber, it has become necessary to use a packaging container with high breathability. That is, it was necessary to commonize the environment by using a packaging container with high breathability and circulating the atmosphere inside the fermentation chamber and the atmosphere inside the packaging container. However, the packaging container for natto is designed to function as a fermentation container during fermentation from the viewpoint of cost efficiency, etc., and to function as a product container after the product is completed, and the fermentation container and the product container are common. For this reason, it has been found that the breathability of the packaging container, which is dominant during fermentation, is a factor that makes it difficult to prevent the intrusion of bacteria other than natto bacteria during product distribution, and this is one of the causes of shortening the shelf life. However, since natto bacteria consume an extremely large amount of oxygen during fermentation, it has also been found that in a packaging container in which the prevention of the intrusion of bacteria other than natto bacteria is highly prioritized, oxygen in the packaging container becomes insufficient during fermentation, making fermentation itself difficult. Therefore, the present inventors have found that it is possible to dramatically extend the shelf life by using a packaging container with lower breathability than conventional ones while enabling the supply of oxygen from the atmosphere in the fermentation chamber into the packaging container.

[0008] As a result, it was found that the possibility of food loss can be significantly reduced in proportion to the extension of the shelf life. Furthermore, it was found that the risk of a significantly hypoxic state in the fermentation chamber can be reduced. In other words, an atmosphere in a fermentation chamber that is in a significantly hypoxic state is highly dangerous to 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 respect, it was found that the production method of the present application is a method that can reduce the risk during production because the oxygen concentration in the fermentation chamber can be maintained higher than in the past.

[0009] That is, the present invention includes the following inventions. [1] A method for producing natto, comprising the following steps (i) to (iii): (i) preparing a packaging container having a low oxygen permeable portion that satisfies at least one of the following (1) to (2): (1) Oxygen permeability is 70cc / cm 2 ·Day · atm or more 850cc / cm 2 ·Day·atm or less (2) Average pore area is 10,000 μm 2 With a through hole of less than (ii) inoculating Bacillus subtilis natto; (iii) carrying out fermentation 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) The temperature of the fermented product during the fermentation period is between 37°C and 53°C. [2] A method for producing natto, comprising the following steps (i) to (iii): (i) preparing a packaging container; (ii) inoculating Bacillus subtilis natto; (iii) A step of carrying out fermentation that satisfies 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) The temperature of the fermented product during the fermentation period is between 37°C and 53°C. (3) During the fermentation period, the oxygen concentration in the packaging container is 10% or less for 8 hours or more. [3] The method for producing natto according to [1] above, further satisfying the following (3) in (iii). (3) During the fermentation period, the oxygen concentration in the packaging container is 10% or less for 8 hours or more. [4] Further, in the (i) above, the packaging container has a low oxygen permeable portion that satisfies at least one of the following (1) to (2). The method for producing natto according to the above [2]. (1) Oxygen permeability is 70cc / cm2 ·Day · atm or more 850cc / cm 2 ·Day·atm or less (2) Average pore area is 10,000 μm 2 With a through hole of less than [5] The method for producing natto according to any one of [1] to [4] above, further satisfying the following (4) in (iii). (4) The oxygen concentration in the packaging container remains below 8% for 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). (5) The time period during which the oxygen concentration in the packaging container falls to 6% or less is between 2.5 hours and 15 hours. [7] The method for producing natto according to any one of [1] to [6] above, further satisfying the following (6) in (iii). (6) The temperature outside the packaging container is 30°C or higher. [8] The method for producing natto according to any one of [1] to [7] above, wherein the opening rate of the low oxygen permeable portion 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 portion is a film.

[10] The method for producing natto according to any one of [1] to [9] above, wherein the lysine content (a) contained in the fermented product stored at 10 ° C. for 10 consecutive 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 ammonia content (b) contained in the fermented product stored continuously for 10 days at 10 ° C. after (iii) above 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 stored continuously for 10 days at 10 ° C. after (iii) above is 125 mg% or less.

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

[12] above, wherein the fermented product stored at 10 ° C. for 10 consecutive days after (iii) has a tyrosine content of 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 stored continuously for 10 days at 10°C after (iii) above 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 the step (iii). (iv) The temperature of the fermented product after (iii) is adjusted to be higher than 53°C.

[16] The method for producing natto according to

[15] above, in which the step (iv) is carried out within 3.5 hours after the step (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 valine content (f) contained in the fermented product stored continuously for 30 days at 10 ° C. after (iv) above is 90 mg % or less.

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

[15] to

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

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

[15] to

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

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

[15] to

[20] above, wherein the tyrosine content (d) contained in the fermented product stored continuously for 30 days at 10°C after (iv) above 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 bitter amino acids (e) contained in the fermented product stored continuously for 30 days at 10°C after (iv) above 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 (iv). (g) Enzyme activity is 7 U / g or less

[24] Natto, characterized in that it is produced through the following steps (i) to (iii). (i) preparing a packaging container having a low oxygen permeable portion that satisfies at least one of the following (1) to (2): (1) Oxygen permeability is 70cc / cm 2 ·Day · atm or more 850cc / cm 2 ·Day·atm or less (2) Average pore area is 10,000 μm 2 With a through hole of less than (ii) inoculating Bacillus subtilis natto; (iii) carrying out fermentation 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) The temperature of the fermented product during the fermentation period is between 37°C and 53°C.

[25] Natto, characterized in that it is produced through the following steps (i) to (iii). (i) preparing a packaging container; (ii) inoculating Bacillus subtilis natto; (iii) A step of carrying out fermentation that satisfies 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) The temperature of the fermented product during the fermentation period is between 37°C and 53°C. (3) During the fermentation period, the oxygen concentration in the packaging container is 10% or less for 8 hours or more.

[26] A packaging container for use in producing natto, the packaging container having a low oxygen permeable portion that satisfies at least one of the following (1) to (2): (1) Oxygen permeability is 70cc / cm 2 ·Day · atm or more 850cc / cm 2·Day·atm or less (2) Average pore area is 10,000 μm 2 With a through hole of less than

[27] Furthermore, the packaging container according to the above

[26] is used for storing the product at 10°C for 14 days or less after fermentation is completed.

[28] Furthermore, the packaging container according to

[26] or

[27] above, wherein the porosity of the low oxygen permeable portion is 0.022% or less.

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

[26] to

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

[30] A film characterized by being used for a natto production container that satisfies at least one of the following (1) to (2): (1) Oxygen permeability is 70cc / cm 2 ·Day · atm or more 850cc / cm 2 ·Day·atm or less (2) Average pore area is 10,000 μm 2 With a through hole of less than

[31] Furthermore, the film according to the above

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

[32] The film according to the above

[30] or

[31] , wherein the porosity of the low oxygen permeable portion is 0.022% or less.

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

[30] to

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

[0010] According to the method for producing natto of the present invention, it is possible to produce natto that has a longer shelf life than conventional methods. The natto of the present invention can be made to have a longer shelf life than conventional natto. According to the packaging container of the present invention, natto having a longer shelf life than conventional natto can be produced. According to the film of the present invention, natto having a longer shelf life than conventional natto can be produced. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described below based on specific embodiments. However, the present invention is not limited to these embodiments. These embodiments are merely examples shown for the sake of convenience, and the present invention is not limited to these in any sense. The present invention can be modified in various ways depending on the purpose and application. In addition, all publications, patents, and patent applications cited in this specification are incorporated herein by reference as they are.

[0012] In addition, in this specification, the expression "and / or" includes both the meanings of "and" and "or." For example, "A and / or B" includes both the meanings of A and B and A or B, and indicates the three cases of A alone, B alone, and both A and B. Furthermore, in this specification, when multiple upper limit values ​​and / or multiple lower limit values ​​are shown for the specification of a numerical range, even if not specifically stated, the specification of a numerical range combining at least the maximum value of the upper limit specification and the minimum value of the lower limit specification is directly described, and further, 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 with "~" 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 with "~".

[0013] [1] Natto manufacturing method (first form) The method for producing natto according to the first embodiment of the present invention is characterized by comprising the following steps: (i) preparing a packaging container; (ii) inoculating; and (iii) fermenting.

[0014] [1-1] Stage (i) Step (i) is a step of preparing a packaging container having a low oxygen permeable portion that satisfies at least one of the following (1) and (2) (packaging container preparation step). (1) Oxygen permeability is 70cc / cm 2·Day · atm or more 850cc / cm 2 ·Day·atm or less (2) Average pore area is 10,000 μm 2 With a through hole of less than

[0015] The packaging container is a container that can accommodate the raw material, which is the material to be fermented by the fermenting bacteria, and the fermenting bacteria inoculated therein, as the main contents (these may be collectively referred to as the material to be fermented). In the present invention, the fermenting bacteria is Bacillus subtilis natto, and the material to be fermented includes soybeans, chickpeas, peas, etc. From this point of view, it has a function as a container for the material to be fermented. Furthermore, it is a container that can be filled with the material to be fermented, sealed, and then used for fermentation as is. That is, from this point of view, it has a function as a fermentation container. Furthermore, it is a container that can be used for aging as is after fermentation is completed. That is, from this point of view, it can have a function as an aging container. Furthermore, it is a container that can be packaged as necessary after aging is completed, and can be shipped as a product as is, and can be distributed. That is, from this point of view, it can have a function as a shipping container and a distribution container. Furthermore, it is a container that can be used as a tableware as is. That is, it is a container that does not have holes, etc. through which liquid seasonings, etc. flow out from the bottom and lower sides of the container, and from this point of view, it can have a function as a tableware. Since the manner in which the fermented material is ingested varies depending on the person consuming it, there is no limitation as to whether the packaging container is used as tableware or not.

[0016] This packaging container satisfies at least one of (1) a predetermined range of oxygen permeability and (2) a predetermined range of average hole area. Of the above, (1) the predetermined range of oxygen permeability may be satisfied in any way. 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 a through hole, or it may be achieved by the oxygen permeability of the member (for example, film) itself, not just a visible opening such as a through hole. Note that the packaging container that requires the oxygen permeability is a container that is in contact with the outside air. In addition, when (1) is satisfied, (2) may or may not be satisfied.

[0017] The oxygen permeability of packaging containers is usually 70cc / cm 2 ·Day · atm or more 850cc / cm 2 ·Day·atm or less, and further 150cc / cm 2 ·Day · atm or more 750cc / cm 2 ·Day·atm or less, and further 230cc / cm 2 ·Day · atm or more 600cc / cm 2 ·Day·atm or less. By being in this range, the activity of Bacillus subtilis natto during the fermentation period can be effectively suppressed. Note that the packaging container after (iii) may or may not satisfy at least one of (i)(1) and (i)(2). The upper limit of the above range is 850cc / cm 2 ·Day·atm or less, but still 830cc / cm 2 ·Day · ATM or less, 810cc / cm 2 ·Day · ATM or less, 800cc / cm 2 ·Day · ATM or less, 780cc / cm 2 ·Day · ATM or less, 760cc / cm 2 ·Day · ATM or less, 750cc / cm 2 ·Day · ATM or less, 730cc / cm 2 ·Day · ATM or less, 700cc / cm2 ·Day · ATM or less, 680cc / cm 2 ·Day · ATM or less, 650cc / cm 2 ·Day · ATM or less, 630cc / cm 2 ·Day · ATM or less, 600cc / cm 2 ·Day · ATM or less, 590cc / cm 2 On the other hand, the lower limit of the above range is 70 cc / cm 2 ·Day·atm or more, but with an additional 100cc / cm 2 ·Day · atm or more, plus 120cc / cm 2 ·Day · atm or more, 150cc / cm 2 ·Day · ATM or higher, 180cc / cm 2 ·Day · ATM or more, 200cc / cm 2 ·Day · ATM or higher, 210cc / cm 2 ·Day · ATM or higher, 230cc / cm 2 ·Day · ATM or higher, 240cc / cm 2 ·Day · ATM or higher, 250cc / cm 2 ·Day·atm or more. The above upper and lower limits can be combined with each other. For example, the oxygen permeability is 120 cc / cm 2 ·Day · atm or more 850cc / cm 2 ·Day·atm and below, 100cc / cm 2 ·Day · atm or more 800cc / cm 2 ·Day·atm or less, 200cc / cm 2 ·Day · atm or more 650cc / cm 2 ·Day·atm or less, 230cc / cm 2 ·Day · atm or more 750cc / cm 2 ·Day·atm or less, 230cc / cm 2 ·Day · atm or more 600cc / cm 2 ·Day·atm or less. Furthermore, by satisfying the above configuration, the activity of natto bacteria after fermentation can be effectively suppressed, and thus a natto bacteria fermented product (particularly natto) with a longer shelf life than usual can be obtained. Specifically, after 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 may usually be 1 day or more, or 3 days or more. Furthermore, by satisfying the above configuration, the container can be used as a packaging container for storage purposes with a shelf life of 14 days or less, or 10 days or less, at an average storage temperature of 10°C. Furthermore, the film satisfying the above configuration may be used in a natto production container, or the film may be attached to the opening of the natto production container.

[0018] The oxygen permeability is measured in accordance with JIS K-7126-2. Specifically, the oxygen permeability (unit: cc / cm) at a temperature of 23±2°C and a relative humidity of 50% is measured using a gas barrier tester (model "OX-TRAN 1 / 50", manufactured by MOCON). 2 ·Day·atm) is measured. If the packaging container is composed of one type of material, the oxygen transmission rate per area of ​​the material is measured and multiplied by the area of ​​the material used in one packaging container to obtain the oxygen transmission rate. If the packaging container is composed of two or more types of materials, the oxygen transmission rate per area of ​​each material is measured and multiplied by the area of ​​each material used in one packaging container to obtain the oxygen transmission rate. Furthermore, if the component of the packaging container has a through hole, all other through holes are masked with aluminum tape and the oxygen transmission rate of only the one through hole to be measured is measured. Then, the oxygen transmission rate is calculated as the sum of the value obtained by multiplying the oxygen transmission rate by the total area of ​​the through holes (measured using a microscope) and the value obtained by multiplying the oxygen transmission rate of the area of ​​the material that does not have a through hole by the area of ​​the area that does not have a through hole.

[0019] An example of a packaging container that can achieve such oxygen permeability is a packaging container that has a bottom and side portions that do not have through holes through which liquids can leak when used as tableware, a cup-shaped portion that has an open portion (a portion that opens upward) that allows the fermented material to be received from above, and a top film portion that seals the open portion after the fermented material is received in the cup-shaped portion. When the top film portion is used to satisfy the above-mentioned oxygen permeability, the above-mentioned oxygen permeability may be satisfied by only a portion of the top film portion, or the above-mentioned oxygen permeability may be satisfied by the entire top film portion (entire surface).

[0020] On the other hand, among the above, (2) the average hole area of ​​the predetermined range may be satisfied in any manner. That is, for example, the average hole area may be satisfied by through holes provided in only a part of the packaging container, or the average hole area may be satisfied by through holes provided in the entire packaging container. Note that the packaging container requiring the average hole 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 a through hole, the average hole area is not limited, but from the viewpoint of effectively suppressing the activity of Bacillus subtilis natto during the fermentation period, the upper limit is 10,000 μm 2 It can be less than 9500 μm 2 or less, and further 9000 μm 2 or less, and further 8500 μm 2 or less, and further 8000 μm 2 Below, 7000μm 2 Below, 6000μm 2 Below, 5000μm 2 Below, 4500μm 2 Below, 4200μm 2 Below, 4000μm 2 Below, 3800μm 2 Below, 3500μm 2 Below, 3400μm 2 Below, 3300μm 2 Below, 3200μm2 The above ranges can more effectively prevent mold from entering through the through holes. On the other hand, the lower limit is 500 μm or less. 2 or more, and further 700 μm 2 More than 800μm 2 More than 900μm 2 More than 1000μm 2 More than 1100μm 2 More than 1200μm 2 The above ranges can ensure better oxygen flow inside and outside the packaging container. The above upper and lower limits can be combined. That is, for example, the average pore area is 500 μm 2 More than 10000μm 2 It can be less than 800 μm 2 More than 8000μm 2 Further, 1000μm 2 More than 5000μm 2 Below that, another 1100μm 2 More than 4000μm 2 Below that, another 1200μm 2 More than 3500μm 2 It can be as follows: Furthermore, by satisfying the above configuration, the activity of natto bacteria after fermentation can be effectively suppressed, and thus a natto bacteria fermented product (particularly natto) with a longer shelf life than usual can be obtained. Specifically, after 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 may usually be 1 day or more, or 3 days or more. Furthermore, by satisfying the above configuration, the container can be used as a packaging container for storage purposes with a shelf life of 14 days or less, or 10 days or less, at an average storage temperature of 10°C. In particular, when used for fermented natto products stored for 3 days or more or 5 days or more in a household refrigerator where mold cleaning is not usually performed thoroughly, it is useful because it reduces the risk of mold contamination during storage in the household refrigerator. There is no particular upper limit, 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 storage in a household refrigerator for 3 days or more or 5 days or more. Furthermore, the film satisfying the above configuration may be used in a natto production container, or the film may be attached to the opening of the natto production container.

[0022] The average hole area means the average hole area of ​​the through holes in a plan view when the through holes are provided in the packaging container. The average hole area represents the arithmetic average of the hole 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, the average hole area represents the arithmetic average of the oxygen permeability of all the through holes in the packaging container. The hole area is the average hole area on the outer surface of the packaging container. The hole area is measured by observing the through holes with a digital microscope VHX-7000 (manufactured by KEYENCE Corporation), and measuring the hole area of ​​the obtained image using the image analysis software installed in the microscope, selecting "automatic area measurement" in the area measurement. The sum of the hole areas is the total hole area. This total hole area is a value calculated by multiplying the average hole area by the number of holes in the entire packaging container.

[0023] Furthermore, when the packaging container has through holes, the total hole area is not limited, but the activity of Bacillus subtilis natto can be effectively suppressed during the fermentation period. This total hole area is, for example, 120,000 μm 2 More than 1,600,000μm 2 or less, and further 300,000 μm 2 More than 1,500,000μm 2 or less, and further 450,000 μm 2 More than 1,400,000μm 2Furthermore, the upper limit of each of the above ranges is 1,600,000 μm or less. 2 Below, 1,500,000μm 2 Below, 1,400,000μm 2 Below, 1,350,000μm 2 Less than 1,300,000μm 2 Below, 1,250,000μm 2 Below, 1,200,000μm 2 Below, 1,150,000μm 2 Below, 1,100,000μm 2 On the other hand, the lower limit of each of the above ranges is 120,000 μm or less. 2 More than 150,000μm 2 More than 180,000μm 2 More than 200,000μm 2 More than 250,000μm 2 More than 300,000μm 2 More than 350,000μm 2 More than 400,000μm 2 More than 450,000μm 2 It can be more than that.

[0024] The porosity (%) of the packaging container is not limited, but from the viewpoint of suppressing the intrusion 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 of 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, or 0.016% or less. Meanwhile, the lower limit of 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, or 0.006% or more. The porosity is the ratio (%) of the total area of ​​the through holes that are actually opened to the total area of ​​the surface of the packaging container on which the through holes are provided. In addition, the actual number of through holes is not limited, but can be, for example, 30 to 1000, further 70 to 850, and further 120 to 750. In addition, by satisfying the above configuration, the intrusion of mold can be suppressed, and thus the expiration date of natto can be extended more than usual. Specifically, after the end of fermentation, 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 may be usually 1 day or more, or 3 days or more. Furthermore, by satisfying the above configuration, the container can be used as a packaging container for storage at an average storage temperature of 10°C with an expiration date of 14 days or less, or 10 days or less.

[0025] The planar shape of the through-hole is not limited, and for example, an elliptical hole, a regular circle hole, a diamond hole, a triangular hole, a trapezoidal hole, a line hole, a rectangular hole, or a cross, an X-shape, a Y-shape, an H-shape, etc. can be used. The hole opening position of the lid material for natto containers may be uniformly opened over the entire surface of the lid area, or may be partially opened. The method of opening fine holes is not particularly limited, and examples of the method include commonly used mechanical perforation, hot needle or laser perforation, but mechanical perforation using a roller method is convenient.

[0026] When a top film portion is employed, the material of the film constituting the top film portion is not limited, and examples thereof include paper, polystyrene foam, various plastics, etc. (for example, films formed from foam sheets made of various synthetic resins such as paper, styrene-modified polyolefin resins, polystyrene, high-impact polystyrene, polystyrene-ethylene copolymer and other polystyrene resins, polyethylene, polypropylene, ethylene-vinyl acetate copolymer and other polyolefin resins, polyethylene terephthalate and other polyester resins, etc.). These may be used alone or in combination of two or more. In addition, the thickness of the film is not limited, but can be, for example, 100 μm or less, 80 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, or 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, polystyrene foam, various plastics, etc. (for example, cup-shaped paper containers, containers molded from foam sheets made of various synthetic resins such as styrene-modified polyolefin resins, polystyrene, high impact polystyrene, polystyrene-ethylene copolymers, polyolefin resins such as polyethylene, polypropylene, ethylene-vinyl acetate copolymers, and polyester 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 fermentation bacteria. From the viewpoints of heat retention during fermentation, lightness when stacked in mass production, lightness during shipping, shock absorption, shape retention when eaten, lightness, and manufacturing costs, paper or polystyrene foam is preferable, and polystyrene foam (specifically, polystyrene is one example) is more preferable. Regarding light transmittance, if activation of photosynthesis or fermentation by light is desired, a highly transparent material should be selected, but if no action by light is required, an opaque material can be used. From the viewpoint of deterioration of quality due to light exposure during distribution and sales, an opaque material can be used.

[0029] In addition, the contents in the packaging container may include, in addition to the above-mentioned main contents (fermented material by fermentation bacteria (soybeans, chickpeas, peas, especially soybeans) and fermentation bacteria (natto bacteria) inoculated on the fermented material), general liquid / gel-like / powdered / solid seasonings, etc., may be enclosed in a small bag or separate structure of the container, etc., as long as they do not affect the fermentation of the fermented material. In addition, there is no restriction on whether or not a thin film-like thin film is laid on the fermented material so that the fermented material does not come into contact with or adhere to the lid of the container and hinder ease of eating, as long as it is in a form that does not affect the fermentation of the fermented material. Similarly, there is no particular restriction on whether or not to open holes in the thin film-like thin film. Furthermore, it is also possible to enclose tableware such as spoons and forks from the viewpoint of improving the ready-to-eat nature. These are distinguished from the fermented material in the container.

[0030] The size of the packaging container is not limited, but from the viewpoint of suitability for individual consumption, it is preferable that the size is such that the content of the fermented material before fermentation can be enclosed in an amount of, for example, 20 g to 300 g. More specifically, when the container is substantially cylindrical, it is preferable that the minimum diameter is, for example, 4 cm to 15 cm and the height is, for example, 4 cm to 10 cm, and when the container is substantially rectangular or square, it is preferable that the minimum width is, for example, 5 cm to 15 cm and the height is, for example, 2 cm to 5 cm.

[0031] [1-2] Stage (ii) Step (ii) is a step of inoculating Bacillus subtilis natto (inoculation step). That is, this is the step of placing the fermentation bacteria necessary for fermentation in the packaging container prepared in the step (i). In the present invention, the fermentation bacteria is Bacillus subtilis natto. Any natto bacteria can be used. For example, Miyagino bacteria (trade name: pure cultured natto bacteria (Miyagino natto bacteria)) (manufactured by Miyagino Manufacturing Co., Ltd.), Takahashi bacteria (trade name: Natto base) (manufactured by Takahashi Yuzo Laboratory Co., Ltd.), Naruse bacteria (trade name: powdered natto bacteria) (manufactured by Naruse Fermentation Chemistry Laboratory), etc., which are common commercially available bacteria, can be used, but various strains such as mutant strains and genetically modified strains having specific properties can also be used. Among them, it is preferable to use the K-245 strain or the No. 7 strain, and it is particularly preferable to use the K-245 strain. The K-245 strain has been internationally deposited under the name of Bacillus subtilis K-245 strain with the accession number NITE BP-01804 at the Patent Biological Depositary of the National Institute of Technology and Evaluation, 2-5-8 Kazusa Kamatari, Kisarazu City, Chiba Prefecture, Japan, on February 25, 2014. The K-245 strain is a mutant obtained by mutating the natto bacteria strain (Bacillus subtilis K-2; NITE BP-1577) described in JP-B-5-60335. The No. 7 strain was internationally deposited on February 25, 2014 at the National Institute of Technology and Evaluation, Patent Microorganisms Depositary (NPMD) (Room 122, 2-5-8 Kazusa Kamatari, Kisarazu City, Chiba Prefecture, Japan 292-0818) under the accession number NITE BP-01805 (identification: Bacillus subtilis No. 7). Natto bacteria are classified as Bacillus subtilis, but are generally classified as a variant of Bacillus subtilis, Bacillus subtilis var. natto or Bacillus subtilis (natto), to distinguish them from Bacillus subtilis, or as Bacillus natto, a closely related species of Bacillus subtilis.

[0032] In step (ii), the state of the natto bacteria to be added as the natto bacteria starter is not particularly limited, but it is preferable to use one in a spore state that can be directly inoculated into the high-temperature raw material to prevent contamination with various bacteria. In order to perform fermentation uniformly, it is preferable to inoculate the natto bacteria starter into the raw material by inoculation or spraying, etc., and then mix the raw material and the natto bacteria uniformly. It is preferable to prepare a spore suspension of the natto bacteria and add it in a liquid state.

[0033] Here, as the spore suspension, a culture solution obtained by culturing the above-mentioned Bacillus subtilis natto in a liquid medium containing components suitable for spore formation can be used. The components of the liquid medium are not particularly limited as long as they enable spore formation and growth of Bacillus subtilis natto and contain medium components such as a carbon source, a nitrogen source, and inorganic salts that are commonly used for culturing Bacillus subtilis natto. The liquid medium may be a synthetic medium or a natural medium. Among the medium components, carbon sources include sugars such as glucose, sucrose, galactose, mannose, starch, and starch hydrolysates, and organic acids such as citric acid, nitrogen sources include peptone, meat extract, casein hydrolysate, ammonia, ammonium sulfate, and ammonium chloride, and 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. The medium may also contain yeast extract, malt extract, soybean flour, vitamins (biotin, etc.), etc. When using a Bacillus subtilis natto mutant strain that requires a specific nutritional component due to gene deletion or the like, the medium composition may be changed as appropriate.

[0034] The amount of bacteria to be inoculated is usually 1 / 100 to 1 / 50 of the amount of steamed soybeans. More specifically, the number of bacteria to be inoculated is not particularly limited as long as it is a bacterial concentration according to the usual method, but is preferably 1×10 per 1 g of soybeans. 3 ~1×10 6 pcs, preferably 1 x 10 3 ~1×10 5 pcs, more preferably 1×103 ~1×10 4 There are 10.

[0035] The temperature of the soybeans when inoculating the natto bacteria can be 55 to 95° C., preferably 60 to 95° C., more preferably 65 to 95° C., even more preferably 70 to 90° C., and particularly preferably 75 to 90° C. In the above range, contamination with various bacteria can be more effectively prevented, and the death of the natto bacteria spores can be more effectively prevented, thereby preventing poor fermentation.

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

[0037] In the present invention, the raw soybeans are heated in liquid to produce steamed or boiled soybeans by a conventional method. Steamed soybeans are preferred in terms of preventing loss of components. Before steaming or boiling, it is desirable to soak the raw soybeans in water and swell them before use. Here, as a specific preparation procedure for steamed soybeans, a method can be adopted in which soybeans are soaked in water at room temperature for about 6 to 24 hours, then drained, and steamed with steam at 100 to 135°C for 10 to 30 minutes. A method of pressure steaming under high pressure conditions of 0.12 to 0.22 MPa can also be adopted. As a specific preparation procedure for boiled soybeans, a method can be adopted in which soybeans are soaked in water at room temperature for about 6 to 24 hours, then boiled in water at 90 to 100°C for 20 to 50 minutes.

[0038] Specifically, the packaging container prepared in step (i) needs to accommodate the fermented material (soybeans, chickpeas, peas, especially soybeans). Therefore, a fermented material accommodation step can be provided in which the fermented material is accommodated in the packaging container. The inoculation step (ii) may be performed before the fermented material accommodation step or after the fermented material accommodation step. Furthermore, the inoculation step (ii) and the fermented material accommodation step may be performed simultaneously. Furthermore, the packaging container preparation step (i) and the inoculation step (ii) may be performed simultaneously, or the packaging container preparation step (i) may be followed by the inoculation step (ii), or, if possible, the packaging container preparation step (i) may be performed after the inoculation step (ii).

[0039] [1-3] Stage (iii) In the first embodiment of the method for producing natto, the step (iii) is a step of performing fermentation that satisfies the following (1) and (2) (fermentation step). (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) The temperature of the fermented product during the fermentation period is between 37°C and 53°C.

[0040] "(1) The average oxygen concentration inside the packaging container during the fermentation period is relatively lower than the average oxygen concentration outside the packaging container" means that the average oxygen concentration inside the packaging container is relatively lower than the average oxygen concentration outside the packaging container during the entire fermentation process, from the start of fermentation to the end of fermentation. The "fermentation process" in the present invention refers to a process of raising the product temperature of the fermented material (soybeans, chickpeas, peas, particularly soybeans) inoculated with Bacillus subtilis natto in step (ii) to 37°C or higher, and generally, the product temperature is controlled so that it does not fall below 37°C. In addition, even if the product temperature falls below 37° C. due to a temporary temperature drop, it is considered to be a fermentation step. In other words, it does not mean that the temperature does not completely fall outside the temperature range, but for example, it means that the fermentation step is satisfied even if the product temperature falls outside the temperature range within a slight temperature range (for example, within 2° C., preferably within 1° C.) and for a short period of time (less than 15 minutes, within 10 minutes, preferably within 5 minutes).

[0041] Here, the start of fermentation refers to the point in time when the fermented material (soybeans, chickpeas, peas, particularly soybeans) and the fermenting bacteria (natto bacteria) coexist and the product temperature of the fermented material first becomes 37°C or higher for 15 consecutive minutes. The end of fermentation refers to the point in time after the fermentation stage (iii) when the product temperature of the fermented material becomes less than 37°C for 15 consecutive minutes. When using the inactivation step (iv) described below in which the temperature of the fermented material exceeds 53°C, the inactivation step (iv) may be provided in the latter half of the entire fermentation process (50% or later, particularly 75% or later).

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

[0043] The oxygen concentration in 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. For example, the main body can be the "FireSting O2-C (4ch)" and the O2 probe can be the "O2 mini sensor OXF900PT-OI (fixed needle)". In concrete terms, a rubber sheet is attached to the ceiling of the packaging container to be measured, and the detection part of the measuring device (the fixed needle in the above O2 probe) is inserted through the rubber sheet so as to be positioned inside the packaging container, and the oxygen concentration in the packaging container is continuously measured every 5 minutes. In this specification, the unit of oxygen concentration is "%", which is the volume ratio of oxygen when the entire atmosphere to be measured is 100% by volume.

[0044] The oxygen concentration outside the packaging container can be measured using an oxygen concentration meter. The oxygen concentration meter can be the same device as the oxygen concentration meter that measures the oxygen concentration inside the packaging container. Specifically, the detection part of the measuring device (a fixed needle in the above O2 probe) is placed 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 is preferably 2% or more. By making this difference 2% or more, the activity of Bacillus subtilis natto during the fermentation period can be effectively suppressed. The lower limit of this difference can be 2% or more, and can be further 2.5% or more, 3% or more, 3.5% or more, 4% or more, 4.5% or more, or 5% or more. On the other hand, the upper limit of this difference is not limited, but can be 16% or less, and can be further 15% or less, 14% or less, 13% or less, or 12%. The above upper and lower limits can be combined with each other. That is, for example, it can be 2% or more and 16% or less, further 3% or more and 14% or less, and further 5% or more and 12% or less.

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

[0047] The time of the entire fermentation process from the start to the end of fermentation is not limited, but from the viewpoint of obtaining natto with excellent taste (particularly bitterness), texture, odor, and stringiness (spinnability), the lower limit is usually 5 hours or more, and can be 6 hours or more, and can be 7 hours or more, 7.5 hours or more, 8 hours or more, 9 hours or more, or 10 hours or more. On the other hand, the upper limit is usually 23 hours or less, and can be 22 hours or less, and can be 21 hours or less, or 20 hours or less. The above upper and lower limits can be combined with each other. 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, or 10 hours or more and 20 hours or less.

[0048] Although the oxygen concentration in the packaging container (not the average oxygen concentration but the oxygen concentration at the time of measurement) is not limited, it is preferable to have a period during the fermentation period during which the oxygen concentration in the packaging container is 10% or less from the viewpoint of effectively suppressing the activity of natto bacteria during the fermentation period. 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, it can be 8 hours or more from the viewpoint of suppressing the activity of natto bacteria during the fermentation period, and can be 8.1 hours or more, 8.2 hours or more, 8.3 hours or more, 8.4 hours or more, or 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 18 hours or less, 15 hours or less, 13 hours or less, 10 hours or less, or 9.7 hours or less. The above upper and lower limits can be combined with each other. That is, for example, it can be 8 hours or more and 20 hours or less, and can be 8.2 hours or more and 15 hours or less, and can be 8.4 hours or more and 10 hours or less.

[0049] Furthermore, from the viewpoint of effectively suppressing the activity of Bacillus subtilis natto during the fermentation period, it is preferable to have a period during which the oxygen concentration in the packaging container is 8% or less during the fermentation period. Although the lower limit of the length of this period (the period during which the oxygen concentration in the packaging container is 8% or less) is not limited, from the viewpoint of suppressing the activity of Bacillus subtilis natto during the fermentation period, it can be 5 hours or more, and furthermore, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, or 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 furthermore, 18 hours or less, 15 hours or less, 13 hours or less, 11 hours or less, or 10.7 hours or less. The above upper and lower limits can be combined with each other. That is, for example, it can be 5 hours or more and 20 hours or less, furthermore, it can be 7 hours or more and 15 hours or less, and furthermore, it can be 9 hours or more and 11 hours or less.

[0050] Furthermore, from the viewpoint of effectively suppressing the activity of Bacillus subtilis natto during the fermentation period, it is preferable to have a period during which the oxygen concentration in the packaging container is 6% or less during the fermentation period. Although the lower limit of the length of this period (the period during which the oxygen concentration in the packaging container is 6% or less) is not limited, from the viewpoint of suppressing the activity of Bacillus subtilis natto during the fermentation period, it can be 2.5 hours or more, and further 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, or 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 14 hours or less, 13 hours or less, 12 hours or less, 11 hours or less, or 10.7 hours or less. The above upper and lower limits can be combined with each other. That is, for example, it can be 2.5 hours or more and 15 hours or less, further 5 hours or more and 13 hours or less, and further 9.5 hours or more and 11 hours or less.

[0051] In the fermentation step (iii), "(2) the product temperature of the fermented material during the fermentation period is 37°C or higher and 53°C or lower" means that the product temperature of the fermented material (soybeans, chickpeas, peas, especially soybeans) is controlled so that it does not become less than 37°C throughout the entire fermentation process from the start of fermentation to the end of fermentation (note that, as mentioned above, a temperature drop to less than 37°C in less than 15 minutes is permitted). From the viewpoint of obtaining natto with excellent taste (especially bitterness), texture, odor, and stringiness (spinnability), the lower limit of this product 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, or 42°C or higher. On the other hand, the upper limit of this product 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, or 46°C or lower. The above upper and lower limits can be combined with each other. That is, for example, it can be 42°C or higher and 53°C or lower, and further it can be 42°C or higher and 46°C or lower.

[0052] The product temperature can be controlled in the fermentation room by using various air conditioning equipment. Examples of air conditioning equipment include air conditioners, ventilators, electric fans, blowers, heaters (including hot air generated by steam heating and hot water heating), and light control equipment. These may be used alone or in combination of two or more types. Specifically, in the fermentation stage (iii), heat is generated due to the activity of the natto bacteria. The temperature in the fermentation room can also be affected by the weather. For this reason, the temperature can be reflected in the product temperature by cooling or heating as necessary.

[0053] In the fermentation step (iii), the temperature outside the packaging container (ambient temperature) is not particularly limited, but can be 30°C or higher. The lower limit of the temperature outside the packaging container can be 30°C or higher, and can be 33°C or higher, 35°C or higher, or 37°C or higher. Meanwhile, the upper limit of the temperature outside the packaging container can be 67°C or lower, and can be 66°C or lower, or 65°C or lower. The above upper and lower limits can be combined with each other. That is, for example, it can be 30°C or higher and 67°C or lower, and can be 35°C or higher and 66°C or lower. The temperature outside the packaging container refers to the temperature of the outer surface of the packaging container.

[0054] [1-4] Stage (iv) In the first embodiment of the method for producing natto, after the fermentation step (iii), an inactivation step (iv) can be provided in which the temperature of the fermented material (soybeans, chickpeas, peas, especially soybeans) is maintained at a temperature above 53°C. That is, by maintaining the temperature above 53°C, it is possible to promote sporulation and / or reduce / eliminate vegetative cells, thereby inhibiting the production of enzymes by live bacteria. In addition, by inactivating various enzyme activities by heating, it is possible to stabilize the quality. Therefore, it is possible to maintain the natto in the state produced up to that point and prevent further fermentation. This makes it possible to maintain the taste (especially bitterness), texture, odor, and stringiness (spinnability) in good conditions.

[0055] The product temperature in this inactivation step (iv) may be more than 53° C., but from the viewpoint of maintaining the taste (particularly bitterness), texture, odor, and stringiness (spinnability) of natto in a good condition, it can be 67° C. or less. The product temperature in this inactivation step (iv) can be more than 53° C. and less than 67° C., more than 53° C. and less than 66° C., or more than 53° C. and less than 65° C. Furthermore, the time for which the above product temperature is maintained is not limited, but from the viewpoint of ensuring deactivation, it can be 0.1 hours or more and 3.5 hours or less, further 0.3 hours or more and 3 hours or less, and further 0.5 hours or more and 2 hours or less.

[0056] The inactivation step (iv) may be carried out after the fermentation step (iii). From the viewpoint of preventing stringiness, the inactivation step (iv) may be carried out within 0 to 3.5 hours, preferably within 0.1 to 3 hours, more preferably within 0.5 to 2 hours, from the end of the fermentation step (iii).

[0057] In the first embodiment of the method for producing natto, when the deactivation step (iv) is provided, the degree of the enzyme activity is not limited, but from the viewpoint of shelf life, the upper limit of the enzyme activity measured in the deactivation step (iv) can be 7U / g or less, and further 6.5U / g or less, 6U / g or less, 5.5U / g or less, 5U / g or less, 4.5U / g or less, 4U / g or less, 3.5U / g or less, 3U / g or less, or 2.5U / g or less. On the other hand, the lower limit can be 0.01U / g or more, and further 0.03U / g or more, 0.05U / g or more, 0.07U / g or more, 0.1U / g or more, 0.3U / g or more, 0.5U / g or more, 0.7U / g or more, 1U / g or more, 1.3U / g or more, 1.5U / g or more, 1.7U / g or more, or 2U / g or more. The upper and lower limits may be combined. For example, the enzyme activity may be 0.01 U / g or more and 7 U / g or less, 0.1 U / g or more and 6 U / g or less, or 1 U / g or more and 5 U / g or less. In this application, the enzyme activity refers to neutral protease activity.

[0058] The method for measuring the above-mentioned enzyme activity is as follows. <Enzyme solution preparation> Add 200 ml of sodium phosphate (20 mM, pH 7) to 20 g of natto and stir with a stirrer at 4°C (on ice) for 30 minutes. Then, transfer only the supernatant to a Falcon tube, being careful not to include any solids. Then, centrifuge at 15,000 rpm for 10 minutes, and store the supernatant in another Eppendorf tube (store 5 x 1 ml in 1.5 ml tubes) and store at -80°C. <Enzyme activity measurement> Mix 50μL of the enzyme solution prepared above, 800μL of substrate (casein (1% in 20mM NaPi pH7)), and 750μL of buffer solution (NaPi pH7), and react at 37℃ for 30 minutes. Add 2400μL of 5% TCA to stop the reaction, and leave at room temperature for 30 minutes. Then, centrifuge at 15000rpm for 10 minutes, take the supernatant in a test tube, and measure the absorbance (280nm) of the supernatant. Similarly, mix 100μL of the enzyme solution prepared above, 800μL of substrate (casein (1% in 20mM NaPi pH7)), and 700μL of buffer solution (NaPi pH7), react at 37℃ for 30 minutes, and measure the absorbance (280nm) of the supernatant. For the blank, a substrate (casein (1% in 20 mM NaPi pH 7)) and a buffer solution (NaPi pH 7) were mixed and reacted, and 5% TCA was added, followed by the addition of the enzyme solution. <Enzyme activity calculation> The enzyme activity required to cleave 1 μg of tyrosine from casein in 1 minute at 37° C. is defined as 1 U, and the number of units is calculated using the following formula. Unit number (U): Absorbance (280 nm) / 1.34 / 4 / 30 (1.34: molar absorbance coefficient of tyrosine, 4: volume of reactor (mL), 30: reaction time (min)) Furthermore, the enzyme activity per gram of natto is calculated using the following formula by dividing the number of units by the weight of natto, which is calculated from the amount of natto extract used in the reaction system. Enzyme activity (U / g) = number of units (U) * reactor volume (4000 μL) / enzyme solution volume (μL) / (buffer solution + natto) (g) / natto (g) The enzyme activity in the present invention can be determined by calculating the arithmetic mean.

[0059] In the first embodiment of the method for producing natto, other steps may be included in addition to the above-mentioned packaging container preparation step (i), fermentation target storage step, inoculation step (ii), fermentation step (iii), and inactivation step (iv). Other stages include a cooling stage, a maturation stage, etc. These other stages may be used alone or in combination of two or more. For example, after a cooling stage in which the natto is cooled to 30°C or less (preferably about 25°C or less), the natto can be moved to a maturation chamber and maturation can begin. The maturation stage can be carried out after the end of fermentation, usually for about 24 to 72 hours at 4 to 10°C. The maturation stage makes it possible to produce the natto product.

[0060] [2] Natto manufacturing method (second form) The method for producing natto according to the second embodiment of the present invention is characterized by comprising the following steps: (i) preparing a packaging container; (ii) inoculating the natto bacteria; and (iii) fermenting the natto.

[0061] [2-1] Stage (i) Step (i) is a step of preparing a packaging container (packaging container preparation step). The packaging container must have an oxygen permeability of 70cc / cm 2 ·Day · atm or more 850cc / cm 2 ·Day·atm or less, and (2) the average pore area is 10,000 μm 2 The packaging container is the same as the packaging container in the method for producing natto of the first embodiment described above, except that at least one of the above is not an essential configuration. In addition, (1) oxygen permeability is 70cc / cm 2 ·Day · atm or more 850cc / cm 2 ·Day·atm or less, and (2) the average pore area is 10,000 μm 2 Although it is not essential that at least one of the above conditions is satisfied, as described in the first embodiment of the method for producing natto, these conditions can be satisfied.

[0062] That is, the packaging container is a container that can accommodate the raw material, which is the material to be fermented by the fermenting bacteria, and the fermenting bacteria inoculated therein, as the main contents (these may be collectively referred to as the material to be fermented). The packaging container can have functions as a container for the material to be fermented, a fermentation container, a maturation container, and after maturation is completed, a shipping container, a distribution container, etc., and can also be used as a tableware as it is. In these respects, the explanation in the first embodiment of the method for producing natto is applied as it is.

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

[0064] The oxygen permeability of the packaging container is 70cc / cm 2 ·Day·atm or less than 850cc / cm 2 ·Day·atm may exceed 70cc / cm 2 ·Day · atm or more 850cc / cm 2 It is preferable that the fermentation temperature is set to 1.0·Day·atm or less. As explained in the first embodiment, by setting the fermentation temperature in this range, the activity of Bacillus subtilis natto can be effectively suppressed during the fermentation period. The upper limit of the above range, the lower limit of the above range, and combinations thereof are the same as those described in the first embodiment of the method for producing natto.

[0065] A packaging container that can achieve such oxygen permeability is, for example, a packaging container having a cup-shaped portion and a top film portion that seals the open portion after the fermented material is placed in the cup-shaped portion, which is common to 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 portion, or by the entire top film portion (whole surface), and in this respect, the explanation in the method for producing natto of the first embodiment is applied as it is.

[0066] In addition, when the packaging container has through holes, the average hole area is not limited, but can be in the same range from the same viewpoint as the packaging container in the first form of the method for producing natto. In addition, when the packaging container has through holes, the total hole area is not limited, but can be in the same range from the same viewpoint as the packaging container in the first form of the method for producing natto. Furthermore, the porosity (%) of the packaging container is not limited, but can be in the same range from the same viewpoint as the packaging container in the first embodiment of the method for producing natto.

[0067] In addition, the number of through holes is not limited, but can be in the same range from the same viewpoint as the packaging container in the first embodiment of the method for producing natto. Furthermore, the shape of the through-hole is not limited, but can be a similar shape from the same viewpoint as the packaging container in the first embodiment of the method for producing natto. When a top film portion is employed, the material of the film constituting the top film portion is not limited, but can be made of the same material from the same viewpoint as the packaging container in the first form of the method for producing natto. In addition, the thickness of the film is not limited, but can be in the same range from the same viewpoint as the packaging container in the first embodiment of the method for producing natto. Besides, the material constituting the packaging container is not limited, and the same material can be used from the same viewpoint as the packaging container in the first embodiment of the method for producing natto.

[0068] In addition, as the contents in the packaging container, in addition to the main contents described above in the first embodiment of the method for producing natto, other contents may be enclosed in the packaging container in the first embodiment of the method for producing natto, as long as they do not affect the fermentation of the fermented material. In addition, the contents in the packaging container in the first embodiment of the method for producing natto are also the same as those in the packaging container in the first embodiment of the method for producing natto, such as laying a thin film on the fermented material, whether or not holes are made in the thin film, and enclosing tableware such as spoons and forks. Furthermore, the size of the packaging container is the same as in the first embodiment of the method for producing natto.

[0069] [2-2] Stage (ii) Step (ii) is a step of inoculating Bacillus subtilis natto (inoculation step). That is, it is a step of placing fermentation bacteria necessary for fermentation in the packaging container prepared in the step (i). In the present invention, the fermentation bacteria is Bacillus subtilis natto. The explanation of step (ii) explained in the first embodiment of the method for producing natto is applied to step (ii) as it is.

[0070] [2-3] Stage (iii) The step (iii) is a step (fermentation step) in which fermentation is carried out so as to satisfy 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) The temperature of the fermented product during the fermentation period is between 37°C and 53°C. (3) During the fermentation period, the oxygen concentration in the packaging container is 10% or less for 8 hours or more.

[0071] In step (iii), the explanation in the first embodiment of the method for producing natto is applied as is to "(1) the average oxygen concentration inside the packaging container during the fermentation period is relatively lower than the average oxygen concentration outside the packaging container." And, although the specific difference between the average oxygen concentration inside the packaging container and the average oxygen concentration outside the packaging container is not limited, the explanation in the first embodiment of the method for producing natto is applied as is. In addition, the average oxygen concentration inside the packaging container and the average oxygen concentration outside the packaging container are not limited, but the explanation in the first embodiment of the method for producing natto is applied as it is. Furthermore, the time for the entire fermentation process from the start to the end of fermentation is not limited, but the explanation for the first embodiment of the method for producing natto is applied as it is. In step (iii), with regard to "(2) the product temperature of the fermented material during the fermentation period is 37°C or higher and 53°C or lower", the explanation in the first embodiment of the method for producing natto is applied as is.

[0072] In step (iii), "(3) the time during the fermentation period during which the oxygen concentration in the packaging container (not the average oxygen concentration but the oxygen concentration at the time of measurement) is 10% or less is 8 hours or more", so that the activity of natto bacteria can be effectively suppressed during the fermentation period. 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 8 hours or more from the viewpoint of suppressing the activity of natto bacteria, but it can be further set to 8.1 hours or more, 8.2 hours or more, 8.3 hours or more, 8.4 hours or more, or 8.5 hours or more. On the other hand, the upper limit of the length of this period is not limited, but can be set to 20 hours or less, and further set to 18 hours or less, 15 hours or less, 13 hours or less, 10 hours or less, or 9.7 hours or less. The above upper and lower limits can be combined with each other. That is, for example, it can be set to 8 hours or more and 20 hours or less, further set to 8.2 hours or more and 15 hours or less, or further set to 8.4 hours or more and 10 hours or less.

[0073] Furthermore, it is preferable that the fermentation period has a period during which the oxygen concentration in the packaging container is 8% or less, from the viewpoint of effectively suppressing the activity of natto bacteria during the fermentation period. Although the lower limit of the length of this period (the period during which the oxygen concentration in the packaging container is 8% or less) is not limited, from the viewpoint of suppressing the activity of natto bacteria, it can be 5 hours or more, and furthermore, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, or 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 furthermore, 18 hours or less, 15 hours or less, 13 hours or less, 11 hours or less, or 10.7 hours or less. The above upper and lower limits can be combined with each other. That is, for example, it can be 5 hours or more and 20 hours or less, furthermore, it can be 7 hours or more and 15 hours or less, and furthermore, it can be 9 hours or more and 11 hours or less.

[0074] Furthermore, it is preferable that the fermentation period has a period during which the oxygen concentration in the packaging container is 6% or less, from the viewpoint of effectively suppressing the activity of natto bacteria during the fermentation period. Although the lower limit of the length of this period (the period during which the oxygen concentration in the packaging container is 6% or less) is not limited, from the viewpoint of suppressing the activity of natto bacteria, it can be 2.5 hours or more, and further 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, or 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 14 hours or less, 13 hours or less, 12 hours or less, 11 hours or less, or 10.7 hours or less. The above upper and lower limits can be combined with each other. That is, for example, it can be 2.5 hours or more and 15 hours or less, further 5 hours or more and 13 hours or less, and further 9.5 hours or more and 11 hours or less.

[0075] [2-4] Stage (iv) In the second embodiment of the method for producing natto, a deactivation step (iv) can be provided after the fermentation step (iii) in which the temperature of the fermented material (soybeans, chickpeas, peas, particularly soybeans) is maintained at more than 53° C. For the deactivation step (iv), the explanation for the first embodiment of the method for producing natto is applied as it is.

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

[0077] [3] Natto obtained by the present method (first and second forms) (3-1) The natto obtained by the method for producing natto according to the first embodiment is The natto is characterized by being produced through the following steps (i) to (iii). (i) preparing a packaging container that satisfies at least one of the following (1) to (2); (1) Oxygen permeability is 70cc / cm 2 ·Day · atm or more 850cc / cm2 ·Day·atm or less (2) Average pore area is 10,000 μm 2 is less than (ii) inoculating Bacillus subtilis natto; (iii) carrying out fermentation 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) The temperature of the fermented product during the fermentation period is between 37°C and 53°C. The details are as described above.

[0078] (3-2) The natto obtained by the method for producing natto according to the second embodiment is The natto is characterized by being produced through the following steps (i) to (iii). (i) preparing a packaging container; (ii) inoculating Bacillus subtilis natto; (iii) A step of carrying out fermentation that satisfies 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) The temperature of the fermented product during the fermentation period is between 37°C and 53°C. (3) During the fermentation period, the oxygen concentration in the packaging container is 10% or less for 8 hours or more. The details are as described above.

[0079] The natto obtained by this method can contain one or more free amino acids selected from 20 types of 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 a composition, separate from the amino acids that constitute proteins and peptides. 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), the type of optical isomer is not particularly limited unless otherwise specified. That is, each amino acid may be an L-form, a D-form, or a DL-form containing an arbitrary ratio of L-form and D-form.

[0080] The total content of free amino acids contained in the fermented product (natto) obtained by this method and stored continuously for 10 days at 10 ° C. after the fermentation step (iii) is not limited, but can be 50 mg% or more in total content measured by the method for measuring amino acid content described later. This makes it possible to obtain natto with excellent storage stability. The lower limit of the total content of free amino acids can be further set to 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 mg5 or more, or 230 mg% or more. On the other hand, the upper limit of the total content of free amino acids is not limited, but can be, for example, 930 mg% or less, and 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, or 730 mg% or less. The above upper and lower limits can be each combined. That is, for example, it can be 50 mg% or more and 930 mg% or less, further 150 mg% or more and 800 mg% or less, and further 210 mg% or more and 750 mg% or less. Even if the storage temperature is not 10°C due to a temporary temperature change, it is considered to be natto stored at 10°C for 10 consecutive days. That is, it does not mean that the temperature is not completely exceeded, but for example, it means that the requirements of the natto are met even if the temperature is exceeded within a slight temperature range (for example, within 2°C, preferably within 1°C) and for a short time (less than 15 minutes, within 10 minutes, preferably within 5 minutes).

[0081] <Method for measuring amino acid content> 5g of natto is crushed and suspended in 5% TCA, then placed in a 50ml measuring flask and filled up with 5% TCA. The measuring flask is then placed in an ultrasonic cleaner and left for 30 minutes, after which the suspension is transferred to a centrifuge tube and centrifuged at 7,500pm for 5 minutes. The supernatant after centrifugation is diluted 10-fold with 0.02N hydrochloric acid, and filtered through a 0.22μm filter. The sample is then measured using an amino acid analyzer (high-speed amino acid analyzer, Hitachi High-Tech Corporation, model "LA8080").

[0082] The fermented material (natto) obtained by this method and stored at 10°C for 10 consecutive days after the fermentation step (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), may satisfy two or more, may satisfy three or more, may satisfy four or more, or may satisfy all five. Furthermore, it may satisfy the total content of the above-mentioned free amino acids. (a) Lysine content is 90 mg% or less (b) Ammonia content is 160 mg% or less (c) Glutamic acid content is 125 mg% or less (d) Tyrosine content is 120 mg% or less (e) The total content of bitter amino acids is 580 mg% or less

[0083] The natto obtained by this method includes a lysine (Lys) content (a) contained in the fermented product (natto) stored at 10°C for 10 consecutive days after the fermentation step (iii), but the content measured by the above-mentioned method for measuring the amino acid content can be 90 mg% or less. This makes it possible to obtain natto with reduced bitterness. The upper limit of the lysine content can be further set to 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, or 50 mg% or less. On the other hand, the lower limit of the lysine content is not limited, but can be, for example, 5 mg% or more, and can be further set to 10 mg% or more, 13 mg% or more, 15 mg% or more, 18 mg% or more, or 20 mg% or more. The above upper and lower limits can be combined with each other. That is, for example, it can be 5 mg% or more and 90 mg% or less, further it can be 10 mg% or more and 75 mg% or less, and further it can be 20 mg% or more and 65 mg% or less.

[0084] The content of (b) ammonia (NH3) contained in the fermented product (natto) obtained by this method and stored at 10°C for 10 consecutive days after the fermentation step (iii) is not limited, but the content measured by the above-mentioned method for measuring the amino acid content can be 160 mg% or less. This makes it possible to obtain natto with a suppressed odor (ammonia odor). The upper limit of this ammonia content can be further set to 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, or 90 mg% or less. On the other hand, the lower limit of the ammonia content is not limited, but can be, for example, 5 mg% or more, and further 10 mg% or more, 15 mg% or more, 20 mg% or more, 25 mg% or more, or 30 mg% or more. The above upper and lower limits can be combined with each other. That is, for example, it can be 5 mg% or more and 160 mg% or less, further it can be 15 mg% or more and 130 mg% or less, and further it can be 30 mg% or more and 110 mg% or less. The degree of inhibition of fermentation occurring after the fermentation step (iii) of the produced natto (after the inactivation step (iv) in the case where the above-mentioned inactivation step (iv) is included) can be determined using the amount of ammonia contained in the natto as an indicator. Ammonia is considered to be generated by assimilating various nitrogen compounds contained in soybeans by Bacillus subtilis natto.

[0085] The content of (c) glutamic acid (Glu) contained in the fermented product (natto) obtained by this method and stored at 10°C for 10 consecutive days after the fermentation step (iii) is not limited, but the content measured by the above-mentioned method for measuring the amino acid content can be 125 mg% or less. This makes it possible to obtain natto with reduced astringency. The upper limit of the glutamic acid content can be further set to 120 mg% or less, 115 mg% or less, 110 mg% or less, 105 mg% or less, 100 mg% or less, or 95 mg% or less. On the other hand, the lower limit of the glutamic acid content is not limited, but can be, for example, 5 mg% or more, and can be further set to 10 mg% or more, 15 mg% or more, 20 mg% or more, 25 mg% or more, 30 mg% or more, or 35 mg% or more. The above upper and lower limits can be combined with each other. That is, for example, it can be 5 mg% or more and 125 mg% or less, further it can be 15 mg% or more and 115 mg% or less, and further it can be 25 mg% or more and 110 mg% or less.

[0086] The content of (d) tyrosine (Tyr) contained in the fermented material (natto) obtained by this method and stored continuously for 10 days at 10°C after the fermentation step (iii) is not limited, but the content measured by the above-mentioned method for measuring the amino acid content can be 120mg% or less. This can prevent the natto from having a crunchy texture. The upper limit of the tyrosine content can be further set to 115mg% or less, 110mg% or less, 100mg% or less, or 95mg% or less. On the other hand, the lower limit of the tyrosine content is not limited, but can be, for example, 5mg% or more, and can be further set to 10mg% or more, 15mg% or more, 20mg% or more, or 25mg% or more. The above upper and lower limits can be combined with each other. That is, for example, it can be set to 5mg% or more and 120mg% or less, further set to 15mg% or more and 110mg% or less, and further set to 20mg% or more and 100mg% or less.

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

[0088] In the natto obtained by the method provided with the inactivation step (iv), the total content of free amino acids contained in the fermented product (natto) stored continuously for 30 days at 10°C after the inactivation step (iv) is not limited, but the total content measured by the above-mentioned method for measuring the amino acid content can be 1900mg% or less. This makes it possible to obtain natto with excellent storage properties. The upper limit of the total content of free amino acids can be further set to 1850mg% or less, 1800mg% or less, 1750mg% or less, 1700mg% or less, 1680mg% or less, 1650mg% or less, 1630mg% or less, or 1600mg% or less. On the other hand, the lower limit of the total content of free amino acids is not limited, but can be, for example, 300mg% or more, and further 400mg% or more, 500mg% or more, 550mg% or more, 600mg% or more, 630mg% or more, 650mg% or more, or 670mg% or more. The above upper and lower limits can be combined with each other. That is, for example, it can be 300 mg% or more and 1900 mg% or less, further 450 mg% or more and 1750 mg% or less, and further 600 mg% or more and 1650 mg% or less. Even if the storage temperature is not 10°C due to a temporary temperature change, it is considered to be natto stored at 10°C for 30 consecutive days. That is, it does not mean that the temperature is not completely exceeded, but for example, it means that the requirements of the natto are met even if the temperature is exceeded within a slight temperature range (for example, within 2°C, preferably within 1°C) and for a short time (less than 15 minutes, within 10 minutes, preferably within 5 minutes).

[0089] The fermented material (natto) obtained by this method and stored at 10°C for 30 consecutive 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), may satisfy two or more, may satisfy three or more, may satisfy four or more, or may satisfy all five. Furthermore, it may satisfy the total content of the above-mentioned free amino acids. (a) Lysine content is 115 mg% or less (b) Ammonia content is 190 mg% or less (d) Tyrosine content is 200 mg% or less (e) The total content of bitter amino acids is 1100 mg% or less (f) Valine content is 90 mg% or less

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

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

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

[0093] In the natto obtained by the method provided with the inactivation step (iv), the content of (d) tyrosine (Tyr) contained in the fermented product (natto) stored continuously for 30 days at 10°C after the inactivation step (iv) is not limited, but the content measured by the above-mentioned method for measuring the amino acid content can be 200mg% or less. This can prevent the natto from having a crunchy texture. The upper limit of the tyrosine content can be further set to 195mg% or less, 193mg% or less, 190mg% or less, 187mg% or less, 185mg% or less, 183mg% or less, or 180mg or less. On the other hand, the lower limit of the tyrosine content is not limited, but can be, for example, 20mg% or more, and can further be 30mg% or more, 40mg% or more, 50mg% or more, 60mg% or more, or 70mg% or more. The above upper and lower limits can be combined with each other. That is, for example, it can be 20 mg% or more and 200 mg% or less, further it can be 40 mg% or more and 190 mg% or less, and further it can be 60 mg% or more and 180 mg% or less.

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

[0095] The present invention will be described in more detail below with reference to examples. However, these examples are merely illustrative and are not intended to limit the present invention in any way.

[0096] [1] Natto production 〈1〉Production of natto in Experimental Examples 1-15 and 17-31 (1) Packaging preparation stage (i) A container (natto container) having a cup-shaped portion made of expanded polystyrene (PSP) and an opening ratio (×10―4 %) and average pore area (μm 2 A top film having a thickness of 100 μm and a thickness of 100 μm were prepared. The container having a cup-shaped portion has a substantially negligible oxygen permeability, and the through-holes provided in the top film enable the oxygen permeability of the packaging container (Tables 1 to 6) to be achieved.

[0097] The oxygen permeability of the packaging container was measured in accordance with JIS K-7126-2. Specifically, a gas barrier tester (model "OX-TRAN 1 / 50", manufactured by MOCON) was used to measure the oxygen permeability (unit: cc / cm) of the packaging container (i.e., the packaging container in which the top film portion is formed by attaching the above-mentioned top film to the cup opening of the container having the above-mentioned cup-shaped portion) at a temperature of 23±2°C and a relative humidity of 50%. 2 The oxygen permeability of the entire packaging container was calculated by masking all other through holes with aluminum tape, measuring the oxygen permeability of only one through hole to be measured, and multiplying the oxygen permeability by the total area of ​​the through holes (measured using a microscope) and multiplying the oxygen permeability of the area of ​​the member that does not have a through hole by the area of ​​the area that does not have a through hole, and the oxygen permeability is shown in Tables 1 to 6.

[0098] (2) Inoculation step (ii) Dried soybeans were soaked in water for 16 hours, drained, and then packed at 1.6 kg / cm 2 The soybeans were then steamed under pressure for 30 minutes. A natto bacteria liquid containing the natto bacteria K-245 strain (Bacillus subtilis K-245; NITE BP-01804) was added so that 5,000 natto bacteria were contained per gram of steamed soybeans, and the mixture was lightly homogenized to obtain a fermented product. The obtained fermented material was placed in an amount of 40 g each in the above-mentioned container having a cup-shaped portion, and then covered with the above-mentioned top film.

[0099] (3) Fermentation stage (iii) The fermentation material was placed in a lidded packaging container, which was then placed in a programmed incubator with a gas phase temperature set at 43° C., and fermentation was carried out for 16 hours. The average oxygen concentration in the packaging container during the fermentation period was measured using an oxygen concentration meter (consisting of a main unit and an O2 probe, with a FireSting O2-C (4ch) as the main unit and an O2 mini sensor OXF900PT-OI (fixed needle) as the O2 probe). Specifically, a rubber sheet was attached to the ceiling of the packaging container, and the detection unit of the measuring device (the fixed needle of the O2 probe) was inserted through the rubber sheet so that it was positioned inside the packaging container, and the oxygen concentration in the packaging container was continuously measured every 5 minutes, and the average value of the oxygen concentrations measured every 5 minutes over 16 hours was calculated. 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 detector of the measuring device (fixed needle in the case of the O2 probe) was positioned around the outside of the packaging container, and the oxygen concentration outside the packaging container was continuously measured every 5 minutes, and the average value of the oxygen concentrations measured every 5 minutes over 16 hours was calculated. The results are shown in Tables 1 to 6. In addition, from the above measurement results, the time when the oxygen concentration in the packaging container would reach 6% or less, the time when the oxygen concentration in the packaging container would reach 8% or less, and the time when the oxygen concentration in the packaging container would reach 10% or less were calculated, and the results are shown in Tables 1 to 6. Furthermore, when the temperature of the fermented material was measured during the fermentation period, the product temperature was 46 to 50°C. The product temperature rose with the heat of fermentation and reached a steady state. In addition, the temperature of the outer surface of the packaging container during the fermentation period was always 30°C or higher. These temperatures were measured using a TPF1100 fixed needle temperature mini sensor.

[0101] (4) Cooling and maturation stages After the fermentation stage was completed, the product temperature was cooled to 20° C. Then, the product was transferred to a 4° C. refrigerated room and left to stand at a product temperature of about 5° C. for 8 hours to mature, thereby obtaining natto.

[0102] 2. Production of natto in Experimental Example 16 The packaging container preparation step (i) and the inoculation step (ii) were carried out in the same manner as in Experimental Examples 1 to 15 and 17 to 31. Thereafter, 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 was 8.0% as shown in Table 2. Thereafter, the natto was obtained through the cooling step and the maturation step in the same manner as in Experimental Examples 1 to 15 and 17 to 31.

[0103] 〈3〉 Production of natto in Experimental Examples 32 to 46 As in the cases of 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 incubator's gas phase temperature was set to 60° C., and the inactivation step (iv) was carried out for 0.5 hours. After that, as in the cases of Experimental Examples 1 to 15 and 17 to 31, the fermentation step (iii) was followed by a cooling step and a maturation step to obtain natto.

[0104] [2] Evaluation <1> Measurement of various amino acids and ammonia Each of the natto samples from Experimental Examples 1 to 31 obtained in [1]〈1〉 and [1]〈2〉 above was stored at 10°C for 10 consecutive days, after which 5 g of each of the stored natto samples was crushed and suspended in 5% TCA, then placed in a 50 ml measuring flask and filled up with 5% TCA. The measuring flask was then placed in an ultrasonic cleaner and left for 30 minutes, after which 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 0.02 N hydrochloric acid, and 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 ammonia content using an amino acid analyzer (high-speed amino acid analyzer, Hitachi High-Tech Corporation, model "LA8080"). The lysine content was measured using the "Lys (mg%) 10°C" column in Tables 1 to 4. The ammonia content is shown in the "NH3 (mg%) 10°C x 10 days" column of Tables 1 to 4, the glutamic acid content is shown in the "Glu (mg%) 10°C x 10 days" column of Tables 1 to 4, the tyrosine content is shown in the "Tyr (mg%) 10°C x 10 days" column of Tables 1 to 4, and the total amount of the eight amino acids, valine, methionine, isoleucine, leucine, tyrosine, phenylalanine, lysine and arginine, in the "Bitter amino acids (mg%) 10°C x 10 days" column of Tables 1 to 4.

[0105] <2> Measurement of spinnability Each of the natto samples from Experimental Examples 1 to 31 obtained in [1] <1> and [1] <2> above was stored at 10°C for 10 consecutive days, and was then stirred with chopsticks 30 times for 10 seconds. A lump of natto (approximately 20 grams) was then picked up and evaluated based on how difficult it was for the natto grains to fall off the chopsticks. A comprehensive evaluation was performed according to the following evaluation criteria, and the results are shown in Tables 1 to 4. 5: Very strong (When a lump of mixed natto grains is picked up with chopsticks, it remains in the air and does not fall for more than 3 seconds) 4: Strong (When a lump of mixed natto grains is picked up with chopsticks, it takes more than 1 second and less than 3 seconds for it to be held in the air and fall) 3: Normal (When the mixed natto grains are picked up with chopsticks, they cannot be held in the air and the grains fall off) 2: Weak (strings form but no clumps of natto grains form) 1: Very weak (no strings)

[0106] <3> Sensory evaluation The sensory evaluation was carried out according to the following procedure. First, as sensory inspectors who would perform each sensory test, we conducted prior training in discrimination of food taste, texture, appearance, etc., and selected inspectors who had particularly excellent records, experience in product development, and ample knowledge of food quality such as taste, texture, appearance, etc., and who could make absolute evaluations for each sensory inspection item. Specifically, we conducted the following discrimination training A) to C), and selected inspectors who had particularly excellent records, ample knowledge of food quality such as taste and texture, and who could make absolute evaluations for each sensory inspection item.

[0107] A) A taste quality identification test in which one aqueous solution of each of the five tastes (sweetness: the taste of sugar, sourness: the taste of tartaric acid, umami: the taste of monosodium glutamate, saltiness: the taste of sodium chloride, bitterness: the taste of caffeine) was prepared at a concentration close to the threshold value of each component, and two distilled waters were added to these to make a total of seven samples, in which the subject was required to accurately identify the sample of each taste. B) A concentration difference discrimination test to accurately distinguish the differences in concentration between five slightly different saline solutions and an acetic acid solution. C) A three-point discrimination test 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 testers performed a sensory evaluation of the bitterness of each of the natto samples from Experimental Examples 1 to 31 obtained in [1] <1> and [1] <2> above, which had been stored at 10°C for ten consecutive days, according to the following evaluation criteria. The evaluation was performed by each tester selecting one number from a five-level scale that was closest to their own evaluation. The evaluation results were tabulated by calculating the arithmetic mean of the scores of the ten testers, and rounding off any decimal places. The results are shown in the "Sensory evaluation (bitterness)" column of Tables 1 to 4. 5: No bitterness is felt, very pleasant. 4: Almost no bitterness is noticeable, which is preferable. 3: Not much bitterness is felt, and it is somewhat preferable. 2: Slightly bitter taste, not very pleasant 1: Bitter taste is felt and is undesirable.

[0109] <4> Overall evaluation The natto of each of Experimental Examples 1 to 31 obtained in [1] <1> and [1] <2> above was stored at 10°C for 10 consecutive days, and was then comprehensively evaluated according to the following evaluation criteria, and the results are shown in Tables 1 to 4. Note that in Experimental Example 1, since there was no fermentation or the fermentation was insufficient, there was almost no stringiness and the texture was also poor. 5: The taste (especially the bitterness), texture, smell, and stringiness (spinnability) are excellent and very desirable. 4: Excellent taste (especially bitterness), texture, smell, and stringiness (spinnability), and is desirable. 3: The taste (especially bitterness), texture, smell, and stringiness (spinnability) are somewhat excellent, and the rating is somewhat preferable. 2: The taste (especially bitterness), texture, smell, and stringiness (spinnability) are somewhat poor and somewhat undesirable. 1: The taste (especially bitterness), texture, odor, and stringiness (spinnability) are not excellent and are not desirable.

[0110] 5. Measurement of enzyme activity Using each of the natto of Experimental Examples 32 to 46 obtained in [1] <3> above (natto before being stored at 10°C for 30 consecutive days), an enzyme solution was prepared according to the following procedure, and the enzyme activity of the enzyme solution was measured according to the following procedure. The results are shown in Tables 5 to 6. <Enzyme solution preparation> 200 ml of sodium phosphate (20 mM, pH 7) was added to 20 g of natto and stirred with a stirrer at 4°C (on ice) for 30 minutes, after which only the supernatant was transferred to a Falcon tube, taking care not to let any solid matter get in. It was then centrifuged at 15,000 rpm for 10 minutes, and the supernatant was stored in another Eppendorf tube (1 ml x 5 tubes stored in 1.5 ml tubes) and stored at -80°C.

[0111] <Enzyme activity measurement> 50 μL of the enzyme solution prepared above, 800 μL of substrate (casein (1% in 20 mM NaPi pH 7)), and 750 μL of buffer solution (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 the mixture was left at room temperature for 30 minutes. After that, the mixture was centrifuged at 15000 rpm for 10 minutes, the supernatant was taken in 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 substrate (casein (1% in 20 mM NaPi pH 7)), and 700 μL of buffer solution (NaPi pH 7) were mixed and reacted at 37 ° C for 30 minutes, and the absorbance (280 nm) of the supernatant was measured. For the blank, the substrate (casein (1% in 20 mM NaPi pH 7)) was mixed with a buffer solution (NaPi pH 7) and reacted, and after addition of 5% TCA, the enzyme solution was added.

[0112] <Enzyme activity calculation> The enzyme activity required to cleave 1 μg of tyrosine from casein in 1 minute at 37° C. is defined as 1 U, and the number of units is calculated using the following formula. Unit number (U): Absorbance (280 nm) / 1.34 / 4 / 30 (1.34: molar absorbance coefficient of tyrosine, 4: volume of reactor (mL), 30: reaction time (min)) Furthermore, the enzyme activity per gram of natto is calculated using the following formula by dividing the number of units by the weight of natto, which is calculated from the amount of natto extract used in the reaction system. Enzyme activity (U / g) = number of units (U) * reactor volume (4000 μL) / enzyme solution volume (μL) / (buffer solution + natto) (g) / natto (g) The enzyme activity was determined by calculating the arithmetic mean of these values.

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

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

[0115] <8> Overall rating Each of the natto of Experimental Examples 32 to 46 obtained in [1] <3> above was stored at 10°C for 30 consecutive days and subjected to a comprehensive evaluation according to the following evaluation criteria. The results are shown in Tables 5 to 6. 5: The taste (especially the bitterness), texture, smell, and stringiness (spinnability) are excellent and very desirable. 4: Excellent taste (especially bitterness), texture, smell, and stringiness (spinnability), and is desirable. 3: The taste (especially bitterness), texture, smell, and stringiness (spinnability) are somewhat excellent, and the rating is somewhat preferable. 2: The taste (especially bitterness), texture, smell, and stringiness (spinnability) are somewhat poor and somewhat undesirable. 1: The taste (especially bitterness), texture, odor, and stringiness (spinnability) are not excellent and are not desirable.

[0116] [Table 1]

[0117] [Table 2]

[0118] [Table 3]

[0119] [Table 4]

[0120] [Table 5]

[0121] [Table 6] [Industrial Applicability]

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

Claims

1. A method for producing natto, comprising the following steps (i) to (iii). (i) preparing a packaging container having a low oxygen permeable portion that satisfies at least one of the following (1) to (2): (1) Oxygen permeability is 70cc / cm ２ ・Day・ATM or more 850cc / cm ２ ・Day・atm or less (2) Average pore area is 10,000 μm ２ With a through hole of less than (ii) inoculating the natto bacteria; (iii) performing fermentation 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) The temperature of the fermented material during the fermentation period is between 37°C and 53°C.

2. A method for producing natto, comprising the following steps (i) to (iii). (i) providing a packaging container; (ii) inoculating the natto bacteria; (iii) A step of carrying out fermentation that satisfies 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) The temperature of the fermented material during the fermentation period is between 37°C and 53°C. (3) During the fermentation period, the oxygen concentration in the packaging container is 10% or less for 8 hours or more.

3. The method for producing natto according to claim 1, further comprising satisfying the following (3) in (iii). (3) During the fermentation period, the oxygen concentration in the packaging container is 10% or less for 8 hours or more.

4. The method for producing natto according to claim 2, further comprising: (i) a packaging container having a low oxygen permeable portion that satisfies at least one of the following (1) to (2). (1) Oxygen permeability is 70cc / cm ２ ・Day・ATM or more 850cc / cm ２ ・Day・atm or less (2) Average pore area is 10,000 μm ２ With a through hole of less than

5. The method for producing natto according to claim 1 or 2, further comprising satisfying the following (4) in (iii). (4) The time during which the oxygen concentration in the packaging container is 8% or less is 5 hours or more.

6. The method for producing natto according to claim 1 or 2, further comprising satisfying the following (5) in (iii). (5) The time during which the oxygen concentration in the packaging container falls to 6% or less is 2.5 hours or more and 15 hours or less.

7. The method for producing natto according to claim 1 or 2, further comprising satisfying the following (6) in (iii). (6) The temperature outside the packaging container is 30° C. or higher.

8. The method for producing natto according to claim 1 or 4, wherein the opening rate of the low oxygen permeable portion is 0.022% or less.

9. The method for producing natto according to claim 1 or 4, wherein the low oxygen permeable site is a film.

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

11. The method for producing natto according to claim 1 or 2, further comprising the following step (iv) after the step (iii). (iv) Adjust the temperature of the fermented product after (iii) to a temperature of more than 53° C.

12. The method for producing natto according to claim 11, wherein the time during which the product temperature exceeds 53 ° C. is 3.5 hours or less.

13. The method for producing natto according to claim 11, wherein the fermented product stored continuously at 10 ° C. for 30 days after (iv) satisfies at least one of the following (a) to (b) and (d) to (f). (a) A lysine content of 115 mg% or less (b) Ammonia content is 190 mg% or less (d) Tyrosine content is 200 mg% or less (e) The total content of bitter amino acids is 1100 mg% or less. (f) A valine content of 90 mg% or less.

14. The method for producing natto according to claim 11, further satisfying the following (g) after (iv). (g) Enzyme activity is 7 U / g or less.

15. Natto characterized by being produced through the following steps (i) to (iii). (i) preparing a packaging container having a low oxygen permeable portion that satisfies at least one of the following (1) to (2): (1) Oxygen permeability is 70cc / cm ２ ・Day・ATM or more 850cc / cm ２ ・Day・atm or less (2) Average pore area is 10,000 μm ２ With a through hole of less than (ii) inoculating the natto bacteria; (iii) performing fermentation 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) The temperature of the fermented material during the fermentation period is between 37°C and 53°C.

16. Natto characterized by being produced through the following steps (i) to (iii). (i) providing a packaging container; (ii) inoculating the natto bacteria; (iii) A step of carrying out fermentation that satisfies 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) The temperature of the fermented material during the fermentation period is between 37°C and 53°C. (3) During the fermentation period, the oxygen concentration in the packaging container is 10% or less for 8 hours or more.

17. A packaging container characterized by being used for producing natto having a low oxygen permeable portion that satisfies at least one of the following (1) to (2). (1) Oxygen permeability is 70cc / cm ２ ・Day・ATM or more 850cc / cm ２ ・Day・atm or less (2) Average pore area is 10,000 μm ２ With a through hole of less than

18. The packaging container according to claim 17, further comprising a container for storing the product at 10° C. for 14 days or less after completion of fermentation.

19. The packaging container according to claim 17 or 18, wherein the low oxygen permeable portion has a porosity of 0.022% or less.

20. Further, the packaging container according to claim 17 or 18 is used in the method for producing natto according to claim 1.

21. A film characterized by being used for a natto production container that satisfies at least one of the following (1) to (2). (1) Oxygen permeability is 70cc / cm ２ ・Day・ATM or more 850cc / cm ２ ・Day・atm or less (2) Average pore area is 10,000 μm ２ With a through hole of less than

22. The film according to claim 21, further comprising a storage method for up to 14 days at 10° C. after fermentation.

23. The film according to claim 21 or 22, wherein the low oxygen permeable portion has a porosity of 0.022% or less.

24. The film according to claim 21 or 22, which is used in the method for producing natto according to claim 1.

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