JP2009201466A - Method for producing natto, and natto obtained by the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing Natto by which an improvement in texture such as remaining of skin and promotion of fermentation and aging can sufficiently be carried out even when Natto is produced by using black soybeans with thick seed coats without causing contamination etc., by various germs, and to provide the Natto obtained by the same. <P>SOLUTION: The method for producing the Natto comprises dipping dried soybeans in water, steaming the soybeans, inoculating the steamed soybeans with Bacillus natto, and then carrying out fermentation. The treatment involves refrigerating and freezing the soybeans after dipping, and then thawing the frozen soybeans prior to the steaming to thereby obtain the Natto. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing natto and natto obtained thereby, and more specifically, a method for producing natto, which is particularly effective as a method for producing black soybean natto made from black soybeans with thick seed coats. About the natto produced.

  Natto is excellent in taste and nutrition, but it also has various biological regulation functions. Natto is one of the most important traditional foods in Japan.

  The seed coat color of soybean used as a raw material for natto is usually yellow and yellowish white, but in recent years, the health benefits of anthocyanin pigments contained in the seed coat are expected and there is a high-class feeling. Therefore, black soybeans are increasingly used.

  By the way, commercially available natto is usually manufactured by the following processes. That is, first, the raw material soybean is washed with water, then immersed in water for 8 to 24 hours, and then steamed. After inoculating the natto suspension into the steamed soybean in this manner, the soybean is subdivided into a container such as a cup and fermented as it is at a predetermined temperature for 15 to 48 hours. Thereafter, the whole container is cooled at 10 ° C. or lower for 1 to 2 days and aged, whereby a commercialized natto can be obtained.

Even when natto is produced using black soybean as a raw material, the production is basically performed in the same process as described above. In addition, in recent years, as a method for producing natto specialized in specific black soybeans (large light black soybeans (medium light black soybeans) and medium grain black soybeans (Tokachi black soybeans)), The method for producing black soybean natto is characterized in that the water temperature is kept at around 10 ° C. under inflow and the tank is immersed for 40 to 48 hours while supplying oxygen. It has been proposed (Patent Document 1).
JP-A-1-243958

  However, when black soybeans are made into natto using the conventional natto manufacturing method, the texture remains badly when it is eaten, or the fermentation is insufficient and the original taste of natto is poor. There is a problem that it is difficult to become. This problem is thought to be due to the fact that the seed coat of black soybean is particularly thicker and stronger than yellow soybean or yellowish white soybean. That is, the seed coat of soybean is formed by laminating an epidermis palisade cell layer, a watch glass cell layer, and a spongy parenchyma cell layer in this order from the outside. There is a cuticle layer, and the central part is lignined, and it is difficult to collapse when immersed in water or boiled. In particular, in the seed coat of black soybean, the above-mentioned epidermis cell layer is thicker and stronger than that of yellow soybean or yellowish white soybean, regardless of the particle size of beans.

  On the other hand, as disclosed in Patent Document 1, when water immersion is performed for a long time (40 to 48 hours), there is a risk of spoilage due to various bacteria during the immersion. The manufacturing method disclosed in Patent Document 1 requires complicated operations such as water temperature management and water replacement in order to prevent such corruption. Moreover, there is a possibility that nutrients of black soybeans may flow out due to such long-time immersion in water or replacement of water.

  The present invention has been made in view of such circumstances, and even when producing natto using black soybeans or the like having a thick seed coat without causing contamination by various germs, the texture of the skin remains, etc. The present invention relates to a method for producing natto that can sufficiently improve and promote fermentation and ripening, and natto obtained thereby.

  In order to achieve the above object, the present invention is a method for producing natto in which dried soybeans are immersed in water and then steamed, inoculated with natto bacteria and fermented in the steamed soybeans, prior to the cooking. The first method is a method for producing natto in which the soybeans after immersion are frozen, frozen and then thawed. The second method is natto obtained by the method.

  That is, the present inventors have intensively studied to solve the above problems. In the process of research, in the natto manufacturing method, the soybean seeds are thick and strong (black soybeans) by simply adding a simple process of freezing and freezing soybeans and then thawing them between the water soaking and steaming processes. Etc.) was found to be able to improve the poor texture such as the rest of the skin and to produce soft natto. Moreover, in this manufacturing method, after steaming, while the product temperature of the beans is still high (70-90 ° C.), natto bacteria are inoculated and manufactured as it is, so there is almost no risk of contamination by various bacteria. As a result, the inventors have found that the original umami taste, which has been poor in black soybeans, can be sufficiently extracted, and have reached the present invention.

  Here, FIG. 1 is obtained by collecting seed coats from black soybean natto obtained by the production method of the present invention and photographing the cross section with a scanning electron microscope. In FIG. 1, (a) is an electron micrograph (magnification 1000 times) showing the entire cross section of the seed coat, and (b) is an enlarged main part near the outer surface of the seed coat (near the epidermis-like cell layer). It is a photograph (magnification 3000 times), and (c) is an enlarged photograph (magnification 3000 times) of the main part near the inside of the seed coat (near the spongy parenchyma cell layer). On the other hand, FIG. 2 is a cross-sectional image of the seed coat of black soybean natto obtained by a conventional manufacturing method in which freezing and thawing processes are not performed, and in FIG. , An electron micrograph showing the entire cross-section of the seed coat (magnification 1000 times), (b ') is an enlarged photograph (magnification 3000 times) of the main part near the outer surface of the seed coat (near the epidermis palisade cell layer), (C ′) is an enlarged photograph (magnification 3000 times) of the main part near the inside of the seed coat (near the spongy parenchyma cell layer). And comparing these, the seed coat (FIG. 1) of black soybean natto that had been subjected to freeze-thaw treatment before cooking had collapsed epidermis-like cell layers, and a large number of natto bacteria (in the figure, elongated oval) It can be seen that the invading material from the seed coat surface reaches the spongy parenchyma cell layer. On the other hand, the seed coat of black soybean natto by the conventional manufacturing method (Fig. 2) shows almost no collapse of the epidermis-like cell layer and many natto bacteria are seen outside the seed coat. It turns out that it has hardly penetrated to the inside. And this is considered to be a factor that the bad texture such as the skin residue was improved in the production method of the present invention, and that the original umami taste was sufficiently drawn. In other words, since the umami component peculiar to natto is produced when soybean protein is decomposed by the action of protease produced by natto bacteria, a large number of natto bacteria reach the inside of black soybean by the production method of the present invention. Thus, it is considered that sufficient umami components were obtained, and the poor texture was improved by the collapse of the epidermis-like cell layer as described above.

  As described above, the method for producing natto of the present invention includes a step of immersing dried soybeans in water, then steaming the soybeans, inoculating the fermented natto and fermenting the steamed soybeans prior to the cooking. The soybeans after the immersion are subjected to a simple process of freezing, freezing, and then thawing. Therefore, even when producing natto using black soybeans with thick seed coats, etc. without causing contamination by various germs, sufficiently improve the texture such as the remaining skin and promote fermentation and ripening. Can do. And the quality of black soybean natto, where the seed coat has been thick and strong, has a poor texture compared to natto made from yellow soybeans and yellowish white soybeans, and has not been fully fermented by natto bacteria. However, the natto of the present invention is improved by the above-mentioned production method, and as a result, the natto of the present invention has an unprecedented taste.

  In particular, when the Bacillus natto is Bacillus subtilis KAORI II (FERM P-14771), the production of ammonia by Bacillus subtilis KAORI II and FERM P-14771 is suppressed, and umami is extracted and softening is sufficiently promoted. be able to.

  Further, when the treatment of immersing dried soybeans in water is performed at a water temperature of 5 to 25 ° C. for 8 to 24 hours, a higher quality natto can be obtained without causing nutrient outflow or decay.

  Next, embodiments of the present invention will be described in detail.

  The method for producing natto of the present invention is as described above, after immersing dried soybeans in water, steaming the soybeans, inoculating and fermenting natto bacteria on the cooked soybeans, Prior to steaming, the biggest feature is that the soaked soybean is frozen, frozen and then thawed.

  Examples of soybeans used in the above production method include yellow soybeans, yellowish white soybeans, black soybeans, and blue soybeans. Above all, black soybeans are of good quality with the conventional natto manufacturing method, which has a bad effect on the texture, such as the skin remaining when eaten, and the fermentation is insufficient and the original taste of natto is poor. Although there was a problem that it is difficult, these problems are preferably solved by applying the production method of the present invention, which is preferable. Further, since black soybean has advantages such as the expected health effect of anthocyanin pigments contained in seed coats, the production method of the present invention is also useful in that it can be advantageously applied to such black soybeans. . The soybean varieties and particle sizes are not particularly limited in the production method of the present invention.

  When the treatment of immersing the soybean (dried soybean) in water is carried out at a water temperature of 5 to 25 ° C. for 8 to 24 hours, a higher quality natto can be obtained without causing outflow of nutrients and decay. Therefore, it is preferable. In addition, this immersion process is normally performed using the water equivalent to 3 times amount with respect to dry soybean. Moreover, you may wash | clean soybeans suitably before the said immersion process. Moreover, in order to remove stone beans, this soybean may be passed through a sorter as appropriate.

  As described above, the soybeans after the immersion treatment are subjected to a freezing treatment and a thawing treatment, which are the characteristics of the present invention. The freezing treatment is performed so that the soybeans immersed in water can be completely frozen, and in particular, it is preferably a treatment of slowly freezing at −5 to −30 ° C. from the viewpoint of improving the quality. . In addition, the thawing process is performed so that the frozen soybeans can be completely thawed, and the thawing process is performed in an environment of 5 to 40 ° C. until the product temperature of the soybeans reaches about 5 to about room temperature. It is preferable to do.

Steaming soybeans after the thawing treatment is, for example, degassed at 0.4 to 0.6 kg / cm ² for 5 to 15 minutes, and then to 0.6 to 2.5 kg / cm ² over 5 to 15 minutes. The pressure is increased and maintained at the same pressure for 15 to 60 minutes, and then the pressure is reduced to normal pressure by degassing for 5 to 15 minutes.

  For inoculation of natto bacteria into the above-mentioned steamed soybean, natto bacteria spore suspension commonly used in the natto industry, natto bacteria isolated and acquired from the natural world, and improved breeding natto bacteria, etc. Can be used. Specific examples include spore suspensions of Takahashi bacteria (Takahashi Yuzo Laboratory), Miyagino bacteria (Miyagino Natto Seisakusho), and Naruse bacteria (Naruse Fermentation Chemistry Laboratory), which are commercially available natto bacteria. Further, when the Bacillus natto is Bacillus subtilis KAORI II (FERM P-14771) disclosed in Japanese Patent No. 2851811, it produces umami while suppressing the production of ammonia as compared with ordinary Bacillus natto. In addition, it is preferable in the production method of the present invention since the softening can be sufficiently promoted.

  And the target natto can be obtained by fermenting the soybean planted in this way. When producing as commercially available natto, the fermentation is usually performed after filling the inoculated soybean into a packaging container. And the said fermentation is performed by storing the inoculated soybean for 15 to 48 hours in a 40 degreeC environment.

  When the fermentation process is completed, the natto is sufficiently aged by cooling the whole packaging container at 10 ° C. or lower for 1-2 days until it is shipped as a product. When this ripening step is completed, the product can be shipped as a product.

  The natto of the present invention thus obtained is not contaminated by various bacteria, and even if it is made of black soybean with a thick seed coat, it does not have a bad texture such as the skin residue and is soft. Moreover, fermentation and aging are also sufficient, and the taste is excellent.

  Next, examples will be described together with comparative examples. However, the present invention is not limited to these examples.

The dried black soybean (medium light black) was washed and then immersed in water at 15 ° C. for 18 hours. Next, after thoroughly draining the water of the black soybean, it was frozen in a freezer at −20 ° C. for 20 hours and frozen. Then, this black soybean was thawed at room temperature over 20 hours. Immediately after thawing, the black soybeans were placed in a pressure kettle and steamed. The natto fungal spore suspension was sprayed on the steamed soybean thus obtained. The spore suspension of Bacillus subtilis KAORI II (FERM P-14771) was used as the natto fungal spore suspension, and the number of inoculated plants was 10 ³ to 10 ⁴ per gram of steamed soybean. It sprayed so that it might become. Then, the steamed soybeans inoculated in this way are filled into a Styrofoam container for natto, and then the surface of the filled steamed soybean is covered with a perforated polyethylene film, and the foamed polystyrene container is covered with a lid. Fermented at 40 ° C. for 24 hours. After completion of the fermentation, the black soybean natto of Example 1 was obtained by cooling and aging at 5 ° C. for 24 hours.

[Comparative Example 1]
The freezing and thawing treatment before the steaming process was not performed on the black soybean after the water immersion. Other than that was carried out similarly to Example 1, and manufactured black soybean natto.

  The hardness of the black soybean natto of Example 1 and Comparative Example 1 thus obtained and the amount of formol nitrogen were measured according to the following criteria. And the measurement result was combined with Table 1 of the postscript, and was shown.

〔Hardness〕
The hardness (g) of black soybean natto was measured with a digital force gauge (PGD-2, manufactured by Maruhishi Science Machinery Co., Ltd.).

[Formol nitrogen content]
1 g of amino nitrogen of natto was measured by the formol titration method, and the value was defined as “formol nitrogen amount”. In addition, it shows that an umami | flavor ingredient (amino body nitrogen) is rich, so that this value is large.

  From the results of Table 1 above, it can be seen that the black soybean natto of Example 1 is softer and richer in umami components than the black soybean natto of Comparative Example 1 obtained by a general natto manufacturing method.

  Next, sensory evaluation of the black soybean natto of Example 1 and Comparative Example 1 was also performed by 19 professional panelists. As for the evaluation method, each panelist gives each item (appearance, stringing, fragrance / flavor, texture, taste, overall) in the order of 1, 2, 3, 4 and 5 in ascending order. Based on the above, the average of 19 panelists was taken. The results are also shown in Table 2 below.

  From the results of Table 2 above, the black soybean natto of Example 1 is clearly highly evaluated in terms of texture, taste, and overall evaluation as compared with the black soybean natto of Comparative Example 1 obtained by a general manufacturing method of natto. It can be seen that it is. It can also be seen that the measurement results shown in Table 1 support this sensory evaluation.

  In addition, seed coats were collected from the black soybean natto of Example 1 and the black soybean natto of Comparative Example 1, and the cross section thereof was observed with a scanning electron microscope. The cell layer collapsed, and it was confirmed that many natto bacteria invaded from the seed coat surface and reached the spongy parenchyma cell layer (see FIG. 1). On the other hand, in the seed coat of black soybean natto of Comparative Example 1, almost no collapse of the epidermis palisade cell layer occurred, and many natto bacteria were seen outside the seed coat, but almost up to the inside of the seed coat. It was confirmed that no intrusion occurred (see FIG. 2). This is considered to be the reason why the bad texture such as the remaining skin of the black soybean natto of Example 1 was improved and the original taste of natto was sufficiently extracted.

  Instead of the natto fungus spore suspension used in Example 1, a spore solution of Takahashi fungus (Takahashi Yuzo Laboratory), Miyagino fungus (Miyagino Natto Seisakusho) or Naruse fungus (Naruse Fermentation Chemistry Laboratory) is used. Other than that, even when black soybean natto was produced under the same conditions as in Example 1, as with black soybean natto in Example 1, it was softer and richer in umami components than the black soybean natto in Comparative Example 1. It was confirmed by experiments that

  As black soybeans, instead of the mesophyll black used in Example 1, a small black sengoku was used, and as Bacillus subtilis Kaori II, Takahashi fungus (Yuzo Takahashi Laboratory) A black soybean natto was prepared under the same conditions as in Example 1 except that the spore solution of either Miyagino or Naruse (Naruse Fermentation Chemistry Laboratories) was used.

  The natto thus obtained was stored in a refrigerator for 23 days. And the sensory evaluation of the strength of the ammonia smell emitted from such natto after long-term storage was carried out according to the following criteria by 12 professional panelists. And the result of averaging the evaluation was combined with Table 3 of the postscript, and was shown.

[Standard]
◎ ... I don't mind the ammonia odor at all.
○ ... I don't mind the ammonia odor.
Δ: A little ammonia odor.
X: Strong enough to worry about the ammonia odor.

  From the results of Table 3 above, it can be seen that when the storage period after the end of fermentation is long, the odor of ammonia tends to increase depending on the Bacillus natto. In addition, this tendency is seen also in the case of natto obtained by the general manufacturing method which does not perform freezing and thawing processing. However, in the production method of the present invention, it is known that there is a tendency that the ammonia odor tends to be slightly stronger even if the same Bacillus natto is used because the degradation of the protein is easier to proceed than in the case of the conventional production method. .

  However, as apparent from the results of Table 3 above, when Bacillus subtilis Kaori II is used as a natto bacterium, the generation of ammonia odor is suppressed as compared to other natto bacteria, From the viewpoint of long-term storage, it can be seen that it is preferable to use Bacillus subtilis Kaori II in the production method of the present invention. In addition, it was confirmed by experiment that any black soybean natto was soft and rich in umami components, like the black soybean natto of Example 1.

  The method for producing natto according to the present invention is useful in that it can be applied to beans with thick seed coats such as black soybeans to obtain an unprecedented natto with excellent taste. It can also be applied to conventional natto materials such as.

It is an electron micrograph which shows an example of the seed coat cross section of the black soybean natto obtained by the manufacturing method of this invention, (a) is the whole (1000 times magnification), (b) is the outer surface vicinity of a seed coat ( (Magnification 3000 times) and (c) is near the inside of the seed coat (magnification 3000 times). It is an electron micrograph which shows an example of the seed coat cross section of the black soybean natto obtained by the conventional manufacturing method, (a ') is the whole (1000 times magnification), (b') is the outer surface vicinity of a seed coat (Magnification 3000 times) and (c ′) is near the inside of the seed coat (magnification 3000 times).

Claims (5)

  After immersing the dried soybeans in water, steaming the soybeans, inoculating the fermented natto and fermenting natto into the steamed soybeans, prior to the cooking, freezing the frozen soybeans and freezing them. Then, a method of producing natto, characterized by performing a process of thawing.   The method for producing natto according to claim 1, wherein the soybean is black soybean.   The method for producing natto according to claim 1 or 2, wherein the Bacillus natto is Bacillus subtilis KAORI II (FERM P-14771).   The method for producing natto according to any one of claims 1 to 3, wherein the treatment of immersing the dried soybeans in water is performed at a water temperature of 5 to 25 ° C for 8 to 24 hours.   It is obtained by the manufacturing method as described in any one of Claims 1-4, Natto characterized by the above-mentioned.