Method for producing soybean protein composition and soybean protein composition

Abstract

[Problem] To provide: a method for producing a soybean protein composition by which a protein composition that has soybeans as a raw material and has high protein content can be obtained without the use of chemicals such as organic solvents, acids, and alkalis; and a soybean protein composition. [Solution] This method for producing a soybean protein composition comprises: a soy milk separation step in which soybeans are subjected to extraction to separate soy milk and soy pulp; an enzymatic degradation step in which a proteolytic enzyme is added to the soy milk to degrade proteins contained in the soy milk; and a fermentation step in which sugar-assimilating microorganisms are added to the soy milk to assimilate sugar contained in the soy milk.

Description

Method for producing a soy protein composition and soy protein composition , ,

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[0001] The present invention relates to a method for producing a soy protein composition having a high content of soy protein using soybeans as a raw material and a soy protein composition.

[0002] Conventionally, as a method for producing soy protein using soybeans as a raw material, (A) water is added to defatted soybeans and crushed to form a slurry, the slurry is centrifuged to separate and remove okara, acid is added to the obtained water-soluble fraction (defatted soy milk) to adjust the pH to the isoelectric point to precipitate soy protein, the supernatant (soy whey) is separated and removed to obtain an acidic slurry, alkali is added to this acidic slurry to neutralize it, and it is dried by spray drying or the like. Also, (B) there is a method of water-extracting concentrated soy protein to remove okara, and then drying the obtained soy protein solution by spray drying or the like.

[0003] International Publication No. 2007 / 66694

[0004] However, in the conventional method for producing a soy protein composition, when producing a protein composition having a high content of soy protein, it is necessary to perform defatting using an organic solvent such as hexane, and then perform chemical treatment using an acid or an alkali. However, such a method has a high environmental load because it uses an organic solvent, an acid, an alkali, etc., and there is a possibility that components derived from chemicals remain in the product. In recent years, from the viewpoint of maintaining health, active intake of protein is widely demanded, and a method for producing a soy protein composition having a high content of soy protein without performing these chemical treatments is desired.

[0005] An object of the present invention is to provide a method for producing a soy protein composition and a soy protein composition that can obtain a protein composition having a high content of soy protein using soybeans as a raw material without using chemical agents such as organic solvents, acids, and alkalis. <00000The present invention is essentially a method for producing a soy protein composition as described in any of the following (1) to (7): (1) A method for producing a soy protein composition comprising: a soy milk separation step of squeezing soybeans to separate them into soy milk and okara; an enzymatic decomposition step of adding a proteolytic enzyme to the soy milk to decompose the proteins contained in the soy milk; and a fermentation step of adding sugar-assimilating microorganisms to the soy milk to assimilate the sugars contained in the soy milk. (2) A method for producing a soy protein composition as described in (1) above, wherein whole soybeans from which the skins have been removed are used in the soy milk separation step. (3) A method for producing a soy protein composition as described in (1) or (2) above, comprising: a solid-liquid separation step of centrifuging the soy milk after the enzymatic decomposition step or the fermentation step to separate it into a supernatant and a precipitate; and a step of obtaining soy protein from the supernatant. (4) A method for producing a soy protein composition as described in (3) above, wherein the pH of the soy milk after the enzymatic decomposition step or the fermentation step is adjusted to 6.0 or less before performing the solid-liquid separation step. (5) A method for producing the soy protein composition according to (3) above, further comprising: (6) A method for producing the soy protein composition according to (5) above, wherein in the juice production step, the precipitate is pressed after the solid-liquid separation step to obtain pressed juice; (7) A method for producing the soy protein composition according to (5) above, wherein in the juice production step, the okara is added to the precipitate and pressed; (8) A method for producing the soy protein composition according to (5) above, wherein in the juice separation step, the pH of the pressed juice is adjusted to 6.0 or less before the pressed juice is separated into supernatant and precipitate. Furthermore, the present invention is characterized by the soy protein composition according to (8) or (9) below. (8) A soy protein composition that does not contain residues of organic solvents, acidic chemicals, and alkaline chemicals, and has a soy protein content of 80% by mass or more. (9) The soy protein composition according to (8) above, wherein a proteolytic enzyme is added to soy milk produced from whole soybeans from which the skins of the soybeans have been removed, thereby enzymatically decomposing the proteins contained in the soy milk to release and remove lipids from the proteins, and sugar-assimilating microorganisms are added to assimilate the sugars contained in the soy milk to remove the sugars.Furthermore, the present invention is characterized by the following soy protein compositions: (10) The soy protein composition according to any one of (1) to (7) above, which does not contain residues of organic solvents, acidic chemicals, and alkaline chemicals. (11) The soy protein composition according to any one of (1) to (7) or (10) above, which has a soy protein content of 80% by mass or more. (12) The soy protein composition according to any one of (1) to (7), (10), or (11) above, which is obtained by adding a proteolytic enzyme to soy milk produced from whole soybeans from which the skin of the soybean has been removed to enzymatically decompose the proteins contained in the soy milk, thereby freeing and removing lipids from the proteins, and by adding a sugar-assimilating microorganism to assimilate the sugars contained in the soy milk, thereby removing the sugars.

[0007] According to the present invention, lipids and carbohydrates can be efficiently removed by enzymatic decomposition and fermentation of soy milk obtained by squeezing soybeans, without using organic solvents or chemical substances such as acids and alkalis, thereby obtaining a soy protein composition with a high soy protein content.

[0008] This flowchart shows an example of the production of the soy protein composition according to this embodiment. This flowchart shows another example of the production of the soy protein composition.

[0009] The present invention relates to a method for producing a soy protein composition with a high soy protein content using soybeans as raw material, and to a soy protein composition. In particular, it is characterized by producing a soy protein composition having a high concentration of soy protein by removing fat, ash, and carbohydrates from raw soybeans by combining known food processing technologies such as extraction and separation with enzymatic decomposition and fermentation methods, without using organic solvents such as hexane, or chemicals such as acidic or alkaline chemicals. Furthermore, in raw soybeans, the seed coat accounts for about 10%, and the seed coat is composed almost entirely of fiber (carbohydrates). In the present invention, by removing the hulls in the pretreatment, about 10% of the carbohydrates are removed from the raw material, increasing the protein concentration at the start of processing and enabling highly efficient recovery of soy protein. The following describes embodiments of the method for producing a soy protein composition according to the present invention.

[0010] The soy protein composition according to this embodiment uses whole soybeans as a raw material. The whole soybeans used as a raw material are not particularly limited, and whole grain soybeans, whole fat soybeans, processed defatted soybeans, etc., can be used, but in the following description, whole grain soybeans will be used as an example. Furthermore, the type of soybean is not particularly limited, and white soybeans, yellow soybeans, mung beans, black soybeans, etc., can be used.

[0011] Figure 1 is a flowchart showing an example of the production of a soy protein composition according to this embodiment. As shown in Figure 1, in this embodiment, first, the raw material soybeans are hulled (step S101). There are various products that use soybeans as raw materials, such as tofu, soy milk, natto, miso, soy sauce, and soybean oil, but hulled soybeans are rarely used in these products. The method of hulling soybeans is not particularly limited, and can be appropriately selected from, for example, a method of hulling soybeans by rubbing them together using a known hulling device, a method of hulling soybeans by applying friction to the surface of the soybeans with rollers or discs, a method of hulling soybeans by hitting them against a wall with high-speed rotating blades or rollers, or other known methods. In this embodiment, a soy protein composition with a high protein content can be produced by using hulled soybeans from which the skin, which contains almost no protein, has been removed.

[0012] Next, the hulled soybeans are soaked in water or the like to allow them to absorb water (step S102). The temperature of the water used for soaking is not particularly limited; room temperature water or hot water may be used. The amount of water is preferably 2 to 3 times the total weight of the soybeans. The soaking time is also not particularly limited; for example, if water is used, the soaking time can be set to 2 to 24 hours. In addition, a pH adjusting agent such as baking soda may be added to the soaking water as appropriate to improve the water absorption of the soybeans.

[0013] The hulled soybeans, after soaking in water, are polished into a slurry (soybean paste) using a wet grinder, then squeezed to separate into soy milk and okara (soybean pulp) (step S103). The crushing method is not particularly limited, but known wet grinders such as grinders, colloid mills, stone mills, disc mills, and homogenizers can be used. In this embodiment, the soybeans are crushed after soaking in water, but instead of this configuration, the soybeans can be crushed using a dry grinder such as a hammer mill before soaking in water, and then the crushed soybeans can be soaked in water.

[0014] Furthermore, the method of extracting juice after crushing soybeans to form a slurry (soy milk) is not particularly limited, but for example, it is possible to separate the slurry into solid and liquid by filtering it with a filter or cloth using a filtration juicer, to separate the slurry into solid and liquid using a decanter-type centrifuge, or to extract the juice using a screw press or piston press. It is also possible to heat the slurry before extracting the juice (for example, by heating it at 100°C for about 10 minutes), but it is preferable to crush and extract the juice without heating because protein denaturation will occur.In addition, although this embodiment exemplifies a configuration for producing soy milk from hulled soybeans, it is not limited to this configuration, and it is also possible to separate soybeans into soy milk and okara by crushing and extracting juice with the skin on.

[0015] Next, the obtained soy milk is subjected to an enzymatic hydrolysis treatment (step S104). Specifically, water is added to the soy milk separated in step S103, and proteolytic enzymes such as endoproteases like papain and pepsin, and / or exoproteases like aminopeptidases and carboxypeptidases are added to the water-added soy milk. Endoproteases have high decomposition power, and exoproteases can improve the taste. By performing enzymatic hydrolysis, soy protein and lipids can be separated, making it easier to remove the lipids. In other words, in soy milk, soy protein and lipids form an emulsion, and it was difficult to separate soy protein and lipids by centrifugation alone. In this embodiment, by enzymatically decomposing the soy protein that forms an emulsion with lipids, the emulsion of soy protein and lipids is demulsified, and it becomes possible to separate soy protein and lipids by centrifugation described later.

[0016] The proteolytic enzyme used in step S104 is not particularly limited, but commercially available enzyme preparations used for food products can be used. In addition to using a purified enzyme preparation, or by alternatively, the enzyme hydrolysis of soy milk can also be performed by adding enzyme-active foods such as mushrooms or fruits. Furthermore, the conditions for the enzyme hydrolysis treatment are not particularly limited, but it can be performed at a temperature suitable for the enzyme used (for example, 45-55°C for papain) for 30-120 minutes.

[0017] After the enzymatic hydrolysis treatment, the soy milk is heated to deactivate the enzymes and sterilize it. The heating conditions are not particularly limited and can be any temperature exceeding the deactivation temperature of the enzyme used or conditions that meet the sterilization requirements for general foods. For example, heating at 90-100°C for 0-30 minutes can deactivate the enzymes and sterilize the soy milk.

[0018] Furthermore, in step S105, a process is carried out to remove water-soluble sugars in the soy milk by using sugar-assimilating microorganisms. The sugar-assimilating microorganisms can be sugar-assimilating yeasts or lactic acid bacteria commonly used in food fermentation, and the type is not particularly limited.

[0019] Specifically, as sugar-assimilating yeasts, species commonly used in brewing and bread fermentation can be used. Examples include yeasts such as Saccharomyces cerevisiae, Saccharomyces bayanus, Candida utilis, Kluyveromyces lactis, and Pichia pastoris, as well as commercially available brewing yeast starters and dry yeast for bread.

[0020] Furthermore, as sugar-assimilating lactic acid bacteria, strains commonly used in the production of yogurt and cheese can be used, such as Lactobacillus casei, Lactobacillus plantarum, Lactobacillus helveticus, Lactobacillus bulgaricus, Lactobacillus gasseri, Lactobacillus acidophilus, Lactobacillus lactis, Lactobacillus salivarius, Lactobacillus gallinarum, and Lactobacillus... amylovorus, Lactobacillus brevis, Lactobacillus fermentum, Lactobacillus mali, Lactobacillus delbrueckii, Lactobacillus sanfranciscensis, Lactobacillus panis, Lactobacillus comensis, Lactobacillus italicus, Lactobacillus rhamnosus, Lactobacillus calvatus, Lactobacillus hilgardii, Lactobacillus reuteri, Lactobacillus pastorianus, Lactobacillus buchneri, Lactobacillus Lactobacillus spp., such as Lactobacillus cellobiosus, Lactobacillus fructivorans, Streptococcus thermophilus, Streptococcus lactis, Streptococcus Streptococcus spp. such as Lactococcus diacetylactis, Lactococcus lactis Examples include the Lactococcus genus, such as Lactosoccus lactis and Lactococcus lactis cremoris, the Leuconostoc genus, such as Leuconostoc mesenteroides cremoris and Leuconostoc lactis, and commercially available lactic acid bacteria starters.

[0021] These sugar-assimilating microorganisms may be used individually or in combination of two or more. Furthermore, the fermentation conditions are not particularly limited; fermentation can be carried out at a temperature suitable for each microorganism for a duration sufficient to consume the sugars. For example, commercially available beer brewing yeast can be fermented at 20-40°C for 12-48 hours. After fermentation is complete, the fermentation liquid is heated to sterilize the sugar-assimilating microorganisms used in fermentation. The heating conditions are not particularly limited and can be any conditions necessary for sterilizing the sugar-assimilating microorganisms used; for example, it can be heat-sterilized by heating at 90-100°C for 0-30 minutes.

[0022] In step S106, the soy milk fermented in step S105 is centrifuged to separate it into a supernatant containing soy protein and a precipitate containing lipids, fiber, and cells of sugar-assimilating microorganisms. The precipitate (lipids, fiber, and cells of sugar-assimilating microorganisms) is then removed to obtain a supernatant containing soy protein. To separate the soy protein from the lipids, fiber, and sugar-assimilating microorganisms, it is preferable to use a centrifuge with a centrifugal force of 10,000 to 20,000 G, more preferably 12,000 to 18,000 G, and even more preferably 14,000 to 16,000 G.

[0023] Furthermore, it is preferable to adjust the pH of the soy milk before centrifugation. Specifically, it is preferable to set the pH of the soy milk to 4.0 or higher and 6.0 or lower, and more preferably to 4.5 or higher and 5.5 or lower. If the pH is below 4.0, the acidity will be strong and the taste will be impaired. Also, if the pH is higher than 6.0, good separation of soy protein and fat cannot be obtained, and it will not be possible to obtain a high concentration of soy protein. The pH adjusting agent is not particularly limited, but it is preferable to use edible substances such as fermented lactic acid or fruit juice. The centrifuge is also not particularly limited as long as it is one that is generally used in food processing, and the centrifugal conditions are also not particularly limited as long as they can remove lipids and fiber from the soy milk.

[0024] Furthermore, it is generally known that the isoelectric point of soy protein is around pH 5, and that when the pH of soy milk containing soy protein is set to 4.0 or higher and 6.0 or lower, the soy protein tends to precipitate. However, in this embodiment, by reducing the molecular weight of the soy protein through enzymatic decomposition, the soy protein is less likely to precipitate even when the pH is set to 4.0 or higher and 6.0 or lower, and the soy protein can be recovered in the supernatant after centrifugation (separated from precipitates such as fiber). In addition, when lipids contained in soy milk are centrifuged, some of them settle together with insoluble ash and carbohydrates (fiber), and the remainder separates as an oil layer in the upper layer of the supernatant containing soy protein. Therefore, in this embodiment, by recovering the supernatant (middle layer) containing soy protein using a three-phase separation centrifuge, lipids, fiber, and microbial cells of sugar-assimilating microorganisms can be removed.

[0025] In step S107, the supernatant liquid containing soy protein, which was centrifuged in step S106, is concentrated. The concentration method is not particularly limited, and vacuum evaporation concentrators or membrane concentrators commonly used in food applications can be used. The concentration is also not particularly limited, and any concentration suitable for the dryer in the next drying step is acceptable. For example, it can be 50% or less in Brix, preferably 40% or less, and more preferably 30-40%.

[0026] In step S108, the soy protein composition is powdered by drying the supernatant liquid concentrated in step S107. The method for drying the supernatant liquid is not particularly limited, and general food drying equipment such as spray dryers, freeze dryers, and vacuum dryers can be used.

[0027] As described above, the method for producing the soy protein composition according to this embodiment involves using whole soybeans as raw materials, preparing soy milk from hulled soybeans, performing an enzymatic decomposition treatment in which the prepared soy milk is decomposed with a proteolytic enzyme to separate the protein from the lipids forming an emulsion, and fermenting the soy milk with sugar-assimilating microorganisms to assimilate the sugars contained in the soy milk and remove them. As a result, it is possible to remove lipids and sugars contained in soy milk without using organic solvents or chemical substances such as acids and alkalis as in the conventional method, thus reducing the burden on the environment and providing a soy protein composition with a high soy protein content of 80% by mass or more, preferably 83% by mass or more, and more preferably 85% by mass or more, which is also health-conscious. Furthermore, in the soy protein composition according to this embodiment, since the soy protein is decomposed by the enzymatic decomposition step, it is possible to obtain a soy protein composition with high solubility in water and good digestibility and absorption.

[0028] The soy protein content in the soy protein composition can be measured by known methods such as the Kjeldahl method, combustion method, Biuret method, Bradford method, Lowry method, infrared spectroscopy, and mass spectrometry.

[0029] Figure 2 is a flowchart showing another example of the production of a soy protein composition. In the production method of the soy protein composition shown in Figure 2, steps S201 to S206 are the same as steps S101 to S106 shown in Figure 1, so their explanation is omitted. In the example shown in Figure 2, in order to increase the total amount of soy protein composition, the okara obtained in step S203 and the precipitate obtained in step S206 are pressed again, and soy protein is recovered from the pressed juice as well.

[0030] Specifically, as shown in Figure 2, in step S207, the precipitate (containing lipids and fibers, etc.) obtained by centrifugation in step S206 is subjected to a pressing process. In particular, in this embodiment, the okara obtained by juicing in step S203 is mixed with the precipitate obtained by centrifugation in step S206, and the mixture is pressed with a screw press or the like to obtain pressed juice. By adding okara in this way, the okara functions as a lipid adsorbent, which further promotes the separation of lipids.

[0031] In step S208, the juice obtained in step S207 is centrifuged. Specifically, in step S208, similar to step S206, the juice can be separated into a supernatant containing soy protein and a precipitate containing lipids and fiber by centrifuging with a centrifugal force of, for example, 10,000 to 20,000 G using a centrifuge to separate the protein from the lipids and fiber. Also in step S208, similar to step S206, it is preferable to adjust the pH of the juice obtained in step S207 to be between 4.0 and 6.0, more preferably between 4.5 and 5.5, and then centrifuge the pH-adjusted juice.

[0032] In step S209, the supernatant obtained from centrifugation in step S206 is mixed with the supernatant obtained from centrifugation in step S208. Then, in steps S210 and S211, similar to steps S107 and S108 shown in Figure 1, the supernatant mixed in step S209 is concentrated, and the concentrated supernatant is dried and powdered. This results in a powdered soy protein composition.

[0033] Thus, in the example shown in Figure 2, the total amount of soy protein composition can be increased compared to the example shown in Figure 1 by not only using the supernatant liquid obtained by centrifugation in step S206, but also by pressing the okara obtained in step S203 and the precipitate obtained in step S206 again and recovering soy protein from the resulting juice. However, since the soy protein content in the soy protein composition is higher in the example shown in Figure 1, the manufacturing method can be switched depending on the application.

[0034] Examples of the method for producing the soy protein composition according to the present invention are described below.

[0035] (Test Example 1) In Test Example 1, whole soybeans were hulled and then soaked overnight (for about 15 hours) in 2-3 kg of water per 1 kg of hulled whole soybeans to allow them to absorb water. After that, the hulled soybeans that had absorbed water were made into a slurry using a wet grinder called a Mascolloider, and then the slurry was separated into soy milk and okara using a juicer (Yanagiya Co., Ltd. Squeezer). Furthermore, after adding an equal to 1.5 times the amount of water to the separated soy milk, papain and exo-type protease (Amano Enzyme Protease P6) were added to perform enzymatic hydrolysis. The enzymatic hydrolysis treatment was carried out at 45-55°C for 60 minutes. In addition, after enzymatic hydrolysis, the soy milk containing the proteolytic enzyme was heated at 90-100°C for 15 minutes to inactivate the proteolytic enzyme, and then cooled.

[0036] Next, in Test Example 1, soy milk was pH-adjusted, and the pH-adjusted soy milk was centrifuged to obtain a supernatant liquid containing soy protein. This supernatant liquid was then concentrated and dried to powderize it, obtaining a powdered soy protein composition. In Test Example 1, the Brix of the supernatant liquid before concentration and the soy protein content in the dried soy protein composition were measured. Table 1 below shows the pH of the pH-adjusted soy milk after enzymatic decomposition (before centrifugation), the Brix of the supernatant liquid after centrifugation, and the protein content after drying. In Test Example 1, the soy protein content in the soy protein composition was measured by the combustion method. In Test Example 1, the Brix of the supernatant liquid was measured using a sugar meter (handheld refractometer).

[0037]

[0038] As shown in Table 1 above, in Example 1, the pH was 6.2, which is higher than 6 compared to Examples 2-4. In this case, the Brix in the supernatant was 5.2% lower than in Examples 2-4, and the soy protein content after drying was also lower at 74.8%. In contrast, in Examples 2-4, the pH of the soy milk after pH adjustment was 6 or lower. In this case, the Brix in the supernatant was 5.8% higher than in Example 1, and the soy protein content after drying was also higher at 80% or higher. In particular, in Examples 3 and 4, where the pH of the soy milk after pH adjustment was 5 or lower, the soy protein content after drying was the highest at 81%. However, the protein composition of Example 4 had a strong sour taste, and its flavor was lower compared to Example 3.

[0039] (Test Example 2) In Test Example 2, after enzymatic decomposition was carried out in the same manner as in Test Example 1, the soy milk was centrifuged to separate it into supernatant (A) and precipitate. The precipitate and the mixture of okara (soybean pulp) produced during soy milk production were then pressed to obtain juice. The pH of the juice was then adjusted, and the pH-adjusted juice was centrifuged to obtain supernatant (B) containing soy protein. Supernatant (A) and supernatant (B) were then combined, and the combined supernatant (A+B) was concentrated and dried to produce a powder. In Test Example 2, the Brix of the combined supernatant (A+B) before concentration and the soy protein content after drying were measured. Table 2 below shows the measurement results for the pH of the juice, the Brix of the supernatant before concentration, and the protein content of the soy protein composition after drying. In Test Example 2, as in Test Example 1, the soy protein content in the soy protein composition was measured by the combustion method, and the Brix of the supernatant was measured using a sugar meter (handheld refractometer).

[0040]

[0041] As shown in Table 2 above, in Example 5, the pH was 6.2, which is higher than 6 compared to Examples 6-8. In this case, the Brix in the supernatant was 5.4%, which is lower than in Examples 6-8, and the soy protein content after drying was 74.8%, which is lower. In contrast, in Examples 6-8, the pH was 6 or lower. In this case, the Brix in the supernatant was 6.0%, which is higher than in Example 5, and the soy protein content after drying was also higher, at 80% or more. In particular, in Examples 7 and 8, where the pH of the soy milk after pH adjustment was 5 or lower, the soy protein content after drying was the highest at 81%. However, the protein composition of Example 8 had a strong sour taste and was less palatable compared to Example 7.

[0042] Furthermore, comparing Test Example 1 and Test Example 2, the protein content after drying was similar in both Test Example 1, where soy protein was obtained only from the supernatant obtained by centrifuging enzymatically hydrolyzed soy milk, and Test Example 2, where soy protein was also obtained from the pressed juice of the precipitate obtained by centrifuging enzymatically hydrolyzed soy milk. From this, it was found that if the total amount of soy protein is to be increased, the soy protein composition can be manufactured using the method of Test Example 2, and if the manufacturing process is to be simplified, the soy protein composition can be manufactured using the method of Test Example 1, thereby producing soy protein compositions with similar protein content.

[0043] (Test Example 3) In Test Example 3, it was tested whether a soybean protein composition having a soybean protein content of 85% by mass or more could be obtained by the method for producing a soybean protein composition according to the present embodiment. Specifically, similar to Test Example 1, enzymatic hydrolysis using a proteolytic enzyme was carried out until enzymatic inactivation and cooling, then the pH was adjusted to 5.0, and the pH-adjusted soy milk was centrifuged at 15,000 G to obtain a supernatant (A) containing soybean protein and a precipitate. Also, similar to Test Example 2, after separating the supernatant (A) and the precipitate, the mixture of the precipitate and okara generated during soy milk production was juiced to obtain a juice. Then, the pH of the juice was adjusted, and the juice adjusted to pH 5.0 was centrifuged to obtain a supernatant (B) containing soybean protein. Further, the supernatant (A) and the supernatant (B) were blended, and a commercially available sugar-assimilating yeast for beer brewing was added to the blended supernatant (A + B), and fermentation was carried out at 30°C for 16 hours. After fermentation, the soy milk to which the sugar-assimilating yeast was added was heated at 90°C for 30 minutes for sterilization. Next, the soy milk was centrifuged at 15,000 G using a high-speed centrifuge to separate the soy milk into a supernatant containing soybean protein and a precipitate containing lipids, fibers, and cells of saccharifying microorganisms, and the supernatant containing soybean protein was recovered. Then, the recovered supernatant was concentrated using a vacuum evaporation concentrator until the Brix reached 40%, and thereafter, the concentrate was dried using a spray dryer to obtain a powdery protein composition.

[0044] For the powdery soybean protein composition obtained in Test Example 3 (hereinafter referred to as the soybean protein composition according to Example 9), the content rate of each component was measured. Table 3 shows the content rate of each component of the soybean protein composition according to Example 9. Also, in Table 3, the analysis results of each component of the whole soybeans used as raw materials are also shown for reference. Note that the following Table 3 is a table showing the measurement results of the component content rates (weight %) of the raw whole soybeans and the soybean protein composition according to Example 9. Also, in Test Example 3, similar to Test Example 1, the content of soybean protein was measured by the combustion method.

[0045] As shown in Table 3 above, in raw whole soybeans, the content of soy protein is as low as 41.1%, while the fat content is 21.7% and the carbohydrate content is 23.0%, indicating that there is a large amount of fat and carbohydrates. In contrast, in the soy protein composition according to Example 9, the fat content is as low as 1.7% and the carbohydrate content is 7.5%. Accordingly, the content of soy protein is as high as 85.3% by mass. Thus, it was possible to make the content of soy protein in the soy protein composition 85% by mass or more. As described above, from the results of Test Example 3, for the soy milk produced from shelled whole soybeans, by performing an enzymatic decomposition step of adding a proteolytic enzyme to decompose the protein contained in the soy milk and a fermentation step of adding sugar-assimilating microorganisms to the soy milk to assimilate the carbohydrates contained in the soy milk, it was found that a soy protein composition with a high soy protein concentration of 85.3% by mass could be obtained.

[0046] As described above, in the method for producing a soy protein composition according to the present embodiment, in order to increase the content of soy protein, a soy milk separation step of squeezing soybeans to separate them into soy milk and okara, an enzymatic decomposition step of adding a proteolytic enzyme to the soy milk to decompose the protein contained in the soy milk, and a fermentation step of adding sugar-assimilating microorganisms to the soy milk to decompose the carbohydrates contained in the soy milk are provided. By doing so, a soy protein composition with a soy protein content of 80% by mass or more, preferably 83% by mass or more, and more preferably 85% by mass or more can be obtained. In particular, in the method for producing a soy protein composition according to the present embodiment, without using chemical agents such as organic solvents such as hexane, acidic chemicals, and alkaline chemicals, by combining known food processing techniques such as extraction and separation with enzymatic decomposition and fermentation methods, fat, ash, and carbohydrates can be removed from raw soybeans, and a soy protein composition with a high concentration of soy protein can be obtained.

[0047] Furthermore, in this embodiment, by using whole soybeans with the hulls removed in the soy milk separation process, the protein content in the soy protein composition can be further increased. Specifically, in raw soybeans, the seed coat accounts for about 10%, and this seed coat consists almost entirely of fiber (carbohydrates). In this embodiment, by performing a dehulling process to remove the seed coat of the raw soybeans as a pretreatment, about 10% of the carbohydrates in the raw soybeans are removed from the beginning, increasing the concentration of soy protein in the raw material at the start of processing, and enabling more efficient recovery of soy protein. Moreover, in this embodiment, by adjusting the pH of the soy milk after the enzymatic decomposition process or fermentation process to 6.0 or lower before performing the solid-liquid separation process, the protein content in the soy protein composition can be further increased.

[0048] In addition, after the solid-liquid separation process, the precipitate obtained in the solid-liquid separation process can be pressed to obtain pressed juice, the pressed juice can be separated into supernatant and precipitate by centrifugation, and the supernatant can be concentrated and / or dried to increase the total amount of the soy protein composition. Furthermore, when producing the pressed juice, the protein content of the soy protein composition can be further increased by adding okara (soybean pulp) to the precipitate and pressing it, and by adjusting the pH of the pressed juice to 6.0 or less before separating the pressed juice into supernatant and precipitate.

[0049] Although preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the embodiments described above. Various modifications and improvements can be made to the above embodiments, and such modified or improved forms are also included within the technical scope of the present invention.

Claims

1. A method for producing a soy protein composition, comprising: a soy milk separation step of extracting juice from soybeans and separating it into soy milk and okara; an enzymatic decomposition step of adding a proteolytic enzyme to the soy milk to decompose the proteins contained in the soy milk; and a fermentation step of adding sugar-assimilating microorganisms to the soy milk to assimilate the sugars contained in the soy milk.

2. The method for producing a soy protein composition according to claim 1, wherein whole soybeans from which the skin of the soybean has been removed are used in the soy milk separation step.

3. A method for producing a soy protein composition according to claim 1, comprising: a solid-liquid separation step of centrifuging the soy milk after the enzymatic decomposition step or the fermentation step to separate it into a supernatant liquid and a precipitate; and a step of obtaining soy protein from the supernatant liquid.

4. The method for producing a soy protein composition according to claim 3, wherein the soy milk after the enzymatic decomposition step or the fermentation step is adjusted to a pH of 6.0 or lower before the solid-liquid separation step is performed.

5. A method for producing a soy protein composition according to claim 3, further comprising: a juice production step of obtaining juice by pressing the precipitate after the solid-liquid separation step; a juice separation step of separating the juice into a supernatant and a precipitate by centrifugation; and a step of obtaining soy protein from the supernatant separated in the juice separation step.

6. The method for producing a soy protein composition according to claim 5, wherein in the pressing juice production step, the okara is added to the precipitate and pressed.

7. The method for producing a soy protein composition according to claim 5, wherein in the juice separation step, the pH of the juice is adjusted to 6.0 or less, and then the juice is separated into supernatant and precipitate.

8. A soy protein composition that does not contain residues of organic solvents, acidic chemicals, or alkaline chemicals, and has a soy protein content of 80% by mass or more.

9. The soy protein composition according to claim 8, wherein a proteolytic enzyme is added to enzymatically decompose the proteins contained in soy milk, thereby freeing and removing lipids from the proteins, and a sugar-assimilating microorganism is added to assimilate the sugars contained in the soy milk, thereby removing the sugars.

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