JP7760564B2 - Manufacturing method of packaged soybean rice - Google Patents

Description

The present invention relates to a method for producing retort-packaged soybean rice using artificial rice (soybean rice) made primarily from soybeans.

Rice, the staple food of the Japanese people, is relatively high in calories due to its high starch content. Therefore, patients with diseases such as obesity or diabetes may have to limit their rice intake, resulting in an increasing number of people who are unable to feel satisfied with their daily meals.
Furthermore, in recent years, nutritional disorders associated with decreased food intake among the elderly, frailty (frailty), and muscle loss associated with aging (the onset of sarcopenia) have become problems, and the Ministry of Health, Labor, and Welfare's "Dietary Reference Intakes for Japanese (2020 Edition)" recommends consuming sufficient amounts of protein daily to prevent frailty in the elderly. However, rice, the staple food of the Japanese people, is low in protein, and it is not possible to ingest the necessary protein from rice alone. Therefore, the applicant has proposed artificial rice (soybean rice), which is made primarily from soybeans, as an artificial rice that can be used as a substitute for staple rice and is high in protein (Patent Document 1).

Soybean rice can be eaten by absorbing water in the same way as rice and then cooking it in a rice cooker or microwave oven, but for easier consumption, there is a demand for a form that can be eaten simply by reheating.
Among cooked rice products, sealed cooked rice foods (packaged cooked rice) that can be eaten simply by reheating in a microwave oven or in hot water and can be stored at room temperature for a long period of time are widely available as a convenient form of eating. Known methods for producing this packaged cooked rice include a method in which cooked cooked rice is packed into a container in a sterile facility and sealed (Patent Document 2), and a method in which rice and water are packed into a container, sealed, and then cooked and sterilized (Patent Document 3).
However, there is no known method for producing artificial rice made primarily from soybeans that can be easily eaten and stored at room temperature for a long period of time.

Japanese Patent Application Laid-Open No. 2022-82347 Japanese Patent Application Publication No. 5-176696 Japanese Patent Application Publication No. 9-149766

The present invention aims to provide a technology that can prevent soybean rice from sticking together in retort-packaged products (hereinafter referred to as packaged soybean rice) produced by sealing soybean rice soaked in water and water in a container and heating under pressure, making it possible to easily eat soybean rice. Another objective of the present invention is to provide packaged soybean rice with an excellent appearance and texture by preventing sticking that occurs during the heating and pressurization process.

The inventors conducted extensive research to solve the above-mentioned problems and discovered that by using an acidic solution when soybean rice is soaked in water, and by using an acidic solution when soybean rice and water are placed in a container and sealed after soaking, it is possible to prevent sticking of pressurized and heated packaged soybean rice. This resulted in packaged soybean rice with excellent appearance and texture, which led to the completion of the present invention.

The present invention was completed based on these findings and includes the following technical ideas.
[1] A method for producing packaged soybean rice, the method comprising the steps of: a soaking step of soaking soybean rice in a soaking liquid; a packaging step of sealing the soybean rice after soaking and a filling liquid in a container; and a heating step of pressurizing and heating the soybean rice, wherein the pH of the soaking liquid and the filling liquid is 2.2 to 3.7, and the pH of the packaged soybean rice after the heating step is 5.3 to 6.7.
[2] The manufacturing method according to [1], which uses soybean rice obtained by a manufacturing method including a kneading step of adding water to raw materials containing soybean flour, soybean protein, and transglutaminase and kneading them together, a shaping step of extruding the kneaded mixture to obtain a rice-like product, and a drying step of heating and drying the rice-like product, wherein the temperature in the kneading step and the shaping step is 40°C or less, the temperature in the drying step is 30 to 100°C, and the raw materials have a mixing ratio of soybean flour to soybean protein of 30:70 to 90:10.
[3] The manufacturing method according to [1] or [2], wherein the total amount of water absorbed by the soybean rice after soaking and the amount of the filling liquid is 1.5 to 2.8 parts by weight per 1 part by weight of the soybean rice.
[4] The manufacturing method described in [3], wherein in the soybean rice soaking step or the packaging step, a portion of the soybean rice is replaced with grains, and the dry weight ratio of the soybean rice to grains is 100:0 to 30:70.
[5] The manufacturing method described in [2], wherein the soybean rice contains starches as raw materials.

According to the method of the present invention, an acidic solution is used when soybean rice is soaked in water, and an acidic solution is also used in the filling liquid when the soaked soybean rice and filling liquid are sealed in a container. This prevents the packaged soybean rice from sticking together during the pressurized heat treatment, resulting in packaged soybean rice with an excellent appearance and texture.

The following describes the embodiments of the present invention. The present invention is not limited to the following description.

In this specification, "soybean rice" refers to artificial rice made primarily from soybeans, which is molded into the shape of rice grains and dried, and has the following characteristics (a), (b), or (c).
(i) Soybean rice obtained by a production method comprising: a kneading step of adding water to and kneading raw materials containing soy flour, soy protein, and transglutaminase; a shaping step of extruding the kneaded mixture to obtain a rice-like product; and a drying step of heating and drying the rice-like product, wherein the temperature in the kneading step and the shaping step is 40°C or less, the temperature in the drying step is 30 to 100°C, and the raw materials are soy flour and soy protein in a mixing ratio of 30:70 to 90:10.
(ii) Soybean rice obtained by the manufacturing method described in (i), wherein the raw material contains a total of 50 parts by weight or more of soy flour and soy protein as solids per 100 parts by weight of the total raw material solids.
(c) Soybean rice obtained by the manufacturing method described in (a) or (b), in which the raw material contains starches.

(I) Method for Producing Soybean Rice First, the method for producing soybean rice will be described in detail.
(soy flour)
The soybean flour used for soybean rice can be any ordinary soybean flour. Specifically, for example, it is prepared by crushing dehulled soybeans, appropriately heating them, and drying them. From the viewpoint of flavor, such as the unpleasant odor and taste characteristic of soybeans, it is preferable to use soybean flour in which enzyme activity such as lipoxygenase has been inactivated by heat treatment.
The soybean raw material used for the soybean flour is not particularly limited, and whole soybeans, dehulled soybeans, cracked soybeans, etc. can be used.
The type of soybean used for the soybean flour is not particularly limited and may be selected depending on the desired flavor, such as yellow soybeans, white soybeans, green soybeans, black soybeans, and kurakake soybeans. For example, from the viewpoint of color tone, white soybeans and yellow soybeans are preferred when a color tone similar to that of white rice is desired.
Soybean flour is processed, for example, by dehulling soybeans, heating them, grinding them, and drying them. The heat treatment may be performed before, after, or after the dehulling process, or after the grinding process, and is not particularly limited. If pre-dehulled soybeans are used, the dehulling process is not necessary.
The soybean dehulling treatment is not particularly limited, and any commonly used known method may be used. Specific examples include grinding, dry crushing, dry dehulling using a millstone, polishing, and flash heating, and may be carried out using a commercially available dehulling machine. When a heating method is used, the activity of enzymes such as lipoxygenase can be inactivated or suppressed by heating at the same time as the dehulling treatment.
The heat treatment of soybeans is not particularly limited as long as it can inactivate or suppress the activity of enzymes such as lipoxygenase by heating, and any commonly used known method may be used. The heating method may be either dry heating or wet heating, and examples of dry heating include roasting and heating with hot air.
The soybean grinding process is not particularly limited, and any commonly used known method may be used. Examples of grinding methods include dry grinding, wet grinding, and freeze grinding, and the grinding may be carried out using a commercially available grinder. The particle size of the resulting soybean flour is, for example, 100 μm or less, preferably 25 μm or less. From the viewpoint of improving the texture of the final soybean rice, the smaller the particle size of the soybean flour, the more preferable it is. The amount of soybean flour used can be adjusted depending on the desired texture, flavor, and moldability of the soybean rice, and soybean rice with excellent taste, flavor, and texture can be obtained by adjusting the mixing ratio with the soybean protein described below.

(soy protein)
The soybean protein used in soybean rice is not particularly limited, and for example, either isolated soybean protein or concentrated soybean protein can be used, or a combination of these can be used.
Soy protein isolate is obtained by removing non-protein compounds from defatted soybeans, and by purifying the soy protein to a protein content of, for example, about 90% or more on a dry matter basis. Examples of soy protein isolates that can be used include commercially available products and products prepared using soy protein as a raw material. Soy protein concentrate is obtained by removing most of the fats and oils and water-soluble non-protein compounds from defatted soybeans, and by purifying the soy protein to a protein content of, for example, about 70% or more on a dry matter basis.
Concentrated soy protein can be, for example, a commercially available product or one prepared using soy protein as a raw material. Soy protein can be in various forms, such as powder, granules, or fiber, but the soy protein used in soy rice is powder. Using granular or fibrous soy protein is undesirable because it results in uneven texture and appearance of the soy rice. The amount of soy protein used can be adjusted depending on the desired texture, flavor, and moldability of the soy rice, and soy rice with excellent taste, flavor, and texture can be obtained by adjusting the mixing ratio with the soy flour described above.

(mixing ratio of soy flour and soy protein)
The mixing ratio of soy flour and soy protein can be adjusted depending on the texture, flavor, and moldability of the desired soy rice. When the auxiliary ingredients described below are not used, the mixing ratio of soy flour and soy protein in the raw material is preferably adjusted to a range of 30 parts by weight:70 parts by weight to 90 parts by weight:10 parts by weight based on the total raw material solids, as this provides good moldability. A more preferable ratio is 30 parts by weight:70 parts by weight to 50 parts by weight:50 parts by weight, as this provides a better texture. A mixing ratio of soy flour and soy protein of 25 parts by weight or less based on the total raw material solids is unsuitable because the kneaded product obtained by mixing and kneading the soy flour and soy protein lacks viscosity and cannot be molded in the process of extruding the kneaded product to obtain a rice-like product, as described below.
Furthermore, if the amount of soybean flour exceeds 90 parts by weight relative to the total raw material solid content, the kneaded mixture will be too sticky, and the rice-shaped products extruded from the kneaded mixture will not break apart but will stick together, resulting in molding defects, making this unsuitable.

(Transglutaminase)
The action of the transglutaminase used in soybean rice is to catalyze the formation of cross-links between glutamic acid residues and lysine residues through isopeptide bonds in the proteins contained in the soybean flour and soybean protein mentioned above, thereby polymerizing them and giving the proteins elasticity.
The transglutaminase used for soybean rice may be any conventionally known transglutaminase, and may be commercially available or prepared by a unique method. Examples include Activa TG-H, Activa TG-K, Activa TG-M, Activa TG-AK, Activa TG-B, and Activa TG-S (all manufactured by Ajinomoto Co., Inc.). These transglutaminases may be used alone or in combination of two or more.
The amount of transglutaminase used can be adjusted depending on the desired texture of the soybean rice, and is not particularly limited. For example, 0.005 to 1.0 parts by weight of transglutaminase may be used relative to the total raw material solid content, and preferably 0.01 to 0.2 parts by weight of transglutaminase can be added and used to impart elasticity to the texture of the soybean rice.

(auxiliary raw materials)
The auxiliary ingredients used in soybean rice are not essential but can be used as appropriate for the purpose of improving the texture, flavor, moldability, and storage stability of the target soybean rice. The raw materials used as the auxiliary ingredients are not particularly limited, but starches such as rice flour and modified starch, thickening polysaccharides such as alginic acid, sugars other than starches such as monosaccharides and dextrin, and dietary fiber materials such as cellulose can be used.

(Starches)
Although the starches used in soybean rice are not essential, their use can impart the flavor and texture unique to cooked rice to the soybean rice.
The starches are not particularly limited in terms of their raw material or type, and examples thereof include grain starches such as rice flour, glutinous rice flour, corn starch, waxy corn starch, potato starch, sweet potato starch, tapioca starch, and cassava starch, and processed starches such as highly branched cyclic dextrin, heat-moisture treated starch, hydroxypropyl starch, starch acetate, hydroxyalkyl starch, and phosphate cross-linked starch, and at least one of these can be used as necessary.
The amount of starch used is not particularly limited, but if the flavor of cooked rice is particularly preferred, soybean rice with a flavor unique to cooked rice can be obtained by including 3 parts by weight or more, preferably 5 parts by weight or more, and more preferably 10 parts by weight or more of starch relative to the total solid content of the raw material.

(Thickening polysaccharides)
The thickening polysaccharide is not particularly limited, and examples thereof include sodium alginate, propylene glycol alginate, gum arabic, arabinogalactan, alginic acid, gum ghatti, curdlan, carrageenan, glucomannan, furcellaran, karaya gum, locust bean gum, xanthan gum, gellan gum, native gellan gum, guar gum, psyllium seed gum, tamarind seed gum, tara gum, tragacanth gum, pectin, pullulan, welan gum, cassia gum, gelatin, agar, etc. The use of thickening polysaccharides can impart elasticity and stickiness to the texture of soybean rice and improve its water retention.

(Dietary fiber material)
Examples of dietary fiber materials include cellulose, polydextrose, indigestible dextrin, enzymatic hydrolyzate of guar gum, low-molecular-weight sodium alginate, psyllium husk, inulin, water-soluble soybean polysaccharides, gum arabic, corn fiber, etc. The use of dietary fiber materials can impart elasticity and stickiness to the texture of soybean rice and improve its water retention and flavor.

(Sugars other than starches)
As the sugars other than starches, any sugars available for food can be used, including, for example, reduced starch syrups such as glucose, fructose, galactose, mannose, maltose, lactose, sucrose, trehalose, maltitol, and sorbitol. These sugars can impart effects such as making the soybean rice fluffy when cooked and when left for a while after cooking, as well as the effect of inhibiting protein hardening and starch retrogradation.

Soybean rice is made by kneading soy flour, soy protein, and transglutaminase with water, forming them into a rice-like shape, and then heating and drying them to activate the transglutaminase, allowing it to act on the protein.

(Kneading process)
First, the main ingredients, soy flour and soy protein, are mixed uniformly. If a secondary ingredient is used, it is mixed at the same time as the main ingredient. Next, transglutaminase is dissolved in cold water, and the solution and the powder mixture are mixed and kneaded.
In the kneading step, the amount of water added during kneading can be set as appropriate; for example, when the total weight of the ingredients including water is 100 parts by weight, water is preferably added in the range of 30 to 60 parts by weight, more preferably 45 to 55 parts by weight. If the amount of water added is too high or too low, molding defects will occur in the molding step described below, and the desired rice-like product will not be obtained. Furthermore, if the amount of water added is too low, transglutaminase will not be able to act sufficiently in the drying step described below, and a desirable texture will not be obtained.
The kneading step is carried out under conditions where the product temperature of the kneaded product is 40° C. or less so as not to accelerate the reaction between transglutaminase and protein. It is preferable that the main raw materials and auxiliary raw materials to be used as raw materials are cooled in a refrigerator in advance.
The kneading method may be any method as long as the raw materials can be mixed uniformly, and the type of kneader is not particularly limited, but it is preferable to use a kneader equipped with a cooling chiller.

(molding process)
The kneaded material obtained in the kneading step is fed to a screw extruder, and while being further kneaded, it is extruded and cut through a die attached to the tip of the extruder to form rice grain-like shapes. In this step, the kneaded material is compressed and extruded, thereby obtaining rice-like products with a dense structure. The type of extruder used for forming is not particularly limited, but a squeezer or extruder can be used, and preferably one equipped with a cooling chiller is preferred.
The forming step is carried out under conditions where the product temperature of the rice-shaped product is 40°C or less so as not to accelerate the reaction between transglutaminase and protein.
If the product temperature exceeds 40°C during the preceding kneading and shaping steps, the activation of transglutaminase in the kneaded product will be accelerated, and the structured product will collapse upon extrusion, resulting in a decrease in the shape retention of the resulting rice-like shaped product and the generation of many cracks and scraps. Furthermore, soybean rice will be imparted with excessive elasticity, making it impossible to obtain a desirable texture.

(drying process)
The rice-like formed product obtained in the forming step is dried at 100°C or less, and at the same time, the activation of transglutaminase is enhanced, and as the drying progresses, the rice-like formed product is dried to a predetermined dry state, and at the same time, the transglutaminase is deactivated or inactivated.
In the drying process, drying at 100°C or below not only produces a product with good color tone with little discoloration, but also enhances the reaction between transglutaminase and protein, which causes the proteins in the rice-like product to cross-link with each other and become polymerized, imparting appropriate elasticity and improved shape retention to the soybean rice, resulting in soybean rice with excellent texture and cooking resistance.
The temperature in the drying step is 100°C or less, preferably 50 to 100°C, and drying for 30 to 210 minutes is preferred. More preferably, drying is performed at 60 to 90°C and for 35 to 90 minutes. This is preferred because not only does it provide a product with a good texture and color, but it also has high drying efficiency and a short drying time, resulting in high productivity. While the lower limit temperature is not particularly limited, drying at a low temperature is not preferred because it results in poor drying efficiency and a long drying time.
The predetermined dry state is preferably a moisture content of 12% by weight or less, more preferably 10% by weight or less, and even more preferably 8% by weight or less, which is preferable because reducing the moisture content can prevent deterioration and browning caused by microorganisms during storage.
The dryer to be used is not particularly limited, but a hot air band dryer, a hot air flow dryer, a hot air shelf dryer, or the like can be used.

Thus, the above method makes it possible to produce soybean rice that retains the shape of the rice grains without crumbling during cooking, has a hardness and elastic texture similar to cooked rice, is high in protein and low in carbohydrates, and is an excellent substitute for cooked rice with excellent taste, flavor, and texture.

(II) Method for Producing Packaged Soybean Rice Next, a method for producing packaged soybean rice using the soybean rice obtained above, which can be easily eaten and can be stored at room temperature for a long period of time, will be described in detail.
(Soaking process)
In the soaking step, the soybean rice is soaked in a soaking solution having an acidic pH to absorb the soaking solution. After soaking, the soybean rice is drained using a colander or the like to obtain soaked soybean rice.

The soaking liquid is prepared by dissolving an acid in water to adjust the pH to an acidic level. The soaking liquid can be adjusted appropriately within the pH range of 2.2 to 3.7 to ensure that the pH of the packaged soybean rice is 5.3 to 6.7. For example, when adjusting the pH of the soaking liquid to 3.5 using 10% (w/v) acetic acid (pH 2.3), 99 parts by weight of water can be added to 1 part by weight of 10% (w/v) acetic acid. If the pH of the soaking liquid is lower than 2.2, the amount of water absorbed by the soybean rice will decrease, resulting in a hard texture for the packaged soybean rice. If the pH of the soaking liquid is higher than 3.7, the effect of inhibiting sticking will be weakened.

The acid used in the soaking solution may be any organic acid, inorganic acid, or salt thereof used in the food industry, and these acids may be synthetic, natural, or produced by fermentation, or may be a salt thereof, or a combination of two or more acids. Examples of organic acids that may be used include acetic acid, gluconic acid, citric acid, lactic acid, fumaric acid, malic acid, and ascorbic acid, while examples of inorganic acids that may be used include phosphoric acid and hydrochloric acid.

The amount of water absorbed by the soaking liquid during the soaking process can be adjusted appropriately within the range of 0.8 to 1.2 parts by weight per 1 part by weight of soybean rice. The amount of soaking liquid should be 1.2 parts by weight or more per 1 part by weight of soybean rice, and may be adjusted to, for example, 2 to 5 parts by weight. The soaking time should be 30 minutes or more when the temperature of the soaking liquid is 15°C, for example.

(packaging process)
In the packaging step, the soaked soybean rice obtained in the soaking step and the filling solution having an acidic pH are placed in a heat-resistant plastic container and then sealed.

The filling liquid is prepared by dissolving an acid in water to adjust the pH to an acidic level. The filling liquid can be adjusted appropriately within the pH range of 2.2 to 3.7 so that the pH of the packaged soybean rice is 5.3 to 6.7. For example, when adjusting the filling liquid to pH 3.5 using 10% (w/v) acetic acid (pH 2.3), 99 parts by weight of water can be added to 1 part by weight of 10% (w/v) acetic acid. If the pH of the filling liquid is lower than 2.2, the amount of water absorbed by the soybean rice after soaking in the heating process described below will decrease, resulting in a hard texture. If the pH is higher than 3.7, the effect of inhibiting adhesion will be weakened. The pH of the filling liquid may be different from the pH of the soaking liquid.

The acid used in the filling liquid may be any organic acid, inorganic acid, or salt thereof used in the food industry. These acids may be synthetic, natural, or produced by fermentation, or may be salts of these acids, or a combination of two or more acids may be used. Organic acids include acetic acid, gluconic acid, citric acid, lactic acid, fumaric acid, malic acid, and ascorbic acid, while inorganic acids include phosphoric acid and hydrochloric acid. The acid used in the filling liquid may be different from the acid used in the soaking liquid.

The amount of filling liquid is the sum of the amount of soaking liquid absorbed by the soybean rice after soaking in the soaking process (hereinafter referred to as the "amount of water absorbed by the soybean rice after soaking") and the amount of filling liquid (hereinafter referred to as the "total liquid amount"), and can be adjusted so that the total liquid amount is 1.5 to 2.8 parts by weight per 1 part by weight of soybean rice. From the perspective of texture, however, it is preferable to adjust it to a range of 2.0 to 2.7 parts by weight. If the total liquid amount is less than 1.5 parts by weight, the texture of the packaged soybean rice will be hard. If the total liquid amount is more than 2.8 parts by weight, the soybean rice after soaking will not be able to absorb the entire amount of filling liquid, and the appearance and texture of the packaged soybean rice will be significantly inferior.

(Heating process)
In the heating step, the soybean rice sealed in the packaging step is subjected to a pressure heating treatment, thereby cooking the soybean rice and ensuring its shelf life at room temperature. The heating step imparts a desirable flavor, texture, and shelf life to the soybean rice, thereby completing the packaged soybean rice of the present invention with reduced sticking.

The heating temperature and time can be adjusted as appropriate as long as the soybean rice is cooked and sterilized under conditions that result in an F value of 4 or higher. For example, the heating temperature and time can be adjusted to 105°C to 130°C and 20 to 120 minutes, depending on the content volume of the final packaged soybean rice product and the amount of sterilization treatment.

(grain)
In the present invention, the soybean rice can be partially replaced with grains such as rice in the soaking or packaging process. The dry weight ratio of soybean rice to grains is, for example, in the range of 100:0 to 30:70. The grains may be mixed in dry form, or may be mixed after pre-absorption. The amount of filling liquid can be adjusted appropriately depending on the type of grain used, the amount added, and whether or not it has absorbed water. Grains that can be used include rice, brown rice, barley, Job's tears, oats, glutinous barley, black rice, red rice, millet, foxtail millet, and barnyard millet, and a combination of multiple grains may also be used.
When using grains, the amount of water required for normal rice cooking of the grains to be used can be confirmed in advance to determine the amount of filler liquid required for the grains to be mixed. For example, when using white rice, the amount of water required for cooking can be adjusted as needed to achieve the desired firmness, and can be appropriately adjusted within a range of, for example, 1.0 to 1.5 parts by weight per 1 part by weight of white rice. When 1 part by weight of white rice is soaked for 1 hour, the amount of water absorbed by the white rice is approximately 0.2 to 0.25 parts by weight. Therefore, when mixing white rice (dry), the amount of filler liquid should be approximately 1.0 to 1.5 times the amount of white rice, and when mixing soaked white rice, the amount of filler liquid should be approximately 0.75 to 1.3 times the amount of white rice.
Furthermore, when brown rice is used, the amount of water required to cook 1 part by weight of brown rice can be adjusted to the desired firmness, and can be appropriately adjusted, for example, within the range of 1.0 to 2.0 parts by weight per 1 part by weight of brown rice. Since the amount of water absorbed by brown rice when 1 part by weight of brown rice is soaked for 5 hours is approximately 0.2 to 0.25 parts by weight, when mixing brown rice (dried), the amount of filler liquid should be approximately 1.0 to 2.0 times the amount of brown rice, and when mixing soaked brown rice, the amount of filler liquid should be approximately 0.75 to 1.8 times the amount of white rice.

Thus, the manufacturing method of the present invention suppresses the sticking that occurs when heated under pressure, making it possible to provide packaged soybean rice with excellent appearance and texture.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, the following examples were carried out at room temperature (25°C ± 5°C) and atmospheric pressure. Unless otherwise specified, the percentages stated below mean "% by weight."

(1) Method for Producing Soybean Rice An example of a method for producing soybean rice used in the present invention will be described.

<Examples 1 and 2, Comparative Examples 1 to 3>
The following examples and comparative examples were carried out using the following raw materials and conditions unless otherwise specified.
(Soybean rice production)
First, the manufacturing method of Example 1 will be described below.
The raw materials used were soybean flour, powdered soybean protein (isolated soybean protein, manufactured by Fuji Oil Co., Ltd.), and transglutaminase (manufactured by Ajinomoto Co., Inc.).
Soybean flour was prepared by heating whole soybeans (Toyomasari, produced in Hokkaido) at 115°C for 20 minutes with hot air, then dehulling the soybeans with a dehuller and grinding them with a grinder. The average particle size of the resulting soybean flour was 20-30 μm.
Next, 2000 g of soy flour and 2750 g of soy protein that had been refrigerated at 10° C. or below were powder-mixed, and then 1 g of transglutaminase was dissolved in 5249 g of water at 10° C., and these were mixed and kneaded uniformly to obtain a kneaded mixture. At this time, the product temperature of the kneaded mixture was 20° C. or below.
The kneaded mixture was then fed to a screw extruder equipped with a die at the end, and extruded while circulating chilled water (10°C) in the outer jacket of the extruder rotor. Simultaneously, the mixture was cut to obtain rice-shaped extrusions. The product temperature of the rice-shaped extrusions was 25°C or lower. The size of the rice-shaped extrusions was adjusted to 7 mm in length, 2 mm in width, and 2-3 mm in thickness.
The rice-like product was then supplied to a steam convection oven (Fujimak Co., Ltd., product number FCCM6) and dried on a hot air rack without humidification at 80°C (the oven's set temperature) for 45 minutes, then transferred to a tray and air-cooled to 35°C or less to obtain soybean rice. The obtained soybean rice had a moisture content of 10% to 14%.
In Example 2, the same procedure as in Example 1 was carried out except that the raw soy protein was changed from isolated soy protein to concentrated soy protein (manufactured by Matsuda Sangyo Co., Ltd.), and a sample of Example 2 was obtained.
As comparative examples, those using transglutaminase were prepared using only soy flour as the raw material (Comparative Example 1), those using only soy protein (Comparative Example 2), and those not using transglutaminase were prepared using soy flour and soy protein (Comparative Example 3). These were all prepared in the same manner as in Example 1 except for the raw materials.

(Cooked soybean rice)
400 g of water was added to 200 g of the soybean rice obtained in the Examples and Comparative Examples, and the rice was cooked in a rice cooker in the usual manner. After stirring well with a rice scoop, the rice was steamed in the rice cooker for 10 minutes.

(Evaluation of soybean rice)
The soybean rice obtained in the Examples and Comparative Examples was evaluated for its formability during production and for its sensory evaluation (texture, appearance, taste and flavor) after cooking. The sensory evaluation was carried out by five trained panelists for sensory evaluation of palatability, who tasted the rice and evaluated it according to the following evaluation criteria, and the results were compiled. In the sensory evaluation, rice that was not cooked due to poor forming was marked with "-". The results are shown in Table 1.
[Evaluation criteria for formability]
◎: The grain surface is smooth and can be molded without crumbling or cracking.
○: No crumbling or cracking and can be molded.
△: There is some crumbling, but it can be molded.
×: Unable to mold, or many crumbles and cracks.
[Evaluation criteria for sensory evaluation]
(Texture)
◎: It has a texture similar to cooked rice and is delicious.
○: The texture is decent and it's delicious.
△: The texture is slightly bad and the taste is inferior.
×: The texture is bad and it is not tasty.
(Appearance)
Good: Little discoloration, crumbling, or sticking, and looks good.
△: There is a problem with either discoloration, crumbling during cooking, or adhesion, and the appearance is poor.
×: There are many problems with discoloration, crumbling during cooking, or adhesion, and the appearance is poor.
(Taste/Flavor)
Good: No burnt or bitter taste, with a delicious soybean flavor.
△: Slightly burnt or bitter, or has little soybean flavor and is inferior in flavor.
×: Burnt, bitter and not tasty.

[Table 1]

From the results in Table 1, when soy flour was used alone without soy protein (Comparative Example 1), the dough was too sticky and poorly molded, while when soy protein was used alone without soy flour (Comparative Example 2), the dough was not sticky and could not be molded. Furthermore, when transglutaminase was not used (Comparative Example 3), the dough was easy to mold, but gelation occurred during cooking, resulting in poor texture and appearance. These results demonstrate that soy flour, soy protein, and transglutaminase are essential ingredients for the soy rice used in this invention. Furthermore, although the stickiness and adhesiveness differ depending on the type of soy protein, both isolated soy protein (Example 1) and concentrated soy protein (Example 2) were able to provide a good texture.

Example 1, Comparative Example 4: Study of the Enzyme Reaction Process of Soybean Rice A test was conducted in which transglutaminase was activated and reacted in the kneading process of Example 1. Specifically, 2,000 g of soy flour stored at room temperature and 2,750 g of soy protein were powder-mixed, and then 1 g of transglutaminase was dissolved in 5,249 g of water at 50°C, and the mixture was kneaded uniformly. The product temperature immediately after kneading was 40°C. The kneaded product was placed in a bag, sealed, placed in an incubator, and maintained at 40°C for 1 hour. It was then fed to an extruder and dried to obtain a soybean rice sample of Comparative Example 4. The molding and drying processes were carried out under the same conditions as in Example 1. The results are shown in Table 2.

[Table 2]

The results in Table 2 show that when transglutaminase was activated and allowed to act during the kneading process (Comparative Example 4), the rice-like formed product crumbled and cracked, and the quality after cooking was also affected by the loss of shape and poor texture. It was found that for the soybean rice used in the present invention, it is essential to activate and allow transglutaminase to act during the drying process.

Examples 3 and 4, Comparative Examples 5 and 6: Study of Temperature Conditions in the Kneading and Forming Processes of Soybean Rice. The temperature conditions of the kneaded product from the kneading process to the forming process were studied to determine the moldability of the rice-like shaped product. Specifically, the temperature of the water added was adjusted so that the product temperature from the kneading process to the forming process was 25°C (Example 3), 40°C (Example 4), 45°C (Comparative Example 5), or 50°C (Comparative Example 6). The kneading process was completed within 20 minutes from the start of kneading to the end of forming, and the resulting granular shaped product was dried to obtain each soybean rice sample. The same procedures as in Example 1 were followed, except for the temperature conditions from the kneading process to the forming process. The results are shown in Table 3.

[Table 3]

From the results in Table 3, it was found that when the product temperature from the kneading process to the shaping process was 40°C or higher (Example 4, Comparative Examples 5 and 6), the rice-like shaped product crumbled slightly, reducing moldability and resulting in a poor texture and appearance after cooking. In particular, when the product temperature was 45°C or higher (Comparative Examples 5 and 6), the transglutaminase was overly activated and acted upon, resulting in the soybean rice being too elastic after cooking and resulting in a poor texture. From these results, it was found that for the soybean rice used in the present invention, it is essential to keep the product temperature of the kneaded product from the kneading process to the shaping process below 40°C.

Example 1, Comparative Example 7: Examination of the necessity of drying soybean rice In the drying process of Example 1, a test was conducted in which transglutaminase was activated and acted on without heat drying. Specifically, the rice-like product obtained after the shaping process was placed in a bag, sealed, and then placed in an incubator. After the product temperature reached 55°C, the bag was maintained for 60 minutes to activate and act on the transglutaminase, yielding a soybean rice sample of Comparative Example 7. The conditions for the kneading and shaping processes were the same as those for Example 1. The results are shown in Table 4.

[Table 4]

The results in Table 4 show that when no drying treatment was performed (Comparative Example 7), the quality of the cooked rice was somewhat high in cracks and had a crumbly, brittle texture. This demonstrates that it is essential for the soybean rice used in the present invention to be kept in a dry state during the drying process.

<Examples 5 to 8, Comparative Example 8>: Study of the blending ratio of soy flour and soy protein in soy rice Tests were conducted in which the blending ratio of soy flour and soy protein was changed in the raw material of Example 1. Specifically, only the blending ratio of soy flour and soy protein was increased or decreased, and the water and transglutaminase were used in the same manner as in Example 1 to obtain each soy rice sample. The conditions for the kneading, molding, and drying processes were the same as in Example 1. The results are shown in Table 5. In Table 5, each value indicates the weight percentage per total weight of the raw material, and the value in parentheses indicates the ratio of soy flour to soy protein.

[Table 5]

The results in Table 5 show that when the soy flour mixing ratio relative to the total raw material solids was 25% by weight or less (soy protein was 75% by weight or more) (Comparative Example 8), the dough was not sticky enough to hold together and could not be shaped. Furthermore, when the soy flour mixing ratio relative to the total raw material solids was 90% by weight or more (soy protein was 10% by weight or less) (Example 8), the dough was too sticky, causing the extruded grains to stick together, resulting in a product with poor shaping ability, texture, and appearance.

<Examples 9 to 15, Comparative Examples 9 and 10>: Study of the drying temperature for soybean rice In the drying process of Example 1, tests were conducted with different drying temperatures and times. Specifically, soybean rice samples were obtained by drying at each temperature until the moisture content was 8% by weight or less. The conditions for the kneading and molding processes were the same as in Example 1. The results are shown in Table 6.

[Table 6]

The results in Table 6 show that when the drying temperature exceeded 100°C (Comparative Examples 9 and 10), discoloration and burning occurred, resulting in a poor appearance. Furthermore, when the drying temperature was in the range of 60-90°C (Examples 11-14), the product was excellent in all aspects: texture, appearance, taste, and flavor.

Example 16: Study of modified starch in soybean rice. A test was conducted in which a portion of the soy flour and soy protein in the raw materials of Example 1 was replaced with modified starch. Specifically, 1590 g of soy flour and 2170 g of soybean protein were powder-mixed with 1000 g of modified starch (heat-moisture treated starch, manufactured by Matsutani Chemical Industry Co., Ltd.), and the process was repeated as in Example 1 to obtain the soybean rice sample of Example 16. The conditions for the kneading, molding, and drying processes were the same as in Example 1. The results are shown in Table 7. In Table 7, each value indicates the weight percentage per total weight of the raw materials, and the values in parentheses indicate the proportions of soy flour, soy protein, and modified starch.

[Table 7]

The results in Table 7 show that using processed starch makes it possible to produce soybean rice with excellent formability, texture, taste, and flavor.

(2) Manufacturing Method of Packaged Soybean Rice An example of the manufacturing method of packaged soybean rice according to the present invention will be described.

<Examples 17 to 20, Comparative Example 11>: Investigation of pH of soaking solution and filling solution Unless otherwise specified, the following Examples and Comparative Examples were carried out using the soybean rice obtained in Example 16 under the following conditions.

[Manufacturing method]
The manufacturing method of Example 17 will be described below.
250 g (2.5 parts by weight) of soybean rice was added to 100 g (1 part by weight) of a soaking solution prepared by dissolving acetic acid in water and adjusting the pH to 3.73, and the rice was soaked for 60 minutes to allow it to absorb water. The soybean rice that had absorbed water was placed in a colander, left to stand for 5 minutes, and drained to obtain soybean rice after soaking. The weight of the soybean rice after soaking was measured, and the amount of soaking solution absorbed by the soybean rice after soaking (amount of water absorbed by the soybean rice after soaking) was measured.
After soaking, 99.0 g of the soybean rice and 69.0 g of a filling solution prepared by dissolving acetic acid in water and adjusting the pH to 3.73 were filled into a container and sealed. Next, the container was pressurized and heated in a retort sterilizer under conditions such that the F value became 8, and then cooled to 35° C. or less to obtain packaged soybean rice.
For Examples 18 to 20, the same procedure as in Example 17 was carried out, except that the pH of the soaking liquid and the filling liquid was changed to 3.50 (Example 18), 3.27 (Example 19), and 3.04 (Example 20), respectively, and packaged soybean rice was obtained. For Comparative Example 11, packaged soybean rice was obtained, similarly to Example 17, except that water (pH 7.59) was used instead of acetic acid for the soaking liquid and the filling liquid. At this time, the pH of the soaking liquid and the filling liquid was 7.59.

[pH Measurement]
The pH was measured using a pH meter (manufactured by Horiba, Ltd., product number D-51) connected to a pH electrode (manufactured by Horiba, Ltd., product number 9615S). When measuring a solid, the pH electrode was inserted into the solid and the measurement was performed.

[Evaluation of packaged soybean rice]
The packaged soybean rice obtained in the Examples and Comparative Examples was heated in a microwave oven (manufactured by Sharp Corporation, product number RE-S203-H) at 600 watts for 30 seconds and subjected to a sensory evaluation (adhesion, texture, taste and flavor). The sensory evaluation was conducted by five trained panelists who tasted the rice and evaluated it according to the following evaluation criteria, and the results were summarized. The results are shown in Table 8.
[Evaluation criteria for sensory evaluation]
(binding)
Good: The whole thing is not solidified, can be loosened with a little force using chopsticks, and looks good.
△: The whole is a little hard, but can be loosened with chopsticks and looks rather good.
×: The whole is strongly hardened and looks bad.
(Texture)
〇: Moderately soft, with a texture similar to cooked rice, and delicious.
△: A little hard, but the texture is good and it's tasty.
×: Hard. The core remains. Not tasty.
(Taste/Flavor)
Good: No sourness, has a soybean flavor and is delicious.
△: A slight sourness is felt, but the soybean flavor is delicious.
×: It has a strong sour taste and is not tasty.

[Table 8]

The results in Table 8 show that when the pH of the packaged soybean rice was between 5.50 and 6.64, sticking was suppressed, resulting in packaged soybean rice with a good appearance, texture, taste, and flavor. On the other hand, when the pH was 6.86 or higher (Comparative Example 11), although the taste and flavor was excellent, the rice stuck together and became very hard, and the texture was poor.

Examples 21 to 26: Study of Acid Type and pH The type and pH of the acid used in the soaking solution and the filling solution were studied. Specifically, packaged soybean rice was obtained in the same manner as in Example 17, except that the acid used in the soaking solution and the filling solution was changed to citric acid (pH 3.03 in Example 21, pH 2.23 in Example 22), fermented lactic acid (pH 3.21 in Example 23, pH 2.34 in Example 24), or glucono-delta-lactone (pH 3.00 in Example 25, pH 2.27 in Example 26), and various measurements and evaluations were then performed in the same manner. The results are shown in Table 9.

[Table 9]

The results in Table 9 show that even when acids other than acetic acid are used in the soaking and filling solutions, sticking is suppressed, and packaged soybean rice with a good appearance, texture, taste, and flavor is obtained.

Examples 27-28: Study of Grain Blending. The mixing of soybean rice with rice or other grains was investigated during the packaging process. In Example 27, 41.7 g of soybean rice after soaking, 49.4 g of grains (a 2.5:1 mixture of unabsorbed white rice and unabsorbed brown rice), and 74.9 g of filler liquid were packed into a container and sealed. In Example 28, 79.0 g of soybean rice after soaking, 22.0 g of grains (a mixture of unabsorbed white rice and unabsorbed brown rice), and 65.0 g of filler liquid were packed into a container and sealed. Packaged soybean rice was obtained in the same manner as in Example 18, except for the above changes, and various measurements and evaluations were performed in the same manner. The results are shown in Table 10.

[Table 10]

The results in Table 10 show that even when soybean rice and grains were added in a ratio of 0.30:0.70, sticking was suppressed, and packaged soybean rice containing grains was obtained that had a good appearance, texture, taste, and flavor (Example 27).

Claims (4)

a soaking step of soaking the soybean rice in a soaking liquid;
a packaging step of sealing the soybean rice and the filling liquid in a container after soaking;
a heating step of pressurizing and heating the mixture,
The pH of the soaking liquid and the filling liquid is 2.2 to 3.7, and the pH of the packaged soybean rice after the heating step is 5.3 to 6.7;
a kneading step of adding water to a raw material containing soybean flour, soybean protein, and transglutaminase to prepare the soybean rice, and kneading the raw material;
a molding step of extruding the kneaded mixture to obtain rice-shaped molded products;
a drying step of heating and drying the rice-shaped product,
the temperatures in the kneading step and the molding step are 40°C or less,
the temperature in the drying step is 30 to 100°C;
A method for producing packaged soybean rice, characterized in that the raw material is obtained by a production method in which the mixing ratio of soybean flour to soybean protein is 30:70 to 90:10 . The method according to claim 1 , wherein the soybean rice contains starch as a raw material. The manufacturing method described in claim 1 or 2, wherein the total amount of water absorbed by the soybean rice after soaking and the amount of the filling liquid is 1.5 to 2.8 parts by weight per 1 part by weight of the soybean rice. The method according to claim 3, wherein in the soybean rice soaking step or the packaging step, a portion of the soybean rice is replaced with grains, and the dry weight ratio of the soybean rice to grains is 100:0 to 30:70.