JP7378996B2 - Tofu, raw tofu, food, and method for suppressing tofu swelling - Google Patents

Description

The present invention relates to tofu, raw tofu, foods, and a method for suppressing the rise of tofu.

Tofu is one of the ingredients widely used in cooking. However, tofu suffers from the problem of so-called ``scalding,'' in which small holes form when heated.

For example, Patent Document 1 proposes a method for producing cut tofu in which firmness is suppressed.

Japanese Patent Application Publication No. 2010-75105

However, there is an additional need for tofu that can be suppressed from boiling during heating without impairing the texture and the like.

The present invention has been made in view of the above situation, and aims to provide tofu that is suppressed from boiling during heating and has excellent texture.

The present inventors have discovered that the above-mentioned problems can be solved by using tofu containing a specific peptide, and have completed the present invention. Specifically, the present invention provides the following.

(1) Tofu containing a peptide derived from soybean protein that shows a maximum peak at an elution time of 24 to 28 minutes in a peptide chromatograph obtained under the following conditions.
(Conditions for peptide chromatography)
Equipment used: High performance liquid chromatograph (UHPLC), manufactured by Shimadzu Corporation Detector: Fluorescence detector Column: Product name "TSKgel G200SW 10 μm" (7.5 mm I.D. x 30 cm), manufactured by Tosoh Co., Ltd. Column temperature: 25 ℃
Elution buffer composition: 40% acetonitrile, 0.1% acetic acid Flow rate: 0.5ml/min

(2) Tofu containing a partial decomposition product of a protein selected from the group consisting of β-conglycinin a subunit, b subunit, glucinin Acidic subunit, and glucinin Basic subunit.

(3) The tofu according to (1) or (2), wherein the total amount of free amino acids is 200 mg/100 g or more and 10,000 mg/100 g or less.

(4) The tofu according to any one of (1) to (3), which is made from soy milk from germinated soybeans and/or soy milk treated with proteolytic enzymes.

(5) The tofu according to any one of (1) to (4), which contains gluconolactone in an amount of 0.10% by mass or more.

(6) Raw tofu that shows a breaking point after the following heating test and breaking stress test.
(Heating test)
Tofu is immersed in water and wrapped in a retort bag (made of nylon poly(NYPE)), and left to stand at 1 atm and 90° C. for 20 minutes.
(Rupture stress test)
The tofu after the heating test is cut into a size of 10 mm x 10 mm x 10 mm, and this is placed on a sample stand. Next, using a creep meter physical property testing system (model: RE2-33005B, manufactured by Yamadensha), a plunger with a diameter of 30 mm was inserted into the tofu placed on the sample stage from the top direction at a speed of 1.0 mm per second. The breaking load is measured by penetrating at a strain rate of 85%.

(7) Retort-sterilized tofu that shows a breaking point in the following breaking stress test.
(Rupture stress test)
Cut tofu into a size of 10 mm x 10 mm x 10 mm and place it on a sample stand. Next, using a creep meter physical property testing system (model: RE2-33005B, manufactured by Yamadensha), a plunger with a diameter of 30 mm was inserted into the tofu placed on the sample stage from the top direction at a speed of 1.0 mm per second. The breaking load is measured by penetrating at a strain rate of 85%.

(8) A retort-sterilized food containing the tofu according to any one of (1) to (7).

(9) A method for suppressing the rise of tofu using soymilk from germinated soybeans and/or soymilk treated with proteolytic enzymes as a raw material.

According to the present invention, tofu that is suppressed from rising during heating and has excellent texture is provided.

It is a figure showing the result of the peptide analysis of the soybean raw material used in the example. FIG. 2 is a diagram showing the results of electrophoresis of peptides contained in soybean raw materials used in Examples. It is a figure which shows the result of the breaking stress test after heating about the tofu produced in the Example. It is a figure which shows the state after heating about the tofu produced in the Example. It is a figure which shows the observation result of the cross section after heating about the tofu produced in the Example. It is a figure which shows the state after heating about the tofu produced in the Example.

Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not particularly limited thereto.

<Tofu of the present invention>
The tofu of the present invention contains a peptide that satisfies the following requirements (P1) and/or (P2). Hereinafter, the following peptides are also simply referred to as "P1" and "P2."
(P1) A peptide derived from soybean protein that shows a maximum peak at an elution time of 24 to 28 minutes in a peptide chromatograph obtained under the following conditions.
(Conditions for peptide chromatography)
Equipment used: High performance liquid chromatograph (UHPLC), manufactured by Shimadzu Corporation Detector: Fluorescence detector Column: Product name "TSKgel G200SW 10 μm" (7.5 mm I.D. x 30 cm), manufactured by Tosoh Co., Ltd. Column temperature: 25 ℃
Elution buffer composition: 40% acetonitrile, 0.1% acetic acid Flow rate: 0.5ml/min
(P2) A partial decomposition product of a protein selected from the group consisting of β-conglycinin a subunit, b subunit, glucinin Acidic subunit, and glucinin Basic subunit.

As a result of studies conducted by the present inventors, it was surprisingly discovered that tofu containing the above-mentioned peptide has suppressed bulging even after heating, and also has excellent texture.

Both P1 and P2 have a relatively smaller molecular weight than proteins that are abundantly contained in normal tofu. In the present invention, it is presumed that by incorporating a peptide with a small molecular weight in this way, protein denaturation and structural changes in tofu due to heating are suppressed, and as a result, boiling is suppressed. Note that P1 may include P2.

Regarding P2, the a subunit, b subunit, glucinin Acidic subunit, and glucinin Basic subunit of β-conglycinin have molecular weights of 72 kDa, 53 kDa, 37 to 42 kDa, and 20 kDa, respectively. Therefore, P2, which is a partial decomposition product of these, has a molecular weight smaller than the above molecular weight.

The lower limit of the content of P1 in the tofu of the present invention is preferably 0.1% by mass or more, more preferably 0.3% by mass or more based on the tofu. The upper limit of the content of P1 in the tofu of the present invention is preferably 10% by mass or less, more preferably 10% by mass or less based on the tofu.

The lower limit of the content of P2 in the tofu of the present invention is preferably 0.1% by mass or more, more preferably 0.3% by mass or more based on the tofu. The upper limit of the content of P2 in the tofu of the present invention is preferably 10% by mass or less, more preferably 5.0% by mass or less, based on the tofu.

When the tofu of the present invention contains a relatively large amount of free amino acids, it is easier to suppress the rise of the tofu. For example, the lower limit of the total amount of free amino acids in the tofu of the present invention is preferably 200 mg/100 g or more, more preferably 600 mg/100 g or more, and even more preferably It is 1000 mg/100g or more, even more preferably 1500 mg/100g or more. The upper limit of the total amount of free amino acids in the tofu of the present invention does not need to be excessive, and is preferably 10,000 mg/100 g or less, more preferably 8,000 mg/100 g or less, even more preferably 5,000 mg/100 g, even more preferably It is 3000mg/100g or less.

The reason that when the tofu of the present invention contains a relatively large amount of free amino acids, the rise is more likely to be suppressed is surmised as follows. Among the proteins contained in soybeans, which are the raw materials for tofu, β-conglycinin is known to produce fibrous proteins, oligopeptides, etc. during the decomposition process by proteolytic enzymes. As a result of studies conducted by the present inventors, it was discovered that such fibrous proteins, oligopeptides, and the like may contribute to the construction of the network structure of tofu. The fact that the tofu of the present invention contains a relatively large amount of free amino acids means that it also contains a large amount of the above-mentioned fibrous proteins and oligopeptides, which helps build a strong tofu network structure. , it is thought that crowding is suppressed.

The lower limit of the total amount of free amino acids in the tofu of the present invention is preferably 200 mg/100 g or more, more preferably 600 mg/100 g or more, still more preferably 1000 mg/100 g or more, and even more, from the viewpoint of easily suppressing the rise of tofu. Preferably it is 1500mg/100g or more. The upper limit of the total amount of free amino acids in the tofu of the present invention does not need to be excessive, and is preferably 10,000 mg/100 g or less, more preferably 8,000 mg/100 g or less, even more preferably 5,000 mg/100 g, even more preferably It is 3000mg/100g or less.

Examples of free amino acids and their content that may be included in the tofu of the present invention include the following.
Glutamic acid: 15-30mg/100g
Alanine: 10-20mg/100g
Aspartic acid: 0.5-3mg/100g
Lysine: 2-5mg/100g
Histidine: 2-5mg/100g
Phenylalanine: 2-5mg/100g
Methionine: 0.5-3mg/100g
Threonine: 1.5-5mg/100g
Leucine: 1-5mg/100g
Isoleucine: 1-5mg/100g
Valine: 1.5-5mg/100g
Arginine: 20-50mg/100g
Glycine: 2-5mg/100g
Serine: 2-5mg/100g
Tyrosine: 1.5-5mg/100g

Among the free amino acids mentioned above, the tofu of the present invention tends to have large amounts of glutamic acid, alanine, threonine, and serine, which can affect taste. Therefore, the tofu of the present invention can be a tofu with good palatability.

The tofu of the present invention may have an isoelectric point of 2.0 to 6.8. Isoelectric points are determined by acid titration.

(soy milk)
The tofu of the present invention is made from soymilk obtained from soybeans. Although the soybean from which soymilk is derived is not particularly limited, it is preferable to use germinated soybeans as a raw material from the viewpoint of easily obtaining tofu containing P1 and/or P2. Further, as the soymilk, soymilk from germinated soybeans and/or soymilk treated with a proteolytic enzyme is preferable.

In the present invention, the term "germinated soybean" refers to soybeans that have been subjected to the germination treatment described below, and also includes soybeans in which sprouts are not clearly recognized.

As a result of the studies conducted by the present inventors, germinated soybeans contain more small molecular weight peptides (P1, P2, etc.) and free amino acids than normal soybeans (soybeans that have not been germinated). discovered. It was found that the same holds true for soy milk and tofu made from germinated soybeans. Therefore, by using soymilk from germinated soybeans as a raw material, the tofu of the present invention can be easily produced.

As the germinated soybean, any soybean that has been subjected to germination treatment (treatment that promotes germination) can be used. Conventionally known methods can be used for the germination treatment, such as a method in which soybeans are soaked in water and then exposed to air. Other methods include the methods of Japanese Patent No. 5795676 and Japanese Patent No. 5722518.

The raw material for the tofu of the present invention preferably contains soymilk from germinated soybeans. When using soymilk obtained from normal soybeans (soybeans that have not been germinated) as a raw material for the tofu of the present invention, it may be mixed with soymilk from germinated soybeans, or it may be used in combination with soymilk obtained from normal soybeans. By adding/or P2, soymilk, which is a raw material for the tofu of the present invention, can be easily prepared.

In the present invention, "proteolytic enzyme-treated soymilk" refers to soymilk obtained from any soybean that has been treated with a proteolytic enzyme.

As a result of studies by the present inventors, it has been found that any soymilk (for example, commercially available soymilk) treated with proteolytic enzymes contains many small molecular weight peptides (P1, P2, etc.) and free amino acids. discovered. Therefore, by using proteolytic enzyme-treated soymilk as a raw material, the tofu of the present invention can be easily produced.

The soybean from which the soymilk subjected to proteolytic enzyme treatment is derived is not particularly limited, and both germinated soybeans and ungerminated soybeans can be used, and a combination of these can also be used.

The proteolytic enzyme is not particularly limited as long as it can decompose proteins contained in soymilk. Examples include enzymes such as protease and peptidase (gingipain, cysteine protease, etc.). Purified products can be used as the proteolytic enzyme, and foods containing the enzyme can also be used. Examples of foods containing proteolytic enzymes include raw ginger, papaya, kiwi fruit, and their juices.

Conditions for the proteolytic enzyme (amount of enzyme used, temperature, time, etc.) are not particularly limited as long as the enzyme is not deactivated and the proteins in soymilk can be sufficiently decomposed. For example, the temperature condition may be 10 to 50°C. Enzyme treatment time may be 1 to 72 hours.

Conventionally known methods can be used as methods for producing soymilk. For example, soybean milk may be obtained by soaking soybeans in water, expanding them, grinding them, and then removing fibers (bean curd). Soy milk may be subjected to sterilization treatment, etc., if necessary.

<Tofu manufacturing method>
The tofu of the present invention can be obtained by adding a coagulant to soybean milk and filling the mixture into appropriate molds or packaging it in containers. As the coagulant, those used in the production of tofu can be used. Other conditions are not particularly limited, and those commonly used in tofu production can be adopted.

As a result of studies conducted by the present inventors, it has been found that when gluconolactone is used as a coagulant, it is easier to obtain tofu that is more inhibited from rising during heating. The lower limit of the amount of gluconolactone is preferably 0.10% by mass or more, more preferably 0.30% by mass or more based on the tofu, from the viewpoint of easily obtaining tofu with excellent texture and flavor. The upper limit of the amount of gluconolactone is preferably 0.40% by mass or less, more preferably 0.35% by mass or less, from the viewpoint of not impairing the flavor of tofu. However, the coagulant other than gluconolactone may be used, or a combination of a plurality of coagulants (for example, gluconolactone and other coagulants) may be used.

In the production of tofu according to the present invention, tofu having a good texture can be obtained without the use of emulsifiers that have been used in conventional tofu production. Such emulsifiers include glycerin fatty acid esters (monoglycerin fatty acid esters, diglycerin fatty acid esters, organic acid monoglycerides, polyglycerin fatty acid esters, polyglycerin condensed ricinoleate esters), sucrose fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acids Examples include esters, stearoyl lactate, yucca extract, saponin, lecithin, polysorbate, and the like. However, embodiments in which such an emulsifier is included in the present invention are not excluded. For example, the tofu of the present invention may contain the emulsifier, preferably 0.5% by mass or less, more preferably 0.1% by mass or less, based on the tofu.

In the production of tofu according to the present invention, tofu having a good texture can be obtained without the use of thickeners that have been used in conventional tofu production. Examples of such thickeners include the following. Pectin, carrageenan, xanthan gum, native gellan gum, deacylated gellan gum, tamarind seed gum, guar gum, locust bean gum, tara gum, glucomannan, alginic acid, sodium alginate, curdlan, gum arabic, agar, tragacanth gum, karaya gum, gati gum, pullulan Thickening polysaccharides such as , ramsan gum, psyllium seed gum, macrohomopsis gum, fermented cellulose, microfibrous cellulose, water-soluble cellulose ethers (methyl cellulose, hydroxypropyl cellulose, hydroxymethyl propyl cellulose, etc.); corn starch, waxy corn starch, sweet potato starch , raw starches such as wheat starch, tapioca starch, potato starch, and rice starch, and processed starches that have undergone processing such as crosslinking, etherification, and esterification. However, embodiments in which such a thickener is included in the present invention are not excluded. For example, the tofu of the present invention may contain preferably 0.5% by mass or less, more preferably 0.1% by mass or less of the above-mentioned thickener, based on the tofu.

In the production of tofu according to the present invention, tofu having a good texture can be obtained without containing protein aids that have been used in conventional tofu production. Examples of such protein aids include proteins other than those derived from soybean milk, and specific examples include the following. Egg-derived proteins such as whey protein, egg protein, and albumin; soybean protein; wheat protein; myosin protein; gelatin; collagen; plasma protein, etc. However, embodiments in which such a protein auxiliary agent is included in the present invention are not excluded. For example, the tofu of the present invention may contain preferably 0.5% by mass or less, more preferably 0.1% by mass or less of the protein auxiliary agent based on the tofu.

The tofu of the present invention can be prepared as a retort-sterilized food product as appropriate. In the present invention, "retort sterilization" means that a packaged food is subjected to pressure and heat treatment at a temperature of about 100 to 150°C. In the present invention, "food" may be tofu itself, or may be a cooked product made from tofu (mapo tofu, hot and sour soup, sundubu, miso soup, etc.).

The tofu of the present invention can be prepared as an aseptically filled food product (a product in which the food product is sterilized and the packaging material is sterilized separately, and then the food product is packaged). However, the preparation of such products requires significant equipment costs. According to the present invention, a packaged product in which bulging is well suppressed can be obtained by simple retort sterilization, so aseptic filling is not required in the production of the tofu of the present invention.

<Characteristics of tofu>
As mentioned above, the tofu of the present invention is suppressed from boiling even when heated, and has excellent texture. Whether or not the swelling during heating is suppressed can be determined visually or by microscopic observation. Texture can be evaluated as chewiness, smoothness, etc. when eating tofu.

Even when the tofu of the present invention is heated, its structural change is suppressed. Whether a structural change has occurred due to heating can be evaluated, for example, by the following heating test and breaking stress test.

The tofu of the present invention may be raw tofu that exhibits a breaking point after the following heating test and in the breaking stress test. Note that "raw tofu" refers to tofu that has not been subjected to heat treatment (for example, heat treatment at 90° C. or higher). The term "breaking point" refers to the ultimate point at which an external force is applied to tofu and the stress against the external force is no longer able to withstand, causing the tofu to break.
(Heating test)
Soak the tofu in water, wrap it in a retort bag (made of nylon poly (NYPE)) (product name "Meiwa Pax BRS-1624S", manufactured by Meiwa Pax Co., Ltd.), and leave it for 20 minutes at 1 atm and 90°C. .
(Rupture stress test)
The tofu after the heating test is cut into a size of 10 mm x 10 mm x 10 mm, and this is placed on a sample stand. Next, using a creep meter physical property testing system (model: RE2-33005B, manufactured by Yamadensha), a plunger with a diameter of 30 mm was inserted into the tofu placed on the sample stage from the top direction at a speed of 1.0 mm per second. The breaking load is measured by penetrating at a strain rate of 85%.

When the tofu of the present invention is raw tofu, it can be used as it is, or it can be used for heating and cooking. Examples of heating cooking include heating using fire, hot water, oil, etc., heating using a microwave oven, etc.

For example, the tofu of the present invention can be retort sterilized tofu that exhibits a breaking point in the breaking stress test below.
(Rupture stress test)
Cut tofu into a size of 10 mm x 10 mm x 10 mm and place it on a sample stand. Next, using a creep meter physical property testing system (model: RE2-33005B, manufactured by Yamadensha), a plunger with a diameter of 30 mm was inserted into the tofu placed on the sample stage from the top direction at a speed of 1.0 mm per second. The breaking load is measured by penetrating at a strain rate of 85%.

<How to prevent tofu from rising>
As described above, by using soymilk from germinated soybeans and/or soymilk treated with proteolytic enzymes as a raw material, tofu with suppressed firming can be obtained.

Further, in the production of tofu, by blending P1 and/or P2, tofu with suppressed firmness can be obtained. The blending amount of P1 and/or P2 can be adjusted as appropriate depending on the texture of the tofu to be obtained.

The present invention will be described in more detail below based on Examples, but the present invention is not limited to these Examples.

<Test 1: Amino acid analysis of tofu obtained from various soybean ingredients>
Amino acid analysis was performed on tofu obtained from two types of soybean raw materials: germinated soybeans and regular soybeans.

(1) Preparation of soybean raw materials After washing "Toyomasari" grown in Hokkaido with 30 ppm sodium hypochlorite, watering was repeated every 3 hours for 15 hours to produce germinated soybeans. In addition, soaked soybeans made by soaking "Toyomasari" grown in Hokkaido in water for 15 hours were used as regular soybeans.

(2) Preparation of soybean milk Soybean raw material was swollen with water so that the mass was 2.25 times the mass of dried soybeans. Next, the soybean raw material was ground while adding water approximately 2.5 times the mass of the swollen soybean raw material. The ground soybean juice was heated to extract proteins and other soluble components, and then filtered. The filtrate was collected to obtain soymilk with a final solid content of 11.3%.

(3) Preparation of tofu Glocono delta lactone (0.34% by mass based on soymilk) was added to each soymilk obtained in the above (2) and coagulated to obtain tofu.

(4) Amino acid analysis The tofu obtained above was analyzed for amino acids under the following conditions to determine the amount of free amino acids. The results are shown in Table 1.
Equipment used: High performance liquid chromatograph (UHPLC), manufactured by Shimadzu Corporation Detector: Fluorescence detector Column: "Inertil ODS-4 HP 3μm" (100 mm L. x 3.0 mm I.D.), manufactured by GL Sciences Co., Ltd. Column temperature :35℃
Elution buffer composition: 15 mmol/L potassium dihydrogen phosphate, 5 mmol/L dipotassium hydrogen phosphate, water/acetonitrile/methanol = 15/45/40 (V/V/V)
Flow rate: 0~1.5min 9.5%, 1.5~6.0min 30%, 6.0~11.0min 40%, 11.0~16.0min 100%
Flow rate: 0.8ml/min

As shown in Table 1, tofu obtained from germinated soybeans had a significantly higher amount of free amino acids than tofu obtained from conventional soybeans.

Among the free amino acids mentioned above, tofu obtained from germinated soybeans had large amounts of glutamic acid, alanine, threonine, and serine, which can affect taste. Therefore, tofu obtained from germinated soybeans was better in taste than tofu obtained from regular soybeans.

<Test 2: Peptide analysis of soybean raw materials>
Peptide analysis of the soybean raw material used in Test 1 was conducted under the following conditions. The results are shown in Figure 1.
Equipment used: High performance liquid chromatograph (UHPLC), manufactured by Shimadzu Corporation Detector: Fluorescence detector Column: Product name "TSKgel G200SW 10 μm" (7.5 mm I.D. x 30 cm), manufactured by Tosoh Co., Ltd. Column temperature: 25 ℃
Elution buffer composition: 40% acetonitrile, 0.1% acetic acid Flow rate: 0.5ml/min

In FIG. 1, the longer the elution time of the fraction, the shorter the molecular weight. As shown in FIG. 1, germinated soybeans showed a maximum peak at an elution time of 24 to 28 minutes, and normal soybeans showed a maximum peak at an elution time of 22 to 28 minutes. From this, it was found that many of the peptides contained in germinated soybeans had smaller molecular weights than peptides normally contained in soybeans.

Based on the results in Figure 1, in Figure 1, we extracted the peak fraction with an elution time of 24-28 minutes for germinated soybeans, and the peak fraction with an elution time of 22-28 minutes for normal soybeans, and performed electrophoresis under the following conditions. I did it. The results are shown in FIG.

(Electrophoresis conditions)
All reagents used for polyacrylamide gel electrophoresis (SDS-PAGE) were manufactured by Wako Pure Chemical Industries.
The running buffer was prepared as follows. Distilled water was added to 3 g of tris(hydroxymethyl)aminomethane, 14.4 g of glycine, and 1 g of sodium lauryl sulfate to make 1 L to obtain a running buffer.
The sample addition solution was prepared as follows. Add distilled water to 0.5 ml of 1.0M tris(hydroxymethyl)aminomethane pH 6.8 solution, 0.154 g of dithiothreitol, 2 ml of 10% sodium lauryl sulfate solution, 0.01 g of Blumphenol blue, and 1 ml of glycerol to make 10 ml. , a sample addition solution was obtained.
100 mg of the specimen was suspended in 1 ml of physiological saline and homogenized using an ultrasonic crusher (manufactured by Tomy Seiko Co., Ltd.). 1 μl of the sample addition solution was added to 10 μl of the homogenized specimen, and the mixture was kept at 95° C. for 10 minutes in an aluminum block constant temperature bath (manufactured by As One Corporation). A gel with an acrylamide concentration of 12.5% was placed in a mini-slab size electrophoresis apparatus (manufactured by Atto Corporation), and a running buffer was added to the anode and cathode sides. The kept specimen was applied to an acrylamide gel, SDS-PAGE was performed using a constant voltage of 30 V, and the protein was stained with a 0.25% Coomassie brilliant blue solution, and the electrophoresis results were observed.

As shown in FIG. 2, bands of β-conglycinin a subunit, b subunit, and glucinin Acidic subunit were clearly observed in normal soybeans. On the other hand, in germinated soybeans, these bands were not clearly observed, indicating that partial decomposition of β-conglycinin a subunit, b subunit, and glucinin Acidic subunit had occurred.

<Test 3: Breaking stress test after heating>
The tofu produced in Test 1 was subjected to a heating test and a breaking stress test using the following methods. The results are shown in FIG.

(Heating test)
Each piece of tofu was completely immersed in water and packaged in a retort bag (made of nylon poly(NYPE)), and allowed to stand at 1 atm and 115° C. for 23 minutes.

(Negotiation stress test)
After the heating test, each tofu was cut into a size of 10 mm x 10 mm x 10 mm, and this was placed on a sample stand. Next, using a creep meter physical property testing system (model: RE2-33005B, manufactured by Yamadensha), a plunger with a diameter of 30 mm was inserted into the tofu placed on the sample stage from the top direction at a speed of 1.0 mm per second. The breaking load was measured by penetrating at a strain rate of 85%.

As shown in Figure 3, tofu obtained from germinated soybeans showed a breaking point. On the other hand, tofu obtained from conventional soybeans crumbled as soon as external force was applied and did not show any breakage point. In addition, tofu obtained from normal soybeans was spongy and no breaking stress was observed. This indicates that tofu obtained from germinated soybeans maintains its three-dimensional structure, which affects the appearance and texture of tofu, even after heating.

<Test 4: Observation of tofu cross section>
After heating the tofu prepared in Test 1 at 90° C. for 20 minutes, the cross section was observed using the following method. The results are shown in FIGS. 4 and 5. FIG. 4 shows the tofu after heating (before cutting). The upper part (A) of FIG. 5 shows the results of cross-sectional observation with the naked eye, and the lower part (B) shows the results of cross-sectional observation with an electron microscope.

As shown in FIGS. 4 and 5, tofu obtained from regular soybeans was found to have firmness after heating. On the other hand, tofu obtained from germinated soybeans showed no firmness after heating and had a fine mesh structure.

<Test 5: Tofu heating test-1>
The tofu prepared in Test 1 was filled into a container made of a retort bag (made of nylon poly(NYPE)), heated at 110° C. to 121° C. for 7 minutes, and evaluated from each viewpoint using the following criteria. The results are shown in Table 2.

(Evaluation criteria)
◎: Very good ○: Good △: Neutral ×: Bad

As shown in Table 2, tofu obtained from germinated soybeans was superior not only in appearance and texture but also in all aspects compared to tofu obtained from regular soybeans.

Although data is not shown, when mapo tofu was cooked and evaluated using the tofu prepared in Test 1, the same results as in Table 2 were obtained. Furthermore, the same results as in Table 2 were obtained even after mapo tofu prepared using the tofu prepared in Test 1 was packed in pouches, retort sterilized, and heated in a microwave oven or the like.

<Test 6: Various evaluations of tofu obtained from proteolytic enzyme-treated soymilk>
Two types of soymilk raw materials were prepared, namely soymilk (commercially available) obtained from regular soybeans and soymilk that had been subjected to enzyme treatment, and amino acid analysis of tofu obtained from these soymilk was performed. .

(1) Preparation of proteolytic enzyme derived from ginger juice 200 g of ginger (raw ginger) was ground and squeezed to obtain ginger juice. The obtained ginger juice was centrifuged at 2000 rpm for 20 minutes, and the supernatant was filtered. 473 μl of 0.1 mM mercaptopropionic acid and ascorbic acid (0.2% based on the filtrate) were added to the filtrate. Hereinafter, the obtained solution was used as a proteolytic enzyme derived from ginger juice. Note that ginger juice is known to contain proteolytic enzymes such as gingipain and cysteine protease.

(2) Enzyme treatment of soy milk Commercially available soy milk (Sujata solid content, 12%) was used as the soy milk obtained from ordinary soybeans. 0.06 ml of proteolytic enzyme derived from ginger juice was added to 60 ml of the soymilk, and the mixture was left in a constant temperature bath at 37° C. for 48 hours. Hereinafter, the soymilk obtained from this process will also be referred to as "enzyme-treated soymilk."
Further, as a target group, 0.06 ml of sterile distilled water was added to 60 ml of commercially available soy milk (Sujata Co., Ltd. solid content, 12%), and the mixture was left in a constant temperature bath at 37° C. for 48 hours. Hereinafter, the soymilk obtained from this process will also be referred to as "regular soymilk".
Both enzyme-treated soymilk and regular soymilk were adjusted with sterile distilled water so that the final solid content was 11.3%.

(3) Preparation of tofu Glocono delta lactone (0.34% by mass based on soymilk) was added to each soymilk obtained in the above (2) and coagulated to obtain tofu.

(4) Amino acid analysis The tofu obtained above was analyzed for amino acids under the following conditions to determine the amount of free amino acids. The results are shown in Table 3.
Equipment used: High performance liquid chromatograph (UHPLC), manufactured by Shimadzu Corporation Detector: Fluorescence detector Column: "Inertil ODS-4 HP 3μm" (100 mm L. x 3.0 mm I.D.), manufactured by GL Sciences Co., Ltd. Column temperature :35℃
Elution buffer composition: 15 mmol/L potassium dihydrogen phosphate, 5 mmol/L dipotassium hydrogen phosphate, water/acetonitrile/methanol = 15/45/40 (V/V/V)
Flow rate: 0~1.5min 9.5%, 1.5~6.0min 30%, 6.0~11.0min 40%, 11.0~16.0min 100%
Flow rate: 0.8ml/min

As shown in Table 3, tofu obtained from enzyme-treated soymilk had a significantly higher amount of free amino acids than tofu obtained from normal soymilk.

<Test 7: Tofu heating test-2>
The tofu produced in Test 6 was filled into a container made of a retort bag (made of nylon poly(NYPE)), heated at 110° C. to 121° C. for 7 minutes, and evaluated from each viewpoint using the following criteria. The results are shown in Table 4 and FIG.

(Evaluation criteria)
◎: Very good ○: Good △: Neutral ×: Bad

As shown in Table 4 and FIG. 6, the tofu obtained from the enzyme-treated soymilk had significantly suppressed firmness compared to the tofu obtained from normal soymilk.

Although data is not shown, when mapo tofu was cooked and evaluated using the tofu prepared in Test 1, the same results as in Table 2 were obtained. Furthermore, even after pouching mapo tofu cooked using the tofu prepared in Test 6, sterilizing it in a retort, and heating it in a microwave oven, the same results as in Table 4 and Figure 6 were obtained. It was done.

Claims (9)

Tofu containing a peptide derived from soybean protein that shows a maximum peak at an elution time of 24 to 28 minutes in a peptide chromatograph obtained under the following conditions.
(Conditions for peptide chromatography)
Measurement target: Soybean raw material
Equipment used: High performance liquid chromatograph (UHPLC), manufactured by Shimadzu Corporation Detector: Fluorescence detector Column: Product name "TSKgel G200SW 10 μm" (7.5 mm I.D. x 30 cm), manufactured by Tosoh Co., Ltd. Column temperature: 25 ℃
Elution buffer composition: 40% acetonitrile, 0.1% acetic acid Flow rate: 0.5ml/min The tofu according to claim 1, comprising a partial decomposition product of a protein selected from the group consisting of β-conglycinin a subunit, b subunit, glucinin acidic subunit, and glucinin basic subunit. The tofu according to claim 1 or 2, wherein the amount of glutamic acid is 15 mg/100 g or more and 31.1 mg/100 g or less . The tofu according to any one of claims 1 to 3, which is made from soymilk from germinated soybeans and/or soymilk treated with proteolytic enzymes. The tofu according to any one of claims 1 to 4, containing gluconolactone in an amount of 0.10% by mass or more. The tofu according to any one of claims 1 to 5, which is raw tofu that exhibits a breaking point after the following heating test and in the breaking stress test.
(Heating test)
Tofu is immersed in water and wrapped in a retort bag (made of nylon poly(NYPE)), and left to stand at 1 atm and 90° C. for 20 minutes.
(Rupture stress test)
The tofu after the heating test is cut into a size of 10 mm x 10 mm x 10 mm, and this is placed on a sample stand. Next, using a creep meter physical property testing system (model: RE2-33005B, manufactured by Yamadensha), a plunger with a diameter of 30 mm was inserted into the tofu placed on the sample stage from the top direction at a speed of 1.0 mm per second. The breaking load is measured by penetrating at a strain rate of 85%. The tofu according to any one of claims 1 to 5, which is retort-sterilized tofu that exhibits a breaking point in the following breaking stress test.
(Rupture stress test)
Cut tofu into a size of 10 mm x 10 mm x 10 mm and place it on a sample stand. Next, using a creep meter physical property testing system (model: RE2-33005B, manufactured by Yamadensha), a plunger with a diameter of 30 mm was inserted into the tofu placed on the sample stage from the top direction at a speed of 1.0 mm per second. The breaking load is measured by penetrating at a strain rate of 85%. A retort-sterilized food product comprising the tofu according to any one of claims 1 to 7. A method for suppressing the rise of tofu,
The tofu is the tofu according to any one of claims 1 to 7,
A method for suppressing firming of tofu, wherein the tofu is obtained using soymilk from germinated soybeans and/or soymilk treated with proteolytic enzymes as a raw material.

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