JPH01112962A - Preparation of frozen bean curd - Google Patents

Abstract

PURPOSE:To prepare the titled bean curd preservable over a long period and keeping the same color, palatability, taste and flavor as those of commercially available bean curd even after thawing, by adding powdery soya milk to cooled soya milk, deaerating the mixture, adding a coagulant to prepare a bean curd and quickly freezing the product. CONSTITUTION:Powdery soya milk is added to soya milk cooled to <=25 deg.C to increase the coagulable solid content to >=15wt.%. The cooled soya milk mixture is added with 1-15wt.% of sugars, agitated at a high speed to uniformly mix the solid components and other components, deaerated, and mixed with glucono-delta-lactone as a coagulant for bean curd. The obtained mixture is heated at >=80 deg.C for >=30min to coagulate the soya milk and the prepared bean curd is cooled and quickly frozen to obtain the objective bean curd.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention allows tofu, which is generally considered difficult to preserve, to be frozen and stored for a predetermined period of time, then thawed and cooked so that it remains unfrozen even when eaten. This invention relates to a method for producing frozen tofu that has an excellent texture similar to that of tofu.

``Prior art'' As is well known, tofu is made by extracting the soluble components of soybeans with boiling water, adding magnesium salts, calcium salts, etc. to this, and precipitating the heat-denatured proteins together with soybean oil and water. It is solidified (gelled), placed in a mold box, and molded. This tofu is an excellent nutritious food that has a high water-holding capacity and a high content of high-quality protein, fat, and calcium.It has a smooth texture and unique elasticity, and has been popular among Japanese people since ancient times as a food that goes well with rice meals. It is a food that has deep roots in the diet of many people.

As shown in Figure 1, this tofu is a gel (tofu) made of a protein solution.When frozen, ice crystals form and become porous, and when stored frozen, the ice crystals gradually grow and the protein is trapped between the ice. -5-8 between close protein molecules
-The exchange reaction progresses to form a tight and elastic spongy tissue. In this case, even if the tofu is thawed, its water-holding capacity is significantly reduced and it is easily dehydrated, making it impossible to maintain its original water-holding capacity and smooth texture and flavor. In other words, tofu is denatured by freezing and storage, and even when thawed, it usually does not return to its unique smooth texture and elasticity. Since ancient times, people have focused on this freezing denaturation of tofu, dehydrating and drying frozen tofu to make use of this spongy tissue, and creating a product called ``frozen tofu'' where you can enjoy the texture and flavor of the resulting skeletal structure. ing. However, in recent years, as low-temperature distribution has become widespread, there is a desire to be able to freeze perishable tofu for long-term storage, and to make it possible to return to its original state by thawing without causing denaturation when frozen. Demand has arisen, and research is underway in various fields.

For example, one that emulsifies soy milk (Special Publication No. 56-31942)
No.), those containing starches and/or carbonates (Special Publication No. 62-16625), and those containing starches and/or carbonates and emulsifying soymilk (Japanese Patent Publication No. 16625-1983)
No. 897), after adjusting the pH, immersing it in an aqueous solution containing dissolved sugars and salt and freezing it (Special Publication No. 59-203)
No. 45), Tofu with high solid content (Unexamined Japanese Patent Publication No. 6
1-254158).

"Problems to be Solved by the Invention" As mentioned above, various methods have been developed to prevent freezing denaturation of tofu, but none have been satisfactory.
Frozen tofu foods are not yet very popular as a commercial product. The present inventor has researched the further freezing denaturation of heat-denatured soybean protein, and has tried to minimize the number of ice crystals, and even if they occur, to keep them as small as possible, and to make the gel as uniform and strong as possible. We have developed a manufacturing method that makes it difficult to form and undergo dehydration and denaturation. This enables long-term storage without denaturing even when frozen, and when thawed, it is possible to restore tofu with the same texture and flavor as fresh (unfrozen) tofu.

``Means for Solving the Problems'' The present invention involves preparing soymilk from whole soybeans or defatted soybeans in a conventional manner, cooling it to below 25°C, and adding powdered soymilk to the cooled soymilk to improve its coagulation properties. A certain solid content is 15% (
At the same time, 1% to 15% sugar is added to the cooled soymilk, stirred at high speed to uniformly mix the solids and other ingredients, and after deaeration, a coagulant for tofu is added. glucono delta-lactone was added and mixed, and then the mixture was heated at a temperature of 80° C. or higher for 30 minutes or more to coagulate soymilk to prepare tofu, and then the tofu was cooled and quickly frozen. This is a method for producing frozen tofu characterized by the following.

Hereinafter, the present invention will be explained in detail based on the drawings.

First, when manufacturing tofu, the material blending and preparation process up to just before gelation is carried out under temperature control that is cooled to 25° C. or lower.

Generally, when a coagulant is added to heated soymilk, soybean protein molecules entrap the dispersed soybean oil and water and form a gel. When coagulating the soymilk, the solid content and coagulation temperature of the soymilk affect the gel properties of tofu. For example, the greater the amount of water added or the higher the coagulation temperature, the firmer the tofu becomes. Therefore, it is necessary to adjust the coagulation timing and coagulation rate so that the soymilk does not coagulate suddenly and inadvertently, so the soymilk is cooled to below 25°C, preferably below 15°C.

Further, in the present invention, the reason why the temperature must be controlled to keep the material blending and preparation process at 25° C. or lower is to ensure that the addition of saccharides described below can be carried out successfully. In other words, when monosaccharides and oligosaccharides are added to raw materials such as soy milk, which have a high temperature, they do not mix easily evenly even when stirred, and tend to separate immediately. When the mixture is cooled to a certain temperature, the saccharides are easily mixed, and the gel strength upon coagulation can be greatly uniformized.

Next, powdered soymilk is added to soymilk so that the coagulable solid content is 15% (weight ratio) or more, preferably 20% (weight ratio).
Make it so that it becomes more than that. This is expected to have effects such as preventing freeze denaturation, imparting elasticity, and improving water retention.
This is because the high solids content of soymilk forms tofu with high gel strength.

Next, add 1% sugar to this chilled soymilk that has been cooled to below 25℃.
Add ~15% and stir at high speed to evenly mix with the solids and other ingredients.

The saccharide may be either an oligosaccharide or a monosaccharide, for example. If the amount of sugar added is less than 1%, the effect of preventing freeze denaturation will be insufficient, and if it is more than 15%, the gel strength will be weakened and the sweetness will be too strong.

Saccharides generally have the effect of improving frozen physical properties such as preventing protein denaturation, ice crystal formation, and ice crystal growth, as well as improving flavor through moderate sweetness, as well as preventing crystal precipitation and improving moisture retention. Therefore, when sugars are added, their effect of improving frozen physical properties prevents freezing denaturation of the frozen tofu according to the present invention, and their moisturizing property improving effect prevents deterioration of the flavor of tofu.

Furthermore, by adding an appropriate amount of saccharide, it has the effect of enhancing the appropriate gel strength during gel formation of soymilk. The present inventor took note of this knowledge and added sugars, which have not conventionally been added to tofu, directly into the raw material to obtain tofu with strong gel strength.

Next, the mixture containing the raw materials and additives is stirred at high speed to uniformly mix the solids and other ingredients.

Mixing here does not mean dissolving the solids in warm soymilk, which is easy to process, but rather mixing the solids uniformly in the cooled soymilk solution by stirring, thereby eliminating powder distortion and lumps. be.

Next, the air bubbles in the soy milk are removed through a degassing process.

If the air bubbles inside the soymilk are not removed, they will remain in the tofu and will not only prevent the formation of a strong gel, but also cause oxidation and browning, making it extremely difficult to maintain the unique color tone of tofu. Such denaturation due to insufficient degassing is likely to become apparent when stored for a long period of time by freezing.
This can be a major cause of product quality deterioration, so you need to be very careful.

Thereafter, glucono delta lactone (G, D, L,) as a coagulant for tofu is added and thoroughly mixed.

It is important to ensure that the coagulant is sufficiently mixed throughout the soymilk, and uneven coagulation due to insufficient mixing will greatly affect the gel strength of the product after freezing.

Calcium sulfate, calcium chloride, magnesium chloride, glucono delta lactone (G, D, L, etc.) are generally known as coagulants for tofu, but depending on the coagulation period,
Glucono delta-lactones (G, D,
L,) was selected. The glucono delta lactone (G,
D.

When using L,), if the amount added is too little, the coagulation power will be weak, and if it is too much, it will be too hard and taste sour, so the amount added relative to the amount of soy milk is 0.31 %〜
0.34% is desirable.

After adding the glucono delta lactones (G, D, L,), the mixture is heated at a temperature of 80° C. or higher for 30 minutes or more to coagulate the soymilk at once to prepare tofu. the result,
The gel properties of the prepared tofu had a dense and uniform structure, and a strong gel was formed, making it difficult to dehydrate even when frozen.

Gluconodelactone (G.

D, L, ) are white crystals with the structural formula shown in Figure 2. They dissolve well in water, and when heated, they gradually decompose into gluconic acid, making soymilk acidic, and thus producing ionic carboxyl The group (-Coo-) is a molecular carboxyl group (
COOH), and the charge on the molecule as a whole is neutralized. As a result, the electrostatic repulsion between molecules decreases, and -5-3- bonds and hydrophobic bonds are formed between molecules due to hydrophobic groups and -SH groups exposed to the outside through thermal denaturation.
(see Figure 3), that is, glucono delta lactones (G, D, L,) coagulate proteins in soy milk that tend to precipitate by thermally decomposing and making soy milk acidic. This process is called acid precipitation.

Its characteristics are that it does not react unless heated, that the reaction is slow, and that it has a high water retention capacity. The property of G, D, and L that they do not react unless they are heated means that if the temperature is controlled and the raw materials are kept at a low temperature, it is possible to mix solids and sugars without causing a reaction. , it is possible to perform sufficient pretreatment before solidification. In this way, once preparations are completed in the ideal state,
Since the temperature can be raised in a timely manner and the coagulation reaction can be caused quickly, tofu (gel) with good coagulation properties can be obtained. Moreover, G, D.

Since L has a slow coagulation speed compared to other coagulants, it forms a gel with a dense structure, high water-holding capacity, and evenness and uniformity. G like this.

Using D and L, the coagulation reaction is controlled by temperature control, the solid content is increased, and sugar is added to coagulate tofu, which has a strong gel strength and is less likely to form ice crystals.

In the present invention, the special tofu prepared in this manner is finally cooled and rapidly frozen to obtain frozen tofu. The reason for rapid freezing is to prevent large ice crystals from forming or growing inside the food and to prevent freezing denaturation from occurring due to slow freezing. As a result, the tofu according to the present invention, which was frozen and stored for a predetermined period of time and then thawed, had almost no difference in gel strength or hardness from before freezing even when cooked.

By performing the above-mentioned processing, it was possible to make frozen tofu, and by using this as a raw material and cutting it into appropriate sizes and adding sauce etc. to it, it was possible to make frozen prepared foods.

``Example'' Example 1> Soy milk is prepared from whole soybeans or defatted soybeans in a conventional manner, and then cooled to 20°C. To 100 parts of this cooled soymilk with a solids content of 11%, 15 parts of powdered soymilk with a solids content of 97% was added to make the solids content 21.8%, and then 5 parts of sorbitol was added and stirred at high speed. After homogeneously mixing and degassing G, D, and L, 0.31% of G, D, and L are mixed, and the above mixture is heated at 90°C for 30 minutes to coagulate the soymilk, thereby removing moisture. 74.56% tofu was prepared. The tofu is then cooled and heated using liquid nitrogen.
Frozen tofu was obtained by rapid freezing at 0°C. After storing this tofu in the freezer for three months, I cooked it and compared the quality of the resulting tofu with that of regular tofu.

Table 1 shows the results. The test product, that is, the thawed frozen tofu product, was superior in both color tone and texture to the frozen tofu product. Furthermore, the quality is quite similar to that of fresh (unfrozen) commercially available tofu.

Second Example> Soy milk is prepared from whole soybeans or defatted soybeans in a conventional manner, and then cooled to 25°C. This cooled solids content 14%
To 85 parts of soy milk, add 15 parts of water and 12 parts of powdered soy milk with a solid content of 97% to make the solid content 21.0%,
To this cooled soymilk, 8 parts of saccharide oligodose (see Table 3) manufactured by Mitsubishi Chemical Industries, Ltd. was added and stirred at high speed to uniformly mix the solids and other ingredients. After degassing, further
, D, and L at 0.34%, the above mixture was heated at 80°C for 40 minutes to coagulate soymilk, and the moisture content was 73.75%.
Tofu was prepared, and then the tofu was cooled and quickly frozen at -30°C using a freezer to obtain frozen tofu. After storing this in the freezer for 2 months, thawing it and making it 2 cmX 2 cmX
Cut into 1 cm pieces and add 50% tofu and 50% sauce.
The quality of the resulting mapo tofu was compared with that of mapo tofu made using regular tofu.

Table 2 shows the results. The test product, that is, a product made from frozen tofu, was superior in color tone, texture, and flavor compared to a product made from frozen ordinary tofu. Furthermore, there is almost no difference when compared to products made from raw commercially available tofu.

Table 1 Sensory test results for Example 1 The above evaluation was performed by 10 panelists, and the evaluation criteria were as follows.

0 points Not good at all 5 points Slightly similar to tofu 10 points Totally tofu itself Table 2 Sensory test results of Example 2 The above evaluation was evaluated by 10 panelists, and the evaluation criteria are as follows. .

0 points: Very poor.

5 points average.

10 points: Very good.

Table 3 Analysis value "Efficacy" of Fl "Oligodose" (trademark) of Mitsubishi Chemical Industries, Ltd. As shown in Unegami, the present invention provides a method for producing frozen tofu, which has been considered difficult in the past. It is something to do.

The frozen tofu obtained by the production method of the present invention has a strong gel and
Almost no ice crystals form and it is protected against freezing denaturation, so even if you store it refrigerated at -30 degrees for 2 to 3 months and thaw it, it will retain the same color tone and taste as raw commercially available tofu (silken tofu). It is possible to restore tofu with texture and flavor. That is, the frozen tofu produced according to the present invention can be stored for a long time while maintaining its quality, and can be distributed and sold at low temperatures as a type of frozen food.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the mechanism by which proteins become spongy when tofu is frozen.
, L, ) and the structural formula of gluconic acid produced by thermal decomposition. FIG. 3 is a schematic diagram of the denaturation of protein molecules and the intermolecular bonding reaction.

Claims (1)

[Claims] Powdered soymilk is added to soymilk that has been cooled to 25°C or below so that the coagulable solids content is 15% or more (by weight), and 1% to 15% of sugars are added to this cooled soymilk and stirred at high speed. to uniformly mix solids and other ingredients,
After degassing, glucono delta lactone is added as a coagulant for tofu and mixed, and then the above mixture is heated to 80°C.
A method for producing frozen tofu, characterized in that the soybean milk is coagulated by heating at the above temperature for 30 minutes or more to prepare tofu, and then the tofu is cooled and quickly frozen.