Method of producing frozen food

Abstract

To provide a method of producing a frozen food, the method not needing to package a main food material and an auxiliary food material separately even if the auxiliary food material is highly fluid and contains much soup, or the food is eaten after being poured separately with much soup; and to provide a method of producing a frozen food that does not lose the original texture or flavor of the main food material when cooked in a microwave, etc., the method enabling the main food material and the auxiliary food material to be simultaneously in an appropriate heated state and to have a superior appearance.SOLUTION: A method of producing a frozen food consisting of rice as a main food material and an auxiliary food material containing much soup includes the steps of filling a container with cooked rice, freezing the filled cooked rice, placing the auxiliary food material containing much soup directly onto the frozen cooked rice, and refreezing the food materials.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing frozen foods. More specifically, it relates to a method for manufacturing frozen foods in which a side ingredient with a lot of juice is directly filled on cooked rice, which is the main ingredient.

Background Art

[0002] In recent years, various foods have been sold along with changes in eating habits and lifestyles. Among them, frozen foods are accepted by consumers and have been steadily increasing in sales because of the ease of cooking, good taste, and quality.

[0003] Among frozen foods, there are some in which a liquid such as a sauce, which is a side ingredient, is entangled or mixed with cooked rice or noodles, which are the main ingredients, at the time of eating. In such frozen foods, during microwave heating cooking, the texture of the main ingredient may deteriorate because the main ingredient absorbs the moisture of the side ingredient. Therefore, many of them are packaged separately with the main ingredient and the side ingredient. Alternatively, in the case of a sauce with high viscosity and low fluidity, there are some that prevent moisture migration during transportation or heating by interposing a film or the like between the main ingredient and the side ingredient (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] On the other hand, among so-called donburi dishes such as beef bowl, chicken and egg bowl, and tempura bowl, although not the source, there are also those where sauce or tare (hereinafter sometimes simply referred to as "sauce etc.") is poured over the rice. When the amount of sauce etc. is small, there is no particular problem. However, in the case where the rice is soaked in the sauce or tare like what is called "drowning in sauce", the texture of the rice deteriorates as the rice absorbs the moisture of the sauce or tare as described above. Furthermore, since the sauce or tare has high fluidity, it is difficult to prevent the contact between the main ingredient and the side ingredient only by interposing a film like the above-mentioned source. Therefore, when the amount of sauce etc. is large, it is necessary to separately package the side ingredient including the sauce or tare and the main ingredient.

[0006] However, when separately packaging the main ingredient and the side ingredient, there are problems such as an increase in manufacturing cost and the need for individual heat cooking, which is time-consuming. Also, in consideration of environmental issues, reduction of the materials used for the container is required.

[0007] The present invention has been made in view of the above problems. That is, the first object of the present invention is that even for a side ingredient with high fluidity and a lot of juice, or a food ingredient that is eaten with an extra amount of juice such as sauce separately, it is not necessary to package the main ingredient and the side ingredient separately. The second object is to provide a method for manufacturing a frozen food that can simultaneously bring the main ingredient and the side ingredient to an appropriate heating state without impairing the original texture and taste of the main ingredient when heating and cooking in a microwave oven etc., and is also excellent in appearance.

Means for Solving the Problems

[0008] To achieve the above object, the inventor of the present invention focused on the filling method of the side ingredient and conducted intensive studies. As a result, it was newly found that by freezing the main ingredient in advance, the moisture absorption of the main ingredient can be suppressed, and the invention was completed.

[0009] In order to solve the above problems, the present invention provides a method for manufacturing a frozen food comprising a main ingredient of rice and a side ingredient with a lot of juice. The method includes a step of filling cooked rice into a container, a step of freezing the filled cooked rice, a step of directly filling a side ingredient with a lot of juice onto the frozen cooked rice, and then a step of freezing again. The method is characterized by being a method for manufacturing a frozen food comprising these steps.

[0010] In order to solve the above problems, the present invention provides a method for manufacturing a frozen food comprising a main ingredient of rice and a side ingredient arranged on the main ingredient. The method includes a step of filling cooked rice into a container, a step of freezing the filled cooked rice, a step of arranging the side ingredient on the frozen cooked rice, a step of further adding juice, and a step of freezing again after the step of adding the juice. The method is characterized by being a method for manufacturing a frozen food comprising these steps.

[0011] According to such a configuration, by freezing the main ingredient first, the moisture in the main food becomes ice and fills the gaps in the main ingredient tissue. That is, even if the juice tries to soak into the main ingredient tissue, the soaking path is blocked by ice, so it becomes difficult for the juice to soak into the main ingredient tissue. As a result, it is considered that the main ingredient becomes less likely to absorb the juice, and a decrease in texture can be prevented. In addition, by freezing the main ingredient in advance, it is possible to prevent the outflow of nutrients from the main ingredient to the juice, so the original taste of the main ingredient can be maintained. Here, "a lot of juice" described in the claims means a highly fluid liquid.

Effects of the Invention

[0012] According to the present invention, it is possible to suppress the main ingredient from absorbing the juice contained in the side ingredient or the juice added separately, so that a decrease in the texture of the main ingredient can be prevented. In addition, it is possible to provide a method for manufacturing a frozen food that is excellent in appearance by bringing the main ingredient and the side ingredient into an appropriate heating state at the same time without impairing the original texture and taste of the main ingredient. Furthermore, even for a side ingredient with high fluidity and a lot of juice, it is not necessary to package the main ingredient and the side ingredient separately, so materials can be reduced.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0014] Hereinafter, preferred embodiments for carrying out the present invention will be described. Note that the embodiments described below show an example of typical embodiments of the present invention, and the scope of the present invention is not construed narrowly thereby.

[0015] The frozen food according to the present invention may be any that contains at least a main ingredient and a side ingredient. The frozen food according to the present invention is characterized in that the main ingredient is frozen before the main ingredient and the side ingredient are integrated. The freezing method used in the present invention is not particularly limited, but it is preferable to freeze so as to rapidly pass through the temperature range in which ice crystals grow. For that purpose, it is preferable to perform rapid freezing. Also, it is preferable to cool the main ingredient once before freezing it. By cooling, the growth of ice crystals can be suppressed more than freezing the main ingredient immediately after heating as it is, and the loss of energy required for freezing can be reduced.

[0016] As the main ingredient used in the present invention, cooked rice such as polished rice and brown rice is preferred. Also, it may be a granular substance in the form of grains made of rice flour or starch. Here, the granular substance in the form of grains refers to a kneaded product mainly made of rice flour or resistant starch that imitates the shape of grains. Further, grains refer to the seeds of cereals, which are the seeds of Poaceae crops such as rice, and may include pseudo-cereals such as buckwheat, amaranth, and quinoa.

[0017] In the present invention, it is preferable to use polished rice as the main ingredient. As the polished rice, short-grain rice is preferred, but medium-grain rice or long-grain rice may also be used. Also, as the type of rice, Japonica rice is preferred, but Indica rice or Javanica rice may also be used. Furthermore, the cooked rice used in the present invention is the one that has been cooked once. The cooking method is not particularly limited, and it may be cooked by a normal method such as gas cooking, electric cooking, IH cooking, cooking by steaming, or cooking using superheated steam. Also, the amount of water added during cooking may be appropriately adjusted so that cooked rice with a desired texture of stickiness and firmness can be obtained after cooking. For example, the amount of water added can be appropriately adjusted so that the cooking yield is 1.6 to 2.6 (corresponding to 49 to 68% moisture after cooking) for cooking. Here, the cooking yield is the weight ratio of the rice after cooking to the weight of the rice before cooking. Alternatively, it may be cooked with a water addition rate of 130 to 180%. The water addition rate is the weight ratio of water to the weight of the rice before cooking. For example, "cooking polished rice with a water addition rate of 160%" means cooking in the ratio of "100 g of polished rice before cooking + 160 g of water". Note that during cooking, enzymes such as oil, emulsifier, polymerized phosphate, antioxidant, and amylase may be added as necessary. Also, seasonings such as salt, soy sauce, and sugar may be used for seasoning.

[0018] The side ingredient is not particularly limited as long as it is a type of what is called so-called donburi, but it is preferably an ingredient that requires sauce or the like. Also, it is preferably an ingredient that can be eaten even if the main ingredient is dipped in sauce or the like. Specifically, examples include oyakodon, nikujaga, gyudon, butadon, tempura, simmered tempura, kalbi kuppa, soup curry, and the like. The side ingredient may initially be in a state with a lot of juice, or it may be made into a state with a lot of juice by separately adding sauce or the like. The manufacturing method of the side ingredient is not particularly limited as long as it is cooked according to existing cooking methods.

[0019] The present invention is more effective for low-viscosity sauce or the like among sauces or the like. That is, the lower the viscosity of the sauce or the like, the larger the area where the main ingredient and the sauce or the like come into contact. However, in the present invention, even if the area where the main ingredient comes into contact becomes larger, it is possible to suppress the main ingredient from absorbing water such as sauce. In the present invention, when the viscosity of the sauce or the like is measured with a B-type viscometer, rotor No. 1, at 40 °C, and a rotation speed of 20 rpm, the effect is easily felt when it is 180 mPa·s or less.

Example

[0020] Hereinafter, the present invention will be described in more detail based on examples.

[0021] Commercially available rice (Koshihikari) was cooked with a water addition rate of 140%. The obtained cooked rice was loosened and cooled, and 150 g each was filled into a container with a capacity of 550 mL. At this time, the temperature of the cooked rice was 50 to 60 °C. Then, it was leveled so as to have approximately the same thickness. Cold air was blown onto the container filled with the cooked rice, and it was cooled until the cooked rice reached 40 °C to obtain cooled cooked rice.

[0022] 100 mL of water, 30 mL of soy sauce, and 30 g of sugar were mixed and brought to a boil to prepare a solution imitating the sauce for beef bowl (hereinafter, sometimes referred to as "sauce-like solution"). The obtained solution was allowed to cool naturally until it reached room temperature. At this time, the viscosity measured with a B-type viscometer, rotor No. 1, at 40 °C, and a rotation speed of 20 rpm was 28 mPa·s.

[0023] (Test Example 1) The cooled cooked rice was put into a quick-freezer and left standing at -35°C for 10 minutes to obtain frozen cooked rice. For the obtained frozen cooked rice, a soy sauce-flavored solution in an amount sufficient to immerse the cooked rice (150 mL in this example) was added, and immediately put into a quick-freezer and left standing at -35°C for 60 minutes to be frozen. This was designated as Test Example 1.

[0024] (Test Example 2) In Test Example 1, the one without adding the soy sauce-flavored solution and remaining as frozen cooked rice was designated as Test Example 2.

[0025] (Test Example 3) For the cooled cooked rice, a soy sauce-flavored solution in an amount sufficient to immerse the cooked rice (150 mL in this example) was added, and immediately put into a quick-freezer and left standing at -35°C for 90 minutes to be frozen. This was designated as Test Example 3.

[0026] Test Examples 1 to 3 were thawed by heating at 600 W for 6 minutes. Approximately 20 g of the cooked rice in each test example immediately after the thawing was immediately immersed in liquid nitrogen and freeze-dried to obtain Samples 1 to 3. On the other hand, the cooked rice in each test example that was the same until being immersed in liquid nitrogen after heating and thawing by a microwave oven but without being freeze-dried was designated as Samples 4 to 6. For Test Examples 1 and 3, after the thawing was completed, the contents in the container were drained with a strainer to separate the cooked rice and the soy sauce-flavored solution.

[0027] Immediately after the thawing was completed, for the cooked rice (Samples 1 to 3) immediately frozen with liquid nitrogen, the cross-section was confirmed at magnifications of 30, 150, and 600 times using a scanning electron microscope (SEM: JCM-6000 manufactured by JEOL Ltd.). The images of each sample are shown in Fig. 1. Also, for Samples 1 to 3, the cross-section was confirmed at magnifications of 50 and 200 times using a digital microscope (VHX-5000 manufactured by Keyence Corporation). The images of each sample are shown in Fig. 2.

[0028] For the cooked rice (Samples 4 to 6) that was not freeze-dried after being immersed in liquid nitrogen, the cross-section was confirmed with a digital microscope (VHX-5000 manufactured by Keyence Corporation). The images of each sample are shown in Fig. 3.

[0029] Sample 2 is the one obtained by directly freezing and thawing the cooked rice. As is clear from FIG. 1, in Sample 2, it can be seen that both the central part of the rice grain (hereinafter referred to as the "core") and the outermost part of the rice grain (hereinafter referred to as the "surface layer") have a dense structure in which they are closely packed (see 150, 600 times magnification). It can be seen that Sample 3 has large cavities inside as compared with Sample 2. Further, it can be seen that a bubble structure is formed around the cavities, and on the surface layer side, the bubble structure is rougher and sparser than around the cavities (see 30, 150 times magnification). Furthermore, it can be seen that there are a large number of fine bubble structures on the surface layer (see 600 times magnification). On the other hand, it can be seen that Sample 1 has smaller internal cavities as compared with Sample 3 (see 600 times magnification). Also, it can be seen that the bubble structure formed around the internal cavities in Sample 1 is finer and denser than that of Sample 3 (see 150 times magnification). Note that, unlike Sample 2, although a bubble structure was formed on the surface layer side of Sample 1, the bubbles were extremely smaller than the bubble structure of Sample 3 (see 600 times magnification).

[0030] FIG. 2 is a digital microscope image of Samples 1 to 3. Looking at FIG. 2, it can be seen that only the surface layer of Sample 1 is stained (see 200 times magnification), whereas in Sample 3, the sauce and the like have penetrated beyond the surface layer and are stained (see 200 times magnification). Also, a gap is recognized between the surface layer side and the core side of Sample 3. It is considered that the said gap is caused by moisture migration occurring from the surface layer side toward the core side and the moisture remaining directly under the surface layer sublimating by freeze-drying. This is also suggested from FIG. 3 described later. Specifically, in Sample 6 of FIG. 3, it can be seen that the surface layer part shows a liquefied appearance due to moisture migration directly under the surface layer, and moreover, the layer is thickened (see 200 times magnification). Such a state is not recognized in Samples 4 and 5. On the other hand, as far as seen from the microscope images of FIG. 2, Samples 1 and 2 did not show the visual difference as shown in FIG. 1. From these facts, it was suggested that when freezing after adding soy sauce or the like, not only does the soy sauce or the like penetrate beyond the surface layer of the rice grains to the core side, but also voids are likely to form inside the rice grains due to the penetrated moisture.

[0031] Figure 3 is an image of a cross-section of cooked rice soaked in liquid nitrogen after thawing by a microwave oven, viewed with a digital microscope. Different from Figure 2, the cross-section is uneven because freeze-drying was not performed and the frozen moisture melted during observation. As is clear from Figure 3, it can be seen that the soy sauce has penetrated to the core of the rice in Sample 6. Also, it can be seen that the periphery of the surface layer of Sample 6 is thickened (see 200 times magnification). On the other hand, it can be seen that although the soy sauce has penetrated beyond the surface layer in Sample 4, it has not reached the core (see 200 times magnification). Also, it can be seen that the amount of soy sauce or the like that has penetrated is less than that of Sample 6.

[0032] Subsequently, a taste comparison was conducted between Samples 4 and 6. Sample 4 was in a state of being immersed in the thawed soy sauce-like solution, and the tension on the surface of the rice grains and the graininess of the rice could be felt during chewing. On the other hand, in Sample 6, no tension on the surface of the rice grains was felt during chewing, and the texture was soft and without a chewy feeling.

[0033] Next, in Test Examples 1 and 3, the same experiment was conducted with tonkatsu placed as a side dish. The filling timing of the tonkatsu was that in Test Example 1, filling was performed after freezing the cooked rice. In Test Example 3, the tonkatsu was filled on top of the cooked rice from the beginning. Furthermore, temperature sensors were installed at the center of the cooked rice layer served in both Test Examples 1 and 3 and directly below the tonkatsu (between the tonkatsu and the cooked rice), and the temperature changes at each site were measured.

[0034] The results are shown in Fig. 4. The elapsed time in the figure represents the elapsed time since the start of the operation. First, look at Test Example 1. Test Example 1 is a test example in which only the cooked rice was frozen first. It can be seen that the temperature at the center of the cooked rice layer drops rapidly at the start of freezing. And after 10 minutes of freezing, it can be seen that the temperature at the center of the cooked rice layer has dropped to -25°C or lower. Next, when the tonkatsu is filled and then the soup-like solution is filled, the temperature of the cooked rice layer rises to a temperature close to 0°C. After that, the temperature drops again, and it can be seen that it takes about 14 minutes after filling the soup-like solution for the temperature directly under the tonkatsu to reach 0°C or lower. Also, 56 minutes after being put into the quick-freezing machine after filling the soup-like solution, both the temperature directly under the tonkatsu and the center of the cooked rice layer have dropped below -15°C, which is a temperature suitable for storing frozen foods.

[0035] Subsequently, look at Test Example 3. Test Example 3 is a test example in which the side dish tonkatsu is filled on top of the cooked rice and then frozen after filling the soup-like solution. The results of Test Example 3 are shown in Fig. 5. It can be seen that the temperature at the center of the cooked rice layer and the temperature directly under the tonkatsu drop at the same rate at the start of freezing. This rate of drop was slower than that of Test Example 1. After that, when the temperature reaches 0°C, the temperature directly under the tonkatsu becomes horizontal for a while and maintains 0°C for some time. On the other hand, the center of the cooked rice layer did not become horizontal, although the rate of drop became slower than the initial rate. The temperature directly under the tonkatsu, which had become horizontal, then started to drop again and reached -15°C earlier than the center of the cooked rice layer. Also, the rate when it started to drop again was almost the same as the rate of drop before reaching 0°C. 10 minutes after the delay in the temperature directly under the tonkatsu, the center of the cooked rice layer also reached -15°C. 68 minutes after being put into the quick-freezing machine, both the temperature directly under the tonkatsu and the center of the cooked rice layer dropped below -15°C.

[0036] In Test Examples 1 and 3, looking at the passing (staying) time in the maximum ice crystal formation temperature zone, for the center part of the cooked rice layer, Test Example 1 tended to have a longer time. On the other hand, directly under the tonkatsu, Test Example 3 tended to have a longer time. Since cooked rice contains a lot of moisture, if the passing time in the maximum ice crystal formation temperature zone is long, ice crystals are likely to grow inside the rice grains and the tissue inside the rice grains is likely to be destroyed. However, as is also clear from Figure 1, in Test Example 1, it cannot be said that the tissue inside the rice grains has been destroyed that much. This is probably because the freezing of the cooked rice in Test Example 1 was rapid and solidly frozen to the core of the rice grains. When filled with tonkatsu or sauce-like solution, even if the surface layer of the rice grains melted, the core of the rice grains did not melt, preventing the formation of ice crystals inside the rice grains. On the other hand, although the inside of the rice grains did not melt, the surface layer melted, so it is considered that the surface layer absorbed sauce or the like and fine bubbles were formed on the surface layer side when frozen later. This is also clear from the SEM photograph of Test Example 1, and the dense layer present in the intermediate layer is considered to be the remains of the layer formed by the first freezing. In addition, it is considered that the texture could be maintained because the core of the rice grains did not melt.

[0037] In contrast, in Test Example 3, it is considered that ice crystals were generated inside because the freezing of the cooked rice took time and the tissue inside the rice grains was destroyed. It is considered that the large bubbles in the SEM image of Figure 1 were due to ice crystals. Furthermore, not only the generation of ice crystals but also the absorption of sauce or the like is considered to have destroyed the tissue on the surface layer side. Thus, it is considered that the original texture of the rice grains was impaired by the formation of various-sized bubbles throughout the rice grains.

[0038] As described above, according to the present invention, since it is possible to suppress the absorption of the juice contained in the side ingredient or separately added juice by the main ingredient, it is possible to prevent the deterioration of the texture of the main ingredient.

Claims

1. A method for manufacturing a frozen food comprising a main ingredient of rice and a secondary ingredient with a lot of juice, a step of filling a container with cooked rice, a step of freezing the filled cooked rice, a step of filling a secondary ingredient with a lot of juice directly onto the frozen cooked rice and then freezing again, comprising the above steps, a method for manufacturing a frozen food.

2. A method for manufacturing a frozen food comprising a main ingredient of rice and a secondary ingredient arranged on the main ingredient, a step of filling a container with cooked rice, a step of freezing the filled cooked rice, a step of arranging a secondary ingredient on the frozen cooked rice and then adding more juice, a step of freezing again after the step of adding the juice, comprising the above steps, a method for manufacturing a frozen food.

Images