Microwave heating method for packaged foods

Abstract

This invention provides a microwave heating method for food packaged in resin packaging, which allows for adjustment of the heating state without causing uneven heating or overheating. [Solution] A method for heating food contained in a resin packaging material by microwave heating, characterized in that the food is a food with a water activity of 0.6 or higher, and the outer surface of the resin packaging material is covered with a material capable of absorbing microwaves while microwave heating is performed.

Description

Technical Field

[0001] The present invention relates to a method for heating food packaged in a resin packaging material by a microwave oven. More specifically, it relates to a heating method by microwave oven heating that can prevent overheating of the food and heat it uniformly without impairing the taste.

Background Art

[0002] When heating food by a microwave oven, the food in the oven is irradiated with microwaves, and the water molecules contained in the food are vibrated to heat the food through the temperature rise of the water. With the spread of such microwave ovens, heating food directly in the packaging material in the microwave oven is highly convenient and widely used because there is no need to transfer the food taken out of the packaging material to a dish.

[0003] When heating food in a packaged state, it is desirable that the packaging material has heat resistance compatible with microwave oven heating, and in the case of foods such as mochi that become highly viscous upon heating, the heated contents can be easily separated from the packaging material without adhering to the packaging material.

[0004] In order to solve such problems, Patent Document 1 below describes a microwave oven heating compatible container in which an edible wax or an edible oil coating layer having a melting point in the range of 50 to 95°C is provided on the inner surface of the container, and the coating layer that becomes liquid during microwave oven heating can prevent the adhesion of solid food in a viscous state to the inner surface of the container. Also, Patent Document 2 below describes a mochi packaging body in which mochi is housed in a container, and a solid coating of an edible wax or an edible oil having a melting point in the range of 50 to 95°C is formed on the entire surface of the mochi.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] The microwave-safe container described in Patent Document 1 above allows for the separation of foods that become sticky when heated, such as mochi, from the container without them adhering to it. However, because it uses edible wax with a low melting point, there is a risk that the edible wax may migrate to the food, potentially impairing its taste. Furthermore, since Patent Document 2 described above involves directly coating cut mochi with edible wax, its application is limited to solid foods with a uniform surface like cut mochi, and, similar to Patent Document 1 described above, there is a risk of impairing the taste. Furthermore, when heating food in a microwave oven, if the microwave's power (wattage) or heating time is incorrectly adjusted, uneven heating can occur, or excessive heating can damage the packaging of oily foods, or cause foods that become sticky when heated, such as mochi, to stick to the packaging, or result in food not being cooked to the desired degree. Adjusting these settings is not easy.

[0007] Therefore, the object of the present invention is to provide a microwave heating method that allows for adjustment of the heating state of food stored in resin packaging without causing uneven heating or overheating. Another object of the present invention is to provide a microwave heating method using a resin packaging material that allows for easy separation from the packaging material without the contents becoming sticky when heated, such as mochi (rice cake). [Means for solving the problem]

[0008] The present invention provides a method for heating food contained in a resin packaging material using microwave heating, characterized in that the food is a food with a water activity of 0.6 or higher, and the outer surface of the resin packaging material is covered with a substance capable of absorbing microwaves before microwave heating is performed.

[0009] In the heating method of the present invention, (1) The substance capable of absorbing microwaves is water, and the resin packaging material is immersed in water. Heat in a microwave oven while the food is in a dry state or covered with a water-containing material. (2) The power output (W) × heating time (sec) per 1g of the food is 600 (J / g) ) Heat to a temperature exceeding 2.0 (3) The food contains oil, (4) The food is a food that becomes viscous after heating. (5) At least the inner surface of the resin packaging material contains an amide compound with a melting point of more than 130°C. It is present, or it has an uneven surface. (6) The amide compound contains N,N'-ethylenebisstearamide. and, (7) The resin packaging material is equipped with an automatic steaming mechanism. (8) The resin packaging material is a self-supporting packaging material. (9) The unfolded surface area ratio (Sdr) of the irregularities is 0.2 or more. This is preferable. [Effects of the Invention]

[0010] In the microwave heating container of the present invention, by heating food contained in a resin packaging material in a microwave oven while the outer surface of the resin packaging material is covered with a material that can absorb microwaves, it is possible to control the microwave heating of the food inside the resin packaging material, enabling uniform heating of the food and preventing overheating, thereby effectively preventing damage to the packaging material, even with foods that are high in oil. Furthermore, because a coating made of a specific amide compound is formed on the inner surface of the resin packaging material that comes into contact with the food, or because an uneven surface is formed, even if the contents, such as mochi (rice cake), become viscous when heated, can be easily separated from the packaging material. [Brief explanation of the drawing]

[0011] [Figure 1] This figure illustrates an example of the microwave heating method of the present invention. [Modes for carrying out the invention]

[0012] In the microwave heating method of the present invention, by heating food contained in a resin packaging material with a microwave-absorbing material (hereinafter sometimes referred to as "microwave-absorbing material") without removing it from the packaging material, the microwaves generated from the microwave oven are dispersed and absorbed not only by the food in the packaging material but also by the microwave-absorbing material. As a result, the heating of the food in the packaging material is controlled, preventing rapid and excessive heating of the food, and preventing overheating and uneven heating of the food. In other words, the heating method of the present invention not only allows for heating similar to that performed by heating at low power (200W or less) or in defrost mode of a microwave oven, but also allows microwave-absorbing material heated simultaneously with the food to indirectly heat the food from the surroundings through the packaging material, enabling more efficient and thorough heating of food than simply heating at low power.

[0013] (Food products packaged in plastic packaging) In the heating method of the present invention, it is important that the food contained in the resin packaging has a water activity of 0.6 or higher, and is not limited to food that can be heated in a microwave oven. In the heating method of the present invention, since it is possible to heat the food stored in the resin packaging material without opening it, it is possible to uniformly heat various products such as individually packaged mochi, retort foods in pouches, and individually packaged bread. Among them, in addition to mochi that becomes viscous upon heating and foods with a large amount of oil such as curry and stew, when cooking various ingredients with different water activities in a bag, it is possible to control the heating state to prevent local overheating and heat uniformly, which is particularly suitable.

[0014] (Resin packaging material) In the heating method of the present invention, as the resin packaging material, the form is not limited as long as it can store food, such as a bag (pouch), cup, tray, bottle, etc. With such a storage-capable packaging material, it is possible to immerse it in a microwave-absorbing substance such as water without affecting the food in the packaging material. Note that the packaging material capable of storing food only needs to prevent direct contact between the food and the microwave-absorbing substance during heating, and does not necessarily need to be airtight. In the heating method of the present invention, since the resin packaging material containing the food is heated by controlling the microwave by microwave oven heating, the resin constituting the resin packaging material does not necessarily have to have high heat resistance, but when using water or the like as the microwave-absorbing substance, it is necessary to have moisture resistance. Also, it is sufficient that the main component of the packaging material is resin, and it may include a layer made of a material other than resin, such as paper or an inorganic vapor deposition layer, as an intermediate layer.

[0015] Examples of the resin constituting the resin packaging material include, but are not limited to, olefin resins such as polyethylene and polypropylene, cyclic olefin resins, polystyrene resins, acrylonitrile-styrene copolymer resins, acrylonitrile-butadiene-styrene copolymer resins, poly(meth)acrylic resins, polycarbonate resins, polyvinyl alcohol resins, ethylene-vinyl alcohol copolymers, saponified ethylene-vinyl ester copolymers, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polyamide resins such as various nylons, polyurethane resins, acetal resins, cellulose resins, polyvinylidene chloride resins, etc. It is desirable that it has a multilayer structure composed of these resins. Suitable resin packaging materials include, but are not limited to, a packaging bag (pouch) composed of a laminate having a gas barrier layer such as an ethylene-vinyl alcohol copolymer or an inorganic vapor deposition layer as an inner layer and an outer layer of polypropylene, polyethylene or polyethylene terephthalate, and a cup or tray formed by thermoforming such a laminate. The thickness of the resin packaging material may be the same as that of conventionally known packaging bags (pouches), cups, trays, etc., and is not limited thereto, but it is desirable that it is in the range of 12 to 1000 μm for packaging bags (pouches) and 0.1 to 10 mm for cups and trays.

[0016] In the heating method of the present invention, as the resin packaging material for storing food, it is preferable that an amide compound having a melting point exceeding 130 °C or irregularities are formed at least on the inner surface. Amide compounds with a melting point above 130°C function as a slip agent by leaching a small amount from the inner surface of the resin packaging material. This makes it possible to easily separate foods such as mochi (rice cakes) that become viscous when heated from the inner surface of the resin packaging material. Furthermore, because the melting point is above 130°C, it is possible to prevent excessive bleed-out of the amide compound during microwave heating, which would cause it to adhere excessively to the food. A suitable amide compound with a melting point above 130°C is N,N'-ethylenebisstearamide. Specifically, it is preferable that the amide compound is contained in an amount of 0.05 to 3 parts by mass per 100 parts by mass of resin constituting the inner layer of the resin packaging material, because this allows an appropriate amount of the amide compound to seep out onto the surface of the inner layer of the resin packaging material, making it easy to separate the food without impairing the flavor of the food.

[0017] Furthermore, the presence of irregularities on the inner surface of the resin packaging reduces the contact area between the food, which becomes viscous when heated, and the inner surface of the resin packaging, making it easier to separate the food from the resin packaging. The surface irregularities on the inner surface of the resin packaging material are not restricted as long as they reduce the contact area with food, but preferably, the unfolded surface area ratio (Sdr) is 0.2 or higher. If the unfolded surface area ratio is smaller than the above range, it may not be possible to adequately prevent food from adhering to the inner surface of the resin packaging material compared to when it is above the above value. The unfolded surface area ratio (Sdr) is a parameter representing surface properties as defined in ISO 25178, and it represents how much the unfolded area (surface area) of the defined region has increased compared to the projected area of ​​the defined region. An Sdr of 0.2 or higher means that the irregularities are formed so that the surface area is 1.2 times or more than that of a smooth inner surface.

[0018] As mentioned above, the resin packaging material used in the heating method of the present invention can be any container such as a pouch, cup, or tray, but it is preferable that it has an automatic steam release mechanism that can release the internal pressure when the internal pressure in the resin packaging material rises due to microwave heating. The heating method of the present invention prevents overheating, so there is little risk of the resin packaging material bursting, but by having an automatic steam release mechanism, the food is efficiently heated by the steam in the packaging material until the automatic steam release mechanism is released, while effectively preventing the bag from bursting due to internal pressure and burns from steam when opening. For the automatic steaming mechanism, known mechanisms used in pouches, trays, etc., can be used.

[0019] In the heating method of the present invention, microwave heating is performed with the outer surface of the resin packaging containing the food covered with a microwave-absorbing material. In particular, when a liquid such as water is used as the microwave-absorbing material, the liquid such as water is placed in a container, and the resin packaging is placed in it and heated. This is preferable because the resin packaging has the ability to stand on its own and maintain a stable state in the liquid. Examples of self-standing packaging materials include containers such as cups, trays, and bottles, as well as bags with a bottom, such as standing pouches.

[0020] (Microwave-absorbing material) As a material capable of absorbing microwaves (microwave-absorbing material), it is preferable to use a medium that is solely intended for microwave absorption, such as water or salt water. However, by using a soup or other substance that can be heated and consumed on its own, it is also possible to heat it simultaneously with the food inside the resin packaging. Furthermore, when using salt water, the degree of microwave absorption can be controlled by changing the concentration, and by increasing the salt concentration, it becomes possible to heat the food inside the resin packaging more slowly.

[0021] One method for covering a plastic packaging containing food with a microwave-absorbing material is as follows: If the microwave-absorbing material is a liquid such as water or saltwater, place it in a container and immerse the plastic packaging containing the food directly in the microwave-absorbing material in the container. Alternatively, water or saltwater can be soaked into paper towels or similar materials, and the plastic packaging can be wrapped around it from the outside. When immersing a resin packaging material containing food in a liquid such as water, it is preferable for the entire resin packaging material to be immersed, as this allows the food to be heated slowly and improves the heat transfer efficiency from the microwave-absorbing material. However, it is also acceptable for a portion of the resin packaging material not to be in contact with the microwave-absorbing material (e.g., floating in the liquid). If food is heated in a microwave oven with part of it not covered by microwave-absorbing material, the presence of microwave-absorbing material in the surrounding area or nearby can prevent overheating of the exposed food. It is preferable that the liquid coverage rate on the packaging material be 10% or more, and it is desirable that the liquid coverage rate on the food be 50% or more, preferably 60% or more, more preferably 70% or more, and most preferably 80% or more. Furthermore, the more microwave-absorbing material is used to immerse the plastic packaging containing the food, the slower the food can be heated. However, using too much material reduces thermal efficiency. Therefore, in the case of water, it is preferable to use a range of 0.0005 to 20g per gram of food being heated.

[0022] (Heating conditions) In the heating method of the present invention, it is preferable to heat the food in the resin packaging material using a microwave oven so that the microwave oven power (W) × heating time (sec) per 1 g of food exceeds 60 (J / g), and more preferably exceeds 600 (J / g). Heating at 60 (J / g) or less makes it difficult to sufficiently heat the food, regardless of the type or amount of microwave-absorbing material. The upper limit cannot be determined definitively, as it depends on the type of food, the water activity value, or the type and amount of microwave-absorbing material, but it is desirable that it be 10,000 (J / g) or less. Specifically, for example, in the case of individually packaged mochi (50g), it is preferable to heat each piece of mochi in a microwave oven so that the microwave temperature is in the range of 300 to 8000 (J / g) when immersed in 60 to 1000 ml of water as a microwave-absorbing material. [Examples]

[0023] (Experimental Example 1) Individually packaged mochi (50g) in bags 1-3 shown below were placed in a paper cup (capacity 270ml) containing 200ml of water, so that the water covered 70% of the packaging and 80% of the food (see Figure 1). The mochi was then heated in a 500W microwave for the time shown in Table 1, and the condition of the mochi inside the bag was visually evaluated. The results are shown in Table 1. Bags 1-3 were made by cutting the following three types of film to a size of 60mm x 110mm and sealing them in a center pillow style. Bag 1: Commercially available film (inner layer LDPE, total film thickness 70μm) Bag 2: Inner layer contains 1% by mass of N,N'-ethylenebistearate LLDPE film. Film (total film thickness 100 μm) Bag 3: LLDPE film with an inner surface of Sdr 0.47 (total film thickness 60μ) m)

[0024] (Experimental Example 2) The mochi, individually packaged in the three types of resin packaging used in Experimental Example 1, was heated in a 500W microwave oven for the time shown in Table 1, and the condition of the mochi inside the resin packaging was visually evaluated. The results are shown in Table 1.

[0025] The evaluation criteria are as follows: ×: The mochi is hard overall (undercooked) △: Some parts are hard, but it is soft. ○: Overall soft and delicious ▼: Although it has softened overall, it sticks to the inside of the bag and is difficult to separate.

[0026] [Table 1] [Industrial applicability]

[0027] The microwave heating method of the present invention can heat food uniformly without causing overheating, and is therefore suitable for heating plastic packaging materials containing foods that tend to become sticky when heated, such as mochi rice cakes or foods with a high oil content.

Claims

1. A method for heating food contained in a resin packaging material using microwave heating, The aforementioned food is a food with a water activity of 0.6 or higher. A heating method characterized by performing microwave heating while the outer periphery of the resin packaging material is covered with a material capable of absorbing microwaves.

2. The heating method according to claim 1, wherein the substance capable of absorbing microwaves is water, and the resin packaging material is heated in a microwave oven while immersed in water or covered with a water-containing component.

3. The heating method according to claim 1 or 2, wherein the output power (W) × heating time (sec) per gram of the food is heated to more than 600 (J / g).

4. The heating method according to claim 1 or 2, wherein the food contains oil.

5. The heating method according to claim 1 or 2, wherein the food is a food that is viscous after heating.

6. The heating method according to claim 1 or 2, wherein at least the inner surface of the resin packaging material contains an amide compound with a melting point exceeding 130°C, or an irregularity is formed thereon.

7. The heating method according to claim 6, wherein the amide compound contains N,N'-ethylenebisstearamide.

8. The heating method according to claim 1 or 2, wherein the resin packaging material is equipped with an automatic steaming mechanism.

9. The heating method according to claim 1 or 2, wherein the resin packaging material is a self-supporting packaging material.

10. The heating method according to claim 6, wherein the ratio of the unfolded interface area (Sdr) of the irregularities is 0.2 or more.

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