JPH0157945B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat sterilization method using microwaves, and more specifically, when a sealed container filled with food is heat sterilized by irradiating microwaves, the sealed container is This invention relates to an improved heat sterilization method that prevents bursting.

Recently, not only have there been an increase in the variety of foods that can be canned or bottled, but containers to store them have also been developed that utilize a variety of materials and take advantage of the performance of each material. There is. Food stored in containers often undergoes a sterilization process.
placed in the distribution process.

Conventionally known sterilization methods include aseptic filling, in which a previously sterilized food is filled into a container that has also been sterilized in advance, and sealed, and a method in which the food is filled into a container and then the food and the container are sealed. There are various methods of sterilization.

The latter sterilization method is divided into two methods: one used in the can manufacturing process and the other used in the so-called retort food manufacturing process.In both methods, the internal pressure inside the container increases during heat sterilization. Care has also been taken to prevent the container from bursting.
That is, in the case of can manufacturing, a high-strength metal plate is selected as the material for can manufacturing, and the heat sterilization temperature is selected to be 120° C. or lower. On the other hand, in the case of retort food, conditions are selected in which the container filled with the food is pressurized with a gas mixture of air and steam and heat sterilized.

Recently, a method of sterilizing foods by microwave irradiation has been proposed (see, for example, Japanese Patent Application Laid-Open No. 53-127849, US Pat. No. 3,961,569, etc.), and some practical applications are being considered. Even in such a method of heat sterilizing foods using microwave irradiation, the internal pressure of the container increases during heat sterilization, causing the problem of container rupture.
When using a sterilization method using microwave irradiation, containers made of strong metal materials cannot be used, so containers made of non-metallic materials that are not very strong and have low microwave dielectric loss must be used. . Foods filled in containers made of such materials are often sterilized only under conditions that do not damage the containers, and are not completely sterilized. For example, JP-A No. 52-68785 discloses methods such as heating the food only to a certain extent to prolong its shelf life without sealing the container, or limiting the heat sterilization to a temperature below 100°C even when the container is sealed. As proposed in 2006, when food-filled containers are heated and sterilized by microwave irradiation, the pressure difference between the pressure inside the food-filled container and the microwave irradiation chamber is reduced to prevent the containers from bursting. This is the current situation.

However, if the container is not sealed like the former, complete sterilization cannot be achieved even with microwave irradiation, so it cannot be used to sterilize foods for long-term storage. On the other hand, even for sealed food containers like the latter, the heat sterilization temperature is 100℃.
According to the inventors' experimental results, in the following cases, PH
It was found that for foods with a pH of 4 or less, bacterial growth after heat sterilization is extremely small, but for foods with a pH higher than this, bacterial growth after heat sterilization is large.

The present inventor has completed the present invention as a result of intensive studies aimed at providing a microwave heat sterilization method that eliminates the above-mentioned drawbacks that existed in the conventional technology.

Therefore, the gist of the present invention is to sterilize a food-filled container made of a material with low microwave dielectric loss by heating it with microwaves, in which the food-filled container is sealed and filled with food. Made of material with low wave dielectric loss,
The container is housed in a container having a plurality of micropores in its wall surface, and the container wall is made of a material with low dielectric loss in the gap formed by the inner wall surface of the container and the outer circumferential wall surface of the food filling container. Microwave heating characterized in that the container is filled with powder that cannot pass through micropores provided in the container, the container is covered with a lid, and microwaves are irradiated from the outside of the container to heat and sterilize the food-filled container. It depends on the sterilization method.

The method of the present invention will be explained in detail below.

Foods to which the method of the present invention can be applied are foods that are usually canned or bottled, such as seafood, meat, vegetables, fruits, and fresh sweets, all of which preferably contain liquid ingredients.

In the present invention, a container that can be used as a food filling container is made of a material with low microwave dielectric loss. Materials with low microwave induction loss include polystyrene, polyethylene, polypropylene, ethylene-vinyl acetate copolymer and partially saponified products thereof, polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polyamides, synthetic resins such as polyfluoroethylene, Examples include paper, but the material is not limited to these examples.

Containers for filling foods include those manufactured integrally from synthetic resin or paper, and those manufactured integrally from a laminated product of a synthetic resin film and paper, such as those described in Japanese Utility Model Application Publication No. 53-89085. A laminated product of a synthetic resin film and paper, such as
Examples include composite containers made of a synthetic resin frame.

The shapes of food filling containers are cylindrical, polygonal prism,
The shape may be a truncated cone, an inverted truncated cone, a truncated polygonal pyramid, an inverted polygonal truncated pyramid, other polyhedral shapes, or a bag-like shape, which can be appropriately selected depending on the food.

In the method of the present invention, the food filling container is filled with food and sealed using an appropriate means with a lid made of a material with low microwave dielectric loss that can be used for manufacturing the food filling container. .

In the method of the present invention, the food filling container is
It is housed in a separately prepared housing made of a material with low microwave dielectric loss and having a plurality of fine holes in the wall surface.

The container serves to indirectly prevent the food-filled container from expanding and being damaged when the food-filled container accommodated therein is irradiated with microwaves and heated.

The material with low microwave dielectric loss constituting the container can be appropriately selected from materials with low microwave dielectric loss suitable for manufacturing the food filling container. The shape of the container may be a cylindrical shape, a polygonal prism shape, a truncated cone shape, an inverted truncated cone shape, a polygonal pyramid shape, an inverted polygonal truncated pyramid shape, or any other polyhedral shape manufactured integrally from the above-mentioned material.

This container has a structure that can be closed. Since the food filling container is accommodated in this container, the size of the container is such that even when the food filling container is accommodated, a void remains. The container can also be sized to accommodate a plurality of food-filled containers.

The container is provided with a plurality of micropores in its wall surface. The micropores are formed on the wall surface of the container when the container is filled with a food-filled container and powder and granules (described later), and the lid is closed, and the food-filled container is irradiated with microwaves to heat and sterilize the food-filled container. The function is to eliminate pressure other than the pressure caused by the thermal expansion of the stored food, for example, when there is gas or liquid in the cavity of the container, the pressure that is applied to the inner wall surface of the container due to thermal expansion is eliminated. Furthermore, when the food filling container is forcibly cooled after the heat sterilization is completed, it functions to quickly guide the cooling medium to the outer wall surface of the food filling container.

The size, shape, etc. of the micropores provided in the wall surface of the container can be changed depending on the capacity of the container, but polygons such as circles, triangles, and squares with a maximum diameter of 0.1 mm to 5 mm are preferable. The micropores may be provided at any of the side wall surface, the lid wall surface, and the bottom wall surface, or may be provided in combination on different wall surfaces. The number of micropores provided in the wall surface of the container may be two or more as long as the strength of the wall surface of the container is not weakened too much.

In the present invention, the gap formed between the inner wall surface of the container and the outer peripheral wall surface of the food filling container is filled with powder particles that are made of a material with low dielectric loss and cannot pass through the fine holes provided in the container wall surface. Fill the body and cover it.

Examples of the material constituting the granular material include the aforementioned synthetic resin materials used for manufacturing food filling containers. The appearance of the granular material may be spherical, cylindrical, prismatic, truncated cone, truncated pyramid, or a three-dimensional shape that is a combination of these shapes.

The size of these powder particles is preferably such that it does not pass through the fine holes provided in the wall surface of the container, and depending on the size of the fine holes provided in the wall surface of the container Just choose your body.

FIG. 1 is a longitudinal sectional view showing an example of a state in which a food filling container is housed in a container, the gap is filled with powder and the lid is closed. In the figure, 1 is a food container, 2 is a food product, 3 is a container, 4 is a lid, 5 is a fine hole, 6 is a clamp, and 7 is a powder material.

In the method of the present invention, as illustrated in FIG. 1, the food filling container 1 is housed in the container 3, and after filling the gap in the container with the powder 7, the lid 4 is clamped with the clamp 6, etc. from the outside of this containment body,
Irradiate with microwaves. Microwaves have a frequency of
Refers to the range of 300 to 33,000 megahertz (MHz). In this frequency range, the frequencies currently permitted for non-detection purposes are 915MHz, 2450M
Hz, 5800MHz and 22125MHz, of which
915MHz and 2450MHz are commonly used.

Microwaves irradiated from the outside of the container pass through the wall surface of the container with small dielectric loss, the granular material filled in the void portion of the container, and the wall surface of the food filling container, and reach the food. As the microwave passes through the food, it converts into thermal energy and heats the food.

The heating temperature for heat sterilization by microwave irradiation according to the method of the present invention is set to a temperature necessary to sterilize the germs of the food stored in the food container and the residual bacteria adhering to the food container. This temperature varies depending on the type of residual bacteria (microorganisms) contained in the food and the type of bacteria adhering to the food container, but it should be at least 60℃.
It is in the range of 120℃. The material and structure of the food container used should be selected according to the sterilization temperature. The heating time may be at least a time sufficient to kill germs within the above temperature range, and it is preferable that the range be as short as possible. The time period during which germs can be killed can be determined by appropriate experiments depending on the type of bacteria.

After heating and sterilizing with microwave irradiation, the container is cooled by immersing it in a cold water medium such as cold water, or by forcibly injecting a compressed cooling medium through micro holes provided in the wall of the container. After cooling to around room temperature, it is preferable to remove the clamp, remove the lid, and take out the food-filled container.

The powder and granules can be collected and reused.

The method of the present invention has the following technical effects,
Its industrial utility value is extremely large.

(1) When using the method of the present invention, a food-filled container is housed in a container, the cavity of the container is filled with powder made of a material with low dielectric loss, the lid is closed, and the container is heated by irradiation with microwaves. Since it is sterilized, even if the internal pressure of the food filling container increases, it will not burst.

(2) When using the method of the present invention, since the container is not a closed type, it is not only easy to accommodate the food filling container in the container, but also the heating operation by irradiating microwaves and the cooling operation are extremely easy. It's easy.

Hereinafter, the present invention will be explained in more detail based on Examples, but the present invention is not limited to the above examples unless it exceeds the gist thereof.

Example 1 A thin polyethylene film with a thickness of 20μ is provided on the outer surface,
40μ thick polyethylene thin film on inner surface, 20μ thick
A flanged inverted truncated conical container (opening part) with a capacity of 200 ml made of 280 μ thick paper with a three-layer laminated film consisting of a partially saponified ethylene-vinyl acetate copolymer thin film and a 40 μ thick polyethylene thin film. Diameter 75mm, bottom wall diameter 64mm, height 56mm),
188 ml of warm water heated to 60°C was added. The opening flange of this container is covered with a lid made of a laminate of a 100μ thick biaxially oriented polystyrene sheet, a 20μ thick ethylene-vinyl acetate copolymer partially saponified thin film, and a 40μ thick polyethylene thin film. ,
Use an ultrasonic adhesive machine (manufactured by Bronson) to attach the flange part.
Glued and sealed using Model 5170).

The above container is made of polymethyl methacrylate, has an opening diameter of 90 mm, a bottom wall diameter of 80 mm, and a height of
It is an inverted cone-shaped container of 70 mm and wall thickness of 7 mm,
The specimen was housed in a container having a large number of through holes of 1 mm in diameter in the wall. The gap formed between the outer circumferential wall of the container and the inner wall of the container was filled with polypropylene spheres with a diameter of 3 to 5 mm and covered (first
(see figure).

The upper container was placed in a commercially available microwave oven (microwave frequency: 2450MHz, 500W) and irradiated with microwaves. The temperature of the water stored in the container is 85
Even when the water temperature reached 98°C, no swelling of the container lid was observed, and no rupture of the container occurred even when the water temperature reached 98°C.

Comparative Example 1 In the same procedure as in the example described in Example 1,
A container filled with water was prepared.

When the container filled with water was placed in the same microwave oven used in Example 1 and started heating without being placed in the container, when the internal temperature of the container reached 75°C, the lid of the container A bulge was observed;
The container burst when the temperature reached 90℃.

The above two examples show that when the method of the present invention is used, even if the food-filled container is heated to a high temperature, the container is less likely to burst. Since high temperature heating is possible, food-filled containers can be sterilized more effectively.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing an example of a state in which a food filling container is housed in a container, the gap is filled with powder and the lid is closed. In the figure, 1 is a food container, 2 is a food product, 3 is a container, 4 is a lid, 5 is a fine hole, 6 is a clamp, and 7 is a powder.

Claims (1)

[Claims] 1. When heating and sterilizing a food-filled container made of a material with low microwave dielectric loss and sealed with food by microwave, the food-filled container is made of a material with low microwave dielectric loss and the wall surface is The food filling container is housed in a container having a plurality of micropores, and a gap formed between the inner wall surface of the container and the outer peripheral wall surface of the food filling container is made of a material with low dielectric loss, and the container wall surface is made of a material with low dielectric loss. Microwave heating characterized in that the container is filled with powder that cannot pass through micropores provided in the container, the container is covered with a lid, and microwaves are irradiated from the outside of the container to heat and sterilize the food-filled container. Sterilization method.