JPS5813372A - Heat sterilization method using microwave - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for heat sterilization using microwaves, and more specifically, the present invention relates to a heat sterilization method using microwaves.
The present invention relates to an improved heat sterilization method that prevents a sealed container from bursting during heat sterilization by irradiating microwaves.

In recent years, not only have there been an increase in the variety of foods that can be canned or bottled, but containers for housing these foods have also been developed using many different materials. Foods stored in containers often go through a sterilization process before being distributed.

Traditionally known sterilization methods, such as aseptic filling,
There are two main types of methods: a method in which a previously sterilized food is filled into a container that has also been sterilized in advance, and a method in which the food and the container are sterilized together after the food is filled into the container.

The latter sterilization method is the same as that used in the can manufacturing process.
In both methods, care is taken to prevent the container from bursting even if the internal pressure inside the container increases during heat sterilization. That is, in the case of can manufacturing, a high-strength metal plate is selected as the material for can manufacturing, and the conditions of heat sterilization temperature of 771120° C. or lower are also selected. 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 food sterilization method using microwave irradiation has been proposed (see, for example, Japanese Patent Laid-Open No. 33-27 Zageta, U.S. Pat. is being considered. Even in such heat sterilization methods of 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 heat radiation, it is not possible to use a container made of a metal material with high strength, so a container made of a non-metallic material that is not very strong and has low microwave dielectric loss must be used. No. 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, without sealing the container, heat the food only to a certain extent to prolong its shelf life, or even if the container is sealed, sterilize it by heating at a temperature below 100 degrees Celsius, according to Tokkai Sho! As proposed in Publication No. 2-TG71#,
At present, when food-filled containers are heated and sterilized by microwave irradiation, the pressure difference between the pressure inside the food-filled containers and the microwave irradiation chamber is reduced to prevent the containers from bursting.

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 in the case of a sealed food container like the latter, if the heat sterilization temperature is 100°C or lower, according to the inventors' experimental results, food with a pH of 70°C or lower cannot be added. 1.
.

Bacterial growth after heat sterilization is extremely small, but it was found that for foods with a higher pH than this, bacterial growth after heat sterilization was found in dogs. Furthermore, JP-A-3.2-617r
As described in Publication No. J, even if a method of sterilization is adopted by reducing the pressure difference between the pressure of the food filling container and the microwave irradiation chamber, heating spots may occur if there is a gaseous portion inside the container. The disadvantage is that complete sterilization cannot be achieved. In other words, what is heated by microwave irradiation is
The food in the food-filled container is hardly heated at the gas portion of the container wall that does not come into contact with the food. This is because the container wall is made of a material with low microwave dielectric loss, and because the wall is thin, the heat is dissipated with good heat dissipation efficiency.

Therefore, by leaving the food-filled container still or placing it on a conveyor belt and irradiating it with microwaves, the temperature of the food inside the container can be raised to a temperature that does not allow the survival of germs. However, since the wall portion of the food-filled container that is in contact with the internal gas is at a low temperature, residual bacteria adhering to the inner wall will not be killed. Moreover, if microwave irradiation is continued, the food filled in the container will be heated above the appropriate temperature and deteriorate, and the moisture contained in the food will turn into steam and the vapor pressure will become excessive.

The present inventors have completed the present invention as a result of extensive studies aimed at providing a microwave heat sterilization method that eliminates the drawbacks of conventional techniques.

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 and sealing the food-filled container by microwave. The container is housed in a container made of a material with a small microwave dielectric loss, and 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 a liquid having a large dielectric loss and closed. The present invention resides in a microwave heat sterilization method characterized in that the food filling container is heat sterilized by irradiating microwaves from the outside of the container.

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 normally canned, such as seafood, meat, vegetables, fruits, and fresh sweets. All of them preferably contain a liquid component.

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

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 disclosed in Japanese Utility Model Application Publication No. 1983-J'riogs. Composite containers made of a laminated product of paper and paper, plastic containers made of synthetic resin materials, and a frame made of synthetic resin, etc., are listed.

The shape of the food filling container may be cylindrical, polygonal prism, truncated cone, inverted truncated cone, polygonal truncated pyramid, inverted polygonal truncated pyramid, or other polyhedral shape, and is selected as appropriate depending on the food. be able to.

In the method of the present invention, the food filling container is filled with food and sealed by appropriate means.

Separately prepared food containers filled with food and sealed,
It is housed in a container made of a material with low microwave dielectric loss.

The materials that make up the entire container have low microwave dielectric loss.
The material can be appropriately selected from materials suitable for manufacturing the food filling container. The container may have 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 with low microwave dielectric loss. It's fine. Since this housing body accommodates the food filling container, the size of the housing portion of the housing body is such that a space is formed even when the food filling container is housed therein. The container can also be a dog cage capable of accommodating a plurality of food-filled containers.

In the method of the present invention, a food-filled container is housed in a container, and a gap formed between the inner wall surface of the container and the outer peripheral wall surface of the food-filled container is filled with a liquid having a large dielectric loss and closed.

Examples of liquids with large dielectric loss include water and an aqueous solution containing an electrolyte such as sodium chloride. These liquids may be heated to a predetermined temperature in advance. To close the container, it is preferable to place a backing over the opening of the container, place the lid on top of the backing, and use an auxiliary tool such as a bolt nut or a spring to tighten the backing.

FIG. 1 is a longitudinal cross-sectional view showing an example of a state in which a food filling container is accommodated in the container, the gap is filled with liquid, and the container is closed. In the figure, / indicates the food container, λ indicates the food, 3 indicates the gas portion, t indicates the 9 bodies contained, y indicates the liquid, Otsu indicates the lid, 7 indicates the backing, g indicates the bolt, and ri indicates the naratra.

In the method of the present invention, as illustrated in FIG. 1, a food-filled container is housed in a container, the gap in the container is filled with a liquid with a large dielectric loss, and the container is closed. Irradiate with microwaves. Microwaves have frequencies in the range of 300 to 30,000 megahertz (Mn2). In this frequency range, use for purposes other than detection is currently permitted: Ri/, t Mn2
Microwaves irradiated from the outside of the container pass through the wall of the container with small dielectric loss, heat the liquid while passing through the liquid with large dielectric loss, and the attenuated microwaves penetrate the wall of the food-filled container. It passes through, reaches the food, and heats the food as well.

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 in the food stored in the food container and the residual bacteria adhering to the food container. This temperature varies depending on the type of microorganisms contained in the food, the type of microorganisms adhering to the food container, etc.
The range is from ℃ to 130℃. The heating time may be at least a time sufficient to kill microorganisms within the above temperature range, and within that range, the heating time is preferably as short as possible. The time period during which microorganisms can be killed can be determined by appropriate experiments depending on the type of microorganism.

After heating and sterilizing the food by irradiating it with microwaves, open the container, let the liquid that filled the cavity of the container flow out, and then take out the food filling container and adjust the temperature of the stored food as soon as possible. , it is preferable to cool it to around room temperature.

The method of the present invention has the following characteristics, and its industrial utility value is extremely high.

(1) When using the method of the present invention, the food-filled container is housed in the container, the cavity of the container is filled with liquid, the container is closed, and the food-filled container is heated and sterilized by irradiation with microwaves. Even if the internal pressure of the beam increases, the beam will not break/slide.

(2) When using the method of the present invention, even if there is a gaseous portion in the food filling container that does not come into contact with the food, the container wall in this gaseous portion is heated by the liquid filled in the container, so that no adhesion occurs. It is possible to completely kill all the germs that are present, and complete sterilization can be achieved.

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

Example: An inverted truncated conical container with a capacity of isoml and 7 flanges, made of paper 300μ thick, with a polypropylene thin film 20μ thick on the outer surface and a goμ thick polypropylene thin film on the inner surface. , soybean pog and 100 ml of water were placed in the container, and a polypropylene film with a thickness of 200 μm was layered on the opening flange of this container, and the container was sealed by heat-bonding.

As above, the food light filled with food and sealed □□, □−
１．Yo□□Wow.

It was housed in a lidded container made of polypropylene (see figure 7 in Fig. 7) with a thickness of 0 mrn and a capacity of 0 ml, and the cavity was filled with water, as shown in the longitudinal section in Fig. 1. The lid was overturned via the packing 7, and the lid was fixed with bolts and nuts to close the container.

The above container was placed in a commercially available microwave oven (microwave frequency 2.≠DMn2), heated to the internal temperature of the food filling container f/30°C, and held at this temperature for 5 minutes to sterilize it. . After 5 minutes had passed, the container was removed from the microwave oven, the nut was removed from the bolt of the container, the lid was removed, water was poured out, and the food-filled container was taken out. The food-filled container did not burst, and no deformation such as expansion was observed. The food-filled container after heat sterilization was rapidly cooled with cold water.

Even when the food-filled container after sterilization was left at a constant temperature of 37° C. for two weeks, no change in the color of the contents was observed. ! ! In addition, when the food-filled container was opened and the status of bacterial growth inside the container was observed, no bacteria were observed.

Comparative Example 1 A food-filled container was prepared in the same manner as in the example described in Example.

When this food-filled container was placed in the same microwave oven used in Example 1 to begin heating, the internal temperature of the food-filled container reached 10j'C.
My food container burst.

Example λ The outer layer has a polyamide thin film with a thickness of 10 μm, and the inner layer has a polyamide thin film with a thickness of 10 μm.
A bag-like container was prepared from a laminated film with a thin polyethylene film of μ. This bag-like container was filled with 1 ml of commercially available soy milk (Mapron, manufactured by Mitsubishi Chemical Industries, Ltd.), and the opening was sealed by thermal bonding.

This food filling container is housed in the same lidded polypropylene container used in Example 1, and the cavity is filled with water.
It was heated and sterilized under the same conditions as in the example described in Example.

The food-filled container was not damaged.The food-filled container after heat sterilization was rapidly cooled with cold water.

Even when the food-filled container after sterilization was left at a constant temperature of 37° C. for λ weeks, no change in the color of the contents was observed. Furthermore, when the food-filled containers were opened and the status of bacterial growth inside the containers was observed, no bacteria were observed at all.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing an example of a state in which a food filling container is housed in a container and the gap is filled with liquid and closed according to the method of the present invention. In the figure, l is the food container, c is the food, 3 is the gas part,
G is the container, j is the liquid, O is the lid, 7 is the backing, ♂
indicates bolt, ri indicates oak), respectively. Applicant Mitsubishi Monsite Kasei Co., Ltd. 15- Ko 1 Figure

Claims (2)

[Claims] (1) A food-filled container made of a material with low microwave dielectric loss is filled with food and sealed, and the food-filled container is heated and sterilized using microwaves.
The microwave is housed in a container made of a material with low dielectric loss, and 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 a liquid with large dielectric loss and closed; A method for heat sterilization using microwaves, characterized in that the food filling container is heat sterilized by irradiating microwaves from the outside of the container. (2) The microwave heat sterilization method according to claim 1, wherein the liquid having a large dielectric loss is water.