JPS5843771A - Heating method by means of microwaves - Google Patents

Abstract

PURPOSE:When food products of a solid-liquid mixture are heated by the irradiation of microwaves, an electrolyte is added to the liquid component of the food products to permit uniform heating without undesirable local heating. CONSTITUTION:When fish, meat, vegetables, fruits or their cooked products containing solids and liquid are put in vessels made of low microwave dielectric loss, tightly sealed and they are heated by the irradiation of microwaves, an electrolyte such as sodium chloride is added to the liquid component of the food product by 0.03-2wt%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of heating food by microwave irradiation.

More specifically, the present invention relates to the microwave method for preparing solid-liquid mixed foods.

Traditionally, the methods of filling, sterilizing, and preserving food into containers include:
The canning method, the bottle method, the so-called retort preservation method, etc., involve filling food into gas-impermeable containers and sterilizing them by heating.
There are known ways to preserve it.

Heat sterilization of canned or bottled food is carried out using heated water or heated steam at a temperature of around 720° C., and requires heating for a fairly long period of time to exhibit a sterilization effect.

Heating for a long time in this way is not preferable because the flavor and quality of the food will be impaired. In the case of so-called retort food, the food stored in a thin plate bag is shaped into a thin plate, the heating temperature is increased, and the heating time is shortened.
Techniques are used to ensure that the quality of the food is not compromised. However, the containers used in this method are limited to bag-like containers, and there are also restrictions on the foods to which it can be applied.

Recently, a method of heat sterilization of food using microwave irradiation has been proposed (for example, see Japanese Patent Application Laid-open No. 53-HA-4T9, U.S. Patent No. 2. Rigohe! No. 69, etc.), and some of them have been put into practical use. is being considered.

In such a method of heating and sterilizing foods using microwave irradiation, the microwaves are converted into thermal energy while passing through objects with large dielectric loss filled in containers, and the dielectric loss of liquids, solid foods, etc. is reduced. It is used to heat large items.

If the food that is filled in a container and heated by microwave irradiation is a solid-liquid mixed food, only the temperature of the liquid portion increases and the temperature of the solid portion does not follow this.
Even if this was followed, there were problems such as part of the solid portion being heated excessively or not being heated sufficiently.

Under such circumstances, the inventors of the present invention have developed microphone 1,...

As a result of intensive study to provide an improved method for uniformly heating a solid-liquid mixed food by filling it in a container made of a material with low mouth wave dielectric loss and sealing it, irradiating it with microwaves, we have developed this book. This led to the completion of the invention.

Therefore, the gist of the present invention is to provide a method for heating a food-filled container made of a material with low microwave dielectric loss by filling the solid-liquid mixed food with a sealed food container by irradiating the solid-liquid food container with microwaves. A microwave heating method characterized by adding an electrolyte to a liquid component of a liquid mixed food.

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 prepared foods thereof. These contain a liquid component, and is the content of the liquid component 4 tO weight % or more? A preferable range is 2% by weight or less.

This liquid component is not contained in the solid food itself. It may also be something that exists.

In the present invention, an electrolyte is added to the liquid component of the solid-liquid mixed food stored in a container.

When no electrolyte is added to the liquid component, the microwave dielectric loss of this liquid component is generally not so large, so the microwaves are concentrated in the center of the food container.
The disadvantage is that the solid food in this area is overheated.

On the other hand, when a high concentration electrolyte is added to the liquid component, the microwave dielectric loss of this liquid component is large, and the microwave is absorbed by the high concentration electrolyte solution and does not reach the center of the food container. , a problem arises in that the solid food in the central portion is not heated. Therefore, the concentration of the electrolyte added to the liquid component must be selected within a preferred range.

This concentration depends on the type of food, the proportion of solids and liquids in the food,
Various changes can be made depending on the size of the container containing the food, the frequency of the microwave irradiated to the food-filled container, etc. It is best to choose within the range of 2% by weight.

In the present invention, the container that can be used as a food filling container is made of a material with low microwave dielectric loss.

Examples of materials with low microwave dielectric loss include glass, polystyrene, polyethylene, polypropylene, ethylene-vinyl acetate copolymer and partially saponified products thereof, polyethylene terephthalate, polybutylene terephthalate, polycarbonate, and Boriao. kind, poly, yao V, 7
Examples include synthetic resins, paper, etc.
’ is not limited to those listed above.

Food filling containers 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 Utility Model Publication No. 63-r90.
Composite containers made of a laminate of synthetic resin film and paper and a synthetic resin frame, as described in RJ Publication, include inverted truncated cone, polygonal truncated pyramid, inverted truncated pyramid, and others. It may be polyhedral or bag-shaped, and can be selected as appropriate depending on the type of 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 to manufacture the food filling container. do.

In the method of the present invention, a food container filled with food and then sealed is heated by irradiating it with microwaves. Microwaves have a frequency of 30θ to 30.000 megahertz (MHz
).

The frequencies currently permitted for use are 9/jMHz, 441! OMHz.

S/θθMHz and −S/′ 2 j MH2, of which 9/jMEZ and Q41jOMHz are generally used.

The heating temperature when heating by irradiating microwaves according to the method of the present invention is the
2) and food! The temperature should be up to a temperature that can be used to sterilize any residual bacteria that may have adhered to the container.

This temperature varies depending on the type of bacteria contained in the food and the type of bacteria attached to the food container, but
! It is in the range of θ°C.

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 required to kill germs is
depending on the type of fungus.

It can be determined by appropriate experiments.

When food-filled containers are heated by microwave irradiation, they expand and may even burst, so use a cassette to prevent damage and store the food-filled containers in a separately prepared container. It is possible to adopt a method of heating the material while preventing damage using a liquid, powder, compressed air, or the like.

In the method of the present invention, the food-filled container is heated by irradiating the food-filled container with microwaves according to the procedure described above. After heating, it is preferable to cool the food-filled container to a desired temperature as soon as possible.

When using the method of the present invention, since an electrolyte is added to the liquid component of the solid-liquid mixed food, the liquid component to which the electrolyte has been added has a large dielectric loss when irradiated with microwaves. Unable to concentrate, I filled the container. It has the effect of uniformly heating the contents, and has extremely high industrial utility value.

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

Example / Inner diameter Otsu! Cod, height/jO fins in a cylindrical glass container, about 2 in diameter, pre-steamed and then cooled to room temperature! Add the pine mushrooms.

Furthermore, 4t'jOcc of a saline solution having a concentration of 0.7% by weight was added. Thickness in this container! The polypropylene lid of the vessel was placed on top. Two thermocouples were inserted into the center of the glass container to measure the temperature of the liquid and the pine mushroom.

A container filled with the above-mentioned pine mushrooms and saline solution was heated to a frequency of 24t! It was placed in a microwave oven with an output of 0 MHz and an output of zoow, and irradiated with microwaves.

The temperature of the pine mushroom and the temperature of the liquid were measured after a certain period of time had elapsed from the start of microwave irradiation. The results are shown in Table 7.

In the example described in Comparative Example/Example/, microwave irradiation was performed in the same manner as described on the same side, except that the saline solution sealed in a glass container was 1% by weight. The temperature of the pine mushroom and the temperature of the liquid were measured.

The results are shown in Table 1.

Note: Rice temperature difference = liquid (temperature) - pine mushroom (temperature).

According to Table 1, in the example, the temperature difference between the temperature of the pine mushroom and the liquid is extremely small and the temperature of the liquid is heated uniformly, but in the case of the comparative example, this is extremely large, indicating that the heating is not uniform. . □゛Example 2 ゛:'□゛A composite material in which a 10μ thick polypropylene thin film is laminated on the front and back sides of a 300μ thick paper, the inner diameter of the upper opening is 7! An inverted truncated cone-shaped container with a lower inner diameter of 6θ, a height of tOwa, and a capacity of λθO− with 7 flange at the opening was prepared.

In this container, put 6 to 7 pine mushrooms with a diameter of about aO ~ 26 m that have been steamed in advance and cooled to room temperature, and then add a concentration of θ,! A saline solution of % by weight was added to make the weight of the contents contained in the container /op.

The thickness of the open loflazine part of this container! A polypropylene lid was placed on the vessel. A thermocouple was inserted into the container through the lid so that the temperature of the liquid and the temperature of the pine mushrooms could be measured.

Container filled with the above pine mushroom and saline solution at 1 frequency Q4t! It was placed in a microwave oven with an output of soow at OMHz, and irradiated with microwaves.

One minute after the start of microwave irradiation, the temperature of the liquid and the temperature of each pine mushroom were measured. Measurement was carried out using 1.2 containers (container number/%2).

The results are shown in Table 2.

Comparative Example: In the example described in Example 2, a container (container number 3)
Except for using tap water as a substitute for the saline solution in the
Irradiate the ipsilateral side with microwaves in the same manner as described above,
The temperature of the pine mushroom and the temperature of the liquid were measured.

The results are shown in Table 3.

Table - (Example) Table 3 (Comparative example 2) From Table 1 and Table 3, the following is clear.

(1) When the method of the present invention is followed, the standard deviation of the temperature of the pine mushroom is small, indicating that it is heated uniformly.

(2) On the other hand, when no electrolyte is added to the liquid component as in the comparative example, some mushrooms exhibit significantly high temperatures, and the standard deviation of the temperature of mushrooms is large. Local heating cannot be avoided.

Example 3 Composite material cover with a 20μ thick polypropylene thin film laminated on the front and back sides of a 300μ thick paper, the inner diameter of the upper opening? !
Proverb, lower inner diameter tjwm, height 41j, capacity/4tOm
An inverted truncated conical container with 7 lunges at the opening of g was prepared.

Into this container are button-shaped cod mushrooms with a diameter of about 2 lbs that have been steamed, cooled, and then cooled to room temperature! The container was further filled with a saline solution having a concentration of 0.3% by weight.

A three-layer film consisting of polypropylene with a thickness of 10θμ, polyvinyl alcohol with a thickness of 20μ and polypropylene with a thickness of 100μ was sealed on the open bottom 7 flange of this container by ultrasonic welding.゛The food-filled sealed container prepared as above was
m, height 90 mm, thickness / θ It is housed in a cylindrical container with a lid made of cod polymethyl methacrylate, and the gap between the outer wall of the food filling container and the inner wall of the container is filled with air.
It was closed under 3% pressure.

This container has a frequency of 241! OMHz, output! OθW
I placed it in a microwave oven and started irradiating it with microwaves.

The internal temperature of the food filling container containing pine mushrooms is approximately /20
When reaching °C, microwave irradiation was discontinued.

This containment body! After being left at room temperature for a minute, the container was forcibly cooled with cooling water, and the food-filled container was removed from the container.

Even if this food-filled container was left at a constant temperature of 37° C. for two weeks, no change in the color of the contents was observed. Furthermore, when the food-filled container was opened and the status of bacterial growth inside the container was observed, no bacterial growth was observed.

Example In the example described in Example 3, a sodium phosphate aqueous solution with a concentration of 0.09% was used instead of the saline solution sealed in the container, but in the same manner as in the method described in Example 3. Microwave irradiation and post-processing.

Food filled containers heated by microwave irradiation are heated to 32°C.
Even after being left at a constant temperature for one week, no bacteria were observed.

The above results indicate that, as in Example 3, when there is an electrolyte solution of an appropriate concentration in the food container, uniform heating is achieved by microwave irradiation, and the food, container, etc. This indicates that the remaining bacteria that adhered to the sample have been killed.

Approximately 2 in diameter after steaming and cooling to room temperature! Cod mushrooms were added, and a saline solution having a concentration of λ and j% by weight was added and heated.

A three-layer film of the same type as used in Example 3 was placed over the opening of this container, and the container was sealed by ultrasonic welding.

The container thus sealed is placed in a cylindrical container with a lid made of the same polymethyl methacrylate used in Example 3, and the gap between the food-filled container and the inner wall of the container is filled with air. Mu! The noodles were placed under pressure and closed.

This container has a frequency of J, 4tj OM Hz, and an output! Place it in an OθW microwave oven and irradiate it with microwaves.
It was heated until the internal temperature reached about 7.20°C.

After heating, remove the container from the microwave and! After being left at room temperature for a minute, the container was forcibly cooled with cooling water, and the food-filled container was taken out from the container.

After leaving this food-filled container at a constant temperature of 32°C for one week, it was opened and the status of bacterial growth inside the container was observed.
Bacterial growth was observed.

This result shows that when there is an electrolyte solution with too high a concentration in the food filling container, there will be areas where the microwave irradiation is insufficiently heated, resulting in insufficient sterilization.

Claims (2)

[Claims] (1) A heating method using microwaves, which is characterized in that a container made of a material with low microwave dielectric loss is filled with a solid-liquid mixed food, and a sealed food electrolyte is added thereto. (2) The concentration of electrolyte added to the liquid component is θ, Oj
The microwave heating method according to claim 1, wherein the amount is in the range of 2% by weight.