JPS58216681A - Thermal sterilization of packaged food with microwave - Google Patents

Abstract

PURPOSE:To prevent the overheating of the outer part of the packaged food, and prevent the expansion and burst of the packaged food with heat, by contacting the packaged food with air having a proper temperature during the thermal sterilization with microwave radiation, thereby cooling the outer part of the food. CONSTITUTION:The thermal sterilization of the packaged food 2 is carried out by transferring the food 2 by the belt conveyor 1, and irradiating with microwave radiation generated by the microwave generator and emitted from the antenna 7 in the inner air duct 5 of the heating chamber 4. In the course of the thermal sterilization, the air in the air duct 3 is sucked into the air duct 5 by operating the suction fan 12, thereby cooling the outer part of the packaged food 2 under heating and preventing the overheating of the part. The temperature of the air blown to the food 2 is 10-60 deg.C, and is dependent on the intensity of the microwave radiation. Generally, higher intensity of the microwave radiation demands the lower temperature of the air.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for heating and sterilizing packaged foods using microwaves, in particular, during the heat sterilization, air at an appropriate temperature is brought into contact with the packaged food to cool the outer part thereof. The present invention relates to a microwave heat sterilization method for packaged foods that prevents parts from overheating and rupturing the packaged foods.

Microwaves are electromagnetic waves that are also called ultra-high frequency waves.
．． Wavelength of 3-3 cIcm, i.e. 1-100GI
It is said to have a frequency of IZ, and has recently attracted attention as a means of heating food following high-frequency heating, and is being applied to microwave ovens and the like.

Microwaves have a loss coefficient [(permittivity ε) x (permittivity -
Heat generation is small in materials with a small δ)], but materials with a large loss coefficient generate a lot of heat, and because they have the property of reflecting when they hit metal, it is difficult to heat packaged foods using A-size packaging with a small loss coefficient. It is an effective means.

When heating food using microwaves, place the food inside a metal container and radiate microwaves from the magnetron antennas on both sides.The microwaves will be reflected by the metal walls, so the food will be heated from the top, bottom, left and right. It can be irradiated with microwaves and can be heated entirely.

Furthermore, even if food is packaged in materials with a low loss coefficient, such as plastic or paper, microwaves will pass through these packaging materials without absorbing them, so only the food inside can be heated. can. For this reason, microwaves are an effective means for heating packaged foods, especially hermetically packaged foods, for sterilization or cooking.

However, heating by microwaves heats the food from the part where the microwave hits the food, so the packaged food is heated from the outside part. Furthermore, since foods are generally a mixture of many types each having a different loss coefficient, the heat generated by microwaves inside the food tends to be non-uniform. This creates a temperature difference between the outer and inner parts of the packaged food.

Furthermore, in the case of irregularly shaped foods, especially flat shaped foods, for example, in the case of a hamburger steak, the periphery is heated from three directions, while the center is heated from two directions. Although the temperature is high, the central part is not yet heated, and the temperature difference can reach 40°C. Such a temperature difference becomes a fatal defect when heat sterilizing packaged foods, especially hermetically packaged foods. This is because while the center of the food has not yet reached the temperature for heat sterilization, the outer or surrounding parts have already been heated to 100°C, causing water to boil and cause the package to expand or burst. This is because it makes you

In order to prevent the packaging from bursting during heat sterilization, when heat sterilizing packaged foods using microwaves, has it been attempted to place the entire metal gap under pressure?
This method has the disadvantage that not only the equipment itself is expensive, but also the operating costs are high. Furthermore, since the outer or peripheral portion of the food itself is exposed to high temperatures for a long period of time, the outer or peripheral portion becomes harder than the central portion, resulting in a disadvantage in that the texture deteriorates.

Furthermore, in the case of flat packaged foods, heating sterilization using microwaves was attempted by fitting a metal jig into the side of the food, but this method required extra steps to remove and remove the jig. It has the disadvantage of requiring

The present inventors have conducted extensive research to overcome the above-mentioned deficiencies in microwave heat sterilization of packaged foods. They discovered that overheating can be prevented and completed the present invention.

An object of the present invention is to provide a heat sterilization method for heating packaged foods using microwaves in which the entire food is heated uniformly and the package does not expand or burst.

The present invention is directed to a packaged food product which is characterized in that when the packaged food product is heat sterilized by irradiating the packaged food product with microwaves, air is blown onto the packaged food product being heated to prevent the package from expanding or bursting during heating. This is a heat sterilization method.

The present invention also provides a microwave heat sterilization method for packaged food according to item 2, wherein the packaged food is a flat food, and at least a portion of the side surface thereof is coated with a material capable of reflecting microwaves. This is a method for heat sterilization of packaged foods characterized by:

In the microwave heat sterilization of the present invention, the temperature of the air blown onto the packaged food is 10-60°C (preferably 20°C).
The temperature of the air to be blown is related to the strength of the microwave.

Generally, when the strength of microwaves is high, the humidity of the air should be low.

The strength of the microwave is 2 kW or less, preferably i kW or less, particularly preferably 500 W per 100 g of packaged food.
It is as follows. When the strength of the microwave is 2 kW or more, the food heats up too quickly, and blowing air cannot completely suppress overheating, making it impossible to prevent the food packaging from expanding or bursting.

The microwave heat sterilization method for packaged foods of the present invention includes:
It is particularly effective for heat sterilization of hermetically packaged foods, particularly flat-shaped hermetically packaged foods such as hamburger steaks. When heat sterilizing a hermetically packaged food that has a flat shape, it is particularly effective to cover part or all of the sides of the food with a material that can reflect microwaves, such as metal foil such as aluminum foil. . When heating a flat packaged food using microwaves, the flat part of the food is heated from two directions, top and bottom, while the surrounding area of the food is heated from three directions: top, bottom and sides. By coating the sides of the food with a material that can reflect microwaves, microwave heating from the side of the food is blocked, and the food is heated from both the top and bottom directions. Overheating can be prevented.

The material that coats the sides of the flat food product needs to be a material that can reflect microwaves without transmitting them. As such materials, 4. Since aluminum foil is known, it is preferable to use aluminum foil from the viewpoint of cost, but 11. of the present invention. Not limited to aluminum foil or metal foil.

An example of an apparatus for heat sterilization using microwaves according to the present invention will be explained with reference to the drawings.

In Figs. 1 and 6, 1 is a belt conveyor that conveys the packaged food 2, and 6 is a metal ventilation duct on the 1'' side, which also has the function of preventing microwaves from leaking to the outside. . 4 is a heating chamber surrounded by a metal wall to reflect microwaves, and an internal ventilation duct 5 made of a material such as polyethylene that transmits microwaves without absorbing them runs through the heating chamber. .

6 is a microwave generator having an antenna 7;
9 is a waveguide that guides the microwave to the heating chamber 4, and 9 is a stirrer that stirs the microwave within the heating chamber 4. Reference numeral 10 denotes a metal outlet-side ventilation duct, which also has the function of preventing leakage of microwaves to the outside.

In FIG. 1, 11 is a metal suction duct;
is a fan for air suction, and the air duct 6 on the inlet side
Air is blown from the internal ventilation duct 5 to the outlet 1-. ．． I
The air is blown inside the side air duct 10.

In FIG. 6, 16 is an air circulation duct, 14 is an air circulation fan, 15 is a temperature control device, and 16 is a damper that adjusts the speed of the circulating air flow.

Furthermore, 17 is an outside air intake port.

In FIGS. 1 and 6, when the heald conveyor 1 is moved in the direction of the arrow and the packaged food 2 is placed on the left end, the packaged food 2 passes through the internal ventilation duct 5 from the ventilation duct 6 on the entrance side. It is sent to the side ventilation duct 10. The microwaves generated by the antenna 7 of the microwave generator 6 are sent to the heating chamber 4 through the waveguide 8 and are scattered inside the chamber by the starter 9, but the microwaves are scattered by the metal surrounding the heating chamber 4. Reflected on the wall, polyethylene internal ventilation duct 5
The packaged food 2 passing through is irradiated from the top, bottom, left and right directions to heat the packaged food 2.

In FIG. 1, while the packaged food is being heated in the internal ventilation duct 5, the suction fan 12 is operated to suck the air inside each duct, and as a result, the air is blown into each duct.

That is, the air in the ventilation duct 6 on the population side taken in from the entrance is sucked into the ventilation duct 5, cools the outside part of the packaged food 2 that is being heated, and prevents the outside part of the packaged food 2 from overheating. The air is sucked from the suction duct 11 to the suction fan 12 . Further, the air taken in from the outlet and inside the outlet-side ventilation duct 10 contacts the packaged food 2 that has been heated in the exit-side ventilation duct 10 in a countercurrent manner, cooling it while passing through the suction duct 11. The air is sucked by the suction fan 12. In FIG. 6, while the packaged food 2 is being heated in the internal ventilation duct 5, by operating the air circulation fan 14, the air circulation duct 16 (outlet side ventilation duct) 10s internal ventilation duct 5. Circulating air through the ventilation duct 6 and the air circulation duct 16 on the "Person 1" side,
Air is blown onto the packaged food 2 that is being heated by microwaves.

This cools the outer part of the packaged food 2 that is being heated and prevents the outer part from overheating.

If the air temperature is out of a predetermined temperature range, the temperature control device 15 is activated, and if the wind speed is out of the predetermined range, the damper 16 is adjusted.

Of course, these adjustments can also be made automatically by connecting a terminal device such as a suitable detector to a computer.

Again in FIGS. 1 and 6, the packaged food 2 that has been heat sterilized is taken out from the air duct 10 on the exit side.

Next, some specific examples of packaged foods in which at least a portion of the side surfaces are coated with metal foil when heat sterilizing flat packaged foods in the present invention will be described with reference to the drawings.

Figure 2 shows an example of using a packaging material in which plastic film is laminated with aluminum foil.

FIG. 2B is a longitudinal cross-sectional view of a packaged hamburger steak, where 21 is the hamburger steak, 22 is the part whose side surface 1 is covered with aluminum foil, and 26 is the flat part. , the part wrapped in plastic film without aluminum foil.

The packaged hamburger steak shown in Figure 2B is made by placing the hamburger steak in the bag-shaped packaging shown in Figure 2A and vacuum packaging the entire steak.

Packaging 4J' 11 of the 21st MA is a packaging made of plastic film laminated with aluminum foil, but after packaging, the part 23 corresponding to the flat shaped part of the hamburger steak is not laminated with aluminum foil, but only with plastic film. be.

Figure 6 is an example of a packaged food product in which a hamburger steak wrapped in plastic film is further wrapped in aluminum foil.

FIG. 6 13 is a vertical cross-sectional view of the packaged food after double packaging, where 31 is a hamburger steak, 32 is the plastic film in which it was wrapped, and 6ro is a hamburger steak wrapped in a plus deck film. The aluminum foil 66 used for wrapping the hamburger steak is provided with an opening 34 at a portion corresponding to the flattened portion of the hamburger steak.

In this example, a plastic film laminated with aluminum foil can be used instead of the aluminum foil 33, and the opening portion 64 may be made of only a plastic film without the aluminum foil 33. The double-wrapped food product shown in FIG. 6B is produced by placing a hamburger steak vacuum-packed with a plastic film into the packaging box shown in FIG. 3A, and then sealing the portion 65.

FIGS. 4 and 5 show an example of a packaged food in which only the sides of a hamburger steak are covered with aluminum foil when the steak is packaged.

FIG. 4C is a longitudinal cross-sectional view of the packaged food, where 41 is a hamburger steak and 42 is a cylindrical ring-shaped aluminum foil covering the side surface of the packaged food, which has the shape shown in FIG. 4A. 46 is a plastic film of the type shown in FIG. 4B, and 44 is a plastic film that seals the upper surface of the film.

The packaged food shown in FIG.
around the cylindrical ring-shaped metal foil 4 shown in FIG. 4A.
2, a hamburger steak 41 is placed therein, a plastic film 44 is placed on top of the hamburger steak 41, and the whole is vacuum packaged.

FIG. 5B is a longitudinal cross-sectional view of the packaged food, in which 51 is a hamburger steak, 52 is a metal foil covering the sides of the food, and 56 is a plastic film wrapping the whole food.

The packaged food shown in FIG. 5-13 is made by placing a disc ring-shaped aluminum foil 52 (Z and 52b) above and below the hamburger steak 51 shown in FIG. 5A, and placing a plastic film 56 above and below it. It is made by vacuum packaging the entire product.

In the specific example below, a hamburger steak is used as an example of a flat-shaped food, and aluminum foil is used as an example of metal foil, but other flat-shaped foods are used instead of the hamburger steak, and Other metal foils can be used instead of aluminum foil. Further, instead of the metal foil, a layer that reflects microwaves but does not transmit them can also be used. Also, in place of the plastic film of the packaging material, other coating materials with a small loss coefficient can be used.

The microwave heat sterilizer shown in Fig. 1 is mounted on Fig. 4 G, and air at a temperature of 22°C is sent cocurrently at a wind speed of 477 L/sec, and sterilized while being irradiated with microwaves under the conditions shown in the table below. did. The results are shown in the table below, and a product that can be stored for 0 days at a temperature of 10'C was obtained.

In order to obtain a shelf life of 10'C and 30 days, the conventional method
It required immersion in boiling water at 8°C for 6D minutes, but
In this example, it was possible to sterilize the product in 7 minutes or less so that it had the same shelf life.

table

[Brief explanation of the drawing]

FIG. 1 is a side view of a specific example of an apparatus for heat sterilization of the present invention, FIG. 2A is a perspective view of a packaging material for packaged food to be heat sterilized in a specific example of the present invention, and FIG. 2B is a , a vertical cross-sectional view of a packaged food to be heat sterilized in an example of the present invention;
FIG. 6A is a perspective view of a packaging material for a packaged food to be heat sterilized in a specific example of the present invention, FIG. 6B is a longitudinal sectional view of a packaged food to be heat sterilized in a specific example of the present invention, and FIG. 4A FIG. 4 is a perspective view of a cylindrical ring-shaped aluminum foil used for packaging packaged food to be heat sterilized in one embodiment of the present invention.
3 is a perspective view of a package 44 of nine packaged items to be heat sterilized in one embodiment of the present invention, FIG. FIG. 5 is a partial perspective view of the material of the packaged food to be heat sterilized in one embodiment of the present invention, and FIG. 5 is a vertical sectional view of the packaged food to be heat sterilized in one embodiment of the present invention. FIG. 6 is a side view of another specific example of the apparatus for heat sterilization of the present invention. 1: Belt conveyor 21.31.41.51: Humber 2: Packaged food Gusteakro:
Inlet side ventilation duct 22 Part covered with aluminum foil 4: Heating chamber 23 Part covered with aluminum foil 5:
Internal ventilation duct Covered part 6: Microwave generator 32.4644.53: Blastin 9:
Stirrer Kufilm 10: Exit 1" side ventilation duct 6 Ro, 42.52 Ni Aluminum foil 12: Suction fan 64 2 open "1 part 45: Searching part 1,)) Applicant H wooden frame A name polishing cost Ka ! Person 斤り士 Tsu 1) Showl J Soto 3 屓 A 3rd fertilizer 8 Long' irises Flour 4 椙C L ふ 5 Gi: 15 ノ1%A

Claims (1)

[Claims] (1) In the heat sterilization method in which packaged food is irradiated with microwaves, air at a humidity of 10-60°C is blown onto the food while it is being heated, thereby reducing the expansion of the packaged food during heating. A heat sterilization method characterized by preventing rupture. (2) The heat sterilization method according to claim 1, wherein the microwave intensity is 2 kW or less per 100 g of food. (6) The heat sterilization method according to item 1 or 2 of the scope of patent Ii, characterized in that the wind speed is 2 m/sec or more. (4) Any one of claims 1 to 6, characterized in that the packaged food is a flat-shaped food, and at least a portion of its side surface is coated with a material that reflects microwaves. Heat sterilization method described in Crab. (5) Packaged food is packaged by placing a cylindrical ring-shaped foil made of a material that reflects microwaves on the side of the flat food and wrapping it with a material that transmits microwaves. The heat sterilization method according to claim 4, characterized in that: (6) For packaged foods, a disk-shaped ring made of foil made of a microwave-reflecting material is placed on the top and bottom surfaces of the flat food so that the edge of the disk protrudes beyond the edge of the flat food. The heat sterilization method according to claim 4, wherein the method is packaged with a material that does not transmit microwaves. (h) The heat sterilization method according to any one of claims 4 to 6, characterized in that the material that reflects microwaves is metal foil. (8) The metal foil is aluminum foil. (9) The heat sterilization method according to claim 7, characterized in that the food in a flat form is a hamburger steak. Heat sterilization method described in Crab.