JP2004275141A - Method for heating packaged food and apparatus therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for uniformly and efficiently heating a food packaged in a container by high-frequency dielectric heating while preventing a spark-induced damage of the container to lose the sterilized sealing and provide an apparatus for the heating of the packaged food. <P>SOLUTION: A packaged material 9 produced by packaging a food (cooked rice) 7 in a container 6 is placed between a pair of electrodes 31, 32. At least one of the electrodes 31 is pressed against a lid 8 of the packaged material 9 with a pressing mechanism such as an actuator 38 to essentially eliminate the gap such as head space 39 between the electrodes 31, 32. A high-frequency voltage is applied from a high-frequency power source 33 to effect the thermal sterilization of the cooked rice 7 by the high-frequency dielectric heating. There is essentially no head space 39 and, accordingly, the heating efficiency is improved, the uneven heating is prevented and the discharging phenomenon to cause the damage of the lid material 8 and the container 6 is prevented. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for sterilizing packaged food.
[0002]
[Prior art]
BACKGROUND ART Conventionally, foods such as cooked rice and prepared foods have been distributed and marketed after being filled in tray-shaped or cup-shaped containers and then sealed by sealing a lid material. In order to prevent the package from containing oxygen that degrades the quality of food, the air remaining in the remaining space, such as the head space or the gap between foods, is inerted with nitrogen gas, etc., prior to sealing the container with the lid. Replacement with gas has been performed. By such gas replacement with an inert gas, it is possible to greatly reduce (for example, to about 0.2%) the oxygen present in air at about 20%.
[0003]
In order to remove oxygen still remaining in a head space or the like in a container, it has been proposed that the container itself contains iron powder and the iron powder absorbs oxygen. However, it takes many days for the iron powder to completely absorb the oxygen remaining in the container, during which time the food may be degraded by the remaining oxygen. In the food packaging process, measures against bacteria floating in the air, such as treatment in sterile air, have been taken, but it is difficult to completely sterilize the atmosphere.
[0004]
In consideration of the above circumstances, food such as cooked rice at a temperature of 40 ° C to 50 ° C at the time of hermetic packaging is reheated from 60 ° C to a maximum of about 90 ° C by increasing the temperature by 20 ° C to 40 ° C as post-heating, It has been studied to sterilize various germs such as mold. It is conceivable that the reheating of the packaged food is usually carried out by passing the packaged food through a heating tunnel which is disposed in the middle of the container and has a high temperature when the package is carried out. However, the reheating using a heating tunnel requires a long heating distance and a long passing time for heating, thus increasing the length of the heating tunnel and preparing a recooling step for recooling to about 50 ° C. There is a problem that enlargement of the size cannot be avoided.
[0005]
Other methods of reheating the food in the package include microwave heating and high-frequency dielectric heating. Heating by microwave heating has a problem that it is difficult to heat the whole food without unevenness due to local heating due to a short wavelength. On the other hand, high-frequency dielectric heating is advantageous in that such heating unevenness does not occur and a large space is not required as a heating station. As an example of heating the packaged food by high-frequency dielectric heating, after filling the container with the food in a non-aseptic filling process having a plurality of filling series, sealing in a shell, the frequency of 1 MHz to several GHz generated by a high-frequency oscillator There has been proposed a method for producing sterilized food in which food in a container is sterilized by dielectric heating in an electric field (see Patent Document 1).
[0006]
According to the method for producing sterilized food by high-frequency dielectric heating, as shown in FIG. 4, the sterilizer 50 has a vacuum tube-type high-frequency oscillator 52 with a frequency of 13.56 MHz and an output of 7 kW. The heating unit 54 is connected via a tuning circuit 53 including a variable capacitance capacitor and a variable impedance coil. The heating unit 54 includes an upper electrode plate 55a and a lower electrode plate 55b, which are two upper and lower electrode plates, and a shell 56 formed of an insulator. The high-frequency oscillator 52 is connected to the upper electrode plate 55a via the tuning circuit 53, and the lower electrode plate 55b is grounded. A press cylinder 57 is connected to the upper electrode plate 55a, and can be pressed toward the lower electrode plate 55b. The shell 56 is located between the upper electrode plate 55a and the lower electrode plate 55b, and has a space for disposing a sample to be heated in the center thereof. After the space at the center of the shell 56 is sealed, high-frequency oscillation is performed by the high-frequency oscillator 52, so that the food in the shell 56 is heated.
[0007]
Foods are sterilized in a short time, and many kinds of sterilized foods can be easily manufactured continuously or simultaneously. Since the process is performed with the upper and lower shells simply sandwiched between electrodes, a head space usually remains in the container sealed with the lid material. FIG. 5 is a side view showing a state where a package in which food (rice cooked rice) is packaged in a container is heated by conventional high-frequency dielectric heating. The package 9 is placed in a state of being sandwiched between electrode plates 31 and 32 each having a surface extending over the entire surface of the lid 8 and the bottom 37. The electrode plates 31 and 32 are connected to a high-frequency power supply 33 by wiring 34. If the head space 39 remains above the cooked rice 7 in the container 6, the dielectric heating efficiency at the time of high-frequency dielectric heating deteriorates. Further, if the thickness of the cooked rice 7 varies depending on the location even in the same package 9, the heating temperature varies depending on the thickness, so that the cooked rice 7 has temperature unevenness. Further, when the steam generated by heating the cooked rice 7 is included in the head space 39 during the dielectric heating, a discharge phenomenon may occur, and damage to the container 6 and the lid member 8 such as generation of holes due to sparks may occur. It becomes a problem. Further, at the time of high-frequency dielectric heating, a pressure rise occurs inside the container 6 due to the temperature rise or the generation of steam. Therefore, it is necessary to consider a measure against the pressure rise.
[0008]
In order to make the height of the headspace uniform, it is conceivable to press the food surface with a Teflon (registered trademark) processing press plate before sealing and sealing the lid, but if the food is cooked rice There is a possibility that the grain of cooked rice may be crushed at the time of direct pressing by the pressing plate, thereby lowering the commercial value.
[0009]
[Patent Document 1]
JP-A-10-262624 (paragraphs [0043]-[0045], FIG. 4)
[0010]
[Problems to be solved by the invention]
Therefore, when high-frequency dielectric heating having various advantages is employed as the reheating means, when a food packaged in a container is heated by high-frequency dielectric heating, a space such as a head space in the container is generated between the electrodes. There is a problem to be solved in order to increase the heating efficiency of the food and to secure the uniformity of the heating, and to prevent the occurrence of the discharge phenomenon which causes the damage of the container, by minimizing the amount of heat generated. .
[0011]
An object of the present invention is to efficiently and uniformly heat food packaged in a container by high-frequency dielectric heating, and to prevent damage to the container that would cause sterilization and sealing to occur due to sparks. An object of the present invention is to provide a method and an apparatus for heating packaged food.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, a method for heating packaged food according to the present invention includes a high-frequency voltage between the electrodes in a state where a package made of a food and a container for containing the food is sandwiched between two opposed electrodes. In the method of heating a packaged food for heat sterilizing the packaged food by applying pressure, by pressing at least one of the electrodes against the package, a gap other than the food is substantially formed between the electrodes. And applying the high-frequency voltage in a state without any problem.
[0013]
According to this method of heating packaged food, a package consisting of a food and a container for accommodating the food is sandwiched between two opposing electrodes, and at least one electrode is pressed against the package, so that the food is placed between the electrodes. In this state, a high-frequency voltage is applied between both electrodes. By making a state in which substantially no gap exists between the electrodes, the food having a uniform thickness can be heat-sterilized efficiently and uniformly. In addition, since such a state makes it possible for the headspace to be substantially nonexistent, the high-frequency dielectric heating may cause damage to the container in the headspace due to the vaporized water in the food. It is possible to prevent the generation of potential sparks.
[0014]
The apparatus for heating packaged food according to the present invention comprises two opposing electrodes sandwiching a package consisting of a food and a container for accommodating the food, and a high-frequency voltage between the electrodes for heating and sterilizing the packaged food. A high-frequency power supply for applying a high-frequency voltage, and applying the high-frequency voltage in a state in which substantially no void other than the food is formed between the electrodes, at least one of the electrodes is It is provided with a pressing mechanism for pressing the package.
[0015]
According to the packaged food heating device, the package composed of the food and the container for accommodating the food is placed between the two opposed electrodes. In this state, the pressing mechanism is operated, and at least one electrode is pressed against the container so that a gap other than the food is not substantially formed between the electrodes. Since a high frequency voltage is applied between the electrodes from the high frequency power supply, the food is heat-sterilized by dielectric heating. Since there is substantially no gap between the electrodes, the food can be efficiently and uniformly sterilized by heating. Also, since there is virtually no headspace, sparks that can damage the container in the headspace can also occur in the headspace due to the vapors of moisture in the food during high frequency dielectric heating. Can be prevented.
[0016]
In this method of heating packaged food, the container is a tray-shaped container that is hermetically sealed by welding a lid material to a flange portion around the opening, and the electrode or the tray-shaped member disposed on the lid material side. The electrodes arranged on the bottom side of the container can be pressed against the lid or the bottom of the tray-shaped container, respectively. In this packaged food heating apparatus, the container is a tray-shaped container that is hermetically sealed by welding a lid material to a flange around the opening, and the pressing mechanism is disposed on the lid material side. The electrode disposed on the bottom of the tray-shaped container or the electrode may be pressed against the bottom of the tray-shaped container. The tray-shaped container has a wide mouth, and the inside of the container is hermetically sealed by welding a lid material covering the opening to a flange formed around the opening. When the lid is pressed by the electrode, the lid is deformed to the inside of the container, so that the gas inside the container is compressed and moves to the side, so that the gap between the lid and the top surface of the packaged food is reached. The head space that tends to be formed in the head can be reduced as much as possible. Further, when the bottom of the container is pressed with the electrode, the bottom is deformed in a lifting manner to push up the packaged food, so that the lid and the top surface of the packaged food are pressed in the same manner as when the lid is pressed. The head space that tends to be formed therebetween can be reduced as much as possible.
[0017]
In this method and apparatus for heating packaged food, the food can be cooked rice. The rice grains of freshly cooked cooked rice are very easily crushed. Even with freshly cooked rice, it is expected that the influence is reduced as much as possible by pressing the electrode from the outside of the container to reduce the head space as compared with the case where rice grains are directly pressed.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a method and an apparatus for heating packaged food according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic side view showing a main part of one embodiment of a packaged food heating apparatus according to the present invention, and FIG. 2 is a schematic side view showing a main part of another embodiment of a packaged food heating apparatus according to the present invention. FIG. 3 is a schematic side view showing a gas replacement packaging apparatus to which the packaged food heating apparatus according to the present invention is applied subsequently.
[0019]
Before describing the packaged food heating apparatus according to the present invention, the gas replacement packaging apparatus shown in FIG. 3 to which the packaged food heating apparatus according to the present invention is applied subsequently will be described. The gas displacement packaging apparatus 1 shown in FIG. 3 is applied to an aseptic filling and sealing step, and is made of a synthetic resin such as polypropylene or the like which has been subjected to heat welding or has been treated, and is formed into a tray-shaped container 6 (one). In the following description, a reference numeral is given only to the portion. A rice container 7 (refer to FIGS. 1 and 2) is filled with rice 7 (refer to FIGS. 1 and 2), and the remaining space such as the head space of the container 6 containing the rice 7 as a content is filled. A package 9 in which cooked rice 7 is sealed in a container 6 by heat-sealing a lid member 8 made of a synthetic resin film that has been heat-sealed or treated in a state where the gas is replaced with an inert gas such as nitrogen gas. This is an apparatus for manufacturing. The gas replacement packaging apparatus 1 includes a container and contents transfer station 2, a chamber station 3 for performing spraying of steam and nitrogen gas as an inert replacement gas, and a container containing cooked rice 7 in order in the transport direction. 6 is provided with a sealing station 4 for heat-sealing the lid 8 and a package removing station 5 for removing the package 9 of the cooked rice 7 sealed with the lid 8.
[0020]
The container and contents transfer station 2 is configured as a sterile closed space including a transfer portion 2a of the container 6 and a contents filling portion 2b located downstream of the transfer portion 2a for filling the rice 7 as the contents. ing. Although not shown, the container and contents transfer station 2 is entirely surrounded by a chamber, and sterile air is supplied to the inside thereof, and the container 6 is sterilized to be sterile. In the transfer section 2a, the container 6 is supplied onto a receiving table 16 as a container holder described later by a container supply mechanism (not shown). The container 6 placed on the cradle 16 is filled with cooked rice 7 as a content in the content filling section 2b.
[0021]
The chamber station 3 is a station for spraying steam and nitrogen gas as an inert gas onto the container 6 containing the cooked rice 7. Nitrogen is supplied to the inside and is appropriately exhausted. Put in the atmosphere. In the chamber station 3, a chamber 10 is provided, and when the containers 6 containing the cooked rice 7 supported by the receiving table 16 are sequentially conveyed, the chamber 10 is placed in a remaining space such as the head space of the containers 6 passing therethrough. The remaining air is replaced with nitrogen gas.
[0022]
Each of the above-mentioned container and contents transfer station 2, chamber station 3, closing station 4, and package taking-out station 5 is connected to the transport path of the upper traveling portion 15d of the transport device 15 such as a magnetic conveyor. Are arranged in order along. The transfer device 15 includes a drive sprocket 15a, a driven sprocket 15b, and a chain 15c wound around the drive sprocket 15a and the driven sprocket 15b. The container 6 is transported together with the cradle 16 by attracting the magnet provided in the container 16. Thereafter, the cradle 16 is appropriately washed and dried while being conveyed through the lower traveling portion 15f, and is carried into the container and contents transfer station 2 at a position returning to the upper traveling portion 15e.
[0023]
The closing station 4 includes a cover material roll 12 on which the cover material 8 is wound, and a surplus cover material winding unit 13 for winding a cover material surplus portion 8a generated by cutting the cover material 8. A seal mechanism 20 is provided between the lid roll 12 and the surplus lid winding section 13. The lid 8 is sterilized by a UV lamp (not shown) before heat sealing, and is conveyed through a sterile space covered with a cover (not shown). The sealing mechanism 20 includes, in order from the upstream side, a first seal portion 21 for applying an annular heat seal around an opening in the container 6 containing the cooked rice 7 to the lid material 8 fed from the lid material roll 12, and a first seal portion 21. A second seal portion 22 disposed downstream of the portion 21 in the transport direction; a cooling portion 23 disposed downstream of the second seal portion 22 to cool a heat-sealed seal region; And a lid material cutting portion 24 for cutting the lid material 8 while trimming the lid material 8 for each container 6.
[0024]
After the package 9 is taken out at the package take-out station 5, the package 9 is once cooled, and then subjected to a high-frequency dielectric heating treatment by a packaged food heat sterilizer as illustrated in FIG. 1 or FIG. . In the high-frequency dielectric heating treatment, it is preferable to batch-treat a plurality of packages 9 by batch processing.
[0025]
As shown in FIG. 1, the packaged food heat sterilizer 30 is connected to two electrode plates 31, 32 for high-frequency dielectric heating and connected to the electrode plates 31, 32 by wirings 34, and applies a high-frequency voltage. An oscillator 33 as a high-frequency power supply is provided. The container 6 for accommodating the cooked rice 7 is a tray-shaped container having a flange portion 36 formed around the wide-opening portion 35, and the lid member 8 extended to cover the opening portion 35 has a flange portion. 36 is hermetically sealed by welding. The package 9 made of the tray-shaped container 6 and the cooked rice 7 is placed between the electrode plate 31 on the lid 8 side and the electrode plate 32 on the bottom 37 side.
[0026]
In the example shown in FIG. 1, the upper electrode plate 31 facing the lid 8 is pressed against the lid 8 by an appropriate actuator (for example, a piston 38) as a pressing mechanism. Since the electrode plate 31 has a contour that fits in the opening 35 of the container 6, the lid 8 can be pushed inward of the container 6 without being obstructed by the flange 36 of the container 6. . By pressing the lid 8, the lid 8 is deformed into the inside of the container 6, compressing the inert gas and driving it to the side 39 a, so that the lid 8 is formed between the lid 8 and the upper surface of the cooked rice 7. The head space 39 can be reduced as much as possible. As a result, the space between the top of the cooked rice 7 and the lid 8 is reduced, and substantially no gap remains between the electrode plates 31 and 32 except for the cooked rice 7.
[0027]
A high-frequency voltage of 1 MHz to 50 MHz, for example, 5 MHz, is applied between the electrode plates 31 and 32 from the oscillator 33 between the electrode plates 31 and 32 in a state where substantially no gap other than the cooked rice 7 is formed between the electrode plates 31 and 32. . As an example of the heating, for example, a 200 g heavy cooked rice was heated at a power of 3 kW for 30 seconds to obtain a temperature rise of 50 ° C. The pressing force of the electrode is 50 to 60 kg, and is 1 kg / cm ² in terms of the pressure applied to the container 6. In addition, at the time of heating, warm water may be passed through the electrode or hot air may be blown to heat the package 9 from the periphery.
[0028]
Since substantially no gap is formed between the electrode plates 31 and 32, the cooked rice 7 is efficiently heat-sterilized by dielectric heating. In addition, since a head space cannot substantially exist in the container 6 above the cooked rice 7, a discharge phenomenon occurs due to the vapor in which the water in the cooked rice 7 evaporates during high-frequency dielectric heating. Can be prevented. Therefore, it is possible to prevent damage such as opening of a hole in the container 6 or the lid member 8 due to a spark in the head space. Further, the cooked rice 7 is heated in a state where its thickness is uniform, so that it is possible to heat and sterilize it evenly and uniformly. Since the cooked rice 7 is pressed indirectly by the electrode plates 31 and 32 via the lid 8 and the bottom 37 of the container 6, the grains of the cooked rice 7 are not directly crushed, and the commercial value is reduced. Absent. In order to prevent the inner pressure of the package 9 from rising when the electrode plates 31 and 32 are pressed, the lid 8 near the flange is lifted, and the seal is set back, it is preferable to fix the package around the flange. Recooling of the package 9 reheated by dielectric heating can be performed in a state where cooling water is brought into contact with the electrode plates 31 and 32, but forced cooling is also possible.
[0029]
FIG. 2 is a schematic side view showing another embodiment of the packaged food heating apparatus according to the present invention. In the heating device 40 shown in FIG. 2, the package 9 is pressed by the electrode plate 31 from the lid 8 side in the embodiment shown in FIG. This is an example of pressing from the bottom 37 side. Other structures are the same as those of the heating device 30 shown in FIG. 1, and therefore, the same components are denoted by the same reference numerals, and the description thereof will not be repeated. It is preferable that the size of the electrode plate 32 be slightly smaller than the bottom 37 of the container 6 so that the bottom 37 is easily deformed. When the electrode plate 32 is pressed against the bottom 37 of the container 6 by the actuator 48, the container 6 is deformed in such a manner that the bottom 37 is lifted, pushing up the rice 7 to compress the inert gas and drive it to the side 39a. The head space 39 that tends to be formed between the upper surface of the cover 7 and the cover member 8 can be reduced as much as possible. Therefore, substantially no gap remains between the electrode plates 31 and 32 except for the cooked rice 7. Since the mode of the sterilization heating is the same as the description of the previous embodiment, the description will not be repeated.
[0030]
Although the embodiment of the apparatus for heating the packaged food has been described above, the electrode plates 31 and 32 are pressed against the lid 8 and the bottom 37 of the container 6, respectively, so that the lid 8 and the bottom 37 are simultaneously deformed. Can be. In this case, pressing mechanisms are arranged on both the upper and lower sides of the package 9, and the size of the electrode plates 31, 32 is also set to a size that easily deforms the lid 8 and the bottom 37. Further, the electrode plates 31 and 32 do not need to be single plates, but may be divided into a plurality of plates. Further, the pressing area of the electrode plates 31 and 32 against the package 9 does not need to be the entire surface of the lid member 8 or the bottom 37 of the container 6, but may be limited to a certain extent that the head space 39 can be crushed. .
[0031]
【The invention's effect】
The method for heating packaged food according to the present invention, as described above, when heating a package by high-frequency dielectric heating, which has various advantages as a heating means, faces a package consisting of a food and a container in which the food is packaged. By sandwiching between two electrodes and further pressing at least one electrode against the package, a space such as a head space in the container is substantially not generated between the electrodes, so that the thickness becomes uniform. The food can be efficiently heated by dielectric heating, and can be heat-sterilized almost uniformly without unevenness. In addition, since a head space cannot be substantially present in such a state, the occurrence of sparks in the head space caused by the vapor of moisture in the food during high-frequency dielectric heating is prevented, It is possible to prevent damage to containers including lids and packaging materials that would cause sterilization and sealing.
[Brief description of the drawings]
FIG. 1 is a schematic side view showing an embodiment of a packaged food heating apparatus according to the present invention.
FIG. 2 is a schematic side view showing another embodiment of the packaged food heating apparatus according to the present invention.
FIG. 3 is a side view schematically showing a food packaging device to which the packaged food heating device according to the present invention is applied.
FIG. 4 is an explanatory diagram illustrating a conventional heating method using high-frequency dielectric heating.
FIG. 5 is a side view showing a state in which a package in which food is packaged in a container is heated by conventional high-frequency dielectric heating.
[Explanation of symbols]
Reference Signs List 6 container 7 cooked rice 8 lid material 9 package 30, 40 heating device 31, 32 electrode plate 33 high frequency power supply 35 opening 36 flange portion 37 bottom portion 38 pressing mechanism 39 head space

Claims (6)

Heating of a packaged food that heat-sterilizes the packaged food by applying a high-frequency voltage between the electrodes while a package consisting of a food and a container for storing the food is sandwiched between two opposed electrodes. Heating the packaged food by applying at least one of the electrodes to the package to apply the high-frequency voltage without substantially forming a gap other than the food between the electrodes. Method. The container is a tray-shaped container that is hermetically sealed by welding a lid material to a flange portion around an opening, and is disposed on the electrode disposed on the lid material side or on a bottom side of the tray-shaped container. 2. The method for heating packaged food according to claim 1, wherein the performed electrodes are pressed against the lid or the bottom of the tray-shaped container, respectively. The method for heating packaged food according to claim 2, wherein the food is cooked rice. A packaged food comprising two opposed electrodes sandwiching a package consisting of a food and a container for accommodating the food, and a high-frequency power supply for applying a high-frequency voltage between the electrodes to heat and sterilize the packaged food. In the heating device, in order to apply the high-frequency voltage in a state in which substantially no gap other than the food between the electrodes is formed, from having a pressing mechanism that presses at least one of the electrodes against the package. A packaged food heating device. The container is a tray-shaped container that is hermetically sealed by welding a lid material to a flange portion around the opening, and the pressing mechanism applies the electrode disposed on the lid material side to the lid material. 5. The apparatus for heating a packaged food according to claim 4, further comprising pressing the electrode arranged on the bottom side of the tray-shaped container against the bottom of the tray-shaped container. 6. The packaged food heating device according to claim 4, wherein the food is cooked rice.

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