JP3676125B2 - Microwave sterilization method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a microwave sterilization method, and more particularly, to a microwave sterilization method in a case where an object to be sterilized such as food or pet food has a gap and is accommodated in a storage container and sealed.
[0002]
[Prior art]
In order to prevent deterioration during distribution and storage of so-called normal temperature foods, sterilization is usually required, and various sterilization methods have been devised mainly by heat sterilization methods such as retort sterilization methods. ing.
On the other hand, heat sterilization is effective for sterilization, but also has a close influence on alteration of food components, and a microwave sterilization method that can heat the inside of food in a short time has attracted attention (Japanese Patent Publication No. 56). -24542, JP-B-60-58668, JP-A-56-131132, JP-A-6-296478, JP-A-11-149, etc.).
[0003]
Of these, Japanese Patent Publication No. 56-24542 or Japanese Patent Publication No. 60-58668 attempted to sterilize at a temperature of 100 ° C. or higher by performing microwave heating while substantially balancing the internal pressure and external pressure of the food packaging container. In addition, Japanese Patent Laid-Open No. 56-131132 performs microwave heating as a pre-treatment for retort sterilization.
[0004]
JP-A-6-296478 is provided with a pressure chamber, which is pressurized to 0.5 to 2.8 kg / cm ² and irradiated with microwaves to raise the food temperature to 100 to 130 ° C., Under these temperature and pressure conditions, the temperature is maintained for a predetermined time in a dry heat heating atmosphere at a relative humidity of 0 to 30% and 130 ° C. or lower.
Furthermore, in JP-A-11-149, the target food filled and sealed in a microwave permeable packaging container is microwave-heated in a steam-containing atmosphere pressurized to about 0.5 to 3.0 kg / cm ² . A method for producing a sterilized food that can be distributed at room temperature is disclosed.
[0005]
[Problems to be solved by the invention]
However, when the present inventors examined, in the general microwave sterilization method as shown in the above-mentioned Japanese Patent Publication No. 56-24542 or Japanese Patent Publication No. 60-58668, even when theoretically sufficient heating is performed, It has become clear that bacterial growth may be spotted during later storage, and in particular, there are many cases where bacteria remain or adhere to the food surface.
As a result of further investigation on this point, the surface of the food after the sterilization was finished because the bacteria remained on the inner wall of the food container because the surface of the food was not sufficiently heated and the bacteria remained. It was revealed that the bacteria reattached.
[0006]
That is, FIG. 1 shows a food container 14 in which a food (object to be sterilized) 10 is stored and sealed with a gap 12. When microwave irradiation is performed from the outside of the container 14, the food 10 having moisture or the inner wall of the container 14 in contact with the food 10 is sufficiently heated and sterilized, but the container 14 in contact with the gap portion 12. The inner wall stops being heated by water vapor generated from the food 10, and the temperature of the outside of the container 14 hardly rises due to the nature of microwave heating. Therefore, the outside air around the container 14 acts to cool the container 14, and this portion It is considered that the temperature rise itself is insufficient and proper sterilization is not performed. Such a problem is unlikely to occur when the container 14 is filled with food, but a tray made of synthetic resin is used for recent normal temperature distribution food so that it can be eaten as it is by heating it with a microwave oven or the like. In many cases, food is stored with a gap in the container, and sterilization of the inner wall of the container in contact with the gap has become extremely important.
[0007]
In the technique described in Japanese Patent Laid-Open No. Hei 6-296478, a pressure chamber is provided as described above and kept in a dry-heated atmosphere for a predetermined time. The problem is that the equipment cost is high, and the amount of water vapor introduced into the pressurizing chamber is also large, and since heating by dry heat is used, the heating efficiency is low and the running cost is high.
[0008]
Furthermore, in the technique disclosed in Japanese Patent Application Laid-Open No. 11-149, since heating by microwave irradiation and cooling by cooling water or the like are performed under pressure, a large pressurizing chamber is required, and the equipment cost is increased. In order to pressurize a large pressurizing chamber with water vapor, a large amount of water vapor is required, and microwave energy is also consumed to heat these water vapors, which increases the running cost. .
The present invention has been made in view of the above-described problems of the prior art, and the object thereof can be sufficiently sterilized including the inner wall of the container even when the object to be sterilized has a gap and is accommodated in the container. The object is to provide a microwave sterilization method.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a microwave sterilization method according to the present invention includes a microwave permeable storage container in which an object to be sterilized is stored and sealed with a gap, and the volume of the storage container is 1.5. having an internal volume of 5.0 times, and housed in a transmitted microwave and the desired sterilization temperature does not Oite substantially deformed in a sealed container, after sealing, a step of sterilizing the container, And a step of cooling the storage container.
Here, in the step of sterilizing the storage container, while the sealed container is moved to the next process side, pressurized water vapor is introduced into the sealed container so that the internal pressure of the storage container and the internal pressure of the sealed container are substantially balanced. Microwave irradiation is performed from the outside of the sealed container, and the inside of the sealed container is set to a relative humidity of 50 to 100%, a pressure of 1.0 to 3.0 kg / cm ² , and a temperature of 100 ° C. or higher for a predetermined time. Sterilize.
Further, in the step of cooling the storage container, the storage container is cooled by introducing a coolant into the sealed container while moving the sealed container to the next process side.
[0010]
In the method, a plurality of sealed containers are attached around the rotating body, and the process of storing the storage container in the sealed container, the process of heating the storage container, the process of cooling the storage container, and the storage The step of removing the container from the sealed container is preferably performed while the rotating body is rotating.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, as described above, the storage container in which the article to be sterilized is stored in a sealed container having an internal volume of 1.5 to 5.0 times the volume of the storage container, and sealed, Since pressurized water vapor (water vapor or water vapor and air) is introduced into this sealed container and microwaves are irradiated from the outside of the sealed container, a large pressurized chamber is not required, and the equipment cost can be reduced. Since only the pressurized water vapor or the cooling liquid is introduced into the small sealed container, the amount of water vapor or the cooling liquid required is small, the running cost is low, and the heating and cooling speed are increased.
[0012]
In addition, since microwaves are irradiated into a relatively small sealed container, it can be used to heat the water vapor in the sealed container, the storage container, and the object to be sterilized. Compared to irradiating a relatively large pressure chamber with microwaves (used to heat water vapor in the pressurization chamber and the storage container and the object to be sterilized), the microwave energy is used without waste.
Preferred embodiments of the present invention will be described below with reference to the drawings.
FIG. 2 shows a sealed container 150 used in the microwave sterilization method according to an embodiment of the present invention. The portion corresponding to FIG.
[0013]
The sealed container 120 shown in the figure contains a food container (storage container) 114 that is sealed with the food 110 contained therein, and is closed, and both the containers 114 and 120 are microwave permeable. It consists of a synthetic resin having heat resistance. The sealed container 120 is provided with a water vapor introduction pipe 122.
The sealed container 120 in the state shown in FIG. 2 is introduced into a continuous microwave sterilizer 130 as shown in FIG. 3, for example.
[0014]
In FIG. 3, the continuous microwave sterilizer 130 includes an introduction side filter zone 132, a microwave zone 134, and a discharge side filter zone 136, and the sealed container 120 is a glass having excellent heat resistance and wear resistance. It is placed on a belt conveyor 138 made of fiber-containing epoxy resin, enters from the introduction side filter zone 132, passes through the microwave zone 134 and the discharge side filter zone 136 in order, and exits to the outside. The microwave zone 134 receives microwave irradiation from the waveguide 140 and is sterilized by heating.
In addition, since the ferrite is attached to the inner walls of the filter zones 132 and 136 and has a relatively narrow tunnel shape, the microwave irradiated in the microwave zone 134 does not leak outside. .
[0015]
In this embodiment, when performing microwave irradiation in the microwave zone 134, the sealed container 120 is supplied with pressurized steam by the steam introduction pipe 122. This water vapor becomes an object of heating by microwaves, and the internal atmosphere of the sealed container 120, that is, the external atmosphere of the food container 114 becomes a high temperature like the food 110. As a result, in the food container 114, the food 110 and the portion in contact with the food 110 are of course, and the inner wall portion of the container that is not in direct contact with the food 110 also becomes sufficiently hot, and heat sterilization is performed. In addition, the increase in the internal pressure of the food container 114 due to the thermal expansion of air and water vapor accompanying the heating of the food 110 is offset by the pressure of the pressurized water vapor, and the food container 114 formed of an easily deformable material is greatly deformed. Or, no damage will occur.
[0016]
For example, when food such as shrimp, hamburger, broccoli, fish fillets, seafood is heated at 135 ° C. for 60 seconds by irradiating with microwaves, the pressure of the sealed container 120 is 1.5 to 2.0 kg / cm. ² (gauge pressure), pressurized steam is used so that the difference between the internal pressure of the food container 114 and the internal pressure of the sealed container 120 is at most within the range of ± 0 to 0.5 kg / cm ² (gauge pressure). adjust.
Then, after the sterilization is completed, that is, when reaching the discharge side filter zone 136, cooling water (preferably 20 ° C. or less) as a coolant is introduced from the introduction pipe 122, and the food 110 is rapidly cooled. Therefore, the quality change due to the residual heat of the food 110 is suppressed to a minimum.
[0017]
As described above, according to the continuous microwave sterilization apparatus according to the present embodiment, not only food, but also the food container 114 is entirely heat sterilized, and recontamination of food due to falling bacteria from the inner wall of the container. Can be significantly reduced. Furthermore, the container deformation accompanying the increase in the internal pressure of the food container 114 can be suppressed by the pressurized steam, and the deterioration of the food component due to the residual heat can be efficiently suppressed by the rapid cooling of the food by introducing the cooling water after sterilization. In particular, the present invention is effective when the food container (storage container) is a thin flexible resin container.
[0018]
In the present invention, the relative humidity in the sealed container at the time of microwave sterilization needs to be 50 to 100%, preferably 70 to 90%. The internal pressure is usually 1.0 to 3.0 kg / cm ² (gauge pressure) although it depends on the ultimate pressure of the food container.
In addition, the storage container is a microwave-permeable synthetic resin having heat resistance at a sterilization temperature (130 ° C. or higher), such as polyethylene terephthalate, polybutylene terephthalate, copolymer polyester, polyethylene naphthalate, polypropylene, and polyamide. A container composed of a single layer of a thermoplastic resin, a container provided with at least one of these resin layers, or a container having a mixed resin layer obtained by mixing these resins is preferable.
[0019]
Furthermore, in the present embodiment, the “inner volume close to the volume of the storage container” of the sealed container 120 means an internal volume that is about 1.5 to 5.0 times the volume of the storage container.
In addition, although the example which performs microwave heating, introduce | transducing water vapor | steam is shown by the said Unexamined-Japanese-Patent No. 56-13112, this technique presupposes performing retort sterilization later, and is flexible with a space | gap part. However, if the retort sterilization is performed, bacteria remaining on the inner wall of the food container are not a problem. Therefore, this prior art is intended for liquid or semi-liquid food filled in a soft bag or the like. Furthermore, in this prior art, since steam is introduced into the kettle itself, it is extremely difficult to perform sterilization continuously.
[0020]
In this regard, in the present invention, the microwave zone 134 that performs microwave irradiation is not particularly required to have pressure resistance, airtightness, and the like, and there is an advantage that a general-purpose microwave continuous sterilization apparatus can be used.
FIG. 4 shows an example of a detailed structure of a sealed container characteristic of the present invention. FIG. 4A is a top view and FIG. 4B is a side sectional view. Note that the portions corresponding to those in FIG.
A sealed container 220 shown in the figure includes a main body 250, a lid body 252, and a mounting table 254.
[0021]
Each of these parts is formed of a glass fiber-containing epoxy resin having excellent heat resistance and pressure resistance and high microwave transmission efficiency. It is also preferable to use a fluororesin or the like.
Specifically, the sealed container 220 according to the present embodiment contains a tray-like food container (storage container) 214 (140 mm × 170 mm × 20 mm thick) in which a food is stored and an opening is sealed by heat sealing. It is stored in an epoxy resin sealed container (diameter 230 mm x height 40 mm), closed with a lid 252, and pressurized steam is introduced at a pressure of 1.71 to 2.64 kg / cm ² (sterilization temperature 130 to 140 ° C.). In addition, auxiliary pressure (+0.5 kg / cm ² ) is applied with air so that the food container 214 containing the ingredients does not rupture.
[0022]
As shown in detail in FIG. 5, the main body 250 is formed in a bottomed cylindrical shape in which concave portions 255 a and 255 b are provided in two stages.
Further, a mounting table 254 (see FIG. 6) having protrusions 256 a, 256 b, 256 c, and 256 d is fixed to the bottom surface on the inner surface side of the main body 250 by a tap 258. The protrusion 256 prevents the food container 214 from coming into close contact with the sealed container 220, and the pressurized water vapor spreads around the entire outer periphery of the food container, so that proper heat sterilization is performed.
[0023]
Further, as shown in detail in FIG. 7, the lid 252 is detachably fixed to the main body 250 by a tap 262, and introduction paths 262a, 262b,... 262h communicating with the inside of the sealed container 220 are formed. Yes. The lid body 252 and the main body 250 can be maintained in an airtight state by the O-ring 264.
The introduction path 262a is provided with a thermometer 266 for monitoring the temperature inside the container, the introduction paths 262b and 262d are selectively supplied with cooling water (coolant) or water vapor by valves 268a and 268b, and the introduction path 262c is provided with a container. A pressure adjustment valve 270 for adjusting the pressure in 220, a pressure gauge 272 for monitoring the pressure in the container 220 in the introduction path 262e, and a discharge port in the introduction paths 262f and 262h via the flow rate adjustment valve 274, Air 276 to be introduced is connected to the introduction path 262g when the pressure adjustment in the container 220 is insufficient only by the introduction of water vapor.
[0024]
When the sealed container 220 enters the microwave zone 134 shown in FIG. 3, the pressurized water vapor is introduced into the sealed container 220 through the valve 268b, while the temperature and pressure in the sealed container 220 are measured by a thermometer 266. The internal pressure is adjusted by the pressure adjustment valve 270 according to the expected pressure in the food container 214. That is, the temperature and pressure in the food container 214 caused by the irradiation energy in the microwave zone are predicted experimentally or theoretically, and the internal pressure of the sealed container 220, that is, the external pressure of the food container 214 is almost balanced with the internal pressure of the container 214. It is adjusted as follows. Note that by introducing hot water vapor, loss of microwave irradiation energy can be reduced, and the heating efficiency of the food container 214 can be increased. Further, when the above-described introduction of water vapor is insufficient to balance the internal pressure of the food container 214, the air 276 is supplied from the introduction path 262g.
[0025]
When the sealed container 220 reaches the discharge-side filter zone 136, the valve 268b is closed, the valve 268a is opened, and cooling water is introduced into the container 220. At this time, the cooling effect can be improved by sequentially replacing the cooling water in the flow state via the flow rate adjusting valve 274.
If the monitor of the thermometer 266 confirms that the cooling water temperature, that is, the temperature of the food container 214 has sufficiently decreased, the cooling water in the container 220 is discharged.
As described above, when the sealed container 220 according to the present embodiment is used, the pressure and temperature in the sealed container 220 are strictly controlled, and the food container 214 is not easily damaged or deformed. The food container 214 is properly sterilized to every corner.
[0026]
In the embodiment, the sealed container 220 is linearly moved. For example, a pocket on which 6 to 24 sealed containers can be fixed is provided on the outer periphery of a rotary type rotating body, and fixed to each pocket. Air, water vapor, and cooling water pipes are connected to the sealed container, and after the food is stored in the sealed container fixed in the pocket and closed, After the introduction of water vapor and air, the food container and water vapor are rapidly heated by irradiating microwaves, and when the sterilization temperature is reached, the power of the microwave is reduced or the microwave irradiation is stopped for a predetermined time. After maintaining the sterilization temperature, cooling water is introduced into the sealed container to cool the food container and the sealed container, and then the sealed container is opened to remove the food container from the sealed container. Is It becomes ECTS, loading of food containers it is possible to close the accommodating position and the take-out position of the food containers, it is convenient to carry-out.
[0027]
In addition, although the example which used the cooling water as a coolant was demonstrated in the said Example, it is not restricted to this, For example, liquid nitrogen etc. can be introduce | transduced and it can also cool more rapidly.
[0028]
【The invention's effect】
As described above, according to the microwave sterilization method of the present invention, the content of the storage container in which the object to be sterilized is stored with a gap is 1.5 to 5.0 times the volume of the storage container. by introducing steam into and sealed in a sealed container of a product sealed in the container during the microwave sterilization, it is possible to perform sterilization of the sterilization product container inner wall every corner with less energy consumption, after sterilization It becomes possible to suppress the contamination of the sterilized material by the bacteria falling from the inner wall of the container.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a problem of the present invention.
FIG. 2 is an explanatory diagram of a sealed container according to the first embodiment of the present invention.
FIG. 3 is an explanatory diagram of a continuous microwave sterilization apparatus in which the sterilization method of the present invention is used.
FIG. 4 is a detailed explanatory view of a sealed container characteristic of the present invention.
5 is an explanatory diagram of the main body of the container shown in FIG. 4. FIG.
6 is an explanatory diagram of a mounting table for the container shown in FIG. 4. FIG.
7 is an explanatory view of a lid of the container shown in FIG.
[Explanation of symbols]
10,110 Food (to be sterilized)
12, 112 Cavity 14, 114, 214 Food container (easily deformable storage container )
1 20,220 Sealed container 130 Continuous microwave sterilizer

Claims (2)

A microwave permeable storage container in which the object to be sterilized is stored and sealed with a gap, has an inner volume of 1.5 to 5.0 times the volume of the storage container, and transmits microwaves. and housed in a sealed container that does not Oite substantially deformed to the desired sterilization temperature, after sealing,
While moving the sealed container to the next process side, microwave irradiation is performed from the outside of the sealed container while introducing pressurized water vapor into the sealed container so that the internal pressure of the storage container and the internal pressure of the sealed container are substantially balanced, Sterilizing the container for a predetermined time by setting the inside of the sealed container to a relative humidity of 50 to 100%, a pressure of 1.0 to 3.0 kg / cm ² , and a temperature of 100 ° C. or higher ;
A step of cooling the storage container by introducing a coolant into the sealed container while moving the sealed container to the next process side;
Microwave sterilization method characterized by comprising a. 2. The microwave sterilization method according to claim 1 , wherein a plurality of sealed containers are attached around the rotating body, the storage container is accommodated in the sealed container, the storage container is sterilized, and the storage container is cooled. A microwave sterilization method comprising performing a step and a step of taking out the storage container from the sealed container while the rotating body is rotating.

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