JPH025389B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a method for sterilizing foods by microwave irradiation, and in particular, the packaging does not rupture or deform even when sterilized continuously under normal pressure. This relates to a microwave sterilization method for food that does not cause serious damage.

[Prior art and its problems]

Currently, in order to distribute sealed food packages at room temperature for long periods of time, food is sterilized using the retort sterilization method. However, this retort sterilization method uses a heat medium of 100℃ or higher and heat sterilizes under pressure.
Sterilization took a long time, ranging from 20 to 60 minutes. Therefore, the texture, taste, aroma, etc. of the food to be sterilized,
It had the disadvantage of impairing the color etc.

Since this retort sterilization method performs sterilization under pressure, advanced technology is required to adjust the pressure in order to prevent the package from bursting.

As an alternative to the retort sterilization method, a sterilization method using a microfluid that can be heated in a short time has attracted attention, and the United States Army Research Institute has announced a method that sterilizes by irradiating microwaves under pressure, similar to the retort sterilizer. However, since this method involves microwave irradiation under pressure, it is difficult to adjust the pressure like the retort sterilization method, and the sterilization equipment is complicated and expensive, making it difficult to be widely used.

In addition, as a sterilization method using microwaves, as shown in Japanese Patent Publication No. 58-26949, a package containing an object to be sterilized is sealed in a pressure-resistant container made of a material that can transmit microwaves, and the A method of sterilizing containers by irradiating them with microwaves from outside the container has been proposed.

According to this method, the package can be sterilized by sealing it in a pressure-resistant container and irradiating it with microwaves. However, since microwaves are irradiated all at once, uneven heating tends to occur, and food with a low moisture content can be sterilized. Burning may occur in some cases.

Further, there is no disclosure regarding the method of degassing, and if degassing is not performed sufficiently, temperature unevenness may occur in the package, which may lead to rupture.

Furthermore, since it is a closed system, it takes time to store and take out packages of objects to be sterilized, making it difficult to sterilize them continuously.

[Means for solving problems]

A bag sealed on three sides is filled with food with a moisture content of 20% or more, and a hole, slit or corner with a diameter of 1 to 5 mm is cut in the top of the sealed package with a thickness of 35 mm or less to remove air. The package is housed in a support made of a material that can transmit microwaves and has a storage part with a volume and shape that is approximately the same as that of the package, with the degassing part facing upward. After heating and deaerating the package so that the internal temperature becomes 100 to 105°C, and sealing the degassing port of the package, irradiate the support with microwaves from the outside as described above, This is a microwave sterilization method for food that involves heating the package to an internal temperature of 125°C or higher, holding it for a certain period of time, sterilizing the food, and then cooling it.

At this time, the material of the bag to be filled with the food is a microwave-permeable material, the inner surface is made of a heat-sealable laminated material, and the thickness is preferably 0.35 mm or less.

The specific laminated material is suitably a film having a composition of stretched nylon/unstretched polypropylene or stretched nylon/unstretched nylon/unstretched polypropylene, with a total thickness of about 80 to 120 microns.

On the other hand, the support is made of a heat-resistant, pressure-resistant, and microwave-transmissible material, specifically, polycarbonate, Teflon, ceramic, wood, or a material in which glass fiber is mixed with the polycarbonate or Teflon.

Then, the structure of the bag and support will be explained according to the drawings.

That is, FIGS. 1 a to 1 c are explanatory diagrams showing an example of the package 10, and the multi-dotted portions indicate sealed portions.

FIG. 1a shows a bag in which the contents are filled and sealed, and then a hole 11 with a diameter of 1 to 5 mm is provided to serve as a deaeration port.

Further, in FIG. 1b, a slit 12 is used as a deaeration port instead of a hole.

The support, as shown in FIGS. 2 and 3,
It consists of two side walls 15 and 16 forming a storage section 14 having approximately the same shape as the outer diameter of the package to be stored, and windows 17 and 18 for hermetically sealing the degassing port of the package at the upper part of the side walls. Furthermore, at least one side wall is provided with a measurement port 20 for temperature inspection to detect the heating state of the package. Of course, the two side walls have a sandwiching structure so that the package does not open even if it expands due to heating.

Here, if measurement ports for temperature inspection are provided on both side walls, water or air will flow better in the next cooling step, and the cooling effect will be even better.

Of the two heatings in the present invention, the first heating time can be performed within 6 minutes, and the second heating time can be performed within 4 minutes.

The final cooling step is performed by blowing cold air or cold water from the outside of the support containing the package for 70 to 75 minutes.
After cooling to 0.degree. C., the package is removed from the support.

[Effect]

According to the method of the present invention, not only the initial heating but also the initial heating ensures degassing of the package, so that the subsequent heating for sterilization can also be performed under normal pressure.

Since it can be operated under normal pressure in this way, it is easy to operate and the sterilizer can be downsized.

Continuous sterilization is possible by providing a large number of supports in the device and feeding them continuously, and sterilization conditions can be easily changed by adjusting the transfer speed and microwave output.

Since the package can be heated within 10 minutes, it is now possible to sterilize beefsteak, grilled fish, etc., which could not be produced using conventional retort sterilization methods, and can be applied to a wide range of foods that contain more than 20% moisture. It became possible.

〔Example〕

After filling 120 g of beefsteak and 30 g of seasoned sauce into a bag made of a laminated film of stretched nylon film (15μ)/unstretched polypropylene film (70μ) and having a size of 130 x 170 mm and sealed on three sides, Figure 1. The package is made of glass fiber-filled Teflon and has a sealed opening and a hole of 3 mm in diameter as shown in Fig. It is stored in a support with a measurement port for temperature testing on the top and a window for sealing on the top.

A large number of supports are placed on a belt conveyor,
It has a structure that allows it to move continuously at a speed of 0.4 m/min.

While storing this package, the support body was passed through a first heating section with a length of 1.2 m each equipped with three 600 W microwave oscillators (manufactured by Sanyo Electric) that irradiated microwaves in waveguides on both sides. Performed deaeration work. The passage time through this first heating section was 3 minutes, and the temperature inside the package was measured with an infrared sensor through the measurement port of the support, and was found to be 100 to 102°C.

Next, the degassing port of the package was sealed, and then the package was passed through a second heating section having a length of 1.2 m and equipped with the same microwave oscillator as the first heating section, one on each side, to perform sterilization. The passage time of this second heating section is 3 minutes,
When the temperature of the package was measured in the same way as above, it was 128
It was warm at ℃.

Furthermore, the support containing the package was allowed to pass through the holding section for 1 minute, and then cooled with cold air at 5℃ for 3 minutes, and when the temperature of the package reached 70 to 75℃, the package was moved to the support. It was taken out and sterilized.

The beefsteak in this package did not turn into a Yamato-ni-like state, which is the case with retort sterilization, and had a flavor close to well-done.

On the other hand, when this package was stored in a constant temperature bath at 60℃ for two weeks, the condition of the package was inspected, and the number of viable bacteria was as follows.
100 pieces/g or less and no gas generation was observed within the package.

〔effect〕

The sterilization method of the present invention uses pressurized heat sterilization at 100℃ or higher under normal pressure, and can sterilize in 1/5 to 1/10 the time compared to the conventional retort method. It can be sterilized without losing taste or color.

In addition, the initial heating fills the package with water vapor, which allows more complete degassing than the vacuum degassing method, and makes the temperature distribution inside the package more uniform.
There is no problem with the half-life depth of microwaves, and uniform heating sterilization is possible without uneven heating.

Furthermore, if there is a pinhole in the package during the first heating, the temperature will not rise to a predetermined level, so that the presence or absence of pinholes in the package can be checked at the same time as the first heating.

[Brief explanation of drawings]

1A to 1C are explanatory diagrams showing an example of the package at the time of initial heating, FIG. 2 is an explanatory diagram of the support, and FIG. 3 is a cross-sectional explanatory diagram of FIG. 2 A-A'. 10... Packaging body, 11... Hole, 12... Slit, 13... Inquiry part, 14... Storage part, 15,1
6... Side wall, 17, 18... Window, 20... Measurement port.

Claims (1)

[Claims] 1. After filling a bag sealed on three sides with the contents and completely sealing the mouth, a deaeration port is installed in the upper part of the bag by means of a hole with a diameter of 1 to 5 mm, a slit, or cutting out a corner. After forming and preheating and degassing,
A method for microwave sterilization of food, which comprises sealing the deaeration port and then sterilizing it by microwave heating.