JP2018029520A - Sterilization method using pulsed plasma and object to be sterilized - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sterilization method using pulsed plasma capable of effectively sterilizing an object to be sterilized, such as food, packaged with a packaging container or the like in a packaged state, and even in a state where objects to be sterilized overlap with each other inside the packaging container, and to provide an object to be sterilized.SOLUTION: A method for sterilizing an object to be sterilized 3a, 3b in a packaging container 2a, 2b using pulsed plasma includes: a step of arranging the object to be sterilized 1 packaged with the packaging container 2a, 2b between a first electrode 6a and a second electrode 6b of a plasma generator; and a step of applying a pulse voltage between the first electrode 6a and the second electrode 6b of the plasma generator to generate pulsed plasma inside the packaging container 2a, 2b. A dielectric 4 is inserted into the object to be sterilized 3a, 3b, and a space 5 is formed between the object to be sterilized 3a, 3b and the dielectric 4. In the step of generating the pulsed plasma, an electric field having the magnitude capable of obtaining a sterilizing effect is generated in the space 5.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sterilization method using pulsed plasma and an object to be sterilized (object to be sterilized). In particular, the present invention relates to a sterilization method using pulsed plasma and an object to be sterilized, which can effectively sterilize an object to be sterilized such as food packaged in a packaging container. .

In recent years, there has been much talk about food safety, because food safety is closely related to our lives. In order to ensure food safety, sterilization of food is indispensable, and it can be said that we can live daily life with peace of mind by preventing damage from food poisoning. There are various factors that cause food poisoning, but the main cause is often caused by bacteria.
Various sterilization methods are known. For example, heat sterilization can be used for foods and is the most reliable, easy and inexpensive method for sterilization. However, in this method, there is a possibility that the flavor and texture of food are changed by heating. In addition, chemical sterilization with chemicals, etc. is limited in the scenes where it can be applied, which may cause changes in the quality of food due to chemicals and the problem of residual fungicides. There is also a problem that it is not suitable for sterilization. Furthermore, UV sterilization can be sterilized even if it is a packaged food if the package is UV transmissive, but there is a problem in terms of efficiency, such as the portion that is not irradiated with UV is not sterilized. .

  As a method for solving these problems of conventional sterilization methods, a sterilization method using pulsed plasma has been studied. The pulse plasma sterilization method is a method in which a pulse streamer discharge is caused by pulse power or silent discharge to generate sterilizing active species and ultraviolet rays to perform sterilization. The generated active species oxidizes the cell membrane and cell wall of the fungus and decomposes them to sterilize them. The sterilization is also performed by the generated ultraviolet light penetrating the cell wall and cell membrane and directly acting on DNA to destroy the physiological function of the fungus. In the pulse plasma sterilization method, it is expected that a powerful sterilization effect is produced by combining these energy phenomena in a complex manner. In addition, the plasma sterilization method can be said to be a method that can be carried out without selecting bacteria, because it also has an effect on heat-resistant bacteria that cannot be heat-sterilized. Furthermore, the active species generated in the plasma sterilization method are only generated temporarily and disappear rapidly after the reaction, so that it is not necessary to take measures against problems associated with the residual active species. For this reason, the pulse plasma sterilization method is expected as a sterilization method that can be used not only in food sterilization but also in various technical fields such as environment, biotechnology, recycling, materials, medicine, and nanotechnology.

  As a sterilization method using plasma, for example, Japanese Patent Application Laid-Open No. 2010-187648 (Patent Document 1) discloses a sterilization method for sterilizing an object to be sterilized by performing a plasma irradiation process for irradiating the object to be sterilized with air plasma. Foods are listed as sterilized items.

  JP 2013-510398 A (Patent Document 2) discloses the use of a plasma generator, in which the plasma generator is positioned in front of the first electrode and the first electrode. A structure and an insulating layer sandwiched between the first electrode and the second electrode structure, the second electrode structure having a plurality of second electrode portions defining a gap portion therebetween The width of the gap portion is w, each of the second electrode portions has a front surface, each of the gap portions has a front surface, and the front surface of the second electrode portion and the front surface of the gap portion are The height difference between the front surface of each second electrode portion and the front surface of the adjacent gap portion is h, and h is at most 1 mm, and the ratio w / h Is at least 1, and the packaging container to be processed is the packaging container processing table And using the plasma generating device, wherein the generated plasma is positioned substantially entirely within the packaging container to be processed, comprising the steps of: Yes.

JP 2010-187648 A Special table 2013-510398 gazette

  However, in the conventional plasma sterilization method, for example, when sterilized foods and the like packaged in a packaging container or the like in a packaged state, the articles to be sterilized overlap each other inside the packaging container. However, no examination has been made as to whether or not the overlapping portions can be sufficiently sterilized.

  The present invention effectively sterilizes food to be sterilized, which is packaged in a packaging container, even if the sterilized material overlaps inside the packaging container in a packaged state. An object of the present invention is to provide a sterilization method using pulsed plasma and an object to be sterilized.

In the case of sterilizing the objects to be sterilized in the packaging container using pulse plasma, the present inventors, for example, when the objects to be sterilized overlap each other inside the packaging container, By inserting a dielectric into the part and forming a space between the article to be sterilized and the dielectric, an electric field having a magnitude that can provide a sterilizing effect can be generated in this space. I found out that it can be solved.
Although not bound by any theory, if the shape is possible, a sharp corner is formed where three substances with different dielectric constants such as food to be sterilized, dielectric, and air intersect. This can induce a phenomenon (triple junction) that concentrates the electric field on this part. As a result, a large electric field intensity capable of generating pulsed plasma can be obtained, and the bactericidal effect can be improved effectively. it is conceivable that.

That is, the present invention is a method for sterilizing an object to be sterilized in a packaging container using pulse plasma, and the object to be sterilized packed by the packaging container is converted into the first electrode and the second electrode of the plasma generator. And a step of generating a pulsed plasma inside the packaging container by applying a pulse voltage between the first electrode and the second electrode of the plasma generating device. In addition, a dielectric is inserted in the article to be sterilized, and a space is formed between the article to be sterilized and the dielectric, and in the step of generating the pulse plasma, a sterilizing effect is produced in the space. The above-mentioned sterilization method is characterized by generating an electric field having such a magnitude that can be obtained.
In the sterilization method of the present invention, the electric field preferably has a magnitude exceeding 50 kV, more preferably 100 kV or more.

Further, in the sterilization method of the present invention, in the space formed between the article to be sterilized and the dielectric, the surface of the dielectric facing the article to be sterilized and the article to be sterilized facing the dielectric The depth of the space defined as the distance between the surface of the object is preferably 3 mm or less, more preferably less than 2 mm.
Furthermore, in the sterilization method of the present invention, it is desirable that the dielectric is a polyimide resin.

  The present invention also relates to an article to be sterilized, which is packaged by a packaging container and sterilized using pulsed plasma, and a dielectric is inserted into the article to be sterilized, and the article to be sterilized and the dielectric A space is formed between the body, and the space is configured to generate an electric field having a magnitude that can provide a sterilizing effect by generating pulsed plasma inside the packaging container. The packaged article to be sterilized is characterized.

  According to the present invention, it is effective even if the items to be sterilized such as food packaged in the packaging container remain in the packaged state and the items to be sterilized overlap each other inside the packaging container. Can be sterilized. That is, the present invention is expected to have effects such as prevention of food poisoning, suppression of bacterial growth, and long-term storage of food without risk associated with safety, etc., compared to conventional sterilization methods. Is.

It is a cross-sectional schematic diagram of one form of the packaged article to be sterilized according to the present invention. It is a circuit diagram of an example of the plasma generator which can be used for the sterilization method of the present invention.

Hereinafter, modes for carrying out the present invention will be described.
The present invention is a method for sterilizing an object to be sterilized in a packaging container using pulsed plasma.
The object to be sterilized by the sterilization method of the present invention is typically food, for example, fresh food or processed food such as meat, fish, vegetables, fruits, etc., but is not limited thereto, animal feed and medical use. Widely includes instruments that need to be sterilized, such as instruments.
In addition, Escherichia coli is typically assumed as a bacterium to be targeted by the sterilization method of the present invention, but is not limited to Escherichia coli and includes other bacteria that cause food poisoning.
In the present invention, these objects to be sterilized are packaged in a packaging container, and the objects to be sterilized inside the packaging container are sterilized while being packaged. The packaging container is not particularly limited as long as it is a container that is normally used for packaging an object to be sterilized, but by applying a pulse voltage to an electrode disposed outside the packaging container, It is necessary to be able to generate pulsed plasma inside the packaging container.
A specific method or apparatus for generating pulsed plasma will be described later, but is not particularly limited as long as it is generally used, and is suitably used if it is used for sterilization of various foods and containers. can do.

The sterilization method of the present invention includes a step of disposing an object to be sterilized packaged in a packaging container between a first electrode and a second electrode of a plasma generator, a first electrode of the plasma generator, and a first electrode. And applying a pulse voltage between the two electrodes to generate a pulsed plasma inside the packaging container.
In the sterilization method of the present invention, a dielectric is inserted into the article to be sterilized, and a space is formed between the article to be sterilized and the dielectric, and in the step of generating pulsed plasma, sterilization is performed in this space. It is characterized by generating an electric field having a magnitude that can provide an effect.

FIG. 1 is a schematic cross-sectional view of one embodiment of the packaged article to be sterilized according to the present invention.
The packaged article to be sterilized 1 is disposed inside the container between the upper part 2a and the lower part 2b of the packaging container so that the first part 3a and the second part 3b of the article to be sterilized overlap each other. . And the dielectric 4 is inserted between the 1st part 3a and the 2nd part 3b of to-be-sterilized material. Further, a space 5 is formed in the second portion 3b of the article to be sterilized. This space 5 is defined as the distance between the surface of the dielectric 4 facing the second part 3 b of the object to be sterilized and the surface of the second part 3 b of the object to be sterilized facing the dielectric 4. Has a depth d. In the present invention, such a packaged article 1 to be sterilized is disposed between the first electrode 6a and the second electrode 6b of the plasma generator. Next, a pulse voltage is applied between the first electrode 6a and the second electrode 6b to generate pulsed plasma inside the packaging container between the upper part 2a and the lower part 2b of the packaging container. In that case, in this invention, the electric field of the magnitude | size with which the sterilization effect is acquired is generated in the space 5 formed in the 2nd part 3b of the to-be-sterilized thing.

In the sterilization method of the present invention, as the sterilization effect in the space 5, it is desirable that the magnitude of the electric field exceeds 50 kV from the viewpoint of at least ensuring the effect of reducing the number of bacteria (sterilization). From the viewpoint of sterilizing, it is more desirable that the magnitude of the electric field is 100 kV or more.
The magnitude of the electric field generated in the space 5 is applied between the first electrode 6a and the second electrode 6b using a two-dimensional electrostatic solution / static magnetic field calculation software such as an electrostatic field static magnetic field analysis kit. It can be calculated by inputting necessary parameters such as the magnitude of the pulse voltage to be sterilized and the dielectric constants of the article to be sterilized (3a, 3b) and the dielectric 4.

  In the sterilization method of the present invention, the depth d of the space 5 is determined based on the magnitude of the pulse voltage applied between the first electrode 6a and the second electrode 6b, the object to be sterilized (3a, 3b), and the dielectric. 4 can be appropriately determined according to a value such as a dielectric constant of 4. In one embodiment of the present invention, the depth d of the space 5 is 3 mm as a sterilizing effect in the space 5 from the viewpoint of ensuring an sterilizing effect by generating an electric field that reduces at least the number of bacteria (sterilization). Desirably, the depth d of the space 5 is more preferably less than 2 mm from the viewpoint of obtaining a further sterilizing effect by generating an electric field that sterilizes a large proportion of bacteria.

  The dielectric 4 used in the sterilization method of the present invention is not particularly limited as long as it can generate a desired electric field in the space 5, but has a relatively low dielectric constant and a high withstand voltage. It is preferred to use materials. In addition, the dielectric 4 has mechanical characteristics (such as elastic modulus) such that the space 5 formed in the second portion 3b of the article to be sterilized can maintain a desired shape and dimensions (particularly depth). It is preferable to have it. As the dielectric 4, it is desirable to use a polyimide resin from the viewpoint of excellent durability and being relatively thin and easy to handle. Although the thickness of the dielectric 4 depends on the material used, for example, when a polyimide resin is used, it is preferably about 10 μm to 150 μm.

FIG. 2 is a circuit diagram of an example of a plasma generator that can be used in the sterilization method of the present invention. This apparatus includes a capacitor 7, a pulse transformer 8, a trigger tron gap switch 9, and a trigger circuit 10.
Referring to FIG. 2, the operation of the plasma generator is as follows. The capacitor 7 is charged with a charge from a DC high voltage via a resistor. The charging voltage can be appropriately determined according to the circuit configuration and the like, but the higher the charging voltage, the higher the bactericidal effect.
After charging, the triggertron gap switch 9 is operated to transfer the accumulated charge to the primary coil of the pulse transformer 8. The pulse voltage boosted by the mutual inductance of the pulse transformer 8 is applied to the electrodes (6a, 6b) of the discharge reactor.

A pulse voltage for generating a trigger discharge is generated using the trigger circuit 10, and a pulse voltage of several kV is applied to the trigger electrode using the trigger gap switch 9, so that a high voltage and a large current are generated at a repetition frequency of several kHz or less. Switching can be performed.
The number of pulse repetitions is preferably 10 pps or more. Further, the higher the number of times of application, the higher the sterilizing effect is obtained. Depending on the applied voltage, at least 20 shots, preferably 100 shots or more, more preferably 1000 shots or more are preferable.

  In the sterilization method of the present invention, an electrode having an arbitrary shape can be used as the electrodes (6a, 6b) of the plasma generator. The larger the electrode size, the higher the bactericidal effect.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples.

(Plasma generator)
The plasma generator shown in the circuit diagram of FIG. 2 was used. This device is composed of a capacitor, a pulse transformer, a trigger tron gap switch, and a trigger circuit.
The operation of the circuit is as follows. Charge is charged from a DC high voltage to a ceramic capacitor having a capacity of 2700 pF (N4700, Murata Manufacturing Co., Ltd., withstand voltage of 30 kV) through a resistance of 3 MΩ. After charging, the triggertron gap switch is operated to transfer the accumulated charge to the primary coil of the pulse transformer. The pulse voltage boosted by the mutual inductance of the pulse transformer is applied to the electrodes sandwiching the packaged food. The charging resistance was 3 MΩ so that the allowable current of the power source would not exceed 10 mA when the charging voltage was 30 kV.
The pulse transformer uses a ferrite core (PC40T manufactured by TDK Co., Ltd., 75 × 20 × 15) as the core, and the turns ratio of the primary winding and the secondary winding on the charging capacitor side is 1: 6.
Using a trigger circuit to generate a pulse voltage for generating a trigger discharge, and applying a pulse voltage of several kV to the trigger electrode using a trigger gap switch, high voltage and large current switching can be achieved with a repetition rate of 40 pps or less. Made it possible to do.

(Evaluation method of bactericidal effect)
As the fungus, E. coli (Escherichia coli (Migula) Castellani and Chalmers): ATCC Number 11229) was used. When using Escherichia coli, what was cultured for about 18 to 24 hours was used as the bacterial solution. The number of bacteria at this time was about 2.5 × 10 ⁹ CFU / ml.
The bactericidal effect was evaluated by measuring the number of viable bacteria after the pulse plasma treatment and before the treatment using the colony count method. That is, first, the bacterial solution was diluted 10 ⁶ times with pure water, and 100 μl of the diluted solution was inoculated on a nutrient agar medium as a simulated food. Thereafter, the nutrient agar medium before and after the plasma treatment inoculated with the bacterial solution were cultured in an incubator. Since one colony is formed for one bacterium, the number of surviving bacteria was determined by counting the number of colonies that appeared on the agar.
The ratio of the number of viable bacteria after the treatment to the number of viable bacteria before the pulse plasma treatment was used as a survival rate (Survival ratio [%]) as an index of the bactericidal effect.

(Calculation method of electric field strength)
Electrostatic Static Magnetic Field Analysis Kit SATE (Static-field Analysis Toolkit) mesh creation software (Mesh) and electrostatic field solver (EStat) are two-dimensional electrostatic solution and static magnetic field calculation software manufactured by Advanced Science Laboratory. The electric field distribution calculation and electric field strength calculation in the simulated food were performed.

Example 1
A plastic petri dish (As One Co., Ltd., material: polystyrene) having a diameter of 90 mm was prepared as a simulated packaging container. In this petri dish, 35 ml (thickness 5.5 mm) of a nutrient agar medium (manufactured by OXOID Ltd.) was filled as a simulated food assuming an object to be sterilized. A space having a diameter of 32 mm and a depth of 0.5 mm was formed near the center of the agar medium.
A treatment liquid was inoculated into the formed space, and a polyimide film (Kapton (registered trademark) manufactured by Toray DuPont Co., Ltd.) having a thickness of 12.5 μm and a diameter of 85 mm was disposed thereon as a dielectric. Further thereon, a nutrient agar medium having a diameter of 60 mm and a thickness of 3 mm was arranged.
The simulated packaging container was placed between the electrodes of the plasma generator, and a pulse voltage was applied between the electrodes to generate pulsed plasma inside the simulated packaging container to sterilize the simulated food. At that time, the charging voltage of the plasma generator was 16 kV, the number of pulse repetitions was 40 pps, and the number of applications was 1000 shots.
As a result of evaluating the bactericidal effect, the survival rate was about 10%.
In this case, the electric field strength of the space is considered to be about 325 kV / cm.

(Example 2)
The simulated food was sterilized in the same manner as in Example 1 except that the depth of the space was 1 mm.
As a result of evaluating the bactericidal effect, the survival rate was about 28%.
In this case, the electric field strength of the space is considered to be about 175 kV / cm.

(Example 3)
The simulated food was sterilized in the same manner as in Example 1 except that the depth of the space was 1.5 mm.
As a result of evaluating the bactericidal effect, the survival rate was about 48%.
In this case, the electric field strength of the space is considered to be about 125 kV / cm.

Example 4
The simulated food was sterilized in the same manner as in Example 1 except that the depth of the space was 3 mm.
As a result of evaluating the bactericidal effect, the survival rate was about 97%.
In this case, the electric field strength of the space is considered to be about 70 kV / cm.

(Comparative Example 1)
The simulated food was sterilized in the same manner as in Example 1 except that the depth of the space was 4 mm.
As a result of evaluating the bactericidal effect, the survival rate was 100%, and the bactericidal effect was not recognized.
In this case, the electric field strength of the space is considered to be about 50 kV / cm.

(Comparative Example 2)
The simulated food was sterilized in the same manner as in Example 1 except that no space was formed in the agar medium.
As a result of evaluating the bactericidal effect, the survival rate was 100%, and the bactericidal effect was not recognized.

(Comparative Example 3)
The simulated food was sterilized in the same manner as in Example 1 except that no polyimide film was inserted between the upper and lower two agar media.
As a result of evaluating the bactericidal effect, the survival rate was 100%, and the bactericidal effect was not recognized.

DESCRIPTION OF SYMBOLS 1 Packaged object 2a, 2b Packaging container 3a, 3b Object to be sterilized 4 Dielectric 5 Space 6a, 6b Electrode 7 Capacitor 8 Pulse transformer 9 Triggertron gap switch 10 Trigger circuit

Claims (7)

A method of sterilizing an object to be sterilized in a packaging container using pulse plasma,
Disposing the article to be sterilized packed by the packaging container between the first electrode and the second electrode of the plasma generator; and
Applying a pulse voltage between the first electrode and the second electrode of the plasma generator to generate a pulsed plasma inside the packaging container;
Including
A dielectric is inserted into the article to be sterilized,
A space is formed between the object to be sterilized and the dielectric,
In the step of generating the pulsed plasma, an electric field having a magnitude capable of obtaining a bactericidal effect is generated in the space.
The said sterilization method characterized by the above-mentioned.   The sterilization method according to claim 1, wherein the magnitude of the electric field exceeds 50 kV.   The sterilization method according to claim 2, wherein the magnitude of the electric field is 100 kV or more.   In the space formed between the object to be sterilized and the dielectric, the distance between the surface of the dielectric facing the object to be sterilized and the surface of the object to be sterilized facing the dielectric The sterilization method according to any one of claims 1 to 3, wherein a depth of the defined space is 3 mm or less.   The sterilization method according to claim 4, wherein the depth of the space is less than 2 mm.   The sterilization method according to any one of claims 1 to 5, wherein the dielectric is a polyimide resin. A product to be sterilized using a pulsed plasma packaged by a packaging container,
A dielectric is inserted into the article to be sterilized,
A space is formed between the object to be sterilized and the dielectric,
The space is configured to generate an electric field having a magnitude capable of obtaining a sterilizing effect by generating pulsed plasma inside the packaging container.
The packaged article to be sterilized is characterized by the above.

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