JP2010187648A - Sterilization method using air plasma - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sterilization method by plasma irradiation, capable of sufficiently sterilizing a sterilizing object such as vegetables or fruits at a relatively low cost without deteriorating quality of the sterilizing object. <P>SOLUTION: The sterilizing object such as vegetables or fruits is sterilized by a plasma irradiation process to irradiate the object with air plasma. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for sterilizing food to be sterilized, particularly foods such as vegetables and fruits, by irradiating with air plasma. Further, the present invention relates to a method of performing not only sterilization but also drying and washing.

  As methods for drying instant food ingredients and the like, typical methods currently employed include freeze-drying (FD) and hot-air drying (AD).

The freeze-drying method (FD) has little loss of nutritional value of ingredients, is excellent in reconstitution with water and hot water, and is widely used for drying protein-rich materials and flavored vegetables.
However, in the case of raw vegetables, especially foreign vegetables, the contamination by microorganisms is severe, and they are contaminated with 100,000 to 1 million microorganisms per gram. Many of these microorganisms grow on bacterial spores and are not easily killed by heating. If they are not sufficiently sterilized, they can cause rot of processed foods. Is important to.

For this reason, many dried vegetables are dried by the hot air drying method (AD).
However, even with this hot air drying method, sufficient heating temperature and treatment time are required for sterilization. Therefore, the quality of vegetables, such as fragrance, color, and nutritional value, is impaired.

  Therefore, there is a demand for a sterilization / drying method that sufficiently sterilizes and does not impair the quality of vegetables.

Therefore, the inventors of the present application have previously proposed sterilization by irradiating food or the like with oxygen plasma (see Patent Document 1).
By irradiating oxygen plasma, bacteria such as microorganisms adhering to the surface of the material can be sterilized and removed without deteriorating the quality of the material such as food.
Further, by using oxygen gas, the processing cost can be reduced as compared with the case where plasma is generated using a special gas.

JP 2006-333824 A

By the way, if vegetables are irradiated with oxygen plasma, moisture will be diffused to some extent, and it will become wilted.
Therefore, it is necessary to supply moisture in order for the vegetables after plasma irradiation to have a crunchy and crunchy state.
In order to supply moisture, for example, ice is put in a sufficient amount of water to make cold water, lemon juice is dripped in it, and it is immersed for about the same time (about 30 minutes) as the plasma irradiation time, and then cold water Pull up from.
Therefore, in order to obtain a crunchy state, it is necessary to perform a process of supplying moisture before shipping as a product, which increases the manufacturing cost of the product.

In the case of irradiating oxygen plasma or nitrogen plasma, oxygen gas or nitrogen gas is required as a raw material of plasma, so that the raw material cost is increased.
Furthermore, the freeze-drying method (FD) and the hot air drying method (AD) both require a large cost for the drying process.

  In order to solve the above-mentioned problems, in the present invention, it is possible to sufficiently sterilize the object to be sterilized at a relatively low cost without damaging the quality of the object to be sterilized such as vegetables or fruits. A sterilization method by plasma irradiation is provided.

  The sterilization method by plasma irradiation of the present invention performs a plasma irradiation process of irradiating air plasma on an object to be sterilized to sterilize the object to be sterilized.

In the plasma irradiation step of the sterilization method of the present invention, it is also possible to irradiate air plasma while stirring the object to be sterilized.
In the sterilization method of the present invention, the food to be sterilized can be food, and further, the food to be sterilized can be food containing vegetables or fruits.
In the sterilization method of the present invention, the object to be sterilized can be further dried in the decompression step and the plasma irradiation step before the plasma irradiation step.
In the sterilization method of the present invention, a hydrophilic functional group is further introduced into the surface of the sterilized product (food containing vegetables or fruits) during the plasma irradiation step, and the sterilized product after the plasma irradiation step. It is also possible to carry out a step of washing.

  According to the sterilization method of the present invention described above, it is possible to generate a sterilization action by air plasma at a relatively low temperature by irradiating with air plasma.

Further, according to the sterilization method of the present invention, it is possible to introduce a hydrophilic functional group (for example, a nitro group or a second amide group) onto the surface of an object to be sterilized such as food by irradiation with air plasma. Become. As a result, it is possible to restore a crisp and crunchy state when the article to be sterilized is returned to water, and to enhance the drainage effect of bacteria when the article to be sterilized is washed.
In particular, when a hydrophilic functional group is introduced into the surface of a food containing vegetables or fruits in the plasma irradiation step, and the step of cleaning the sterilized material is performed after the plasma irradiation step, the hydrophilic functional group is used. Since the introduction of the group enhances the drainage effect of the bacteria, the bacteria can be efficiently discharged and sterilized in the washing step.

According to the above-described present invention, it is possible to generate a sterilization action at a relatively low temperature, and it is possible to perform sterilization sufficiently without deteriorating the quality of the irradiated object.
Further, according to the present invention, since air plasma is used, the cost of the plasma raw material can be greatly reduced as compared with the case of using special material plasma, oxygen plasma, or nitrogen plasma, The irradiated object can be sterilized at a low cost.
In particular, when the article to be sterilized is a food, it is possible to sufficiently sterilize while maintaining quality such as aroma, color and nutritional value.

  Further, in the plasma irradiation step, when the air plasma is irradiated while stirring the object to be sterilized, the sterilization efficiency can be improved.

  In addition, when the object to be sterilized is dried in the decompression process and the plasma irradiation process before the plasma irradiation process, not only sterilization but also the object to be sterilized can be dried.

  In addition, when a hydrophilic functional group is introduced on the surface of food containing vegetables or fruits in the plasma irradiation process, and the sterilized product is washed after the plasma irradiation process, not only sterilization In addition, the sterilization of the article to be sterilized can be performed efficiently.

It is a schematic block diagram of one form of the plasma irradiation apparatus for performing the sterilization method of this invention. (A)-(c) It is a photograph which shows the change by the plasma irradiation of the raw food mixed vegetable of vegetable group 1, and a Japanese radish. (A)-(c) It is a photograph which shows the change by the plasma irradiation of the dry ramen ingredients of vegetable group 2. FIG. It is a photograph which shows the state of the vegetable of the vegetable group 3 after air plasma irradiation. (A)-(e) It is a photograph which shows the state which immersed each vegetable of FIG. 4 in water, and returned. It is a photograph which shows the culture result of raw food mixed vegetables (vegetable salad). It is a photograph which shows the culture result of a Japanese radish. It is a photograph which shows the culture | cultivation result of a dry ramen ingredient material. It is a photograph which shows the culture result of dry onion. It is a photograph of a stirring type low temperature plasma apparatus. It is the identification result by FT-IR of the original sample of Hijiki. It is the identification result by FT-IR of the sample irradiated with the air plasma of Hijiki. It is an atom identification result by XPS survey measurement of the original sample of Hijiki. It is the identification result of the atom by XPS survey measurement of the sample irradiated with the air plasma of Hijiki. It is a figure which shows the change of the colony number of a microbe by the frequency | count of washing of hijiki. It is a medium photograph of a hijiki buffered with silver ion water.

Hereinafter, specific embodiments of the present invention will be described.
In the present invention, sterilization is performed by irradiating an object to be sterilized (for example, food or spices including vegetables and fruits) with air plasma.

The air plasma can be generated by introducing air after the inside of the plasma generator is depressurized to a predetermined vacuum state.
At this time, air plasma can be generated at a low temperature of 70 ° C. or lower.

By depressurization before the generation of air plasma, some dehydration can be performed from vegetables and fruits, and then sterilization and dehydration can be performed by generating air plasma at low temperature and irradiating with air plasma . That is, in the sterilization method of the present invention, it is possible to dry the irradiated object in the decompression step and the plasma irradiation step before the plasma irradiation step.
For example, only pressure reduction is performed for 60 minutes to dehydrate to some extent, and then air plasma is irradiated for 30 minutes to perform sterilization and dehydration.
By irradiating the air plasma in a low temperature state, the quality of the sterilized object such as vegetables and fruits due to heating can be prevented and sufficiently sterilized.
By irradiating with air plasma, bacteria attached to the surface of an object to be sterilized such as vegetables and fruits can be reduced as much as possible.

In the sterilization method of irradiating oxygen plasma described in Patent Document 1, it is considered that bacteria are killed by the oxidizing power of ozone (O ₃ ) and hydroxyl radical (.OH).
In addition, it is considered that bacteria are killed by the action of nitrogen radicals or the like in the sterilization method in which nitrogen plasma is irradiated.

In contrast, in the present invention, since air plasma is irradiated, in addition to ozone and hydroxyl radical, nitrogen monoxide (NO) radical and superoxide anion radical (. It is thought that bacteria are killed by peroxynitrite (ONOO ⁻ ) radicals generated by reaction with O ₂ ⁻ ) and having strong oxidizing power.
Therefore, according to the present invention, the sterilization effect can be enhanced by irradiating with air plasma, as compared with the case of irradiating only oxygen plasma or the case of irradiating only nitrogen plasma.
Further, according to the present invention, since air is used as a plasma raw material (precursor), the plasma raw material is less expensive than the case of irradiating only oxygen plasma or the case of irradiating only nitrogen plasma. The cost of sterilization by irradiation can be greatly reduced.

Furthermore, according to the present invention, by introducing air plasma, a hydrophilic functional group (for example, a nitro group or a second amide group) is introduced into the surface of an object to be irradiated including organic substances such as food. Is possible.
Thereby, it is considered that when an irradiated object such as food after plasma irradiation is returned to water, it can be restored to a fresh and crunchy state.
In addition, the hydrophilic functional group can enhance the drainage effect of the bacteria when the object to be sterilized is washed.

In the sterilization method of the present invention, the sterilization efficiency can be increased and the sterilization time can be shortened by stirring the irradiated object in the plasma irradiation step.
When an object to be irradiated is placed on a flat plate and the surface of the object to be irradiated is irradiated with plasma, there are irradiation unevenness and an irradiation amount limitation.
On the other hand, by stirring the irradiation object, the plasma irradiation surface is not limited, and the sterilization can be performed with a small dose by improving the sterilization efficiency.

Depending on the nature of the vegetables and fruits, it is preferable to cut them with a knife, peel them, or subdivide the leaves into appropriate sizes. Thereby, sterilization can be performed more efficiently.
For example, leafy vegetables such as cabbage can be sterilized more efficiently if they are subdivided for each leaf rather than the whole because bacteria may exist in the gap between the leaves.

In spices such as pepper and sesame seeds, attachment of thermophilic bacteria (spore bacteria) is more problematic than general live bacteria.
In order to sterilize thermophilic bacteria (spore bacteria), it is necessary to perform sterilization treatment at a higher temperature than in the case of sterilizing general living bacteria. was there.
Therefore, a method capable of sterilizing thermophilic bacteria (spore bacteria) at low temperatures is highly desired in the spice industry.
On the other hand, by sterilizing spices by the sterilization method of the present invention, it becomes possible to sterilize thermophilic bacteria (spore bacteria) at a low temperature of 70 ° C. or less, so that the scent of spices is not impaired. Sterilization can be performed.

Also, porous foods such as mainsprings, hijiki, mushrooms, etc. tend to inhabit bacteria inside the food, and the survival rate of the bacteria increases as the inside of the food.
Conventionally, porous foods have been sterilized by increasing the number of washings or boil heat treatment, which is not efficient.
On the other hand, by applying the sterilization method of the present invention, it is possible to introduce hydrophilic functional groups onto the surface of the porous food by irradiating air plasma. Thereby, it is thought that it becomes possible to improve the drainage effect of bacteria when washed, and it becomes possible to remove many bacteria by washing the irradiated object after plasma irradiation with water or the like.
In order to introduce a hydrophilic functional group onto the surface of the food, it is more effective to irradiate the dry food with air plasma.

  By performing sterilization by the sterilization method of the present invention, for example, it is possible to eat the entire skin without removing the bag-like skin that wraps citrus fruits such as oranges and oranges, and the skin of grapes and the like. It is done.

In hospital food, from the viewpoint of preventing food poisoning, raw vegetables are often sterilized by heating without being used as they are.
On the other hand, by applying the method of the present invention and setting the air plasma irradiation conditions so as to be sufficiently sterilized, it is also possible to provide raw vegetables and fruits as hospital foods It is considered to be.

And, in the sterilization method of the present invention, since sterilization is performed by plasma irradiation, there is no residue of radioactive substances and chemicals, as in the case of sterilization using radiation irradiation or chemicals, and the alteration of the target object Since it does not occur, it is harmless to the human body.
In addition, foods sterilized by plasma irradiation are excellent in water-absorbing and restoring properties with water and hot water, and have enhanced aroma, color, and nutritional value compared to conventional foods that have been dried and sterilized.

  In the sterilization method of the present invention, when the object to be sterilized is further dried, it is possible to perform sterilization and drying in a one-step process, so that the conventional freeze-drying method, hot air drying method, etc. Compared with the method, the processing cost can be greatly reduced.

Furthermore, the food sterilized and dried by the plasma irradiation method according to the present invention is not completely dry compared with the food sterilized and dried by the conventional FD method or AD method, but the bacteria are sufficiently killed. Therefore, it does not corrode for a long time.
That is, according to the present invention, food that can be stored for a long period of time and sterilized can be produced.

The schematic block diagram of one form of the plasma irradiation apparatus for performing the sterilization method of this invention is shown in FIG.
This apparatus uses the plasma reaction tube furnace 5 to perform the plasma irradiation process according to the method of the present invention.
The plasma reaction tube furnace 5 includes a reaction tube for generating plasma, and a copper pipe 4 is wound around the reaction tube. The reaction tube is composed of, for example, a quartz tube.
The plasma reaction tube furnace 5 is an external induction type low-pressure low-temperature plasma furnace. For this reason, there is no electrode inside the plasma reaction tube furnace 5, and stable precursor plasma can be obtained uniformly over a large volume, and three-dimensional plasma irradiation can be performed.
Further, since the plasma reaction tube furnace 5 is composed of a quartz tube, it does not react with the plasma gas when plasma is generated, and the plasma gas permeates the quartz and directly acts on the internal working gas. is there.
In a normal usage form of the plasma irradiation apparatus, a gas cylinder for generating gas plasma is connected to the plasma reaction tube furnace 5, but in the present invention, in order to generate air plasma, in the atmosphere instead of the gas cylinder. An air suction device 6 for sucking the air is connected to the plasma reaction tube furnace 5.
This apparatus includes a high frequency power source 3 that supplies a high frequency for performing high frequency heating. High-frequency induction heating can be performed on the plasma reaction tube furnace 5 by supplying high-frequency power from the high-frequency power source 3 to the copper pipe of the electromagnetic induction coil 4.
The apparatus includes a water tank 1 and a pumping pump 2 for supplying cooling water to be fed into the high-frequency power source 3 and the copper pipe 4. In the water tank 1, the internal water is held at a constant temperature. The pumping pump 2 can circulate cooling water inside the copper pipe 4.
A liquid nitrogen trap 7 and a trap 8 containing slaked lime are connected to the rear stage of the plasma reaction tube furnace 5 as a trap part for capturing dangerous reaction exhaust gas.
At the subsequent stage, a Pirani vacuum gauge 9 and a vacuum pump 10 for measuring the degree of vacuum are provided as a vacuum exhaust device. For example, an oil rotary pump is used as the vacuum pump 10. By evacuating the inside of the plasma reaction tube furnace 5 with the vacuum pump 10, plasma can be generated at a low temperature.
Furthermore, in order to process the exhaust gas from the vacuum pump 10, an electric suction machine 11 that performs forced suction and a scrubber (exhaust gas cleaning device) 12 are provided in the subsequent stage.

And by the sterilization method of this invention, it can sterilize as demonstrated below, for example using the plasma irradiation apparatus shown in FIG.
First, an object to be sterilized (for example, vegetables or fruits) is put into the plasma reaction tube furnace 5.
Next, the inside of the plasma reaction tube furnace 5 is evacuated using the vacuum pump 10.
After reaching a predetermined initial vacuum state, air is introduced into the plasma reaction tube furnace 5 through the air suction device 6 in the roughing state.
When a predetermined degree of vacuum is reached, high frequency power is supplied from the high frequency power source 3 to the copper pipe 4 to generate air gas plasma in the plasma reaction tube furnace 5.
Active species are generated in the air gas plasma, and the object to be sterilized can be sterilized by a combined action of ozone, hydroxyl radical, nitric oxide radical, peroxynitrite radical, etc. excited by the active species. In addition, depending on the conditions, the object to be sterilized can also be dried.
Finally, the sterilized material to be sterilized is taken out by opening the doors attached to both ends of the plasma reaction tube furnace 5, and the sterilization process is completed.

The plasma irradiation apparatus for performing the method of the present invention is not limited to the apparatus configuration shown in FIG.
The apparatus configuration shown in FIG. 1 is experimental and suitable for performing plasma irradiation on a relatively small amount of an object.
In the case of sterilizing a large amount of articles to be sterilized, an apparatus configuration suitable for mass processing may be used.

Vegetables were actually sterilized and dried using the apparatus shown in FIG.
The plasma reaction tube furnace 5 is made of quartz and has an outer diameter of 300 mm, an inner diameter of 290 mm, and a length of 1000 mm so that the inside can be easily seen from a transparent quartz tube. The copper pipe 4 having a diameter of 6 mm was used and wound around the reaction tube furnace 5 made of quartz 38 times.
The high frequency power supply 3 was set to oscillate a high frequency.

<Vegetable group 1>
Cut vegetable mixed vegetables (cabbage, corn, broccoli, carrot, mizuna, daikon, radish, sunny lettuce, purple cabbage) that are commercially available as vegetable group 1 and the root parts of the commercially available radish radish were cut off. Things were prepared.

FIG. 2 shows changes caused by plasma irradiation for these raw mixed vegetables and radish of Japanese vegetable group 1. 2, (a) is a photograph before plasma irradiation, (b) is during air plasma irradiation, and (c) is a picture taken out of the furnace after 30 minutes of air plasma irradiation.
From FIG. 2 (c), it can be seen that the sample after plasma irradiation, especially the radish, is dehydrated and wilted.

<Vegetable group 2>
As the vegetable group 2, a commercially available dried ramen material by the FD method (freeze drying method) was prepared. The breakdown includes wakame (from China), carrot (from France), corn (from the United States), kelp (from Hokkaido), chopping (from China), and konoe (from China).

About the dry ramen ingredient of these vegetable groups 2, the change by plasma irradiation is shown in FIG. In FIG. 3, (a) is a photograph before plasma irradiation, (b) is during air plasma irradiation, and (c) is a picture taken out of the furnace after 30 minutes of air plasma irradiation.
From FIG. 3 (c), the material after the plasma irradiation was hardly observed visually before the irradiation.

<Vegetable group 3>
As the vegetable group 3, white leek (round cut), white leek (diagonal cut), Kinusa, cabbage flakes, spinach and salad vegetables were prepared.

Each vegetable of these vegetable groups 3 is placed side by side on a single quartz plate, placed in the plasma reaction tube furnace 5 of the plasma irradiation apparatus shown in FIG. 1, and exposed to a vacuum state for 60 minutes. Irradiated with air plasma for 30 minutes.
The state of the vegetable of the vegetable group 3 after air plasma irradiation is shown in the photograph of FIG.
As shown in FIG. 4, it is in a dry state by air plasma irradiation.

Furthermore, the dried vegetables were immersed in water and returned.
Each vegetable in the returned state is shown in the photograph of FIG. In FIG. 5, (a) is white leek, (b) is kinusaya, (c) is spinach, (d) is cabbage flakes, and (e) is salad vegetables.
As can be seen from the photographs in FIG. 5, the size and color are almost restored to the state before irradiation.
Moreover, although it is not understood from the photograph, the scent was almost restored to the state before irradiation.

  The dried vegetables shown in FIG. 4 and FIG. 5 are not completely dried compared to those by the conventional FD method or AD method, but do not corrode for a long time because the bacteria are sufficiently killed.

(Bacteria culture test for vegetables)
About vegetables, the fungus culture test was done and the sterilization effect by plasma irradiation was investigated.
First, the ingredients after plasma irradiation of the vegetable group 1 and the vegetable group 2 shown in FIG. 2 and FIG. 3 are: (1) raw mixed vegetables, (2) kaiware radish, (3) dried ramen ingredients, (4 ) Dry onion, divided into four types.
For the four types of ingredients, three types of samples were prepared: an original (raw state) sample without plasma irradiation, a sample with oxygen plasma irradiation, and a sample with air plasma irradiation. In the oxygen plasma irradiation and air plasma irradiation, the irradiation time was unified to 30 minutes.

Subsequently, each sample obtained was placed in a sample bag (sterilized) containing 100 ml of distilled water, stirred for 1 minute, and then bacteria adhering to the surface of each ingredient were released into distilled water. This liquid was used as a test liquid.
1 ml was taken from the obtained test solution, spread on a petri film, and cultured in an incubator. The culture conditions were an incubator temperature of 35 ° C., a carbon dioxide concentration of 5%, and a culture time of 48 hours.

Hereinafter, the results of culturing each of the four types of ingredients will be sequentially described.
(1) The culture result of raw mixed vegetables (vegetable salad) is shown in the photograph of FIG. In FIG. 6, the top is the original (non-irradiated) sample, the left Air is the air plasma irradiated sample, and the right O ₂ is the oxygen plasma irradiated sample. This photo shows the situation of colonies (red spots) of general viable bacteria, and the same applies to the other ingredients below.
As can be seen from the photograph in FIG. 6, the number of colonies was about 800 in the original case, but decreased to 34 when irradiated with air plasma, and decreased to about 65 in the case of oxygen plasma.
That is, the air plasma shows stronger sterilization power than the oxygen plasma.

(2) The results of cultivating radish radish are shown in the photograph of FIG. The arrangement of the sample is the same as in FIG.
From the photograph of FIG. 7, the number of colonies was as large as about 1425 in the original case, but decreased to 93 when irradiated with air plasma, and decreased to about 189 in the case of oxygen plasma. When air plasma or oxygen plasma is irradiated, the number of colonies is clearly reduced.

(3) The results of culturing the dried ramen material are shown in the photograph of FIG. The sample arrangement is the same as in FIGS.
From FIG. 8, it can be seen that the number of colonies is 13 in the case of the original, whereas the number of colonies is reduced to half or less when air plasma or oxygen plasma is irradiated.

(4) The results of cultivating dried onions are shown in the photograph of FIG. The sample arrangement is the same as in FIGS.
From FIG. 9, even in the original case, the number of colonies is as small as about 2, but it is further reduced to 0 when air plasma or oxygen plasma is irradiated.

  Table 1 summarizes the results of the bacterial culture test of the above four types of vegetables.

  As the above results show, the sterilizing effect of bacteria by air plasma irradiation of the method of the present invention clearly appears.

(Bactericidal effect of spices)
Then, the bactericidal effect of the bacteria adhering to spices (black pepper and black sesame) by the sterilization method of the present invention was examined.

<Disinfection of black pepper>
First, black pepper was prepared, and a sample in an original state not irradiated with plasma and a sample irradiated with air plasma were prepared.
The sample irradiated with air plasma produced a sample (No. 1) with an irradiation time of 0.5 hour and a sample (No. 2, No. 3) with an irradiation time of 4 hours.
For each sample, thermophilic bacteria adhering to black pepper were examined by the agar medium method.
Table 2 summarizes the air plasma irradiation conditions and the number of surviving thermophilic bacteria (per gram) of each sample.

According to Table 2, about 30000 / g of the bacteria survived in the original, but when the plasma was irradiated with air plasma at an anode voltage of 3 kV for 30 minutes, it died to the order of half of about 15000 / g. In addition, when irradiated for 4 hours, the number of bacteria was greatly attenuated to about 20 to 60 / g, and the bactericidal effect by low temperature plasma was shown.
Therefore, it can be seen that the bactericidal effect of thermophilic bacteria (spore bacteria) can be improved by increasing the irradiation time.
In addition, it cannot be said that it is an efficient sterilization method when the irradiation time is 4 hours, so there is room for devising the irradiation conditions so that a large sterilization effect can be obtained with a shorter irradiation time.

<Disinfection of black sesame>
Next, Myanmar black sesame was prepared and sterilized using a stirring type low temperature plasma apparatus.
A photograph of the stirring type low-temperature plasma irradiation apparatus used is shown in FIG.
The apparatus shown in FIG. 10 uses a cylindrical quartz tube having a diameter of 250 mm and a length of 250 mm as a stirring reactor, and a ceramic blade through which cooling water circulates is provided at the center of the reactor. It is configured to be able to stir up to a maximum of 60 rpm by moving the blades with a motor.
The outline of the apparatus is a structure in which the quartz tube reactor shown in FIG. 1 is miniaturized and a stirring blade is attached in the furnace.
In the photograph in FIG. 10, for the sake of convenience, the electrode tube coil having a diameter of 6 mm is removed for 10 turns so that the internal aspect can be confirmed.

Then, 2 kg of Myanmar black sesame was inserted into the stirring reactor of the apparatus shown in FIG. 10, the stirring speed was kept constant at 60 rpm, and plasma was irradiated to the black sesame for 2 hours while stirring.
There are five types of plasma gas: hydrogen, hydrogen + nitrogen, hydrogen + oxygen, hydrogen + air, and air. For each sample, the general viable bacteria can be determined from the original state before plasma treatment and the state after plasma treatment. The fungus culture test was conducted in the same manner as the test method for vegetables described above.
Table 3 shows the results of the plasma gas (sterilization conditions) and the fungus culture test for each sample. In addition, the difference between the number of colonies in the original state and the number of colonies after plasma treatment, that is, the number of colonies reduced by dividing the number of colonies by the original number of colonies is calculated as the “bactericidal effect”. These are also shown in Table 3.

From Table 3, it can be seen that the sterilization effect is greatest when the air plasma is irradiated. When the air plasma is irradiated, the D value is about 2 hours. This D value is an index representing the sterilization performance (death time), and is a time for decaying to 1/10 of the original number of bacteria. For example, when the original number of bacteria is 500 CFU / ml, it refers to the time to reach 1/10 of 50 CFU / ml. Here, CFU is an abbreviation for colony forming unit and literally means the number of bacterial colonies.
In addition, when the black sesame was sterilized in the same manner as the other irradiation conditions of the air plasma without stirring the black sesame, the D value was about 4 hours. That is, by sterilizing black sesame while stirring, it is possible to reduce the D value to about half that when not stirring.

(Sterilization of porous food)
Subsequently, the sterilization effect of the porous food by the sterilization method of the present invention was examined.
As a porous food, spring (Chinese) and Hijiki (Korean) were prepared, and for each food, an original sample and a sample irradiated with air plasma for 2 hours were prepared.
Then, 90 ml of PBS solution (phosphate buffer solution) is put into a sterilized stomacher bag (bag for separating and extracting bacteria), and further 10 g of a food sample is added. PBS is used as a role to keep the pH constant so that a fatal influence does not occur even if some foreign matter (falling bacteria) enters from the outside during the operation.
Next, the bacteria were separated from the food by a stomaching process (separation and extraction process of bacteria for 30 seconds by mechanical processing), and this was used as a stock solution (diluted solution to the 10th power).
Furthermore, for bacteriological examinations, in principle, if the number of bacteria is not within 30 to 300 CFU / ml on one plate, the data reliability becomes poor. Therefore, the stock solution was diluted so as to be hit within that range. The dilution method is to mix 1 ml of the stock solution with 9 ml of PBS solution to prepare a 10 1 dilution, and further mix 1 ml of the mixture with 9 ml of a new PBS solution to produce a 10 square dilution. Thereafter, in the same manner, from 10 3 to 10 7 dilution liquids were prepared.
Each diluted solution was examined for the number of various bacteria (general live bacteria, coliforms, heat-resistant bacteria, fungi). The test results are shown in Tables 4 and 5. Table 4 shows the case of the mainspring, and Table 5 shows the case of the hijiki.

From Table 4 and Table 5, the number of bacteria tended to increase in the sample irradiated with plasma.
It was also found that sterilization of the internal bacteria was difficult due to the effect of only the surface sterilization of low temperature plasma.

Here, in order to clarify the reason why the number of bacteria in the plasma irradiation sample increased in the test results shown in Tables 4 and 5, further experiments were performed.
First, the mass of the original sample and the sample irradiated with air plasma for 2 hours was measured to examine the change in mass.
Table 6 shows the mass of hijiki before and after plasma irradiation and the dry amount as measurement results.

  From the results in Table 6, it was found that the dry amount before and after plasma irradiation was only 0.35 g, which was a slight decrease with respect to the total mass.

Next, the influence of the water absorption difference, that is, the water absorption effect due to the binding of hydrophilic groups to the surface of hijiki by plasma irradiation was investigated.
For the original sample and the sample irradiated with air plasma for 2 hours, the amount of water absorbed after 10 g of sample was immersed in 300 ml of purified water for 45 minutes was measured. The 45 minute water immersion time is the return time with the dry hijiki water used.
Table 7 shows the measurement results.

From Table 7, it can be seen that the amount of water absorbed is increased by 26 ml by air plasma irradiation.
From this, it is considered that the state of the surface of the hijiki is changed by the irradiation of air plasma.

Next, the functional groups on the surface of the hijiki were identified by FT-IR (Fourier transform infrared spectrophotometer) for each of the original and hijiki samples irradiated with air plasma.
The identification results are shown in FIGS. FIG. 11 shows the identification result of the original sample, and FIG. 12 shows the identification result of the sample irradiated with air plasma.

From the results of FIG. 12, in the seaweed sample irradiated with air plasma, - increasing (NHCO) of secondary amide group (1300 cm ^-1) and -NO ₂ nitro groups (890 cm ^-1) was confirmed. That is, it can be seen that these functional groups increase the water absorption effect due to hydrogen bonding.

Next, the abundance of atoms in each sample of hijiki before and after plasma irradiation was quantified by XPS (X-ray photoelectron spectroscopy).
FIG. 13 shows the result of atom identification by XPS survey measurement of the original sample of Hijiki. FIG. 14 shows the result of atom identification by XPS survey measurement of a sample irradiated with hijiki air plasma for 2 hours.
Further, the ratio of atoms by XPS multi-measurement of FIGS. 13 and 14 is calculated and shown in Table 8.

From the results shown in FIGS. 13 and 14 and Table 8, it was found that oxygen components contained in hijiki increased by 10% and nitrogen atoms increased by 0.53% after air plasma irradiation.
Considering together with the results of identification of the functional groups on the surface of hijiki by FT-IR, the nitro group contained oxygen atoms, so the nitro group was bound inside the hijiki porous material, and the drainage effect of the bacteria was improved. That was proved.

Next, the effect of draining bacteria by the number of washings of each sample of hijiki before and after plasma irradiation was examined.
Each sample of Hijiki was washed for 10 minutes under running water, and this state was designated as Run1.
Then, the sample in the state of Run1 was washed again under the same conditions, and this state was designated as Run2.
Furthermore, the sample in the Run2 state was washed again under the same conditions, and this state was designated as Run3.
About the sample of each state of Run1, Run2, Run3, the number of bacteria was investigated by the bacteriological examination by the Petri film method. Specifically, using 10 g of the washed sample, 1 ml of the stock solution was extracted from each sample by the same stomaching treatment as described above, and this stock solution was put on a Petrifilm medium (a medium dedicated to general viable bacteria manufactured by 3M). Was inoculated and a fungus culture test was conducted to determine the number of bacteria. The culture conditions were an incubator room temperature of 37 ° C., a 5% CO ₂ atmosphere, and a culture time of 48 hours.
Red spots (bacterial colonies: colonies) appearing on the Petri film after culture were counted, and the number of colonies per ml was calculated. The result is shown in FIG.

From the results shown in FIG. 15, the washing and discharging amount of the bacteria in the state of Run1 in which the original sample was immersed and absorbed in purified water for 10 minutes is 620 colonies, and in Run2, it is greatly attenuated to 74 colonies. However, Run3 tended to increase to 123 colonies.
This is because water is more easily penetrated into the interior each time washing is performed, and the water absorption time is increased, so that the bacteria in the interior are easily moved, and as a result, more is discharged.
In contrast, in the sample irradiated with plasma using air as a precursor, 2805 colonies were discharged in Run1. Compared to the original, it is about 4.5 times. That is, most of the bacteria are discharged at the first time, 71 colonies for Run2 and 24 colonies for Run3, and the washing discharge amount of the bacteria decreases.

Here, looking at the total number of bacteria in Run 1 to Run 3 of the original and the plasma-irradiated sample, the original sample was 817 colonies, and the plasma-irradiated sample was found to have a bacteria drainage effect of 3.5 times that of 2900 colonies.
That is, it can be seen that in the conventional washing and draining process, the bacteria inside can not be washed efficiently, but a large amount of bacteria can be discharged in the initial stage by performing the sterilization method by air plasma irradiation of the present invention.

Next, the bactericidal effect of general viable bacteria adhering to the hijiki by the silver ion solution was verified.
The above-mentioned hijiki was buffered for about 30 seconds with a silver ion solution having a concentration of 100 ppm.
As a result, a medium photograph of hijiki buffered with silver ion water is shown in FIG.
From the photograph in FIG. 16, it can be seen that the general bacteria and thermophilic bacteria in hijiki were completely sterilized by buffering with a silver ion solution.

Next, the bactericidal effect by air plasma irradiation in a wet state was verified.
The above-mentioned hijiki was irradiated with air plasma in a state containing water for 2 hours, and a fungus culture test of the bacteria adhering to the surface of each sample before and after the plasma irradiation was performed. In the fungus culture test, as described above, a 10 square dilution (1/100) was prepared, and the number of colonies of general viable bacteria after the culture was counted. The results are shown in Table 9.

From Table 9, when the air plasma was irradiated to the elbow containing water, a large difference in sterilizing effect was not obtained between the original and the sample irradiated with air plasma.
That is, it was found that the subsequent water washing with the binding of the hydrophilic group to the hijiki surface in a dry state plays an important role in sterilization (discharge of bacteria from the plasma irradiation object).

The following knowledge was obtained from the examples described above.
(1) General viable bacteria adhering to the surface of commercially available raw vegetables could be killed and reduced to 1/20 or less by air plasma irradiation according to the present invention.
(2) When the plasma irradiation conditions are the same, air plasma has a higher sterilization effect than oxygen plasma or nitrogen plasma.
(3) Since the hydrophilic functional group can be introduced onto the surface of the food by the air plasma irradiation of the present invention, it is possible to obtain a food excellent in restoring force with water or hot water. In addition, it becomes possible to enhance the scent and color as compared to the untreated original food.
(4) By the air plasma irradiation of the present invention, thermophilic bacteria (spore bacteria) adhering to spices and the like can be sterilized at a low temperature. Moreover, the residual amount of thermophilic bacteria (spore bacteria) can be reduced by increasing irradiation time.
(5) By sterilizing the object to be sterilized while stirring, the D value can be reduced as compared with the case of not stirring. In the case of black sesame, the D value could be reduced to about half.
(6) Since the hydrophilic functional group can be introduced to the surface of the food by the air plasma irradiation of the present invention, the effect of draining bacteria during washing can be enhanced.
(7) It was found that complete sterilization was possible when hijiki, a porous food, was buffered with silver ion water.
(8) In order to introduce a hydrophilic functional group to the surface of the food, it is more effective to irradiate the dry food with air plasma.

  The present invention is not limited to the above-described embodiments and examples, and various other configurations can be taken without departing from the gist of the present invention.

  1 water tank, 2 pumping pump, 4 copper pipe, 5 plasma reaction tube furnace, 6 air suction device, 10 vacuum pump

Claims (6)

Perform the plasma irradiation process to irradiate the object to be sterilized with air plasma,
A sterilization method for sterilizing the article to be sterilized.   The sterilization method according to claim 1, wherein in the plasma irradiation step, the air plasma is irradiated while stirring the object to be sterilized.   The sterilization method according to claim 1, wherein the object to be sterilized is food.   The sterilization method according to claim 3, wherein the sterilized product is a food containing vegetables or fruits.   The sterilization method according to claim 1, wherein the object to be sterilized is dried in the decompression step and the plasma irradiation step before the plasma irradiation step. During the plasma irradiation step, a hydrophilic functional group is introduced on the surface of the object to be sterilized,
The sterilization method of Claim 4 which performs the process of wash | cleaning a to-be-sterilized object after the said plasma irradiation process.