JP2944199B2 - Sterilization method of experimental animal feed by electron beam irradiation - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for sterilizing feed for clean laboratory animals by electron beam irradiation.

[Prior art] Clean animals (including sterile animals) such as mice and rats intended for use in animal experiments are sterilized or used not only in the breeding environment but also in feeds for breeding (experimental animal feed). Conventionally, sterilization has been performed due to environmental restrictions such as breeding in a clean state. Conventional methods for sterilizing feed include high-pressure steam sterilization and cobalt-
Either radiation sterilization method using gamma rays from 60 (hereinafter referred to as gamma ray sterilization method) or gas sterilization method using ethylene oxide gas, but gas sterilization method has high carcinogenicity due to residual gas. From the point of view, it is practically hardly used at present, and sterilization is performed by high-pressure steam sterilization or gamma-ray sterilization.

In the case of the high-pressure steam sterilization method, in the sterilization step, first, a laboratory animal feed contained in a container such as a bag or a can is placed in an autoclave. Next, after the inside of the autoclave is evacuated, steam is supplied and the temperature is maintained at 121 ° C. for 20 minutes. Thereafter, exhaust steam and vacuum evacuation are performed, and finally, hot air supply and drying are performed to complete the sterilization process.

On the other hand, in gamma ray sterilization, sterilization is performed according to the following procedure. The experimental animal feed previously packed in a plastic bag or can is placed in a cardboard box of a fixed size, and the cardboard box is further placed in a carton case. Next, the case is placed on a conveyor and moved to a cobalt-60 irradiation room, and a predetermined amount of gamma rays are irradiated in the irradiation room to sterilize the case. Gamma ray sterilization conditions for a cobalt-60 irradiation facility that is currently operating to perform sterilization on a commercial scale are as follows: Sterilization doses range from 10LGy to 50KGy, and are irradiated in air at room temperature. The irradiation time (sterilization time) required for one carton case in a normal commercial scale facility (500,000 Ci) is about 2.0 hours for 10KGy irradiation and about 10 hours for 50KGy irradiation.

The outline of both the high-pressure steam sterilization method and the gamma-ray sterilization method, which are the current sterilization methods, has been described above. Each method has advantages and disadvantages.

The high-pressure steam sterilization method is advantageous in that sterilization costs can be reduced from the economic point of view, and that the equipment is simple and easy to maintain and manage. It is disadvantageous in that it becomes harder or more brittle), the vitamin components in the feed deteriorate, and the preference for sterile feed decreases. Further, after sterilization, moisture due to steam remains in the feed, which shortens the storage period of the feed. On the other hand, in the gamma ray sterilization method, contrary to the former sterilization method, there is almost no change in physical properties of the feed after sterilization, the deterioration of vitamin components is small, and sterilization does not affect the storage period of the feed, etc. However, on the other hand, there are disadvantages such as high sterilization cost and difficulty in maintaining and managing a gamma irradiation facility.

As described above, gamma ray sterilization is superior to high-pressure steam sterilization in terms of changes in the physical properties of feed, deterioration of vitamin components, and palatability due to sterilization, but this is quantitatively determined by experiments. Is shown in According to Kuwahara et al.'S experimental report (31st Annual Meeting of the Japan Society of Experimental Animal Science, 1984), in physical property changes, the hardness of feed changed by up to several tens of percent before and after high-pressure steam sterilization, whereas before and after irradiation with gamma-ray sterilization. It has been found that there is almost no change in hardness. Also, regarding vitamin degradation, especially vitamin
Degradation of B ₁ is while hardly a gamma sterilization, greatly deteriorates the high-pressure steam sterilization, it has been found that more than half as compared with the untreated deteriorates. Furthermore, the palatability has been found to be 2-3 times higher than that for steam-sterilized feed from the preference ratio for gamma-ray-sterilized feed. However, gamma ray sterilization, which is an excellent sterilization method, is a drawback of this sterilization method as described above in terms of sterilization processing capacity, maintenance and management of gamma ray irradiation equipment, sterilization cost, etc., and these are inferior to high-pressure steam sterilization method. It is.

As shown the current irradiation conditions in gamma sterilization,
Since irradiation of one carton case requires 2.0 hours or more, the gamma-ray sterilization method significantly reduces the productivity of the sterilization process, and the sterilization cost is necessarily high. Further, since the half-life of cobalt-60 is about 5.3 years, the activity of cobalt-60 decreases with time, that is, the amount of gamma irradiation per unit time decreases, and the irradiation time (sterilization time) increases. As the time increases, the sterilization capacity is increasingly reduced, further increasing the cost of sterilization. For example, in the case of a 500,000 Ci commercial irradiation facility, the irradiation time, which required 10 hours for 50KGy irradiation at the time of completion of the facility, doubles to 20 hours after about 5 years, and the productivity of the sterilization process has passed over time. Will be dropped with you. However, in commercial irradiation facilities, in order to keep the irradiation time (sterilization time) as constant as possible, cobalt-
The replenishment of 60 sources is currently underway, but the replenishment of these sources is currently a problem. Since the gamma-ray source Cobalt-60 is not produced in Japan, all irradiation facilities in Japan rely on imports from the Canadian Atomic Energy Authority (AECL), resulting in supply instability and safety during transportation. In addition to securing a large amount of radiation, the cost of the radiation source itself is high, and the maintenance cost of the irradiation facility is high, and the sterilization processing capacity is low. .

Despite being an excellent sterilization method, gamma ray sterilization is not so widespread due to the problems described so far, and currently only accounts for 5 to 6% of the total sterilized feed. As a proposal, a sterilization method by electron beam irradiation is shown,
No specific irradiation conditions are presented, and no special features are disclosed, so that the irradiation conditions, productivity, etc. are considered to be comparable to those of gamma-ray sterilization, and its practical use is not yet known. .

[Problems to be Solved by the Invention] As the development of better new drugs or the establishment of advanced technologies in the field of biotechnology is progressing steadily, the demands on the quality of experimental animals will become increasingly severe in the future. Can be easily guessed. To meet such demands, breeding in a clean environment, including aseptic conditions that are more controlled than ever, is necessary.
There is a demand for a feed that has no change in physical properties due to sterilization and has no component deterioration.

The present inventors have already invented and applied for a patent for a novel sterilization method for experimental animal feed using a high-energy electron beam and having excellent productivity as a new sterilization method to respond to such a demand. However, there is no existing commercial electron beam irradiation facility for carrying out the invention of this application, and at present the implementation of the invention has not been easy. Therefore, in the present invention, for the purpose of using the existing 5MeV or less medium energy electron beam (more than 1MeV and 5MeV or less) irradiation facility in the present invention, electron beam irradiation conditions that can be sterilized even with medium energy,
It is another object of the present invention to establish a packaging form in consideration of the restriction of electron beam transmission ability due to low energy.

[Means for Solving the Problems] As a novel sterilization method having the advantages of gamma ray sterilization from cobalt-60 and the advantages of high-pressure steam sterilization, the present inventors have used electron beams. We have found electron beam sterilization.

As a result of further study of the invention already filed, the present inventors have found that sterilization is possible even when the energy and the current value of the electron beam exceed the ranges already filed. That is, the electron beam energy, the energy of 3 MeV to 5 MeV, and the current value are
The present inventors have found that even if the amount exceeds 10 mA and up to 40 mA, it can be sterilized without affecting the animal feed components particularly with respect to vitamins, and have proposed the present invention. In this case, since the electron beam penetrating ability in the electron beam energy range proposed this time is small, the thickness of the object to be irradiated should be uniform, or when performing double-sided irradiation, the reversal from the front side to the back side is performed. At times, it is required that feed powder and feed solids in bags (including containers) do not move in the bags, but for this requirement, the present inventors vacuum degassed inside bags with high gas barrier properties. Have found that the packaging style to be used is sufficient. Furthermore, the packaging form in which the inside of the bag is vacuum degassed is also an excellent feature as the packaging form in the following points.

(1) Since the feed is fixed in bags by vacuum degassing, the solid feed is broken during transportation and other handling,
Collapse can be prevented.

(2) Since the pinhole formed in the bag is inspected by vacuum degassing packaging, the sterilization state can be inspected by swelling of the bag after degassing.

(3) The volume of the feed packed in the bag shrinks due to vacuum degassing, and the handling becomes easy because the volume becomes small.

Low energy less than 1 MeV or 5 MeV
Medium-energy electron beams up to medium energy have been used for the purpose of improving plastics and rubber products, or for sterilizing medical devices, but there are no applications for sterilizing experimental animal feed. The present invention provides unprecedented knowledge and techniques regarding sterilization methods for experimental animal feed, since the effect of radiation on vitamins and the like was not clear.

An electron beam is one of radiations similar to gamma rays in terms of chemical and physical effects in terms of radiation effects on substances, but gamma rays are radiations that differ greatly in terms of penetrative power to an irradiated object. The difference is that radioisotopes are the source of gamma rays, whereas electron beams are radiation that is generated electrically by an electron accelerator.
Therefore, it can be said that the electron beam irradiation facility does not require replenishment of the radiation source as in the gamma ray irradiation facility, and operates the accelerator only at the time of irradiation, thereby facilitating the maintenance and management of the facility.
Furthermore, while gamma rays from cobalt-60 are radiation with a constant energy of 1.25 MeV, electron beams can freely control the magnitude of energy and current by the performance of the electron accelerator, which means that productivity can be controlled. It becomes possible to set irradiation conditions according to an object to be irradiated.
In addition, the use efficiency of gamma rays is low because it is applied to the entire space of the generated gamma rays, whereas the use efficiency of electron beams is high because electrons are emitted only to the object to be irradiated. Productivity grows. The present inventors have focused on such characteristics of the electron beam and have found a method of sterilizing experimental animal feed using the electron beam.

The electron beam sterilization method by the present inventors is a method in which an object to be irradiated is loaded on a conveyor and carried into an electron beam irradiation chamber and sterilized by electron beam irradiation as in the case of the gamma ray sterilization method. 3-5MeV, current value exceeds 10mA,
Characterized in the range up to 40mA.

[Operation] The magnitude of the energy of the irradiated electrons is proportional to the transmission distance in the irradiated object for the irradiated object having the same specific gravity. FIG. 1 shows the relationship between the energy of the electron beam and the transmission distance of the electron beam in the irradiated sample having an average specific gravity of 1.0. Specific gravity d
The transmission distance of the electron beam into the sample having an average specific gravity of 1.0 = the transmission distance (cm) of the electron beam in the sample to be irradiated has a relationship of specific gravity d. For electrons with 5 MeV energy, the transmission distance is about 2.2
〜3.1cm (corresponding to the average specific gravity 0.7 ~ 0.5), with energy of 5MeV, about 1.4 ~ 2cm for irradiated electrons (average specific gravity
Corresponds to 0.7-0.5. ). Therefore, in the electron beam sterilization according to the present invention, the thickness that can be sterilized is 3 in order on both sides of the cardboard box filled with the experimental animal feed (average specific gravity: 0.5).
Assuming irradiation of 〜5 MeV, the thickness of the vacuum pack is about 2 cm to about 8 cm from FIG. 1 (average specific gravity 1.0).

Next, regarding the current value of the irradiation electrons, the inventors have at most
It is up to 40 mA, preferably 20 mA to 30 mA. The larger the current value of the irradiated electrons, the larger
Although the irradiation dose per unit time increases and the productivity increases, the maximum is set to 40 mA in consideration of the heat generation of the experimental animal feed due to the large current or the vitamin deterioration due to the heat.

Irradiation electron energy as preferred in the present invention, and
Assuming a commercial electron accelerator capable of irradiating 3 MeV electrons with a current value of 25 mA from the current value range, the specific gravity is 0.5
10kg per hour for experimental animal feed
Approximately 7.0m ^{3 for} y irradiation and 1.4m ^{3 for} 50KGy irradiation. This throughput is 10% of gamma sterilization with 500,000 Ci cobalt source.
0.2 m ^3, it is seen that extremely high productivity of about 35 times that in the 0.04 m ³ at 50KGy in KGy. Therefore, even in the energy current range proposed by the present invention, the sterilization cost is significantly reduced as compared with the gamma sterilization method.

At present, there are two types of electron accelerators, one of which is an electrostatic type (DC type) accelerator and the other type is a DC type (AC type). The former is difficult in principle to produce high-energy electron beams.Accelerators that accelerate electrons up to 5 MeV energy have been manufactured so far, but those that accelerate electrons with energies exceeding that Has not been realized. On the other hand, in the case of the linear accelerator, as described above, although the magnitude of the current value is limited by the acceleration principle, the electron energy can be accelerated infinitely in principle, and the desired energy level can be increased. Can accelerate the electrons up to.

Therefore, a DC type accelerator is suitable from the energy and current value ranges according to the present invention. After the electron beam irradiation, the temperature rise of the experimental animal feed (solid sample), the effect on the vacuum packaging form, and the degree of vitamin degradation were evaluated in consideration of the heat generated by the increase in the current value range.

Examples of the present invention will be described in the following order. In each of the examples, an electron beam generated from a DC accelerator is used.

[Example 1] A solid sample (wheat, bran, corn, soybean meal, whitefish meal, brewer's yeast, alfalfa meal, mineral mixture, vitamin mixture) for a mouse and a rat of 14 mmφ x an average length of 18 mm was put in a polyethylene bag of 500 g 90 μm. After spreading the solid feed inside the bag so that the solid feeds do not overlap each other in the bag, set the inside to the vacuum setting pointer -1000 mbar using MULTIVAC A300 type, deaeration by automatically processing the vacuum speed, This was subjected to electron beam sterilization.
The electron beam accelerator used was a DC type, and irradiation was performed at an electron beam energy of 3 MeV and a current value of 20 mA. The irradiation of the feed placed on the stainless steel belt conveyor with 5 Mrad of electron beam from above was completed in a short time within 30 seconds per bag. When irradiating the same feed as above in a separate bag that had not been vacuum degassed, the temperature inside the solid feed was also measured using a thermocouple. As a result of the measurement, the central temperature of the solid feed was 55 ° C on average, and it was found that there was no practical problem with the vacuum-packed packaging form and vitamin deterioration of the feed at such a temperature rise.

[Example 2] Irradiation was performed in the same manner as in Example 1 except that only the current value of the electron beam was changed to 25 mA.
° C, and even at this current value, the packaging form of the vacuum pack was sound.

[Example 3] After 500 g of the solid feed as in Example 1 was put in a plastic bag, the feed in the bag was spread over the entire bag so that the feeds did not overlap, and the mouth of the plastic bag was opened without degassing. Heat seal,
Six same bags were prepared, placed in a cardboard box in a stacked manner, and irradiated with an electron beam from above. Electron beam irradiation is a DC type accelerator, electron energy, 5 MeV, current value, 10
Performed in mA. After irradiation, the sterilization test was performed on each of the six stacked stages. As a result, all the stages other than the first stage were positive as shown in Table 1, but the first stage was negative and the 5 MeV electron If the linear energy is 14mmφ solid feed, irradiation from one side (in the case of single-sided irradiation), sterilization is possible if the thickness of the first step (14mm) in this type of packaging, confirmed.

* Indicator bacteria: B. pumilas Dose marker: Radiochromic film ◎ Number of test samples 10 pellets, thioglycolate medium,
Aseptic test results show the number of positive specimens after culturing for 7 days. [Effect of the Invention] As described above, the method of the present invention for performing sterilization treatment by electron beam irradiation has an irradiation energy of 3 MeV to 5 MeV, a current value exceeding 10 mA, It is characterized by short-time irradiation of up to 40 mA, is more productive than conventional gamma-ray sterilization, is easier to maintain, and meets the demands that there is no change in the physical properties of the feed due to sterilization and no degradation of the ingredients. A new sterilization method that can be sufficiently answered is provided, and at the same time, a package form suitable for electron beam irradiation is established by bagging and vacuum degassing the feed.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the energy of an electron beam and the transmission distance of an electron beam in an irradiation object having an average specific gravity of 1.0.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) A23K 1/18 A23L 3/005

Claims (1)

(57) [Claims] 1. A fixed amount of feed for clean experimental animals is packed in bags, the inside of which is evacuated to vacuum, and irradiated with energy.
A method for sterilizing an experimental animal feed with improved productivity, comprising irradiating an electron beam from 3 MeV to 5 MeV, an electric current value exceeding 10 mA and up to 40 mA for a short time.