Sterilization device and sterilization method

Abstract

Provided is a sterilization device for irradiating an electron beam more uniformly over the entire surface of food and imparting a sterilization effect based on the electron beam to the entire surface. The device comprises: an electron beam generating unit (10) for irradiating an electron beam (EB) to a processed object (e.g., a raw egg) (40); a mounting platform (22) for the processed object (40); and a slit (SL) disposed between the processed object (40) and the electron beam generating unit (10), wherein the slit unit (SL) has a plurality of openings and is disposed above a high point of the processed object (40). Thus, the processed object (40) is irradiated with an electron beam (EB) via the slit (SL), so that the electron beam can be irradiated more uniformly over the entire surface and imparting a sterilization effect based on the electron beam to the entire surface. In addition, the influence of bremsstrahlung X-rays generated by the irradiation of the electron beam on the interior of the processed object (40) can be reduced, and the dose of X-rays irradiated to the interior of the processed object (40) (the portion that becomes the edible portion) can be suppressed to a small level to meet the standards specified by laws and regulations.

Description

Technical Field

[0001] The present invention relates to a sterilization device and a sterilization method, and in particular to a technology effective for surface sterilization of food having a shell or skin covering an edible part. Background Art

[0002] When washing eggs, the cuticle on the surface of the eggshell is removed, and the micropores (stomata) in the eggshell become open. Therefore, microorganisms such as Salmonella can easily enter the micropores, which may contaminate the surface of the washed eggs.

[0003] In response to such contamination, chemical sterilization (wet sterilization) is performed. However, in chemical sterilization, there is a concern about the influence of residual chemical. For example, the flavor may be reduced due to the odor generated by the residual chemical. In addition, there is a concern about environmental pollution caused by the waste liquid.

[0004] Therefore, a dry and non-heat treatment (dry sterilization), that is, a treatment using ultraviolet rays, has been put into practical use. In addition, a dry and non-heat treatment (dry sterilization), that is, a treatment using radiation, is being studied.

[0005] For example, Patent Document 1 discloses an electron beam sterilization device, which includes: an electron beam irradiation mechanism having an irradiation window for irradiating an electron beam; a conveying mechanism for conveying a parison (article) within an irradiation area of ​​the electron beam irradiated from the irradiation window; and magnets arranged opposite to each other across a conveying path for conveying the parison by the conveying mechanism. According to this device, a magnetic field along the irradiation direction of the electron beam irradiated from the irradiation window is generated by the opposing magnets, and while the parison passes between the opposing magnets, the electron beam irradiated from the irradiation window is deflected by the magnetic field and irradiated to the parison, thereby efficiently sterilizing the article.

[0006] In addition, Patent Document 2 discloses a method and apparatus for treating poultry eggs using an electron beam for sterilizing calcium shells, and discloses a method comprising the steps of moving at least one egg through a flow path of an electron beam source and irradiating the egg to irradiate the calcium shell with various doses, and comprising the following steps: using an electron beam to irradiate the entire area of ​​the calcium shell of the egg over a large area, inserting elements in the path of the electron beam to distribute the irradiation over the entire area of ​​the calcium shell, and irradiating the calcium shell over a large area with a dose set within a prescribed target dose range; or using an electron beam source to irradiate an egg that is rotating / has been rotated within the path of the electron beam; or using an electron beam source to irradiate an egg that is held at a zero degree position on one side in a device arranged upstream of a rotating device.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2017-209136

[0010] Patent Document 2: Japanese Patent Application No. 2019-527046 Summary of the invention

[0011] Technical problem to be solved by the invention

[0012] As mentioned above, methods for sterilizing food are roughly divided into wet sterilization and dry sterilization. For example, when only the surface of eggs is sterilized, hypochlorous acid is used for wet sterilization. However, in such sterilization methods, there are problems of residual drugs and waste liquid as mentioned above.

[0013] In addition, in the treatment using ultraviolet rays (dry sterilization), the sterilization effect is limited to the surface of the egg, and there is a possibility that the inside (for example, the inside of the micropores in the eggshell) cannot be fully sterilized. In addition, if there is dirt on the surface of the egg, there is a possibility that the sterilization is not good.

[0014] In contrast, the electron beam treatment (dry sterilization) can sterilize not only the surface of the egg but also a certain depth of the eggshell, and is useful because it can sterilize through dirt on the surface of the egg.

[0015] However, in an ellipsoidal treatment object such as an egg, the distances from the electron beam source to the end and the center of the surface are different, so when the electron beam is irradiated, the surface dose will be different, making it difficult to irradiate the entire surface of the egg with the electron beam uniformly. In addition, if the irradiation intensity of the electron beam is increased in order to achieve a sterilization effect on the entire surface of the egg, the dose of the bremsstrahlung X-ray generated by the irradiation of the electron beam will increase, resulting in an increase in the internal dose of the egg.

[0016] On the other hand, even in the method of making the surface dose of the electron beam uniform by a magnetic field as described above, bremsstrahlung X-rays are generated when the electron stream is bent, which increases the internal dose of the egg.

[0017] The object of the present invention is to provide a sterilization device and a sterilization method, which can irradiate an electron beam more evenly over the entire surface of a food having a shell or a skin covering an edible part, and impart a sterilization effect based on the electron beam to the entire surface. In addition, the object of the present invention is to provide a sterilization device and a sterilization method, which can irradiate an electron beam over the entire surface of a food having a shell or a skin covering an edible part, and reduce the influence of bremsstrahlung X-rays generated by the irradiation of the electron beam on the edible part, and can suppress the dose of X-rays irradiated to the edible part to a small level to meet the standards specified by laws and regulations.

[0018] Technical solutions for solving technical problems

[0019] (1) The sterilization device of the present invention sterilizes a treatment object by irradiating an electron beam, and comprises: an electron beam irradiation portion for irradiating the treatment object with an electron beam; a mounting portion for the treatment object; and a slit portion arranged between the treatment object and the electron beam irradiation portion, the slit portion having a plurality of openings and being arranged above a high point of the treatment object.

[0020] (2) The sterilization method of the present invention sterilizes a treatment object having an edible portion and a surface portion covering the edible portion by irradiating an electron beam, and comprises: (a) a process of preparing an electron beam irradiation device, wherein the electron beam irradiation device comprises: an electron beam irradiation portion for irradiating the treatment object with an electron beam; a carrying portion for the treatment object; and a slit portion arranged between the treatment object and the electron beam irradiation portion; and (b) a process of carrying the treatment object on the carrying portion and irradiating the treatment object with an electron beam through the slit portion, wherein the slit portion in the process (b) has a plurality of openings and is arranged above a high point of the treatment object.

[0021] Effects of the Invention

[0022] According to the sterilization device and sterilization method of the present invention, for a food having a shell or skin covering an edible part, an electron beam can be irradiated more uniformly on the entire surface thereof, and an electron beam-based sterilization effect can be imparted to the entire surface thereof. In addition, for a food having a shell or skin covering an edible part, an electron beam can be irradiated on the entire surface thereof, and the influence of bremsstrahlung X-rays generated by the irradiation of the electron beam on the edible part can be reduced, and the dose of X-rays irradiated to the edible part can be suppressed to a small level to meet the standards specified by laws and regulations. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a cross-sectional view and a perspective view showing the electron beam irradiation device and the electron beam irradiation method according to the first embodiment.

[0024] Figure 2This is a cross-sectional view showing a state where an electron beam is irradiated onto an object to be processed without passing through a slit.

[0025] Figure 3 This is a schematic diagram showing the state of the electron beam irradiated to the slit or the metal thin film and the state of the bremsstrahlung X-ray.

[0026] Figure 4 This diagram shows the structure of a raw egg.

[0027] Figure 5 It is a diagram showing a surface dose measurement model 1.

[0028] Figure 6 It is a diagram showing a surface dose measurement model 1.

[0029] Figure 7 It is a diagram showing the internal dose measurement model 2.

[0030] Figure 8 It is a diagram showing the internal dose measurement model 2.

[0031] Fig. 9 Graph showing the surface dose of irradiated sample A.

[0032] Fig.10 is a graph showing surface dose based on simulation.

[0033] Fig.11 is a graph showing the internal dose based on simulation.

[0034] Fig.12 is a graph showing surface dose.

[0035] Fig.13 This means that slit 1 ( A diagram showing simulation results of the dose near the surface of an egg with a spacing of 1.5 mm).

[0036] Fig.14 is a graph showing surface dose.

[0037] Fig.15 This is a diagram showing the simulation results of the dose near the surface of the egg when the slit A is used.

[0038] Fig.16 Graphs showing the internal dose measurement results and the internal dose simulation results of the internal dose measurement model 2.

[0039] Fig.17 It is a schematic cross-sectional view showing the electron beam irradiation device according to the second embodiment.

[0040] Fig.18This is a perspective view showing the structure of a transport unit used in the electron beam irradiation device (sterilization device) according to the second embodiment.

[0041] Fig.19 It is a schematic cross-sectional view of the conveying portion in the Y direction.

[0042] Fig. 20 It is a schematic cross-sectional view of the conveying portion in the X direction.

[0043] Fig.21 It is a diagram showing an example of the structure of the support member.

[0044] Fig. 22 It is a diagram showing an example of the structure of a slit.

[0045] Fig.23 This is a diagram showing the relationship between the height of the region of the object to be processed and the area of ​​the opening. DETAILED DESCRIPTION

[0046] (Implementation Method 1)

[0047] Hereinafter, embodiments of the present invention will be described in detail based on the drawings. Note that in the following description, A to B represent greater than A and less than B (the same applies to the subsequent Embodiment 2, etc.).

[0048] Figure 1 It is a cross-sectional view and a perspective view showing the electron beam irradiation device and the electron beam irradiation method according to the present embodiment.

[0049] Figure 1 The electron beam irradiation device (sterilization device) shown in (A) includes an electron beam generating unit 10 and an irradiation chamber 20. The electron beam EB is irradiated from the electron beam generating unit 10 to a treatment object (irradiated object, treatment object such as raw eggs) 40 disposed on a mounting table (mounting unit) 22 of the irradiation chamber 20. It should be noted that the detailed structure of the electron beam irradiation device (sterilization device) refers to the description of Embodiment 2.

[0050] Here, in this embodiment, the electron beam EB is irradiated to the object to be processed 40 through the slit (slit portion, slit member) SL, so that the electron beam can be irradiated more uniformly on the entire surface thereof, and the electron beam-based sterilization effect can be imparted to the entire surface thereof. In addition, the influence of the bremsstrahlung X-rays generated by the irradiation of the electron beam on the interior (edible part) of the object to be processed can be reduced.

[0051] like Figure 1 As shown in (B), the slit SL has a metal rod 50 and a metal spacer 50s. For example, 4 long round rods and 6 short round rods are prepared, and the long round rods are 1.5 mm in diameter (sometimes represented as ) aluminum round bars, short round bars are arranged between the long round bars and at both ends of the long round bars as spacers. Thus, it is possible to form The slits SL are spaced 1.5 mm apart.

[0052] Here, the metal rod 50 and the metal spacer 50s are made of the same metal, but may be made of different metals. The width of the metal rod 50 that becomes the shielding part and the width of the metal spacer 50s that becomes the opening part can be adjusted. Carbon rods 50 and carbon spacers 50s may be used instead of metal. In addition, the slit SL may be formed by a combination of a metal rod and a carbon spacer, or a combination of a carbon rod and a metal spacer.

[0053] In addition, as the slit SL, a slit having a plurality of linear openings on a rectangular metal plate may be used. For example, by arranging linear openings with a width of 1.5 mm at intervals of 1.5 mm, a slit having a width of 1.5 mm and a width of 1.5 mm may be formed. Figure 1 (B) Slit SL of the same shape.

[0054] As the constituent material of the slit SL, it is preferable to use a material with good conductivity such as metal (for example, aluminum (Al), iron (Fe), copper (Cu), lead (Pb), titanium (Ti), tungsten (W)), carbon (C), etc. In addition, it is preferable to use a material with a small thermal expansion coefficient.

[0055] The slit SL is disposed at the highest position (referred to as a high point) of the object to be processed (here, raw eggs) 40. In the case of raw eggs, the high point is substantially the center portion in a plan view viewed from above.

[0056] Thus, according to the present embodiment, since the object to be processed 40 is irradiated with the electron beam EB through the slit SL, the electron beam can be irradiated more uniformly on the entire surface thereof, and the electron beam-based sterilization effect can be imparted to the entire surface thereof. In addition, the object to be processed 40 can be irradiated with the electron beam on the entire surface thereof, and the influence of the bremsstrahlung X-rays generated by the irradiation of the electron beam on the interior of the object to be processed 40 can be reduced, and the dose of X-rays irradiated to the interior of the object to be processed 40 (the portion that becomes the edible portion) can be suppressed to a small value to meet the standards prescribed by laws and regulations.

[0057] In contrast, Figure 2As shown in the figure, when the electron beam is directly irradiated to the object 40 to be treated without passing through the slit SL, the intensity of the electron beam is high at a high position of the object 40 to be treated (here, the raw egg), and the intensity of the electron beam is low at a low position of the object 40 to be treated (here, the raw egg). Therefore, if the intensity of the electron beam required for sterilization is set according to the position (high position) where the intensity of the electron beam is high, the sterilization power will be reduced at the low position. On the contrary, if the intensity of the electron beam required for sterilization is set according to the position (low position) where the intensity of the electron beam is low, the intensity of the electron beam becomes too high at the high position, and in particular, the internal dose caused by the bremsstrahlung X-ray becomes large. Figure 2 This is a cross-sectional view showing the case where the object to be processed is irradiated with an electron beam without passing through a slit. It should be noted that the high part of the object to be processed (here, a raw egg) 40 corresponds to the part (central part) where the distance between the object to be processed and the electron beam irradiation device (electron beam irradiation section) is small, and the low part of the object to be processed (here, a raw egg) 40 corresponds to the part (end part) where the distance between the object to be processed and the electron beam irradiation device (electron beam irradiation section) is large. In addition, the slit SL is arranged roughly parallel to the electron beam irradiation section, so the height of the object to be processed (here, a raw egg) 40 can also be determined based on the distance between the object to be processed and the slit SL.

[0058] Figure 3 Schematic diagram showing the electron beam irradiated to the slit or metal film and the bremsstrahlung X-ray. Here, as a method of reducing the dose at a high point of the object to be processed (raw egg in this case) 40, there is a method of irradiating the electron beam EB via the metal film MF. However, when the metal film MF is used, the irradiated electrons collide with the metal atoms constituting the metal film MF and are scattered. Therefore, the energy of the electrons is reduced, and the dose on the surface of the object to be processed is reduced. In addition, the generation rate of the bremsstrahlung X-rays due to electron scattering is also increased ( Figure 3 (B)).

[0059] In contrast, Figure 3 As shown in (A), when the slit SL is used, there are metal parts and space parts, and the electrons that pass through the space part are irradiated to the object to be processed while maintaining their energy. In addition, by keeping the distance between the slit SL and the object to be processed at a certain level or more, the surface dose of the electrons that pass through the space part becomes uniform. Moreover, compared with the metal film MF, the generation rate of bremsstrahlung X-rays is reduced, so it is more effective to use the slit SL.

[0060] Thus, in this embodiment, by irradiating the electron beam through the slit SL, the electron beam can be irradiated more uniformly on the entire surface of the object to be processed, and the entire surface can be given a sterilization effect based on the electron beam. In addition, the surface of the object to be processed can be efficiently sterilized without increasing the internal dose (especially the absorbed dose of X-rays (bremsstrahlung) XL).

[0061] Specifically, the electron beam EB is irradiated from the electron beam generating unit 10 through the slit SL toward the eggshell of the raw egg (the object to be processed 40) having the yolk 1 and the egg white 2, thereby sterilizing to a certain depth from the surface of the eggshell (for example, sterilizing of Salmonella) (see Figure 4 ). In addition, in the electron beam irradiation through the slit, since the irradiation time until the predetermined surface dose is reached increases, the absorbed dose of X-rays (bremsstrahlung X-rays) XL in the edible part (yolk 1 and egg white 2) inside the eggshell increases. However, due to the shielding effect of the slit on X-rays, the absorbed dose of X-rays will not be increased extremely, and for example, it can be reduced to meet the standards stipulated by laws and regulations (for example, 0.1Gy=100mGy). It should be noted that by irradiating with an electron beam of 1kGy, Salmonella was reduced to 1 / 10000, and by irradiating with an electron beam of 3kGy, Salmonella was reduced to below the detection limit.

[0062] Example

[0063] Next, the sterilization treatment of raw eggs using the electron beam irradiation device (sterilization device) and the sterilization method according to the present embodiment will be described in more detail using examples.

[0064] First, the shape of the raw egg will be described.

[0065] Figure 4 is a diagram showing the structure of a raw egg. Figure 4 As shown, a raw egg has an eggshell 4 and an egg yolk 1 and an egg white 2 inside the eggshell 4. The egg yolk 1 and the egg white 2 are connected by an egg band 3. There is a cuticle 5 on the outside of the eggshell 4, and an eggshell membrane 7 on the inner wall of the eggshell 4. A plurality of pores 6 are provided in the eggshell 4. The cuticle 5 can be removed by washing. In addition, there is an air chamber at the blunt end of the raw egg. The following simulated sample was produced based on the structure of such a raw egg.

[0066] As the electron beam irradiation device, a low energy electron accelerator (EC-250 manufactured by Iwasaki Electric Co., Ltd.) was used to irradiate electron beams at an acceleration voltage of 120 kV. A slit SL was arranged below the irradiation portion (irradiation window) of the low energy electron accelerator to irradiate electron beams.

[0067] <Surface dosimetry model 1>

[0068] In order to evaluate the absorbed dose on the surface, a model 1 using the following irradiation sample and slit was prepared. Figure 5 and Figure 6 It is a diagram showing a surface dose measurement model 1. Figure 5 It is a top view. Figure 6 is with Figure 5 The cross-sectional view corresponding to the AA section.

[0069] Raw eggs (washed eggs, M size) with cleaned surfaces were prepared. The raw eggs were cracked open along the outer periphery in the short-diameter direction, the contents and eggshell membranes were removed, and the eggs were dried to obtain eggshells on the blunt end side. A chemical process indicator label (Crosstex) C was wrapped and attached to the central part of the outer periphery of the eggshell on the blunt end side to prepare a simulated eggshell sample (raw egg simulated sample, irradiated sample) A.

[0070] Prepare 9 long round rods and 16 short round rods to make The slits SL are spaced 1.5 mm apart, wherein the long round rod is Aluminum round bars.

[0071] The slit SL was arranged above the high part of the simulated sample A of the eggshell so as to intersect with the chemical process indication label C.

[0072] The electron beam EB was irradiated at an acceleration voltage of 120 kV using a low-energy electron accelerator (EC-250 manufactured by Iwasaki Electric Co., Ltd.) The distance between the slit SL and the simulated sample A of the eggshell was set to 3 mm.

[0073] <Internal dosimetry model 2>

[0074] In order to evaluate the internal absorbed dose (bremsstrahlung dose of X-rays), a model 2 using the following irradiation sample and slit was prepared. Figure 7 and Figure 8 It is a diagram showing the internal dose measurement model 2. Figure 7 It is a top view. Figure 8 is with Figure 7 The cross-sectional view corresponding to the AA section.

[0075] 2% liquid agar was poured into a lunch box (Tupper), solidified, and then cut into 50mm×70mm pieces to make agar CD with a thickness of 13mm. Five TLD elements (TLD100: manufactured by ThermoFisher Scientific) sealed with polyethylene films were arranged on the upper and lower parts of the agar CD, respectively, and the whole was wrapped with plastic wrap. In addition, a circular calcium carbonate layer L with a thickness of 0.4mm and a diameter of 2.0cm was set on the upper part of the agar as an egg simulation sample (raw egg simulation sample, irradiation sample) B. The calcium carbonate layer L corresponds to the egg shell, and the agar CD corresponds to the inside of the raw egg (edible part, yolk and egg white).

[0076] Prepared as 18 long round bars and 34 short round bars (spacers) of aluminum round bars are used to make The slits SLa are 1.5 mm apart. The aluminum round bars are made of 25 long round bars and 48 short round bars. The slits SLb are spaced 1.0 mm apart.

[0077] The slit SL was arranged above the simulated egg sample B so as to intersect the arrangement direction of the TLD elements.

[0078] The electron beam EB was irradiated at an acceleration voltage of 120 kV using a low-energy electron accelerator (EC-250 manufactured by Iwasaki Electric Co., Ltd.) The distance between the slit SL and the simulated sample B of the eggshell was set to 3 mm.

[0079] <Simulation>

[0080] Using the particle and heavy ion transport calculation code PHITS (Version 2.96), a model based on the structure of the above-mentioned models 1 and 2 was created. Since the eggshell (main component: CaCO3) has pores, the density was set to 2.0, the density of the edible part was set to be equal to that of water, and the atmosphere was set to standard air. The dose distribution of the electron beam and the bremsstrahlung X-ray when the egg was irradiated with an electron beam was evaluated by Monte Carlo simulation. As parameters, the acceleration voltage, the position (length) of the slit, the distance between the slit and the object, the diameter of the round rods constituting the slit, the interval between the round rods, the material of the round rods, etc. can be considered. By selecting several of these parameters for simulation, the relationship between each parameter and the dose (surface dose, internal dose) was clarified.

[0081] [Example 1]

[0082] Through the surface dose measurement model 1 ( Figure 5 , Figure 6 ) and measured the surface dose of irradiated sample A.

[0083] Fig. 9 : is a graph showing the surface dose of irradiated sample A. The horizontal axis represents the length (position, mm), and the vertical axis represents the dose (kGy). In addition, the arrows represent the configuration positions of the slits SL. Fig. 9 As shown, in the case of "with slit", compared with the case of "without slit", it can be confirmed that the surface dose is reduced near the high point of the irradiated sample A, and it can be confirmed that the slit SL improves the uniformity of the surface dose.

[0084] [Example 2]

[0085] In the above-mentioned Example 1, aluminum was used as the constituent material of the slit, but the above-mentioned simulation evaluated the case where carbon (C), aluminum (Al), iron (Fe), copper (Cu), and lead (Pb) were used as the constituent material of the slit. The surface dose was calculated using the parameters based on the above-mentioned Model 1 except for the material of the round rod.

[0086] Fig.10 The figure shows the surface dose based on the simulation. The horizontal axis represents the length (position, cm) and the vertical axis represents the dose (kGy). Fig.10 As shown in the figure, it can be confirmed that the surface dose can be uniformized in any case of using carbon (C), aluminum (Al), iron (Fe), copper (Cu), and lead (Pb) as the constituent material of the slit. In terms of the material of the slit, there is no significant difference in the effect of uniformizing the surface dose among carbon (C), aluminum (Al), iron (Fe), copper (Cu), and lead (Pb).

[0087] [Example 3]

[0088] In the above-mentioned Example 1, aluminum was used as the constituent material of the slit, but the internal dose was evaluated by simulation for the case where carbon (C), aluminum (Al), titanium (Ti), iron (Fe), and tungsten (W) were used as the constituent material of the slit. The internal dose was calculated using the parameters based on the above-mentioned Model 2 except for the material of the round rod.

[0089] Fig.11 This is a graph showing the internal dose based on simulation. The horizontal axis represents the element and the vertical axis represents the dose (mGy). The elements are arranged from the left in order of atomic number from small to large. Fig.11 As shown in the figure, when carbon (C), aluminum (Al), titanium (Ti), iron (Fe), and tungsten (W) are used as the constituent materials of the slit, the greater the atomic number of the constituent material of the slit, the smaller the internal dose. It can be seen that even in low-energy electron beam irradiation of eggs, by using a slit made of a material with a large atomic number (especially metal), the X-ray dose of the edible part can be reduced.

[0090] [Example 4]

[0091] The influence of the slit spacing when an electron beam is irradiated through a slit was evaluated by simulation. Specifically, a plurality of slits are used as slits. The aluminum round bar is provided with slits 1 ( The interval is 1.5 mm), the interval is set to 1.0 mm slit 2 ( The interval is 1.0 mm), the interval is set to 0.5 mm slit 3 ( The surface dose was measured with the parameters other than the interval between the round bars (0.5 mm). The surface dose was calculated using the parameters based on the above-mentioned model 1. In addition, the surface dose was measured in the same manner for the case where no slit was used (no slit).

[0092] Fig.12This is a graph showing surface dose. The horizontal axis represents length (position, cm), and the vertical axis represents dose (Dose, kGy). In addition, the slit is configured between the position of -2 cm and the position of 2 cm. Fig.12 As shown in FIG. 1 , when no slit is used (no slit), as the pitch decreases from 1.5 mm to 0.5 mm, the surface dose value decreases. This shows that the smaller the slit pitch is, the higher the surface dose suppression effect is.

[0093] Fig.13 This means that slit 1 ( 1.5 mm spacing) in the case of a simulation result of the dose near the surface of the egg. As shown in the figure, the color below the slit 1 (SL) is lighter than that above the slit 1 (SL), and it can be seen that the dose is suppressed by the slit 1 (SL).

[0094] Here, in Fig.12 In the diagram of The shape of the graph is similar to that of the case where the slit is used (1.5 mm) and the case where the slit is not used (no slit). Fig. 9 The shapes of the graphs shown are similar, and it can be seen that the simulation results used in this embodiment are very consistent with the results of the embodiment based on specific experiments.

[0095] [Example 5]

[0096] The influence of the change in the interval between the slits when the electron beam is irradiated through the slits was evaluated by simulation. Specifically, a plurality of slits are arranged. Tungsten round rod (refer to Fig.15 ), using slits A with varying pitches at the center and both ends of the tungsten round rod and slits B with constant pitches ( The surface dose was measured by using the parameters based on the above-mentioned model 1 except for the spacing of the round bars. As slit A, a slit with a pitch of 0.5 mm in the center and a pitch of 1.0 mm at both ends was used. The surface dose was calculated using the parameters based on the above-mentioned model 1 except for the spacing of the round bars.

[0097] Fig.14 This is a graph showing surface dose. The horizontal axis represents length (position, mm), and the vertical axis represents dose (Dose, kGy). In addition, the slit is arranged at a position from -2 cm to 2 cm, or from -4 cm to 4 cm. Fig.14 As shown, compared with the case where no slit is used (no slit), the case where slit B is used ( The side using slit A (1.5 mm interval) suppressed the surface dose value, and the side using slit B suppressed the surface dose value. In addition, the side using slit A made the surface dose value more uniform compared to slit B.

[0098] As described above, it can be seen that the surface dose can be made more uniform by making the intervals between the slits denser in the center (higher part) of the egg and making the intervals between the slits sparser in the end (lower part) of the egg.

[0099] Fig.15 This is a diagram showing the simulation result of the dose near the surface of the egg when the slit A is used. As shown in the figure, the color below the slit A (SL) is lighter than that above the slit A (SL), and it can be seen that the dose is suppressed by the slit A. In addition, the color directly below the two ends of the slit A (SL) is darker than that directly below the center of the slit A (SL), and it can be seen that the color concentration on the surface of the egg is further uniform.

[0100] [Example 6]

[0101] The internal dose of the irradiated sample B was measured by the internal dose measurement model 2. In addition, the internal dose was measured in the same manner when the slit was not used. In addition, the internal dose was calculated by simulation using parameters based on the model 2. In addition, the internal dose was measured in the same manner when the slit was not used.

[0102] Fig.16 Graphs showing the internal dose measurement results and internal dose simulation results of the internal dose measurement model 2. The TLD element on the agar in the case of the slit SL with a spacing of 1.5 mm (refer to Figure 7 , Figure 8 ) produces an internal dose of about 9 mGy, using The internal dose generated by the TLD element on the agar when the slit SL was 1.0 mm apart was about 9.5 mGy, and the internal dose generated by the TLD element on the agar when there was no slit was about 12.5 mGy. The measured values ​​obtained in this example showed a high consistency with the results obtained by simulation.

[0103] In the above-mentioned Examples 1 to 6, the surface dose and the internal dose are consistent with the specific measurement results and simulation results, and it can be seen that the slit can be designed through simulation.

[0104] (Summary of processing conditions)

[0105] In the above-mentioned embodiment, the acceleration voltage is set to 120 kV, but the acceleration voltage can be adjusted within a range of less than 1 MV, for example, not less than 80 kV and not more than 150 kV.

[0106] In addition, the surface dose can be adjusted within a range of 0.1 kGy to 10 kGy.

[0107] The internal dose is preferably set to 0.1 Gy (=100 mGy) or less, which is a reference value of the internal dose allowed in food inspections, etc. It should be noted that the internal dose measurement result described in Example 6 is much lower than this reference value.

[0108] (Implementation Method 2)

[0109] In this embodiment, an example in which an electron beam is irradiated through a slit while rotating the object to be processed will be described.

[0110] Fig.17 It is a schematic cross-sectional view showing the electron beam irradiation device according to the present embodiment.

[0111] Fig.17 The electron beam irradiation device (sterilization device) shown includes an electron beam generating unit 10 and an irradiation chamber 20. The electron beam is irradiated to a processed object (irradiated object such as a raw egg) 40 arranged in the irradiation chamber 20 via an irradiation window (irradiation window) 30 provided in the electron beam generating unit 10. The processed object 40 is arranged on a conveying unit 21 such as a conveyor and is conveyed. Here, in the present embodiment, the processed object 40 is conveyed while rotating on the conveying unit 21. In this way, the processed object 40 that is conveyed while rotating is irradiated with an electron beam through the slit SL, so that the electron beam can be irradiated more evenly on the entire surface thereof, and a sterilization effect based on the electron beam can be imparted to the entire surface thereof. Moreover, as a result, the influence of the bremsstrahlung X-rays generated by the irradiation of the electron beam on the interior (edible part) of the processed object can be reduced.

[0112] Note that the structure of the slit SL can be configured similarly to that of the first embodiment, and therefore, the structure other than the slit SL will be described in detail herein.

[0113] The electron beam generating unit 10 includes a terminal 12 for generating an electron beam in a chamber, and a space (acceleration space) for accelerating the electron beam generated by the terminal 12. The space (acceleration space) of the electron beam generating unit 10 is maintained at 10°C by a vacuum exhaust system 28 to prevent the electrons from colliding with gas molecules and losing energy and to prevent oxidation of the filament 12a. -3 ~10 -5The terminal 12 has a linear filament 12a for emitting thermal electrons and a grid 12c for controlling the thermal electrons generated by the filament 12a.

[0114] In addition, the electron beam generating unit 10 includes: a heating power supply (not shown) for heating the filament 12a to generate thermal electrons; a control DC power supply (not shown) for applying a voltage between the filament 12a and the grid 12c; and an accelerating DC power supply 16c for applying a voltage (acceleration voltage) between the grid 12c and a window foil 32 provided in the irradiation window portion 30.

[0115] The irradiation chamber 20 includes an irradiation space for irradiating the electron beam to the object to be processed (irradiated object) 40. The object to be processed 40 is transported in the irradiation chamber 20 by a conveyor 21 such as a conveyor. Figure 1 In the irradiation chamber 20, the electron beam is transported from the back side of the paper to the front side. In addition, a beam collector 24 is provided in the irradiation chamber 20. The beam collector 24 absorbs the electron beam that has passed through the object to be processed 40. It should be noted that the electron beam generating unit 10 and the irradiation chamber 20 are surrounded by lead shielding plates to prevent the secondary X-rays generated when the electron beam is irradiated from leaking to the outside.

[0116] In addition, the irradiation chamber 20 is set to an atmosphere such as an inert gas or air according to the treatment content. In the case of sterilization treatment (sterilization treatment), the irradiation atmosphere in the irradiation chamber 20 is set to air (an atmosphere in which oxygen exists), and the object to be treated is sterilized by electron beam. In this case, ozone is generated from oxygen by electron beam irradiation, and then reacts with nitrogen in the atmosphere to generate nitrogen oxides. Nitrogen oxides corrode the window foil 32, so the generation of nitrogen oxides can be controlled by sending dry air from the blower 29 into the irradiation chamber 20.

[0117] The irradiation window portion (irradiation window) 30 includes a window foil 32 and a window frame portion 34 made of copper. The window frame portion 34 is used to support the window foil 32. The window frame portion 34 is formed with a rectangular (rectangular) opening. The width of the opening is, for example, about 1 cm, and its long side direction is arranged along a direction orthogonal to the conveying direction.

[0118] In addition, in the irradiation window portion 30, a cooling flow path (not shown) is formed inside in order to cool the window foil 32 whose temperature rises due to the irradiation of the electron beam. The window frame portion 34 is detachably mounted on the irradiation opening portion of the electron beam generating portion 10. The window foil 32 is detachably attached to the lower surface of the window frame portion 34. As the window foil 32, a metal foil such as aluminum foil or titanium (Ti) foil is used.

[0119] In the electron beam irradiation device of the present embodiment, when the filament 12a is energized and heated by a heating power supply, the filament 12a emits thermal electrons, and the emitted thermal electrons are attracted in all directions by the control voltage of the control DC power supply applied between the filament 12a and the grid 12c. Among them, only the thermal electrons that have passed through the grid 12c are effectively extracted as an electron beam. Then, the electron beam extracted from the grid 12c is accelerated in the acceleration space by the acceleration voltage of the acceleration DC power supply 16c applied between the grid 12c and the window foil 32, passes through the window foil 32, and irradiates the processed object that is transported while rotating in the irradiation chamber 20 below the irradiation window portion 30. It should be noted that the current value generated by the flow of the electron beam extracted from the grid 12c is called the electron beam current. The larger the electron beam current, the greater the amount of the electron beam.

[0120] In the electron beam irradiation device, the acceleration voltage, electron beam current, the conveying speed (irradiation time) of the processed object, the distance between the electron beam irradiation unit and the processed object, etc. are set to specified values, and then the processed object is irradiated with electron beams. The energy given to the electron beam is determined by the acceleration voltage. That is, the higher the acceleration voltage is set, the greater the kinetic energy obtained by the electron beam, and as a result, the electron beam can reach a position deep from the surface of the processed object. Therefore, by changing the setting value of the acceleration voltage, the penetration depth of the electron beam to the processed object can be adjusted.

[0121] Fig.18 1 is a perspective view showing the structure of a conveying unit used in the electron beam irradiation device (sterilization device) of the present embodiment. Fig.19 and Fig. 20 They are schematic cross-sectional views of the conveying unit in the Y direction and the X direction, respectively.

[0122] like Figures 18 to 20 As shown, the conveying unit 21 has a plurality of rollers 21a extending in the Y direction orthogonal to the conveying direction (here, the X direction). The roller 21a has a plurality of roller paths L. The roller 21a has an axis 21d and truncated cone members 21c arranged at both ends of the axis 21d on the roller paths L, and a space (gap) 21b is formed between the truncated cone members 21c. The truncated cone members 21c are arranged so that the front end gradually tapers toward the space (gap) 21b.

[0123] The object to be processed (here, raw eggs) 40 is carried on each roller L in the form of a truncated cone member 21c that spans both sides of the space (gap) 21b. The object to be processed (here, raw eggs) 40 rotates by the truncated cone member 21c rotating around the axis 21d. In addition, the axis 21d of the roller is rotatably connected to a chain or a belt (not shown), and the chain moves in the conveying direction (here, the X direction, see the dotted arrow), thereby rotating the object to be processed (here, raw eggs) 40 while being conveyed in the X direction.

[0124] Therefore, use Fig.17 The electron beam irradiation device shown in the figure can sterilize the surface of the food by rotating the food having a shell or skin covering the edible part as the processed object 40 and irradiating the food with electron beams through the slit SL. In addition, the absorbed dose of X-rays (bremsstrahlung X-rays) XL in the edible part of the food (egg yolk 1 and egg white 2) will not be locally increased, and can be reduced to meet the standards stipulated by laws and regulations (e.g., 0.1 Gy = 100 mGy).

[0125] (Summary of processing conditions)

[0126] Various processing conditions in this embodiment are described.

[0127] In the present embodiment, the acceleration voltage can also be adjusted within a range of less than 1 MV, for example, 80 kV to 150 kV.

[0128] In addition, the surface dose can be adjusted within a range of 0.1 kGy to 10 kGy.

[0129] The internal dose is preferably set to 0.1 Gy (=100 mGy) or less. 0.1 Gy (=100 mGy) is a reference value of the internal dose allowed in food inspections and the like.

[0130] In consideration of the impact on the food, the rotation speed of the food as the object to be processed is preferably set to 0.3 rpm to 5 rpm.

[0131] In consideration of the sterilization rate, the conveying speed of the food to be processed is preferably set to 0.1 m / min to 5 m / min.

[0132] (Implementation 3)

[0133] In this embodiment, various application examples according to the above-described embodiment will be described.

[0134] (Application Example 1)

[0135] In Embodiment 1, the slit SL uses an aluminum round bar, but as described above, metals other than aluminum may be used as components of the slit, and alloys, metal compounds, etc. may also be used. In addition, carbon may be used in addition to metals, and a multilayer structure of metal and / or carbon may also be used. In particular, it is preferred to use a material with low thermal expansion and high thermal conductivity.

[0136] In addition, the cross-sectional shape of the rod may be an ellipse, a rectangle (square, rectangular), or other polygonal shapes other than a circle. In addition, a round rod support member may be used instead of the spacer. Fig.21 is a diagram showing an example of the structure of the supporting member. Fig.21 As shown in (A) of FIG. 5 , a support member PL having a hole P for inserting a round rod 50 may also be used. Fig.21 As shown in (B), a support member PL having a recessed portion Q for placing the round bar 50 may be used. By making the size of the hole P and the recessed portion Q larger than the cross section of the round bar 50, deformation and distortion of the slit can be prevented even if the round bar 50 thermally expands.

[0137] (Application Example 2)

[0138] In the first embodiment, an aluminum round bar is used as the slit SL. However, as described above, a slit in which a plurality of linear openings OA are provided on a rectangular metal plate may be used.

[0139] Fig. 22 is a diagram showing an example of a slit structure. Fig. 22 As shown in (A), a slit having a linear opening of 1.5 mm in width can also be used at intervals of 1.5 mm. In this case, the slit SL is arranged so that the opening OA extends in the short-diameter direction of the egg as the processing object 40, and the egg can be rotated in the short-diameter direction.

[0140] In addition, for example, Fig. 22 As shown in (B), a slit with a width of 0.5 mm in the central opening OAc and a width of 1.0 mm in the openings OAe near both ends may be used. The width between the openings (shielding portion) is 0.5 mm. It should be noted that the width between the openings (shielding portion) can be set to a certain size (density).

[0141] In this case, the slit SL is arranged so that the opening portion extends in the short-diameter direction of the egg as the processing object 40, and the egg can be rotated in the short-diameter direction.

[0142] For example, the width between the openings (shielding portions) can be adjusted between 0.3 mm and 3 mm, and the slit is preferably set so that the surface dose of each part on the surface of the treatment object (such as an egg) 40 converges between 1 kGy and 3 kGy.

[0143] In the second embodiment, the eggs as the processing object 40 are transported while being rotated, but the processing object 40 may be irradiated with an electron beam while being rotated at a fixed position.

[0144] In addition, for example, Fig. 22 As shown in (C), Fig. 22 The slit shown in (A) is Fig. 22 The slits shown in (B) are overlapped and used. In this case, the openings (shielding parts) exist in a mesh shape. Therefore, a mesh-shaped metal plate of this shape can also be used as a slit.

[0145] (Application Example 3)

[0146] The slits may be designed so that the height of a predetermined section of the object to be processed (eg, eggs) 40 corresponds to the area of ​​the opening. Fig.23 This is a diagram showing the relationship between the height of the region of the object to be processed and the area of ​​the opening.

[0147] like Fig.23 As shown in (A), a plurality of regions a are set in a top view observed from above the object to be processed (e.g., egg) 40. The opening of the slit is set in a manner corresponding to the average height of the object to be processed (e.g., egg) 40 in the region a. For example, if the average height is above the first benchmark, the opening ratio is set to about 30%. In addition, if the average height is between the first benchmark and the second benchmark, the opening ratio is set to about 60%. In addition, if the average height is below the second benchmark, the opening ratio is set to about 90%. In other words, if the average height of the object to be processed (e.g., egg) 40 in the region a is high, it is set to a small opening OAs, if the average height is medium, it is set to a medium opening OAm, and if the average height is low, it is set to a large opening OAb ( Fig.23 (B)). It should be noted that Fig.23 In (B), the opening OA corresponding to the area a is set to one, but it can also be as follows Fig.23 As shown in (C), a plurality of openings OA corresponding to the region a are provided, and the total area is defined as the aperture ratio.

[0148] In this way, the opening of the slit can be set based on the surface shape (three-dimensional shape) of the object 40 to be processed.

[0149] (Application Example 4)

[0150] In the above-mentioned embodiment, raw eggs are used as an example of the processed object 40, but the processed object (irradiated object) can be any food having an edible part and a surface part (such as a shell or skin) covering the edible part. The sterilization device and sterilization method of this embodiment can be appropriately used for the sterilization treatment of such food.

[0151] Such food includes, in addition to eggs, fruits, crustaceans, etc. For example, fruits include oranges, lemons, grapefruits, apples, pears, grapes, peaches, etc. In addition, crustaceans include shrimps, crabs, etc. Lemons and grapefruits have unevenness (pores) on the surface of the outer skin, and are suitable for the sterilization method of this embodiment.

[0152] In addition, citrus fruits that are roughly spherical or ellipsoidal, or cylindrical objects can be irradiated while rotating, and thus the sterilization method of the second embodiment can be applied.

[0153] In the application to articles other than food, the sterilization or disinfection of pharmaceutical containers and food packaging materials made of materials such as plastic and / or paper, glass, etc. can be cited. Since they do not need to consider the dose of bremsstrahlung X-rays irradiated to the irradiated parison (article), they are effective in suppressing local radiation irradiation degradation and / or quality reduction of the parison (article) raw materials caused by uneven irradiation. In particular, it is suitable for the mold prevention treatment of roughly spherical or ellipsoidal citrus fruits and cylindrical food packaging.

[0154] As mentioned above, the invention completed by the present inventors has been specifically described based on the embodiments thereof, but the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the gist thereof.

[0155] Description of Reference Numerals

[0156] 1: yolk; 2: egg white; 3: egg band; 4: eggshell; 5: cuticle; 6: pores; 7: eggshell membrane; 10: electron beam generating unit; 12: terminal; 12a: filament; 12c: grid; 16c: DC power supply for acceleration; 20: irradiation chamber; 21: conveying unit; 21a: roller; 21b: space (gap); 21c: frustum cone component; 21d: axis; 22: mounting platform; 24: beam collector; 28: vacuum exhaust system; 29: blower; 30: irradiation window; 32: window foil; 34: window frame; 40: object to be processed; 50: rod; 50s: spacer; a: area; C: indicator label; CD: agar; EB: electron beam; L: roller; MF: metal film; OA: opening; PL: supporting component; P: hole; Q: recess; SL: slit; XL: bremsstrahlung.

Claims

1. A sterilization device for sterilizing an object to be treated by irradiating an electron beam. The sterilization device comprises: An electron beam irradiation unit irradiates the object to be processed with an electron beam; A loading portion for the processing object; and a slit portion disposed between the object to be processed and the electron beam irradiation portion, The processing object has a high point and a low point lower than the high point, The slit portion has a plurality of openings and is disposed above the high portion of the object to be processed, wherein an opening ratio of the slit portion in a second region corresponding to the high portion is smaller than an opening ratio in a first region corresponding to the low portion, The aperture ratio in the first region refers to the ratio of the area of ​​the opening located in the first region to the area of ​​the first region, and the aperture ratio in the second region refers to the ratio of the area of ​​the opening located in the second region to the area of ​​the second region.

2. The sterilization device according to claim 1, wherein: The slit portion has a plurality of linear openings, and the width of the linear openings at the high position is smaller than the width of the linear openings at the low position.

3. The sterilization device according to claim 1, wherein: The mounting section is a conveying section that conveys the object to be processed while rotating the object to be processed so that the object to be processed passes within an irradiation region of the electron beam from the electron beam irradiation section.

4. The sterilization device according to claim 3, wherein: The transport unit includes a plurality of axially supported rollers, and the object to be processed is transported while rotating in a direction opposite to a rotation direction of the rollers.

5. The sterilization device according to claim 1, wherein: The surface dose of the treatment object is greater than or equal to 0.1 kGy and less than or equal to 10 kGy.

6. The sterilization device according to claim 1, wherein: The X-ray dose inside the treatment object is 0.1 Gy or less.

7. The sterilization device according to claim 1, wherein: The object to be processed is a food having an edible portion and a surface portion covering the edible portion.

8. A sterilization method for sterilizing an object to be treated by irradiating it with an electron beam. The sterilization method has the following features: (a) preparing an electron beam irradiation device, the electron beam irradiation device comprising: an electron beam irradiation portion for irradiating the object to be processed with an electron beam; a portion for carrying the object to be processed; and a slit portion disposed between the object to be processed and the electron beam irradiation portion; and (b) placing the object to be processed on the placing portion and irradiating the object with an electron beam through the slit portion, The processing object has a high point and a low point lower than the high point, The slit portion in the step (b) has a plurality of openings and is disposed above the high portion of the object to be processed, and an opening ratio of the slit portion in a second region corresponding to the high portion is smaller than an opening ratio in a first region corresponding to the low portion. The aperture ratio in the first region refers to the ratio of the area of ​​the opening located in the first region to the area of ​​the first region, and the aperture ratio in the second region refers to the ratio of the area of ​​the opening located in the second region to the area of ​​the second region.

9. The sterilization method according to claim 8, wherein: The slit portion has a plurality of linear openings, and the width of the linear openings at the high position is smaller than the width of the linear openings at the low position.

10. The sterilization method according to claim 8, wherein: The mounting unit is a conveying unit that conveys the object to be processed while rotating the object to be processed so that the object to be processed passes within an irradiation area of ​​the electron beam from the electron beam irradiation unit. The step (b) is a step of irradiating the object to be processed with an electron beam while rotating the object to be processed.

11. The sterilization method according to claim 9, wherein: The width of the linear opening of the slit portion at the high position and the width of the linear opening at the low position are set by simulation according to the surface shape of the object to be processed.

12. The sterilization method according to claim 8, wherein: The surface dose of the treatment object is greater than or equal to 0.1 kGy and less than or equal to 10 kGy.

13. The sterilization method according to claim 8, wherein: The X-ray dose inside the treatment object is 0.1 Gy or less.

14. The sterilization method according to claim 8, wherein: The object to be processed is a food having an edible portion and a surface portion covering the edible portion.

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