Patent Application
20230320388
The present invention relates to a sterilizing device and a sterilizing method, and, more particularly relates to a technique effectively applied to a surface sterilizing process for a food having a shell or an outer skin covering an eatable part.
In hen's egg, a cuticular layer on a surface of an eggshell is removed by washing, so that micropores (air holes) inside the eggshell are exposed. Because of this, microbes such as salmonella are easy to penetrate the micropores, and there is a risk of contamination of the washed egg surface.
Against such contamination, pharmaceutical sterilization (wet sterilization) is performed. However, in the pharmaceutical sterilization, there is concern about influence of residue of pharmaceuticals. For example, flavor such as smell can be deteriorated by the residue of pharmaceuticals. Also, there is concern about environmental pollution due to effluent.
Therefore, a process making use of ultraviolet ray, that is, a dry unheated process (dry sterilization) is practically applied. And, a process making use of radioactive ray, that is, a dry unheated process (dry sterilization) is studied.
For example, a Patent Document 1 discloses an electron-beam sterilizing device including: an electron-beam irradiator means with an irradiation window emitting electron beam; a delivery means delivering a parison (object) within an irradiation region of the electron beam emitted through the irradiation window; and magnets facing each other to interpose a delivery path therebetween for the parison delivered by the delivery means. According to the device, a magnetic field along an irradiation direction of the electron beam emitted through the irradiation window can be generated by the facing magnets, and the object can be efficiently sterilized by irradiating the parison with the electron beam emitted through the irradiation window and polarized by the magnetic field while the parison passes between the facing magnets to irradiate the parison.
A Patent Document 2 discloses a process method and a device for poultry eggs using an electron beam flux in sterilization of a calcareous shell. In the method including: a step of moving at least one egg through a beam path of an electronic beam source; and a step of irradiating the egg to irradiate the calcareous shell at various doses, the method further includes: a step of using an electron beam and widely irradiating all regions of the calcareous shell of the egg, and causing an element inserted into a path of the electron beam to distribute the irradiation over all regions of the calcareous shell to widely irradiate the calcareous shell at a dose being set within a predetermined target does range; a step of using an electron beam source and irradiating an egg that is rotating/already-rotated in the path of the electron beam; or a step of using an electron beam source and irradiating an egg that is held so that one side is positioned at zero degree inside a device arranged in an upstream of a rotating device.
As described above, methods of sterilizing foods are roughly classified into the wet sterilization and the dry sterilization. For example, in the case of the sterilization for only the surface of the hen's egg, wet sterilization making use of hypochlorous acid is applied. However, such a sterilizing method has problems of the residue of pharmaceuticals and the effluent as described above.
In the process making use of the ultraviolet ray (dry sterilization), the sterilizing effect is limited to only the surface of the hen's egg, and there is concern of failure to sufficiently sterilize an inside of the egg (such as an inside of the micropore in the eggshell). When dirt is adhered to the surface of the hen's egg, there is concern of failure in the sterilization.
On the other hand, in the process making use of the electron beam (dry sterilization), the sterilization is possible for not only the surface of the hen's egg but also the inside ranging from the eggshell to a certain depth. And, this method is effective since the electron beam can penetrate the dirt of the surface of the hen's egg and make the sterilization.
However, an end portion and a center portion of a surface of an oval sphere process target such as a hen's egg are different from each other in terms of a distance from an electron beam source, and therefore, cause a different degree of a surface dose at the time of the irradiation with the electron beam, and, as a result, it is difficult to evenly irradiate the entire surface of the hen's egg with the electron beam. And, increase in an irradiation intensity of the electron beam for providing the sterilizing effect to the entire surface of the hen's egg increases a dose of bremsstrahlung X ray generated by the irradiation with the electron beam, and undesirably increases an internal does of the hen's egg.
Meanwhile, for example, even a method of equalizing the surface dose of the electron beam by using the magnetic field as described above generates the bremsstrahlung X ray when the electron beam is bent, and therefore, undesirably increases the internal does of the hen's egg.
A purpose of the present invention is to provide a sterilizing device and a sterilizing method configured to evenly irradiate an entire surface of a food having an eggshell or an outer skin covering an eatable part with electron beam to provide a sterilizing effect based on the electron beam to the entire surface. Also, a purpose of the present invention is to provide a sterilizing device and a sterilizing method configured to suppress an X-ray irradiation dose on an eatable part of a food having an eggshell or an outer skin covering the eatable part to be low so as to satisfy a criterion value regulated in a law or others by reducing influence of bremsstrahlung X ray on the eatable part due to the irradiation with the electron beam while irradiating an entire surface of the food with electron beam.
According to a sterilizing device or a sterilizing method of the present invention, an entire surface of a food having a shell or an outer skin covering an eatable part can be evenly irradiated with electron beam, and a sterilizing effect based on the electron beam can be provided to the entire surface. And, an X-ray irradiation dose on an eatable part of a food having an eggshell or an outer skin covering the eatable part can be suppressed to be low so as to satisfy the criterion value regulated in a law or others by reducing influence of bremsstrahlung X ray on the eatable part due to the irradiation with the electron beam while an entire surface of the food is irradiated with the electron beam.
Hereinafter, embodiments of the present invention will be explained in detail on the basis of the drawings. In the following explanation, note that a term “A to B” means a term “equal to or larger than A and equal to or smaller than B” (the same goes for a second embodiment and others described later).
The electron-beam irradiator (sterilizing device) shown in
In the present embodiment, when a process-target object 40 is irradiated with the electron beam EB through the slit (slit unit, slit member) SL, its entire surface can be evenly irradiated with the electron beam, so that the sterilizing effect based on the electron beam can be provided to the entire surface. And, the influence of the bremsstrahlung X ray on the inside contents (eatable part) of the process-target object caused by the irradiation with the electron beam can be made small.
As shown in
In this case, the metallic bar 50 and the metallic spacer 50s are made of the same metal. However, these members may be made of a metal different from each other. When the diameters φ of the metallic bar 50 and the metallic spacer 50s are changed, combination of a width of the metallic bar 50 that is a shielding portion and a width of the metallic spacer 50s that is an opening can be adjusted. In place of the metallic members, a carbon bar 50 and a carbon spacer 50s may be used. Alternatively, the slit SL may be made of combination of the metallic bar and the carbon spacer or combination of the carbon bar and the metallic spacer.
Alternatively, as the slit SL, a quadrangular metallic panel with a plurality of linear openings may be used. For example, when the linear openings each having a width of 1.5 mm are arranged at a pitch of 1.5 mm, the slit SL having the same shape as that of
As a constituent material of the slit SL, it is preferable to use a material having a favorable electric conductivity such as metal (such as aluminium (Al), iron (Fe), copper (Cu), lead (Pb), titanium (Ti) and tungsten (W)), carbon (C) or others. And, it is preferable to use a material having a small thermal expansion coefficient.
This slit SL is arranged on the highest portion (also referred to as high portion) of the process-target object (in this case, the raw egg) 40. In the case of the raw egg, the high portion is a substantially center portion in a plan view viewed from above.
As described above, according to the present embodiment, since the process-target object 40 is irradiated with the electron beam EB through the slit SL, its entire surface can be evenly irradiated with the electron beam, and the sterilizing effect based on the electron beam can be provided to its entire surface. And, an X-ray irradiation dose on an inside (that is a part to be an eatable part) of the process-target object 40 can be suppressed to be low so as to satisfy the criterion value regulated in a law or others by reducing influence of bremsstrahlung X ray on the process-target object 40 due to the irradiation with the electron beam while an entire surface of the process-target object is irradiated with the electron beam.
On the other hand, when the process-target object 40 is directly irradiated with the electron beam not through the slit SL as shown in
On the other hand, in the case of the usage of the slit SL as shown in
As described above, in the present embodiment, the object is irradiated with the electron beam through the slit SL, and, as a result, its entire surface can be more evenly irradiated with the electron beam, and the sterilizing effect based on the electron beam can be provided to its entire surface. Also, the surface of the process-target object can be efficiently sterilized without the increase of the internal dose (particularly the absorbed dose of the X ray (bremsstrahlung X ray) XL).
Specifically, when an eggshell of the raw egg (process-target object 40) having a yolk 1 and an albumen 2 is irradiated with the electron beam EB through the slit SL from the electron-beam irradiator unit 10, a part having a certain depth from the surface of the eggshell can be sterilized (such as the sterilization of salmonella) (see
The sterilizing process for the raw egg, making use of the electron-beam irradiator (sterilizing device) and the sterilizing method of the present embodiment, will be more specifically explained below with reference to working example.
First, a shape of the raw egg will be explained.
A low-energy electron accelerator (EC-250: produced by IWASAKI ELECTRIC CO., LTD.) was used as the electron-beam irradiator, and the irradiation with the electron beam having an acceleration voltage of 120 kV was performed. The irradiation with the electron beam was performed while the slit SL was arranged below an irradiation unit (irradiation window) of the low-energy electron accelerator.
<Surface Dose Measuring Model 1>
A model 1 using the following irradiation specimen and slit was prepared in order to evaluate the surface absorbed dose. Each of
The raw egg, a surface of which was washed, (washed egg, M size) was prepared. A blunt-end eggshell was obtained by cracking of the raw egg to be along an outer circumference in a minor radius direction, followed by removal of the inner contents and the eggshell membrane and drying of the egg. A chemical process indicator label (Crosstex) C was wound around and pasted on a center portion of the outer circumference of the blunt-end eggshell to prepare the eggshell simulation specimen (raw-egg simulation sample, irradiation specimen) A.
Nine long circular bars and sixteen short circular bars each of which is an aluminium circular bar having φ of 1.5 mm were prepared, and the slit SL having φ of 1.5 mm and the pitch of 1.5 mm was formed.
The slit SL was arranged above the high portion of the eggshell simulation specimen A to cross the chemical process indicator label C.
A low-energy electron accelerator (EC-250: produced by IWASAKI ELECTRIC CO., LTD.) was used, and the irradiation with the electron beam EB having the acceleration voltage of 120 kV was performed. The distance between the slit SL and the eggshell simulation specimen A was set to 3 mm.
<Internal Dose Measuring Model 2>
A model 2 using the following irradiation specimen and slit was prepared in order to evaluate the internal absorbed dose (the dose of the bremsstrahlung X ray). Each of
A liquid agar of 2% was poured in a Tupperware (food storage container) and was solidified, and then, was cut to have a size of “50 mm×70 mm” to prepare an agar “CD” having a thickness of 13 mm. Five TLD elements (TLD100: produced by Thermo Fisher Scientific, Inc.) each upper portion and lower portion of which are shielded with a polyethylene film were arranged and were covered with a plastic wrap as a whole. A circular calcium carbonate layer L having a thickness of 0.4 mm and a diameter of 2.0 cm was formed in the upper portion of the agar to prepare the egg simulation specimen (raw-egg simulation sample, irradiation specimen) B. The calcium carbonate layer L corresponds to the eggshell, and the agar CD corresponds to the inside contents (eatable part, yolk and albumen) of the raw egg.
Eighteen long circular bars and thirty four short circular bars (spacers) each of which is an aluminium circular bar having φ of 1.5 mm were prepared, and a slit SLa having φ of 1.5 mm and the pitch of 1.5 mm was formed. Also, twenty five long circular bars and forty eight short circular bars each of which is an aluminium circular bar having φ of 1.0 mm were prepared, and a slit SLb having φ of 1.0 mm and the pitch of 1.0 mm was formed.
The slit SL was arranged above the egg simulation specimen B to cross the arrangement direction of the TLD element.
The low-energy electron accelerator (EC-250: produced by IWASAKI ELECTRIC CO., LTD.) was used, and the irradiation with the electron beam EB having the acceleration voltage of 120 kV was performed. The distance between the slit SL and the eggshell simulation specimen B was set to 3 mm.
<Simulation>
The Particle and Heavy Ion Transport code System PHITS (Version 2.96) was used for creation of the model in conformity with the configurations of the models 1 and 2. A density of the eggshell (main component: CaCO3) was set to 2.0 because of having pores, a density of the eatable part was set to be equal to that of water, atmosphere was set to the standard air, and the dose distributions of the electron beam and the bremsstrahlung X ray in the irradiation with the electron beam on the egg were evaluated under the Monte Carlo simulation. As parameters, the acceleration voltage, a slit position (length), the distance between the slit and the process-target object, the diameter of the circular bar configuring the slit, the pitch of the circular bar, the material of the circular bar and others are conceivable. From the simulation under selection of some of these parameters, relation between each parameter and the dose (surface dose, internal dose) was revealed.
The surface dose of the irradiation specimen A was measured in the surface dose measuring model 1 (
In the working example 1, aluminium was used as the constituent material of the slit. However, cases of usages of carbon (C), aluminium (Al), iron (Fe), copper (Cu) and lead (Pb) as the constituent material of the slit were evaluated using the simulation. The surface dose was calculated using the parameters in conformity with the model 1 other than the material of the circular bar.
In the working example 1, aluminium was used as the constituent material of the slit. However, the internal dose in each of cases of usages of carbon (C), aluminium (Al), titanium (Ti), iron (Fe), and tungsten (W) as the constituent material of the slit was evaluated based on the simulation. The internal dose was calculated using the parameters in conformity with the model 2 other than the material of the circular bar.
Influence of the slit pitch in the irradiation with the electron beam through the slit was evaluated based on the simulation. Specifically, a plurality of aluminium circular bars having φ of 1.5 mm were used as the slit, and the surface dose was measured using a slit 1 (φ of 1.5 mm, pitch of 1.5 mm) arranged at a pitch of 1.5 mm, a slit 2 (φ of 1.5 mm, pitch of 1.0 mm) arranged at a pitch of 1.0 mm and a slit 3 (φ of 1.5 mm, pitch of 0.5 mm) arranged at a pitch of 0.5 mm. The surface dose was calculated using the parameters in conformity with the model 1 other than the pitch of the circular bar. The surface dose in the case without the slit (no slit) was also similarly measured.
In this case, in the graph of
Influence of the change of the slit pitch in the irradiation with the electron beam through the slit was evaluated based on the simulation. Specifically, a plurality of tungsten circular bars having φ of 1.5 mm were arranged as the slit (see
As seen from this, it is revealed that the further evenness of the surface dose is achieved when the slit pitch at the center portion (high portion) of the egg is densified while the slit pitch at the end portion (low portion) of the egg is isolated (made less dense).
The internal dose of the irradiation specimen B was measured based on the internal dose measuring model 2. The internal dose in the case without the slit was also similarly measured. Also, the internal dose was calculated based on the simulation using the parameters in conformity with the model 2. The internal dose in the case without the slit was also similarly measured based on the simulation.
In the working examples 1 to 6, the specific measurement results of both the surface dose and the internal dose match with the simulation results, and therefore, it is revealed that the slit can be designed based on the simulation.
(Summary of Process Condition)
In the working examples, the acceleration voltage was set to 120 kV. However, the acceleration voltage can be adjusted in a range that is, for example, equal to or higher than 80 kV and equal to or lower than 150 kV.
The surface dose can be adjusted in a range that is equal to or higher than 0.1 kGy and equal to or lower than 10 kGy.
The internal dose is preferable to be equal to or lower than 0.1 kGy (=100 mGy) that is an allowable criterion value of the internal dose in the test for food or others. Note that the measurement results of the internal dose explained in the working example 6 are significantly lower than this criterion value.
In the present embodiment, an example of irradiation with the electron beam through the slit at the same time of rotation of the process-target object will be explained.
The electron-beam irradiator (sterilizing device) shown in
Note that the structure of the slit SL can be configured to be the same structure as the first embodiment, and therefore, a structure other than that of the slit SL will be explained in detail herein.
The electron-beam generator unit 10 includes a terminal 12 generating the electron beam inside a chamber and a space (acceleration space) where the electron beam that is generated in the terminal 12 is accelerated. And, the space (acceleration space) of the electron-beam generator unit 10 is kept in a vacuum state of about 10−3 to 10−5 Pa by a vacuum exhaust system 28 in order to prevent energy loss due to collision of the electrons with gas molecules and prevent oxidation of a filament 12a. The terminal 12 includes the linear filament 12a releasing thermal electrons and a grid 12c controlling the thermal electrons generated in the filament 12a.
And, the electron-beam generator unit 10 includes a heating power supply (not illustrated) for use in heating the filament 12a to generate the thermal electrons, a controlling direct-current power supply (not illustrated) applying a voltage to a gap between the filament 12a and the grid 12c, and an accelerating direct-current power supply 16c applying a voltage (acceleration voltage) to a gap between the grid 12c and a window foil 32 arranged in the irradiation window unit 30.
The irradiation chamber 20 includes an irradiation space where the process-target object (irradiation-target object) 40 is irradiated with the electron beam. The process-target object 40 is delivered through the irradiation chamber 20 by a delivery unit 21 such as a conveyor in a direction, for example, from a depth side of a sheet of
The inside of the irradiation chamber 20 is under atmosphere of an inert gas, ambient air or others in accordance with a process content. In the case of the sterilizing process (disinfection process), the irradiation atmosphere inside the irradiation chamber 20 is set to be under the ambient air (atmosphere containing oxygen), and the process-target object is sterilized by the electron beam. In this case, ozone is generated from the oxygen by the electron-beam irradiation, and then, is reacted with nitrogen in the ambient air, so that NOx is generated. Since the NOx corrodes the window foil 32, the generation of the NOx can be controlled by blowing of dry air from a blower 29 into the irradiation chamber 20.
The irradiation window unit (irradiation window) 30 includes the window foil 32 and a window frame unit 34 made of copper. The window frame unit 34 is used for supporting the window foil 32. In the window frame unit 34, a rectangular-shaped (quadrangular-shaped) opening is formed. A width of the opening is, for example, about 1 cm, and its longitudinal direction is arranged in a direction that is orthogonal to the deliver direction.
And, inside the irradiation window unit 30, a cooling passage (not illustrated) is formed in order to cool the window foil 32, a temperature of which is increased by the electron-beam irradiation. The window frame unit 34 is detachable to the irradiation opening of the electron-beam generator unit 10. The window foil 32 is detachably adhered to a lower surface of the window frame unit 34. As the window foil 32, a metal foil such as an aluminum foil or a titanium (Ti) foil is used.
In the electron-beam irradiator of the present embodiment, when the filament 12a is heated through the electric current by the heating power supply, the filament 12a releases the thermal electrons, and the released thermal electrons are attracted everywhere by a control voltage of the controlling direct-current power supply applied between the filament 12a and the grid 12c. Among the thermal electrons, only thermal electrons that pass the grid 12c are effectively extracted as the electron beam. Then, the electron beam that is extracted from the grid 12c is accelerated in the acceleration space by an acceleration voltage of the accelerating direct-current power supply 16c applied between the grid 12c and the window foil 32, and then, penetrates the window foil 32, and the process-target object that is delivered through the irradiation chamber 20 below the irradiation window unit 30 while rotating is irradiated with the electron beam. Note that an electric current value generated by the flow of the electron beam extracted from the grid 12c is referred to as beam electric current. The larger the beam electric current is, the more the electron beam is.
In the electron-beam irradiator, predetermined values are set to the acceleration voltage, the beam electric current, a delivery speed (irradiation time) of the process-target object, a distance between the electron-beam irradiator unit and the process-target object and others, and then, the electron-beam irradiation process is performed to the process-target object. The energy applied on the electron beam is defined by the acceleration voltage. In other words, the higher the set acceleration voltage is, the larger the resultant kinetic energy of the electron beam is. As a result, the electron beam can reach a position deep from the surface of the process-target object. Therefore, by the change in the setting value of the acceleration voltage, the penetrating depth of the electron beam in the process-target object can be adjusted.
As shown in
The process-target object (in this case, the raw egg) 40 is placed at each lane L so as to straddle these circular truncated cone members 21c on both sides of the space (gap) 21b. When the circular truncated cone member 21c rotates about the shaft 21d, the process-target object (in this case, the raw egg) 40 rotates. The shaft 21d of the roller is joined to a chain or a belt (not illustrated) so as to be rotatable. By movement of this chain in the delivery direction (in this case, the X direction, see a dashed arrow), the process-target object (in this case, the raw egg) 40 is delivered in the X direction while rotating.
Therefore, when the electron-beam irradiator as shown in
(Summary of Process Conditions)
Various process conditions of the present embodiment will be explained.
Also in the present working example, the acceleration voltage can be adjusted to be lower than 1 MV such as a range that is, for example, equal to or higher than 80 kV and equal to or lower than 150 kV.
The surface dose can be adjusted in a range that is, for example, equal to or higher than 0.1 kGy and equal to or lower than 10 kGy.
The internal dose is preferably equal to or lower than 0.1 Gy (=100 mGy) that is the allowable internal dose criterion value in the test for the food or others.
In consideration of the impact on the food, the rotation speed of the food that is the process-target object is preferably 0.3 rotation/seconds to 5 rotation/seconds.
In consideration of the sterilizing speed, the delivery speed of the food that is the process-target object is preferably 0.1 m/minutes to 5 m/minutes.
In the present embodiment, various application examples according to the above-described embodiments will be explained.
In the first embodiment, the aluminium circular bar was used as the slit SL. However, as described above, as the constituent member of the slit, a metal other than aluminium may be used, or an alloy, metallic compound or others may be used. Other than the metal, carbon may be used, or a multilayered structure made of metal or carbon may be used. It is particularly preferable to use a material having a small thermal expansion and a large thermal conductivity.
The cross-sectional shape of the bar may be not the circular shape but ellipsoidal, quadrangular (square, rectangular) or other polygonal shape. In place of the spacer, a circular bar supporting member may be used.
(Second Application Example)
In the first embodiment, the aluminium circular bar was used as the slit SL. However, as described above, a quadrangular metallic plate having a plurality of linear openings OA may be used.
For example, as shown in
In this case, the slit SL can be arranged so that the opening extends in the minor radius direction of the egg that is the process-target object 40, and the egg can be rotated in the minor radius direction.
For example, the width of the gap (shielding portion) between the openings can be adjusted in a range of 0.3 mm to 3 mm, and the width of the opening can be adjusted in a range of 0.3 mm to 3 mm, and it is preferable to set the slit so that the surface dose of each portion on the surface of the process-target object (such as the egg) 40 is within 1 kGy to 3 kGy.
In the second embodiment, the egg that is the process-target object 40 is delivered while rotating. However, the process-target object 40 may be irradiated with the electron beam while rotating at a fixed position.
For example, as shown in
A slit may be designed so that a height of a predetermined section of the process-target object (such as the egg) 40 corresponds to an area of the opening.
As shown in
In this manner, the opening of the slit can be set in accordance with the surface shape (three-dimensional shape) of the process-target object 40.
In the working example, the raw egg has been explained as the example of the process-target object 40. However, the process-target object (irradiation-target object) needs to be only a food having the eatable part and the surface part (such as the shell or the outer skin) covering the eatable part, and the sterilizing device and the sterilizing method of the present embodiment can be preferably used for the sterilizing process of such foods.
As such foods, not only the eggs but also fruits, crustaceans and others are exemplified. As the fruits, for example, oranges, lemons, grapefruits, apples, pears, grapes, peaches and others are exemplified. As the crustaceans, shrimps, crabs and others are exemplified. The lemons and the grapefruits have surface asperity (holes) on its outer surface, and the sterilizing method of the present embodiment is preferably used for these foods.
Also, the substantially spherical or oval spherical citrus fruits or cylindrical objects can be irradiated while rotating, and therefore, the sterilizing method of the second embodiment is applicable to these objects.
As application to other items than the foods, the sterilization and the disinfection of medical containers, food packing medium and others made of plastic, paper, glass or others are exemplified. For these items, it is unnecessary to consider the dose of the bremsstrahlung X ray on the irradiation-target parison (object), and therefore, the method is effective for suppressing the partial deterioration of the radiant-ray irradiation or the partial deterioration of the quality of the parison (object) due to unevenness of the irradiation. Particularly, the sterilizing device and the sterilizing method are preferable to the mold-resistant process for the substantially spherical or oval spherical citrus fruits and the cylindrical food packages. In the foregoing, the invention made by the present inventors has been concretely described on the basis of the embodiments. However, it is needless to say that the present invention is not limited to the foregoing embodiments, and various modifications and alterations can be made within the scope of the present invention.
While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-134382 | Aug 2020 | JP | national |
This application is a National Stage application of International Patent Application No. PCT/JP2021/020909, filed on Jun. 1, 2021, which claims priority to Japanese Patent Application No. 2020-134382, filed on Aug. 7, 2020, each of which is hereby incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/020909 | 6/1/2021 | WO |
