Method For Irradiating Foodstuffs And Other Consumables, Pharmaceuticals And The Like, And A Package For Same

Abstract

The material to be irradiated is placed with an oxygen binding medium into a gas-tight package and irradiated. The oxygen which may be present in the package becomes bound by the oxygen binding medium so that the irradiated material and/or the material of the package do not become adversely effected by the oxygen.

Description

This invention relates to a method for irradiating foodstuffs, other consumables, pharmaceuticals, medical requirements and the like as well as a package for the same.

It has been known to irradiate various materials such as foodstuffs, pharmaceuticals, and the like by packaging the material in a gas-tight covering and by thereafter exposing the packaged material to an ionizing radiation, preferably gamma radiation. Such irradiation has already been successfully employed not only for the sterilization of catgut, hypodermic syringes of plastic material but also for the destruction of undesirable micro-organisms on or in foodstuffs and other consumables. The last mentioned application refers to a sterilizing treatment which is intended to destroy all micro-organisms which have an adverse effect on durability or only those micro-organisms which prevent the substances from being kept fresh for a short period.

However, it has been found that the presence of oxygen in the interior of the sealed package prior to irradiation may cause difficulties which may become greater since the enclosed gaseous oxygen may be converted under the effect of ionizing irradiation into ozone or even into nascent oxygen. Oxygen, particularly in one of the aforementioned highly reactive forms, can give rise to a wide variety of harmful effects depending on the nature of the packaged material or of the packaging material itself. In the first place, there is oxidation of the packaged material itself, also foodstuffs and other consumables containing fats and albumen for example fish and meat products can be adversely affected. In other cases, any oxygen that may be present may unfavorably continue the ripening process of fruit, for example strawberries, which have been exposed to a preserving irradiation, thus impairing the visual condition and taste of the packaged material. Furthermore, in many cases it is not possible to destroy resistant and durable forms of micro-organisms, for example spores. A correspondingly increased radiation dose or duration of radiation or radiation intensity also increases the danger of harmful oxidation of the packaged material in conjunction with the formation of ozones or nascent oxygen. Oxygen in an irradiated package for foodstuffs and other consumables may also have an adverse effect on aromatic substances.

In addition to the above disadvantages in the preserving treatment of foodstuffs and other consumables, it has been found that in the sterilizing irradiation or medical material and medical apparatus, the plastics material usually employed for forming the package or, as in the case of catgut, the packaged material itself has been adversely affected by the irradiation due to the oxygen present in the package. For example, the oxygen may embrittle the plastics packaging material owing to oxidation. Similar detrimental effects may also be observed in the irradiation of natural or synthetic catgut.

It is known in connection with the difficulties described hereinabove to partially eliminate the quantity of oxygen present in the package by evacuation or to displace it by means of an inert gas. However, such measures are expensive and involve complicated packaging machines so that this method of solving the indicated problems efficiently is possible only in very few cases.

Accordingly, it is an object of the invention to permit the application of an irradiation method in which the harmful effects of oxygen, increased by the use of ionizing radiation on the material disposed in the closed packaged or on the package itself is substantially eliminated.

It is another object of the invention to protect a packaged material against adverse effects from oxygen during irradiation.

It is another object of the invention to maintain a packaged foodstuff in a protected state for a relatively long period of time.

Briefly, the invention provides a method and a package which preserves materials such as foodstuffs, consumables, pharmaceuticals, and the like over long time periods without adverse effects from entrapped oxygen in the package upon the package being subjected to radiation and the like.

The method resides in the steps of packaging the material to be irradiated in a gas-tight covering along with a medium capable of binding oxygen and of exposing the sealed material to an ionizing irradiation. During the time of irradiation, as well as thereafter, any gases in the interior of the covering come into contact with the oxygen binding medium and become bound.

In the method according to the invention, the oxygen can be bound either chemically or physically. For example, adsorption media are particularly suitable for physical binding. Also, since it is known that irradiation causes adsorbing substances and chemical substances to have an increased binding capacity; media such as silica gel which is particularly activated as regards its oxygen binding capacity by ionizing radiation can be used. With such characteristics, it is in some cases possible to dispense with special measures which protect the oxygen binding medium against premature contact with atmospheric oxygen while the package is not yet sealed.

In carrying out the invention, is is advisable to use the oxygen binding medium in small, particulate or porous form, both for chemical as well as for physical binding as the increased surface area obtained by this measure accelerates and intensifies the binding process.

The package of the invention includes the material to be irradiated, the oxygen binding medium and a gas-tight covering enclosing the material and medium therein in sealed relation.

In one embodiment, the interior of the gas-tight covering is constructed as a support for the oxygen binding medium.

In another embodiment, the oxygen binding medium is appropriately disposed within its own gas-permeable covering or sheath such as a perforated cartridge. This separates the medium from the packaged material thus preventing undesirable contact between the binding medium and the material. It is furthermore recommended that the gas-permeable covering for the oxygen binding material be joined to the gas-impermeable covering for the material to be irradiated. The binding medium and the packaged material is then automatically separated when the package is opened.

In another embodiment, the oxygen binding medium may be disposed in a gas-permeable foil which is coated onto the gas-tight covering enclosing the material to be irradiated. Such a gas-permeable foil is advantageously constructed of polyethylene while the use of packaging material having aluminum foil is recommended for the gas-tight covering. Aluminum has a relatively high transmittance for the ionizing radiation, readily reflects incident heat radiation and is very suitable as hygienic packaging material.

As oxygen binding media of high binding intensity are naturally endangered by premature exhaustion of their binding capacity, the oxygen binding media can, in another embodiment, be brought into contact with the oxygen only after sealing of the package for the material to be irradiated. This may be achieved by disposing the oxygen binding medium in a gas-impermeable covering which is opened only after sealing of the gas-tight covering for the material to be irradiated.

The material for the packages of the kind heretofore described can be easily prefabricated and provided it is protected by a suitable hermetically sealed packaging against premature exhaustion of the binding capacity can be stored or transported to the location of use for any desired period of time.

By means of the invention, it is possible to perform irradiation for preservation or sterilization without the need for the complicated and expensive removal of the oxygen from the package for the material to be irradiated. Instead, the gaseous oxygen disposed in the package is bound and thus does not cause any harmful oxidation of the irradiated material or any of the other detrimental effects. At the same time, it is possible for the radiation dose to be substantially increased without having to anticipate any increased oxidation of the irradiated material.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a sealed package prepared for irradiation with an enclosed cartridge containing oxygen binding media according to the invention;

FIG. 2 illustrates an enlarged view of the cartridge of FIG. 1;

FIG. 3 illustrates an embodiment of the invention in which the oxygen binding medium is disposed in a gas-permeable covering joined to the interior of a packaging material;

FIG. 4 illustrates a gas-permeable foil in which the oxygen binding medium is disposed according to the invention;

FIG. 5 illustrates an embodiment according to the invention in which the oxygen binding medium is disposed in a gas-impermeable covering which is opened only after the gas-tight covering for the material to be irradiated is closed.

Referring to FIG. 1, the package 11 consists of a material which is as far as possible impermeable to gas, for example, a paper-like packaging material with an inlaid aluminum foil and a plastic coating on the interior. The package 11 contains a material 12, for example fresh meat, and is hermetically sealed by means of a welding seal 13 so that the material 12 is enclosed in a substantially gas-tight package. A cartridge 14 of oxygen binding medium is also enclosed within the interior of the package 11.

Referring to FIGS. 1 and 2, the cartridge 14 comprises a cylinder 15, forming a gas-permeable covering which is closed at the endfaces by means of lids 16. The interior of the cartridge 14 contains the oxygen binding medium for example, in the form of granular material 17 which is in physical contact with the gases in the interior of the package covering by means of apertures 18 in the wall of the cylinder 15.

After the package 11 has been sealed with the material 12 and oxygen binding medium 17 therein, the material 12 in the package 11 can be exposed to an ionizing radiation as is known. During such a time, and thereafter, any oxygen in the package interior is, at least, partially bound by the medium 17.

Referring to FIG. 3, the package can also be formed of a foil-like packaging material 21 which forms the gas-tight covering for the material to be irradiated. The material 21 may be formed of a plastic foil which can also be lined in any desired manner with paper or metal foil. This package also includes a tubular chamber 22 on the material side which forms the interior of the package. This tubular chamber 22 is joined by means of flanges 23 to the foil 21, namely by welds 24 and, prior to welding, is filled with a granular medium 25 capable of binding oxygen. The medium 25 comes into physical contact with the oxygen in the package through apertures 26 in the chamber wall.

In use, any oxygen which is entrapped in a package constructed of the material described hereinabove (FIG. 3) is bound by the medium 25. When the packaged material is removed from the gas-tight covering 21, automatic provision is made to ensure that the covering 21 and the packaged material are separated from each other.

Referring to FIG. 4, the oxygen binding medium 31 can also be incorporated into a gas-permeable foil 32 so that strips of the foil 32 can be used in the formation of packages. For example, the oxygen binding medium 31 in a pulverized or granular form is disposed in a gas-permeable foil 32 of polyethylene. The foil 32 is appropriately obtained in such a manner that the small, particulate binding medium is admixed to the polyethylene during extrusion. By suitable selection of the particle size and the degree of admixture, preferably 0.5 to 10 percent, it is possible to influence the binding rate of the oxygen. A foil-like material 33 for the gas-tight impermeable covering of a package is then coated with the foil 32. The gas-tight covering 33 and the foil 32 therefore represent a web-like packaging material which can be easily processed. This type of packaging material is appropriately stored in reels and the oxygen binding medium is protected against premature exhaustion due to the ingress of atmospheric oxygen, for example by hermetic sealing in evacuated containers. In some cases, it is advisable to omit the coating from those positions which later coincide with the zone of a welding seam when the package is formed. In some cases also it is possible to embed the oxygen binding material directly into the plastics coating of paper-like packaging materials.

Referring to FIG. 5, the oxygen binding medium can also be stored within gas-impermeable coverings which are opened only after the covered medium has been sealed into a package. For example, the oxygen binding medium 44 in small particulate form is filled in a container 41 made of fragile gas-impermeable material such as a thin glass. The container 41 in turn is placed within a small gas-permeable material such as a small textile bag 43 which is closed by means of a clip 42. The small bag 43 with the container 41 is then enclosed in the package in place of the cartridge 14 shown in FIG. 1. In order to provide physical contact between the medium 44 and the oxygen entrapped in the package, the thin wall of the container 41 is broken from the exterior by applying pressure or a blow. The medium 44 thus comes into contact with the oxygen which diffuses through the wall of the small bag 43. In this way, it is possible to control the timing of the beginning of oxygen binding by the medium 44. The protective container is appropriately destroyed immediately after the package is sealed.

Media suitable for binding oxygen include those capable of binding oxygen chemically as well as those capable of inducing binding by physical means. All readily oxidizing inorganic material are particularly suitable as chemically acting media. Metals such as manganese, aluminum and magnesium in small particulate form are particularly suitable although it is recommended that the media be stored in a protective atmosphere, for example nitrogen, in the interior of a container according to FIG. 5 as a protection against premature oxidation. However, organic compounds with a suitable binding activity relative to oxygen are also feasible.

The previously mentioned silica gel having a particle size of for example 0.01 to 5 mm is very suitable for physical binding of the oxygen. Silica gel is characterized by the surprising property that is adsorption capacity relative to oxygen is substantially increased by irradiation with ionizing rays by virtue of a structural change resulting from the irradiation. Furthermore, it is absolutely non-toxic and acts practically without thermal effects. Another medium for physical binding of oxygen is bentonite.

In every case, an increase of the surface area of the oxygen binding medium is recommended by using the medium in small particulate form such that the ratioes of surface area to volume of the particulate are relatively large. It would however also be possible to employ the oxygen binding medium in the form of a porous or spongy member.

In order to treat the packaged material, the package should be made as impermeable to gas as is possible. In practice, however, a certain exchange of gas is possible under some circumstances even with lined packaging material having a plastics coating and a metal foil insert. The gas-impermeable property of the covering for the material to be irradiated is therefore meant to imply impermeability to gas as obtainable under practical conditions. Further, in order to improve the impermeability of aluminum foil it is advisable to apply a lacquer coating on the foil web, at least on one side.

Claims

What is claimed is:

1. A package comprising

a material to be irradiated;

a gas-tight covering enclosing said material in sealed relation; and

a medium within said covering capable of binding oxygen, said medium having a surface area exposed to the interior of said covering and having an oxygen binding capacity which increases upon irradiation.

2. A package as set forth in claim 1 wherein said medium is a coating on the interior of said covering.

3. A package as set forth in claim 1 which further comprises a foil coating the interior of said covering and wherein said medium is disposed in said foil.

4. A package as set forth in claim 1 wherein said medium is silica gel.

5. A package as set forth in claim 1 wherein said medium is in the form of small particulates having relatively large ratioes or surface area to volume.

6. A package as set forth in claim 1 wherein said medium is in the form of a porous structure.

7. A package as set forth in claim 1 which further comprises a gas permeable covering about said medium within said gas-tight covering.

8. A package as set forth in claim 1 which further comprises a gas impermeable covering about said medium within said gas-tight covering; said gas impermeable covering being adapted to be opened within said gas-tight covering to communicate said medium with said material.

9. A package as set forth in claim 1 wherein said medium is bentonite.

10. A package as set forth in claim 1 wherein said medium is capable of chemically binding with oxygen.

11. A package as set forth in claim 1 wherein said medium is capable of physically binding with oxygen.