EP1173754A1

EP1173754A1 - Leakage indicator, method to produce the leakage indicator and a package provided with a leakage indicator

Info

Publication number: EP1173754A1
Application number: EP99959462A
Authority: EP
Inventors: Eero VTT Bio-ja elintarviketekniikka HURME; Maria VTT Bio-ja elintarviketekniikka SMOLANDER; Timo VTT Bio-ja elintarviketekniikka PULLINEN; Raija VTT Bio-ja elintarviketekniikKA AHVENAINEN; Seppo UPM-Kymmene Corporation KARISALO; H kan Raflatac Oy SAXEN
Original assignee: UPM Kymmene Oy
Current assignee: UPM Kymmene Oy
Priority date: 1999-04-28
Filing date: 1999-12-09
Publication date: 2002-01-23
Also published as: WO2000067014A1; FI990958A; FI990958A0

Abstract

In the method for manufacturing and attaching to a package a leakage indicator which reacts with oxygen in controlled atmosphere food packages, the leakage indicator is reduced and attached to packaging material (11) in such a manner that the said leakage indicator attached to the packaging material has been reduced at latest before the moment when the package is ready.

Description

Leakage indicator , method to produce the leakage indicator and a package provided with a leakage indicator

The object of this invention is a leakage indicator, a method of manufacturing the same, and a package provided with a leakage indicator. The package comprises a packaging space made of packaging material and enclosed from the surrounding environment, the leakage indicator being attached in contact with the said packaging space. If the package is damaged, the leakage indicator reacts with the oxygen leaking into the package and thus indicates that the packaged product may possibly be damaged.

The terms leakage indicator or indicator, indicator agent and indicator colouring agent are used in this patent application. An indicator colouring agent refers to a colouring agent, the colour of which is different depending on whether it is in an oxidised state or a reduced state, in other words, it is a so-called redox-type colouring agent. An indicator agent refers to a mixture or a solution, which includes other substances in addition to the indicator colouring agent. A leakage indicator or an indicator refers to a ready-made product, which includes an indicator agent, film materials and possibly substance layers on the surfaces of the film materials. When the packaging material forms the backing film of the leakage indicator, the indicator without backing film is referred to as the leakage indicator.

Furthermore, the terms oxygen-tight film and a film with controlled oxygen permeability are used in this application. The oxygen permeability of oxygen- tight film is in the same range as that of food packaging material, i.e. practically impermeable to oxygen. The permeability of a film with controlled oxygen permeability can vary greatly depending on the planned application of the leakage indicator, generally varying between 1-10,000 ml/m² 24 h-atrn. The general idea is that the fiim with controlled oxygen permeability allows through it an amount of oxygen that causes the oxidation of the indicator agent and the resulting colour change.

The term ready-made package is used in this application when a packaging space is made of packaging material and enclosed from the environment, the said packaging space containing a foodstuff packed in a protective gas, and the leakage indicator being attached to the packaging material. Sub-processes of the packaging process may occur in different order, but the ready-made package has all the above-mentioned characteristics of a ready-made package.

Foodstuff liable to deterioration is generally packed in a vacuum or a protective gas, such as carbon dioxide or nitrogen. In this way the foodstuff keeps longer, as there is no oxygen available for microbial growth. In connection with the packaging or in the distribution chain from the factory to the consumer, the package may, however, be damaged in such a way that the surrounding oxygen leaks into the interior of the package. Thus, the shelf life of the foodstuff is substantially reduced and the product might already have become spoiled before the sell-by-date.

A leakage indicator that reacts with oxygen, placed in connection with a controlled atmosphere food package, thus indicates when the package is damaged and the contents are possibly no longer usable. On the other hand, in connection with the packaging, a small amount of residual oxygen (equal or less than 3.0%) might remain in the controlled atmosphere food package, and the indicator should not react with this oxygen.

Known oxygen indicators are presented, for example, in the following publications:

US 4349509 presents an indicator which reacts with oxygen and which can be attached to its substrate by means of printing or coating. The substrate is a sheet-like cellulose-based material or a plastic material. The indicator comprises a reducing agent, a colouring agent which changes colour depending on whether it is in a reduced state or an oxidised state a thickening agent, and a solvent.

US 5096813 presents an indicator based on a combination of a separate colour indicator and a separate oxygen-sensitive material. The oxygen indicator is ready for use. The colour indicator is generally in the form of a printing ink.

JP 55041875 presents an oxygen scavenger/oxygen indicator combination in which the oxygen scavenger and the oxygen indicator are in a pouch in the same space or separated from each other by means of a partition wall. The principal application of the indicator is to ensure that the oxygen scavenger works, but it can also be used to indicate a leakage in the package. GB 2298273 presents a leakage indicator composition in which there is a carrier agent, ferrocyanide, L-ascorbic acid and a ferrous component, for instance, ferrous sulphate or ferrous chloride. The indicator functions both as an oxygen scavenger and an as oxygen indicator.

EP 0666977 presents an indicator agent, which includes a reducing agent, an indicator colouring agent and an oxygen scavenger. The indicator agent is enclosed in between two walls in such a manner that the walls delimit the enclosed space, in other words, the leakage indicator forms a kind of a pad. The walls are of double material with controlled oxygen permeability. In connection with the packaging, the oxygen-free interspace between the layers of the double material acts as a buffer against atmospheric oxygen in order to protect the leakage indicator, which is in a reduced state. In connection with the packaging, the indicator is placed inside the package, without however attaching the said indicator to the packaging material.

EP 0627363 presents a food package containing an indicator that changes its colour when the concentration of gas flowing into the package reaches a predetermined level. The indicator may comprise a name label or printed material formed on the surface of the package. The indicator may be separated from the packaged product by means of a gas permeable film. The indicator may be a carbon dioxide indicator or an oxygen indicator.

The problem with known leakage indicators is the reducing of said indicators and keeping them in a reduced state, and also the placing of the leakage indicator in the package in such a way that it will not hamper the packaging of the foodstuff.

An indicator according to the invention aims at avoiding the above-mentioned drawbacks. Thus, the leakage indicator is characterised in that the leakage indicator attached to the packaging material has already been reduced, at latest before the moment when the package is ready.

No method has previously been presented to implement the foregoing. The method presented here is characterised in that the leakage indicator is reduced and attached to the packaging material in such a manner that the leakage indicator attached to the packaging material has been reduced, at latest before the moment when the package is ready.

A further object of the invention is a package provided with a leakage indicator, the package being characterised in that the leakage indicator attached to the packaging material has been reduced, at latest before the moment when the package is ready.

With the indicator according to the invention a reliably functioning indication of leakage in a package can be obtained, the said indicator not reacting with small amounts of oxygen, for example, with residual oxygen left in the package in the course of the packaging, or with oxygen with which it is temporarily in contact in the packaging machine. An oxygen scavenger is not necessarily needed in the structure of the leakage indicator, and the leakage indicator is in a ready-to-use state in the package before the foodstuff is packed, or else the said indicator can be attached in a ready-to-use state to the outer surface of the package immediately after the packaging. It also remains stationary in its place and thus its position needs no attention in connection with the packaging - there is, for instance, no danger of the leakage indicator becoming wet due to liquid leaking from the foodstuff. Thus, the structure of the leakage indicator is simple, and industrial packaging of the package provided with the leakage indicator is easy.

A leakage indicator according to the invention is formed either of a film which is folded around the indicator agent and the edges of which are closed, or of two films between which the indicator agent is enclosed. The fiim forming that surface of the leakage indicator that forms the interface with the packaging space has controlled oxygen permeability. The backing film is generally an oxygen-tight film but it can also be oxygen-permeable, provided that the indicator is attached to the inner surface of the packaging material. It is unnecessary to purchase several film materials if the same type of film is used on both surfaces of the leakage indicator. The film material may be any film that possesses suitable oxygen permeability properties, for example, a plastic film or coated paper. The choice of the film can also contribute to the prevention of reoxidation of the leakage indicator after reduction, in other words, by choosing a fiim, which is permeated by oxygen at an appropriately slow pace. The effect of light on the colour of the indicator agent can be reduced by the use of colour films. The oxygen permeability of the film may be based on the thickness of the material, the general structural permeability or porosity of the material, or on micro perforation of the material. The film may also consist of several superimposed layers of material. The properties of the film are chosen to be such that the indicator reacts at a desired level with oxygen that has leaked into the package. If the film is too permeable, the indicator colouring agent may become oxidised during the manufacture of the package or the packaging, or due to the residual oxygen remaining in the package after packaging. If, on the other hand, the film is too dense, the foodstuff may already be seriously damaged but the leakage indicator does not react with oxygen leaking into the package.

The leakage indicator may also be formed in such a manner that the packaging material functions as the backing film of the leakage indicator. In this way the leakage indicator is joined directly to form an integral part of the packaging material. In this case, film with controlled oxygen permeability can be attached on top of the indicator agent, or the said film can form the entire package locally or the inner surface of a part of it.

The indicator agent may be solid or liquid. A liquid indicator agent, for instance, a water-based indicator agent, is more homogeneous than a solid one and, in addition to this, substances that control chemical reactions can be added to a liquid. A liquid indicator agent can be thickened to make it gelatinous, for example, with starch, or it can be adsorbed into a carrier material, for instance, paper, non-woven fabric or some polymer-based material.

The indicator agent comprises at least a colouring agent, a reducing agent, and reduction-stimulating and/or reoxidation-retardant agents. The colouring agent may be any one that becomes oxidised and changes its colour due to the influence of the oxygen in the air, and does not react with the protective gas used in the package, for example, nitrogen or carbon dioxide. Such colouring agents are, for instance, methylene blue, gallocyanine or methylene red. Combinations of different colouring agents can also be used.

The purpose of the reducing agent is to reduce the colouring agent and to keep it reduced. The reducing agents used may, for instance, be carbohydrates, preferably reducing saccharides such as glucose. The reduction-stimulating and/or reoxidation-retardant agents may, for example, be titanium dioxide, riboflavin and/or L-cysteine. When the indicator agent contains reduction-stimulating and/or reoxidation-retardant agents, it withstands storage in protective gas better than without any additives. Thus, the colour of the leakage indicator only changes when the food package is broken.

The slowing down of reoxidation is important because with the method according to the invention, the leakage indicators are reduced before the packaging of the foodstuff in a package provided with a leakage indicator, or before attaching the leakage indicator to the packaging material, at the later of these two points of time, and thus the reduced leakage indicators are momentarily in contact with the oxygen of the ambient air. If reduction- stimulating and/or reoxidation-retardant agents are used in the indicator agent, it is not necessary to use an oxygen scavenger, since the leakage indicators which have had the above-mentioned substances added to their indicator agent do not react with the residual oxygen left in the package in the course of packaging.

Moreover, the indicator agent may contain alkaline substances and fillers. The alkaline substances, for instance, sodium hydroxide (NaOH), sodium carbonate (Na₂CO₃) or sodium bicarbonate (NaHCO₃), slow down the oxidation reaction. The purpose is to avoid too fast oxidation reactions, whereby the leakage indicator would change its colour due to the momentary contact with air, for example, when the leakage indicator is attached to the packaging material before packaging.

The fillers used may, for instance, be kaolin, silicon oxide or talc.

An oxygen scavenger can also be incorporated in the leakage indicator, although this is not necessary. The oxygen scavenger is placed between the films in the same way as the indicator agent, but the oxygen scavenger is in its own space separate from the indicator agent. The oxygen scavenger may be a powder or a liquid, for example, an oxygen scavenger that is based on an enzyme reaction, or a solution containing iron or its compounds, citric or acetic acid, alcohol and water.

The components of the indicator agent are combined in normal ambient conditions, and the indicator agent, thickened or adsorbed into a carrier material, is seamed between the films. The leakage indicator together with a separate oxygen scavenger is placed in an oxygen-free space, for instance, a nitrogen atmosphere, whereby the indicator agent becomes reduced. During the reduction, the preferable temperature range is 15-35 degrees Celcius and the reducing time 3-60 days.

The reduction of the indicator agent can be accelerated by supplying energy to the process by means of either heat or light. For example, a halogen light, micro- or ultrasonic waves may function as sources of energy. When using applications of this kind, attention must be paid to the limitations imposed by the raw materials of the leakage indicator, for instance, the limitations resulting from the melting point of the raw materials.

The package's packaging material, from which the packaging space enclosed from the surrounding environment is formed, may be any material suitable for the packaging of foodstuffs, for example, plastic or liquid packaging board. In the case where the leakage indicator is attached to the inside of the package, the packaging material must be at least partly transparent. This can be achieved, for instance, by using a transparent film as a lid for the package, in which case, the other packaging material can be opaque.

The invention will be explained in further detail in the following with reference to the accompanying drawings, in which

figure 1 is a cross-sectional view showing alternative ways of attaching the leakage indicator to the package,

figure 2 shows the joining of the oxygen scavenger to the leakage indicator,

figure 3 is a cross-sectional view showing the structure of the leakage indicator according to an advantageous embodiment of the invention,

figure 4 illustrates a web roll formed of leakage indicators,

figure 5 presents the storage cassette of a web roll formed of leakage indicators, figure 6 shows the effect of reduction-stimulating and/or reoxidation- retardant agents on the functioning of the leakage indicator, and

figure 7 depicts the effect of storage life, lighting and a leakage in the package on the colour of the indicator.

There are several alternative ways to attach the leakage indicator to the packaging material. Figure 1 a illustrates a package in which the indicator is attached to the inside of the packaging material 1 by means, for example, of seaming or gluing. The backing fiim 2 has been attached to the packaging material 1 , and it can either be oxygen-tight or with controlled oxygen permeability. The film with controlled oxygen permeability 3 forms an interface with the packaging space delimited by the packaging material 1 and is seamed and/or glued to the backing film 2 in such a manner that the indicator agent 4 remains entirely inside the films. If the indicator is attached to the inside of the package, at least partial transparency is required of the packaging material 1 and the backing film 2, in order for the colour change of the indicator agent 4 to be perceivable. A leakage indicator placed inside of the package has been reduced before the packaging of the foodstuff.

Figure 1b depicts a package in which the leakage indicator has been attached to the packaging material 1. The oxygen-tight backing film comprises a packaging material 1 against which the indicator agent 4 is placed. Thus, the outer surface of the indicator is simultaneously the outer surface of the packaging material. The film 3 with controlled oxygen permeability is attached on top of the indicator agent 4 either locally or in such a manner that it forms the inner surface of the packaging material 1 throughout the area of the whole package, or a part of it. The film 3 with controlled oxygen permeability has been seamed and/or glued to the packaging material 1 in such a way that the indicator agent 4 remains entirely inside the film 3 and the packaging material 1. In this alternative, too, the leakage indicator has been reduced before the packaging of the foodstuff.

Figure 1c shows a package in which the indicator is outside the package. The indicator is attached to the packaging material 1 , for example, by seaming or gluing. The film 3 with controlled oxygen permeability is against the surface of the packaging material 1. The part of the packaging material 1 remaining under the film 3 of with controlled oxygen permeability has been perforated before the attachment of the indicator. The oxygen-tight backing film 2, which in this alternative is outermost and seamed to the outer surface of the packaging material 1 , prevents oxygen reaching the indicator agent 4 by any other way than by the holes in the packaging material 1 , or if the packaging film is film with controlled oxygen permeability, by any other way than from the inside of the package through the packaging material. The indicator on the outside of the package may be attached to the packaging material either before the packaging of the foodstuff, in which case the indicator is in a reduced state during the packaging of the foodstuff, or immediately after the packaging, when the reduced leakage indicator is being attached to the package.

In figures 1a to 1c, a packaged foodstuff is referred to by the letter F.

The function of the oxygen scavenger is to remove the residual oxygen remaining in the package and the oxygen diffusing into the package through the packaging material. The use of an oxygen scavenger in a leakage indicator according to the invention is not necessary, but the oxygen scavenger may be attached to the indicator if desired. As shown in figure 2, the oxygen scavenger is placed between the backing film 2 and the film 3 with controlled oxygen permeability. The indicator agent 4 and the oxygen scavenger 10 are separated from each other by a seam 5, in such a manner that the indicator agent 4 and the oxygen scavenger are totally separated. The oxygen scavenger 10 can also be totally separated from the leakage indicator in such a way that the oxygen scavenger and the films surrounding it form a separate piece, which is then attached to the package. The oxygen scavenger 10 may be a powder or a liquid, for example, a substance that removes oxygen on the basis of an enzyme reaction, or a solution containing iron or its compounds, citric or acetic acid, alcohol and water.

Figure 3 illustrates the structure of the leakage indicator according to an advantageous embodiment of the invention (for the sake of clarity, the parts of the leakage indicator are shown separately), the said structure comprising a film 2, a film 3 with controlled oxygen permeability, layers 6 and 7 of adhesive, and the indicator agent 4. The indicator agent 4 has been enclosed from the environment by seaming films 2 and 3 together with seam 5. The product in question is meant to be attached to the inside of the packaging space and, thus film 2 can be oxygen-tight or oxygen-permeable. Layers 6 and 7 of adhesive have been applied to both sides of film 2, the layers of adhesive being self- adhesive glue for attaching the leakage indicator to the package and for attaching§ film 2 to film 3. The layer of glue 7 is not essential.

In one embodiment, films 2 and 3 depicted in figure 3 have an oxygen removing effect, and they function as oxygen scavengers in relation to the indicator colouring agent.

In the following, a method applicable in the production of leakage indicators is described. A roll, which has a multiplicity of reduced leakage indicators I adjacent to and consecutively to one another, as presented in figure 4, is placed in a cassette, which is shown in figure 5. The cassette may also contain a roll that is formed solely of indicators placed consecutively to one another. An oxygen-free gas flow is arranged in the cassette in such a manner that a slight overpressure is created. The gas is introduced into the cassette via a gas inlet 9. The gas is lighter than oxygen, for example, nitrogen or a gas mixture. The leakage indicator web and the gas flow are discharged through a gap 8. The cassette incorporates a gas flow guide 7, which ensures that the web comes as little as possible into contact with the oxygen in the air when the web is being unrolled. The gas flow being discharged from the cassette is directed by guide 7 to flow parallel to the web and thus to form a layer of protective gas on the web outside the cassette as well. The web is taken to the packaging machine packed in the cassette. At the packaging machine, the leakage indicators in the web are detached from it or cut off and attached to the packaging material. In the following phase, the foodstuff is packed, and the package is closed.

The invention is illustrated by way of the following examples, which are not such as to limit the scope of invention.

Example 1.

An indicator agent was produced in normal ambient conditions, the composition of the indicator agent being

- methylene blue 10.0 mg

- riboflavin 2.5 mg - L-cysteine 32.5 mg

- titanium dioxide 32.5 mg

- glucose 3,200 mg

- saturated NaHCO₃ solution 6 ml Methylene blue changes its colour depending on whether it is in an oxidised or a reduced state. In an oxidised state, the colour is blue, and in a reduced state, it is white. Glucose reduces the indicator colouring agent, and riboflavin, L- cysteine and titanium dioxide function as reduction-stimulating and/or reoxidation-retardant agents. Sodium bicarbonate mixed with water slows down the rate of the oxidation reaction of methylene blue.

An indicator according to figure 3 was manufactured of two films and the indicator agent 4, which was adsorbed into a 15 x 15 mm piece of paper. The layer against the surface of the package was formed by film 2, which was a 65 micro m thick polyamide / ethylene/vinyl alcohol /polyethylene film, provided on both its sides with a layer 6 of adhesive, which was a self-adhesive glue. The outer surface of the indicator was fiim 3 which was also a 65 micro m thick polyamide/ ethylene/vinyl alcohol /polyethylene film. The indicator agent 4 was placed between the afore-mentioned films 2 and 3 in such a manner that seam 5 was formed around the paper.

The indicators were placed in oxygen-tight pouches together with a separate oxygen scavenger, whereafter the pouches were filled with nitrogen gas and closed. The pouches were stored at room temperature in the dark for 9 weeks, and during this time, the indicators had become reduced.

Example 2.

Ascorbic acid (AA), riboflavin (RF), L-cysteine (L-k) and titanium dioxide (TiO₂) were added to the indicator agent of leakage indicators manufactured in normal ambient conditions, the ratio of the substances being 1 :1 in relation to the molar quantity of methylene blue. The reduction was carried out in an oxygen-free state at 30 degrees Celcius. The leakage indicators were packed in a reduced state in packages containing nitrogen as a protective gas. The packages were stored at 5 degrees Celcius.

Figure 6 shows the effect of reduction-stimulating and/or reoxidation-retardant agents on the functioning of the leakage indicator. Some of the packages were broken after 4 and some after 7 days of storage (dotted lines ), and a number were kept in intact packages (continuous line). It was possible to state that the addition of ascorbic acid did not have the desired effect, but the indicators, which contained riboflavin, L-cysteine and titanium dioxide, withstood storage better than those without a reduction-stimulating and/or a reoxidation-retardant agent, and the said leakage indicator functioned equally well when the package was damaged.

Example 3.

The indicators according to figure 1 were attached to a film which was used as a lid for a food package. When the lid was attached, the indicator remained inside the package. 250 g of frozen meatballs were packed in 600 ml polypropylene containers, after which the containers were closed with the aforementioned film. The gas composition of the containers was 20% carbon dioxide and 80% nitrogen, the amount of residual oxygen being approximately 1%.

In order to simulate the distribution chain of food packages, the meatball packages were stored at 5 degrees Celcius for 17 days in the dark and then for 2 days in the light and finally 6 days in the dark. Some of the packages were kept intact, a number of them had a hole made in the lid after 3 days with a tungsten filament, the diameter of which was either 95 micro m or 800 micro m.

The colour of the indicators was monitored during the experiment both visually and with a Minolta spectrophotometer using the L,a,b colour determination scale. A graphic representation of the results of the colour measurement is shown in figure 7, in which the value of the L-coordinate is presented as a function of the storage time. The value of the L-coordinate, 100, stands for a white surface and the value 0 stands for a black surface. Thus, the change in the degree of darkness of the indicator can be monitored by the change in the value of the L-coordinate.

The colour of the indicator remained light in the intact meatball packages (the change in the colour during the storage was from light to light grey).The 800 micro m hole was discovered in 1 to 2 days (the colour changed from light to blue), and the 95 micro m hole was discovered in 4 to 7 days (the colour changed from light to blue). Light did not have a considerable impact on the colour. Light changed the colour that had turned to blue to a shade of violet, but the violet tone changed back to blue in the dark. To a person skilled in the art it is clear that the invention is not limited to the afore-mentioned examples, but it can vary within the scope of the attached Claims. The leakage indicator can be used in a variety of food packages, for example, in meatball, frankfurter or ready-to-eat food packages. The packaging material can be shaped into pouches or containers which may have a separate lid or a lid formed of the same material. If the leakage indicator is attached to the inside of the package, the packaging material must be either partially or totally transparent. If, on the other hand, the indicator is outside the package, transparency of the packaging material is not essential. It suffices that the packaging material is permeable to oxygen at the point of the leakage indicator.

The composition and the state of the indicator agent may vary, as may the means of attachment of the leakage indicator to the packaging material. The main point is that the leakage indicator has been reduced and attached to the material in such a manner that the leakage indicator is in the reduced state at latest at the moment when the package is ready.

Claims:

Claims

1. A method for manufacturing and attaching to a package a leakage indicator which reacts with oxygen in controlled atmosphere food packages, characterised in that the leakage indicator is reduced and attached to packaging material in such a manner that the said leakage indicator attached to the packaging material has been reduced at latest before the moment when the package is ready.

2. A method as claimed in Claim 1 , characterised in that the leakage indicator comprises an indicator agent (4) enclosed inside a film material, which at least partly is film with controlled oxygen permeability.

3. A method as claimed in Claim 2, characterised in that the leakage indicator comprises a film (3), with controlled oxygen permeability and a backing film (2), between which two films the indicator agent (4) is enclosed.

4. A method as claimed in Claim 3, characterised in that the backing film (2) is made of a separate film (2).

5. A method as claimed in Claim 3, characterised in that the backing film (2) is made of the packaging material (1).

6. A method as claimed in any of the preceding Claims 2-5 mentioned above, characterised in that the indicator agent (4) is produced in such a manner that at least an indicator colouring agent, a reducing agent, a reduction-stimulating and/or a reoxidation-retardant agent are used in its production.

7. A method as claimed in Claim 6, characterised in that the reduction- stimulating and/or reoxidation-retardant agents are riboflavin, L-cysteine and titanium dioxide.

8. A method as claimed in any of the preceding Claims 2-7 mentioned above, characterised in that auxiliary agents are added to the indicator agent (4).

9. A method as claimed in Claim 8, characterised in that the auxiliary agents are liquid substances, for instance water, with which other components of the indicator agent are mixed, an alkaline substance which controls the oxidation reaction, and fillers.

10. A method as claimed in any of the Claims 2-9 mentioned above, characterised in that the indicator agent (4) is thickened or adsorbed into a carrier material.

11. A method as claimed in Claim 10, characterised in that paper, non-woven fabric or some polymer based material is used as a carrier material.

12. A method as claimed in Claim 10, characterised in that the indicator agent is thickened with starch.

13. A method as claimed in any of the Claims 2-12 mentioned above, characterised in that the indicator agent is enclosed in between films (2, 3) or between a film (3) and a packaging material (1) by means of seaming or gluing.

14. A method as claimed in any of the preceding Claims, characterised in that the leakage indicator is reduced by enclosing it in an oxygen-free atmosphere with a separate oxygen scavenger, which is not part of the structure of the leakage indicator.

15. A method as claimed in any of the preceding Claims, characterised in that the leakage indicator or the packaging material to which the said leakage indicator is attached, is stored in an oxygen-free atmosphere.

16. A method as claimed in any of the preceding Claims, characterised in that the leakage indicator is attached to the packaging material.

17. A method as claimed in any of the preceding Claims, characterised in that the leakage indicator is attached to the packaging material by means of seaming or gluing.

18. A method as claimed in Claim 16 or 17, characterised in that the leakage indicator is attached to the inside of the packaging material by attaching the backing film (2) to the inner surface of the packaging material (1).

19. A method as claimed in Claim 16 or 17, characterised in that the leakage indicator is attached to the outside of the packaging material (1) by attaching the film (3) with controlled oxygen permeability to the outer surface of the packaging material (1 ), the said outer surface being perforated at the leakage indicator.

20. A leakage indicator for controlled atmosphere food packages, characterised in that the leakage indicator attached to the packaging material has been reduced at latest before the moment when the package is ready.

21. A leakage indicator as claimed in Claim 20, characterised in that the leakage indicator comprises an indicator agent (4) which has been enclosed inside a film material, which is at least partly film with controlled oxygen permeability.

22. A leakage indicator as claimed in Claim 20 or 21 , characterised in that the leakage indicator comprises of a film (3) with controlled oxygen permeability and of a backing film (2) between which the indicator agent (4) has been enclosed.

23. A leakage indicator as claimed in Claim 22, characterised in that the backing film (2) has been made of a separate film (2).

24. A leakage indicator as claimed in Claim 22, characterised in that the backing film (2) has been made of a packaging material (1).

25. A leakage indicator as claimed in Claims 20-24 mentioned above, characterised in that the indicator agent (4) comprises an indicator colouring agent, a reducing agent, a reduction-stimulating and/or a reoxidation-retardant agent.

26. A leakage indicator as claimed in Claim 25, characterised in that the reduction-stimulating and/or reoxidation-retardant agents are riboflavin, L- cysteine and titanium dioxide.

27. A package provided with a leakage indicator which reacts with oxygen, the said package comprising a packaging space made of packaging material and enclosed from the surrounding environment, and a leakage indicator attached to the packaging material, characterised in that the leakage indicator attached to the packaging material has been reduced at latest before the moment when the package is ready.