STERILISING MEDIUM, METHOD FOR PREPARING THE STERILISING MEDIUM, METHOD FOR STERILISING PACKAGING MATERIAL FOR FOOD PACKAGING AND THE USE OF A SPREADING AGENT COMPOSITION IN A STERILISING MEDIUM

TECHNICAL FIELD

The present invention relates to a sterilising medium for sterilisation of packaging material for food packaging containing an aqueous solution of hydrogen peroxide and a spreading agent additive composition. The invention also relates to a method of preparing the sterilising medium, the method of sterilising a laminated packaging material, or a container thereof, for food packaging and to the use of the spreading agent composition in a sterilising medium containing hydrogen peroxide for the sterilisation of packaging material or containers for food packaging.

PRIOR ART AND PROBLEMS

In the production of aseptically packaged food, several factors interplay in order to obtain a food product that can remain on the shelf for a long time without deteriorating in taste and nutritional quality. It is important that the food product as such is sterile to such a degree that micro-organisms do not multiply during long- term storage, that the filling of the product into the package takes place under aseptic conditions in clean machines in a clean environment, and that the package itself is capable of keeping the product unaffected by surrounding moisture, light, oxygen gas and bacteria for a long time. It is, of course, of highest importance that the packaging material or package is sterile, i.e. free from microorganisms, at the moment the food product is filled into it. Sterilisation of packaging machines, packaging material or packages to be filled may be achieved in various ways, e.g. by applying a chemical sterilising liquid or gas- phase mediums onto the surfaces to be sterilised, by UV-light or by electron

beam irradiation or by combinations of such methods. Of course, thorough cleaning in the first place and rinsing with sterile water also contributes significantly to the resulting aseptic environment in a packaging machine.

Packaging containers of the single use disposable type for liquid and high- viscosity flowable foods are often produced from a packaging laminate of the type comprising a core layer of paper or paperboard and outermost liquid tight, heat sealable layers of polyolefin. Commonly occurring such packaging containers are marketed i.a. under the trademarks Tetra Brik Aseptic® or Tetra Classic Aseptic® and are principally employed for liquid foods such as milk, fruit juices etc. The packaging material in these known packaging containers is typically a laminate comprising a bulk core layer of paper or paperboard and outer, liquid-tight layers of thermoplastics. In order to render the packaging container light- and gas-tight, in particular oxygen gas-tight, for example for the purpose of aseptic packaging and packaging of fruit juices, the laminate for these packaging containers is normally provided with at least one additional layer, most commonly an aluminium foil, which moreover renders the packaging material thermo-sealable by inductive thermo-sealing which is a rapid and efficient sealing technique for obtaining mechanically strong, liquid- and gas-tight sealing joints or seams during the production of the containers. On the inside of the laminate, i.e. the side intended to face the contents of a container produced from the laminate, there is an outermost layer, applied to the aluminium foil, which outermost, inside layer may be composed of several part layers, comprising adhesive polymers and/or polyolefins.

Such packaging containers are generally produced by means of modern packaging machines of the type that form, fill and seal packages from a web or from prefabricated blanks of packaging material. From a web, for example, packaging containers are produced in that the web is reformed into a tube by both of the longitudinal edges of the web being united to one another in an overlap joint. The tube is filled with the intended liquid food product and is divided into individual packages by repeated transversal seals of the tube at a distance from one another below the level of the contents in the tube. The packages are separated from the tube by incisions in the transverse seals and are given the

desired geometric configuration, normally parallelepipedic or tetrahedron-shaped, by fold formation along prepared crease lines in the packaging material.

Before the formation of the tube and the filling of the product into the tube, the web typically passes through a bath with a liquid sterilising agent. So-called squee-gee rollers, remove the surplus of sterilising liquid by squeezing it away from the web, before the tube is dried with hot sterile air. Other methods of sterilising such a tube of packaging material, than simply dipping the web by leading it through a deep bath of sterilising medium, are spraying, gas phase condensation or, most commonly, coating of the packaging material web with a roller, for applying the liquid evenly onto the surface of the packaging material web.

One very commonly used sterilising agent, which is suitable both for liquid and gas-phase sterilising mediums is hydrogen peroxide, H2O2. Normally, for application in the food industry, hydrogen peroxide is employed as an aqueous solution at a concentration of about 35 weight-%, but also higher concentrations are feasible, e.g. up to 50 weight-%. Also other sterilising agents such as per- acetic acid are often used.

The effect of the sterilisation is to a large extent depending on the ability of the sterilising medium to spread out evenly across the surface to be sterilised and on the wetting characteristics of the particular surface. When the surface tension is too high, the sterilising medium forms larger droplets and is not distributed evenly on the surface. There are two main problems arising as a consequence to this. The first is that the sterilisation will be less efficient because the sterilising agent is not affecting the entire surface and because too much sterilising medium is used in the regions of the larger droplets and too little in the regions there between. The second problem is that residuals of sterilising medium will remain on the surface after sterilisation because the larger droplets are difficult to remove satisfactorily at high production speed in the packaging machine.

The two problems are entangled with each other, because a better distribution of hydrogen peroxide on the web will help the evaporation of droplets at drying and, consequently, leads to lower residuals of peroxide in the packages.

The two problems are further pronounced at high speed production, because the sterilising agent then only has a minimum time to act on the surface

to be sterilised and must be removed very quickly before the filling of the food product. The problem is also particularly pronounced when the surface to be sterilised is extra smooth and glossy such as is the case for certain film qualities used as an outermost layer of a packaging laminate. As an example, highly viscous products require an outermost material surface, directed towards the inside of the packaging container, onto which the viscous food product does not stick, in order to facilitate emptying of the package. Naturally, also the sterilising agent does not spread and remain evenly coated onto such a "non-stick" surface. Also, certain film qualities used for an inner strip attached to the innermost layer, for covering the longitudinal seal on the inside of the package, have such non- wetting characteristics. Although it is possible to keep the sterilisation process under close control in order to reach sufficient and adequate sterilisation with the presently used hydrogen peroxide sterilising medium, it is desirable to have a wider operation window for the relevant parameters, such as production speed and contact time, temperatures and concentrations of the sterilising agent.

In order to remedy these problems to some extent, it has been known for a long time to blend the aqueous hydrogen peroxide solution with a non-ionic wetting agent called "Tween™ 20" a polyethylene glycol 20 sorbitan mono laurate. A certain spreading effect is obtained, but it leaves room for improvement, especially for high speed production and when variations in process conditions are difficult to control.

From EP1384670, it is known to use wetting agents, i.a. either fatty acid esters or lecithin, in an aqueous sterilising solution of a hypochlorous acid- containing chlorine-based sterilising agent. However, sufficient sterilisation effect at a short contact time will only be possible if the sterilisation method also involves heat sterilisation.

It is known from US 5,858,933 to use chemically modified lecithin in combination with a fatty ester as a lubricant additive for coating a paper web with clay-coating during paper manufacturing, resulting in improved coating quality due to improved viscosity control, improved runnability and less problems of the coating such as calcification, streaking, whiskering e.t.c. These properties are dependent on how well the particles and pigments are dispersed in the coating composition.

It is further known from US 4,200,551 to improve dispersibility of non- modified crude lecithin in water by adding a non-ionic emulsifier.

However, it has hitherto not been contemplated to develop these findings about lecithin compounds into a suitable spreading agent additive composition for aqueous hydrogen peroxide sterilising mediums.

DISCLOSURE OF THE INVENTION

It is, therefore, an object of the present invention to overcome or alleviate the above-described problems.

It is a general object of the invention to provide a hydrogen peroxide-based sterilising medium which has improved spreading properties onto the surface to be sterilised.

Consequently, it is an object to provide a hydrogen peroxide-based sterilising medium that is more efficient and may improve the robustness of the sterilisation process, i.e. is less sensitive to variations in process conditions, and thus functions well also at higher production speeds of a packaging machine. More specifically, it is an object to provide a hydrogen peroxide-based sterilising medium that has an improved sterilisation effect. A specific object of a preferred embodiment of the invention is to provide a hydrogen peroxide-based sterilising medium that has an optimised sterilisation effect regarding wetting and consumption of the sterilising medium.

A further specific object of the invention is to provide a hydrogen peroxide- based sterilising medium that leaves a reduced amount of residues on the surface after sterilisation.

Yet a further object of the invention is to provide a hydrogen peroxide- based sterilising medium that functions well for smooth and glossy surfaces with low wetting ability.

These objects are attained according to the present invention by the hydrogen peroxide-based sterilising medium, as defined in claim 1. Preferred embodiments of the sterilising medium of the invention are as defined in claims 2- 11.

These objects are thus attained according to the present invention by a sterilising medium containing an aqueous solution of hydrogen peroxide and a spreading agent additive composition comprising a compound selected from the group consisting of lecithin and chemically modified lecithin and further comprising a non-ionic emulsifier.

The sterilising agent most commonly used is hydrogen peroxide due to its excellent killing effect on bacteria and its comparatively low cost and good health and safety characteristics in connection with food applications. Aqueous hydrogen peroxide solutions of concentrations of up to 50 weight-% are feasible for this invention and solutions of up to about 35 weight-% are commercially available for applications in food industry. Preferably, a concentration of from 30 to 40 weight-%, most preferably of 35 weight-%, is used in a sterilising medium according to the invention.

Lecithin is regarded as a well tolerated and non-toxic surfactant. It is approved by the United States Food and Drug Administration for human consumption with the status "Generally Recognized As Safe" (GRAS) and is also approved by the EU as a food additive. In biochemistry, lecithin is usually used as a synonym for phosphatidylcholine, a phospholipid which is the major component of a phosphatide fraction which may be isolated from egg yolk or soy beans. Commercial lecithin, is a mixture of phospholipids in oil. The main phospholipids in lecithin from soya or sun flower oil are phosphatidyl choline, phosphatidyl inositol, phosphatidyl ethanolamine and phosphatide acid. To adapt the performance of lecithins, they may be chemically modified.

Suitable chemically modified lecithins for the present invention are normally able to dispers more readily into water than crude lecithin and typically has an iodine value (I.V.) of less than 50. The iodine value is related to the number of ethylenic unsaturations in the molecule of the relevant substance. The chemical modification generally introduces hydrophilic substituents into the fatty acid ester group, which in turn renders the lecithin more hydrophilic. Preferably, such chemically modified lecithins are hydroxylated or acetylated lecithins, saponified hydroxylated lecithin or saponified acetylated lecithin or mixtures thereof. Other chemically modified lecithins may be obtained by reactions with

enzymes, such as lipase. Most preferably, a chemically modified lecithin according to the invention is hydroxylated lecithin.

It has, however, unexpectedly been found that also unmodified, crude lecithin disperses and functions very well in an aqueous solution of hydrogen peroxide. Likely, this is due to a chemical reaction or interaction between the unmodified lecithin and the aqueous hydrogen peroxide, such that the initially unmodified lecithin in fact finally becomes chemically modified, most likely with hydroxyl groups as in hydroxylated ledithin.

Although a lecithin compound works to some extent as a sole spreading agent for a sterilising medium containing aqueous hydrogen peroxide, it has surprisingly been found that when combined in a spreading agent composition with a non-ionic emulsifier, the spreading ability of the hydrogen peroxide-based sterilising medium is significantly improved. Preferably, the non-ionic emulsifier is a polyoxylalkylene derivative of a fatty acid glyceride or a polyoxyalkylene derivative of a partial fatty acid ester or a hexitol anhydride or a mixture of such emulsifiers. Representative examples of polyoxyalkylene derivatives of partial fatty acid esters and hexitol anhydrides are POE (polyoxyethylene) 20 sorbitan monostearate, POP (polyoxypropylene) 20 sorbitan monostearate, POE 20 sorbistan tristearate, POE 10 sorbitan distearate, POE 15 mannitan monopalmitate, POE 10 mannitan dimyristate, POE 20 sorbitan dioleate, POE 20 sorbitan monooleate, POE 20 sorbitan trioleate, POE 20 galactitan monostearate, POE 20 galactitan dioleate, POE 30 sorbitan monostearate, POE 20 monolaurate, POE 20 sorbitan monopalmitate, POE 5 sorbitan monooleate and the like. Polyoxylalkylene derivatives of fatty acid mono- and diglycerides are according to the formula

(I) CH2(r2)CH(R3)CH2(R4)

wherein at least two of the (R2), (R3), and (R4) members are selected from the group consisting of a fatty acid ester having at least 12 carbon aroms and a polyoxylkylene moiety represented by the formula

-(-OCH2CH(Y)-)n— OY

wherein n represents an average number of repeating oxylkylene untis, Y is either hydrogen or methyl and the remaining R1 , R2 or R3 member of the Formula (I) composition is either hydroxyl, a polyoxyalkylene moiety or a fatty acid ester.

More preferably, the non-ionic emulsifier is an alkoxylated sorbitan fatty acid ester, and most preferably a polyethylene glycol 20 sorbitan fatty acid ester. A preferred, well functioning example is polyethylene glycol 20 sorbitan mono laurate, also called "Tween™ 20". It has been found that the sterilising medium should preferably comprise from 0,1 to 0,4 weight-% of the unmodified or chemically modified lecithin. At above 0,4 weight-%, the sterilising medium becomes oily and more difficult to remove from the sterilised surface at drying. At below 0,1 weight-% of the lecithin, the consumption or uptake of the sterilising agent, i.e. hydrogen peroxide, becomes too low, i.e. too little hydrogen peroxide is transferred to the surface to be sterilised and the sterilisation effect is too low to be reliable.

The lecithin compound is mixed with a non-ionic emulsifier, thus further improving the spreading and, preferably, the concentration of the non-ionic emulsifier should be from 0,1 to 0,3 weight-% in the sterilising medium. Optimally, the sterilising medium comprises from 0,2 to 0,3 weight-% of the chemically modified lecithin and from 0,1 to 0,2 weight-% of the non-ionic emulsifier. Absolutely best and optimally preferred, the sterilising medium comprises about 0,3 weight-% of the chemically modified lecithin and from 0,1 to 0,2 weight-% of the non-ionic emulsifier. Expressed in a different way, the spreading agent additive composition should most preferably comprise from 60 to 75 weight-% of the chemically modified lecithin and from 25 to 40 weight-% of the non-ionic emulsifier, calculated on the total weight of the spreading agent composition.

According to another aspect of the invention, the hydrogen peroxide-based sterilising medium according to the invention is prepared by first adding a spreading agent additive compound selected from the group consisting of lecithin and chemically modified lecithin to an aqueous solution of hydrogen peroxide or deionized water at a weight ratio of from 1 :5 to 1 :20, preferably at about 1 :10, stirring the mixture to obtain a stable emulsion, adding the thus obtained aqueous

spreading agent lecithin emulsion to an aqueous solution of the hydrogen peroxide sterilising medium, at some stage adding a non. ionic emulsifier and finally stirring to obtain a stable hydrogen peroxide sterilising medium. It is not very important for the end result at what stage the non-ionic emulsifier is added, but preferably, the non-ionic emulsifier is first added into the spreading agent additive lecithin emulsion to form a spreading agent additive composition. Alternatively, the non-ionic emulsifier may be added directly into the aqueous hydrogen peroxide sterilising medium in the form of a separate stable aqueous emulsion. According to a third aspect of the invention, a method of sterilising a packaging material or a container for food packaging, by applying the sterilising medium of the invention onto the surface to be sterilised, is described. According to one preferred embodiment of the method of the invention, the sterilising medium is applied by means of dipping the packaging material into a bath of the sterilising liquid. According to another preferred embodiment of the method of the invention, the sterilising medium is applied by means of coating the packaging material by means of a transfer roller transferring liquid sterilising medium from a bath of the sterilising liquid to the packaging material surface. According to yet a further embodiment of the method of the invention, the sterilising medium is applied by means of spraying of the liquid sterilising medium onto the packaging material surface to be sterilised.

According to a further aspect of the invention, a spreading agent composition comprising a compound selected from the group consisting of unmodified lecithin and chemically modified lecithin and further comprising a non- ionic emulsifier, is used in an aqueous hydrogen peroxide sterilising medium for the sterilisation of packaging material or containers for food packaging.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, preferred embodiments of the invention will be described with reference to the drawings, of which:

Fig. 1a is schematically showing how a web of a packaging laminate is led through a deep bath of a liquid sterilising medium in an aseptic packaging machine of the kind that is normally used for producing Tetra Brik Aseptic® packages, and Fig. 1 b is schematically showing such a packaging machine for the manufacturing of filled packaging containers from a packaging laminate in a continuous form, fill and seal process,

Fig. 2 is schematically showing how a web of a packaging laminate is led through a shallow bath of a liquid sterilising medium in an alternative sterilisation process, Fig. 3 is schematically showing how a web of a packaging laminate may be coated with a sterilising medium by the sterilising liquid from a shallow bath via a transfer roller to one side of the web, in a further alternative sterilisation process,

Fig. 4 is schematically showing how a web of a packaging laminate may be coated with a sterilising medium by spraying the sterilising liquid onto one side of the web and, where appropriate, subsequently irradiating the surface to be sterilised with UV irradiation, in a packaging machine of the kind that is normally used for producing packages intended for chilled ESL (Extended Shelf Life) storage,

Fig. 5a through 5j are showing UV photographs of the distribution or spreading of the sterilising medium liquid applied on a packaging material having a surface to be sterilised of very smooth blown film, by a standard application roller according to the method of Figure 2, above. The UV pictures are taken by including a fluorescent agent, i.e. Tinopal® into the sterilising medium.

Fig. 6a, 6b and 6 c, show the effect of the sterilising medium on the residual content of sterilising liquid when using the sterilising process as described in connection with Figure 2, above.

Fig. 1a thus shows the principle of a packaging and sterilisation process 10 in which a web of packaging laminate is led through a deep bath 12 of a liquid sterilising medium in an aseptic packaging machine of the kind that is normally used for producing Tetra Brik Aseptic® packages. Normally, the hold time, during which sterilisation takes place on the packaging material surface, is the total time during which the packaging material web is soaked in the bath of sterilising liquid. More or less immediately after the web exits from the bath, it is drained by so-

called squee-gee rollers 13 of rubber, which squeeze the liquid away from the web, and subsequently it is dried by hot sterile air. When sterilising by this process, there is no actual wetting problem, because the surface to be sterilised is immersed and in direct contact with liquid all across the surface during sufficient time. However, there may still be an issue of how big the droplets on the surface are after the web has passed the squee-gee rollers and thus of how easily they may be removed at drying, and thus also of sterilising liquid residual content on the sterilised surface. After the sterilising operation, the web is formed into a tube 14, filled with liquid food product 15, sealed and divided into separate packages 16.

In Fig. 1b an example of a packaging machine 10b for the continuous high speed packaging of Tetra Brik® Aseptic packages is shown. The web of laminated packaging material is un-rolled from a reel 11 at the back of the machine, and led through a bath of sterilising liquid 12 just after applying a longitudinal seal cover strip 11 ^' of thermoplastic polymer. After drying and evaporating off the sterilising liquid, the web is formed into a tube 14 which is longitudinally sealed and almost in the same operation filled 15 with the food product through a pipe 15 ^' entering the top of the tube, transversally sealing of the tube beneath the surface of the filled food product and chopping off 16 the separate packages and finally folding and forming the packages into their final shape 17.

In Fig. 2 a sterilising process 20 a is used, according to which the packaging material surface is not in direct contact with the liquid more than during a part of the total "hold time", i.e. the time during which the sterilising medium acts upon the surface, in that the packaging materia! web is dipped into a bath during a limited time, a so-called shallow bath. The experiments carried out as described hereinafter were made in a machine using this sterilisation system, by dipping the web of packaging material 21 into a shallow bath 22. Squee-gee rollers 23 are removing surplus of sterilisation liquid from the web and then the web is led through a heating chamber 25. In order to improve the efficency of this sterilisation process and reduce the sterilising medium residual content, the system is equipped with a special so-called blister roller 24 with a rough surface, which breaks down the liquid droplets on the packaging material surface to

smaller ones, in the heating chamber 25. In order to improve the efficiency still further, an extra heating and drying unit 26, with additional supply of heat and air flow, may be connected to the heating chamber 25.

In Figure 3, a sterilising process is used, according to which the packaging material surface is coated with sterilising medium by roller application, i.e. a transfer roller 33 transfers the liquid sterilising medium from a shallow bath 32 to the packaging material 31 surface. The coated surface is subsequently dried by a heating element (not shown). When applying sterilising medium according to this process, with a specially designed transfer roller, a more even coating of the surface is attainable, compared to when merely immersing the web into the liquid. It has been seen that better spreading of the sterilising medium across the packaging material surface is achieved when lecithin solely is used as spreading agent additive, compared to when using the conventional additive Tween™ 20 alone, in which latter case the spreading was not good. By the sterilisation method of Fig. 4, the intention may be to produce a packaging container with lower requirements on shelf storage life, such as packages for chilled ESL storage. Aseptic sterilisation methods are, however, also feasible involving spraying of sterilising liquid onto the packaging material surface to be sterilised. A web of packaging material 41 is led through a chamber 44, in which sterilising liquid is sprayed onto the entire surface of the web by means of a spray nozzle 42, and subsequently led past a UV-lamp 43 for irradiation of the same surface with sterilising UV-light, before the web is dried and then formed into a tube, filled and finally sealed into separate packages.

EXAMPLES

A chemically modified lecithin that was used in the Examples is ALCOLEC® Aquasperse A from American Lecithin Company. This product is a hydroxylated lecithin which has water dispersibility characteristics. After the chemical modification, the lecithin remains oil soluble, but also becomes water dispersible and capable of forming oil-in-water emulsions. The modified lecithin was mixed with aqueous hydrogen peroxide or deionised water by using a mixer, or by shaking in a container with a tight lid, in order to obtain a stable emulsion. Then the diluted lecithin mixture dispersed readily into the hydrogen peroxide solution. Optical inspection of the wetting ability of the lecithin-containing sterilising mediums was made by the inclusion of a fluorescent agent called Tinopal® in the sterilising medium and UV photography of the coated surface. Various amounts of the modified lecithin and/or the non-ionic emulsifier polyethylene glycol 20 sorbitan monolaurate (Tween™ 20) was mixed with 35 weight-% aqueous solution of hydrogen peroxide according to Table 1. The concentration of Tinopal was 2 weight-% in all Examples. The UV photos in Figures 5a through 5j, correspond to the respective Examples in the same order as presented in the Table. The first three Examples are Reference Examples, either comprising no spreading agent at all or only Tween 20.

Examples 1-7 show that acceptable wetting is obtained when using the modified lecithin alone and at various concentrations and mixtures with Tween™ 20, but that optimised properties also as regards the consumption, i.e. the up- take of hydrogen peroxide solution, are obtained with the conditions according to Examples 2-4. With "consumption" is meant the amount of sterilising agent that is carried by the web and passed through the squee-gee rollers and entered into the heating chamber. If the consumption is too low, evidently the sterilisation effect will be in-sufficient and un-reliable. The effect of the sterilising medium on the residual content on a sterilised surface was investigated and the results presented in Figures 6a - 6c. The well recognised Chemets® ferric thiocyanate method was used. According to this method, an ampoule with reagent, i.e. ferrous ion and ammonium thiocyanate in acid solution, is immersed into a package filled with deionised water. If any trace of hydrogen peroxide is remaining in the package at filling with deionised water, it will oxidize the ferrous iron in the ampoule to the ferric state and form a red thiocyanate complex. The red colour will have different shades depending on the concentration. For approval, the residual content should be less than 0,4 ppm. In the diagrams, the residual content in ppm, is shown by the Y-axis, while the time after start-up is shown on the X-axis. The measurements of residual content were made on packages at various points in time after start-up of the packaging machine (using a sterilisation system according to Figure 2 above), i.e. at 1, 30, 60, 90, 102 and 105 seconds after start-up, and 1 , 2 (3 packages),3,6,9,12,15,18,20 (2+5 packages),23,26 and 29 minutes after start-up. It can be seen that as the machine gets warm and the process reaches a steady- state, the residual content values stabilise at a lower level. Test runs were done at three different conditions, i.e. in connection with Figure 6a with normal settings of the machine and using chemically modified lecithin (hydroxylated lecithin) as wetting agent, in Figure 6b without all arrangements made in order to reduce the residual content, such as i.a. extra air flow and heat after the heating chamber and a blister roller acting upon the web inside the heating chamber, but with the hydroxylated lecithin as wetting agent. In connection with Figure 6c, the machine was run at the same settings as in Figure 6b, but with Tween™ 20 as the sole

wetting agent instead of the hydroxylated lecithin. The concentration of the hydrogen peroxide in the three tests was roughly the same and, thus, does not influence the outcome of the tests. It can be seen in Figure 6c that by running the sterilisation without any arrangement for reducing the residues of sterilising liquid with merely Tween™ 20 added to the aqueous hydrogen peroxide, the residual content of hydrogen peroxide is at an unacceptable level. By making the arrangements mentioned above, the residual contents would be lowered to below 0,4 ppm, but not as much as in the case when hydroxylated lecithin is used instead as the wetting agent. In Figures 6a and 6b, the residual contents are very low, both with and without the extra arrangements in the sterilisation system, but better, of course, in the first case.

The Examples with reference to Figures 5 and 6, were repeated by using unmodified lecithin instead of the hydroxylated lecithin, i.e. Leciprime™ 1400 IP from Cargill. The same results were obtained regarding wetting, uptake/consumption as well as residual contents of hydrogen peroxide in the packages. This is probably, according to a working theory, due to the unmodified lecithin becoming chemically modified when mixed with hydrogen peroxide. In the resulting sterilising medium, whether mixing with chemically modified lecithin or normal unmodified lecithin, you will end up with the same ingredients and total composition. This effect obtained, when using also unmodified lecithin, was unexpected and surprising. The effect is also highly advantageous, because normal, unmodified lecithin is cheaper and easier to find on the market.

Finally, it should be noted that the invention is not limited by the embodiments shown and described above, but may be varied within the scope of the claims.