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Method for preserving foodstuffs

Method for preserving foodstuffs description/claims

This application is a National Stage application of International Application No. PCT/CH2006/000063, filed on Feb. 1, 2006, which claims priority of Swiss application number 00219/05, filed on Feb. 10, 2005.

1. Field of the Invention

The present invention relates to a method for stabilizing foods and in particular pasteurizing foods in which the foods in a moist state inside a container suitable as a shipping and retail package and having a vent opening are heated by microwaves for a limited period of time but at least long enough so that hot steam forms in the container and escapes through the vent opening.

For further use for shipping and retail, the vent opening of the container must be sealed, even if it is very small, to prevent contamination of the foodstuffs with microorganisms and possibly even leakage of fluid out of the container.

2. Description of the Prior Art

A method of the aforementioned type is known from WO 2004/045985 A1, for example. In this method, a container having a flexible bottom and a flexible cover film is used, with a valve being arranged in it as a vent opening. The valve opens automatically during heating under the influence of the excess pressure generated in the container and thereby allows steam to escape. Even shortly after heating, with the onset of cooling and the resulting drop in pressure, the valve automatically closes again. Subsequently, there is a further drastic drop in pressure with further cooling and due to the condensation of the vapor which practically creates a vacuum in the container. The flexible bottom and the flexible cover film of the container bulge inward under the influence of the vacuum and thereby securely enclose the foodstuffs present in the container between them.

The same effect is utilized as described in WO 00/03605 A1 and in WO 03/087993 A1 to achieve a tight and secure sheathing of the foodstuffs with an especially flexible cover film.

EP 1 076 012 A1 describes a preparation method for foods in which the foodstuffs in a moist state are heated with microwaves in a container with a partially flexible cover film and an excess pressure valve for a limited period of time, but at least long enough until steam forms in the container and escapes through an excess pressure valve. This known method is available and is suitable in particular for bringing foods in a raw fresh state on the market in a container and only preparing them in the container in a microwave oven by the end user immediately before consuming them. Due to microwave steam preparation under elevated pressure, the foodstuffs are prepared in an extremely gentle manner from their raw state within only a few minutes, whereby their nutritional content, their consistency, color and natural taste are largely preserved.

However, as part of this usage, it would be unfavorable for a vacuum to develop in the container as described above. The foodstuffs which have just been prepared freshly would be crushed by the covering film bulging inward and liquid might also be pressed out of them. This would destroy the very attractive appearance of the foodstuffs, which has just been achieved. Furthermore, the container as such would be deformed in an unattractive manner. EP 1 076 012 A1 solves this problem by a special design of the excess pressure valve. The valve is altered during the heating process so that it can no longer close again or at least can no longer close immediately. This prevents the development of a vacuum in the container. The destruction of the valve in the method according to EP 1 076 012 A1 does not constitute a problem because the foodstuffs here are intended for consumption immediately after being prepared. The container is also designed only for a single use and then is no longer needed. To render the foodstuffs stable through heating at the manufacturer's before the shipping and retail phase, the method according to EP 1 076 012 A1 would not be suitable, however, because of the excess pressure valve being destroyed there.

To at least partially avoid the vacuum problem, EP 1 359 097 A1 proposes that in a corresponding method, the microwave treatment in pasteurization should be of such dimensions that the resulting vacuum is no longer great enough to destroy or completely deform the container. In practice, however, this means that for effective pasteurization at a lower temperature, heating must be continued for a longer period of time than in EP 1 076 012 A1 by a factor of at least 10, so that the advantages achieved with the preparation method according to EP 1 076 012 A1 and through the short preparation times would be virtually lost again completely.

Patches are also known in which a vent opening without a valve is actively closed again after heating, e.g., with an adhesive patch. In this case, the sealing of the container could basically wait until the container and the foods have cooled sufficiently and an equalization of pressure through the vent opening has been established. However, the time required for this would be substantial and would be a burden on an effective production rate. Due to the air flowing into the container during this pressure equalization phase, microorganisms could also enter the container and impair the stability of the foodstuffs. To have the equalization of pressure performed under a sterile protective gas atmosphere would at the very least be complex in terms of equipment.

It is possible to provide for the foodstuffs to be heated again by the end user before the foods are consumed and again for this to be done in the container, optionally with the use of microwave heating. Since the foodstuffs have at least partially been pre-prepared through the prior heating to make them stable and/or pasteurize them, simply warming them here is usually sufficient. In this context we also speak of regeneration in contrast with preparation from the raw state. However an excess pressure situation might nevertheless also develop in the container. If there is a valve that opens automatically, it may play a role in pressure release. If a vent opening has been sealed again with an adhesive patch after stabilizing the contents, then an automatic pressure release may no longer be available. Accordingly, the end user is often required to puncture the container before heating it, for example, or expose the sealed vent opening again, e.g., by removing the adhesive patch applied to it. However, adhesive patches which become detached with heating and thereby automatically release the vent opening again have already become known.

Finally, EP 1 359 097 A1 also cites in the introduction other methods of the state of the art, including heating containers without a vent opening under a backpressure, but they are not very economical and they require complicated and expensive plant technology.

The object of the present invention is to provide a method of stabilizing and in particular pasteurizing foodstuffs of the type defined in the introduction with which the advantages of the preparation method known from EP 1 076 012 A1 can also be achieved by the manufacturer and thus also prior to the shipping and retail phases.

This object is achieved according to the present invention, namely by a method for stabilizing foodstuffs in which the foodstuffs are in a moist state inside a container suitable as a shipping and retail package and having a vent opening. The foodstuffs are heated with microwaves for a limited period of time but at least until hot steam has formed in the container and escapes through the vent opening. A gas is injected into the container for at least partial compensation of the pressure drop in the container after the end of the heating. The core of the invention thus consists of the fact that a gas is injected into the container for at least partial compensation of the pressure drop in the container after the end of heating.

Injection of the gas may be performed easily and rapidly in only a few seconds and under a pressure of a few bar, e.g., using a cannula. To this end, the cannula may be inserted through the vent opening. However, the cannula is preferably used to puncture a wall of the container, and the container is flushed with the gas while expelling vapor through the vent opening. It is thermally advantageous if the injection gas is precooled.

A gas having little or no oxygen content is also preferred as the injection gas with which, in addition to the steam, the oxygen which is still present in the container but is especially harmful for the stability of the foodstuffs is flushed out of the container. Especially good stabilities can be achieved when an inert gas such as nitrogen or an antibacterial gas such as CO2 or a mixture of these two gases is used as the injection gas.

The seal on the puncture hole optionally created in the container wall during injection of the gas can be accomplished easily, e.g., by applying an adhesive patch to the container wall.

• Provisional Patent
• Utility Patent

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