METHOD FOR PACKING FRESH VEGETABLE PRODUCTS INTO A MODIFIED ATMOSPHERE

The present invention relates to a method for packing fresh vegetable products like fresh-cut vegetables, fruit, root crops, lettuce, mushrooms, etc. and e.g. fresh flowers into a modified atmosphere.

Fresh-cut vegetable and fruit etc. have already for a longer time been packed into a modified atmosphere (modified atmosphere packaging, MAP), and it has become even a certain type of a standard on the market. In the MAP packaging, the products are packed into an air-tight or breathable foil or corresponding airtight or breathable package, after which the space including the product is filled with a gas mixture, and the foil or package is sealed airtight. The gas mixture used in the MAP packaging is generally a gas mixture consisting of nitrogen and carbon dioxide in desired proportions, whereby the aim is to decrease the amount of oxygen as much as possible. By means of this kind of packaging and a strict hygiene standard, even shelf lives of 10 days for lettuce have been achieved. With this technology, the shelf life of lettuce and root crops has been significantly increased. For packaging of vegetables and fruit this technology has not been efficient.

A problem with MAP packaging of vegetables and fruit has been the fact that the packed product has continued ripening inside the package, in other words, the product has not been taken to a "sleeping condition" so that the vital functions of the vegetable and fruit would significantly decrease. In that state, the product would not respire and usually would not produce ethylene as much as it would in the normal condition after the fresh-cutting. In addition, one problem with the MAP packaging of prior art has been that the packed product can go bad very quickly after getting to contact with the normal atmosphere. This is because certain products do not stand the new radical change of atmosphere.

One alternative way for packing that kind of fresh products is to pack the products into vacuums of different grades. There one problem is the damages caused by the vacuum to the cellular texture of the product to be packed. In that case, quite light

vacuums must be used for fragile products, whereby the benefits gained from the vacuum package decrease or they are totally vanished.

With the MAP packaging method according to the present invention, it is possible to improve the shelf life of packed products and to eliminate problems with the MAP packaging according to prior art. The solution in accordance with the invention is suitable for packaging fresh-cut fruit, root crop, lettuce and mushrooms, and even fresh flowers. With the method according to the invention, these products can also be packed as whole. With the solution according to the invention, self lives of even 14 days can be achieved for sensitive products.

In the MAP packaging method according to the invention, the atmosphere to be created within the package to be in contact with the product to be packed is comprised of gas having substantially higher oxygen content than normal atmosphere and inert gas like nitrogen. The oxygen content of the normal atmosphere is 21%. With adequately high oxygen content the ripening of the product to be packed can be almost totally stopped, which substantially increases the eventual preservation time.

The product, after being removed from the package to be in contact with the normal atmosphere, continues ripening as usual, and no spoilage that is typical for the solutions of prior art will occur.

More precisely, the method according to the invention is characterized by what is stated in the characterizing part of Claim 1.

The interest of the applicant in using protective atmosphere for packing fresh-cut vegetable was woken after the applicant found out that in Europe and in the United States lettuce has already for a long time been successfully packed into protective atmosphere. The content of the gas mixture used in these known methods has been generally 1-5 % oxygen, 70-75% carbon dioxide and 20-25% nitrogen. The applicant, however, did not find any solution for packing more sensitive products like tomatoes, sweet pepper, cucumber, zucchini, honey melon or cantaloupe into protective atmosphere.

The applicant started to develop himself the protective atmosphere packaging particularly with respect to these more sensitive products.

Example 1.

The applicant tried first the known protective atmosphere mixture that was meant for the food industry. The content of this protective atmosphere most generally used in the food industry was 5% oxygen, 75% nitrogen and 20% carbon dioxide. The mixture in question did not work at all with sensitive and fresh-cut products, because based on the test it appeared that the used protective atmosphere mixture accelerated the deterioration of the products. This was caused by the fact that the packed products started sweating quite much and they got colour defects. The product packages also swell strongly due to the increased respiration of the product.

Example 2.

Based on the results of the Example 1, additional tests were made, to remove the unwanted reactions of the Example 1. In these tests the oxygen content was increased to 50% and the carbon dioxide content to 50%. When using this protective atmosphere it appeared that oxygen disappeared from the package and the amount of carbon dioxide increased. The used protective atmosphere did not work as desired, because a very strong vacuum formed into the package, when the carbon dioxide either absorbed to the products or shrunk in the cold. In addition, odor and color defects were observed in the product.

Example 3.

Based on the previous tests, in the following tests protective atmosphere was used, having an oxygen content of 90%, carbon dioxide totally removed and replaced with nitrogen content of 10%. Nitrogen was chosen to this test series because it is a neutral gas not reacting with anything but acting simply as filling gas. It was shown by the results of the tests that sill a strong vacuum formed in the packages when the packed product had respired oxygen and produced carbon dioxide to the package. The results were, however, encouraging for the use of these gases as protective atmosphere,

because the results proved that the preservability improved and the odor and color defects disappeared.

Example 4.

In these tests the oxygen content of the protective atmosphere was changed to 80% and the nitrogen content to 20% based on the previous tests. It was shown by the results of the tests that now there was enough nitrogen, so as to act with adequate efficiency as filling gas, when the product respired oxygen, thus preventing generation of a strong vacuum. When the products respired, carbon dioxide still was formed in the package, but the content of it was very small, although increasing in the course of time. It was also shown by the results, that when using the gas mixture in question, the preservability of the packed products had increased perceptually assessed to 14 days.

In the above described examples an essential requirement of the packing apparatus has been that with said apparatus the products are packed with a gas flushing method so as to avoid any damages to the products to be packed like those caused by the vacuum packaging. In addition, the products to be packed as well as the equipment used for packaging must be especially sterile and the cold chain of the products must be unbroken. The storing temperature of the products was in the given examples from +1 to +4 ⁰ C.

The better self life of products provided by the packing method according to the invention is based on the fact that the high oxygen content prevents the growth of some bacteria totally and reduces the growth of some other bacteria. In order to prevent/reduce the bacterial action, the amount of oxygen in the package must be from 40 to 90%. Oxygen content as high as that has effect on the density of respiration, color, composition, metabolism of the vegetable and reduces mold and microbiological deterioration. In addition, the products having a high liquid content greatly benefit from the packing method according to the invention, because it minimizes the liquid escape from the tissue of the product.

Another advantageous application of the method in accordance with the invention is the packing of flowers, providing self lives of several weeks, at its best.

The application of the method according to the present invention with the usual MAP packing devices does not require anything else except packing to be performed with gas flushing. The reason for that is that sensitive products cannot be packed as usual by evacuating with vacuum the existing atmosphere from the package and by replacing it with a new MAP atmosphere, because in that case the cell membranes of a sensitive product do not stand the stress caused by the vacuum, and the cell membranes break, whereby the product starts to loose liquid and the product goes bad very quickly.