Improved packaging method that causes and maintains the preferred red color of fresh meat

(74) Agent

Curwood Inc, 2200 Badger Avenue, US-WI54904 OSHKOSH, USA Dan Θ Siegel, 512 Oak Hill Drive, US-IL62223 BELLEVILLE, USA Zacco Norway AS, PO Box 2003 Vika, 0125 OSLO, Norway

<td> (54)</td><td>Designation</td><td>Food wrapping film and wrapping process that produces and retains the preferred red color of fresh meat</td>

<td> (56)</td><td>cited</td><td></td>

<td></td><td>publications</td><td>US 6623773 B2 US 2925346 A</td>

<td> (57)</td><td>Summary</td><td></td>

The present invention is a method of improving the visual appearance of a food product (12) and a film (22) used in the method. The film includes an effective amount of a nitrogen-containing mixture contained within or applied to one side of the film and adapted to touch a food item held within a food packaging container (10). Upon contact of the food item within the container, the mixture containing nitrogen, nitrous oxide gas inside the container forms due to the contact of the mixture with and the solution in the juices of the food product. Thus, the physical contact of the packaging film with the food product causes a preferred reddish freshness to appear on the display surface (100) of the food item without affecting the appearance, performance or color of the interior of the food product.

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Field of the Invention

The present invention relates to food wrapping and, more particularly, to a method and a wrapping film adapted to transfer a material to a food surface to promote an attractive appearance of the food product contained in the packaging.

BACKGROUND AND SUMMARY OF THE INVENTION

By itself, color remains the single most important quality characteristic of meat that affects its marketability. Consumers use color as an indicator of freshness. The color of meat comes from myoglobin. This is a complicated pigmented protein present in the muscle tissue of all animals. Its biological function is for oxygen storage and release. It achieves this function by reversible binding of molecular oxygen, thereby creating an intracellular source of oxygen for the mitochondria. Flesh and poultry contain smaller amounts of myoglobin than beef and are thus lighter in color than beef.

Myoglobin consists of a non-protein moiety designated heme and a protein moiety designated globin. The protein portion is a large polypeptide chain that determines the three-dimensional configuration of the myoglobin molecule. The home part consists of a jematoma in a flat ring. The globule part surrounds the heme group and interacts with it in a way that stabilizes the molecule. The heme group is the reaction center of myoglobin. It has an open binding site that attracts a ligand. The ligand must be small enough to fit in the cavity and have the correct electron configuration to bind to the jematome. Oxygen fulfills these conditions perfectly and this is how myoglobin performs its biological function for transporting oxygen from the blood to the mitochondria.

As oxygen enters the heavens, its oxygen configuration changes the shape of the globule to the molecule in a way that affects light absorption properties. It is the presence or absence of a ligand in the cerebellum and the ligand itself that affects visible color changes in myoglobin.

When there is no ligand in the cerebellum, myoglobin is in its natural state. This form of the molecule is called deoxymyoglobin. Its color is purple. When oxygen is present at high concentrations, such as the level of the earth's atmosphere, it is drawn into the celestial cavity and deoxymyoglobin becomes oxymyoglobin. Its color is red. If oxygen pressure becomes low, it tends to be cleaved from the oxymyoglobin molecule. When this happens, there is a tendency for the oxygen to pick up an electron from the jematome and leave it in the ferrous state. As this occurs, a water molecule moves into the celestial cavity and becomes the ligand that affects light absorption. The oxidized form of myoglobin with H₂0 in the artificial hemegroup is referred to as metmyoglobin and its color is brown. When the chemical state of iron changes from bivalent (Fe⁺²) to threefold (Fe⁺³), the three-dimensional structure of the globular part changes in a way that allows water into the heavens. The oxidation of the jematome always causes a bright color.

Other variables that affect the stability of the globin also affect the attraction of the oxygen heme group and the tendency of the chemical state of the jematome to be oxidized. Acidity and high temperature, such as that associated with boiling, can denature the globin portion thus leading to instability of the heme group. In the absence of stabilizing ligands, the oxidation of the heme home is automatic when the globin is denatured.

In fresh meat (postmortem muscle tissue), oxygen is continually associated and separated from the heme complex. Thus, it is the mutual abundance of three forms of the muscle pigment that determines the visible color of fresh meat. In summary, they include deoxymyoglobin (reduced myoglobin) which is purple; oxymyoglobin (oxygenated myoglobin) which is red; and methyoglobin (oxidized myoglobin) which is brown.

Deoxymyoglobin information dominates immediately after the animal is slaughtered. Thus freshly cut meat has a purple color. This purple color can persist for a long time if the pigment is not exposed to oxygen. Cutting or painting exposes the pigment to oxygen in the atmosphere, and the purple color is rapidly converted to either high red (oxymyoglobin) or brown (metmyoglobin). Although deoxymyoglobin is technically fresher, it is the red or fresh flesh color that consumers use as their primary criterion for perception of freshness.

Changes in the percentage of each of these forms continue to occur as long as fresh meat is exposed to oxygen. The immediate conversion of the purple color to the desired high red or undesired brown depends on the partial pressure of oxygen at the surface. The purple color is favored at the very low oxygen levels. It dominates at levels of 0-0.2%. The tan is favored when the partial pressure of oxygen is only slightly higher (0.2% to 5.0%). Consumer acuity begins when the mutual amount of methmyoglobin is 20%. A clear tan is evident at 40% methmyoglobin, which typically renders the meat indelible.

Biochemical reactions that occur in muscle tissue after death are important for fresh flesh color. These reactions are caused by the presence of active glycolytic enzymes which convert oxygen into carbon dioxide. The effect on flesh color is the presence of reducing coenzymes that continuously convert methmyoglobin back into the deoxymyoglobin. These reducing coenzymes are called metmyoglobin reductases, and their activity is called "MRA" which is an abbreviation for metmyoglobin reducing activity. MRA can be described as the muscle ability to reduce metmyoglobin back to its natural deoxymyoglobin state. It is lost when the oxidizable substrates are reduced or when heat or acid denatures the enzymes. When the enzymes lose their activity or are denatured, the iron in the heme pigment automatically oxidizes to the metmyoglobin information and the brown color stabilizes and dominates.

MRA persists for a period of time after death depending on the extent of exposure of the meat tissue to oxygen. During this time, oxygen is continuously consumed by the meat tissue. The oxygen consumption rate is referred to as “OCR”. When meat that has a high OCR is exposed to oxygen, oxygen pressure is reduced so rapidly that the methyoglobin is favored below the viewing surface. If it is close to the viewing surface, the perceived color of the meat is affected. The MRA is important to minimize this layer of metmyoglobin formed between the fresh surface and the purple interior. As the MRA wears out, the brown methyoglobin layer thickens and migrates toward the surface, thus ending the display durability. When the MRA is high, the metmyoglobin layer is thin and sometimes not visible to the naked eye.

There is a practical relationship between MRA and OCR for the specifications of a package intended for retail sale to extend the desired meat appearance as long as possible. Canned sealed films with oxygen barrier films will cause a low oxygen pressure on the meat surface. Thus, metmyoglobin formation occurs and the display surface changes to an undesirable brown color. However, if the OCR is large enough to stay in front of the oxygen migrating over the wrapping film, and the MRA is good enough to reduce the surface methmyoglobin formed, then natural deoxymyoglobin replaces metmyoglobin. After a period of time, the perceived color changes from brown to purple. Both of these colors are unacceptable to the consumer. For this reason, vacuum wrapping by itself has historically become an unacceptable format for box-ready fresh meat. On the other hand, vacuum packaging is the choice format for cooked and preserved processed meat in which the myoglobin pigment is denatured by heat and stabilized by the presence of nitrite. When oxygen is eliminated from a canned processed meat packing, the color and taste of the product deteriorates more slowly than when oxygen is present.

Some uses of fresh meat are suitable for vacuum wrapping due to its inherent benefits in protecting product quality. For example, vacuum packaging is usually used for original and sub-original wholesale as well as frozen steaks. The color of the product is not crucial in these applications. However, the color of the detail pieces is very critical and the color caused by vacuum packing is unacceptable. Thus, the industry has not been able to take advantage of the benefits of vacuum packaging for box-ready applications.

As mentioned earlier, the artificial home group is responsible for color. Relevant literature shows us that ligands different from oxygen and water also affect the flesh color. For example, cyanide and fluorine cause a brown color, carbon monoxide (CO) causes the preferred high red color, and nitrogen monoxide (NO) causes a dull red color. In particular, methods for treating fresh meat with carbon monoxide have been developed for ready-to-use packaging applications. The right red myoglobin complex is preferred as carboxy myoglobin.

Sodium nitrite also affects color when added meat. This approved additive is a commonly known preservative used in the storage process for products such as ham, lose ham, bologna and hot sausages. Its effects on meat color and bacterial growth are the basis for its widespread use in the meat industry. Almost immediately after its addition, the raw meat color changes to a grayish tan. This is a commonly experienced event. The pigment associated with the characteristic brown color of raw stored meat is sometimes referred to as nitric oxide methyoglobin. It has been shown that nitrite is reduced to nitrogen monoxide gas by dissolution in meat juices. Nitrogen monoxide is the simplest known thermally stable paramagnetic molecule (i.e., a molecule with an unpaired electron). When contacted with raw meat in the presence of oxygen, nitrite and nitrogen monoxide turn the color brown by encouraging the dissolution of oxygen from the oxy myoglobin complex. The presence of oxygen oxidizes available nitrogen monoxide to nitrite, thus reducing its availability to bind to the myoglobin molecule. During these conversion processes, the heme group loses an electron to form brown metmyoglobin.

When boiling in the presence of nitrogen monoxide, the globular portion of the methyoglobin molecule denatures and the nitrogen monoxide attaches to the whole pocket. Since nitric oxide has an unpaired electron, its presence in the heme group encourages the reduction of the jematome back to its bivalent state. The color changes to pink or reddish brown depending on the relative amount of myoglobin in the muscle tissue. Boiled stored bottle or poultry is pink and cooked stored beef is more of a reddish brown color.

The denatured (boiled) myoglobin complex with nitrogen monoxide as its ligand is called nitrosohemochrome. In the absence of oxygen, this pigment is very stable, however, it possibly oxidizes the presence of the oxygen nitrosohemochrome and the color changes to greyish brown. As a result, the packaging format is the choice for processed meat vacuum packaging with a costly barrier film. This protects the nitrosohemochrome from oxidation with oxygen so that the color is stable for months.

The traditional wrapping format used by the fresh meat retailer is to wrap a thin PVC film around a foam board that supports the product. The film is permeable to oxygen, so the initial color of the meat is bright red. However, the durability of the high red color is only about three days. This packing format is thus undesirable because the color often becomes unacceptable before it can be exhibited or sold. As a result, a packing format is required which retains the fresh meat color for a longer period of time for the centralized packing procedure.

Alternatively, an atmosphere modified with high oxygen content can be used. Currently, it is the most commonly used cash-ready packaging format. Pre-formed oxygen barrier bowls of this type are filled and sealed on high-speed equipment. The bowl is typically either formed of foam with an oxygen barrier layer or of a rigid oxygen barrier plastic. An oxygen-rich gas is then flushed into the bowl before canning a clear film on top of the bowl. In this case, the film used for the lid also has an oxygen barrier film as well as some weak creep properties. The product is dissolved within the package, as the film does not touch the meat, so there is a considerable space between the film and the product (top spot), which allows the gas to affect the flesh color. Centralized or regional packing machines currently produce whole muscle pieces and ground beef with this type of packing. The atmosphere with high oxygen content in the package produces a dense fresh color that lasts longer than when compared to meat exposed to only atmospheric levels of oxygen. The maximum shelf life is about 14 days for ground beef and 10 days for whole pieces of muscle. As for the modified atmosphere within these packages, the most common approach is to use a mixture containing 60-80% oxygen and residual carbon dioxide. The partial pressure of oxygen at the meat surface provides enough oxygen for enzyme activity as well as reactions with myoglobin. The surface myoglobin pigment is converted to oxy myoglobin before tissue respiration consumes the excess oxygen, and the result is the formation of a thicker layer of surface oxy myoglobin and consequently an extension of exhibition life. As the MRA decreases toward the end of the color display lifetime, the thick oxymyoglobin layer oxidizes to metmyoglobin.

The high oxygen packaging format also has further shortcomings. More specifically, the actual exhibition life is much shorter than 14 days because exposure to light actually catalyzes or accelerates the oxidation of the high red color to the undesirable brown. Furthermore, whole pieces of muscle fade more quickly than measured products when exposed to light. As a result, they are priced and printed with a three-day sale date at the storage level, greatly reducing the available sales time for the meat. Oxidation hardness, chemo-methoglobin development and premature burning are also quality issues due to the long exposure to an elevated oxygen level. Furthermore, the distinctive top space in the individual packing occupies space in the box, thereby increasing transport and storage costs. The top class is less attractive to the consumer than the tightly wrapped piece of meat.

Recently, the use of carbon monoxide was approved as a component of the gas used for the clear-pack with modified atmosphere. It has been shown to effectively extend the shelf life. As mentioned earlier, when carbon monoxide is the ligand of the myoglobin complex, the highly red preferred color develops. This is a very suitable method to extend the color life and as such is currently pursuing a number of commercial uses of the industry. This type of modified atmosphere gasket will have no oxygen and only 0.4% carbon monoxide to develop the desired effect. A top spot is required by this method and development of the preferred high red color will be obstructed at any point of contact between the flesh and the film. U.S. Patents 4522835, 6113962, 6270829 and 6521275 disclose methods utilizing carbon monoxide and other gases to effect and preserve the desired fresh meat color.

Another approach used by some packaging companies to allow centralized packaging and economics of scale is to use the traditional PVC-wrapped format with its oxygen-permeable film inside another oxygen barrier package. One or more of the traditional packages are wrapped in a main package which is flushed with a gas with little or much oxygen to extend the shelf life of the packages contained therein. If low oxygen gas is used, the meat freshens when the individual bowls are removed from their main package. It does a good job of prolonging the color life, but sometimes freshness is difficult because atmospheric levels of oxygen do not need appropriately through the film covering the meat surface. The high oxygen gas approach is limited to a regional level of distribution because the shelf life is shorter than the modified low oxygen atmosphere gaskets discussed above. As such, the main package approach is usually more used for bottling and poultry.

Other packaging formats to improve the appearance of packaged food products have also been uncovered by others in the industry. Such a format, for example, uses carbon monoxide (CO) as part of the gas which is flushed into a secondary or outer main gasket. The carbon monoxide penetrates through the permeable inner gasket and affects the color of the food product in a manner similar to oxygen, causing the food product to refresh. However, since there is no oxygen present in the gas which includes the carbon monoxide that is flushed into the package to oxidize the myoglobin, the red color developed by carbon monoxide is more stable. It therefore lasts longer than the red color caused by oxygen. This extension of the time before the red color turns to brown consequently increases the attractiveness of the food product for a consumer and the likelihood of the sale of the product to a consumer. However, the format without oxygen or with carbon monoxide requires special packaging equipment and an additional outer gasket to achieve the desired effect.

In addition to the aforementioned formats, a variety of other additives and gases have been used and uncovered in prior art to enhance or extend the bacteriological and color-shelf life of box-ready fresh meat. For example, U.S. Patent No. 4683139 discloses a method of enhancing and preserving fresh meat color for up to two weeks. The method uses direct additives which include the phosphate salt, ascorbic acid or alkali metal salts and a complex salt formant, such as citric acid, in combination with a modified packing atmosphere. This patent and the references cited there refer to the stabilization of the color of fresh meat effected by the presence of oxygen.

Several patents also mention the use of pressurized gases as a device for treating meat prior to wrapping, thereby intensifying and stabilizing the preferred red color. U.S. Patent 6716464 discloses use of the oxygen gas in this way. Again, these methods emphasize the importance of the red color of fresh meat.

Other methods that actively enhance the packing atmosphere to cause the meat color to change are disclosed in US Patent 5481852 and US Patent 5989613.

The display life of the gaskets formed by these methods is very short and oxygen is used as the agent to effect the color change. Similarly, the method disclosed in US Patents 5866184 and 5711978 uses perforations in the bowl or lid of a modified atmospheric packer to effect a passive entry of oxygen into the meat surface at a time just prior to retail display. US patents 5759650, 5591468 and 4055672 disclose methods in which an outer barrier film layer is removed to leave behind a permeable film layer. When the barrier layer is removed just before exposition, atmospheric oxygen spreads into the meat surface, thereby effecting the preferred color change. Further, US Patents 5989610, 5597599 and 5352467 disclose the use of a variety of gases and additives. All of these methods are attempted to effect and preserve the oxygenated (red) form of the meat pigment for an extended period of time.

US patents 6046243, 5965264 and 5888528 relate to the encapsulation and subsequent release of biosidal gases for the purpose of braking, controlling, killing and preventing microbiological contamination. Nitrite and nitrogen monoxide are mentioned in the patents as agents for achieving these special effects. Uses for meat wrapping are also mentioned more specifically with regard to chlorine dioxide as the active antibacterial agent. US Patent Application 2004/0137202 discloses a method for coating a touch film surface of a food wrapper with active ingredients or agents that perform a variety of secondary effects or functions. Nitrite is mentioned in this method for a preservative function.

Furthermore, several patents reveal the use of nitrite in the packaging material as a corrosion inhibitor. They include US Patent Nos. 6533962, 6465109, 6033599 and

5281471. US Patent No. 5271471 is a broad statement which also mentions vacuum wrapping and food wrapping.

In US Patent No. 6623773, a fresh food piece packed in a packaging material comprising a substrate suitable for contact with food and a food processing layer comprising a predetermined amount of edible adhesive applied to a food contact surface of the substrate and a storage or marinating agent mixed in, maintained and calibrated by adhesive.

US 2925346 A discloses a method of packaging stored meat products to provide an attractive, strongly colored product and to prevent color deterioration in said product. The process comprises placing the product in a container, removing oxygen from the product and the container, filling the container with a gaseous nitric oxide and then sealing said container.

Prior art technologies relate to methods of affecting flesh color by means of passive or active treatments and the meat with gases or chemicals. Some of these methods also utilize physical properties of the package to assist in reshaping the color of fresh meat including tear-off barriers, perforations, and packs of multiple film layers. However, none of these technologies indicate to us anything about selection for the preferred red color of fresh meat using nitrite, nitrate or nitrogen monoxide. Furthermore, none of these methods are capable of producing and preserving the preferred red color of fresh meat in a vacuum package.

It is therefore desirable to develop a new packaging format that produces and retains the red display color of the meat food product and has the appearance that more closely resembles the packaging format traditionally offered to the consumer.

Summary of the Invention

It is a principal object of the present invention to provide and preserve the preferred red color on the surface of fresh meat. The color in question is typically associated with fresh meat which has been exposed to oxygen to produce the oxygenated red form of the meat pigment. The present process achieves this objective by using a nitric oxide-containing mixture, for example, nitrite or nitrate mixtures in a packing format which significantly prolongs the desirable color of a meat food product. More particularly, the present invention produces and retains the preferred red color using a nitric oxide-containing mixture, for example, nitrite or nitrate, in a manner that allows reaction with the meat myoglobin pigment to form nitroxymyoglobin, as defined herein.

The present invention provides a food wrapping film 22 for use in producing and stabilizing a desirable color on a display surface 100 of a raw food product 12 containing myoglobin, with no detrimental effect on the surface surface color of the food product, the film being a barrier to oxygen and comprising:

a) a food touch layer 24 capable of touching the food product held within a package formed with the film; and

b) a nitric oxide-containing mixture 30 which is in and / or distributed on the surface of the food contact layer in an amount equal to 0.327 g m.² (0.211 mg in²) or less.

Further, the present invention provides a food wrapping container including a film 22 as indicated above and a bowl 14, 16, 18 adapted to hold a food item 12 therein, the bowl being a barrier to oxygen, the film being positioned over the bowl to retain the food item. in this.

Still further, the present invention provides a method of wrapping a food item 12 to create and stabilize a desirable color on a display surface 100 of the food item with no detrimental effect on the bottom surface color of the food item, comprising the steps of:

a) providing a film 22 as claimed in any one of the preceding claims; and

b) touching the film with the food item to form a food item gasket 10.

The present invention also provides vacuum packed meat comprising an uncooked meat product 12 vacuum packed in the films or container as set forth above, the film 22 or container having a first oxygen barrier polymer layer and a second surface layer 24 containing a mixture 30 containing nitric oxide selected from a group consisting of sodium nitrite, sodium nitrate, potassium nitrite, potassium nitrate and mixtures thereof, in an amount sufficient to transfer between 0.00124 gm.² and 0.00248 g m² (0.0008 and 0.016 mg in²) to the uncooked meat product within 96 hours.

The present process achieves the purposes of producing conditions within the meat packing which allow the formation of nitroxymyoglobin. More specifically, it has been shown that when meat is exposed to sodium nitrite after vacuum wrapping in a barrier film, its color changes from red to brown during the minute. However, surprisingly and unexpectedly after a period of time (1-5 days), the color changes back to bright red. Thus, during this time period, the dominant pigment on the meat surface changes from oxymyoglobin to metmyoglobin to nitroxymyoglobin. This is due to the elimination of oxygen and the reduction of methmyoglobin causing nitroxymyoglobin to be formed. The vacuum applied during the packing step is unable to eliminate the oxygen absorbed in the meat surface because it was bound to the hemoglobin of the myoglobin complex. However, the OCR and MRA of the meat are capable of eliminating this oxygen and reducing the maintenance of the methyoglobin pigment. Several days may be needed to allow enough time for this change to happen. As soon as the methyoglobin pigments are reduced, the nitroxy myoglobin pigments begin to dominate and the color of the meat product surface turns to the preferred high red.

It is another object of the present invention to provide conditions which allow the nitroxy myoglobin to be formed on the visible surfaces of meat without extending fully through the thickness of the meat. More specifically, a nitrite or a nitrate is sprayed on or incorporated into the wrapping film as file forms seal layers for the film positioned directly above and in contact with the food product. The amount of nitrite to effect this effective conversion of surface deoxymyoglobin to nitroxymyoglobin relates to the concentration of myoglobin molecules naturally present in the packaged meat product. This amount varies widely between types of meat, with beef and lamb being larger than pork and poultry. Furthermore, there are differences in the concentration of myoglobin molecule between individual animals and their age, gender or upbringing. Individual muscle type and slaughter conditions further affect the rate and efficiency of conversion of the myoglobin molecules. Thus, the present invention utilizes to effect nitroxymyoglobin forming only on the display surface of the fresh meat to leave the center of the product in its natural myoglobin state. In particular, the desired depth with improved color penetration provided by the method is preferably less than about mm (0.375 inch) and more preferably less than about 6 mm (0.25 inch).

Numerous other objects, features and advantages of the present invention will be made apparent by the following detailed discussion seen in conjunction with the drawings.

Brief description of the drawings

The drawings illustrate the best way at present provided in the practice of the present invention.

The drawings are:

Fig. 1 is an isometric view of a package including the packaging film containing a nitric oxide;

FIG. 2A is a cross-sectional view of the wrapping film of FIG. 1 wherein the nitrogen-containing mixture is sprayed onto the film;

FIG. 2B is a cross-sectional view of the wrapping film of FIG. 1 wherein the nitric oxide is included in the film; and

FIG. 3 is an isometric view of a vacuum package including the wrapping film of the present invention.

Detailed Description of the Invention

The unnatural (crude) nitrogen monoxide myoglobin complex is of major importance to the present process and the packaging film of the invention. The current scientific references refer to "nitrogen monoxide methyoglobin" as the pigment formed from the exposure of raw meat to nitrite. Little research has been done on the reduced form of this pigment. The terminology of the pigment is uneven. Researchers refer to it as "nitrogen monoxide myoglobin", "nitrosomyoglobin" or "nitrosyl haemochromagen" among others. In order to avoid confusion, in this publication, the unnatural and reduced form of the nitrogen monoxide myoglobin complex will be referred to as nitroxy myoglobin.

As mentioned earlier, the display surface of raw fresh meat is in fact the combination of three myoglobin forms. Pigments on the surface and under the surface contribute to the color. When meat is exposed to the atmosphere, oxymyoglobin dominates the percentage of pigments and the color is high red. When the raw fresh meat is exposed to nitrogen monoxide, the meth myoglobin predominates on the surface and the color is brown. However, beneath the surface the color is dull red and deep in the core the color is high red. The perceived color of nitrite-treated meat is a combination of four pigments that include nitroxymyoglobin. If no oxygen is present and the metmyoglobin is reduced to deoxymyoglobin, the nitroxymyoglobin information will begin to exceed the number of the other three forms. Conditions need to be just right for everyone to reduce the metmyoglobin. The results of experiments with the method according to the present invention suggest that the color of nitroxymyoglobin is the same as oxymyoglobin and carboxymyoglobin. Thus, when nitroxymyoglobin is the dominant form of the myoglobin pigment on the meat surface, the perceived color is bright red.

Referring now to the drawing figures in which like reference numerals denote equal parts throughout the disclosure, a food package in accordance with the present invention, such as a bowl, is illustrated in FIG. 1 generally at 10. The package 10 may have any desired shape depending on the size and configuration of the food product 12 with a display surface 100 to be contained therein. In accordance with this invention, the method can advantageously be used with any tissue containing myoglobin or hemoglobin, and has particular relevance to food products harvested from: cattle such as beef, pork, veal, lamb, sheep, chicken or turkey meat; game, such as animal meat, quail meat and duck meat; and fish meat, fish or seafood products. The terms '' meat food product '' or '' food product '' used throughout this disclosure refer to any of the meat types referred to above. The meat can be in a variety of forms including the original, sub-original and detail pieces as well ground, finely divided or mixed.

Further, the package 10 can be formed from any number of suitable materials, such as foam and plastic material, which are well-known for use in forming food packages or trays 10. In fact, the film alone can be used to package the food by means of a bag or bags that are vacuum-packed around the meat, and the film may or may not be heat shrinkable. In a particularly preferred embodiment, the food product 12 is a meat, such as fresh red meat, with an upper meat surface 13a and an opposite lower surface (not shown) associated with a continuous meat side wall surface 13b packed with a film in accordance with the present invention. In a preferred package, food is vacuum-packed in a bowl, such as a packing bowl 10, which includes a lower wall 14, a pair of side walls 16 extending upwardly from the lower wall 14, and a pair of end walls 18 extending upwardly from the lower the wall 14 and is connected to the side walls 16. The respective walls 14, 16 and 18 which form the packing bowl 10, file forms a housing 20 within which the food product 12 can be positioned. The food product 12 is retained within the packing bowl 10 by a wrapping film 22 positioned above the food product 12 and the bowl 10 and securing at each end of the bowl 10. The packing film 22 can be secured to the packing bowl 10 in any suitable manner, such as by heat shrinkage, heat sealing, adhesive or any other suitable method.

Referring now to FIG. 2A and 2B, the wrapping film 22 may be formed from any suitable and preferably at least generally transparent packaging material and may be formed to have one or more layers. In a preferred embodiment, the film 22 includes multiple layers to allow the film 22 to act movable for its intended purpose. In a particularly preferred embodiment, the wrapping film 22 includes an inner sealing layer 24 having a food touch surface 25, and an outer layer 26.1 additionally, one or more inner layers 28a and 28b may be included in the wrapping film 22. The invention contemplates the use of films having 1,2,3. , 4,5,6,7,8,9, or more layers.

The sealing layer 24 includes an amount of a nitric oxide, a nitrite or a nitrate mixture 30 used to control the displayed color of the food product 12. Nitrate or nitrite mixture 30 is then applied to or included in the formation of the layer 24 and optionally layers 26 and 28. The mixture 30 may be applied to the meat touch surface 25 of layer 24 or include in the sealing layer 24 in any conventional manner, as long as it is evenly spread over the touch surface 25 of layer 24 and / or throughout layer 24 to allow any length of the film 22 which includes layer 24, includes approximately equal amounts of the mixture 30 within the seal layer 24 for uniform transfer to meat via the surface 25.1 of the embodiment where the mixture 30 is incorporated within the seal layer 24, the thickness of the seal layer 24 is adjusted to optimize the migration of the mixture 30 from the layer 24 by contact with the top and bottom layers. the side surfaces 13a and 13b of the food product 12. The layer thicknesses and / or the amount of the mixture 30 for the layer can be adjusted thereby varying the rate of migration of the mixture 30 out of the layer 24, as desired. The film 22 may also be formed with an adhesive layer 34 disposed between the layers 24 and 28 of the film 22. The adhesive 34 may contain the nitrogen-containing mixture 30 to release the mixture 30 through the layer 24 in a controlled manner depending on the materials used in forming the layer 24.

experimental

The wrapping film 22 of this invention was developed by experiments in which a variety of chemicals were sprayed onto raw meat prior to vacuum wrapping. The chemicals used were various reducing agents and oxidizing agents that were tested in an effort to influence the myoglobin-reducing activity (MRA) and the oxygen consumption rate (OCR) of the raw meat. The purpose was to stabilize the respiratory conditions of the meat, thereby slowing myoglobin oxidation after exposure to oxygen. Commonly used meat additives were also evaluated. The chemicals included a variety of phosphates, sulfites, acids and alkalis, salts, various forms of ascorbic acid, antioxidants, oxygen complex salts, plant extracts, such as rosemary extract, and others which are beyond the scope of and do not necessarily relate to this disclosure.

In the course of these experiments, sodium nitrite and sodium nitrate were tested. Very small amounts of nitrite or nitrate have been shown to affect the color of vacuum packed meat. More particularly, when nitrite was coated on the inner touch film surface or a vacuum gasket, the color would turn to brown immediately after evacuation of oxygen away from the viewing surface. However, unexpectedly and surprisingly in some experiments, the preferred red color gradually replaced the brown color and remained stable for several months.

As a result of the test performed, it is assumed without any desire to bind by this assumption that nitrogen monoxide (NO) gas is formed which results from the reduction of the nitrite on the gasket and this gas affects the color of the meat food product. The nitrogen monoxide gas is believed to have a similar effect on freshness as carbon monoxide gas. Experiments in which meat food products were affected with nitrite showed that the fresh color occurs only in the absence of oxygen. It is the initial small amount of residual oxygen that causes initial browning of the food product. It was shown that when the residual oxygen is high, a longer time is required for the initial brown color to be replaced by the preferred red color. In the initial experiments, five days were required for the red color to develop completely. The freshness of the muscle and the special piece also affect this '' freshness time ''. When a poor barrier film is used for the packaging material, the time required to achieve the desired freshness is also extended. This is because oxygen travels through the film, causing and retaining the brown or dark color of the meat within.

In an effort to shorten the freshness period, extended vacuum times were used during packaging of the food product. It was observed that when a high vacuum level was applied, the freshness time decreased. With greater vacuum levels, it was also observed that when the food product surface was sprayed, dusted or otherwise coated with a water-based solution of nitrite, the freshness time could be reduced to approximately 60 hours. When the nitrite solution was sprayed, dusted or otherwise applied to the inner surface of the package and allowed to dry before packaging, the freshness time was reduced to approximately 48 hours. In addition, it was observed that the freshness time is generally shorter for pork than beef. Less than 24 hours was required for pork. Improved pork (pork with about 10% or less added mixture of water, salt and phosphate) showed a shorter freshness time than unprocessed pork. Cattle that were more than 20 days postmortem were found to require the longest freshness of up to 72 hours. On the other hand, 10 days of postmortem beef cured for 24 hours. This illustrated that the higher oxygen consumption rate for fresher meat is important to minimize freshness time.

The red color developed by the use of nitrite or nitrate in this way is very stable and does not turn brown during boiling. The uncontrolled addition of nitrite or nitrate can be a problem in that a visibly "well-prepared" indication of cooking for the food product is difficult to obtain when the nitrous oxide gas (or color change material) penetrates through intact muscle or ground meat to depths that almost reach the center of the individual. the part. It is therefore important to control the level of nitrite used so that it is used only sufficiently to achieve a very shallow penetration of the color effect (believed to be due to nitrogen monoxide penetration) of the display surface of the food product. As the depth of nitrogen monoxide gas penetration increases, the interior color is no longer affected at boiling temperatures, which usually turn the color to brown or gray. When this happens, it is not possible to boil the product to the usual appearance of a well-made level. Thus, it is important to minimize the amount of nitrite exposure to the meat display surface.

This can be achieved by adding nitrite to the touch surface 32 of the seal layer 24 or the wrapping film 22. After vacuum wrapping, the film 22 touches the viewing surface 100 of the food product 12. Nitrite from the film surface 24 is dissolved in the meat juices and broken down into nitrogen monoxide to obtain the desired result. Best results occur when the nitrite level is controlled so that only sufficient nitrogen monoxide is released to affect the pigments within the display surface 100 of the food product 12. The nitrite level required for this result is less than one tenth (1/10) of the nitrite usually used for storage. In fact, part of the focus of the present process is controllable to release only sufficient nitrogen monoxide to affect the display surface 100 of the meat 12. Nitrite levels typically associated with storage are so high that their effect on color lasts after cooking. In a preferred embodiment, the level of nitrite that can be used in the process of the invention is so small that in most embodiments, it is not analytically detectable as nitrite or nitrate in the finished product by commonly used test methods. Furthermore, the amount is sufficient to effectively preserve the entire product 12.

More particularly in one example of the present invention, the nearest 0.25 inch (~ 6 mm) of beef exposed to the film containing the correct nitrite level was tested for nitrite. It is an important observation that after short (about 48 hours) and long (about 7-10 days) exposure periods, no nitrite was measured in the meat (minimum detection level = 2.0 ppm). Thus, a very small amount of sodium nitrite is needed for its desired effect. Although the preferred penetration depth of the nitrite is about 6 mm (~ 0.25 inch), it is also acceptable for the nitrite to penetrate deeper into the viewing surface to a maximum of about 10 mm (-0.375 inch).

In previous studies when nitrite was coated on the film surface, levels higher than 20 ppm were observed. At these levels, the nitrite appeared to penetrate the viewing surface very deeply. When cooking, it was not possible to achieve a "well-made" appearance level of odor in the meat. The pink color produced by the nitroxy myoglobin was present in the core of the meat piece. These experiments evaluated films that touched both sides of the piece of meat. Subsequent evaluations with a bowl that did not contain nitrite on the meat touch surface still demonstrated a significant penetration depth when evaluating the higher levels of nitrite. However, when the 20000 ppm sealing film was applied to the skin wrap, the penetration was less than 3/16 inch (~ 4.76 mm). It was demonstrated that at this level, subsequent cooking behavior is similar to the control after 30 days of frozen storage prior to cooking. Both the core and the surface of the meat are browned during cooking. A thin layer of pink often remains between the surface and the core.

The preferred embodiment of this method is to use the treated film 22 for a vacuum seal 10 ', as shown in FIG. 3. During vacuum wrapping, all air is removed from the inside of the gasket 10 'so that the film 22 intimately touches the upper surface 13a and the side surface 13b, i.e. the viewing surface 100 of the meat 12. Best results are obtained when the touching wrapping film 22 effectively prevents the entry of oxygen from the atmosphere after packing. This is due to small amounts of oxygen accelerating unacceptable discoloration, as discussed earlier. Thus, it is desirable to minimize the exposure time of the raw meat to oxygen during the cutting or grinding procedures that occur prior to packing. Residual oxygen that absorbed into the meat surface during the cutting and grinding procedures is eliminated by the postmortem respiratory activities of the raw meat tissue. Since time is required for this to occur, the process works best when the nitrite solution into the juices occurs gradually. It has been shown that incorporation of nitrite mixture 30 into thin polymer sealing layer 24 of a multilayer wrapping film 22 yielded better results than coating or dusting of nitrite mixture 30 on inner film surface 24 where all of the mixture 30 is readily available to display surface 100.1. as favorable to the present process encapsulating the nitrite mixture 30 or otherwise protecting it in a manner which controls or delays the release of nitric oxide.

One of the best types of vacuum packs in the industry is referred to as a '' skin pack ''. This type of gasket generally uses a rigid bowl to support the product. The clear top film is formed around the product during the vacuum packing procedure. The thin film forms a skin around the entire viewing surface of the product. There seems to be no film on the product surface. Thus, an excellent fresh meat appearance can be achieved when used with a skin-wrapping film.

It is contemplated that oxygen barrier bowls with or without the surfaces containing nitrite or nitrate can be used with wrapping films in accordance with the present invention. The oxygen barrier dish may maintain a fresh purple color on the meat against the bowl touching surface, which color will freshen red after settling and exposure to oxygen, or the dish may contain nitrite or nitrate on the surface, as is done with the film of the invention.

Another use of the present method is to use it with the vacuum packaging of storage processed meats such as ham, lunch meat, bologna and hot sausages.

They are most commonly packaged with barrier films to preserve their distinctive color. This color is much more stable than fresh meat and typically lasts more than 60 days. When color bleaching occurs, it can be attributed to an oxidation of the nitrosohemochrome pigment. This is most likely due to the depletion of residual nitrite and the entry of very small amounts of oxygen through the wrapping film. Advantageously, the present process retains a residual nitrite level at the film 22 against the meat touch surface thereby extending the color life.

To control the rate and amount of nitric oxide gas released from the inner film surface after packaging, impregnation or penetration of nitrite or nitrate mixture 30 into the polymer comprising film touch surface layer 24 would allow a slow and controlled release of the mixture. Polymer films for this purpose were prepared using 0.1,000, 5,000, 10,000,20,000 and 25,000 parts per million of sodium nitrite included in the surface layer 24 (based on the weight of the surface layer 24). It was shown that even the lowest amount of nitrite tested resulted in the preferred red color formation in the food product. Furthermore, different types of food products showed different results with differing nitrite levels present in the film 22. For example, pork showed the best results with a film having 10,000 ppm of nitrite, where beef had the best results with a 20,000 ppm nitrite level in film 22. Thus, the nitrite level required in film 22 relates to produce the desirable and stable color, the level of myoglobin present in the food product.

Although the disclosure of the present invention has been disclosed with regard to nitrite, it will be appreciated that the invention requires the use of a sodium or potassium salt of nitrite or nitrate or mixtures thereof, and these commonly available materials or less common oxides of nitrogen may be useful. is used in the present invention.

The film surface will preferably have 0.0155 gm.² (0.01 mg per square inch) or less, and more preferably 0.0119 gm '(0.0077 mg per square inch) or less of nitric oxide agent, such as nitrite, to avoid an undesirable deep penetration of the agent into a contacted meat. . This amount minimizes fuzziness to produce a favorable transparent gasket. The film containing nitric oxide will advantageously have good optical properties and be transparent. Advantageously, the film will have a cloudiness value less than 25%, preferably less than 20% and more preferably less than 15% as measured by ASTM D-1003-52. The surface will preferably have at least 0.00124 gm.² (0.0008 mg per square inch) and advantageously at least 0.00248 gm² (0.0016 mg per square inch) in a transferable amount to effect an appropriate color change over 96 hours after contact with an uncooked meat in an oxygen barrier vacuum-packed environment.

Advantageously for use with beef, an amount of at least 1 ppm (based on the weight of the beef) available on the nitrite or nitrate treated surface of the film can be advantageously used. Similar to pork, only 0.5 ppm (based on the weight of the pork) can be used for similar effect. It has been demonstrated that films containing 10,000 ppm (0.164 gm² (0.106 mg per square inch) of nitrite (in the form of sodium nitrite), after 48 hours will make available for transfer 0.00264 gm '² (0.0017 mg per square inch) to the surface of meat. At 20,000 ppm (0.327 gm² (0.211 mg / square inch)) is 0.0199 gm² (0.0077 mg / square inch) available for transfer at 48 hours.

Although the disclosure of the invention above relates to its use for fresh red meat, this method also provides advantages when applied to fresh fish. More particularly, when the wrapping film and method is used for vacuum-packed fresh fish, its bacteriological safety is enhanced. At present, the safety of a low oxygen pack of fresh fish is at greater risk than a pack of oxygen permeability or high oxygen content, because the low oxygen pack produces conditions that favor the growth of certain bacteria, such as Clostridium botulinum. The higher oxygen package is preferred for this reason and is actually authorized by regulatory bodies. However, the presence of increased oxygen levels also allows the bacteria that grow faster to break down the product more quickly. Nitrite or nitrate and nitrogen monoxide gas inhibit the ability of the clostridium bacterium to produce its venom. The presence on the surface of a vacuum pack therefore reduces this risk and extends the bacteriological shelf life of the fish.

Food products, such as pork, beef, etc., which have been improved, also work well with the method and film of the present invention. More particularly, common ingredients for improvement, which include antioxidants, such as rosemary extract or erythorbate, help to accelerate the degradation of nitrite or nitrogen monoxide. Other ingredients for these enhancement types, such as sodium phosphate, help stabilize the myoglobin pigment and raise the oxygen consumption rate of the meat tissues.