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

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

BACKGROUND AND SUMMARY OF THE INVENTION [0002] Color alone remains the only essential quality feature of meat that affects its sale. For consumers, color is an indicator of freshness. The color of the meat comes from myoglobin. It is a complex pigment protein present in the muscle tissue of all animals. Its biological function is to store and supply oxygen. It performs this function by binding molecular oxygen, thereby creating an intracellular source of oxygen for the mitochondrion. Pork and poultry contain less amounts of myoglobin than beef, so they are lighter in color than beef.

[0003] Myoglobin consists of a non-protein part called heme and a protein part called globin. The protein portion is a large polypeptide chain that determines the three-dimensional configuration of myoglobin. Hem consists of an iron atom in a flat ring. Globin surrounds the heme group and interacts with it in a way that stabilizes the molecule. The heme group is the reactive center of myoglobin. It contains an open binding site that attracts ligands. The ligand must be small enough to fit into the heme pocket and have the appropriate electron configuration to bind to the iron atom. Oxygen perfectly meets these requirements, and thus in this way myoglobin performs its biological function of transporting oxygen from the blood to the mitochondrion.

[0004] When oxygen enters the heme pocket, its electron configuration changes the shape of the globin that is part of the molecule in a way that affects the radiation absorption characteristics. Visible changes in myoglobin color are caused by the presence or absence of the ligand in the haem pocket and the ligand itself.

[0005] When there is no ligand in the haem pocket, myoglobin is in its native state. This form of the molecule is referred to as deoxymyoglobin. Her color is purple. If oxygen is present in high concentrations, such as levels in the Earth's atmosphere, then it is pushed into the haem pocket and deoxymyoglobin turns into oxymyoglobin. Her color is red. If the oxygen pressure is low, then it tends to dissociate from the oxymyoglobin molecule. In this case, oxygen tends to take the electron from the iron atom and leave it in the iron (III) state. When this happens, a water molecule travels into the heme pocket and becomes a ligand that affects light absorption. The oxidized form of myoglobin with H2O in the prosthetic heme group is referred to as metmyoglobin and its color is brown. If the chemical state of iron changes from iron (II) (Fe⁺²) on iron (III) (Fe⁺³), the three-dimensional structure of the globin changes in a way that allows water to enter the heme pocket. Oxidation of the iron atom always produces a brown color.

[0006] Other variables that affect globin stability also affect the affinity of the heme group for oxygen and the tendency for the iron atom to become oxidized. Acidity and high temperatures, such as those associated with cooking, can cause denaturation of globin and thus lead to hemostability. In the absence of stabilizing ligands, if the globin has dented, heme iron oxidation is automatic.

[0007] In fresh meat (muscle tissue after slaughter), oxygen is continuously associated and de-associated with the heme complex. Therefore, there is a relative prevalence of three forms of muscle pigment that determines the visual color of fresh meat. In summary, these forms include deoxymyoglobin (reduced myoglobin), which is purple; oxymyoglobin (oxygen-saturated myoglobin) which is red; and metmyoglobin (oxidized myoglobin), which is brown.

[0008] Immediately after slaughter, deoxymyoglobin dominates. Therefore, freshly cut meat is purple. This purple color can persist for a long time if the pigment is not exposed to oxygen. Cutting or milling exposes the pigment to oxygen in the atmosphere and the purple color quickly transforms into either bright red (oxymyoglobin) or brown (metmyoglobin). Although deoxymyoglobin is technically fresher, the primary criterion used by consumers when assessing freshness is red or bloody meat color.

[0009] Changes in the relative content of each form continue as fresh meat is exposed to oxygen. The immediate conversion of purple to the desired bright red or undesirable brown depends on the oxygen pressure on the surface. Purple is favored at very low oxygen levels. It dominates at levels of 0-0.2%. The brown color is favored when the partial strait of oxygen is only slightly larger (0.2% to 5.0%). Consumers begin to notice adverse changes when the relative level of metmyoglobin is 20%. The pronounced brown color is evident at 40% metmyoglobin, which typically means no sealing of the meat.

[0010] After the animal's death, biochemical reactions that affect the color of fresh meat occur in muscle tissue. These reactions are caused by the presence of active glycolytic enzymes that convert oxygen into carbon dioxide. The presence of reducing coenzymes that continually convert metmyoglobin back to deoxymyoglobin has an effect on meat color. These reducing coenzymes are called metmyoglobin reductases and their activity is referred to as "MRA", which is an abbreviation for metmyoglobin reducing activity. MRA activity can be described as the ability of a muscle to reduce metmyoglobin back to its natural state - deoxymyoglobin. This activity is lost when the oxidizable substrates are depleted or if the heat or acid causes the enzymes to denature. When the enzymes lose their activity or denature, the heme pigment iron automatically oxidizes to form metmyoglobin, which causes stabilization and dominance of brown color.

[0011] MRA activity is maintained for a period of time after death depending on the degree of muscle tissue exposure to oxygen. During this time, oxygen is continuously consumed by the meat tissue. The oxygen consumption rate is referred to as "OCR". When meat with high OCR is

When exposed to oxygen, the oxygen pressure drops so quickly that metmyoglobin is favored under the visible surface. This affects the perceived color of the meat when close to the visible surface. MRA activity is important for minimizing this layer of metmyoglobin that forms between the coating and the purple interior. As the MRA "consumes," the brown layer of metmyoglobin expands and migrates toward the surface, thus reducing exhibition durability. If the MRA activity is high, the metmyoglobin layer is thin and sometimes invisible to the naked eye.

[0012] There is a practical link between MRA and OCR with the retail packaging specification to extend the desired meat appearance as long as possible. Hermetic packaging with oxygen barrier films means that the oxygen pressure on the surface is low. Accordingly, metmyoglobin is produced and the visible surface changes with undesirable brown color. However, if the OCR is high enough to "overtake" the oxygen that migrates through the packaging film, and MRA activity is sufficient to reduce surface metmyoglobin, then native 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 packaging alone in the past was not an acceptable format for fresh meat in the packaging system for retail portions ready for case-ready display. On the other hand, vacuum packaging is the format of choice for cooked meats and sausages, in which myoglobin denatures under the influence of elevated temperature and is stabilized by the presence of nitrite. If oxygen is eliminated from the sausage packaging, then the color and smell of the product deteriorate more slowly than when oxygen is present.

[0013] Some uses of fresh meat are suitable for vacuum packaging because of its inherent benefits in protecting product quality. For example, vacuum packaging is commonly used for essential cuts and smaller parts, as well as for frozen steaks. Product color is not critical to these applications. However, the color of retail portions is extremely critical and the color caused by vacuum packaging is unacceptable. Therefore, the industry was not able to take advantage of the benefits of vacuum packaging in a "case ready" system.

[0014] As mentioned earlier, the prosthetic heme group is responsible for the color. Ligands other than oxygen or water, which also affect meat color, have been discussed in the literature. For example, cyanide and fluoride cause brown, carbon monoxide (CO) produces a bright red color, and nitric oxide (NO) produces a cherry color. In particular, a method of treating fresh meat with carbon monoxide has been developed for use in case ready packaging. The bright red myoglobin complex is referred to as carboxymyoglobin.

[0015] Sodium nitrite, when added to meat, also affects the color. This approved additive is a well-known preservative used in the preservation processes of products such as ham, luncheon meat, mortadella and hot dogs. The effect on meat color and bacterial growth form the basis for its widespread use in the meat industry. Almost immediately after adding it, the color of raw meat changes to gray-brown. This is a phenomenon

EP 1 737 651 B1 frequently encountered. The pigment associated with the characteristic brown color of raw preserved meat is sometimes referred to as the nitric oxide-metmyoglobin complex. It has been shown that nitrite is reduced to nitric oxide gas during dissolution in meat juices. Nitric oxide is the simplest known paramagnetic molecule (i.e. a molecule with an unpaired electron). Under the influence of contact with raw meat in the presence of oxygen, nitrite and nitric oxide take on a brown color by enhancing the dissociation of oxygen from the oxymyoglobin complex. The presence of oxygen causes the oxidation of nitric oxide to nitrite, thus reducing its availability for association with a myoglobin molecule. During these conversion processes, the heme group loses an electron to form brown metmyoglobin.

[0016] Under the influence of cooking nitric oxide, the globin of the metmyoglobin molecule denatures and nitric oxide is attracted to the heme pocket. Because nitric oxide has an unpaired electron, its presence in the heme group activates the reduction of the iron (III) atom back to iron (II). The color changes to rusty red or pink, depending on the relative amount of myoglobin in the muscle tissue. Cooked preserved pork or poultry is pink, and cooked preserved beef has a more rusty red color.

[0017] The denatured (heat treated) complex of myoglobin with nitric oxide as its ligand is called nitrosohemochrome. In the absence of oxygen, this pigment is very stable, however, the presence of oxygen eventually causes oxidation of nitrosohemochrome and the color changes to gray-brown. As a result, the packaging format of choice for processed meat is vacuum packaging with foil that is a significant barrier to oxygen. This protects nitrosohemochrome against oxidation by oxygen so that the color is stable for months.

[0018] The conventional packaging format used by retailers for fresh meat is to draw a thin PVC film around the foam tray that holds the product. This foil is permeable to oxygen so that the initial color of the meat is bright red. However, the shelf life for the bright red is only about three days. Accordingly, this packaging format is undesirable because the color often becomes unacceptable before being displayed or sold. As a result, a packaging format that stabilizes the fresh color of meat for a longer time is required for centralized packaging operations.

[0019] As an alternative, a high oxygen content modified atmosphere tray may be used. Currently, it is the most commonly used case-ready packaging system. Pre-formed trays with this type of oxygen barrier are filled and sealed on devices ensuring high speed of this process. The tray is typically a foam tray with an oxygen barrier layer or a rigid plastic oxygen barrier. The tray is then flushed with oxygen-rich gas before the hermetic closure with a transparent film on top. In this case, the film used for covering also has the properties of an oxygen barrier film, and also has some shrinking properties. The product is free inside the packaging because the film does not adhere to the meat, so that a significant space (free space) is created between the film and the product, which allows gas color modification. Centralized or local packaging machines currently produce whole portions of meat and ground beef in such packages.

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The high-oxygen atmosphere in the packaging produces a thick layer of colored coating on the surface, more durable compared to meat exposed only to atmospheric oxygen levels. The maximum achievable shelf life is about 14 days for ground beef and 10 days for whole portions of meat. Since this refers to the modified atmosphere inside the packaging, the most common approach is to use a 60-80% oxygen blend, the rest being carbon dioxide. The partial pressure of oxygen on the surface of the meat provides enough oxygen for the activity of the enzyme, as well as the reaction with myoglobin. Surface pigment - myoglobin is converted to oxymyoglobin before excess oxygen is consumed by tissue respiration, which results in the creation of a thicker surface layer of oxymyoglobin and, consequently, an increase in display durability. However, due to depletion of MRA at the end of the exhibition shelf life, the thick layer of oxymyoglobin oxidizes to metmyoglobin.

[0020] The high oxygen packaging format has additional disadvantages. More specifically, the current display durability is much shorter than 14 days, because exposure to light actually catalyzes or accelerates the oxidation of a bright red color to undesirable brown. In addition, whole portions of meat lose color faster than ground products when exposed to light. As a result, they are priced and labeled with a three-day shelf life in the retail store, which significantly reduces the period of meat sale. Qualitative features caused by prolonged exposure to elevated oxygen levels include aerobic rancidity, metmyoglobin formation in the core, and premature browning. In addition, the characteristic free space in a single package takes up space in the carton, increasing transport and storage costs. The free space is also less attractive to the consumer than tightly wrapped portions of meat.

[0021] Recently, carbon monoxide has been approved as a component of gases for use in a modified atmosphere of "case ready" packaging. It has been shown that this gas effectively extends the shelf life. As mentioned earlier, if carbon monoxide is a ligand of the myoglobin complex, then a bright red favorable color is formed. This is a very suitable way to extend color life and many commercial applications are currently being implemented in industry. This type of modified atmosphere packaging will not contain oxygen, but only 0.4% carbon monoxide to achieve the desired effect. In this method, free space is required and the formation of a favorable bright red color will be inhibited at every contact of the film with the meat. U.S. Patent Nos. 4,522,835, 6,113,962, 6, 270,829 and 6,521,275 describe methods of using carbon monoxide and other gases to induce and maintain a fresh meat color.

[0022] Another approach used by some packaging facilities to enable centralized packaging and to provide economies of scale is the use of conventional PVC foil wrapping with oxygen permeable foil inside another oxygen barrier package. One or more conventional packages are wrapped in a high oxygen or low oxygen gas flushed cardboard packaging to extend the shelf life of the packaging contained therein. If a low oxygen gas is used, the meat will tarnish when the individual trays are removed from the carton. Is

EP 1 737 651 B1 is beneficial for extending the color fastness, but sometimes the formation of the coating is difficult because the oxygen at the level of the content in the atmosphere does not properly penetrate the foil covering the surface of the meat. The high oxygen gas approach is limited to the local distribution level because the shelf life is shorter than for the modified low oxygen atmosphere package described above. As such, the bulk carton approach is more commonly used for pork and poultry.

[0023] Another packaging format for improving the appearance of packaged food products is also disclosed. For example, carbon monoxide (CO) is used in one such format as part of the gas injected into the secondary or outer carton packaging. Carbon monoxide penetrates the permeable inner packaging and affects the color of the food product like oxygen, causing a coating to form on the surface of the food product. However, due to the lack of oxygen in the carbon monoxide gas injected into the packaging to oxidize myoglobin, the red color developed by carbon monoxide is more durable. Therefore, it is more long-lasting than the red color caused by oxygen. This extension of the color change time from red to brown consequently increases the attractiveness of the food product to the consumer and the likelihood of selling the product to the consumer. However, the format using carbon monoxide in the absence of oxygen requires special packaging equipment and additional outer packaging to achieve the desired effect.

[0024] In addition to the previously mentioned formats, various other additives and gases have been used and disclosed in the art to improve and extend the bacteriological shelf life and color shelf life for fresh meat packaged in a "case ready" system. For example, US Patent 4,683,139 describes a method of enhancing and maintaining the color of fresh meat for up to two weeks. This method uses direct additives including phosphate salts, ascorbic acid or alkali metal salts, and masking agents such as citric acid in combination with a modified packaging atmosphere. In this patent and references cited, the color of fresh meat is stabilized by the presence of oxygen.

[0025] Many patents also describe the use of compressed gases as agents for treating meat before packaging so as to intensify and consolidate the beneficial red color. U.S. Patent 6,716,464 discloses the use of oxygen in this manner. Again, these methods emphasize the importance of the red color of fresh meat.

[0026] Other methods in which the packaging atmosphere is actively exchanged to change the color of the meat are described in US Patent No. 5,481,852 and US Patent 5,989,613. The display durability of packaging produced by these methods is very short and as a color change agent used is oxygen. Similarly, the method described in US Patent Nos. 5,866,184 and 5,711,978 uses perforations in a tray or cover for a modified atmosphere package to allow oxygen to passively enter the meat surface just before retail display. U.S. Patent Nos. 5,759,650, 5,591,468 and 4,055,672 describe methods in which the outer layer of barrier film is removed leaving a permeable film layer. When the barrier layer is removed immediately before exposure, atmospheric oxygen diffuses into the meat surface causing a favorable color change. In addition, U.S. Patent Nos. 5,989,610, 5,597,599 and 5,352

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467 the use of various gases and additives is described. The goal of all these methods is to develop and preserve the oxygen-saturated (red) form of meat pigment for a longer period of time.

[0027] US Patent Nos. 6,046,243, 5 965 264 and 5 888 528 relates to the encapsulation and subsequent release of biocidal gases to delay, control or prevent microbial contamination. Nitrite and nitric oxide are mentioned in patents as measures to achieve these specific effects. Meat packaging applications are also mentioned in detail with respect to chloride dioxide as the active antibacterial ingredient. United States Patent Application No. 2004/0137202 discloses a method of coating the contacting surface of a food wrapping film with active ingredients or agents that give different secondary effects or perform different functions. Nitrite in this method is mentioned in the context of its preservative effect.

[0028] In addition, many patents disclose the use of nitrite in packaging material as corrosion inhibitors. These include US Patent Nos. 6,533,962, 6,465,109, 6,033,599, and 5,281,471. US Patent No. 5,271,471 is a broad disclosure that also includes vacuum packaging and packaged food.

[0029] WO-A-2004/039683 discloses a multifunctional food wrapper comprising fabric, glue and having yet another additional function. A fabric with many protrusions integrated into this fabric and with spaces between them is provided. The adhesive is placed within the space between the protuberances. At least one secondary function may be performed by chemical or physical means placed within the adhesive, fabric and / or protuberances.

[0030] In US-A-2001/0055640, a fresh food product is wrapped in a packaging material comprising a food contact substrate and a food treatment layer containing a predetermined amount of edible adhesive applied to that food contact substrate and a preservative or marinating agent admixed to, maintained and characterized by glue.

[0031] WO-A-03/009709 discloses a method of producing a modified atmosphere package comprising providing the first package with a non-barrier portion substantially oxygen permeable. A retail portion of raw meat is placed in the first pack and the first pack is sealed. A second package substantially oxygen-impermeable is provided. The first package is covered with the second package without sealing the second package so as to create a pocket between the first and second packages. A gas mixture is delivered to the pocket.

[0032] EP-A-0473091 discloses an extruded film article, such as a pouch, consisting of a mixture of a thermoplastic polymer such as a copolymer of ethylene vinyl acetate and olefin oxide, a polymer such as polyethylene oxide with a modifier such like liquid smoke absorbed in the mixture. The modifier is transferable from the film to the receiving surface, such as food in fluid contact with the film.

EP 1 737 651 B1 [0033] Abstract in English JP-A-57-155975 refers to foods, especially processed meat products, such as ham, sausage, etc., which are wrapped in a film of sparingly soluble pullulan containing a natural or synthetic dye , flavoring, spices, etc., and which withstands the process of packing raw meat or raw meat products at room temperature, but dissolves at the temperature of the normal cooking process.

[0034] WO-A-96/14760 discloses a method of extending the shelf life of fresh food products such as meat, poultry, seafood, vegetables and fruits, using a foil pad with an adhesive layer and a preservative or marinating agent attached to foil with glue. The food is sealed in a pad with a preservative or marinating agent in close contact with the food and the packaging is kept at a temperature of about 0 ° C until it is substantially preserved or marinated.

[0035] US-A-2925346 discloses a process of packaging preserved meat products to provide an attractive, brightly colored product and inhibit color distribution in this product. The process involves placing the product in a container, removing oxygen from the product and container, refilling the container with nitrogen gas and then sealing the container.

[0036] Techniques belonging to the prior art relate to methods of modifying meat color by means of passive or active meat processing with gases or chemicals. Some of these methods also use the physical properties of the packaging to activate the color transformation of fresh meat, including peelable barriers, perforations and packages with multiple layers of film. However, none of these techniques give any guidance on the selection of a favorable red color for fresh meat with nitrite, nitrate or nitric oxide. Furthermore, none of these methods ensures the production and stabilization of the beneficial red color of fresh meat in a vacuum package.

[0037] In view of the above, it is desirable to develop a new packaging format allowing the production and stabilization of the visible red color of the meat food product, with a appearance reminiscent of a packaging format traditionally offered to consumers.

SUMMARY OF THE INVENTION [0038] The main purpose of the present invention is to develop and stabilize the beneficial red color on the surface of fresh meat. The color of interest is that typically specific to fresh meat that has been exposed to oxygen to produce the oxidized red form of the meat pigment. The present method achieves this goal by using a nitric oxide-based compound, e.g., nitrite or nitrate compounds, in a packaging format that significantly increases the shelf life of the desired color of the meat food product. More specifically, the present invention allows the development and stabilization of a beneficial red color by using a compound based on nitric oxide on

EP 1 737 651 B1 example of nitrites or nitrates in a manner that allows reaction with myoglobin being a meat pigment to form the nitroxymyoglobin as defined herein.

[0039] The present invention provides food packaging film in the form as claimed in claim 1, to which reference should be made at this time. Preferred but optional features of the film are listed in claims 2 to 10. The invention also provides a food packaging container according to claim 11 and a food packaging method according to claim 14, wherein both the container and the method uses the film according to the invention. Claims 12 and 13 and 15 to 19 list preferred but optional features of the container and methods, respectively. Claim 20 lists the vacuum-packed meat provided by the invention and the use of the film according to the invention.

[0040] The present invention enables the objectives to be achieved by creating conditions within the packaging of meat food products that allow the production of nitroxymyoglobin. More specifically, it has been found that if raw meat is exposed to sodium nitrite after vacuum packaging in a barrier film, its color changes from red to brown within minutes. However, unexpectedly, after a longer period of time (1-5 days) the color turns bright red back. Accordingly, during this period of time, the dominant pigment on the meat surface changes from oxymyoglobin to metmyoglobin and to nitroxymyoglobin. This is because the elimination of oxygen and the reduction of metmyoglobin allow the formation of nitroxymyoglobin. The vacuum that is used during the packaging stage is not able to eliminate the oxygen absorbed on the surface of the meat because it is bound in the heme pocket of the myoglobin complex. However, thanks to OCR and MRA activity, it is possible to eliminate oxygen and reduce other metmyoglobin pigments. The color change may take several days. After reducing metmyoglobin pigments, nitroxymyoglobin pigments begin to dominate and the color on the surface of meat products changes to a favorable bright red.

[0041] Another object of the present invention is to create conditions that allow the production of nitroxymyoglobin on visible meat surfaces without spreading deep into the meat. More specifically, nitrites or nitrates are sprayed on or introduced into the packaging film forming a sealing layer for the film placed directly above it in contact with the food product. The amount of nitrite affecting the effective conversion of surface deoxymyoglobin to nitroxymyoglobin depends on the concentration of myoglobin molecules naturally present in the packaged meat product. This amount varies significantly between different types of meat, with beef and lamb higher than for pork and poultry. In addition, there are fluctuations in the concentration of myoglobin molecules for individual animals, depending on their age, sex or race. Muscle type and slaughter conditions also affect the speed and efficiency of converting myoglobin molecules. Accordingly, the present invention is used to induce nitroxymyoglobin formation only on the visible surface of fresh meat leaving myoglobin in the middle of the product in a natural state. Particularly, the desired depth of improved color penetration provided by the present invention is preferably less than about 10 mm (0.375 inches) and more preferably less than about 6 mm (0.25 inches).

[0042] Many other objects, features and advantages of the present invention will be apparent from the detailed description below, together with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS [0043] The drawings illustrate the best mode of carrying out the invention currently considered in implementing the present invention.

[0044] In the drawings:

Fig. 1 is an isometric view of a packaging consisting of a packaging film containing nitric oxide;

Fig. 2A is a cross-sectional view of the packaging film of Fig. 1 where a nitrogen-containing compound is sprayed onto the film;

Fig. 2B is a cross-sectional view of the packaging film of Fig. 1, wherein nitric oxide is introduced into the film; and

Fig. 3 is an isometric view of a vacuum package containing the packaging film of the present invention.

DETAILED DESCRIPTION OF THE INVENTION [0045] Undenatured (crude) nitric oxide and myoglobin complex is essential for the method of the present invention and packaging film. In current literature, the "nitric oxide-metmyoglobin complex" is described as a pigment formed under the exposure of raw meat to nitrite. Little research has been done into the reduced form of this pigment. The terminology for pigments is inconsistent. Scientists refer to them as, among others, 'nitric oxide-myoglobin complex', 'nitrosomyoglobin', or 'nitrosylhemochromagen'. To avoid confusion, in this specification the undenatured and reduced form of the nitric oxide and myoglobin complex will be referred to as nitroxymyoglobin.

[0046] As mentioned earlier, the visible surface of unprocessed fresh meat currently contains a combination of three forms of myoglobin. Pigments on the surface and below the surface affect the color. If the meat is exposed to atmospheric air, oxymyoglobin dominates the percentage of pigments and the color is bright red. When raw fresh meat is exposed to nitric oxide, metmyoglobin dominates on the surface and the color is brown. However, below the surface, the color of the meat is dull red, and deep inside the color is bright red. The perceived color of nitrite-treated meat is a combination of four pigments including nitroxymyoglobin. In the absence of oxygen and reduction of metmyoglobin to deoxymyoglobin, nitroxymyoglobin begins to dominate the other three forms. Conditions must be adequate for the reduction of all four forms of metmyoglobin. The results of the experiments for the method of the present invention suggest that the color of nitroxymyoglobin is the same as that of oxymyoglobin and carboxymyoglobin. Accordingly, when nitroxymyoglobin is the predominant myoglobin pigment on the meat surface, the perceived color is bright red.

[0047] Currently, with reference to the figures in which reference numbers designate similar elements described throughout the disclosure, the packaging of the food product of the present invention, such as a tray, is shown in Figure 1 essentially as 10. Packaging 10 has any desired shape, depending on the size and configuration of the food product 12 mixed therein having a visible surface 100. According to the present invention, the method can be advantageously used for any type of tissue containing myoglobin or hemoglobin and particularly applies to food products derived from: livestock such as beef, pork, veal, lamb, mutton, chicken or turkey; venison such as quail and duck; and fish, fish products or seafood. The terms "meat food product" or "food product" used in this application refer to each of the above types of meat. Meat can take a variety of forms, including basic cuts, smaller parts and retail portions, as well as minced meat, in minced or mixed form.

[0048] Furthermore, the package 10 may consist of a large number of suitable materials, such as foams and plastics, known as materials for the packaging of food products or trays 10. In fact, the film itself can be used to package food using pouches, bags Vacuum meat packing, and the film can be heat shrink or not. In a particularly preferred embodiment, the food product 12 is meat, such as fresh red meat with an upper surface 13a and an opposed bottom surface (not shown) that join through the surface of the meat sidewall 13b, packaged with the film of the present invention. In a preferred package, the food product is vacuum-packed into a tray drawn on the product on a tray, such as a packaging tray 10 including a bottom wall 14, a pair of side walls 16 protruding upwardly from the bottom wall 14, and a pair of end walls 18 protruding upward from the bottom wall 14 and connected to the side walls 16. The respective walls 14, 16 and 18 forming the packaging tray 10 form a housing 20 in which the food product 12 can be placed. The food product 12 is held within the packaging tray 10 by means of the packaging film 22 placed on the food product 12 and the tray 10, and attached at each end to the tray 10. The packaging film 22 can be attached to the tray 10 by any suitable means, e.g. thermal shrinking, welding, gluing or any other suitable method.

[0049] Currently, with reference to Figures 2A and 2B, the packaging film 22 can be made of any suitable and preferably at least substantially transparent packaging material, and may consist of one or more layers. In a preferred embodiment, the film 22 consists of a plurality of layers to allow the film 22 to perform various functions for its intended purpose. In a particularly preferred embodiment, the packaging film 22 consists of an inner sealing layer 24 having meat contact surface 25 and an outer layer 26. In addition, one or more inner layers 28a may be incorporated into the packaging film 22. The present invention contemplates the use of films having 1, 2, 3, 4, 5, 6, 7, 8, 9 or more layers.

[0050] The sealing layer 24 contains nitric oxide, nitrite or nitrate 30 in an amount used to control the exposed color of the food product 12. Then, nitrate or nitrite 30

EP 1 737 651 B1 is applied to or incorporated into the produced layer 24, and optionally layers 26 and 28. Compound 30 may be applied to the meat contact surface of layer 24 or introduced into the sealing layer 24 by any conventional method, provided that the contact surface 25 of the layer 24 is evenly distributed and / or throughout the entire layer 24 so that each length of film 22 comprising layer 24 contained approximately similar amounts of compound 30 within the sealing layer 24 for uniform transfer to meat through surface 25. In an embodiment in which compound 30 is introduced within the sealing layer 24, the thickness of the sealing layer 24 is adjusted to optimize the migration of compound 30 from the layer 24 during contact with the top surface and side surfaces 13a and 13b of the food product 12. The thickness of the layer and / or the amount of compound 30 for layer 24 can be adjusted to modify the migration rate of compound 30 from layer 24 as needed. Also, film 22 may include an adhesive layer 34 sandwiched between layers 24 and 28 of film 22. Adhesive 34 may contain a nitrogen compound 30 to release compound 30 through layer 24 in a controlled manner, depending on the materials used to form layer 24.

EXPERIMENTAL PART [0051] The packaging film 22 of the present invention was developed based on experiments in which various chemicals were sprayed on raw meat prior to vacuum packaging. The chemicals used were various reducing and oxidizing agents that were tested to modify myoglobin reducing activity (MRA) and oxygen consumption rate (OCR) of raw meat. The goal was to stabilize the respiratory conditions of the meat to slow down the oxidation of myoglobin after exposure to oxygen. Commonly used meat additives were also evaluated. Chemicals included various phosphates, sulfates, acids and alkali, salts, various forms of ascorbic acid, antioxidants, oxygen masking agents, plant extracts such as rosemary extract and other compounds outside this range and not necessarily related to the present disclosure [0052] During these experiments, sodium nitrite and sodium nitrate were tested. It has been found that very small amounts of nitrite or nitrate affect the color of vacuum packed meat. More specifically, when the nitrites were coated on the inside contact surface of the vacuum package, the color changed to brown immediately after removal of oxygen from the visible surface. However, surprisingly, in some experiments, the beneficial red color gradually replaced the brown color and was stable for many months.

[0053] Based on the test, it can be concluded, without going into theoretical considerations, that nitric oxide gas (NO) is formed as a result of the reduction of nitrite on the packaging and that the gas affects the color of the meat food product. Nitric oxide gas is believed to have a similar effect on the formation of surface coating as carbon monoxide gas. In studies in which meat food products were contacted with nitrites, it was found that color in the form of a coating on the surface occurs only in the absence of oxygen. It is this initial small amount of residual oxygen that causes the food product to brown. It has been found that if the amount of residual oxygen is high, longer time is required to change the brown color to a favorable red color. In initial experiments, for the full development of red

Five days were required. Freshness of muscles and specific portions also affects the discussed "time to create a coating". Also, when using a weak barrier film for the packaging material, the time necessary to achieve the desired surface coating is increased. This is because oxygen migrates through the film causing and fixing a brown or dark color inside the meat.

[0054] In order to reduce the time to produce a coating on the surface, an extended vacuum time is used when packaging the food product. It has been observed that if a high level of vacuum is applied, the time for the formation of a coating on the surface decreases. At high vacuum levels it has also been observed that if an aqueous solution of nitrite is sprayed, sprayed or otherwise coated on the surface of the food product, the time for the formation of the coating on the surface can be reduced to about 60 hours. When the nitrite solution is sprayed, sprayed or otherwise applied to the inner surface of the package and left to dry before packaging, the time for producing the coating on the surface is reduced to about 48 hours. In addition, it has been observed that, generally, the coating time on the surface is shorter for pork than for beef. For pork, less than 24 hours was required. Improved pork (pork with about 10% or less addition of a mixture of water, salt and phosphate) showed a shorter production time of surface coating than non-improved pork. Beef, more than 20 days after slaughter, required a longer time to produce a coating on the surface, up to 72 hours. On the other hand, 10 days after slaughtering, beef raided within 24 hours. This is illustrated by the fact that a higher oxygen consumption rate of fresher meat is important to minimize the time it takes for the coating to surface.

[0055] The red color resulting from the use of nitrites or nitrates in this way is very durable and the color does not change into brown during cooking. The uncontrolled addition of nitrites or nitrates can be a problem in that the visual indicator of "cooking" a food product during cooking is difficult to obtain if nitric oxide gas (or material that changes color) penetrates an entire portion of muscle or minced meat to a depth almost reaching the middle of a single serving. In view of the above, it is important to control the level of nitrite used so that only an amount sufficient to obtain a very shallow color penetration (believed to be caused by nitric oxide penetration) of the visible surface of the food product is used. As the depth of nitric oxide penetration increases, the internal color is no longer affected by the cooking temperature, which normally turns brown or gray. If this phenomenon occurs, it is not possible to cook the product to obtain the appearance of a "cooked" product. In view of the above, it is important to minimize the amount of nitrite to which the visible surface of the meat is exposed.

[0056] This goal can be achieved by adding nitrites to the contact surface 32 of the sealing layer 24 or the packaging film 22. After vacuum packaging, the film 22 contacts the visible surface 100 of the food product 12. The nitrites from the surface of the film 24 dissolve in meat juices and break down to form nitric oxide with the desired effect. The best results are obtained when nitrite levels are controlled so that only enough nitrous oxide is released to develop coloration within the visible surface

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100 food product 12. The level of nitrite required to achieve this effect is less than one-tenth (1/10) of the nitrite typically used for canning. Indeed, partly the purpose of the present method is to control the supply of sufficient nitric oxide to modify only the visible surface 100 of meat 12. The level of nitrite typically associated with preserving is so high that the color persists even after cooking. In a preferred embodiment, the level of nitrite that can be used in the method of the present invention is so low that in most embodiments it is not analytically detectable as nitrite or nitrate in the final product by conventional tests. In addition, the quantity is insufficient for the effective maintenance of the whole product 12.

[0057] More specifically, in one example of the present invention, beef with a directly adjacent 0.25 inch layer thickness exposed to a film containing a suitable level of nitrite was tested for its content. An important observation is that after a short (about 48 hours) and a long (about 7-10 days) exposure period, no nitrite was detected in the meat (minimum detection level = 2.0 ppm). Accordingly, a very small amount of sodium nitrite is needed to achieve the desired effect. While the preferred nitrite penetration depth is about 0.25 inches (~ 6 mm), deeper nitrite penetration into the visible surface is also acceptable, up to a maximum of about 0.375 inches (~ 10 mm).

[0058] In previous studies, when nitrites were coated on the film surface, concentrations above 20 ppm were observed. At this level, nitrites seemed to penetrate the visible surface very deeply. Under the influence of cooking, it was impossible to achieve the aroma sensation of meat indicating the level of "cooking" for visual collection. The pink color produced by nitroxymyoglobin was present in the meat core. These studies evaluated the film adhering to both sides of the meat piece. Another assessment of the nitrite-free tray on the surface adjacent to the meat also found a significant penetration depth with higher nitrite levels. However, when 20,000 ppm sealing film was used on the packaging being drawn on the product, the penetration was less than 3/16 inch. At this level, it was found that the characteristics of further cooking are similar to the control sample after 30 days storage in refrigerated conditions before cooking. Both the core and surface of the meat turn brown when cooking. A thin layer of pink color remains between the surface and the core.

[0059] A preferred way of carrying out this method is to use a suitably treated film 22 for vacuum packaging 10 'as shown in Fig. 3. During vacuum packaging, all air is removed from the interior of the packaging 10' so that the film 22 adheres exactly to the upper surface 13a and the side surface 13b, i.e. the visible surface 100 of meat 12. The best results are obtained when the adjacent packaging film 22 effectively prevents oxygen from entering the surroundings after packaging. This is necessary because small amounts of oxygen accelerate unwanted discoloration as described earlier. Accordingly, it is desirable to minimize the exposure time of raw meat to oxygen during cutting and milling procedures prior to packaging. The residual oxygen absorbed on the meat surface during cutting and grinding is eliminated by the post-slaughter breathing processes of raw meat tissue. Because it takes time, the way works

Preferably, the dissolution of nitrite in meat juices occurs gradually. It has been found that the introduction of the nitrite compound 30 into the thin polymer sealing layer 24 of the multilayer packaging film 22 gives better results than coating or spraying of the nitrite compound 30 on the inner surface of the film 24, where all compound 30 is directly accessible to the visible surface 100. In one embodiment of the invention, it is contemplated that the nitrite compound may be encapsulated or otherwise protected as allowing the present process to control or delay the release of nitric oxide.

[0060] One of the best-looking vacuum packages is referred to in industry as a drawn package on a product. This type of packaging generally uses a rigid tray to support the product. A transparent top film is applied around the product during vacuum packing procedures. Thin film is stretched over the entire visible surface of the product. It looks like there is no film on the product. Accordingly, an excellent appearance of fresh meat can be achieved when this method is carried out using a stripped packaging film.

[0061] It is contemplated that oxygen barrier trays with or without surfaces containing nitrites or nitrates can be used in conjunction with the packaging films of the present invention. The oxygen barrier tray may allow the meat to retain its fresh purple color on the surface adjacent to the tray, which will result in the formation of a red coating on the surface after uncoiling and exposure to oxygen, or the tray may contain nitrites or nitrates on its surface as with the films of the present invention.

[0062] Another application of the present method is the use of it for vacuum packaging of sausages such as luncheon meat, mortadella and hot dogs. They are usually vacuum-packed with barrier films to maintain their characteristic color. This color is much more durable than the color of fresh meat and typically lasts longer than 60 days. Loss of color, if it occurs, can be attributed to the oxidation of the nitozohemachrome pigment. Most likely, this is due to the depletion of residual nitrite and the penetration of very small amounts of oxygen through the packaging film. The present method advantageously allows the level of residual nitrite to be maintained on the contact surface of the film 22 with the meat, extending the color shelf life.

[0063] To control the rate and amount of nitric oxide gas released from the outer surface of the film after packaging, the impregnation or permeation of the nitrite or nitrate compound 30 in a polymer comprising a surface layer adhering to the film 24 allows slow and controlled release of the compound. Polymer films for this purpose were prepared using 0, 1,000, 5,000, 10,000, 20,000 and 25,000 parts per million sodium nitrite introduced into surface layer 24 (relative to the weight of surface layer 24). It was found that even a smaller amount of nitrite tested induces the production of a favorable red color in the food product. In addition, different results were obtained for different types of food products with different levels of nitrite present in film 22. For example, for pork the best results were obtained for films with a nitrite content of 10,000 ppm, while for beef the best results were obtained with a nitrite level of 20,000 ppm in film 22.

Accordingly, the level of nitrite in film 22 necessary to produce the desired and permanent color is related to the level of myoglobin present in the food product.

[0064] Although the description of the present invention has been made with respect to nitrites, it should be obvious that the invention contemplates the use of sodium or potassium salts of nitrites or nitrates, or mixtures thereof, and these commonly available materials or less common nitrogen oxides may find use in the present invention .

[0065] Preferably, the surface film will contain 0.01 mg per square inch (0.0155 gm^-2) or less, and more preferably 0.0077 mg per square inch (0.0119 gm^-2) or less, an agent based on nitric oxide, e.g. nitrite, to avoid undesirable deep penetration of the agent into the meat during adherence. This amount minimizes haze in order to obtain a preferably transparent package. Preferably, the film containing nitric oxide based compounds will have good optical properties and will be transparent. Preferably, the film will have haze preferably less than 25 percent, preferably less than 20 percent and more preferably less than 15 percent, as measured by ASTM D-1003 52. Preferably, the surface will contain at least 0.0008 mg per square inch (0.00124 gm^-2) and preferably at least 0.0016 mg per square inch (0.00248 gm^-2) the quantity transferable to produce the appropriate color change within 96 hours after contact with raw meat in an oxygen barrier vacuum packaging environment.

[0066] Preferably, in the case of beef, an amount of at least 1 ppm (based on the weight of beef) available on the surface of the film treated with nitrite or nitrate may be used. Similarly, in the case of pork, to achieve a similar effect, only 0.5 ppm (based on the weight of pork) can be used. A film containing 10,000 ppm was found. (0.106 mg per square inch (0.164 gm^-2) nitrite (as sodium nitrite) after 48 hours will be able to transfer 0.0017 mg per square inch (0.00264 gm^-2) on the surface of the meat. At the level of 20,000 ppm (0.211 mg / square inch (0.327 gm^-2)) after 48 hours, 0.0077 mg / square inch (0.0119 gm^-2).

[0067] Although the above description of the invention relates to the application to fresh red meat, this method may also be advantageous for fresh fish. More specifically, when the packaging film and method is applied to vacuum-packed fresh fish, bacteriological safety is improved. At present, the safety of packaging fresh fish with low oxygen content is at greater risk than permeable or high oxygen packaging, because the low oxygen packaging creates conditions conducive to the development of certain bacteria, such as Clostridium botulinum. For this reason, packaging with a higher oxygen content is preferred and currently recommended by regulatory agencies. However, the presence of increased oxygen levels also allows faster bacterial growth, resulting in faster product degradation. Nitrites or nitrates and nitric oxide gas inhibit the ability of Clostridium to produce toxins. Accordingly, their presence on the surface of the vacuum pack reduces the risk and extends the bacteriological shelf life of the fish.

[0068] Food products such as pork, beef etc. that have been improved are also suitable for use according to the method and using the film of the present invention. More specifically, typical components of improvement agents, including antioxidants, such as extract

Rosemary or isoascorbate, promote the breakdown of nitrite to nitric oxide. Other ingredients of this type of improvement agents, such as sodium phosphate, help stabilize the myoglobin pigment and increase the rate of oxygen consumption of meat tissues.

[0069] Various alternative embodiments of the present invention are also contemplated as falling within the scope of the following claims, particularly indicating and explicitly claiming the object considered to be the invention.

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