MXPA06011165A - Improved packaging method that causes and maintains the preferred red color of fresh meat - Google Patents

Abstract

The present invention is a method for improving the visual appearance of a food product (12) and a film (22) utilized in the method. The film includes an effective amount of a nitrogen-containing compound contained within or applied to one side of the film and adapted to contact a food item held within a food packaging container (10). Upon contacting the food item within the container, the nitrogen-containing compound forms nitrous oxide gas within the container, because of the contact of the compound with and dissolution into the juices of the food product. Thus, the physical contact of the packaging film with the food product causes a preferred reddish bloom to appear on the viewing surface (100) of the food item without effecting the appearance, performance or color of the interior of the food product.

Description

IMPROVED PACKING METHOD THAT CAUSES AND MAINTAINS THE PREFERRED RED COLOR OF FRESH MEAT FIELD OF THE INVENTION The present invention relates to food packaging, and more specifically to a packaging method and film adapted to transfer a material to a food surface to promote an attractive appearance of the food product contained in the package.

BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION By itself, color remains the most important quality characteristic of meat that affects its commercialization. Consumers use color as an indicator of freshness. The color of the meat comes from myoglobin. This is a complex pigmented protein present in the muscle tissue of all animals. Its biological function is storage and delivery of oxygen. It achieves this function by reversibly binding molecular oxygen, thereby creating an intracellular source of oxygen for the mitochondria. Pigs and poultry contain lower amounts of myoglobin than beef and are therefore lighter in color than beef. Myoglobin consists of a non-protein portion called heme and a protein portion called globin. The protein portion is a large polypeptide chain that determines the three-dimensional configuration of the myoglobin molecule. The heme portion consists of an iron atom in a flat ring. The globin portion 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 has an open binding site that attracts a ligand. The ligand must be small enough to fit in the heme pocket and have the proper electron configuration to bind to the iron atom. Oxygen meets these requirements perfectly and that is how myoglobin performs its biological function to transport oxygen from the blood to the mitochondria. When oxygen enters the heme pocket, its electronic configuration changes the shape of the globin portion of the molecule in a way that affects the light absorption characteristics. It is the presence or absence of a ligand in the heme pocket and the ligand itself which affects the visible changes of color of the myoglobin. When there is no ligand in the heme pocket, the 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 in the Earth's atmosphere, it is pulled towards the heme pocket and the deoxymyoglobin becomes oxymyoglobin. Your color is red. If the oxygen tension becomes low, it tends to dissociate from the oxymyoglobin molecule. When this happens, there is a tendency for oxygen to capture an electron from the iron atom and leave it in the ferric state. As this happens, a molecule of water moves into the heme pocket and becomes the ligand that affects the absorption of light. The oxidized form of myoglobin with H2O in the heme prosthetic group is referred to as metmyoglobin and its color is brown. When the chemical state of iron changes from ferrous (Fe + 2) to ferric (Fe + 3), the three-dimensional structure of the globin part changes in a way that allows the water in the heme pocket. The oxidation of the iron atom always causes a brown color. Other variables that affect the stability of the globin portion also affect the affinity of the heme group for oxygen and the tendency of the chemical state of the iron atom to become oxidized. Acidity and high temperature, such as that associated with cooking, can denature the globin part, thus leading to the instability of the heme group. In the absence of stabilizing ligands, the oxidation of heme iron is automatic when the globin is denatured. In fresh meat (postmortem muscle tissue), oxygen is continuously associating and dissociating from the heme complex. In this way, the relative abundance of three forms of the muscular pigment is what determines the visual color of fresh meat. In summary, they include deoxymyoglobin (reduced myoglobin), which is purple; oxymyoglobin (oxygenated myoglobin), which is red; and metmyoglobin (oxidized myoglobin), which is brown. The form deoximioglobina dominates right after the animal is sacrificed. In this way, the freshly cut meat has a purple color. This purple color can last 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 is rapidly converted to either bright red (oxymyoglobin) or brown (methyoglobin). Even though deoxymyoglobin is technically cooler, it is the red or bright color of meat that consumers use as their main criterion to perceive freshness. Changes in the relative percentage of each of these forms continue to occur if fresh meat is more exposed to oxygen. The immediate conversion of the purple color to the desirable bright red or undesirable coffee depends on the partial pressure of oxygen on the surface. The purple color is favored at very low oxygen levels. Dominates at levels of 0-0.2%. The brown color is favored when the partial pressure of oxygen is only slightly higher (0.2% to 5.0%). Consumer discrimination begins when the relative amount of metmyoglobin is 20%. A distinctly brown color is evident at 40% metmyoglobin, which usually means that the meat is not sold. There are biochemical reactions that occur in muscle tissue after death that are important for the color of fresh meat. These reactions are caused by the presence of enzymatic glycolytic enzymes that convert oxygen to carbon dioxide. The effect on the color of the meat is the presence of reducing coenzymes that continuously convert the metmyoglobin back to deoxymyoglobin. These reducing coenzymes are called methyoglobin reductases, and their activity is called "MRA", which is an abbreviation for reducing activity of metmyoglobin. It is lost when the oxidizable substrates are suppressed or when the heat or acid denatures the enzymes. When the enzymes lose their activity or are denatured, the iron in the heme pigment is automatically oxidized to the methyoglobin form and the brown color stabilizes and dominates. MRA persists for a period after death, depending on the amount of exposure of the meat tissue to oxygen. During this time, oxygen is continually 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, the oxygen tension is reduced so rapidly that metmyoglobin is favored below the surface that is seen. If it is close to the surface that is seen, the perceived color of the flesh is affected. MRA is important to minimize this layer of metmyoglobin that forms between the shiny surface and the purple interior. As the MRA wears out, the brown methyoglobin layer thickens and migrates to the surface, thereby fermenting the exhibition life. When the MRA is high, the metmiogloblna layer is thin and sometimes it is 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, in order to prolong the desirable appearance of the meat as much as possible. Packs hermetically sealed with films that are an oxygen barrier, will cause a low oxygen tension on the surface of the meat. In this way, the formation of metmyoglobin occurs and the surface that is seen changes to an undesirable brown color. However, if the OCR is high enough to stay ahead of the oxygen that migrates through the packaging film, and the MRA is good enough to reduce the metmyoglobin that forms on the surface, then the natural deoxymyoglobin replaces the metmyoglobin. After a period, the perceived color changes from brown to purple. Both colors are unacceptable to the consumer. For this reason, vacuum packaging by itself has historically been an unacceptable format for ready-to-eat fresh meat. On the other hand, vacuum packaging is the format of choice for cooked and cured processed meats, where the myoglobin pigment is denatured by heat and stabilized by the presence of nitrite. When oxygen is removed from a package of processed cured meat, the color and flavor of the product deteriorate slower than when oxygen is present. Some applications of fresh meat are suitable for vacuum packing due to their inherent advantages to protect the quality of the product. For example, vacuum packing is commonly used for primary and sub-prime cuts of wholesale sales, as well as for frozen fillets. Product color is not critical in these applications. However, the color of retail cuts is very critical and the color caused by vacuum packing is unacceptable. In this way, the industry has not been able to capitalize on the benefits of vacuum packing for ready-made applications. As mentioned previously, the heme prosthetic group is responsible for the color. The relevant literature shows that different ligands of oxygen or water also affect the color of the meat. For example, cyanide and fluorine cause a brown color, carbon monoxide (CO) causes a preferred bright red color and nitric oxide (NO) causes an opaque red color. In particular, the methods for treating fresh meat with carbon monoxide have been developed for ready-to-pack packing applications. The bright red myoglobin complex is referred to as carboxymyoglobin. Sodium nitrite also affects color when added to meat. This improved additive is a commonly known preservative used in the curing process for products, such as hams, sausages, sausage and hot dogs. Its effects on meat color and bacterial growth are the basis of its wide use in the meat industry. Almost immediately after its addition, the color of the raw meat changes to a grayish coffee. This is a commonly experienced event. The pigment associated with the brown color characteristic of raw cured meat is sometimes referred to as nitric oxide methyoglobin. It has been shown that nitrite is reduced to nitric oxide upon dissolution in meat juices. Nitric oxide is the simplest known thermally stable paramagnetic molecule (ie, a molecule with an unpaired electron). Upon contact with raw meat in the presence of oxygen, nitrite and nitric oxide change the brown color by encouraging oxygen dissociation from the oxymyoglobin complex. The presence of oxygen oxidizes available nitric oxide to nitrite, thus reducing its availability to associate with the myoglobin molecule. During these conversion processes, the heme group loses an electron, thus forming the brown methyoglobin.

When cooked in the presence of nitric oxide, the globin portion of the metmyoglobin molecule is denatured and the nitric oxide is attracted to the heme pocket. Because nitric oxide has an unpaired electron, its presence in the heme group encourages the reduction of the iron atom back to its ferrous state. The color changes to pink or brown depending on the relative amount of myoglobin in muscle tissue. The boiled cooked pork or poultry is pink and the cooked cured beef is more of a brown color. The complex of denatured myoglobin (cooked) 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 oxidizes the nitrosohemochrome and the color changes to grayish coffee. As a result, the packaging format of choice for processed meat is vacuum packed with a film of high barrier. This protects the nltrosohemochrome from oxygen by oxygen, so that the color is stable for months. The conventional packaging format used for the retail grocer for fresh meat is to stretch a thin PVC film around a foam tray that supports the product. The film is permeable to oxygen, so that the initial color of the meat is bright red. However, the shelf life for the bright red color is only about three days. In this way, this packaging format is undesirable because the color frequently becomes unacceptable before it can be displayed or sold. As a result, a packaging format that maintains the color of fresh meat for a longer period is required for the centralized packing operation. As an alternative, a modified atmosphere tray with a high oxygen content can be used. Currently, it is the commonly used portfolio sleeve packaging format. The pre-formed oxygen barrier trays of this type are filled and sealed in high speed equipment. This tray is usually either formed of foam with an oxygen barrier layer or a rigid oxygen barrier plastic. A gas rich in oxygen is then discharged into the tray before sealing a clear film on the top of the tray. In this case, the film used for the lid also has an oxygen barrier film as well as some light shrinkage properties. The product is loose inside the packaging, since the film has no contact with the meat, so that there is considerable space between the film and the product (upper space), allowing the gas to affect the color of the meat. Centralized or regional packers currently manufacture whole muscle cuts and ground beef with this type of packaging. The high oxygen content atmosphere in the package creates a coarse bright color that lasts longer when compared to meat that is exposed to only atmospheric levels of oxygen. Maximum achievable shelf life is approximately 14 days for ground beef and 10 days for whole muscle cuts. Since it belongs to the modified atmosphere within these packages, the most common approach is to use a mixture containing 60-80% oxygen and the rest of carbon dioxide. The partial pressure of oxygen on the surface of the meat provides enough oxygen for enzymatic activity, as well as for reactions with myoglobin. The surface myoglobin pigment is converted to oxyimoglobin before the respiration of tissue consumes the excess oxygen and the result is the formation of a thicker layer of surface oxymyoglobin and consequently an extension of the life of the display. However, as the MRA is decreased towards the end of the color display life, the thick oxymyoglobin layer is oxidized to metmyoglobin. The high oxygen packaging format also has additional disadvantages. More specifically, the actual display life is much shorter than 14 days because the exposure to light actually catalyzes or accelerates the oxidation of bright red color to undesirable coffee. In addition, whole muscle cuts fade more quickly than milled products when exposed to light. As a result, they are labeled with a sell date of up to three days at the store level, greatly reducing the time available for meat sales. In addition, oxidizing rancidity, development of core methyoglobin and premature darkening are matters of quality due to long exposure to a high oxygen level. Additionally, the upper space characteristic of the individual package takes up space in the box, thereby increasing shipping and storage costs. The upper space 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 modified atmosphere jacket. It has been shown to effectively lengthen the shelf life. As mentioned previously, when carbon monoxide is the ligand of the myoglobin complex, the preferred bright red color develops. This is a very suitable method to extend the life of the color and as such, a variety of commercial applications are currently being pursued by the industry. This type of modified atmosphere packaging will have no oxygen and only 0.4% carbon monoxide to produce the desired effect. A superior space is required by this method and the development of the preferred bright red color will be blocked in any place where there is contact between the meat and the film. U.S. Patents 4,522,835, 6,1, 13,962, 6,270,829 and 6,521, 275 disclose methods that use carbon monoxide and other gases to cause and maintain the color of desirable fresh meat. Another approach used by some packers to enable centralized packing and economies of scale is to use the conventional PVC wrap format with its oxygen permeable film inside another oxygen barrier package. One or more of the conventional packages are overwrapped in a master package that is discharged with either a high or low oxygen gas to extend the shelf life of the packages contained therein. If low oxygen gas is used, the meat blooms when the individual trays are removed from their master package. It does a good job of extending the life of color, but sometimes the florescence is difficult because atmospheric oxygen levels do not adequately penetrate the film covering the surface of the meat. The high oxygen gas approach is limited to a regional distribution level because the shelf life is shorter than the low oxygen modified atmosphere packaging described above. As such, the master package approach is most commonly used for pork and poultry. Other packaging formats to intensify the appearance of packaged food products are also described by others in the industry. For example, one such format uses carbon monoxide (CO) as part of the gas that is discharged in an external or secondary master package. Carbon monoxide penetrates the permeable inner packaging and affects the color of the food product in a manner similar to oxygen, causing the food product to flourish. However, because there is no oxygen present in the gas including carbon monoxide that is discharged into the package to oxidize myoglobin, the red color developed by carbon monoxide is more stable. Therefore, it lasts longer than the red color caused by oxygen. This extension of the time before the red color turns brown, consequently increases the attractiveness of the food product to a consumer and the probability of selling the product to a consumer. However, the carbon monoxide / oxygen-free format requires special packaging equipment and an additional outer packaging to achieve the desired effect. In addition to the previously mentioned formats, a variety of other additives and gases have been used and discussed before in the prior art to intensify or extend the color and bacteriological shelf life of ready-to-eat fresh meat. For example, U.S. Patent 4,683, 139 describes a method for intensifying and maintaining the color of fresh meat for up to two weeks. The method uses direct additives that include phosphate salts, ascorbic acid, or alkali metal salts, and a sequestering agent, such as citric acid, in combination with a modified packing atmosphere. This patent, and references cited herein, refers to stabilizing the color of fresh meat that is caused by the presence of oxygen. Several patents also describe the use of pressurized gases as a means to treat meat before packing, in order to intensify and stabilize the preferred red color. The patent 6,716,464 describes the use of oxygen gas in this manner. Again, these methods emphasize the importance of the red color of fresh meat. Other methods that actively exchange the packing atmosphere to cause the color of the meat to change are described in U.S. Patent 5,481, 852 and U.S. Patent 5,989,613. This display life of the packaging formed by these methods is very short and oxygen is used as the agent that causes the color change. Similarly, the method described in US Pat. Nos. 5, 866, 184 and 5,71,1978 uses perforations in the tray or lid of a modified atmosphere gasket to allow a passive entry of oxygen to the surface of the meat in a fair moment anfes of the retail exhibition. U.S. Patents 5,759,650, 5,591, 468 and 4,055,672 describe methods where an outer barrier film layer is removed leaving behind a film permeable layer. When the barrier layer is removed just before the display, atmospheric oxygen diffuses to the surface of the meat, causing the preferred color change. In addition, U.S. Patents 5,989,610, 5,597,599 and 5,342,467 describe the use of a variety of gases and additives. All these methods are attempts to cause and maintain the oxygenated (red) form of the meat pigment for a prolonged period.

US Patents 6,046,243, 5,965,264 and 5,888,528 relate to the encapsulation and subsequent release of biocidal gases for the purpose of retarding, controlling, killing or preventing microbiological contamination. Nitrite and nitric oxide are mentioned in patents as agents to achieve these specific effects. Applications to meat packaging are also mentioned more specifically with respect to chlorine dioxide as the active antibacterial agent. US Patent Application 2004/0137202 discloses a method for coating a contact film surface of a food wrap with ingredients or active agents that perform a variety of side effects or functions. Nitrite is mentioned in this method for a conservation function. further, several patents describe the use of nitrite in the packaging material as a corrosion inhibitor. They include US patents nos. 6,533,962, 6,465, 109, 6,033,599 and 5,281, 471. The American patenle no. 5,271, 471 is a broad description, which also mentions vacuum packing and packaged foods. The above technologies refer to methods to affect the color of meat using passive or active meat treatments with gases or chemicals. Some of these methods also employ physical packaging properties to assist in the transformation of fresh meat color, which include removable barriers, perforations and packaging with multi-layer layers. However, none of these technologies show us anything about selecting the preferred red color of fresh meat using nitrite, nitrate or nitric oxide. Additionally, none of these methods are capable of creating and maintaining the preferred red color of fresh meat in a vacuum package. Therefore, it is desirable to develop a novel packaging format that creates and maintains the red color of the meat food product and has the appearance that most closely resembles the packaging format traditionally offered to the consumer.

BRIEF DESCRIPTION OF THE INVENTION The main objective of the present invention is to cause and maintain the preferred red color on the surface of fresh meat. The color of interest is that normally associated with fresh meat that has been exposed to oxygen to create the oxygenated red pigment form of the meat. The present method accomplishes this objective by using nitrite or nitrate compounds in a packaging form that significantly extends the desirable color of a meat food product. More specifically, the present invention elicits and maintains the preferred red color by using nitrite or nitrate in a manner that allows reaction with the meat myoglobin pigment to form the nitroxymyoglobin as defined herein. The present invention achieves the objectives by creating conditions within the meat food package that allow nitroxymyoglobin to be formed. More specifically, it has been found that when raw meat is exposed to sodium nitrite after vacuum packing in a barrier film, its color changes from red to brown in minutes. However, surprisingly and unexpectedly after a period (1-5 days), the color changes back to bright red. Thus, during this period the predominant pigment on the meat surface changes from oxymyoglobin to metmyoglobin to nitroxymyoglobin. This is because the elimination of oxygen and reduction of metmyoglobin allows the formation of nitroxymyoglobin. The vacuum that is applied during the packing step is not able to remove the oxygen that is absorbed on the surface of the meat, because it was bound in the heme pocket of the myoglobin complex. However, the OCR and MRA of the meat are able to remove this oxygen and reduce the remaining metmyoglobin pigments. It may take several days to allow enough time for this change to occur. Once the methyoglobin pigments are reduced, the nitroxymyoglobin pigments come back to dominate and the color on the product surface of the meat changes to the preferred bright red. Another objective of the present invention is to create conditions that allow nitroxymyoglobin to form on the visible surfaces of the meat without spreading through the thickness of the meat. More specifically, a nitrite or nitrate is sprayed onto or incorporated into the packaging film which forms the sealing layer for the film which is positioned directly on and in contact with the food product. The amount of nitrite to affect efficient conversion of surface deoxymyoglobin to nitroxymyoglobin is related to the concentration of myoglobin molecules that are naturally present in the meat product being packaged. This amount varies greatly between types of meat with beef and lamb being older than pork and poultry. Additionally, there are variations in the concentration of myoglobin molecule between individual animals and their age, sex or breed. The individual muscle type and killing conditions additionally affect the speed and efficiency of the conversion of myoglobin molecules. In this way, the present invention is used to cause the formation of nitroxymyoglobin only on the surface that is seen of the fresh meat, leaving the center of the product in its natural myoglobin state. Specifically, the desired depth of improved color penetration provided by the method is preferably less than about 10 mm (0.375 in), and more preferably less than about 6 mm (0.25 in). Numerous other objects, features and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings illustrate the best mode currently envisaged for practicing the present invention. In the drawings: FIG. 1 is an isometric view of a package incorporating the packaging film containing a nitrogen oxide; FIG. 2A is a cross-sectional view of the packaging film of FIG. 1, wherein the nitrogen-containing compound is sprayed onto the film; FIG. 2B is a cross-sectional view of the emaque film of FIG. 1, where nitrogen oxide is incorporated in the film; and FIG. 3 is an isometric view of a vacuum package incorporating the packaging film of the present invention.DETAILED DESCRIPTION OF THE INVENTION The non-denatured nitric oxide myoglobin complex (crude) is of greater importance for the packaging method and film of the present invention. The current scientific teachings describe the "nitric oxide methyoglobin" as the pigment that is formed from the exposure of raw meat to nitrite. Little research has been done on the reduced form of this pigment. The terminology for the pigment is inconsistent. Researchers refer to it as "nitric oxide myoglobin", "nitrosomyoglobin" or "nitrosylhemocromagen" among others. In order to avoid confusion, in this writing the non-denatured and reduced form of the nitric oxide myoglobin complex will be referred to as nitroxymyoglobin. As mentioned previously, the surface that is seen of untreated fresh meat is actually the combination of three forms of myoglobin. The pigments on the surface and the subsurface contribute to the color. When the meat is exposed to the atmosphere, the oxymyoglobin dominates the relative percentage of the pigments and the color is a bright red. When raw fresh meat is exposed to nitric oxide, metmyoglobin dominates the surface and the color is brown. However, below the surface, the flesh color is dull red and in the nucleus the color is bright red. The perceived color of meat treated with nitrite is a combination of four pigments that include nitroxymyoglobin. If oxygen is not present and metmyoglobin is reduced to deoxymyoglobin, the nitroxymyoglobin form will begin to outperform the other three forms. The conditions have to be correct for all the metmyoglobin to be reduced. The results of experiments with the method of the present invention suggest that the color of nitroxymyoglobin is the same as oxymyoglobin and carboxymyoglobin. Thus, when nitroxymyoglobin is the predominant form of myoglobin pigment on the surface of meat, the perceived color is bright red. Referring now to the drawings, in which like reference numerals designate like parts throughout the description, a food package according to the present invention, such as a tray, is illustrated in FIG. 1 generally as 10. The package 10 can have any desired shape depending on the size and configuration of the food product 12 having a surface that looks 100 to be contained therein. In accordance with this invention, the method can be advantageously employed with any tissue-containing myoglobin or hemoglobin and is of particular relevance to allmenium products collected from: livestock, such as, beef, pork, veal, lamb, mutton, chicken or turkey; game animals, such as, deer, quail, duck; and fish, fishery products or seafood. The phrases "meat food product" or "food product" used throughout this application refer to any of the types of meat referred to above. Meat can be in a variety of forms including primary, suppressive and retail cuts as well as ground, shredded or mixed. Additionally, the package 10 can be formed of any number of suitable materials, such as foam and plastic materials, which are well known for use in the formation of food packages or trays 10. In fact, the film alone can be used to pack the food by means of a bag or bag, which is vacuum packed around the meat and the film can be shrinkable with heat or not. In a particular preferred embodiment, the food product 12 is a meat, such as fresh red meat having an upper meat surface 13a, and opposed bottom surface (not shown) connected by a side wall surface of continuous meat 13b, which It is packaged by a film according to the present invention. In a preferred package, the food is vacuum packed in a tray, such as packing tray 10, which includes a bottom wall 14, a pair of side walls 16 extending upwardly from the bottom wall 14 and a pair of end walls 18 extending upwardly from the bottom wall 14 and they are connected to the side walls 16. The respective walls 14, 16 and 18 forming the packing tray 10 form an enclosure 20 within which the food product 12 can be positioned. The food product 12 is retained within the packaging tray 10 by a packaging film 22 positioned on the food product 12 and tray 10 and secured at each end to the tray 10. The packaging film 22 can be secured to the tray. 1 0 in any suitable manner, such as by heat shrink, heat seal, an adhesive or any other suitable method. Referring now to FIGS. 2A and 2B, the packaging film 22 can be formed from any suitable packaging material and preferably at least generally transparent, and can be formed to have one or more layers. In a preferred embodiment, the film 22 includes a number of layers to allow the film 22 to operate movably for its intended purposes. In a particularly preferred embodiment, the packaging film 22 includes an inner sealing layer 24 having a meat contact surface 25 and an outer layer 26. Additionally, one or more internal layers 28a and 28b can be incorporated into the packaging film 22. The invention contemplates the use of films having 1, 2, 3, 4, 5, 6, 7, 8, 9 or more layers. The sealant layer 24 includes an amount of a nitrogen oxide, a nitrite or a nitrate compound that is used to control the color displayed of the food product 12. Then the nitrate or nitrite compound 30 is applied to or incorporated into the formation of the layer 24 and optionally layers 26 and 28. The compound 30 can be applied to the meat contact surface 24 of layer 24 or incorporated in the sealant layer 24 in any conventional manner, as long as it is uniformly dispersed over the surface 25 of layer 24 and / or through full layer 24 to allow any length of film 22 incorporating layer 24 to include approximately similar amounts of compound 30 within sealing layer 24 for uniform transfer to the meat via the surface 25. In the embodiment where the compound 30 is incorporated within the sealing layer 24, the thickness of the sealing layer 24 is adjusted to optimize it migration of the compound 30 from the layer 24 on contact with the upper and lateral surfaces 13a and 13b of food product 12. The thicknesses of layer and / or amount of compound 30 for layer 24 can be adjusted in order to vary the speed of the migration of compound 30 out of layer 24, as desired. In addition, the film 22 can also be formed with a layer of adhesive 34 disposed between the layers 24 and 28 of the film 22. The adhesive 34 can contain the nitrogen-containing compound 30 in order to release the compound 30 through the layer 24. in a controlled manner depending on the materials used to form layer 24.

EXPERIMENTAL PHASE The packaging film 22 of this invention was developed using experiments in which a variety of chemicals were sprayed onto raw meat prior to vacuum packing. The chemicals used were various reducing agents and oxidizing agents, which were tested in an attempt to affect the myoglobin reducing activity (MRA) and oxygen consumption rate (OCR) of the raw meat. The objective was to stabilize the respiratory conditions of the meat in order to delay the oxidation of myoglobin after exposure to oxygen. The commonly used meat additives were also evaluated. The chemicals included a variety of phosphates, sulfites, acids and alkalis, salts, different forms of ascorbic acid, antioxidants, oxygen sequestering agents, plant extracts such as rosemary extract and others that are beyond the reach of, and not necessarily related to, with this description. In the course of these experiments, sodium nitrite and sodium nitrate were tested. It was found that very small amounts of nitrite or nitrate affected the color of vacuum packed meat. More specifically, when nitrite was coated on the interior contact film surface of a vacuum package, the color turned brown immediately after evacuating the oxygen from the surface seen. However, unexpectedly and surprisingly, in some experiments the preferred red color gradually displaced the brown color and remained stable for several months. As a result of the test performed, it is believed, without wanting to bind to a belief, that nitric oxide (NO) gas forms as a result of the reduction of nitrite in the package and this gas affects the color of the meat food product. It is believed that nitric oxide gas has a similar effect on florescence as carbon monoxide gas. The trials where the meat food products had contact with nitrite found that the color florescence occurs only in the absence of oxygen. It is the small initial amount of residual oxygen that causes the initial darkening of the food product. It was found 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, it took five days for the red color to fully develop. The freshness of the muscle and the specific cut also affect this "bloom time". In addition, when a poor barrier film is used for the packaging material, the time necessary to achieve the desired bloom is prolonged. This is because the oxygen migrates through the film causing and maintaining the brown or dark color of the meat inside.

In efforts to shorten the flowering time, prolonged vacuum times were used during the packing of the food product. It was observed that when a high level of vacuum was applied, the freshness time decreased. With higher vacuum levels, it was also observed that when the food product surface was sprayed, sprayed or otherwise coated with a water-based nitrite solution, the freshness time could be reduced to about 60 hours. When the nitrite solution was atomized, sprayed or otherwise applied on the inner surface of the package and allowed to dry before packing, the bloom time was reduced to approximately 48 hours. Additionally, it was observed that the general blooming time is shorter for pigs than for res. It took less than 24 hours for pork. The intensified pig (pork with approximately 10% or less of the mixture of water, salt and added phosphate) exhibited a shorter flowering time than the non-intensified pig. The beef that was more than 20 days postmortem seemed to require the longest flowering time of up to 72 hours. On the other hand, the 10-day postmortem res blossomed in 24 hours. This illustrated that the higher oxygen consumption rate of fresher meat is important to minimize the flowering time. The red color developed by the application of nitrate or niíraío in this way is very stable and does not turn brown during cooking. The addition of uncontrolled nitrite or nitrate can be a problem since a visually perceptible "well-cooked" cooked indication is difficult to achieve when the nitric oxide gas (or material that changes color) penetrates intact muscle or ground beef to depths that almost reach the center of the individual portion. Therefore, it is important to control the level of nitrite used, so that only enough is used to achieve a very shallow penetration through the color effect (thought to be caused by the penetration of nitric oxide) from the surface that is See the food product. As the depth of the nitric oxide gas penetration increases, the internal color is no longer affected by the firing temperatures that normally change the brown or gray color. When this occurs, it is not possible to cook the product to the normal appearance of a well-cooked level. In this way, it is important to minimize the amount of nitrite exposure to the surface that is seen from the meat. This objective can be achieved by adding nitrite to the contact surface 32 of the sealing layer 24 or the packaging film 22. After vacuum packing, the film 22 contacts the visible surface 100 of the food product 12. The nitrite of the Film surface 24 is dissolved in the meat juices and decomposed into nitric oxide to achieve the desired result. Better results occur when the level of nitrite is controlled, so that only enough nitric oxide is released to affect the pigments within the surface 100 of the food product 12. The level of nitrite required for this result is less than one tenth (1/10) of the nitrite commonly used for curing. In fact, it is part of the central point of the present method to controllably deliver only enough nitric oxide to affect the surface seen 100 of the meat 12. The nitrite levels normally associated with curing are so high that their effect on color It lasts after cooking. In a preferred embodiment, the level of nitrite that can be used in the present inventive method is so small that in most modalities it is not analytically detectable as nitrite or nitrate in the finished product by commonly used test methods. Additionally, the amount is insufficient to effectively cure the complete product 12. More specifically, in one example of the present invention, 0.635 cm (0.25 in) of beef that was exposed to the film containing the appropriate level of nitrite was tested for nitrite. An important observation is that after short (approximately 48 hours) and long (approximately 7-10 days) exposure periods, no nitrite was measured in the meat (minimum detection level = 2.0 ppm). In this way, a very small amount of sodium nitrite is necessary for its desired effect. Although the preferred penetration depth of nitrite is approximately 0.25 in (~ 6 m), it is also acceptable for nitrite to penetrate deeper into the surface that is seen at a maximum of approximately 0.375 in (~ 10 mm). In previous studies when the nitrite was coated on the film surface, concentrations of levels greater than 20 ppm were observed. At these levels, the nitrite seemed to penetrate the surface that looks very deeply. When cooking, it was not possible to reach a level of appearance of odor of "well cooked" meat. The pink color created from nitroxymyoglobin was present in the core of the carte cut. These trials evaluated the film that contacted both sides of the meat cut. Subsequent evaluations with a tray containing no nitrite on the meat contact surface still found a significant depth of penetration when higher nitrite levels were evaluated. Nevertheless, when the 20,000 ppm sealing film was used in the skin pack package, the penetration was less than 0.476 cm (3/16 in). It was found that at this level, the subsequent cooking performance is similar to the control after 30 days of refrigerated storage before cooking. Both the core and the surface of the meat darkened during cooking. A thin layer of pink often remains between the surface and the core. The preferred modality of this method is to use the treated film 22 for a 10S vacuum package as shown in FIG. 3. During vacuum packing all the air is removed from the interior of the package 10 ', so that the film 22 intimately counted the upper surface 13a and side surface 13b, i.e. the surface that is seen 100 of the meat 12. Better results are achieved when the contact packing film 22 effectively prevents the ingress of oxygen from the atmosphere after packing. This is because small amounts of oxygen accelerate unacceptable discoloration as previously described. In this way, it is desirable to minimize the exposure time for raw meat to oxygen during the cutting or milling processes that occur prior to packing. The residual oxygen that was absorbed on the surface of the meat during the cutting and grinding operations is eliminated by the postmortem respiratory activities of the raw meat tissue. Because it takes time for this to happen, the method works best when the nitrite solution in the juices of the meat occurs gradually. It was found that incorporating the nitrite compound 30 into the thin polymer sealant layer 24 of a multilayer packaging film 22 gave better results than coating or spraying the nitrite compound 30 on the interior film surface 24, where all the composite 30 is immediately available to the surface seen 100. In one embodiment of the invention, encapsulating the nitrite compound 30, or otherwise protecting it so as to control or retard the release of nitric oxide, is contemplated as beneficial to the present method. One of the best-looking types of vacuum packaging is referred to in the industry as a "skin pack." This type of packaging generally uses a rigid tray that supports the product. The transparent top film is formed around the product during the vacuum packing processes. The thin film forms a skin around the surface that looks complete with the product. It seems as if there is no film on the surface of the product. In this way, an excellent appearance of fresh meat can be achieved when this method is used with a skin packaging film.

It is contemplated that the oxygen barrier trays with or without the nitrate or nitrate containing surfaces may be employed with packaging films according to the present invention. The oxygen barrier tray can keep the fresh purple color in the flesh to the tray contact surface, which will bloom red after unwrapping and exposing it to oxygen or the tray may contain nitrite or nitrate on its surface as is done with the inventive movie. Another application of the present method is to use it with the vacuum packing of cured processed meats, such as ham, sausages, sausage and hot dogs. They are most commonly vacuum packed with barrier films to maintain their characteristic color. This color is much more stable than fresh meat and normally lasts more than 60 days. When color fading occurs, it is attributable to an oxidation of the nitrosohemacrome pigment. This most likely occurs due to the suppression of residual nitrite and the entry of very small amounts of oxygen through the packaging film. The present method advantageously maintains a residual nitrile level in the film 22 for the meat contact surface, thereby extending the life of the color. To control the velocity and amount of nitric oxide gas that is released from the inner film surface after packing, impregnating or permeating the nitrite or nitrate compound 30 in the polymer comprising the film contact surface layer 24, would allow a 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 of sodium nitrite incorporated in the surface layer 24 (based on the weight of the surface layer 24). It was found that even the lowest amount of nitrite tested induced the preferred red color formation in the food product. In addition, different types of food products showed different results with different levels of nitrite present in film 22. For example, the pig showed the best results with a film having 10,000 ppm of nitrite, when the beef had the best results with a level of nitrite of 20,000 ppm in the film 22. In this way, the level of nitrite needed in the film 22 to produce the desirable and stable color is related to the level of myoglobin present in the food product. Although the description of the present invention has been described with respect to nitrite, it will be appreciated that the contemplated use of the invention of a sodium or potassium salt of nitrite or nitrate or mixtures thereof and these commonly available materials or nitrogen oxides less common, can be usefully employed in the present invention. Preferably, the surface of the film will have 0.01 mg per 6.4516 cm2 (per square inch) or less, and more preferably 0.0077 mg per 6.4516 cm2 (per square inch) or less, of the nitrogen oxide agent, e.g., nitrite, to avoid undesirably deep penetration of the agent into a meat during contact. This amount minimizes the mist to produce a benignly transparent package. In a beneficial way, the film containing nitrogen oxide will have good optical properties and will be transparent. Advantageously, the film of preference will have a haze value of 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 have at least 0.0008 mg per 6.451 6 cm2 (per square inch) and beneficially at least 0.0016 mg per 6.4516 cm2 (per square inch) in a transferable amount, in order to effect an adequate color change within 96 hours after contacting an uncooked meat in a vacuum-sealed oxygen barrier environment. Advantageously, for use with beef, an amount of at least 1 ppm (based on the weight of the beef) available on the surface brought with niirite or nitrate from the film can be advantageously used. Similarly, for pork only 0.5 ppm (based on pig weight) can be used for a similar effect. It has been found that the film containing 10,000 ppm (0.106 mg per 6.4516 cm2 (per square inch)) of nitrite (in the form of sodium nitrite) after 48 hours, will be made available to transfer 0.0017 mg per 6.4516 cm2 (per inch) square) to the surface of meat. At 20,000 (0.21 1 mg / 6.4516 cm2 (per square inch)), 0.0077 mg / 6.4516 cm2 (per square inch) is available for transference in 48 hours. Although the description of the above invention refers to its application to fresh red meat, this method also offers benefits when applied to fresh fish. More specifically, when the film and packing method is applied to fresh vacuum packed fish, it improves its bacteriological safety. Currently, the safety of a fresh low-oxygen fish package is at greater risk than a high-oxygen or oxygen-permeable package, because the low-oxygen package creates conditions that favor the growth of certain bacteria, such as Clostridium botulinum. The packaging of higher oxygen content is preferred for this reason and is currently mandatory by regulatory agencies. However, the presence of increased levels of oxygen also allows bacteria that grow faster to degrade the product more quickly. Nitrite or nitrate and nitric oxide gas inhibit the ability of the bacterium Clostridum to produce its toxin. Thus, its presence on the surface of a vacuum package reduces this risk and prolongs bacteriological shelf life for fish. Food products, such as pork, beef, etc., which have been intensified also work well with the method and film of the present invention. More specifically, common enhancement ingredients that include antioxidants such as rosemary extract and eritorbate accelerate the decomposition of nitrite to nitric oxide. Other ingredients in these types of enhancements, such as sodium phosphate, help stabilize the myoglobin pigment and increase the oxygen consumption rate of meat tissues. Various alternative embodiments of the present invention are contemplated as falling within the scope of the following claims which point in particular and distinctly claim the matter in question with respect to the invention.

Claims (27)

1. CLAIMS 1 . A food packaging film to be used to create and stabilize a desirable color on a surface that is seen of a food product containing crude myoglobin without detrimentally affecting the color of the subsurface of the food product, the film comprising: a) a contact layer of food capable of contacting the food product maintained inside a package formed with the film; and b) an effective amount of a nitrogen oxide-containing compound applied to the food count layer and capable of interacting with the food product containing myoglobin to produce the desirable color.
2. 2. The packaging film of claim 1, wherein the food packaging film is an oxygen barrier.
3. 3. The packaging film of claim 1, wherein the nitrogen oxide-containing compound forms nitric oxide when in contact with the food product.
4. 4. The packaging film of claim 3, wherein the nitrogen oxide-containing compound is a nitrate.
5. 5. The packaging film of claim 4, wherein the compound concomiting ni- ogen oxide is a sodium nitrite.
6. 6. The packaging film of claim 1, wherein the nitrogen oxide-containing compound is present in an amount sufficient to affect the surface seen of the food product.
7. 7. The packaging film of claim 6, wherein the nitrogen oxide-containing compound is applied to the surface of the food contact layer.
8. 8. The packaging film of claim 6, wherein the nitrogen oxide-containing compound is incorporated into the feed-in-food layer.
9. 9. The packaging film of claim 1, further comprising at least one additional layer positioned on the food contact layer.
10. 10. The packaging film of claim 9, wherein the food contact layer is an adhesive. eleven .
11. The packaging film of claim 10, wherein the at least one additional film layer is disposed in the food contact layer.
12. 12. The packaging film of claim 1, wherein the film is adapted to vacuum pack the food article.
13. 13. A food packaging container comprising: a) a tray adapted to hold a food article in it; and b) a film positioned on the tray to hold the food article therein, the film including an effective amount of a nitrogen-containing compound and adapted to be in contact with the food article held within the tray.
14. 14. The food packaging container of claim 13, wherein the film is used to vacuum pack the food item in the tray and substantially eliminate the presence of oxygen between the film and the tray.
15. 15. The food packaging container of claim 13, wherein the nitrogen-containing compound is applied to the tray.
16. 16. A method for packaging a food article to prolong a desirable appearance for the food article, the method comprises the steps of: a) providing a film including a nitrogen oxide and b) contacting the film with the food article to form a package for the article food The method of claim 16, further comprising the step of evacuating oxygen from between the film and the food article after contacting the film with the food article. The method of claim 17, further comprising the step of introducing other gases or gas mixture between the film and the food article after evacuating the oxygen. The method of claim 16, wherein the step of providing the film having the nitrogen oxide comprises the steps of: a) providing a packaging film; and b) apply the nitrogen oxide to the film. 20. The method of claim 1 9, wherein the step of applying the nitrogen oxide to the film comprises permeating the film with the nitrogen oxide. twenty-one . The method of claim 1, wherein the step of applying the nitrogen oxide to the film comprises applying the nitrogen oxide to the film in an amount sufficient to affect the surface seen of the food article. 22. The method of claim 18, wherein the step of applying the nitrogen oxide to the film comprises applying the nitrogen oxide to a contact surface of the film, which contacts the food article. 23. The method of claim 16, further comprising the step of evacuating oxygen from between the film and the food article before contacting the film with the food article. The method of claim 16, further comprising the step of treating the food article with the nitrogen oxide before contacting the film with the food article. 25. A method for creating and stabilizing a desirable color in a food product, the method comprising the step of contacting a surface that is seen of the food product with an effective amount of a nitrogen-containing compound. 26. The method of claim 25, wherein the step of contacting the surface that is seen comprises releasing the nitrogen-containing compound into contact with the food product in a controlled manner. 27. A vacuum packaged meat comprising an uncooked meat product packaged in a multilayer polymeric film, having a first polymeric oxygen barrier layer and a second surface layer containing a nitrogen oxide, selected from a group consisting of of sodium nitrate, sodium nitrate, potassium nitrite, potassium nitrate and mixtures thereof, in an amount sufficient to transfer between 0.0008 and 0.016 milligrams per 6.4516 cm2 (per square inch) to the uncooked meat product within 96 hours.