The present invention relates to a method of preserving the freshness and color life of meat products, and also to a method of matching the color life to the microbial life of the meat products.
An increasingly popular method of providing fresh meat in the retail environment is case-ready packaging, whereby the meat product is processed and packaged in a retail package by a meat packer that may be quite distant from the retail facility. Case-ready packaging is especially appealing to large retail organizations that specialize in highly efficient logistics and supply chain management, because it enables them to provide an otherwise relatively perishable product in their stores with minimum investment in special infrastructure. The challenge for these organizations, even with their world-class distribution capability, is shelf life. The time between processing fresh meat until the product is sold to the consumer averages over 10 days, and may be as high as 21 days.
It is quite difficult to provide good quality and good looking fresh meat products to consumers with a shelf life as high as 21 days. The dual challenges for shelf life of this magnitude are microbial growth and product color. Microbial growth is related to the geometric multiplication of spoilage bacteria that causes fresh meat products to spoil. Product color is related to the shift in color spectrum of the myoglobin constituents in fresh meats.
Meat scientists have researched the effect of the oxidative states of myoglobin on the color of fresh meat. Fully fresh, recently processed meat is dominated by the presence of oxymyoglobin, which has oxygen attached to the myoglobin base molecule and is bright pink-red in color in the so-called “bloomed” state. If fresh meat is placed in an oxygen-depleted environment, the oxygen is lost and the myoglobin turns to the deoxymyoglobin state, which takes on a deep purple-brown color. This product may still be very fresh, but its color is not familiar, and consumers may be reluctant to purchase product with this appearance. As fresh meat ages, the myoglobin progressively turns to the metmyoglobin state that is characterized by the brown color familiarly associated with old and possibly spoiled meat.
In the ongoing efforts to provide increased shelf life fresh meats, it has been learned that various modified atmosphere case-ready packages may be employed to mitigate the previously mentioned effects of microbial growth and color loss. Microbial growth in fresh meat can be suppressed by the use of atmospheres that spoilage bacteria do not thrive in. For example, many spoilage bacteria are aerobic, so they don't multiply well in an oxygen-deprived atmosphere. Case-ready modified atmosphere packaging (MAP) with a low oxygen atmosphere can delay spoilage in fresh meats. Unfortunately, low oxygen packaging causes the color of the fresh product to be dominated by deoxymyoglobin, with its characteristic purple-brown color. Case-ready MAP products with a high oxygen atmosphere can delay spoilage due to a high concentration of carbon dioxide, and the oxygen concentration extends the oxymyoglobin state to maintain the preferred pink-red color state. High oxygen MAP is generally more successful for delivery of case-ready fresh meat in the retail distribution marketplace than low oxygen MAP, but even with its better characteristics, it is generally limited to less than 10 days of shelf life.
In the ongoing search for methods of extending the shelf life of fresh meats, scientists have discovered that carbon monoxide is capable of extending color life. Carbon monoxide reacts with myoglobin in a way very similar to the way it reacts with hemoglobin—the basic oxygen and carbon dioxide carrying constituent in blood. Carbon monoxide has high affinity for the oxygen-carrying site in both hemoglobin and myoglobin, and binds approximately 240 times more strongly than oxygen or carbon dioxide. In the case of hemoglobin, a concentration of carbon monoxide may lead to death because the body may be deprived of necessary oxygen. In the case of myoglobin, the presence of carbon monoxide forms a special state of myoglobin labeled carboxymyoglobin. Carboxymyoglobin has a color spectrum that is nearly identical to oxymyoglobin, and causes meat to look identical to fresh meat that is dominated by the presence of oxymyoglobin. Meat processors and retailers have discovered that carbon monoxide as a MAP additive, even in low concentrations, lessens the color loss in fresh meat for significantly extended periods of time. A popular MAP atmosphere called “low oxygen” or “low ox” includes 70% nitrogen, 29.6% carbon dioxide and 0.4% carbon monoxide, with very minute levels of oxygen (if any) being present.
Iradiation technology has been utilized for decades as a means for reduction of micro flora in fresh and frozen food products. Applications of irradiation have included reduction of harmful food borne pathogens such as E. coli 0157:H7, Salmonella, and Listeria, as well as common spoilage bacteria for extension of shelf life. Irradiation has more recently been employed in systems and processes that package the irradiated meat products with modified atmosphere packaging to extend shelf life for case-ready retail applications.
While the combination of these technologies has generally extended the shelf life of fresh meat products, the desired 21 days (or more) of shelf life has been elusive, primarily due to color life limitations. What is needed is a process for extension of both the shelf (microbial) life and color life of fresh meat products.
The microbial life and color life of fresh meat products are extended by placing fresh meat in a tray, sealing the fresh meat in the tray in an atmosphere that excludes oxygen and contains carbon monoxide, and applying ionizing radiation to the tray containing the fresh meat. The color life of the fresh meat in the tray may be controlled (such as to be less than or equal to the microbial life) by employing a permeable element and an impermeable element to seal the fresh meat in the tray. The impermeable element is removed at a time after ionizing radiation has been applied, so that the atmosphere that excludes oxygen and contains carbon monoxide is exchanged for ambient atmosphere, resulting in predictable limiting of color life of the fresh meat.
In order to extend both the shelf life and color life of fresh meat products, a process according to the present invention is employed. This process is illustrated in
In one particular embodiment, the low oxygen, carbon monoxide-containing modified atmosphere is introduced into the tray containing the fresh meat product and is allowed to dwell there for an extended period of time before the fresh meat product is irradiated. Allowing the carbon monoxide of the modified atmosphere gas to dwell sets the color of the fresh meat product to a greater extent than would otherwise occur, so that a higher dose of irradiation can be applied to the fresh meat product without causing discoloration.
In some embodiments, it is desirable to control the length of the color life of fresh meat products to ensure that the color life fails before the microbial life, so that consumers have a reliable indication that the product may be spoiled and should not be consumed. Experience has shown that carbon monoxide MAP packaging may be so successful at preserving the color life of packaged fresh meat products such as ground beef, that in some cases these products may have a very wholesome looking fresh appearance, but may in fact be quite spoiled. This situation is addressed as discussed below with respect to
The tray of
An alternate process for the tray of
Referring now to
The tray of
In addition, the tray of
In another embodiment, the meat product may be placed in tray 1, permeable lid film 12 may be applied to tray 1, and gas impermeable bag 10 may enclose tray 1 and permeable lid film 12 before ionizing radiation is applied (in an atmosphere that excludes oxygen, as mentioned above). Again, in this embodiment, no oxygen is present in the irradiation environment because of the fact that the atmosphere in tray 1 (sealed by permeable lid film 12) is a low oxygen blend that substantially excludes oxygen, the atmosphere within gas impermeable bag 10 is filled with a low oxygen blend that substantially excludes oxygen, and the irradiation environment around the product is also controlled to exclude oxygen in some embodiments.
This configuration is ideal for extended storage life of fresh meat products. When it is time for the fresh meat product to be placed on the retail shelf, the enclosing impermeable bag is removed. At this point, the modified atmosphere begins to diffuse across the permeable lid film and the concentrations of MAP gas are exchanged with ambient air until they reach ambient air concentrations. Of particular interest is the concentration of carbon monoxide, as well as the characteristics of the fresh meat that has been exposed to the carbon monoxide. Research has shown that the carbon monoxide binds to myoglobin in a manner very similar to the way it binds to hemoglobin in blood. While the affinity of carbon monoxide to hemoglobin is approximately 240 times greater than oxygen, this binding is reversible with a half-life of approximately 4.5 hours.
In retail applications, it is desirable for the rate of release of carbon monoxide to be controlled to match the required display shelf life expected while being coordinated with the spoilage life of the fresh meat product. For example, in relatively high volume retail environments such as super stores, it may be desirable to have a week of display shelf life. To achieve one week of display shelf life, the gas permeable lid film should be selected so that enough carbon monoxide is exchanged with the ambient atmosphere that the carbon monoxide level is below the color maintenance level 7 days after the enclosing impermeable bag is removed. Other retail applications such as convenience stores may require longer display shelf life, such as two weeks. In such applications, the gas permeable lid film should be selected with a lower permeability to cause a slower exchange of carbon monoxide with the ambient atmosphere.
As in the tray configuration of
Management of shelf life expiration of fresh meat products processed and distributed according to the present invention is essentially the same as any other perishable product with a posted expiration date. The expiration date affixed or printed on the trays is determined by the microbial life of the product. The color life of fresh meat in storage according to the present invention is generally longer than the microbial storage life of the product until the gas impermeable bag or film is removed. Once this step is completed, the color life of the product is very predictably limited so that the color of the product becomes a meaningful indication of the state of freshness of the product. Specifically, in many embodiments it is desirable for the permeability of the permeable film to be selected in a way that provides a color life of a particular length of time, and for the dose of ionizing radiation to be selected in a way that provides a microbial life of a particular length of time that has a known relationship to the color life. For example, in some embodiments, it is desirable for the color life to match the microbial life. In other embodiments, it is desirable for the color life to be slightly less than the microbial life. The permeability of the permeable film over the tray and the dose of ionizing radiation are controllable variables that allow this correspondence between microbial life and color life to be achieved.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
This application claims the benefit of U.S. Provisional Application No. 60/781,529 filed Mar. 10, 2006 for EXTENDED STORAGE LIFE FRESH MEAT by B. Dalziel, V. Kennedy and S. Koenck. The aforementioned U.S. Provisional Application No. 60/781,529 is hereby incorporated by reference in its entirety.
Number | Date | Country | |
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60781529 | Mar 2006 | US |