CA2049760A1 - Ultra-high temperature pasteurization process - Google Patents
Ultra-high temperature pasteurization processInfo
- Publication number
- CA2049760A1 CA2049760A1 CA 2049760 CA2049760A CA2049760A1 CA 2049760 A1 CA2049760 A1 CA 2049760A1 CA 2049760 CA2049760 CA 2049760 CA 2049760 A CA2049760 A CA 2049760A CA 2049760 A1 CA2049760 A1 CA 2049760A1
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- Prior art keywords
- food product
- product
- approximately
- meat
- temperature
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
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Landscapes
- Meat, Egg Or Seafood Products (AREA)
- Food Preservation Except Freezing, Refrigeration, And Drying (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method of preserving raw food products, such as beef, poultry and fish, is provided. The method comprises the steps of simultaneously exposing all surfaces of the food product to a high temperature preferably between approximately 700°C-1200°C for a time period sufficient to effectively denature proteins and destroy microorganisms on the entire surface of the product to a substantially uniform depth of less than about 4.0 mm. After heat pasteurization of the product surface, the product is rapidly cooled at a relatively low temperature of about minus 50°C for approximately two minutes. The product is then vacuum packaged and stored in a refrigerated environment. Neat products preserved in accordance with the method of this invention enjoy a refrigerated shelf life of up to 120 days without surface discoloration or unacceptable spoilage by microorganisms. During the heating step, the product also may be placed on a grill to produce an appetizing grill pattern on the product to facilitate cooking in a microwave oven after storage.
A method of preserving raw food products, such as beef, poultry and fish, is provided. The method comprises the steps of simultaneously exposing all surfaces of the food product to a high temperature preferably between approximately 700°C-1200°C for a time period sufficient to effectively denature proteins and destroy microorganisms on the entire surface of the product to a substantially uniform depth of less than about 4.0 mm. After heat pasteurization of the product surface, the product is rapidly cooled at a relatively low temperature of about minus 50°C for approximately two minutes. The product is then vacuum packaged and stored in a refrigerated environment. Neat products preserved in accordance with the method of this invention enjoy a refrigerated shelf life of up to 120 days without surface discoloration or unacceptable spoilage by microorganisms. During the heating step, the product also may be placed on a grill to produce an appetizing grill pattern on the product to facilitate cooking in a microwave oven after storage.
Description
2~97~
BACKGROUND OF THE INVENTION
The present invention relates to methods o~
preserving food products and, more particularly, to a method of pressrving a raw food product by utilizing high temperature pasteurization of the product surface.
In the course of processing meat food products, such as beef, poultry and fish, the product often is pre-cut into meal size portions, such as steaks, roasts or the like. After pre-cutting, if the product is not frozen by conventional method3 for long term storage, it is refrigerated and usually packaged in some form for shipment to a customer and ultimate sale to the public. Unless the food product is intended to be sold and cooked promptly, certain precautions must be taken to adequately preserve the product. Depending upon the particular packaging and storage methods employed, the storage or so-called shelf life of the product can vary widely.
It is well known that meat food products tend to spoil during refrigerated storage and eventually must be reprocessed or thrown away if they are not used within a ~pecified time period. If the internal muscle of the meat is sterile, as is the case with most retail cuts of meat, spoilage generally occurs as a surface phenomenon in khe form of loss of bloom and growth of microorganisms. Loss of bloom occurs when the fresh, healthy cherry red (oxymyoglobin) appearance of the meat is lost and replaced by sur~ace discoloration. For example, the development of myoglobin (purple) and metmyoglobin ~brown) will discolor meat products by giving them an 7 ~ ~
unappetizing appearance. The growth of microorganisms occurs when the meat has been stored too long.
Typical ones include both mesophilic and psychrotrophic spoilage microorganisms, and vegetative pathogens (e.g. Salmonella, Listeria and Clostridium).
The number of such microorganisms increases in proportion to the initial load and the length of storage.
As a general rule, meat tends to become discolored before it is totally spoiled by the growth of baaterial microorganisms. Indeed, according to one study, 50% to 75% surface discoloration was found to have occurred in fresh beef steaks after only four days of retail display (using four primal cut packaging/pre-cutting treatments). Discoloration is a very undesirable characteristic of meat products.
In fact, according to one survey, consumers will adversely discriminate against fresh beef steaks when greater than 25% of the product surface is discolored.
Recent consumer concerns about pathogenic bacteria in raw animal tissues suggssts the likelihood of further discrimination against discolored meat, as well as consumer fears about the safety and wholesomeness of raw products.
Under these circumstances, retail fresh meat establishments have very few alternatives when disposing of discolored meat. Some alternatives include discarding it as waste, reducing the price of the product, retrimming it and/or processing it into another form, such as ground beef. All of these alternatives, however, involve a loss of value, especially when higher priced cuts are involved.
7 ~ (3 Over the years, various approaches have been taken to attempt to increase the storage life and to maintain the quality of fresh meat, such as beef, poultry, fish and other food products. One approach involves packaging the meat product in an oxygen permeable film after pre-cutting, and then storing the packaged product in a refrigerated environment.
Unfortunately, this approach results in a relatively short storage life of only about 2-3 days and historically has resulted in 10% - 20% waste.
Another prior approach involves packaging the meat product in an oxygen impermeable film followed by refrigsration. This approach, utilizing an oxygen impermeable film, increases the storage life of the meat product by comparison to the approach using oxygen permeable film. In general, fish products usually have a storage life of one week using this approach, poultry products usually have a storage life of two to three weeks, and beef products generally have a storage life of three to four weeks.
Storage in oxygen impermeable film, however~
is not without its disadvantages. When oxygen impermeable film is used, it is usually used in conjunction with a vacuum packaging technique. As a result of this packaging technique, the food product usually displays an unappetizing purple (myoglobin) color. The growth of anaerobic microorganisms also occurs. For example, lactic acid bacteria can become dominant on vacuum packaged meats, even when they are stored at 1 4C, according to one study. When vacuum pacXaging is employed, flavor intensity also tend~ to suffer. It also has been attributed to reducing the ~497~
juiciness and tenderness of the meat.
Also, in vacuum packaging, it has been found that primal beef cuts tend to lose ~uality after 45 60 days of storage. Of course, these conclusions depend on the storage temperature, the degree of evacuation within the packaging, the permeability of the packaging film, the initial load and composition o~ the primal. In some cases, the bacterial sounts of retail cuts of beef have had a signifi~ant corre-lation with the bacterial counts of vacuum packagedprimals, as reported in one study.
Accordingly, there has existed a definite need for a method of preserving raw meat products, such as beef, poultry, fish and other food products, that extends the shelf life of the product while maintaining a high standard of quality. There further has existed a definite need for a method of preserving food products that, in addition to controlling the growth of surface microorganisms, provides an attractive appearance to the food product, both at the time of purchase by the ultimate customer and after proper cooking. The present invention satisfies these needs and provides further related advantages.
SUMMARY~ OF THE INVENTION
The presPnt invention provides a method of preserving food products, and especially fresh raw meat products, such as beef, poultry and fish. The method involves simultaneously exposing all surfaces of the food product to a very high temperature for a short period of time, followed by rapid cooling and vacuum packaging ~or storage in a refrigerated 2~97~
environment. Meat products preserved in accordance with the method of this invention have been found to enjoy a refrigerated shelf life of up to 120 days without surface discoloration or spoilage from micro organisms. The method of the present invention furthermore is intended to be simple to practice, reliable in use and relatively inexpensive to implement.
More particularly, the method includes placing the food product in a high temperature oven capable of producing a substantially constant and uniform temperature preferably in the range of approximately 700C to 1200C surrounding khe food product. In the preferred embodiment, the product is supported in the oven on a ceramic grill adapted to produce an attractive and appetizing grill pattern on the product. Depending upon the temperature of the oven, the product preferably is exposed to the high temperature from anywhere between approximately 5-60 seconds. Of course, the specific time period of exposure will vary depending upon the temperature of the oven and the type of meat product to be pre-served~ Thus, under some circumstances, exposure may be for less than 5 seconds or for more than 60 seconds. Whatever temperature and time period are selectedl however, they must be sufficient to cause substantially uniform denaturation of proteins and destruction of microorganisms on all surfaces of the product without cooking the interior portion of the product.
Optimal temperature ranges are 900C-1100C
for 10-30 seconds. When a meat product is exposed to 20ll~9 ~3 these high temperatures, microorganisms on the surface of the product are destroyed, and proteins are denatured, while producing an attractive and appetizing appearance to the product. This pasteurization of the product surfacP (i.e., denaturation of proteins and destruction of microorganisms), is substantially uniform and preferably occurs to a depth of approximately 0.5 mm.
- 4.0 mm.
After the surface of the meat product has been fully pasteurized by the fir~t heating step of the method, the product is removed from the oven compartment and quickly cooled for a predetermined period of time at a relatively low temperature. In the preferred embodiment, the product is cooled for approximately two minutes at a temperature of about minus 50C. In one aspect of the invention, a carbon dioxide chiller, containing either solid or liquid carbon dioxide, is used. This step rapidly cools the product surfaces, so that the product may be handled and quickly transferred to the next processing step. Cooling of the product also prevents it from continuing to cook after it has been removed from the high temperature oven. By stopping further cooking, the pasteurized surface area of the product is reliably kept within a desired range of thickness of between about 0.5 mm. to 4.0 mm. Moreover, internal temperatures of the raw, uncooked center of the product are kept below about 15C.
Next, the food product is packaged in a wrapping suitable for storing the product in a refrigerated environment. In this aspect of the invention, the product preferably is packaged in a 2~9 r~Q
~lexible, oxygen impermeable film that may be formed and wrapped around the product utilizing vacuum packaging techniques. Other packaging techniques may be used, but vacuum packaging is the most advantageous for long term storage.
As quickly as possible after the product has been vacuum packaged, it is stored in a re~rigerated environment. When the product is to be cooked within 120 days after being preserved, then storage in a refrigerated environment of about 4-5C is appropriate. However, when long term storage and preservation in excess of 120 days is needed, the packaged product should be stored in a freezer at below 0C, and preferably at about minus 21C.
Meat products preserved in accordance with the method of this invention result in a raw product with an attractive, cooked appearance. Hence, the natural catheptic enz~mes inside the raw meat muscle remain active to tenderize the meat and allow the product to continue to wet age without surface spoilage. Thus, the product tends to have lower shear values after refrigerated storage for 10-20 days by comparison with raw, unpreserved products which must be consumed within 2-3 days and therefore have higher shear values when stored in the same refrigerated environment.
In addition, heat pasteurization o~ the product surface forms a barrier to moisture that effectively seals the product surface and stabilizes its appearance. ~his has particular advantages when the preserved product is to be cooked using microwave energy. It is believed that the barrier to moisture 2~97~
will result in a more even h0at distribution when the product is cooked in a microwave oven. Stabilization of the product surface also provides the product with an attractive and appetizing appearance, both before and after cooking~ Furthermore, discoloration of the product surface is prevented, such as when oxymyoglobin (cherry red) is reduced to form myoglobin (purple), oxidized to form metmyoglobin (brown), or denatured by heat to form globin ferrihemochrome ~grey), all of which are unattractive and unappetizing.
Pasteurization of the product surface controls the growth of vegetative pathogens on a raw meat product. If cooling and vacuum packaging after heat pasteurization are conducted under sterile conditions, consumers could be provided with a raw meat product free of vegetative pathogens, such as Salmonella and Listeria. Moreover, both mesophilic and psychrotrophic spoilage microorganismæ are controlled by the mPthod of this invention. In one test, meat sample6 treated by the method were held in a refrigerated environment at about 4.4C for 120 days without any significant deleterivus ahanges in quality. Also, it is possible to heat pasteuriz~ the surfaces of both retail cuts of meat and large carcass primals, with the only limiting factor being the size of the oven.
Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.
2~7~l~
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate the invention. In such drawings:
FIG. 1 is a front pexspective view of a high temperature oven employed in the method of the present invention:
FIG. 2 is a front perspective view of a ceramic grill for supporting the food product inside.
the oven;
FIG. 3 is a perspective view of a low temperature chiller employed in the method of the present invention;
FIG. 4 is a perspective assembly view, showing the food product being inserted into a flexible package for storage;
FIG. 5 is a perspective view of a refrigeration device, showing packaged food products in refrigerated storage after they have been preserved by the method of this invention;
FIG. 6 is a perspective view of a microwave oven for cooking the food product after it has been removed from its packaging; and FIG~ 7 is a cross-sectional elsvational view of the food product after it has been preserved by the method of the present invention, and before it has been cooked.
~ o ~
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is embodied in a method of preserving food products and, as pre6entl~Y
practiced and contemplated, the method has particular application in preserving fresh, raw meat products, such as beef, poultry and fish. As used herein, the term "meat" refers to animal tissue used as food.
Hence, the category of meat includes land animals such as beef and pork, aquatic animals such as fish and shellfish, and winged animals such as chickens and turkeys. While the method of the present invention presently has focused its application on meat products, such as the meat product referred to by the reference numeral 10 in the exemplary drawings, it is contemplated that the method also will have use in connection with the preservation of other, non-animal food products, such as vegetables and other food products subject to spoilage by bacterial microorganisms.
The accompanying drawings illustrate various items of equipment used to practice the method of this invention. FIG. 1 is a perspective view of an ultra high temperature oven 12 used in the first step of the method. As explained in more detail below, this first step involves simultaneously exposing all surfaces of the food product 10 to a very high temperature, preferably in the range of approximately 700C to 1200C. To this end, the oven 12 includes a power unit 14 having a conventional on-off switch 16 and appropriate controls 18 to monitor and regulate the temperature inside an oven compartment 20 mounted on top of the power unit. Inside the oven compartment ~97~,~
20, one or more electric coils 22 are mounted on the interior walls 24 to create heat and to raise the temperature inside the compartment to a selested level.
In the preferred embodiment, the oven compartment 20 is capable of reaching temperatures at least as high as 300C, and preferably as high as 1300C, and of being accurately regulated to maintain a constant temperature of anywhere between these ranges. 5ince a conventional oven, such as a household oven, generally does not reach temperatures higher than about 260C ~500F), the term "high temperature" means a temperature above about 300C.
Free access to the inside of the oven compartment 20 is provided by an opening 26 in the front of the compartment. It is noted that the opening 26 will have a door (not shown) to control fluctuations in temperatuxes. The door is not shown for purposes of clarity in the drawings. Opening and closing the door during loading and unloading requires about 5 seconds. The opening 26 provides relatively unrestricted access to the food product 10, which is especially important when the oven 12 is operated at high temperatures, such as 1000~C and higher, where it is necessary to insert and then remove the ood product in a matter of only 10-20 seconds.
High temperature ovens 12, such as the one described above, are commercially available from Barnstead/Thermolyne of Dubuque, Iowa 52001.
Presently, a Type 47900 furnace from Thermolyne is being used. It will be understood, however, that other types of high temperature ovens or furnace~ may ~97~
be used to practice the first step of the method. For example, gas or other non-electric heating sources can be used to provide the necessary high temperatures.
Larger ovens ~or high volume processing also may be used. The use of high temperature ovens having high velocity air streams to heat the surface of the product also could be feasible to carry out the high temperature treatment even faster. Whatever high temperature oven is selected, however, it should be capable of supplying heat at a substantially constant and uniform temperature surrounding the food product inside the oven compartment.
As mentioned above, the first step in the method of preserving the food product 10 is to simultaneously expose all surfaces of the product to a very high temperature, preferably in the range of about 700C to 1200C. The specific temperature and time period will vary depending on the type of meat product 10 to be preserved. Specific examples of this first step of the process, setting forth specific temperatures and time periods of exposure for various types of meat products, are described in greater detail below. Whatever temperature and time period are selected, however, they must be sufficient to cause substantially uniform denaturation of proteins and destruction of microorganisms on all surfaces of the product 10. This is accomplished by placing the food product 10 inside the oven compartment 20 at a specified temperature for a predetermined amount of time. Optimal temperature ranges are 900C -1100C
for 10-30 seconds. When exposed to these high temperatures inside the oven compartment 20, microorganisms on the surface of the product 10 are destroyed, and proteins are denatured. This 2~97~
pasteurization of the product surface is subskantially uniform and occurs to a depth of approximately 0.5 mm.
- 4.0 mm. for meat produats.
In the preferred embodiment, the meat product 10 is supported inside the oven compartment 20 on a grill 28. As shown in FIG. 2, the grill 28 comprises a plurality of spaced, cylindrical bars 30 arranged in a parallel, horizontal manner by two support members 32 and 34. When the cylindrical bars lo 30 are constructed from ceramic material, a non-stick gril~ing surface is provided. Ceramic materials ~or grills 28 of this type are available from Coors Ceramics in Golden, Colorado 80401. A non-stick grilling surface is preferred 80 that the process will not be delayed or interrupted by the meat 10 adhering to the very hot grill.
When the meat product 10 i8 placed on the grill 28 inside the oven compartment 20, contact with the cylindrical bars 30 of the grill burns a pattern o~ spaced, parallel lines 36 on the meat, much like the grill pattern of a steak on an outdoor barbecue.
If the meat product lO is turned or flipped over on the grill 28 during the heating process, then both sides of the product will display the grlll pattern 36. This aspect of the method is mostly cosmetic in nature and provides an appetizing and attractive appearance ko the meat product lO. Contact with the grill 28 also provides a charcoal-cooked flavor to the product lO. By increasing or decreasing the area of contact between the meat product 10 and the grill 28, the intensity of the charcoal flavor can be controlled. This can be an important ~actor in ¢onsumer acceptability. The application of the grill ~97~
pattern does not, however, have any significant effect on the pasteurization process of the invention.
High temperature treatment of the product surfaces has several important advantages. Chief among them is the uni~orm pasteurizakion of the product surface which destroys microorganisms, such as mesophilic and psychrotrophic spoilage organisms and vegetative pathogens. This surface pasteurization extends to a uniform depth of approximately 0.5 mm. -4.0 mm. As shown in FIG. 7, the treated areacomprises a thin hand 38 over the entire surface area of the product lO. Since the heat is applied constantly and uniformly, all surfaces of the product are pasteurized, even when an uneven product surface is involved. Pasteurization of the product surface in accordance with the method of this invention also effectively denatures proteins on the product surface, such as oxymyoglobin (cherry red).
By denaturing these proteins, the development of myoglobin (purple) and metmyoglobin (brown), unappetizing pigments that discolor the product surface, is prevented. Further processing and refrigerated storage of the meat product lO in accordance with the method of this invention provides a refrigerated shalf life of up to 120 days. This is about twice the shelf life of meat products preserved by prior methods.
After the surface of the meat product lO has been fully pasteurized by the first step of the method, the product is removed from the oven compartment 20. The next step of the method is to quickly cool the product 10 for a predetermined period of time at a relatively low temperature. In the pre-2~ 76~
ferred embodiment, the product 10 is cooled forapproximately two minutes at a temperature of about minus 50c. One known device capable of producing such low temperatures includes a carbon dioxide chiller 40, as illustrated in FIG. 3. The chiller 40 may use either solid or liquid carbon dioxide.
Chillers of this type are commercially available from Liquid Air Corp. of Phoenix, Arizona 85029. Other low temperature cooling devices also may be used.
When the meat product 10 is removed from the oven compartment 20, its sur~aces are extremely hot.
The subsequent step of cooling the product at minus 50C rapidly cools the product surfaces so that the product may be handled and quickly transferred at a low temperature for further processing. The cooling step also prevents the product 10 from continuing to cook after it has been removed from the oven compartment 20~ By stopping further cooking, the pasteurized surface area of the product 10, as represented by the thin band 38 of FIG. 7, is reliably kept within a range o~ thickness of between about 0.5 mm. to 4.0 mm.
After cooling, the food product 10 is packaged in a package or wrapping 42, such as that shown in FIG. 4, suitable for storing the product in a refrigerated environment. In the preferred embodiment, the product 10 is packaged in a flexible plastic film that may be formed and wrapped around the product 10. The film is preferably oxygen impermeable, and vacuum packaging techniques are used to withdraw all air from inside the package 42 once the package has been sealed. Vaauum packaged products 44 held in refrigerated storage have a shelf life of 2~7~
about 120 days. Other packaging technigues may be used, but vacuum packaging is the most advantageous for long term storage. Alt~rnative packaging for shorter term storage includes a conventional styrofoam tray with an oxygen permeable plastic overwrap (not shown). This alternative form of packaging has been found to provide a shelf life of between 14-21 days.
As soon as possible after the product 10 has been vacuum packaged, the packaged product 44 is stored in a refrigerated environment, such as the exemplary household refrigerator 46 illustrated in FIG. 5. The refrigerator 46 is shown with two cooling compartments, one being a freezer 48 maintained at a temperature below minus 21C, and the other being a cooling compartment 50 maintained at a temperature of between about 4-5C. When the product 10 is to be cooked within 120 days after being preserved by the present method, then storage in the cooling compartment 50 is appropriate. When long term preservation in excess of 120 days i~ needed, the packaged product 44 is stored in the freezer 48.
During the high temperature pasteurization of the product surface, the internal temperature of the meat 10 is raised to only about 15-16C (where the meat sample is approximately 1.25-1.30 cm. thick).
Immediately after heat pasteurization of the surface, the product 10 is rapidly cooled for about two minutes in the carbon dioxide chiller 40 discussed above. As a result of this rapid heating and cooling process, the interior portion 52 of the product 10 surrounded by the thin, pasteurized urface band 38, remains completely raw and uncooked. (FIG. 7). This allows ~9r4t~0 the natural catheptlc enzymes, inside the muscle, to be unaf~ected by the preservakion method. During storage in the cooling compartment 5n, these enzymes are not denatured and are allowed to remain active to tenderize the meat lo. Hence, the product lo continues to wet age, without surface spoilage as in the case of dry, untreated meat.
Tests have shown that shear values of both vacuum packaged raw loin steaks treated in accordance with tha method of this invention, and vacuum packaged, untreated raw loin steaks, were found to have decreased after ten days of storage at 4.4C. In this xegard, shear value is the force in kilograms required to shear a 1.30 cm. core of cooked tissue.
In tests conducted 10 and 20 days after refrigerated storage at 4.4C, both the untreated and preserved steaks were cooked in a microwave ovPn to 74C.
Thereafter, the shear values for each were determined.
The results of the tests indicated that preserved steaks treated by the method of this invention had lower shear values than the untreated steaks. For example, the shear value of the untreated steak was 10.25 kg. at inception, 7.5 kg. after 10 days, and 6.4 kg~ after 20 days. The shear values of the preserved steak were 9.75 kg. at inception, 3.9 kg. after 10 days and 4.1 kg. after 20 days. Thus, another advantage of the method of this invention is that it tends to provide a more tender product 10 after cooking.
The pasteurized surface of the meat product 10 also forms a barrier to moisture and effectively seals the product surface. This prevents the 108s 0 water and dehydration of the product 10. During ~n~97~
subsequent cooking of the product lo~ it is believed that khis barrier to moisture will result in a more even heat distribution when microwave energy i5 used as the cooking medium. It is further contemplated that the preservation method of this invention also may improve the fl~vor of meat products cooked by microwave energy.
In accordance with the inventionl meat products 10 preserved by the foregoing method have been found to enjoy a shelf life of up to 120 days when stored in the cooling compartment 50 at 4-5OC
after vacuum packaging. The success of the method is believed to be attributable to the high temperature pasteurization step, followed by rapid cooling and vacuum packaging. This heat treatment, ~ollowed by rapid cooling and exclusion of oxygen from the final packaged product 44, seems to effectively control microbial growth and chemical changes in the product 10 during refrigerated storage. As a result, spoilage and surface discoloration of the meat 10 are retarded for up to 120 days.
Another advantage provided by the preservation method of this invention includes the stabilization of the product surface. Since denaturation of surface proteins is in the range of about 0.5 mm. - 4.0 mm., the resulting meat product is a raw product with a cooked appearance.
Physical changes in the meat surface are minimized due to the relatively short exposure of the meat to the very high oven temperatures.
The surface appearance is ~urther enhanced by placing the meat 10 in contact with the ceramic 2~49r~b~f,,~
grill 28 during the heating step, which provides the meat surface with an attractiva and appetizing yrilled pattern 36. ~hus, consumers desiring to use a microwave oven 54, such as the one shown in FIG. 6, to cook higher priced cuts of meat can do so, since meak preserved by the present method will have an attractive and appetizing appearance, both before and after cooking. The use of cooking plates having microwave interactive materials, such as susceptors, which become very hot when exposed to microwave energy, are not needed to brown the product 10.
Moreover, the uneven and unapp~tizing pink and grey appearance of raw meats cooked in a microwave oven is eliminated due to surface stabilization by the present preSQrvation method.
The method of this invention also can be utilized to maintain and perhaps increase the value of discolored retail cuts of meat which have lost bloom, but have not yet spoiled from microbial growth. Thus, the present method provides an economical and safe means for converting a discolored fresh cut of meat into a fresh steak with an attractive and appetizing appearance. The preserved product 10 is also provided in a convenient, vacuum packaged form 44. This is especially useful for convenient storage of the product 10 in a household refrigerator 46 and for subse~uent cooking in a microwave oven 54 or other cooking appliance.
In addition to its use on fresh raw meats, the method also can be used to pasteurize the surface of pre-cooked meats/ to control spoilage and improve appearance. For example, white poultry meat that has been cooked in water has no browned or cooked ~9~0 appearance on its surface. The method of this invention advantageously allows surface browning of the cooked poultry product, while also pasteurizing the surface to increase its shelf life.
Specific temperatures and time periods of exposure in the first step of the method will now be dcscribed for various types of meat products 10.
Since this information represents the preferred temperatures and time periods of exposure for specific meat products, it should not be construed in any manner that would limit the scope of application of this invention. Rather, it should be understood that this information is being provided for purposes of example and illustration and not by way of limitation.
The following table represents a compilation of test data indicating preferred temperatures and time periods of exposure for beef, turkey and fish (Tilapia), in both the fresh and frozen states. The far left column indicates the type of meat product.
The next column to the right bears the heading "E/T/S," where E - total time period of exposure in seconds, T = thickness in millimeters of the denatured product surface corresponding to the thin band shown in FIG. 7, and S = the percentage of shrinkage o~ the product after exposure to high temperature. The remaining columns to the right reflect the temperature in C to which the product was exposed. Time periods of exposure (E) were selected to result in a desirable appearance of the meat product after heat treatment (i.e., without undercooking or burning of the surface).
o Product E~T/S 1100C 1000C 900C 800C _ 700C
E (sec)15 20 25-30 30-35 40-45 Fresh T (mm)2.2 2.5 2.9-3.1 3~9-3.7 2.8-3.1 Beef S (%)10.311.810.9-12.2 8.9-9.4 6.9-7.5 E (sec)20 40 70 60 60-80 Frozen T (mm)2.2 2.3 2.0 2.3 1.8-2.3 Beef S (%)14.018.3 18.2 11.3 11.3-10.8 .
E (sec) 10 15 20 40 60 Fresh T (mm)2.12.2 2.3 3.2 4.2 Turkey S (%)6.5 7.5 7.4 9.5 9.2 _ E (sec) 20 35 40-60 60 60-80 Frozen T (mm)1.61.7 1.0-1.9 2.1 1.9-2.4 Turkey S (%)10.011.411.3-15.8 10.0 6.8-9.3 . _ _ E (sec) 10 15 20-30 30 40 Fresh T (mm)1.71.7 2.0-3.1 2.3 1.9 Fish S (%)9.712.510.6-16.3 11.9 7.9 . _ _ E (sec) 20 35 60 60 80-100 Frozen T (mm)1.31.9 2.2 2.6 2.8-2.9 Fish S (%)_ 15.217.0 24.2 18.2 16.2-24.2 2~97~
It will be appreciated that higher or lower temperatures and shorter or longer periods of exposure than those set forth above may be utilized. In general, however, lower temperatures and longer periods o~ exposure produce a greater depth o~
denaturation, higher final internal temperatures and greater shrinkage of the meat product 10. Thu~, lower temperatures and longar exposure periods tend to detract from product ~uality. Of course, higher temperaturas and shorter periods of exposure also are possible/ utilizing sophisticated heating equipment.
At this time, however~ exposure periods of less than ~ive seconds have not been attained in view of the time required to physically insert and remove the meat products 10 from the oven 12 shown in FIG. 1.
Moreover, at temperatures approaching 1300C, the edges of the product 10 are more susceptible to burning and creating an undesirable appearance unless the period of exposure is extremely short.
Therefore, it is contemplated that development of appropriate oven technology will snable rapiA, high volume process1ng of meat products 10 in a controlled environment. It is also contemplated that large meat masses may be processed in accordance with the invention, with the size of the oven 12 generally being the only limiting factor. When high processing rates are desired, shorter exposure periods will increase production.
Based on current test results, the best temperature for heat treatment seems to be near 1100C. Exposure periods o~ 5-10 seconds at 1100C
2~7~3 using the equipment illustrated in the accompanying drawing~ produces a fresh meat product 10 with an attractive grilled appearance, with a denaturation depth of less than 1 mm., shrink of less than 11 percent, and a final internal temperature of no greater than about 15C.
From the foregoing, it will be appreciated that the present invention provides a quick and convenient method of preserving food products 10.
After heat pasteurization of the product surface, the product 10 is quickly cooled and then vacuum packaged for convenient refrigerated storage of up to 120 days without sur~ace discoloration or spoilage from microorganisms. When removed from storage, the product 10 is ready for cooking in a microwave oven 54 or other cooking device.
While a particular form of the invention has been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention.
Therefore, it is not intended that the invention be limited, except as by the appended claims.
BACKGROUND OF THE INVENTION
The present invention relates to methods o~
preserving food products and, more particularly, to a method of pressrving a raw food product by utilizing high temperature pasteurization of the product surface.
In the course of processing meat food products, such as beef, poultry and fish, the product often is pre-cut into meal size portions, such as steaks, roasts or the like. After pre-cutting, if the product is not frozen by conventional method3 for long term storage, it is refrigerated and usually packaged in some form for shipment to a customer and ultimate sale to the public. Unless the food product is intended to be sold and cooked promptly, certain precautions must be taken to adequately preserve the product. Depending upon the particular packaging and storage methods employed, the storage or so-called shelf life of the product can vary widely.
It is well known that meat food products tend to spoil during refrigerated storage and eventually must be reprocessed or thrown away if they are not used within a ~pecified time period. If the internal muscle of the meat is sterile, as is the case with most retail cuts of meat, spoilage generally occurs as a surface phenomenon in khe form of loss of bloom and growth of microorganisms. Loss of bloom occurs when the fresh, healthy cherry red (oxymyoglobin) appearance of the meat is lost and replaced by sur~ace discoloration. For example, the development of myoglobin (purple) and metmyoglobin ~brown) will discolor meat products by giving them an 7 ~ ~
unappetizing appearance. The growth of microorganisms occurs when the meat has been stored too long.
Typical ones include both mesophilic and psychrotrophic spoilage microorganisms, and vegetative pathogens (e.g. Salmonella, Listeria and Clostridium).
The number of such microorganisms increases in proportion to the initial load and the length of storage.
As a general rule, meat tends to become discolored before it is totally spoiled by the growth of baaterial microorganisms. Indeed, according to one study, 50% to 75% surface discoloration was found to have occurred in fresh beef steaks after only four days of retail display (using four primal cut packaging/pre-cutting treatments). Discoloration is a very undesirable characteristic of meat products.
In fact, according to one survey, consumers will adversely discriminate against fresh beef steaks when greater than 25% of the product surface is discolored.
Recent consumer concerns about pathogenic bacteria in raw animal tissues suggssts the likelihood of further discrimination against discolored meat, as well as consumer fears about the safety and wholesomeness of raw products.
Under these circumstances, retail fresh meat establishments have very few alternatives when disposing of discolored meat. Some alternatives include discarding it as waste, reducing the price of the product, retrimming it and/or processing it into another form, such as ground beef. All of these alternatives, however, involve a loss of value, especially when higher priced cuts are involved.
7 ~ (3 Over the years, various approaches have been taken to attempt to increase the storage life and to maintain the quality of fresh meat, such as beef, poultry, fish and other food products. One approach involves packaging the meat product in an oxygen permeable film after pre-cutting, and then storing the packaged product in a refrigerated environment.
Unfortunately, this approach results in a relatively short storage life of only about 2-3 days and historically has resulted in 10% - 20% waste.
Another prior approach involves packaging the meat product in an oxygen impermeable film followed by refrigsration. This approach, utilizing an oxygen impermeable film, increases the storage life of the meat product by comparison to the approach using oxygen permeable film. In general, fish products usually have a storage life of one week using this approach, poultry products usually have a storage life of two to three weeks, and beef products generally have a storage life of three to four weeks.
Storage in oxygen impermeable film, however~
is not without its disadvantages. When oxygen impermeable film is used, it is usually used in conjunction with a vacuum packaging technique. As a result of this packaging technique, the food product usually displays an unappetizing purple (myoglobin) color. The growth of anaerobic microorganisms also occurs. For example, lactic acid bacteria can become dominant on vacuum packaged meats, even when they are stored at 1 4C, according to one study. When vacuum pacXaging is employed, flavor intensity also tend~ to suffer. It also has been attributed to reducing the ~497~
juiciness and tenderness of the meat.
Also, in vacuum packaging, it has been found that primal beef cuts tend to lose ~uality after 45 60 days of storage. Of course, these conclusions depend on the storage temperature, the degree of evacuation within the packaging, the permeability of the packaging film, the initial load and composition o~ the primal. In some cases, the bacterial sounts of retail cuts of beef have had a signifi~ant corre-lation with the bacterial counts of vacuum packagedprimals, as reported in one study.
Accordingly, there has existed a definite need for a method of preserving raw meat products, such as beef, poultry, fish and other food products, that extends the shelf life of the product while maintaining a high standard of quality. There further has existed a definite need for a method of preserving food products that, in addition to controlling the growth of surface microorganisms, provides an attractive appearance to the food product, both at the time of purchase by the ultimate customer and after proper cooking. The present invention satisfies these needs and provides further related advantages.
SUMMARY~ OF THE INVENTION
The presPnt invention provides a method of preserving food products, and especially fresh raw meat products, such as beef, poultry and fish. The method involves simultaneously exposing all surfaces of the food product to a very high temperature for a short period of time, followed by rapid cooling and vacuum packaging ~or storage in a refrigerated 2~97~
environment. Meat products preserved in accordance with the method of this invention have been found to enjoy a refrigerated shelf life of up to 120 days without surface discoloration or spoilage from micro organisms. The method of the present invention furthermore is intended to be simple to practice, reliable in use and relatively inexpensive to implement.
More particularly, the method includes placing the food product in a high temperature oven capable of producing a substantially constant and uniform temperature preferably in the range of approximately 700C to 1200C surrounding khe food product. In the preferred embodiment, the product is supported in the oven on a ceramic grill adapted to produce an attractive and appetizing grill pattern on the product. Depending upon the temperature of the oven, the product preferably is exposed to the high temperature from anywhere between approximately 5-60 seconds. Of course, the specific time period of exposure will vary depending upon the temperature of the oven and the type of meat product to be pre-served~ Thus, under some circumstances, exposure may be for less than 5 seconds or for more than 60 seconds. Whatever temperature and time period are selectedl however, they must be sufficient to cause substantially uniform denaturation of proteins and destruction of microorganisms on all surfaces of the product without cooking the interior portion of the product.
Optimal temperature ranges are 900C-1100C
for 10-30 seconds. When a meat product is exposed to 20ll~9 ~3 these high temperatures, microorganisms on the surface of the product are destroyed, and proteins are denatured, while producing an attractive and appetizing appearance to the product. This pasteurization of the product surfacP (i.e., denaturation of proteins and destruction of microorganisms), is substantially uniform and preferably occurs to a depth of approximately 0.5 mm.
- 4.0 mm.
After the surface of the meat product has been fully pasteurized by the fir~t heating step of the method, the product is removed from the oven compartment and quickly cooled for a predetermined period of time at a relatively low temperature. In the preferred embodiment, the product is cooled for approximately two minutes at a temperature of about minus 50C. In one aspect of the invention, a carbon dioxide chiller, containing either solid or liquid carbon dioxide, is used. This step rapidly cools the product surfaces, so that the product may be handled and quickly transferred to the next processing step. Cooling of the product also prevents it from continuing to cook after it has been removed from the high temperature oven. By stopping further cooking, the pasteurized surface area of the product is reliably kept within a desired range of thickness of between about 0.5 mm. to 4.0 mm. Moreover, internal temperatures of the raw, uncooked center of the product are kept below about 15C.
Next, the food product is packaged in a wrapping suitable for storing the product in a refrigerated environment. In this aspect of the invention, the product preferably is packaged in a 2~9 r~Q
~lexible, oxygen impermeable film that may be formed and wrapped around the product utilizing vacuum packaging techniques. Other packaging techniques may be used, but vacuum packaging is the most advantageous for long term storage.
As quickly as possible after the product has been vacuum packaged, it is stored in a re~rigerated environment. When the product is to be cooked within 120 days after being preserved, then storage in a refrigerated environment of about 4-5C is appropriate. However, when long term storage and preservation in excess of 120 days is needed, the packaged product should be stored in a freezer at below 0C, and preferably at about minus 21C.
Meat products preserved in accordance with the method of this invention result in a raw product with an attractive, cooked appearance. Hence, the natural catheptic enz~mes inside the raw meat muscle remain active to tenderize the meat and allow the product to continue to wet age without surface spoilage. Thus, the product tends to have lower shear values after refrigerated storage for 10-20 days by comparison with raw, unpreserved products which must be consumed within 2-3 days and therefore have higher shear values when stored in the same refrigerated environment.
In addition, heat pasteurization o~ the product surface forms a barrier to moisture that effectively seals the product surface and stabilizes its appearance. ~his has particular advantages when the preserved product is to be cooked using microwave energy. It is believed that the barrier to moisture 2~97~
will result in a more even h0at distribution when the product is cooked in a microwave oven. Stabilization of the product surface also provides the product with an attractive and appetizing appearance, both before and after cooking~ Furthermore, discoloration of the product surface is prevented, such as when oxymyoglobin (cherry red) is reduced to form myoglobin (purple), oxidized to form metmyoglobin (brown), or denatured by heat to form globin ferrihemochrome ~grey), all of which are unattractive and unappetizing.
Pasteurization of the product surface controls the growth of vegetative pathogens on a raw meat product. If cooling and vacuum packaging after heat pasteurization are conducted under sterile conditions, consumers could be provided with a raw meat product free of vegetative pathogens, such as Salmonella and Listeria. Moreover, both mesophilic and psychrotrophic spoilage microorganismæ are controlled by the mPthod of this invention. In one test, meat sample6 treated by the method were held in a refrigerated environment at about 4.4C for 120 days without any significant deleterivus ahanges in quality. Also, it is possible to heat pasteuriz~ the surfaces of both retail cuts of meat and large carcass primals, with the only limiting factor being the size of the oven.
Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.
2~7~l~
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate the invention. In such drawings:
FIG. 1 is a front pexspective view of a high temperature oven employed in the method of the present invention:
FIG. 2 is a front perspective view of a ceramic grill for supporting the food product inside.
the oven;
FIG. 3 is a perspective view of a low temperature chiller employed in the method of the present invention;
FIG. 4 is a perspective assembly view, showing the food product being inserted into a flexible package for storage;
FIG. 5 is a perspective view of a refrigeration device, showing packaged food products in refrigerated storage after they have been preserved by the method of this invention;
FIG. 6 is a perspective view of a microwave oven for cooking the food product after it has been removed from its packaging; and FIG~ 7 is a cross-sectional elsvational view of the food product after it has been preserved by the method of the present invention, and before it has been cooked.
~ o ~
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is embodied in a method of preserving food products and, as pre6entl~Y
practiced and contemplated, the method has particular application in preserving fresh, raw meat products, such as beef, poultry and fish. As used herein, the term "meat" refers to animal tissue used as food.
Hence, the category of meat includes land animals such as beef and pork, aquatic animals such as fish and shellfish, and winged animals such as chickens and turkeys. While the method of the present invention presently has focused its application on meat products, such as the meat product referred to by the reference numeral 10 in the exemplary drawings, it is contemplated that the method also will have use in connection with the preservation of other, non-animal food products, such as vegetables and other food products subject to spoilage by bacterial microorganisms.
The accompanying drawings illustrate various items of equipment used to practice the method of this invention. FIG. 1 is a perspective view of an ultra high temperature oven 12 used in the first step of the method. As explained in more detail below, this first step involves simultaneously exposing all surfaces of the food product 10 to a very high temperature, preferably in the range of approximately 700C to 1200C. To this end, the oven 12 includes a power unit 14 having a conventional on-off switch 16 and appropriate controls 18 to monitor and regulate the temperature inside an oven compartment 20 mounted on top of the power unit. Inside the oven compartment ~97~,~
20, one or more electric coils 22 are mounted on the interior walls 24 to create heat and to raise the temperature inside the compartment to a selested level.
In the preferred embodiment, the oven compartment 20 is capable of reaching temperatures at least as high as 300C, and preferably as high as 1300C, and of being accurately regulated to maintain a constant temperature of anywhere between these ranges. 5ince a conventional oven, such as a household oven, generally does not reach temperatures higher than about 260C ~500F), the term "high temperature" means a temperature above about 300C.
Free access to the inside of the oven compartment 20 is provided by an opening 26 in the front of the compartment. It is noted that the opening 26 will have a door (not shown) to control fluctuations in temperatuxes. The door is not shown for purposes of clarity in the drawings. Opening and closing the door during loading and unloading requires about 5 seconds. The opening 26 provides relatively unrestricted access to the food product 10, which is especially important when the oven 12 is operated at high temperatures, such as 1000~C and higher, where it is necessary to insert and then remove the ood product in a matter of only 10-20 seconds.
High temperature ovens 12, such as the one described above, are commercially available from Barnstead/Thermolyne of Dubuque, Iowa 52001.
Presently, a Type 47900 furnace from Thermolyne is being used. It will be understood, however, that other types of high temperature ovens or furnace~ may ~97~
be used to practice the first step of the method. For example, gas or other non-electric heating sources can be used to provide the necessary high temperatures.
Larger ovens ~or high volume processing also may be used. The use of high temperature ovens having high velocity air streams to heat the surface of the product also could be feasible to carry out the high temperature treatment even faster. Whatever high temperature oven is selected, however, it should be capable of supplying heat at a substantially constant and uniform temperature surrounding the food product inside the oven compartment.
As mentioned above, the first step in the method of preserving the food product 10 is to simultaneously expose all surfaces of the product to a very high temperature, preferably in the range of about 700C to 1200C. The specific temperature and time period will vary depending on the type of meat product 10 to be preserved. Specific examples of this first step of the process, setting forth specific temperatures and time periods of exposure for various types of meat products, are described in greater detail below. Whatever temperature and time period are selected, however, they must be sufficient to cause substantially uniform denaturation of proteins and destruction of microorganisms on all surfaces of the product 10. This is accomplished by placing the food product 10 inside the oven compartment 20 at a specified temperature for a predetermined amount of time. Optimal temperature ranges are 900C -1100C
for 10-30 seconds. When exposed to these high temperatures inside the oven compartment 20, microorganisms on the surface of the product 10 are destroyed, and proteins are denatured. This 2~97~
pasteurization of the product surface is subskantially uniform and occurs to a depth of approximately 0.5 mm.
- 4.0 mm. for meat produats.
In the preferred embodiment, the meat product 10 is supported inside the oven compartment 20 on a grill 28. As shown in FIG. 2, the grill 28 comprises a plurality of spaced, cylindrical bars 30 arranged in a parallel, horizontal manner by two support members 32 and 34. When the cylindrical bars lo 30 are constructed from ceramic material, a non-stick gril~ing surface is provided. Ceramic materials ~or grills 28 of this type are available from Coors Ceramics in Golden, Colorado 80401. A non-stick grilling surface is preferred 80 that the process will not be delayed or interrupted by the meat 10 adhering to the very hot grill.
When the meat product 10 i8 placed on the grill 28 inside the oven compartment 20, contact with the cylindrical bars 30 of the grill burns a pattern o~ spaced, parallel lines 36 on the meat, much like the grill pattern of a steak on an outdoor barbecue.
If the meat product lO is turned or flipped over on the grill 28 during the heating process, then both sides of the product will display the grlll pattern 36. This aspect of the method is mostly cosmetic in nature and provides an appetizing and attractive appearance ko the meat product lO. Contact with the grill 28 also provides a charcoal-cooked flavor to the product lO. By increasing or decreasing the area of contact between the meat product 10 and the grill 28, the intensity of the charcoal flavor can be controlled. This can be an important ~actor in ¢onsumer acceptability. The application of the grill ~97~
pattern does not, however, have any significant effect on the pasteurization process of the invention.
High temperature treatment of the product surfaces has several important advantages. Chief among them is the uni~orm pasteurizakion of the product surface which destroys microorganisms, such as mesophilic and psychrotrophic spoilage organisms and vegetative pathogens. This surface pasteurization extends to a uniform depth of approximately 0.5 mm. -4.0 mm. As shown in FIG. 7, the treated areacomprises a thin hand 38 over the entire surface area of the product lO. Since the heat is applied constantly and uniformly, all surfaces of the product are pasteurized, even when an uneven product surface is involved. Pasteurization of the product surface in accordance with the method of this invention also effectively denatures proteins on the product surface, such as oxymyoglobin (cherry red).
By denaturing these proteins, the development of myoglobin (purple) and metmyoglobin (brown), unappetizing pigments that discolor the product surface, is prevented. Further processing and refrigerated storage of the meat product lO in accordance with the method of this invention provides a refrigerated shalf life of up to 120 days. This is about twice the shelf life of meat products preserved by prior methods.
After the surface of the meat product lO has been fully pasteurized by the first step of the method, the product is removed from the oven compartment 20. The next step of the method is to quickly cool the product 10 for a predetermined period of time at a relatively low temperature. In the pre-2~ 76~
ferred embodiment, the product 10 is cooled forapproximately two minutes at a temperature of about minus 50c. One known device capable of producing such low temperatures includes a carbon dioxide chiller 40, as illustrated in FIG. 3. The chiller 40 may use either solid or liquid carbon dioxide.
Chillers of this type are commercially available from Liquid Air Corp. of Phoenix, Arizona 85029. Other low temperature cooling devices also may be used.
When the meat product 10 is removed from the oven compartment 20, its sur~aces are extremely hot.
The subsequent step of cooling the product at minus 50C rapidly cools the product surfaces so that the product may be handled and quickly transferred at a low temperature for further processing. The cooling step also prevents the product 10 from continuing to cook after it has been removed from the oven compartment 20~ By stopping further cooking, the pasteurized surface area of the product 10, as represented by the thin band 38 of FIG. 7, is reliably kept within a range o~ thickness of between about 0.5 mm. to 4.0 mm.
After cooling, the food product 10 is packaged in a package or wrapping 42, such as that shown in FIG. 4, suitable for storing the product in a refrigerated environment. In the preferred embodiment, the product 10 is packaged in a flexible plastic film that may be formed and wrapped around the product 10. The film is preferably oxygen impermeable, and vacuum packaging techniques are used to withdraw all air from inside the package 42 once the package has been sealed. Vaauum packaged products 44 held in refrigerated storage have a shelf life of 2~7~
about 120 days. Other packaging technigues may be used, but vacuum packaging is the most advantageous for long term storage. Alt~rnative packaging for shorter term storage includes a conventional styrofoam tray with an oxygen permeable plastic overwrap (not shown). This alternative form of packaging has been found to provide a shelf life of between 14-21 days.
As soon as possible after the product 10 has been vacuum packaged, the packaged product 44 is stored in a refrigerated environment, such as the exemplary household refrigerator 46 illustrated in FIG. 5. The refrigerator 46 is shown with two cooling compartments, one being a freezer 48 maintained at a temperature below minus 21C, and the other being a cooling compartment 50 maintained at a temperature of between about 4-5C. When the product 10 is to be cooked within 120 days after being preserved by the present method, then storage in the cooling compartment 50 is appropriate. When long term preservation in excess of 120 days i~ needed, the packaged product 44 is stored in the freezer 48.
During the high temperature pasteurization of the product surface, the internal temperature of the meat 10 is raised to only about 15-16C (where the meat sample is approximately 1.25-1.30 cm. thick).
Immediately after heat pasteurization of the surface, the product 10 is rapidly cooled for about two minutes in the carbon dioxide chiller 40 discussed above. As a result of this rapid heating and cooling process, the interior portion 52 of the product 10 surrounded by the thin, pasteurized urface band 38, remains completely raw and uncooked. (FIG. 7). This allows ~9r4t~0 the natural catheptlc enzymes, inside the muscle, to be unaf~ected by the preservakion method. During storage in the cooling compartment 5n, these enzymes are not denatured and are allowed to remain active to tenderize the meat lo. Hence, the product lo continues to wet age, without surface spoilage as in the case of dry, untreated meat.
Tests have shown that shear values of both vacuum packaged raw loin steaks treated in accordance with tha method of this invention, and vacuum packaged, untreated raw loin steaks, were found to have decreased after ten days of storage at 4.4C. In this xegard, shear value is the force in kilograms required to shear a 1.30 cm. core of cooked tissue.
In tests conducted 10 and 20 days after refrigerated storage at 4.4C, both the untreated and preserved steaks were cooked in a microwave ovPn to 74C.
Thereafter, the shear values for each were determined.
The results of the tests indicated that preserved steaks treated by the method of this invention had lower shear values than the untreated steaks. For example, the shear value of the untreated steak was 10.25 kg. at inception, 7.5 kg. after 10 days, and 6.4 kg~ after 20 days. The shear values of the preserved steak were 9.75 kg. at inception, 3.9 kg. after 10 days and 4.1 kg. after 20 days. Thus, another advantage of the method of this invention is that it tends to provide a more tender product 10 after cooking.
The pasteurized surface of the meat product 10 also forms a barrier to moisture and effectively seals the product surface. This prevents the 108s 0 water and dehydration of the product 10. During ~n~97~
subsequent cooking of the product lo~ it is believed that khis barrier to moisture will result in a more even heat distribution when microwave energy i5 used as the cooking medium. It is further contemplated that the preservation method of this invention also may improve the fl~vor of meat products cooked by microwave energy.
In accordance with the inventionl meat products 10 preserved by the foregoing method have been found to enjoy a shelf life of up to 120 days when stored in the cooling compartment 50 at 4-5OC
after vacuum packaging. The success of the method is believed to be attributable to the high temperature pasteurization step, followed by rapid cooling and vacuum packaging. This heat treatment, ~ollowed by rapid cooling and exclusion of oxygen from the final packaged product 44, seems to effectively control microbial growth and chemical changes in the product 10 during refrigerated storage. As a result, spoilage and surface discoloration of the meat 10 are retarded for up to 120 days.
Another advantage provided by the preservation method of this invention includes the stabilization of the product surface. Since denaturation of surface proteins is in the range of about 0.5 mm. - 4.0 mm., the resulting meat product is a raw product with a cooked appearance.
Physical changes in the meat surface are minimized due to the relatively short exposure of the meat to the very high oven temperatures.
The surface appearance is ~urther enhanced by placing the meat 10 in contact with the ceramic 2~49r~b~f,,~
grill 28 during the heating step, which provides the meat surface with an attractiva and appetizing yrilled pattern 36. ~hus, consumers desiring to use a microwave oven 54, such as the one shown in FIG. 6, to cook higher priced cuts of meat can do so, since meak preserved by the present method will have an attractive and appetizing appearance, both before and after cooking. The use of cooking plates having microwave interactive materials, such as susceptors, which become very hot when exposed to microwave energy, are not needed to brown the product 10.
Moreover, the uneven and unapp~tizing pink and grey appearance of raw meats cooked in a microwave oven is eliminated due to surface stabilization by the present preSQrvation method.
The method of this invention also can be utilized to maintain and perhaps increase the value of discolored retail cuts of meat which have lost bloom, but have not yet spoiled from microbial growth. Thus, the present method provides an economical and safe means for converting a discolored fresh cut of meat into a fresh steak with an attractive and appetizing appearance. The preserved product 10 is also provided in a convenient, vacuum packaged form 44. This is especially useful for convenient storage of the product 10 in a household refrigerator 46 and for subse~uent cooking in a microwave oven 54 or other cooking appliance.
In addition to its use on fresh raw meats, the method also can be used to pasteurize the surface of pre-cooked meats/ to control spoilage and improve appearance. For example, white poultry meat that has been cooked in water has no browned or cooked ~9~0 appearance on its surface. The method of this invention advantageously allows surface browning of the cooked poultry product, while also pasteurizing the surface to increase its shelf life.
Specific temperatures and time periods of exposure in the first step of the method will now be dcscribed for various types of meat products 10.
Since this information represents the preferred temperatures and time periods of exposure for specific meat products, it should not be construed in any manner that would limit the scope of application of this invention. Rather, it should be understood that this information is being provided for purposes of example and illustration and not by way of limitation.
The following table represents a compilation of test data indicating preferred temperatures and time periods of exposure for beef, turkey and fish (Tilapia), in both the fresh and frozen states. The far left column indicates the type of meat product.
The next column to the right bears the heading "E/T/S," where E - total time period of exposure in seconds, T = thickness in millimeters of the denatured product surface corresponding to the thin band shown in FIG. 7, and S = the percentage of shrinkage o~ the product after exposure to high temperature. The remaining columns to the right reflect the temperature in C to which the product was exposed. Time periods of exposure (E) were selected to result in a desirable appearance of the meat product after heat treatment (i.e., without undercooking or burning of the surface).
o Product E~T/S 1100C 1000C 900C 800C _ 700C
E (sec)15 20 25-30 30-35 40-45 Fresh T (mm)2.2 2.5 2.9-3.1 3~9-3.7 2.8-3.1 Beef S (%)10.311.810.9-12.2 8.9-9.4 6.9-7.5 E (sec)20 40 70 60 60-80 Frozen T (mm)2.2 2.3 2.0 2.3 1.8-2.3 Beef S (%)14.018.3 18.2 11.3 11.3-10.8 .
E (sec) 10 15 20 40 60 Fresh T (mm)2.12.2 2.3 3.2 4.2 Turkey S (%)6.5 7.5 7.4 9.5 9.2 _ E (sec) 20 35 40-60 60 60-80 Frozen T (mm)1.61.7 1.0-1.9 2.1 1.9-2.4 Turkey S (%)10.011.411.3-15.8 10.0 6.8-9.3 . _ _ E (sec) 10 15 20-30 30 40 Fresh T (mm)1.71.7 2.0-3.1 2.3 1.9 Fish S (%)9.712.510.6-16.3 11.9 7.9 . _ _ E (sec) 20 35 60 60 80-100 Frozen T (mm)1.31.9 2.2 2.6 2.8-2.9 Fish S (%)_ 15.217.0 24.2 18.2 16.2-24.2 2~97~
It will be appreciated that higher or lower temperatures and shorter or longer periods of exposure than those set forth above may be utilized. In general, however, lower temperatures and longer periods o~ exposure produce a greater depth o~
denaturation, higher final internal temperatures and greater shrinkage of the meat product 10. Thu~, lower temperatures and longar exposure periods tend to detract from product ~uality. Of course, higher temperaturas and shorter periods of exposure also are possible/ utilizing sophisticated heating equipment.
At this time, however~ exposure periods of less than ~ive seconds have not been attained in view of the time required to physically insert and remove the meat products 10 from the oven 12 shown in FIG. 1.
Moreover, at temperatures approaching 1300C, the edges of the product 10 are more susceptible to burning and creating an undesirable appearance unless the period of exposure is extremely short.
Therefore, it is contemplated that development of appropriate oven technology will snable rapiA, high volume process1ng of meat products 10 in a controlled environment. It is also contemplated that large meat masses may be processed in accordance with the invention, with the size of the oven 12 generally being the only limiting factor. When high processing rates are desired, shorter exposure periods will increase production.
Based on current test results, the best temperature for heat treatment seems to be near 1100C. Exposure periods o~ 5-10 seconds at 1100C
2~7~3 using the equipment illustrated in the accompanying drawing~ produces a fresh meat product 10 with an attractive grilled appearance, with a denaturation depth of less than 1 mm., shrink of less than 11 percent, and a final internal temperature of no greater than about 15C.
From the foregoing, it will be appreciated that the present invention provides a quick and convenient method of preserving food products 10.
After heat pasteurization of the product surface, the product 10 is quickly cooled and then vacuum packaged for convenient refrigerated storage of up to 120 days without sur~ace discoloration or spoilage from microorganisms. When removed from storage, the product 10 is ready for cooking in a microwave oven 54 or other cooking device.
While a particular form of the invention has been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention.
Therefore, it is not intended that the invention be limited, except as by the appended claims.
Claims (30)
1. A method of preserving a raw, solid food product, comprising the steps of:
(a) simultaneously exposing all surfaces of the food product to a high temperature in excess of about 300°C for a period of time that is only long enough to cause substantially uniform denaturation of proteins and destruction of microorganisms on all surfaces of the food product, thereby maintaining the food product in a substantially raw condition;
(b) rapidly cooling the food product for a predetermined period of time at a relatively low temperature; and (c) packaging the food product in a wrapping suitable for storing the food product in a refrigerated environment.
(a) simultaneously exposing all surfaces of the food product to a high temperature in excess of about 300°C for a period of time that is only long enough to cause substantially uniform denaturation of proteins and destruction of microorganisms on all surfaces of the food product, thereby maintaining the food product in a substantially raw condition;
(b) rapidly cooling the food product for a predetermined period of time at a relatively low temperature; and (c) packaging the food product in a wrapping suitable for storing the food product in a refrigerated environment.
2. The method of claim 1, wherein the high temperature is in the range of approximately 700°C to 1200°C.
3. The method claim 2, wherein the food product is exposed to the high temperature for a time period sufficient to cause substantially uniform denaturation of proteins and destruction of microorganisms on all surfaces of the food product to a depth of less than about 4.0 mm.
4. The method of claim 3, wherein the food product is exposed to the high temperature for a time period of between approximately 5 seconds to 60 seconds.
5. The method of claim 2, wherein the step of cooling the food product includes cooling the food product at approximately minus 50°C for approximately 2 minutes.
6. The method of claim 5, wherein the food product is cooled in a carbon dioxide chiller.
7. The method of claim 5, wherein the step of packaging the food product includes the step of vacuum packaging the food product in an oxygen impermeable wrapping.
8. The method of claim 5, further comprising the step of storing the food product in a refrigerated environment after it has been packaged.
3. The method of claim 8, wherein the step of storing the food product includes storing the food product in a refrigerator or a freezer.
10. The method of claim 8, wherein the refrigerated environment is at a temperature of between approximately 4°C to 5°C.
11. The method of claim 3, wherein the step of exposing the food product to a high temperature includes placing the food product in an oven.
12. The method of claim 11, further comprising the step of supporting the food product on a ceramic grill inside the oven to burn a grill pattern on the product.
13. The method of claim 1, wherein the food product comprises meat, including beef, poultry, fish or other animal tissue used as food.
14. A food product preserved by the method of claim 1.
15. The food product of claim 14, wherein the food product comprises meat, including beef, poultry, fish or other animal tissue used as food.
16. A method of preserving a raw, solid food product, comprising the steps of:
(a) simultaneously exposing all surfaces of the food product to a high temperature for a period of time sufficient to cause substantially uniform denaturation of proteins and destruction of microorganisms on all surfaces of the food product to a depth of less than about 5 mm, (b) rapidly cooling the food product for a predetermined period of time at a relatively low temperature: and (c) packaging the food product in a wrapping suitable for storing the food product in a refrigerated environment.
(a) simultaneously exposing all surfaces of the food product to a high temperature for a period of time sufficient to cause substantially uniform denaturation of proteins and destruction of microorganisms on all surfaces of the food product to a depth of less than about 5 mm, (b) rapidly cooling the food product for a predetermined period of time at a relatively low temperature: and (c) packaging the food product in a wrapping suitable for storing the food product in a refrigerated environment.
17. The method of claim 16, wherein the food product is exposed to a temperature of between approximately 600°C to 1200°C.
18. The method of claim 17, wherein the internal temperature of the food product does not exceed approximately 25°C during the step of simultaneously exposing all surfaces of the food product to a high temperature.
19. The method of claim 16, wherein the food product is fresh beef that is exposed to a temperature of approximately 1,100°C for approximately 15 seconds.
20. The method of claim 16, wherein the food product is fresh poultry or fish that is exposed to a temperature of approximately 1,100°C for approximately 10 seconds.
21. The method of claim 16, wherein the food product is fresh beef that is exposed to a temperature of approximately 1,000°C for approximately 20 seconds.
22. The method of claim 16, wherein the food product is fresh poultry or fish that is exposed to a temperature of approximately 1,000°C for approximately 15 seconds.
23. The method of claim 16, wherein the food product is fresh beef that is exposed to a temperature of approximately 900°C for approximately 25-30 seconds.
24. The method of claim 16, wherein the food product is fresh poultry that is exposed to a temperature of approximately 900°C for approximately 20 seconds.
25. The method of claim 16, wherein the food product is fresh fish that is exposed to a temperature of approximately 900°C for approximately 20-30 seconds.
26. The method of claim 16, wherein the food product comprises meat, including beef, poultry, fish or other animal tissue used as food.
27. A food product preserved by the method of claim 16.
28. The food product of claim 27, wherein the food product comprises meat, including beef, poultry, fish or other animal tissue used as food.
29. A method of preserving raw meat, comprising the steps of:
(a) simultaneously exposing all surfaces of the meat to a high temperature in the range of about 700°C to about 1200°C for a period of time that is only long enough to cause substantially uniform denaturation of proteins and destruction of microorganisms on all surfaces of the meat to a depth of less that about 5 mm;
(b) rapidly cooling the meat at a temperature below 0°C for a predetermined period of time;
(c) packaging the meat in a wrapping suitable for storing the meat in a refrigerated environment;
and (d) storing the packaged meat in a refrigerated environment.
(a) simultaneously exposing all surfaces of the meat to a high temperature in the range of about 700°C to about 1200°C for a period of time that is only long enough to cause substantially uniform denaturation of proteins and destruction of microorganisms on all surfaces of the meat to a depth of less that about 5 mm;
(b) rapidly cooling the meat at a temperature below 0°C for a predetermined period of time;
(c) packaging the meat in a wrapping suitable for storing the meat in a refrigerated environment;
and (d) storing the packaged meat in a refrigerated environment.
30. A meat product preserved according to the process of claim 29.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US57335890A | 1990-08-27 | 1990-08-27 | |
| US573,358 | 1990-08-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2049760A1 true CA2049760A1 (en) | 1992-02-28 |
Family
ID=24291665
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2049760 Abandoned CA2049760A1 (en) | 1990-08-27 | 1991-08-23 | Ultra-high temperature pasteurization process |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2049760A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2934120A1 (en) * | 2008-07-22 | 2010-01-29 | Vitreenne D Abattage Jean Roze | Pieces of meat i.e. red meat, treating method for microwave oven, involves marking part of surface of meat pieces while maintaining cold and raw meat, where marking is placed on surface of meat pieces without interposition of coating |
| US20110183051A1 (en) * | 2010-01-28 | 2011-07-28 | Skender David J | Roasting Apparatus and Packaging System for Providing a Cooked Food Product Having a Long Shelf Life |
-
1991
- 1991-08-23 CA CA 2049760 patent/CA2049760A1/en not_active Abandoned
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2934120A1 (en) * | 2008-07-22 | 2010-01-29 | Vitreenne D Abattage Jean Roze | Pieces of meat i.e. red meat, treating method for microwave oven, involves marking part of surface of meat pieces while maintaining cold and raw meat, where marking is placed on surface of meat pieces without interposition of coating |
| US20110183051A1 (en) * | 2010-01-28 | 2011-07-28 | Skender David J | Roasting Apparatus and Packaging System for Providing a Cooked Food Product Having a Long Shelf Life |
| US8445049B2 (en) * | 2010-01-28 | 2013-05-21 | David J. Skender | Roasting apparatus and packaging system for providing a cooked food product having a long shelf life |
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