Patent Publication Number: US-7214398-B2

Title: Method for producing a pH enhanced comminuted meat product

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 09/965,337, filed Sep. 27, 2001, and entitled “METHOD FOR PRODUCING A PH ENHANCED COMMINUTED MEAT PRODUCT,” now U.S. Pat. No. 6,713,108, which is a continuation of U.S. patent application Ser. No. 09/213,190, filed Dec. 17, 1998, now U.S. Pat. No. 6,389,838 B1, and entitled “APPARATUS AND METHOD FOR REDUCING MICROBE CONTENT IN FOODSTUFFS BY pH AND PHYSICAL MANIPULATION.” The Applicant claims the benefit of each of these applications pursuant to 35 U.S. C. §120. The entire content of each of these applications is incorporated herein by this reference. The entire content of U.S. Pat. No. 5,871,795 is also hereby incorporated herein by reference. The content of U.S. Pat. No. 5,871,795 was incorporated by reference in the parent application Ser. No. 09/213,190. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates to meat processing. More particularly, the invention relates to a method for adding ammonia to a comminuted meat product to produce a pH enhanced comminuted meat product. 
     BACKGROUND OF THE INVENTION 
     Almost all foods are processed in some way before reaching the consumer. Meat products, for example, are separated from unusable or undesirable elements or components, ground or chopped, mixed or blended, and often times frozen for distribution. Even lightly processed meats are cut, trimmed, and then packaged for sale or distribution. 
     Microbes are part of the natural decay process of organic material and invariably appear or grow in foodstuffs as they are processed or handled. Although some microbes may be relatively benign, others contribute to spoilage and some can cause serious illness if consumed. Lactic acid producing bacteria are examples of benign microbes while some strains of  E. Coli , Salmonella, Staph, and Listeria bacteria are examples of pathogens and can cause serious illness. 
     It is desirable to control the growth of pathogen microbes or reduce pathogen microbe count in foodstuffs. Historically, microbe growth has been reduced by chemical preservatives that remain in the product and are ultimately ingested by the consumer. However, a growing population of consumers has expressed a desire for food products that are free of traditional chemical preservatives. Alternatively to traditional chemical preservatives, heat has been used to kill microbes in foodstuffs. However, heat processing or sterilization often has an undesirable effect on the quality or characteristics of the foodstuff and may make the product undesirable to the consumer. Also, heat sterilization in meats can kill all microbes, leaving the meat susceptible to the rapid growth of dangerous microbes or pathogens after sterilization, should the previously sterilized meat be exposed to such microbes. 
     The prior related application Ser. No. 09/213,190, now U.S. Pat. No. 6,389,838 B1 discloses an apparatus and method for physically manipulating a pH modified comminuted meat product to reduce the microbe content in the resulting product. The process includes freezing the pH modified meat product and then physically manipulating the frozen material to produce relative movement between points within the material. This process of treating a pH modified meat product, which may be referred to as “freeze/stress processing,” has been found to greatly reduce the live microbe count in the resulting product. 
     SUMMARY OF THE INVENTION 
     It is a general object of the invention to provide a method for producing a pH enhanced comminuted meat product. The pH enhanced comminuted meat product produced according to the invention is well suited for use in freeze/stress processing to dramatically reduce live microbe content in the resulting product. 
     The method of producing a pH enhanced comminuted meat product according to the invention includes placing ammonia in contact with an initial comminuted meat product. This contact with ammonia results in an intermediate meat product having a pH higher than the initial comminuted meat product. Once the intermediate meat product is produced, the method includes releasing or removing ammonia from the surface of the intermediate meat product and then applying mechanical action to the intermediate meat product. This mechanical action helps drive ammonia deposited on the intermediate meat product into the meat and helps distribute the ammonia in the meat product. Removing ammonia from the surface of the intermediate meat helps ensure that the mechanical action does not cause too much ammonia to be absorbed into the intermediate meat product, and produce an overly ammoniated product. 
     One preferred form of the invention applies ammonia in the form of a gas at relatively high pressures. Using high pressure ammonia gas allows the ammonia gas pressure to be held for only a very short operating period, on the order of seconds or fractions of a second, and still raise the pH at the surface of the meat product to a desired level. 
     As used in this disclosure and the following claims, the “surface” of the meat product means generally any surface that may be exposed to the ammonia. For example, the surface of ground meat may include the entire surface of each piece of ground meat and not just the surface of the aggregate made up of individual ground pieces. 
     While the preferred forms of the present invention apply ammonia in the form of a gas, it will be appreciated that the ammonia may be applied in solution with water within the scope of the invention. It is believed that the ammonia gas goes into solution in water in the initial meat product to form an ammonium hydroxide solution generally at the surface of the intermediate meat product. Where ammonia is added in the form of an ammonium hydroxide solution, it is believed that the ammonium hydroxide solution simply mixes with the water in the initial meat product to produce the desired intermediate meat product. 
     The method of the invention may be performed as a continuous process with an apparatus such as that disclosed in U.S. Pat. No. 5,433,142 or as a batch process. In either case, the apparatus for performing the process includes a container for containing the initial meat product and ammonia and also means for placing the initial meat product and ammonia in the container and for removing the intermediate meat product from the container after treatment. The continuous process apparatus also preferably includes means for compressing ammonia gas in contact with the meat product to the operating pressure and means for releasing the pressure after the operating period. In the batch process, the meat product may be held in a pressure vessel and ammonia gas may be introduced into the vessel under the desired operating pressure. 
     The ammonia releasing or removing step serves to remove any excess or free ammonia from the intermediate meat product. In one form of the invention, the ammonia releasing or removing step may include rinsing the surface of the intermediate meat product with a suitable inert gas or a liquid. In another preferred form of the invention, the ammonia releasing or removing step includes placing the previously treated meat under a vacuum to draw off excess ammonia gas from the intermediate product. In addition to applying a vacuum to the treated product, the temperature of the intermediate product may be increased to help release ammonia gas from the product. The intermediate meat product may also be agitated or blended while applying a vacuum. 
     The mechanical action according to the invention may be applied in a number of different fashions. The agitation or blending while removing ammonia from the surface of the intermediate meat product may be referred to as a primary mechanical action. Pumping the intermediate meat product through a conduit also applies the desired mechanical action to the intermediate meat product. An initial mechanical action by pumping the intermediate meat product may be applied prior to the primary mechanical action. A secondary mechanical action by pumping the intermediate meat product may be applied after the primary mechanical action. 
     These and other objects, advantages, and features of the invention will be apparent from the following description of the preferred embodiments, considered along with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing method steps performed according to one preferred form of the invention. 
         FIG. 2  is a mostly diagrammatic view of an apparatus for performing a method embodying the principles of the invention in a continuous process. 
         FIG. 3  is a partial longitudinal section view of the compressor used in the apparatus shown in  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a method embodying the principles of the invention for using ammonia gas as a treatment gas to modify the pH of an initial comminuted meat product to produce a pH enhanced meat product. The method  4  shown in  FIG. 1  includes first, at block  5 , placing ammonia gas under a desired operating pressure in contact with the surface of the initial comminuted meat product. As shown at block  6 , the method next includes holding the ammonia gas and meat product under the operating pressure for an operating period sufficient to increase the pH of the initial meat product to a desired level. After holding the meat product and ammonia gas under the operating pressure for the operating period, the method depicted in  FIG. 1  includes releasing the gas pressure at block  7 . This releasing step is preferably done quickly or instantaneously to put the maximum physical stress on the microbes then existing in the meat product. 
     Although  FIG. 1  illustrates the ammonia gas application, hold, and release steps as separate steps, the time for performing each step may be very short. Applying and releasing the ammonia gas may be done almost instantaneously, with the operating period representing the short time between pressurization and release. Short treatment times or operating periods are obtained by using an operating pressure that is at or above the equilibrium vapor pressure or vapor pressure of the ammonia gas at the temperature of the meat product being treated. For example, when the meat product is held at 38 degrees F., the operating pressure for ammonia gas must be 55.7 psig or more to produce the desired pH increase in a short period of time, on the order of one to thirty seconds or less. At 60 degrees F., the ammonia gas operating pressure would be at or above 92.9 psig. At higher operating pressures, between 2,500 to 3,000 psi, for example, the operating period may be less than 1 second to achieve a significant pH increase. The preferred operating pressure ranges from 2000 psi to 4500 psi, while the temperature of the meat product being treated is maintained in a temperature ranging from 33 degrees F. to 110 degrees F. 
     The method  4  shown in  FIG. 1  concludes with step  8 , removing the ammonia gas from the meat product being processed. This gas removal step removes the free ammonia gas but leaves the meat product with the desired increased pH. The gas removal step may include simply applying a vacuum to evacuate the gas or flushing the meat product with an inert food processing gas such as Nitrogen, Oxygen, or Helium. With either applying a vacuum or flushing with an inert gas, the method may additionally include applying heat to the meat product being processed to help remove excess ammonia gas. 
     When ammonia gas is in contact with the initial meat product being processed, it is believed that the moisture in the meat product absorbs the ammonia gas to form ammonium hydroxide (NH 4 OH). The free hydroxyl ions from the ammonium hydroxide in the meat product produce the increased pH. It will therefore be appreciated that the desired pH change may be accomplished by applying ammonia in any fluid form. That is, the ammonia may be applied as a gas which is absorbed in water in the initial meat product to form ammonium hydroxide solution, or the ammonia may be added in the form of ammonium hydroxide solution (aqueous ammonia) which mixes with the moisture in the initial meat product to produce the desired intermediate meat product having an increased pH with respect to the initial meat product. 
     The same pressurization, hold, and release cycle shown in  FIG. 1  may be employed for decreasing the pH of the treated meat product. However, in this cycle the treatment gas comprises a suitable pH lowering gas such as carbon dioxide gas or a suitable liquid or solid pH lowering material dispersed in a suitable carrier gas. The method includes placing the treated meat product with increased pH in contact with the pH lowering gas at a neutralizing pressure, holding the pressure for a neutralizing period, and releasing the pressure after the desired period. As with the release step in the pH increasing method, the release step in the pH lowering method preferably comprises releasing the pressure substantially instantaneously to physically stress the microbes in the meat product. The neutralizing pressure is preferably a pressure above the vapor pressure of the treatment gas at the temperature of the meat product being processed. 
     As with the pH increasing method according to the steps shown in  FIG. 1 , the pH lowering method preferably concludes with the step of removing the pH lowering treatment gas from contact with the meat product being processed. This step may include subjecting the meat product to a vacuum or flushing the meat product with an inert food processing gas. Additionally the step of removing the treatment gas may include heating the meat product to help remove excess pH lowering gas from the meat product, additional pH increasing gas, or their reaction products. 
     THE TREATMENT APPARATUS 
       FIGS. 2 and 3  show a preferred apparatus  10  for processing ground meat, or the like, according to the method of the invention. Referring to  FIG. 2 , the apparatus  10  includes means, in this case processing conduit  12 , for containing the initial meat product and treatment gas under the desired operating pressure. The pressure is applied by a compressor or pump  14  driven by a suitable motor  16 . A flow-restricting valve or other device  18  is associated with the conduit  12  for holding a back-pressure against the pressure applied by the compressor  14 . The flow-restricting valve  18  opens to an output container  20 , which is used in removing excess treatment gas from the intermediate meat product. The initial meat product to be processed in the apparatus  10  is pumped from an in-take container  22  by feed pump  26  to the compressor  14 , and the treatment gas supply  24  provides treatment gas which is then compressed in contact with the initial meat product. 
     The form of the invention shown in  FIG. 2  provides for continuous processing with continuous meat product intake, compression with the treatment gas, holding under the operating pressure, and then pressure release. In this continuous processing form of the invention, other processing equipment may be connected in the conduit  12  or elsewhere for performing other functions on the meat product before the treatment gas pressure is released at device  18 . 
       FIG. 3  illustrates the preferred compressor or pump  14 . The compressor  14  includes a cylinder head  30  with a piston  32  adapted to reciprocate within a cylinder  34  which opens into a chamber  36  in the cylinder head. As seen from the perspective of  FIG. 3 , the piston  32  would move transverse to the plane of the paper. An inlet manifold  38  is connected to the cylinder head  30  with an inlet valve  40 , and an outlet manifold  42  is connected to the cylinder head via an outlet valve  44 . Although  FIG. 3  is broken away to show only one piston and cylinder arrangement in the cylinder head  30 , it will be readily apparent to those skilled in the art that the compressor  14  could, and preferably would, include additional piston and cylinder arrangements. In one preferred form, compressor  14  includes three separate pistons. 
     The inlet manifold  38  includes an inlet manifold passage  50  through which the meat product reaches the inlet valve  40 . The illustrated inlet valve  40  is a check valve comprising a seat  52 , ball  54 , and ball retainer  56 , and defines an inlet passage  58  to the cylinder head chamber  36 . Similarly, the outlet valve  44  comprises a check valve having a seat  60 , ball  62 , and ball retainer  64 , and defines an outlet passage  66  connecting the cylinder head chamber  36  to a passage  68  extending through the outlet manifold  42 . 
     The treatment gas is preferably supplied to the compressor  14  for compressing with the initial meat product, even though in other forms of the invention the treatment gas may simply be applied to the initial meat product under the desired operating pressure. The illustrated form of the invention shows two alternate injection points for injecting treatment gas to place the treatment gas in contact with the initial meat product. The first treatment gas injection port  70  extends through the seat  52  of the inlet valve  40  on the inlet manifold side of the inlet valve ball  54 . Treatment gas injected into the inlet manifold passage  50  through this first injection port  70  under a suitable pressure is drawn into the cylinder head chamber  36  along with the initial meat product. The alternate, second injection port  72  extends into the inlet passage  58  on the cylinder head side of the inlet valve ball  54 . Thus the treatment gas injected through this second port  72  is injected directly into the cylinder head chamber  36  for compressing with the initial meat product. 
     Referring again to  FIG. 2 , after releasing the treatment gas pressure at valve  18 , the treated, intermediate meat product travels through output conduit  80  to the output container  20 . The excess treatment gas removal step described with reference to  FIG. 1  (block  8 ) may be performed by applying a vacuum to container  20  with vacuum pump  82 . The vacuum pump  82  may discharge into a gas recovery system  84  for recovering the treatment gas or for disposing of the gas. Also, the container  20  may have associated with it a motor  86  for driving an agitator or blender mechanism (not shown) within the container. Applying mechanical action by blending or agitating intermediate meat product in the container helps expose the meat product to the vacuum to ensure better removal of excess or free treatment gas. In addition to the application of a vacuum and the agitation of the meat product, the product may be heated to a desired temperature to help release treatment gas. The heat may be applied by a heating element as the meat product travels through the output conduit  80 . The heating element  90  is associated with the conduit  80  and may be controlled through a heater control  92 . The heat may be applied electrically or with any other suitable heating device to heat the meat to a desired temperature. Also, heat may be applied earlier in the process if desired. For example, the meat product may be heated in conduit  12  by a suitable process. 
     The treated meat product is removed from the container  20  through a suitable pump  94  mounted at the bottom of a hopper  96 , which forms the bottom of container  20 . Alternatively to the pump  94 , an auger may be used to remove meat product from container  20 . In any event, the pump or auger is operated at a rate sufficient to maintain a level of meat product in the container  20 . Maintaining a level of meat product in the bottom of container  20  allows better control of the vacuum applied to the container through vacuum pump  82 . 
     The intermediate, pH increased meat product which is produced by apparatus  10  will commonly be subjected to further processing for storage or shipment. For example, the meat product may be tempered and put through a suitable process for separating fat from lean meat. Also, the final lean meat product may be frozen and chipped for packaging and shipment. 
     Mechanical action according to the invention is applied to the meat product or intermediate meat product at three separate points in the form of the invention illustrated in  FIG. 2 . The primary mechanical action is applied to the intermediate meat product by the blender mechanism in output container  20 , driven by motor  86 . An initial mechanical action is applied to the initial/intermediate meat product as it is acted upon by compressor  14  and forced through conduit  12 . Also, a secondary mechanical action is applied to the intermediate meat product as it is pumped or augered from output container through output conduit  98 . 
     The operation of apparatus  10  may now be described with reference to  FIGS. 2 and 3 . The apparatus  10  shown in  FIG. 2  uses the reciprocating piston pump or compressor  14  to place the initial meat product in contact with the treatment gas under the operating pressure. As shown in  FIG. 2 , the feed pump  26  pumps meat product from the intake container  22  to the inlet manifold passage  50  ( FIG. 3 ) of the compressor  14  under an inlet pressure. Referring now to  FIG. 3 , as the piston  32  withdraws into the cylinder  34 , it creates a low pressure in the cylinder head chamber  36  causing the ball  62  of the outlet valve  44  to seat and the ball  54  of the inlet valve  40  to unseat, drawing the initial meat product into the cylinder head from the inlet manifold passage  50 . When the first treatment gas injection port  70  is used, treatment gas is injected into the inlet manifold passage  50  and the treatment gas is drawn into the cylinder head chamber  36  along with the initial meat product. Alternatively, when the second port  72  is used, the treatment gas is injected directly into the cylinder head chamber  36  preferably during the intake stroke of the piston  32  or just as the piston starts on the compression stroke. In either case, when the piston  32  returns through the cylinder  34  in the compression stroke, it increases the pressure in the cylinder head chamber  36  causing the inlet ball  54  to seat in the inlet valve  38 . The pressure continues to rise in the cylinder head chamber  36  until the pressure passes the pressure held in the outlet manifold passage  66  and processing conduit  12  by the flow restricting back-pressure device  18 . At this point, the outlet valve ball  62  unseats to allow the meat products and treatment gas under the operating pressure to move into the outlet manifold passage  66 . 
     The pumping or compressing process continues each cycle of the piston  32  to compress the initial meat product and treatment gas and transport the compressed treatment gas and meat product through the outlet manifold passage  66  and into the processing conduit  12 . In this continuous pressurizing, holding, and releasing process, the pump speed and the processing conduit length are chosen to provide travel time of the meat product and compressed treatment gas in the processing conduit  12  equal to the required operating period to produce the desired pH altering effect in the initial meat product. 
     After holding the initial meat product in contact with the treatment gas under the operating pressure for the operating period to produce the desired intermediate meat product, the method continues with the step of releasing the pressure across the flow restricting device  18 . Preferably, the pressure is released substantially instantaneously across the device  18  as the intermediate meat product is delivered into the output container  20 : The step of removing the treatment gas may be performed in the output container  20  by applying the desired vacuum to the container with vacuum pump  82  alone and preferably by agitating the material in the container  20  with a suitable blender mechanism (not shown) driven by motor  86 . Heat may be applied to the meat product through heater  90  to assist in treatment gas removal under the vacuum. 
     Alternatively to the continuous processing method possible with the apparatus  10  shown in  FIGS. 2 and 3 , the method of the invention encompasses a batch process. In this batch process, the step of placing the meat product in contact with the treatment gas under the operating pressure includes placing the meat product in a pressure vessel and then applying the treatment gas under the operating pressure. The operating pressure is then simply held on the pressure vessel for the operating period. This batch method is preferable, or may be required, for some meat products that cannot easily be passed through the valves of a reciprocating compressor as shown in  FIG. 3 . In any event, in the batch process, the step of releasing the pressure may be accomplished simply by releasing treatment gas pressure through a suitable pressure release device associated with the pressure vessel. 
     Operating or neutralizing pressures at near atmospheric pressure provide significant pH effect. However, the lower operating pressures require longer operating periods to produce a given pH modification. Alternatively, relatively high operating or neutralizing pressures, from at or above the vapor pressure of the treatment gas at the temperature of the meat being processed to several thousand psi may be employed in the method of the invention to produce the desired pH effect at a shorter operating period and also to produce microbe kill by physically stressing the microbes. Also, multiple pressurization, hold, and release cycles may be employed within the scope of the invention to produce the desired pH altering effects. The different pressurization cycles may have different pressure, duration, and treatment gas all within the scope of the invention. 
     EXAMPLE NO. 1 
     The method of improving the quality of meat according to the invention was tested in the production of Lean Finely Textured Beef from trimmings consisting of lean meat and approximately 70% fat. Pure anhydrous NH 3  gas was injected into trimmings being processed through a pump apparatus similar to the apparatus shown best in  FIG. 3 . The NH 3  gas was injected into the pump through a port just prior to the piston compression stroke, resulting in an immediate distribution of the gas to the product under pressure. The pump outlet was to a conduit similar to conduit  12  shown in  FIG. 2 , in which pressure was maintained at approximately 4,000 psi through an outlet orifice which performed the back pressure function of the outlet valve  18  shown in  FIG. 2 . The flow rate through the pump and conduit held the NH 3  gas in contact with the trimmings for approximately 2 to 2.5 minutes. Through the compression process, the material was held at a temperature of approximately 40 degree F. While being held at the elevated pressure, the material was tempered from 40 degree F. to 108 degree F. and then the pressure was reduced at the orifice. The treated and heated material was then centrifuged to remove fat, leaving a lean portion with 4% to 6% fat, which was then frozen, chipped, and packaged. Also, the identical process was performed for a control, without any NH 3  gas injection. 
     The pH of the material injected with NH 3  was 7.45, as compared to 6.36 for the untreated product. Thus, the NH 3  gas treatment provided a 17.14% increase in pH in the finished product after freezing. 
     Both the control and test products were cooked and evaluated for flavor and aroma. The sensory tests for flavor and aroma found no detectible differences between the control and NH 3  treated product. Particularly, the NH 3  treated product had no detectible NH 3  aroma, either while thawing, during cooking, or after being cooked. Also, the NH 3  treatment and increased pH did not affect the taste of the cooked product as compared to the untreated product. The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit the scope of the invention. Various other embodiments and modifications to these preferred embodiments may be made by those skilled in the art without departing from the scope of the following claims. For example, the vacuum for helping to remove excess treatment gas may be applied in the output conduit  80  or at some other point in the process rather than in the output container  20  as discussed above. Also, heat may be applied as desired while the material being processed passes through the output conduit  80 , or at any other suitable point in the process such as in the output container  20  or in the treatment conduit  12  shown in  FIG. 2 .