Method for reducing microbe content in foodstuffs by pH and physical manipulation

Abstract
A manipulating apparatus (10) receives a plurality of previously frozen pieces of pH modified foodstuffs or workpieces (23) and physically manipulates or stresses the workpieces while they remain in a frozen state. The physical manipulation causes relative movement between various points within the volume of the workpieces (23) and kills microbes within the foodstuff. One preferred pH modifying arrangement includes a supply of NH3 gas (11) and a pump (9) for placing the comminuted foodstuffs to be processed and the NH3 gas together under an operating pressure for a period of time sufficient to increase the pH of the foodstuffs.
Description




TECHNICAL FIELD OF THE INVENTION




This invention relates to food processing, and more particularly, to reducing microbe content in processed foodstuffs. The invention encompasses a method for manipulating the pH of foodstuffs and then physically manipulating the foodstuffs to reduce microbe content.




BACKGROUND OF THE INVENTION




Most foods are processed in some way before reaching the consumer. For example, vegetables may be washed, trimmed, blanched, and than frozen prior to distribution. Meat products also require significant processing before reaching the consumer. At the very least, the animal carcass is cut into segments and the larger cuts of meat or fillets are cut from these initial segments. Other usable elements remaining after separating the larger cuts of meat are then separated from the remaining unusable elements such as bone and then ground or chopped, mixed, and then commonly frozen for distribution.




Foodstuffs are inevitably exposed to microbes as the foodstuffs are processed or handled. Microbes are part of the natural decay process of organic material and may be deposited on foodstuffs through the air or by contact between the foodstuff and contaminated equipment or other material. Although some microbes may be relatively benign, others contribute to spoilage and some can cause serious illness. Lactic acid producing bacteria are examples of benign microbes, while some strains of


E. Coli,


Salmonella, Listeria, and Staph bacteria are examples of pathogenic microbes which can cause serious illness when ingested by humans.




Even with careful processing practices, foodstuffs may be exposed to pathogenic microbes during processing or initial handling. The risk of illness from dangerous microbes which may be present in foodstuffs is reduced by a careful handling and cooking of the foodstuffs by the consumer. In larger cuts of meat for example, dangerous microbes may only be present on the surface of the meat and are readily killed in the cooking process.




Ground or chopped and mixed foodstuffs, including ground beef, may carry dangerous microbes which are killed only after thoroughly cooking the material. The reason for this is that dangerous microbes residing at the surface of a larger piece of the foodstuff may be distributed throughout the final ground or chopped product as the large piece is ground and mixed together with other pieces. Thorough cooking is required in order to kill microbes residing in the center of a piece of ground and mixed foodstuff.




It is desirable to control the growth of microbes and reduce microbe content in foodstuffs. Microbe content and growth in foodstuffs may be reduced by applying chemical additives or preservatives to the foodstuff. These chemical additives or preservatives, however, may not be acceptable to consumers, or may have undesirable effects on foodstuffs.




Alternatively to chemical additives or preservatives, heat may be used to kill microbes in foodstuffs. However, heat processing or sterilization often has undesirable effects on the quality or characteristics of the foodstuff and may make the food product undesirable to the consumer.




SUMMARY OF THE INVENTION




It is an object of the invention to provide a method for reducing microbe content in comminute foodstuffs, particularly commninuted meats.




The method of the invention comprises modifying the pH of a foodstuff and then physically manipulating or applying stress to the foodstuff while the foodstuff is in a frozen state. The physical manipulation produces significant relative movement within the foodstuff. In this sense “relative movement” means movement between one point in the foodstuff and adjacent points in the foodstuff. While the mechanism by which the process reduces live microbe count is not fully understood, pH modification followed by physical manipulation according to invention has been shown to significantly reduce microbe content in the treated foodstuffs.




The process according to the invention may be performed as a continuous process or as a batch process. In either case, the pH of the foodstuff to be processed is first modified by suitable means. Preferably after the pH modification, the foodstuff is cooled by a suitable freezer to a process temperature no greater than or below the freezing point of the foodstuff to place the foodstuff in a frozen state. As used in this disclosure and the accompanying claims, the “freezing point of the foodstuff” means the temperature at which ice crystals begin to form in the foodstuff to be processed. The frozen foodstuff is then formed into workpieces. A manipulating arrangement manipulates the frozen workpieces to produce relative movement preferably throughout each workpiece. The manipulating arrangement may define a working area and operate to manipulate each workpiece as it passes or is drawn through the working area.




The pH of the foodstuff may be modified in any suitable manner. For example, a higher pH foodstuff such as lean finely textured beef may be mixed with a regular ground beef to modify the pH of the resulting mixture. The process of producing lean finely textured beef, which increases pH with respect to the starting material, also represents a suitable pH modifying step. Also, a foodstuff may be placed in contact with NH


3


(Ammonia) in gaseous or aqueous form to increase the pH of the foodstuff. U.S. patent application Ser. No. 08/803,322, now U.S. Pat. No. 5,871,795, the disclosure of which is hereby incorporated herein by this reference, discloses a pH modifying apparatus and method which may be employed in this invention. pH modification within the scope of the invention also encompasses decreasing pH. The pH of a foodstuff may be decreased by placing the foodstuff in contact with a pH reducing material such as CO


2


, for example.




In one form of the invention, the manipulating arrangement comprises first and second spaced apart rollers, with the working area defined between the first and second rollers. The rollers are preferably driven in a counter-rotating fashion to draw a workpiece there between. The spacing between the first and second rollers is smaller than an initial thickness of each workpiece so that each frozen workpiece is compressed and allowed to spread out laterally as it passes between the rollers.




Each roller may include a plurality of the spaced apart longitudinal ridges. The ridged rollers may be rotated such that each ridge on one roller registers with the space between a pair of adjacent ridges on the opposite roller as the rollers are rotated, similar to the cogs of two intermeshed gears. However, the ridges preferably do not touch, but maintain a minimum clearance. This ridged roller form of manipulating arrangement has the advantage that the frozen workpiece not only spreads out laterally as it is drawn between the rollers but is also bent between the opposing ridges on the counter-rotating rollers.




Another form of manipulating arrangement within the scope of the invention comprises two opposing plates with a suitable actuator, or actuators, for pressing the opposing plates together. The process includes placing a plurality of workpieces between the two plates and then operating the actuator arrangement to press the plates together to significantly reduce the volume between the plates. The relative movement of the plates presses the previously frozen workpieces into a block of frozen material. In this arrangement, the desired relative movement in the workpieces occurs as the workpieces deform to fill the voids left between adjacent workpieces when the workpieces were initially placed in the area between the opposing plates.




Regardless of the particular manipulating arrangement employed to manipulate the frozen workpieces according to the invention, a manipulator temperature control system preferably controls the temperature of the manipulating arrangement surfaces which come in contact with the frozen workpieces. The manipulator temperature control system may cool the surfaces of the manipulating arrangement to ensure that heat from the surfaces of the manipulating arrangement does not raise the temperature of the workpieces to a temperature above the desired process temperature. Alternatively, the manipulator temperature control system may heat the manipulating arrangement surfaces and thereby heat the frozen workpieces from a lower process temperature to the freezing temperature or even slightly above the freezing temperature. Also, maintaining the surfaces of the manipulating arrangement at a temperature near the process temperature or slightly above the process temperature also helps prevent the workpieces from sticking to the manipulator surfaces.




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 diagrammatic representation of a foodstuff pH and physical manipulation system embodying the principles of the invention.





FIG. 2

is a partial longitudinal section view of a manipulating arrangement suitable for use as the manipulating arrangement shown diagrammatically in FIG.


1


.





FIG. 3

is a partial transverse section view taken along line


3





3


in FIG.


2


.





FIG. 4

is an enlarged diagrammatic side view of a piece of foodstuff being drawn between the rollers of a preferred manipulating arrangement.





FIG. 5

is a view in section taken along line


5





5


in FIG.


4


.





FIG. 6

is a view in section taken along line


6





6


in FIG.


4


.





FIG. 7

is a partial section view showing an alternate manipulating arrangement embodying the principles of the invention.











DESCRIPTION OF THE PREFERRED EMBODIMENTS




Referring to

FIG. 1

, an apparatus


10


for manipulating foodstuffs is associated with a pH manipulating system


8


and a suitable freezer


12


. A transport device


14


is positioned between the freezer


12


and manipulating apparatus


10


. A second to transport device


16


may be positioned at an outlet from the manipulating apparatus


10


for transporting treated foodstuffs to further processing equipment.




The illustrated pH manipulating system


8


includes a pump


9


, NH


3


supply


11


, pressure reduction arrangement


13


, and a system


15


for removing excess NH


3


. Conduit


17


transfers pH modified foodstuff to freezer


12


. Pump


9


preferably comprises a piston pump with an injection arrangement (not shown) for injecting a measured amount of NH


3


from supply


11


into the foodstuff stream either during compression or prior to compression. The pump preferably compresses the NH


3


and foodstuff to a pressure at or above the vapor pressure of the NH


3


at the temperature of the foodstuff. As disclosed in U.S. patent application Ser. No. 08/803,322, now U.S. Pat. No. 5,871,795, this treatment pressure has been found to rapidly increase the pH of foodstuffs. Pressure reduction arrangement


13


may comprise any suitable device or arrangement for releasing the pressure developed by pump


9


. Device


15


may comprise an arrangement for applying a vacuum or any other arrangement for drawing off excess NH


3


after the treatment pressure is released at device


13


.




Those skilled in the art will appreciate that many arrangements other than the system


8


shown in

FIG. 1

may be used to modify the pH of the foodstuff. For example, the foodstuff may be treated in batches in a vessel into which a suitable pH modifying gas is introduced. Also, a liquid material such as aqueous NH


3


may be applied to the foodstuff under pressure or otherwise. Any pH modifying material may be used to modify the pH of the foodstuff within the scope of the invention. Although the invention preferably comprises increasing the pH of the foodstuff, pH modification within the scope of the invention also encompasses decreasing the pH of the foodstuff. Decreasing the pH may be accomplished by applying a pH decreasing material, such as CO


2


gas, to the foodstuff preferably under pressure as described above with reference to FIG.


1


. Furthermore, no pH modifying material may be needed for processing certain foodstuffs. For example, reducing the fat content of a comminuted beef product may change the pH of the material sufficiently within the scope of the invention, as may mixing a reduced fat product with a regular comminuted product.




The pH modification required according to the invention may be minimal. However, the pH modification step according to the invention preferably comprises modifying the pH of the foodstuff by at least approximately 3% from the original pH of the foodstuff. For example, a foodstuff having an original pH of approximately 5.5 is preferably treated to increase its pH to at least approximately 5.67. Treatment times to modify the pH may range from on the order of approximately one second to three minutes or more.




Freezer


12


freezes the pH modified foodstuff and cutter


18


cuts the frozen foodstuff into workpieces which are then placed on transport device


14


. Transport device


14


transports the workpieces to manipulating apparatus


10


. Manipulating apparatus


10


physically manipulates the frozen foodstuff to produce relative movement between different points in the volume of the foodstuff. This relative movement occurs preferably throughout the entire volume of the foodstuff during the treatment process. It is believed that the relative movement caused by manipulating apparatus


10


damages the cell walls of microbes in the foodstuff, thereby killing the microbes. This damage to the microbes may be accomplished as ice crystals are pressed against the microbe cell walls in the course of the manipulation. The microbes may also become brittle at the processing temperature employed by the invention and the manipulation may serve to damage the cell walls in this relatively brittle state. Although the mechanism by which microbe kill is accomplished is not fully understood, tests of the apparatus and process according to the invention indicate significant microbe kill.




The freezer


12


may be any suitable device capable of cooling the foodstuff to a process temperature no greater than or below the freezing point of the foodstuff. For example, freezer


12


may comprise a roller-type freezer as disclosed in U.S. Pat. Nos. 4,138,768 and 4,192,899, which are incorporated herein by this reference. Regardless of the particular type of freezer employed, freezer


12


preferably freezes the foodstuff in less than thirty (30) minutes and optimally in less than about ten (10) minutes. The roller-type freezer disclosed in U.S. Pat. Nos. 4,138,768 and 4,192,899 is particularly well-suited for rapidly freezing foodstuffs into thin sheets of material which may then be cut into small sections. Freezing times of approximately 2 minutes may be obtained using these roller-type freezers. Regardless of the freezer type, rapid freezing is preferable for purposes of this invention because rapid freezing produces relatively smaller ice crystals as compared to a slow freezing process. It is believed that the smaller ice crystals produced by rapidly freezing a foodstuff improve microbe kill during the manipulation or stressing step according to the invention.




Freezer


12


also preferably has associated with it a forming arrangement for forming the pH modified foodstuff into workpieces comprising discrete pieces of foodstuff. The forming arrangement may comprise the cutting system


18


such as the cutting system shown in U.S. Pat. No. 4,192,899. This cutting arrangement


18


cuts workpieces from the sheet of frozen foodstuff produced by freezer


12


. Alternatively, the foodstuff may be formed into workpieces in an unfrozen state and then frozen to the process temperature. In any event, the workpieces preferably comprise approximately half-inch by half-inch squares having a thickness of approximately 0.25 to 0.125 inches. Although larger workpieces may be used within the scope of invention, the thickness of workpieces is preferably less than 0.75 inches. The thinness of the workpiece helps ensure relative movement throughout the volume of the workpiece as the workpiece is manipulated according to the invention. Also, thin sheets or workpieces of foodstuff may be cooled more quickly to the process temperature.




Transport device


14


preferably comprises a vibrating conveyor capable of receiving the frozen workpieces from freezer


12


and cutter system


18


, and transporting the workpieces to an inlet


20


associated with manipulating apparatus


10


. Details of the transport device


14


are not shown in the figures since a number of different types of conveying devices may be employed within the scope of the invention, and in any event the details of such conveying devices are well within the knowledge of those skilled in the present field. Transport device


14


preferably moves the frozen workpieces quickly to the manipulating device


10


so that the workpieces are manipulated as quickly as possible after being frozen to the process temperature. It is believed that microbes which have been maintained at the process temperature for a long period of time can survive the manipulation better. In the preferred form of the invention, manipulating device


10


, freezer


12


, and transport device


14


are situated and operated such that the workpieces are manipulated according to the invention as quickly as possible after reaching the process temperature, and preferably no more than about ten (10) minutes, about thirty (30) minutes, or about one hour, or as much as 24 hours, after the workpieces reach the process temperature, although longer periods may be used within the scope of the invention.




One preferred manipulating apparatus


10


is shown in

FIGS. 2 and 3

. Manipulating apparatus


10


includes a chute


22


through which workpieces


23


drop from the transport device


14


shown in FIG.


1


. The illustrated manipulating apparatus


10


includes two spaced apart rollers


24


and


25


within a chamber


26


. Rollers


24


and


25


are positioned within chamber


26


with their longitudinal axes extending substantially parallel to each other. Chamber walls


28


are positioned on either side of the two rollers. Rollers


24


and


25


are spaced apart with a minimum clearance between the roller surfaces which is less than an initial thickness of the workpieces


23


. For example, workpieces


23


may be approximately 0.25 to 0.125 inches thick and the clearance between the opposing surfaces of rollers


24


and


25


may be approximately 0.10 inches. The spaced apart rollers


24


and


25


define a working area W extending from the point of minimum clearance between the roller surfaces upwardly to a point at which workpieces


23


first make contact with both rollers.




At least one of the rollers


24


or


25


is driven by a suitable drive motor so as to rotate about its longitudinal axis. The direction of rotation is toward the opposing roller. In the illustrated form of the invention, both rollers


24


and


25


are driven by a single drive motor


30


in a counter rotating fashion toward each other. Drive motor


30


drives first roller


24


directly through shaft


32


and timing gears


34


and


35


cooperate to drive the second roller


25


. Timing gear


34


is mounted on drive shaft


32


while timing gear


35


is mounted on drive shaft


33


which is rigidly connected to second roller


25


. Although not shown in the drawings, those skilled in the art will appreciate that drive motor


30


includes a suitable transmission arrangement for transmitting power to the first drive shaft


32


. The drive motor


30


and associated transmission arrangement may be adapted for driving rollers


24


and


25


at a constant speed, or may be adapted to vary the speed to suit different processing rates.




Although rollers


24


and


25


may have a substantially smooth outer surface, the illustrated preferred rollers include longitudinally extending ridges


38


. Rollers


24


and


25


are rotated in synchronization through the timing gears


34


and


35


so that each ridge


38


on one roller registers between adjacent ridges on the opposing roller similarly to the cogs of two intermeshed gears. However, the ridges


38


on the opposing rollers preferably do not touch, but always maintain a minimum clearance between the opposing roller surfaces, for example approximately 0.10 inches.




The manipulating apparatus


10


shown in

FIGS. 2 and 3

also preferably includes a manipulator temperature control system for cooling or warming the outer surfaces of rollers


24


and


25


, that is, the surfaces of the manipulating apparatus (machine surfaces) which may come in contact with workpieces


23


. Maintaining the outer surface of rollers


24


and


25


at a temperature near the process temperature prevents the rollers from heating workpieces


23


above the process temperature as the workpieces come in contact with the roller surfaces. A roller outer surface temperature which is near but just above the particular process temperature being employed also helps prevent workpieces


23


from sticking to the rollers


24


and


25


and may also enhance microbe kill as discussed below. For example, the outer surfaces of the rollers


24


and


25


may be maintained at approximately 32 degrees Fahrenheit where the process temperature is approximately 28 degrees Fahrenheit or lower.




The illustrated temperature control system includes for each roller


24


and


25


an inlet


40


and an outlet


41


. A channel


42


extends near the outer surface of the respective roller and is preferably formed as a continuous spiral groove between an inner roller member


44


and an outer roller member


45


. A temperature controlling fluid is circulated through an inlet duct


48


associated with respective roller drive shaft


32


and


33


into the inlet


40


, through the continuous spiral channel


42


, and out through outlet port


41


and outlet duct


49


formed in respective drive shaft. Any suitable fluid may be circulated through the temperature control system for cooling or heating the outer surfaces of rollers


24


and


25


preferably to a temperature near the processing temperature, that is, the temperature of the frozen workpieces as they pass between the rollers. The system for producing the temperature control fluid, directing the fluid into inlet duct


48


, and receiving the returning fluid from outlet duct


49


is omitted from the drawings so as not to obscure the invention in unnecessary detail. Such system is within the knowledge of those skilled in the art.




The roller-type manipulating apparatus


10


shown in

FIGS. 2 and 3

also preferably includes gas injection ports


52


. Any suitable gas such as clean air may be injected through the gas injection ports


52


so as to flow over the outer surfaces of rollers


24


and


25


. The injected gas helps clean the roller surfaces and separate foodstuff material which may partially stick to the roller surfaces.




In operation, the roller-type manipulating apparatus


10


shown in

FIGS. 2 and 3

receives a plurality of workpieces


23


into chamber


26


immediately above rollers


24


and


25


. As at least one of the rollers is rotated toward the opposite roller or both rollers are rotated toward each other in counter rotating fashion, workpieces


23


are drawn into the working area W and through the area of minimum clearance between the rollers. This action in shown best in

FIGS. 4 through 6

. Referring to

FIGS. 4 and 5

each frozen workpiece retains generally its initial shape before passing into the working area W between rollers


24


and


25


. However, as shown in

FIG. 6

, the workpiece material is forced to spread out laterally as the workpiece passes through the working area W and ultimately through the area of minimum clearance between rollers


24


and


25


. This spreading of the workpiece material causes relative movement between points within the volume of the material. For example, referring to

FIG. 5

, a central point A in workpiece


23


resides a distance d to a point B at one corner of the workpiece. However, as the workpiece


23


spreads out as it passes between rollers


24


and


25


as shown in

FIG. 6

, the distance d between point A and point B changes significantly. This relative movement would occur even if rollers


24


and


25


each had a smooth outer surface. The ridged rollers


24


and


25


have the added advantage of forcing the workpiece material to bend around the opposing ridges


38


. This bending in the workpiece material produces additional relative movement between various points within the material.




In the preferred form of the invention, the manipulating arrangement causes relative movement throughout the volume of the foodstuff being processed. Relative movement throughout the foodstuff ensures consistent microbe kill throughout the foodstuff. However, manipulation which produces relative movement in only a portion of the material being processed produces microbe kill in that portion of the material in which the relative movement occurs. Significant microbe kill can be accomplished according to the invention by manipulating the frozen comminuted foodstuff so as to produce relative movement in at least approximately twenty percent of the volume of the foodstuff. In the roller-type manipulating arrangement disclosed in

FIGS. 1 through 6

, the extent of relative movement in the workpieces is controlled primarily by the clearance between the rollers relative to the initial thickness of the workpieces. A clearance between rollers equal to ninety-five percent (95%) or less of the total initial thickness of the individual workpieces produces the desired relative movement in a significant volume of the foodstuffs being processed.





FIG. 7

shows an alternate manipulating arrangement


60


according to the invention. In the form of invention shown in

FIG. 7

, workpieces (not shown in

FIG. 7

) are collected in an area


62


bounded by at least one movable plate. The form of invention shown

FIG. 7

has both a movable top plate or platen


64


and a movable bottom plate or platen


65


. Both top plate


64


and bottom plate


65


are movable along axis M relative to chamber walls


68


. A top actuator


70


is associated with top plate


64


while a bottom actuator


71


is associated with bottom plate


65


. Actuator


70


may comprise a suitable hydraulic or pneumatic piston and cylinder unit for positioning the top plate


64


along the axis M. Actuator


71


may similarly comprise a piston and cylinder arrangement for positioning bottom plate


65


along axis M. Chamber walls


68


may each have a structure


72


which allows a temperature control fluid to be circulated there through for cooling or heating the chamber walls to a temperature near the process temperature similarly to the rollers


24


and


25


discussed above with particular reference to

FIGS. 2 and 3

.




In operation, numerous small workpieces (not shown in

FIG. 7

) are randomly arranged in the area


62


defined by bottom plate


65


and chamber walls


68


. The random arrangement of rigid small workpieces in the area


62


leaves numerous voids between the individual workpieces. Once the area is filled to a desired point, top actuator


70


is operated to move the top plate downwardly toward bottom plate


65


and into the area


62


defined between the chamber walls


68


. A lowered position of top plate


64


is shown in phantom in FIG.


7


. As top plate


64


advances toward bottom plate


65


, the workpieces deform to fill the voids in the volume. This deformation produces relative movement throughout each workpiece.




Top plate


64


may be advanced downwardly until the individual workpieces (not shown in

FIG. 7

) in area


62


deform to produce substantially a solid block of material. At is point, bottom actuator


71


may be operated to move bottom plate


65


downwardly along axis M as top plate


64


continues downwardly. This downward movement of both top plate


64


and bottom plate


65


pushes the block formed from the frozen workpieces out from between chamber walls


68


. Once the block clears chamber walls


68


, the block of frozen material may be transferred by suitable means to another location for packaging for further processing.




Manipulating apparatus


60


shown in

FIG. 7

is used in connection with a freezer and a transport device which are not shown in the drawing. The freezer may be the same type of freezer discussed with reference to FIG.


1


. The transport device may be any suitable conveyor or other device for transporting the frozen, pH modified workpieces from the freezer to the chamber area


62


. The freezer preferably freezes the workpieces in less than 30 minutes and optimally in less than 10 minutes. Relatively small workpieces are preferable for use in the manipulating arrangement shown in FIG.


7


. Workpieces having a size on the order of 0.5 inches by 0.5 inches by 0.25 inches ensure consistent relative movement within each workpiece. However larger or smaller thin pieces of frozen comminuted or ground foodstuffs may be effectively treated with the apparatus


60


shown in FIG.


7


.




The manipulating process according to the invention is particularly applicable to comminuted foodstuffs. As used in this disclosure and in the following claims, a comminuted foodstuff may comprise any ground, chopped, or mixed foodstuff which is made up of relatively small pieces of foodstuffs which have been cut down or otherwise formed from larger pieces. The invention is well suited for treating ground meat such as beef, pork, or poultry. In the following examples, the process was applied to comminuted beef products. However, the invention may be used to treat substantially any comminuted foodstuff.




The manipulation according to the invention provides an immediate reduction in microbe count. However, microbe count decreases further for a period of time after the manipulation is performed. It is therefore preferable to use the processed foodstuffs no sooner than approximately 24 hours after the manipulation is performed. In this sense “use” the foodstuffs means cook the product or incorporate it into another food product.




Regardless of the particular manipulation arrangement used, it may be desirable to cause at least a portion of each workpiece to go to an unfrozen state during the physical manipulation step. As used in this disclosure and the following claims, an “unfrozen” state means a state in which some, but not necessarily all, ice crystals formed in the foodstuff when the foodstuff was cooled to the process temperature go back to a liquid state. Placing a portion of each workpiece in an unfrozen state may be accomplished by the pressure applied in the manipulation step or may be accomplished by increasing the temperature of a portion of each workpiece during the manipulation step to the freezing point of the foodstuff or slightly above the freezing point. After physically manipulating or stressing the workpieces, each workpiece is re-frozen to the process temperature, that is, a temperature no greater than or below the freezing point of the foodstuff. The workpieces may be re-frozen by cooling them in a suitable freezing device or by allowing the still frozen portions of the workpieces to re-freeze the adjacent unfrozen portions. Also, re-freezing may be accomplished in some cases simply by removing the pressure applied during the manipulation step.




EXAMPLE I




A test was performed using a block-type manipulation apparatus similar to that illustrated in FIG.


7


. Two batches of foodstuffs were processed in the apparatus. A first batch comprised regular ground beef having a pH of approximately 5.25 to 5.5. A second batch was made up of ground beef mixed with 15% (by weight) lean finely textured beef having a pH of approximately 6.25 to 6.5. The ground beef used in the second batch was taken from the same lot as the ground beef used in the first batch. It will be noted that the pH increase in the second batch was accomplished by mixing the higher pH lean finely texture beef with the lower pH ground beef.




The first batch comprising regular ground beef was first processed through a grinder having 0.125 inch diameter grinder plate openings. Five samples of the ground beef material were taken at the grinder output, the samples taken approximately 10 seconds apart. The ground beef was then cooled to approximately 28 degrees Fahrenheit (a temperature below the freezing point of the ground beef material) in about two minutes using a roller-type freezing machine described above. The frozen ground beef was cut into workpieces with a cutting machine associated with the roller-type freezer, the workpieces being about one-eighth inch thick and measuring approximately one-half inch by one-half inch. Five samples were taken at the output of the freezer/cutter arrangement.




The workpieces of ground beef at the process temperature were then placed in a block-type manipulating device similar to that shown in FIG.


7


. The working area of the device was filled loosely with the workpieces and then the volume of the loose collection of workpieces was reduced by about 50% to form a block of frozen ground beef. The volume reduction was achieved by advancing a top plate. The block of material was then removed from the manipulating device and samples of material were cored at various locations around the block. These cores were mixed together and five samples of frozen material were then collected from the mix of cored material.




Tables 1 through 3 show the results of bacteria tests performed on the various samples described above. Tests were conducted for Total Plate count (TPC),


E. Coli


count, Coliform count, and Staph count. Tests were also conducted to detect the presence of Salmonella and Listeria. Table 1 shows the results for the five samples taken at the grinder output. Table 2 shows the results for the five samples taken at the freezer/cutter output. Table 3 shows the bacteria test results for the five samples taken from the material removed from the frozen block. Comparing Table 3 to Tables 1 and 2, the freezing and manipulation alone produced a reduction in Coliform and Staph counts in the ground beef.


















TABLE 1









Sample




TPC






E. Coli






Coliform




Staph




Sal.




List











1




7,800




20




150




43




Neg




Neg






2




6,000




40




130




23




Neg




Pos






3




13,000 




10




720




 7




Neg




Neg






4




4,600




30




490




 9




Pos




Neg






5




4,700




90




910




43




Neg




Pos






Avg




7,220




38




480




25




N/A




N/A




























TABLE 2









Sample




TPC






E. Coli






Coliform




Staph




Sal.




List





























1




20,000




10




250




23




Pos




Neg






2




 9,200




40




490




4




Neg




Pos






3




16,000




10




720




9




Neg




Neg






4




 5,100




10




130




7




Neg




Neg






5




 6,900




20




680




23




Neg




Neg






Avg




11,440




18




454




13.2




N/A




N/A




























TABLE 3









Sample




TPC






E. Coli






Coliform




Staph




Sal.




List





























1




7,600




10




110




9




Neg




Neg






2




5,900




20




200




3




Neg




Neg






3




6,100




10




270




3




Neg




Pos






4




  750




10




210




9




Neg




Neg






5




6,700




20




400




3




Neg




Neg






Avg




5,410




14




238




5.4




N/A




N/A














The second batch of beef material, comprising the ground beef mixed with 15% lean finely textured beef, was processed in the same fashion as the first batch and samples were taken in the same fashion and at the same points. Tables 4 through 6 show the results of bacteria tests performed on the samples from the second batch. Table 4 shows the results for the five samples taken at the grinder output. Table 5 shows the results for the five samples taken at the freezer/cutter output. Table 6 shows the bacteria test results for the five samples taken from the material removed from the frozen block. Comparing the Table 6 test results with those of Tables 4 and 5, there was a marked reduction in Total Plate count,


E. Coli


count, Coliform count, and Staph count in the samples taken after pH manipulation and manipulation in the block-type manipulation device. The “<” symbol in Table 6 indicates that the observed count was less than the minimum resolution for the test. Also, all tests for Salmonella and Listeria were negative in the material subjected to both pH manipulation and physical manipulation according to the invention.


















TABLE 4









Sample




TPC






E. Coli






Coliform




Staph




Sal.




List











1




29,000




 90




720




 7




Neg




Neg






2




 8,600




 40




490




 4




Pos




Neg






3




13,000




180




270




43




Pos




Neg






4




 4,600




220




1,600  




23




Neg




Pos






5




 6,000




110




200




23




Neg




Pos






Avg




12,240




128




656




20




N/A




N/A




























TABLE 5









Sample




TPC






E. Coli






Coliform




Staph




Sal.




List





























1




5,800




10




110




9




Neg




Neg






2




3,400




40




200




4




Neg




Pos






3




3,900




10




270




7




Neg




Neg






4




3,100




10




210




4




Neg




Neg






5




5,300




20




400




9.1




Neg




Neg






Avg




4,300




18




238




6.6




N/A




N/A




























TABLE 6









Sample




TPC






E. Coli






Coliform




Staph




Sal.




List











1




2,900




<10




10




<3




Neg




Neg






2




2,700




<10




<10 




<3




Neg




Neg






3




2,000




<10




10




<3




Neg




Neg






4




  300




<10




<10 




<3




Neg




Neg






5




  900




<10




10




<3




Neg




Neg






Avg




1,760




<10





<3




N/A




N/A














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, a screw press or compressor may be used as the manipulating device in place of the block forming arrangement shown in

FIG. 8

or roller-type manipulating device shown in

FIGS. 2 and 3

. Also, although the invention is described as processing individual workpieces formed from the foodstuff to be treated, the roller-type treatment apparatus such as that shown in

FIGS. 2 and 3

may operate on a substantially continuous strand or strands of frozen foodstuff. Each such strand is to be considered an equivalent of the workpieces described above and set out in the following claims.



Claims
  • 1. A process for manipulating comminuted foodstuffs to decrease live microbe content therein, the process comprising:(a) modifying the pH of a comminuted foodstuff to produce a pH modified foodstuff; (b) cooling the pH modified foodstuff to a temperature below the freezing point of the pH modified foodstuff; (c) forming the pH modified foodstuff into at least one workpiece; and then (d) producing relative movement between points throughout a portion of the workpiece of the pH modified foodstuff while that portion of the workpiece is at a temperature below the freezing point of the pH modified foodstuff.
  • 2. The method of claim 1 further comprising the step of controlling the temperature of machine surfaces which come in contact with the workpiece in the course of producing relative movement within the workpiece.
  • 3. The method of claim 1 wherein the step of modifying the pH of the comminuted foodstuff to produce the pH modified foodstuff comprises placing the comminuted foodstuff in contact with NH3 gas.
  • 4. The method of claim 3 further comprising the step of placing the comminuted foodstuff and NH3 gas under an operating pressure at least equal to the vapor pressure of NH3 gas at the temperature of the comminuted foodstuff.
  • 5. The method of claim 1 wherein the step of modifying the pH of the comminuted foodstuff to produce the pH modified foodstuff comprises placing the comminuted foodstuff in contact with a solution of NH3 in water.
  • 6. The method of claim 1 wherein the step of modifying the pH of the comminuted foodstuff to produce the pH modified foodstuff comprises reducing the fat content of the comminuted foodstuff.
  • 7. The method of claim 1 further comprising the steps of:(a) causing an additional portion of the workpiece to go to an un-frozen state while producing the relative movement in the workpiece; and (b) placing the entire workpiece in a frozen state after producing the relative movement in the workpiece.
  • 8. A process for manipulating comminuted foodstuffs to decrease live microbe content therein, the process comprising:(a) modifying the pH of a comminuted foodstuff to produce a pH modified foodstuff (b) cooling the pH modified foodstuff to a temperature below the freezing point of the pH modified foodstuff; and (c) physically manipulating the pH modified foodstuff to produce relative movement between points substantially throughout the pH modified foodstuff while the pH modified foodstuff is at a temperature below the freezing point of the pH modified foodstuff.
  • 9. The method of claim 8 further comprising the step of controlling the temperature of machine surfaces which come in contact with the pH modified foodstuff in the course of producing relative movement therein.
  • 10. The method claim 8 wherein the step of modifying the pH of the comminuted foodstuff to produce the pH modified foodstuff comprises placing the comminuted foodstuff in contact with NH3 gas.
  • 11. The method of claim 10 further comprising the step of placing the comminuted foodstuff and NH3 gas under an operating pressure at least equal to the vapor pressure of NH3 gas at the temperature of the comminuted foodstuff.
  • 12. The method of claim 8 wherein the step of modifying the pH of the comminuted foodstuff to produce the pH modified foodstuff comprises placing the comminuted foodstuff in contact with a solution of NH3 in water.
  • 13. The method of claim 8 wherein the step of modifying the pH of the comminuted foodstuff to produce the pH modified foodstuff comprises reducing the fat content of the comminuted foodstuff.
  • 14. The method of claim 8 further comprising the steps of:(a) causing an additional portion of the pH modified foodstuff to go to an un-frozen state while producing the relative movement in the pH modified foodstuff; and (b) placing substantially the entire pH modified foodstuff in a frozen state after producing the relative movement.
  • 15. A process for manipulating comminuted foodstuffs to decrease live microbe content therein, the process comprising:(a) modifying the pH of a comminuted foodstuff to produce a pH modified foodstuff; and (b) physically manipulating the pH modified foodstuff to produce relative movement between points throughout a portion of the pH modified foodstuff while that portion of the pH modified foodstuff is at a temperature below the freezing point of the pH modified foodstuff.
  • 16. The method of claim 15 further comprising the step of controlling the temperature of machine surfaces which come in contact with the pH modified foodstuff in the course of producing relative movement therein.
  • 17. The method of claim 15 wherein the step of modifying the pH of the comminuted foodstuff to produce the pH modified foodstuff comprises placing the comminuted foodstuff in contact with NH3 gas.
  • 18. The method of claim 15 wherein the step of modifying the pH of the comminuted foodstuff to produce the pH modified foodstuff comprises placing the comminuted foodstuff in contact with a solution of NH3 in water.
  • 19. The method of claim 15 wherein the step of modifying the pH of the comminuted foodstuff to produce the pH modified foodstuff comprises reducing the fat content of the comminuted foodstuff.
  • 20. The method of claim 15 further comprising the steps of:(a) causing an additional portion of the pH modified foodstuff which is below the freezing point to go to an un-frozen state while producing the relative movement in the pH modified foodstuff; and (b) placing substantially the entire pH modified foodstuff in a frozen state after producing the relative movement in the pH modified foodstuff.
CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of pending U.S. patent application Ser. No. 09/213,190, filed Dec. 17, 1998, now U.S. Pat. No. 6,389,838 and entitled APPARATUS AND METHOD FOR REDUCING MICROBE CONTENT IN FOODSTUFFS BY pH AND PHYSICAL MANIPULATION, which is a continuation-in-part of U.S. patent application Ser. No. 09/144,928, filed Sep. 1, 1998, and entitled APPARATUS AND METHOD FOR MANIPULATING FOODSTUFFS TO REDUCE MICROBE CONTENT, now U.S. Pat. No. 6,054,164.

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Entry
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Continuation in Parts (1)
Number Date Country
Parent 09/144928 Sep 1998 US
Child 09/213190 US