Abstract:
The present invention is a method for pasteurization or sterilization of liquid food products using high pressure in a continuous or semi-continuous flow. The invention involves pressurizing and depressurizing the liquid product for a sufficient duration of time to achieve a 2.5 log cycle reduction in microorganisms. The uniform application of high pressure to the liquid food product coupled with a controlled pH and temperature of the liquid food product, the setting and maintaining the pressurizing media temperature, and the rapid depressurization resulting in cellular disruption of the microorganisms within the liquid product inactivating or destroying the microorganisms, such as vegetative microorganisms, while preserving the functionality of the liquid product.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to the field of non-thermal microbial inactivation of liquid food products, and more particularly to non-thermal pasteurization. 
       BACKGROUND OF THE INVENTION 
       [0002]    Food processing involves the transformation of raw animal or plant materials into consumer-ready products, with the objective of stabilizing food products by preventing or reducing negative changes in quality. To consumers, the most important attributes of a food product are its sensory characteristics (e.g. texture, flavor, aroma, shape and color). These determine an individual&#39;s preference for specific products. A goal of food manufacturers is to develop and employ processing technologies that retain or create desirable sensory qualities or reduce undesirable changes in food due to processing. PHysical (e.g. heating, freezing, dehydration, and packaging) and chemical (e.g. reduction of pH or use of preservatives) preservation methods continue to be used extensively and continue to evolve at a rapid rate in order to improve the efficiency and effectiveness of these processes. The most common method of food preservation used today is thermal treatment (e.g. pasteurization, sterilization). Although heating food effectively reduces levels of microorganisms, such as vegetative microorganisms, such processing can alter the natural taste and flavor of food and destroy vitamins. 
         [0003]    Consumer-oriented food products and modified food products for preparing popular dished that have the properties of fresh ingredients are highly desirable for their economy, high nutrition, convenience, and appeal as a food. Moreover, these food products, which include discrete flavored particles, i.e. pieces, that are added to the food product before cooking to enhance and modify the natural food product and provide discrete zones of independent natural flavor, texture, shape, and color. However, the effects of thermal pasteurization on such combinations contain major drawbacks, i.e. it may lose the texture, consistency and mouth feel of discrete particle in the food product. When food products and modified food product in accordance with the present invention, these drawbacks are avoided. 
         [0004]    Several alternatives to thermal inactivation of micro-organisms exists, such as microwaves, infrared, ultra violet, gamma radiation, ionized radiation, E-beam radiation, high intensity laser or non coherent light pulses, ultrasound, ohmic heating, pulsed electric fields, high voltage electric discharges, bacterial enzymes, mild heat with slight pressurization, extrusion cooking, high pressure batch processing, high pressure throttling, and combinations of such. 
         [0005]    Microbial inactivation by high pressure (“HP”) is the result of a combination of factors. The primary site for pressure-induced microbial inactivation is the cell membrane (e.g. modification in permeability and ion exchange). Microorganisms are resistant to selective chemical inhibitors due to their ability to exclude such agents from the cell, mainly by the action of the cell membrane; however, if the membrane becomes damaged, this tolerance is lost. In addition, HP causes changes in cell morpHology and biochemical reactions, protein denaturation and inhibition of genetic mechanisms. Other mechanisms of action, which may be responsible for microbial inactivation, include the denaturation of key enzymes and the disruption of ribosomes. 
         [0006]    High pressure micro-organism inactivation through high pressure is effective for certain applications, the technology has the disadvantages of being a batch process with long process times due to the pressurization and depressurization of the vessel combined with the loading and unloading of the contents. In an effort to overcome these disadvantages, investigators have developed pulse-type mechanisms, which are essentially multiple batch processes that fill and evacuate in a throttling manner as to provide a continual flow of post-pressurized product. This type of system is mechanically intensive and economically laborious. 
         [0007]    Therefore, it would be advantageous to devise a method of assuring the protections of pasteurization, maintaining the desired functionality of a liquid food product, such as liquid egg product, and to improve the commercial feasibility of the process. 
       SUMMARY OF THE INVENTION 
       [0008]    Accordingly, the present invention involves a method and an apparatus for using high pressure to ensure microorganism, such as vegetative microorganism, inactivation in liquid products, and in particular liquid egg products. The product is subjected to high pressures of approximately 70,000 to 87,000 pounds per square inch (psi). This high pressure coupled with adjusting the temperature of the pre-pressurized food product, to the desired temperature, adjustment of pH of the pre-pressurized food product, to the desired pH, and maintaining a desired temperature of the pressurizing media disrupts the cellular function of the microorganisms, such as vegetative microorganisms, causing death or inactivation of the microorganism. 
         [0009]    High pressure pasteurization (“HPP”), also known as high hydrostatic pressure processing or ultra-high pressure processing, is to be used to pasteurize egg white, whole eggs, egg substitutes, and egg yolk at elevated pressures of approximately 70,000 to 87,000 pounds per square inch (“psi”) at a specified temperature and for a specified time. The pressure within the chamber is created via a reduction in the pressure chamber volume or a positive displacement of the pressurizing material. Under these conditions, HPP has been found to be effective in inactivating many microorganisms, such as vegetative microorganisms, commonly found in foods. As compared to canned foods or conventionally pasteurized juices and milk, HPP significantly reduces the process temperature and time, which results in foods with improved characteristics such as better retention of freshness, flavor, texture, color, and nutrients. 
         [0010]    Demand for products that appeal to consumer sensory perceptions such as aroma, texture, color, shape, and flavor equate to fresh and wholesome food. The Isostatic Rule is applicable to High Pressure Pasteurization and states that pressure is instantaneously and uniformly transmitted throughout a sample under pressure, whether the sample is in direct contact with the pressure medium or hermetically seated in a flexible package that transmits pressure. Pressure is transmitted in a uniform (isostatic) and quasi-instantaneous manner throughout the sample; the time necessary for pressure processing is therefore independent of sample size, in contrast to thermal processing. 
         [0011]    The present invention provides consumers with the safety of pasteurization in a product where the individual components of combined food products retain their natural characteristics despite the combination. For example, in a liquid egg product it may be desirous to add cheese to the egg product. However, the use of thermal pasteurization will change the characteristics of the egg and the cheese creating a mushy non-natural looking product. This non-natural product may lack the taste, texture, shape and color that the consumer comes to expect. Additionally, thermal processing may reduce the moisture of the ingredients and thus the size of the food particle within the egg product. 
         [0012]    The use of high-pressure pasteurization eliminates the need for maintaining particle size in order to achieve adequate pasteurization of additional food ingredients. Therefore, the addition of chunk cheese, whole vegetables, or meat pieces to a liquid egg product is equally pasteurized regardless of particle size. 
         [0013]    In the present invention, the waste associated with plate degradation of the food product is eliminated due to the consistent pressure and thus pasteurizing of the food product despite distribution of the product within the chamber. Because of the uniformity of effect created by the High Pressure there is no over or under processing of the food material. Therefore, no additional validation is required when adding food components in combination prior to pasteurization. 
         [0014]    The present invention involves preparing the food product, such as liquid egg product, as to pH and temperature, heating the pressurizing media to a desired temperature, subjecting the product to pressures up to 87,000 psi, and then rapidly depressurizing the pressurizing chamber or removing the food product from the high-pressure environment. The high pressure coupled with a rapid return to ambient pressure destroys microorganisms, such as vegetative microorganisms, by interrupting their cellular functions. Within a living bacteria cell, many pressure sensitive processes such as protein function, enzyme action, and cellular membrane function are impacted by high pressure resulting in the inability of the bacteria to survive. While small macromolecules that are responsible for flavor, aroma, and nutrition are typically not changed by pressure additional sensory perception may still be impacted by high pressure. In particular are the effects on liquid egg products. Liquid egg white partially coagulates when treated at pressure greater that 500 MPa, and strong self-supporting gels are formed at pressure higher than 600 MPa. However the hardness and elastic modulus of the gels remained significantly lower than those of gels obtained by heat treatment, or by longer pressurization times. The present invention utilizes pH and temperature to accentuate the effects of high-pressure on microorganisms and minimize the effects on protein and lipid components of the food product, such as liquid egg product through a reduction in pressurization times. 
         [0015]    The liquid product will be subjected to the high pressure environment via a continuous or semi-continuous flow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which: 
           [0017]      FIG. 1  is a diagram illustrating a method for pasteurizing material using high-pressure in accordance with an exemplary embodiment of the present invention; 
           [0018]      FIG. 2  is a side elevation view of a semi-continuous or continuous high-pressure pasteurization apparatus in accordance with an exemplary embodiment of the present invention. 
           [0019]      FIG. 3  is a side elevation view of a pre-packaged high-pressure pasteurization apparatus in accordance with an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    It is believed that the present invention and many of its attendant advantages will be understood by the foregoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely an explanatory embodiment thereof, it is the intention of the following claims to encompass and include such changes. 
         [0021]    It will be appreciated by those skilled in the art that liquid and non-liquid egg products pose unique problems during pasteurization resulting from changes to lipid and protein content of the egg products. Albumen represents an extensively used food ingredient, mostly because of its functional properties. The gelling, emulsifying, and foaming properties of fresh albumen are fundamental for the production and for assessing the final properties (texture, flavor, etc.), of many foods. However, most of the functional properties of egg albumen are lost or modified after even the mildest heat treatments (such as pasteurization), that are normally used for the sanitation of egg components. Moreover, the use of high pressure, for pasteurization of egg products, sufficient to achieve the desired vegetative microorganism inactivation likewise has unique problems. While the pressure-treated egg products retain their natural flavor and nutritional values other sensory perceptions are changed. Liquid egg white partially coagulates when treated at pressure greater that 500 MPa, and strong self-supporting gels are formed at pressure higher than 600 MPa. However the hardness and elastic modulus of the gels remained significantly lower than those of gels obtained by heat treatment, or by longer pressurization times. The present invention utilizes pH and temperature to accentuate the effects of high-pressure on microorganism, such as vegetative microorganisms and minimize the effects on protein and lipid components of the food product, such as liquid egg product. 
         [0022]    Referring generally to  FIG. 1 , a method of pressure processing a material is shown. In a present embodiment, the method  100  includes preparing a material into at least one of a liquid or slurry  102 . The material described in the method is a liquid egg product. The liquid egg product includes at least one nutritional ingredient. The method  100 , includes adjusting the pH of the food material to a range between 4.0 and 9.0 ( 104 ). Additionally the method  100 , prescribes that the temperature, at normal atmosphere, of the liquid egg product be between 40 degrees Fahrenheit and 120 degrees Fahrenheit and the slurry be at between 40 degrees Fahrenheit and 160 degrees Fahrenheit prior to placement in the pressure chamber  106 . 
         [0023]    In a present embodiment, the pressurizing media is set to a defined temperature  108 . The food product is placed into a pressurization chamber where a pressurizing material is pressurized  110 . Examples of pressurizing material include liquid or gas. The pressurizing media is set and maintained at a temperature of 40 degrees Fahrenheit and 120 degrees Fahrenheit. The method for achieving the pressurization may include reducing the area of the pressure chamber or expanding the content volume within the chamber. The method  100 , includes the de-pressurization of the food material  112 . 
         [0024]    In an embodiment of the present invention, the food material is in a liquid form. The pH of the liquid material is adjusted to a desired pH of between 4.0 and 9.0. The pH is adjusted with the use of NaOH and HCL, however other chemicals may be used for this purpose. For example, KOH may be utilized in place of NaOH. 
         [0025]    In further embodiments, the addition of antimicrobial agents such as Acetates, Benzoates, Diacetates, Dimethyl Dicarbonate, Lactates, Nitrates, Propionates, Sorbates, Sulfites, and carbon dioxide further enhance the effects of high pressure pasteurization. The effects of the antimicrobial agents are synergistically enhanced by the high pressure processing. 
         [0026]    In further embodiments, the temperature of the pressurizing material is maintained between 40 degrees Fahrenheit and 120 degrees Fahrenheit (At normal atmosphere). 
         [0027]    In the present embodiment, as the pressure is exerted on the liquid product within the pressure vessel the resulting high pressure is transferred to the food product and disrupts the cellular function of the microorganism, such as vegetative microorganisms. This results in the destruction or inactivation of microorganism, such as vegetative microorganisms, achieving a 2.5 to 3.0 log reduction in microorganism, such as vegetative microorganisms in the liquid product. 
         [0028]    In a further embodiment, the food material is subjected to the desired high pressure for a time sufficient to kill or deactivate the desired pathogens present. In a current embodiment of the invention, the pressure within the chamber is between 70,000 psi and 87,000 psi. In a current embodiment, the time necessary to achieve a 3.0 log reduction on a liquid egg product is between 4 and 6 minutes. 
         [0029]    Table 1 illustrates the effect of HPP on Listeria species at 70,000 psi for 4 minutes: 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Sample 
                   
                 Counts 
                 Log Decrease following 
               
               
                 Description 
                 Processed 
                 (cfu/g)* 
                 processing 
               
               
                   
               
             
             
               
                 Pasteurized egg 
                 No 
                 8.5 × 10 4   
                   
               
               
                 Pasteurized egg 
                 Yes 
                 &lt;100 
                 &gt;2.92 
               
               
                 Un-pasteurized egg 
                 No 
                 6.8 × 10 4   
               
               
                 Un-pasteurized egg 
                 Yes 
                 &lt;100 
                 &gt;2.83 
               
               
                   
               
               
                 *Refers to duplicate samples 
               
             
          
         
       
     
         [0030]    Table 2, illustrates the effect of HPP on Salmonella species at 70,000 psi for 4 minutes: 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Sample 
                   
                   
                 Log Decrease 
               
               
                 Description 
                 Processed 
                 Counts (cfu/g)* 
                 following processing 
               
               
                   
               
             
             
               
                 Pasteurized egg 
                 No 
                 1.50 × 10 5   
                   
               
               
                 Pasteurized egg 
                 Yes 
                 &lt;100 
                 &gt;3.18 
               
               
                 Un-pasteurized 
                 No 
                 8.25 × 10 5   
               
               
                 egg 
               
               
                 Un-pasteurized 
                 Yes 
                 &lt;100 
                 &gt;3.92 
               
               
                 egg 
               
               
                   
               
               
                 *Refers to duplicate samples 
               
             
          
         
       
     
         [0031]    Table 3, illustrates the effect of HPP on Bacillus subtilis at 87,000 psi for 4 minutes: 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Preprocess 
                 Processing 
                 Counts (cfu/g)* 
                 Counts 
                   
               
               
                 Sample 
                 Product 
                 Water 
                 Before 
                 (cfu/g)* After 
                 Log 
               
               
                 Description 
                 Temperature 
                 Temperature 
                 processing 
                 Processing 
                 Decrease 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Slurry pH 
                 40 
                 40 
                 5.85 × 10 5   
                 7.35 × 10 5   
                 −0.1 
               
               
                 4.6 
                 120 
                 120 
                 5.50 × 10 5   
                 4.55 × 10 4   
                 1.1 
               
               
                 (pH 
                 160 
                 120 
                 2.70 × 10 5   
                 4.50 × 10 2   
                 2.78 
               
               
                 adjusted 
               
               
                 with HCL 
               
               
                 Slurry pH 6 
                 40 
                 40 
                 5.30 × 10 5   
                 3.65 × 10 5   
                 0.16 
               
               
                   
                 120 
                 120 
                 4.45 × 10 5   
                 5.10 × 10 5   
                 −0.06 
               
               
                   
                 160 
                 120 
                 4.20 × 10 5   
                 6.50 × 10 3   
                 1.81 
               
               
                 Slurry pH 9 
                 40 
                 40 
                 7.50 × 10 5   
                 4.75 × 10 5   
                 0.2 
               
               
                 (pH 
                 120 
                 120 
                 5.70 × 10 5   
                 6.75 × 10 4   
                 0.93 
               
               
                 adjusted 
                 160 
                 120 
                 4.55 × 10 5   
                 4.15 × 10 4   
                 1.04 
               
               
                 with NaOH 
               
               
                   
               
               
                 *Refers to duplicate samples 
               
             
          
         
       
     
         [0032]    In a further embodiment the food product is egg white, whole egg, or egg product with or without additional ingredients such as dairy, vegetable, and meat products. 
         [0033]    A further embodiment is directed to an apparatus for subjecting a liquid or slurry material to high pressure in a pulse, semi-continuous, or continuous flow. Examples would include the use of liquid, gas, or mechanical means to create pressure within a pressure chamber. 
         [0034]    In a further embodiment the liquid material is held in a mixing and holding tank or chamber  202 , which is connected to a positive displacement pump  204 . The positive displacement pump includes an inlet, which is at ambient pressure and a outlet, which is at high pressure. The outlet of the positive displacement pump is constructed with a pressure valve and attachment  206 , to attach to a pressure chamber. In one example the positive displacement pump pumps liquid material into the pressure chamber and continues to fill the pressure chamber until a desired pressure is achieved. Upon achieving the desired pressure within the chamber, the liquid material is maintained at said pressure for a defined period. Upon reaching the defined time limits a high pressure valve allows for escape of the liquid material at a rate consistent with the pumping speed of the positive displacement pump such as to maintain the time and pressure for the deactivation of the micro-organisms within the liquid material. 
         [0035]    In an additional example, the liquid material is pumped through a tube  212 , which is constructed within the high-pressure chamber  208 . A resilient membrane  210 , within the pressure chamber reduces the volume of the chamber and causes a pressurizing media to exert a defined amount of pressure on the tube within the chamber. The tube, which contains the liquid material remains pliable and thus as the liquid material is coursing the tube it is subjected to the same pressure as the tube. The liquid material then exits the tube through a reduced orifice, or high pressure valve  214 , to maintain the integrity of the tube while time and pressure limits are met. The liquid material undergoes rapid de-pressurization upon exiting the tube and returns to ambient pressure. The high-pressure valve is attached to a sterile fill chamber  216 , which receives the pasteurized liquid material from the high-pressure chamber container. 
         [0036]    In a further embodiment, the food product is pre-packaged and the package and contents are introduced to the pressure chamber  304 , via a first star valve  302 . The first star valve  302  is in contact with the pressure chamber creating a air tight seal which, when the first star valve  302  is rotated, the packaged food product falls to a moving system that transports the packaged food product to a second star valve  306 . The second star valve  306 , is in contact with the pressure chamber  304  to allow for evacuation of the packaged food product following the pressurization cycle. The pressurizing media may be gas or liquid and is maintained at pressure via a reduction of volume within the high pressure chamber container, such as a resilient bag or a positive displacement pump that receives pressurizing material from external holding tank  308 . The pre-packaged food product is thus subjected to the pressurizing media, thereby upon pressurization of the chamber the contents of the package follow the Isostatic Rule.