Patent Publication Number: US-2010112151-A1

Title: High-voltage pulsed electrical field for antimicrobial treatment

Description:
The present application claims the benefit of U.S. provisional patent application No. 61/111,577, filed Nov. 5, 2008 and entitled “High-Voltage Pulsed Electrical Field for Antimicrobial Treatment,” the entire disclosure of which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a method and system for antimicrobial treatment. In particular, this invention relates to a method and system for fluid media treatment to inactivate harmful microorganisms using high-voltage nanosecond pulsed electrical field. 
     BACKGROUND 
     A high intensity pulsed electric field (“PEF”) may be employed for treating fluid medium, such as liquid products (including, but not limited to, liquid foods and medicines), to inactivate biocontamination, such as bacteria, fungi, spores etc. PEF inactivates microorganisms causing damage to their cell membranes or injuring their subcellular structure. 
     Conventional PEF processing systems include a pulsed high voltage generator and electrodes for creating an electric field in a treatment chamber. PEF processes use high voltage pulses to generate short duration pulsating electric fields in a product. The short duration of pulses is preferred to prevent undesirable heating of the treated product. 
     PEF systems generally require direct physical and electrical contact between the medium being treated and the electrodes during the treatment. Such systems typically generate a field strength within a range of 5-100 kV/cm and have a pulse duration in the range of about 0.1-100 microseconds. 
     However, using a 0.1-100 microseconds pulse duration may be less effective when attempting to treat packaged products (treatment of a medium not in direct contact with the electrodes) because of the high energy loss due to various reasons—e.g. the packaging materials and air gaps between electrodes and packaging may diminish the effect of the pulse. Additionally, high energy pulses may not be able to be applied to treat foods with high electrical conductivity because intensive electric current may cause electrical breakdown of the food and change its organoleptic properties. 
     BRIEF SUMMARY 
     Aspects of the invention may overcome disadvantages in the prior art, provide devices and methods for non-contact antimicrobial treatment of packaged products, and prevent the electrical breakdown of dielectric packaging material, which may occur when a high voltage pulsed electrical field is applied. In certain aspects, this may be accomplished by creating a quasi-uniform electrical field of high intensity in products placed into dielectric containers of complex shape. 
     It will be appreciated by those skilled in the art, given the benefit of the following description of certain exemplary embodiments of the beverage and other beverage products disclosed here, that at least certain embodiments of the invention have improved or alternative formulations suitable to provide desirable taste profiles, nutritional characteristics, etc. These and other aspects, features and advantages of the invention or of certain embodiments of the invention will be further understood by those skilled in the art from the following description of exemplary embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is illustrated by way of example and not limited in the accompanying figures in which like reference numerals indicate similar elements and in which: 
         FIG. 1  shows an illustrative pulsed electric field treatment device according to some embodiments of the present invention; 
         FIG. 2A  depicts an illustrative chart of the output of the high voltage generator in some embodiments of the invention; 
         FIG. 2B  depicts an illustrative chart of the pulse packet formed on electrodes in some embodiments of the invention; 
         FIG. 3  shows an illustrative application of a pulsed electric field treatment device to a conveyer-escalator type filling line according to aspects of the invention; and 
         FIG. 4  shows an illustrative application of a pulsed electric field treatment device to a conveyer-rotator type filling line according to aspects of the invention. 
         FIG. 5  shows an illustrative flow chart of a method that may be used to treat a product in a container according to aspects of the invention. 
         FIG. 6A  shows an illustrative complex electrode shape according to aspects of the invention. 
         FIG. 6B  shows a second illustrative complex electrode shape according to aspects of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In accordance with various aspects of the disclosure, a method and system for treatment of a product to inactivate harmful microorganisms using a high-voltage nanosecond pulsed electrical field is disclosed. The product to be treated can be any of various items including products containing oil and/or water, foodstuffs, beverages, pharmaceuticals, nutraceuticals, etc. The products may be packaged in many types of containers including bottles, which may be made from a polymer such as polyethylene terephthalate. In the following description of the various embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration various embodiments in which the invention may be practiced. Certain embodiments are described as “illustrative” or “exemplary,” which indicates that these embodiments are just examples of potential embodiments and are not to be interpreted as preferred or sole embodiments. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention. 
       FIG. 1  depicts an exemplary pulsed electric field treatment system  100  for processing products. Treatment system  100  may include high voltage generator  110 , treatment assembly  120 , and one or more electrodes  140 . Treatment assembly  120  may be filled with a medium  130  having high dielectric permeability, generally higher than approximately 30. In some embodiments, medium  130  may be de-ionized water, generally having a high dielectric permeability of approximately 80. The system may be used to treat a product  150 , which may be contained by a product container  160 . 
     One embodiment depicted in  FIG. 1  may include two electrodes  140  that may be connected to generator  110  via wires  172 ,  174 . In some embodiments, one of electrodes  140  may be grounded. In at least one embodiment, a space  190  may be formed between the electrodes  140  and may form a treatment zone where a product may be treated by an electrical field. 
     The container  160  containing product  150  may be made of a dielectric material. The container  160  may have regular or complex shape. In certain embodiments, the thickness of the walls of container  160  may be in the range of 50 micrometers to 1 millimeter. In some embodiments, the thickness of the walls of container  160  may be between 50 and 400 micrometers. In aspects of the invention, limiting the thickness of the walls of container  160  may minimize energy losses in the walls of container  160 . 
     Generator  110  may produce high-voltage single-polarity or dual-polarity electrical pulses. Exemplary amplitudes  220  of such pulses may range from 100 to 1000 kilovolts as depicted in  FIG. 2A . In certain embodiments, the output voltage generated by generator  110  may be selected by determining the electrical field strength desired inside product  150  to inactivate undesirable and/or harmful microorganisms. Energy losses that may occur due to container  160  thickness, gaps  180  between electrodes  140  and container  160 , size of container  160 , and product&#39;s  150  properties may be taken into account in determining the electrical field strength desired and/or the output voltage to be generated. In some embodiments, the electrical field strength inside product  150  is in the range of 10 to 100 kilovolts/centimeter. 
     In one embodiment, the pulse generated by generator  110  may have a duration  230  of approximately 5 to 50 nanoseconds and a rise time  240  of approximately 1 nanosecond. The nanosecond rise time may generate an electrical field of high intensity that may be delivered to the product through the dielectric material of the walls of container  160  and through the gaps between electrodes  140  and the walls of container  160  without significant losses. Pulses having short duration may avoid undesirable heating and may reduce the cost of running generator  110  due to reduced energy consumption during treatment of product  150 . 
     The number of pulses, pulse frequency, shape, and the input pulse voltage may vary based on the type of product  150  being treated, the type of microorganism contamination for which product  150  is being treated, and the required time of treatment. In some embodiments, between 1 and 10,000 pulses may be generated with an input pulse voltage in the range of 100 to 1000 kilovolts. In certain embodiments, the frequency of pulses generated may be between 1 and 10,000 Hz. 
     Electrodes  140 , together with the container  160  may be placed into treatment assembly  120 , which may be filled by medium  130  having high dielectric permeability. Electrodes  140  and container  160  do not need to be in direct contact, allowing a gap  180 . 
     Electrodes  140  may be made of various materials and may be of many shapes and sizes. In some embodiments, electrodes  140  are composed of a metal material. In one embodiment, electrodes  140  may be made of stainless steel. Stainless steel electrodes  140  may reduce electron emission from the metal to the surrounding media  130  when subjected to an electric field. Reduction of electron emission may minimize the probability of the electrical breakdown of the dielectric material of container  160 . 
     In certain embodiments, electrodes  140  may be flat plates. This shape may provide a quasi-uniform electrical field inside product  150 . The size of electrodes  140  and inter-electrode space  190  may vary depending on the size of container  160 . In other embodiments, electrodes may have a complex shape as depicted in  FIGS. 6A and 6B . The embodiment depicted in  FIG. 6A  shows electrodes  140  having a complex shape similar to the exterior shape of container  160 . In some embodiments, electrodes  140  may be of an exact shape to match the shape of container  160  such that electrodes  140  are in direct contact with container  160 . In other embodiments, electrodes  140  may not be in direct contact with container  160  such that there is a gap between electrodes  140  and container  160 . 
     Similarly, in some embodiments depicted in  FIG. 6B , electrodes  140  may directly contact container  160  whereas other embodiments may leave a gap between electrodes  140  and container  160 . The embodiment depicted in  FIG. 6B  employs a sponge  644  or sponge-like material. In such embodiments, electrodes  140  may be attached to a surface of sponge  644  and electrodes  140  may be composed of a flexible metalized film. Flexible electrodes  140  attached to a sponge  644  may allow the electrodes to form a complex shape similar to the shape of the exterior of container  160 . In some embodiments, the assembly may also include an electrode holder  646  to which sponge  644  may be attached. Electrode holder  646  may provide a firm surface to grip or attach to the rest of the assembly. There are many other possible electrode configurations. The embodiments depicted in  FIGS. 6A and 6B  are merely illustrative of two possible embodiments. Other embodiments may include depositing electrodes on the surface of container  160  such as part of a bottle label or design, embedding electrodes into aspects of the treatment assembly (such as attaching electrodes to portions of the assembly that grip or transfer container  160 , etc. In other embodiments, at least one of electrodes  140  may have a knife-point edge or be a point-source electrode. 
     In some embodiments, electrodes  140  may have a length comparable to the pulse  230  wavelength. In such embodiments, numerous pulses  230  may be reflected from both ends of electrodes  140  and form a pulse packet  250  within product  150  as shown in  FIG. 2B . The formation of pulse packet  250  may result in increasing efficacy of the inactivation of harmful microorganisms by affecting the microorganisms&#39; membranes or injuring their subcellular structure. As can be seen in  FIG. 2B , the formation of pulse packet  250  within product  150  from a single generated pulse  230  (as depicted in  FIG. 2A ) may increase the number of voltage swings that product  150  is subjected to as compared to a traditional single pulse. Subjecting product  150  to an increased number of voltage swings may assist in breaking down the organisms&#39; membranes and ripping the organisms apart. Therefore, when using electrodes  140  with a length approximately equal to the pulse wavelength, which may allow for favorable conditions to obtain resonance and maintain maximum pulse amplitude, each pulse  230  generated by generator  110  may result in an electrical field present in product  150  that includes a group of pulses, or a pulse packet  250 , without requiring additional energy from generator  110 . Variation in the length of electrodes  140  may provide different combinations of pulse interactions in the pulse packet  250  (i.e., different amplitudes, frequencies, and rise times). 
     In accordance with different sized product containers, certain embodiments may have a space between electrodes  140  (the “treatment zone”  190  or inter-electrode space) ranging from approximately 1 to approximately 10 centimeters. For containers  160  made of different dielectric materials, different gaps  180  between electrodes  140  and container  160  may be used. In some embodiments, gaps  180  may be between 0.1 millimeters and 2 centimeters, depending on the electrical breakdown properties of the dielectric material of container  160 , the thickness of the walls of container  160 , and the shape of container  160 . In one embodiment, treatment of the packaged product  150  may simultaneously inactivate microorganisms&#39; in product  150  and in the inner surface of container  160 . In such embodiments, the need to separately disinfect container  160  may be eliminated and the total cost of production may therefore be reduced. 
     In some embodiments, treatment assembly  120  may be filled with a medium  130 . In one embodiment, medium  130  may have a high dielectric permeability, which may assist in: (i) forming a quasi-uniform electrical field in all parts of the product  150 , which is placed into container  160  (container  160  may be of a complex or regular shape); (ii) avoiding the electrical breakdown of the dielectric material of container  160  by diminishing the effect of electrical voltage concentrators, which generally exist on electrodes&#39;  140  surface, (iii) passing an electrical field of high intensity to product  150  through the gaps between electrodes  140  and the walls of container  160  without significant losses. Embodiments including a medium  130  having a high dielectric permeability may result in less significant losses than embodiments including a medium having low dielectric permeability, such as air gaps. In certain embodiments, medium  130  may also have low conductivity. 
     Exemplary Process 
     In an exemplary method of treating a product with a pulsed electrical field to inactivate biocontamination in the product or the interior of the product container, a treatment assembly may be filled with a medium  130 . In some embodiments, a container meant to hold a product may be sterilized in step  510  and the product may be placed into the container in step  520 . Alternatively, the product may be placed into the container in step  520  and the container may be sterilized  510  after the product is in the container. The container may then be sterilized separately from the product in step  510 , or, alternatively, the container may be sterilized when an electrical pulse is generated in step  540 , described below. In step  530 , the container may be placed into the treatment assembly. The container may be placed in the treatment assembly in any of a variety of ways, including, for example, manually placing the container in the treatment assembly, placing the container on a conveyor line, etc. An electrical pulse may be generated in step  540 . The electrical pulse may be generated using a high voltage generator or any other system capable of producing an electrical pulse with the desired characteristics, such as field strength, duration, etc. In certain embodiments, a series of electrical pulses may be generated. In some embodiments, the wavelength of the pulse generated may be comparable to the length of the electrodes such that a pulse packet is generated. 
     EXAMPLES 
     The following examples are specific embodiments of the present invention but are not intended to limit it. 
     Example 1 
       FIG. 3  depicts one possible embodiment of the present invention that may be integrated with a conveyer line  310 . Conveyor line  310  may be used for filling container  360  with product  350 . The example shown in  FIG. 3  depicts beverages as product  350  and bottles as container  360 . The pulsed electrical field treatment device  100  may be placed along conveyer line  310 . Treatment assembly  320  may include an area that may be filled with a medium  330 . In some embodiments, medium  330  may be a medium having a high dielectric permeability. In one embodiment, medium  330  may be de-ionized water. Conveyor  310  may transport product containers  360  to treatment assembly  320 . In one embodiment, product containers  360  may be bottles. In certain embodiments, product containers  360  may be polyethylene terephthalate (PET) bottles. Optionally, a segment of conveyer line  310  may be modified to create a conveyer-escalator  315 . Product containers  360  may be transported along conveyor line  310  and, when transported to conveyer-escalator  315 , product containers  360  may enter treatment assembly  320 . As product  350  in product containers  360  pass through treatment assembly  320  along conveyor line  310 , product  350  and container  360  may pass between two electrodes  140 . At certain time intervals, product  350  and container  360  may be treated by electrical field pulses generated between electrodes  140 . High voltage pulses may be transmitted to electrodes  140  via wires  172 ,  174  from generator  110 . As a result, undesirable and/or harmful microorganisms in product  350  and on the inner surface of container  360  may be inactivated. 
     Example 2 
       FIG. 4  depicts another possible embodiment of the present invention that may be integrated with a conveyer line (not shown). Conveyor line may be used for filling container  460  with product  450 . In the embodiment depicted in  FIG. 4 , conveyer line may include conveyer-rotator  415 . In one embodiment, product containers  460  may be bottles and product  450  may be beverages. In certain embodiments, product containers  460  may be PET bottles. The pulsed electrical field treatment device  100  may be placed along conveyor line. Treatment assembly  420  may include an area that may be filled with a medium  430 . In some embodiments, medium  430  may be a medium having a high dielectric permeability. In one embodiment, medium  430  may be de-ionized water. Conveyor may transport product containers  460  to treatment assembly  420 . Container  460  may then enter a cell  417  of conveyer-rotator  415 , which may then transport container  460  to treatment assembly  420 . At certain time intervals, product  450  and container  460  may be treated by electrical field pulses generated between electrodes  140 . High voltage pulses may be transmitted to electrodes  140  via wires  172 ,  174  from generator  110 . As a result, undesirable and/or harmful microorganisms in product  450  and on the inner surface of container  460  may be inactivated. Variations of the described embodiment are also possible. For example, in some embodiments, electrodes  140  may be connected to or a part of cell  417 , such that portions of the interior lining of cell  417  may constitute electrodes  140  (one portion constituting a ground electrode and another portion constituting a charged electrode). 
     Aspects of the invention have been described in terms of illustrative embodiments thereof. Numerous other embodiments, modifications and variations within the scope and spirit of the appended claims will occur to persons of ordinary skill in the art from a review of this disclosure. For example, one of ordinary skill in the art will appreciate that the steps illustrated in the figures may be performed in other than the recited order, and that one or more steps illustrated may be optional in accordance with aspects of the disclosure. Given the benefit of the above disclosure and description of exemplary embodiments, it will be apparent to those skilled in the art that numerous alternative and different embodiments are possible in keeping with the general principles of the invention disclosed here. Those skilled in this art will recognize that all such various modifications and alternative embodiments are within the true scope and spirit of the invention.