WO2015028822A1

WO2015028822A1 - Disinfection of packaged articles

Info

Publication number: WO2015028822A1
Application number: PCT/GB2014/052637
Authority: WO
Inventors: Malcolm Snowball
Original assignee: Ozonica Limited
Priority date: 2013-08-29
Filing date: 2014-08-29
Publication date: 2015-03-05
Also published as: GB201315415D0; GB2517729A

Abstract

A method of disinfecting a packaged article is provided. The method comprises providing a first electric field extending into the package 100 of the packaged article 10 such that, in use, the first electric field causes a discharge producing ozone within a disinfection region 107 of the package. The method also comprises providing a second electric field extending into the package of the packaged article such that, in use, the second electric field drives an electric potential difference across the packaged article into the disinfection region of the packaged article.

Description

DISINFECTION OF PACKAGED ARTICLES

Field of the invention

The present invention relates to methods and apparatus for the disinfection of packaged articles such as packaged food and drink products.

Background of the invention

The shelf life of food is substantially shortened due to the presence of microorganisms in the food, which can cause the food to deteriorate. Not only does shelf life affect the economic viability of food producers but it has a direct effect on public health, since the presence of certain microorganisms in food can be hazardous if the food is ingested. These problems can be exacerbated if the food is not kept sufficiently refrigerated, since the microorganisms in the food can multiply rapidly. In order to overcome the above-mentioned problems, it has been proposed to pasteurise food. However, a disadvantage of pasteurisation is that the process is lengthy and can only be used on certain types of food. Furthermore, the pasteurisation process affects the taste of the food and is costly to perform, since it uses a substantial amount of energy, a great deal of which is discharged into the working environment. In one known method, the food is packaged in an atmosphere which inhibits the fast reproduction of microorganisms. One such an approach is to package the food product within a carbon dioxide atmosphere. This has proved to be difficult to control, environmentally unfriendly and expensive to run. GB2457057 discloses an alternative method in which the food product is disinfected by irradiating it with UV light through its sealed packaging. This method requires the packaging material to pass the disinfection wavelengths (around 260 nm) at high efficiencies, otherwise high power is required to get sufficient UV intensity into the package to disinfect the food. Present packaging materials are poor transmitters of these UV wavelengths and therefore special packaging materials need to be used. Such packaging materials are expensive and necessitate modifications to the existing packaging processes, which mean that the whole food industry will have to change its packaging equipment or develop a whole new family of packaging materials.

In order to achieve adequate disinfection inside a sealed package it is necessary that all of the product surfaces are irradiated with the UV light. This is extremely difficult to achieve, for example in the case of sliced meat or cheese where the light will not reach between the slices therefore the disinfection effect will be marginal and therefore the shelf life will not be improved. The method also suffers from susceptibility to dust and dirt, since the UV lamps must be clean at all times and it will be appreciated that the general environment in the food processing industry does not lend itself to this. This method also has the added disadvantage that the UV light must have a clear "window" to penetrate the package i.e. no labeling or printing on the package. This makes the packaging process inflexible and forces packaging process redesign. It is well known that ozone is a highly oxidising gas, which is a very efficient disinfector of microorganisms. Ozone has a very short life (about 20 minutes) before it naturally reverts back to oxygen and therefore ideally suited for extending the shelf life of food sold in sealed packages and for killing other harmful microorganisms that may be contained in the food such as e-coli.

GB2457057 also discloses a method in which the food product is further disinfected in its sealed package by creating ozone inside the package using UV light of ozone producing wavelengths. Ozone, being a gas with very efficient disinfection properties, will permeate everywhere inside the sealed package and will therefore disinfect the product. Unfortunately this method suffers from the same disadvantages as the above-mentioned UV disinfection method, in that the packaging materials to pass such UV wavelengths are even more special and are expensive to buy and process. Also, the ozone producing wavelengths are in the vacuum UV range (around 185 nm) and known packaging materials pass these wavelengths inefficiently and hence are energy inefficient.

In practice, the amount of ozone produced by UV methods is relatively low and is significantly affected by atmospheric humidity. Accordingly, in a fixed flow process where the time to dose each package is fixed, it is very difficult to get a consistent ozone dose. This method also produces nitrous oxide as a by-product from the gas inside the package which is undesirable, since nitrous oxide combined with water produces nitric acid which will damage the product. Another drawback to this approach is that there is an amount of unwanted ozone produced in the gas spaces surrounding the UV lamp, which must be neutralized as free ozone is a regulated substance because the presence of ozone in the atmosphere presents a health hazard. This method also has the added disadvantage that the UV must have a clear window to penetrate the package i.e. no labeling or printing on the package. This makes the packaging process inflexible and forces packaging process redesign. Another known method of sterilising food comprises creating ozone inside a sealed package using conventional corona discharge methods. This entails a metal electrode placed either side of the sealed package and a high voltage ac supply coupled to the electrodes. The high voltage creates a corona discharge between the electrodes, which then converts some of the oxygen in the gas in the package to ozone.

Whilst this method avoids some of the problems with the UV irradiation method, it still suffers from some serious shortcomings. The method uses metal electrodes, which heat up to a significantly high temperature during operation and therefore need to be force cooled. These electrodes are in close proximity to the packaging material and hence have to be cooled to less than 70 degrees centigrade; otherwise the packaging material is degraded. This usually requires water cooling with its associated pumping and heat exchanger systems. This method is a discharge system, which means that electrons are discharged between the electrodes under high voltage conditions: as a consequence there is erosion and hence deterioration of the electrodes leading to short electrode life and hence poor reliability. Discharges of this technology are uncontrolled avalanche types, which not only penetrate the packaging material but also the product and can be very detrimental to some products. This method usually cannot be repeated more than once as the product deterioration due to repeated corona discharge is unacceptable. Corona discharge whilst producing medium to high levels of ozone also suffers from inconsistent ozone production due to atmospheric humidity and worse produces high levels of nitrous oxide from the nitrogen in the gas inside the package. As a consequence this method is usually confined to applications where the packaging environment is pure oxygen and hence no nitrous oxide is formed. To package product in oxygen is both difficult to control and expensive. International Patent application WO2010/1 16191 discloses a plasma-generating apparatus and method in which two electrodes are arranged so that, upon the application of a sufficiently high voltage, the electromagnetic field between the electrodes creates cold plasma energetic enough to convert oxygen in gas into ozone and other reactive oxygen based species. Further work by the same inventor has provided a variety of practical configurations of electrodes.

In practical systems which use the application of electric field to generate ozone for disinfection of packaged articles, dielectric breakdown of components of the apparatus, and of the package, can be a significant problem. The need to replace damaged apparatus or the wastage of packaged articles may have adverse environmental implications.

The inventor has also recognised that not all microorganisms in a packaged article may be exposed to the ozone, for example if they are buried in a wrinkle on fatty tissue or held between layers of sliced meat or cheese, for example. In these cases the disinfection effect may still not be satisfactory and as a result shelf life will still be compromised.

Summary of the invention

A first aspect of the invention provides a method of disinfecting a packaged article, the method comprising:

providing a first electric field extending into the package of the packaged article to produce, for example, plasma within a disinfection region of the package, and

providing a potential difference across the packaged article and into the disinfection region to subject the packaged article to a second electric field.

A second aspect of the invention provides a packet disinfector for disinfecting packaged articles, comprising:

a first electric field applier configured to provide an alternating voltage to cause a first electric field extending into the package of the packaged article to produce, for example, plasma within a disinfection region of the package; and

a second electric field applier configured to provide a potential difference extending across the packaged article and into the disinfection region, to subject the packaged article to a second electric field. The first electric field may comprise an alternating field, with a frequency of at least 50 Hz. The alternating field may comprise, for example, a radio frequency (RF) field with a frequency of between 3 kHz and 300 GHz. The first electric field may cause a discharge that produces ozone to aid disinfection. The potential difference may be provided by a pulsed DC electric field. The pulsed DC electric field may be provided by a rectified AC voltage supplying the second electric field applier. Advantageously, in this and other related aspects of the invention, the potential difference provided by the second electrical field may drive charged matter from the packaged article toward the disinfection region. The method may further comprise controlling the potential difference across the packaged article. The potential difference may be controlled so that it does not exceed a selected limit. For example, the potential difference may be controlled so that it does not exceed 80 kV, or does not exceed 60 kV. For example, the potential difference may be at least 10 kV.

At least one of the first and second electric fields may comprise pulsed electric fields. The duty cycle of the fields may be varied to control the power supplied to the package. The duty cycle of the first and/or second electric fields may be at least 10 %, or at least 15 %, or at least 20 %. For example, the duty cycle may be at most 80 %, or at most 50 %.

The second electric field may be transverse to the first electric field. The second electric field may comprise a DC electric field. The DC electric field may include electric fields that are slightly alternating but substantially biased in one polarity. For example, the DC electric field may comprise pulses of one polarity each followed by an undershoot of relatively lower magnitude pulses of a second polarity. The second electric field may be provided when the first electric field is producing ozone. For example, the second electric field may be controlled so that the magnitude of the second electric field is relatively higher when the first electric field is generating ozone or plasma than when it is not. The second electric field may comprise an alternating field with a non-zero DC component, for example a time- varying signal with a non-zero time average such as a pulse train, a square wave or a sine wave superimposed on a DC offset. The first electric field may be provided by a first electric field applier, and the second electric field may be provided by a second electric field applier. The second electric field applier may be referenced to the first electric field applier such that the potential difference that subjects the article to the second electric field comprises a potential difference between the second electric field applier and the first electric field applier. Referencing the electric field appliers may comprise electrically coupling the electric field appliers. For example, the electric field appliers may be conductively coupled. The electric field appliers may be referenced by being coupled to a common reference voltage, such as an earth, for example a floating earth.

The phase of the second electric field may be referenced to the phase of the first electric field. Referencing the phases of the electric fields may comprise synchronising the phases of the electric fields or referencing the phases to have a phase difference, such as a controlled, a variable, or a constant phase difference. For example, the second electric field may be provided when the first electric field is producing ozone. The second electric field may not be provided when the first electric field is not producing ozone.

The electric field appliers may comprise a power supply or supplies, a transformer, an oscillator and an electrode assembly. The power supply and/or oscillator may have an inductance and a capacitance, and so the electric field appliers may have a resonant frequency.

The first electric field applier may comprise a first electrode assembly with a first electrode and a second electrode. The first electrode and the second electrode may be in a substantially coplanar arrangement. The first electrode assembly may comprise a dielectric arranged between the first electrode and the second electrode. The dielectric may have a breakdown voltage of at least 20 kV per mm. The dielectric may be selected from a list comprising: fused quartz, borosilicate glass, boron nitride, shapal®, mica, and synthetic mica such as synthetic fluorophlogopite. The first electrode and the second electrode may be interleaved.

The second electric field applier may have a second electrode assembly. The second electrode assembly may comprise an electrode. The second electrode assembly may be in a plane parallel to the first electrode assembly. The second electrode assembly may be powered by a high voltage power supply. The high voltage power supply may be configured to provide a voltage of at least 5 kV, or at least 10 kV, or at least 20 kV, or at least 40 kV, for example, at most 80 kV. The high voltage power supply may use two transformers with their primaries in parallel and their secondaries in series. At least one of the first electric field applier and the second electric field applier may be earthed. The first and second field appliers may have respective electrode assemblies that may be spaced apart to receive a package therebetween. A first electrode assembly may be provided adjacent to the disinfection region of the package. For example, a first electrode assembly may be provided on one side of the package, and a second electrode assembly may be provided on the opposite side of the package. The package may further have a conductive portion. The second electric field applier may be in contact with the conductive portion. For example, the second electrode assembly may have an electrode in contact with the conductive portion. The disinfection region may comprise a gas space within the package.

A third aspect of the invention provides a method of disinfecting packaged articles, the method comprising:

providing an alternating voltage to cause an electric field to extend into the package of the packaged article;

obtaining a signal based on power supplied to the package; and

controlling a frequency of the alternating voltage, based on the obtained signal, to control the power supplied to the package. A fourth aspect of the invention provides a packet disinfector for disinfecting packaged articles, comprising:

an electric field applier configured to provide an alternating voltage to cause an electric field to extend into the package of the packaged article and cause a discharge, producing, for example, plasma within a disinfection region of the package;

wherein the packet disinfector further has a controller configured to obtain a signal based on the power supplied to the package, and to control the frequency of the electric field applier, based on the obtained signal, to control the power supplied to the package.

A fifth aspect of the invention provides a packet disinfector configured to perform the method of any one of the first and/or third aspects of the invention.

The signal based on power supplied to the package may be based on power consumed, for example, by an electric field applier or an electric field. For example, the power consumed may be the power consumed by an oscillator or a power supply. The signal may be based on current and/or voltage, and/or may be a phase difference. In one example, controlling the power comprises limiting the voltage, for example holding the voltage within a selected range, and varying the frequency of the alternating voltage. For example this may enable the power to be controlled to remain within a selected range.

In another example, controlling the power comprises controlling the driving frequency of a power supply to an electric field applier to control the power supplied to the package. For example, the driving frequency of a power supply may be controlled. Additionally or alternatively, an inductance and/or a capacitance of an electric field applier may be controlled to control the resonant frequency of the alternating voltage. For example, the inductance and/or capacitance of a power supply and/or an oscillator of the electric field applier may be controlled.

Any aspects of the inventions, in so far as they are compatible, may be combined with any other aspects of the invention.

For example method aspects may be combined with apparatus aspects, and features described with reference to the operation of particular elements of apparatus may be provided in methods which do not use those particular types of apparatus. In addition, each of the features of each of the embodiments is intended to be separable from the features which it is described in combination with, unless it is expressly stated that some other feature is essential to its operation. Each of these separable features may of course be combined with any of the other features of the embodiment in which it is described, or with any of the other features or combination of features of any of the other embodiments described herein.

Brief Description of the Drawings

Embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 shows a general schematic view of an apparatus for packaging a packaged article and for generating ozone in the package and providing a potential difference across the packaged article;

Fig. 2 shows a schematic view of a first electric field applier for generating ozone in a package and a second electric field applier providing a potential difference across a packaged article;

Fig. 3 shows a schematic view of a first electrode assembly and a second electrode assembly for generating ozone in a package and providing a potential difference across a packaged article whereby the resonant frequency of a power supply can be controlled; 5 Fig. 4 shows a flow chart illustrating a method of disinfecting a packaged article.

Detailed Description of the Invention

In overview, methods and apparatus of the disclosure may be generally employed in systems substantially similar to that shown in Fig. 1.

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Fig. 1 shows an article 10 to be packaged. Downstream from article 10 on a conveyor belt (not shown) is a packaging apparatus 200.

Sealed package 100 has a gas space 107 and a conductive portion 105. The conductive 15 portion 105 is on the base of the package 100 and forms an outer surface to the package 100. The gas space 107 is within and towards the top of the package 100. The gas space 107 contains, amongst other gases, oxygen.

Downstream from the packaging apparatus 200 on the conveyor belt is packet disinfector 20 50. The packet disinfector 50 has two electric field appliers, first electric field applier 160, and second electric field applier 162. The electric field appliers 160, 162 are coupled to respective first and second programmable logic computers 140, 142. The electric field appliers 160, 162 comprise respective power supplies 120a, 120b, respective oscillators 130a, 130b, respective transformers 150, 152 and respective electrode assemblies 103, 25 101.

For example, first electric field applier 160 comprises a power supply 120a. The power supply 120a is coupled to the programmable logic computer 140 and an oscillator 130a. The oscillator 130a is coupled to the programmable logic computer 140, oscillator 130b of 30 the second electric field applier 162, and transformer 150. Transformer 150 is coupled to a first electrode assembly 103. Second electric field applier 162 comprises a power supply 120b. The power supply 120b is coupled to the programmable logic computer 142 and an oscillator 130b. The oscillator 130b is coupled to the programmable logic computer 142, oscillator 130a of the first electric field applier 160, and transformer 152. Transformer 152 is coupled to a second electrode assembly 101.

The two electrode assemblies 101 , 103 are spaced apart to receive a package 100 between them. The second electrode assembly 101 is in a plane parallel to the first electrode assembly 103.

The first electric field applier 160 is arranged to provide a first electric field extending into the package 100 of the packaged article 10. The programmable logic computer 140 controls the power supply 120a to operate oscillator 130a. The output from the oscillator causes the first electric field to emanate from the first electrode assembly 103. The second electric field applier 162 is arranged to provide a potential difference across the packaged article 10 and into the gas space 107 of the package 100, to produce a second electric field. The programmable logic computer 142 controls the power supply 120b to operate oscillator 130b. The output from the oscillator 130b causes a potential difference between the first electrode assembly 103 and the second electrode assembly 101. In this way, the packet disinfector 50 is arranged to provide a first electric field extending into the package 100 of the packaged article 10 to cause a discharge producing ozone within a disinfection region of the package 100, and provide a potential difference across the packaged article 10 and into the disinfection region to subject the packaged article to a second electric field.

Figs. 2 and 3 show the configuration of the packet disinfector 50 in more detail. The first electrode assembly 103 comprises two electrodes, 103a and 103b, which are interleaved in a substantially coplanar arrangement. The first electrode assembly 103 comprises a dielectric arranged between the first electrode 103a and the second electrode 103b, while the second electrode assembly 101 comprises one electrode 101 a. The electrode 101 a is in the form of a plate, covering substantially the entire area of the conductive portion 105 of the package 100.

Each electrode assembly 101 , 103 is coupled to respective oscillators 130a, 130b and power supplies 120a, 120b. The power supply 120b for the second electrode assembly 101 comprises a high voltage power supply, capable of providing a voltage output to the second electrode assembly 101 of at least 40 kV. Between each oscillator 130a, 130b and electrode assembly 101 , 103 is a respective transformer 150, 152. The transformer 152 for the second electrode assembly 101 comprises two additive polarity high voltage transformers, with their primaries in parallel and their secondaries in series. The electrode assemblies 101 , 103 are conductively coupled by referencing lines 1 17, 1 19. Referencing line 1 19 is coupled in parallel to the oscillator 130a of the first electric field applier and in parallel to the oscillator 130b of the second electric field applier 162. Referencing line 1 17 is coupled in parallel to an output from the transformer 150 of the first electric field applier and in series to an output of the transformer 152 of the second electric field applier. Referencing line 1 17 is earthed.

The second electric field applier 162 has a rectifying diode 1 15 located between the second electrode assembly 101 and the transformer 152.

Voltage and current sensors 109, 1 1 1 are coupled between the first electric field applier 160 and the first programmable logic computer 140, while a second voltage sensor 1 13 is coupled between the second electric field applier 162 and the second programmable logic computer 142. For the first electric field applier, the voltage and current sensors 109, 1 1 1 are located between the transformer 150 and the first electrode assembly 103. For the second electric field applier, the second voltage sensor 1 13 is coupled to the transformer 152 and to the second electrode assembly 101 , and before the rectifying diode 1 15. Packaging apparatus 200 is operable to package article 10 into a sealed package 100. The conveyor belt is operable to transport the article 10 into the packaging apparatus 200, and to transport the packaged article 100 from the packaging apparatus to the packet disinfector 50. The first electrode assembly 103 is arranged to be held against the package 100 adjacent the gas space 107. The second electrode assembly 101 is arranged to be held against the conductive portion 105. In this way, one electrode assembly 103 is on one side of the package 100 and the other electrode assembly 101 on the opposite side of the package 100.

The first electric field applier 160 is arranged to provide a first electric field extending into the package 100 of the packaged article 10. The first electric field is a pulsed alternating field with a frequency of 40 kHz. The first electric field has a duty cycle of 20 %, and operates in 50 ms bursts. The first electric field causes a discharge within the gas space 107 of the package, producing disinfecting ozone. The gas space 107 therefore comprises a disinfection region.

The second electric field applier 162 is arranged to provide a potential difference across the packaged article 10 and into the gas space 107 of the package 100, to produce a second electric field. The second electric field is a pulsed DC field. The pulsed DC field is provided from an AC input using rectifier 115.

The potential difference produces a second electric field transverse to the first electric field. The potential difference is controlled by the programmable logic computers 140, 142 that act as respective controllers for the electric field appliers 130a, 130b, so that the potential difference does not exceed a selected limit. In this case the selected limit is 80 kV. The programmable logic computers 140, 142 also control the second electric field applier 162 so that the potential difference and hence the second electric field are provided when the first electric field is applied. In this case, the first electric field and the second electric field are controlled so that the phases of the fields are synchronised.

Voltage and current sensors 109, 1 1 1 are arranged to obtain the current and voltage output from the electric field applier 130a to the first electrode assembly 103 and feed this information to the programmable logic computer 140. Voltage sensor 1 13 obtains the voltage output from the electric field applier 130b and feeds this information to the programmable logic computer 142.

The programmable logic computers 140, 142 can obtain a signal based on power supplied to the electric field appliers 160, 162. The power supplied is based on the current and voltage applied to the electrode assemblies 101 , 103 as measured by current and voltage sensors 109, 1 1 1 and 1 13.

Both electric field appliers 160, 162 have an inductance and a capacitance, and so the electric field appliers 160, 162 have a resonant frequency. For example, the electrodes 103a, 103b of the first electrode assembly 103 and the electrode 101 a of the second electrode assembly 101 have an inductance and a capacitance, and the secondary of the transformers 150, 152 have an inductance. Referencing line 1 17 is earthed so that the electric field appliers 130a, 130b have a common earth. Referencing line 1 17 conductively couples the electric field appliers 160, 162 so that a potential difference can be applied to the packaged article 10 between the first electrode assembly 103 and the second electrode assembly 101. By coupling the 5 electrode assemblies in this way, the electric field produced by the electric field appliers 160, 162 can be referenced to be in phase using the programmable logic computers 140, 142.

The packet disinfector 50 is arranged to disinfect the package 100 according to the method 10 as shown in Fig. 4, and the package 100 can then be passed on by the conveyor belt ready for storage, delivery or use as appropriate.

The conveyor belt transports the article 10 into a packaging apparatus 200. The packaging apparatus 200 packages the article 10 into a sealed package 100. The conveyor belt 15 transports the article from the packaging apparatus 200 to the packet disinfector 50.

Fig. 4 illustrates a method of disinfecting packaged articles using the apparatus of Figs 1 to 3. The method comprises providing 200 with the first electric field applier 160 and electrode assembly 103 a first electric field extending into the package 100 of the packaged article 20 10.

The method also comprises providing 202 with the second electric field applier 162, powered by a second power supply 120b, a potential difference across the packaged article 10.

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The method also comprises obtaining 204 a signal based on power supplied to the electric field appliers 130a, 130b.

The method also comprises controlling 206 the power supplied to the package 100 by 30 controlling the driving frequencies of the power supplies 120a, 120b to the electric field appliers, based on the obtained signal.

In this way, without wishing to be bound by theory, it is believed that the potential difference provided by the second electric field applier 162 causes charged matter, such as microorganisms, to be driven into the disinfection region 107. This helps to ensure the packaged article 10 is sufficiently disinfected in order to provide an adequate shelf life.

In some configurations, the system may not comprise a conveyor belt. For example, the package 100 and packaged article 10 may be moved between the packaging apparatus 200 and the packet disinfector 50 manually.

If the gas space does not contain oxygen, disinfecting plasma may still be produced by the first electric field provided by the first electric field applier 160. For example, the gas space may comprise nitrogen. In some configurations the gas space may comprise a number of gases. The conductive portion 105 of the package 100 may comprise any conductive element to provide electrical coupling between the packaged article and the second electric field applier, for example, the conductive portion 105 may comprise a foil tray. In some configurations, the package 100 may not comprise a conductive portion, for example the coupling between the second electric field applier and the packaged article may be capacitive rather than conductive.

In some configurations, the packet disinfector 50 may comprise more than two electric field appliers. In some configurations the programmable logic computers 140, 142 may be replaced by any other device capable of acting as a controller for the electric field appliers 160, 162. In some configurations, the packet disinfector 50 may comprise only one electric field applier and/or one programmable logic computer. In some configurations the packet disinfector 50 may not comprise a programmable computer at all. In some configurations the packet disinfector 50 will have other means to control the electric fields applied to the package 100. The programmable logic computer 140, 142 make comprise any controller, such as a general purpose processor configured with a computer program product configured to program the processor to operate according to any one of the methods described herein. In addition, the functionality of such a processor may be provided by an application specific integrated circuit, ASIC, or by a field programmable gate array, FPGA, or by a configuration of logic gates, or by any other control apparatus.

In some configurations, the transformers 150, 152 may comprise additive polarity transformers or reverse polarity transformers. The transformer 152 for the second electric field applier 130b and second electrode assembly 101 may comprise one transformer. In some configurations the electric field appliers 160, 162 may comprise no transformer.

In some configurations, the power supply 120b and electric field applier 130b may be slaved to the power supply 120a and electric field applier 130b. In other configurations, the second electric field applier 130b may be coupled to the same power supply as the first electric field applier 130b, so that there is only one power supply.

In some configurations, the first electric field may a pulsed alternating field with a frequency of at least 50 Hz. For example, the first electric field may be a radio frequency RF field, which may have a frequency of between 3 kHz and 300 GHz. The first electric field may have a duty cycle of at least 20 %, for example at least 40 %. The first electric field may operate in bursts of at least 50 ms or less than 50 ms. While first electrode assembly 103 is described above as being located in a plane parallel to the second electrode assembly 101 , in other configurations the electrode assemblies may be configured in other orientations. For example, the first and second electrode assemblies 103, 101 may be in the same plane, or the second electrode assembly 103 may be in a plane perpendicular to the first electrode assembly 103. Therefore, while the first and second electric fields described above are transverse to each other, in some configurations the electric fields may be in other orientations. For example, the electric fields may be parallel to each other.

In some configurations, the first electrode assembly 103 may comprise more than two electrodes. Similarly, while the electrode 101 a of the second electrode assembly 101 in the example described above is in the form of a plate, the second electrode assembly 101 may be in other shapes and may comprise more than one electrode. If there are at least two electrodes, in some configurations the electrodes of the electrode assemblies 103, 101 may follow a serpentine or zigzag path. The electrodes may comprise interdigitated elongate fingers.

In some configurations, the first and/or second electrode assembly 103 may be adapted to surround at least part of the package 100, for example it may comprise a partial or complete ring adapted to be placed around the package 100. ln some configurations, the second electrode assembly 101 may comprise a conductive member in contact with the conductive portion 105 of the package 100. The conductive member may, for example, comprise a clamp that clamps on to a region of the conductive 5 portion 105 of the package 105.

In some configurations, the signal based on power supplied by the electric field appliers 160, 162 may be the power supplied to at least one of the power supplies 120a, 120b. In this case, the voltage and current sensors 109, 1 1 1 , 113 may be coupled to the electric field 10 applier between the oscillators 130a, 130b and the power supplies 120a, 120b, or before the power supplies 120a, 120b. In some configurations, the signal may be the power supplied to at least one of the oscillators 130a, 130b. In this case, the voltage and current sensors 109, 1 1 1 , 1 13 may be coupled to the electric field appliers 160, 162 before the power supplies 120a, 120b.

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In some configurations, the power control of the electric field appliers 160, 162 may be optional. For example, the packet disinfector 50 may not have voltage and current sensors 109, 1 1 1 and 1 13. In this way, the method of disinfecting a packaged article may not comprise obtaining 204 a signal based on power supplied to the electric field appliers 130a, 20 130b. The method of disinfecting a packaged article may also not comprise controlling 206 the power supplied to the package 100.

In some configurations, the electric fields may be referenced so that the phases of the electric fields have a constant phase difference or a variable phase difference. In some 25 configurations, the electric field appliers 160, 162 may have only one referencing line. In some configurations, the electric field appliers may not have any referencing lines. Instead the electric field appliers 160, 162 may be referenced in some other way. For example, the electric field appliers 160, 162 may be capacatively coupled. In some configurations the electric field appliers 160, 162 may not be referenced at all.

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In some configurations, the rectifying diode 1 15 may be located elsewhere in the electric field applier 162. In other configurations, the electric field applier 162 may not comprise a rectifying diode. In such configurations, the input for the second electric field may be, for example, a square wave input. The present invention is applicable to the disinfection of perishable and non- perishable products in sealed packages across a wide range of applications. The following list is by no means exhaustive and includes food items, bottled drinks, bottled sauces, produce such as salad, medical tools and instruments, baby's bottles etc. Other examples and variations will be apparent to the skilled reader in the context of the present disclosure.

Claims

CLAIMS:

1. A method of disinfecting packaged articles, the method comprising:

providing with an electric field applier an alternating electric field extending into the package of the packaged article to cause a discharge producing ozone within a disinfection region of the package;

obtaining a signal based on power supplied to an electric field applier; and controlling the frequency of the alternating electric field, based on the obtained signal, to control the power supplied to the package.

2. The method of claim 1 wherein controlling the frequency comprises controlling the frequency of a voltage that provides the electric field based on the obtained signal to maintain the amplitude of the voltage within a selected range.

3. The method claim 1 or 2 wherein controlling the power comprises maintaining the power within a selected range.

4. The method of claim 2 or 3 comprising controlling the driving frequency of a power supply coupled to an electric field applier to control the power supplied to the package.

5. A method of disinfecting a packaged article, the method comprising:

providing a first electric field extending into the package of the packaged article to cause a discharge producing ozone within a disinfection region of the package, and providing a potential difference across the packaged article and into the disinfection region to subject the packaged article to a second electric field.

6. The method of claim 5 wherein the first electric field is an alternating electric field; the method further comprising:

obtaining a signal based on power supplied to provide the first electric field and controlling the frequency of the first electric field based on the obtained signal, to control the power supplied to the package, for example further comprising the methods of any of claims 2 to 4.

7. The method of claim 5 or 6 wherein the second electrical field is configured to drive charged matter from the packaged article towards the disinfection region.

8. The method of any of claims 5 to 7 wherein at least one of the first and second electric fields comprise pulsed electric fields.

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9. The method of any of claims 5 to 8 further comprising controlling the potential difference across the packaged article so that it does not exceed 80 kV.

10. The method of any of claims 5 to 9 wherein the second electric field comprises a DC 10 electric field.

1 1. The method of any of claims 5 to 10 wherein the first electric field comprises an alternating electric field.

15 12. The method of any of claims 5 tol l wherein the second electric field comprises a field transverse to the first electric field.

13. The method of any of claims 5 to 12 wherein the first electric field is provided by a first electric field applier, and the second electric field is provided by a second electric field 20 applier, the method further comprising referencing the second electric field applier to the first electric field applier such that the potential difference of the second electric field comprises a potential difference between the second electric field applier and the first electric field applier.

25 14. The method of any of claims 5 to 13 wherein the method further comprises referencing the phase of the second electric field to the phase of the first electric field.

15. The method of claims 5 to 14 wherein the second electric field is provided when the first electric field is producing ozone, and the second electric field is not provided when the

30 first electric field is not producing ozone.

16. A packet disinfector configured to perform the method of any one of the previous claims.

17. A packet disinfector for disinfecting packaged articles, comprising:

an electric field applier configured to provide an alternating voltage to cause an electric field to extend into the package of the packaged article to produce ozone within a disinfection region of the package;

5 wherein the packet disinfector comprises a controller configured to obtain a signal based on the power supplied to the package by the electric field applier, and to control the frequency of the alternating voltage based on the obtained signal to control the power supplied to the package.

10 18. The packet disinfector of claim 17 wherein the controller is configured to control the frequency of the alternating voltage based on the obtained signal to maintain the voltage within a selected range.

19. The method of claim 17, or claim 18 wherein the controller is configured to maintain 15 the power within a selected range.

20. A packet disinfector for disinfecting packaged articles, comprising:

a first electric field applier configured to provide an alternating voltage to cause a first electric field extending into the package of the packaged article to produce ozone within 20 a disinfection region of the package; and

a second electric field applier configured to provide a potential difference extending across the packaged article and into the disinfection region, to subject the packaged article to a second electric field.

25 21. The packet disinfector of claim 20, wherein the packet disinfector further has a controller configured to obtain a signal based on power supplied, and to control the frequency of the alternating voltage, based on the obtained signal, to control the power supplied to the package.

30 22. The packet disinfector of claim 16 or 18 in which the controller is configured to control at least one of an inductance and a capacitance of the electric field applier to control the frequency of the alternating voltage.

23. The packet disinfector of any one of claims 16 to 22 wherein the second electric field applier is powered by a high voltage power supply of at least 5 kV.

24. The packet disinfector of any one of claims 16 to 23, wherein the first electric field applier comprises a first electrode assembly comprising a first electrode and a second electrode in a substantially coplanar arrangement.

25. The packet disinfector of any of claims 20, or 21 to 24 as dependent thereon wherein the second electric field applier is adapted to be coupled electrically with a conductive portion of a package.

26. The packet disinfector of any of claims 20, or 21 to 25 as dependent thereon wherein the first and second electrode assemblies are spaced apart to receive a package therebetween, so that the first electrode assembly is adjacent to the package to produce ozone within a disinfection region.

27. The packet disinfector of any one of claims 24 to 26 wherein the second electric field applier comprises an electrode assembly in a plane parallel to the first electrode assembly.

28. The packet disinfector of claim 26 or 27 wherein the first electrode assembly is adapted to be adjacent to the disinfection region of the package.

29. The packet disinfector of any one of claims 26 to 28, configured to provide the first electrode assembly on one side of the package, and the second electrode assembly on the opposite side of the package.

30. The packet disinfector of any one of claims 16 to 29 configured to provide the disinfection region in a gas space within the package.

31. The packet disinfector of any one of claims 16 to 30 wherein at least one of the first electric field applier and the second electric field applier are earthed.

32. A method of disinfecting substantially as described herein with reference to, and as illustrated in, the accompanying drawings.

33. A packet disinfector substantially as described herein with reference to, and illustrated in, the accompanying drawings.