GB2487796A

GB2487796A - Pulsed electric field treatment using boron doped diamond electrodes

Info

Publication number: GB2487796A
Application number: GB1102076.5A
Authority: GB
Inventors: Nickolas Charles Edward Speakman
Original assignee: CORDON Ltd
Current assignee: CORDON Ltd
Priority date: 2011-02-07
Filing date: 2011-02-07
Publication date: 2012-08-08
Also published as: GB201102076D0

Abstract

A treatment chamber 100 for a treatment apparatus for preserving pumpable food products in a pulsed electric field comprises an inlet 110 for receiving the food products, an outlet 120 for expelling the treated food products, a first electrode 130 abd a second electrode placed between the inlet and the outlet. The electrodes are electrically insulated from each other and being arranged such that upon application of a potential across the first electrode and the second electrode a food product in the treatment chamber is subjected to an electric field. The first and second electrodes are boron-doped diamond electrodes. Boron doped diamond electrodes are able to withstand high field strengths and pulsation frequencies and do not degrade to produce toxic degradation products.

Description

FOOD PRODUCT TREATMENT CHAMBER, TREATMENT APPARATUS AND

TREATMENT METHOD

FIELD OF THE INVENTION

The present invention relates to a treatment chamber for a treatment apparatus for preserving pumpable food products in a pulsed electric field, the treatment chamber comprising an inlet for receiving the food products, an outlet for expelling the treated food products, a first electrode placed between the inlet and the outlet, a second electrode placed between the inlet and the outlet, said first electrode and second electrode being electrically insulated from each other and being arranged such that upon application of a potential across the first electrode and the second electrode a food product in the treatment chamber is

subjected to an electric field.

The present invention further relates to a treatment apparatus including such a treatment chamber.

The present invention yet further relates to a method of treating food products using such a treatment apparatus.

BACKGROUND OF THE INVENTION

The preference of consumers for fresh foods has led to the development of mild preservation technologies. Food producers are looking for solutions to prevent the growth of micro-organisms without compromising the initial quality of products. New processes are being evaluated and products have found their way to the market. Most remarkable are the preservation processes whereby products are subjected to a physical treatment at temperatures less than those required for heat pasteurisation. Consequently, the initial quality of products is no longer adversely affected by heating. Preservatives are less frequently required to extend the shelf life of products. The absence of additives is an important issue regarding regulatory aspects both in Europe and the United States. The importance lies in the fact that both the European Food Safety Authority (EFSA) and the United States Food and Drug Administration (FDA) distinguish processes where physical treatment takes place from processes where additives are used.

Pulsed electric field (PEF) processing is a non-thermal method of food preservation that uses short bursts of electricity for microbial inactivation and causes minimal or no detrimental effect on food quality attributes. PEF can be used for processing liquid and semi-liquid food products. PEF processing offers high quality fresh-like liquid foods with excellent flavor, nutritional value, and shelf-life. Since it preserves foods without using heat, foods treated this way retain their fresh aroma, taste, and appearance. PEF has also been applied to enhance extraction of sugars and other cellular content from plant cells, such as sugar beets, and for the breakdown of starch. PEF also found application in reducing the solid volume (sludge) of wastewater.

In the food industry, PEF processing involves treating foods placed between electrodes by voltage pulses in the order of 20-80 kV, usually for a few microseconds per pulse. The applied high voltage results in an electric field that causes microbial inactivation. The electric field may be applied in the form of exponentially decaying, square wave, bipolar, or oscillatory pulses and at ambient, sub-ambient, or slightly above-ambient temperature. After the treatment, the food is packaged aseptically and stored under refrigeration.

PEF treatment has lethal effects on various vegetative bacteria, mold, and yeast. Efficacy of spore inactivation by PEF in combination with heat or other hurdles is a subject of current research. A series of short, high-voltage pulses breaks the cell membranes of vegetative microorganisms in liquid media by expanding existing pores (electroporation) or creating new ones. Pore formation is reversible or irreversible depending on factors such as the electric field intensity, the pulse duration, and number of pulses. The membranes of PEF-treated cells become permeable to small molecules; permeation causes swelling and eventual rupture of the cell membrane. This process is sometimes also referred to as lysing.

PEF is an energy efficient process compared to thermal pasteurization.

The PEF processing typically adds only £0.02-E0.051L to final food costs. A commercial-scale PEF system can process between 1,000 and 5,000 liters of liquid foods per hour and this equipment is scalable. Application of PEF technology has been successfully demonstrated for the pasteurization of foods such as juices, milk, yogurt, soups, and liquid eggs. However, the technology suffers from some limitations that prohibit large scale industrial application of the technology.

A PEF treatment chamber typically consists of at least two electrodes and insulation that forms a volume, i.e., PEF treatment zone, where the foods receive pulses. The electrodes are made of inert metallic materials, such as titanium. An example of such a treatment chamber is disclosed in US patent No. US 6,393,975 B2. One limitation is that the maximum particle size in the liquid must be smaller than the gap of the treatment region in the chamber in order to ensure proper treatment. Enlargement of the gap is not trivial as this requires an increase of the pulse intensity to achieve the same level of PEF pasteurization.

Current electrode materials are unable to cope with such intensity increases, which is expressed by electrode degradation, leading to the emission of electrode materials in the treated food, as for instance has been reported in V. Heinz, S. Toepfl, and D. Knorr, Proceedings of the TEE European Pulsed Power Symposium 21, 1-6, (2002). As many electrode metals are toxic, such emissions are of course completely unacceptable. This is a problem that has existed for at least a couple of decades and has so far not been adequately solved.

This problem is further exacerbated when the treatment chamber is subjected to food stuffs with varying pH, e.g. different fruit juices, as it has been found that such pH variations accelerate the degradation of metal electrode materials through corrosion.

To date, problem of food contamination with electrode debris has been compensated for by the introduction of large dead volumes in the treatment chamber in the form of transition zones at the inlet and outlet. This however equates to inefficient treatment chamber designs as such dead volumes not only lead to overly bulky designs but also causes electrical leakage, which has a detrimental effect on the uniformity of the generated electrical field, which compromises quality assurance of the treated food products. A further consequence of the instability of the electrodes is that the PEF system has to be regularly shut down for remedial maintenance work, e.g. to replace degraded components. Moreover, the ongoing degradation of the electrodes means that the operational parameters of the treatment chambers are constantly shifting due to the change in electrode response caused by this degradation, which makes it very difficult to ensure a constant treatment quality for the PEF process.

In addition, generation of high voltage pulses having sufficient peak power, typically in the megawatt domain, is another limitation in processing large quantities of fluid economically, not in the least because electrode materials are unable to withstand such peak powers as previously explained. The emergence of solid-state pulsed power systems, which can be arbitrarily sized by combining switch modules in series and parallel, removes this limitation. However, this does increase the complexity and therefore the cost of PEF treatment systems, which prohibits large-scale integration of such systems in industrial environments on economic grounds.

Hence, there exists a need to improve PEF treatment systems to facilitate wide-scale industrial application of the technology in a feasible manner in terms of economic and toxicological considerations.

SUMMARY OF THE INVENTION

The present invention seeks to provide a treatment chamber that addresses at least some of the aforementioned economic and toxicological considerations.

The present invention further seeks to provide a food treatment apparatus including such a treatment chamber.

The present invention yet further seeks to provide a food treatment method using such an apparatus including such a treatment chamber.

According to an aspect of the present invention, there is provided a treatment chamber for a treatment apparatus for preserving pumpable food products in a pulsed electric field, the treatment chamber comprising an inlet for receiving the food products, an outlet for expelling the treated food products, a first electrode placed between the inlet and the outlet, a second electrode placed between the inlet and the outlet, said first electrode and second electrode being electrically insulated from each other and being arranged such that upon application of a potential across the first electrode and the second electrode a food product in the treatment chamber is subjected to an electric field, wherein the first electrode and the second electrode are boron-doped diamond electrodes.

The present inventor has surprisingly found that boron-doped diamond (BDD) electrodes are able to withstand significantly higher electric field densities than the state of the art electrodes used in PEF processing systems. It has been experimentally determined by the present inventor that BDD electrodes show no evidence of carbon emission into the food products even when applying megawatt pulses to the electrodes. In fact, wherein for prior art metal electrodes the power supply had to be chosen carefully to avoid electrode degradation by the application of excessive pulse energies, it has been found that for BDD electrodes no such degradation occurs with the strongest of the commercially available power supplies. In addition, the BDD electrodes may be operated at pulse frequencies in excess of 100 MHz without detrimental effects to the electrode integrity. This for instance makes it possible to increase the inner diameter, i.e. the diameter of the flow path, of the treatment chamber to at least 10 mm, which is a factor 10 higher than the inner diameter of the state of the art treatment chambers. Consequently, it becomes possible to treat much larger volumes of food products in a single treatment chamber, thus obviating the need to place multiple treatment chambers in series or parallel to achieve industrial scale food throughput volumes. It is noted that although the use of BDD electrodes in redox-reaction based treatment of fluids such as waste water streams is well known, it has not been previously recognized that such electrodes can be advantageously applied in PEF food treatment systems.

Suitable BDD electrodes may for instance be derived from the DiamoxlM and DiapodlM reactors marketed by Advanced Oxidation Limited. These are reactors specifically designed for the chemical free disinfection and purification of water. These reactors may be redesigned by removing all but the outermost BDD electrodes in the reactors such that they become suitable for PEF applications as these adjusted configurations facilitate the generation of the required field strength between the BDD electrodes.

It is preferred that the BDD electrodes are solid BDD electrodes as they have been found to be most resilient to the application of the high electric field densities. However, the use of composite BDD electrodes, e.g. electrodes in which a layer of boron-doped diamonds is adhered to a carrier such as a titanium carrier may also be considered as long as the carrier is not in flu idic contact with the food product, such that contamination of the food product with the carrier material can be avoided during use of the treatment chamber. Although solid wafer diamond electrodes have a better lifetime, i.e. suffer less degradation than composite BDD electrodes, it is noted that laminated electrodes having BDD electrode surfaces still exhibit a marked improvement in resilience compared to prior art metal electrodes such as titanium electrodes. This makes it more straightforward to maintain the desired consistency in the quality of the treatment process, and furthermore significantly reduces the downtime of the treatment apparatus as pads do not need frequent replacing.

Preferably, a layer of electrically insulating material is sandwiched between the first electrode and the second electrode, said layer comprising the inlet, the outlet and a meandering conduit connecting the inlet to the outlet. This can dramatically increase the dwell time of the food product inside the treatment chamber, which allows for a significant improvement of the treatment results without requiring an increase or change in electrode control pulse frequency and/or intensity.

In a further advantageous embodiment, the meandering conduit comprises at least one member for introducing turbulence into the food stream. This is particularly advantages for inhomogeneous food products, e.g. juices, where a substantially laminar flow may cause inconsistencies in the treatment of the food product due to local variations in the electrical field to which the food product has been subjected inside the treatment chamber. The introduction of turbulence ensures that the whole volume of such inhomogeneous food products is subjected to the same averaged electrical field, thereby increasing the homogeneity of the PEF treatment.

According to another aspect of the present invention, there is provided a treatment apparatus for preserving pumpable food products in a pulsed electric field, comprising the treatment chamber of any of claims 1-11; a pulse generator conductively coupled to at least the first electrode and the second electrode; and a pump for pumping the food products through the treatment chamber. Such a treatment apparatus benefits from the presence of the treatment chamber of the present invention in that it can be adapted to operate at higher electric field densities and with larger flow cell diameters, thereby facilitating industrial scale application without toxicological concerns originating from electrode breakdown.

In a particularly advantageous embodiment, the pulse generator is arranged to generate an oscillating pulsed electric field between the first electrode and the second electrode, preferably with an oscillating frequency of at least 100 MHz. The application of an oscillating PEF, in particular a PEF having an oscillating frequency of at least 100 MHz, improves the efficiency of irreversible cell degradation of e.g. bio-organisms in the food products, thus resulting in a more effective pasteurization. Such frequencies cannot be achieved with a state of the art treatment apparatus as the electrode material will start to contaminate the food product well below such oscillating frequencies.

In addition, due to the fact that the BDD electrodes are capable of generating a much higher field density, the pulse generator design can be dramatically simplified as the maximum voltage that needs to be generated is much lower compared to existing PEF treatment systems.

In accordance with yet another aspect of the present invention, there is provided a method of preserving pumpable food products, the method comprising providing the treatment apparatus of any of claims 12-14; pumping a food product through the treatment chamber of the treatment apparatus; and whilst residing in the treatment chamber, subjecting the food product to a pulsed electric field by generating suitable control signals with the pulse generator and applying the control signals to the boron doped diamond electrodes. This method ensures an effective pasteurization of the food product without contaminating the food product with the electrode material.

Further advantageous aspects of the present invention have been defined by the dependent claims and are described in more detail in the detailed

description.

BRIEF DESCRIPTION OF THE EMBODIMENTS

Embodiments of the invention are described in more detail and by way of non-limiting examples with reference to the accompanying drawings, wherein: FIG. 1-6 schematically depict example embodiments of a treatment chamber of the present invention; FIG. 7 schematically depicts an example embodiment of a treatment apparatus of the present invention; and FIG. 8 depicts an example pulse sequence for controlling an embodiment of a treatment chamber of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

The present invention is based on the insight that many design constraints of existing PEF systems can be lifted by the integration of BDD electrodes in the treatment chambers of such systems. In particular, increased treatment chamber flow diameter and increased electric field densities can be applied without the risk of electrode material releasing into the food product under treatment. In addition, due to the fact that BDD electrodes have been found to be extremely stable and furthermore provide well-defined electric fields, the treatment chamber design can be improved in terms of efficiency by the reduction of the dead volume in the chamber, thus reducing electrical leakage and improving the homogeneity or

uniformity of the generated electric field.

Although the present invention is particularly applicable to the food treatment industry because of the improved toxicological aspects of the present invention, it should be understood that the invention may be applied in any PEF system, such as for instance waste stream treatment systems.

The present invention may be used to improve any existing PEF system design. For instance, the present invention is not limited to a particular electrode shape. BDD electrodes can be successfully applied in for instance PEF systems based on flat plate, cross-field and co-field treatment chambers.

FIG. I is a non-limiting example of a flat plate electrode-based treatment chamber 100 having an inlet 110, an outlet 120 and flat plate BDD electrodes and 140 on either side of the flow path between the inlet 110 and the outlet 120. Pane (a) gives a front view and pane (b) gives a cross-sectional view of the flow chamber 100 along the dashed line shown in pane (a). The BDD electrodes 130 and 140 may be separated by insulating wall sections 150, such that the perimeter of the flow path is defined by the BDD electrodes 130 and 140 and the insulating wall sections 150. The insulating wall sections 150 may be made of any suitable insulating material. In operation, one of the BDD electrodes 130 and is connected to a positive potential and the other of the BDD electrodes 130 and 140 is connected to a negative potential, e.g. ground, thereby generating an electric field across the flow path through the treatment chamber 100. As the operation of such treatment chambers is known per se, this will not be further explained for the sake of brevity.

FIG. 2 is a non-limiting example of another electrode-based treatment chamber 100 having an inlet 110, an outlet 120, a first BDD electrode 130 placed in the centre of the flow path, thereby defining the inner diameter of the flow path, -10-and a second BDD electrode 140 defining the outer diameter of the flow path. In other words, the outer BDD electrode 140 envelopes the inner BDD electrode 130, with the space between the two electrodes defining the flow path and electrically insulating the electrodes from each other. Pane (a) gives a front view and pane (b) gives a cross-sectional view of the flow chamber 100 along the dashed line shown in pane (a).

FIG. 3 is a non-limiting example of yet another electrode-based treatment chamber 100 having an inlet 110, an outlet 120. Here, annular BDD electrodes separated by annular insulating sections 150 define the inner wall of the treatment chamber 100. A first BDD electrode 140 is placed between the inlet and a first one of the annular insulating sections 150, a second BDD electrode 130 is placed between the first one and a second one of the annular insulating sections 150 and a third BDD electrode 140' is placed between the second one of the annular insulating sections 150 and the outlet 120. Pane (a) gives a front view and pane (b) gives a cross-sectional view of the flow chamber along the dashed line shown in pane (a). The arrows in pane (b) depict the field lines of the electric field generated by the treatment chamber 100 in operation.

FIG. 4 shows a preferred embodiment of a BDD electrode-based treatment chamber 100 having an inlet 110 and an outlet 120. In this embodiment, a stacked design is provided in which an electrically insulating material 150 is sandwiched between a first BDD electrode wafer 130 and a second BDD electrode wafer 140. In this embodiment, the BDD electrodes 130 and 140 preferably are solid BDD electrodes. The inlet 110 and outlet 120 are both formed in a sidewall of the electrically insulating layer 150. In FIG. 4, the inlet 110 and outlet 120 are formed in the same sidewall by way of non-limiting example only. It is equally feasible to locate the inlet 110 and outlet 120 in different sidewalls of the electrically insulating layer 150, e.g. in opposite sidewalls.

The inlet 110 is in fluidly connected to the outlet 120 through a meandering conduit 152, which is shown in FIG. 5, which depicts a cross-section -Il -of the treatment chamber 100 along the dashed line shown in FIG. 4. The meandering conduit increases the dwell time of the food product in the treatment chamber 100, which has the advantage that an improved homogeneity of the PEF treatment can be obtained. This is particularly relevant where it proves practically or economically unfeasible to create a perfect homogeneous electrical field between the upper BDD electrode 130 and the lower BDD electrode 140, as the meandering through the treatment chamber 100 causes such local variations

in the electrical field to cancel out.

The conduit 152 may optionally comprise one or more members 154, e.g. propellers or other types of rotating wheels, or fixed members, which for instance may be wedge-shaped, that disrupt a laminar flow of the food product through the treatment chamber, i.e. that cause turbulence in this flow. This ensures that the food product flow is sufficiently mixed during its passage through the conduit 152 that any gradients present in the electrical field from the top electrode 130 to the bottom electrode 140 do not cause localized differences in the effectiveness of the PEF treatment of the food product, as the effect of these gradients is cancelled out by the incorporation of the one or more members 154.

The stacked design of FIG. 4 is not limited to a single layer 150. This is shown in FIG. 6, where two electrically insulating layers 150 are present in the stacked design, each with respective inlets 110 and outlets 120, interconnected by a conduit 152 (not shown). The outer electrodes of the stacked design in FIG. 6 are BDD electrodes 130 of a first polarity, whereas the stacked design further comprises an intermediate BDD electrode 140 of an opposite polarity located in between the two electrically insulating layers 150. It will be immediately apparent to the skilled person that such a stacked treatment chamber may be extended to comprise any suitable number of electrically insulating layers 150 and BDD electrodes.

It is reiterated that FIG. 1-6 show non-limiting examples of flow chamber designs. These designs may be altered without departing from the present invention. For instance, intermediate electrodes may be included in the design to improve the flexibility of the design such that it can be used in multiple application -12 -domains. This is typically achieved by selecting a subset of the electrodes in the operation of the treatment chamber 100 for a particular application domain.

FIG. 7 schematically depicts a non-limiting example embodiment of the treatment apparatus 400 of the present invention. A power supply 410 is connected to the BDD electrodes of the treatment chamber 100 via a high-voltage switch 450. A charge capacitor 430 has a first plate connected to the positive terminal of the power supply 410 via a charge resistor 420 and a second plate connected to the negative terminal of the power supply 410, which may be ground. The high-voltage switch 450 is conductively coupled to the first plate of the charge capacitor 430, preferably through a protective resistor 440. In operation, the charge capacitor 430 is constantly charged by the power supply 410, and the high-voltage switch 450 is periodically closed, i.e. switched to a conductive state, each time the charge capacitor 430 has reached a predefined charge level, e.g. is fully charged. To this end, the treatment apparatus 400 may comprise a controller (not shown) for periodically closing the high-voltage switch 450. The switch 450 is kept closed for a short period of time, i.e. for the duration of the voltage pulse to be applied to the BDD electrodes of the treatment chamber 100, such that the BDD electrodes are periodically provided with voltage pulses 500 as shown in FIG. 8. As the maximum voltage value of the voltage pulses 500 may be reduced compared to prior art applications due to the high efficiency of the BDD electrodes in the treatment chamber 100, the pulse generation stage of the treatment apparatus 400 can be realized in a straightforward and cost-effective manner.

In a preferred embodiment, the pulse generator defined by the power supply 410, the charge capacitor 430 and the high-voltage switch 450 is adapted to generate a series of pulses at a pulse frequency in the MHz domain, preferably MHz or more. It has been found that BDD electrodes can withstand such high pulse frequencies without detrimental side-effects.

The treatment apparatus 400 typically further comprises a pump (not shown) for pumping food products through the treatment chamber 100. -13-

In operation, a food product is pumped through the treatment chamber of the treatment apparatus 400. Whilst residing in the treatment chamber 100, the food product is subjected to a pulsed electric field generated by voltage pulses 500 to the BDD electrodes. As explained, these voltage pulses 500 may be generated by applying suitable control signals to the pulse generation stage.

At this point, some further surprising advantages of the treatment chamber of the present invention are recited. It is known per se that the pulse patterns of PEF treatment systems can be adapted such that ohmic heating occurs in the food products undergoing treatment. This allows for in-situ pasteurization in addition to the PEF treatment. However, in PEF systems comprising metal or metal oxide electrodes, such ohmic heating accelerates the degradation of the electrode material, which makes it unfeasible to include ohmic heating cycles in the PEF treatment. However, it has been found that BDD electrodes do not suffer any negative side-effects such as degradation during such ohmic heating cycles, such that the treatment chamber of the present invention is also suitable for use in a PEF treatment set-up that includes ohmic heating steps.

A further surprising and environmentally attractive advantage of the treating meat products in the treatment chamber of the present invention is as follows. Meat products, in particular pork-based meats such as ham, are pre-treated with NaCI and phosphates to increase the osmotic pressure in the environment of the meat cells to facilitate the extraction of myosin from the cells to assist in the aggregation of the meat, as the myosin acts as a binding agent. It has been found that when treating meats in the treatment chamber of the present invention, sufficient levels of myosin were released from the meat cells without requiring the addition of phosphates and/or other salts. The treatment chamber of the present invention facilitates the manufacture of durable meat products having good consistency without having to achieve such consistency by using additives.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not -14 -be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several distinct elements. In the device claim enumerating several means, several of these means can be embodied by one and the same item of hardware.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. -15-

Claims

CLAIMS1. A treatment chamber (100) for a treatment apparatus (400) for preserving pumpable food products in a pulsed electric field, the treatment chamber comprising an inlet (110) for receiving the food products, an outlet (120) for expelling the treated food products, a first electrode (130) placed between the inlet and the outlet, a second electrode (140) placed between the inlet and the outlet, said first electrode and second electrode being electrically insulated from each other and being arranged such that upon application of a potential across the first electrode and the second electrode a food product in the treatment chamber is subjected to an electric field, wherein the first electrode and the second electrode are boron-doped diamond electrodes.
2. The treatment chamber of claim 1, wherein a layer of electrically insulating material (150) is sandwiched between the first electrode (130) and the second electrode (140), said layer comprising the inlet (110), the outlet (120) and a meandering conduit (152) connecting the inlet to the outlet.
3. The treatment chamber of claim 2, wherein the meandering conduit (152) comprises at least one member (154) for introducing turbulence into the flow through said conduit.
4. The treatment chamber (100) of claim 1, wherein both the first electrode (130) and the second electrode (140) extend from the inlet (110) to the outlet (120), and wherein the treatment chamber further comprising at least one section of electrically insulating material (150) extending from the inlet to the outlet, said at least one section electrically insulating the first electrode from the second electrode.
5. The treatment chamber (100) of claim 1, wherein both the first electrode (130) and the second electrode (140) extend from the inlet (110) to the outlet -16 - (120), said first electrode (130) defining the inner wall of the treatment chamber and said second electrode (140) being placed inside the volume delimited by said inner wall such that the flow path of the pumpable food product through the treatment chamber is defined between the first electrode (130) and the second electrode (140).
6. The treatment chamber (100) of claim 1, wherein the first electrode (140) and the second electrode (130) define different sections of the inner wall of the treatment chamber, the treatment chamber further comprising an electrically insulating inner wall section (150) separating said different sections from each other.
7. The treatment chamber (100) of claim 6, further comprising a third electrode (140') defining a further section of said inner wall and a further electrically insulating inner wall section (150), wherein the first electrode (140) is located between the inlet (110) and the electrically insulating inner wall section (150), the second electrode (130) is located between the electrically insulating inner wall section (150) and the further electrically insulating inner wall section, and the third electrode (140') is located between the further electrically insulating inner wall section and the outlet (120).
8. The treatment chamber (100) of any of claims 1-6, further comprising at least one intermediate electrode placed in between the first electrode (130) and the second electrode (140).
9. The treatment chamber (100) of any of claims 1-8, wherein the inner diameter of the treatment chamber is at least 10 mm.
10. The treatment chamber (100) of any of claims 1-8, wherein the boron doped diamond electrodes are DiamoxTM or a DiapodTM reactor electrodes. -17-
11. The treatment chamber (100) of any of claims 1-8, wherein the boron doped diamond electrodes are solid diamond wafer electrodes.
12. A treatment apparatus (400) for preserving pumpable food products in apulsed electric field, comprising:the treatment chamber (100) of any of claims 1-11; a pulse generator (410, 420, 430, 440) conductively coupled to at least the first electrode (130) and the second electrode (140); and a pump for pumping the food products through the treatment chamber.
13. The treatment apparatus (400) of claim 12, wherein the pulse generator (410, 420, 430, 440) is arranged to generate a high frequency pulsed electric field between the first electrode (130) and the second electrode (140).
14. The treatment apparatus (400) of claim 13, wherein the pulse generator is adapted to generate the pulsed electric field with a pulse frequency of at least MHz.
15. A method of preserving pumpable food products, the method comprising: providing the treatment apparatus (400) of any of claims 12-14; pumping a food product through the treatment chamber (100) of the treatment apparatus; and whilst residing in the treatment chamber, subjecting the food product to a pulsed electric field by generating suitable control signals with the pulse generator and applying the control signals to the boron doped diamond electrodes (130, 140).
16. The method of claim 15, wherein the pumpable food product is a meat product.