Freshness preservation device and freshness preservation method

Abstract

To provide a freshness keeping device and method which apply an electromagnetic field to a perishable item to achieve more uniform freshness keeping.SOLUTION: A freshness keeping device 1 comprises: two electrodes 2 facing each other; a power supply 20 for applying a voltage between the electrodes 2; and a perishable item placement part 3 provided in a space sandwiched between the two electrodes 2. The two electrodes 2 are configured so that the density of lines of electric force 10 in an electric field generated between the two electrodes 2 by the power supply 20 is uniform at least in a space occupied by a perishable item 9 placed on the perishable item placement part 3. The freshness of the perishable item 9 placed on the perishable item placement part 3 is kept by penetration of the lines of electric force 10 in the electric field generated between the two electrodes 2 by the power supply 20 through the inside of the perishable item 9.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a freshness preservation device and a freshness preservation method. [Background technology]

[0002] Traditionally, various methods have been used to maintain the freshness of perishable goods that require preservation, such as meat, fish, vegetables, fruits, and flowers. Freezing and salting are used to preserve food, but these methods result in a loss of freshness. The most commonly used method to maintain the freshness of perishable goods is to maintain low temperatures. Refrigeration technology, which maintains freshness by maintaining a temperature of around 4 degrees Celsius, is widely used for both commercial and domestic purposes. The temperature range of around 4 degrees Celsius is chosen because it is necessary to maintain the temperature as low as possible without causing freezing.

[0003] The reason for maintaining low temperatures to preserve freshness for perishable goods in general is to suppress bacterial activity. Low temperature maintenance technology is commonly used as it is the only technology with a known mechanism for preserving freshness while suppressing bacterial activity. While this type of low temperature maintenance is useful, it only maintains freshness for a few days. Therefore, there is a demand for technology that can extend the period during which freshness can be maintained.

[0004] Meanwhile, methods of applying an electromagnetic field to food have been proposed for the purpose of preserving the quality and freshness of food. For example, a processing device and processing method have been proposed in which, before the grinding process of various plants to be pulverized for consumption, the edible material is piled on an electrode to which a voltage is applied, or an electrode is inserted into the pile of edible material, and the electrode acts as a monopole antenna to emit electromagnetic waves, exposing the edible material to the electromagnetic field (see, for example, Patent Document 1).

[0005] In addition, an electric field processing refrigerated storage cabinet has been proposed which has a plurality of mounted electrodes on which the storage material is placed in contact, and a plurality of vertically movable electrodes each facing the mounted electrodes, and stores the material in an electromagnetic field generated by applying an AC voltage of the same polarity to the mounted electrodes and the movable electrodes (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2003-189789 A (Patent 3668848) [Patent Document 2] Special Publication No. 2012-527216 (Patent 5593235) Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the devices and methods described in the above-mentioned Patent Documents 1 and 2, although an alternating current electromagnetic field is applied to preserve freshness, the mechanism of action is unknown. As a result, the problems with the technology have not been identified or improved, and for example, the effect of preserving freshness in fresh produce is uneven and unpredictable, which is an issue.

[0008] The present invention aims to solve the above-mentioned problems by providing a freshness preservation device and a freshness preservation method that can apply an electromagnetic field to fresh produce with a simple configuration, thereby achieving more uniform freshness preservation regardless of whether the electromagnetic field is direct current or alternating current. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the freshness preservation device of the present invention comprises two electrodes facing each other, a power source that applies a voltage between the electrodes, and a fresh food placement section that is located in the space between the two electrodes, and is characterized in that the freshness of the fresh food is preserved by applying a voltage between the two electrodes and allowing the electric field lines of the electric field generated between the electrodes to pass through the fresh food placed in the fresh food placement section.

[0010] In addition, the freshness preservation method of the present invention uses a freshness preservation device comprising two electrodes facing each other, a power source that applies a voltage between the electrodes, and a fresh food placement section that is located in the space between the two electrodes, and is characterized in that by applying a voltage between the two electrodes, an electric field is generated between the electrodes, and the electric force lines of the generated electric field are passed through the fresh food placed in the fresh food placement section, the movement of active oxygen, which is a polar molecule contained in the fresh food, is constrained by the electric field, thereby suppressing the spread of oxidation of organic matter in the fresh food by active oxygen, and / or suppressing the energy supply from active oxygen to bacteria, thereby suppressing bacterial activity. [Effects of the Invention]

[0011] According to the freshness preservation device and freshness preservation method of the present invention, the electric field lines generated between two opposing electrodes are passed through the fresh produce, thereby achieving more uniform freshness preservation regardless of whether the electromagnetic field is direct current or alternating current, based on a clear mechanism of action in which the movement of active oxygen, which is a polar molecule, is constrained by the electric field lines. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a perspective view conceptually showing the configuration of a freshness preservation device according to one embodiment of the present invention; [Figure 2] FIG. 10 is a perspective view conceptually showing the configuration of a freshness preservation device according to another embodiment. [Figure 3] FIG. 10 is a perspective view conceptually showing the configuration of a freshness preservation device according to yet another embodiment. [Figure 4] FIG. 10 is a side view conceptually showing the configuration of a freshness preservation device according to yet another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] A freshness preservation device and a freshness preservation method according to one embodiment of the present invention will be described below with reference to the drawings.

[0014] As shown in Figure 1, freshness preservation device 1 includes two electrodes 2 facing each other, a power source 20 that applies a voltage between electrodes 2, and a fresh food placement section 3 provided in the space between the two electrodes 2. The two electrodes 2 are configured so that the density of electric field lines 10 of the electric field generated between the two electrodes 2 by power source 20 is uniform at least in the space occupied by fresh food 9 placed in fresh food placement section 3.

[0015] The two electrodes 2 facing each other may be any two electrodes facing each other. Each electrode 2 may be configured as a single electrode by combining multiple electrode elements. Such electrodes 2 or electrode elements may be flat or curved. Furthermore, they are not limited to being plate-shaped, and it is sufficient that the surfaces of the two electrodes 2 facing each other are predetermined flat or curved surfaces.

[0016] The power source 20 is only required to be capable of applying a DC or AC voltage between the two electrodes 2, and the electric field generated between the two electrodes 2 is not limited to a DC electric field and may be an AC electric field. The number of power sources 20 is not limited to one, and multiple power sources 20 may be provided. For example, if each of the two electrodes 2 is composed of multiple electrode elements, multiple power sources 20 may be used to apply voltages individually to each of the multiple electrode elements or to a group of electrode elements. The two opposing electrodes 2 and power sources 20 are only required to form an electric field with a uniform density of electric field lines 10 at least in the space occupied by the fresh food 9.

[0017] The fresh product placement unit 3 is not limited to a placement table on which fresh products 9 are placed, but may be anything capable of placing fresh products 9 in the space where freshness preservation is performed, such as a conveyor that can be moved, or a structure or moving object that suspends fresh products 9 from above. Freshness preservation is possible in the space sandwiched between two opposing electrodes, but if metal parts are placed in that space, they will absorb the electric field lines, reducing the effectiveness of freshness preservation. For this reason, the fresh product placement unit 3 is made of a material that does not disrupt the density of the electric field lines 10. It is preferable to use shelves or pallets made of plastic or wood. Metal shelves, etc. should not be installed.

[0018] An electric field is generated between the two electrodes 2 by the power source 20, and electric field lines 10 of the electric field pass through the fresh products 9 placed in the fresh product placement section 3. The freshness of the fresh products 9 is maintained by the uniform density of the electric field lines 10 passing through the interior of the fresh products 9. The principle behind this is explained below.

[0019] (Mechanism of freshness preservation by electromagnetic fields) There are two key points to maintaining the freshness of fresh produce: eliminating the effects of active oxygen and stopping bacterial activity. (1) Active oxygen oxidizes nearby organic matter in fresh produce, reducing its freshness. Therefore, by binding active oxygen, it is possible to suppress the reaction in which active oxygen moves and oxidizes the organic matter in fresh produce one after another. (2) Furthermore, bacteria use active oxygen to obtain the energy they need to function. Therefore, by binding active oxygen, the bacteria cannot obtain energy, and bacterial activity can be stopped. If these two points are applied, eliminating the effects of active oxygen and stopping bacterial activity can achieve the maintenance of fresh produce's freshness.

[0020] Incidentally, water, active oxygen, biomolecules, and the like generally have polarization within their molecules. These molecules are collectively called polar molecules. When a space containing a substance containing polar molecules is sandwiched between two electrodes 2 and a voltage is applied between the two opposing electrodes, an electric field is generated between the two electrodes, and electric field lines 10 are defined. In the absence of an electric field, polar molecules can move around due to Brownian motion, etc. Furthermore, in the presence of an electric field, polar molecules are bound along the electric field lines, just as a magnetic needle is bound in the direction of the magnetic field lines, and when the electric field weakens, the binding loosens and they can move across the electric field lines.

[0021] Furthermore, if there is a non-uniformity in the density of electric field lines, polar molecules will be subjected to a force generated based on that non-uniformity and will move according to that force. Conversely, in a space where electric field lines exist at a constant density, no force based on the non-uniformity in the density of electric field lines will be generated, and polar molecules will only be able to thermally move along the electric field lines. Thermal movement can be suppressed by lowering the temperature as needed.

[0022] Freshness preservation device 1 has two mechanisms for preserving freshness: it can bind polar molecules such as active oxygen using electric field lines 10 in space, regardless of whether the electromagnetic field is direct current or alternating current, thereby achieving freshness preservation. In other words, freshness preservation device 1 focuses on active oxygen, which is a polar molecule, and incorporates this mechanism of action to capture active oxygen with electric field lines 10, eliminate the effects of the movement of active oxygen, stop bacterial activity, and preserve the freshness of fresh produce. Freshness preservation device 1 can achieve more uniform freshness preservation regardless of whether the electromagnetic field is direct current or alternating current, thanks to its clear mechanism of action of binding polar molecules with electric field lines 10.

[0023] (Uniform density of electric field lines) Within a space where freshness preservation is expected, it is necessary to establish a uniform freshness preservation ability within the space. To achieve this, as mentioned above, the density of electric field lines within the space where freshness preservation is expected must be uniform. For example, in the case of two opposing electrodes 2 made of rectangular parallel plates, the density of electric field lines can be easily made constant in the center. However, at the ends of the electrodes, the electric field lines diverge, the density of the electric field lines decreases, and they no longer become uniform.

[0024] In order to preserve the freshness of more fresh produce, it is necessary to create a wider space (called a freshness preservation space) with a constant density of electric field lines between the two electrodes 2. For this reason, each electrode 2 is not limited to a simple flat plate electrode, and may have, for example, a concave structure or a structure combining multiple electrode elements. The shape of the two opposing electrodes 2 that can form a wider space with a uniform electric field density can be determined by electromagnetic field simulation using the finite element method.

[0025] (floating electrode) Figure 2 shows one method for expanding a freshness preservation space with a constant density of electric field lines. Freshness preservation device 1 is the same as freshness preservation device 1 shown in Figure 1, but with floating electrodes 4 installed to surround the space sandwiched between two electrodes 2. In this embodiment, there are eight floating electrodes 4, with two sets of four electrodes each surrounding the space sandwiched between two opposing, disk-shaped electrodes 2 from above, below, left, and right in a frame-like fashion. There is no limit to the number of floating electrodes 4 installed, nor is there any limit to the number of sets, the method of configuring the sets, or whether or not to configure a set. The floating electrodes 4 surrounding the freshness preservation space can suppress the spread of electric field lines, thereby expanding the effective freshness preservation space.

[0026] Freshness preservation device 1 is configured, for example, by arranging two opposing electrodes 2 and a floating electrode 4 on the inner wall of a container that encloses the space in which the freshness preservation function is to be exerted. Floating electrode 4 may be held on the inner wall of the container in an electrically insulated state. There are no limitations on the material or shape of the inner wall of the container, and there are no limitations on the circulation of air or the inflow of light. Information on the appropriate placement and configuration of floating electrode 4 can be obtained by electromagnetic field simulation.

[0027] (capacitor coupling) Figure 3 shows another method for expanding the freshness preservation space with a constant density of electric field lines. Freshness preservation device 1 is the same as freshness preservation device 1 shown in Figure 2, but includes capacitors 5 that electrically connect two electrodes 2 and floating electrodes 4. In this embodiment, two opposing electrodes 2 and eight floating electrodes 4 are electrically connected by 11 capacitors. In this case, too, electromagnetic field simulation can be used to determine various quantities.

[0028] (applied voltage, generated electric field) There are no particular limitations on the power supply 20, as long as it can apply any one of a DC voltage, an AC voltage consisting of, for example, a sine wave, and an AC voltage consisting of, for example, a square wave or triangular wave to the two electrodes 2. Furthermore, the power supply 20 may be capable of generating, in the space between the two electrodes 2, an electric field that is a temporal or spatial combination of the electric fields generated by applying any of these voltages.

[0029] When the voltage applied by power supply 20 is a sine wave, sine wave voltages are easy to boost and are commonly used, but they have a weakness due to the waveform being a sine wave: the voltage drops for long periods during the cycle, sometimes reaching zero. Periodically, the voltage drops, weakening the electric field, lowering the density of the electric field lines and weakening the force binding polar molecules, which periodically reduces the freshness-preserving effect and reducing the overall effect.

[0030] The voltage applied between the two opposing electrodes may be direct current. In the case of direct current, the density of the electric field lines is constant over time, and the effect of binding polar molecules is stably obtained. However, if water molecules or ionized substances are present, for example, near an unprotected electrode, there is a risk that the electrode material will be eluted due to the effects of electrolysis.

[0031] The voltage applied between the two opposing electrodes may be, for example, a rectangular wave alternating voltage. With an alternating rectangular wave, the voltage remains constant except during alternation, eliminating the time during which the effect of the electric field lines weakens, and the time during which the voltage becomes zero during alternation can be reduced, thereby achieving a desired freshness-preserving effect. There are no particular restrictions on the magnitude of the voltage applied between the two opposing electrodes, but it is preferable that the strength of the electric field formed between the two electrodes be 100 V / m or greater.

[0032] When the voltage applied between the two opposing electrodes is, for example, a sine wave AC voltage or, for example, a square wave or triangular wave AC voltage, its frequency is preferably 10 Hz or more and 10 kHz or less. If it is less than 10 Hz, the effect of the electric field lines weakens for a long time, making it impossible to restrain polar molecules that are beginning to move due to Brownian motion. Frequencies above 10 kHz are undesirable because the wavelength of the electromagnetic waves becomes shorter, becoming shorter than the wavelength of the freshness-preserving space, resulting in uneven freshness-preserving effects within the freshness-preserving space. It is more preferable to set the AC or AC voltage applied by power source 20 to a frequency of 50 Hz or more and 1 kHz or less.

[0033] (Bonding and grounding of electrodes via resistors) The freshness preservation device 1 shown in Figure 4 is the same as the freshness preservation device 1 shown in Figure 1, except that each of the two electrodes 2 is equipped with a resistor 6, the two electrodes 2 are connected to each other via the resistor 6, and the two electrodes 2 are grounded through their connection point 61.

[0034] Power supply 20 applies a voltage between electrodes 2 so that an AC or alternating electric field is generated in the space between the two electrodes 2. Freshness preservation device 1 of this embodiment can improve the freshness preservation effect when the voltage applied to the two opposing electrodes 2 is AC or alternating. Furthermore, the configuration of this embodiment, which includes resistor 6 and is grounded, may be applied to freshness preservation device 1 shown in Figures 2 and 3 above. [Example]

[0035] Example 1 A freshness-keeping device equivalent to freshness-keeping device 1 shown in Figure 1 was installed in a concrete room with a floor area of ​​3m x 5m and a height of 3m. Two electrodes 2 were each a square with sides of 2.5m. One electrode 2 was installed on a 3m square wall, and the other electrode 2 was installed on the opposing wall. A 1kV, 50Hz AC voltage (sine wave) was applied to the installed freshness-keeping device.

[0036] In the center of the room, an 80 cm high wooden workbench was set up as fresh food placement area 3. 30 g of chicken thigh meat was placed in a petri dish with a lid, placed on the workbench, and left for 3 days with the freshness preservation device running. The temperature in the room was set to 20°C.

[0037] When the odor was smelled after 3 days, the odor level was determined to be level 2 on the 6-level odor intensity scale shown in Table 1 below.

[0038] (Table 1) Six-level odor intensity rating system ============================ 0: Odorless 1: Smell that can barely be detected (detection threshold) 2: Weak odor that can be identified (recognition threshold) 3: Easily detectable odors 4: Strong odor 5: Strong odor ============================

[0039] Commercially available chicken thighs are usually contaminated with Campylobacter and Escherichia coli, and if left at room temperature, an odor would be generated as the bacteria multiply. However, the odor intensity was 2, and the results of Example 1 show that the freshness-keeping device suppressed microbial activity.

[0040] (Comparative Example 1) In Comparative Example 1, the freshness preservation device of Example 1 was used, but the device was not driven and no voltage was applied to electrode 2. As in Example 1, 30 g of chicken thigh meat was placed in a petri dish with a lid, placed on a workbench, and left for 3 days without driving the device. The room temperature was set to 20°C.

[0041] When the odor was smelled after three days, the level of malodor based on Table 1 was an intensity of 5. This confirmed the effectiveness of the freshness preservation device in Example 1. In other words, chicken thighs normally sold commercially are contaminated with Campylobacter and Escherichia coli, and in Comparative Example 1, the freshness preservation device was not activated and the chicken was left at room temperature, so the freshness preservation effect of the freshness preservation device was not achieved, and it is thought that this was the cause of the odor caused by bacterial growth.

[0042] Example 2 A device equivalent to the freshness-keeping device 1 shown in Figure 2 was installed inside a metal storage cabinet with an inner floor area of ​​2.5m x 4m and a height of 2m. Two electrodes 2 were each a square with sides of 1.8m. One electrode 2 was installed on a 2.5m x 2m wall, and the other electrode 2 was installed on the opposing wall. The two electrodes 2 were installed 4m apart. Three sets of floating electrodes 4 were installed at equal intervals, each spaced 1m apart. The electrode parts that make up each set of floating electrodes 4 were fixed to the inner wall of the storage cabinet using ceramic insulators, electrically insulated from the storage cabinet and floating. A DC voltage of 2kV was applied to the electrodes 2 of the installed freshness-keeping device.

[0043] A 60 cm high plastic workbench was installed in the center of the storage facility as fresh product storage area 3. 200 g of swordfish lean meat was prepared. The myoglobin metmyoglobin ratio was measured (see Inohara Kota, Onoue Yukino, and Kimura Ikuo, "Study on a method for measuring the metmyoglobin ratio of fish muscle myoglobin," Journal of the Japanese Society of Fisheries Science, 81(3), 456-464 (2015)), which was found to be 10%. 200 g of swordfish lean meat was placed in a petri dish with a lid, placed on the workbench, and left for 6 days with the freshness-keeping device running. The temperature inside the storage facility was set to 7°C.

[0044] The myoglobin metmyoglobin conversion rate was measured after 6 days and was found to be 15%. Myoglobin metmyoglobin conversion is related to active oxygen, but the low metmyoglobin conversion rate suggests that the effects of the electromagnetic field in the freshness-preserving device suppressed the effects of active oxygen.

[0045] (Comparative Example 2) In Comparative Example 2, the freshness preservation device of Example 2 was used, but the device was not driven and no voltage was applied to electrode 2. As in Example 2, 200 g of swordfish lean meat was placed in a petri dish with a lid, placed on a workbench, and left for 6 days without driving the device. The temperature inside the chamber was set at 7°C.

[0046] The metmyoglobin rate was measured after 6 days and was found to be 70%. This high metmyoglobin rate suggests that in Comparative Example 2, the freshness preservation device was not operated, which prevented the effects of active oxygen from being suppressed, leading to increased metmyoglobin and food deterioration.

[0047] Example 3 A device equivalent to the freshness preservation device 1 shown in Figure 3 was installed inside a metal storage facility with an inner floor area of ​​1.5m x 2m and a height of 1.8m. Two electrodes 2 were each rectangular with sides of 1.2m x 1.4m. One electrode 2 was installed on a 1.5m x 1.8m wall, and the other electrode 2 was installed on the opposing wall. The two electrodes 2 were installed 2m apart.

[0048] Three sets of floating electrodes 4 were installed at equal intervals, with a distance of 0.5 m between each set. The three sets of floating electrodes 4 and the electrode components that make up each set were connected to each other via capacitors 5. Each floating electrode 4 was fixed to the inner wall of the storage cabinet using ceramic insulators, electrically insulated from the storage cabinet and kept in a floating state. All capacitors 5 used were 100 pF. An alternating square wave voltage of 1.5 kV and a frequency of 900 Hz was applied to electrode 2 of the installed freshness preservation device.

[0049] A 60 cm high plastic work table was installed in the center of the storage cabinet as the fresh food storage area 3. Three cherry tomatoes were placed in a Ziploc® bag, sealed, and placed on the work table. The freshness-keeping device was left running for 8 days. The temperature inside the cabinet was set to 20°C.

[0050] Even after eight days, no mold had grown. Mold growth requires metabolites secreted by bacteria, but the lack of mold growth suggests that the electromagnetic field of the freshness-keeping device inhibited the movement of active oxygen, thereby suppressing bacterial activity.

[0051] (Comparative Example 3) In Comparative Example 3, the freshness preservation device of Example 3 was used, but the device was not driven and no voltage was applied to electrode 2. As in Example 3, three cherry tomatoes were placed in a Ziploc® bag, sealed, placed on a workbench, and left for 8 days without driving the freshness preservation device. The temperature inside the bag was set to 20°C.

[0052] After leaving it for 8 days, mold had grown. From the result of mold growth, it is thought that in Comparative Example 3, the movement of active oxygen could not be suppressed and bacterial activity could not be suppressed because the freshness preservation device was not operated.

[0053] As described above, a freshness preservation device using this technology can suppress reactions related to active oxygen and maintain the freshness of food. It is effective in preventing deterioration of meats such as beef, pork, chicken, and fish by preventing metmyocarditis, and in suppressing microorganisms in salads and other vegetables.

[0054] (How to keep fresh) The freshness preservation method of the present invention uses the freshness preservation device 1 shown in Figures 1 to 4 above to pass electric field lines 10 through fresh produce 9 placed in the fresh produce placement section 3, and uses the electric field to constrain the movement of active oxygen, a polar molecule contained in the fresh produce 9, thereby suppressing the spread of oxidation of organic matter in the fresh produce 9 by the active oxygen, and suppressing the supply of energy from the active oxygen to bacteria, thereby suppressing bacterial activity, thereby preserving the freshness of the fresh produce 9.

[0055] The present invention is not limited to the above configuration and various modifications are possible. For example, the configurations of the above-described embodiments can be combined. The density of electric field lines can be defined as the number of electric field lines passing through a unit cross section perpendicular to the electric field lines passing through a point of interest. Furthermore, as long as the electric field lines used to preserve freshness are parallel to each other at least inside the fresh product, the freshness-preserving effect can be achieved even if the density is not strictly constant. Therefore, the two opposing electrodes 2 may be capable of generating an electric field having such electric field lines. [Explanation of symbols]

[0056] 1. Freshness preservation device 10 Electric field lines 2 electrodes 20 Power supply 3 Perishable product placement department 4 Floating electrode 5 Capacitors 6 resistor 9 Perishables

Claims

1. The device comprises two electrodes facing each other, a power source that applies a voltage between the electrodes, and a fresh food placement section that is provided in a space sandwiched between the two electrodes, The two electrodes are configured to generate electric field lines of an electric field generated between the two electrodes by applying a voltage between the two electrodes so that the density of the electric field lines is uniform at least in a space occupied by fresh products placed in the fresh product placement section, and to transmit the electric field lines to the fresh products placed in the fresh product placement section, A freshness preservation device characterized by maintaining the freshness of fresh produce by restricting the movement of active oxygen, a polar molecule contained in the fresh produce, along the electric field lines, thereby suppressing the spread of oxidation of organic matter in the fresh produce by active oxygen.

2. The freshness preservation device according to claim 1, characterized in that the power supply applies a voltage between the electrodes so that the electric field generated between the electrodes is 100 V / m or more.

3. The freshness preservation device according to claim 1 or 2, characterized in that the power source applies a sine wave AC voltage or a square wave or triangular wave AC voltage having a frequency of 10 Hz or more and 10 kHz or less between the electrodes.

4. A freshness preservation device as described in any one of claims 1 to 3, characterized in that each of the two electrodes is composed of a plurality of electrode elements, a plurality of power sources are provided, and the plurality of power sources are used to apply voltage individually to each of the plurality of electrode elements or to a group of the electrode elements, so that the density of the electric field lines of the electric field generated between the two electrodes by the plurality of power sources is uniform at least in the space occupied by the fresh food placed in the fresh food placement section.

5. A freshness preservation device as described in any one of claims 1 to 4, characterized in that it further comprises a floating electrode installed in an electrically insulated state so as to surround the space sandwiched between the two electrodes in order to make the space in which the density of electric field lines is uniform wider.

6. The freshness preservation device according to claim 5, further comprising a capacitor that electrically connects the two electrodes and the floating electrode.

7. A freshness preservation device as described in any one of claims 1 to 6, characterized in that the power supply is configured to generate an electric field in the space sandwiched between the two electrodes by applying either a direct current voltage, an alternating current voltage consisting of a sine wave, or an alternating current voltage consisting of a rectangular wave or a triangular wave to the two electrodes, or an electric field generated by a temporal or spatial combination of these electric fields.

8. The two electrodes are connected to each other via resistors provided in each electrode, and are grounded through the connection point. The freshness preservation device according to any one of claims 1 to 7, characterized in that the power source applies a voltage between the electrodes so as to generate an alternating current electric field or an alternating electric field in the space sandwiched between the two electrodes.

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