JP7803638B2 - Freshness preservation device and freshness preservation method - Google Patents

Description

The present invention relates to a freshness preservation device and a freshness preservation method.

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 allows for the lowest possible temperature without causing freezing.

The reason for maintaining low temperatures to preserve freshness for perishable goods in general is to suppress bacterial activity. Low temperature maintenance techniques are commonly used as they are the only techniques with a known mechanism for preserving freshness while suppressing bacterial activity. While maintaining low temperatures is a useful technique, 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.

Meanwhile, methods have been proposed for applying electromagnetic fields to food in order to preserve its quality and freshness. For example, before the grinding process of various plants to be pulverized for consumption, a processing device and processing method have been proposed in which 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).

An electric field processing refrigerated storage cabinet has also been proposed, which has multiple mounted electrodes on which the storage material is placed in contact, and multiple vertically movable electrodes facing each other, 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).

JP 2003-189789 A (Patent 3668848) Special Publication No. 2012-527216 (Patent 5593235)

However, while the devices and methods described in the aforementioned Patent Documents 1 and 2 aim to preserve freshness by applying an alternating electromagnetic field, the mechanism of action is unknown. As a result, the problems with the technology have not been identified or improved, and issues remain, such as the uneven and unpredictable effectiveness of preserving freshness in perishable products.

The present invention aims to solve the above-mentioned problems by providing a freshness preservation device and freshness preservation method that uses a simple configuration to apply an electromagnetic field to fresh products, thereby achieving more uniform freshness preservation regardless of whether the electromagnetic field is direct current or alternating current.

To achieve the above objectives, the freshness preservation device of the present invention comprises two opposing electrodes, a power source that applies a voltage between the electrodes, and a fresh food placement section located in the space between the two electrodes. By applying a voltage between the two electrodes, the electric field lines of the electric field generated between the electrodes are transmitted through the fresh food placed in the fresh food placement section, thereby preserving the freshness of the fresh food.

Furthermore, the freshness preservation method of the present invention uses a freshness preservation device comprising two opposing electrodes, a power source that applies a voltage between the electrodes, and a fresh food placement section disposed in the space between the two electrodes. By applying a voltage between the two electrodes, an electric field is generated between the electrodes, and the electric field lines of the generated electric field are transmitted through the fresh food placed in the fresh food placement section, thereby restricting the movement of active oxygen, which is a polar molecule contained in the fresh food, thereby suppressing the spread of oxidation of organic matter in the fresh food by active oxygen and/or suppressing bacterial activity by suppressing the supply of energy from active oxygen to bacteria.

The freshness preservation device and freshness preservation method of the present invention allow the electric field lines generated between two opposing electrodes to pass through fresh produce, thereby achieving more uniform freshness preservation regardless of whether the electromagnetic field is direct current or alternating current, thanks to a clear mechanism of action in which the movement of active oxygen, a polar molecule, is constrained by the electric field lines.

1 is a perspective view conceptually showing the configuration of a freshness preservation device according to one embodiment of the present invention; FIG. 10 is a perspective view conceptually showing the configuration of a freshness preservation device according to another embodiment. FIG. 10 is a perspective view conceptually showing the configuration of a freshness preservation device according to yet another embodiment. FIG. 10 is a side view conceptually showing the configuration of a freshness preservation device according to yet another embodiment.

Below, a freshness preservation device and freshness preservation method according to one embodiment of the present invention will be described with reference to the drawings.

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

The two electrodes 2 facing each other may simply be 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 the opposing surfaces of the two electrodes 2 may simply be flat or curved.

The power supply 20 is only required to be able to apply 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 supplies 20 is not limited to one, and multiple power supplies 20 may be provided. For example, if each of the two electrodes 2 is composed of multiple electrode elements, multiple power supplies 20 may be used to apply voltages individually to each of the multiple electrode elements or to groups of electrode elements. The two opposing electrodes 2 and power supplies 20 are only required to be able to form an electric field with a uniform density of electric field lines 10 in at least the space occupied by the fresh food 9.

The fresh product placement unit 3 is not limited to a platform 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 is maintained in the space sandwiched between two opposing electrodes, but if metal parts are placed in this 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.

An electric field is generated between the two electrodes 2 by the power source 20, and the electric field lines 10 of this 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.

(Mechanism of freshness preservation using 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 necessary for their activity. Therefore, by binding active oxygen, the bacteria cannot obtain energy, and bacterial activity can be stopped. By applying these two points, it is possible to eliminate the effects of active oxygen and stop bacterial activity, thereby maintaining the freshness of fresh produce.

By the way, 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, when an electric field is present, 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.

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 in accordance with that force. Conversely, in a space where electric field lines exist at a constant density, no force based on 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 if necessary.

The mechanism of action of freshness preservation device 1 is based on two points: the ability to 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 uses electric field lines 10 to capture the active oxygen, eliminating the effects of the movement of active oxygen and stopping bacterial activity, thereby preserving the freshness of fresh produce. With a clear mechanism of action in which electric field lines 10 bind polar molecules, freshness preservation device 1 can achieve more uniform freshness preservation, regardless of whether the electromagnetic field is direct current or alternating current.

(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 described 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 portion. However, at the ends of the electrodes, the electric field lines diverge, the density of the electric field lines decreases, and they become non-uniform.

In order to preserve the freshness of more fresh produce, it is necessary to create a wider space between the two electrodes 2 where the density of electric field lines is constant (called the freshness preservation space). 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 will create a wider space with a uniform electric field density can be determined by electromagnetic field simulations using the finite element method.

(Floating electrode)
Figure 2 shows one method for expanding a freshness preservation space with a constant density of electric field lines. The freshness preservation device 1 is the same as the 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, and two sets of four electrodes each surround the space sandwiched between two opposing circular electrodes 2 from above, below, left, and right in a frame-like manner. 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 sets. The floating electrodes 4 surrounding the freshness preservation space can suppress the spread of electric field lines, thereby expanding the effective freshness preservation space.

The 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. The floating electrode 4 simply needs to 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 the floating electrode 4 can be obtained through electromagnetic field simulation.

(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. Even in this case, electromagnetic field simulation can be used to determine various quantities.

(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 alternating voltage consisting of, for example, a rectangular wave or a triangular wave to the two electrodes 2. Furthermore, the power supply 20 may be capable of generating, in the space sandwiched 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.

When the voltage applied by power supply 20 is a sine wave, sine wave voltages are easy to boost and are commonly used, making them easy to use. However, the sine wave waveform has a weakness: the voltage is low for long periods of time during the cycle, and can even become zero. Periodically, the voltage decreases, weakening the electric field, reducing the density of the electric field lines and weakening the force binding polar molecules. This periodically reduces the freshness-preserving effect, reducing the overall effectiveness.

The voltage applied between the two opposing electrodes may be direct current. With direct current, the density of the electric field lines remains constant over time, providing a stable effect of binding polar molecules. However, if water molecules or ionized substances are present, for example, near an unprotected electrode, there is a risk that the electrode material may be eluted due to the effects of electrolysis.

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 when alternating, so there is no time when the effect of the electric field lines weakens, and the time when the voltage becomes zero during alternation can be shortened, 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 more.

When the voltage applied between two opposing electrodes is, for example, a sine wave AC voltage, or, for example, a rectangular wave or triangular wave AC voltage, its frequency is preferably 10 Hz or higher and 10 kHz or lower. If it is below 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. If the frequency exceeds 10 kHz, the wavelength of the electromagnetic waves becomes shorter, becoming shorter than the wavelength of the freshness-preserving space, which is undesirable as it results in uneven freshness-preserving effects within the freshness-preserving space. It is more preferable to set the AC or AC voltage applied by the power source 20 to a frequency of 50 Hz or higher and 1 kHz or lower.

(Bonding and grounding of electrodes via resistors)
The freshness preservation device 1 shown in Figure 4 is 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.

The power supply 20 applies a voltage between the two electrodes 2 so that an AC or alternating electric field is generated in the space between them. The freshness preservation device 1 of this embodiment can enhance 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 a resistor 6 and is grounded, may also be applied to the freshness preservation device 1 shown in Figures 2 and 3 above.

Example 1
A freshness preservation device equivalent to freshness preservation 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 preservation device.

An 80 cm high wooden workbench was installed in the center of the room as the 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 three days with the freshness preservation device running. The temperature inside the room was set to 20°C.

When smelled three days later, the odor level was determined to be level 2 on the 6-level odor intensity rating scale shown below (Table 1).

(Table 1) Six-level odor intensity rating system == ...
0: Odorless 1: Barely detectable odor (detection threshold)
2: A weak smell that can be identified (recognition threshold)
3: Easily detectable odor 4: Strong odor 5: Overpowering odor == ...

Commercially available chicken thighs are usually contaminated with Campylobacter and E. coli, and if left at room temperature, bacterial growth would produce an odor. However, the odor intensity was 2, indicating that the freshness-keeping device suppressed microbial activity.

(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.

When the odor was smelled after three days, the odor level based on Table 1 was rated an intensity of 5. This confirmed the effectiveness of the freshness preservation device in Example 1. In other words, commercially available chicken thighs are usually contaminated with Campylobacter and E. coli, and in Comparative Example 1, the freshness preservation device was left at room temperature without being operated, so the freshness preservation effect of the freshness preservation device was not achieved, and odor due to bacterial growth was likely generated.

Example 2
A device equivalent to the freshness preservation device 1 shown in Figure 2 was installed inside a metal storage cabinet with an inner floor 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 surface, 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 components constituting 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 preservation device.

A 60 cm high plastic workbench was installed in the center of the storage facility as the fresh product placement area 3. 200 g of swordfish lean meat was prepared. The myoglobin metmyoglobin conversion rate was measured (see Inohara Kota, Onoue Yukino, and Kimura Ikuo, "Study on a method for measuring the metmyoglobin conversion rate of fish muscle myoglobin," Journal of the Japanese Society of Fisheries Science, 81(3), 456-464 (2015)), and was found to be 10%. 200 g of this 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.

The myoglobin metmyoglobin conversion rate was measured after six days and was found to be 15%. Reactive oxygen is involved in the conversion of myoglobin to metmyoglobin, 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.

(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.

When the myoglobin metmyoglobin rate was measured after six days, it 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.

Example 3
A device equivalent to the freshness preservation device 1 shown in Figure 3 was installed inside a metal storage cabinet with an inner floor 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.

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 were 100 pF. An alternating rectangular wave voltage of 1.5 kV and a frequency of 900 Hz was applied to electrode 2 of the installed freshness preservation device.

A 60 cm high plastic workbench was installed in the center of the storage facility as the fresh food storage area 3. Three cherry tomatoes were placed in Ziploc® bags, sealed, and placed on the workbench. They were then left for 8 days with the freshness preservation device running. The temperature inside the storage facility was set to 20°C.

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.

(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.

After leaving it for eight days, mold had grown. The mold growth suggests that in Comparative Example 3, the freshness preservation device was not activated, which meant that the movement of active oxygen could not be suppressed, and therefore bacterial activity could not be suppressed.

As described above, a freshness-preserving device using this technology can suppress reactions involving active oxygen, thereby maintaining the freshness of food. It is effective in preventing deterioration of meats such as beef, pork, chicken, and fish by preventing metmyocarditis, and for vegetables such as salads, by suppressing microorganisms.

(Method of preserving freshness)
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.

The present invention is not limited to the above configuration and can be modified in various ways. For example, the configurations of the above-mentioned 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 perishable item, they can still achieve a freshness-preserving effect even if their density is not strictly constant. Therefore, the two opposing electrodes 2 may be capable of generating an electric field with such electric field lines.

REFERENCE SIGNS LIST 1 Freshness preservation device 10 Electric field lines 2 Electrode 20 Power supply 3 Perishable food placement section 4 Floating electrode 5 Capacitor 6 Resistor 9 Perishable food

Claims (8)

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 . The freshness preservation device described in 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. The freshness-preserving device according to claim 1 or 2, characterized in that the power supply 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. 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. A freshness preservation device as described in any one of claims 1 to 4, characterized in that it further comprises a floating electrode that is 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 larger. The freshness preservation device described in claim 5, further comprising a capacitor electrically connecting the two electrodes and the floating electrode. The freshness preservation device according to any one of claims 1 to 6, characterized in that the power supply is configured to generate an electric field in the space between the two electrodes by applying either a DC voltage, an AC voltage consisting of a sine wave, or an AC voltage consisting of a square wave or triangular wave to the two electrodes, or an electric field created by a temporal or spatial combination of these electric fields. The two electrodes are connected to each other via resistors provided in each electrode, and are grounded through the connection point.
A freshness preservation device as described in any one of claims 1 to 7, characterized in that the power source applies a voltage between the electrodes so that an alternating current electric field or an alternating electric field is generated in the space sandwiched between the two electrodes.