FOOD PRESERVING DEVICE WITH ELECTROSTATICALLY ATOMIZING UNIT AND PROCESS OF PRESERVING PERISHABLE FOOD

TECHNICAL FIELD

The present invention relates to a food preserving device with an electrostatically atomizing unit which generates charged minute water particles for preserving a perishable food, and a process of preserving the perishable food.

BACKGROUND ART

JP 2006-061072 A disclose to spray charged minute water particles directly to a perishable food for keeping the freshness thereof through an effect of sterilizing the food. However, the uncovered food is susceptible to being dried out in the surrounding air which renders an adverse effect. In view of this insufficiency, the inventors study the use of a plastic film designed to wrap various foods and found that the charged minute water particles can well permeate through the plastic film to reach the food through an activation diffusion effect for improved preservation of the food.

DISCLOSURE OF THE INVENTION

In view of the above finding, the present invention has been achieved to provide a food preserving device capable of keeping the freshness of a perishable food over a long period of time. The food preserving device in accordance with the present invention includes an electrostatically atomizing unit and a container configured to store a perishable food wrapped with a plastic film. The atomizing unit includes an emitter electrode, water supply means configured to supply water to the emitter electrode, and a high voltage applying means configured to apply a high voltage to said emitter electrode to electrostatically atomize the water on the emitter electrode into the charged minute water particles capable of permeating through the plastic film. The atomizing unit is disposed to spray a mist of the charged minute water particles to the food wrapped with the plastic film and stored in the container. Thus, the charged minute water particles are allowed to permeate through the plastic film to reach the food for sterilization of the food, in addition to an effect of keeping the food free from being dried out by the plastic film.

In a preferred embodiment, the food preserving device includes a housing which is divided by a partition into the container and an air flow compartment. The air flow compartment is provided with a fan which introduces an outside air through an inlet port of the housing to generate a forced air flow directed to the container through an outlet port at one end of the partition. The atomizing unit is disposed within the air flow compartment to carry the mist of the charged minute water particles on the forced air flow. The outlet port is provided with a swinging fan for uniformly dispersing the mist carrying forced air flow into the container for effectively applying the mist to the food through the plastic film.

In this connection, the air flow compartment is preferred to include a separator which separates a first flow path from a second flow path. The first flow path extends from the inlet port through the fan to the outlet port for directing the forced air flow towards the container. The second flow path extends from the inlet port to the outlet port not through the fan so as to develop an additional air flow caused by being sucked by the forced air flow to be directed into the container thought the outlet port. The atomizing unit is disposed within the second flow path so as to successfully carrying the mist of the charged minute water particles on the forced air flow directed towards the container.

Preferably, the device includes a humidifier which is disposed in the first flow path downstream of the fan to add moisture to the forced air flow independently of the mist for increasing the humidity in the container in order to keep the food fresh over a prolonged time period.

Further, the food preserving device may include a filter for removing a germ and/or virus suspended in the air carrying the mist. For example, the first flow path may be provided with a first filter upstream of the fan prior to the moisturization by the humidifier, and the second flow path may be provided with a second filter upstream of the atomizing unit for effectively removing the germs or viruses prior to the generation of the mist.

Preferably, the atomizing unit is configured to generate the charge minute water particles in the number of 0.15 x 10 ¹⁴ per second or more for improving the sterilization effect.

The present invention also proposes a process of preserving a perishable food using the atomizing unit of the above configuration for keeping the freshness of the food. The process includes steps of supplying water to the emitter electrode, and applying a high voltage to the emitter electrode to generate the mist of the charged minute water particles, wrapping the perishable food with a plastic film permeable to the charged minute water particles, and spraying the mist of the charged minute water particles to the perishable food through the plastic film. Preferably, the plastic film has a thickness of 250 μm or less, and is made of a material selected from a group consisting of poly vinylidene chloride (PDVC), polyethylene, and poly vinyl chloride (PVC).

In the above process, the emitter electrode is preferred to be cooled for condensation of water from within the surrounding air on the emitter electrode.

These and still other advantageous features of the present invention will become more apparent from the following detailed description of the embodiment when taken in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a food preserving device in accordance with a preferred embodiment of the present invention;

FIG. 2 is a sectional view of an electrostatically atomizing unit employed in the above device for generating charged minute water particles;

FIG. 3 is a schematic view illustrating how the charged minute water particles permeate through a plastic film;

FIGS. 4Aand 4B are schematic views illustrating a structure of the plastic film;

FIG. 5 is a schematic view illustrating an instrument used for an experimental test;

FIG. 6 is a set of pictures demonstrating a result of the experimental test;

FIG. 7 is a set of pictures demonstrating a result of another experimental test;

FIG. 8 is a graph illustrating the result of the above test;

FIG. 9 is a set of pictures demonstrating a result of a further experimental test;

FIG. 10 is a graph illustrating the result of the above test;

FIG. 11 is a set of pictures demonstrating a result of a still further experimental test; and

FIG. 12 is a graph illustrating the result of the above test.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1 , an explanation is now made to a food preserving device in accordance with a preferred embodiment of the present invention. The device includes a housing 100 divided by a partition 110 into a container 120 and an air flow compartment 130. The container 120 is provided to store a perishable food 160 such as meat, vegetable, fruit, and seafood, and is provided with a door 128. The food 160 is placed in a tray 124 and is wrapped with a plastic film 126. The air flow compartment 130 is provided with a fan 140 driven by a motor to introduce an outside air through an inlet port 132 so as to generate a forced air flow leading to the container 130 through an outlet port 112 in the upper end of the partition 110. Disposed in the air flow compartment 130 is an electrostatically atomizing unit 10 which generates a mist of charged minute water particles to be carried on the forced air flow directed to the container 130 in order to spray the mist on the food 160 wrapped with the plastic film 170.

The air flow compartment 130 includes a separator 134 which separates a first flow path from a second flow path. The first flow path extends from the inlet port 132 through the fan 140 to the outlet port 112 at the upper end of the compartment 130 for directing the forced air flow towards the outlet port. The second flow path extends from the inlet port 132 to the outlet port 112 not through the fan to develop an additional air flow which is caused by being sucked from the forced air flow to flow towards the outlet port 112 and into the container 120. The atomizing unit 10 is disposed in the second flow path so as to carry the mist of the charged minute water particles on the forced air flow directed towards the container 120. A filter 135 is disposed in the first flow path upstream of the fan 140 to remove impurities, particularly germs or viruses carried on the incoming air. A like filter 136 is disposed in the second flow path upstream of the atomizing unit 10. The compartment 130 also includes a humidifier 138 which is disposed in the first flow path downstream of the fan 140 for moisturizing the air directed into the container 130. The humidifier 138 incorporates a moisturizing element which absorbs water supplied from a tank (not shown) and vaporizes the water. The filters may be made of any material that is capable of entrapping at least one of the germ and virus.

Further, the device includes a controller 150 which controls, based upon an output of a humidity sensor 152 exposed in the container 120, the humidifier 138 for regulating the humidity of the air directed to the container 120 at an optimum level for preserving the food.

As shown in FIG. 2, the atomizing unit 10 includes a cylindrical barrel 12 carrying an emitter electrode 60 projecting through a bottom of the barrel 12, and an opposed electrode 24 which is disposed in an opposite relation to the emitter electrode 20. The oppose electrode 24 is shaped from an electrically conductive substrate with a circular opening 26 which has an inner periphery spaced by a predetermined distance from a discharge end 22 at the tip of the emitter electrode 20 to define a discharge port of discharging the mist. The atomizing unit 10 includes cooling means 30 and a high voltage source 50. The cooling means 30 is coupled to cool the emitter electrode 20 in order to condense the water content carried in the surrounding air on the emitter electrode 20, thereby supplying the water thereto. The high voltage source 50 is provided to apply a high voltage across the emitter electrode 20 and the opposed electrode 24 so as to charge the water on the emitter electrode 20 and atomize it into the charged minute water particles to be discharged out through the discharge port 26 in the form of the mist. The cooling means 30 is realized by a Peltier module having a cooling side coupled to the emitter electrode 20 at its one end away from the discharge end 22, and having thermo-electric elements which, upon being applied with a predetermined voltage, cools the emitter electrode to a temperature below a dew point of the water. The Peltier module has a plurality of thermo-electric elements arranged in parallel with each between thermal conductors 31 and 32 to cool the emitter electrode 20 at a cooling rate determined by a variable voltage given from a cooling electric source circuit 40. One thermal conductor 31 defining the cooling side is coupled to the emitter electrode 20, while the other thermal conductor 32 defining the heat radiation side is provided with a heat radiator 36. The Peltier module is fixed between the bottom of the barrel 12 and the heat radiator 36 with its cooling side conductor 31 in heat transfer contact with a root of the emitter electrode 20. The high voltage source 50 includes a high voltage generation circuit which applies a predetermined high voltage across the emitter electrode 20 and the grounded opposed electrode 20 to give a negative or positive voltage (for example, - 4.6 kV) to the emitter electrode 20, thereby generating the mist of the charged minute water particles of nanometer size in the order of 10 nm to 30 nm. The resulting mist is carried on the air which is directed into the container 120 through the outlet port 112 to be sprayed on the food. The outlet port 112 is provided with a swinging fan 114 for uniformly dispersing the forced air flow carrying the mist into the container 120. It is noted in this connection that the mist can successfully entrap radical existing in the air within the charged minute water particles so as to keep its activity for a prolonged period of time. The radical includes, for example, a hydroxyl radical which is highly reactive with germs and/or viruses for effective sterilization of the food when entrapped with the charged minute water particles.

The unit 10 is disposed with its opposed electrode 24 spaced away from the emitter electrode 20 towards the outlet port 112 so as to attract the charged minute water particles for guiding the same along the air flow directed to the container 130, i.e., the food therein. Alternatively, when the unit 10 is dispensed with the opposed electrode, an equivalent electrode can be realized by a portion of the housing positioned downstream of the unit 10 for expelling the charged minute water particles towards the container 130.

The atomizing unit 10 is controlled by a controller (not shown) to generate the charged minute water particles in the number of 0.5 x 10 ¹⁴ (30 μmol/l) per one minute or more to give an improved sterilization effect to the food wrapped with the plastic film 170, as demonstrated in the below.

The plastic film used for wrapping the food has a thickness of 250 μm or less, and is made of a material selected from a group of polyvinylidene chloride (PDVC), polyethylene (PE), and polyvinyl chloride (PVC). The polyvinylidene (PDVC) film is commercially available as a food wrapping film of home use, while the polyethylene (PE) or polyvinyl chloride (PVC) is available as that of industrial use. Generally, the film of the industrial use has greater permeability to oxygen gas that that of the home use.

As shown in a schematic view of FIG. 3 which is somewhat exaggerate with regard to the plastic film 170, when filled in the container 120 at a high concentration, a large number of charged minute water particles stuck on the plastic film 170 are caused to diffuse or dissolved into the film due to a concentration difference between the opposite sides of the film, as indicated by black arrows, and are subsequently released from the film to reach the food 160 for making the sterilization effect on the food, while the moisture or the water content of the food 160 is blocked from escaping out through the film as indicated by while arrows. Thus, the food is expected to keep its freshness over a prolonged period of time.

The diffusion of the particles in the film can be explained by a mechanism shown in FIGS. 4A and 4B. The film is known to have a crystalline area R1 where polymer chains appear regularly, and a non-crystalline area R2 where the polymer chains are intermingled. As shown in FIG. 4B, the non-crystalline area R2 is known to have clearances or spaces S given by free volumes between the polymer chains. The space S will vary constantly as a consequence of thermal motion of the polymer chains, and is therefore regarded to diffuse the charged minute water particles therethrough.

Now, an explanation is given to various experimental tests for demonstrating the sterilization effect of spraying the mist of the charged minute water particles to the food wrapped with the plastic film. As schematically shown in FIG. 5, one of the tests was made with the use of the container 120 having a volume of 70 I, and being kept at a temperature of 5 ⁰ C and a humidity of 99 %. A single atomizing unit 10 was used to constantly generate the charged minute water particles in the number of 0.5 x 10 ¹⁴ (30 μmol/l) per one minute for spraying the mist thereof onto three specimens of indigo carmine, the first one (A) wrapped with the PDVC film, the second one (B) wrapped with the PE film, and the third one (C) not wrapped with the film. The indigo carmine was employed as an alternative substance to the food, and becomes bluish when oxidized, and becomes colorless when reduced. The test was done over a period of 12 days for continuously spraying the mist to the oxidized indigo carmine, i.e., bluish one. For comparison a purpose, the same three specimens were left unexposed to the mist for the same period of time. As shown in FIG. 6, all the specimens exposed to the mist become colorless after the elapse of 9 to 12 days, while the same specimens not exposed to the mist remain bluish. That is, the specimens wrapped with any one of the plastic films see the same reducing effect as the specimen not wrapped with the plastic film. On the other hand, the specimens not sprayed with the mist do not see the reducing effect. This demonstrates that either one of the plastic films is permeable to the charged minute water particles to give the reducing effect to the specimens.

Next, another test was made to examine variations in weight, appearance, and the sense of touch with regard to a cheese as one perishable food 160, as shown in FIG. 7. Two specimens of the cheese, one wrapped with the plastic film, the other not wrapped with the film were stored in the container 20 over 15 days with a temperature being kept constantly at 5 ⁰ C, and with the relative humidity being kept at 99 % for the first 7 days, and at 70 % for the last 8 days. The mist of the charged minute water particles were generated in the number of 0.5 x 10 ¹⁴ (30 μmol/l) per one minute and sprayed continuously over the period of 15 days. For comparison, the like specimens and were stored in the container at the same environmental conditions but not being exposed to the mist of the charged minute water particles. FIG. 8 shows the test result from which it is found that the specimen [1] of cheese wrapped with the plastic film and exposed to the mist sees a minimum weight reduction than any one of the three specimens, one [2] wrapped with the film but not exposed to the mist, another [3] not wrapped with the film but exposed to the mist, and the other [4] not wrapped with the film and not exposed to the mist. With this consequence, the specimen wrapped with the film and exposed to the mist remains soft, while the other specimens becomes hardened due to the reduction of the water content. Also, it is found that the non-wrapped specimens show no substantial difference therebetween in the weight reduction, sense of touch, and color, irrespective of being exposed to the mist or not.

A further test was made to examine the like variations with regard to hams as the food, with the same conditions as in the above test of FIGS. 7 and 8. As shown in FIGS. 9 and 10, it is also found that the specimen [1] of the ham wrapped with the plastic film and exposed to the mist sees a minimum weight reduction than any one of the three specimens, one [2] wrapped with the film but not exposed to the mist, another [3] not wrapped with the film but exposed to the mist, and the other [4] not wrapped with the film and not exposed to the mist. With this consequence, the specimen [1] wrapped with the film and exposed to the mist remains soft, while the other specimens becomes hardened due to the reduction of the water content. Also, it is found that the non-wrapped specimens are too decomposed to see no substantial difference therebetween in the appearance and the sense of touch.

A still further test was made to examine the like variations with regard to a beef as one perishable food, as shown in FIGS. 11 and 12. Two specimens of the beef, one (A) wrapped with the polyethylene (PE) film, the second one (B) not wrapped with the film were stored in the above mentioned container over 3 days with a temperature being kept at 5 ⁰ C, and with a relative humidity kept at 70 %. The mist of the charged minute water particles were generated in the number of 0.5 x 10 ¹⁴ (30 μmol/l) per one minute and sprayed continuously over the period of 3 days. For comparison, the like specimens and were stored in the container at the same environmental conditions but not being exposed to the mist of the charged minute water particles. FIG. 12 shows the test result from which it is found that no substantial difference in the weight reduction between the specimen [1] of the beef wrapped with the plastic film of PE and exposed to the mist and the specimen [2] wrapped with the same film but not exposed to the mist, but a considerable difference in the weight reduction is seen between the wrapped specimens [1], [2] and the non-wrapped specimens [3], [4]. Further, there is a considerable difference between the appearance and the sense of touch between the specimen [1] and [2]. While, on the other hand, the non-wrapped specimens are too decomposed to see no substantial difference therebetween in the appearance and the sense of touch. With this consequence, the specimen [1] wrapped with the film and exposed to the mist is found to be most effective to keep the freshness.

A sterilization effect was examined with regard to the two specimens of the beef, one wrapped with the film of polyethylene (PE) and the other wrapped with the film of polyvinylidene chloride (PDVC). One group of the specimens were stored in the like container and subjected to the spray of the mist over 3 days, while another group of the specimens were stored in the container for 3 days without be exposed to the mist for comparison. The mist of the charged minute water particles were generated and sprayed under the same condition as made in the above test of FIGS. 11 and 12. The sterilization effect is evaluated in terms of the number of germs (cfu/cm ² ) appearing in the specimens before and after the elapse of 3 days. The number of germs was measured in accordance with the known plate dilution method. The result is shown in table below.

As apparent from the table, it is estimated that the radicals carried by the charged minute water particles permeated successfully through either of the films to prevent proliferation of the germs in the beef.