Food coating method and coating device

Abstract

To provide a method for keeping freshness of food by forming a coat on the surface of the food and a device therefor.SOLUTION: A food coating method includes applying an aqueous solution or alcohol solution of a water-soluble and biocompatible base compound to the surface of food, and then irradiating the surface of the food with plasma or an electron beam to subject the base compound to a polymerization reaction, thereby forming a polymerized thin film on the surface of the food.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for coating food products. [Background technology]

[0002] In recent years, food waste (food that is still edible but is thrown away) has become a problem, and interest in reducing food waste is growing. However, food spoilage is unavoidable, and a lot of food is wasted for that reason. For example, in the case of fruits and vegetables, freshness gradually decreases during distribution after harvest, and there is a limited time that they can be stored after reaching the consumer.

[0003] Known food freshness preservation technologies that contribute to reducing food waste include packaging materials such as modified atmosphere (MA) films and antibacterial films. Other freshness preservation technologies besides packaging materials include, for example, ethylene gas absorbing and decomposing agents and alcohol sustained-release agents. Furthermore, research into food coating technologies using plant-derived extracts and the like has recently been conducted. However, there remains a need for food freshness preservation technologies, including fresh foods such as fruits and vegetables, as well as processed foods. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2014 / 038674 [Non-patent literature]

[0005] [Non-Patent Document 1] Daisuke Ishii and Takahiko Hariyama, Self-supporting organic thin film: Surface protection effect of "nanosuit" formed by mimicking extracellular substances, Japan Science and Technology Agency New Technology Briefing, 2015.12.08, https: / / shingi.jst.go.jp / past_abst / abst / 2015 / cips / tech_property.html, https: / / shingi.jst.go.jp / past_abst / abst / p / 15 / cips / cips06.pdf Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above circumstances, an object of the present invention is to provide a method and an apparatus for preserving the freshness of food by forming a film on the surface of the food. [Means for solving the problem]

[0007] The present inventor has proposed a technique for producing a thin film using a biocompatible compound, etc., which is difficult to form into a film, as a raw material, and has actually confirmed that a thin film can be formed on the body surface of a living mosquito larva using a nonionic surfactant (see Patent Document 1). The thin film described in Patent Document 1 has a composition that is continuously graded from the surface of the thin film to the cross-sectional direction of the thin film, and has a different structure on the front and back, which is similar to the cuticle of an organism, so it is expected to exhibit excellent membrane properties (gas barrier properties, liquid permeability) similar to the skin and outer interface of an organism. Therefore, the thin film was expected to be applied as a food packaging material.

[0008] However, with regard to the thin film described in Patent Document 1, it is not entirely clear whether such a thin film can be formed on the surface of materials other than minute biological samples such as those used for electron microscope observation, particularly on the surface of food, and there is room for further study regarding the method and device configuration for this purpose.

[0009] Therefore, as a result of intensive research, the present inventors have found that the above object can be achieved by the following configuration.

[0010] [1] A method for coating food, comprising applying an aqueous solution or an aqueous alcohol solution of a water-soluble and biocompatible raw compound to the surface of a food, and then irradiating the surface of the food with plasma or an electron beam to polymerize the raw compound and form a thin polymerized film on the surface of the food. [2] The coating method according to [1], wherein the raw material compound is a compound having a polyalkylene glycol chain in its molecule. [3] The coating method according to [1] or [2], characterized in that the aqueous solution or aqueous alcohol solution of the raw material compound further contains at least one additive selected from amino acids, sugars, and amphipathic compounds other than the raw material compound. [4] The coating method according to any one of [1] to [3], wherein the additive is a saccharide. [5] The coating method according to any one of [1] to [4], characterized in that the food is fresh fruit or vegetable. [6] The coating method according to any one of [1] to [4], wherein the food is meat, seafood, or processed food made from meat and / or seafood. [7] The coating method according to any one of [1] to [4], wherein the food is a carbohydrate-rich food such as cooked rice, mochi, noodles, bread, or buns. [8] A food coating device comprising an application means for applying an aqueous solution or an alcoholic aqueous solution of a water-soluble and biocompatible raw material compound to the surface of a food, and an irradiation means for irradiating the surface of the food with plasma or an electron beam, and characterized in that it performs the coating method described in any of [1] to [7]. Effect of the Invention

[0011] According to the present invention, a water-soluble and biocompatible raw compound applied to the surface of a food is irradiated with plasma or an electron beam, thereby forming a thin polymeric film (i.e., a coating) of the raw compound on the surface of the food, and the surface of the food is coated with the thin polymeric film (coating). This polymeric thin film suppresses the loss of moisture (transpiration) from inside the food, and also prevents the intrusion of germs from the outside, suppressing their proliferation. Furthermore, during the process of forming the polymeric thin film, plasma or electron beams are applied to kill or inactivate pathogens such as bacteria and viruses that were originally attached to the surface of the food. This improves or controls conditions such as the gas environment (oxygen, carbon dioxide, ethylene gas, etc.), temperature, humidity, and microorganisms that affect the freshness of food, and extends the shelf life of food under favorable conditions. The inventors have long considered the possibility that the barrier properties of such polymeric thin films could be used to protect foods, and have published an article about this in, for example, Non-Patent Document 1. However, it was surprising and unexpected that the polymeric thin film can actually inhibit the intrusion of bacteria and the like from the outside, and further that it works synergistically with the inactivation effect of plasma or electron beam irradiation to obtain remarkable effects as shown in the following examples. Thus, the present invention provides a method for preserving the freshness of food by forming a film on the surface of the food. The present invention also provides an apparatus for use in the above method. [Brief description of the drawings]

[0012] [Figure 1] Photographs showing the results of Example 1 conducted using fruit grapes (Delaware). Lower right: Group 1, upper right: Group 2, lower left: Group 3, upper left: Group 4. [Diagram 2] Photographs showing the results of Example 1 conducted using fruit grapes (Delaware). Lower right: Group 1a, upper right: Group 2a, lower left: Group 3a, upper left: Group 4a [Diagram 3]Photographs showing the results of Example 2 using raisins, a processed food. Lower right: Group 5, upper right: Group 6, lower left: Group 7, upper left: Group 8 [Figure 4] Photographs showing the results of Example 2 using raisins, a processed food. Lower right: Group 5a, upper right: Group 6a, lower left: Group 7a, upper left: Group 8a DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described in detail. The following description of the components may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment.

[0014] As used herein, the term "food" refers to anything provided for consumption by animals (including feed, fodder, etc.), and typically refers to anything provided for consumption by humans.

[0015] Examples of foods include fresh produce (vegetables, fruits, wild plants, mushrooms, etc.), seafood, and meat, which are collectively referred to as fresh foods. Here, vegetables include leafy vegetables, root vegetables, and fruit vegetables, classified according to the part used. Fruits refer to fruits that are used for food. Wild plants refer to plants that grow wild in the mountains and are used for food. Mushrooms refer to organisms classified as fungi that form fruit bodies of a macroscopic size, or the fruit bodies themselves that are used for food. Seafood refers to aquatic animals such as fish and shellfish that are used for food. Meat refers to meat that is used for food. In addition, research and development of artificial substitute meat artificially produced from plant lipids and proteins, and cultured meat obtained by culturing animal cells has also progressed in recent years. The present invention can also be used for these artificial meats (including seafood).

[0016] The food may also be a processed food made from the above-mentioned fruits and vegetables, seafood, and / or meat, and the raw materials are subjected to some processing. For example, the food may be a food that is cooked by boiling, steaming, stewing, baking, deep-frying, or the like before being distributed to consumers as a product (e.g., boiled shrimp, grilled fish, roast beef, roast pork, etc.), or a food prepared using a variety of ingredients (e.g., gyoza, shumai, hamburger steak, sausage, ham, kamaboko, fish cake, etc.).

[0017] Foods to which the food coating method of the present invention can be applied can also be classified according to the amount of nutrients they contain.Specific examples include foods that contain a lot of carbohydrates (sugar) (e.g., cooked rice, rice cakes, noodles, bread, buns, etc., also called staple foods), foods that contain a lot of protein (e.g., meat, seafood, eggs, soybeans, soybean processed foods, etc., also called main dishes), and foods that contain a lot of vitamins, minerals, and dietary fiber (e.g., vegetables, mushrooms, seaweed, etc., also called side dishes).

[0018] In this specification, the term "coating" of a food refers to a state in which a thin film formed by polymerizing a water-soluble and biocompatible raw compound described later is formed on at least a part or the entire surface of the food. In other words, as long as the polymerized thin film is formed on at least a part of the surface of the food, the effect of the present invention can be obtained, and the polymerized thin film does not necessarily have to be formed on the entire surface of the food. In other words, it should be noted that the formation of the polymerized thin film on the entire surface of the food is not an essential condition for obtaining the effect of the present invention. Furthermore, the location and range of coating can be set according to the size of the food to be coated (hereinafter also simply referred to as the "target food"), the size (surface area), shape (unevenness, etc.), properties (wettability, etc.) of the surface to which the aqueous solution of the raw compound or the aqueous alcohol solution described later is to be applied, or according to the conditions required for preserving the freshness of the target food.

[0019] Taking grapes used in the following examples as an example, it is known that grape berries (grains) are susceptible to damage from mold and the like in the places where the stalk is (or was) attached and where the skin is damaged, and that even if germs attach to other places, the antibacterial properties of the grapes themselves can kill the germs or inhibit their growth. Therefore, when the target food is grapes, it is sufficient that the above-mentioned polymeric thin film is formed on at least a part of the surface of the grape berries (grains). In this way, the location and range of the coating can be determined according to the type of target food.

[0020] The food coating method according to an embodiment of the present invention (hereinafter also referred to as the "coating method according to the present embodiment") is characterized in that an aqueous solution or an aqueous alcohol solution of a water-soluble and biocompatible raw compound is applied to the surface of a food, and then the raw compound is polymerized by irradiating the surface of the food with plasma or an electron beam, thereby forming a polymerized thin film on the surface of the food.

[0021] In the coating method of this embodiment, the biocompatibility of the raw material compound means that the raw material compound can be consumed by animals (typically humans).

[0022] As the raw material compound, a compound having a hydrophilic functional group can be used, and for example, a compound having a polyalkylene glycol chain in the molecule can be mentioned.

[0023] In addition, as the raw material compound, a compound having the property of forming a film by polymerization by irradiation with plasma or electron beam can be used. Therefore, the raw material compound may be a compound having no polymerization active group, or may be a compound having a polymerization active group. In the latter case, the raw material compound may be a compound having at least one double bond selected from a carbon-carbon double bond, a carbon-nitrogen carbon-carbon double bond, and a carbon-oxygen double bond.

[0024] Specifically, raw material compounds include glycerin and glycerin substitutes; polysorbates such as polysorbate 20, polysorbate 40, polysorbate 60, polysorbate 65, polysorbate 80, and polysorbate 85, and polysorbate substitutes.

[0025] Glycerin is a trihydric alcohol (so-called polyhydric alcohol), has a hydroxyl group in the molecule, and is a low vapor pressure substance. Glycerin also has viscosity. Substances with these characteristics can be used as substitutes for glycerin. Specifically, examples of glycerin substitutes include polyethylene glycol, polyvinyl alcohol, triglyceride, polyresorcinol, polyphenol, tannic acid, urushiol, and saponin.

[0026] In this specification, "polysorbates" refers to those prepared by reacting sorbitan fatty acid esters (nonionic surfactants) with ethylene oxide. Currently available polysorbates include polysorbate 20 (Tween 20), polysorbate 40 (Tween 40), polysorbate 60 (Tween 60), polysorbate 65 (Tween 65), polysorbate 80 (Tween 80), and polysorbate 85 (Tween 85), but polysorbates that can be used as raw materials are not limited to these. In addition, substances classified as nonionic surfactants similar to polysorbates can be used as substitutes for polysorbates. Specifically, examples of substitutes for polysorbates include polyoxyethylene alkyl ethers, polyoxyethylene hydrogenated castor oil, polyoxyethylene mono fatty acid esters, sucrose fatty acid esters, polyglycerin fatty acid esters, alkyl polyglycosides, and N-methyl alkyl glucamides.

[0027] The raw material compounds as described above are dissolved in water at an appropriate concentration taking into consideration the viscosity, etc., to prepare an aqueous solution of the raw material compounds. The raw material compounds may be used alone or in combination of two or more. In addition, lower alcohols may be used in combination to form an alcohol aqueous solution for the purposes of coating properties and drying characteristics for food, or for manufacturing reasons when adding additives described below, etc. The lower alcohol is preferably undenatured ethanol, and the preferred amount of the lower alcohol to be added is 1 to 80 weight percent, more preferably 5 to 30 weight percent.

[0028] The content of glycerin, glycerin substitute, polysorbates, and / or polysorbate substitutes in the aqueous solution or aqueous alcohol solution of the raw material compound is not particularly limited, but is preferably 0.01 to 10 percent by weight, and more preferably 0.1 to 2 percent by weight.

[0029] The aqueous solution or alcoholic solution of the raw material compound may further contain at least one additive selected from amino acids, sugars, and amphipathic compounds other than the raw material compound. By containing the additive, the wettability of the aqueous solution or alcoholic solution of the raw material compound to the surface of the target food is improved, and the polymerization property of the raw material compound can be increased when the surface of the food coated with the aqueous solution or alcoholic solution of the raw material compound is irradiated with plasma or electron beam.

[0030] Examples of amino acids include isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine, and histidine (all essential amino acids), as well as tyrosine, cysteine, aspartic acid, asparagine, serine, glutamic acid, glutamine, proline, glycine, alanine, and arginine (all non-essential amino acids), and derivatives thereof. Examples of the sugars include monosaccharides, polysaccharides, and derivatives thereof. Examples of the monosaccharides include glucose, fructose, etc. Examples of the polysaccharides include disaccharides such as sucrose and trehalose, oligosaccharides, starch, glucomannan, hyaluronic acid, pullulan, guar gum, xanthan gum, propylene glycol, carboxymethylcellulose, etc. Examples of amphiphilic compounds other than the raw material compounds include amphoteric surfactants such as lauryl dimethylaminoacetate betaine, dodecylaminomethyl dimethylsulfopropyl betaine, and 3-(tetradecyldimethylaminio)propane-1-sulfonate, as well as amphiphilic compounds (biosurfactants) derived from microorganisms such as rhamnolipid, sophorolipid, and mannosylerythritol lipid.

[0031] The content ratio of the additive in the aqueous solution or aqueous alcohol solution of the raw material compound is not particularly limited, and may be at least lower than the content ratio of the raw material compound described above. Specifically, for example, in an embodiment in which the raw material compound is glycerin, a glycerin substitute, polysorbates, and / or polysorbates substitutes, the content is preferably 0.001 weight percent to less than 10 weight percent, and more preferably 0.01 weight percent to less than 2 weight percent.

[0032] Regarding the embodiment in which the aqueous solution of the raw material compound or the aqueous alcohol solution contains the additive, according to the inventor's preliminary experiment, when a 1% aqueous solution of Tween 20 used in the examples of Patent Document 1 is used as the aqueous solution of the raw material compound, the Tween 20 aqueous solution is partially repelled by the surface of some types of fruits and vegetables, making it difficult to apply the solution uniformly and form a polymerized thin film. However, it has been found that by using an aqueous solution of Tween 20 containing a certain amount of the additive, the wettability of the surface of the fruits and vegetables is improved, making it possible to apply the solution more uniformly and increasing the stability of the polymerized thin film. It has also been found that the surface tension of some foods can be controlled by using undenatured ethanol in combination. Among them, the above-mentioned effects on the target foods (fruits and vegetables) were particularly notable when sugars were used as additives and at least one of them was included in an amount of about 0.005 weight percent.

[0033] From these results, the present inventors speculate that the additives play a role in enhancing the buffer effect (buffering action) and polymerization strength of the aqueous solution of the raw material compound or the aqueous alcohol solution by containing the additives at a predetermined ratio. Therefore, in the coating method of the present embodiment, it is considered effective to adjust the selection (combination) of the raw material compound and additives and their content ratios, as well as the composition of the solvent, according to the type of the target food. In addition, the selection (combination) of the raw material compound and additives and their content ratios, as well as the composition of the solvent, may be adjusted according to the preservation and storage environment of the coated food.

[0034] In addition, the aqueous solution or aqueous alcohol solution of the raw material compound may further contain auxiliary ingredients, as necessary, such as sweeteners, colorants, flavorings, etc. for improving the flavor and appearance of food, nutritional enhancers for enhancing the nutritional components of food, and preservatives, antioxidants, etc. for improving the shelf life of food, which are generally called food additives. In addition, the aqueous solution or aqueous alcohol solution of the raw material compound may further contain, as necessary, a hydrophobic compound such as lipids or proteins and a dispersion thereof dispersed with a surfactant, or an inorganic compound or metal nanoparticles and a dispersion thereof dispersed with a surfactant.

[0035] In this embodiment, the method of applying the aqueous solution or alcoholic solution of the raw compound to the surface of the food is not particularly limited, and can be appropriately selected according to the size of the target food, and the size (surface area), shape (unevenness, etc.), and properties (wettability, etc.) of the surface to which the aqueous solution or alcoholic solution of the raw compound is applied. For example, the aqueous solution or alcoholic solution of the raw compound may be applied to the surface of the target food using an application means such as a sprayer, or the aqueous solution of the raw compound or the alcoholic solution may be applied to the surface of the target food using an application means such as a brush. In addition, the aqueous solution or alcoholic solution of the raw compound may be applied to the surface of the target food using a known application device such as a spin coating device. Alternatively, a part or the entire surface of the target food may be immersed in the aqueous solution or alcoholic solution of the raw compound placed in a specified container for a certain period of time.

[0036] The polymerization reaction by irradiation with plasma can be carried out using a device such as a reaction tube used in conventional plasma polymerization, an atmospheric pressure plasma irradiation device, etc. The gas species (atmosphere) used is not particularly limited, and examples thereof include rare gases (argon, helium, etc.), inert gases such as nitrogen, oxygen, hydrogen, ammonia, etc. These gas species may be used alone or in combination of two or more to form a mixed gas.

[0037] Polymerization reaction by electron beam irradiation can be carried out using a conventional electron beam irradiation device, etc. Electron beams are obtained by passing an electric current through a filament placed at the center of a chamber kept in vacuum, heating it and releasing thermoelectrons, which are extracted to a grid, converted into an electron current by an accelerating voltage, and emitted to the outside world through a window, and the structure of an electron microscope, a small electron beam tube, or a module structure in which these are arranged can be used.

[0038] By irradiating the plasma or electron beam, the polymerization reaction of the raw material compound proceeds from the irradiated surface to the irradiated surface, which results in a gradient of polymerization density from the irradiated surface to the irradiated surface. Therefore, on the surface of the food on which the polymerized thin film is formed, the loss of moisture (transpiration) inside the food is suppressed (moisture retention effect), and the intrusion of germs from the outside is prevented, suppressing the proliferation of germs (antibacterial effect). Furthermore, by irradiating the food with plasma or electron beam during the process of forming the polymerized thin film, pathogens such as bacteria and viruses that were originally attached to the surface of the food (before the aqueous solution of the raw material compound or the alcohol aqueous solution was applied) can be killed or inactivated (sterilization effect). This improves or controls conditions such as the gas environment (oxygen, carbon dioxide, ethylene gas, etc.), temperature, humidity, and microorganisms that affect the freshness of food, and extends the shelf life of the food under favorable conditions.

[0039] Thus, according to the coating method of the present embodiment, a film is formed on the surface of food, thereby obtaining the above-mentioned moisture retention effect, antibacterial effect, and sterilization effect, thereby enabling the freshness of the food to be maintained.

[0040] As described above, the coating method of the present embodiment can be carried out by using separate means or devices for applying an aqueous solution or an aqueous alcohol solution of a raw material compound to the surface of a food and irradiating the surface of the food with plasma or electron beams. Alternatively, the coating method of the present embodiment can be carried out by using a device equipped with an application means for applying an aqueous solution or an aqueous alcohol solution of a water-soluble and biocompatible raw material compound to the surface of the food and an irradiation means for irradiating the surface of the food with plasma or electron beams. The device may be a so-called dedicated device for carrying out the coating method of the present embodiment, or may be added as a function of an existing device. In the latter case, an example is a device in which the above application means and the above irradiation means are added to a preservation device such as a conventional freezer or refrigerator. In this case, a user (such as a food producer, consumer, processor, distributor, or retailer) can preserve the food by freezing or refrigerating the food in a state in which the coating method of the present embodiment is applied to the food.

[0041] Hereinafter, the embodiments of the present invention will be described in more detail based on examples. However, the scope of the present invention should not be construed as being limited by the following examples. EXAMPLES

[0042] [Example 1] The food to be coated was the fruit grape (Delaware). Polysorbate 20 (Tween 20) was used as a raw material compound, and an aqueous solution of the raw material compound was prepared by adding 0.005 weight percent of a sugar as an additive to an aqueous solution containing 1 weight percent of Tween 20 (1% aqueous solution of Tween 20).

[0043] Grapes were removed from bunches of grapes purchased from a greengrocer, and a total of 16 grapes were divided into four groups of four grapes each. The grapes were then placed into separate glass petri dishes for each group and left to stand in an incubator set to 37°C for four days. <Processing conditions> Group 1: An aqueous solution of the raw material compound is sprayed onto the surface of grape berries using a sprayer, and then the surface of the grape berries is irradiated with plasma in an argon atmosphere using a plasma irradiation device. Group 2: The surface of the grape berries was sprayed with an aqueous solution of the raw compound using a sprayer (without plasma irradiation). Group 3: The surface of grape grains was irradiated with plasma in an argon atmosphere using a plasma irradiation device (without application of an aqueous solution of the raw compound). Group 4: The surface of the grapes was neither coated with an aqueous solution of the raw compound nor irradiated with plasma (untreated). The distance between the plasma nozzle of the plasma irradiation device and the surface of the object was set to 1 cm, and the irradiation time was set to 3 minutes. The same applies to the following examples.

[0044] The results are shown in Figure 1. The four photographs shown in Figure 1 are group 1 (bottom right), group 2 (top right), group 3 (bottom left), and group 4 (top left).

[0045] As can be seen from the photograph in Figure 1, in groups 2, 3, and 4, mold growth was visible on the surface of the grapes, especially in the areas not covered by the skin (the junction with the spikelet and its surroundings), whereas in group 1, mold growth was clearly suppressed compared to groups 2 to 4. Furthermore, in group 1, the skin remained firmer than in groups 2 to 4, suggesting that water evaporation was suppressed.

[0046] Next, to prepare a fungal solution, the spikelets and branches from which the grapes (fruit) had been removed were soaked in distilled water for 24 hours. The four groups prepared in the same manner as above were then subjected to the following treatments. After that, the grapes for each group were placed on separate glass petri dishes and left to stand in an incubator set at 37°C for four days. <Processing conditions> Group 1a: An aqueous solution of the raw material compound is sprayed onto the surface of grape berries using a sprayer, the surface of the grape berries is irradiated with plasma in an argon atmosphere using a plasma irradiation device, and then a bacterial liquid is sprayed onto the surface of the grape berries using a sprayer. Group 2a: An aqueous solution of the raw material compound was sprayed onto the surface of grape berries using a sprayer, and then a bacterial liquid was sprayed onto the surface of the grape berries using a sprayer (without plasma irradiation). Group 3a: The surface of grape berries was irradiated with plasma in an argon atmosphere using a plasma irradiation device, and then the bacterial liquid was sprayed onto the surface of the grape berries using a sprayer (no aqueous solution of the raw compound was applied). Group 4a: The surface of the grape berries is sprayed with a bacterial liquid using a sprayer (no application of an aqueous solution of the raw compound or plasma irradiation is performed).

[0047] The results are shown in Figure 2. The four photographs shown in Figure 2 are group 1a (bottom right), group 2a (top right), group 3a (bottom left), and group 4a (top left).

[0048] As can be seen from the photograph in FIG. 2, in groups 2a, 3a, and 4a, mold was observed on the surface of the grape berries, especially on the parts not covered with skin (the junction with the spikelet and its surroundings), as in groups 2 to 4 described above, while mold growth was clearly suppressed in group 1a compared to groups 2a to 4a. It is noteworthy that in groups 2a to 4a, the application of the fungal liquid to the surface of the grape berries tended to increase mold growth in all groups compared to when the fungal liquid was not applied, while in group 1a, the degree of mold growth was the same as in group 1 or only slightly increased. Furthermore, in group 1a, the skin was kept firmer than groups 2a to 4a, as in group 1, suggesting that evaporation of water was suppressed.

[0049] In addition, surprisingly, it was initially expected that a certain bactericidal effect would be obtained even when the plasma irradiation was performed without applying an aqueous solution of the raw material compound to the surface of the grape berries (i.e., Group 3 and Group 3a), but contrary to this expectation, the expected effect (inhibitory effect on mold growth) was not observed under the conditions used in this example. This suggests that although the above-mentioned sterilization effect can be obtained by irradiating the surface of the grape berries with plasma, it is difficult to prevent the invasion of germs from the outside and the proliferation of germs after plasma irradiation, that is, to obtain the above-mentioned antibacterial effect. Furthermore, it was found that even when the aqueous solution of the raw compound was applied to the surface of grape berries without irradiating them with plasma, as in Group 2 and Group 2a, the above-mentioned sterilization and antibacterial effects were hardly obtained.

[0050] These results confirm that the food coating method of the present invention forms a film on the surface of the food, and that this film provides the above-mentioned moisture retention, antibacterial and sterilizing effects, thereby enabling the food to retain its freshness.

[0051] [Example 2] The food to be coated was raisins, a processed food. As a raw material compound, polysorbate 20 (Tween 20) was used, and an aqueous solution of the raw material compound was prepared in the same manner as in Example 1.

[0052] A total of 20 commercially available raisins were divided into four groups of five raisins each and subjected to the following treatments. The raisins were then placed in separate glass petri dishes for each group and left to stand in an incubator set at 37°C for four days. <Processing conditions> Group 5: An aqueous solution of the raw material compound is sprayed onto the surface of raisin grains using a sprayer, and then the surface of the raisin grains is irradiated with plasma in an argon atmosphere using a plasma irradiation device. Group 6: The surface of raisin grains was sprayed with an aqueous solution of the raw compound using a sprayer (without plasma irradiation). Group 7: Using a plasma irradiation device, the surface of raisin grains is irradiated with plasma in an argon atmosphere (without application of an aqueous solution of the raw compound). Group 8: The surface of the raisin grains was neither coated with the aqueous solution of the raw compound nor irradiated with plasma (untreated).

[0053] The results are shown in Figure 3. The four photographs shown in Figure 3 are group 5 (bottom right), group 6 (top right), group 7 (bottom left), and group 8 (top left).

[0054] As can be seen from the photograph in Figure 3, in groups 6, 7, and 8, mold growth was clearly visible to the naked eye over a wide area of ​​the surface of the raisins, whereas in group 5, mold growth was significantly suppressed compared to groups 6 to 8. Furthermore, in group 5, no significant changes were observed in the appearance (color, luster, etc.) of the surface of the raisins compared to the state before they were placed in the incubator, suggesting that the moisture content was maintained close to the state when they were removed from the packaging.

[0055] Next, a bacterial liquid was prepared in the same manner as in Example 1, and the four groups prepared in the same manner as above were subjected to the following treatment. After that, the raisins were placed on separate glass petri dishes for each group and left to stand in an incubator set at 37°C for four days. <Processing conditions> Group 5a: An aqueous solution of the raw material compound is sprayed onto the surface of raisin grains using a sprayer, the surface of the raisin grains is irradiated with plasma in an argon atmosphere using a plasma irradiation device, and then a bacterial liquid is sprayed onto the surface of the raisin grains using a sprayer. Group 6a: An aqueous solution of the raw material compound was sprayed onto the surface of raisins using a sprayer, and then a bacterial liquid was sprayed onto the surface of the raisins using a sprayer (without plasma irradiation). Group 7a: The surface of raisin grains is irradiated with plasma in an argon atmosphere using a plasma irradiation device, and then the bacterial liquid is sprayed onto the surface of the raisin grains using a sprayer (no application of an aqueous solution of the raw material compound). Group 8a: The bacterial liquid is sprayed onto the surface of raisins using a sprayer (no aqueous solution of the raw compound is applied, nor is plasma irradiated).

[0056] The results are shown in Figure 4. The four photographs shown in FIG. 4 are group 5a (lower right), group 6a (upper right), group 7a (lower left), and group 8a (upper left).

[0057] As can be seen from the photograph in Fig. 4, in groups 6a, 7a, and 8a, mold growth was clearly visible to the naked eye over a wide area of ​​the surface of the raisins, as in groups 6 to 8 described above, whereas mold growth was significantly suppressed in group 5a compared to groups 6a to 8a. Note that in group 5a, mold growth was greater than in group 5 due to the application of the bacterial liquid to the surfaces of the raisins, but the appearance (color, luster, etc.) of the surface of the parts where mold growth was not observed seemed to maintain a moisture content close to that when they were removed from the packaging material.

[0058] In addition, as described above with regard to Example 1 using grapes, initially, it was expected that a certain degree of bactericidal effect would be obtained even when plasma irradiation was performed without applying an aqueous solution of the raw compound to the surface of the raisin grains (i.e., Groups 7 and 7a). However, contrary to this expectation, the expected effect (inhibition of mold growth) was not observed under the conditions used in this Example. Furthermore, even when the aqueous solution of the raw material compound was applied to the surface of raisins without irradiating them with plasma, as in Groups 6 and 6a, no inhibitory effect on mold growth was observed.

[0059] From these results, it was confirmed that the food coating method of the present invention is not limited to application to fresh produce such as fruits, but can also be applied to processed foods made from fresh produce, and that a film is formed on the surface of the food, which provides the above-mentioned moisture retention, antibacterial and sterilizing effects, thereby maintaining the freshness of the food. [Industrial Applicability]

[0060] The food coating method according to the present invention is a method for preserving the freshness of food by forming a film on the surface of the food. The method of the present invention can be carried out by applying an aqueous solution or an aqueous alcohol solution of a water-soluble and biocompatible raw material compound to the surface of the food and irradiating the surface of the food with plasma or an electron beam, so that the device configuration can be relatively simple. Therefore, the present invention is expected to be applied in various situations such as food production, processing, distribution, retail, and preservation, and is expected to contribute to reducing food waste.

Claims

1. A method for coating food, comprising the steps of: applying an aqueous solution or an aqueous alcohol solution of a water-soluble and biocompatible raw compound to a surface of a food; and then irradiating the surface of the food with plasma or an electron beam to polymerize the raw compound, thereby forming a polymerized thin film on the surface of the food, A coating method, wherein the aqueous solution or aqueous alcohol solution of the raw material compound further contains a saccharide as an additive.

2. 2. The coating method according to claim 1, wherein the raw material compound is a compound having a polyalkylene glycol chain in the molecule.

3. The coating method described in claim 1, characterized in that the raw material compound is at least one compound selected from glycerin, polyethylene glycol, polyvinyl alcohol, triglyceride, polyresorcinol, polyphenol, tannic acid, urushiol and saponin; polysorbates such as polysorbate 20, polysorbate 40, polysorbate 60, polysorbate 65, polysorbate 80 and polysorbate 85, and nonionic surfactants.

4. The coating method according to claim 3, characterized in that the content of the sugar in the aqueous solution or aqueous alcohol solution of the raw material compound is from 0.001 weight percent to less than 10 weight percent.

5. 5. The coating method according to claim 1, wherein the food is fruit or vegetable.

6. 5. The coating method according to claim 1, wherein the food is meat, seafood, or a processed food made from meat and / or seafood.

7. 5. The coating method according to claim 1, wherein the food is a carbohydrate-rich food such as cooked rice, mochi, noodles, bread, or buns.

8. 8. A food coating apparatus comprising: a coating means for coating a surface of a food with an aqueous solution or an alcoholic aqueous solution of a water-soluble and biocompatible raw compound, the aqueous solution or the alcoholic aqueous solution further containing a sugar as an additive; and an irradiation means for irradiating the surface of the food with plasma or an electron beam, the food coating apparatus comprising: a coating means for coating a surface of the ... the water-soluble and biocompatible raw compound, the aqueous solution or the alcoholic aqueous solution further containing a sugar as an additive;

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