Cover for container for preserving freshness of citrus fruits and method for preserving freshness of citrus fruits

Abstract

To provide a technique that can hold freshness of citrus fruit for a longer period of time.SOLUTION: A cover for a citrus fruit freshness holding container is made of a synthetic resin film, a moisture permeability of the synthetic resin film at 40°C, 90% RH is 5 to 1,000 [g / m2 day atm].SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cover for a container for preserving the freshness of citrus fruits and a method for preserving the freshness of citrus fruits. [Background technology]

[0002] Citrus fruits such as Unshu mandarins are sometimes stored in agricultural containers after harvesting and shipped after a certain period of storage. In addition, agricultural containers are generally box-shaped with a mesh structure and an open top for the reasons of good breathability, strength, light weight, ease of storage, and sufficient storage capacity. Therefore, if harvested citrus fruits are stored in an agricultural container as is, the surface of the citrus fruits will dry out and wilt, significantly reducing their commercial value.

[0003] On the other hand, agricultural crops such as citrus fruits continue to breathe even after harvesting. Therefore, if they are covered with a non-breathable cover to prevent drying, the humidity increases due to the respiration of the citrus fruits, causing condensation, which makes the citrus fruits more susceptible to mold.

[0004] In addition, the more active the respiration of agricultural products, the more likely they are to deteriorate, and the greater the weight loss (transpiration rate) immediately after harvest. Therefore, in order to maintain the freshness of agricultural products, it is important to suppress respiration.

[0005] A technique for preserving harvested citrus fruits for a long period of time is described, for example, in Patent Document 1. Patent Document 1 discloses a storage cover for citrus fruits, which is made of a breathable sheet material having an air permeability of 100 sec / 100 cc to 5000 sec / 100 cc. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Utility Model Registration No. 3129141 Summary of the Invention [Problem to be solved by the invention]

[0007] However, although the technology described in Patent Document 1 suppresses the occurrence of condensation by ensuring breathability, the ventilation causes active respiration of citrus fruits, and the weight loss amount cannot be sufficiently reduced. In addition, good breathability also tends to reduce humidity, which causes the surface of citrus fruits to dry out easily, leading to problems with appearance such as the tendency for them to wilt.

[0008] The present inventors have conducted extensive research into how to suppress mold growth on harvested citrus fruits stored in agricultural containers, while reducing wilting due to drying and limiting the respiration of the citrus fruits to maintain their freshness. As a result, they have found that controlling the moisture permeability of the cover that covers the agricultural container at 40°C and 90% RH is effective, and have completed the present invention. [Means for solving the problem]

[0009] According to the present invention, A cover for a citrus freshness-keeping container made of a synthetic resin film, The moisture permeability of the synthetic resin film at 40° C. and 90% RH is 5 to 1000 [g / m 2 A cover for a citrus freshness-keeping container is provided which is

[0010] According to the present invention, there is also provided a method for preserving freshness of citrus fruits using the above-mentioned cover for a citrus freshness-preserving container, A method for preserving the freshness of citrus fruits is provided, which comprises covering an agricultural container containing citrus fruits with the citrus freshness-preserving container cover. Effect of the Invention

[0011] According to the present invention, a technique can be provided that can maintain the freshness of citrus fruits for a longer period of time. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a schematic perspective view showing an example of a method of using the cover for a citrus freshness-keeping container according to this embodiment. [Diagram 2] FIG. 2 is a schematic perspective view showing an example of a method of using the cover for a citrus freshness-keeping container according to this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments of the present invention will be described in detail. In this specification, the term "approximately" means that the range includes a range that takes into consideration manufacturing tolerances and assembly variations, unless otherwise specified. In this specification, the expression "a to b" in the explanation of a numerical range means a or more and b or less, unless otherwise specified. For example, "1 to 5% by mass" means "1% by mass or more and 5% by mass or less."

[0014] <Cover for citrus freshness-keeping container> The cover for a citrus freshness-keeping container of this embodiment is intended to cover a known container used to store harvested citrus fruits. The covering is not limited to a continuous covering, but may be discontinuous or have an opening in part. Specifically, in the case of a rectangular parallelepiped container, the top and sides of the top, sides, and bottom may be covered, or all of the sides may be covered.

[0015] The cover for a citrus freshness-keeping container of this embodiment (hereinafter also simply referred to as the "cover") is made of a synthetic resin film, and the moisture permeability of the synthetic resin film at 40°C and 90% RH is 5 to 1000 [g / m 2 ·day·atm]. This makes it possible, when harvested citrus fruits are stored in agricultural containers, to suppress the growth of mold on the citrus fruits, reduce wilting due to drying, and limit the respiration of the citrus fruits to maintain their freshness. The moisture permeability at 40°C and 90% RH is preferably 25 to 900 [g / m 2 ·day·atm], and more preferably 50 to 800 [g / m2 ·day·atm]. According to the cover of this embodiment, by setting the moisture permeability at 40°C and 90% RH to the lower limit or more, water vapor can easily pass through, the increase in humidity inside the cover can be reduced, and the occurrence of condensation can be suppressed. On the other hand, by setting the moisture permeability at 40°C and 90% RH to the upper limit or less, respiration and transpiration of citrus fruits can be appropriately maintained, weight loss can be suppressed, freshness can be easily maintained, and wilting of the citrus peel due to drying can be suppressed.

[0016] The moisture permeability at 40° C. and 90% RH can be measured by a method in accordance with JIS Z0208 (cup method).

[0017] In addition, the moisture permeability at 40°C and 90% RH can be adjusted by applying known techniques such as the selection of the material of the synthetic resin film described below, the manufacturing method of the synthetic resin film, the layer structure of the synthetic resin film, and control of the through holes.

[0018] The shape of the cover in this embodiment is not particularly limited as long as it can cover the container, and may be, for example, a sheet shape, a bag shape, etc. Among these, a bag shape is preferable from the viewpoint of being able to easily cover a known container. When the cover of the present embodiment is in the form of a bag, it is preferable that at least a part of the periphery of the bag excluding the opening has a heat-sealed portion, which makes it possible to easily preserve the freshness of citrus fruits.

[0019] In addition, in this embodiment, citrus fruits refer to the fruits of plants belonging to the Rutaceae family, Rutaceae subfamily. Specific examples of citrus fruits include oranges such as navel oranges, Valencia oranges, and blood oranges; mandarin oranges such as Unshu mandarins, mandarin oranges, ponkan oranges, Kishu mandarins, Ancore, Dandelion, koji, shekwasha, Tachibana, and Shiranui; miscellaneous citrus fruits such as Natsudaidai, Hassaku, Hyuganatsu, Sanboukan, Kawachibankan, Kinukawa, and Naruto; tangor and tanzero fruits such as Tankan, Iyokan, Murcott, Kiyomi, Orlando, Mineola, and Seminole; limes such as Mexican lime and Tahiti lime; lemons such as Lisbon lemon, Eureka lemon, Diamante, and Etlogue; pomelo fruits such as Banpeiyu and Tosa Buntan; grapefruits such as Duncan, Marsh, Thompson, and Ruby Red; yuzu fruits such as yuzu, kabosu, sudachi, hanayu, and Kizu; kumquat and trifoliate orange. Among these, from the viewpoint of obtaining a good freshness-preserving effect, mandarin oranges are preferable, and Unshu mandarin oranges are more preferable.

[0020] The synthetic resin film will be further described below.

[0021] [Synthetic resin film] From the viewpoint of allowing the citrus fruits accommodated in the container to be visually observed from the outside, the synthetic resin film is preferably transparent or translucent, and more preferably transparent.

[0022] The synthetic resin constituting the synthetic resin film is not particularly limited as long as it can be used for packaging agricultural products and fruits and vegetables, and any known synthetic resin can be used. Examples of the polyethylene and ethylene copolymers include various polyethylenes and ethylene copolymers, polypropylene, polyvinyl chloride, polystyrene, acrylic resins, polyester resins such as polyethylene terephthalate and polylactic acid, and polyamide resins such as nylon 6. These may be homopolymers, copolymers of two or more types, or blends of two or more types of these homopolymers or copolymers. Specific examples of the polyethylene and ethylene copolymers include copolymers or ionomers such as ethylene-vinyl alcohol copolymers, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, metallocene-linear low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-propylene copolymer, and ethylene-α-olefin copolymer. These may be used alone or in combination, or may be mixed with other resins.

[0023] Among these, from the viewpoint of appropriately controlling the air permeability, polyester resins such as polyethylene, ethylene-vinyl alcohol copolymer, polypropylene, polystyrene, and polylactic acid, and polyamide resins such as nylon are preferred, and one or more types selected from nylon, polylactic acid, polystyrene, and ethylene-vinyl alcohol copolymer are more preferred, and nylon is even more preferred.

[0024] The above nylons may be nylon 6, nylon 11, nylon 12, nylon 66, nylon 6·10, nylon 6·12, nylon 6·T, nylon 6·I, nylon 9T, nylon M5T, polymetaxylylene adipamide (MXD nylon), etc., which may be used alone or in combination of two or more thereof. Among these, nylon 6, nylon 11, nylon 12 and nylon 66 are preferred alone or in combination of two or more thereof, and nylon 6 and nylon 66 are more preferred alone or in combination of two or more thereof. Moreover, it is preferable that the nylon is unoriented.

[0025] The above ethylene-vinyl alcohol copolymer is preferred from the viewpoint of obtaining good heat sealability. The ethylene content in the ethylene-vinyl alcohol copolymer resin is preferably 20 to 48 mol%, more preferably 40 to 48 mol%. By adjusting the ethylene content, it is possible to further improve the heat sealability and adjust the moisture permeability.

[0026] The molding method of the synthetic resin film is not particularly limited, but may be extrusion, inflation, calendering, etc. When the synthetic resin film has a multi-layer structure, it is preferably produced by a co-extrusion inflation method.

[0027] When molding a synthetic resin film, additives such as an anti-fogging agent may be kneaded into the film, if necessary, or two or more types of resins may be blended together. The antifogging agent may include a nonionic surfactant. This makes it possible to effectively suppress condensation. Examples of the nonionic surfactant include glycerin fatty acid ester, polyglycerin fatty acid ester, polyethylene glycol fatty acid ester, polyethylene glycol sorbitan fatty acid ester, polyoxyethylene alkyl ether, sorbitan fatty acid ester, alkyl diethanolamine, and alkyl diethanolamide.

[0028] In addition, the synthetic resin film may be stretched or annealed, and may further include a sealant layer. By stretching, the rigidity, pinhole resistance, water vapor / oxygen barrier properties, and appearance of the synthetic resin film can be improved. Examples include stretched nylon, stretched polylactic acid, and stretched polystyrene.

[0029] The synthetic resin film may be used as a single layer or as a multi-layer structure of two or more layers. In the case of a multi-layer structure, the resins contained in each layer may be the same or different. For example, the same resin may be selected from nylon, polylactic acid, polystyrene, and ethylene-vinyl alcohol copolymer, or different resins may be selected to form each layer to form a multi-layer structure. Among these, it is preferable to have at least a layer made of nylon.

[0030] Thickness The average thickness of the synthetic resin film is preferably 10 μm or more and 150 μm or less, more preferably 15 μm or more and 100 μm or less, and even more preferably 20 μm or more and 50 μm or less. By making the average thickness of the synthetic resin film equal to or greater than the lower limit, it becomes easier to control the oxygen permeability and moisture permeability to a higher degree and the strength of the cover can be increased, whereas by making the average thickness of the synthetic resin film equal to or less than the upper limit, the handleability of the cover can be improved, appropriate moisture permeability and oxygen permeability can be obtained, and production costs can be reduced.

[0031] [Through hole] The cover of the present embodiment may or may not have a through hole.

[0032] In the case where the film has a through hole, the planar shape of the through hole may be, for example, a circle, a polygon, or a slit. The circle is not limited to a perfect circle, but includes an approximately circular shape. In addition to the circle, the shape may be a semicircle or a crescent shape. The polygon may be a shape surrounded by three or more line segments, such as a triangle, a rectangle, or a pentagon. The slit is a cut or narrow gap that penetrates the synthetic resin film, and may be a straight line, a curve, an L-shape, an X mark, or the like, and its length is not particularly limited.

[0033] The average diameter of the through holes is preferably 30 μm to 1100 μm, more preferably 40 μm to 500 μm, and further preferably 50 μm to 200 μm.

[0034] The through holes can be formed by any known method, such as a processing method using a hot needle, a method of perforating with a laser beam, or a method using a mold such as a roll cutter.

[0035] [Oxygen permeability] The oxygen transmission rate of the synthetic resin film of the present embodiment at 23° C. and 60% RH is preferably 2 cc / m from the viewpoint of maintaining the respiration of citrus fruits and maintaining their freshness. 2 ·day·atm or more, and more preferably 5cc / m 2 ·day·atm or more, and more preferably 300cc / m 2 ·day·atm or higher. On the other hand, the oxygen permeability of the synthetic resin film at 23° C. and 60% RH is preferably 50,000 cc / m from the viewpoint of suppressing the respiration of citrus fruits and preserving their freshness. 2 ·day·atm or less, and more preferably 10000cc / m 2 ·day·atm or less, and more preferably 7500cc / m 2 ·day·atm or less.

[0036] The oxygen permeability can be adjusted by selecting the material of the synthetic resin film, the manufacturing method of the synthetic resin film, the layer structure of the synthetic resin film, the through holes, and the like.

[0037] <How to keep citrus fruits fresh> The method for preserving freshness of citrus fruits in this embodiment is a method for preserving freshness of citrus fruits using the above-mentioned citrus freshness-preserving container cover, in which an agricultural container containing citrus fruits is covered with the citrus freshness-preserving container cover. This makes it possible to suppress the growth of mold and reduce wilting while preserving the freshness of the citrus fruits in the agricultural container. After the agricultural container containing the citrus fruits is covered with the citrus freshness-preserving container cover, the citrus fruits may be stored as is indoors or refrigerated, but from the viewpoint of effectively suppressing the growth of mold, it is preferable to store the citrus fruits at room temperature.

[0038] Next, the packaging form using the citrus freshness-keeping container cover will be described with reference to Figs. 1 and 2 show a bag-shaped citrus freshness-keeping container cover placed over an agricultural container containing agricultural produce. That is, the bag is placed over the top of the agricultural container, covering the peripheral walls (all sides) of the agricultural container. In this case, the bottom of the bag is located on the top of the agricultural container. In addition, Figure 1 shows a configuration in which the opening of the bag is not closed and the bottom of the agricultural container is exposed, while Figure 2 shows a configuration in which the opening of the bag is closed and the bottom (bottom) of the agricultural container is closed. In order to ensure appropriate breathability, it is preferable that at least a part of the bottom (bottom surface) of the agricultural container is not covered, and it is more preferable that the entire surface is exposed.

[0039] In addition, when the cover is in sheet form, the method of covering the peripheral wall (entire side surface) of the agricultural container by placing the sheet on the top surface of the agricultural container in the same manner as in the case of the bag-shaped cover can be used. The bottom surface of the agricultural container can be covered by the sheet, or can be partially or entirely exposed.

[0040] In addition, the above-mentioned bags and sheets can be bound together by any known method. For example, the open portion may be heat sealed, or the bags and sheets may be bound together using materials such as back sealing tape, cable ties, rubber bands, or crimps.

[0041] In addition, in the citrus freshness preservation method of this embodiment, from the viewpoint of further improving the freshness preservation effect, it is preferable to control the packaging form according to the moisture permeability at 40°C and 90% RH of the synthetic resin film constituting the cover for the citrus freshness preservation container. Specifically, the moisture permeability is 30 to 1000 [g / m 2 ·day·atm], and more preferably 50 to 1000 [g / m 2In the case of a freshness-preserving container having a moisture permeability of 5 to 900 [g / m 2 ·day·atm], more preferably 5 to 800 [g / m 2 In the case of [100-1500m2], it is preferable that a part of the bottom surface of the agricultural container is exposed and the other surfaces are covered by the citrus freshness-keeping container cover. This makes it easier to maintain the temperature and humidity of the space inside the citrus freshness-keeping container cover within a more appropriate range.

[0042] The agricultural containers used in the method for preserving freshness of citrus fruits of this embodiment are also called collection containers, harvest containers, etc., and in this embodiment, any known containers can be used without any particular limitation. Specifically, agricultural containers have, for example, air permeable walls (all sides) and a bottom (bottom surface). In addition, agricultural containers have a mesh structure, and therefore have high air permeability and are lightweight. The size of the agricultural container is not particularly limited, and the citrus fruits may be stored in a flat or stacked manner. From the standpoint of ease of handling, etc., a rectangular box-like agricultural container with an open top is preferable. Agricultural containers may be made of resin, wood, vines, or cloth.

[0043] Furthermore, according to the method for preserving freshness of citrus fruits of this embodiment, the weight loss rate of the stored citrus fruits is 0.05% by weight or more and less than 1% by weight per day. In other words, according to the method for preserving freshness of citrus fruits of this embodiment, the average weight retention rate of the stored citrus fruits per day is more than 99% by weight and 99.05% by weight or less. This provides a high freshness retention effect. In general, the freshness of agricultural products is evaluated, for example, by the amount of weight loss (amount of transpiration), and it is said that a weight loss of 5% compared to the weight at harvest significantly impairs the quality of the product as a marketable product.

[0044] In addition, in the method for preserving freshness of citrus fruits according to the present embodiment, it is preferable to maintain the average temperature in the space covered by the cover for a citrus freshness-preserving container at 15° C. or higher and 20° C. or lower, and the average relative humidity at 80% or higher and 98% or lower. This makes it possible to obtain a more remarkable freshness-preserving effect. The space covered by the cover for a citrus freshness-keeping container refers to the space surrounded by the cover to the extent that outside air does not directly enter, and refers to the space inside the agricultural container. For example, if the cover is bag-shaped and the bag is placed over the top of the agricultural container and the opening is sealed at the bottom, it refers to the space near the top surface of the citrus fruits contained in the agricultural container. In other words, it is the temperature measured on the top surface of the agricultural produce contained in the topmost layer of the container. The temperature and humidity are intended to be within the above-mentioned ranges on average during the period during which freshness is maintained, starting immediately after the citrus fruits are covered with the citrus freshness-keeping container cover.

[0045] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various configurations other than those described above can also be adopted. Below, examples of reference forms are given. 1. A cover for a citrus freshness-keeping container made of a synthetic resin film, The moisture permeability of the synthetic resin film at 40° C. and 90% RH is 5 to 1000 [g / m 2 A cover for citrus freshness-keeping containers. 2. The cover for a citrus freshness-keeping container according to 1., wherein the thickness of the synthetic resin film is 10 to 150 μm. 3. A cover for a citrus freshness-keeping container as described in 1. or 2., wherein the synthetic resin film contains one or more materials selected from the group consisting of nylon, polylactic acid, polystyrene, and ethylene-vinyl alcohol copolymer. 4. A cover for a citrus freshness-keeping container as described in any one of 1. to 3., wherein the cover for the citrus freshness-keeping container is bag-shaped. 5. A cover for a citrus freshness-keeping container as described in any one of 1. to 4., wherein the synthetic resin film includes non-oriented nylon. 6. A cover for a citrus freshness-keeping container as described in any one of 1. to 5., wherein the synthetic resin film has a multi-layer structure. 7. A cover for a citrus freshness-keeping container as described in any one of 1. to 6., wherein the synthetic resin film contains an anti-fogging agent. 8. The cover for a citrus freshness-keeping container according to claim 7, wherein the anti-fogging agent comprises a non-ionic surfactant. 9. A cover for a citrus freshness-keeping container as described in any one of 1. to 8., wherein the citrus fruit is a mandarin orange. 10. A method for preserving the freshness of citrus fruits using a cover for a citrus freshness-preserving container according to any one of 1. to 9., A method for preserving the freshness of citrus fruits, comprising covering an agricultural container containing citrus fruits with the citrus freshness preservation container cover. 11. The method for preserving the freshness of citrus fruits according to claim 10, wherein the agricultural container has air permeable walls and a bottom. 12. The method for preserving the freshness of citrus fruits described in 10. or 11., wherein the weight loss rate of the stored citrus fruits is 0.05% by weight or more and less than 1% by weight per day. 13. A method for preserving the freshness of citrus fruits described in any one of claims 10 to 12, wherein the average temperature within the space covered by the cover for the citrus freshness-preserving container is 15°C or higher and 20°C or lower, and the average relative humidity is 80% or higher and 98% or lower. 14. A method for preserving the freshness of citrus fruits described in any one of claims 10 to 13, in which the entire surface of the agricultural container except for the bottom is covered with the citrus freshness-preserving container cover. EXAMPLES

[0046] Next, the present invention will be described in detail with reference to examples, but the content of the present invention is not limited to the examples.

[0047] <1> Citrus freshness container cover The following citrus freshness-keeping container covers were prepared: Citrus freshness container cover A (procedure) Nylon (UBE Nylon (registered trademark) 5033B, manufactured by Ube Industries) and ethylene-vinyl alcohol copolymer resin (EVOH: manufactured by Kuraray Co., Ltd., product name: E173B) were prepared, and each was put into the extruder part (two places) of an air-cooled inflation device capable of co-extrusion of two layers, heated and melted, and extruded into a ring-shaped die, from which a two-layered tubular molten resin (nylon on the outside, EVOH on the inside) of the melt of each material was extruded. Air at 50°C or less was fed into the extruded tubular molten resin to expand the molten resin while forming a film, and a tubular synthetic resin film was obtained at a film-forming speed of 60 m / min. The obtained tubular synthetic resin film was bottomed and sealed with a bottoming bag making machine to produce a large bag (inner dimensions 1200 mm x 1000 mm, thickness 25 μm: nylon layer 21 μm, EVOH layer 4 μm) to obtain a bag-shaped citrus freshness-keeping container cover A.

[0048] Citrus freshness container cover B (procedure) Nylon (UBE Nylon (registered trademark) 1030B, manufactured by Ube Industries, Ltd.) was charged into a T-die extruder, and a synthetic resin film was produced by the extrusion T-die method. The obtained synthetic resin film was cut and two pieces were stacked together, and heat-sealed on three sides using an impulse sealer (manufactured by Fuji Impulse, FI-400Y-10PK) to form a 10 mm wide heat-sealed area at 190°C for a sealing time of 1 second, producing a large bag (inner dimensions 1200 mm x 900 mm, thickness 20 μm), and a bag-shaped citrus freshness-keeping container cover B was obtained.

[0049] Citrus freshness container cover C (procedure) A polylactic acid film (Terramac TF (registered trademark) manufactured by Unitika Ltd.) was prepared and a large bag (inner dimensions 1200 mm x 900 mm, thickness 15 μm) was made in the same manner as cover B described above, to obtain bag-shaped cover C for citrus freshness-keeping containers.

[0050] Citrus freshness container cover D A nonwoven fabric made of high density polyethylene (Tyvek (registered trademark) manufactured by DuPont Co., Ltd.) was prepared and used in sheet form.

[0051] Citrus freshness container cover E (procedure) A biaxially stretched transparent polypropylene (PP) film (OPP film) was prepared and a large bag (inner dimensions 1200 mm x 900 mm, thickness 40 μm) was made in the same manner as cover B described above, to obtain cover E for a bag-shaped citrus freshness-keeping container.

[0052] <2> measurement The following measurements were carried out using each citrus freshness-keeping container cover. ·Moisture permeability (40℃, 90%RH) [g / m 2 ·Japan ·ATM] The measurement was performed by the cup method in accordance with JIS Z 0208.

[0053] The following measurements were carried out using each citrus freshness-keeping container cover. Oxygen permeability (23℃, 60%RH) [cc / m 2 ·day·atm] (1) Nitrogen gas filling After the sheet-like cover was formed into a bag shape, each bag was sealed by heat sealing or the like, and then the bag was degassed using an aspirator or the like. Degassing was performed until both sides of the bag were stuck together. Next, the bag was filled with nitrogen gas (purity 99.9% or more) using a white hard syringe. The amount of nitrogen gas injected was adjusted to the bag size, and as much as possible was injected within the range where the film constituting the bag was not tensioned by the injected nitrogen gas and was slightly loose, and was measured using the scale of the white hard syringe. The degassing and injection of nitrogen gas was performed, for example, by piercing the bag with a syringe needle. When piercing the syringe needle, double-sided tape was attached to the film constituting the bag, and an adhesive tape made of polypropylene film (hereinafter referred to as "PP tape") was further attached on top of this. After the syringe needle was removed, the pinhole was quickly blocked with PP tape. The tape attached to the bag was 4.5 cm long. 2 It fits within the following area: Furthermore, when the film constituting the bag was a microporous film, the micropores were not blocked with tape. (2) Initial oxygen concentration measurement The initial oxygen concentration (C0) in the bag was measured immediately after filling with nitrogen gas (t=0). The gas in the bag was sampled, and the initial oxygen concentration (C0) in the bag was determined by gas chromatography (TCD). C0 was 0.2% or less, and if it exceeded this, the process was repeated. The amount of sampling gas used for oxygen concentration measurement was 10cc or less. When injected into gas chromatography, a fixed amount of approximately 1cc was injected. In addition, measurements of standard gases (two or more points including approximately 1% and approximately 10% oxygen) were also performed by injecting the same amount of gas, and a calibration curve was created. (3) Storage of bags The bags used to measure the initial oxygen concentration were stored at 23°C and 60% RH (in a temperature and humidity chamber). The bags were placed so that no objects were placed on top of them and the air from the temperature and humidity chamber fan did not directly hit the bags. (4) Measurement of oxygen concentration in the bag during storage and calculation of oxygen transmission rate The oxygen concentration inside the bag is measured at 3 to 5 points in total, at least 2 points within the range of 1% to 7% immediately after filling with nitrogen gas and after 3 hours or more have passed, and a proportional relationship (correlation coefficient of 0.98 or more) must be established between the elapsed time t (hr) and the oxygen concentration inside the bag. If the correlation coefficient does not hold, the test was repeated. If the oxygen transmission rate of the film constituting the bag is too high and the oxygen concentration inside the bag increases too quickly and this condition cannot be met, a bag can be created by laminating a part of the film with a smaller oxygen transmission rate than the film being measured and a known film of the same material, and the same procedure can be repeated. In this case, the surface area of ​​the bag is excluding the part that is laminated with another known film, and the oxygen transmission rate of the measured film is determined by subtracting the oxygen transmission rate of the known film part from the calculated oxygen transmission rate. The oxygen transmission rate was calculated using the value for the longer elapsed time according to the following formula (1). F = 1.143 × (Ct-C0) × V / t (1) However, F: oxygen permeation rate (cc / bag day atm) Ct: Oxygen concentration in the bag t hours after filling with nitrogen gas (%) C0: Oxygen concentration in the bag immediately after filling with nitrogen gas (%) V: Amount of nitrogen gas filled (cc) t: Time elapsed since gas filling (hr)

[0054] <3> Freshness preservation experiment The following experiments were conducted using each citrus freshness-keeping container cover. Example 1 We offer a deep agricultural container (594 x 400 x 255 mm: mesh structure, made of resin) and a shallow agricultural container (594 x 400 x 170 mm: mesh structure, made of resin). 24 kg of Satsuma mandarins were evenly placed in each of the prepared agricultural containers, and the agricultural containers were stacked from the bottom up in the order of deep type to shallow type, and then a bag-shaped citrus freshness-keeping container cover A was placed on top of them. At this time, the top and all sides of the agricultural container were covered, and the opening of the citrus freshness-keeping container cover A was left open, leaving the bottom of the agricultural container exposed. The agricultural container was placed on a platform 150 mm high to ensure ventilation from the bottom of the agricultural container. The samples were stored at room temperature in a room away from direct sunlight and a freshness retention experiment was conducted.

[0055] Example 2 A freshness-retention experiment was carried out in the same manner as in Example 1, except that the bottom of the agricultural container was not exposed. Specifically, the top, all sides, and bottom of the agricultural container were covered, and the opening of cover A for citrus freshness-keeping containers was folded over the bottom of the lower agricultural container so that the bottom was not exposed, and the cover was placed on a platform 150 mm high.

[0056] Example 3 A freshness preservation experiment was carried out in the same manner as in Example 1, except that cover B for citrus freshness preservation container was used instead of cover A for citrus freshness preservation container in Example 1.

[0057] Example 4 A freshness retention experiment was conducted in the same manner as in Example 1, except that a total of five agricultural containers were prepared: three deep agricultural containers and two shallow agricultural containers, the same as in Example 1. Specifically, 24 kg of Satsuma mandarins were evenly placed in each of the prepared agricultural containers, and the agricultural containers were stacked from the bottom up in the following order: deep, shallow, deep, shallow, deep, and then a bag-shaped citrus freshness-keeping container cover A was placed on top of them.

[0058] Example 5 A freshness preservation experiment was carried out in the same manner as in Example 1, except that cover C for citrus freshness preservation container was used instead of cover A for citrus freshness preservation container in Example 1.

[0059] Comparative Example 1 A freshness preservation experiment was carried out in the same manner as in Example 2, except that cover D for a citrus freshness preservation container was used instead of cover A for a citrus freshness preservation container in Example 1. In addition, since the citrus freshness-keeping container cover D is in the form of a sheet, it is placed over the agricultural container by wrapping it from above.

[0060] Comparative Example 2 A freshness preservation experiment was carried out in the same manner as in Example 1, except that cover E for citrus freshness preservation container was used instead of cover A for citrus freshness preservation container in Example 1.

[0061] Comparative Example 3 A freshness preservation experiment was conducted in the same manner as in Example 1, except that the cover A for citrus freshness preservation containers in Example 1 was not used.

[0062] <4> Freshness retention rating (1) Unshu mandarins were taken out from storage and evaluated by multiple panelists for each of the following items: "discoloration," "withering (wrinkling)," and "discoloration and wilting of the stem." The results were evaluated according to the following criteria, and the average scores were calculated. In addition, the presence or absence of "mold" was confirmed, and the ratio of the number of unshu mandarins with mold to the total number of unshu mandarins was taken as the mold occurrence rate (%). The evaluation was carried out once a day, and any items that had deteriorated or had mold on them were removed after each evaluation. Furthermore, the "freshness retention period" was calculated as follows, and the results are shown in Table 1. Evaluation criteria 4: Good 3: Slightly deteriorated (purchase) 2: Obvious deterioration (no merchantability) 1: Severe deterioration (cannot be eaten) The "freshness retention period" is defined as the day before the earliest of the following dates on which a deterioration in quality was confirmed: The day when at least one of the above items has an evaluation result of less than 3.0, or the day when the mold occurrence rate reaches 20% or more.

[0063] (2) Weight retention rate The weight retention rate (%) was calculated by the ratio of the weight (g) of the Satsuma mandarins after 35 days of storage to the weight (g) of the Satsuma mandarins before covering them with the citrus freshness-keeping container cover. The results are shown in Table 2.

[0064] (3) Relative humidity A humidity sensor was placed near the top surface of the top shelf of the Satsuma mandarin oranges in the agricultural container, and the humidity was measured every hour. The average relative humidity during the freshness retention period was calculated. The results are shown in Table 1.

[0065] (4)Temperature A temperature sensor was placed near the top surface of the top shelf of the Satsuma mandarin oranges in the agricultural container, and the temperature was measured every hour. The average relative humidity during the freshness retention period was calculated. The results are shown in Table 1.

[0066] [Table 1]

Claims

1. Moisture permeability at 40°C and 90% RH is 5 to 1000 [g / m ２ A storage unit in which an agricultural container containing citrus fruits is covered with a citrus freshness-keeping container cover made of a synthetic resin film having a viscosity of 100 / sq.m. (excluding storage units in which an agricultural container containing citrus fruits is covered with a citrus freshness-keeping container cover having a lid that has a ceiling opening area that can be freely adjusted to be fully closed, half open, or fully open).

2. The container according to claim 1 , wherein the agricultural container has a peripheral wall and a bottom that are breathable.

3. 3. The container according to claim 1 or 2, wherein the entire surface of the agricultural container except for the bottom portion is covered with the citrus freshness-keeping container cover.

4. A freshness preservation method comprising a step of covering an agricultural container housing citrus fruits with a citrus freshness preservation container cover made of a synthetic resin film having a moisture permeability of 5 to 1000 [g / m2·day·atm] at 40°C and 90% RH to form a storage body (excluding a freshness preservation method for a storage body in which an agricultural container housing citrus fruits is covered with a citrus freshness preservation container cover having a lid whose ceiling opening area can be freely adjusted to be fully closed, half open or fully open).

5. The method for preserving freshness of citrus fruits according to claim 4, wherein the agricultural container has a peripheral wall and a bottom that are breathable.

6. 6. The method for preserving freshness of citrus fruits according to claim 4 or 5, wherein the entire surface of the agricultural container except for the bottom portion is covered with the cover for a citrus freshness-preserving container.

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