WO2002074656A1

WO2002074656A1 - Liquid-absorbing sheet for packaging perishable food

Info

Publication number: WO2002074656A1
Application number: PCT/JP2002/002482
Authority: WO
Inventors: Katsunori Saito; Takeshi Banba
Original assignee: Showa Denko Plastic Products Co,, Ltd.
Priority date: 2001-03-15
Filing date: 2002-03-15
Publication date: 2002-09-26

Abstract

A liquid-absorbing sheet provided with a discrimination mark is to develop wherein the discrimination mark can be easily distinguished when packaging is carried out using a film so that it is easy to check whether or not an appropriate surface of the liquid-absorbing sheet, which is disposed inside the package, is directe toward a food, but the discrimination mark cannot be easily distinguished or gives no abnormal impression after liquid is absorbed therein. The liquid-absorbing sheet incorporates a packaging material (1) having housed therein a sheet-shaped liquid-absorbing material (1) containing a polymer absorbent and/or a wetting agent, the packaging material having one outer layer having a liquid permeable film (3) and another outer layer having a liquid impermeable or semipermeable film (2), wherein at least a portion of one side of the liquid-absorbing sheet has a discrimination mark in a color similar to the color of the perishable food.

Description

DESCRIPTION

LIQUID-ABSORBING SHEET FOR PACKAGING PERISHABLE FOOD

TECHNICAL FIELD

The present invention relates to a liquid-absorbing sheet for packaging perishable foods, the liquid-absorbing sheet being capable of absorbing and thereby removing drips seeping out during storage or circulation of perishable foods such as meat, vegetables, fruits, or fish and preventing the perishable food from discoloring or deteriorating in the quality for a long period of time. More specifically, the present invention relates to a liquid-absorbing sheet for packaging perishable foods, the liquid-absorbing sheet being provided with a discrimination mark which prevents the misuse of front and back sides of the liquid-absorbing sheet when the liquid-absorbing sheet is used, and gives no abnormal impression even after the absorption of liquid. The present invention also relates to a method for producing a packaged perishable food product using this liquid-absorbing sheet for perishable foods.

BACKGROUND ART When a perishable food (hereinafter occasionally simply referred to as "food") such as meat or fish is vacuum-packaged with a gas-impermeable film and stored in a chilled temperature zone or stored in a frozen state and then thawed, a liquid called "drips" such as blood and body fluid seeps out. These drips are pooled in a space between the food and the gas-impermeable film and if this state is left as it is, cause deterioration in the quality, such as discoloration of a food which is in contact with the drips, and the commercial value of the food is extremely lowered. If the discolored portion of the food is removed so as to avoid this problem, the yield of commercial products decreases in proportion. Furthermore, the drips are liable to provide a hotbed for the proliferation of bacteria and there arise many problems such as shortened shelf life.

In order to overcome these problems, studies have been made on the method for removing drips from a packaged perishable food. The method for removal first considered is to package a food while laying it in contact with a sheet- shaped liquid-absorbing material and remove the drips seeping out during the storage by the occasional absorption to the liquid-absorbing material. The liquid-absorbing material used here is a capillary liquid-absorbing material such as paper pulp having a hydrophilic surface and capable of absorbing and retaining drips by the capillary phenomenon, a so-called polymer water absorbent, a composite material thereof, or the like.

However, there are problems in that the capillary liquid- absorbing material is poor in the strength as a sheet material and in that the polymer water absorbent which is generally in the form of powder or granular cannot be brought into contact directly with a food. To overcome these problems, a liquid- absorbing sheet for perishable foods (hereinafter occasionally simply referred to as "liquid-absorbing sheet") has been proposed in which the outer surface of a liquid-absorbing material is covered with a liquid permeable film such as nonwoven fabric. By such means, the absorption of drips is greatly improved. However, the foods themselves became dry in some cases since this liquid-absorbing sheet actively absorbs water inside the food from the contact surface of the food, as well as the drips seeping from the food such as meat or fish. As a liquid-absorbing sheet which can remedy the above problems, there has been proposed a liquid-absorbing sheet where a cover-type packaging material is used in which a liquid permeable film is used for one surface and a liquid impermeable or semipermeable film is used for the other surface. These liquid-absorbing sheets absorb only the drips seeping out from a food such as meat or fish but not positively absorb water inside the food from the surface which is in contact with the food, so that the food itself can be prevented from becoming dry. Furthermore, this liquid- absorbing sheet absorbs and thereby removes the drips seeping out and staying at the bottom and recessed parts of the food where the food and the liquid-absorbing sheet are in contact with each other, so that the food can be prevented from discoloring or deteriorating in the quality for a long period of time and the yield can be maintained.

Such a liquid-absorbing sheet is used while maintaining the food in contact with the surface of the liquid-impermeable film or liquid-semipermeable film so as to avoid direct or local water absorption from the inside of the food. Therefore, means for discriminating the front surface from the back surface is designed to the sheet-shaped liquid-absorbing material, such as coloring or printing. However, since colors or patterns working out to a clear discrimination mark are not used by taking account of the impression on consumers or for giving good looking of the commercial product, the front and back surfaces are poorly discriminated and the packaging is sometimes performed to bring the food into direct contact with the opposite surface, that is, the liquid-permeable film surface. Once packaged as such, this cannot be easily detected from the outside.

DISCLOSURE OF INVENTION The object of the present invention is to develop a liquid-absorbing sheet provided with a discrimination mark wherein the discrimination mark can be easily distinguished when packaging is carried out using a gas impermeable film or the like so that it is easy to check whether or not an appropriate surface of the liquid-absorbing sheet, which is disposed inside the package, is directed toward a food, while even after packaging, the discrimination mark can be easily distinguished when the opposite surface faces the food by being viewed from outside, but the discrimination mark cannot be easily distinguished by consumers or gives no abnormal impression after liquid is absorbed therein.

The above-described object of the present invention can be attained by developing:

(1) a liquid-absorbing sheet for packaging a perishable food, incorporating a packaging material having housed therein a sheet-shaped liquid-absorbing material containing a polymer absorbent and/or a wetting agent, the packaging material having one outer layer having a liquid permeable film and another outer layer having a liquid impermeable or semipermeable film, wherein at least a portion of one side of the liquid-absorbing sheet has a discrimination mark in a color similar to the color of the perishable food;

(2) the liquid-absorbing sheet for packaging a perishable food as described (1) above, wherein the perishable food is beef, and the color of the discrimination mark is a reddish color;

(3) the liquid-absorbing sheet for packaging a perishable food as described in (1) above, wherein the perishable food is a vegetable or fruit, and the color of the discrimination mark is a greenish, yellowish, or brownish color;

(4) the liquid-absorbing sheet for packaging a perishable food as described in (1) above, wherein the perishable food is chicken, pork, or fish, and the color of the discrimination mark is a pinkish, yellowish, or brownish color;

(5) the liquid-absorbing sheet for packaging a perishable food as described in any one of (1) to (4) above, wherein at least a portion of the periphery of the liquid impermeable or semipermeable film has the discrimination mark;

(6) the liquid-absorbing sheet for packaging a perishable food as described in any one of (1) to (4) above, wherein at least a portion of the periphery of the liquid permeable film has the discrimination mark;

(7) the liquid-absorbing sheet for packaging a perishable food as described in (1) to (6) above, wherein the liquid semipermeable film is a polyethylene or polypropylene film having formed therein pores;

(8) the liquid-absorbing sheet for packaging a perishable food as described in (1) to (7) above, wherein the sheet-shaped liquid-absorbing material contains at least one wetting agent selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol monoethyl ether, 1,3-butylene glycol, glycerin, polyethylene glycol, polypropylene glycol, polyglycerin, xylitol, sorbitol, maltitol, methyl cellulose and carboxymethyl cellulose; (9) a method for producing a packaged perishable food product, the method incorporating the step of having liquid absorbed by bringing a perishable food into contact with a surface of the liquid impermeable or semipermeable film of the liquid-absorbing sheet for packaging a perishable food as described in any one of (1), (2), (4), (5), (7), and (8) above, and by vacuum-packaging the perishable food and the liquid-absorbing sheet with a gas impermeable film; and (10) a method for producing a packaged perishable food product, the method incorporating the step of having liquid absorbed by allowing the surface of the liquid permeable film of the liquid-absorbing sheet for packaging a perishable food as described in any one of (1), (3), (4), and (6) to (8) above to face a perishable food, and by packaging the perishable food and the liquid-absorbing sheet.

BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a plan view and a cross-sectional view of the liquid-absorbing sheet of Example 1 according to the present invention .

Fig. 2 is a plan view and a cross-sectional view of the liquid-absorbing sheet of Example 2 according to the present invention.

Fig. 3 is a plan view and a cross-sectional view of the liquid-absorbing sheet of Example 3 according to the present invention.

Fig. 4 is a plan view and a cross-sectional view of the liquid-absorbing sheet of Example 4 according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION The packaging material for use in the liquid-absorbing sheet of the present invention is constructed such that one surface is formed of a liquid permeable film and the other surface is formed of a liquid impermeable or semipermeable f i lm .

The liquid permeable film for use in the liquid-absorbing sheet of the present invention may be any generally available film insofar as it is water-permeable and water-resistant, has pores having sizes small enough to prevent leakage of the liquid-absorbing material, particularly powder-form polymer water absorbent, is preferably heat-sealable and is acceptable as a film for packaging foods. For example, the liquid permeable film may be any one member selected from the group consisting of woven fabrics, knitted fabrics and nonwoven fabrics of natural fiber, semisynthetic fiber, synthetic fiber or synthetic resin, or may be a laminate thereof.

The liquid-permeable film may also be a polyethylene film, polypropylene film, polyester film or moisture-proof cellophane, for example, where fine communicating holes are formed by known mechanical or electrical means or using a laser; a foamed polyethylene sheet having communicating holes; or a mesh sheet.

These liquid permeable films, which are so-called water- passing films, have a porosity of 1% or more and therefore, can be clearly distinguished from the liquid semipermeable film. This liquid permeable film is provided for allowing drips which have seeped out from a surface of a food, the surface not in contact with the liquid-absorbing sheet, and which have reached the liquid-absorbing sheet due to vibration during transportation, gravity or the like, to pass therethrough and to be quickly absorbed inside the liquid- absorbing sheet.

Examples of the liquid impermeable film used for the surface opposite the liquid permeable film include polyethylene film, polypropylene film, polyvinylidene chloride film, polyester film, moisture-proof cellophane and polyethylene laminated aluminum foil. Among these, a polyethylene film and a polypropylene film are preferred because these films do not contain or generate substances having a possibility of contaminating the food, have neither water-absorbing property nor water permeability by themselves, have flexibility and good releasability from the food press- fixed to the film, and are heat-sealable and inexpensive.

The liquid semipermeable film can be produced by forming pores using known mechanical or electrical means or a laser on the above-described liquid impermeable film. However, unlike the liquid permeable film, this liquid semipermeable film must have an extremely low water-passing property and the porosity thereof is limited.^"

More specifically, the pores are formed to have a diameter of 0.05 to 0.5 mm, preferably from 0.1 to 0.3 ram, and a porosity P of 0.01 to 0.4%, preferably from 0.01 to 0.2%. These pores are preferably distributed uniformly throughout the liquid semipermeable film. The shape of the pore is not particularly limited insofar as the above-described diameter and porosity are satisfied.

The porosity P as used herein is a % value obtained by the formula: (total area of pores/total area of liquid semipermeable film)xl00. In the case where the pores have the same area s, the porosity P is obtained by the formula: (area

s per one pore x number n of pores x 100) /(total area of liquid semipermeable film) . When a food is preserved using the liquid-absorbing sheet of the present invention by bringing its liquid impermeable or semipermeable film surface into contact with the food and vacuum-packaging the whole, the drips seeping out from a food in contact with the liquid semipermeable film are introduced inside the liquid-absorbing sheet through the pores.

Accordingly, for absorbing only the drips without dehydrating the food which is in contact with the liquid-absorbing sheet, the pore diameter d is preferably from 0.05 to 0.5 mm.

The liquid permeable film and the liquid impermeable or semipermeable film are both preferably heat-sealable and form respective surfaces of the packaging material of the liquid- absorbing sheet. The peripheral part of these two films are heat-sealed, whereby the films of the liquid-absorbing sheet can be prevented from separating and the polymer water absorbent or the like housed therein can be prevented from leaking out.

The sheet-shaped liquid-absorbing material is used for absorbing drips seeping out from a food and any material may be used insofar as it does not adversely affect the human body in storing the food.

The sheet-shaped liquid-absorbing material preferably does not release the drips or water once absorbed, under the application of a pressure or the like and for this purpose. Therefore, the sheet-shaped liquid-absorbing material preferably contains a polymer liquid absorbent such as a polymer water absorbent. The polymer water absorbent used in the sheet-shaped liquid-absorbing material may be any known polymer insofar as it has a capability of absorbing water or drips and is allowable in view of food safety. These are generally a water-soluble polymer having a three-dimensionally crosslinked structure and a large number of polymers are known therefor .

Preferred examples of the polymer water absorbent include crosslinked products of polymers obtained by the graft polymerization or the graft polymerization and then hydrolysis of a polysaccharide such as starch or cellulose with one or more member selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid salts, methacrylic acid salts, acrylic acid esters, methacrylic acid esters, acrylamides, methacrylamides, acrylonitrile, methacrylonitrile, maleic acid, sulfonated styrene, polyvinyl pyridine, and oligomers or co-oligomers thereof; crosslinked products of one or more member selected from the group consisting of polyethylene oxide, polypropylene oxide, polyvinyl pyrrolidone, sulfonated polyethylene, polyvinyl pyridine, polyacrylic acid salts, polymethacrylic acid salts, polyacrylamides and polymethacrylamides; vinyl acetate/acrylic acid salt copolymers; isobutylene/maleic anhydride copolymers; polyvinyl alcohol/maleic acid copolymers; and crosslinked products of carboxymethyl cellulose. Examples of commercially available polymer water absorbents for use in the liquid- absorbing sheet include PX-402A (produced by Showa Denko K.K.), Sunwet IM-300 (produced by Sanyo Chemical Industries, Ltd.), Aquakeep 10SH (produced by Seitetsu Kagaku Kogyo K.K.) and Aqualic CA (produced by Nippon Shokubai Kagaku Kogyo Co., Ltd. ) .

In the sheet-shaped liquid-absorbing material of the present invention, the above-described polymer water absorbent is preferably sandwiched by capillary liquid-absorbing materials capable of absorbing a liquid using a capillary phenomenon. The capillary liquid-absorbing material is a sheet-like formed article capable of absorbing and holding drips or water by a capillary phenomenon and holds the polymer water absorbent and at the same time, preferably a wetting agent which is described later. Examples thereof include paper, pulp, pulp sheet obtained by forming pulp into a sheet, absorbent cotton, gauze, woven fabric, knitted fabric, nonwoven fabric, sponge, polyurethane foam having communicated holes, viscose foam having communicated holes and vinylon foam having communicated holes.

The polymer water absorbent is generally a powder or a granule in the dry state and therefore, may be incorporated into the liquid-absorbing sheet by scattering and holding it like a layer between two capillary liquid-absorbing material layers or by inserting and holding it inside communicated holes of one capillary liquid-absorbing material layer. Furthermore, commercially available products where a polymer water absorbent is sandwiched by capillary liquid-absorbing materials, such as paper diaper, sanitary napkin and high water-absorbing sheet used in the field of soil improver, may also be used as the liquid-absorbing material.

The polymer water absorbent non-reversibly absorbs drips or water introduced through the capillary liquid-absorbing material layer after the passing thereof through pores of the liquid semipermeable film or fine communicated pores of the liquid permeable film and unlike normal capillary liquid- absorbing materials, allows no back-flow of the once absorbed drips or water even when a pressure or an impact is applied from outside. In the present invention, the sheet-shaped liquid- absorbing material preferably contains a wetting agent. Generally, the polymer absorbent becomes hard in the dry state and may damage the packaging material film or the gas impermeable film entirely wrapping the food due to impact or friction at the time of transportation or movement. The wetting agent added keeps the softness of the polymer absorbent even in the dry state and therefore, prevents the above-described damage, so that pinholes of, for example, the gas impermeable film used for the vacuum-packaging can be decreased.

In the case where the above-described capillary liquid- absorbing material has a hydrophobic surface, the initial water absorption is generally not sufficient. However, when this hydrophobic surface is covered by a wetting agent, the initial water absorption is greatly improved and the drips or water introduced from pores of the liquid semipermeable film or fine communicated pores of the liquid permeable film can be swiftly absorbed. The amount of the wetting agent used is not particularly limited insofar as it is such an amount to make the liquid-absorbing material flexible and cause substantially no leakage even under the application of a pressure. The optimum amount thereof is experimentally determined by taking account of the construction material, constitution and total capillary wall area of the liquid-absorbing material used.

Examples of the wetting agent include polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol monoethyl ether, 1,3-butylene glycol and glycerol; polyhydric alcohol polymerization products such as polyethylene glycol, polypropylene glycol and polyglycerol; sugar alcohols such as xylitol, sorbitol and maltitol; and methyl cellulose and carboxymethyl cellulose. These are used in the form of an aqueous solution, if desired. Among these, glycerol is preferred in view of wettability and safety.

When a packaged perishable food product is manufactured by vacuum-packaging a food and a liquid-absorbing sheet using a gas impermeable film so as to absorb liquid, the food and the liquid-absorbing sheet are used in close contact with each other. At this time, it is preferable that the surface of the liquid impermeable or semipermeable film of the liquid- absorbing sheet be brought into contact with the food. By doing so, the food itself is prevented from becoming dry due to contact with the liquid permeable film.

When a packaged perishable food product is manufactured by packaging a food and a liquid-absorbing sheet by a packaging method other than vacuum-packaging so as to absorb liquid, it is preferable that the surface of the liquid permeable film of the liquid-absorbing sheet face the food, in a manner opposite to that in vacuum-packaging, and that the food and the liquid-absorbing sheet be packaged. By doing so, the absorption of liquid becomes faster in comparison with a case in which the surface of the liquid impermeable or semipermeable film faces the food.

As described above, an effective method of using the liquid-absorbing sheet includes selecting a surface of the liquid-absorbing sheet to face the food in accordance with the mode of packaging, and placing the liquid-absorbing sheet so that at least a portion of the liquid-absorbing sheet is under the bottom portion of the food when the packaged food product is transported or stored.

In order to produce the packaged perishable food product by packaging a food with the liquid-absorbing sheet of the present invention and by allowing the liquid-absorbing sheet to absorb liquid, it is preferable that the liquid-absorbing sheet be used in a manner such that the side of the liquid- absorbing sheet on which the discrimination mark is provided faces the food. By using the liquid-absorbing sheet in this manner, mischoice of front or back side of the liquid- absorbing sheet against user's intention can be easily recognized from outside by eye when packaging is carried out, and the discrimination mark becomes indistinctive after liquid is absorbed.

Specific modes of packaging for each example of food are as follows: when the food is meat such as beef, pork, and chicken, fish, fish meat, or the like, the food is in contact with the surface of the liquid impermeable or semipermeable film while the food and the liquid-absorbing sheet are vacuum- packaged using a gas impermeable film; and when the food is fish, fish meat, a vegetable, fruit, or the like, packaging is employed in which the liquid-absorbing sheet is placed under the food in a manner such that the surface of the liquid permeable film faces the food.

The gas impermeable film used for vacuum-packaging may be a gas impermeable film such as polyethylene, polypropylene or polyvinyl chloride, a shrink film or the like, which are generally used for the vacuum packaging of foods. Also, at this time, the vacuum degree may be sufficient if it is high enough to give close contact between the food and the liquid- absorbent sheet or the gas-impermeable film.

For the discrimination mark used in the liquid-absorbing sheet of the present invention, the coloring for the discrimination mark may be made on the sheet-shaped liquid- absorbing material or packaging material itself or the discrimination mark surface may be distinguished by inserting a colored film or tape, a string or the like, by putting a sticker, by printing a mark or the lime, or by a like manner. The easiest way is to provide the discrimination mark to the liquid impermeable or semipermeable film and this is a preferred embodiment.

As for the design of discrimination mark, the above- described film as a whole may be uniformly colored or a pattern of stripes or small polka dots may be used. According to respective uses, a small pattern of fish, cattle, chicken, pig, vegetable, fruit, or the like may be designed and a color may be selected therefor.

As the color of the discrimination mark, a color capable of, upon absorption of drips, turning into the same color as the drips or into a similar color which can make the discrimination mark indistinct is selected. Specific examples of combinations of the food and the color are as follows: a reddish color is preferable on a liquid-absorbing sheet to be used for packaging beef; a greenish, yellowish, or brownish color is preferable on a liquid-absorbing sheet to be used for packaging a vegetable or fruit; and a pinkish, yellowish, or brownish color is preferable on a liquid-absorbing sheet to be used for packaging chicken, pork, or fish.

The discrimination mark may be sufficient if the front and back surfaces of the liquid-absorbing sheet can be clearly discriminated and therefore, may be provided either on the front surface or the back surface but is preferably provided on the side which is invisible from outside so that the discrimination mark cannot be viewed from the outside after the packaging.

The color dye which can be used for the coloring of the discrimination mark is not limited insofar as it is a color dye usable in the packaging of foods. For example, when the construction material of the tape or film is polyolefin, color dyes described in Polyolefin Nado Eisei Kyogi Kai, Polyolefin Nado Goseij ushi -Sei Shokuhin Hoso Nado-ni Kansuru Posi tive List (Posi tive List Regarding Synthetic Resin-Made Food Packaging Such As Polyolefin) can be used. Specific examples of color dyes are red dyes such as food red which is classified as a food or food additive, yellow dyes such as β- carotenes, green dyes such as chlorophylls, and brown dyes, which are mixtures of the aforesaid dyes. In order to print on a film or a sticker, the above- described color dye may be dissolved in a solvent usable for foods, such as water or ethanol .

Examples of the perishable food to which the liquid- absorbing sheet for packaging perishable foods of the present invention can be applied include vegetables and fruit, and various perishable foods which give drips of a reddish color, such as partial meat of cattle or pig, subdivided meat or partial meat of chicken or the like, and frozen, chilled or perishable fish meats of tuna, bonito, salmon or the like.

Examples (Example 1) As shown in Fig. 1, a liquid impermeable film 2 was entirely colored red using a red color masterbatch at the production of the film, a non-colored polyethylene and polypropylene-made nonwoven fabric (liquid permeable film) 3 was superposed thereon, and the three sides were heat-sealed to form a cover-type packaging material. A pulp (sheet-shaped liquid-absorbing material) 1 having supported thereon a polymer absorbent was inserted into the packaging material and the inlet port was heat-sealed to obtain a liquid-absorbing sheet for packaging perishable foods.

(Example 2)

As shown in Fig. 2, a cover-type packaging material was obtained using a non-colored polyethylene film 5 in place of the colored liquid impermeable film 2 in Example 1. A sheet- shaped liquid absorbent 1 prepared in the same manner as in Example 1 was housed therein, a red polyethylene film tape 4 was inserted between the polyethylene film 5 and the sheet- shaped liquid absorbent 1, and the inlet port was heat-sealed to obtain a liquid-absorbing sheet for packaging perishable foods. When the polyethylene film 5 and the nonwoven fabric 3 were formed into a cover-type packaging material, the tape was sandwiched and sealed at the heat-sealed parts so as not to move inside the cover-type packaging material.

(Example 3)

As shown in Fig. 3, a solution obtained by dissolving food red in ethanol was printed on the liquid impermeable film 5 using an inkjet printer and dried in place of inserting the red-color polyethylene film tape in Example 2. Reference numeral 6 indicates the food red printed on the liquid impermeable film 5.

(Example 4)

As shown in Fig. 4, a red film sticker 7 was affixed in place of inserting the red-color polyethylene film tape in Example 2. The sticker was affixed using a starch or heat- sealed, and there was no problem in view of hygiene of foods.

INDUSTRIAL APPLICABILITY In the liquid-absorbing sheet for packaging perishable foods of the present invention, a discrimination mark is provided to the perishable food side using a harmless coloring agent usable for the packaging of foods, so that the possibility of causing a misuse can be greatly reduced before packaging, the liquid absorbing sheet which is misused can be easily identified after the packaging, the liquid-absorbing sheet after absorbing drips can conceal or veil its use by the color of drips, and the package can be prevented from giving an abnormal impression to consumers.

Claims

1. A liquid-absorbing sheet for packaging a perishable food, incorporating a packaging material having housed therein a sheet-shaped liquid-absorbing material containing a polymer absorbent and/or a wetting agent, the packaging material having one outer layer having a liquid permeable film and another outer layer having a liquid impermeable or semipermeable film, wherein at least a portion of one side of the liquid-absorbing sheet has a discrimination mark in a color similar to the color of the perishable food.

2. The liquid-absorbing sheet for packaging a perishable food as claimed in claim 1, wherein the perishable food is beef, and the color of the discrimination mark is a reddish color.

3. The liquid-absorbing sheet for packaging a perishable food as claimed in claim 1, wherein the perishable food is a vegetable or fruit, and the color of the discrimination mark is a greenish, yellowish, or brownish color.

4. The liquid-absorbing sheet for packaging a perishable food as claimed in claim 1, wherein the perishable food is chicken, pork, or fish, and the color of the discrimination mark is a pinkish, yellowish, or brownish color.

5. The liquid-absorbing sheet for packaging a perishable food as claimed in claim 1, wherein at least a portion of the periphery of the liquid impermeable or semipermeable film has the discrimination mark.

6. The liquid-absorbing sheet for packaging a perishable food as claimed in claim 1, wherein at least a portion of the periphery of the liquid permeable film has the discrimination mark.

7. The liquid-absorbing sheet for packaging a perishable food as claimed in claim 1, wherein the liquid semipermeable film is a polyethylene or polypropylene film having formed therein pores.

8. The liquid-absorbing sheet for packaging a perishable food as claimed in claim 1, wherein the sheet-shaped liquid- absorbing material contains at least one wetting agent selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol monoethyl ether, 1,3- butylene glycol, glycerin, polyethylene glycol, polypropylene glycol, polyglycerin, xylitol, sorbitol, maltitol, methyl cellulose and carboxymethyl cellulose.

9. A method for producing a packaged perishable food product, the method incorporating the step of having liquid absorbed by bringing a perishable food into contact with a surface of the liquid impermeable or semipermeable film of the liquid-absorbing sheet for packaging a perishable food as described in any one of claims 1, 2, 4, 5, 7, and 8, and by vacuum-packaging the perishable food and the liquid-absorbing sheet with a gas impermeable film.

10. A method for producing a packaged perishable food product, the method incorporating the step of having liquid absorbed by allowing the surface of the liquid permeable film of the liquid-absorbing sheet for packaging a perishable food as described in any one of claims 1, 3, 4, and 6 to 8 to face a perishable food, and by packaging the perishable food and the liquid-absorbing sheet.