JPH046065A - Method for maintaining freshness of perishable food - Google Patents

Abstract

PURPOSE:To simply maintain freshness of a perishable food by wrapping the perishable food by using a film comprising antibacterial zeolite particles and vinyl alcohol polymer. CONSTITUTION:A film comprises antibacterial zeolite particles for supporting metallic ions selected in silver, copper and zinc and vinyl alcohol polymer. The antibacterial zeolite particles for supporting metallic ions are such that natural or synthesized zeolite made of aluminosilicate supports one or two kinds of metallic ions with ion exchanged. polyvinyl alcohol and ethylene-vinyl alcohol copolymer among the vinyl alcohol polymers is especially preferable from a point of view of antibacterial property and maintenance of freshness of perishable foods. A blending ratio of antibacterial zeolite particles to the vinyl alcohol polymer is not limited specifically but preferably 0.1 to 10%, more preferably 0.5 to 5% and further more preferably 1 to 3%.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for preserving the freshness of fresh foods.

[Conventional technology] If fresh fish is left as it is after landing, it rapidly loses its freshness through hardening and softening, and eventually rots.

In order to maintain the freshness of fresh fish, it is important to reduce the rate of self-decomposition caused by the action of internal enzymes, and to suppress spoilage due to the proliferation of microorganisms. It is extremely well known that keeping fish at low temperatures is an effective method for this purpose.

The most effective way to maintain freshness is to keep fish at -20°C.
A method called "freezing", in which food is stored frozen at a low temperature of -60°C, is commonly used.

However, this method has the problem that the meat becomes soft and the quality is significantly reduced.

The most commonly used method for preserving the freshness of fresh fish is the so-called ice storage method. This method involves cooling and preserving fresh fish by covering it with crushed ice.

This method is the most commonly used freshness preservation method in the distribution of fresh fish, but when this method is used, there is a problem that the period of time during which freshness can be preserved is not long enough for practical use.

[Problems to be Solved by the Invention] The purpose of the present invention is to improve the ice storage method, which is extremely simple to implement and is the most cost-effective method, to improve the production of coastal fisheries, fish within 200 nautical miles, and imports. To provide a method that can easily prevent deterioration in the freshness of fresh fish and maintain the freshness of fresh foods such as meat and vegetables.

[Tanu's Means to Solve the Problem] The present inventors have conducted intensive studies on a method that can maintain the freshness of fresh foods for a long period of time even when using an ice storage method. The present inventors have discovered that when fresh foods are packaged using a film made of a polymer, their freshness can be maintained for a long period of time even when stored in ice, leading to the completion of the present invention.

The antibacterial zeolites used in the present invention are those described in Japanese Patent Publication No. 63-28402 and Japanese Patent Publication No. 63-54013.

The present invention will be explained in detail below.

The film in the present invention is a film made of antibacterial zeolite particles and vinyl alcohol polymer that support metal ions selected from silver, copper, and zinc.

The zeolite particles used in the present invention have a specific surface area of 150 m
”/g (based on anhydrous zeolite) or more, and the molar ratio of the zeolite constituents is 1.
It should be 4 or less, preferably 11 or less.

In the present invention, the antibacterial zeolite particles supporting the above-mentioned metal ions are particles in which natural or synthetic zeolite made of aluminosilicate supports one or more of the above-mentioned metal ions through ion exchange.

The solution of water-soluble salts of silver, copper, and zinc used in the present invention easily undergoes ion exchange with the zeolite defined in the present invention, so using this phenomenon, the necessary metal ions are isolated. Alternatively, it is possible to support the zeolite stationary phase by mixing, but the zeolite particles supporting metal ions must have a specific surface area of 150 m"/g or more and Sin!/Aff, O.

Two conditions must be met: the molar ratio is 14 or less. It has been found that if this is not the case, a target product with effective antibacterial properties cannot be obtained.

This is thought to be due to the fact that the absolute amount of metal ions fixed on the zeolite is insufficient in a state where the effect can be exerted. In other words, this is considered to be due to the physicochemical properties of the zeolite, such as the amount of exchange groups, exchange rate, and accessibility.

Therefore, 5io, known as molecular sieve
Olides with a large t/A12tOs molar ratio are completely unsuitable for the present invention.

In addition, in zeolite with a SiO*/Al2tOs molar ratio of 14 or less, it is possible to uniformly support metal ions having antibacterial properties, and for this reason, sufficient antibacterial properties can only be obtained by using such zeolite. It turns out. In addition, 5in1/A of zeolite (
The acid resistance and alkali resistance of zeolite with a high silica ratio and an ltos molar ratio exceeding 14 are Sin! However, their synthesis requires a long time, and from an economic point of view, it is not advisable to use zeolites with such high silica ratios. The aforementioned SIO! /AQtOz≦14 natural or synthetic zeolite can be used satisfactorily from the viewpoint of acid resistance and alkali resistance in the fields in which the present composition is usually considered, and is also inexpensive and advantageous from an economic point of view. . From this point of view, 5rat/h (ltos molar ratio is 1
Must be 4 or less.

The molar ratio of 5iO=/AQtOs used in the present invention is 1
As the zeolite material of 4 or less, any natural or synthetic zeolite can be used. For example, analcime (5if) is a natural zeolite.
t/Al2tOs=3.6~5.6), Chabazite: SiO2/AQtO
z = 3.2-6.0 and 6,4-7.6), clinoptilolite (C11noptilolite: Si
O*/AQfCh=8.5~lf1.5), Erionite (Er1oniLe: 5ift/A(!
tos=5.8~7.4), Faojasite (Fa
ujasite: 5iO1/AQtOs = 4
．． 2-4.6), mordenite
: 5ift/AltOs=8.34~10.0)
, Ph1llipsite:
SiO*/AdtO, = 2.6 to 4.4). These typical natural zeolites are suitable for the present invention.

On the other hand, a typical synthetic zeolide is A-type zeolide (SiOt/Al2xOs=1.4-2.4)
, X-type zeolide (Siow/A1210-
= 2~3), Y-type zeolide (SiOx/Al2
tOs = 3~6), mordenite (5ift/A
(!!0-=Q~10), etc., and these synthetic zeolites are suitable as the zeolite material of the present invention. Particularly preferred are synthetic A-type zeolides,
X-type zeolides, Y-type zeolides and synthetic or natural mordenites.

There are no particular restrictions on the shape and particle size of the zeolite, but it is preferably in the form of powder particles, and the smaller the particle size is, for example, preferably 5 microns or less, particularly 2 microns or less.

Examples of the vinyl alcohol polymer used in the present invention include polyvinyl alcohol, ethylene-vinyl alcohol copolymer, etc. Among the vinyl alcohol polymers used in the present invention, polyvinyl alcohol and ethylene-vinyl alcohol copolymer are used. is particularly preferable in terms of antibacterial properties and maintaining the freshness of fresh foods.

The vinyl alcohol polymer of the present invention has a degree of polymerization of 1000 to
10,000, preferably 1,300 to 8,000, more preferably 1,500 to 6,000, saponification degree of 95 mol% or more,
It is preferable to use 98 mol% or more, particularly preferably 99.0 mol% or more. If the degree of polymerization is low, the strength will be low, and if it is too high, the flexibility of the film in the dry state will decrease, which is not preferable. The higher the degree of saponification, the better, because if the degree of saponification is low, the amount of elution increases, making it impossible to use it for food applications.

There is no particular restriction on the ethylene content in the case of the ethylene-vinyl alcohol copolymer, but it is preferably 5 to 60 mol% from the viewpoint of antibacterial properties and maintaining the freshness of fresh foods.
More preferably 0 to 50 mol%.

The blending ratio of antibacterial zeolite particles to vinyl alcohol polymer is not particularly limited, but is preferably 0.1 to 1.
0%, more preferably 0.5-5%, even more preferably 1-3%.

The method of mixing the antibacterial zeolite particles and the vinyl alcohol polymer is not particularly limited.

When the vinyl alcohol polymer is water-soluble, it is preferable to mix antibacterial zeolite particles into the aqueous solution of the vinyl alcohol polymer before producing the film. In the case of polyvinyl alcohol with a degree of saponification close to 100%, it is difficult to dissolve in water at room temperature, so it is preferable to completely dissolve the polyvinyl alcohol by heating the water in which the polyvinyl alcohol has precipitated to 80° C. or higher. An antibacterial polyvinyl alcohol film is produced by casting from an aqueous solution of vinyl alcohol polymer mixed with antibacterial zeolite particles.

Ethylene whose vinyl alcohol polymer is water-insoluble
In the case of a vinyl alcohol copolymer, antibacterial zeolite particles are mixed with the polymer when it is melted, and a film is produced by melt molding.

The thickness of the film of the present invention is not particularly limited, but is 15 to 10 g.
OuII is preferred; if the film thickness is less than 15 atn, the strength in a water-absorbed state is low and unsuitable for actual use. Moreover, if it exceeds 90 μm, it is too thick and is therefore unsuitable for packaging fish and the like.

When the vinyl alcohol polymer constituting the film of the present invention is heat-treated at 75° C. or higher, the antibacterial properties and freshness retention performance of fresh foods are significantly improved.

The heat treatment is preferably carried out at a temperature of 75°C or higher, preferably 85°C or higher, more preferably 100°C or higher, even more preferably 120°C or higher. There are no particular restrictions on the heat treatment time, but it is 1 second to 60 minutes, preferably 30 seconds to 1 minute. A higher heat treatment temperature is preferable because the higher the heat treatment temperature, the lower the elution amount.However, if the heat treatment temperature is raised too much, the vinyl alcohol polymer may decompose. Therefore, the maximum heat treatment temperature should be 240°C or lower.

The film of the present invention does not exhibit its effects unless it comes into direct contact with food. For this reason, it is preferable that a film made of a vinyl alcohol polymer used for antibacterial purposes be heat-treated to reduce the amount of vinyl alcohol polymer eluted.

The film of the present invention is used for packaging fresh foods such as vegetables, meat, fish and shellfish, and can maintain high freshness even when stored in ice.

[Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to these examples in any way. In the following, "%" means "weight%" unless otherwise specified.
” means.

Reference example! Here, an example will be shown in which antibacterial zeolite is produced by supporting silver ions on A-type zeolide through ion exchange.

Composition formula 0.98+1a, 0 ・1 (hOs ・1.9S
250 g of dry powder of sodium type A-type zeolide was prepared and washed with warm water so that the pH of the furnace solution was around 9. Approximately 900+oQ of 0.12M AgNOs aqueous solution was added.

The resulting slurry was stirred at 25°C for about 4 hours, filtered, and then washed with water until the solid phase was free of excess Ag'. The water-washed solids were dried at 100''-110°C, then crushed and dried under reduced pressure at a temperature of about 250°C.

The physical properties of the obtained antibacterial zeolite solid particles are as follows: Example 1 A 30% by weight aqueous solution of polyvinyl alcohol with a degree of polymerization of 2000 and a degree of saponification of 99.5 mol% was prepared. The aqueous solution was heated to 90°C to completely dissolve the polyvinyl alcohol. The polyvinyl alcohol solution was cooled to 70° C., and the antibacterial zeolite prepared in Reference Example 1 was added in an amount of 1% by weight based on the polyvinyl alcohol and mixed. A polyvinyl alcohol film was produced by casting on a rotating drum heated to 7D"C. By spraying steam onto the polyvinyl alcohol film thus obtained, the film was made flexible. The thickness was 304 m.

The polyvinyl alcohol film thus obtained was heat treated at xao° C. for 2 minutes.

The elution amount of this polyvinyl alcohol film was measured according to the standard test method No. 20 of the Ministry of Health and Welfare of 1981. The elution amount was 4 μg/m (l). This confirmed that the antibacterial polyvinyl alcohol film produced by this method was suitable for direct contact with foods.

The antibacterial properties of this polyvinyl alcohol film were tested. The test bacterium is Escherichia coli
It was used. Transfer this to ordinary agar medium (medium used: Mull).
The cells were cultured at 37° C. for 18 hours. The test cells were suspended in a phosphate buffer (pH 7.2) to make a suspension of 10 cells/mff, which was diluted and used in the test.

Pressure contact method was used to measure antibacterial performance. That is, inject 1 o- of bacterial liquid into the bottom of a bag-shaped film, spread the bacterial liquid from the outside and expel the air, then seal it with a heat seal, store it at 25°C in a horizontally pressurized state, and store it at a specified temperature. After some time, it was opened and measured.

The number of bacteria at the start is 9.5x 10'cells/m
(It was set as l.

When the number of viable bacteria per 1 m 2 was measured 30 minutes after the start of the experiment, the number of viable bacteria on the antibacterial film was zero. This indicates that the polyvinyl alcohol film mixed with antibacterial zeolite has extremely high antibacterial properties.

Comparative Example 1 1% by weight of the antibacterial zeolite prepared in Reference Example 1 was added to 72 polypropylene chips and mixed. The mixture was then heated to a temperature of 240'C and further mixed at this temperature. An antibacterial film having a thickness of 30 μm was prepared by hot pressing the thus prepared chip, and its antibacterial properties were measured in the same manner as in Example 1. The results are shown in Table 1.

Comparative Examples 2 and 3 Various antibacterial films were prepared in the same manner as in Comparative Example 1, except that the type of resin to be mixed and the mixing temperature were changed, and the antibacterial performance of each film was measured. The results are shown in Table 1.

Example 2 Degree of polymerization 1000. An ethylene-vinyl alcohol copolymer with a saponification degree of 99.5 mol% and an ethylene content of 30 mol% and an antibacterial zeolite prepared in Reference Example 1 were added at 1% by weight to the ethylene-vinyl alcohol copolymer. After mixing, a film having a thickness of 30 μm was produced by melt extrusion at 230° C.

The antibacterial performance of the film was measured in the same manner as in Example 1. The results are shown in Table 1.

Example 3 The performance of a polyvinyl alcohol antibacterial film was evaluated with respect to the freshness of fish when stored, using Japanese sardines as a material.

Fresh Japanese sardines were packaged in the antibacterial polyvinyl alcohol film prepared in Example 1. In this state, it was stored in a refrigerator with an internal temperature of 0°C. In order to prevent the Japanese sardine from drying out, it was stored in an airtight container made of polyethylene.

The polyvinyl alcohol film was completely adhered to the surface of the Japanese sardine when it was observed 30 minutes after packaging.

Under these conditions the storage period and value (indicator of freshness:
Fisheries Science Series [4], Plil, April 15, 1972
(Published in Japanese, edited by the Japan Fisheries Society).

Even after 11 days of storage, the viscosity value of the Japanese sardine was about 25%, and it was sufficiently edible. The results are shown in FIG.

Comparative Example 4 Japanese sardines were placed in the refrigerator under the same conditions as in Example 3, except that they were not wrapped in antibacterial polyvinyl alcohol film. I saved this. The results are shown in FIG.

After 11 days of storage, the value was about 50%, and the freshness had significantly decreased.

[Effects of the Invention] As is clear from the above examples, the method for preserving the freshness of fresh foods of the present invention has high antibacterial properties, and the period of freshness preservation is sufficiently long for practical use.

The film made of the vinyl alcohol polymer according to the present invention has the characteristic that when it comes into contact with a food such as fish that has moisture on its surface, it naturally wraps around the food.

In other words, when food with a wet surface is packaged with a film made of vinyl alcohol polymer mixed with antibacterial zeolite particles, the film made of vinyl alcohol polymer naturally adheres to the food, and as a result, the surface of the food is Since it has the characteristic that all bacteria are almost completely killed, the freshness period of fresh food is long enough for practical use, and its practicality is extremely high.

[Brief explanation of drawings]

FIG. 1 shows the progression of the values (indicator of freshness) of Japanese sardines in Example 3 and Comparative Example 4.・: Example 3 (packaged with antibacterial polyvinyl alcohol) ○: Comparative example 4 (no packaging) Patent Deko Dai Co., Ltd.

Claims (5)

[Claims] (1) A method for preserving the freshness of fresh foods, which comprises packaging fresh foods using a film made of antibacterial zeolite particles and a vinyl alcohol polymer. (2) The method for preserving the freshness of fresh foods according to claim 1, wherein the film is heat-treated at a temperature of 75° C. or higher. (3) The method for preserving the freshness of fresh foods according to claim 1 or 2, wherein the vinyl alcohol polymer is polyvinyl alcohol. (4) The method for preserving the freshness of fresh foods according to claim 1 or 2, wherein the vinyl alcohol polymer is an ethylene-vinyl alcohol copolymer. (5) The method for preserving the freshness of fresh foods according to any one of claims 1 to 4, wherein the fresh foods are vegetables, fish and shellfish, or meat.