JPH078222B2 - Methods for freezing biological tissue - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improved method for freezing biological tissues, particularly a freezing method suitable for use with foods such as fish, meat, and fruit.

BACKGROUND ART Currently, meat and fish foods are stored in freezers for 20 minutes.
However, this freezing method has the problem that ice crystals form in the meat or fish during freezing, which significantly destroys the freshness and flavor of the meat or fish.

That is, for biological tissues to be frozen, such as fish, meat, leafy vegetables, and fruits, the temperature varies slightly depending on the type, but it is generally between -1°C and
The temperature range for maximum ice crystal formation is -5°C. Therefore, when biological tissue passes through this temperature range during a temperature drop, the water in the biological tissue crystallizes into needle-like crystals, and the grown crystals damage or destroy the cells, fibers, or cell membranes and fiber membranes of the biological tissue.

If cells, fibers, etc. are damaged in this way, the delicious flavor of the meat juices, etc., known as drips, will leak out when the biological tissue is thawed, which significantly reduces the value of the biological tissue as a food. In addition, the meat juices, etc., may sublimate during frozen storage, causing the biological tissue to become dehydrated.

In response to this, in recent years, a method has been developed for preserving meat, fish, etc. by cooling them to a temperature range immediately adjacent to the maximum ice crystal formation temperature range.

In this way, even if the food is cooled to 0°C or below, ice crystals will not form within the tissue, so the freshness and flavor of the food will be maintained.

However, it is quite difficult to maintain the temperature of food within a narrow temperature range between approximately 0° C. and the temperature range at which maximum ice crystals form.

In other words, in the food distribution process, controlling the temperature of food within such a narrow temperature range during transportation is
This poses a problem of requiring a great deal of cost.

Furthermore, because the food is not frozen, its cells, fibers,
Another problem is that the cell membrane or fiber membrane is soft and easily damaged during transportation.

Furthermore, since the cooling temperature is relatively high, not only is the effect of killing bacteria and bacteriostatic action small, but there is also the problem that food cannot be stored for a long period of time of more than one month.

Another method involves immersing biological tissue in an extremely low temperature liquid such as liquid nitrogen to rapidly freeze it. This method is not suitable for freezing meat, fish, etc. In other words, if biological tissue such as meat or fish is immersed in liquid nitrogen directly or while placed in a container such as a synthetic resin film, it will be cooled so rapidly that the temperature difference between the outside and inside of the biological tissue will become large. This temperature difference will cause distortion,
The problem arises that the biological tissue is pulverized.

Therefore, when freezing biological tissue using an ultra-low temperature liquid such as liquid nitrogen, the biological tissue is first slowly frozen in low temperature nitrogen gas above the liquid nitrogen container,
Thereafter, it may be possible to immerse the sample in liquid nitrogen.

However, such freezing procedures are time-consuming and costly, and cannot be used to freeze large quantities of meat, fish, etc.

Furthermore, liquid nitrogen is expensive to produce and easily vaporizes, resulting in significant losses as it gradually evaporates while stored in a container. Furthermore, there are problems with the evaporation of large amounts of vaporized nitrogen into the air during the freezing of biological tissues.

In particular, gaseous nitrogen has a lower specific gravity than air, so it diffuses rapidly into the air. Therefore, freezing with liquid nitrogen is very costly, and so it has traditionally only been used for some expensive meats and fish.

Disclosure of the Invention The present invention has been made in consideration of the above-mentioned problems of the prior art, and provides a method for freezing biological tissue without using liquid nitrogen, by passing through the maximum ice crystal formation temperature zone in a short time, without forming needle-shaped ice crystals, and therefore without damaging or damaging the cells, fibers, cell membranes, or fiber membranes of the biological tissue to be frozen.
The object of the present invention is to provide a method for freezing biological tissue that can freeze the biological tissue.

The invention provides a method for freezing biological tissues by adjusting the pH and osmotic pressure to be equal to the pH and osmotic pressure of the biological tissue to be frozen;
The above object is achieved by immersing the product in an antifreeze solution cooled to 6°C to -79°C and freezing it.

In addition, the above-mentioned object can be achieved by placing the biological tissue in a container together with a liquid whose pH and osmotic pressure have been adjusted to be equal to those of the biological tissue to be frozen, and then immersing the biological tissue in an antifreeze solution cooled to -9°C to -150°C to freeze it.

In addition, the above-mentioned object can be achieved by placing the biological tissue in the container together with an aqueous solution of glycerin or a glycerin derivative containing an ester at a concentration of 0.1 to 20%, and then immersing the biological tissue in this state in the antifreeze solution to freeze it.

The above object is also achieved by adjusting the pH and osmotic pressure of the aqueous solution of glycerin or a glycerin derivative to be equal to the pH and osmotic pressure of the biological tissue to be frozen.

In addition, when the biological tissue is a marine fish, the marine fish is
The above object is achieved by placing the seaweed in a container together with a seawater solution containing glycerin or a glycerin derivative containing an ester at a concentration of about 20%, and then immersing the seaweed in this state in the antifreeze solution to freeze it.

The biological tissue is leafy vegetables, which are wrapped in a water-absorbent material and placed in a sealed container, and then immersed in an antifreeze solution to freeze them, thereby achieving the above object.

Furthermore, when leafy vegetables are placed in the sealed container, the air is removed from the sealed container before sealing, thereby achieving the above object.

The above object can also be achieved by pre-cooling the biological tissue to a temperature range immediately adjacent to the temperature range at which maximum ice crystal formation occurs, and then immersing the tissue in the antifreeze solution to freeze it.

In this invention, meat, fish, etc. are frozen using antifreeze, i.e., a specific heat of which is approximately the same as that of air, whereas conventionally meat, fish, etc. are frozen using low-temperature air.
The biological tissue is cooled by the liquid, so that the biological tissue instantly passes through the temperature range for maximum ice crystal formation, freezing the biological tissue without forming needle-shaped ice crystals.

Therefore, the water in the biological tissue is frozen in granular form,
No cells, fibers, cell membranes or fiber membranes are damaged or destroyed.

BEST MODE FOR CARRYING OUT THE INVENTION The following provides a detailed description of an embodiment of the present invention.

In the first embodiment of the method of the present invention, an ethylene glycol aqueous solution is used as the antifreeze, and this is cooled to a temperature below -6°C, close to the freezing point which varies depending on the concentration of ethylene glycol, and biological tissue such as meat or fish is immersed in the solution to freeze it.

The amount of ethylene glycol is determined by the amount of the biological tissue to be frozen,
That is, the size is selected appropriately depending on the size of the fish, meat, etc.

Generally, the specific heat of a liquid is about 20 times that of air, and the thermal conductivity of the liquid is also higher than that of air.

Therefore, liquids can cool biological tissue approximately 20 times faster than air.

Thus, rapid cooling of biological tissues can reach temperatures of -1°C to
The maximum ice crystal formation temperature range between -5°C is passed in a very short time, and the water in the cells does not have time to grow into needle-shaped crystals, so they freeze in granular form.

Therefore, the needle-like crystals can penetrate the cells, fibers, and
Cell or fiber membranes are not damaged or destroyed.

Therefore, even if the biological tissue is thawed, cell fluid, body fluids between fibers, etc. will not leak out, and the freshness of the biological tissue will be maintained for a long period of time.

According to the inventor's experiments, when small fish are fresh, their bodies become warped or twisted due to rigor mortis, and this warping or twisting returns to normal over time. However, small fish frozen using the method of the above example retained their rigor mortis even after thawing.

In addition, in the above embodiment, since the biological tissue is instantaneously cooled to an ultra-low temperature, most of the bacteria that adhere to the tissue, such as Bordetella, Erysipelas, Leptospira, Brumola, Staphylococcus, Streptococcus, and Escherichia coli, are killed.
In addition, Anisakis larvae, which are known to parasitize marine fish and shellfish, are instantly killed, and the bacteriostatic effect after freezing is also far superior to other freezing methods.

Furthermore, in the above examples, ethylene glycol or its aqueous solution is used as the antifreeze solution, but ethylene glycol is approved for use under the food hygiene regulations of Japan and is safe and harmless.

Next, examples of freezing methods according to specific types of biological tissue will be described.

First, relatively small freshwater fish, such as sweetfish and young herons, are placed in a sealed package made of synthetic resin film together with an aqueous solution of glycerin with a concentration of about 2%, and then immersed in the antifreeze solution to be frozen.

In this way, the glycerin coating covers and protects the cells or cell membranes of the fish, and the glycerin aqueous solution speeds up the conduction of cold and heat within the package, allowing the freshwater fish to be frozen at almost the same rate as if it were directly immersed in antifreeze, and is also convenient to handle.

Furthermore, biological tissue is usually thawed by immersing the package in water at room temperature. In this case, the frozen biological tissue cracks due to the sudden rise in temperature. However, the inventors have confirmed through experiments that when the biological tissue is protected by a glycerin solution, thawing occurs slowly and cracks do not occur.

Next, in the case of relatively small saltwater fish, the saltwater fish is placed in a sealed package made of synthetic resin film or the like together with a sterilized seawater solution containing 2% glycerin, and then immersed in antifreeze to freeze.
Furthermore, for freezing small fish such as sardines, herrings, and sweetfish, i.e., milt or white fish of a few centimeters or less, a sterilized seawater solution or aqueous solution containing 0.1% glycerin is used.

In this case, experiments have confirmed that fish can be frozen and preserved more freshly by freezing them using a liquid obtained by adding glycerin to the water or seawater in which they live to achieve the required concentration.

In other words, by adjusting the osmotic pressure and pH of the water or seawater that comes into contact with the fish to be frozen to be equal to the osmotic pressure and pH of the fish, it is possible to suppress the penetration of the fish's cellular fluids and body fluids and to prevent changes in pH, thereby preventing the destruction of biological tissue. Incidentally, the pH value for freshwater fish is approximately 6.8 to 7.0, and for saltwater fish it is approximately 7.0 to 7.2.

Next, large fish such as salmon, tuna, bonito, etc. are sealed in a synthetic resin film package, the air is removed, and a solution of seawater or water in which they live and 2% glycerin is added is poured into them, and then they are immersed in the antifreeze solution and frozen.

Alternatively, the fish may be immersed in the antifreeze solution without using a package. In this case, it is preferable to adjust the pH and osmotic pressure of the antifreeze solution to match those of the biological tissue to be frozen.

As mentioned above, glycerin or a glycerin derivative including an ester can be used to adjust the osmotic pressure of seawater or water.
Glucose, citric acid, etc. can be used.

The minimum temperature of the antifreeze solution differs depending on whether the biological tissue to be frozen is immersed in the antifreeze solution as is or whether it is placed in a package such as a synthetic resin film, either alone or together with the glycerin solution described above, and then immersed in the antifreeze solution for freezing.

In other words, if biological tissue is directly immersed in antifreeze solution at a temperature lower than -79°C, some of the tissue may be destroyed. However, if the tissue is sealed in a package together with a glycerin solution, the package and the glycerin solution absorb the thermal shock, and no destruction of the biological tissue due to sudden cooling is observed, even when the tissue is immersed in antifreeze solution cooled to, for example, -150°C.

Next, in the case of leafy vegetables, the leafy vegetables are wrapped in a water-absorbent material such as thick Japanese paper, and then placed in a sealed container, which is then sealed after the air has been removed.

In this state, the leafy vegetables are immersed in an antifreeze solution to freeze them.

In this way, moisture contained in the air in the sealed container does not adhere to the surface of the leafy vegetables, and damage to the leafy vegetables due to so-called frost burn caused by such adhesion is prevented.

Furthermore, root vegetables such as wasabi and ginseng are frozen in a glycerin solution with a concentration of about 2% in the same manner as in the case of freshwater fish.

In the case of mushrooms such as matsutake and shiitake, chips of pine or pine needles are placed in a sealed container together with the matsutake, and the sealed container is immersed in an antifreeze solution to freeze.

In the case of shiitake mushrooms, chips of shiitake wood or chips of shiitake leaves are placed in a sealed container together with the shiitake mushrooms, and then immersed in an antifreeze solution and frozen.

This has been confirmed through experiments, and it has been confirmed that the food can be stored in a more fresh state for a longer period of time than if it were simply placed in a container and frozen.

Here, if the biological tissue is cooled to a temperature close to the maximum ice crystal formation temperature range prior to freezing as described above, and then immersed in an antifreeze solution and frozen as described above, the maximum ice crystal formation temperature range can be passed through even more rapidly. Furthermore, pre-cooling the biological tissue reduces the thermal shock when immersed in the antifreeze solution, allowing the use of a lower temperature antifreeze solution.

The temperature of antifreeze solution rises when biological tissue is immersed in it, but if the biological tissue is pre-cooled as much as possible, the temperature rise is small. Furthermore, pre-cooling reduces the thermal shock given to the biological tissue, allowing the antifreeze solution to be kept at a lower temperature, thereby keeping the temperature rise of the antifreeze solution low.

In the above embodiment, the antifreeze is kept at a temperature of -6°C to -150°C.
However, this temperature is appropriately selected depending on the type of biological tissue to be frozen.

Furthermore, when a glycerin solution or a glycerin seawater solution is placed in a sealed container together with biological tissue and frozen, the glycerin concentration is not limited to 0.1% or 2%, and experiments have confirmed that a range of 0.1 to 20% is effective.

Furthermore, in the above examples, the antifreeze is ethylene glycol or a solution thereof in water or seawater, but the present invention is not limited to this, and any antifreeze that has a certain degree of hydrophilicity and does not freeze in the range of -6°C to -150°C will suffice.

Therefore, an antifreeze solution containing propylene glycol, an alcohol-based antifreeze solution such as ethyl alcohol, methyl alcohol, or propyl alcohol, or an aqueous solution of sodium chloride or potassium chloride may be used.

However, alcohol-based antifreeze is highly flammable, so explosion prevention measures are necessary. Also, toxic antifreeze such as methyl alcohol should only be used when freezing biological tissue in a sealed container.

In the above example, the cooling temperature of the antifreeze solution when biological tissue is directly immersed is -6°C to -79°C. The upper limit of -6°C is determined in relation to the temperature range for maximum ice crystal formation, and -79°C is determined as the limit value for preventing tissue crushing, similar to that which occurs when biological tissue is rapidly frozen and then immersed in liquid nitrogen, etc.

When biological tissue is immersed in antifreeze solution while placed in a sealed container such as a synthetic resin film, the lower limit of the cooling temperature of the antifreeze solution is set to -150°C. This is determined based on the possible limit value for antifreeze solutions that are difficult to evaporate at room temperature.

In addition, in the above examples, glycerin is used, but this is not limited to glycerin,
In addition to glycerin, it also includes glycerin derivatives including esters. Furthermore, the liquid placed in the sealed container together with the biological tissue is not limited to a solution of glycerin, etc., as long as it is adjusted to have approximately the same pH and osmotic pressure as the biological tissue.

In the above example of leafy vegetables, the leafy vegetables were contained in a water-absorbent material, and the air was removed from the sealed container to dehumidify and deoxidize them, but dehumidification, dehydration, or deoxidation may also be achieved by enclosing a desiccant or deoxidant in the sealed container, or by using both.

The inclusion of such desiccant and oxygen absorber is not limited to leafy vegetables, but can also be used to cool other biological tissues.

INDUSTRIAL APPLICABILITY According to the present invention, the temperature range for maximum ice crystal formation, at which the water contained in the biological tissue turns into needle-shaped crystals, can be instantaneously passed through during cooling, thereby preventing damage or destruction of cells, fibers, cell membranes or fiber membranes of the biological tissue due to needle-shaped crystals. Furthermore, the pH and osmotic pressure of the liquid in contact with the biological tissue can be controlled to
The pH and osmotic pressure of the biological tissue can be adjusted to be equal to those of the biological tissue, and the permeation of cell fluids and body fluids and changes in pH can be suppressed, so that the biological tissue can be frozen and stored in a fresh state for a long period of time without losing its flavor.

Furthermore, the above-mentioned cooling can be performed continuously at low cost.
It can be done in large quantities.

Claims (10)

[Claims] [Claim 1] A method for freezing biological tissues, such as meat, fish, vegetables, and fruits, by immersing and freezing the biological tissues in an antifreeze solution whose pH and osmotic pressure have been adjusted to be equal to those of the biological tissue to be frozen and which has been cooled to between -6°C and -79°C. 2. A method for freezing biological tissue according to claim 1, wherein the biological tissue is pre-cooled to a temperature range immediately adjacent to the temperature range at which maximum ice crystal formation occurs, and then immersed in the antifreeze solution to freeze the tissue. [Claim 3] A method for freezing biological tissue, comprising placing the biological tissue in a container together with a liquid whose pH and osmotic pressure have been adjusted to be equal to those of the biological tissue to be frozen, and then immersing the biological tissue in an antifreeze solution cooled to -6°C to -150°C to freeze it. [Claim 4] A method for freezing biological tissue as described in claim 3, wherein the biological tissue is placed in the container together with an aqueous solution of glycerin or a glycerin derivative containing an ester at a concentration of 0.1 to 20%, and in this state is immersed in the antifreeze solution to freeze. 5. The pH and osmotic pressure of the aqueous solution of glycerin or a glycerin derivative are adjusted to the pH and osmotic pressure of the biological tissue to be frozen.
5. The method for freezing biological tissue according to claim 4, wherein the pH and osmotic pressure are adjusted to be equal. 6. When the biological tissue is a saltwater fish, the saltwater fish is placed in the container together with a seawater solution of glycerin or a glycerin derivative containing an ester at a concentration of 0.1 to 20%,
4. The method for freezing biological tissue according to claim 3, wherein the biological tissue is immersed in the antifreeze solution in this state to be frozen. 7. The method of claim 6, wherein the pH and osmotic pressure of the seawater solution containing said glycerin or glycerin derivative are adjusted to be equal to those of the biological tissue to be frozen.
Item 4. A method for freezing biological tissue. 8. The biological tissue is a leafy vegetable, and the leafy vegetable is wrapped in a water-absorbent material and placed in a sealed container, and in this state is stored at -6°C to
A method for freezing biological tissues, characterized by immersing the tissue in an antifreeze solution cooled to -150°C. 9. The method for freezing biological tissue according to claim 8, wherein when placing the leafy vegetables in the sealed container, the air is removed from the sealed container before sealing. [Claim 10] A method for freezing biological tissue described in any one of claims 3 to 9, in which the biological tissue is pre-cooled to a temperature range immediately adjacent to the temperature range at which maximum ice crystal formation occurs, and then immersed in the antifreeze solution to freeze it.