WO2012036166A1 - Freezing method and freezing device - Google Patents

Abstract

In this freezing method, an object to be frozen is immersed in a nonfreezing water solution or an ice slurry that contains a clathrate hydrate of carbon dioxide, and then is frozen. Preferably, the nonfreezing water solution or ice slurry contains an alcohol.

Description

Freezing method and freezing apparatus

The present invention relates to a freezing method and a freezing apparatus.

Patent Document 1 discloses that an object to be frozen is frozen by a cooling medium adjusted to an ice slurry in a temperature range of −20 ° C. to −50 ° C.

JP 2011-17512 A

However, in the freezing method disclosed in Patent Document 1, since ice in the ice slurry inhibits convection, the amount of drip generated at the time of thawing despite the endothermic heat due to the melting latent heat of ice is the object to be frozen in the brine. This was not much different from the brine freezing performed by soaking. The drip contains umami components and nutrients of food, and the amount of drip generated upon thawing has a great effect on the freezing quality of the object to be frozen such as food.

In view of the above points, an object of the present invention is to provide a freezing method and a freezing apparatus capable of further reducing the amount of drip generated when the object to be frozen is thawed.

The freezing method of the present invention is characterized in that an object to be frozen is immersed in an ice slurry or an antifreeze aqueous solution containing carbon dioxide inclusion hydrate and frozen.

According to the freezing method of the present invention, carbon dioxide clathrate hydrate is contained in an aqueous solution in an ice slurry or an antifreeze aqueous solution. Therefore, in addition to being cooled by being immersed in an ice slurry or an antifreeze aqueous solution, the object to be frozen is cooled by the endothermic heat of the melting latent heat of the particulate carbon dioxide clathrate hydrate. Therefore, the freezing speed of the object to be frozen increases.

Therefore, the ice nuclei generated in the object to be frozen do not grow into large-sized ice crystals and damage to the object to be frozen is reduced, so that high-quality freezing with a small amount of drip generated during thawing can be realized. . The melting of carbon dioxide clathrate hydrate means that carbon dioxide molecules that have entered the cage structure of water molecules by hydrogen bonding are separated from the water molecules. Under normal pressure, clathrate hydrate of carbon dioxide is formed at −55 ° C. or lower.

Since ice has a large latent heat of melting, the freezing speed of the object to be frozen increases due to the melting of the ice around the object to be frozen. However, in the case of an ice slurry, the convection of the aqueous solution is significantly hindered by the ice in the ice slurry and heat transfer is reduced. Therefore, in a temperature zone where carbon dioxide inclusion hydrate is not produced, high-quality freezing with a smaller amount of drip than brine freezing cannot be realized despite the endothermic heat due to the latent heat of melting of ice.

On the other hand, in the temperature zone where the inclusion hydrate of carbon dioxide is generated, even in the case of ice slurry, the drip amount is greatly reduced as compared with brine freezing, and high-quality freezing can be realized.

In the freezing method of the present invention, the freezing temperature of the aqueous solution in the ice slurry or the antifreeze aqueous solution needs to be lower than the temperature at which the aqueous solution can contain carbon dioxide clathrate hydrate. Therefore, the ice slurry or the antifreeze aqueous solution preferably contains alcohol. The ice slurry or antifreeze aqueous solution may be adjusted by cooling an alcohol water mixed solution such as ethanol.

In addition, it is preferable that the to-be-frozen thing is low moisture content things, such as meat, such as seafood and animal meat, and a biological sample. Low moisture content means a moisture content of less than 90%.

The freezing apparatus of the present invention is characterized in that means for supplying carbon dioxide gas is provided in a container in which an ice slurry or an antifreeze aqueous solution at a temperature lower than the temperature at which carbon dioxide inclusion hydrate is generated is provided.

According to the freezing device of the present invention, the freezing method of the present invention can be easily realized concretely.

The graph which shows the relationship between the drip rate at the time of defrosting after freezing a sample, and refrigerant | coolant temperature. The graph which shows the relationship between the drip rate at the time of defrosting after freezing a sample, and refrigerant | coolant temperature. The graph which shows the relationship between ethanol aqueous solution density | concentration and coagulation temperature. The graph which shows the production | generation conditions of a carbon dioxide inclusion hydrate. Explanatory drawing of the freezing apparatus which concerns on this invention.

[Freezing principle]
The damage of the object to be frozen at the time of freezing includes damage due to cracks and cracks that increase in proportion to the endothermic rate, and damage due to ice crystal size growth that decreases in inverse proportion to the endothermic rate. When considering only the freezing of the object to be frozen without considering the storage and thawing of the object to be frozen, the damage at the time of freezing can be considered as the sum of the two damages.

割 れ Cracking during freezing is damage that causes cracking or deformation in the outer layer of the object to be frozen. Cracking is caused by the expansion of the outer layer portion that was first frozen due to heat absorption from the surface layer during freezing inside. Damage due to ice crystal size growth is caused by the growth of ice crystal nuclei generated in the object to be frozen and the size of the ice crystal becoming large.

If the object to be frozen is animal meat or fish meat with a low moisture content of 65% to 85%, if the thickness is thin, there is little damage due to cracking, and damage due to ice crystal size growth in the object to be frozen is The main cause of damage. On the other hand, if the object to be frozen has a high moisture content of more than 90%, such as single cells or tissue pieces, damage due to cracks in the object to be frozen becomes a main factor of damage to the object to be frozen during freezing.

The growth of ice crystal size can be suppressed by rapidly freezing the object to be frozen and reducing the exposure time to a freezing temperature of about 0 ° C. due to latent heat of solidification. For that purpose, it is important to freeze at a high cooling rate.

〔Evaluation methods〕
Conventionally, the quality of food by freezing or thawing has been evaluated by a method of measuring the amount of drip at the time of thawing, the elastic value after thawing, the ice crystal size in the frozen state, or a sensory test. However, the measured values differ greatly depending on the food parts, and there are problems in the accuracy and reproducibility of the evaluation. Therefore, if there is not much difference in food quality due to freezing, the superiority or inferiority of freezing cannot be distinguished, which has been an obstacle to developing new freezing methods.

Therefore, the inventor of the present application first developed a method for evaluating the quality of freezing by measuring the amount of drip at the time of thawing, using Takano tofu as a model for low moisture content foods such as seafood and meat such as animal meat. .

As a low moisture content food model, a sample formed by mixing 1.5 wt% agar aqueous solution with Takano tofu powder was used. The moisture content of this sample is about 80%, which is close to the moisture content of meat such as seafood and animal meat, which is 65% to 85%. Specifically, Koya tofu was crushed with a grater and powdered. Then, 7% by weight of Takano tofu powder with respect to the weight of water was mixed with the boiled 1.5% by weight agar aqueous solution, stirred for 5 minutes, placed in the container, and cooled with ice water to solidify the contents. . And after removing the condensed water droplets in the container, die-cutting was performed using a cylindrical mold having an inner diameter of 12 mm to obtain a cylindrical sample having a diameter of 12 mm and a height of 10 mm. Further, the molded sample was stored in a plastic bag with a chuck and refrigerated at 4 ° C. for 1 day.

Using this sample, the drip rate was determined as follows.

First, after measuring the weight Wep of the sample before freezing, the bag sample was frozen under various conditions without being put in a container or bag. Then, the sample was placed in a centrifuge tube (Spitz tube) in a frozen state, and naturally thawed by centrifuging at 220 G for 40 minutes using a swing rotor centrifuge. Then, the sample was taken out from the centrifuge tube, the weight Wer was measured, and the freezing drip rate Rer was obtained by the formula (1) based on the weight difference between the samples before and after freezing.

Rer = 100 × (Wep-Wer) / Wep (1)

On the other hand, after measuring the weight Wer of the sample before freezing, the unfrozen sample was centrifuged at 220 G for 40 minutes using a swing rotor centrifuge. Then, the weight Wc of the sample after centrifugation was measured, and the centrifugal drip rate Rc was determined by the formula (2) based on the difference in weight of the sample before and after centrifugation.

Rc = 100 × (Wc−Wep) / Wep (2)

Finally, from the difference between the freezing drip rate Rer and the centrifugal drip rate Rc, the drip rate Re was obtained by Equation (3), and the difference in the drip rate Re depending on the freezing conditions was compared.

Re = Rer-Rc (3)

However, because of variations in sample production, the drip rate Re was compared using samples of the same production lot.

Since the sample was refrigerated and stored in a sealed bag for 1 day after molding, water droplets on the surface adhered to the bag and a certain amount of water evaporated in the bag, so the error could be reduced. Furthermore, since it thawed during centrifugation, the drip generated during the thawing could be separated without being reabsorbed by agar or Takano tofu. In addition, since a swing rotor centrifuge is used, the sample can be squeezed in the vertical direction, and the error can be reduced.

〔Evaluation results〕
FIG. 1 and FIG. 2 are graphs showing the relationship between the drip rate Re and the refrigerant temperature according to the type of medium (hereinafter referred to as “contact refrigerant”) that is cooled by contacting with the sample.

In FIG. 1, the case where the sample is frozen in a state where the sample is placed on the resin plate with air as the atmosphere in the freezer is plotted with rhombuses, and the approximate straight line is shown with a short broken line. In the freezer, the case of freezing with the sample placed on an aluminum plate with air as the atmosphere was plotted in a circle, and the approximate straight line was shown by a one-dot chain line. When the sample was frozen by immersing it in a 90% aqueous ethanol solution (ethanol brine) (hereinafter referred to as “brine freezing”), it was plotted with a square, and the approximate straight line was shown with a long broken line. Further, when the sample is frozen by immersing it in an ice slurry of an ethanol aqueous solution cooled with dry ice (hereinafter referred to as “ice slurry + CO ₂ freezing”), it is plotted with a triangle, and the approximate straight line is shown with a solid line. It was.

In FIG. 2, when the sample is frozen by immersing it in an ice slurry of an aqueous ethanol solution cooled in a freezer (hereinafter referred to as “ice slurry freezing”), it is plotted with a hollow triangle, and its approximate straight line Is shown by a two-dot chain line. Furthermore, the case where the sample was frozen by immersing it in an ice slurry of an aqueous ethanol solution cooled with dry ice was plotted with an intermediate coating triangle, and the approximate straight line was shown by a solid line.

Brine freezing was performed by natural convection. Further, in ice slurry freezing and ice slurry + CO ₂ freezing, the ice slurry freezing start temperature varies depending on the ethanol concentration in the ethanol aqueous solution. Therefore, the ethanol concentration of the aqueous ethanol solution was determined so as to be below the curve indicating the relationship between the ethanol concentration of the aqueous ethanol solution and the solidification temperature shown in the graph of FIG.

As can be seen from FIG. 1, in the high temperature range around −20 ° C., brine freezing has a smaller drip rate Re than ice slurry + CO ₂ freezing. This is thought to be because convection does not occur in the ice slurry.

On the other hand, in the low temperature zone around −50 ° C., the ice slurry + CO ₂ freezing has a smaller drip rate Re than the brine freezing. This is presumably because the inclusion hydrate of carbon dioxide is formed at -55 ° C under normal pressure, and the latent heat of dissolution of the inclusion aqueous solution contributes. This is understood from the fact that an inclusion hydrate of carbon dioxide is produced below the curve shown in the graph of FIG.

However, when dry ice is immersed in an aqueous ethanol solution and cooled, even if the average temperature of the aqueous ethanol solution is around −40 ° C., the area around the dry ice is locally −55 ° C. or lower. It is thought that it is formed.

As can be seen from FIG. 2, in the high temperature zone around −20 ° C., the drip rate Re between ice slurry freezing and ice slurry + CO ₂ freezing is the same, but the low temperature zone around −50 ° C. Then, it can be said that ice slurry + CO ₂ freezing has a smaller drip rate Re than brine freezing.

In the method of immersing an object to be frozen in the ice slurry disclosed in Patent Document 1, the convection of the aqueous solution is inhibited by ice, and the latent heat of ice cannot be fully utilized for cooling. Therefore, the object to be frozen is cooled only by the cooling itself by being immersed in the ice slurry and the cooling by the latent heat of the surrounding ice, so that the freezing speed is not sufficient. Therefore, a relatively large amount of drip is generated at the time of thawing due to the damage caused by the ice crystals generated in the object to be frozen growing to a large size, and it is not possible to realize a sufficiently high quality freezing.

On the other hand, in the present invention, the object to be frozen is cooled not only by being immersed in an ice slurry or an antifreeze aqueous solution but also by the endothermic endothermic heat of the particulate carbon dioxide clathrate hydrate. . Therefore, the freezing speed of the object to be frozen increases. Therefore, since ice crystals generated in the object to be frozen do not grow to a large size, damage to the object to be frozen is reduced, and high-quality freezing with a small amount of drip generated during thawing can be realized.

[Freezing device]
As shown in FIG. 5, the freezing apparatus 1 according to the present invention supplies carbon dioxide to a freezing tank 2 that contains a refrigerant composed of an ice slurry or an antifreeze aqueous solution at a temperature lower than the temperature at which carbon dioxide inclusion hydrate is generated. Carbon dioxide supply means 3 is provided.

The ice slurry or antifreeze aqueous solution is prepared from an alcohol aqueous solution. In addition, as alcohol, when a to-be-frozen thing is a foodstuff, since there is no toxicity, it is preferable that it is ethanol. In addition, alcohol is not limited to ethanol, Ethylene glycol, propylene glycol, etc. may be sufficient.

Under normal pressure, carbon dioxide clathrate hydrate is formed at −55 ° C. or lower. Therefore, referring to FIG. 3, the ethanol concentration in the ice slurry or antifreeze aqueous solution may be 60% by weight. preferable. However, under normal pressure, carbon dioxide clathrate hydrate is formed if it is locally −55 ° C. or lower even at an average of −40 ° C. or lower. Therefore, referring to FIG. The ethanol concentration in the aqueous solution may be 40% by weight.

Further, if the freezing temperature of the aqueous solution in the ice slurry or the antifreeze aqueous solution is equal to or lower than the temperature at which the aqueous solution can contain the clathrate hydrate of carbon dioxide, the ice slurry or the antifreeze aqueous solution is composed of an aqueous solution other than the alcohol aqueous solution. It may be a thing.

Here, the carbon dioxide supply means 3 includes an aeration pipe 4 disposed in the freezing tank 2, a gas cylinder 5 filled with liquefied carbon dioxide gas provided outside the freezing tank 2, and the aeration pipe 4 and the gas cylinder 5. It is composed of a regulator 7 interposed in the gas pipe 6 to be connected. By adjusting the regulator 7, carbon dioxide having an appropriate pressure is released from the diffuser 4 into the refrigerant accommodated in the freezing tank 2.

In addition, the freezer 2 is provided with a cooler 8 for cooling the refrigerant at around −60 ° C. The cooler 8 includes an evaporator 9, a condenser 10, a compressor 11 and an expansion valve 12.

When carbon dioxide gas is supplied by the carbon dioxide supply means 3 into the refrigerant cooled to around −60 ° C. by the cooler 8, an inclusion hydrate of carbon dioxide in the refrigerant is formed. By immersing the object to be frozen in this inclusion hydrate, high-quality freezing can be realized.

Also, in the case of ice slurry, the amount of ice produced is reduced to the area where convection occurs, and instead the amount of carbon dioxide inclusion hydrate produced is much smaller than the ice slurry ice. By doing so, it is possible to increase the freezing speed of the object to be frozen while maintaining the convection in the ice slurry.

The carbon dioxide supply means 3 may supply dry ice into the freezing tank 2.
Further, when the contact refrigerant is an ethanol aqueous solution, the object to be frozen may be immersed in water or salt water to form a water layer on the surface layer, and then immersed in a cooled ethanol aqueous solution directly without packaging and frozen. Alternatively, paste-like starch or protein may be attached to the surface of the object to be frozen and then frozen, and the paste may be washed away after thawing.

Furthermore, a layer of water or a paste is provided on the surface of the object to be frozen so that air does not enter and the object to be frozen is wrapped with a resin film for food packaging having a thickness of about 10 μm, and then brine or ice It may be frozen by dipping in a slurry. As a result, the thermal resistance is reduced, and freezing with a higher cooling rate is possible. In addition, since water and glue on the surface layer are first frozen to form a frozen capsule, it is possible to prevent ethanol from contaminating a frozen object such as food.

Claims (3)

A freezing method characterized by immersing an object to be frozen in an ice slurry or an antifreeze aqueous solution containing carbon dioxide inclusion hydrate. The freezing method according to claim 1, wherein the ice slurry or the antifreeze aqueous solution contains alcohol. A freezing apparatus comprising means for supplying carbon dioxide gas into a container containing an ice slurry or an antifreeze aqueous solution at a temperature lower than the temperature at which carbon dioxide inclusion hydrate is generated.

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