JP2015055396A - Freezing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a freezing method capable of obtaining a sufficiently high supercooling degree by detecting release of supercooling.SOLUTION: The freezing method includes: a supercooling formation step for cooling an object so that the object becomes a supercooling state where the object is not frozen even at a temperature of a freezing point or less by means for respectively detecting a temperature of coolant gas and a surface temperature of the object; a supercooling release detection step for detecting that the supercooling state is released; and a quick cooling step for quickly cooling the object when the supercooling state is released. When a temperature difference between the temperature of the coolant gas and the surface temperature of the object exceeds a previously determined range in the supercooling formation step, reduction in the temperature of the coolant gas is stopped, and when the temperature difference is returned to the previously determined range, reduction in the temperature of the coolant gas is restarted.

Description

  The present invention relates to a freezing method using a cooling gas, and more particularly to a freezing method in which an object is frozen through a supercooled state.

  When freezing biological substances such as foods and cells, ice crystals generated in the cells or in the cell gaps damage the cell tissues. In addition, when freezing a solution, the concentration may become non-uniform due to freeze concentration of the frozen product during the freezing process. In order to avoid these problems, it is used to freeze through a so-called supercooled state that does not freeze below the freezing point. This is because an object that has been frozen through a supercooled state generates uniform ice crystals that are not needle-like and granular, and thus damage to the cell tissue is reduced.

  In addition, freezing in the freezing process after the release of the supercooled state reduces the possibility of ice crystals growing, and avoids quality degradation factors other than ice crystals. Can do. In addition, the greater the degree of supercooling (the difference between the minimum temperature reached in the supercooled state and the freezing temperature), the more ice nuclei that are formed at the start of freezing, resulting in finer crystals. Is also known to be able to maintain a state closer to that before freezing.

  As a method of freezing an object using supercooling as described above, after maintaining the supercooled state for a predetermined time, releasing the supercooled state, and further rapidly cooling and freezing (for example, Patent Document 1), A method of controlling cooling so that the difference between the surface temperature measured by the surface temperature measuring means and the core temperature calculated from the surface temperature becomes small until the core temperature of the object reaches the freezing point (for example, Patent Document 2) ) Is done.

Japanese Patent No. 4253775 Japanese Patent No. 4827788

  However, in the freezing method described in Patent Document 1, since the supercooling state is released after a predetermined time has elapsed, a sufficient degree of supercooling may not be obtained or the supercooling state may have already been released. . Further, even in the freezing method described in Patent Document 2, there is a case where a sufficient degree of supercooling cannot be obtained by cooling until the core temperature reaches the freezing point. Further, depending on the object, it may be difficult to calculate the core temperature from the surface temperature, and the core temperature may not be measured correctly.

  Then, this invention aims at providing the freezing method which can acquire sufficient supercooling degree by detecting cancellation | release of supercooling.

  In order to achieve the above object, the freezing method of the present invention includes a means for detecting the temperature of the cooling gas and a means for detecting the surface temperature of the target object in the freezing method in which the target object is cooled by a cooling gas and frozen. A subcooling forming step for cooling the object so that it is not frozen even at a temperature below the freezing point, a supercooling release detecting step for detecting that the supercooling state is released, and the supercooling. It is characterized by comprising a rapid cooling step of rapidly cooling the object when the state is released.

  Further, when the temperature difference between the cooling gas temperature and the surface temperature exceeds a predetermined range in the supercooling formation step, the cooling gas temperature reduction is stopped, and the temperature difference is determined in advance. When the temperature returns to within the range, the cooling gas temperature reduction is resumed, and the subcooling release detecting step is performed at 5 ° C. within 10 seconds when the surface temperature of the object is below the freezing temperature. It is detected that the supercooled state is released when the temperature rises by 0.5 ° C. or more at a rate of 0.1 ° C./second from / second.

  According to the freezing method of the present invention, the supercooling release detection step is performed, in particular, at a rate of 5 ° C./second to 0.1 ° C./second within 10 seconds when the surface temperature of the object is below the freezing temperature. By detecting that the supercooling state is released when the temperature rises by more than ° C., the release of the supercooling can be reliably grasped. In addition, when the temperature difference between the temperature of the cooling gas and the surface temperature of the target object exceeds a predetermined range in the supercooling formation process, cooling is temporarily stopped and returned to the predetermined range. A sufficient degree of supercooling can be obtained by repeating the resumption of cooling.

It is explanatory drawing which shows an example of the freezing apparatus which enforces the freezing method of this invention. It is a figure which shows the temperature change of a supercooling formation process and a supercooling cancellation | release. It is a figure which shows the temperature change in Example 1 of this invention. It is an enlarged view of the figure which shows the temperature change in Example 1 of this invention. It is a figure which shows the temperature change in Example 2 of this invention. It is an enlarged view of the figure which shows the temperature change in Example 2 of this invention.

  FIG. 1 shows an example of a refrigeration apparatus for carrying out the freezing method of the present invention. The refrigeration apparatus 10 includes a sample chamber 11 that accommodates the object 1 and a rectifying chamber 13 that surrounds the sample chamber 11 with a blowing plate 12 interposed therebetween. A liquefied nitrogen gas in a storage tank (container) (not shown) is introduced from the liquefied nitrogen inlet 14, and the liquefied nitrogen gas is injected from the liquefied nitrogen injection port 17 toward the stirring fan 18 through the needle valve 15 and the electromagnetic valve 16.

  The agitating fan 18 driven by the motor 19 sucks the cooling gas in the sample chamber 11, sends the cooling gas into the rectifying chamber 13, vaporizes the injected liquefied nitrogen gas, and diffuses it as the cooling gas. The blowing plate 12 has an opening ratio limited by a punching hole or the like. Further, by making the sectional area of the gas flow direction of the rectifying chamber 13 more than five times the opening area of the blowing plate 12, it is uniform in the sample chamber 11. Cooling gas is sent to

  Furthermore, when the liquefied nitrogen gas is jetted and vaporized, the pressure in the rectifying chamber 13 increases, so that the flow rate of the cooling gas flowing from the blowing plate 12 into the sample chamber 11 is prevented from changing. 11 is provided with a pressure adjusting mechanism 20 that exhausts a part of the cooling gas without going through 11, and an exhaust port 21 for lowering the internal pressure rising by the cooling gas supplied into the sample chamber 11 is provided. .

  Further, a cooling gas temperature sensor 22 that measures the temperature of the cooling gas in the rectifying chamber 13, a surface temperature sensor 23 that measures the surface temperature of the object 1, and a core temperature sensor 24 that measures the core temperature are provided. . Further, a heater 25 for heating the cooling gas is provided in the vicinity of the stirring fan 18.

The needle valve 15 and the electromagnetic valve 16 are controlled based on the cooling gas temperature detected by the cooling gas temperature sensor 22 or the temperature difference between the cooling gas temperature and the surface temperature of the object 1 detected by the surface temperature sensor 23. By adjusting the flow rate of the liquefied nitrogen gas, controlling the rotation speed of the motor 19 to adjust the amount of stirring of the cooling gas, or operating the heater 25,
The temperature of the cooling gas can be controlled.

  Next, the temperature change at which the object 1 is brought into a supercooled state using the refrigeration apparatus 10 and the supercooled state is released will be described with reference to FIG. The object 1 uses 3% gelatin, and the temperature of the cooling gas is maintained from 20 ° C. to 0 ° C. for the first 10 minutes, maintained at 0 ° C. for the next 60 minutes, and from 0 ° C. for the subsequent 100 minutes. It is controlled to be −10 ° C. In the first 10 minutes, as the cooling gas temperature decreases, the surface temperature and core temperature of the object 1 decrease. Thereafter, when the cooling gas temperature is maintained at 0 ° C., the surface temperature and the core temperature of the object 1 continue to decrease while the gradient is slightly relaxed. Thereafter, when the cooling gas temperature gradually decreases from 0 ° C., the surface temperature and core temperature of the object 1 further decrease below the freezing point (0 ° C.) with the surface temperature being slightly lower. The object 1 is in a supercooled state. Thereafter, after a certain period of time, the surface temperature and the core temperature of the object 1 rapidly rise to the vicinity of the freezing point, and the supercooling is released. The object 1 is in a supercooling state in which it does not freeze even at a temperature below the freezing point, and until the supercooling is released is the supercooling formation process of the present application. According to FIG. 2, since the temperature control is performed so that the temperature of the cooling gas gradually decreases after the supercooling is released, the temperature of the object that has risen to the freezing point remains in the vicinity of the freezing point.

  Next, FIG. 3 and FIG. 4 show the temperature change at the time of rapid cooling when the object 1 is made 3% gelatin and the supercooling state is detected in the same supercooling formation process as described above, and when the supercooling release is detected. FIG. 4 is an enlarged view of FIG. 3 in which the display temperature range is 20 ° C. to −10 ° C. When it is detected that the surface temperature of the object 1 has risen by 1 ° C. within 5 seconds below the freezing point (0 ° C.), it is determined that the supercooling has been released and the cooling gas is reduced to −100 for 1 minute. Control to be at ℃.

  As shown in FIG. 3 and FIG. 4, when the supercooling release is detected and the cooling gas is rapidly cooled to −100 ° C., the surface temperature of the object 1 also decreases immediately after rising near the freezing point, It can be seen that the core temperature stays near the freezing temperature for a while, but then the temperature rapidly decreases.

  As described above, in the freezing process after the release of the supercooled state, if the object is rapidly cooled to freeze the object, it is possible to prevent the ice crystals from being enlarged and to avoid quality deterioration factors other than the ice crystals.

  Furthermore, under the same conditions as in the first embodiment, when the supercooling release is detected and the cooling gas temperature is controlled, in the supercooling formation step, the surface temperature of the object 1 is below the freezing point (0 ° C.). When the temperature difference from the cooling gas temperature is 0.5 ° C. or more, control is performed so as to stop the liquefied nitrogen gas injection and stop the cooling gas temperature drop. FIG. 5 and FIG. 6 show the temperature change when controlling to restart the cooling gas temperature reduction by restarting the injection of the liquefied nitrogen gas when the temperature is lower than ° C. FIG. 6 is an enlarged view of FIG. 5 in which the display temperature range is 20 ° C. to −10 ° C.

  As shown in FIG. 6, in the supercooling formation step, when the temperature difference between the surface temperature and the cooling gas temperature becomes 0.5 ° C. or more, the temperature control program for lowering the temperature of the cooling gas is stopped, When the temperature control program for lowering the temperature of the cooling gas is started four times when the temperature is lower than 0.5 ° C., the time of the supercooling state becomes longer than that of the first embodiment, and the supercooling is performed. It can be seen that the degree can be increased.

  As described above, by increasing the degree of supercooling, the ice crystals formed in the object become finer, and it is possible to maintain a state closer to that before freezing even after thawing.

  Note that the refrigeration apparatus to which the freezing method of the present invention is applied is not limited to the above-described one, as long as the surface temperature of the object and the cooling gas temperature (atmosphere temperature) can be measured and the temperature control of the cooling gas is possible. Good. Also, in the event that the supercooling release detection process cannot detect the release of supercooling, if the cooling gas temperature or surface temperature reaches a predetermined temperature, or if a predetermined time has passed, it is A temperature control program for starting the refrigeration process may be implemented.

  DESCRIPTION OF SYMBOLS 1 ... Object, 10 ... Refrigeration apparatus, 11 ... Sample chamber, 12 ... Outlet plate, 13 ... Rectification chamber, 14 ... Liquid nitrogen inlet, 15 ... Needle valve, 16 ... Electromagnetic valve, 17 ... Liquid nitrogen injection port, 18 ... Stirring fan, 19 ... Motor, 20 ... Pressure adjusting mechanism, 21 ... Exhaust port, 22 ... Cooling gas temperature sensor. 23 ... Surface temperature sensor, 24 ... Core temperature sensor, 25 ... Heater

Claims (3)

In a freezing method in which an object is cooled by a cooling gas and frozen,
Means for detecting the temperature of the cooling gas and means for detecting the surface temperature of the object;
A supercooling formation step of cooling the object so as to be in a supercooling state in which the object is not frozen even at a temperature below the freezing point;
A subcooling release detection process for detecting that the supercooling state has been released;
A freezing method comprising a rapid cooling step of rapidly cooling the object when the supercooled state is released. When the temperature difference between the temperature of the cooling gas and the surface temperature exceeds a predetermined range in the supercooling formation step, the cooling gas temperature stops decreasing and the temperature difference is determined in advance. The freezing method according to claim 1, wherein when the temperature falls within the range, the temperature of the cooling gas is restarted. The supercooling release detecting step is in a supercooled state when the surface temperature of the object rises by 0.5 ° C or more at a rate of 5 ° C / second to 0.1 ° C / second within 10 seconds at or below the freezing temperature. The freezing method according to claim 1, wherein the freezing method detects that is released.

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