Cooling methods

Abstract

A novel method for cooling water-containing materials is provided. [Solution] A cooling method for a hydrated object includes a preservation cooling step in which the temperature at the center of the object decreases before the temperature at the surface of the object decreases in at least a portion of the temperature range from -5.0°C to -1.0°C.

Description

[Technical Field]

[0001] The present invention relates to a cooling method, and in particular to a method for cooling an object containing moisture (hereinafter sometimes referred to as a "moisture-containing object"). [Background technology]

[0002] Conventionally, methods for cooling water-containing materials such as food products include a vacuum cooling method, a blast chiller method, and an electromagnetic induction method.

[0003] Various attempts have been made to establish a method for efficiently cooling food and the like while maintaining quality. For example, Patent Document 1 proposes a cooling method that can prevent the cooled object from drying out and shorten the cooling time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-060186 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been a need for a new cooling method for water-containing materials such as foods and cell dispersions. Therefore, an object of the present application is to provide a new cooling method that differs from conventional cooling methods. [Means for solving the problem]

[0006] One example of a cooling method for achieving the above-mentioned object is [1] a cooling method for a hydrated object, characterized in that it includes a storage preparation cooling step in which the temperature at the center of the object drops before the temperature at the surface of the object in at least a portion of the temperature range of -5.0°C or higher and -1.0°C or lower.

[0007] [2] Furthermore, it is preferable that the cooling method of [1] above further includes a basic cooling step, prior to the storage preparation cooling step, in which the object is kept in a temperature range of -1.0°C or higher and -0.1°C or lower, and cooled so that the entire object reaches a state of temperature equilibrium.

[0008] [3] In the cooling method of [1] or [2] above, it is preferable that the storage preparation cooling step includes preventing stagnation of temperature drop at least in the center of the object within a temperature range of -3.0°C or higher and -1.0°C or lower. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a novel method for cooling a water-containing material. [Brief explanation of the drawings]

[0010] [Figure 1] 10 is a cooling curve in a cooling method according to an example. [Figure 2] 10 is a cooling curve in another example of a cooling method. [Figure 3] 10 is a cooling curve in a cooling method according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of a cooling method according to one example of the present invention will be described below. The cooling method of the present invention is a cooling method that corresponds to frozen storage. The object to be cooled by the cooling method of the present invention is not particularly limited as long as it is a water-containing object, and may include foods such as vegetables, seafood, meat, fruit, confectionery, and grains, as well as medical compositions such as cell dispersions. In the following description, "°C" in temperature notation means Celsius.

[0012] (Cooling method) A cooling method according to one example of the present invention is a cooling method for a water-containing object. This cooling method is characterized by including a pre-storage cooling step in which the temperature at the center of the object drops before the temperature at the surface of the object in at least a portion of the temperature range of -5.0°C to -1.0°C. Furthermore, the cooling method of the present invention preferably further includes a basic cooling step, prior to the pre-storage cooling step, in which the object is kept in a temperature range of -1.0°C to -0.1°C and cooled so that the entire water-containing object reaches a state of temperature equilibrium. This cooling method is a novel cooling method that differs from conventional cooling methods. Furthermore, this cooling method can improve the quality of the object after cooling.

[0013] According to one example cooling method, the center of an object is cooled first in the so-called "maximum ice crystal formation zone," which is between -5.0°C and -1.0°C. Conventional cooling methods cool the surface of an object first, resulting in heat exchange with the warmer center, lowering the temperature of the entire object. This typically results in frost or a thin ice film forming on the surface of the object. While frost or an ice film on the surface of an object can cause freezing degradation, it can also promote cooling of the object.

[0014] According to one example cooling method, the temperature at the center of the object drops slightly before the temperature at the surface of the object in at least a portion of the temperature range of -5.0°C to -1.0°C. This effectively prevents the formation of an ice film on the surface of the object. Furthermore, even though the center of the object cools slightly first, the temperature of the entire object drops while maintaining approximately temperature equilibrium, thereby preventing the growth of ice crystals within the object. As a result, the formation of large ice crystals within the object can be effectively prevented, improving the quality of the cooled object.

[0015] <Hydrate> The water-containing material used in the cooling method is a material to be cooled that contains water. The water content of the water-containing material is not particularly limited, but may be, for example, 10.0% to 99.9%, or less, and may also be, for example, 98.0% or less. The water content can be measured according to the loss on drying method. Many foods, particularly fresh fruits, vegetables, seafood, and meat, have a high water content (e.g., 40.0% or more). While they have a juicy texture and are difficult to preserve, the cooling method of the present invention can effectively cool such water-containing materials and maintain their quality even when refrigerated. Specifically, by suppressing ice crystal formation, density changes after refrigerated storage and thawing can be suppressed and shape retention can be improved. Examples of water-containing materials include, but are not limited to, foods such as vegetables, seafood, meat, fruits, confectioneries, and grains, as well as medical compositions such as cell dispersions.

[0016] As described above, the cooling method is characterized by controlling the temperature of the center of the object to decrease before the temperature of the surface layer of the object. Here, the "center" of the object (water-containing object) refers to a region that includes a length within 50% of the center when an imaginary line (hereinafter referred to as the "imaginary line") is drawn from the center of gravity of the object to the surface. Furthermore, the "surface layer" of the object (water-containing object) refers to a region that includes a length within 20% of the surface of the imaginary line of the object.

[0017] <Basic cooling process> In the basic cooling step, prior to the pre-storage cooling step (a cooling step in a temperature range of -5.0°C to -1.0°C), the object is kept in a temperature range of -1.0°C to -0.1°C and cooled so that the entire object is in a state of temperature equilibrium. By carrying out this basic cooling step, it becomes possible to cool the object while maintaining good temperature equilibrium in the subsequent pre-storage cooling step, further improving the quality of the object.

[0018] The basic cooling process can be carried out, for example, by the following method. First, an object is placed in a first refrigerator. The first refrigerator is a refrigerator capable of maintaining the temperature of the object at a constant temperature within a temperature range of -1.0°C or higher and -0.1°C or lower. By cooling the object in such a first refrigerator, the object can be cooled while maintaining good temperature equilibrium within the object. The basic cooling process can be carried out using a device that has a mechanism for continuously emitting a constant temperature range of cold air. Specifically, heat is exchanged between the cold air ambient temperature within the device and the object, such as food, stored therein, and cooling is continued until the temperature is the same as the ambient temperature within the device. Here, it is preferable to continue emitting the same amount of cold air medium at the same temperature within the device even after the basic cooling process is completed.

[0019] <Storage preparation cooling process> In the pre-storage cooling step, the temperature at the center of the object drops before the temperature at the surface of the object in at least a portion of the temperature range of -5.0°C to -1.0°C. By carrying out this pre-storage cooling step, it is possible to suppress the growth of ice crystals within the object, thereby further improving the quality of the object after cooling. The pre-storage cooling step is an important step in achieving the storage conditions of -18°C or below in accordance with the Codex standard and in decreasing the temperature to that temperature.

[0020] Furthermore, in the pre-storage cooling process, it is preferable to prevent the temperature drop at least at the center of the object from stagnating in the temperature range of -3.0°C or higher and -1.0°C or lower. Here, in this specification, "no stagnating temperature drop" means that the temperature drop rate is -0.01°C / min or higher. By preventing the temperature drop at least at the center of the object from stagnating in the temperature range of -3.0°C or higher and -1.0°C or lower, it is possible to further suppress the growth of ice crystals within the object. As a result, the quality of the object after cooling can be further improved.

[0021] The following method, for example, can be used to perform the pre-storage cooling process. First, the object is placed in the second refrigerator. For example, if the cold air used to create the atmosphere inside the refrigerator is designated as the base cold air, the second refrigerator preferably includes a mechanism that can utilize this base cold air to first generate heat-returning cold air from a portion of the base cold air to serve as preparatory cold air for heat exchange. However, most of this base cold air and heat-returning cold air do not directly exchange heat with the food. Preferably, less than 1% of the total amount of heat-returning cold air is sent to the object, and the sent cold air is immediately collected. In this way, by allowing only a small portion of the cold air to exchange heat with the food, the object is cooled under a gentle temperature gradient, further suppressing the growth of ice crystals within the object. In one example, the temperature inside the second refrigerator may be about -20°C, for example, -15°C to -22°C, and preferably -18°C to -21°C, the basic cold air may be about -30°C, for example, -27°C to -33°C, and the preparatory cold air (heat return cold air) may be about -25°C, for example, -22°C to -27°C, or -23°C to -26°C.

[0022] Furthermore, the cooling method according to one example may optionally include a further cooling step following the pre-storage cooling step. This cooling step is a step of cooling the object to a desired temperature range below −5.0°C. Specifically, it may be a temperature-lowering step of lowering the object's temperature to a target temperature of −18°C or lower according to the Codex standard. Even when such a cooling step is performed, since the entire object is in a state of approximate temperature equilibrium after the pre-storage cooling step described above, cooling can proceed while the entire object is maintained in a state of approximate temperature equilibrium within that temperature range. Thus, according to the cooling method according to one example disclosed herein, the entire object is maintained in a state of approximate temperature equilibrium, thereby suppressing ice crystal growth and enabling the production of a high-quality cooled product.

[0023] <Cooling theory> The novel cooling theory that supports the cooling method of the present invention will now be described. Until now, when refrigerated objects, especially food, go through a series of freezing operations such as freezing, low-temperature storage, and thawing, quality deterioration occurs, typified by deterioration in texture, color, and dripping. These changes are caused by the complex interaction of numerous physical and biochemical factors, making it difficult to fully understand the mechanisms of quality deterioration.

[0024] For example, according to the inventors' considerations, the water contained in fish flesh immediately after the cessation of vital activities is thought to be in a state similar to bound water, and even if pressure is applied to the fish flesh, for example by crushing it, phenomena such as water leakage and dripping are unlikely to occur. However, as time passes after the cessation of vital activities, components that contribute to the water-retaining capacity in the tissue disappear, and the compatibility of water with other components in the tissue tends to be lost.

[0025] Therefore, with the aim of contributing to the maintenance of food quality, the present inventors investigated a method that can significantly extend the shelf life of foods, including fresh foods, while suppressing the loss of nutritional components and preventing the growth of harmful microorganisms during storage. As a result of this investigation, the present inventors newly discovered that, as described above, when cooling an object, the temperature of the center of the object (food) to be cooled can be controlled so that it drops before the temperature of the surface layer in at least a portion of the temperature range from -5.0°C to -1.0°C, thereby maintaining a high level of food quality. This cooling method is believed to be able to suppress the occurrence of lipid oxidation and myoglobin oxidation in meat, fish, and shellfish, even when the object is stored at a temperature of -18°C or below, as specified in the Codex standard.

[0026] The inventors' idea is not to maintain the temperature inside the refrigerator within a predetermined temperature range, as in methods using conventional refrigeration equipment, but to cool the food itself. As described above, by maintaining the object within a narrow temperature range of -1.0°C or more and cooling the entire object so that it reaches temperature equilibrium, and then implementing a specific cooling mode in which "the temperature at the center of the object drops before the temperature at the surface," it is possible to promote approximately uniform cooling of the entire food object.

[0027] In this way, it is believed possible to bind the water contained within the food's structure. If the water in the food's structure can be "bound," the relationship between the water and other nutrients in the food's structure will resemble that of bound water, making it possible to further lower the freezing point of the food. This phenomenon is expected to promote the uniformity of the temperature throughout the food. Furthermore, this phenomenon is expected to prevent the loss of compatibility between water and other components within the structure, thereby strengthening the structure and allowing the food to maximize its unique characteristics. These characteristics include the aroma, color, taste, and texture of each food. It is believed that a method based on the inventors' theory can improve all aspects of the food, including its nutrients and texture.

[0028] Based on the above theory, it is believed that the cooling method of the present invention makes it possible to preserve objects such as food while maintaining their quality. [Example]

[0029] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0030] Example 1 <Sample preparation> A piece of yellowfin tuna (yellowfin tuna fillet) taken out of the refrigerator and cut into 3cm cubes was used as the test sample. First, temperature sensors were inserted into the center (area corresponding to the center of gravity) and the surface (area within 20% of the surface) of the yellowfin tuna (water content: 70%), and then the tuna was placed in an aluminum tray.

[0031] <Cooling test> <<Basic cooling process>> The tray containing the sample and temperature sensor was then placed in a first refrigerator (X-Charge unit, manufactured by XEN GROUP Co., Ltd.), and the temperature of the object was maintained in the temperature range of -1.0°C or higher and -0.1°C or lower, and the entire object was cooled to reach temperature equilibrium. <<Storage preparation cooling process>> The vats that had undergone the basic cooling process were placed in a second cooling chamber, where a pre-storage cooling process was carried out. The second cooling chamber was configured so that the cold air flowing into the chamber would not come into direct contact with the objects. In the second cooling chamber, cold air at -25°C was circulated within the chamber. Less than 1% of this cold air was directed toward the objects. When the temperature of the objects was in the range of -5.0°C to -1.0°C, the temperature at the center of the objects dropped before the temperature at the surface of the objects. <<Further cooling process>> Furthermore, the object that had undergone the storage preparation cooling step was further cooled to around −20° C. Then, the vat that had reached a temperature of −20° C. was stored in a freezer stocker that can control the temperature at −20° C. or below.

[0032] Figure 1 shows the temperature change measured by the temperature sensor. Figure 1 shows the temperature change throughout the basic cooling process through the pre-storage cooling process, with the vertical axis representing temperature (°C) and the horizontal axis representing elapsed time (minutes). Figure 1 also shows an enlarged view of a portion of the basic cooling process (a process in which the sample is cooled to achieve temperature equilibrium by maintaining the temperature in the range of -1.0°C to -0.1°C) and the pre-storage cooling process (a cooling process in which the temperature at the center of the sample drops before the temperature at the surface of the sample in the temperature range of -5.0°C to -1.0°C). Figure 1 clearly shows that the temperature at the center of the sample drops before the temperature at the surface of the sample during the basic cooling process. Figure 1 also clearly shows that the temperature at the center of the sample drops before the temperature at the surface of the sample during the pre-storage cooling process.

[0033] Example 2 A beef block (moisture content: 40%) was cooled in the same manner as in Example 1. The beef block used had a perimeter of 25.1 cm with the longitudinal axis as the axis. Figure 2 shows the temperature changes measured by the temperature sensor. It is clear from Figure 2 that in the basic cooling process, the temperature of the entire object is in equilibrium in the range of -1.0°C to -0.1°C. It is also clear from Figure 2 that in the storage preparation cooling process, the temperature at the center of the object drops before the temperature at the surface of the object.

[0034] Example 3 Strawberries (moisture content: 90%) were cooled in the same manner as in Example 1. The strawberries used were "Sanukihime." Strawberries are broadly divided into three layers and are classified as fruit vegetables. The insoluble vegetable fiber content of strawberries is approximately 0.9 g / 100 g. Because of their delicate nature, strawberries are generally considered to be difficult to withstand pressure when frozen.

[0035] (Comparative Example 1) Yellowfin tuna slices cut into 3 cm cubes were cooled using a standard refrigerator-freezer (Panasonic refrigerator-freezer (commercial use), model number: SRR-K1281B).

[0036] (Comparative Example 2) A beef block was cooled using a standard refrigerator-freezer (Panasonic commercial refrigerator-freezer, model number SRR-K1281B). The beef block used had a circumference of 24.0 cm, with the longitudinal axis as the axis. Figure 3 shows the temperature changes measured by a temperature sensor. Note that the beef block was kept at 4.5°C in the refrigerator and immediately transferred to the freezer (around 10 minutes into the graph). It is clear that the temperature at the surface of the beef block dropped faster than the center immediately after cooling in the freezer began.

[0037] (Comparative Example 3) The strawberries were cooled using a general refrigerator-freezer (Panasonic refrigerator-freezer (for commercial use), model number: SRR-K1281B). The strawberries used were the same variety as in Example 3: "Sanukihime."

[0038] <Quality evaluation: Yellowfin tuna> The cooled objects (yellowfin tuna) obtained in Example 1 and Comparative Example 1 were placed on a porcelain plate and naturally thawed for 60 minutes at a temperature of 14°C, and the presence or absence of dripping was evaluated. In the yellowfin tuna treated in Comparative Example 1, dripping occurred in the areas where the object was in contact with the plate, and the shape was beginning to collapse, but in the yellowfin tuna treated in Example 1, no dripping was visible. For the yellowfin tuna of Example 1, a person entered the refrigerator at -14°C and attempted to manually cut it with a knife (Kai Corporation's "Seki Magoroku Akane Santoku Knife 165mm", triple-layer stainless steel). As a result, the yellowfin tuna fillet did not break and pieces of sashimi were successfully cut out. In addition, the yellowfin tuna that had been cooled in the same manner as in Comparative Example 1 was taken out of the refrigerator at -14°C and immediately tried to cut with a knife in the same manner as in Example 1. However, the blade could not be inserted into the fence by hand, and cutting was not possible. Furthermore, even when an attempt was made to cut the fence, the fence broke and it was not possible to cut it into sashimi pieces.

[0039] <Quality evaluation: beef block> The percentage change in perimeter was calculated for the cooled objects (beef blocks) obtained in Example 2 and Comparative Example 2. After cooling to -20°C, the perimeter of the beef block in Example 2 was 100% of the perimeter before the experiment, i.e., unchanged. On the other hand, the perimeter of the beef block in Comparative Example 2 was 106.25% of the perimeter before the experiment. These results suggest that the cooling method of the present invention suppressed the formation of large ice crystals inside the food.

[0040] <Quality Evaluation: Strawberry> The cooled objects (strawberries) obtained in Example 3 and Comparative Example 3 were placed on a porcelain plate and allowed to thaw naturally for 60 minutes at a temperature of 14°C, and the presence or absence of dripping was evaluated. In the strawberries treated in Comparative Example 3, dripping occurred at the area where the object was in contact with the plate, and the shape was beginning to collapse, but in the strawberries treated in Example 3, no dripping was visible. Furthermore, when each of the strawberries for which drip observation had been performed was cut, the strawberries of Comparative Example 3 were cut but lost their shape, whereas the strawberries of Example 3 retained their shape even after cutting and had excellent shape retention.

[0041] From the results of the above Examples and Comparative Examples, it can be seen that in Examples 1 to 3 in which the cooling step of the present invention was carried out, cooled products of excellent quality were obtained. [Industrial Applicability]

[0042] According to the present invention, it is possible to provide a novel method for cooling a water-containing material.

Claims

1. A cooling method for a water-containing object, comprising: A basic cooling step is carried out in which the object is kept at a temperature range of -1.0°C or more and -0.1°C or less and cooled so that the entire object is in a temperature equilibrium state, and then A preservation cooling step is carried out in which less than 1% of the cold air circulated in the refrigerator in which the object is placed is sent to the object side, and the temperature at the center of the object is lowered before the temperature at the surface of the object in at least a part of the temperature range of -5.0°C or higher and -1.0°C or lower. Cooling method.

2. The cooling method according to claim 1, further comprising preventing stagnation of temperature drop at least at the central portion of the object in the temperature range of −3.0° C. or higher and −1.0° C. or lower in the preservation cooling step.

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