CN115428823A - A step-by-step adjustment magnetic field-assisted quick-freezing and fresh-keeping method and device - Google Patents

Abstract

The invention provides a quick-freezing preservation method assisted by regulating a magnetic field step by step, which comprises the following steps: food preservation is divided into three stages: in the first stage, food is placed in a fresh-keeping device and cooled to a first critical value, and a first magnetic field is applied; the second stage is to apply a second magnetic field to lower the temperature of the food to a second threshold value at the first magnetic field strength; the third stage is that the food is cooled to a third critical value under the condition of the second magnetic field intensity; the first magnetic field is a static magnetic field, the second magnetic field is an alternating magnetic field, and the first magnetic field intensity is greater than the second magnetic field intensity. The invention carries out three-stage cooling on food, wherein the first stage is that the food is naturally frozen to a set temperature in the preservation device, the second stage and the third stage are added with magnetic fields with different strengths, the second stage is that water molecules are dispersed, so that ice crystals form small individuals in the later stage, and the third stage is that water rapidly passes through a crystallization zone, so that the formation of a part of ice crystals can be inhibited.

Description

A step-by-step adjustment magnetic field-assisted quick-freezing and fresh-keeping method and device

technical field

The invention relates to the technical field of freezing and fresh-keeping, and more specifically relates to a step-by-step magnetic field-assisted quick-freezing and fresh-keeping method and device.

Background technique

Frozen preservation generally refers to facilities that are refrigerated by certain equipment and can be artificially controlled and maintained at a stable low temperature. It is widely used in food preservation and other fields. There are many methods for assisting food freezing by combining external physical methods, such as electric field assisting method, magnetic field assisting method, overpressure assisting method, radiation assisting method, pulse assisting method, light assisting method, film assisting method, etc. Among them, the technology of magnetic field-assisted fresh-keeping is an emerging fresh-keeping method in recent years. It has the advantages of simple operation, low implementation cost, non-toxic and harmless, no environmental pollution, and little impact on the quality characteristics of the food itself.

At present, the time and intensity of magnetic field-assisted freezing treatment are closely related to the effect of food preservation. If the magnetic field treatment is not enough, the beneficial effect will not be achieved, or if the treatment is excessive, it may even have a negative effect. Usually, when samples are frozen in a refrigerator or cold storage, the cooling efficiency of the system is low, and the sample stays in the "maximum ice crystal formation zone" for too long, and it is easy to form larger ice crystals with uneven distribution, resulting in too large ice crystals to puncture the cell membrane and cell wall, and tissue structure. Due to mechanical damage, a large amount of water will be lost after the sample is thawed, the cells cannot be restored to the original state, and the quality of the sample after thawing is seriously reduced.

The magnetic field has a great influence on the formation of ice crystals during the freezing process and has been reported. For example, studies have found that under the action of a magnetic field, the dipole moment of the transition and vibration state of water molecules changes, and the surface tension, viscosity, rheological properties, refractive index, dielectric constant, and conductivity of water change. Under the action of different magnetic fields, such as rotating magnetic field, pulsed magnetic field, and alternating magnetic field, the low-frequency alternating magnetic field has a greater impact on the freezing and crystallization of NaCl solution, and this magnetic field has a significant inhibitory effect on the formation of ice crystals during the phase transition process of its solution. .

At present, during the working process of magnetic field-assisted freezing processing equipment, the magnetic field participates in the freezing process of food throughout the process. Compared with the case without magnetic field participation, it can reduce ice crystals, but it still does not achieve the best fresh-keeping effect.

For example, the invention patent with publication number CN105486017B discloses a low-temperature freezing device based on a magnetic field and a food freezing method thereof. The present invention discloses a low-temperature freezing device based on a magnetic field, including a low-temperature chamber and related freezing equipment. Wherein, the cryogenic freezer also includes a magnetic field generating device, the magnetic field generating device includes a first magnetic field generating unit that generates a steady magnetic field and a second magnetic field generating unit that generates an alternating magnetic field; the first magnetic field generating unit and The second magnetic field generating unit is correspondingly arranged so that the steady-state magnetic field and the alternating magnetic field form a predetermined angle to generate a preset composite spatial magnetic field in the low-temperature chamber. By setting alternating magnetic fields and steady-state magnetic fields interlaced at predetermined angles, a corresponding composite space magnetic field is formed in the low-temperature chamber, so that the water in the water-containing food maintains the original distribution state during the freezing process, avoiding the redistribution and loss of water. It can better maintain the freshness of food before freezing. The invention mainly solves the problem of water loss and redistribution of water-containing food caused by freezing technology during the refrigeration and thawing process. But how to optimize the magnetic freezing process to better suppress the formation of ice crystals, there is currently no definite solution.

Contents of the invention

The technical problem to be solved by the present invention is how to suppress the formation of ice crystals during food refrigeration.

The present invention realizes solving above-mentioned technical problem by following technical means:

A step-by-step magnetic field-assisted quick-freezing preservation method comprises the following steps:

Food preservation is divided into three stages:

In the first stage, the food is placed in the fresh-keeping device to cool down to the first critical value and the first magnetic field is applied;

The second stage is to apply a second magnetic field to reduce the temperature of the food to a second critical value under the condition of the first magnetic field strength;

The third stage is to cool the food down to a third critical value under the second magnetic field strength;

The first magnetic field is a static magnetic field, the second magnetic field is an alternating magnetic field, and the strength of the first magnetic field is greater than that of the second magnetic field.

The invention lowers the temperature of the food in three stages. The first stage is that the food is naturally frozen to the set temperature in the fresh-keeping device. The second stage and the third stage add magnetic fields of different strengths. The second stage is to let the water particles disperse. , so that the individual ice crystals formed in the later stage are small, and the water quickly passes through the crystallization zone in the third stage, which can inhibit the formation of part of the ice crystals.

Further, the first critical value is that the central temperature of the food is 4°C; the first magnetic field strength of the fruit food is 200-600Gs; the second critical value is that the central temperature of the food is 0°C; the second magnetic field strength is 20-600Gs. 60Gs, frequency 50Hz; the third critical value is the core temperature of the food is -5°C; select the corresponding freezing rate according to the volume of the fruit in the first magnetic field environment and the second magnetic field environment.

Further, the first critical value is that the central temperature of food is 4°C; the first magnetic field strength of meat food is 600-800Gs, the second critical value is that the central temperature of food is 0°C; the second magnetic field strength is 10-800Gs. 50Gs, frequency 50Hz; the third critical value is the core temperature of the food is -5°C; select the corresponding freezing rate according to the volume of the fruit in the first magnetic field environment and the second magnetic field environment.

Furthermore, fruits are frozen in an environment of -40 to -30°C.

Further, the meat is frozen in an environment of -50 to -40°C.

The present invention also provides an adjustable magnetic field assisted quick-freezing and fresh-keeping device, which is applied to the above method. The fresh-keeping device includes a quick-freezing chamber (1), and two pairs of magnetic coils are fixed horizontally and vertically in the quick-freezing chamber (1); a tray (7) is installed on the bottom wall of the quick-freezing chamber (1), and The tray is located in the magnetic action area formed by two pairs of magnetic coils. The tray (7) is provided with a plurality of placement cavities, and the food is placed on the tray (7) corresponding to the placement cavities to obtain the approximate volume of the food.

Further, the fresh-keeping device also includes a control box; the control box is provided with a food type selection knob and a plurality of freezing gear knobs; a controller is arranged in the control box; the controller controls the food according to the selected food type and freezing gear. The application intensity and application time of the two pairs of magnetic force coils.

Further, the two opposite side walls of the inner cavity of the quick-freezing chamber (1) are respectively equipped with first excitation coils (2), and the two first excitation coils (2) are arranged oppositely; the inner chamber of the quick-freezing chamber (1) A second excitation coil (3) is installed on the top wall, an integrated board (4) is fixedly connected to the inner bottom of the quick-freezing chamber (1), and a third excitation coil (5) is fixedly connected to the upper end of the integrated board (4). The upper end of the integrated board (4) is rotatably connected with a rotating shaft (6), the rotating shaft (6) passes through the center of the third excitation coil (5), and the upper end of the rotating shaft (6) is fixedly connected with a tray (7); The first exciting coil (2), the second exciting coil (3) and the third exciting coil (5) are all electrically connected to the integration board (4).

Further, a motor chamber (9) is also provided below the quick-freezing chamber (1), and a motor is placed in the motor chamber (9), and the output end of the motor is connected to the rotating shaft to drive the rotating shaft to rotate .

Further, the first exciting coil (2) and the second exciting coil (3) include a coil support (13) and a surrounding electric coil (14), and the outer end of the surrounding electric coil (14) is wrapped with a waterproof adhesive layer ( 15), the coil support (13) is fixedly connected to the inner wall of the quick-freezing chamber (1), the surrounding electric coil (14) is fixedly connected to the outer end of the coil support (13), and is electrically connected to the integrated board (4).

The advantages of the present invention are:

The invention lowers the temperature of the food in three stages. The first stage is that the food is naturally frozen to the set temperature in the fresh-keeping device. The second stage and the third stage add magnetic fields of different strengths. The second stage is to let the water particles disperse. , so that the individual ice crystals formed in the later stage are small, and the water quickly passes through the crystallization zone in the third stage, which can inhibit the formation of part of the ice crystals.

Divide food into two categories: fruit and meat, and you can achieve the best frozen and fresh-keeping effect of food by selecting the corresponding mode.

The present invention can arbitrarily control the direction and size of the magnetic field generated by the first excitation coil, the second excitation coil, and the third excitation coil to meet the requirements of suitable parameters for different types of food, and any number of them can be turned on or off during use. This combined method makes a multi-dimensional magnetic field space generated in the center of the quick-freezing chamber.

By setting the rotating shaft and the tray, when the items are subjected to magnetic field-assisted freezing, the items can be subjected to a uniform magnetic field with the rotation of the tray, so that the items can be frozen to produce fine and uniform ice crystals. In particular, the tray is designed as a structure with multiple placement cavities, and the corresponding placement cavities can be selected according to the size of the food, so that the corresponding control mode can be selected to achieve the best freezing effect.

Description of drawings

1 is a three-dimensional schematic diagram of the overall structure of an adjustable magnetic field-assisted quick-freezing and fresh-keeping device in an embodiment of the present invention;

2 is a three-dimensional schematic diagram of the internal structure of an adjustable magnetic field-assisted quick-freezing and fresh-keeping device in an embodiment of the present invention;

3 is a schematic structural diagram of an excitation coil of an adjustable magnetic field-assisted quick-freezing and fresh-keeping device in an embodiment of the present invention;

Fig. 4 is a comparison diagram of experimental effects of small tomatoes in Example 1 of the present invention, the left side is the appearance and intracellular ice crystal effect after thawing without a magnetic field, and the right side is the appearance and intracellular ice crystal effect after thawing with a magnetic field;

Fig. 5 is a comparison diagram of the experimental effect of pork in Example 4 of the present invention. The left side shows the appearance and intracellular ice crystal effect after thawing without a magnetic field, and the right side shows the appearance and intracellular ice crystal effect after thawing with a magnetic field.

detailed description

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the present invention Examples, not all examples. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

Please refer to Figure 1-3, an adjustable magnetic field assisted quick-freezing and fresh-keeping device, including a quick-freezing chamber 1, a pair of first excitation coils 2 are installed in the inner cavity of the quick-freezing chamber 1, and a second excitation coil 2 is installed on the inner top of the quick-freezing chamber 1. The excitation coil 3 is fixedly connected to the integrated board 4 at the bottom of the quick-freezing chamber 1. The integrated board 4 is located on the lower side of a pair of first excitation coils 2. The upper end of the integrated board 4 is fixedly connected to the third excitation coil 5. The upper end of the integrated board 4 is rotatably connected. There is a rotating shaft 6, the third exciting coil 5 is located outside the rotating shaft 6, the upper end of the rotating shaft 6 is fixedly connected with a tray 7, the tray 7 is located between a pair of first exciting coils 2 and the lower side of the second exciting coil 3, and the electric circuit on the right side of the quick-freezing chamber 1 A control box 8 is connected, and a motor cavity 9 is arranged below the quick-freezing chamber 1. The front end of the quick-freezing chamber 1 is rotatably connected to a door 10, and a digital display screen 11 is installed at the front end of the door 10. The polarity and the excitation strength of the second excitation coil 3 and the third excitation coil 5 are adjusted in multiple ways, so that in the quick-freezing chamber 1, the size, distribution and direction of the magnetic field that can be changed arbitrarily are generated, so that the induced organisms include various types of food, water, etc. Products, fruits and vegetables, agricultural products and fresh meat appear fine ice crystals during the freezing process to avoid mechanical damage to cells caused by large ice crystals. After thawing, the sample juice loss is reduced and the quality is better.

Please refer to Fig. 1, 3, a pair of first exciting coil 2 and second exciting coil 3 comprise coil support 13, surrounding electric coil 14, surrounding electric coil 14 outer ends are wrapped with waterproof adhesive layer 15, coil support 13 and quick-freezing chamber 1 The inner wall of the surrounding electric coil 14 is fixedly connected to the outer end of the coil support 13, and is electrically connected to the integrated board 4. The third excitation coil 5 includes the coil support 13 and the surrounding electric coil 14, and is electrically connected to the integrated board 4. By setting the first One excitation coil 2, the second excitation coil 3, and the third excitation coil 5 can be turned on or off in use, and any number of them can be turned on or off, so that a multi-dimensional magnetic field space is generated at the center of the quick-freezing chamber 1 in a variety of combinations. By setting the waterproof adhesive layer 15, the waterproof adhesive layer 15 protects the electric current that is energized around the electric coil 14 from being exposed, and at the same time prevents the condensed water in the quick-freezing chamber 1 from affecting the surrounding electric coil 14 during the freezing process.

Please refer to Figures 1 and 2, the rotating shaft 6 is electrically connected to the motor, and a sealing rubber ring 16 is installed at the connection with the inner bottom of the quick-freezing chamber 1. By setting the rotating shaft 6 and the tray 7, when the magnetic field assisted freezing is carried out to the items, the items follow the The rotation of the tray 7 can be subjected to a uniform magnetic field to realize the freezing of the items to produce fine and uniform ice crystals. By setting the sealing rubber ring 15, the cold air in the quick-freezing chamber 1 is prevented from flowing out, and at the same time, the juice and condensed water of the items are prevented from seeping down and affecting the normal operation of the motor. Work.

Please refer to Fig. 1, 2, the rotary switch 12, the gear knob 17 of a plurality of stalls are installed on the control box 8, and the rotary switch 12 has different food types options, and the gear knob 17 can select different freezing rates according to the volume. A controller is provided in the control box 8, and the controller is electrically connected with the integrated board to control the power supply of the excitation coil. Through the controller, the first excitation coil 2, the second excitation coil 3, and the third excitation coil 5 can be arbitrarily controlled to generate The direction and size of the magnetic field to meet the appropriate parameter requirements of different types of food.

In this embodiment, the tray 7 is provided with a plurality of placement chambers representing different volumes, and an appropriate placement chamber is selected according to the size of the food currently to be frozen, and each placement chamber corresponds to a knob level of a freezing rate. According to the currently selected placement cavity, turn the knob to the corresponding position, then the controller can control the magnetic field application time and freezing rate according to the current selection.

Please refer to Figure 1, the control temperature of the quick-freezing chamber 1 is between -30 and -50°C. By setting the temperature in the quick-freezing chamber 1, the temperature can be adjusted between -30 and -50°C, so that various items can be adapted to different temperatures during freezing. Freshness needs.

In the present invention, first open the door 10, put the food that needs to be kept fresh on the tray 7 in the quick-freezing chamber 1, then close the door 10, start the motor, the rotating shaft 6 drives the tray 7 to start rotating, and turn the knob switch 12 to adjust to Appropriate freezing temperature, then start the control box 8, adjust the current and voltage of the control box 8 according to the appropriate magnetic field size and combination mode required by the actual parameters, and transmit the electrical signal to each excitation coil through the integrated board 6 to achieve the appropriate magnetic field parameters. Quick freezing chamber 1 The magnetic field inside starts to assist food freezing and fresh-keeping until the freezing is finished at an appropriate time. All temperature, time and magnetic field parameters are transmitted to the digital display screen 11 through the integrated board 6 for display. Compared with the prior art, this scheme can Realize by carrying out multiple adjustments to the polarity and excitation strength of the first excitation coil 2, the second excitation coil 3 and the third excitation coil 5, so that the size, distribution and direction of the magnetic field that can be changed arbitrarily in the quick-freezing chamber 1 are generated, In order to induce organisms including various foods, aquatic products, fruits and vegetables, agricultural products and fresh meat to appear fine ice crystals during the freezing process, avoid mechanical damage to cells caused by large ice crystals, reduce the loss of sample juice after thawing, and have better quality.

The method of using the above-mentioned fresh-keeping device to freeze food is as follows:

Example 1

The method of freezing and freshing small tomatoes is as follows:

A small tomato with a volume of about (2.5×2×2) cm ³ is placed in the cavity corresponding to the tray on which the fresh-keeping device is placed, and the corresponding magnetic field strength and freezing rate are selected through the knob to activate the fresh-keeping device. It takes about 24 minutes to cool down to the center temperature of the small tomatoes at -30°C to 4°C. Then, during the process from 4°C to 0°C, the first magnetic field is applied, the first magnetic field is a static magnetic field, the strength is 200Gs, the application time is 6 minutes, and the freezing rate is 0.67°C/min; finally, during the process from 0°C to -5°C A second magnetic field is applied, the second magnetic field is an alternating magnetic field, the intensity is 20Gs, the frequency is 50Hz, the application time is 8 minutes, and the freezing rate is 0.63° C./min. The magnetic field was withdrawn after the tomato reached -5°C.

The small tomatoes frozen according to the above method were taken out and thawed naturally at room temperature at 25°C for 15 minutes to test their water loss rate and compare with the control sample without applying two stages of magnetic field. It was found that the cooling time of the small tomatoes assisted by two magnetic fields and those frozen without the magnetic field was shortened by 1.12 minutes, and the water loss rates of the samples after thawing were 7.06% and 39.28%, respectively, and the frozen tomatoes were frozen without the magnetic field. After thawing, the skin of the small tomatoes shrank significantly, and the pulp was soft and collapsed. As shown in Figure 4, the left side of Figure 4 shows the appearance and intracellular ice crystal effect after thawing without a magnetic field, and the right side shows the appearance and intracellular ice crystal effect after thawing with a magnetic field;

Example 2

A small tomato with a volume of about (2.5×2×2) cm ³ is placed in the cavity corresponding to the tray on which the fresh-keeping device is placed, and the corresponding magnetic field strength and freezing rate are selected through the knob to activate the fresh-keeping device. It takes about 24 minutes to cool down to the center temperature of the small tomatoes at -30°C to 4°C. Then, during the process from 4°C to 0°C, the first magnetic field is applied, the first magnetic field is a static magnetic field, the strength is 300Gs, the application time is 6 minutes, and the freezing rate is 0.67°C/min; finally, during the process from 0°C to -5°C The second magnetic field is applied, the second magnetic field is an alternating magnetic field, the intensity is 40Gs, the frequency is 50Hz, the application time is 8 minutes, and the freezing rate is 0.63° C./min. The magnetic field was withdrawn after the tomato reached -5°C.

The small tomatoes frozen according to the above method were taken out and thawed naturally at room temperature at 25°C for 15 minutes to test their water loss rate and compare with the control sample without applying two stages of magnetic field. It was found that the cooling time of the small tomatoes assisted by two magnetic fields and those frozen without the magnetic field was shortened by 1.74 minutes, and the water loss rates of the samples after thawing were 5.39% and 39.28%, respectively, and the frozen tomatoes were frozen without the magnetic field. After thawing, the skin of the small tomatoes shrank significantly, and the pulp was soft and collapsed.

Example 3

A small tomato with a volume of about (2.5×2×2) cm ³ is placed in the cavity corresponding to the tray on which the fresh-keeping device is placed, and the corresponding magnetic field strength and freezing rate are selected through the knob to activate the fresh-keeping device. It takes about 24 minutes to cool down to the center temperature of the small tomatoes at -30°C to 4°C. Then, in the process of dropping from 4°C to 0°C, apply the first magnetic field, the first magnetic field is a static magnetic field, the strength is 400Gs, the application time is 6 minutes, and the freezing rate is 0.67°C/min; finally, in the process from 0°C to -5°C The second magnetic field is applied, the second magnetic field is an alternating magnetic field, the intensity is 60Gs, the frequency is 50Hz, the application time is 8 minutes, and the freezing rate is 0.63° C./min. The magnetic field was withdrawn after the tomato reached -5°C.

The small tomatoes frozen according to the above method were taken out and thawed naturally at room temperature at 25°C for 15 minutes to test their water loss rate and compare with the control sample without applying two stages of magnetic field. It was found that the cooling time of the tomatoes assisted by two magnetic fields and those frozen without the magnetic field was shortened by 1.04 minutes. After thawing, the skin of the small tomatoes shrank significantly, and the pulp was soft and collapsed.

Example 4

The method of freezing and keeping fresh apples is as follows:

An apple with a volume of about (8×8×6.5) cm ³ is placed in the cavity corresponding to the tray on which the fresh-keeping device is placed, and the corresponding magnetic field strength and freezing rate are selected through the knob to activate the fresh-keeping device. It takes about 35 minutes to cool down to the core temperature of the apples at -40°C to 4°C. Then, in the process of dropping from 4°C to 0°C, apply the first magnetic field, the first magnetic field is a static magnetic field, the strength is 400Gs, the application time is 8 minutes, and the freezing rate is 0.50°C/min; finally, in the process from 0°C to -5°C The second magnetic field is applied, the second magnetic field is an alternating magnetic field, the intensity is 20Gs, the frequency is 50Hz, the application time is 12 minutes, and the freezing rate is 0.42° C./min. The magnetic field was withdrawn after the apple reached -5°C.

The apples frozen according to the above method were taken out and thawed naturally at room temperature 25°C for 25 minutes to test their water loss rate and compare with the control sample without applying two magnetic fields. The results showed that the cooling time of the apples assisted by two magnetic fields and the apples frozen without applying the magnetic field was shortened by 1.07 minutes, and the water loss rate of the samples after thawing was 2.12% and 5.48%, respectively, and the apples frozen without applying the magnetic field Significant epidermal shrinkage and loss of firmness after thawing.

Example 5

An apple, with a volume of about (8×8×6.5) cm3, is placed in the tray corresponding to the fresh-keeping device in the cavity, and the corresponding magnetic field strength and freezing rate are selected through the knob to start the fresh-keeping device. It takes about 35 minutes to cool down to the core temperature of the apples at -40°C to 4°C. Then, in the process of dropping from 4°C to 0°C, apply the first magnetic field, the first magnetic field is a static magnetic field, the strength is 500Gs, the application time is 8 minutes, and the freezing rate is 0.50°C/min; finally, in the process from 0°C to -5°C A second magnetic field is applied, the second magnetic field is an alternating magnetic field, the intensity is 25Gs, the frequency is 50Hz, the application time is 12 minutes, and the freezing rate is 0.42° C./min. The magnetic field was withdrawn after the apple reached -5°C.

The apples frozen according to the above method were taken out and thawed naturally at room temperature 25°C for 25 minutes to test their water loss rate and compare with the control sample without applying two magnetic fields. It was found that the cooling time of apples assisted by two magnetic fields and apples frozen without applying the magnetic field was shortened by 1.36 minutes, and the water loss rates of the samples after thawing were 1.97% and 5.48%, respectively, and the apples frozen without applying the magnetic field Significant epidermal shrinkage and loss of firmness after thawing.

Example 6

A peach, with a volume of about (7×6.5×6.5) cm3, is placed in the tray corresponding to the fresh-keeping device in the cavity, and the corresponding magnetic field strength and freezing rate are selected through the knob to activate the fresh-keeping device. It takes about 35 minutes to lower the temperature to the center temperature of the peaches at -35°C to 4°C. Then, in the process of dropping from 4°C to 0°C, apply the first magnetic field, the first magnetic field is a static magnetic field, the strength is 600Gs, the application time is 8 minutes, and the freezing rate is 0.50°C/min; finally, in the process from 0°C to -5°C The second magnetic field is applied, the second magnetic field is an alternating magnetic field, the intensity is 30Gs, the frequency is 50Hz, the application time is 12 minutes, and the freezing rate is 0.42° C./min. The magnetic field was withdrawn after the peaches reached -5°C.

The peaches frozen according to the above method were taken out and thawed naturally at room temperature 25°C for 25 minutes to test their water loss rate and compare with the control sample without applying two magnetic fields. It was found that the cooling time of the peaches assisted by two magnetic fields and the peaches frozen without applying the magnetic field was shortened by 1.14 minutes, and the water loss rates of the samples after thawing were 2.45% and 6.67%, respectively, and the peaches frozen without applying the magnetic field Significant epidermal shrinkage and loss of firmness after thawing.

Example 7

For pork (5×5×8) cm ³ , the tray on which the fresh-keeping device is placed corresponds to the cavity, and the corresponding magnetic field strength and freezing rate are selected through the knob, and the fresh-keeping device is activated. It takes about 29 minutes to cool down to the center temperature of the pork at -50°C to 4°C, and then apply the first magnetic field during the process of dropping from 4°C to 0°C. The first magnetic field is a static magnetic field with a strength of 600Gs. The time is 6 minutes, the freezing rate is 0.67°C/min; finally, the second magnetic field is applied from 0°C to -5°C, the second magnetic field is an alternating magnetic field, the intensity is 10Gs, the frequency is 50Hz, the application time is 10 minutes, the freezing rate 0.5°C/min. Remove the magnetic field after the pork reaches -5°C.

The pork frozen according to the above method was then taken out and thawed naturally at room temperature 25° C. for 30 minutes to test its water loss rate and compare it with the control sample without applying two stages of magnetic field. It was found that the cooling time of the pork frozen with the assistance of two magnetic fields and the pork frozen without applying the magnetic field was shortened by 1.97 minutes, and the water loss rate of the sample after thawing was 3.12% and 12.74%, respectively, and the pork frozen without applying the magnetic field Significant color deepening after thawing. As shown in Figure 5, the left side of Figure 5 shows the appearance and intracellular ice crystal effect after thawing without a magnetic field, and the right side shows the appearance and intracellular ice crystal effect after thawing with a magnetic field;

Example 8

For pork (5×5×4) cm ³ , the tray on which the fresh-keeping device is placed corresponds to the cavity, and the corresponding magnetic field strength and freezing rate are selected through the knob, and the fresh-keeping device is activated. It takes about 29 minutes to cool down to the center temperature of the pork at -45°C to 4°C, and then apply the first magnetic field during the process of dropping from 4°C to 0°C. The first magnetic field is a static magnetic field with a strength of 600Gs. The time is 6 minutes, the freezing rate is 0.67°C/min; finally, the second magnetic field is applied from 0°C to -5°C, the second magnetic field is an alternating magnetic field, the intensity is 10Gs, the frequency is 50Hz, the application time is 10 minutes, the freezing rate 0.5°C/min. Remove the magnetic field after the pork reaches -5°C.

The pork frozen according to the above method was then taken out and thawed naturally at room temperature 25° C. for 30 minutes to test its water loss rate and compare it with the control sample without applying two stages of magnetic field. It was found that the cooling time of the pork frozen with the assistance of two magnetic fields and the pork frozen without applying the magnetic field was shortened by 1.97 minutes, and the water loss rate of the sample after thawing was 3.12% and 12.74%, respectively, and the pork frozen without applying the magnetic field Significant color deepening after thawing. As shown in Figure 5, the left side of Figure 5 shows the appearance and intracellular ice crystal effect after thawing without a magnetic field, and the right side shows the appearance and intracellular ice crystal effect after thawing with a magnetic field;

Example 9

For shrimps (1×1.5×8) cm ³ , the tray on which the fresh-keeping device is placed corresponds to the cavity, and the corresponding magnetic field strength and freezing rate are selected through the knob to start the fresh-keeping device. It takes about 29 minutes to cool down to the central temperature of the shrimp at -40°C to 4°C, and then apply the first magnetic field during the process of dropping from 4°C to 0°C. The first magnetic field is a static magnetic field with a strength of 700Gs. The time is 6 minutes, the freezing rate is 0.67°C/min; finally, the second magnetic field is applied from 0°C to -5°C, the second magnetic field is an alternating magnetic field, the intensity is 30Gs, the frequency is 50Hz, the application time is 10 minutes, the freezing rate 0.5°C/min. The magnetic field was withdrawn after the shrimp reached -5°C.

The shrimps frozen according to the above method were then taken out and thawed naturally at room temperature 25°C for 20 minutes to test their water loss rate and compare with the control sample without applying a periodic magnetic field. The results showed that the cooling time of the shrimp frozen by two magnetic fields and the shrimp frozen without the magnetic field was shortened by 1.54 minutes, and the water loss rate of the samples after thawing was 4.76% and 10.43%, respectively.

In the above embodiment, the food is cooled in three stages. The first stage is that the food is naturally frozen to 4°C in the fresh-keeping device, and the second stage is that the first magnetic field is applied in the range of 4-0°C. For fruit, the first magnetic field is between 200Gs and 600Gs, and for meat, it is between 600Gs and 800Gs. The principle is that water molecules are connected by hydrogen bonds to form associated water molecules with a certain structure. While associating, the hydrogen bonds are broken and separated. Water molecules are always in this dynamic equilibrium process. This process requires energy. The thermal motion of water molecules is provided, and the magnetic field can provide Lorentz force, destroying the formation of hydrogen bonds, making the water molecules relatively discrete, and the effect is most obvious at 4°C to 0°C, and it saves the most energy consumption. The third stage is to apply the second magnetic field at 0°C to -5°C. For fruit, the magnetic field strength is 20-60Gs, and the frequency is 50H; for meat, the magnetic field strength is 10-50Gs, and the frequency is 50Hz. The principle is the maximum ice crystal formation zone: the temperature range in which a large number of ice crystals are formed in food is called the maximum ice crystal formation zone. Generally, the maximum ice crystal formation zone of food is 0～-5℃. It is generally believed that the central temperature of the food stays within the temperature range of the maximum ice crystal formation zone for no more than 30 minutes, which meets the requirements of rapid freezing. The magnetic field can affect electrons to accelerate the spin of water molecules, so that the heat exchange rate can be accelerated, and it can quickly pass through the maximum ice crystal formation zone, reducing the formation of ice crystals. To sum up, the second stage is to let the water particles disperse, so that the individual ice crystals formed in the later stage are small, and the third stage water passes through the crystallization zone quickly, which can inhibit the formation of part of the ice crystals.

In the above embodiments, since the fruit has a large water content, the free hydrothermal motion is relatively severe, and a relatively low magnetic field strength can have a relatively large impact. Meat has more bound water, less free water, and the movement of free water is relatively stable, so it needs a stronger magnetic field to drive, so the first magnetic field strength of fruits is smaller than that of meat. When the internal temperature of the fruit drops below 0 degrees, the free water in the fruit gradually forms ice crystals, and the magnetic field can inhibit the formation of crystal nuclei. The fruit has a large water content and forms more crystal nuclei than meat, so the second The magnetic field strength of fruits is greater than that of meat.

The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be described in the foregoing embodiments Modifications are made to the recorded technical solutions, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. A quick-freezing preservation method assisted by step-by-step magnetic field adjustment is characterized by comprising the following steps:

the food preservation is divided into three stages:

in the first stage, the food is cooled to a first critical value and a first magnetic field is applied;

the second stage is to apply a second magnetic field to lower the temperature of the food to a second threshold value at the first magnetic field strength;

the third stage is that the food is cooled to a third critical value under the condition of the second magnetic field intensity;

the first magnetic field is a static magnetic field, the second magnetic field is an alternating magnetic field, and the first magnetic field intensity is greater than the second magnetic field intensity.

2. The quick-freezing preservation method assisted by a step-by-step magnetic field as claimed in claim 1, wherein the first critical value is that the temperature of the center of the food is 4 ℃; the first magnetic field intensity of the fruit food is 200-600 Gs, and the second critical value is that the central temperature of the food is 0 ℃; the second magnetic field intensity is 20-60 Gs, and the frequency is 50Hz; the third critical value is that the center temperature of the food is-5 ℃; and selecting corresponding freezing rates according to the volumes of the fruits in the first magnetic field environment and the second magnetic field environment.

3. The quick-freezing preservation method assisted by a step-by-step magnetic field as claimed in claim 1, wherein the first critical value is that the temperature of the center of the food is 4 ℃; the first magnetic field intensity of meat food is 600-800 Gs, and the second critical value is that the central temperature of the food is 0 ℃; the second magnetic field intensity is 10-50 Gs, and the frequency is 50Hz; the third critical value is that the center temperature of the food is-5 ℃; and selecting corresponding freezing rates according to the volumes of the fruits in the first magnetic field environment and the second magnetic field environment.

4. The quick-freezing preservation method assisted by a step-by-step magnetic field as claimed in claim 2, wherein the fruits are frozen in an environment of-40 to-30 ℃.

5. The quick-freezing preservation method assisted by a step-by-step magnetic field as claimed in claim 3, wherein the meat is frozen at-50 to-40 ℃.

6. A quick-freezing fresh-keeping device assisted by step-by-step adjustment of a magnetic field is applied to the method as claimed in any one of claims 1 to 5, and is characterized by comprising a quick-freezing chamber (1), wherein two pairs of horizontal and vertical magnetic coils are fixed in the quick-freezing chamber (1); the bottom wall of the quick freezing chamber (1) is rotatably provided with a tray (7), the tray is positioned in a magnetic action area surrounded by two pairs of magnetic force lines, the tray (7) is provided with a plurality of placing cavities, and food is placed on the tray (7) and correspondingly placed in the cavities to obtain the approximate volume of the food.

7. The adjustable magnetic field assisted quick-freezing preservation device as claimed in claim 6, wherein the preservation device further comprises a control box; the control box is provided with a food type selection knob and a plurality of freezing gear knobs; a controller is arranged in the control box; the controller controls the application intensity and application time of the two pairs of magnetic coils according to the selected food kind and the freezing gear.

8. An adjustable magnetic field assisted quick-freezing and fresh-keeping device as claimed in claim 6, wherein two opposite side walls of the inner cavity of the quick-freezing chamber (1) are respectively provided with a first excitation coil (2), and the two first excitation coils (2) are oppositely arranged; a second excitation coil (3) is installed on the inner top wall of the quick freezing chamber (1), an integrated plate (4) is fixedly connected to the inner bottom end of the quick freezing chamber (1), a third excitation coil (5) is fixedly connected to the upper end of the integrated plate (4), a rotating shaft (6) is rotatably connected to the upper end of the integrated plate (4), the rotating shaft (6) penetrates through the center of the third excitation coil (5), and a tray (7) is fixedly connected to the upper end of the rotating shaft (6); the first excitation coil (2), the second excitation coil (3) and the third excitation coil (5) are all electrically connected with the integrated board (4).

9. The quick-freezing and fresh-keeping device with the assistance of the adjustable magnetic field as claimed in claim 8 is characterized in that a motor cavity (9) is further arranged below the quick-freezing chamber (1), a motor is placed in the motor cavity (9), and the output end of the motor is in transmission connection with the rotating shaft to drive the rotating shaft to rotate.

10. The auxiliary quick-freezing and fresh-keeping device with the adjustable magnetic field as claimed in claim 5, wherein: first excitation coil (2) and second excitation coil (3) include coil brace (13), encircle electric coil (14), it has waterproof glue layer (15) to encircle electric coil (14) outer end parcel, the inner wall fixed connection of coil brace (13) and quick-freeze room (1), encircle electric coil (14) and coil brace (13) outer end fixed connection, be connected with integrated board (4) electricity.

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