Radio frequency auxiliary freezing system and freezing method thereof

Abstract

The invention discloses a radio frequency assisted freezing system which comprises a radio frequency generation module, a radio frequency processing module, a low-temperature freezing module and an optical fiber temperature measurement module, the radio frequency generation module can provide stable pulse radio frequency signals and comprises a radio frequency generator, a relay pulse generator and an impedance matcher, and the relay pulse generator and the impedance matcher are electrically connected with the radio frequency generator. The radio frequency processing module is used for providing a radio frequency action space for food and comprises a radio frequency processing device, the low-temperature freezing module can provide freezing cooling capacity for the system and comprises a low-temperature refrigerator, the impedance matcher and the radio frequency processing device are arranged in the low-temperature refrigerator, and the optical fiber temperature measuring module is arranged on the outer side of the low-temperature refrigerator; and the optical fiber temperature measurement module is used for accurately monitoring the food temperature. Through the synergistic effect of the radio frequency field and low-temperature freezing, the crystallization process of water molecules in the food can be effectively interfered, the food is promoted to generate an obvious supercooling phenomenon, a large number of ice nucleuses are formed at the temperature lower than the freezing point in an explosive mode finally, and the final quality of the frozen food is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of freezing and preservation technology, and in particular to a radio frequency assisted freezing system and its freezing method. Background Technology

[0002] Freezing is one of the most widely used preservation technologies in the food industry. By significantly reducing the rate of chemical reactions within food and inhibiting microbial metabolic activity, it can preserve the original flavor, nutritional value, and sensory quality of food to the greatest extent, providing a core guarantee for long-term storage and transportation. However, the final quality of frozen food is highly dependent on the crystallization behavior of water molecules during the freezing process, especially the size and distribution of ice crystals, which has become a key factor determining the quality of frozen food.

[0003] In traditional freezing technologies, slow freezing methods such as forced-air freezing and plate freezing, due to their gradual cooling rate, easily cause water inside food cells to gradually seep into the extracellular space, forming large ice crystals. These large ice crystals compress and damage the microstructure of food, such as muscle fiber bundle breakage and loss of cell membrane integrity, ultimately leading to severe juice loss after thawing, accompanied by problems such as hardening of texture and deterioration of flavor. To address this deficiency, rapid freezing technologies such as liquid nitrogen flash freezing have emerged. These technologies can simultaneously form small, uniform ice crystals inside and outside food cells through extremely rapid cooling rates, effectively protecting the microstructure of food and significantly improving frozen quality. However, liquid nitrogen is expensive as a refrigerant, and its drastic cooling process can easily create excessive temperature gradients inside food, causing cracking, which greatly limits the widespread application of this technology in large-scale industrial production. Therefore, how to reduce ice crystal size without increasing processing costs, or how to reduce freezing costs while ensuring ice crystal quality, has become a pressing technical challenge in the food freezing industry.

[0004] To overcome traditional technological bottlenecks, researchers have developed various novel assisted freezing technologies in recent years, including high-pressure assisted freezing, ultrasonic assisted freezing, electric field assisted freezing, magnetic field assisted freezing, microwave assisted freezing, and radio frequency assisted freezing. Among these, radio frequency assisted freezing technology has gradually become a research hotspot in the field due to its outstanding advantages such as strong penetration capability, low equipment investment cost, high energy utilization efficiency, and easy compatibility with automated batch production and continuous flow processing. Radio frequency refers to electromagnetic waves with frequencies between 3kHz and 300MHz, with 27.12MHz being the most widely used radio frequency frequency in the food processing field. The core principle of radio frequency assisted freezing is to apply a radio frequency field during the food freezing process. Through the polarization and vibration of water molecules in the food by the radio frequency field, the nucleation and growth process of ice crystals is interfered with, thereby refining the ice crystal size and improving the freezing quality. Existing studies have confirmed that, compared with liquid nitrogen freezing alone, pork samples treated with radio frequency assisted liquid nitrogen freezing showed significantly reduced ice crystal size, more intact microstructure, lower drip loss rate after thawing, and quality indicators such as texture and color that are closer to fresh meat, fully demonstrating the great potential of radio frequency assisted technology in the freezing and processing of livestock and poultry meat.

[0005] Despite the promising prospects of radio frequency (RF) assisted freezing technology, existing RF assisted freezing systems still suffer from several unresolved defects, severely hindering their industrial application: First, the choice of refrigeration source is inappropriate. Existing systems mostly rely on liquid nitrogen as the refrigeration medium, leading to high freezing costs and excessive temperature gradients that can damage food structure, compounding the inherent defects of traditional liquid nitrogen freezing. Second, the design of RF systems has shortcomings. Most mainstream equipment uses self-oscillating RF systems, which have low modularity, cannot achieve precise adjustment of output power, and have large fluctuations in operating frequency, making it difficult to form stable coordination with the freezing system and limiting the technology's adaptability. Third, the core technology effect has not been fully explored. Existing RF assisted freezing technology has not yet achieved a supercooling-promoting effect on food, presumably related to insufficient exploration of RF application parameters (such as power, pulse mode, and electric field strength). The absence of supercooling, a key step in refining ice crystals, means that the potential for quality improvement by RF technology has not been fully realized. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a radio frequency assisted freezing system that can solve the technical problems of existing radio frequency assisted freezing systems, such as high cost due to reliance on liquid nitrogen refrigeration, large temperature gradient that easily causes food cracking, low modularity of self-oscillating radio frequency systems, inaccurate power and frequency adjustment, and insufficient potential for quality improvement due to failure to achieve supercooling promotion. At the same time, the present invention also provides a radio frequency assisted freezing method, which is applied to the radio frequency assisted freezing system.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A radio frequency assisted refrigeration system includes a radio frequency generation module, a radio frequency processing module, a low-temperature refrigeration module, and a fiber optic temperature measurement module. The radio frequency (RF) generation module provides a stable pulsed RF signal. It includes an RF generator and a relay pulse generator and an impedance matching device electrically connected to it. The RF generator has an external control port and an output port. The external control port of the RF generator is electrically connected to the relay pulse generator, and the output port of the RF generator is electrically connected to the impedance matching device. The impedance matching device internally houses a vacuum variable capacitor and a fixed inductor. The radio frequency (RF) processing module is used to provide an RF operating space for food. It includes an RF processing device comprising a processing cavity, an upper aluminum electrode plate suspended and fixed inside the processing cavity, and a lower aluminum electrode plate positioned below the upper aluminum electrode plate via a lifting platform. An impedance matching device is electrically connected to the upper aluminum electrode plate through its signal output terminal, and is electrically connected to the lower aluminum electrode plate and grounded through its housing. The low-temperature freezing module provides freezing capacity to the system and includes a low-temperature freezer. The impedance matching device and radio frequency processing device are placed inside the low-temperature freezer, and an optical fiber temperature measurement module is installed on the outside of the low-temperature freezer. The optical fiber temperature measurement module is used to achieve accurate monitoring of food temperature. It includes a temperature measurement host and a display screen electrically connected to it, and an optical fiber temperature measurement probe. The temperature measuring end of the optical fiber temperature measurement probe extends into the processing cavity of the radio frequency processing device to be inserted into the geometric center of the food to be processed.

[0008] Furthermore, the RF generator is equipped with an output power display window, a reflection power display window, and a power adjustment knob; the external control port and the output port are integrated on the rear side of the RF generator, and the output port is electrically connected to an impedance matching device through a coaxial cable.

[0009] Furthermore, the relay pulse generator is set to a "10s on / 20s off" cycle mode. By precisely controlling the radio frequency duty cycle, the system heat generation is limited. It can dynamically adjust the switching cycle according to the food freezing stage, ensuring both the supercooling effect and avoiding food heating caused by continuous radio frequency, thus ensuring freezing quality.

[0010] Furthermore, the impedance matching device is provided with two vacuum variable capacitors and one fixed inductor. The two vacuum variable capacitors are connected in series at the input and output terminals of the impedance matching device, respectively, and the fixed inductor is connected in parallel between the two vacuum variable capacitors. The three form a π-type impedance matching circuit. Each vacuum variable capacitor is provided with an adjustment knob that can adjust its capacitance.

[0011] Furthermore, the processing chamber is made of stainless steel in a rectangular cavity structure with an opening on the front side for easy food handling. The upper aluminum electrode plate is made of high-purity aluminum and is suspended and fixed inside the processing chamber by an insulating bracket. The insulating bracket is rigidly connected to the side wall of the processing chamber by bolts. The upper aluminum electrode plate is electrically connected to the signal output terminal of the impedance matching device through a wire, serving as the receiving electrode for radio frequency signals. The lifting platform includes a bottom platform connected to the bottom surface of the lower aluminum electrode plate, a bracket at the top of the bottom platform, an adjustment handle through the bracket for adjusting the lifting of the bracket, and a top platform at the top of the bracket. The lower aluminum electrode plate is made of high-purity aluminum and is placed on the top platform of the lifting platform located at the center of the bottom surface of the processing chamber. By rotating the adjustment handle of the lifting platform, the height of the lower aluminum electrode plate can be freely adjusted, thereby controlling the distance between the upper and lower aluminum electrode plates. The lower aluminum electrode plate is electrically connected to the outer shell of the impedance matching device and is grounded together with the outer shell, serving as the grounding electrode for the radio frequency electric field.

[0012] Furthermore, the impedance matching device is fixed inside the low-temperature freezer and placed horizontally beside the radio frequency processing device to avoid mutual interference; the measuring end of the fiber optic temperature probe extends through the sealed interface provided by the low-temperature freezer into the processing chamber and is fixed to a polypropylene sample plate located at the center of the surface of the lower aluminum electrode plate. The food to be processed is placed on the surface of the polypropylene sample plate, and the measuring end of the fiber optic temperature probe is inserted into the geometric center of the food to ensure real-time monitoring of the core temperature inside the food. The monitoring data is processed by the temperature measuring host and displayed on the display screen in real time.

[0013] The core working principle of this invention to achieve the supercooling effect is as follows: A stable pulsed radio frequency signal is generated by a radio frequency generator, which is controlled by a relay pulse generator to a "10s on / 20s off" cyclic mode. When the output power of the radio frequency generator is set to 50W, the average power of the system is 16.7W. This pulse mode can avoid the heat generated by continuous radio frequency affecting the freezing rate. The radio frequency signal is transmitted losslessly between the upper and lower aluminum plates through an impedance matching device. The two vacuum variable capacitors and one fixed inductor inside the impedance matching device form a π-type impedance matching circuit. By adjusting the adjustment knob of the vacuum variable capacitor, the reflected power can be reduced to 0, ensuring lossless transmission of radio frequency energy, thereby forming a uniform high-frequency alternating electric field between the upper and lower aluminum plates. The food to be processed is placed on the surface of the polypropylene sample plate, in a synergistic environment of high-frequency alternating electric field and stable low temperature provided by the low-temperature freezer. The radio frequency field is polarized... The process of cooling food causes water molecules to vibrate at high frequencies, interfering with the crystallization process and slowing down the formation of initial ice crystals. Simultaneously, the continuous cooling of the freezer lowers the food temperature until it remains liquid even below its freezing point, creating a significant supercooling state. A fiber optic temperature sensor monitors the core temperature at the geometric center of the food in real time, providing accurate data for determining the supercooling point. The lifting platform of the radio frequency processing unit allows for adjustable electrode spacing from 2cm to 7cm, flexibly adjusting according to the food thickness to ensure the food remains within the core area of ​​the electric field, improving the uniformity of the supercooling effect. When the food temperature reaches the critical supercooling point, under the combined effect of continuous radio frequency field disturbance and the low-temperature environment, a large number of ice nuclei explosively form within the food. Compared to ordinary freezing, the size of the generated ice crystals is significantly smaller, effectively avoiding mechanical damage to food cells from large ice crystals and ultimately improving the quality of the frozen food.

[0014] The present invention also provides a radio frequency assisted freezing method, which is applied to the above-mentioned radio frequency assisted freezing system, and the specific steps include: Step S1: Preliminary Preparations Turn on the power of the low-temperature freezer and set its internal temperature to -30℃. Run it continuously for 30 minutes until the temperature stabilizes. Take a certain weight of the food to be processed and place it in the center of the polypropylene sample plate. Then insert the fiber optic temperature probe into the geometric center of the food to be processed, ensuring that the temperature measuring end is in close contact with the food. Finally, place the polypropylene sample plate stably on the upper surface of the lower aluminum plate. Step S2: Parameter Adjustment Depending on the thickness of the food to be processed, adjust the upper and lower aluminum plates to a suitable distance using the adjustment handle of the rotating lifting platform; turn on the relay pulse generator and set the pulse cycle mode to "10s on / 20s off"; turn on the radio frequency generator and set the output power to 50W using the power adjustment knob, at which point the average system power is 16.7W. Step S3: Impedance Matching and RF Startup Press the "Output" and "External Control" buttons of the RF generator in sequence. The relay pulse generator starts to control the pulse output of the RF signal. The signal is transmitted to the impedance matching device via cable. Slowly rotate the adjustment knob of the vacuum variable capacitor of the impedance matching device and observe the reflected power display window of the RF generator until the reflected power drops to 0, completing the impedance matching. At this time, the RF energy is transmitted without loss to form a high-frequency alternating electric field between the upper and lower aluminum plates. The food to be processed receives the RF field. Step S4: Freezing the food to be processed The core temperature change of the food to be processed is monitored in real time by the display screen of the fiber optic temperature measurement system. The food is rapidly cooled by the cold air in the low-temperature freezer and undergoes supercooling under the action of the radio frequency field, eventually completing the crystallization phase transition and achieving freezing. After a period of time, the power of all equipment is turned off, the food is taken out, and the entire freezing process is completed.

[0015] Compared with the prior art, the technical solution described in this invention has the following beneficial effects: 1. This invention utilizes the synergistic effect of radio frequency field and low-temperature freezing to effectively interfere with the crystallization process of water molecules in food, causing the food to undergo significant supercooling and ultimately resulting in the explosive formation of a large number of ice nuclei at temperatures below freezing point. Compared to ordinary freezing, the ice crystals generated by this invention are significantly smaller, effectively avoiding mechanical damage to food cells caused by large ice crystals, thereby reducing water loss during thawing, while maximizing the preservation of the food's textural properties, protecting the integrity of the food's microstructure, and significantly improving the final quality of frozen food. 2. This invention uses a 50Ω radio frequency system, which is more modular than a self-oscillating radio frequency system, making it easier to integrate and adapt with a freezing system; at the same time, the frequency is stable, and continuous power adjustment with a precision of 1W can be achieved through the power adjustment knob of the radio frequency generator, which can accurately match the needs of different types and sizes of food. 3. This invention uses radio frequency combined with low-temperature air freezing to provide a stable -30°C low-temperature environment with a low-temperature freezer, replacing expensive refrigerants such as liquid nitrogen and significantly reducing equipment operating costs; at the same time, it eliminates the need for complex refrigerant storage and transportation devices, making operation more convenient and safer, avoiding the potential risks of using refrigerants such as liquid nitrogen, and is more suitable for the needs of continuous industrial production. 4. The radio frequency processing device of this invention adopts a design with a fixed upper electrode plate and an adjustable lower electrode plate. The electrode plate spacing can be adjusted from 2cm to 7cm through the lifting platform, which can be flexibly adjusted according to the thickness of the food to ensure that the food is always in the core area of ​​the electric field and improve the uniformity of the supercooling effect. At the same time, the configured fiber optic temperature measurement system has the advantages of anti-electromagnetic interference and high temperature measurement accuracy. The fiber optic temperature measurement probe fixed on the polypropylene sample plate can monitor the core temperature of the geometric center of the food in real time, providing accurate data for judging the supercooling point and controlling the freezing endpoint, effectively avoiding over-freezing or under-freezing, and ensuring the stability of freezing quality. Other beneficial effects of this invention will be further explained in the following specific embodiments. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Figure 1 This is a schematic diagram of the radio frequency assisted refrigeration system described in this invention; Figure 2 This is a schematic diagram of the radio frequency processing device described in this invention; Figure 3 This is a side view of the lifting platform in the radio frequency assisted refrigeration system of the present invention. Figure 4 This is a comparison chart of thawing drip loss in the experimental examples described in this invention; Figure 5 This is a comparison diagram of the textural properties of the experimental examples described in this invention; Figure 6 These are comparative microstructure diagrams of the experimental examples described in this invention; The components include: 1. Radio frequency generator; 2. Relay pulse generator; 3. Impedance matching device; 4. Radio frequency processing device; 401. Processing chamber; 402. Upper aluminum electrode plate; 403. Lifting platform; 404. Lower aluminum electrode plate; 405. Polypropylene sample plate; 5. Low temperature freezer; 6. Temperature measuring host; 7. Display screen; 8. Fiber optic temperature probe. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] like Figures 1 to 3 As shown, the present invention provides a radio frequency assisted refrigeration system. It includes a radio frequency generation module, a radio frequency processing module, a cryogenic freezing module, and a fiber optic temperature measurement module. The radio frequency (RF) generation module provides a stable pulsed RF signal. It includes an RF generator 1 and a relay pulse generator 2 and an impedance matching device 3 electrically connected to it. The RF generator 1 has an external control port and an output port. The external control port of the RF generator 1 is electrically connected to the relay pulse generator 2, and the output port of the RF generator 1 is electrically connected to the impedance matching device 3. The impedance matching device 3 internally houses a vacuum variable capacitor and a fixed inductor. The radio frequency (RF) processing module is used to provide an RF action space for food. It includes an RF processing device 4, which comprises a processing cavity 401, an upper aluminum electrode plate 402 suspended and fixed inside the processing cavity 401, and a lower aluminum electrode plate 404 positioned below the upper aluminum electrode plate 402 via a lifting platform 403. An impedance matching device 3 is electrically connected to the upper aluminum electrode plate 402 through its signal output terminal, and is electrically connected to the lower aluminum electrode plate 404 and grounded through its housing. The low-temperature freezing module provides freezing capacity to the system and includes a low-temperature freezer 5. The impedance matching device 3 and the radio frequency processing device 4 are placed inside the low-temperature freezer 5. An optical fiber temperature measurement module is set on the outside of the low-temperature freezer 5. The optical fiber temperature measurement module is used to achieve accurate monitoring of food temperature. It includes a temperature measuring host 6 and a display screen 7 electrically connected to it, and an optical fiber temperature measuring probe 8. The temperature measuring end of the optical fiber temperature measuring probe 8 extends into the processing cavity 401 of the radio frequency processing device 4 to be inserted into the geometric center of the food to be processed.

[0019] In the embodiments described in this invention, the radio frequency generator 1 is equipped with an output power display window, a reflected power display window, and a power adjustment knob. The maximum design power of the radio frequency generator 1 is 1kW, and it can continuously adjust the output power with an accuracy of 1W. The actual effective transmission power generated by the radio frequency generator 1 is the difference between the output power and the reflected power. The power adjustment and dual power display design of the radio frequency generator 1 can accurately control the electric field strength, adapt to different types and sizes of food, improve the system's versatility, and the 1kW maximum power reserve meets the needs of special working conditions. In actual operation, low power can achieve the supercooling effect, resulting in low energy consumption. The external control port and the output port are integrated on the rear side of the radio frequency generator 1, and the output port is electrically connected to the impedance matching device 3 through a coaxial cable.

[0020] This invention uses a 50Ω radio frequency system. Compared with a self-oscillating radio frequency system, the 50Ω radio frequency system has a high degree of modularity, which makes it easy to integrate with the refrigeration system. In addition, the frequency is stable during operation and the output power can be precisely adjusted. The relay pulse generator 2 connected to the external control port can also precisely control the radio frequency pulse mode and duty cycle, thereby limiting the excessive generation of heat and protecting the refrigeration rate from being affected.

[0021] In the embodiments described in this invention, the relay pulse generator 2 can control the switching state of the radio frequency generator 1 and can also freely set the switching duration to achieve pulsed radio frequency transmission. Specifically, in this embodiment, the relay pulse generator 2 is set to a "10s on / 20s off" cycle mode, which limits the system heat generation by precisely controlling the radio frequency duty cycle. It can dynamically adjust the switching cycle according to the food freezing stage, ensuring both the supercooling effect and avoiding food temperature rise caused by continuous radio frequency, thus ensuring freezing quality. It should be noted that when the power of the RF generator 1 is set to 50W, in the above-mentioned "10s on / 20s off" pulse cycle mode, the average power of the system is only 16.7W. At this power, the heat generated by the RF generator module and the food materials is almost negligible.

[0022] In the embodiments described in this invention, the impedance matching circuit 3 includes two vacuum variable capacitors and one fixed inductor. The two vacuum variable capacitors are connected in series at the input and output terminals of the impedance matching circuit 3, respectively, and the fixed inductor is connected in parallel between the two vacuum variable capacitors. The three components form a π-type impedance matching circuit. The use of vacuum variable capacitors improves the accuracy and stability of impedance adjustment, adapting to impedance changes of different food loads. The two vacuum variable capacitors are labeled C1 and C2. Each vacuum variable capacitor is equipped with an adjustment knob to adjust its capacitance. By rotating the adjustment knobs of C1 and C2, the real part of the system impedance can be precisely adjusted to 50Ω and the imaginary part to 0Ω. At this time, the reflected power of the RF generator 1 is displayed as 0, ensuring that the RF energy is transmitted to the subsequent processing module without loss. It should be noted that during the process of the power of the radio frequency generator 1 being transmitted to the upper aluminum plate 402 and the lower aluminum plate 404, some of the energy is absorbed by the food material, and most of the other unused energy is ultimately consumed as heat in the inductor of the impedance matching device 3. The pulse mode design of the aforementioned relay pulse generator 2 can further reduce the overall heat accumulation. Impedance matching unit 3 is equipped with a signal output terminal and a grounded housing to ensure the directional transmission of radio frequency energy.

[0023] In the embodiments described in this invention, the processing cavity 401 is a rectangular cavity structure made of stainless steel, with an opening on its front side for easy food handling. The processing cavity 401 provides a stable operating environment for the radio frequency electric field. The stainless steel material shields against radio frequency signal leakage, ensuring operational safety. Its semi-enclosed structure also helps maintain a stable internal temperature and reduces cooling loss. The upper aluminum electrode plate 402 is made of high-purity aluminum and is suspended and fixed inside the processing cavity 401 by an insulating bracket. The insulating bracket is connected to the side wall of the processing cavity 401 by screws. A rigid connection is used to ensure the stable position of the upper aluminum electrode plate 402, and the distance between the upper surface of the upper aluminum electrode plate 402 and the upper wall of the processing cavity 401 is 10cm. The upper aluminum electrode plate 402 is electrically connected to the signal output terminal of the impedance matching device 3 through a wire, serving as the receiving electrode for radio frequency signals. The lifting platform 403 includes a bottom platform connected to the bottom surface of the lower aluminum electrode plate 404, a bracket located at the top of the bottom platform, an adjustment handle penetrating the bracket and used to adjust the lifting of the bracket, and a top platform located at the top of the bracket. The lower aluminum electrode plate... Material 404 is made of high-purity aluminum and is placed on the top platform of the lifting platform 403, which is located at the center of the bottom surface of the processing chamber 401. The height of the lower aluminum electrode 404 can be freely adjusted by rotating the adjustment handle of the lifting platform 403, thereby controlling the distance between the upper and lower aluminum electrode 402. The adjustable range of the distance between the upper and lower aluminum electrode 402 and 404 is 2cm-7cm. Under the same output power, the distance between the upper and lower aluminum electrode 402 and 404... The smaller the distance between the upper aluminum plate 402 and the lower aluminum plate 404, the stronger the electric field strength formed between them. Both the upper aluminum plate 402 and the lower aluminum plate 404 are made of high-purity aluminum, which has excellent conductivity and ensures a uniform distribution of the radio frequency electric field. The design of a fixed upper aluminum plate 402 and an adjustable lower aluminum plate 404 allows the distance between them to be flexibly adjusted according to the thickness of the food, ensuring that the food is always in the core area of ​​the electric field and improving the uniformity of the supercooling effect. The lower aluminum electrode plate 404 is electrically connected to the outer shell of the impedance matching device 3 and is grounded together with the outer shell, serving as the grounding electrode of the radio frequency electric field. It forms a uniform high-frequency alternating electric field parallel to and directly opposite the upper aluminum electrode plate 402, causing the water molecules inside the food material to vibrate violently. Under appropriate power and electric field strength, the radio frequency field can effectively inhibit the formation of ice crystal nuclei, causing the food material to become supercooled.

[0024] In the embodiments described in this invention, the impedance matching device 3 is fixed inside the low-temperature freezer 5 and placed horizontally beside the radio frequency processing device 4 to avoid mutual interference. The low-temperature freezer 5 is set to a temperature of -30°C during operation to provide stable low-temperature cooling for food freezing. This invention uses a combination of radio frequency and low-temperature air freezing to replace expensive refrigerant liquid nitrogen, reducing temperature gradients and preventing food cracking, making it more economical and practical overall. The fiber optic temperature measurement module has the advantages of strong anti-electromagnetic interference capability and high temperature measurement accuracy, and can capture changes in the core temperature of food in real time, providing accurate data for determining the supercooling point and controlling the freezing endpoint. To avoid over-freezing or under-freezing, the temperature measuring end of the fiber optic temperature probe 8 extends through the sealed interface of the low-temperature freezer 5 into the processing chamber 401 and is fixed to a polypropylene sample plate 405 located at the center of the surface of the lower aluminum electrode plate 404. The polypropylene sample plate 405 is made of insulating material, which can avoid interference with the radio frequency electric field and has stable chemical properties, so it does not react with food. The food to be processed is placed on the surface of the polypropylene sample plate 405, and the temperature measuring end of the fiber optic temperature probe 8 is inserted into the geometric center of the food to ensure real-time monitoring of the core temperature inside the food. The monitoring data is processed by the temperature measuring host 6 and displayed in real time on the display screen 7.

[0025] This invention has a significant supercooling-promoting effect on food. Specifically, the radio frequency field can interfere with the crystallization of water molecules in food, causing supercooling. Ultimately, a large number of ice nuclei are explosively formed at temperatures below freezing, thereby reducing the size of the final ice crystals. Compared to ordinary freezing without radio frequency, water molecules in food materials undergoing radio frequency-assisted freezing begin to freeze at even lower temperatures. At this point, a large number of ice crystal nuclei are explosively generated. Due to the greatly increased number of ice crystal nuclei, the size of the final ice crystals is significantly reduced, effectively protecting the food's microstructure from damage caused by excessively large ice crystals.

[0026] Based on the above, the core working principle of this invention to achieve the supercooling effect is as follows: RF generator 1 generates a stable pulse RF signal, which is controlled by relay pulse generator 2 to a "10s on / 20s off" cyclic mode. When the output power of RF generator 1 is set to 50W, the average power of the system is 16.7W. This pulse mode can avoid the heat generated by continuous RF affecting the freezing rate. The RF signal is transmitted losslessly between the upper aluminum plate 402 and the lower aluminum plate 404 via impedance matching device 3. The two vacuum variable capacitors and one fixed inductor inside the impedance matching device 3 form a π-type impedance matching circuit. By adjusting the adjustment knob of the vacuum variable capacitor, the reflected power can be reduced to 0, ensuring lossless transmission of RF energy, thereby forming a uniform high-frequency alternating electric field between the upper aluminum plate 402 and the lower aluminum plate 404. The food to be processed is placed on the surface of the polypropylene sample plate 405, and is subjected to the synergistic effect of the high-frequency alternating electric field and the stable low temperature provided by the low-temperature freezer 5. In the environment, the radio frequency field polarizes water molecules within the food and causes them to vibrate at high frequencies, interfering with the crystallization process of water molecules within the food and delaying the formation of initial ice crystals. Simultaneously, the continuous cooling of the low-temperature freezer 5 causes the food temperature to continuously decrease until it remains liquid even below its freezing point, forming a significant supercooling state. The fiber optic temperature probe 8 of the fiber optic temperature measurement module monitors the core temperature of the food's geometric center in real time, providing accurate data for determining the supercooling point. The lifting platform 403 of the radio frequency processing device 4 can achieve an adjustable electrode spacing of 2cm-7cm, which can be flexibly adjusted according to the thickness of the food to ensure that the food is always in the core area of ​​the electric field, improving the uniformity of the supercooling effect. When the food temperature reaches the supercooling critical point, under the synergistic effect of the continuous disturbance of the radio frequency field and the low-temperature environment, a large number of ice nuclei are explosively formed within the food. Compared with ordinary freezing, the size of the generated ice crystals is significantly smaller, thereby effectively avoiding mechanical damage to food cells by large ice crystals and achieving an improvement in the final quality of frozen food.

[0027] The present invention also provides a radio frequency assisted freezing method, which is applied to the above-mentioned radio frequency assisted freezing system, and the specific steps include: Step S1: Preliminary Preparations Turn on the power of the low-temperature freezer 5 and set its internal temperature to -30℃. Run it continuously for 30 minutes until the temperature stabilizes. Take a certain weight of the food to be processed and place it at the center of the surface of the polypropylene sample plate 405. Then insert the fiber optic temperature probe 8 into the geometric center of the food to be processed, ensuring that the temperature measuring end is in close contact with the food to be processed. Then place the polypropylene sample plate 405 stably on the upper surface of the lower aluminum electrode plate 404. Step S2: Parameter Adjustment Based on the thickness of the food to be processed, adjust the distance between the upper aluminum plate 402 and the lower aluminum plate 404 using the adjustment handle of the rotating lifting platform 403; turn on the power of the relay pulse generator 2 and set the pulse cycle mode to "10s on / 20s off"; turn on the power of the radio frequency generator 1 and set the output power to 50W using the power adjustment knob. At this time, the average power of the system is 16.7W. Step S3: Impedance Matching and RF Startup Press the "Output" and "External Control" buttons of the RF generator 1 in sequence. The relay pulse generator 2 starts to control the pulse output of the RF signal. The signal is transmitted to the impedance matching device 3 via cable. Slowly rotate the adjustment knob of the vacuum variable capacitor of the impedance matching device 3 and observe the reflected power display window of the RF generator 1 until the reflected power drops to 0, completing the impedance matching. At this time, the RF energy is transmitted without loss to form a high-frequency alternating electric field between the upper aluminum plate 402 and the lower aluminum plate 404. The food to be processed receives the RF field. Step S4: Freezing the food to be processed The display screen 7 of the fiber optic temperature measurement system monitors the core temperature change of the food to be processed in real time. The food to be processed is rapidly cooled by the cold air in the low-temperature freezer 5, and supercooling occurs under the action of the radio frequency field, eventually completing the crystallization phase transition and achieving freezing. After a period of time, the power of all equipment is turned off, the food is taken out, and the entire freezing process is completed.

[0028] To further verify the technical effectiveness of the radio frequency assisted freezing system and method of the present invention, based on the above, the present invention selects beef foreleg meat as the experimental subject and provides the following experimental examples: Experimental parameter settings: The temperature of the low-temperature freezer 5 was set to -30℃, the radio frequency parameters were set to 50W pulse mode (pulse cycle parameters: 10s on / 20s off), and the distance between the upper and lower aluminum plates was set to 7cm. At the same time, a normal freezing group without radio frequency was set up as a control group, and the other experimental conditions of the control group were kept the same as those of the above experimental group.

[0029] Experimental results: Under the above parameters, the experimental group of beef foreleg meat was supercooled to an average of -4.6℃ during radiofrequency assisted freezing, which is 3℃ supercooled compared to the freezing point of -1.6℃. The control group of beef foreleg meat did not exhibit supercooling, with a supercooling of 0℃. The following are the comparative results of the quality data for beef foreleg meat from the two experimental groups: 1. Water loss due to thawing dripping: such as Figure 4As shown, the thawing drip loss of beef foreleg meat in the radio frequency assisted freezing group (50W pulse) was significantly lower than that in the ordinary freezing control group (0W). This indicates that beef foreleg meat treated with radio frequency assisted freezing has better water retention. The core reason is that the ice crystals formed during the freezing process are smaller, which greatly reduces the mechanical damage of ice crystals to beef foreleg meat cells and reduces the loss of intracellular water. 2. Texture properties: such as Figure 5 As shown, using the firmness of fresh beef foreleg as a reference, the firmness of the conventionally frozen control group (0W) beef foreleg significantly increased, while the firmness of the radio frequency assisted freezing group (50W pulse) beef foreleg showed no significant difference from the fresh group. This indicates that radio frequency assisted freezing can maximize the preservation of the textural properties of beef foreleg, maintaining good tenderness. 3. Microstructure: such as Figure 6 As shown, the microstructure of beef foreleg meat from the radio frequency assisted freezing group (50W pulse) was significantly better than that from the ordinary freezing control group (0W). The white areas in the figure represent the spaces left by ice crystals. It can be clearly observed that the ice crystal spaces in the radio frequency assisted freezing group were smaller, meaning that the ice crystals formed during the freezing process were smaller, proving that the microstructure of the meat was effectively protected and the overall quality was superior.

[0030] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A radio frequency assisted refrigeration system, characterized in that: It includes a radio frequency generation module, a radio frequency processing module, a cryogenic freezing module, and a fiber optic temperature measurement module. The radio frequency (RF) generation module provides a stable pulsed RF signal. It includes an RF generator and a relay pulse generator and an impedance matching device electrically connected to it. The RF generator has an external control port and an output port. The external control port of the RF generator is electrically connected to the relay pulse generator, and the output port of the RF generator is electrically connected to the impedance matching device. The impedance matching device internally houses a vacuum variable capacitor and a fixed inductor. The radio frequency (RF) processing module is used to provide an RF operating space for food. It includes an RF processing device comprising a processing cavity, an upper aluminum electrode plate suspended and fixed inside the processing cavity, and a lower aluminum electrode plate positioned below the upper aluminum electrode plate via a lifting platform. An impedance matching device is electrically connected to the upper aluminum electrode plate through its signal output terminal, and is electrically connected to the lower aluminum electrode plate and grounded through its housing. The low-temperature freezing module provides freezing capacity to the system and includes a low-temperature freezer. The impedance matching device and radio frequency processing device are placed inside the low-temperature freezer, and an optical fiber temperature measurement module is installed on the outside of the low-temperature freezer. The optical fiber temperature measurement module is used to achieve accurate monitoring of food temperature. It includes a temperature measurement host and a display screen electrically connected to it, and an optical fiber temperature measurement probe. The temperature measuring end of the optical fiber temperature measurement probe extends into the processing cavity of the radio frequency processing device to be inserted into the geometric center of the food to be processed.

2. The radio frequency assisted refrigeration system according to claim 1, characterized in that: The RF generator is equipped with an output power display window, a reflection power display window, and a power adjustment knob; the external control port and the output port are integrated on the rear side of the RF generator, and the output port is electrically connected to an impedance matching device through a coaxial cable.

3. The radio frequency assisted refrigeration system according to claim 1, characterized in that: The relay pulse generator is set to a "10s on / 20s off" cycle mode. By precisely controlling the radio frequency duty cycle, it limits the heat generation of the system. It can dynamically adjust the switching cycle according to the food freezing stage, ensuring both the supercooling effect and avoiding the food temperature rise caused by continuous radio frequency, thus ensuring the freezing quality.

4. The radio frequency assisted refrigeration system according to claim 1, characterized in that: The impedance matching circuit includes two vacuum variable capacitors and one fixed inductor. The two vacuum variable capacitors are connected in series at the input and output terminals of the impedance matching circuit, respectively, and the fixed inductor is connected in parallel between the two vacuum variable capacitors. The three components form a π-type impedance matching circuit. Each vacuum variable capacitor is equipped with an adjustment knob that can adjust its capacitance.

5. The radio frequency assisted refrigeration system according to claim 1, characterized in that: The processing chamber is a rectangular hollow structure made of stainless steel, with an opening on the front side for easy food handling. The upper aluminum electrode plate is made of high-purity aluminum and is suspended and fixed inside the processing chamber by an insulating bracket. The insulating bracket is rigidly connected to the side wall of the processing chamber by bolts. The upper aluminum electrode plate is electrically connected to the signal output terminal of the impedance matching device by a wire, serving as the receiving electrode for radio frequency signals. The lifting platform includes a bottom platform connected to the bottom surface of the lower aluminum electrode plate, a bracket at the top of the bottom platform, an adjustment handle through the bracket for adjusting the lifting of the bracket, and a top platform at the top of the bracket. The lower aluminum electrode plate is made of high-purity aluminum and is placed on the top platform of the lifting platform located at the center of the bottom surface of the processing chamber. The height of the lower aluminum electrode plate can be freely adjusted by rotating the adjustment handle of the lifting platform, thereby controlling the distance between the upper and lower aluminum electrode plates. The lower aluminum electrode plate is electrically connected to the housing of the impedance matching device and is grounded together with the housing, serving as the grounding electrode of the radio frequency electric field.

6. The radio frequency assisted refrigeration system according to claim 1, characterized in that: The impedance matching device is fixed inside the low-temperature freezer and placed horizontally beside the radio frequency processing device to avoid mutual interference. The temperature measuring end of the fiber optic temperature probe extends through the sealed interface provided by the low-temperature freezer into the processing chamber and is fixed to the upper surface of the polypropylene sample plate located at the center of the surface of the lower aluminum electrode plate. The food to be processed is placed on the surface of the polypropylene sample plate, and the temperature measuring end of the fiber optic temperature probe is inserted into the geometric center of the food to ensure real-time monitoring of the core temperature inside the food. The monitoring data is processed by the temperature measuring host and displayed on the display screen in real time.

7. A radio frequency assisted freezing method, wherein the method is applied to the radio frequency assisted freezing system according to any one of claims 1 to 6, characterized in that: The specific steps include: Step S1: Preliminary Preparations Turn on the power of the low-temperature freezer and set its internal temperature to -30℃. Run it continuously for 30 minutes until the temperature stabilizes. Take a certain weight of the food to be processed and place it in the center of the polypropylene sample plate. Then insert the fiber optic temperature probe into the geometric center of the food to be processed, ensuring that the temperature measuring end is in close contact with the food. Finally, place the polypropylene sample plate stably on the upper surface of the lower aluminum plate. Step S2: Parameter Adjustment Depending on the thickness of the food to be processed, adjust the upper and lower aluminum plates to a suitable distance using the adjustment handle of the rotating lifting platform; turn on the relay pulse generator and set the pulse cycle mode to "10s on / 20s off"; turn on the radio frequency generator and set the output power to 50W using the power adjustment knob, at which point the average system power is 16.7W. Step S3: Impedance Matching and RF Startup Press the "Output" and "External Control" buttons of the RF generator in sequence. The relay pulse generator starts to control the pulse output of the RF signal. The signal is transmitted to the impedance matching device via cable. Slowly rotate the adjustment knob of the vacuum variable capacitor of the impedance matching device and observe the reflected power display window of the RF generator until the reflected power drops to 0, completing the impedance matching. At this time, the RF energy is transmitted without loss to form a high-frequency alternating electric field between the upper and lower aluminum plates. The food to be processed receives the RF field. Step S4: Freeze the food to be processed The core temperature change of the food to be processed is monitored in real time by the display screen of the fiber optic temperature measurement system. The food is rapidly cooled by the cold air in the low-temperature freezer and undergoes supercooling under the action of the radio frequency field, eventually completing the crystallization phase transition and achieving freezing. After a period of time, the power of all equipment is turned off, the food is taken out, and the entire freezing process is completed.

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