Method for thawing frozen catfish fillets with the aid of magneto-electric coupling and application thereof

Abstract

The application discloses a method for thawing frozen channel catfish fillets by using magnetoelectric coupling, and comprises the following steps: placing the frozen channel catfish fillets into a sealed bag and placing the sealed bag into a magnetoelectric coupling freezing and refrigerating box; inserting a thermocouple temperature probe into the center of the meat sample to monitor the temperature in real time; and stopping the magnetoelectric coupling when the temperature reaches a predetermined temperature, thereby completing the thawing. The method can reduce the damage of the channel catfish during thawing, improve the quality stability of the thawed channel catfish, and has high thawing efficiency.

Description

Technical Field

[0001] This invention relates to the field of aquatic product thawing technology, specifically to a method and application for thawing frozen catfish fillets using magnetoelectric coupling-assisted thawing. Background Technology

[0002] With the continuous optimization of residents' dietary structure and consumption upgrade, pre-processed aquatic products have received widespread attention due to their high nutritional value, convenience, and diverse processing methods. Catfish, as one of my country's important freshwater farmed fish, has advantages such as tender flesh, few bones, high protein content, and a balanced fat composition, making it a promising candidate for the aquatic product processing industry. However, due to the seasonality of raw material supply and the limitations imposed by processing and distribution needs, frozen storage has become one of the most common preservation methods for catfish, and the thawing process is a crucial and indispensable step in the processing of frozen aquatic products.

[0003] Existing research has shown that thawing methods and processing conditions significantly affect the physical structure and biochemical properties of fish meat. When thawing time is too long, endogenous enzymes within the fish tissue gradually regain activity, easily triggering protein degradation and lipid oxidation reactions. Simultaneously, this provides favorable conditions for microbial growth and reproduction, accelerating the deterioration of aquatic product quality. Conversely, thawing too quickly or using improper methods can lead to cell structure damage, significant juice loss, nutrient loss, and a significant reduction in the water-holding capacity, tenderness, and overall sensory quality of the fish meat. Therefore, choosing a scientifically sound thawing method is crucial for ensuring the suitability for processing and the stability of the quality of frozen catfish.

[0004] At present, traditional methods such as low temperature thawing, room temperature thawing, and running water thawing are widely used in aquatic product processing, but they generally have problems such as long thawing time, high energy consumption, or significant quality damage

[25] . In recent years, new assisted thawing technologies such as ultrasound, magnetic field, and electric field have gradually attracted attention because they can regulate ice crystal behavior, shorten thawing time, and improve product quality. Among them, magnetoelectric coupling assisted thawing is expected to show unique advantages in reducing thawing damage and inhibiting quality deterioration through the synergistic effect of magnetic field and electric field. However, its application research in freshwater fish, especially catfish, is still relatively limited, and the relevant mechanism and quality effect need to be systematically elucidated. Summary of the Invention

[0005] The present invention aims to provide a method for thawing frozen catfish fillets using magnetoelectric coupling. The method of thawing catfish fillets using magnetoelectric coupling has high thawing efficiency and high quality stability of catfish after thawing.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: a method for thawing frozen catfish fillets using magnetoelectric coupling, comprising: placing the frozen catfish fillets in a sealed bag and placing it in a magnetoelectric coupling freezer; inserting a thermocouple thermometer probe into the center of the meat sample to monitor the temperature in real time; and stopping the magnetoelectric coupling when the temperature reaches a predetermined temperature, thereby completing the thawing process.

[0007] The magnetoelectric coupling freezer / refrigerator is configured with the following parameters: temperature 4℃-25℃, electric field strength 4.5kV-22.5kV, magnetic field strength 1mT-9mT, and magnetic field efficiency 0.1 Hz-0.9 Hz.

[0008] The magnetoelectric coupling freezer / refrigerator is configured with the following parameters: temperature 10℃, electric field strength 15 kV, magnetic field strength 4 mT, and magnetic field efficiency 0.3 Hz. The thermocouple thermometer probe is inserted into the center of the meat sample to a depth of 2cm-3cm, and the predetermined temperature is 2℃-4℃.

[0009] The method described is applied in the thawing of frozen catfish fillets and the processing of pre-processed fish products.

[0010] Beneficial effects: This invention clarifies the effect of the thawing process on the tissue structure and quality stability of fish meat, and optimizes the parameters of the magnetoelectric coupling assisted thawing technology, which can reduce the damage of catfish during thawing and improve the quality stability of thawed catfish. Attached Figure Description

[0011] Figure 1 The effect of thawing method on the thawing time of frozen catfish fillets; Figure 2 The effect of thawing method on the thawing loss rate of frozen catfish fillets; Figure 3 The effect of thawing method on the loss rate of frozen catfish fillets during steaming; Figure 4 The effect of thawing method on the water-holding capacity of frozen catfish fillets; Figure 5 The effect of thawing method on pH of frozen catfish fillets; Figure 6 The effect of thawing method on the whiteness value of frozen catfish fillets; Figure 7 The effect of thawing method on TVB-N of frozen catfish fillets; Figure 8 The effect of thawing method on the total bacterial count of frozen catfish fillets; Figure 9 The effect of thawing temperature on the water-holding capacity of frozen catfish fillets; Figure 10 The effect of electric field strength on the water-holding capacity of frozen catfish fillets; Figure 11 The effect of magnetic field strength on the water-holding capacity of frozen catfish fillets; Figure 12 The effect of magnetic field frequency on the water-holding capacity of frozen catfish fillets; Figure 13 The elastic contour plot and response surface plot of catfish fillets are shown. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure. Example 1

[0013] Frozen catfish fillets were removed from a -18℃ freezer and randomly divided into 5 groups. Each group was thawed using one of the following 5 methods. During thawing, a thermocouple probe was inserted 2-3 cm into the center of the sample to observe the temperature change at the center. The thawing endpoint was set at 2-4℃. Thawing time was recorded, and various parameters were measured.

[0014] Magnetoelectric coupling assisted thawing: Frozen catfish fillets were placed in sealed bags and then placed in a magnetoelectric coupling freezer / refrigerator. The temperature was set to 4℃, the magnetic field strength to be 5.0 mT, the magnetic field frequency to be 0.5 Hz, and the electric field strength to be 13.5 kV. All thawing processes were completed when the core temperature of the meat sample reached 2-4℃. The magnetoelectric coupling freezer / refrigerator model was MEF20-Pro, manufactured by Indust (Wuxi) Induction Technology Co., Ltd.

[0015] Comparative test examples: Low-temperature thawing: Frozen catfish fillets were placed in a sealed bag and thawed in a 4°C freezer; Room temperature thawing: Frozen catfish fillets were placed in a sealed bag and placed on a test bench for thawing at room temperature (25°C); Running water thawing: Frozen catfish fillets in a sealed bag were placed under running tap water, with the water flow evenly washing the surface of the fillets at a flow rate of approximately 60 mL / s; Ultrasonic thawing: Frozen catfish fillets were placed in a sealed bag and immersed in an ultrasonic cleaner at a water temperature of 20°C, a working frequency of 40 kHz, and a power of 200 W. Example 2

[0016] 1) The effect of thawing method on the thawing time of frozen catfish fillets Different thawing methods resulted in significant differences in the thawing time of frozen catfish fillets (P<0.05). For example... Figure 1As shown, ultrasound-assisted thawing requires the shortest time, followed by running water thawing, while cryogenic thawing requires the longest time. This is because ultrasound generates high-frequency vibrations through cavitation, directly disrupting the ice crystal structure and significantly accelerating the thawing process. Furthermore, the synergistic effect of the thermal and mechanical effects of ultrasound improves heat conduction efficiency, thus shortening the thawing time. Compared to traditional cryogenic thawing, magnetoelectric coupling-assisted thawing significantly shortens the thawing time, even at 4°C, it is still 32.6% faster than traditional cryogenic thawing. This efficiency improvement stems from the synergistic effect of the magnetic and electric fields. The pulsed magnetic field enhances the speed of heat transfer by vibrating and accelerating the movement of water molecules, while the electrostatic field promotes the uniform propagation of heat within the frozen sample by optimizing the electric field distribution of water molecules and charged particles. When used in combination, the pulsed magnetic field enhances the randomness of molecular motion and the transfer of kinetic energy, while the electrostatic field makes the energy distribution in this process more efficient and uniform, ultimately leading to faster thawing.

[0017] This result indicates that magnetoelectric coupling-assisted thawing can effectively reduce thawing time through the synergistic effect of both.

[0018] 2) The effect of thawing method on the thawing loss rate of frozen catfish fillets Remove the frost from the frozen catfish using absorbent paper, weigh the fish fillets using a balance, and record the weight as m1. After thawing, pat the surface dry with kitchen paper and weigh the fillets again, recording the weight as m2. Repeat this process three times and take the average value.

[0019] Thawing loss rate / % = (m1-m2) / m1×100.

[0020] In the formula: m1 is the mass of catfish before thawing / g; m2 is the mass of catfish after thawing / g.

[0021] Depend on Figure 2It was found that the thawing loss rate of the magnetoelectric coupling-assisted thawing group was significantly lower than that of other thawing methods (P<0.05). Magnetoelectric coupling-assisted thawing accelerates heat transfer through the combined action of pulsed magnetic fields and electrostatic fields. These two fields induce alternating currents and magnetic effects within the material, enhancing the movement of water molecules and other molecules, thereby accelerating the uniform conduction of internal heat. Compared to traditional thawing methods, magnetoelectric coupling can uniformly heat frozen samples in a shorter time, avoiding the problems caused by uneven heat distribution during prolonged thawing. This uniform heating effectively prevents local overheating or excessively rapid melting, reducing rapid water loss. Furthermore, traditional thawing methods may lead to excessive water seepage during thawing due to slow heat conduction, while magnetoelectric coupling technology reduces the leakage of water from the surface and interior of the fish fillets by optimizing energy transfer during the thawing process. The combined effect of electric and magnetic fields also promotes the binding and retention of water molecules at the molecular level, avoiding unnecessary water loss. Therefore, magnetoelectric coupling-assisted thawing significantly reduces the thawing loss rate of catfish fillets compared to traditional thawing methods and ultrasonic thawing.

[0022] 3) The effect of thawing method on the loss rate of frozen catfish fillets during steaming. Weigh a sample of a certain size (approximately 3×2×2 cm) and steam it in an 85℃ water bath for 25 minutes. Weigh the sample before steaming. After steaming, allow it to cool naturally to room temperature (20℃), wipe the surface of the fish meat dry with kitchen paper, and weigh it again. Repeat this process 3 times and take the average value.

[0023] Cooking loss rate / % = (m1-m2) / m1×100 Where: m1 is the mass of fish meat before steaming / g; m2 is the mass of fish meat after steaming / g. Loss during steaming or boiling is due to the thermal denaturation of myofibrils, which damages the muscle structure and causes a large amount of juice and soluble substances to seep out. This is related to the juiciness and water retention capacity of meat. Figure 3 It was found that the ultrasonic-assisted thawing group had the highest cooking loss rate, followed by magnetoelectric coupling-assisted thawing, room temperature thawing, and running water thawing, while the low-temperature thawing group had the lowest cooking loss rate. This phenomenon indicates that low-temperature thawing has certain advantages in slowing down protein thermal denaturation and maintaining the stability of muscle tissue structure, thereby effectively improving the water retention of fish fillets and reducing the loss of juices and soluble nutrients during heating. In comparison, although ultrasonic-assisted thawing can accelerate the thawing process, the mechanical vibration and cavitation effect generated by ultrasound during the process may damage the muscle microstructure, leading to cell membrane rupture, making it easier for water and soluble substances to seep out during heating, increasing cooking loss. Although magnetoelectric coupling-assisted thawing can improve the uniformity of heat conduction and reduce some structural damage through the synergistic effect of magnetic and electric fields, compared with low-temperature thawing, its physical field effect still causes a certain degree of microscopic damage to muscle tissue, resulting in a higher cooking loss than the low-temperature group.

[0024] 4) The effect of thawing method on the water-holding capacity of frozen catfish fillets After thawing, the samples were placed at room temperature (25℃) for 30 minutes. Excess moisture was removed with absorbent paper. Sample M0 was wrapped in three layers of filter paper and placed in a 100 mL centrifuge tube. The sample was centrifuged at 5000 r / min for 10 minutes. The sample was then removed, the filter paper was removed, and the sample was weighed as M1. Each sample group was repeated three times, and the average value was taken.

[0025] WHC / % = M1 / ​​M0 × 100% In the formula: M0 is the sample mass before centrifugation / g; M1 is the sample mass after centrifugation / g.

[0026] The water-holding capacity of catfish muscle refers to its ability to retain internal water without loss under external force. As shown in Figure 4, the water-holding capacity of the magnetoelectric coupling assisted thawing group was significantly higher than that of the other groups (P < 0.05), reaching 75.53%. This result indicates that magnetoelectric coupling assisted thawing can effectively improve the water-holding capacity of fish meat and reduce water loss. This is mainly because during magnetoelectric coupling assisted thawing, the synergistic effect of the pulsed magnetic field and electrostatic field promotes the uniform melting of ice crystals, avoiding cell structure damage caused by localized thawing. Simultaneously, a moderate magnetic field can stabilize cell membrane structure to a certain extent, reducing intracellular water leakage and enhancing the muscle's water retention capacity.

[0027] 5) The effect of thawing method on the pH of frozen catfish fillets Take 1 g of sample, add 9 mL of distilled water, homogenize, and then measure the pH value of the sample using a pH meter. Each group has 3 replicates.

[0028] pH value is one of the important indicators for evaluating the freshness of fish. It reflects the acidity or alkalinity of the fish to a certain extent and has a significant impact on various aspects of the fish, including its color, tenderness, flavor, water retention, and shelf life. Figure 5 It was found that the pH values ​​of the low-temperature thawing and ultrasound-assisted thawing groups were significantly higher than those of the room temperature, running water, and magnetoelectric coupling assisted thawing groups (P < 0.05). The pH value of pulsed magnetic field assisted thawing was the lowest, at 7.28. This may be because the low-temperature thawing time is longer, and the fish samples have already entered the autolysis and decay process. At this time, nitrogenous substances such as proteins will decompose to produce alkaline substances such as amino acids, ammonia, hydrogen sulfide, and indole, resulting in a higher pH value.

[0029] 6) The effect of thawing method on the whiteness value of frozen catfish fillets First, the catfish samples were cut into cuboids measuring 3 cm × 2 cm × 1 cm, and then their colorimetry was measured using a colorimeter. The colorimeter was preheated for 30 minutes before use and calibrated using a standard white plate. Each sample was measured in parallel six times. The L* value represents the lightness of the sample, the a* value represents red-green hue, the b* value represents yellow-blue hue, and W represents whiteness, where W is calculated using the following formula: The decrease in whiteness is mainly due to the destruction of pigments in fish meat by intermediate products such as free radicals generated from fat oxidation, causing browning. Figure 6 It was found that the whiteness values ​​of the low-temperature, ultrasound-assisted, and magnetoelectric coupling-assisted thawing groups were significantly higher than those of the room-temperature and running water thawing groups (P < 0.05), indicating that these three methods better preserved the appearance quality of the fish meat and slowed down browning. Low-temperature thawing, through a slower temperature change, effectively avoided the aggravation of oxidation reactions during rapid thawing, thus maintaining a high whiteness value. Although ultrasound-assisted thawing was faster, appropriate ultrasound action could promote uniform melting of ice crystals, reduce tissue damage, and thus reduce the degree of oxidation. Magnetoelectric coupling-assisted thawing, through the synergistic effect of magnetic and electric fields, accelerated heat transfer while avoiding excessively high local temperatures, slowing down lipid oxidation and pigment degradation, further maintaining a good whiteness value of the fish meat. In contrast, during room-temperature and running water thawing, the longer thawing time or the increased mechanical damage to the tissue by the water flow easily accelerated lipid oxidation and pigment degradation, resulting in a significant decrease in whiteness value.

[0030] 7) The effect of thawing method on the texture of frozen catfish fillets Before measurement, the samples were placed at room temperature (around 25℃) for 0.5 h to eliminate the influence of low temperature. The fish fillet samples were 2cm × 2cm × 1cm in size. A flat-bottomed cylindrical probe p / 30 (30 mm diameter) was used. The testing speed was 3 mm / s before the test, 1 mm / s during the test, and 1 mm / s after the test. The compression degree was 50%, and the probe type was Auto-5 g. Hardness, elasticity, cohesion, and chewiness were selected as the TPA values ​​for analyzing the elasticity of the fish paste gel. Six replicates were performed for each sample.

[0031] Table 1 shows that the thawing method significantly affects the hardness, elasticity, and chewiness of the catfish fillets. In terms of hardness, the ultrasonic-assisted thawing group had the highest hardness, while the magnetoelectric coupling-assisted thawing group had the lowest (1966.55±288.55 gf), significantly lower than the other groups (P < 0.05). Lower hardness values ​​generally indicate a more tender texture and less mechanical damage to the fish's structure. Regarding elasticity, running water thawing showed the highest value, but the overall difference was not significant, with only the low-temperature thawing group exhibiting slightly lower elasticity. Furthermore, in terms of chewiness, both the ultrasonic-assisted and running water thawing groups showed high chewiness, while the magnetoelectric coupling-assisted thawing group had the lowest chewiness (254.83±60.83 gf), not significantly different from the low-temperature thawing group, but significantly lower than the other groups (P < 0.05). In summary, magnetoelectric coupling-assisted thawing of catfish fillets maintained low hardness and chewiness without significantly affecting their elasticity and cohesion. This indicates that this thawing method effectively avoids textural degradation caused by ice crystal damage or uneven heating, preserving the tenderness and integrity of the fish. Previous research has shown that magnetoelectric coupling-assisted thawing, through the synergistic effect of magnetic and electric fields, promotes uniform melting of ice crystals, reduces damage to cell membranes and muscle fiber structures, and thus optimizes the textural properties of the fish.

[0032] Table 1. Effects of thawing method on the texture of frozen catfish fillets 8) The effect of thawing method on TVB-N of frozen catfish fillets The determination was carried out in accordance with the national standard GB 5009.228-2016 "National Food Safety Standard - Determination of Volatile Basic Nitrogen in Food".

[0033] The TVB-N value is one of the important indicators reflecting the freshness of aquatic products. It is closely related to the degree of degradation of nitrogenous compounds and is widely used as an indicator of the degradation and freshness of aquatic products. Figure 7It was found that among the five thawing methods, magnetoelectric coupling-assisted thawing had the lowest TVB-N value, at 6.24 mg / 100mL. This is mainly because the synergistic effect of the magnetic and electric fields positively impacted the internal structure and metabolic processes of the fish fillets. On one hand, magnetoelectric coupling-assisted thawing, through stable and uniform energy input, effectively avoided localized overheating or uneven thawing, reducing structural damage to muscle tissue and thus lowering the protein degradation rate. On the other hand, the combined effect of the magnetic and electric fields improved cell membrane integrity, enhanced selective permeability, and slowed the leakage of nitrogenous substances from the cells. Furthermore, moderate magnetic and electric fields could inhibit the growth and reproduction of microorganisms, further slowing down the decomposition and metabolism of proteins, amino acids, and other substances by microorganisms, reducing the accumulation of nitrogenous volatile substances, which is consistent with the total bacterial count results discussed later.

[0034] 9) The effect of thawing method on the total bacterial count of frozen catfish fillets The total bacterial count was determined in accordance with GB 4789.2-2010 (National Food Safety Standard for Microbiological Examination of Food: Determination of Total Colony Count).

[0035] Depend on Figure 8 It was found that compared with low temperature, room temperature, running water, and ultrasonic-assisted thawing, the pulsed magnetic field-assisted thawing group had the lowest total bacterial count, at 5.31 log. This phenomenon is mainly attributed to the combined inhibitory effect of the magnetic and electric fields on microorganisms during magnetoelectric coupling-assisted thawing. Previous studies have shown that electric fields can disrupt the integrity of microbial cell membranes, inducing electroperforation, increasing cell membrane permeability, and even causing irreversible damage, leading to loss of cell contents and inhibiting microbial growth and metabolism. The introduction of a magnetic field may further affect intracellular and membrane potential stability, thus interfering with microbial physiological activities. Furthermore, magnetoelectric coupling-assisted thawing has the advantages of accelerating thawing speed and improving heat transfer uniformity, avoiding excessively high or low local temperatures during thawing, reducing the time the product spends in the optimal temperature range for microbial growth, and effectively inhibiting microbial reproduction. Therefore, compared with traditional thawing methods, magnetoelectric coupling-assisted thawing not only shortens thawing time but also delays microbial growth to a certain extent, improving the microbiological quality of frozen aquatic products during thawing.

[0036] The test results show that different thawing methods have a significant impact on the quality of frozen catfish fillets. While traditional room temperature thawing and running water thawing are simple to operate, they easily lead to increased juice loss, deterioration of color and texture, and a relatively high risk of microbial growth. Low-temperature thawing can better maintain sample quality, but it has a longer thawing time and lower efficiency. Ultrasonic-assisted thawing can shorten the thawing time to some extent, but its effect on improving some quality indicators is limited. In contrast, magnetoelectric coupling-assisted thawing shows better comprehensive advantages in thawing efficiency, water retention, texture characteristics, and microbial control, indicating its good application potential in the thawing process of frozen catfish fillets. Therefore, magnetoelectric coupling-assisted thawing was selected as the subject of further research, and its key process parameters were further optimized to obtain a more stable and high-quality thawing effect, providing a good raw material foundation for subsequent processing of fish fillets into crispy meat.

[0037] Example 3 Single-factor experimental design for thawing frozen catfish fillets To study the thawing process of frozen catfish fillets, thawing temperature, electric field strength, magnetic field strength, and magnetic field frequency were selected as factors to be investigated, and single-factor experiments were conducted using the thawing loss rate, water holding capacity, and textural properties of the frozen catfish fillets as evaluation indicators.

[0038] (1) Effect of thawing temperature on the quality of catfish The thawing temperatures were set to 4, 10, 15, 20, and 25°C, respectively, with a fixed electric field strength of 13.5 kV, a magnetic field strength of 5 mT, and a magnetic field frequency of 0.5 Hz.

[0039] like Figure 9 As shown, with increasing thawing temperature, the water-holding capacity of the catfish fillets first increased and then decreased, reaching its maximum at 10℃ (78.44%), significantly higher than other groups (P < 0.05). This phenomenon may be attributed to the fact that a suitable thawing temperature facilitates the uniform melting of ice crystals, reduces mechanical damage to cell structures, and promotes the water retention capacity of muscle tissue. Excessively high thawing temperatures, on the other hand, can lead to rapid, localized thawing, increased water loss, and more severe damage to cell structures, ultimately reducing water-holding capacity.

[0040] The effect of thawing on the textural properties of frozen catfish fillets was tested, and the results are shown in Table 2. There were no significant differences in chewiness and cohesion between the catfish thawed under different temperatures using magnetoelectric coupling (P > 0.05). The hardness was highest at 15℃, while moderate hardness and good elasticity were observed at 10℃. Considering both water retention and textural properties, 10℃ was selected as the temperature for subsequent magnetoelectric coupling-assisted thawing.

[0041] Table 2 Effect of thawing temperature on the textural properties of frozen catfish fillets Note: Different letters indicate significant differences between samples (P < 0.05).

[0042] (2) Effect of electric field strength on the quality of catfish The electric field strengths were set to 4.5, 9, 13.5, 18, and 22.5 kV, respectively, the thawing temperature was fixed at 10℃, the magnetic field strength was 5 mT, and the magnetic field frequency was 0.5 Hz.

[0043] Depend on Figure 10 It was found that the electric field strength had a significant impact on the water-holding capacity of frozen catfish fillets thawed with magnetoelectric coupling (P < 0.05). With increasing electric field strength, the water-holding capacity first increased and then decreased, reaching its highest value at an electric field strength of 13.5 kV. As the electric field strength continued to increase, the water-holding capacity significantly decreased (P < 0.05). This may be because an electric field of appropriate strength can produce a mild electrical stimulation to the cell membrane, thereby increasing the selective permeability of the membrane structure and promoting uniform melting of ice crystals, reducing cell structural damage, and thus improving the water-holding capacity of muscle tissue. However, when the electric field strength is too high, the electric field may induce electroporation of the cell membrane, disrupting cell membrane integrity, causing intracellular water to leak out and leading to tissue structural damage, thereby reducing water-holding capacity. Related studies have shown that high-intensity electric field treatment can significantly alter the structure of myofibril proteins and affect the water-binding state; therefore, reasonable control of the electric field strength is an important factor in maintaining the structural stability and water retention capacity of meat products.

[0044] The effect of electric field strength on the textural properties of frozen catfish fillets was tested, and the results are shown in Table 3. At an electric field strength of 13.5 kV, the fillets exhibited moderate hardness, and the best elasticity, chewiness, and cohesion. Considering both water retention and textural properties, 13.5 kV was selected as the electric field strength for subsequent magnetoelectric coupling-assisted thawing.

[0045] Table 3 Effect of electric field strength on the textural properties of frozen catfish fillets (3) The effect of magnetic field strength on the quality of catfish The magnetic field strengths were set to 1, 3, 5, 7, and 9 mT, respectively, the thawing temperature was fixed at 10℃, the electric field strength was 13.5 kV, and the magnetic field frequency was 0.5 Hz.

[0046] like Figure 11As shown, magnetic field strength has a significant impact on the water-holding capacity of frozen catfish fillets thawed with magnetoelectric coupling (P < 0.05). With increasing magnetic field strength, water-holding capacity initially increases and then decreases, reaching a maximum of 79.30% at 3 mT. A suitable magnetic field strength helps regulate the orientation and movement of water molecules, promotes uniform melting of ice crystals, and reduces cell structure damage, thereby effectively improving the product's water-holding capacity. However, when the magnetic field strength exceeds a certain range, excessively strong magnetic fields may damage cell membrane structures, leading to significant water loss and a marked decrease in water-holding capacity.

[0047] The effect of magnetic field strength on the textural properties of frozen catfish fillets was tested, and the results are shown in Table 4. There was no significant difference in the chewiness of catfish fillets thawed with magnetoelectric coupling under different magnetic field strengths, while the fillets exhibited moderate hardness, optimal elasticity, and cohesion at 3 mT. Considering both water retention and textural properties, 3 mT was selected as the magnetic field strength for subsequent magnetoelectric coupling-assisted thawing.

[0048] Table 4. Effect of magnetic field strength on the textural properties of frozen catfish fillets (4) The effect of magnetic field frequency on the quality of catfish The magnetic field frequencies were set to 0.1, 0.3, 0.5, 0.7, and 0.9 Hz, respectively, the thawing temperature was fixed at 10℃, the electric field strength was 13.5 kV, and the magnetic field strength was 5 mT.

[0049] Depend on Figure 12 It was found that the magnetic field frequency had a significant impact on the water-holding capacity of frozen catfish fillets thawed with magnetoelectric coupling (P < 0.05). Overall, the water-holding capacity showed a trend of first increasing and then decreasing with changes in magnetic field frequency. The highest water-holding capacity, reaching 78.18%, was observed at a magnetic field frequency of 0.3 Hz. A suitable magnetic field frequency helps to stimulate beneficial resonance between water molecules and cell structures, promoting uniform thawing of ice crystals, reducing mechanical damage to cell membranes and muscle tissue, and improving the water-holding capacity of the fillets. However, when the frequency is too low or too high, the effect of the magnetic field weakens, and it may even have an adverse effect on the tissue structure, leading to significant water loss and a decrease in water-holding capacity.

[0050] The effect of magnetic field frequency on the textural properties of frozen catfish fillets was tested, and the results are shown in Table 5. At a magnetic field frequency of 0.3 Hz, the catfish fillets exhibited moderate hardness and chewiness, while exhibiting optimal elasticity and cohesion. Considering both water retention and textural properties, 0.3 Hz was selected as the magnetic field frequency for magnetoelectric coupling-assisted thawing.

[0051] Table 5. Effect of magnetic field frequency on the textural properties of frozen catfish fillets Example 4

[0052] Based on the results of the single-factor experiments, the thawing temperature for frozen catfish fillets was determined to be 10℃. According to the Box-Behnken central composite design principle, electric field strength (A), magnetic field strength (B), and magnetic field frequency (C) were selected as the three independent variables in the response surface methodology. Using the elasticity index as the response value, a three-factor, three-level response surface optimization experiment was designed using Design-Expert 13 to further analyze the impact of each factor on the quality of the frozen catfish fillets during the thawing process and to find the most suitable process parameters. The response surface methodology factor level table is shown in Table 6.

[0053] Table 6 Response Surface Experiment Factor Levels SPSS 19 was used to perform analysis of variance and significance analysis on the data in the single-factor experiment. The data are expressed as mean ± standard deviation. At the same time, Origin 2021 software and Design-Expert 13 were used to draw charts and perform response surface optimization design.

[0054] (1) Establishment and analysis of response surface regression model The electric field strength, magnetic field strength, and magnetic field frequency of magnetoelectric coupling-assisted thawing are important factors in the thawing process of frozen catfish fillets. These three factors have a significant impact on the water-holding capacity, hardness, and elasticity of the fillets. Considering the changing patterns of each indicator and the requirements of subsequent fish fillet crisping processing on the raw material's tissue state, elasticity is relatively sensitive to changes in processing conditions and can reflect the integrity of the fish meat's tissue structure and its processing adaptability to a certain extent. Therefore, using elasticity as the response value, a three-factor, three-level optimization experiment was conducted based on the Box-Behnken central composite design principle. A total of 17 sets of experiments were carried out, including 14 analytical experiments and 3 zero-point replication experiments. The experimental results are shown in Table 7.

[0055] A quadratic multiple regression analysis was performed on the response surface methodology results using Design-Expert 13, with elasticity as the evaluation index. The resulting regression equation is: Elasticity Y = 0.42 + 0.01A + 0.0075B + 0.005C + 0.0025AB + 0.0025AC - 0.0175BC - 0.0187A 2 - 0.0087B 2 - 0.0188C 2 .

[0056] Table 7 Response Surface Experimental Design and Results As can be seen from Table 8, for the regression model, P = 0.0032 < 0.01, and the lack-of-fit term is 0.8032, which is not significant, indicating that this regression model has a high goodness of fit and truly reflects the actual situation. The coefficient of determination R 2 = 0.9270, indicating that the mathematical regression model established by the experiment has a good goodness of fit. The adjusted coefficient R 2 Adj = 0.8331, indicating that the model can explain 83.31% of the response value changes. Among the first-order terms of the factors, A, B, and the interaction term BC, as well as the second-order terms A2 and C2, have a significant impact on the elasticity of catfish fillets (P < 0.05). The first-order term C and the interaction terms AB, AC, and the second-order term B2 have no significant impact on the elasticity of catfish fillets (P > 0.05). From this, it can be known that the primary and secondary order of the influence of each factor designed in this experiment on elasticity is electric field strength (A) > magnetic field strength (B) > magnetic field frequency (C).

[0057] Table 8 Analysis of variance of the elasticity regression model Note: "*" indicates significant difference (0.01 < P < 0.05), and "**" indicates extremely significant difference (P < 0.01).

[0058] (3)Results of response surface and contour line analysis Through software processing, based on regression analysis and regression equation fitting, the response surface and the corresponding contour line analysis diagram are obtained. In the response surface diagram, if the graph is steeper, the interaction effect between the two is more significant. The degree of their interaction can be judged according to the shape of the contour line diagram. If the graph is elliptical and dense, the interaction phenomenon is more obvious.

[0059] From Figure 13 it can be seen that the contour line diagram of the electric field strength and the magnetic field strength (AB) is a dense ellipse, and the response surface diagram shows an obvious bending trend, indicating that there is an obvious interaction between the two and it has a relatively significant impact on the elasticity of catfish fillets. The contour line diagram of the electric field strength and the magnetic field frequency (AC) is close to a circle, indicating that the interaction between the two is weak, but the slope of its response surface diagram is steep, indicating that it has a strong impact on the elasticity of catfish fillets. In addition, the slope of the response surface diagram of the magnetic field strength and the magnetic field frequency (BC) is large, the contour line shows an obvious ellipse, and the distribution is relatively dense, indicating that there is a significant interaction effect between the two. The reasonable matching of the magnetic field strength and the frequency plays an important role in optimizing the elasticity of catfish fillets.

[0060] Response surface methodology analysis showed that the optimal thawing process parameters, using elasticity as an indicator, were: electric field strength 14.841 kV, magnetic field strength 4.191 mT, and magnetic field frequency 0.275 Hz. Under these conditions, the elasticity value was 0.423. Considering operational convenience, the optimized parameters were modified to an electric field strength of 15 kV, a magnetic field strength of 4 mT, and a magnetic field frequency of 0.3 Hz. To verify the reliability of the response surface methodology, the above optimized formulation parameters were used to thaw catfish fillets, and their quality was measured. The results showed an elasticity of 0.423 ± 0.004.

[0061] The above description is merely 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 method for thawing frozen catfish fillets using magnetoelectric coupling-assisted thawing, characterized in that, include: Place the frozen catfish fillets in a sealed bag and put them in a magneto-coupled freezer. Insert a thermocouple thermometer probe into the center of the meat sample to monitor the temperature in real time. Stop the magneto-coupled process when the temperature reaches the preset temperature, and the thawing is complete.

2. The method for thawing frozen catfish fillets using magnetoelectric coupling as described in claim 1, characterized in that, The magnetoelectric coupling freezer / refrigerator is configured with the following parameters: temperature 4℃-25℃, electric field strength 4.5kV-22.5kV, magnetic field strength 1mT-9mT, and magnetic field efficiency 0.1 Hz-0.9 Hz.

3. The method for thawing frozen catfish fillets using magnetoelectric coupling as described in claim 2, characterized in that, The magnetoelectric coupling freezer is configured with the following parameters: temperature 10℃, electric field strength 15 kV, magnetic field strength 4 mT, and magnetic field efficiency 0.3 Hz.

4. The method for thawing frozen catfish fillets using magnetoelectric coupling as described in claim 1, characterized in that, The thermocouple thermometer probe is inserted into the center of the meat sample to a depth of 2cm-3cm, and the predetermined temperature is 2℃-4℃.

5. The application of the method according to any one of claims 1-4 in the thawing of frozen catfish fillets and the processing of pre-processed fish products.

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