Meat ice crystal temperature point rapid measurement method and system based on low-field nuclear magnetic resonance

Abstract

The invention belongs to the field of food detection, and particularly relates to a meat ice crystal temperature point rapid measurement method and system based on low-field nuclear magnetic resonance. By optimizing test parameters of the low-field nuclear magnetic resonance spectrometer and combining accurate temperature control of the low-temperature constant-temperature module, continuous acquisition of gradient cooling signals from normal temperature to-80 DEG C can be realized only by directly putting a meat sample into a low-temperature-resistant sealed sample tube, and a moisture phase change inflection point is determined through a change curve of a transverse relaxation time T2 spectrum. The corresponding temperature is the ice crystal temperature point. The method has the advantages of no damage to samples in the detection process, no pollution, simple and easy operation, low instrument and equipment maintenance cost, good stability and high reliability, and can be used in field environments such as food processing workshops and refrigeration houses. The detection result is high in accuracy, the actual condition of the ice crystal point of the chicken can be accurately reflected, and a scientific basis is provided for optimization of a freezing process.

Description

Technical Field

[0001] This invention relates to the field of food testing, and in particular to a method and system for rapid measurement of ice crystal temperature points in meat products based on low-field nuclear magnetic resonance. Background Technology

[0002] Meat storage is a method of preserving meat in daily life and industrial production. Its scientific basis and standardization are extremely important for the development of the food industry, food safety, and the protection of consumer rights. Meat is rich in high-quality protein, water, and various nutrients. It naturally has the characteristics of being prone to the growth of pathogenic bacteria and the occurrence of fat oxidation and protein degradation. If the storage conditions are not proper, not only will quality problems such as darkening of color, loosening of meat, loss of juice, and deterioration of flavor occur in a short period of time, causing the product to lose its commercial value, but it may also pose foodborne safety risks due to the large-scale proliferation of microorganisms or the accumulation of harmful substances such as biogenic amines, threatening consumer health.

[0003] Precise measurement of the ice crystal temperature point in meat products allows for microscopic optimization of ice crystal formation and distribution, thereby maximizing the preservation of core quality characteristics. This reduces mechanical damage to myofiber cells caused by ice crystals during ultra-low temperature freezing, maintains cell membrane integrity, and minimizes juice loss after thawing. It also effectively preserves the meat's inherent bright red color, firmness, elasticity, and natural umami flavor, preventing rancidity and toughness caused by fat oxidation and protein denaturation. Furthermore, precise storage solutions based on the ice crystal temperature point (such as stabilizing storage temperatures near this point) completely solidify all moisture in the meat, thoroughly inhibiting the growth of pathogenic bacteria, parasite survival, and biochemical deterioration reactions such as fat oxidation and biogenic amine accumulation, thus extending the meat's shelf life.

[0004] There are various techniques for determining the ice crystal temperature point in meat products, including differential scanning calorimetry (DSC), cryogenic thermometry, and resistance thermometry. However, each of these methods has different limitations on the sample. Traditional methods generally require destructive pretreatment of the meat, such as crushing, electrode insertion, and sealing, which not only makes sample recovery and reuse impossible and cumbersome but also easily introduces human error. Furthermore, existing technologies are significantly affected by the characteristics of the meat matrix. For example, salt in high-salt processed meats (sausages, hams) can easily alter the system's conductivity or phase transition heat flow signal, and fat crystals in high-fat meats can mask the characteristic signal of water freezing, leading to poor measurement stability and large errors (the error of conventional methods can reach ±2-3℃). In addition, some methods (such as DSC) have problems such as high operational thresholds, long processing times, and expensive instrument costs, making it difficult to meet the dual needs of rapid detection in industry and precise analysis in academic research.

[0005] Therefore, there is an urgent need to design a detection method that is simple to operate, highly accurate, and stable. Summary of the Invention

[0006] The technical problem to be solved by this invention is to design a rapid measurement method and system for ice crystal temperature points in meat products. Based on the advantage of low-field nuclear magnetic resonance technology in specifically identifying hydrogen nuclei signals in liquid water, a meat product ice crystal temperature point detection system with strong resistance to matrix interference and no need for complex pretreatment is constructed, thereby solving the existing technical problems.

[0007] To address the aforementioned technical problems, this invention provides a rapid method for measuring the ice crystal temperature of meat products based on low-field nuclear magnetic resonance, specifically including the following steps: Step S1: Select fresh meat tissue, cut it into pieces, absorb the surface moisture, place it in a low-temperature resistant sample tube, and seal the tube opening.

[0008] Step S2: Place the sealed sample tube in the temperature control probe of the low-field NMR spectrometer, and use the CPMG sequence to acquire the NMR transverse relaxation time T2 spectrum of the sample.

[0009] Step S3: Control the sample temperature using a reverse heating program, with a heating range of t ℃ to 0 ℃. Set the heating rate and the temperature stabilization time for each step. At each temperature stabilization point, acquire nuclear magnetic resonance signals using a CPMG pulse sequence to obtain the transverse relaxation time T2 spectrum of the sample at different temperatures.

[0010] Step S4: Determine the inflection point of the water phase transition by the change curve of the transverse relaxation time T2 spectrum. The corresponding temperature is the ice crystal temperature point.

[0011] Furthermore, in step S1 of this invention, when selecting meat samples, fascia and adipose tissue are avoided, and the volume of the sample cut is 1 cm³. 3 ~2 cm 3 .

[0012] Furthermore, in step S1 of this invention, the sample tube is a polytetrafluoroethylene sample tube, and the volume of the sample tube matches the volume of the sample.

[0013] Furthermore, in step S2 of this invention, the magnetic field strength of the low-field nuclear magnetic resonance spectrometer is 0.2 T to 0.6 T, and the magnet temperature is controlled at 32℃ ± 2℃.

[0014] Furthermore, in step S3 of this invention, the range of the initial temperature t for heating is... .

[0015] Furthermore, in step S3 of this invention, the heating rate is 1 °C / step, and the temperature stabilization time for each step is 5 minutes.

[0016] Furthermore, in this invention, the transverse relaxation time T2 spectrum of the sample is obtained by software calculation provided by the low-field nuclear magnetic resonance spectrometer system. The complex decay curve is transformed into a transverse relaxation time T2 spectrum by inversion through a joint iterative correction algorithm and a fast non-negative least squares algorithm. The horizontal axis of the T2 spectrum is the relaxation time, and the vertical axis is the amplitude of the corresponding signal. Different peaks in the spectrum correspond to different states of water content.

[0017] In a further step of this invention, in step S4, the changes in the transverse relaxation time T2 spectrum of liquid water in meat at different temperatures are tracked, and the peak area ratios of free water, non-flowing water and bound water and the dynamic changes in the total peak area are quantified. When the total peak area drops to the lower limit of instrument detection and the fluctuation is ≤1% of the initial total peak area, the corresponding temperature is the ice crystal temperature point of the meat.

[0018] This invention also provides a rapid measurement system for the ice crystal temperature of meat products based on low-field nuclear magnetic resonance, employing the aforementioned rapid measurement method for the ice crystal temperature of meat products based on low-field nuclear magnetic resonance, and including the following modules: The sample carrier module is used to hold the meat samples to be tested.

[0019] The nuclear magnetic resonance detection module is used to apply radio frequency pulses to the sample and acquire hydrogen nucleus resonance signals. The nuclear magnetic resonance detection module includes a magnetic field generating unit and a signal acquisition unit. The magnetic field generating unit can generate a low-field magnetic field, and the signal acquisition unit uses the CPMG sequence to acquire the transverse relaxation time T2 signal of the sample.

[0020] A precise temperature control module, connected to the sample carrier module, is used to control the sample temperature to change according to a preset program and has a temperature stability control function.

[0021] The data processing module is communicatively connected to the nuclear magnetic resonance detection module. It is used to receive the relaxation signal acquired by the signal acquisition unit, convert the relaxation signal decay curve into a T2 spectrum through an inversion algorithm, quantify the peak area and total peak area corresponding to bound water and non-flowing water, and determine the ice crystal temperature point of chicken meat based on the fluctuation of the total peak area.

[0022] Furthermore, the present invention also includes a control module, which is electrically connected to the nuclear magnetic resonance detection module, the precision temperature control module, and the data processing module, respectively, for coordinating the collaborative work of each module and controlling the synchronous execution of temperature changes and signal acquisition.

[0023] The present invention provides a rapid measurement method and system for the ice crystal temperature of meat products based on low-field nuclear magnetic resonance (NMR). By optimizing the test parameters of the low-field NMR instrument and combining it with the precise temperature control (accuracy ±0.1 ℃) of the low-temperature isothermal module, the method allows for continuous acquisition of gradient cooling signals from room temperature to -80 ℃ simply by placing the meat sample directly into a low-temperature resistant sealed sample tube. By tracking the changes in the transverse relaxation time (T2) spectrum of liquid water in the meat product at different temperatures, the method quantifies the dynamic changes in the peak area ratios of free water, immobile water, and bound water, as well as the total peak area. When the total peak area drops to the instrument's detection limit, with fluctuations ≤1% of the initial value, the corresponding temperature is the ice crystal temperature of the meat product.

[0024] This invention can accurately and quickly obtain ice crystal temperature data for different types of meat products. It not only provides core technical support for optimizing ultra-low temperature freezing processes for meat (such as setting the final freezing temperature and controlling the cooling rate) and formulating ultra-long shelf-life storage plans (such as ultra-low temperature preservation of reserve meat and high-value meat), but can also be widely applied to food science academic research (such as analyzing the mechanism of "freezing temperature-moisture state-quality correlation"), quality control and testing in the meat product industry, and safety supervision of cold chain logistics. It has important industrial application value and academic research significance.

[0025] The present invention has the following beneficial effects: (1) It does not require destructive pretreatment of meat products, and the samples can be completely recovered for subsequent quality correlation analysis (such as observation of ice crystal structure and determination of juice loss rate), and the measurement process does not damage or contaminate the samples.

[0026] (2) The measurement results are highly accurate (error ≤ ±1 ℃), have strong resistance to matrix interference, and are not affected by the salt content, fat content and processing auxiliary materials of meat products. They are suitable for the detection of ice crystal temperature points of fresh livestock meat, poultry meat, aquatic products and various processed meat products.

[0027] (3) It has good stability, with a measurement deviation of ≤ ±0.5 ℃ for parallel samples, which can effectively avoid signal interference and operational errors of traditional methods.

[0028] (4) The detection process is safe and environmentally friendly. No chemical reagents are required. The radio frequency radiation dose of low field nuclear magnetic resonance meets safety standards and is harmless to the human body. The instrument is easy to operate and the maintenance cost is controllable. Attached Figure Description

[0029] The specific embodiments of the present invention will be further explained below with reference to the accompanying drawings.

[0030] Figure 1 This is a flowchart of the rapid measurement method for ice crystal temperature points in meat products based on low-field nuclear magnetic resonance according to the present invention.

[0031] Figure 2The T2 spectrum is the T2 spectrum of the fresh chicken sample detected in Example 1.

[0032] Figure 3 This is a diagram showing the changes in moisture migration during the low-temperature freezing process of chicken in Example 1.

[0033] Figure 4 This is a signal change diagram of the chicken low-temperature freezing process in Example 1.

[0034] Figure 5 This is a system block diagram of the rapid measurement system for ice crystal temperature points in meat products based on low-field nuclear magnetic resonance according to the present invention. Detailed Implementation Example 1

[0035] Combination Figure 1 As shown in the figure, the rapid measurement method for ice crystal temperature points in meat products based on low-field nuclear magnetic resonance in this embodiment specifically includes the following steps: Step S1: Select fresh meat tissue, cut it into pieces, absorb the surface moisture with filter paper, place it in a low-temperature resistant sample tube and seal the tube opening to prevent moisture in the air from condensing on the sample surface at low temperatures and interfering with the signal.

[0036] In this embodiment, preferably, in step S1, when selecting the meat sample, fascia and adipose tissue are avoided, and the sample volume is cut to 1 cm³. 3 ~2 cm 3 .

[0037] In this embodiment, preferably, in step S1, the sample tube is a polytetrafluoroethylene sample tube, and the volume of the sample tube matches the volume of the sample, which can just accommodate the test sample, without leaving excess air or exceeding the measurement range.

[0038] Step S2: Place the sealed sample tube in the temperature control probe of the low-field NMR spectrometer, and use the CPMG sequence to acquire the NMR transverse relaxation time T2 spectrum of the sample.

[0039] In this embodiment, preferably, in step S2, the magnetic field strength of the low-field nuclear magnetic resonance spectrometer is 0.2 T~0.6 T, and the magnet temperature is controlled at 32℃±2℃.

[0040] Step S3: Control the sample temperature using a reverse heating program, with a heating range of t ℃ to 0 ℃. Set the heating rate and the temperature stabilization time for each step. At each temperature stabilization point, acquire nuclear magnetic resonance signals using a CPMG pulse sequence to obtain the transverse relaxation time T2 spectrum of the sample at different temperatures.

[0041] In this embodiment, preferably, in step S3, the range of the initial temperature t for heating is: .

[0042] In this embodiment, preferably, in step S3, the heating rate is 1 °C / step, and the temperature stabilization time for each step is 5 minutes.

[0043] In this embodiment, preferably, the transverse relaxation time T2 spectrum of the sample is calculated by the software built into the low-field nuclear magnetic resonance spectrometer system. After the instrument applies a radio frequency pulse to the sample, the hydrogen nuclei in the water are excited and resonate, then release energy to return to the ground state. The instrument collects the echo attenuation curve of this process, which is a comprehensive signal of the water state. Since the original signal cannot directly characterize the water distribution, an inversion is performed using a joint iterative correction algorithm and a fast non-negative least squares algorithm to transform the complex attenuation curve into a transverse relaxation time T2 spectrum. The horizontal axis of the T2 spectrum is the relaxation time, and the vertical axis is the amplitude of the corresponding signal. Different peaks in the spectrum correspond to different states of water.

[0044] Step S4: Determine the inflection point of the water phase transition by the change curve of the transverse relaxation time T2 spectrum. The corresponding temperature is the ice crystal temperature point.

[0045] In this embodiment, preferably, in step S4, the changes in the transverse relaxation time T2 spectrum of liquid water in meat at different temperatures are tracked, and the peak area ratios of free water, non-flowing water and bound water and the dynamic changes in the total peak area are quantified. When the total peak area drops to the lower limit of instrument detection and the fluctuation is ≤1% of the initial total peak area, the corresponding temperature is the ice crystal temperature point of the meat.

[0046] In this embodiment, taking the detection of ice crystal temperature in chicken meat as an example, the specific operation is as follows: Select fresh chicken breast or thigh meat, avoiding tendons and fat when selecting samples, and ensure that the moisture content of the chicken meat is uniform. Cut it into 2 cm × 1 cm × 1 cm cuboids, use filter paper to absorb the moisture on the sample surface, and quickly place it into a low-temperature resistant polytetrafluoroethylene sample tube to avoid moisture evaporation. Seal the tube opening to prevent moisture in the air from condensing on the sample surface at low temperatures and interfering with the signal.

[0047] The sample tube was placed in the sample temperature control probe slot of an NMRC12-010V nuclear magnetic resonance analyzer manufactured by Suzhou Newmai Analytical Instruments Co., Ltd. The analyzer had a resonance frequency of 12 MHz, a magnet strength of 0.50 T ± 0.02 T, a coil diameter of 10 mm, and a magnet temperature of 32 ℃. Signal acquisition was performed using the CPMG sequence in the "Newmai NMR Analysis and Measurement Software" to obtain the fresh sample NMR T2 spectrum. The measurement results are as follows: Figure 2 As shown: Figure 2This reflects the distribution characteristics of water in different states in fresh chicken. The horizontal axis of the T2 spectrum represents relaxation time, and the vertical axis represents the amplitude of the corresponding signal. Different peaks in the spectrum correspond to water in different states. Two main types of water can be identified from the graph (fresh chicken usually contains three types of water, but the bound water signal is weaker in the graph): Bound water T21: corresponds to a weak signal (amplitude close to 0) in the 0.01~10 ms interval of the graph, with an extremely short relaxation time (usually 1~10 ms). It is water tightly bound to the hydrophilic groups of chicken proteins (such as myosin), with very low mobility, and its content is usually 5%~10%. Non-flowing water + free water (merged peak): corresponds to a strong peak (highest amplitude) near 100 ms in the graph. In fresh chicken meat, this type of water actually comprises two states: immobile water (T22): relaxation time approximately 40–60 ms, which is water trapped within myofibrils, accounting for 70%–80% (playing a key role in chicken tenderness and water retention); and free water (T22): relaxation time approximately 150–400 ms, which is extracellular free water. The peaks of these two types of water in the figure merge into a single broad peak, indicating that the difference in mobility between immobile and free water in fresh chicken meat is small, and the water distribution is uniform.

[0048] The sample temperature was controlled by a reverse heating program of 1℃ / step within the range of -30℃ to 0℃, with each step stabilizing for 5 minutes. Nuclear magnetic resonance signals were acquired using a CPMG pulse sequence, and the T2 relaxation time variation curves were measured. The low-field NMR T2 relaxation spectra of chicken meat at different low-temperature freezing temperatures are shown below. Figure 3 As shown: Figure 3 This reflects the migration and changes in the moisture state of chicken during freezing. Low-temperature curve: The peak position shifts towards a shorter T2 range (shorter relaxation time), indicating a reduced degree of freedom of water movement. This is because at low temperatures, the less mobile water in the chicken gradually transforms into bound water (or is bound by ice crystals), resulting in a tighter bond between water and the chicken matrix. High-temperature curve: The peak position is relatively longer within the T2 range, and the signal intensity distribution is more dispersed, indicating that the water is still mainly composed of less mobile water, with a weaker migration degree. Peak shape differences: The peaks of the low-temperature curve are more "sharp and concentrated," while the peaks of the high-temperature curve are relatively "broad and gentle," reflecting a simpler moisture state at low temperatures (mainly bound water) and a more complex moisture state at high temperatures (coexistence of multiple moisture states).

[0049] Changes in low-field NMR signal during the cryogenic freezing process of chicken, such as Figure 4 As shown, Figure 4 This reflects the dynamic signal response of hydrogen nuclei (mainly corresponding to water) during the freezing stage. The significant drop in signal intensity is a direct result of the large-scale formation of ice crystals. Ice crystals alter the hydrogen nucleus environment of water, reducing the detectability of the signal. The final stable low signal indicates that only a small amount of easily detectable bound water remains in the chicken meat during the later stages of freezing.

[0050] In this embodiment, fresh chicken breast and chicken thigh meat were sampled and tested on both sides. The test results are shown in Tables 1 and 2. T21 represents bound water, and A21 is its corresponding signal quantity, also known as peak area; T22 represents non-flowing water, and A22 is its corresponding signal quantity, also known as peak area. Fresh meat has no free water or a very small proportion of free water, which is negligible. The peak area of ​​different water types divided by the total peak area represents the proportion. Table 1 shows the test results of relaxation time-signal quantity changes during the low-temperature freezing process of chicken breast meat, and Table 2 shows the test results of relaxation time-signal quantity changes during the low-temperature freezing process of chicken thigh meat.

[0051] Table 1:

[0052] Table 2:

[0053] The transverse relaxation time (T2) spectrum of liquid water in meat products was tracked at different temperatures. The peak area ratios of free water, non-flowing water, and bound water were quantified, along with the dynamic changes in the total peak area. When the total peak area dropped to the instrument's detection limit, with fluctuations ≤ 1% of the initial total peak area, the corresponding temperature was identified as the ice crystal temperature point of the meat product. In this embodiment, the ice crystal temperature point of chicken meat was found to be -24 ℃.

[0054] Low-field nuclear magnetic resonance (NMR) technology, with its non-destructive and high-throughput detection advantages, combined with freeze-thaw control technology, can rapidly and accurately locate the critical temperature (i.e., ice crystal point) of free water in chicken meat during low-temperature processing by capturing the dynamic changes of hydrogen nucleus relaxation signals in real time. This detection method not only avoids the shortcomings of traditional detection methods (such as differential scanning calorimetry) that are complex and time-consuming, but also controls the signal deviation rate of repeated detection to within 5%, demonstrating excellent stability and consistency of detection results. It fully meets the stringent requirements of the food industry for "accuracy to ±0.5℃" in chicken ice crystal point detection. This technology combination can be deeply integrated into core links such as chicken processing (e.g., quick-frozen prepared meat product production) and cold chain storage (e.g., temperature monitoring during long-distance transportation). By accurately controlling the ice crystal point, it can reduce the mechanical damage of ice crystals to muscle fibers, thereby improving the water retention, tenderness, and other quality indicators of chicken products, providing efficient and reliable technical support for the whole-chain quality control of food enterprises.

[0055] This invention's detection process is non-destructive and non-contaminated to the sample, simple and easy to operate, with low instrument maintenance costs. It can be used in on-site environments such as food processing workshops and cold storage facilities, exhibiting good stability and high reliability. The detection results of this invention are highly accurate, precisely reflecting the actual ice crystal point of chicken meat, providing a scientific basis for optimizing freezing processes. Example 2

[0056] Combination Figure 5 As shown, the rapid measurement system for meat ice crystal temperature points based on low-field nuclear magnetic resonance in this embodiment adopts the rapid measurement method for meat ice crystal temperature points based on low-field nuclear magnetic resonance in Embodiment 1, and includes the following modules: The sample carrier module is used to hold the meat samples to be tested.

[0057] The nuclear magnetic resonance detection module is used to apply radio frequency pulses to the sample and acquire hydrogen nucleus resonance signals. The nuclear magnetic resonance detection module includes a magnetic field generating unit and a signal acquisition unit. The magnetic field generating unit can generate a low-field magnetic field, and the signal acquisition unit uses the CPMG sequence to acquire the transverse relaxation time T2 signal of the sample.

[0058] A precise temperature control module, connected to the sample carrier module, is used to control the sample temperature to change according to a preset program and has a temperature stability control function.

[0059] The data processing module is communicatively connected to the nuclear magnetic resonance detection module. It is used to receive the relaxation signal acquired by the signal acquisition unit, convert the relaxation signal decay curve into a T2 spectrum through an inversion algorithm, quantify the peak area and total peak area corresponding to bound water and non-flowing water, and determine the ice crystal temperature point of chicken meat based on the fluctuation of the total peak area.

[0060] In this embodiment, preferably, a control module is also included, which is electrically connected to the nuclear magnetic resonance detection module, the precision temperature control module, and the data processing module, respectively, to coordinate the collaborative work of each module and control the synchronous execution of temperature changes and signal acquisition.

[0061] Many specific details have been set forth in the foregoing description to provide a thorough understanding of the present invention. However, the above description is merely a preferred embodiment of the present invention, and the present invention can be implemented in many other ways different from those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed above. Furthermore, any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, using the methods and techniques disclosed above, without departing from the scope of the present invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A rapid method for measuring the ice crystal temperature point of meat products based on low-field nuclear magnetic resonance, characterized in that: Includes the following steps: Step S1: Select fresh meat tissue, cut it into pieces, absorb the surface moisture, place it in a low-temperature resistant sample tube and seal the tube opening; Step S2: Place the sealed sample tube in the temperature control probe of the low-field NMR spectrometer, and use the CPMG sequence to acquire the NMR transverse relaxation time T2 spectrum of the sample. Step S3: The sample temperature is controlled by a reverse heating program, with a heating range of t ℃~0 ℃. The heating rate and temperature stabilization time for each step are set. At each temperature stabilization point, nuclear magnetic resonance signals are acquired using a CPMG pulse sequence to obtain the transverse relaxation time T2 spectrum of the sample at different temperatures. Step S4: Determine the inflection point of the water phase transition by the change curve of the transverse relaxation time T2 spectrum. The corresponding temperature is the ice crystal temperature point.

2. The method for rapid measurement of ice crystal temperature points in meat products based on low-field nuclear magnetic resonance according to claim 1, characterized in that: In step S1, when selecting meat samples, avoid fascia and adipose tissue, and cut the sample to a volume of 1 cm³. 3 ~2cm 3 .

3. The method for rapid measurement of ice crystal temperature points in meat products based on low-field nuclear magnetic resonance according to claim 1, characterized in that: In step S1, the sample tube is a polytetrafluoroethylene sample tube, and the volume of the sample tube matches the volume of the sample.

4. The method for rapid measurement of ice crystal temperature points in meat products based on low-field nuclear magnetic resonance according to claim 1, characterized in that: In step S2, the magnetic field strength of the low-field nuclear magnetic resonance spectrometer is 0.2 T to 0.6 T, and the magnet temperature is controlled at 32℃±2℃.

5. The method for rapid measurement of ice crystal temperature points in meat products based on low-field nuclear magnetic resonance according to claim 1, characterized in that: In step S3, the initial temperature t for heating is in the range of -80°C. -25.

6. The method for rapid measurement of ice crystal temperature points in meat products based on low-field nuclear magnetic resonance according to claim 1, characterized in that: In step S3, the heating rate is 1 °C / step, and the temperature stabilization time for each step is 5 minutes.

7. The method for rapid measurement of ice crystal temperature points in meat products based on low-field nuclear magnetic resonance according to claim 1, characterized in that: The transverse relaxation time T2 spectrum of the sample was calculated by the software built into the low-field nuclear magnetic resonance spectrometer system. The complex decay curve was transformed into a transverse relaxation time T2 spectrum by using a joint iterative correction algorithm and a fast non-negative least squares algorithm. The horizontal axis of the T2 spectrum is the relaxation time, and the vertical axis is the amplitude of the corresponding signal. Different peaks in the spectrum correspond to different states of water content.

8. The method for rapid measurement of ice crystal temperature points in meat products based on low-field nuclear magnetic resonance according to claim 1, characterized in that: In step S4, the changes in the transverse relaxation time T2 spectrum of liquid water in meat at different temperatures are tracked, and the peak area ratios of free water, non-flowing water and bound water and the dynamic changes in the total peak area are quantified. When the total peak area drops to the lower limit of instrument detection and the fluctuation is ≤1% of the initial total peak area, the corresponding temperature is the ice crystal temperature point of the meat.

9. A rapid measurement system for ice crystal temperature points in meat products based on low-field nuclear magnetic resonance, characterized in that: The rapid measurement method for ice crystal temperature points in meat products based on low-field nuclear magnetic resonance, as described in any one of claims 1-8, includes the following modules: The sample carrier module is used to hold the meat samples to be tested; The nuclear magnetic resonance detection module is used to apply radio frequency pulses to the sample and acquire hydrogen nucleus resonance signals. The nuclear magnetic resonance detection module includes a magnetic field generating unit and a signal acquisition unit. The magnetic field generating unit can generate a low-field magnetic field, and the signal acquisition unit uses a CPMG sequence to acquire the transverse relaxation time T2 signal of the sample. A precise temperature control module, connected to the sample carrying module, is used to control the sample temperature to change according to a preset program and has a temperature stability control function. The data processing module is communicatively connected to the nuclear magnetic resonance detection module. It is used to receive the relaxation signal acquired by the signal acquisition unit, convert the relaxation signal decay curve into a T2 spectrum through an inversion algorithm, quantify the peak area and total peak area corresponding to bound water and non-flowing water, and determine the ice crystal temperature point of chicken meat based on the fluctuation of the total peak area.

10. The rapid measurement system for ice crystal temperature points of meat products based on low-field nuclear magnetic resonance according to claim 9, characterized in that: It also includes a control module, which is electrically connected to the nuclear magnetic resonance detection module, the precision temperature control module, and the data processing module, respectively, to coordinate the collaborative work of each module and control the synchronous execution of temperature changes and signal acquisition.

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