Low-temperature low-loss pig slaughtering pre-cooling process

Abstract

The invention discloses a low-temperature low-loss pig slaughtering pre-cooling process, and relates to the technical field of meat product processing. The process comprises the following steps: spraying the surface of the carcass to form a liquid water-containing film; the carcass is fed into a pre-cooling room for gradient pre-cooling, the temperature is controlled to be reduced from-5 DEG C to-8 DEG C to-15 DEG C to-18 DEG C at the speed of 0.1 DEG C / min to 0.2 DEG C / min in the starting stage, the relative humidity is maintained to be 92%-98%, and the water-containing film is gradually frozen to release phase change latent heat; the icing area proportion is monitored in real time, and when the icing area proportion reaches 70%-85%, a rapid cooling stage is started; in the rapid cooling stage, the temperature is controlled to be-20 DEG C to-23 DEG C, and the airflow speed is controlled to be 2.2 m / s to 3.0 m / s until the carcass center temperature is reduced to 4 DEG C to 7 DEG C. Cold impact is relieved through a phase change buffering mechanism, precooling loss can be reduced, and meat quality can be improved.

Description

Technical Field

[0001] This invention relates to the field of meat processing technology, and more specifically, to a low-temperature, low-loss pre-cooling process for pig slaughter. Background Technology

[0002] Chilled fresh meat has become the main form of pork consumption due to its good eating quality and long shelf life. After slaughter, the carcass temperature of pigs is high, requiring pre-cooling to rapidly lower the carcass temperature, inhibit microbial growth, and extend shelf life. Weight loss caused by the evaporation of surface moisture during pre-cooling is one of the main problems faced by slaughterhouses, directly impacting their economic benefits. At the same time, the pre-cooling method also has a significant impact on the eating quality of pork, including its color, water retention capacity, and tenderness.

[0003] Existing precooling processes mainly include single-stage cooling and two-stage cooling. Single-stage cooling involves directly placing the hot carcass into a cold storage room at 0°C to 4°C for 16 to 24 hours, resulting in high precooling losses. Two-stage cooling first cools the carcass in a rapid cooling room at -20°C to -30°C for about 90 minutes, then transfers it to a precooling room at 0°C to 4°C to achieve a balanced temperature. This helps reduce precooling losses, but the problem of muscle contraction and water loss due to cold shock still exists.

[0004] Chinese patent CN104273200A discloses a method for processing live pigs, which involves pre-cooling pork carcasses at -30℃ for 1 hour, then further pre-cooling them at -20℃ for 6 hours after cutting them up, achieving cooling through two stages of pre-cooling at different temperatures. Although this method achieves the pre-cooling effect, both stages of pre-cooling use constant low temperatures. The first stage of strong cooling at -30℃ can easily cause rapid freezing on the carcass surface, forming an ice shell that hinders the dissipation of internal heat, and the muscle contraction is quite significant.

[0005] Chinese patent CN103815000A discloses a method for reducing pre-cooling losses in pig carcasses. This method involves extending the carcass' time on track and increasing the number of spray cycles to lower the carcass temperature to 28°C to 30°C before it enters the rapid cooling chamber, followed by rapid cooling and acid removal for maturation. While this method reduces the temperature difference between the carcass and the cold storage through spray cooling, thus helping to reduce pre-cooling losses, the multiple spray cycles increase production steps and time, placing higher demands on production line layout, and it does not address the cold shock problem during the rapid cooling start-up phase. Summary of the Invention

[0006] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a low-temperature, low-loss pre-cooling process for pig slaughter to solve the problems of high pre-cooling loss, significant muscle contraction, and need to improve meat quality in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a low-temperature, low-loss pre-cooling process for pig slaughter, comprising the following steps: S1. Surface spraying treatment. The carcasses of slaughtered pigs are sprayed to form a liquid water-containing film on the surface of the carcass. This liquid water-containing film serves as a medium for the subsequent phase change buffering process.

[0008] S2. Gradient Precooling During Start-up. The carcass is placed in a precooling chamber for gradient precooling, which includes a start-up phase. During the start-up phase, the temperature in the precooling chamber is gradually reduced from an initial temperature of -5°C to -8°C at a cooling rate of 0.1°C / min to 0.2°C / min to -15°C to -18°C. The relative humidity in the precooling chamber is maintained at 92% to 98%, and the airflow velocity is controlled at 0.8 m / s to 1.2 m / s. Through the synergistic effect of the cooling rate and humidity, the liquid water film on the surface of the carcass gradually freezes during the cooling process. The latent heat of phase change released by the freezing of water buffers the thermal shock of cold air to the carcass.

[0009] S3. Icing Level Monitoring and Phase Switching. During the startup phase, the icing level on the carcass surface is monitored in real time. When the icing area on the carcass surface reaches 70% to 85%, the startup phase ends and the carcass transitions to the rapid cooling phase.

[0010] S4. Rapid Cooling Stage. During the rapid cooling stage, the temperature of the pre-cooling room is maintained at -20°C to -23°C, the relative humidity naturally drops to 82% to 88%, the airflow speed is increased to 2.2m / s to 3.0m / s, and cooling continues until the center temperature of the thickest part of the carcass drops to 4°C to 7°C.

[0011] Furthermore, the start-up phase described in S2 includes a film-forming sub-phase and a phase change buffer sub-phase. The film-forming sub-phase controls the pre-cooling room temperature to be maintained at -5°C to -8°C, the relative humidity to be maintained above 98%, and the airflow velocity to be below 1.0 m / s for 8 to 12 minutes, so that a uniformly thick liquid water-containing film is formed on the surface of the carcass.

[0012] The phase change buffer sub-stage controls the pre-cooling room temperature to gradually decrease from -5°C to -8°C to -15°C to -18°C at a rate of 0.1°C / min to 0.2°C / min, while maintaining the relative humidity at 92% to 95%, so that the liquid water film on the carcass surface gradually freezes and continuously releases the latent heat of phase change.

[0013] Furthermore, in the phase change buffering sub-stage, the phase change buffering process is determined by monitoring the residence time of the carcass surface temperature near 0°C. When the residence time of the surface temperature in the range of -1°C to +1°C reaches 15 min to 25 min, it is confirmed that the freezing process of the liquid water film on the carcass surface releases the latent heat of phase change.

[0014] Furthermore, the real-time monitoring of the degree of icing on the carcass surface described in S3 adopts infrared thermal imaging. By analyzing the temperature distribution image of the carcass surface, the proportion of the area with a temperature range of -1℃ to +1℃ to the total area of ​​the carcass surface is identified and calculated, and this proportion is taken as the proportion of the icing area on the carcass surface.

[0015] When the area of ​​the region with a temperature between -1℃ and +1℃ detected by infrared thermal imaging reaches its maximum value and then begins to decrease, it is determined that the proportion of the carcass surface covered with ice reaches 70% to 85%.

[0016] Furthermore, S2 and S4 implement zoned control of the temperature, humidity, and airflow velocity in the pre-cooling room, specifically including: The airflow velocity in the area corresponding to the hind legs of the carcass is increased by 20% to 30% compared to other areas of the carcass, so that the cooling rate of the hind legs is synchronized with that of the whole body; The relative humidity of the abdominal region of the carcass should be maintained 3% to 5% higher than that of other areas of the carcass to prevent excessive water loss in the thin-walled abdominal area. Infrared radiation was applied to the corresponding area on the back of the carcass to slow down its cooling rate, so that the temperature drop curves of the center of each part of the carcass tended to be synchronized.

[0017] The power density of the infrared radiation applied to the corresponding region on the back of the carcass is 0.1 W / cm². 2 Up to 0.3W / cm 2 It also dynamically adjusts based on the temperature feedback from the dorsal surface of the carcass.

[0018] Furthermore, the surface spraying treatment in S1 uses a solution containing food-grade additives, wherein the food-grade additives are at least one of glycerol or sorbitol, with a total mass concentration of 2% to 6%, the spraying time is 18s to 25s, and the spraying pressure is 0.22MPa to 0.28MPa.

[0019] The additive is used to lower the freezing point of the aqueous film, thereby extending the phase change buffer zone to a lower temperature range.

[0020] Furthermore, after the temperature at the center of the thickest part of the carcass in S4 drops to 4°C to 7°C, the carcass is transferred out of the pre-cooling room and sent to the maturation room at 0°C to 4°C for acid removal and maturation for 16 to 24 hours.

[0021] In the above technical solution, a uniform water-containing film is formed through the film-forming sub-stage, providing a medium for phase change buffering; the cooling rate and humidity are controlled through the phase change buffering sub-stage, allowing the water film to slowly freeze and release the latent heat of phase change, buffering the thermal shock of cold air to the carcass; the proportion of ice-forming area is monitored in real time through infrared thermal imaging, enabling precise switching between the start-up stage and the rapid cooling stage; zoned control ensures synchronous cooling of different parts of the carcass, avoiding localized overcooling or delayed cooling; additives are used to adjust the freezing point of the water-containing film, expanding the process's adaptability to different carcass types; and final quality improvement is achieved through aging and aging. All steps work together to achieve a low-temperature, low-loss pre-cooling process for pig slaughter.

[0022] The technical effects and advantages of this invention are as follows: This invention creates a high-humidity environment and controls the cooling rate during the rapid cooling initiation phase, allowing the water-containing film on the carcass surface to gradually freeze at a controllable rate. The latent heat of phase change released during the freezing process buffers the direct thermal shock of cold air to the carcass, preventing muscle contraction due to rapid cooling, helping to maintain the integrity of muscle cells, reducing intracellular water loss, and thus improving the water retention and tenderness of pork.

[0023] This invention employs infrared thermal imaging to monitor the degree of icing on the carcass surface in real time, and dynamically controls the switching of stages based on the proportion of iced area. This adaptive control method can adapt to differences in carcass size and fat thickness, ensuring that each carcass receives an optimized cooling curve. It avoids overcooling or undercooling caused by uniform parameters, and helps to further improve the consistency of precooling effect.

[0024] This invention employs a zoned control strategy during the rapid cooling phase, adjusting wind speed, humidity, and infrared radiation intensity separately for different parts of the carcass, such as the hind legs, abdomen, and back, to synchronize the temperature drop curves of each part. This differentiated control avoids the microbial risks caused by delayed cooling of the hind legs, while preventing localized frostbite caused by excessive cooling of the abdomen and back, thus helping to improve the overall uniformity of carcass cooling and meat quality.

[0025] This invention effectively reduces moisture loss from carcass evaporation during precooling by controlling a gradient cooling process involving water film formation, phase change buffering, and rapid cooling. Compared to existing technologies, this invention establishes a complete technical path from surface water film formation to phase change buffering and rapid cooling. The synergistic effect of each step improves meat quality while reducing precooling losses, demonstrating promising prospects for industrial application. Attached Figure Description

[0026] Figure 1 This is a linear flow diagram of the low-temperature, low-loss precooling process of the present invention.

[0027] Figure 2 This is a linear flowchart of the phase change buffer and adaptive control of the present invention. Detailed Implementation

[0028] 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.

[0029] As attached Figures 1 to 2 The low-temperature, low-loss pre-cooling process for pig slaughter shown is implemented as follows: Example 1 This embodiment applies the process to standard fattening pigs weighing 100kg to 120kg.

[0030] The control system adopts a distributed control architecture. A host industrial computer runs control software and connects to multiple PLCs via a communication protocol. Each PLC is responsible for controlling the refrigeration unit and fan, the humidifier and nozzles, and acquiring data from the infrared heating element and sensors. The host computer periodically reads sensor data, runs the core control algorithm, and then sends the setpoints to each PLC for execution.

[0031] The temperature-humidity coupled control adopts a feedforward-feedback composite control: when the humidity deviation exceeds the set value, the feedforward controller adjusts the cooling capacity in advance to offset the heat load change caused by humidification, and the feedback controller uses a PID algorithm for fine adjustment.

[0032] S1: Surface Spraying Treatment. The slaughtered pig carcasses are transported to the spraying station. The spraying system consists of multiple fan-shaped nozzles arranged around the carcass, with the nozzles positioned at a certain distance from the carcass surface. A solution containing food-grade additives, specifically glycerin, is used for spraying at a total mass concentration of 3%. The spraying time is 20 seconds, and the spraying pressure is 0.25 MPa.

[0033] During the spraying process, by adjusting the spraying time and pressure, a uniformly thick liquid water-containing film is formed on the surface of the carcass. The water film thickness should be controlled between 0.4mm and 0.6mm. The surface temperature of the carcass after spraying should be approximately 30℃ to 32℃. After spraying, the carcass should remain on the ambient temperature track section for no more than 3 minutes to avoid excessive evaporation of the water film.

[0034] A 3D laser contour scanner is installed in front of the spraying station to scan the contour of the back of the carcass and calculate the carcass volume. (unit: dm) ) and hind leg thickness (Unit: mm).

[0035] Control system according to and Automatic adjustment of process parameters: film formation time Cooling rate and switching threshold This allows the process parameters to be adapted to the carcass dimensions.

[0036] S2: Start-up Phase. The sprayed carcasses are transported along the suspended track into the pre-cooling room. The pre-cooling room is a sealed storage unit equipped with a variable frequency refrigeration unit, a variable frequency fan, an ultrasonic humidifier, and multi-point temperature and humidity sensors.

[0037] The initial temperature of the pre-cooling room was set to -6℃, the relative humidity to 98%, and the airflow velocity to 1.0 m / s. Under these conditions, [the system was maintained]. This is the film-forming sub-stage. This stage utilizes a high-humidity, low-wind-velocity environment to ensure the stable existence of the liquid aqueous film on the carcass surface and prevent it from being blown away, thus controlling the film thickness. Maintain uniformity.

[0038] In a preferred embodiment, the temperature of the film-forming sub-stage can be adjusted from -5°C to -8°C depending on the size of the carcass, the humidity can be adjusted from 98% to 100%, and the time can be adjusted from 8 min to 12 min.

[0039] This then enters the phase transition buffer sub-stage. The control system uses... The cooling rate of ℃ / min linearly decreases the precooling room temperature from -6℃ to -16℃ (denoted as the termination temperature). The cooling process is achieved by adjusting the compressor frequency to ensure that the temperature tracks the set curve.

[0040] Meanwhile, the relative humidity is maintained between 93% and 95%: the humidifier is turned on when the humidity is below the lower limit and stopped when it is above the upper limit, and the cooling capacity is adjusted synchronously through the feedforward controller to compensate for the heat load change caused by humidification. The airflow velocity is maintained between 1.0 m / s and 1.2 m / s.

[0041] During this process, through the synergistic effect of cooling rate and high humidity conditions, the liquid water film on the surface of the carcass begins to slowly freeze under the cooling effect. The latent heat released by the phase change of water molecules continuously offsets the coldness of the cold air, thereby slowing down the sudden drop in carcass surface temperature and preventing muscle cold contraction.

[0042] In a preferred embodiment, the cooling rate of the phase change buffer sub-stage can be adjusted from 0.1℃ / min to 0.2℃ / min, the termination temperature can be adjusted from -15℃ to -18℃, and the humidity can be adjusted from 92% to 98%.

[0043] An infrared thermal imager is installed on the ceiling of the pre-cooling room to collect images of the temperature distribution on the carcass surface in real time. The imager lens points vertically downwards, covering the entire carcass area, and periodically collects image data which is then transmitted to the industrial control computer.

[0044] The industrial computer analyzes and processes the image, identifies the carcass outline, extracts the area with a temperature range of -1℃ to +1℃, and calculates the proportion of this area to the total surface area of ​​the carcass as the icing area proportion. This temperature range corresponds to the phase transition plateau period in the water freezing process; by detecting this temperature range, the frozen areas can be identified.

[0045] During the phase transition buffer sub-stage... The value gradually increases from 0, reaches a peak, stabilizes, and then begins to decline, indicating that most of the water film has completed freezing. In this embodiment, The value reached 80% of the peak value (i.e.) After 0°C, the temperature began to drop, and the residence time near 0°C was 22 minutes, indicating that the phase change buffering process was sufficient.

[0046] S3: Phase Switching. When... When the value reaches its peak and then shows a downward trend after multiple consecutive samplings, the control system determines that the proportion of the carcass surface ice area has reached the switching threshold. The switching condition is met. At this point, the startup phase ends immediately, and the system enters the rapid cooling phase. During the switching instant, the control system completes the following operations sequentially within a short time: first, it resets the target temperature of the chiller unit; then, it adjusts the fan speed to rapid cooling mode; and finally, it shuts off the humidifier.

[0047] S4: Rapid Cooling Stage. Maintain the pre-cooling room temperature at -22℃, allow the relative humidity to naturally drop to around 85% (humidity gradually decreases as humidification stops), and increase the airflow velocity to 2.5 m / s. Simultaneously activate zone control: In infrared thermal imaging, three regions of interest (ROIs) are defined based on the carcass outline and prior anatomical location: ROI1 (Rear Leg): The area with a certain height and width above the bottom of the outline; ROI2 (abdomen): The area of ​​a certain height and width in the middle of the outline; ROI3 (Back): The area at the top of the outline with a certain height and width.

[0048] As the carcass moves forward on the track, the ROI position in the image coordinate system is dynamically tracked by a tracking algorithm to ensure the accuracy of temperature extraction.

[0049] Hind leg region: Average temperature at which ROI1 was extracted The target temperature drop curve is set to be consistent with the overall trend. Based on the deviation between the measured temperature in the rear leg area and the target temperature, a PID control algorithm is used to calculate the wind speed correction coefficient. This makes the actual wind speed in the rear leg area... , The overall wind speed is set at 2.5 m / s. The value is limited to between 1.2 and 1.5; values ​​outside this range are taken as boundary values. In this embodiment, the wind speed in the rear leg region... It is 3.0 m / s.

[0050] Abdominal region: Average temperature at which ROI2 was extracted Set the target humidity for this area. ,in The overall relative humidity is 85%. The humidity level is 3% to 5%. The measured humidity is adjusted by changing the flow rate of the abdominal humidifier nozzle. The deviation is less than 1%. In this embodiment, the relative humidity of the abdominal region... It remains between 88% and 90%.

[0051] Back region: Average temperature at which ROI3 was extracted Based on the deviation between the measured temperature and the target temperature in the back area, the infrared radiation power density of the back is dynamically adjusted. This allows the cooling rate of the back to be synchronized with the overall cooling rate. The value range is 0.1 W / cm. 2 Up to 0.3W / cm 2 In this embodiment 0.2W / cm 2 .

[0052] After 70 minutes of continuous cooling, the temperature of the thickest part of the carcass (center of the hind legs) was measured at 6°C using an insertion temperature probe. Once the target temperature of 4°C to 7°C was reached, the carcass was automatically transferred out of the pre-cooling chamber.

[0053] After the carcasses are transferred out, the pre-cooling room automatically returns to its initial settings (temperature -6℃, humidity 98%, wind speed 1.0m / s) to prepare for the next batch of carcasses to enter.

[0054] Mature aging and acid removal: After being transferred from the pre-cooling room, the carcasses are sent to the maturation room for acid removal and maturation. The maturation room is equipped with a cold air evaporator, with a temperature control accuracy of ±0.5℃. The temperature in the maturation room is controlled between 0℃ and 4℃, the relative humidity is 85% to 90%, and the airflow speed is 0.2m / s to 0.5m / s. The pH value is periodically measured by inserting a wireless pH meter 50mm to 60mm deep into the center of the hind legs. When the pH value drops to 5.6 to 5.8, acid removal is considered complete. If the pH does not reach the target within 24 hours, the acid removal time is extended, but not exceeding 30 hours.

[0055] Tests showed that the pre-cooling loss rate of the carcass processed in this embodiment was 0.9%, the meat was bright red, and the muscle had good water retention. Example 2

[0056] This embodiment is implemented for large-weight pigs weighing 130kg to 150kg with a thicker fat layer. The maturation and aging process is the same as in Embodiment 1.

[0057] S1: Surface spraying treatment. A solution containing food-grade additives is used, with sorbitol as the additive, and its total mass concentration is 5%. The spraying time is 25 seconds, and the spraying pressure is 0.28 MPa. After spraying, a liquid water-containing film forms on the carcass surface, with a film thickness of... The thickness ranges from 0.6 mm to 0.8 mm. Due to the large size of the carcass, the spraying time is appropriately extended to ensure full coverage. The dwell time after spraying should not exceed 3 minutes. Measurements were taken using laser scanning. dm , mm, the control system automatically adjusts the process parameters accordingly, and calculates... min, ℃ / min, %.

[0058] S2: Start-up Phase. The initial temperature of the pre-cooling room is set to -8℃, relative humidity to 99%, and airflow velocity to 0.8 m / s. The film formation sub-phase is maintained... min, to ensure uniform adhesion of the water film on the surface of the thick fat carcass.

[0059] In the phase change buffer sub-stage, the cooling rate is set to ℃ / min, gradually decreasing from -8℃ to the final temperature The temperature was maintained at ℃, relative humidity at 92% to 94%, and airflow velocity at 0.8 m / s to 1.0 m / s. Infrared thermal imaging monitoring showed the proportion of icing area. The temperature gradually increases from 0, and the residence time in this region near 0°C is 25 minutes, which is longer than that in Example 1. This is because the large body weight has a large heat capacity, which prolongs the phase change buffering process.

[0060] S3: Phase Switching. When... When the peak value is reached (75% in this embodiment) and the sampling shows a downward trend after multiple consecutive samplings, the switching condition is determined to be met. At this point, the startup phase ends and the rapid cooling phase begins. The control logic for the switching instant is the same as in Embodiment 1.

[0061] S4: Rapid cooling stage. The temperature of the pre-cooling room is maintained at -23℃, the relative humidity naturally drops to 83%, and the airflow speed is increased to 2.8m / s.

[0062] The zone control parameters are adjusted to: wind speed in the rear leg area. 3.3 m / s Take 1.25), relative humidity in the abdominal area Maintaining at 88% to 90%, the infrared radiation power density in the back region 0.25W / cm 2 (Due to the thick fat layer, more heat is needed to prevent overcooling). After 85 minutes of continuous cooling, the center temperature of the thickest part of the carcass dropped to 7°C. It was then transferred out of the pre-cooling room and sent to the 0°C maturation room for 24 hours of acid removal and maturation. The pre-cooling room automatically reset.

[0063] Tests showed that the pre-cooling loss rate of the carcass processed in this embodiment was 1.1%, and the tenderness of the meat was significantly improved. Example 3

[0064] In this embodiment, near-infrared spectroscopy is used to monitor the degree of ice formation on the carcass surface as an alternative monitoring method to infrared thermal imaging. Other steps (S1, S2, S4, and ripening and acid removal) are the same as in Example 1.

[0065] S1: Same as Example 1.

[0066] S2: The parameters for the startup phase are the same as in Example 1, but the monitoring method is different.

[0067] S3: Stage Switching. A near-infrared spectral probe is installed in the pre-cooling chamber, positioned at a certain distance from the carcass surface and irradiated at a specific angle. The reflectance spectrum is periodically collected.

[0068] The industrial control computer analyzes the spectral data and calculates the ice-water index by monitoring the change in the intensity of the liquid water absorption peak at 1450 nm. It is used to characterize the degree of icing on the surface of the carcass.

[0069] When the surface of the carcass is pure liquid water, The value is relatively high; as freezing progresses, the intensity of the liquid water absorption peak gradually weakens. The value decreased.

[0070] In this embodiment, the initial The value is 1.15, when When the value drops to 0.8 (according to calibration experiments, this value corresponds to approximately 75% of the ice-covered area), and multiple consecutive samples are taken... If all values ​​are below 0.8, the switching condition is met, the startup phase ends, and rapid cooling begins.

[0071] S4: Rapid cooling stage is the same as in Example 1.

[0072] The mature acid removal process is the same as in Example 1. Example 4

[0073] This embodiment uses the conductivity method to monitor the degree of freezing as an alternative monitoring method to infrared thermal imaging. Other steps (S1, S2, S4, and ripening and acid removal) are the same as in embodiment 1.

[0074] S1: Same as Example 1.

[0075] S2: The parameters for the startup phase are the same as in Example 1.

[0076] S3: Stage Switching. A conductivity monitoring station is set up on the straight section of the suspended track before entering the pre-cooling chamber, and a retractable contact probe is installed. The probe is driven by a pneumatic cylinder, and the contact pressure is constant. When the carcass reaches the monitoring position, the probe extends and lightly touches the surface of the hind leg of the carcass to measure the resistance value between the two points.

[0077] The probe retracts immediately after measurement to avoid affecting the movement and cooling of the carcass. In the initial state (right after spraying), the liquid water film resistance is low, and the reference resistance is used for measurement. The resistance is 0.5 MΩ. As icing progresses, the resistance gradually increases. The control system records the resistance in real time. ,when When it reaches 5MΩ (according to the calibration, (corresponding to 80% of the icing area), and multiple consecutive samplings. If all values ​​are higher than 5MΩ, the switching condition is met, and the startup phase ends.

[0078] S4: Rapid cooling stage is the same as in Example 1.

[0079] The mature acid removal process is the same as in Example 1. Example 5

[0080] This example verifies the applicability of the process for different additive combinations. Other steps (S2 to S4, maturation and acid removal) are the same as in Example 1.

[0081] S1: The surface spraying treatment uses a mixed solution containing glycerol and sodium lactate, wherein the mass concentration of glycerol is 2% and the mass concentration of sodium lactate is 1%. The spraying time is 22s and the pressure is 0.24MPa. Other steps are the same as in Example 1.

[0082] Parameters S2 to S4 are the same as in Example 1. Monitoring showed that, due to the additive lowering the freezing point, the residence time of the carcass surface temperature in the -1.5℃ to -0.5℃ range during the phase change buffer sub-stage was extended to 24 minutes, and the proportion of icing area increased. After reaching 75% of its peak, it began to decline, and the switching conditions were met.

[0083] The mature acid removal process is the same as in Example 1. Example 6

[0084] This embodiment focuses on describing the detailed implementation of partition control. S1 to S3 are the same as in Embodiment 1.

[0085] S4: During the rapid cooling phase, the specific logic of the zone control is as follows: Hind leg region: The average temperature of the hind leg region (defined as a rectangular ROI covering the hind leg contour) was extracted using infrared thermal imaging. .

[0086] The target temperature drop curve is set to be consistent with the overall trend. Based on the deviation between the measured temperature in the rear leg area and the target temperature, a PID control algorithm is used to calculate the wind speed correction coefficient. This makes the actual wind speed in the rear leg area... , The overall wind speed is set at 2.5 m / s. The value is limited to between 1.2 and 1.5; if it exceeds the range, the boundary value is used.

[0087] Abdominal region: Extract the average temperature of the abdominal region Set the target humidity for this area. ,in The overall relative humidity is 85%. The humidity level is 3% to 5%. The measured humidity is adjusted by changing the flow rate of the abdominal humidifier nozzle. The deviation is less than 1%.

[0088] Back area: Extract the average temperature of the back area Based on the deviation between the measured temperature and the target temperature in the back area, the infrared radiation power density of the back is dynamically adjusted. This allows the cooling rate of the back to be synchronized with the overall cooling rate. The value range is 0.1 W / cm. 2 Up to 0.3W / cm 2 .

[0089] All control parameters are updated periodically to ensure synchronized cooling of all parts of the carcass. Each output quantity has a safety limit.

[0090] The mature acid removal process is the same as in Example 1.

[0091] The control system of an industrial production line periodically executes the following decision-making cycle: (1) Read data from infrared thermal imaging and temperature and humidity sensors; (2) Calculate the proportion of the icing area Temperature in each region , , ; (3) If it is in the startup phase and Continue phase transition buffering; if However, it has not yet reached its peak; monitoring continues. (4) If After reaching the peak, the temperature shows a downward trend after multiple consecutive samplings, so switch to rapid cooling. (5) Calculate the temperature deviation of the rear leg during the rapid cooling stage, and calculate the wind speed correction coefficient using PID control. Adjust the rear leg wind speed after limiting the amplitude; (6) Adjust the amount of humidification on the abdomen according to the abdominal temperature and target humidity; (7) Adjust the back infrared power according to the back temperature and the target temperature; (8) Wait for the next cycle.

[0092] The key terms in the above embodiments are explained as follows: Latent heat of phase change: The heat absorbed or released by a substance during a phase change (such as from liquid to solid). When water freezes, it releases approximately 334 kJ / kg.

[0093] Film-forming sub-stage: The sub-process in the initiation stage that maintains a high humidity and low temperature environment to form a stable water film on the carcass surface.

[0094] Phase change buffering sub-stage: a sub-process in the start-up stage that controls the slow freezing of the water film and uses latent heat to buffer the cold shock.

[0095] Ice-covered area ratio: The proportion of the carcass surface temperature near the freezing point, representing the degree of icing.

[0096] PID control: Proportional-Integral-Derivative control, a feedback control algorithm that adjusts based on the proportional, integral, and derivative of the deviation.

[0097] ROI: Region of Interest, refers to a specific area in an image that needs to be analyzed in detail.

[0098] The above embodiments are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention, such as adjusting the type of additives, changing the model of the monitoring sensor, or optimizing the control algorithm, should be included within the scope of protection of the present invention.

Claims

1. A low-temperature, low-loss pre-cooling process for pig slaughter, characterized in that, Includes the following steps: S1: Spray the surface of the pig carcass after slaughter to form a liquid water-containing film on the carcass surface; S2: The carcass is sent into a precooling room for gradient precooling. The gradient precooling includes a start-up phase, in which the temperature of the precooling room is controlled to gradually decrease from an initial temperature of -5℃ to -8℃ to -15℃ to -18℃ at a cooling rate of 0.1℃ / min to 0.2℃ / min. The relative humidity of the precooling room is controlled to be maintained at 92% to 98%, and the airflow velocity of the precooling room is controlled to be 0.8m / s to 1.2m / s. Through the synergistic effect of the cooling rate and the humidity, the liquid water film on the surface of the carcass gradually freezes during the cooling process. S3: During the start-up phase, monitor the degree of icing on the carcass surface in real time. When the proportion of icing area on the carcass surface reaches 70% to 85%, end the start-up phase and enter the rapid cooling phase. S4: During the rapid cooling phase, the temperature of the pre-cooling room is maintained at -20°C to -23°C, the relative humidity naturally drops to 82% to 88%, the airflow speed is increased to 2.2m / s to 3.0m / s, and cooling continues until the center temperature of the thickest part of the carcass drops to 4°C to 7°C.

2. The low-temperature, low-loss pre-cooling process for pig slaughtering according to claim 1, characterized in that, The start-up phase described in S2 includes a film-forming sub-phase, in which the temperature of the pre-cooling room is maintained at -5°C to -8°C, the relative humidity is maintained at above 98%, the airflow velocity is below 1.0 m / s, and this is maintained for 8 to 12 minutes, so that a uniformly thick liquid water-containing film is formed on the surface of the carcass.

3. The low-temperature, low-loss pre-cooling process for pig slaughtering according to claim 2, characterized in that, The start-up stage described in S2 includes a phase change buffering stage after the film formation stage. In the phase change buffering stage, the temperature of the pre-cooling room is controlled to gradually decrease from -5°C to -8°C to -15°C to -18°C at a rate of 0.1°C / min to 0.2°C / min, while the relative humidity is controlled to be maintained at 92% to 95%, so that the liquid water-containing film on the surface of the carcass gradually freezes and continuously releases the latent heat of phase change.

4. The low-temperature, low-loss pre-cooling process for pig slaughtering according to claim 3, characterized in that, In the phase change buffering sub-stage, the phase change buffering process is determined by monitoring the residence time of the carcass surface temperature near 0°C. When the residence time of the surface temperature in the range of -1°C to +1°C reaches 15 min to 25 min, it is confirmed that the freezing process of the liquid water film on the carcass surface releases the latent heat of phase change.

5. The low-temperature, low-loss pre-cooling process for pig slaughtering according to claim 1, characterized in that, The real-time monitoring of the degree of icing on the carcass surface described in S3 uses infrared thermal imaging. By analyzing the temperature distribution image of the carcass surface, the proportion of the area with a temperature range of -1℃ to +1℃ to the total area of ​​the carcass surface is identified and calculated. This proportion is taken as the proportion of the icing area on the carcass surface.

6. The low-temperature, low-loss pre-cooling process for pig slaughtering according to claim 5, characterized in that, When the area of ​​the region with a temperature between -1℃ and +1℃ detected by infrared thermal imaging reaches its maximum value and then begins to decrease, it is determined that the proportion of the carcass surface covered with ice reaches 70% to 85%.

7. The low-temperature, low-loss pre-cooling process for pig slaughtering according to any one of claims 1 to 6, characterized in that, In S2 and S4, the temperature, humidity, and airflow speed of the pre-cooling room are controlled by zones. Specifically, the airflow speed in the area corresponding to the hind legs of the carcass is increased by 20% to 30% compared to other areas of the carcass, the relative humidity in the area corresponding to the abdomen of the carcass is maintained at 3% to 5% higher than other areas of the carcass, and infrared radiation is applied to the area corresponding to the back of the carcass to slow down its cooling rate.

8. The low-temperature, low-loss pre-cooling process for pig slaughtering according to claim 7, characterized in that, The power density of the infrared radiation applied to the corresponding region on the back of the carcass is 0.1 W / cm². 2 Up to 0.3W / cm 2 It also dynamically adjusts based on the temperature feedback from the dorsal surface of the carcass.

9. The low-temperature, low-loss pre-cooling process for pig slaughtering according to any one of claims 1 to 6, characterized in that, The surface spraying treatment described in S1 uses a solution containing food-grade additives, wherein the food-grade additives are at least one of glycerol or sorbitol, with a total mass concentration of 2% to 6%, the spraying time is 18s to 25s, and the spraying pressure is 0.22MPa to 0.28MPa.

10. The low-temperature, low-loss pre-cooling process for pig slaughtering according to any one of claims 1 to 6, characterized in that, After the temperature at the center of the thickest part of the carcass in S4 drops to 4°C to 7°C, the carcass is transferred out of the pre-cooling room and sent to the maturation room at 0°C to 4°C for 16 to 24 hours of acid removal and maturation.

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