A method and system for precise control of flavor substance loss in pre-made canned food with multi-field coupling

Abstract

This invention relates to the field of food processing technology and discloses a method and system for precise control of flavor substance loss in pre-made canned goods using multi-field coupling. The method first screens key flavor fingerprint substances and establishes an activity coefficient correction model based on the oil-water ratio of the food matrix. During sterilization, a multi-component thermodynamic calculation unit calculates the target flavor retention pressure value in real time, including the saturated vapor pressure of pure water, the dynamic volatilization partial pressure of flavor substances, and the thermal expansion partial pressure of the headspace gas. The method introduces a dynamic mass transfer correction coefficient, determines the mass transfer state based on the temperature change rate, and establishes hysteresis pressure relief control through a gain correction coefficient during the cooling stage to physically suppress microscopic flash evaporation caused by heat transfer hysteresis. Finally, a PID split-range control logic is used to drive a proportional intake and exhaust regulating valve to achieve closed-loop tracking of the target pressure. This invention effectively suppresses the phase change volatilization of flavor substances and significantly improves the flavor retention rate of pre-made canned goods by actively constructing a positive pressure differential environment.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, specifically to a method and system for precise control of flavor substance loss in pre-made canned goods using multi-field coupling. Background Technology

[0002] Pre-prepared canned foods commonly employ high-temperature, high-pressure sterilization processes in industrial production to achieve commercial sterility and extend shelf life. In traditional autoclave control systems, pressure control strategies are typically set based on the thermodynamic relationship between the saturated vapor pressure of pure water and temperature. The control system defaults to treating the food matrix inside the can as a pure water system, determining the target pressure value within the autoclave solely by looking up tables or calculating the partial pressure of water vapor at real-time temperature.

[0003] However, actual pre-prepared food systems are complex multi-component mixtures containing water, oils, various volatile organic compounds (VOCs), and dissolved gases. According to thermodynamic principles, the total saturated vapor pressure of a mixed solution is determined by the partial pressures of the solvent and each solute. Existing pressure control methods neglect the contribution of VOCs to the total system pressure, resulting in calculated target pressure settings that are lower than the actual bubble point pressure of the food at high temperatures. When the ambient pressure inside the sterilizer cannot fully cover the total internal pressure of the canned food mixture, a pressure gradient will form at the liquid-phase interface, driving highly volatile flavor compounds to flash evaporate or accelerate desorption. This leads to irreversible mass transfer of flavor compounds from the liquid phase to the gas phase. The pressure control deviation caused by the lack of a thermodynamic model is the main technical reason for the fading of characteristic flavors and loss of aroma in pre-prepared canned foods after heat processing. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method and system for precise control of flavor substance loss in pre-made canned goods through multi-field coupling, solving the problem of aroma loss after thermal processing caused by the lack of a thermodynamic model in existing technologies.

[0005] The first aspect of this invention provides a method for precise control of flavor substance loss in pre-made canned goods through multi-field coupling, comprising the following steps: Step 1: A multi-component gas-liquid equilibrium model of key flavor fingerprint substances in the pre-prepared canned food matrix is ​​pre-constructed, and the model parameters are stored in the control system's database. The construction process includes selecting 1 to 3 volatile organic compounds (VOCs) with the highest flavor contribution from the pre-prepared canned food as key flavor fingerprint substances, determining the initial mole fraction of these key flavor fingerprint substances in a specific food matrix and their activity coefficients as a function of temperature, and establishing a fugacity interaction logic describing the distribution relationship of the key flavor fingerprint substances between the gas and liquid phases.

[0006] Step 2: During the sterilization process, sensors are used to collect real-time temperature and physical pressure values ​​inside the sterilization vessel.

[0007] Step 3: Using the collected real-time temperature value and the multi-component gas-liquid phase equilibrium model, calculate the target flavor retention pressure required to inhibit the migration of key flavor fingerprint substances from the liquid phase to the gas phase at the current moment. The target flavor retention pressure is calculated by coupling and superimposing the saturated vapor pressure component of water, the dynamic volatile partial pressure component of key flavor fingerprint substances, the thermal expansion partial pressure component of headspace gas, and a preset safety pressure margin.

[0008] The logic for determining the dynamic volatile partial pressure of the key flavor fingerprint substances is as follows: based on the pure component saturated vapor pressure, initial mole fraction and activity coefficient of each key flavor fingerprint substance at the current real-time temperature, the sum of the theoretical mixing partial pressures is calculated and then multiplied by a dynamic mass transfer correction coefficient.

[0009] The dynamic mass transfer correction coefficient is a non-equilibrium adjustment parameter determined based on the rate of change of real-time temperature, used to compensate for kinetic deviations in the unsteady-state mass transfer process. The specific control strategy is as follows: When the sterilization process is in the heating stage or the heat preservation stage where the absolute value of the temperature change rate is less than the preset threshold, the dynamic mass transfer correction coefficient is set to the baseline value.

[0010] When the sterilization process enters the cooling stage and the temperature shows a downward trend, the dynamic mass transfer correction coefficient is adjusted to a gain value greater than the reference value, thereby increasing the calculated target flavor retention pressure value and forming a positive pressure differential environment at the gas-liquid interface to inhibit volatilization.

[0011] Step 4: Using the calculated target flavor retention pressure value as a dynamic setpoint, the opening of the air inlet valve or exhaust valve of the sterilizer is adjusted by the PID controller so that the real-time physical pressure value inside the sterilizer tracks the target flavor retention pressure value.

[0012] Furthermore, the method includes parameter correction logic based on the characteristics of the food matrix. The control system corrects the activity coefficients of key flavor fingerprint substances according to preset oil-to-water ratio parameters in the food formula. When the oil content in the food matrix increases, for fat-soluble key flavor fingerprint substances, the system uses a reduced activity coefficient in the calculation to reflect the dissolving and binding effect of the oil matrix on the flavor substances.

[0013] Furthermore, the method employs a delayed pressure relief control strategy during the cooling phase. Initially, in the early stages of cooling, based on the increased dynamic mass transfer correction coefficient, the control system maintains the target flavor retention pressure at a high pressure, which does not decrease linearly with the decrease in the saturated vapor pressure of pure water. At this time, the control system drives the exhaust valve to maintain a small opening or remain closed. Until the real-time temperature drops below the inflection point temperature where the gas-liquid partition coefficient of the key flavor fingerprint substances changes significantly, the control system restores the dynamic mass transfer correction coefficient to the reference value and controls the exhaust valve to open for rapid pressure relief.

[0014] Furthermore, the method includes container pressure differential tolerance limiting logic, and the control system presets a maximum allowable pressure differential threshold for the packaging container. Before executing control, the system determines whether the difference between the calculated target flavor retention pressure value and the theoretical total pressure inside the container exceeds the maximum allowable pressure differential threshold. If the determination result is that it exceeds the threshold, the system limits the target flavor retention pressure value within a safe limit range to prevent permanent physical deformation of the packaging container.

[0015] A second aspect of this invention provides a multi-field coupled, precise control system for the loss of flavor substances in pre-made canned goods, the system comprising: The data acquisition module has its input end connected to a temperature sensor and a pressure transmitter installed on the sterilization vessel, and is configured to acquire the real-time temperature value and the real-time physical pressure value inside the sterilization vessel at a preset frequency.

[0016] The multi-component thermodynamic calculation unit stores the multi-component gas-liquid phase equilibrium model and related thermodynamic parameters of key flavor fingerprint substances. This unit is configured to receive real-time temperature values ​​and, based on the aforementioned superposition logic and dynamic mass transfer correction coefficient, periodically calculate the target flavor retention pressure value.

[0017] The pressure control module has its signal input connected to the multi-component thermodynamic calculation unit and its output connected to the drive mechanism of the inlet and outlet valves of the sterilizer. This module is configured to receive the target flavor retention pressure value as a setpoint and drive the proportional control valve to achieve closed-loop control of the pressure inside the sterilizer.

[0018] This invention provides a method and system for precise control of flavor substance loss in pre-made canned goods through multi-field coupling. It has the following beneficial effects: 1. This invention expands the basis for sterilization reactor pressure control from a single water saturated vapor pressure to a mixed partial pressure including volatile organic compounds by constructing a multi-component gas-liquid phase equilibrium model incorporating key flavor fingerprint substances. This method overcomes the technical deficiency of traditional thermal sterilization processes, which suffer from low pressure setpoints due to neglecting solute partial pressures. It ensures that the physical pressure inside the reactor can cover the bubble point pressure of the mixed solution, thereby reducing the mass transfer driving force for flavor substances migrating from the liquid phase to the gas phase at the thermodynamic level and minimizing flavor substance volatilization losses during high-temperature processing.

[0019] 2. This invention introduces a dynamic mass transfer correction coefficient based on the rate of temperature change, and accordingly implements a hysteresis depressurization strategy during the cooling phase. This strategy addresses the non-equilibrium mass transfer characteristics at the gas-liquid interface in the initial stage of cooling. By maintaining an environmental pressure higher than the theoretical equilibrium value, it prevents microscopic flash evaporation caused by the rate of pressure decrease in the vessel exceeding the rate of temperature decrease during cooling, effectively suppressing the rapid escape of highly volatile components in the initial stage of cooling and maintaining the concentration of flavor substances in the product liquid phase.

[0020] 3. This invention utilizes the existing temperature sensors, pressure transmitters, and regulating valves in the sterilization autoclave, and achieves multi-field coupled control by embedding a thermodynamic calculation model into the controller. Compared to existing technologies that require the addition of a gas analyzer or modification of the autoclave structure, this invention only requires updating the control logic and can be implemented on general industrial sterilization autoclaves. Without changing the original mechanical structure and safety standards of the equipment, it achieves precise control of the thermal processing of complex food systems, with lower implementation costs and good industrial compatibility. Attached Figure Description

[0021] Figure 1 This is a flowchart of the present invention; Figure 2 This is a schematic diagram of the system logic architecture of the present invention; Figure 3 This is a schematic diagram of the control system architecture of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will now be clearly and completely described 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.

[0023] See attached document Figure 1 , Figure 1 This is a flowchart of a method for precise control of flavor substance loss in pre-made canned goods using multi-field coupling, according to an embodiment of the present invention. (Refer to the attached diagram.) Figure 2 , Figure 2This is a schematic diagram of the system logic architecture according to an embodiment of the present invention. (See attached diagram.) Figure 3 , Figure 3 This is a schematic diagram of a control system architecture according to an embodiment of the present invention.

[0024] This invention provides a method for precise control of flavor substance loss in pre-made canned goods through multi-field coupling, the method comprising the following steps: Step S1: Pre-construct a multi-component gas-liquid phase equilibrium model of key flavor fingerprint substances in the pre-made canned food matrix and store it in the control system.

[0025] Step S2: During the sterilization process, the real-time temperature and physical pressure values ​​inside the sterilization vessel are collected.

[0026] Step S3: Using the real-time temperature value and combined with the multi-component gas-liquid phase equilibrium model, calculate the target flavor retention pressure value required to inhibit the migration of key flavor fingerprint substances from the liquid phase to the gas phase at the current moment.

[0027] Step S4: Using the target flavor retention pressure value as a dynamic setpoint, the opening of the air inlet valve or exhaust valve of the sterilizer is adjusted by the PID controller so that the real-time physical pressure value inside the sterilizer tracks the target flavor retention pressure value.

[0028] like Figure 2 As shown, the hardware system implementing this method mainly includes a sterilization autoclave body, a data acquisition module, a multi-component thermodynamic calculation unit, and a pressure execution control module. The sterilization autoclave body is a pressure-bearing, sealed container used to hold pre-made canned products to be processed.

[0029] The data acquisition module includes a temperature sensor and a pressure transmitter installed inside the sterilization autoclave. The temperature sensor is a PT100 platinum resistance thermometer or a thermocouple, configured to detect the real-time temperature of the fluid medium inside the autoclave. The pressure transmitter is configured to detect the real-time physical pressure value of the environment inside the vessel. The signal outputs of the temperature sensor and pressure transmitter are electrically connected to the analog input interface of the multi-component thermodynamics calculation unit via shielded cables. The data acquisition sampling frequency is set to 10Hz to 50Hz to ensure the capture of transient changes in temperature and pressure.

[0030] The multi-component thermodynamics computing unit is an industrial control computer or programmable logic controller with floating-point arithmetic capabilities. The internal memory of this computing unit contains a pre-loaded database of multi-component gas-liquid phase equilibrium models for specific products.

[0031] The pressure control module includes a proportional intake regulating valve connected to the inlet pipe of the sterilizer and a proportional exhaust regulating valve connected to the exhaust pipe. The input of the proportional intake regulating valve is connected to a compressed air source or a high-pressure steam source, and the output of the proportional exhaust regulating valve is connected to the atmosphere or a recovery network. The control signal output interface of the multi-component thermodynamic calculation unit is electrically connected to the actuators of the proportional intake regulating valve and the proportional exhaust regulating valve, respectively, for adjusting the valve opening percentage.

[0032] In step S1, the physical basis for constructing the multi-component gas-liquid phase equilibrium model is Dalton's law of partial pressures and a modified Raoult law. To suppress the volatilization of flavor substances, the total pressure inside the autoclave must be greater than or equal to the sum of the partial pressures of each component. In this embodiment, the total pressure requirement inside the sterilization autoclave is decoupled into four independent physical quantities: water vapor partial pressure, volatile organic compound mixed partial pressure, air thermal expansion partial pressure, and safety margin.

[0033] Key flavor fingerprints refer to volatile components that, in headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (GC-MS), have an aroma activity value greater than 1 and a retention index within a preset range. Specifically, the mass concentration of key flavor fingerprints in the food matrix is ​​determined using the GC-MS internal standard method and converted to a mole fraction.

[0034] In step S3, the multi-component thermodynamic calculation unit calculates the received real-time temperature value. The target flavor retention pressure value is calculated using the following mathematical model. : The definitions and determination methods of the symbols in the above formulas are as follows: Current moment The target flavor retention pressure value, in MPa; The real-time temperature value inside the vessel, measured in Kelvin (K). At temperature The saturated vapor pressure of pure water, expressed in MPa; this value is determined by the IAPWS-IF97 industrial standard formula or the Antoine equation. The values ​​are obtained through real-time calculations, where A, B, and C are Antoine constants for water. The total number of key flavor fingerprint substances selected, with values ​​ranging from 1 to 3; Sequence index of key flavor fingerprint substances; : No. The initial mole fraction of a key flavor fingerprint substance in the liquid phase is a dimensionless parameter; this value is a constant, determined in the laboratory and pre-set in the control system. : No. Key flavor fingerprint substances at current temperature The saturated vapor pressure of the pure components is given in MPa; this value is calculated in real time based on the Antoine equation parameters corresponding to each substance. : No. Key flavor fingerprint substances at current temperature The activity coefficient in a specific food matrix is ​​a dimensionless parameter; this coefficient has a functional relationship with temperature, and is expressed using an empirical formula. Perform calculations, where and These are the characteristic constants determined and fitted through gas-liquid equilibrium experiments; The dynamic mass transfer correction factor is a function of time. and rate of temperature change The function is a dimensionless parameter; The headspace gas inside the tank at temperature The partial pressure of thermal expansion under the given condition is expressed in MPa; its calculation formula is as follows: ,in This refers to the initial absolute pressure applied when the can is sealed. Let be the initial absolute temperature at the time of sealing, and assume that the headspace volume remains constant in the rigid container; : The preset engineering safety pressure margin value, in MPa, with a range of 0.01MPa to 0.05MPa, is used to compensate for sensor measurement errors and elastic deformation tolerance of packaging materials.

[0035] In step S4, the multi-component thermodynamic calculation unit calculates the... As a setpoint (SV), the real-time physical pressure value As a process value (PV), it is input to the PID control algorithm module, and the pressure inside the vessel is kept stable through closed-loop regulation.

[0036] The method for precise control of flavor substance loss in pre-made canned food through multi-field coupling provided by this invention includes the following sub-steps in the specific execution process of step S1: S11: Perform full-spectrum analysis of volatile components in pre-prepared canned food matrix to screen key flavor fingerprint substances; S12: Determine the initial mole fraction and basic thermodynamic parameters of key flavor fingerprint substances; S13: Establish an activity coefficient correction logic based on the oil-water ratio of the food matrix, and generate a parameter library for a multi-component gas-liquid phase equilibrium model.

[0037] In step S11, the screening logic is based on the olfactory threshold theory of flavor substances. Since there are many types of volatile substances in food, but not all of them contribute significantly to the final flavor, this embodiment only performs pressure control on key components whose concentration exceeds the human sensory threshold.

[0038] The specific procedure involves using headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (GC-MS) to perform qualitative and quantitative analysis on pre-cooked canned food samples. First, the sample is placed in a constant-temperature, sealed headspace vial and adsorbed at the equilibrium temperature for 30 to 60 minutes to ensure phase equilibrium is established between the headspace and the sample. Subsequently, the chromatographic peaks of volatile organic compounds are resolved, and the compound names are determined by comparison with a mass spectrometry library.

[0039] Next, the aroma activity value (OAV) of each detected compound was calculated. The formula for calculating OAV is as follows: ,in For compounds Mass concentration in the matrix, For compounds The olfactory threshold in water, The values ​​were obtained by consulting the Leffingwell database. The compounds were identified as potential characteristic flavor compounds and ranked from highest to lowest OAV value. The top 1 to 3 compounds were selected as the "key flavor fingerprints" for this control system. For example, in canned braised pork, ethyl acetate, acetaldehyde, or specific aldehydes were selected as key flavor fingerprints.

[0040] In step S12, the initial molar fraction of the key flavor fingerprint substance in the liquid phase is determined. This value is calculated based on the amount of ingredients in the formula or the results of physicochemical testing. The calculation formula is: in, For the quality of key flavor fingerprint substances, Its molar mass, This refers to the total mass of the food matrix. This is the average molar mass of the matrix. For pre-made canned foods with water as the main dispersion medium (moisture content >70%), this value is approximately taken as the molar mass of water, which is 18 g / mol. For low-moisture, high-solids systems, this value is calculated as a weighted average based on the molar masses of water, protein, and fat in the formula.

[0041] The initial mole fraction The parameters are stored as constant parameters in the database of the control system, and the saturated vapor pressure of the pure components of each key flavor fingerprint substance is determined. The calculation parameters are used. This embodiment uses the Antoine equation to describe... With temperature Relationship: in, The Antoine constants for the corresponding substances are obtained by consulting the NIST chemical database or relevant thermodynamic handbooks and entered into the control system.

[0042] In step S13, the activity coefficient is established. The calculation and correction logic is as follows. The activity coefficient reflects the deviation between the actual solution and the ideal solution, and this deviation is mainly affected by the intermolecular interaction forces between solute and solvent molecules.

[0043] First, determine the basal activity coefficient. In a laboratory setting, a simulated solution with an aqueous phase composition approximating that of the food matrix was prepared, and vapor-liquid equilibrium (VLE) measurements were conducted in a sealed high-pressure reactor. The concentrations of the gaseous components were measured at different temperature points, covering a sterilization temperature range such as 80°C to 130°C, and the activity coefficient was calculated using a modified Raoult's law. The experimental data were then fitted as a function of temperature. in, and These are the characteristic constants obtained from the fitting.

[0044] Furthermore, for food matrices containing oils, the control system incorporates oil-to-water ratio correction logic. The physical principle behind this is that most key flavor fingerprint substances, especially esters and aldehydes, are lipophilic. In an oil-water coexisting system, flavor substances are redistributed between the oil and aqueous phases according to their partition coefficients. As the proportion of the oil phase increases, more flavor substances dissolve in the oil phase, leading to a decrease in their effective concentration in the aqueous phase, and consequently, a reduction in their partial pressure in the gas phase.

[0045] This invention defines a matrix correction factor. The activity coefficient is corrected. The corrected activity coefficient is... The calculation formula is as follows: The specific expanded form of the modified model is as follows: The symbols are defined as follows: The oil-water volume ratio of the food matrix, i.e., the ratio of the volume of oil to the volume of water in the formula, is determined by the production formula of the pre-made canned food and is input into the control system as a preset parameter. : No. Octyl alcohol-water partition coefficients of key flavor fingerprint substances. Based on a general physicochemical approximation, the octanol-water partition coefficient is used to represent the distribution behavior of substances in an oil-water system. This value is a dimensionless constant, obtained by consulting chemical property databases.

[0046] The control system reads the formula during operation. Parameters and substances Combined with real-time temperature Calculated The final output is the corrected activity coefficient. Used for the total pressure calculation in step S3. When When the denominator increases, the denominator term increases. Less than 1, calculated This reduces the target flavor retention pressure value. The corresponding weight of flavor compounds is consistent with the physical fact that oils adsorb flavor compounds, thereby reducing volatility.

[0047] In the multi-field coupled method for precise control of flavor substance loss in pre-made canned food provided by this invention, step S3 specifically includes the following sub-steps: S31: Calculate the saturated vapor pressure component of pure water based on the current real-time temperature value; S32: Calculate the dynamic volatile partial pressure components of key flavor fingerprint substances based on the current real-time temperature value and model parameters; S33: Calculate the thermal expansion partial pressure components of the headspace gas based on the current real-time temperature value and initial sealing state parameters; S34: The above three components are superimposed with the preset safety pressure margin to output the target flavor retention pressure value.

[0048] In step S3, the physical principle is based on Dalton's law of partial pressures. As a closed thermodynamic system, the total internal pressure of the pre-made canned food is composed of the vapor pressure of the solvent in the liquid phase, the volatile partial pressure of the solute, and the thermal expansion pressure of the non-condensable gas in the headspace. To prevent permanent deformation of the packaging container during sterilization and to inhibit the phase change and volatilization of flavor substances, the external physical pressure applied inside the can must be constantly balanced and slightly higher than the theoretical total pressure inside the can. The multi-component thermodynamic calculation unit periodically executes the above calculation logic at a frequency of not less than 10 Hz to achieve real-time tracking of pressure changes inside the can.

[0049] In step S31, the saturated vapor pressure component of pure water is calculated. The control system reads the current real-time temperature value. Since water is the main component of pre-made canned goods, its saturated vapor pressure is the primary contributor to the internal pressure of the can. The control system utilizes the pre-set Antoine equations for calculations and introduces a unit conversion factor: in, , , Let be the Antoine constant for water, with the following values: =5.11564, =1687.537, =230.17 applies to the temperature range, and the constant's unit is bar. The coefficient 0.1 in the formula is used to convert the calculation result from bar to MPa. Used to convert Kelvin temperature to Celsius to match constant standards.

[0050] In step S32, the dynamic volatile partial pressure components of the key flavor fingerprint substances are calculated. This component characterizes the thermodynamic driving force for the migration of all key flavor compounds from the liquid phase to the gas phase in the mixed solution at the current temperature. The calculation formula is as follows: in: The amount of key flavor fingerprint substances, in this embodiment =3; : refers to the first Key flavor fingerprint substances; : The current real-time temperature value; The first step determined in step S1 The activity coefficient of a substance at the current temperature; The first determined in step S1 The initial mole fraction of the substance; : the first The saturated vapor pressure of a substance in its pure components at the current temperature is calculated using the Antoine equation corresponding to that substance. : Dynamic mass transfer correction coefficient. This coefficient is based on the real-time temperature change rate. The determined dimensionless parameters are used to correct mass transfer deviations under non-equilibrium conditions. The specific logic for determining their values ​​will be explained in detail in subsequent step S4.

[0051] In step S33, the partial pressure components of thermal expansion of the headspace gas are calculated. This component reflects the physical pressure generated by the thermal expansion of residual air inside the can. Based on engineering approximations, it is assumed that the can container is a rigid body with a constant headspace volume, and that the residual gas follows the ideal gas law, i.e., Charles's Law. The calculation formula is as follows: in, Current temperature Partial pressure of the lower headspace gas, in MPa; The initial total absolute pressure at the moment of sealing the pre-made can, in MPa. The calculation formula is: ,in The pressure is the local atmospheric pressure (usually taken as 0.101 MPa). The vacuum reading (absolute value, e.g., 0.06 MPa) set for the sealing machine.

[0052] : The core temperature of the pre-made canned food at the moment of sealing, in Kelvin (K). This value is acquired by an online temperature probe during the sealing process and transmitted to the control system.

[0053] In step S34, component superposition calculation is performed to determine the final target flavor retention pressure value. Its calculation logic is as follows: in, This is the preset engineering safety pressure margin value, in MPa; The value range is from 0.01 MPa to 0.03 MPa. The determination of this threshold is based on two factors: first, the control deadband of the pressure transmitter and regulating valve, typically ±0.005 MPa; and second, the maximum allowable additional differential pressure of the packaging material within its elastic deformation range. In this embodiment, The pressure is set at 0.02 MPa to create a stable positive pressure differential environment, ensuring that even when there are slight fluctuations in the control system, the pressure inside the vessel is not lower than the internal pressure inside the tank, thereby effectively preventing microscopic flash evaporation of flavor substances.

[0054] The method for precise control of flavor substance loss in pre-made canned food with multi-field coupling provided by this invention includes the following specific steps for determining the dynamic mass transfer correction coefficient and implementing the hysteresis depressurization strategy: S41: Calculate the rate of temperature change at the current moment based on continuously collected real-time temperature values; S42: Determine the current mass transfer kinetics state based on the temperature change rate and process stage markers; S43: During the heating and isothermal stages, the dynamic mass transfer correction coefficient is set as the baseline value to maintain gas-liquid equilibrium control. S44: During the cooling phase, the dynamic mass transfer correction coefficient after the gain is calculated based on the cooling rate, and hysteresis depressurization control is executed. S45: Monitor whether the real-time temperature value drops to the gas-liquid distribution inflection point temperature. If so, reset the dynamic mass transfer correction coefficient and perform rapid depressurization.

[0055] Before executing the above steps, the physical thermodynamic principles of this control strategy need to be explained: During the cooling process of industrial sterilization, due to the thermal resistance between the food matrix and the packaging material, the rate of temperature decrease at the center of the can inevitably lags behind the rate of temperature decrease inside the sterilizing autoclave. If the control system only depressurizes based on the saturation pressure corresponding to the ambient temperature inside the autoclave, the inside of the can will still be at a relatively high temperature, and its corresponding internal saturated vapor pressure will be higher than the ambient pressure inside the autoclave. This causes an outward expansion force inside the packaging container, driving the dissolved flavor substances to undergo violent flash desorption at the liquid phase interface. This step introduces a correction term based on the rate of temperature change to artificially create an overpressure environment inside the autoclave that is higher than the saturation pressure corresponding to the ambient temperature, thereby physically compensating for the pressure loss caused by the lag in heat transfer.

[0056] In step S41, the multi-component thermodynamic calculation unit performs differential calculations on the acquired real-time temperature sequence. To eliminate the interference of sensor noise on the differential results, a five-point moving average method combined with the backward difference method is used to calculate the rate of temperature change. Calculation formula: in, The rate of temperature change at the previous moment, expressed in K / s; The current temperature value after applying a moving average filter, in Kelvin (K). : The filtered temperature value of the previous calculation cycle, in K; The time interval for calculating the cycle is set to 0.1s to 0.5s in this embodiment.

[0057] In steps S42 and S43, the system will calculate the... Compare with a preset state determination threshold. When Time (of which) The zero-point drift tolerance (valued at 0.01 K / s) determines whether the system is in a "heating" or "holding" state. At this point, the mass transfer process between the gas and liquid phases is approximately in thermodynamic equilibrium, and the system is set with a dynamic mass transfer correction coefficient. At this point, the target flavor retention pressure value It is mainly determined by the static equilibrium partial pressure, and the valve action is controlled to closely follow the saturated vapor pressure curve.

[0058] In step S44, when If the duration exceeds the preset confirmation time limit (e.g., 2 seconds), the system is determined to enter the "cooling" state.

[0059] To suppress flashing caused by heat transfer hysteresis, the system calculates the dynamic mass transfer correction coefficient after gain. The calculation uses a linear gain model: in: Hysteresis damping coefficient, in units of This coefficient is an empirical physical quantity positively correlated with the thermal inertia of the product. It is determined by performing a center temperature puncture test on prefabricated cans of a specific specification and measuring the maximum temperature difference lag time under standard cooling conditions. . The value of and Proportional, the specific correspondence is as follows ,in This is a proportionality constant (usually taken as 0.5). For a 500g tin can, The temperature is typically set to 20 to 30; for flexible packaging bags, due to faster heat transfer, Set to 10 to 15. : The absolute value of the rate of temperature decrease.

[0060] The calculation obtained from this The value is greater than 1.0. Substituting this value into the formula in step S32 will significantly increase the weighting of the partial pressure of key flavor fingerprint substances. This makes the final calculated target flavor retention pressure value... During the cooling phase, the temperature does not drop significantly immediately as it decreases. Instead, it remains in a relatively high-pressure range to create a delayed pressure relief effect. This high-pressure environment physically counteracts the excess vapor pressure generated inside the can due to the temperature lag, thereby inhibiting liquid-phase boiling.

[0061] In step S45, the system defines the gas-liquid distribution inflection point temperature. This threshold is determined based on the Antoine equation curve characteristics of the key flavor compounds. When the temperature is below this value, the saturated vapor pressure of the flavor compounds drops below 0.01 MPa, and the volatilization driving force becomes negligible. In this embodiment, the azeotropic point of ethyl acetate and water is used as a reference, and the threshold is set... The system monitors the temperature inside the reactor in real time, setting it to 85℃. .when At this time, maintain the calculation logic in step S44 to maintain high pressure differential control. At this point, it indicates that the temperature has dropped to a safe zone where the volatility of flavor compounds is significantly reduced. At this point, the system forcibly resets the dynamic mass transfer correction coefficient to [value missing]. =1.0, and drive the exhaust valve to increase the opening, so that the pressure inside the vessel drops rapidly to atmospheric pressure, thereby shortening the process time and improving production efficiency.

[0062] The multi-field coupled method for precise control of flavor substance loss in pre-made canned goods provided by this invention includes the following sub-steps in step S4 (which includes pressure regulation execution): S51: Calculate the deviation between the current target pressure setpoint and the real-time physical pressure value; S52: Uses a discrete PID control algorithm to perform proportional, integral and derivative operations on the deviation and outputs a normalized control quantity; S53: Based on split-range control logic, normalized control quantities are mapped to the opening commands of intake and exhaust valves; S54: Drives the proportional intake control valve or proportional exhaust control valve to perform actions, and eliminates pressure deviation in a closed loop.

[0063] In step S51, the multi-component thermodynamic calculation unit reads the target flavor retention pressure value at the current moment. Real-time physical pressure value The arithmetic unit calculates the pressure deviation. The calculation formula is: when When the pressure inside the vessel is lower than the target value required to suppress the volatilization of flavor substances, the system needs to perform a pressurization operation; otherwise, a depressurization operation is performed.

[0064] In step S52, the positional discrete PID algorithm is used to calculate the control output. Its control principle lies in using a proportional term (P) to respond to the current deviation magnitude, an integral term (I) to eliminate steady-state error, and a derivative term (D) to predict the deviation change trend to suppress overshoot. The calculation formula is as follows: The definitions and parameter settings of each symbol in the above formula are as follows: The normalized control output at the current moment is limited to the range of [−100%, +100%]; : Proportional gain coefficient. This coefficient is inversely proportional to the free volume of the sterilizer. For standard sterilizers with a volume of 2-5 cubic meters, due to the high compressibility of the gas and the slow system response, a larger gain needs to be set to improve the response speed. In this embodiment, it is set to 8.0 to 12.0. and : These represent the pressure deviations at the current time and the previous sampling time, respectively; From the start of control =0 to the current time = Cumulative deviation; Sampling period, set to 0.1s; Integration time constant. Set to 20s to 40s. Too small an integration time will cause the system to oscillate around the target value, while too large an integration time will result in slow elimination of steady-state error. The differential time constant is set to 1.0s to 3.0s.

[0065] In step S53, a split-range control strategy is employed to distribute the single-path control output to two actuators with opposite physical actions. The physical purpose of this strategy is to avoid simultaneous opening of the intake and exhaust valves (Fighting Mode), thereby reducing ineffective compressed air loss and preventing pressure fluctuations. Simultaneously, considering the mechanical friction and positioner dead zone of the pneumatic regulating valve, a dead zone threshold is set at the intake and exhaust switching point. The specific valve opening mapping logic is as follows: Boosting zone: When Time: Proportional intake control valve opening proportional exhaust regulating valve opening .

[0066] Pressure relief zone: At that time: proportional intake control valve opening; proportional exhaust control valve opening. .

[0067] Dead zone preservation: when hour:, At this point, the pressure inside the vessel is within the steady-state allowable error range, and all valves remain closed. The value ranges from 1.0% to 3.0%, and the specific value is determined according to the accuracy class of the regulating valve positioner. In this embodiment, the value is 2.0%.

[0068] In step S54, the multi-component thermodynamic calculation unit outputs the calculated data through the analog output module (AO). and It is converted into a 4-20mA standard industrial current signal. This signal drives the electric valve positioner connected to the regulating valve, which controls the valve core to produce corresponding linear or angular displacement by changing the driving gas source pressure, thereby precisely regulating the gas flow rate entering or leaving the sterilizer and achieving closed-loop tracking of the target flavor retention pressure value.

[0069] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for precise control of flavor substance loss in pre-made canned food through multi-field coupling, characterized in that, Includes the following steps: Step S1: Pre-construct a multi-component gas-liquid phase equilibrium model of key flavor fingerprint substances in the pre-made canned food matrix and store it in the control system; Step S2: During the sterilization process, the real-time temperature and physical pressure values ​​inside the sterilization vessel are collected. Step S3: Using the real-time temperature value and the multi-component gas-liquid phase equilibrium model, calculate the target flavor retention pressure value required to inhibit the migration of key flavor fingerprint substances from the liquid phase to the gas phase at the current moment; Step S4: Using the target flavor retention pressure value as a dynamic setpoint, the opening of the air inlet valve or exhaust valve of the sterilizer is adjusted by the PID controller so that the real-time physical pressure value inside the sterilizer tracks the target flavor retention pressure value. The target flavor retention pressure value in step S3 is determined by the coupled superposition of the saturated vapor pressure component of water, the dynamic volatile partial pressure component of key flavor fingerprint substances, and the thermal expansion partial pressure component of headspace gas.

2. The method for precise control of flavor substance loss in pre-made canned food through multi-field coupling as described in claim 1, characterized in that: The construction of a multi-component gas-liquid phase equilibrium model in step S1 includes: selecting 1-3 volatile organic compounds in the pre-made canned food that have the highest contribution to flavor as key flavor fingerprint substances; The initial molar fraction of the key flavor fingerprint substance in a specific food matrix and its activity coefficient as a function of temperature were determined. Establish a fugacity interaction logic that can describe the distribution relationship of key flavor fingerprint substances between the gas and liquid phases.

3. The method for precise control of flavor substance loss in pre-made canned food through multi-field coupling according to claim 2, characterized in that: The specific logic for calculating the target flavor retention pressure value in step S3 is as follows: the following four pressure components are summed and calculated: First component: The saturated vapor pressure of pure water calculated based on the current real-time temperature value; The second component is the flavor inhibition dynamic pressure term, which is the sum of the theoretical mixing partial pressures calculated from the pure component saturated vapor pressure, initial mole fraction, and activity coefficient of each key flavor fingerprint substance at the current real-time temperature, and then multiplied by a dynamic mass transfer correction coefficient. The third component: the partial pressure of thermal expansion of the headspace gas inside the tank, calculated based on the ideal gas state and real-time temperature value; The fourth component: the preset engineering safety pressure margin value.

4. The method for precise control of flavor substance loss in pre-made canned food through multi-field coupling according to claim 3, characterized in that: The dynamic mass transfer correction coefficient is a non-equilibrium adjustment parameter determined based on the rate of change of real-time temperature values. When the sterilization process is in the heating stage or the heat preservation stage where the absolute value of the temperature change rate is less than the preset threshold, the dynamic mass transfer correction coefficient is set to a base value of 1.0; when the sterilization process enters the cooling stage and the temperature shows a downward trend, the dynamic mass transfer correction coefficient is adjusted to a gain value greater than 1.0 in order to build an overpressure barrier at the gas-liquid interface and suppress rapid mass transfer under non-equilibrium conditions.

5. The method for precise control of flavor substance loss in pre-made canned food through multi-field coupling according to claim 3, characterized in that: The activity coefficient is set as a variable relating to temperature and the oil-to-water ratio of the food matrix. The control system corrects the effective concentration of key flavor fingerprint substances based on the preset oil-to-water ratio parameters of the food formula. When the oil content in the food matrix increases, the activity coefficient with a reduced value is used when calculating the flavor inhibition dynamic pressure term for fat-soluble key flavor fingerprint substances.

6. The method for precise control of flavor substance loss in pre-made canned food through multi-field coupling according to claim 4, characterized in that: In step S4, during the cooling phase, a delayed pressure relief control strategy is implemented. In the initial stage of cooling, based on the dynamic mass transfer correction coefficient greater than 1.0, the target flavor retention pressure value calculated by the control system is maintained at a high pressure and does not decrease linearly with the decrease of the saturated vapor pressure of pure water. The control system drives the exhaust valve to maintain a small opening or a closed state until the real-time temperature value drops below the inflection point temperature where the gas-liquid partition coefficient of the key flavor fingerprint substance changes abruptly. At this point, the control system restores the dynamic mass transfer correction coefficient to the reference value of 1.0 and controls the exhaust valve to open for rapid depressurization.

7. The method for precise control of flavor substance loss in pre-made canned food through multi-field coupling according to claim 3, characterized in that: The calculation logic for the thermal expansion partial pressure of the headspace gas inside the tank is based on the sealing temperature and sealing pressure at the initial moment of the sterilization process. Using the ideal gas law, the physical partial pressure of the residual air in the sealed headspace at the current real-time temperature value is calculated.

8. The method for precise control of flavor substance loss in pre-made canned food through multi-field coupling according to claim 1, characterized in that: Step S4 also includes logic for limiting the pressure differential of the container: The control system has a preset maximum tolerance pressure difference threshold for the packaging container; before executing the control, the system determines whether the difference between the calculated target flavor retention pressure value and the theoretical total pressure inside the container exceeds the maximum tolerance pressure difference threshold. If the limit is exceeded, the target flavor retention pressure value will be forcibly limited to a safe limit to prevent permanent physical deformation of the packaging container.

9. The method for precise control of flavor substance loss in pre-made canned food through multi-field coupling according to claim 1, characterized in that: The calculation process in step S3 is performed periodically at a frequency of not less than 10 Hz to form a continuous state observation of the volatilization trend of flavor substances.

10. A multi-field coupled precision control system for the loss of flavor substances in pre-made canned food, used to execute the multi-field coupled precision control method for the loss of flavor substances in pre-made canned food as described in any one of claims 1 to 9, characterized in that the system include: The data acquisition module is configured to acquire real-time temperature and physical pressure values ​​inside the sterilization vessel via sensors. The multi-component thermodynamic calculation unit is configured to store a multi-component gas-liquid phase equilibrium model of key flavor fingerprint substances, and calculates the target flavor retention pressure value by superimposing components based on real-time temperature value and dynamic mass transfer correction coefficient. The pressure control module is configured to receive the target flavor retention pressure value and drive the proportional regulating valve to achieve closed-loop control of the pressure inside the reactor.

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