A method of monitoring the temperature of particles during a sterilization process and a method of assessing the microbiological safety of a fruit sauce containing particles

Abstract

The application provides a method for monitoring the temperature of particles in a sterilization process and a method for evaluating the microbial safety of a particle-containing jam. The method comprises the following steps: obtaining the density, thermal conductivity, specific heat capacity and thermal diffusivity of the particles; obtaining the flow rate, pipe diameter, pipe length of different sections and temperature of the sterilization machine under working conditions; obtaining the temperature rise and fall curves of the particle-containing material liquid in each section according to the above parameters; obtaining the temperature rise and fall functions of the particle-containing material liquid in each section according to the temperature rise and fall curves of the particle-containing material liquid in each section; obtaining a three-dimensional model of the particles by taking the temperature rise and fall functions of the particle-containing material liquid in each section as the temperature boundary conditions of the particle surface; obtaining the temperature distribution nephogram of the particle cross section in each time period in each section according to the three-dimensional model of the particles; obtaining the temperature change rule curve of the particle center according to the temperature distribution nephogram; and monitoring the temperature of the particles according to the temperature change rule curve.

Description

Technical Field

[0001] This invention relates to a method for monitoring the temperature of particles during sterilization and a method for assessing the microbial safety of jams containing particles, belonging to the field of dairy product technology. Background Technology

[0002] Fruit pieces are an important additive in room temperature yogurt and acidic dairy beverages. Adding fruit pieces can bring an ultimate experience in the flavor and taste of the product, which is loved by consumers.

[0003] From a scientific perspective, the design of a fruit pasteurizer is determined by the sterilization intensity inside the fruit pieces, not by the sterilization intensity of the liquid (i.e., jam). To kill the target bacteria, the core temperature of the fruit pieces must reach a specified temperature and be maintained for a certain time to achieve the desired sterilization intensity. The challenge lies in the fact that the core temperature of the fruit pieces cannot be measured within the pasteurizer, making it impossible to clearly understand the temperature changes. In practical applications, numerous gradient experiments are typically conducted, and shelf-life validation is used for trial and error. However, this consumes significant time and financial resources, and only sterilization process parameters for a single type of fruit can be determined. Changing the size or type of fruit pieces further complicates the debugging and application of the pasteurizer, making it time-consuming and labor-intensive. Moreover, to ensure food safety, the heat intensity is usually increased, which can lead to a loss of flavor and texture, increased energy consumption, and higher production costs. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a method for monitoring the temperature of particles during the sterilization process and a method for assessing the microbial safety of jam containing particles based on this method.

[0005] To achieve the above objectives, the present invention provides a method for monitoring the temperature of particles during the sterilization process, comprising the following steps:

[0006] Obtain the particle density, thermal conductivity, specific heat capacity, and thermal diffusivity;

[0007] Obtain the flow rate, pipe diameter, pipe length of different sections, and temperature of different sections of the sterilizer under operating conditions;

[0008] Based on the particle density, thermal conductivity, specific heat capacity, thermal diffusivity, as well as the flow rate, pipe diameter, pipe length of different sections, and temperature of different sections of the sterilizer under working conditions, the temperature rise and fall curves of the particulate-containing liquid in each section are obtained.

[0009] The temperature rise and fall functions of the particulate-containing liquid in each section are obtained based on the temperature rise and fall curves of the liquid containing particulate matter in each section.

[0010] The temperature rise and fall functions of the granular liquid in each section are used as the temperature boundary conditions on the particle surface to obtain the three-dimensional model of the particles.

[0011] Based on the 3D model of the particle, temperature distribution cloud maps of the particle cross-section at different time periods in each section are obtained. Based on the temperature distribution cloud maps, temperature change curves at the particle center are obtained. Based on these temperature change curves, the temperature of the particle is monitored.

[0012] In the above method, the particles can be fruit and vegetable granules, etc., and the granule-containing liquid can be jam containing fruit and vegetable granules, etc.

[0013] In the above method, preferably, the thermal conductivity, specific heat capacity, and thermal diffusivity are obtained by a transient thermal constant detector.

[0014] In the above method, preferably, the process section includes a heating section, a holding section, and a cooling section.

[0015] In the above method, preferably, the heating and cooling function of the particulate liquid in the heating section is T = a + bt, where T is the particle temperature in °C, a and b are coefficients, and t is the time the particles stay in the sterilization process, that is, the time calculated from the time the particles enter the sterilizer in seconds.

[0016] In the above method, preferably, the heating and cooling function of the cooling section is T = c - dt, where T is the particle temperature in °C, c and d are coefficients, and t is the time the particles stay in the sterilization process in seconds.

[0017] In the above method, the temperature of the process section is kept constant, and there is no change in temperature rise or fall. Therefore, the temperature rise and fall function of the particulate liquid in the process section is kept constant, that is, T = e, where e is a fixed temperature value.

[0018] In the above method, preferably, the method further includes converting the heating and cooling functions of the particulate-containing liquid in each section into a C++ parameter file executable by OpenFOAM software.

[0019] In the above method, preferably, the three-dimensional model of the particle is obtained using OpenFOAM software.

[0020] In the above method, preferably, the three-dimensional model of the particles uses the temperature rise and fall function of the particle-containing liquid in each process section as the temperature boundary of the particle wall.

[0021] In the above method, preferably, the particle cross-section passes through the center of the particle.

[0022] In the above method, preferably, the temperature change curve is generated from calculated data output by OpenFOAM software. The horizontal axis of the temperature change curve represents heating time, and the vertical axis represents temperature. Furthermore, it includes both the temperature change curve of the particle center and the temperature change curve of the liquid containing particles (e.g., jam).

[0023] The present invention also provides a method for assessing the microbial safety of jam containing particles, comprising the following steps:

[0024] The temperature change curve at the center of the granules obtained by the above method is used to assess the internal heating of the granules during the sterilization process of the jam containing granules, that is, to assess the microbial safety of the jam containing granules.

[0025] According to a specific embodiment of the present invention, in the actual sterilization production process, the above-mentioned method for assessing the microbial safety of jam containing particles can be performed as follows: monitoring the temperature of the liquid containing particles in the sterilizer to obtain a temperature change curve of the particle center; comparing the temperature change curve of the particle center with the temperature change curve of the liquid containing particles (e.g., jam) to determine the delay in the particle center reaching the predetermined sterilization temperature relative to the liquid containing particles (e.g., jam) reaching the predetermined sterilization temperature:

[0026] If there is no delay, then it can be determined that the sterilization intensity at the center of the particles meets the requirements, and the microbial safety of the jam containing particles meets the requirements.

[0027] If there is a delay, but the predetermined sterilization temperature can be reached within the predetermined sterilization time, it is determined that the sterilization intensity at the particle center does not meet the requirements, and the microbial safety of the jam containing particles does not meet the requirements. In this case, the problem of insufficient sterilization intensity can be solved by adjusting the flow rate and pipe diameter by increasing the length of the holding pipe, or by appropriately increasing the opening of the steam valve or the hot water flow rate to ensure that the sterilization intensity at the particle center meets the requirements.

[0028] If there is a delay and the predetermined sterilization temperature cannot be reached within the predetermined sterilization time, it is determined that the sterilization intensity at the particle center does not meet the requirements, and the microbial safety of the jam containing particles does not meet the requirements. In this case, it is difficult to solve the problem of insufficient sterilization intensity by general adjustments. Instead, numerical simulation can be used to specify the heating and cooling rate of the particle surface so that the sterilization temperature and time at the particle center achieve the required sterilization process parameters. Then, reverse engineering can be used to adjust the opening of the steam valve or the hot water flow of the sterilizer, or modify the sterilizer pipeline to achieve the desired sterilization intensity at the particle center.

[0029] Fruit particle sterilizers, as crucial equipment in the sterilization process, can sterilize jams containing fruit particles. However, due to hardware limitations, it's impossible to directly measure the internal temperature of the fruit particles, making it difficult to determine whether the heat treatment intensity has been achieved. This invention fills this gap by utilizing numerical simulation technology. By detecting the specific heat capacity and thermal conductivity of the fruit particles, and extracting the real-time temperature function of the liquid in the sterilizer as a simulated boundary condition for the particle surface, transient heat transfer simulation can be performed, allowing for real-time monitoring of the particle's internal temperature. Simultaneously, sterilization process parameters can be adjusted based on the monitoring results, thereby addressing issues such as insufficient sterilization intensity at the center of the fruit particles and unacceptable microbial safety of the jam.

[0030] The present invention has the following advantages:

[0031] The method of the present invention can quickly assess the internal heating of the granules during the sterilization process of jam containing granules, ensuring the overall microbial safety of the granule-containing process;

[0032] Determining the sterilization process parameters for jam through numerical simulation can reduce the number of experiments, significantly lowering workload and R&D costs. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a three-dimensional model of the particle.

[0034] Figure 2 This is a temperature distribution cloud map of cross-sections of yellow peach berries at different time periods in each work section.

[0035] Figure 3 The temperature change curves are shown for the centers of yellow peach jam and yellow peach granules with side lengths of 5mm, 7mm, and 20mm.

[0036] Figure 4 Temperature change curves at the center of aloe vera jam and aloe vera granules with side lengths of 5mm, 7mm, and 20mm.

[0037] Figure 5 Temperature change curves are shown for the centers of cheese ball jam and sodium alginate, with diameters of 5mm, 7mm, and 20mm. Detailed Implementation

[0038] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0039] Example

[0040] Select particle samples: yellow peach granules (cubic shape, with side lengths of 5mm, 7mm, and 20mm respectively), aloe vera granules (cubic shape, with side lengths of 5mm, 7mm, and 20mm respectively) and cheese popping balls (double-layer structure, with cheese on the inner side and sodium alginate on the outer side, with diameters of 5mm, 7mm, and 20mm respectively) are used as the research objects in this study.

[0041] A Hot Disk TPS3500 transient thermal constant analyzer (detection error of approximately 2%) is used to detect its thermal conductivity, thermal diffusivity and specific heat capacity:

[0042] The detection ambient temperature is 18-20°C. A sample holder is used to fill a space with a diameter of 20mm and a depth of 14mm with the sample, and the probe is placed in the middle of the sample for testing. The test results are shown in Table 1.

[0043] Table 1 Thermophysical parameters of fruit granules

[0044]

[0045] Determine the boundary conditions for calculating the center temperature of particles

[0046] A currently used fruit granule sterilizer is selected. Through the flow rate under its normal working conditions, the overall density of the jam (measured with uniform jam, ρ=m / V), the pipeline diameter, the pipeline lengths of heating section 1, heating section 2, holding section, cooling section 1 and cooling section 2, and the temperature monitored by temperature probes in each section, the specific data are shown in Table 2:

[0047] Table 2

[0048]

[0049] According to the data recorded in Table 2, the temperature rise and fall functions of the material-carrying liquid (jam) in each section are summarized. For example, the temperature rise and fall function of a yellow peach granule with a side length of 7 mm is specifically as follows:

[0050] Heating section 1: T1=20.7+0.53t (0s≤t≤132.49s), the unit of T1 is °C;

[0051] Heating section 2: T2=90.3+0.13t (132.49s<t≤264.98s), the unit of T2 is °C;

[0052] Holding section: T3=107.5 (264.98s<t≤384.98s), the unit of T3 is °C;

[0053] Cooling section 1: T4=110-0.38t (384.98s<t≤530.72s), the unit of T4 is °C;

[0054] Cooling section 2: T5=54.1-0.28t(530.72s<t≤649.96s), the unit of T5 is °C;

[0055] Wherein, t is the residence time of the particles in each section during the sterilization process, and the unit is s.

[0056] Convert the temperature rise and fall functions of the material-carrying liquid (jam) in each section into an executable C++ parameter file for OpenFOAM software, bring this parameter file together with thermal conductivity, specific heat capacity and thermal diffusivity into the user-defined interface of OpenFOAM software for file compilation. After successful compilation, this temperature change condition is used as the temperature boundary condition for the surfaces of yellow peach, aloe and cheese balls to obtain a three-dimensional model of the particles, for example Figure 1 shown therein, (a) is the particle model of yellow peach and aloe, and (b) is the particle model of cheese balls.

[0057] According to the three-dimensional model of the particles, the temperature distribution nephogram of the particle cross-section in each time period of each section is obtained by OpenFOAM software. For example, Figure 2 shows the temperature distribution nephogram of the cross section of 5 mm side-length yellow peach granules under the time periods of temperature rising section 1, temperature rising section 2, holding section, cooling section 1 and cooling section 2. The temperature of the granules can be visually displayed and monitored through the nephogram, which is difficult to be monitored by conventional physical methods.

[0058] According to the temperature distribution nephogram, corresponding data are extracted by OpenFOAM software ( Figure 1 the horizontal line therein is the data extraction position), and the temperature change rule curve of the particle center is obtained based on these data, as shown in Figures 3-5 , wherein, Figure 3 is the temperature change rule curve of the center of yellow peach jam and cubic fruit granules with side lengths of 5 mm, 7 mm and 20 mm, Figure 4 is the temperature change rule curve of the center of aloe jam and cubic fruit granules with side lengths of 5 mm, 7 mm and 20 mm, Figure 5 is the temperature change rule curve of the center of cheese ball jam and sodium alginate spherical particles with diameters of 5 mm, 7 mm and 20 mm.

[0059] Judge according to the temperature change rule curve whether the center of the fruit granules meets the corresponding sterilization intensity:

[0060] as shown in Figure 3As shown: For yellow peach jam and fruit pieces, under the same heating conditions, if the sterilization process parameters are set at 107.5℃ / 120s: the time for the center of cube-shaped fruit pieces with sides of 5mm and 7mm to reach 107.5℃ is delayed by 15s and 35s respectively compared to the liquid jam; the time for the center of cube-shaped fruit pieces with sides of 20mm to reach the highest sterilization temperature is delayed by 180s compared to the liquid jam, and the center temperature of the fruit pieces cannot reach 107.5℃, reaching a maximum of only 101.63℃. At the same heating time of 100s, the center temperature of cube-shaped fruit pieces with sides of 5mm, 7mm, and 20mm is 4.9℃, 9.9℃, and 47.9℃ lower than the jam temperature, respectively.

[0061] like Figure 4 As shown: For aloe vera jam and fruit pieces, under the same heating conditions, if the sterilization process parameters are set at 107.5℃ / 120s: the time for the center of cube-shaped fruit pieces with sides of 5mm and 7mm to reach 107.5℃ is delayed by 13.5s and 21.5s respectively compared to the liquid jam; the time for the center of cube-shaped fruit pieces with sides of 20mm to reach the highest sterilization temperature is delayed by 149s compared to the liquid jam, and the center temperature of the fruit pieces cannot reach 107.5℃, reaching a maximum of only 102.69℃. At the same heating time of 100s, the center temperature of cube-shaped fruit pieces with sides of 5mm, 7mm, and 20mm is 4.8℃, 9.2℃, and 47℃ lower than the jam temperature, respectively.

[0062] like Figure 5 As shown: For cheese balls, jam, and fruit pieces, under the same heating conditions, if the sterilization process parameters are set at 107.5℃ / 4s: relative to the 107.5℃ of the jam liquid, the highest temperatures at the center of the sodium alginate layer, the 5mm diameter, and the 7mm diameter fruit pieces are 107.31℃, 106.85℃, and 106.0℃, respectively, with the 5mm and 7mm diameter fruit pieces reaching their highest temperatures delayed by 7s and 17s, respectively; the 20mm diameter fruit pieces reach their highest sterilization temperature 120s later than the jam liquid, and the temperature at the center of the fruit pieces cannot reach 107.5℃, reaching a maximum of only 87.29℃. At the same heating time of 100s, the temperatures at the outer sodium alginate layer, and the centers of the 5mm, 7mm, and 20mm diameter fruit pieces are 1.8℃, 5.6℃, 11.6℃, and 49.9℃ lower than the jam temperature, respectively.

[0063] According to the design principle of sterilization intensity, the sterilization intensity at the center of the fruit pieces determines the asepticity of the jam. Therefore, from... Figure 3 , Figure 4 , Figure 5Analysis of the temperature change curves at the center of the fruit pieces and the jam shows that for peach pieces, aloe vera pieces with side lengths of 5mm, 7mm, and 20mm, and cheese balls with diameters of 5mm, 7mm, and 20mm, there is a delay in reaching the specified sterilization temperature of 107.5℃, and the temperature at the center of larger fruit pieces does not reach the specified sterilization temperature. Therefore, it can be determined that the sterilization intensity at the center of the fruit pieces does not meet the requirements, and the microbial safety of the jam does not meet the requirements.

[0064] For situations where the sterilization temperature can be reached but there is a delay (such as yellow peach pieces, aloe vera pieces, and corresponding jams with side lengths of 5mm and 7mm), this can be achieved by adjusting the flow rate and pipe diameter, increasing the length of the retaining pipe, or appropriately increasing the opening of the steam valve or the hot water flow rate.

[0065] For cases where the specified sterilization temperature cannot be reached and the difference is large (such as yellow peach pieces and aloe vera pieces with a side length of 20mm, and cheese balls and corresponding jams with diameters of 5mm, 7mm, and 20mm), the heating and cooling rate of the specified particle surface can be numerically simulated to make the sterilization temperature / time at the center of the fruit pieces achieve the required sterilization process parameters. This can be achieved by using reverse engineering methods to adjust the opening of the steam valve or the hot water flow of the sterilizer and modify the sterilizer pipeline.

Claims

1. A method for monitoring the temperature of particles during a sterilization process, comprising the following steps: Obtain the particle density, thermal conductivity, specific heat capacity, and thermal diffusivity; Obtain the flow rate, pipe diameter, pipe length of different sections, and temperature of different sections of the sterilizer under operating conditions; Based on the particle density, thermal conductivity, specific heat capacity, thermal diffusivity, as well as the flow rate, pipe diameter, pipe length of different sections, and temperature of different sections of the sterilizer under working conditions, the temperature rise and fall curves of the particulate-containing liquid in each section are obtained. The temperature rise and fall functions of the particulate-containing liquid in each process section are obtained based on the temperature rise and fall curves of the liquid in each process section; wherein, the process section includes a heating section, a holding section and a cooling section; the temperature rise and fall function of the particulate-containing liquid in the heating section is T=a+bt, and the temperature rise and fall function of the cooling section is T=c-dt, where T is the particle temperature in °C, a, b, c and d are coefficients, and t is the residence time of the particles in sterilization in seconds; The temperature rise and fall functions of the granular liquid in each section are used as the temperature boundary conditions on the particle surface to obtain the three-dimensional model of the particles. Based on the three-dimensional model of the particle, temperature distribution cloud maps of the particle cross-section at different time periods in each section are obtained using OpenFOAM software. Based on the temperature distribution cloud maps, the temperature change curve of the particle center is obtained, and the temperature of the particle is monitored based on the temperature change curve.

2. The method according to claim 1, wherein, The thermal conductivity, specific heat capacity, and thermal diffusivity are obtained using a transient thermal constant detector.

3. The method according to claim 1, wherein, The method also includes converting the heating and cooling functions of the particulate-containing liquid in each process section into a C++ parameter file executable by OpenFOAM software.

4. The method according to claim 1 or 3, wherein, The three-dimensional model of the particle was obtained using OpenFOAM software.

5. The method according to claim 1, wherein, The three-dimensional model of the particles uses the temperature rise and fall functions of the particle-containing liquid in each process section as the temperature boundary of the particle surface.

6. The method according to claim 4, wherein, The three-dimensional model of the particles uses the temperature rise and fall functions of the particle-containing liquid in each process section as the temperature boundary of the particle surface.

7. The method according to claim 1, wherein, The particle cross section passes through the center of the particle.

8. A method for assessing the microbiological safety of jam containing particles, comprising the following steps: The temperature change curve at the center of the particles obtained by the method according to any one of claims 1-7 is used to evaluate the internal heating of the particles in the pasteurization process, i.e., to evaluate the microbial safety of the paste. The above method for assessing the microbial safety of jam containing particles is as follows: The temperature of the liquid containing particles in the sterilizer is monitored to obtain a temperature change curve at the particle center; the temperature change curve at the particle center is compared with the temperature change curve of the liquid containing particles to determine the delay in the particle center reaching the predetermined sterilization temperature relative to the liquid containing particles reaching the predetermined sterilization temperature. If there is no delay, then it can be determined that the sterilization intensity at the center of the particles meets the requirements, and the microbial safety of the jam containing particles meets the requirements. If there is a delay, but the predetermined sterilization temperature can be reached within the predetermined sterilization time, it is determined that the sterilization intensity of the particle center does not meet the requirements, and the microbial safety of the jam containing particles does not meet the requirements. If there is a delay and the predetermined sterilization temperature cannot be reached within the predetermined sterilization time, it is determined that the sterilization intensity of the particle center does not meet the requirements, and the microbial safety of the jam containing particles does not meet the requirements.

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