Method for monitoring temperature of particles in sterilization process and method for evaluating microbial safety of jam containing particles

Abstract

The invention provides a method for monitoring the temperature of particles in the sterilization process and a method for evaluating the microbial safety of particle-containing jam. The method comprises the following steps: acquiring the density, heat conductivity coefficient, specific heat capacity and thermal diffusion coefficient of particles; obtaining the flow, the pipeline diameter, the pipeline length of different working sections and the temperature of different working sections of the sterilization machine under the working condition; according to the parameters, obtaining a temperature increasing and decreasing curve of the particle-containing feed liquid of each working section; according to the heating and cooling curve of the particle-containing feed liquid of each workshop section, obtaining a heating and cooling function of the particle-containing feed liquid of each workshop section; obtaining a three-dimensional model of the particles by taking the temperature rising and falling functions of the particle-containing feed liquid of each working section as temperature boundary conditions of the surfaces of the particles; and according to the three-dimensional model of the particles, obtaining a temperature distribution cloud picture of the particle cross section in each time period of each working section, according to the temperature distribution cloud picture, obtaining a temperature change rule curve of the particle center, and according to the temperature change rule curve, monitoring the temperature of the particles.

Description

Technical Field

[0001] The invention relates to a method for monitoring the temperature of particles during the sterilization process and a method for evaluating the microbial safety of jam containing particles, belonging to the technical field of dairy products. Background Art

[0002] Fruit pulp is an important additive to room temperature yogurt and acidic milk drinks. Adding fruit pulp can bring the ultimate experience to the flavor and taste of the product, and is deeply loved by consumers.

[0003] For fruit sterilization, from a scientific point of view, the sterilization intensity inside the fruit determines the design of the fruit sterilizer, not the sterilization intensity of the carrier liquid (i.e., jam). In order to kill the target bacteria, the temperature at the center of the fruit is required to reach a specified temperature and maintain it for a certain period of time to achieve the specified sterilization intensity. The difficulty lies in that the temperature at the center of the particles cannot be measured in the fruit sterilizer, and the temperature change at the center of the particles cannot be clearly understood. In the actual application process, a large number of gradient experiments are generally carried out, and the shelf life verification is used for exploration, but this will cost a lot of time and money, and can only determine the sterilization process parameters of one fruit. If the size of the fruit is changed or the type of fruit is changed, the debugging and application of the fruit sterilizer is also time-consuming and laborious. In addition, in order to ensure food safety, the heating intensity is usually increased, which will cause the loss of taste and flavor of the fruit, increase the energy consumption of the equipment, and increase certain production costs. Summary of the invention

[0004] In order to solve the above technical problems, the object of the present invention is to provide a method for monitoring the temperature of particles during the sterilization process and a method for evaluating the microbial safety of jam containing particles based on the method.

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

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

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

[0008] According to the density, thermal conductivity, specific heat capacity, thermal diffusion coefficient of the particles, the flow rate of the sterilizer under working conditions, the pipe diameter, the pipe length of different sections, and the temperature of different sections, the temperature rise and fall curves of the particle-containing liquid in each section are obtained;

[0009] According to the temperature rise and fall curves of the particle-containing liquid in each section, a temperature rise and fall function of the particle-containing liquid in each section is obtained;

[0010] Taking the temperature rise and fall function of the particle-containing liquid in each process section as the temperature boundary condition on the particle surface, a three-dimensional model of the particle is obtained;

[0011] According to the three-dimensional model of the particle, a temperature distribution nephogram of the particle cross-section in each time period of each process section is obtained. According to the temperature distribution nephogram, a temperature change law curve of the particle center is obtained. According to this temperature change law curve, the temperature of the particle is monitored.

[0012] In the above method, the particle can be fruit and vegetable particles, etc., and the particle-containing liquid can be jam containing fruit and vegetable particles, 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 temperature rise and fall function of the particle-containing 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 residence time of the particle in sterilization, that is, the time calculated from when the particle enters the sterilizer, in s.

[0016] In the above method, preferably, the temperature rise and fall 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 residence time of the particle in sterilization, in s.

[0017] In the above method, the holding section is at a constant temperature without temperature rise and fall changes. Therefore, the temperature rise and fall function of the particle-containing liquid in the holding section is a fixed value, that is, T = e, and e is a fixed temperature value.

[0018] In the above method, preferably, the method further includes converting the temperature rise and fall function of the particle-containing liquid in each process 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 by OpenFOAM software.

[0020] In the above method, preferably, the three-dimensional model of the particle takes 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 the calculation data output by the OpenFOAM software. The abscissa of the temperature change curve is the heating time, and the ordinate is the temperature. Moreover, it includes both the temperature change curve of the particle center and the temperature change curve of the particle-containing liquid (such as jam).

[0023] The present invention also provides a method for evaluating the microbial safety of particle-containing jam, which comprises the following steps:

[0024] Evaluate the heat reception situation inside the particles during the sterilization process of the particle-containing jam according to the temperature change curve of the particle center obtained by the above method, that is, evaluate the microbial safety of the particle-containing jam.

[0025] According to the specific implementation of the present invention, in the actual sterilization production process, the above method for evaluating the microbial safety of particle-containing jam can be carried out in the following way: monitor and obtain the temperature of the particle-containing liquid in the sterilizer to obtain the temperature change curve of the particle center; compare the temperature change curve of the particle center and the temperature change curve of the particle-containing liquid (such as jam) in the temperature change curve to determine the delay of the particle center reaching the predetermined sterilization temperature relative to the particle-containing liquid (such as jam) reaching the predetermined sterilization temperature:

[0026] If there is no delay, it can be determined that the sterilization intensity of the particle center meets the requirements, and the microbial safety of the particle-containing jam meets the requirements;

[0027] If there is a delay, but it can reach the predetermined sterilization temperature 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 particle-containing jam does not meet the requirements; in this case, it can be adjusted by increasing the length of the holding pipe for the corresponding flow rate and pipe diameter to solve the problem that the sterilization intensity does not meet the requirements, or appropriately increasing the opening of the steam valve or the hot water flow rate to solve it, so that the sterilization intensity of the particle center meets the requirements;

[0028] If there is a delay and it cannot reach the predetermined sterilization temperature 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 particle-containing jam does not meet the requirements; in this case, it is generally difficult to solve the problem that the sterilization intensity does not meet the requirements by general adjustment. The heating and cooling rate of the particle surface can be specified according to numerical simulation, so that the sterilization temperature and time of the particle center achieve the required sterilization process parameters. Thus, by using the reverse engineering method, adjust the opening of the steam valve or the hot water flow rate of the sterilizer, and transform the sterilizer pipeline method to achieve adjustment, so that the sterilization intensity of the particle center meets the requirements.

[0029] As an important process equipment for sterilization, the fruit granule sterilizer can sterilize fruit granule-containing jam. However, due to hardware limitations, it is impossible to directly measure the temperature inside the fruit granules, which brings difficulties in judging whether the heat treatment intensity of the fruit granules has reached the required level. The present invention can exactly fill this gap by means of numerical simulation technology. By detecting the specific heat capacity, thermal conductivity and other thermophysical parameters of the fruit granules and extracting the real-time temperature function of the liquid in the fruit granule sterilizer as the simulated boundary condition on the surface of the fruit granules, transient heat transfer simulation of the fruit granules can be carried out to monitor the temperature inside the granules in real time. At the same time, according to the monitoring results, the sterilization process parameters can be adjusted in a timely manner, thus solving the problems of insufficient sterilization intensity at the center of the fruit granules and non-compliance of the microbial safety of the jam with the requirements.

[0030] The present invention has the following advantages:

[0031] The method of the present invention can quickly evaluate the heating situation inside the granules during the sterilization process of the granule-containing jam, and ensure the microbial safety of the whole granule-containing process;

[0032] By determining the jam sterilization process parameters through numerical simulation, the number of experiments can be reduced, and the workload and R & D costs can be greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0034] Figure 2 It is a cloud chart of the temperature distribution of the cross-section of the yellow peach fruit granules at different time periods in each section.

[0035] Figure 3 It is a curve of the temperature change law of the center of the yellow peach jam and the yellow peach fruit granules with side lengths of 5 mm, 7 mm, and 20 mm.

[0036] Figure 4 It is a curve of the temperature change law of the center of the aloe vera jam and the aloe vera fruit granules with side lengths of 5 mm, 7 mm, and 20 mm.

[0037] Figure 5 It is a curve of the temperature change law of the center of the cheese ball jam and the cheese ball fruit granules with sodium alginate and diameters of 5 mm, 7 mm, and 20 mm. DETAILED DESCRIPTION OF THE INVENTION

[0038] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0039] Embodiment

[0040] Select granular samples: yellow peach fruit grains (cubic shape, side lengths are 5 mm, 7 mm, and 20 mm respectively), aloe fruit grains (cubic shape, side lengths are 5 mm, 7 mm, and 20 mm respectively), and cheese boba balls (double-layer structure, with cheese inside and sodium alginate outside, ball diameters are 5 mm, 7 mm, and 20 mm respectively) as the research objects for this study.

[0041] Use a Hot Disk TPS3500 (detection error is about 2%) transient thermal constant detector to detect its thermal conductivity, thermal diffusivity, and specific heat capacity:

[0042] Detect the environmental temperature: 18 - 20 °C. Use a sample holder to fill the sample into a space with a diameter of 20 mm and a depth of 14 mm. Place the probe in the middle of the sample for testing. The test results are shown in Table 1.

[0043] Table 1 Thermal physical properties of fruit grains

[0044]

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

[0046] Select a certain existing fruit grain sterilizer. Through its flow rate under normal working conditions, the density of the whole jam (measured with uniform jam, ρ = m / V), pipeline diameter, heating section 1, heating section 2, holding section, cooling section 1, cooling section 2 pipeline lengths, and the temperatures monitored by temperature probes in each section, the specific data are shown in Table 2:

[0047] Table 2

[0048]

[0049] Based on the data recorded in Table 2, summarize the heating and cooling functions of the loading liquid (jam) in each section. For example, the heating and cooling function of yellow peach particles with a cube side length of 7 mm is specifically as follows;

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

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

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

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

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

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

[0056] Convert the temperature rise and fall functions of the carrier liquid (jam) in each section into a C++ parameter file executable by the OpenFOAM software. Bring this parameter file, along with the thermal conductivity, specific heat capacity, and thermal diffusivity, into the user-defined interface of the OpenFOAM software for file compilation. After successful compilation, use this temperature change condition as the temperature boundary condition on the surfaces of yellow peaches, aloe vera, and cheese balls to obtain a three-dimensional model of the particles. For example, Figure 1 as shown, where (a) is the model of yellow peach and aloe vera particles, and (b) is the model of cheese ball particles.

[0057] According to the three-dimensional model of the particles, obtain the temperature distribution nephogram of the particle cross-section at each time period in each section through the OpenFOAM software. For example, Figure 2 shows the temperature distribution nephogram of the cross-section of a yellow peach fruit granule with a side length of 5 mm at the corresponding time periods of heating section 1, heating section 2, holding section, cooling section 1, and cooling section 2. Through this nephogram, the temperature of the fruit granule can be visually displayed and monitored, which is difficult to monitor by conventional physical means.

[0058] According to the temperature distribution nephogram, extract the corresponding data by the OpenFOAM software ( Figure 1 the horizontal line in it is the data extraction position), and obtain the temperature change law curve of the particle center based on these data. For example, Figures 3 - 5 as shown, where Figure 3 is the temperature change law 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 law curve of the center of aloe vera jam and cubic fruit granules with side lengths of 5 mm, 7 mm, and 20 mm, Figure 5 is the temperature change law curve of the center of cheese ball jam and spherical particles of sodium alginate with diameters of 5 mm, 7 mm, and 20 mm.

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

[0060] such as Figure 3As shown: For yellow peach jam and fruit granules, under the same heating conditions, if the sterilization process parameters are set at 107.5°C / 120s: The time for the centers of cube fruit granules with side lengths of 5 mm and 7 mm to reach 107.5°C is delayed by 15 s and 35 s respectively compared to the jam liquid; the time for the center of the cube fruit granule with a side length of 20 mm to reach the highest sterilization temperature is delayed by 180 s compared to the jam liquid, and the temperature at the center of the fruit granule cannot reach 107.5°C, with the highest only reaching 101.63°C. At the same heating time of 100 s, the center temperatures of cube fruit granules with side lengths of 5 mm, 7 mm, and 20 mm are 4.9°C, 9.9°C, and 47.9°C lower than the jam temperature respectively.

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

[0062] As Figure 5 shown: For cheese ball jam and fruit granules, under the same heating conditions, if the sterilization process parameters are set at 107.5°C / 4s: Compared to 107.5°C of the jam liquid, the highest temperatures at the centers of the sodium alginate layer, fruit granules with diameters of 5 mm and 7 mm can reach 107.31°C, 106.85°C, and 106.0°C respectively, and the times for the centers of the fruit granules with diameters of 5 mm and 7 mm to reach the highest temperature are delayed by 7 s and 17 s respectively; the time for the center of the fruit granule with a diameter of 20 mm to reach the highest sterilization temperature is delayed by 120 s compared to the jam liquid, and the temperature at the center of the fruit granule cannot reach 107.5°C, with the highest only reaching 87.29°C. At the same heating time of 100 s, the center temperatures of the sodium alginate outer layer, fruit granules with diameters of 5 mm, 7 mm, and 20 mm are 1.8°C, 5.6°C, 11.6°C, and 49.9°C lower than the jam temperature respectively.

[0063] According to the design principle of sterilization intensity, the sterilization intensity at the center of the fruit granule determines the sterility of the jam. Then from Figure 3 、 Figure 4 、 Figure 5Analysis of the temperature change curves of the fruit granule centers and the jam shows that for yellow peach fruit granules with side lengths of 5 mm, 7 mm, and 20 mm, aloe fruit granules, and cheese ball fruit granules with diameters of 5 mm, 7 mm, and 20 mm, there is a time delay in reaching the specified sterilization temperature of 107.5 °C, and the central temperature of the large-sized fruit granules cannot reach the specified sterilization temperature. It can thus be determined that the sterilization intensity at the fruit granule centers does not meet the requirements, and the microbial safety of the jam does not meet the requirements.

[0064] For cases where the sterilization temperature can be reached but there is a time delay (such as yellow peach fruit granules and aloe fruit granules with side lengths of 5 mm and 7 mm and the corresponding jams), it can be achieved by increasing the holding tube length through the corresponding flow rate and pipe diameter, or by 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 significant (such as yellow peach fruit granules and aloe fruit granules with side lengths of 20 mm, and cheese ball fruit granules with diameters of 5 mm, 7 mm, and 20 mm and the corresponding jams), the required sterilization process parameters for the sterilization temperature / time at the fruit granule centers can be achieved by numerically simulating the heating and cooling rates on the surfaces of the specified particles, and by using the reverse engineering method to adjust the opening of the steam valve or the hot water flow rate of the sterilizer and to modify the sterilizer pipeline.

Claims

1. A method for monitoring the temperature of particles during the sterilization process, which comprises the following steps: Obtain the density, thermal conductivity, specific heat capacity, and thermal diffusivity of the particles; Obtain the flow rate, pipeline diameter, pipeline lengths of different sections, and temperatures of different sections of the sterilizer under working conditions; Based on the density, thermal conductivity, specific heat capacity, thermal diffusivity of the particles, and the flow rate, pipeline diameter, pipeline lengths of different sections, and temperatures of different sections of the sterilizer under working conditions, obtain the heating and cooling curves of the particle-containing liquid in each section; Obtain the heating and cooling functions of the particle-containing liquid in each section based on the heating and cooling curves of the particle-containing liquid in each section; Using the heating and cooling functions of the particle-containing liquid in each section as the temperature boundary conditions on the particle surface, obtain the three-dimensional model of the particle; Based on the three-dimensional model of the particle, obtain the temperature distribution nephogram of the particle cross-section at each time period in each section, and based on the temperature distribution nephogram, obtain the temperature change law curve of the particle center, and realize the monitoring of the temperature of the particle according to this temperature change law curve.

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

3. The method according to claim 1, wherein, the sections include a heating section, a holding section, and a cooling section.

4. The method according to claim 3, wherein, the heating and cooling function of the particle-containing 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 residence time of the particle during sterilization in s.

5. The method according to claim 3, wherein, 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 residence time of the particle during sterilization in s.

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

7. The method according to claim 1 or 6, wherein, the three-dimensional model of the particle is obtained by OpenFOAM software.

8. The method according to claim 1 or 7, wherein, the three-dimensional model of the particle uses the heating and cooling functions of the particle-containing liquid in each section as the temperature boundary on the particle wall.

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

10. A method for evaluating the microbial safety of particle-containing jam, which includes the following steps: Evaluate the heat reception situation inside the particles during the sterilization process of the particle-containing jam, that is, evaluate the microbial safety of the particle-containing jam, according to the temperature change law curve of the particle center obtained by the method according to any one of claims 1-9.

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