Method for detecting moisture content of roasted beef based on electrical characteristics

Abstract

The invention discloses a method for detecting the moisture content of roasted beef on the basis of electrical characteristics, and belongs to the technical field of food nondestructive testing. According to the method, a high-precision digital bridge system is constructed, an optimization method for beef electrical characteristic detection is determined, and the influence of voltage and frequency on a beef electrical characteristic change rule is analyzed; electrical parameters such as shunt capacitance (Cp), impedance (Z) and conductance (G) of the beef steak are measured in real time through a high-precision digital bridge system; a multiple regression model of the electrical parameters and the moisture content is established, and real-time prediction of the moisture content is achieved; by adopting the method disclosed by the invention, the moisture content of the roasted beef steak at any moment and any position can be predicted, the problems of incapability of real-time monitoring and high technical cost of near infrared and the like of a traditional drying method are solved in actual production, and the method has the advantages of non-destructiveness, high precision and simplicity and convenience in operation, and is suitable for intelligent control of meat processing.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of non-destructive testing of food products, and in particular to a method for detecting the moisture content of a grilled steak based on electrical properties. BACKGROUND

[0002] Grilled beef products, as a representative of high-protein foods, play an important role in the global meat consumption market due to their rich nutritional value and unique flavor characteristics. Electrical property detection technology, with its non-destructive and rapid response characteristics, has become an important research tool for meat quality analysis. During the grilling process of beef, the moisture content of beef not only directly affects its tenderness, taste and processing suitability, but also is a key quality indicator for evaluating the freshness and degree of corruption of the product. The coupling of water migration with protein denaturation, fat melting and other physical fields leads to significant changes in its dielectric properties, and this change has a certain mapping relationship with the moisture content.

[0003] Currently, the existing national standard for meat moisture detection is "Limit of Moisture in Livestock and Poultry Meat" (GB 18394-2020). To meet this standard, meat moisture detection techniques are mainly divided into two categories: traditional methods and modern non-destructive detection techniques. Traditional methods such as drying, although have low equipment costs, have a detection period of several hours, which completely cannot meet the technical needs of real-time detection for modern food industry. Modern non-destructive detection techniques such as near-infrared spectroscopy and nuclear magnetic resonance, although the measurement results are accurate and reliable, have limitations such as high equipment purchase cost, large system size, and long time consumption for single detection (usually several minutes), making it difficult to achieve large-scale application in modern production lines or market circulation links. It is particularly worth noting that existing electrical property detection research has problems such as not establishing a grilling process-specific frequency-moisture response model, lacking a multi-parameter collaborative analysis mechanism, and being unable to directly quantify and real-time monitor the internal moisture content of grilled beef.

[0004] In terms of grilling process, when the temperature rises to 40-60℃, myosin denaturation initiates initial water loss; at 60-75℃, collagen transformation intensifies water migration; and above 100℃, evaporation dominates. This dynamic change process poses high requirements for detection technology. Therefore, developing a method for detecting the moisture content of grilled steaks based on electrical properties to achieve real-time and accurate monitoring of moisture content during the grilling process has become a technical bottleneck that needs to be broken through in the field of meat processing quality control. SUMMARY

[0005] The purpose of the present application is to solve the problems mentioned in the prior art background, and provide a method for detecting the moisture content of grilled beef based on electrical properties, which constructs a high-precision digital bridge system to determine the optimization method of beef electrical property detection; the parallel capacitance Cp, impedance Z and conductance G of beef are measured in real time by a high-precision digital bridge system; a multiple regression model of electrical parameters and moisture content is established to realize real-time prediction of moisture content.

[0006] A method for detecting the moisture content of grilled beef based on electrical properties, comprising the following steps: Step one, sample preparation 1) Raw material selection: select fresh beef, and perform 24 h acid removal treatment under the condition of 0-4℃; 2) Primary processing: remove surface fat and fascial tissue using a sterile scalpel on a sterile operating table, and cut n pieces of 3.5cm×3.5cm×1.5cm beef pieces and one piece of 1.5cm thick whole beef along the muscle fiber direction.

[0007] Step two, grilled beef piece sample 1) The prepared beef pieces are balanced to room temperature in a standard experimental environment with a temperature of 20±1℃ and a relative humidity of 50±5%; 2) Set the oven to an up-and-down hot air circulation heating mode, with a wind speed of 0.5 m / s, and set the temperature to 170℃, and preheat for 10 min; 3) Number the beef pieces, and sequentially number them as the first beef piece, the second beef piece, the third beef piece, …, the n-th beef piece; For each beef piece, the following operations are performed: Place the beef piece on the grill, adjust the position of the beef piece so that its center coincides with the geometric center of the oven, with a three-dimensional positioning error of less than 1 cm, and the end point temperature of the beef piece is 72℃, select any time, and take out the beef piece; the cooking time of each beef piece is different, and n beef piece samples are obtained.

[0008] Step three, processing steps of beef piece sample for measuring electrical properties 1) Fine segmentation: divide the n beef pieces at different temperatures into two beef slices along the vertical muscle fiber direction, and ensure that the cutting surface is flat; 2) Stabilization treatment: place the cut beef slices in an environment with a temperature of 4℃ and a relative humidity of 85% for 10 min; then seal and store; each beef piece sample is divided into two beef slices, one of which is used for electrical property testing, i.e. n beef slices are used for electrical property testing, and the other is used for moisture testing, i.e. n beef slices are used for moisture testing.

[0009] Step four, establishment of the model of electrical properties and moisture content Impedance Z, parallel capacitance Cp and conductance G were selected as the electrical property characteristic parameters of beef. The electrical property of n pieces of beef slices for electrical property test was measured under the condition of 1 kHz and 1 V. T2 grade pure copper plate with purity of ≥99.9% was selected as the electrode plate. The electrode plate was fixed in parallel on the PTFE insulation base, wherein the weight of PTFE was about 1 N. The time required for the electrical property data of a single beef sample to be stable was determined under the condition of 1 kHz and 1 V. The data measurement stability of the electrode plate was verified by measuring different sites of the electrode plate, so as to ensure that the values measured in the test were correct. The actual moisture content of n pieces of beef slices for moisture content measurement was measured by direct drying method. Direct drying method, also known as weight method or thermogravimetric method, is a method for determining the moisture content by measuring the mass difference of the sample before and after heating through evaporation of water in the sample. The current national standard is “Limit of Moisture in Livestock and Poultry Meat” (GB 18394-2020).

[0010] Statistics and analysis: Based on the values of electrical properties and moisture content measured above, all test data were averaged. Test data analysis was arranged using Excel 2016 (Microsoft, Washington, USA), plotted using Origin 9.0 (Origin Lab, Massachusetts, USA), and processed using curve fitting of results and other data processing methods. Finally, the model for predicting moisture content from electrical properties was established. Moisture content = a + b × Cp - c × G - d × Z Wherein a, b, c and d are the coefficients of the inverse regression model. In addition, 8 pieces of beef blocks were prepared, which had the same size as the n pieces of beef blocks. The accuracy of the model was verified. The model verification standard was R² = 0.989 and MAE = 0.43%. The model was applicable to the monitoring of the moisture content in the range of 55-75%.

[0011] Step five, application of the moisture content model A whole beef steak with a thickness of 1.5 cm was used. The moisture content at different distances from the center point and different cooking times was measured. The cooking conditions were 170°C and 1440 s.

[0012] In step one, fresh beef from the 8-12 intercostal parts of the longissimus dorsi muscle of beef that met the health quarantine standards was selected as the raw material.

[0013] In step one, the scalpel was sterilized with 75% ethanol after being used for 5 times.

[0014] The open circuit / short circuit calibration of the electric property measurement system in step four needs to be carried out, the instrument is preheated for 40 minutes, and any point of the electrode plate can be selected for measurement.

[0015] In step four, 28 characteristic frequency points are selected in the frequency range of 1 kHz-5 MHz, and 10 characteristic voltage points are selected in the voltage range of 0.5-5V. The influence of different frequencies (1 kHz-5 MHz) and voltages (0.5-5V) on the electrical properties of beef is studied, which can provide key parameter support for meat quality nondestructive testing, processing technology optimization and emerging food technology (such as pulsed electric field sterilization, radio frequency thawing). By analyzing the changes of impedance, dielectric constant, etc., the freshness, moisture content and microbial contamination of beef can be quickly evaluated, and the microscopic mechanisms such as cell membrane electroporation or protein polarization are also revealed. This study helps to develop efficient online detection sensors, optimize electric field assisted processing technology, and improve the food electrical property database, which has important significance for improving the intelligent level of meat processing and product safety.

[0016] In step five, the model verification adopts the stratified sampling method, and the samples are taken at a distance of 1-5 cm from the center point along the long axis direction of the beef steak. The stratified sampling method is only the application of the model, and the actual moisture content is not verified again; stratified sampling is required in the later chapters of the experimental design, and also conforms to the moisture content at any time and any position; significance: the stratified sampling research on the change of moisture content of beef steak can accurately reveal the spatial distribution rule of water migration in the cooking process. By comparing the moisture gradient changes of the surface dehydration layer, the middle transition layer and the center reserved area, data support is provided for optimizing the cooking parameters (such as temperature and time). This research not only helps to improve the tenderness and juiciness of beef steak, but also lays a theoretical foundation for the development of moisture control technology in the industrialized processing of meat, which has important significance for improving product quality and standardized production.

[0017] Preferably, eight key roasting time nodes of beef steak are selected for the electric property measurement of step three and the beef moisture content measurement of step four.

[0018] The beneficial effects of the present application are: The present application makes the judgment of moisture content during the roasting process of beef steak convenient, simple, economical and practical, and does not damage the integrity of the roasted meat; the mathematical model based on the porous medium theory at the pore scale can better reflect the actual roasting process by analyzing the heat and mass transfer phenomena of the porous medium; the changes of temperature, humidity and other physical quantities of the position of the roasted food to be studied can be given; the application of the present application can predict the temperature and moisture content of meat products during the roasting process under different roasting process conditions, which is helpful to the stability of product quality.

[0019] The moisture content change of beef steak at different positions (0-5 cm) from the center to the edge during the roasting process (0-1440 s) is predicted by the electrical property and moisture content model, and a three-dimensional relationship model of roasting time-space position-moisture content is established for the first time. During the roasting process, the moisture loss shows a significant spatial gradient characteristic, and the farther from the center, the more significant the loss (the moisture loss at 5 cm is 50% at 1440 s, while the center is only 3.6%). And the time and moisture loss are nonlinearly positively correlated. Based on this finding, the application can be applied to the temperature field optimization control system of the intelligent roasting equipment, and the internal moisture gradient of the beef steak can be accurately controlled by dynamically adjusting the heating parameters, effectively solving the technical problem of "dry outside and wet inside" in the traditional roasting process. The technical scheme of the application provides an innovative moisture retention solution for the meat processing field, which can significantly improve the quality uniformity and taste of the roasted beef steak.

[0020] The partial English abbreviations described in the application are explained as follows: PTFE is polytetrafluoroethylene, which is a high-performance synthetic fluoropolymer with excellent insulation performance, with a volume resistivity of more than 10^18 ohm-cm, which can effectively block current conduction under an experimental voltage of 0.5-5V, avoiding leakage interference of the measurement system.

[0021] The EDTA solution is an ethylenediamine tetraamine acid solution.

[0022] MAE is the mean absolute error, which is a statistical index for evaluating the accuracy of a prediction model, representing the average of the absolute difference between the predicted value and the true value. The smaller the MAE value, the smaller the prediction error of the model, the higher the precision, and the average deviation of the prediction can be more intuitively reflected. It is suitable for regression analysis tasks such as beef electrical property modeling, and helps to optimize the fitting effect of experimental data. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The flowchart of the embodiment of the application is shown in the figure; Figure 2 The main part diagram of the digital bridge system constructed in the embodiment of the application is shown in the figure; Figure 3 The instrument preheating and electrode plate measurement position uncertainty evaluation diagram of the embodiment of the application is shown in the figure; Figure 4 The frequency change law curve of the electrical physical quantity of beef block of the embodiment of the application is shown in the figure; Figure 5 The voltage change law curve of the electrical physical quantity of beef block of the embodiment of the application is shown in the figure; Figure 6 The roasting beef electrical property parameter and moisture content change law curve of the embodiment of the application is shown in the figure; Figure 7A roasted beef moisture content verification law curve of an embodiment of the present application; Figure 8 A sampling schematic of an embodiment of the present application at a distance of 1-5 cm from a center point along a long axis direction of a beef steak; Figure 9 Moisture content prediction of different positions in a beef steak roasting process of an embodiment of the present application. DETAILED DESCRIPTION

[0024] Referring to Figures 1 to 9 , an embodiment of the present application is shown.

[0025] A method for detecting the moisture content of a roasted beef based on electrical characteristics, comprising the following steps: Step one, sample preparation 1) Raw material selection: select fresh beef from the 8-12 intercostal part of the longissimus dorsi muscle that meets health quarantine standards, and perform 24 h of acid removal treatment under 0-4℃ conditions; 2) Primary processing: use a sterile scalpel to remove surface fat and fascial tissue on a sterile operating table, and cut out 13 pieces of 3.5 cm x 3.5 cm x 1.5 cm beef pieces and one piece of 1.5 cm thick whole beef steak along the muscle fiber direction; the scalpel is sterilized with 75% ethanol every 5 times of use during fine division.

[0026] Step two, roasted beef piece sample 1) Equilibrate the prepared beef pieces to room temperature in a standard experimental environment with a temperature of 20±1℃ and a relative humidity of 50±5%; 2) Set the oven to an up-and-down hot air circulation heating mode, with a wind speed of 0.5 m / s, a set temperature of 170℃, and preheat for 10 min; 3) Number the beef pieces, with the first beef piece, the second beef piece, the third beef piece, …, the thirteenth beef piece. For each beef piece, the following operations are performed: Place the beef piece on the grill, adjust the position of the beef piece so that its center coincides with the geometric center of the oven, with a three-dimensional positioning error of less than 1 cm, and the final temperature of the beef piece is 72℃, select any time, and take out the beef piece; the roasting time of each beef piece is different, and 13 beef piece samples are obtained.

[0027] Step three, beef piece sample processing step for measuring electrical characteristics 1) Fine division: divide the 13 beef pieces at different temperatures into two beef slices along the vertical muscle fiber direction, trim to 0.5 cm thick, and ensure that the cut surface is flat; 2) Stabilization treatment: the cut beef slices were placed in an environment with a temperature of 4°C and a relative humidity of 85% for 10 min; then sealed and stored; each beef block sample was divided into two portions of beef slices, one of which was used for electrical property testing, i.e., 13 beef slices were used for electrical property testing, and the other was used for moisture testing, i.e., 13 beef slices were used for moisture testing.

[0028] Step four, establishment of electrical property and moisture content model A high-precision digital bridge measurement system was constructed: the measurement device included a TH2826 precision LCR digital bridge instrument, a HIOKI-9140 four-terminal test fixture, and a self-made beef electrical property test clamping square parallel plate electrode device; the electrode plate was made of T2 grade pure copper plate with a size of 40 mm x 40 mm x 0.5 mm and a purity of ≥99.9%; the electrode plate was fixed in parallel on a PTFE insulating base, and the weight of the PTFE was 1N; the LCR digital tester must be zeroed for open and short circuits before each measurement, and preheated for 40 min. By measuring different points on the electrode plate, the data measurement stability of the electrode plate was verified to ensure the correctness of the values measured in the test.

[0029] Electrical parameter measurement and optimization: impedance Z, parallel capacitance Cp, and conductance G were selected as the electrical property characteristic parameters of beef; the LCR tester was set to a test voltage of 1 V and a frequency of 1 kHz, and the electrical properties of n beef slices used for electrical property testing were measured; the values of parallel capacitance (Cp), impedance (Z), and conductance (G) were measured, and each sample was measured 3 times to take the average value; after measuring 5 beef block samples, the electrodes were cleaned with 0.1 mol / L EDTA solution; by measuring different points on the electrode plate, the data measurement stability of the electrode plate was verified.

[0030] The actual moisture content of n beef slices used for moisture content measurement was measured by the direct drying method (direct drying method, also known as weight method or thermogravimetric method, is a method for determining the moisture content by measuring the mass difference before and after heating the sample by evaporating the water in the sample. The current national standard is "Limit of Moisture in Livestock and Poultry Meat" (GB 18394-2020)).

[0031] Table 1 was obtained

[0032] Statistics and analysis: Based on the measured electrical properties and water content values, all experimental data were analyzed using the mean value. The experimental data were analyzed using Excel 2016 (Microsoft, Washington, USA) for sorting, Origin 9.0 (Origin Lab, Massachusetts, USA) for plotting, and curve fitting for the results. Finally, the model for predicting water content from electrical properties was established by back calculation: Water content = 72.50 + 0.62Cp-0.02Z+0.10G Another 8 pieces of beef were prepared for verification, and the size was the same as the above 13 pieces of beef. The model was verified to be accurate: the model verification standard was R²=0.989, MAE=0.43%, and was suitable for monitoring the water content in the range of 55-75%.

[0033] As shown in Figure 4 , Figure 5 , 28 characteristic frequency points (1, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10, 12, 15, 20, 25, 30, 40, 50, 70, 100, 300, 500, 800, 1000, 1500, 2000, 3000, 5000 kHz) were selected in the frequency range of 1 kHz-5 MHz; 10 characteristic voltage points (0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 V) were selected in the voltage range of 0.5-5 V. This part of the experiment is to observe the influence of voltage and frequency on the measurement of beef electrical properties; the results are as follows: by measuring and analyzing the electrical properties of beef at different frequencies (1 kHz-5 MHz), it can be observed that there is a clear frequency-dependent rule. In the low frequency band (1-100 kHz), the parallel capacitance (Cp) and impedance (Z) show higher values, which reflects the hindering effect of cell membrane polarization on current. As the frequency rises above 1 MHz, these parameters decrease significantly, indicating that the cell membrane capacitance effect is weakened, and the current is more easily penetrated into the cell interior. This frequency response characteristic provides a sensitive indicator for non-destructive detection of the microstructure changes of beef (such as cell integrity and water state). From the influence of voltage (0.5-5 V) on electrical parameters, the parameters change gently in the low voltage zone (<2 V), which conforms to the linear dielectric response; when the voltage exceeds 3 V, the conductance (G) and admittance (Y) appear nonlinear jump, and the loss factor (D) increases significantly, indicating that cell membrane electroporation or enhanced ion migration may occur. This voltage threshold effect has important application value: below 3 V, it is suitable for quality detection (to avoid tissue damage), while in the high voltage range of 3-5 V, it can be used for the development of electric field assisted processing technology (such as accelerated curing or non-thermal sterilization). The research results not only deepen the understanding of the electrical properties of beef, but also provide a theoretical basis for optimizing the electromagnetic processing technology of the meat industry.

[0034] Step five, application of the moisture content model Using 1.5 cm thick whole beef, the moisture content was measured at different distances from the center point and different cooking times, with the cooking conditions being 170°C and 1440 s. The model verification used a stratified sampling method, with sampling being performed at 1-5 cm from the center point along the long axis of the beef.

[0035] The cooking test used an NB-HM3810 type combined oven (temperature control accuracy ±1°C). A K-type thermocouple (accuracy ±0.3°C) was inserted into the center of the beef, and a 1.5 cm thick whole beef was placed on a grill preheated to 170°C for 10 minutes. Eight key monitoring points were set at 0-1400 s (0 s, 200 s, 400 s, 600 s, 800 s, 1000 s, 1200 s, 1400 s), and the electrical property measurement described in step three and the beef moisture content measurement described in step four were performed.

Claims

1. A method of detecting the moisture content of a grilled steak based on electrical properties, characterized in that, Comprising the following steps: Step one, sample preparation 1) raw material selection: select fresh beef, under the condition of 0-4℃, carry out 24 h of acid removal treatment; 2) primary processing: use sterile surgical knife on a sterile operating table to remove surface fat and fascial tissue, cut n pieces of 3.5cm×3.5cm×1.5cm beef pieces and a piece of 1.5cm thick whole beef steak along the muscle fiber direction; Step two, roasted beef piece sample 1) the prepared beef pieces are balanced to room temperature in a standard experimental environment with a temperature of 20±1℃ and a relative humidity of 50±5%; 2) set the oven to an up-and-down hot air circulation heating mode, the wind speed is 0.5 m / s, set the temperature to 170℃, preheat for 10 min; 3) number the beef pieces, and the first beef piece, the second beef piece, the third beef piece, …, the n beef piece are numbered in turn; For each beef piece, the following operation is performed: Place the beef piece on the grill, adjust the position of the beef piece so that the center coincides with the geometric center of the oven, the three-dimensional positioning error is less than 1 cm, the end point temperature of the beef piece is 72℃, select any time, take down the beef piece; the roasting time of each beef piece is different, n beef piece samples are obtained; Step three, treatment step of beef piece sample for measuring electrical properties 1) fine segmentation: cut the n beef pieces at different temperatures into two beef slices along the vertical muscle fiber direction, and ensure that the cutting surface is flat; 2) stabilization treatment: place the cut beef slices in an environment with a temperature of 4℃ and a relative humidity of 85% for 10 min; then seal and store; each beef piece sample is divided into two beef slices, one of which is used for electrical property testing, i.e. n beef slices are used for electrical property testing, and the other is used for moisture testing, i.e. n beef slices are used for moisture testing; Step four, establishment of electrical property and moisture content model Select impedance Z, parallel capacitance Cp and conductance G as the electrical property characteristic parameters of beef, measure under the condition of 1 kHz, 1 V, measure the electrical properties of n beef slices for electrical property testing; measure the actual moisture content of n beef slices for moisture content measurement by direct drying method; Through the above measured electrical property and moisture content values, use Origin 9.0 software to plot, perform curve fitting and other data processing methods of the results, and finally establish the model of predicting moisture content from electrical properties: Moisture content = a + b × Cp - c × G - d × Z Where a, b, c, d are the numerical coefficients of the back regression model; Step five, application of moisture content model Use a 1.5cm thick whole beef steak to measure the moisture at different distances from the center and different roasting times, and the roasting conditions are: 170℃, 1440 s.

2. A method of detecting the moisture content of a grilled steak based on electrical properties according to claim 1, characterized in that: In the raw material selection of step one, fresh beef from the 8-12 intercostal part of the longissimus dorsi muscle of the cow that meets the health quarantine standards is selected.

3. A method of detecting the moisture content of a grilled steak based on electrical properties according to claim 1, characterized in that: In the fine segmentation of step one, the surgical knife is sterilized with 75% ethanol every 5 times of use.

4. A method of detecting the moisture content of a grilled steak based on electrical properties according to claim 1, characterized in that: In step four, the electrical property measurement system needs to be calibrated for open circuit / short circuit, and the instrument is preheated for 40 minutes.

5. A method of detecting the moisture content of a grilled steak based on electrical properties according to claim 1, characterized in that: The 28 characteristic frequency points are selected in the frequency range of 1 kHz-5 MHz in the fourth step; and the 10 characteristic voltage points are selected in the voltage range of 0.5-5 V.

6. A method of detecting the moisture content of a grilled steak based on electrical properties according to claim 1, characterized in that: The layered sampling method is used in the model verification in the fifth step, and the samples are taken at the positions 1-5 cm away from the center point along the long axis of the beefsteak.

7. A method of detecting the moisture content of a grilled steak based on electrical properties according to claim 1, characterized in that: The eight key roasting time nodes of the beefsteak are selected to perform the electrical property measurement in the third step and the beef moisture content measurement in the fourth step.

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