Preparation method and application of pork cold storage-freezing cross-temperature zone time and temperature indicator

Abstract

The invention relates to a preparation method and application of a pork refrigeration-freezing cross-temperature zone time temperature indicator. The invention belongs to the technical field of time and temperature indicators, particularly relates to a preparation method and application of a pork refrigeration-freezing cross-temperature zone time and temperature indicator, and aims to solve the problems that an existing time and temperature indicator is limited in applicable temperature range and prone to denaturation under extreme conditions. The method comprises the following steps: 1, preparing reducing sugar into a solution with distilled water, and recording the solution as a solution A; 2, amino acid and a reaction catalyst are prepared into a solution with distilled water, and the solution is marked as a solution B; 3, the container is divided into two sealed areas by a switch; the liquid A and the liquid B are placed in the two sealed areas respectively, the switch is in a closed state, and preparation of the indicator is completed. When in use, the switch is rotated from a vertical state to a parallel state. The indication temperature range of the time temperature indicator covers normal temperature, refrigeration and freezing areas, and the pork quality can be accurately indicated at-18-25 DEG C.

Description

Technical Field

[0001] The invention belongs to the technical field of time-temperature indicators, and in particular to a preparation method and application of a pork refrigeration-freezing cross-temperature zone time-temperature indicator. Background Art

[0002] Food quality and safety have always been one of the main concerns of society. Currently, food spoilage is often delayed by refrigeration or freezing. Although refrigeration or freezing can delay food spoilage, during the cold chain transportation, perishable products cannot be kept at a specific temperature due to handling and transshipment. With the fluctuation of temperature during transportation and the extension of storage time, perishable products are prone to chain breaks, which makes its intrinsic quality change and difficult to detect by appearance. This causes food safety and food waste problems. Time temperature indicators can not only predict the safety of perishable products, but also indicate the remaining shelf life of perishable products. This not only avoids a series of diseases caused by the accidental ingestion of perishable products, but also avoids the waste caused by conservative estimates of the shelf life of perishable products. Therefore, it is very necessary to study the use of safe, environmentally friendly and stable materials to prepare TTI to monitor food quality.

[0003] The working principle of traditional enzymatic TTI (time temperature indicator) is that the substrate is hydrolyzed under the action of enzymes, resulting in a decrease in the pH value of TTI, causing the color of the pH color developer to change. However, TTI prepared by microorganisms has high requirements for the application environment. When the temperature is too high, the enzyme activity is inactivated. When the temperature is too low, TTI cannot be started. The applicable temperature is limited, and it is easy to denature under extreme conditions. Therefore, this type of TTI is suitable for specific scenarios. Summary of the invention

[0004] The present invention aims to solve the problem that the existing time and temperature indicators have limited applicable temperatures and are prone to denaturation under extreme conditions, and to provide a preparation method and application of a pork refrigeration-freezing cross-temperature zone time and temperature indicator.

[0005] The method for preparing a pork refrigeration-freezing temperature-spanning time-temperature indicator of the present invention is specifically carried out according to the following steps:

[0006] 1. Prepare a solution of reducing sugar with distilled water, referred to as solution A;

[0007] 2. Prepare the amino acid and the reaction catalyst into a solution using distilled water, which is referred to as solution B;

[0008] 3. The container is divided into two sealed areas by a switch; liquid A and liquid B are placed in the two sealed areas respectively, and the switch is in a closed state, thus completing the preparation of the pork refrigeration-freezing cross-temperature zone time temperature indicator.

[0009] The pork refrigeration-freezing temperature-crossing time and temperature indicator of the present invention is applied to indicate the quality of pork under different circulation environments through the color change of the pork refrigeration-freezing temperature-crossing time and temperature indicator.

[0010] Beneficial effects of the present invention:

[0011] The invention proposes a preparation scheme of a refrigeration-freezing cross-temperature zone time-temperature indicator based on the Maillard reaction characteristics. The prepared time-temperature indicator has the characteristics of simple preparation process, convenient use, economy, environmental protection, safety and stability.

[0012] The time-temperature indicator produced by the present invention can accurately indicate the quality of pork at -18 to 25°C. Compared with the existing time-temperature indicators, the temperature monitoring range is wider and can be applied to the quality monitoring of products in normal temperature, refrigerated or frozen environments to solve the problems existing in some time-temperature indicators in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the structure of the pork refrigeration-freezing cross-temperature zone time-temperature indicator prepared in Example 1;

[0014] Figure 2 The color change diagram of TTI under different reducing sugar and amino acid combinations;

[0015] Figure 3 The graph is the absorbance change of TTI under different reducing sugar and amino acid combinations;

[0016] Figure 4 It is the color change diagram of TTI under orthogonal experiment; 1 represents 0.5mol / L xylose-1.5mol / L glycine-0.75mol / L K2HPO4, 2 represents 0.5mol / L xylose-2mol / L glycine-1.25mol / L K2HPO4, 3 represents 0.5mol / L xylose-2.5mol / L glycine-1mol / L K2HPO4, 4 represents 1mol / L xylose-1.5mol / L glycine-1.25mol / LK2HPO4, 5 represents 1mol / L xylose-2mol / L glycine-1mol / L K2HPO4, 6 represents 1mol / L xylose-2.5mol / L glycine-0.75mol / L K2HPO4, 7 represents 1.5mol / L xylose-1.5mol / L glycine-1mol / L K2HPO4, 8 represents 1.5mol / L xylose-2mol / L glycine-0.75mol / L K2HPO4, 9 represents 1.5mol / L xylose-2.5mol / L glycine-1.25mol / L K2HPO4;

[0017] Figure 5 It is the absorbance change diagram of TTI under orthogonal experiment; 1 represents 0.5mol / L xylose-1.5mol / L glycine-0.75mol / L K2HPO4, 2 represents 0.5mol / L xylose-2mol / L glycine-1.25mol / L K2HPO4, 3 represents 0.5mol / L xylose-2.5mol / L glycine-1mol / L K2HPO4, 4 represents 1mol / L xylose-1.5mol / L glycine-1.25mol / L K2HPO4, 5 represents 1mol / L xylose-2mol / L glycine-1mol / L K2HPO4, 6 represents 1mol / L xylose-2.5mol / L glycine-0.75mol / L K2HPO4, 7 represents 1.5mol / L xylose-1.5mol / L glycine-1mol / LK2HPO4, 8 represents 1.5mol / L xylose-2mol / L glycine-0.75mol / L K2HPO4, 9 represents 1.5mol / L xylose-2.5mol / L glycine-1.25mol / L K2HPO4;

[0018] Figure 6 The color change diagram of the pork refrigeration-freezing cross-temperature zone time-temperature indicator prepared in Example 1 at different temperatures;

[0019] Figure 7 The Fourier infrared spectrum of the pork refrigeration-freezing cross-temperature zone time-temperature indicator prepared in Example 1;

[0020] Figure 8 The UV-visible absorption curves of the pork refrigeration-freezing cross-temperature zone time-temperature indicator prepared in Example 1 at different temperatures;

[0021] Fig. 9 This is a color difference fitting diagram of the pork refrigeration-freezing cross-temperature zone time-temperature indicator prepared in Example 1;

[0022] Fig.10 The fitting curve for calculating the activation energy of the pork refrigeration-freezing cross-temperature zone time-temperature indicator prepared in Example 1;

[0023] Fig.11 This is a graph showing the effect of storage temperature on pork weight loss rate over time;

[0024] Fig.12 This is a graph showing the effect of storage temperature on pH value over time;

[0025] Fig.13 This is a graph showing the effect of storage temperature on TVB-N value over time;

[0026] Fig.14It is a comparison curve of temperature monitoring conditions of different refrigerated cold chain transportation;

[0027] Fig.15 Comparative photos of pork quality monitoring by the pork refrigeration-freezing cross-temperature zone time-temperature indicator prepared in Example 1 under different cold chain logistics;

[0028] Fig.16 This is a graph showing the impact of different cold chain logistics on the weight loss rate of pork over time;

[0029] Fig.17 This is a graph showing the effect of different cold chain logistics on pH value over time;

[0030] Fig.18 This is a graph showing the impact of different cold chain logistics on TVB-N values ​​over time. DETAILED DESCRIPTION

[0031] Specific implementation method 1: In this implementation method, a method for preparing a pork refrigeration-freezing cross-temperature zone time temperature indicator is specifically carried out according to the following steps:

[0032] 1. Prepare a solution of reducing sugar with distilled water, referred to as solution A;

[0033] 2. Prepare the amino acid and the reaction catalyst into a solution using distilled water, which is referred to as solution B;

[0034] 3. The container is divided into two sealed areas by a switch; liquid A and liquid B are placed in the two sealed areas respectively, and the switch is in a closed state, thus completing the preparation of the pork refrigeration-freezing cross-temperature zone time temperature indicator.

[0035] The present embodiment adopts the Maillard reaction to realize the indication function. The Maillard reaction is a non-enzymatic browning reaction between reducing sugar and amino acid. Its reaction mechanism is completely different from the enzymatic reaction and does not rely on the action of enzymes. Therefore, there are no enzyme-related problems such as inactivation of enzyme activity due to high temperature, inability to start TTI due to low temperature, and easy denaturation of enzymes under extreme conditions. Its reaction process is mainly affected by factors such as reaction substrate concentration and temperature, but there is no situation where key reaction substances (such as enzymes) are inactivated due to high temperature. It can react within a wider temperature range, as long as the temperature conditions can meet the basic requirements for the occurrence of the Maillard reaction, and it will not be completely ineffective due to high temperature like enzymatic TTI. Although the reaction rate of the Maillard reaction may slow down in a low temperature environment, there will be no situation similar to the enzymatic reaction that cannot be started. It is just that the reaction progress will be relatively delayed, and it can still gradually react with the combined effect of time and temperature and produce corresponding color changes to realize the indication function.

[0036] The Maillard reaction system is relatively more adaptable to the environment. As long as the basic elements such as the presence of reaction substrates (reducing sugars, amino acids, catalysts, etc.) and suitable temperature conditions are guaranteed, the reaction can proceed and play an indicating role. Unlike enzymatic TTI, it is not easily affected by various environmental factors, resulting in unstable performance.

[0037] The Maillard reaction is based on a complex chemical reaction between reducing sugars and amino acids. It produces products of different colors through the formation and transformation of a series of intermediates. The driving factor of the color change is the chemical process of the Maillard reaction itself, not the single mechanism of enzymatic hydrolysis to change pH value that is easily affected by the environment, as does enzymatic TTI.

[0038] Specific embodiment 2: This embodiment is different from specific embodiment 1 in that the reducing sugar in step 1 is D-xylose, D-ribose or L-(+)-arabinose. The rest is the same as specific embodiment 1.

[0039] Specific embodiment 3: This embodiment is different from specific embodiment 1 or 2 in that the concentration of liquid A is 0.50 mol / L, 1.00 mol / L, 1.50 mol / L, 2.00 mol / L or 2.50 mol / L. The rest is the same as specific embodiment 1 or 2.

[0040] Specific embodiment 4: This embodiment is different from specific embodiment 1 in that: the amino acid in step 2 is glycine, L-lysine or L-alanine; the reaction catalyst is K2HPO4. The rest is the same as specific embodiment 1.

[0041] Specific embodiment 5: This embodiment is different from specific embodiment 1 in that the concentration of the amino acid in the B solution in step 2 is 1.00mol / L, 1.50mol / L, 2.00mol / L, 2.50mol / L, 3.00mol / L or 3.50mol / L, and the concentration of the reaction catalyst is 0.50mol / L, 0.75mol / L, 1.00mol / L, 1.25mol / L, 1.50mol / L, 1.75mol / L or 2.00mol / L. The rest is the same as specific embodiment 1.

[0042] Specific implementation example 6: This implementation example is different from the specific implementation example 1 in that the volume ratio of liquid A to liquid B in step 3 is 1:1. The rest is the same as the specific implementation example 1.

[0043] Specific implementation method seven: The application of the pork refrigeration-freezing temperature-crossing time and temperature indicator in this implementation method is to indicate the quality of pork under different circulation environments through the color change of the pork refrigeration-freezing temperature-crossing time and temperature indicator.

[0044] Specific embodiment eight: This embodiment differs from specific embodiment seven in that when the pork refrigeration-freezing temperature-crossing time-temperature indicator is used, the switch is rotated from vertical to parallel by turning the knob, so that liquid A contacts liquid B, and then the container is gently shaken to fully mix liquid A and liquid B. The rest is the same as specific embodiment seven.

[0045] Specific embodiment 9: This embodiment is different from specific embodiment 7 in that the temperature monitoring range of the pork refrigeration-freezing cross-temperature zone time temperature indicator is -18 to 25° C. The rest is the same as specific embodiment 7.

[0046] Specific embodiment 10: This embodiment is different from specific embodiment 7 in that the color change refers to the change of the pork refrigeration-freezing cross-temperature zone time temperature indicator from transparent, light yellow, yellow, blue-green, light brown, dark brown to brown-black over time. The rest is the same as specific embodiment 7.

[0047] The beneficial effects of the present invention are verified by the following examples:

[0048] Example 1: A method for preparing a pork refrigeration-freezing temperature-span time-temperature indicator is specifically carried out according to the following steps:

[0049] 1. Prepare a solution of reducing sugar with distilled water, which is referred to as solution A; the concentration of solution A is 1.00 mol / L;

[0050] 2. The amino acid and the reaction catalyst are prepared into a solution with distilled water, which is referred to as solution B; the concentration of the amino acid in the solution B is 2.00 mol / L, and the concentration of the reaction catalyst is 1.00 mol / L;

[0051] 3. The container is divided into two sealed areas by a switch; liquid A and liquid B are placed in the two sealed areas respectively, and the switch is in a closed state, thus completing the preparation of the pork refrigeration-freezing cross-temperature zone time temperature indicator; the volume ratio of liquid A to liquid B is 1:1.

[0052] Fourth, different concentrations of xylose, glycine and K2HPO4 were selected for single factor experiment, each experiment was repeated 3 times and the average value was taken; the concentrations of xylose, glycine and K2HPO4 were (0.50, 1.00, 1.50, 2.00, 2.50 mol / L), (1.00, 1.50, 2.00, 2.50, 3.00, 3.50 mol / L) and (0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.00 mol / L), respectively;

[0053] 5. Select three factors respectively, and select the three concentrations obtained from the single factor experiment in step S4 for orthogonal test. Color change, absorbance value and EC50 close to 5 are regarded as evaluation indicators; the three concentrations of xylose, glycine and K2HPO4 are (0.50, 1.00, 1.50 mol / L), (1.50, 2.00, 2.50 mol / L) and (0.75, 1.00, 1.25 mol / L), respectively;

[0054] 6. Record TTI color. Under constant temperature and humidity conditions, use a handheld pipette to dispense 0.30 mL of the mixed reaction solution into a 96-well microplate and store it at 4°C. Subsequently, use a camera to record the color change history of TTI and take photos at intervals of 1 day. In order to reduce the influence of ambient light and box color, place the sample in a photo box with a size of 23 cm × 22 cm × 24 cm, equipped with a ring light on the top and a white background cloth on the bottom and sides.

[0055] 7. Determine the absorbance of TTI. Set the measurement wavelength of the UV spectrophotometer to 420nm, and use distilled water as the control group. Repeat the measurement for each sample 3 times, and take the average value as the final test result.

[0056] 8. TTI infrared spectrum measurement. Use Fourier transform infrared spectrometer in attenuated total reflection (ATR) mode to measure 4000-500cm -1 The spectrum is in the range of 4 cm -1 , the number of scans is 32 times.

[0057] 9. Determination of UV-Vis absorption spectrum. First, mix the A solution and the B solution in the above step 3 in equal volume ratio and store them at 4°C. Then, measure the spectrum of TTI at different time points (0, 2, 4, 6, 8, 10 days). In addition, measure the spectrum of TTI stored at different temperature conditions (25, 15, 4, -1, -10, -18°C) at 7 days. During the measurement, set the UV-spectrophotometer scanning parameters to 200-800nm, the scanning interval to 10nm, use distilled water as the reference solution, and repeat the measurement for each sample 3 times.

[0058] like Figure 1The figure shows a schematic diagram of the structure of a refrigeration-freezing cross-temperature zone time temperature indicator, which is mainly composed of four parts. 1 is xylose, 2 is glycine, and 3 is K2HPO4. Since the Maillard reaction solution prepared by xylose and glycine has excellent reactivity, obvious color change, and low price, xylose and glycine are used as reaction substrates of the Maillard reaction, and K2HPO4 is used as a catalyst for the reaction. 4 is a sealing device for containing the Maillard reaction solution, which has good transparency and mechanical properties, and strong impact resistance.

[0059] The method of matching the cross-temperature time temperature indicator with the food index is: prepare the reaction solution of xylose and glycine according to the proportion and concentration determined in step five, use K2HPO4 as a catalyst, mix evenly, observe the color change of the solution and characterize it. According to the relationship between the change of color over time, fit the response function of the color difference and time, and then build a kinetic model. The corresponding activation energy can be obtained by calculation using the Arrhenius equation. In the kinetic analysis of TTI, the activation energy difference between food and TTI is required to be less than 25kJ / mol to determine whether the two can match, and the closer the activation energy of food and TTI is, the more accurately TTI can monitor changes in food quality.

[0060] The method described in Example 1 was used to respectively configure the D-xylose / L-lysine experimental group, the D-xylose / L-alanine experimental group, the D-ribose / glycine experimental group, the D-ribose / L-lysine experimental group, the D-ribose / L-alanine experimental group, the L-(+)-arabinose / glycine experimental group, the L-(+)-arabinose / L-lysine experimental group, and the L-(+)-arabinose / L-alanine experimental group.

[0061] like Figure 2 As shown, the Maillard reaction is a condensation reaction between hydroxyl and amino functional groups. It appears brown or dark brown at the end of the reaction, and the color change can be clearly distinguished by the naked eye. The first condition for TTI preparation is that it can give people a significant color change or deformation, and can quickly and accurately judge the quality change of the product. Because 4℃ is a common cold chain storage temperature and the refrigeration temperature of household refrigerators, the Maillard reaction type TTI base liquid is selected at 4℃. Figure 3 It can be seen that the TTI under the combination of xylose and glycine gradually changed from colorless to light yellow, yellow, light blue, blue, brown, and black within 10 days. The color change is more obvious and there are more stages of color change.

[0062] like Figure 3As shown, the reaction was carried out at 4°C. It can be seen from the figure that the absorbance of xylose-glycine no longer changed after 7 days, indicating that the reaction reached the end point. Within 7 days, the absorbance growth rate of xylose-glycine was more uniform than that of other combinations. From the perspective of absorbance change, xylose-glycine can be used as an alternative base solution for subsequent exploration of TTI concentration.

[0063] like Figure 4 As shown in the figure, three TTIs with uniform color changes and moderate reaction rates were obtained through orthogonal experiments, laying the foundation for further exploring the performance of TTI. As can be seen from the figure, the color changes of combinations 1, 2, and 3 are slow, and the three groups did not reach the reaction endpoint on the 10th day. Among them, combination 1 reacts the slowest and the color change is the least obvious. Looking at combinations 4 to 9, combination 9 has the highest reaction rate, and no obvious color change can be seen after the 7th day. From the perspective of color change, the color changes of combinations 4 to 8 are relatively moderate.

[0064] like Figure 5 The figure shows the absorbance changes of 9 groups of TTI within 10 days. It can be seen from the figure that the absorbance of 3 groups of TTI did not reach 3. The absorbance of combination 1 was only 0.81 at 10 days, which was too low and the reaction rate was too slow. The absorbance of combination 9 exceeded 3 on the 7th day, and the reaction endpoint was reached at this time. Looking at the absorbance changes within 10 days, the reaction rates of combinations 4 to 8 were relatively moderate, which can also be verified in the color changes.

[0065] like Figure 6 As shown, under different isothermal storage conditions, the longer the TTI reaction time, the stronger the color change. The initial color of TTI is colorless, and as the reaction proceeds, the color of TTI shows characteristic colors of light yellow, yellow, blue-green, light brown, dark brown, and brown-black, and as the temperature increases, the time for TTI to reach the reaction endpoint is also shortened. The temperature in the present invention covers room temperature, refrigerated temperature, and ice temperature to match the monitoring ability of TTI of food under different storage conditions.

[0066] like Figure 7 As shown in Figure 2, the internal changes of TTI during the reaction were analyzed by measuring the Fourier transform infrared spectra of TTIA solution, TTI B solution and 0, 2, 4, 6, 8 and 10 days. -1 There are obvious strong and broad OH stretching vibration peaks near 1 633, 1 516 and 1 331 cm -1 The characteristic peaks near the C=O stretching, NH bending, CN stretching and NH deformation are respectively caused by. After the A solution and B solution are mixed, the peak of amide I changes from 1633cm -1 Move to 1 629cm -1, indicating the formation of a Schiff base (C=O). In addition, 1 516 cm -1 The intensity of the absorption band at 1 509 cm is reduced, which is due to the interaction between the carbonyl group of xylose and the amine group of glycine. -1 The absorption peak at 1516 cm -1 , indicating the formation of new hydrogen bonds. 1412cm -1 The absorption peaks at 1071 and 987 cm-1 may be caused by CH deformation. -1 The absorption bands near represent CO stretching vibrations. The TTI spectrum results show that CO, CH, C=O, C=C, C=N, amide I, amide II, amide III, CN, NH, CH, etc. may be involved in the formation of melanin. With the increase of TTI storage time, the overall change trend of the spectrum is not large, so it is speculated that the mixing of TTIA liquid and B liquid caused a benign interaction. Except for slight differences in peak position and peak intensity, there is no obvious difference in the FTIR spectrum, and no new peaks are observed in the spectrum, indicating that no new covalent bonds are formed after the mixing of A liquid and B liquid. It shows that the cross-temperature time-temperature indicator made of xylose and glycine as raw materials can better indicate the quality of food.

[0067] like Figure 8 The figure shows the UV spectra of TTI at different temperatures. As can be seen from the figure, with the increase of storage temperature, the UV absorption intensity of TTI gradually increases, indicating the progress of the reaction and the accumulation of products. In the early stage of the reaction, the absorption peak was observed to be red-shifted, which may be caused by the formation of Schiff base. It can be seen from the figure that when TTI is stored at -1℃, an absorption peak appears at 270nm. The substance that appears at this time may be an α-dicarbonyl compound. Combined with the color change of TTI, it can be inferred that the substance produced at 270nm may be the precursor of the blue substance. In the middle and late stages of the reaction, obvious characteristic peaks appear at 580nm and 630nm. At this time, the color of TTI is blue. The blue substance that appears may be a dimer formed by the polymerization of yellow pyrrolopyrrole-2-carboxaldehyde. In addition, absorption peaks are generated at 220nm and 210nm at -10℃ and -18℃, respectively. The absorption peaks here are generated in the ultraviolet light region, but no absorption peaks are generated in the visible light region, which is also mutually confirmed by the color of TTI.

[0068] A. Measurement of color change: Place the reaction system at 25, 15, 4, -1, -10, and -18°C, respectively, and test the corresponding chromaticity value at regular intervals using an automatic colorimeter.

[0069] B. Determination of kinetic parameters: Plot the curves of the color difference value changing with time under constant temperature conditions of 25, 15, 4, -1, -10, and -18°C, respectively, and fit them using the zero-order kinetic reaction equation (1) to calculate the corresponding k 25℃ , k 15℃ , k 4℃ , k -1℃ , k -10℃ , k -18℃ The corresponding activation energy is then calculated according to the Arrhenius equation (2).

[0070] y=kt+b (1)

[0071]

[0072] In formula (1), y is the TTI color difference value; t is time, days; k and b are fitting parameters; in formula (2), k is the reaction rate; A is the prefactor; Ea is the activation energy, J / mol; T is the absolute temperature, K; R is the gas constant (8.314 J / mol·k).

[0073] The calculation results are shown in Table 1;

[0074] Table 1 TTI kinetic fitting parameters at different storage temperatures

[0075]

[0076] The color difference fitting diagram of the reaction system is shown in Fig. 9 As shown, in the initial stage of the reaction, the color change follows the zero-order kinetic reaction equation, and the reaction stabilizes after reaching the end point. Moreover, the higher the temperature, the faster the color change.

[0077] Table 2 Time-temperature indicator activation energy fitting results

[0078]

[0079] According to formula (2), the reciprocal of temperature is taken as the horizontal coordinate, and the logarithm of the slope of the color difference value change is taken as the vertical coordinate. The fitting curve is as follows: Fig.10 As shown, the activation energy is 79.44 kJ / mol. The activation energy range of the matching food should be within 54.44-104.44 kJ / mol.

[0080] like Fig.11 , Fig.12 , Fig.13As shown in the figure, the weight loss rate, pH value and TVB-N value of pork change at different temperatures. According to the figure, the reaction rate of pork indicators at different temperatures can be calculated. Then, with lnk as the vertical coordinate, linear fitting can be performed to calculate the activation energy of pork juice loss rate, pH value and TVB-N value. From Table 3, it can be seen that the difference with TTI activation energy does not exceed 25kJ / mol. The corresponding R 2 and activation energies are shown in Table 3;

[0081] Table 3 Activation energy fitting results of various pork indicators

[0082]

[0083] like Fig.13 As shown in the figure, in order to verify the accuracy of TTI monitoring of pork, we took the temperature changes of actual cold chain transportation as the starting point, and designed three transportation chains under refrigeration and freezing conditions to simulate the process of pork transportation chain interruption. Multiple temperature changes were set during transportation, sales and home storage, and TTI and pork were stored at corresponding temperatures.

[0084] like Figures 15 to 18 As shown in the figure, during the cold chain circulation of pork, the time temperature indicator is used to monitor pork for up to 180 days. Fig.15 It can be seen that TTI did not reach the end point of the reaction at 180 days, and there was no obvious color change in the pork. Fig.16 It is known that in cold chain transportation, the juice loss rate shows an upward trend, and the rate of increase is the fastest in 0-15 days. It is relatively large in e-commerce logistics. During storage, the free water in the pork gradually increases with the extension of time, and the juice loss rate continues to increase. The reason is that with the extension of storage and transportation time, the fibrin in the muscle is constantly oxidized, which reduces the water holding capacity of fresh cold pork. According to national standards, when the pH value is 5.8-6.2, pork is first-grade fresh meat; when the pH is 6.3-6.6, pork is second-grade fresh meat; when the pH is greater than 6.7, the pork has deteriorated. Fig.17 It can be seen that the pH value of e-commerce logistics was 6.32 on the 108th day, and the pork was already grade 2 fresh meat. Fig.18 In the simulation, the TVB-N value of pork in e-commerce logistics increased faster than that of the other two groups. At 180 days, the TVB-N value was 18.67 mg / 100 g, and the pork was already sub-fresh meat at this time, which is consistent with the conclusion obtained by judging the freshness of pork by pH value. It can be concluded that in the simulation of frozen pork logistics, the quality change of pork under dynamic temperature can be more accurately matched with TTI. That is, the time-temperature indicator across the temperature zone can more accurately monitor the quality change of pork.

Claims

1. A method for preparing a pork refrigeration-freezing cross-temperature zone time temperature indicator, characterized in that The preparation method of the pork refrigeration-freezing cross-temperature zone time temperature indicator is specifically carried out according to the following steps:

1. Prepare a solution of reducing sugar with distilled water, referred to as solution A; 2. Prepare the amino acid and the reaction catalyst into a solution using distilled water, which is referred to as solution B; 3. The container is divided into two sealed areas by a switch; liquid A and liquid B are placed in the two sealed areas respectively, and the switch is in a closed state, thus completing the preparation of the pork refrigeration-freezing cross-temperature zone time temperature indicator.

2. The method for preparing a pork refrigeration-freezing temperature range time-temperature indicator according to claim 1, characterized in that The reducing sugar in step 1 is D-xylose, D-ribose or L-(+)-arabinose.

3. The method for preparing a pork refrigeration-freezing temperature-spanning time-temperature indicator according to claim 1, characterized in that The concentration of solution A in step 1 is 0.50 mol / L, 1.00 mol / L, 1.50 mol / L, 2.00 mol / L or 2.50 mol / L.

4. The method for preparing a pork refrigeration-freezing temperature-spanning time-temperature indicator according to claim 1, characterized in that In step 2, the amino acid is glycine, L-lysine or L-alanine; and the reaction catalyst is K2HPO4.

5. The method for preparing a pork refrigeration-freezing temperature-spanning time-temperature indicator according to claim 1, characterized in that The concentration of amino acids in the B solution in step 2 is 1.00 mol / L, 1.50 mol / L, 2.00 mol / L, 2.50 mol / L, 3.00 mol / L or 3.50 mol / L, and the concentration of the reaction catalyst is 0.50 mol / L, 0.75 mol / L, 1.00 mol / L, 1.25 mol / L, 1.50 mol / L, 1.75 mol / L or 2.00 mol / L.

6. The method for preparing a pork refrigeration-freezing temperature-spanning time-temperature indicator according to claim 1, characterized in that The volume ratio of liquid A to liquid B in step 3 is 1:

1.

7. Application of the pork refrigeration-freezing temperature-span time-temperature indicator prepared by the method of claim 1, characterized in that The color change of the temperature indicator of pork refrigeration-freezing cross-temperature zone indicates the quality of pork under different circulation environments.

8. The use of the pork refrigeration-freezing temperature-span time-temperature indicator according to claim 7, characterized in that When the pork refrigeration-freezing cross-temperature zone time and temperature indicator is used, the switch is rotated from vertical to parallel by turning the knob, so that liquid A contacts liquid B, and then the container is gently shaken to fully mix liquid A and liquid B.

9. The use of the pork refrigeration-freezing temperature-span time-temperature indicator according to claim 7, characterized in that The temperature monitoring range of the pork refrigeration-freezing cross-temperature zone time temperature indicator is -18 to 25°C.

10. The use of the pork refrigeration-freezing temperature-span time-temperature indicator according to claim 7, characterized in that The color change refers to the color change of the pork refrigeration-freezing cross-temperature zone time-temperature indicator from transparent, light yellow, yellow, blue-green, light brown, dark brown to brown-black as time passes.

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