Preparation method of fluorescent label for indicating freshness of chicken

Abstract

The invention belongs to the field of food packaging materials, and provides a preparation method of a fluorescent label for specific detection of putrescine, tyramine and cadaverine, and the preparation method comprises the following steps: dispersing rhodamine B into an ethanol solution to prepare an indicator I; dissolving polymethylacrylic acid and hydroxytetraphenyl ethylene in tetrahydrofuran, and preserving heat to obtain an indicator II; dissolving zein in an ethanol solution, heating and stirring, cooling, and adding a plasticizer to obtain a loaded matrix solution; uniformly mixing the indicator I and the indicator II, slowly adding the loaded matrix solution to obtain a film-forming solution, degassing, casting, spreading, drying, and balancing temperature and humidity to obtain the fluorescent label. The fluorescent label prepared by the invention is wide in concentration response range to putrescine, tyramine and cadaverine solutions, low in detection limit, sensitive in response and high in color discrimination, and can accurately indicate the freshness of fresh chicken.

Description

Technical Field

[0001] This invention belongs to the field of food packaging materials, and specifically relates to a method for preparing a freshness indicator label for chicken. Background Technology

[0002] Chicken products are popular with consumers due to their high nutritional value and delicious taste. However, even during refrigeration, the quality of fresh chicken can still change due to endogenous chemical reactions and microbial growth, and the quality of fresh chicken is difficult to assess in a timely manner. Consumers' immediate judgment of chicken freshness during the sales process is a significant factor influencing their purchasing behavior. Therefore, developing labels that clearly reflect the freshness of fresh chicken is an important way to solve this problem.

[0003] Currently, there are some reported methods or means for indicating freshness. Wang Lin et al. disclosed a fluorescent label for the freshness of meat products in cold storage and its preparation method in patent (CN202310917769), using Rhodamine B and fluorescein as fluorescent dyes to indicate the freshness of meat in cold storage. Liu Xiuying et al. disclosed a method for preparing and applying a ratiometric fluorescent response sensor label for salmon freshness in patent (CN202110346921), using Rhodamine B and tetraphenylethylene as fluorescent dyes to indicate the freshness of salmon meat. However, both of these patents can only indicate the freshness of pork, beef, and salmon meat, and neither can specifically detect the characteristic biogenic amines (putrescine, cadaverine, tyramine) in the chicken spoilage process. Huang Xiaowei et al. disclosed a method for preparing a pH-controlled anthocyanin indicator membrane and its application in patent (CN202311505019). The patent uses anthocyanins as an indicator and zein as a loading matrix. During the spoilage of chicken, it exhibits a pink to blue-purple color change. However, as the meat spoils, it only responds when the pH of the meat exceeds 6, resulting in a slow response. Wang Wenliang et al. disclosed a method for preparing a dual-mode biomass / paper-based label for indicating food freshness in patent (CN202311437774). This patent uses a rhodamine derivative as an indicator and paper as a loading matrix. During the spoilage of pork, it exhibits a green to yellow color change under ultraviolet light. However, it detects acidic gases containing sulfides and cannot detect alkaline gases containing biogenic amines released during spoilage.

[0004] Characteristic biogenic amines are those that are absent or virtually absent in fresh meat, but are produced during spoilage. Therefore, using them as a criterion for freshness testing is reliable. Fresh chicken produces three characteristic biogenic amines during refrigeration: putrescine, cadaverine, and tyramine. The typical concentration ranges for putrescine are: fresh: 0–5 mg / L, slightly fresh: 5–10 mg / L, spoiled: 10–50 mg / L; for cadaverine: fresh: 0–5 mg / L, slightly fresh: 5–10 mg / L, spoiled: 10–25 mg / L; and for tyramine: fresh: 0–10 mg / L, slightly fresh: 10–50 mg / L, spoiled: 50–100 mg / L. Currently, there is a lack of specific indicator labels for detecting the characteristic biogenic amines released during chicken spoilage. Existing color-response labels suffer from problems such as limited color change, slow response speed, high detection limits, and narrow detection ranges. Therefore, developing labels that specifically respond to the characteristic biogenic amines released during the refrigeration of chicken, with fast response speed, low detection limit, and wide detection range, is of practical significance for timely reflection of chicken freshness.

[0005] Traditional fluorescent dyes exhibit fluorescence quenching upon aggregation. Fluorescence quenching refers to the weakening or disappearance of fluorescence intensity emitted by a fluorescent substance under specific conditions. Essentially, excited-state fluorescent molecules release energy through non-radiative energy transfer pathways, leading to a decrease in fluorescence efficiency. This mainly includes: Collisive quenching: Fluorescent molecules collide with a quencher, losing energy as heat. Static quenching: Fluorescent molecules form a non-fluorescent complex with the quencher, directly hindering excitation. Energy transfer: Excited-state molecules transfer energy to an acceptor. Charge transfer: Electron transfer occurs between electron donors and acceptors. Due to fluorescence quenching, fluorescent dyes cannot maintain stable luminescence properties during several days of refrigeration of chicken, limiting their application in indicating the freshness of fresh chicken. Summary of the Invention

[0006] [Technical Issues] Currently, there is a lack of indicator labels specifically designed to detect the characteristic biogenic amines released during chicken spoilage. Existing color-response labels suffer from limitations such as monotonous color changes, slow response speed, high detection limits, and narrow detection ranges. Traditional fluorescent dyes exhibit fluorescence quenching upon aggregation, restricting their application in indicating the freshness of fresh chicken. There is a need for a fluorescent label with a clear color change, fast response speed, low detection limit, and wide detection range, capable of specifically detecting putrescine, tyramine, and cadaverine while avoiding fluorescence quenching, to accurately indicate the freshness of fresh chicken.

[0007] [Technical Solution] The first objective of this invention is to provide a method for preparing a fluorescent tag that specifically detects putrescine, tyramine, and cadaverine, comprising the following steps: S1. Preparation of indicator: Rhodamine B was dispersed in an ethanol solution and placed at -2~10℃ for 1~3 days to obtain indicator I; polymethacrylic acid and hydroxytetraphenylene were dissolved in tetrahydrofuran and kept at the temperature to obtain indicator II; S2. Preparation of the load matrix: Dissolve zein in an ethanol solution, heat and stir, cool, add plasticizer and continue stirring to obtain the load matrix solution; S3. Preparation of film-forming solution: Indicator I and indicator II are mixed and then slowly added to the loading matrix solution to obtain the film-forming solution, which is then degassed. S4. Film Formation: The film-forming solution is cast and spread, dried, and then the temperature and humidity are balanced to obtain the fluorescent tag.

[0008] In one embodiment of the present invention, in step S1, the ethanol solution is a mixture of ethanol and water, and the volume fraction of ethanol is 90-98%.

[0009] In one embodiment of the present invention, in step S1, the amount of Rhodamine B added relative to the ethanol solution is 0.2~0.4 g / L.

[0010] In one embodiment of the present invention, in step S1, the Rhodamine B ethanol solution is sonicated at -2~10℃ for 20~30 min, and then placed at -2~10℃ for 1~3 days.

[0011] In one embodiment of the present invention, in step S1, the amount of polymethacrylic acid added relative to tetrahydrofuran is 10~30 mg / mL, and the amount of hydroxytetraphenylene added relative to tetrahydrofuran is 0.5~1.5 mg / mL.

[0012] In one embodiment of the present invention, in step S1, the molecular weight of polymethacrylic acid Mw is 60,000 to 100,000.

[0013] In one embodiment of the present invention, in step S1, the heat preservation temperature is 20~30℃ and the heat preservation time is 8~12h.

[0014] In one embodiment of the present invention, in step S2, the ethanol solution is a mixture of ethanol and water, and the volume fraction of ethanol is 70-80%.

[0015] In one embodiment of the present invention, in step S2, the amount of zein added relative to the ethanol solution is 60~100 mg / mL, and the amount of plasticizer added relative to the ethanol solution is 18~28 mg / mL.

[0016] In one embodiment of the present invention, in step S2, the plasticizer is selected from one or more of glycerol, sorbitol, polyethylene glycol, and citrate esters.

[0017] In one embodiment of the present invention, in step S2, the heating temperature is 60~75℃, and the heating and stirring time is 20~40 min; after cooling to 20~30℃, glycerol is added and stirring is continued for 10~15 min.

[0018] In one embodiment of the present invention, in step S2, the stirring speed is 300~1000 r / min.

[0019] In one embodiment of the present invention, in step S3, the mixing volume ratio of indicator I, indicator II and the supporting matrix solution is 8~12:1:6.5~8.5.

[0020] In one embodiment of the present invention, in step S4, the thickness of the film-forming solution is 0.2~0.8 mL / cm. 2 .

[0021] In one embodiment of the present invention, in step S4, the drying conditions are 40~50℃ for 18~30 h.

[0022] In one embodiment of the present invention, in step S4, the membrane is placed at an ambient temperature of 20~30℃ and a relative humidity of 40%~50% for 1~2 days to balance the temperature and humidity.

[0023] A second objective of this invention is to provide a fluorescent tag prepared by the above-described method.

[0024] A third objective of this invention is to provide the application of the aforementioned fluorescent label in the detection of meat freshness; said application includes the detection of chicken freshness.

[0025] Invention Principle: When chicken begins to spoil during transportation and storage, the characteristic biogenic amines produced permeate into the label. The hydroxytetraphenylene-polymethacrylic acid complex responds rapidly: under alkaline conditions, polymethacrylic acid deprotonates, and electrostatic repulsion causes the polymer chains to extend, inducing the aggregation of hydroxytetraphenylene molecules and producing blue fluorescence. However, when hydroxytetraphenylene molecules aggregate excessively, their fluorescence intensity weakens, and the blue fluorescence gradually disappears. Subsequently, the protonated biogenic amines cause Rhodamine B to open its ring, producing pinkish-purple fluorescence. Furthermore, the hydroxytetraphenylene-polymethacrylic acid complex responds quickly, while Rhodamine B responds slowly, thus resulting in the transition from blue fluorescence to pinkish-purple fluorescence. A zein-based substrate ensures the stability of the reaction product, resulting in clear and lasting color, while maintaining the integrity of the label's overall structure. After irradiation with ultraviolet light, consumers or supply chain personnel can intuitively and in real-time assess the freshness of the chicken by observing the degree of color change on the label.

[0026] Beneficial effects: The freshness indicator label prepared by this invention exhibits excellent biogenic amine response performance, with a concentration response range of 2–1000 mg / L for putrescine, tyramine, and cadaverine solutions. The detection limits for putrescine, tyramine, and cadaverine solutions are 1.59, 1.27, and 2.59 mg / L, respectively, and the response time to 10 mg / L putrescine, cadaverine, and tyramine is 20 min, achieving sensitive response to low concentrations of biogenic amines.

[0027] In the freshness indicator label prepared by this invention, the indicator has a strong interaction with the supporting matrix and low sensitivity to aqueous solutions, ensuring the stability of the indicator. Under ultraviolet light, the indicator label shows a significant color difference change (ΔE > 80) in 5000 mg / L ammonia solution within 20 min.

[0028] The loading matrix of this invention uses zein, which has the advantages of being safe and non-toxic, and is an environmentally friendly material.

[0029] The freshness indicator label prepared by this invention exhibits a color change from orange-yellow to blue to light pinkish-purple to dark pinkish-purple under ultraviolet light during the storage of chicken, with high color differentiation.

[0030] The freshness indicator label prepared by this invention responds to characteristic biogenic amines (putrescine, cadaverine, tyramine) during the chicken spoilage process, thus broadening the field of specific indicators of chicken freshness and providing a solution for timely judgment of the freshness of raw chicken. Attached Figure Description

[0031] Figure 1 A flowchart illustrating the process for preparing indicator labels.

[0032] Figure 2 These are scanning electron microscope (SEM) images of the films prepared in Example 1 and Comparative Examples 1-3.

[0033] Figure 3 The water contact angle is the water contact angle of the membranes prepared in Example 1 and Comparative Examples 2-4.

[0034] Figure 4 The graph shows the color difference changes of the films prepared in Example 1 and Comparative Examples 1-3 in response to 5000 mg / L ammonia water.

[0035] Figure 5 Example 1 shows the color difference changes and linear fitting of the label under visible and ultraviolet light for different concentrations of putrescine, tyramine, and cadaverine.

[0036] Figure 6The fluorescence and visible spectra of the indicator label solution for chicken spoilage in Example 1 are shown.

[0037] Figure 7 Example 1: Color difference changes of indicator labels for monitoring chicken stored at 4°C under visible and ultraviolet light.

[0038] Figure 8 The sensitivity of the label to putrescine, cadaverine, and tyramine is shown in Example 1.

[0039] Figure 9 The sensitivity of the membrane prepared in Comparative Example 4 to putrescine, cadaverine, and tyramine was determined. Detailed Implementation

[0040] The materials used in the following comparative examples are: Rhodamine B (CAS: 81-88-9), polymethacrylic acid (CAS: 25087-26-7), hydroxytetraphenylene (CAS: 76115-06-5), tetraphenylene (CAS: 632-51-9), zein (CAS: 9010-66-6), and glycerol (CAS: 56-81-5).

[0041] Example 1 A method for preparing a fluorescent tag (zein-rhodamine B-hydroxytetraphenylene-polymethacrylic acid membrane) for the specific detection of putrescine, tyramine, and cadaverine includes the following steps: S1. Preparation of the indicator: 30 mg of Rhodamine B was added to 100 mL of 95% ethanol solution and stirred until uniformly dispersed. The solution was then sonicated at 4℃ for 20 min and stored at 4℃ for 1 day to obtain indicator I. 0.2 g of polymethacrylic acid (Mw = 80000) and 10 mg of hydroxytetraphenylene were dissolved in 10 mL of tetrahydrofuran and incubated at 25℃ for 12 h. Under physical adsorption, a hydroxytetraphenylene-polymethacrylic acid complex solution was formed, thus obtaining indicator II. S2. Preparation of the loading matrix: Take 5.6 g of zein and 70 mL of 75% ethanol, stir at 70℃ and 600 r / min for 30 min, cool to 25℃, add 1.68 g of glycerol, and continue stirring for 1 min to obtain the loading matrix solution. S3. Preparation of film-forming solution: Indicator I and indicator II are mixed and then slowly added to the loading matrix solution to obtain the film-forming solution. The solution is sonicated at 25°C for 20 min and allowed to stand for 12 h to completely remove air bubbles from the film-forming solution. S4. Film Formation: 30 mL of film-forming solution was cast and spread onto a glass culture dish with a diameter of 10.6 cm. The dish was dried at 40℃ for 24 h and then placed at an ambient temperature of 20~30℃ and a relative humidity of 40%~50% for 1 day to obtain the fluorescent tag.

[0042] Preparation process as follows Figure 1 As shown.

[0043] Comparative Example 1 The preparation method of the zein membrane differs from that of Example 1 only in that the loading matrix solution prepared in step S2 is used as the film-forming solution.

[0044] Comparative Example 2 The preparation method of the zein-rhodamine B membrane differs from that of Example 1 only in that indicator II is not added to the film-forming solution in step S3.

[0045] Comparative Example 3 The preparation method of the zein-hydroxytetraphenylene-polymethacrylic acid membrane differs from that of Example 1 only in that no indicator is added to the film-forming solution in step S3.

[0046] Comparative Example 4 The preparation method of the zein-rhodamine B-tetraphenylethylene-polymethacrylate membrane differs from that of Example 1 only in that hydroxytetraphenylethylene is replaced with tetraphenylethylene.

[0047] Figure 2 This is a scanning electron microscope image, which shows the zein membrane ( Figure 2 A), Zein-Rhodamine B membrane ( Figure 2 B), zein-hydroxytetraphenylene-polymethacrylate film ( Figure 2 C) and zein-rhodamine B-hydroxytetraphenyl-polymethacrylic acid indicator label ( Figure 2 The microscopic morphological characteristics of D). Figure 1 As shown in A, at a magnification of 1000x, the surface texture can be observed more clearly: some natural granular or fibrous structures can be seen on the surface, which are characteristic of the aggregation of zein. Figure 2 As shown in Figure B, when Rhodamine B is added to a zein solution, it cannot be uniformly dispersed at the molecular level in the hydrophobic protein matrix. During film formation, Rhodamine B and zein undergo microphase separation. Simultaneously, Rhodamine B and zein have a strong interaction, leading to subtle changes in the surface texture. Figure 1 As shown in C, at a magnification of 1000x, the changes in the morphology of the zein matrix interface caused by the addition of the TPE-OH / PMAA complex can be observed more clearly. Figure 2As shown in D, Rhodamine B did not adsorb onto the TPE-OH / PMAA complex, but was dispersed on the interface of zein itself.

[0048] Figure 3 The results of the water contact angle experiment are shown. The experimental method involves releasing 2-3 μL of water droplets above the test material and measuring the water contact angle. Due to surface tension, the water droplet and the test material form a certain angle, which is the water contact angle. The water contact angle reflects the hydrophilicity or hydrophobicity of the test material; the larger the angle, the stronger the hydrophobicity and the weaker the hydrophilicity. After the addition of RhB, the water contact angle of the membrane increased slightly compared to the zein membrane, but statistically, there was no significant difference in the water contact angle between the zein membrane and the zein-rhodamine B membrane (P>0.05). After the addition of TPE-OH / PMAA, the water contact angles of the zein-hydroxytetraphenyl-polymethacrylate (HTHPT) film (51.50°±0.91°) and the zein-rhodamine B-hydroxytetraphenyl-polymethacrylate (HTHPT) indicator tag (51.97°±2.42°) were significantly larger than those of the zein film, the zein-rhodamine B film, and the zein-rhodamine B-HTHPT-polymethacrylate (P<0.05). This is due to the hydrophobicity of the TPE-OH / PMAA complex. The test results indicate that the water sensitivity of the tag decreases after the addition of the TPE-OH / PMAA complex, improving the tag's stability in aqueous solutions and preventing water from quenching Rhodamine B molecules.

[0049] 5000 mg / L ammonia solution was dropped onto the prepared indicator label. After the color of the indicator label stopped changing, photos of the indicator label before and after the color change were taken under the same lighting conditions. The L, a, and b values ​​were obtained from the photos using image processing software, and the color difference was calculated. Figure 4 The color response of zein membrane, zein-rhodamine B membrane, zein-hydroxytetraphenyl-polymethacrylic acid membrane, and zein-rhodamine B-hydroxytetraphenyl-polymethacrylic acid indicator label to 5000 mg / L ammonia solution under visible and ultraviolet light is shown, along with corresponding photographs. The criterion for evaluating color difference change value is as follows: when the color difference change value (ΔE) is in the range of 0~1, it is indistinguishable to the naked eye; only when ΔE > 5 can it be distinguished by the naked eye. The formula for calculating ΔE is shown in formula (1). Figure 4As shown in Figure A, the ΔE values ​​of all groups under ultraviolet light were significantly higher than those under visible light (P < 0.05). Among them, the ΔE value of the zein-rhodamine B-hydroxytetraphenyl-polymethacrylic acid indicator tag under ultraviolet light (82.72 ± 3.51) was significantly higher than that of the zein film, zein-rhodamine B film, and zein-hydroxytetraphenyl-polymethacrylic acid film (35.55 ± 1.08, 67.47 ± 2.23, 50.99 ± 1.11, respectively) (P < 0.05). Therefore, the zein-rhodamine B-hydroxytetraphenyl-polymethacrylic acid indicator tag was selected for further response experiments. Figure 4 As can be seen from B, after contact with 5000 mg / L ammonia water, the zein-rhodamine B-hydroxytetraphenylene-polymethacrylic acid indicator label underwent a significant color change under ultraviolet light within 20 min.

[0050]

[0051] In formula (1), L represents brightness, a represents the deviation value from green to red, and b represents the deviation value from blue to yellow.

[0052] Figure 5 The changes in ΔE values ​​of the zeaxanthin-rhodamine B-hydroxytetraphenylphenyl-polymethacrylic acid indicator label for different concentrations of putrescine, cadaverine, and tyramine were demonstrated. Figure 5 A) and its linear fit ( Figure 5 B). Among them, the fitting equations for the color difference change (Y) of putrescine, cadaverine, and tyramine and their concentration (X) are: Y=1.54x+26.03, Y=3.01x+14.61, Y=1.08x+17.26, respectively, with R-squared values ​​of 0.994, 0.998, and 0.995. It can be concluded that the color difference change of the indicator label has a good linear response to the concentration change of putrescine, cadaverine, and tyramine. According to the calculation formula (2) for the detection limit, the detection limits of the label for putrescine, cadaverine, and tyramine are calculated to be 1.59 mg / L, 1.27 mg / L, and 2.59 mg / L, respectively. It can be seen that the detection limits of the zein-rhodamine B-hydroxytetraphenylethylene-polymethacrylic acid indicator label for putrescine, cadaverine, and tyramine are low.

[0053]

[0054] In formula (2), SD_△E is the standard deviation of the color difference change of the control group label, and b is the slope.

[0055] Add 1 mL of various biogenic amine solutions with a concentration of 10 mg / L to 30 mL of the zein-rhodamine B-hydroxytetraphenyl-polymethacrylic acid solution (film-forming solution) prepared in Example 1, and test the absorbance and fluorescence intensity of the solution. Figure 6 The fluorescence and visible spectra of zein-rhodamine B-hydroxytetraphenylethylene-polymethacrylic acid solution on characteristic and non-characteristic biogenic amines during chicken spoilage, as well as a control group, are presented. Figure 6 As shown in Figure A, the absorbance values ​​of putrescine, cadaverine, and tyramine at the characteristic wavelengths were significantly higher than those of the blank group and other biogenic amine solutions. This indicates that putrescine, cadaverine, and tyramine produced more reaction products with Rhodamine B and hydroxytetraphenyl-polymethacrylic acid. Figure 6 As can be seen from Figure B, in the fluorescence spectrum, compared with the blank group and the control group, the addition of putrescine, cadaverine, and tyramine induced the solution to produce a new characteristic absorption peak at 470 nm. This result indicates that the fluorescence of hydroxytetraphenylene-polymethacrylic acid is activated by putrescine, cadaverine, and tyramine, thus demonstrating that the Rhodamine B-hydroxytetraphenylene-polymethacrylic acid tag solution has a specific response to putrescine, cadaverine, and tyramine.

[0056] Seal the indicator label and 50-60 g of chilled fresh chicken with plastic wrap and store at 4°C. Take photos of the color of the indicator label daily under the same light conditions, record the L, a, and b values, and calculate the color difference. Figure 7 This study demonstrates the changes in ΔE values ​​and corresponding photographs of chicken meat during chilled storage using a zein-rhodamine B-hydroxytetraphenylethylene-polymethacrylic acid indicator label. Figure 7 It can be seen that the ΔE value shows a positive correlation with the extension of storage days. On day 8, compared with the initial label, the color difference change under ultraviolet light reached 71.25 ± 3.72. According to the evaluation criteria for color difference change value: when the color difference change value (ΔE) is in the range of 0 to 1, it is not distinguishable to the naked eye; only when ΔE > 5 can it be distinguished to the naked eye. On day 8, the zein-rhodamine B-hydroxytetraphenylethylene-polymethyl methacrylate indicator label has undergone a significant color difference change compared to day 0. Therefore, it can be seen that the label of this invention has an indicative function for the freshness of chilled chicken.

[0057] A 10 mg / L biogenic amine was dropped onto an indicator label, and the color change of the indicator label was photographed under the same lighting conditions.

[0058] Figure 8 The sensitivity of the zeaxanthin-rhodamine B-hydroxytetraphenylethylene-polymethacrylic acid indicator label to putrescine, cadaverine, and tyramine was demonstrated. From Figure 8It can be seen that in the initial response phase of 0-30 min, TPE-OH / PMAA mainly plays an indicative role. According to the definition of response time, the time required to reach 90% of the maximum color difference within 30 min is taken as the response time. Therefore, the response time of the label to 10 mg / L biogenic amine is 20 min. It can be concluded that the zein-rhodamine B-hydroxytetraphenylethylene-polymethacrylic acid indicator label has good sensitivity for low concentrations of putrescine, cadaverine, and tyramine.

[0059] Figure 9 The sensitivity of the zein-rhodamine B-tetraphenylethylene-polymethacrylate membrane to putrescine, cadaverine, and tyramine was demonstrated. The zein-rhodamine B-tetraphenylethylene-polymethacrylate membrane did not exhibit the fluorescence response corresponding to the tetraphenylethylene / polymethacrylate complex to 10 mg / L of putrescine, cadaverine, and tyramine. Comparative Example 4 showed significantly worse detection limits for putrescine, cadaverine, and tyramine than Example 1, and its specificity for these substances was also significantly worse than that of Example 1.

[0060] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a fluorescent tag for specifically detecting putrescine, tyramine, cadaverine, characterized in that, The method comprises the following steps: S1, preparation of an indicator: dispersing rhodamine B into an ethanol solution, and placing the solution at -2-10℃ for 1-3 days to obtain an indicator I; dissolving polymethyl acrylic acid and hydroxyl tetraphenyl ethane into tetrahydrofuran, and keeping the solution to obtain an indicator II; S2, preparation of a loading matrix: dissolving zein into an ethanol solution, heating and stirring, adding a plasticizer after cooling, and continuously stirring to obtain a loading matrix solution; S3, preparation of a film-forming solution: mixing the indicator I and the indicator II, slowly adding the mixture into the loading matrix solution, and degassing to obtain a film-forming solution; S4, film preparation: casting and spreading the film-forming solution, drying, and balancing temperature and humidity to obtain a fluorescent tag.

2. The production method according to claim 1, characterized by, In step S1, the volume fraction of ethanol in the ethanol solution is 90-98%, and the addition amount of rhodamine B in the ethanol solution is 0.2-0.4 g / L; the rhodamine B ethanol solution is ultrasonically treated at -2-10℃ for 20-30 min, and then placed at -2-10℃ for 1-3 days.

3. The production method according to claim 1, characterized by, In step S1, the addition amount of polymethyl acrylic acid in tetrahydrofuran is 10-30 mg / mL, and the addition amount of hydroxyl tetraphenyl ethane in tetrahydrofuran is 0.5-1.5 mg / mL; the molecular weight of polymethyl acrylic acid is 60000-100000; the temperature for keeping is 20-30℃, and the time for keeping is 8-12 h.

4. The production method according to claim 1, characterized by, In step S2, the volume fraction of ethanol in the ethanol solution is 70-80%, the addition amount of zein in the ethanol solution is 60-100 mg / mL, and the addition amount of a plasticizer in the ethanol solution is 18-28 mg / mL; the plasticizer is selected from one or more of glycerol, sorbitol, polyethylene glycol, and citric acid esters.

5. The production method according to claim 1, characterized by, In step S2, the heating temperature is 60-75℃, and the time for heating and stirring is 20-40 min; the temperature is cooled to 20-30℃, glycerol is added and continuously stirred for 10-15 min; the stirring speed is 300-1000 r / min.

6. The method of claim 1, wherein, In step S3, the mixing volume ratio of the indicator I, the indicator II, and the loading matrix solution is 8-12:1:6.5-8.

5.

7. The production method according to claim 1, characterized by, The thickness of the film-forming solution spread in step S4 is 0.2 to 0.8 mL / cm 2 .

8. The production method according to claim 1, characterized by, In step S4, the drying condition is 40-50℃ for 18-30 h; the film is placed at an ambient temperature of 20-30℃ and a relative humidity of 40%-50% for 1-2 days to balance the temperature and humidity.

9. The fluorescent tag prepared by the preparation method in any one of claims 1-8.

10. The fluorescent tag in claim 9 is applied in meat freshness detection.

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