Aquatic product freshness detection indication label based on colorimetric-fluorescence bimodal signal as well as preparation method and application of aquatic product freshness detection indication label

Abstract

The invention discloses an aquatic product freshness detection indication label based on a colorimetric-fluorescence bimodal signal as well as a preparation method and application of the aquatic product freshness detection indication label, and belongs to the technical field of intelligent food packaging. The preparation method comprises the following steps: dissolving casein in water, heating, stirring, refrigerating and standing to obtain a casein solution; adjusting the pH value of the casein solution to 12, adding curcumin, and uniformly stirring to obtain a curcumin / casein mixed solution; adjusting the pH value of the curcumin / casein mixed solution to 7-9 to obtain a casein encapsulated curcumin solution; dissolving carboxymethyl cellulose and sodium alginate in water to obtain a carboxymethyl cellulose-sodium alginate solution; and adding the casein encapsulated curcumin solution and glycerol into the carboxymethyl cellulose-sodium alginate solution, adjusting the pH value to be acidic, and drying to form the film. The label prepared by the invention has relatively strong mechanical property and excellent degradation property, and can intelligently detect the freshness of shrimp and fish meat aquatic products through color and fluorescence double signals.

Description

Technical Field

[0001] This invention relates to the field of intelligent food packaging technology, specifically to a colorimetric-fluorescence dual-modal signal aquatic product freshness detection indicator label, its preparation method, and its application. Background Technology

[0002] With increasing consumer focus on food quality and safety, the development of real-time, non-destructive freshness indication technologies has become a research hotspot in the food packaging industry. pH-responsive indicator labels based on natural pigments have attracted significant attention due to their environmental friendliness and visibility. Curcumin, in particular, is considered an ideal indicator due to its significant pH-dependent color change (yellow → reddish-brown) and fluorescence properties. However, existing technologies face the following bottlenecks:

[0003] Curcumin's stability is a concern: free curcumin is easily degraded by light, heat, and oxidation, leading to rapid decay of the indicator signal. Existing encapsulation technologies, such as liposome encapsulation, are complex and costly, while nanoparticle loading poses biocompatibility risks.

[0004] Limitations of single-response mode: Existing indicator tags mostly rely on a single color response, which results in poor visibility under complex lighting conditions. On the other hand, the design of tags with dual fluorescence response suffers from low response sensitivity and narrow linear range due to limitations in carrier materials.

[0005] Insufficient compatibility with matrix materials: Traditional matrices such as gelatin have poor mechanical strength, and chitosan is prone to swelling in high humidity environments, leading to label structure failure. Although sodium alginate / carboxymethyl cellulose composite systems show potential, there are no reports of synergistic effects with protein-pigment composite particles.

[0006] Lack of specific monitoring for aquatic products: Existing indicator labels are mostly designed for meat, while volatile amines produced during the spoilage of high-protein aquatic products such as shrimp and fish have unique release kinetics, and conventional labels have problems such as mismatched response thresholds and obvious hysteresis.

[0007] Chinese patent application CN118307820A discloses a method for preparing a biodegradable smart indicator tag that uses pH-driven three-dimensional structural changes of soy protein isolate to in-situ encapsulate anthocyanins. This tag possesses properties such as UV resistance, hydrophobicity, real-time monitoring, high barrier properties, and biodegradability. The technical solution involves preparing a soy protein isolate / sodium carboxymethyl cellulose (CMC)-based film using a solution casting method with a certain mass of soy protein isolate, sodium carboxymethyl cellulose (CMC), tannic acid, glycerol, and anthocyanins. The pH of the film solution is adjusted by tannic acid, driving the soy protein isolate molecular chains to contract and encapsulate anthocyanins. The freshness of meat is observed in real time based on changes in the film's color. This method features low energy consumption, a simple and environmentally friendly process, ease of large-scale production, good batch-to-batch repeatability, effectively reduced anthocyanin migration, enhanced hydrophobicity and barrier properties of the film, and good UV resistance. It holds promise for widespread application in meat freshness indication; however, its reliance solely on color response limits its applicability. Summary of the Invention

[0008] The technical problem to be solved by this invention is how to monitor the freshness of aquatic products in real time with visualization.

[0009] The present invention solves the above-mentioned technical problems through the following technical means:

[0010] A method for preparing a colorimetric-fluorescence dual-modal signal aquatic product freshness detection indicator label includes the following steps:

[0011] S1. Dissolve casein (Cas) in water, heat, stir, and then refrigerate and let stand to obtain a casein solution;

[0012] S2. Adjust the pH of the casein solution to 12, add curcumin (Cur), and stir until homogeneous to obtain a curcumin / casein mixed solution;

[0013] S3. Adjust the pH of the curcumin / casein mixed solution to 7-9 to obtain a casein-encapsulated curcumin solution;

[0014] S4. Dissolve carboxymethyl cellulose and sodium alginate in water to obtain a carboxymethyl cellulose-sodium alginate solution; add casein-encapsulated curcumin solution and glycerol to the carboxymethyl cellulose-sodium alginate solution, adjust the pH to acidic, and dry to form a film to obtain the colorimetric-fluorescence dual-modal signal aquatic product freshness detection indicator label.

[0015] Preferably, in S1, the ratio of casein to water is 0.1–3 g / 100 mL; in S4, the mass ratio of carboxymethyl cellulose to sodium alginate is 1 / 3–3 / 1; and the total concentration of carboxymethyl cellulose and sodium alginate in the carboxymethyl cellulose-sodium alginate solution is 0.5–2 g / 100 mL.

[0016] Preferably, in S1, the heating temperature is 30–50°C; the refrigeration temperature is 0–5°C, and the time is 8–24 hours.

[0017] Preferably, in S2, the mass ratio of casein to curcumin in the casein solution is 1 g / 10 to 90 mg.

[0018] Preferably, in S3, the pH is adjusted to 7.

[0019] Preferably, in step S3, the curcumin / casein mixed solution is adjusted to pH 7-9 and then centrifuged to obtain a casein-encapsulated curcumin solution; the centrifugation speed is 5000-10000 rpm, the time is 5-20 min, and the temperature is 0-10℃.

[0020] Preferably, in step S4, the mass ratio of the casein-encapsulated curcumin solution to the solute in the carboxymethyl cellulose-sodium alginate solution is 1 / 10 to 1 / 2, and the amount of glycerol added is 20% to 40% of the mass of the solute in the carboxymethyl cellulose-sodium alginate solution.

[0021] Preferably, in S4, the pH is adjusted to 4-6.

[0022] The present invention also proposes a colorimetric-fluorescence dual-modal signal aquatic product freshness detection indicator label, which is prepared using the aforementioned method for preparing a colorimetric-fluorescence dual-modal signal aquatic product freshness detection indicator label.

[0023] The present invention also proposes the application of the colorimetric-fluorescence dual-modal signal aquatic product freshness detection indicator label in the detection of aquatic product freshness.

[0024] Preferably, the aquatic product is fish or shrimp.

[0025] The advantages of this invention are:

[0026] This invention encapsulates curcumin within casein, enabling it to exhibit a yellow-green fluorescence. This also improves the thermal and photostability of curcumin. Furthermore, using carboxymethyl cellulose and sodium alginate as a base, the resulting composite label exhibits excellent mechanical properties and hydrophobicity. This composite label changes color and fluorescence according to pH changes during the spoilage process of aquatic products, thus enabling visual detection of the freshness of these products. Consumers can observe both color and fluorescence changes on the label to promptly understand the quality status of the food, reducing the risk of health problems caused by accidentally consuming spoiled food.

[0027] This invention innovatively proposes a pH-driven method for preparing casein-curcumin composite particles (Cur@Cas), achieving efficient encapsulation and enhanced stability of the pigment through protein self-assembly. Furthermore, it is compounded with a sodium alginate / carboxymethyl cellulose matrix to construct a smart tag with dual color and fluorescence signal outputs. This design overcomes the limitations of a single response mode, achieving highly sensitive and specific responses to spoilage characteristics of aquatic products through the synergistic effect of casein's expanded pH response domain and the osmotic regulation of the polysaccharide matrix. Attached Figure Description

[0028] Figure 1 The graph shows the thermal stability test results of curcumin in the Cur@Cas solution prepared in Example 1 of this invention;

[0029] Figure 2 The image shows the photostability test results of curcumin in the Cur@Cas solution prepared in Example 1 of this invention;

[0030] Figure 3 The fluorescence spectra of the Cur@Cas solutions prepared in Examples 1 and 6 of this invention are shown.

[0031] Figure 4 The images show daylight photographs and fluorescence spectra of Cur@Cas solutions prepared at different pH values ​​in Examples 1 and 7 of this invention.

[0032] Figure 5 Sunlight and fluorescence photographs of CS, Cas / CS, Cur / CS, and Cur@Cas / CS tags prepared in Examples 2, 3, 4, and 5 of this invention;

[0033] Figure 6 Infrared spectra of CS, Cas / CS, Cur / CS, and Cur@Cas / CS tags prepared in Examples 2, 3, 4, and 5 of this invention;

[0034] Figure 7 Mechanical tensile diagrams of the CS, Cas / CS, Cur / CS, and Cur@Cas / CS tags prepared in Examples 2, 3, 4, and 5 of this invention;

[0035] Figure 8 The figures show the water contact angle test results of the CS, Cas / CS, Cur / CS, and Cur@Cas / CS tags prepared in Examples 2, 3, 4, and 5 of this invention;

[0036] Figure 9 The graph shows the natural degradation test results of the CS and Cur@Cas / CS tags prepared in Examples 2 and 5 of this invention;

[0037] Figure 10 This is a photograph of the ammonia response test results of the Cur@Cas / CS tag prepared in Example 5 of the present invention;

[0038] Figure 11 These are photos of the freshness test results of shrimp and fish meat with Cur@Cas / CS tags prepared in Example 5 of this invention;

[0039] Figure 12 This is a schematic diagram illustrating the process of preparing the Cur@Cas / CS tag according to the present invention;

[0040] Figure 13 These are photographs of the freshness test results of shrimp and fish meat labeled in Examples 2-4 of this invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0043] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0044] Example 1

[0045] Synthesis of casein-encapsulated curcumin solution (Cur@Cas):

[0046] 2.0 g of casein (Cas) was dissolved in 100 mL of deionized water to a concentration of 20 mg / mL. The solution was heated at 40 °C, stirred until homogeneous, and then refrigerated at 4 °C for 12 h to obtain a Cas solution. The pH of the Cas solution was adjusted to 12 using 4 mol / L sodium hydroxide solution, and 100 mg of curcumin (Cur) was added and stirred until homogeneous to obtain a curcumin / casein mixed solution. The curcumin / casein mixed solution was then adjusted to neutral using 1 mol / L hydrochloric acid solution and centrifuged at 8000 rpm for 10 min at 5 °C to obtain a casein-encapsulated curcumin solution (Cur@Cas).

[0047] Example 2

[0048] Synthesis of carboxymethyl cellulose-sodium alginate tag (CS):

[0049] Dissolve 0.375g of carboxymethyl cellulose (CMC) and 0.375g of sodium alginate in 50mL of deionized water to obtain a mixed solution of carboxymethyl cellulose and sodium alginate; pour 25mL of the mixed solution into a mold with a diameter of 9cm and dry at 50℃ for 24h to obtain the CS label.

[0050] Example 3

[0051] Synthesis of casein / carboxymethyl cellulose-sodium alginate tag (Cas / CS):

[0052] 0.375 g of carboxymethyl cellulose (CMC) and 0.375 g of sodium alginate (SA) were dissolved in 50 mL of deionized water to obtain a CMC-SA solution; 0.2 g of casein was dissolved in 10 mL of deionized water to obtain a casein solution. The CMC-SA solution and the casein solution were mixed, and 225 mg of glycerol was added. The pH was adjusted to 5 using 1 mol / L hydrochloric acid solution. 25 mL of the mixture was poured into a 9 cm diameter mold and dried at 50 °C for 24 h to obtain the Cas / CS label.

[0053] Example 4

[0054] Synthesis of curcumin / carboxymethyl cellulose-sodium alginate tag (Cur / CS):

[0055] 0.375 g of carboxymethyl cellulose and 0.375 g of sodium alginate were dissolved in 50 mL of deionized water to obtain a carboxymethyl cellulose-sodium alginate solution; 0.01 g of curcumin was dispersed in 10 mL of deionized water to obtain a curcumin dispersion, which was added to the carboxymethyl cellulose-sodium alginate solution, and then 225 mg of glycerol was added. The pH was adjusted to 5 using 1 mol / L hydrochloric acid solution; 25 mL of the mixed solution was poured into a mold with a diameter of 9 cm and dried at 50 °C for 24 h to obtain the Cur / CS label.

[0056] Example 5

[0057] Synthesis of casein-encapsulated curcumin / carboxymethyl cellulose-sodium alginate tag (Cur@Cas / CS):

[0058] 0.375 g of carboxymethyl cellulose and 0.375 g of sodium alginate were dissolved in 50 mL of deionized water to obtain a carboxymethyl cellulose-sodium alginate solution; then 225 mg of glycerol and 10 mL of the Cur@Cas solution prepared in Example 1 were added, and the pH was adjusted to 5 using 1 mol / L hydrochloric acid solution; 25 mL of the mixed solution was poured into a mold with a diameter of 9 cm and dried at 50 °C for 24 h to obtain the Cur@Cas / CS label. The process is illustrated in the diagram below. Figure 12 As shown.

[0059] Example 6

[0060] The only difference from Example 1 is that the pH of the Cas solution was adjusted to 9, 10, or 11.

[0061] Example 7

[0062] The only difference from Example 1 is that the pH of the curcumin / casein mixed solution was adjusted to 8, 9, 10, and 11.

[0063] Example 8

[0064] Synthesis of casein-encapsulated curcumin / carboxymethyl cellulose-sodium alginate tag (Cur@Cas / CS):

[0065] 1.2 g of casein (Cas) was dissolved in 100 mL of deionized water, heated at 30 °C, stirred until homogeneous, and then refrigerated at 5 °C for 24 h to obtain a Cas solution. The pH of the Cas solution was adjusted to 12 using 4 mol / L sodium hydroxide solution, and 100 mg of curcumin (Cur) was added and stirred until homogeneous to obtain a curcumin / casein mixed solution. The curcumin / casein mixed solution was then adjusted to neutral using 1 mol / L hydrochloric acid solution and centrifuged at 5000 rpm for 20 min at 0 °C to obtain a casein-encapsulated curcumin solution (Cur@Cas).

[0066] 0.125g carboxymethyl cellulose and 0.375g sodium alginate were dissolved in 50mL of deionized water to obtain a carboxymethyl cellulose-sodium alginate solution; then 200mg glycerol and 10mL of the prepared Cur@Cas solution were added, and the pH was adjusted to 4 with 1mol / L hydrochloric acid solution; 25mL of the mixed solution was poured into a mold with a diameter of 9cm and dried at 50℃ for 24h to obtain the Cur@Cas / CS label.

[0067] Example 9

[0068] Synthesis of casein-encapsulated curcumin / carboxymethyl cellulose-sodium alginate tag (Cur@Cas / CS):

[0069] Dissolve 3.0 g of casein (Cas) in 100 mL of deionized water, heat at 50 °C, stir until homogeneous, and refrigerate at 0 °C for 8 h to obtain a Cas solution. Adjust the pH of the Cas solution to 12 using 4 mol / L sodium hydroxide solution, add 100 mg of curcumin (Cur), stir until homogeneous, and obtain a curcumin / casein mixed solution. Adjust the pH of the curcumin / casein mixed solution to neutral using 1 mol / L hydrochloric acid solution, and centrifuge at 10 °C and 10,000 rpm for 5 min to obtain a casein-encapsulated curcumin solution (Cur@Cas).

[0070] 0.75 g of carboxymethyl cellulose and 0.25 g of sodium alginate were dissolved in 50 mL of deionized water to obtain a carboxymethyl cellulose-sodium alginate solution; then 225 mg of glycerol and 10 mL of the prepared Cur@Cas solution were added, and the pH was adjusted to 6 with 1 mol / L hydrochloric acid solution; 25 mL of the mixed solution was poured into a mold with a diameter of 9 cm and dried at 50 °C for 24 h to obtain the Cur@Cas / CS label.

[0071] Comparative Example 1

[0072] The only difference from Example 5 is that 0.375g of PVA was used instead of sodium alginate to prepare the label for detecting the freshness of shrimp and fish. This comparative example has poor hydrophobic properties; the label swells during the shrimp and fish freshness detection process, which is detrimental to practical applications.

[0073] The thermal stability of curcumin in the Cur@Cas solution prepared in Example 1 was tested by encapsulating curcumin with casein and heating at 80°C for 120 min. The results are as follows. Figure 1 As shown, the stability of curcumin was significantly improved after encapsulation with casein, and the curcumin retention rate increased by 62.95%, while the color change was small and the initial color was basically maintained.

[0074] The photostability of curcumin in the Cur@Cas solution prepared in Example 1 was tested by irradiating curcumin and casein-encapsulated curcumin under a xenon lamp for 120 min. The results are as follows. Figure 2 As shown, the stability of curcumin was significantly improved after encapsulation with casein, and the curcumin retention rate increased by 57.50%, while the color change was small and the initial color was basically maintained.

[0075] Figure 3 The fluorescence spectra of the Cur@Cas solutions prepared in Examples 1 and 6 above are shown. Using different pH-driven casein encapsulation methods, when the pH of the casein solution was adjusted to 9-11, the Cur@Cas solution prepared in Example 6 showed almost no fluorescence; when the pH was adjusted to 12, the Cur@Cas solution showed a significant fluorescence characteristic peak at 506 nm, indicating that when the pH of the casein solution was adjusted to 12, the Cur@Cas solution prepared in Example 1 possessed fluorescence properties.

[0076] Figure 4 The images show daylight photographs and fluorescence spectra of the Cur@Cas solutions prepared at different pH values ​​in Examples 1 and 7 above. The fluorescence intensity of the Cur@Cas solutions varied at different pH values. As the pH increased from 7 to 11, the fluorescence intensity of the Cur@Cas solutions continuously decreased, and the maximum emission wavelength continuously shifted to the left. Visually, the color of the Cur@Cas solutions changed from yellow to brownish-red, and the fluorescence intensity continuously decreased.

[0077] Figure 5 Sunlight and fluorescence photographs of the CS, Cas / CS, Cur / CS, and Cur@Cas / CS tags prepared in Examples 2, 3, 4, and 5 above. The CS tag prepared in Example 2 is transparent and exhibits no fluorescence. The Cas / CS tag prepared in Example 3 is transparent and exhibits weak blue fluorescence. The Cur / CS tag prepared in Example 4 is deep yellow and exhibits no fluorescence. The Cur@Cas / CS tag prepared in Example 5 is light yellow and exhibits strong yellow-green fluorescence.

[0078] Figure 6 Infrared spectra of the CS, Cas / CS, Cur / CS, and Cur@Cas / CS tags prepared in Examples 2, 3, 4, and 5 above. At 3274 cm⁻¹ -1 2927cm -1 1595cm -1 1409cm -1 and 1025cm -1 The characteristic peaks correspond to stretching vibrations of hydroxyl groups (O–H), alkyl chains (C–H), carboxylic acid groups (C=O), and glycosidic bonds (C–O–C). These peaks are consistent with the functional groups of carboxymethyl cellulose and sodium alginate, confirming the successful preparation of the tag. The center is at 3274 cm⁻¹. -1 The broad O–H peaks indicate a strong hydrogen bond interaction between carboxymethyl cellulose and sodium alginate.

[0079] Figure 7 Tensile mechanical diagrams of the CS, Cas / CS, Cur / CS, and Cur@Cas / CS labels prepared in Examples 2, 3, 4, and 5 above are shown. The labels were cut into dumbbell shapes, fixed with clamps, and tested using a universal tensile testing machine at a tensile rate of 10 mm / min. Figure 7 It can be seen that CS, Cas / CS, Cur / CS, and Cur@Cas / CS tags possess good mechanical properties. Among them, the Cur@Cas / CS tag has a strain of 4.11%, a stress of 70.70 MPa, and a toughness of 1.75 MJ / m. 3 Its Young's modulus is 2682.62 MPa. Its excellent mechanical properties meet the practical application requirements for indicating the freshness of aquatic products.

[0080] Figure 8The water contact angle test results for the CS, Cas / CS, Cur / CS, and Cur@Cas / CS labels prepared for Examples 2, 3, 4, and 5 above are shown in the figure. The water contact angles of the CS, Cas / CS, Cur / CS, and Cur@Cas / CS labels are 69.88°, 88.44°, 82.84°, and 90.30°, respectively. The Cur@Cas / CS label possesses suitable hydrophilic and hydrophobic properties, which satisfies the adsorption response of analytes in indicating the freshness of aquatic products while preventing the label from absorbing water and becoming damaged.

[0081] Figure 9 The graph shows the natural degradation test results of the CS and Cur@Cas / CS tags prepared in Examples 2 and 5 above. After burying the CS and Cur@Cas / CS tags in soil for natural degradation for 15 days, the mass retention rates of the CS and Cur@Cas / CS tags were 17.30% and 22.13%, respectively, indicating that the CS and Cur@Cas / CS tags have excellent natural degradation performance and are environmentally friendly.

[0082] Figure 10 The image shows the ammonia response test results of the Cur@Cas / CS tag prepared in Example 5 above. When the Cur@Cas / CS tag was placed in an ammonia vapor atmosphere for 5 minutes, the tag's color gradually changed from yellow to brownish-red, and the fluorescence intensity continuously decreased, indicating that the Cur@Cas / CS tag has both color and fluorescence responses to ammonia. After the ammonia vapor was removed, the Cur@Cas / CS tag was placed in an air atmosphere for 2 minutes. The tag's color gradually changed from brownish-red to yellow, and the fluorescence intensity continuously increased, indicating that the Cur@Cas / CS tag is reusable.

[0083] Figure 11 and 13 The images show the results of freshness detection for shrimp and fish using the Cur@Cas / CS tag prepared in Example 5 and the CS, Cas / CS, and Cur / CS tags prepared in Examples 2-4. When the Cur@Cas / CS tag was placed in a container containing fresh shrimp and fish for 48 hours, the shrimp and fish gradually spoiled, and the tag color gradually changed from yellow to brownish-red, with the fluorescence intensity continuously weakening. This indicates that the Cur@Cas / CS tag can intelligently detect the freshness of aquatic products using a colorimetric-fluorescence dual-modal signal. After being reused four times, the tag still exhibited a strong colorimetric-fluorescence dual-modal signal response. In contrast, the CS, Cas / CS, and Cur / CS tags prepared in Examples 2-4 showed no significant changes during the spoilage of the shrimp and fish, and therefore could not detect the freshness of aquatic products.

[0084] To address the shortcomings of existing curcumin indicators, such as poor stability, a single response mode (only colorimetric response), and insufficient adaptability to matrix environments, this invention first employs a pH-driven method to induce casein self-assembly, encapsulating curcumin within the hydrophobic chamber of casein to prepare Cur@Cas composite particles. This improves the water solubility, thermal stability, and photostability of curcumin. These composite particles exhibit a characteristic color change (bright yellow → brownish-red) and fluorescence quenching effect within the pH range of 7-11. Furthermore, Cur@Cas is blended with a carboxymethyl cellulose / sodium alginate composite matrix, and a dual-signal output tag is constructed through casting. This tag possesses strong mechanical properties and excellent degradation performance, enabling intelligent detection of the freshness of shrimp and fish products using both color and fluorescence signals. This invention features a simple and environmentally friendly process, and the resulting tag combines high sensitivity with resistance to environmental interference, providing an innovative solution for aquatic product quality monitoring.

[0085] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a colorimetric-fluorescence dual-modal signal indicator label for detecting the freshness of aquatic products, characterized in that: Includes the following steps: S1. Dissolve casein in water, heat, stir, and then refrigerate and let stand to obtain a casein solution; S2. Adjust the pH of the casein solution to 12, add curcumin, and stir until homogeneous to obtain a curcumin / casein mixed solution. S3. Adjust the pH of the curcumin / casein mixed solution to 7-9 to obtain a casein-encapsulated curcumin solution; S4. Dissolve carboxymethyl cellulose and sodium alginate in water to obtain a carboxymethyl cellulose-sodium alginate solution; Casein-encapsulated curcumin solution and glycerol were added to carboxymethyl cellulose-sodium alginate solution, the pH was adjusted to acidic, and the mixture was dried to form a film to obtain the aquatic product freshness detection indicator label with colorimetric-fluorescence dual-modal signal.

2. The method for preparing the aquatic product freshness detection indicator label with colorimetric-fluorescence dual-modal signal according to claim 1, characterized in that: In S1, the ratio of casein to water is 0.1–3 g / 100 mL; in S4, the mass ratio of carboxymethyl cellulose to sodium alginate is 1 / 3–3 / 1; and in the carboxymethyl cellulose-sodium alginate solution, the total concentration of carboxymethyl cellulose and sodium alginate is 0.5–2 g / 100 mL.

3. The method for preparing the aquatic product freshness detection indicator label with colorimetric-fluorescence dual-modal signal according to claim 1, characterized in that: In S1, the heating temperature is 30–50°C; the refrigeration temperature is 0–5°C, and the time is 8–24 hours.

4. The method for preparing the aquatic product freshness detection indicator label with colorimetric-fluorescence dual-modal signal according to claim 1, characterized in that: In S2, the mass ratio of casein to curcumin in the casein solution is 1 g / 10 to 90 mg.

5. The method for preparing the aquatic product freshness detection indicator label with colorimetric-fluorescence dual-modal signal according to claim 1, characterized in that: In S3, the pH is adjusted to 7.

6. The method for preparing the aquatic product freshness detection indicator label with colorimetric-fluorescence dual-modal signal according to claim 1, characterized in that: In step S3, the curcumin / casein mixed solution is adjusted to pH 7-9 and then centrifuged to obtain a casein-encapsulated curcumin solution; the centrifugation speed is 5000-10000 rpm, the time is 5-20 min, and the temperature is 0-10℃.

7. The method for preparing the aquatic product freshness detection indicator label with colorimetric-fluorescence dual-modal signal according to claim 1, characterized in that: In S4, the mass ratio of the casein-encapsulated curcumin solution to the carboxymethyl cellulose-sodium alginate solution is 1 / 10 to 1 / 2, and the amount of glycerol added is 20% to 40% of the mass of the solute in the carboxymethyl cellulose-sodium alginate solution.

8. The method for preparing a freshness indicator label for aquatic products using a colorimetric-fluorescence dual-modal signal according to any one of claims 1-7, characterized in that: In S4, adjust the pH to 4-6.

9. A colorimetric-fluorescence dual-modal signal indicator label for detecting the freshness of aquatic products, characterized in that: The label is prepared using the method described in any one of claims 1-8 for preparing a freshness indicator label for aquatic products using a colorimetric-fluorescence dual-modal signal.

10. The application of a colorimetric-fluorescence dual-modal signal aquatic product freshness detection indicator label as described in claim 9 in the detection of aquatic product freshness.

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