High-stability intelligent indicating label for freshness of aquatic products as well as preparation method and application of high-stability intelligent indicating label

Abstract

The invention belongs to the technical field of food safety detection, and provides a high-stability aquatic product freshness intelligent indication label as well as a preparation method and application thereof, and the stability of the anthocyanin-based aquatic product freshness intelligent indication label is remarkably improved through the color assisting effect of UiO-66-NH2 and gentisic acid on anthocyanin. The preparation method comprises the following steps: completely dissolving sodium alginate, cooling to room temperature, sequentially adding glycerol, an anthocyanin extracting solution, a gentisic acid solution and a UiO-66-NH2 resuspension under continuous stirring, uniformly stirring, and drying in a blast drying oven at 35 DEG C to form a film, thereby obtaining the high-stability intelligent indication label for freshness of aquatic products. The preparation method is simple and easy to operate, the prepared indication label can greatly improve the storage stability of the anthocyanin label under the dark condition, and meanwhile, the label can sensitively and accurately respond to changes of freshness of aquatic products.

Description

Technical Field

[0001] The present invention relates to the technical field of food safety detection, and in particular to a high-stability intelligent freshness indicator label for aquatic products and a preparation method and application thereof. Background Art

[0002] Aquatic products have become an indispensable part of people's dining tables. However, since aquatic products are rich in protein and high in water content, they are extremely susceptible to lipid oxidation, protein and nucleic acid hydrolysis caused by endogenous enzymes and exogenous microbial contamination during transportation, storage and sales, resulting in spoilage and the production of spoiled odors. In particular, during the meat spoilage process, toxic and harmful metabolites such as trimethylamine will continue to accumulate, causing the meat to lose its edible value and even pose a potential threat to consumers' health. With the improvement of the economy and living standards, the fast-paced lifestyle, and the shift in people's demand for food from "quantity" to "quality", the public's demand for nutritious, safe and fresh food has increased, which undoubtedly poses a higher challenge to the prepared food industry in ensuring food safety. Traditional methods for evaluating the freshness of meat, such as volatile basic nitrogen content (based on Chinese national standard GB 5009.228-2016) and total colony count measurement (based on Chinese national standard GB 4789.2-2022), as well as sensory evaluation, can provide accurate food freshness information. However, due to their cumbersome operation, long detection cycle, destructive detection, and the need for professional operators, it is difficult to achieve rapid and non-destructive freshness detection on site. Therefore, a low-cost, real-time, and visual monitoring method is urgently needed.

[0003] Smart food freshness indicator labels can intuitively reflect food spoilage changes caused by physiological or microbial growth through color changes without opening the food packaging, providing non-destructive and real-time monitoring of the freshness of animal-derived perishable foods such as livestock meat, poultry meat, and aquatic products. In recent years, research on freshness indicator labels responsive to biogenic amines has attracted much attention. Among them, the selection of colorants is crucial to the sensitivity and scope of application of freshness indicator labels. Natural pigments, especially anthocyanins, are favored compared to chemical synthetic pigments because of their environmental friendliness, high cost-effectiveness, and avoidance of toxicity issues. However, the stability of anthocyanins is easily affected by external conditions such as pH, oxygen, and light, and cannot be stored for a long time. Therefore, improving the stability of anthocyanin-based food freshness smart indicator labels is the key to promoting their commercialization.

[0004] To this end, the present invention provides a preparation method and application of a high-stability intelligent indicator label for freshness of aquatic products. Summary of the invention

[0005] In order to make up for the deficiencies of the prior art, the present invention provides a highly stable intelligent indicator label for freshness of aquatic products, and a preparation method and application thereof. An intelligent indicator label for freshness with good storage stability and capable of visually monitoring the freshness of aquatic products, and a preparation method and application thereof. The present invention incorporates UiO-66-NH2 and gentisic acid into anthocyanin indicator labels, utilizes the excellent ultraviolet absorption and fluorescence properties of UiO-66-NH2, and the interaction such as hydrogen bonding with anthocyanin, and the auxiliary color effect between gentisic acid and anthocyanin, thereby synergistically improving the storage stability of anthocyanin indicator labels and achieving long-term preservation in actual storage environments.

[0006] The present invention is realized by the following technical scheme: a method for preparing a high-stability intelligent indicator label for freshness of aquatic products, which specifically comprises the following steps: Step S1: using 55% to 65% (v / v) ethanol solution as an extractant, extracting anthocyanins from anthocyanin-rich plant tissue at a solid-to-liquid ratio of 1:10, and extracting for 4 h to 6 h to obtain anthocyanin extract; concentrating the anthocyanin extract to 150 mL to 200 mL using a rotary evaporator to obtain anthocyanin concentrate; Step S2: 197 mg of 2-aminoterephthalic acid, 253 mg of zirconium tetrachloride, and 27.6 mL of glacial acetic acid were dissolved in 230 mL of N,N-dimethylformamide (DMF), ultrasonicated in an ultrasonic environment for 1 hour, and then transferred to a 300 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene, and reacted in a vacuum drying oven at 120°C for 24 hours (negative pressure 0.085 mPa~0.090 mPa); after the reaction was completed, the reactor was taken out, cooled to room temperature in a room temperature environment, and then opened, centrifuged at 8000 rpm to remove the supernatant, washed with DMF 3 times, activated with methanol for 24 hours, and activated the precipitate in a vacuum drying oven at 60°C after centrifugation to obtain UiO-66-NH2; Step S3: dispersing sodium alginate powder in water, stirring at 85°C-90°C until completely dissolved, and then cooling to room temperature to obtain a sodium alginate solution; adding glycerol, anthocyanin concentrate, gentisic acid and UiO-66-NH2 to the sodium alginate solution in sequence, stirring evenly and drying in a 35°C forced air drying oven to form a film, thereby obtaining an intelligent indicator label for freshness of aquatic products; before use, immersing the label in a calcium chloride solution for cross-linking, then taking it out, rinsing the label surface with clean water and then using it.

[0007] As a preferred embodiment, the concentration of the sodium alginate solution is 1 wt%-3 wt%.

[0008] As a preferred embodiment, the volume ratio of the anthocyanin concentrate to the sodium alginate solution is 1:10.

[0009] As a preferred embodiment, the mass ratio of gentisic acid to sodium alginate solution is 4 mg~24 mg:20 mL.

[0010] As a preferred solution, the dosage ratio of UiO-66-NH2 to sodium alginate solution is 4 mg~24 mg:20 mL.

[0011] As a preferred solution, the concentration of the calcium chloride solution is 1wt%~5wt%, the volume is 10 mL, and the cross-linking time is 1min.

[0012] A highly stable intelligent indicator label for freshness of aquatic products, characterized in that it is prepared by the above method.

[0013] A high-stability aquatic product freshness intelligent indicator label is used to reflect the freshness of aquatic products. It is prepared by the above preparation method, and its specific application is as follows: 1) Pasting the aquatic product freshness intelligent indicator label prepared by the method for preparing a high-stability aquatic product freshness intelligent indicator label on the packaging of the aquatic product to be tested, and storing it at 0-37°C; 2) Record the color change of the label and combine it with the TVB-N change of the sample to achieve qualitative judgment of the freshness of the aquatic product to be tested: Based on the TVB-N content, the freshness level of aquatic products can be judged visually: When TVB-N is less than 20 mgN / 100 g, it is in a fresh state; when TVB-N is between 20 mgN / 100 g and 30 mgN / 100 g, it is in a semi-fresh state; when TVB-N is greater than 30 mgN / 100 g, it is in a corrupt state; When the label is purple-red, the aquatic product to be tested is fresh; When the edge of the label turns green, the aquatic product to be tested is in a semi-fresh state; When all labels turn green and the green color gradually deepens, the TVB-N index of the aquatic product to be tested is close to the corruption threshold and it is not suitable for consumption.

[0014] Due to the adoption of the above technical scheme, the present invention has the following beneficial effects compared with the prior art: the present invention utilizes the pH-responsive color change of plant anthocyanins to present blue or green in an alkaline environment, thereby realizing non-destructive, real-time, and visual judgment of the freshness of aquatic products; in addition, plant anthocyanins are safe and edible, greatly reducing the threat to human health caused by pigment migration.

[0015] The present invention introduces UiO-66-NH2 and gentisic acid into the intelligent indicator label, which greatly enhances the storage stability of the anthocyanin indicator label.

[0016] The preparation method of the present invention does not require the use of complex instruments and equipment, has low material cost, is easy to produce in batches, and is simple to operate.

[0017] Additional aspects and advantages of the present invention will become apparent from the following description or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1 SEM images of UiO-66-NH2 in Example 1, the label of Comparative Example 1, and the label of Example 1; Figure 1 In the figure, Figure A is a SEM image of UiO-66-NH2, Figure B is a SEM image of the surface of the label of Example 1 at a scale of 10 μm, Figure C is a SEM image of the cross-section of the label of Example 1 at a scale of 10 μm, and Figure D is a SEM image of the cross-section of the label of Example 1 at a scale of 1 μm.

[0019] Figure 2 The stability changes of the labels of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6 and Comparative Example 3 under storage conditions of 37° C. in the dark. Figure 2 Figure A shows the change in color difference values ​​of different labels when placed in a light-proof environment at 37°C for 48 hours, and Figure B shows the significant difference analysis of color difference after different labels were placed in a light-proof environment at 37°C for 36 hours and 48 hours.

[0020] Figure 3 This is a comparison chart of the ammonia response performance of the labels of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, and Comparative Example 3.

[0021] Figure 4 The stability changes of the labels of Example 1, Example 7, Example 8, Example 9, Example 10, Example 11 and Comparative Example 2 under storage conditions of 37° C. in the dark. Figure 2 Figure A shows the change in color difference values ​​of different labels when placed in a light-proof environment at 37°C for 36 hours, and Figure B shows the significant difference analysis of color difference after different labels were placed in a light-proof environment at 37°C for 24 hours and 36 hours.

[0022] Figure 5 This is a comparison chart of the ammonia response performance of the labels of Example 1, Example 7, Example 8, Example 9, Example 10, Example 11, and Comparative Example 2.

[0023] Figure 6 The stability changes of the labels of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 under room temperature and light-proof environment.

[0024] Figure 7 The stability changes of the labels of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 in a light-proof environment at 4°C.

[0025] Figure 8 The color change of the label of Example 1 between pH 2 and pH 12.

[0026] Fig. 9 The TVB-N changes of shrimps stored at 25°C for different time periods, and the corresponding color difference changes of the label of Example 1.

[0027] Fig.10 The diagrams are the states of shrimps at different times in a 25°C storage environment, and the corresponding color change diagram of the label of Example 1.

[0028] Fig.11 The TVB-N changes of shrimps in a 4°C storage environment at different times, and the corresponding color difference value changes of the label of Example 1.

[0029] Fig.12 1 is a diagram showing the states of shrimps at different times in a 4°C storage environment, and a corresponding diagram showing the color changes of the label of Example 1.

[0030] Fig.13 This is a correlation analysis between the changes in TVB-N and the corresponding label color parameters when shrimp are stored at 25℃ and 4℃. Fig.13 In the figure, Figure A is the correlation analysis between the changes in TVB-N and the corresponding label color parameters of shrimp stored at 25°C, and Figure B is the correlation analysis between the changes in TVB-N and the corresponding label color parameters of shrimp stored at 4°C. DETAILED DESCRIPTION

[0031] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0032] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0033] The present invention proposes a method for preparing a high-stability intelligent indicator label for freshness of aquatic products, which specifically comprises the following steps: Step S1: Extraction of anthocyanins: Anthocyanins are extracted from anthocyanin-rich plant tissues using an alcohol method with an alcohol solution as the extraction solvent to obtain anthocyanin solution, and then the anthocyanin extract is concentrated to a volume of 150 mL to 200 mL using a rotary evaporator to obtain anthocyanin concentrated solution.

[0034] It should be noted that, in some preferred embodiments of the present invention, the plants rich in anthocyanins are one or more of purple cabbage, purple sweet potato, black carrot, carnation, blueberry, rose, and black wolfberry.

[0035] In some preferred embodiments of the present invention, anthocyanins are extracted from anthocyanin-rich plant tissues using a 55% to 65% (v / v) ethanol solution as an extractant at a solid-to-liquid ratio of 1:10, and the anthocyanin extract is obtained for 4 h to 6 h; the anthocyanin extract is concentrated to 150 mL to 200 mL using a rotary evaporator to obtain an anthocyanin concentrate; Specifically prepared by the following steps: take plant tissue rich in anthocyanins, wash it, cut it into small pieces, dry it in a 50°C blast drying oven, and then use a crusher to crush the dried plant tissue into powder. The obtained plant tissue rich in anthocyanins is dispersed in a 55%~65% (v / v) ethanol aqueous solution, continuously extracted at 400 rpm in the dark for 4h~6h, and then filtered repeatedly with Whatman no.4 filter paper to remove impurities to obtain the anthocyanin extract. Wherein, in some preferred embodiments of the present invention, the plant tissue rich in anthocyanins is cut into thin strips. In some preferred embodiments of the present invention, the temperature of the stirring treatment is room temperature, the stirring time is 4h~6h, and the stirring speed is 400 rpm. In some preferred embodiments of the present invention, the drying temperature is 50°C. In some preferred embodiments of the present invention, the specific setting parameters of the rotary evaporator are: 40°C, 60rpm~70 rpm.

[0036] Step S2: Preparation of UiO-66-NH2: UiO-66-NH2 was prepared by a solution heat method.

[0037] It should be noted that in order to improve the storage stability of the anthocyanin indicator label, the present invention utilizes the excellent ultraviolet absorption and fluorescence properties of UiO-66-NH2. At the same time, its rich functional groups can form hydrogen bonds and other interactions with the hydroxyl groups of anthocyanins, thereby improving the light stability and thermal stability of the anthocyanin indicator label.

[0038] The UiO-66-NH2 used in the present invention is prepared by a solvothermal method, and the specific steps are: 197 mg of 2-aminoterephthalic acid, 253 mg of zirconium tetrachloride, and 27.6 mL of glacial acetic acid are dissolved in 230 mL of N,N-dimethylformamide (DMF), ultrasonicated in an ultrasonic environment for 1 hour, then transferred to a 300 mL stainless steel high-pressure reactor containing a polytetrafluoroethylene liner, and reacted in a 120°C vacuum drying oven for 24 hours (negative pressure 0.085 mPa~0.090 mPa); after the reaction is completed, the reactor is taken out, cooled to room temperature in a room temperature environment, and then opened, centrifuged at 8000 rpm to remove the supernatant, washed with DMF 3 times, activated with methanol for 24 hours, and activated the precipitate in a 60°C vacuum drying oven after centrifugation to obtain UiO-66-NH2; The UiO-66-NH2 used in the present invention is prepared by a solvothermal method, and the obtained UiO-66-NH2 has a particle size of 425±75 nm and a specific surface area of ​​approximately 1149.77 m 2 / g.

[0039] Step S3: mixing with sodium alginate solution: dispersing sodium alginate powder in water, stirring at 85°C-90°C until completely dissolved, and then cooling to room temperature to obtain a sodium alginate solution; adding glycerol, anthocyanin concentrate, gentisic acid and UiO-66-NH2 to the sodium alginate solution in sequence, stirring evenly and drying in a 35°C forced air drying oven to form a film, thereby obtaining the aquatic product freshness intelligent indicator label prepared by the method for preparing a high-stability aquatic product freshness intelligent indicator label; before use, immersing the label in a calcium chloride solution for cross-linking, then taking it out, rinsing the label surface with clean water and using it.

[0040] The molecular weight of the sodium alginate selected in the present invention is 20,000-50,000, and the viscosity is 15-60 mpa·s. In some preferred embodiments of the present invention, the concentration of the sodium alginate solution is 1 wt%-3 wt% to ensure that the sodium alginate solution has good fluidity and dispersibility.

[0041] In some preferred embodiments of the present invention, the amount of glycerol added is 150 μL to 200 μL; In some preferred embodiments of the present invention, the dosage ratio of the anthocyanin concentrate to the sodium alginate solution is: 1 mL~3 mL:20 mL.

[0042] In some preferred embodiments of the present invention, the dosage ratio of the gentisic acid solution to the sodium alginate solution is: 4 mg~24 mg:20 mL; it should be noted that the gentisic acid solution needs to be dissolved in 2 mL of 50% (v / v) ethanol aqueous solution.

[0043] In some preferred embodiments of the present invention, the dosage ratio of UiO-66-NH2 to sodium alginate solution is 4 mg~24 mg:20 mL; it should be noted that UiO-66-NH2 needs to be evenly dispersed by ultrasound in 1 mL of water before addition.

[0044] In some preferred embodiments of the present invention, the concentration of the calcium chloride solution is 1wt%~5wt%, the volume is 10mL, and the cross-linking time is 1min.

[0045] It should be noted that the formation process of the smart indicator label requires continuous drying in a 35° C. forced air drying oven until a film is formed.

[0046] The second object of the present invention is to provide an intelligent indicator label for freshness of aquatic products having good storage stability obtained by the above preparation method.

[0047] The third object of the present invention is to provide a method for preparing a high-stability aquatic product freshness intelligent indicator label, and use the prepared aquatic product freshness intelligent indicator label in reflecting the freshness of food.

[0048] A high-stability aquatic product freshness intelligent indicator label is used to reflect the freshness of aquatic products. The specific applications are as follows: 1) The prepared aquatic product freshness intelligent indicator label is pasted on the packaging of the aquatic product to be tested and stored at 0-37°C; 2) Record the color change of the smart indicator label to achieve visual identification of the freshness of the aquatic product to be inspected through the color change of the label; it should be noted that the camera parameters should be set to: ISO speed = 50, aperture value = f / 1.6, exposure time = 1 / 172 seconds when taking pictures.

[0049] 3) According to the "National Food Safety Standard of China GB 5009.228-2016 Determination of Volatile Basic Nitrogen in Food", the TVB-N values ​​of aquatic products at different storage times are measured, and the color change of the label is correlated with the TVB-N of the aquatic product, so as to qualitatively judge the freshness of the aquatic product based on the color state of the label.

[0050] According to the color response change of the label, the freshness of the aquatic product to be tested can be visually judged according to the following standards: When TVB-N is less than 20 mgN / 100 g, it is in a fresh state; when TVB-N is between 20 mgN / 100 g and 30 mgN / 100 g, it is in a semi-fresh state; when TVB-N is greater than 30 mgN / 100 g, it is in a corrupt state; When the label is purple-red, the aquatic product to be tested is fresh; When the edge of the label turns green, the aquatic product to be tested is in a semi-fresh state; When all labels turn green and the green color gradually deepens, the TVB-N index of the aquatic product to be tested is close to the corruption threshold and it is not suitable for consumption.

[0051] Combine the following Figures 1 to 13 The high-stability aquatic product freshness intelligent indicator label and its preparation method and application according to the embodiment of the present invention are specifically described.

[0052] In the following embodiments of the present invention, the UiO-66-NH2 used is prepared by the following steps: 197 mg 2-aminoterephthalic acid, 253 mg zirconium tetrachloride, and 27.6 mL glacial acetic acid are dissolved in 230 mL N, N-dimethylformamide (DMF), ultrasonicated in an ultrasonic environment for 1 hour, and then transferred to a 300 mL stainless steel high-pressure reactor containing a polytetrafluoroethylene liner, and reacted in a vacuum drying oven at 120°C for 24 hours (negative pressure 0.085 mPa~0.090 mPa); after the reaction is completed, the reactor is taken out and cooled to room temperature under room temperature, and then the reactor is opened, and the supernatant is removed by centrifugation at 8000 rpm, and the precipitate is washed with DMF (the precipitate is resuspended in 50 mL DMF and stirred for 1 hour) 3 times, and then activated with methanol for 24 hours, and the precipitate is activated in a vacuum drying oven at 60°C after centrifugation to obtain UiO-66-NH2.

[0053] Example 1 This embodiment provides a method for preparing a high-stability aquatic product freshness intelligent indicator label, which is achieved by the following steps: Step 1, extraction of purple cabbage anthocyanins: Wash the purple cabbage leaves and crush them into flakes, and completely dry them in a 50°C forced air drying oven. Use a crusher to crush the dried purple cabbage leaves. Take 50 g of purple cabbage leaf powder, disperse it in 500 mL of 60% ethanol aqueous solution, and stir and extract it at 400 rpm in the dark for 4 h. Then use Whatman no.4 filter paper to repeatedly filter the extract to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator, and the rotary evaporation parameters were 40°C and 60 rpm. Finally, the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain a purple cabbage anthocyanin concentrate.

[0054] Step 2, mixing with sodium alginate: 2 g of sodium alginate is completely dissolved in 98 g of water at 85°C, and then cooled to room temperature to obtain a 2 wt% sodium alginate solution. Take 20 mL of sodium alginate solution, add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 16 mg of gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution by volume), and 20 mg of UiO-66-NH2 (dispersed in 1 mL of water) in sequence under continuous stirring at 400 rpm, and after stirring evenly, pour into a disposable plastic culture dish with a diameter of 90 mm, and then dry in a 35°C blast drying oven to form a film. After film formation, carefully peel off the film from the culture dish with tweezers, and then cut it into a 15 mm*15 mm square, and obtain the aquatic product freshness intelligent indicator label prepared by the method for preparing a high-stability aquatic product freshness intelligent indicator label. Before use, soak the label in 10 mL 5 wt% calcium chloride solution for cross-linking for 1 min, then take it out and rinse the label surface with clean water before use.

[0055] Example 2 This embodiment provides a method for preparing a high-stability aquatic product freshness intelligent indicator label, which is achieved by the following steps: Step 1, extraction of purple cabbage anthocyanins: Wash the purple cabbage leaves and crush them into flakes, and completely dry them in a 50°C forced air drying oven. Use a crusher to crush the dried purple cabbage leaves. Take 50 g of purple cabbage leaf powder, disperse it in 500 mL of 60% ethanol aqueous solution, and stir and extract it at 400 rpm in the dark for 4 h. Then use Whatman no.4 filter paper to repeatedly filter the extract to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator, and the rotary evaporation parameters were 40°C and 60 rpm. Finally, the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain a purple cabbage anthocyanin concentrate.

[0056] Step 2, mixing with sodium alginate: 2 g of sodium alginate is completely dissolved in 98 g of water at 85°C, and then cooled to room temperature to obtain a 2 wt% sodium alginate solution. Take 20 mL of sodium alginate solution, add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 4 mg of gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution by volume), and 20 mg of UiO-66-NH2 (dispersed in 1 mL of water) in sequence under continuous stirring at 400 rpm, and after stirring evenly, pour into a disposable plastic culture dish with a diameter of 90 mm, and then dry in a 35°C blast drying oven to form a film. After film formation, carefully peel off the film from the culture dish with tweezers, and then cut it into a 15 mm*15 mm square, and obtain the aquatic product freshness intelligent indicator label prepared by the method for preparing a high-stability aquatic product freshness intelligent indicator label. Before use, soak the label in 10 mL 5 wt% calcium chloride solution for cross-linking for 1 min, then take it out and rinse the label surface with clean water before use.

[0057] That is, the difference between this embodiment and embodiment 1 is that the dosage of gentisic acid in this embodiment is 4 mg.

[0058] Example 3 This embodiment provides a method for preparing a high-stability aquatic product freshness intelligent indicator label, which is achieved by the following steps: Step 1, extraction of purple cabbage anthocyanins: Wash the purple cabbage leaves and crush them into flakes, and completely dry them in a 50°C forced air drying oven. Use a crusher to crush the dried purple cabbage leaves. Take 50 g of purple cabbage leaf powder, disperse it in 500 mL of 60% ethanol aqueous solution, and stir and extract it at 400 rpm in the dark for 4 h. Then use Whatman no.4 filter paper to repeatedly filter the extract to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator, and the rotary evaporation parameters were 40°C and 60 rpm. Finally, the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain a purple cabbage anthocyanin concentrate.

[0059] Step 2, mixing with sodium alginate: 2 g of sodium alginate is completely dissolved in 98 g of water at 85°C, and then cooled to room temperature to obtain a 2 wt% sodium alginate solution. Take 20 mL of sodium alginate solution, add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 8 mg of gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution by volume), and 20 mg of UiO-66-NH2 (dispersed in 1 mL of water) in sequence under continuous stirring at 400 rpm, and after stirring evenly, pour into a disposable plastic culture dish with a diameter of 90 mm, and then dry in a 35°C blast drying oven to form a film. After film formation, carefully peel off the film from the culture dish with tweezers, and then cut it into a 15 mm*15 mm square, and obtain the aquatic product freshness intelligent indicator label prepared by the method for preparing a high-stability aquatic product freshness intelligent indicator label. Before use, soak the label in 10 mL 5 wt% calcium chloride solution for cross-linking for 1 min, then take it out and rinse the label surface with clean water before use.

[0060] That is, the difference between this embodiment and embodiment 1 is that the dosage of gentisic acid in this embodiment is 8 mg.

[0061] Example 4 This embodiment provides a method for preparing a high-stability aquatic product freshness intelligent indicator label, which is achieved by the following steps: Step 1, extraction of purple cabbage anthocyanins: Wash the purple cabbage leaves and crush them into flakes, and completely dry them in a 50°C forced air drying oven. Use a crusher to crush the dried purple cabbage leaves. Take 50 g of purple cabbage leaf powder, disperse it in 500 mL of 60% ethanol aqueous solution, and stir and extract it at 400 rpm in the dark for 4 h. Then use Whatman no.4 filter paper to repeatedly filter the extract to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator, and the rotary evaporation parameters were 40°C and 60 rpm. Finally, the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain a purple cabbage anthocyanin concentrate.

[0062] Step 2, mixing with sodium alginate: 2 g of sodium alginate is completely dissolved in 98 g of water at 85°C, and then cooled to room temperature to obtain a 2 wt% sodium alginate solution. Take 20 mL of sodium alginate solution, add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 12 mg of gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution by volume), and 20 mg of UiO-66-NH2 (dispersed in 1 mL of water) in sequence under continuous stirring at 400 rpm, and after stirring evenly, pour into a disposable plastic culture dish with a diameter of 90 mm, and then dry in a 35°C blast drying oven to form a film. After film formation, carefully peel off the film from the culture dish with tweezers, and then cut it into a 15 mm*15 mm square, and obtain the aquatic product freshness intelligent indicator label prepared by the method for preparing a high-stability aquatic product freshness intelligent indicator label. Before use, soak the label in 10 mL 5 wt% calcium chloride solution for cross-linking for 1 min, then take it out and rinse the label surface with clean water before use.

[0063] That is, the difference between this embodiment and embodiment 1 is that the dosage of gentisic acid in this embodiment is 12 mg.

[0064] Example 5 This embodiment provides a method for preparing a high-stability aquatic product freshness intelligent indicator label, which is achieved by the following steps: Step 1, extraction of purple cabbage anthocyanins: Wash the purple cabbage leaves and crush them into flakes, and completely dry them in a 50°C forced air drying oven. Use a crusher to crush the dried purple cabbage leaves. Take 50 g of purple cabbage leaf powder, disperse it in 500 mL of 60% ethanol aqueous solution, and stir and extract it at 400 rpm in the dark for 4 h. Then use Whatman no.4 filter paper to repeatedly filter the extract to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator, and the rotary evaporation parameters were 40°C and 60 rpm. Finally, the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain a purple cabbage anthocyanin concentrate.

[0065] Step 2, mixing with sodium alginate: 2 g of sodium alginate is completely dissolved in 98 g of water at 85°C, and then cooled to room temperature to obtain a 2 wt% sodium alginate solution. Take 20 mL of sodium alginate solution, add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 20 mg of gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution by volume), and 20 mg of UiO-66-NH2 (dispersed in 1 mL of water) in sequence under continuous stirring at 400 rpm, and after stirring evenly, pour into a disposable plastic culture dish with a diameter of 90 mm, and then dry in a 35°C blast drying oven to form a film. After film formation, carefully peel off the film from the culture dish with tweezers, and then cut it into a 15 mm*15 mm square, and obtain the aquatic product freshness intelligent indicator label prepared by the method for preparing a high-stability aquatic product freshness intelligent indicator label. Before use, soak the label in 10 mL 5 wt% calcium chloride solution for cross-linking for 1 min, then take it out and rinse the label surface with clean water before use.

[0066] That is, the difference between this embodiment and embodiment 1 is that the dosage of gentisic acid in this embodiment is 20 mg.

[0067] Example 6 This embodiment provides a method for preparing a high-stability aquatic product freshness intelligent indicator label, which is achieved by the following steps: Step 1, extraction of purple cabbage anthocyanins: Wash the purple cabbage leaves and crush them into flakes, and completely dry them in a 50°C forced air drying oven. Use a crusher to crush the dried purple cabbage leaves. Take 50 g of purple cabbage leaf powder, disperse it in 500 mL of 60% ethanol aqueous solution, and stir and extract it at 400 rpm in the dark for 4 h. Then use Whatman no.4 filter paper to repeatedly filter the extract to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator, and the rotary evaporation parameters were 40°C and 60 rpm. Finally, the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain a purple cabbage anthocyanin concentrate.

[0068] Step 2, mixing with sodium alginate: 2 g of sodium alginate is completely dissolved in 98 g of water at 85°C, and then cooled to room temperature to obtain a 2wt% sodium alginate solution. Take 20 mL of sodium alginate solution, add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 24 mg of gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution by volume), and 20 mg of UiO-66-NH2 (dispersed in 1 mL of water) in sequence under continuous stirring at 400 rpm, and after stirring evenly, pour into a disposable plastic culture dish with a diameter of 90 mm, and then dry in a 35°C blast drying oven to form a film. After film formation, carefully peel off the film from the culture dish with tweezers, and then cut it into a 15 mm*15 mm square, and obtain the aquatic product freshness intelligent indicator label prepared by the method for preparing a high-stability aquatic product freshness intelligent indicator label. Before use, soak the label in 10 mL 5 wt% calcium chloride solution for cross-linking for 1 min, then take it out and rinse the label surface with clean water before use.

[0069] That is, the difference between this embodiment and embodiment 1 is that the dosage of gentisic acid in this embodiment is 24 mg.

[0070] Example 7 This embodiment provides a method for preparing a high-stability aquatic product freshness intelligent indicator label, which is achieved by the following steps: Step 1, extraction of purple cabbage anthocyanins: Wash the purple cabbage leaves and crush them into flakes, and completely dry them in a 50°C forced air drying oven. Use a crusher to crush the dried purple cabbage leaves. Take 50 g of purple cabbage leaf powder, disperse it in 500 mL of 60% ethanol aqueous solution, and stir and extract it at 400 rpm in the dark for 4 h. Then use Whatman no.4 filter paper to repeatedly filter the extract to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator, and the rotary evaporation parameters were 40°C and 60 rpm. Finally, the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain a purple cabbage anthocyanin concentrate.

[0071] Step 2, mixing with sodium alginate: 2 g of sodium alginate is completely dissolved in 98 g of water at 85°C, and then cooled to room temperature to obtain a 2 wt% sodium alginate solution. Take 20 mL of sodium alginate solution, add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 16 mg of gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution by volume), and 4 mg of UiO-66-NH2 (dispersed in 1 mL of water) in sequence under continuous stirring at 400 rpm, and after stirring evenly, pour into a disposable plastic culture dish with a diameter of 90 mm, and then dry in a 35°C blast drying oven to form a film. After film formation, carefully peel off the film from the culture dish with tweezers, and then cut it into a 15 mm*15 mm square, and obtain the aquatic product freshness intelligent indicator label prepared by the method for preparing a high-stability aquatic product freshness intelligent indicator label. Before use, soak the label in 10 mL of 5 wt% calcium chloride solution for cross-linking for 1 min, then take it out and rinse the label surface with clean water before use.

[0072] That is, the difference between this embodiment and embodiment 1 is that the amount of UiO-66-NH2 used in this embodiment is 4 mg.

[0073] Example 8 This embodiment provides a method for preparing a high-stability aquatic product freshness intelligent indicator label, which is achieved by the following steps: Step 1, extraction of purple cabbage anthocyanins: Wash the purple cabbage leaves and crush them into flakes, and completely dry them in a 50°C forced air drying oven. Use a crusher to crush the dried purple cabbage leaves. Take 50 g of purple cabbage leaf powder, disperse it in 500 mL of 60% ethanol aqueous solution, and stir and extract it at 400 rpm in the dark for 4 h. Then use Whatman no.4 filter paper to repeatedly filter the extract to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator, and the rotary evaporation parameters were 40°C and 60 rpm. Finally, the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain a purple cabbage anthocyanin concentrate.

[0074] Step 2, mixing with sodium alginate: 2 g of sodium alginate is completely dissolved in 98 g of water at 85°C, and then cooled to room temperature to obtain a 2 wt% sodium alginate solution. Take 20 mL of sodium alginate solution, add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 16 mg of gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution by volume), and 8 mg of UiO-66-NH2 (dispersed in 1 mL of water) in sequence under continuous stirring at 400 rpm, and after stirring evenly, pour into a disposable plastic culture dish with a diameter of 90 mm, and then dry in a 35°C blast drying oven to form a film. After film formation, carefully peel off the film from the culture dish with tweezers, and then cut it into a 15 mm*15 mm square, and obtain the aquatic product freshness intelligent indicator label prepared by the method for preparing a high-stability aquatic product freshness intelligent indicator label. Before use, soak the label in 10 mL 5 wt% calcium chloride solution for cross-linking for 1 min, then take it out and rinse the label surface with clean water before use.

[0075] That is, the difference between this embodiment and embodiment 1 is that the amount of UiO-66-NH2 used in this embodiment is 8 mg.

[0076] Example 9 This embodiment provides a method for preparing a high-stability aquatic product freshness intelligent indicator label, which is achieved by the following steps: Step 1, extraction of purple cabbage anthocyanins: Wash the purple cabbage leaves and crush them into flakes, and completely dry them in a 50°C forced air drying oven. Use a crusher to crush the dried purple cabbage leaves. Take 50 g of purple cabbage leaf powder, disperse it in 500 mL of 60% ethanol aqueous solution, and stir and extract it at 400 rpm in the dark for 4 h. Then use Whatman no.4 filter paper to repeatedly filter the extract to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator, and the rotary evaporation parameters were 40°C and 60 rpm. Finally, the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain a purple cabbage anthocyanin concentrate.

[0077] Step 2, mixing with sodium alginate: 2 g of sodium alginate is completely dissolved in 98 g of water at 85°C, and then cooled to room temperature to obtain a 2 wt% sodium alginate solution. Take 20 mL of sodium alginate solution, add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 16 mg of gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution by volume), and 12 mg of UiO-66-NH2 (dispersed in 1 mL of water) in sequence under continuous stirring at 400 rpm, and after stirring evenly, pour into a disposable plastic culture dish with a diameter of 90 mm, and then dry in a 35°C blast drying oven to form a film. After film formation, carefully peel off the film from the culture dish with tweezers, and then cut it into a 15 mm*15 mm square, and obtain the aquatic product freshness intelligent indicator label prepared by the method for preparing a high-stability aquatic product freshness intelligent indicator label. Before use, soak the label in 10 mL 5 wt% calcium chloride solution for cross-linking for 1 min, then take it out and rinse the label surface with clean water before use.

[0078] That is, the difference between this embodiment and embodiment 1 is that the amount of UiO-66-NH2 used in this embodiment is 12 mg.

[0079] Example 10 This embodiment provides a method for preparing a high-stability aquatic product freshness intelligent indicator label, which is achieved by the following steps: Step 1, extraction of purple cabbage anthocyanins: Wash the purple cabbage leaves and crush them into flakes, and completely dry them in a 50°C forced air drying oven. Use a crusher to crush the dried purple cabbage leaves. Take 50 g of purple cabbage leaf powder, disperse it in 500 mL of 60% ethanol aqueous solution, and stir and extract it at 400 rpm in the dark for 4 h. Then use Whatman no.4 filter paper to repeatedly filter the extract to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator, and the rotary evaporation parameters were 40°C and 60 rpm. Finally, the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain a purple cabbage anthocyanin concentrate.

[0080] Step 2, mixing with sodium alginate: 2 g of sodium alginate is completely dissolved in 98 g of water at 85°C, and then cooled to room temperature to obtain a 2 wt% sodium alginate solution. Take 20 mL of sodium alginate solution, add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 16 mg of gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution by volume), and 16 mg of UiO-66-NH2 (dispersed in 1 mL of water) in sequence under continuous stirring at 400 rpm, and after stirring evenly, pour into a disposable plastic culture dish with a diameter of 90 mm, and then dry in a 35°C blast drying oven to form a film. After film formation, carefully peel off the film from the culture dish with tweezers, and then cut it into a 15 mm*15 mm square, and obtain the aquatic product freshness intelligent indicator label prepared by the method for preparing a high-stability aquatic product freshness intelligent indicator label. Before use, soak the label in 10 mL 5 wt% calcium chloride solution for cross-linking for 1 min, then take it out and rinse the label surface with clean water before use.

[0081] That is, the difference between this embodiment and embodiment 1 is that the amount of UiO-66-NH2 used in this embodiment is 16 mg.

[0082] Embodiment 11 This embodiment provides a method for preparing a high-stability aquatic product freshness intelligent indicator label, which is achieved by the following steps: Step 1, extraction of purple cabbage anthocyanins: Wash the purple cabbage leaves and crush them into flakes, and completely dry them in a 50°C forced air drying oven. Use a crusher to crush the dried purple cabbage leaves. Take 50 g of purple cabbage leaf powder, disperse it in 500 mL of 60% ethanol aqueous solution, and stir and extract it at 400 rpm in the dark for 4 h. Then use Whatman no.4 filter paper to repeatedly filter the extract to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator, and the rotary evaporation parameters were 40°C and 60 rpm. Finally, the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain a purple cabbage anthocyanin concentrate.

[0083] Step 2, mixing with sodium alginate: 2 g of sodium alginate is completely dissolved in 98 g of water at 85°C, and then cooled to room temperature to obtain a 2 wt% sodium alginate solution. Take 20 mL of sodium alginate solution, add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 16 mg of gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution by volume), and 24 mg of UiO-66-NH2 (dispersed in 1 mL of water) in sequence under continuous stirring at 400 rpm, and after stirring evenly, pour into a disposable plastic culture dish with a diameter of 90 mm, and then dry in a 35°C blast drying oven to form a film. After film formation, carefully peel off the film from the culture dish with tweezers, and then cut it into a 15 mm*15 mm square, and obtain the aquatic product freshness intelligent indicator label prepared by the method for preparing a high-stability aquatic product freshness intelligent indicator label. Before use, soak the label in 10 mL 5 wt% calcium chloride solution for cross-linking for 1 min, then take it out and rinse the label surface with clean water before use.

[0084] That is, the difference between this embodiment and embodiment 1 is that the amount of UiO-66-NH2 used in this embodiment is 24 mg.

[0085] Comparative Example 1 This comparative example provides an intelligent indicator label for freshness of aquatic products, and the only difference between this comparative example and Example 1 is that UiO-66-NH2 and gentisic acid are not added in this comparative example.

[0086] Comparative Example 2 This comparative example provides an intelligent indicator label for freshness of aquatic products, and the only difference between this comparative example and Example 1 is that UiO-66-NH2 is not added in this comparative example.

[0087] Comparative Example 3 This comparative example provides an intelligent label indicating the freshness of aquatic products, and the only difference between this comparative example and Example 1 is that gentisic acid is not added in this comparative example.

[0088] Experimental Section In the following experimental section, for the sake of ease of expression, "label" will be used instead of "high-stability aquatic product freshness intelligent indication label" or "aquatic product freshness intelligent indication label".

[0089] 1. Microscopic morphology test The present invention respectively carried out SEM test on UiO-66-NH2 and label prepared in Example 1, and the results are as follows: Figure 1 shown. Figure 1In the figure, Figure A is the SEM image of UiO-66-NH2, Figure B is the surface morphology of the label at a scale of 10 μm, Figure C is the cross-sectional morphology of the label at a scale of 10 μm, and Figure D is the cross-sectional morphology of the label at a scale of 1 μm.

[0090] Depend on Figure 1 It can be seen that the particle size of the prepared UiO-66-NH2 is 425 ± 75 nm. When the purple cabbage anthocyanidins, UiO-66-NH2 and gentisic acid are mixed with the sodium alginate solution, the label surface is relatively rough, fine cracks can be observed in the cross section, and a large amount of UiO-66-NH2 can be observed in the enlarged image, with regular and complete shapes.

[0091] 2. Optimization process of label composition 1) Effect of gentisic acid addition on label stability at 37°C In order to explore the effect of different amounts of gentisic acid added on the thermal stability of the label, the present invention encapsulates Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, and Comparative Example 3 in a double-sided adhesive containing a transparent PET release film to simulate real storage conditions. The 7 labels are placed in a light-proof environment at 37°C at the same time, and the color parameters (L, a, b) of the labels are recorded and the color difference ΔE value is calculated using a colorimeter every 2 hours. The calculation formula is as follows: .

[0092] Among them, L0, a0, b0 represent the initial brightness value, red-green color and blue-yellow color of the label respectively; L1, a1, b represent the brightness value, red-green color and blue-yellow color of the label after accelerated test respectively.

[0093] It should be noted that it is generally believed that the color change can be observed by the naked eye when the ΔE value exceeds 5. Therefore, all stability evaluation indicators of the present invention are judged by whether the ΔE value exceeds 5: When ΔE<5, the color change of the label cannot be distinguished by the naked eye; when ΔE≥5, the color change of the label can be observed by the naked eye.

[0094] The longer different tags maintain the ΔE<5 state, the better the stability of the tags.

[0095] The test results are as follows Figure 2 As shown. Figure 2 A and 2B show that as the storage time increases, the ΔE of the label continues to rise, and the thermal stability of the label continues to increase with the increase in the amount of gentisic acid added. After 36 hours of storage, the color difference values ​​of the labels prepared by the preparation method of the embodiment are all less than 5, while the comparative example exceeds 5. After 48 hours of storage, the color difference values ​​of all labels are more than 5, and the color difference change of the label prepared by the preparation method of the embodiment is significantly lower than that of the comparative example.

[0096] 2) Effect of gentisic acid addition on label ammonia response In order to explore the effect of different amounts of gentisic acid added on the ammonia response performance of the label, the present invention placed Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, and Comparative Example 3 above 20 mL, 14.28 mM ammonia solution, and took photos with a mobile phone every 1 min to record the color change of the label. It should be noted that the camera parameters should be set to: iso speed = 50, aperture value = f / 1.6, exposure time = 1 / 172 seconds when taking pictures.

[0097] from Figure 3 It can be seen that with the addition of gentisic acid, the color difference ΔE value of the label after contact with ammonia gas changes more than that of comparative example 3. This is because after the addition of gentisic acid, the microenvironment pH of the label changes toward the acidic direction, making the color change richer.

[0098] Based on the above analysis and the differences in stability of different labels at 37°C, the final amount of gentisic acid added was determined to be 16 mg.

[0099] 3) Effect of UiO-66-NH2 addition on the stability of the label at 37°C In order to explore the effect of different UiO-66-NH2 addition amounts on the thermal stability of the label, the present invention encapsulates Example 1, Example 7, Example 8, Example 9, Example 10, Example 11, and Comparative Example 2 in a double-sided adhesive containing a transparent PET release film to simulate real storage conditions. The 7 labels are placed in a light-proof environment at 37°C at the same time, and the color parameters (L, a, b) of the labels are recorded and the color difference ΔE value is calculated using a colorimeter every 2 hours.

[0100] The test results are as follows Figure 4 As shown. Figure 4 A and 4B show that as the storage time increases, the ΔE of the labels continues to rise, and the UV stability of the labels continues to improve with the increase in the amount of UiO-66-NH2 added. After 24 hours of storage, the ΔE values ​​of some labels exceeded 5, and the stability of Comparative Example 2 was the worst. After 36 hours of storage, the color difference values ​​of all labels exceeded 5, and the color difference changes of the labels prepared by the preparation method of the embodiment were lower than those of the comparative examples.

[0101] 4) Effect of UiO-66-NH2 addition on label ammonia response In order to explore the effect of different UiO-66-NH2 addition amounts on the ammonia response performance of the label, the present invention places Example 1, Example 7, Example 8, Example 9, Example 10, Example 11, and Comparative Example 2 above 20 mL, 14.28 mM ammonia solution, and takes pictures with a mobile phone every 1 min to record the color change of the label. It should be noted that the camera parameters should be set to: iso speed = 50, aperture value = f / 1.6, exposure time = 1 / 172 seconds when taking pictures.

[0102] from Figure 5 It can be seen that with the addition of UiO-66-NH2 content, the color difference ΔE value of the label after contact with ammonia shows a trend of first increasing and then decreasing relative to Comparative Example 2. Adding a small dose of UiO-66-NH2 can increase the opacity of the label, thereby increasing the color difference value; and as the amount of addition continues to increase, on the one hand, the diffusion distance of ammonia is extended, and on the other hand, the amino and carboxyl groups in the UiO-66-NH2 ligand interact with ammonia, extending the retention time of ammonia, so the color difference value gradually decreases.

[0103] Based on the above analysis, combined with the stability differences of different tags at 37°C and the ammonia response performance, the final addition amount of UiO-66-NH2 was determined to be 20 mg.

[0104] (II) Storage stability of label under actual storage conditions In order to study whether the simultaneous addition of UiO-66-NH2 and gentisic acid can improve the stability of the label, Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were encapsulated in a double-sided tape containing a transparent PET release film, and stored in a light-proof environment at room temperature and 4°C, respectively. The color parameters (L, a, b) of the label were recorded using a colorimeter at regular intervals and the color difference ΔE value was calculated.

[0105] Depend on Figure 6 It can be seen that, under room temperature and light-proof environment, the stability of different labels is ranked from low to high as follows: Comparative Example 1≈Comparative Example 2<Comparative Example 3<Example 1, with the number of days that the color difference ΔE value does not exceed 5 as the evaluation index: Comparative Example 1≈Comparative Example 2<Comparative Example 3<Example 1. Example 1 prepared by the present invention has the best stability under room temperature and light-proof environment, reaching 30 days, and has the stability performance conditions for application in practice, which is more than twice the stability of the label prepared by the comparative preparation method.

[0106] Depend on Figure 7 It can be seen that under a light-proof environment at 4° C., the ΔE values ​​of all labels prepared according to the embodiments and comparative examples did not exceed 5 within 2 months, demonstrating that they all had good stability.

[0107] 3. pH-responsive color change of the label The label of Example 1 was immersed in 8 mL of buffer solutions with pH values ​​ranging from 2 to 12 for 10 min, and then taken out to observe the color change of the label in different pH environments.

[0108] like Figure 8 The color change of the label in different buffers. It can be seen that the label is purple-red at pH 2-4, purple at pH 5 and 6, blue at pH 7, blue-green at pH 8, green at pH 9-11, and yellow-green at pH 12, which proves that the label prepared in Example 1 has the ability to reflect pH changes and can be used for freshness monitoring with alkaline gases such as ammonia and amines as characteristic corruption gases.

[0109] 3. Monitoring the freshness of Penaeus vannamei The label of Example 1 was pasted on the top of the inner part of the white shrimp package, and the shrimps were stored at 25° C. and 4° C. respectively. Fig. 9 and Fig.11 The changes in TVB-N of white shrimp during different storage periods and the corresponding label color difference ΔE values ​​were described. Fig.10 and Fig.12 The color changes of the shrimp corresponding to the label during storage were recorded.

[0110] The present invention tests the TVB-N value of whiteleg shrimp under different storage conditions during storage, and the test results are as follows: Fig. 9 As shown. Under 25℃ storage conditions, white shrimp is in a fresh state from 0 to 8 hours; after 8 hours, its TVB-N value exceeds 20 mgN / 100 g for the first time, entering a sub-fresh state; and after 12 hours, white shrimp exceeds the corruption threshold and is completely corrupt and inedible. Under 4℃ storage conditions, white shrimp reaches a sub-fresh state after 48 hours, and its TVB-N value exceeds 30 mgN / 100 g after 84 hours, reaching a corrupt state and is not suitable for consumption.

[0111] Fig.10 The color changes of the corresponding labels in the packaging of white shrimp at 25℃ were recorded. After 8 hours of storage at 25℃, the edges of the labels turned green, and then the green gradually spread to the center and deepened, turning completely green after 10 hours. Fig. 9 The curve of the label color difference ΔE value changing over time is also recorded in the figure. We can see that as time goes by, the ΔE value continues to rise and is positively correlated with the change of TVB-N. Therefore, we can draw the following conclusions: When the label is purple-red, the aquatic product to be tested is fresh; When the edge of the label turns green, the aquatic product to be tested is in a semi-fresh state; When all labels turn green and the green color gradually deepens, the TVB-N index of the aquatic product to be tested is close to the corruption threshold and it is not suitable for consumption.

[0112] Fig.12 The color changes of the corresponding labels in the packaging of white shrimp at 4°C were recorded. After 48 hours, the labels changed from purple-red to purple-blue, and then gradually changed from purple to green. After about 80 hours, the labels completely turned green, and then the green color deepened. Fig.11 The curve of the label color difference ΔE value changing over time is also recorded in the figure. We can see that as time goes by, the ΔE value continues to rise and is positively correlated with the change of TVB-N. Therefore, we can draw the following conclusions: When the label is purple-red, the aquatic product to be tested is fresh; When the label is purple-blue, the aquatic product to be tested is in a semi-fresh state; When all labels turn green and the green color gradually deepens, the TVB-N index of the aquatic product to be tested is close to the corruption threshold and it is not suitable for consumption.

[0113] Fig.13 The correlation between TVB-N and label color parameters was described, and the results showed that there was a strong correlation between the color change of the label prepared by the present invention and the freshness of the white shrimp, and the freshness of the white shrimp could be qualitatively judged according to the color change of the label.

[0114] In summary, the high-stability intelligent indicator label for freshness of aquatic products of the present invention, as well as its preparation method and application, utilize the excellent ultraviolet absorption and fluorescence properties of UiO-66-NH2, the rich functional groups in the ligand to produce hydrogen bonds and other interactions with anthocyanins, and the auxiliary color interaction between gentisic acid and anthocyanins, thereby synergistically improving the storage stability of the anthocyanin indicator label; at the same time, alkaline gases such as ammonia and amines produced by aquatic products during the spoilage process are utilized to induce pH-responsive color changes in the label, and the label also realizes the visual qualitative judgment of the freshness of aquatic products.

[0115] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "specific embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0116] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a high-stability intelligent label for indicating freshness of aquatic products, characterized in that , specifically including the following steps: Step S1: using 55% to 65% (v / v) ethanol solution as an extractant, extracting anthocyanins from anthocyanin-rich plant tissue at a solid-to-liquid ratio of 1:10, and extracting for 4 h to 6 h to obtain anthocyanin extract; concentrating the anthocyanin extract to 150 mL to 200 mL using a rotary evaporator to obtain anthocyanin concentrate; Step S2: 197 mg 2-aminoterephthalic acid, 253 mg zirconium tetrachloride, and 27.6 mL glacial acetic acid were dissolved in 230 mL N, N-dimethylformamide (DMF), ultrasonicated for 1 hour in an ultrasonic environment, and then transferred to a 300 mL stainless steel high-pressure reactor containing polytetrafluoroethylene lining, and reacted in a vacuum drying oven at 120°C for 24 hours (negative pressure 0.085 mPa~0.090 mPa); after the reaction was completed, the reactor was taken out, cooled to room temperature in a room temperature environment, and then opened, centrifuged at 8000 rpm to remove the supernatant, washed with DMF 3 times, activated with methanol for 24 hours, and activated the precipitate in a vacuum drying oven at 60°C after centrifugation to obtain UiO-66-NH2; Step S3: dispersing sodium alginate powder in water, stirring at 85°C-90°C until completely dissolved, and then cooling to room temperature to obtain a sodium alginate solution; adding glycerol, anthocyanin concentrate, gentisic acid and UiO-66-NH2 to the sodium alginate solution in sequence, stirring evenly and drying in a 35°C forced air drying oven to form a film, thereby obtaining an intelligent indicator label for freshness of aquatic products; before use, immersing the label in a calcium chloride solution for cross-linking, then taking it out, rinsing the label surface with clean water and then using it.

2. The method for preparing a high-stability intelligent indicator label for freshness of aquatic products according to claim 1, characterized in that: The concentration of the sodium alginate solution is 1 wt%-3 wt%.

3. The method for preparing a high-stability intelligent label indicating freshness of aquatic products according to claim 1, characterized in that: The volume ratio of the anthocyanin concentrate to the sodium alginate solution is 1:

10.

4. The method for preparing a high-stability intelligent indicator label for freshness of aquatic products according to claim 1, characterized in that: The mass ratio of the gentisic acid to the sodium alginate solution is 4 mg to 24 mg: 20 mL.

5. The method for preparing a high-stability intelligent indicator label for freshness of aquatic products according to claim 1, characterized in that: The dosage ratio of the UiO-66-NH2 to the sodium alginate solution is 4 mg~24 mg:20 mL.

6. The method for preparing a high-stability intelligent indicator label for freshness of aquatic products according to claim 1, characterized in that: The concentration of the calcium chloride solution is 1 wt% to 5 wt%, the volume is 10 mL, and the cross-linking time is 1 min.

7. A highly stable intelligent label for indicating freshness of aquatic products, characterized in that: The method is prepared by any one of claims 1 to 6.

8. Application of a high-stability intelligent indicator label for freshness of aquatic products for reflecting the freshness of aquatic products, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 6, and its specific application is as follows: 1) Pasting the aquatic product freshness intelligent indicator label prepared by the method for preparing a high-stability aquatic product freshness intelligent indicator label on the packaging of the aquatic product to be tested, and storing it at 0-37°C; 2) Record the color change of the label and combine it with the TVB-N change of the sample to achieve qualitative judgment of the freshness of the aquatic product to be tested: Based on the TVB-N content, the freshness level of aquatic products can be qualitatively judged by naked eye visualization: When TVB-N < 20 mgN / 100 g, it is in fresh state; When TVB-N is 20 mgN / 100 g~30 mgN / 100 g, it is in a sub-fresh state; When TVB-N>30 mgN / 100 g, it is in a corrupt state; When the label is purple-red, the aquatic product to be tested is fresh; When the edge of the label turns green, the aquatic product to be tested is in a semi-fresh state; When all labels turn green and the green color gradually deepens, the TVB-N index of the aquatic product to be tested is close to the corruption threshold and it is not suitable for consumption.

Images