High-stability intelligent freshness indicating label for aquatic products and preparation method and application thereof

Abstract

The application belongs to the technical field of food safety detection, and provides a high-stability water product freshness intelligent indication label and a preparation method and application thereof. The stability of the water product freshness intelligent indication label based on anthocyanin is significantly improved through the synergistic auxiliary color effect of UiO-66-NH2 and gentisic acid on anthocyanin. The preparation method is as follows: after sodium alginate is completely dissolved and cooled to room temperature, glycerol, anthocyanin extract, gentisic acid solution and UiO-66-NH2 resuspension are sequentially added under continuous stirring, and then the mixture is uniformly stirred and dried into a film in a 35 DEG C air-drying oven, so that the high-stability water product freshness intelligent indication label is obtained. The preparation method is simple and easy to operate, the prepared indication label can greatly improve the storage stability of the anthocyanin label under light-proof conditions, and the label has the functions of sensitive and accurate response to the change of water product freshness.

Description

TECHNICAL FIELD

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

[0002] Aquatic products have become an indispensable part of people's table, but due to the high protein and water content of aquatic products, they are prone to lipid oxidation, endogenous enzyme and exogenous microbial contamination leading to protein and nucleic acid hydrolysis during transportation, storage and sales, thereby causing spoilage and accompanying putrefactive odor. Especially in the process of meat spoilage, toxic and harmful metabolites such as trimethylamine are continuously accumulated, making the meat lose its edible value and even posing a potential threat to the health of consumers. With the improvement of economy and living standards, the fast-paced lifestyle, and the change of people's demand for food from "quantity" to "quality", the public's demand for nutritious, safe and fresh food is increasing, which undoubtedly poses higher challenges to the pre-prepared food industry in ensuring food safety. Traditional methods for evaluating meat freshness, such as volatile base nitrogen content (according to Chinese national standard GB 5009.228-2016) and total bacterial count measurement (according to Chinese national standard GB 4789.2-2022), as well as sensory evaluation, although can provide accurate food freshness information, but due to its cumbersome operation, long detection period, destructive detection and the need for professional operators, it is difficult to realize on-site rapid and non-destructive freshness detection, therefore, a low-cost, real-time, visual monitoring method is urgently needed.

[0003] The food freshness intelligent indication label can intuitively reflect the food spoilage changes caused by physiological or microbial growth through color change 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, freshness indication labels responsive to biogenic amines have attracted much attention. Among them, the selection of color developing agent is crucial to the sensitivity and application range of freshness indication label. Natural pigments, especially anthocyanins, are preferred over chemically synthesized pigments due to their environmental friendliness, cost-effectiveness and avoidance of toxicity problems. 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 food freshness intelligent indication label based on anthocyanins is the key point to promote its commercialization process.

[0004] Therefore, the present application provides a preparation method and application of a high-stability intelligent freshness indication label for aquatic products. SUMMARY

[0005] In order to make up for the deficiencies of the prior art, the application provides a high-stability aquatic product freshness intelligent indication label and a preparation method and application thereof.The freshness intelligent indication label has good storage stability and can realize visual monitoring of aquatic product freshness.The application improves the storage stability of the anthocyanin indication label by incorporating UiO-66-NH2 and gentisic acid in the anthocyanin indication label, using the excellent ultraviolet absorption and fluorescence characteristics of UiO-66-NH2 and the hydrogen bond interaction between anthocyanin and UiO-66-NH2, and the auxiliary color effect between gentisic acid and anthocyanin, so that long-term preservation in an actual storage environment is realized.

[0006] The application is realized by the following technical scheme: a preparation method of a high-stability aquatic product freshness intelligent indication label, specifically comprising the following steps:

[0007] Step S1: anthocyanin is extracted from plant tissues rich in anthocyanin by using 55% to 65% (v / v) ethanol solution as an extracting agent and a solid-liquid ratio of 1:10, and the extraction is carried out for 4 h to 6 h to obtain an anthocyanin extract; the anthocyanin extract is concentrated to 150 mL to 200 mL by using a rotary evaporator to obtain an anthocyanin concentrate;

[0008] Step S2: 197 mg of 2-amino terephthalic acid, 253 mg of zirconium tetrachloride and 27.6 mL of glacial acetic acid are dissolved in 230 mL of N,N-dimethylformamide (DMF), ultrasonic treatment is performed in an ultrasonic environment for 1 hour, then the reaction kettle is transferred to a 300 mL stainless steel high-pressure reaction kettle containing a polytetrafluoroethylene liner, and reaction is performed in a 120℃ vacuum drying box for 24 hours (negative pressure 0.085 mPa to 0.090 mPa); after the reaction is completed, the reaction kettle is taken out and cooled to room temperature in a room temperature environment, then opened, centrifuged at 8000 rpm to remove the supernatant, washed with DMF for 3 times, activated with methanol for 24 hours, and after centrifugation, the precipitate is activated in a 60℃ vacuum drying box to obtain UiO-66-NH2;

[0009] Step S3: sodium alginate powder is dispersed in water, stirred at 85℃ to 90℃ until completely dissolved, then cooled to room temperature to obtain a sodium alginate solution; glycerol, the anthocyanin concentrate, gentisic acid and UiO-66-NH2 are sequentially added to the sodium alginate solution, uniformly stirred and dried into a film in a 35℃ air drying oven to obtain the aquatic product freshness intelligent indication label; before use, the label is soaked in a calcium chloride solution for crosslinking, then taken out, rinsed with clean water to clean the label surface and ready for use.

[0010] As a preferred scheme, the concentration of the sodium alginate solution is 1 wt%-3 wt%.

[0011] As a preferred solution, the volume ratio of the anthocyanin concentrate solution to the sodium alginate solution is 1:10.

[0012] As a preferred solution, the mass ratio of gentisic acid to the sodium alginate solution is 4 mg-24 mg:20 mL.

[0013] As a preferred solution, the dosage ratio of UiO-66-NH2 to the sodium alginate solution is 4 mg-24 mg:20 mL.

[0014] As a preferred solution, the concentration of the calcium chloride solution is 1 wt%-5 wt%, the volume is 10 mL, and the crosslinking time is 1 min.

[0015] A high-stability aquatic product freshness intelligent indication label is prepared by the above method.

[0016] The application of a high-stability aquatic product freshness intelligent indication label in reflecting the freshness of aquatic products is prepared by the above preparation method, and the specific application is as follows:

[0017] 1) The aquatic product freshness intelligent indication label prepared by the above preparation method is pasted on the upper part of the packaging of the aquatic product to be detected and stored at 0-37℃.

[0018] 2) The color change of the label is recorded, and the TVB-N change of the sample is combined to realize the qualitative discrimination of the freshness of the aquatic product to be detected:

[0019] According to the obtained TVB-N content, the visual qualitative judgment of the freshness grade of aquatic products is realized:

[0020] When TVB-N<20 mgN / 100 g, it is in a fresh state;

[0021] When TVB-N is 20 mgN / 100 g-30 mgN / 100 g, it is in a sub-fresh state;

[0022] When TVB-N>30 mgN / 100 g, it is in a state of corruption;

[0023] When the label is purple red, the aquatic product to be detected is in a fresh state;

[0024] When the edge of the label appears green, the aquatic product to be detected is in a sub-fresh state;

[0025] When the label turns green all over and the green color gradually deepens, the TVB-N index of the aquatic product to be detected approaches the corruption threshold, and it is not suitable for consumption.

[0026] Compared with the prior art, the application has the following beneficial effects: the application utilizes the pH-responsive color change of plant anthocyanins, and the plant anthocyanins present blue or green in an alkaline environment, so that the freshness of aquatic products can be nondestructively, real-timely and visually distinguished; in addition, the plant anthocyanins are safe and edible, and the threat to human health caused by pigment migration is greatly reduced.

[0027] The application introduces UiO-66-NH2 and gentisic acid into the intelligent indicating label, and the storage stability of the anthocyanin indicating label is greatly enhanced.

[0028] The preparation method of the application does not need to use complex instruments and equipment, has low material cost, is easy to mass-produce, and is simple to operate.

[0029] Additional aspects and advantages of the application will become apparent in the light of the following detailed description of the application. BRIEF DESCRIPTION OF DRAWINGS

[0030] The above and / or additional aspects and advantages of the application will become apparent and be readily understood by practice of the application, from the following detailed description, from the accompanying drawings, and from the claims.

[0031] 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, A is the SEM image of UiO-66-NH2, B is the SEM image of the surface of the label of Example 1 at a scale of 10 μm, C is the SEM image of the cross section of the label of Example 1 at a scale of 10 μm, and D is the SEM image of the cross section of the label of Example 1 at a scale of 1 μm.

[0032] Figure 2 Stability changes of the labels of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6 and Comparative Example 3 under 37℃ light-avoiding storage conditions. Figure 2 In the figure, A is the change of the color difference value of different labels during 48 hours of placement in a 37℃ light-avoiding environment, and B is the significant difference analysis of the color difference of different labels after 36 hours and 48 hours of placement in a 37℃ light-avoiding environment.

[0033] Figure 3 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.

[0034] Figure 4 Stability changes of the labels of Example 1, Example 7, Example 8, Example 9, Example 10, Example 11 and Comparative Example 2 under 37℃ light-avoiding storage conditions. Figure 2In the middle, A is the color difference value change of different labels in 37℃ dark environment for 36 hours, B is the significant difference analysis of color difference of different labels in 37℃ dark environment after 24 hours and 36 hours.

[0035] Figure 5 The ammonia response performance comparison chart of the labels of Example 1, Example 7, Example 8, Example 9, Example 10, Example 11, Comparative Example 2.

[0036] Figure 6 The stability change of the labels of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 in room temperature dark environment.

[0037] Figure 7 The stability change of the labels of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 in 4℃ dark environment.

[0038] Figure 8 The color change of the label of Example 1 in the pH range of 2-12.

[0039] Figure 9 The TVB-N change of shrimp in 25℃ storage environment for different time, and the corresponding color difference value change of the label of Example 1.

[0040] Figure 10 The state diagram of shrimp in 25℃ storage environment for different time, and the corresponding color change diagram of the label of Example 1.

[0041] Figure 11 The TVB-N change of shrimp in 4℃ storage environment for different time, and the corresponding color difference value change of the label of Example 1.

[0042] Figure 12 The state diagram of shrimp in 4℃ storage environment for different time, and the corresponding color change diagram of the label of Example 1.

[0043] Figure 13 The correlation analysis between the TVB-N change of shrimp in 25℃ and 4℃ storage environment and the corresponding label color parameter change. Figure 13 In the middle, A is the correlation analysis between the TVB-N change of shrimp in 25℃ storage environment and the corresponding label color parameter change, B is the correlation analysis between the TVB-N change of shrimp in 4℃ storage environment and the corresponding label color parameter change. DETAILED DESCRIPTION

[0044] In order to enable a more clear understanding of the above-mentioned objects, features and advantages of the present application, the present application will be further described in detail below with reference to 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.

[0045] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, however, the present application can also be implemented in other different manners from those described herein, and therefore, the protection scope of the present application is not limited by the specific embodiments disclosed below.

[0046] The present application provides a preparation method of a high-stability aquatic product freshness intelligent indicating label, specifically comprising the following steps:

[0047] Step S1: extraction of anthocyanins: using an alcohol solution as an extraction solvent, anthocyanins are extracted from plant tissues rich in anthocyanins by an alcohol method to obtain an anthocyanin solution, and then the volume of the anthocyanin extraction liquid is concentrated to 150 mL-200 mL using a rotary evaporator to obtain an anthocyanin concentrated solution.

[0048] It should be noted that, in some preferred embodiments of the present application, the plant tissues rich in anthocyanins are one or more of purple cabbage, purple sweet potato, black carrot, delphinium, blueberry, rose and black wolfberry.

[0049] In some preferred embodiments of the present application, 55%-65% (v / v) of an ethanol solution is used as an extraction agent, and anthocyanins are extracted from plant tissues rich in anthocyanins at a solid-liquid ratio of 1:10 to obtain an anthocyanin extraction liquid by leaching for 4-6 h; the anthocyanin extraction liquid is concentrated to 150 mL-200 mL using a rotary evaporator to obtain an anthocyanin concentrated solution.

[0050] Specifically, the anthocyanin extraction liquid is obtained by the following steps: taking plant tissues rich in anthocyanins, washing and cutting into small pieces, drying in a 50℃ air-drying oven, and then crushing the dried plant tissues into powder using a crushing instrument. The obtained plant tissues rich in anthocyanins are dispersed in a 55%-65% (v / v) ethanol aqueous solution, and leached for 4-6 h under 400 rpm in the dark, and then repeatedly filtered with Whatman no. 4 filter paper to remove impurities. In some preferred embodiments of the present application, the plant tissues rich in anthocyanins are cut into thin strips. In some preferred embodiments of the present application, the stirring temperature is room temperature, the stirring time is 4-6 h, and the stirring speed is 400 rpm. In some preferred embodiments of the present application, the drying temperature is 50℃. In some preferred embodiments of the present application, the specific setting parameters of the rotary evaporator are 40℃, 60-70 rpm.

[0051] Step S2: Preparation of UiO-66-NH2: UiO-66-NH2 was prepared by a dissolution-heat method.

[0052] It should be noted that, in order to improve the storage stability of anthocyanin indicating label, the application utilizes the excellent ultraviolet absorption and fluorescence characteristics of UiO-66-NH2, and at the same time, the rich functional groups can form hydrogen bonds and other interactions with the hydroxyl groups of anthocyanin, thereby improving the light stability and thermal stability of the anthocyanin indicating label.

[0053] The UiO-66-NH2 used in the application is prepared by a solvent-thermal method, and the specific steps are as follows: 197 mg of 2-amino terephthalic acid, 253 mg of zirconium tetrachloride, and 27.6 mL of glacial acetic acid are dissolved in 230 mL of N,N-dimethylformamide (DMF), and ultrasonic treatment is performed in an ultrasonic environment for 1 hour, and then the reaction mixture is transferred to a 300 mL stainless steel high-pressure reaction kettle with a polytetrafluoroethylene liner, and the reaction is carried out in a vacuum drying oven at 120℃ for 24 hours (negative pressure of 0.085 mPa to 0.090 mPa); after the reaction is completed, the reaction kettle is taken out and cooled to room temperature in a room temperature environment, and then opened, and the supernatant is removed by centrifugation at 8000 rpm, and the precipitate is washed with DMF for 3 times, and then activated with methanol for 24 hours, and after centrifugation, the precipitate is activated in a vacuum drying oven at 60℃, and the UiO-66-NH2 is obtained.

[0054] The UiO-66-NH2 used in the application is prepared by a solvent-thermal method, and the UiO-66-NH2 obtained has a particle size of 425±75 nm and a specific surface area of about 1149.77 m 2 / g.

[0055] Step S3: Mixing with sodium alginate solution: sodium alginate powder is dispersed in water, stirred at 85℃ to 90℃ until completely dissolved, and then cooled to room temperature to obtain a sodium alginate solution; glycerol, anthocyanin concentrate, gentisic acid and UiO-66-NH2 are sequentially added to the sodium alginate solution, and after stirring, the mixture is dried into a film in a 35℃ air-drying oven, thereby obtaining the water product freshness intelligent indicating label prepared by the preparation method of the high-stability water product freshness intelligent indicating label; before use, the label is soaked in a calcium chloride solution for crosslinking, and then taken out and washed with clean water to clean the surface of the label.

[0056] The sodium alginate used in the application has a molecular weight of 20-50 thousand and a viscosity of 15-60 mpa·s. In some preferred embodiments of the application, the concentration of the sodium alginate solution is 1 wt% to 3 wt%, so as to ensure that the sodium alginate solution has good fluidity and dispersibility.

[0057] In some preferred embodiments of the present application, the amount of glycerol added is 150 μL to 200 μL.

[0058] In some preferred embodiments of the present application, the ratio of the amount of cyanidin concentrate to the amount of sodium alginate solution is 1 mL to 3 mL to 20 mL.

[0059] In some preferred embodiments of the present application, the ratio of the amount of gentisic acid solution to the amount of sodium alginate solution is 4 mg to 24 mg to 20 mL. It should be noted that the gentisic acid solution needs to be dissolved in 2 mL of 50% (v / v) aqueous ethanol solution.

[0060] In some preferred embodiments of the present application, the ratio of the amount of UiO-66-NH2 to the amount of sodium alginate solution is 4 mg to 24 mg to 20 mL. It should be noted that the UiO-66-NH2 needs to be uniformly dispersed in 1 mL of water before being added.

[0061] In some preferred embodiments of the present application, the concentration of the calcium chloride solution is 1 wt% to 5 wt%, the volume is 10 mL, and the crosslinking time is 1 min.

[0062] It should be noted that the formation process of the intelligent indicator label needs to be continuously dried in a 35℃ air-drying oven until a thin film is formed.

[0063] A second object of the present application is to provide a water product freshness intelligent indicator label prepared by the above preparation method, which has good storage stability.

[0064] A third object of the present application is to provide the use of a water product freshness intelligent indicator label prepared by the preparation method of a high-stability water product freshness intelligent indicator label in reflecting the freshness of food.

[0065] The use of a high-stability water product freshness intelligent indicator label in reflecting the freshness of water products, specifically as follows:

[0066] 1) The prepared water product freshness intelligent indicator label is pasted above the packaging of the water product to be detected, and is stored at a temperature of 0 to 37℃.

[0067] 2) The color change of the intelligent indicator label is recorded, so as to realize the visual discrimination of the freshness of the water product to be detected by the color change of the label. It should be noted that the camera parameters should be set as follows when taking pictures: iso speed is 50, aperture value is f / 1.6, and exposure time is 1 / 172 seconds.

[0068] 3) According to the "Chinese national standard GB 5009.228-2016 food safety national standard food determination of volatile nitrogen" to determine the TVB-N value of aquatic products under different storage time, the color change of the label is correlated with the TVB-N of the aquatic products, so as to realize the qualitative discrimination of the freshness state of the aquatic products according to the color state of the label.

[0069] According to the color response change of the label, the freshness of the aquatic products to be detected is visually discriminated according to the following standards:

[0070] TVB-N<20 mgN / 100 g is fresh state;

[0071] TVB-N is 20 mgN / 100 g~30 mgN / 100 g is sub-fresh state;

[0072] TVB-N>30 mgN / 100 g is putrid state;

[0073] When the label is purple red, the aquatic products to be detected are in fresh state;

[0074] When the label edge appears green, the aquatic products to be detected are in sub-fresh state;

[0075] When the label turns green all over and the green color gradually deepens, the TVB-N index of the aquatic products to be detected approaches the corruption threshold, and it is not suitable to be eaten.

[0076] The following will be combined Figures 1 to 13 The high-stability aquatic product freshness intelligent indicating label and the preparation method and application of the embodiment of the application will be specifically described.

[0077] In each of the following embodiments of the application, the UiO-66-NH2 is prepared by the following steps: 197 mg of 2-amino terephthalic acid, 253 mg of zirconium tetrachloride and 27.6 mL of glacial acetic acid are dissolved in 230 mL of N,N-dimethylformamide (DMF), ultrasonic treatment is carried out in an ultrasonic environment for 1 hour, then it is transferred to a 300 mL stainless steel high-pressure reaction kettle with a polytetrafluoroethylene liner, and reaction is carried out in a vacuum drying box at 120 DEG C for 24 hours (negative pressure 0.085 mPa~0.090 mPa); after the reaction is completed, the reaction kettle is taken out and cooled to room temperature at room temperature, then the reaction kettle is opened, the supernatant is removed by centrifugation at 8000 rpm, the precipitate is washed with DMF (the precipitate is resuspended in 50 mL of DMF, and continuous stirring is carried out for 1 hour) 3 times, then methanol is activated for 24 hours, the precipitate is activated in a vacuum drying box at 60 DEG C after centrifugation, and UiO-66-NH2 is obtained.

[0078] Example 1

[0079] The embodiment provides a preparation method of a high-stability aquatic product freshness intelligent indicating label, and the method is realized through the following steps:

[0080] Step 1, extraction of purple cabbage anthocyanins: clean the purple cabbage leaves, crush them into pieces, and completely dry them in a 50°C air-drying oven. Crush the dried purple cabbage leaves using a crushing instrument. Take 50 g of the purple cabbage leaf powder, disperse it in 500 mL of an ethanol aqueous solution with a volume fraction of 60%, and continuously stir for 4 h under light shielding at 400 rpm. Then, repeatedly filter the extract using Whatman no. 4 filter paper to obtain a purple cabbage anthocyanin extract. Concentrate the anthocyanin extract using a rotary evaporator, and the rotary evaporation parameters are 40°C and 60 rpm. Finally, concentrate the purple cabbage anthocyanin extract to 150 mL to obtain a purple cabbage anthocyanin concentrate.

[0081] Step 2, mixing with sodium alginate: dissolve 2 g of sodium alginate in 98 g of water at 85°C, and then cool to room temperature to obtain a 2 wt% sodium alginate solution. Take 20 mL of the sodium alginate solution, and continuously stir at 400 rpm to add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 16 mg of a gentisic acid solution (dissolved in 2 mL of an ethanol aqueous solution with a volume fraction of 50%), and 20 mg of UiO-66-NH2 (dispersed in 1 mL of water) in sequence. After uniform stirring, pour the mixture into a disposable plastic petri dish with a diameter of 90 mm, and then dry the mixture into a film in a 35°C air-drying oven. After film formation, carefully remove the film from the petri dish with tweezers, and then cut the film into a square with a size of 15 mm*15 mm to obtain an aquatic product freshness intelligent indicating label prepared by the preparation method of the high-stability aquatic product freshness intelligent indicating label. Before use, immerse the label in 10 mL of a 5 wt% calcium chloride solution for crosslinking for 1 min, then take out the label, wash the surface of the label with clean water, and then use the label.

[0082] Example 2

[0083] The embodiment provides a preparation method of a high-stability aquatic product freshness intelligent indicating label, and the method is realized through the following steps:

[0084] Step 1, extraction of purple cabbage anthocyanins: The purple cabbage leaves were washed clean and then broken into pieces, and dried completely in a 50℃ air-drying oven. The dried purple cabbage leaves were ground using a grinder. 50 g of the dried purple cabbage leaf powder was dispersed in 500 mL of 60% ethanol aqueous solution, and continuously stirred at 400 rpm for 4 h in the dark. The extract was then filtered repeatedly using Whatman no. 4 filter paper to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator at 40℃ and 60 rpm, and the final volume of the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain the purple cabbage anthocyanin concentrate.

[0085] Step 2, mixing with sodium alginate: 2 g of sodium alginate was completely dissolved in 98 g of water at 85℃, and then cooled to room temperature to obtain a 2 wt% sodium alginate solution. 20 mL of the sodium alginate solution was added with 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), and 20 mg of UiO-66-NH2 (dispersed in 1 mL of water) under continuous stirring at 400 rpm. After stirring evenly, the mixture was poured into a 90 mm diameter disposable plastic petri dish, and then dried into a film in a 35℃ air-drying oven. After film formation, the film was carefully removed from the petri dish with tweezers, and then cut into a 15 mm*15 mm square to obtain the water product freshness intelligent indicator label prepared by the preparation method of the high-stability water product freshness intelligent indicator label.

[0086] The difference between this embodiment and Example 1 is that the amount of gentisic acid used in this embodiment is 4 mg.

[0087] Example 3

[0088] This embodiment provides a preparation method of a high-stability water product freshness intelligent indicator label, and the method is achieved by the following steps:

[0089] Step 1, extraction of purple cabbage anthocyanins: Clean the purple cabbage leaves and crush them into pieces, then dry them completely in a 50℃ air-drying oven. Grind the dried purple cabbage leaves using a grinder. Take 50 g of the purple cabbage leaf powder and disperse it in 500 mL of 60% ethanol aqueous solution, then continuously stir it under light shielding at 400 rpm for 4 h. Then filter the extract solution repeatedly using Whatman no. 4 filter paper to obtain the purple cabbage anthocyanin extract solution. Concentrate the anthocyanin extract solution using a rotary evaporator, with the rotary evaporation parameters being 40℃ and 60 rpm. Finally, concentrate the purple cabbage anthocyanin extract solution to 150 mL to obtain the purple cabbage anthocyanin concentrate solution.

[0090] Step 2, mixing with sodium alginate: Dissolve 2 g of sodium alginate in 98 g of water at 85℃ to obtain a 2 wt% sodium alginate solution, then cool it to room temperature. Take 20 mL of the sodium alginate solution and add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate solution, 8 mg of the gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution), and 20 mg of UiO-66-NH2 (dispersed in 1 mL of water) successively under continuous stirring at 400 rpm. After stirring uniformly, pour the mixture into a 90 mm diameter disposable plastic petri dish, then dry it into a film in a 35℃ air-drying oven. After film formation, carefully remove the film from the petri dish using tweezers, then cut it into a 15 mm*15 mm square to obtain the water product freshness intelligent indication label prepared by the preparation method of the high-stability water product freshness intelligent indication label.

[0091] The difference between this embodiment and Example 1 is that the gentisic acid used in this embodiment is 8 mg.

[0092] Example 4

[0093] This embodiment provides a preparation method of a high-stability water product freshness intelligent indication label, and the preparation method is achieved by the following steps:

[0094] Step 1, extraction of purple cabbage anthocyanins: The purple cabbage leaves were washed clean and then broken into pieces, and dried completely in a 50℃ air-drying oven. The dried purple cabbage leaves were ground using a grinder. 50 g of the dried purple cabbage leaf powder was dispersed in 500 mL of 60% ethanol aqueous solution, and continuously stirred at 400 rpm for 4 h in the dark. The extract was then filtered repeatedly using Whatman no. 4 filter paper to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator at 40℃ and 60 rpm, and the final volume of the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain the purple cabbage anthocyanin concentrate.

[0095] Step 2, mixing with sodium alginate: 2 g of sodium alginate was completely dissolved in 98 g of water at 85℃, and then cooled to room temperature to obtain a 2 wt% sodium alginate solution. 20 mL of the sodium alginate solution was added with 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 12 mg of the gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution), and 20 mg of UiO-66-NH2 (dispersed in 1 mL of water) under continuous stirring at 400 rpm. After stirring evenly, the mixture was poured into a 90 mm diameter disposable plastic petri dish, and then dried into a film in a 35℃ air-drying oven. After film formation, the film was carefully removed from the petri dish with tweezers, and then cut into a 15 mm*15 mm square to obtain the water product freshness intelligent indicator label prepared by the preparation method of the high-stability water product freshness intelligent indicator label.

[0096] The difference between this embodiment and Example 1 is that the amount of gentisic acid used in this embodiment is 12 mg.

[0097] Example 5

[0098] This embodiment provides a preparation method of a high-stability water product freshness intelligent indicator label, and the method is achieved by the following steps:

[0099] Step 1, extraction of purple cabbage anthocyanins: The purple cabbage leaves were washed clean and then broken into pieces, and dried completely in a 50℃ air-drying oven. The dried purple cabbage leaves were ground using a grinder. 50 g of the dried purple cabbage leaf powder was dispersed in 500 mL of 60% ethanol aqueous solution, and continuously stirred at 400 rpm for 4 h in the dark. The extract was then filtered repeatedly using Whatman no. 4 filter paper to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator at 40℃ and 60 rpm, and the final volume of the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain the purple cabbage anthocyanin concentrate.

[0100] Step 2, mixing with sodium alginate: 2 g of sodium alginate was completely dissolved in 98 g of water at 85℃, and then cooled to room temperature to obtain a 2 wt% sodium alginate solution. 20 mL of the sodium alginate solution was added with 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 20 mg of the gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution), and 20 mg of UiO-66-NH2 (dispersed in 1 mL of water) under continuous stirring at 400 rpm. After stirring evenly, the mixture was poured into a 90 mm diameter disposable plastic petri dish, and then dried into a film in a 35℃ air-drying oven. After film formation, the film was carefully removed from the petri dish with tweezers, and then cut into a 15 mm*15 mm square to obtain the water product freshness intelligent indicator label prepared by the preparation method of the high-stability water product freshness intelligent indicator label.

[0101] The difference between this embodiment and Example 1 is that the amount of gentisic acid used in this embodiment is 20 mg.

[0102] Example 6

[0103] This embodiment provides a preparation method of a high-stability water product freshness intelligent indicator label, and the method is achieved by the following steps:

[0104] Step 1, extraction of purple cabbage anthocyanins: The purple cabbage leaves were washed clean and then broken into pieces, and dried completely in a 50℃ air-drying oven. The dried purple cabbage leaves were ground using a grinder. 50 g of the dried purple cabbage leaf powder was dispersed in 500 mL of 60% ethanol aqueous solution, and continuously stirred at 400 rpm for 4 h in the dark. The extract was then filtered repeatedly using Whatman no. 4 filter paper to obtain the purple cabbage anthocyanin extract. The anthocyanin extract was concentrated using a rotary evaporator at 40℃ and 60 rpm, and the final volume of the purple cabbage anthocyanin extract was concentrated to 150 mL to obtain the purple cabbage anthocyanin concentrate.

[0105] Step 2, mixing with sodium alginate: 2 g of sodium alginate was completely dissolved in 98 g of water at 85℃, and then cooled to room temperature to obtain a 2 wt% sodium alginate solution. 20 mL of the sodium alginate solution was added with 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 24 mg of the gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution), and 20 mg of UiO-66-NH2 (dispersed in 1 mL of water) under continuous stirring at 400 rpm. After stirring evenly, the mixture was poured into a 90 mm diameter disposable plastic petri dish, and then dried into a film in a 35℃ air-drying oven. After film formation, the film was carefully removed from the petri dish with tweezers, and then cut into a 15 mm*15 mm square to obtain the water product freshness intelligent indicator label prepared by the preparation method of the high-stability water product freshness intelligent indicator label.

[0106] The difference between this embodiment and Example 1 is that the amount of gentisic acid used in this embodiment is 24 mg.

[0107] Example 7

[0108] This embodiment provides a preparation method of a high-stability water product freshness intelligent indicator label, and the method is achieved by the following steps:

[0109] Step 1, extraction of purple cabbage anthocyanins: Clean the purple cabbage leaves and crush them into pieces, then dry them completely in a blast drying oven at 50℃. Grind the dried purple cabbage leaves using a grinder. Take 50 g of the purple cabbage leaf powder and disperse it in 500 mL of 60% ethanol aqueous solution, then continuously stir it under light shielding at 400 rpm for 4 h. Then filter the extract solution repeatedly using Whatman no. 4 filter paper to obtain the purple cabbage anthocyanin extract solution. Concentrate the anthocyanin extract solution using a rotary evaporator with the parameters of 40℃ and 60 rpm, and finally concentrate the purple cabbage anthocyanin extract solution to 150 mL to obtain the purple cabbage anthocyanin concentrate.

[0110] Step 2, mixing with sodium alginate: Dissolve 2 g of sodium alginate in 98 g of water at 85℃ to obtain a 2 wt% sodium alginate solution, then cool it to room temperature. Take 20 mL of the sodium alginate solution and add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 16 mg of the gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution), and 4 mg of UiO-66-NH2 (dispersed in 1 mL of water) successively under continuous stirring at 400 rpm. After stirring uniformly, pour the mixture into a disposable plastic petri dish with a diameter of 90 mm, then dry it into a film in a blast drying oven at 35℃. After film formation, carefully remove the film from the petri dish with tweezers, then cut it into a square with a side length of 15 mm to obtain the water product freshness intelligent indication label prepared by the preparation method of the high-stability water product freshness intelligent indication label.

[0111] The difference between this embodiment and Example 1 is that the amount of UiO-66-NH2 used in this embodiment is 4 mg.

[0112] Example 8

[0113] This embodiment provides a preparation method of a high-stability water product freshness intelligent indication label, and it is achieved by the following steps:

[0114] Step 1, extraction of purple cabbage anthocyanins: Clean the purple cabbage leaves and crush them into pieces, then dry them completely in a blast drying oven at 50℃. Grind the dried purple cabbage leaves using a grinder. Take 50 g of the purple cabbage leaf powder and disperse it in 500 mL of 60% ethanol aqueous solution, then continuously stir it under light shielding at 400 rpm for 4 h. Then filter the extract solution repeatedly using Whatman no. 4 filter paper to obtain the purple cabbage anthocyanin extract solution. Concentrate the anthocyanin extract solution using a rotary evaporator with the parameters of 40℃ and 60 rpm, and finally concentrate the purple cabbage anthocyanin extract solution to 150 mL to obtain the purple cabbage anthocyanin concentrate solution.

[0115] Step 2, mixing with sodium alginate: Dissolve 2 g of sodium alginate in 98 g of water at 85℃ to obtain a 2 wt% sodium alginate solution, then cool it to room temperature. Take 20 mL of the sodium alginate solution and add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate solution, 16 mg of a gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution), and 8 mg of UiO-66-NH2 (dispersed in 1 mL of water) successively under continuous stirring at 400 rpm. After stirring uniformly, pour the mixture into a disposable plastic petri dish with a diameter of 90 mm, then dry it into a film in a blast drying oven at 35℃. After film formation, carefully remove the film from the petri dish with tweezers, then cut it into a square with a side length of 15 mm to obtain the water product freshness intelligent indication label prepared by the preparation method of the high-stability water product freshness intelligent indication label.

[0116] The difference between this embodiment and Example 1 is that the amount of UiO-66-NH2 used in this embodiment is 8 mg.

[0117] Example 9

[0118] This embodiment provides a preparation method of a high-stability water product freshness intelligent indication label, and it is achieved by the following steps:

[0119] Step 1, extraction of purple cabbage anthocyanins: Clean the purple cabbage leaves and crush them into pieces, then dry them completely in a blast drying oven at 50℃. Grind the dried purple cabbage leaves using a grinder. Take 50 g of the purple cabbage leaf powder and disperse it in 500 mL of 60% ethanol aqueous solution, then continuously stir it under light shielding at 400 rpm for 4 h. Then filter the extract solution repeatedly using Whatman no. 4 filter paper to obtain the purple cabbage anthocyanin extract solution. Concentrate the anthocyanin extract solution using a rotary evaporator with the parameters of 40℃ and 60 rpm, and finally concentrate the purple cabbage anthocyanin extract solution to 150 mL to obtain the purple cabbage anthocyanin concentrate solution.

[0120] Step 2, mixing with sodium alginate: Dissolve 2 g of sodium alginate in 98 g of water at 85℃ to obtain a 2 wt% sodium alginate solution, then cool it to room temperature. Take 20 mL of the sodium alginate solution and add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate solution, 16 mg of a gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution), and 12 mg of UiO-66-NH2 (dispersed in 1 mL of water) successively under continuous stirring at 400 rpm. After stirring uniformly, pour the mixture into a disposable plastic petri dish with a diameter of 90 mm, then dry it into a film in a blast drying oven at 35℃. After film formation, carefully remove the film from the petri dish with tweezers, then cut it into a square with a side length of 15 mm to obtain the water product freshness intelligent indication label prepared by the preparation method of the high-stability water product freshness intelligent indication label.

[0121] The difference between this embodiment and Example 1 is that the amount of UiO-66-NH2 used in this embodiment is 12 mg.

[0122] Example 10

[0123] This embodiment provides a preparation method of a high-stability water product freshness intelligent indication label, and it is achieved by the following steps:

[0124] Step 1, extraction of purple cabbage anthocyanins: Clean the purple cabbage leaves and crush them into pieces, then dry them completely in a blast drying oven at 50℃. Grind the dried purple cabbage leaves using a grinder. Take 50 g of the purple cabbage leaf powder and disperse it in 500 mL of 60% ethanol aqueous solution, then continuously stir it under light shielding at 400 rpm for 4 h. Then filter the extract solution repeatedly using Whatman no. 4 filter paper to obtain the purple cabbage anthocyanin extract solution. Concentrate the anthocyanin extract solution using a rotary evaporator with the parameters of 40℃ and 60 rpm, and finally concentrate the purple cabbage anthocyanin extract solution to 150 mL to obtain the purple cabbage anthocyanin concentrate solution.

[0125] Step 2, mixing with sodium alginate: Dissolve 2 g of sodium alginate in 98 g of water at 85℃ to obtain a 2 wt% sodium alginate solution, then cool it to room temperature. Take 20 mL of the sodium alginate solution and add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate solution, 16 mg of a gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution), and 16 mg of UiO-66-NH2 (dispersed in 1 mL of water) successively under continuous stirring at 400 rpm. After stirring uniformly, pour the mixture into a disposable plastic petri dish with a diameter of 90 mm, then dry it into a film in a blast drying oven at 35℃. After film formation, carefully remove the film from the petri dish with tweezers, then cut it into a square with a side length of 15 mm to obtain the water product freshness intelligent indication label prepared by the preparation method of the high-stability water product freshness intelligent indication label.

[0126] The difference between this embodiment and Example 1 is that the amount of UiO-66-NH2 used in this embodiment is 16 mg.

[0127] Example 11

[0128] This embodiment provides a preparation method of a high-stability water product freshness intelligent indication label, and it is achieved by the following steps:

[0129] Step 1, extraction of purple cabbage anthocyanins: Clean the purple cabbage leaves and crush them into pieces, then dry them completely in a blast drying oven at 50℃. Grind the dried purple cabbage leaves using a grinder. Take 50 g of the ground purple cabbage leaves and disperse them in 500 mL of 60% ethanol aqueous solution. Stir the mixture continuously at 400 rpm for 4 h in the dark. Then filter the mixture repeatedly using Whatman no. 4 filter paper to obtain the purple cabbage anthocyanin extract. Concentrate the anthocyanin extract using a rotary evaporator at 40℃ and 60 rpm. Finally, concentrate the purple cabbage anthocyanin extract to 150 mL to obtain the purple cabbage anthocyanin concentrate.

[0130] Step 2, mixing with sodium alginate: Dissolve 2 g of sodium alginate in 98 g of water at 85℃ to obtain a 2 wt% sodium alginate solution. Then cool the solution to room temperature. Take 20 mL of the sodium alginate solution and add 200 μL of glycerol, 2 mL of the purple cabbage anthocyanin concentrate, 16 mg of the gentisic acid solution (dissolved in 2 mL of 50% ethanol aqueous solution), and 24 mg of UiO-66-NH2 (dispersed in 1 mL of water) successively under continuous stirring at 400 rpm. After stirring, pour the mixture into a 90 mm diameter plastic petri dish and dry it in a blast drying oven at 35℃ to form a film. Carefully remove the film from the petri dish using tweezers and cut it into a 15 mm*15 mm square to obtain the water product freshness intelligent indicator label prepared by the method of the present embodiment. Before use, immerse the label in 10 mL of 5 wt% calcium chloride solution for 1 min for crosslinking, then remove the label and rinse the surface of the label with clean water.

[0131] The difference between the present embodiment and Example 1 is that the amount of UiO-66-NH2 used in the present embodiment is 24 mg.

[0132] Comparative Example 1

[0133] The present comparative example provides a water product freshness intelligent indicator label, and the difference between the present comparative example and Example 1 is that the present comparative example does not add UiO-66-NH2 and gentisic acid.

[0134] Comparative Example 2

[0135] The present comparative example provides a water product freshness intelligent indicator label, and the difference between the present comparative example and Example 1 is that the present comparative example does not add UiO-66-NH2.

[0136] Comparative Example 3

[0137] This comparative example provides an intelligent indicator label for the freshness of aquatic products, and the only difference between this comparative example and Example 1 is that gentian acid is not added to this comparative example.

[0138] Experimental Section

[0139] For ease of description, the term "label" will be used in the following experimental section instead of "high-stability aquatic product freshness intelligent indicator label" or "aquatic product freshness intelligent indicator label".

[0140] (a) Microscopic morphology testing

[0141] The present invention performed SEM tests on the UiO-66-NH2 and the tag prepared in Example 1, and the results are as follows. Figure 1 As shown. Figure 1 In the image, A is the SEM image of UiO-66-NH2, B is the surface morphology of the tag at the 10 μm scale, C is the cross-sectional morphology of the tag at the 10 μm scale, and D is the cross-sectional morphology of the tag at the 1 μm scale.

[0142] Depend on Figure 1 It can be seen that the particle size of the prepared UiO-66-NH2 is 425±75 nm. When purple cabbage anthocyanins, UiO-66-NH2 and gentian acid are mixed with sodium alginate solution, the label surface is relatively rough, and fine cracks can be observed in the cross-section. In the magnified image, a large amount of UiO-66-NH2 is observed to be stacked, with a regular and complete shape.

[0143] (II) Optimization process of label composition

[0144] 1) Effect of gentic acid addition on label stability at 37℃

[0145] To investigate the effect of different amounts of gentianic acid added on the thermal stability of the labels, Examples 1, 2, 3, 4, 5, 6, and Comparative Example 3 were encapsulated in double-sided adhesive containing a transparent PET release film to simulate real storage conditions. The seven labels were simultaneously placed in a light-protected environment at 37°C. Every two hours, the color parameters (L, a, b) of the labels were recorded using a colorimeter, and the color difference ΔE value was calculated using the following formula: .

[0146] Where L0, a0, and b0 represent the initial brightness, red-green hue, and blue-yellow hue of the label, respectively; and L1, a1, and b represent the brightness, red-green hue, and blue-yellow hue of the label after accelerated testing, respectively.

[0147] It should be noted that it is generally considered that the ΔE value exceeding 5 can be observed by the naked eye. Therefore, all the stability evaluation indexes of the present application are judged by whether ΔE exceeds 5 or not.

[0148] 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.

[0149] The longer the time for different labels to keep ΔE < 5, the better the stability of the label.

[0150] The test results are shown in Figure 2 It can be seen from Figure 2 A and 2B that with the extension of storage time, the ΔE of the label continues to rise, and the thermal stability of the label is continuously improved with the increase of the addition amount of gentisic acid. After 36 hours of placement, the color difference values of the labels prepared according to the preparation method of the examples are all less than 5, while those of the comparative examples exceed 5. After 48 hours of placement, the color difference values of all the labels exceed 5, and the color difference change of the labels prepared according to the preparation method of the examples is significantly lower than that of the comparative examples.

[0151] 2) Effect of gentisic acid addition amount on ammonia response of label

[0152] To explore the effect of different gentisic acid addition amounts on the ammonia response performance of the label, the present application places example 1, example 2, example 3, example 4, example 5, example 6 and comparative example 3 above 20 mL of 14.28 mM ammonia solution, and takes a photo every 1 min with a mobile phone to record the color change of the label. It should be noted that when taking a photo, the camera parameters should be set as: iso speed is 50, aperture value is f / 1.6, and exposure time is 1 / 172 seconds.

[0153] It can be seen from Figure 3 With the addition of gentisic acid content, the color difference ΔE value change of the label after contacting with ammonia is higher than that of comparative example 3, which is because the addition of gentisic acid changes the pH of the microenvironment of the label to the acidic direction, so that the color change is more abundant.

[0154] Based on the above analysis, combined with the stability difference of different labels at 37℃, it is finally determined that the addition amount of gentisic acid is 16 mg.

[0155] 3) Effect of UiO-66-NH2 addition amount on the stability of label at 37℃

[0156] To explore the effect of different amounts of UiO-66-NH2 on the thermal stability of the label, the present application encapsulates Example 1, Example 7, Example 8, Example 9, Example 10, Example 11, and Comparative Example 2 in double-sided tape containing transparent PET release film to simulate real storage conditions. The 7 labels are placed in a 37°C light-free environment at the same time, and the color parameters (L, a, b) of the labels are recorded every 2 hours using a color difference meter and the color difference ΔE value is calculated.

[0157] The test results are shown in Figure 4 . As can be seen from Figure 4 A and 4B, with the extension of storage time, the ΔE of the labels continues to rise, and the ultraviolet stability of the labels continuously improves with the increase of the amount of UiO-66-NH2 added. After 24 hours, the ΔE value of part of the labels exceeds 5, and the stability of Comparative Example 2 is the worst. After 36 hours, the color difference value of all labels exceeds 5, and the color difference change of the labels prepared by the preparation method of the examples is lower than that of the comparative examples.

[0158] 4) Effect of UiO-66-NH2 amount on label ammonia response

[0159] To explore the effect of different amounts of UiO-66-NH2 on the ammonia response performance of the label, the present application places Example 1, Example 7, Example 8, Example 9, Example 10, Example 11, and Comparative Example 2 above 20 mL of 14.28 mM ammonia solution, and takes a photo every 1 min to record the color change of the label using a mobile phone. It should be noted that when taking a photo, the camera parameters should be set as follows: iso speed is 50, aperture value is f / 1.6, and exposure time is 1 / 172 seconds.

[0160] As can be seen from Figure 5 , with the addition of UiO-66-NH2 content, the color difference ΔE value of the label after contacting with ammonia gas shows a trend of first increasing and then decreasing compared with Comparative Example 2. Small dose of UiO-66-NH2 can increase the opacity of the label, thus increasing the color difference value; and with the continuous increase of the amount, on the one hand, the diffusion distance of ammonia gas is prolonged, and on the other hand, the amino and carboxyl groups in the UiO-66-NH2 ligand interact with ammonia gas, thus prolonging the retention time of ammonia gas, and thus the color difference value gradually decreases.

[0161] Based on the above analysis, combined with the stability difference of different labels at 37°C and the ammonia response performance, the amount of UiO-66-NH2 added is finally determined to be 20 mg.

[0162] (II) Storage stability of the label under actual storage conditions

[0163] To study whether the simultaneous addition of UiO-66-NH2 and gentisic acid can play a role in improving the stability of the label, the labels of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 were packaged in double-sided tape containing transparent PET release film, and were placed in room temperature and 4°C light-protected environments, respectively. The color parameters (L, a, b) of the labels were recorded every other day using a color difference meter and the color difference ΔE value was calculated.

[0164] From Figure 6 It can be seen that, in the room temperature light-protected environment, the number of days that the color difference ΔE value does not exceed 5 is used as the evaluation index, and the stability of different labels from low to high is in the order of: Comparative Example 1≈Comparative Example 2<Comparative Example 3<Example 1. The label prepared by the present application has the best stability in the room temperature light-protected environment, reaching 30 days, and has the stability performance conditions for practical application, which is more than twice the stability of the labels prepared by the preparation methods of the comparative examples.

[0165] From Figure 7 It can be seen that, in the 4°C light-protected environment, the ΔE values of all labels prepared according to the examples and comparative examples do not exceed 5 within 2 months, proving that they all have good stability.

[0166] (Three) pH-responsive color change of the label

[0167] The label of Example 1 was immersed in 8 mL of buffer with pH values of 2-12 for 10 min, respectively, and then taken out to observe the discoloration of the label in different pH environments.

[0168] As Figure 8 The discoloration of the label in different buffers. It can be seen that the label presents 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, proving that the label prepared in Example 1 has the ability to reflect pH changes and can be applied to freshness monitoring of ammonia and amine alkaline gas characteristic spoilage gas.

[0169] (Three) Monitoring of the freshness of South American white shrimp

[0170] The label of Example 1 was pasted on the upper part of the inside of the South American white shrimp package, and was stored at 25°C and 4°C, respectively. Figure 9 and Figure 11 The changes of TVB-N of South American white shrimp during different storage periods and the changes of the color difference ΔE values of the corresponding labels are described, Figure 10 and Figure 12 The color changes of the corresponding labels of the shrimp during storage were recorded.

[0171] The application detects the TVB-N value of Penaeus vannamei under different storage conditions during storage, and the test results are shown in Figure 9 Under the storage condition of 25 DEG C, Penaeus vannamei is in fresh state at 0-8 hours; after 8 hours, the TVB-N value of Penaeus vannamei first exceeds 20 mgN / 100 g, and enters the sub-fresh state; and after 12 hours, Penaeus vannamei exceeds the spoilage threshold and is completely spoiled and inedible.

[0172] Figure 10 The color change of the label in the packaging of Penaeus vannamei under the storage environment of 25 DEG C is recorded. Under the storage environment of 25 DEG C, the label appears partial green at the edge after 8 hours, and then the green gradually spreads to the center and deepens, and the label is completely green after 10 hours. Figure 9 The change curve of the label color difference ΔE value with time is also recorded in the application, and we can see that the ΔE value continuously rises with the extension of time, and there is a positive correlation with the change of TVB-N. Therefore, we can draw the following conclusions:

[0173] When the label is purple red, the water product to be detected is in fresh state;

[0174] When the label appears green at the edge, the water product to be detected is in sub-fresh state;

[0175] When the label is completely green and the green gradually deepens, the TVB-N index of the water product to be detected is close to the spoilage threshold, and it is not suitable to be eaten.

[0176] Figure 12 The color change of the label in the packaging of Penaeus vannamei under the storage environment of 25 DEG C is recorded. Under the storage environment of 25 DEG C, the label appears partial green at the edge after 8 hours, and then the green gradually spreads to the center and deepens, and the label is completely green after 10 hours. Figure 11 The change curve of the label color difference ΔE value with time is also recorded in the application, and we can see that the ΔE value continuously rises with the extension of time, and there is a positive correlation with the change of TVB-N. Therefore, we can draw the following conclusions:

[0177] When the label is purple red, the water product to be detected is in fresh state;

[0178] When the label appears purple blue, the water product to be detected is in sub-fresh state;

[0179] When the label is completely green and the green gradually deepens, the TVB-N index of the water product to be detected is close to the spoilage threshold, and it is not suitable to be eaten.

[0180] Figure 13 The correlation between TVB-N and the label color parameter is expressed, and the results prove that the label color change prepared by the application has a strong correlation with the freshness of the white shrimp, and the freshness of the white shrimp can be qualitatively judged according to the color change of the label.

[0181] In summary, the high-stability freshness intelligent indicating label for aquatic products and the preparation method and application thereof utilize the excellent ultraviolet absorption and fluorescence characteristics of UiO-66-NH2, the interaction of the rich functional groups in the ligand and the hydrogen bond of anthocyanin, and the auxiliary color interaction between gentisic acid and anthocyanin, and synergistically improve the storage stability of the anthocyanin indicating label; meanwhile, the alkaline gas such as ammonia and amine generated in the spoilage process of aquatic products is utilized to induce the pH-responsive color change of the label, and the label realizes the visual qualitative discrimination of the freshness of aquatic products.

[0182] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "a specific embodiment" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily mean 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.

[0183] The above only is the preferred embodiment of the present application, and is not used to limit the present application, and the present application can have various changes and variations for the person skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a high-stability intelligent freshness indicating label for aquatic products, characterized in that , specifically comprising the following steps: Step S1: extracting anthocyanins from plant tissues rich in anthocyanins with 55%~65% v / v ethanol solution as the extracting agent at a solid-liquid ratio of 1:10, and leaching for 4 h~6 h to obtain an anthocyanin extract; concentrating the anthocyanin extract to 150 mL~200 mL using a rotary evaporator to obtain an anthocyanin concentrate; Step S2: 197 mg of 2-amino terephthalic acid, 253 mg of zirconium tetrachloride, 27.6 mL of glacial acetic acid were dissolved in 230 mL of N,N-dimethylformamide (DMF), and ultrasonic treatment was performed for 1 hour in an ultrasonic environment, and then transferred to a 300 mL stainless steel autoclave with a polytetrafluoroethylene liner, and reacted in a vacuum oven at 120°C for 24 hours, with a negative pressure of 0.085 mPa-0.090 mPa; after the reaction was completed, the autoclave was taken out and cooled to room temperature in a room temperature environment, and then opened, and the supernatant was removed by centrifugation at 8000 rpm, washed with DMF for 3 times, and then activated with methanol for 24 hours, and the precipitate was activated in a vacuum oven at 60°C after centrifugation, to obtain UiO-66-NH2; and the particle size of the obtained UiO-66-NH2 was 425±75 nm, and the specific surface area was about 1149.77 m 2 / g. Step S3: dispersing sodium alginate powder in water, stirring at 85℃~90℃ until completely dissolved, and then cooling to room temperature to obtain a sodium alginate solution; adding glycerol, the anthocyanin concentrate, gentisic acid and UiO-66-NH2 to the sodium alginate solution in sequence, and stirring uniformly, and then drying in a 35℃ air-drying oven to form a film, thereby obtaining the freshness intelligent indicating label for aquatic products; before use, the label is soaked in a calcium chloride solution for crosslinking, and then taken out and rinsed with clean water to clean the label surface, and then used; the concentration of the sodium alginate solution is 1 wt%-3 wt%, the volume ratio of the anthocyanin concentrate to the sodium alginate solution is 1:10, the mass ratio of gentisic acid to the sodium alginate solution is 4 mg~24 mg:20 mL, the dosage ratio of UiO-66-NH2 to the sodium alginate solution is 4 mg~24 mg:20 mL, the concentration of the calcium chloride solution is 1 wt%~5 wt%, the volume is 10 mL, and the crosslinking time is 1 min; by incorporating UiO-66-NH2 and gentisic acid into the anthocyanin indicating label, the storage stability of the anthocyanin indicating label is improved in cooperation by virtue of the excellent ultraviolet absorption and fluorescence characteristics of UiO-66-NH2 and the hydrogen bonding interaction between UiO-66-NH2 and anthocyanin and the synergistic effect between gentisic acid and anthocyanin.

2. A high-stability water product freshness intelligent indicating label, characterized in that, The high-stability freshness intelligent indicating label for aquatic products is prepared by the preparation method of claim 1.

3. The application of a high-stability water product freshness intelligent indicating label for reflecting the freshness of water products, characterized in that, The high-stability freshness intelligent indicating label for aquatic products is prepared by the preparation method of claim 1, and is specifically applied as follows: 1) The high-stability freshness intelligent indicating label for aquatic products prepared by the preparation method is pasted on the upper part of the packaging of the aquatic product to be detected, and is stored at 0~37℃; 2) The color change of the label is recorded, and the TVB-N change of the sample is combined to realize qualitative discrimination of the freshness of the aquatic product to be detected: According to the obtained TVB-N content, visual qualitative judgment of the freshness grade of the aquatic product is realized: TVB-N<20 mgN / 100 g, the aquatic product to be detected is in a fresh state; TVB-N is 20 mgN / 100 g~30 mgN / 100 g, the aquatic product to be detected is in a sub-fresh state; TVB-N>30 mgN / 100 g, the aquatic product to be detected is in a state of corruption; When the label is purple red, the aquatic product to be detected is in a fresh state; When the edge of the label appears green, the aquatic product to be detected is in a sub-fresh state; When the label turns green all over and the green color gradually deepens, the TVB-N index of the aquatic product to be detected approaches the corruption threshold, and it is not suitable for consumption.

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