Preparation method and application of food freshness indication intelligent label of anthocyanin-based composite nanomaterial

Abstract

The invention discloses a preparation method and application of a food freshness indication intelligent label of an anthocyanin-based composite nano material, and belongs to the technical field of biological polysaccharide application. The composite nano material is prepared by encapsulating anthocyanin through ZIF-8 and is ingeniously combined with the hydrogel, so that the anthocyanin can be better protected, and the structural stability of the anthocyanin can be improved. The combination of the hydrogel and the nano composite material is more beneficial to enrichment of volatile amine gas and improvement of freshness sensing sensitivity. Compared with other indication labels, the freshness indication label provided by the invention is more suitable for being applied in the aspect of freshness monitoring of food, especially aquatic products, is crucial to quality monitoring in an aquatic product supply chain, and also can promote the development of the field of food safety detection.

Description

Technical Field

[0001] The invention relates to a food freshness indicator label, in particular to a preparation method and application of a food freshness indicator intelligent label made of anthocyanin-based composite nanomaterials, and belongs to the field of biopolysaccharides. Background Art

[0002] my country is a major aquatic country, with an annual output of more than 65 million tons of aquatic products, providing 30% of high-quality animal protein for Chinese residents. The healthy development of the aquatic industry not only conforms to the country's new development trend of "solving food and clothing" to "nutrition diversity", but is also an important part of the country's food security and big food concept. However, aquatic products have tender tissues and high water and protein content. They are easily affected by microbial activities during processing and transportation, causing corruption and deterioration. The protein and fat in aquatic products are easily affected by endogenous enzymes and microorganisms, accumulating biogenic amines, which reduces the freshness of aquatic products. Freshness detection technology faces challenges such as low portability, poor perception performance, and difficulty in naked eye identification. Therefore, the development of a freshness detection method that is easy to operate, fast to respond, and intelligently perceived is of great significance for the timely control of the deterioration of aquatic product quality.

[0003] Anthocyanidins are glycoside derivatives, which are substances that can change color with changes in pH. Among the many freshness detection methods, freshness indicator cards using anthocyanins as indicators have quickly become a research hotspot in this field, thanks to their advantages such as wider color changes in a wide pH range. However, most indicator cards with added anthocyanins have the disadvantage of not changing color significantly during freshness monitoring, making them difficult to identify or distinguish with the naked eye. In addition, most of the freshness studies based on anthocyanin color change are to incorporate free anthocyanins into a polymer matrix, and anthocyanins have structural instability, which limits the universality of the label. Therefore, improving the rapid response of anthocyanins and maintaining the structural stability of anthocyanins are the key to improving the sensitivity and universality of freshness indicator labels.

[0004] Metal-Organic Frameworks (MOFs) are a class of three-dimensional porous crystalline materials composed of organic ligands containing nitrogen, oxygen aromatic acids or bases and inorganic metal ions or metal clusters connected by coordination bonds. Zeolitic Imidazolate Framework-8 (ZIF-8) is a MOF with good biocompatibility and low toxicity, and is one of the most stable MOFs structures. It has a large specific surface area and high porosity, and can show excellent gas adsorption performance and high stability. This advantage enables ZIF-8 to show great gas adsorption and enrichment capabilities in an environment where amine gases are produced by the corruption of aquatic products. Therefore, if anthocyanins are encapsulated with ZIF-8, the structural stability of anthocyanins can be enhanced, and the universality of freshness indicator labels in different environments can be improved.

[0005] Porous hydrogels have high free water content and complex and highly organized 3D network structures, good hygroscopicity, and have shown great potential in improving the sensitivity of pH indicators to spoiled gases in aquatic products. At the same time, hydrogels also have the advantages of rapid response, low cost and simple operation, and have been proven to be one of the effective methods for monitoring the freshness of fish. Therefore, multifunctional MOFs can be combined with fast-responsive porous hydrogels to load anthocyanin pH indicators to form an amine-responsive signal amplification system to construct an efficient and sensitive scallop freshness indicator label. When scallops are corrupted and produce amine gases, ZIF-8 can adsorb the gases and enrich them in the porous structure of the hydrogel, causing the pH value in the freshness indicator label to change, resulting in structural changes in anthocyanins and color changes, thereby achieving rapid and sensitive detection of scallop freshness.

[0006] Chinese patent CN118599140A discloses a preparation method and application of a freshness indicator label, which specifically comprises adding polysaccharide to a fish gelatin solution and stirring to dissolve to prepare a hydrogel solution; adding anthocyanin to the hydrogel solution and stirring to obtain anthocyanin hydrogel, and after incubation, obtaining the target product anthocyanin hydrogel freshness indicator label.

[0007] Chinese patent CN115782264A discloses a method for preparing an intelligent visual food freshness indicator label, which specifically comprises preparing a membrane liquid based on pectin, chitosan and beeswax, drying the membrane to obtain a membrane sheet, and then preparing a natural pigment concentrate and starch gel, and then mixing the two to obtain a pigment starch gel; loading the gel into a 3D printing material barrel, and obtaining a single-layer hydrophobic membrane indicator label through 3D printing.

[0008] Chinese patent CN112378906A discloses a method for preparing a meat freshness indicator label based on natural pigments. The specific steps are: dissolving carrageenan powder in deionized water, stirring thoroughly, adding glycerin to obtain a carrageenan solution; dissolving natural pigments (anthocyanidins and curcumin) to obtain an indicator solution; adding the indicator solution to the carrageenan solution, degassing, and pouring into a polystyrene culture dish to obtain a completely gelled indicator film. Summary of the invention

[0009] The purpose of the present invention is to provide a food freshness indicator label and a preparation method and application thereof. The freshness indicator label is particularly suitable for monitoring the freshness of aquatic products.

[0010] In order to solve the above technical problems, the present invention provides a hydrogel composed of a composite nano material composed of anthocyanin and ZIF-8 and sodium alginate and bovine serum albumin.

[0011] Specifically, the present invention provides the use of a nanocomposite material of ZIF-8 encapsulating anthocyanin on a food freshness indicator label, and the use of a hydrogel prepared from sodium alginate and bovine serum albumin on a food freshness indicator label.

[0012] Furthermore, the present invention combines the above-mentioned ZIF-8 encapsulated anthocyanin nanocomposite material with a hydrogel prepared from sodium alginate and bovine serum albumin to prepare a food freshness indicator label.

[0013] ZIF-8 (Zeolitic Imidazolate Framework-8) is a MOFs with good biocompatibility and low toxicity. It is one of the most stable MOFs structures, with a large specific surface area and high porosity, and can show excellent gas adsorption performance and high stability. This advantage enables ZIF-8 to show great gas adsorption and enrichment capabilities in environments where amine gases are produced by food corruption, especially aquatic products.

[0014] The food freshness indicator label provided by the present invention is prepared according to the following method:

[0015] (1) Preparation of ZIF-8 encapsulated anthocyanin nanocomposites:

[0016] A zinc nitrate hexahydrate methanol solution and a 2-methylimidazole methanol solution were prepared, and mixed with anthocyanin in a volume ratio of 1:2 to prepare a composite nanomaterial;

[0017] (2) The solution of step (1) is mixed with a sodium alginate solution and a bovine serum albumin solution, and then cross-linked with a CaCl2 solution to obtain a freshness indicator label.

[0018] The specific method for preparing the freshness indicator label comprises the following steps:

[0019] (1) Dissolve zinc nitrate hexahydrate (1.05 g) in 35 mL of anhydrous methanol and 2-methylimidazole (2.31 g) in 70 mL of anhydrous methanol. Dissolve 20 mg of anthocyanin in the methanol solution of 2-methylimidazole and quickly add the zinc nitrate solution to the 2-methylimidazole solution under magnetic stirring. After stirring for 1 h, the solution becomes a blue suspension, indicating that the nanocomposite material is synthesized.

[0020] (2) Prepare a 2% sodium alginate solution and a 2% BSA solution. Dissolve the nanocomposite obtained in step (1) in 10 mL of 2% bovine serum albumin solution, and then mix with 10 mL of 2% sodium alginate solution. Stir for 1 h under magnetic stirring, and then ultrasonicate for 30 min. Add the gel solution to a customized mold, freeze at -20 °C for 1 h, and then thaw at room temperature for 30 min. Repeat the freeze-thaw cycle 3 times. Finally, cross-link with 5% CaCl2 solution for 10 min to obtain the final freshness indicator label.

[0021] Preferably, the anthocyanins in the above step (1) are derived from blueberries.

[0022] Furthermore, the 2% sodium alginate solution prepared in step (2) above needs to be heated and dissolved at 60° C. Sodium alginate tends to form lumps when dissolved in water, and hot water helps to accelerate the dissolution.

[0023] Furthermore, the amount of the nanocomposite material added in the above step (2) is 0.3 g.

[0024] Furthermore, in the above step (2), the nanocomposite material needs to be ultrasonically treated for 5 min when dissolved in a 2% bovine serum albumin solution. The nanocomposite material is prone to agglomeration, and ultrasonic treatment can make it dispersed evenly.

[0025] Beneficial effects of the present invention:

[0026] The invention provides a scallop freshness indicator label, aiming to solve the problems of poor structural stability of anthocyanin as a freshness indicator and low sensitivity of a freshness indicator label based on anthocyanin.

[0027] The present invention combines ZIF-8 and anthocyanin for the first time to prepare a freshness indicator label. The freshness indicator label uses ZIF-8 to encapsulate anthocyanin, thereby improving the stability of anthocyanin, and uses composite nanomaterials to improve the response sensitivity to volatile amine gases.

[0028] The present invention prepares a scallop freshness indicator label, and proves the advantages of the freshness indicator label in terms of stability and sensitivity. The freshness indicator label is applied to the monitoring of the freshness of scallops. By measuring the changes in TVB-N of the scallops during storage and the R, G, and B values ​​of the corresponding freshness indicator label, it can be found that the freshness indicator label can indicate the freshness of the scallops in real time. The practicality of the label is verified by the corresponding relationship between the changes in its R, G, and B values ​​and the corruption of the scallops, and the freshness indicator label is expected to be applied to the freshness monitoring of other aquatic products. This is crucial for quality monitoring in the aquatic product supply chain, and will also promote the development of the field of food safety testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the release index of anthocyanins in ethanol solution with and without MOFs added to the freshness indicator label. The results show that the addition of MOFs can significantly improve the stability of anthocyanins.

[0030] Figure 2 is the color difference of the freshness indicator labels prepared with and without MOFs in ammonia (C d ). The results show that adding MOFs can significantly improve the response sensitivity of the tag.

[0031] Figure 3 is the color difference between the freshness indicator label with MOFs added and MOFs acid hydrolyzed in ammonia (C d ). The results show that adding MOFs can significantly improve the response sensitivity of the tag.

[0032] Figure 4 It is the change of TVB-N value during storage of scallops at 4℃.

[0033] Figure 5 The freshness indicator label monitors the corresponding R, G, and B values ​​of scallops during storage at 4°C. The results show that the freshness indicator label can indicate the freshness of scallops in real time.

[0034] Figure 6 It is a freshness indicator label monitoring the physical picture of scallops during storage at 4°C and the physical picture of scallops. DETAILED DESCRIPTION

[0035] Example 1

[0036] This embodiment provides an implementation process of a freshness indicator label, and the specific technical solution steps are as follows:

[0037] (1) Weigh 1.05 g of zinc nitrate hexahydrate into a 250 mL beaker and dissolve it in 35 mL of anhydrous methanol. Weigh 2.31 g of 2-methylimidazole into a 250 mL beaker and dissolve it in 70 mL of anhydrous methanol. Weigh 20 mg of anthocyanin and dissolve it in the methanol solution of 2-methylimidazole. Quickly add the zinc nitrate solution to the 2-methylimidazole solution under magnetic stirring, then stir for 1 h. Centrifuge at 10,000 rpm for 15 min, collect the product and wash it with methanol three times. Dry the blue product in an oven at 40 °C for 24 h to obtain a nanocomposite material.

[0038] (2) Weigh 2 g of sodium alginate into a 250 mL beaker and dissolve it in 100 mL of ultrapure water. Weigh 2 g of bovine serum albumin into a 250 mL beaker and dissolve it in 100 mL of ultrapure water. Take 10 mL of 2% bovine serum albumin solution, then add the nanocomposite obtained in step (1) and ultrasonicate for 5 min.

[0039] (3) Take 10 mL of 2% sodium alginate solution and mix it with the solution obtained in step (2), stir it under magnetic stirring for 1 h, and then ultrasonically treat it for 30 min.

[0040] (4) The solution obtained in step (3) was added to a customized mold, frozen at -20°C for 1 h, and then thawed at room temperature for 30 min. This freeze-thaw cycle was repeated 3 times. Finally, the final freshness indicator label was prepared by cross-linking with 5% CaCl2 solution for 10 min.

[0041] Example 2

[0042] This embodiment provides an implementation process of a freshness indicator label without adding MOFs, and the specific technical solution steps are as follows:

[0043] (1) Weigh 2 g of sodium alginate into a 250 mL beaker and dissolve it in 100 mL of ultrapure water. Weigh 2 g of bovine serum albumin into a 250 mL beaker and dissolve it in 100 mL of ultrapure water. Take 10 mL of 2% bovine serum albumin solution, then add 20 mg of anthocyanidins and ultrasonicate for 5 min.

[0044] (2) Take 10 mL of 2% sodium alginate solution and mix it with the solution obtained in step (1), stir it under magnetic stirring for 1 h, and then ultrasonically treat it for 30 min.

[0045] (3) The solution obtained in step (2) was added to a customized mold, frozen at -20°C for 1 h, and then thawed at room temperature for 30 min. This freeze-thaw cycle was repeated 3 times. Finally, the final freshness indicator label was prepared by cross-linking with 5% CaCl2 solution for 10 min.

[0046] Example 3 Experimental comparison results of freshness indicator labels prepared in Example 1 and Example 2

[0047] The relevant experiments of this embodiment are conducted based on the freshness indicator labels prepared in Embodiments 1 and 2, specifically:

[0048] 1. Proof of improved stability of anthocyanins. The specific experimental process and experimental conclusions are as follows:

[0049] The freshness indicator labels with and without MOFs were dissolved in 95% ethanol solution, and the release index of anthocyanins in the labels with and without MOFs was evaluated to prove the improvement of anthocyanin stability by MOFs. 1.0 g of freshness indicator label was weighed, dissolved in 30 mL of 95% ethanol solution, and then incubated in the dark for 0 to 240 minutes. The absorbance of the supernatant at 517 nm was measured at 5, 10, 40, 70, 100, 130, 160, 190, 210, and 240 minutes, respectively. The calculation equation for the release index is as follows:

[0050]

[0051] Where M represents the amount of anthocyanins released from the tag at a certain time point, M ∞ Represents the total amount of anthocyanins released at equilibrium.

[0052] The results show that the release of anthocyanins in the freshness indicator label with MOFs follows the zero-order kinetic model, and the fitting equation is y = 3.1844*10 -4 x+0.8214,R 2 =0.9435. The release of anthocyanins in the freshness indicator label without adding MOFs follows the Ritger and Peppas model, and the fitting equation is y = 0.8457x 0.0284 , R 2 =0.9837, indicating that Fickian diffusion is the main diffusion mechanism, which means that anthocyanins can easily migrate from the freshness indicator label without MOFs. Therefore, the addition of MOFs can significantly improve the sensitivity of the freshness indicator label. The specific results are shown in Figure 1 and Figure 2 . Figure 1 is the release index of anthocyanins in ethanol solution of freshness indicator labels prepared with and without MOFs. Figure 1The results showed that the addition of MOFs can significantly improve the stability of anthocyanins. Figure 2 is the color difference of the freshness indicator labels prepared with and without MOFs in ammonia (C d ). Figure 2 The results show that the addition of MOFs can significantly improve the response sensitivity of the tag.

[0053] 2. Proof of improved sensitivity of freshness indicator labels. The specific experimental process and experimental conclusions are as follows:

[0054] Freshness indicator labels with and without MOFs were attached to the top of a cylindrical closed space with a diameter of 22 mm and a height of 22 mm, and 1 mL of 5000 mM ammonia water was added to the bottom to simulate food spoilage. The color difference (C d Next, the freshness indicator label with MOFs was placed in acetic acid for 30 minutes and then attached to the top of a cylindrical closed space with a diameter of 22 mm and a height of 22 mm. 1 mL of 5000 mM ammonia was added to the bottom to simulate food spoilage. The color difference (C d ). Color difference (C d ) is calculated as follows:

[0055]

[0056]

[0057] The R, G, and B values ​​of the freshness indicator label are extracted by taking an image with a smartphone, where x represents the number of days of storage and R x , G x and B x Represents the color characteristic value of the freshness indicator label at different storage times, R b , G b and B b Indicates the color characteristic value of the background when there is no freshness indicator label.

[0058] The results showed that a large number of holes appeared on the surface of the freshness indicator label after acetic acid treatment, which means that MOFs have disintegrated and only anthocyanins are left in the system. By comparison, it was found that the color difference (C d ) is significantly higher, indicating that MOFs can significantly improve the sensitivity of freshness indicator labels. Figure 3 , Figure 3 is the color difference between the freshness indicator label with MOFs added and MOFs acid hydrolyzed in ammonia (C d ). Figure 3The results show that adding MOFs can significantly improve the response sensitivity of the tag.

[0059] Example 4 The experimental results of the freshness indicator label prepared in Example 1 were specifically studied on scallops.

[0060] The relevant experiments of this embodiment are conducted based on the freshness indicator label prepared in Example 1, specifically:

[0061] 1. The corruption of scallops during storage and the monitoring effect of freshness indicator labels. The specific experimental process and experimental conclusions are as follows:

[0062] Fresh scallops weighing 1.65 kg were placed in a transparent plastic sealed box (287 mm × 186 mm × 105 mm), and a freshness indicator label (16 mm) was attached tightly to the inner top of the sealed box. The color change of the freshness indicator label was recorded every 12 h and the color difference (C d ). At the same time, the TVB-N value of scallops was determined. The TVB-N value was determined in accordance with GB 5009.228-2016 National Food Safety Standard Determination of Volatile Basic Nitrogen in Foods, and three parallel experiments were performed.

[0063] For specific results, see Figure 4-Figure 6 The results showed that when the TVB-N value was <10 mg / 100g, the scallops were fresh, when it was between 10 mg / 100g-15 mg / 100g, the scallops were considered not fresh, when it was between 15 mg / 100g-30 mg / 100g, the scallops were judged to be slightly corrupt, and when the TVB-N value was >30 mg / 100g, the scallops were deteriorated. The R, G, and B values ​​of the freshness indicator label increased with the increase of TVB-N value, and the linear equation of R value was y=1.2516x+51.4096 (R 2 =0.9787), the linear equation of G value is y=1.3899x+70.4463 (R 2 =0.9908), the linear equation of B value is y=1.2625x+81.3922 (R 2 =0.9832). Therefore, the freshness of scallops can be reflected by measuring the R, G, and B values ​​of the freshness indicator label, and the practicality of the freshness indicator label is verified.

Claims

1. Application of ZIF-8 encapsulated anthocyanin nanocomposites in food freshness indicator labels.

2. Application of hydrogel prepared by sodium alginate and bovine serum albumin in food freshness indicator labels.

3. Application of ZIF-8 encapsulated anthocyanin nanocomposites and hydrogels prepared from sodium alginate and bovine serum albumin in the preparation of food freshness indicator labels.

4. The use according to claim 3, characterized in that: The food is aquatic product.

5. A food freshness indicator label, characterized in that: It includes a composite nanomaterial composed of anthocyanin and ZIF-8 and a hydrogel composed of sodium alginate and bovine serum albumin.

6. A method for preparing a food freshness indicator label, characterized in that: The following steps are involved: (1) Preparation of ZIF-8 encapsulated anthocyanin nanocomposites: A zinc nitrate hexahydrate methanol solution and a 2-methylimidazole methanol solution were prepared, and mixed with anthocyanin in a volume ratio of 1:2 to prepare a composite nanomaterial; (2) The solution of step (1) is mixed with a sodium alginate solution and a bovine serum albumin solution, and then cross-linked with a CaCl2 solution to obtain a freshness indicator label.

7. The method for preparing a food freshness indicator label according to claim 6, characterized in that: The specific steps are as follows: (1) Dissolve 1.05 g zinc nitrate hexahydrate in 35 mL anhydrous methanol and 2.31 g 2-methylimidazole in 70 mL anhydrous methanol; dissolve 20 mg anthocyanin in the methanol solution of 2-methylimidazole, and quickly add the zinc nitrate solution to the 2-methylimidazole solution under magnetic stirring; after stirring for 1 h, the solution becomes a blue suspension, indicating that the nanocomposite material is synthesized; (2) Prepare a 2% sodium alginate solution and a 2% bovine serum albumin solution. Dissolve the nanocomposite obtained in step (1) in 10 mL of 2% bovine serum albumin solution, and then mix with 10 mL of 2% sodium alginate solution. Stir for 1 h under magnetic stirring, and then ultrasonicate for 30 min. Add the gel solution into a customized mold, freeze at -20°C for 1 h, and then thaw at room temperature for 30 min. Repeat the freeze-thaw cycle for 3 times. Finally, cross-link with 5% CaCl2 solution for 10 min to obtain the final freshness indicator label.

8. Use of the food freshness indicator label according to any one of the above claims for indicating the freshness of food.

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