Co-MOF-coated CEO intelligent active packaging film and preparation method and application thereof

Abstract

The invention belongs to the technical field of food packaging materials, and particularly relates to a Co-MOF (at) CEO intelligent active packaging film and a preparation method and application thereof. Cinnamon essential oil is embedded in a cobalt-based metal organic framework to form composite nanoparticles with antibacterial and ammonia-sensitive functions, then the composite nanoparticles and potato starch are mixed, a film is formed through a solution casting method, and the intelligent active packaging film is obtained. According to the preparation method of the intelligent active packaging film provided by the invention, the water solubility of the potato starch packaging film is reduced, the prepared intelligent active packaging film has good antibacterial, antioxidant activity, mechanical and barrier properties and good sensitivity to ammonia, the freshness of meat can be monitored in real time only through the color change of the packaging film, and the method is suitable for large-scale popularization and application. The fresh-keeping and freshness visual monitoring of food such as fish meat and the like can be realized at the same time, and the method has a good application prospect in the field of intelligent active packaging.

Description

Technical Field

[0001] This invention belongs to the field of food packaging materials technology, specifically relating to a Co-MOF@CEO intelligent active packaging film, its preparation method, and its application. Background Technology

[0002] With the simultaneous improvement of economic levels and food safety awareness, the quality and safety of aquatic products have become a key issue of social concern. Aquatic products are rich in protein and various bioactive substances, occupying an important position in the dietary nutritional structure. However, aquatic products are extremely susceptible to spoilage during storage and distribution. Fish, as a typical high-protein food, has tissues rich in endogenous enzymes and microbial flora, which can continue to multiply and metabolize even under cold chain conditions, accelerating tissue degradation. At the same time, temperature fluctuations during transportation further exacerbate the risk of microbial proliferation, leading to quality deterioration, loss of nutritional value, and potentially causing significant food safety hazards. Therefore, establishing a rapid and reliable fish freshness assessment system is of great practical significance for protecting consumer health and maintaining the economic benefits of the industry.

[0003] Currently, conventional methods for detecting fish freshness mainly include sensory evaluation, microbiological testing, and chemical index analysis. However, these methods are generally cumbersome, time-consuming, highly dependent on professional personnel, and prone to human error, making it difficult to meet the urgent need for real-time, non-destructive testing in the modern food supply chain. In recent years, metal-organic frameworks (MOFs) have attracted widespread attention due to their tunable structure and function. Among them, cobalt-based metal-organic frameworks (Co-MOFs) not only possess excellent antibacterial properties, but their Co-O and Co-N groups can also interact with volatile ammonia compounds, exhibiting high sensitivity to ammonia gas, thus showing potential applications in smart packaging and freshness indication. On the other hand, cinnamon oil (CEO), as a natural functional extract, has good antibacterial and antioxidant properties, which can effectively enhance the bioactivity of packaging materials. Although potato starch (PS) has good film-forming properties, pure starch films are highly hydrophilic and lack sufficient barrier properties, limiting their practical application in food packaging. Although some studies have introduced active ingredients into starch matrices to improve membrane performance, there is still a lack of packaging materials that can simultaneously achieve preservation and freshness monitoring. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a Co-MOF@CEO intelligent active packaging film, its preparation method, and its application. This packaging film possesses excellent antibacterial and antioxidant activity, as well as mechanical and barrier properties. It exhibits good sensitivity to ammonia and can monitor the freshness of meat in real time through color changes, thus achieving the integration of food preservation and freshness monitoring for fish and other foods. It has promising application prospects in the field of intelligent active packaging.

[0005] To achieve the above objectives, the specific technical solution of the present invention is as follows: The first aspect of the present invention provides a Co-MOF@CEO smart active packaging film, the smart active packaging film comprising a film-forming matrix and composite nanoparticles dispersed in the film-forming matrix; the film-forming matrix is ​​potato starch; the composite nanoparticles are formed by encapsulating cinnamon essential oil in a cobalt-based metal-organic framework.

[0006] A second aspect of this invention provides a method for preparing the Co-MOF@CEO smart active packaging film described above, comprising the following steps: Cobalt-based metal-organic frameworks and cinnamon essential oil were placed in an organic solvent environment, so that the cobalt-based metal-organic frameworks were dispersed in an organic solvent solution in which cinnamon essential oil was dissolved, and the cinnamon essential oil was embedded in the pores of the cobalt-based metal-organic frameworks. After evaporating the organic solvent, composite nanoparticles were obtained. The composite nanoparticles were dissolved in water, and plasticizer and potato starch were added. After stirring, a starch film-forming solution was obtained. After the starch film-forming solution is solidified and molded, the Co-MOF@CEO smart active packaging film is obtained.

[0007] The Co-O / Co-N groups of the cobalt-based metal-organic framework interact with volatile ammonia, exhibiting good sensitivity to ammonia. Adding safe and non-toxic cinnamon essential oil to potato starch, which serves as the film-forming matrix, endows it with antibacterial and antioxidant activities, extending the antibacterial efficacy of the antibacterial film. Modifying potato starch with composite nanoparticles improves the performance of the potato starch film, while also giving it ammonia-sensitive and antibacterial properties.

[0008] Furthermore, the organic solvent is chloroform or ethanol.

[0009] Furthermore, the organic solvent is chloroform. Chloroform has a low boiling point and evaporates rapidly and completely under normal pressure and moderate heating. This is crucial for the subsequent formation of the thin film; chloroform does not chemically react with the cobalt-based metal-organic framework and cinnamon oil, thus maintaining the stability of the components.

[0010] Furthermore, the dispersion is ultrasonic dispersion, the dispersion temperature is 20℃~30℃, and the dispersion time is 25min~35min.

[0011] Furthermore, the cobalt-based metal-organic framework is obtained by reacting a cobalt salt and trimesic acid as an organic ligand via a solvothermal method; the molar ratio of the cobalt salt to trimesic acid is 14~15:9~10.

[0012] Furthermore, the temperature of the solvothermal reaction is 195℃~205℃, and the reaction time is 15h~16h.

[0013] Furthermore, the solvothermal reaction temperature is 120°C and the reaction time is 15 hours.

[0014] Furthermore, the cobalt-based metal-organic framework is prepared by dissolving cobalt nitrate hexahydrate and trimesic acid in an ethanol solution, and then reacting them in a closed reaction vessel at 120°C for 15 hours to obtain the cobalt-based metal-organic framework.

[0015] Furthermore, the volume ratio of ethanol to water in the ethanol solution is 1:1.

[0016] Furthermore, the ratio of the cobalt-based metal-organic framework, cinnamon oil, and organic solvent is 0.9g~1.0g:3.9mL~4.0mL:9mL~10mL.

[0017] Furthermore, the ratio of the cobalt-based metal-organic framework, cinnamon oil, and organic solvent is 1g:4mL:10mL.

[0018] Furthermore, the plasticizer is glycerol; the mass ratio of glycerol, potato starch and composite nanoparticles is 0.8:2:0.025~0.1.

[0019] Furthermore, the composite nanoparticles dissolve in water at a temperature of 34°C to 35°C; the curing temperature is 44°C to 45°C.

[0020] Furthermore, the composite nanoparticles dissolve in water at a temperature of 35°C; the curing temperature is 45°C.

[0021] A third aspect of the present invention provides an application of the Co-MOF@CEO intelligent active packaging film in monitoring the freshness of food, wherein the food is fresh meat, seafood products or processed meat products.

[0022] The fourth aspect of the present invention provides an application of the Co-MOF@CEO intelligent active packaging film as a food preservation film, wherein the food preservation film has antibacterial activity or antioxidant activity.

[0023] Furthermore, the antibacterial effect is to inhibit Staphylococcus aureus and / or Escherichia coli.

[0024] Furthermore, the food is fresh meat, seafood products, or processed meat products.

[0025] The Co-O and Co-N groups in cobalt-based metal-organic frameworks interact with volatile ammonia, exhibiting good sensitivity to ammonia. Therefore, Co-MOF@CEO smart active packaging films can be used as intelligent packaging materials for detecting the freshness of fresh meat, seafood, or processed meat products. Cinnamon essential oil is a natural functional essential oil with antibacterial and antioxidant properties. Potato starch (PS) has good film-forming ability, but pure PS easily absorbs moisture, which is not conducive to its application in food packaging. However, incorporating antibacterial and antioxidant compounds into the film-forming matrix can significantly improve the gas barrier properties of hydrophilic films. Therefore, composite nanoparticles can be added to it, which not only significantly improves the tensile strength, UV shielding ability, and gas barrier ability of the film, but also forms a smart active packaging film with good antibacterial and antioxidant activity. Most importantly, it can visualize and monitor the freshness of fish in real time through color changes.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a Co-MOF@CEO intelligent active packaging film, its preparation method, and its application. Cinnamon essential oil is embedded in a cobalt-based metal-organic framework to form composite nanoparticles with both antibacterial and ammonia-sensitive functions. These composite nanoparticles are then mixed with potato starch and formed into a film using a solution casting method, resulting in an intelligent active packaging film. This packaging film exhibits excellent antibacterial and antioxidant activity, mechanical and barrier properties, and good sensitivity to ammonia. It can monitor the freshness of meat in real time through color changes, achieving integrated preservation and freshness monitoring of foods such as fish and meat. It has promising application prospects in the field of intelligent active packaging. Details are as follows:

[0027] (1) Intelligent response mechanism: The ammonia sensitivity of cobalt-based metal-organic framework (indicating ammonia produced by fish spoilage through color change) and the antibacterial function of cinnamon essential oil are integrated into a single packaging system to achieve an intelligent packaging upgrade from "passive preservation" to "active monitoring + active antibacterial".

[0028] (2) Material composite technology: Compared with traditional technology, the composite nanoparticles formed in the preparation of this invention are composite nanomaterials formed by introducing cinnamon essential oil molecules into the porous structure of cobalt-based metal-organic framework through an encapsulation method, which solves the problems of easy migration and poor stability of traditional antibacterial agents.

[0029] (3) Ammonia response color change and antibacterial function produce synergistic effect: When the ammonia concentration is detected to increase, the antibacterial activity of cinnamon essential oil is simultaneously triggered, and a three-in-one preservation system of "monitoring-early warning-antibacterial" is constructed.

[0030] (4) Application scenarios: Specifically designed for the preservation needs of high-protein aquatic products (such as shrimp and salmon), it solves the pain point that existing packaging cannot simultaneously achieve freshness monitoring and long-term antibacterial effect. The transparency of the packaging film is adjustable, making it easy for consumers to intuitively judge the state of the food.

[0031] (5) Preparation process: Compared with the traditional preparation process, the present invention utilizes low temperature film formation technology to avoid the damage of active ingredients to high temperature processing, and adopts solution blending-self-assembly process to achieve molecular-level uniform dispersion of cobalt-based metal-organic framework and cinnamon essential oil.

[0032] In summary, the Co-MOF@CEO / PS smart active packaging film provided by this invention has significant advantages in terms of ammonia sensitivity, long-lasting antibacterial effect, and overall packaging performance, and is particularly suitable for packaging high-value aquatic products that require real-time monitoring and continuous freshness. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 The color response of the smart active packaging film under an ammonia atmosphere is shown. A, B, C, D, and E represent samples of pure PS film, 0.05% Co-MOF@CEO / PS composite film, 0.1% Co-MOF@CEO / PS composite film, 0.15% Co-MOF@CEO / PS composite film, and 0.2% Co-MOF@CEO / PS composite film, respectively; 0 min, 5 min, 10 min, 20 min, 40 min, 60 min, 120 min, and 180 min represent the duration of exposure to volatile ammonia. L* Indicates brightness. b* Indicates yellowness. ΔE The letter a indicates color difference; lowercase letters a, b, c, d, e, f, g, h indicate significant differences between groups.

[0035] Figure 2 The structural characterization results are for Co-MOF and Co-MOF@CEO. Figure 2 In the image, A represents the SEM image of Co-MOF. Figure 2 B in the figure is the SEM image of Co-MOF@CEO. Figure 2 C in the diagram represents the reaction of Co-MOF with ammonia. Figure 2 In the diagram, D represents the XRD patterns of Co-MOF, Co-MOF@CEO, and Co-MOF@CEO after ammonia treatment. Figure 2 E in the figure represents the FTIR spectra of Co-MOF, Co-MOF@CEO, and Co-MOF@CEO after ammonia treatment.

[0036] Figure 3 The antibacterial effect of Co-MOF and Co-MOF@CEO is shown in the figure. Figure 3 The top row of column A shows the antibacterial effects of Co-MOF and Co-MOF@CEO against Staphylococcus aureus. Figure 3 The bottom row of A in the diagram shows the antibacterial effects of Co-MOF and Co-MOF@CEO on Escherichia coli. Figure 3 B in the figure represents the ammonia sensitivity diagram of Co-MOF@CEO.

[0037] Figure 4 Here is a surface SEM image of the Co-MOF@CEO / PS composite film. Figure 4 In the image, 'a' represents the SEM image of a pure PS film. Figure 4 In the image, b represents the SEM image of the 0.05% Co-MOF@CEO / PS composite membrane. Figure 4 In the image, c represents the SEM image of the 0.1% Co-MOF@CEO / PS composite membrane. Figure 4 The image shows the SEM image of the 0.15% Co-MOF@CEO / PS composite membrane, where d represents 0.15%. Figure 4 The 'e' in the image represents the SEM image of the 0.2% Co-MOF@CEO / PS composite membrane.

[0038] Figure 5 The FTIR and XRD spectra of the Co-MOF@CEO smart active packaging film are shown. Figure 5 In the image, A represents the FTIR spectrum. Figure 5 B in the image represents the XRD pattern. Figure 5 Curves (a) for both A and B are PS films. Figure 5 Curves (b) for both A and B are 0.05% Co-MOF@CEO intelligent active packaging film. Figure 5 Curves (c) for both A and B are 0.1% Co-MOF@CEO / PS composite membranes. Figure 5 Curves (d) for both A and B are 0.15% Co-MOF@CEO / PS composite membranes. Figure 5 Curve (e) for both A and B is 0.2% Co-MOF@CEO / PS composite membrane.

[0039] Figure 6 The tensile strength (TS) and elongation at break (EB) of the Co-MOF@CEO smart active packaging film are measured. Figure 6 In the figure, 'a' represents the TS and EB diagrams of a pure PS film. Figure 6In the figure, b represents the TS and EB values ​​of the 0.05% Co-MOF@CEO smart active packaging film. Figure 6 The TS and EB graphs for c in the figure represent the 0.1% Co-MOF@CEO smart active packaging film. Figure 6 The TS and EB graphs for d represent the 0.15% Co-MOF@CEO smart active packaging film. Figure 6 The TS and EB figures for 0.2% Co-MOF@CEO smart active packaging film are shown in Figure 1.

[0040] Figure 7 The image shows the optical properties of the Co-MOF@CEO / PS composite film. Figure 7 In the image, A represents a photograph of the Co-MOF@CEO / PS film. The black dotted lines separate different samples, and the background paper with black English text is used to highlight the film's light transmittance. Figure 7 In the diagram, B represents the transmittance of the composite film. Curve (a) represents the pure PS film, curve (b) represents the 0.05% Co-MOF@CEO / PS composite film, curve (c) represents the 0.1% Co-MOF@CEO / PS composite film, curve (d) represents the 0.15% Co-MOF@CEO / PS composite film, and curve (e) represents the 0.2% Co-MOF@CEO / PS composite film.

[0041] Figure 8 The functional performance diagram of the Co-MOF@CEO / PS composite membrane. Figure 8 Figure A shows the antibacterial effect of the composite membrane against Escherichia coli and Staphylococcus aureus. Figure 8 In the figure, B represents the antioxidant effect of the composite membrane. Figure 8 In the figure, C represents the plate experiment diagram of the composite membrane against Escherichia coli and Staphylococcus aureus.

[0042] Figure 9 This image shows the application effect of Co-MOF@CEO / PS composite film on the preservation of grass carp. Figure 9 In Figure A, the color indicator diagram of the Co-MOF@CEO / PS composite film on grass carp is shown. The top row of images, from left to right, shows fresh grass carp stored for 0h, 12h, 24h, and 36h, along with the colors of different Co-MOF@CEO / PS composite films. The bottom row of images, from left to right, shows four groups of Co-MOF@CEO / PS composite films at storage times of 0h, 12h, 24h, and 36h. Within each group, from left to right, the films are pure PS film (0%), 0.05% Co-MOF@CEO / PS composite film, 0.1% Co-MOF@CEO / PS composite film, 0.15% Co-MOF@CEO / PS composite film, and 0.2% Co-MOF@CEO / PS composite film. Figure 9B in the text refers to the composite film used during grass carp storage. ΔE Value map, ΔE The sensitivity of the membrane to the visual response of grass carp freshness. Figure 9 In the figure, C represents the change in TVB-N (volatile basic nitrogen) content during the storage of grass carp. The lowercase letters a, b, c, and d in the figure indicate that there are significant differences between groups. Detailed Implementation

[0043] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods, and the materials and reagents used in the following embodiments are commercially available unless otherwise specified.

[0044] Example 1: A Co-MOF@CEO smart active packaging film, prepared by the following steps: S1: Dissolve 15 mmol of cobalt nitrate hexahydrate and 10 mmol of trimesic acid in 120 mL of a mixed solution (the mixed solution was obtained by mixing deionized water and anhydrous ethanol solution in a 1:1 volume ratio), then transfer the solution to a reaction vessel, heat at 120 °C for 18 h, remove the reaction vessel, and wash the product multiple times with anhydrous ethanol and deionized water to remove unreacted precursors and residual solvents. Dry the precipitate at 65 °C to obtain Co-MOF nanoparticles. S2: Add 4 mL of CEO and 1 g of Co-MOF to 10 mL of chloroform, then sonicate at 25 °C for 30 min to mix CEO, chloroform and Co-MOF evenly, and then place in an air drying oven at 40 °C to completely evaporate the solvent to obtain composite nanoparticles with antibacterial effect, labeled as Co-MOF@CEO. Step 3: Disperse 0.075g of Co-MOF@CEO in 50mL of ultrapure water and incubate in a magnetically stirred water bath at 35℃ for 30min to obtain a mixed dispersion. Step 4: Add 0.8g glycerin and 2g PS to the mixed dispersion, and stir thoroughly in an 80℃ magnetically stirred water bath to obtain a starch film-forming solution. Apply the starch film-forming solution evenly to a 12cm diameter film. After drying in a 45°C air drying oven on a 12 cm plastic plate, the film is peeled off to obtain the Co-MOF@CEO intelligent active packaging film, namely the 0.15% CoMOF@CEO / PS composite film.

[0045] Example 2: A Co-MOF@CEO smart active packaging film, prepared by the following steps: S1: Dissolve 15 mmol of cobalt nitrate hexahydrate and 10 mmol of trimesic acid in 120 mL of a mixed solution (the mixed solution was obtained by mixing deionized water and anhydrous ethanol solution in a 1:1 volume ratio), then transfer the solution to a reaction vessel, heat at 120 °C for 18 h, remove the reaction vessel, and wash the product multiple times with anhydrous ethanol and deionized water to remove unreacted precursors and residual solvents. Dry the precipitate at 65 °C to obtain Co-MOF nanoparticles. S2: Add 4 mL of CEO and 1 g of Co-MOF to 10 mL of chloroform, then sonicate at 25 °C for 30 min to mix CEO, chloroform and Co-MOF evenly, and then place in an air drying oven at 40 °C to completely evaporate the solvent to obtain the composite nanoparticle Co-MOF@CEO with antibacterial effect. Step 3: Disperse 0.05g of Co-MOF@CEO in 50mL of ultrapure water and stir in a magnetically stirred water bath at 35℃ for 30 min to obtain a mixed dispersion. Step 4: Add 0.8g glycerin and 2g PS to the mixed dispersion, and stir thoroughly in an 80℃ magnetically stirred water bath to obtain a starch film-forming solution. Apply the starch film-forming solution evenly to a 12cm diameter film. After drying in a 45°C air drying oven on a 12 cm plastic plate, the film is peeled off to obtain the Co-MOF@CEO intelligent active packaging film, namely the 0.1% Co-MOF@CEO / PS composite film.

[0046] Example 3: A Co-MOF@CEO smart active packaging film, prepared by the following steps: S1: Dissolve 15 mmol of cobalt nitrate hexahydrate and 10 mmol of trimesic acid in 120 mL of a mixed solution (the mixed solution was obtained by mixing deionized water and anhydrous ethanol solution in a 1:1 volume ratio), then transfer the solution to a reaction vessel, heat at 120 °C for 18 h, remove the reaction vessel, and wash the product multiple times with anhydrous ethanol and deionized water to remove unreacted precursors and residual solvents. Dry the precipitate at 65 °C to obtain Co-MOF nanoparticles. S2: Add 4 mL of CEO and 1 g of Co-MOF to 10 mL of chloroform, then sonicate at 25 °C for 30 min to mix CEO, chloroform and Co-MOF evenly, and then place in an air drying oven at 40 °C to completely evaporate the solvent to obtain the composite nanoparticle Co-MOF@CEO with antibacterial effect. Step 3: Disperse 0.025% Co-MOF@CEO in 50mL of ultrapure water and stir in a magnetically stirred water bath at 35℃ for 30 min to obtain a mixed dispersion; Step 4: Add 0.8g glycerin and 2g PS to the mixed dispersion, and stir thoroughly in an 80℃ magnetically stirred water bath to obtain a starch film-forming solution. Apply the starch film-forming solution evenly to a 12cm diameter film. After drying in a 45°C air drying oven on a 12 cm plastic plate, the film is peeled off to obtain the Co-MOF@CEO intelligent active packaging film, namely the 0.05% Co-MOF@CEO / PS composite film.

[0047] Example 4: A Co-MOF@CEO smart active packaging film, prepared by the following steps: S1: Dissolve 15 mmol of cobalt nitrate hexahydrate and 10 mmol of trimesic acid in 120 mL of a mixed solution (the mixed solution was obtained by mixing deionized water and anhydrous ethanol solution in a 1:1 volume ratio), then transfer the solution to a reaction vessel, heat at 120 °C for 18 h, remove the reaction vessel, and wash the product multiple times with anhydrous ethanol and deionized water to remove unreacted precursors and residual solvents. Dry the precipitate at 65 °C to obtain Co-MOF nanoparticles. S2: Add 4 mL of CEO and 1 g of Co-MOF to 10 mL of chloroform, then sonicate at 25 °C for 30 min to mix CEO, chloroform and Co-MOF evenly, and then place in an air drying oven at 40 °C to completely evaporate the solvent to obtain the composite nanoparticle Co-MOF@CEO with antibacterial effect. Step 3: Disperse 0.1g of Co-MOF@CEO in 50mL of ultrapure water and stir in a magnetically stirred water bath at 35℃ for 30 min to obtain a mixed dispersion; Step 4: Add 0.8g glycerin and 2g PS to the mixed dispersion, and stir thoroughly in an 80℃ magnetically stirred water bath to obtain a starch film-forming solution. Apply the starch film-forming solution evenly to a 12cm diameter film. After drying in a 45°C air drying oven on a 12 cm plastic plate, the film is peeled off to obtain the Co-MOF@CEO intelligent active packaging film, namely the 0.2% Co-MOF@CEO / PS composite film.

[0048] Example 5: A Co-MOF@CEO smart active packaging film, prepared by the following steps: S1: Dissolve 14 mmol of cobalt nitrate hexahydrate and 10 mmol of trimesic acid in 120 mL of a mixed solution (the mixed solution was obtained by mixing deionized water and anhydrous ethanol solution in a 1:1 volume ratio), then transfer the solution to a reaction vessel, heat at 120 °C for 18 h, remove the reaction vessel, and wash the product multiple times with anhydrous ethanol and deionized water to remove unreacted precursors and residual solvents. Dry the precipitate at 65 °C to obtain Co-MOF nanoparticles. S2: Add 4 mL of CEO and 1 g of Co-MOF to 10 mL of chloroform, then sonicate at 20 °C for 35 min to mix CEO, chloroform and Co-MOF evenly, and then place in an air drying oven at 40 °C to completely evaporate the solvent to obtain the composite nanoparticle Co-MOF@CEO with antibacterial effect. Step 3: Disperse 0.075g of Co-MOF@CEO in 50mL of ultrapure water and stir in a magnetically stirred water bath at 35℃ for 30 min to obtain a mixed dispersion. Step 4: Add 0.8g glycerin and 2g PS to the mixed dispersion, and stir thoroughly in an 80℃ magnetically stirred water bath to obtain a starch film-forming solution. Apply the starch film-forming solution evenly to a 12cm diameter film. A Co-MOF@CEO intelligent active packaging film was obtained by drying the film in a 12 cm plastic plate at a constant temperature of 45°C in an air drying oven and then peeling it off.

[0049] Example 6: A Co-MOF@CEO smart active packaging film, prepared by the following steps: S1: Dissolve 15 mmol of cobalt nitrate hexahydrate and 9 mmol of trimesic acid in 120 mL of a mixed solution (the mixed solution was obtained by mixing deionized water and anhydrous ethanol solution in a 1:1 volume ratio), then transfer the solution to a reaction vessel, heat at 120 °C for 18 h, remove the reaction vessel, and wash the product multiple times with anhydrous ethanol and deionized water to remove unreacted precursors and residual solvents. Dry the precipitate at 65 °C to obtain Co-MOF nanoparticles. S2: Add 4 mL of CEO and 1 g of Co-MOF to 10 mL of chloroform, then sonicate at 30 °C for 25 min to mix CEO, chloroform and Co-MOF evenly, and then place in an air drying oven at 40 °C to completely evaporate the solvent to obtain the composite nanoparticle Co-MOF@CEO with antibacterial effect. Step 3: Disperse 0.075g of Co-MOF@CEO in 50mL of ultrapure water and incubate in a magnetically stirred water bath at 35℃ for 30min to obtain a mixed dispersion. Step 4: Add 0.8g glycerin and 2g PS to the mixed dispersion, and stir thoroughly in an 80℃ magnetically stirred water bath to obtain a starch film-forming solution. Apply the starch film-forming solution evenly to a 12cm diameter film. A Co-MOF@CEO intelligent active packaging film was obtained by drying the film in a 12 cm plastic plate at a constant temperature of 45°C in an air drying oven and then peeling it off.

[0050] Comparative Example 1: A potato starch packaging film, prepared by the following steps: Add 0.8g glycerol and 2g PS to 50mL of ultrapure water, and stir thoroughly in a magnetically stirred water bath at 80℃ to obtain a starch film-forming solution. Spread the starch film-forming solution evenly on a plastic plate with an area of ​​12cm×12cm, and dry it at a constant temperature in an air drying oven at 45℃. Then peel off the film to obtain potato starch packaging film, i.e., PS film.

[0051] Experiment Example 1: Performance Testing of Smart Active Packaging Film The Co-MOF@CEO / PS composite membranes prepared in Examples 1-4 and the PS membrane prepared in Comparative Example 1 were used as experimental subjects to conduct relevant performance tests.

[0052] 1. Thickness Measurement. The Co-MOF@CEO / PS composite membranes prepared in Examples 1-4 and the PS membrane prepared in Comparative Example 1 were cut into 6 cm × 1 cm shapes, and their thicknesses were measured using a thickness gauge.

[0053] 2. Water vapor transmission rate. Weighing bottles containing 5g of CaCl2 (mouth diameter 5 cm) were sealed with different membranes, and the weights were recorded. The bottles were then placed in a 25℃, 97% RH environment for 72 hours, and the weights were recorded again. The water vapor transmission rate was calculated as follows:

[0054] ; In the formula, G is the weight increase of the glass bottle when constant weight is achieved (g); L is the thickness of the membrane (m); and A represents the effective sealing area of ​​the composite membrane (m²). 2 ); t is the total time (s); ∆P is the water vapor pressure difference across the membrane (Pa).

[0055] 3. Oxygen Transmission Rate. First, seal the mouths of glass bottles containing 3g of oxygen absorber (5cm in diameter) using different membranes, weigh them, and record the weight. Then, place the glass bottles at 25℃ and 90%RH for 48 hours, weigh them again, and record the weight. Determine the oxygen transmission rate using the formula:

[0056] ; In the formula, G is the weight increase of the glass bottle when constant weight is achieved (g); A represents the effective area covered by the composite film (m²). 2 ); t represents the storage time (h).

[0057] 4. Swelling Degree. The membrane was divided into 2 cm × 2 cm sections, and the initial weight W1 was recorded. Each section was then placed in a glass beaker containing 40 mL of distilled water and kept at 25°C for 10 min. The sample was then removed, the surface moisture was wiped dry, and the weight W2 was recorded. The swelling degree was calculated as follows:

[0058] ; In the formula, W1 is the initial weight (g) of the composite membrane; W2 is the weight (g) of the composite membrane after immersion.

[0059] 5. Opacity. The absorbance (A) of different films at 600 nm was measured. 600 The opacity of the composite film is calculated using the following formula:

[0060] ; In the formula, X is the thickness of the composite membrane (mm).

[0061] Table 1 Performance test results of smart active packaging film Note: Lowercase letters a, b, c, and d in the table indicate significant differences between groups.

[0062] The results are shown in Table 1. The thickness of the PS membrane was 71.96 μm. After adding 0.05%, 0.1%, 0.15%, and 0.2% Co-MOF@CEO, the membrane thickness increased to 73.57 μm, 77.30 μm, 80.67 μm, and 81.79 μm, respectively. Comparison of the water vapor transmission rates of the PS membrane and different Co-MOF@CEO / PS composite membranes revealed that the incorporation of Co-MOF@CEO significantly reduced the water vapor transmission rate of the pure PS membrane. The composite membrane with 0.15% Co-MOF@CEO showed a greater reduction in water vapor transmission rate: the PS membrane's water vapor transmission rate was 0.53 × 10⁻⁶. −10 g / Pa·s·m, decreased to 0.40×10 after adding 0.15% Co-MOF@CEO. −10 g / Pa·s·m. By comparing the oxygen permeability of PS membranes and different Co-MOF@CEO / PS composite membranes, it was found that the incorporation of Co-MOF@CEO significantly reduced the oxygen permeability of pure PS membranes. The composite membrane with 0.15% Co-MOF@CEO showed a greater reduction in oxygen permeability. The oxygen permeability of the pure PS membrane was 0.85 × 10⁻⁶ g / Pa·s·m. −7 g / cm2 •s. Adding 0.15% Co-MOF@CEO reduced the concentration to 0.43 × 10⁻⁶. −7 g / cm 2 •s. Compared with different composite films, the 0.1% Co-MOF@CEO / PS composite film has the lowest swelling degree, while the 0.2% Co-MOF@CEO / PS composite film has higher opacity.

[0063] Experimental Example 2: Color Response of Smart Active Packaging Film under Ammonia Atmosphere The sensitivity of the Co-MOF@CEO / PS composite membrane to ammonia was determined. First, a 3 cm diameter composite membrane was fixed 5 cm above the top of a container containing 5 mL of ammonia. Then, a colorimeter was used to measure the color change of the composite membrane from 0 min to 180 min. The results are as follows: Figure 1 As shown.

[0064] from Figure 1 It can be seen that the pure PS film shows almost no color change, while the Co-MOF@CEO / PS composite film exhibits a significant color change, indicating that the Co-MOF@CEO / PS composite film has a clear color indication response to volatile ammonia. The color change values ​​of the pure PS film and the Co-MOF@CEO / PS composite film were subsequently measured. With increasing exposure time to volatile ammonia, the brightness of the Co-MOF@CEO / PS composite film increased. L* Gradually decreasing, while yellowness... b* Rapidly increasing, ΔE The concentrations also increased significantly. After 40 min, the concentrations of 0.05%, 0.1%, 0.15%, and 0.2% Co-MOF@CEO / PS composite membranes increased significantly. ΔE The values ​​increased to 7.54, 10.88, 14.91 and 21.78 respectively. ΔE A value greater than 5 indicates that the composite membrane undergoes a color change that is visible to the naked eye, indicating that the Co-MOF@CEO composite membrane has a clear color indication for ammonia, and the 0.2% Co-MOF@CEO / PS composite membrane is more sensitive to ammonia.

[0065] Experimental Example 3: Performance Characterization of Co-MOF and Co-MOF@CEO Taking Example 1 as an example, the morphology of Co-MOF and Co-MOF@CEO was observed using scanning electron microscopy; the functional group changes of Co-MOF and Co-MOF@CEO were observed using Fourier transform infrared spectroscopy; and the crystal structure of Co-MOF and Co-MOF@CEO was observed using X-ray diffraction. The results are as follows: Figure 2 As shown.

[0066] Figure 2In the figure, A and B represent the SEM morphology of Co-MOF and Co-MOF@CEO, respectively. It can be seen that obvious voids are formed on the surface of Co-MOF@CEO, indicating that CEO is successfully loaded into Co-MOF. Figure 2 D in the figure represents the X-ray diffraction patterns of Co-MOF and Co-MOF@CEO: sharp diffraction peaks were observed at 2θ = 9.8°, 14.34°, 18.41°, 19.59°, 22.26°, 29.13°, 30.05° and 33.73°, respectively, indicating that Co-MOF and Co-MOF@CEO were successfully prepared and have good crystallinity. Figure 2 C in the diagram represents the reaction between Co-MOF@CEO and ammonia. Figure 2 In the figure, E represents the FTIR spectrum of Co-MOF and Co-MOF@CEO, with the absorption peak appearing at 3467 cm⁻¹. −1 (OH stretching), 1376 cm −1 (CO stretching) and 750 cm −1 (Co-O tensile vibration). Compared with Co-MOF, Co-MOF@CEO shows a new absorption peak at 1626 cm⁻¹. −1 (C=C tensile vibration) and 1677 cm −1 (C=O tensile vibration) indicates that CEO was successfully loaded into the pores of Co-MOF. After ammonia treatment (treatment method as in Example 2), Co-MOF@CEO reached 1376 cm⁻¹. −1 The absorption band migrated to 1382 cm. −1 This may be because a new hydrogen bond forms between Co-MOF@CEO and ammonia. The spectrum of ammonia-treated Co-MOF@CEO is at 690 cm⁻¹. −1 A new characteristic absorption band appeared, which was caused by the Co-N stretching vibration. These results indicate that Co-MOF@CEO adsorbs ammonia by forming new interactions and Co-N bonds.

[0067] Experimental Example 4: Ammonia Sensitivity of Co-MOF@CEO Following the ammonia sensitivity determination method in Example 2, the Co-MOF@CEO smart active packaging film prepared in Example 1 was placed in an ammonia atmosphere for 5 minutes, and the color change of the Co-MOF@CEO smart active packaging film before and after placement was observed.

[0068] like Figure 3 As shown, the Co-MOF@CEO smart active packaging film showed a significant color change after being placed in an ammonia atmosphere for 5 minutes. This result strongly demonstrates that the prepared Co-MOF has good ammonia indication capabilities.

[0069] Experimental Example 5: SEM Characterization of Pure PS Film and Different Co-MOF@CEO / PS Composite Films Figure 4 The morphology of pure PS membranes and different Co-MOF@CEO / PS composite membranes was observed using SEM. It can be seen that the pure PS membrane has a uniform surface structure and is free of pores. After adding Co-MOF@CEO, the surface roughness of the resulting Co-MOF@CEO / PS composite membrane increased. Simultaneously, particles were observed on the surface of the composite membrane, proving that Co-MOF@CEO was successfully incorporated into the PS membrane. Notably, compared to other Co-MOF@CEO / PS composite membranes, no obvious impurities or particles were found in the surface image of the 0.15% Co-MOF@CEO / PS composite membrane. This may be because 0.15% Co-MOF@CEO is uniformly dispersed in the starch membrane with less agglomeration.

[0070] Experimental Example 6: FTIR and XRD characterization of pure PS film and different Co-MOF@CEO / PS composite films Figure 5 The functional group changes and crystal structures of pure PS films and different Co-MOF@CEO / PS composite films were observed by FTIR and XRD, respectively.

[0071] Figure 5 In the figure, A represents the FTIR spectra of the pure PS film and the Co-MOF@CEO / PS composite film. No new absorption peaks were observed in the Co-MOF@CEO / PS composite film, indicating that no new chemical bonds were formed. Spectra show that all composite films exhibit broad absorption peaks (3000 cm⁻¹). −1 -3700 cm −1 This is attributed to the stretching vibration of the hydroxyl group. There is also an absorption peak at 2930 cm⁻¹. −1 (CH tensile vibration) and 1648 cm −1 At (OH bending vibration) location. 1153 cm −1 The peak observed at this point is due to CO stretching. PS is polymerized from monosaccharides and contains a relatively high number of CO-C bonds. 1026 cm⁻¹ −1 The absorption band at 577 cm⁻¹ is a characteristic peak of potato starch, corresponding to the COC stretching vibration. In the spectrum, 577 cm⁻¹... −1 The absorption band at that location is attributed to the skeletal vibration of the pyranose ring in the monosaccharide.

[0072] Figure 5In the figure, B represents the crystal structure of the pure PS film and different Co-MOF@CEO / PS composite films. XRD patterns show that the pure PS film has a broad diffraction peak at 2θ = 3°–16°, which is a characteristic peak of PS. Compared to the pure PS film, the position and width of the peak did not change significantly after Co-MOF@CEO incorporation, indicating that the crystal integrity of the film was not affected, and that Co-MOF@CEO has good compatibility with the PS matrix.

[0073] Experimental Example 7: Determination of Mechanical Properties of Different Membranes Figure 6 To measure the elongation at break (EB) and tensile strength (TS) of different Co-MOF@CEO / PS composite membranes (6 cm × 1 cm), samples were cut into 6 cm × 1 cm shapes. The results showed that the TS and EB of the pure PS membrane were 2.45 MPa and 123.93%, respectively. The TS increased with increasing Co-MOF@CEO content. When the Co-MOF@CEO addition was 0.15%, the TS of the Co-MOF@CEO / PS composite membrane increased to 6.68 MPa. Meanwhile, with increasing Co-MOF@CEO addition, the EB of the pure PS membrane decreased from 123.93% to 49.88%. The TS of the Co-MOF@CEO / PS composite membrane showed a decreasing trend with increasing Co-MOF@CEO content.

[0074] Experiment Example 8: Determination of the appearance and transmittance of different membranes The color of different Co-MOF@CEO / PS composite films was measured using a colorimeter. ΔL* , Δa* , Δb* ). ΔE The formula for calculating the value is as follows:

[0075] ; The transmittance of different Co-MOF@CEO / PS composite films in the range of 200 nm to 800 nm was determined using a UV-Vis spectrophotometer.

[0076] Figure 7 In the figure, A represents the appearance of pure PS film and different Co-MOF@CEO / PS composite films: the uniform PS film is transparent and colorless, and the Co-MOF@CEO / PS composite films obtained after adding different amounts of Co-MOF@CEO maintain good uniformity in appearance.

[0077] Figure 7 In the figure, B represents the transmittance of different Co-MOF@CEO / PS composite films. Firstly, pure PS films exhibit high transmittance for both ultraviolet and visible light, with a transmittance at 280 nm (T0). 280 ) and 660 nm (T660 The transmittance at 280 nm and 660 nm were 33.07% and 70.46%, respectively. After adding Co-MOF@CEO, the transmittance of the Co-MOF@CEO / PS composite film decreased at 280 nm and 660 nm. Simultaneously, the ultraviolet transmittance of the Co-MOF@CEO / PS composite film at 280 nm was almost zero.

[0078] Experiment Example 9: Determination of the antibacterial properties of different membranes against Staphylococcus aureus and Escherichia coli First, the five composite membranes were divided into 6 mm diameter discs and sterilized under ultraviolet light. Then, 100 μL of Escherichia coli suspension and Staphylococcus aureus suspension (10 μL each) were respectively used. 6 The CFU / mL of the composite membrane was placed on a petri dish and spread evenly using a spreader. Then, the different composite membranes were placed on petri dishes and incubated at 37 °C for 24 h to observe the growth of microorganisms around the five composite membranes.

[0079] Determination of the antioxidant properties of the composite membrane: 50 mg of the composite membrane was weighed and placed in 5 mL of DPPH ethanol (0.1 mM). The resulting mixed solution was placed in a light-protected environment and reacted for 30 min. A blank experiment was performed using the DPPH ethanol solution without the composite membrane. Then, the absorbance values ​​of the mixed solution (A1) and the blank experiment (A0) were measured at 517 nm. The formula for the DPPH free radical scavenging rate is as follows:

[0080] ; Figure 8 A comparison of the antibacterial effects of pure PS membranes and different Co-MOF@CEO / PS composite membranes against Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli) was shown in Figure A. Pure PS membranes showed no antibacterial activity, while Co-MOF@CEO / PS composite membranes exhibited significant antibacterial activity. The antibacterial effect of the Co-MOF@CEO / PS composite membranes further improved with increasing Co-MOF@CEO content. The composite membrane showed better inhibitory effects against Staphylococcus aureus than against Escherichia coli.

[0081] Figure 8 In the figure, B represents the antioxidant capacity of the composite membrane. Pure PS membrane has no antioxidant capacity. With the addition of Co-MOF@CEO, the antioxidant capacity of the 0.2% Co-MOF@CEO / PS composite membrane reaches its maximum (30.72%).

[0082] Experiment Example 10: The Color Indication Effect of Different Membranes on Grass Carp The color indication effect of Co-MOF@CEO / PS composite membranes on grass carp. Different Co-MOF@CEO / PS composite membranes (10 mm × 10 mm) were fixed in the top space of a plastic box containing 30 g grass carp samples and stored at 25 ℃ and 55%RH for 36 h. The color change of the composite membranes was measured at 0 h, 12 h, 24 h, and 36 h. The volatile basic nitrogen (TVB-N) content of grass carp was determined according to GB 5009.288-2016.

[0083] Figure 9 In this context, A represents the color indication function of the composite membrane for grass carp. Figure 9 B in the text refers to the composite film used during grass carp storage. Δ E value; Figure 9 C in the figure represents the TVB-N value of grass carp during storage. Firstly, the pure PS film showed no significant color change. ΔE The values ​​remained relatively stable. However, the Co-MOF@CEO / PS composite membrane showed a significant color change (turning brown) after grass carp were stored for 24 hours. ΔE The TVB-N value increased sharply to over 35. The TVB-N value also reflects the spoilage of the fish. After 12 h, 24 h, and 36 h, the TVB-N value of the fish increased from the initial 4.89 mg / 100 g to 13.31 mg / 100 g, 29.9 mg / 100 g, and 40.27 mg / 100 g, respectively. After 24 h, the TVB-N value of the fish exceeded the limit specified in GB 2733-2015 (20 mg / 100 g), indicating that the fish was no longer edible. With prolonged storage, the color of the fish gradually darkened (light yellow → gray → yellow → dark yellow). After 12 h, the fish had a slight rotten odor. After 24 h, it was severely spoiled, accompanied by yellow mucus, and the muscles did not recover after acupressure. By 36 h, a strong pungent odor was produced, and the mucus became more cloudy. As the quality of the fish changes, the color of the membrane also changes. Therefore, the Co-MOF@CEO / PS composite membrane can effectively monitor the freshness of the fish.

[0084] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0085] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A Co-MOF@CEO smart active packaging film, characterized in that, The intelligent active packaging film includes a film-forming matrix and composite nanoparticles dispersed in the film-forming matrix; the film-forming matrix is ​​potato starch; the composite nanoparticles are formed by encapsulating cinnamon essential oil in a cobalt-based metal-organic framework.

2. A method for preparing the Co-MOF@CEO intelligent active packaging film according to claim 1, characterized in that, Includes the following steps: Cobalt-based metal-organic frameworks and cinnamon essential oil were placed in an organic solvent environment, allowing the cinnamon essential oil to be embedded in the pores of the cobalt-based metal-organic framework. After evaporating the organic solvent, composite nanoparticles were obtained. The composite nanoparticles were dissolved in water, and plasticizer and potato starch were added. After stirring, a starch film-forming solution was obtained. After the starch film-forming solution is solidified and molded, the Co-MOF@CEO smart active packaging film is obtained.

3. The preparation method according to claim 2, characterized in that, The organic solvent is chloroform or ethanol; the dispersion is ultrasonic dispersion, the dispersion temperature is 20℃~30℃, and the dispersion time is 25min~35min.

4. The preparation method according to claim 2, characterized in that, The cobalt-based metal-organic framework is obtained by reacting cobalt salt and trimesic acid via a solvothermal method; the molar ratio of the cobalt salt to trimesic acid is 14~15:9~10.

5. The preparation method according to claim 4, characterized in that, The solvothermal reaction temperature is 195℃~205℃, and the reaction time is 15h~16h.

6. The preparation method according to claim 2, characterized in that, The ratio of the cobalt-based metal-organic framework, cinnamon oil, and organic solvent is 0.9g~1.0g: 3.9mL~4.0mL: 9mL~10mL.

7. The preparation method according to claim 2, characterized in that, The plasticizer is glycerol, sorbitol or propylene glycol; the mass ratio of glycerol, potato starch and composite nanoparticles is 0.8:2:0.025~0.

1.

8. The preparation method according to claim 2, characterized in that, The curing temperature is 44℃~45℃.

9. The application of the Co-MOF@CEO intelligent active packaging film according to claim 1 in food freshness monitoring, characterized in that, The food items are fresh meat, seafood, or processed meat products.

10. The application of the Co-MOF@CEO intelligent active packaging film according to claim 1 as a food preservation film, characterized in that, The food preservation film is a food preservation film with antibacterial or antioxidant activity.

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