Humidity-responsive edible polysaccharide-cyclodextrin metal organic framework fresh-keeping film and preparation method thereof

Abstract

The present invention relates to the field of active food packaging, specifically to a humidity-responsive edible polysaccharide-cyclodextrin metal-organic framework (MOF) cling film and its preparation method. The preparation method utilizes an in-situ growth method. By adjusting the cellulose addition ratio and utilizing the complexation between the abundant hydroxyl groups on the polysaccharide matrix and potassium ions, γ-CD-MOFs nanoparticles are fixed to the polysaccharide film surface. Finally, a polysaccharide solution that is most conducive to the in-situ growth of the γ-cyclodextrin metal-organic framework is selected to prepare the composite film. Carvacrol is then loaded via physical adsorption to achieve humidity-responsive controlled release.

Description

Technical Field

[0001] The invention relates to the field of food active packaging, and in particular to a humidity-responsive edible polysaccharide-cyclodextrin metal organic framework fresh-keeping film and a preparation method thereof. Background Art

[0002] Fresh fruits and vegetables continue to undergo physiological metabolic activities such as respiration and transpiration after harvest. This high water activity leads to elevated temperatures and humidity within the relatively closed packaging environment, promoting the growth and reproduction of microorganisms and contributing to their rotting and spoilage. Therefore, developing efficient antibacterial preservation technologies is crucial for post-harvest fruit and vegetable storage and preservation.

[0003] In order to extend the shelf life of fresh fruits and vegetables, existing technologies for inhibiting microorganisms in the storage environment include packaging films that add functional active substances to the packaging matrix, such as "water-absorbing and moisture-control films", "anti-fog coatings", "antibacterial films", and "antibacterial gases". Among them, "water-absorbing and moisture-control films" and "anti-fog coatings" only reduce microorganisms by absorbing moisture in the package or regulating humidity, but such packaging cannot completely inhibit the growth and reproduction of microorganisms. Generally, "antibacterial films" kill bacteria on the surface of food by adding some metals or metal oxides (such as silver and zinc oxide) to the packaging material, but this type of antibacterial agent is a contact antibacterial agent, which is difficult to kill microorganisms in the environment and easily migrates to the surface or interior of food, posing certain food safety risks. "Antibacterial gas" generally uses gases such as chlorine dioxide and sulfur dioxide to effectively kill bacteria, but such chemical gases also have certain food toxicity. The above preservation methods or technical functions are relatively simple or difficult to meet the requirements of green and sustainable development.

[0004] Antimicrobial active packaging is an advanced food preservation technology that not only prevents microbial contamination of food, but also effectively inhibits microorganisms by adding antimicrobial active substances, thereby extending the shelf life of food. Essential oils are broad-spectrum natural biological preservatives derived from plants. Antimicrobial packaging with essential oils as active substances has become a research hotspot in the field of food preservation. However, essential oils have problems such as volatility, insolubility in water, sensitivity to light and heat, easy oxidation and deterioration, and pungent odor, which have become obstacles to their application in food preservation. In recent years, nano-encapsulation carriers can achieve effective encapsulation and long-term sustained release of essential oils, providing an opportunity to overcome the limitations of essential oils. Metal-organic frameworks (MOFs) are new porous nanomaterials composed of metal ions / clusters and organic ligands, which have been proven to effectively improve the stability and bioavailability of essential oils. However, most MOFs materials contain non-food-grade organic linkers and transition metal ions, have certain biological toxicity and non-degradability, and are difficult to be directly used in food preservation. γ-cyclodextrin (γ-CD) and potassium ions (K +) self-assemble to form green, edible γ-cyclodextrin-metal-organic framework (γ-CD-MOF) nanocarriers, which not only stabilize essential oils within their abundant nanopores but also exhibit good edibility, biocompatibility, and biodegradability. However, when used directly, γ-CD-MOF nanoparticles tend to agglomerate, failing to achieve the desired preservation effect. Advanced composite materials composed of γ-CD-MOF and natural polymer membranes represent an important step forward in promoting the use of nanomaterials for food preservation. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a humidity-responsive edible polysaccharide-cyclodextrin metal organic framework cling film and a preparation method thereof for active food packaging. The specific scheme is as follows:

[0006] A humidity-responsive edible polysaccharide-cyclodextrin metal-organic framework cling film is prepared. Chitosan-cellulose (CS-CEL) is used as an edible polysaccharide matrix, and γ-cyclodextrin metal-organic framework (γ-CD-MOFs) nanoparticles are in situ grown on its surface. Carvacrol (CAR) is loaded as an antibacterial agent by physical adsorption to obtain a humidity-responsive edible polysaccharide-cyclodextrin metal-organic framework cling film, namely, CAR@γ-CD-MOFs / CS-CELL composite film.

[0007] A method for preparing a humidity-responsive edible polysaccharide-cyclodextrin metal organic framework fresh-keeping film, comprising the following steps:

[0008] (1) preparing chitosan-cellulose polysaccharide matrix;

[0009] (2) The polysaccharide matrix is ​​immersed in an aqueous solution of γ-cyclodextrin and potassium ions, forming nucleation sites of γ-CD-MOFs under the action of methanol vapor, and growing into γ-CD-MOFs crystals under the action of methanol and hexadecyltrimethylammonium bromide;

[0010] (3) The polysaccharide film of in situ grown γ-CD-MOFs nanoparticles was immersed in a carvacrol solution, shaken, fully adsorbed, washed with ethanol, and vacuum dried to obtain a humidity-responsive controlled-release composite film loaded with carvacrol.

[0011] The specific process of preparing the chitosan-cellulose polysaccharide matrix in step (1) is as follows: using chitosan solution as a film-forming agent, mixing it with a cellulose dispersion, fully stirring, casting, and drying to form a film to obtain a chitosan-cellulose polysaccharide-based composite film.

[0012] The specific steps are as follows: preparing a chitosan acetic acid aqueous solution as a film-forming solution and stirring overnight; dispersing cellulose in water and stirring overnight to obtain a uniform cellulose dispersion; mixing the chitosan solution and the cellulose dispersion and stirring thoroughly to obtain a polysaccharide mixed solution; pouring the mixed solution into a mold using a solution casting method and drying in an oven overnight to obtain a polysaccharide matrix. The cellulose concentration is 1% w / v, 3% w / v, or 5% w / v.

[0013] The specific process of step (2) is as follows: γ-CD and KOH are added to deionized water and ultrasonically dissolved, filtered with a 0.45 μm filter membrane, the polysaccharide film prepared in step (1) is immersed in the above solution, sealed, and methanol vapor is passed through to gradually form γ-CD-MOFs nucleation sites on the surface of the polysaccharide matrix, and then CTAB and methanol solution are added, and the reaction is continued at room temperature to form γ-CD-MOFs crystals, which are washed with isopropanol, activated in dichloromethane, dried in a vacuum oven, and placed in a dry environment for use.

[0014] The specific process of loading carvacrol in step (3) is as follows: immersing 50 mg of the polysaccharide film of the in situ grown γ-CD-MOFs nanoparticles prepared in step (2) in a 20 mg / mL ethanol solution of carvacrol, shaking overnight to fully adsorb carvacrol, taking it out, washing it with anhydrous ethanol to remove unloaded carvacrol, and vacuum freeze-drying it.

[0015] Metal-organic frameworks (MOFs) are novel porous nanomaterials composed of metal ions / clusters self-assembled with organic ligands. They possess a uniform and stable crystal structure, high porosity, high loading rate, and tunable physicochemical properties, making them suitable carriers for essential oils. Although MOF nanoparticles have been shown to effectively improve the stability and utilization of essential oils, most currently used MOFs contain non-food-grade organic linkers and transition metal ions, exhibiting certain biotoxicity and non-degradability, making them difficult to directly apply in food preservation. γ-cyclodextrin (γ-CD) not only serves as an effective encapsulation carrier for essential oil molecules but also self-assembles with potassium ions (K+) to form green and edible γ-cyclodextrin-metal-organic framework (γ-CD-MOF) nanocarriers, stabilizing essential oil molecules within their porous structure and increasing the loading rate. γ-CD-MOF also exhibits excellent biosafety for use in food preservation. However, γ-CD-MOF nanoparticles tend to agglomerate when used directly, preventing effective preservation.

[0016] Carvacrol is one of the main active ingredients in oregano essential oil and the most extensively studied essential oil component in the field of food preservation. Currently, most research focuses on incorporating carvacrol into polymer matrices, microcapsules, or nanoparticles to create active packaging materials to achieve slow release of carvacrol. While these carriers can, to a certain extent, prevent premature release of antimicrobial agents, they still suffer from low loading rates, uncontrollable release rates, and non-degradability. Therefore, the development of high-load, non-toxic, and pollution-free stimuli-responsive controlled-release active packaging materials, particularly those that trigger essential oil release in the high humidity of fresh food storage environments to achieve antibacterial and preservation purposes, holds broad application prospects and research value in the food industry.

[0017] The preparation method provided by the present invention utilizes an in situ growth method. By regulating the addition ratio of cellulose and utilizing the complexation effect of abundant hydroxyl groups and potassium ions on the surface of the polysaccharide matrix, γ-CD-MOFs nanoparticles are fixed on the surface of the polysaccharide film. Finally, a polysaccharide solution that is most conducive to the in situ growth of the γ-cyclodextrin metal-organic framework is selected to prepare a composite film. Carvacrol is loaded by physical adsorption to achieve humidity stimulus-responsive controlled release.

[0018] Compared with other food active packaging materials, the present invention has the following advantages:

[0019] (1) The preservative film provided by the present invention uses chitosan and cellulose polysaccharide as a matrix. γ-cyclodextrin metal-organic framework nanoparticles are in situ grown on the matrix surface through the coordination of hydroxyl groups and potassium ions, acting as an encapsulation carrier for carvacrol, preventing the premature release of the antimicrobial agent. Under the stimulation of a high humidity environment, the γ-cyclodextrin metal-organic framework nanoparticle structure is destroyed, releasing carvacrol to act on microorganisms, achieving an antibacterial and fresh-keeping effect.

[0020] (2) The method of the present invention utilizes the hydrophobic cavity and nanoporous structure of γ-cyclodextrin metal organic framework nanoparticles as a carrier of carvacrol, significantly improving the encapsulation efficiency and loading rate of carvacrol and prolonging the action time of the antibacterial agent.

[0021] (3) The present invention uses chitosan, cellulose and cyclodextrin as the base materials, all of which are natural, non-toxic, edible polysaccharides, and adopts a simple, efficient and green synthesis method to improve the safety and environmental protection of the active packaging material.

[0022] (4) The edible polysaccharide-cyclodextrin metal organic framework cling film prepared by the present invention can stimulate the release of antimicrobial agents in a high humidity environment. Compared with other sustained-release active packaging systems, it does not require external stimulation factors to achieve the effect of controlled release of antimicrobial agents, thereby improving the bioavailability of antimicrobial agents. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1ac are the morphological images of the polysaccharide matrix with different cellulose concentrations added in Example 1;

[0024] Figure 2 ac are the morphological images of γ-CD-MOFs grown when different cellulose concentrations were added to the polysaccharide matrix in Example 2;

[0025] Figure 3 is a morphology diagram of γ-CD-MOFs nanoparticles in Example 2;

[0026] Figure 4 is the loading rate of carvacrol on the polysaccharide film of the in situ grown γ-CD-MOFs in Examples 4-7;

[0027] Figure 5 is the release rate of carvacrol under different relative humidity conditions;

[0028] Figure 6 is the antibacterial effect of different materials on Escherichia coli and Staphylococcus aureus;

[0029] Figure 7 is the effect of different material treatments on the morphology of Escherichia coli and Staphylococcus aureus;

[0030] Figure 8 The antibacterial effect of polysaccharide-cyclodextrin metal organic framework plastic wrap on Botrytis cinerea;

[0031] Figure 9 This is a morphology diagram of the humidity-responsive edible polysaccharide-cyclodextrin metal-organic framework composite film prepared in Example 5. DETAILED DESCRIPTION

[0032] Example 1

[0033] A method for preparing a humidity-responsive edible polysaccharide-cyclodextrin metal organic framework fresh-keeping film, comprising the following steps:

[0034] (1) Dissolve 2g of chitosan powder in 100mL (1%, v / v) acetic acid aqueous solution and stir at room temperature overnight to obtain a 2% (w / v) chitosan solution. Add 1g, 3g, and 5g of cellulose powder to 100mL of deionized water, respectively, and stir at room temperature for 12h to obtain cellulose dispersions with concentrations of 1wt%, 3wt%, and 5wt%. Mix the chitosan solution with cellulose dispersions of different concentrations, stir thoroughly for 24h, and cast into films. Field emission scanning electron microscopy showed that the surface of the prepared film was rougher when the cellulose content was 5%. The film morphology is as follows Figure 1 shown.

[0035] (2) Add 1.62gγ-CD and 0.56g KOH to 50mL deionized water, sonicate for 1h until the solution is completely dissolved, and filter with a 0.45μm filter membrane. Take 100mg of polysaccharide membrane and immerse it in a 150mL small beaker containing the above solution without sealing. Then place the beaker in a large beaker containing 100mL methanol, seal it, and place it in a 50℃ oven to react for 12h. After the reaction is completed, add 50mL methanol solution and 400mg CTAB to the small beaker and continue to react at room temperature for 3h. After the reaction is completed, wash it three times with isopropanol, activate it in dichloromethane for 2 days, and vacuum dry it at 50℃ for 6h to finally obtain the γ-CD-MOFs / CS-CELL composite membrane.

[0036] (3) The γ-CD-MOFs / CS-CELL composite membrane (50 mg) was placed in an ethanol solution of carvacrol (20 mg / mL) and shaken overnight for full adsorption. The membrane was washed with ethanol three times to remove the unencapsulated carvacrol and dried under vacuum at 50 °C for 2 h to obtain the CAR@γ-CD-MOFs / CS-CELL composite membrane.

[0037] Example 2

[0038] (1) Dissolve 2g of chitosan powder in 100mL (1%, v / v) acetic acid aqueous solution and stir at room temperature overnight to obtain a 2% (w / v) chitosan solution. Add 1g, 3g, and 5g of cellulose powder to 100mL of deionized water and stir at room temperature for 24h to obtain cellulose dispersions with concentrations of 1wt%, 3wt%, and 5wt%. Mix the chitosan solution with cellulose dispersions of different concentrations and stir them thoroughly for 24h to prepare CS-CELL polysaccharide membranes. Figure 2 As shown in Figure 3, the higher the cellulose content, the more γ-CD-MOF crystals grow on the surface of the polysaccharide film.

[0039] (2) Add 1.62g γ-CD and 0.56g KOH to 50mL deionized water, sonicate for 1h until the solution is completely dissolved, and filter with a 0.45μm filter membrane. Take 100mg CS-CELL polysaccharide membrane and immerse it in a 150mL small beaker containing the above solution without sealing. Then place the beaker in a large beaker containing 100mL methanol, seal it, and place it in a 50℃ oven to react for 3h, 6h, 12h, and 24h. After the reaction is completed, add 50mL methanol solution and 400mg CTAB to the small beaker and continue to react at room temperature for 3h. After the reaction is completed, wash it three times with isopropanol, activate it in dichloromethane for 2 days, and vacuum dry it at 50℃ for 6h to finally obtain a γ-CD-MOFs / CS-CELL composite membrane. When the first stage reaction time was 12h and the second stage reaction time was 3h, more nucleation sites were formed on the surface of the CS-CELL polysaccharide membrane, and γ-CD-MOFs grew uniformly on the surface of the CS-CELL polysaccharide matrix. Field emission transmission electron microscopy showed that the size of the grown γ-CD-MOFs particles was nanometer-scale ( Figure 3 ).

[0040] (3) The γ-CD-MOFs / CS-CELL composite membrane (50 mg) was placed in an ethanol solution of carvacrol (20 mg / mL) and shaken overnight for full adsorption. The membrane was washed with ethanol three times to remove the unencapsulated carvacrol and dried under vacuum at 50 °C for 2 h to obtain the CAR@γ-CD-MOFs / CS-CELL composite membrane.

[0041] Example 3

[0042] (1) Dissolve 2g of chitosan powder in 100mL (1%, v / v) acetic acid aqueous solution and stir at room temperature overnight to obtain a 2% (w / v) chitosan solution. Add 5g of cellulose powder to 100mL of deionized water and stir at room temperature for 24h to obtain a 5wt% cellulose dispersion. The chitosan solution was mixed with cellulose dispersions of varying concentrations and stirred for 24h to prepare CS-CELL polysaccharide membranes.

[0043] (2) Add 1.62g of γ-CD and 0.56g of KOH to 50mL of deionized water, sonicate for 1h until the solution is completely dissolved, and filter with a 0.45μm filter membrane. Take 100mg of CS-CELL polysaccharide membrane and immerse it in a 150mL small beaker containing the above solution without sealing. Then place the beaker in a large beaker containing 100mL of methanol, seal it, and place it in a 50℃ oven to react for 12h. After the reaction is completed, add 50mL of methanol solution and 400mg of CTAB to the small beaker and continue to react at room temperature for 3h. After the reaction is completed, wash it three times with isopropanol, activate it in dichloromethane for 2 days, and vacuum dry it at 50℃ for 6h to finally obtain a γ-CD-MOFs / CS-CELL composite membrane.

[0044] (3) The γ-CD-MOFs / CS-CELL composite membrane (50 mg) was placed in an ethanol solution of carvacrol (5 mg / mL) and shaken overnight for full adsorption. The membrane was washed with ethanol three times to remove the unencapsulated carvacrol and dried under vacuum at 50 °C for 2 h to finally obtain the CAR@γ-CD-MOFs / CS-CELL composite membrane.

[0045] Example 4

[0046] (1) Dissolve 2g of chitosan powder in 100mL (1%, v / v) acetic acid aqueous solution and stir at room temperature overnight to obtain a 2% (w / v) chitosan solution. Add 5g of cellulose powder to 100mL of deionized water and stir at room temperature for 24h to obtain a 5wt% cellulose dispersion. The chitosan solution was mixed with cellulose dispersions of varying concentrations and stirred for 24h to prepare CS-CELL polysaccharide membranes.

[0047] (2) Add 1.62g of γ-CD and 0.56g of KOH to 50mL of deionized water, sonicate for 1h until the solution is completely dissolved, and filter with a 0.45μm filter membrane. Take 100mg of CS-CELL polysaccharide membrane and immerse it in a 150mL small beaker containing the above solution without sealing. Then place the beaker in a large beaker containing 100mL of methanol, seal it, and place it in a 50℃ oven to react for 12h. After the reaction is completed, add 50mL of methanol solution and 400mg of CTAB to the small beaker and continue to react at room temperature for 3h. After the reaction is completed, wash it three times with isopropanol, activate it in dichloromethane for 2 days, and vacuum dry it at 50℃ for 6h to finally obtain a γ-CD-MOFs / CS-CELL composite membrane.

[0048] (3) The γ-CD-MOFs / CS-CELL composite membrane (50 mg) was placed in an ethanol solution of carvacrol (10 mg / mL) and shaken overnight for full adsorption. The membrane was washed with ethanol three times to remove the unencapsulated carvacrol and dried under vacuum at 50 °C for 2 h to finally obtain the CAR@γ-CD-MOFs / CS-CELL composite membrane.

[0049] Example 5

[0050] (1) Dissolve 2g of chitosan powder in 100mL (1%, v / v) acetic acid aqueous solution and stir at room temperature overnight to obtain a 2% (w / v) chitosan solution. Add 5g of cellulose powder to 100mL of deionized water and stir at room temperature for 24h to obtain a 5wt% cellulose dispersion. The chitosan solution was mixed with cellulose dispersions of varying concentrations and stirred for 24h to prepare CS-CELL polysaccharide membranes.

[0051] (2) Add 1.62g of γ-CD and 0.56g of KOH to 50mL of deionized water, sonicate for 1h until the solution is completely dissolved, and filter with a 0.45μm filter membrane. Take 100mg of CS-CELL polysaccharide membrane and immerse it in a 150mL small beaker containing the above solution without sealing. Then place the beaker in a large beaker containing 100mL of methanol, seal it, and place it in a 50℃ oven to react for 12h. After the reaction is completed, add 50mL of methanol solution and 400mg of CTAB to the small beaker and continue to react at room temperature for 3h. After the reaction is completed, wash it three times with isopropanol, activate it in dichloromethane for 2 days, and vacuum dry it at 50℃ for 6h to finally obtain a γ-CD-MOFs / CS-CELL composite membrane.

[0052] (3) The γ-CD-MOFs / CS-CELL composite membrane (50 mg) was placed in an ethanol solution of carvacrol (20 mg / mL) and shaken overnight for full adsorption. The membrane was washed with ethanol three times to remove the unencapsulated carvacrol and dried under vacuum at 50 °C for 2 h to obtain the CAR@γ-CD-MOFs / CS-CELL composite membrane.

[0053] Example 6

[0054] (1) Dissolve 2g of chitosan powder in 100mL (1%, v / v) acetic acid aqueous solution and stir at room temperature overnight to obtain a 2% (w / v) chitosan solution. Add 5g of cellulose powder to 100mL of deionized water and stir at room temperature for 24h to obtain a 5wt% cellulose dispersion. The chitosan solution was mixed with cellulose dispersions of varying concentrations and stirred for 24h to prepare CS-CELL polysaccharide membranes.

[0055] (2) Add 1.62g of γ-CD and 0.56g of KOH to 50mL of deionized water, sonicate for 1h until the solution is completely dissolved, and filter with a 0.45μm filter membrane. Take 100mg of CS-CELL polysaccharide membrane and immerse it in a 150mL small beaker containing the above solution without sealing. Then place the beaker in a large beaker containing 100mL of methanol, seal it, and place it in a 50℃ oven to react for 12h. After the reaction is completed, add 50mL of methanol solution and 400mg of CTAB to the small beaker and continue to react at room temperature for 3h. After the reaction is completed, wash it three times with isopropanol, activate it in dichloromethane for 2 days, and vacuum dry it at 50℃ for 6h to finally obtain a γ-CD-MOFs / CS-CELL composite membrane.

[0056] (3) The γ-CD-MOFs / CS-CELL composite membrane (50 mg) was placed in an ethanol solution of carvacrol (40 mg / mL) and shaken overnight for full adsorption. The membrane was washed with ethanol three times to remove the unencapsulated carvacrol and dried under vacuum at 50 °C for 2 h to finally obtain the CAR@γ-CD-MOFs / CS-CELL composite membrane.

[0057] Example 7

[0058] (1) Dissolve 2g of chitosan powder in 100mL (1%, v / v) acetic acid aqueous solution and stir at room temperature overnight to obtain a 2% (w / v) chitosan solution. Add 5g of cellulose powder to 100mL of deionized water and stir at room temperature for 24h to obtain a 5wt% cellulose dispersion. The chitosan solution was mixed with cellulose dispersions of varying concentrations and stirred for 24h to prepare CS-CELL polysaccharide membranes.

[0059] (2) Add 1.62g of γ-CD and 0.56g of KOH to 50mL of deionized water, sonicate for 1h until the solution is completely dissolved, and filter with a 0.45μm filter membrane. Take 100mg of CS-CELL polysaccharide membrane and immerse it in a 150mL small beaker containing the above solution without sealing. Then place the beaker in a large beaker containing 100mL of methanol, seal it, and place it in a 50℃ oven to react for 12h. After the reaction is completed, add 50mL of methanol solution and 400mg of CTAB to the small beaker and continue to react at room temperature for 3h. After the reaction is completed, wash it three times with isopropanol, activate it in dichloromethane for 2 days, and vacuum dry it at 50℃ for 6h to finally obtain a γ-CD-MOFs / CS-CELL composite membrane.

[0060] (3) The γ-CD-MOFs / CS-CELL composite membrane (50 mg) was placed in an ethanol solution of carvacrol (60 mg / mL) and shaken overnight for full adsorption. The membrane was washed with ethanol three times to remove the unencapsulated carvacrol and dried under vacuum at 50 °C for 2 h to obtain the CAR@γ-CD-MOFs / CS-CELL composite membrane. Figure 4 As shown in the figure, the γ-CD-MOFs / CS-CELL composite membrane was immersed in five concentrations of carvacrol solutions. The higher the concentration, the higher the loading rate. When the concentration of carvacrol exceeded 20 mg / mL, the loading rate of carvacrol on the CAR@γ-CD-MOFs / CS-CELL composite membrane was basically the same, indicating that the amount of carvacrol in the pores of γ-CD-MOFs reached saturation.

[0061] The release behavior of carvacrol from the humidity-responsive edible polysaccharide-cyclodextrin metal organic framework cling film prepared by the present invention at different relative humidity (22%, 43%, 75%, 98%) was studied. The results are as follows: Figure 5As shown in the figure, at a humidity of 22%, only about 15% of carvacrol was released on the 12th day. At a humidity of 43%, about 33% of carvacrol was released on the 12th day. At a humidity of 75%, 85% of carvacrol was released. At a humidity of 98%, carvacrol was almost completely released on the 10th day. Therefore, the release results indicate that the release of carvacrol from the edible polysaccharide-cyclodextrin metal-organic framework plastic wrap can be triggered by high humidity and that the plastic wrap can be stored at low humidity.

[0062] The antibacterial effect of humidity-responsive edible polysaccharide-cyclodextrin metal organic framework plastic wrap on Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus was studied. Figure 6 As shown. The antibacterial experiment was divided into four groups, namely the blank group without any treatment, the CS-CELL polysaccharide film treatment group, the γ-CD-MOFs treatment group and the CAR@γ-CD-MOFs / CS-CELL composite film treatment group. The experimental results showed that the nutrient agar plates of the blank group, CS-CELL group and γ-CD-MOFs group were full of bacteria, while the CAR@γ-CD-MOFs / CS-CELL composite film group had almost no colony growth. This is because carvacrol is released from the pores of γ-CD-MOFs and acts on bacteria, destroying the bacterial cell membrane, causing the contents to seep out and causing bacterial death. And the bacterial morphology was observed by field emission scanning electron microscopy and found that ( Figure 7 ), the bacteria in the blank group, CS-CELL group, and γ-CD-MOFs group maintained a plump and relatively smooth morphology, while the bacteria treated with the CAR@γ-CD-MOFs / CS-CELL composite membrane underwent wrinkled deformation, which was consistent with the antibacterial test results.

[0063] Further research was conducted on the antibacterial effect of humidity-responsive edible polysaccharide-cyclodextrin metal organic framework cling film on Botrytis cinerea. Figure 8 As shown in the figure, the mycelium of Botrytis cinerea in the blank group without material treatment covered the entire plate of potato glucose medium, while the growth of Botrytis cinerea in the CAR@γ-CD-MOFs / CS-CELL composite membrane group was significantly inhibited.

[0064] The edible cling film provided by the present invention can regulate the release of the antimicrobial agent carvacrol by utilizing the humidity of the packaging environment, achieving controlled-release antimicrobial preservation. The edible polysaccharide film loaded with γ-CD-MOFs nanocarriers not only has high porosity and high encapsulation efficiency, but is also a green, edible nanocarrier with broad application prospects in the field of food preservation.

[0065] The above content describes the technical principles, beneficial effects and features of the present invention. It should be pointed out that the above is only a preferred embodiment of the present invention, but is not limited to the above embodiments. For technicians in the technical field to which the present invention belongs, they can make some improvements and optimizations without departing from the content of the present invention, which should be regarded as belonging to the scope of protection of the present invention.

Claims

1. A method for preparing a humidity-responsive edible polysaccharide-cyclodextrin metal organic framework cling film, characterized by: Chitosan-cellulose was used as an edible polysaccharide matrix, and γ-cyclodextrin metal organic framework nanoparticles were in situ grown on its surface. Carvacrol was loaded as an antibacterial agent by physical adsorption to obtain a humidity-responsive edible polysaccharide-cyclodextrin metal organic framework preservative film, namely CAR@γ-CD-MOFs / CS-CELL composite film. The specific steps are as follows: (1) Preparation of chitosan-cellulose polysaccharide matrix; (2) The polysaccharide matrix is ​​immersed in an aqueous solution of γ-cyclodextrin and potassium ions, forming nucleation sites of γ-CD-MOFs under the action of methanol vapor, and growing into γ-CD-MOFs crystals under the action of methanol and hexadecyltrimethylammonium bromide; (3) The polysaccharide film of in situ grown γ-CD-MOFs nanoparticles was immersed in a carvacrol solution, shaken, fully adsorbed, washed with ethanol, and vacuum dried to obtain a humidity-responsive controlled-release composite film loaded with carvacrol; The specific process of loading carvacrol in step (3) is as follows: immersing 50 mg of the polysaccharide film of the in situ grown γ-CD-MOFs nanoparticles prepared in step (2) in a 20 mg / mL ethanol solution of carvacrol, shaking overnight to fully adsorb carvacrol, taking it out, washing it with anhydrous ethanol to remove unloaded carvacrol, and vacuum drying; The specific process of preparing the chitosan-cellulose polysaccharide matrix in step (1) is as follows: using chitosan solution as a film-forming agent, mixing it with a cellulose dispersion, fully stirring, casting, and drying to form a film to obtain a chitosan-cellulose polysaccharide-based composite film.

2. The method for preparing a humidity-responsive edible polysaccharide-cyclodextrin metal organic framework fresh-keeping film according to claim 1, characterized in that: The specific steps of preparing the chitosan-cellulose polysaccharide matrix in step (1) are as follows: preparing a chitosan acetic acid aqueous solution as a film-forming solution and stirring it overnight; dispersing cellulose in water and stirring it overnight to obtain a uniform cellulose dispersion; mixing the chitosan solution and the cellulose dispersion and stirring them thoroughly to obtain a polysaccharide mixed solution; pouring the mixed solution into a mold by a solution casting method, and drying it in an oven overnight to obtain a polysaccharide matrix.

3. The method for preparing a humidity-responsive edible polysaccharide-cyclodextrin metal organic framework fresh-keeping film according to claim 2, characterized in that: The concentration of the cellulose uniform dispersion is 1% w / v, 3% w / v or 5% w / v.

4. The method for preparing a humidity-responsive edible polysaccharide-cyclodextrin metal organic framework fresh-keeping film according to claim 1, wherein: The specific process of step (2) is as follows: γ-CD and KOH are added to deionized water and ultrasonically dissolved, filtered with a 0.45 μm filter membrane, the polysaccharide film prepared in step (1) is immersed in the above solution, sealed, and methanol vapor is passed through to gradually form γ-CD-MOFs nucleation sites on the surface of the polysaccharide matrix, and then CTAB and methanol solution are added, and the reaction is continued at room temperature to form γ-CD-MOFs crystals, which are washed with isopropanol, activated in dichloromethane, dried in a vacuum oven, and placed in a dry environment for use.

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