Antibacterial fresh-keeping composite film and preparation method and application thereof

Abstract

The application discloses a bacteriostatic fresh-keeping composite film and a preparation method and application thereof, and relates to the technical field of film materials. The bacteriostatic fresh-keeping composite film is prepared by introducing modified ZIF-8 and silver heterojunction particles into a film-forming base with chitosan and pueraria powder as main components, wherein the modified ZIF-8 is loaded with paeonol and has a bacteriostatic fresh-keeping function, and the prepared bacteriostatic fresh-keeping film can effectively delay the corruption process of fruits. Since the film material adopts natural degradable components, meets the requirements of green environmental protection and sustainable development, and has a strong market application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of film materials, in particular to a bacteriostatic fresh-keeping composite film and a preparation method and application thereof. BACKGROUND

[0002] With the improvement of people's living standards, higher requirements are put forward for food preservation. Fresh-keeping film is a fresh-keeping material used in daily life and has a direct impact on the preservation effect. In order to achieve better bacteriostatic effect, bacteriostatic ingredients are often added to the fresh-keeping film to prepare bacteriostatic fresh-keeping film. The bacteriostatic fresh-keeping film can be used as a carrier of various food antioxidants and bacteriostatic agents, and has a fresh-keeping function for food.

[0003] The traditional bacteriostatic fresh-keeping film is mainly made of petroleum-based raw materials, which is not easy to degrade and difficult to recycle. In addition, the preservation effect of the bacteriostatic fresh-keeping film needs to be improved, and it cannot meet the long-term preservation requirements of strawberries and other perishable fruits.

[0004] Therefore, the present application is proposed. SUMMARY

[0005] The present application aims to provide a bacteriostatic fresh-keeping composite film and a preparation method and application thereof, and to significantly improve the preservation effect of the bacteriostatic fresh-keeping composite film.

[0006] The present application is implemented as follows:

[0007] In a first aspect, the present application provides a bacteriostatic fresh-keeping composite film, which comprises a film-forming matrix and an efficacy component dispersed in the film-forming matrix. The film-forming matrix comprises chitosan and pueraria powder, and the efficacy component comprises modified ZIF-8 and silver heterojunction particles. The modified ZIF-8 comprises a ZIF-8 carrier and a paeonol loaded on the ZIF-8 carrier.

[0008] In an optional embodiment, the mass ratio of the pueraria powder, chitosan, silver heterojunction particles and modified ZIF-8 is (1000-10000):(1000-2000):(10-50):(50-300).

[0009] Preferably, when preparing the modified ZIF-8, the molar ratio of zinc salt, imidazole organic ligand and paeonol is controlled to be 1:(2-34):(2.3-2.4).

[0010] Preferably, the silver heterojunction particles comprise silver carbonate and silver oxide.

[0011] In a second aspect, the present application provides a preparation method of the bacteriostatic fresh-keeping composite film of the foregoing embodiments, which comprises:

[0012] In the process of preparing the ZIF-8 material, paeonol is introduced to load the paeonol on the generated ZIF-8 material to obtain the modified ZIF-8.

[0013] The silver heterojunction particles are prepared by a silver ion precipitation reaction in a solution.

[0014] The film-forming matrix, the silver heterojunction particles and the modified ZIF-8 are mixed to prepare a film-forming solution, and the film-forming solution is used for film formation.

[0015] In an optional embodiment, the process for preparing the modified ZIF-8 comprises:

[0016] The zinc salt and the imidazole organic ligand are respectively dissolved to obtain a zinc salt solution and a ligand solution, and the paeonol and the organic solvent are mixed to obtain a paeonol solution;

[0017] The paeonol solution and the zinc salt solution are mixed, and then mixed with the ligand solution for reaction, followed by solid-liquid separation, and the obtained solid material is washed and dried;

[0018] Preferably, the paeonol solution and the zinc salt solution are mixed and stirred for 0.5h-2h, and then mixed with the ligand solution for stirring for 2h-5h.

[0019] In an optional embodiment, the molar ratio of the zinc salt, the imidazole organic ligand and the paeonol is 1:(2-34):(2.3-2.4).

[0020] Preferably, the zinc salt is Zn(NO3)2·6H2O, and the imidazole organic ligand is 2-methylimidazole.

[0021] Preferably, the solvent used for preparing the zinc salt solution and the ligand solution is water, the solvent used for preparing the paeonol solution is an organic alcohol solvent, the concentration of the zinc salt solution is 0.05mmol / mL-0.20mmol / mL, the concentration of the ligand solution is 1.0mmol / mL-2.5mmol / mL, and the concentration of the paeonol solution is 0.05mmol / mL-0.20mmol / mL.

[0022] In an optional embodiment, the process for preparing the silver heterojunction particles comprises: mixing silver nitrate, water and a surfactant to obtain a mixed solution, heating the mixed solution to 50℃-70℃, mixing with a carbonate for 2h-6h, followed by solid-liquid separation, and washing and drying the obtained solid material.

[0023] Preferably, the surfactant is polyvinylpyrrolidone with a molecular weight of 8000Mw-360000Mw.

[0024] Preferably, the carbonate is selected from at least one of sodium carbonate and potassium carbonate.

[0025] In an optional embodiment, the mass ratio of silver nitrate and surfactant is 1:(8-10), and the molar ratio of silver nitrate to carbonate radical ion in carbonate is 1:(1-3).

[0026] In an optional embodiment, the process of preparing the film-forming solution comprises:

[0027] The chitosan and the aqueous acetic acid solution are mixed and dissolved to obtain a chitosan solution;

[0028] The pueraria powder is dispersed in hot water at 93-98℃ and stirred for 30-90min to obtain a paste;

[0029] The paste is mixed with a plasticizer, and then cooled to 55-70℃ and mixed with the chitosan solution and stirred for 10-60min, and then the silver heterojunction particles are added and stirred for 5-60min, and when the temperature is reduced to 35-45℃, the modified ZIF-8 is mixed and stirred for 10-60min, and then defoaming treatment is performed;

[0030] Preferably, the mass ratio of pueraria powder, chitosan, silver heterojunction particles and modified ZIF-8 is (1000-10000):(1000-2000):(10-50):(50-300);

[0031] Preferably, the plasticizer is glycerol, and the mass ratio of glycerol to chitosan is (10-50):100;

[0032] Preferably, the volume fraction of acetic acid in the aqueous acetic acid solution is 0.05-0.2%, and the mass fraction of chitosan in the chitosan solution is 1%-2%;

[0033] Preferably, the mass ratio of pueraria powder and hot water is (1-10):(95-105).

[0034] In an optional embodiment, the film-forming solution is poured into a film-forming container, and then dried to form a film.

[0035] In a third aspect, the application provides the use of the antibacterial and fresh-keeping composite film of any one of the preceding embodiments or prepared by the preparation method of any one of the preceding embodiments in the preparation of antibacterial and fresh-keeping packaging materials.

[0036] The application has the following beneficial effects: The application introduces modified ZIF-8 and silver heterojunction particles into a film-forming matrix mainly composed of chitosan and pueraria powder, wherein the modified ZIF-8 is loaded with paeonol, has antibacterial and fresh-keeping functions, and the prepared antibacterial and fresh-keeping film can effectively delay the spoilage process of fruits. Since the film material uses natural degradable components, it meets the requirements of green environmental protection and sustainable development, and has strong market application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those of ordinary skill in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0038] Figure 1 Fig. 1 is SEM morphology diagrams of ZIF-8, PAE@ZIF-8 and silver heterojunction; (A) represents ZIF-8, (B) represents PAE@ZIF-8, and (C) represents silver heterojunction;

[0039] Figure 2 Fig. 2 is infrared spectra and X-ray diffraction patterns of the three materials; (A) represents the infrared spectrum, and (B) represents the X-ray diffraction pattern;

[0040] Figure 3 Fig. 3 is an X-ray diffraction pattern of a nanocomposite film;

[0041] Figure 4 Fig. 4 is a fresh-keeping effect diagram of different nanocomposite films on raspberries;

[0042] Figure 5 Fig. 5 is a weight loss rate result diagram of raspberries. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described as follows. The specific conditions not mentioned in the embodiments are carried out according to conventional conditions or the conditions suggested by the manufacturer. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be purchased in the market.

[0044] The embodiments of the present application provide a preparation method of a bacteriostatic fresh-keeping composite film. Chitosan and pueraria powder are used as a film-forming matrix, and ZIF-8 material loaded with paeonol (PAE@ZIF-8) and silver heterojunction are added therein. The composite film has high efficient bacteriostatic fresh-keeping function and can effectively delay the corruption process of fruits. The preparation steps are as follows:

[0045] S1, preparation of modified ZIF-8

[0046] In the process of preparing ZIF-8 material, paeonol is introduced to load paeonol on the generated ZIF-8 material to obtain modified ZIF-8. ZIF-8 material becomes an ideal carrier due to its high specific surface area and porosity, and is widely used in adsorption and release of active ingredients. By loading active molecules paeonol, ZIF-8 can exert its excellent function to stably release these active ingredients, thereby realizing various functional applications. Paeonol is loaded into ZIF-8 by one-pot synthesis method, and it is found that the loading rate of ZIF-8 to paeonol can reach 36.33%, and the slow-release effect can be achieved.

[0047] It should be noted that paeonol (Paeonol, PAE) is a natural phenolic compound widely present in the root bark of peony. It has antioxidant, anti-inflammatory, antibacterial, antitumor and other biological activities. Paeonol contains phenolic hydroxyl groups in its chemical structure, which can effectively scavenge free radicals, delay cell aging, and has strong antioxidant capacity. In addition, paeonol also has certain antibacterial effect, which can inhibit the growth of various pathogenic microorganisms. In the field of food, paeonol is gradually concerned and applied in the research and development of preservative film due to its natural antibacterial and antioxidant properties. By adding paeonol to the preservative film material, the shelf life of food can be effectively prolonged, and food oxidation and bacterial contamination can be prevented, and the taste and nutritional value of food can be maintained. Since it is natural, the application of paeonol in preservative film not only meets the trend of green environmental protection, but also reduces the dependence on artificially synthesized chemicals, and has important market prospects. Therefore, the application of paeonol in preservative film can not only improve the preservation effect, but also enhance the biodegradability of the film material.

[0048] It should be noted that zinc-based metal organic framework (ZIF-8) is composed of zinc ions and 2-methyl imidazole as ligand, which has a topological structure similar to zeolite. The advantages of ZIF-8 include good thermal stability and chemical stability, especially strong hydrolysis resistance in humid environment. In addition, ZIF-8 also has high specific surface area and porosity, which is suitable for adsorption and release of active ingredients. Although ZIF-8 has many advantages, it also has some disadvantages, such as the need for organic solvent in its synthesis process, which may cause environmental pollution. In addition, the pore structure and chemical stability of ZIF-8 still need to be improved under certain specific conditions to ensure its stability in long-term application.

[0049] In the embodiments of the present application, ZIF-8 has high specific surface area and adjustable pore structure, which can effectively adsorb and slow-release active substances such as antioxidants, antibacterial agents and preservatives, thereby prolonging the shelf life of food. In addition, they can also effectively isolate external gases, reduce the oxidation and water loss of food, and maintain the taste and nutrition of food.

[0050] In some embodiments, the process of preparing modified ZIF-8 includes: dissolving zinc salt and imidazole organic ligands to obtain zinc salt solution and ligand solution, respectively; mixing paeonol and an organic solvent to obtain paeonol solution; mixing the paeonol solution and zinc salt solution, and then mixing and reacting them with the ligand solution; followed by solid-liquid separation; and washing and drying the obtained solid material. Paeonol and zinc salt are first mixed evenly before the ligand is added for reaction, so that paeonol is loaded onto the formed ZIF-8 material to prepare modified ZIF-8. Specifically, the solid-liquid separation method is not limited and can be centrifugal filtration, with a centrifugation speed of 7000 r / min-9000 r / min (e.g., 8000 r / min) and a centrifugation time of 10 min-20 min (e.g., 15 min); the washing solvent can be water, and the number of washes is unlimited; the drying method is not limited and can be vacuum freeze drying, with a drying time of 10 h-15 h.

[0051] In some embodiments, the paeonol solution and zinc salt solution are first mixed and stirred for 0.5h-2h (e.g., 0.5h, 1.0h, 1.5h, 2.0h, etc.), and then the ligand solution is slowly added and stirred for 2h-5h (e.g., 2h, 3h, 4h, 5h, etc.). By controlling the mixing time, the reaction is made sufficient, and the paeonol is uniformly loaded. Before mixing the paeonol solution and zinc salt solution, the paeonol solution, zinc salt solution, and ligand solution can all be sonicated to ensure complete dissolution.

[0052] In some embodiments, the molar ratio of zinc salt, imidazole organic ligand, and paeonol is 1:(2-34):(2.3-2.4). Adjusting the amounts of zinc salt, imidazole organic ligand, and paeonol can further improve the preservation effect. The zinc salt can be Zn(NO3)2·6H2O, but is not limited to it; the imidazole organic ligand can be 2-methylimidazole, but is not limited to it. The molar ratio of zinc salt, imidazole organic ligand, and paeonol can be 1:2:2.30, 1:5:2.31, 1:8:2.32, 1:10:2.33, 1:13:2.34, 1:15:2.35, 1:20:2.36, 1:23:2.37, 1:25:2.38, 1:30:2.39, 1:34:2.40, etc.

[0053] In some embodiments, the solvent used to prepare the zinc salt solution and ligand solution is water, and the solvent used to prepare the paeonol solution is an organic alcohol solvent (such as methanol, but not limited to this). The concentration of the zinc salt solution is 0.05 mmol / mL-0.20 mmol / mL, the concentration of the ligand solution is 1.0 mmol / mL-2.5 mmol / mL, and the concentration of the paeonol solution is 0.05 mmol / mL-0.20 mmol / mL. Solution concentrations within the above ranges allow for better dissolution of the reaction raw materials, ensuring a complete reaction. The total amount of water used refers to the total amount of water used to prepare the zinc salt solution and ligand solution. The total amount of water used per gram of imidazole organic ligand can be 6 mL, 7 mL, 8 mL, etc., and the corresponding amount of organic alcohol solvent can be 15 mL, 16 mL, 17 mL, 18 mL, etc.

[0054] S2, Preparation of silver heterojunction particles

[0055] Silver heterojunction particles were prepared by utilizing the precipitation reaction of silver ions in solution. The antibacterial effect of silver was then leveraged to further enhance the preservation effect of the composite membrane. Silver heterojunctions were synthesized via a hydrothermal method, utilizing their ability to release silver ions and exert bactericidal effects to provide antibacterial functionality to the membrane material.

[0056] In some embodiments, the preparation process of silver heterojunction particles includes: mixing silver nitrate, water, and a surfactant to obtain a mixed solution; heating the mixed solution to 50℃-70℃ (e.g., 50℃, 60℃, 70℃, etc.); then reacting it with carbonate for 2h-6h (e.g., 2h, 3h, 4h, 5h, 6h, etc.); followed by solid-liquid separation; and washing and drying the obtained solid material. During the reaction, anions and carbonate ions combine and precipitate, while a small amount of anions are oxidized, ultimately yielding brown silver heterojunction particles (AgH) containing Ag2CO3 and Ag2O. The addition of a surfactant can effectively prevent excessive particle growth, which would affect the dispersion effect in the composite membrane.

[0057] Specifically, the solid-liquid separation method is not limited, and centrifugal filtration can be used; the washing method is not limited, and water washing can be used; drying can be carried out in a vacuum drying oven, and the drying temperature can be controlled at 50℃-70℃, and the drying time can be 10h-15h.

[0058] In some embodiments, the surfactant can be polyvinylpyrrolidone (PVP) with a molecular weight of 8000 Mw-360000 Mw, such as 8000 Mw, 10000 Mw, 50000 Mw, 100000 Mw, 200000 Mw, 300000 Mw, 360000 Mw, etc. Molecular weights within the above range can effectively control the particle size of silver heterojunctions. The carbonate is selected from at least one of sodium carbonate and potassium carbonate, and the carbonate can be any one or more of the above.

[0059] In some embodiments, the mass ratio of silver nitrate to surfactant is 1:(8-10), such as 1:8, 1:9, 1:10, etc., and the molar ratio of silver nitrate to carbonate ions in carbonate is 1:(1-3), such as 1:1, 1:2, 1:3, etc. By adjusting the amount of each raw material, the silver ions can react fully, and the resulting silver heterojunction particles have a suitable particle size.

[0060] It should be noted that silver heterojunctions (AgH) possess excellent optical, electrical, and catalytic properties. Their main advantage lies in their strong antibacterial properties, effectively inhibiting the growth of microorganisms in food and thus extending its shelf life. Furthermore, the photocatalytic properties of silver heterojunctions enable them to decompose harmful substances under ultraviolet light irradiation, further improving food safety. In the food packaging field, the antibacterial properties and photocatalytic activity of silver heterojunctions offer immense potential. By applying silver heterojunctions to packaging materials, food contamination and spoilage can be effectively inhibited, improving food quality and shelf life, making them particularly suitable for packaging perishable foods and in high-humidity environments.

[0061] S3. Preparation of antibacterial and food-preserving composite film

[0062] A film-forming solution was prepared by mixing a film-forming matrix, silver heterojunction particles, and modified ZIF-8. The film was then formed using this solution to obtain a composite film with antibacterial and preservative properties. In the food packaging field, the adsorption properties of ZIF-8 can effectively capture and release components beneficial to food preservation, such as antioxidants and antibacterial agents. Furthermore, combining this with silver heterojunction materials can further enhance the antibacterial properties of the packaging film. The silver heterojunction not only releases silver ions but also effectively inhibits the growth and reproduction of common bacteria in food, reducing the risk of food spoilage. By combining ZIF-8-loaded paeonol with silver heterojunctions, the resulting composite material exhibits strong antibacterial properties, significantly extending the shelf life of food, and is particularly suitable for packaging perishable foods.

[0063] In some embodiments, the process of preparing the film-forming solution includes: (1) mixing and dissolving chitosan and an aqueous acetic acid solution to obtain a chitosan solution; (2) dispersing kudzu root powder in hot water at 93℃-98℃ and stirring for 30min-90min to completely gelatinize the kudzu root powder and obtain a paste; (3) mixing the paste with a plasticizer, then cooling it to 55℃-70℃ and mixing it with the chitosan solution for 10min-60min, then adding silver heterojunction particles and stirring for 5min-60min, and when the temperature is reduced to 35℃-45℃, mixing it with modified ZIF-8 and stirring for 10min-60min, and then performing defoaming treatment.

[0064] It should be noted that by adjusting the order and temperature of adding each raw material, it is easier to disperse the raw materials evenly. For example, if silver heterojunction particles are added at around 40°C, they are prone to aggregation, which is not conducive to preparing a uniform film.

[0065] Specifically, in step (2) above, the temperature of the hot water can be 93℃, 94℃, 95℃, 96℃, 97℃, 98℃, etc., and the stirring time can be 30min, 40min, 50min, 60min, 70min, 80min, 90min, etc. In step (3) above, the temperature at which the chitosan solution is added can be 55℃, 60℃, 65℃, 70℃, etc., and the stirring time can be 10min, 20min, 30min, 40min, 50min, 60min, 70min, 80min, 90min, etc.; the stirring time after adding the silver heterojunction particles can be 5min, 10min, 20min, 30min, 40min, 50min, 60min, etc.; the temperature at which the modified ZIF-8 is added can be 35℃, 40℃, 45℃, etc., and the stirring time can be 10min, 20min, 30min, 40min, 50min, 60min, etc. The defoaming treatment method is not limited; it can be done by ultrasonic removal, and the ultrasonic time can be 1 min to 5 min.

[0066] It should be noted that chitosan itself possesses natural antibacterial properties and is a biodegradable material with excellent biocompatibility. Based on this, combined with natural ingredients such as kudzu root powder, the prepared nanocomposite film not only possesses multiple functions including anti-oxidation and antibacterial properties, but also effectively slows down the oxidation process of fruits and vegetables, reduces moisture loss, and maintains the freshness and nutritional components of food. This film material not only protects food but also degrades naturally after application, avoiding the environmental pollution caused by traditional plastic packaging. Therefore, the composite material formed by combining ZIF-8-loaded paeonol with silver heterostructures exhibits significant antibacterial and preservation effects. Furthermore, the combination with natural materials such as chitosan and kudzu root powder allows this composite film to not only extend the shelf life of food and maintain its taste and nutrition but also meet the needs of environmental protection and sustainable development. Its biocompatibility and biodegradability make it an ideal choice for the future development of the food packaging industry.

[0067] In some embodiments, the mass ratio of kudzu root powder, chitosan, silver heterojunction particles and modified ZIF-8 is (1000-10000):(1000-2000):(10-50):(50-300). By adjusting the mass of the above main raw materials, the active ingredients in the prepared composite film are evenly dispersed, resulting in a better preservation and antibacterial effect. Specifically, the mass ratio of kudzu root powder, chitosan, silver heterojunction particles, and modified ZIF-8 can be 1000:1000:10:50, 2000:1100:15:80, 3000:1200:20:100, 4000:1300:25:130, 5000:1400:30:150, 6000:1500:35:180, 7000:1600:40:200, 8000:1700:43:250, 9000:1800:45:280, 10000:2000:50:300, etc.

[0068] Furthermore, the plasticizer can be glycerol, with a glycerol to chitosan mass ratio of (10-50):100, such as 10:100, 20:100, 30:100, 40:100, 50:100, etc. The volume fraction of acetic acid in the acetic acid aqueous solution is 0.05-0.2%, such as 0.05%, 0.10%, 0.15%, 0.20%, etc. By adjusting the amount of acetic acid aqueous solution, the mass fraction of chitosan in the chitosan solution is made to be 1%-2%, such as 1.0%, 1.3%, 1.5%, 1.8%, 2.0%, etc.

[0069] The mass ratio of kudzu root powder to hot water is (1-10):(95-105). Within this range, the active ingredients can be better dispersed, resulting in a uniform composite film. Specifically, the mass ratio of kudzu root powder to hot water can be 1:95, 3:98, 5:100, 8:102, 10:105, etc.

[0070] In some embodiments, the method of film formation is not limited. For example, the film-forming solution can be poured into a film-forming container and then dried to form a film. The film-forming container can be a petri dish with a diameter of 15 cm, the drying temperature can be 30℃-40℃, and the drying time can be 30h-40h.

[0071] This invention provides an antibacterial and preservative composite film, comprising a film-forming matrix and active ingredients dispersed within the matrix. The film-forming matrix includes chitosan and kudzu root powder, while the active ingredients include modified ZIF-8 and silver heterojunction particles. The modified ZIF-8 comprises a ZIF-8 carrier and paeonol loaded onto the ZIF-8 carrier. This antibacterial and preservative film can effectively delay the spoilage process of fruit. Preservation experiments using raspberry as a model fruit showed that the film material exhibits excellent effects in extending the shelf life of fruit. Because the film material uses natural and biodegradable components, it meets the requirements of green environmental protection and sustainable development, and has strong market application prospects. Furthermore, the slow-release properties of ZIF-8 and the antibacterial effect of the silver heterojunction further improve the overall performance of the film material. In summary, the nano-preservative composite film shows great application potential in the field of food preservation, inhibiting bacterial growth, extending the shelf life of food, and meeting environmental protection requirements, thus possessing broad application prospects.

[0072] In some embodiments, the mass ratio of kudzu root powder, chitosan, silver heterojunction particles, and modified ZIF-8 is (1000-10000):(1000-2000):(10-50):(50-300); when preparing modified ZIF-8, the molar ratio of zinc salt, imidazole organic ligand, and paeonol is controlled to be 1:(2-34):(2.3-2.4). By controlling the amount of key raw materials used in the preparation process, the antibacterial and preservation effects of the product can be improved.

[0073] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0074] Example 1

[0075] This embodiment provides a method for preparing an antibacterial and food-preserving composite film, the steps of which are as follows:

[0076] (1) Preparation of modified ZIF-8

[0077] A zinc salt solution was obtained by dissolving 1 mmol Zn(NO3)2·6H2O in 10 mL of deionized water, and a ligand solution was obtained by dissolving 16 mmol 2-methylimidazole in 10 mL of deionized water. A paeonol solution was obtained by dissolving 2.4 mmol paeonol in 20 mL of methanol. The zinc salt solution, ligand solution, and paeonol solution were sonicated at room temperature (approximately 25°C) to ensure complete dissolution.

[0078] The paeonol solution was mixed with the zinc salt solution and magnetically stirred for 1 hour. Then, the ligand solution was slowly added and magnetically stirred for 3 hours. The mixture was centrifuged and filtered (centrifugation conditions: 8000 r / min, 15 min). The mixture was washed with water and freeze-dried under vacuum for 12 hours to obtain the paeonol-loaded ZIF-8 material (PAE@ZIF-8).

[0079] Note: In this embodiment, the molar ratio of zinc salt, imidazole organic ligand and paeonol is 1:16:2.4.

[0080] (2) Preparation of silver heterojunction particles

[0081] 0.1 mmol of AgNO3 was dissolved in 1 mL of deionized water, and then added to 10 mL of PVP aqueous solution (PVP concentration of 1.88 mol / L, molecular weight of PVP used is 8000 Mw). The resulting mixture was magnetically stirred at room temperature for 1 hour. After the solution temperature was raised to 60 °C, 1 mL of 0.1 mol / L sodium carbonate solution was added, and the mixture was stirred at this temperature for 4 hours. After centrifugation and filtration, the mixture was washed three times at room temperature and dried in a vacuum drying oven at 60 °C for 12 hours to obtain a brown Ag2CO3 / Ag2O silver heterojunction (AgH).

[0082] Note: In this embodiment, the mass ratio of silver nitrate to PVP is 1:8.8, and the molar ratio of silver nitrate to carbonate ions in carbonate is 1:1.

[0083] (3) Preparation of antibacterial and freshness-preserving composite film

[0084] First, dissolve 2g of chitosan in 100mL of 0.1% v / v acetic acid and stir until completely dissolved. Then, disperse 5g of kudzu root powder in 100mL of 95℃ water and stir for 60min to complete gelatinization of the kudzu root powder. Next, add 0.6g of glycerol as a plasticizer and stir until completely homogeneous. When the temperature of the kudzu root powder drops to 60℃, pour in the chitosan solution and mix for 30min. Then, add 40mg of AgH granules and stir for 20min. When the temperature of the solution drops to 40℃, add 100mg of PAE@ZIF-8 and stir for 20min. Finally, sonicate for 2min to remove air bubbles. Pour the film-forming solution into a 15cm diameter petri dish and dry at 35℃ in an oven for 36 hours to obtain a mixed film of chitosan, kudzu root powder, PAE@ZIF-8, and AgH (CS-KP-AgH). Before testing the film's performance, the film was conditioned at 25°C and 50% relative humidity until a constant weight was achieved.

[0085] Note that in this embodiment, the mass ratio of kudzu root powder, chitosan, silver heterojunction particles and modified ZIF-8 is 5000:2000:40:100; the mass ratio of glycerol to chitosan is 30:100; and the mass ratio of kudzu root powder to hot water is 5:100.

[0086] Example 2

[0087] The only difference from Example 1 is that the mass ratio of kudzu root powder, chitosan, silver heterojunction particles and modified ZIF-8 in step (3) is different. The mass ratio of this example is 5000:2000:10:100. The mass of kudzu root powder remains unchanged. The mass of chitosan, silver heterojunction particles and modified ZIF-8 are adjusted accordingly. The amount of other raw materials remains unchanged.

[0088] Example 3

[0089] The only difference from Example 1 is that the mass ratio of kudzu root powder, chitosan, silver heterojunction particles and modified ZIF-8 in step (3) is different. The mass ratio in this example is 5000:2000:20:100. The mass of kudzu root powder remains unchanged. The mass of chitosan, silver heterojunction particles and modified ZIF-8 are adjusted accordingly. The amount of other raw materials remains unchanged.

[0090] Example 4

[0091] The only difference from Example 1 is that the mass ratio of glycerol to chitosan in step (3) is different. The mass ratio in this example is 10:100. Only the amount of glycerol is changed, while the amount of other raw materials remains the same.

[0092] Example 5

[0093] The only difference from Example 1 is that the mass ratio of glycerol to chitosan in step (3) is different. The mass ratio in this example is 20:100. Only the amount of glycerol is changed, while the amount of other raw materials remains the same.

[0094] Comparative Example 1

[0095] This comparative example provides a pure chitosan membrane (CS). The specific steps are as follows: First, 2g of chitosan was dissolved in 100mL of 0.1% v / v acetic acid and stirred until completely dissolved. Then, 0.06g of glycerol was added as a plasticizer and stirred until completely homogeneous. When the temperature of the kudzu root powder dropped to 60℃, the chitosan solution was poured in and mixed and stirred for 30 minutes. Finally, the mixture was sonicated for 2 minutes to remove air bubbles. The film-forming solution was poured into a 15cm diameter petri dish and dried in an oven at 35℃ for 36 hours to obtain the pure chitosan membrane (CS).

[0096] Comparative Example 2

[0097] This comparative example provides a chitosan and kudzu root powder mixed membrane (CS-K). The specific steps are as follows: First, dissolve 2g of chitosan in 100mL of 0.1% v / v acetic acid and stir until completely dissolved. Then, disperse 5g of kudzu root powder in 100g of water at 95℃ and stir for 60min to complete gelatinization of the kudzu root powder. Then, add 0.06g of glycerol as a plasticizer and stir until completely homogeneous. When the temperature of the kudzu root powder drops to 60℃, pour in the chitosan solution and mix for 30min. Finally, sonicate for 2min to remove air bubbles. Pour the film-forming solution into a 15cm diameter petri dish and dry at 35℃ in an oven for 36 hours to obtain the chitosan and kudzu root powder mixed membrane (CS-K).

[0098] Comparative Example 3

[0099] This comparative example provides a chitosan-kudzu root powder and PAE@ZIF-8 mixed membrane (CS-KP). The specific steps are as follows: First, dissolve 2g of chitosan in 100mL of 0.1% v / v acetic acid and stir until completely dissolved. Then, disperse 5g of kudzu root powder in 100g of 95℃ water and stir for 60min to complete gelatinization of the kudzu root powder. Then, add 0.06g of glycerol as a plasticizer and stir until completely homogeneous. When the temperature of the kudzu root powder drops to 60℃, pour in the chitosan solution and mix for 30min. When the temperature of the solution drops to 40℃, add 100mg of PAE@ZIF-8 and stir for 20min. Finally, sonicate for 2min to remove air bubbles. Pour the film-forming solution into a 15cm diameter petri dish and dry at 35℃ in an oven for 36 hours to obtain the chitosan-kudzu root powder and PAE@ZIF-8 mixed membrane (CS-KP).

[0100] Comparative Example 4

[0101] Comparative Example 4 provides commercially available PVC film.

[0102] Experimental Example 1

[0103] The antibacterial and antimicrobial preservation films prepared in Example 1 and Comparative Examples 1-4 were subjected to preservation and antimicrobial tests:

[0104] Raspberries of similar size, color, and freshness were selected for a practical preservation experiment. Specifically, the raspberries were washed and disinfected with deionized water. Then, the raspberries were wrapped with pure chitosan film (CS), a mixture of chitosan and kudzu root powder (CS-K), a mixture of chitosan, kudzu root powder, and PAE@ZIF-8 (CS-KP), a mixture of chitosan, kudzu root powder, PAE@ZIF-8, and AgH (CS-KP-AgH), and commercially available PVC film. Untreated raspberries served as a control group. The treated raspberries were then placed at room temperature, and changes in their appearance and quality were studied.

[0105] from Figure 1 The SEM images show that ZIF-8 has a dodecahedral structure with an average diameter of 90.56 ± 17.31 nm. After PAE modification, the nanoparticles changed from a dodecahedral structure to a spherical structure with more uniform size and an average diameter of 42.65 ± 3.79 nm. The bulk structure of AgH has a rough surface with many small spherical particles attached. These may be small particles of silver oxide attached to the surface of silver carbonate.

[0106] Please refer to Figure 2 In the infrared spectrum of PAE@ZIF-8, the intensity of many absorption bands of ZIF-8 was significantly weakened or disappeared, indicating that PAE is mainly encapsulated in the material or partially adsorbed on the surface of ZIF-8. Meanwhile, at 1636 cm⁻¹... -1 The absorption band at that point is the characteristic peak of PAE's C=O, proving the successful loading of PAE onto ZIF-8. Furthermore, it can be observed that ZIF-8 and PAE@ZIF-8 have many very similar absorption bands, indicating that PAE@ZIF-8 forms a complete structure.

[0107] The crystal structure of the composite film was studied by XRD analysis, and its spectrum is as follows: Figure 3 As shown, the appearance of the peak near 20.5 degrees indicates the amorphous structure of chitosan. The addition of kudzu root powder and nanomaterials did not change the peak position, but weakened the peak intensity. This indicates that hydrogen bonds are formed between chitosan and starch in kudzu root powder, restricting the movement of molecular bonds and inhibiting the crystallization process. It also demonstrates the complete structure of the nanocomposite film and its successful synthesis.

[0108] from Figure 4As can be seen, the raspberries in the control group lost moisture rapidly, shrinking to almost half their original size after 5 days. The raspberries wrapped in CS and CS-K showed slight shrinkage, but holes were observed in the CS group raspberries due to significant water loss. The raspberries wrapped in CS-KP began to turn white on the 5th day. Raspberries wrapped in commercially available PVC developed mold on the 3rd day. This indicates that CS-KP-AgH successfully extended the shelf life of the raspberries.

[0109] Figure 5 The changes in the weight loss rate of raspberries were shown. The control group raspberries experienced the fastest weight loss. By day 5, the weight loss exceeded half, reaching 54.92%. The weight loss rates of raspberries coated with CS, CS-K, and CS-KP were 48.06%, 45.92%, and 44.83%, respectively. The weight loss rate of raspberries packaged with CS-KP-AgH was relatively low, at 36.22%. Although the weight loss of PVC-treated raspberries was relatively small, the impermeability of the film may have led to faster spoilage. Therefore, the prepared nanocomposite film has a certain preservation effect.

[0110] Experimental Example 2

[0111] The performance of the antibacterial preservation films prepared in Examples 1-7 was tested, and the results are shown in Table 1.

[0112]

[0113] As shown in Table 1, the composite film prepared in the embodiments of the present invention has superior antibacterial and preservation effects. Comparison of Examples 1-5 reveals that variations in a single factor can affect various properties of the membrane, such as water vapor permeability, membrane thickness, and ABTS free radical scavenging rate. Through comparison, it was found that the composite film prepared in this invention has good barrier properties and antioxidant capacity, and its moderate thickness enables it to exert an antibacterial effect, effectively extending the shelf life of raspberries.

[0114] Example 1 is the optimal example. The antibacterial preservation film prepared in Example 1 has low water vapor permeability, which can effectively block external moisture; the film thickness is moderate and the color of the film is also dark, which can effectively block ultraviolet rays; it has strong antioxidant properties and good antibacterial properties.

[0115] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An antibacterial and preservative composite film, characterized in that, The film-forming matrix includes a film-forming matrix and an active ingredient dispersed in the film-forming matrix. The film-forming matrix includes chitosan and kudzu root powder. The active ingredient includes modified ZIF-8 and silver heterojunction particles. The modified ZIF-8 includes a ZIF-8 carrier and paeonol loaded on the ZIF-8 carrier. The mass ratio of kudzu root powder, chitosan, the silver heterojunction particles, and the modified ZIF-8 is (1000-10000):(1000-2000):(10-50):(50-300). When preparing the modified ZIF-8, the molar ratio of zinc salt, imidazole organic ligand, and paeonol was controlled to be 1:(2-34):(2.3-2.4). The silver heterojunction particles comprise silver carbonate and silver oxide; the preparation process of the silver heterojunction particles includes: mixing silver nitrate, water, and a surfactant to obtain a mixed solution, heating the mixed solution to 50℃-70℃, then mixing and reacting it with carbonate for 2h-6h, followed by solid-liquid separation, and washing and drying the obtained solid material; the surfactant is polyvinylpyrrolidone with a molecular weight of 8000Mw-360000Mw; the carbonate is selected from at least one of sodium carbonate and potassium carbonate; the mass ratio of silver nitrate to the surfactant is 1:(8-10), and the molar ratio of silver nitrate to carbonate ions in the carbonate is 1:(1-3).

2. A method for preparing the antibacterial and preservative composite film according to claim 1, characterized in that, include: Paeonol was introduced during the preparation of ZIF-8 material, and paeonol was loaded onto the generated ZIF-8 material to obtain modified ZIF-8; when preparing the modified ZIF-8, the molar ratio of zinc salt, imidazole organic ligand and paeonol was controlled to be 1:(2-34):(2.3-2.4). Silver heterojunction particles are prepared by precipitation reaction of silver ions in solution. The preparation process of the silver heterojunction particles includes: mixing silver nitrate, water and a surfactant to obtain a mixed solution; heating the mixed solution to 50℃-70℃; reacting it with a carbonate for 2h-6h; then separating the solid and liquid components; washing and drying the obtained solid material; the surfactant is polyvinylpyrrolidone with a molecular weight of 8000Mw-360000Mw; the carbonate is selected from at least one of sodium carbonate and potassium carbonate; the mass ratio of silver nitrate to the surfactant is 1:(8-10); and the molar ratio of silver nitrate to carbonate ions in the carbonate is 1:(1-3). A film-forming solution is prepared by mixing the film-forming matrix, the silver heterojunction particles, and the modified ZIF-8, and a film is formed using the film-forming solution. The film-forming matrix includes chitosan and kudzu root powder, and the mass ratio of kudzu root powder, chitosan, the silver heterojunction particles, and the modified ZIF-8 is (1000-10000):(1000-2000):(10-50):(50-300).

3. The preparation method according to claim 2, characterized in that, The process for preparing the modified ZIF-8 includes: Zinc salt and imidazole organic ligands were dissolved to obtain zinc salt solution and ligand solution, respectively. Paeonol was mixed with an organic solvent to obtain paeonol solution. The paeonol solution and the zinc salt solution are mixed and then reacted with the ligand solution. After solid-liquid separation, the resulting solid material is washed and dried.

4. The preparation method according to claim 3, characterized in that, First, mix and stir the paeonol solution and the zinc salt solution for 0.5h-2h, then mix and stir with the ligand solution for 2h-5h.

5. The preparation method according to claim 3, characterized in that, The zinc salt is Zn(NO3)2·6H2O, and the imidazole organic ligand is 2-methylimidazole.

6. The preparation method according to claim 5, characterized in that, The solvent used to prepare the zinc salt solution and the ligand solution is water, and the solvent used to prepare the paeonol solution is an organic alcohol solvent. The concentration of the zinc salt solution is 0.05 mmol / mL to 0.20 mmol / mL, the concentration of the ligand solution is 1.0 mmol / mL to 2.5 mmol / mL, and the concentration of the paeonol solution is 0.05 mmol / mL to 0.20 mmol / mL.

7. The preparation method according to claim 2, characterized in that, The process of preparing the film-forming solution includes: Chitosan and an aqueous acetic acid solution were mixed and dissolved to obtain a chitosan solution; Disperse kudzu root powder in hot water at 93℃-98℃ and stir for 30min-90min to obtain a paste; The paste is mixed with a plasticizer, then cooled to 55℃-70℃ and mixed with a chitosan solution for 10min-60min. The silver heterojunction particles are then added and stirred for 5min-60min. When the temperature is reduced to 35℃-45℃, the modified ZIF-8 is mixed and stirred for 10min-60min, followed by defoaming treatment.

8. The preparation method according to claim 7, characterized in that, The plasticizer is glycerol, and the mass ratio of glycerol to chitosan is (10-50):

100.

9. The preparation method according to claim 7, characterized in that, The volume fraction of acetic acid in the acetic acid aqueous solution is 0.05-0.2%, and the mass fraction of chitosan in the chitosan solution is 1%-2%.

10. The preparation method according to claim 7, characterized in that, The mass ratio of kudzu root powder to hot water is (1-10):(95-105).

11. The preparation method according to claim 7, characterized in that, The film-forming solution is poured into a film-forming container and then dried to form a film.

12. The application of the antibacterial and fresh-keeping composite film of claim 1 or the antibacterial and fresh-keeping composite film prepared by any one of claims 2-11 in the preparation of antibacterial and fresh-keeping packaging materials.

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