Preservative film agent and preparation method thereof

Abstract

The invention discloses a preservative film agent and a preparation method thereof, and belongs to the technical field of preservation. The preservative film agent comprises the following raw materials: polyvinyl alcohol, hydroxy propyl cellulose, glycerol and an antibacterial agent, wherein the antibacterial agent is a cinnamyl aldehyde-loaded Pickering emulsion; a Pickering emulsion is dispersed in a PVA / HPC composite film agent, and a solvent pouring method is adopted to prepare the composite film with antibacterial performance. According to the invention, polyvinyl alcohol and hydroxy propyl cellulose are selected to form a film together so as to overcome the defects of a traditional film agent, and the cinnamyl aldehyde-loaded Pickering emulsion is dispersed in a composite film agent prepared from PVA / HPC, so that the comprehensive preservative film agent with good preservation effect and antibacterial ability is obtained.

Description

Technical Field

[0001] This invention belongs to the field of food preservation technology, specifically relating to a food preservation film agent and its preparation method. Background Technology

[0002] Fresh produce, especially fruits and vegetables, suffers significant losses of 20% to 40% in the food supply chain after the agricultural production stage. Strawberries, a popular fruit rich in nutrients, are perishable and susceptible to bacterial contamination (such as E. coli and Salmonella) during growth, harvesting, transportation, and storage. All these factors can cause significant changes in their quality parameters, including color, texture, and levels of bioactive compounds. Chemically synthesized preservatives are the primary method for preventing and managing post-harvest microbial diseases in fruits and vegetables due to their effective preservation and antiseptic properties; however, their use can have adverse effects on human health. Traditional methods also employ cryopreservation and modified atmosphere packaging (MAP) technologies to extend fruit shelf life, but cryopreservation only inhibits microbial growth, not kills them. These methods are not only time-consuming and uneconomical but also severely affect the appearance, texture, and flavor of the fruit. Furthermore, fruits are often not kept fresh in refrigerated conditions when placed on shelves. Therefore, developing a green and cost-effective method to extend the shelf life of perishable foods remains a significant challenge.

[0003] Cinnamaldehyde, as a natural material, possesses excellent properties such as antibacterial and antioxidant effects. It is a hydrophobic aromatic aldehyde, selected as a model without safety concerns at recommended intake levels. It exhibits strong antibacterial activity, having been shown to effectively inhibit the growth of a range of microorganisms, including bacteria, molds, and yeasts, and has been reported to inhibit the production of toxins by these microorganisms. However, cinnamaldehyde has poor solubility in water, and its molecules are sensitive to oxygen, light, and high temperatures, directly limiting its application in the food industry.

[0004] Traditional food wraps are made from materials such as polyethylene (PE) and polyvinyl chloride (PVC). While they offer advantages such as ease of use, moderate breathability, and good stretchability, their slow degradation and resulting environmental pollution are significant problems. Polyvinyl alcohol (PVA) and hydroxypropyl cellulose (HPC) have been experimentally validated as raw materials for film preparation, and as environmentally friendly and readily biodegradable materials, they are also beneficial to the environment. Although PVA is a promising biodegradable packaging material, it also has some drawbacks for food packaging, such as poor UV and water vapor barrier properties, low mechanical strength, poor water resistance, and lack of antibacterial properties. To overcome these limitations, novel PVA / cellulose nanocrystal (CNC) / titanium dioxide (TiO2) nanocomposites have been developed and applied.

[0005] Based on this, the present invention designs a comprehensive preservation film agent with good preservation effect and antibacterial ability by using Pickering emulsion loaded with cinnamaldehyde as the antibacterial component and using polyvinyl alcohol and hydroxypropyl cellulose to form a film. Summary of the Invention

[0006] One objective of this invention is to provide a food preservation film agent, the raw materials of which include: polyvinyl alcohol, hydroxypropyl cellulose, glycerin and an antibacterial agent;

[0007] The ratio of polyvinyl alcohol, hydroxypropyl cellulose, glycerin, and antibacterial agent is 0.2–0.4 g : 0.1–0.2 g : 0–0.2 g : 1 mL;

[0008] The antibacterial agent is a Pickering emulsion loaded with cinnamaldehyde.

[0009] Furthermore, the polyvinyl alcohol is PVA 0588.

[0010] Furthermore, the ratio of PVA 0588, HPC, glycerin, and antibacterial agent is 0.23g:0.13g:0.13g:1mL.

[0011] Further, the preparation process of the cinnamaldehyde-loaded Pickering emulsion is as follows: chitosan is dissolved in acetic acid to prepare a chitosan solution with a mass percentage concentration of 0.50%; the chitosan solution is mixed with a 1 mg / mL sodium tripolyphosphate solution, with a mass ratio of chitosan to sodium tripolyphosphate of 5:1, centrifuged, the supernatant is discarded, pure water is added for resuspension and ultrasonic dispersion is performed to obtain a chitosan nanoparticle suspension; the chitosan nanoparticle suspension is used as the aqueous phase and mixed with the oil phase cinnamaldehyde at a volume ratio of 95:5, and ultrasonicated to obtain the Pickering emulsion.

[0012] The second objective of this invention is to provide a method for preparing the above-mentioned food preservation film agent, which involves mixing polyvinyl alcohol, hydroxypropyl cellulose, glycerin and water, then adding an antibacterial agent, pouring the mixture into a mold and drying it to form a film.

[0013] This invention first prepares chitosan-sodium tripolyphosphate particles via ionic crosslinking. The chitosan concentration and the ratio of chitosan to sodium tripolyphosphate are investigated, while particle size is used to screen the optimal chitosan concentration and ratio. Results show that the chitosan-sodium tripolyphosphate particles have the smallest particle size when the ratio is 5:1. Next, using these particles as a stabilizer and cinnamaldehyde as the oil phase, a Pickering emulsion with antibacterial properties is prepared. By screening the ratio of nanoparticles to cinnamaldehyde and the ultrasonic time, a highly stable Pickering emulsion is obtained. Single-factor screening and Box-Behnken response surface methodology are used to screen the optimal formulation of the PVA and HPC composite film. Results show that the optimal formulation is 0.13 g HPC, 2.3 g PVA (0588), and 0.13 g glycerol. A composite membrane with antibacterial properties was prepared by dispersing Pickering emulsion in a PVA / HPC composite membrane agent and using a solvent casting method. The results showed that the prepared composite membrane agent had significant antibacterial properties.

[0014] This invention selects polyvinyl alcohol and hydroxypropyl cellulose to form a film together to overcome the defects of traditional film agents. It disperses a Pickering emulsion loaded with cinnamaldehyde in a composite film agent prepared by PVA / HPC, and obtains a comprehensive preservation film agent with good preservation effect and antibacterial ability. Attached Figure Description

[0015] Figure 1 Images of emulsions stained with FITC and Nile Red, respectively, taken under a fluorescence microscope.

[0016] Figure 2 In the image, the left image is a SEM image of the blank membrane, and the right image is a SEM image of the Pickering emulsion membrane.

[0017] Figure 3 The infrared spectra of PVA0588, PH-WP membrane, PH-PE membrane, HPC, and PH membrane were measured using a Fourier transform infrared spectrometer.

[0018] Figure 4 The water vapor transmission rate of PH-PE membrane, PH-WP membrane and PH membrane is measured using the weight loss method.

[0019] Figure 5 In the table, A represents the results of the E.coil antibacterial plate, and B represents the results of the SA antibacterial plate.

[0020] Figure 6 This is an image showing the effect of the antibacterial zone.

[0021] Figure 7 and Figure 8 These are photographs of live and dead bacteria, namely Escherichia coli and Staphylococcus aureus.

[0022] Figure 9 Image showing the effect of saving strawberries.

[0023] Figure 10 This is a graph showing the weight loss of strawberries. Detailed Implementation

[0024] The preferred embodiments of the present invention will now be described in detail with reference to specific examples. It should be understood that the following examples are given for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications and substitutions to the present invention without departing from its spirit and essence.

[0025] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0026] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0027] Example 1

[0028] I. Formulation Investigation of Blank Film Formulation

[0029] 1. Single-factor screening of blank film agents

[0030] First, single-factor screening was conducted to determine the type and dosage of PVA, the dosage of HPC, and the dosage of glycerol. The specific design is shown in Table 1 below. The constant-temperature water bath stirrer was turned on and the temperature was set to 80℃ for preheating. 10g of PVA0588, 10g of PVA1588, and 10g of HPC were accurately weighed and added to 90mL of deionized water respectively. The mixture was heated and stirred in a water bath for 0.5h to prepare a 10% (w / v) solution. The solution was poured into a reagent bottle, cooled, and stored. 5mL of each PVA and HPC solution was measured, and deionized water was added to a final volume of 30mL. The solutions were poured into a film mold and dried to form a film. The film was then demolded and packaged.

[0031] Table 1. Single-factor screening table

[0032]

[0033]

[0034] The single-factor screening included HPC dosage, PVA dosage and type, and glycerol dosage. Preliminary screening was based on membrane performance, including membrane surface smoothness, stretchability, and ease of demolding. Results showed that membranes prepared with PVA of type 1588 exhibited high brittleness, while those prepared with PVA of type 0588 met expectations. The composite membrane prepared using PVA and HPC in combination showed better tensile strength than the PVA membrane, and demolding was easier with glycerol.

[0035] 2. Box-Behnken Response Surface Design

[0036] Based on single-factor screening, Box-Behnken response surface methodology was used to optimize the formulations and select the optimal film formulation. In Design Expert software, Box-Behnken design was selected, and the indicators to be optimized, evaluation criteria, and addition ranges were input to generate the formulations. The characteristics of each film formulation were then evaluated based on demolding performance, film surface appearance, and folding performance. After preparation and evaluation according to the programmed formulation list, the predicted optimal ratio was generated and verified to obtain the optimal blank film formulation. The Box-Behnken design influencing factors A: PVA (0588) ranged from 0.2 to 0.4 g; influencing factor B: HPC ranged from 0.1 to 0.2 g; and influencing factor C: glycerol ranged from 0 to 0.2 g. Seventeen formulations were generated sequentially, and after film fabrication, the corresponding data were entered according to the three evaluation indicators.

[0037] Table 2. Box-Behnken Design Results

[0038]

[0039]

[0040] Table 3. Regression Analysis of Tensile Properties

[0041]

[0042] Table 4. Regression analysis of surface smoothness

[0043]

[0044] Table 5. Regression analysis of demolding difficulty

[0045]

[0046] Regression analysis in the table shows that the equation for tensile properties is linear, while the equations for surface smoothness and demolding ease are quadratic. Within a given range, tensile properties are directly proportional to the amount of glycerol and PVA used. Meanwhile, surface smoothness and demolding ease, within a given range, exhibit a quadratic relationship with the three influencing factors.

[0047] Finally, the optimal formulation was obtained by setting targets based on the expected values ​​of each response using Design Expert software. The results showed that the optimal formulation ratio for the blank membrane was: 0.23g PVA (0588), 0.13g HPC, and 0.13g glycerol. The model predicted a tensile strength of 2.647, a surface smoothness of 2.822, and a demolding ease of 10.829. Blank membranes were prepared based on the obtained optimal formulation, and their performance was evaluated. The results are shown in Table 6. The results indicate that the optimized predicted values ​​are not significantly different from the actual measured values, suggesting that this design can yield a better formulation.

[0048] Table 6. Evaluation of Actual Film Formation Indicators

[0049]

[0050] Therefore, the optimal prescription was determined to be 0.23g PVA (0588), 0.13g HPC, and 0.13g glycerin.

[0051] II. Preparation and Characterization of Pickering Emulsion

[0052] Pickering emulsion was prepared according to the formulation and process described in patent CN119185199A, as follows:

[0053] Chitosan powder was dissolved in acetic acid to prepare a chitosan solution with a mass percentage concentration of 0.50%. The chitosan solution was then mixed with a sodium tripolyphosphate solution (1 mg / mL) at a mass ratio of 5:1. The mixture was centrifuged at 10000 × g for 35 min at 4 °C, the supernatant was discarded, and the mixture was resuspended in 1 mL of pure water and ultrasonically dispersed to obtain a chitosan nanoparticle suspension. The aqueous chitosan nanoparticle suspension was then mixed with an oil phase of cinnamaldehyde at a volume of 5% (v / v), and the mixture was ultrasonically sonicated at 300 W for 2 min to prepare a Pickering emulsion.

[0054] FITC and Nile Red were dissolved in DMSO to obtain solutions 1 and 2 at 1 mg / mL. 30 μL of solution 1 was added dropwise to 3 mL of the chitosan nanoparticle aqueous phase, and the mixture was incubated in the dark for 20 min. A Pickering emulsion was prepared using the stained aqueous phase, and 10 μL of solution 2 was added to the emulsion and incubated for 20 min. The mixture was then observed under a fluorescence microscope.

[0055] Next, chitosan-sodium tripolyphosphate particles used in Pickering emulsions were prepared using FITC staining, and the oil phase of the emulsion was stained with Nile Red. The results are as follows: Figure 1As shown in the figure, green fluorescence represents chitosan-sodium tripolyphosphate particles, and red fluorescence represents the oil phase. The Merge diagram shows that the oil phase is encapsulated by chitosan-sodium tripolyphosphate particles, indicating that an oil-in-water Pickering emulsion was successfully prepared, and the small droplets in the Pickering emulsion are evenly distributed and stable.

[0056] III. Preparation and Characterization of Films Loaded with Pickering Emulsion

[0057] A pH-PE membrane with antibacterial activity was prepared by adding Pickering emulsion to a matrix made of HPC and PVA. The membrane formulation consisted of 0.23 g PVA (0588), 0.13 g HPC, and 0.13 g glycerol. The added Pickering emulsion formulation used a matrix of 5% (v / v) cinnamaldehyde oil phase and 95% (v / v) aqueous phase. The aqueous phase used 0.5% chitosan nanoparticles in a mass ratio of 5:1 to sodium tripolyphosphate to prepare 1 mL of Pickering emulsion. The preparation process involved mixing 10 wt% PVA (0588) solution, 10 wt% HPC solution, and 0.13 g glycerol, adding 1 mL of Pickering emulsion, and then adding double-distilled water to a final volume of 20 mL. The mixture was then poured into a mold and dried in an oven to form a membrane.

[0058] Simultaneously, a blank membrane (pH membrane) was prepared: the formula consisted of 0.23g PVA (0588), 0.13g HPC, and 0.13g glycerol. The preparation process involved first mixing the blank membrane agent with a 10wt% PVA (0588) solution, a 10wt% HPC solution, and 0.13g glycerol. Second-distilled water was added to a final volume of 20mL, and the mixture was thoroughly mixed. The mixture was then poured into a mold and dried in an oven to form the membrane.

[0059] Aqueous membrane (PH-WP membrane): The formulation consists of 0.23g PVA (0588), 0.13g HPC, and 0.13g glycerol. The aqueous phase uses 0.5% chitosan nanoparticles in a mass ratio of 5:1 to sodium tripolyphosphate. The preparation process involves first mixing the blank membrane agent with 10wt% PVA (0588) solution, 10wt% HPC solution, and 0.13g glycerol. Then, 0.95mL of the aqueous phase is added, followed by double-distilled water to a final volume of 20mL. The mixture is then poured into a mold and dried in an oven to form the membrane.

[0060] The surface and cross-sectional properties of the prepared thin film were investigated using scanning electron microscopy. Figure 2 It can be observed that the cross-section of the blank film is rough due to the poor compatibility and different densities of HPC and PVA; adding Pickering emulsion to the blank film can improve its smoothness and reduce bubble generation.

[0061] from Figure 3The results show that the finished PH-PE membrane has characteristic peaks of PVA and HPC. Literature review indicates that the characteristic peak for cinnamaldehyde is at 1496 cm⁻¹. -1 and 1388cm -1 As can be seen from the infrared curve of the PH-PE membrane, it contains the above characteristic peaks, verifying that the prepared Pickering emulsion membrane successfully encapsulates the Pickering emulsion. In the infrared spectrum of PVA, the broad and intense peak of the hydroxyl group appears in the range of 3200–3550 cm⁻¹. -1 In the specified range, this peak is formed by intermolecular hydrogen bonds. As shown in the figure, PVA is encapsulated in all the prepared films, verifying the PVA0588 component. (3440cm) -1 The hydroxyl stretching vibration peak at the position is a characteristic infrared peak of HPC, and this characteristic peak can also be observed in the PH-PE membrane in the figure.

[0062] The vapor transmission rates of PH-PE, PH-WP, and PH membranes were measured using the gravimetric loss method. Specifically, 50g of double-distilled water was weighed into each open container, and then sealed using the PH, PH-WP, and PH-PK membranes respectively, with the weight recorded as w0. A blank control group without sealing was included. The weight was then measured every 24 hours to obtain the final weight w. n The weight loss rate was obtained as (w n -w n-1 ) / w0. By Figure 4 As can be observed, the slope of water evaporation indicates that the coated pH membrane, pH-PE membrane, and pH-WP membrane all have a good ability to reduce water loss. In contrast, the weight of the uncoated group decreases rapidly, with a larger slope than the coated group. This verifies the good water retention capacity of the fabricated membranes.

[0063] IV. Evaluation of the antibacterial properties of the film

[0064] 1. Antibacterial plate experiment

[0065] Dissolve 1.0 g of pH membrane, pH-PE membrane, and pH-WP membrane separately in deionized water, and add deionized water to make up to 5 mL. Vortex to mix and prepare solutions 6, 1, and 4, respectively. Add 1 mL of Pickering emulsion (PE), 50 μL of cinnamaldehyde essential oil, and 1 mL of aqueous phase (WP) to EP tubes, and add water to make up to 5 mL. Sonicate to mix and prepare solutions 2, 5, and 3, respectively. Spread each of the above solutions onto a culture medium that has been evenly coated with 2 mL of Escherichia coli culture, and set up a blank control group. Then spread each solution onto a culture medium that has been evenly coated with 2 mL of Staphylococcus aureus culture, and set up a blank control group. Incubate at 37℃ for one day and observe the state and color changes of the culture medium.

[0066] The antibacterial board effect is as follows Figure 5As shown, a clear antibacterial effect can be observed. The PH-PE membrane, cinnamaldehyde, and PE groups are lighter in color than the blank group, indicating that these groups of solutions have antibacterial effects. The remaining groups of solutions are darker in color, and their antibacterial effects are not significant. In the above antibacterial experiments, the WP group and the PH membrane group have the worst antibacterial effect. It can be clearly seen that colonies grew in both groups in the E. coli antibacterial plate, and similarly, in the Staphylococcus aureus antibacterial plate, both groups also had a large number of yellow dot-like colonies. Interestingly, the transparent blank areas that appeared in the PH-PE group antibacterial plate were not colonies, but rather gaps formed after the coated solution dried and formed a film. This phenomenon did not appear in the Staphylococcus aureus antibacterial plate, which is speculated to be due to the more uniform coating of the Staphylococcus aureus solution. The white dots in the cinnamaldehyde and PE groups are also not colonies; these two groups of solutions are naturally white and naturally dried into white dots in the incubator.

[0067] 2. Antibacterial zone test

[0068] Spread 400 μL of *E. coli* and 400 μL of *Staphylococcus aureus* culture evenly on a medium-sized dish. Make six wells in each dish, numbered 1 to 6. Add 250 μL of each of the corresponding solutions (1-6) to each well. Make a well in the center (number 7) and add 250 μL of PBS solution. Incubate at 37°C for one day, observing the culture medium condition and the size of the inhibition zone.

[0069] The antibacterial ring effect is as follows Figure 6 As shown, a significant antibacterial effect can be observed. The pH-PE membrane, cinnamaldehyde, and PE groups are lighter in color than the control group, indicating that these groups of solutions have an antibacterial effect. The remaining groups of solutions are darker in color, suggesting a less pronounced antibacterial effect. Furthermore, the pH-WP group, pH membrane group, and WP group did not produce inhibition zones; the surrounding area was almost entirely covered with bacteria, indicating an insignificant antibacterial effect.

[0070] 3. Bacterial live / dead staining fluorescence experiment

[0071] Using the prepared solution, 0.25 mL of each solution was added to 4.75 mL of bacterial suspension and incubated at 37°C for 2 hours. After balancing the two solutions, centrifuged at 10,000 rpm for 5 minutes at room temperature, discarding the supernatant. The suspension was then resuspended in 5 mL of physiological saline, balanced again, and centrifuged at 10,000 rpm for 5 minutes at room temperature, discarding the supernatant and resuspending again in 5 mL of physiological saline. 100 μL of the suspension was added to 1 μL of staining working solution and incubated at 37°C in the dark for 15 minutes. After incubation, 10 μL of the bacterial suspension was added to a glass slide and sealed with a 24 mm square coverslip. Finally, the staining effect of live and dead bacteria was observed under a fluorescence microscope.

[0072] Bacterial live and dead staining, such as Figure 7 and8 As shown in the figure. DMAO staining is green, marking live bacteria, and PI staining is red, marking dead bacteria. Figure 7 Images showing live and dead bacteria of E. coli. Figure 8 Images show the live and dead bacteria of Staphylococcus aureus. A large number of dead bacteria can be observed in the PH-PE group, PE group, and cinnamaldehyde group, verifying the antibacterial effect of the finished membrane. Meanwhile, a large number of green bacteria are present in the blank group, aqueous phase membrane group, aqueous phase group, and blank membrane group, with very few dead bacteria, indicating that the antibacterial effect of these groups is not significant.

[0073] Example 2

[0074] Study on the Preservation Effect of Films Containing Pickering Emulsion on Fruits

[0075] The prepared film was applied to the preservation of fresh strawberries, and its effect on strawberry quality was studied. Freshly picked strawberries were purchased from the local market. The strawberries were then randomly divided into three groups, sealed with PH, PH-WP, and PH-PE films respectively, and a blank control group without film sealing was set up. The samples were stored at room temperature. The strawberry samples were stored for 5 days, and indicators, including strawberry weight and appearance, were measured once a day. The weight loss rate of the strawberries was determined, and the surface was wiped dry with paper before the test.

[0076] The formula is as follows:

[0077] Weight loss (%) = ((W0-W) t ) / W0)×100,

[0078] In the formula, W0 is the initial weight of the strawberry sample, W t The weight of strawberries sampled at a specific time. Three strawberry samples were measured for each group.

[0079] like Figure 9 The finished film exhibited a significant preservation and antibacterial effect. The unfilmed group spoiled first, the PH group showed no significant antibacterial effect, and the PH-PE group demonstrated excellent preservation ability. This validated the antibacterial effect of the prepared film. No contamination by other microorganisms was observed in the PH-PE group during preservation. In contrast, the unfilmed group showed gray-green and white mold on the spoiled parts, while the PH film and PH-WP groups only showed one type of white mold, likely the common Rhizopus stolonifer, which is frequently found in mechanically damaged fruits. Furthermore, mold spots appeared on the unfilmed and PH-WP groups on day 5. Although no mold spots appeared on day 5 in the PH film group, the tips of the strawberries showed signs of yellowing, indicating poor preservation in these groups. After 6 days, all four groups of strawberries shrank and faded in color. However, the PH-PE group showed less color fading. This experiment validated the fruit preservation ability of PH-PE.

[0080] Strawberry weight loss results as follows Figure 10 As shown, the blank group had the highest weight loss rate, while the weight loss rates of the other three coated groups were basically the same, with no significant changes. This indicates that the prepared film has good water retention capacity. This figure also corroborates that in the above strawberry preservation experiment, the PH-PE group had the best preservation ability and the lowest water loss rate.

Claims

1. A preservative film agent, characterized by, The raw materials include polyvinyl alcohol, hydroxypropyl cellulose, glycerol and an antibacterial agent; The polyvinyl alcohol, hydroxypropyl cellulose, glycerol and the antibacterial agent are in a ratio of 0.2-0.4 g: 0.1-0.2 g: 0-0.2 g: 1 mL; The antibacterial agent is a Pickering emulsion loaded with cinnamaldehyde.

2. The preservative film agent according to claim 1, characterized by, The polyvinyl alcohol is PVA 0588.

3. The preservative film agent according to claim 1, characterized by, The PVA 0588, HPC, glycerol and the antibacterial agent are in a ratio of 0.23 g: 0.13 g: 0.13 g: 1 mL.

4. The preservative film agent according to claim 1, characterized by, The preparation process of the Pickering emulsion loaded with cinnamaldehyde is as follows: chitosan is dissolved in acetic acid to prepare a chitosan solution with a mass percentage of 0.50 %; the chitosan solution is mixed with a 1 mg / mL sodium tripolyphosphate solution, and the mass ratio of chitosan to sodium tripolyphosphate is 5:1; after centrifugation, the supernatant is discarded, pure water is added for resuspension and ultrasonic dispersion to obtain a chitosan nanoparticle suspension; the chitosan nanoparticle suspension is mixed with oil-phase cinnamaldehyde as the water phase at a volume ratio of 95:5, and ultrasonic dispersion is performed to prepare the Pickering emulsion.

5. The method of preparing a preservative film agent according to any one of claims 1 to 4, characterized in that, The polyvinyl alcohol, hydroxypropyl cellulose, glycerol and water are mixed, and then the antibacterial agent is added, poured into a mold and dried into a film.

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