Antibacterial film and preparation method thereof

Abstract

The invention belongs to the technical field of bio-based high polymer materials, and particularly relates to an antibacterial film and a preparation method thereof.According to the antibacterial film and the preparation method thereof, traditional lysozyme is replaced with fibrotic lysozyme, seville orange flower essential oil Pickering emulsion is added, and the flexibility and the antibacterial performance of the antibacterial film are remarkably improved. Specifically, the fibrotic lysozyme is a rigid fiber aggregate formed after acid heat induction treatment, not only maintains the original antibacterial activity, but also enhances the structural stability, so that the fibrotic lysozyme continuously plays an antibacterial role in a complex application environment. Besides, by adding the seville orange flower essential oil Pickering emulsion, the elongation at break of the antibacterial film is greatly improved, and the effect is unexpected by technicians in the field, so that the unexpected technical effect is reflected.

Description

Technical Field

[0001] The present application belongs to the technical field of bio-based polymer materials, and specifically relates to a degradable antibacterial film comprising a biopolymer, lysozyme fibrils and a daisy Pickering emulsion. Background Art

[0002] Biodegradable films are packaging or agricultural films made primarily from biodegradable materials that can be completely decomposed into water, carbon dioxide, and harmless mineral salts through microbial action. These films are environmentally friendly and meet the requirements of sustainable development. Common types include polyhydroxyalkanoate-based biodegradable films, starch-based biodegradable films, polylactic acid-based biodegradable films, polycaprolactone-based biodegradable films, and gelatin-based biodegradable films. Gelatin-based biodegradable films are widely used in various fields due to their excellent biocompatibility, superior film-forming properties, and environmental friendliness.

[0003] Gelatin, a macromolecular hydrophilic colloid derived from the partial hydrolysis of animal connective tissue collagen, can form a glassy film after drying due to its unique helical structure and stable network structure formed by hydrogen bonds. It exhibits advantages such as non-toxicity, good gelation, excellent compatibility and biodegradability. However, although gelatin has great application potential in the field of packaging materials, its insufficient mechanical properties limit its effectiveness when used alone. To address this problem, researchers have explored various improvement methods, including blending gelatin with other natural polymer materials such as chitosan, sodium alginate, and cellulose, as well as modifying it using physical cross-linking, chemical cross-linking, and enzymatic cross-linking techniques to obtain a gelatin film-forming matrix with excellent film-forming properties.

[0004] To enhance the antimicrobial efficacy of degradable films, gelatin film-forming matrices are often combined with active substances with antimicrobial properties to form composite antimicrobial films. Lysozyme, due to its natural antimicrobial properties, is often added to such film-forming matrices as an active ingredient. However, lysozyme is often affected by various factors in complex application environments, significantly reducing its actual antimicrobial efficacy. To ensure that lysozyme maintains high activity within the gelatin film-forming matrix, the film-forming matrix must be specially designed. For example, patent application number 202510180864.4 discloses a film-forming matrix based on sodium alginate and gelatin. This matrix uses calcium chloride as a crosslinker, utilizing the fact that L-glucuronic acid in alginate, in the presence of divalent calcium ions, can interact with deprotonated carboxyl groups to form a stable egg-box structure, thereby enhancing the immobilization of lysozyme. However, while this approach significantly improves the stability of lysozyme and the antimicrobial properties of the film, the addition of calcium ions for crosslinking increases the film's hardness and brittleness, which to some extent limits its application as a packaging material in the food industry. Summary of the Invention

[0005] To solve the technical problem of the current gelatin-lysozyme composite antibacterial film in which it is difficult to achieve both antibacterial properties and flexibility, the present application provides an antibacterial film with high elongation at break and good antibacterial effect, which is achieved specifically through the following technical solutions: A method for preparing an antibacterial film comprises: mixing raw materials comprising gelatin, sodium alginate, lysozyme fibrils, glycerol, and a dapoxetine Pickering emulsion to obtain an antibacterial film casting solution; wherein the mass volume concentration of gelatin in the antibacterial film casting solution is 4-6 g / ml, and the mass ratio of gelatin, sodium alginate, lysozyme fibrils, glycerol, and dapoxetine Pickering emulsion is 1:0.03:0.0002:0.2:(0.01-0.05); the dapoxetine Pickering emulsion is obtained by homogenizing and ultrasonically treating nano-esterified starch as solid colloidal particles, a mixed oil phase of dapoxetine essential oil and a carrier oil as a dispersed phase, and water as a continuous phase; and wherein the mass volume concentration of the solid colloidal particles, the mass volume concentration of the dapoxetine essential oil, and the mass volume concentration of the carrier oil are 3-8%, 1-3%, and 4-6%, respectively.

[0006] Preferably, the lysozyme fibrils are fibrous aggregates containing a β-pleated structure.

[0007] Preferably, the fibrous aggregates are obtained by subjecting lysozyme to acid-heat induction treatment.

[0008] Preferably, the preparation step of the nano-esterified starch comprises: esterifying the refined starch with 2-octenylsuccinic anhydride under alkaline conditions to introduce amphiphilic groups on the surface of the refined starch to obtain esterified starch.

[0009] Preferably, the preparation step of the nano-esterified starch further comprises: gelatinizing the suspension of the esterified starch, cooling the suspension to make the system temperature lower than the gelatinization temperature to promote recrystallization of the esterified starch, and performing ultrasonic crushing to obtain the nano-esterified starch.

[0010] Preferably, the refined starch is obtained by removing protein from crude starch through alkali washing, and the content of amylopectin in the crude starch is higher than that of amylose.

[0011] An antibacterial film is prepared by any of the above-mentioned preparation methods.

[0012] Preferably, the elongation at break of the antibacterial film is greater than 20%.

[0013] Compared with the prior art, this application has the following beneficial effects: The present application significantly improves the flexibility and antibacterial properties of the antibacterial film by replacing traditional lysozyme with fibrous lysozyme and adding daisy Pickering emulsion. Specifically, fibrous lysozyme is a rigid fiber aggregate formed after acid-heat induction treatment, which not only maintains the original antibacterial activity, but also enhances the structural stability, so that it can continue to play an antibacterial role in complex application environments. In addition, the addition of daisy Pickering emulsion greatly improves the elongation at break of the antibacterial film, reflecting an unexpected technical effect. Specifically, performance tests show that under optimal conditions, the elongation at break of the antibacterial film of the present application is increased by more than 1 times, showing higher flexibility. In actual applications, when the antibacterial film is used to package strawberries, the preservation effect is significantly improved, the corruption and deterioration phenomena are effectively reduced, and the shelf life is extended. In summary, the present application has developed a new antibacterial film with high flexibility, excellent antibacterial properties and good preservation effect, which provides a reliable choice for food packaging and other application fields that require efficient antibacterial protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] To clearly introduce the embodiments, the following briefly introduces the drawings: Figure 1 The graphs for measuring different film thicknesses are shown below; Figure 2 The Lab values ​​and color difference values ​​of different films are shown; Figure 3 The following are the appearance pictures of different films; Figure 4 Tensile strength (TS) and elongation at break (EAB) of films of different thicknesses; Figure 5 is the UV absorption spectrum and opacity of different films; Figure 6 is the differential scanning calorimeter (DSC) curve of different films; Figure 7 Thermogravimetric (TGA) curves and differential thermogravimetric (DTG) curves of different films; Figure 8 The water contact angle diagram of different films; Figure 9 The water vapor transmission rate diagram of different films; Figure 10 The oxygen transmission rate diagram of different films; Figure 11 These are pictures of the preservation experiment of different films. DETAILED DESCRIPTION

[0015] The present application will be further described below in the form of specific embodiments. Those skilled in the art will be able to implement the present application based on these descriptions. In addition, the embodiments of the present application involved in the following description are generally only embodiments of a portion of the present application, rather than all embodiments. Therefore, based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making any creative efforts should fall within the scope of protection of the present application. Example 1. Preparation of antibacterial film

[0016] This embodiment discloses a method for preparing an antibacterial film, comprising the following steps: Preparation of lysozyme fibrils: The pH of a 2% (wt) lysozyme solution was adjusted to 2.0 with 1 M HCl and then heated at 90°C for 8 h to induce fibril formation. After heating, the sample was immediately cooled in an ice bath and stored at 4°C.

[0017] Preparation of Daidahlia Pickering Emulsion: Crude starch was dissolved in water at a ratio of 1:5 (w / v) to form a suspension. The pH of the starch slurry was adjusted to 9.0 using 1 M NaOH, then gently stirred for 30 minutes and allowed to stand overnight. The suspension, which had been allowed to stand overnight, was neutralized to a pH of 7.0 using 1 M HCl. The suspension was then washed three times with deionized water to remove residual NaCl. The washed starch was dried in an oven at 45°C for 24 hours. After drying, it was pulverized into a powder and passed through a 100-mesh sieve for storage for further use. The resulting product is referred to as refined starch.

[0018] Refined starch was dispersed in distilled water to prepare a 10% (w / v) starch suspension. The suspension was continuously stirred in a 35°C water bath while adjusting the pH to 8.5. 2-Octenylsuccinic anhydride (v / v = 0.2) diluted in anhydrous ethanol was slowly added in multiple additions over 2 hours, maintaining a constant pH of 8.5. The reaction was terminated by adjusting the pH to 6.5 with 1 M HCl. Subsequently, esterified sweet potato starch was obtained by centrifugation at 2,000 rpm for 5 minutes. The obtained esterified sweet potato starch was washed three times with deionized water and three times with 70% ethanol. The starch was freeze-dried and stored until further use.

[0019] Esterified sweet potato starch was prepared into a 2% (w / v) starch suspension and maintained in a boiling water bath at 100°C for 30 minutes for complete gelatinization. After cooling the starch paste to 50°C, it was sonicated for 10 minutes using an ultrasonic disruptor. Ultrasonication was performed at an amplitude of 80%, with an on-time of 5 seconds and a rest time of 3 seconds. Immediately after sonication, the starch slurry was dropwise added to anhydrous ethanol and rapidly precipitated under magnetic stirring to re-extract the starch. The precipitate, obtained by centrifugation at 2,000 rpm for 5 minutes at 4°C, was nano-esterified sweet potato starch. The nano-esterified sweet potato starch was then freeze-dried in a freeze dryer.

[0020] Daisy flower essential oil was completely dissolved in 5% (w / v) soybean oil at concentrations of 1%, 2%, and 3% (w / v), respectively, as the oil phase. This oil phase was mixed with deionized water (as the aqueous phase) and 5% (w / v) nanoesterified sweet potato starch was added. The mixture was homogenized at 10,000 rpm for 3 minutes. The homogenized mixture was then sonicated at 480 W for 15 minutes. Homogenization was performed in an ice bath to obtain a uniform and stable nanoemulsion and minimize the adverse effects of high temperature on emulsion stability and the activity of the essential oil.

[0021] Preparation of antibacterial film: Dissolve 5g of gelatin (G) in 100mL of distilled water and stir at 60°C for 30min until completely dissolved. Add 3% (w / w) sodium alginate (SA) and 0.02% (w / w) lysozyme fibrils to the gelatin solution and continue stirring for 1h to thoroughly mix. Add 20% (w / w) glycerol to the gelatin and disperse evenly for 15min. Add the previously prepared Daphne dauphinae Pickering emulsion to the mixture at ratios of 0%, 1%, 3%, and 5% (w / w) of Daphne dauphinae essential oil to the gelatin solution, respectively, and stir thoroughly to obtain a film casting solution. Pour 20g of the film casting solution into a polytetrafluoroethylene mold (10 cm × 10 cm) and air-dry at room temperature for 24h before peeling and storing in a desiccator for later use. Using the same method, the daikon radish Pickering emulsion content was added to the above solution at a ratio of 0%, 1%, 3% and 5% of the dry weight of gelatin, and stirred thoroughly. The films were named G / S / L, G / S / L@EO-P (1%), G / S / L@EO-P (3%) and G / S / L@EO-P (5%), respectively. Specific film information is shown in the table below: Table 1. Composition and addition ratio of film casting solution Film name Main components and addition ratio of thin film casting solution G / S Gelatin, sodium alginate, glycerin G / S / L Gelatin, sodium alginate, lysozyme fibrils, glycerol G / S / L@EO-P (1%) Gelatin, sodium alginate, lysozyme fibrils, glycerol, 1% Dacryma-Pickering emulsion G / S / L@EO-P (3%) Gelatin, sodium alginate, lysozyme fibrils, glycerol, 3% Dacryma-Pickering emulsion G / S / L@EO-P (5%) Gelatin, sodium alginate, lysozyme fibrils, glycerol, 5% Dacryma Pickering emulsion Example 2: Preparation of antibacterial film

[0022] The difference between this embodiment and embodiment 1 is that the film casting solution The mass volume concentration of gelatin in the antibacterial film casting solution is 4%, and the mass ratio of gelatin, sodium alginate, lysozyme fibrils, glycerol and dahliae Pickering emulsion is 1:0.03:0.0002:0.2:0.01; in the dahliae Pickering emulsion, the mass volume concentration of the solid colloidal particles is 3%, the mass volume concentration of the dahliae essential oil is 1%, and the mass volume concentration of the carrier oil is 4%. Example 3: Preparation of antibacterial film

[0023] The difference between this embodiment and embodiment 1 is that the film casting solution The mass volume concentration of gelatin in the antibacterial film casting solution is 6%, and the mass ratio of gelatin, sodium alginate, lysozyme fibrils, glycerol and dahliae Pickering emulsion is 1:0.03:0.0002:0.2:0.05; in the dahliae Pickering emulsion, the mass volume concentration of the solid colloidal particles is 8%, the mass volume concentration of the dahliae essential oil is 3%, and the mass volume concentration of the carrier oil is 6%. Example 4: Preparation of antibacterial film

[0024] The difference between this embodiment and embodiment 1 is that the film casting solution The mass volume concentration of gelatin in the antibacterial film casting solution is 4%, and the mass ratio of gelatin, sodium alginate, lysozyme fibrils, glycerol and dahliae Pickering emulsion is 1:0.03:0.0002:0.2:0.03; in the dahliae Pickering emulsion, the mass volume concentration of the solid colloidal particles is 5%, the mass volume concentration of the dahliae essential oil is 2%, and the mass volume concentration of the carrier oil is 5%. Performance test 1. Film thickness and appearance measurement

[0025] The film thickness was measured using a digital micrometer (with an accuracy of 1 μm). Figure 1 The color change of the composite film was measured using a handheld colorimeter. The film sample was placed on a white standard plate, and its L* (brightness), a* (redness and greenness), and b* (yellowness and blueness) values ​​were measured, and the color difference value (ΔE) was calculated at the same time. ( Figure 2 ). Use a digital camera to take pictures of the film samples to visually characterize their transparency, uniformity and surface smoothness ( Figure 3 ).

[0026] See attached Figure 1 and 2It can be found that the thickness of the prepared films ranges from 85 nm to 120 nm. Specifically, the addition of 3% and 5% concentrations of Pickering emulsion significantly increased the film thickness, which is mainly attributed to the increase in the solid content in the film. With the increase in the amount of Pickering emulsion added, the opacity of the film increased significantly. The L value (brightness) of the film decreased significantly, while the b value (yellow-blueness) of the G / S-based film showed an overall upward trend. The a value (redness-greenness) of all films was slightly negative, and the b value was slightly positive, indicating that the film had an overall yellow-green hue. At the same time, with the increase in the concentration of Pickering emulsion, the color difference value (ΔE) of the film increased significantly. These phenomena are consistent with the changing trend of the transparency of the film-forming solution, further verifying the significant effect of Pickering emulsion on the optical properties of the film. Performance test 2. Mechanical properties determination

[0027] The tensile strength (TS) and elongation at break (EAB) of the film were measured using a universal material testing machine ( Figure 4 ).

[0028] The mechanical properties of films are key indicators for evaluating their quality during food processing, transportation and storage. Figure 4 As shown in the figure, the addition of lysozyme fibrils significantly improved the TS and EAB values ​​of the composite film. This is mainly due to the formation of more intermolecular hydrogen bonds between the lysozyme fibrils and the polysaccharide matrix, thereby enhancing the mechanical strength and flexibility of the film.

[0029] With increasing loading of the Daphne Pickering emulsion, the TS of the films increased, while the EAB decreased. The G / S / L@EO-P5 film with 5% Daphne Pickering emulsion exhibited a maximum TS of 67.95 MPa. Although fats and oils typically reduce the strength of gelatin films, the high TS exhibited by this composite film may be attributed to the interfacial interactions between the essential oil nanoemulsion stabilized by esterified sweet potato starch and the polymer matrix via hydrogen bonding, particularly the interaction between the active components of the Daphne essential oil and the gelatin hydroxyl groups. Furthermore, the G / S / L@EO-P1 film with 1% Daphne Pickering emulsion exhibited the highest EAB (23.57%), indicating superior flexibility under load. Compared to the G / S film without lysozyme fibrils, the film with 3% Daphne Pickering emulsion also exhibited a significantly higher elongation at break, further demonstrating the excellent mechanical properties of the film under tensile conditions. Performance Test 3: Determination of UV Protection Capacity

[0030] The UV-visible spectra were recorded by full-band scanning in the wavelength range of 200 nm to 800 nm using a UV-visible spectrophotometer. The opacity of the film was evaluated by the absorbance value at 600 nm (A600). Figure 5 ).

[0031] like Figure 5 As shown in the figure, the UV-visible light absorbance of the composite film increases significantly with the increase of the content of the Pickering emulsion of the daisy flower, which directly indicates that its UV shielding ability is effectively improved. Among them, the absorbance of the G / S / L@EO-P5 film reaches its maximum at 288 nm. The study believes that this enhancement effect is mainly attributed to the phenolic compounds rich in the daisy flower essential oil, which have the ability to absorb ultraviolet radiation. The opacity analysis results of the film show that the G / S / L@EO-P5 film has the highest opacity, which is consistent with the visual appearance observation results of the film ( Figure 3 ), further demonstrating the excellent UV shielding properties of the composite film. Notably, the visible light transmittance of the G / S / L film containing lysozyme fibrils increased, which is speculated to be related to the cross-linked structure between the lysozyme fibrils, gelatin, and sodium alginate. Performance test 4: Thermal stability of the film

[0032] The glass transition temperature (Tg) and other thermal transition behaviors of the films were determined by differential scanning calorimetry (DSC). Figure 6 The thermal decomposition behavior of the film was analyzed by thermogravimetric analysis (TGA / DTG), and the thermal stability of the film was evaluated by recording the thermogravimetric curve and differential thermogravimetric curve ( Figure 7 ).

[0033] TGA and DTG analysis ( Figure 7 ) showed that all films exhibited similar thermal decomposition processes in the temperature range of 25~600 °C, mainly including the evaporation of water and essential oils in the initial stage, the decomposition of glycerol in the intermediate stage, and the thermal degradation of the polymer skeleton in the main stage. After the addition of lysozyme fibrils, the thermal degradation temperature of the film increased significantly, indicating that its thermal stability was significantly improved. The study believes that this is attributed to the formation of a stronger film network structure between the lysozyme fibrils and the G / S matrix, thereby improving the heat resistance of the film. Although the thermal stability of the film showed a slight downward trend with the increase in the addition amount of daisy Pickering emulsion, the overall thermal stability remained at a high level compared with the G / S film without daisy Pickering emulsion. According to research, this may be attributed to the enhanced intermolecular interactions between the components in the composite film and the addition of the oil phase in the film matrix. DSC analysis ( Figure 6) showed that compared with the G / S film, all films loaded with active ingredients exhibited higher glass transition temperatures (Tg). Among them, the G / S / L@EO-P5 film had the highest Tg midpoint, reaching 86.77 °C. The study believes that the increase in Tg is mainly due to the enhanced intermolecular interactions between polymers (such as hydrogen bonds and electrostatic interactions). These interactions restrict the movement of macromolecular chains and reduce the free volume and intermolecular distance in the film. In summary, the addition of EO-ONS-P described in the present invention significantly improves the thermal properties of the composite film by enhancing intermolecular interactions, providing solid theoretical and technical support for its application in high-temperature environments. Performance Test 5. Determination of film hydrophobicity

[0034] The hydrophilicity and hydrophobicity of the film were evaluated using a contact angle meter ( Figure 8 ).

[0035] like Figure 8 As shown, the water contact angle (WCA) of the G / S film without lysozyme fibrils was 98.75°. The introduction of lysozyme fibrils significantly enhanced the film's hydrophobicity, resulting in an increase in the water contact angle. The incorporation of a Pickering nanoemulsion loaded with daisy essential oil (EO-ONS-P) reduced the water contact angles of the composite films. This demonstrates the good compatibility of EO-ONS-P with the G / S / L-based film. Importantly, all prepared composite films exhibited water contact angles above 90°, indicating excellent surface hydrophobicity. This high hydrophobicity contributes to effective steric hindrance, effectively preventing external moisture penetration and protecting the food from water loss, endowing the film with excellent moisture-barrier properties in humid environments. Performance test 6. Film water vapor transmission rate test

[0036] The water vapor transmission rate of the film was measured by weighing method ( Figure 9 ).

[0037] like Figure 9 As shown in the figure, the WVP of the G / S film without lysozyme fibrils was the highest (6.70×10 -7 g·m -1 ·h -1 ·Pa -1 The WVP of the G / S-based films decreased slightly after the addition of lysozyme fibrils, which was attributed to the strengthening of the cross-linked network through hydrogen bonding. The WVP of the films generally decreased after the introduction of the dapoxetine Pickering emulsion. In particular, the WVP of the G / S / L@EO-P5 film was the lowest, at only 5.49×10 -7 g·m -1 ·h -1 ·Pa -1The decrease in WVP was mainly attributed to the formation of a long and tortuous water vapor transmission path in the film by the Pickering emulsion, while the hydrophobicity of the emulsion droplets reduced the permeability. Performance test 7. Film oxygen transmission rate test

[0038] The oxygen transmission rate of the film was measured by the deoxidizer method ( Figure 10 ).

[0039] like Figure 10 As shown in Figure 2, the incorporation of the dapoxetine Pickering emulsion significantly reduced the oxygen transmission rate (OP) of the films. In particular, the OP of the G / S / L@EO-P5 film was reduced to the lowest, reaching 2.59 g·m -2 ·h -1 The study attributed this to the oily compounds reducing the mobility of gelatin chains and creating tortuous pathways within the film, effectively hindering gas permeation. These results strongly suggest that the addition of the Daidahlia Pickering emulsion significantly improves the film's oxygen barrier properties, providing important support for its application in food packaging. Performance Test 8: Determination of the Effect of Film on Preserving Strawberries

[0040] Fresh strawberries were washed with deionized water and randomly divided into five groups. Each group of strawberries was covered with four films and all samples were stored at room temperature for 6 days ( Figure 11 ).

[0041] like Figure 11 As shown, compared to the strawberries packaged with the G / S film in the control group, which showed obvious signs of mold and deterioration after 3 days of storage, the strawberries packaged with the Daidaihua Pickering emulsion film provided by the present invention maintained their bright color during this period and showed no obvious deterioration. After 7 days of storage, the strawberries treated with the G / S film had already shown severe mold and corruption. In contrast, the strawberries packaged with the G / S / L@EO-P5 film (loaded with 5% EO-ONS-P) remained intact throughout the 7-day storage and preservation experiment, showing no signs of deterioration, directly demonstrating its excellent antioxidant and antibacterial properties. Even the G / S / L@EO-P1 film, with a lower addition level, had a significantly better preservation effect than the control group. These results intuitively and strongly demonstrate that the composite film provided by the present invention can significantly extend the shelf life of strawberries, providing strong support for its efficient application in fruit packaging.

Claims

1. A method for preparing an antibacterial film, characterized in that: The preparation method comprises: mixing raw materials including gelatin, sodium alginate, lysozyme fibrils, glycerol and dahliae Pickering emulsion to obtain an antibacterial film casting solution; the mass volume concentration of gelatin in the antibacterial film casting solution is 4-6 g / ml, and the mass ratio of gelatin, sodium alginate, lysozyme fibrils, glycerol and dahliae Pickering emulsion is 1:0.03:0.0002:0.2:(0.01-0.05); the dahliae Pickering emulsion is obtained by homogenizing and ultrasonically treating nano-esterified starch as solid colloidal particles, a mixed oil phase of dahliae essential oil and carrier oil as a dispersed phase, and water as a continuous phase; in the dahliae Pickering emulsion, the mass volume concentration of the solid colloidal particles is 3-8%, the mass volume concentration of the dahliae essential oil is 1-3%, and the mass volume concentration of the carrier oil is 4-6%.

2. The method for preparing an antibacterial film according to claim 1, characterized in that: The lysozyme fibrils are fibrous aggregates containing a β-pleated structure.

3. The method for preparing an antibacterial film according to claim 2, characterized in that: The fibrous aggregates are obtained by subjecting lysozyme to acid-heat induction treatment.

4. The method for preparing an antibacterial film according to claim 1, characterized in that: The preparation steps of the nano-esterified starch include: esterifying refined starch with 2-octenylsuccinic anhydride under alkaline conditions to introduce amphiphilic groups on the surface of the refined starch to obtain esterified starch.

5. The method for preparing an antibacterial film according to claim 4, characterized in that: The preparation step of the nano-esterified starch further includes: gelatinizing the suspension of the esterified starch, cooling the suspension to make the system temperature lower than the gelatinization temperature, promoting the recrystallization of the esterified starch, and performing ultrasonic crushing to obtain the nano-esterified starch.

6. The method for preparing an antibacterial film according to claim 4 or 5, characterized in that: The refined starch is obtained by removing protein from crude starch through alkali washing, and the content of amylopectin in the crude starch is higher than that of amylose.

7. An antibacterial film prepared by the preparation method according to any one of claims 1 to 6.

8. The antibacterial film according to claim 7, characterized in that: The elongation at break of the antibacterial film is greater than 20%.

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