Active packaging film, method for preparing the same, and use thereof

Abstract

The application relates to an active packaging film and a preparation method and application thereof, and the preparation method is as follows: preparing essential oil@polydopamine capsules by self-polymerization oxidation under alkaline conditions; preparing a soybean protein isolate solution; preparing a carboxymethyl cellulose solution; blending and configuring essential oil@polydopamine capsules, the soybean protein isolate solution, the carboxymethyl cellulose solution and a plasticizer into a film-forming solution, performing vacuum degassing, adopting a solution casting method to form a film, demolding after drying, and obtaining the active packaging film. Compared with the prior art, the preparation method adopted by the application is simple in operation, non-toxic and harmless, low in cost, the polydopamine capsules are covalently combined with the soybean protein isolate and the carboxymethyl cellulose to form a cross-linking network structure such as a phenolic amine, and the prepared active packaging film has good mechanical properties, antioxidant properties, antibacterial properties and degradability, and has potential application value in the field of food packaging and preservation.

Description

Technical Field

[0001] This invention relates to the field of food packaging materials technology, and in particular to an active packaging film, its preparation method, and its application. Background Technology

[0002] The spoilage, nutrient and flavor loss of fresh fruit are related to microbial contamination, oxidative imbalance, and ultraviolet radiation. Food packaging acts as a physical barrier to protect food from external factors, playing a crucial role in food quality and safety. Traditional petroleum-based plastic films are non-degradable and non-recyclable, posing significant risks to the environment and human health. Bio-based soy protein isolate (SPI) and carboxymethyl cellulose (CMC) offer advantages such as low cost, abundant sources, biodegradability, biocompatibility, and recyclability, making them potential alternatives to traditional plastic films. Plant essential oils, as natural antibacterial agents, can be added to membrane matrices as natural active ingredients, imparting antibacterial and antioxidant activities. However, single essential oils have drawbacks such as large dosage requirements, strong odors, and instability. Microencapsulation of essential oils can improve their stability and controlled release, allowing them to be mixed with membrane matrices to prepare active packaging films for use in food packaging, achieving longer shelf lives. Therefore, developing multifunctional active packaging films that are biodegradable and possess antibacterial, antioxidant, and ultraviolet-barrier properties is of great significance in the food packaging field. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art by providing an active packaging film, its preparation method, and its application. Using soy protein isolate (SPI) and carboxymethyl cellulose (CMC) as bio-based materials, the active packaging film is prepared by adding polydopamine capsules loaded with aromatic antibacterial essential oils. The polydopamine capsules can covalently crosslink with the film substrate, effectively improving the tensile strength and elongation at break of the film while avoiding the use of crosslinking agents. The prepared active packaging film has excellent antioxidant and UV blocking properties and can continuously release essential oils, giving the film excellent antibacterial properties.

[0004] The objective of this invention can be achieved through the following technical solutions:

[0005] The first objective of this invention is to provide a method for preparing an active packaging film, the method comprising the following steps:

[0006] S1. Essential oils@polydopamine capsules were prepared by oxidative self-polymerization under alkaline conditions.

[0007] S2. Dissolve soy protein isolate in an alkaline aqueous solution, heat and stir for a certain time to obtain a soy protein isolate solution;

[0008] S3. Dissolve carboxymethyl cellulose in an aqueous solution, heat and stir for a certain period of time to obtain a carboxymethyl cellulose solution;

[0009] S4. The essential oil@polydopamine capsules obtained in step S1, the soy protein isolate solution obtained in step S2, the carboxymethyl cellulose solution obtained in step S3, and the plasticizer are mixed in a certain proportion to prepare a film-forming solution. After vacuum degassing, a film is formed by solution casting. After drying, the film is demolded to obtain the active packaging film.

[0010] Further, the specific process of step S1 is as follows: add the essential oil to a mixed solution of deionized water and anhydrous ethanol, add dopamine hydrochloride and Tris buffer solution under magnetic stirring at 200-600 rpm, continue stirring for 12-24 hours, and obtain essential oil@polydopamine capsules after washing with water and centrifuging 2-4 times.

[0011] Further, the specific process of step S2 is as follows: dissolve soy protein isolate in an aqueous solution, adjust the pH to 9-10 with NaOH solution, and stir continuously at 60-90℃ for 50-70 minutes to obtain a soy protein isolate solution.

[0012] Further, the specific process of step S3 is as follows: carboxymethyl cellulose is dissolved in an aqueous solution, and heated and stirred at 40-60℃ for 20-40 minutes to obtain a carboxymethyl cellulose solution.

[0013] Further, the specific process of step S4 is as follows: Using the solution blending method, the essential oil@polydopamine capsules obtained in step S1, the soy protein isolate solution obtained in step S2, the carboxymethyl cellulose solution obtained in step S3, and the plasticizer are stirred under magnetic stirring for 1 hour to obtain a film-forming solution. After vacuum degassing, the solution is poured into a mold to form a film using the solution casting method. After drying at room temperature, the film is demolded and placed in a desiccator to equilibrate for no less than 48 hours to obtain a multifunctional active packaging film based on polydopamine capsules and soy protein isolate-carboxymethyl cellulose.

[0014] Furthermore, in step S1, the essential oil is an antibacterial essential oil.

[0015] Furthermore, in step S1, the essential oil is a blend of Litsea cubeba essential oil and cinnamon essential oil.

[0016] Further, in step S2, the percentage of soy protein isolate in the soy protein isolate solution is 2.0-5.0%.

[0017] Further, in step S3, the mass percentage of carboxymethyl cellulose in the carboxymethyl cellulose solution is 1.0-2.0%.

[0018] Further, in step S4, the plasticizer is glycerin, and the amount of plasticizer added accounts for 2.0-3.0% of the mass percentage of the film-forming liquid.

[0019] Further, in step S4, the essential oil@polydopamine capsule accounts for 0.1-1% of the mass percentage of the film-forming solution.

[0020] Furthermore, in step S4, the mass ratio of soybean protein isolate solution to carboxymethyl cellulose solution in the film-forming solution is 1:1.

[0021] Furthermore, in step S1, the essential oil@polydopamine capsules have a smooth spherical morphology and good dispersibility, and the average particle size range is about 200-300 nm through the control of preparation conditions.

[0022] The second objective of this invention is to provide an active packaging film, which is prepared by the above-described preparation method. The active packaging film is a multifunctional active packaging film based on polydopamine capsules, consisting of soy protein isolate and carboxymethyl cellulose.

[0023] A third objective of this invention is to provide an application of the above-mentioned active packaging film, using the active packaging film in the field of food preservation.

[0024] Furthermore, the active packaging film is used as a food packaging material in the field of food preservation.

[0025] Furthermore, the active packaging film is used as a food packaging material for the preservation of perishable fruits. The specific steps are as follows: the active packaging film is used to package perishable fruits at room temperature, and their appearance is observed at regular intervals.

[0026] Furthermore, the perishable fruit includes blueberries.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1) The essential oil@polydopamine capsules prepared by this invention are prepared in one step without the addition of surfactants during the reaction process. They have the advantages of being safe, simple to prepare, and green to synthesize. The prepared essential oil@polydopamine capsules have a smooth spherical morphology and good dispersibility. By controlling the preparation conditions, the average particle size range is about 200-300 nm.

[0029] 2) The polydopamine capsules of the present invention can form covalent crosslinks with the film substrate, which can effectively improve the tensile strength and elongation at break of the film while avoiding the use of crosslinking agents, and effectively enhance the mechanical properties of the active packaging film.

[0030] 3) In the active packaging film prepared by the present invention, the addition of essential oil@polydopamine capsules endows the active packaging film with excellent antibacterial, antioxidant, and ultraviolet blocking properties. The prepared active packaging film has excellent antioxidant and ultraviolet blocking properties and can continuously release essential oil, giving the film excellent antibacterial properties.

[0031] 4) The active packaging film prepared by the present invention exhibits good biodegradability and low in vitro cytotoxicity.

[0032] 5) The active packaging film prepared by this invention is applied to the preservation of perishable fruits and has a good protective effect on perishable fruits, effectively extending their shelf life. The prepared active packaging film is a green and multifunctional active food packaging material with potential application prospects in food packaging. Attached Figure Description

[0033] Figure 1 a is the TEM image of the essential oil@polydopamine capsules prepared in Example 1; Figure 1 b is a SEM image of the essential oil@polydopamine capsules prepared in Example 1;

[0034] Figure 2 ab are SEM surface images of the active packaging films of Examples 1-4 and the comparative example soy protein isolate-carboxymethyl cellulose film; Figure 2 cd is a SEM cross-sectional view of the active packaging film of Examples 1-4 and the comparative example soy protein isolate-carboxymethyl cellulose film;

[0035] Figure 3 Mechanical strength diagrams of the active packaging films of Examples 1-4 and the comparative example of soy protein isolate-carboxymethyl cellulose film;

[0036] Figure 4 The graphs show the DPPH and ABTS free radical scavenging rates of the active packaging films of Examples 1-4 and the comparative soybean protein isolate-carboxymethyl cellulose film.

[0037] Figure 5 The UV blocking performance of the active packaging films of Examples 1-4 and the comparative example soy protein isolate-carboxymethyl cellulose film is shown in the diagram.

[0038] Figure 6 Antibacterial images of the active packaging films of Examples 1-4 and the comparative example of soy protein isolate-carboxymethyl cellulose film;

[0039] Figure 7 Biodegradation diagrams of the active packaging films of Examples 1-4 and the comparative example of soy protein isolate-carboxymethyl cellulose film;

[0040] Figure 8Cytotoxicity diagrams of the active packaging films of Examples 1-4 and the comparative example of soy protein isolate-carboxymethyl cellulose film;

[0041] Figure 9 Images show the active packaging films of Examples 1-4 and the comparative example of soy protein isolate-carboxymethyl cellulose film for blueberry preservation. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0043] The mechanism of this technical solution is as follows: Using soy protein isolate (SPI) and carboxymethyl cellulose (CMC) as bio-based materials, an active packaging film is prepared by adding polydopamine capsules loaded with aromatic antibacterial essential oils. Polydopamine can form covalent bonds with SPI and CMC, effectively improving the mechanical properties of the active packaging film while avoiding the use of cross-linking agents. SPI and PDA capsules can undergo Michael addition and Schiff base reactions, and PDA capsules can form numerous hydrogen bonds with CMC. Furthermore, the addition of nanoparticles (PDA capsules) to the polymer system can provide toughening and strengthening effects. In addition, the addition of essential oils@polydopamine capsules endows the active packaging film with excellent antibacterial, antioxidant, and UV-blocking properties. Applying this active packaging film to the preservation of perishable fruits—blueberries—can effectively maintain their freshness, extend their shelf life, and reduce quality loss. It has significant market application value in the food packaging field.

[0044] Any preparation methods, materials, structures, or composition ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0045] All other raw materials used in the following examples are commercially available.

[0046] The essential oil used in the examples is an antibacterial essential oil, which is a blend of Litsea cubeba essential oil and cinnamon essential oil in a ratio of 2:1.

[0047] Example 1

[0048] This embodiment provides a method for preparing an active packaging film, the method comprising the following steps:

[0049] S1. Preparation of essential oil@polydopamine capsules: 3 mL of antibacterial essential oil was added to water and ethanol at a volume ratio of 5:1 to form a microemulsion; 3 mL of 25 mg / mL dopamine hydrochloride solution and 15 mL of Tris buffer were added under magnetic stirring at 500 rpm, stirred for 24 h, washed with water and centrifuged 3 times to obtain essential oil@polydopamine capsules;

[0050] S2. Preparation of soy protein isolate solution: Weigh 5g of soy protein isolate into 100mL of deionized water, adjust the pH to 10 with NaOH solution, heat in an 80℃ water bath and stir continuously for 1h to allow it to fully swell until a yellow transparent soy protein isolate solution is obtained.

[0051] S3. Preparation of carboxymethyl cellulose solution: Weigh 2g of carboxymethyl cellulose into 100mL of deionized water, heat in a 50℃ water bath, and stir continuously for 30min to allow it to fully swell until a colorless and transparent carboxymethyl cellulose solution is obtained.

[0052] S4. Preparation of active packaging film: Take 0.025g of essential oil@polydopamine capsules, 9.7g of soy protein isolate solution, 9.7g of carboxymethyl cellulose solution and 0.6g of glycerin and stir magnetically for 1 hour to mix thoroughly. Defoam under vacuum for 30 minutes to obtain active packaging film liquid. Cast the film-forming liquid evenly into a polytetrafluoroethylene mold and dry at room temperature for 48 hours to remove moisture. After peeling off the film, the active packaging film is obtained, namely the soy protein isolate-carboxymethyl cellulose active packaging film of polydopamine capsules.

[0053] Example 2

[0054] The difference from Example 1 is that the mass of the essential oil@polydopamine capsules is 0.05g when preparing the active packaging film in step S1. All other contents are the same as in Example 1.

[0055] Example 3

[0056] The difference from Example 1 is that the mass of the essential oil@polydopamine capsules is 0.1g when preparing the active packaging film in step S1. All other contents are the same as in Example 1.

[0057] Example 4

[0058] The difference from Example 1 is that the mass of the essential oil@polydopamine capsules is 0.2g when preparing the active packaging film in step S1. All other contents are the same as in Example 1.

[0059] Example 5

[0060] The difference from Example 1 is that the preparation of the soy protein isolate solution in step S2 is as follows: 5g of soy protein isolate is weighed into 100mL of deionized water, and the pH is adjusted to 9 with NaOH solution. The solution is heated in a 60℃ water bath and stirred continuously for 70min to allow it to swell fully until a yellow transparent soy protein isolate solution is obtained. The other contents are the same as in Example 1.

[0061] Example 6

[0062] The difference from Example 1 is that the preparation of the soy protein isolate solution in step S2 is as follows: 5g of soy protein isolate is weighed into 100mL of deionized water, and the pH is adjusted to 9.5 with NaOH solution. The solution is heated in a 90℃ water bath and stirred continuously for 50min to allow it to swell fully until a yellow transparent soy protein isolate solution is obtained. The other contents are the same as in Example 1.

[0063] Comparative Example

[0064] S1. Preparation of soy protein isolate solution: Weigh 5g of soy protein isolate into 100mL of deionized water, place it in a water bath and heat to 80℃, and stir continuously for 1h to allow it to fully swell until a yellowish-brown transparent soy protein isolate solution is obtained.

[0065] S2. Preparation of carboxymethyl cellulose solution: Weigh 2g of carboxymethyl cellulose into 100mL of deionized water, place it in a water bath and heat to 50℃, stir continuously for 1h to allow it to fully swell until a colorless and transparent carboxymethyl cellulose solution is obtained.

[0066] S3. Preparation of soy protein isolate-carboxymethyl cellulose film: Take 9.7g of soy protein isolate solution, 9.7g of carboxymethyl cellulose solution and 0.6g of glycerol and stir magnetically for 1 hour to mix thoroughly. Defoam under vacuum for 30 minutes to obtain blank comparative packaging film liquid. Cast the film liquid evenly into a polytetrafluoroethylene mold and dry at room temperature for 48 hours to remove moisture. After peeling off the film, the soy protein isolate-carboxymethyl cellulose film is obtained.

[0067] Application examples

[0068] The active packaging film was used to package blueberries at room temperature, and their appearance was observed at regular intervals.

[0069] Performance testing:

[0070] (1) TEM of essential oil@polydopamine capsules: The capsules were diluted to a suitable concentration with anhydrous ethanol and ultrasonically dispersed at room temperature for 5 min. The ethanol dispersion of the capsules was dropped onto a copper grid and allowed to dry naturally. The sample was observed using a Tecnai G220TEM with a test voltage of 200 kV.

[0071] SEM of essential oil@polydopamine capsules: The morphology of the samples was observed using an S-3400N scanning electron microscope. The ethanol dispersion of essential oil@polydopamine capsules was dropped onto a silicon wafer, dried, and then sputter-coated with gold. Testing was performed at an accelerating voltage of 1.0 kV. The results are as follows: Figure 1 As shown.

[0072] Depend on Figure 1 As shown in ab, the essential oil@polydopamine capsules exhibit smooth, spherical particles with good dispersibility, an average particle size of approximately 283 nm, and a polydispersity index (PDI) value of 0.157. These results indicate that the prepared essential oil@polydopamine capsules possess a regular and uniform morphology.

[0073] (2) SEM of active packaging film: The active packaging films of Examples 1-4 and the comparative soybean protein isolate-carboxymethyl cellulose film were fixed on conductive adhesive and sputtered with gold. The surface and cross-sectional morphology of the film samples were observed using an S-4800 field emission scanning electron microscope at an accelerating voltage of 2kV.

[0074] Depend on Figure 2 It can be seen that the surface of the comparative example of soy protein isolate-carboxymethyl cellulose film is smooth and flat. Figure 2 a) The active packaging films of Examples 1-4 become rough, and the polydopamine capsules are uniformly distributed inside and on the surface of the substrate. Figure 2 b). The cross-sectional morphology of the comparative soybean protein isolate-carboxymethyl cellulose film is a dense structure. Figure 2 c) The cross-sectional structure of the active packaging films in Examples 1-4 remains uniform and dense. Figure 2 d) indicates that the polydopamine capsules are compatible with the soy protein isolate-carboxymethyl cellulose film matrix.

[0075] (3) Mechanical properties of the active packaging film: The active packaging films of Examples 1-4 and the comparative example soy protein isolate-carboxymethyl cellulose film were cut into pieces of 1×10 cm. Their mechanical properties were measured using a universal tensile testing instrument at a tensile testing rate of 50 mm / min. The tensile strength and elongation at break of the films were obtained based on the stress-strain curves. The results are as follows: Figure 3 As shown.

[0076] The addition of essential oil@polydopamine capsules can improve the tensile strength and elongation at break of the film. At an addition level of 1%, the tensile strength of the film can increase by approximately 8 times, and the elongation at break by 2.8 times. This is mainly due to the hydrogen bonds formed between the polydopamine capsules and soy protein isolate-carboxymethyl cellulose, and the covalent bonds formed between the essential oil@polydopamine capsules and soy protein through Schiff base or Michael addition reactions, thus giving the active packaging film greater tensile strength.

[0077] (4) Antioxidant properties test of active packaging film:

[0078] ① Determination of DPPH (1,1-diphenyl-2-trinitrophenylhydrazine) free radical scavenging ability: Prepare a 0.1 mM DPPH ethanol solution. Take 1 × 2 cm (approximately 50 mg) of the active packaging film from Examples 1-4 and the comparative example of soy protein isolate-carboxymethyl cellulose film and place them in the DPPH ethanol solution. After reacting the test solution in the dark at room temperature for 30 min, measure its absorbance value at 517 nm and record it as A. i The absorbance of the DPPH ethanol solution without a thin film was measured at 517 nm and denoted as A. j The results are as follows Figure 4 As shown.

[0079] The formula for calculating DPPH free radical scavenging rate is:

[0080] ② Determination of ABTS (2,2'-adiazono-3-ethylbenzothiazoline-6-sulfonic acid) free radical scavenging ability: 5 mL of 7 mmol / L ABTS solution was mixed with 88 μL of 140 mmol / L potassium persulfate solution and incubated overnight at room temperature in the dark to obtain an ABTS stock solution. The stock solution was diluted with anhydrous ethanol to obtain an absorbance of 0.70 ± 0.02 nm at 734 nm. 1 × 2 cm (approximately 50 mg) of the active packaging film from Examples 1-4 and the comparative example of soy protein isolate-carboxymethyl cellulose film were placed in the ABTS ethanol solution. After reacting the test solution in the dark at room temperature for 15 min, the absorbance value was measured at 734 nm and recorded as A. The absorbance value of the ABTS ethanol solution without the film was measured at 734 nm and recorded as A0. The results are as follows: Figure 4 As shown.

[0081] The formula for calculating the ABTS free radical scavenging rate is:

[0082] Depend on Figure 4 It can be seen that, compared with pure soy protein isolate-carboxymethyl cellulose film, the active packaging film with added essential oil@polydopamine capsules significantly enhances the DPPH free radical scavenging activity and ABTS free radical scavenging activity. When the concentration of essential oil@polydopamine capsules is 1%, the scavenging rate of DPPH free radicals reaches 66% and the scavenging rate of ABTS free radicals reaches more than 90%, which is mainly attributed to the quenching of free radicals by polydopamine and essential oils.

[0083] (5) UV blocking performance of active packaging film: The UV blocking performance of the active packaging film of Examples 1-4 and the comparative soybean protein isolate-carboxymethyl cellulose film sample was studied in the range of 200-900nm using a UV-1900 UV-Vis spectrometer. Each sample was measured three times.

[0084] Depend on Figure 5 It is known that soy protein isolate-carboxymethyl cellulose film cannot completely block ultraviolet rays below 400nm, while the active packaging films of Examples 1-4 absorb almost all ultraviolet rays below 400nm, achieving 100% ultraviolet shielding. The excellent UV protection performance of the active packaging film mainly stems from the absorption of ultraviolet light by the electron transitions of the benzene ring of polydopamine and quinone polymers. Therefore, the active packaging film can protect food from photo-oxidation and discoloration.

[0085] (6) Antibacterial test of active packaging film:

[0086] The antibacterial activity of the film samples against foodborne pathogenic Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus) was evaluated using colony counting methods. First, 20 mm × 20 mm active packaging films as described in Examples 1-4 were prepared and sterilized by UV irradiation on each side for 30 min. Then, 100 μL of a 10% concentration was... 6 CFU / mL bacterial suspensions were transferred to 5 mL PBS solutions containing different sterile film samples and incubated at 37°C for 24 hours. 100 μL of the incubated suspensions were plated onto sterile agar plates and incubated at 37°C for 24 hours to determine antibacterial activity. Bacterial suspensions without film samples were used as controls. Triples were performed for each test.

[0087] like Figure 6 As shown, pure soy protein isolate-carboxymethyl cellulose film did not exhibit any antibacterial activity against the tested microorganisms. However, after the addition of essential oil@polydopamine capsules, the film showed concentration-dependent antibacterial activity against both *Escherichia coli* and *Staphylococcus aureus*, with the 1% essential oil@polydopamine capsule film showing particularly significant antibacterial activity. The antibacterial activity of the active packaging film is mainly due to the release of the active ingredients of the essential oil in the capsules, which disrupts the bacterial cell membrane and thus inhibits bacterial growth.

[0088] (7) Biodegradation test of active packaging film:

[0089] The biodegradability of the film samples was assessed using an outdoor natural soil embedding method. 1cm × 1cm portions of the active packaging films from Examples 1-4 were wrapped in plastic mesh and buried 15-20cm below the soil surface. The weight of the active packaging films from Examples 1-4 was measured at different times. Here, m1 is the original weight of the film sample, and m2 is the weight of the film sample after degradation. The results are shown below. Figure 8 As shown.

[0090] The formula for calculating the weight degradation rate is:

[0091] Depend on Figure 7 It can be seen that after 32 days, the decomposition rate of the active packaging films in Examples 1-4 all significantly increased to over 90%, indicating that the active packaging film of soy protein isolate-carboxymethyl cellulose based on essential oil@polydopamine capsules can effectively solve the environmental pollution problem caused by traditional plastic films.

[0092] (8) In vitro cytotoxicity of the active packaging films: The cytotoxicity of the active packaging films of Examples 1-4 and the comparative soy protein isolate-carboxymethyl cellulose film samples was detected using the CCK-8 assay. NIH3T3 cells were cultured in 4 and 6 mg / mL medium, respectively, and the absorbance was measured at 450 nm. Each sample was measured three times.

[0093] have Figure 8 It can be seen that the cell viability of all film samples is above 65%. The cell viability of the active packaging films in Examples 1-4 is not significantly different from that of the comparative soy protein isolate-carboxymethyl cellulose film samples, indicating that the active packaging films have good biocompatibility and are suitable for further application in food packaging.

[0094] (9) Blueberry Preservation Test with Active Packaging Film: Blueberries were coated with the active packaging films of Examples 1-4 and the comparative example soy protein isolate-carboxymethyl cellulose film, and stored together with uncoated blueberries at room temperature. The morphological changes of the blueberries were recorded daily by photograph. The results are as follows: Figure 9 As shown.

[0095] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing an active packaging film, characterized in that, The preparation method includes the following steps: S1. Essential oils@polydopamine capsules were prepared by oxidative self-polymerization under alkaline conditions. S2. Dissolve soy protein isolate in an alkaline aqueous solution, heat and stir for a certain time to obtain a soy protein isolate solution; S3. Dissolve carboxymethyl cellulose in an aqueous solution, heat and stir for a certain period of time to obtain a carboxymethyl cellulose solution; S4. The essential oil@polydopamine capsules obtained in step S1, the soy protein isolate solution obtained in step S2, the carboxymethyl cellulose solution obtained in step S3, and the plasticizer are mixed in a certain proportion to prepare a film-forming solution. After vacuum degassing, a film is formed by solution casting. After drying, the film is demolded to obtain the active packaging film. In step S1, the essential oil is a blend of Litsea cubeba essential oil and cinnamon essential oil; In step S2, the percentage of soy protein isolate in the soy protein isolate solution is 2.0-5.0%; In step S3, the carboxymethyl cellulose solution contains 1.0-2.0% carboxymethyl cellulose by mass. In step S4, the plasticizer is glycerin, and the amount of plasticizer added accounts for 2.0-3.0% of the mass percentage of the film-forming solution. In step S4, the essential oil@polydopamine capsules account for 0.1-1% of the mass percentage of the film-forming solution; In step S4, the mass ratio of soybean protein isolate solution to carboxymethyl cellulose solution in the film-forming solution is 1:1; The specific process of step S1 is as follows: Add the essential oil to a mixed solution of deionized water and anhydrous ethanol, add dopamine hydrochloride and Tris buffer solution under magnetic stirring at 200-600 rpm, continue stirring for 12-24 hours, and obtain essential oil@polydopamine capsules after washing with water and centrifuging 2-4 times. Using soy protein isolate and carboxymethyl cellulose as bio-based materials, an active packaging film was prepared by adding essential oils to polydopamine capsules. In this process, polydopamine forms covalent bonds with soy protein isolate and carboxymethyl cellulose. Soy protein isolate and polydopamine undergo Michael addition and Schiff base reactions, and polydopamine forms hydrogen bonds with carboxymethyl cellulose.

2. The method for preparing an active packaging film according to claim 1, characterized in that, The specific process of step S2 is as follows: Dissolve soy protein isolate in an aqueous solution, adjust the pH to 9-10 with NaOH solution, and stir continuously at 60-90 ℃ for 50-70 min to obtain soy protein isolate solution.

3. The method for preparing an active packaging film according to claim 1, characterized in that, The specific process of step S3 is as follows: Dissolve carboxymethyl cellulose in an aqueous solution, heat and stir at 40-60 ℃ for 20-40 min to obtain a carboxymethyl cellulose solution.

4. The method for preparing an active packaging film according to claim 1, characterized in that, The specific process of step S4 is as follows: Using the solution blending method, the essential oil@polydopamine capsules obtained in step S1, the soy protein isolate solution obtained in step S2, the carboxymethyl cellulose solution obtained in step S3, and the plasticizer are stirred under magnetic stirring for 1 h to obtain a film-forming solution. After vacuum degassing, the solution is poured into a mold to form a film using the solution casting method. After drying at room temperature, the film is demolded and placed in a desiccator to equilibrate for no less than 48 h to obtain an active packaging film.

5. The method for preparing an active packaging film according to claim 1, characterized in that, In step S1, the average particle size of the essential oil@polydopamine capsules is 200-300 nm.

6. An active packaging film prepared by the preparation method according to any one of claims 1-5, characterized in that, The active packaging film is a multifunctional active packaging film based on essential oil@polydopamine capsules, consisting of soy protein isolate and carboxymethyl cellulose.

7. An application of an active packaging film prepared by the preparation method according to any one of claims 1-5, characterized in that, The active packaging film is used in the field of food preservation.

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