Antioxidant-antibacterial bifunctional starch-based composite film and preparation method and application thereof

Abstract

The application discloses an antioxidant-antibacterial dual-functional starch-based composite film and a preparation method and application thereof. The preparation method comprises the following steps: sequentially performing ultrasonic treatment and pullulanase enzymolysis treatment on a starch suspension to obtain a modified starch film-forming solution; adding a nano-composite loaded with an antioxidant and a metal organic framework material loaded with an antibacterial agent into the modified starch film-forming solution in sequence, and then adding a plasticizer to form a film to obtain the antioxidant-antibacterial dual-functional starch-based composite film. The composite film comprises a modified starch matrix, a nano-composite loaded with an antioxidant and a metal organic framework material loaded with an antibacterial agent. The preparation process is simple, physical, biological and self-assembly methods are used throughout the process, the obtained composite film has excellent mechanical properties, high barrier property, significant antioxidant and broad-spectrum antibacterial activity, and can be completely biodegraded, and can be widely applied to the field of food preservation packaging.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable packaging materials technology, specifically relating to an antioxidant-antibacterial dual-functional starch-based composite film, its preparation method, and its application. Background Technology

[0002] Starch-based biodegradable films are strong candidates to replace traditional petroleum-based plastic packaging. However, the weak mechanical strength, poor barrier properties, and lack of active functions to inhibit food spoilage of natural starch films limit their practical application. Existing technologies typically employ single physical or enzymatic methods to modify starch, or directly incorporate a functional factor (such as polyphenols or metal ions) to improve performance, but these methods suffer from limited modification effects, single function, and easy deactivation or uncontrollable release of active ingredients. For example, directly adding polyphenols may lead to uneven dispersion due to aggregation; adding antibacterial agents may affect the mechanical integrity of the film. Furthermore, the use of chemical crosslinking agents (such as glutaraldehyde) to enhance the network structure introduces safety risks.

[0003] Current technology CN118772454A discloses a high-strength starch composite film, which uses a starch-polysaccharide blending technology to enhance the mechanical properties of the film, but does not involve the nano-encapsulation technology of functional factors; CN114381042A discloses an indicator film containing anthocyanins, which uses encapsulation technology to load anthocyanins in a carrier for pH response indication. However, this technology mainly focuses on the color stability of anthocyanins during storage, and does not address the protection of the antioxidant activity of anthocyanins during film formation, nor does it solve the technical problems of uneven dispersion of anthocyanins in the starch matrix and synergistic effect with antibacterial function; some studies have also disclosed the antibacterial application of PCL@ZIF-8 nanofibers, but do not involve the synergistic effect with antioxidant function or its application in starch films.

[0004] Therefore, developing a process that uses a fully bio-based, non-chemical cross-linking method to systematically construct starch-based composite films that combine high strength and stability with synergistic antioxidant and antibacterial functions is of great value. Summary of the Invention

[0005] The main objective of this invention is to provide an antioxidant-antibacterial dual-functional starch-based composite film, its preparation method, and its application, so as to overcome the shortcomings of the existing starch-based active film construction process being blind and the performance being difficult to optimize synergistically.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes: The first aspect of this invention provides a method for preparing an antioxidant-antibacterial bifunctional starch-based composite film, comprising: The starch suspension was subjected to ultrasonic treatment and pullulanase hydrolysis in sequence to obtain a modified starch film-forming solution. An antioxidant-antibacterial dual-functional starch-based composite film was prepared by sequentially adding an antioxidant-loaded nanocomposite and an antibacterial-loaded metal-organic framework material to the modified starch film-forming solution, followed by adding a plasticizer to form a film. The antioxidant-loaded nanocomposite has a core-shell structure, wherein the core is an antioxidant and the shell is a nanocomposite, and the antibacterial agent is encapsulated in the pores of a metal-organic framework material.

[0007] A second aspect of the present invention provides an antioxidant-antibacterial bifunctional starch-based composite film prepared by the above preparation method, comprising: a modified starch matrix, a nanocomposite loaded with an antioxidant, and a metal-organic framework material loaded with an antibacterial agent. The antioxidant-loaded nanocomposite and the antibacterial metal-organic framework material form a physically cross-linked dual-network structure with the modified starch matrix. The antioxidant-loaded nanocomposite has a core-shell structure, wherein the core is the antioxidant and the shell is the nanocomposite. The antibacterial agent is encapsulated in the pores of the metal-organic framework material.

[0008] A third aspect of the present invention provides the application of the above-described antioxidant-antibacterial bifunctional starch-based composite film in the field of food preservation packaging.

[0009] Compared with the prior art, the present invention has at least the following beneficial effects: (1) Construction strategy innovation: This invention proposes for the first time a step-by-step construction and optimization strategy of “substrate strengthening → quantitative introduction of antioxidant function → synergistic introduction of antibacterial function”, which simplifies the performance regulation of complex multi-component systems, making the process clear and controllable, and overcoming the blindness of one-step blending method.

[0010] (2) Active ingredient protection technology: The present invention has a nano-encapsulation structure of antioxidant unit, which encapsulates proanthocyanidins inside quaternized chitosan / sodium tripolyphosphate nanoparticles instead of simply mixing them, so that they are protected from oxidative damage during film formation and maintain high antioxidant activity; The present invention also has a pore encapsulation structure of antibacterial unit, which encapsulates ε-PL in the pores of ZIF through in-situ synthesis, so as to achieve sustained release of antibacterial agent, avoid burst release, and extend antibacterial efficacy; The nano-encapsulation technology protects antioxidant and antibacterial agent respectively, preventing them from being deactivated during film formation, and significantly improving the utilization rate and stability of functional factors.

[0011] (3) Synergistic enhancement of structure: The nanostructures of the two functional units of the present invention form a double network structure with the modified starch matrix, which produces a synergistic enhancement effect, making the tensile strength of the film reach more than 7 MPa, which is significantly improved compared with pure modified starch film.

[0012] (4) Performance synergistic optimization: This invention achieves synergistic maximization of mechanical strength, antioxidant and antibacterial activity through step-by-step optimization, rather than simple superposition.

[0013] (5) Green and safe process: The present invention adopts physical, biological and self-assembly methods throughout the process, without using any chemical cross-linking agents, the raw materials are safe and biocompatible, and the film can be completely degraded.

[0014] (6) Excellent preservation effect: The dual-function film of the present invention has shown a preservation effect far exceeding that of single-function film and commercial PE film in the blueberry preservation experiment. It can effectively inhibit spoilage, maintain quality and extend shelf life. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a graph showing the tensile strength and elongation at break of films with different amounts of antioxidant units added in Example 1 of the present invention; Figure 2 This is a schematic diagram showing the DPPH scavenging rate relationship of films with different amounts of antioxidant units added in Example 1 of the present invention; Figure 3 This is a schematic diagram showing the relationship between ABTS scavenging rates of films with different amounts of antioxidant units added in Example 1 of the present invention; Figure 4 This is a comparison chart of tensile strength and elongation at break of films with simple ε-PL and ZIF and films with ε-PL@ZIF added in Example 1 of the present invention (both based on the optimal antioxidant system); Figure 5 The image shows a physical photograph of the antioxidant-antibacterial bifunctional starch-based composite film prepared according to an embodiment of the present invention. Figure 6 The image shows the antibacterial activity of the bifunctional film (UPB-1.5NPs / ε-PL@ZIF) obtained in Example 1 of this invention against Escherichia coli, Staphylococcus aureus, and Botrytis cinerea. Figure 7 This is a schematic diagram showing the inhibition rate of the bifunctional film obtained in Example 1 of the present invention against Escherichia coli; Figure 8 This is a schematic diagram showing the inhibition rate of the bifunctional film obtained in Example 1 of the present invention against Staphylococcus aureus; Figure 9This is a schematic diagram showing the inhibition rate of the bifunctional film obtained in Example 1 of the present invention against Botrytis cinerea; Figure 10 The images show a comparison of the appearance of blueberries packaged in the bifunctional film of Example 1, the pure modified starch film of Comparative Example 1, and the commercial PE film after storage at 4 °C for 9 days. Detailed Implementation

[0017] In view of the problems existing in the prior art, after in-depth research, an antioxidant-antibacterial dual-functional starch-based composite film is provided, along with its preparation method and application.

[0018] The following will provide a further explanation of the technical solution, its implementation process, and its principles.

[0019] The first aspect of this invention provides a method for preparing an antioxidant-antibacterial bifunctional starch-based composite film, comprising: The starch suspension was subjected to ultrasonic treatment and pullulanase hydrolysis in sequence to obtain a modified starch film-forming solution. An antioxidant-antibacterial dual-functional starch-based composite film was prepared by sequentially adding an antioxidant-loaded nanocomposite and an antibacterial-loaded metal-organic framework material to the modified starch film-forming solution, followed by adding a plasticizer to form a film. The antioxidant-loaded nanocomposite has a core-shell structure, wherein the core is an antioxidant and the shell is a nanocomposite, and the antibacterial agent is encapsulated in the pores of a metal-organic framework material.

[0020] In some embodiments, the concentration of the starch suspension is 3 to 8 wt%.

[0021] In some implementations, the ultrasonic treatment has a power of 200-300 W and a duration of 8-15 min.

[0022] In some embodiments, the pullulanase hydrolysis treatment involves adding 15-25 U / g starch at a temperature of 50-60 °C for 3-5 h.

[0023] In some embodiments, the modified starch film-forming solution contains 3 to 8 wt% modified starch.

[0024] In this invention, a synergistic physical process of "first ultrasound, then enzymatic hydrolysis" is employed. Biological modification methods use ultrasound to disrupt the particle structure, greatly increasing enzyme action sites and enabling precise enzymatic hydrolysis to cleave molecular chains, thereby generating a substrate suitable for forming a high-strength, dense network structure.

[0025] In some embodiments, the antioxidant-loaded nanocomposite is prepared by ionogel method. In a typical embodiment, the preparation method of the antioxidant-loaded nanocomposite includes the following steps: First, a 2 mg / mL aqueous solution of quaternized chitosan (HACC) is prepared and filtered; then, under continuous stirring at 800 rpm, proanthocyanidins (PC) (3 mg / mL) and sodium tripolyphosphate (TPP) (2 mg / mL) solutions are added dropwise to the HACC solution, and stirred for 1 h; the resulting suspension is centrifuged at 12000 rpm for 10 min, the precipitate is collected, washed several times with deionized water, and then freeze-dried at -42℃ for 24 h to obtain dry powdered proanthocyanidin quaternized chitosan nanoparticles (HPNPs) for later use. Nanoparticles prepared without the addition of PC are named quaternized chitosan nanoparticles (HNPs).

[0026] In some embodiments, the nanocomposite is formed by crosslinking quaternized chitosan with sodium tripolyphosphate.

[0027] In some embodiments, the antioxidant includes proanthocyanidins. The proanthocyanidins used in this invention have better stability, as they are mostly dimers or polymers, and are more resistant to changes in light, heat, and pH. Furthermore, proanthocyanidins have more phenolic hydroxyl groups, and their ability to scavenge free radicals is generally superior to that of anthocyanins, resulting in stronger antioxidant properties.

[0028] Furthermore, the mass ratio of the quaternized chitosan, sodium tripolyphosphate, and proanthocyanidins is 1:(0.3~0.6):(0.2~0.6).

[0029] In some embodiments, the mass ratio of the antioxidant-loaded nanocomposite to the modified starch is (0.6~0.8):100.

[0030] In this invention, proanthocyanidin-loaded nanocomposites (HPNPs) are independently constructed as antioxidant units. Proanthocyanidins are encapsulated within nanoparticles formed from quaternized chitosan / sodium tripolyphosphate using an ionogel method, forming a core-shell structure that protects them from oxidation. Besides improving stability and isolating them from external environmental influences, the core-shell structure also enables controlled, sustained release, extending the shelf life. Furthermore, the core-shell structure improves material compatibility and enhances the tensile strength of the composite film.

[0031] In some embodiments, the metal-organic framework material includes, but is not limited to, zeolite imidazole ester framework materials.

[0032] In some embodiments, the antimicrobial agent includes, but is not limited to, ε-polylysine.

[0033] In some embodiments, the metal-organic framework material loaded with antibacterial agent is prepared by in-situ synthesis.

[0034] In a typical implementation, the specific steps of preparing the metal-organic framework material loaded with the antibacterial agent are as follows: First, 2-methylimidazole (0.8 mol·L⁻¹) is prepared separately. - ¹), ε-PL (12 g·L) - ¹) and zinc nitrate hexahydrate (0.8 mol·L⁻¹) - ¹) solution. Subsequently, 10 mL of 2-methylimidazole solution, 1 mL of ε-PL solution, and 1 mL of zinc nitrate hexahydrate solution were taken and thoroughly mixed at 500 rpm. After 30 min, the mixture was centrifuged at 10000 rpm for 10 min, washed twice with deionized water, and freeze-dried to obtain the product, denoted as ε-PL@ZIF. For comparison, a pure ZIF sample was synthesized using the same procedure without the addition of ε-PL solution as a control.

[0035] Furthermore, the loading amount of the antibacterial agent in the metal-organic framework loaded with the antibacterial agent is 5.0~5.2 wt%.

[0036] In some embodiments, the mass-to-volume ratio of the antimicrobial-loaded metal-organic framework material to the modified starch film-forming solution is (15-35 mg): 9 mL.

[0037] In some embodiments, the plasticizer is 1 to 5 wt% of the modified starch.

[0038] In this invention, an antibacterial unit is introduced into a system already containing antioxidant units. ε-PL is encapsulated within the porous structure of ZIF using an in-situ synthesis method, solving the deliquescence problem of ε-PL, enhancing its stability, and achieving an improved membrane performance. By comparing the effects of ε-PL alone, ZIF, and ε-PL@ZIF on film properties (especially mechanical strength), antibacterial units that can further maintain or enhance various membrane properties are screened. This step ensures that the addition of antibacterial function synergistically enhances the overall performance of the film.

[0039] In some more specific embodiments, the preparation method specifically includes the following steps: (1) Substrate synergistic modification: Cassava starch was prepared into a suspension with a mass concentration of 5%, and ultrasonically treated at a power of 200~300W for 8~15 min; then pullulanase of 15~25 U / g starch was added at 50~60℃, and the reaction was carried out for 3~5 h; the enzyme was inactivated by heating and cooled to obtain the modified starch film-forming solution.

[0040] (2) Construction and optimization of antioxidant system: Quaternary ammonium chitosan, sodium tripolyphosphate and proanthocyanidins were self-assembled in aqueous solution at a mass ratio of 1:(0.3~0.6):(0.2~0.6) to prepare nanocomposite suspension.

[0041] (3) Construction and integration of antibacterial systems: Preparation of zeolite imidazolium ester framework materials (ZIF) and zeolite imidazolium ester framework materials loaded with ε-polylysine (ε-polylysine). ε-PL@ZIF powder. ε-PL@ZIF is synthesized in situ by pre-dissolving ε-PL in a 2-methylimidazole solution and then reacting it with zinc salt, so that ε-PL is encapsulated inside the channels during the ZIF crystal growth process.

[0042] (4) Film formation: The above modified starch film-forming liquid, the quaternized chitosan / sodium tripolyphosphate nanocomposite loaded with proanthocyanidins and the zeolite imidazole ester framework material loaded with ε-polylysine are mixed, and then 2wt% plasticizer is added. After homogenization, degassing, casting and drying, an antioxidant-antibacterial dual-function starch-based composite film is obtained.

[0043] A second aspect of the present invention provides an antioxidant-antibacterial bifunctional starch-based composite film prepared by the above preparation method, comprising: a modified starch matrix, a nanocomposite loaded with an antioxidant, and a metal-organic framework material loaded with an antibacterial agent. The antioxidant-loaded nanocomposite has a core-shell structure, wherein the core is an antioxidant and the shell is a nanocomposite, and the antibacterial agent is encapsulated in the pores of a metal-organic framework material.

[0044] In some embodiments, the thickness of the antioxidant-bifunctional starch-based composite film is 0.1 to 0.2 mm.

[0045] In some embodiments, the antioxidant-bifunctional starch-based composite film comprises 90-98 wt% modified starch matrix, 1-8 wt% antioxidant-loaded nanocomposite, 0.2-0.8 wt% antibacterial-loaded metal-organic framework material, and 1-5 wt% glycerol. In some embodiments, the modified starch matrix includes a modified cassava starch matrix.

[0046] In some embodiments, the antioxidant-loaded nanocomposite comprises a quaternized chitosan / sodium tripolyphosphate nanocomposite loaded with proanthocyanidins.

[0047] In some embodiments, the metal-organic framework material loaded with the antimicrobial agent includes a zeolite imidazole ester framework material loaded with ε-polylysine.

[0048] In some embodiments, the tensile strength of the antioxidant-antibacterial bifunctional starch-based composite film is above 6 MPa.

[0049] In some embodiments, the antioxidant-antibacterial bifunctional starch-based composite film has a scavenging rate of more than 50% for ABTS free radicals.

[0050] In some embodiments, the antioxidant-antibacterial bifunctional starch-based composite film has an antibacterial rate of greater than 70% against Escherichia coli and Staphylococcus aureus.

[0051] In some embodiments, the antioxidant-antibacterial bifunctional starch-based composite film exhibits complete biodegradability in a 28-day soil degradation experiment.

[0052] A third aspect of the present invention provides the application of the above-described antioxidant-antibacterial bifunctional starch-based composite film in the field of food preservation packaging.

[0053] In some implementations, the food includes berries.

[0054] In some preferred embodiments, the berry fruit is blueberry.

[0055] The technical solution of the present invention will be further described below with reference to the embodiments. Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available. Other unmentioned raw materials and instruments are all conventionally selected and do not involve the core technical means of the present invention.

[0056] Example 1 (1) Synergistic modification of cassava starch (substrate preparation): Weigh 5 g of cassava starch and dissolve it in 95 g of deionized water to prepare a 5% suspension. Sonicate the solution at 240 W for 10 min. Then, place it in a 55 °C water bath, add pullulanase (20 U / g starch), and magnetically stir for 4 h. Inactivate the enzyme by heating in a 90 °C water bath for 10 min to obtain modified starch base solution M, which contains approximately 5 wt% modified cassava starch. This base solution M serves as the common substrate for all subsequent examples.

[0057] (2) Preparation and screening of antioxidant units: S1. Quaternary ammonium chitosan, sodium tripolyphosphate, and proanthocyanidins were prepared into aqueous solutions of 2 mg / mL, 2 mg / mL, and 3 mg / mL, respectively. Under stirring, the latter two were added dropwise to the former, maintaining a final mass ratio of 1:0.45:0.2. The reaction was allowed to proceed for 1 h. Finally, the precipitate was redispersed uniformly in a measured amount of deionized water to prepare an antioxidant nanocomposite (HPNPs) resuspension containing 2.22 wt% of antioxidant-loaded nanocomposites.

[0058] S2. Optimization of Addition Amount: Multiple portions of the modified cassava starch film-forming solution prepared in Example 1 were accurately measured, each with a volume of 9 mL (measured to contain 450 mg of cassava starch on a dry basis per 9 mL). Different volumes of the above-mentioned HPNPs resuspension were added to each 9 mL portion of film-forming solution, setting the volume addition gradient as follows: 0.4 mL, 0.8 mL, 1.2 mL, 1.5 mL, and 1.8 mL. Subsequently, 2 wt% glycerol was added to each sample as a plasticizer. After thorough homogenization, air bubbles were removed, and the mixtures were cast into a flat mold and dried at 35 °C and 50% relative humidity for 10 h to prepare a series of antioxidant films.

[0059] S3. Performance Testing: Determine the mechanical properties and DPPH and ABTS free radical scavenging rates of each film. The specific testing method is as follows: (1) Mechanical properties: The tensile properties of the membrane were evaluated using a physical property tester. Before the test, the membrane samples, which were equilibrated at 25 ℃ and 50 ± 5% relative humidity for 24 h, were cut into rectangular strips of 50 mm × 10 mm. Then, tensile tests were performed at a constant tensile rate of 2 mm / min. Each sample was tested three times.

[0060] (2) Antioxidant activity: DPPH: Take 10 mg of the film and put it into 95% ethanol solution for 1 h to obtain film extract. Add 3 mL of DPPH (0.1 mM) and 1 mL of film extract. After the mixture stands in the dark for 3 h, read the absorbance at a wavelength of 517 nm.

[0061] ABTS: Mix 7 mM ABTS solution with an equal volume of 2.45 mM K2S2O8 solution and allow to react completely in a dark room for 16 h. Then dilute the mixture with 50% ethanol until the absorbance at 734 nm is 0.70 ± 0.02. For testing, add 3 mL of diluted ABTS solution to 1 mL of the film extract, react in the dark for 10 min, and then read the absorbance at 734 nm.

[0062] All experiments were repeated four times. The DPPH and ABTS free radical scavenging rates were calculated using the following formulas: ×100 Where A0 is the absorbance of the DPPH / ABTS solution without the film, and A1 is the absorbance after the film reacts with the solution.

[0063] Test results are as follows Figures 1-3 As shown.

[0064] Figure 1 The graph shows the tensile strength and elongation at break of films with different amounts of antioxidant units added in Example 1. UPB is a starch film modified by ultrasonication followed by pullulanase, and UPB-nNPs represents the addition of n mL of nanoparticles to the starch film solution modified by ultrasonication followed by pullulanase, where n is 0, 0.4, 0.8, 1.2, 1.5, or 1.8.

[0065] Figure 2 This is a schematic diagram showing the DPPH scavenging rate relationship of films with different amounts of added antioxidant units in Example 1. Figure 3 This is a schematic diagram showing the relationship between ABTS scavenging rates of films with different amounts of added antioxidant units in Example 1.

[0066] a. Mechanical properties show that the tensile strength of the film continuously increases as the addition amount increases from 0.4 mL to 1.5 mL. When the addition amount increases to 1.8 mL, the tensile strength of the film shows a decreasing trend.

[0067] b. Antioxidant activity showed that the ABTS scavenging rate increased with increasing addition amount.

[0068] The optimal addition amount of the antioxidant nanocomposite was determined to be 1.5 mL by testing its mechanical strength and antioxidant activity.

[0069] (3) Screening of antibacterial units S1. Preparation of antibacterial unit: a. ZIF: Mix 2-methylimidazole (0.8 mol / L) and zinc nitrate hexahydrate (0.8 mol / L) solution at a volume ratio of 10:1, stir for 30 min, centrifuge, wash and freeze dry.

[0070] b. ε-PL@ZIF: An in-situ synthesis method was adopted. ε-PL (final concentration 12 g / L) was added to the 2-methylimidazole solution in advance to make it completely dissolved, and then mixed with the zinc salt solution so that ε-PL was encapsulated inside the channel during the growth of ZIF crystals. The same method was used.

[0071] S2. Screening and Optimization: Use a base solution containing the optimal antioxidant system. Experiments were conducted in three groups: Group I: 0.4 wt% (20 mg) of ε-PL powder was added.

[0072] Group II: Add 0.4wt% (20 mg) of ZIF powder.

[0073] Group III: 0.4 wt% (20 mg) of ε-PL@ZIF powder was added to each group. 2 wt% glycerol was added to each group. After thorough homogenization, air bubbles were removed, and the mixtures were cast into flat molds and dried at 35 °C and 50% relative humidity for 10 h to prepare a series of films.

[0074] S3. Performance testing: Test the mechanical properties (tensile strength and elongation at break) of all films. Figure 4 This is a comparison of tensile strength and elongation at break of films with simple ε-PL, ZIF, and ε-PL@ZIF added in Example 1 (all based on the optimal antioxidant system). UPB-1.5NPs / ε-PL is the film prepared by simply adding ε-PL in Example 1; UPB-1.5NPs / ZIF is the film prepared by simply adding ZIF in Example 1; and UPB-1.5NPs / ε-PL@ZIF is the film prepared by adding ε-PL@ZIF in Example 1. The results show that the TS of Group III (ε-PL@ZIF) film is significantly higher than that of the other two groups.

[0075] S4. Release Experiment: The films of Group I and Group II were immersed in different food simulants, and the absorbance of the immersion solutions was measured at 214 nm (for ε-PL) and 278 nm (for proanthocyanidins). The results showed that the ε-PL and proanthocyanidins in the Group II film exhibited significant sustained-release effects.

[0076] (4) Preparation of antioxidant-antibacterial dual-functional starch-based composite film Take 9 mL of membrane base solution M, add 1.5 mL of HPNPs and 20 mg of ε-PL@ZIF powder, and add 2 wt% glycerol. Homogenize at high speed for 5 min, sonicate to remove bubbles for 2 min, cast on a plate, and dry at 35 ℃ and 50% RH for 10 h. Peel off the membrane to obtain the final bifunctional membrane UPB-1.5NPs / ε-PL@ZIF. The actual product is as follows... Figure 5 As shown.

[0077] Performance testing a. Mechanical properties: The tensile strength is 7.67 MPa, which is 28% higher than that of pure modified starch film (Comparative Example 1).

[0078] b. Antibacterial and antioxidant properties: such as Figure 6-9As shown, it exhibits significant antibacterial effects against Escherichia coli and Staphylococcus aureus, with an antibacterial rate of approximately 83%, and an inhibition rate of 50% against Botrytis cinerea. The ABTS clearance rate is approximately 60%.

[0079] c. Barrier properties: Water vapor permeability is reduced by 17%.

[0080] d. Blueberry Preservation Application: Using fresh blueberries as the test material, four groups were set up: unpackaged (CK), commercially available PE film packaging, comparative example 1 film packaging, and the UPB-1.5NPs / ε-PL@ZIF film packaging of this invention, stored at 4 ± 1 ℃. Figure 10 As shown, after 9 days of storage, the UPB-1.5NPs / ε-PL@ZIF membrane group maintained the best appearance and firmness of blueberries, had the lowest rot rate, and retained significantly higher rates of titratable acid, anthocyanins, and other nutrients than other groups, demonstrating the best overall preservation effect.

[0081] Example 2 The difference between this embodiment and Embodiment 1 is that: (1) Substrate modification parameters: Weigh 3 g of cassava starch and dissolve it in 97 g of deionized water. The starch suspension concentration is 3wt%. The ultrasonic treatment power is 200 W and the time is 8 min. The enzymatic hydrolysis temperature is 50 ℃ and the time is 3 h. The pullulanase addition amount is 15 U / g starch. (2) Antioxidant unit parameters: Quaternary ammonium chitosan: TPP: proanthocyanidins mass ratio 1:0.3:0.2, HPNPs to film-forming liquid volume ratio 0.4:9; (3) Antibacterial unit parameters: ε-PL@ZIF addition amount 15 mg; (4) Film-forming parameters: 1 wt% of plasticizer glycerin was added.

[0082] The remaining steps are the same as in Example 1.

[0083] Performance results: tensile strength 6.35 MPa, ABTS removal rate 51.2%, antibacterial rate against Escherichia coli and Staphylococcus aureus approximately 70.5%, inhibition rate against Botrytis cinerea 42%, and water vapor transmission rate reduced by 17.3%.

[0084] Example 3 The difference between this embodiment and Embodiment 1 is that: (1) Substrate modification parameters: starch suspension concentration 8 wt%, ultrasonic treatment power 300 W, time 15 min, enzymatic hydrolysis temperature 60 ℃, time 5 h, pullulanase addition amount 25 U / g starch; (2) Antioxidant unit parameters: Quaternary ammonium chitosan: TPP: proanthocyanidins mass ratio 1:0.6:0.6, HPNPs to film-forming liquid volume ratio 1.8:9; (3) Antibacterial unit parameters: ε-PL@ZIF addition amount 35 mg; (4) Film-forming parameters: 5 wt% of plasticizer glycerin was added.

[0085] The remaining steps are the same as in Example 1.

[0086] Performance results: tensile strength 6.75 MPa, ABTS removal rate 50.6%, antibacterial rate against Escherichia coli and Staphylococcus aureus approximately 83.2%, inhibition rate against Botrytis cinerea 57%, and water vapor permeability reduced by 15%.

[0087] Comparative Example 1 This comparative example uses only pure modified starch film.

[0088] Using only the base solution M from Example 1, 2wt% glycerol was added, and film was formed using the same process.

[0089] Its tensile strength is about 4.37 MPa, it has almost no antioxidant and antibacterial activity, its barrier properties are reduced, and its water vapor permeability is about 17% higher than that of Example 1. The preservation effect of blueberries is basically the same as that of the unpackaged group.

[0090] Comparative Example 2 This comparative example uses a single antioxidant film (optimal addition amount). Using base solution M, 1.5 mL of HPNPs were added, and 2 wt% glycerol was added to form a film.

[0091] Its tensile strength decreased compared to Example 1, to about 6.0 MPa. Its antioxidant performance was not significantly different from that of Example 1. The ABTS scavenging rate was about 60%. Due to the lack of ε-PL@ZIF antibacterial units, it had no antibacterial effect. Its water vapor transmission rate was about 10% higher than that of Example 1. The shelf life of blueberries was extended by 2 days compared to the blank group, but much shorter than that of Example 1.

[0092] Comparative Example 3 This comparative example uses a single antioxidant film (not the optimal amount).

[0093] Film was formed by adding 1.8 mL of HPNPs (in excess) and 2 wt% glycerol to base solution M.

[0094] Its tensile strength decreased compared to Example 1, to approximately 4.8 MPa, demonstrating that excessive addition is detrimental to mechanical properties. Due to the increased antioxidant content, the membrane's antioxidant capacity improved, with an ABTS scavenging rate of approximately 75%. However, its water vapor barrier properties decreased, and its water vapor permeability was 13% higher. It exhibited no antibacterial activity, and the blueberry shelf life was extended by 2 days compared to the control group, but still significantly shorter than that of Example 1.

[0095] Comparative Example 4 This comparative example uses an antioxidant and antibacterial dual membrane (non-metallic organic framework loading).

[0096] Using base solution M, 1.5 mL of HPNPs were added, along with ε-PL (without ZIF loading) and 2 wt% glycerol to form a film.

[0097] Its tensile strength decreased compared to Example 1, to approximately 5.3 MPa; the ABTS removal rate was approximately 55%; the antibacterial rate against Escherichia coli was approximately 78%; and the inhibitory rate against Botrytis cinerea was approximately 47%, demonstrating that directly adding antimicrobial peptides is detrimental to mechanical properties. Barrier properties decreased, with water vapor permeability 12% higher than in Example 1; the shelf life of blueberries was extended by 4 days compared to the unpackaged group, but the preservation effect was not as good as in Example 1.

[0098] Comparative Example 5 This comparative example uses a membrane with directly added antioxidants and no nanocomposite shell.

[0099] Using base solution M, add 1.5 mL of proanthocyanidin solution and 2 wt% glycerol to form a film.

[0100] Its tensile strength decreased compared to Example 1, to approximately 5.1 MPa, and its antioxidant properties also decreased compared to Example 1. The ABTS scavenging rate was approximately 53%, and since no ε-PL@ZIF was added, it had no antibacterial activity. The membrane density decreased, and the water vapor permeability was 14% higher than that of Example 1. The blueberry preservation performance was significantly lower than that of Example 1.

[0101] In addition, the present invention has also conducted experiments with other raw materials, process operations and process conditions described in this specification, with reference to the foregoing embodiments, and has obtained relatively ideal results in all cases.

[0102] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A method for preparing an antioxidant-antibacterial bifunctional starch-based composite film, characterized in that, include: The starch suspension was subjected to ultrasonic treatment and pullulanase hydrolysis in sequence to obtain a modified starch film-forming solution. An antioxidant-antibacterial dual-functional starch-based composite film was prepared by adding an antioxidant-antibacterial dual-functional starch-based composite film to the modified starch film-forming solution, followed by the addition of a plasticizer. The antioxidant-loaded nanocomposite has a core-shell structure, wherein the core is an antioxidant and the shell is a nanocomposite, and the antibacterial agent is encapsulated in the pores of a metal-organic framework material.

2. The preparation method according to claim 1, characterized in that: The concentration of the starch suspension is 3-8 wt%; And / or, the power of the ultrasonic treatment is 200~300 W, and the time is 8~15 min; And / or, the pullulanase hydrolysis treatment involves adding 15-25 U / g starch at a temperature of 50-60 °C for 3-5 h; And / or, the modified starch film-forming solution contains 3-8 wt% modified starch.

3. The preparation method according to claim 1, characterized in that, The antioxidant-loaded nanocomposite was prepared by ionogel method; And / or, the nanocomposite is formed by crosslinking quaternized chitosan with sodium tripolyphosphate; And / or, the antioxidants include proanthocyanidins.

4. The preparation method according to claim 3, characterized in that: The mass ratio of the quaternized chitosan, sodium tripolyphosphate, and proanthocyanidins is 1:(0.3~0.6):(0.2~0.6). The mass ratio of the antioxidant-loaded nanocomposite to the modified starch is (0.6~0.8):

100.

5. The preparation method according to claim 1, characterized in that: The metal-organic framework material includes zeolite imidazolate framework material; And / or, the antimicrobial agent includes ε-polylysine; And / or, the metal-organic framework material loaded with antibacterial agent is prepared by in-situ synthesis; And / or, the plasticizer includes glycerin.

6. The preparation method according to claim 5, characterized in that: The loading amount of the antibacterial agent in the metal-organic framework supporting the antibacterial agent is 5.0~5.2 wt%; And / or, the mass-to-volume ratio of the antibacterial metal-organic framework material to the modified starch film-forming solution is (15~35 mg): 9 mL; And / or, the plasticizer is 1 to 5 wt% of the modified starch.

7. The antioxidant-antibacterial bifunctional starch-based composite film prepared by the preparation method according to any one of claims 1-6, characterized in that, include: Modified starch matrix, antioxidant-loaded nanocomposites, and antibacterial metal-organic framework materials; The antioxidant-loaded nanocomposite and the antibacterial metal-organic framework material form a physically cross-linked dual-network structure with the modified starch matrix. The antioxidant-loaded nanocomposite has a core-shell structure, wherein the core is the antioxidant and the shell is the nanocomposite. The antibacterial agent is encapsulated in the pores of the metal-organic framework material.

8. The antioxidant-antibacterial dual-functional starch-based composite film according to claim 7, characterized in that: The thickness of the antioxidant-bifunctional starch-based composite film is 0.1~0.2 mm; And / or, the antioxidant-bifunctional starch-based composite film comprises 90-98 wt% modified starch matrix, 1-8 wt% nanocomposite loaded with antioxidant, 0.2-0.8 wt% metal-organic framework material loaded with antibacterial agent, and 1-5 wt% glycerol; And / or, the modified starch matrix includes a modified cassava starch matrix; And / or, the antioxidant-loaded nanocomposite includes a quaternized chitosan / sodium tripolyphosphate nanocomposite loaded with proanthocyanidins. And / or, the metal-organic framework material loaded with antibacterial agent includes a zeolite imidazole ester framework material loaded with ε-polylysine; And / or, the tensile strength of the antioxidant-antibacterial bifunctional starch-based composite film is above 6 MPa; And / or, the antioxidant-antibacterial bifunctional starch-based composite film has a scavenging rate of ABTS free radicals greater than 50%; And / or, the antioxidant-antibacterial bifunctional starch-based composite film has an antibacterial rate of greater than 70% against Escherichia coli and Staphylococcus aureus.

9. The application of the antioxidant-antibacterial dual-functional starch-based composite film according to claim 7 or 8 in the field of food preservation packaging.

10. The application according to claim 9, characterized in that: The food includes berries, preferably blueberries.

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