Antioxidant and antibacterial food packaging material based on multi-field synergy and gradient ultrasound and preparation method thereof

Abstract

The application belongs to the technical field of food packaging materials, and particularly relates to an antioxidant and bacteriostatic food packaging material based on multi-field synergy and gradient ultrasonic and a preparation method thereof, the preparation method comprising the following steps: mixing a metal salt solution with the polyphenol polysaccharide blend to obtain a metal-polyphenol polysaccharide blending system; performing gradient power ultrasonic treatment on the metal-polyphenol polysaccharide blending system, wherein the gradient power ultrasonic treatment comprises at least two ultrasonic stages with gradually increased power; and forming the ultrasonically treated blending system into a gel to obtain the food packaging material. The application has the beneficial effect that two-step addition enables metal ions and polyphenols to form a uniform metal-polyphenol coordination network; and gradient power ultrasonic treatment realizes bubble removal, molecular chain stretching and rearrangement in stages under the premise of protecting the activity of polyphenols, and finally constructs an antioxidant and bacteriostatic food packaging material free of bubble defects and stable in structure.

Description

Technical Field

[0001] This invention belongs to the field of food packaging materials technology, specifically relating to an antioxidant and antibacterial food packaging material based on multi-field synergy and gradient ultrasound and its preparation method. Background Technology

[0002] Food packaging materials play a crucial role in preserving freshness, extending shelf life, and maintaining food quality. In recent years, with increasing consumer demand for health and environmental protection, the development of active packaging with antioxidant and antibacterial functions has become a research hotspot. Polysaccharide-based materials, due to their good biocompatibility, biodegradability, and film-forming properties, are widely used to replace traditional plastic packaging.

[0003] To further enhance the bioactivity of food packaging materials, existing technologies often incorporate polyphenols into polysaccharide packaging materials, utilizing their excellent antioxidant and antibacterial properties to improve the bioactivity of the food packaging. For example, Chinese patent application CN111171385A discloses a starch-crosslinked tea polyphenol antibacterial and biodegradable food packaging material, which uses a crosslinking agent to crosslink starch and tea polyphenols to overcome the instability of tea polyphenols. Another example is Chinese patent application CN120310064A, which discloses a chitosan-carrageenan blended composite film containing crabapple peel extract and vitamin C, enhancing the film's antioxidant and antibacterial capabilities by adding natural extracts and vitamin C.

[0004] However, existing technologies still have many shortcomings. In polysaccharide-polyphenol composite packaging materials, the phenolic hydroxyl groups in polyphenol molecules are easily oxidized by oxygen in the air, causing their antioxidant activity to rapidly decline during processing and storage, resulting in insufficient durability. Furthermore, traditional preparation methods often rely on simple mechanical stirring, making it difficult to achieve uniform cross-linking between polyphenol and polysaccharide molecules. This easily leads to incomplete network structures, poor mechanical properties, and a large number of residual air bubbles in the system. This increases the contact area between polyphenols and air, making them more susceptible to oxidation, and also causes structural defects in hydrogel formation, affecting the material's density and functionality.

[0005] To address issues such as residual bubbles, uneven cross-linking, and the easy oxidation of polyphenols, ultrasonic treatment is commonly used in existing technologies to assist in the preparation of composite gel materials. However, conventional ultrasonic treatment often employs a fixed power mode, making it difficult to simultaneously achieve a balance between efficient defoaming, orderly network construction, and polyphenol stability protection during the process. While lower-power ultrasound can avoid polyphenol oxidation and network damage, it results in low bubble removal efficiency and insufficient molecular cross-linking. Higher power, although helpful in defoaming and promoting cross-linking, exacerbates polyphenol degradation and localized network destruction, limiting further improvements in material performance.

[0006] Current research suggests enhancing the antibacterial properties of materials by introducing metal ions to coordinate with polyphenols. However, the metal ion addition process often lacks precise timing and rate control under multi-field synergistic conditions, leading to uneven metal ion distribution, excessively rapid local cross-linking, or aggregate formation. This fails to effectively leverage the synergistic antioxidant and antibacterial effects between metals and polyphenols / polysaccharides. Furthermore, the addition of metal ions affects the uniformity, transparency, and stability of food packaging materials. Without precise control, it may lead to ion migration or leaching, posing potential food safety risks and limiting its large-scale application in food packaging. Summary of the Invention

[0007] The technical problem to be solved by this invention is to address the problems of easy oxidation of polyphenols, uneven cross-linking, excessive bubble residue, and uncontrollable metal ion distribution in existing polysaccharide-polyphenol composite packaging materials, which lead to unstable performance. This invention provides an antioxidant and antibacterial food packaging material based on multi-field synergy and gradient ultrasound and its preparation method.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing an antioxidant and antibacterial food packaging material based on multi-field synergy and gradient ultrasound, comprising the following steps:

[0009] Under the combined effect of a thermal field and a mechanical stirring field, a polyphenol solution is added to a polysaccharide solution at a flow rate of 0.1-0.5 mL / min using a peristaltic pump to obtain a polyphenol-polysaccharide blend.

[0010] Under the combined effect of a thermal field and a mechanical stirring field, a metal salt solution was added to the polyphenol-polysaccharide blend at a flow rate of 0.1-0.5 mL / min using a peristaltic pump to obtain a metal-polyphenol-polysaccharide blend system.

[0011] The metal-polyphenol-polysaccharide blend system is subjected to gradient power ultrasonic treatment, which includes at least two ultrasonic stages with progressively increasing power.

[0012] The ultrasonically treated blend system is gelled to obtain the food packaging material.

[0013] Another technical solution provided by the present invention is: to provide an antioxidant and antibacterial food packaging material based on multi-field synergy and gradient ultrasound prepared by the above-mentioned method for preparing antioxidant and antibacterial food packaging material based on multi-field synergy and gradient ultrasound.

[0014] The beneficial effects of this invention are as follows: This application reconstructs the mixing and cross-linking steps in the traditional preparation process into a two-step time-controlled process of premixing polyphenols and polysaccharides followed by adding metal ions. Combined with gradient power ultrasonic treatment as a core process, the metal-polyphenol-polysaccharide blend system is subjected to staged physicochemical regulation through at least two ultrasonic stages with progressively increasing power. The two-step addition strategy avoids local aggregation caused by the instantaneous and violent reaction between metal ions and polyphenols, laying the foundation for the formation of a uniform metal-polyphenol coordination network. Gradient power ultrasonic treatment, through an energy-increasing manner, sequentially achieves the gradual removal of bubbles within the system, the full extension and rearrangement of macromolecular chain segments, and ultimately drives efficient coordination and cross-linking of metal-polyphenols. Thus, without the need for additional chemical cross-linking agents, a food packaging material with no bubble defects, a dense and uniform structure, and synergistic enhancement of the metal-polyphenol-polysaccharide ternary network is constructed, significantly improving the material's antioxidant durability and broad-spectrum antibacterial activity. Attached Figure Description

[0015] Figure 1 The figure shows the experimental results of food packaging materials treated with different methods according to specific embodiments of the present invention against Staphylococcus aureus.

[0016] Figure 2 Experimental results on Escherichia coli using food packaging materials with different treatment methods according to specific embodiments of the present invention;

[0017] Figure 3 The diagram shows the antibacterial effects of food packaging materials processed in different ways according to specific embodiments of the present invention against Escherichia coli and Staphylococcus aureus.

[0018] Figure 4 The effects of different treatment methods of composite hydrogels on DPPH free radical scavenging rate in specific embodiments of the present invention. Detailed Implementation

[0019] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0020] The key concept of this invention lies in:

[0021] 1. This invention innovatively combines a thermal field, a mechanical stirring field, and an ultrasonic energy field in a sequential and coordinated manner, employing a stepped ultrasonic process to construct a dynamic and controllable preparation environment for composite hydrogels, based on the precise matching of the material system state and reaction requirements at each stage. First, gentle heating reduces the viscosity of the polysaccharides in the system, enhancing molecular mobility and providing favorable initial conditions for subsequent mechanical stirring and ultrasonic action. Mechanical stirring is introduced on top of the thermal field to achieve preliminary mixing and homogenization of the reaction components at a macroscopic scale, preventing localized overheating or deposition. Through staged and precise control of the hydrogel solution using a gradient ultrasonic energy field, a three-stage mode with increasing power is employed to process the composite hydrogel according to the different structural requirements during the reaction process.

[0022] The first stage, low power (100-300W), primarily utilizes the cavitation effect of ultrasound to generate microjets and shear forces, physically breaking down initial aggregates, initially dispersing nanoparticles, and preliminarily eliminating microbubbles within the system. This provides a low-defect, homogeneous environment for the molecular-level interactions of the composite hydrogel. The second stage, medium power (300-500W), moderately enhances the ultrasonic energy, promoting the movement, extension, and rearrangement of polymer chains. Simultaneously, it accelerates the migration and adsorption of functional molecules such as polyphenols to the interface, facilitating the effective formation of non-covalent interactions such as hydrogen bonds. Continuous ultrasound further integrates and removes the bubbles refined in the low-power stage. The third stage, high power (500-700W), applies high-intensity ultrasound, providing higher local energy to drive coordination reactions between metal ions and polyphenol ligands. The intense ultrasound action fully exposes the reaction sites, ensuring rapid and uniform formation of coordination bonds, enabling efficient metal-polyphenol coordination reactions. The advanced gradient ultrasound effectively avoids the problems that single high-intensity ultrasound may cause, such as the breakage of macromolecular chains between hydrogels, inactivation of active ingredients, or excessive bubbles. It promotes the coordination reaction between metal ions and polyphenol molecules, and effectively improves the antioxidant and antibacterial properties of the composite hydrogel.

[0023] 2. This invention also employs a peristaltic pump to control the addition rate of the metal ion solution. By precisely setting the flow rate of the peristaltic pump, metal ions are slowly and constantly added to the polyphenol / polymer system under continuous stirring and ultrasonic action. This overcomes the technical difficulties commonly encountered in coordination reactions, such as uneven distribution of metal ions and rapid local cross-linking leading to aggregation or gelation. This allows the coordination reaction between metal ions and polyphenols to occur almost synchronously and gradually throughout the entire system, effectively avoiding instantaneous over-cross-linking, particle aggregation, or the formation of uneven hard lumps due to excessively high local concentrations. This ensures that polyphenols can effectively coordinate with metal ions, maximizing the utilization of their antioxidant and antibacterial active centers and promoting the antioxidant and antibacterial properties of the composite hydrogel.

[0024] This invention provides a method for preparing an antioxidant and antibacterial food packaging material based on multi-field synergy and gradient ultrasound, comprising the following steps:

[0025] Under the combined effect of a thermal field and a mechanical stirring field, a polyphenol solution is added to a polysaccharide solution at a flow rate of 0.1-0.5 mL / min using a peristaltic pump to obtain a polyphenol-polysaccharide blend.

[0026] Under the combined effect of a thermal field and a mechanical stirring field, a metal salt solution was added to the polyphenol-polysaccharide blend at a flow rate of 0.1-0.5 mL / min using a peristaltic pump to obtain a metal-polyphenol-polysaccharide blend system.

[0027] The metal-polyphenol-polysaccharide blend system is subjected to gradient power ultrasonic treatment, which includes at least two ultrasonic stages with progressively increasing power.

[0028] The ultrasonically treated blend system is gelled to obtain the food packaging material.

[0029] The beneficial effects of this invention are as follows: This application reconstructs the mixing and cross-linking steps in the traditional preparation process into a two-step time-sequential control method of premixing polyphenols and polysaccharides and adding metal ions, and combines the core process of "gradient power ultrasonic treatment" to carry out phased physicochemical regulation of the metal-polyphenol and polysaccharide blend system through at least two ultrasonic stages with successively increasing power.

[0030] A peristaltic pump was used to add reactants at a constant flow rate of 0.1-0.5 mL / min. By precisely controlling the addition rate of reactants, the cross-linking and coordination reactions between polyphenols and polysaccharides, and between metal ions and polyphenols, were ensured to proceed synchronously and uniformly at both the macroscopic and microscopic scales. This technological improvement fundamentally avoids the instantaneous violent reactions, agglomeration, or formation of uneven precipitation caused by excessively high local concentrations. It is a key process guarantee for achieving uniform material structure, stable performance, and good reproducibility, and provides an ideal reaction precursor system for subsequent gradient ultrasonic treatment.

[0031] The two-step addition strategy described above avoids local aggregation caused by the instantaneous and violent reaction between metal ions and polyphenols, laying the foundation for the formation of a uniform metal-polyphenol coordination network. The gradient power ultrasonic treatment, through an energy increment, sequentially achieves the gradual removal of bubbles in the system, the full extension and rearrangement of macromolecular chain segments, and ultimately drives the efficient coordination and cross-linking of metal-polyphenols. Thus, without the need for additional chemical cross-linking agents, a food packaging material with no bubble defects, a dense and uniform structure, and synergistic enhancement of the metal-polyphenol-polysaccharide ternary network is constructed, significantly improving the material's antioxidant durability and broad-spectrum antibacterial activity.

[0032] Furthermore, in the above-mentioned method for preparing antioxidant and antibacterial food packaging materials based on multi-field synergy and gradient ultrasound, the gradient power ultrasound treatment includes:

[0033] In the first ultrasonic stage, the ultrasonic power is 100-300 W and the processing time is 5-10 min;

[0034] In the second ultrasonic stage, the ultrasonic power is 300-500 W and the processing time is 10-20 min;

[0035] In the third ultrasonic stage, the ultrasonic power is 500-700 W and the processing time is 20-30 min.

[0036] As described above, the first ultrasonic stage (100-300W, 5-10min) utilizes the cavitation effect of gentle ultrasound for initial dispersion and defoaming, providing a homogeneous initial environment for subsequent reactions and preventing the direct destruction of active molecules by intense cavitation. The second ultrasonic stage (300-500W, 10-20min) promotes the movement, extension, and rearrangement of polymer chain segments through energy enhancement, accelerating the migration of functional molecules such as polyphenols to the reaction interface and facilitating the formation of non-covalent interactions such as hydrogen bonds. The third ultrasonic stage (500-700W, 20-30min) provides sufficient energy through high-intensity ultrasound to drive efficient and rapid coordination reactions between metal ions and polyphenols, strengthening the network structure. The synergistic effect of these three stages balances the contradictions between defoaming, cross-linking promotion, and activity preservation, optimizing the structural uniformity and functionality of the material.

[0037] Furthermore, in the above-mentioned method for preparing antioxidant and antibacterial food packaging materials based on multi-field synergy and gradient ultrasound, the temperature of the thermal field is 60-75℃, the rotation speed of the mechanical stirring field is 300-1000 rpm, and the stirring time is 20-60 min.

[0038] As described above, the mild heat treatment can reduce the viscosity of the polysaccharide solution, improve the molecular thermal mobility, and provide an energy basis for intermolecular interactions; appropriate mechanical stirring achieves macroscopically uniform mixing, preventing local overheating or uneven concentration. The synergistic effect of both creates favorable initial conditions for subsequent molecular-level cross-linking and coordination, ensuring the homogeneity and controllability of the reaction system.

[0039] Furthermore, in the above-mentioned method for preparing antioxidant and antibacterial food packaging materials based on multi-field synergy and gradient ultrasound, the polysaccharide in the polysaccharide solution is selected from at least one of carrageenan, agarose, sodium alginate, chitosan, and bacterial nanocellulose; based on the total volume of the polysaccharide solution, the mass-volume concentration of the polysaccharide is 60-100 g / L.

[0040] As described above, a concentration range of 60-100 g / L is the preferred range to ensure the formation of a continuous network framework with a certain mechanical strength, while avoiding excessive viscosity that would affect subsequent mixing and reaction, thus providing the material with good film-forming properties and structural support.

[0041] Furthermore, in the above-mentioned method for preparing antioxidant and antibacterial food packaging materials based on multi-field synergy and gradient ultrasound, the polyphenols in the polyphenol solution are selected from at least one of epigallocatechin gallate, tannic acid, gallic acid, and proanthocyanidins; based on the total volume of the polyphenol solution, the mass-volume concentration of the polyphenols is 30-50 g / L.

[0042] As described above, a concentration range of 30-50 g / L ensures that there are enough active sites to coordinate with metal ions, forming an effective metal-polyphenol network, while avoiding self-aggregation caused by excessive concentration, thereby maximizing its functional activity.

[0043] Furthermore, in the above-mentioned method for preparing antioxidant and antibacterial food packaging materials based on multi-field synergy and gradient ultrasound, the metal ions in the metal salt solution are Zn²⁺. + Fe³ + Ag + At least one of the following; the mass-volume concentration of the metal ion is 50-70 mg / L, based on the total volume of the metal salt solution.

[0044] As described above, the aforementioned ions possess broad-spectrum antibacterial activity. By coordinating with polyphenols, they stabilize the polyphenol molecular structure and slow down its oxidative deactivation. On the other hand, they fix the metal ions in the material network, achieving a long-lasting and safe antibacterial effect and avoiding the food safety risks caused by their rapid migration. The concentration range of 50-70 mg / L is a key parameter for achieving effective coordination and cross-linking while ensuring the biosafety of the material.

[0045] Furthermore, in the above-mentioned method for preparing antioxidant and antibacterial food packaging materials based on multi-field synergy and gradient ultrasound, the volume ratio of the polysaccharide solution, polyphenol solution and metal salt solution is (70-100):100:(1-30).

[0046] As described above, the above ratio ensures that, on the basis of the polysaccharide forming a continuous backbone, there is a sufficient amount of polyphenols to interact with and form a preliminary network, and that the metal ions can fully coordinate with the polyphenols to form stable metal-polyphenol complexes, without destroying the polysaccharide network or producing cytotoxicity due to excessive amounts.

[0047] Furthermore, in the above-mentioned method for preparing antioxidant and antibacterial food packaging materials based on multi-field synergy and gradient ultrasound, the gelation molding step includes: pouring the ultrasonically treated blend system into a mold and letting it stand at 4-30℃ for 2-24 h to gel and form a hydrogel.

[0048] As described above, the gelation molding conditions are limited to standing at 4-30℃ for 2-24 hours after casting. This mild standing condition provides sufficient time for the various interactions within the ultrasonically treated system (such as hydrogen bonds, coordination bonds, and van der Waals forces) to fully rearrange and optimize. Through this process, the system ultimately forms a more thermodynamically stable and structurally more complete network structure, eliminating internal stress and ensuring the material's mechanical properties, stability, and functional durability.

[0049] Another technical solution provided by the present invention is: to provide an antioxidant and antibacterial food packaging material based on multi-field synergy and gradient ultrasound prepared by the above-mentioned method for preparing antioxidant and antibacterial food packaging material based on multi-field synergy and gradient ultrasound.

[0050] Example 1

[0051] A method for preparing an antioxidant and antibacterial food packaging material based on multi-field synergy and gradient ultrasound includes the following steps:

[0052] S1: Under the synergistic effect of heating and stirring, carrageenan, epigallocatechin gallate (EGCG), and zinc chloride solutions (containing the mass-volume concentration of metal ions) were prepared, with concentrations of 70 (g / L), 40 (g / L), and 60 (mg / L), respectively.

[0053] S2: Add 10 mL of EGCG solution to 7 mL of carrageenan solution at a rate of 0.5 mL / min under the combined action of a thermal field and a mechanical stirring field. Maintain the temperature at 70℃, rotate the stirring wheel at 500 rpm, and continue stirring for 30 min to allow cross-linking to occur between EGCG and carrageenan molecules.

[0054] S3: Add 3 mL of zinc chloride solution to the mixed solution in S2 at a rate of 0.1 mL / min under the combined action of a thermal field and a mechanical stirring field. Maintain the temperature at 70℃, the stirring speed at 500 rpm and continue stirring for 30 min to allow cross-linking to occur between zinc ions, EGCG and carrageenan molecules.

[0055] S4: Under the action of an ultrasonic energy field, the solution obtained in step S3 is subjected to gradient power ultrasonic treatment. The specific parameters are set as follows: power 300 W, treatment for 5 minutes; then the power is increased to 500 W, treatment for 10 minutes; finally the power is adjusted to 700 W, treatment for 20 minutes, in order to eliminate bubbles in the system and promote cross-linking between composite hydrogel molecules.

[0056] S5: The bubble-free blend system treated in step S4 is poured into a film-forming mold and left to stand at 25°C for 2 hours to produce food packaging materials with antioxidant and antibacterial properties.

[0057] Example 2

[0058] A method for preparing an antioxidant and antibacterial food packaging material based on multi-field synergy and gradient ultrasound includes the following steps:

[0059] S1: Under the synergistic effect of heating and stirring, carrageenan, epigallocatechin gallate (EGCG), and zinc chloride solutions (containing metal ions at mass-volume concentrations) were prepared, with concentrations of 60 (g / L), 40 (g / L), and 50 (mg / L), respectively.

[0060] S2: 10 mL of EGCG solution was added to 7 mL of carrageenan solution at a rate of 0.5 mL / min under the combined action of a thermal field and a mechanical stirring field. The temperature was maintained at 60℃, the stirring speed was 300 rpm, and the mixture was stirred continuously for 60 min to allow cross-linking to occur between EGCG and carrageenan molecules.

[0061] S3: Add 3 mL of zinc chloride solution to the mixed solution in S2 at a rate of 0.1 mL / min under the combined action of a thermal field and a mechanical stirring field. Maintain the temperature at 60℃, the stirring speed at 300 rpm and continue stirring for 60 min to allow cross-linking to occur between zinc ions, EGCG and carrageenan molecules.

[0062] S4: Under the action of an ultrasonic energy field, the solution obtained in step S3 is subjected to gradient power ultrasonic treatment. The specific parameters are set as follows: power 100 W, treatment for 5 minutes; then the power is increased to 300 W, treatment for 10 minutes; finally the power is adjusted to 500 W, treatment for 20 minutes, in order to eliminate bubbles in the system and promote cross-linking between composite hydrogel molecules.

[0063] S5: The bubble-free blend system treated in step S4 is poured into a film-forming mold and left to stand at 4°C for 24 hours to produce food packaging materials with antioxidant and antibacterial properties.

[0064] Example 3

[0065] A method for preparing an antioxidant and antibacterial food packaging material based on multi-field synergy and gradient ultrasound includes the following steps:

[0066] S1: Under the combined effect of heating and stirring, solutions of carrageenan, proanthocyanidins, and zinc chloride (containing metal ions at mass-volume concentrations) were prepared, with concentrations of 100 (g / L), 50 (g / L), and 70 (mg / L), respectively.

[0067] S2: 10 mL of proanthocyanidin solution was added to 7 mL of carrageenan solution at a rate of 0.5 mL / min under the combined action of a thermal field and a mechanical stirring field. The temperature was maintained at 60℃, the stirring speed was 300 rpm, and the mixture was stirred continuously for 20 min to allow cross-linking to occur between proanthocyanidin and carrageenan molecules.

[0068] S3: Add 3 mL of zinc chloride solution to the mixed solution in S2 at a rate of 0.1 mL / min under the combined action of a thermal field and a mechanical stirring field. Maintain the temperature at 60℃, the stirring speed at 300 rpm and continue stirring for 20 min to allow cross-linking to occur between zinc ions, proanthocyanidins and carrageenan molecules.

[0069] S4: Under the action of an ultrasonic energy field, the solution obtained in step S3 is subjected to gradient power ultrasonic treatment. The specific parameters are set as follows: power 200 W, treatment for 10 minutes; then the power is increased to 400 W, treatment for 20 minutes; finally the power is adjusted to 600 W, treatment for 30 minutes, in order to eliminate bubbles in the system and promote cross-linking between composite hydrogel molecules.

[0070] S5: The bubble-free blend system treated in step S4 is poured into a film-forming mold and left to stand at 30°C for 12 hours to produce food packaging materials with antioxidant and antibacterial properties.

[0071] Comparative Example 1

[0072] A method for preparing a food packaging material includes the following steps:

[0073] The rest is the same as in Example 1, except that no metal ions are added to the raw materials.

[0074] S1: Carrageenan and EGCG solutions were prepared under the synergistic effect of heating and stirring, with concentrations of 70 (g / L) and 40 (g / L), respectively.

[0075] S2: Add 10 mL of EGCG solution to 10 mL of carrageenan solution at a rate of 0.5 mL / min under the combined action of a thermal field and a mechanical stirring field. Maintain the temperature at 70℃, the stirring speed at 500 rpm and continue stirring for 30 min to allow cross-linking to occur between EGCG and carrageenan molecules.

[0076] S3: Under the action of an ultrasonic energy field, the solution obtained in step S2 is subjected to gradient power ultrasonic treatment. The specific parameters are set as follows: power 300 W, treatment for 5 minutes; then the power is increased to 500 W, treatment for 10 minutes; finally the power is adjusted to 700 W, treatment for 20 minutes, in order to eliminate bubbles in the system and promote cross-linking between composite hydrogel molecules.

[0077] S4: The bubble-free blend system treated in step S3 is poured into a film-forming mold and left to stand at 25°C for 2 hours to produce food packaging materials with antioxidant and antibacterial properties.

[0078] Comparative Example 2

[0079] A method for preparing a food packaging material includes the following steps:

[0080] The rest is the same as in Example 1, except that no advanced ultrasonic treatment is performed.

[0081] S1: Under the combined effect of heating and stirring, solutions of carrageenan, EGCG, and zinc chloride (containing the mass-volume concentration of metal ions) were prepared, with concentrations of 70 (g / L), 40 (g / L), and 60 (mg / L), respectively.

[0082] S2: Add 10 mL of EGCG solution to 7 mL of carrageenan solution at a rate of 0.5 mL / min under the combined action of a thermal field and a mechanical stirring field. Maintain the temperature at 70℃, rotate the stirring wheel at 500 rpm, and continue stirring for 30 min to allow cross-linking to occur between EGCG and carrageenan molecules.

[0083] S3: Add 3 mL of zinc chloride solution to the mixed solution in S2 at a rate of 0.1 mL / min under the combined action of a thermal field and a mechanical stirring field. Maintain the temperature at 70℃, the stirring speed at 500 rpm and continue stirring for 30 min to allow cross-linking to occur between zinc ions, EGCG and carrageenan molecules.

[0084] S4: Under the action of an ultrasonic energy field, the solution obtained in step S3 is subjected to ultrasonic treatment with a power of 700W for 35 minutes to eliminate bubbles in the system and promote cross-linking between composite hydrogel molecules.

[0085] S5: The bubble-free blend system treated in step S4 is poured into a film-forming mold and left to stand at 25°C for 2 hours to produce food packaging materials with antioxidant and antibacterial properties.

[0086] Comparative Example 3

[0087] A method for preparing a food packaging material includes the following steps:

[0088] The rest is the same as in Example 1, except that ultrasonic treatment is not performed.

[0089] S1: Under the combined effect of heating and stirring, solutions of carrageenan, EGCG, and zinc chloride (containing the mass-volume concentration of metal ions) were prepared, with concentrations of 70 (g / L), 40 (g / L), and 60 (mg / L), respectively.

[0090] S2: 10 mL of EGCG solution was added to 7 mL of carrageenan solution at a rate of 0.5 mL / min under the combined action of a thermal field and a mechanical stirring field. The temperature was maintained at 70℃, the stirring speed was 500 rpm, and the mixture was stirred continuously for 30 min to allow cross-linking to occur between EGCG and carrageenan molecules.

[0091] S3: Add 3 mL of zinc chloride solution to the mixed solution in S2 at a rate of 0.1 mL / min under the combined action of a thermal field and a mechanical stirring field. Maintain the temperature at 70℃, the stirring speed at 500 rpm and continue stirring for 30 min to allow cross-linking to occur between zinc ions, EGCG and carrageenan molecules.

[0092] S4: The bubble-free blend system treated in step S3 is poured into a film-forming mold and left to stand at 25°C for 2 hours to produce food packaging materials with antioxidant and antibacterial properties.

[0093] Comparative Example 4

[0094] A method for preparing a food packaging material includes the following steps:

[0095] The rest is the same as in Example 1, except that the crosslinking process is not precisely controlled.

[0096] S1: Under the combined effect of heating and stirring, solutions of carrageenan, EGCG, and zinc chloride (containing the mass-volume concentration of metal ions) were prepared, with concentrations of 70 (g / L), 40 (g / L), and 60 (mg / L), respectively.

[0097] S2: Add 10 mL of EGCG solution to 7 mL of carrageenan solution, maintain the temperature at 70℃, and stir continuously at 500 rpm for 30 min to allow cross-linking to occur between EGCG and carrageenan molecules.

[0098] S3: Add 3 mL of zinc chloride solution to the mixed solution in S2, maintain the temperature at 70°C, and stir continuously at 500 rpm for 30 min to allow cross-linking to occur between zinc ions, EGCG and carrageenan molecules.

[0099] S4: Under the action of an ultrasonic energy field, the solution obtained in step S3 is subjected to gradient power ultrasonic treatment. The specific parameters are set as follows: power 300 W, treatment for 5 minutes; then the power is increased to 500 W, treatment for 10 minutes; finally the power is adjusted to 700 W, treatment for 20 minutes, in order to eliminate bubbles in the system and promote cross-linking between composite hydrogel molecules.

[0100] S5: The bubble-free blend system treated in step S3 is poured into a film-forming mold and left to stand at 25°C for 2 hours to produce food packaging materials with antioxidant and antibacterial properties.

[0101] Performance Testing and Effect Analysis

[0102] The performance of the food packaging materials (samples) prepared in Example 1 and Comparative Examples 1-4 was tested, and the results are as follows:

[0103] 1. Antibacterial performance test

[0104] The antibacterial activity of each sample against Staphylococcus aureus (Gram-positive bacteria) and Escherichia coli (Gram-negative bacteria) was determined using the oscillation contact method and the filter paper diffusion method. Figure 1 and Figure 2 It is the oscillating contact method. Figure 3 It is the filter paper diffusion method, and the results are as follows: Figure 1 , Figure 2 and Figure 3 As shown.

[0105] Example 1: The highest inhibition rate was observed against both test bacteria. Figure 1 , Figure 2 ), and the inhibition zone is clear, the largest ( Figure 3 This indicates that it possesses the strongest broad-spectrum antibacterial activity. This is attributed to the metal ion (Zn²⁺). + The synergistic antibacterial effect of EGCG, and the uniform and stable metal-polyphenol network resulting from gradient ultrasound and precise addition.

[0106] Comparative Example 1 (without metal ions): The antibacterial rate was significantly lower than that of Example 1 ( Figure 1 , Figure 2This indicates that the introduction of metal ions is crucial to enhancing the antibacterial properties of the material. The antibacterial ability of a standalone polyphenol-polysaccharide network is limited.

[0107] Comparative Example 2 (non-gradient ultrasound): The antibacterial rate was less than that of Example 1, indicating that fixed power ultrasound cannot achieve the multiple effects brought about by gradient ultrasound (such as efficient defoaming, uniform cross-linking, and sufficient coordination), resulting in defects in the material structure and uneven distribution of active ingredients, thus affecting the antibacterial performance.

[0108] Comparative Example 3 (without ultrasound): The antibacterial rate was lower than that of Example 1, and the material itself may contain visible air bubbles. This indicates that the absence of ultrasound treatment cannot effectively eliminate air bubbles and promote cross-linking, resulting in a loose material structure, extensive oxidation and deactivation of polyphenols, and ineffective coordination of metal ions.

[0109] Comparative Example 4 (without precise control): The antibacterial rate was less than that of Example 1, which indicates that rapid addition led to an excessively fast local reaction, resulting in the formation of uneven aggregates, failing to form a uniform and effective metal-polyphenol network, and some polyphenols may have been destroyed due to the intense local reaction.

[0110] 2. Antioxidant performance test

[0111] The antioxidant activity of each sample was determined using the DPPH free radical scavenging method, and the results are as follows: Figure 4 As shown.

[0112] Example 1 showed the highest DPPH radical scavenging rate, which was attributed to the protection of polyphenol activity by gradient ultrasound, while metal coordination further stabilized the polyphenol structure and slowed down its oxidation.

[0113] Comparative Example 1 (without metal ions): lowest scavenging rate. This indicates that without the coordination protection of metal ions, polyphenols are more easily oxidized and have poor antioxidant durability.

[0114] Comparative Example 2 (non-gradient ultrasound): The clearance rate was lower than that of Example 1, indicating that fixed-power ultrasound failed to optimally protect the activity of polyphenols.

[0115] Comparative Example 3 (without ultrasound): The clearance rate was lower than that of Example 1, and a large amount of polyphenols had been oxidized and deactivated during the preparation process.

[0116] Comparative Example 4 (without precise control): The clearance rate was lower than that of Example 1, indicating that the uneven crosslinking and aggregates could not effectively protect the polyphenols, and some polyphenols were deactivated in the localized violent reaction.

[0117] In summary, this invention successfully prepared a uniform, bubble-free, and network-stable metal-polyphenol-polysaccharide hydrogel through the synergistic effects of multiple fields (thermal field, stirring field, and ultrasonic energy field), gradient ultrasound, and precise control of the addition via a peristaltic pump. Compared with the comparative examples, the material of this invention (Example 1) achieved significantly better antibacterial and antioxidant properties than existing technologies. In particular, Comparative Example 1 demonstrated the indispensability of metal ions, Comparative Examples 2 and 3 demonstrated the unique advantages of the gradient ultrasound process, and Comparative Example 4 demonstrated the importance of precisely controlling the crosslinking process.

[0118] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing an antioxidant and antibacterial food packaging material based on multi-field synergy and gradient ultrasound, characterized in that, Includes the following steps: Under the combined effect of a thermal field and a mechanical stirring field, a polyphenol solution is added to a polysaccharide solution at a flow rate of 0.1-0.5 mL / min using a peristaltic pump to obtain a polyphenol-polysaccharide blend. Under the combined effect of a thermal field and a mechanical stirring field, a metal salt solution was added to the polyphenol-polysaccharide blend at a flow rate of 0.1-0.5 mL / min using a peristaltic pump to obtain a metal-polyphenol-polysaccharide blend system. The metal-polyphenol-polysaccharide blend system is subjected to gradient power ultrasonic treatment, which includes at least two ultrasonic stages with progressively increasing power. The ultrasonically treated blend system was gelled to obtain the food packaging material. The gradient power ultrasound processing includes: In the first ultrasonic stage, the ultrasonic power is 100-300 W and the processing time is 5-10 min; In the second ultrasonic stage, the ultrasonic power is 300-500 W and the processing time is 10-20 min; The third ultrasonic stage involves an ultrasonic power of 500-700 W and a processing time of 20-30 min. The metal ions in the metal salt solution are Zn. 2+ Fe 3+ Ag + At least one of them.

2. The method for preparing antioxidant and antibacterial food packaging materials based on multi-field synergy and gradient ultrasound according to claim 1, characterized in that, The temperature of the thermal field is 60-75℃, the rotation speed of the mechanical stirring field is 300-1000 rpm, and the stirring time is 20-60 min.

3. The method for preparing antioxidant and antibacterial food packaging materials based on multi-field synergy and gradient ultrasound according to claim 1, characterized in that, The polysaccharide in the polysaccharide solution is selected from at least one of carrageenan, agarose, sodium alginate, chitosan, and bacterial nanocellulose; the mass-volume concentration of the polysaccharide is 60-100 g / L based on the total volume of the polysaccharide solution.

4. The method for preparing antioxidant and antibacterial food packaging materials based on multi-field synergy and gradient ultrasound according to claim 1, characterized in that, The polyphenols in the polyphenol solution are selected from at least one of epigallocatechin gallate, tannic acid, gallic acid, and proanthocyanidins; the mass-volume concentration of the polyphenols is 30-50 g / L based on the total volume of the polyphenol solution.

5. The method for preparing antioxidant and antibacterial food packaging materials based on multi-field synergy and gradient ultrasound according to claim 1, characterized in that, Based on the total volume of the metal salt solution, the mass-volume concentration of the metal ions is 50-70 mg / L.

6. The method for preparing antioxidant and antibacterial food packaging materials based on multi-field synergy and gradient ultrasound according to claim 1, characterized in that, The volume ratio of the polysaccharide solution, polyphenol solution and metal salt solution is (70-100):100:(1-30).

7. The method for preparing antioxidant and antibacterial food packaging materials based on multi-field synergy and gradient ultrasound according to claim 1, characterized in that, The gelation molding step includes: pouring the ultrasonically treated blend into a mold and letting it stand at 4-30℃ for 2-24 hours to gel and form a hydrogel.

8. An antioxidant and antibacterial food packaging material based on multi-field synergy and gradient ultrasound, characterized in that, It is prepared by any one of claims 1-7.

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