Preservative film as well as preparation method and application thereof

Abstract

The invention provides a preservative film as well as a preparation method and application thereof. Comprising a colloidal film and a protein film compounded with the colloidal film, the colloidal film comprises a colloidal matrix and an active substance loaded on the colloidal matrix, and the active substance comprises a compound of cinnamyl aldehyde and tannic acid. According to the preservative film provided by the invention, the antibacterial function and the antioxidant function are integrated into the same film material by constructing an asymmetric compound system of a colloidal film and a protein film. The colloidal film loaded with the cinnamyl aldehyde and tannic acid compound can directly play a fresh-keeping role; the protein film forms a barrier to the outside. According to the structure, space coupling of physical barrier and biological activity is achieved in design, and a core foundation is laid for directional release and function synergy of active ingredients.

Description

Technical Field

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

[0002] With the continued growth in global demand for fresh food and increasing consumer focus on food safety, nutritional quality, and shelf life, food packaging technology is rapidly developing towards functionalization, intelligence, and green practices. Traditional inert packaging materials (such as polyethylene and polypropylene) primarily provide physical isolation and protection, but are insufficient to proactively address spoilage issues caused by microbial growth, enzymatic reactions, and oxidative deterioration during storage, transportation, and sales. Therefore, active packaging and smart packaging have emerged, integrating functional components such as antibacterial agents, antioxidants, and humidity regulators to endow packaging materials with the ability to actively maintain or improve the quality of their contents. This has become a significant development trend in the food packaging industry.

[0003] While current research has developed various antibacterial / antioxidant packaging materials, significant limitations remain. On one hand, the problem of functional singularity is prominent: common antibacterial or antioxidant films are often designed only for a specific spoilage factor, making it difficult to synergistically address the multiple challenges of microbial contamination and oxidative rancidity commonly present in food spoilage. On the other hand, the uncontrollable and non-directional release of active ingredients constitutes a technological bottleneck. Most active packaging uses a symmetrical film structure, resulting in the indiscriminate release of functional ingredients (such as tea polyphenols, silver ions, and carvacrol) on both sides of the film. This not only reduces the effective release concentration and shortens the duration of action on the food contact surface, leading to ineffective loss of active ingredients and increased costs, but also raises potential ecological safety concerns due to uncontrolled release into the environment from the non-contact side. Furthermore, some active ingredients (such as volatile antibacterial agents) are easily lost during processing and storage, affecting the long-term stability and functional reliability of the product.

[0004] Therefore, how to construct an asymmetric structure that can release functional ingredients in a targeted manner during the preparation and application of active packaging films, so as to synergistically exert antibacterial and antioxidant effects, effectively solve the problems of loss, low efficiency and potential environmental release caused by the bidirectional release of active ingredients in traditional symmetric films, and further improve the stability of active ingredients in processing and storage, is a technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0005] This invention provides a food preservation film, its preparation method, and its application. This film integrates antibacterial and antioxidant functions into a single membrane material by constructing an asymmetric composite system of a colloidal membrane and a protein membrane. The colloidal membrane loaded with a cinnamaldehyde and tannic acid complex can directly exert its preservation effect; the protein membrane forms an external barrier. This structure achieves spatial coupling between physical barrier and biological activity through design, laying a core foundation for the targeted release and functional synergy of active ingredients.

[0006] The present invention provides a food preservation film, comprising a colloidal film and a protein film composited with the colloidal film; the colloidal film comprises a colloidal matrix and an active substance loaded on the colloidal matrix, the active substance comprising a complex of cinnamaldehyde and tannic acid.

[0007] According to one embodiment of the present invention, the complex of cinnamaldehyde and tannic acid is prepared by a process including the following steps: stirring a mixture containing cinnamaldehyde, tannic acid and a first solvent at room temperature for 20 min to 30 min, and then sonicating it at 0℃ to 4℃ for 20 min to 40 min to obtain the complex of cinnamaldehyde and tannic acid.

[0008] According to one embodiment of the present invention, the mass ratio of cinnamaldehyde to tannic acid is (3~6):1.

[0009] According to one embodiment of the present invention, the first solvent includes water.

[0010] According to one embodiment of the present invention, the mass ratio of the gel matrix to the active substance is (100~200):1.

[0011] According to one embodiment of the present invention, the adhesive matrix comprises gelatin.

[0012] According to one embodiment of the present invention, the thickness of the colloidal membrane is 290 μm to 300 μm.

[0013] According to one embodiment of the present invention, the protein membrane comprises zein.

[0014] According to one embodiment of the present invention, the thickness of the protein membrane is 25 μm to 30 μm.

[0015] In another aspect, the present invention provides a method for preparing a food preservation film, comprising the following steps: performing a film-forming treatment on a first film-forming liquid for forming the protein film to form the protein film; applying a second film-forming liquid to the surface of the protein film to form the colloidal film, thereby obtaining the food preservation film; wherein the second film-forming liquid comprises the colloidal matrix and the active substance.

[0016] According to one embodiment of the present invention, the first film-forming solution further includes glycerol and a protein raw material for forming the protein film, wherein the mass of the glycerol accounts for 10% to 15% of the mass of the protein raw material.

[0017] According to one embodiment of the present invention, the preparation process of the first film-forming solution includes: mixing a protein raw material for forming the protein film with a second solvent to obtain a first solution, wherein the second solvent includes an ethanol solvent; adding glycerol to the first solution and mixing evenly to obtain the first film-forming solution.

[0018] According to one embodiment of the present invention, the process of performing film-forming treatment on the first film-forming liquid for forming the protein film includes: casting the first film-forming liquid into a film, and after a first drying, forming the protein film.

[0019] According to one embodiment of the present invention, the second film-forming liquid further includes sodium alginate, wherein the mass of sodium alginate accounts for 3% to 5% of the mass of the colloidal matrix.

[0020] According to one embodiment of the present invention, the second film-forming liquid further includes glycerol, wherein the mass of the glycerol accounts for 10% to 15% of the mass of the gel matrix.

[0021] According to one embodiment of the present invention, the second film-forming liquid further includes a third solvent, wherein the third solvent includes water.

[0022] According to one embodiment of the present invention, the preparation process of the second film-forming solution includes: dissolving sodium alginate and glycerol in a second solution containing the colloidal matrix at a temperature of 55°C to 60°C to obtain a third solution; controlling the temperature of the third solution to 40°C to 45°C, and then adding the active substance thereto and mixing evenly to obtain the second film-forming solution.

[0023] According to one embodiment of the present invention, a second film-forming liquid is applied to the surface of the protein membrane by casting, and after a second drying, the colloidal membrane is formed.

[0024] In another aspect, the present invention provides the application of the aforementioned preservation film or the preservation film prepared according to the aforementioned method in the preservation of fruits and vegetables.

[0025] The implementation of this invention has at least the following beneficial effects: The preservation film provided by this invention, by constructing an asymmetric colloidal membrane-protein membrane bilayer system, helps to achieve precise spatial separation and synergy of functions. The protein membrane, with its highly hydrophobic properties, effectively blocks the intrusion of environmental moisture and prevents food moisture loss, maintaining stable humidity. The colloidal membrane, with its hydrophilic properties, adheres tightly to the food surface, serving as a highly efficient carrier for the cinnamaldehyde and tannic acid complex. Tannic acid delays oxidative spoilage by scavenging free radicals and inhibiting enzyme activity; cinnamaldehyde inhibits the proliferation of microorganisms by disrupting their cell structure. The synergistic effect of these two components in the colloidal membrane allows for simultaneous intervention in the chemical and biological pathways of food spoilage. This design, through precise multi-target intervention of spoilage factors, provides an innovative solution for long-term preservation of fresh food. Attached Figure Description

[0026] Figure 1 The images show the antibacterial zone effect of the plastic wrap in Example 1 and the comparative example. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. The specific embodiments listed below are merely descriptions of the principles and features of this invention, and the examples given are only for explaining this invention and are not intended to limit the scope of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0028] This invention provides a food preservation film, including a colloidal film and a protein film composited with the colloidal film; the colloidal film includes a colloidal matrix and an active substance loaded on the colloidal matrix, the active substance including a complex of cinnamaldehyde and tannic acid.

[0029] According to the inventors' research, the aforementioned food preservation film achieves precise spatial separation and efficient integration of physical barrier functions and biochemical activity functions by constructing an asymmetric composite system of colloidal and protein membranes (asymmetric Janus membrane structure). The protein membrane possesses low surface energy and high hydrophobicity, which helps prevent water vapor from the environment from penetrating into the membrane, while also preventing excessive moisture loss from the food interior and maintaining a stable humidity microenvironment. The colloidal membrane has high surface energy and strong hydrophilicity, allowing it to adhere tightly to the surface of water-containing foods, forming good interfacial contact; simultaneously, its colloidal matrix provides an efficient and stable functional carrier for the complex of cinnamaldehyde and tannic acid. Tannic acid primarily functions to scavenge free radicals, block lipid oxidation chain reactions, and inhibit polyphenol oxidase activity, thereby delaying chemical oxidation and enzymatic browning of food; while cinnamaldehyde inhibits spoilage bacteria and fungi by disrupting the cell membrane structure of microorganisms and interfering with their energy metabolism and genetic material synthesis. Both coexist within the matrix of the colloidal membrane, enabling a combined intervention on the main biological and chemical pathways of food spoilage (microbial proliferation and oxidative deterioration), resulting in complementary or even enhanced preservation effects. Therefore, this preservation film, through its asymmetric structural design and synergistic configuration of the active complex, achieves multi-target intervention against food spoilage factors, providing an innovative solution for the precise and long-lasting preservation of fresh food.

[0030] In some embodiments, the cinnamaldehyde-tannic acid complex is prepared by a process including the following steps: stirring a mixture containing cinnamaldehyde, tannic acid, and a first solvent at room temperature for 20-30 minutes, followed by ultrasonic treatment at 0-4°C (i.e., ice bath conditions) for 20-40 minutes to obtain the cinnamaldehyde-tannic acid complex. By controlling the conditions of the above preparation process within the aforementioned range, cinnamaldehyde and tannic acid are covalently bonded, which helps to form a stable and uniform cinnamaldehyde-tannic acid complex, facilitating uniform dispersion during subsequent film formation and maintaining biological activity.

[0031] Specifically, the room temperature mentioned above can be 25℃~30℃, for example, 25℃, 26℃, 27℃, 28℃, 29℃, 30℃ or any combination thereof.

[0032] For example, the stirring time of the mixture of the first solvent at room temperature can be a range of 20 min, 22 min, 24 min, 26 min, 28 min, 30 min, or any two of these; the temperature conditions of the ultrasonic treatment can be a range of 0°C, 1°C, 2°C, 3°C, 4°C, or any two of these; and the time of the ultrasonic treatment can be a range of 20 min, 25 min, 30 min, 35 min, 40 min, or any two of these.

[0033] In some embodiments, the mass ratio of cinnamaldehyde to tannic acid can be (3~6):1, for example, a range of 3:1, 4:1, 4.5:1, 5:1, 6:1, or any combination thereof. A mass ratio of not less than 3:1 helps to provide sufficient antibacterial components to ensure the inhibitory effect on microorganisms; a mass ratio of not more than 6:1 provides sufficient tannic acid to achieve synergistic stabilization and antioxidant functions; controlling the mass ratio within the above range is beneficial to balancing the three core properties of antibacterial, antioxidant, and stability, making the complex more functional.

[0034] In some embodiments, the first solvent includes water. Water helps improve the solubility and dispersibility of tannic acid, promoting its full reaction with cinnamaldehyde; water as a solvent can reduce the irritation and cost of the system, improving product safety and economy; it is compatible with aqueous systems commonly used in subsequent colloidal membrane preparation, helping to simplify the process and improve production efficiency.

[0035] Specifically, before mixing cinnamaldehyde with tannic acid and the first solvent, cinnamaldehyde needs to be dissolved in a fourth solvent to obtain a cinnamaldehyde solution; the fourth solvent includes ethanol. Ethanol helps improve the initial dispersion of cinnamaldehyde in the aqueous phase, allowing it to enter the aqueous phase in the form of fine droplets. This creates favorable conditions for the subsequent rapid adsorption and coating of tannic acid molecules at the oil-water interface.

[0036] In some embodiments, the mass ratio of the colloidal matrix to the active substance can be (100~200):1, for example, 100:1, 120:1, 140:1, 160:1, 180:1, 200:1, or any combination thereof. A mass ratio of not less than 100:1 helps the colloidal matrix to have sufficient load-bearing capacity and film-forming strength, reducing the risk of the film being fragile and easily broken; a mass ratio of not more than 200:1 helps to ensure sufficient content of active substances and improve the preservation effect; controlling the mass ratio within the above range is beneficial to balancing the mechanical properties and preservation function of the colloidal film, making the preservation film both durable and effective.

[0037] In practice, cinnamaldehyde is dissolved in a fourth solvent at room temperature to obtain a cinnamaldehyde solution; tannic acid is dissolved in a first solvent to obtain a tannic acid solution; the cinnamaldehyde solution and the tannic acid solution are mixed and magnetically stirred for 20 to 30 minutes, and then ultrasonically defoamed at 0 to 4°C (i.e., ice bath conditions) for 20 to 40 minutes to obtain a complex of cinnamaldehyde and tannic acid.

[0038] In some embodiments, the aforementioned adhesive matrix includes gelatin. Gelatin helps form a flexible, crack-resistant colloidal film, improving the actual performance of the cling film; gelatin's loading and controlled release of active substances can make the preservation effect last longer; gelatin is a natural biodegradable material, which helps reduce the environmental impact of cling film after use, aligning with the trend of green environmental protection.

[0039] In some embodiments, the thickness of the colloidal film can be 290 μm to 300 μm, for example, 290 μm, 292 μm, 294 μm, 296 μm, 298 μm, 300 μm, or any combination thereof. A thickness of not less than 290 μm helps to provide sufficient loading of active substances, extend the shelf life, and improve the tear resistance of the film layer; a thickness of not more than 300 μm helps to reduce the resistance to the release of active substances, promote the rapid formation of an antibacterial environment on the surface of fruits and vegetables, and is less likely to excessively hinder the normal respiration of fruits and vegetables; controlling the thickness within the above range is beneficial to achieving a better balance between preservation effect, performance and adaptability to fruits and vegetables.

[0040] In some embodiments, the protein membrane includes zein. Zein is a hydrophobic protein containing a large number of hydrophobic amino acid residues. After forming a membrane, it can create a dense hydrophobic structure, which helps to block the intrusion of external water vapor and oxygen, reducing water loss and oxidative spoilage of fruits and vegetables. The disulfide bonds between its molecular chains can enhance the mechanical strength of the membrane and improve its stability. Zein has good film-forming properties and can form a stable composite interface with colloidal membranes.

[0041] In some embodiments, the thickness of the protein film can be 25 μm to 30 μm, for example, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, or any combination thereof. A thickness of not less than 25 μm helps to form a denser barrier structure, better blocking external moisture and microorganisms, and improving the preservation effect; a thickness of not more than 30 μm helps to ensure that the film layer has a certain degree of flexibility, better conforming to the surface contours of fruits and vegetables, while reducing material usage and production costs; controlling the thickness within the above range is conducive to achieving a balance between barrier performance and ease of use, and improving the overall quality of the composite preservation film.

[0042] The preservation film provided by this invention achieves precise spatial separation and synergy of functions through the construction of an asymmetric colloidal membrane-protein membrane bilayer system. The protein membrane, with its highly hydrophobic properties, helps to block the intrusion of environmental moisture and prevent food moisture loss, maintaining stable humidity. The colloidal membrane, with its hydrophilic properties, adheres tightly to the food surface, serving as a highly efficient carrier for the cinnamaldehyde and tannic acid complex. Tannic acid delays oxidative spoilage by scavenging free radicals and inhibiting enzyme activity; cinnamaldehyde inhibits microbial cell proliferation by disrupting microbial cell structure. The synergistic effect of these two components within the colloidal membrane allows for simultaneous intervention in both the chemical and biological pathways of food spoilage. This design provides an innovative long-term preservation solution for fresh food through precise multi-target intervention of spoilage factors.

[0043] This invention also provides a method for preparing the above-mentioned food preservation film, comprising the following steps: performing a film-forming treatment on a first film-forming liquid used to form the above-mentioned protein film to form the above-mentioned protein film; applying a second film-forming liquid to the surface of the above-mentioned protein film to form the above-mentioned colloidal film, thereby obtaining the above-mentioned food preservation film; wherein the second film-forming liquid comprises the above-mentioned colloidal matrix and the above-mentioned active substance.

[0044] According to the inventors' research, the above preparation method first prepares a protein membrane as a substrate, utilizing its good film-forming stability to provide support for the subsequent coating of the colloidal membrane. The initial formation of the protein membrane helps maintain its dense structure and avoids swelling or interfacial mixing when the second film-forming liquid is applied later. Applying the second film-forming liquid containing the colloidal matrix and active substances to the surface of the formed protein membrane helps to achieve tight bonding of the bilayer membrane, improves the bonding strength between the membrane layers, and reduces the risk of delamination during use.

[0045] In some embodiments, the first film-forming solution further includes glycerol and a protein raw material for forming the protein membrane; the mass ratio of glycerol to the mass ratio of the protein raw material can be 10% to 15%, for example, 10%, 11%, 12%, 13%, 14%, 15%, or any combination thereof. The addition of glycerol can significantly improve the flexibility and tear resistance of the protein membrane, reducing the risk of membrane breakage during use; controlling the glycerol ratio within the above range helps maintain the hydrophobic barrier properties of the protein membrane and prevents the membrane structure from becoming loose due to plasticizing effects.

[0046] In some embodiments, the preparation process of the first film-forming solution includes: mixing the protein raw material used to form the protein film with a second solvent to obtain a first solution, wherein the second solvent includes ethanol; adding glycerol to the first solution and mixing evenly to obtain the first film-forming solution. The step of mixing the protein raw material with the second solvent before adding glycerol helps the protein to fully dissolve and then uniformly plasticize, making the first film-forming solution more stable.

[0047] Specifically, the protein raw materials used to form the protein membrane include zein.

[0048] Specifically, in the first solution, the mass of the protein raw material accounts for 3% to 5% of the total mass of the first solution, for example, 3%, 3.5%, 4%, 4.5%, 5%, or any combination thereof.

[0049] In some embodiments, the process of treating the first film-forming solution used to form the protein film includes: casting the first film-forming solution into a film, followed by a first drying process to form the protein film. The casting process is simple and easy to operate.

[0050] Specifically, the drying temperature of the first drying process can be 30℃~40℃, for example, 30℃, 32℃, 34℃, 35℃, 38℃, 40℃ or any combination thereof; the drying time can be 2 h~3 h, for example, 2 h, 2.2 h, 2.5 h, 2.8 h, 3 h or any combination thereof.

[0051] In some embodiments, the second film-forming liquid further includes sodium alginate, wherein the mass ratio of sodium alginate to the mass of the colloidal matrix is ​​3% to 5%, for example, 3%, 3.5%, 4%, 4.5%, 5%, or any combination thereof. The addition of sodium alginate helps to improve the tensile strength and water resistance of the colloidal film, reducing the softening problem of the film layer caused by surface moisture of fruits and vegetables; the synergistic effect of sodium alginate and gelatin can enhance the loading capacity of active substances and reduce the loss of active substances; sodium alginate is a natural biodegradable material, further improving the environmental friendliness and safety of the product.

[0052] In some embodiments, the second film-forming solution further includes glycerol, and the mass ratio of glycerol to the mass of the colloidal matrix can be 10% to 15%, for example, 10%, 11%, 12%, 13%, 14%, 15%, or any combination thereof. Glycerol, as a plasticizer, can intercalate between the molecular chains of gelatin and sodium alginate, disrupting strong intermolecular interactions and increasing the flexibility of the film. Controlling the mass ratio of glycerol within the above range helps to ensure that the colloidal film possesses good flexibility without causing the film to become sticky or the active substances to be released too quickly due to excessive glycerol content. The hydrophilicity of glycerol can also regulate the swelling properties of the colloidal film, enabling controlled release of active substances.

[0053] In some embodiments, the preparation process of the second film-forming solution includes: dissolving sodium alginate and glycerol in a second solution containing the aforementioned gel matrix at 55°C to 60°C to obtain a third solution; controlling the temperature of the third solution at 40°C to 45°C, then adding the aforementioned active substance and mixing thoroughly to obtain the second film-forming solution. 55°C to 60°C is a suitable dissolution temperature for gelatin, allowing gelatin molecules to fully expand and dissolve. Simultaneously, the solubility of sodium alginate is also high at this temperature, and glycerol can be completely dissolved. At this temperature, the molecular chains of gelatin and sodium alginate begin to cross-link initially, forming a stable solution system and preventing molecular aggregation caused by subsequent temperature reduction. Lowering the temperature of the third solution to 40°C to 45°C helps retain the antibacterial and antioxidant activities of the active substance, maintaining a good preservation effect.

[0054] For example, the dissolution temperature of the sodium alginate and glycerol can be a range of 55°C, 56°C, 57°C, 58°C, 59°C, 60°C or any two of these; the temperature of the third solution can be 40°C to 45°C, for example, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C or any two of these.

[0055] In some embodiments, the second film-forming liquid further includes a third solvent, which includes water. Water, as the third solvent, dissolves gelatin and sodium alginate, providing a medium for their cross-linking reaction and film formation. Both gelatin and sodium alginate are hydrophilic substances, readily dissolving in water to form a homogeneous solution. The polar environment of water helps disperse the active substance complex and prevents aggregation.

[0056] Specifically, the above-mentioned colloidal matrix is ​​mixed with a third solvent to obtain a second solution.

[0057] Specifically, in the second solution, the mass of the colloidal matrix accounts for 3% to 5% of the total mass of the second solution, for example, 3%, 3.5%, 4%, 4.5%, 5%, or any combination thereof.

[0058] In some embodiments, a second film-forming solution is applied to the surface of the protein membrane by casting, and after a second drying process, the colloidal membrane is formed. Casting helps control the thickness precision of the colloidal membrane and improves the consistency of the preservation effect; room temperature natural drying avoids the damage of active substances to high temperatures and retains the complete preservation function; slow drying makes the colloidal membrane structure dense and the surface smooth, improving its binding strength with the protein membrane and its adhesion to the surface of fruits and vegetables, thus extending the shelf life.

[0059] Specifically, the temperature for the second drying process can be room temperature.

[0060] In specific implementation, the protein raw material is mixed with the second solvent and magnetically stirred at 50℃~55℃ for 20 min~30 min to obtain the first solution; glycerol is added to the first solution, the system temperature is kept constant, and magnetic stirring is continued for 20 min~30 min, followed by ultrasonic defoaming for 20 min~40 min to obtain the first film-forming liquid; the colloidal matrix is ​​mixed with the third solvent to obtain the second solution; sodium alginate and gelatin are added to the second solution at 55℃~60℃ to dissolve, resulting in the third solution; the temperature of the third solution is controlled at 40℃~45℃, and the above-mentioned active substances are added to it, and magnetic stirring is carried out for 20 min~30 min to mix evenly to obtain the second film-forming liquid; the first film-forming liquid is cast into a film, and after the first drying, a protein film is formed; the second film-forming liquid is cast onto the surface of the protein film, and after the second drying, a colloidal film is formed to obtain the plastic wrap.

[0061] The preservation film prepared by the method provided by the present invention integrates antibacterial and antioxidant functions into the same membrane material by constructing an asymmetric composite system of colloidal membrane and protein membrane. It achieves spatial coupling of physical barrier and biological activity from the design perspective, laying the core foundation for the targeted release and functional synergy of active ingredients.

[0062] This invention also provides an application of the above-described preservation film or the preservation film prepared according to the above-described preservation film preparation method in the preservation of fruits and vegetables.

[0063] According to the inventors' research, applying the preservation film provided by this invention to the preservation of fruits and vegetables helps reduce the rate of decay and water loss during storage, and better maintains the color, firmness, and flavor of fruits and vegetables; it can extend the shelf life of various fruits and vegetables (such as walnuts, broccoli, strawberries, etc.) and reduce post-harvest losses; the ingredients of the preservation film are natural and safe, and it is not likely to cause secondary pollution to fruits and vegetables, thus improving the safety of eating fruits and vegetables; it is easy to use, can adapt to the preservation needs of fruits and vegetables of different shapes, and has broad application prospects.

[0064] The present invention will be further described below through specific embodiments.

[0065] In the following examples and comparative examples, the ultrasonic defoaming process was performed using an ultrasonic power of 300W, which will not be described in detail here.

[0066] Example 1

[0067] S1. Dissolve 5g of zein in a 90% ethanol solution (ethanol accounts for 90% of the total mass of the ethanol solution), stir at 50℃ for 30 min to prepare a 5% first solution (zein content accounts for 5% of the total mass of the first solution); add 15% glycerol (glycerol content accounts for 15% of the zein content) to the first solution, continue stirring for 30 min, and sonicate to defoam for 10 min to form the first film-forming solution (zein film-forming solution).

[0068] S2. At room temperature, 40 mg of cinnamaldehyde was dissolved in 200 μL of ethanol solution to obtain cinnamaldehyde solution; 10 mg of tannic acid was dissolved in 10 mL of deionized water to obtain tannic acid solution with a concentration of 1 mg / mL; the cinnamaldehyde solution and tannic acid solution were mixed, magnetically stirred for 30 min, and then ultrasonically defoamed for 30 min under ice bath conditions to obtain a complex of cinnamaldehyde and tannic acid.

[0069] S3. Dissolve 5g of gelatin in distilled water to form a 5% second solution (the mass of gelatin accounts for 5% of the total mass of the second solution); at 60℃, add 3% sodium alginate (the mass of sodium alginate accounts for 3% of the mass of gelatin) and 15% glycerol (the mass of glycerol accounts for 15% of the mass of gelatin) to dissolve and obtain a third solution; control the temperature of the third solution at 45℃, and then add 20% of the complex of cinnamaldehyde and tannic acid (the total mass of the complex of cinnamaldehyde and tannic acid accounts for 20% of the mass of the gelatin solution), and stir magnetically for 20 min to mix evenly to obtain the second film-forming solution (gelatin film-forming solution).

[0070] S4. Cast the first film-forming solution into a film and dry it at 35°C for 2.5 h to form a protein film with a thickness of 28 μm; cast the second film-forming solution onto the protein film and dry it at room temperature to form a colloidal film with a thickness of 296 μm, thus obtaining a plastic wrap.

[0071] The difference between Example 2 and Example 1 is that in step S2 of Example 2, cinnamaldehyde is 10 mg, the mass ratio of cinnamaldehyde to tannic acid is 1:1, and other preparation conditions are the same as in Example 1.

[0072] The difference between Example 3 and Example 1 is that in step S2 of Example 3, the amount of cinnamaldehyde is 60 mg, the mass ratio of cinnamaldehyde to tannic acid is 6:1, and the other preparation conditions are the same as in Example 1.

[0073] The difference between Example 4 and Example 1 is that in step S2 of Example 4, the amount of cinnamaldehyde is 80 mg, the mass ratio of cinnamaldehyde to tannic acid is 8:1, and the other preparation conditions are the same as in Example 1.

[0074] The difference between Example 5 and Example 1 is that in step S2 of Example 5, the amount of cinnamaldehyde is 30 mg, the mass ratio of cinnamaldehyde to tannic acid is 3:1, and the other preparation conditions are the same as in Example 1.

[0075] The difference between Example 6 and Example 1 is that in step S4 of Example 6, the thickness of the protein membrane is 20 μm, while the other preparation conditions are the same as in Example 1.

[0076] The difference between Example 7 and Example 1 is that in step S4 of Example 7, the thickness of the protein membrane is 35 μm, while the other preparation conditions are the same as in Example 1.

[0077] The difference between Example 8 and Example 1 is that in step S4 of Example 8, the thickness of the protein membrane is 25 μm, while the other preparation conditions are the same as in Example 1.

[0078] The difference between Example 9 and Example 1 is that in step S4 of Example 9, the thickness of the protein membrane is 30 μm, while the other preparation conditions are the same as in Example 1.

[0079] The difference between Example 10 and Example 1 is that in step S4 of Example 10, the thickness of the colloidal film is 280 μm, while the other preparation conditions are the same as in Example 1.

[0080] The difference between Example 11 and Example 1 is that in step S4 of Example 11, the thickness of the colloidal film is 310 μm, while the other preparation conditions are the same as in Example 1.

[0081] The difference between Example 12 and Example 1 is that in step S4 of Example 12, the thickness of the colloidal film is 290 μm, while the other preparation conditions are the same as in Example 1.

[0082] The difference between Example 13 and Example 1 is that in step S4 of Example 13, the thickness of the colloidal film is 300 μm, while the other preparation conditions are the same as in Example 1.

[0083] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not add the complex of cinnamaldehyde and tannic acid, that is, step S2 is omitted.

[0084] Comparative Example 2

[0085] Dissolve 4g of zein in a 90% ethanol solution (the ethanol accounts for 90% of the total mass of the ethanol solution), add 0.6g of glycerol, stir at 50℃ for 25 min, cast into a film, and dry at 35℃ for 2.5 h to obtain a plastic wrap.

[0086] Comparative Example 3

[0087] Dissolve 5g of gelatin in distilled water to form a 5% second solution (the mass of gelatin accounts for 5% of the total mass of the second solution); add 3% sodium alginate (the mass of sodium alginate accounts for 3% of the mass of gelatin) and 15% glycerin (the mass of glycerin accounts for 15% of the mass of gelatin) at 60℃ to dissolve, cast into a film, and dry at room temperature to obtain a plastic wrap.

[0088] The DPPH (1,1-diphenyl-2-trinitrophenylhydrazine) radical scavenging rate and ABTS (2,2'-azido-bis-3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging rate of the plastic wrap in the examples and comparative examples were determined by the following methods:

[0089] (1) Determination of DPPH free radical scavenging rate

[0090] First, accurately weigh 0.1 g of plastic wrap sample, cut it into small pieces, and place it in a stoppered conical flask. Add 10 mL of 70% ethanol aqueous solution (ethanol accounts for 70% of the total mass of the ethanol aqueous solution). Extract the sample by shaking at 50℃ in the dark for 3 hours. Then, centrifuge the mixture at 4000 rpm for 10 minutes. The resulting supernatant is the sample extract to be tested. Simultaneously, prepare a 0.1 mmol / L DPPH-ethanol working solution and store it in the dark. For measurement, mix 2.0 mL of the sample extract with 2.0 mL of the DPPH working solution thoroughly. React at room temperature in the dark for 30 minutes, and then measure the absorbance at 517 nm, denoted as A. 样品 The background absorbance of the sample was measured using an equal volume of 70% ethanol solution instead of DPPH solution, and denoted as A. 空白 The initial absorbance of the DPPH solution was measured using an equal volume of 70% ethanol solution instead of the sample extract, and denoted as A. 对照 DPPH free radical scavenging rate (%) = [(1-A] 样品 -A 空白 ) / A 对照 ]×100%.

[0091] (2) Determination of ABTS free radical scavenging rate

[0092] An equal volume of 7.0 mmol / L ABTS aqueous solution and 2.45 mmol / L potassium persulfate aqueous solution were mixed and allowed to stand at room temperature in the dark for 12-16 h to generate ABTS. + Stock solution; before use, dilute with phosphate buffered saline (PBS, 0.01 M, pH 7.4) or anhydrous ethanol to correct the absorbance at 734 nm to 0.70 ± 0.02, thus obtaining ABTS. +Working solution. Sample pretreatment is the same as the DPPH method: Accurately weigh 0.1 g of plastic wrap sample, extract with 10 mL of 70% ethanol aqueous solution (ethanol mass accounts for 70% of the total mass of the ethanol aqueous solution) at 50℃ in the dark for 3 h, centrifuge and collect the supernatant as the test solution. For determination, take 0.1 mL of sample extract and 3.9 mL of ABTS... + The working solutions were mixed and vortexed until homogeneous. After reacting at room temperature in the dark for 6 minutes, the absorbance was immediately measured at a wavelength of 734 nm and denoted as A. 样品 Use 0.1 mL of 70% ethanol instead of the sample solution as a reaction control, denoted as A. 对照 The absorbance was measured by mixing 0.1 mL of sample extract with 3.9 mL of dilution solvent (PBS or ethanol), and recorded as A. 空白 ABTS free radical scavenging rate (%) = [(1-A] 样品 -A 空白 ) / A 对照 ]×100%.

[0093] Table 1

[0094]

[0095] As shown in Table 1, the antioxidant activity of Examples 1-13 provided by the present invention is significantly better than that of Comparative Examples 1-3. The DPPH and ABTS radical scavenging rates of Example 1 reached 83.75% and 89.13%, respectively, while the DPPH and ABTS radical scavenging rates of Comparative Example 1 (Janus membrane without active substance) were only 37.29% and 27.87%; the DPPH and ABTS radical scavenging rates of Comparative Example 2 (monolayer zein membrane) were 38.57% and 43.25%; and the DPPH and ABTS radical scavenging rates of Comparative Example 3 (single gelatin membrane) were as low as 29.46% and 1.8%. This indicates that the significant improvement in the antioxidant performance of the food preservation film provided by the present invention is not due to the membrane substrate itself, but mainly due to the cinnamaldehyde-tannic acid complex loaded in the colloidal membrane. Further analysis shows that the asymmetric structure (Janus structure) of the present invention is crucial for maintaining the stability and function of the active ingredients. The ABTS removal rate of Comparative Example 3 (single gelatin membrane) was only 1.8%, indicating that hydrophilic active ingredients (especially tannins) may be more easily lost or degraded during processing or testing without the protection of an outer protein membrane. However, Example 1, using the same gelatin substrate as Comparative Example 3, exhibited extremely high antioxidant activity. This strongly validates that the physical barrier formed by the hydrophobic protein membrane helps protect the inner active substances and reduces their ineffective loss, thus solving the common problem of easy loss of volatile or water-soluble active ingredients in traditional membranes. The data in Table 1 not only empirically demonstrate that the present invention, by introducing a cinnamaldehyde-tannin complex into the Janus structure, can achieve a leap in antioxidant activity, but also confirms the unique technical advantages of its asymmetric bilayer design in stabilizing active ingredients and achieving functional synergy.

[0096] Using Example 1 as a representative of the present invention, the antibacterial properties and applications in fruit and vegetable preservation of the preservation films of Example 1 and Comparative Examples 1-3 were determined by the following methods:

[0097] (3) Determination of the antibacterial properties of plastic wrap

[0098] The in vitro antibacterial effect of plastic wrap on *Penicillium citrinum* was determined using the agar diffusion method (inhibition zone method). The specific method is as follows: a concentration of 1×10⁻⁶ was prepared. 6 A CFU / mL suspension of Penicillium citrinum spores was prepared. 0.1 mL of this spore suspension was evenly spread onto a potato dextrose agar (PDA) plate using a sterile spreader. A 6 mm diameter disc of the plastic wrap sample was aseptically punched and aseptically attached to the center of the inoculated plate. The plate was then incubated at 28°C for 3-5 days. After incubation, the diameter of the inhibition zone was measured.

[0099] Table 2. Diameter of inhibition zones in the examples and comparative examples

[0100]

[0101] From Table 2 and Figure 1 As can be seen, Example 1 exhibited significant antibacterial activity against *Penicillium citrinum*, with an inhibition zone diameter of 23.43 ± 0.04 mm, indicating that its active ingredient could diffuse and inhibit the growth of *Penicillium citrinum*. In contrast, Comparative Example 1 (without the complex of cinnamaldehyde and tannins), Comparative Example 2 (only the hydrophobic membrane of zein), and Comparative Example 3 (only the hydrophilic membrane of gelatin) did not produce measurable inhibition zones. This comparative result clearly demonstrates that the preservation film provided by this invention has antibacterial function, providing direct experimental evidence for the application of the preservation film of this invention in the preservation of fruits and vegetables susceptible to fungal contamination.

[0102] (4) Determination of the application of plastic wrap in fruit and vegetable preservation

[0103] To evaluate the actual protective effect of different plastic wraps on the storage quality of fruits and vegetables, a simulated shelf-life storage experiment was conducted, with the decay rate assessed periodically. The specific methods are as follows: First, fresh walnuts, broccoli, and strawberries of uniform size, color, and maturity, free from mechanical damage or pests, were selected as experimental materials and randomly grouped. After weighing and recording the initial mass of each group of fruits and vegetables, they were wrapped or sealed with plastic wrap, with unpackaged samples serving as a blank control group. All treated samples were placed in a constant temperature and humidity chamber simulating ambient temperature storage (temperature set at 20℃, relative humidity controlled at 85%), avoiding direct sunlight. The decay status of each group was observed and recorded periodically (walnuts: every 2 days; broccoli: every 4 days; strawberries: every 3 days). The criteria for judging decay were: visible mold spots, softening, oozing juice, or decay exceeding 5% of the fruit's surface area. During each inspection, the number of rotten fruits in each group is counted, and the rot rate (%) is calculated using the formula: (number of rotten fruits / total number of fruits in the group) × 100%.

[0104] Table 3. Rot rate (%) of fresh walnuts in the examples and comparative examples

[0105]

[0106] Table 4. Broccoli rot rate (%) in the examples and comparative examples

[0107]

[0108] Table 5. Strawberry rot rate (%) in the examples and comparative examples.

[0109]

[0110] The preservation film provided in Example 1 of this invention exhibits significant and consistent advantages in delaying the spoilage of various fruits and vegetables. Specifically, for fresh walnuts (see Table 3), the spoilage rate of Example 1 group (56.17%) on day 10 was significantly lower than that of Comparative Examples 1-3. For broccoli (see Table 4), the preservation effect of Example 1 was more prominent compared to Comparative Examples 1-3, with a spoilage rate of only 7.17% on day 20. For perishable strawberries (see Table 5), the advantage of Example 1 was extremely obvious, delaying the onset of spoilage to day 9, and the spoilage rate of Example 1 (37.50%) on day 12 was far lower than that of Comparative Examples 1-3. The experimental results show that Example 1 can effectively delay the spoilage process of three kinds of fruits and vegetables, significantly reducing their spoilage rate during the critical storage period, especially with the most significant improvement in preservation effect on perishable fruits and vegetables such as strawberries.

[0111] In summary, this invention successfully achieves spatial coupling and functional synergy between physical barrier and bioactivity by constructing an asymmetric Janus membrane structure loaded with active complexes. The bilayer design precisely separates the hydrophobic barrier and hydrophilic sustained-release functions, which helps stabilize and protect the active ingredients, solving the problems of easy volatility and loss of active substances in traditional functional membranes. Simultaneously, the loaded cinnamaldehyde and tannic acid produce a synergistic effect at the molecular level, giving the film outstanding antibacterial and antioxidant functions. In practical applications, this design exhibits broad-spectrum and long-lasting preservation effects, significantly delaying the spoilage process of various fruits and vegetables, especially providing protection for high-moisture and perishable fruits and vegetables, thus demonstrating significant application value in extending shelf life and reducing post-harvest losses. This invention provides innovative ideas for developing next-generation, efficient, and intelligent active packaging materials.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A type of food preservation film, characterized in that, The invention includes a colloidal membrane and a protein membrane composited with the colloidal membrane; the colloidal membrane includes a colloidal matrix and an active substance loaded on the colloidal matrix, the active substance including a complex of cinnamaldehyde and tannic acid.

2. The food preservation film according to claim 1, characterized in that, The cinnamaldehyde-tannic acid complex is prepared by the following steps: a mixture containing cinnamaldehyde, tannic acid and a first solvent is stirred at room temperature for 20 min to 30 min, and then ultrasonically treated at 0℃ to 4℃ for 20 min to 40 min to obtain the cinnamaldehyde-tannic acid complex.

3. The food preservation film according to claim 2, characterized in that, The mass ratio of cinnamaldehyde to tannic acid is (3~6):1; And / or, the first solvent includes water.

4. The food preservation film according to claim 1, characterized in that, The mass ratio of the colloidal matrix to the active substance is (100~200):1; And / or, the adhesive matrix includes gelatin.

5. The food preservation film according to claim 1, characterized in that, The thickness of the colloidal membrane is 290 μm to 300 μm.

6. The food preservation film according to claim 1, characterized in that, The protein membrane includes zein; And / or, the thickness of the protein membrane is 25 μm to 30 μm.

7. A method for preparing the plastic wrap according to any one of claims 1-6, characterized in that, Includes the following steps: The first film-forming solution used to form the protein film is subjected to a film-forming treatment to form the protein film; The second film-forming solution is applied to the surface of the protein membrane to form the colloidal membrane, thereby obtaining the preservation film; wherein the second film-forming solution includes the colloidal matrix and the active substance.

8. The method for preparing the food preservation film according to claim 7, characterized in that, The first film-forming solution further includes glycerol and a protein raw material for forming the protein film, wherein the mass of the glycerol accounts for 10% to 15% of the mass of the protein raw material; And / or, the preparation process of the first film-forming solution includes: mixing the protein raw material used to form the protein film with a second solvent to obtain a first solution, wherein the second solvent includes ethanol solvent; adding glycerol to the first solution and mixing evenly to obtain the first film-forming solution; And / or, the process of treating the first film-forming solution used to form the protein film includes: casting the first film-forming solution into a film, and after a first drying, forming the protein film.

9. The method for preparing the food preservation film according to claim 7, characterized in that, The second film-forming solution also includes sodium alginate, wherein the mass of sodium alginate accounts for 3% to 5% of the mass of the colloidal matrix; The second film-forming solution also includes glycerol, wherein the mass of glycerol accounts for 10% to 15% of the mass of the colloidal matrix; And / or, the second film-forming solution further includes a third solvent, said third solvent including water; And / or, the preparation process of the second film-forming solution includes: dissolving sodium alginate and glycerol in a second solution containing the colloidal matrix at a temperature of 55°C to 60°C to obtain a third solution; The temperature of the third solution is controlled at 40℃~45℃, and then the active substance is added to it and mixed evenly to obtain the second film-forming solution; And / or, the second film-forming solution is applied to the surface of the protein membrane by casting, and after a second drying process, the colloidal membrane is formed.

10. The application of a preservation film according to any one of claims 1-6 or a preservation film prepared according to the preparation method of any one of claims 7-9 in the preservation of fruits and vegetables.

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