A corn protein-based composite film with synergistic degradation of ethylene and antibacterial property and a preparation method thereof

Abstract

This invention discloses a corn protein-based composite film for synergistic degradation of ethylene and antibacterial effects, and its preparation method, belonging to the field of food active packaging materials and fruit and vegetable preservation technology. The composite film comprises zein, quercetin, and the plasticizer glycerol. The quercetin content is 0.5%–3% of the zein content, and the film is obtained by casting. The quercetin is uniformly dispersed in the zein matrix. The preparation method is as follows: zein is dissolved in an 80%–95% ethanol aqueous solution, and glycerol is added and mixed. Quercetin is dissolved in anhydrous ethanol and stirred in the dark. The two are mixed to obtain a film-forming solution, which is poured into a mold and dried at 20–30°C and 50%–80% relative humidity for 24–48 hours before the film is removed. This invention utilizes the adsorption and enrichment of ethylene by zein, and the photocatalytic effect of visible light-excited reactive oxygen species generated by quercetin synergistically achieves efficient ethylene degradation. Simultaneously, the reactive oxygen species generated by this photocatalysis achieve an antibacterial effect, combining the advantages of natural raw materials, simple preparation, and ease of large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of food active packaging materials and fruit and vegetable preservation technology, and particularly relates to a corn protein-based composite film that synergistically degrades ethylene and has antibacterial properties, and its preparation method. Background Technology

[0002] With the continuous growth in consumer demand for fresh agricultural products, post-harvest preservation of fruits and vegetables has become a critical issue urgently needing to be addressed in the global food supply chain. Harvested fruits and vegetables exhibit high metabolic activity, continuously releasing large amounts of ethylene gas. Ethylene, as an endogenous ripening hormone, accelerates respiration, promotes chlorophyll degradation, and induces tissue softening and quality deterioration, making it a core contributing factor to the rapid ripening, aging, and spoilage of fruits and vegetables. Simultaneously, the proliferation of microorganisms in the packaging environment exacerbates spoilage, resulting in significant post-harvest economic losses. Therefore, developing highly efficient preservation packaging materials that integrate ethylene regulation and antibacterial functions is of great significance for extending the shelf life of fruits and vegetables and reducing food waste.

[0003] In existing technologies, the preparation of ethylene adsorption membrane materials using zein as a single film-forming matrix has been reported. This technology uses zein as the film-forming matrix and prepares homogeneous protein membranes via a casting method. It relies on the hydrophobic surface and microporous structure formed by the large number of hydrophobic amino acids (including leucine, alanine, and proline) in zein molecules to physically adsorb and enrich ethylene, thereby reducing the ethylene concentration inside the packaging and delaying the ripening of fruits and vegetables (see "Preparation of Ultrasonic-Assisted Zein-Based Ethylene Adsorption Membrane and its Preservation Performance for Bananas"). However, this technology has significant shortcomings: it can only achieve physical adsorption of ethylene, the membrane material easily reaches adsorption saturation, and the adsorbed ethylene is prone to desorption under fluctuating environmental conditions, failing to completely degrade or remove ethylene at the molecular level; simultaneously, this single protein membrane lacks antibacterial function, cannot inhibit the reproduction of microorganisms in the packaging space, and cannot solve the problem of fruit and vegetable spoilage caused by microbial infection; furthermore, the ethylene adsorption capacity of this membrane is low, the adsorption efficiency is limited, and the overall preservation effect is singular, making it difficult to meet the urgent need for multifunctional synergistic preservation in practical applications. The aforementioned defects stem from the inherent limitations in its material structure and composition: the film-forming matrix is ​​a homogeneous structure of single corn protein, and the system only contains hydrophobic adsorption sites and physical micropores, lacking active components that can chemically convert or degrade ethylene; no antibacterial active substances have been introduced, and it lacks the structural basis to kill or inhibit microorganisms; furthermore, it lacks overall functional synergistic design, and the number and efficiency of adsorption sites have a natural upper limit, making it impossible to achieve continuous and efficient removal of ethylene.

[0004] To address the limitations of single adsorption functions, researchers further explored a strategy of introducing inorganic photocatalysts into plant protein matrices to endow membrane materials with ethylene photocatalytic degradation capabilities. This technology uses a composite protein of wheat gluten and zein as the membrane matrix, incorporates ferulic acid as an antibacterial and antioxidant component, and dops titanium dioxide (TiO2) nanoparticles as an inorganic photocatalyst. Nanofiber membranes with a core-shell structure are prepared via electrospinning. Under illumination, TiO2 is excited to generate electron-hole pairs and further produce reactive oxygen species, thereby oxidizing and degrading ethylene. Simultaneously, the thiol groups in the composite matrix can chemically adsorb ethylene, while ferulic acid endows the system with antibacterial function, ultimately constructing a triple-functional system of "ethylene adsorption + photocatalytic degradation + antibacterial" (see "Electrospun wheat gluten / zein nanofibers loaded with ferulic acid and TiO2 as potential food active packaging", Food Research International, 2025, 221: 117285). Despite the progress made in functional integration, this technology still suffers from several critical drawbacks: The system still relies on TiO2 as an inorganic photocatalyst, which has limited biocompatibility and poses a potential safety risk of nanoparticle migration when in direct or indirect contact with food. This does not meet current consumer and market expectations for fully edible, natural, and green food packaging materials. Furthermore, the significant differences in surface polarity and interfacial energy between inorganic TiO2 particles and the plant protein matrix result in only weak electrostatic interactions and a lack of strong covalent or hydrogen bonds, leading to localized aggregation of TiO2 particles during film formation. This reduces the uniformity of the nanofiber structure and inhibits light absorption and catalytic efficiency. Additionally, the core-shell electrospinning process is highly dependent on specialized equipment, involves complex process parameter control, and has low production efficiency, making it difficult to achieve large-scale production to support industrial applications. From a structural and compositional perspective, the root cause of the above problems lies in the following: the core functional component is TiO2 inorganic semiconductor particles, which are non-natural food-grade substances. Inevitably, there are potential risks of food contact migration and biocompatibility in the material structure; the interfacial bonding force between TiO2 inorganic particles and plant proteins is weak, relying only on weak physical interactions, which cannot achieve highly uniform and stable dispersion of nanoparticles in organic matrices, thus leading to structural agglomeration and failure; the core-shell electrospinning structure has a complex process route, which cannot be achieved through simple casting methods, thus limiting its production versatility and cost controllability.

[0005] In addition, some studies have used gelatin as the main film-forming matrix and prepared zein-quercetin nanoparticles using the antisolvent method. After blending the nanoparticles with different addition amounts, gelatin / zein-quercetin nanocomposite films were prepared by casting method (see “Enhancing mechanical and blocking properties of gelatinfilms using zein-quercetin nanoparticle and applications for strawberrypreservation”, Food Chemistry, 2025, 464: 141895). However, this technical solution still has several performance defects: First, the ethylene adsorption capacity of the gelatin-based film matrix is ​​extremely weak, and it cannot effectively capture and enrich the ethylene gas released by fruits and vegetables during storage, thus failing to slow down the ripening and aging process of fruits and vegetables induced by ethylene; Second, the quercetin in this solution only plays a conventional antioxidant and antibacterial role as a static antioxidant and antibacterial agent. Its core photodynamic function as a natural photosensitizer, which can efficiently generate highly reactive oxygen species with strong oxidizing activity under visible light excitation, has not been activated and utilized. The membrane material as a whole lacks visible light response characteristics and cannot achieve ethylene degradation and photodynamic antibacterial effects through photodynamic mechanisms; Third, the membrane structure is a simple physical blend of gelatin matrix and zein-quercetin particles, lacking a synergistic structural design targeting the coupling mechanism of "ethylene adsorption and enrichment-photocatalytic degradation". Its preservation efficiency relies solely on a single mode of action of passive barrier, static antioxidant and basic antibacterial, resulting in limited overall preservation effect. The aforementioned defects have clear structural and compositional causes: From the perspective of the film-forming phase structure, the gelatin matrix molecular structure lacks hydrophobic adsorption sites, fundamentally lacking the ability to adsorb ethylene gas; from the perspective of the structural distribution of functional components, quercetin is encapsulated inside zein nanoparticles and further dispersed in the gelatin continuous phase matrix. This multi-layered encapsulated composite structure spatially blocks the effective contact between quercetin and incident visible light, preventing quercetin from being photoexcited to generate reactive oxygen species, thus completely losing its photodynamic potential; from the perspective of the overall membrane structure design, the membrane is a physically blended homogeneous structure, failing to construct a spatial coupling structure between "hydrophobic adsorption sites" and "photosensitive active sites," fundamentally lacking the structural basis required for the efficient synergistic adsorption and enrichment of ethylene and the in-situ degradation of ethylene by reactive oxygen species.

[0006] In summary, while existing research on active packaging materials for fruit and vegetable preservation has made some progress in functional aspects such as ethylene adsorption, photocatalytic degradation, and antibacterial properties, several common or specific defects still exist: First, there is a lack of an adsorption-degradation synergistic mechanism; single adsorption materials are easily saturated and cannot completely eliminate ethylene, resulting in low ethylene degradation efficiency. Second, the chemically synthesized photosensitizers or inorganic semiconductor catalytic materials used have poor biosafety and pose risks of food contact residues and migration. Third, the organic synergy between ethylene degradation and antibacterial functions has not been achieved, failing to fully meet the dual requirements of ethylene regulation and microbial inhibition in fruit and vegetable preservation. Fourth, the compatibility between the film-forming matrix and the active functional components is generally poor; some matrices lack sufficient biodegradability and environmental friendliness, and existing preparation technologies are costly and complex, severely restricting the industrial transformation and market application of related technological achievements. Therefore, there is an urgent need to develop a new generation of food preservation packaging materials that combine high-efficiency ethylene degradation capability with excellent antibacterial activity, good biosafety, and scalable production characteristics to overcome current technological bottlenecks. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a corn protein-based composite membrane for synergistic ethylene degradation and antibacterial activity, as well as its preparation method. This membrane possesses both high ethylene degradation capacity and excellent antibacterial activity, while also exhibiting good biosafety and scalable production characteristics.

[0008] To achieve the above objectives, this invention provides a zein-based composite membrane for synergistic degradation of ethylene and antibacterial effects. The composite membrane comprises zein, quercetin, and glycerol as a plasticizer, wherein the mass of quercetin is 0.5% to 3% of the mass of zein, and the mass of glycerol as a plasticizer is 10% to 30% of the mass of zein. The composite membrane is obtained by casting zein and quercetin together in a solvent system, with quercetin uniformly dispersed in the zein matrix. Under visible light irradiation, the quercetin in the composite membrane is excited to generate reactive oxygen species, and the zein matrix has an adsorption and enrichment effect on ethylene. The two work synergistically to achieve the degradation of ethylene, while the reactive oxygen species generated by this photocatalysis achieve an antibacterial effect.

[0009] Furthermore, the quercetin accounts for 1% to 2.5% of the mass of zeaxanthin.

[0010] Furthermore, the quercetin is present at a mass of 1.5% to 2% of the zeaxanthin content.

[0011] Furthermore, the wavelength range of the visible light is 400~700 nm.

[0012] The present invention also provides a method for preparing the corn protein-based composite film according to the above, comprising the following steps: (1) Dissolve zein in an 80%~95% ethanol aqueous solution and stir at 60~80℃ for 0.5~2 hours to obtain a zein solution; (2) Add glycerol, a plasticizer, to the zein solution obtained in step (1) and stir until homogeneous. The amount of glycerol added is 10% to 30% of the zein content. (3) Dissolve quercetin in anhydrous ethanol and stir for 1 to 3 hours at 15 to 30°C in the dark to obtain a quercetin solution. The amount of quercetin added is 0.5% to 3% of the amount of zeatin-soluble protein. (4) After cooling the solution obtained in step (2) to room temperature, add the quercetin solution obtained in step (3) and stir for 0.5 to 2 hours to obtain the film-forming solution; (5) Pour the film-forming liquid obtained in step (4) into the mold and dry it for 24 to 48 hours at a temperature of 20 to 30°C and a relative humidity of 50% to 80%. The corn protein-based composite film is obtained by peeling off the film.

[0013] Furthermore, the amount of quercetin added in step (3) is 1% to 2.5% of the amount of zein protein.

[0014] Furthermore, the film-forming liquid described in step (5) is subjected to vacuum degassing treatment before being poured into the mold.

[0015] Furthermore, the drying temperature in step (5) is 25°C, the relative humidity is 60%~75%, and the drying time is 30~40 hours.

[0016] The present invention also provides a fruit and vegetable preservation packaging material comprising the above-mentioned corn protein-based composite film, or comprising a corn protein-based composite film prepared by the above-mentioned preparation method.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects: (1) This invention constructs a synergistic system for the physical adsorption and enrichment of ethylene by zein and the visible light catalytic chemical degradation of ethylene by quercetin. The zein matrix efficiently adsorbs and enriches ethylene gas through its hydrophobic amino acid residues and active functional groups such as thiol groups. Quercetin generates reactive oxygen species under visible light excitation, and utilizes the high oxidizing activity of reactive oxygen species to catalytically degrade the adsorbed and enriched ethylene molecules in situ. This overcomes the defects of traditional single physical adsorption membranes in adsorption saturation and desorption, and significantly improves the ethylene removal efficiency. Experimental data show that the composite membrane of this invention can achieve an ethylene removal rate of more than 51.3% under visible light irradiation, which is more than twice that of 16.4% under light-shielded conditions.

[0018] (2) The composite film of the present invention possesses both highly efficient inherent antibacterial activity and visible light-dynamic antibacterial activity. Quercetin itself has inherent antibacterial properties, and under visible light excitation, it can further generate a large amount of reactive oxygen species, killing or inhibiting foodborne pathogens in the packaging environment. Experimental data show that the composite film of the present invention has an antibacterial rate of 58.5% against Staphylococcus aureus under dark conditions, and the antibacterial rate jumps to 99.6% after 30 minutes of visible light irradiation, demonstrating a significant synergistic antibacterial effect.

[0019] (3) This invention uses quercetin of natural origin as a photosensitizer to replace traditional inorganic semiconductor photocatalysts such as TiO2. The raw materials have high biosafety and are environmentally friendly, effectively avoiding the migration risk and biocompatibility hazards of inorganic nanoparticles in food contact, and meeting the requirements of green packaging and food safety.

[0020] (4) The present invention uses zein as the film-forming matrix, which is widely available, renewable and biodegradable; quercetin is tightly bound to zein through intermolecular hydrogen bonds, and is uniformly dispersed in the matrix and not easy to agglomerate, overcoming the defect of weak interfacial bonding between traditional inorganic photocatalysts and organic matrix; within the preferred content range, the introduction of quercetin also improves the tensile strength (from 12.5 MPa to 15.8 MPa), elongation at break (from 3.8% to 5.1%) and water vapor barrier properties of the composite film.

[0021] (5) The present invention uses the casting method, which is simple and requires low equipment, to form a film. Compared with complex processes such as electrospinning, it is easier to scale up and produce on a large scale. It has lower manufacturing costs and good industrial adaptability, providing a practical and feasible technical solution for the commercial application of fruit and vegetable preservation packaging materials. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 Staphylococcus aureus under different treatment conditions ( S. aureus Photographs of agar plates (a) and colony counts under the corresponding conditions (b).

[0024] Figure 2 The graph shows the ethylene degradation efficiency of different treatment groups. Detailed Implementation

[0025] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0026] All raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0027] There are no particular restrictions on the purity of any of the raw materials used in this invention. However, this invention preferably uses raw materials of analytical grade or purity commonly used in the field of chemical synthesis.

[0028] Raw material source and specifications The zein (ZN) used in the following examples was a commercially available food-grade product with a protein content ≥92% and a number-average molecular weight of approximately 25-35 kDa; quercetin (QUC) purity ≥95% (HPLC grade); anhydrous ethanol, glycerol, etc., were all analytical grade reagents, and deionized water was used in the experiments. In the following examples, the LED light source parameters were: white LED, wavelength range 400-700 nm, optical power density 20 mW / cm². 2 Irradiation distance: 10 cm.

[0029] Overall technical solution for composite membrane preparation process This invention provides a method for preparing a corn protein-based composite membrane that synergistically degrades ethylene and has antibacterial properties. The membrane uses corn gliadin as the film-forming matrix, quercetin as the natural photosensitizer as the active functional component, and glycerol as the plasticizer. The corn protein-quercetin composite membrane is prepared by casting. Specifically, zein is dissolved in an 80%–95% ethanol aqueous solution and stirred at 60–80°C for 0.5–2 hours to obtain a homogeneous zein solution (ZN solution). After cooling to room temperature, 10%–30% of the plasticizer glycerol based on the mass of zein is added and stirred until homogeneous. Separately, quercetin is dissolved in anhydrous ethanol and stirred at 15–30°C under light-protected conditions for 1–3 hours to obtain a quercetin solution (QUC solution). After cooling the zein solution to room temperature, the quercetin solution is added and stirred for 0.5–2 hours to obtain a film-forming solution. This film-forming solution is poured into a mold and dried in an artificial climate chamber at 20–30°C and 50%–80% relative humidity for 24–48 hours. The resulting membrane is then peeled off to obtain a zein-quercetin composite membrane (ZN-QUC composite membrane). The mass of quercetin is 0.5%–3% of the zein mass.

[0030] Example 1 Weigh 1 g of zein (ZN) and add it to 30 mL of 90% ethanol aqueous solution. Stir in a 70°C water bath for 1 hour to obtain a homogeneous and transparent ZN solution. Add 0.2 g of glycerol (i.e., 20% of the ZN mass) to the above ZN solution and continue stirring for 20 minutes to ensure the plasticizer is fully dispersed. Separately weigh 0.02 g of quercetin (QUC) and dissolve it in 10 mL of anhydrous ethanol. Stir in the dark at 25°C for 2 hours to obtain a QUC solution. Cool the ZN solution to room temperature (25±2°C), then add the above QUC solution and stir for 1 hour to obtain a homogeneous ZN-QUC film-forming solution free of visible particles. The film-forming solution was slowly poured into a 12 cm diameter polytetrafluoroethylene circular mold and placed in an artificial climate chamber. It was dried for 36 hours at a temperature of 25°C and a relative humidity of 75% RH. The complete corn protein-quercetin composite film (marked as ZN-QUC-20) could then be peeled off the mold. The film was uniform in color, light yellow, and approximately 65±5 μm thick.

[0031] Meanwhile, following the same method described above, without adding QUC solution, a pure zein membrane (labeled as ZN membrane) was prepared using only ZN solution and glycerol as a control sample, with a membrane thickness of approximately 60 ± 5 μm.

[0032] Example 2 This embodiment is basically the same as Example 1, except that the amount of quercetin added is 0.01 g (i.e., 1% of the mass of QUC as ZN), which is dissolved in 5 mL of anhydrous ethanol under light and stirred. Other operating conditions remain unchanged, and a corn protein-quercetin composite membrane (labeled as ZN-QUC-10) with a thickness of approximately 62±5 μm is obtained.

[0033] Example 3 This example is basically the same as Example 1, except that the amount of quercetin added is 0.03 g (i.e., QUC mass is 3% of ZN), and it is dissolved in 15 mL of anhydrous ethanol under light and stirred. Other operating conditions remain unchanged, and a corn protein-quercetin composite membrane (labeled as ZN-QUC-30) with a membrane thickness of approximately 68±5 μm is obtained.

[0034] Example 4 1 g of zein was weighed and added to 25 mL of 85% ethanol aqueous solution, and stirred at 75℃ for 1.5 hours to obtain Zn solution; 0.15 g of glycerol (15% of Zn mass) was added and stirred for 20 minutes; 0.015 g of quercetin was weighed and dissolved in 8 mL of anhydrous ethanol, and stirred at 20℃ in the dark for 2.5 hours; after cooling the Zn solution to room temperature, QUC solution was added and stirred for 1 hour; the film-forming solution was poured into a glass mold and dried in an artificial climate chamber at 28℃ and 60% RH for 30 hours, and the film was peeled off to obtain ZN-QUC composite membrane (labeled as ZN-QUC-15), with a membrane thickness of approximately 63±5 μm.

[0035] Example 5 1.5 g of zein was weighed and added to 45 mL of 90% ethanol aqueous solution, and stirred at 70℃ for 1 hour to obtain Zn solution; 0.375 g of glycerol (25% of Zn mass) was added and stirred for 20 minutes; 0.0375 g of quercetin (i.e., QUC mass of Zn) was weighed and dissolved in 18 mL of anhydrous ethanol, and stirred at 25℃ in the dark for 2 hours; after the Zn solution was cooled to room temperature, the QUC solution was added and stirred for 1 hour; the film-forming solution was poured into a polytetrafluoroethylene mold with a diameter of 12 cm and dried at 25℃ and 75% RH for 40 hours to obtain Zn-QUC composite membrane (labeled as ZN-QUC-25) with a thickness of approximately 75±10 μm.

[0036] Example 6 This embodiment is basically the same as Embodiment 1, except that the film-forming solution is vacuum degassed for 10 minutes before being poured into the mold to eliminate air bubbles. The resulting ZN-QUC composite film has a smooth surface without obvious air bubble defects, and the film thickness is approximately 65±5 μm, and is labeled as ZN-QUC-20 (degassed).

[0037] Comparative Example 1 In this comparative example, gelatin was used instead of zein as the film-forming matrix. 1 g of gelatin was weighed and dissolved in 30 mL of deionized water, stirred at 60 °C for 1 hour, and 0.2 g of glycerol was added and stirred until homogeneous. 0.02 g of quercetin was weighed and dissolved in 10 mL of anhydrous ethanol and stirred in the dark for 2 hours. After the gelatin solution was cooled to room temperature, the quercetin solution was added and stirred for 1 hour. The film-forming solution was poured into a polytetrafluoroethylene mold and dried at 25 °C and 75% RH for 36 hours to obtain a gelatin-quercetin composite film (labeled GEL-QUC-20).

[0038] The gelatin matrix lacks ethylene adsorption sites formed by the enrichment of hydrophobic amino acids, and therefore lacks intrinsic ethylene physical adsorption and enrichment capabilities. It cannot synergize with the photocatalytic function of quercetin. Therefore, although quercetin can generate ROS under light conditions, the lack of matrix pre-enrichment of ethylene results in a much lower ethylene removal efficiency than the ZN-QUC composite membrane of this invention.

[0039] Comparative Example 2 In this comparative example, tea polyphenols (TP), a natural antioxidant that does not have visible light response properties, were used to replace quercetin. 1 g of zein was weighed and dissolved in 30 mL of 90% ethanol, stirred at 70°C for 1 hour, and then 0.2 g of glycerol was added and stirred. Separately, 0.02 g of tea polyphenols was weighed and dissolved in 10 mL of anhydrous ethanol, stirred in the dark for 2 hours. The mixing and preparation process was the same as in Example 1, resulting in a zein-tea polyphenol composite membrane (labeled ZN-TP-20).

[0040] Tea polyphenols do not show significant absorption in the visible light region and cannot be used as photosensitizers to generate ROS under visible light. Therefore, although the ZN-TP membrane can physically adsorb ethylene by relying on the intrinsic adsorption capacity of the zein matrix, it does not generate new ethylene catalytic degradation function under visible light irradiation due to the lack of photocatalytically active components. The overall ethylene removal efficiency is significantly lower than that of the ZN-QUC membrane of this invention.

[0041] Comparative Example 3 In this comparative example, the amount of quercetin added was 0.003 g (i.e., QUC mass was 0.3% of ZN), and the other conditions were the same as in Example 1. 1 g of zein was weighed and dissolved in 30 mL of 90% ethanol, stirred at 70°C for 1 hour, and then 0.2 g of glycerol was added and stirred. 0.003 g of quercetin was weighed and dissolved in 2 mL of anhydrous ethanol, stirred in the dark for 2 hours, and the mixing and preparation process was the same as in Example 1, resulting in a ZN-QUC-3 composite membrane.

[0042] Due to the low quercetin loading, the density of photosensitive active sites in the membrane is insufficient, resulting in a low total amount of ROS generated under visible light irradiation. Consequently, the photocatalytic degradation of ethylene and photodynamic antibacterial capabilities are significantly weaker than those of the composite membranes within the preferred range.

[0043] Comparative Example 4 In this comparative example, the amount of quercetin added was 0.05 g (i.e., 5% of the ZN mass in QUC), and the other conditions were the same as in Example 1. 1 g of zein was weighed and dissolved in 30 mL of 90% ethanol, stirred at 70°C for 1 hour, and then 0.2 g of glycerol was added and stirred. 0.05 g of quercetin was weighed and dissolved in 20 mL of anhydrous ethanol, stirred in the dark for 2 hours, and the mixture was used to prepare a ZN-QUC-50 composite membrane. However, when the quercetin loading was too high, it easily aggregated and crystallized inside the membrane, which not only damaged the overall structural integrity of the film but also increased light scattering loss, leading to a significant decrease in photocatalytic efficiency. Simultaneously, the mechanical properties of the composite membrane deteriorated, making it difficult to meet the application requirements of actual food packaging.

[0044] Comparative Example 5 In this comparative example, the quercetin solution was prepared without any light-shielding measures and stirred under natural indoor light conditions, with all other conditions being the same as in Example 1. The resulting ZN-QUC-L composite membrane was significantly darker, turning a deep brown. UV-Vis spectroscopy analysis showed a significant decrease in the intensity of the characteristic absorption peak of quercetin, indicating that quercetin underwent partial photooxidative degradation under light irradiation, losing some of its photosensitizing activity. In subsequent ethylene degradation and antibacterial tests, the ethylene removal rate and photodynamic antibacterial activity of this membrane were significantly lower than those of the membrane sample prepared in the dark in Example 1.

[0045] Comparative Example 6 In this comparative example, the film-forming and drying conditions were 25°C and 90% RH, with the remaining conditions being the same as in Example 1. Under high humidity, the evaporation rate of the film-forming solution was too slow, extending the drying time to over 60 hours; the resulting membrane surface showed localized whitening, softening, abnormally high water vapor permeability, and decreased barrier performance. This indicates that controlling the appropriate drying humidity is crucial for obtaining a ZN-QUC composite membrane with excellent overall performance.

[0046] Comparative Example 7 Following the method disclosed in the prior art (Food Research International, 2025, 221: 117285), a zein-supported nano-TiO2 composite membrane was prepared. 1 g of zein was dissolved in 30 mL of 90% ethanol, and 0.2 g of glycerol and 0.02 g of nano-TiO2 (P25 type, average particle size approximately 21 nm) were added. After ultrasonic dispersion for 30 min and stirring for 1 hour, a ZN-TiO2 membrane was prepared according to the casting conditions of Example 1. Although this membrane exhibited some ethylene degradation ability under ultraviolet light irradiation, it showed almost no catalytic activity in the visible light region (400–700 nm) due to the band gap limitation of TiO2 (~3.2 eV); furthermore, there was no strong interaction between the TiO2 particles and the protein matrix, and local TiO2 aggregates were visible under SEM observation.

[0047] Performance test examples Test Example 1: Photodynamic Antibacterial Performance Test The representative foodborne pathogen Staphylococcus aureus (Staphylococcus aureus) Staphylococcus aureus , S. aureus The photodynamic antibacterial activity of the composite film of the present invention was investigated using [the film] as the research object. S. aureus Freshly incubated overnight, then diluted with sterile phosphate buffer to a bacterial suspension concentration of approximately 10. 6 CFU / mL. 200 μL of bacterial suspension was evenly coated onto the ZN membrane and ZN-QUC-20 membrane prepared in Example 1, respectively. The following treatment groups were set up: (1) Control group: bacterial suspension placed in a dark environment, no membrane treatment; (2) ZN group: bacterial suspension on ZN membrane, dark environment; (3) ZN-QUC group: bacterial suspension on ZN-QUC-20 membrane, dark environment; (4) ZN-QUC + Group 1: Bacterial suspensions were placed on ZN-QUC-20 membranes and continuously irradiated with LED visible light for 30 min; all treatments were performed at 37°C for 30 min. After treatment, bacterial suspensions from each group were collected, serially diluted, and spread onto PCA agar plates. After incubation at 37°C for 24 hours, the total number of colonies was counted. Simultaneously, antibacterial tests were performed on the films prepared in Examples 2-5, Comparative Examples 1-3, Comparative Examples 5, and Comparative Example 7 using the same method. Colony counts were recorded under both dark and light conditions, and the antibacterial rate was calculated.

[0048] See results Figure 1 , Figure 1 For different treatment conditions S. aureus Photomicrograph of agar plates (a) and colony counts under the corresponding conditions (b). Figure 1 As shown, compared with the control group and the ZN group, the ZN-QUC treatment group under dark conditions... S. aureus The number of bacterial colonies was significantly reduced, which is attributed to the inherent antibacterial properties of quercetin itself; while under visible light irradiation, ZN-QUC + The colony count in the treated group was significantly reduced further compared to ZN-QUC, demonstrating stronger antibacterial efficacy. This indicates that quercetin not only generates highly reactive oxygen species (ROS) under visible light excitation to exert photodynamic antibacterial effects, but also exhibits a significant synergistic effect between its inherent antibacterial activity and photodynamic activity, thereby greatly enhancing the antibacterial capability of the composite membrane. Detailed antibacterial data for each example and comparative example are summarized in Table 1.

[0049] Test Example 2: Ethylene Degradation Performance Test 100 ppm of ethylene standard gas was injected into multiple sealed gas sampling bags. Then, the ZN membrane and ZN-QUC-20 membrane prepared in Example 1 were placed into their respective gas bags and sealed. The following experimental groups were set up: (1) ZN group: protected from light throughout; (2) ZN-QUC group: protected from light throughout; (3) ZN-QUC group: protected from light throughout. + Group: First, avoid light for 10 hours, and then turn on LED visible light irradiation for 2 hours in the later stage of the reaction; (4) Light control group: Take ZN-QUC-20 membrane and avoid light for 12 hours as control. All experiments were carried out at room temperature (25±2℃). After the reaction, the residual ethylene concentration in each gas bag was detected by gas chromatography, and the ethylene removal rate was calculated according to (initial concentration-residual concentration) / initial concentration×100%. The ethylene degradation test was carried out on the films prepared in Examples 2-5, Comparative Examples 1-3, Comparative Examples 5 and Comparative Examples 7 according to the same method, and the data were recorded and summarized in Table 2.

[0050] See results Figure 2 , Figure 2 Ethylene degradation efficiency for different treatment groups. Figure 2 As shown, the ZN membrane exhibits a certain ethylene scavenging ability, mainly due to the physical adsorption and chemisorption of ethylene molecules by a large number of hydrophobic amino acid residues and active functional groups such as thiol groups in the zein molecule, thus possessing intrinsic ethylene scavenging function. The ethylene scavenging efficiency of the ZN-QUC group under completely dark conditions was not significantly different from that of the ZN group, confirming that quercetin itself does not possess significant ethylene degradation activity without light excitation. In stark contrast, under visible light irradiation for 2 hours, the ZN-QUC... + The ethylene removal rate of group 1 was significantly higher than that of the previous two groups (more than doubled), which fully demonstrates that quercetin can generate ROS under visible light excitation. The high oxidizing activity of ROS allows for the efficient catalytic degradation of ethylene molecules, which have been adsorbed and enriched by the zein matrix, into smaller molecule products. This achieves a synergistic effect of physical adsorption enrichment and photocatalytic chemical degradation, endowing the composite membrane with excellent ethylene removal performance. Detailed ethylene degradation data for each example and comparative example are summarized in Table 2.

[0051] Test Example 3: Characterization Test and Overall Performance Data Table 1. Ultraviolet-Visible Absorption Spectroscopy The ZN film and ZN-QUC-20 film of Example 1 were scanned using a UV-Vis spectrophotometer. The results showed that the pure ZN film had almost no absorption in the visible light region; while the ZN-QUC-20 film showed a distinct quercetin characteristic absorption band in the 350-450 nm range, extending into the visible light region, confirming that quercetin retains its ability to respond to visible light in the composite film.

[0052] 2. Mechanical properties and water vapor barrier properties Tensile tests and water vapor transmission rate (WVTR) tests were conducted on the membrane samples of Examples 1-6 and Comparative Examples 1, 4, and 5 according to standard methods. The data are summarized in Table 3.

[0053] 3. Fruit preservation application experiment Fresh strawberries of uniform ripeness were selected and placed in packaging boxes lined with different films. They were stored under conditions of light-protected storage and daily exposure to visible light for 8 hours (simulating retail display lighting conditions), respectively, and stored at 25℃ for 5 days. The weight loss rate, firmness retention rate, rot rate, and soluble solids content were measured, and the results are summarized in Table 4.

[0054] Table 1. Comparison of antibacterial properties of different film samples against Staphylococcus aureus Note: Antibacterial rate = [(number of colonies in control group - number of colonies in experimental group) / number of colonies in control group] × 100%; Lighting conditions: white LED irradiation for 30 min.

[0055] As shown in Table 1, the ZN-QUC-20 membrane exhibits an antibacterial rate of 58.5% under dark conditions, which jumps to 99.6% after illumination, demonstrating a significant photodynamic enhancement. With a loading of 2%–3%, the antibacterial rate under illumination consistently exceeds 99.5%. In Comparative Example 2, the ZN-TP-20 membrane shows no significant difference in antibacterial rate under light and dark conditions, confirming that tea polyphenols have no visible light response. In Comparative Example 7, the ZN-TiO2 membrane achieves a visible light antibacterial rate of only 80.0%, far lower than that of this invention.

[0056] Table 2 Comparison of ethylene degradation performance of different film samples Table 2 shows that the ethylene removal rate of the ZN-QUC-20 membrane under light-shielded conditions was only 16.4%, close to that of the pure ZN membrane (15.8%). After 2 hours of visible light irradiation, it jumped to 51.3%, demonstrating a synergistic effect of adsorption and photocatalysis. The low removal rate of the GEL-QUC-20 membrane proves that the gelatin matrix lacks ethylene adsorption capacity. The removal rate of the ZN-TP-20 membrane is comparable to that of the pure ZN membrane, verifying that tea polyphenols have no visible light photocatalytic ability to degrade ethylene. The catalytic activity is insufficient when the quercetin loading is too low, and the improvement slows down after exceeding 2%. The removal rate of the ZN-TiO2 membrane under visible light is only 19.8%, highlighting the visible light photocatalytic advantage of the quercetin in this invention.

[0057] Table 3 Comparison of comprehensive physical properties of representative thin film samples As shown in Table 3, when the quercetin content increases from 0 to 2%, the tensile strength and elongation at break first increase and then decrease, with the optimal values ​​observed at 2%. After exceeding 3%, the tensile strength and elongation at break drop sharply, leading to the brittleness of the membrane in Comparative Example 4. Water vapor permeability decreases with increasing quercetin content. The membrane in Example 6, after defoaming treatment, exhibits superior mechanical and barrier properties.

[0058] Table 4 Results of strawberry preservation application test (stored at 25℃ for 5 days) Table 4 shows that the ZN-QUC-20 membrane of this invention resulted in a strawberry weight loss rate of only 5.8%, a rot rate of 10.5%, and a firmness retention rate of 82.5% under light conditions. All indicators were significantly better than those of the light-shielded group, the pure ZN membrane group, and Comparative Example 7, demonstrating the outstanding synergistic preservation effect of adsorption-photocatalysis.

[0059] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A corn protein-based composite membrane for synergistic ethylene degradation and antibacterial properties, characterized in that, The composite membrane comprises zein, quercetin, and glycerol as a plasticizer, wherein the mass of quercetin is 0.5% to 3% of the mass of zein, and the mass of glycerol as a plasticizer is 10% to 30% of the mass of zein. The composite membrane is obtained by casting zein and quercetin together in a solvent system, with quercetin uniformly dispersed in the zein matrix. Under visible light irradiation, the quercetin in the composite membrane is excited to generate reactive oxygen species, and the zein matrix has an adsorption and enrichment effect on ethylene. The two work synergistically to achieve the degradation of ethylene, and at the same time, the reactive oxygen species generated by this photocatalysis achieve an antibacterial effect.

2. The corn protein-based composite membrane according to claim 1, characterized in that, The quercetin is present at a mass of 1% to 2.5% of the zeaxanthin content.

3. The corn protein-based composite membrane according to claim 2, characterized in that, The quercetin is present at a mass of 1.5% to 2% of the zeaxanthin content.

4. The corn protein-based composite membrane according to claim 1, characterized in that, The wavelength range of the visible light is 400~700 nm.

5. A method for preparing a corn protein-based composite membrane according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Dissolve zein in an 80%~95% ethanol aqueous solution and stir at 60~80℃ for 0.5~2 hours to obtain a zein solution; (2) Add glycerol, a plasticizer, to the zein solution obtained in step (1) and stir until homogeneous. The amount of glycerol added is 10% to 30% of the zein content. (3) Dissolve quercetin in anhydrous ethanol and stir for 1 to 3 hours at 15 to 30°C in the dark to obtain a quercetin solution. The amount of quercetin added is 0.5% to 3% of the amount of zeatin-soluble protein. (4) After cooling the solution obtained in step (2) to room temperature, add the quercetin solution obtained in step (3) and stir for 0.5 to 2 hours to obtain the film-forming solution; (5) Pour the film-forming liquid obtained in step (4) into the mold and dry it for 24 to 48 hours at a temperature of 20 to 30°C and a relative humidity of 50% to 80%. The corn protein-based composite film is obtained by peeling off the film.

6. The preparation method according to claim 5, characterized in that, The amount of quercetin added in step (3) is 1% to 2.5% of the amount of zein protein.

7. The preparation method according to claim 5, characterized in that, The film-forming liquid described in step (5) is subjected to vacuum degassing treatment before being poured into the mold.

8. The preparation method according to claim 5, characterized in that, The drying temperature in step (5) is 25°C, the relative humidity is 60%~75%, and the drying time is 30~40 hours.

9. A fruit and vegetable preservation packaging material, characterized in that, The membrane comprises a corn protein-based composite membrane according to any one of claims 1 to 4, or a corn protein-based composite membrane prepared by any one of claims 5 to 8.

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