Degradable nanocomposite preservative film with antibacterial and gas regulating functions

Abstract

This invention discloses a biodegradable nanocomposite preservation film with antibacterial and gas-regulating effects, belonging to the field of food preservation technology. The nanocomposite preservation film is prepared by the following method: water, glycerol, cellulose nanofiber dispersion, sodium carboxymethyl cellulose solution, and calcium chloride solution are added sequentially to okra mucilage and stirred until homogeneous; then, chitosan porous microspheres loaded with curcumin are added and stirred until homogeneous; the mixture is degassed and cast into a mold, then dried in an oven to form a peelable nanocomposite preservation film. This invention uses okra mucilage and chitosan porous microspheres as substrates, and curcumin as the active ingredient, to construct a biodegradable nanocomposite preservation film with antibacterial and gas-regulating effects. This preservation film not only spontaneously constructs a low-oxygen, moderately carbon dioxide microenvironment inside the packaging through asymmetric gas selective permeability, but also achieves long-term sustained release of the antibacterial molecule curcumin, resulting in excellent preservation effects.

Description

Technical Field

[0001] This invention belongs to the field of food preservation technology, specifically relating to a biodegradable nanocomposite preservation film with antibacterial and gas regulation effects. Background Technology

[0002] Fresh fruits and vegetables have a high water content and strong metabolic activity. Even after harvesting, they continue to undergo respiration and transpiration, leading to continuous water loss, accelerated sugar consumption, and gradual softening of cell structure. Combined with microbial infection and oxidation, these products are highly susceptible to browning, rotting, and quality deterioration within just a few days. Traditional food preservation technologies, such as plastic packaging, low-temperature logistics, and chemical preservatives, while partially effective, face challenges related to unsustainability, high energy consumption, and potential health and environmental risks.

[0003] In recent years, the rise of edible films and coatings has paved the way for green packaging, but their functions are often limited and they cannot dynamically respond to the complex physiological and microbial changes during food preservation. The key scientific bottleneck lies in how to combine the dynamic, adaptive regulatory mechanisms of nature with fully edible and biodegradable material systems to create a green and sustainable packaging that can actively intervene in the microenvironment and has no environmental burden after use.

[0004] Therefore, developing the next generation of green packaging materials that combine high-efficiency preservation, environmental friendliness, and safety has become an urgent problem to be solved in the fields of food science, materials engineering, and sustainable development. Summary of the Invention

[0005] This invention provides a biodegradable nanocomposite food preservation film with antibacterial and gas-regulating effects, wherein the nanocomposite food preservation film is prepared by the following method: Water, glycerol, cellulose nanofiber dispersion, sodium carboxymethyl cellulose solution, and calcium chloride solution were added sequentially to okra mucilage and stirred until homogeneous. Then, chitosan porous microspheres loaded with curcumin were added and stirred until homogeneous. After degassing the mixture, it was cast into a mold and dried in an oven to form a peelable nanocomposite preservation film.

[0006] In the above technical solution, the amounts of each component are as follows: okra mucilage 100-150 g, water 100-150 mL, glycerol 5-10 g, cellulose nanofiber dispersion 1-2 g, sodium carboxymethyl cellulose solution 20-30 mL, calcium chloride solution 1-5 mL, and chitosan porous microspheres loaded with curcumin 5-50 mg.

[0007] In the above technical solution, the concentration of the cellulose nanofiber dispersion is 0.5~2 wt%, the concentration of the sodium carboxymethyl cellulose solution is 1~5 wt%, and the concentration of the calcium chloride solution is 1~10 wt%. The solvent for the above dispersions or solutions is water.

[0008] In the above technical solution, the okra mucilage is prepared by the following method: Select fresh okra pods or flowers, wash them thoroughly, crush them, add water, and soak them; stir constantly while soaking; then fold a sterile degreased gauze in half, put the soaked okra pods or flowers in, squeeze them hard to separate the solid and liquid, take the liquid and centrifuge it, and take the supernatant after centrifugation to obtain okra mucilage.

[0009] In the above method for preparing okra mucilage, the mass ratio of water to okra pods or okra flowers is 1:(1~3).

[0010] In the above method for preparing okra mucilage, the soaking conditions are: soaking at 80~100 ℃ for 3~5 h.

[0011] In the above technical solution, the chitosan porous microspheres loaded with curcumin are prepared by the following method: Curcumin was dissolved in ethyl acetate, and Tween 80 and chitosan acetate solution were added. The mixture was stirred and ultrasonically emulsified for 5-10 min to ensure uniform emulsification. Then, under stirring, Span 80 and liquid paraffin were added. After uniform emulsification, glutaraldehyde was added, and the crosslinking reaction was carried out for 5-10 h. The reaction was continued for 5-10 h under a water bath at 40-60℃. After the reaction was completed, the mixture was centrifuged, the upper oil phase was discarded, and the mixture was washed with petroleum ether. After natural drying, chitosan porous microspheres loaded with curcumin were obtained.

[0012] In the above method for preparing chitosan porous microspheres loaded with curcumin, the amounts of each component are as follows: curcumin 10-50 mg, ethyl acetate 5-10 mL, Tween 80 0.05-0.2 g, chitosan acetate solution 10-20 mL, Span 80 2-10 mL, liquid paraffin 200-300 mL, and glutaraldehyde 0.1-1 mL.

[0013] In the above method for preparing chitosan porous microspheres loaded with curcumin, the concentration of the chitosan acetate solution is 0.5~2 wt%.

[0014] This invention provides the application of the above-mentioned nanocomposite preservation film in food preservation; the food includes, but is not limited to, pasta, fruits and vegetables, meat, seafood and other foods.

[0015] The beneficial effects of this invention are as follows: This invention utilizes okra mucilage and chitosan porous microspheres as substrates, with curcumin as the active ingredient, to construct a biodegradable nanocomposite preservation film with antibacterial and gas-regulating effects. This film not only spontaneously creates a low-oxygen, moderately carbon dioxide microenvironment within the packaging through asymmetric gas selective permeability, but also achieves long-term sustained release of the antibacterial molecule curcumin. In tests simulating complex temperature-fluctuating cold chain logistics processes, this preservation film can be successfully applied to agricultural products with typical perishable characteristics, demonstrating excellent preservation effects. Attached Figure Description

[0016] Figure 1 This is a SEM image of chitosan porous microspheres (PCMs).

[0017] Figure 2 The diagram shows the particle size distribution of the curcumin-chitosan porous microspheres (Cur-PCMs) (A), the particle size volume distribution of the Cur-PCMs (B), the nitrogen adsorption and desorption isotherms of the Cur-PCMs at 77 K (C), and the pore size distribution of the Cur-PCMs (D).

[0018] Figure 3 XRD diffraction patterns (A), FTIR spectra (B), TGA thermogravimetric curves (C), and DTG differential thermogravimetric curves (D) for films with different formulations.

[0019] Figure 4 A comparison diagram of the water contact angles of various plastic wraps.

[0020] Figure 5 This diagram simulates the variation of water contact angle of various plastic wraps under cold chain logistics transportation conditions.

[0021] Figure 6 A comparison chart of water vapor transmission rates for various plastic wraps.

[0022] Figure 7 This is a comparison chart of the gas barrier properties of various plastic wraps; where A is the CO2 transmittance, B is the O2 transmittance, and C is the CO2 / O2 gas selectivity coefficient.

[0023] Figure 8 This is a comparison chart of the moisture content and solubility of various plastic wraps.

[0024] Figure 9 This is a comparison chart of the moisture content and solubility of the plastic wrap used in Example 2 and commercially available plastic wrap.

[0025] Figure 10 A visual comparison of the transparency of various plastic wraps.

[0026] Figure 11 A comparison chart of the light transmittance (A) and opacity (B) of various plastic wraps.

[0027] Figure 12 The images show the degradation experiment of the plastic wrap in the soil environment in Example 2.

[0028] Figure 13 Statistical and visual diagrams of plant growth height in pot experiments on soil degradation.

[0029] Figure 14 Curcumin release rate curves of the preservation film in Example 2 under different temperature and pH conditions.

[0030] Figure 15 This is to demonstrate the antioxidant properties of the plastic wrap in Example 2.

[0031] Figure 16 Representative photos of various plastic wraps were taken to simulate the cold chain logistics process of button mushrooms (after being placed at 4°C for 2 days, and then at 25°C for 4 days).

[0032] Figure 17 The curves showing the changes in surface color difference L value (brightness) of Agaricus bisporus (A), surface color difference a value (B), and surface color difference b value (C) are shown.

[0033] Figure 18 The curves showing the changes in titratable acidity (A), soluble solids (B), and hardness (C) of Agaricus bisporus are shown.

[0034] Figure 19 The graph shows the correlation analysis of the weight loss rate of Agaricus bisporus. Detailed Implementation

[0035] The materials used in this invention are as follows: Chitosan was purchased from Shanghai Maokang Biotechnology Co., Ltd. Curcumin was purchased from Beijing Bailingwei Technology Co., Ltd. Tween 80, sorbitan oleate (Sban 80), and calcium chloride were purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Pentylene glycol, ethyl acetate, and anhydrous ethanol were purchased from Sinopharm Chemical Reagent Co., Ltd. Okra, button mushrooms, strawberries, mangoes, bananas, and avocados were all purchased from Chengyang Agricultural Market. Cellulose nanofiber (CNF) dispersion (1.0 wt%, water as solvent) was purchased from Guilin Qihong Technology Co., Ltd. (diameter 4~20 nm, length 1000~3000 nm, crystal structure type I cellulose). Sodium carboxymethyl cellulose (CMC-Na) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd. (viscosity 5000~15000 mPa·s, USP grade).

[0036] In this invention, okra mucilage is a natural polysaccharide matrix, rich in soluble dietary fiber such as pectin, and is widely available, making it suitable as a primary film-forming matrix. Chitosan itself is a natural antibacterial polymer with inhibitory effects on various microorganisms. By preparing it into porous microspheres and embedding curcumin within them, it not only mimics the slow-release protective effect of plant secondary metabolites but also possesses excellent gas regulation and water vapor barrier properties.

[0037] Curcumin molecules are loaded into the mesoporous network structure of chitosan porous microspheres. The release of curcumin requires overcoming the binding forces such as electrostatic interactions and hydrogen bonds within the microspheres, as well as the physical barriers formed by the polysaccharide matrix, to achieve its gradual release. This sustained-release design mimics the sustained protective effect of plant secondary metabolites, maintaining effective antioxidant and antibacterial activity concentrations over a longer time window, thus achieving long-term food preservation.

[0038] In this invention, okra mucilage is prepared by the following method: Select fresh okra pods or flowers, wash them thoroughly, and set aside. Slice or crush the okra pods, or crush the okra flowers, and soak them in distilled water at a ratio of 1:2 (distilled water to okra pods or flowers). The soaking temperature should be 90℃, and the soaking time should be 4 hours. Stir constantly during soaking at a speed of 100 rpm. Then, fold a 10cm × 5cm sterile degreased gauze in half, place an appropriate amount of soaked okra inside, and squeeze firmly to separate the solid and liquid. Centrifuge the liquid at 12000 rpm and 4℃. After centrifugation, collect the supernatant to obtain okra mucilage.

[0039] The okra mucilage used in the following experiments of this invention is prepared from okra pods.

[0040] In this invention, the chitosan porous microspheres are prepared by the following method: Chitosan was dissolved in a 3% (v / v) acetic acid solution to prepare a 1% (w / w) chitosan acetic acid solution. The specific preparation method is as follows: 3% acetic acid solution preparation: 3 mL glacial acetic acid, 97 mL water; 1% chitosan acetic acid solution preparation: 1 g chitosan, 99 g aqueous acetic acid solution, removing undissolved chitosan and impurities.

[0041] Take 15 mL of chitosan acetate solution, add 0.1 g of emulsifier Tween 80 and 5 mL of ethyl acetate, mechanically stir and sonicate for 5 min to ensure uniform emulsification. Then, under stirring at 560 rpm, add 4.5 mL of emulsifier Span 80 and 225 mL of liquid paraffin. After uniform emulsification, add 0.4 mL of glutaraldehyde (diluted to 5 mL with 1,4-dioxane) (dilution is beneficial for spheroidization and better dispersibility due to the strong nature of glutaraldehyde). The crosslinking reaction is carried out at room temperature for 5 h. The mixture is then heated to 50 °C in a water bath and the reaction is continued for 5 h to allow the ethyl acetate in the inner oil phase to evaporate as completely as possible. After the reaction is complete, centrifuge at 4000 rpm for 6 min, discard the upper oil phase, and wash three times with petroleum ether. After natural drying, chitosan porous microspheres (PCMs) are obtained.

[0042] In this invention, the chitosan porous microspheres loaded with curcumin are prepared by the following method: Chitosan was dissolved in a 3% (v / v) acetic acid solution to prepare a 1% (w / w) chitosan acetic acid solution. The specific preparation method is as follows: 3% acetic acid solution preparation: 3 mL glacial acetic acid, 97 mL water; 1% chitosan acetic acid solution preparation: 1 g chitosan, 99 g aqueous acetic acid solution, removing undissolved chitosan and impurities.

[0043] 30 mg of curcumin was dissolved in 5 mL of ethyl acetate. 0.1 g of emulsifier Tween 80 and 15 mL of chitosan acetate solution were added. The mixture was mechanically stirred and ultrasonically emulsified for 5 min to ensure homogeneity. Then, under stirring at 560 rpm, 4.5 mL of emulsifier Span 80 and 225 mL of liquid paraffin were added. After homogeneity, 0.4 mL of glutaraldehyde (diluted to 5 mL with 1,4-dioxane) was added (because glutaraldehyde is too potent, dilution promotes spheroidization and better dispersibility). The crosslinking reaction was carried out at room temperature for 5 h. The mixture was then heated to 50 °C in a water bath and the reaction was continued for 5 h to allow the ethyl acetate in the inner oil phase to evaporate as completely as possible. After the reaction was complete, the mixture was centrifuged at 4000 rpm for 6 min, the upper oil phase was discarded, and the mixture was washed three times with petroleum ether. After natural drying, chitosan porous microspheres loaded with curcumin (Cur-PCMs) were obtained.

[0044] I. Scanning Electron Microscope Image In this invention, chitosan porous microspheres (PCMs) are the core functional component of the food preservation film system. To reveal their morphology and structural characteristics, the microsphere powder was directly sprinkled onto a silicon wafer with double-sided adhesive using a scanning electron microscope (SEM). After fixing the silicon wafer with conductive adhesive and sputtering gold for 120 seconds, the surface morphology of the chitosan microspheres was observed using a scanning electron microscope.

[0045] Test results are as follows Figure 1 As shown: Chitosan porous microspheres (PCMs) exhibit a regular and complete spherical geometry, with no obvious aggregation between microspheres. Under high magnification, the surface of PCMs is not smooth and dense, but rather features a highly developed, interconnected network of wrinkles and porous structures. This rough and porous surface feature greatly increases the specific surface area of ​​the microspheres, providing abundant physical attachment sites for their tight cross-linking with the cling film substrate. More importantly, it provides ample physical space for the large-scale adsorption of curcumin (Cur). Furthermore, this "sponge-like" microstructure provides sufficient physical space reserves for the controlled and sustained release of Curcumin.

[0046] II. Particle size, pore size and thermodynamic characteristics Besides microstructure, the particle size of microspheres directly affects their dispersion uniformity in composite films and their ability to regulate the diffusion path of gas molecules.

[0047] The particle size distribution of the microspheres was automatically analyzed using an S3500 laser particle size analyzer (manufacturer: Microtrac, USA). After drying at 50 °C for 6 h, the pore structure of PCMs and Cur-PCMs was measured using an AutoPore IV 9500 mercury porosimetry analyzer (manufacturer: Micromeritics, USA). After vacuum degassing and activation at 80 °C for 12 h, the nitrogen adsorption and desorption isotherms of Cur-PCMs at 77 K were determined using a surface area analyzer (manufacturer: BELSORPmax, Japan).

[0048] Test results are as follows Figure 2 As shown: From the distribution of PCMs ( Figure 2 A) It can be seen that the size distribution of the microspheres exhibits a typical unimodal distribution characteristic, indicating that the microsphere system has good size uniformity and dispersion stability. It is worth noting that by comparing the median diameter (D50) before and after loading Cur, it was found that... Figure 2 (B) The D50 of the PCMs before loading was 42.3 μm; however, after successful loading of curcumin, the D50 of Cur-PCMs significantly increased to 50.1 μm. This moderate expansion of particle size indirectly proves that Cur has successfully entered and occupied the internal pores of the PCMs or firmly adhered to their surface, and the intercalation of guest molecules leads to a certain degree of physical expansion of the polymer microsphere framework. Furthermore, the pore size distribution of the PCMs before and after Cur loading was measured, such as... Figure 2As shown in Figure D, the curves reveal that the internal pore size distribution of PCMs ranges from 4 to 6 nm, while the pore size of Cur-PCMs is mainly concentrated in the range of 2 to 4 nm. This mesoporous pore size (2–4 nm) not only enables efficient physical encapsulation of the small-molecule hydrophobic antibacterial agent (curcumin), but also effectively limits the "burst release" phenomenon of curcumin in the initial contact with high humidity environments through capillary condensation and steric hindrance, thus endowing the microsphere system with long-term and stable antibacterial release efficacy. Furthermore, its pore thermodynamic characteristics were further characterized through nitrogen adsorption-desorption experiments at 77 K, such as… Figure 2 As shown in Figure C, the adsorption-desorption isotherms of Cur-PCMs exhibit typical type IV isotherm characteristics, accompanied by a significant hysteresis loop in the region of higher relative pressure. This classic mesoporous physicochemical behavior confirms the existence of a permeable mesoporous network within the microspheres.

[0049] Other materials used in this invention, unless otherwise stated, are commercially available. Other terms used in this invention, unless otherwise specified, generally have the meanings commonly understood by those skilled in the art. The invention is further described in detail below with reference to specific embodiments and data. The following embodiments are merely illustrative and not intended to limit the scope of the invention in any way.

[0050] Example 1

[0051] The steps for preparing OM-Cur-PCMs thin films are as follows: Add 136 g of okra mucilage to a beaker, then add 136 mL of deionized water and stir magnetically for 30 min at room temperature until homogeneous. Add 8 g of glycerol and stir until completely compatible, then add 1.36 g of CNF dispersion (1.0 wt%, water solvent) and stir until the system is homogeneous. Slowly add 24 mL of sodium carboxymethyl cellulose (CMC-Na) solution (2.0 wt%, water solvent) and continue stirring at room temperature for 40 min. Slowly add 2.68 mL of calcium chloride solution (5.0 wt%, water solvent) and stir to form a cross-linked structure. Then add 7.5 mg of chitosan porous microspheres loaded with curcumin (Cur-PCMs) and stir until homogeneous. After degassing the mixture, cast it into an A4-sized glass mold and dry it in a 50°C oven to form a peelable nanocomposite food preservation film, namely OM-Cur-PCMs film.

[0052] Example 2

[0053] The steps for preparing OM-Cur-PCMs thin films are as follows: Add 136 g of okra mucilage to a beaker, then add 136 mL of deionized water and stir magnetically for 30 min at room temperature until homogeneous. Add 8 g of glycerol and stir until completely compatible. Then add 1.36 g of CNF dispersion (1.0 wt%, water solvent) and stir until the system is homogeneous. Slowly add 24 mL of sodium carboxymethyl cellulose (CMC-Na) solution (2.0 wt%, water solvent) and continue stirring at room temperature for 40 min. Slowly add 2.68 mL of calcium chloride solution (5.0 wt%, water solvent) and stir to form a cross-linked structure. Then add 17.5 mg of chitosan porous microspheres loaded with curcumin (Cur-PCMs) and stir until homogeneous. After degassing the mixture, cast it into an A4-sized glass mold and dry it in a 50°C oven to form a peelable nanocomposite food preservation film, namely OM-Cur-PCMs film.

[0054] Example 3

[0055] The steps for preparing OM-Cur-PCMs thin films are as follows: Add 136 g of okra mucilage to a beaker, then add 136 mL of deionized water and stir magnetically for 30 min at room temperature until homogeneous. Add 8 g of glycerol and stir until completely compatible, then add 1.36 g of CNF dispersion (1.0 wt%, water solvent) and stir until homogeneous. Slowly add 24 mL of sodium carboxymethyl cellulose (CMC-Na) solution (2.0 wt%, water solvent) and continue stirring at room temperature for 40 min. Slowly add 2.68 mL of calcium chloride solution (5.0 wt%, water solvent) and stir to form a cross-linked structure. Then add 27.5 mg of chitosan porous microspheres loaded with curcumin (Cur-PCMs) and stir until homogeneous. After degassing the mixture, cast it into an A4-sized glass mold and dry it in a 50°C oven to form a peelable nanocomposite food preservation film, namely OM-Cur-PCMs film.

[0056] Comparative Example 1 The steps for preparing the OM membrane are as follows: Add 136 g of okra mucilage to a beaker, then add 136 mL of deionized water and stir magnetically for 30 min at room temperature until well mixed. Add 8 g of glycerol and stir until completely compatible, then add 1.36 g of CNF dispersion (1.0 wt%, water solvent) and stir until the system is homogeneous. Slowly add 2.68 mL of calcium chloride aqueous solution (5.0 wt%, water solvent) and stir to form a cross-linked structure. After degassing the mixture, cast it into an A4-sized glass mold and dry it in a 50°C oven to form a peelable nanocomposite food preservation film, i.e., OM film.

[0057] Comparative Example 2 The steps for preparing the OM-CMC membrane are as follows: Add 136 g of okra mucilage to a beaker, then add 136 mL of deionized water and stir magnetically for 30 min at room temperature until well mixed. Add 8 g of glycerol and stir until completely compatible, then add 1.36 g of CNF dispersion (1.0 wt%, water solvent) and stir until the system is homogeneous. Slowly add 24 mL of sodium carboxymethyl cellulose (CMC-Na) solution (2.0 wt%, water solvent) and continue stirring at room temperature for 40 min. Slowly add 2.68 mL of calcium chloride solution (5.0 wt%, water solvent) and stir to form a cross-linked structure. After degassing the mixture, cast it into an A4-sized glass mold and dry it in a 50℃ oven to form a peelable nanocomposite food preservation film, namely OM-CMC film.

[0058] III. Crystal phase, chemical structure and thermal stability The long-lasting preservation function of composite membranes depends not only on the chemical properties of each component, but also on the molecular-scale interactions between components and the resulting hierarchical structure. The crystal phase, chemical interactions, and thermodynamic stability of OM membranes, OM-CMC membranes, and OM-Cur-PCMs membranes (Example 2) were systematically characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA / DTG).

[0059] The crystal structure of the samples was analyzed using a Bruker D8 ADVANCE X-ray diffractometer (Bruker GmbH, Germany). The instrument was equipped with a Cu Kα radiation source (λ = 0.154 nm), operating at 40 kV and 40 mA. Scanning was performed in θ / θ mode, with a 2θ range of 5–80° (covering all characteristic peak regions), a step size of 0.02, and a dwell time of 2 s. Thermogravimetric analysis (TGA) was performed using a Mettler Toledo thermogravimetric analyzer (model: TGA103030247) to evaluate the thermal degradation behavior of the samples in the range of 20–600°C. The test conditions were as follows: heating rate of 25°C / min, air atmosphere, and flow rate of 50 mL / min. Data were acquired using the instrument's STARe software, and derivative thermogravimetric (DTG) curves were obtained by differentiating the TG curves using the software. Fourier transform infrared (FTIR) spectra of each sample were measured using a Fourier transform infrared spectrometer, with a scanning range of 500–4000 cm⁻¹. -1 The resolution is 4 cm. -1 The number of scans was 64. Different samples (OM membrane, OM-CMC membrane, OM-Cur-PCMs membrane) were characterized.

[0060] Test results are as follows Figure 3 As shown: Figure 3A shows the X-ray diffraction patterns of three different membrane formulations to analyze the effect of each component introduction on the membrane crystal structure. The OM membrane exhibits distinct diffraction peaks at approximately 16.7° and 22.7° at 2θ, mainly attributed to the typical crystalline structure of nanofibers (CNFs) in the okra natural polysaccharide network, providing a rigid framework support for the membrane matrix. Upon addition of CMC-Na, the XRD pattern of the OM-CMC membrane changed significantly. As a cellulose derivative, the carboxymethyl substituents introduced into the CMC-Na molecular chain disrupt the original regular crystalline arrangement of cellulose, leading to a significant decrease in crystallinity. Specifically, the sharp diffraction peaks originally located at 16.7° and 22.7° disappeared, and a broad and weak diffuse peak appeared near 2θ ≈ 20°, exhibiting typical amorphous characteristics. After introducing curcumin-loaded chitosan porous microspheres (Cur-PCMs) into the OM-CMC matrix, a new diffraction peak appeared at 12.1°, which is attributed to the characteristic crystalline peak of chitosan, thus confirming the successful introduction of the chitosan porous microspheres. It is noteworthy that curcumin, as the active ingredient loaded in the chitosan porous microspheres, exhibits multiple strong characteristic diffraction peaks in its bulk crystalline state (located at 2θ ≈ 8.9°, 12.2°, 14.5°, and 17.2°, respectively). However, due to the low amount of PCMs added and the fact that curcumin is encapsulated within the porous network structure of the microspheres, its diffraction signal may be extremely weak, making it difficult to clearly identify in XRD detection. This indirectly suggests that curcumin may exist in the microspheres in a partially amorphous or highly dispersed microcrystalline form, which is beneficial for its subsequent sustained-release behavior.

[0061] FTIR spectroscopy further confirmed the compatibility mechanism between the above components at the chemical bond level. Figure 3 B). Of all membrane samples, 3330 cm⁻¹ -1 The strong, broad absorption peak at this point is attributed to the stretching vibrations of the polysaccharide backbone (cellulose, okra mucilage), glycerol, and the large number of hydroxyl (OH) groups in the residual water. Compared to the OM membrane, the composite membrane exhibits a significant broadening and even a slight wavenumber shift in its absorption peak at this point, which precisely demonstrates the formation of a dense intermolecular hydrogen bond network within the system. Furthermore, at 2890 cm⁻¹... -1 CH stretching vibration peak at 1025~1050 cm⁻¹ -1 The characteristic fingerprint peaks at the 895 cm⁻¹ site, which are attributed to the polysaccharide COC and COH backbones, are also present. -1 The characteristic absorption peak of the β-glycosidic bond of cellulose was stably present in all three formulations without significant peak splitting. This indicates that the incorporation of CMC-Na and the construction of the cross-linked network of Cur-PCMs did not disrupt the basic molecular skeleton of okra polysaccharide and cellulose; the three formed a homogeneous and stable composite system through abundant hydrogen bonding.

[0062] Thermal stability is a key indicator for evaluating the practicality of food preservation materials. Figure 3 The TGA curves of C show that all membrane samples exhibit a typical three-stage mass loss process, indicating that the membrane material has reasonable thermal stability. The first stage, from room temperature to 150°C, involves the evaporation of free and bound water; the second stage, at 200–350°C, is the main chain thermal decomposition stage, involving violent reactions such as glycosidic bond breaking, dehydration, and decarboxylation; the third stage (>400°C) involves further carbonization of residual organic matter and thermal decomposition of inorganic components. It is noteworthy that in the DTG curves ( Figure 3 (D) The maximum thermal degradation rate temperature (Tmax) of the OM film is relatively low, while the Tmax of the OM-Cur-PCMs composite film with added CMC-Na and PCMs shifts significantly towards higher temperatures. This indicates that, on the one hand, CMC-Na and PCMs have high inherent thermal resistance; on the other hand, the dense intermolecular cross-linked network confirmed by the FTIR restricts the thermal movement of polymer chain segments. This excellent thermal resistance ensures that the food preservation film maintains its structural and performance integrity in different transportation environments.

[0063] IV. Surface wettability, water vapor transmission rate and gas selective barrier properties Surface hydrophilicity / hydrophobicity and barrier properties are important parameters that determine the preservation efficiency of packaging materials in cold chain logistics. Good hydrophobicity can effectively resist the invasion of external liquid water and the accumulation of condensate during refrigeration, maintaining the stability of the internal microenvironment of the packaging.

[0064] 1. Surface wettability The wettability of the thin film surface was evaluated by static water contact angle (WCA) testing. The wettability of OM-Cur-PCMs was characterized using an optical contact angle meter (model: DSA100S, Krüger GmbH, Germany). Before testing, the OM-Cur-PCMs samples were cut to appropriate sizes and fixed flat on the sample stage to avoid wrinkles or stretching deformation. Using the optical contact angle meter, the contact angle of deionized water on the sample surface was measured over time at room temperature via the seated drop method. A 5 μL water droplet was placed on the membrane surface, and the contact angle change was continuously recorded from 0 to 18 s (data collected every 3 s). The test environment temperature was room temperature (25 ± 1°C).

[0065] Test results are as follows Figure 4 and Figure 5 As shown: The blank okra-based membrane (OM) exhibited a water cohesion (WCA) of 91.3°, demonstrating inherent weak hydrophilicity, primarily attributed to the abundant free hydroxyl and carboxyl groups on the okra polysaccharide chains. The hydrophobicity of the composite membrane was significantly enhanced after the introduction of PCMs. The WCAs of Examples 1, 2, and 3 increased to 111.0°, 114.7°, and 122.0°, respectively. This reversal of surface wettability was mainly caused by changes in the microstructure. The uniform distribution of microspheres on the membrane surface created micron-level roughness, trapping air pockets and thus promoting the formation of a Cassie-Baxter non-wetting state for water droplets on the surface.

[0066] Furthermore, we placed four different film formulations at 4°C for 4 days, followed by 25°C for 4 days, to simulate the impact of temperature changes on WCA during cold chain logistics transportation. During the 8-day continuous test, although the WCA of all film groups gradually decreased over time and with changes in ambient temperature, the composite film with added PCMs remained consistently within a highly hydrophobic range (>100°C). This excellent resistance to hydration effectively prevents damage to the packaging film structure from exudates from fruits and vegetables or environmental condensation.

[0067] 2. Water vapor transmission rate (WVP) measurement The water vapor permeability of OM-Cur-PCMs samples was determined by gravimetric method. At room temperature (25 ± 1°C), 10 mL of distilled water was added to a 15 mL centrifuge tube. The prepared sample membrane was tightly sealed to the centrifuge tube opening, ensuring no leakage. The centrifuge tube was then placed in a desiccator containing silica gel to maintain a relative humidity close to 0%. The centrifuge tube was weighed every 2 hours for 10 consecutive hours. The measurements were performed in triplicate. The change in mass over time was recorded, and the mass loss due to water vapor permeation per unit time (Δm / t) was calculated. The water vapor permeability (WVP) of the membrane was calculated using the following formula.

[0068] In the formula, ∆m is the mass difference of the sample before and after (g), X is the film thickness (mm), and S is the area of ​​the centrifuge tube opening (cm²). 2 ), t is the time interval (h); ∆P is the saturated vapor pressure of pure water at 25°C, ∆P = 3167 Pa. The WVP unit of OM-Cur-PCMs is g·mm·kPa. -1 ·h -1 ·m 2 The experimental results are expressed as the average of three parallel determinations.

[0069] Test results are as follows Figure 6 As shown: The water vapor transmission rate (WVP) of the membrane increases with the increase of PCMs dosage, and is comparable to that of the OM membrane at 0.11 g mm kPa. -1 h -1 m -2 This contrasts sharply with the extremely low WVP of the plastic wrap. Perishable fruits and vegetables often have extremely high transpiration rates after harvest. If the WVP of the plastic wrap is too low, condensation will form inside the packaging during cold chain logistics. This excessively humid environment will accelerate microbial growth, leading to spoilage of the fruits and vegetables. However, by adding PCMs to the film, it is equivalent to embedding a large number of pores on the film surface, significantly increasing the WVP. This allows the composite film to dynamically balance the humidity within the microenvironment.

[0070] 3. Gas selective barrier properties Oxygen permeability (OP) test: The oxygen transmission rate (OTR) of OM-Cur-PCMs was determined using a gas transmission rate tester. A 25 cm² effective area was cut from the film under test. 2 A circular sample was prepared. High-vacuum silicone grease was evenly applied to the sealed area of ​​the test chamber to prevent gas leakage. The film was placed flat on the lower chamber, and the upper chamber was locked before starting the test. The test conditions were 23 ℃ and 0% RH. The instrument automatically recorded the OTR value after steady-state operation, where d is the film thickness. The oxygen permeability of the film was calculated using the following formula.

[0071] Each sample was tested in triplicate, and the results are expressed as mean ± standard deviation.

[0072] Carbon dioxide transmission rate test: An effective area of ​​25 cm² was cut from the film to be tested. 2 A circular sample was prepared. High-vacuum silicone grease was evenly applied to the sealed area of ​​the test chamber to prevent gas leakage. The film was then placed flat on the lower chamber, and the upper chamber was locked before starting the test. The test conditions were 23 ℃ and 0% RH. During the test, one side of the sample was exposed to high-purity carbon dioxide gas (100% CO2), while the other side was purged with high-purity nitrogen gas. The carbon dioxide that passed through the film was carried by the nitrogen gas to the infrared detector for quantitative detection. The instrument automatically recorded the CO2 TR value after steady-state operation.

[0073] Test results are as follows Figure 7 As shown: Compared to pure OM membranes, the composite membranes containing PCMs show increased absolute permeability for both O2 and CO2, with the increase in CO2 permeability (CP) far exceeding that of O2 permeability (OP). Therefore, the gas selectivity coefficient (S = CP / OP) of the composite membranes exhibits a qualitative leap: the selectivity coefficient of the OM membrane is only about 2.8, while the selectivity coefficients of Examples 2 and 3 soar to approximately 6.8 and 8.2, respectively. This asymmetric gas transport behavior can spontaneously create a dynamic regulated atmosphere microenvironment with low oxygen and moderate carbon dioxide levels inside the packaging, providing strong material support for delaying oxidative decay and physiological maturation of perishable foods.

[0074] V. Analysis of Water Resistance and Optical Properties The interaction between the membrane and water is crucial for assessing its stability, and strong hydrophilicity and poor water resistance are common bottlenecks faced by the vast majority of pure polysaccharide-based films. Furthermore, optical properties not only affect consumers' visual perception but also relate to the photo-oxidative spoilage of food.

[0075] 1. Determination of moisture content and water solubility Moisture content (MC) test: OM-Cur-PCMs were cut into squares (40 × 40 mm) and equilibrated for 7 days at 25°C in a desiccator containing saturated salt solution (K₂SO₄, RH 94.6%). Afterwards, the samples were dried to constant weight in a hair dryer at 105°C. The moisture content (MC) of the samples was calculated using the following formula: In the formula, m0 is the mass of the sample after equilibrium, and m1 is the mass after drying at 105℃.

[0076] Solubility (WS) test: OM-Cur-PCMs were cut into squares (40×40 mm) and equilibrated at 25°C for 48 hours in a desiccator containing silica gel, and then weighed. The samples were then placed in beakers containing 50 mL of deionized water, shaken at 120 rpm for 3 hours, filtered through a 100-mesh filter cloth, and dried to constant weight in a 105°C dryer. The solubility of the samples was calculated using the following formula.

[0077] In the formula, m0 is the mass of the sample after equilibrium, and m1 is the mass after drying at 105℃.

[0078] Test results are as follows Figure 8 As shown: Pure OM membranes exhibit high water content (approximately 22%) and solubility, which is closely related to the abundant hydrophilic groups in their polysaccharide components. After the introduction of PCMs, both the MC and WS of the composite membrane significantly decreased, consistent with the aforementioned surface wettability phenomenon. On one hand, the hydrophobic groups on the PCM surface form a dense network with the polysaccharide chains, blocking a large number of free hydrophilic hydroxyl groups and reducing the water-binding capacity of the membrane; on the other hand, the physical occupancy effect of the microspheres increases the tortuosity of water molecule penetration.

[0079] To highlight the practical value of the food preservation film of this invention, the water resistance of the OM-Cur-PCMs film was compared with that of various commercially available or widely studied bio-based films (sodium alginate, pectin, gelatin, chitosan, etc.). Figure 9 As shown, the composite membrane of this invention exhibits significantly better water resistance than most single-component biopolymer membranes, demonstrating strong commercial competitiveness.

[0080] 2. Optical performance analysis Transparency test: The transparency of OM-Cur-PCMs was visually evaluated using a comparative method. Different membrane samples (CK, Comparative Example 1, Example 1, Example 2, and Example 3) were laid flat on a background with text as a reference and observed and photographed under constant illumination. The transparency of the membrane was qualitatively evaluated based on the clarity of the text and pattern on the background: the clearer the background, the higher the transparency; if the membrane appears opaque or blurry, the transparency is lower.

[0081] Measurement of transmittance: The composite film was cut into 10×40 mm rectangular strips and placed on the smooth side of a cuvette. Using air as a control group, the transmittance of the film was measured in the range of 200–800 nm using a UV spectrophotometer.

[0082] Opacity of the membrane: Measured using a UV-Vis spectrophotometer equipped with an integrating sphere. The film to be tested is cut to a suitable size, and its thickness χ (mm) is accurately measured. The transmittance T of the film is recorded at a specific wavelength (e.g., 550 nm or the entire wavelength range). The opacity μ is calculated using the formula μ = ln(T) / χ, which represents the attenuation of light per unit length propagated in the film, in mm. -1 ).

[0083] Test results are as follows Figure 10 and Figure 11 As shown: The visual transparency of the composite film can be seen from the intuitive text coverage test. The pure OM film has excellent transparency, while the visual transparency of the composite film decreases as the PCM loading increases.

[0084] In the visible light region (400–800 nm), the transmittance of the composite film decreases with increasing microsphere content. However, in Example 2, it remains above 50%, primarily due to light scattering caused by the refractive index difference between the chitosan microspheres and the matrix, a fact confirmed by the opacity data. More importantly, the composite film exhibits very low transmittance in the ultraviolet region (200–400 nm), demonstrating excellent UV blocking capabilities. This natural barrier function effectively prevents photoinduced degradation of vitamins, pigments, and lipids in fruits and vegetables.

[0085] VI. Biodegradability Traditional petroleum-based plastics are extremely difficult to degrade in the natural environment, becoming a heavy burden on global environmental governance. Developing active packaging materials with full biodegradability is an inevitable choice for achieving sustainable agricultural development.

[0086] 1. Soil biodegradation experiment All films were cut into rectangles of a fixed size and placed in pores with a diameter of <0.5mm. 2 The film was placed on a gauze screen. Then, 65 grams of Marine Forest Potting Soil (CA, USA) was added to a 10cm × 10cm square plastic planting pot, and the film was buried 2cm below the soil surface. Samples were stored in a sealed room at 25°C and 30-50% (RH). Every other day, 8 mL of water was gently added to each sample. Weekly, two different films were sampled without replacement and photographed under natural light and a lightbox to measure biodegradation.

[0087] 2. Soil degradation toxicology experiment: Two groups of potted plants were set up: CK and Example 2, with three pots in each group and plants of similar growth in each pot. A circular piece of Example 2 plastic wrap with a diameter of 90 mm was placed at the bottom of the pot in the Example 2 group, while no plastic wrap was placed in the CK group. The potted plants were placed in a suitable environment for cultivation. The height of the exposed plants (cm) was measured on Day 0 and Day 10, and top and side photos were taken to compare the growth differences between the two groups and to conduct a toxicological evaluation.

[0088] Test results are as follows Figure 12 and Figure 13 As shown: Initially, the composite membrane exhibits a complete physical morphology and good flexibility when buried in the soil. By day 5, under the combined effects of soil microorganisms, moisture, and thermal stress, the membrane rapidly undergoes physical degradation, showing obvious cracks and mechanical breakage, losing its original continuous structure. By day 15, the composite membrane in the soil has almost completely disintegrated into fragments, leaving only a small number of indistinct film remnants; most of the material has been decomposed and absorbed by soil microorganisms. This is because OM-Cur-PCMs are composed of okra mucilage natural polysaccharides, cellulose, and chitosan, which can serve as a high-quality carbon source for bacteria and fungi (such as actinomycetes and Aspergillus) in the soil. Microorganisms attack the polysaccharide backbone by secreting extracellular enzymes such as cellulase, chitinase, and pectinase, breaking it down into low-molecular-weight oligosaccharides or monosaccharides, which are ultimately metabolized into carbon dioxide and water through respiration. This phenomenon of complete macroscopic disintegration within just 15 days stands in stark contrast to the fact that commercial PE or PP plastic wrap takes hundreds of years to degrade, fully demonstrating the extremely high bioavailability and degradation potential of OM-Cur-PCMs in the natural environment.

[0089] To eliminate the potential phytotoxicity of degradation products, this invention further conducted a potted plant toxicity verification experiment. A composite preservative film prepared in Example 2 was placed at the bottom of the pots in the experimental group. Comparison of the growth of plants in the control and experimental groups over 10 days revealed no significant difference in plant height between the two groups. Visual examination of the photographs showed that the leaf morphology, stem thickness, and overall growth of the plants in the experimental group did not exhibit any toxic symptoms such as inhibition, yellowing, or deformity. This indicates that the preservative film of this invention has no toxic effects.

[0090] VII. Release Kinetics and Antioxidant Analysis 1. Curcumin release rate determination The in vitro release behavior of OM-Cur-PCMs (Example 2) was investigated using centrifugation. Approximately 10 mg of drug-loaded microspheres were weighed into a centrifuge tube, and 5 mL of release medium (PBS with pH 7.4 or pH 6.0 containing 0.5% Tween-80) was added. The tubes were incubated at 4°C and 25°C with constant shaking (100 rpm). Samples were taken at preset time points (0–192 h), centrifuged at 8000 rpm for 5 min, and 2 mL of the supernatant was collected. An equal volume of fresh medium was added at the same temperature. The absorbance of the supernatant was measured at 425 nm, and the cumulative release rate was calculated. Each experiment was repeated three times. The curcumin release rate was calculated using the following formula: Where Ci is the concentration of curcumin in the release medium at the i-th sampling (μg / mL), V0 is the initial release medium volume, Vs is the sampling volume each time (2 mL), and m is the total curcumin loading in the microspheres (μg).

[0091] The test results are as follows Figure 14 As shown: During the 192-hour testing period, none of the groups exhibited a "burst release effect," but rather a stable "slow release" phase, eventually reaching a plateau of "complete release." This indicates that OM-Cur-PCMs possess the potential for long-lasting sustained release. Notably, OM-Cur-PCMs displayed significant pH- and temperature-dependent release characteristics. Regarding pH, the release rate was consistently higher in a neutral environment (pH 7.4) than in a slightly acidic environment (pH 6.0). This phenomenon may be because under neutral or slightly alkaline conditions, the polysaccharide network undergoes deprotonation, leading to increased electrostatic repulsion between molecular chains and network swelling, thereby opening diffusion channels for curcumin. At pH 6.0, however, hydrogen bonds are more tightly bound, inhibiting diffusion. Since the surface of fresh fruits and vegetables is typically slightly acidic, the initial release of curcumin is relatively controlled, which is beneficial for exerting a more prolonged protective effect under neutral or low-acid food or environmental conditions. Regarding temperature, the release rate at room temperature (25℃) is higher than that under refrigeration (4℃). This is attributed to the fact that the low temperature significantly reduces the free volume of polymer segments and the thermal kinetic energy of curcumin molecules, limiting their outward diffusion. This intelligent response characteristic—slow release under refrigeration (4℃, corresponding to a real cold chain environment) and moderate release at room temperature (when fruits and vegetables are displayed after being taken out of storage)—better meets the dynamic needs of perishable foods for preservatives at different logistics stages. This sustained release capability endows the composite film with excellent and long-lasting antioxidant properties.

[0092] 2. Calculation of free radical scavenging rate DPPH: Weigh a certain amount of OM-Cur-PCMs sample, cut it into small pieces, add anhydrous ethanol, and extract by sonication for 30 min at room temperature. After centrifugation, take the supernatant as the test solution. Prepare DPPH solution and ABTS solution and store them in the dark. Mix 2 mL of DPPH solution or ABTS solution with 2 mL of the test solution, react at room temperature in the dark for 30 min, and measure the absorbance at 517 nm and 734 nm, respectively. Calculate the DPPH / ABTS radical scavenging rate (%) according to formula (10).

[0093] A0 and A1 refer to the absorbance of the blank control and the sample, respectively. The experiment was repeated three times, and the average value was taken.

[0094] The test results are as follows Figure 15 As shown: Thanks to the presence of curcumin, a natural polyphenol compound with multiple phenolic hydroxyl groups in its molecular structure, it can donate hydrogen atoms to free radicals through the hydrogen atom transfer (HAT) mechanism, effectively terminating free radical chain reactions and thus exhibiting excellent antioxidant activity. The sustained-release effect of PCMs ensures the continuous release of curcumin over a longer period, enabling OM-Cur-PCMs to maintain stable antioxidant capacity throughout the entire shelf life, effectively inhibiting lipid oxidation and enzymatic browning reactions on the food surface.

[0095] VIII. Evaluation of Preservation Effect Button mushrooms (Agaricus bisporus) have extremely high water content and lack a protective epidermal structure, making them very susceptible to moisture loss, tissue softening, surface browning, and microbial infection after harvesting. These problems result in an extremely short shelf life.

[0096] After being harvested, packed, and covered with film, button mushrooms first undergo post-harvest cold storage at 4°C and low-temperature transportation, and then are transferred to a 25°C environment for sale and home storage. This logistics model with temperature fluctuations is more practically challenging than single constant-temperature storage.

[0097] To verify the preservation effect of the OM-Cur-PCMs of this invention, continuous storage experiments were conducted on button mushrooms at 4℃ and 25℃, following the model described above, and relevant indicators were tested. The storage time at each temperature environment was flexibly adjusted according to the characteristics of the fruits and vegetables, and groups with commercial polyethylene preservation film (PE), uncovered film (Control), and Example 2 were set up.

[0098] Color difference test: The L*, a*, and b* values ​​of *Agaricus bisporus* samples in the OM-Cur-PCMs cold chain logistics simulation experiment were determined using a colorimeter. The measurements were performed in triplicate, and the results are expressed as mean ± standard deviation. L* represents lightness (0–100, black to white), a* represents red-green value (positive value is red, negative value is green), and b* represents yellow-blue value (positive value is yellow, negative value is blue).

[0099] Titratable acid content: The determination was performed according to GB / T 12456-2008. Weigh 5.00 g of thoroughly homogenized *Agaricus bisporus* sample, dilute to 100 mL with carbon dioxide-free distilled water, shake well, and filter. Accurately pipette 20.0 mL of the filtrate into an Erlenmeyer flask, add 2-3 drops of 1% phenolphthalein indicator, and titrate with 0.05 mol / L NaOH standard solution until a faint red color appears and persists for 30 seconds. Record the volume of NaOH. A blank control was also performed. The titratable acid content is expressed as the mass fraction (%) of the main organic acid (malic acid in *Agaricus bisporus*).

[0100] Determination of soluble solids content (TSS): The determination was performed according to the refractometer method for the determination of soluble solids content in fruits and vegetables, as per NY / T 2637-2014. A handheld refractometer was used, and the zero point was calibrated with distilled water before measurement (zeroing was performed at 20℃; if the temperature changed, the calibration table should be consulted). 2-3 drops of the sample solution were added to the prism surface, and the reading was taken at room temperature. The measurement was repeated three times, and the average value was taken as the soluble solids content of the sample. The result was expressed as a percentage (%).

[0101] hardness: Three uniformly sized button mushrooms without mechanical damage were selected. Puncture or compression tests were performed using a texture analyzer.

[0102] Determination of weight loss rate: The weight loss rate of the samples was determined by weighing. Several uniformly sized, undamaged, and uniformly mature Agaricus bisporus (at least three fruiting bodies) were selected. The initial mass (W0) was measured at the beginning of storage (day 0), and the immediate mass (W0) was measured every 2 days during storage using an electronic balance. t The weight loss rate (W) is calculated using the following formula: Each treatment was measured three times, and the results are expressed as mean ± standard deviation.

[0103] The test results are as follows Figures 16-19 As shown: Color and appearance are the most critical indicators that determine the commercial value of button mushrooms. Figure 16 Representative photographs of button mushrooms from the Example 2 group, PE group, and Control group are shown from day 0 to day 6 of storage. The Control group exhibited the most rapid and severe browning, with obvious browning, surface wrinkling, and edge cracking appearing on the surface as early as day 2. Cross-sections showed that the flesh tissue had softened and discolored significantly, rendering it unmarketable. While the PE film has some water retention, it lacks air permeability regulation, leading to condensation on the inner wall, accelerating microbial growth and spoilage. Browning appeared on the surface of the button mushroom caps, and cross-sections showed that the internal tissue had turned black. The button mushrooms in the Example 2 group maintained a white cap color and smooth surface throughout the storage period, without significant browning or softening. Cross-sections on day 6 showed that the flesh tissue remained firm and dense, with minimal difference from fresh samples. This phenomenon was precisely quantified by colorimetric indicators, such as... Figure 17 As shown, during the entire storage period, the brightness (L value) of Group 2 was significantly higher than the other two groups, and the decrease was the slowest, indicating that OM-Cur-PCMs had the most significant inhibitory effect on browning of the surface of Agaricus bisporus. The a value, representing red-green deviation, and the b value, representing yellow-blue deviation, showed the smallest increase, further confirming the effective inhibition of browning reaction by OM-Cur-PCMs.

[0104] Postharvest spoilage of fruits and vegetables is often accompanied by the loss of a large amount of nutrients. For example... Figure 18 As shown, the contents of titratable acid (TA) and soluble solids (SSC) in *Agaricus bisporus* decreased with prolonged storage time, due to their continuous consumption as substrates for respiration. The packaging group in Example 2 significantly slowed the rate of decrease in TA and SSC. This indicates that OM-Cur-PCMs can effectively suppress the peak respiratory metabolism of *Agaricus bisporus*, and the slow release of curcumin within the membrane may inhibit the metabolism of postharvest pathogens, thereby reducing the additional energy consumption of *Agaricus bisporus*.

[0105] The hardness of the Control group showed a sharp decline within 6 days, while the Example 2 group maintained high hardness at the end of the logistics cycle, significantly better than the PE and Control groups. The reason for this is that OM-Cur-PCMs effectively delayed cell wall degradation by maintaining a low O2 microenvironment, exhibiting the strongest hardness retention ability. More importantly, after 6 days of fluctuating temperature storage, such as... Figure 19 As shown, the weight loss rate of button mushrooms in Example 2 was much lower than that in the Control group, and even better than that in the PE film group, achieving an excellent dynamic balance between preventing water loss from fruit pulp transpiration and reducing condensation inside the packaging.

[0106] As can be seen from the above analysis, during the storage process, the OM-Cur-PCMs composite preservation film can dynamically regulate the gas exchange of the internal microenvironment of the packaging, effectively block the invasion of external microorganisms, and balance the concentration of O2, CO2 and H2O inside the packaging, thus playing a typical modified atmosphere packaging effect.

[0107] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A biodegradable nanocomposite food preservation film with antibacterial and gas-regulating effects, characterized in that, The nanocomposite food preservation film is prepared by the following method: Water, glycerol, cellulose nanofiber dispersion, sodium carboxymethyl cellulose solution, and calcium chloride solution were added sequentially to okra mucilage and stirred until homogeneous. Then, chitosan porous microspheres loaded with curcumin were added and stirred until homogeneous. After degassing the mixture, it was cast into a mold and dried in an oven to form a peelable nanocomposite preservation film.

2. The nanocomposite food preservation film according to claim 1, characterized in that, The amounts of each component are as follows: okra mucilage 100-150 g, water 100-150 mL, glycerin 5-10 g, cellulose nanofiber dispersion 1-2 g, sodium carboxymethyl cellulose solution 20-30 mL, calcium chloride solution 1-5 mL, and chitosan porous microspheres loaded with curcumin 5-50 mg.

3. The nanocomposite food preservation film according to claim 1, characterized in that, The concentration of the cellulose nanofiber dispersion is 0.5-2 wt%, the concentration of the sodium carboxymethyl cellulose solution is 1-5 wt%, and the concentration of the calcium chloride solution is 1-10 wt%.

4. The nanocomposite food preservation film according to claim 1, characterized in that, The okra mucilage is prepared by the following method: Select fresh okra pods or flowers, wash them thoroughly, crush them, add water, and soak them; stir constantly while soaking; then fold a sterile degreased gauze in half, put the soaked okra pods or flowers in, squeeze them hard to separate the solid and liquid, take the liquid and centrifuge it, and take the supernatant after centrifugation to obtain okra mucilage.

5. The nanocomposite food preservation film according to claim 4, characterized in that, The mass ratio of water to okra pods or okra flowers is 1:(1~3).

6. The nanocomposite food preservation film according to claim 4, characterized in that, The soaking conditions are: soaking at 80~100 ℃ for 3~5 h.

7. The nanocomposite food preservation film according to claim 1, characterized in that, The chitosan porous microspheres loaded with curcumin were prepared by the following method: Curcumin was dissolved in ethyl acetate, and Tween 80 and chitosan acetate solution were added. The mixture was stirred and ultrasonically emulsified for 5-10 minutes to ensure uniform emulsification. Then, under stirring, Span 80 and liquid paraffin were added. After uniform emulsification, glutaraldehyde was added, and the crosslinking reaction was carried out for 5-10 hours. The reaction was continued for 5-10 hours under a water bath at 40-60°C. After the reaction was completed, the mixture was centrifuged, the upper oil phase was discarded, and the mixture was washed with petroleum ether. After natural drying, chitosan porous microspheres loaded with curcumin were obtained.

8. The nanocomposite food preservation film according to claim 7, characterized in that, The amounts of each component are as follows: curcumin 10-50 mg, ethyl acetate 5-10 mL, Tween 80 0.05-0.2 g, chitosan acetate solution 10-20 mL, Span 80 2-10 mL, liquid paraffin 200-300 mL, and glutaraldehyde 0.1-1 mL.

9. The nanocomposite food preservation film according to claim 8, characterized in that, The concentration of the chitosan acetate solution is 0.5~2 wt%.

10. The application of the nanocomposite preservation film according to any one of claims 1 to 9 in food preservation.

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