Konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid, and preparation method and application thereof

Abstract

The application discloses a konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid, a preparation method and application thereof, and belongs to the technical field of aerogel material preparation. A cobalt acetate solution and a copper acetate solution are added to a trimesic acid solution, and after stirring and reaction, the CuCo-MOF is obtained through washing and vacuum drying; after the konjac glucomannan solution, the carboxymethyl chitosan solution and glycerol are uniformly mixed and stirred, the mixed solution is obtained; the CuCo-MOF dispersion liquid obtained by ultrasonic dispersion of the CuCo-MOF in anhydrous ethanol and a gallic acid solution are sequentially added to the mixed solution and uniformly stirred, and the konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid is obtained through standing and freeze-drying. The ethylene adsorption of the composite aerogel reaches 10.67 mg / m 3 / h, the ABTS clearance rate reaches 93.84%, the antibacterial rate is close to 100%, the humidity response can release GA, the composite aerogel can be used for strawberry preservation, the weight loss rate is only 1.81%, and the shelf life is significantly prolonged.

Description

Technical Field

[0001] This invention belongs to the field of aerogel material preparation technology, specifically relating to a konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid, its preparation method, and its application. Background Technology

[0002] Delicate and perishable fruits and vegetables, such as strawberries, blueberries, and cherries, are highly susceptible to mechanical damage and microbial contamination during postharvest logistics due to their fragile tissues and high water content, resulting in significant losses (Liu F, Kuai L, Lin C, et al. Respiration-triggered release of cinnamaldehyde from a biomolecular schiffbase composite for preservation of perishable food [J]. Advanced Science, 2024, 11(9): 2306056.). Currently, commercial preservation mainly relies on cold chain logistics and traditional plastic films (such as PE films). However, these passive packaging methods cannot provide sufficient mechanical cushioning, nor can they actively remove the ethylene gas and excessive condensate that accumulate inside the packaging. This makes it easy to induce secondary microbial outbreaks in the packaging microenvironment (Cocetta G, Natalini A. Ethylene: Management and breeding for postharvest quality invegetable crops. A review [J]. Frontiers in Plant Science, 2022, 13:968315.).

[0003] Building upon the successful construction of a two-dimensional basic food preservation film system, this paper aims to further overcome the limitations of traditional films in terms of physical cushioning and achieve morphological innovation in material structure. Aerogels, as an advanced solid material with extremely high porosity, ultra-low density, and a continuous three-dimensional porous network, have shown great potential in the food packaging field in recent years. Compared with traditional two-dimensional films, the unique honeycomb skeleton of aerogels not only provides excellent mechanical cushioning protection for delicate fruits and vegetables, but its rich internal three-dimensional channels also provide ample microscopic space for moisture regulation and the adsorption / release of active gases (Chen C, Zhang Y, Cui H, et al. Aerogels in active packaging for food preservation: A comprehensive review of applications [J]. Trends in Food Science & Technology, 2026, 169: 105549.). Konjac glucomannan (KGM) and carboxymethyl chitosan (CMCS), as two abundant and highly biocompatible natural polysaccharides, provide a physicochemical basis for gelation and cross-linking due to the large number of hydroxyl, carboxyl, and amino groups on their molecular chains (Pan Z, Zhong W, Xu J, et al. Effects of oregano essentialoil pickering emulsion and zno nanoparticles on the properties and antibacterial activity of konjac glucomannan / carboxymethyl chitosannano composite films [J]. RSC Advances, 2024, 14(10): 6548-56.). However, pure KGM / CMCS (KC) aerogels often suffer from insufficient mechanical strength, poor water resistance, and lack of intrinsic antibacterial activity.

[0004] Therefore, there is an urgent need to develop an active preservation packaging material that can take into account mechanical protection, microenvironment humidity control, and targeted removal of ethylene. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel, its preparation method and application, so as to solve the technical problem that existing fruit and vegetable preservation packaging materials are difficult to achieve efficient ethylene removal, controlled release of active substances, anti-oxidation, broad-spectrum antibacterial properties and good mechanical properties and thermal stability at the same time.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid, comprising: Cobalt acetate solution and copper acetate solution were added to trimesic acid solution, stirred and reacted, washed and dried under vacuum to obtain CuCo-MOF; After mixing and stirring the konjac glucomannan solution, carboxymethyl chitosan solution and glycerol evenly, a mixed solution is obtained; CuCo-MOF was ultrasonically dispersed in anhydrous ethanol to obtain a CuCo-MOF dispersion. The CuCo-MOF dispersion and gallic acid solution were added to the mixed solution in sequence and stirred evenly. After standing and freeze-drying, CuCo-MOF and gallic acid konjac glucomannan / carboxymethyl chitosan composite aerogel was obtained.

[0007] Preferably, the cobalt acetate solution is prepared by dissolving cobalt acetate in deionized water; the copper acetate solution is prepared by dissolving copper acetate in deionized water; and the trimellitic acid solution is prepared by dissolving trimellitic acid in a mixture of ethanol and deionized water. The molar ratio of total metal ions of cobalt acetate and copper acetate to pyromellitic acid is (0.6~1.0):(0.3~0.5); the molar ratio of cobalt acetate to copper acetate is 1:2~2:1. In a mixture of ethanol and deionized water, the volume ratio of ethanol to deionized water is 2:1 to 4:1.

[0008] Preferably, the stirring reaction conditions are: stirring reaction at 80~100 ℃ for 0.5~1.5 h.

[0009] Preferably, the washing conditions are: washing with deionized water 2-4 times, followed by methanol exchange for 2-4 days; the vacuum drying conditions are: vacuum drying at 50-70 °C for 10-14 h.

[0010] Preferably, the concentration of the konjac glucomannan solution is 1.5 wt% to 2.5 wt%; the concentration of the carboxymethyl chitosan solution is 1.5 wt% to 2.5 wt%. The volume ratio of konjac glucomannan solution to carboxymethyl chitosan solution is 2:1 to 1:2; The amount of glycerol added is 20wt%~40wt% of the total mass of polysaccharides; the polysaccharides are konjac glucomannan and carboxymethyl chitosan.

[0011] Preferably, the mixing time is 0.5 to 1.5 hours.

[0012] Preferably, the ultrasonic dispersion time of CuCo-MOF in anhydrous ethanol is 1~10 min; the gallic acid solution is prepared by dissolving gallic acid in deionized water; The amount of CuCo-MOF added is 1wt%~5wt% of the total mass of polysaccharides; the amount of gallic acid added is 0.5wt%~1.5wt% of the total mass of polysaccharides; the polysaccharides are konjac glucomannan and carboxymethyl chitosan.

[0013] Preferably, the standing time is 10~14 h; the freeze-drying conditions are: freezing at -80~-20 ℃ for 10~14 h, followed by freeze-drying at a vacuum degree ≤100 Pa and -60~-40 ℃ for 36~60 h.

[0014] The present invention also discloses a CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel, which is prepared by the above-mentioned preparation method of CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel.

[0015] This invention also discloses the application of the above-mentioned CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel in the preparation of food preservation packaging materials, antibacterial materials, antioxidant materials, ethylene adsorption materials, humidity-responsive slow-release materials, or fruit and vegetable preservation materials.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid. First, bimetallic CuCo-MOF is synthesized, and then it is introduced together with gallic acid (GA) into a polysaccharide matrix composed of konjac glucomannan (KGM) and carboxymethyl chitosan (CMCS). The composite aerogel is obtained by static gelation and freeze-drying. The unsaturated metal sites (CuCo-MOF) in CuCo-MOF... 2+ / Co 2+ The metal ion forms a π-complex with ethylene molecules (the metal ion accepts π electrons from ethylene to form a σ bond, while simultaneously feeding back d electrons to the empty antibonding orbitals of ethylene). Combined with the physical adsorption sites provided by the three-dimensional porous structure of the aerogel, this achieves highly efficient and reversible chemisorption of ethylene. Test data shows that when the MOF addition amount is 4%, the ethylene adsorption capacity reaches 10.66667±0.8 mg / m³. 3 / h, significantly higher than the 0.99 mg / m² of pure KC and the KC / GA control group. 3Gallic acid, through its abundant phenolic hydroxyl groups, forms hydrogen bonds with the polysaccharide matrix and embeds itself in the aerogel network. Simultaneously, the introduction of CuCo-MOF synergistically enhances antioxidant activity; the ABTS radical scavenging rate continuously increases from 16.61% to 94.14% with increasing MOF addition (reaching 93.84±0.72% at 4%). Cu released from CuCo-MOF... 2+ / Co 2+ Metal ions can disrupt bacterial cell membrane integrity and induce oxidative stress. In conjunction with the phenolic hydroxyl structure of GA, the antibacterial rates of the composite aerogel against *Escherichia coli* and *Staphylococcus aureus* approach 99.34±0.41% and 99.21±0.41%, respectively, when the MOF addition reaches 5%. Furthermore, GA, as a natural cross-linking agent, enhances the intermolecular chain interactions, and CuCo-MOF particles, as rigid fillers, are uniformly dispersed in the polymer network, enhancing the skeletal load-bearing capacity. This increases the aerogel hardness from 2343.40 g for pure KC to approximately 7980.92 g at a 4% addition, while maintaining a low density (≤0.02713 g / cm³). 3 It possesses high porosity (≥68%). Through a synergistic mechanism of chemical adsorption as the main component and physical adsorption as the auxiliary component, as well as the synergistic effect of antioxidant and antibacterial properties of GA and CuCo-MOF, a multifunctional integrated structure was achieved, laying the foundation for the subsequent preparation of high-performance preservation materials.

[0017] This invention discloses a CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel. A dense three-dimensional porous network structure is formed using KGM and CMCS as matrices, with GA embedded as a crosslinking agent. CuCo-MOF particles are distributed on the pore wall surface or embedded within the framework. The obtained CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel exhibits lightweight properties, with a maximum density (5% CuCo-MOF) of only 0.02713 ± 0.00040 g / cm³. 3It can be stably placed on the blade without causing significant pressure. With increasing CuCo-MOF addition, the density increases and the porosity decreases (from 76.55% to 68.07%), but the introduction of CuCo-MOF improves the stability of the network structure by enhancing intermolecular interactions. Water vapor adsorption performance is significantly improved; the water vapor adsorption rate of KC / GA / CuCo-MOF-4% reaches 42.39±0.52%, far exceeding the 4.98±0.21% of pure KC. This is attributed to the high water-binding capacity conferred by the large number of -OH groups on the main chain molecule and the low crystallinity, providing a structural basis for humidity-responsive release. TGA testing shows that the residual mass of the pure KC film at 700℃ is 25.33%, while the residual mass of KC / GA / CuCo-MOF-4% increases to 28.55%, indicating that the stable and dense network formed by CuCo-MOF with the matrix through hydrogen bonds effectively suppresses thermal decomposition kinetics. Mechanical testing showed that the product's hardness continuously increased with increasing CuCo-MOF content, reaching 7980.92 g (5% addition). Meanwhile, its elasticity and resilience rebounded to above 0.72 and 0.17 respectively after the addition exceeded 3%, indicating that an appropriate doping level resulted in a more stable three-dimensional network structure, possessing both high load-bearing capacity and good elastic recovery performance. The ethylene adsorption capacity reached 10.66667±0.8 mg / m³ at a 4% CuCo-MOF addition. 3 The / h release rate is attributed to the synergistic effect of Cu / Co bimetallic compounds, which optimizes the electronic structure and pore environment of the MOF, enhancing its binding energy to ethylene. Humidity-responsive release tests showed that at relative humidity of 30%, 60%, and 90%, the release amounts of GA after 48 hours were 2.08, 2.47, and 2.92 μg / mL, respectively, exhibiting a stable, sustained-release characteristic positively correlated with humidity. The mechanism is that under high humidity, the hydrophilic polysaccharide network swells, and pore expansion accelerates the diffusion and dissolution of GA molecules. Antioxidant tests showed that the product achieved a high ABTS free radical scavenging rate of 93.84±0.72% (4% CuCo-MOF). Antibacterial tests showed that the inhibition rate against two common foodborne pathogens reached over 84% at 3% CuCo-MOF addition, and approached 100% at 5%. This invention, through its dense three-dimensional network structure and multiple activities including efficient ethylene removal, intelligent sustained release, and antibacterial and antioxidant effects, effectively inhibits postharvest respiratory metabolism and blocks microbial infection in fruits and vegetables.

[0018] This invention discloses the application of CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel in the preparation of food preservation packaging materials, antibacterial materials, antioxidant materials, ethylene adsorption materials, humidity-responsive slow-release materials, or fruit and vegetable preservation materials. In the application to fruit and vegetable preservation materials / food preservation packaging materials: KC / GA / CuCo-MOF-4% aerogel was applied to the preservation packaging of strawberries at 25℃. After 8 days of storage, the results are as follows: [Appearance quality...] In terms of appearance, the unpackaged group and the PE film group showed severe spoilage on day 6, while the aerogel preservation group maintained excellent appearance quality. Regarding spoilage rate, the blank group and the PE film group reached 94.44% and 66.67% respectively, while the aerogel group only reached 33.33%. In terms of weight loss rate, the aerogel group maintained 1.81±0.24%, far lower than the unpackaged group's 22.53±1.63% and the PE group's 7.65±0.75%. Regarding hardness, the aerogel group maintained 1.78±0.03 kg / cm² after 7 days. 2 (10 5 Pa), higher than the PE group's 1.49 kg / cm². 2 Regarding titratable acid content, after 8 days, the aerogel group still reached 0.8±0.04%, while the PE group was only 0.7±0.02%. In terms of soluble solids, the aerogel group remained relatively stable throughout the storage period. These effects are attributed to the dense three-dimensional network structure of the aerogel effectively inhibiting strawberry respiration and reducing water and nutrient loss. Simultaneously, the antioxidant and antibacterial effects of GA and CuCo-MOF synergistically delayed microbial proliferation, and the ethylene adsorption capacity of CuCo-MOF further delayed the fruit ripening and senescence process. In terms of antibacterial material application: the product exhibited concentration-dependent broad-spectrum antibacterial activity against Escherichia coli and Staphylococcus aureus. When the MOF addition reached 5%, the inhibition rate exceeded 99%, approaching complete inhibition. The mechanism is that the metal ions released by MOF disrupt the integrity of bacterial cell membranes and induce oxidative stress. In the application of antioxidant materials: the ABTS free radical scavenging rate of the product continuously increases with the increase of MOF addition, reaching over 94%. GA provides phenolic hydroxyl active sites, and the metal sites of CuCo-MOF form a synergistic effect with GA. Furthermore, MOF itself may have adsorption or catalytic scavenging effects on free radicals. In the application of ethylene adsorption materials: the product's ethylene adsorption capacity reaches 10.67 mg / m³. 3 / h, efficient and reversible chemical adsorption is achieved through the π-complexation of Cu / Co bimetals, and the three-dimensional porous structure of the aerogel provides diffusion channels and physical adsorption sites, enabling efficient capture of ethylene at room temperature and pressure. In the application of humidity-responsive controlled-release materials: the GA release rate of the product is positively correlated with humidity, exhibiting excellent environmentally responsive controlled-release performance. It can automatically adjust the release behavior of antioxidant / antibacterial active substances according to the actual humidity conditions inside the packaging, achieving on-demand preservation. Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating the preparation process and application of the KC / GA / CuCo-MOF composite aerogel of the present invention; Figure 2 This is a flowchart illustrating the preparation process of the KC / GA / CuCo-MOF composite aerogel of the present invention. Figure 3 Scanning electron microscope image (a) of CuCo-MOF of the present invention; Fourier transform infrared spectrum of CuCo-MOF and H3BTC (b); X-ray diffraction pattern of CuCo-MOF and H3BTC (c). Figure 4 This is a schematic diagram of the cross-sectional microstructure of the KC / GA / CuCo-MOF composite aerogel of the present invention (doping amount 0%~5%); wherein, (a) is KC; (b) is KC / GA; (c) is KC / GA / CuCo-MOF-1%; (d) is KC / GA / CuCo-MOF-2%; (e) is KC / GA / CuCo-MOF-3%; (f) is KC / GA / CuCo-MOF-4%; and (g) is KC / GA / CuCo-MOF-5%. Figure 5 Fourier transform infrared spectra (a) and X-ray diffraction patterns (b) of different aerogels of the present invention. Figure 6 The morphology and physical properties of the KC / GA / CuCo-MOF composite aerogel of the present invention are characterized; (a) is a picture of the aerogel placed on the leaf, (b) is the density, (c) is the porosity, and (d) is the change of water vapor adsorption capacity with CuCo-MOF loading. Figure 7 Thermogravimetric curves (a) and derivative thermogravimetric curves (b) of the KC / GA / CUCO-MOF composite aerogel of the present invention are shown. Figure 8 The compression properties of the KC / GA / CuCo-MOF-4% composite aerogel of the present invention are shown in (a) macroscopic morphology image of the aerogel with CuCo-MOF doping amount of 4% after compression; (b) hardness, (c) elasticity, and (d) curves of rebound force as a function of CuCo-MOF loading amount. Figure 9 The following are the results of the present invention: ethylene removal efficiency, GA release behavior and antioxidant properties of KC / GA / CUCO-MOF composite aerogel; (a) the effect of different CuCo-MOF loading on ethylene removal efficiency; (b) the standard curve of GA; (c) the release kinetic curve of GA under different relative humidity (RH) environments; (d) the scavenging rate of ABTS free radicals by the composite material. Figure 10Evaluation of the antibacterial properties of the KC / GA / CUCO-MOF composite aerogel of this invention; (a) Evaluation of the antibacterial properties of different samples against Escherichia coli (Escherichia coli) E. coli ) and Staphylococcus aureus ( S. aureus (a) Colony count image of sample pair; (b) Image of sample pair. E. coli (c) Statistics on the antibacterial rate of the sample pair; S. aureus Statistics on antibacterial rate; Figure 11 This invention relates to the practical application of KC-based composite aerogels; (a) shows the appearance; (b) shows the putrefaction rate; and (c) shows the weight loss rate. Figure 12 The changes in hardness (a), titratable acidity (b), and total soluble solids content (c) of strawberries during storage are shown in this invention. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0022] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0023] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0024] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0025] In this invention, unless otherwise specified, the numerical range "a~b" is an abbreviation for any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "6~22" indicates that all real numbers between "6~22" have been listed in this document, and "6~22" is simply an abbreviation for these numerical combinations.

[0026] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0027] The term “and / or” as used in this invention refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0028] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0029] This invention discloses a method for preparing konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid, comprising the following steps: 1) Synthesis of CuCo-MOF 11) Preparation of solution A Cobalt acetate and copper acetate are mixed at a specific molar ratio of 1:2 to 2:1, preferably 1:2. The total metal ion content is 0.6 to 1.0 mmol, preferably 0.8 mmol. The above metal salts are dissolved separately in 15 to 25 mL of deionized water, preferably 20 mL of deionized water, and stirred thoroughly until completely dissolved to obtain solution A.

[0030] 12) Preparation of solution B Take 0.3-0.5 mmol of pyromellitic acid (H3BTC), preferably 0.4 mmol, and dissolve it in a mixture of 10-20 mL of ethanol and 3-8 mL of deionized water, preferably 15 mL of ethanol and 5 mL of deionized water. Stir until completely dissolved to obtain solution B. The volume ratio of ethanol to deionized water is 2:1 to 4:1, preferably 3:1.

[0031] 13) Mixed reaction Add the prepared solution A to solution B, mix well, and react at 80~100 ℃ for 0.5~1.5 h, preferably at 90 ℃ for 1 h, to obtain the reaction product.

[0032] 14) Post-processing After the reaction is complete, the product is washed with deionized water 2 to 4 times, preferably 3 times; then exchanged with methanol for 2 to 4 days, preferably 3 days; finally, it is vacuum dried at 50 to 70 °C for 10 to 14 h, preferably at 60 °C for 12 h, to obtain the blue product CuCo-MOF.

[0033] Following the above method, the product was synthesized using a molar ratio of cobalt acetate to copper acetate of 1:2, and the resulting product was denoted as the sample.

[0034] 2) Preparation of CuCo-MOF and gallic acid konjac glucomannan / carboxymethyl chitosan composite aerogel (KC / GA / CuCo-MOF composite aerogel) 21) Preparation of Solution A (polysaccharide matrix) A konjac glucomannan solution and a carboxymethyl chitosan solution are mixed at a certain volume ratio of 2:1 to 1:2, preferably 1:1. The concentration of the konjac glucomannan solution is 1.5wt% to 2.5wt%, preferably 2wt%, and the stirring temperature is 45 to 85℃, preferably 65℃, for 0.5 to 1.5 h, preferably 1 h. The concentration of the carboxymethyl chitosan solution is 1.5wt% to 2.5wt%, preferably 2wt%, and the mixture is stirred at room temperature for 0.5 to 1.5 h, preferably 1 h. The total volume of the mixed solution is 80 to 120 mL, preferably 100 mL, and the stirring time is 0.5 to 1.5 h, preferably 1 h. Glycerin is then added, with the amount of glycerin added being 20wt% to 40wt%, preferably 30wt%, of the total mass of the polysaccharides (konjac glucomannan and carboxymethyl chitosan). The mixture is stirred until homogeneous to obtain solution A.

[0035] 22) Preparation of solution B Take CuCo-MOF, the amount of which is 1wt%~5wt% of the total mass of polysaccharides, preferably 4wt%, and add it to 3~8 mL of anhydrous ethanol, preferably 5 mL of anhydrous ethanol. Sonicate for 1-10 min to obtain solution B.

[0036] 23) Preparation of solution C Gallic acid (GA) is added at an amount of 0.5wt% to 1.5wt% of the total mass of the polysaccharide, preferably 1wt%. It is dissolved in 3 to 8 mL of deionized water, preferably 5 mL of deionized water, and stirred until completely dissolved to obtain solution C.

[0037] 24) Mixing and Molding Add solutions B and C, prepared above, sequentially to solution A, mix thoroughly, and accurately measure 20-30 g (preferably 25 g) per well into a 6-well plate. Allow to stand at room temperature for 10-14 h (preferably 12 h) to form a nascent gel.

[0038] 25) Freeze-drying The nascent gel was frozen in a freezer at -80 to -20 ℃ for 10 to 14 h, preferably at -80 ℃ for 12 h. Then it was transferred to a freeze dryer and freeze-dried at a vacuum degree ≤100 Pa and a cold trap temperature of -60 to -40 ℃ (preferably -50 ℃) for 36 to 60 h, preferably 48 h, to obtain the final product CuCo-MOF and gallic acid konjac glucomannan / carboxymethyl chitosan composite aerogel.

[0039] Table 1. Main reagents used in this invention

[0040] Table 2 Main instruments used in this invention

[0041] This invention proposes a multi-scale composite synergistic modification strategy. First, gallic acid (GA), a natural phenolic compound, is introduced. GA not only possesses excellent antioxidant and antibacterial activities but can also crosslink with the polysaccharide matrix through hydrogen bonds and covalent bonds, enhancing the aerogel network and endowing it with environmentally responsive release properties. Second, metal-organic frameworks (MOFs) with great application potential are introduced. CuCo-MOFs, with their ultra-high specific surface area, tunable pore structure, and abundant unsaturated metal sites (Cu... 2+ / Co 2+ It can specifically and efficiently adsorb ethylene molecules through π-complexation; at the same time, metal ions can endow the material with strong broad-spectrum antibacterial properties.

[0042] This invention upgrades the structure of the previously developed basic material system, using KGM and CMCS as the gel framework, GA as the crosslinking and activator, and CuCo-MOF as the functional nanofiller. The aim is to prepare a novel bioaerogel integrating buffering and pressure resistance, targeted ethylene scavenging, humidity-responsive drug release, and antibacterial and antioxidant properties. By characterizing its microstructure and physicochemical properties, the interfacial interactions and performance enhancement mechanisms among the multiple components are explored in depth. Using strawberry as a model, the actual preservation efficacy of this composite aerogel in postharvest storage of fruits and vegetables is comprehensively evaluated. This invention represents a leap from basic corrosion protection to three-dimensional structured multi-effect protection in packaging materials, aiming to provide a highly forward-looking solution for the active packaging design of high-end fresh foods. The experimental process is as follows: Figure 1 As shown.

[0043] join Figure 1This diagram illustrates the preparation process and application of the KC / GA / CuCo-MOF composite aerogel of this invention. As shown, the preparation of this composite aerogel mainly involves three stages: raw material mixing, molding, and drying. First, CuCo-MOF, konjac glucomannan, carboxymethyl chitosan (KC), and gallic acid (GA) are mixed uniformly in a certain proportion. Then, the mixture is poured into a mold, and the system is frozen to set its shape. Finally, vacuum freeze-drying is used to remove the solvent, resulting in a KC / GA / CuCo-MOF composite aerogel with a porous network structure. Regarding its functions and applications, the diagram further reveals the multiple mechanisms of action of this aerogel. First, the components interact through hydrogen bonds, enhancing the structural stability of the material and facilitating the adsorption of target small molecules. Second, due to the introduction of gallic acid and carboxymethyl chitosan, the aerogel exhibits excellent antibacterial and antioxidant properties, inhibiting microbial growth and delaying food oxidative spoilage. Thirdly, the porous structure of CuCo-MOF endows the material with efficient ethylene adsorption and moisture absorption capabilities, thereby effectively regulating the packaging microenvironment, reducing ethylene concentration, and maintaining suitable humidity in preservation applications, ultimately achieving the goal of maintaining freshness. In summary, this schematic diagram clearly demonstrates the complete technical path of KC / GA / CuCo-MOF aerogel from raw materials to functional finished products, highlighting its synergistic application potential in the field of food preservation (especially fruit and vegetable preservation).

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0045] Example 1 A method for preparing konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid includes the following steps: 1) Synthesis of CuCo-MOF Cobalt acetate was dissolved in 20 mL of deionized water and stirred thoroughly until completely dissolved to obtain solution A1; copper acetate was dissolved in 20 mL of deionized water and stirred thoroughly until completely dissolved to obtain solution A2; wherein the molar ratio of cobalt acetate to copper acetate was 1:2, and the total amount of metal ions was 0.8 mmol.

[0046] Take another 0.4 mmol of pyromellitic acid (H3BTC) and dissolve it in a mixture of 15 mL of ethanol and 5 mL of deionized water. Stir until completely dissolved to obtain solution B.

[0047] Then, solutions A1 and A2 were added to solution B, mixed thoroughly, and reacted at 90 °C for 6 h. After the reaction was complete, the product was washed three times with deionized water, then exchanged with methanol for three days, and finally dried under vacuum at 60 °C for 12 h to obtain the blue product CuCo-MOF.

[0048] 2) Preparation of CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel First, prepare solution A (polysaccharide matrix): Mix 2wt% KGM solution and 2wt% CMCS solution at a ratio of 1:1 (100mL), then add 30wt% glycerol of the total polysaccharide mass, and stir for 1 hour.

[0049] Prepare solution B separately: Add 1 wt% CuCo-MOF (based on the total mass of polysaccharides) to 5 mL of anhydrous ethanol and sonicate for 5 min.

[0050] Solution C was prepared by dissolving GA (1% by mass of total polysaccharides) in 5 mL of deionized water. Solutions B and C were added sequentially to solution A and mixed thoroughly. 25 g of the mixture was accurately measured per well and injected into a 6-well plate. The plate was allowed to stand at room temperature for 12 h to form a nascent gel. The nascent gel was then frozen at -80 °C for 12 h, and subsequently freeze-dried in a freeze dryer (vacuum ≤100 Pa, cold trap temperature -50 °C) for 48 h to obtain a CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel (KC / GA / CuCo-MOF-1%). The preparation process is as follows: Figure 2 As shown.

[0051] The only difference between KC / GA / CuCo-MOF-2%, KC / GA / CuCo-MOF-3%, KC / GA / CuCo-MOF-4%, KC / GA / CuCo-MOF-5% and KC / GA / CuCo-MOF-1% is the mass of CuCoMOF added; all other conditions are the same.

[0052] join Figure 2 The flowchart shows the preparation process of the KC / GA / CuCo-MOF composite aerogel of the present invention. As can be seen from the figure, the preparation of the composite aerogel mainly includes the steps of raw material ratio, mixing and dissolving, cross-linking reaction, freeze-setting and vacuum freeze-drying.

[0053] Example 2 A method for preparing konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid includes the following steps: 1) Synthesis of CuCo-MOF Cobalt acetate was dissolved in 15 mL of deionized water and stirred thoroughly until completely dissolved to obtain solution A1; copper acetate was dissolved in 15 mL of deionized water and stirred thoroughly until completely dissolved to obtain solution A2; wherein the molar ratio of cobalt acetate to copper acetate was 2:1, and the total amount of metal ions was 1.0 mmol.

[0054] Take another 0.5 mmol of pyromellitic acid (H3BTC) and dissolve it in a mixture of 20 mL of ethanol and 5 mL of deionized water (ethanol:deionized water volume ratio = 4:1). Stir until completely dissolved to obtain solution B.

[0055] Then, solutions A1 and A2 were added to solution B, mixed thoroughly, and reacted at 100 °C for 1.5 h. After the reaction was complete, the product was washed four times with deionized water, then exchanged with methanol for four days, and finally dried under vacuum at 70 °C for 10 h to obtain the blue product CuCo-MOF.

[0056] 2) Preparation of CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel First, prepare solution A (polysaccharide matrix): Mix 1.5 wt% KGM solution and 1.5 wt% CMCS solution at a volume ratio of 2:1 (total volume 80 mL). Stir the KGM solution at 45 ℃ for 1.5 h and the CMCS solution at room temperature for 1.5 h. After mixing, continue stirring for 1.5 h. Then add 20 wt% glycerol, which accounts for 20 wt% of the total mass of polysaccharides, and stir until homogeneous.

[0057] Prepare another solution B: Add 3 wt% CuCo-MOF (based on the total mass of polysaccharides) to 3 mL of anhydrous ethanol and sonicate for 6 min.

[0058] Prepare solution C: Dissolve 1.5 wt% GA in 3 mL of deionized water and stir until completely dissolved.

[0059] Solution B and solution C were added to solution A sequentially and mixed thoroughly. 20 g of solution was accurately measured for each well and injected into a 6-well plate. The mixture was allowed to stand at room temperature for 14 h to form a nascent gel. The nascent gel was then frozen at -50 ℃ for 14 h, and subsequently freeze-dried in a freeze dryer (vacuum ≤100 Pa, cold trap temperature -60 ℃) for 60 h to obtain a CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel.

[0060] Example 3 A method for preparing konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid includes the following steps: 1) Synthesis of CuCo-MOF Cobalt acetate was dissolved in 25 mL of deionized water and stirred thoroughly until completely dissolved to obtain solution A1; copper acetate was dissolved in 25 mL of deionized water and stirred thoroughly until completely dissolved to obtain solution A2; wherein the molar ratio of cobalt acetate to copper acetate was 1:1, and the total amount of metal ions was 0.6 mmol.

[0061] Take another 0.3 mmol of pyromellitic acid (H3BTC) and dissolve it in a mixture of 10 mL of ethanol and 5 mL of deionized water (ethanol:deionized water volume ratio = 2:1). Stir until completely dissolved to obtain solution B.

[0062] Then, solutions A1 and A2 were added to solution B, mixed thoroughly, and reacted at 80 °C for 0.5 h. After the reaction was complete, the product was washed twice with deionized water, then exchanged with methanol for 2 days, and finally dried under vacuum at 50 °C for 14 h to obtain the blue product CuCo-MOF.

[0063] 2) Preparation of CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel First, prepare solution A (polysaccharide matrix): Mix 2.5 wt% KGM solution and 2.5 wt% CMCS solution at a volume ratio of 1:2 (total volume 120 mL). Stir the KGM solution at 85 ℃ for 0.5 h and the CMCS solution at room temperature for 0.5 h. After mixing, continue stirring for 0.5 h. Then add 40 wt% glycerol, which accounts for 40 wt% of the total mass of polysaccharides, and stir until homogeneous.

[0064] Prepare another solution B: Add 5 wt% CuCo-MOF (based on the total mass of polysaccharides) to 8 mL of anhydrous ethanol and sonicate for 1 min.

[0065] Prepare solution C: Dissolve GA (0.5 wt% of total polysaccharide) in 8 mL of deionized water and stir until completely dissolved.

[0066] Solution B and solution C were added to solution A sequentially and mixed thoroughly. 30 g of solution was accurately measured for each well and injected into a 6-well plate. The mixture was allowed to stand at room temperature for 10 h to form a nascent gel. The nascent gel was then frozen at -20 ℃ for 10 h, and subsequently freeze-dried in a freeze dryer (vacuum ≤100 Pa, cold trap temperature -40 ℃) for 36 h to obtain a CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel.

[0067] Example 4 A method for preparing konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid includes the following steps: 1) Synthesis of CuCo-MOF Cobalt acetate was dissolved in 20 mL of deionized water and stirred thoroughly until completely dissolved to obtain solution A1; copper acetate was dissolved in 20 mL of deionized water and stirred thoroughly until completely dissolved to obtain solution A2; wherein the molar ratio of cobalt acetate to copper acetate was 1:1 and the total amount of metal ions was 0.8 mmol.

[0068] Take another 0.4 mmol of pyromellitic acid (H3BTC) and dissolve it in a mixture of 12 mL of ethanol and 4 mL of deionized water (ethanol:deionized water volume ratio = 3:1). Stir until completely dissolved to obtain solution B.

[0069] Then, solutions A1 and A2 were added to solution B, mixed thoroughly, and reacted at 90 °C for 1 h. After the reaction was complete, the product was washed three times with deionized water, then exchanged with methanol for 3 days, and finally dried under vacuum at 60 °C for 12 h to obtain the blue product CuCo-MOF.

[0070] 2) Preparation of CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel First, prepare solution A (polysaccharide matrix): Mix 2 wt% KGM solution and 2 wt% CMCS solution at a 1:1 volume ratio (total volume 100 mL). Stir the KGM solution at 65 ℃ for 1 h and the CMCS solution at room temperature for 1 h. After mixing, continue stirring for 1 h. Then add 30 wt% glycerol, which accounts for 30 wt% of the total mass of polysaccharides, and stir until homogeneous.

[0071] Prepare another solution B: Add 4 wt% CuCo-MOF (based on the total mass of polysaccharides) to 5 mL of anhydrous ethanol and sonicate for 10 min.

[0072] Prepare solution C: Dissolve 1 wt% of GA in 5 mL of deionized water and stir until completely dissolved.

[0073] Solution B and solution C were added to solution A sequentially and mixed thoroughly. 25 g of solution was accurately measured for each well and injected into a 6-well plate. The mixture was allowed to stand at room temperature for 12 h to form a nascent gel. The nascent gel was then frozen at -80 ℃ for 12 h, and subsequently freeze-dried in a freeze dryer (vacuum ≤100 Pa, cold trap temperature -50 ℃) for 48 h to obtain a CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel.

[0074] Comparative Example 1 A method for preparing KC includes the following steps: Konjac glucomannan solution (KGM) and carboxymethyl chitosan solution (CMCS) were mixed at a volume ratio of 1:1. The concentration of the konjac glucomannan solution was 2% wt, the stirring temperature was 65℃, and the stirring time was 1 h; the concentration of the carboxymethyl chitosan solution was 2% wt, and the stirring time was 1 h at room temperature. The total volume of the mixed solution was 100 mL, and the stirring time was 1 h. Glycerin was then added at 30% wt of the total polysaccharide mass, and the mixture was stirred until homogeneous. 25 g of the mixture was accurately measured and injected into each well of a 6-well plate. The mixture was allowed to stand at room temperature for 12 h to form a nascent gel. The nascent gel was then frozen at -80℃ for 12 h. It was then transferred to a freeze dryer and freeze-dried at a vacuum degree ≤100 Pa and a cold trap temperature of -50℃ for 48 h to obtain the final product KC.

[0075] Comparative Example 2 A method for preparing KC / GA includes the following steps: Konjac glucomannan solution and carboxymethyl chitosan solution were mixed at a volume ratio of 1:1. The concentration of the konjac glucomannan solution was 2% wt, the stirring temperature was 65℃, and the stirring time was 1 h; the concentration of the carboxymethyl chitosan solution was 2% wt, and the stirring was carried out at room temperature for 1 h. The total volume of the mixed solution was 100 mL, and the stirring time was 1 h. Glycerin was then added at 30% wt of the total polysaccharide mass, and the mixture was stirred until homogeneous to obtain solution A. Gallic acid (GA) was added at 1% wt of the total polysaccharide mass and dissolved in 5 mL of deionized water, stirred until completely dissolved to obtain solution B. Solution B was added to solution A, mixed thoroughly, and 25 g was accurately measured for each well and injected into a 6-well plate. The mixture was allowed to stand at room temperature for 12 h to form a primary gel. The primary gel was then frozen at -80℃ for 12 h. The product was then transferred to a freeze dryer and freeze-dried for 48 h under conditions of vacuum ≤100 Pa and cold trap temperature -50 ℃ to obtain the final product KC / GA.

[0076] Morphological and structural characterization of CuCo-MOF and aerogel Observation was performed using a scanning electron microscope (SEM) at 10 kV. The samples underwent gold sputtering pretreatment before observation. Fourier transform infrared spectroscopy (FT-IR) was used at 4000–400 cm⁻¹. -1 Within range (resolution 4 cm) -1 The functional groups of the thin film were characterized. Furthermore, X-ray diffraction (XRD) (40 kV) was used at 5–90° (2 θThe crystal morphology of the thin film was analyzed at a rate of 5° / min within the range of )

[0077] Physical performance testing The dimensions and weight of the aerogel were measured using calipers and an analytical balance, respectively, to determine its bulk density. Bulk density (ρ) b (g / cm³) is calculated according to the following formula (1-1): (1-1) In the formula: m — mass (g); A – Cross-sectional area (cm²) 2 ); h — thickness (cm).

[0078] The porosity of the aerogel samples was determined by gravimetric method. Completely dried aerogel samples were immersed in anhydrous ethanol for 24 h. The aerogel porosity was calculated using the following formula: (1-2) In the formula: W1 — Mass of the aerogel before immersion in ethanol (g); W2 — Mass of the aerogel after immersion in ethanol (g); V — Volume of the aerogel before immersion in ethanol (cm³) 3 ); ρ ethanol —The density of ethanol (0.8075 g / cm³) 3 ).

[0079] The water vapor adsorption capacity (WVAC) of the aerogel was determined according to the previously described method. After each weighing of the aerogel sample, it was placed in a constant temperature and humidity chamber (25±1 °C, 100% relative humidity) for 24 h, and then weighed again. The water vapor adsorption capacity (WVAC) was calculated according to the following formula: (1-3) In the formula: M2 — Mass of the aerogel after adsorbing water vapor (g); M1 — Mass of the aerogel before water vapor adsorption (g).

[0080] Mechanical properties The mechanical properties of the aerogel were determined using a physical property analyzer. The aerogel samples were compressed to 60% at a test speed of 0.5 mm / s. The test results are presented as hardness and elasticity values.

[0081] Thermogravimetric analysis Thermogravimetric analysis was used to test the thermal stability of the samples, with a heating temperature range of 30 to 800 °C. The heating rate and nitrogen flow rate were set to 10 °C / min and 20 mL / min, respectively.

[0082] Ethylene adsorption performance Aerogel was placed into a gas sampling bag and 160 ppm of ethylene gas was injected. After 5 hours, the amount of ethylene remaining in the bag was measured using a VOC detector.

[0083] Humidity-responsive release of gallic acid The kinetics of GA release from aerogels under different relative humidities were determined at 25 ℃. A standard curve for GA was plotted by utilizing the characteristic absorption peak of the GA benzene ring structure in the 270 nm UV region. First, the initial GA loading in the aerogels was determined: three aerogel samples (mass m0) that had not undergone release experiments were taken, and 20 mL of 50% ethanol solution was added. The samples were ultrasonically extracted at 25 ℃ for 30 min, allowed to stand, and the supernatant was discarded. Then, 10 mL of 50% ethanol was added and the extraction was repeated once. The two extracts were combined, transferred to a 50 mL volumetric flask, and diluted to volume with 50% ethanol. After shaking, the mixture was filtered or centrifuged to obtain a clear initial extract. Simultaneously, a blank aerogel was taken, and a blank extract was obtained using the same procedure. The absorbance was measured at 270 nm using 50% ethanol as a reference, and these were recorded as Ainitial and Ablank, respectively. The corrected absorbance Acorrected was calculated. 校1 =A 初始 -A 空白 Substituting this into the standard curve yields the concentration C.

[0084] Antioxidant activity ABTS (7 mM) and potassium persulfate (2.45 mM) were dissolved in deionized water and left to stand at room temperature in the dark for 16 h. The reaction solution was then diluted with deionized water, and the absorbance at 734 nm was measured to be 0.700 ± 0.005. A certain mass of aerogel was weighed and mixed with 4 mL of ABTS solution. After reacting the mixture in the dark at 25 ℃ for 30 min, the absorbance at 734 nm was measured using a full-wavelength microplate reader. The ABTS free radical scavenging activity was calculated using the following formula (1-4): (1-4) In the formula: A0 – Absorbance of the blank group; A1 – Absorbance of the experimental group.

[0085] Antibacterial properties The antibacterial activity of aerogel against two foodborne pathogens, *Escherichia coli* (ATCC 25922) and *Staphylococcus aureus* (ATCC 25922), was evaluated. Aerogel (100 mg) was mixed with bacterial solution (50 mL, 10 mL) at different concentrations.6 The mixture (CFU / mL) was incubated at 37°C for 12 h. Then, 100 μL of the mixture was inoculated into the culture medium and incubated at 37°C for another 48 h. The antibacterial activity of the film was assessed by counting bacterial colonies. The inhibition rate (%) was calculated using the following formula (1-5): (1-5) In the formula: A – The number of surviving cells in the blank culture dish; B – The number of surviving cells in the culture dish with the added membrane.

[0086] Strawberry freshness test In this preservation study, strawberries with intact appearance, good physical structure, and no initial rot were selected to evaluate the preservation effect of the composite film. Three groups of strawberries (six strawberries per group) were placed in pre-sterilized commercial food packaging boxes. Three packaging treatments were included: a blank control group (unpackaged), a PE film packaging group (commercial sample group), and a KC / GA / CuCo-MOF-4% aerogel packaging group. All samples were from the same batch. The storage experiment was conducted under constant conditions of 25±2 ℃ and 65-70% relative humidity for 8 days. During storage, strawberries were randomly selected from the packaging boxes every two days for photographic evaluation of appearance, and the spoilage rate, weight loss rate, firmness value, TSS, and TA were measured. Fruit weight loss is calculated using formula (1-6): where M0 (g) and M1 (g) are the weights of cherry tomatoes measured after 0 days of storage and every 3 days, respectively.

[0087] (1-6) Fruit firmness was measured using a handheld hardness tester. The procedure was as follows: after zeroing the device, apply uniform pressure vertically to the cherry tomatoes until the scale of the hardness tester aligned with the tangent on the fruit surface. The result is expressed as the maximum penetrating pressure achieved upon cracking.

[0088] The spoilage rate (%) is calculated using formula (1-7) based on the ratio of the number of tomatoes showing visible signs of spoilage to the total number of fruits (6 units) in each sample group: (1-7) Grind 5 g of the strawberries to be tested in a mortar and pestle, then centrifuge at 40 ℃ and 6000 r / min for 10 min. Measure the samples using a refractometer, three times per group, and record the data as the average.

[0089] Titratable acidity was determined by acid-base titration. 5 g of sample was ground evenly and diluted to 100 mL with ultrapure water. After mixing, the solution was allowed to stand for 30 min. 20 mL of the filtrate was taken, 2 drops of phenolphthalein indicator (1% w / v) were added, and titrated to the endpoint with sodium hydroxide solution (0.1 mmol / L). The titratable acid was calculated using formula (1-8): (1-8) In the formula: V – Total volume of pulp (mL); C—Concentration of NaOH (mol / L); V1 — Volume of NaOH solution consumed in titration of the filtrate (mL); V0 — Volume of NaOH solution consumed in the titration of distilled water (mL); V s — The volume of filtrate used during the titration process (mL); m — Sample mass (g); K—the conversion factor for the major acid, meaning the number of grams of the major acid equivalent to 1 mmol of sodium hydroxide (NaOH), calculated with reference to citric acid (0.070) (g / mmol).

[0090] Data Analysis All experiments were repeated at least three times, and results are expressed as mean ± standard deviation. One-way ANOVA combined with Duncan's multiple range test (P < 0.05) was used to process the data. Statistical analysis was performed using SPSS 27 software (SPSS Inc., Chicago, USA), and a statistically significant difference was defined as p < 0.05.

[0091] Morphological and structural characterization of CuCo-MOF Figure 3 Here are scanning electron microscope images (a) of the CuCo-MOF of this invention; Fourier transform infrared spectra of CuCo-MOF and H3BTC (b); X-ray diffraction patterns of CuCo-MOF and H3BTC (c); and the morphology of the synthesized CuCo-MOF material was characterized by SEM, with the results shown below. Figure 3 As shown in (a), the CuCo-MOF material exhibits a granular morphology with uneven particle size distribution and significant agglomeration, which is closely related to the structural characteristics of the MOF material itself and the interfacial interactions during the synthesis process.

[0092] The synthesized compounds were fully characterized by FT-IR to examine their structural features in detail. Figure 3(b) Comparison of the FT-IR spectra of the H3BTC ligand and the CuCo-MOF sample. In the infrared spectrum of the H3BTC ligand, a peak at 1721.52 cm⁻¹ can be observed. -1 The strong absorption peaks nearby are attributed to the stretching vibration of C=O in the carboxyl group (-COOH), and the peak at 1275.79 cm⁻¹. -1 The CO stretching vibration peaks are within the specified range. However, in the spectrum of CuCo-MOF, these characteristic peaks are significantly weakened or almost disappear, while the peaks at 1623.26 cm⁻¹ are absent. -1 and 1371.2 cm -1 Two new sets of strong absorption peaks appeared nearby, attributed to the asymmetric and symmetric stretching vibrations of the coordinated carboxylate group, respectively. The appearance of these two characteristic peaks indicates that the carboxyl group in H3BTC has been deprotonated and reacted with the metal ion (Cu). 2+ / Co 2+ Coordination occurred. Furthermore, at 489.71 cm... -1 In the low wavenumber region, CuCo-MOF exhibits a new weak absorption peak compared to H3BTC, which can be attributed to the stretching vibration of the metal-oxygen (MO) bond, providing direct evidence for the formation of a coordination bond between the metal and the ligand oxygen atom. FT-IR spectral analysis fully confirms that in the CuCo-MOF sample, the H3BTC ligand binds to Cu through its carboxyl oxygen atom. 2+ / Co 2+ The ions successfully coordinated, forming a stable bimetallic organic framework structure, rather than a physical mixture.

[0093] In the XRD pattern of ligand H3BTC, a series of sharp characteristic diffraction peaks can be observed, mainly concentrated in the 5-30° range. θ Within this range, this corresponds to the crystal structure formed by the orderly stacking of H3BTC molecules. However, in the spectra of the CuCo-MOF sample, the characteristic diffraction peaks of H3BTC completely disappear, indicating that the ligands no longer exist in a free state but are fully involved in the coordination reaction. The CuCo-MOF spectra show a new set of sharp and high-intensity diffraction peaks in the low-angle region of 5-15°, with the most significant characteristic peak located at 2°. θ = around 7.19°, 9.91°, 12.03° and 13.74°. The appearance of strong diffraction peaks in the low-angle region is a typical feature of metal-organic framework materials with long-range ordered pore structures, corresponding to the diffraction of specific crystal planes of MOFs.

[0094] Morphological and structural characterization of aerogels Figure 4This is a schematic diagram of the cross-sectional microstructure of the KC / GA / CuCo-MOF composite aerogel of the present invention (doping amount 0%~5%); wherein, (a) is KC; (b) is KC / GA; (c) is KC / GA / CuCo-MOF-1%; (d) is KC / GA / CuCo-MOF-2%; (e) is KC / GA / CuCo-MOF-3%; (f) is KC / GA / CuCo-MOF-4%; (g) is KC / GA / CuCo-MOF-5%; as shown below. Figure 4 As shown, pure KC aerogel exhibits a typical porous network structure with relatively uniform pore distribution and smooth, continuous pore walls. The introduction of GA, as a natural crosslinking agent, further enhances the interaction between macromolecular chains, resulting in a denser framework, more regular pore structure, and smaller pore size in the KC / GA composite aerogel. After doping with different proportions of CuCo-MOF, MOF particles are mainly distributed on the pore wall surface or embedded within the framework. When the doping concentration is low (1%–3%), MOF particles are relatively uniformly dispersed in the matrix, and the composite material maintains a relatively complete pore structure. When the doping concentration increases to 4%, local aggregation of particles begins to occur, and the surface roughness increases significantly. When the doping concentration further increases to 5%, excessive MOF particles gradually block some pores, leading to a decrease in porosity, a more irregular pore structure, and even framework collapse or cracks in some areas. Overall, appropriate doping with CuCo-MOF can increase the active sites of the material while maintaining a porous structure, but excessively high doping concentrations can adversely affect the microstructural integrity of the aerogel. Figure 5 The Fourier transform infrared spectra (a) and X-ray diffraction patterns (b) of different aerogels of this invention are shown below; Figure 5 As shown in (a), for KC aerogels, the FT-IR is in the range of 3400-3200 cm⁻¹. -1 A broad and strong absorption peak is observed at 2920.57 cm⁻¹, attributed to the stretching vibrations of OH and NH, indicating the presence of a rich hydrogen bond network in the system. -1 An absorption peak for the stretching vibration of CH is present at 1589.08 cm⁻¹, which may be the absorption peak of intramolecular and intermolecular hydroxyl groups in the polysaccharide molecule. -1 The nearby peak is mainly attributed to the stretching vibration of the benzene ring bonds, 1412.5 cm⁻¹. -1 The absorption peak appearing nearby is the bending vibration absorption peak of CH2, at 1022.31 cm⁻¹. -1 The prominent peaks are related to the asymmetric stretching vibrations of COC and the vibrations of the CO bond. These characteristics together confirm the successful recombination of KGM and CMCS, and that the two form a stable three-dimensional network structure through intermolecular hydrogen bonds.

[0095] After incorporating GA into the aerogel, compared with KGM / CMCS aerogel, the diameter was 3289.4 cm. -1 The characteristic peaks broaden and shift slightly towards lower wavenumbers, indicating that GA forms additional hydrogen bond interactions with the KC matrix through its abundant phenolic hydroxyl groups, thereby embedding itself within the aerogel network. FT-IR shows that the aerogels treated with GA and CuCo-MOF exhibit peaks at 450–1600 cm⁻¹. -1 The weakening intensity at the characteristic band and the slight shift in the position of the functional group absorption peaks indicate that these functional groups mainly interact through electrostatic interactions.

[0096] Furthermore, the effects of GA and CuCo-MOF on the crystal structure of the aerogel matrix were analyzed by XRD, such as... Figure 5 As shown in (b), the diffraction pattern of the KC aerogel exhibits a broad peak (20.9°), indicating that it is mainly amorphous. With the addition of GA and CuCo-MOF, the intensity of these peaks decreases significantly, which may be due to the hydrogen bonds between these additives and the aerogel matrix, affecting the original crystal structure of the matrix.

[0097] Physical properties Figure 6 The morphology and physical properties of the KC / GA / CUCO-MOF composite aerogel of this invention are characterized; (a) is a picture of the aerogel placed on a leaf, (b) shows the density, (c) shows the porosity, and (d) shows the change in water vapor adsorption capacity with CuCo-MOF loading; the density and porosity of the aerogel are as follows. Figure 6 As shown in (b) and (c), the density of the aerogel increases significantly with increasing CuCo-MOF concentration, but the density of KC / GA / CuCo-MOF-5%, which has the highest CuCo-MOF concentration, is only 0.02713 ± 0.00040 g / cm³. 3 It still belongs to low-density, lightweight materials, such as Figure 6 As shown in (a), KC / GA / CuCo-MOF-5% can be stably placed on the blade without causing significant pressure.

[0098] like Figure 6 As shown in (c), the porosity decreases with increasing CuCo-MOF concentration. This is because the introduction of CuCo-MOF occupies part of the pore space, disrupting the orderliness of molecular chain crosslinking. When the CuCo-MOF concentration is 1%, the porosity is 76.55 ± 0.13%. When the CuCo-MOF concentration increases to 5%, the porosity decreases to 68.07 ± 0.72%. With increasing CuCo-MOF addition, the degree of crosslinking between aerogel components increases and the pore size decreases, which is consistent with the SEM observations of the aerogel. Figure 4The addition of CuCo-MOF may improve the stability of the aerogel network structure by enhancing intermolecular interactions, thereby improving the physical properties of the aerogel.

[0099] Bioactive aerogels, due to their excellent water absorption capacity, can easily absorb excess liquid accumulated inside food packaging and remove residual liquid, thereby inhibiting microbial growth and ultimately extending the shelf life of food. Therefore, the excellent water absorption properties exhibited by aerogels while maintaining structural integrity are crucial for food packaging applications. The water vapor adsorption rate of aerogels is as follows... Figure 6 As shown in Figure (d), the water adsorption capacity of KC aerogel is 4.98±0.21%, which is due to the formation of hydrogen bonds between KGM and CMCS. These bonds reduce the availability of free hydroxyl groups and further inhibit its water absorption capacity. The addition of GA and CuCo-MOF significantly increases the hygroscopic capacity of the aerogel. The water vapor adsorption rates of KC / GA, KC / GA / CuCo-MOF-1%, KC / GA / CuCo-MOF-2%, KC / GA / CuCo-MOF-3%, KC / GA / CuCo-MOF-4%, and KC / GA / CuCo-MOF-5% are 31.51±0.22%, 29.61±0.66%, 34.60±0.69%, 38.84±0.46%, 42.39±0.52%, and 51.76±1.07%, respectively. This is because the presence of numerous -OH groups on the main chain molecules and the low crystallinity of the prepared air gels all enhance the water-binding capacity of these polymers. Furthermore, the free side groups of the polymers can interact with water through hydrogen bonds, leading to a decrease in the cohesive force of the polymer matrix and thus enhancing its water vapor absorption capacity.

[0100] Thermal stability and mechanical property testing Figure 7 Thermogravimetric curves (a) and derivative thermogravimetric curves (b) of the KC / GA / CUCO-MOF composite aerogel of this invention are shown. Thermogravimetric analysis (TGA) and derivative thermogravimetric analysis (DTG) were used to evaluate the residual mass ratio and mass loss of the developed aerogel with increasing temperature, respectively. All TGA curves exhibited three-stage degradation characteristics (e.g., Figure 7(As shown in (a)). The first stage (below 150 °C) corresponds to the removal of physically adsorbed weakly bound water and chemically adsorbed strongly bound water; the second stage (150-330 °C) is the main decomposition stage, involving the decomposition of KGM and CMCS backbones and the degradation of incorporated GA and CuCo-MOF; the third stage (330-519 °C) corresponds to the further decomposition of the polymer matrix and the combustion of residual carbon. At 700 °C, the residual mass of the original KC film was 25.33%. With the increase of CuCo-MOF loading, the residual mass of KC / GA / CuCo-MOF-4% increased to 28.55%, indicating that the introduction of CuCo-MOF enhanced the thermal stability of the film, which is attributed to the hydrogen bonds formed between the extract and the polymer. However, when CuCo-MOF increased to 5%, the residual mass of KC / GA / CuCo-MOF-4% was 27.53%. This is because particle agglomeration disrupted the uniformity of part of the network structure, resulting in a slight decrease in thermal stability (based on residual mass). Figure 7 The differential thermogravimetric (DTG) curves shown in Figure (b) reveal that all films exhibit rapid degradation in the 125–340 °C range, with the maximum decomposition rate occurring at approximately 218 °C. Consistent with the TGA results, the KC / GA / CuCo-MOF-4% aerogel shows the smallest peak value, indicating that its thermal decomposition kinetics are effectively suppressed. This enhanced thermal stability can be attributed to the more stable and dense network structure formed between CuCo-MOF and the KC / GA matrix through hydrogen bonding and electrostatic interactions.

[0101] Figure 8 The compressibility of the KC / GA / CuCo-MOF-4% composite aerogel of this invention is shown in Figure 1. (a) is a macroscopic image of the aerogel with 4% CuCo-MOF doping after compression; (b) shows the hardness, (c) the elasticity, and (d) the resilience curves as a function of CuCo-MOF loading. In the packaging field, the excellent compressive strength of aerogel helps reduce mechanical damage that may occur during product transportation and handling. Simultaneously, the material maintains the integrity of its pore structure under pressure, which facilitates the release of active substances. An ideal aerogel needs sufficient strength and compressive elasticity to support the weight of fruit without decomposing or deforming. The mechanical properties of the KC / GA / CuCo-MOF composite aerogel are as follows: Figure 8 As shown. Figure 8As shown in Figure (b), with the increase of CuCo-MOF content, the hardness of the composite aerogel showed a trend of first significantly increasing and then leveling off, while the elasticity and resilience showed a pattern of first decreasing and then slightly increasing. Specifically, the hardness of pure KC aerogel was 2343.40±186.75 g. After the introduction of GA, the hardness increased to 2850.81±13.74 g, indicating that GA formed effective hydrogen bond interactions with the polysaccharide matrix. With further addition of CuCo-MOF, the hardness continued to increase with the increase of MOF content, gradually rising from 4409.16±442.10 g (1% CuCo-MOF) to 7980.92±154.58 g (5% CuCo-MOF). This is attributed to the uniform dispersion of CuCo-MOF particles as rigid fillers in the polymer network, which enhanced the load-bearing capacity of the skeleton. However, the changes in elasticity and resilience were more complex, such as... Figure 8 As shown in (c) and (d), at low CuCo-MOF additions (1%-3%), the elasticity decreased from 0.85±0.006 (KC) to approximately 0.66, and the resilience also remained at a low level (0.14-0.15). This may be because the introduction of CuCo-MOF disrupted the original polysaccharide network continuity, limiting the flexibility of the molecular chains. When the CuCo-MOF content further increased to 4% and 5%, the elasticity and resilience rebounded to approximately 0.72 and above 0.17, respectively. It is speculated that a more stable three-dimensional network structure was formed at high CuCo-MOF content, or the interface between CuCo-MOF and the matrix was enhanced, thereby improving the deformation recovery ability of the network to a certain extent. Overall, CuCo-MOF doping effectively improved the mechanical strength of the aerogel, but a good elastic recovery performance could only be achieved when the addition amount exceeded 3%.

[0102] Ethylene adsorption capacity Figure 9 This invention relates to the ethylene removal efficiency, GA release behavior, and antioxidant properties of the KC / GA / CUCO-MOF composite aerogel; (a) the effect of different CuCo-MOF loadings on the ethylene removal efficiency; (b) the standard curve of GA; (c) the release kinetic curves of GA under different relative humidity (RH) environments; and (d) the scavenging rate of the composite material for ABTS free radicals. Figure 9As shown in Figure (a), the results indicate that the adsorption capacity of pure KC and the KC / GA control group was extremely low (both 0.99 mg / m³ / h), while the adsorption capacity was significantly improved after the introduction of MOF. Furthermore, the adsorption capacity showed a continuous upward trend as the MOF addition increased from 1% to 4%, gradually increasing from 3.50667±0.48 mg / m³ / h to 10.66667±0.8 mg / m³ / h. When the addition reached 5%, the adsorption capacity decreased slightly (10.51333±1.37 mg / m³ / h), which may be attributed to the agglomeration of excessive MOF particles or blockage of the pore structure. Considering all factors, the composite aerogel exhibited the best ethylene adsorption performance when the MOF addition was 4%.

[0103] The improved adsorption performance is mainly attributed to the unsaturated metal sites (CuCo-MOF) in CuCo-MOF. 2+ / Co 2+ The π-complexion between the metal ion and ethylene molecules: Metal ions accept π electrons from ethylene to form σ bonds, while simultaneously feeding back d electrons to the empty antibonding orbitals of ethylene, thus achieving efficient and reversible chemisorption of ethylene. The synergistic effect of the mixed metals (especially Co:Cu = 2:1) may optimize the electronic structure and pore environment of the MOF, enhancing the binding energy for ethylene and further improving the adsorption capacity. In addition, the three-dimensional porous structure of the aerogel provides diffusion channels and physical adsorption sites for ethylene. This material achieves efficient ethylene capture at room temperature and pressure through a synergistic mechanism of chemisorption-dominant and physisorption-assisted adsorption, demonstrating its application potential in the field of fruit and vegetable preservation.

[0104] Humidity-responsive release Based on mechanical properties and ethylene adsorption capacity, KC / GA / CuCo-MOF-4% composite aerogel was selected as the research object. Figure 9 The GA release can be obtained from the standard curve in (b). Figure 9 As shown in Figure (c), at 30% relative humidity (RH), the release of GA was 2.08 μg / mL after 48 h, with the overall release curve showing an initial increase followed by fluctuation. At 60% RH, the release was slightly higher than under low humidity conditions, remaining at 2.47 μg / mL after 48 h, exhibiting a relatively stable sustained-release characteristic. At 90% RH, the release of GA increased significantly further, reaching 2.92 μg / mL after 48 h, with the overall release level significantly higher than under medium and low humidity conditions.

[0105] The results indicate that increased ambient humidity significantly promotes the release of GA from the aerogel matrix. This is mainly attributed to the swelling of the hydrophilic polysaccharide network in the aerogel under high humidity conditions, leading to pore expansion and thus accelerating the diffusion and dissolution of GA molecules. Furthermore, the temporary decrease in the release curve at 12 h may be related to the re-adsorption of GA in the release medium or local concentration equilibrium, while the subsequent rebound indicates that the release process can continue. Overall, the KC / GA / CuCo-MOF composite aerogel can achieve continuous GA release under different humidity conditions, and the release rate is positively correlated with humidity, exhibiting good environmentally responsive controlled-release performance. This is beneficial for adjusting the release behavior of antioxidant or antibacterial active substances in food packaging according to actual humidity conditions.

[0106] Antioxidant activity like Figure 9 As shown in Figure (d), the ABTS radical scavenging ability of the composite aerogel continuously increases with the increase of CuCo-MOF content. The ABTS scavenging rate of pure KC aerogel is only 16.61±0.69%, while the scavenging rate increases significantly to 67.27±0.63% after the introduction of GA, indicating that GA, as a strong antioxidant, provides abundant phenolic hydroxyl active sites for the system. After further doping with CuCo-MOF, the scavenging rate steadily increases with the increase of MOF content: when the MOF content is 1%, the scavenging rate increases to 73.19±0.54%; as the content gradually increases to 2%, 3%, and 4%, the scavenging rates reach 83.46±0.93%, 91.42±0.55%, and 93.84±0.72%, respectively; when the MOF content reaches 5%, the scavenging rate further increases to 94.14±0.69%. This result indicates that the introduction of CuCo-MOF can synergistically enhance the antioxidant activity of the aerogel, which may be attributed to the metal sites (CuCo-MOF) in the MOF. 2+ / Co 2+ The synergistic effect between KC / GA and GA, as well as the adsorption or catalytic scavenging effect of MOF itself on free radicals, are observed. It is noteworthy that when the MOF addition exceeds 4%, the increase in scavenging rate tends to plateau, indicating that the system is close to saturation in antioxidant performance at 4%. Considering all factors, KC / GA / CuCo-MOF composite aerogel exhibits excellent free radical scavenging ability, and a 4% MOF addition is the optimal formulation.

[0107] Antibacterial properties Figure 10 Evaluation of the antibacterial properties of the KC / GA / CUCO-MOF composite aerogel of this invention; (a) Evaluation of the antibacterial properties of different samples against Escherichia coli (Escherichia coli) E. coli ) and Staphylococcus aureus ( S. aureus (a) Colony count image of sample pair; (b) Image of sample pair. E. coli(c) Statistics on the antibacterial rate of the sample pair; S. aureus The antibacterial rate was statistically analyzed; the growth inhibition rate of aerogels against Escherichia coli and Staphylococcus aureus was calculated using the plate count method to evaluate the antibacterial activity of aerogels. The growth inhibition effects and inhibition rates of different aerogels against the two bacteria were as follows: Figure 10 As shown, with the increase of CuCo-MOF addition, the antibacterial activity of the composite aerogel against Escherichia coli and Staphylococcus aureus showed a significant concentration-dependent increasing trend. Pure KC aerogel had no inhibitory effect on Escherichia coli and an inhibition rate of only 8.33±9.55% against Staphylococcus aureus; after the introduction of GA, the inhibition rates increased to 8.63±8.61% and 13.75±13.17%, respectively, indicating that GA endows the aerogel with basic antibacterial ability through its phenolic hydroxyl structure. Further doping with CuCo-MOF significantly enhanced the antibacterial properties: when the MOF content was 1%, the inhibition rates against *Escherichia coli* and *Staphylococcus aureus* reached 21.57±6.3% and 30.83±13.77%, respectively; when the MOF content reached 3%, the inhibition rates increased sharply to 84.64±2.15% and 92.12±1.02%, showing highly efficient antibacterial activity; further increasing the MOF content to 5% resulted in inhibition rates approaching 99.34±0.41% (*Escherichia coli*) and 99.21±0.41% (*Staphylococcus aureus*), nearing complete inhibition. These results indicate that the introduction of CuCo-MOF significantly enhanced the broad-spectrum antibacterial properties of the aerogel, and the mechanism may be attributed to the Cu released from the MOF. 2+ / Co 2+ Metal ions disrupt bacterial cell membrane integrity and induce oxidative stress. Overall, the KC / GA / CuCo-MOF composite aerogel exhibits excellent antibacterial properties, which increase with increasing MOF content, achieving almost complete antibacterial activity at concentrations of 3% or higher.

[0108] Strawberry freshness test Figure 11 This invention relates to the practical application of KC-based composite aerogel; (a) shows the appearance; (b) shows the spoilage rate; and (c) shows the weight loss rate. The core value of preservation packaging materials lies in their ability to effectively extend the shelf life of food. Figure 11 As shown, when KC / GA / CuCo-MOF-4% aerogel is applied to strawberries, its dense three-dimensional network structure enables the controlled and sustained release of antibacterial compounds while maintaining the optimal microenvironment within the packaging, thereby extending the shelf life of the strawberries. Figure 11Figure (a) shows the state of strawberries under different packaging conditions at 25 ℃. Both unpackaged and PE-film-packaged strawberries showed slight rotting on day 4. After 6 days, the unpackaged and PE-film-packaged strawberries showed severe spoilage, while the strawberries preserved with KC / GA / CuCo-MOF-4% aerogel maintained excellent appearance and quality, fully demonstrating the superior effectiveness of this aerogel in maintaining freshness over extended storage periods.

[0109] During storage, strawberries are susceptible to infection by pathogenic microorganisms, leading to tissue softening and spoilage. Therefore, the rate of decay has become a core indicator for evaluating the sensory quality and commercial value of fruits and vegetables. Figure 11 As shown in (b), the decay rates of the control group and the PE group reached 94.44% and 66.67% respectively on day 8. In contrast, the decay rate of strawberries packaged with KC / GA / CuCo-MOF aerogel was only 33.33%. This significant reduction in decay rate highlights the superior performance of the composite aerogel in blocking microbial invasion, inhibiting water loss, and slowing oxidative degradation, thereby effectively maintaining the overall quality of the fruit.

[0110] Strawberries experience continuous respiration, leading to water and nutrient loss during storage and consequently, weight loss. For example... Figure 11 As shown in (c), unpackaged strawberries experienced a weight loss rate of 22.53 ± 1.63% after 8 days, primarily due to the lack of a protective barrier, which accelerated moisture evaporation and increased the risk of microbial spoilage in the exposed environment. In contrast, PE film, with its inherent moisture-blocking properties, reduced the weight loss rate to 7.65 ± 0.75%. Among them, KC / GA / CuCo-MOF-4% aerogel exhibited the best performance, significantly improving the preservation effect. Its dense three-dimensional network structure maintained the weight loss rate at 1.81 ± 0.24% after 7 days of storage, effectively inhibiting the respiratory metabolism of strawberries. Furthermore, the antioxidant activity and antibacterial effect of GA and CuCo-MOF delayed microbial proliferation, synergistically reducing moisture loss and spoilage rates.

[0111] Figure 12 This invention describes the changes in firmness (a), titratable acidity (b), and total soluble solids content (c) of strawberries during storage. Strawberry firmness is a key indicator of freshness, directly affecting the preservation of fruit texture and flavor. Figure 12 As shown in Figure (a), the firmness of all four groups of strawberries decreased with prolonged storage time. Specifically, the firmness of the unpackaged group decreased from an initial value of 3.08 ± 0.29 kg / cm². 2 (10 5 The Pa value dropped sharply to 1.05 ± 0.18 kg / cm³. 2 (10 5The increased pressure (Pa) was mainly attributed to the degradation of cell wall polysaccharides by pectinase and the accelerated microbial activity. Strawberries packaged in PE film maintained a firmness of 1.49 kg / cm². 2 (10 5 (Pa), thanks to its basic barrier properties. Notably, strawberries packaged with KC / GA / CuCo-MOF-4% aerogel maintained a firmness of 1.78±0.03 kg / cm² after 7 days. 2 (10 5 The measured values ​​(Pa) indicate that the aerogel effectively inhibits strawberry respiration, reducing water and nutrient loss. This improved firmness retention can be attributed to enhanced moisture resistance and the release of CuCo-MOF, which prevents the decomposition of organic matter in the fruit by bacteria, thus reducing firmness.

[0112] Titratable acid content (TA) is an important indicator of strawberry flavor quality and is closely related to fruit metabolic activity and microbial processes. For example... Figure 12 As shown in (b), the total acid value (TA) of strawberries began to decrease after the first day, and this change was positively correlated with the ripeness of the strawberries. After 8 days, the TA values ​​of the unpackaged group and the PE film group decreased to 0.49±0.02% and 0.7±0.02%, respectively. The TA value of the KC / GA / CuCo-MOF-4% aerogel group decreased at a slower rate, still reaching 0.8±0.04%. Soluble solids (TSS) is another key indicator of strawberry quality. Figure 12 As shown in Figure (c), the TSS (Total Sediment Saturation) of all groups initially showed an upward trend. However, the TSS of the unpackaged group and the PE film group decreased to 7.1±0.52% and 8.8±0.35% respectively by day 8. In contrast, the TSS of the KC / GA / CuCo-MOF-4% aerogel group only decreased slightly and remained relatively stable throughout the storage period. Therefore, KC / GA / CuCo-MOF-4% aerogel can be used as a food packaging material to extend the shelf life of fruits.

[0113] In summary, this invention discloses a konjac glucomannan / carboxymethyl chitosan composite aerogel based on gallic acid, its preparation method, and its application. Using KGM and CMCS as matrices and GA as a crosslinking agent, a KC / GA / CuCo-MOF composite bioaerogel was successfully prepared. The addition of 4%~5% CuCo-MOF significantly improved the hardness, and this composite aerogel exhibited both high load-bearing capacity and good elasticity. In terms of functional properties, when the CuCo-MOF addition was 4%, the aerogel exhibited the optimal ethylene adsorption capacity (10.66±0.8 mg / m³). 3With its humidity-responsive intelligent slow-release function, it exhibits an antioxidant scavenging rate of up to 93.84±0.72%, and achieves near-complete inhibition against Escherichia coli and Staphylococcus aureus. Applying this optimally formulated aerogel to strawberry preservation packaging significantly reduced fruit weight loss after 8 days of storage, effectively delaying the decline in firmness and nutritional indicators (TA, TSS). This composite aerogel, with its dense three-dimensional network structure and multiple excellent activities including efficient ethylene removal, intelligent slow release, antibacterial and antioxidant properties, is an ideal active food preservation packaging material.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid, characterized in that, include: Cobalt acetate solution and copper acetate solution were added to trimesic acid solution, stirred and reacted, washed and dried under vacuum to obtain CuCo-MOF; After mixing and stirring the konjac glucomannan solution, carboxymethyl chitosan solution and glycerol evenly, a mixed solution is obtained; CuCo-MOF was ultrasonically dispersed in anhydrous ethanol to obtain a CuCo-MOF dispersion. The CuCo-MOF dispersion and gallic acid solution were added to the mixed solution in sequence and stirred evenly. After standing and freeze-drying, CuCo-MOF and gallic acid konjac glucomannan / carboxymethyl chitosan composite aerogel was obtained.

2. The preparation method of konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid according to claim 1, characterized in that, The cobalt acetate solution is prepared by dissolving cobalt acetate in deionized water; the copper acetate solution is prepared by dissolving copper acetate in deionized water; the pyromellitic acid solution is prepared by dissolving pyromellitic acid in a mixture of ethanol and deionized water. The molar ratio of the total metal ions of cobalt acetate and copper acetate to pyromellitic acid is (0.6~1.0):(0.3~0.5); the molar ratio of cobalt acetate to copper acetate is 1:2~2:

1. In the mixture of ethanol and deionized water, the volume ratio of ethanol to deionized water is 2:1 to 4:

1.

3. The preparation method of konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid according to claim 1, characterized in that, The conditions for the stirring reaction are: stirring at 80~100 ℃ for 0.5~1.5 h.

4. The preparation method of konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid according to claim 1, characterized in that, The washing conditions are: washing with deionized water 2-4 times, followed by methanol exchange for 2-4 days; the vacuum drying conditions are: vacuum drying at 50-70 °C for 10-14 h.

5. The preparation method of konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid according to claim 1, characterized in that, The concentration of the konjac glucomannan solution is 1.5 wt% to 2.5 wt%; the concentration of the carboxymethyl chitosan solution is 1.5 wt% to 2.5 wt%. The volume ratio of the konjac glucomannan solution to the carboxymethyl chitosan solution is 2:1 to 1:

2. The amount of glycerol added is 20wt%~40wt% of the total mass of the polysaccharide; the polysaccharide is konjac glucomannan and carboxymethyl chitosan.

6. The method for preparing konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid according to claim 1, characterized in that, The mixing and stirring time is 0.5~1.5h.

7. The method for preparing konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid according to claim 1, characterized in that, The CuCo-MOF was ultrasonically dispersed in anhydrous ethanol for 5-15 minutes; the gallic acid solution was prepared by dissolving gallic acid in deionized water. The amount of CuCo-MOF added is 1wt%~5wt% of the total mass of the polysaccharide; the amount of gallic acid added is 0.5wt%~1.5wt% of the total mass of the polysaccharide; the polysaccharide is konjac glucomannan and carboxymethyl chitosan.

8. The method for preparing konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid according to claim 1, characterized in that, The settling time is 10~14 h; the freeze-drying conditions are: freezing at -80~-20 ℃ for 10~14 h, followed by freeze-drying at a vacuum degree ≤100 Pa and -60~-40 ℃ for 36~60 h.

9. Konjac glucomannan / carboxymethyl chitosan composite aerogel based on CuCo-MOF and gallic acid, characterized in that, The aerogel was prepared using the method described in any one of claims 1-8 for the preparation of CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel.

10. The application of the CuCo-MOF and gallic acid-based konjac glucomannan / carboxymethyl chitosan composite aerogel as described in claim 9 in the preparation of food preservation packaging materials, antibacterial materials, antioxidant materials, ethylene adsorption materials, humidity-responsive slow-release materials, or fruit and vegetable preservation materials.

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