A double-layer aerogel packaging pad and a preparation method and application thereof

Abstract

This invention discloses a double-layer aerogel packaging pad, its preparation method, and its application. The aerogel packaging pad includes an upper agar layer, a lower gelatin layer, and a natural antibacterial agent. The aerogel pad of this invention comprises a hydrophilic agar layer and a hydrophobic gelatin layer. The soft agar layer wraps around fruits and vegetables, providing ample cushioning, while the gelatin layer, with its certain mechanical strength, provides sufficient resistance to compressive stress, thereby preventing mechanical damage to fruits and vegetables caused by external collisions or compression during transportation. The aerogel packaging pad not only has extremely high water absorption and water vapor absorption capacity but also possesses an intelligent humidity regulation function of "rapid absorption and slow release." It maintains the humidity inside the packaging pad at a suitable level, preventing the fresh fruits and vegetables from wilting due to dehydration and inhibiting the growth of microorganisms caused by excessive moisture, significantly extending the shelf life of fruits and vegetables.

Description

Technical Field

[0001] This invention belongs to the field of fruit and vegetable preservation technology, specifically relating to a double-layer aerogel packaging pad, its preparation method, and its application. Background Technology

[0002] Strawberries are beloved by consumers for their high nutritional value, excellent flavor, and appealing appearance. However, research shows that approximately 30% of agricultural products suffer varying degrees of mechanical damage post-harvest, which accelerates nutrient loss, ripening, senescence, and spoilage, thus shortening shelf life and leading to food waste. Post-harvest water loss in fruits and vegetables is also a key factor affecting their quality. Studies indicate that fruits and vegetables can lose up to 45% of their moisture during storage, which not only increases their susceptibility to pathogen infection but also leads to the loss of flavor nutrients and a decrease in fruit firmness. Furthermore, research by the Food and Agriculture Organization of the United Nations has found that bacterial contamination causes the loss of nearly half of all fruits and vegetables each year. Therefore, effectively controlling mechanical damage, water loss, and microbial growth is crucial for extending the shelf life of fruits and vegetables and reducing food loss.

[0003] Traditional methods for delaying fruit and vegetable spoilage typically involve placing soft, non-biodegradable foam pads or absorbent mats under delicate fruits and vegetables such as strawberries. However, these traditional materials are derived from petroleum and are non-biodegradable, limiting their effectiveness in addressing environmental problems. While numerous studies have explored food preservation films and the addition of antimicrobial agents to inhibit bacterial growth, these films suffer from poor mechanical properties, insufficient thermal stability, easy dissolution, and difficulty in effectively releasing antimicrobial agents. Furthermore, there is a potential risk of component migration when fruits and vegetables are coated for preservation.

[0004] Aerogels are typically low-density, mesoporous nanoscale porous solid materials prepared through a sol-gel process, with pore sizes ranging from 2 to 50 nm. During preparation, ice crystal sublimation creates voids in the network structure, resulting in properties such as low density, high specific surface area, large porosity, lightweight, low deformation, and low thermal conductivity. In the context of sustainable development, proteins and polysaccharides are widely studied for aerogel preparation due to their excellent properties, including tunable structure, biocompatibility, renewability, biodegradability, and low cost and availability. Cellulose is widely available and commonly used in aerogel preparation; however, cellulose primarily originates from lignocellulosic materials, and research on aerogels involving agricultural byproduct cellulose is currently limited. Furthermore, the application scenarios for aerogel materials remain relatively limited, currently focusing mainly on meat and aquatic products, with less research on fruits and vegetables, and their functions are relatively singular and lack multifunctionality. Summary of the Invention

[0005] In order to more effectively preserve fruits and vegetables, especially those with easily damaged peels (such as strawberries, apples, pears, grapes, tomatoes, etc.) and reduce environmental pollution caused by traditional preservation materials, this invention provides the following technical solutions.

[0006] In a first aspect, the present invention provides an aerogel packaging pad, the aerogel packaging pad comprising an upper agar layer and a lower gelatin layer.

[0007] The applicant ingeniously designed an aerogel pad comprising an agar layer and a gelatin layer. The agar layer, being hydrophilic and flexible, better preserves fruits and vegetables while preventing damage to the peel. The gelatin layer, being hydrophobic and possessing a certain degree of mechanical strength, reduces moisture loss from the surface of fruits and vegetables and prevents damage from external pressure.

[0008] Preferably, the agar layer is composed of agar solution and cellulose solution, and the gelatin layer is composed of gelatin solution and cellulose solution.

[0009] Furthermore, the concentration of the agar solution is 0.5~2.5 wt%, for example: 0.5%, 1%, 1.5 wt%, 1.8 wt%, 2.0 wt%, 2.2 wt%, 2.5 wt%.

[0010] Furthermore, the concentration of the gelatin solution is 1 to 5 wt%, for example: 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%.

[0011] Furthermore, the concentration of the cellulose solution is 0.5~2 wt%, for example: 0.5 wt%, 0.7 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2.0 wt%.

[0012] Preferably, the volume ratio of the agar layer to the gelatin layer is 1:2 to 5, for example: 1:2, 1:3, 1:4, 1:5.

[0013] Preferably, the aerogel packaging pad may also contain an antibacterial agent.

[0014] Furthermore, the antibacterial agent is a natural antibacterial agent, which includes, but is not limited to, bio-essential oils, calcium lactate, compound lecithin, tea polyphenols, or ε-polylysine.

[0015] Furthermore, the natural antibacterial agent is added to the cellulose solution, and the concentration of the antibacterial agent in the cellulose solution is 0.1~1 wt%, for example: 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%.

[0016] In one specific embodiment of the present invention, the aerogel packaging pad consists of an upper agar layer and a lower gelatin layer.

[0017] In a second aspect, the present invention provides a method for preparing the aerogel packaging pad described in the first aspect, the method comprising the following steps: (1) Prepare agar solution, gelatin solution and cellulose solution; (2) The agar solution and the cellulose solution are mixed to prepare an agar layer precursor solution, and the gelatin solution and the cellulose solution are mixed to prepare a gelatin layer precursor solution; (3) Pour the agar layer precursor solution into the mold, then add the gelatin layer precursor solution, let stand and dry to obtain the aerogel pad; Optionally, the cellulose solution contains 0-1 wt% of an antibacterial agent.

[0018] Preferably, in step (1), the concentration of the agar solution is 0.5~2.5 wt%, for example: 0.5 wt%, 1 wt%, 1.5 wt%, 1.8 wt%, 2.0 wt%, 2.2 wt%, 2.5 wt%.

[0019] Furthermore, the concentration of the gelatin solution is 1 to 5 wt%, for example: 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%.

[0020] Furthermore, the concentration of the cellulose solution is 0.5~2 wt%, for example: 0.5 wt%, 0.7 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2.0 wt%.

[0021] Furthermore, the cellulose solution contains an antibacterial agent.

[0022] Furthermore, the antibacterial agent is a natural antibacterial agent, including but not limited to bio-essential oils, calcium lactate, compound lecithin, tea polyphenols, or ε-polylysine.

[0023] Furthermore, the concentration of the antibacterial agent in the cellulose solution is 0.1~1 wt%, for example: 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%.

[0024] Preferably, in step (2), the mixing volume ratio of the agar solution and the cellulose solution mixed therewith is 1 to 5:1, for example: 1:1, 2:1, 3:1, 4:1, 5:1.

[0025] Preferably, in step (2), the volume ratio of the gelatin solution to the cellulose solution mixed therewith is 1 to 5:1, for example: 1:1, 2:1, 3:1, 4:1, 5:1.

[0026] Preferably, the volume ratio of the agar layer precursor solution to the gelatin layer precursor solution is 1:2 to 5, for example: 1:2, 1:3, 1:4, 1:5.

[0027] Preferably, in step (3), the settling time is ≥1.5 h; for example: 1.5 h, 2.0 h, 2.5 h, 3 h.

[0028] The drying methods include freeze drying, supercritical drying, and atmospheric pressure drying.

[0029] Thirdly, the present invention provides the application of the aerogel packaging pad described in the first aspect or the aerogel packaging pad prepared according to the preparation method described in the second aspect in the preservation of fruits and vegetables.

[0030] Preferably, the fruits and vegetables include, but are not limited to, strawberries, apples, pears, grapes, or tomatoes.

[0031] The beneficial effects of this invention are: 1. The aerogel pad of the present invention comprises a hydrophilic agar layer and a hydrophobic gelatin layer. The soft agar layer wraps around fruits and vegetables, providing sufficient cushioning, while the gelatin layer with a certain mechanical strength provides sufficient resistance to compression stress, thereby avoiding mechanical damage to fruits and vegetables caused by external collisions or compression during transportation.

[0032] 2. The aerogel packaging pad of this invention contains a natural antibacterial agent. Compared with traditional absorbent pads or single-function plastic wrap, the aerogel packaging pad of this invention not only has extremely high water absorption and water vapor absorption capacity, effectively removing excess moisture inside the packaging, but also possesses an intelligent humidity regulation function of "rapid absorption and slow release." This maintains the humidity inside the packaging pad at a suitable level, preventing fresh fruits and vegetables from wilting due to dehydration, and inhibiting the growth of microorganisms caused by excessive moisture, significantly extending the shelf life of fruits and vegetables. Attached Figure Description

[0033] Figure 1 The figures show the mechanical properties-stress-strain curves of aerogels. A is the stress-strain curve of gelatin + wheat bran cellulose aerogel, and B is the stress-strain curve of agar + wheat bran cellulose aerogel. Figure 2The figures show the compressive strength, compressive modulus, and compressive yield stress of aerogels. A represents the compressive strength of gelatin + wheat bran cellulose aerogel, B represents the compressive modulus of gelatin + wheat bran cellulose aerogel, C represents the compressive yield stress of gelatin + wheat bran cellulose aerogel, D represents the compressive strength of agar + wheat bran cellulose aerogel, E represents the compressive modulus of agar + wheat bran cellulose aerogel, and F represents the compressive yield stress of agar + wheat bran cellulose aerogel. Figure 3 The figures show the solubility of aerogels. A represents the solubility of gelatin + wheat bran cellulose aerogel, and B represents the solubility of agar + wheat bran cellulose aerogel. Figure 4 The images show aerogel packaging pads with different volume ratios of agar and gelatin layers. A has a volume ratio of 2:1, B has a volume ratio of 1:1, and C has a volume ratio of 1:2. Figure 5 The figure shows the stress-strain curve of the aerogel. Figure 6 The figure shows the compressive strength of the aerogel; Figure 7 The figure shows the compressive modulus of the aerogel; Figure 8 The figure shows the compressive yield stress of the aerogel. Figure 9 The figure shows the water absorption capacity of the aerogel; Figure 10 The figure shows the water vapor absorption capacity of the aerogel; Figure 11 The moisture absorption properties of the bilayer aerogel are shown at 60% humidity. Figure 12 The moisture absorption properties of the bilayer aerogel are shown at 80% humidity. Figure 13 The moisture absorption properties of the bilayer aerogel are shown in the figure at 100% humidity. Figure 14 The desorption properties of the bilayer aerogel are shown at 43% humidity. Figure 15 The results of the qualitative and quantitative antibacterial experiments of the bilayer aerogel are shown. (a) shows the inhibition zones of bilayer aerogels with different concentrations of ε-polylysine against Escherichia coli and Staphylococcus aureus (①-⑤ correspond to PL0, PL2, PL4, PL6, and PL8, respectively); (b) shows the diameter of the inhibition zones of the bilayer aerogel against Escherichia coli and Staphylococcus aureus; (c) shows the quantitative experimental results of the antibacterial effect of the bilayer aerogel against Escherichia coli; and (d) shows the quantitative experimental results of the antibacterial effect of the bilayer aerogel against Staphylococcus aureus. Detailed Implementation

[0034] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Some of the reagents used in the embodiments of this invention are as follows: Wheat bran cellulose: Shaanxi Panier Biotechnology Co., Ltd.; Gelatin: Maclean Biotechnology Co., Ltd.; Agar: Shanghai Yuanye Biotechnology Co., Ltd.

[0036] ε-Polylysine: Shanghai Yuanye Biotechnology Co., Ltd.

[0037] Escherichia coli and Staphylococcus aureus: Beijing Hengkang Tiansheng Biotechnology Co., Ltd.

[0038] Example 1: Selection of concentrations for agar solution and gelatin solution (1) Preparation of gelatin + wheat bran cellulose aerogel (G / WBC) Agar was dissolved in deionized water at 60°C to prepare gelatin precursor solutions of 1 wt%, 2 wt%, 3 wt%, 4 wt%, and 5 wt%, respectively. The gelatin precursor solutions of different concentrations were then sol-gelled at 60°C for 30 min, followed by preliminary gelation at room temperature. At a volume ratio of 3:1 (gelatin precursor solution to wheat bran cellulose suspension), different concentrations of gelatin precursor solutions were mixed evenly with 1 wt% wheat bran cellulose suspension to form hydrogels. The gelatin / wheat bran cellulose hydrogels were poured into molds and crosslinked at ambient temperature for 2 h. The prepared hydrogels were pre-cooled at -80°C for 12 h, and then freeze-dried in a freeze dryer for 72 h to obtain gelatin + wheat bran cellulose aerogels (G / WBC). Simultaneously, a control sample of pure gelatin aerogel was prepared.

[0039] (2) Preparation of agar + wheat bran cellulose aerogel (A / WBC) Agar was dissolved in deionized water at 96℃ to prepare agar precursor solutions of 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, and 2.5 wt%, respectively. The agar precursor solutions of different concentrations were then mixed at 96℃ for 30 min to induce sol-gelation, followed by preliminary gelation at room temperature. Agar precursor solutions of different concentrations were mixed with 1 wt% wheat bran cellulose suspension at a volume ratio of 3:1 to form hydrogels. The agar / wheat bran cellulose hydrogels were poured into molds and crosslinked at ambient temperature for 2 h. The prepared hydrogels were pre-cooled at -80℃ for 12 h, and then freeze-dried in a freeze dryer for 72 h to obtain agar + wheat bran cellulose aerogels (A / WBC). Simultaneously, a control sample of pure agar aerogel was prepared.

[0040] (3) The mechanical properties of the aerogel were determined using a universal testing machine equipped with a 100 N force sensor. Cylindrical aerogel specimens with a diameter of 30 mm and a thickness of 5 mm were compressed to 80% of their original height at a rate of 1 mm / min, with all specimens having the same height-to-diameter ratio. The test parameters included stress-strain curves, compressive strength, compressive modulus, and compressive yield stress.

[0041] Figure 1 The stress-strain curves of the composite aerogels were displayed, showing that all samples exhibited three characteristic stages: first, the elastic deformation stage (0%-20% strain), then the plastic deformation stage (20%-60% strain), and finally the densification region (60%-80% strain). This indicates that all samples exhibit the typical compressive behavior of bio-based aerogel porous materials. The addition of high concentrations of gelatin and agar resulted in deeper stress-strain curves, more closely resembling the compressive behavior of bio-based aerogels.

[0042] Figure 2 The compressive strength, compressive modulus, and compressive yield stress of the composite aerogel are shown. (From...) Figure 2 As can be seen from AC, the compressive strength and compressive modulus of the G / WBC composite aerogel both increase with increasing gelatin concentration, indicating that higher gelatin concentrations enhance the aerogel's hardness. This superior hardness stems from the uniform porous structure of gelatin, which facilitates uniform stress distribution. From the yield stress perspective, there is no significant difference between adding 4 wt% and 5 wt% gelatin concentrations. Based on the principle of low-cost selection, the composite aerogel with 4 wt% gelatin was chosen. Figure 2The DF analysis shows that the compressive modulus and compressive yield stress of the A / WBC composite aerogel both increase with increasing gelatin concentration. There is no significant difference in compressive strength between 2 wt% and 2.5 wt% agar. Based on the principle of low-cost selection, the composite aerogel with 2 wt% agar was chosen.

[0043] Depend on Figure 2 A comparison of the two composite aerogel materials shows that the compressive strength of the G / WBC composite aerogel is about four times higher than that of the A / WBC composite aerogel. However, the compressive modulus of the A / WBC composite aerogel is much lower than that of the G / WBC composite aerogel, indicating that it has a good buffering and energy absorption effect. Both materials have their own advantages as aerogel materials.

[0044] Example 2 Preparation of a bilayer aerogel (agar layer: gelatin layer ratio 1:2) (1) Prepare 2 wt% agar solution, 4 wt% gelatin solution and 1 wt% wheat bran cellulose solution respectively.

[0045] (2) Take agar solution and cellulose solution respectively, mix them in a volume ratio of 3:1 to prepare agar layer precursor solution; take gelatin solution and cellulose solution respectively, mix them in a volume ratio of 3:1 to prepare gelatin layer precursor solution.

[0046] (3) Take the agar layer precursor solution and the gelatin precursor solution in a volume ratio of 1:2. Then pour the agar layer precursor solution into the mold and add the gelatin layer precursor solution. Let the hydrogel stand at ambient temperature for 2 h to eliminate trapped air and promote cross-linking. Then pre-cool the hydrogel at -80℃ for 12 h and freeze-dry it in a freeze dryer to obtain a bilayer aerogel.

[0047] Comparative Example 1: Preparation of Mixed Non-Layered Aerogels The specific preparation process is the same as in Example 2, except that 2 wt% agar solution and 4 wt% gelatin solution are first mixed at a volume ratio of 1:2, and then 1% cellulose solution is added at a volume ratio of 3:1 between the mixed solution and the cellulose solution. After mixing, the mixture is poured into a mold.

[0048] Comparative Example 2: Preparation of cellulose + agar monolayer aerogel A 2 wt% agar solution was initially gelled. Then, 1% cellulose solution was added at a volume ratio of 3:1 (agar solution to cellulose solution). The mixture was poured into a mold and allowed to stand at ambient temperature for 2 hours to eliminate trapped air and promote cross-linking. The hydrogel was then pre-cooled at -80°C for 12 hours and freeze-dried in a freeze dryer to obtain a cellulose + agar monolayer aerogel.

[0049] Comparative Example 3: Preparation of cellulose / gelatin monolayer aerogel A 4 wt% gelatin solution was initially gelled. Then, 1% cellulose solution was added at a volume ratio of 3:1 (gelatin solution to cellulose solution). The mixture was poured into a mold, and the hydrogel was allowed to stand at ambient temperature for 2 hours to eliminate trapped air and promote cross-linking. The hydrogel was then pre-cooled at -80°C for 12 hours and freeze-dried in a freeze dryer to obtain a cellulose + gelatin monolayer aerogel.

[0050] Comparative Example 4: Preparation of a bilayer aerogel (agar layer: gelatin layer ratio of 2:1) The specific preparation process is the same as in Example 2, except that the volume ratio of the agar layer precursor solution to the gelatin layer precursor solution is 2:1.

[0051] Comparative Example 5: Preparation of a bilayer aerogel (agar layer: gelatin layer = 1:1) The specific preparation process is the same as in Example 2, except that the volume ratio of the agar layer precursor solution to the gelatin layer precursor solution is 1:1.

[0052] Performance determination experiment of aerogel samples Take the aerogel samples from Example 2 and Comparative Examples 1 to 5, and measure the mechanical strength, water absorption capacity, water vapor adsorption capacity, moisture absorption and desorption properties of the aerogel samples.

[0053] (1) The mechanical properties of the aerogel were determined using a universal testing machine equipped with a 100 N force sensor. Cylindrical aerogel specimens with a diameter of 30 mm and a thickness of 5 mm were compressed to 80% of their original height at a rate of 1 mm / min, with all specimens maintaining the same height-to-diameter ratio. The test parameters included stress-strain curves, compressive strength, compressive modulus, and compressive yield stress. like Figure 5 As shown, the stress-strain curves of all samples exhibit the typical three-stage compression behavior of bio-based porous aerogel materials: elastic deformation (0-20% strain), plastic deformation (20-60% strain), and densification region (60-80% strain). Overall, group 1:2 has high stress-strain curves.

[0054] like Figure 6 As shown, the samples, arranged in descending order of compressive strength, are: Sample 2 of Example, Sample 5 of Comparative Example, Sample 3 of Comparative Example, Sample 2 of Comparative Example, Sample 4 of Comparative Example, and Sample 1 of Comparative Example. This demonstrates that the aerogel with a volume ratio of agar layer to gelatin layer of 1:2 is harder and can withstand greater forces to maintain its integrity.

[0055] like Figure 7As shown, the compressive modulus of the sample in Example 2 is similar to that of the sample in Comparative Example 1, but much lower than that of the sample in Comparative Example 3. This indicates that the aerogel with a volume ratio of agar layer to gelatin layer of 1:2 has a low modulus energy, but also has a certain energy absorption and buffering capacity.

[0056] like Figure 8 As shown, in terms of compressive yield stress, the sample in Example 2 has the highest compressive yield stress, followed by Comparative Example 5, Comparative Example 3, Comparative Example 2, Comparative Example 4, and Comparative Example 2. This demonstrates that aerogels with an agar layer to gelatin layer volume ratio of 1:2 exhibit strong "rigidity" and "strength" under pressure, indicating that aerogel materials are durable and reliable.

[0057] (2) Water absorption capacity was tested using the gravimetric method to assess the water retention performance of the material. The dried aerogel was immersed in water, ensuring that the pores were completely filled with water. At 37°C, the aerogel was placed in a beaker containing 15 mL of distilled water and soaked for 24 hours, with tests conducted at regular intervals. Its water absorption capacity (WAC) was then measured. The WAC of the aerogel was calculated using the formula: In the formula, W1 and W2 represent the mass of the sample before and after water absorption (in grams), respectively.

[0058] like Figure 9 As shown, the samples, ordered from highest to lowest water absorption capacity (WAC%), are: Sample 2 (2449.55±31.37), Sample 3 (2386.89±19.25), Sample 5 (2217.82±30.13), Sample 4 (2151.15±20.98), Sample 2 (2100.90±63.28), and Sample 1 (1563.90±55.08). This is because the uniform porous structure of the gelatin / cellulose-based aerogel provides ample space for moisture storage.

[0059] (3) Measurement of water vapor absorption capacity (WVAC) of aerogel. The weighed and dried aerogel sample was placed in a constant temperature and humidity chamber and left to stand for 24 h at 25℃ and 100% relative humidity (RH). The WVAC was calculated according to the following formula.

[0060] In the formula, m1 and m2 represent the initial and final sample masses (g), respectively, measured before and after exposure to water vapor.

[0061] like Figure 10As shown, the samples, ranked from highest to lowest water vapor absorption capacity (WVAC%), are: Sample 2 (1.95±0.010), Sample 4 (1.94±0.05), Sample 5 (1.90±0.11), Sample 3 (0.84±0.01), Sample 1 (0.98±0.12), and Sample 2 (0.85±0.06). There was no significant difference in WVAC% among Sample 2, Sample 4, Sample 5, and Sample 3 (p>0.05), all exhibiting excellent performance. This is because the dense network formed by hydrogen bonds enhances water adsorption, making it a promising candidate for fruit preservation under high humidity conditions.

[0062] like Figures 11-14 As shown, at 60% humidity, the moisture absorption rate of the aerogels in Example 2, Comparative Example 3, and Comparative Example 4 increased with storage time. Within the first 3 hours, Example 2 reached 9% of its total moisture absorption capacity, while Comparative Example 3 and Comparative Example 4 reached 7.5% of their total moisture absorption capacity, indicating that the bilayer aerogel absorbs moisture rapidly. Figure 11 At 80% humidity, the moisture absorption rate of the aerogels in Example 2, Comparative Example 3, and Comparative Example 4 increased with storage time. Within the first 3 hours, Example 2 and Comparative Example 3 reached 14% of their total moisture absorption capacity, and Comparative Example 4 reached 12% of its total moisture absorption capacity, indicating that the bilayer aerogel absorbs moisture rapidly. Figure 12 At 100% humidity, the moisture absorption of the aerogels in Examples 2, 3, and 4 increased with storage time, reaching approximately 30% of their total moisture absorption capacity within the first 3 hours, indicating that the bilayer aerogels absorb moisture rapidly. Figure 13 At a relative humidity of 43%, the desiccation rates of the aerogels in Example 2, Comparative Example 3, and Comparative Example 4 were 13%, 9%, and 7%, respectively. Figure 14 This indicates that the double-layer gel can stably lock in moisture and release it slowly, effectively preventing the formation of condensation inside the packaging and providing a more stable high-humidity environment for fruits and vegetables.

[0063] Example 3: Preparation of a bilayer aerogel (including antibacterial agent) The specific process is the same as in Example 2, except that different concentrations of ε-polylysine (ε-PL) are added to the cellulose solution. The concentrations of ε-PL are 0 wt% (PL0 group), 0.2 wt% (PL2 group), 0.4 wt% (PL4 group), 0.6 wt% (PL6 group), and 0.8 wt% (PL8 group).

[0064] Aerogel samples from Example 2 (Control group), PL0 group, PL2 group, PL4 group, PL6 group and PL8 group were taken respectively for antibacterial ability testing.

[0065] (1) Escherichia coli and Staphylococcus aureus were inoculated into LB liquid medium and cultured at 37°C for 20 h. 200 μL of bacterial solution was evenly spread on the surface of LB solid medium, and sterilized aerogel samples were placed on the surface of the solid medium and cultured at 37°C for 24 h. The distance from the edge of the sample to the edge of the inhibition zone was measured.

[0066] like Figure 15 As shown in Figures AB, the inhibition zone diameters of the aerogels in groups PL0, PL2, PL4, PL6, and PL8 against *E. coli* were 0 mm, 1.44±0.07 mm, 2.08±0.11 mm, 3.28±0.24 mm, and 4.36±0.18 mm, respectively. The inhibition zone diameters against *S. aureus* were 0 mm, 1.41±0.02 mm, 2.57±0.09 mm, 3.54±0.08 mm, and 5.36±0.24 mm, respectively. Compared with group PL0, the inhibitory effects of each group with added ε-PL showed significant differences against both bacteria. This demonstrates that the ε-PL-loaded aerogel has excellent antibacterial effects.

[0067] (2) Inoculate Escherichia coli and Staphylococcus aureus separately into LB liquid medium and incubate with shaking. OD of bacterial culture 600 After the concentration reached 0.6, the mixture was diluted 1000 times. 0.5 g of aerogel material was dispersed into the bacterial suspension under shaking to ensure sufficient contact between the material and the bacteria. The mixture was incubated at 37°C for 12 h, and the change in the OD value of the bacterial suspension was measured within 12 h. The inhibition rate was calculated using the following formula.

[0068] In the formula: OD0 represents the absorbance value of the supernatant of the bacterial culture in the Control group (without aerogel), lg(1 / trans); OD represents the absorbance value of the supernatant containing aerogel bacterial solutions loaded with different concentrations of antibacterial agents, lg(1 / trans).

[0069] like Figure 15 As shown in CD, the OD values ​​of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) 600 The curves show that, with increasing culture time, the OD values ​​of the Control group and the PL0 group... 600The OD of PL2, PL4, PL6, and PL8 groups gradually increased. 600 The gradual decrease indicates that the aerogel without ε-PL loading exhibited only weak antibacterial activity compared to the blank control group, possibly due to the physical adsorption of bacteria by its porous structure. However, after loading with ε-PL, the antibacterial performance of the aerogel was significantly improved, with inhibition rates against both *Escherichia coli* and *Staphylococcus aureus* approaching or exceeding 90%. This is because ε-PL enhances the electrostatic interaction between the aerogel and bacterial cells, thereby improving the antibacterial effect.

[0070] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An aerogel packaging pad, characterized in that, The aerogel packaging pad includes an upper agar layer and a lower gelatin layer. The agar layer is composed of an agar solution and a cellulose solution, and the gelatin layer is composed of a gelatin solution and a cellulose solution.

2. The aerogel packaging pad according to claim 1, characterized in that, The concentration of the agar solution is 0.5-2.5 wt%, the concentration of the gelatin solution is 1-5 wt%, and the concentration of the cellulose solution is 0.5-2 wt%.

3. The aerogel packaging pad according to claim 1, characterized in that, The volume ratio of the agar layer to the gelatin layer is 1:2~5.

4. The aerogel packaging pad according to claim 1, characterized in that, The aerogel packaging pad also contains an antibacterial agent.

5. The aerogel packaging pad according to claim 4, characterized in that, The concentration of the antibacterial agent in the cellulose solution is 0~1 wt%.

6. The method for preparing the aerogel packaging pad according to claim 1, characterized in that, The preparation method includes the following steps: (1) Prepare agar solution, gelatin solution and cellulose solution; (2) The agar solution and the cellulose solution are mixed to prepare an agar layer precursor solution, and the gelatin solution and the cellulose solution are mixed to prepare a gelatin layer precursor solution; (3) Pour the agar layer precursor solution into the mold, then add the gelatin layer precursor solution, let stand and dry to obtain the aerogel pad.

7. The preparation method according to claim 6, characterized in that, In step (1), the concentration of the agar solution is 0.5~2.5 wt%, the concentration of the gelatin solution is 1~5 wt%, the concentration of the cellulose solution is 0.5~2 wt%, and the cellulose solution contains 0~1 wt% of antibacterial agent.

8. The preparation method according to claim 6, characterized in that, In step (2), the volume ratio of the agar solution to the cellulose solution mixed therewith is 1~5:1; and / or The volume ratio of the gelatin solution to the cellulose solution mixed therewith is 1 to 5:

1.

9. The preparation method according to claim 6, characterized in that, In step (3), the volume ratio of the agar layer precursor solution to the gelatin layer precursor solution is 1:2~5; and / or In step (3), the settling time is ≥1.5 h; and / or The drying method is freeze drying.

10. The application of the aerogel packaging pad according to any one of claims 1-5 or the aerogel packaging pad prepared according to any one of claims 6-9 in the preservation of fruits and vegetables.

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