Preparation method and application of genipin cross-linked and nanofiber-reinforced carboxymethyl chitosan antifogging preservative film

Abstract

The invention discloses a preparation method of a genipin cross-linked synergistic nanofiber reinforced carboxymethyl chitosan antifogging preservative film, which comprises the following steps: (1) dissolving carboxymethyl chitosan in deionized water, sequentially adding gelatin, genipin, glycerol and carboxylated cellulose nanofiber, stirring in a water bath, and standing for defoaming to obtain a mixed film solution; and (2) uniformly coating the mixed film solution in a tape casting manner, performing vacuum drying, and balancing to obtain the carboxymethyl chitosan antifogging preservative film. In a gelatin and glycerol system, carboxymethyl chitosan is taken as a main hydrophilic matrix, natural cross-linking agents genipin and carboxylated cellulose nanofibers are introduced, and finally, the high-performance carboxymethyl chitosan-based antifogging preservative film is prepared through a tape casting method, and the antifogging preservative film is good in performance. The invention also discloses an application of the carboxymethyl chitosan antifogging preservative film in preservation of fresh fruits and vegetables.

Description

Technical Field

[0001] This invention relates to a food preservation film, and more particularly to a method for preparing a genipin crosslinked synergistic nanofiber reinforced carboxymethyl chitosan anti-fog food preservation film and its application. Background Technology

[0002] During the storage and transportation of fresh fruits and vegetables after harvest, respiration and transpiration generate a large amount of water vapor inside the packaging. When the inner surface temperature of the packaging material is below the dew point, the water vapor condenses into discrete water droplets, causing the packaging to fog. Fogging not only hinders consumers' observation of the product's appearance and affects their purchasing desire, but the condensed water droplets also provide a favorable environment for the growth of microorganisms (such as molds and bacteria). The metabolic activities of microorganisms destroy the nutritional components of food and produce putrefactive substances, accelerating the spoilage of fruits and vegetables and shortening their shelf life. Currently, research on extending the shelf life of food focuses on developing packaging materials with excellent barrier, antibacterial, antioxidant, and ultraviolet shielding functions. However, anti-fogging capability, as a key characteristic for maintaining dryness, transparency, and sustained antibacterial properties inside the packaging, is often overlooked. Therefore, developing functional packaging materials that can effectively prevent fogging is crucial for ensuring the quality of fruits and vegetables.

[0003] Existing anti-fogging strategies are mainly based on hydrophobic or hydrophilic mechanisms. Hydrophobic strategies use self-assembly technology and surface grafting modification to create hydrophobic surfaces and reduce water droplet adhesion. However, the water droplets formed are prone to rolling onto food surfaces, potentially accelerating food spoilage, thus limiting their applicability in food packaging. In contrast, hydrophilic anti-fogging films utilize the material's own hydrophilic groups (such as -OH and -COOH) to absorb and rapidly spread condensate, forming a uniform and transparent water film that avoids light scattering, making them more suitable for food packaging. Among numerous candidate materials, carboxymethyl chitosan (CMC) is considered an ideal substrate for preparing hydrophilic anti-fogging films due to its excellent film-forming properties, biocompatibility, biodegradability, and rich hydrophilic groups. However, pure CMC films suffer from poor mechanical strength and are prone to swelling and dissolving in wet conditions, limiting their practical application. Although many studies have attempted to improve the overall performance of CMC films, existing solutions generally suffer from complex processes, insufficient safety, or limited performance improvements, making it difficult to balance practicality and biocompatibility. Summary of the Invention

[0004] This invention addresses the problems of poor mechanical strength and easy swelling and dissolution of pure carboxymethyl chitosan films in the prior art. It provides a method for preparing a carboxymethyl chitosan anti-fog preservation film reinforced by genipin crosslinking and nanofibers. The process is simple, highly operable, and the resulting carboxymethyl chitosan anti-fog preservation film has good overall performance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a genipin crosslinked synergistic nanofiber reinforced carboxymethyl chitosan anti-fog preservation film according to the present invention includes the following steps: (1) Dissolve carboxymethyl chitosan in deionized water, then add gelatin, genipin, glycerol, and carboxylated cellulose nanofibers in sequence. Stir in a water bath, then allow to stand to defoam, obtaining a mixed membrane solution. Genipin can react with the amino groups on the carboxymethyl chitosan molecular chain to form a stable covalent cross-linked structure, thereby improving the mechanical properties and stability of the membrane. Carboxylated cellulose nanofibers can form a strong interfacial bond with the genipin / carboxymethyl chitosan cross-linked network through physical interactions such as hydrogen bonding, playing a dual role of nano-reinforcement and microstructure regulation, ultimately achieving synergistic optimization of the mechanical properties, water resistance, optical properties, and biosafety of the carboxymethyl chitosan-based membrane. (2) After the mixed film liquid is uniformly coated by casting, it is vacuum dried and then balanced to obtain carboxymethyl chitosan anti-fog preservation film.

[0006] Preferably, in step (1), the mass-volume ratio of carboxymethyl chitosan to deionized water, glycerol, and carboxylated cellulose nanofibers is 2g:100mL:0.625mL:50mL, and the mass ratio of carboxymethyl chitosan to gelatin and genipin is 2:1:0.01.

[0007] Preferably, the gelatin is added in the form of a gelatin solution, which is prepared by dissolving gelatin in deionized water at 60°C, wherein the mass-to-volume ratio of gelatin to deionized water is 1 g: 25 mL.

[0008] Preferably, in step (1), the mixture is stirred in a water bath at 40°C for 24 hours.

[0009] Preferably, in step (2), the product is vacuum dried at 40°C.

[0010] Application of a carboxymethyl chitosan anti-fog preservation film in the preservation of fresh fruits and vegetables.

[0011] Therefore, this invention has the following beneficial effects: Addressing the problem of fogging on the inner surface of fruit and vegetable packaging under high humidity conditions, leading to quality deterioration, this invention uses carboxymethyl chitosan as the main hydrophilic matrix in a gelatin and glycerin system. It introduces the natural crosslinking agent genipin and carboxylated cellulose nanofibers, forming a stable three-dimensional network structure through Schiff base reaction and hydrogen bonding. Through a synergistic strategy of genipin crosslinking and carboxylated cellulose nanofiber reinforcement, a high-performance carboxymethyl chitosan-based anti-fog preservation film is finally obtained via a casting method. This anti-fog preservation film exhibits excellent performance. Based on the abundant hydrophilic groups on the film surface, it maintains high water vapor transmission rate (WVP) and moisture absorption rate (MA), effectively inhibiting fogging on the film surface. The anti-fog time is extended by more than 5 times compared to PE film. Simultaneously, it enables rapid adsorption and spreading of condensate, preventing water droplets from falling inside the packaging and effectively reducing the risk of microbial growth. In addition, the composite film has a low oxygen permeability (OP) and good shielding effect against ultraviolet rays in the 200–300 nm band. It can be used for packaging of easily oxidized and ultraviolet-sensitive foods. Using it as a packaging material for the preservation of fresh fruits and vegetables can extend the overall shelf life of fresh fruits and vegetables. It provides a feasible design idea and theoretical basis for developing high-performance, green and multifunctional food packaging materials based on natural polysaccharides. Attached Figure Description

[0012] Figure 1 This is a comparison chart of water contact angle measurement results.

[0013] Figure 2 This is a comparison chart of moisture absorption rate (Ma) measurement results. Different lowercase letters indicate significant differences between groups (p < 0.05).

[0014] Figure 3 This is a comparison chart of water vapor permeability (WVP) measurement results. Different lowercase letters indicate significant differences between groups (p < 0.05).

[0015] Figure 4 This is a comparison chart of oxygen permeability (OP) measurement results. Different lowercase letters indicate significant differences between groups (p < 0.05).

[0016] Figure 5 This is a comparison chart of ultraviolet transmittance measurement results.

[0017] Figure 6 This is a comparison chart of water solubility test results. Different lowercase letters indicate significant differences between groups (p < 0.05).

[0018] Figure 7 These are photos comparing blueberries on the second day of storage in a blueberry preservation experiment.

[0019] Figure 8 This is a graph showing the changes in blueberries during an 8-day storage period in a blueberry preservation experiment. Detailed Implementation

[0020] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0021] In this invention, chitosan (molecular weight 300 kDa) and carboxymethyl chitosan (BR, water-soluble, degree of substitution ≥60%) were sourced from Shanghai Maclean Biochemical Technology Co., Ltd.; genipin (purity ≥98%) was sourced from Shanghai Aladdin Biochemical Technology Co., Ltd.; carboxylated cellulose nanofibers (length 100-500 nm, diameter 4-20 nm, carboxyl content 1.2-3.0 mmol / g) were sourced from Guilin Qihong Technology Co., Ltd.; and blueberries were sourced from Xianfeng Fruit, Zhoushan City, Zhejiang Province, China.

[0022] Example 1 (1) Dissolve 2g of carboxymethyl chitosan in 100mL of deionized water, and add 1g of gelatin, 10mg of genipin, 0.625mL of glycerol and 50mL of carboxylated cellulose nanofibers in sequence. Stir in a 40℃ water bath for 24h, and let stand to defoam to obtain a mixed membrane solution; wherein the gelatin is added in the form of gelatin solution. The gelatin solution is prepared by dissolving gelatin in deionized water at 60℃, and the mass-volume ratio of gelatin to deionized water is 1g:25mL. (2) After uniformly coating 15 mL of the mixed film solution by casting, vacuum dry at 40 °C and after equilibration, carboxymethyl chitosan anti-fog preservation film is obtained.

[0023] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that genipin and carboxylated cellulose nanofibers were not added; otherwise, they were exactly the same as in Example 1.

[0024] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that no carboxylated cellulose nanofibers were added; otherwise, they are exactly the same as Example 1.

[0025] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that carboxymethyl chitosan is replaced with chitosan, and the rest is exactly the same as Example 1.

[0026] I. Performance testing of the films obtained in Example 1 and Comparative Examples 1-3 (a) Measurement of water contact angle The water contact angle of the sample was statically measured using a contact angle goniometer (JC2000DM). A 2 μL droplet of water was dispensed onto the sample surface using a syringe, the contact angle was recorded, and a photograph was taken. The water contact angle measurement results are as follows: Figure 1 As shown.

[0027] according to Figure 1It can be seen that the water contact angle of the film prepared in Example 1 is significantly reduced, indicating a significant improvement in surface hydrophilicity. In contrast, the water contact angles of the films prepared in Comparative Examples 1-3 are relatively high. Therefore, the low contact angle (high hydrophilicity) of the film prepared in Example 1 provides a surface property basis for its rapid water film spreading and long-lasting anti-fogging effect.

[0028] (ii) Measurement of moisture absorption rate (Ma) and water vapor permeability (WVP) Method for determining moisture absorption rate (Ma): At room temperature, accurately weigh the dried sample m0 and place it in a weighing bottle with a diameter of 3cm. Then place the weighing bottle in a desiccator containing saturated sodium chloride aqueous solution (relative humidity RH=70%). After 24 hours, weigh the sample m1 and calculate the moisture absorption rate Ma according to formula (1): Ma (%) = (m1-m0) / m0×100%.

[0029] Water vapor permeability (WVP) determination method: Weigh the sample bottle containing 3g anhydrous calcium chloride / 1.2g oxygen absorber (0.2g reduced iron powder, 0.6g sodium chloride, 0.4g activated carbon) initially. Cover the bottle opening with a film, and seal the opening with multiple layers of rubber bands where the film contacts the film. The WVP of the sample film is calculated using the formula: WVP (kg·m³) -1 ·s -1 ·Pa -1 ) = (ΔM × d) / (A × t × ΔP), where: ΔM is the increase in weight of the centrifuge tube (kg), d is the thickness of the film (m), and A is the area of ​​the film (m²). 2 ), t is the equilibrium time (s), and ΔP is the water vapor pressure difference across the membrane, which is 2.375×103 Pa under the experimental conditions.

[0030] Moisture absorption rate (MA) and water vapor transmission rate (WVP) are key indicators for evaluating the humidity control capability of food packaging films. Both of them together affect the stability of the internal microenvironment and the preservation effect.

[0031] The moisture absorption rate (MA) measurement results are as follows: Figure 2 As shown. From Figure 2It can be seen that the film prepared in Example 1 exhibits the highest moisture absorption rate of 23.5%, while the film prepared in Comparative Example 3 shows a significantly lower moisture absorption rate, the lowest being 6.2%. This is due to the fundamental difference in their chemical structures and crosslinking behaviors. Carboxymethyl chitosan molecules are rich in strongly hydrophilic functional groups such as -COOH and -OH, exhibiting high hydrophilicity. The crosslinking of genipin does not consume these main hydrophilic groups, but rather reacts with -NH2 in the system to construct a loose three-dimensional network. This network avoids the tight packing of molecular chains, forming numerous pores and channels, significantly increasing the accessible surface area and diffusion path of water molecules, allowing water molecules to fully bind with the internal hydrophilic groups. Simultaneously, the surface of carboxylated cellulose nanofibers is also rich in hydrophilic hydroxyl groups, further providing abundant hydrogen bonding sites. The synergistic effect of genipin, carboxymethyl chitosan, and carboxylated cellulose nanofibers may form a composite structure with interpenetrating network characteristics, endowing the material with extremely strong moisture absorption and retention capabilities. The film prepared in Comparative Example 3 showed the opposite trend. Genipin crosslinking directly consumed the -NH2 hydrophilic groups on the chitosan chains, reducing the number of free hydrophilic sites. Therefore, although carboxylated cellulose nanofibers are hydrophilic materials themselves, their dominant role in the chitosan system is to enhance crosslinking and promote densification, ultimately leading to a decrease in overall moisture absorption capacity.

[0032] Water vapor transmission rate (WVP) such as Figure 3 As shown. A higher WVP helps to expel moisture generated by the respiration of fruits and vegetables in a timely manner, inhibiting fogging and microbial growth inside the packaging, thereby extending shelf life. The film prepared in Comparative Example 3 has the highest WVP. The film prepared in Example 1 has a similar WVP value to the film prepared in Comparative Example 3, but the underlying mechanisms are different. In Example 1, the introduction of genipin and carboxymethyl chitosan significantly increased the WVP by approximately 126%. This is mainly attributed to the following mechanisms: on the one hand, genipin crosslinks with carboxymethyl chitosan, optimizing the network structure and potentially forming more interconnected channels; on the other hand, both carboxymethyl chitosan and carboxymethyl cellulose nanofibers carry negative charges (-COO-, -OH), resulting in electrostatic repulsion in the aqueous phase. This, to some extent, hinders the complete fusion of carboxymethyl cellulose nanofibers and the carboxymethyl chitosan / genipin network, leading to a microscopically loose and porous structure that provides a rapid diffusion path for water molecules. Furthermore, the transport of water molecules in the polymer mainly occurs through amorphous regions, and the increase in interfacial regions in the composite material further promotes the permeation and diffusion of water molecules. In contrast, in Comparative Example 3, the crosslinking of genipin directly consumed some of the hydrophilic groups (-NH2) and formed a more dense network structure, thus resulting in a decrease in overall WVP. Although chitosan becomes positively charged under acidic conditions (-NH3),... +), and negatively charged carboxylated cellulose nanofibers can be combined through electrostatic attraction, but the addition of excessive carboxylated cellulose nanofibers may cause local aggregation and interface defects, which in turn form a small number of rapid water vapor channels, resulting in a slight increase in the WVP of the film prepared in Comparative Example 3.

[0033] In summary, the film prepared in Example 1 possesses both high moisture barrier properties (WVP) and excellent moisture absorption capacity, forming a synergistic humidity management mechanism of rapid moisture absorption and efficient moisture permeability. This allows it to absorb condensate in a timely manner and accelerate the outward diffusion of water vapor, effectively maintaining a suitable humidity level inside the packaging and inhibiting droplet formation and microbial growth. While the film prepared in Comparative Example 3 exhibits strong moisture barrier properties, its moisture absorption capacity is limited, resulting in a relatively weaker humidity regulation function. This difference fundamentally stems from the different molecular structures, charge characteristics, and interaction modes between the two polysaccharides and genipin / carboxylated cellulose nanofibers, ultimately manifesting as drastically different moisture treatment performances. This provides a theoretical basis for selecting packaging materials for different fruit and vegetable preservation scenarios.

[0034] (III) Oxygen permeability (OP) measurement Place the sample vial in a desiccator (80% RH) containing saturated sodium chloride solution and leave it at room temperature for 24 hours. Remove the membrane and weigh it again. The OP of the sample membrane is calculated using the formula: OP (kg·m³). -1 ·s -1 ) = (m1 - m0) / (d × S), where: m0 and m1 are the weights of the beaker before and after the experiment (kg), d is the time (s), and S is the area (m²). 2 ).

[0035] The oxygen concentration inside the packaging directly affects the respiration rate and shelf life of fruits and vegetables. OP measurement results are as follows: Figure 4 As shown. According to Figure 4 It is evident that the film prepared in Example 1 had the lowest OP value, indicating that the introduction of genipin and carboxylated cellulose nanofibers significantly reduced the OP value of the film, demonstrating a marked improvement in its oxygen barrier performance. This effect is mainly attributed to the following synergistic mechanism: Genipin, as a crosslinking agent, forms Schiff bases and other covalent bonds with the -NH2 groups in the polysaccharide chains, constructing a dense three-dimensional network structure. This not only enhances intermolecular forces but also restricts chain segment movement and free volume, thereby significantly increasing the diffusion path and migration resistance of oxygen molecules. Simultaneously, carboxylated cellulose nanofibers, as a high aspect ratio nano-reinforcing phase, can form a tortuous physical barrier network in the polymer matrix, further extending the oxygen permeation path. Furthermore, since oxygen is a nonpolar molecule with low solubility in polar polysaccharide matrices, the combined effect of these two factors significantly reduces the OP value. The chemical crosslinking of genipin and the physical barrier of carboxylated cellulose nanofibers synergistically construct a highly efficient gas barrier system, providing a key material basis for maintaining a low-oxygen environment within packaging and delaying the senescence of fruits and vegetables.

[0036] (iv) Tensile strength (TS) and elongation at break (EAB) determination: The TS and EAB of the film were tested at room temperature using an electric tensile testing machine (China-ZQ-990LA). The sample was 40 mm long and 20 mm wide, and stretched at a rate of 50 mm / min. Each sample was tested at least three times.

[0037] The formula for calculating TS is: TS (MPa) = F / S, where: F is the maximum tensile strength of the membrane (N); S is the cross-sectional area of ​​the membrane (cm²). 2 ).

[0038] The formula for calculating EAB is: EAB (%) = (L1 - L) / L1 × 100%, where: L1 is the breaking elongation distance of each film (mm); L is the initial length of the film (mm).

[0039] Good mechanical properties are crucial for packaging materials to maintain structural integrity during transportation and storage. The tensile strength (TS) and elongation at break (EAB) results are shown in Table 1. TS reflects the material's ability to resist external forces, while EAB characterizes its flexibility and deformation potential. The tensile strength of the film prepared in Example 1 reached 28.93 MPa, more than three times higher than the 8.67 MPa of the film prepared in Comparative Example 3, indicating that the combined effect of genipin and carboxylated cellulose nanofibers significantly improved the mechanical properties of the film. Genipin can react with the -NH2- groups in the system through amide bonds and Schiff bases to form covalent crosslinks, constructing a robust three-dimensional network structure. This network can effectively transfer and disperse stress, thereby improving macroscopic strength. Simultaneously, carboxylated cellulose nanofibers, as a high aspect ratio and high modulus nanoreinforcing phase, can be uniformly dispersed in the matrix and bond with the polymer through strong hydrogen bonds. Under stress, they bear the load and inhibit microcrack propagation, producing a significant nanoreinforcing effect. The EAB value decreased after the introduction of carboxylated cellulose nanofibers. This may be because the high-modulus rigid nanofiller, carboxylated cellulose nanofibers, has a significant modulus difference with the flexible CMC matrix. During stretching, stress tends to concentrate at the interface between the two phases and cannot be dispersed through the flexible deformation of the matrix, ultimately leading to a decrease in the flexibility of the composite film, manifested as a lower EAB value. This phenomenon of increased strength accompanied by decreased flexibility is also a typical mechanical behavior characteristic of rigid nanofiller-reinforced polymer systems. Overall, the combined effect of genipin and carboxylated cellulose nanofibers improved the mechanical properties of the film.

[0040] Table 1. Results of Tensile Strength (TS) and Elongation at Break (EAB) of Thin Films

[0041] Note: Different lowercase letters indicate significant differences between groups (p < 0.05).

[0042] (v) Measurement of ultraviolet transmittance The film was cut into rectangular sample strips (12×35mm), and the ultraviolet shielding performance of the film in the wavelength range of 200-800nm ​​was measured using a Labsphere UV-2000F (USA) with air as a reference.

[0043] The color and transparency of food packaging films are important factors influencing consumers' visual perception and purchasing intentions. Ultraviolet transmittance measurement, for example... Figure 5 As shown. According to Figure 5 It is evident that the introduction of genipin significantly alters the color of the composite membrane: the carboxymethyl chitosan-based membrane appears purple, while the chitosan-based membrane turns blue-green. This color change is attributed to genipin's role as an iridoid crosslinking agent. Its active aldehyde group (-CHO) reacts with the amino group (-NH2) in carboxymethyl chitosan and gelatin via a Schiff base reaction, subsequently undergoing oxidation to form a chromophore with an extended conjugated structure, thus imparting the material's characteristic color. This conjugated system also enhances the film's absorption capacity in the ultraviolet region (especially 200-300 nm), significantly improving its UV shielding performance, with a transmittance below 7%. This UV blocking function helps protect photosensitive nutrients (such as anthocyanins) in fresh fruits and vegetables from photo-oxidative degradation, thereby maintaining their quality. It is worth noting that the introduction of carboxylated cellulose nanofibers to improve mechanical properties slightly weakened the UV shielding performance (transmittance increased slightly from about 2% to 7%), which may be due to the dilution of the local concentration of genipin chromophores by the dispersion of carboxylated cellulose nanofibers in the matrix. Nevertheless, the film prepared in Example 1 still maintains a high UV blocking rate of about 93%, exhibiting good photoprotection capabilities.

[0044] (vi) Determination of water solubility (WS) The sample was dried at 40℃ for 24 hours and weighed (m1). A 2cm × 2cm film sample was then immersed in distilled water at room temperature for 24 hours. The remaining sample in the water was filtered out, dried at 105℃ for 24 hours, and weighed (m2). The WS calculation formula is: WS (%) = (m1 - m2) / m1 × 100%.

[0045] Water solubility is a key indicator for evaluating the stability of food packaging films in real-world humid environments. The water solubility test results are as follows: Figure 6 As shown. According to Figure 6It can be seen that the film prepared in Comparative Example 1 has a water solubility as high as 80% due to its rich hydrophilic groups; however, after introducing genipin and carboxylated cellulose nanofibers, the water solubility of the film prepared in Example 1 was significantly reduced to 21%, and the stability was improved by 4 times. This improvement is mainly attributed to the efficient cross-linking effect of genipin: the ester group in its molecule can undergo nucleophilic substitution with the -NH2 on the carboxymethyl chitosan and gelatin chains to form amide bonds; at the same time, the dihydropyran ring of genipin is ring-opened by the nucleophilic attack of -NH2 to generate an active aldehyde intermediate, which in turn forms a Schiff base (C=N) or a complex heterocyclic conjugated structure. These reactions together construct a stable three-dimensional covalent cross-linked network between carboxymethyl chitosan / gelatin and genipin, which greatly inhibits the dissolution and swelling of polymer molecular chains in water. In addition, the addition of carboxylated cellulose nanofibers further enhances the rigidity of the network, and the abundant hydroxyl groups on its surface can form a dense hydrogen bond network with the -COOH, residual -NH2 on the carboxymethyl chitosan chain and the genipin cross-linking points. The synergistic effect of chemical crosslinking and physical hydrogen bonding significantly improves the crosslinking density of the system, making the film structure more compact, thereby effectively blocking the penetration and diffusion of water molecules and improving the stability of the composite membrane in high humidity environments.

[0046] Blueberry Preservation Experiment Fresh blueberries that were undamaged, plump, free from spoilage, and uniform in color and size were selected for the experiment. The preservation experiment was divided into four groups according to the type of film used: blueberries coated with the films prepared in Example 1 and Comparative Examples 1-3. The blueberries were placed in disposable petri dishes and stored at room temperature for 8 days. Photos of the blueberries, both whole and in the disposable petri dishes, were taken every 2 days. The photos taken on the second day are shown below. Figure 7 As shown, photos of blueberries during storage are as follows: Figure 8 As shown.

[0047] from Figure 7 As can be seen, the film prepared in Example 1 is highly transparent in appearance and can clearly present the appearance of blueberries, demonstrating excellent and long-lasting anti-fogging ability. In contrast, the films of Comparative Examples 1 to 3 are darker in color, and obvious fogging appeared on the film of Comparative Example 1 on the second day of storage.

[0048] from Figure 8 It can be seen that the film prepared in Example 1 has the best inhibitory effect on blueberry rot. The blueberries did not rot after being stored for 8 days and remained relatively plump. In contrast, the blueberries in Comparative Examples 1 to 3 showed varying degrees of shriveling and rot.

[0049] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A method for preparing a genipin-crosslinked synergistic nanofiber-reinforced carboxymethyl chitosan anti-fog food preservation film, characterized in that, Includes the following steps: (1) Dissolve carboxymethyl chitosan in deionized water, and add gelatin, genipin, glycerin and carboxylated cellulose nanofibers in sequence. Stir in a water bath and let stand to defoam, to obtain a mixed membrane solution. (2) After the mixed film liquid is uniformly coated by casting, it is vacuum dried and then balanced to obtain carboxymethyl chitosan anti-fog preservation film.

2. The method for preparing a genipin crosslinked synergistic nanofiber reinforced carboxymethyl chitosan anti-fog preservation film according to claim 1, characterized in that, In step (1), the mass-volume ratio of carboxymethyl chitosan to deionized water, glycerol, and carboxylated cellulose nanofibers is 2g:100mL:0.625mL:50mL, and the mass ratio of carboxymethyl chitosan to gelatin and genipin is 2:1:0.

01.

3. The method for preparing a genipin crosslinked synergistic nanofiber reinforced carboxymethyl chitosan anti-fog preservation film according to claim 1 or 2, characterized in that, The gelatin is added in the form of a gelatin solution, which is prepared by dissolving the gelatin in deionized water at 60°C, with a mass-to-volume ratio of 1g gelatin to 25mL deionized water.

4. The method for preparing a genipin crosslinked synergistic nanofiber reinforced carboxymethyl chitosan anti-fog preservation film according to claim 1, characterized in that, In step (1), the mixture is stirred in a 40°C water bath for 24 hours.

5. The method for preparing a genipin crosslinked synergistic nanofiber reinforced carboxymethyl chitosan anti-fog preservation film according to claim 1, characterized in that, In step (2), vacuum drying is performed at 40°C.

6. The application of the carboxymethyl chitosan anti-fog preservation film prepared by the method for preparing genipin crosslinked synergistic nanofiber reinforced carboxymethyl chitosan anti-fog preservation film as described in claims 1-5 in the preservation of fresh fruits and vegetables.

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