An anti-fog fresh-keeping coating and a preparation method thereof

Abstract

This invention belongs to the field of food preservation and functional coating technology, and relates to an anti-fogging preservation coating and its preparation method. The coating uses chitosan modified by Schiff base crosslinking with tea polyphenols as the main film-forming material, and introduces glycerol as a synergistic component. It is also compounded with film-forming aids, plasticizers, surfactants, and preservatives to form a transparent and stable coating. The modified chitosan constructs a ternary crosslinking structure with tea polyphenols and terephthalaldehyde, which not only improves the material's antioxidant and antibacterial properties but also avoids the toxicity problems associated with traditional crosslinking agents. The resulting coating exhibits excellent transparency and anti-fogging properties, with a light transmittance of over 90%. The anti-fogging clarity recovery time is significantly shortened, effectively extending the shelf life of fruits and vegetables. The coating of this invention shows significant advantages in transparency, anti-fogging, antioxidant properties, and shelf life, and is green, safe, widely applicable, and has industrialization potential.

Description

Technical Field

[0001] This invention relates to the field of food preservation and functional coating technology, specifically to an anti-fog preservation coating and its preparation method. Background Technology

[0002] During post-harvest storage, transportation, and sales, fruits and vegetables continuously release moisture through respiration, and changes in external humidity easily lead to the formation of condensation droplets on their surfaces and coatings. The formation of these droplets reduces surface transparency, blurring the appearance of the fruits and vegetables, and increases humidity inside the packaging, providing suitable conditions for bacterial and mold growth, ultimately accelerating spoilage and shortening shelf life. Current technologies often use chitosan, sodium alginate, and carboxymethyl cellulose as film-forming materials to form an edible film on the surface of fruits and vegetables to block oxygen and reduce moisture evaporation, achieving a certain degree of preservation. However, these coatings are prone to condensation under refrigeration or high humidity conditions, typically resulting in a significant decrease in light transmittance after one to two days of storage, causing the fruit and vegetable surface to lose clarity and affecting product display.

[0003] To improve film strength and stability, researchers often use glutaraldehyde or formaldehyde to chemically cross-link chitosan. While this method can enhance the mechanical properties and water resistance of the film, it has potential toxicity and can darken the film color and reduce transparency, which is detrimental to food preservation applications. Existing chitosan-tea polyphenol composite systems are mostly physically combined, resulting in limited structural stability. They are prone to precipitation under high humidity conditions, making it difficult to maintain long-term anti-fogging and antibacterial effects. Commonly used additive systems mainly include plasticizers and preservatives, which can improve flexibility or delay microbial growth, but have limited effect on improving transparency and anti-fogging performance. Therefore, existing anti-fogging preservation coatings still suffer from insufficient transparency, poor anti-fogging effect, and short preservation period. There is an urgent need to develop a new type of coating material that is green, safe, structurally stable, and simultaneously possesses anti-fogging, antioxidant, and preservation functions. Summary of the Invention

[0004] To overcome the problems of insufficient anti-fogging performance, poor safety of crosslinking agents, low structural stability, and limited shelf life in the prior art, the present invention aims to provide an anti-fogging and preservative coating and its preparation method. The present invention uses chitosan modified by crosslinking with tea polyphenol Schiff base as the main film-forming material, and introduces glycerol, an organic small molecule not previously used in this field, as a synergistic component. Simultaneously, film-forming aids, plasticizers, surfactants, and preservatives are combined, and a stable coating is prepared under optimized ratios and process conditions. This coating exhibits good transparency, excellent surface anti-fogging performance, and significant antibacterial and antioxidant effects, effectively extending the shelf life of fruits and vegetables and meeting the application requirements of food preservation. The coating of the present invention is safe and environmentally friendly, with strong anti-fogging performance, high transparency, and significant preservation effect.

[0005] The objective of this invention can be achieved through the following technical solutions: An anti-fog and freshness-preserving coating, the coating comprising the following raw materials in parts by weight: 10-30 parts of chitosan modified by cross-linking with tea polyphenol Schiff base; 5-15 parts of glycerin; 3-10 parts of film-forming aid; 2-8 parts of plasticizer; 0.5-2 parts of surfactant; 0.1-1 parts of preservative; and 40-70 parts of deionized water.

[0006] Optionally, the chitosan modified by cross-linking with tea polyphenol Schiff base comprises the following raw materials in parts by weight: 10-30 parts chitosan; 3-10 parts tea polyphenols; and 0.2-2 parts terephthalaldehyde.

[0007] Optionally, the preparation method of chitosan modified by tea polyphenol Schiff base crosslinking includes the following steps: (1) Dissolve chitosan in dilute acetic acid solution to obtain chitosan solution; (2) Add tea polyphenols to the chitosan solution and disperse them evenly under stirring conditions; (3) Add terephthalaldehyde as a crosslinking agent to make the amino group on the chitosan molecule react with the aldehyde group in a Schiff base reaction, and at the same time combine with tea polyphenols to form a ternary crosslinking structure. Continue the reaction until the system is stable. (4) Chitosan modified by cross-linking of tea polyphenol Schiff base was obtained by dialysis purification and drying.

[0008] Optionally, the reaction conditions for step (1) are: stirring and dissolving in 0.5%–2% acetic acid solution at a temperature of 20–30°C for 0.5–2 hours; the reaction conditions for step (2) are: stirring continuously at room temperature for 30–60 minutes to fully disperse the tea polyphenols; the reaction conditions for step (3) are: adding terephthalaldehyde at a pH of 5.0–6.0 at a reaction temperature of 25–40°C for 1–3 hours; and the reaction conditions for step (4) are: dialysis with deionized water for 24–48 hours followed by freeze drying.

[0009] Optionally, the film-forming aid is a mixture of polyvinyl alcohol and hydroxypropyl methylcellulose in a mass ratio of 2:1; the plasticizer is a mixture of propylene glycol and sorbitol in a mass ratio of 1:1; the surfactant is a mixture of Tween-80 and nonylphenol polyoxyethylene ether in a mass ratio of 3:1; and the preservative is a mixture of potassium sorbate and sodium benzoate in a mass ratio of 1:1.

[0010] Optionally, a method for preparing an anti-fog and food-preserving coating includes the following steps: S1, dissolve the chitosan modified by cross-linking with tea polyphenol Schiff base in deionized water to obtain a homogeneous solution; S2, add glycerin, film-forming aid, plasticizer, surfactant and preservative in sequence, mix evenly under stirring to obtain coating liquid; S3. Apply the coating liquid evenly to the surface of fruits and vegetables by coating or spraying, and then air dry or dry with hot air to form a transparent anti-fog and freshness-preserving coating.

[0011] Optionally, the reaction conditions for step S1 are stirring at room temperature (20–30°C) for 30–60 min.

[0012] Optionally, the reaction conditions for step S2 are stirring at 25–40°C for 0.5–2 hours.

[0013] Optionally, the reaction conditions for step S3 are hot air drying at 40–50°C for 10–30 min.

[0014] The beneficial effects of this invention are: This invention utilizes a stable ternary crosslinking network constructed from chitosan modified with tea polyphenol Schiff bases. This network enables the film to maintain high transparency and uniformity even under high humidity and low temperature conditions, significantly improving anti-fogging performance. Simultaneously, the chemical intercalation of tea polyphenols endows the coating with durable antioxidant and antibacterial properties, avoiding the toxicity and color deepening problems caused by traditional crosslinking agents. The introduction of glycerol, a small molecule not previously used in this field, as a synergistic component not only improves the coating's flexibility but also inhibits water vapor condensation by regulating the hydrophilic / hydrophobic balance, thus achieving a synergistic improvement in both anti-fogging and preservation. These effects are not yet achieved in existing chitosan-based coating systems, demonstrating significant inventive advantages. Attached Figure Description

[0015] The invention will now be further described with reference to the accompanying drawings.

[0016] Figure 1 The infrared spectra of chitosan modified by Schiff base crosslinking with tea polyphenols are compared with those of chitosan. Figure 2 A bar chart comparing the transmittance results of samples with different ratios; Figure 3 A bar chart comparing the clear recovery time of anti-fog samples with different formulation ratios; Figure 4 A bar chart comparing the free radical scavenging rates of samples with different ratios; Figure 5 A bar chart comparing the diameters of the inhibition zone for samples with different formulation ratios; Figure 6 A bar chart comparing the preservation periods of samples with different ratios. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments. However, the present invention is not limited to the following embodiments. Equivalent adjustments made without departing from the spirit and essence of the present invention should also be considered to fall within the protection scope of the present invention.

[0018] Example 1 The purpose of this embodiment is to verify the performance of the prepared coating in terms of transparency, anti-fogging, and preservation effect when each component is taken at its upper limit.

[0019] S1. Weigh 30 parts of chitosan and dissolve it in 100 parts of 1.5% acetic acid solution, stirring for 30 minutes until completely dissolved; add 10 parts of tea polyphenols to the solution and stir at room temperature for 40 minutes to disperse it evenly; then add 2 parts of terephthalaldehyde to adjust the pH to 5.5, and react at 30℃ for 2 hours to allow the amino and aldehyde groups of chitosan molecules to react to form a Schiff base structure and bind tea polyphenols; after dialyzing the product with deionized water for 36 hours, freeze-dry to obtain chitosan powder modified by tea polyphenol Schiff base crosslinking. S2, add 30 parts of chitosan modified by cross-linking with tea polyphenol Schiff base to 70 parts of deionized water and stir until completely dissolved; then add 15 parts of glycerin, 10 parts of film-forming aid (polyvinyl alcohol and hydroxypropyl methylcellulose in a mass ratio of 2:1), 8 parts of plasticizer (propylene glycol and sorbitol in a mass ratio of 1:1), 2 parts of surfactant (Tween-80 and nonylphenol polyoxyethylene ether in a mass ratio of 3:1) and 1 part of preservative (potassium sorbate and sodium benzoate in a mass ratio of 1:1) in sequence, and stir at 30°C for 1.5 h to obtain a uniform coating liquid; S3. Spray the coating liquid evenly onto the surface of fresh cucumbers and dry it in hot air at 45℃ for 20 minutes to form a transparent anti-fog and freshness-preserving coating.

[0020] Example 2 The purpose of this embodiment is to verify the overall performance of the coating under balanced ratio conditions when the intermediate values ​​of each component are taken.

[0021] S1. Weigh 20 parts of chitosan and dissolve it in 100 parts of 1% acetic acid solution. Stir for 40 min, add 6 parts of tea polyphenols, and stir at room temperature for 30 min. Then add 1 part of terephthalaldehyde, adjust the pH to 5.5, and react at 30℃ for 2 h to obtain the cross-linked modified product. After dialyzing with deionized water for 24 h, freeze dry to obtain chitosan cross-linked with tea polyphenol Schiff base. Figure 1 The comparison of the infrared spectra of chitosan before and after modification is shown. Unmodified chitosan has an infrared spectrum at 3400 cm⁻¹. -1 A distinct O–H stretching vibration peak appears nearby, at 1650 cm⁻¹. -1 The C=O stretching vibration peak appears at 1635 cm⁻¹, which is a typical characteristic; after cross-linking modification with tea polyphenol Schiff base, the peak appears at 1635 cm⁻¹ in the spectrum. -1 The appearance of a new C=N stretching vibration peak nearby, along with the superposition of the C=O and C=N peaks, proves that the chitosan amino group and the terephthalaldehyde aldehyde group underwent a Schiff base reaction; 1260 cm⁻¹ -1 A strong Ar–O absorption peak appears at 700–760 cm⁻¹, and continues in the range of 700–760 cm⁻¹.-1 The presence of aromatic ring skeletal vibration peaks in the region indicates the successful introduction of tea polyphenols; the enhanced intensity and broadening of the O–H stretching peaks after modification indicate enhanced hydrogen bonding; overall comparison shows that the chitosan structure undergoes significant changes after Schiff base crosslinking and tea polyphenol grafting, forming a stable ternary crosslinked network structure. S2, dissolve 20 parts of chitosan modified by tea polyphenol Schiff base crosslinking in 55 parts of deionized water and stir evenly; then add 10 parts of glycerol, 6 parts of film-forming aid (polyvinyl alcohol and hydroxypropyl methylcellulose in a mass ratio of 2:1), 5 parts of plasticizer (propylene glycol and sorbitol in a mass ratio of 1:1), 1 part of surfactant (Tween-80 and nonylphenol polyoxyethylene ether in a mass ratio of 3:1), and 0.5 parts of preservative (potassium sorbate and sodium benzoate in a mass ratio of 1:1) in sequence, and stir at 30°C for 1 hour to obtain the coating liquid; S3. Apply the coating liquid evenly to the surface of fresh tomatoes and dry it with hot air at 40℃ for 15 minutes to obtain a transparent anti-fog preservation coating.

[0022] Example 3 The purpose of this embodiment is to verify the feasibility and performance of the coating under extremely low addition conditions when each component is taken to the lower limit.

[0023] S1, 10 parts of chitosan were weighed and dissolved in 100 parts of 0.5% acetic acid solution and stirred for 30 min; 3 parts of tea polyphenols were added and stirred at room temperature for 30 min; then 0.2 parts of terephthalaldehyde were added, the pH was adjusted to 5.0, and the reaction was carried out at 25℃ for 1 h; the product was dialyzed with deionized water for 48 h and then freeze-dried to obtain chitosan modified by Schiff base crosslinking of tea polyphenols. S2, 10 parts of chitosan modified by cross-linking with tea polyphenol Schiff base were added to 40 parts of deionized water and stirred evenly; then 5 parts of glycerol, 3 parts of film-forming aid (polyvinyl alcohol and hydroxypropyl methylcellulose in a mass ratio of 2:1), 2 parts of plasticizer (propylene glycol and sorbitol in a mass ratio of 1:1), 0.5 parts of surfactant (Tween-80 and nonylphenol polyoxyethylene ether in a mass ratio of 3:1) and 0.1 parts of preservative (potassium sorbate and sodium benzoate in a mass ratio of 1:1) were added sequentially and stirred at 25°C for 0.5 h to obtain the coating liquid; S3. Spray the coating liquid evenly onto the surface of fresh apples and let it air dry under natural conditions for 30 minutes to obtain a transparent anti-fog preservation coating.

[0024] Comparative Example 1 The purpose of this comparative example is to verify the differences in anti-fogging properties and structural stability of the coating when only tea polyphenols are used without the addition of aldehyde crosslinking agents.

[0025] S1, 20 parts of chitosan were weighed and dissolved in 100 parts of 1% acetic acid solution, stirred for 40 min, then 6 parts of tea polyphenols were added, and stirred at room temperature for 30 min to obtain a chitosan-tea polyphenol complex solution. This solution was dialyzed against deionized water for 24 h and then freeze-dried to obtain tea polyphenol-chitosan complex.

[0026] S2, dissolve 20 parts of tea polyphenol composite chitosan in 55 parts of deionized water and stir evenly; add 10 parts of glycerin, 6 parts of film-forming aid (polyvinyl alcohol and hydroxypropyl methylcellulose in a mass ratio of 2:1), 5 parts of plasticizer (propylene glycol and sorbitol in a mass ratio of 1:1), 1 part of surfactant (Tween-80 and nonylphenol polyoxyethylene ether in a mass ratio of 3:1), and 0.5 parts of preservative (potassium sorbate and sodium benzoate in a mass ratio of 1:1) in sequence, and stir at 30°C for 1 hour to obtain the coating liquid.

[0027] S3. Apply the coating liquid evenly to the surface of fresh tomatoes and dry it with hot air at 40℃ for 15 minutes to obtain an anti-fog and freshness-preserving coating.

[0028] Comparative Example 2 The purpose of this comparative example is to verify the difference in transparency and antioxidant properties of the coating when only aldehyde crosslinking is used without the introduction of tea polyphenols.

[0029] S1. Weigh 20 parts of chitosan and dissolve it in 100 parts of 1% acetic acid solution. Stir for 40 min, then add 1 part of terephthalaldehyde to adjust the pH to 5.5. React at 30℃ for 2 h to obtain the cross-linked product. After dialyzing the product with deionized water for 24 h, freeze-dry to obtain aldehyde-crosslinked chitosan.

[0030] S2, dissolve 20 parts of aldehyde crosslinked chitosan in 55 parts of deionized water and stir until homogeneous; then add 10 parts of glycerol, 6 parts of film-forming aid (polyvinyl alcohol and hydroxypropyl methylcellulose in a mass ratio of 2:1), 5 parts of plasticizer (propylene glycol and sorbitol in a mass ratio of 1:1), 1 part of surfactant (Tween-80 and nonylphenol polyoxyethylene ether in a mass ratio of 3:1), and 0.5 parts of preservative (potassium sorbate and sodium benzoate in a mass ratio of 1:1). Stir at 30°C for 1 hour to obtain the coating liquid.

[0031] S3. Apply the coating liquid evenly to the surface of fresh tomatoes and dry it with hot air at 40℃ for 15 minutes to obtain an anti-fog and freshness-preserving coating.

[0032] Comparative Example 3 The purpose of this comparative example is to verify the difference in flexibility and anti-fogging properties of the coating when glycerol, a small organic molecule, is not added.

[0033] S1. Weigh 20 parts of chitosan and dissolve it in 100 parts of 1% acetic acid solution. Stir for 40 min, add 6 parts of tea polyphenols, and stir at room temperature for 30 min. Then add 1 part of terephthalaldehyde to adjust the pH to 5.5, and react at 30℃ for 2 h to obtain the cross-linked modified product. After dialyzing the product with deionized water for 24 h, freeze-dry to obtain chitosan cross-linked with tea polyphenol Schiff base.

[0034] S2, dissolve 20 parts of modified chitosan in 55 parts of deionized water and stir evenly; add 6 parts of film-forming aid (polyvinyl alcohol and hydroxypropyl methylcellulose in a mass ratio of 2:1), 5 parts of plasticizer (propylene glycol and sorbitol in a mass ratio of 1:1), 1 part of surfactant (Tween-80 and nonylphenol polyoxyethylene ether in a mass ratio of 3:1), and 0.5 parts of preservative (potassium sorbate and sodium benzoate in a mass ratio of 1:1) in sequence, and stir at 30°C for 1 hour to obtain the coating liquid.

[0035] S3. Apply the coating liquid evenly to the surface of fresh tomatoes and dry it with hot air at 40℃ for 15 minutes to obtain a transparent anti-fog preservation coating.

[0036] Performance testing Transparency test The coating solutions obtained in the examples and comparative examples were uniformly coated onto the surface of a glass slide. After drying, a transparent film was prepared. The transmittance was measured at a wavelength of 600 nm using a UV-Vis spectrophotometer. The test was repeated three times, and the average value was taken. The higher the transmittance, the better the transparency of the coating.

[0037] Anti-fog performance test The coating liquids obtained in the examples and comparative examples were uniformly coated onto the surface of a transparent glass slide. After drying, the slide was placed in a saturated steam environment at 90°C for 2 minutes, and then quickly transferred to an environment at 25°C and 60% relative humidity. The change in scattering intensity was continuously monitored over 0–5 minutes using a laser scattering instrument. The lower the scattering intensity and the faster the clarity recovery, the better the anti-fog performance of the coating.

[0038] Antioxidant performance test Take 2g of each coating sample, cut it into small pieces, and place it in 10mL of methanol solution. Extract by sonication for 30min, and use the supernatant for DPPH free radical scavenging experiment. Mix the sample solution with an equal volume of 0.1mmol / L DPPH ethanol solution, react in the dark for 30min, and then measure the absorbance at 517nm wavelength to calculate the free radical scavenging rate. The higher the scavenging rate, the stronger the antioxidant performance.

[0039] Antibacterial performance test Using *Escherichia coli* and *Staphylococcus aureus* as indicator strains, after culturing to the logarithmic growth phase, the coating solutions of each sample were evenly spread on the surface of agar plates. After drying, bacterial suspension (1×10⁻⁶) was inoculated in the center of the plate. 6(CFU / mL). Incubate at 37℃ for 24 hours, then measure the colony diameter or inhibition zone size. A larger inhibition zone indicates better antibacterial performance of the coating.

[0040] Preservation performance test Fresh tomatoes or cucumbers of uniform size were selected and randomly divided into six groups. Each group was treated with the coatings obtained in Examples 1-3 and Comparative Examples 1-3, respectively, with an uncoated blank control included. The samples were stored at 25°C and 60% relative humidity for 7 days, and the weight loss rate, appearance gloss, and spoilage rate were recorded every 24 hours. Low weight loss rate, high appearance retention, and low spoilage rate indicate excellent preservation performance of the coating.

[0041] Table 1. Performance test results of anti-fog and food-preserving coating As can be seen from the data in Table 1, Examples 1 to 3 are superior to the comparative examples in terms of transparency, anti-fogging properties, antioxidant properties, antibacterial properties, and shelf life, indicating that the formulation design of the present invention has significant advantages. Among them, Figure 2 Example 2 showed the best performance, with a light transmittance of 94.0%, which is higher than 91.2% of Example 1 and 89.0% of Example 3, and is also significantly better than 81.7% to 85.1% of Comparative Examples 1 to 3, indicating that the coating formed under this ratio has the best transparency. Figure 3 Regarding anti-fog performance, the clarity recovery time of Example 2 was only 1.0 minute, which was faster than the 1.3 minutes of Example 1 and the 1.5 minutes of Example 3, while the comparative examples were all above 2.0 minutes. This indicates that the coating modified by crosslinking of tea polyphenol Schiff base and synergistically with glycerol can significantly inhibit droplet condensation and quickly restore clarity.

[0042] Figure 4 In terms of antioxidant performance, the free radical scavenging rate of Example 2 was as high as 90.3%, which was significantly better than 84.5% of Example 1 and 82.1% of Example 3, while the comparative example was only between 61.7% and 70.8%, indicating that the Schiff base cross-linking structure and tea polyphenol embedding could maximize the retention of activity under these conditions. Figure 5 In terms of antibacterial performance, the diameter of the antibacterial ring in Example 2 reached 16.2 mm, which is higher than that of Example 1 (14.8 mm) and Example 3 (13.5 mm), while the comparative examples were only between 9.5 mm and 11.1 mm, indicating that the coating has a stronger inhibitory effect on putrefactive bacteria. Figure 6 Regarding the preservation period, Example 2 was able to maintain the product for 7 days, which is better than the 6 days of Example 1 and Example 3, while the comparative example could only maintain it for 4 to 5 days, which is obviously insufficient.

[0043] In summary, all the embodiments are superior to the comparative examples. In particular, Example 2 achieves the best balance in terms of transparency, anti-fogging properties, antioxidant properties, antibacterial properties, and shelf life, which fully demonstrates the inventiveness and significant technical effect of the synergistic effect of tea polyphenol Schiff base crosslinked modified chitosan and glycerol in this invention.

Claims

1. An anti-fog and food-preserving coating, characterized in that, The coating comprises the following raw materials in parts by weight: 10-30 parts of chitosan modified by crosslinking with tea polyphenol Schiff base; 5-15 parts of glycerin; 3-10 parts of film-forming aid; 2-8 parts of plasticizer; 0.5-2 parts of surfactant; 0.1-1 parts of preservative; and 40-70 parts of deionized water.

2. The anti-fog and food-preserving coating according to claim 1, characterized in that, The chitosan modified by cross-linking with tea polyphenol Schiff base comprises the following raw materials in parts by weight: 10-30 parts chitosan; 3-10 parts tea polyphenols; and 0.2-2 parts terephthalaldehyde.

3. The anti-fog and food-preserving coating according to any one of claims 1 or 2, characterized in that, The preparation method of the chitosan modified by tea polyphenol Schiff base crosslinking includes the following steps: (1) Dissolve chitosan in dilute acetic acid solution to obtain chitosan solution; (2) Add tea polyphenols to the chitosan solution and disperse them evenly under stirring conditions; (3) Add terephthalaldehyde as a crosslinking agent and continue the reaction until the system is stable; (4) Chitosan modified by cross-linking of tea polyphenol Schiff base was obtained by dialysis purification and drying.

4. The anti-fog and food-preserving coating according to claim 3, characterized in that, The reaction conditions for step (1) are: stirring and dissolving in 0.5% to 2% acetic acid solution at a temperature of 20 to 30°C for 0.5 to 2 hours; the reaction conditions for step (2) are: stirring continuously at room temperature for 30 to 60 minutes; the reaction conditions for step (3) are: adding terephthalaldehyde at a pH of 5.0 to 6.0 at a reaction temperature of 25 to 40°C for 1 to 3 hours; and the reaction conditions for step (4) are: dialysis with deionized water for 24 to 48 hours followed by freeze drying.

5. The anti-fog and food-preserving coating according to claim 1, characterized in that, The film-forming aid is a mixture of polyvinyl alcohol and hydroxypropyl methylcellulose in a mass ratio of 2:1; the plasticizer is a mixture of propylene glycol and sorbitol in a mass ratio of 1:1; the surfactant is a mixture of Tween-80 and nonylphenol polyoxyethylene ether in a mass ratio of 3:1; and the preservative is a mixture of potassium sorbate and sodium benzoate in a mass ratio of 1:

1.

6. A method for preparing an anti-fog preservation coating, wherein the anti-fog preservation coating is as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1, dissolve the chitosan modified by cross-linking with tea polyphenol Schiff base in deionized water to obtain a homogeneous solution; S2, glycerol, film-forming aid, plasticizer, surfactant and preservative are added in sequence and mixed evenly under stirring to obtain coating liquid; S3. Apply the coating liquid evenly to the surface of fruits and vegetables by coating or spraying, and then air dry or dry with hot air to form a transparent anti-fog and freshness-preserving coating.

7. The method for preparing an anti-fog and food-preserving coating according to claim 6, characterized in that, The reaction conditions for step S1 are stirring at room temperature (20–30°C) for 30–60 minutes.

8. The method for preparing an anti-fog and food-preserving coating according to claim 6, characterized in that, The reaction conditions for step S2 are stirring at 25–40°C for 0.5–2 hours.

9. The method for preparing an anti-fog and food-preserving coating according to claim 6, characterized in that, The reaction conditions for step S3 are hot air drying at 40-50°C for 10-30 minutes.

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