Nanometer composite film for storage and transportation of apples and preparation method thereof

Abstract

This invention relates to the field of preservation films, specifically to a nanocomposite film for apple storage and preservation and its preparation method, comprising a base film and a coating liquid. This invention combines a cellulose nanocrystal base film with an evaporation-induced self-assembled layered ordered structure with a superhydrophobic cellulose ester coating. A cyclodextrin-laccase cascade system is integrated in the base film to specifically capture and enzymatically degrade the pathogenic factors of tiger skin disease. A micro-nano rough structure is constructed in the coating to encapsulate humidity-triggered microencapsulated degradation enzymes. Compared with existing technologies, this invention simultaneously achieves multiple effects on a single film: passive regulation of the respiratory microenvironment, active removal of stored pathogens, surface anti-condensation, and accelerated degradation on demand after disposal. It leaves no harmful residues throughout its entire life cycle and has broad application prospects in the cold chain logistics and green packaging of fresh agricultural products.

Description

Technical Field

[0001] This invention relates to the field of food preservation films, and more particularly to a nanocomposite film for apple storage and preservation and its preparation method. Background Technology

[0002] As a typical climacteric fruit, apples continuously release ethylene and accumulate α-farnesene during post-harvest storage and transportation. The conjugated trienes, oxidation products of α-farnesene, easily induce tiger skin disease, leading to browning of the peel and a sharp drop in commercial value. At the same time, the fruit's transpiration and the temperature difference in the cold chain cause continuous condensation inside the packaging. Water droplets are obstructed from sliding off and accumulate on the fruit surface, creating a localized high-humidity environment that induces mold infection and rot. Existing plastic wraps mostly rely on adding chemical antioxidants or anti-fogging agents to alleviate the above problems, but these functions are independent of each other and it is difficult to achieve synergistic regulation of multiple functions on a single film.

[0003] In existing technologies, although traditional cellulose-based food preservation films have good transparency and breathability, they generally have inherent defects such as moisture absorption, softness, and poor water resistance due to the high hydroxyl content of cellulose molecular chains. To improve hydrophobicity, existing technologies often introduce siloxanes or fluorocarbons for surface treatment, which not only increases material costs and environmental burden, but also makes the hydrophobic layer prone to peeling and failure during storage and transportation friction. In addition, traditional functional films cannot degrade on their own after disposal, and the residual film remains in the soil for a long time, posing a continuous pressure on the ecological environment.

[0004] Therefore, based on the relevant technologies mentioned above, there is an urgent need to develop a nanocomposite film for apple storage, transportation, and preservation, and its preparation method. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a nanocomposite film for apple storage and preservation and its preparation method, so as to solve the problems of single function, poor water resistance and non-degradability in the prior art.

[0006] To achieve the above objectives, the present invention provides a nanocomposite film for apple storage and preservation and its preparation method.

[0007] A nanocomposite film for storing and preserving apples includes a base film and a coating liquid. The base film is composed of cellulose nanocrystals, a carrier complex, a first crosslinking agent, and glycerol. The carrier complex is composed of modified oxidized nanocellulose, laccase, and a second crosslinking agent; The first crosslinking agent is polyethylene glycol diglycidyl ether, used to construct a crosslinking network between cellulose nanocrystals in the base layer membrane; the second crosslinking agent is polyethylene glycol diglycidyl ether. The coating solution is composed of cellulose stearate, cellulose nanocrystals, carnauba wax emulsion, microencapsulated cellulase, sodium carboxymethyl cellulose with high degree of substitution, and triethyl citrate.

[0008] Preferably, the preparation steps of the base layer membrane are as follows: Step A1: Under light-protected conditions, add cellulose nanocrystals to deionized water and sonicate for 10-20 minutes at a power of 150-250W. Once sonication is complete, a suspension is obtained. Step A2: Add the carrier complex to the suspension and stir for 25-35 min at 150-250 rpm. Add glycerol and stir for 8-12 min. Add 0.1 mol / L sodium hydroxide solution and adjust the pH to 6.8-7.2. Then add the first crosslinking agent, polyethylene glycol diglycidyl ether. Heat to 20-25℃ and reduce the stirring speed to 100-140 rpm. React for 30-40 min. Once the reaction is complete, degas under vacuum to obtain the film-forming solution. Step A3: Cast the film-forming liquid into a polytetrafluoroethylene mold, place it in a constant temperature and humidity chamber, heat it to 24-26℃, relative humidity 55%-65%, and let it stand for 46-50 hours. After standing, place it in an oven, heat it to 70-80℃, and cure it for 50-70 minutes. After curing, cool it to 20-30℃, and the film thickness is 20-30μm to obtain the base film.

[0009] The cellulose nanocrystals have a crystallinity of 75%-90%, a length of 100-300 nm, a diameter of 5-20 nm, and an aspect ratio of 15-40.

[0010] Preferably, the mass ratio of cellulose nanocrystals to deionized water in step A1 is 0.05-0.06:1; In step A2, the mass ratio of the carrier complex, suspension, glycerol and the first crosslinking agent is 0.035-0.036:1:0.0074-0.0078:0.0036-0.004.

[0011] Preferably, the preparation steps of the carrier complex are as follows: Modified oxidized nanocellulose was added to 0.1 mol / L phosphate buffer, laccase was added, the temperature was raised to 20-30℃, and the mixture was stirred for 2-3 hours at a speed of 100-140 rpm. The second crosslinking agent, polyethylene glycol diglycidyl ether, was added, and the mixture was stirred for 4-5 hours. After the reaction was completed, the mixture was centrifuged and washed to obtain the carrier complex.

[0012] Preferably, the mass ratio of the modified oxidized nanocellulose, laccase, and the second crosslinking agent polyethylene glycol diglycidyl ether is 1:0.20-0.22:0.32-0.34.

[0013] Preferably, the preparation steps of the modified oxidized cellulose nanoparticles are as follows: Step B1: Add nanocellulose filaments to deionized water, heat to 20-30℃, sonicate for 25-35 minutes at a power of 150-250W, and after sonication is complete, obtain a filament suspension. Step B2: Under a nitrogen atmosphere, β-cyclodextrin is added to the fiber suspension, the temperature is raised to 45-55℃, and the mixture is stirred for 25-35 min at a speed of 250-350 rpm. Sodium hypophosphite catalyst is added, and the mixture is stirred for 8-12 min. The stirring speed is reduced to 180-220 rpm, and 1 mol / L hydrochloric acid solution is added to adjust the pH to 3.4-3.6. 1,2,3,4-butanetetracarboxylic acid crosslinking agent is added, and the temperature is raised to 110-130℃. The reaction is carried out for 3-4 h. After the reaction is completed, the temperature is lowered to 20-30℃, and the mixture is purified by dialysis with deionized water and freeze-dried to obtain modified oxidized nanocellulose.

[0014] The nanocellulose filaments have a diameter of 10-50 nm, a length of 1-5 μm, an aspect ratio of 50-200, and a crystallinity of 55%-70%. Preferably, the mass ratio of the nanocellulose filaments to deionized water in step B1 is 0.4-0.6:1; The mass ratio of β-cyclodextrin, fiber suspension, catalyst and crosslinking agent in step B2 is 0.074-0.078:1:0.0046-0.005:0.018-0.022.

[0015] Preferably, the preparation steps of the coating liquid are as follows: Step C1: Add cellulose stearate to ethyl acetate, heat to 40-50℃, stir for 50-70 min at 250-350 rpm, cool to 20-30℃, add cellulose nanocrystals, and sonicate for 8-12 min at 200-300 W. After sonication is complete, a suspension is obtained. Step C2: Add carnauba wax emulsion with a solid content of 10%wt to the suspension, stir at 200-300 rpm for 25-35 min, then reduce the speed to 80-120 rpm, add microencapsulated cellulase and sodium carboxymethyl cellulose with a high degree of substitution, stir for 14-16 min, add triethyl citrate, stir for 4-6 min, after stirring is complete, degas under vacuum to obtain the coating solution; The high degree of substitution of sodium carboxymethyl cellulose ranges from 0.8 to 1.2.

[0016] The mass ratio of cellulose stearate to cellulose nanocrystals is 1:0.22-0.26; The mass ratio of the carnauba wax emulsion, suspension, microencapsulated cellulase, highly substituted sodium carboxymethyl cellulose, and triethyl citrate is 0.08-0.12:1:0.005-0.0052:0.006-0.0062:0.0018-0.0022.

[0017] Preferably, the preparation steps of the microencapsulated cellulase are as follows: Step D1: Add sodium alginate to deionized water, heat to 15-25℃, stir for 100-140 min at 350-450 rpm, after stirring, let stand to degas for 25-35 min, add cellulase, reduce the speed to 150-250 rpm, stir for 15-25 min, after stirring, add 2% calcium chloride solution, let stand to solidify for 30-40 min, filter through a 200-mesh filter, wash and dry to obtain microcapsules; Step D2: Add chitosan to a 1% acetic acid aqueous solution, heat to 20-30℃, stir for 2-3 hours, add microcapsules, soak for 8-12 seconds, after soaking is complete, air dry naturally for 2-3 hours, sieve to obtain microencapsulated cellulase. The mass ratio of sodium alginate, cellulase, and calcium chloride solution is 0.004-0.006:0.004-0.006:1. The mass ratio of chitosan to microcapsules is 1.4-1.6:1.

[0018] A method for preparing a nanocomposite film for apple storage and preservation, the specific steps of which are as follows: Lay the base film flat on a clean, horizontal glass table. Add the coating liquid to the spray gun's storage tank. The nozzle diameter is 0.7-0.9 mm, the spraying pressure is 0.14-0.16 MPa, the spraying distance is 14-16 cm, the moving speed is 4-6 cm / s, and the wet film thickness is 45-55 μm. After spraying, let it stand for 30-40 minutes, then vacuum dry. After peeling off the film, place it in a constant temperature chamber at 20-30℃ for equilibration for 22-26 hours to obtain the composite film.

[0019] In this invention, although the first crosslinking agent, polyethylene glycol diglycidyl ether, and the second crosslinking agent, polyethylene glycol diglycidyl ether, are the same compound, they are added in different steps and play different roles: the second crosslinking agent is added during the preparation stage of the carrier complex to crosslink and fix the laccase onto the surface of the modified oxidized nanocellulose, forming a stable enzyme-carrier complex, which exists in the final product as an enzyme-carrier crosslinking network; the first crosslinking agent is added during the film-forming stage of the base film to construct a crosslinking network between cellulose nanocrystals, imparting mechanical strength to the film and regulating the pitch of the layered ordered structure, which also exists in the final product as a cellulose nanocrystal crosslinking network. The two crosslinking processes are independent of each other, each forming an independent crosslinking system, which together constitute the functional framework of the base film.

[0020] The beneficial effects of this invention are: This invention provides a nanocomposite membrane for apple storage and preservation, and its preparation method. The invention combines a cellulose nanocrystal base layer with an evaporation-induced self-assembled layered ordered structure with a superhydrophobic cellulose ester coating. A cyclodextrin-laccase cascade system is integrated into the base layer to specifically capture and enzymatically degrade the pathogenic factors of tiger skin disease. A micro-nano rough structure is constructed in the coating to encapsulate humidity-triggered microencapsulated degradation enzymes. Compared with existing technologies, this invention simultaneously achieves multiple effects on a single membrane: passive regulation of the respiratory microenvironment, active removal of storage pathogens, surface anti-condensation, and accelerated degradation on demand after disposal. It leaves no harmful residues throughout its entire life cycle and has broad application prospects in the cold chain logistics and green packaging of fresh agricultural products. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0022] Example 1: Preparation of a modified oxidized cellulose nanoparticle: S1: Add 40g of nanocellulose fibers to 100mL of deionized water, heat to 20℃, sonicate for 35min at 150W, and sonication is completed to obtain a fiber suspension. S2: Under a nitrogen atmosphere, 7.4 g of β-cyclodextrin was added to 100 g of fiber suspension, the temperature was raised to 45 °C, and the mixture was stirred for 35 min at 250 rpm. 0.46 g of sodium hypophosphite catalyst was added, and the mixture was stirred for 12 min. The stirring speed was reduced to 180 rpm, and 1 mol / L hydrochloric acid solution was added to adjust the pH to 3.4-3.6. 1.8 g of crosslinking agent 1,2,3,4-butanetetracarboxylic acid was added, the temperature was raised to 130 °C, and the reaction was carried out for 3 h. After the reaction was completed, the temperature was lowered to 30 °C, and the mixture was purified by dialysis with deionized water and freeze-dried to obtain modified oxidized nanocellulose.

[0023] Example 2: Preparation of a modified oxidized cellulose nanoparticle: S1: Add 50g of nanocellulose fibers to 100mL of deionized water, heat to 25℃, sonicate for 30min at 200W, and sonication is completed to obtain a fiber suspension. S2: Under a nitrogen atmosphere, 7.6 g of β-cyclodextrin was added to 100 g of fiber suspension, the temperature was raised to 50 °C, and the mixture was stirred for 30 min at 300 rpm. 0.48 g of sodium hypophosphite catalyst was added, and the mixture was stirred for 10 min. The stirring speed was reduced to 200 rpm, and 1 mol / L hydrochloric acid solution was added to adjust the pH to 3.4-3.6. 2 g of crosslinking agent 1,2,3,4-butanetetracarboxylic acid was added, and the temperature was raised to 120 °C. The reaction was carried out for 3.5 h until the reaction was complete. The mixture was then cooled to 25 °C, purified by dialysis with deionized water, and freeze-dried to obtain modified oxidized nanocellulose.

[0024] Example 3: Preparation of a modified oxidized cellulose nanoparticle: S1: Add 60g of nanocellulose fibers to 100mL of deionized water, heat to 30℃, sonicate for 25min at 250W, and sonication is completed to obtain a fiber suspension. S2: Under a nitrogen atmosphere, 7.8 g of β-cyclodextrin was added to 100 g of fiber suspension, the temperature was raised to 55 °C, and the mixture was stirred for 25 min at 350 rpm. 0.5 g of sodium hypophosphite catalyst was added, and the mixture was stirred for 8 min. The stirring speed was reduced to 220 rpm, and 1 mol / L hydrochloric acid solution was added to adjust the pH to 3.4-3.6. 2.2 g of crosslinking agent 1,2,3,4-butanetetracarboxylic acid was added, and the temperature was raised to 110 °C. The reaction was carried out for 4 h until it was complete. The mixture was then cooled to 20 °C, purified by dialysis with deionized water, and freeze-dried to obtain modified oxidized nanocellulose.

[0025] Example 4: Preparation of a carrier complex: 10g of modified oxidized nanocellulose (Example 1) was added to 100mL of 0.1mol / L phosphate buffer, 2g of laccase was added, the temperature was raised to 20℃, and the mixture was stirred for 3h at 100rpm. 3.2g of polyethylene glycol diglycidyl ether was added, and the mixture was stirred for 5h. After the reaction was completed, the mixture was centrifuged and washed to obtain the carrier complex.

[0026] Example 5: Preparation of a carrier complex: 10g of modified oxidized nanocellulose (Example 2) was added to 100mL of 0.1mol / L phosphate buffer, 2.1g of laccase was added, the temperature was raised to 25℃, and the mixture was stirred for 2.5h at 120rpm. 3.3g of polyethylene glycol diglycidyl ether was added, and the mixture was stirred for 4.5h. After the reaction was completed, the mixture was centrifuged and washed to obtain the carrier complex.

[0027] Example 6: Preparation of a carrier complex: 10g of modified oxidized nanocellulose (Example 3) was added to 100mL of 0.1mol / L phosphate buffer, 2.2g of laccase was added, the temperature was raised to 30℃, and the mixture was stirred for 2h at 140rpm. 3.3g of polyethylene glycol diglycidyl ether was added, and the mixture was stirred for 4h. After the reaction was completed, the mixture was centrifuged and washed to obtain the carrier complex.

[0028] Example 7: Preparation of a base layer membrane: S1: Under light-protected conditions, 5g of cellulose nanocrystals were added to 100g of deionized water and sonicated for 10min at a power of 250W. After sonication was completed, a suspension was obtained. S2: Add 3.5g of the carrier complex (Example 4) to 100g of suspension, stir for 25min at 250rpm, add 0.74g of glycerol, stir for 8min, add 0.1mol / L sodium hydroxide solution, adjust the pH to 6.8-7.2, then add 0.36g of crosslinking agent polyethylene glycol diglycidyl ether, heat to 25℃, reduce the stirring speed to 100rpm, react for 40min, the reaction is complete, vacuum degassing, and obtain the film-forming solution; S3: Cast 100g of film-forming liquid into a polytetrafluoroethylene mold, place it in a constant temperature and humidity chamber, heat it to 24℃, relative humidity 65%, let it stand for 46h, after standing is complete, place it in an oven, heat it to 80℃, cure for 50min, after curing is complete, cool it to 30℃, the film thickness is 20-30μm, and the base film is obtained.

[0029] Example 8: Preparation of a base layer membrane: S1: Under light-protected conditions, 5.5g of cellulose nanocrystals were added to 100g of deionized water and sonicated for 15min at a power of 200W. After sonication was completed, a suspension was obtained. S2: Add 3.55g of the carrier complex (Example 5) to 100g of suspension, stir for 30min at 200rpm, add 0.76g of glycerol, stir for 10min, add 0.1mol / L sodium hydroxide solution, adjust the pH to 6.8-7.2, then add 0.38g of crosslinking agent polyethylene glycol diglycidyl ether, heat to 23℃, reduce the stirring speed to 120rpm, react for 35min, the reaction is complete, vacuum degassing, and obtain the film-forming solution; S3: Cast 100g of film-forming liquid into a polytetrafluoroethylene mold, place it in a constant temperature and humidity chamber, heat it to 25℃, relative humidity 60%, let it stand for 48h, after standing is complete, place it in an oven, heat it to 75℃, cure for 60min, after curing is complete, cool it to 25℃, the film thickness is 20-30μm, and the base film is obtained.

[0030] Example 9: Preparation of a base layer membrane: S1: Under light-protected conditions, 6g of cellulose nanocrystals were added to 100g of deionized water and sonicated for 20min at a power of 150W. After sonication was completed, a suspension was obtained. S2: Add 3.6g of the carrier complex (Example 6) to 100g of suspension, stir for 35min at 150rpm, add 0.78g of glycerol, stir for 12min, add 0.1mol / L sodium hydroxide solution, adjust the pH to 6.8-7.2, then add 0.4g of crosslinking agent polyethylene glycol diglycidyl ether, heat to 20℃, reduce the stirring speed to 140rpm, react for 30min, the reaction is complete, vacuum degassing, and obtain the film-forming solution; S3: Cast 100g of film-forming liquid into a polytetrafluoroethylene mold, place it in a constant temperature and humidity chamber, heat it to 26℃, relative humidity 55%, let it stand for 50h, after standing is complete, place it in an oven, heat it to 70℃, cure for 70min, after curing is complete, cool it to 20℃, the film thickness is 20-30μm, and the base film is obtained.

[0031] Example 10: Preparation of a microencapsulated cellulase: S1: Add 0.8g of sodium alginate to 200mL of deionized water, heat to 15℃, stir for 140min at 350rpm, after stirring is complete, let stand to degas for 35min, add 0.8g of cellulase, reduce the speed to 150rpm, stir for 25min, after stirring is complete, add 200mL of 2% calcium chloride solution, let stand to solidify for 30min, filter through a 200-mesh filter, wash and dry to obtain microcapsules; S2: Add 1.4g of chitosan to 100mL of 1% acetic acid aqueous solution, heat to 20℃, stir for 3h, add 1g of microcapsules, soak for 8s, after soaking is complete, air dry naturally for 2h, sieve to obtain microencapsulated cellulase. Example 11: Preparation of a microencapsulated cellulase: S1: Add 1g of sodium alginate to 200mL of deionized water, heat to 20℃, stir for 120min at 400rpm, after stirring is complete, let stand to degas for 30min, add 1g of cellulase, reduce the speed to 200rpm, stir for 20min, after stirring is complete, add 200g of 2% calcium chloride solution, let stand to solidify for 35min, filter through a 200-mesh filter, wash and dry to obtain microcapsules; S2: Add 1.5g of chitosan to 100mL of 1% acetic acid aqueous solution, heat to 25℃, stir for 2.5h, add 1g of microcapsules, soak for 10s, after soaking is complete, air dry naturally for 2.5h, sieve to obtain microencapsulated cellulase. Example 12: Preparation of a microencapsulated cellulase: S1: Add 1.2g of sodium alginate to 200mL of deionized water, heat to 25℃, stir for 100min at 450rpm, after stirring is complete, let stand to degas for 25min, add 1.2g of cellulase, reduce the speed to 250rpm, stir for 15min, after stirring is complete, add 200g of 2% calcium chloride solution, let stand to solidify for 40min, filter through a 200-mesh filter, wash and dry to obtain microcapsules; S2: Add 1.6g of chitosan to 100mL of 1% acetic acid aqueous solution, heat to 30℃, stir for 2h, add 1g of microcapsules, soak for 12s, after soaking is complete, air dry naturally for 2h, sieve to obtain microencapsulated cellulase. Example 13: Preparation of a coating liquid: S1: Add 100g of cellulose stearate to 150mL of ethyl acetate, heat to 40℃, stir for 70min at 250rpm, cool to 30℃, add 22g of cellulose nanocrystals, sonicate for 8min at 300W, and sonicate to obtain a suspension. S2: Add 8g of carnauba wax emulsion with a solid content of 10%wt to 100g of suspension, stir at 200rpm for 35min, then reduce the speed to 80rpm, add 0.5g of microencapsulated cellulase (Example 10) and 0.6g of sodium carboxymethyl cellulose with a high degree of substitution, stir for 16min, add 0.18g of triethyl citrate, stir for 4min, after stirring is complete, degas under vacuum to obtain the coating solution.

[0032] Example 14: Preparation of a coating liquid: S1: Add 100g of cellulose stearate to 150mL of ethyl acetate, heat to 45℃, stir for 60min at 300rpm, cool to 25℃, add 24g of cellulose nanocrystals, sonicate for 10min at 250W, and sonicate to obtain a suspension. S2: Add 10g of carnauba wax emulsion with a solid content of 10%wt to 100g of suspension, stir at 250rpm for 30min, then reduce the speed to 100rpm, add 0.51g of microencapsulated cellulase (Example 11) and 0.61g of sodium carboxymethyl cellulose with a high degree of substitution, stir for 15min, add 0.2g of triethyl citrate, stir for 5min, after stirring is complete, degas under vacuum to obtain coating solution.

[0033] Example 15: Preparation of a coating liquid: S1: Add 100g of cellulose stearate to 150mL of ethyl acetate, heat to 50℃, stir for 50min at 350rpm, cool to 20℃, add 26g of cellulose nanocrystals, and sonicate for 12min at 200W. After sonication is complete, a suspension is obtained. S2: Add 12g of carnauba wax emulsion with a solid content of 10%wt to 100g of suspension, stir at 300rpm for 25min, then reduce the speed to 120rpm, add 0.52g of microencapsulated cellulase (Example 12) and 0.62g of sodium carboxymethyl cellulose with a high degree of substitution, stir for 14min, add 0.22g of triethyl citrate, stir for 6min, after stirring is complete, degas under vacuum to obtain the coating solution.

[0034] Example 16: A method for preparing a nanocomposite film for apple storage and preservation: The base film (Example 7) was laid flat on a clean, horizontal glass table. The coating liquid (Example 13) was then added to the spray gun storage tank. The nozzle diameter was 0.7 mm, the spraying pressure was 0.16 MPa, the spraying distance was 14 cm, the moving speed was 6 cm / s, and the wet film thickness was 45-55 μm. After spraying, the film was left to stand for 30 min, then vacuum dried. After peeling off the film, the film was placed in a constant temperature chamber at 30°C for equilibration for 22 h to obtain the composite film.

[0035] Example 17: A method for preparing a nanocomposite film for apple storage and preservation: The base film (Example 8) was laid flat on a clean, horizontal glass table. The coating liquid (Example 14) was then added to the spray gun storage tank. The nozzle diameter was 0.8 mm, the spraying pressure was 0.15 MPa, the spraying distance was 15 cm, the moving speed was 5 cm / s, and the wet film thickness was 45-55 μm. After spraying, the film was left to stand for 35 min, then vacuum dried. After peeling off the film, the film was placed in a constant temperature oven at 25 °C for equilibration for 24 h to obtain the composite film.

[0036] Example 18: A method for preparing a nanocomposite film for apple storage and preservation: The base film (Example 9) was laid flat on a clean, horizontal glass table. The coating liquid (Example 15) was then added to the spray gun's storage tank. The nozzle diameter was 0.9 mm, the spraying pressure was 0.14 MPa, the spraying distance was 16 cm, the moving speed was 4 cm / s, and the wet film thickness was 45-55 μm. After spraying, the film was left to stand for 40 min, then vacuum dried. After peeling off the film, the film was placed in a constant temperature chamber at 20°C for equilibration for 26 h to obtain the composite film.

[0037] Comparative Example 1: Compared with Example 16, in the preparation process of the nanocomposite film for apple storage and preservation, the base film and coating liquid components were directly mixed in the same proportion and then cast into a single-layer homogeneous film in one go. The remaining steps and parameters were the same, and will not be repeated in this comparative example. Finally, a composite film was obtained.

[0038] Comparative Example 2: Compared with Example 16, this comparative example only replaces the "carrier complex" with "cellulose nanocrystals". All other steps and parameters are the same, and will not be repeated here. The final composite membrane is obtained.

[0039] Comparative Example 3: Compared with Example 16, this comparative example only replaces "sodium carboxymethyl cellulose with high degree of substitution" with "cellulose stearate". All other steps and parameters are the same, and will not be repeated in this comparative example. The final composite membrane is obtained.

[0040] Comparative Example 4: Compared with Example 16, this comparative example only replaces "cellulose nanocrystals" with "cellulose stearate". All other steps and parameters are the same, and will not be repeated here. The final composite film is obtained.

[0041] Comparative Example 5: This comparative example differs from Example 16 only in that “β-cyclodextrin” is replaced with “corn starch”. All other steps and parameters are the same, and will not be repeated here. The final composite membrane is obtained.

[0042] Comparative Example 6: Compared with Example 16, this comparative example does not use a spraying method to apply the coating liquid to the surface of the base film during the composite film preparation process. Instead, the coating liquid is cast separately into an independent film and then stacked with the base film in a physical bonding manner. All other steps and parameters are the same, and a composite film is finally obtained.

[0043] Performance testing: Tiger Skin Disease Occurrence Index Test Refer to the testing standard GB / T 36770-2018; Take the composite films of Examples 16-18 and Comparative Examples 1-6 respectively, and cut them into 30cm×40cm packaging bags; Select the same batch of Red Fuji apples, each weighing 200±20g, with uniform maturity, free from pests, diseases and mechanical damage, and place them in a cardboard box. The cardboard box dimensions are 40cm×30cm×25cm, with 30 apples per box. Each cardboard box is lined with a layer of corrugated cardboard partition. Experimental group: Apples were placed in the packaging bags prepared in Examples 16-18 and Comparative Examples 1-6, respectively. The bags were sealed and placed in a constant temperature chamber at 0±5℃ and 90%±3% relative humidity for 120 days. Samples were then taken for testing. Control group: Apples were placed directly in the constant temperature chamber without any wrapping, and the experimental conditions were the same; After processing, the apples were taken out and placed at room temperature of 20℃ for 24 hours. The number of fruits of each grade was counted for each fruit. At the same time, the apples were graded according to the percentage of browning area on the peel to the total surface area of ​​the fruit. Tiger Skin Disease Severity Classification level Browning area percentage Level 0 No browning Level 1 Browning area <5% Level 2 Browning area 5%-15% Level 3 Browning area: 15%-30% Level 4 Browning area > 30% Calculation formula: α-Farnese scavenging rate test Gas chromatography-mass spectrometry was used. In a 0℃ cold storage, seal one corner of the packaging bag with a silicone rubber septum, use a 50μL injection needle to penetrate the septum, extract 20mL of air from the packaging, inject it into a vacuum headspace vial, and seal it. Place the headspace vial in a 40℃ constant temperature water bath for equilibration for 15 min, insert the aged CAR / PDMS (75μm) SPME extraction head into the headspace vial, push out the fiber head, perform headspace extraction and adsorption at 40℃ for 30 min, and analyze with GC-MS. GC-MS conditions: Column: HP-5MS capillary column; Injector temperature: 250℃; Desorption time: 5 min; Initial temperature: 50℃; Hold for 2 min; Increase to 180℃ at 10℃ / min; Increase to 280℃ at 25℃ / min; Hold for 5 min; Carrier gas: Helium; Flow rate: 1.0 mL / min. Mass spectrometry conditions: EI source, 70 eV, ion source temperature 230℃, quadrupole temperature 150℃, scan mode SIM, m / z 69, 93, 123, m / z 81, 95; The α-farnesene standard and the conjugated triene standard were diluted with n-hexane to 0.1, 0.5, 1.0, 5.0, 10.0 and 50.0 μg / mL, respectively. 1 μL of each standard was injected into a 20 mL headspace vial, and SPME enrichment and GC-MS analysis were performed under the same conditions as the samples.

[0044] Formulas for calculating the concentrations of α-farnesene and conjugated trienes: In the formula: C: Analyte concentration in headspace sample (ng / mL); A s : Sample peak area; a: Slope of the standard curve; b: Standard curve intercept; Formula for calculating α-farnesene scavenging rate: using Comparative Example 2 without carrier-added complex as the reference standard. In the formula: C 对比例2 : Concentration of α-farnesene in the packaging of Comparative Example 2; C 样品 : Concentration of α-farnesene inside the membrane packaging to be tested.

[0045] Formula for calculating conjugated triene inhibition rate: Table 1 Test Results of Examples and Comparative Examples project Incidence rate (%) DI (%) Clearance rate (%) Inhibition rate (%) Example 16 1.8 0.5 94.6 92.3 Example 17 1.6 0.4 95.8 93.7 Example 18 1.4 0.4 96.2 94.1 Comparative Example 1 8.2 5.6 62.4 58.7 Comparative Example 2 15.6 11.2 / / Comparative Example 3 1.9 0.5 93.8 91.5 Comparative Example 4 1.7 0.5 94.1 92.0 Comparative Example 5 11.3 7.8 31.5 28.4 Comparative Example 6 4.6 2.8 78.3 74.9 Hydrophobicity test The optical contact angle measuring instrument was used in accordance with the GB / T 30693-2014 testing standard. Composite membranes from Examples 16-18 and Comparative Examples 1-6 were taken and cut into 3cm×5cm pieces. They were wiped with anhydrous ethanol, placed in a constant temperature chamber at 25±1℃ and 50±5% relative humidity for 4 hours to equilibrate. Five measurement points were selected at different locations on the membrane material. 5μL of deionized water was added using the pendant drop method, and the contact angle was measured with an optical contact angle meter. The contact angle was recorded and the average value was taken. For the roll-off angle test, the membrane material was placed horizontally and then slowly tilted. The critical tilt angle at which the water droplet began to roll off was recorded. Table 2 Hydrophobicity test results of the examples and comparative examples project Water contact angle (°) Roll angle (°) Example 16 152.3 6.5 Example 17 154.6 5.8 Example 18 155.2 5.2 Comparative Example 1 148.5 12.3 Comparative Example 2 153.1 6.8 Comparative Example 3 153.4 6.2 Comparative Example 4 101.6 23.5 Comparative Example 5 153.2 6.1 Comparative Example 6 139.8 18.7 Oxygen and carbon dioxide pass rate test Referring to the GB / T 1038-2000 testing standard, a differential pressure gas permeation analyzer was used. Take the composite films of Examples 16-18 and Comparative Examples 1-6 respectively, cut them into circular samples with a diameter of 8cm, test the thickness with a thickness gauge, and then place the samples at a temperature of 23±2℃ and a relative humidity of 50±5% for 24h. The upper and lower chambers of the test chamber are simultaneously evacuated to below 27 Pa and degassed for 3 hours. The vacuum valve of the lower chamber is closed, and the upper chamber is evacuated for another 1 hour. High-purity oxygen is then introduced into the upper chamber to 0.1 MPa. The gas permeation instrument is used for testing. Then the oxygen is replaced with carbon dioxide, and the above steps are repeated. Calculation formula: In the formula: GTR: Gas Transmission Rate, unit: cm³ 3 / (m 2 ·24h·0.1MPa) Δp / Δt: Under steady-state transmission conditions, the pressure change per unit time on the low-pressure side, expressed in Pa / h. V: Volume of the low-pressure chamber, in cm³ 3 ; A: Effective test area of ​​the sample, in m²; T0: Standard state temperature, 273.15 K; p0: Standard pressure, 1.0133 × 10⁻⁶ 5 Pa; Θ: Test temperature, in °C; P1-P2: Pressure difference across the sample, in Pa.

[0046] Table 3. Results of oxygen and carbon dioxide throughput tests in the examples and comparative examples. project <![CDATA[O2GTR(cm 3 / (m 2 ·24h·0.1MPa))]]> <![CDATA[CO2GTR(cm 3 / (m 2 ·24h·0.1MPa))]]> <![CDATA[CO2 / O2 Permeability Ratio]]> Example 16 281 1176 4.19 Example 17 278 1180 4.24 Example 18 284 1178 4.15 Comparative Example 1 352 862 2.45 Comparative Example 2 291 1192 4.10 Comparative Example 3 283 1174 4.15 Comparative Example 4 286 1182 4.13 Comparative Example 5 288 1185 4.11 Comparative Example 6 326 948 2.91 Degradation performance test Refer to the testing standard GB / T 19277.1-2025; Mature compost: Total dry solids content 50%-55%, volatile solids content ≥ 60% of total dry solids, pH value 7.0-8.5, carbon-nitrogen ratio (C / N) 20-30:1, dark brown appearance, no foul odor; Take the composite films of Examples 16-18 and Comparative Examples 1-6 respectively, cut them into 2cm×2cm pieces, prepare 30 pieces of each type of film, place them in a constant temperature and humidity chamber at 25±1℃ and 50±5% relative humidity, equilibrate for 24h, weigh them, and record the initial mass (m0). Spread the well-rotted compost into a plastic box with drainage holes at the bottom, to a thickness of 10 cm. Place the test piece in a nylon bag and spread it on the compost. Cover it with another 10 cm thick layer of compost. Spray with deionized water to adjust the moisture content of the compost to 60%±5%. Place it in a constant temperature chamber at 28±2℃. Add deionized water every 3 days for 90 days. After the sample was removed, it was rinsed in deionized water, dried, cooled to room temperature, weighed, and the mass after degradation (m) was recorded. t ); Calculation formula: In the formula: m0: Initial mass of the sample (mg); m t : Dry weight of the sample (mg) after degradation for t days; Table 4 Degradation performance test results of the examples and comparative examples project 30-day weight loss rate (%) 60-day weight loss rate (%) 90-day weight loss rate (%) Example 16 3.2 8.7 76.4 Example 17 2.8 7.9 78.1 Example 18 3.5 9.1 75.8 Comparative Example 1 4.8 18.6 42.7 Comparative Example 2 3.1 8.2 73.5 Comparative Example 3 2.9 4.1 12.4 Comparative Example 4 3.3 8.9 74.8 Comparative Example 5 3.0 8.3 75.1 Comparative Example 6 3.4 11.2 55.6 Comprehensive Preservation Index Test Referencing the GB / T 10651-2008 testing standard, a fruit firmness tester was used. Fruits wrapped with composite films from Examples 16-18 and Comparative Examples 1-6 were stored in a cold storage for 120 days. After being taken out, they were weighed and their mass M1 was recorded. Calculation formula: In the formula, M0: the weight of the apples before packaging; M1: the weight of the apples after 120 days of storage.

[0047] After the fruits wrapped with composite film in Examples 16-18 and Comparative Examples 1-6 were taken out of the cold storage, they were placed at room temperature of 20±1℃ for 12 hours to warm up. At the equator of the fruit, a circular peel with a thickness of about 1 mm and a diameter of about 2 cm was evenly peeled off with a peeler. The fruit hardness was tested with a fruit hardness tester, the fruit hardness was recorded, 20 data points were collected, and the average value was calculated. Take 20g of the pulp from the fruit that has completed the hardness test, juice it, stir it with a glass rod, let it stand and separate into layers, take the clear juice from the top layer, measure it with a refractometer, and record the soluble solids content. Table 5. Test results of comprehensive preservation indicators for the examples and comparative examples project Water loss rate (%) <![CDATA[Fruit firmness (kg / cm 2 ).]]> Soluble solids content (%) Example 16 1.9 7.8 13.2 Example 17 1.7 7.9 13.4 Example 18 1.6 8.1 13.5 Comparative Example 1 3.5 6.9 11.8 Comparative Example 2 2.1 6.2 11.2 Comparative Example 3 2.0 7.6 13.1 Comparative Example 4 4.8 7.5 12.3 Comparative Example 5 2.2 6.8 11.6 Comparative Example 6 2.8 7.4 12.6 Data Analysis: As shown in Tables 1-5, the nanocomposite film for apple storage and preservation prepared in this invention exhibits excellent performance in all aspects. The incidence of apple scab is only 1.4%-1.8%, the disease index is controlled at 0.4-0.5, the α-farnesene scavenging rate is as high as 94.6%-96.2%, and the conjugated triene inhibition rate reaches 92.3%-94.1%. The water contact angle exceeds 152°, and the roll-off angle is less than 7°, exhibiting typical superhydrophobic and low-adhesion characteristics. The CO2 / O2 permeability ratio is 4.15-4.24, significantly higher than that of ordinary cellulose films, demonstrating excellent passive modified atmosphere capabilities. The film remains stable for the first 60 days of preservation, while the degradation rate reaches 75.8%-78.1% after 90 days, achieving significant accelerated time-sequential degradation. Fruit water loss is controlled at 1.6%-1.9%, and firmness is maintained at 7.8-8.1 kg / cm². 2 The soluble solids content is 13.2%-13.5%, and the preservation effect is comprehensive and excellent.

[0048] In contrast, Comparative Example 1, where the base film and coating solution components were directly mixed and cast into a single-layer homogeneous film, resulted in the cyclodextrin-laccase active center being embedded and obscured by hydrophobic wax. α-Farnesene could not effectively contact the enzyme's active site, leading to a rise in the incidence of laccase disease to 8.2% and a sharp drop in clearance rate to 62.4%. Simultaneously, the wax component was uniformly dispersed within the membrane rather than concentrated on the surface, reducing the water contact angle to 148.5° and increasing the roll-off angle to 12.3°, failing to form superhydrophobic and low-adhesion characteristics. Furthermore, the layered ordered structure formed by the evaporation-induced self-assembly of cellulose nanocrystals was destroyed, essentially eliminating the anisotropic selective permeability of gases, with the CO2 / O2 permeability ratio dropping to 2.45, indicating a near-complete loss of anisotropic selective permeability. Microencapsulated cellulase was prematurely exposed to a water environment in a homogeneous membrane, and its weight loss rate reached 18.6% after 60 days. However, the accelerated degradation kinetics were insufficient in the later stages, and the weight loss rate was only 42.7% after 90 days. This comparative example shows that even if all functional components are present, if they are not spatially partitioned in an asymmetric manner, mutual interference and functional cancellation will occur between the components. Comparative Example 2, lacking the addition of a carrier complex, lost the specific capture of α-farnesene by cyclodextrin and the enzymatic removal function of laccase, resulting in a high incidence of tiger skin disease (15.6%), a disease index of 11.2%, and a decrease in fruit firmness to 6.2 kg / cm². 2 The reason is that the active disease prevention cascade pathway of "molecular recognition-enzymatic removal" is missing, and α-farnesene and its oxidation product conjugated trienes continue to accumulate in the packaging, which accelerates the occurrence of tiger skin disease and fruit softening. Comparative Example 3, lacking the addition of highly substituted sodium carboxymethyl cellulose, lacked the hygroscopic swelling trigger switch, resulting in a weight loss of only 12.4% after 90 days, indicating a near-complete loss of degradation function. This is because, although the microencapsulated cellulase was well embedded in the membrane, the lack of stress from the swelling and cracking of the membrane matrix under soil moisture caused by sodium carboxymethyl cellulose prevented the effective release of cellulase from the microcapsules, leading to the failure of the time-sequential degradation mechanism. In Comparative Example 4, due to the absence of cellulose nanofibers, the coating could not construct the micro / nano secondary rough structure required for superhydrophobicity. The water contact angle decreased to 101.6°, the roll-off angle increased to 23.5°, and the fruit water loss rate reached as high as 4.8%. This is because the coating surface only contained low surface energy materials but lacked micro / nano rough structures. Water droplets became trapped in the surface's microscopic pits and could not suspend, resulting in a hydrophilic wetting state and an increased roll-off angle. In contrast, the rough structure constructed by the cellulose nanofibers in this example could trap an air cushion layer beneath the water droplets, causing them to spherically suspend above the surface tip, thus achieving superhydrophobicity and low adhesion. In Comparative Example 5, because β-cyclodextrin was replaced with ordinary corn starch, it was unable to form a hydrophobic cavity for specific molecular recognition and inclusion of α-farnesene, resulting in a clearance rate of only 31.5% and an incidence of tiger skin disease rising to 11.3%. This is because corn starch lacks the unique "internal hydrophobic-external hydrophilic" truncated cone-shaped cavity structure of cyclodextrin, which cannot selectively capture and enrich nonpolar α-farnesene molecules, leading to an unobstructed oxidation pathway and a high incidence of tiger skin disease. Comparative Example 6, due to the failure to integrate the two membrane layers into a single composite and their mere physical bonding, experienced micro-displacement of the two membrane layers under the pressure of the fruit surface bonding. This allowed water vapor to penetrate the interlayer interface, forming water film channels. Consequently, the superhydrophobic outer layer effect was short-circuited by the interlayer water film, resulting in a decrease in the water contact angle to 139.8° and an increase in the roll-off angle to 18.7°. The CO2 / O2 transmission ratio decreased to 2.91, partially impairing the modified atmosphere function. Furthermore, the interlayer water film interfered with the hygroscopic swelling behavior of sodium carboxymethyl cellulose in the coating layer. The degradation trigger signal was diluted and delayed by the interlayer water accumulation, resulting in a 60-day weight loss of 11.2% and a 90-day weight loss of only 55.6%, significantly weakening the sequential degradation efficiency. In summary, Comparative Example 1 demonstrates that functional components need to be enriched in different spatial regions to achieve synergistic effects, and homogeneous mixing will lead to mutual entrapment and functional cancellation. Comparative Example 6 further proves that functional regions must form a continuous, interface-free whole, and the infiltration of water vapor into the physically bonded interface will cause the functions of each layer to be short-circuited. Comparative Examples 1 and 6 together prove from different perspectives that the asymmetric integrated composite structure is a necessary prerequisite for the realization of multifunctional synergy in this invention.

[0049] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

[0050] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A nanocomposite film for storing and preserving apples, characterized in that, The coating includes a base film and a coating liquid, wherein the base film is composed of cellulose nanocrystals, a carrier complex, a first crosslinking agent, and glycerol; The carrier complex is composed of modified oxidized nanocellulose, laccase, and a second crosslinking agent; The first crosslinking agent is polyethylene glycol diglycidyl ether, used to construct a crosslinking network between cellulose nanocrystals in the base layer membrane; the second crosslinking agent is polyethylene glycol diglycidyl ether. The coating solution is composed of cellulose stearate, cellulose nanocrystals, carnauba wax emulsion, microencapsulated cellulase, sodium carboxymethyl cellulose with high degree of substitution, and triethyl citrate.

2. The nanocomposite film for apple storage and preservation according to claim 1, characterized in that, The preparation steps of the base layer membrane are as follows: Step A1: Under light-protected conditions, add cellulose nanocrystals to deionized water and sonicate for 10-20 minutes at a power of 150-250W. Once sonication is complete, a suspension is obtained. Step A2: Add the carrier complex to the suspension and stir for 25-35 min at 150-250 rpm. Add glycerol and stir for 8-12 min. Add 0.1 mol / L sodium hydroxide solution and adjust the pH to 6.8-7.

2. Then add the first crosslinking agent, polyethylene glycol diglycidyl ether. Heat to 20-25℃ and reduce the stirring speed to 100-140 rpm. React for 30-40 min. Once the reaction is complete, degas under vacuum to obtain the film-forming solution. Step A3: Cast the film-forming liquid into a polytetrafluoroethylene mold, place it in a constant temperature and humidity chamber, heat it to 24-26℃, relative humidity 55%-65%, and let it stand for 46-50 hours. After standing, place it in an oven, heat it to 70-80℃, and cure it for 50-70 minutes. After curing, cool it to 20-30℃, and the film thickness is 20-30μm to obtain the base film.

3. The nanocomposite film for apple storage and preservation according to claim 2, characterized in that, The mass ratio of cellulose nanocrystals to deionized water in step A1 is 0.05-0.06:1; In step A2, the mass ratio of the carrier complex, suspension, glycerol and the first crosslinking agent is 0.035-0.036:1:0.0074-0.0078:0.0036-0.

004.

4. The nanocomposite film for apple storage and preservation according to claim 2, characterized in that, The preparation steps of the carrier complex are as follows: Modified oxidized nanocellulose was added to 0.1 mol / L phosphate buffer, laccase was added, the temperature was raised to 20-30℃, and the mixture was stirred for 2-3 hours at a speed of 100-140 rpm. The second crosslinking agent, polyethylene glycol diglycidyl ether, was added, and the mixture was stirred for 4-5 hours. After the reaction was completed, the mixture was centrifuged and washed to obtain the carrier complex.

5. The nanocomposite film for apple storage and preservation according to claim 4, characterized in that, The mass ratio of the modified oxidized nanocellulose, laccase, and the second crosslinking agent polyethylene glycol diglycidyl ether is 1:0.20-0.22:0.32-0.

34.

6. The nanocomposite film for apple storage and preservation according to claim 4, characterized in that, The preparation steps of the modified oxidized nanocellulose are as follows: Step B1: Add nanocellulose filaments to deionized water, heat to 20-30℃, sonicate for 25-35 minutes at a power of 150-250W, and after sonication is complete, obtain a filament suspension. Step B2: Under a nitrogen atmosphere, β-cyclodextrin is added to the fiber suspension, the temperature is raised to 45-55℃, and the mixture is stirred for 25-35 min at a speed of 250-350 rpm. Sodium hypophosphite catalyst is added, and the mixture is stirred for 8-12 min. The stirring speed is reduced to 180-220 rpm, and 1 mol / L hydrochloric acid solution is added to adjust the pH to 3.4-3.

6. 1,2,3,4-butanetetracarboxylic acid crosslinking agent is added, and the temperature is raised to 110-130℃. The reaction is carried out for 3-4 h. After the reaction is completed, the temperature is lowered to 20-30℃, and the mixture is purified by dialysis with deionized water and freeze-dried to obtain modified oxidized nanocellulose.

7. The nanocomposite film for apple storage and preservation according to claim 6, characterized in that, The mass ratio of nanocellulose filaments to deionized water in step B1 is 0.4-0.6:1; The mass ratio of β-cyclodextrin, fiber suspension, catalyst and crosslinking agent in step B2 is 0.074-0.078:1:0.0046-0.005:0.018-0.

022.

8. The nanocomposite film for apple storage and preservation according to claim 1, characterized in that, The preparation steps of the coating liquid are as follows: Step C1: Add cellulose stearate to ethyl acetate, heat to 40-50℃, stir for 50-70 min at 250-350 rpm, cool to 20-30℃, add cellulose nanocrystals, and sonicate for 8-12 min at 200-300 W. After sonication is complete, a suspension is obtained. Step C2: Add carnauba wax emulsion with a solid content of 10%wt to the suspension, stir at 200-300 rpm for 25-35 min, then reduce the speed to 80-120 rpm, add microencapsulated cellulase and sodium carboxymethyl cellulose with a high degree of substitution, stir for 14-16 min, add triethyl citrate, stir for 4-6 min, after stirring is complete, degas under vacuum to obtain the coating solution; The mass ratio of cellulose stearate to cellulose nanocrystals is 1:0.22-0.26; The mass ratio of the carnauba wax emulsion, suspension, microencapsulated cellulase, highly substituted sodium carboxymethyl cellulose, and triethyl citrate is 0.08-0.12:1:0.005-0.0052:0.006-0.0062:0.0018-0.0022.

9. The nanocomposite film for apple storage and preservation according to claim 8, characterized in that, The preparation steps of the microencapsulated cellulase are as follows: Step D1: Add sodium alginate to deionized water, heat to 15-25℃, stir for 100-140 min at 350-450 rpm, after stirring, let stand to degas for 25-35 min, add cellulase, reduce the speed to 150-250 rpm, stir for 15-25 min, after stirring, add 2% calcium chloride solution, let stand to solidify for 30-40 min, filter through a 200-mesh filter, wash and dry to obtain microcapsules; Step D2: Add chitosan to a 1% acetic acid aqueous solution, heat to 20-30℃, stir for 2-3 hours, add microcapsules, soak for 8-12 seconds, after soaking is complete, air dry naturally for 2-3 hours, sieve to obtain microencapsulated cellulase. The mass ratio of sodium alginate, cellulase, and calcium chloride solution is 0.004-0.006:0.004-0.006:

1. The mass ratio of chitosan to microcapsules is 1.4-1.6:

1.

10. A method for preparing a nanocomposite film for apple storage and preservation according to any one of claims 1-9, characterized in that, The specific steps of the preparation method are as follows: Lay the base film flat on a clean, horizontal glass table. Add the coating liquid to the spray gun's storage tank. The nozzle diameter is 0.7-0.9 mm, the spraying pressure is 0.14-0.16 MPa, the spraying distance is 14-16 cm, the moving speed is 4-6 cm / s, and the wet film thickness is 45-55 μm. After spraying, let it stand for 30-40 minutes, then vacuum dry. After peeling off the film, place it in a constant temperature chamber at 20-30℃ for equilibration for 22-26 hours to obtain the composite film.

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