Amphiphilic chitosan and plant nanocellulose composite coating fresh-keeping material as well as preparation method and application thereof

Abstract

The invention discloses an amphiphilic chitosan and plant nanocellulose composite coating fresh-keeping material, which is prepared from the following ingredients in percentage by mass: 0.5 to 20 percent of amphiphilic chitosan, 0.1 to 5.0 percent of plant nanocellulose, 0.5 to 10.0 percent of coalescing agents, 0.1 to 3.0 percent of antioxidants and the balance deionized water. Wherein the amphiphilic chitosan is prepared from chitosan, quaternary phosphonium salt and sorbic acid. Amphipathic chitosan of the material has hydrophilic groups such as amino and carboxyl and a sorbate hydrophobic group, has hydrophilicity and hydrophobicity at the same time, and is extremely easy to combine with substances such as a coalescing agent, plant nanocellulose and an antioxidant to form a stable polymeric membrane layer, so that the mechanical property after membrane formation is remarkably improved, and the material has a good application prospect. Meanwhile, the plant nanocellulose particles can be stably coated in the polymeric membrane material layer, so that the mechanical property of the material is enhanced, and lasting and efficient antibacterial and antioxidant effects are realized. The invention further discloses a preparation method and application of the amphiphilic chitosan and plant nanocellulose composite coating fresh-keeping material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of fresh-keeping materials, and particularly relates to an amphiphilic chitosan-plant nanocellulose composite coating fresh-keeping material and a preparation method and application thereof. BACKGROUND

[0002] Chitosan is a natural polysaccharide derived from crustaceans (such as shrimp, crab) or fungi, and has the advantages of good biocompatibility, biodegradability and good antibacterial activity. In recent years, natural polymer polymers such as chitosan have become a research hotspot in the food industry as coating fresh-keeping materials.

[0003] The amino groups (-NH2) and hydroxyl groups (-OH) on the molecular chain of chitosan endow it with the ability to bind to negatively charged substances (such as bacterial cell walls), thereby inhibiting microbial growth. Studies have shown that chitosan coating can delay fruit and vegetable spoilage through physical barrier and antibacterial effects, such as inhibiting browning and nutrient loss. Unmodified chitosan has problems such as poor water solubility, poor compatibility and low mechanical strength of the formed film, which limits its practical application.

[0004] In the prior art, the water solubility and functional activity of chitosan are improved through chemical modification such as quaternization and carboxymethylation. Chinese patent CN113278093A discloses a chitosan quaternary ammonium salt quaternary phosphonium salt derivative, which significantly enhances the antibacterial property and film-forming property of chitosan. However, such modification may affect the compatibility and mechanical properties of chitosan, and the mechanical strength and toughness of the coating film are poor. The addition of nanocellulose (CNC) or nanosilica (SiO x )can enhance the mechanical strength and barrier properties of the film. For example, after modification by a surfactant, nanosilica is uniformly dispersed in the chitosan matrix, and the tensile strength and water vapor barrier property of the composite film are significantly improved, but the dispersion stability of the nanoparticles is sensitive to process conditions, which easily leads to performance fluctuations. The performance of chitosan coating can also be improved by loading functional additives, such as embedding plant essential oils (such as thyme essential oil, cinnamon essential oil) or natural antibacterial agents (such as tea polyphenols) to form a slow-release system, which can effectively improve the antibacterial property and antioxidant property of the chitosan coating. However, essential oils are volatile and inactivated, and need to be stably loaded by microcapsule technology (such as Pickering emulsion), which increases the complexity of preparation and production cost. In a high humidity environment, unmodified chitosan coating is prone to swelling and rupture, which limits its application. Solving the adaptability and stability of chitosan coating materials to high humidity environments (humidity 80%~95%) while enhancing the mechanical properties and preservation effect of the coating film is an urgent problem that needs to be solved for chitosan coating fresh-keeping materials. SUMMARY

[0005] The present application aims to provide an amphiphilic chitosan plant nanocellulose composite coating fresh-keeping material and a preparation method and application thereof, and to solve the technical problems of low mechanical strength and poor moisture resistance of traditional chitosan coating fresh-keeping materials by combining molecular modification technology and nanocellulose compounding technology to construct a new coating fresh-keeping material with multiple functions such as antibacterial, modified atmosphere (i.e. adjusting the concentrations of oxygen and carbon dioxide), antioxidant, etc., and high mechanical strength and humidity adaptability.

[0006] According to a first aspect of the present application, an amphiphilic chitosan plant nanocellulose composite coating fresh-keeping material is provided, comprising, in mass percentage: 0.5-20% of amphiphilic chitosan, 0.1-5.0% of plant nanocellulose, 0.5-10.0% of film-forming aid, 0.1-3.0% of antioxidant, and the balance of deionized water. The amphiphilic chitosan is prepared from a system composed of chitosan, quaternary phosphonium salt and sorbic acid, and specifically, the amphiphilic chitosan is prepared by introducing water-soluble quaternary phosphonium salt and fat-soluble sorbic acid into chitosan molecules through peracylation reaction.

[0007] In some embodiments, the amphiphilic chitosan is prepared by the following steps: (1) adding chitosan to an ice acetic acid solution, and then performing ultrasonic defoaming to obtain a chitosan solution; (2) dissolving quaternary phosphonium salt in an organic solvent, then adding 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), N-hydroxysuccinimide (NHS) and sorbic acid to the organic solvent, and obtaining a mixed solution after reaction, and then adding the mixed solution dropwise to the chitosan solution for reaction; (3) dialyzing the product obtained in step (2), washing and freeze-drying to obtain the product.

[0008] In some embodiments, the amphiphilic chitosan is prepared by the following steps: (1) adding chitosan to an ice acetic acid solution, and then performing ultrasonic defoaming to obtain a chitosan solution; (2) dissolving quaternary phosphonium salt in an organic solvent, then adding 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), N-hydroxysuccinimide (NHS) and sorbic acid to the organic solvent, and obtaining a mixed solution after reaction, and then adding the mixed solution dropwise to the chitosan solution for reaction; (3) dialyzing the product obtained in step (2) for 24-48 h, washing and freeze-drying to obtain the product.

[0009] In some embodiments, in step (1), the glacial acetic acid solution is prepared by dissolving glacial acetic acid in water to obtain a 1-3% (v / v) glacial acetic acid solution. Preferably, the glacial acetic acid solution is a 1% (v / v) glacial acetic acid solution.

[0010] In some embodiments, the plant nanocellulose is a plant nanocellulose treated by 1,3-propanesultone or glyceryl stearate sulfonate.

[0011] In some embodiments, in step (1), the ratio of the mass of chitosan to the volume of the glacial acetic acid solution is 1:10-1:100.

[0012] In some embodiments, in step (2), the organic solvent is dimethyl sulfoxide (DMSO).

[0013] In some embodiments, the quaternary phosphonium salt is selected from at least one of 4-carboxybutyltriphenylphosphonium bromide and 2-carboxyethyltriphenylphosphonium bromide.

[0014] In some embodiments, in step (2), the amount of the quaternary phosphonium salt is 6-10% of the mass of chitosan, and the ratio of the mass of the quaternary phosphonium salt to the volume of the organic solvent is 1:(260-670) g / mL. Preferably, the amount of the quaternary phosphonium salt is 6.68% of the mass of chitosan, and the ratio of the mass of the quaternary phosphonium salt to the volume of the organic solvent is 1:500 g / mL.

[0015] In some embodiments, in step (2), the amount of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride is 0.6-35% of the mass of chitosan, the amount of N-hydroxysuccinimide is 0.6-35% of the mass of chitosan, and the amount of sorbic acid is 6-68% of the mass of chitosan.

[0016] In some embodiments, in step (3), the dialysis is performed by using a dialysis bag with a molecular weight cut-off of 3000-4000. Preferably, the dialysis is performed by using a dialysis bag with a molecular weight cut-off of 3500.

[0017] In some embodiments, in step (3), the temperature for freeze-drying is -10°C to -80°C.

[0018] In some embodiments, the plant nanocellulose is selected from at least one of pineapple leaf nanocellulose and sisal nanocellulose.

[0019] In some embodiments, the plant nanocellulose has a particle size of 1-200 nanometers.

[0020] In some embodiments, the film forming aid is selected from at least one of shellac, gum arabic and zein, and the antioxidant is selected from at least one of tea polyphenol, quercetin and chlorogenic acid.

[0021] According to a second aspect of the present application, a preparation method of the amphiphilic chitosan plant nanocellulose composite coating fresh-keeping material is provided, comprising the following steps: (1) dissolving the amphiphilic chitosan in water to obtain an amphiphilic chitosan aqueous solution with a concentration of 0.1-2.0 wt%, and dissolving the film forming aid in water to obtain a film forming aid aqueous solution with a concentration of 0.5-5.0 wt%; (2) ultrasonically dispersing the plant nanocellulose with water to obtain a nanocellulose suspension with a solid content of 1-5%, and adding 1,3-propane sulfonate lactone or glycerol stearate sulfonate to the nanocellulose suspension; (3) under the condition of a rotation speed of 400-800 rpm, adding the film forming aid aqueous solution prepared in step (1) to the amphiphilic chitosan aqueous solution prepared in step (1), and continuing to stir after the addition is completed to obtain an amphiphilic chitosan mixed solution; (4) stirring the amphiphilic chitosan mixed solution, the product of step (2) and the antioxidant under the condition of a rotation speed of 400-800 rpm to obtain the product.

[0022] It should be noted that in step (2), the purpose of adding 1,3-propane sulfonate lactone or glycerol stearate sulfonate to the nanocellulose suspension is to perform sulfonated treatment on the plant nanocellulose to enhance its dispersibility and stability.

[0023] In some embodiments, in step (2), the amount of 1,3-propane sulfonate lactone or glycerol stearate sulfonate is 1-55% of the mass of the plant nanocellulose.

[0024] In some embodiments, in step (3), the amount of the film forming aid in the film forming aid aqueous solution is 0.5-5.0% of the mass of the amphiphilic chitosan aqueous solution.

[0025] In some embodiments, in step (4), the mass ratio of the amphiphilic chitosan mixed solution, the product of step (2) and the antioxidant is (100-50):(50-10):(5-0.5).

[0026] According to a third aspect of the present application, the application of the amphiphilic chitosan plant nanocellulose composite coating fresh-keeping material is provided. The amphiphilic chitosan plant nanocellulose composite coating fresh-keeping material can be applied to fruit coating fresh-keeping agents, and is applied to fruits in a dipping coating or spraying manner to achieve the effects of antibacterial and antioxidant, modified oxygen and carbon dioxide concentration, and physical isolation.

[0027] The amphiphilic chitosan has hydrophilic groups such as amino and carboxyl groups and a sorbate hydrophobic group, and has hydrophilicity and hydrophobicity, so that the amphiphilic chitosan can be easily combined with film forming aids, plant nanocellulose and antioxidants and other substances to form a stable high molecular film layer, and the mechanical properties after film forming are significantly improved, and the plant nanocellulose particles can be stably coated in the high molecular film material layer to enhance the mechanical properties of the material and achieve long-lasting and efficient antibacterial and antioxidant effects. In addition, the amphiphilic chitosan, plant nanocellulose and other substances have good biocompatibility and are safe and non-toxic green pollution-free materials.

[0028] The beneficial effects of the present application include: 1. The present application modifies chitosan by adding quaternary phosphonium salt and sorbic acid, which is to modify chitosan to be amphiphilic, i.e. to connect hydrophilic quaternary phosphonium salt and hydrophobic sorbic acid on the chitosan molecule. The present application modifies chitosan to be amphiphilic, which gives chitosan the property of having both hydrophilicity and hydrophobicity, can effectively improve the compatibility of chitosan, realize stable compatibility and effective uniform dispersion with other composite components, can greatly improve the compatibility of chitosan solution and nanocellulose, so that chitosan and plant nanocellulose can be stably compounded together, thereby effectively improving the mechanical properties of single chitosan coating material.

[0029] 2. The amphiphilic chitosan plant nanocellulose composite coating preservative material provided by the present application not only can realize long-lasting and efficient antibacterial and antioxidant effects, but also can form a high molecular coating layer to effectively isolate harmful microorganisms and regulate the respiration of fruits, and has the advantages of antibacterial, antioxidant and air conditioning (adjusting the concentrations of oxygen and carbon dioxide) and other functions.

[0030] 3. The present application uses high molecular film forming substances such as shellac, gum arabic and corn protein, which has good film forming performance and contains hydrophilic groups such as hydroxyl and carboxyl groups in the high molecule, can form stable hydrogen bonds with the amphiphilic chitosan and plant nanocellulose material, and can be stably and efficiently combined together through intermolecular forces, and the high molecular film layer formed by the composite material has good mechanical properties such as tensile strength and elongation at break, solving the problem of poor mechanical properties and easy breakage of traditional chitosan coating materials.

[0031] 4. The raw materials used in the present application are all natural materials, which have good biocompatibility, biodegradability, non-toxicity and other characteristics, and are a green pollution-free material, which has good safety to the environment, plants and animals and human body.

[0032] 5、The application combines molecular modification technology and nanocellulose complex technology to construct a new type of coating preservation material with multiple functions such as antibiosis, air conditioning, antioxidant, etc., which are coordinated and synergistic, and also has high mechanical strength and humidity adaptability, solves the problem of single function of traditional single chitosan coating preservation material, and overcomes the defects of low mechanical strength and poor moisture resistance of pure chitosan coating material.

[0033] 6、The amphiphilic chitosan plant nanocellulose composite coating preservation material prepared in the application can form a film on the surface of fruits through dipping, brushing, spraying and the like, not only can realize long-lasting and efficient antibacterial and bactericidal effect, but also the formed composite polymer coating layer can effectively isolate harmful microorganisms and regulate the respiration of fruits, has the multifunctional advantages of antibiosis, physical barrier and air conditioning, solves the defect of single function of traditional chitosan coating material, and effectively improves the antibacterial protection effect of chitosan coating material on fruits. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is a Fourier infrared spectrum of chitosan, quaternary phosphonium salt, sorbic acid and amphiphilic chitosan in the application example 1. Figure 2 (A) is the stability test result graph of the chitosan plant nanocellulose composite coating preservation material of the comparative example 2, and (B) is the stability test result graph of the amphiphilic chitosan plant nanocellulose composite coating preservation material of the application example 1. Figure 3 It is a scanning electron microscope graph of the amphiphilic chitosan plant nanocellulose composite coating preservation material of the application. Figure 4 It is a picture of each group on the 0-8th day in the application test of litchi preservation. DETAILED DESCRIPTION

[0035] The application will be further described in detail below in combination with the drawings, but the embodiments of the application are not limited thereto. The raw materials and reagents involved in the following examples can be obtained from commercial channels.

[0036] The amphiphilic chitosan plant nanocellulose composite coating preservative material of the present application, firstly, the amphiphilic chitosan is prepared by grafting quaternary phosphonium salt and sorbic acid onto chitosan. Then, the nanocellulose suspension is prepared by sulfonating natural plant nanocellulose with propane sulfone lactone to enhance the dispersibility of the nanocellulose suspension and the compatibility of the nanocellulose suspension with the amphiphilic chitosan. Next, the amphiphilic chitosan is formulated into an aqueous solution and mixed with a film-forming aid to obtain an amphiphilic chitosan mixed solution. Finally, the amphiphilic chitosan mixed solution and the plant nanocellulose suspension after sulfonation are mixed in a certain volume ratio, a film-forming aid and an antioxidant are added, and an amphiphilic chitosan plant nanocellulose composite coating preservative material is obtained after emulsification.

[0037] Example 1 The present embodiment provides a preparation method of an amphiphilic chitosan plant nanocellulose composite coating preservative material, comprising the following steps: 1. Preparation of amphiphilic chitosan (1) Dissolve glacial acetic acid in deionized water to prepare a 1% (v / v) glacial acetic acid solution, add 1.50 g of chitosan to 150 mL of the glacial acetic acid solution, and react under the condition of constant temperature water bath magnetic stirring at 60°C for 2 h, then ultrasonic defoaming for 10 min, and cool to room temperature after standing to obtain a chitosan solution.

[0038] (2) Dissolve 0.1 g of 4-carboxybutyltriphenylphosphonium bromide in 50 mL of dimethyl sulfoxide (DMSO), then add 0.01 g of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), 0.01 g of N-hydroxysuccinimide (NHS) and 0.1 g of sorbic acid to the DMSO, and react for 1 h, then add the DMSO dropwise to the chitosan solution, and react under constant temperature conditions at 70°C for 6 h.

[0039] (3) After the product obtained in step (2) is dialyzed at room temperature for 24 h using a dialysis bag with a molecular weight cut-off of 3500, wash with distilled water, then freeze-dry at -50°C to obtain amphiphilic chitosan.

[0040] 2. Preparation of amphiphilic chitosan plant nanocellulose composite coating preservative material (1) Formulate the amphiphilic chitosan into an amphiphilic chitosan aqueous solution with a concentration of 0.1 wt%, and formulate the film-forming aid shellac into a shellac aqueous solution with a concentration of 0.5 wt%, for standby use.

[0041] (2) Ultrasonically disperse 1 g of pineapple leaf nanocellulose with distilled water to obtain a nanocellulose suspension with a solid content of 1%, and add 0.01 g of 1,3-propane sulfone lactone to sulfonate the plant nanocellulose to enhance its dispersibility and stability.

[0042] (3) Slowly drop the aqueous solution of shellac into the amphiphilic chitosan solution prepared in step (1) under the condition of 400 rpm, and continue to stir uniformly after the dropping is completed, to obtain an amphiphilic chitosan mixed solution.

[0043] (4) Take 100 g of the amphiphilic chitosan mixed solution, and add 2.0 g of the plant nanocellulose suspension and 1.0 g of the antioxidant tea polyphenol to the amphiphilic chitosan mixed solution, and stir uniformly under the condition of 400 rpm to prepare an amphiphilic chitosan plant nanocellulose composite coating fresh-keeping material.

[0044] Comparative Example 1 The present comparative example provides a preparation method of quaternary phosphonium salt chitosan, comprising the following steps: (1) Dissolve glacial acetic acid in deionized water to prepare a 1% (v / v) glacial acetic acid solution, and add 1.50 g of chitosan to 150 mL of the glacial acetic acid solution, and dissolve under magnetic stirring in a 60°C constant temperature water bath, and ultrasonic defoaming for 10 min, and then cool to room temperature to obtain a chitosan solution.

[0045] (2) Dissolve 0.1 g of 4-carboxybutyltriphenylphosphonium bromide in 50 mL of dimethyl sulfoxide (DMSO), and then add 0.01 g of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and 0.01 g of N-hydroxysuccinimide (NHS) to the DMSO, and then magnetically stir uniformly, and then drop the DMSO mixture into the chitosan solution obtained in step (1), and react at 70°C for 6 h.

[0046] (3) Use a dialysis bag with a molecular weight cut-off of 3500 to dialyze the product obtained in step (2) at room temperature for 24 h, and then wash with distilled water, and then freeze-dry at -50°C to obtain an amphiphilic chitosan.

[0047] The Fourier infrared spectrum of the amphiphilic chitosan prepared in Example 1, the quaternary phosphonium salt chitosan prepared in Comparative Example 1, chitosan, and sorbic acid was tested, and the results are shown in Figure 1 From Figure 1 it can be seen that the modified amphiphilic chitosan molecule has new infrared characteristic absorption peaks at 2920 cm -1 , 1638 cm -1 and 1528 cm -1 . Among them, 2920 cm -1 and 1528 cm -1 are characteristic absorption peaks in the quaternary phosphonium salt molecule, and 1638 cm -1The characteristic absorption peak of sorbic acid molecule. It is shown that the quaternary phosphonium salt and sorbic acid have been successfully grafted into the molecule of chitosan, and the amphiphilic chitosan has been successfully prepared.

[0048] Comparative Example 2 The present comparative example provides a preparation method of a chitosan nanocellulose composite coating preservative material, comprising the following steps: (1) Prepare a chitosan aqueous solution with a concentration of 0.1 wt%, and prepare a shellac aqueous solution with a concentration of 0.5 wt% as a film forming aid, for standby use.

[0049] (2) Ultrasonically disperse 1 g of pineapple leaf nanocellulose with distilled water to obtain a nanocellulose suspension with a solid content of 1%, and add 0.01 g of 1,3-propane sulfonate lactone to the nanocellulose for sulfonated treatment, to enhance the dispersibility and stability thereof.

[0050] (3) Slowly drop the shellac aqueous solution into the chitosan aqueous solution prepared in step (1) under the condition of a rotation speed of 400 rpm, and continue to stir uniformly after the dropping is completed, to obtain a chitosan mixed solution.

[0051] (4) Weigh 100 g of the chitosan mixed solution, and add 2.0 g of the plant nanocellulose suspension and 1.0 g of the antioxidant tea polyphenol to the chitosan mixed solution, and stir uniformly under the condition of a rotation speed of 400 rpm, to prepare a chitosan plant nanocellulose composite coating preservative material.

[0052] Place the amphiphilic chitosan plant nanocellulose composite coating preservative material prepared in Example 1 and the chitosan plant nanocellulose composite coating preservative material prepared in Comparative Example 2 under normal temperature and pressure conditions, and perform stability testing, and the results are shown in Table 1. Figure 2 As can be seen from Table 1, the composite suspension prepared from the chitosan without modification and the pineapple leaf nanocellulose appears to be stratified after being placed under normal temperature and pressure conditions for 5 days, while the amphiphilic chitosan plant nanocellulose composite coating preservative material does not appear to be stratified under the same conditions for 10 days, and the stability is significantly improved. Figure 2

[0053] Perform scanning electron microscope testing on the amphiphilic chitosan plant nanocellulose composite coating preservative material prepared in Example 1, and the results are shown in Table 2. Figure 3 As can be seen from Table 2, the amphiphilic chitosan and the plant nanocellulose in the amphiphilic chitosan plant nanocellulose composite coating preservative material can be stably combined together, and the surface and cross section are flat and dense. Figure 3

[0054] Example 2 ​​The present embodiment provides a preparation method of an amphiphilic chitosan plant nanocellulose composite coating preservation material, comprising the following steps: 1. Preparation of amphiphilic chitosan (1) Dissolve glacial acetic acid in deionized water to prepare a 1% (v / v) glacial acetic acid solution, and then add 1.50 g of chitosan to 150 mL of the glacial acetic acid solution. Stir the mixture in a constant temperature water bath at 60°C for 8 hours, and then perform ultrasonic defoaming for 15 minutes. Let the mixture cool to room temperature to obtain a chitosan solution.

[0055] (2) Dissolve 0.1 g of 4-carboxybutyltriphenylphosphonium bromide in 50 mL of dimethyl sulfoxide (DMSO), and then add 0.5 g of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), 0.5 g of N-hydroxysuccinimide (NHS), and 1.0 g of sorbic acid to the DMSO. After reacting for 5 hours, add the DMSO dropwise to the chitosan solution, and then react at a constant temperature of 70°C for 12 hours.

[0056] (3) Use a dialysis bag with a molecular weight cut-off of 3500 to dialyze the product obtained in step (2) at room temperature for 48 hours. Then, wash the product with distilled water, and then freeze-dry the product at -80°C to obtain amphiphilic chitosan.

[0057] 2. Preparation of amphiphilic chitosan plant nanocellulose composite coating preservation material (1) Prepare a 2.0 wt% amphiphilic chitosan aqueous solution, and prepare a 5.0 wt% gum arabic aqueous solution as a film-forming aid, and then reserve the solutions.

[0058] (2) Ultrasonically disperse 1 g of pineapple leaf nanocellulose in distilled water to obtain a nanocellulose suspension with a solid content of 5%, and then add 0.5 g of 1,3-propane sulfonic acid lactone to the nanocellulose to perform sulfonization treatment, thereby enhancing the dispersibility and stability of the nanocellulose.

[0059] (3) Slowly add the gum arabic aqueous solution to the amphiphilic chitosan aqueous solution prepared in step (1) at a rotation speed of 800 rpm, and then continue to stir the mixture until it is uniform to obtain an amphiphilic chitosan mixture.

[0060] (4) Weigh 100 g of the amphiphilic chitosan mixture, and then add 20 g of the plant nanocellulose suspension (the product obtained in step (2)) and 10 g of the antioxidant quercetin to the amphiphilic chitosan mixture. Stir the mixture at a rotation speed of 800 rpm until it is uniform to obtain an amphiphilic chitosan plant nanocellulose composite coating preservation material.

[0061] Example 3 The present embodiment provides a preparation method of an amphiphilic chitosan plant nanocellulose composite coating preservation material, comprising the following steps: 1. Preparation of amphiphilic chitosan (1) Dissolve glacial acetic acid in deionized water to prepare a 1% (v / v) glacial acetic acid solution, add 1.50 g of chitosan to 150 mL of the glacial acetic acid solution, and react under the condition of a 60°C constant temperature water bath and magnetic stirring for 6 h, then perform ultrasonic debubbling for 12 min, and cool to room temperature after standing to obtain a chitosan solution.

[0062] (2) Dissolve 0.1 g of 4-carboxybutyltriphenylphosphonium bromide in 50 mL of dimethyl sulfoxide (DMSO), then add 0.1 g of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), 0.1 g of N-hydroxysuccinimide (NHS), and 0.5 g of sorbic acid to the DMSO, and react for 3 h, then add the DMSO dropwise to the chitosan solution, and react under the condition of a 70°C constant temperature for 8 h.

[0063] (3) After dialysis of the product obtained in step (2) at room temperature for 36 h using a dialysis bag with a molecular weight cut-off of 3500, perform washing treatment using distilled water, then perform freeze-drying at -70°C to obtain amphiphilic chitosan.

[0064] 2. Preparation of amphiphilic chitosan plant nanocellulose composite coating preservation material (1) Prepare an amphiphilic chitosan aqueous solution with a concentration of 1.0 wt% from the amphiphilic chitosan, and prepare a zein aqueous solution with a concentration of 3.0 wt% from the film-forming aid zein, for standby use.

[0065] (2) Ultrasonically disperse 1 g of pineapple leaf nanocellulose with distilled water to obtain a nanocellulose suspension with a solid content of 3%, and add 0.1 g of 1,3-propane sulfonic acid lactone to the plant nanocellulose for sulfonated treatment to enhance the dispersibility and stability thereof.

[0066] (3) Slowly add the zein aqueous solution to the amphiphilic chitosan aqueous solution prepared in step (1) under the condition of a rotation speed of 600 rpm, and continue to stir uniformly after the addition is completed to obtain an amphiphilic chitosan mixed solution.

[0067] (4) Weigh 100 g of the amphiphilic chitosan mixed solution, 10 g of the plant nanocellulose suspension (product obtained in step (2)), and 10 g of the antioxidant chlorogenic acid, and stir uniformly under the condition of a rotation speed of 600 rpm to prepare an amphiphilic chitosan plant nanocellulose composite coating preservation material.

[0068] Comparative Example 3 The present comparative example provides a preparation method of a chitosan film material, comprising the following steps: The chitosan is dissolved in deionized water, filtered, ultrasonically defoamed, and then poured into a mold. The mold is dried at room temperature for 24-48 hours or accelerated drying in an oven at 40°C. After the solvent is volatilized, a chitosan film is formed.

[0069] Comparative Example 4 The present comparative example provides a preparation method of an amphiphilic chitosan film material, comprising the following steps: The amphiphilic chitosan prepared in Example 1 is dissolved in deionized water, filtered, ultrasonically defoamed, and then poured into a mold. The mold is dried at room temperature for 24-48 hours or accelerated drying in an oven at 40°C. After the solvent is volatilized, an amphiphilic chitosan film is formed.

[0070] Litchi preservation application test The litchis are divided into an ultrapure water control group, a prochloraz control group, a pure chitosan control group, and a composite material group.

[0071] 1. Test grouping Test group: composite material group, treated with the amphiphilic chitosan plant nanocellulose composite coating preservation material prepared in Example 1; Control group 1: ultrapure water control group, treated with ultrapure water; Control group 2: prochloraz control group, treated with a 0.5wt% prochloraz aqueous solution; Control group 3: pure chitosan control group, treated with a 0.5wt% pure chitosan solution.

[0072] 2. Experimental treatment method The preservation effect of the materials in each experimental group on litchis is determined by using the dip coating method. First, 1 kg of freshly picked litchi samples are soaked in ultrapure water, a 0.5% prochloraz aqueous solution, a 0.5% pure chitosan solution, and the amphiphilic chitosan plant nanocellulose composite coating preservation material prepared in Example 1, respectively. After soaking for 1 hour, the litchi samples are taken out and stored under normal temperature and pressure conditions. The appearance and degree of rotting of the litchi samples in each test group are observed at different times to determine the preservation application effect.

[0073] The litchi preservation application effect is as shown in Table 2. Figure 4 From Table 2, it can be seen that the litchi samples treated with the amphiphilic chitosan plant nanocellulose composite coating preservation material prepared in Example 1 have the best preservation effect. Figure 4It can be seen that in the first 6 days, the fruits of the blank control group and the pure chitosan treatment group gradually appeared mildew, and the color of the peel became dark. The prochloraz control group and the composite material treatment group of the application did not appear mildew or spots. On the 8th day, the prochloraz control group appeared mildew and spots, and the blank control group and the pure chitosan treatment group appeared obvious browning and mildew, completely losing the edible value, and the fruits of the composite material group still had no mildew smell and the peel color was bright. It shows that the amphiphilic chitosan plant nanocellulose composite coating preservation material improves the antibacterial activity, and the physical isolation effect of coating and the antibacterial effect of amphiphilic chitosan produce a synergistic antibacterial effect, thereby reducing the mildew and browning of fruits during storage. The room temperature shelf life of litchi can be extended to 6-8 days.

[0074] Mechanical strength test of composite coating material 1. Test object Test group: amphiphilic chitosan plant nanocellulose composite coating preservation material prepared in examples 1-3; Control group 1: chitosan film material prepared in comparative example 3; Control group 2: amphiphilic chitosan film material prepared in comparative example 4.

[0075] 2. Test method The tensile strength and elongation at break of the coating were tested according to the standard ASTM D882-12 to characterize its mechanical strength performance. The sample film was cut into a size of 15mm×40mm, and 5 points were taken on each sample film with a screw micrometer to measure the thickness, and the average value was taken. The sample was tested under the condition of T=25℃, RH=80%-95% high humidity. Open the Material Test V4.3 software on the computer connected with the tensile testing machine, set the tensile speed to 10mm / min, stop the tensile testing machine after the film breaks, and then read the tensile strength and elongation at break. Each group of samples was repeated 5 times, and the average value was taken.

[0076] 3. Test results Fruit storage and preservation is usually carried out under high humidity (RH=80%-95%) conditions, so it is an important indicator to evaluate the coating preservation material to still have good mechanical strength under high humidity conditions. Coating preservation materials with high tensile strength and high elongation at break are not easy to break during use, have better physical barrier effect and modified atmosphere preservation effect, and can significantly improve the preservation effect of coating.

[0077] The tensile strength value and the elongation at break value of the coating film materials of different test groups under high humidity (humidity is 80%~95%) conditions are shown in Table 1. From the results of Table 1, it can be seen that the mechanical properties of the amphiphilic chitosan plant nanocellulose composite coating film preservation materials obtained in Examples 1~3 are better than those of the pure chitosan film material without compounding and the amphiphilic chitosan material control group; the amphiphilic chitosan plant nanocellulose composite coating film preservation material of Example 1 has the largest tensile strength value, and the amphiphilic chitosan plant nanocellulose composite coating film preservation material of Example 3 has the largest elongation at break value, which has excellent performance, indicating that the composite coating film preservation material obtained by combining the molecular modification technology and the nanocellulose compounding technology has high mechanical strength and humidity adaptability. The test results show that the compounding of plant nanocellulose and amphiphilic chitosan can effectively improve the mechanical strength of chitosan, so that it still has good mechanical strength under high humidity conditions.

[0078] Table 1 Comparison of tensile strength value and elongation at break value of different coating film materials

[0079] The above only describes some embodiments of the present application. For those skilled in the art, without departing from the inventive concept, several modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. Amphiphilic chitosan plant nanocellulose composite coating fresh-keeping material, characterized in that, Calculated by mass percentage, it includes: amphiphilic chitosan 0.5-20%, plant nanocellulose 0.1-5.0%, film-forming aid 0.5-10.0%, antioxidant 0.1-3.0%, and the balance is deionized water; Among them, the amphiphilic chitosan is prepared from a system consisting of chitosan, quaternary phosphate and sorbic acid.

2. The amphiphilic chitosan plant nanocellulose composite coating preservative material according to claim 1, characterized in that The amphiphilic chitosan is prepared by the following steps: (1) adding chitosan to a glacial acetic acid solution, and then performing ultrasonic degassing to obtain a chitosan solution; (2) dissolving the quaternary phosphonium salt in an organic solvent, then adding 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide and sorbic acid to the organic solvent, reacting to obtain a mixed solution, and adding the mixed solution dropwise to the chitosan solution for reaction; (3) The product obtained in step (2) is dialyzed, washed and freeze-dried to obtain the product.

3. The amphiphilic chitosan plant nanocellulose composite coating preservative material according to claim 2, characterized in that: In step (1), the ratio of the mass of the chitosan to the volume of the glacial acetic acid solution is 1:10 to 1:

100.

4. The amphiphilic chitosan plant nanocellulose composite coating preservative material according to claim 2, characterized in that: In step (2), the quaternary phosphonium salt is selected from at least one of 4-carboxybutyltriphenylphosphonium bromide and 2-carboxyethyltriphenylphosphonium bromide; the amount of the quaternary phosphonium salt is 6-10% of the mass of the chitosan; the amount of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride is 0.6-35% of the mass of the chitosan; the amount of N-hydroxysuccinimide is 0.6-35% of the mass of the chitosan; and the amount of sorbic acid is 6-68% of the mass of the chitosan.

5. The amphiphilic chitosan plant nanocellulose composite coating preservative material according to claim 1, characterized in that: The plant nanocellulose is selected from at least one of pineapple leaf nanocellulose and sisal nanocellulose; and the particle size of the plant nanocellulose is 1 to 200 nanometers.

6. The amphiphilic chitosan plant nanocellulose composite coating preservative material according to claim 1, characterized in that: The film-forming aid is selected from at least one of shellac, gum arabic and zein; and the antioxidant is selected from at least one of tea polyphenols, quercetin and chlorogenic acid.

7. The method for preparing the amphiphilic chitosan plant nanocellulose composite coating fresh-keeping material according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) dissolving amphiphilic chitosan in water to obtain an amphiphilic chitosan aqueous solution with a concentration of 0.1-2.0 wt %, and dissolving a film-forming agent in water to obtain a film-forming agent aqueous solution with a concentration of 0.5-5.0 wt %; (2) ultrasonically dispersing plant nanocellulose with water to obtain a nanocellulose suspension with a solid content of 1 to 5%, and adding 1,3-propane sultone or stearyl glyceryl sulfonate to the nanocellulose suspension; (3) adding the film-forming aid aqueous solution prepared in step (1) dropwise to the amphiphilic chitosan aqueous solution prepared in step (1) at a rotation speed of 400 to 800 rpm, and continuing to stir after the addition is completed to obtain an amphiphilic chitosan mixed solution; (4) stirring the amphiphilic chitosan mixed solution, the product of step (2) and the antioxidant at a rotation speed of 400-800 rpm to obtain.

8. The method for preparing the amphiphilic chitosan plant nanocellulose composite coating fresh-keeping material according to claim 7, characterized in that: In step (2), the amount of 1,3-propane sultone or stearyl glyceryl sulfonate is 1 to 55% of the mass of the plant nanocellulose; In step (3), the amount of the film-forming aid in the film-forming aid aqueous solution is 0.5-5.0% of the mass of the amphiphilic chitosan aqueous solution.

9. The method for preparing the amphiphilic chitosan plant nanocellulose composite coating fresh-keeping material according to claim 7, characterized in that: In step (4), the mass ratio of the amphiphilic chitosan mixed solution, the product of step (2) and the antioxidant is (100-50): (50-10): (5-0.5).

10. Use of the amphiphilic chitosan plant nanocellulose composite coating preservative material according to any one of claims 1 to 6 in the preparation of a fruit coating preservative.

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