Natural antibacterial coating fresh-keeping material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of organic polymer material modification and composite coating preservation, in particular to a natural antibacterial coating preservation material as well as a preparation method and application thereof. The preparation method comprises the following steps: dispersing an amphiphilic antibacterial chitosan derivative into a solvent A to obtain a water phase; adding essential oil into the water phase, homogenizing, and carrying out ultrasonic emulsification to obtain a Pickering emulsion; dissolving a film-forming material in a dispersing agent, and adding a plasticizer to obtain a film-forming base solution; and mixing the Pickering emulsion, the film-forming base solution and water, adding nano reinforced particles and a binder, homogenizing, and degassing to obtain the natural antibacterial coating fresh-keeping material. The antibacterial material is grafted in a natural polymer material chitosan molecular structure, meanwhile, the organic polymer material and the plant essential oil are compounded, the natural antibacterial coating fresh-keeping material with multiple antibacterial functions is constructed, the natural antibacterial coating fresh-keeping material is used for postharvest fresh keeping of tropical fruits, and the fresh-keeping effect is good.

Description

Technical Field

[0001] The invention relates to the field of organic polymer material modification technology and composite coating preservation technology, and in particular to a natural antibacterial coating preservation material and a preparation method and application thereof. Background Art

[0002] Traditional chemical preservatives have problems such as high toxicity, single function, and harmful to health. As people's demand for green, organic, healthy and safe food increases, the requirements for food preservative materials are also getting higher and higher. Green, efficient and safe preservation technology and new preservatives have become a hot spot in international research. In recent years, coating preservation technology has attracted widespread attention at home and abroad due to its green, safe and easy use. Coating preservation is to soak and coat fruits with polymer coating liquid. The film layer formed on the surface of the fruit after drying can inhibit the respiration of the fruit and isolate harmful microorganisms. At present, coating preservation materials are usually made of wax, natural resin, lipid, gelatin, starch and other polymer film-forming substances to make an appropriate concentration of aqueous solution or emulsion, which is applied to the surface of the fruit by dipping, smearing, spraying and other methods. After air drying, a thin transparent film is formed, which becomes an effective barrier between the fruit and the outside atmosphere, inhibiting gas exchange, thereby forming a low oxygen and high carbon dioxide atmosphere to inhibit the respiration of the fruit after harvest and delay the rapid ripening of the fruit. However, the existing coating preservation materials generally only have physical isolation effects, no antibacterial and antioxidant effects, single functions, and the preservation effect needs to be further improved.

[0003] Therefore, constructing a natural antibacterial coating preservation material with multiple antibacterial functions is of great significance in the field of composite coating preservation technology. Summary of the invention

[0004] Based on the above content, the present invention provides a natural antibacterial coating preservation material and its preparation method and application. The present invention constructs a natural antibacterial coating preservation material with multiple antibacterial functions by grafting antibacterial materials into the molecular structure of natural polymer material chitosan, and compounding organic polymer materials and plant essential oils, and uses it for the post-harvest preservation of tropical fruits, with good preservation effect.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention is a method for preparing a natural antibacterial coating fresh-keeping material, comprising the following steps:

[0007] dispersing the amphiphilic antibacterial chitosan derivative in solvent A to obtain an aqueous phase;

[0008] Add the essential oil to the aqueous phase and homogenize (homogenize at a speed of 10000-12000 r / min for 5-30 min), and ultrasonic emulsify (output power of 100W-250W, ultrasonic time of 5-10 min; intermittent pulse working mode: pulse width of 2.0-3s, intermittent time of 2.0-5s) to obtain a Pickering emulsion;

[0009] Dissolving the film-forming material in a dispersant and adding a plasticizer to obtain a film-forming base liquid;

[0010] The Pickering emulsion, the film-forming base liquid and water are mixed, and nano-reinforced particles and a binder are added, homogenized (homogenized by a high-speed shearing machine at a speed of 10000-12000 r / min for 3-8 min), and degassed (15-30 min) to obtain the natural antibacterial coating fresh-keeping material;

[0011] The structural formula of the amphiphilic antibacterial chitosan derivative is shown in Formula I:

[0012]

[0013] In formula I, m, n, s, and t are independently natural numbers ≥ 1;

[0014] X is one of F, Cl, Br, I, HSO3, HCO3, H2PO4, NO3, CH3CH2COO, CH3COO, and HCOO;

[0015] The R1 and R2 are independently aromatic hydrocarbon groups or derivative groups thereof; R3 is an organic acid with antibacterial properties: one or more of citric acid, malic acid, tartaric acid, ascorbic acid, sorbic acid, benzoic acid, phenyllactic acid, formic acid, and lactic acid; R4 is an organic acid with hydrophobic properties: one or more of cholic acid, deoxycholic acid, ricinoleic acid, eleostearic acid, linoleic acid, linoleic acid, linoleic acid, or oleic acid.

[0016] The introduction of the Pickering emulsion in the present invention can, on the one hand, improve the uniformity of the dispersion of the plant essential oil in the membrane matrix and improve the release and stability of the essential oil; on the other hand, the emulsion-stabilized particles can play the role of a nano-enhancer and can significantly reduce the tendency of the membrane's mechanical properties to decrease due to the addition of the essential oil, thereby ensuring the membrane's mechanical stability.

[0017] When preparing Pickering emulsion, too high a homogenization speed, too high an ultrasonic emulsification power, or too long an ultrasonic time will cause the solution temperature to be too high, rendering the essential oil inactive. In addition, too high a rotation speed will cause the solution to splash. Too low a homogenization speed, too short an ultrasonic emulsification power, or too short an ultrasonic time will cause the essential oil to be unevenly dispersed and fail to achieve the purpose of emulsification.

[0018] In a preferred embodiment of the present invention, the solvent A is one or more of water, methanol, ethanol, acetone, isopropanol, chloroform, ethyl acetate, tetrahydrofuran and N,N-dimethylformamide; the mass concentration of the amphiphilic antibacterial chitosan derivative in the aqueous phase is 0.5%-3%; the essential oil is at least one of thyme essential oil, galangal essential oil, tea tree essential oil, lemon essential oil, citronella essential oil, oil peel essential oil, mustard essential oil, peppermint essential oil, cinnamon essential oil, clove essential oil, garlic essential oil, almond essential oil, eucalyptus essential oil, ylang-ylang essential oil and lavender essential oil; the volume concentration of the essential oil in the Pickering emulsion is 0.5%-10%.

[0019] In a preferred embodiment of the present invention, the film-forming material is at least one of chitosan, carboxymethyl chitosan, quaternary ammonium chitosan, quaternary phosphonium chitosan, soluble starch, cellulose, polyvinyl alcohol, zein, cyclodextrin, gelatin, konjac glucomannan and pullulan; the plasticizer is at least one of ethylene glycol, glycerol, sorbitol, polyethylene glycol with a molecular weight lower than 4000, ethylenediamine and triethanolamine; the mass concentration of the film-forming material in the film-forming base liquid is 0.5%-10%; the amount of the plasticizer added is 20%-50% of the mass of the film-forming material; and the dispersant is water or ethanol.

[0020] In a preferred embodiment of the present invention, the volume ratio of the Pickering emulsion to the film-forming base liquid and water is (1-9):(1-9):10.

[0021] In a preferred embodiment of the present invention, the nano-reinforced particles are at least one of nano-cellulose, TiO2, nano-SiO2, nano-CaCO3, nano-ZnO, nano-MgO, nano-Au, and nano-Ag; the binder is at least one of konjac gum, gum arabic, gellan gum, carrageenan, oxidized starch, cationic starch, etherified starch, esterified starch, wheat protein, corn protein, and gelatin; the nano-reinforced particles are 1%-10% of the mass of the film-forming material; and the added amount of the binder is 0.5%-5% of the mass of the film-forming material.

[0022] The natural antibacterial coating fresh-keeping material constructed by the present invention can improve the mechanical properties of the film layer by adding nano-reinforced particles in the film liquid, thereby ensuring that the coating material has good stability, so as to better ensure the durability of the antibacterial fresh-keeping effect of the coating; at the same time, the coating material forms a protective film after solidification on the surface of fruits and vegetables, which can reduce the respiration of fruits and vegetables and further extend the fresh-keeping time.

[0023] In a preferred embodiment of the present invention, the method for preparing the amphiphilic antibacterial chitosan derivative comprises the following steps:

[0024] The chitosan is dissolved in solvent B, and then lipase, carboxyl quaternary phosphonium salt, antibacterial organic acid and hydrophobic organic acid are added, mixed and reacted, and then rotary evaporation is performed, water is added, and the mixture is allowed to stand for stratification, and the upper layer is taken and centrifuged (1000-8000rpm), dialyzed (dialysis bag molecular weight cutoff is 3500-12000), and freeze-dried (for 24-72h) in sequence to obtain the amphiphilic antibacterial chitosan derivative;

[0025] The solvent B is one or more of water, isopropanol, chloroform, ethyl acetate, tetrahydrofuran, N,N-dimethylformamide, and dimethyl sulfoxide;

[0026] The lipase is at least one of immobilized Candida antarctica lipase, immobilized Rhizomucor miehei lipase, immobilized Thermomyces lipase, acrylic resin recombinant lipase from Aspergillus niger, Amano acyltransferase, acyltransferase I from Aspergillus meleus, APSAmano lipase lipase, Lipozyme CACB, TLZM, and Lipozyme 435; the concentration of the lipase in the solvent B is 5-100 mg / mL;

[0027] The carboxyl quaternary phosphonium salt is one or more of 5-carboxypentyl-triphenylphosphonium bromide, 4-carboxybutyl-tritylphosphonium bromide and 3-carboxypropyl-tritylphosphonium iodide;

[0028] The antibacterial organic acid is one or more of citric acid, malic acid, tartaric acid, ascorbic acid, sorbic acid, benzoic acid, phenyllactic acid, formic acid, and lactic acid;

[0029] The hydrophobic organic acid is one or more of cholic acid, deoxycholic acid, ricinoleic acid, eleostearic acid, linoleic acid, linoleic acid, linoleic acid or oleic acid.

[0030] In a preferred embodiment of the present invention, the mass ratio of the chitosan to the lipase, the carboxyl quaternary phosphonium salt, the antibacterial organic acid and the hydrophobic organic acid is 0.5:(0.5-10):(0.5-2.5):(0.5-2.5):(0.5-2.5); the viscosity average molecular weight of the chitosan is 1.2×10 3 -2.5×10 5 , the degree of deacetylation is ≥80%; the concentration of chitosan in the solvent B is 5-100 mg / mL; the temperature of the reaction (amidation reaction) is 25-80° C., and the time is 12-36 hours.

[0031] The invention grafts carboxyl quaternary phosphonium salt and antibacterial organic acid into chitosan to make it antibacterial. The higher the grafting rate of carboxyl quaternary phosphonium salt and antibacterial organic acid is, the better the antibacterial effect of the product is. In addition, hydrophobic organic acid is grafted to make chitosan amphiphilic. The invention controls the amount of reactants by comprehensively considering the influence of grafting of quaternary phosphonium salt and antibacterial organic acid on chitosan, so that the grafting rate of quaternary phosphonium salt is between 10% and 30%, the grafting rate of antibacterial organic acid is between 10% and 20%, and the grafting rate of hydrophobic organic acid is between 10% and 20%. The product in this grafting range has good water solubility and strong antibacterial performance.

[0032] The method of chitosan amidation reaction involved in the present invention is carried out by biological enzyme (lipase) catalysis. Compared with traditional chemical catalysis, it has mild reaction conditions, simple processing, and does not require harsh conditions such as high temperature and high pressure. At the same time, it avoids the degradation of the main functional groups of the grafted antibacterial active substances due to external environments such as high temperature, strong acid or strong alkali during the structural modification process, thereby reducing their activity.

[0033] The second technical solution of the present invention is a natural antibacterial coating fresh-keeping material prepared according to the preparation method.

[0034] The third technical solution of the present invention is the application of the natural antibacterial coating fresh-keeping material in the preservation of fruits and vegetables.

[0035] In a preferred embodiment of the present invention, the natural antibacterial coating preservative material is diluted 100-1000 times by volume to obtain a coating liquid; the coating liquid is applied to the surface of fruits and vegetables by spraying, smearing or dipping, and then washed and dried.

[0036] The fruits and vegetables are at least one of mango, pineapple, banana, pitaya, lychee, longan, eggplant, cucumber, green pepper, tomato, potato and the like.

[0037] The present invention discloses the following technical effects:

[0038] 1. The present invention constructs an amphiphilic antibacterial chitosan derivative, and the antioxidant activity and antibacterial performance of the covalent polymer are significantly improved compared with chitosan. In addition, after chitosan is covalently bonded with a hydrophobic organic acid, its surface hydrophobicity is improved, and its emulsification performance is enhanced. Therefore, the amphiphilic antibacterial chitosan derivative can be used as an effective antioxidant emulsifier and prevent the oxidation of the loaded active substance to a certain extent.

[0039] 2. The present invention constructs a plant essential oil Pickering emulsion using an amphiphilic antibacterial chitosan derivative as a stabilizer. The constructed stabilizer is amphiphilic and can improve the loading capacity and stabilizing ability of the essential oil. At the same time, the plant essential oil with antibacterial activity is compounded in the coating material in the form of an emulsion, which can slowly release the plant essential oil, thereby prolonging the preservation effect of the composite coating preservative material.

[0040] 3. The natural antibacterial coating fresh-keeping material prepared by the present invention can be applied to fruits and vegetables by convenient spraying, coating or dipping, is simple to operate and easy to use, can significantly improve the application efficiency, and reduce the damage to fruits and vegetables. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0042] Figure 1 The infrared spectra (FTIR) of chitosan and amphiphilic antibacterial chitosan derivatives in Example 1;

[0043] Figure 2 The X-ray diffraction patterns (XRD) of the chitosan and the amphiphilic antibacterial chitosan derivatives in Example 1;

[0044] Figure 3 The HNMR spectra of chitosan and the amphiphilic antibacterial chitosan derivatives in Example 1;

[0045] Figure 4 The microscopic morphology of the Pickering emulsion of cinnamon essential oil stabilized by the amphiphilic antibacterial chitosan derivative in Example 1;

[0046] Figure 5 This is a comparison chart of the antibacterial properties of the natural antibacterial coating fresh-keeping materials prepared in Example 1;

[0047] Figure 6 The preservation effect of the natural antibacterial coating preservation material prepared in Example 1 on mangoes. CK is a blank control group (CK), PVA is a pure polyvinyl alcohol coating treatment group, and PP is a natural antibacterial coating preservation material coating treatment group;

[0048] Figure 7 The preservation effect of the natural antibacterial coating preservation material on litchi prepared in Example 2 is shown in FIG. CK is a blank control group (CK), CS is a pure chitosan coating treatment group, and CP is a natural antibacterial coating preservation material coating treatment group.

[0049] Figure 8 This is the preservation effect of the natural antibacterial coating preservation material prepared in Comparative Example 1 on litchi. DETAILED DESCRIPTION

[0050] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0051] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0052] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0053] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0054] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0055] The technical solutions described in the present invention, unless otherwise specified, are all conventional solutions in the art, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0056] The immobilized Candida antarctica lipase used in the examples of the present invention was purchased from Shanghai Yuanye Biotechnology Co., Ltd., with an enzyme activity of 10,000 PLU / g.

[0057] The acyltransferase used in the examples of the present invention is specifically Amano acyltransferase, purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd., with an enzyme activity of ≥30,000 U / g.

[0058] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0059] Example 1

[0060] (1) Preparation of amphiphilic antibacterial chitosan derivatives

[0061] ① Weigh 0.5g chitosan (viscosity average molecular weight is 1.2×10 5 , deacetylation degree ≥90%) was dissolved in 100 mL of water and tetrahydrofuran (volume ratio 1:1) mixed solution, followed by adding 0.5 g of immobilized Antarctic Candida lipase (5 mg / mL), and then adding 0.5 g of carboxyl quaternary phosphonium salt (5-carboxypentyl-triphenylphosphonium bromide, CTPB), 0.5 g of antibacterial organic acid (sorbic acid, SA), and 0.5 g of hydrophobic organic acid (cholic acid, CA), respectively, and stirring and mixing at 500 r / min magnetic stirring. The reaction was carried out at 25 ° C for 36 hours.

[0062] ② The organic solvent was removed from the solution after the reaction by rotary evaporation, and then an appropriate amount of deionized water was added to make the volume 100 mL, and the solution was allowed to stand for stratification, and the upper layer liquid was centrifuged (at a rate of 1000 rpm) to remove the lipase in the lower layer, and then dialyzed (dialysis bag molecular weight cutoff of 3500) to remove the unreacted antibacterial organic acid and hydrophobic organic acid, and then freeze-dried (24 hours) to obtain the amphiphilic antibacterial chitosan derivative. Among them, the grafting rate of quaternary phosphonium salt in the amphiphilic antibacterial chitosan derivative is 10.5%, the grafting rate of antibacterial organic acid is 18.9%, and the grafting rate of hydrophobic organic acid is 11.2%.

[0063] (2) Preparation of Pickering emulsions stabilized with cinnamon essential oil by amphiphilic antibacterial chitosan derivatives

[0064] A certain amount of amphiphilic antibacterial chitosan derivative was weighed and dispersed in distilled water to prepare a dispersion with a concentration (g / mL) of 1.5% (w / v) as the aqueous phase, and then cinnamon essential oil (oil phase) was slowly dripped into the aqueous phase and homogenized for 3 minutes using a high-speed shearing machine at a speed of 12000r / min, and then treated by a concentrated ultrasonic emulsification disperser, wherein the output power of the ultrasonic treatment was 250W, the ultrasonic time was 5min, the pulse width was 2.0s, and the interval time was 2.0s, to form a Pickering emulsion (abbreviated as: Pickering emulsion) of amphiphilic antibacterial chitosan derivative stabilizing cinnamon essential oil. The final concentration of cinnamon essential oil in the Pickering emulsion was 0.5% (v / v).

[0065] (3) Preparation of natural antibacterial coating preservation materials

[0066] Weigh a certain amount of polyvinyl alcohol (PVA) and dissolve it in deionized water, add 20% (based on the dry weight of PVA) of glycerol (plasticizer), stir evenly to prepare a PVA film-forming base liquid with a PVA concentration of 10% (w / v) (g / mL). Take 5.0mL of Pickering emulsion of amphiphilic antibacterial chitosan derivative stabilized cinnamon essential oil, 45mL of deionized water and 50mL of PVA film-forming base liquid (emulsion volume: water volume: film-forming liquid volume = 1:9:10), add 1% of nano-TiO2 (nano-enhanced particles) based on the dry weight of the film-forming material, namely PVA, and 0.5% of carrageenan (binder). Then use a high-speed shearing machine to homogenize at a speed of 10000r / min for 3min, and then degas in a vacuum environment for 30min to form an emulsion active film film-forming solution, and the total volume of the film-forming solution is 100mL. That is, a natural antibacterial coating preservation material is obtained.

[0067] (4) Effect of natural antibacterial coating materials on postharvest preservation of mangoes

[0068] Mangoes with basically uniform size, color and maturity and free from pests, diseases and mechanical damage were selected, and they were soaked and disinfected in 0.05% (v / v) sodium hypochlorite aqueous solution for 5 min (2 to 10 min is acceptable), then washed with distilled water, and after naturally drying, the mangoes were divided into three groups.

[0069] Control group (CK): no treatment. PVA coating group (PVA): mangoes were immersed in the PVA film-forming matrix solution for 5 min (5 to 10 min), and then taken out and dried naturally. Natural antibacterial coating preservative material coating group (PP): the natural antibacterial coating preservative material in step (3) was diluted 100 times to obtain a coating solution, and then mangoes were immersed in the coating solution for 5 min (5 to 10 min), and then taken out and dried naturally.

[0070] The mangoes after the above three treatments were stored in a constant temperature and humidity chamber at 25°C and a relative humidity of 50%.

[0071] Example 2

[0072] (1) Preparation of amphiphilic antibacterial chitosan derivatives

[0073] ① Weigh 0.5g chitosan (viscosity average molecular weight is 1.2×10 3, deacetylation degree ≥ 80%) was dissolved in 100 mL of water and dimethyl sulfoxide (volume ratio 1:1) mixed solution, followed by adding 10.0 g of Amano acyltransferase (100 mg / mL), and then adding 2.5 g of carboxyl quaternary phosphonium salt (4-carboxybutyl-trityl phosphonium bromide), 2.5 g of antibacterial organic acid (benzoic acid), and 2.5 g of hydrophobic organic acid (ricinoleic acid), respectively, and stirred and mixed evenly under 1000 r / min magnetic stirring. The reaction was carried out at 80°C for 12 hours.

[0074] ② The organic solvent was removed from the solution after the reaction by rotary evaporation, and then an appropriate amount of deionized water was added to make the volume 100 mL, and the solution was allowed to stand for stratification, and the upper layer liquid was centrifuged (at a rate of 8000 rpm) to remove the lipase in the lower layer, and then dialyzed (dialysis bag molecular weight cutoff of 12000) to remove the unreacted antibacterial organic acid and hydrophobic organic acid, and then freeze-dried (72 hours) to obtain the amphiphilic antibacterial chitosan derivative. Among them, the grafting rate of quaternary phosphonium salt in the amphiphilic antibacterial chitosan derivative is 28.5%, the grafting rate of antibacterial organic acid is 10.9%, and the grafting rate of hydrophobic organic acid is 12.3%.

[0075] (2) Preparation of Pickering emulsions stabilized with cinnamon essential oil by amphiphilic antibacterial chitosan derivatives

[0076] A certain amount of amphiphilic antibacterial chitosan derivative was weighed and dispersed in distilled water to prepare a dispersion with a concentration (g / mL) of 3.0% (w / v) as the aqueous phase, and then cinnamon essential oil (oil phase) was slowly dripped into the aqueous phase and homogenized for 30 minutes using a high-speed shearing machine at a speed of 10000r / min, and then treated by a concentrated ultrasonic emulsification disperser, wherein the output power of the ultrasonic treatment was 100W, the ultrasonic time was 10min, the pulse width was 3.0s, and the interval time was 5.0s, to form a Pickering emulsion of cinnamon essential oil stabilized by amphiphilic antibacterial chitosan derivative. The volume concentration of cinnamon essential oil in the final Pickering emulsion was 10.0% (v / v).

[0077] (3) Preparation of natural antibacterial coating preservation materials

[0078] A certain amount of chitosan (CS) was weighed and dissolved in an acetic acid aqueous solution with a volume concentration of 1.0% (the volume concentration of the acetic acid aqueous solution can be 0.5-1.0%), and 50% (based on the dry weight of CS) of glycerol (plasticizer) was added, and after stirring evenly, a CS film-forming base liquid with a CS concentration of 0.5% (w / v) (g / mL) was prepared. 45.0mL of Pickering emulsion of amphiphilic antibacterial chitosan derivative stabilized cinnamon essential oil, 5mL of deionized water and 50mL of CS film-forming base liquid were mixed (emulsion volume: water volume: film-forming liquid volume = 9:1:10), and 1% of nano-SiO2 (nano-enhanced particles) based on the film-forming material, i.e., the dry weight of CS, and 5% of cationic starch (binder) were added. Then, a high-speed shearing machine was used to homogenize at a speed of 12000r / min for 8min, and then degassed in a vacuum environment for 15min to form an emulsion active film film-forming solution, and the total volume of the film-forming solution was 100mL. That is, a natural antibacterial coating fresh-keeping material is obtained.

[0079] (4) Effect of natural antibacterial coating materials on postharvest preservation of litchi

[0080] Select lychees that are basically the same in size, color, and maturity and free of pests and diseases and mechanical damage, soak them in 0.05% (v / v) sodium hypochlorite aqueous solution for disinfection for 5 minutes (2 to 10 minutes is acceptable), then wash them with distilled water, and after drying naturally, divide the lychees into three groups.

[0081] Control group (CK): No treatment was performed. Chitosan coating group (CS): Mango was immersed in CS film-forming matrix solution for 5 min (5 to 10 min), and then taken out and dried naturally. Natural antibacterial coating preservative material coating group (CP): The natural antibacterial coating preservative material in step (3) was diluted 1000 times to obtain a coating solution, and then litchi was immersed in the coating solution for 5 min (5 to 10 min), and then taken out and dried naturally.

[0082] The three groups of treated litchi were stored in a constant temperature and humidity chamber at 25°C and a relative humidity of 75%.

[0083] The test results of Example 1-2 are as follows ( Figure 1-3 The amphiphilic antibacterial chitosans in the above all refer to amphiphilic antibacterial chitosan derivatives):

[0084] 1. The structural functional groups of the chitosan and the amphiphilic antibacterial chitosan derivatives of Example 1 were tested by infrared spectroscopy using a German Tensor 27 infrared spectrometer (FT-IR).

[0085] The specific steps are as follows: Use Fourier transform infrared spectrometer to test the infrared spectrum of the sample, with a spectral resolution of 4cm -1 , scanning range 4000cm -1 Up to 650cm-1 , 16 times. Infrared spectroscopy was performed on chitosan and amphiphilic antibacterial chitosan derivatives to analyze the changes in functional groups.

[0086] FTIR spectrum can reflect the information of characteristic groups in the complex, and in the infrared spectrum data, the amide I band (1600cm -1 -1700cm -1 ) and amide II bands (1500cm -1 -1560cm -1 ), which is often used to analyze the changes in acylation groups. Therefore, FTIR can be used to reveal the interaction between chitosan and carboxyl quaternary phosphonium salts, antibacterial organic acids and hydrophobic organic acid molecules, and to understand the influence of chitosan covalent structure. Figure 1 The infrared spectra of chitosan and the amphiphilic antibacterial chitosan derivatives of Example 1 are shown. Chitosan has the following infrared spectra at 3415, 2953, and 2873 cm -1 The characteristic peaks of OH, NH, -CH2- stretching vibration absorption are at 1650 and 1570 cm -1 The characteristic peak of -C=O stretching vibration is 1074cm -1 The peak is the characteristic peak of COC.

[0087] The amphiphilic antibacterial chitosan derivatives produced by the reaction of chitosan with carboxyl quaternary phosphonium salt (5-carboxypentyl-triphenylphosphonium bromide, CTPB), antibacterial organic acid (sorbic acid, SA) and hydrophobic organic acid (cholic acid, CA) were detected at 3318, 2960 and 2873 cm -1 The characteristic peaks of OH, NH, -CH2- stretching vibration absorption are at 1644, 1570cm -1 The characteristic peak of the stretching vibration of the acyl-C=O at 3029cm -1 New characteristic peaks appeared, which were -CH=CH- stretching vibration, indicating that the antibacterial organic acid (sorbic acid, SA) was successfully grafted; at 2960 and 2873 cm -1 The characteristic absorption peaks of -CH2- stretching vibration at 1473, 1417, and 1361 cm -1 A new absorption peak appeared, which was a characteristic peak of benzene ring, indicating that the carboxyl quaternary phosphonium salt (5-carboxypentyl-triphenylphosphonium bromide, CTPB) was successfully grafted. The above analysis results proved that the amphiphilic antibacterial chitosan was successfully prepared.

[0088] 2. X-ray diffraction analysis is a structural analysis method that uses X-ray diffraction formed by crystals to analyze the spatial distribution of atoms inside a substance. The crystal structure analysis of the structures of different substances in the examples was performed using a Japanese Rigaku Smartlab 9KW. Figure 2 The XRD spectra of the chitosan and the amphiphilic antibacterial chitosan derivatives of Example 1 are shown.

[0089] The specific steps are as follows: grind the sample into powder in an agate mortar, then take an appropriate amount of powder and put it into the sample slot, gently flatten the surface with a glass slide, and then put it into the X-ray diffractometer for testing. The parameters are set as follows: the scanning angle is 5°-80°, and the scanning rate is set to 4° / min.

[0090] X-ray diffractometers can be used to analyze material crystal types and related diffraction information, and also help reveal the compatibility between composite materials. Figure 2 As shown in the figure, the XRD spectrum of chitosan shows that it has multiple sharp diffraction peaks between 10°-30°, among which the maximum diffraction peak has a wider characteristic diffraction peak at 2θ=20.05°, and a flat shoulder-shaped diffraction peak appears at 2θ=10.7°. This is because the chitosan macromolecule has good regularity and is easier to form a crystalline structure, and its crystallinity increases with the increase of deacetylation degree; however, the XRD curve of amphiphilic antibacterial chitosan is generally different from that of chitosan. The XRD curves of sugars are similar, with a broad characteristic diffraction peak, but the peak position shifts to the right to 22.08°. In addition, the diffraction peak of the amphiphilic antibacterial chitosan at 2θ of 10.7° basically disappears, indicating that when chitosan is grafted with carboxyl quaternary phosphonium salt (5-carboxypentyl-triphenylphosphonium bromide, CTPB), antibacterial organic acid (sorbic acid, SA) and hydrophobic organic acid (cholic acid, CA), the lattice structure parameters of the macromolecule change, indicating that chitosan has undergone grafting modification.

[0091] 3. Pass 1 The chemical structure of the amphiphilic antibacterial chitosan derivatives was further analyzed by H-NMR spectroscopy. The chitosan of Example 1 and the amphiphilic antibacterial chitosan were analyzed by using the Avance 600 NMR spectrometer of Bruker, Germany. 1 H-NMR spectrum analysis.

[0092] The specific steps are as follows: take a certain amount of chitosan and amphiphilic antibacterial chitosan derivatives, dissolve them with an appropriate amount of D2O mixed solution, and perform nuclear magnetic resonance hydrogen spectrum measurement after the samples are completely dissolved.

[0093] Figure 3 The chitosan and the amphiphilic antibacterial chitosan derivative of Example 1 1H-NMR spectrum. For chitosan, the obvious peak at δ = 1.87 ppm is attributed to the methyl (CH3) group (H-7) of N-acetylglucosamine, and the chemical shift value at δ = 3.0-4.0 ppm is attributed to the ring protons of chitosan. 1 In the H-NMR spectrum, the new peak at δ=7.0~8.0ppm (Hf) was attributed to the benzene ring, -CH=CH- proton. Also, the new peaks at δ=3.41, 2.39 and 1.25~1.72ppm were attributed to the methylene group, confirming that the carboxyl quaternary phosphonium salt (5-carboxypentyl-triphenylphosphonium bromide-CTPB) and the antibacterial organic acid (sorbic acid-SA) were grafted onto the chain of chitosan. In addition, the new peaks at δ=0.87, 0.76 and 0.54ppm, which were attributed to the proton signals of the methyl (CH3) groups (H-c1, H-b1 and H-a1) of the hydrophobic organic acid (cholic acid-CA), respectively appeared in the amphiphilic antibacterial chitosan. 1 In the H-NMR spectrum, this shows that the hydrophobic organic acid (cholic acid, CA) is grafted onto the chain of chitosan. The above analysis results prove the successful preparation of amphiphilic antibacterial chitosan derivatives.

[0094] 4. The microstructure of the Pickering emulsion of cinnamon essential oil stabilized by the amphiphilic antibacterial chitosan derivative of Example 1 was observed using an EVOS XL Core inverted optical microscope produced by Thermo Fisher Scientific, USA.

[0095] Figure 4 The microscopic morphology and particle size distribution of the Pickering emulsion of Example 1. It can be seen from the figure that the particle size distribution of the Pickering emulsion is relatively uniform and presents a normal distribution, and the average particle size is 6.32 μm.

[0096] 5. Prepare bacterial suspension by plate colony counting method. Activate and culture the lyophilized powder of Escherichia coli and Staphylococcus aureus twice. Use the activated bacteria on the culture medium, take 1 bacterial loop and inoculate it into 100mL nutrient broth liquid culture medium, shake and culture at 37℃ and 200 times / min for 24 hours, and then dilute it. Use an adjustable micropipette to draw up the bacterial suspension, dilute it 10 times with sterile saline, count the plates, observe under a microscope, and prepare it to a concentration of 10 6 CFU / mL suspension of Escherichia coli and Staphylococcus aureus is reserved. The determination is carried out by sterile filter paper method. In advance, a round sterilized filter paper with a diameter of 8mm is immersed in the composite coating liquid. Take 15mL of sterilized culture medium and inject it into a sterilized culture dish, cool and solidify for use. Use a sterile pipette to take 50μL of 10 6CFU / mL suspensions of Escherichia coli and Staphylococcus aureus were evenly spread on PDA culture medium. Sterile filter paper sheets soaked in coating solution were placed in the center of the culture medium coated with different bacterial suspensions. In addition, filter paper sheets soaked in sterile water were used as blank control groups. All were placed in a 37℃ constant temperature incubator for 48 days. Finally, the size of the inhibition zone was measured with a vernier caliper. Figure 5 This is a comparison chart of the antibacterial performance of the natural antibacterial coating fresh-keeping material of Example 1 and the blank control group. It can be seen from the figure that the natural antibacterial coating fresh-keeping material has good antibacterial performance against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus).

[0097] 6. Figure 6 The preservation effect of the natural antibacterial coating preservation material prepared in Example 1 on mangoes is shown in Figure 1. CK is the blank control group (CK), PVA is the pure polyvinyl alcohol coating treatment group, and PP is the natural antibacterial coating preservation material coating treatment group. The appearance images of mangoes in different coating treatment groups stored at 25°C and 50% relative humidity for 15 days are shown in Figure 1. Figure 5 As shown. At the beginning of storage, the skin color of all mangoes was yellow-green, with no obvious machine damage and pests. On the 3rd day, due to the high respiration intensity of the CK group fruit, the skin color began to turn yellow. On the 6th day, the CK group was basically half mature, and the skin turned yellow over a large area. At this time, the PVA group and the PP group showed only slight yellowing due to the good barrier properties of the coating. On the 9th day of storage, obvious black spots appeared on the skin of the CK group mangoes, accompanied by slight shrinkage and water loss. By the 12th day, black spots appeared on the surface of the CK group mangoes, indicating that they had been infected by microorganisms, and the fruit skin showed obvious shrinkage. By the 12th day, a large number of black spots appeared on the surface of the CK group mangoes, and they had lost their edible value. Comparing the two groups of coating preservation, a small amount of brown spots appeared on the surface of the PVA group fruit on the 12th day, and the brown spots expanded and turned black on the 15th day, indicating that the PVA group fruit was infected by microorganisms at this time and the quality began to decline. The fruit samples in the PP group had no water loss during the entire storage period, except that the skin color turned slightly yellow, with only a few black spots, and still had the edible value of the commodity. This shows that the active emulsion coating material formed by the compounding of the amphiphilic antibacterial chitosan stabilized cinnamon essential oil Pickering emulsion and the PVA matrix can effectively delay the ripening of mango fruits and prevent them from losing water and rotting during post-harvest storage.

[0098] 7. Figure 7The preservation effect of the natural antibacterial coating preservation material prepared in Example 1 on litchi. CK is a blank control group (CK), CS is a pure chitosan coating treatment group, and CP is a natural antibacterial coating preservation material coating treatment group. The treated litchi was stored in a constant temperature and humidity chamber at 25°C and a relative humidity of 75%. In the early stage of storage, the skin color of all litchis was red, and there was no obvious machine damage and pests and diseases. On the second day, due to the high respiration intensity of the fruit in the CK group, the color of the litchi skin began to turn brown. On the fourth day, the skin of litchis in the CK group and the CS coating group turned brown. At this time, the CP group had better antibacterial properties because the coating contained an amphiphilic antibacterial chitosan stabilized cinnamon essential oil Pickering emulsion, and the litchi skin did not turn brown. On the sixth day of storage, a large amount of browning appeared on the skin of litchis in the CK group and the CS coating group, and even mildew spots appeared in the CK group. The CP group had bright colors and the fruit was in good condition. On the 8th day, a large number of mold spots appeared on the surface of litchi in the CK and CS coating groups, indicating that they had been infected by microorganisms. At the same time, the fruit skin showed obvious shrinkage, and the litchi fruit had lost its edible value. The CP group was still bright in color, with only a small number of brown spots, and still had fruit edible value, while the surface of litchi in the CK group had black spots in patches. The above results show that the natural antibacterial coating preservation material formed by the compounding of the Pickering emulsion of cinnamon essential oil stabilized by amphiphilic antibacterial chitosan derivatives and the CS film-forming base liquid can effectively inhibit the ability of litchi skin browning and mold growth, while maintaining the quality of litchi fruit, and has the effect of extending the shelf life of litchi.

[0099] Comparative Example 1

[0100] The only difference from Example 2 is that the preparation of the amphiphilic antibacterial chitosan derivative in step (1) is omitted, and the amphiphilic antibacterial chitosan derivative in step (2) is replaced by an equal mass of chitosan mixture, wherein the chitosan mixture is chitosan (viscosity average molecular weight is 1.2×10 3 , deacetylation degree ≥80%): a mixture of 4-carboxybutyl-trityl phosphonium bromide: benzoic acid: ricinoleic acid in a mass ratio of 0.5:2.5:2.5:2.5; the remaining steps and parameters are the same as those in Example 2.

[0101] The natural antibacterial coating fresh-keeping material prepared in Comparative Example 1 was subjected to the same effect verification as in Example 2. The results are as follows: Figure 8 As shown; Figure 8 The figure is a diagram showing the preservation effect of the coating preservation material prepared in comparative example 1 on litchi. The results show that on the 8th day, a large amount of browning appeared on the surface of the litchi, and the preservation effect was poorer than that of Example 2. This shows that compared with simple physical mixing, the natural antibacterial coating preservation material prepared by grafting modified chitosan has a better preservation effect on litchi.

[0102] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a natural antibacterial coating fresh-keeping material, characterized in that: The following steps are involved: dispersing the amphiphilic antibacterial chitosan derivative in solvent A to obtain an aqueous phase; Adding essential oil to the aqueous phase for homogenization and ultrasonic emulsification to obtain a Pickering emulsion; Dissolving the film-forming material in a dispersant and adding a plasticizer to obtain a film-forming base liquid; The Pickering emulsion, the film-forming base liquid and water are mixed, and nano-enhanced particles and a binder are added, homogenized, and degassed to obtain the natural antibacterial coating fresh-keeping material; The structural formula of the amphiphilic antibacterial chitosan derivative is shown in Formula I: In formula I, m, n, s, and t are independently natural numbers ranging from 1 to 1000; X is one of F, Cl, Br, I, HSO3, HCO3, H2PO4, NO3, CH3CH2COO, CH3COO, and HCOO; R1 and R2 are independently aromatic hydrocarbon groups or derivative groups thereof; R3 is one or more of citric acid, malic acid, tartaric acid, ascorbic acid, sorbic acid, benzoic acid, phenyllactic acid, formic acid, and lactic acid; R4 is one or more of cholic acid, deoxycholic acid, ricinoleic acid, eleostearic acid, linoleic acid, linoleic acid, linoleic acid, or oleic acid.

2. The method for preparing the natural antibacterial coating fresh-keeping material according to claim 1, characterized in that: The solvent A is one or more of water, methanol, ethanol, acetone, isopropanol, chloroform, ethyl acetate, tetrahydrofuran and N,N-dimethylformamide; the mass concentration of the amphiphilic antibacterial chitosan derivative in the water phase is 0.5%-3%; the essential oil is at least one of thyme essential oil, galangal essential oil, tea tree essential oil, lemon essential oil, citronella essential oil, oil peel essential oil, mustard essential oil, peppermint essential oil, cinnamon essential oil, clove essential oil, garlic essential oil, almond essential oil, eucalyptus essential oil, ylang-ylang essential oil and lavender essential oil; the volume concentration of the essential oil in the Pickering emulsion is 0.5%-10%.

3. The method for preparing the natural antibacterial coating fresh-keeping material according to claim 1, characterized in that: The film-forming material is at least one of chitosan, carboxymethyl chitosan, quaternary ammonium salt chitosan, quaternary phosphonium salt chitosan, soluble starch, cellulose, polyvinyl alcohol, zein, cyclodextrin, gelatin, konjac glucomannan and pullulan; the plasticizer is at least one of ethylene glycol, glycerol, sorbitol, polyethylene glycol with a molecular weight lower than 4000, ethylenediamine and triethanolamine; the mass concentration of the film-forming material in the film-forming base liquid is 0.5%-10%; the added amount of the plasticizer is 20%-50% of the mass of the film-forming material; and the dispersant is water or ethanol.

4. The method for preparing the natural antibacterial coating fresh-keeping material according to claim 1, characterized in that: The volume ratio of the Pickering emulsion to the film-forming base liquid and water is (1-9):(1-9):

10.

5. The method for preparing the natural antibacterial coating fresh-keeping material according to claim 1, characterized in that: The nano-reinforced particles are at least one of nano-cellulose, TiO2, nano-SiO2, nano-CaCO3, nano-ZnO, nano-MgO, nano-Au, and nano-Ag; the binder is at least one of konjac gum, gum arabic, gellan gum, carrageenan, oxidized starch, cationic starch, etherified starch, esterified starch, wheat protein, corn protein, and gelatin; the nano-reinforced particles account for 1%-10% of the mass of the film-forming material; and the added amount of the binder is 0.5%-5% of the mass of the film-forming material.

6. The method for preparing the natural antibacterial coating fresh-keeping material according to claim 1, characterized in that: The preparation method of the amphiphilic antibacterial chitosan derivative comprises the following steps: Dissolving chitosan in solvent B, then adding lipase, carboxyl quaternary phosphonium salt, antibacterial organic acid and hydrophobic organic acid, mixing and reacting, then rotary evaporation, adding water and standing for stratification, taking the upper layer liquid and sequentially centrifuging, dialysis and freeze drying to obtain the amphiphilic antibacterial chitosan derivative; The solvent B is one or more of water, isopropanol, chloroform, ethyl acetate, tetrahydrofuran, N,N-dimethylformamide, and dimethyl sulfoxide; The lipase is at least one of immobilized Candida antarctica lipase, immobilized Rhizomucor miehei lipase, immobilized Thermomyces lipase, acrylic resin recombinant lipase from Aspergillus niger, Amano acyltransferase, acyltransferase I from Aspergillus meleus, APSAmano lipase lipase, Lipozyme CACB, TLZM, and Lipozyme 435; the concentration of the lipase in the solvent B is 5-100 mg / mL; The carboxyl quaternary phosphonium salt is one or more of 5-carboxypentyl-triphenylphosphonium bromide, 4-carboxybutyl-tritylphosphonium bromide and 3-carboxypropyl-tritylphosphonium iodide; The antibacterial organic acid is one or more of citric acid, malic acid, tartaric acid, ascorbic acid, sorbic acid, benzoic acid, phenyllactic acid, formic acid, and lactic acid; The hydrophobic organic acid is one or more of cholic acid, deoxycholic acid, ricinoleic acid, eleostearic acid, linoleic acid, linoleic acid, linoleic acid or oleic acid.

7. The method for preparing the natural antibacterial coating fresh-keeping material according to claim 6, characterized in that: The mass ratio of the chitosan to the lipase, carboxyl quaternary phosphonium salt, antibacterial organic acid and hydrophobic organic acid is 0.5:(0.5-10):(0.5-2.5):(0.5-2.5):(0.5-2.5); the viscosity average molecular weight of the chitosan is 1.2×10 3 -2.5×10 5 , the deacetylation degree is ≥80%; the concentration of chitosan in the solvent B is 5-100 mg / mL; the reaction temperature is 25-80° C., and the reaction time is 12-36 hours.

8. The natural antibacterial coating fresh-keeping material prepared according to the preparation method according to any one of claims 1 to 7.

9. Use of the natural antibacterial coating fresh-keeping material as claimed in claim 8 in the preservation of fruits and vegetables.

10. The use according to claim 9, characterized in that: The natural antibacterial coating preservation material is diluted 100-1000 times by volume to obtain a coating liquid; the coating liquid is applied to the surface of fruits and vegetables by spraying, smearing or dipping, and then washed and dried.

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