Nanofiber preservative film as well as preparation method and application thereof

Abstract

The invention provides a nanofiber preservative film and a preparation method of the nanofiber preservative film. The nanofiber preservative film is prepared from the following raw materials: pullulan, polyvinyl alcohol, thymol and titanium dioxide nanoparticles. And the dispersibility of titanium dioxide nanoparticles in the nanofiber preservative film is remarkably improved by adopting an electrostatic spinning technology.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of food active packaging materials, and particularly relates to a preparation method of a nanofiber preservative film with high ethylene degradation and antibacterial properties, a nanofiber preservative film obtained by the preparation method, and application of the nanofiber preservative film. BACKGROUND

[0002] The postharvest shelf life of respiration climacteric fruits and vegetables is short, and the main reasons include fruit softening and aging induced by ethylene and spoilage caused by microbial infection. Therefore, in order to effectively prolong the shelf life of fruits and vegetables and significantly reduce postharvest losses, it is necessary to improve the ethylene elimination rate and the antibacterial rate at the same time when developing active packaging for fruits and vegetables.

[0003] In the reported ethylene removal studies, activated carbon, clay and nanotubes are used as ethylene adsorbents, or potassium permanganate is used to oxidize ethylene. However, the adsorption efficiency of physical adsorbents is limited, and there is also a problem of moisture absorption failure. Chemical oxidants are prone to chemical residue problems. Photocatalysts can oxidize and decompose ethylene in the fruit and vegetable storage environment by using an external light source, which can be recycled and has mild reaction conditions. Titanium dioxide is a typical photocatalyst. However, titanium dioxide is prone to agglomeration in practical application, which reduces its specific surface area and seriously affects the photocatalytic efficiency.

[0004] Natural biological antibacterial agents play an important role in the postharvest preservation of fruits and vegetables due to their safety and environmental friendliness. These natural biological antibacterial agents mainly include animal-derived lysozyme, chitosan and its derivatives, plant-derived extracts and essential oils, etc. Thymol is a phenolic compound extracted from thyme, which has broad-spectrum antibacterial properties and inhibits most gram-positive bacteria and has antifungal effects. It can destroy the normal structure of the cell membrane or cell wall of microorganisms, affect the normal metabolism of microorganisms, and thus inhibit the growth and reproduction of microorganisms. However, thymol is prone to volatilization and oxidation when exposed to air, is sensitive to heat, and has a pungent odor, which limits its application in food preservation.

[0005] There is still a need for improved fruit and vegetable preservation packaging and methods for preparing the same. SUMMARY

[0006] To solve the above problems, the present application provides an improved nanofiber preservative film, a preparation method thereof, and the application of the nanofiber preservative film in fruit and vegetable antibacterial and ethylene degradation.

[0007] Specifically, the present application adopts the following technical solutions:

[0008] 1. A nanofiber preservative film, which is obtained by a preparation method using the following raw materials:

[0009] pullulan,

[0010] polyvinyl alcohol,

[0011] thymol, wherein the mass fraction of thymol is 0.2-5% relative to the total mass of the pullulan and polyvinyl alcohol; and

[0012] titanium dioxide nanoparticles, wherein the mass fraction of the titanium dioxide nanoparticles is 20-80% relative to the total mass of the pullulan and polyvinyl alcohol.

[0013] 2. A method for preparing the nanofiber preservative film of claim 1, comprising the following steps:

[0014] S1-preparing a matrix solution, which is an aqueous solution of pullulan and polyvinyl alcohol;

[0015] S2-adding thymol to the matrix solution to obtain a mixed solution of thymol and matrix, wherein the added mass fraction of thymol is 0.2-5% relative to the total mass of the pullulan and polyvinyl alcohol;

[0016] S3-adding titanium dioxide nanoparticles to the mixed solution of thymol and matrix to obtain a spinning precursor solution, wherein the added mass fraction of the titanium dioxide nanoparticles is 20-80% relative to the total mass of the pullulan and polyvinyl alcohol dry matter; and

[0017] S4-electrospinning the spinning precursor solution to obtain the nanofiber preservative film.

[0018] Further, step S1 comprises:

[0019] S11-adding pullulan to distilled water and stirring to obtain an aqueous solution of pullulan with a mass fraction of 8-12%;

[0020] S12-adding polyvinyl alcohol to distilled water and stirring to obtain an aqueous solution of polyvinyl alcohol with a mass fraction of 8-12%;

[0021] S13-mixing the aqueous solution of pullulan obtained in step S11 and the aqueous solution of polyvinyl alcohol obtained in step S12 uniformly at a volume ratio of (1-5):(5-1) to obtain a matrix solution of pullulan and polyvinyl alcohol.

[0022] Further, step S2 comprises:

[0023] S21-preparing a thymol ethanol solution, wherein the volume fraction of thymol relative to the total volume of the thymol ethanol solution is 50-90%;

[0024] S22-adding thymol ethanol solution into the matrix solution and stirring uniformly to obtain a thymol / pullulan / polyvinyl alcohol solution, wherein the added mass fraction of the thymol is 0.5-1% relative to the total mass of the pullulan and polyvinyl alcohol.

[0025] Further, the volume fraction of thymol in the thymol ethanol solution relative to the total volume of the thymol ethanol solution is 70-80% by volume.

[0026] Further, step S3 comprises:

[0027] adding titanium dioxide nanoparticles with a mass fraction of 20-80% relative to the total mass of the dry substance of the pullulan and polyvinyl alcohol, ultrasonic treatment for 0.5-2h, stirring for 12-24h to obtain the spinning precursor solution.

[0028] Further, the average particle size of the titanium dioxide nanoparticles is 5-10nm.

[0029] Further, step S4 comprises drawing the spinning precursor solution into a syringe with a 20-22G needle, adjusting the distance from the needle to the syringe to 15-20cm, and then stretching the spinning precursor solution into nanofibers by the action of an external electrostatic field and stacking the nanofibers layer by layer on a receiver to form a nanofiber preservative film.

[0030] Further, the setting parameters of electrospinning are as follows: the pushing speed of the syringe is 0.5-1mL / h, the spinning time is 5-15h, the spinning voltage is 15-25kV, the ambient temperature is 20-30℃, and the relative humidity is 45-55%.

[0031] 3. Application of the above nanofiber preservative film in fruit and vegetable antibacterial and ethylene degradation.

[0032] The present application also achieves the following advantages:

[0033] (1) The nanofiber preservative film prepared by the present application uses ultrasonic treatment combined with electrospinning technology to significantly improve the dispersibility of titanium dioxide nanoparticles, so that when the addition amount of titanium dioxide nanoparticles is 40% or more, uniform diameter nanofibers can still be obtained. Further, the loading rate of the nanofiber film to titanium dioxide nanoparticles is more than 40%.

[0034] (2) The nanofiber film prepared by the present application can obtain titanium dioxide / thymol / pullulan / polyvinyl alcohol nanofibers with uniform fiber thickness and smoothness without beading, significantly improving the photocatalytic activity specific surface area of titanium dioxide nanoparticles, and better achieving the effects of degrading ethylene produced during fruit and vegetable storage and inhibiting microbial growth.

[0035] (3) The nanofiber preservative film prepared by the application has significant advantages compared to the cast film. The unique pore structure of the film material gives the film material more excellent air permeability, allowing ethylene gas molecules to diffuse freely in the fiber gap, increasing the contact between ethylene molecules and titanium dioxide nanoparticles, thereby improving the efficiency of titanium dioxide photocatalytic degradation of ethylene.

[0036] (4) The electrospinning technology used in the application enables the preparation of a preservative film at room temperature, maintaining the chemical stability and biological activity of the active ingredient thymol.

[0037] (5) The nanofiber film loaded with thymol and titanium dioxide nanoparticles prepared by the application has the dual functions of long-acting antibacterial and ethylene degradation, and can be effectively applied to the long-term storage and preservation of fruits and vegetables. Under the condition of external light source irradiation, titanium dioxide nanoparticles can continuously generate hydroxyl radicals and superoxide anion radicals, fully exerting their photocatalytic activity, thereby achieving sustained antibacterial effect and ethylene degradation. At the same time, thymol in the nanofiber film will be slowly released into the fruit and vegetable storage environment, further inhibiting the growth of microorganisms.

[0038] BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The viscosity of the spinning solution with different mass fractions of thymol added in Examples 1, 2, 3 and 4 of the application is shown.

[0040] Figure 2 The ethylene degradation rate of the nanofiber preservative film in Examples 2, 5, 6 and 7 of the application is shown.

[0041] Figure 3 The photo shows the comparison of the antibacterial effect of the nanofiber preservative film and the blank control group on Botryosphaeria dothidea in Example 2 of the application.

[0042] Figure 4 The photo shows the preservation effect of the nanofiber preservative film on kiwi fruit over time in Example 2 of the application. DETAILED DESCRIPTION

[0043] The embodiments of the application are described in detail below. The embodiments described below are exemplary and are used to explain the application, and cannot be understood as a limitation of the application. If a specific technique or condition is not specified in the embodiments, it is carried out according to the technique or condition described in the literature in the art or according to the product instruction. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be obtained by market purchase.

[0044] ​In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application.

[0045] On the contrary, the present application covers any substitution, modification, equivalent method and scheme made within the essence and scope of the present application defined by the claims. Further, in order to make the public have a better understanding of the present application, some specific details are described in the following detailed description of the present application. The present application can also be completely understood without the description of these details by those skilled in the art.

[0046] The existing food active packaging material faces many challenges, including serious nanoparticle agglomeration, low photocatalytic efficiency, too fast release rate of natural antibacterial active ingredients, great influence of preparation process on the biological activity of antibacterial agents, and low antibacterial efficiency. In view of these problems, the present application provides a kind of nanofiber preservative film with high efficiency ethylene degradation and antibacterial property and its preparation method, which is used for food preservation. The method uses polyvinyl alcohol and pullulan aqueous solution as the base material, adds different proportions of titanium dioxide and thymol as the electrospinning liquid, optimizes the addition proportion of titanium dioxide and thymol, and uses electrospinning technology to prepare a nanofiber film with uniform morphology, smooth surface and continuity. The nanofiber film not only has high antibacterial performance, but also can effectively degrade ethylene, and is suitable for the preservation of kiwi fruit and other fruits and vegetables during storage.

[0047] In particular, the electrospinning technology used in the present application is a simple and efficient method for preparing nanofiber. Under normal temperature and pressure, the polymer solution is continuously stretched into micro / nanofiber by the action of an external electric field, and is stacked layer by layer on the receiver to form a nanofiber film. The electrospun nanofiber can efficiently load organic or inorganic nanoparticles. The specific surface area of the generated fiber film is large, and the porosity is high, which is beneficial to the uniform dispersion of nanoparticles and improves the specific surface area of the nanoparticles to play functional activity. At the same time, the bioactive ingredients are encapsulated inside the nanofiber, which can realize the slow release of the bioactive ingredients. In addition, since the electrospinning technology is a normal temperature preparation process, the chemical stability and biological function of the bioactive substances can be maintained during the preparation process.

[0048] In order to achieve the above effects, in one aspect, the present application provides a kind of nanofiber preservative film, the nanofiber preservative film is obtained by using the following raw materials preparation method:

[0049] pullulan,

[0050] polyvinyl alcohol,

[0051] thymol, a mass fraction of the thymol being 0.2-5% relative to the total mass of the pullulan and polyvinyl alcohol; and

[0052] titanium dioxide nanoparticles, a mass fraction of the titanium dioxide nanoparticles being 20-80% relative to the total mass of the pullulan and polyvinyl alcohol.

[0053] In a second aspect, the present application further provides a preparation method of the nanofiber preservative film, comprising the following steps:

[0054] S1-preparing a matrix solution by mixing a pullulan aqueous solution and a polyvinyl alcohol aqueous solution;

[0055] S2-adding thymol to the matrix solution to obtain a mixed solution of thymol and the matrix, a mass fraction of the thymol being 0.2-5% relative to the total mass of the dry substances of the matrix solution;

[0056] S3-adding titanium dioxide nanoparticles to the thymol / pullulan / polyvinyl alcohol matrix solution to obtain a spinning precursor solution, a mass fraction of the titanium dioxide nanoparticles being 20-80% relative to the total mass of the dry substances of the pullulan and polyvinyl alcohol; and

[0057] S4-electrospinning the spinning precursor solution to obtain the nanofiber preservative film.

[0058] Specifically, the preparation method provided by the present application can comprise the following steps:

[0059] (1) preparing a pullulan / polyvinyl alcohol matrix solution;

[0060] (2) adding thymol to the pullulan / polyvinyl alcohol matrix solution in different proportions to prepare a spinning precursor solution 1 (thymol / pullulan / polyvinyl alcohol matrix solution);

[0061] (3) adding titanium dioxide nanoparticles to the thymol / pullulan / polyvinyl alcohol matrix solution in different proportions to prepare a spinning precursor solution 2;

[0062] (4) preparing the spinning precursor solution 2 into a nanofiber preservative film by electrospinning technology.

[0063] Further, the specific process of step (1) for preparing the pullulan / polyvinyl alcohol matrix solution is as follows: preparing an 8-12% (w / w) pullulan aqueous solution and an 8-12% (w / w) polyvinyl alcohol aqueous solution, and then mixing the prepared pullulan aqueous solution and polyvinyl alcohol aqueous solution uniformly at a volume ratio of 1:1 to obtain the pullulan / polyvinyl alcohol matrix solution.

[0064] Further, the specific process of step (2) for preparing the spinning precursor solution 1 is as follows: adding thymol ethanol solution to the pullulan / polyvinyl alcohol mixed solution at 0.2-5% (w / w), stirring for 12-24 h, and fully mixing to obtain the thymol / pullulan / polyvinyl alcohol spinning solution (spinning precursor solution 1).

[0065] Further, the specific process of step (3) for preparing the spinning precursor solution 2 is as follows: preparing the thymol / pullulan / polyvinyl alcohol spinning solution, wherein the addition amount of thymol is 1% (w / w), then adding different proportions of nano-titanium dioxide at 20-80% (w / w), and ultrasonicating for 0.5-2 h and stirring for 12-24 h to obtain the titanium dioxide / thymol / pullulan / polyvinyl alcohol spinning solution (spinning precursor solution 2).

[0066] Further, the electrospinning in step (4) includes a single-axis electrospinning technique. The specific process of preparing the nanofiber membrane by the single-axis electrospinning technique is as follows: adding the spinning precursor solution prepared in steps (2) and (3) to a syringe with a 20-22G needle, adjusting the distance from the needle to the syringe to 15-20 cm, setting the syringe advance speed to 0.5-1 mL / h, spinning for 5-15 h, the spinning voltage being 15-25 kV, the ambient temperature being 20-30℃, and the relative humidity being 45-55%, to obtain the nanofiber preservative film.

[0067] Further, step S1 includes:

[0068] S11-adding pullulan to distilled water and stirring to obtain a pullulan aqueous solution with a mass fraction of 8-12%;

[0069] S12-adding polyvinyl alcohol to distilled water and stirring to obtain a polyvinyl alcohol aqueous solution with a mass fraction of 8-12%;

[0070] S13-mixing the pullulan aqueous solution obtained in step S11 and the polyvinyl alcohol aqueous solution obtained in step S12 uniformly at a volume ratio of (5-1):(1-5) to obtain a pullulan and polyvinyl alcohol matrix solution.

[0071] Further, step S2 includes:

[0072] S21-preparing a thymol ethanol solution, wherein the volume fraction of thymol relative to the total volume of the thymol ethanol solution is 70-80%;

[0073] S22-adding thymol ethanol solution into pullulan / polyvinyl alcohol matrix solution at a mass ratio of 0.2-5%, and stirring uniformly to obtain thymol / pullulan / polyvinyl alcohol matrix solution, wherein the mass ratio is a percentage relative to the total mass of pullulan / polyvinyl alcohol dry substance.

[0074] Preferably, thymol ethanol solution is added into pullulan / polyvinyl alcohol matrix solution at a mass ratio of 0.5-1%.

[0075] Further, step S3 comprises:

[0076] Further, titanium dioxide nanoparticles are added at a mass fraction of 20-80% relative to the total mass of pullulan / polyvinyl alcohol dry substance, and ultrasonic treatment is performed for 0.5-2h, and stirring is performed for 12-24h to obtain the spinning precursor solution.

[0077] Further, titanium dioxide nanoparticles are added at a mass fraction of 20-80% relative to the total mass of pullulan / polyvinyl alcohol dry substance.

[0078] Further, step S4 comprises: sucking the spinning precursor solution into a syringe with a 20-22G needle, adjusting the distance from the needle to the syringe to 15-20cm, and then stretching the spinning precursor solution into nanofibers by the action of an external electrostatic field, and stacking the nanofibers layer by layer on a receiver to form a nanofiber membrane.

[0079] Further, the setting parameters of electrospinning are as follows: the pushing speed of the syringe is 0.5-1mL / h, the spinning time is 5-15h, the spinning voltage is 15-25kV, the ambient temperature is 20-30℃, and / or the relative humidity is 45-55%.

[0080] The nanofiber preservative film provided by the application has a large specific surface area and high porosity, which is conducive to the uniform dispersion of nanoparticles and improves the specific surface area of the nanoparticles to play a functional activity. At the same time, the bioactive ingredients are encapsulated in the nanofibers of the nanofiber preservative film, which can achieve the slow release of the bioactive ingredients. In addition, since the electrospinning technology is a normal-temperature preparation process, the chemical stability and biological function of the bioactive substances can be maintained during the preparation process.

[0081] In a third aspect, the application also provides the use of the above-mentioned fiber preservative film in fruit and vegetable antibacterial and / or fruit and vegetable ethylene degradation. In particular, the nanofiber film loaded with titanium dioxide and thymol is prepared by using electrospinning technology, and finally the nanofiber film with good structure and moderate drug loading is selected to be used for photocatalytic degradation of ethylene, antibacterial and preservation of kiwi fruit and other fruits and vegetables.

[0082] In summary, the present application provides a nanofiber preservative film with high ethylene degradation and antibacterial properties and a preparation method thereof, in which a spinning solution is prepared with pullulan and polyvinyl alcohol as spinning base materials, thymol and titanium dioxide are added to the spinning solution, and a nanofiber film loaded with titanium dioxide and thymol is prepared by using electrospinning technology.

[0083] The present application is further described in detail below by examples.

[0084] Example 1

[0085] Example 1 provides a nanofiber preservative film with high ethylene degradation and antibacterial properties and a preparation method thereof, in which the specific steps are as follows:

[0086] (1) 10 g of polyvinyl alcohol was weighed into 100 mL of distilled water and stirred at 80°C for 3 h, and then cooled to room temperature to obtain a polyvinyl alcohol aqueous solution; 10 g of pullulan was weighed into 100 mL of distilled water, and stirred at room temperature for 5 h until the pullulan was completely dissolved to obtain a pullulan aqueous solution. 10 mL of the polyvinyl alcohol aqueous solution and 10 mL of the pullulan aqueous solution were measured and mixed, and stirred at 25°C for 12 h to obtain a pullulan / polyvinyl alcohol mixed aqueous solution;

[0087] (2) 4 mL of thymol was measured and added to 5 mL of ethanol to prepare a thymol ethanol solution with a concentration of 80% (v / v). The thymol ethanol solution was added to the pullulan / polyvinyl alcohol mixed aqueous solution at a mass fraction of 0.5% (relative to the total mass percentage of the pullulan / polyvinyl alcohol dry substances), and thoroughly mixed to obtain a thymol / pullulan / polyvinyl alcohol solution;

[0088] (3) 0.8 g of titanium dioxide nanoparticles with a mass fraction of 40% (w / w) was weighed and added to the thymol / pullulan / polyvinyl alcohol solution, and then ultrasonically treated for 1 h and stirred for 12 h to obtain a uniform and stable spinning solution;

[0089] (4) The spinning solution was taken up using a 20 mL syringe, a 21G stainless steel needle was mounted on the syringe, the needle was connected to the positive electrode of a high-voltage power supply, and the receiving plate was connected to the negative electrode of the high-voltage power supply. The spinning temperature was 25°C, and the relative humidity was 50%. The specific parameters were set as follows: the spinning voltage was 24 kV, the injection speed of the syringe was 0.8 mL / h, the distance from the needle to the receiver was 15 cm, and the spinning time was 12 h to obtain a nanofiber preservative film.

[0090] Example 2

[0091] (1) 10 g of polyvinyl alcohol was weighed into 100 mL of distilled water and stirred at 80°C for 3 h, and then cooled to room temperature to obtain a polyvinyl alcohol aqueous solution; 10 g of pullulan was weighed into 100 mL of distilled water and stirred at room temperature for 5 h until the pullulan was completely dissolved to obtain a pullulan aqueous solution. 10 mL of the polyvinyl alcohol aqueous solution and 10 mL of the pullulan aqueous solution were measured and mixed, and stirred at 25°C for 12 h to obtain a mixed pullulan / polyvinyl alcohol aqueous solution;

[0092] (2) 4 mL of thymol was measured and added into 5 mL of ethanol to prepare a thymol ethanol solution at 80% (v / v). The thymol ethanol solution was added into the mixed pullulan / polyvinyl alcohol aqueous solution at a mass fraction of 1% (relative to the total mass of the dry matter of the pullulan / polyvinyl alcohol), and mixed well to obtain a thymol / pullulan / polyvinyl alcohol solution;

[0093] (3) 0.8 g of titanium dioxide nanoparticles at 40% (w / w) was weighed and added into the thymol / pullulan / polyvinyl alcohol solution, and ultrasonically treated for 1 h, and then stirred for 12 h to obtain a uniform and stable spinning solution;

[0094] (4) The spinning solution was taken with a 20 mL syringe, a 21G stainless steel needle was mounted on the syringe, the needle was connected to the positive electrode of a high-voltage power supply, and the receiving plate was connected to the negative electrode of the high-voltage power supply. The spinning temperature was 25°C and the relative humidity was 50%. The specific parameters were set as follows: the spinning voltage was 24 kV, the pushing speed of the syringe was 0.8 mL / h, the distance from the needle to the receiver was 15 cm, and the spinning time was 12 h to obtain a nanofiber preservative film.

[0095] Example 3

[0096] This example relates to a nanofiber preservative film with high ethylene degradation and antibacterial properties and a preparation method thereof. The specific preparation process is according to steps (1), (2), (3) and (4) of Example 1, and the only difference is that the mass fraction of the thymol ethanol solution added in step (2) is 2%.

[0097] Example 4

[0098] This example relates to a nanofiber preservative film with high ethylene degradation and antibacterial properties and a preparation method thereof. The specific preparation process is according to steps (1), (2), (3) and (4) of Example 1, and the only difference is that the mass fraction of the thymol ethanol solution added in step (2) is 5%.

[0099] Example 5

[0100] The present example relates to a nanofiber preservative film with high ethylene degradation and antibacterial properties and a preparation method thereof. The specific preparation process is according to the steps (1) (2) (3) (4) of Example 2, the only difference is that 0.4 g of titanium dioxide nanoparticles with a mass fraction of 20% is added in step (3).

[0101] Example 6

[0102] The present example relates to a nanofiber preservative film with high ethylene degradation and antibacterial properties and a preparation method thereof. The specific preparation process is according to the steps (1) (2) (3) (4) of Example 2, the only difference is that 1.2 g of titanium dioxide nanoparticles with a mass fraction of 60% is added in step (3).

[0103] Example 7

[0104] The present example relates to a nanofiber preservative film with high ethylene degradation and antibacterial properties and a preparation method thereof. The specific preparation process is according to the steps (1) (2) (3) (4) of Example 2, the only difference is that 1.6 g of titanium dioxide nanoparticles with a mass fraction of 80% is added in step (3).

[0105] Comparative Example 1

[0106] The preservative film of Comparative Example 1 is prepared according to the preparation method of Example 2, except that step (2) is omitted.

[0107] Comparative Example 2

[0108] The preservative film of Comparative Example 2 is prepared according to the preparation method of Example 2, except that step (3) is omitted.

[0109] Comparative Example 3

[0110] The preservative film of Comparative Example 3 is prepared according to the preparation method of Example 2, except that step (1) is as follows: 10 g of polyvinyl alcohol is weighed into 100 mL of distilled water, and stirred at 80°C for 3 h, and cooled to room temperature to obtain a polyvinyl alcohol aqueous solution. That is, the polyvinyl alcohol aqueous solution is prepared instead of the pullulan / polyvinyl alcohol mixed aqueous solution for subsequent operations.

[0111] Comparative Example 4

[0112] The preservative film of Comparative Example 4 is prepared according to the preparation method of Example 1, except that step (1) is as follows: 10 g of pullulan is weighed into 100 mL of distilled water, and stirred at room temperature for 5 h until the pullulan is completely dissolved to obtain a pullulan aqueous solution. That is, the pullulan aqueous solution is prepared instead of the pullulan / polyvinyl alcohol mixed aqueous solution for subsequent operations.

[0113] Comparative Example 5

[0114] The preservative film of Comparative Example 5 was prepared according to the preparation method of Example 1, except that the electrospinning parameters of step (4) were as follows: the injection speed of the syringe was 2 mL / h, the spinning time was 20 h, the spinning voltage was 30 kV, the ambient temperature was 30 °C, and the relative humidity was 55%.

[0115] Comparative Example 6

[0116] The preservative film of Comparative Example 6 was prepared according to the preparation method of Example 1, except that the electrospinning parameters of step (4) were as follows: the injection speed of the syringe was 0.4 mL / h, the spinning time was 4 h, the spinning voltage was 13 kV, the ambient temperature was 20 °C, and / or the relative humidity was 45%.

[0117] Test Example

[0118] - Viscosity measurement of the spinning precursor solution

[0119] The viscosity of the spinning solution was determined using a rotary rheometer (DHR-20, TA Instruments, USA). The specific test conditions were as follows: a parallel aluminum plate fixture (diameter 20 mm) was selected, the plate gap was set to 1.0 mm, and the sample loading was 1 mL; the sample was scanned at a shear rate range of 0.01-100 s -1 at a constant temperature of 25 °C.

[0120] - SEM test of the nanofiber film

[0121] The nanofiber preservative films obtained in Examples 1-7 and Comparative Examples 1-6 were observed using a scanning electron microscope (JSM-7800F, JEOL). The observation results are shown in Table 2.

[0122] - Measurement of the ethylene degradation rate of the nanofiber preservative film

[0123] A saturated potassium sulfate solution was added to a headspace bottle (250 mL), followed by 1 g of the nanofiber preservative film prepared in Example 2, 5, 6, or 7, which was placed in the headspace bottle. After 5 h, the relative humidity in the headspace bottle was stabilized at 98%, and ethylene gas was injected into the headspace bottle to make the ethylene concentration in the bottle 200 ppm. The headspace bottle was irradiated using a xenon lamp (wavelength 200-1100 nm, power 1.5 kW), and the ethylene concentration in the bottle was detected every hour. The ethylene content was detected using gas chromatography-mass spectrometry.

[0124] - Measurement of the antibacterial rate of the nanofiber preservative film on postharvest kiwifruit

[0125] The antibacterial experiment was divided into four groups: a control group without any treatment, Example 2 group, Comparative Example 1 group, and Comparative Example 2 group. 20 mg of nanofiber membrane samples from each of the control, Example 2, Comparative Example 1, and Comparative Example 2 groups were immersed in a suspension of *Botrytis cinerea* spores and shaken on a shaker for 5 hours. 10 μL of the mixture was then dropped into the center of a potato dextrose agar plate, treated with light, and incubated at 28°C for 4 days.

[0126] The inhibition rate indicates the degree to which an antimicrobial substance inhibits the growth of microorganisms, usually expressed as a percentage (%), and is calculated using the following formula:

[0127]

[0128] in:

[0129] • Dc: Colony diameter (mm) of the control group (untreated);

[0130] • Dt: Colony diameter (mm) of the treatment group (with added antibacterial substance).

[0131] Kiwi fruit preservation effect test

[0132] The study investigated the preservation effect of the nanofiber preservation film used in the blank control group and Example 2 on kiwifruit. Kiwifruit of uniform weight and with smooth surfaces were selected and placed in storage boxes, with four kiwifruit in each box. Simultaneously, 1g of nanofiber film was placed in each box as a preservation pad. The kiwifruit were stored at room temperature for 17 days, and irradiated with a xenon lamp for 4 hours daily.

[0133] Results and Discussion

[0134] like Figure 1 As shown, the viscosity of the spinning solution increases with increasing thymol content. When the thymol content in the spinning solution is equal to or less than 1%, the viscosity of the spinning solution does not change significantly. When the thymol content is 2%, the viscosity of the spinning solution increases sharply, causing spinning difficulties. The phenolic hydroxyl groups of thymol can form hydrogen bonds with the hydroxyl groups of pullulan and polyvinyl alcohol, enhancing intermolecular forces and leading to an increase in solution viscosity.

[0135] The degradation properties of the nanofiber food preservation film prepared in this invention on ethylene were investigated. For example... Figure 2 As shown, the light exposure times required for the complete degradation of ethylene by nanofiber membranes containing 20%, 40%, 60%, and 80% nano-titanium dioxide were 8 h, 4 h, 2 h, and 5 h, respectively. When the titanium dioxide content was below 60%, the degradation rate of ethylene by the nanofiber membrane increased with the increase of titanium dioxide content. When the titanium dioxide content was 80%, the degradation rate of ethylene by the nanofiber membrane decreased. This may be because the titanium dioxide nanoparticles agglomerated in the nanofiber membrane, reducing the photocatalytic specific surface area of ​​titanium dioxide.

[0136] The inhibition effect of the nanofiber preservative film of Research Example 2, Comparative Example 1, Comparative Example 2 and the control group on the postharvest pathogenic bacteria Botryosphaeria dothidea of kiwi fruit was studied. The results of the antibacterial rate test are shown in Table 1. Figure 3 The photos showing the comparison of the antibacterial effect of the nanofiber preservative film of Example 2 and the blank control group on Botryosphaeria dothidea are shown. The mycelium of the control group filled the diameter of 6.2 cm of the potato dextrose medium plate under light conditions; while the mycelium of the nanofiber film treatment group of Example 2 hardly grew under light conditions.

[0137] Table 1

[0138]

[0139] The preservation effect of the nanofiber preservative film on kiwi fruit was studied. As shown in Figure 4 Table 2 shows the comprehensive evaluation of the samples of Examples 1-7 and Comparative Examples 1-6, including the SEM evaluation results.

[0140] Table 2

[0141] Table 2

[0142]

[0143]

[0144] The observation results of Examples 1-7 and Comparative Examples 1-6 above show that the TiO2 composite nanofibers prepared under the optimal conditions of Examples 1-5 exhibit excellent performance, including uniform, smooth and continuous morphology without beading, and good dispersibility of TiO2 nanoparticles, and the spinning process is smooth; among them, Examples 3 and 4 have slightly difficult spinning due to slightly high spinning solution viscosity, but the fiber quality is not affected. In contrast, Examples 6 and 7 have uneven fiber thickness and beading phenomenon, which may be related to process parameter fluctuations or decreased dispersibility of nanoparticles. The fiber morphology of Comparative Examples 1-2 is not affected, but the antibacterial property and ethylene degradation performance are significantly reduced, indicating that the addition or modification of TiO2 is crucial for functionality; while Comparative Examples 3-6 have problems such as poor fiber uniformity, uneven spinning and even unable to spin due to improper formulation or process, highlighting the sensitivity of the spinning solution viscosity, conductivity and process parameters. Overall, the uniform dispersion of TiO2, the reasonable regulation of the spinning solution viscosity and the optimization of the electrospinning parameters are the key factors for preparing high-quality functional nanofibers.

[0145] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present application, but not to limit them. Although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application. Any changes or replacements that can be easily thought of by those skilled in the art within the technical scope disclosed by the present application should be covered within the protection scope of the present application.

Claims

1. A nanofiber cling film, characterized by, The nanofiber preservative film is obtained by using the following raw materials: pullulan, polyvinyl alcohol, thymol, wherein the mass fraction of thymol is 0.2-5% relative to the total mass of the pullulan and polyvinyl alcohol; and titanium dioxide nanoparticles, wherein the mass fraction of the titanium dioxide nanoparticles is 20-80% relative to the total mass of the pullulan and polyvinyl alcohol.

2. A method for preparing the nanofiber food preservation film according to claim 1, characterized in that, The method comprises the following steps: S1-preparing a matrix solution, which is an aqueous solution of pullulan and polyvinyl alcohol; S2-adding thymol to the matrix solution to obtain a mixed solution of thymol and matrix, wherein the added mass fraction of the thymol is 0.2-5% relative to the total mass of the pullulan and polyvinyl alcohol dry substances; S3-adding titanium dioxide nanoparticles to the mixed solution of thymol and matrix to obtain a spinning precursor solution, wherein the added mass fraction of the titanium dioxide nanoparticles is 20-80% relative to the total mass of the pullulan and polyvinyl alcohol dry substances; and S4-electrospinning the spinning precursor solution to obtain the nanofiber preservative film.

3. The preparation method according to claim 1, characterized in that, Step S1 comprises: S11-adding pullulan to distilled water and stirring to obtain an aqueous solution of pullulan with a mass fraction of 8-12%; S12-adding polyvinyl alcohol to distilled water and stirring to obtain an aqueous solution of polyvinyl alcohol with a mass fraction of 8-12%; S13-mixing the aqueous solution of pullulan obtained in step S11 and the aqueous solution of polyvinyl alcohol obtained in step S12 uniformly at a volume ratio of (1-5):(5-1) to obtain a pullulan and polyvinyl alcohol matrix solution.

4. The preparation method according to claim 1, characterized in that, Step S2 comprises: S21-preparing a thymol ethanol solution, wherein the volume fraction of thymol relative to the total volume of the thymol ethanol solution is 50-90%; S22-adding the thymol ethanol solution to the matrix solution and stirring uniformly to obtain a thymol / pullulan / polyvinyl alcohol solution, wherein the added mass fraction of the thymol is 0.5-1% relative to the total mass of the pullulan and polyvinyl alcohol dry substances.

5. The preparation method according to claim 4, characterized in that, The volume fraction of thymol in the thymol ethanol solution relative to the total volume of the thymol ethanol solution is 70-80%.

6. The preparation method according to claim 2, characterized in that, Step S3 comprises: adding titanium dioxide nanoparticles with an added mass fraction of 20-80% relative to the total mass of the pullulan and polyvinyl alcohol dry substances, ultrasonicating for 0.5-2 h, and stirring for 12-24 h to obtain the spinning precursor solution.

7. The production method according to claim 6, characterized by, The average particle size of the titanium dioxide nanoparticles is 5-10 nm.

8. The preparation method according to claim 2, characterized in that, Step S4 comprises drawing the spinning precursor solution into a syringe with a 20-22G needle, adjusting the distance from the needle to the syringe to 15-20 cm, and then stretching the spinning precursor solution into nanofilaments by the action of an external electrostatic field and stacking the nanofilaments layer by layer on a receiver to form the nanofiber preservative film.

9. The production method according to claim 8, characterized by, The setting parameters of electrospinning are as follows: the injection speed of the syringe is 0.5-1 mL / h, the spinning time is 5-15 h, the spinning voltage is 15-25 kV, the ambient temperature is 20-30 DEG C, and the relative humidity is 45-55%.

10. The application of the nanofiber preservative film of claim 1 in fruit and vegetable antibacterial and fruit and vegetable ethylene degradation.

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