Preparation method and application of zein nanoparticle composite membrane

Abstract

The invention discloses a preparation method of a zein nanoparticle composite membrane. The preparation method comprises the following steps: S1, preparing a thymol-zein ethanol water solution; s2, preparing the thymol-zein nano particles; s3, preparing a thymol ethanol water solution; s4, preparing a carrageenan base membrane solution; s5, preparing a 5.25 mg / mL potassium chloride solution; s6, preparing a nano particle-carrageenan composite solution; s7, preparing a thymol-carrageenan composite solution; and S8, the nanoparticle-carrageenan composite solution and the thymol-carrageenan composite solution are taken through a solution pouring method and poured into a non-stick coating mold with the side length being 28 cm * 28 cm, drying and film forming are conducted in a constant-temperature incubator, and the thymol-loaded zein nanoparticle filling type composite film has excellent oxidation resistance and antibacterial capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of food packaging, and specifically to a preparation method and application of a composite film filled with thymol-loaded zein nanoparticles. Background Art

[0002] Recently, consumers have become increasingly aware of the environmental challenges posed by the production and disposal of petroleum-based plastic packaging materials. To address these issues, the scientific community has started to focus on the design and development of biodegradable active packaging materials. Biopolymers (polysaccharides, proteins, and / or lipids) are expected to become alternatives to plastic packaging materials due to their excellent characteristics such as being renewable and biodegradable.

[0003] Carrageenan is a film-forming hydrocolloid extracted from red algae, composed of sulfated and non-sulfated galactose units and 3,6-anhydrogalactose units, and is widely used as a film-forming matrix due to its good film-forming property. However, due to the low antibacterial activity of this polysaccharide, its effect in food preservation is still limited. Nevertheless, carrageenan can be used in combination with other natural substances (including essential oils) to improve its antibacterial properties. For example, thymol is an essential oil extracted from plants of the Labiatae family, with strong antibacterial and antioxidant properties. In addition, it has safety as a food additive and has been widely used in food, medicine, and cosmetics. However, thymol has limited water solubility and high volatility, so it is prone to decomposition when exposed to light or heat, resulting in the loss of active ingredients and limiting its efficacy. By encapsulating hydrophobic bioactive compounds inside hydrophobic and outside hydrophilic nanoparticles, their water dispersibility and chemical stability can be improved.

[0004] Nanoparticles refer to particles with diameters between 1 and 1000 nm. These nanoparticles can be composed of various different food components, including polysaccharides, proteins, phospholipids, and lipids. Zein is a hydrophobic protein from corn, and its polypeptide chain is rich in non-polar amino acids, so it is insoluble in water but soluble in alcohol and alkaline solutions. This property enables zein to self-assemble into nanoparticles by methods such as antisolvent precipitation. Zein nanoparticles have been successfully used to encapsulate various hydrophobic bioactive compounds, thereby improving their dispersibility, stability, release characteristics, and biological activity.

[0005] In this study, we fabricated thymol-loaded zein nanoparticles by anti-solvent precipitation and then incorporated them into κ-carrageenan-based films to enhance their preservative properties. We hypothesized that compared with composite films containing free thymol, the addition of thymol-loaded nanoparticles would significantly improve the antioxidant and antibacterial capacities of carrageenan-based composite films. In addition, the ability of these composite films to preserve a fresh food model was also compared. Few studies have directly compared the efficacy of biopolymer composite films containing free and encapsulated essential oils. Therefore, we propose a method for preparing zein nanoparticle composite films. Summary of the Invention

[0006] The object of the present invention is to provide a method for preparing zein nanoparticle composite films to solve the problems raised in the above-mentioned background technology.

[0007] 2. To achieve the above object, the present invention provides the following technical solution: A method for preparing zein nanoparticle composite films, comprising the following steps:

[0008] S1. Prepare an ethanol aqueous solution of thymol and zein;

[0009] S2. Prepare thymol-zein nanoparticles;

[0010] S3. Prepare an ethanol aqueous solution of thymol;

[0011] S4. Prepare a carrageenan-based film solution;

[0012] S5. Prepare a 5.25 mg / mL potassium chloride solution;

[0013] S6. Prepare a nanoparticle-carrageenan composite solution;

[0014] S7. Prepare a thymol-carrageenan composite solution;

[0015] S8. Using the solution casting method, pour the nanoparticle-carrageenan composite solution and the thymol-carrageenan composite solution into a non-stick coated mold with side lengths of 28 cm * 28 cm and dry to form a film in a constant temperature incubator.

[0016] Preferably, the method for preparing the ethanol aqueous solution of thymol and zein in S1 is: Weigh 80.0 mg of thymol and 400.0 mg of zein and dissolve them in 40.0 mL of ethanol aqueous solution, and stir in the dark for 12 hours at 300 rpm / min with a magnetic stirrer.

[0017] Preferably, the preparation method of the thymol - zein nanoparticles in S2 is as follows: Slowly drop 10.0 mL of the solution in S1 into 30.0 mL of distilled water, and stir in the dark at 1200 rpm / min to obtain thymol - zein nanoparticles.

[0018] Preferably, the preparation method of the thymol ethanol aqueous solution in S3 is as follows: Weigh 60.0 mg of thymol and dissolve it in 30.0 mL of ethanol aqueous solution, and stir in the dark at 300 rpm / min with a magnetic stirrer for 30.0 min.

[0019] Preferably, the preparation method of the carrageenan - based film solution in S4 is as follows: Weigh 2400.0 mg of carrageenan, add 100.0 mL of distilled water, stir evenly in a water bath to form a 24 mg / mL carrageenan solution, then add 480.0 mg of glycerol as a plasticizer to the carrageenan solution, and cool the solution to 40 °C to obtain the carrageenan - based film solution.

[0020] Preferably, the preparation method of the 5.25 mg / mL potassium chloride solution in S5 is as follows: Weigh 157.5 mg of potassium chloride, add 30 mL of distilled water, and stir evenly to obtain a 5.25 mg / mL potassium chloride solution.

[0021] Preferably, the preparation method of the nanoparticle - carrageenan composite solution in S6 is as follows: Mix the carrageenan - based film solution in S4, the nanoparticles in S2, and the potassium chloride solution in S5, where the dry mass of the nanoparticles is 360.0 mg, the potassium chloride solution is 9.14 mL, and make up the volume to 238.32 mL to obtain the nanoparticle - carrageenan composite solution.

[0022] Preferably, the preparation method of the thymol - carrageenan composite solution in S7 is as follows: Mix the carrageenan - based film solution in S4, the thymol ethanol aqueous solution in S3, and the potassium chloride solution in S5, where the dry mass of thymol is 60.0 mg, the potassium chloride solution is 9.14 mL, and make up the volume to 238.32 mL to obtain the thymol - carrageenan composite solution.

[0023] An application of a zein nanoparticle composite film: Wrap fish meat with the composite film prepared in S8 and store it at 25 °C.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. The thymol - loaded zein nanoparticle - filled composite film in the present invention has excellent antioxidant and antibacterial abilities.

[0026] 2. The thymol - loaded zein nanoparticle - filled composite film can effectively delay the spoilage of fish meat.

[0027] 3. This method is simple and convenient to use. All the raw materials of the composite film are green, natural, environmentally friendly, and biodegradable materials, and will not cause any pollution to the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Shows the comparison chart of the ultraviolet-visible light transmittance of Sample 1 and Sample 2 in the embodiments and comparative examples of the present invention;

[0029] Figure 2 Shows the scanning electron microscope comparison chart of the surface and cross-section of Sample 1 and Sample 2 in the embodiments and comparative examples of the present invention;

[0030] Figure 3 Shows the comparison chart of the water contact angle of Sample 1 and Sample 2 in the embodiments and comparative examples of the present invention;

[0031] Figure 4 Shows the comparison chart of the thermal stability of Sample 1 and Sample 2 in the embodiments and comparative examples of the present invention;

[0032] Figure 5 Shows the comparison chart of the DPPH radical scavenging rate of Sample 1 and Sample 2 in the embodiments and comparative examples of the present invention;

[0033] Figure 6 Shows the comparison chart of the antibacterial property of Sample 1 and Sample 2 in the embodiments and comparative examples of the present invention;

[0034] Figure 7 Shows the comparison chart of the pictures and total colony counts of mandarin fish meat labeled with Sample 2 during the storage period in the embodiments of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0036] Embodiment 1

[0037] A thymol-loaded nanoparticle-filled carrageenan-based composite film proposed in this embodiment includes the following raw materials: 2400.0 mg of carrageenan, 100.0 mL of distilled water, 480.0 mg of glycerol, 48.0 mg of potassium chloride, and 360.0 mg of ZT nanoparticles.

[0038] It is prepared according to the following method:

[0039] (1) Preparation of carrageenan-based film solution: Weigh 2400.0 mg of carrageenan, add 100.0 mL of distilled water, and stir evenly in a water bath (80 °C, 300 rpm / min) to form a 24 mg / mL carrageenan solution. Then add 1.97 mL of glycerol (20% v / v) as a plasticizer to the carrageenan solution, and cool the solution to 40 °C to obtain the carrageenan-based film solution for later use.

[0040] (2) Preparation of 5.25 mg / mL potassium chloride solution: Weigh 52.5 mg of potassium chloride, add 10 mL of distilled water, and stir evenly to obtain a 5.25 mg / mL potassium chloride solution for later use.

[0041] (3) Preparation of ZT nanoparticle-carrageenan composite solution: Mix the carrageenan-based film solution from (1), the ZT nanoparticles prepared previously, and the potassium chloride solution of S2. The dry mass of the ZT nanoparticles is 360.0 mg, and the potassium chloride solution is 9.14 mL. Make up the volume to 238.32 mL in total to obtain the ZT nanoparticle-carrageenan composite solution.

[0042] (4) Using the solution casting method, pour the ZT nanoparticle-carrageenan composite solution into a non-stick coating mold with sides of 28 cm * 28 cm, and dry it into a film in a constant temperature incubator (30 °C, 72 h). The formed film is stored in a desiccator at room temperature, waiting to measure the performance indicators of the composite film.

[0043] Comparative Example 1

[0044] (1) Preparation of carrageenan-based film solution: Weigh 2400.0 mg of carrageenan, add 100.0 mL of distilled water, and stir evenly in a water bath (80 °C, 300 rpm / min) to form a 24 mg / mL carrageenan solution. Then add 1.97 mL of glycerol (20% v / v) as a plasticizer to the carrageenan solution, and cool the solution to 40 °C to obtain the carrageenan-based film solution for later use.

[0045] (2) Preparation of 5.25 mg / mL potassium chloride solution: Weigh 52.5 mg of potassium chloride, add 10 mL of distilled water, and stir evenly to obtain a 5.25 mg / mL potassium chloride solution for later use.

[0046] (3) Preparation of thymol-carrageenan composite solution: Mix the carrageenan-based film solution from (1), the thymol ethanol aqueous solution prepared previously, and the potassium chloride solution of S2. The dry mass of the thymol ethanol aqueous solution is 60.0 mg, and the potassium chloride solution is 9.14 mL. Make up the volume to 238.32 mL in total to obtain the thymol-carrageenan composite solution.

[0047] (4) Using the solution casting method, pour the thymol-carrageenan composite solution into a non-stick coated mold with side lengths of 28 cm * 28 cm, and dry it into a film in a constant temperature incubator (30 °C, 72 h). The formed film is stored in a desiccator at room temperature, waiting to measure the various performance indicators of the composite film.

[0048] Comparative Example 2

[0049] (1) Preparation of the carrageenan-based film solution: Weigh 2400.0 mg of carrageenan, add 100.0 mL of distilled water, stir evenly in a water bath (80 °C, 300 rpm / min) to form a 24 mg / mL carrageenan solution. Then add 1.97 mL of glycerol (20% v / v) as a plasticizer to the carrageenan solution, and cool the solution to 40 °C to obtain the carrageenan-based film solution for standby.

[0050] (2) Preparation of the 5.25 mg / mL potassium chloride solution: Weigh 52.5 mg of potassium chloride, add 10 mL of distilled water, and stir evenly to obtain a 5.25 mg / mL potassium chloride solution for standby.

[0051] (3) Preparation of the carrageenan composite solution: Mix the carrageenan-based film solution in (1) with the potassium chloride solution in S2, where the potassium chloride solution is 9.14 mL, and make up the volume to 238.32 mL to obtain the carrageenan composite solution.

[0052] (4) Using the solution casting method, pour the carrageenan composite solution into a non-stick coated mold with side lengths of 28 cm * 28 cm, and dry it into a film in a constant temperature incubator (30 °C, 72 h). The formed film is stored in a desiccator at room temperature, waiting to measure the various performance indicators of the composite film.

[0053] Table 1 Dosages of each raw material in Example 1 and Comparative Examples 1-2

[0054]

[0055] Example 2

[0056] In this example, the composite films obtained in Example 1 and Comparative Examples 1-2 (or some of the comparative examples) are used as samples to test the chromaticity, thickness, opacity, thermal properties, antioxidant properties, and antibacterial properties of the composite films. The composite films prepared in Example 1 and Comparative Examples 1-2 are respectively named Car / ZT-NPs (representing Sample 1 in Example 1), Car / Thymol (representing Sample 1 in Comparative Example 1), and Car (representing Sample 2 in Comparative Example 2).

[0057] 1. Color and opacity measurement

[0058] The color of the composite film was measured using a colorimeter and expressed in terms of L*, a*, and b*. The composite film was cut into rectangles measuring 40 mm × 10 mm, and the opacity of the composite film was measured using an ultraviolet-visible spectrophotometer at a wavelength of 600 nm. The formula for calculating opacity is as follows:

[0059]

[0060] Here, A600 is the absorbance of the sample at 600 nm, and x is the thickness of the sample (mm). Each sample was repeated three times.

[0061] 2. Thickness measurement

[0062] The thickness of the composite film was measured using a digital micrometer with a precision of 0.001 mm. There were 5 measurement points on each composite film, and the average thickness value was used for calculation.

[0063] Table 2 shows the color, thickness, and opacity values of different composite films. The brightness (L*) of all carrageenan films was around 90, and there was no significant difference between different samples (p > 0.05). However, after adding ZT-NPs, the yellowness (b*) of the carrageenan film increased significantly from -0.60 to +1.70 (p < 0.05). This effect is attributed to the presence of zein in the nanoparticles (powdered zein is slightly yellow), rather than thymol (transparent and colorless).

[0064] The thicknesses of Car, Car / Thymol, and Car / ZT-NPs were all approximately 33 μm. This indicates that the addition of free or encapsulated thymol does not cause a significant change in the thickness of the carrageenan film. When free thymol was added to the composite film, no change in opacity was observed, but after adding ZT-NPs, a significant increase in opacity was detected (p < 0.05). This increase is attributed to the light scattering effect of the nanoparticles in the composite film.

[0065] Table 2 Color, thickness, and opacity of the composite film

[0066]

[0067] Different superscript letters in the same column of the table indicate significant differences (p < 0.05).

[0068] 3. Ultraviolet-visible light transmittance measurement

[0069] The transmittance of the composite film was measured as follows: The composite film was cut into strips measuring 40 mm × 10 mm and then placed in a cuvette for measurement. An empty cuvette was used as a control. Then, the transmittance in the wavelength range of 200 to 800 nm was measured.

[0070] The transmittance results of the composite film are asFigure 1 As shown, both Car and Car / Thymol exhibit high transmittance in the visible light (400 - 800 nm) and ultraviolet (200 - 400 nm) wavelength ranges. However, the addition of ZT-NPs significantly improves the ultraviolet barrier ability of the composite film, especially in the ultraviolet-visible light (200 - 275 nm), ultraviolet wavelength (275 - 320 nm), and ultraviolet wavelength (320 - 400 nm) regions. The transmittance in the ultraviolet range approaches zero, which is mainly attributed to the light scattering of the nanoparticles. These results indicate that ZT-NPs can inhibit the penetration of ultraviolet light into food, thereby delaying the oxidative degradation of food under light. These results are consistent with the opacity results discussed earlier.

[0071] 4. Determination by Scanning Electron Microscope

[0072] The microstructure of the composite film was determined by the following method. The surface and cross-section of the composite film were observed using a scanning electron microscope at an acceleration voltage of 5 kV with a magnification of 1000 times.

[0073] The scanning electron microscope results of the composite film are as Figure 2 shown. A scanning electron microscope was used to characterize the microstructure of different composite films ( Figure 2 ). All composite films have a uniform cross-sectional microstructure. The surface morphology images show that the pure carrageenan film has a smooth and uniform appearance. However, some irregularities appear on the surface of the carrageenan / thymol film, which may be due to the presence of free thymol that has not been fully incorporated into the carrageenan network. After introducing ZT-NPs into the carrageenan film, the surface morphology becomes rougher, with many granular protrusions. This change in microstructure can be attributed to the presence of some nanoparticles on the surface of the carrageenan film.

[0074] 5. Determination of Water Contact Angle

[0075] The water contact angle of the composite film was determined by the following method. A drop of ultrapure water (2 μL) was dropped onto the surface of the composite film sample (1 cm × 4 cm) using a precision syringe, and then the water contact angle was calculated by taking digital images of the water droplet.

[0076] The water contact angle results of the composite film are as Figure 3As shown, water contact angle (WCA) measurement was used to describe the hydrophobicity of various composite films. The water contact angle of the pure carrageenan film (73.6°) was significantly lower (p < 0.05) than that of the film containing directly dispersed thymol (79.2°), which was attributed to the hydrophobicity of thymol. The WCA of Car / ZT-NPs (83.5°) was significantly higher than that of other composite films, indicating that the composite film became more hydrophobic. This effect was mainly attributed to the increase in the surface roughness of the composite film after the addition of ZT-NPs (as shown by scanning electron microscopy), as well as the strong hydrophobicity of zein.

[0077] 6. Thermal stability determination

[0078] The thermal properties of the composite films were determined by the following method. The composite film (5 mg) was placed in a crucible, and then the crucible was placed in a thermogravimetric analyzer. The mass change of the sample was measured in the range of 25 °C - 600 °C, the nitrogen flow rate was 20 mL / min, and the heating rate was 10 °C / min.

[0079] The thermal stability results of the composite films are as Figure 4 shown Figure 4 Figure A shows the thermogravimetric analysis curves of all composite films, that is, the change in their mass with temperature. The final weight losses of Car, Car / Thymol, and Car / ZT-NPs were 70.8%, 63.5%, and 62.7%, respectively. The lower mass loss of Car / ZT-NPs may be due to its higher initial solid content.

[0080] After adding ZT-NPs to the carrageenan film, the peak position observed around 240 - 250 °C changed ( Figure 4 Figure B), and the temperature increased from about 241 °C to 250 °C, which can be attributed to the intermolecular interactions between ZT-NPs and the surrounding zein / carrageenan matrix. It is speculated that these interactions mean that the composite film must be heated to a higher temperature for the carrageenan to undergo thermal degradation. In summary, adding thymol in the form of nanoparticles can improve the thermal stability of carrageenan films.

[0081] 7. DPPH radical scavenging rate determination

[0082] The antioxidant activity of the composite films was measured by the following method. The composite film (400 mg) was placed in a 50% ethanol solution (4 mL), and then reacted for 6 h under dark conditions at 30 °C. Then, 3 mL of 0.1 mmol DPPH solution prepared with 50% ethanol was added to 2 mL of the extract, and then the absorbance was measured at a wavelength of 517 nm and determined according to the following formula:

[0083]

[0084] Here, A1 represents the absorbance of the mixture of the composite film and DPPH at 517 nm, and A0 represents the absorbance of the pure DPPH solution at 517 nm.

[0085] The results of the DPPH radical scavenging rate of the composite film are as Figure 5 shown. The DPPH radical scavenging effect of the pure carrageenan film is limited, and it can only scavenge 7% of the DPPH radicals. When free thymol is added, the DPPH radical scavenging rate only slightly increases to 11%. In contrast, after adding ZT-NPs to the carrageenan film, the DPPH radical scavenging rate significantly increases to 78%. This result highlights the potential of nanoparticle encapsulation in enhancing the antioxidant activity of essential oils.

[0086] 8. Determination of antibacterial property

[0087] The antibacterial activity of the composite film was measured by the following method. The composite film sample (15 mg) was placed into the bacterial suspension (3 mL, 106 - 107 CFU / mL), and the flask was placed in a bacterial culture shaker (30 °C) for 1 h. The extract was serially diluted and the total number of colonies was calculated.

[0088] The results of the antibacterial property of the composite film are as Figure 7 shown. The antibacterial rates of Car, Car / Thymol, and Car / ZT-NPs are 18.2%, 39.1%, and 63.7% respectively. The results show that incorporating free thymol can improve the antibacterial performance of the composite film, while incorporating encapsulated thymol is more effective. This is because thymol is a good antibacterial agent as it can disrupt the microbial cell membrane and interfere with key biochemical pathways within the cell. Free thymol may not be as effective as encapsulated thymol because free thymol is more volatile and chemically degradable, thus reducing the amount available to inactivate microorganisms. In addition, the small size of the nanoparticles may help them penetrate the bacterial cell wall, thus bringing thymol closer to its site of action.

[0089] Example 3

[0090] In this example, the applicant explored the effect of carrageenan-based composite films filled with thymol-loaded nanoparticles on the quality indicators of mandarin fish, and systematically evaluated the preservation effect of the composite film on mandarin fish. The specific implementation steps are as follows:

[0091] In the experimental group, mandarin fish pieces (10 cm × 5 cm) were completely wrapped with Car / ZT-NPs and Car / Thymol (15 cm × 15 cm), and then stored in an incubator at 25 °C for 24 h. In the control group, mandarin fish pieces (10 cm × 5 cm) were completely wrapped with Car (15 cm × 15 cm), and then stored in an incubator at 25 °C for 24 h. The total viable count (TVC) of mandarin fish was measured, and the measurement method of the total viable count was determined according to the method of GB4789.2-2022.

[0092] The experimental results are as Figure 7 shown. The changes in appearance and total viable count (TVC) were used to evaluate the freshness of fish during storage. Figure 7 Photographs and TVC values of fish samples in different groups after 0 and 24 h are shown. The TVC values of fresh fish and fish treated with Car, Car / Thymol, and Car / ZT-NPs after 24 h were 4.00, 6.89, 6.80, and 6.22 lgCFU / g, respectively. Compared with the pure carrageenan film group, the TVC values of the fish meat in the Car / Thymol and Car / ZT-NPs groups decreased by 18.7% and 78.5% after 24 h, respectively. Compared with the fish packaged with Car / Thymol, the TVC value of the fish packaged with Car / ZT-NPs decreased by 73.5%. There are many reasons for this effect. As mentioned above, the volatilization and chemical degradation of free thymol may be more than that of encapsulated thymol. In addition, free thymol may be released from the film rapidly, while nano-encapsulated thymol may be released more slowly, thus prolonging its antiseptic effect on fish during the whole storage process.

[0093] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device.

[0094] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made in these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a zein nanoparticle composite film, characterized in that: The following steps are involved: S1. preparing a thymol-zein ethanol aqueous solution; S2, preparing thymol-zein nanoparticles; S3, preparing thymol ethanol aqueous solution; S4, preparing carrageenan base film liquid; S5, prepare 5.25 mg / mL potassium chloride solution; S6, preparing a nanoparticle-carrageenan composite solution; S7, preparing a thymol-carrageenan composite solution; S8. Pour the nanoparticle-carrageenan composite solution and the thymol-carrageenan composite solution into a non-stick coating mold with a side length of 28 cm*28 cm by using a solution casting method, and dry them in a constant temperature incubator to form a film.

2. The method for preparing a zein nanoparticle composite film according to claim 1, characterized in that: The preparation method of the thymol-zein ethanol aqueous solution in S1 is as follows: 80.0 mg of thymol and 400.0 mg of zein are weighed and dissolved in 40.0 mL of ethanol aqueous solution, and stirred with a magnetic stirrer at 300 rpm / min in the dark for 12 hours.

3. The method for preparing a zein nanoparticle composite film according to claim 2, characterized in that: The preparation method of the thymol-zein nanoparticles in S2 is: slowly drip 10.0 mL of S1 solution into 30.0 mL of distilled water, and stir in the dark at 1200 rpm / min to obtain thymol-zein nanoparticles.

4. The method for preparing a zein nanoparticle composite film according to claim 3, characterized in that: The preparation method of the thymol ethanol aqueous solution in S3 is: weigh 60.0 mg of thymol and dissolve it in 30.0 mL of ethanol aqueous solution, and stir it with a magnetic stirrer at 300 rpm / min in the dark for 30.0 min.

5. The method for preparing a zein nanoparticle composite film according to claim 4, characterized in that: The preparation method of the carrageenan base film liquid in S4 is as follows: weigh 2400.0 mg of carrageenan, add 100.0 mL of distilled water, stir evenly in a water bath to form a 24 mg / mL carrageenan solution, then add 480.0 mg of glycerol as a plasticizer to the carrageenan solution, and cool the solution to 40° C. to obtain the carrageenan base film liquid.

6. The method for preparing a zein nanoparticle composite film according to claim 5, characterized in that: The preparation method of the 5.25 mg / mL potassium chloride solution in S5 is as follows: weigh 157.5 mg of potassium chloride, add 30 mL of distilled water, stir evenly, and obtain a 5.25 mg / mL potassium chloride solution.

7. The method for preparing a zein nanoparticle composite film according to claim 6, characterized in that: The preparation method of the nanoparticle-carrageenan composite solution in S6 is as follows: the carrageenan base film liquid of S4, the nanoparticles of S2 and the potassium chloride solution of S5 are mixed, wherein the dry mass of the nanoparticles is 360.0 mg, the potassium chloride solution is 9.14 mL, and water is added to a total volume of 238.32 mL to obtain the nanoparticle-carrageenan composite solution.

8. The method for preparing a zein nanoparticle composite film according to claim 7, characterized in that: The preparation method of the thymol-carrageenan composite solution in S7 is as follows: the carrageenan base film liquid of S4, the thymol ethanol aqueous solution of S3 and the potassium chloride solution of S5 are mixed, wherein the dry mass of thymol is 60.0 mg, the potassium chloride solution is 9.14 mL, and water is added to a total volume of 238.32 mL to obtain the thymol-carrageenan composite solution.

9. An application of a zein nanoparticle composite film, characterized in that: The fish meat was wrapped with the composite film prepared by S8 and stored at 25℃.

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