High-performance shellac nano emulsion paint protein film and preparation method thereof

Abstract

The invention discloses a high-performance shellac nano emulsion paint protein film and a preparation method thereof. The preparation method comprises the following steps: S1, preparing a protein film-forming solution; s2, pouring the protein film-forming liquid prepared in the step S1 on a plane template, casting to form a film, drying and taking down to form the film; s3, the shellac ethanol solution and polyethylene glycol are subjected to high-pressure homogenization, and shellac nano emulsion paint liquid is prepared; and S4, uniformly brushing the shell-lac nano emulsion paint solution prepared in the step S3 on two surfaces of the protein film in the step S2, and drying to obtain the shell-lac nano emulsion paint protein film. The preservative has the beneficial effects that the preservative is easy to biodegrade, free of environmental pollution, good in mechanical property, high in heat stability, high in water, light and oxygen blocking capacity and good in antibacterial and antioxidant effect, food spoilage bacteria can be effectively inhibited, oxygenolysis of nutritional ingredients in food can be slowed down, the preservative has good preservation performance, the food quality can be guaranteed, and the shelf life of the food can be prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of food processing, and in particular relates to a high-performance shellac nano-emulsion protein film and a preparation method thereof. Background Art

[0002] The large-scale use of traditional plastic packaging films based on petroleum as raw material matrix has caused great pressure on the ecological environment. In particular, the microplastics generated during the preservation process of food packaging films also pose a potential danger to human health. With the popularization of the "plastic restriction order" and the exacerbation of a series of economic problems caused by energy, resources, and the environment, it is urgent for humans to develop and utilize new packaging materials that are biodegradable, renewable in raw materials, and green and pollution-free.

[0003] As a natural polymer, protein can be rapidly degraded by microorganisms and ultimately return to nature in the form of carbon dioxide, water, and nitrogen. Its source is renewable and it is pollution-free to the environment. Therefore, new packaging films based on protein can alleviate the current environmental problems to a certain extent. According to the source of the film-forming protein raw materials, they can be divided into three categories: animal-derived, plant-derived, and mixed-source protein films. Common animal-derived proteins include: gelatin, collagen, whey protein, casein, fish protein isolate, keratin, etc.; common plant-derived proteins include: soy protein isolate, zein, wheat protein, sorghum protein, rice bran protein, peanut protein, etc. Protein films have good elasticity, high mechanical strength, and good transparency. However, due to the hydrophilicity of the side chain groups of proteins, protein films have strong hygroscopicity and good water solubility, and their barrier properties to moisture, light, oxygen, and microorganisms are poor. They can be optimized by methods such as adding a hydrophobic protective layer.

[0004] Shellac is a natural polymer refined from the secretions of lac insects. It is currently the only animal resin approved for commercial use and has been widely used in food additives, preservatives, and pharmaceutical coating excipients. Shellac resin is composed of laccaic acid and cyclonic acid. Laccaic acid has hydrophobic properties, while cyclonic acid is hydrophilic. These components are interconnected by ester bonds to form an amphiphilic structure, which is insoluble in water but soluble in alcohol or alkaline solutions. Shellac has significant advantages in the food industry, including pH-responsiveness, biodegradability, and biocompatibility. Shellac has amphiphilicity and can undergo self-emulsification. It has been used to prepare edible coatings and microcapsules, and can further be applied to the packaging and preservation of food. The shellac layer in food packaging has good barrier properties and acts as a material exchange barrier, which can effectively limit the migration of moisture, oxygen, carbon dioxide, and aroma, slow down the side effects of the external environment on food, and reduce the oxidation of food and the influence of microorganisms.

[0005] Food packaging can effectively reduce the spoilage of food caused by external factors during storage, transportation, and sales. As a rich source of protein and lipids, meat occupies an important position in people's daily diet. However, during storage, meat is prone to becoming a breeding ground for microorganisms, and the lipid and protein components will also be partially oxidized and decomposed, which will not only seriously affect the shelf life of food but also reduce its nutritional value, resulting in food waste. Therefore, the use of a new type of food packaging film with antibacterial and antioxidant functions can provide a new method to solve this problem.

[0006] Nanoemulsion technology utilizes the amphiphilicity of emulsifiers to disperse the particle diameter into the range of 1 - 100 nm. The surface energy increases, the adsorption capacity and reaction activity are stronger, and it can more effectively contact bacteria and destroy their cell structure, thus having antibacterial effects. The high-pressure homogenization method uses the high hydraulic pressure generated by a piston pump to repeatedly break up droplets into smaller droplets with diameters meeting the nanoemulsion range, which is a commonly used and effective method for preparing nanoemulsions in industry. A new type of food packaging film developed by combining hydrophobic functional components with hydrophilic film-forming matrices using nanoemulsion technology can not only improve the physical and chemical properties of the film but also endow the film with antibacterial, antioxidant, and other functions, thereby extending the shelf life of packaged food. Therefore, nanoemulsion technology plays an important role in the development of new food packaging materials. Summary of the Invention

[0007] In view of this, the present invention aims to propose a high-performance shellac nanoemulsion casein film and its preparation method to solve at least one problem in the background technology. The matrix of this film uses protein, which is easy to be biodegradable, inexpensive, readily available, highly renewable, and has good biocompatibility. Using nanoemulsion technology, a composite paint film is made by covering the protein film with a nano-level emulsified shellac barrier layer of natural antibacterial and antioxidant agents, which can effectively inhibit common food spoilage bacteria, slow down the oxidative decomposition of nutrients in food, ensure food quality, and extend the shelf life of food.

[0008] To achieve the above object, the technical solution of the present invention is realized as follows: A preparation method of a high-performance shellac nanoemulsion casein film, comprising the following steps: S1: Prepare a protein film-forming solution; S2: Pour the protein film-forming solution obtained in step S1 onto a flat template, cast the film, and dry and remove it to form a film; S3: Perform high-pressure homogenization on a shellac ethanol solution and polyethylene glycol to obtain a shellac nanoemulsion paint solution; S4: Evenly brush the shellac nanoemulsion paint solution obtained in step S3 on both sides of the protein film in step S2, and dry to obtain a shellac nanoemulsion casein film.

[0009] Further, the preparation of the protein film-forming solution in step S1 includes mixing protein and water by stirring to obtain an aqueous protein solution, allowing it to stand and swell, adding glycerol, and stirring and mixing to obtain the protein film-forming solution; And / or, the concentration of the aqueous protein solution is 2% - 8%; And / or, the water in the aqueous protein solution is deionized water.

[0010] Further, protein and water are mixed by magnetic stirring, allowed to stand and swell, glycerol is added, and magnetic stirring and mixing are carried out to obtain the protein film-forming solution; And / or, the time for standing and swelling is 1 - 2 hours.

[0011] Further, the protein includes one or two of animal-derived protein and plant-derived protein; And / or, the animal-derived protein includes one or more of gelatin, collagen, whey protein, casein, fish protein isolate, keratin; And / or, the plant-derived protein includes one or more of soy protein isolate, zein, wheat protein, sorghum protein, rice bran protein, peanut protein.

[0012] Further, in step S2, the protein film-forming solution from step S1 is poured onto a flat template, cast into a film, and after drying at room temperature for 20 - 24 hours, it is removed to form a film.

[0013] Further, the preparation of the shellac ethanol solution in step S3 includes: mixing shellac and ethanol by magnetic stirring at a rotation speed of 280 - 320 rpm for 0.8 - 1.2 hours.

[0014] Further, the preparation of the shellac ethanol solution in step S3 includes: the pressure for high-pressure homogenization of the shellac ethanol solution and polyethylene glycol is 10 - 30 MPa, the rotation speed is 4800 - 5200 rpm, and high-pressure homogenization is carried out for 5 - 10 min to obtain the shellac nanoemulsion lacquer; And / or, the high-pressure homogenization process is carried out using a high-speed dispersion homogenizer.

[0015] Further, the drying temperature in step S4 is 70 - 80 °C, and the drying time is 15 - 30 min; And / or, drying is carried out in a drying oven, and the drying oven is a forced-air drying oven.

[0016] Further, the average particle size of the shellac nanoemulsion lacquer in step S3 is 49.35 - 67.32 nm.

[0017] The shellac nanoemulsion paint protein film prepared by the above-mentioned preparation method of a high-performance shellac nanoemulsion paint protein film has a thickness of 0.093 mm to 0.169 mm, a polydispersity index <0.3, a tensile strength of 17.34 to 36.85 MPa, an elongation at break of 55.81% to 82.78%, and a water vapor permeability coefficient of 0.64×10 -11 gm -1 s - 1 Pa~2.81×10 -11 gm -1 s -1 The high-performance shellac nanoemulsion paint protein film of the present invention uses protein (animal-derived gelatin or plant-derived soy protein isolate) as a matrix, and uses nanoemulsification technology to cover the natural antibacterial agent and antioxidant shellac on the protein film in the form of a barrier layer of nano-scale emulsion paint to prepare the shellac nanoemulsion paint protein film.

[0018] Protein molecules can form stable colloids in aqueous solution by relying on the hydration film and double electric layer on their surface, and the internal structure of protein molecules is maintained stable by the disulfide bonds, hydrogen bonds, ionic bonds, hydrophobic interactions and van der Waals forces in the molecules. When the internal interactions are destroyed after certain treatments, the disulfide bonds in the molecules are broken, and the sulfhydryl and hydrophobic groups in the molecules are exposed, the spatial conformation of the protein will be stretched, and the interaction between adjacent proteins will be enhanced to form a stable network matrix structure and a protein film with certain barrier functions. Because the main component of protein is protein, the protein film is easily biodegradable, reduces environmental pollution, and can also improve the sensory and nutritional properties of food; at the same time, because the protein film has good mechanical strength, it can be supplemented with hydrophobic shellac nanoemulsion paint to enhance its barrier effect and reduce its transmittance to substances such as oxygen, water vapor, light and oil to ensure the quality of the packaged food.

[0019] Polyethylene glycol is a high molecular weight polymer with the chemical formula HO(CH 2 CH 2 O) n H, non-irritating, slightly bitter, with good water solubility, viscoelasticity, lubricity, moisture retention, dispersibility and adhesion, mainly used in pharmaceutical preparations and food processing as a solubilizer, stabilizer, antistatic agent and softener. PEG-400 has excellent water solubility, good compatibility with organic components, can combine with drug molecules to form stable complexes or compounds, increase the solubility and stability of drugs, prevent drug crystallization, and is often used to make liquid preparations, such as oral solutions and eye drops.

[0020] Glycerol, also known as propylene glycol, is a simple polyol compound with a chemical formula of C3 H 8 O 3 is a colorless, odorless, sweet-tasting viscous liquid, non-toxic, with certain antibacterial and antiviral properties. It can be miscible with water, alcohols, amines, and phenols in any proportion, and has hygroscopicity. It has been widely used in the fields of food, medicine, cosmetics, etc. During the preparation of a protein-based film, glycerol can combine with protein molecules, acting as a plasticizer to increase the hardness of the final film and improve the mechanical properties of the film.

[0021] Compared with the prior art, a high-performance shellac nanoemulsion protein film and its preparation method according to the present invention have the following advantages: The high-performance shellac nanoemulsion protein film described in the present invention is easily biodegradable, has good mechanical properties, high thermal stability, strong water, light, and oxygen barrier capabilities, excellent antibacterial and antioxidant effects, can effectively slow down the spoilage of the packaged food caused by bacterial contamination and oxidation decomposition of nutrients, has good freshness preservation performance, can ensure the food quality, extend the food shelf life, and solves the problems of environmental pollution of existing food packaging films and easy spoilage of the packaged food. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings: Figure 1 is a schematic diagram of the release amount of volatile basic nitrogen during the refrigeration process of pork packaged with the shellac nanoemulsion protein film described in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0024] The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0025] Example 1: Prepare a high-performance shellac nanoemulsion animal protein film: (1) Prepare a protein film-forming solution: Weigh 0.4000 g of gelatin powder, dissolve it in 10 ml of deionized water, mix it with magnetic stirring, and after standing and swelling for 2 hours, add 0.1600 g of glycerol and mix it with magnetic stirring to prepare a protein film-forming solution.

[0026] (2) Cast film: Pour the protein film-forming solution in step (1) onto a flat template, cast the film, and after drying at room temperature for 20 - 24 hours, remove it to form a film.

[0027] (3) Preparation of shellac nanoemulsion paint solution: Weigh 2 g of shellac particles, dissolve them in 100 ml of ethanol, magnetically stir and mix at a speed of 300 rpm for 1 hour, slowly add 0.2 g of PEG-400, and under a pressure of 30 MPa, perform high-pressure homogenization at a speed of 5000 rpm for 10 min to obtain the shellac nanoemulsion paint solution.

[0028] (4) Preparation of shellac-lacquer protein film: Use a brush to evenly brush the shellac nanoemulsion paint solution in step (3) on both sides of the protein film in step (2), place it in a drying oven, and dry at 75 °C for 30 min to obtain the shellac nanoemulsion paint protein film.

[0029] Through the above steps and material ratios, the shellac nanoemulsion paint animal protein film containing 2% shellac as described in the present invention is obtained.

[0030] Example 2: Preparation of high-performance shellac nanoemulsion paint animal protein film: (1) Preparation of protein film-forming solution: Weigh 0.4000 g of gelatin powder, dissolve it in 10 ml of deionized water, magnetically stir and mix, after standing and swelling for 2 hours, add 0.1600 g of glycerol, and magnetically stir and mix to prepare the protein film-forming solution.

[0031] (2) Casting film formation: Pour the protein film-forming solution in step (1) onto a flat template, cast a film, and after drying at room temperature for 20 - 24 hours, remove it to form a film.

[0032] (3) Preparation of shellac nanoemulsion paint solution: Weigh 4 g of shellac particles, dissolve them in 100 ml of ethanol, magnetically stir and mix at a speed of 300 rpm for 1 hour, slowly add 0.4 g of PEG-400, and under a pressure of 30 MPa, perform high-pressure homogenization at a speed of 5000 rpm for 10 min to obtain the shellac nanoemulsion paint solution.

[0033] (4) Preparation of shellac-lacquer protein film: Use a brush to evenly brush the shellac nanoemulsion paint solution in step (3) on both sides of the protein film in step (2), place it in a drying oven, and dry at 75 °C for 30 min to obtain the shellac nanoemulsion paint protein film.

[0034] Through the above steps and material ratios, the shellac nanoemulsion paint animal protein film containing 4% shellac as described in the present invention is obtained.

[0035] Example 3: Preparation of high-performance shellac nanoemulsion paint animal protein film: (1) Preparation of protein film-forming solution: Weigh 0.4000 g of gelatin powder, dissolve it in 10 ml of deionized water, magnetically stir and mix, after standing and swelling for 2 hours, add 0.1600 g of glycerol, and magnetically stir and mix to prepare the protein film-forming solution.

[0036] (2) Casting into film: Pour the protein film-forming solution from step (1) onto a flat template, cast it into a film, and after drying at room temperature for 20 - 24 hours, remove it to obtain the film.

[0037] (3) Preparing shellac nanoemulsion paint solution: Weigh 8 g of shellac particles, dissolve them in 100 ml of ethanol, magnetically stir and mix at 300 rpm for 1 hour, slowly add 0.8 g of PEG - 400, and under a pressure of 30 MPa, homogenize at 5000 rpm for 10 min to obtain the shellac nanoemulsion paint solution.

[0038] (4) Preparing shellac paint protein film: Use a brush to evenly brush the shellac nanoemulsion paint solution from step (3) on both sides of the protein film from step (2), place it in an oven, and dry at 75 °C for 30 min to obtain the shellac nanoemulsion paint protein film.

[0039] Through the above steps and material ratios, the shellac nanoemulsion paint animal protein film containing 8% shellac described in the present invention is obtained.

[0040] Example 4: Preparing a high - performance shellac nanoemulsion paint plant protein film: (1) Preparing protein film - forming solution: Weigh 0.4000 g of soy protein isolate powder, dissolve it in 10 ml of deionized water, magnetically stir and mix, let it stand and swell for 2 hours, then add 0.1600 g of glycerol, and magnetically stir and mix to prepare the protein film - forming solution.

[0041] (2) Casting into film: Pour the protein film - forming solution from step (1) onto a flat template, cast it into a film, and after drying at room temperature for 20 - 24 hours, remove it to obtain the film.

[0042] (3) Preparing shellac nanoemulsion paint solution: Weigh 2 g of shellac particles, dissolve them in 100 ml of ethanol, magnetically stir and mix at 300 rpm for 1 hour, slowly add 0.2 g of PEG - 400, and under a pressure of 30 MPa, homogenize at 5000 rpm for 10 min to obtain the shellac nanoemulsion paint solution.

[0043] (4) Preparing shellac paint protein film: Use a brush to evenly brush the shellac nanoemulsion paint solution from step (3) on both sides of the protein film from step (2), place it in an oven, and dry at 75 °C for 30 min to obtain the shellac nanoemulsion paint protein film.

[0044] Through the above steps and material ratios, the shellac nanoemulsion paint plant protein film containing 2% shellac described in the present invention is obtained.

[0045] Example 5: Preparing a high - performance shellac nanoemulsion paint plant protein film: (1) Preparation of protein film-forming solution: Weigh 0.4000 g of gelatin powder, dissolve it in 10 ml of deionized water, mix it by magnetic stirring, let it stand and swell for 2 hours, then add 0.1600 g of glycerol, and mix it by magnetic stirring to prepare the protein film-forming solution.

[0046] (2) Casting film formation: Pour the protein film-forming solution in step (1) onto a flat template, cast the film, and after drying at room temperature for 20 - 24 hours, remove it to obtain the formed film.

[0047] (3) Preparation of shellac nanoemulsion paint solution: Weigh 4 g of shellac particles, dissolve them in 100 ml of ethanol, mix them by magnetic stirring at a speed of 300 rpm for 1 hour, slowly add 0.4 g of PEG - 400, and perform high-pressure homogenization at a pressure of 30 MPa and a speed of 5000 rpm for 10 min to obtain the shellac nanoemulsion paint solution.

[0048] (4) Preparation of shellac paint protein film: Use a brush to evenly brush the shellac nanoemulsion paint solution in step (3) on both sides of the protein film in step (2), place it in a drying oven, and dry it at 75 °C for 30 min to obtain the shellac nanoemulsion paint protein film.

[0049] Through the above steps and material ratios, the shellac nanoemulsion paint plant protein film containing 4% shellac described in the present invention is obtained.

[0050] Example 6: Preparation of high-performance shellac nanoemulsion paint plant protein film: (1) Preparation of protein film-forming solution: Weigh 0.4000 g of gelatin powder, dissolve it in 10 ml of deionized water, mix it by magnetic stirring, let it stand and swell for 2 hours, then add 0.1600 g of glycerol, and mix it by magnetic stirring to prepare the protein film-forming solution.

[0051] (2) Casting film formation: Pour the protein film-forming solution in step (1) onto a flat template, cast the film, and after drying at room temperature for 20 - 24 hours, remove it to obtain the formed film.

[0052] (3) Preparation of shellac nanoemulsion paint solution: Weigh 8 g of shellac particles, dissolve them in 100 ml of ethanol, mix them by magnetic stirring at a speed of 300 rpm for 1 hour, slowly add 0.8 g of PEG - 400, and perform high-pressure homogenization at a pressure of 30 MPa and a speed of 5000 rpm for 10 min to obtain the shellac nanoemulsion paint solution.

[0053] (4) Preparation of shellac paint protein film: Use a brush to evenly brush the shellac nanoemulsion paint solution in step (3) on both sides of the protein film in step (2), place it in a drying oven, and dry it at 75 °C for 30 min to obtain the shellac nanoemulsion paint protein film.

[0054] Through the above steps and material ratios, the shellac nanoemulsion paint plant protein film containing 8% shellac described in the present invention is obtained.

[0055] Comparative Example 1: Prepare the packaging film of the comparative example: (1) Prepare the protein film-forming solution: Weigh 0.4000 g of gelatin powder, dissolve it in 10 ml of deionized water, mix it by magnetic stirring, after standing and swelling for 2 hours, add 0.1600 g of glycerol, and mix it by magnetic stirring to prepare the protein film-forming solution.

[0056] (2) Cast film: Pour the protein film-forming solution in step (1) onto a flat template, cast a film, and after drying at room temperature for 20 - 24 hours, remove it to obtain the film.

[0057] (3) Prepare the shellac nano-emulsion paint solution: Weigh 2 g of shellac particles, dissolve them in 100 ml of ethanol, mix them by magnetic stirring at a speed of 300 rpm for 1 hour, slowly add 0.2 g of PEG - 400, and under a pressure of 30 MPa, homogenize it at a speed of 5000 rpm for 10 min to obtain the shellac nano-emulsion paint solution.

[0058] (4) Prepare the single-sided shellac paint protein film: Use a brush to evenly brush the shellac nano-emulsion paint solution in step (3) on one side of the protein film in step (2), place it in an oven, and dry it at 75 °C for 30 min to obtain the shellac nano-emulsion paint protein film.

[0059] Obtain the comparative example of the animal protein film with single-sided shellac paint through the above steps and material ratios.

[0060] Comparative Example 2: Prepare the packaging film of the comparative example: (1) Prepare the protein film-forming solution: Weigh 0.4000 g of soy protein isolate powder, dissolve it in 10 ml of deionized water, mix it by magnetic stirring, after standing and swelling for 2 hours, add 0.1600 g of glycerol, and mix it by magnetic stirring to prepare the protein film-forming solution.

[0061] (2) Cast film: Pour the protein film-forming solution in step (1) onto a flat template, cast a film, and after drying at room temperature for 20 - 24 hours, remove it to obtain the film.

[0062] (3) Prepare the shellac nano-emulsion paint solution: Weigh 2 g of shellac particles, dissolve them in 100 ml of ethanol, mix them by magnetic stirring at a speed of 300 rpm for 1 hour, slowly add 0.2 g of PEG - 400, and under a pressure of 30 MPa, homogenize it at a speed of 5000 rpm for 10 min to obtain the shellac nano-emulsion paint solution.

[0063] (4) Prepare the single-sided shellac paint protein film: Use a brush to evenly brush the shellac nano-emulsion paint solution in step (3) on one side of the protein film in step (2), place it in an oven, and dry it at 75 °C for 30 min to obtain the shellac nano-emulsion paint protein film.

[0064] The plant protein film of shellac paint on one side is obtained as a comparative example through the above steps and material ratios.

[0065] Through corresponding tests on the above-mentioned Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Comparative Example 1, and Comparative Example 2, it shows that the present invention has excellent performances in physical properties, barrier properties, antibacterial properties, antioxidant properties, and freshness preservation properties.

[0066] The test items include: (1) Physical property test of the high-performance shellac nanoemulsion paint protein film.

[0067] The texture analyzer is used to measure the mechanical properties of the film, including tensile property and elongation at break.

[0068] The cup method is used to measure the water vapor transmission rate (water barrier property) of the film.

[0069] The gas analyzer is used to measure the O 2 permeability (oxygen barrier property) of the film.

[0070] The ultraviolet-visible spectrophotometer is used to measure the transmittance and transparency (light barrier property) of the film in the ultraviolet and visible light ranges with wavelengths of 200 - 800 nm.

[0071] The thermogravimetric analyzer is used to analyze the thermal stability of the film.

[0072] The physical properties of the examples and comparative examples are shown in Table 1: Table 1 Comparison table of physical properties of examples and comparative examples After testing, the physical properties and barrier properties of the examples of the present invention are superior to those of the comparative examples.

[0073] (2) Antibacterial property test of the high-performance shellac nanoemulsion paint protein film Prepare film samples with a diameter of 25 mm Select common food spoilage bacteria and pathogenic bacteria, among which Gram-positive bacteria: Bacillus subtilis ( Bacillus subtilis ), Staphylococcus aureus ( Staphylococcus aureas ); Gram-negative bacteria: Escherichia coli ( Escherichia coli ), Salmonella ( Salmonella ), from the Microbial Culture Collection and Management Center of Tianjin University of Science and Technology, and cultured to the logarithmic growth phase in LB medium. Put the above film samples and control films (with diameters of 25 ± 5 mm) into petri dishes, and culture at 37 °C for 24 hours, observe and record the size of the antibacterial zone. The antibacterial effects of the examples and comparative examples are shown in Table 2: Table 2 Comparison table of antibacterial effects of examples and comparative examples It can be seen from the comparison of the diameters of the antibacterial zones that the antibacterial effects of all the examples are better than those of the comparative examples. The antibacterial effect of the double-sided shellac lacquer protein film is better than that of the single-sided shellac lacquer protein film, and the antibacterial effect of the double-sided shellac lacquer protein film gradually increases with the increase of the shellac concentration in the shellac nanoemulsion lacquer liquid, especially the antibacterial effect against Gram-positive bacteria is better.

[0074] (3)Antioxidant property test of high-performance shellac nanoemulsion lacquer protein film The in vitro antioxidant property of the film was determined by the DPPH free radical scavenging ability. Take 6 mL of the film-forming solution and 2 mL of 0.7 mmol·L -1 methanol solution, vortex for 1 min, mix evenly, after dark treatment for 30 min, measure its absorbance at a wavelength of 517 nm using a UV-visible spectrophotometer. Calculate the DPPH free radical scavenging rate of the film sample according to the following formula. The antioxidant effects of the examples and comparative examples are shown in Table 3: Parameters in the formula: A DPPH : Absorbance of DPPH methanol solution at 517 nm; A S : Absorbance of the mixture of the film-forming solution and DPPH methanol at 517 nm.

[0075] Table 3 Comparison table of antioxidant effects of examples and comparative examples It can be seen from the comparison of the free radical scavenging rates that the antibacterial effects of all the examples are better than the antioxidant effects of the comparative examples. The antioxidant effect of the double-sided shellac lacquer protein film is better than that of the single-sided shellac lacquer protein film, and the antioxidant ability of the double-sided shellac lacquer protein film gradually increases with the increase of the shellac concentration in the shellac nanoemulsion lacquer liquid.

[0076] (4)Application test of high-performance shellac nanoemulsion lacquer protein film for packaging chilled fresh meat ① Determination of total number of colonies of chilled fresh meat packaged with high-performance shellac nanoemulsion lacquer protein film According to the method in GB 4789.2-2022 "National Food Safety Standard Food Microbiology Examination - Determination of Total Number of Colonies", the total number of colonies (TVC) of the chilled fresh meat (10 g of fresh pork stored at 4°C) without packaging, packaged with the comparative example, and packaged with the example was measured on the 0th, 1st, 3rd, 5th, and 10th days, as shown in Table 4: Table 4 Total number of colonies of pork packaged with shellac nanoemulsion lacquer protein film during refrigeration (unit: lg(CFU / g)) As can be seen from Table 4, during the refrigeration process of pork in different packaging states, as time goes by, the total number of colonies gradually increases. Among them, the increase in the total number of colonies of the unpackaged pork samples is the most significant. The antibacterial effects of the examples are all better than those of the comparative examples, and the antibacterial effect of the shellac protein film gradually increases with the increase in the shellac concentration in the shellac nanoemulsion lacquer. Therefore, the shellac nanoemulsion lacquer protein film can effectively inhibit the total number of colonies of chilled meat.

[0077] ② Determination of peroxide value of chilled meat packaged with high-performance shellac nanoemulsion lacquer protein film According to GB 5009.227-2023 "National Food Safety Standard - Determination of peroxide value in foods", the peroxide value (POV) was measured for unpackaged, comparative example-packaged, and example-packaged chilled meat after 0, 1, 3, 5, and 10 days, as shown in Table 6: Table 5 Peroxide value (unit: meq / Kg) of pork packaged with shellac nanoemulsion lacquer protein film during refrigeration As can be seen from Table 5, during the refrigeration process of pork in different packaging states, as the storage time extends, its peroxide value gradually increases. Among them, the increase in the peroxide value of the unpackaged pork samples is the most significant. The antioxidant effects of the examples are all better than those of the comparative examples, and the antioxidant ability of the shellac protein film gradually increases with the increase in the shellac concentration in the shellac nanoemulsion lacquer. The shellac nanoemulsion lacquer protein film can effectively inhibit the oxidation of chilled meat.

[0078] ③ Determination of freshness of chilled meat packaged with high-performance shellac nanoemulsion lacquer protein film According to GB 5009.228-2016 "National Food Safety Standard - Determination of volatile basic nitrogen in foods", the semi-micro distillation method was used to detect the quality of the chilled meat samples packaged with the film. The release amount of volatile basic nitrogen (TVB-N) was measured for unpackaged, comparative example-packaged, and example-packaged chilled meat after 0, 1, 3, 5, and 10 days, as Figure 1 shown.

[0079] As Figure 1 can be seen, during the refrigeration process of pork in different packaging states, as time goes by, the amount of volatile basic nitrogen released during the spoilage process gradually increases. Among them, the release amount of volatile basic nitrogen of the unpackaged pork samples is the largest, followed by the samples packaged with the comparative example film, and the release amounts of the examples are significantly lower than those of the comparative examples. Among them, the lower the release amount of volatile basic nitrogen of the film samples with higher shellac concentration in the shellac nanoemulsion lacquer. This result shows that the shellac nanoemulsion lacquer protein film described in the present invention has obvious antibacterial and antioxidant functions, can guarantee the quality of meat, and extend the shelf life of the packaged food.

[0080] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-performance shellac nanoemulsion paint protein film, characterized in that: The method comprises the following steps: S1: preparing a protein film-forming solution; S2: pouring the protein film-forming liquid prepared in step S1 onto a flat template, casting it into a film, and drying and removing it to form a film; S3: high pressure homogenization of the shellac ethanol solution and polyethylene glycol to obtain a shellac nanoemulsion paint solution; S4: evenly brush the shellac nanoemulsion paint solution prepared in step S3 on both sides of the protein film prepared in step S2, and prepare the shellac nanoemulsion paint protein film after drying.

2. The method for preparing a high-performance shellac nanoemulsion paint protein film according to claim 1, characterized in that: The preparation of the protein film-forming solution in step S1 includes mixing protein and water by stirring to obtain a protein aqueous solution, standing to swell, adding glycerol, stirring and mixing to obtain a protein film-forming solution; and / or, the concentration of the aqueous protein solution is 2%-8%; And / or, the water in the aqueous protein solution is deionized water.

3. The method for preparing a high-performance shellac nanoemulsion paint protein film according to claim 2, characterized in that: The protein and water are mixed by magnetic stirring, left to swell, glycerol is added, and mixed by magnetic stirring to prepare a protein film-forming solution; And / or, the swelling time is 1-2 hours.

4. The method for preparing a high-performance shellac nanoemulsion paint protein film according to claim 2, characterized in that: The protein includes one or both of animal source protein and plant source protein; And / or, the animal source protein includes one or more of gelatin, collagen, whey protein, casein, fish protein isolate, and keratin; And / or, the plant-based protein includes one or more of soy protein isolate, zein, wheat protein, sorghum protein, rice bran protein, and peanut protein.

5. The method for preparing a high-performance shellac nanoemulsion paint protein film according to claim 1, characterized in that: In step S2, the protein film-forming liquid of step S1 is poured onto a flat template, cast into a film, and after drying at room temperature for 20-24 hours, the film is removed to form a film.

6. The method for preparing a high-performance shellac nanoemulsion paint protein film according to claim 1, characterized in that: The preparation of the shellac ethanol solution in step S3 includes: mixing shellac and ethanol with magnetic stirring at a rotation speed of 280-320 rpm for 0.8-1.2 hours.

7. The method for preparing a high-performance shellac nanoemulsion paint protein film according to claim 1, characterized in that: The preparation of the shellac ethanol solution in step S3 includes: the shellac ethanol solution and polyethylene glycol are subjected to high-pressure homogenization at a pressure of 10-30 MPa, a rotation speed of 4800-5200 rpm, and high-pressure homogenization for 5-10 minutes to obtain a shellac nanoemulsion paint liquid; And / or, the high pressure homogenization process is performed using a high speed dispersing homogenizer.

8. The method for preparing a high-performance shellac nanoemulsion paint protein film according to claim 1, characterized in that: The drying temperature in step S4 is 70-80°C and the drying time is 15-30 min; And / or, the drying is carried out in a drying oven, and the drying oven is a forced air drying oven.

9. The method for preparing a high-performance shellac nanoemulsion paint protein film according to claim 1, characterized in that: The average particle size of the shellac nanoemulsion paint solution in step S3 is 49.35-67.32 nm.

10. The shellac nanoemulsion paint protein film prepared by the method for preparing a high-performance shellac nanoemulsion paint protein film according to any one of claims 1 to 9, characterized in that: The high-performance shellac nanoemulsion paint protein film has a thickness of 0.093 mm to 0.169 mm, a polydispersity index of <0.3, a tensile strength of 17.34 to 36.85 MPa, an elongation at break of 55.81% to 82.78%, and a water vapor permeability coefficient of 0.64×10 -11 gm -1 s -1 Pa~2.81×10 -11 gm -1 s -1 .

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